Thesis

Geochronology, geochemistry, and isotopic composition (Sr, Nd, Pb) of Tertiary porphyry systems in Ecuador

SCHUTTE, Philip

Abstract

This thesis presents geochronologic, geochemical, and isotopic data on Tertiary arc magmas associated with porphyry-related ore deposits in the northern Andes of Ecuador. In detail, ages on host and porphyry intrusion emplacement (U-Pb zircon) and hydrothermal alteration/mineralization (U-Pb titanite, Re-Os molybdenite) were obtained, combined with whole-rock geochemical analysis of least altered igneous rock samples. These data are discussed in a regional frame with respect to the geodynamic context. The following main conclusions apply: (1) porphyry-related ore deposits in Ecuador are mainly Miocene in age, and represent the northern extension of the Miocene metallogenic belt of northern-central Peru; (2) intrusions associated with mineralization are compositionally highly variable; a systematic association of mineralization with a specific trace element signature cannot be observed; (3) flat slab settings produce favorable exposure conditions for porphyry-related ore deposits; a systematic association of ore deposit formation and seamount chain (Carnegie Ridge) subduction is not observed.

Reference

SCHUTTE, Philip. Geochronology, geochemistry, and isotopic composition (Sr, Nd, Pb) of Tertiary porphyry systems in Ecuador. Thèse de doctorat : Univ. Genève, 2009, no. Sc. 4166

URN : urn:nbn:ch:unige-63675 DOI : 10.13097/archive-ouverte/unige:6367

Available at: http://archive-ouverte.unige.ch/unige:6367

Disclaimer: layout of this document may differ from the published version.

1 / 1 UNIVERSITÉ DE GENÈVE FACULTÉ DES SCIENCES Département de Minéralogie Prof. Urs Schaltegger Dr. Massimo Chiaradia

Geochronology, Geochemistry, and Isotopic Composition (Sr, Nd, Pb) of Tertiary Porphyry Systems in Ecuador

THÈSE

présentée à la faculté des sciences de l'Université de Genève pour obtenir le grade de Docteur ès sciences, mention Sciences de la Terre

par Philip SCHÜTTE de Allemagne

GENÈVE 2010

TABLE OF CONTENTS Acknowledgements ...... iii Abstract ...... v Resumen...... vii Résumé étendu...... xi

CHAPTER I – THEORETICAL BACKGROUND AND AIMS OF THESIS Introduction...... 1 References...... 3

CHAPTER II – GEODYNAMIC CONTROLS ON TERTIARY ARC MAGMATISM IN ECUADOR: CONSTRAINTS FROM U‐PB ZIRCON GEOCHRONOLOGY OF OLIGOCENE‐MIOCENE INTRUSIONS AND REGIONAL AGE DISTRIBUTION TRENDS Abstract ...... 5 Introduction...... 6 Regional Geology of Ecuador ...... 6 Tertiary arc segmentation and geology of investigated magmatic centers...... 8 Analytical techniques and sample material ...... 14 Results ...... 18 Discussion ...... 25 Conclusions...... 34 References...... 34 Appendix I – Accommodation of convergence obliquity at the Ecuadorian margin throughout the Tertiary...... 39 Appendix II – Overriding plate structural controls on the spatio‐temporal distribution of Tertiary plutons in Ecuador...... 42 Appendix III – Accuracy of published K‐Ar (and ZFT) ages of Tertiary intrusions in Ecuador...... 48 Appendix IV – Data tables ...... 54

CHAPTER III ‐ THE MIOCENE METALLOGENIC BELT OF ECUADOR: CONSTRAINTS FROM NEW RE‐OS MOLYBDENITE AND U‐PB TITANITE AGES OF PORPHYRY‐RELATED ORE DEPOSITS Abstract ...... 65 Introduction...... 66 Regional geology and geodynamic setting...... 68 Local geology of Miocene Ecuadorian ore deposits investigated in this study...... 69 Sampling and analytical techniques ...... 73 Results ...... 74 Discussion ...... 76 Conclusions...... 92 References...... 92

i CHAPTER IV ‐ CRUSTAL BASEMENT ARCHITECTURE IN ECUADOR EXPLORED BY SR, ND, AND PB ISOTOPIC COMPOSITIONS OF TERTIARY‐QUATERNARY ARC MAGMAS Abstract ...... 97 Introduction...... 98 Geological framework ...... 100 Methodology ...... 100 Results ...... 103 Discussion ...... 106 Conclusions...... 112 References...... 112 Appendix: Data tables ...... 115

CHAPTER V ‐ ADAKITE‐LIKE FEATURES IN LATE OLIGOCENE TO LATE MIOCENE ECUADORIAN ARC MAGMAS AND THEIR SIGNIFICANCE FOR PORPHYRY‐RELATED ORE DEPOSITS Abstract ...... 119 Introduction...... 120 Tertiary‐Quaternary adakite‐like magmatism in Ecuador...... 120 Regional geology and geodynamic setting...... 122 Sampling and analytical techniques ...... 126 Results ...... 128 Rare earth element distribution patterns ...... 134 Adakite‐like features of Late Tertiary Ecuadorian arc magmas ...... 139 Isotopic constraints on shallow vs. deep crustal magma evolution...... 144 Significance of adakite‐like features for Late Oligocene to Late Miocene porphyry‐related mineralization in Ecuador...... 151 Conclusions...... 152 References...... 153 Appendix I – Rock alteration and element mobility in porphyry‐related hydrothermal systems ...... 157 Appendix II – Data tables...... 159

CHAPTER VI ‐ GENERAL CONCLUSIONS AND OUTLOOK Conclusions...... 179 Outlook...... 180

ii Acknowledgements Big thanks to Massimo Chiaradia for initiating this project, for his continuous and patient support through‐ out its lifetime (both in the lab and in the office), and for doing a superb job with constructive and critical thesis reviewing which was highly appreciated. Successful field work in Ecuador would have been impossi‐ ble without the organizational support of Bernardo Beate whose personal commitment to this project is gratefully acknowledged. Urs Schaltegger, Kalin Kouzmanov, and Othmar Müntener are thanked for accept‐ ing to be part of the committee of this PhD project, and for valuable discussions and critical comments re‐ garding various aspects of the material presented in this thesis during all stages of its compilation over the last couple of years. Urs' administrative support is also gratefully acknowledged. Many individuals at the Universities of Geneva, Lausanne, and Arizona, contributed to the success of this project. As far as Geneva is concerned, my knowledge of the geology of Ecuador improved from valuable discussions with Richard Spikings, Miguel "No More Mr. Nice Guy" Ponce, and, in particular, Diego Vil‐ lagómez, who are all gratefully acknowledged. I also thank Aldo Bendezú for good discussions and for pos‐ ing critical questions which stimulated me to look at geological problems of all sorts from a different per‐ spective, and to think again on many aspects of metallogenesis, magmatism, and tectonics. Big thanks to Maria Ovtcharova, Blair Schoene, and Urs for incredible support in the Geneva zircon lab, with mass spectrometric analysis, and with U‐Pb data reduction. I further thank Fabio Capponi for XRF analysis and Jean‐Marie Boccard for thin section preparation; I had quite a lot of samples for both of them, and they always took it on good‐humored and provided excellent results which were highly appreciated. Thanks for analytical support are further due to Alex Ulianov (MC‐ICP‐MS, Lausanne) and Rosanna Martini (SEM, Ge‐ neva). At the University of Arizona, Fernando Barra and Victor Valencia did a great job in providing Re‐Os molybdenite and U‐Pb zircon analyses for this study, and both are gratefully acknowledged for their valu‐ able contributions. Many administrative aspects of this project were taken care of by Sofia Saldana, Jacque‐ line Berthoud, and Ursula Eigenmann, and I warmly thank each of them. I gratefully acknowledge SEG (Society of Economic Geologists), EDSM (Ecole Doctorale en Sciences des Mi‐ néraux), and the Bourse Lombard for providing travel grants to support congress participation and field‐ work of this project. Thanks in particular to Mike Dungan for investing a lot of time and personal effort into EDSM and for organizing a number of top‐level short courses, as well as for repeated tech support bribery. Furthermore, I am grateful to Lluís Fontboté for encouraging me to participate in several excellent courses and excursions on ore deposits whose informative value was priceless. Many students at Geneva University provided help and advice throughout all stages of this project. In par‐ ticular, I thank Diego Villagómez, Jenny Skoog, Thierry Bineli Betsi, and Régine Baumgartner for lab support in the beginning, Léo Mastrodicasa for advice during the initial stages of computer administration, and Toufik Bekaddour and Diego Villagómez for help with editing the French and Spanish abstracts which was highly appreciated. This project benefited substantially from countless helpful people and exploration companies in Ecuador whose enthusiastic support with logistics and knowledge was key to its success, particularly in a politically sometimes challenging climate. These include (with their affiliations back then): Patricio Salazar (Escuela Politécnica Nacional & Ascendant Copper), Carlos Moncayo and James Stonehouse (Ascendant Copper), Luis Bravo and Edgar Almeida (Dynasty Metals & Mining), Francisco Soria and Miguel Ponce (IMC), Luis Lucero and Patricio Perez Salazar (Iamgold), John Bolaños and Danilo Ortega (Ecuagold), Graeme Smith, Don Allen, and Eduardo Vaca (Atlas Moly), Osman Poma (Channel Resources), and Christian Vallejo (Curimining); apologies for any missing names here. Thanks are also due to the Swiss Embassy in Quito for providing quick and efficient help with sample export, and the Ministerio de Energía y Minas del Ecuador (especially Luis Pilatasig and Fabiola Alcocer) for providing otherwise inaccessible maps and literature. Last but not least, I thank my family for their continuous support in all these years.

iii iv Abstract This Ph.D. thesis presents geochronologic data on Late Tertiary arc magmatism associated with porphyry‐ related ore deposits (Chapter 2), and the timing of intrusion‐related mineralization and alteration in Ecua‐ dor (Chapter 3), as well as on the isotopic (Chapter 4) and geochemical (Chapter 5) composition of Oligo‐ cene‐Miocene arc volcanic and plutonic rocks spatially associated with porphyry systems. Chapter‐specific abstracts precede each part of the thesis and should be consulted for more detailed information on each topic. A general introduction (Chapter 1) explains some of the ideas this project was originally based on, and general conclusions joining its individual parts can be found in Chapter 6. Ecuador hosts a large number of Tertiary arc‐related granitoids and volcanics whose geochronologic char‐ acterization is mostly based on K‐Ar (and zircon fission track) data. Chapter 2 presents the first regional‐ scale dataset of U‐Pb zircon ages for multiple plutons and porphyry intrusions of the Ecuadorian Western Cordillera and southern Sierra region, allowing a robust time calibration of the Tertiary intrusive history of Ecuador. Zircons were dated either by means of isotope dilution thermal ionization mass spectrometry (TIMS) or by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐.MC‐ICP‐MS) Except for a single sample, all investigated intrusions completely lack externally inherited zircons suggesting a dominantly zircon‐poor oceanic basement; antecrystic zircon components are relatively abundant in sev‐ eral plutons indicating that recycling of older arc granitoids took place. Where both K‐Ar and U‐Pb data ex‐ ist for a given intrusive system, ages obtained by the different methods are usually concordant within 1‐4 m.y. implying that K‐Ar data may be used as a semi‐accurate proxy for Tertiary arc magmatism in Ecuador on a regional scale. Spatio‐temporal distribution trends of Tertiary intrusions and arc volcanics indicate a Late Oligocene to Early/Mid‐Miocene arc magmatic flare‐up event in Ecuador comprising widespread ig‐ nimbrite eruption and batholith construction within an overall tensional regional stress field. Initiation of the regional flare‐up event coincides in time with a significant acceleration of Farallon/Nazca‐South Amer‐ ica convergence rates suggesting a positive feedback between faster plate convergence, asthenospheric melt production, mantle‐crust melt flux, and upper crustal arc magmatic productivity in Ecuador. Chapter 3 presents Re‐Os molybdenite and U‐Pb titanite ages related to mineralization and alteration fea‐ tures of latest Oligocene and Miocene porphyry‐related ore deposits in Ecuador. The new geochronologic data allow us to infer that the Miocene metallogenic belt of northern‐central Peru extends northwards into southern Ecuador, and potentially further north until Colombia. Miocene mineralization closely follows the distribution of Miocene arc magmatism in Ecuador. The regional spatio‐temporal distribution of porphyry Cu and associated epithermal mineralization within the Ecuadorian and Peruvian metallogenic belt seg‐ ments is similar. Intersections of Andean (NNE‐) trending structures with arc‐transverse faults and linea‐ ments related to suture zone geometries and block rotation in southern Ecuador represent highly prospec‐ tive sites for Miocene mineralization. The lack of Quaternary arc volcanic cover sequences and overall fa‐ vorable erosion levels are key parameters to preserve and expose widespread Miocene porphyry‐related mineralization in southern Ecuador. In the Western Cordillera of Ecuador porphyry‐related mineralization has locally been preserved, whereas the deeply eroded cores of porphyry systems are exposed at other lo‐ cations and significant parts of the mineralization have been removed. Porphyry systems are often spatially associated with intrusive clusters of batholith dimension, and formed towards the final stages of batholith assembly. Extensive shallow crustal magmatism during peaks of batholith construction may thus be disad‐ vantageous for the formation and preservation of porphyry‐related ore deposits, whereas favorable petro‐ genetic preconditioning of potential porphyry parental melts may occur towards the final phase of batho‐ lith construction. A direct spatio‐temporal association of Miocene porphyry‐related ore deposits and ridge (seamount chain) subduction or pulses of regional compression, as proposed elsewhere in the South American Andes, is not observed in Ecuador. The crustal basement of Ecuador comprises a collage of mostly Paleozoic‐Mesozoic tectono‐stratigraphic units of both continental and oceanic affinity in the Eastern Cordillera, and oceanic plateau units in the Western Cordillera and forearc region which were accreted in the Late Cretaceous. The diffuse paleo‐

v continental suture zone is situated between the Eastern and Western Cordillera ranges where basement units are covered by Tertiary‐Quaternary arc volcanics. Chapter 4 presents a set of 58 new whole‐rock Sr, Nd, and Pb isotopic compositions of Late Oligocene and younger arc volcanics and associated intrusions of the Western Cordillera, its western foothills, and the central‐southern Ecuadorian Sierra region. Combining this new dataset with existing data on Quaternary arc volcanoes allows us to trace basement units of the Late Cretaceous suture zone at depth. Quaternary arc volcanics define distinct isotopic (Sr, Nd, Pb) groups for volcanoes situated teas and west of the regional, roughly margin‐parallel Peltetec Fault, respectively. Late Oligocene to Late Miocene arc volcanics and intrusions of the southern Ecuador Sierra region overlap isotopically with recent arc volcanics in northern Ecuador suggesting along‐arc continuity of similar base‐ ment units at depth. Crustal isotopic contamination of Tertiary‐Quaternary arc magmas mainly takes place at deep to mid‐crustal levels except for granitoids of the Cangrejos‐Zaruma intrusive belt in southern Ecua‐ dor, where additional prominent shallow crustal assimilation is recorded. Isotopic compositions of arc magmas in northern‐central Ecuador follow a systematic across‐arc pattern where they evolve towards progressively more radiogenic 87Sr/86Sr and 207Pb/204Pb, and less radiogenic 143Nd/144Nd compositions at deep to mid‐crustal levels with increasing distance from the trench. This is consistent with regional, east‐ directed underthrusting of accreted oceanic plateau material along a broad suture zone below the paleo‐ continental margin as previously inferred from seismic studies. Chapter 5 presents a comprehensive dataset of the geochemical composition of Late Oligocene to Late Miocene intrusions and arc volcanics associated in space and time with porphyry‐related mineralization in Ecuador, focusing on the spatio‐temporal distribution pattern of adakite‐like geochemical features and ex‐ ploring their significance for porphyry‐related mineralization. The overall spatio‐temporal distribution of adakite‐like features in Ecuadorian arc magmas associated with porphyry systems is semi‐systematic; the relative proportion of adakite‐like (high Sr/Y) magmas increases with decreasing age, and is higher in northern‐central than in southern Ecuador. Broadly increasing Sr/Y and Sm/Dy ratios through time are con‐ sistent with progressively increasing high‐pressure crustal magma differentiation. High Sr/Y magmatism in the Late Tertiary is mainly due to strong Y (and heavy REE) depletion of parental melts at broadly constant Sr contents, where the former is related to fractionation/restite equilibration effects of amphibole, garnet, and titanite. While amphibole (± accessory titanite) fractionation/restite equilibration caused silicic melts to evolve towards adakite‐like compositions in the Early to Mid‐Miocene, combined amphibole and garnet fractionation/restite equilibration in Ecuadorian arc magmas has only been widespread since the Late Mio‐ cene and continues to the present day. A preferential association of adakite‐like features with a specific basement lithology cannot be observed. Increasing crustal thickness favorably influences the occurrence of adakite‐like features on a regional scale, but the latter are further modulated by a set of parameters which dynamically control mineral stabilities and mineral‐melt partitioning coefficients at a local scale. These include magma evolution depth (pressure) in a given crustal column and melt composition (degree of differentiation and melt water content). Por‐ phyry‐related deposits in Ecuador are often associated with intrusive clusters recording multi‐m.y. precur‐ sor magmatism where porphyry emplacement commonly represents a late intrusive event. Porphyry pa‐ rental melts tend to evolve towards more adakite‐like compositions than precursor intrusions if a signifi‐ cant relative age differences with respect to their emplacement exist. In contrast, systematic compositional changes between porphyry and precursor intrusions are not recorded if the relative age difference be‐ tween their respective emplacement events is small. As such, compositional changes between porphyry and precursor magmatism mostly reflect broad changes in arc magma composition through time at a re‐ gional scale. The fact that porphyry‐related ore deposits in Ecuador formed throughout the Late Oligocene to Late Miocene (24‐6 Ma) over a large latitudinal range (c. 0° to 3°30’S) supports the notion that any arc magma of a sufficient volume has the potential to form porphyry‐related mineralization. In some cases adakite‐like magmatism may, however, reflect favorable tectonomagmatic preconditioning of porphyry parental melts for subsequent porphyry‐related mineralization.

vi Resumen Esta tesis de PhD presenta resultados geocronológicos en rocas del arco magmático del Terciario Tardío asociadas a depósitos de pórfidos y epitermales (Capítulo 2) y el tiempo de la mineralización y alteraciones asociadas a las intrusiones (Capítulo 3) así como datos isotópicos (Capítulo 4) y geoquímicos (Capítulo 5) de rocas volcánicas y plutónicas del arco Oligoceno‐Mioceno asociadas con sistemas porfiríticos. Resúmenes específicos de cada capítulo preceden cada parte de la tesis. Una introducción general (Capítulo 1) explica algunas de las ideas generales del proyecto y las conclusiones generales se encuentran en el Capítulo 6. Ecuador presenta un gran número de granitoides y rocas volcánicas relacionadas con el arco magmático Terciario cuyas características geocronológicos han sido mayormente basadas en edades K‐/Ar y en trazas de fisión en zircón. En el Capítulo 2 se presenta el primer set de datos U/Pb en zircón realizado a escala re‐ gional, obtenidos en múltiples plutones e intrusiones porfiríticas en la Cordillera Occidental del Ecuador y en la Sierra Austral, lo que nos ha permitido una calibración robusta de la historia intrusiva durante el Ter‐ ciario en Ecuador. Las dataciones en zircón fueron obtenidas a partir de análisis de espectrometría de masa a partir de disolución isotópicaionización ‐ termal y también a partir de ablación laser. Excepto por una muestra, todas las demás analizadas carecen completamente de zircones heredados lo que sugiere un ba‐ samento oceánico pobre en zircones; la presencia de antecristales es relativamente abundante en muchos plutones lo que indica que granitoides mas antiguos pudieron haber sido reciclados. En rocas plutónicas donde se han obtenido edades K/Ar y U‐Pb se puede observar que los resultados son concordantes entre 1‐4 Ma, lo que sugiere que las edades K/Ar pueden ser usadas como un proxi semi‐ exacto para las rocas del arco magmático en Ecuador a escala regional. Distribuciones espacio temporales de la rocas magmáticas terciarias indican un evento de "flare‐up" desde el Oligoceno Tardío al Mioceno Temprano/Medio el que consistió en una importante y amplia erupción de ignimbrita y así mismo una in‐ tensa formación de batolitos durante un periodo de distensión regional. La iniciación del evento "flare‐up" coincide en el tiempo con una importante aceleración de la convergencia entre las placas Farallón/Nazca – Sudamérica sugiriendo que hay una relación directa entre la convergencia rápida de placas tectónicas, la producción de fundidos astenosféricos, flujo de fundidos manto‐corteza y actividad magmática en la corte‐ za superior del arco. En el Capítulo 3 se presenta edades Re‐Os en molibdenita y U‐Pb en titanita las cuales están relacionadas a mineralizaciones y alteraciones de los depósitos de tipo pórfido y epitermales del Oligoceno Tardío y del Mioceno. Estos nuevos resultados geocronológicos nos permiten inferir que el cinturón metalogénico de los Andes Nor‐centrales del Perú se extendieron al norte hacia el Sur de Ecuador e incluso posiblemente hasta Colombia. La mineralización del Mioceno siguen un patrón de distribución muy parecido a la distribu‐ ción del arco magmático Micénico en Ecuador. La distribución espacio‐temporal de los pórfidos de Cu y mi‐ neralizaciones epitermales asociadas dentro de los cinturones metalogénicos del Ecuador y Perú es muy similar. Las zonas donde se intersecan estructuras de rumbo Andino (NEE) con fallas transversales al arco y lineaciones relacionadas con zonas de sutura y/o bloques rotados en el Sur de Ecuador, representan zonas altamente prospectivas para mineralizaciones miocénicas. La ausencia de cobertura volcánicas cuaternaria y sobre todo la actividad erosiva son factores claves para la preservación y la exposición de las rocas miocénicas de tipo‐pórfido en el Sur de Ecuador. En la Cordillera Occidental del Ecuador las mineralizaciones asociadas al pórfido han sido localmente preservadas, mientras en unas zonas se puede observar el núcleo del sistema de pórfido, en otras zonas las partes más importan‐ tes del sistema han sido removidas debido a una mayor erosión. Los sistemas de pórfidos están a menudo asociados con intrusivos dispersos que se formaron en las etapas finales de la formación de grandes batoli‐ tos. Un magmatismo intenso en la corteza superior durante los mayores picos construcción de batolitos posiblemente no es favorable para la formación y preservación de los depósitos asociados con pórfidos, mas bien las mejores condiciones petrogenéticas se dan cuando los fundidos que forman los pórfidos pue‐

vii den ocurrir hacia la parte final de la formación de los batolitos. En Ecuador no se observa una relación es‐ pacio‐temporal directa entre la edad de los depósitos tipo pórfido y la subducción de ridges oceánicos y/o pulso de compresión regional, como se ha propuesto en muchas otras partes en Sudamérica. El basamento cortical en Ecuador consiste de una serie de unidades tectono‐estratigráficas del Paleozoico‐ Mesozoico de afinidad continental y oceánica en la Cordillera Oriental y rocas relacionadas con un plateau oceánico en la Cordillera Occidental y la costa del Ecuador las cuales fueron acrecionadas en el Cretácico Tardío. La sutura paleocontinental es muy difusa y estaría situada entre la Cordillera Oriental y Occidental donde las unidades del basamento están cubiertas por rocas volcánicas del Arco Terciario‐Cuaternario. En el Capitulo 4 se presenta un set de 58 datos isotópicos de Sr, Nd, Pb en roca total llevadas a cabo en rocas volcánicas e intrusivas del Oligoceno Tardío y más jóvenes, expuestas en la Cordillera Occidental y en la Sie‐ rra Central y Austral del Ecuador. Al combinar estos datos isotópicos con datos existentes en rocas volcáni‐ cas del Cuaternario nos da indicios del basamento que nos permiten trazar posibles zonas de sutura en la profundidad. Rocas volcánicas Cuaternarias definen distintos grupos isotópicos (Sr, Nd, Pb) para volcanes que están si‐ tuados ya sea al este y al oeste de la falla regional de Peltetec. Rocas volcánicas e intrusivas del Oligoceno Tardío al Mioceno tardío en la Sierra Sur del Ecuador se sobrelapan isotópicamente con rocas volcánicas del arco actual presente solamente en el Norte de Ecuador, sugiriendo esto que existe una continuidad en las unidades profundas del basamento a lo largo del arco. Contaminación isotópica cortical de rocas del arco Terciario‐Cuaternario toma lugar a niveles de la corteza media‐profunda, excepto para los granitoides del cinturón intrusivo de Cangrejos‐Zaruma donde se registra una prominente contaminación cortical de corte‐ za superior. Composiciones isotópicas del arco magmático en la Sierra Norte y Centro siguen una sistemáti‐ ca a través del arco donde estas evolucionan progresivamente hacia valores 87Sr/86Sr y 207Pb/204Pb mas ra‐ diogénicos y composiciones de 143Nd/144Nd menos radiogénicas a profundidad de corteza media conforme se incrementa la distancia desde la fosa. Esta observación es consistente con la presencia de rocas del pla‐ teau oceánico a lo largo de una amplia zona de sutura bajo el margen paleocontinental como ha sido inferi‐ do ya por estudios sísmicos. En Capítulo 5 se presenta un set de datos completo y exhaustivo consistente en composiciones geoquími‐ cas de las intrusiones y rocas volcánicas de arco del Oligoceno Tardío‐Mioceno Tardío, las cuales están aso‐ ciados en el espacio‐tiempo con mineralizaciones tipo pórfido en Ecuador, el cual se enfoca en el patrón de distribución espacio‐temporal de características geoquímicas adakíticas y explora además la importancia que estas tienen para las mineralizaciones tipo pórfido. La distribución total espacio‐temporal de las carac‐ terísticas adakíticas en las rocas magmáticas de arco que tienen sistemas porfiríticos asociados es semi‐ sistemática; la proporción relativa de magmas adakíticos (valores de Sr/Y elevados) se incrementa cuando la edad decrece y es mayor en la región Norte y Centro en comparación con la zona Sur. Un amplio incre‐ mento en los valores Sr/Y y Sm/Dy a través del tiempo es consistente con un incremento progresivo de la diferenciación magmática a niveles corticales de presión elevada. Valores altos de Sr/Y en rocas magmáticas del Terciario Tardío es principalmente debido a un fuerte empo‐ brecimiento de Y (y de HREE) en los fundidos parentales cuando se tiene concentraciones aproximadamen‐ te constantes de Sr, en las cuales el Y está relacionado con los efectos de fraccionamiento (y/o equilibrio en la restita) de anfíbol, granate y titanita. Mientras el fraccionamiento (y/o equilibrio en la restita) del anfíbol (+/‐ titanita como accesorio) causa que los fundidos silícicos evolucionen hacia composiciones tipo adakíti‐ cas en el Mioceno Temprano‐Medio, el fraccionamiento (y/o equilibrio en la restita) del anfíbol y el granate combinados, ha sido solo ampliamente existente desde el Mioceno Tardío y continua hasta la actualidad. No se observa una asociación preferencial de las características adakíticas con un tipo específico de litología del basamento. Un incremento del grosor de la corteza influencia favorablemente la ocurrencia de carac‐ terísticas adakíticas a escala regional, pero esta última es posteriormente modulada por una serie de pará‐ metros los cuales controlan dinámicamente las estabilidades minerales y los coeficientes de partición mine‐ ral‐fundido a una escala local. Estos parámetros incluyen la profundidad de evolución del magma (presión)

viii en una columna cortical dada y además incluye la composición del fundido (grado de diferenciación y con‐ tenido de agua del fundido). Depósitos de tipo pórfido y epitermales en Ecuador están a menudo asociados con intrusivos dispersos los cuales graban un magmatismo precursor (a la escala de varios millones de años) donde el emplazamiento del pórfido normalmente representa el último evento de intrusión. Los fundidos parentales que forman los pórfidos tienden a evolucionar hacia composiciones mas adakíticas que las intru‐ siones precursoras si hay una diferencia significativa en las edades de su emplazamiento. Al contrario, no hay evidencia de un cambio composicional entre el pórfido y sus intrusiones precursoras si es que la edad relativa entre sus respectivos emplazamientos es pequeña. De esta manera, los cambios composicionales entre el pórfido y el magmatismo precursor, refleja mayormente cambios grandes a lo lar‐ go del tiempo en la composición magmática del arco. El hecho de que los depósitos de tipo pórfido y epi‐ termales en Ecuador se formaron durante el Oligoceno Tardío‐Mioceno Tardío (24‐6 Ma) a lo largo de un gran rango latitudinal (c. 0° a 3°30’S), soporta la idea de que cualquier magma de arco con un volumen sufi‐ ciente tiene el potencial de formar mineralizaciones económicas. En algunos casos los magmas adakíticos pueden sin embargo, reflejar pre‐condiciones tectono‐magmáticas favorables de los fundidos parentales del pórfido para una subsecuente mineralización relacionada con el pórfido.

ix x Résumé étendu Cangrejos; 20.7±0.9 Ma pour un pluton au nord d’Zaruma; 24.04±0.07 Ma pour une intrusion Le travail de cette thèse présente des données porphyrique à Portovelo, et 92.0±1.6 Ma pour géochronologiques concernant la mise en place une intrusion porphyrique à Curiplaya. des intrusions d’âge Tertiaire supérieures en Sauf l'échantillon de Tres Chorreras, dans toutes Equateur, et sur les événements de minéralisa‐ les intrusions (ou les roches sub‐volcaniques) tion et d'altération hydrothermale liés à ses in‐ étudiées, les zircons hérités sont complètement trusions, ainsi que la composition isotopique et absents suggérant la base de la croûte est océa‐ géochimique des roches volcaniques et plutoni‐ nique et appauvrie en zircons; les zircons de type ques associées à l’arc d’âge Oligocène‐Miocène. "antecryst" sont relativement abondants dans plusieurs plutons indiquant que le recyclage d’un Les granitoïdes d'âge Oligocène‐ ancien arc avait pris place. Lorsque les données Miocène et l'influence des facteurs des deux méthodes de datation géochronologi‐ ques, K‐Ar et U‐Pb, coexistent pour un système géodynamiques pour l'arc magmati‐ intrusif, les âges obtenus par les différentes mé‐ que en Equateur thodes sont généralement concordant et dévoi‐ L’Equateur hôte un très grand nombre de grani‐ lent une différence d'âge entre 1‐4 Ma au maxi‐ toïdes et des roches volcaniques liées à l’arc mum, ce qui implique que les âges de K‐Ar peu‐ d’âge Tertiaire, dont les caractéristiques géo‐ vent être utilisé comme des données semi‐ chronologiques sont principalement basées sur précises pour l’arc magmatique d’âge Tertiaire en les données de la méthode de datation K‐Ar (et Équateur à l'échelle régionale. les traces de fissions sur des zircons). Le chapitre La répartition spatio‐temporelle des intrusions et 1 de cette thèse présente les premières données roches volcaniques d'âge Tertiaires indique un vif régionales des âges U‐Pb des zircons provenant échauffement de magmatisme d’âge Oligocène des intrusions plutoniques et porphyriques de la terminal jusqu’au Miocène inférieure et moyen cordillère Ouest et le sud de la région de Sierra en Équateur, comprenant l'éruption régionale (Fig. 1), permettant une calibration temporale des ignimbrites et la construction des batholites robuste de l’histoire intrusive d'âge Tertiaire en dans un champ de contrainte de tension, généra‐ Equateur. lement à une pente constante du slab. L’initiation Les zircons étaient datés avec deux méthodes, de l’événement d’échauffement régionale coïnci‐ soit parMS TI (spectrométrie de masse par ther‐ de dans le temps avec une accélération impor‐ mo‐ionisation), soit par LA‐MC‐ICP‐MS (émission tante dans le taux de convergence des plaques en plasma induit couplée à la spectrométrie de Sud Amérique et Farallon/Nazca, suggérant une masse et laser ablation). Du nord au sud, les âges relation positive entre une convergence très ra‐ suivants ont été obtenus: 12.87±0.05 Ma pour la pide des plaques, génération nde la fusio partielle batholite d’Apuela à Cuellaje, pénétrée par des dans l'asthénosphère, le flux de la fusion entre dykes porphyriques de 9.01±0.06 Ma à Junin; manteau et croûte, et la productivité de l'arc 25.5±0.7 Ma pour le pluton de Telimbela centra‐ magmatique en Équateur. le; 21.46±0.09 Ma et 21.22±0.17 Ma pour le plu‐ Cela pourrait être envisagée par un taux plus éle‐ ton Balsapamba et une intrusion du dyke porphy‐ vé du fluide généré du slab subducté dans un vo‐ rique dans la zone d’El Torneado respectivement; lume donné dans le coin mantellique, et/ou par 14.84‐15.33 Ma pour le batholite de Chaucha et un changement dans la dynamique des flux as‐ 9.79±0.03 Ma pour une intrusion porphyrique à thénosphériques où des anomalies thermiques Tunas; 20.26±0.07 Ma et 19.89±0.07 Ma pour les positives se développent dans le coin mantellique deux porphyres à Gaby‐Papa Grande; 7.13±0.07 et les taux de reconstitution du matériel du man‐ Ma pour un dôme intra‐caldeira du centre volca‐ teau fertile augmente en réponse du retour nique de Quimsacocha; 30.7±0.7 Ma pour une roche subvolcanique de Saraguro à Tres Chorre‐ ras; 16.04±0.04 Ma pour une intrusion porphyri‐ que à El Mozo ; 26.0±0.7 Ma pour un pluton à

xi

Figure 1: Carte géologique de la région des Cordillères d'Equateur, montrant les éléments géologiques principaux de l'Equateur et l'arc magmatique d'âge Tertiaire. La figure au‐dessous à gauche montre la situation géodynamique du bassin de Panama. Adapté par Litherland et al. (1994), Steinmann (1997), Dunkley & Gaibor (1997), McCourt et al. (1997), Pratt et al. (1997), Hughes et al. (1998), Meschede & Barckhausen (2001), et Palacios et al. (2008). xii du flux induit. L'intensification des transferts de La ceinture métallogénique d'âge chaleur de la conduction et l’advection dans la Miocène en Equateur croûte pourrait déclencher un processus de rela‐ tion positive tectono‐magmatique et thermique, Le chapitre 2 présente les âges calculés grâce aux qui peut faciliter l’intensification de la fusion par‐ méthodes géochronologiques dans la molybdéni‐ tielle de la croûte et le volumineux stockage du te selon le système Re‐Os et dans la titanite selon magma à des niveaux supérieurs, menant à la le système U‐Pb; ces âges sont liés à la minérali‐ construction des batholites, et/ou l’éruption des sation/altération hydrothermale associée avec ignimbrites en Équateur au cours de l'Oligocène des intrusions des gisements de porphyre cupri‐ terminal à Miocène inferieur‐moyen. fère ou épithermaux d’âge Oligocène et Miocène en Équateur.

Figure 2: Distribution spatio‐temporelle des gisements d'âge Miocène associés aux intrusions d'âge Oligocène‐Miocène en Equateur. Il y a de pics de la minéralisation dans le Miocène inférieur avec un deuxième pic dans le Miocène supé‐ rieur. Dans un système batholitique donné (Apuela, Balsapamba‐Telimbela, Chaucha) la minéralisation se manifeste dans un stage final de l'évolution magmatique du batholite par rapport à son construction initiale (après c. 5‐15 m.y.). Pour comparaison les pulses compressives (I = Inca; Q = Quechua) en Equateur (boxes noires; Hungerbühler et al. 2002) et en Pérou (boxes grises: Noble & McKee 1999; boxes blanches: Benavides ‐Cáceres 1999) sont montrées à droite.

xiii

La molybdénite associée à l’altération potassique sites très favorables pour la minéralisation. L'ab‐ et phylliteuse à Junin (gisement porphyre Cu‐Mo) sence de la couverture volcanique quaternaires a donné des âges de 6.63±0.04 Ma et 6.13±0.03 et l'érosion globale des niveaux favorables sont Ma. Les âges calculés selon le système chronolo‐ des paramètres clés pour préserver et exposer gique Re‐Os dans les molybdénites associées à généralement les gisements de porphyres cupri‐ l’altération potassique dans les systèmes porphy‐ fères et épithermaux d’âge Miocène dans le sud riques de Telimbela et Balsapamba sont de de l'Équateur. Dans la Cordillère de l'Ouest de 19.2±0.1 Ma et 21.5±0.1 Ma, respectivement. l'Équateur la minéralisation des porphyres cupri‐ Dans les systèmes porphyriques de Cu‐Mo à fères à été localement préservée, tandis que les Chaucha, les âges obtenus dans des molybdénites cœurs profonds érodés des systèmes porphyri‐ associées aux altérations potassiques et phylli‐ ques sont exposés à d'autres endroits et des par‐ teuses selon le système Re‐Os sont de 9.92±0.05 ties importantes de la minéralisation ont été en‐ Ma (à Tunas‐Naranjos) et 9.5±0.2 Ma (à Gur‐Gur), levés. respectivement. Dans le système porphyrique Alors que les complexes de batholites peuvent Au‐Cu de Gaby, un âge de 20.6±0.1 a été calculé marquer structurellement les sites favorables à la pour la molybdénite selon le système chronologi‐ minéralisation, de vaste magmatisme dans la que Re‐Os pour des brèches hydrothermales sul‐ croûte supérieure pendant les pics de la cons‐ furées (éventuellement associés à une altération truction des batholites peut être désavantageux phylliteuse), et un âge de 20.17±0.16 Ma selon le pour la formation et la préservation des gise‐ système chronologique U‐Pb pour une titanite ments de porphyre cuprifères. En revanche, le associé à l’altération de type Na‐Ca a été obte‐ préconditionnement pétrogénétique favorable nue. Au gisement polymétalliques de Tres Chor‐ des liquides porphyriques parentaux peut se pro‐ reras, les âges obtenus selon le système chrono‐ duire vers la phase finale d'assemblage des ba‐ logique Re‐Os dans les molybdénites sont à tholites. Mais peut‐être applicable pour quelques 12.93±0.07 Ma et 12.75±0.07 Ma, et sont asso‐ gisements, une générale association spatio‐ ciées à une brèche hydrothermale liée à une in‐ temporelle entre la formation de gisements et les trusion et une veine polymétalliques, respecti‐ pulses de compression régional ou la subduction vement. La molybdénite associée à l'altération de des chaînes montagneuses sous‐marines n'est type Na‐Ca dans le système porphyrique Au‐Cu pas observée en l'Équateur (Fig. .2) de Cangrejos a donné un âge de 23.5±0.1 Ma. Les nouvelles données géochronologiques nous La composition isotopique des mag‐ permettent de déduire que la ceinture métallo‐ mas d'âge Oligocène‐Miocène et les génique d’âge Miocène au nord du Pérou s'étend du nord vers le sud de l'Équateur, et potentielle‐ domaines isotopiques de la croûte ment plus au nord jusqu'à la Colombie. La miné‐ équatorienne ralisation d’âge Miocène suit de près la réparti‐ En Equateur, dans la Cordillère Orientale, la base tion de l’arc magmatique d’âge Miocène en Equa‐ de la croûte comprend un ensemble d’unités tec‐ teur, qui se caractérise souvent par des déforma‐ tono‐stratigraphiques de la plupart d’âge Paléo‐ tions syn‐magmatiques. Sur une échelle régiona‐ zoïque et Mésozoïque d'affinité à la fois conti‐ le, la distribution spatio‐temporelle des gise‐ nentale et océanique. Des unités du plateau ments de porphyre cuprifères et épithermaux océanique accumulés au Crétacé supérieur for‐ associée dans les segments de la ceinture métal‐ ment la base de la croûte dans la Cordillère Occi‐ logénique équatorienne et péruvienne est simi‐ dentale et la région d’avant‐arc. La zone de sutu‐ laire. re paléo‐continentale est située entre l'Est et L’intersection des structures Andines (NNE‐) avec l'Ouest de la série de Cordillère où des unités de de failles transversales et des traits liés à des la base de la croûte sont couverts par des roches géométries de zones de sutures et de rotation de volcaniques du Tertiaire et Quaternaire. Un grand blocs dans le sud de l'Equateur représentent des nombre d'information sur la géochimie des ro‐

xiv ches volcaniques du Quaternaire existe pour l'arc de la Zone Volcanique du Nord dans le nord de l'Equateur, alors que les séquences de la couver‐ ture Tertiaire en Équateur centrale et sud sont mal caractérisées isotopiquement. Le chapitre 3 présente un ensemble de 58 nouveaux résultats de roche totales des compositions isotopiques de Sr, Nd et Pb des échantillons Tertiaire de l’arc volcanique et des intrusions associées de la Cor‐ dillère Occidentale et du sud de la région de la Sierra équatorienne. La combinaison de ce nouvel ensemble de données avec les données existan‐ tes sur l’arc volcanique Quaternaire nous permet de suivre les unités basales de la croûte de la zo‐ ne de suture du Crétacé terminal en profondeur. L’arc volcanique d’âge Quaternaire définit des groupes isotopiques distincts pour des volcans situés à l'est et à l'ouest de la faille Peltetec. Les roches volcaniques et les intrusions de la région sud équatorienne de Sierra d’âge Oligocène ter‐ minal‐Miocène terminal chevauchent isotopi‐ quement avec des roches volcaniques récentes à l’est de la faille Peltetec dans le nord de l'Equa‐ teur suggérant ainsi une continuité des unités basales de la croûte similaires en profondeur. Les granitoïdes d’âge Oligocène‐Miocène de la Cordillère Occidentale et sur ses contreforts occi‐ dentaux montrent des compositions isotopiques les plus primitives de Sr et Nd identifiées à ce jour dans l’arc magmatique équatorien d’âge Tertiai‐ re‐Quaternaire; les unités primitives du plateau océanique du Crétacé constituent leurs assimilant en profondeur, entraînant de ces magmas d’arc de devenir plus primitifs isotopiquement avec l'assimilation de la croûte. 87 86 206 204 Figure 3: Diagrammes de Sr/ Sr, εNdinitial, Pb/ Pb, La contamination isotopique crustale du magma 207 204 d’arc d’âge Tertiaire‐Quaternaire a lieu principa‐ et Pb/ Pb vs. Sr/Y; Sr/Y est utilisé comme indica‐ lement à des niveaux profonds à moyens de la teur d'évolution magmatique dans le croûte supérieur vs. inférieur (Sr/Y >30 pour le dernier). Dans l'ordre de croûte à l'exception de la ceinture intrusive des leurs distribution géographique, les centres magmati‐ granitoïdes du Cangrejos‐Zaruma dans le sud de ques forment des groupes isotopiques subparallèles l'Équateur, où plus éminente assimilation de ma‐ pour des valeurs de Sr/Y >30 ce qui implique que les tériau de la croûte supérieure est caractérisé par processus de AFC (assimilation et cristallisation frac‐ une composition de Sr et Pb très radiogéniques, tionnelle) incluent des unités différents à la base de la et une composition isotopique de Nd peu radio‐ croûte. En plus, il y a d'évolution magmatique dans la géniques (Fig. 3). Les compositions isotopiques croûte supérieur pour le Tertiaire supérieur (particuliè‐ du Sr, Nd et Pb des magmas d'arc dans le nord‐ rement pour les intrusions de Cangrejos‐Zaruma) dont central de l'Équateur suivent un schéma systéma‐ l'assimilation comprend des lithologies caractérisées tique dans l'ensemble d’arc où ils évoluent pro‐ par des compositions plus radiogéniques en Sr et moins radiogéniques en Nd. gressivement vers 87Sr/86Sr et

xv 207Pb/204Pb plus radiogéniques, et une composi‐ sions associées dans l'espace et dans le temps tion moins radiogénique en 143Nd/144Nd du pro‐ avec les porphyres cuprifères et la minéralisation fond au moyen niveau de la croûte avec la crois‐ épithermal en Equateur, complétées par des sance de la distance depuis la tranchée. Ceci est données en plusieurs formations de l'arc volcani‐ cohérent avec la poussée régionale du matériel que du même âge. Notre objectif est de décrire la des plateaux océanique accrété le long d'une vas‐ distribution spatio‐temporelle des compositions te zone de suture en dessous de la marge paléo‐ "adakite‐like" dans le contexte de l'évolution continentale comme précédemment déduit à géochimique d'arc du Tertiaire terminal, et d'ex‐ partir des études sismiques. plorer son importance pour les intrusions asso‐ ciées à la minéralisation cuprifère/aurifère en La géochimie des granitoïdes et ro‐ Équateur. ches volcaniques d'âge Oligocène‐ La plupart des intrusions représentent des tonali‐ Miocène et la distribution temporelle tes, granodiorites et diorites quartzeuse modé‐ des compositions "adakite‐like" rément à fortement différenciées et portant de l'hornblende ± biotite, et font souvent partie de Enfin, le chapitre 4 présente un ensemble de plus grands complexes batholitiques d’âge Oligo‐ données de l’Oligocène terminal au Miocène su‐ cène‐Miocène; les roches volcaniques allant périeur de la composition géochimique des intru‐

Figure 4: Diagrammes des éléments de traces et leurs rapports vs. l'âge. La distribution des éléments de traces impli‐ que un épaississement progressif de la croûte pendant l'Oligocène‐Miocène. En plus, des facteurs pétrogénétiques (fractionnement de l'amphibole) contrôlent l'appauvrissement extrême en Y pour les compositions magmatiques silici‐ ques. xvi d'une composition andésitique à dacitique‐ rhyolitique. L'ensemble spatio‐temporel de la distribution des magmas de type "adakite‐like" dans l'arc équatorien est semi‐systématique; la proportion relative des magmas "adakite‐like" augmente avec la diminution de l'âge, et est plus élevé dans le centre‐nord que dans le sud de l'Équateur. Les centres magmatiques caractérisée par, en partie, un magmatisme "adakite‐like" sont principalement encaissés par la Cordillère Occidentale et comprennent Balsapamba (c. 21 Ma), Apuela‐Junin (13‐6 Ma), Chaucha (vers 10 Ma), et Quimsacocha (7 Ma). Les caractéristiques "adakite‐like" (haute Sr/Y) des magmas d’arcs équatoriens d’âge Tertiaire terminal sont princi‐ palement dues à un fort appauvrissement en Y (et les terres rares lourdes) de leurs liquides pa‐ rentaux en gardant les teneurs plus ou moins constantes en Sr, et sont liés au fractionne‐ ment/effets d’équilibration de restite d'amphibo‐ le, grenat, et titanite. Du Miocène inférieur au moyen, le fractionne‐ ment/l'équilibration de restite d’amphibole (± titanite comme accessoire) a causé l’évolution du liquide silicique vers une composition "adakite‐ like". La combinaison du fractionnement/ l’équilibration de restite d’amphibole et grenat dans les magmas d'arc équatorien n'a été généra‐ lisée que depuis le Miocène supérieur. L'appau‐ vrissement de Y par fractionnement/équilibration de restite d'amphibole est très efficace mais seu‐ lement pour les liquides de compositions silici‐ ques. Par contre, le fractionnement/équilibration de restite de grenat produit un appauvrissement fort de Y déjà dans les liquides de compositions plus mafiques, c'est à dire, pendant la phase ini‐ tiale de différenciation. Le fractionnement des plagioclases dans la croûte supérieure affecte certains, mais pas tous les magmas d’arc d’âge Tertiaire dans le sud de l'Equateur; il est d'une importance pétrogénétique mineure pour les in‐ trusions d’âge Miocène de la Cordillère Occiden‐ tale dans le nord‐centre de l'Equateur. Une asso‐ ciation de caractéristiques préférentielles des

Figure 5: Distribution de Sr/Y vs. Y pour les intrusions porphyriques d'âge Tertiaire tardif et les roches intru‐ sives phanéritiques associées avec les porphyres en Equateur. Sauf le porphyre de Cangrejos, tous les porphyres ne montrent pas d'évidence pour l'évolution des liqui‐ des parentaux dans la croûte supérieure (fractionnement de plagioclase). Par contre, les liquides parentaux (sauf Can‐ grejos et Gaby) sont caractérisé par le fractionnement de l'amphibole ± titanite ± grenat aux niveaux plus profonds de la croûte (et/ou les liquides parentaux sont plus riches en H2O) en montrant des compositions "adakite‐like".

xvii compositions "adakite‐like" avec une lithologie Hughes, R.A., Bermudez, R., Espinel, G. (1998): Mapa de la base de la croûte ne peut être observée. geológico de la Cordillera Occidental del Ecuador entre 0°‐1°S, escala 1:200.000. CODIGEM‐Ministerio de En‐ Une variation systématique des éléments traces ergía y Minas‐BGS publs., Quito. (Sr, Y, REE) dans le temps sont révélateurs d’un Hungerbühler, D., Steinmann, M., Winkler, W., Sew‐ progressif épaississement de la croûte équato‐ ard, D., Egüez, A., Peterson, D. E., Helg, U., Hammer, C. rienne de l'Oligocène terminal au Miocène termi‐ (2002): Neogene stratigraphy and Andean geodynam‐ nal (Fig. 4). Tout en augmentant l'épaisseur de la ics of southern Ecuador. Earth Science Reviews 57; 75– croûte influence favorablement l'apparition des 124. compositions "adakite‐like" à l'échelle régionale; Litherland, M., Aspden, J. A., Jemielita, R. A. (1994): ces derniers sont en outre modulées par un en‐ The metamorphic belts of Ecuador. Overseas Memoir semble de paramètres qui contrôlent dynami‐ 11. BGS, Keyworth. quement les stabilités des minéraux et les coeffi‐ cients de partage minéral‐liquide à l'échelle plu‐ McCourt, W. J., Duque, P., Pilatasig, L. F. and Villago‐ tôt locale. Il s'agit notamment de l'évolution du mez, R. (1997): Mapa geológico de la Cordillera Occi‐ dental del Ecuador entre 1° ‐ 2° S., escala 1/200.000. magma en profondeur (pression) dans une co‐ CODIGEM‐Min. Energ. Min.‐BGS publs., Quito. lonne donnée de la croûte et la composition du liquide (degré de différenciation et la teneur en Meschede, M. & Barckhausen, U. (2001): The relation‐ eau). Celui‐ci indique notamment la migration du ship of the Cocos and Carnegie ridges: age constraints magmatisme crustal à une plus grande profon‐ from paleogeographic reconstructions. International Journal of Earth Sciences; 90 386‐392. deur, et/ou en augmentant le contenu en eau du système magmatique. Noble, D. C. & McKee, E. H. (1999): The Miocene met‐ allogenic belt of central and northern Perú. SEG Spe‐ Des changements systématiques dans la compo‐ cial Publication 7; 155‐193. sition entre les intrusions porphyriques et des précurseurs intrusifs ne sont pas enregistrés si la Palacios, O., Pilatasig, L., Sanchez, J., Gordon, D., Shaw, R., Feininger, T. (2008): Mapa geologico binacional différence de temps entre leur mise en place est region sur del Ecuador y norte del Peru. Ingeomin, 1 : faible (Fig. 5). Le fait que la minéralisation de type 500,000. porphyre cuprifère et épithermal "high sulfida‐ tion" en Équateur existe de l'Oligocène terminal Pratt, W. T., Figueroa, J. F., Flores, B. G. (1997): Mapa entier à Miocène supérieur (24‐6 Ma) et une lar‐ geologico de la Cordillera Occidental del Ecuador entre 3°‐4°S. escale 1/200.000. CODIGEM‐Min. Energ. Min.‐ ge latitude de grande taille (c. 0° à 3° 30'S) sou‐ BGS publs., Quito. tient l'idée que toutes les magmas d'un arc de volume suffisant ont le potentiel pour causer de Steinmann, M. (1997): The Cuenca basin of southern minéralisation liée aux intrusions. Le magmatis‐ Ecuador:tectono‐sedimentary history and the Tertiary me de composition "adakite‐like" peut, cepen‐ Andean evolution. PhD Thesis, Institute of Geology ETH Zürich, Switzerland, 176 p. dant, indiquer un favorable environnement tec‐ tono‐magmatique et un préconditionnement fa‐ vorable des liquides porphyriques parentaux pour la minéralisation de type porphyre cuprifère.

Références Benavides‐Cáceres, V. (1999): Orogenic evolution of the Peruvian Andes: The Andean cycle. In: Skinner, B. J. (ed.), Geology and ore deposits of the central Andes. SEG Special Publication 7; 61–107. Dunkley, P. N. & Gaibor, A. (1997): Mapa geologico de la Cordillera Occidental del Ecuador entre 2°‐3° S. es‐ cale 1/200.000. CODIGEM‐Min. Energ. Min.‐BGS publs., Quito.

xviii CHAPTER I THEORETICAL BACKGROUND AND AIMS OF THESIS

melt batch, the silicate melt will become de‐ Introduction pleted in chalcophile metals (such as Cu and Au), Porphyry Cu deposits and associated epithermal thus decreasing its potential for subsequent por‐ and polymetallic vein mineralization, hereafter phyry Cu‐Au mineralization. Although mass bal‐ referred to as "porphyry‐related ore deposits", ance calculations indicate that, in principle, any form as parts of hydrothermal systems related to arc magma (average andesite Cu content 60 ppm; fluid exsolution from shallow crustal intrusions Cline & Bodnar 1991) may contribute to the for‐ (e.g., Seedorff et al. 2005). They can be found in mation of a porphyry‐related ore deposit as long as the integrated magmatic system comprises a subduction zone settings worldwide, and are re‐ 3 garded ase th product of a series of common‐ sufficient volume (≥100 km ; Cline & Bodnar place geologic processes which have to combine 1991), parental melts related to large porphyry‐ favorably to eventually result in economic miner‐ related ore deposits may be expected to be alization (e.g., Tosdal & Richards 2001). Parental highly oxidized, sulfate‐dominated silicate melts melts to porphyry intrusions ultimately derive whose metal budget has not been substantially from the supra‐slab mantle wedge, the latter depleted by metal loss to immiscible sulfide melts fluxed by a volatile‐rich slab component. Subse‐ in or close to the magma source region (Sillitoe quent lower to mid‐crustal magma evolution of 2000; Mungall 2002). porphyry parental melts produces volatile‐ Porphyry‐related ore deposit distribution and size enriched andesitic or more differentiated melt is diachronous through time and space, implying compositions which then ascend to upper crustal that certain tectonomagmatic environments are levels where porphyry intrusive and associated particularly prolific (or unfavorable) for maximiz‐ hydrothermal systems may form. The localization ing the potential of intrusion‐related mineraliza‐ of the latter is often structurally controlled (e.g., tion. Spatio‐temporal clusters of porphyry‐ Richards 2003), although this is not always the related ore deposits may be due to favorable ex‐ case (Sillitoe 2000). posure and preservation conditions, and/or in‐ As far as magma sources and early differentiation creased rates of deposit formation (Wilkinson & Kesler 2009). Considering the latter, the in‐ stages are concerned, a high fO2 is often inferred for porphyry parental melts with the potential to creased abundance of porphyry‐related ore de‐ form high‐tonnage ore deposits (e.g., Sillitoe posits (or their overall larger tonnage) may reflect 2000; Mungall 2002). Depending on the prevail‐ favorable tectonomagmatic settings which, in part, might derive from special geodynamic envi‐ ing fO2, S as a component of a silicate melt com‐ monly occurs in variable proportions of sulfide ronments (Tosdal & Richards 2001). Amongst and sulfate where the melt S solubility is signifi‐ others, the subduction of seamount chains has cantly higher if sulfate, rather than sulfide, forms been proposed to show a positive spatio‐ the dominant S species (e.g. Jugo et al. 2005). If temporal correlation with porphyry‐style miner‐ the S content of a silicate melt aat supr ‐liquidus alization (e.g., in the southern and central Andes; conditions exceeds the melt S solubility, S‐rich Rosenbaum et al. 2005; see also Cooke et al. immiscible liquids will form, which scavenge 2005). Constraining potentially favorable condi‐ lithophile and chalcophile elements from the sili‐ tions for porphyry‐related mineralization is of cate melt (Jugo et al. 2005). If, by virtue of their major interest for the design of regional mineral higher density, S‐rich immiscible melt globules exploration campaigns for this type of ore de‐ coalesce and fractionate from a given silicate posit.

1 In this context, Thieblémont et al. (1997) note Since the works of Thieblémont et al. (1997) and that intrusions associated with porphyry‐style Oyarzun et al. (2001), the notion to associate mineralization often tend to be of "adakitic" "adakitic" magmatism with porphyry‐related ore composition, potentially implying that “adakitic” deposits has gained some appeal in the economic features might be used as a local‐regional explo‐ geology literature (see review by Richards & Ker‐ ration tool for porphyry‐related ore deposits. The rich 2007, and references therein). However, the term "adakite" sensu stricto refers to la specia conclusions of Oyarzun et al. (2001) have been geochemical composition of island arc magmas vigorously debated (Oyarzun et al. 2002; Rabbia indicative of parental melt evolution outside the et al. 2002; Richards 2002; see also Richards & stability field of plagioclase, and melt equilibra‐ Kerrich 2007), in part because a straightforward tion with residual garnet (Defant & Drummond "adakite"‐slab melt correlation cannot be unam‐ 1990). Defant & Drummond (1990) argue that the biguously demonstrated in a continental arc set‐ appropriate P‐T conditions to stabilize or destabi‐ ting where similar chemical signatures (referred lize these mineral phases in an island arc setting to as adakite‐like) may also be acquired through associated with a thin layer of continental crust crustal magma evolution (Richards & Kerrich would apply to slab melting. Modern island arc 2007). Moreover, even in island arc settings ada‐ subduction zones are usually characterized by kite‐like features of arc magmas may be pro‐ low geothermal gradients such that the downgo‐ duced by other processes than slab melting, ei‐ ing slab dehydrates before it melts; augmenting ther in the mantle wedge (e.g., Castillo et al. the local geothermal gradient sufficiently to facili‐ 1999) and/or in the crust (Alonso‐Perez et al. tate slab melting prior to significant slab dehydra‐ 2009). Consequently, the (occasionally) observed tion may only apply to a number of special geo‐ association of adakite‐like magma chemistry and dynamic settings such as subduction zone initia‐ porphyry‐related ore deposits does not necessar‐ tion, subduction of young, hot oceanic litho‐ ily relate to a specific process in the magma sphere (<25 Ma), or, possibly, flat subduction source, but may also reflect certain petrogenetic (e.g., Defant & Drummond 1990; Gutscher et al. processes of crustal magma evolution such as 2000). progressive volatile enrichment, which are equally regarded as favorable for porphyry‐style The empirical observation of Thieblémont et al. mineralization (Sillitoe 2000; Rohrlach & Loucks (1997) might imply that special geodynamic set‐ 2005; Richards & Kerrich 2007). tings facilitating slab melting (of which “adakitic” chemical compositions may be indicative of, but The Late Tertiary Ecuadorian arc system at the see below) favor the formation of porphyry‐ NW South American margin hosts a number of related ore deposits. As slab melting may be a moderate‐tonnage porphyry‐related ore deposits highly effective means of oxidizing the upper (Prodeminca 2000a, b), and regionally connects mantle in the supraslab region, a positive correla‐ with the central‐northern Peruvian Tertiary arc tion between slab melting and porphyry‐related whose Miocene metallogenic belt is of major ore deposit formation had also been envisaged economic importance (e.g., Noble & McKee from theoretical considerations based on ther‐ 1999). Porphyry‐related ore deposits along the modynamic modeling (Mungall 2002). Indeed, Ecuadorian margin formed on the background of Oyarzun et al. (2001) speculate that large por‐ a geodynamic setting characterized by a high de‐ phyry‐related ore deposits (partly associated with gree of complexity involving Late Cretaceous "adakitic" intrusions) of Late Eocene to Early Oli‐ oceanic terrane collision and major strike‐slip gocene age in Chile formed in a special geody‐ partitioning in the upper plate (e.g., Vallejo et al. namic setting (flat subduction) allowing slab 2006), the Late Oligocene break‐up of the Faral‐ melting to take place; in contrast, non‐“adakitic” lon plate and subsequent subduction of newly Paleocene to Early Eocene porphyry‐related ore formed Nazca seafloor, abandoned spreading deposits in Chile are smaller in tonnage, and centers, and oceanic fracture zones at the Ecua‐ might be related to "standard" arc magmatism dorian trench (e.g., Lonsdale 2005), and collision where slab melting does not contribute to arc of the Carnegie Ridge seamount chain with the magma genesis (Oyarzun et al. 2001). margin since the Late Miocene (e.g., Michaud et

2 al. 2009). The overall character of arc magmatism and on their significance for porphyry‐related seems to shift from dominantly non‐adakitic to ore deposits. adakite‐like in the Late Miocene, possibly in re‐ (3) Where appropriate in a given chapter of this sponse to the changing geodynamic regime, al‐ thesis, I test spatio‐temporal correlations of though the timing of the change is only loosely ore deposit formation, variations in arc constrained (Chiaradia et al. 2004, 2009). magma chemistry, and geodynamic changes The highly dynamic nature of the Tertiary Ecua‐ at the Late Tertiary Ecuadorian margin to dorian margin represents an opportunity to study identify potential feedback mechanisms. This the complex interactions between geodynamic includes a critical review of the inferred geo‐ setting, arc magmatism, and ore deposit forma‐ dynamic evolution of the Tertiary Ecuadorian tion. The principal aim of this thesis is to evaluate arc system, and an adjustment of published the mutual relevance of these different factors convergence parameters to the Ecuadorian for each other. As the amount of available state‐ margin (parts of chapters 2 and 3; see also of‐the‐art geochronologic and geochemical data Appendix of Chapter 2). A short synthesis of (outside of this thesis) on Tertiary arc magmatism the results of this analysis is presented in and ore deposits in Ecuador is very limited, the Chapter 6. present work can only serve as a first step to‐ wards a better understanding of the Tertiary Ec‐ References uadorian arc magmatic evolution. Alonso‐Perez, R., Müntener, O., Ulmer, P. (2009): Ig‐ In detail, this thesis aims to address the following neous garnet and amphibole fractionation in the roots issues: of island arcs: experimental constraints on andesitic liquids. Contributions to Mineralogy and Petrology (1) A robust, regional geochronologic framework 157; 541‐558. (as opposed to potentially disturbed ages re‐ lying on the K‐Ar isotopic system) for the Ec‐ Chiaradia, M., Fontboté, L., Beate, B. (2004): Cenozoic uadorian arc segment and its porphyry sys‐ continental arc magmatism and associated mineraliza‐ tems has not been established yet. This work tion in Ecuador. Mineralium Deposita 39; 204–222. presents robust zircon and titanite U‐Pb (ID‐ Chiaradia, M., Müntener, O., Beate, B., Fontignie, D. TIMS, LA‐MC‐ICP‐MS), molybdenite Re‐Os, (2009): Adakite‐like volcanism of Ecuador: lower crust and biotite as well as alunite 40Ar/39Ar (results magmatic evolution and recycling. Contributions to were pending during thesis compilation, but Mineralogy and Petrology 158; 563‐588. will be available for subsequent manuscript Cline, J. S. & Bodnar, R. J. (1991): Can economic por‐ editing) mass spectrometric data allowing the phyry copper mineralization be generated by a typical dating of intrusive and hydrothermal pulses calc‐alkaline melt? Journal of Geophysical Research of several Ecuadorian porphyry systems on a 96, 8113–8126. regional scale. These data are presented in Cooke, D. R., Hollings, P., Walshe, J. L. (2005): Giant Chapters 2 (magmatism) and 3 (hydrothermal porphyry deposits: characteristics, distribution, and systems). tectonic controls. Economic Geology 100; 801‐818. (2) Building on a pilot study by Chiaradia et al. Defant, M. J. & Drummond, M. S. (1990): Derivation of (20004), this thesis provides new and extends some modern arc magmas by melting of young sub‐ existing datasets on Tertiary porphyry‐related ducted lithosphere. Nature 347; 662‐665. arc magma isotopic compositions (Sr, Nd, Pb; Gutscher, M.‐A., Maury, R., Eissen, J.‐P., Bourdon, E. Chapter 4) and geochemistry (multi‐element (2000): Can slab melting be caused by flat subduction? XRF, LA‐ICP‐MS; Chapter 5). These data may Geology 28; 535‐538. be used to track heterogeneous crustal Jugo, P. J., Luth, R. W., Richards, J. P. (2005): An ex‐ basement units at depth, and to broadly con‐ perimental study of the sulfur content in basaltic melts strain the petrogenetic features of Tertiary saturated with immiscible sulfide or sulfate liquids at arc magmatism. Particular emphasis is placed 1300°C and 1.0 GPa. Journal of Petrology 46; 783‐798. on the generation of adakite‐like features,

3 Lonsdale, P. (2005): Creation of the Cocos and Nazca Richards, J. P. (2003): Tectono‐Magmatic Precursors plates by fission of the Farallon Plate: Tectonophysics, for Porphyry Cu‐(Mo‐Au) Deposit Formation. Ec Geol. v. 404, p. 237‐264. 98; 1515‐1533. Michaud, F., Witt, C., Royer, J. Y. (2009): Influence of Richards, J. P. & Kerrich, R. (2007): Adakite‐like rocks: the subduction of the Carnegie volcanic ridge on Ec‐ their diverse origins and questionable role in metal‐ uadorian geology: reality and fiction. In: Kay, S. M., logenesis. Economic Geology 102; 537‐376. Ramos, ,V. A. Dickinson, W. R. (eds.), Backbone of the Rohrlach, B. D. & Loucks, R. R. (2005): Multi‐million‐ Americas: shallow subduction, plateau uplift, and year cyclic ramp‐up of volatiles in a lower crustal ridge and terrane collision. Geological Society of magma reservoir trapped below the Tampakan cop‐ America Memoir 204; doi: 10.1130/2009.1204(10). per‐gold deposit by Mio‐Pliocene crustal compression Mungall, J. E. (2002): Roasting the mantle: slab melting in the southern Philippines. In: Porter, T. M. (ed.), Su‐ and the genesis of major Au and Au‐rich Cu deposits. per Porphyry Copper & Gold Deposits: A Global Per‐ Geology 30; 915‐918. spective; PGC Publishing, Adelaide, v. 92; 36 ‐407. Noble, D. C. & McKee, E. H. (1999): The Miocene met‐ Rosenbaum, G., Giles, D., Saxon, M., Betts, P.G., allogenic belt of central and northern Perú. SEG Spe‐ Weinberg, R.F., Duboz, C. (2005): Subduction of the cial Publication 7; 155‐193. Nazca Ridge and the Inca Plateau: insights into the formation of ore deposits in Peru. Earth and Planetary Oyarzun, R., Marquez, A., Lillo, J., Lopez, I., Rivera, S. Science Letters 239; 18–32. (2001): Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal Seedorff, E., Dilles, J. H., Proffett, J. M. Jr., Einaudi, M. calc‐alkaline magmatism. Mineralium Deposita 36; T., Zurcher, L., Stavast, W. J. A., Johnson, D. A., Barton, 794‐798. M. D. (2005): Porphyry deposits: characteristics and origin of hypogene features. Economic Geology 100th Oyarzun, R., Marquez, A., Lillo, J., Lopez, I., Rivera, S. Anniversary Volume; 251‐298. (2002): Reply to Discussion on "Giant versus small porphyry copper deposits of Cenozoic age in northern Sillitoe, R. H. (2000): Gold‐rich porphyry deposits: de‐ Chile: adakitic versus normal calc‐alkaline magmatism" scriptive and genetic models and their role in explora‐ by Oyarzun et al. (Mineralium Deposita 36; 794‐798, tion and discovery. Society of Economic Geologists 2001). Mineralium Deposita 37; 791‐794. Reviews 13; 315 – 345. Prodeminca (2000a) Evaluacion de distritos mineros Thiéblemont, D., Stein, G., Lescuyer, J.‐L. (1997): del Ecuador, vol 2—Depositos epitermales en la Cor‐ Gisements épithermaux et porphyriques: la connexion dillera Andina. UCP Prodeminca Proyecto MEM BIRF adakite. C. R. Academy of Sciences, Paris, Sciences de 36–55 EC, Quito, Ecuador la terre et des planets/Earth and Planetary Sciences 325; 103‐109. Prodeminca (2000b) Evaluacion de distritos mineros del Ecuador, vol 4—Depositos porfidicos y epi‐ Tosdal, R.M. & Richards, J. P. (2001): Magmatic and mesotermales relacionados con intrusiones de las structural controls on the development of porphyry Cordilleras Occiental y Real. UCP Prodeminca Proyecto Cu±Mo±Au deposits. Reviews in Economic Geology 14; MEM BIRF 36–55 EC, Quito, Ecuador 157–181. Rabbia, O. M., Hernandez, L. B., King, R. W., Lopez‐ Vallejo, C., Spikings, R.A., Luzieux, L., Winkler, W., Escobar, L. (2002): Discussion on "Giant versus small Chew, D., Page, L., (2006): The early interaction be‐ porphyry copper deposits of Cenozoic age in northern tween the Caribbean Plateau and the NW South Chile: adakitic versus normal calc‐alkaline magmatism" American Plate. Terra Nova 18, 264–269 by Oyarzun et al. (Mineralium Deposita 36; 794‐798, Wilkinson, B. H. & Kesler, S. E. (2009): Quantitative 2001). Mineralium Deposita 37; 791‐794. identification of metallogenic epochs and provinces: Richards, J. P. (2002): Discussion on "Giant versus application to Phanerozoic porphyry copper deposits. small porphyry copper deposits of Cenozoic age in Economic Geology 104; 607‐622. northern Chile: adakitic versus normal calc‐alkaline magmatism" by Oyarzun et al. (Mineralium Deposita 36; 794‐798, 2001). Mineralium Deposita 37; 788‐790.

4 CHAPTER II GEODYNAMIC CONTROLS ON TERTIARY ARC MAGMATISM IN ECUA‐ DOR: CONSTRAINTS FROM U‐Pb ZIRCON GEOCHRONOLOGY OF OLI‐ GOCENE‐MIOCENE INTRUSIONS AND REGIONAL AGE DISTRIBUTION TRENDS Abstract We obtained U‐Pb zircon ages of Late Tertiary intrusions in the northern Andes to provide robust time cali‐ bration points for the intrusive geochronologic framework of Ecuador which is mostly based on K‐Ar data. Intrusion emplacement ages range from about 31 to 7 Ma, and mainly pool in the Late Oligocene‐Early Miocene. Where both K‐Ar and U‐Pb data exist for a given intrusive system, ages obtained by the different methods are usually concordant within 1‐4 m.y. implying that K‐Ar ages may be used as proxies for the tim‐ ing of Tertiary arc magmatism on a regional scale. Except for a single sample, the investigated intrusions completely lack externally inherited zircons, in agreement with dominantly zircon‐poor, oceanic crustal basement domains. Spatio‐temporal distribution trends of Tertiary arc magmatism inferred from screened U‐Pb, K‐Ar, and zir‐ con fission track geochronologic data allow tracking of the progressive broadening of a flat slab region be‐ low southernmost Ecuador in the Mid‐ to Late Miocene, and of moderate slab shallowing in northern‐ central Ecuador in the Late Miocene. These regional arc migration patterns correlate in time with the sub‐ duction of the buoyant Inca Plateau and the Carnegie Ridge seamount chain. The temporal distribution of Tertiary Ecuadorian arc magmatism indicates a Late Oligocene‐Early Miocene arc magmatic flare‐up event comprising widespread ignimbrite eruption and batholith construction. Initiation of the flare‐up event coin‐ cides in time with accelerating, less oblique Farallon/Nazca‐South America plate convergence, suggesting a positive feedback between convergence rates, asthenospheric melt production, mantle‐crust melt flux, and upper crustal arc magmatic productivity in Ecuador.

5 Introduction Regional Geology of Ecuador Ecuador’s fundamental physiographic elements The spatio‐temporal distribution of arc magma‐ coincide with major geologic domains and com‐ tism, typically manifested as distinct belt seg‐ prise the flat‐lying western Costa forearc and ments at the Earth's surface, is controlled by the eastern Oriente foreland regions, enclosing be‐ interplay of multiple tectonomagmatic parame‐ tween them the central Andean chain which ters which derive from the complex interactions splits into the Western and Eastern Cordillera, of descending slab, overriding plate, and the separated by the Interandean Depression (IAD; mantle wedge (e.g., Hamilton 1995). A number of Litherland et al. 1994; Fig. 1). Allochthonous ma‐ studies evaluate feedback processes between the fic‐ultramafic oceanic basement domains, inter‐ geodynamic evolution and subduction‐related preted as hotspot‐derived oceanic plateau frag‐ Mesozoic‐Cenozoic arc magmatism along the ments and mainly accreted in the Late Creta‐ western plate edge of South America (e.g. Jaillard ceous, floor the present‐day forearc and frontal & Soler 1996; Kay et al. 2005), but data for the arc regions of Ecuador (e.g., Vallejo et al. 2009). Late Tertiary tectonomagmatic evolution of the Locally, especially in the Western Cordillera and northern Andes are lacking. In this contribution, its western foothills, these oceanic plateau units we are presenting the first dataset of robust U‐Pb host or are tectonically juxtaposed against sev‐ zircon ages of Late Tertiary intrusions in the eral pre‐ and post‐accretionary island arc com‐ northern Andes of Ecuador which to date have plexes of Late Cretaceous‐Early Tertiary age only been characterized by K‐Ar geochronologic (Vallejo et al. 2009). The present‐day main arc is data. built upon IAD basement units which are likely Our new data, combined with previously pub‐ heterogeneous in nature, comprising tectonized lished radiometric age information, allow us to slices of Eastern Cordillera and oceanic plateau discuss the relationships between arc magmatism material (Feininger & Seguin 1983; Spikings et al. and changes in the Tertiary geodynamic regime 2005; Chiaradia et al. 2009). Older Tertiary of the northern Andean margin. Because a side subaerial arc volcanic formations are exposed in outcome of this study (discussed in Chapters 3 the Interandean region south of 2.5°S where ac‐ and 5) is to investigate links between the geody‐ tive volcanism of the Northern Volcanic Zone namic setting, magma chemistry, and intrusion‐ ceases (Hungerbühler et al. 2002). Characteristics related mineralization in Ecuador, our study fo‐ of the major Tertiary arc volcanic formations of cuses on intrusions spatially associated with por‐ Ecuador are listed in Table 1. phyry‐related ore deposits and their respective Two prominent N‐ to NNE‐trending regional fault host rocks. Mineralized porphyry intrusions are zones structure the Western Cordillera (Fig. 2). typically small (few km2 outcrop area), but are The Calacalí‐Pujili‐Pallatanga fault zone (CPPF) thought to represent the uppermost crustal forms the Cordillera's eastern structural limit; it manifestations of significantly larger magmatic intersects the Western Cordillera at 3°S to splay systems at depth, which constitute the major off towards the Gulf of Guayaquil (Winkler et al. source of the mineralizing fluids (e.g., Sillitoe 2005). The Chimbo‐Toachi shear zone (CTSZ) 1973). Therefore, knowledge of the age of em‐ forms the eastern limit of the Macuchi island arc placement of porphyry stocks can serve as a proxy for the timing of more voluminous, not yet unroofed plutonism at depth.

Figure 1 (next page): Simplified geological map of the Cordillera region of Ecuador, focusing on Tertiary arc magmatic units; magmatic centers investigated in this study are marked. Inset shows present‐day geodynamic situation of the Ecuadorian‐Colombian margin and the Panama basin; dark gray areas outline seamount chains (offshore) and Cordil‐ lera ranges (onshore); seafloor features include active spreading centers (thick lines), extinct spreading centers (thin lines), active faults (hairlines), and transform faults/scarps (dashed hairlines). Inset adapted from Meschede & Barck‐ hausen (2001); main map adapted from Litherland et al. (1994), Steinmann (1997), Dunkley & Gaibor (1997), McCourt et al. (1997), Pratt et al. (1997), Hughes et al. (1998), and Palacios et al. (2008).

6 7 sequence (Hughes & Pilatasig 2002). Seismic arc units (Rio Cala arc; Vallejo 2007; Chiaradia studies suggest that, while subvertical in their 2009). uppermost portions, both fault zones extend The Tertiary arc cuts across a fundamental base‐ down to mid‐deep crustal levels where they are ment contrast in the Saraguro arc segment, the defined by 35° E‐dipping fault planes (Guillier et exact location of which is not known (cf. Chapter al. 2001). Tertiary intrusions of the Western Cor‐ 4). It might be located close to the CPPF at ca. dillera are aligned along the CTSZ and, towards its 3°S, or further south towards the Jubones or Pi‐ southern termination, the CPPF (Fig. 1, 2). In SW ñas‐Portovelo faults, and corresponds to the Ecuador the Amotape terrane forms a distinct northern limit of Amotape basement units vs. tectonic unit which extends further south into allochthonous Cretaceous oceanic plateau mate‐ northern Peru (Mitouard et al. 1990; Litherland rial (Litherland et al. 1994; Pratt et al. 1997; Spik‐ et al. 1994). Its Paleozoic basement units, ex‐ ings et al. 2005). Petrologically, most pre‐ posed in the El Oro massif in Ecuador, are mostly Miocene arc units north of 2.5‐3°S and west of covered by volcanic‐sedimentary sequences of the CPPF represent a progressively maturing is‐ the Cretaceous Celica‐Lancones basin (Jaillard et land arc system emplaced in a submarine envi‐ al. 1996). The El Oro massif, interpreted as a mi‐ ronment on oceanic plateau basement. In con‐ crocontinental block accreted to South America trast, subaerial arc magmatism taking place east in the earliest Cretaceous (Litherland et al. 1994), of the CPPF and in southern‐central Ecuador pro‐ represents a major structural break from the duced typical continental arc sequences. main Andean strike further north in that it adds a prominent ESE‐WNW structural trend to the re‐ gional tectonic framework which structurally fo‐ Tertiary arc segmentation and cused intrusion emplacement in across‐arc di‐ geology of investigated magmatic mension (Figs. 1, 2). centers Assembly of multiple exotic terrane fragments, syn‐ and post‐accretionary block rotation and The northern Ecuadorian arc segment fragmentation, large‐scale forearc sliver dis‐ placement,d an an oblique subduction setting, The northern Ecuadorian arc segment comprises concentrated in a narrow range of latitudes, pro‐ the whole Tertiary arc system of central‐northern duced a tectonically heterogeneous Tertiary arc Ecuador (Fig. 2). Its main outcrop unit is the Pa‐ system in Ecuador (e.g., Mitouard et al. 1990; leocene‐Eocene Macuchi Unit, representing a Hungerbühler et al. 2002; Spikings et al. 2005; submarine sequence of pillow lavas and hyalo‐ Vallejo et al. 2009). Therefore, it is useful to in‐ clastites, and their redistributed sedimentary spect the arc in its regional context along the NW equivalents (Hughes & Pilatasig 2002; Vallejo South American margin. Based on their spatial 2007). Due to deep erosion levels in the Western distribution and tectonic context, three major Cordillera, post‐Macuchi arc volcanics are spa‐ Tertiary arc segments (northern, central, and tially underrepresented. Aerially extensive Oligo‐ southern Ecuador) can be distinguished in Ecua‐ cene‐Miocene volcanic cover sequences can be dor (Fig. 2). The regional outcrop pattern of Ter‐ inferred from prominent coeval batholith intru‐ tiary arc magmatic units of NW South America sions in central and northern Ecuador (see be‐ demonstrates an essentially uninterrupted mag‐ low). Locally preserved post‐Macuchi volcanic or matic chain developed along the northern Peru‐ volcaniclastic rocks comprise: (1) minor Saraguro vian (Calipuy) and southern Ecuadorian margin, Group volcanics cropping out in small, isolated geometrically continuous with the central‐ patches in the central Western Cordillera close to northern Ecuadorian arc segments. The north‐ the CPPF. In southern Ecuador, the Saraguro wards continuation of the northern arc segment Group is mainly of Oligocene‐Early Miocene age into southern Colombia is less obvious, as this (Hungerbühler et al. 2002; Tab. 1), but Saraguro area, the Naranjal block, is characterized by a Group (Ocaña Formation) volcanics overlying the high degree of structural complexity including the Paleogene Yunguilla turbidites at the eastern appearance of additional Late Cretaceous island edge of the Western Cordillera have K‐Ar and

8 9 zircon fission track (ZFT) ages of 36‐39 Ma, thus rocks of the Zumbagua Unit in central Ecuador overlapping in age with the youngest Macuchi unconformably overlie Eocene turbidites (Hughes Unit (Dunkley & Gaibor 1997; Tab. 1); (2) the Oli‐ et al. 1998); (4) Pliocene‐Holocene volcanism in gocene‐Early Miocene San Juan de Lachas Forma‐ Ecuador and Colombia, constituting the present‐ tion, contemporaneous with the Saraguro Group, day Northern Volcanic Zone of the Andes, covers crops out in small areas close to the Ecuadorian‐ part of the older arc units of the Western Cordil‐ Colombian border, where it overlies the Macuchi lera and is prominently exposed further east‐ Unit (Vallejo 2007); (3) Miocene volcaniclastic wards in the IAD. Considering the relatively

Figure 2: Regional Tertiary arc outcrop pattern along the NW South American margin showing arc seg‐ ments as discussed in the text (Northern, Central, and Southern Ecuador, and Calipuy, Peru), and major fault systems which con‐ trolled Tertiary intrusion emplacement in Ecuador. Tertiary intrusions (italics) are aligned along major structures (thick lines) or inferred major structures (dashed thick lines). The Raspas complex of the NW El Oro range indicates prox‐ imity to the ancient Amo‐ tape suture zone (Bosch et al. 2002). Age ranges of vol‐ canic‐volcaniclastic forma‐ tions referenced in the leg‐ end are approximate, and refer to the base of the cor‐ responding unit; Calipuy Group volcanism extends throughout most of the Ter‐ tiary (Navarro et al. 2008). Also shown are Wadati‐ Benioff zones (Gutscher et al. 1999a, b; Guillier et al. 2001) outlining the flat slab segment below northern Peru and southern Ecuador. Map compiled from same sources as Fig. 1, plus Gómez Tapias et al. (2006), and Winkler et al. (2005).

10 narrow width of the Macuchi arc segment to the plutons (McCourt et al. 1997; Prodeminca west of the CPPF (mostly 50 km or less) com‐ 2000a). Combined, these intrusive complexes are pared to a typical average arc width of 97 km of batholithic dimension and form the most (Stern 2002), one expects Pliocene‐recent volcan‐ prominent cluster of plutons exposed in western ics to conceal the landward extent of Miocene or central Ecuador. Available K‐Ar ages (hornblende older volcanic sequences spatially associated with or biotite) for the Telimbela‐Chazo Juan pluton the northern Ecuadorian arc segment which, for range from 21‐15 Ma whereas ages for the Balsa‐ example, might constitute the source area for the pamba‐Las Guardias pluton are mostly older (34‐ Paleocene Silante or the Miocene Zumbagua vol‐ 30 Ma) except for two hornblende K‐Ar ages of caniclastic units of the Western Cordillera. 19.8±3.0 Ma and 25.7±0.9 Ma (Kennerley 1980; MMAJ/JICA 1989, 1991; McCourt et al. 1997). Large, mainly Macuchi Unit‐hosted intrusions are Furthermore, the hydrothermal system of a por‐ unroofed in Ecuador's Western Cordillera and its phyry intrusion hosted by the Balsapamba pluton foothills. Relatively few, mostly small‐sized Eo‐ has been dated at 19.7 ± 0.3 Ma (Re‐Os molyb‐ cene stocks and plutons are exposed, with the denite; Chiaradia et al. 2004). Ages reported for Santiago pluton close to the Ecuadorian‐ ythe nearb plutons of Echeandia‐La Industria (27‐ Colombian border representing the only major 23 Ma) and Corazon (16‐14 Ma) closely correlate Eocene plutonic body (Boland et al. 1998). In con‐ in time with these ages (Kennerley 1980; trast, several large Oligocene‐Miocene batholiths MMAJ/JICA 1989, 1991; McCourt et al. 1997). form two regional intrusive clusters and were investigated in this study. The central Ecuadorian arc segment In northern Ecuador the Junin and Cuellaje por‐ The central Ecuadorian arc segment, structurally phyry systems are emplaced in the Apuela‐ bracketed between the Piñas‐Portovelo Fault at Nanegal batholith, which in turn is hosted by vol‐ c. 3° 45' S, and the CPPF at c. 2° 10' S (Fig. 2) hosts caniclastic units ascribed to the Late Cretaceous‐ mainly subaerial volcanic formations spanning Early Tertiary Rio Cala and Macuchi island arc se‐ the whole Tertiary (Tab. 1), with the Oligocene‐ quences (Boland et al. 1998; Prodeminca 2000a; Early Miocene Saraguro Group forming the major Chiaradia 2009). The Apuela‐Nanegal batholith outcrop unit. Several Miocene basins filled with covers an area of 750 km2 thus forming one of volcaniclastic‐sedimentary sequences overlie the the largest Tertiary intrusive complexes in Ecua‐ Saraguro Group volcanics and form prominent dor. It dominantly comprises hornblende‐ and outcrop units in this arc segment (Steinmann biotite‐bearing quartz‐diorites and granodiorites 1997; Hungerbühler et al. 2002). which are punctured by several porphyry stocks and dikes of variable, mainly dacitic, composition. The oldest volcanic formation is the Paleocene (?) Available geochronological data (hornblende, Sacapalca Formation which mainly occurs in the biotite and whole rock K‐Ar; Van Thournout 1991; northwards projection of the Catamayo graben MMAJ/JICA 1992; Boland et al. 1998) indicate a (Hungerbühler et al. 2002), but also well to the period of protracted magmatism from 19 to 6 west of it (Pratt et al. 1997). The Eocene Chinchín Ma, although some K‐Ar ages might reflect ther‐ Formation forms the base of the local Quingeo mal resetting caused by intense hydrothermal basin SW of Cuenca (Steinmann 1997; Hunger‐ alteration associated with porphyry stock em‐ bühler et al. 2002). Post‐Saraguro volcanism is placement. represented by the Sta. Isabel and Quimsacocha formations which overlie older volcanics in the In northern‐central Ecuador the hornblende‐ and southwestern prolongation of the Cuenca basin. biotite‐bearing tonalitic‐granodioritic plutonic The Late Miocene‐Pliocene Tarqui Formation complexes of Telimbela‐Chazo Juan and Balsa‐ represents the youngest major volcanic forma‐ pamba‐Las Guardias host several porphyry intru‐ tion in southern Ecuador, with outcrop areas sions and associated hydrothermal systems; they concentrated along the eastern border of the are situated at a close distance to the western Saraguro arc segment, where it overlies Saca‐ Echeandia‐La Industria and the northern Corazon

11 palca, Chinchín, and Saraguro volcanics (Pratt et In a tectonized zone characterized by regional al. 1997; Hungerbühler et al. 2002). CPPF splay faults, the Gaby‐Papa Grande por‐ phyry system forms a minor intrusive complex. Two major and one minor intrusive centers of The porphyry system is hosted by basalts of the this arc segment were investigated in this study. Pallatanga oceanic plateau unit and consists of Tonalite, quartz‐diorite, and granodiorite units of several small (few km2 in total) intrusive units the Chaucha batholith, exposed adjacent to the comprising a tonalite pluton as well as plagio‐ CPPF, intrude or are tectonically juxtaposed clase‐hornblende porphyry stocks and dikes. against undifferentiated metasedimentary rocks, Prodeminca (2000a) report a K‐Ar age of 19.3 ± mafic lavas of the Pallatanga Unit, sedimentary 1.0 Ma for the Gaby porphyry without providing rocks of the Late Cretaceous‐Eocene Yunguilla further details as to which mineral was used for and Angamarca turbidite series, and Saraguro dating. Group volcanics (Dunkley & Gaibor 1997; Prodeminca 2000a). The Chaucha batholith hosts Apart from these deeply eroded intrusive cen‐ several porphyry intrusions and its SE portion has ters, a number of subvolcanic domes and plugs been dated at 13.3‐9.8 Ma (K‐Ar various minerals; associated with epithermal ore deposits were Kennerley 1980; INEMIN‐AGCD 1989; additional investigated in this work. These comprise the references in Prodeminca 2000a). high sulfidation type epithermal systems of Quimsacocha and El Mozo, as well as the poly‐ Along the northern limit of the Amotape range a metallic vein deposit of Tres Chorreras; spatially series of mainly diorite, quartz‐diorite and grano‐ associated subvolcanics are described or inferred diorite intrusions forms a WNW‐ESE trending belt for each of these deposits (Prodeminca 2000b). hereafter referred to as Cangrejos‐Zaruma intru‐ sive belt. These plutons intrude the southern Quimsacocha forms a topographically prominent flank and partly the hinge of a WNW‐ESE trending caldera of c. 5 km diameter, surrounded by coge‐ regional antiform. Amongst others, the plutonic netic andesitic lavas and breccias, and rhyolitic complexes comprise, from west to east, Cangre‐ ignimbrites (Beate et al. 2001). The caldera hosts jos, Paccha, and El Poglio, and are associated with several rhyodacitic domes whose emplacement several mineralized porphyry intrusions as well as postdates the epithermal mineralization event at a large epithermal vein system at Zaruma and the caldera flank. Zircon fission track ages ob‐ Portovelo (Pratt et al. 1997; Spencer et al. 2002). tained on ignimbrites (5.2‐4.9 Ma) and subvol‐ The regional basement is mostly obscured by canic intra‐caldera domes (3.6 Ma) indicate a overlying Saraguro Group volcanics which form Late Miocene phase of volcanic activity (Beate et the major host lithology for the Tertiary intru‐ al. 2001). Polymetallic veins and mineralized sions, but it is exposed as several metamorphic breccia bodies associated with the Tres Chorreras inliers along the intrusive belt. Towards the east diatreme complex, situated between the the belt is disrupted by a network of Andean‐ Chaucha, Gaby, and Quimsacocha magmatic cen‐ trending (NNE) regional faults, which juxtapose ters, are hosted by silicic volcanic units ascribed units of the Saraguro Group against the Sacapalca to the Saraguro Group (Pratt et al. 1997). Formation further east (Pratt et al. 1997). Prodeminca (2000a) mentions the occurrence of Spencer et al. (2002) regard the Sacapalca‐hosted syn‐ to postmineral intrusions, but we failed to Fierro Urcu porphyry center as the eastern pro‐ clearly identify these in the field due to intense longation of the Cangrejos‐Zaruma intrusive belt. hydrothermal alteration. The El Mozo high sulfi‐ The belt is inferred to be mainly Miocene in age dation type epithermal mineralization occurs at but only a single K‐Ar age of 16.9 ± 0.2 Ma for the the western flank of the Eastern Cordillera. The El Paccha intrusion has been reported so far (Pratt Mozo complex includes strongly altered volcanic et al. 1997). The Paleocene‐Early Eocene San Lu‐ units which are hosted by rhyolitic tuffs of the cas pluton (66‐52 Ma; Aspden et al. 1992), occur‐ uppermost Saraguro Group (La Paz Formation). ring at the eastern termination of the Cangrejos‐ Exploration drill cores encountered altered Zaruma intrusive belt at the border to the Saca‐ granodiorite porphyry intrusions occurring at palca arc segment (Fig. 2), significantly predates shallow depth below the epithermal high western belt plutonism.

12 13 sulfidation mineralization; an alunite K‐Ar age of yielded a Late Cretaceous age. The Curiplaya por‐ 15.4±0.7 Ma is thought to date the high‐ phyry system is thus associated withm magmatis sulfidation alteration and mineralization event of the Tangula batholith, rather than with Terti‐ (Prodeminca 2000b). ary Sacapalca‐Loma Blanca magmatism. The southern Ecuadorian arc segment Analytical techniques and sample Outcrop units of this arc segment south of 3° 45' material S are mainly preserved in the N‐S trending Cata‐ mayo graben at the border between the Eastern We used both isotope dilution thermal ionization Cordillera and the Amotape terrane in southern mass spectrometry (ID‐TIMS; in the following re‐ Ecuador (Figs. 1, 2). An inferred Late Maas‐ ferred to as TIMS) and laser ablation multi‐ trichtian‐Paleocene age of the volcanic Sacapalca collector inductively coupled plasma mass spec‐ Formation is poorly resolved and based on a sin‐ trometry (LA‐MC‐ICP‐MS) for U‐Pb isotopic gle ZFT age of 67±6 Ma (Hungerbühler et al. measurements to obtain age information on our 2002), in conjunction with the Paleocene‐ samples. Samples where, based on the l regiona Miocene ages of several plutons intruding the geological setting (i.e., proximity to basement Sacapalca Formation, including the major Paleo‐ units with a high potential for recycled crustal cene‐Early Eocene San Lucas pluton at the border components; e.g., Noble et al. 1997; Vallejo to the Saraguro arc segment (Aspden et al. 1992; 2007), we suspected significant external zircon Jaillard et al. 1996). Locally, volcanics of the Late inheritance were dated by LA‐MC‐ICP‐MS Eocene‐Early Oligocene Loma Blanca Formation, whereas all other samples were dated by TIMS. forming the base of the Saraguro Group, overlie Samples were crushed and milled to <350 μm, the Sacapalca Formation (Hungerbühler et al. and inclusion‐free zircons suited for isotopic 2002). The major Early to Mid‐Miocene analysis were handpicked from the nonmagnetic 3 Portachuela batholith is exposed in the Eastern heavy mineral (>3.32 g/cm ) fraction using a bin‐ Cordillera directly to the eeast of th Las Aradas ocular. The obtained zircon fractions were either fault (Aspden et al. 1992). In combination with processed for annealing (TIMS) or mounted in several minor, Sacapalca‐hosted intrusions, it epoxy and polished such that grain interiors were demonstrates Early to Mid‐Miocene arc magma‐ exposed for scanning electron microscopy and tism in this region where the young volcanic cathodoluminescence (SEM‐CL) imaging and, cover has not been preserved. where applicable, LA‐MC‐ICP‐MS analysis. We did not study any magmatic centers directly Sample material associated with this arc segment in the present work, but we investigated the Curiplaya porphyry Sampling details are summarized in Table 2. Out‐ system, which is located c. 60 km W of the Cata‐ crop sampling for zircon dating comprised c. 5 kg mayo graben and c. 25 km W of the westernmost of rock material; proximal lithologic contact Loma Blanca and Sacapalca Formation outcrops. zones or rock heterogeneities (xenoliths, en‐ The Curiplaya porphyry intrusions are hosted by claves) were avoided as far as possible. In addi‐ Cretaceous volcanic rocks of the Celica Formation tion, a number of drill core samples were col‐ in the Celica‐Lancones basin and crop out proxi‐ lected for this study; due to its limited availability mal to the major Tangula batholith of Mid‐Late drill core sample quantities are smaller (c. 1‐2 kg). Cretaceous age (Hall & Calle 1982; Palacios et al. Where not directly avoidable during sampling, 2008). The quartz‐diorite porphyry intrusions rock heterogeneities were removed later using a were inferred to be Tertiary in age and are partly diamond‐blade disc saw. For samples where TIMS overlain by dacitic tuffs tentatively assigned to single grain analyses were performed we indi‐ the Loma Blanca Formation. They are structurally vidually imaged ca. 20‐30 zircons/sample by SEM‐ disrupted by a complex network of NNE‐SSW and CL. For zircons where U‐Pb measurements were ESE‐WSW trending faults (Howe International carried out by means of LA‐MC‐ICP‐MS only bulk 2006). However, anticipating our results, a sample (25‐50 zircons) SEM‐CL images were ob‐ Curiplaya porphyry intrusion dated in this study tained which do not provide sufficient resolution

14 to discuss zircon textures in detail. Zircon SEM‐CL tematically over the range of total blank common characteristics are summarized in Table 2 and a Pb amounts (0.5‐7.4 pg). Following the initial an‐ selection of SEM‐CL images is presented in Figure nealing/leaching step sample common Pb con‐ 3. tents were identical within error to total blank common Pb amounts and were thus solely at‐ TIMS analysis tributed to laboratory contamination except for a Zircon single grain (and, in one case, a two‐grain minor number of samples where part (<1.2 pg) of fraction) dissolution and U‐Pb separation at the the common Pb was corrected with the isotopic Department of Mineralogy, University of Geneva, composition of Stacey & Kramers (1975) using an followed the techniques described by Ovtcharova appropriate sample age estimate based on geo‐ et al. (2006). An initial annealing/leaching logical field relationships and published geochro‐ "chemical abrasion" zircon treatment step (Ov‐ nologic data. Whole rock Th and U contents tcharova et al. 2006, based on Mattinson 2005) measured by multi‐element ICP‐MS analysis served to minimize effects of post‐ (Chapter 5) were used as a proxy to estimate crystallizational radiogenic Pb loss which are oth‐ melt Th/U ratios for Th disequilibrium correction. erwise expected to be significant given the high Estimated Th/U ratios are typically in the range of degree of zircon‐fluid interaction displayed by 2‐3, and arbitrary modification of this ratio to up some zircons (Fig. 3). Samples were spiked using to four (a commonly assumed Th/U ratio if geo‐ a mixed 205Pb‐233U‐235U spike solution, and zircon chemical information is lacking; e.g., Ovtcharova dissolution in 63 μl concentrated HF with a trace et al. 2006) does not change the obtained U‐Pb ages beyond analytical uncertainties. of 7N HNO3 took place at 180°C for seven days, followed by evaporation and overnight re‐ The uncertainties of spike and blank Pb isotopic dissolution in 36 μl 3N HCl. composition, mass fractionation correction, and Isotopic analyses at the University of Geneva tracer calibration were propagated to the final were performed using a Thermo Fisher TRITON uncertainties of isotopic ratios and ages of each mass spectrometer equipped with a MasCom‐2 individual analysis. In addition, uncertainties in the decay constants of 238U and 235U (238U: 0.16%, electron multiplier and a digital ion counting sys‐ 235 tem. Loading of U and Pb on previously out‐ U: 0.21%; Jaffey et al. 1971 values with an ad‐ gassed single Re filaments took place using 1 μl of ditional uncertainty factor of 1.5 as suggested by Mattinson (1987) to ensure direct compatibility a silica gel‐H3PO4 mixture (Gerstenberger & Haase 1997). Lead isotopes were measured by with LA‐MC‐ICP‐MS data) were propagated sepa‐ peak‐hopping on the MasCom‐2 electron multi‐ rately and added quadratically to weighted mean or single zircon uncertainties discussed in the plier, and U isotopes as oxides were measured 207 235 either by peak‐hopping on the MasCom‐2 elec‐ text. Pb/ U age information is only used to tron multiplier or, at signal intensities of >3 mV, evaluate the concordancy of individual zircon simultaneously (static mode) on Faraday cups analyses. Concordia plots and weighted average linked to amplifiers equipped with 1012 Ohm re‐ age calculations were prepared using the Isoplot sistors. Mass fractionation of Pb v.3.31 Excel macro of Ludwig (2003). All uncer‐ tainties and error ellipses are reported as 2‐ , (0.08±0.05%/amu) was controlled by SRM‐981 206 238 standard measurements. Mass fractionation of U and weighted mean Pb/ U ages are pre‐ was corrected online by using a double 233U‐235U sented at 95% confidence level. spike solution. LA‐MC‐ICP‐MS analysis The total procedural common lead blank was Epoxy grain mounts of sample zircons and SL‐1 2.07 ± 1.97 pg (average of 20 total blank meas‐ standard zircon fragments for controlling inter‐ urements in the 2007‐2008 period) and has the element fractionation (TIMS age 563.5 ± 3.2 Ma; following isotopic composition (at 2σ uncertainty, Gehrels et al. 2008) were prepared at the Univer‐ fractionation‐corrected): 206/204Pb: 18.36±0.34; sity of Geneva, and isotopic measurements took 207/204Pb: 15.59±0.20; 208/204Pb: 38.00±0.69; the place at the Arizona LaserChron Center, Univer‐ total blank isotopic composition did not vary sys‐ sity of Arizona. Zircons measured by

15 Figure 3: Zircon SEM‐CL images of samples documenting rounded core domains, incremental zircon growth stages, and variable degrees of zircon‐fluid interaction; white scale bar is 100 μm. Note that none of the zircons dated by TIMS showed major external (i.e., xenocrystic) inherited age components. A – Continuous oscillatory zoning pattern (OZP) with resorbed low‐CL internal zone and concordant low‐CL rim; several melt inclusions disturb OZP pattern (E06140). B – Zircon interior with large re‐homogenized low‐CL domains and high‐CL fractures interpreted as altera‐ tion by zircon‐hydrothermal fluid interaction; thin overgrowth rim with well‐developed OZP. High‐CL fractures termi‐ nate against the fresh overgrowth rim possibly indicating alteration of the antecrystic core took place prior to zircon re‐immersion into the melt and final intrusion solifidication (E07032). C – Continuous OZP with minor resorption tex‐ tures (E05090). D – Multiple resorbed OZP domains and overgrowth zones (E06206). E – Zircon with partly resorbed and recrystallized internal domains, as well as conspicuous alteration of the outer rim (E07005). F – Well‐defined OZP domains which are slightly resorbed in places, and alteration along grain margins (E07018).

16 LA‐MC‐ICP‐MS were not annealed/leached prior LA‐MC‐ICP‐MS data reduction to analysis and are thus potentially more likely to The MSWD is usually used for population control display Pb loss features than annealed/leached of zircon LA‐MC‐ICP‐MS data: if the MSWD of all zircons measured by TIMS. However, in most analyzed zircons significantly deviates from unity, cases the magnitude of this effect is probably histograms or cumulative probability plots are smaller than the analytical LA‐MC‐ICP‐MS preci‐ used to statistically evaluate the number of zir‐ sion, such that zircon ages obtained by LA‐MC‐ con populations present. To explain polymodal ICP‐MS are not supposed to be systematically age distributions investigators often invoke ra‐ biased outside of their analytical uncertainty diogenic Pb loss caused by zircon‐fluid interaction range. to reject young zircon ages (e.g., Maksaev et al. Analytical procedures and measurement condi‐ 2004), and zircon inheritance or ‘subtle inheri‐ tions for LA‐MC‐ICP‐MS analysis on a GV Instru‐ tance’ to reject old zircon ages (e.g., Campbell et ments Isoprobe with an attached New al. 2006). Zircon ages at the lower and upper age Wave/Lambda Physik DUV193 Excimer laser are range are then progressively rejected until the outlined in Gehrels et al. (2008). Laser ablation MSWD is decreased to a statistically acceptable spot diameters were 25 or 35 μm. Measurements value, typically on the order of the analyzed were carried out in static mode using Faraday standard zircons (e.g., Bryan et al. 2008). How‐ detectors for 238U, 232Th, 208Pb, 207Pb and 206Pb, ever, unless a large number of zircons are ana‐ and an ion‐counting channel for 204Pb. Back‐ lyzed, the usage of histograms or cumulative ground on‐peak measurement for 20s with the probability plots, where inflection points are used laser off was followed by 20 one‐second integra‐ to identify different zircon spopulation expected tions with the laser on; delay time between two to follow a Gaussian distribution, can fail to samples was 30s. The analyses were corrected for clearly resolve multiple or mixed age populations. common Pb using the measured 204Pb and an as‐ If the magnitude of assigned analytical random sumed initial lead isotopic composition of Stacey errors is correct, the expected MSWD value for a & Kramers (1975). single zircon population following a Gaussian dis‐ Random measurement errors at 2‐б level were tribution is always unity. Deviation from unity propagated into individual analyses. As the used either indicates underestimation of analytical standard material is of significantly older age random errors or reflects real geological scatter than the unknown zircons, relative random errors which might be caused by analytically irresolv‐ of unknowns are typically 2‐3 times higher than able external inheritance, antecrystic compo‐ random errors of the standard zircon. Measured nents or Pb loss features. As outlined by Wendt & low 207Pb intensities (<0.4 mV) resulted in very Carl (1991) a standard deviation can be assigned large errors in the 207Pb/235U and 206Pb/207Pb ra‐ to the MSWD, the size of which depends on the tios producing poorly reliable ages calculated system's degrees of freedom, f, equaling the from these isotopic ratios; we therefore exclu‐ number of unknowns minus two. At 2‐б level, the sively use 206Pb/238U age information. Additional maximum statistically acceptable value of the systematic errors, discussed in detail by Gehrels MSWD is 1+2(2/f)1/2 (Wendt & Carl 1991). et al. (2008), comprise uncertainties of the U de‐ As demonstrated by repeated SL1 standard zircon cay constants (cf. TIMS analytics), SL‐1 standard analyses (weighted mean age of 566.3±2.7 Ma zircon age, fractionation correction, and common with an MSWD = 0.81, n = 31), our assigned ana‐ Pb correction. Systematic errors were propagated lytical random error size is not over‐ or underes‐ separately yielding an average 2‐б error of timated. Yet, MSWD values for a given sample of 1.42±0.54% on 206Pb/238U ages; this average error our dataset without major external inheritance was added quadratically to final weighted mean features are commonly higher than the statisti‐ age uncertainties. cally acceptable value unless a significant number of zircons are excluded from the weighted mean age calculation (see below). Following the rea‐ soning of Wendt & Carl (1991) sample MSWD

17 values exceeding its 2‐б range thus should reflect ‘xenocryst’ which are defined as follows: ‘auto‐ real geological scatter due to external zircon in‐ crysts’ refer to zircons grown from the youngest heritance, antecrystic components, or radiogenic melt batch participating in magma chamber con‐ Pb loss; elevated MSWD values may also reflect struction prior to eruption or final pluton solidifi‐ incorporation of mixed signals ('subtle inheri‐ cation (Miller et al. 2007). In contrast, ‘antecrysts’ tance'), i.e., ablating and mixing different age crystallized from earlier melt batches contribut‐ domains of a given zircon, as the dated zircons ing to incremental pluton growth (Miller et al. are commonly small (<100 μm in the longest di‐ 2007). The maximum age difference between mension) compared to applied laser spot diame‐ antecrysts and autocrysts relates to the duration ters (25‐35 μm). Most of our samples show broad of magmatism at a single volcanic center or plu‐ unimodal age peaks in histogram plots and do ton (up to a few m.y.; Miller et al. 2007), or on a not allow a clear distinction of multiple popula‐ regional pscale (u to >10 m.y.; Bryan et al. 2008). tions on cumulative probability plots. Thus, zircon ‘Xenocrysts’ are incorporated into the magma age scatter from the sources outlined above in‐ from genetically unrelated wall rock units (Miller fluences our dataset, but cannot be clearly re‐ et al. 2007; Bryan et al. 2008). solved at our analytical precision; consequently, It is important to note that porphyry intrusions zircons at the lower and upper age range cannot (dikes or stocks, as applicable for several samples be unambiguously excluded when calculating the below) are considered to represent single, rapidly weighted mean age for a given sample. quenched melt batches (e.g., Seedorff et al. For these reasons, we prefer to include a rather 2005). While they thus might contain antecrystic large number of zircon analyses in the calculation or xenocrystic zircons derived from their parental of weighted mean ages, unless analyses are melts, they are not affected by later melt replen‐ clearly rejectable based on histogram distribution ishment, protracted residual melt crystallization, criteria or significant age offsets. This practice and incremental pluton growth as large phan‐ avoids biasing weighted mean ages by biased zir‐ eritic intrusions potentially are (e.g., Schaltegger con age selection aimed at decreasing the et al. 2009). MSWD. Weighted mean ages built from a broad zircon population are negligibly susceptible to TIMS analysis age bias by radiogenic Pb loss, as these ages of‐ A combined TIMS and LA‐MC‐ICP‐MS results ten show increased individual errors and thus summary is presented in Table 3 whereas de‐ contribute less to the weighted mean age. As it tailed TIMS results are shown in Table A1 (Ap‐ will be shown below, excluding zircons at the pendix). Concordia plots of individual samples, lower and upper age range of a given sample of together with weighted mean 206Pb/238U age dia‐ our dataset (where the MSWD of the whole sam‐ grams are shown in Figure 4. For the following ple zircon population exceeds the statistically results presentation reported single grain and acceptable value) generally allows driving down weighted mean ages are always 206Pb/238U ages the MSWD to a statistically acceptable value where errors include decay constant uncertain‐ without affecting the weighted mean age beyond ties such that these ages can be compared to analytical errors. Weighted mean ages obtained ages obtained from other isotopic systems. Due in this manner thus correspond to a mixture of to extremely low radiogenic Pb contents, sample auto‐ and antecrystic age components reflecting zircons analyzed by TIMS generally show low ra‐ the terminal stages of incremental pluton diogenic/common Pb ratios (<1 for most zircons) growth. producing comparatively high age uncertainties on single zircon analyses. As the MSWD of most Results of our 206Pb/238U ages is significantly below unity, the magnitude of our analytical errors might pos‐ Terminology sibly be overestimated. However, MSWD values In the following sections we repeatedly use the presented below always overlap with the ex‐ terms zircon ‘autocryst’, ‘antecryst’ and pected MSWD uncertainty range (Wendt & Carl 1991) and are thus statistically acceptable.

18 19 Zircons of the Gaby and Papa Grande horn‐ age of 21.34±0.11 Ma with a statistically accept‐ blende‐plagioclase porphyry intrusions (samples able MSWD (MSWD = 0.70), indicating that they E05083 and E05090) yield weighted mean ages of could be treated as a single population. Thus, al‐ 20.26±0.07 Ma (n=5) and 19.89±0.07 Ma (n=6) though there is no statistical justification for dis‐ with MSWD values of 0.10 and 0.11, respectively. carding these two zircon analyses as antecrysts Four zircons obtained from a dacitic intra‐caldera from the weighted mean age, we do exclude dome at Quimsacocha (E06017) yield a weighted them based on cross‐cutting field relationships mean age of 7.13±0.07 Ma (MWSD = 0.23). All and the high precision age obtained on the host zircon analyses are concordant and overlap lithology. Consequently, we prefer the first op‐ within error; we interpret the weighted mean tion and use the age of 21.22±0.17 Ma as em‐ ages to approximate the final emplacement of placement age estimate of the porphyry dike, but the respective intrusions. note that both ages are identical within error. Finally, a single zircon (BA7) of this sample yields Three zircons of the plagioclase‐hornblende por‐ an age of 20.86±0.11 Ma, which we interpret as a phyry exposed in underground workings of the La postcrystallization radiogenic Pb loss feature. Abundancia Mine at Portovelo (E06112) overlap within error and define a weighted mean age of Six zircon analyses of the Apuela batholith at 24.04±0.06 Ma (MSWD = 0.52). Zircon PO2 dis‐ Cuellaje (granodiorite; E06206) overlap within plays negative discordance; the analysis is offset error and yield a weighted mean age of to the left of the Concordia curve (Fig. 4). Re‐ 12.87±0.05 Ma (MSWD = 0.26), interpreted to corded isotopic ratios were stable throughout the approximate the final emplacement pulse of the whole measurement of this sample andt do no granodiorite pluton. Three of these zircon analy‐ indicate any kind of mass spectrometric analytical ses discordantly plot to the right of the Concordia problem. As the analysis is still concordant within curve (Fig. 4) possibly reflecting an imperfect iso‐ error and the 206Pb/238U age does not seem to be topic composition used for common Pb blank significantly affected by this disturbance we in‐ correction for this sample. To some extent, this clude this analysis in the weighted mean age. offset might also represent an effect of Pa dis‐ equilibrium not accounted for during data reduc‐ Four zircons of the Balsapamba pluton (granodio‐ tion (Parrish & Noble 2003). The 206Pb/238U age is rite; E06140) overlap within error and yield a not significantly affected, however, and the weighted mean age of 21.46±0.09 Ma (MSWD = weighted mean age when excluding these three 0.23) which we interpret to approximate final zircon analyses is identical to the weighted mean emplacement pulse of the intrusion. A single zir‐ age of all six zircons. con gives an age of 21.13±0.28 Ma possibly re‐ flecting postcrystallization radiogenic Pb loss Individual zircon ages obtained from the Chaucha caused by hydrothermal alteration and is there‐ batholith (granodiorite; E07003) do not overlap fore excluded; all analyses are concordant. Seven within error and show a continuous age distribu‐ zircons of a hornblende quartz‐diorite porphyry tion along the Concordia curve ranging from dike (E06131) intruding the pluton were analyzed 15.33±0.06 Ma to 14.84±0.07 Ma (Fig. 4). This yielding a somewhat scattered age distribution age distribution might be produced by mixing (Fig. 4): zircons BA5 and BA6 show ages of 21.39‐ variable proportions of antecrystic zircon core 21.41 Ma which is identical to the age of the host domains and autocrystic overgrowth rims. In ad‐ rock (E06140); we thus consider them as ante‐ dition (or alternatively), antecrystic components crysts derived from the latter which is in agree‐ of variable age might be present. Zircon crystalli‐ ment with resorbed core domains observed in zation over a time range of c. 0.5 m.y. is consis‐ some zircon CL images of this sample (Fig. 3). tent with protracted incremental pluton growth Four slightly younger zircons from this sample as observed elsewhere (e.g., Schaltegger et al. (BA1‐4) would then define a weighted mean age 2009). A maximum age for the final pulse of plu‐ of 21.22±0.17 Ma (MSWD = 0.09). The two ton emplacement may be estimated form the slightly older zircons could also be included in a two youngest (i.e., closest to autocrystic) zircons 6‐grain weighted mean age for sample E06131 which overlap within error and yield a weighted (dashed line in Fig. 4) yielding a weighted mean mean age of 14.84±0.07 Ma. Five concordant

20 Figure 4: U‐Pb Concordia diagrams and weighted mean 206Pb/238U age plots of samples dated by TIMS. Error bars and error ellipses correspond to 2‐sigma error ranges. Individual weighted mean ages are presented at 95% confi‐ dence limit with relative and absolute uncertainties as indicated; for additional propagation of the decay constant uncertainty see Table 3. Dashed line in tplo for sample E06131 corresponds to weighted mean age if analyses BA5 and BA6 are included; see text for further explanation. All diagrams were generated using the Isoplot v.3.31 Excel macro (Ludwig 2003).

21 Figure 4 (continued)

22 zircons of a granodioritic porphyry dike (E07005) weighted mean age is 26.0±0.6 Ma (MSWD = intruding the batholith overlap within error and 2.9). Further exclusion of the next three youngest define a weighted mean age of 9.79±0.03 Ma grains produces a within error identical weighted (MSWD = 1.09) which we interpret to approxi‐ mean age of 26.2±0.5 Ma with a statistically ac‐ mate the age of porphyry dike emplacement. A ceptable MSWD of 1.7. As Pb loss or the ante‐ single zircon (CH2) plots slightly off the main age crystic cut‐off age cannot be clearly analytically cluster (Fig. 4); excluding this zircon from the resolved in these grains we use 26.0±0.6 Ma as a weighted mean does not have any effect on the robust estimate for the final pulse of intrusion age but leads to a decrease of the MSWD from emplacement. 1.09 to 0.26. Zircon CH1 has an age of 10.26±0.19 Sample E07011, a strongly altered Saraguro Ma, not overlapping within error with the main Group felsite, contains a xenocrystic zircon core age cluster (Fig. 4), and is thus interpreted as an‐ at 446 Ma with a 34.7 Ma overgrowth rim; a sec‐ tecryst. ond zircon has a xenocrystic (or antecrystic) core Four zircons of the El Mozo granodiorite porphyry age of 37.1 Ma vs. a 30.3 Ma tip age. The histo‐ dike (E07018) overlap within error and define a gram age distribution is clearly polymodal (Fig. 5). weighted mean age of 16.04±0.04 Ma (MSWD = Excluding the 446 eMa cor as xenocryst plus the 0.53) which we interpret to approximate the age next six oldest analyses as xeno‐/antecrystic zir‐ of emplacement of the porphyry dike. Two zir‐ cons we obtain a weighted mean age of 30.7±0.5 cons dated at 16.16±.0.09 Ma and 16.36±0.06 Ma Ma (MSWD = 4.8) for 22 zircon analyses which do not overlap within error with the main age we interpret as dating the timing of final magma cluster (Fig. 4) and are interpreted as antecrysts. chamber assembly prior to eruption of the felsite; there might be a small age difference to the de‐ Four concordant zircon analyses of the Junin positional age of the tuff. Treating the seven granodiorite porphyry stock (E07032) overlap youngest ages as Pb loss results in a weighted within error and yield a weighted mean age of mean age of 30.9±0.3 Ma for the remaining 15 9.01±0.06 Ma (MSWD = 0.36) which we interpret zircons, with a statistically acceptable MSWD of to approximate the age of porphyry stock em‐ 0.83; both ages are identical within error. placement. A single zircon (JU1) shows an older age of 9.48±0.20 Ma (Fig. 4) and is considered as The histogram plot of sample E07023, a horn‐ an antecryst. blende‐biotite granodiorite intrusion north of Zaruma, shows a bimodal age distribution with LA‐MC‐ICP‐MS analysis peaks around 21 Ma and 29.5 Ma (Fig. 5). The Results are presented as weighted mean latter comprises the five oldest analyses and 206Pb/238U age plots and corresponding histo‐ seems to represent an end member xeno‐ or an‐ grams in Figure 5 and in Table 3; detailed analyti‐ tecrystic component yielding a weighted mean cal results are listed in Table A2 (Appendix). In age of 29.5±1.0 Ma. The 15 youngest zircon ages the following results presentation we only refer define a weighted mean age of 20.7±0.8 Ma with to random measurement errors; additional sys‐ a statistically acceptable MSWD of 1.07 which we tematic errors are considered for weighted mean use as a proxy for the last pulse of intrusion em‐ ages presented in Table 3. placement. Five analyses are transitional be‐ tween the two age groups and might reflect vari‐ Zircons obtained from a biotite‐bearing quartz‐ able proportions of the older and younger age diorite intrusion at Cangrejos (sample E06066) groups, and/or antecrystic zircon components of display a broadly unimodal histogram age distri‐ variable age. bution with two minor peaks at the flanks of the major age peak, skewed towards younger ages Sample E07030, a Curiplaya hornblende quartz‐ (Fig. 5). We interpret this pattern as an antecrys‐ diorite porphyry stock, shows two zircon analyses tic age component in the two oldest grains, and a clearly offset from the bulk of the zircon analyses group of zircons which suffered radiogenic Pb (Fig. 5). We interpret these two ages as strongly loss at the younger age range. When excluding influenced by radiogenic Pb loss and exclude the two oldest and three youngest analyses the them from further discussion. Otherwise, the

23 24 histogram age distribution is unimodal, albeit case they are referred to as "inherited" (we addi‐ slightly skewed towards younger ages suggesting tionally use the qualifier "external" to stress the subtle radiogenic Pb loss for some younger xenocrystic character of these zircons, and to set grains. The bulk of sample zircons (n=26) gives a them apart from recycled antecrysts related to weighted mean age of 92.0±1.0 Ma (MSWD = the same magmatic system), as well as during 3.3). Progressively narrowing down the range of magma ascent and later‐stage mid‐shallow analyses by excluding the three oldest and teigh crustal differentiation. The presence of inherited youngest ages produces a within error identical xenocrystic zircon cores with thick magmatic weighted mean age of 92.4±0.7 Ma with a statis‐ overgrowth rims is usually indicative of constant tically acceptable MSWD of 1.3. We prefer to use zircon‐melt immersion and zircon saturation of the first value of 92.0±1.0 Ma which we use as a melts from the magma source region onwards. proxy for emplacement of the porphyry intrusion. Due to rapid dissolution kinetics, preservation of inherited zircons to significant amounts in zircon‐ The zircon age histogram of sample E07045, a undersaturated melts is otherwise only possible if hornblende‐bearing granodiorite intrusion of the these zircons become encapsulated in other crys‐ Telimbela‐Chazo Juan pluton, shows a broadly tallizing minerals (e.g., Hansmann & Oberli 1991; unimodal age distribution which is slightly Miller et al. 2003). In a study of a wide range of skewed towards younger ages, possibly as a re‐ granitoid intrusions in different geodynamic envi‐ sult of radiogenic Pb loss (Fig. 5). Where meas‐ ronments, Miller et al. (2003) observe a bimodal ured separately, zircon core and tip ages overlap distribution pattern with either external zircon within error. Excluding the four oldest grains of inheritance‐poor or ‐rich granitoids; the former this sample, the 24 remaining zircons yield a are mainly of calc‐alkaline type, mostly meta‐ weighted mean age of 25.5±0.6 Ma with an aluminous, and source melt temperatures are on MSWD of 2.2, where the maximum statistically average at least 837°C. acceptable MSWD is 1.6; we interpret this age to approximate final intrusion emplacement. Reject‐ Our TIMS and LA‐MC‐ICP‐MS age data suggest ing the five youngest and three oldest zircons of that the occurrence of externally inherited zircon this group yields a within error identical weighted cores in all intrusions investigated in this study is mean age of 25.5±0.5 Ma with a statistically ac‐ extremely limited. This is in marked contrast to ceptable MSWD of 1.2 for the remaining 16 zir‐ some Paleozoic intrusions in Ecuador where ex‐ cons. ternal zircon inheritance is an abundant feature (Noble et al. 1997). Zircon textural analysis by Discussion SEM‐CL imaging prior to TIMS analysis demon‐ strates the relatively abundant occurrence of dis‐ Causes for limited external zircon in‐ tinct zircon core domains in some Tertiary intru‐ sions (Fig. 3; Tab. 2). These domains do not rep‐ heritance in Tertiary intrusions resent xenocrystic, externally inherited cores, but Zircon xenocrysts can become incorporated into instead seem to reflect antecrystic zircon, or arc magma either in its source region, in which

Figure 5 (previous page): Weighted mean 206Pb/238U age plots, histograms, and cumulative probability density function curves of samples and SL‐1 standard zircon analyzed by LA‐MC‐ICP‐MS. Effects of excluding certain groups of zircons from the calculation of the weighted mean age are illustrated in the plot (outlined with red lines) and discussed further in the text. Preferred weighted mean ages are marked by thin black horizontal lines. Empty boxes = rejected zircon analyses based on histogram age distribution (xenocrysts, Pb loss); gray boxes = zircon analyses potentially influenced by analytically not clearly resolvable antecrystic components or Pb loss; black boxes = zircon analyses accepted for weighted mean age calculation. Weighted mean ages displayed in bold, calculated from zircon analyses marked in gray and black, are preferred as proxies for the final phase of intrusion emplacement (or magma chamber assembly prior to eruption); their MSWD values are not always statistically acceptable for a single zircon population (Wendt & Carl 1991). Weighted mean ages not displayed in bold are calculated only from zircon analyses marked in black and always corre‐ spond to statistically acceptable MSWD values. Note that both weighted mean ages for a given sample are generally identical within error. Also shown are Concordia plot and weighted mean age of SL‐1 standard zircon; the MSWD of 0.81 for the SL‐1 weighted mean 206Pb/238U age suggests analytical random errors are estimated accurately. Error bars, error ellipses, and weighted mean uncertainties correspond to analytical random errors at 2‐ level; see Table 3 for propagation of additional systematic errors. All diagrams generated using the Isoplot v.3.31 Excel macro (Ludwig 2003). 25 distinct autocrystic zircon growth sequences cons such that (if zircons were present; see which do not show significantly different isotopic above) assimilation of zircon antecrysts (sensu age domains, and do not change U‐Pb age con‐ Bryan et al. 2008) originating from arc intrusive cordancy between the 238U/206Pb and 235U/207Pb roots was favored. This scenario is in agreement isotopic systems. Zircon core and tip ages ob‐ with the relatively common occurrence of ante‐ tained by LA‐MC‐ICP‐MS are mostly indistin‐ crystic zircon domains in several samples investi‐ guishable within error. Zircon selection for TIMS gated in this study, and is further compatible with analysis in this study was restricted to picking the reasoning of Dungan & Davidson (2004) fresh‐looking, inclusion‐free zircons to minimize where crustal contamination of arc magmas in a alteration‐induced Pb loss and high common Pb broadly stationary magmatic arc complex tends contents. Single‐graind han picking for mass spec‐ to be restricted to arc intrusive root zones of trometric analysis did not discriminate zircons similar isotopic composition. based on their morphologies, such that a rela‐ (3) Hot, mantle‐derived melts are often zircon‐ tively representative cut of the sample zircon in‐ undersaturated (Miller et al. 2003). In the case of ventory was obtained. Thus, the observed deficit Ecuador, this could apply to deep‐mid crustal of externally inherited zircon components sug‐ domains where hot, mantle‐derived melts tem‐ gested by TIMS age data does not seem to be a porally stall and evolve, i.e., the MASH zone of function of morphology‐selective zircon hand‐ Hildreth & Moorbath (1988), or the hot zone of picking, and is mirrored by our LA‐MC‐ICP‐MS Annen et al. (2006). Granitoid parental melts results. The extremely limited occurrence of ex‐ would only become zircon‐saturated with de‐ ternal zircon inheritance in Tertiary intrusions creasing temperature shortly prior to or during might be due to the following reasons: their final emplacement in the shallow crust. (1) Oceanic plateau basement units (or island arc In a single sample dated in this study, a felsite at intrusive roots) of the Western Cordillera and the Tres Chorreras assigned to the Saraguro Group Interandean region of Ecuador are dominantly (E07011; 30.7±1.6 Ma), a few Early Oligocene primitive and thus zircon‐poor (e.g., Spikings et xeno‐ or antecrystic zircons are present, and a al. 2005; Chiaradia et al. 2009; Vallejo et al. single Ordovician xenocrystic zircon core age with 2009). For the most part, detrital zircon‐bearing a thick Early Oligocene overgrowth rim was de‐ sedimentary formations partly sourced from tected. The latter indicates prolonged melt expo‐ landward metamorphic regions constitute the sure of the xenocrystic core, suggesting the melt only potentially effective assimilant source for was zircon‐saturated. As only a single core of this zircon xenocrysts in the Western Cordillera, as age was identified, it likely does not represent has been demonstrated for the Yunguilla and Sa‐ external source inheritance but rather contami‐ guangal formations, as well as for the sedimen‐ nation during magma ascent. Vallejo (2007) stud‐ tary portions of the Macuchi Unit (Vallejo 2007). ied detrital zircons of the Yunguilla Formation A Late Cretaceous Curiplaya porphyry intrusion, and identified five populations spanning a total situated in the Celica‐Lancones basin north of the age range from the Mesozoic to the Precambrian. Tangula batholith (Fig. 1), does not contain any His subpopulation B1 (384‐639 Ma) overlaps in inherited zircon component indicating a domi‐ age with the inherited Ordovician core at Tres nantly primitive crustal basement, as opposed to Chorreras. Given that the Cretaceous Yunguilla the mature continental basement in the El Oro turbidites were deposited in a wide paleo‐forearc range further north (see also Chapter 4). basin corresponding to the present‐day Western (2) Ascending melts repeatedly exploited the Cordillera and Interandean region (Vallejo 2007), same structures through time (Tab. 4, and further this formation could likely constitute an assimi‐ discussion in the Appendix). Crystallization of arc lant for the Tres Chorreras (Saraguro) parental intrusive root zones along these structures melt. shielded ascending and accumulating melt batches from contamination by xenocrystic zir‐

26 Geodynamic controls on Tertiary arc that he expects his rotational parameters to be magmatism slightly more precise, mainly due to improved accuracy and resolution of the geologic time‐ In order to evaluate feedback reactions between scale. arc magmatism and the geodynamic regime at the Tertiary Ecuadorian margin, we compiled K‐Ar Assuming 25% relative uncertainties for conver‐ and ZFT data from a large number of sources for gence rates plotted in Figure 6 results in within Tertiary volcanic and plutonic rocks in Ecuador, in error overlapping rates throughout most of the addition to U‐Pb data presented in this study Miocene, but allows identification of a peak of (Tab. A3 in the Appendix). As discussed in the nearly orthogonal plate convergence at >120 Appendix, K‐Ar data can largely serve as an accu‐ mm/y in the Late Oligocene‐Early Miocene. Com‐ rate proxy for arc magmatism on a regional, pared to Late Eocene‐Early Oligocene conver‐ multi‐m.y. scale, although at individual magmatic gence rates, the significant acceleration and centers disturbed K‐Ar ages may occasionally oc‐ obliquity change starting at 28.3‐25.8 Ma and cur (e.g., at Apuela/Junin). Where K‐Ar and U‐Pb culminating in the 25.8‐20.2 Ma period is in data for the same lithology are available, maxi‐ agreement with the postulated change in Faral‐ mum age differences between the two methods lon plate motion prior to its fission at 24 Ma and are on the order of 1‐4 m.y. Potentially inaccu‐ initiation of Cocos‐Nazca seafloor spreading at 23 rate and disturbed ages were omitted from the Ma (Lonsdale 2005; Barckhausen et al. 2008). The data base (Tab. A3) such that the data used for change in both convergence rate and obliquity in the following discussion are thought to be accu‐ the 20.2‐16.0 Ma period cannot be clearly re‐ rate for the timing of magmatism on a regional solved at 25% relative uncertainty. It might relate scale. to a short‐term variation caused by the estab‐ lishment of post‐fission independent Nazca plate Tertiary convergence rates and obliquities at the motion commencing at c. 20 Ma when the east‐ Ecuadorian margin ward‐propagating plate rupture eventually inter‐ sected the Meso‐South American trench system; We computed Mid‐ to Late Tertiary (40‐0 Ma) convergence velocities and obliquities at 2°S/82°W, corresponding to the Central Ecuador‐ ian trench (Fig. 6), using the most recent set of available Farallon/Nazca‐South America rota‐ tional parameters (Somoza 1998) and the UNAVCO online plate motion calculator (http://sps.unavco.org/crustal_motion/dxdt/mod el). Along‐arc variations in convergence velocity and obliquity due to the age‐specific position of a given rotation pole are negligible for the small latitudinal difference between southern‐ and northernmost Ecuador (5°S to 1°N). Convergence Figure 6: Convergence parameters from 40‐0 Ma at the parameters in Figure 6 are plotted without uncer‐ Ecuadorian margin. Calculated at 2°S/82°W (present‐ tainty ranges because Somoza (1998) does not day central Ecuadorian trench position) using the Faral‐ quantify the uncertainties associated with his lon/Nazca‐South America rotational poles of Somoza rotation poles. Pardo‐Casas & Molnar (1987) pre‐ (1998). Note discussion of associated uncertainties in sent relative convergence rate uncertainties of c. the text. Also shown are major tectonic events affect‐ 25% for Miocene Farallon/Nazca‐South America ing the Farallon/Nazca plate during the plate reorgani‐ zation in the Oligocene‐Miocene (Lonsdale 2005; convergence rates around 100 mm/y at 10°S. Barckhausen et al. 2008) which comprise: 1 ‐ Farallon Since Somoza’s (1998) study is based on the same plate fission initiates at Farallon‐Pacific spreading cen‐ plate reconstruction systematics as the approach ter and propagates towards South America; 2 – Cocos‐ of Pardo‐Casas & Molnar (1987) it seems justified Nazca seafloor spreading initiates; 3 – plate rupture to apply identical relative uncertainties as a first‐ intersects South American trench; independent Nazca order estimate, although Somoza (1998) notes and eCocos plat motion starts.

27

Figure 7: Pluton and volcanic radiometric age versus latitude plot of southern Ecuador (SE of the CPPF) illustrating along‐arc migration patterns of arc magmatism. Screened radiometric age references are shown in Table A3 (Appen‐ dix); geologically inaccurate ages and duplicate samples were omitted from the database. Minimum ages progressively young northwards (red arrow) from the Peruvian border region (Portachuela batholith) towards the southern end of the present‐day Northern Volcanic Zone (Sangay volcano), likely reflecting northwards slab flattening due to the c. 14‐ 10 Ma inception of the Inca plateau at the northern Peruvian/southern Ecuadorian margin (Gutscher et al. 1999a; Rosenbaum et al. 2005) following a period of protracted arc magmatism throughout most of the Tertiary. this process was accompanied by a reorientation 2.3±0.8 Ma for pyroclastic rocks of the Salapa of the young Cocos‐Nazca spreading center Formation near Loja in southern Ecuador (Hun‐ (Barckhausen et al. 2008). gerbühler et al. 2002) could be in conflict with this model if accurately dating a magmatic event. Along‐arc distribution of Tertiary arc magmatism The mixed average ZFT age of this sample is 2 The Tertiary latitudinal migration pattern of arc 16.4±7.4 Ma (n = 23) with a χ probability of 0%, magmatism through time for southern Ecuador leading these authors to infer a depositional age (SE of the CPPF) is shown in Figure 7. Minimum of 2.3±0.8 Ma based on the youngest zircon. ages of exposed volcanic and plutonic rocks pro‐ Given these statistical ambiguities and the in‐ gressively young northwards. The youngest tense alteration features displayed by the Salapa phases of active arc magmatism in southernmost volcanics (Hungerbühler et al. 2002) the inferred Ecuador are recorded by the Portachuela batho‐ Salapa age might by inaccurate and we therefore lith (c. 4°30'‐5°S) and the Tarqui Formation (c. exclude it from our database. 3°30'S) with ages around 10‐12 Ma; younger Tar‐ qui units occur only further north (e.g., Hunger‐ Across‐arc distribution of Tertiary arc magma‐ bühler et al. 2002). The cessation of active arc tism magmatism in northern Peru and southern Ecua‐ Bulk across‐arc migration patterns may be used dor is temporally and spatially associated with to track changes in slab dip, although structurally the establishment of a flat slab subduction set‐ controlled magma ascent and emplacement, as ting due to subduction of the buoyant Inca pla‐ well as crustal thickening additionally influence teau starting at 14‐10 Ma (Gutscher et al. 1999a; arc magmatic outcrop patterns (e.g., Trumbull et Rosenbaum et al. 2005). The northward decrease al. 2006). Figure 8 illustrates Tertiary longitudinal in minimum ages of arc magmatism towards the migration patterns of arc magmatism through southernmost active arc volcano in Ecuador, San‐ time, combined with radiometric age histograms gay, thus probably reflects the progressive (U‐Pb, K‐Ar, and ZFT data from screened data‐ northward broadening of the flat slab region (see base; see discussion below) for two major Ecua‐ Fig. 2 for present‐day extent). A single ZFT age of dorian arc segments. Data for southern‐ and

28 northernmost Ecuador (4‐5°S and 1°N‐1°S, re‐ relate to slab steepening (increasing hot astheno‐ spectively) are not shown in Figure 8 as for the sphere convection into the mantle wedge, and, former the scarcity of available data does not ultimately, increased crustal melting; see discus‐ allow a reliable analysis of across‐arc migration sion below), similarly to what is inferred in parts patterns, and for the latter the present‐day of the central and southern Andes at that time trench obliquity is high and partly irregular, the (e.g., Mamani et al. 2010). However, the rear arc paleo‐trench configuration cannot be predicted position in all Ecuadorian arc segments remains with confidence, and, consequently, the age‐ relatively stable (Fig. 8) until the Late Miocene longitude distribution of this arc segment is not instead of systematically migrating westwards as directly comparable to the others. might be expected from slab steepening. The radiometric age base in northern‐central Ec‐ Eastward arc migration and broadening during uador (100 km arc strike length) is dominated by the Late Miocene‐Pliocene in all Ecuadorian arc plutonic rock samples. Regional Andean‐ (NNE) segments is consistent with minor‐moderate slab trending structures (mainly the CTSZ) exert a ma‐ flattening, although eastward arc migration (but jor control on pluton emplacement in Ecuador not broadening) could in addition partly relate to (Fig. 2 and Tab. 4; further discussion in the Ap‐ subduction erosion which affects the present‐day pendix) such that the relative stability of the Oli‐ Ecuadorian margin (e.g., Sage et al. 2006). The gocene‐Miocene across‐arc position (Fig. 8) may timing of the landward arc front migration in the partly relate to structurally controlled pluton em‐ Late Miocene can be traced by the youngest plu‐ placement, and the overall arc magmatic outcrop tons exposed in deeply eroded parts of the pattern may be biased trenchwards as major Western Cordillera: c. 6 Ma marks the youngest structures dip 35°E at deep to mid‐crustal levels magmatism in northern Ecuador (Junin porphyry (Guillier et al. 2001). Figure 8 shows that signifi‐ intrusions), whereas the youngest major plutonic cant eastward frontal arc migration occurred in activity in central Ecuador occurred at c. 14‐15 the Mid‐ to Late Miocene; major rear arc east‐ Ma (Telimbela‐Chazo Juan and Corazon intru‐ ward broadening is recorded for the Late Mio‐ sions), either indicating Late Miocene‐Pliocene cene‐Pliocene. eastward arc migration might have proceeded slightly diachronously along the arc, and/or post‐ The radiometric age database for southern‐ 14 Ma plutons exist, but have not been dated yet central Ecuador (200 km arc strike length) com‐ in the Western Cordillera of central Ecuador. The prises a large number of widespread volcanic and age of landward arc migration in northern‐central plutonic samples in subequal proportions. Data Ecuador broadly coincides in time with the arrival for this arc segment are thus potentially more of the Carnegie Ridge seamount chain at the Ec‐ sensitive to record arc migration patterns than uadorian‐Colombian trench at c. 8 Ma (Daly 1989; data for northern‐central Ecuador. The age‐ Gutscher et al. 1999b; Chapter 2); the latter longitude distribution of plutons and volcanics in might induce moderate slab shallowing by virtue southern‐central Ecuador suggests c. 50 km of arc of its buoyancy (e.g., van Hunen et al. 2004). Arc broadening by a westward frontal arc jump in the migration patterns do not indicate any significant Late Oligocene while the rear arc position re‐ pulses of pre‐Late Miocene subduction erosion mained relatively fixed (Fig. 8). Arc broadening is affecting the Ecuadorian margin. reversed by progressive (?) eastward frontal arc migration in the Mid‐Miocene and culminates in Productivity of Tertiary arc magmatism a Late Miocene‐Pliocene period of eastward arc migration comprising both the frontal and rear Radiometric age histograms (Fig. 8) have been arc regions, and mirroring the Late Miocene age‐ used as proxies for plutonic and volcanic rock longitude distribution trend in northern‐central volumes (e.g., Glazner 1991). They can only serve Ecuador. as first‐order proxies for arc magma production because they reflect arc exposure and erosion Although partly structurally controlled, major conditions as well. westward arc broadening in southern‐central Ec‐ uador in the Late Oligocene (Fig. 8) might thus Both major Ecuadorian arc segments display age peaks initiating in the Late Oligocene‐Early Mio‐

29 cene (yellow boxes in Fig. 8). Only in the northern that, as we do not attempted to quantify arc part of the northern Ecuadorian arc segment (not magma production rates at these times, this shown), the peak initiates slightly later in the flare‐up event may not correspond to the scale of Early to Mid‐Miocene. The peak in volcanism es‐ an arc magmatic flare‐up event in the sense of, sentially corresponds to the widespread eruption for example, Ducea & Barton (2007) with magma of upper Saraguro Group volcanics which mainly production rates > 75‐100 km3/m.y. arc km‐1. comprise ignimbrites in its upper portion (Tab. 1). Here, we are using the term flare‐up to indicate The peak in plutonism dominantly reflects the qualitatively a significant increase in arc magma‐ construction of the central Ecuadorian batholith tism compared to the Eocene‐Early Oligocene. A system, the Cangrejos‐Zaruma intrusive belt, and second peak in volcanism occurs in the Late Mio‐ associated smaller intrusions. Combined, this cene and probably reflects the increasing preser‐ peak distribution suggests a relative arc mag‐ vation potential of young volcanic sequences, and matic flare‐up event in Ecuador during the Late eastward arc broadening associated with moder‐ Oligocene‐Early Miocene. It is important to note ate slab flattening.

Figure 8: Pluton and volcanic radiometric age versus longitude plots and age histograms illustrating the Tertiary arc position (migration marked by red arrows) and arc magmatic intensity in Ecuador (from 1‐4°S). Used radiometric ages (U‐Pb, K‐Ar, ZFT) were carefully screened, and potentially inaccurate or duplicate ages have been removed from the database (Appendix Table A3). The Paleocene‐Eocene arc position is relatively stable in all arc segments. Arc broaden‐ ing occurs by a c. 50 km westwards jump of the frontal arc during the Late Oligocene in southern‐central Ecuador; this is not clearly observed in the arc segment further north because of structurally controlled pluton emplacement (along the CTSZ and CPPF) and almost complete erosion of Oligocene‐Miocene volcanic rocks. Progressive eastward migration of the frontal arc at constant rear arc positions during the Early to Mid‐Miocene is followed by a Late Miocene‐Pliocene period of significant eastward broadening of the rear arc. Age histograms show Late Oligocene‐Early Miocene peaks in arc magmatism in all arc segments indicative of a regional arc magmatic flare‐up event (yellow boxes).

30 Glazner (1991) suggests that periods of intense atic migration of the rear‐arc position is not ob‐ plutonism might be associated with oblique con‐ served. vergence settings as the latter result in crustal In addition, the flare‐up event in Ecuador coin‐ strike‐slip deformation and thus space creation cides with a major acceleration in Farallon/Nazca‐ for pluton emplacement. We do not observe any South America convergence rates at the Ecuador‐ systematic correlations between convergence ian trench (Fig. 6). This suggests a feedback obliquity (Fig. 6) and plutonism (Fig. 8) in Tertiary mechanism between the arc magmatic flare‐up Ecuadorian arc magmatism. However, as the Ec‐ event and plate tectonics operates at an astheno‐ uadorian margin represents an oblique subduc‐ spheric scale. The same has been proposed for tion system (where obliquity is variably accom‐ the southern Chilean margin for the same time modated by oblique subduction slip and crustal interval during which neither subducting slab strain partitioning; Ego et al. 1996 and Appendix) properties nor overriding plate motion under‐ the Tertiary margin has probably undergone went any major changes (Jordan et al. 2001). large‐scale crustal strike‐slip deformation throughout the Tertiary such that plutonism was Melt production in the mantle wedge is concen‐ principally continuous. Peak periods of pluton trated in the region where slab dehydration‐ emplacement might in part, however, relate to derived volatiles first encounter fertile mantle reactivation of large strike‐slip fault systems. material of a sufficiently high temperature to in‐ duce partial melting (e.g., Cagnioncle et al. 2007; Asthenospheric controls on a Late Oligocene‐ note that, additionally, decompression melting Early Miocene flare‐up event in Ecuadorian arc might take place in other regions). Subsequently, magmatism the melt fraction may be modified by interaction Mamani et al. (2010) attribute widespread Late of the ascending melt with the surrounding man‐ Oligocene‐Early Miocene ignimbrite eruptions in tle peridotite (e.g., Grove et al. 2003). Several the central Andes to increased crustal melting parameters control increased mantle melting and asthenospheric melt production in response and, by inference, increased arc magma produc‐ to slab steepening. As discussed above, Late Oli‐ tion and development of a broader arc at faster gocene‐Early Miocene arc broadening in south‐ convergence rates and/or during slab steepening. ern‐central Ecuador, and the correlated peaks in These essentially comprise variations in slab‐ arc volcanism and plutonism might also be asso‐ derived volatile flux, the volatile fraction reaching ciated with slab steepening, although a system‐ the zone of partial melting in the supra‐slab

Table 4: Regional structures in Ecuador associated with Tertiary intrusions investigated or referenced in this study

Structure associated intrusions remarks Chimbo-Toachi Santiago, Apuela-Nanegal extends to deep to mid-crustal levels (c. 35°E dip; Guillier et al. shear zone (-Junin/Cuellaje), Corazon, 2001); originally regarded as suture zone for Macuchi island arc (CTSZ) Telimbela-Chazo Juan, (Hughes & Pilatasig 2002), but more recently dismissed as suture Balsapamba-Las Guardias, with autochtonous Macuchi origin (Vallejo 2007; Vallejo et al. 2009) Echeandia

Calacalí-Pujili- Chaucha extends to deep to mid-crustal levels (c. 35°E dip; Guillier et al. Pallatanga fault 2001); western limit of regional suture zone between accreted oce- zone (CPPF) anic plateau units and the paleocontinental margin (Spikings et al. 2005; Vallejo et al. 2009) northern Amo- Cangrejos-Zaruma intrusive bracketed between Piñas-Portovelo and Jubones fault systems; tape suture zone belt Piñas-Portovelo fault joins westwards with La Palma-El Guayabo and Tahuin Dam (Naranjos) faults, delimiting the deeply exhumed metamorphic Raspas complex whose structural position has been related to the ancient Amotape suture zone (Bosch et al. 2002)

See Appendix for a more detailed discussion on structurally controlled intrusion emplacement.

31 mantle wedge by porous flow, mantle wedge mantle wedge is balanced by forced return flow temperatures and the (lateral) extent of the zone of hot, fertile mantle material sourced from a where wet melting occurs, as well as the supply lower backarc region (Kincaid & Sacks 1997); in a rate of fertile mantle material from induced re‐ more realistic three‐dimensional environment turn flow (Fig. 9). The relative importance of each return flow sources could additionally be dy‐ parameter may vary depending on which bound‐ namically distributed in along‐arc dimension (e.g., ary conditions apply (Cagnioncle et al. 2007). Behn et al. 2007). The return flow rate, coupled to the slab velocity, thus directly controls two In a simplified two‐dimensional numerical mantle main parameters for partial melt production in flow model of a slice oriented parallel to the sub‐ the mantle wedge, namely the supply of fertile duction slip, Kincaid & Sacks (1997) show that a mantle material and mantle wedge temperatures temperature‐controlled viscous boundary layer (Cagnioncle et al. 2007). forms in the asthenosphere adjacent to the downgoing slab, where mantle material is Kincaid & Sacks (1997) demonstrate that the dragged downwards parallel to the slab at rates maximum mantle wedge temperature increases proportional to the subduction slip. Removal of as a function of subduction slip; the effect is not asthenospheric boundary layer material from the linear, but becomes more significant for changes

Figure 9: Simplified schematic subduction zone cross section of the Ecuadorian margin as broadly applicable for Late Oligocene‐recent times illustrating multiple stages of arc magma petrogenesis. Progressive slab dehydration takes place below the forearc and main arc regions. Temperature‐controlled formation of a viscous boundary layer couples asthenospheric material with slab motion, and induces return flow into the mantle wedge. In simplified two‐ dimensional models, melt production in the mantle wedge is controlled by the amount of slab‐derived fluids reaching the region of partial melting in the mantle wedge, and by asthenospheric return flow rates providing fertile mantle ma‐ terial and possibly increasing mantle wedge temperatures (e.g., Cagnioncle et al. 2007). These processes operate more vigorously at higher subduction slip velocities and may thus increase partial melt production in the mantle wedge. Note that in a three‐dimensional environment additional along‐arc controls may influence the productivity of partial melting and arc magmatism (e.g., Tamura et al. 2002). Major fault geometries shown in the Figure correspond to the present‐ day configuration based on Guillier et al. (2001); fault systems of the sub‐Andean zone and the Eastern Cordillera are not shown. Upper plate Tertiary pluton distribution suggests strong structural control of major structures (partly su‐ tures) on magma ascent (possibly in part non‐vertical) and pluton emplacement (see Tab. 4 and further discussion in the Appendix). General petrogenetic aspects of cross section adapted from Kincaid & Sacks (1997), Stern (2002), Grove et al. (2003), Annen et al. (2006), and Cagnioncle et al. (2007).

32 from slow‐moderate to fast subduction slips, are not considered in the simplified two‐ whereas it becomes nearly negligible for velocity dimensional models discussed above. increases taking place at already high subduction slips (> c. 100mm/y, depending on the overriding Crust‐mantle wedge feedback impacts on arc plate thickness). Calculating the due‐east Faral‐ magmatism lon/Nazca‐South America convergence rates Increased partial melt production in the mantle (from Fig. 6) as a first‐order proxy for subduction wedge heats the crust of the overriding plate by slip at the Ecuadorian margin reveals a Late Oli‐ advection (due to a larger volume of ascending gocene‐Early Miocene increase from 60‐70 mm/y partial melts) and by increased conductive basal to 120‐140 mm/y thus representing a critical in‐ heat flow into the overlying South American crease from moderate to high subduction slips lithosphere. This implies a higher melt fraction in where a significant effect on maximum mantle a deep crustal hot zone (Annen et al. 2006) and wedge temperature would be expected. could increase the crustal contribution to arc Higher plate convergence rates e(and mor magmatism by lowering the relative thermal trench‐orthogonal convergence), if proportional threshold for assimilation. Increased crustal melt‐ to local subduction slip velocities, might increase ing is inferred for arc magmatic flare‐up events the amount of volatiles introduced into the man‐ elsewhere, and might also be driven by additional tle wedge by slab dehydration, but at the same factors such as crustal thickening or lithospheric time decrease the volatile fraction reaching the delamination (e.g., Ducea & Barton 2007). The region of partial melting by increased downwards widespread occurrence of Late Oligocene‐Early volatile advection due to more vigorous return Miocene silicic ignimbrites as part of the upper flow; the latter effect becomes less pronounced Saraguro Group (Tab. 1) is consistent with in‐ at higher mantle wedge permeability, i.e., faster creased crustal melting. Whole‐rock isotopic volatile migration rates (Cagnioncle et al. 2007; compositions of Tertiary arc units do not show see also Zellmer 2008). In two‐dimensional mod‐ any straightforward systematic variations in the els, faster convergence rates result in higher Late Oligocene‐Early Miocene indicative of bulk rates of mantle partial melt production where the increased continental crust contributions (Chap‐ proportionality between the two may vary as a ter 4). However, this is anticipated as mid‐ to function of the interplay of various control pa‐ deep crustal basement units of the Tertiary arc in rameters (Cagnioncle et al. 2007). Consequently, Ecuador are mostly composed of isotopically the arc magmatic flare‐up event observed in Ec‐ primitive oceanic material, and spatio‐temporal uador during the Late Oligocene‐Early Miocene isotopic variations mainly relate to the tectoni‐ might ultimately reflect increased asthenospheric cally controlled occurrence of continental base‐ melt input into the arc crust driven by increased ment units, and the vertical level of arc magma plate convergence rates, possibly further accen‐ differentiation in the crust, instead of the total tuated by slab steepening. With increasing return amount of crustal contamination (Chapter 4). flow rates, mantle wedge partial melts may be Increased heat flow into the overriding plate trig‐ advected closer towards the trench, thus princi‐ gered a regional uplift event and resulted in re‐ pally causing trenchward arc broadening as ob‐ gional horizontal extension along the Chilean served in the Saraguro arc segment during the main arc in the Late Oligocene‐Early Miocene Late Oligocene‐Early Miocene; however, the vol‐ (Jordan et al. 2001). This tectonic setting is con‐ canic front position might also be controlled by sistent with the inferred tensional environment additional factors such as melt collection in a de‐ during deposition of the Saraguro Group (e.g., compaction channel (Cagnioncle et al. 2007). It is Steinmann 1997) and correlates in time with important to note that along‐arc heterogeneities widespread elevated cooling and exhumation in mantle wedge partial melt production are rates along the Ecuadorian margin in the Mio‐ likely to further influence arc magmatic distribu‐ cene, as inferred from thermochronologic model‐ tion patterns (e.g., Tamura et al. 2002); the latter ing (e.g., Spikings et al. 2005).

33 Conclusions given mantle wedge volume, and by a change in asthenospheric flow dynamics where widespread This study presents the first dataset of robust U‐ positive thermal anomalies develop in the subarc Pb zircon ages on Late Tertiary intrusive rocks of mantle wedge and replenishment rates of fertile Ecuador. The regional distribution trends of Ter‐ mantle material increase in response to more tiary plutons at the Ecuadorian margin mirror the vigorous induced return flow. The latter might along‐ and across‐arc orientations of deeply‐ additionally be influenced by slab steepening. rooted major fault zones suggesting crustal Therefore, we attribute the flare‐up event in arc magma ascent and intrusion emplacement were magmatism to increased melt production in the principally controlled by these structures, further mantle wedge causing increased mantle‐crust modulated by distributed (mainly transpres‐ melt flux and increased heat transfer into the sional) shear in the upper crust. External zircon crust of the overriding plate. As elsewhere (e.g., inheritance in Tertiary intrusions of the Western Ducea & Barton 2007) a positive tectonomag‐ Cordillera and the Interandean region of Ecuador matic‐thermal feedback mechanism may be in‐ is very minor, likely reflecting dominantly zircon‐ duced, facilitating increased partial crustal melt‐ poor oceanic basement units as potential assimi‐ ing, voluminous magma storage at upper crustal lants. In addition, zircon assimilation during levels leading to batholith construction, and/or magma ascent and mid‐ to shallow crustal differ‐ ignimbrite eruption at the Earth’s surface. How‐ entiation was mainly restricted to antecrysts de‐ ever, the Late Oligocene to Early (Mid‐) Miocene rived from intrusive root zones, likely as a result arc magmatic flare‐up event in Ecuador seems to of continuous preferential channeling of arc be mainly triggered by increased asthenospheric magmas through the same, deeply‐rooted struc‐ power input into the lithosphere, instead of tural conduits. compression‐induced crustal thickening or exten‐ Where both K‐Ar and U‐Pb data exist for a given sion‐related lithospheric delamination as inferred lithology, ages obtained by the different methods for flare‐up events in other places (Ducea & Bar‐ are usually concordant within 1‐4 m.y. implying ton 2007). that K‐Ar data may be used as a semi‐accurate proxy for the timing of Tertiary arc magmatism in References Ecuador on a broad, regional scale. Combining previously published K‐Ar and ZFT age informa‐ Annen, C., Blundy, J. D., Sparks, R. S. J. (2006): The tion with newly obtained zircon U‐Pb ages of Ter‐ genesis of intermediate and silicic magmas in deep tiary intrusions allows us to identify a pro‐ crustal hot zones. Journal of Petrology 47; 505‐539. nounced pluton emplacement peak in the Late Aspden, J.A., Harrison, S. H., Rundle, C. C. (1992): New Oligocene to Early (Mid‐) Miocene. The peak in geochronological control for the tectono‐magmatic plutonism temporally coincides with the aerially evolution of the metamorphic basement, Cordillera extensive eruption of Saraguro Group ignim‐ Real,d an El Oro Province of Ecuador. Journal of South brites, and seems to indicate a regional, transient American Earth Sciences 6; 77‐96. arc magmatic flare‐up event in Ecuador involving Bachmann, O., Miller, C. F., de Silva, S. L. (2007): The significant westward arc broadening in central volcanic‐plutonic connection as a stage for under‐ Ecuador. At the time scale resolvable by plate standing crustal magmatism. Journal of Volcanology tectonic reconstructions, initiation of the arc and Geothermal Research 167; 1‐23. magmatic flare‐up event coincides with a change Barckhausen, U., Ranero, C R., Cande, S. C., Engels, M., in Farallon plate motion prior to its fission involv‐ Weinrebe, W. (2008): Birth of an intraoceanic spread‐ ing a significant acceleration of Farallon/Nazca‐ ing center. Geology 36; 767‐770. South America convergence rates, and suggesting Beate B., Monzier M., Spikings R., Cotton J., Silva J., a positive feedback operating between faster Bourdon E., Eissen J.‐P. (2001): Mio‐Pliocene adakite plate convergence rates, asthenospheric melt generation related to flat subduction in southern Ec‐ production and arc magmatic productivity in Ec‐ uador: the Quimsacocha volcanic center. Earth and uador. This might be envisaged by a higher Planetary Science Letters 192; 561–570. amount of slab‐derived fluids introduced into a

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38 Appendix I – Accommodation of struction. These authors show that in the recon‐ structed setting the Manabi and Progreso forearc convergence obliquity at the Ec‐ basins are juxtaposed against Interandean re‐ uadorian margin throughout the gions of Miocene marine transgressions; these depositional environments are correlatable in Tertiary terms of a continuous proximal‐distal basin fa‐ The occurrence of non‐orthogonal plate conver‐ cies, thus indicating that the scale of their dis‐ gence implies two end‐member geodynamic placement estimate is accurate. Consequently, situations where convergence obliquity is either using CPPF slip rates as a proxy for the oblique accommodated by oblique subduction slip or convergence component accommodated by the overriding plate strain partitioning possibly in‐ upper plate, one would assume that the Ecuador‐ cluding forearc sliver displacement (McCaffrey ian margin must have been constantly weakly 1992). Whereas the former is likely to influence decoupled since the Mid‐Miocene. asthenospheric flow dynamics, the latter consti‐ However, the direction of plate convergence at tutes an important factor for crustal magma as‐ the Ecuadorian margin has been almost due east cent and pluton emplacement mechanisms (e.g., since 28.3 Ma (Chapter 2: Fig. 6), paralleling the Glazner 1991). Therefore, the mode of conver‐ present‐day subduction slip (instead of the pre‐ gence obliquity accommodation at a convergent sent‐day direction of convergence). If present‐day plate margin has to be critically evaluated in or‐ subduction slip directions were applied, the cen‐ der to discuss potential controls on overriding tral Ecuadorian margin would be almost com‐ plate magmatism (cf. Appendix II). pletely coupled during most of the Late Oligo‐ Ego et al. (1996) show that the present‐day Ecua‐ cene‐Miocene, and weakly to moderately de‐ dorian margin is weakly decoupled where 75‐90% coupled only from 20.2‐16.0 Ma and from 4.9 Ma of the convergence obliquity are transferred into until the present day. Significant convergence trench‐oblique, due east (87°) subduction slip, obliquity accommodated by major forearc sliver whereas only 10‐25% obliquity are accommo‐ displacement would thus be restricted to these dated by the upper plate. Current dextral forearc periods. Clearly, these considerations are in dis‐ sliver displacement rates along the CPPF can ac‐ agreement with the expected upper plate strike‐ count for most of the northwards increasing up‐ slip displacement from the reconstruction of per plate trench‐parallel component (Ego et al. Hungerbühler et al. (2002), as displacing the 1996), although a number of additional Andean‐ forearc sliver for 100‐130 km since only 4.9 Ma trending fault systems (including the CTSZ and required unrealistically high displacement rates, the Peltetec fault in Ecuador) also accommodate which would be difficult to reconcile with Pleisto‐ convergence obliquity and currently act as a re‐ cene values (Trenkamp et al. 2002). gional restraining bend (Winkler et al. 2005). The Consistent evidence for strain partitioning with a highly oblique subduction slip of the Ecuadorian‐ significant dextral strike‐slip component along Colombian margin is uncharacteristic for the the repeatedly reactivated major fault systems southern‐central Andes where subduction is below the Western Cordillera during the Tertiary mostly trench‐normal; Sébrier & Bellier (1993) exists, although the exact time periods are not suggest that the allochthonous, rheologically always well constrained. Dextral shearing along strong oceanic plateau basement of the northern the CTSZ in northern Ecuador has a minimum age Andes might control the degree of margin de‐ of 48.3±0.6 Ma (hornblende K‐Ar age of foliated coupling of this regional arc segment. diorite emplaced within the CTSZ; Hughes & Pi‐ Using slip rates comparable to Pliocene‐present‐ latasig 2002). A short distance to the west of the day values Hungerbühler et al. (2002) obtain a CTSZ, Chiaradia et al. (2008) show S‐C fabrics in total displacement estimate of 100‐130 km along altered rocks associated with the Macuchi‐hosted the CPPF since the Mid‐Miocene which they use La Plata ore deposit; these authors interpret the to perform a palinspastic forearc sliver recon‐ structures as indicative of Late Eocene dextral

39 transpression related to distributed shearing the Ecuadorian‐Colombian margin to the Nazca‐ along the CTSZ. Mid‐Late Eocene whole‐scale Cocos‐Caribbean plate boundary to the north, dextral strike‐slip motion of the Ecuadorian the transition to the northern Peruvian flat slab forearc sliver along the proto‐CPPF and CTSZ fur‐ segment to the south, and the potential influence ther produced intra‐forearc block rotations of Carnegie Ridge subduction, which all likely in‐ where individual blocks are separated by a set of creases the Miocene subducting slab geometric NNW‐trending sinistral dip‐slip faults (Daly 1989). complexity (e.g., Gutscher et al. 1999; Taboada et The whole structure of the Western Cordillera is al. 2000). The complex margin geometry and out‐ interpreted as a positive flower structure formed crop pattern of Tertiary arc units in Ecuador in response to dextral transpressional reactiva‐ (Chapter 2: Figs. 1; 2) prevents an arc geometry‐ tion of the 35°E‐dipping suture zone forming the based discussion of paleo‐subduction slip direc‐ root of the CPPF, as well as the deeply‐rooted tions even if, for simplicity, subvertical translitho‐ CTSZ (Guillier et al. 2001, and references therein). spheric magma ascent was assumed. Overall, one Finally, Winkler et al. (2005) infer that dextral expects a regionally more homogenous subduc‐ transpression along a restraining bend (including tion geometry along the NW South American the CTSZ, CPPF, Peltetec fault, and Chingual‐La margin prior to the Late Oligocene Farallon plate Sofia fault in Ecuador) has been active since at fission. least 15 Ma, with a pulse of increased activity (3) The Ecuadorian margin and trench geometry since 6 Ma being responsible for the inception of changed through time; the margin geometry the IAD as a full‐, and locally half‐ramp basin. could obviously be strongly influenced by forearc Four possible explanations for the discrepancy sliver displacement. Daly (1989) estimates a between convergence obliquity‐based predicted minimum clockwise trench rotation of 20° since limited strike‐slip motion since the Mid‐Miocene the Oligocene, but does not present any argu‐ and upper plate geological evidence for more ments in favor of this estimate. significant strike‐slip motion exist, and might all (4) The time‐dependent correlation of sedimen‐ be applicable to some degree: tary basin facies by Hungerbühler et al. (2002) (1) Computation of Somoza’s (1998) rotation based on continuous displacement since the Mid‐ poles for the Ecuadorian margin (Chapter 2: Fig. Miocene is inaccurate and overestimates the to‐ 6) slightly underestimates convergence obliquity. tal forearc sliver displacement in the latest Terti‐ However, using convergence parameters calcu‐ ary; instead, forearc sliver displacement of 100‐ lated from Pardo‐Casas & Molnar (1987) instead 130 km along the proto‐CPPF represents cumula‐ yields an even less oblique direction of conver‐ tive, non‐continuous displacement processes gence with respect to the present‐day subduction throughout the whole Tertiary (Witt et al. 2006). slip. While Somoza (1998) does not present any In conclusion, if the present‐day mode of conver‐ rotation pole uncertainties, the uncertainty gence partitioning at the Ecuadorian margin ranges shown by Pardo‐Casas & Molnar (1987) holds some significance for the Tertiary subduc‐ indicate that the precision of the rotation poles is tion system, and at the same time substantial insufficient to further evaluate temporal varia‐ forearc sliver displacement took place since the tions in obliquity at this time scale, as was al‐ Mid‐Miocene, it seems likely that the margin ge‐ ready noted by Daly (1989). Generally, recon‐ ometry and the degree of margin decoupling, i.e., structed convergence parameters always average the component of upper plate accommodation of plate motion over multi‐m.y. periods such that oblique plate convergence, varied through time. any short‐term variations are smoothened out Therefore, overriding versus downgoing plate and thus difficult to detect. strain partitioning in response to changing con‐ (2) The Tertiary paleo‐subduction slip deviated vergence obliquities cannot be reliably predicted from the direction of the present‐day subduction with currently available data, but geological evi‐ slip. Considering a multi‐m.y. lag time, this would dence for multiple phases of Tertiary strike‐slip be a likely response to changes of the conver‐ deformation in the overriding plate exists. From gence direction, especially given the proximity of the Eocene to the Late Oligocene, plate conver‐

40 gence was significantly more oblique with respect convergent subduction: the Andean case. Extended to the present‐day subduction slip (Chapter 2: conference abstracts, ISAG 1993, Oxford, 139‐142. Fig. 6) making short‐term variations in subduction Somoza, R. (1998): Updated Nazca (Farallon)—South slip less likely, such that consistently increased America relative motions during the last 40 My: impli‐ margin decoupling was a likely consequence. cations for mountain building in the central Andean These considerations are in general agreement region. J S Am ;Earth Sc 11 211‐215. with the notion of Witt et al. (2006) discussed Taboada, A., L. A. Rivera, A. Fuenzalida, A. Cisternas, H. above, and would thus be equally applicable if Philip, H. Bijwaard, J. Olaya, and C. Rivera (2000), Geo‐ the Mid‐Miocene sedimentary basin facies corre‐ dynamics of the northern Andes: Subductions and lation of Hungerbühler et al. (2002) was incor‐ intracontinental deformation (Colombia), Tectonics, rect. 19(5), 787–813. Trenkamp, R., Kellog, J. N. Freymueller, J. T. Mora, H. References P. (2002): Wide plate margin deformation, southern Chiaradia, M., Tripodi, D., Fontboté, L., Reza, B. (2008): Central America and northwestern South America, Geologic setting, mineralogy, and geochemistry of the CASA GPS observations: Journal of South American Early Tertiary Au‐rich volcanic‐hosted massive sulfide Earth Sciences, v. 15, p. 157‐171. deposit of La Plate, Western Cordillera, Ecuador. Eco‐ Winkler, W., Villagomez, D., Spikings, R., Abegglen, P, nomic Geology 103; 161‐183. Tobler, S, Eguez, A. (2005): The Chota basin and its Daly, M. C. (1989): Correlation between significance for the inception and tectonic setting if Nazca/Farallon plate kinematics and forearc basin evo‐ the inter‐Andean depression in Ecuador. Journal of lution in Ecuador. Tectonics 8:769–790. South American Earth Sciences 19; 5‐19. Ego, F., Sébrier, M., Lavenu, A., Yepes, H., Egues, A. Witt, C., J. Bourgois, F. Michaud, M. Ordoñez, N. Jimé‐ (1996): Quaternary state of stress in the Northern An‐ nez, and M. Sosson (2006): Development of the Gulf of des and the restraining bend model for the Ecuadorian Guayaquil (Ecuador) during the Quaternary as an ef‐ Andes. Tectonophysics 259; 101‐116. fect of the North Andean block tectonic escape, Tec‐ tonics, 25, TC3017, doi:10.1029/2004TC001723. Glazner, A. F. (1991): Plutonism, oblique subduction, and continental growth: an example from the Meso‐ zoic of California. Geology 19; 784‐786. Guillier, B. Chatelain J.L. Jaillard, E., Yepes, H., Poupinet, G., Fels, J.F. (2001): Seismological evidence on the geometry of the orogenic system in central‐ northern Ecuador (South America): Geophysical Re‐ search Letters, v. 28, p. 3749‐3752. Hughes R. A., Pilatasig L. F. (2002): Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador. Tectonophysics 345:29–48. Hungerbühler, D., Steinmann, M., Winkler, W., Sew‐ ard, D., Egüez, A., Peterson, D. E., Helg, U., Hammer, C. (2002): Neogene stratigraphy and Andean geodynam‐ ics of southern Ecuador. Earth Science Reviews 57; 75– 124. McCaffrey, R. (1992): Oblique Plate Convergence, Slip Vectors, and Forearc Deformation, J. Geophys. Res., 97(B6), 8905–8915. Pardo‐Casas, F. & Molnar, P. (1987): Relative Motion of The Nazca (Farallón) and South American Plates since Late Cretaceous Time. Tectonics 6; 233‐248. Sébrier, M. & Bellier, O. (1993): How is accommodated the parallel‐to‐the‐trench slip compo‐nent in oblique

41 they commonly provide subvertically oriented Appendix II – Overriding plate high‐permeability structures (e.g., Richards structural controls on the spatio‐ 2003). However, particularly in the upper crust, ascending magma may use any available struc‐ temporal distribution of Tertiary tural weakness such that ascent is not necessarily plutons in Ecuador vertical t(Sain Blanquat et al. 1998; Kalakay et al. 2001). Furthermore, the stress regime prevailing Overriding plate tectonics, stress regime and arc at a given time does not control the orientation magmatism show coupled behavior on a regional of pre‐existing structures (Cembrano & Lara to local scale: strike‐slip deformation as a result 2009). Space creation for intrusion emplacement of strain partitioning in the overriding plate is in the upper crust involves displacement of the mainly localized in the rheologically weak arc crustal host rocks, either by means of deforma‐ magmatic zone (Dewey et al. 1998). Melt ascent tion where fault kinetics control emplacement and emplacement in the crust can be efficiently rates (Glazner 1991; Grocott et al. 1994; Acocella focused by structures and is significantly aided by et al. 2008) or/and by ballooning and roof uplift deformation (Saint Blanquat et al. 1998; Vigner‐ (Paterson & Fowler 1993; Saint Blanquat et al. esse & Clemens 2000), and may in turn induce 2006). Thus, emplacement of intrusions along further strike‐slip partitioning (Saint Blanquat et pre‐existing or newly formed structures com‐ al. 1998). Detailed recent reviews of the complex bined with synintrusive deformation does not mechanisms of arc magma ascent and emplace‐ seem to be a general requirement for crustal ment are presented by Richards (2003) and Cem‐ magma ascent or pluton emplacement, but these brano & Lara (2009). In the following, we focus processes are expected to be positively corre‐ on investigating whether and how the spatial and lated, and possibly feedback‐related with each temporal distribution of Tertiary plutonism in other. Ecuador is affected by: (1) the regional signifi‐ cance of structural control for localizing intru‐ The spatial distribution of Tertiary intrusions in sions; and (2) the role of synintrusive deforma‐ Ecuador closely follows the major NNE‐ and ESE‐ tion and the local‐regional stress field on pluton trends of upper plate structures (Fig. 2). In this emplacement. Plutons mapped as Tertiary intru‐ context, plutons are not expected to be directly sions in the Eastern Cordillera have Late Creta‐ localized along major first‐order structures but ceous‐Early Tertiary K‐Ar ages which are poten‐ should rather be emplaced in associated periph‐ tially thermally disturbed on a regional‐scale eral areas of dilation (Richards 2003). Major in‐ (Peltetec event; Litherland et al. 1994), and are trusive belts center on deeply‐rooted faults and thus excluded from any further discussion here. translithospheric suture zones between the mainland and the allochthonous western oceanic A few general considerations apply for these two domain or the southern Amotape terrane, re‐ points. Due to intrinsic overpressuring arc magma spectively: is principally able to ascend and reach the Earth’s surface irrespective of the prevailing local‐ . The N‐ to NE‐trending CTSZ at the western regional stress regime (e.g., Paterson & Fowler flank of the Western Cordillera is spatially 1993; Saint Blanquat et al. 1998; Cembrano & associated and aligned with the northern Lara 2009); a compressional stress component batholiths of Santiago and Apuela‐Nanegal, does not prevent magma from ascending along the central Ecuadorian batholith system pre‐existing or newly formed structures but may (Corazon, Telimbela‐Chazo Juan, Balsa‐ in fact enhance magma ascent by tectonic over‐ pamba‐Las Guardias, Echeandia‐Industria) pressuring (especially at lower crustal levels; as well as multiple small intrusions. Until Saint Blanquat et al. 1998). Local transpressional recently, the CTSZ used to be regarded as a or transtensional stress settings (e.g., associated suture zone (Hughes & Pilatasig 2002) al‐ with restraining or releasing bend geometries of though Vallejo et al. (2006, 2009) proposed large strike‐slip systems; Sylvester 1988) prefer‐ a geodynamic model for the Ecuadorian entially localize rapid magma ascent, because margin where the Macuchi island arc is autochthonous dismissing the suture origin

42 of the CTSZ. Nonetheless, the great strike voluminous Portachuela batholith is em‐ length of the shear zone and seismic stud‐ placed and exhumed along the N‐S trend‐ ies (Guillier et al. 2001) indicate that the ing Las Aradas fault between the Amotape structure extends to deep crustal (possibly terrane and the Eastern Cordillera (Lither‐ transcrustal) levels, although it might not land et al. 1994). be a translithospheric transform fault such The Andean‐trending CTSZ and CPPF show a sub‐ as the CPPF. As described above (Appendix parallel orientation with respect to the central‐ II of Chapter 2), geologic evidence suggests northern Ecuadorian margin and the downgoing multiple phases of dextral transpressional slab, and are thus potentially favorably aligned movement along the shear zone since the with zones of asthenospheric partial melting and Eocene. lithospheric magma ascent. In contrast, the Can‐ . The NE‐ to NNE‐trending CPPF represents grejos‐Zaruma intrusive belt forms a transverse the western limit of a Late Cretaceous su‐ structure with respect to the margin trend, char‐ ture zone below the Western Cordillera acterized by roughly coeval (on a time scale of a (e.g., Vallejo et al. 2006); it has been reacti‐ few m.y.) pluton emplacement at its eastern and vated ase th present‐day CPPF with a dex‐ western end and, by inference, along its whole tral transpressional sense of movement strike length. While the present‐day slab geome‐ and accommodates a significant compo‐ try below this arc segment is likely contorted or nent of the present‐day convergence discontinuous as a result of the flat‐steep slab obliquity (Ego et al. 1996). It is spatially as‐ transition between northern Peru and central sociated with the Chaucha batholith and Ecuador (Gutscher et al. 1999), such geometric multiple smaller intrusions at its southern complexities are unlikely to have existed in the end where it splays off and intersects the Late Oligocene‐Early Miocene when most of the Western Cordillera towards the Gulf of intrusions formed; a continuous subduction of Guayaquil. The preferential emplacement the Farallon plate can be assumed for that time. of Tertiary intrusions along the CPPF and Slab geometry and the orientation of the zone of CTSZ was already noted by Litherland & asthenospheric partial melting alone thus fail to Aspden (1992), although the tectonomag‐ explain the intrusive belt alignment, such that the matic model presented by these authors arc‐transverse pluton emplacement trend must does not withstand modern concepts of arc have been significantly structurally controlled. magma genesis (e.g., Stern 2002; Richards The concentrated occurrence of Oligocene‐ 2003). Miocene plutons along the flanks of the CTSZ . The Cangrejos‐Zaruma intrusive belt occu‐ suggests this structure in part controlled magma pies a central axial position between the ascent and pluton emplacement. Subvertical Piñas‐Portovelo and Jubones fault systems, transcrustal structures are expected to channel‐ probably in the vicinity of the northern ize ascending magma (e.g., Cembrano & Lara limit of Amotape basement (Litherland et 2009). However, at c. 1°30’ S latitude, Guillier et al. 1994). Towards the west, the Piñas‐ al. (2001) show present‐day seismicity patterns Portovelo fault joins with the La Palma‐El defining 35°E dipping planes at mid‐ to deep Guayabo and Tahuin Dam (Naranjos) faults; crustal levels which these authors interpret as these faults delimit the deeply exhumed the traces of the CTSZ and CPPF fault planes, as metamorphic Raspas complex whose struc‐ they intersect these structures at surface levels. tural position has been related to the an‐ Reactivation of the faults caused deformation of cient Amotape suture zone (Bosch et al. their upper portions resulting in subvertical dips 2002). Thus, while the exact location of the close to the surface (Guillier et al. 2001). If a simi‐ northern Amotape suture is concealed be‐ lar, non‐vertical dip had already been established low Tertiary cover sequences, the Cangre‐ during the Oligocene‐Miocene this scenario could jos‐Zaruma belt seems to be emplaced in a be interpreted in the following ways: (1) an addi‐ proximal and subparallel position with re‐ tional deeper subvertical portion of the CTSZ ex‐ spect to the suture zone. Further south, the ists and was exploited by ascending magmas, but

43 is not seismically active at present; (2) the proto‐ tween two major structures, the CPPF and the CTSZ only controlled pluton emplacement (by CTSZ, and second‐order lineaments associated tectonic space creation) at shallow crustal levels, with these structures (but see discussion on addi‐ but did not significantly influence magma ascent tional across‐arc lineaments in Chapter 2). While at depth; (3) significant non‐vertical magma as‐ the batholithic intrusions in central Ecuador cent along the proto‐CTSZ at deep‐ to mid‐crustal (Balsapamba‐Las Guardias, Telimbela‐Chazo Juan, levels took place. Given the deep crustal nature plus associated intrusions) are spatially associ‐ of the CTSZ, we expect it to be principally able to ated with lineaments of various orientations efficiently channelize magmas through the whole mostly trending subparallel to the CTSZ crust, in particular as the mafic‐ultramafic oce‐ (Prodeminca 2000a), none of these have been anic basement units of the Western Cordillera are mapped as faults on regional Western Cordillera rheologically strong and require a high differen‐ maps (Fig. 1; McCourt et al. 1998; Hughes et al. tial stress to fracture. Repeated transpressional 1998). At the southern end of the Western Cordil‐ reactivation of the shear zone throughout the lera, Chaucha batholith emplacement is inferred Tertiary might have aided magma ascent by tec‐ to be generally related to the Bulubulu fault tonic overpressuring. Non‐vertical magma ascent which forms part of the CPPF; a number of asso‐ along thrust ramps has been documented in a ciated NE‐ and NW‐trending faults are thought to number of settings and can be a viable mecha‐ have controlled individual intrusion emplacement nism for magma ascent in an overall transpres‐ and porphyry mineralization (Prodeminca 2000a). sional‐compressional stress regime (e.g., Kalakay Rapid unroofing of the relatively young Chaucha et al. 2001). If magma ascent in the northern Ec‐ batholith was associated with regional contrac‐ uadorian arc segment during the Oligocene‐ tion leading to basin inversion in the Interandean Miocene was partly controlled by east‐dipping region at c. 9 Ma (Hungerbühler et al. 2002). thrust geometries, the zone of partial melting at In the Zaruma region close to the eastern end of depth could extend well to the east of the pre‐ the Late Oligocene‐Early Miocene Cangrejos‐ sent‐day CTSZ, in agreement with the broad Zaruma intrusive belt, growth sequences of intru‐ landwards extent of arc magmatism in the south‐ sion‐hosting Saraguro Group volcanics form ern‐central Ecuadorian arc segments further thickening wedges towards the southern Piñas‐ south. Portovelo fault, indicative of synvolcanic normal While detailed kinematic structural studies of fault slip (Spencer et al. 2002). Further north, a Tertiary pluton emplacement in Ecuador’s West‐ normal slip component, albeit of unconstrained ern Cordillera are lacking, it can be inferred from age, is detected at the E‐W‐trending Jubones the discussion above that distributed shear re‐ fault (Litherland et al. 1994). These observations lated to forearc sliver displacement along the are in agreement with Steinmann’s (1997) pro‐ CPPF and CTSZ, combined with strike‐slip reacti‐ posal of regional horizontal extension during the vation of the older suture zones further east Oligocene‐Early Miocene deposition of Saraguro (Litherland et al. 1994; Winkler et al. 2005) has Group ignimbrites, which are inferred to have been intermittently active throughout the Terti‐ been sourced from fissure eruptions and caldera‐ ary, and probably resulted in partially syntectonic forming events. intrusive activity. Descriptive studies available for Horizontal extension in southern Ecuador was the major intrusions of the Western Cordillera followed by transpression which is recorded by are summarized in Prodeminca (2000a) and gen‐ inversion of the Piñas‐Portovelo fault and folding erally support this notion. Prodeminca (2000a) ein th area north of the fault producing a major note that most intrusions are spatially associated anticline subparallel to the Cangrejos‐Zaruma with second‐order NE‐ to ENE‐trending faults intrusive belt (Spencer et al. 2002), as well as by a which under dextral transpression should pro‐ conjugate set of NE‐trending faults with evidence duce local dilation. for dextral movement (Prodeminca 2000a). Fur‐ In the northern Western Cordillera voluminous thermore, whole‐scale tilting of the Saraguro magmatism of the Apuela‐Nanegal batholith Group volcanic sequence north of the Piñas‐ might be related to its structural position be‐ Portovelo fault is observed (now dipping 30° to

44 the SW; Spencer et al. 2002). Plutons north of the more likely that plutonic activity increased con‐ Piñas‐Portovelo fault which, based on the radio‐ comitant with volcanism during the Late Oligo‐ metric ages obtained in this study, can be in‐ cene to Mid‐Miocene as part of the flare‐up ferred to be of mainly Early Miocene age, show event in arc magmatism discussed in Chapter 2, asymmetric sigmoidal plan‐view geometries in‐ for which larger geodynamic controls are ulti‐ dicative of syntectonic intrusion into a dextral mately inferred. transpressional stress field. Further, Au‐bearing On a local scale, Prodeminca (2000a) note that hydrothermal quartz‐calcite veins in the Zaruma‐ periods of intense magmatism and mineralization Portovelo mining district are related to NW‐ tend to be associated with inferred changes in striking faults moderately dipping to the SW; the local stress regime, particularly at the onset these faults show S‐C fabrics and shear banding, of post‐compressional tensional periods. As dis‐ in agreement with vein formation under dextral cussed above, however, local variations in stress transpression. The veins are interpreted as partly regime might in part reflect coupling between originating from magmatic fluids thus necessitat‐ magmatic and tectonic processes such that local ing roughly coeval and hence syntectonic mag‐ extension might in part be induced by intrusive matism (Spencer et al. 2002). These considera‐ activity. Clearly, detailed structural studies of Ter‐ tions indicate that Late Oligocene‐Early Miocene tiary intrusions hosted by the Western Cordillera magmatism forming the Cangrejos‐Zaruma intru‐ are needed to further discuss the relationships sive belt is at least in part syntectonic in nature. between plutonism and the regional and local Transpressional deformation in this region might tectonic environment. either be related eto th oblique subduction set‐ ting, or, possibly, to the post‐Paleocene 25±12° Significant Tertiary forearc sliver displacement clockwise block rotation inferred for the Amo‐ implies that the plutons of the Western Cordillera tape terrane from paleomagnetic studies (Mi‐ intruded at more southern latitudes than their touard et al. 1990). present‐day position, relative to the Ecuadorian mainland and the “fixed” Tertiary intrusions There does not seem to be a first‐order relation‐ hosted by the southern‐central Ecuadorian arc ship between the intensity of plutonism, in par‐ segments. If the forearc sliver displacement esti‐ ticular the significant increase in the Late Oligo‐ mate of 100‐130 km since the Mid‐Miocene by cene, and changes of the regional stress regime Hungerbühler et al. (2002) is correct, most intru‐ in Ecuador. Steinmann (1997) and Hungerbühler sions will have undergone significant whole‐scale et al. (2002) infer a regional tensional stress field latitudinal displacement, as their timing of em‐ from 40‐20 Ma, with a compressional pulse at c. placement predates the displacement period. 19 Ma, followed by another period of horizontal Alternatively, following the reasoning of Witt et tensional stress in the Interandean region from al. (2006), latitudinal displacement could increase 15‐11 Ma, and compression from 9‐8 Ma. How‐ with pluton age significantly beyond the Mid‐ ever, compared to their detailed studies of Mid‐ Miocene. A forearc sliver displacement of 100‐ Late Miocene sedimentary basins, the geologic 130 km since the Mid‐Miocene implies juxtaposi‐ evidence presented by these authors to constrain tion of the Oligocene‐Early Miocene batholithic the Oligocene‐Early Miocene stress field is rather intrusions of central Ecuador with the volumi‐ limited, as it is solely based on extensional nous, slightly younger intrusions in the Chaucha forearc deformation at that time described by area at the limit between the northern and cen‐ Daly (1989), combined with an inferred cause‐ tral Ecuadorian arc segments. The concentration effect relationship of regional extension and of intrusive activity in this presently highly tec‐ Saraguro Group ignimbrite eruption. Conse‐ tonized region could reflect a concentration of quently, the lack of correlation between varia‐ strike‐slip deformation potentially favorable for tions in the regional stress field and the peak in crustal magma ascent, space creation, and thus shallow crustal arc magmatism initiating in the pluton emplacement (e.g., Glazner 1991; Rich‐ Late Oligocene‐ Early Miocene might be due to ards 2003). Alternatively, or in addition to the insufficient knowledge of the paleo‐stress field at preceding point, a positive asthenospheric heat the Ecuadorian margin. Overall, however, it is anomaly might have locally persisted below the

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47 Hornblende K‐Ar ages of granodiorites of the Appendix III – Accuracy of pub‐ Apuela‐Nanegal batholith are 18.5±0.9 Ma (Van lished K‐Ar (and ZFT) ages of Ter‐ Thournout 1991), 16.5±0.8 Ma (Prodeminca 2000a), and 14.5±0.2 Ma (MMAJ/JICA 1992), with tiary intrusions in Ecuador additional biotite K‐Ar ages of 16.0±0.8 Ma Before the present work the geochronologic (Prodeminca 2000a), 15.8±0.6 Ma (Van framework on the timing of Tertiary plutonism in Thournout 1991) and 13.0±0.6 Ma (MMAJ/JICA Ecuador exclusively relied on K‐Ar (mostly biotite 1992). The latter age, reported by MMAJ/JICA and hornblende fractions, or whole‐rock samples) (1992) for the Cuellaje prospect area, is identical plus few ZFT datations. An exception is Bineli within error with our zircon U‐Pb age of Betsi (2007) who presents two zircon U‐Pb ages 12.87±0.08 Ma on the same lithology, i.e., por‐ of intrusions spatially associated withe th Rio phyry‐hosting hornblende‐biotite‐bearing grano‐ Blanco low sulfidation epithermal deposit in the diorite, and is thus inferred to represent a mag‐ central Western Cordillera of Ecuador. The clo‐ matic cooling age. This indicates that the young‐ sure temperature range (e.g., Chesley 1999) for est pulse of batholith emplacement at Cuellaje the K‐Ar isotopic systems of hornblende (490‐ occurred at relatively shallow crustal levels at 570°C) and, particularly, biotite (260‐350°C) wall rock temperatures <260‐350°C (the biotite K‐ makes these minerals susceptible to thermal dis‐ Ar closure temperature range). Batholith mag‐ turbance by either burial, proximal emplacement matic cooling rates were very high as evidenced of younger intrusions, or, especially, by porphyry‐ by identical zircon and biotite ages; subsequent related hydrothermal alteration where initial burial and reheating to temperatures >260‐350°C fluid temperatures of >500°C for early potassic did not take place. Similarly, we consider the alteration are common (e.g., Seedorff et al. older hornblende K‐Ar ages referred to above to 2005). This issue is even more pertinent for define distinct pulses of batholith emplacement whole‐rock K‐Ar ages, where a reliable closure at shallow crustal levels, since the K‐Ar horn‐ temperature is difficult to estimate, or for ZFT blende and biotite ages of MMAJ/JICA (1992) are data (closure temperature 260±25°C; Foster et al. identical within error. Geochronologic data thus 1996). A field example illustrating this effect is suggest a composite, multi‐intrusive nature of the small El Tingo pluton in southern Ecuador the batholith which is in agreement with detailed with K‐Ar hornblende and biotite ages of 47‐50 geologic and petrographic investigations by Sala‐ Ma (Kennerley 1980) where Hungerbühler et al. zar (2007), defining various, often fault‐ bounded (2002) obtained a Miocene ZFT age of 21±3 Ma. batholith lithologies including tonalite, quartz monzonite, quartz‐diorite and monzogranite, in Zircon U‐Pb age data acquired on Late Tertiary addition to a major granodiorite lithology. intrusions allow us to evaluate whether previ‐ ously reported ages obtained by these methods Age data for the multiple porphyry stocks and represent magmatic cooling, or whether they dikes intruding the batholith define age ranges of have been thermally disturbed, thus partly offset 11.1‐8.8 Ma for the porphyries at Cuellaje (whole towards a younger intrusive or hydrothermal rock K‐Ar; MMAJ/JICA 1992) and 7.9‐5.6 Ma at event, or pluton exhumation. Furthermore, most Junin (whole rock K‐Ar, MMAJ/JICA 1992; biotite‐ K‐bearing minerals are highly susceptible to al‐ hornblende K‐Ar, Prodeminca 2000a). While we teration, and already small amounts of secondary cannot assess the accuracy of the Cuellaje ages, replacement minerals may suffice to produce K‐ ages reported for the Junin porphyries, classified Ar ages of uncertain geological significance, an as "quartziferous porphyry" by MMAJ/JICA (1992) issue which also pertains to Ar‐Ar ages (Snee and Prodeminca (2000a), are significantly 2002). As different types of hydrothermal altera‐ younger than our hornblende granodiorite por‐ tion of variable intensity are a common feature of phyry dike zircon U‐Pb age of 9.01±0.05 Ma. The most intrusive complexes of Ecuador's Western lithological classification as "quartziferous por‐ Cordillera (e.g., Prodeminca 2000a), the accuracy phyry" used by MMAJ/JICA (1992) and of K‐Ar ages can be tested with a relatively altera‐ Prodeminca (2000a) is somewhat ambiguous as tion‐resistant mineral such as zircon. evidenced by their reported 2 m.y. K‐Ar age dif‐

48 ference for "quartziferous porphyry" exceeding hydrothermal alteration affected the biotite analytical errors, and we infer that these K‐Ar and/or hornblende thus rendering these ages ages date cooling or (partial) thermal resetting of potentially inaccurate. In the Balsapamba area, K‐ one or more younger porphyry intrusive events Ar hornblende ages of 33.1±0.4 and 25.7±0.9 Ma and/or their associated hydrothermal systems. are reported (MMAJ/JICA 1989; McCourt et al. Field evidence indicates at least three major and 1997). There, the younger age cluster is more several minor porphyry phases are present at the dominant including our new zircon U‐Pb ages at Junin prospect (Salazar 2007). The 9 Ma horn‐ 21.46±0.08 Ma (batholith) and 21.22±0.17 Ma blende granodiorite porphyry age presented in (porphyry dike), and hydrothermal molybdenite this study seems to define the earliest timing of Re‐Os ages of 19.9±0.3 Ma (Chiaradia et al. 2004) porphyry emplacement, but older pulses of activ‐ and 21.5±0.1 Ma (Chapter 3) related to the ity are likely to have occurred, as indicated by a Balsapamba porphyry system. 9.5±0.2 Ma zircon antecryst. Younger pulses ap‐ Preservation of biotite ages of the older age clus‐ parently center on the 7.9‐7.3 Ma and 6.1‐5.6 Ma ter indicates the batholith has resided at shallow time ranges; further resolving the timing of these crustal levels below the biotite K‐Ar closure tem‐ multiple intrusive events is complicated by petro‐ perature since then. Furthermore, as a systematic graphic evidence of high‐T potassic alteration younging from hornblende to biotite K‐Ar ages overprinted by pervasive phyllic alteration (Sala‐ within the older age cluster is not observed, and zar 2007). Thermal disturbance is evidenced by a biotite K‐Ar ages show intra‐cluster scattering 7.5±0.2 Ma biotite K‐Ar age of altered host outside of their reported uncertainty range, initial granodiorite (Prodeminca 2000a). Continuous batholith emplacement should have taken place multi‐m.y. magmatism focused on the Junin area at relatively shallowl crusta levels where the age might generally have led to a local shallow crustal scatter reflects magmatic cooling from multiple heat anomaly, such that the young K‐Ar ages may intrusions and/or hydrothermal resetting. A shal‐ not be used as accurate estimates for intrusive low crustal emplacement environment at least events of the Junin porphyry stocks and dikes on for the younger part of the batholith is in agree‐ a local scale, although they may be broadly used ment with our field observations of intrusive as proxies for the latter. A further discussion of brecciation along 21.2 Ma porphyry dike margins, the Junin porphyry system is provided in Chapter requiring brittle deformation mechanisms. The 3, where two Re‐Os molybdenite ages (6.13±0.03 19.9±0.3 Ma molybdenite Re‐Os age reported by Ma and 6.63±0.04 Ma) are presented, which sup‐ Chiaradia et al. (2004) is indicative of the addi‐ port the occurrence of several younger porphyry tional presence of a younger, post‐21.2 Ma por‐ intrusive events as inferred from K‐Ar data. phyry intrusion at Balsapamba, since the maxi‐ Previous studies based on hornblende and biotite mum estimate for the lifetime of a large, single K‐Ar ages, and U‐Pb data presented in this work intrusion‐driven hydrothermal system is 0.8 m.y. define two age clusters for the Balsapamba‐Las (Cathles et al. 1997), and typical lifetimes are sig‐ Guardias batholith in central Ecuador. In the Las nificantly shorter still (e.g., Shinohara & Heden‐ Guardias area an earlier peak comprises three quist 1997). This is in agreement with published hornblende and biotite ages ranging from 34.3 to lithological data indicating a composite nature of 30.1 Ma (MMAJ/JICA 1989; McCourt et al. 1997). the batholith (MMAJ/JICA 1989). We attribute In addition, Henderson (1979) reports ages of the limited scatter of ages within a given age 30.8±1 Ma (K‐Ar biotite) and 19.2±3 Ma (K‐Ar cluster to multiple intrusions with two batholith hornblende) on a quartz‐diorite sample from the emplacement peaks during the Early Oligocene same area where he prefers the latter as esti‐ and Early Miocene, where magmatism might mate for the age of pluton emplacement. These have been semi‐continuous in between these ages were recalculated by Kennerley (1980) using peak events, as suggested by a single Late Oligo‐ decay constants of Steiger & Jäger (1977) to cene K‐Ar hornblende age at Balsapamba. 31.7±1 Ma and 19.8±3 Ma. The fact that his Our zircon U‐Pb emplacement age of 25.5±0.7 hornblende K‐Ar age is significantly younger than Ma for the central part of the Chazo Juan‐ the biotite K‐Ar age of the same sample suggests Telimbela batholith significantly predates pub‐

49 lished biotite ± hornblende K‐Ar ages of several granodiorite porphyry dike intruding the batho‐ batholith facies which range in age from 14.5 to lith suggesting that the porphyry‐related hydro‐ 17.5 Ma and 19.1 to 21.4 Ma across the whole thermal system might have thermally reset the batholith (MMAJ/JICA 1989; MMAJ/JICA 1991; surrounding batholith facies, but this cannot be McCourt et al. 1997), again reflecting a multi‐ verified due to uncertainties in the sample loca‐ intrusive batholith assembly. A Re‐Os molyb‐ tion of Müller‐Kahle & Damon (1970). Wide‐ denite age of 19.2±0.1 Ma (Chapter 3) relates to spread porphyry‐related hydrothermal activity is the younger phase of intrusive activity inferred documented by two Re‐Os molybdenite ages of from K‐Ar data. The main pulse of plutonic activ‐ 9.92±0.05 Ma and 9.5±0.2 Ma (Chapter 3). Age ity of the Chazo Juan‐Telimbela batholith and the scatter in the 15‐10 Ma period might reflectl mu ‐ youngest pulse of the Balsapamba‐Las Guardias tiple intrusive events as evidenced by the occur‐ batholith overlap in age. Likewise, the youngest rence of an antecrystic zircon in the quartz‐ plutonic pulse of Chazo Juan‐Telimbela seems to diorite porphyry intrusion dated at 10.3±0.2 Ma coincide with the age of the Corazon intrusion in the present study. The identical hornblende further north. Antecrystic zircons of Early Oligo‐ and biotite ages reported by INEMIN‐AGCD cene age identified in the present study could be (1989) indicate that individual intrusive pulses related to an earlier phase of the Chazo Juan‐ were emplaced at wall rock temperatures below Telimbela batholith construction, contemporane‐ the K‐Ar biotite closure temperature and cooled ous with, or slightly postdating the first intrusive relatively rapidly. Taken in concert, these results peak of Balsapamba‐Las Guardias. These age re‐ suggest that a main phase of the Chaucha batho‐ sults, in conjunction with petrographic similari‐ lith construction occurred during the Mid‐ ties, and the spatial proximity and continuity in Miocene although still earlier intrusive pulses map view suggest that the intrusive complexes of (e.g., in the Early Miocene; Prodeminca 2000a), Balsapamba‐Las Guardias and Chazo Juan‐ similar to Chazo Juan‐Telimbela, cannot bed rule Telimbela, combined with the adjacent Corazon out. and Echeandia‐La Industria complexes and sev‐ A K‐Ar age of 16.9±0.2 Ma reported by Pratt et al. eral smaller satellite intrusions, might represent a (1997) for the Paccha intrusion in the central part single large batholithic system assembled from of the Cangrejos‐Zaruma intrusive belt has, so far, Early Oligocene through Mid‐Miocene times. been the only available age for the whole belt. Ages reported for the Chaucha batholith range The scarcity of available data prevents further from 13.3±0.5 Ma and 13.2±0.5 Ma (K‐Ar horn‐ discussion of the accuracy of this K‐Ar age. In this blende and biotite; INEMIN‐AGCD 1989), study, a relatively tight cluster of Late Oligocene‐ 12.8±0.6 Ma (biotite K‐Ar; Kennerley 1980), Early Miocene emplacement ages was obtained 12.0±0.6 Ma (Snelling 1970), to 9.8±0.3 (whole from zircons for intrusions at Cangrejos, Zaruma, rock K‐Ar; Müller‐Kahle & Damon 1970). In addi‐ and Portovelo attesting coeval pluton emplace‐ tion, INEMIN‐AGCD (1989) provide an age of ment along the whole strike length of the belt. 11±1 Ma for a dacitic porphyry intrusion. The intrusions at Zaruma and Cangrejos contain Prodeminca (2000a) note that these ages might antecrystic zircons of Mid‐Oligocene age demon‐ be disturbed and could significantly postdate strating slightly older magmatic activity in this main batholith emplacement. Our new zircon region. Combined with mainly Late Oligocene‐ ages confirm this notion, and provide a new ba‐ Early Miocene K‐Ar and ZFT ages for volcanic tholith minimum emplacement age of 14.84±0.06 rocks of the Saraguro Group in the area (Pratt et Ma. Ubiquitous zircon antecrysts ranging in age al. 1997; Hungerbühler et al. 2002, and refer‐ from 15.3 to 14.8 Ma testify older pulses of ences therein) this suggests the whole region un‐ magmatism, and a close‐by intrusion at the Rio derwent widespread coeval plutonism and vol‐ Blanco prospect, dated at 15.75±0.04 Ma (zircon canism in the Late Oligocene and Early (‐Mid) U‐Pb TIMS; Bineli Betsi 2007) might represent a Miocene. still older, genetically related batholith facies. The Emplacement ages of around 20 Ma obtained for K‐Ar batholith age of Müller‐Kahle & Damon the porphyry intrusions of Gaby and Papa Grande (1970) is identical to our age of 9.79±0.03 for a overlap within error with a 19.3±1.0 Ma K‐Ar

50 (whole‐rock?) age for the Gaby porphyry stock Quimsacocha volcanic center comprise andesite‐ reported by Prodeminca (2000a), and are further dacite flows and breccias, followed by ignimbrite in agreement with Re‐Os molybdenite (20.6±0.1 eruption and caldera formation; dacitic‐rhyolitic Ma) and U‐Pb hydrothermal titanite (20.2±0.2 caldera‐hosted domes represent the final phase Ma) ages obtained for various porphyry‐related of activity of the volcanic center. Typical dura‐ hydrothermal systems at Gaby (Chapter 3). These tions of volcanic activity at long‐lived arc volca‐ ages coincide with the youngest phases of batho‐ noes are on the order of c. 1 m.y. (e.g., Tatara‐ lith construction further north at Balsapamba‐Las San Pedro; Dungan et al. 2001). As ignimbrite ZFT Guardias, and testify a significant Early Miocene ages of 5.2‐4.9 Ma and an intra‐caldera dome ZFT peak of plutonic activity in the Western Cordillera age of 3.6±0.3 Ma (Beate et al. 2001) significantly of Ecuador. postdate the zircon U‐Pb age obtained for a dac‐ itic dome in the present study, the ZFT ages Our age of 16.04±0.02 Ma for emplacement of a should either reflect exhumation, or thermal dis‐ biotite‐bearing granodiorite porphyry dike at El turbance by a younger hydrothermal system. Mozo, hosted by tuffs of the La Paz Formation Since the Quimsacocha volcanic caldera outline is assigned to the uppermost Saraguro Group well preserved, forming a prominent positive to‐ (Prodeminca 2000b) is contemporaneous with pographic feature at about 4 km altitude, signifi‐ the time range of Sta. Isabel volcanism further cant burial is not a likely option for the caldera‐ north (Hungerbühler et al. 2002). Furthermore, it hosted facies, and hydrothermal fluids, possibly is temporally close to the 16.9±0.2 Ma age of the related to a blind porphyry intrusion, might have Paccha intrusion (Pratt et al. 1997) and the 15.3‐ caused resetting of the ZFT system. Alternatively, 14.8 Ma zircon ages for the Chaucha batholith these ZFT ages could be inaccurate and might not (this study) suggesting relatively wide‐spread have any geological significance, or their preci‐ post‐Saraguro magmatism in southern Ecuador. A sion might be overestimated. previously reported hydrothermal alunite K‐Ar age at El Mozo is 15.4±0.7 Ma (a second age of The zircon U‐Pb age of 30.7±0.5 Ma for a strongly 12.3±0.7 Ma is supposed to be inaccurate due to altered felsite in the Tres Chorreras prospect area significant alunite concentrate contamination by assigned to the Saraguro Group (Pratt et al. 1997) barite; Prodeminca 2000b). The 15.4±0.7 Ma K‐Ar places it at the base of the stratigraphic time alunite age overlaps within error with our zircon range for the Saraguro Formation provided by age, in agreement with the general notion that Hungerbühler et al. (2002), and overlaps with the porphyry intrusions and high‐sulfidation epi‐ time range given by the same authors for the thermal systems are genetically linked and closely Loma Blanca Formation which they regard as the correlated in time (e.g., Shinohara & Hedenquist base of the Saraguro Group in southern Ecuador. 1997). It overlaps with the Late Eocene‐Early Oligocene ZFT ages of Saraguro Group units further north in Volcanic formations genetically related to the the northern Ecuadorian arc segment (Dunkley & Quimsacocha volcanic center were not specifi‐ Gaibor 1997). Taken in combination with an age cally addressed by Hungerbühler et al. (2002) in of 35.77±0.06 Ma (U‐Pb TIMS; Bineli Betsi 2007) their stratigraphic summary of southern Ecuador. for a voluminous quartz‐monzodiorite intrusion Our age of 7.13±0.07 Ma for a Quimsacocha cal‐ inferred to intrude older Saraguro Group volcan‐ dera‐hosted biotite‐hornblende‐bearing dacite ics at the close‐by Rio Blanco prospect (M. Ponce, dome, interpreted as emplacement age, overlaps International Minerals Corporation, pers. comm. with the time range proposed by Hungerbühler et 2009), this suggests that Early Oligocene magma‐ al. (2002) and Pratt et al. (1997) for the Late Mio‐ tism might have been more widespread in south‐ cene, regionally widespread Tarqui Formation, ern‐central Ecuador than previously inferred from and coincides on a regional scale with several spatially isolated outcrops of the Loma Blanca shallow‐level intrusions in the area (cf. summary Formation, although it is clearly subordinate to by Hungerbühler et al. 2002). Our new zircon U‐ Late Oligocene‐Early Miocene volcanism of the Pb age further allows absolute time calibration of Saraguro Formation and the associated intrusive the volcanic stratigraphic sequence provided by activity (Hungerbühler et al. 2002). Beate et al. (2001) where the early phases of the

51 The dismembered Curiplaya porphyry intrusions although they may be of doubtful accuracy at a hosted by the Albian Celica Formation in south‐ local scale to resolve intrusive emplacement ernmost Ecuador were of uncertain age before events at higher precision. A similar conclusion this work; we therefore included them in this can be drawn from a detailed geochronologic study of Tertiary magmatism. The porphyry intru‐ study conducted at the Jurassic Nambija skarn sions occur only a short distance from the com‐ deposit in southern Ecuador: while existing K‐Ar posite Tangula batholith, and thus might repre‐ age data on feldspar and sericite are shown to sent a comagmatic equivalent of this voluminous yield disturbed ages, zircon U‐Pb datations over‐ intrusive complex. A major batholith emplace‐ lap within error with hornblende K‐Ar ages ment pulse is inferred at c. 110 Ma based on (Chiaradia et al. 2009, and references therein). hornblende K‐Ar ages of 111±30 Ma for the Macará intrusion and 110±3 Ma for the Colaisaca References intrusion, where an additional plagioclase K‐Ar Aspden, J. A., Harrison, S. H., Rundle, C. C. (1992): New age of3 108± Ma is available (Kennerley 1980). geochronological control for the tectono‐magmatic Younger K‐Ar ages obtained on biotite from the evolution of the metamorphic basement, Cordillera same locations yielded 48±2 Ma and 93±1 Ma, Real, and El Oro Province of Ecuador. J S Am Earth Sc respectively (Kennerley 1980). Due to their high 6; 77‐96. potential for thermal disturbance the significance Beate, B., Monzier, M., Spikings, R., Cotton, J., Silva, J., of these biotite ages for batholith emplacement Bourdon, E., Eissen, J.‐P. (2001): Mio‐Pliocene adakite is uncertain. Our new zircon U‐Pb age of 92.0±1.0 generation related to flat subduction in southern Ec‐ Ma for a Curiplaya porphyry intrusion demon‐ uador: the Quimasacocha volcanic center. Earth Planet strates the occurrence of post‐110 Ma magma‐ Science Letters 192; 561–570. tism in the area, in agreement with the age range Bineli Betsi, T. (2007): The low‐sulfidation Au‐Ag de‐ expected from the inferred correlation of the posit of Rio Blanco (Ecuador): geology, mineralogy, Tangula and Peruvian Coastal batholiths (Hall & geochronology and isotope geochemistry. Unpub‐ Calle 1982). lished MSc. thesis, University of Geneva, 93 p. In conclusion, comparison of our U‐Pb zircon age Cathles, L.M., Erendi, A.H.J., and Barrie, T. (1997): How data with existing K‐Ar ages on Tertiary intrusive long can a hydrothermal system be sustained by a single intrusive event?: Economic Geology, v. 92, p. rocks in Ecuador shows that several biotite and 766–771. whole rock K‐Ar ages were likely disturbed by younger intrusions and their associated hydro‐ Chesley, J. (1999): Integrative geochronology of ore thermal systems thus failing to detect slightly deposits: new insights into the duration and timing of hydrothermal circulation. In: Lambert DD, Ruiz J (eds) older magmatic pulses (e.g., at Chaucha, Junin, Application of radiogenic isotopes to ore deposit re‐ Telimbela) with age offsets of 1‐4 m.y. Alterna‐ search and exploration. Rev Econ Geol 12:115–141. tively, our zircon ages for these intrusions were derived from previously unsampled lithologies Chiaradia, M., Fontboté, L., Beate, B., (2004): Cenozoic within a given batholith; inconsistencies in pub‐ continental arc magmatism and associated mineraliza‐ tion in Ecuador. Mineralium Deposita 39, 204–222. lished petrographic rock descriptions and sample locations make it difficult to evaluate this issue. Chiaradia, M., Vallance, J., Fontboté. L., Stein, H., In other places hornblende, biotite or whole rock Schaltegger, ,U.l, Coder J., Richards, J., Villeneuve, M., K‐Ar ages coincide within error with U‐Pb zircon Gendall, I. (2009): U‐Pb, Re‐Os, and 40Ar/39Ar geo‐ ages (e.g., at Gaby, Balsapamba, Cuellaje). Re‐ chronology of the Nambija Au‐skarn and Pangui por‐ phyry Cu deposits, Ecuador: implications for the Juras‐ gionally disturbed Neogene K‐Ar age systematics sic metallogenic belt of the Northern Andes. Miner in the Western Cordillera and Interandean re‐ Deposita DOI 10.1007/s00126‐008‐0210‐6 gion, such as documented for the Late Creta‐ ceous to Early Tertiary in the Eastern Cordillera Dungan, M. A., Wulff, A., Thompson, R. (2001): Erup‐ (Peltetec event of Litherland et al. 1994), are not tive Stratigraphy of the Tatara–San Pedro Complex, 36°S, Southern Volcanic Zone, Chilean Andes: Recon‐ observed. We infer that most K‐Ar ages, espe‐ struction Method and Implications for Magma Evolu‐ cially when obtained on hornblende, can be used tion at Long‐lived Arc Volcanic Centers. Journal of Pe‐ as a proxy for magmatism on a regional scale, trology 42; 555‐626.

52 Dunkley, P. N. & Gaibor, A. (1997): Mapa geologico de volcanic rocks, U.S. Atomic Energy Comm. Ann. Prog. la Cordillera Occidental del Ecuador entre 2°‐3° S. es‐ Rep. CC‐689‐130 (Tucson Univ., Arizona), 46‐48. cale 1/200.000. CODIGEM‐Min. Energ. Min.‐BGS Pratt, W. T., Figueroa, J. F., Flores, B. G. (1997): Mapa publs., Quito. geologico de la Cordillera Occidental del Ecuador entre Foster, D. A., Kohn, B. P., Gleadow, A. J. W. (1996): 3°‐4°S. escale 1/200.000. CODIGEM‐Min. Energ. Min.‐ Sphene and zircon fission track closure temperatures BGS publs., Quito. revisited: empirical calibrations from 40Ar/39Ar diffu‐ Prodeminca (2000a) Evaluacion de distritos mineros sion studies of K‐feldspar and biotite. International del Ecuador, vol 2—Depositos epitermales en la Cor‐ Workshop on Fission‐Track Dating, Ghent, Abstracts, dillera Andina. UCP Prodeminca Proyecto MEM BIRF 37. 36–55 EC, Quito, Ecuador. Hall, M. & Calle, J., (1982): Geochronological control Prodeminca (2000b) Evaluacion de distritos mineros for the main Tectono‐Magmatic events of Ecuador: del Ecuador, vol 4—Depositos porfidicos y epi‐ Earth Science Review, v. 10, p. 215‐239. mesotermales relacionados con intrusiones de las Henderson, W. G. (1979): Cretaceous to Eocene vol‐ Cordilleras Occiental y Real. UCP Prodeminca Proyecto canic arc activity in the Andes of northern Ecuador. MEM BIRF 36–55 EC, Quito, Ecuador. Geological Society of London Journal 136; 367‐378. Salazar, F. P. (2007): Geologia, alteracion y mineraliza‐ Hungerbühler, D., Steinmann, M., Winkler, W., Sew‐ cion del porfido de cobre‐molibdeno Junin, Provincia ard, D., Egüez, A., Peterson, D. E., Helg, U., Hammer, C. de Imbabura, Ecuador. MSc thesis Escuela Politecnica (2002): Neogene stratigraphy and Andean geodynam‐ Nacional, Quito; 72 p. ics of southern Ecuador. Earth Science Reviews 57; 75– Seedorff, E., Dilles, J. H., Proffett, J. M., Jr, Einaudi, M. 124. T., Zurcher, L., Stavast, W. J. A., Johnson, D. A., Barton, INEMIN‐AGCD (1989): Estudio del yacimiento de cobre M. D. (2005): Porphyry deposits: characteristics and porfídico de Chaucha. Instituto Ec‐uatoriano de Min‐ origin of hypogene features. Econ Geol 100th Anniver‐ ería, Informe final, 339 p, Quito. sary Volume, pp 251–298. Kennerley J. B. (1980): Outline of the geology of Ecua‐ Shinohara, H., Hedenquist, J. W. (1997): Constraints on dor. Institute of Geological Sciences: Overseas Geology Magma Degassing beneath the Far Southeast Por‐ and Mineral Resources 55; 17 p. phyry Cu–Au Deposit, Philippines. J Petrology 38; 1741‐1752. Litherland, M., Aspden, J. A., Jemielita, R. A. (1994): The metamorphic belts of Ecuador. Overseas Memoir Snee, L. W. (2002): Argon Thermochronology of Min‐ 11. BGS, Keyworth eral DepositsA ‐ Review of Analytical Methods, For‐ mulations, and Selected Applications. USGS Bulletin McCourt, W.J., Duque, P., Pilatasig, L.F. and Villago‐ 2194. mez, R. 1997. Mapa geológico de la Cordillera Occi‐ dental del Ecuador entre 1° ‐ 2° S., escala 1/200.000. Snelling, N. (1970): K‐Ar determinations on samples CODIGEM‐Min. Energ. Min.‐BGS publs., Quito. from Ecuador. Int. Rep. Institute of Geo‐logical Sci‐ ences, London. MMAJ/JICA (1989): Report on the mineral exploration in the Bolivar area, Republic of Ecuador. Consolidated Steiger, R. H. & Jäger, E. (1977): Convention on the use report no. 31, MPN, CR(3), 89‐15. of decay constants in geo‐ and cosmochronology. Earth and Planetary Science Letters 36; 359‐362. MMAJ/JICA (1991): Report on the mineral exploration in the Bolivar area, Republic Ecuador. Consolidated Steinmann, M. (1997): The Cuenca basin of southern report no. 6, MPN, CR(3), 91‐72. Ecuador: tectono‐sedimentary history and the Tertiary Andean evolution. PhD Thesis, Institute of Geology MMAJ/JICA (1992): Report on the cooperative mineral ETH Zu¨rich, Switzerland, 176 p. exploration in the Junin area, Republic of Ecuador. Consolidated report no. 2, MPN, CR(3), 92‐68. Van Thournout, F. (1991): Stratigraphy, magmatism and tectonism in the Ecuadorian northwestern cordil‐ Müller‐Kahle, E. & Damon, P. E. (1970): K‐Ar age of lera: Metallogenic and Geodynamic implications. PhD biotite granodiorite associated with pri‐mary Cu‐Mo thesis, Katholieke Universiteit Leuven, 150 p. mineralization at Chaucha, Ecuador. In Damon, P. E. (ed.), Correlation and chronology of ore deposits and

53 Appendix IV – Data tables

Table A1: Results of U‐Pb age determinations (TIMS) Table A2: Results of U‐Pb age determinations (LA‐MC‐ICP‐MS) Table A3: Age references used for construction of Fig. 7 & Fig. 8

54

55

56

Table A2: Results of U-Pb age determinations (LA-MC-ICP-MS)

concentrations isotopic ratios apparent ages [Ma]

sample U Th Th/U 206 206 ±2σ 207 ±2σ 206 ±2σ corr. 206 ±2σ 207 ±2σ 207 ±2σ

[ppm] [ppm] 204 207 [%] 235 [%] 238 [%] coef. 238 235 206

E07030 PS10-12 21 7 0.36 348 26.7 71 0.06 72 0.0110 12 0.17 70.7 8.7 56 39 -528 1946 PS10-10A 26 8 0.31 504 18.2 83 0.09 84 0.0123 14 0.17 78.5 11 90 73 415 1937 PS10-13 43 16 0.37 600 18.6 155 0.10 156 0.0134 16 0.10 85.7 13 96 143 357 4256 - PS10-10 26 7 0.29 468 35.4 126 0.05 128 0.0135 22 0.17 86.2 19 52 65 1345 4437 PS10-20 54 34 0.63 1002 20.3 45 0.09 45 0.0137 6.0 0.13 87.7 5.2 90 39 162 1060 PS10-5 51 19 0.37 834 24.0 95 0.08 95 0.0137 2.0 0.02 87.8 1.7 77 71 -247 2534 - PS10-25 35 17 0.49 720 33.9 77 0.06 78 0.0137 16 0.21 87.8 14 55 42 1214 2457 PS10-4 38 13 0.33 672 19.8 111 0.10 112 0.0137 6.8 0.06 87.8 5.9 93 99 220 2788 PS10-11 41 18 0.42 474 8.0 41 0.24 48 0.0138 24 0.51 88.3 21 218 93 2038 731 PS10-6 128 98 0.76 1542 19.5 16 0.10 16 0.0139 2.3 0.14 89.2 2.0 95 15 249 376 PS10-17 42 27 0.63 660 20.5 57 0.09 58 0.0140 5.8 0.10 89.6 5.2 91 51 141 1373 PS10-15 43 15 0.36 810 26.0 108 0.07 109 0.0140 6.9 0.06 89.8 6.1 73 76 -449 3053 PS10-19 148 128 0.87 1740 17.4 39 0.11 40 0.0141 4.0 0.10 90.4 3.6 108 40 509 873 PS10-8 84 38 0.45 1242 20.4 22 0.10 22 0.0141 2.3 0.10 90.5 2.1 93 20 147 519 PS10-22A 58 22 0.39 1038 27.9 73 0.07 73 0.0142 2.0 0.03 90.7 1.8 69 48 -646 2058 PS10-2 31 12 0.38 456 30.7 107 0.06 108 0.0144 5.4 0.05 92.2 5.0 64 66 -909 3327 PS10-16 114 91 0.79 1536 22.0 25 0.09 25 0.0144 2.0 0.08 92.4 1.9 88 21 -35 607 PS10-22 44 13 0.30 918 19.6 64 0.10 65 0.0145 9.4 0.14 92.6 8.6 99 61 247 1514 PS10-23A 70 34 0.48 1404 25.7 57 0.08 57 0.0145 2.8 0.05 93.1 2.6 76 42 -428 1525 - PS10-3 30 11 0.36 570 37.4 159 0.05 159 0.0146 7.8 0.05 93.2 7.2 53 82 1530 6311 PS10-9 51 18 0.35 858 18.5 53 0.11 54 0.0146 3.8 0.07 93.4 3.5 105 53 370 1224 PS10-14 94 49 0.52 1230 17.8 63 0.11 63 0.0146 2.0 0.03 93.5 1.9 109 65 463 1435 PS10-1T 158 145 0.92 1920 21.3 18 0.09 18 0.0147 2.0 0.11 93.9 1.9 92 16 42 423 PS10-18 49 28 0.58 702 15.4 46 0.13 46 0.0147 2.9 0.06 94.2 2.7 126 55 777 985 PS10-24 147 111 0.76 2556 22.2 32 0.09 33 0.0148 3.6 0.11 94.4 3.3 89 28 -53 795 PS10-7 53 22 0.42 636 12.1 34 0.17 34 0.0149 2.0 0.06 95.6 1.9 159 50 1257 673 PS10-21 82 32 0.39 1554 25.8 49 0.08 49 0.0150 2.6 0.05 95.7 2.5 78 37 -437 1303 PS10-23 104 94 0.90 2358 25.5 54 0.08 55 0.0152 7.5 0.14 97.1 7.3 80 42 -406 1433

E07011 PS9-5 465 189 0.41 2184 16.0 25 0.04 27 0.0042 11 0.42 26.9 3.1 36 10 696 528 PS9-16 80 42 0.53 420 7.2 73 0.08 74 0.0042 11 0.15 27.1 3.0 79 56 2206 1321 PS9-4 77 42 0.54 582 18.7 127 0.03 128 0.0043 9.6 0.08 27.5 2.6 31 40 345 3217 PS9-18 311 242 0.78 1932 19.5 26 0.03 27 0.0045 4.8 0.18 28.9 1.4 32 8 256 604 PS9-22 417 409 0.98 1992 19.7 26 0.03 26 0.0046 2.0 0.08 29.4 0.6 32 8 228 612 PS9-14 433 552 1.28 2388 19.2 16 0.03 17 0.0046 3.7 0.22 29.5 1.1 33 5 292 373 PS9-3 724 624 0.86 4392 19.9 15 0.03 16 0.0046 2.7 0.17 29.7 0.8 32 5 201 358 PS9-20 1026 1315 1.28 5742 22.6 11 0.03 11 0.0047 3.6 0.31 30.3 1.1 29 3 -98 268 PS9-2 269 238 0.88 1338 17.1 58 0.04 58 0.0047 2.9 0.05 30.3 0.9 38 22 552 1285 PS9-8 741 812 1.10 2352 16.5 13 0.04 16 0.0047 9.9 0.62 30.4 3.0 39 6 621 270 PS9-15 198 160 0.81 1182 17.2 30 0.04 30 0.0048 3.9 0.13 30.7 1.2 38 11 531 665 PS9-6A 420 300 0.71 2778 18.6 22 0.04 23 0.0048 2.0 0.09 30.7 0.6 35 8 356 509 PS9-17 1439 1348 0.94 4830 18.4 10 0.04 11 0.0048 2.0 0.19 30.8 0.6 36 4 390 234 PS9-23 1497 2013 1.34 5970 19.9 8 0.03 8 0.0048 2.5 0.31 30.9 0.8 33 3 210 180 PS9-6 190 134 0.70 462 6.1 29 0.11 30 0.0048 7.3 0.25 31.0 2.3 106 30 2510 486

PS9-13 1678 1701 1.01 10938 20.7 9 0.03 10 0.0048 3.2 0.33 31.0 1.0 32 3 115 212 PS9-24 193 120 0.62 1056 15.8 41 0.04 41 0.0049 3.3 0.08 31.5 1.0 42 17 716 873

57

Table A2 (continued)

concentrations isotopic ratios apparent ages [Ma]

sample U Th Th/U 206 206 ±2σ 207 ±2σ 206 ±2σ corr. 206 ±2σ 207 ±2σ 207 ±2σ

[ppm] [ppm] 204 207 [%] 235 [%] 238 [%] coef. 238 235 206

PS9-25 441 476 1.08 1296 12.5 57 0.05 57 0.0049 3.9 0.07 31.5 1.2 53 29 1189 1142

PS9-9A 103 61 0.60 618 15.0 81 0.05 82 0.0049 6.4 0.08 31.6 2.0 45 36 825 1768 PS9-21 182 126 0.69 786 16.8 86 0.04 86 0.0050 4.1 0.05 32.0 1.3 41 34 591 1951 PS9-7 609 488 0.80 3102 17.0 41 0.04 41 0.0051 2.0 0.05 32.5 0.6 41 16 560 901 PS9-10 1180 1354 1.15 6990 20.3 10 0.03 13 0.0051 7.5 0.58 32.9 2.5 35 4 160 245 PS9-19 126 134 1.06 390 4.3 32 0.17 37 0.0052 19 0.50 33.6 6.3 156 54 3055 523 PS9-12 1404 1875 1.34 6540 17.9 54 0.04 54 0.0053 2.4 0.04 33.9 0.8 40 21 442 1224 PS9-1 399 236 0.59 1356 12.7 34 0.06 34 0.0054 2.3 0.07 34.7 0.8 58 19 1160 673 PS9-9 271 150 0.55 570 5.2 77 0.15 79 0.0056 19 0.24 35.9 6.8 141 105 2769 1323 PS9-2A 133 107 0.80 390 4.5 28 0.18 30 0.0058 8.9 0.30 37.1 3.3 167 46 3011 457 PS9-11 220 173 0.79 1116 12.7 32 0.07 32 0.0066 2.0 0.06 42.3 0.8 70 21 1164 631 PS9-1A 244 86 0.35 12534 15.5 9 0.64 10 0.0716 4.4 0.44 445.7 19 500 39 759 188

E06066 - PS6-14 119 61 0.51 108 58.3 463 0.01 463 0.0029 24 0.05 18.8 4.5 7 32 3374 0 PS6-13 126 59 0.47 876 16.1 865 0.03 865 0.0032 11 0.01 20.3 2.1 27 233 682 0 PS6-12 253 128 0.50 1332 21.1 48 0.02 49 0.0033 8.6 0.18 21.4 1.8 22 11 74 1161 - PS6-4 64 34 0.54 330 35.6 143 0.01 145 0.0034 26 0.18 22.0 5.6 13 19 1364 5208 - PS6-9 78 56 0.73 444 44.8 178 0.01 178 0.0036 14 0.08 23.4 3.4 11 20 2184 2817 PS6-18 217 92 0.42 1026 14.3 36 0.04 36 0.0037 5.0 0.14 23.9 1.2 36 13 922 741 PS6-18A 254 131 0.52 702 8.3 38 0.06 39 0.0039 8.9 0.23 25.1 2.2 64 24 1961 688 PS6-6 87 62 0.71 426 12.1 118 0.05 118 0.0040 2.0 0.02 25.6 0.5 45 52 1258 2551 PS6-2 117 51 0.43 468 10.8 60 0.05 61 0.0040 10 0.16 25.9 2.6 51 30 1484 1172 PS6-10 101 57 0.57 378 11.0 100 0.05 101 0.0040 16 0.16 25.9 4.1 50 49 1442 2049 PS6-20 160 122 0.76 372 7.5 25 0.07 26 0.0040 6.5 0.25 26.0 1.7 72 18 2136 447 PS6-17 144 174 1.21 300 5.3 34 0.11 35 0.0042 8.9 0.25 26.9 2.4 105 35 2731 560 PS6-11 238 124 0.52 660 8.5 35 0.07 35 0.0042 3.8 0.11 26.9 1.0 67 23 1930 632 PS6-19 148 50 0.34 510 6.7 53 0.09 53 0.0042 4.1 0.08 27.1 1.1 84 43 2334 924 PS6-8 97 52 0.53 408 6.0 63 0.10 66 0.0042 20 0.30 27.1 5.4 94 59 2532 1083 PS6-7 116 83 0.72 486 10.8 64 0.05 64 0.0042 3.6 0.06 27.2 1.0 53 33 1477 1237 PS6-3 92 49 0.53 288 3.1 45 0.22 51 0.0049 24 0.47 31.5 7.6 200 94 3583 3265 PS6-1 108 58 0.53 246 4.1 44 0.17 45 0.0051 12 0.26 32.5 3.8 159 66 3136 704

E07023 PS7-19 66 42 0.63 378 12.0 160 0.03 164 0.0026 37 0.23 16.5 6.1 29 48 1276 14 PS7-21 51 37 0.74 270 28.3 225 0.01 230 0.0026 46 0.20 16.7 7.7 13 29 -686 3557 - PS7-19A 57 43 0.75 354 43.4 176 0.01 185 0.0027 55 0.30 17.3 9.6 9 16 2057 2786 PS7-15 71 63 0.90 396 17.3 87 0.02 89 0.0028 17 0.19 18.3 3.1 23 20 525 1996 PS7-8 81 64 0.78 414 29.5 195 0.01 196 0.0029 19 0.10 18.4 3.4 13 26 -800 3372 - PS7-13 82 51 0.63 444 52.7 366 0.01 366 0.0030 15 0.04 19.0 2.8 8 29 2872 0 - PS7-3A 62 44 0.71 348 37.1 139 0.01 140 0.0030 21 0.15 19.1 3.9 11 16 1502 5173 - PS7-20 80 52 0.65 570 39.1 81 0.01 82 0.0032 15 0.19 20.7 3.2 11 9 1675 2890 PS7-1 85 78 0.93 408 23.3 107 0.02 109 0.0032 18 0.17 20.8 3.8 19 21 -171 2854 PS7-3 60 49 0.82 294 27.5 273 0.02 273 0.0033 8.1 0.03 21.4 1.7 17 46 -604 4008 PS7-5A 89 91 1.03 486 26.9 161 0.02 162 0.0034 13 0.08 22.0 2.8 18 28 -539 5262 PS7-10 62 47 0.76 324 11.7 42 0.04 45 0.0034 16 0.35 22.1 3.5 40 18 1326 830 PS7-20A 75 52 0.70 474 29.0 129 0.02 131 0.0034 21 0.16 22.1 4.6 16 21 -752 4004 - PS7-10A 73 66 0.91 360 44.2 140 0.01 141 0.0035 9.4 0.07 22.3 2.1 11 15 2127 1093

58

Table A2 (continued)

concentrations isotopic ratios apparent ages [Ma]

sample U Th Th/U 206 206 ±2σ 207 ±2σ 206 ±2σ corr. 206 ±2σ 207 ±2σ 207 ±2σ

[ppm] [ppm] 204 207 [%] 235 [%] 238 [%] coef. 238 235 206

PS7-5 117 88 0.75 300 5.0 57 0.10 65 0.0036 33 0.50 22.9 7.5 95 60 2836 944

PS7-17 355 536 1.51 582 6.0 67 0.09 68 0.0038 6.2 0.09 24.6 1.5 85 55 2526 1166 PS7-6 62 50 0.81 330 24.7 122 0.02 123 0.0039 15 0.13 25.0 3.8 22 27 -317 3433 PS7-18 344 325 0.94 1230 12.9 51 0.04 53 0.0040 14 0.26 26.0 3.6 43 22 1138 1030 PS7-14 94 56 0.60 612 18.0 79 0.03 79 0.0042 8.1 0.10 26.7 2.2 32 25 435 1820 - PS7-9 75 54 0.73 498 38.8 124 0.02 128 0.0043 32 0.25 27.6 8.7 15 20 1655 4677 - PS7-11 139 89 0.64 780 37.2 49 0.02 49 0.0044 4.0 0.08 28.5 1.1 17 8 1511 1637 PS7-16A 302 416 1.38 1668 18.4 19 0.03 20 0.0045 3.5 0.18 28.8 1.0 34 6 390 433 PS7-7 178 107 0.60 1134 22.5 54 0.03 54 0.0045 4.5 0.08 29.0 1.3 28 15 -84 1340 PS7-16 142 124 0.87 786 17.9 44 0.03 44 0.0045 6.1 0.14 29.1 1.8 35 15 446 982 PS7-2 457 801 1.75 2262 18.3 24 0.04 24 0.0047 2.0 0.08 30.2 0.6 35 8 400 541

E07045 PS8-8 45 20 0.44 276 18.0 56 0.03 60 0.0033 21 0.36 21.0 4.5 25 15 437 1280

PS8-7A 73 56 0.76 408 17.6 120 0.03 123 0.0034 30 0.24 21.8 6.5 27 32 484 2908 PS8-10 53 21 0.39 384 19.4 254 0.03 254 0.0036 14 0.05 23.1 4.5 90 57 2725 1061 PS8-12 28 14 0.51 156 5.3 63 0.09 66 0.0036 19 0.30 23.1 3.1 25 64 257 2127 PS8-24 129 69 0.54 615 16.4 62 0.03 63 0.0037 5.0 0.08 24.1 1.2 31 19 640 1374 PS8-14 72 34 0.47 576 10.3 29 0.05 30 0.0038 9.5 0.31 24.4 2.3 50 15 1574 540 PS8-26 100 29 0.29 535 11.5 70 0.05 70 0.0039 5.2 0.07 24.8 1.3 46 32 1354 1401 PS8-25 136 77 0.57 670 14.3 32 0.04 34 0.0039 9.8 0.29 24.9 2.4 37 12 921 669 PS8-23 134 42 0.31 755 15.7 34 0.03 34 0.0039 2.4 0.07 25.0 0.6 34 11 734 716 PS8-15 89 40 0.45 400 6.5 43 0.08 44 0.0039 10 0.23 25.0 2.5 80 34 2379 736 PS8-18A 69 27 0.39 430 16.3 83 0.03 86 0.0039 23 0.27 25.3 5.8 33 28 652 1863 PS8-7 64 30 0.47 396 15.2 51 0.04 56 0.0039 22 0.40 25.4 5.7 36 20 794 1090 PS8-28 75 27 0.36 440 13.1 74 0.04 75 0.0040 8.3 0.11 25.5 2.1 42 31 1108 1540 PS8-5 71 48 0.68 390 14.0 67 0.04 67 0.0040 7.5 0.11 25.6 1.9 39 26 970 1396 PS8-8A 37 21 0.57 300 15.0 219 0.04 219 0.0040 20 0.09 25.9 5.1 37 79 817 993 PS8-9 59 34 0.58 612 10.9 50 0.05 52 0.0041 13 0.26 26.2 3.5 51 26 1460 967 - PS8-6 30 13 0.43 204 46.4 169 0.01 170 0.0041 17 0.10 26.4 4.6 12 21 2327 2225 PS8-13 55 30 0.55 402 6.2 45 0.09 49 0.0042 19 0.39 26.6 5.1 90 42 2474 778 PS8-18 77 31 0.40 475 16.0 85 0.04 85 0.0042 3.7 0.04 27.1 1.0 36 30 695 1885 PS8-19 86 48 0.56 315 4.8 74 0.12 77 0.0042 22 0.29 27.2 6.1 116 84 2882 1245 PS8-17 86 35 0.41 320 4.4 71 0.14 74 0.0043 20 0.27 28.0 5.6 131 91 3048 1188 PS8-16 80 35 0.43 315 5.5 59 0.11 60 0.0044 6.2 0.10 28.1 1.7 106 60 2684 1004 PS8-22 54 22 0.41 280 5.9 68 0.10 68 0.0044 9.0 0.13 28.2 2.5 100 65 2567 1171 PS8-20 84 36 0.43 315 6.9 54 0.09 55 0.0044 8.3 0.15 28.5 2.3 86 45 2289 946 PS8-2 56 28 0.50 300 5.2 41 0.13 42 0.0049 11 0.27 31.5 3.6 124 49 2759 674 PS8-1 94 65 0.69 288 4.6 58 0.15 59 0.0049 14 0.23 31.8 4.4 139 77 2947 956 PS8-3 49 22 0.45 282 5.3 133 0.13 139 0.0051 38 0.28 33.1 13 127 166 2719 1839 PS8-4 63 33 0.53 246 3.9 59 0.20 69 0.0059 37 0.53 37.6 14 189 120 3208 959

All errors are random errors at 2-sigma level; the additional systematic error of 1.42+/-0.54% for 206Pb/238U ages is considered for weighted mean ages presented in Table 3.

59

Table A3: Age references used for construction of Fig. 7 & Fig. 8. Disturbed ages and duplicate samples were removed. Reference Lithology UTM UTM datation age ±2σ east north method [Ma] [Ma] Aspden et al 1992 Catamayo - bt granodiorite pluton 690000 9560000 K-Ar bt 58 2 Aspden et al 1992 Ishpingo pluton ("unnamed") pluton 765000 9666300 K-Ar bt 39 4 Aspden et al 1992 Pichinal pluton - bt granodiorite pluton 704500 9599900 K-Ar bt 54 4 Aspden et al 1992 Portachuela batholith - bt-bearing felsic pluton 677300 9472300 K-Ar bt 12 1 porphyry Aspden et al 1992 Portachuela batholith - hbl bt granodio- pluton 675500 9474400 K-Ar hbl 20 7 rite Aspden et al 1992 Portachuela batholith - hbl bt granodio- pluton 674500 9476500 K-Ar hbl 24 5 rite Aspden et al 1992 Pungala pluton - hbl bt granodiorite pluton 768000 9800000 K-Ar hbl 42 2 Aspden et al 1992 Pungala pluton - hbl bt granodiorite pluton 768000 9796500 K-Ar bt/hbl 45 4 Aspden et al 1992 San Lucas pluton - bt granodiorite pluton 698500 9574000 K-Ar bt 59 2 Aspden et al 1992 San Lucas pluton - hbl bt granodiorite pluton 694800 9578500 K-Ar hbl 66 4 Aspden et al 1992 San Lucas pluton - hbl granodiorite pluton 692800 9585700 K-Ar bt 52 2 Aspden et al 1992 San Lucas pluton - porphyritic bt pluton 693300 9584900 K-Ar bt 58 2 granodiorite Barberi et al 1988 Cojitambo andesite-dacite volcanic n/a n/a K-Ar 5.2 0.2 Barberi et al 1988 Mangan Fm. - dacitic lava flow volcanic n/a n/a K-Ar 8.0 0.1 Barberi et al 1988 Pisayambo Fm. - andesite volcanic n/a n/a K-Ar 12.2 0.4 Barberi et al 1988 Pisayambo Fm. - andesitic lava flow volcanic n/a n/a K-Ar 7.1 0.3 Barberi et al 1988 Pisayambo Fm. - andesitic lava flow volcanic n/a n/a K-Ar 8.1 0.1 Barberi et al 1988 Pisayambo Fm. - dacite volcanic n/a n/a K-Ar 6.1 0.6 Barberi et al 1988 Pisayambo Fm. - dacitic ignimbrite volcanic n/a n/a K-Ar 11.2 0.4 Barberi et al 1988 Pisayambo Fm. - ignimbrite volcanic n/a n/a K-Ar 15.4 0.7 Barberi et al 1988 Saraguro Fm. - andesite volcanic n/a n/a K-Ar 28.9 1.4 Barberi et al 1988 undefined andesite volcanic n/a n/a K-Ar 6.3 0.1 Beate et al 2001 Quimsacocha ignimbrites volcanic 697400 9662500 ZFT 4.9 0.3 Beate et al 2001 Quimsacocha ignimbrites volcanic 697400 9662500 ZFT 5.2 0.3 Bineli- Betsi 2006 Rio Blanco - microdiorite pluton n/a n/a zircon TIMS 15.8 0.04 Bineli- Betsi 2006 Rio Blanco - qtz monzodiorite pluton n/a n/a zircon TIMS 35.8 0.06 Boland et al 1998 Apuela: Cuellaje - qtz-diorite pluton 772702 38721 K-Ar 16.5 1.1 Boland et al 1998 Cachaco intrusion, E of Santiago pluton 789383 94048 K-Ar 34.7 1.7 batholith Boland et al 1998 Chical-Maldonado (intrusion in San pluton 811656 99597 ZFT 7.5 0.4 Juan Unit) - bt-rich porphyry Boland et al 1998 La Merced (Apuela satellite intrusion) - pluton 789396 71919 K-Ar 15.6 1.1 qtz-diorite Boland et al 1998 Rio Naranjal gabbro intrusion pluton 722591 38709 K-Ar 47 2 Boland et al 1998 San Eduardo intrusion, NE of Santiago pluton 783814 95151 K-Ar 42 2 batholith Boland et al 1998 San Juan de Lachas Fm. - andesitic volcanic 796700 91900 ZFT 23.5 1.5 breccia Boland et al 1998 San Juan de Lachas Fm. - andesitic volcanic 796700 91900 ZFT 25 3 breccia Boland et al 1998 Santiago batholith - granodiorite- pluton 761551 77437 K-Ar 35.8 1.8 tonalite Boland et al 1998 Santiago batholith - granodiorite- pluton 778256 77445 K-Ar 42 2 tonalite Boland et al 1998 Santiago batholith - granodiorite- pluton 778246 94041 K-Ar 45 2 tonalite Boland et al 1998 small diorite pluton S of San Miguel de pluton 733730 0 K-Ar 29 3 Los Bancos Bourgeois et al 1990 Apagua pluton - andesitic porphyry pluton 725501 9891151 K-Ar WR 24.7 1.2 Bourgeois et al 1990 Apagua - dacite volcanic 731254 9893145 K-Ar WR 21.3 1.1 Dunkley & Gaibor 1997 Cisarán - andesite volcanic 730900 9777600 K-Ar 6.9 0.7 Dunkley & Gaibor 1997 Cisarán - andesite volcanic 742900 9744100 K-Ar 7.2 0.4 Dunkley & Gaibor 1997 Molleturo diorite stock pluton 716855 9745631 K-Ar 7.6 0.4 Dunkley & Gaibor 1997 Saraguro Group volcanic 688700 9701200 ZFT 25.7 1.1 Dunkley & Gaibor 1997 Saraguro Group volcanic 722800 9720800 ZFT 27.0 1.0 Dunkley & Gaibor 1997 Saraguro Group volcanic 690700 9679300 ZFT 29.8 1.2 Dunkley & Gaibor 1997 Saraguro Group volcanic 721700 9719200 ZFT 30.2 1.1 Dunkley & Gaibor 1997 Saraguro Group volcanic 699900 9691800 ZFT 34.1 1.3 Dunkley & Gaibor 1997 Saraguro Group volcanic 699800 9725200 ZFT 37.0 1.5 Dunkley & Gaibor 1997 Saraguro Group volcanic 716400 9769200 ZFT 38.6 1.3

60

Table A3 (continued) Reference Lithology UTM UTM datation age ±2σ east north method [Ma] [Ma] Eguez 1986 La Esperie (St. Domingo) diorite pluton 700326 9972354 K-Ar WR 38.6 1.9 Eguez 1986 Pilaló-Zumbagua - porphyritic diorite pluton 733695 9889395 K-Ar WR 24.7 1.2 Eguez 1986 syntectonic intrusions in Mulaute Unit - pluton 733727 9966819 K-Ar hbl 48.3 0.6 foliated diorite Eguez et al 1992 Saraguro Group volcanic 728500 9762000 K-Ar plag 21.0 1.0 Eguez et al 1992 Saraguro Group volcanic 728500 9764800 K-Ar plag 27.0 0.9 Eguez et al 1992 Saraguro Group volcanic 724000 9746700 K-Ar 35.9 0.9 Herbert & Pichler 1983 Amaluza pluton - granodiorite pluton 792500 9712314 K-Ar bt 34 1 Herbert & Pichler 1983 San Lucas pluton - bt granite pluton 694355 9588998 K-Ar bt 52 2 Hughes et al 1998 Chaupicruz - granodiorite pluton 717002 9900465 ZFT 7.0 0.3 Hughes et al 1998 El Tigre, R. Hugshatambo - granodio- pluton 711443 9917057 K-Ar hbl 38.1 0.4 rite Hughes et al 1998 R. Quindigua - granodiorite pluton 728141 9911519 K-Ar bt/hbl 14.8 0.14 Hughes et al 1998 Zumbagua - porphyritic tonalite volcanic 733698 9894925 K-Ar bt/hbl 6.3 0.7 Hungerbühler et al 2002 Chinchin Fm. volcanic 739467 9680826 ZFT 43 4 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 678920 9562364 ZFT 25 3 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 685992 9538147 ZFT 27 4 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 680590 9544440 ZFT 29 3 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 646676 9558934 ZFT 31 3 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 685900 9538200 ZFT 33 3 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 687184 9537098 ZFT 33 4 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 699139 9546868 ZFT 36 7 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 700498 9519437 ZFT 41 5 Hungerbühler et al 2002 Loma Blanca Fm. volcanic 647582 9559391 ZFT 42 3 Hungerbühler et al 2002 Rodanejo pluton pluton 672059 9546653 ZFT 39 6 Hungerbühler et al 2002 Sacapalca Fm. volcanic 646051 9555116 ZFT 67 6 Hungerbühler et al 2002 Saraguro Fm. volcanic 10365 24540 ZFT 19 6 Hungerbühler et al 2002 Saraguro Fm. volcanic 9820 25430 ZFT 19 4 Hungerbühler et al 2002 Saraguro Fm. volcanic 681315 9630791 ZFT 19.1 1.4 Hungerbühler et al 2002 Saraguro Fm. volcanic 10450 27840 ZFT 20 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 735092 9706274 ZFT 21 2 Hungerbühler et al 2002 Saraguro Fm. volcanic 671534 9632381 ZFT 21 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 735732 9702400 ZFT 21.2 1.6 Hungerbühler et al 2002 Saraguro Fm. volcanic 695744 9693134 ZFT 23 2 Hungerbühler et al 2002 Saraguro Fm. volcanic 13480 31070 ZFT 23 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 697035 9625187 ZFT 23 2 Hungerbühler et al 2002 Saraguro Fm. volcanic 735533 9699850 ZFT 23.2 1.8 Hungerbühler et al 2002 Saraguro Fm. volcanic 697311 9624303 ZFT 23 2 Hungerbühler et al 2002 Saraguro Fm. volcanic 726472 9673198 ZFT 26 2 Hungerbühler et al 2002 Saraguro Fm. volcanic 730250 9675252 ZFT 26.0 1.8 Hungerbühler et al 2002 Saraguro Fm. volcanic 680200 9630300 ZFT 26 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 714257 9685269 ZFT 26 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 12250 29500 ZFT 26 5 Hungerbühler et al 2002 Saraguro Fm. volcanic 698991 9674203 ZFT 27 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 730307 9675184 ZFT 27 4 Hungerbühler et al 2002 Saraguro Fm. volcanic 730062 9675245 ZFT 27 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 729721 9675308 ZFT 28 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 720997 9667853 ZFT 28 3 Hungerbühler et al 2002 Saraguro Fm. volcanic 725302 9693138 ZFT 29 3 Hungerbühler et al 2002 St. Isabel Fm. volcanic 698813 9656909 ZFT 8 2 Hungerbühler et al 2002 St. Isabel Fm. volcanic 699931 9642136 ZFT 15.9 1.6 Hungerbühler et al 2002 St. Isabel Fm. volcanic 688300 9629400 ZFT 18 2 Hungerbühler et al 2002 St. Isabel Fm. volcanic 689714 9631727 ZFT 18 3 Hungerbühler et al 2002 St. Isabel Fm. volcanic 683296 9633982 ZFT 18.4 1.6 Hungerbühler et al 2002 St. Isabel Fm. volcanic 698428 9640804 ZFT 19 2 Hungerbühler et al 2002 Tarqui Fm. volcanic 732155 9672200 ZFT 5.1 0.6 Hungerbühler et al 2002 Tarqui Fm. volcanic 729094 9687475 ZFT 5.5 0.6 Hungerbühler et al 2002 Tarqui Fm. volcanic 731940 9672631 ZFT 5.8 0.8 Hungerbühler et al 2002 Tarqui Fm. volcanic 728773 9664281 ZFT 6.0 1.0 Hungerbühler et al 2002 Tarqui Fm. volcanic 720818 9672195 ZFT 6.1 1.0 Hungerbühler et al 2002 Tarqui Fm. volcanic 729453 9664218 ZFT 6.3 0.8 Hungerbühler et al 2002 Tarqui Fm. volcanic 13550 28200 ZFT 6.3 1.0

61

Table A3 (continued) Reference Lithology UTM UTM datation age ±2σ east north method [Ma] [Ma] Hungerbühler et al Tarqui Fm. volcanic 728865 9663789 ZFT 6.6 0.8 2002 Hungerbühler et al Tarqui Fm. volcanic 744998 9700442 ZFT 6.7 0.8 2002 Hungerbühler et al Tarqui Fm. volcanic 723285 9725220 ZFT 6.8 0.8 2002 INEMIN-AGCD 1989 Chaucha batholith - tonalite pluton 666734 9690407 K-Ar bt 13.2 0.5 INEMIN-AGCD 1989 Chaucha batholith - tonalite pluton 666734 9690407 K-Ar hbl 13.3 0.5 INEMIN-AGCD 1989 Chaucha dacitic porphyry pluton 666734 9690407 K-Ar bt 11.0 1.0 Jaillard et al 1996 Palo Blanco pluton - granodiorite pluton 669200 9541800 K-Ar plag 26.6 1.6 Kennerley 1980 Amaluza pluton - granodiorite pluton 770575 9712820 K-Ar hbl 49 2 Kennerley 1980 andesite; Hungerbühler (1997) assigns to pluton 736041 9686336 K-Ar WR 19.7 0.5 El Descanso intrusion Kennerley 1980 andesite; Hungerbühler (1997) assigns to pluton 736690 9686612 K-Ar WR 21 0.6 El Descanso intrusion Kennerley 1980 andesite; Hungerbühler (1997) assigns to volcanic 673135 9632347 K-Ar WR 19.5 0.4 St. Isabel Fm. Kennerley 1980 andesitic porphyry; Hungerbühler (1997) volcanic 698160 9643179 K-Ar WR 14.2 0.5 assigns to St. Isabel Fm.

Kennerley 1980 Chaucha batholith - granodiorite pluton 675428 9679338 K-Ar bt 12.8 0.6 Kennerley 1980 El Tingo pluton - granodiorite pluton 678559 9558619 K-Ar bt 50 3 Kennerley 1980 Las Guardias pluton - qtz-diorite pluton 711358 9800935 K-Ar hbl 20 3 Kennerley 1980 Portachuela batholith - granite pluton 674723 9493201 K-Ar bt 29.0 0.8 Kennerley 1980 rhyolite; Hungerbühler (1997) assigns to St. volcanic 700010 9641978 K-Ar WR 21.4 0.8 Isabel Fm. Kennerley 1980 San Lucas pluton - granodiorite pluton 702191 9573316 K-Ar bt 63 1 Kennerley 1980 Saraguro Group - rhyolite volcanic 672821 9632716 K-Ar WR 26.8 0.7 Lavenu et al 1992 Biblian Fm - rhyolitic tuff volcanic 735300 9701400 K-Ar plag 22.0 0.8 Lavenu et al 1992 Cojitambo - andesite; Hungerbühler (1997): pluton 735300 9695800 K-Ar plag 7.1 0.3 this Cojitambo sample is intrusive, whereas younger Cojitambo ages are from extrusive rocks Lavenu et al 1992 Mangan Fm. - rhyolitic tuff volcanic 733500 9697700 K-Ar plag 16.3 0.7 Lavenu et al 1992 Pisayambo Fm - andesite volcanic 739100 9760300 K-Ar WR 7.9 0.4 Lavenu et al 1992 Pisayambo Fm - andesite volcanic 694400 9596400 K-Ar plag 8.2 0.4 Lavenu et al 1992 Pisayambo Fm - andesite volcanic 737400 9893100 K-Ar plag 9.1 0.5 Lavenu et al 1992 Saraguro Fm - andesite volcanic 728000 9764100 K-Ar WR 21.0 1.0 Lavenu et al 1992 Saraguro Fm - andesite volcanic 724300 9747500 K-Ar plag 35.5 1.3 Lavenu et al 1992 Saraguro Fm. - andesite volcanic 733500 9686600 K-Ar plag 35.3 0.9 McCourt et al 1997 Balsapamba - tonalite-granodiorite pluton 700235 9806476 K-Ar bt/hbl 33.1 0.4 McCourt et al 1997 Chaso Juan - tonalite-granodiorite pluton 708060 9845175 K-Ar bt/hbl 19.5 0.3 McCourt et al 1997 Chaso Juan - tonalite-granodiorite pluton 708060 9845175 K-Ar bt/hbl 20.7 0.2 McCourt et al 1997 Corazon batholith - tonalite-granodiorite pluton 722548 9868388 K-Ar bt/hbl 14.1 0.3 McCourt et al 1997 Corazon batholith - tonalite-granodiorite pluton 728113 9867278 K-Ar bt/hbl 14.8 0.2 McCourt et al 1997 Corazon batholith - tonalite-granodiorite pluton 728117 9872808 K-Ar bt/hbl 14.8 0.4 McCourt et al 1997 Corazon batholith - tonalite-granodiorite pluton 728117 9872808 K-Ar bt/hbl 16.1 0.2 McCourt et al 1997 La Industria tonalite-granodiorite pluton 694671 9806481 K-Ar bt/hbl 23.1 0.8 McCourt et al 1997 La Industria tonalite-granodiorite pluton 694676 9812010 K-Ar bt/hbl 25.6 0.3 McCourt et al 1997 La Industria tonalite-granodiorite pluton 689108 9806486 K-Ar bt/hbl 26.5 0.7 McCourt et al 1997 Las Guardias tonalite-granodiorite pluton 705788 9795411 K-Ar bt/hbl 33.4 0.3 McCourt et al 1997 Las Guardias tonalite-granodiorite pluton 705788 9795411 K-Ar bt/hbl 34.3 0.8 McCourt et al 1997 stock intruding Yunguilla Unit at Juan de pluton 733615 9800911 K-Ar 10.1 0.2 Velasco - porphyritic granodiorite McCourt et al 1997 Tambana pluton pluton 705776 9784352 K-Ar bt/hbl 25.4 0.2 McCourt et al 1997 Telimbela - tonalite-granodiorite pluton 705811 9818635 K-Ar bt/hbl 19.1 0.8 McCourt et al 1997 Telimbela - tonalite-granodiorite pluton 700246 9817534 K-Ar bt/hbl 20.0 0.4 McCourt et al 1997 Telimbela - tonalite-granodiorite pluton 700246 9817534 K-Ar bt/hbl 21.4 0.2 McCourt et al 1997 tonalite dike cutting Apagua Formation pluton 728125 9883869 K-Ar bt/hbl 23.7 0.5 MMAJ/JICA 1989 Balsapamba - qtz-diorite pluton 707560 9807830 K-Ar hbl 25.7 0.9 MMAJ/JICA 1989 Chaso Juan - granodiorite pluton 706170 9845140 K-Ar bt 20.9 0.7 MMAJ/JICA 1989 La Industria - qtz-diorite pluton 690970 9825260 K-Ar hbl 25.5 0.9 MMAJ/JICA 1989 Telimbela - qtz-diorite pluton 703680 9816010 K-Ar bt 19.4 0.6 MMAJ/JICA 1989 Las Guardias - qtz-diorite pluton 708140 9798660 K-Ar hbl 30.1 1.1 MMAJ/JICA 1991 Chaso Juan - diorite pluton n/a n/a K-Ar 17.5 0.6 MMAJ/JICA 1991 Telimbela - hbl qtz-diorite pluton n/a n/a K-Ar 15 3 MMAJ/JICA 1991 Telimbela - qtz porphyry pluton n/a n/a K-Ar 15.7 1.0

62

Table A3 (continued) Reference Lithology UTM UTM datation age ±2σ east north method [Ma] [Ma] MMAJ/JICA 1992 Apuela: Cuellaje - granodiorite pluton 778270 42042 K-Ar bt 13.0 0.6 MMAJ/JICA 1992 Apuela: Junin - granodiorite pluton 767136 27657 K-Ar hbl 14.5 0.2 MMAJ/JICA 1992 Cuellaje andesite porphyry pluton 778270 42042 K-Ar WR 11.1 0.6 MMAJ/JICA 1992 Cuellaje qtz porphyry pluton 778270 42042 K-Ar WR 8.8 0.4 MMAJ/JICA 1992 Junin diorite porphyry pluton 767136 27657 K-Ar WR 7.3 0.3 MMAJ/JICA 1992 Junin qtz porphyry pluton 767136 27657 K-Ar WR 6.1 0.2 Müller-Kahle & Chaucha batholith pluton 675053 9676574 K-Ar WR? 9.8 0.3 Damen 1970 OLADE 1980 Cojitambo andesite-dacite volcanic 735316 9695831 K-Ar 6.3 0.2 Pichler & Aly 1983 Pungala pluton - granodiorite pluton 770721 9802708 K-Ar bt 41.3 1.6 Pratt et al 1997 NE Uzhcurrumi - qtz-diorite volcanic 661100 9635129 K-Ar 19.9 0.2 Pratt et al 1997 Paccha granitoid pluton 644386 9601984 K-Ar 16.9 0.2 Pratt et al 1997 Saraguro Fm. volcanic 650200 9591600 ZFT 21.5 1.6 Pratt et al 1997 Saraguro Fm. volcanic 632400 9635400 ZFT 23.2 1.6 Pratt et al 1997 Saraguro Fm. volcanic 661900 9650900 ZFT 28 2 Pratt et al 1997 Saraguro Fm. - dacitic tuff volcanic 690200 9629700 ZFT 22 2 Pratt et al 1997 Saraguro Fm. - dacitic tuff volcanic 690700 9629300 ZFT 27 2 Pratt et al 1997 Saraguro Fm. - ignimbrite volcanic 702934 9614065 ZFT 22.5 1.8 Pratt et al 1997 Saraguro Fm. - ignimbrite volcanic 703862 9618808 ZFT 25.0 1.8 Pratt et al 1997 Shagli intrusion - granodiorite pluton 683353 9651682 K-Ar 17.6 0.6 Pratt et al 1997 Tarqui Fm. - dacite lava flow volcanic 694100 9595400 ZFT 9.6 1.0 Pratt et al 1997 undefined intrusion pluton 658700 9651500 ZFT 13.9 1.0 Prodeminca 2000 Apuela batholith: granodiorite pluton n/a n/a K-Ar hbl 16.5 0.8 Prodeminca 2000 Junin - qtz porphyry pluton n/a n/a K-Ar bt/hbl 5.9 0.1 Prodeminca 2000 Junin - qtz porphyry pluton n/a n/a K-Ar bt/hbl 7.9 0.3 Rivera et al 1992 Saraguro Fm. - ignimbrite volcanic 697700 9675200 K-Ar bt 26.0 0.8 Rivera et al 1992 Saraguro Fm. - ignimbrite volcanic 696300 9676200 K-Ar bt 27.0 0.7 Snelling 1970 Chaucha batholith - granodiorite-tonalite pluton 666734 9690407 K-Ar 12.0 0.6 Spikings et al. 2005 Saraguro Group volcanic rock volcanic 698100 9724200 ZFT 36 3 Steinmann 1997 Calera pluton - granite pluton 650061 9591480 ZFT 26.5 1.8 Steinmann 1997 Cisarán - andesite volcanic 725300 9693000 ZFT 6.8 0.8 Steinmann 1997 El Prado pluton - granite pluton 658870 9578475 ZFT 24 2 Steinmann 1997 Porotillos pluton - granite pluton 653857 9632490 ZFT 20 4 Steinmann 1997 San Antonio pluton - granite pluton 662162 9634470 ZFT 20 3 this study Apuela: Cuellaje granodiorite (E060206) pluton 772701 44253 zircon TIMS 12.87 0.08 this study Balsapamba granodiorite (E06140) pluton 708028 9809786 zircon TIMS 21.46 0.08 this study Balsapamba granodiorite porphyry pluton 708028 9809786 zircon TIMS 21.22 0.17 (E06131) this study Cangrejos qtz-diorite (E06066) pluton 633163 9614248 zircon 25.7 1.0 ICPMS this study Chaucha dacitic porphyry (Tunas; E07005) pluton 675055 9677495 zircon TIMS 9.79 0.03 this study Chaucha granodiorite batholith (E07003) pluton 675055 9677495 zircon TIMS 14.84 0.06 this study El Mozo granodiorite porphyry (E07018) pluton 714415 9618449 zircon TIMS 16.04 0.02 this study Gaby plag-hbl porphyry (E05083) pluton 644460 9657265 zircon TIMS 20.26 0.06 this study Junin granodiorite porphyry (E07032) pluton 755998 33186 zircon TIMS 9.01 0.05 this study Papa Grande plag-hbl porphyry (E05090) pluton 645570 9656158 zircon TIMS 19.89 0.06 this study Portovelo plag-hbl porphyry (E06112) pluton 653987 9589516 zircon TIMS 24.04 0.06 this study Quimsacocha altered dacite dome pluton 697346 9662472 zircon TIMS 7.13 0.07 (E06017) this study Saraguro at Tres Chorreras - felsite volcanic 663344 9649685 zircon 30.7 0.6 (E07011) ICPMS this study Telimbela granodiorite (E07045) pluton 714543 9834663 zircon 25.5 0.7 ICPMS this study Zaruma granodiorite (E07023) pluton 653270 9599944 zircon 20.9 1.1 ICPMS Vallejo 2007 Cizaran Fm. - andesite volcanic 740461 9806100 Ar-Ar gm 12.2 2.2 Vallejo 2007 Macuchi Unit - andesite volcanic 784106 95939 Ar-Ar gm 35.1 1.7 Vallejo 2007 Macuchi Unit - andesite volcanic 725129 9965028 Ar-Ar plag 42.6 1.3 Vallejo 2007 Pilalo Fm. - andesite volcanic 771610 9996629 Ar-Ar px 64.3 0.4 Vallejo 2007 Pilalo Fm. "intrusion" - andesite volcanic 733838 9919774 Ar-Ar hbl 34.8 1.4 Vallejo 2007 Rio Cala Unit - basaltic andesite volcanic 787170 27797 Ar-Ar px 67 7 Vallejo 2007 San Juan de Lachas Fm. - andesite volcanic 806395 83179 Ar-Ar 32.9 1.2 Vallejo 2007 Silante Fm. - basalt volcanic 763379 9995871 Ar-Ar gm 66 2 Vallejo 2007 Silante Fm. - andesite volcanic 766935 2688 Ar-Ar gm 58 2 Vallejo 2007 Silante Fm. - andesite volcanic 768285 1600 Ar-Ar gm 61.0 1.1 Vallejo 2007 Silante Fm. - basalt volcanic 763379 9995871 Ar-Ar gm 66 2

63

Table A3 (continued) Reference Lithology UTM UTM datation age ±2σ east north method [Ma] [Ma] van Thournout 1991 Apuela pluton - granodiorite pluton 776600 30100 K-Ar bt 15.8 0.6 van Thournout 1991 Apuela pluton - granodiorite pluton 776600 30100 K-Ar hbl 18.5 0.9 van Thournout 1991 hbl-rich intrusion hosted by San Juan de Lachas pluton n/a n/a K-Ar 20 3 Fm. van Thournout 1991 hbl-rich intrusion hosted by San Juan de Lachas pluton n/a n/a K-Ar 36 2 Fm. van Thournout 1991 Macuchi Unit. - gabbro pluton 791000 91500 K-Ar hbl 45 9 van Thournout 1991 Maldonado pluton - granodiorite pluton 822200 101500 K-Ar bt 8.9 0.4 van Thournout 1991 Rio Babosa granodiorite pluton 784100 98500 K-Ar hbl 40 3 van Thournout 1991 Tandapi Unit - diorite pluton 806400 83600 K-Ar hbl 32.6 1.3

Acronyms: qtz - quartz, plag - plagioclase, px - pyroxene, hbl - honrblende, gm - groundmass, WR - whole rock, ZFT - zircon fission track

References Aspden, J.A., S. H. Harrison, C. C. Rundle (1992): New geochronological control for the tectono-magmatic evolution of the metamorphic basement, Cordillera Real, and El Oro Province of Ecuador. J S Am Earth Sc 6; 77-96 Barberi, F., Coltelli, M., Ferrara, G., Innocenti, F., Navarro, J. M., Santacroce, R. (1988): Plio-Quaternary volcanism in Ecuador. Geological Magazine 125; 1-14. Note: the volcanic facies associations of these authors were significantly reinterpreted by Hungerbühler (1997) Beate B, Monzier M, Spikings R, Cotton J, Silva J, Bourdon E, Eissen J-P (2001): Mio-Pliocene adakite generation related to flat subduction in southern Ecuador: the Quimasaco- cha volcanic center. Earth Planet Sci Lett 192:561–570 Bineli Betsi, T. (2007): The low-sulfidation Au-Ag deposit of Rio Blanco (Ecuador): geology, mineralogy, geochronology and isotope geochemistry. MSc. thesis, University of Ge- neva, 93 pp. Boland, M. P., McCourt, W. J., Beate, B. (1998): Mapa geologico de la Cordillera Occidental del Ecuador entre 0°-1° N, 1 : 200,000. Bourgeois, J., Eguez, A., Butterlin, J., de Wever, P. (1990): Evolution géodynamique de la Cordillère occidentale des Andes équateur; la découverte de la formation éocene d'Apa- gua. Comptes Rendus de l'Académie des Sciences, Série 311; 173-180. Dunkley, P. N. & Gaibor, A. (1997): Mapa geologico de la Cordillera Occidental del Ecuador entre 2°-3° S. escale 1/200.000. CODIGEM-Min. Energ. Min.-BGS publs., Quito. Eguez, A. (1986): Evolution Cénozoique de la Cordillère Occidentale Septentrionale d'Equateur (0°15' LS à 1°10' LS): Les Minéralisations associées. PhD thesis, Université Pierre et Marie Curie, Paris; 116 p. Eguez, A., Dugas, F., Bonhomme, M. (1992): Las Unidades Huigra y Alausi en la Evolucion Geodinamica del Valle Interandino del Ecuador. Boletin Geologico Ecuatoriano 3; 47- 56. Herbert, H. J. & Pichler, H. (1983): K-Ar ages of rocks from the Eastern Cordillera of Ecuador. Zeitschrift der Deutschen Geologischen Gesellschaft 134; 483-493. Hughes, R.A., Bermudez, R. & Espinel, G. (1998): Mapa geológico de la Cordillera Occidental del Ecuador entre 0°-1°S, escala 1:200.000. CODIGEM-Ministerio de Energía y Minas-BGS publs., Quito, Nottingham. Hungerbühler, D. (1997): Tertiary basins in the Andes of southern Ecuador (3º00´-4º20´): Sedimentary evolution, deformation and regional tectonic implications. PhD Thesis, Institute of Geology ETH Zurich, Switzerland, p. 182.

Hungerbühler D, Steinmann M, Winkler W, Seward D, Egüez A, Peterson DE, Helg U, Hammer C (2002): Neogene stratigraphy and Andean geodynamics of southern Ecuador. Earth Sci Rev 57:75–124 INEMIN-AGCD (1989): Estudio del yacimiento de cobre porfídico de Chaucha. Instituto Ec-uatoriano de Minería, Informe final, 339 p, Quito. Jaillard E & Soler P (1996): Cretaceous to early Paleogene tectonic evolution of the northern Central Andes (0–18 ) and its relations to geodynamics. Tectonophysics 259:41–53 Kennerley J. B. (1980): Outline of the geology of Ecuador. Institute of Geological Sciences: Overseas Geology and Mineral Resources 55; 17 p. Lavenu, A., Noblet, C., Bonhomme, G., Eguez, A., Dugas, F., Vivier, G. (1992): New K-Ar ages dates of Neogene to Quaternary volcanic rocks from the Ecuadorian Andes: Implica- tions for the relationship between sedimentation, volcanism and tectonics. Journal of South American Earth Sciences 5; 309-320. McCourt, W.J., Duque, P., Pilatasig, L.F. and Villagomez, R. 1997. Mapa geológico de la Cordillera Occidental del Ecuador entre 1° - 2° S., escala 1/200.000. CODIGEM-Min. Energ. Min.-BGS publs., Quito. MMAJ/JICA (1989): Report on the mineral exploration in the Bolivar area, Republic of Ecuador. Consolidated report no. 31, MPN, CR(3), 89-15. MMAJ/JICA (1991): Report on the mineral exploration in the Bolivar area, Republic Ecuador. Consolidated report no. 6, MPN, CR(3), 91-72 MMAJ/JICA (1992): Report on the cooperative mineral exploration in the Junin area, Republic of Ecuador. Consolidated report no. 2, MPN, CR(3), 92-68. Müller-Kahle, E. & Damen, P. E. (1970): K-Ar ages of a bt granodiorite associated with primary Cu-Mo mineralization at Chaucha, Ecuador. U.S. Atomic Energy Commission, Annual Progress Report CCO-689-130; 46-48. OLADE (1980): Informe Geo-Volcanologico: proyecto de investigacion geotermica de la Republica del Ecuador. Organ. Latinoam. Energ., ubpublished report, Quito, 54p. Pratt, W. T., Figueroa, J. F., Flores, B. G. (1997): Mapa geologico de la Cordillera Occidental del Ecuador entre 3°-4°S. escale 1/200.000. CODIGEM-Min. Energ. Min.-BGS publs., Quito. Prodeminca (2000) Evaluacion de distritos mineros del Ecuador, vol 2—Depositos epitermales en la Cordillera Andina. UCP Prodeminca Proyecto MEM BIRF 36–55 EC, Quito, Ecuador Rivera, M., Eguez, A., Beate, B. (1992): El volcanismo neogeno de los Andes australes: sus manifestaciones en la zone entre Cuenca y Soldados, Ecuador. Conference abstract, Secundas Jornadas en Ciencias de la Tierra, Escuela Politecnica Nacional, Quito, 56-57. Snelling, N. (1970): K-Ar determinations on samples from Ecuador. Int. Rep. Institute of Geo-logical Sciences, London. Spikings, R. A., Winkler, W., Hughes, R. A., Handler, R. (2005): Thermochronology of alloch-thonous terranes in Ecuador: Unravelling the accretionary and post-accretionary history of the Northern Andes. Tectonophysics 399; 195-220. Steinmann, M. (1997): The Cuenca basin of southern Ecuador:tectono-sedimentary history and the Tertiary Andean evolution. PhD Thesis, Institute of Geology ETH Zu¨rich, Swit- zerland, 176 pp. Vallejo, C.(2007): Evolution of the Western Cordillera in the Andes of Ecuador (Late Cretaceous-Paleogene). Unpublished PhD Thesis, ETHZ, Zürich, Switzerland, 208 pp. Van Thournout, F. (1991): Stratigraphy, magmatism and tectonism in the Ecuadorian northwestern cordillera: Metallogenic and Geodynamic implications. PhD thesis, Katholieke Universiteit Leuven, 150 pp.

64 CHAPTER III THE MIOCENE METALLOGENIC BELT OF ECUADOR: CONSTRAINTS FROM NEW Re‐Os MOLYBDENITE AND U‐Pb TITANITE AGES OF PORPHYRY‐RELATED ORE DEPOSITS Abstract This study presents Re‐Os molybdenite and U‐Pb titanite ages related to hydrothermal pulses of mineraliza‐ tion and alteration of latest Oligocene and Miocene porphyry‐related ore deposits in Ecuador. Molybdenite associated with potassic‐phyllic alteration at the Junin Cu‐Mo porphyry deposit yielded ages of 6.63±0.04 Ma and 6.13±0.03 Ma. Re‐Os ages of molybdenite associated with potassic alteration at the Telimbela and Balsapamba porphyry systems are 19.2±0.1 Ma and 21.5±0.1 Ma, respectively. At the Chaucha Cu‐Mo por‐ phyry system, Re‐Os ages of 9.92±0.05 Ma (Tunas‐Naranjos) and 9.5±0.2 Ma (Gur‐Gur) were obtained for molybdenite associated with potassic‐phyllic alteration. At the Gaby Au‐Cu porphyry, a Re‐Os molybdenite age of 20.6±0.1 Ma for a sulfide‐cemented hydrothermal breccia (possibly related to phyllic alteration), and a U‐Pb age of 20.17±0.16 Ma for titanite associated with Na‐Ca alteration were obtained. At the Tres Chor‐ reras polymetallic deposit, Re‐Os molybdenite ages are 12.93±0.07 Ma and 12.75±0.07 Ma, and are associ‐ ated with an intrusion‐related hydrothermal breccia and a polymetallic vein, respectively. Molybdenite as‐ sociated with Na‐Ca alteration at the Cangrejos Au‐Cu porphyry system yielded an age of 23.5±0.1 Ma. Our new geochronologic data allow us to infer that the Miocene metallogenic belt of northern‐central Peru extends northwards into southern Ecuador, and potentially further north until Colombia. Intersections of the Andean (NNE‐) trending magmatic arc with arc‐transverse faults and lineaments related to suture zone geometries and block rotation in southern Ecuador represent highly prospective sites for Miocene por‐ phyry‐related mineralization. Porphyry‐related ore deposits in Ecuador are often associated with intrusive clusters of batholith dimen‐ sions, where porphyry‐related pulses of hydrothermal activity often occur towards the end of batholith as‐ sembly. Thus, while batholith complexes may mark structurally favorable sites for mineralization, extensive shallow crustal magmatism during peak periods of batholith construction may be disadvantageous for the formation and preservation of porphyry‐related ore deposits. The lack of Quaternary arc volcanic cover sequences due to a local flat slab setting, and overall favorable erosion levels are key parameters to preserve and expose widespread Miocene epithermal and porphyry Cu mineralization in southern Ecuador. In the Western Cordillera of Ecuador porphyry Cu mineralization has locally been preserved, whereas the deeply eroded cores of porphyry systems are exposed at other loca‐ tions where significant parts of the mineralization have been removed. Although possibly applicable for single ore deposits, a general, direct spatio‐temporal association between Miocene ore deposit formation and seamount chain ("ridge") subduction or regional compressive pulses, as sometimes proposed for parts of the central and southern Andes, is not observed in Ecuador.

65 While the broad extent of the Miocene metal‐ Introduction logenic belts of Peru and Chile is relatively well Porphyry‐related (porphyry Cu, epithermal, and established, the northward belt continuation into Cordilleran vein type) ore deposits in western Ecuador is less certain. In fact, in his seminal in‐ South America typically occur in elongated metal‐ vestigation of intrusion‐related metallogenic logenic belts of several 100 km strike length belts of the Andes, Sillitoe (1988) depicted a pro‐ which regionally link deposits of a similar age (Sil‐ nounced metallogenic gap for Ecuador as only a litoe 1988). Additional sub‐belts may be defined single Miocene porphyry Cu deposit (Chaucha) where the density of ore deposits and geochro‐ was relatively well known at that time. Over the nologic control on the timing of mineralization last two decades, Ecuador has increasingly are sufficiently high (e.g., central‐northern Peru; moved into the focus of exploration activities of Noble & McKee 1999). Porphyry‐related ore de‐ public and privately owned companies as well as posits of the Andes are intimately associated with several government agencies, resulting in the arc magmatism resulting from the subduction of discovery and re‐assessment of a significant the Farallon/Nazca plate at the South American number of Miocene and older porphyry‐related margin (Sillitoe 1988). Consequently, metal‐ ore deposits (Prodeminca 2000a, 2000b; USGS logenic belts tend to follow the overall spatio‐ 2009). In combination with their Jurassic equiva‐ temporal distribution of arc magmatism which is lents, the Miocene ore deposits contain the bulk mainly dictated by the subducting slab geometry of the country's resources in Cu, Mo, Au, and Ag and upper plate structures (e.g., Kay et al. 1999; (Prodeminca 2000a). Miocene mineralization Tosdal & Richards 2001; Richards 2003). types mainly comprise porphyry‐style (e.g., Junin, Chaucha, Gaby), high sulfidation (e.g., Quimsaco‐ Further geodynamic and tectonomagmatic con‐ cha), intermediate sulfidation (e.g., Portovelo‐ trols may operate, causing particularly prolific Zaruma), and low sulfidation (e.g., Rio Blanco) intervals of mineralization in certain belt seg‐ epithermal deposits. Although some of these ore ments, where it is important to distinguish in‐ deposits have a long‐standing history of artisanal creased rates of porphyry‐related ore deposit production, partly since Inca times, many of Ec‐ formation from optimum conditions of ore de‐ uador's mineral resources remain undeveloped posit exposure and preservation (at constant to date (Prodeminca 2000a, 2000b; Spencer et al. rates of deposit formation; Wilkinson & Kesler 2002; USGS 2009). Where quantitatively assessed 2009). Possible factors which have been pro‐ (e.g., Tab. 1, for deposits investigated in this posed to show a positive feedback with porphyry‐ study), their tonnage seems to lag behind that of related mineralization at regional to local scales some giant ore deposits of the Miocene Peruvian include the subduction of bathymetric anomalies metallogenic belt (e.g., Noble & McKee 1999; such as seamount chains ("ridges"), and their ef‐ Rosenbaum et al. 2005). fects on crustal deformation (e.g., Rosenbaum et al. 2005; Cooke et al. 2005), intense hydration of In this contribution we present ten new Re‐Os the crust and evolving arc magmas by flat slab molybdenite ages related to porphyry‐style or dehydration (James & Sacks 1999) or amphibole epithermal mineralization (complemented by a break‐down (Kay et al. 1999), and a broadly fa‐ U‐Pb titanite age related to hydrothermal altera‐ vorable stress regime and its bearing on the ge‐ tion) at several Miocene ore deposits in southern, ometry of crustal structures and transcrustal central, and northern Ecuador (Figs. 1, 2). Com‐ magma ascent (Tosdal & Richards 2001; Richards bined with recent geochronologic works on Late 2003). Furthermore, progressive volatile enrich‐ Tertiary igneous rocks (Chapter 2) and available ment of porphyry intrusive parental melts at mid‐ literature data (Prodeminca 2000a, 2000b, and to deep crustal levels might represent a favorable references therein), our new geochronologic data magmatic preconditioning stage for subsequent allow us to assess the Miocene metallogenic po‐ intrusion‐related mineralization at shallower lev‐ tential of Ecuador, its connectivity with the els (Rohrlach & Loucks 2005; Chiaradia et al. northern‐central Peruvian Miocene metallogenic 2009a). belt, and its relation with the geodynamic evolu‐ tion of the Ecuadorian margin.

66 Figure 1: Simplified geological map of Tertiary arc magmatic units at the NW South American margin, location of irregular bathymetric features of the sub‐ ducting Nazca plate, and Late Oligocene‐Miocene intrusion‐ related ore deposits. Only ore deposits dated in this study are displayed for Ecuador; deposit data for northern Peru and southern Colombia from Sillitoe (1988) and Noble et al. (2004), slightly modified to account for recent discoveries. Major struc‐ tures (undifferentiated; mostly thrust faults which have been variably reactivated during the Tertiary) from references com‐ piled in Chapter 1, and addition‐ ally Mégard (1984) and McNulty et al. (1998) for northern Peru; major structures of the Eastern Cordilleras of Ecuador and Peru are not shown. Ore deposits in Peru all plot in the Mid‐Miocene to Early Pliocene Cu metal‐ logenic belt of Sillitoe (1988); ore deposits in southern Ecuador fit well into the northward projec‐ tion of this belt in space and time. Ore deposit density further north is lower, but suggests that the Miocene Cu belt might be broadly continuous into Colom‐ bia, following the magmatic arc. Hypothetic positions of older, already subducted oceanic fea‐ tures such as the Inca plateau are not shown, but might be of metallogenetic significance (e.g., Rosenbaum et al. 2005). The Curiplaya porphyry intrusions in southernmost Ecuador are of Late Cretaceous age (Chapter 1) and do not form part of the Mio‐ cene metallogenic belt.

67 Regional geology and geody‐ sively produced since the break‐up of the Faral‐ lon plate in the Early Miocene (Lonsdale 2005). namic setting The ENE‐trending scarp currently intersects the Since the Late Cretaceous the Ecuadorian sub‐ Ecuadorian trench at 3°S implying that old Faral‐ duction system has been influenced by a series of lon crust is now subducted below southern Ecua‐ major geodynamic events starting with the c. 75‐ dor (and further south in Peru) whereas young 70 Ma accretion of oceanic plateau fragments Nazca crust is subducted below central‐northern which floor the present day forearc region and Ecuador (and further north in Colombia); Mio‐ possibly parts of the Interandean Depression cene plate motions (Somoza 1998) dictate that (e.g., Vallejo et al. 2009). Throughout the Tertiary the scarp progressively swept southwards along oblique plate convergence between the Faral‐ the margin (Gutscher et al. 1999). The Carnegie lon/Nazca and the South American plates has Ridge seamount chain collided with the Ecuador‐ been accommodated by combined oblique sub‐ ian margin in the Late Miocene (‐Pliocene?) al‐ duction slip and trench‐parallel forearc sliver dis‐ though the exact timing of initial collision is still a placement where the former is the dominant matter of debate, and complicated by jumps of mechanism at the present day (Daly 1989; Ego et the Cocos‐Nazca spreading center and a possibly al. 1996). The offshore Grijalvas scarp separates segmented seamount track (Lonsdale & Klitgord Farallon and Nazca seafloor, the latter progres‐ 1978; Daly 1989; Gutscher et al. 1999;

Figure 2: Geological map of the southern Ecuadorian Sierra region showing position of mineral deposits investigated in this study (Ar‐Ar data is still pending and will be supplemented as it becomes available). Note that a larger number of ore deposits occurs in this area (Prodeminca 2000a, b). Black diamonds correspond to U‐Pb zircon intrusive ages (in Ma: Chapter 1, and Bineli Betsi, 2007, for Rio Blanco intrusions). White diamonds correspond to intrusive ages obtained by K‐Ar (and in one case zircon fission track) geochronology (Aspden et al. 1992; Pratt et al. 1997). Only ages consid‐ ered as relevant for intrusion emplacement are shown. Ages of Saraguro Group volcanics are mostly 19‐29 Ma (ZFT; Hungerbühler et al. 2002). Adapted from Litherland et al. (1994), Pratt et al. (1997) and Dunkley & Gaibor (1997).

68

Spikings et al. 2001; Witt et al. 2006). Ridge colli‐ tems such as Junin, Balsapamba, and Telimbela, sion seems to have caused shallowing of the sub‐ partly associated with minor epithermal minerali‐ duction angle from c. 30‐35° to 25‐30° below cen‐ zation (Prodeminca 2000a). Older porphyry sys‐ tral‐northern Ecuador in the Late Miocene‐ tems have not been described, but a number of Pliocene, whereas the subduction angle had been Au‐rich Eocene volcanic‐hosted massive sulfide broadly constant during the Oligocene‐Miocene deposits occur (Chiaradia & Fontboté 2001; (Guillier et al. 2001; Chapter 2). Establishment of Chiaradia et al. 2008). a flat slab geometry below northern Peru and The Late Oligocene to Early Miocene Saraguro southernmost Ecuador, associated with a gap in Group constitutes the major outcrop unit of the arc magmatism, initiated in the Mid‐ to Late Mio‐ southern Ecuadorian Sierra north of the Piñas‐ cene (e.g., James & Sacks 1999; Gutscher et al. Portovelo fault (Fig. 2). It overlaps in age with the 1999; Chapter 2). The flat slab segment and the Calipuy Group in northern Peru and is partly accompanying cessation of arc magmatism seem overlain by volcaniclastic‐sedimentary formations to have broadened progressively towards south‐ of the Cuenca and associated intramontane ba‐ ern‐central Ecuador where Quaternary arc vol‐ sins, and by Mid‐ to Late Miocene arc volcanic canism is restricted to the area north of c. 2.5°S, formations (Sta. Isabel, Quimsacocha, Tarqui; and Late Miocene arc volcanic formations cover Chapter 2). As in northern Peru, extensive Qua‐ small areas between c. 2.5° and 4°S (Gutscher et ternary volcanic cover sequences are absent in al. 1999; Chapter 2). southern Ecuador creating a favorable erosion The Andean chain hosts the bulk of Tertiary arc level for the exposure of Miocene mineralization magmatic products and splits into a western and (Fig. 2). eastern Cordillera in central‐northern Ecuador, The Saraguro Group volcanics are punctured by which are separated by a number of elongated numerous intrusions including the major Cangre‐ basins referred to as Interandean Depression jos‐Zaruma intrusive belt, and host a large num‐ (Litherland et al. 1994; Winkler et al. 2005). In ber of epithermal and porphyry Cu deposits southern Ecuador, the Andean structural NNE which are, as shown below, mainly of Miocene trend is disrupted where the Western Cordillera age (Fig. 2). The ore deposits of southern Ecuador swings towards the Gulf of Guayaquil and is re‐ define two main districts referred to asy Azua placed by the El Oro micro‐continental block and El Oro districts, respectively (Prodeminca which underwent clockwise rotation during the 2000a, b; Fig. 1, 2). Additional pre‐Miocene Terti‐ Cretaceous‐Tertiary resulting in an arc‐transverse ary mineralization in the southern Ecuadorian structural trend at the present day (Mitouard et Sierra was not identified in the present study but al. 1990; Litherland et al. 1994). cannot be ruled out. Pre‐Tertiary mineralization is Late Oligocene‐Miocene arc volcanics are mostly evidenced by the Late Cretaceous Curiplaya por‐ eroded in the Western Cordillera of central‐ phyry intrusions in SW Ecuador (Fig. 1; Chapter northern Ecuador such that their deeper‐seated 2), and the highly prolific Jurassic period of min‐ plutonic equivalents are unroofed (Chapter 2). eralization in the Eastern Cordillera, including, These plutons are aligned along major fault zones amongst others, the Fruta del Norte, Mirador, of several 100’s km strike length which extend and Nambija deposits (Gendall et al. 2000; Stew‐ down to mid‐ to deep crustal levels where they art & Leary 2007; Chiaradia et al. 2009b). are defined by 35°E dipping fault planes (Guillier et al. 2001). The possible eastward continuation Local geology of Miocene Ecua‐ of Late Oligocene‐Miocene arc magmatism is concealed below Quaternary arc volcanic cover dorian ore deposits investigated sequences of the Interandean Depression (Fig. 1; in this study Chapter 2). Miocene ore deposits of the Western Cordillera and its western foothills mostly repre‐ Seven ore deposits of northern, central and, sent moderately to deeply eroded porphyry sys‐ mainly, southern Ecuador were sampled for Re‐ Os molybdenite dating in this study. These

69 70 comprise deposits with porphyry‐style minerali‐ served in places (MMAJ/JICA 1991). Overall, Cu zation (from north to south: Junin, Telimbela, mineralization related to the Balsapamba por‐ Balsapamba, Chaucha, Gaby, Cangrejos) and one phyry systems (mainly the El Torneado zone) breccia‐related epi‐ to mesothermal deposit (Tres seems to have been mostly eroded, whereas Chorreras) whose metallogenic classification is various exploration targets in the Telimbela por‐ not entirely clear (Prodeminca 2000a). In addi‐ phyry system have a higher mineralization poten‐ tion, hydrothermal titanite was sampled for U‐Pb tial, especially in brecciated areas (MMAJ/JICA dating at the Gaby yporphyr system. General geo‐ 1991). logical features of these deposits are summarized The Chaucha Cu‐Mo porphyry system is one of in Table 1. Typical alteration and mineralization the earliest described porphyry Cu deposits in characteristics of these deposits are shown in Ecuador (e.g., Goossens & Hollister 1973). It is Figure 3, and geological maps are provided for a situated next to the major Bulubulu fault system number of key deposits where more detailed at the SE end of the Mid‐Miocene Chaucha ba‐ geochronologic studies were carried out (Fig. 4‐ tholith and comprises at least two major por‐ 7). phyry intrusions (Tunas and Gur‐Gur) hosted by The Junin Cu‐Mo porphyry system is hosted by pre‐Tertiary metapelites, Saraguro Group volcan‐ the Mid‐Miocene Apuela batholith (Fig. 1; Chap‐ ics, and older intrusive phases of the Chaucha ter 2). It occurs in the center of a belt of three batholith (Figs. 2, 6; Prodeminca 2000a; Micon porphyry deposits (including El Pacto to the SW 2005b; Chapter 2). The spatial distribution of hy‐ and Cuellaje to the NE; plus a meso‐ (?) to epi‐ drothermal alteration reflects the trends of prin‐ thermal Au deposit at El Corazon) which are cipal tectonic structures and overall affects an aligned in NE directions parallel to the Chimbo‐ area of several km2; highest ore grades are en‐ Toachi shear zone, and are collectively referred countered in zones of transitional potassic‐phyllic to as Imbaoeste district (MMAJ/JICA 1998; alteration both in porphyry stocks and batholith Prodeminca 2000a; Micon 2005a; Chapter 2). The host units (Micon 2005b). Junin prospect comprises a well developed zone The Gaby‐Papa Grande Au‐Cu porphyry system of phyllic‐potassic alteration partly extending comprises multiple Early Miocene porphyry and downwards to 600 m depth, centered on multiple phaneritic intrusions (stocks and dikes) emplaced hornblende granodiorite porphyry dikes of vari‐ in oceanic plateau basalts (Pallatanga Unit), oc‐ able thickness striking NNE to ENE and dipping curring at a short distance to the epithermal Bella 45‐70° to the SE (Fig. 4; Salazar 2007). Local struc‐ Rica Au vein system (Fig. 2, 7; Prodeminca 2000a; tures show a major ~NE trend and secondary N‐ Srivastava et al. 2008; Chapter 2). Gold (‐Cu) por‐ NW structures which were repeatedly active at phyry mineralization seems to be associated with pre‐, syn‐, and postmineral times, and are in‐ sodic‐calcic alteration (mostly as free Au) and is ferred to have controlled porphyry dike em‐ particularly well developed in previously frac‐ placement by facilitating local dilation (Micon tured porphyry intrusions and hydrothermal 2005a). breccias which show an overall NW distribution The Balsapamba and Telimbela Cu‐Mo porphyry trend (Srivastava et al. 2008). Local high‐grade systems define the Bolivar district in central Ec‐ mineralization is structurally controlled and asso‐ uador and occur in the western foothills of the ciated with phyllic alteration (e.g., Tama vein; Fig. Western Cordillera (Fig. 1); they represent deeply 7; Srivastava et al. 2008). The Gaby and Papa eroded porphyry systems hosted by various fa‐ Grande porphyry systems are separated by the E‐ cies of the central Ecuadorian Oligocene‐Miocene W striking Guanache normal fault resulting in a batholith (MMAJ/JICA 1991; Prodeminca 2000a; deeper exposure level of the Gaby relative to the Chapter 2). Hydrothermal alteration (mainly Papa Grande sector (Prodeminca 2000a). potassic ± sodic‐calcic) is centered on multiple Tres Chorreras constitutes the northernmost end‐ hornblende quartz‐diorite porphyry dikes which member of a series of tourmaline‐bearing breccia are aligned with mainly NE‐, but also N‐, NW‐, pipe‐related deposits emplaced along the NE‐ and ENE‐trending structures (Prodeminca 2000a). trending La Tigrera fault in the southern Local advanced argillic alteration has been ob‐

71 Figure 3: Typical alteration and mineralization features of Late Tertiary porphyry systems of Ecuador (A‐D = macro‐; E‐H = micro‐photographs). A – Multiple veinlets of cp‐qtz and qtz‐ms‐py‐mo cross‐cutting granodiorite porphyry with per‐ vasive potassic and phyllic alteration (Junin). B – Hydrothermal breccia with subangular hbl‐plag porphyry clasts (with sodic‐calcic alteration) and bt‐qtz cement (related to Tama vein; Gaby). C – Multiple mt and qtz‐mt veinlets with ep haloes cross‐cutting hbl qtz‐diorite porphyry (Cangrejos). D – Reopened mt‐qtz vein filled with later qtz and ser halo cross‐cutting tonalite with bt‐chl alteration, plus multiple thin cp‐qtz veinlets (Chaucha batholith at Tunas). E – hbl‐ bearing granodiorite porphyry with pervasive potassic alteration where bt flakes completely replace hbl phenocrysts

72 Ecuadorian Sierra. Its position corresponds to the 8. Pure molybdenite concentrates of 10‐60 projected intersection of three regional linea‐ mg/sample were obtained from massive molyb‐ ments, namely the La Tigrera fault, the SE‐ denite or quartz‐molybdenite veinlets of samples trending Galena fault, and the NNE‐trending Bu‐ listed in Table 2 using a microdrill, followed by lubulu fault (Fig. 2; Prodeminca 2000a). Lithologi‐ handpicking to purify the concentrates. Where cal units at Tres Chorreras comprise a number of molybdenite occurred as fine‐grained flakes in diorite‐granodiorite intrusions emplaced inc silici the matrix of hydrothermal breccias (Gaby, Saraguro Group volcanics and volcaniclastics, Balsapamba; Fig. 9) samples were crushed to which are associated with several breccia pipes <300 μm and washed to remove clay particles, and a subcircular to irregularly‐shaped agglomer‐ followed by molybdenite handpicking from the ate‐filled structure interpreted as a large dia‐ heavy (> 3.32 g/cm3) non‐magnetic mineral frac‐ treme (Prodeminca 2000a). Gold mineralization tion > 80 μm. Rhenium and Os were separated at in quartz veinlets is partly hosted by various the University of Arizona according to the proce‐ breccia bodies and by the diatreme structure. In dures described in Barra et al. (2003, 2005). addition, a younger set of polymetallic veins oc‐ Weighted molybdenite fractions were spiked cur (Prodeminca 2000a). While broadly classified with 185Re and 190Os and dissolved in a Carius as meso‐ to epithermal mineralization tube using 8 ml inverse aqua regia (3 ∙ 16N HNO3 (Prodeminca 2000a), some of the deposit's geo‐ + 1 ∙ 10N HCl); 2‐3 ml of hydrogen peroxide (30%) logic features such as tourmaline‐bearing hydro‐ were added to the mixture to ensure complete thermal breccias are typically porphyry‐related sample oxidation and spike equilibration. The (e.g., Seedorff et al. 2005), whereas other fea‐ tube was heated to 240°C for c. 8 h, and the solu‐ tures such as polymetallic vein mineralogy are tion subsequently treated in a two‐stage distilla‐ similar to Cordilleran vein‐type deposits (e.g., tion process for Os separation (Nägler & Frei Fontboté & Bendezú 2009). 1997). Osmium was further purified using a mi‐ crodistillation technique, similar to that of Birck The Late Oligocene‐Early Miocene Cangrejos Au‐ et al. (1997), and loaded on Pt filaments with Cu porphyry system occurs at the western end of Ba(OH) to enhance ionization. After Os separa‐ the Cangrejos‐Zaruma intrusive belt (Fig. 2; Chap‐ 2 tion, the remaining acid solution was dried and ter 2). It comprises multiple nested intrusions later dissolved in 0.1 N HNO . Rhenium was ex‐ punctured and intruded by a number of porphyry 3 tracted and purified through a two‐stage column dikes and breccia pipes (Potter 2004). Gold is as‐ using AG1‐X8 (100–200 mesh) resin and loaded sociated with sulfides or occurs in quartz veinlets on Pt filaments with Ba(SO) . whose distribution is structurally controlled and 4 includes all intrusive lithologies; highest Au Samples were analyzed by negative thermal ioni‐ grades are associated with quartz‐tourmaline zation mass spectrometry (Creaser et al. 1991) on veinlets (Potter 2004). a VG 54 mass spectrometer at the University of Arizona. Rhenium and Os were measured with Sampling and analytical tech‐ Faraday collectors. Molybdenite ages were calcu‐ lated using an 187Re decay constant of niques 1.666 ∙10‐11 year‐1 (Smoliar et al. 1996). Errors are Sampling details are listed in Table 2 and further reported at the 2σ level and cmprise the propa‐ illustrated on Figures 4 to 7. Molybdenite sam‐ gated uncertainties of the Re decay con‐ ples used for Re‐Os datation are shown in Figure

Figure 3 (caption continued from previous page): and form "shreddy" disseminations in the porphyry matrix (Gur‐Gur porphyry, Chaucha). F – Sodic‐calcic alteration‐related vein with ttn, act, ep, and po‐cp cross‐cutting plag‐hbl porphyry (Gaby). G – Plag‐qtz porphyry with chl background alteration, cross‐cut by ep‐py‐cp veinlet (Telimbela). H – Porphyritic granodiorite with pervasive silicification and ms alteration (Gur‐Gur porphyry, Chaucha. Mineral abbreviations: ab – albite, act – actinolite, bt – biotite, chl – chlorite, cp – chalcopyrite, ep – epidote, hbl – hornblende, jsp – jasper‐like silica; mo – molybdenite, mt – magnetite, ms – muscovite, plag – plagioclase, po – pyrrhotite, py – pyrite, qtz – quartz, rt – rutile, ser – sericite, sl ‐ sphalerite; tm – tourmaline, ttn – titanite. ). Scale bar is 2 cm for macro‐, and 1 mm for mi‐ cro‐photographs. 73 stant (0.31%), spike calibration for 185Re (0.08%) gated to the final uncertainties of isotopic ratios and 190Os (0.15%), and individual weighting and and ages of each individual analysis. Uncertain‐ analytical random errors. Weighted mean ages ties in the decay constants of 238U and 235U (Jaffey were calculated using the Isoplot v3.31 Excel et al. 1971) were propagated separately and macro (Ludwig 2003). added quadratically to the weighted mean age. Concordia plots and weighted mean age calcula‐ Hydrothermal titanite forms part of the sodic‐ tions were prepared using the Isoplot v.3.31 Excel calcic alteration assemblage at the Gaby por‐ macro of Ludwig (2003). All uncertainties and phyry system (Tab. 2). Titanite from the crushed error ellipses are reported as 2σ and weighted and milled <400 μm grain size fraction of sample mean 206Pb/238U ages are presented at 95% con‐ E05077 was separated using standard Wilfley ta‐ fidence level. ble and heavy mineral (> 3.32 g/cm3) separation techniques, and handpicked from the slightly magnetic fraction (0.8‐1.25 A @ 20° side tilt) us‐ Results ing a Frantz magnetic separation table. The ti‐ Table 3 shows Re‐Os data for the ten molyb‐ tanite fraction underwent a bulk two‐step wash‐ denite concentrates analyzed in this study. Total ing process at 140°C (30 m in. each) using (1) a Re and 187Os concentrations range between 35‐ mixture of concentrated HF and 7N HNO3, and (2) 1019 ppm and 4.7‐250 ppb, respectively. Two Re‐ 6N HCl, followed by rinsing in ultrapure H2O and Os molybdenite ages of 6.63±0.04 Ma and acetone. Titanite multi‐grain fractions (n = 4‐7) 205 233 235 6.13±0.03 Ma were obtained for quartz‐ were spiked using a mixed Pb‐ U‐ U spike molybdenite veinlets at the Junin porphyry sys‐ solution, and were dissolved in 63 μl concen‐ tem. This veinlet type is related to potassic or trated HF with a trace of 7N HNO3 at 110°C for transitional potassic‐phyllic alteration at Junin seven days. Uranium and Pb were separated us‐ (Salazar 2007). The new Re‐Os molybdenite age ing an HCl‐based anion exchange chromatogra‐ at Telimbela (19.2±0.1 Ma) was obtained on a phy, and loaded individually on separate Re fila‐ molybdenite‐quartz veinlet related to potassic ments using the Si‐gel technique (Gerstenberger alteration. A Re‐Os molybdenite age of 21.5±0.1 & Haase 1997). Measurement routines on a Tri‐ for the El Torneado zone of the Balsapamba plu‐ ton thermal ionization mass spectrometer at the ton relates to molybdenite as part of a hydro‐ University of Geneva were identical to those out‐ thermal breccia matrix consisting of mineral lined for zircon analysis in Chapter 2. phases of a potassic alteration assemblage (Tab.

Total analytical common Pb (Pbc) was attributed 2). Two Re‐Os molybdenite ages at Chaucha to both laboratory blank (isotopically constrained comprise the Tunas‐Naranjos sector (9.92±0.05 by repeated measurements as 206Pb/204Pb = Ma) and the Gur‐Gur sector (9.5±0.2 Ma; Fig. 6). 17.87±0.36, 207Pb/204Pb = 15.16±0.34, 208Pb/204Pb The former age was obtained on molybdenite = 36.75±1.11) and Pbc included in titanite (iso‐ associated with potassic‐phyllic alteration hosted topic composition estimated at t = 20 Ma accord‐ by biotite‐bearing granodiorite, and the latter age ing to Stacey & Kramers 1975). Lab blanks were was obtained on molybdenite hosted by grano‐ highly variable (15‐81 pg), but constant in iso‐ diorite porphyry with phyllic alteration. A Re‐Os topic composition; therefore, individual propor‐ molybdenite age of 20.6±0.1 Ma was obtained at tions of titanite Pbc vs. Pbc introduced by labora‐ the Gaby porphyry system where molybdenite tory contamination were calculated assuming a forms part of a hydrothermal breccia matrix (Tab. constant Pbc concentration in titanite which was 2). At Tres Chorreras we dated molybdenite as obtained iteratively by balancing the weight of part of a hydrothermal breccia matrix the titanite fraction vs. the total amount of Pbc, (12.93±0.07 Ma), and as part of a massive poly‐ yielding an average titanite Pbc concentration of metallic vein (12.75±0.07 Ma). Finally, a molyb‐ 229±14 pg/mg. The uncertainties of spike and denite‐quartz veinlet associated with sodic‐calcic blank Pb isotopic composition, mass fractionation alteration at Cangrejos gave a Re‐Os molybdenite correction, and tracer calibration were propa‐ age of 23.5±0.1 Ma.

74 Table 2: Description of samples used for molybdenite Re-Os and titanite U-Pb datation Deposit/sample Location/drill core Description Junin E06194 35050 N, 761383 E; hbl granodiorite porphyry (potassic, overprinted by phyllic alteration); 0° 19' 1'' N, 78° 39' 6'' W; qtz-mo (-cp) veinlet with fine-grained mo flakes MJJ-29 @ 305m

E06199 35050 N, 761383 E; hbl granodiorite porphyry (potassic, overprinted by phyllic alteration); 0° 19' 1'' N, 78° 39' 6'' W; mo-qtz veinlets with coarse-grained mo flakes MJJ-29 @ 498m

Telimbela E07037 9817260 N, 705670 E; hbl tonalite (potassic, overprinted by propylitic alteration); multiple 1° 39' 9'' S, 79° 9' 5'' W; mo-qtz veinlets with coarse-grained mo flakes MJE-9 @ 49m Balsapamba E08003 9808050 N, 707840 E; brecciated hbl granodiorite (potassic-phylic alteration) with breccia 1° 44' 9'' S, 79° 7' 54'' W; matrix (+veinlets?) of chl-bt-qtz-mt with mo-cp-py; fine-grained mo MJE-3 @ 42m flakes in breccia matrix Chaucha E07006 (Naranjos 9676800 N, 676140 E; altered host tonalite (potassic-phyllic) with intense qtz, qtz-cp, cp-mt- sector, adjacent to 2° 55' 23'' S, 79° 24' 55'' qtz veining, and thick qtz vein with mo concentrated at vein margins Tunas porphyry) W; NA-30 @ 53m (fine-grained mo flakes) E06175 (Gur-Gur 9676700 N, 677800 E; altered granodiorite porphyry (phyllic) with py-qtz and qtz-py-mo porphyry) 2° 55' 26'' S, 79° 24' 1'' W; veinlets (fine-grained mo flakes) core-5 @ 80m Gaby-Papa Grande E05075 9661850 N, 643400 E; hydrothermal breccia with altered (qtz-ser), subangular porphyry 3° 3' 31'' S, 79° 42' 35'' W; clasts; breccia matrix comprises qtz, po, cp±mo, and goe, hm, jar GD-08 @ 151m (later oxidation?); mo as fine-grained flakes E05077 9661850 N, 643400 E; hbl-plag porphyry with strong pervasive Na-Ca alteration including 3° 3' 31'' S, 79° 42' 35'' W; act, chl, ep, ttn, and sulfides (mainly po); anhedral-euhedral ttn GD-08 @ 340m grains of c. 50-500 μm size in porphyry matrix or replacing hbl (along with other minerals) Tres Chorreras E07010 9650150 N, 663591 E; hydrothermal breccia with subangular clasts of altered volcanics and 3° 9' 51'' S, 79° 31' 40'' W matrix of tm, mt (repl. by hm + goe), mo, jsp; mo as coarse-grained flakes E07012 9650052 N, 663543 E; massive polymetallic vein with cp-mo-jsp-sl; host rock = completely 3° 9' 54'' S, 79° 31' 42'' W replaced by clay minerals (pyrophyllite?); mo as coarse-grained flakes Cangrejos E06065 9614000 N, 633200 E; bt-bearing qtz-diorite with weak pervasive Na-Ca alteration; abun- 3° 29' 29'' S, 79° 48' 3'' W dant qtz veinlets and single mo-qtz veinlet (coarse-grained mo flakes)

Same mineral abbreviations as in Table 1, plus goe (goethite), jar (jarosite). Coordinates as PSAD-56 projection.

Hydrothermal titanite is associated with sodic‐ gests an imperfect characterization of the Pbc calcic alteration at the Gaby porphyry system isotopic composition, but the homogeneous dis‐ where a U‐Pb titanite age of 20.17±0.16 Ma was tribution of 206Pb/238U ages implies that 206Pb/238U obtained (Fig. 9; Tab. 4). High scatter between age systematics were not significantly affected by individual 207Pb/235U ages for Gaby titanite sug‐ this issue.

75 Discussion Ma, 6.1±0.2 Ma, and 5.9±0.1 Ma (MMAJ/JICA 1992; Prodeminca 2000a). The youngest Re‐Os age thus overlaps (within error) with and con‐ Integration of Re‐Os molybdenite and firms the youngest K‐Ar ages, whereas the 6.6 Ma U‐Pb titanite ages into the geochro‐ Re‐Os molybdenite age evidences an additional nologic framework of individual ore hydrothermal pulse previously not detected by K‐ deposits Ar dating. In agreement with geological and petrographic studies (Salazar 2007), the variable The new Re‐Os molybdenite ages at Junin age range reflects multiple intrusive events and (6.63±0.04 and 6.13±0.03 Ma) are significantly hydrothermal systems at Junin. Following a major younger than the U‐Pb zircon age of 9.01±0.06 period of host batholith construction from c. 19 Ma of a hornblende granodiorite porphyry dike to 12 Ma (Chapter 2, and references therein) re‐ from the same drill core (Fig. 5; Chapter 2). As the peated porphyry dike emplacement associated relative Re‐Os age difference of 0.5 m.y. is out‐ with several hydrothermal systems occurred be‐ side the maximum life span of a moderately‐ tween 9 and 6 Ma. Previously obtained K‐Ar ages sized, single intrusion‐driven hydrothermal sys‐ of 7.9 and 7.3 Ma (overlapping with each other tem at shallow depth (e.g., Marsh et al. 1997) this within error) might either reflect an additional age distribution suggests that widespread potas‐ intrusive event at that time, or might relate to sic‐phyllic alteration is related to several (at least older intrusive events (such as porphyry dike em‐ two) post‐9 Ma porphyry systems. Published placement at 9.01 Ma) and subsequent distur‐ whole rock and biotite/hornblende K‐Ar ages of bance of the K‐Ar isotopic system by younger in‐ Junin porphyry intrusions are 7.9±0.3 Ma, 7.3±0.3 trusive/hydrothermal pulses.

Figure 4: Geological map of the Junin Cu‐Mo±Ag porphyry system (adapted from MMAJ/JICA 1998).

76

Table 3: Re-Os data for molybdenite of Miocene Ecuadorian ore deposits Deposit/sample weight Total Re 187Re 187Os age ± 2б [mg] [ppm] [ppm] [ppb] [Ma] Junin E06199 39 294.4 184.3 18.8 6.13 ± 0.03 E06194 16 408.8 255.9 28.3 6.63 ± 0.04 Telimbela E07037 60 312.8 195.8 62.6 19.2 ± 0.1 Balsapamba E08003 14 580.1 363.1 130.4 21.5 ± 0.1 Chaucha E07006 30 354.6 222.0 36.7 9.92 ± 0.05 E06175 11 70.4 44.1 7.0 9.5 ± 0.2 Gaby-Papa Grande E05075 44 442.9 277.3 95.0 20.6 ± 0.1 Tres Chorreras E07010 55 641.0 401.3 86.4 12.93 ± 0.07 E07012 52 35.3 22.1 4.7 12.75 ± 0.07 Cangrejos E06065 50 1019 637.9 249.9 23.5 ± 0.1

Propagated total age uncertainties (c. 0.5%) include uncertainties in the Re decay constant (0.31%), 185Re (0.08%) and 190Os (0.15%) spike calibration, weighting, and analytical random errors. Weighted mean ages were calculated using the Isoplot v.3.31 Excel macro (Ludwig 2003).

A Re‐Os molybdenite age of 19.2±0.1 Ma over‐ reference ages were also obtained within the El laps with several K‐Ar ages obtained on various Torneado zone of the northern Balsapamba plu‐ facies of the Telimbela pluton (19.1‐19.4 Ma; ton. These ages are significantly younger than MMAJ/JICA 1989; McCourt et al. 1997) where the previously published K‐Ar ages of the Balsapamba total age range of the Telimbela pluton is 25.5‐ pluton (33.1‐25.7 Ma; MMAJ/JICA 1989; McCourt 14.5 Ma (K‐Ar hornblende, biotite, and whole et al. 1997) and show that the Balsapamba and rock data; MMAJ/JICA 1989, 1991; McCourt et al. Telimbela plutons, along with the spatially asso‐ 1997; Chapter 2). This suggests that formation of ciated plutons of Chaso Juan, Las Guardias, El Co‐ the porphyry system occurred after some 6 m.y. razon, and La Industria, were formed at broadly of pluton construction, and was still followed by similar times and constitute an intrusive complex younger plutonic activity. A K‐Ar age of 15.7±1.0 of batholith dimension (cf. Chapter 2). The inte‐ Ma was obtained on a “quartz‐porphyry” grated geochronologic results for the Balsapamba (MMAJ/JICA 1991) possibly indicating further de‐ and Telimbela plutons demonstrate that multiple velopment of porphyry systems towards the end porphyry‐related hydrothermal pulses occurred of pluton assembly. in a relatively short time span during the Early Miocene, following a multi‐m.y. history of batho‐ Our new Re‐Os molybdenite age of 21.5±0.1 Ma lith construction. from the El Torneado zone of the northern Balsa‐ pamba pluton significantly predates a previously Molybdenite associated with hydrothermal al‐ obtained Re‐Os molybdenite age of 19.7±0.3 Ma teration at the Tunas‐Naranjos and Gur‐Gur por‐ from the same area (Chiaradia et al. 2004). It is phyry systems at Chaucha yields different Re‐Os identical with the U‐Pb zircon age of the major ages (9.92±0.05 Ma vs. 9.5±0.2 Ma). Both por‐ pluton lithology (hornblende‐bearing granodio‐ phyry systems comprise different intrusive rite; 21.5±0.1 Ma; Chapter 2), and overlaps within lithologies, alteration characteristics, and host error with the U‐Pb zircon age of a quartz‐diorite rocks, and occur at >2 km distance to each other porphyry dike (21.2±0.2 Ma; Chapter 2); both (e.g., Prodeminca 2000a; Fig. 6). Combined with

77 the Re‐Os relative age difference of 0.4 m.y. (again, as in Junin, well outside the maximum life span of a single intrusion‐driven hydrothermal system at shallow depth) these characteristics suggest that the Tunas and Gur‐Gur intrusions define two distinct porphyry systems separated in time and space, although they might ultimately be related to the same parental magmatic system at depth. The 9.92±0.05 Ma Re‐Os age obtained on molyb‐ denite hosted by biotite‐bearing granodiorite with potassic‐phyllic alteration dated at 14.8±0.1 Ma (U‐Pb zircon; Chapter 2) closely approaches but pre‐dates the U‐Pb zircon age (9.79±0.03 Ma; Chapter 2) of a close‐by granodiorite porphyry dike in the Tunas sector at Chaucha whose em‐ placement might have been associated with a hydrothermal porphyry system. The age differ‐ ence between the non‐overlapping zircon and molybdenite ages might be due to an overestima‐ tion of the molybdenite age by minor alteration‐ induced Re‐loss (e.g., Barra et al. 2003), underes‐ timated analytical uncertainties, or, possibly, an underestimation of the zircon age by subtle ra‐ diogenic Pb loss (Chapter 2). Similar to Junin and Balsapamba‐Telimbela, porphyry deposit forma‐ tion at Chaucha postdates the major batholith construction period. Multiple intrusive phases are present at Gaby and Papa Grande (Fig. 7) where the main lithologies, represented by hornblende‐plagioclase porphyry stocks, have been dated at 20.26±0.07 Ma (Gaby) and 19.89±0.07 Ma (Papa Grande; U‐Pb zircon; Chapter 2). At Gaby, the dated main porphyry body is additionally cut by multiple porphyry dikes. The age of hydrothermal titanite (20.17±0.16 Ma) associated with sodic‐calcic al‐ teration at Gaby overlaps within error with the age of the main porphyry intrusion, consistent with a close relationship between intrusion em‐ placement and fluid circulation causing sodic‐ calcic alteration.

Figure 5: Simplified lithology‐alteration drill core log of Junin core MJJ‐29 showing multiple porphyry intrusive phases and locations of samples dated in this study and in Chapter 2. The mining company's internal lithologic classification, as applied here, does not strictly correspond to the classification used throughout this study such that minor differences in the distribution of intrusive bodies exist. For example, "coarse‐grained quartz‐feldspar porphyry" corresponds to "hornblende granodiorite porphyry" in our (BGS‐based) classification scheme. Hornblende granodiorite porphyry was dated at 9.01 Ma (E07032; Chapter 2) and seems to represent the oldest porphyry intrusion at Junin dated so far, where the wall rock (Apuela batholith) is >12.9 Ma (Chapter 2). Molybdenite Re‐Os and various K‐Ar ages indicate younger porphyry intrusions were emplaced until c. 6 Ma. Adapted from Salazar (2007). 78 In contrast, our new Re‐Os molybdenite age (20.6±0.1 Ma) is older than the previously dated

porphyry intrusion. The age difference might be due to an overestimate of the Re‐Os molybdenite age caused by Re loss of molybdenite which, for example, might accompany crystallographic transformations from 3R to 2H polytypes (McCandless et al. 1993; see also Barra et al. 2003). Alternatively, one or more additional pre‐ 20.6 Ma porphyry intrusions might be present at Gaby, which exsolved fluids responsible for mo‐ lybdenite precipitation. Earlier intrusive activity

at Gaby is evidenced by the occurrence of an un‐ dated tonalite intrusion closely associated with and (according to field relationships) predating

the porphyry intrusions (Fig. 7).

The two Re‐Os molybdenite ages at Tres Chor‐ reras (12.93±0.07 Ma and 12.75±0.07 Ma) do not overlap within error. The older age dates the tim‐ ing of hydrothermal brecciation possibly related to the emplacement of spatially associated por‐ phyry intrusions for which no ages are available at present (Prodeminca 2000a). The younger age dates the timing of polymetallic mineralization. Both ages are significantly younger than their volcanic host units (30.7±0.7 Ma; Chapter 2). The

small age difference (180 k.y.) between porphyry‐ style and polymetallic mineralization might indi‐ cate that both events ultimately relate to the

same magmatic‐hydrothermal system, but more detailed geologic studies of the Tres Chorreras deposit are required before any qualified conclu‐ sions can be drawn.

A quartz‐diorite of the Cangrejos intrusive com‐ plex has a U‐Pb zircon age of 26.0±0.7 Ma (Chap‐ ter 2) and is intruded by plagioclase‐hornblende porphyry (Potter 2004). The new molybdenite age of 23.5±0.1 Ma might thus be related to a hydrothermal system generated by the post‐26 Ma porphyry intrusion. These ages are signifi‐ cantly older than a K‐Ar age of 16.9±0.2 Ma ob‐ tained on the Paccha intrusion in the center of the Cangrejos‐Zaruma intrusive belt (Fig. 2; Pratt

et al. 1997) which had previously been proposed as an age reference for the Cangrejos porphyry system (Potter 2004). In contrast, these ages are broadly similar to U‐Pb zircon ages of intrusions in the Portovelo‐Zaruma mining district (20.7±0.9 Ma and 24.0±0.1 Ma; Chapter 2) at the western end of the Cangrejos‐Zaruma intrusive belt.

79

Figure 6: Geological map of the Chaucha Cu‐Mo porphyry system showing locations of dated samples. Samples for U‐ Pb zircon datation (Chapter 1) were collected from surface outcrop exposure whereas samples for Re‐Os molybdenite datation (this study) are drill core samples (cf. Tab. 2). Adapted from Micon (2005b).

A quartz‐diorite of the Cangrejos intrusive com‐ in the Portovelo‐Zaruma mining district (20.7±0.9 plex has a U‐Pb zircon age of 26.0±0.7 Ma (Chap‐ Ma and 24.0±0.1 Ma; Chapter 2) at the western ter 2) and is intruded by plagioclase‐hornblende end of the Cangrejos‐Zaruma intrusive belt. porphyry (Potter 2004). The new molybdenite age of 23.5±0.1 Ma might thus be related to a Magmatic characteristics of the Mio‐ hydrothermal system generated by the post‐26 cene metallogenic belt of Ecuador Ma porphyry intrusion. These ages are signifi‐ cantly older than a K‐Ar age of 16.9±0.2 Ma ob‐ Miocene Ecuadorian ore deposits investigated in tained on the Paccha intrusion in the center of this study are always intimately associated with the Cangrejos‐Zaruma intrusive belt (Fig. 2; Pratt intrusive activity (e.g., Fig. 2; Chapter 2). Several et al. 1997) which had previously been proposed porphyry Cu deposits in Ecuador (Junin, Balsa‐ as an age reference for the Cangrejos porphyry pamba‐Telimbela, Chaucha) are associated with system (Potter 2004). In contrast, these ages are the final pulses of batholith‐scale intrusive sys‐ broadly similar to U‐Pb zircon ages of intrusions tems, which record protracted periods of precur‐ sor magmatism over several million years. To

80 visualize this, we have plotted the distribution of tion of precursor intrusive magmatism (e.g., Har‐ intrusive and mineralization‐/alteration‐related ris et al. 2004; Barra et al. 2005). radiometric ages for several Ecuadorian arc seg‐ Systematic across‐arc variations with respect to ments (Fig. 10). All major batholith systems of the timing of magmatism and mineralization do Ecuador associated with ore deposits show a not seem to exist in southern Ecuador (Fig. 2, 10). similar pattern where porphyry deposits form c. 5 Instead, both magmatism and metallogenesis m.y. (Chaucha), 10‐13 m.y. (Junin), or. 13‐15 m.y seem to span the whole width of the arc segment (Balsapamba‐Telimbela) after initialization of ba‐ at a given time, in agreement with an inferred tholith magmatism. A similar precursor intrusive period of arc broadening in the Early Miocene history might be inferred for the Cangrejos por‐ (Chapter 2). Mid‐Miocene intrusion emplacement phyry system, although available geochronologic (c. 16 Ma; Chapter 2) and advanced argillic altera‐ data is too scant to quantify this. Similar observa‐ tion (15.4 Ma; K‐Ar alunite; Prodeminca 2000b) at tions have been made elsewhere in the Miocene the El Mozo high‐sulfidation epithermal deposit, metallogenic belts of Chile and Peru (e.g., Sillitoe situated at the easternmost margin of the Mio‐ 1988) and in the Jurassic metallogenic belt of Ec‐ cene metallogenic belt, broadly coincide in time uador (Chiaradia et al. 2009b). The only potential with Mid‐Miocene Chaucha batholith magmatism deviation from this pattern is represented by the (15‐10 Ma; Chapter 2), polymetallic mineraliza‐ Gaby porphyry system, where geochronologic tion at Tres Chorreras (12.9‐12.8 Ma), and mag‐ evidence points to a rather short‐lived intrusive matism (15.7 Ma, U‐Pb zircon) and hydrothermal system and directly associated large intrusive alteration (18.9 Ma, Ar‐Ar sericite) at the Rio bodies are absent. Blanco low‐sulfidation deposit (Bineli Betsi 2007), Multi‐million year batholith assembly signals effi‐ all situated at the western side of the belt. The cient channeling of arc magmas ascending timing of mineralization may differ profoundly at through the crust resulting in large, repeatedly a given position within the metallogenic belt: for replenished mid‐ to shallow crustal magmatic example, the neighboring (at c. 40 km distance) systems; catastrophic, caldera‐forming ignimbrite Gaby and Chaucha porphyry systems formed at c. eruptions often accompany voluminous batho‐ 20 Ma and 10 Ma, respectively. These considera‐ lith‐related magmatism (e.g., Bachmann et al. tions corroborate recent results of Noble et al. 2007). Thus, shallow crustal batholith sites repre‐ (2004) for the northern‐central Peruvian metal‐ sent a potentially favorable environment for the logenic belt where mineralization was partly coe‐ formation of porphyry‐related ore deposits as val at the western and eastern belt extremities. they provide large volumes of magma and ther‐ mal energy to drive hydrothermal systems (e.g., Structural characteristics of the Mio‐ Cline & Bodnar 1991). However, intense shallow cene metallogenic belt of Ecuador crustal magmatism might have negative implica‐ tions for mineralization (e.g., due to dispersed or The principal spatial distribution of Tertiary intru‐ catastrophic volatile loss instead of focused fluid sions in Ecuador mimics the major upper plate exsolution) or its preservation (e.g., destruction structures (Chapter 2); these include the Chimbo‐ of mineralization by subsequent intrusive pulses). Toachi shear zone in central‐northern Ecuador During the waning stages of batholith assembly, (associated with the Apuela batholith including on the other hand, less vigorous magma replen‐ the Junin porphyry system, and the Balsapamba‐ ishment and downwards migration of the focus Telimbela intrusions), the Calacali‐Pallatanga‐ of magmatic activity might represent a favorable Pujili fault zone in central Ecuador (associated tectonomagmatic environment to form and pre‐ with the Chaucha batholith), and the diffuse serve porphyry‐related ore deposits where pro‐ northern limit of the Amotape terrane, probably gressive melt volatile‐enrichment at mid‐crustal bracketed between the Piñas‐Portovelo and levels takes place (e.g., Rohrlach & Loucks 2005; Jubones faults (associated with the Cangrejos‐ Chiaradia et al. 2009a). In this context, the ton‐ Zaruma intrusive belt; Fig. 2). nage of potentially formed ore deposits is not The locations of single Miocene ore deposits and, expected to directly correlate with the total dura‐ especially, ore deposit clusters in Peru are partly

81 82 controlled by intersections of the regional mag‐ tion of Miocene sub‐belt metallogenesis in matic belt with variably oriented arc‐transverse northern‐central Peru (Noble & McKee 1999; structures (e.g., Noble & McKee 1999). Southern note, however, that some disagreement as to the Ecuador hosts a number of first‐ and second‐ timing of the different Quechua phases in north‐ order arc‐transverse structures which represent a ern‐central Peru exists, with different time ranges structurally favorable environment for porphyry‐ proposed by Benavides‐Cáceres, 1999, and Noble related mineralization (Tosdal & Richards 2001; & McKee, 1999) and might therefore be of similar Richards 2003). Arc ‐transverse structures might importance in southern Ecuador. A number of relate to collision tectonics between the tectonic studies assess the Miocene deformation parautochthonous Ecuadorian mainland and the history of southern Ecuador. The Late Oligocene‐ allochthonous forearc block, which undergoes Early Miocene stress field was probably mostly dextral displacement along major fault zones of characterized by horizontal extension, as evi‐ the Western Cordillera in an oblique subduction denced by growth sequences of Saraguro Group setting (Ego et al. 1996; Prodeminca 2000a). Al‐ volcanics forming thickening wedges towards the ternatively, or additionally, transpressional de‐ southern Piñas‐Portovelo fault, indicative of syn‐ formation creating arc‐transverse structures in volcanic normal fault slip (Spencer et al. 2002). southern Ecuador might partly relate to the post‐ Horizontal extension in southern Ecuador was Paleocene 25±12° clockwise block rotation in‐ followed by transpression which is recorded by ferred for the Amotape terrane from paleomag‐ inversion of the Piñas‐Portovelo fault and folding netic studies (Mitouard et al. 1990). in the area north of the fault producing a major The identification of possible arc‐transverse anticline subparallel to the Cangrejos‐Zaruma structures in central‐northern Ecuador is ham‐ intrusive belt (Spencer et al. 2002), as well as by a pered by Quaternary volcano‐sedimentary cover conjugate set of NE‐trending faults with evidence sequences of the Interandean Depression. A pos‐ for dextral movement (Prodeminca 2000a). A sible tool for identifying concealed arc‐transverse compressive pulse at 19 Ma is constrained by the structures might be the structural correlation of age of Saraguro Group volcanics unconformably Tertiary intrusions of the Western Cordillera (e.g., overlying deformed sedimentary rocks of the the Apuela batholith) with Tertiary intrusions ex‐ Jacapa Formation in southern Ecuador (Hunger‐ posed in the Eastern Cordillera (Aspden et al. bühler 1997). Furthermore, whole‐scale tilting 1992), analogous to the structural grain of the (30° to the SW) of the Saraguro Group volcanic Late Oligocene‐Early Miocene Cangrejos‐Zaruma sequence north of the Piñas‐Portovelo fault is intrusive belt in southern Ecuador, which con‐ observed (Spencer et al. 2002). Small plutons nects eastwards with the Paleocene‐Eocene San north of the Piñas‐Portovelo fault which, based Lucas pluton (Fig. 2). However, the existing geo‐ on the radiometric age systematics discussed in chronologic framework for Ecuador’s Eastern Chapter 2, can be inferred to be of mainly Early Cordillera is largely based on K‐Ar data, which Miocene age, show asymmetric sigmoidal plan‐ commonly show thermally disturbed Late Creta‐ view geometries indicative of syntectonic intru‐ ceous to Early Tertiary ages (Aspden et al. 1992). sion into a dextral transpressional stress field Therefore, further U‐Pb zircon geochronologic (Spencer et al. 2002). Geologic evidence thus studies of undeformed Eastern Cordillera intru‐ documents a change from a dominantly tensional sions are required to unambiguously confirm to a transpressional stress field in southern Ecua‐ their Tertiary age before meaningful structural dor in the Early Miocene, which is broadly cor‐ correlations are possible. relative in time with the Quechua 1 event of No‐ ble & McKee (1999). Following a period of Mid‐ Short‐lived compressional Quechua events have Miocene extension a second, major compressive been proposed to control the onset or termina‐

Figure 7 (previous page): Geological map of the Gaby and Papa Grande Au‐Cu porphyry systems, and sampling loca‐ tions for geochronology. Samples for U‐Pb zircon datation (Chapter 1) were collected from surface outcrop exposure whereas samples for Re‐Os molybdenite and U‐Pb titanite datation are drill core sample (cf. Tab. 2). Adapted from Sri‐ vastava et al. (2008).

83 84 pulse at c. 9 Ma led to widespread basin inversion presented in this study as well as geometric con‐ in southern Ecuador (Hungerbühler et al. 2002) tinuity in map view (Fig. 1) strongly suggest that and is approximately correlative with the the Miocene metallogenic belt of northern‐ Quechua 2 event of Noble & McKee (1999). central Peru is continuous at least until southern Ecuador. Due to the relatively sparse occurrence Ages obtained in this study show that Miocene of Miocene ore deposits in central‐northern Ec‐ mineralization in Ecuador clearly predates, partly uador and southern Colombia, the northward overlaps with, and postdates the regional continuation of the belt is less well defined. “Quechua 1” and “Quechua 2” events (Fig. 10). However, given the continuous distribution of The “Quechua 3” event seems to terminate Mio‐ Miocene magmatism along the Ecuadorian mar‐ cene mineralization in Ecuador. This relationship gin (Chapter 2), and the punctual occurrence of is rather coincidental, however, as it correlates Miocene ore deposits in central‐northern Ecua‐ with the cessation of arc magmatism in southern dor (Junin, Balsapamba, Telimbela), the metal‐ Ecuador where minimum ages progressively logenic belt might continue further northwards young northwards until the southern end of the and connect with the metallogenic belt segment active Northern Volcanic Zone in response to slab of Colombia (Fig. 1; Sillitoe 1988). flattening below southern Ecuador (and northern Peru; Chapter 2). We therefore argue that re‐ The typically vertically stacked environments of gional compressive events do not seem to signifi‐ epithermal vs. porphyry‐style mineralization (e.g., cantly control Miocene metallogenesis in Ecua‐ Fontboté & Bendezú 2009) imply that the erosion dor. Rather, favorable conditions for intrusion level at the deposit scale constitutes a major con‐ emplacement and mineralization at structurally trol factor for the exposed ore deposit type. This favorable sites (see above) might be associated in is well exemplified in the western foothills of the time with local stress regime changes, particu‐ Western Cordillera in Ecuador which are deeply larly at the onset of local post‐compressional dila‐ eroded and mostly present the cores of Miocene tion (Prodeminca 2000a). porphyry systems (Prodeminca 2000a). In con‐ trast, large parts of the Azuay district in southern The connectivity between the Mio‐ Ecuador are less deeply eroded and preserve cene metallogenic belts of northern‐ abundant Miocene epithermal mineralization (Prodeminca 2000b). Quaternary volcanics of the central Peru and Ecuador northern‐central Ecuadorian Interandean Depres‐ Sillitoe (1988) popularized the concept of seg‐ sion can be expected to conceal Tertiary arc mented metallogenic belts in the Andes and magmatic units (Chapter 2) and, potentially, Mio‐ placed a fundamental segment boundary at 5°S, cene mineralization at relatively shallow depth. corresponding to the Huancabamba Deflection The close geometric similarity between the Peru‐ (Fig. 1). Due to a lack of geochronologic data for vian and Ecuadorian belt segments calls for a Ecuadorian ore deposits at that time Sillitoe closer inspection of their respective geologic (1988) noted that the continuity of the northern‐ characteristics which are summarized in Table 5. central Peruvian Miocene metallogenic belt to‐ Both belt segments essentially host ore deposits wards Ecuador is uncertain. Geochronologic data

Figure 8 (previous page): Typical mineralization/alteration assemblages for molybdenite samples dated in this study (red rectangles mark used vein type). A – hornblende granodiorite porphyry with pervasive potassic, overprinted by phyllic alteration, cut by multiple mo‐qtz veinlets (Junin). B – hbl‐bt granodiorite with weak pervasive chl‐act alteration, vein‐ like aggregates of bt‐ep‐py‐cp, and thin qtz‐py‐mo‐cp and mo‐qtz veinlets (Telimbela). C – Vein breccia of grano‐ diorite with weak chl‐ep‐ab‐rt alteration; breccia matrix = ms‐bt‐qtz with disseminated cp‐py‐mo (Balsapamba). D – Hydrothermal breccia with plag porphyry clasts (with strong ser alteration) and matrix of qtz‐chl‐rt‐goe‐sulfides (po‐cp‐ mo); ser (phyllic) alteration seems to postdate brecciation such that the breccia matrix mineralogy might not be original (Gaby). E – Tonalite with strong chl‐ser/ms alteration and hydrothermal rt (possibly residual from earlier potassic al‐ teration?); cut by multiple veinlets of qtz‐py (with ser halo), mt‐cp‐qtz‐mo, and qtz‐mo (Chaucha). F – Banded cp‐mo‐ jsp‐sl veins with pervasive clay alteration (Tres Chorreras). G – Jigsaw breccia with angular, silicified volcanic clasts in jsp‐tm‐mo‐mt matrix (Tres Chorreras). Scale bar is 2 cm. Same mineral abbreviations as in Fig. 3.

85 of the same types and age range with the possi‐ age with the younger age peak identified in Peru, ble exception of skarn and Cordilleran vein type and polymetallic mineralization at Tres Chorreras deposits; the latter, although very common in (12.9‐12.8 Ma) and advanced argillic alteration at Peru (Noble & McKee 1999; Fontboté & Bendezú El Mozo (15.4 Ma; Prodeminca 2000b) tend to 2009), are not clearly described as such in Ecua‐ overlap with the older age peak in Peru. In gen‐ dor. This difference might only be an apparent eral, however, data for Ecuador are too scarce to one, caused by different ore deposit classification allow a representative statistical treatment at standards in Ecuador, and/or could be related to this point. Qualitatively, deposit formation in the the scarcity of reactive limestone host units in Ecuadorian belt segment additionally tends to Ecuador compared to their abundant occurrence peak in the Early Miocene, comprising the por‐ in Peru (e.g., the Pucará Group; Noble & McKee phyry Cu deposits of Telimbela, Balsapamba, 1999) where they host economically important Gaby‐Papa Grande, and Cangrejos; there is no polymetallic replacement bodies (Fontboté & equivalent peak in the northern‐central Peruvian Bendezú 2009). Contrasting deep crustal base‐ belt segment at that time. One might speculate ment compositions in Ecuador and Peru (oceanic that this age difference partly relates to a sam‐ vs. continental; Tab. 5) do not seem to produce pling bias due to differential exposure levels in major differences in metallogenesis between various ore deposit districts. these arc segments, although crustal contribu‐ As noted above, Early Miocene ore deposits in tions may influence commodity proportions of the Western Cordillera and in the Cangrejos‐ porphyry Cu deposits elsewhere (e.g., Mo; See‐ Zaruma intrusive belt of Ecuador represent rela‐ dorff et al. 2005). tively deeply eroded porphyry systems domi‐ The temporal distribution pattern of the north‐ nated by sodic‐calcic and potassic alteration zo‐ ern‐central Peruvian Miocene metallogenic belt nes (e.g., Prodeminca 2000a; Fig. 3). In contrast, shows two maxima for radiometric mineralization the younger Ecuadorian porphyry deposits such ages at 15‐13 Ma and 10‐7 Ma (Noble & McKee as Chaucha and Junin consistently display wide‐ 1999; note that these maxima are not weighted spread phyllic alteration zones indicating that by tonnage). A few Ecuadorian porphyry Cu de‐ they have been less deeply eroded. Spikings et al. posits such as Chaucha (c.) 9.5‐9.9 Ma and Junin (2005) show that increased Mid‐ to Late (several events between 9 and 6 Ma) overlap in

Figure 9: Concordia plot and weighted mean 206Pb/238U average age for hydrothermal titanite related to sodic‐calcic alteration at the Gaby porphyry system.

86 Miocene cooling rates inferred from thermo‐ magmatic cycle under favorable exposure levels chronologic modeling relate to the rapid exhuma‐ (Kay et al. 1999; Richards 2003). tion of fault blocks in the Western Cordillera of The distribution pattern of Tertiary arc magma‐ Ecuador. Similarly, N‐S contraction (see discus‐ tism in northern‐central Ecuador suggests a sion above) might have driven Mid‐ to Late Mio‐ broadly stable slab dip until the Late Miocene cene exhumation of the Cangrejos‐Zaruma intru‐ when minor slab shallowing occurred, possibly sive belt which intrudes the hinge and southern related to subduction of the Carnegie Ridge sea‐ flank of a regional antiform north of the inverted mount chain (Chapter 2). Slab shallowing might Piñas‐Portovelo fault (Prodeminca 2000a; thus contribute to generating a favorable expo‐ Spencer et al. 2002). It might thus be speculated sure level for young ore deposits in northern Ec‐ that younger ore deposits in deeply eroded uador (such as Junin) by causing an eastward mi‐ blocks were completely removed by erosion; a gration of Late Miocene to Quaternary arc vol‐ higher density of geochronologic studies on Ec‐ canism. Similarly, progressive broadening of the uadorian ore deposits in less deeply eroded fault flat slab region below southern Ecuador (and blocks might preferentially reveal younger min‐ northern Peru) since the Mid‐Miocene generated eralization ages. This includes, for example, a a favorable exposure level for porphyry‐related large number of potentially younger epithermal ore deposits in this arc segment where post‐Late deposits in the Azuay district of Ecuador (e.g., Miocene volcanic cover sequences are lacking Prodeminca 2000b). (Chapter 2). Geodynamic impacts on the spatio‐ Rosenbaum et al. (2005) present geodynamic temporal distribution of Miocene ore reconstructions constraining the collisional timing of anomalous oceanic bathymetric features, the deposits in Ecuador Inca plateau and the Nazca ridge, with respect to Two geodynamic factors have been proposed to the Peruvian margin. These authors observe an influence the formation of porphyry‐related ore apparent spatio‐temporal coincidence between deposit in the Andes and elsewhere: slab shal‐ bathymetric high collision and Miocene ore de‐ lowing‐flattening (e.g., James & Sacks 1999; Kay posit formation (note, however, that these au‐ et al., 1999; see also review by Richards, 2003, thors do not quantify any uncertainties for their and references therein) and the subduction of reconstruction models), and propose that a direct bathymetric highs, i.e. seamount chains (“ridges”; link exists between the two. In this context it is e.g., Rosenbaum et al. 2005; Cooke et al. 2005). interesting to investigate the metallogenic re‐ As they represent overthickened oceanic crust, sponse to collision of the Carnegie Ridge with the the subduction of seamount chains may contrib‐ Colombian‐Ecuadorian margin. ute to slab shallowing by virtue of their relative The timing of initial collision of the Carnegie buoyancy, thus mutually linking ridge collision Ridge with the Colombian‐Ecuadorian margin and flat subduction (e.g., van Hunen et al. 2004). cannot be accurately determined because, unlike Slab dehydration during periods of flat subduc‐ for other ridges such as the Nazca Ridge, a sym‐ tion may lead to intense hydration of the overly‐ metric mirror hotspot track of the Carnegie Ridge ing crust; subsequent slab re‐steepening and does not exist. While the Cocos Ridge was formed trenchward migration of hot asthenosphere at the same time at the Galapagos hotspot as the leaves the thus rheologically weakened crust Carnegie Ridge, it does not represent a direct highly susceptible to deformation and melting mirror image due to repeated jumps of the which is potentially favorable for metallogenesis Nazca‐Cocos spreading center across the hotspot (James & Sacks 1999). Shallowing of the slab position (Barckhausen et al. 2008). Furthermore, principally results in the landward migration of the leading edge of both ridges has been sub‐ the locus of arc magmatism on the upper plate, ducted (e.g., Gutscher et al. 1999). Consequently, and may result in porphyry‐related ore deposit the shape of the subducted part of the Carnegie formation at the end of a given tectono‐

87 Figure 10: Spatio‐temporal distribution of Miocene ore deposits and associated Oligocene‐Miocene plutons of Ecuador. Mineralization essentially comprises the whole Miocene (and the latest Oligocene: Cangrejos porphyry, 23.5±0.1 Ma) and seems to peak in the Early Miocene, with a second, broader peak in the Mid‐ to Late Miocene. A general spatio‐ temporal correlation between ore deposit formation and Carnegie Ridge subduction or compressive pulses is not ob‐ served. In a given batholith system (Apuela, Balsapamba‐Telimbela, Chaucha) preserved porphyry‐related mineraliza‐ tion tends to occur after a significant lag time with respect to initiation of batholith construction (c. 5‐15 m.y.); miner‐ alization is concomitant with the last pulse of magmatism and final batholith assembly for Apuela and Chaucha, but followed by minor ongoing magmatism at Balsapamba‐Telimbela (though note that the latter observation is solely based on K‐Ar ages which are susceptible to disturbance by younger hydrothermal alteration events). Mineraliza‐ tion/alteration ages compiled from this study or references discussed in the text; magmatic ages from compilation in Chapter 2. Note that only intrusions spatially associated with mineralization are shown. Compressive pulses in Ecuador (black boxes; Hungerbühler et al. 2002 and references therein), and northern‐central Peru (gray boxes: Noble & McKee 1999; white boxes: Benavides‐Cáceres 1999) are shown for comparison (I = Inca; Q = Quechua). Note that minimum size of boxes, corresponding to 1 m.y., was arbitrarily chosen and does not reflect the actual duration of compressive event. See text for further discussion.

88 Table 5: Comparison of geological features of the Miocene metallogenic belts of Peru and Ecuador northern-central Peru Ecuador Main commodities Au, Cu, base metals Au, Cu Mineralization age range 23 - 6 Ma 24 - 6 Ma Mineralization peaks 15 - 13 Ma; 8 - 7 Ma not enough data available to evaluate Ore deposit types porphyry Au-Cu, porphyry Cu-Mo, porphyry Au-Cu, porphyry Cu-Mo, high-, high-sulfidation epithermal, Cordil- intermediate-, low-sulfidation epithermal leran vein, skarn Main host lithologies of ore Mesozoic shelf carbonates and Late Cretaceous-Paleogene island arc vol- deposits sediments canics (northern Ecuador) and oceanic pla- teau units (central Ecuador) Neogene volcanics-intrusions Paleozoic-Mesozoic metasediments (south- ern Ecuador) Neogene volcanics-intrusions (southern Ecuador) Deep crustal basement units Mature continental crust Oceanic plateau crust (Western Cordillera) Oceanic ± continental crust (southern Ecua- dorian Sierra) Continental crust (Cangrejos-Zaruma intru- sive belt) Data for Ecuador from this study and Prodeminca (2000a, 2000b). Data for Peru from Noble & McKee (1999) and Noble et al. (2004). Note that the age of the oldest deposit dated in this study (Cangrejos: 23.5 Ma) corresponds to the latest Oligocene

Ridge is not known, although it seems to be visi‐ 1998) and of the hotspot‐South Amer‐ ble in seismicity distribution patterns by causing a ica/Farallon/Nazca reference systems (Müller et seismic gap (Gutscher et al. 1999). al. 1993; Rosenbaum et al. 2005). This approach enables us to reconstruct the ridge assuming ei‐ Predicting the initial collision of the Carnegie ther a fixed hot spot, or a fixed South America as Ridge with the Ecuadorian margin thus requires a reference. Results are presented as a series of kinematic reconstruction of the ridge track time slices in Figure 11 and yield initial collision through time assuming a fixed origin at the Gala‐ estimates of 8±3.5 Ma (hotspot‐Farallon/Nazca pagos hotspot, followed by progressive stepwise and Farallon/Nazca‐South America reference sys‐ rotation using rotation poles for a given plate tec‐ tems) and 5±4.5 Ma (hotspot‐Farallon/Nazca and tonic reference system. Previous reconstructions hotspot‐South America reference systems). Er‐ in this manner obtained initial collision estimates rors include a 25% relative uncertainty estimate around 8 Ma (using rotation poles of Pilger 1984; for the angular velocity of a given rotation pole e.g., Daly 1989; Gutscher et al. 1999), although (cf. Chapter 2) and a ±50 km uncertainty for the Lonsdale & Klitgord )(1978 estimated a more re‐ hotspot location. Both ages overlap within error cent collision at c. 1 Ma. Using minimum/ maxi‐ and are in good agreement with previous propo‐ mum plate convergence rates of Pardo‐Casas & sitions of initial Carnegie Ridge collision at c. 8 Molnar (1987) instead of rotation pole data, Spik‐ Ma. It should be noted, however, that (1) these ings et al. (2001) estimated an initial collision of calculations (like all plate tectonic reconstruc‐ the Carnegie Ridge with the Ecuadorian margin at tions) are based on the assumption of a plate be‐ 9 or 15 Ma, respectively, for a starting reference having as a rigid entity which might not be strictly time of 22 Ma. true at plate margins (e.g., Cox & Hart 1986), and We have performed a kinematic Carnegie Ridge (2) the reconstructions model a linear hotspot reconstruction using the same starting reference track whereas spreading center jumps (Barck‐ time (22 Ma) as Spikings et al. (2001), and the hausen et al. 2008) might have caused ridge seg‐ most recent sets of available rotation poles of the mentation. Nazca‐South America reference system (Somoza

89 Figure 11: Total reconstructions of the position of a reference point originating at coordinates of the central Galapagos hotspot at different times (boxes in the upper left) throughout the Miocene using the methods described in Cox & Hart (1986). The reference point serves as a proxy for the leading edge of the offshore Carnegie Ridge seamount chain. Two different reference frames were used: a fixed South American plate and the relative motions of hotspots and the Nazca/Farallon plate (Müller et al. 1993; Somoza 1998), or a fixed hotspot and the relative motions of South America and the Nazca/Farallon plate (Müller et al. 1993; Rosenbaum et al. 2005). The different reference frames constrain ini‐ tial Carnegie Ridge collision at 8±3.5 Ma or 5±4.5 Ma, respectively. Note that in the fixed South America‐based recon‐ struction, reference point positions are theoretical and only become geologically relevant at the trench where the Nazca/Farallon and South American plates are in direct contact. In contrast, for fixed hotspot‐based reconstructions offshore locations have geological relevance. Carnegie Ridge seamounts dated by Christie et al. (1992) were rotated back to their origin to test rotation pole accuracy; they mostly overlap with the hotspot starting position suggesting that the former are accurately estimated.

90

Figure 11 (continued)

The time‐space distribution of Ecuadorian por‐ speculate that ridge collision causes increased phyry‐related ore deposits shows that there is no deformation in the upper plate which might aid spatio‐temporal coincidence between ore deposit ore deposit formation. As discussed by MacMillan formation and Carnegie ridge collision, except for et al. (2004) and Michaud et al. (2009), however, the Junin porphyry Cu‐Mo deposit (Fig. 10). Ore a direct causative relation between ridge‐trench deposits in southern Ecuador also predate the collision and geological features (such as defor‐ arrival of the inferred Inca plateau at the Peru‐ mation) of the overriding plate usually cannot be Ecuador trench, which Rosenbaum et al. (2005) demonstrated unambiguously. An exception is estimate at c. 14‐12 Ma. Rosenbaum et al. (2005) the forearc region where, depending on its

91 rheological strength, ridge collision either induces able sites for porphyry‐related mineralization. uplift, or indentation and conjugated strike‐slip However, extensive shallow crustal magmatism faulting (Hampel et al. 2004). Cooke et al. (2005) associated with peaks in batholith construction note that ridge collision (and flat subduction) is (potentially including catastrophic voluminous no requirement for the formation of average‐size ignimbrite eruptions) might prove disadvanta‐ porphyry‐related ore deposits, but might consti‐ geous from a metallogenic perspective. In con‐ tute a positive trigger mechanism for the forma‐ trast, during the waning stages of batholith as‐ tion of giant ore deposits. More detailed studies sembly when thermal relaxation occurs and the exploring the potential connection between Car‐ focus of magmatism migrates from upper to‐ negie Ridge‐margin collision, tectonomagmatic wards deeper crustal levels favorable petroge‐ processes, and porphyry‐related mineralization at netic preconditioning of potential porphyry pa‐ Junin might contribute to unravel these mecha‐ rental melts for subsequent porphyry‐related nisms in more detail. mineralization might take place. A general direct relationship in space and time Conclusions between seamount chain subduction or pulses of We have presented the first regionally extensive regional compression and ore deposit formation dataset of radiometric ages on Miocene ore de‐ is not observed in Ecuador except, perhaps, for posits of Ecuador based on the Re‐Os (molyb‐ the Junin porphyry Cu‐Mo deposit in NW Ecua‐ denite) and U‐Pb (titanite) isotopic systems. dor. The subduction of bathymetric anomalies These new data allow us to infer that the Mio‐ such as the Carnegie Ridge or the Inca Plateau cene metallogenic belt of northern‐central Peru may, however, have a metallogenetically favor‐ extends northwards into southern Ecuador, and able effect by their influence on slab dip (with a potentially further north until Colombia. The ages potential lag time of several m.y.) and thus sur‐ of intrusions and their related hydrothermal sys‐ face migration patterns of arc magmatism culmi‐ tems in Ecuador coincide with the age range of nating in an arc magmatic gap. The latter results porphyry‐related ore deposits in northern‐central in favorable exposure levels of Miocene por‐ Peru and range from 6 to 23.5 Ma. phyry‐related ore deposits in southern Ecuador and northern Peru. Miocene porphyry‐related mineralization is rela‐ tively widespread in southern Ecuador, and facili‐ References tated by metallogenetically favorable factors in‐ cluding (1) a structural setting providing abun‐ Aspden, J.A., Harrison, S. H., Rundle, C. C. (1992): New dant arc‐transverse structures to channelize geochronological control for the tectono‐magmatic magmas and fluids; (2) widespread Miocene evolution of the metamorphic basement, Cordillera magmatism and synmagmatic deformation; (3) Real, and El Oro Prov‐ince of Ecuador. Journal of South American Earth Sciences 6; 77‐96. erosion levels suitable to preserve Miocene min‐ eralization; and (4) lack of extensive Quaternary Bachmann, O., Miller, C. F., de Silva, S. L. (2007): The cover sequences in a flat slab segment. Miocene volcanic ‐plutonic connection as a stage for under‐ porphyry systems in the Western Cordillera and standing crustal magmatism. Journal of Volcanology its western foothills may be deeply eroded such and Geothermal Re‐search 167; 1‐23. that the bulk of the ore body is eroded, but are Barckhausen, U., Ranero, C R., Cande, S. C., Engels, M., well‐preserved in some fault blocks. Weinrebe, W. (2008): Birth of an intraoceanic spread‐ ing center. Geology 36; 767‐770. Porphyry‐related ore deposits in Ecuador are of‐ ten (at Junin, Telimbela, Balsapamba, and Barra, F., Ruiz, J., Mathur, R., Titley, S. (2003): A Re‐Os Chaucha) associated with variably long‐lived study on sulfide minerals from the Bagdad porphyry Cu‐Mo deposit, northern Arizona, United States. Min‐ magmatic cycles of batholith construction where eralium Deposita 38; 585–596. batholithic precursor magmatism has lifetimes of 5‐15 m.y. Batholithic complexes are associated Barra, F., Ruiz, J., Valencia, V. A., Ochoa‐Landín, L., with elevated transcrustal melt flux and accumu‐ Chesley, J. T., Zurcher, L. (2005): Laramide porphyry lation, and may thus represent potentially favor‐ Cu‐Mo mineralization in northern Mexico: age nco‐

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96 CHAPTER IV CRUSTAL BASEMENT ARCHITECTURE IN ECUADOR EXPLORED BY Sr, Nd, AND Pb ISOTOPIC COMPOSITIONS OF TERTIARY‐QUATERNARY ARC MAGMAS Abstract The crustal basement of Ecuador comprises a collage of mostly Paleozoic‐Mesozoic tectono‐stratigraphic units of both continental and oceanic affinity in the Eastern Cordillera, and oceanic plateau units in the Western Cordillera and forearc region which were accreted in the Late Cretaceous. The diffuse paleo‐ continental suture zone is bracketed by the regional Andean‐ (NNE) trending Peltetec and Calacali‐ Pallatanga‐Pujili fault zones, and is situated between the Eastern and Western Cordillera ranges where basement units are covered by Tertiary‐Quaternary arc volcanics. An extensive body of isotope geochemi‐ cal information exists for Quaternary arc volcanics of the Northern Volcanic Zone in northern Ecuador, whe‐ reas Tertiary cover sequences in southern‐central Ecuador are poorly characterized isotopically. In this study we are presenting a set of 58 new whole‐rock Sr, Nd, and Pb isotopic compositions of Late Oligocene and younger intrusions and arc volcanics of the Western Cordillera, its western foothills, and the central‐ southern Ecuadorian Sierra region. Combining this new dataset with existing data on Quaternary arc volca‐ noes allows us to trace basement units of the Late Cretaceous suture zone at depth. Quaternary arc volcanics define distinct isotopic groups for volcanoes situated east and west of the Peltetec Fault, respectively. Late Oligocene to Late Miocene arc volcanics and intrusions of the southern Ecuador Sierra region overlap isotopically with recent arc volcanics east of the Peltetec Fault in northern Ecuador suggesting along‐strike continuity of similar basement units at depth. Late Oligocene to Late Miocene grani‐ toids of the Western Cordillera and its western foothills show the most primitive Sr and Nd isotopic compo‐ sitions identified in Tertiary‐Quaternary Ecuadorian arc magmas so far; primitive Cretaceous oceanic pla‐ teau units constitute their assimilants at depth, causing these arc magmas to become isotopically more primitive while assimilating crustal material. Crustal isotopic contamination of Tertiary‐Quaternary arc magmas mainly takes place at deep to mid‐crustal levels except for granitoids of the Cangrejos‐Zaruma in‐ trusive belt in southern Ecuador, where additional prominent shallow crustal assimilation produces highly radiogenic Sr and Pb, and low radiogenic Nd isotopic compositions of evolving arc magmas. Isotopic Sr, Nd, and Pb compositions of arc magmas in northern‐central Ecuador follow a systematic across‐ arc pattern where they evolve towards progressively more radiogenic 87Sr/86Sr and 207Pb/204Pb, and less ra‐ diogenic 143Nd/144Nd compositions at deep to mid‐crustal levels with increasing distance from the trench. This is consistent with regional underthrusting of accreted oceanic plateau material along a broad suture zone below the paleo‐continental margin as previously inferred from seismic studies.

97 Introduction nental margin (Pratt et al. 2005). Exotic Creta‐ ceous oceanic plateau fragments floor the West‐ Geochemical studies in the southern and central ern Cordillera and forearc region (e.g., Mamberti Andes have revealed pronounced variations in Sr, et al. 2003; Vallejo et al. 2009). Geophysical stud‐ Nd, and Pb isotopic compositions of arc magmas. ies yield contradictory results with respect to the These variations are mainly attributed to crustal geometry of the boundary between the accreted contamination effects where lateral and vertical oceanic plateau material and the parautochtho‐ basement heterogeneity (Davidson & de Silva nous paleocontinental domain below the Inter‐ 1992; Wörner et al. 1992), crustal thickness (Hil‐ andean Depression (IAD) between Ecuador’s dreth & Moorbath 1988), and the extent of direct Eastern and Western Cordilleras. Based on gra‐ magma‐crust interaction (Dungan & Davidson vimetric data Feininger & Seguin (1983) suggest 2004) are inferred to be the major control factors that continental Eastern Cordillera basement for the isotopic variability of arc magmas. Crustal floors the IAD; in contrast, Guillier et al. (2001) isotopic imprints on arc magmas may be super‐ provide seismic evidence for regional‐scale un‐ posed on continent‐scale mantle wedge isotopic derthrusting of oceanic plateau material below variability (Chiaradia & Fontboté 2002) which the IAD. might, for example, involve source contamination While isotopic data for individual arc volcanic by subduction erosion (e.g., Stern & Skewes centers and the accreted oceanic domains are 2005). In a given arc segment, the isotopic char‐ readily available (see references in Figs. 1, 2), on‐ acteristics of Tertiary‐Quaternary arc magmas ly a single study has attempted to comprehen‐ may be used to outline different crustal base‐ sively assess the Pb isotopic composition of the ment domains (e.g., Wörner et al. 1992; Mamani different terrane basement units on a regional et al. 2008, 2010). scale (Chiaradia et al. 2004a). In this contribution, In the northern Andes, significant crustal base‐ we are presenting 58 new whole‐rock Sr, Nd, and ment variations occur both in along‐ and across‐ Pb isotopic compositions of Late Oligocene and arc dimension. The Tertiary‐Quaternary arc sys‐ younger granitoids and volcanic formations (and tem of Ecuador is constructed on a basement some of their host lithologies) of the Western collage of multiple tectono‐stratigraphic units Cordillera, its western foothills, and the central‐ separated by major NNE‐trending fault zones (Li‐ southern Ecuadorian Sierra region. We are com‐ therland et al. 1994). Juxtaposed against the cra‐ bining these new data with published isotopic tonic basement of the Amazon foreland basin, compositions of basement units and Quaternary several Paleo‐ to Mesozoic continental and island arc volcanoes to discuss tectonic implications of arc units form the major basement units of the isotopic variations in the crustal basement of the Eastern Cordillera (Fig. 1; Litherland et al. 1994), IAD and the southern Ecuadorian Sierra, and how alternatively interpreted as autochthonous conti‐

Figure 1 (next page): Left: Topographic map of northern Andean margin showing gravity anomaly isolines [mgal] of Feininger & Seguin (1983) in the Cordillera region (thick white lines). Note the overall lower elevation in southern Ecuador‐northern Peru compared to central‐northern Ecuador where oceanic plateau units are underthrusting the continental margin. Right: Simplified geological map of the Ecuadorian Andes showing crustal basement units, major fault systems (straight ;lines dashed where inferred; adapted from Winkler et al. 2005), Late Cretaceous‐Tertiary arc volcanic units and intrusions, and Quaternary arc volcanoes relevant for this study. New Sr, Nd, and Pb isotopic data presented in this study were obtained on Late Tertiary granitoids and volcanics (and the Late Cretaceous Curiplaya intrusions).c Ar volcanoes and intrusions are color‐coded according to their isotopic composition reflecting crustal 87 86 206 204 207 204 basement domains as discussed in the text (yellow: εNdinitial >5, Sr/ Sr <0.7038, Pb/ Pb <18.9, Pb/ Pb 87 86 206 204 207 204 <15.62; blue: εNdinitial = 4‐6, Sr/ Sr = 0.7038‐0.7044, Pb/ Pb <19.03, Pb/ Pb <15.60; green: εNdinitial = 3‐6, 87 86 206 204 207 204 87 86 206 204 Sr/ Sr = 0.7040‐0.7043, Pb/ Pb < 19.14, Pb/ Pb < 15.64; brown: εNdinitial > ‐2, Sr/ Sr < 0.7049, Pb/ Pb 207 204 87 86 206 204 207 204 <19.08, Pb/ Pb <15.70; dark‐gray: εNdinitial <1, Sr/ Sr >0.7047, Pb/ Pb >18.9, Pb/ Pb >15.62). Volcanoes where only a single isotopic analysis is available (Quilotoa, Sangay, Chalupas) are marked with a question mark and not color‐coded unless the isotopic signature is unambiguous. Note the systematic across‐arc distribution pattern of arc magma isotopic compositions in northern Ecuador as discussed in the text. General geological features of map modified from Chapter 2. 98

99 they relate to the proposed suture zone geome‐ Eastern and Western Cordillera ranges. Major tries of oceanic plateau units and the paleoconti‐ arc‐parallel fault systems thought to bracket the nental Ecuadorian margin. No attempt is being diffuse suture zone between oceanic plateau made here to extend the discussion towards iso‐ units and the paleo‐continental margin below the topically discerning the complex Eastern Cordil‐ IAD (Calacali‐Pallatanga‐Pujili fault zone, CPPF, lera basement (Litherland et al. 1994; Pratt et al. and Peltetec fault, PF; Winkler et al. 2005) tend 2005). to dip subvertically at the surface, but define c. 35°E dipping fault planes at mid‐ to deep crustal Geological framework levels implying that oceanic material forms the deep crustal root of the IAD (Guillier et al. 2001; Paleozoic and subordinate Precambrian base‐ Jaillard et al. 2005); a tectonized mélange of con‐ ment units of Ecuador’s Eastern Cordillera host a tinental crust and oceanic plateau units is in‐ number of major batholiths and volcanics result‐ ferred at shallow crustal depth (e.g., Spikings et ing from intense Triassic‐Jurassic arc magmatism al. 2005). In contrast, IAD basement units similar (Litherland et al. 1994). While Litherland et al. to the parautochthonous Eastern Cordillera have (1994) tend to interpret major batholith bounda‐ been inferred in previous studies (Chaucha ter‐ ries as suture zones delineating a number of both rane; Feininger & Seguin 1983; Litherland et al. oceanic‐ and continental‐affinity allochthonous 1994). terranes (Fig. 1), Pratt et al. (2005) regard most of these contacts as intrusive and infer an autoch‐ Seismic studies constrain the crustal thickness in thonous crustal basement for Ecuador’s Eastern Ecuador to 40‐50 km below the Western Cordil‐ Cordillera. Overthickened oceanic crust, partly lera in the present‐day frontal arc, and to 50‐75 associated with the Caribbean‐Colombian oce‐ km below the IAD and the Eastern Cordillera in anic plateau (CCOP) and mainly accreted in the the present‐day main arc region (Guillier et al. Late Cretaceous, is juxtaposed against the East‐ 2001). The significantly lower mean elevation of ern Cordillera basement along a suture zone the Ecuadorian Andes compared to the Central comprising parts of the IAD (e.g., Mamberti et al. Andean Altiplano region of only slightly higher 2003; Jaillard et al. 2005; Spikings et al. 2005; Val‐ crustal thickness might be isostatically supported lejo et al. 2009). The allochthonous oceanic pla‐ by a column of continental crust underthrusted teau units host several pre‐ and post‐accretionary by high‐density oceanic plateau material, follow‐ island arc systems of Late Cretaceous to Early ing the inferred suture zone geometry at depth Tertiary age (Rio Cala and Macuchi units; e.g., (Guillier et al. 2001). Periods of crustal thickening Chiaradia 2009; Vallejo et al. 2009). Mid‐ to Late in Ecuador are not as well constrained as in the Tertiary arc magmatism in northern‐central Ec‐ southern‐central Andes; tectonic crustal thicken‐ uador, resulting from the subduction of the Faral‐ ing by westwards basal forearc wedging seems to lon/Nazca plate below the accreted oceanic pla‐ have occurred throughout the Tertiary with a ma‐ teau material, focused on the Western Cordillera jor period of thickening affecting the Andean region and only sporadically affected the Eastern main arc region since the Late Miocene (Jaillard Cordillera until the Late Miocene, when major et al. 2005). landwards arc broadening towards the Eastern Cordillera is recorded (Chapter 2). Active arc vol‐ Methodology canism of the Northern Volcanic Zone (NVZ) in Samples for isotopic analysis were collected from Ecuador covers the whole range from the Eastern outcrop exposures or drill cores in Ecuador ac‐ to the Western Cordillera, and from the Colom‐ cording to the locations marked in Figure 1. Gra‐ bian border until Sangay volcano at c. 2° S (Fig. 1). nitoids and arc volcanic formations investigated Tertiary‐Quaternary volcano‐sedimentary cover in this study are of Late Oligocene or younger age sequences conceal the basement of the IAD and (Fig. 1; Chapter 2). Intrusive rocks comprise the central Ecuadorian Sierra region between the hornblende‐ and biotite‐bearing tonalites, grano‐

100 diorites, quartz‐diorites, and granodiorite por‐ Lead, Sr and Nd isotope ratios were measured on phyries emplaced along major fault zones of the a Thermo TRITON mass spectrometer on Faraday Western Cordillera, its western foothills, and in cups in static mode. Lead was loaded on Re fila‐ the Sierra region of central‐southern Ecuador. ments using the silica gel technique and all sam‐ Sampled volcanic rocks of the IAD and the south‐ ples (and standards) were measured at a pyrome‐ ern Ecuadorian Sierra comprise (1) the wide‐ terd‐controlle temperature of 1220 °C. Lead iso‐ spread Late Oligocene to Early Miocene Saraguro tope ratios were corrected for instrumental frac‐ Group, composed of andesitic‐dacitic lava flows tionation by a factor of 0.07% per amu based on and tuffs, and dacitic‐rhyolitic ignimbrites; and more than 90 measurements of the SRM981 (2) the Late Miocene Quimsacocha volcanic cen‐ standard and using the standard values of Todt et ter which forms a caldera with associated ande‐ al. (1996). External reproducibilities (2σ) of the sitic‐dacitic lava flows and dacitic‐rhyolitic standard ratios are 0.05% for 206Pb/204Pb, 0.08% domes. In addition, we compiled isotopic data of for 207Pb/204Pb and 0.10% for 208Pb/204Pb. Stron‐ NVZ volcanic centers which, from north to south, tium was loaded on single Re filaments with a Ta comprise Imbabura, Cayambe, Pululagua, Pichin‐ oxide solution and measured at a pyrometer‐ cha, Chacana, Ilalo, Atacazo, Antisana, Cotopaxi, controlled temperature of 1490 °C. 87Sr/86Sr val‐ Chalupas, Quilotoa, and Sangay volcano. Sumaco ues were internally corrected for fractionation volcano, occupying a back‐arc position 380 km using a 88Sr/86Sr value of 8.375209. Raw values from the trench, was not included in the compila‐ were further corrected for external fractionation tion because its magmas are significantly en‐ by a value of +0.03‰, determined by repeated riched in Sr and Nd, minimizing the isotopic lev‐ measurements of the SRM987 standard erage of potential crustal assimilants (Chiaradia (87Sr/86Sr=0.710250). External reproducibility (2σ) et al. 2009). of the SRM987 standard is 7 ppm. Neodymium was loaded with 1 M HNO and measured with All sample preparation steps and isotopic analy‐ 3 the double filament technique. 143Nd/144Nd val‐ ses were performed at the Department of Miner‐ ues were internally corrected for fractionation alogy, University of Geneva. Samples were using a 146Nd/144Nd value of 0.7219 and the 144Sm cleaned with water, crushed using a steel jaw interference on 144Nd was monitored on the mass crusher, and powdered (<70 μm) using an agate 147Sm and corrected using a 144Sm/147Sm value of disc mill. Preparation for isotopic analysis used 0.206700. The external reproducibility (2σ) of the the techniques of Chiaradia (2009) and refer‐ JNdi‐1 standard (Tanaka et al. 2000) is 4 ppm. ences therein. Powdered samples (100‐150 mg Part of the Nd isotope ratios were measured on a each) were loaded into screw‐sealed 20 ml Teflon seven‐collector Finnigan MAT 262 thermal ioniza‐ vials and leached overnight at room temperature tion mass spectrometer with extended geometry using 3 M HCl to dissolve alteration minerals such and stigmatic focusing using double Re filaments as carbonates with potential isotopic disequilib‐ where 143Nd/144Nd was measured in a semidy‐ rium compositions. Sample‐leachate mixture cen‐ namic mode (quadruple collectors, measurement trifugation and subsequent leachate discarding jumping mode). was followed by two‐fold sample residue rinsing and centrifugation using deionized water. Sam‐ Neodymium isotopic ratios were age‐corrected ples were then dissolved in a mixture of 4 ml con‐ and recalculated to initial 143Nd/144Nd values us‐ centrated HF and 1 ml 15 M HNO3 at 140°C for ing appropriate age estimates (Tab. 1) and sam‐ seven days, followed by sample drying on a hot ple compositions (Chapter 5). Strontium isotopic plate, re‐dissolution in 3 ml 15 M HNO3 at 140°C ratios were not age‐corrected because of signifi‐ for three days, and a final drying step on a hot cant alteration‐induced modifications of whole plate. Strontium and Nd separation was carried rock Rb contents rendering Rb‐based 87Sr/86Sr out using cascade columns with Sr‐spec, TRU‐ corrections to hypothetic initial values geologi‐ spec and Ln‐spec resins following a modified cally meaningless. Most samples are character‐ method after Pin et al. (1994). Lead was further ized by Rb/Sr ratios of 0.1 or below, and age purified with an AG‐MP1‐ M anion exchange resin in hydrobromic medium.

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Table 1: Whole rock 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb com- positions of investigated magmatic centers in Ecuador

87 143 206 207 208 Sample Magmatic center Sr Nd εNd εNdin Pb Pb Pb age age 86Sr 144Nd 204Pb 204Pb 204Pb [Ma] ref.* Neogene intrusions E06209 Apuela (Junin) 0.70365 0.51298 6.7 6.8 18.769 15.595 38.442 15 1 E06200 Apuela (Cuellaje) 0.70374 0.51295 6.0 6.1 18.754 15.565 38.394 13 2 E06202 Apuela (Cuellaje) 0.70379 0.51296 6.3 6.4 18.875 15.594 38.548 13 2 E05127 Junin 0.70376 0.51297 6.4 6.5 18.853 15.602 38.533 9 2 E06211 Junin 0.70378 0.51295 6.1 6.2 18.856 15.583 38.474 9 2 E07032 Junin 0.70377 0.51296 6.3 6.4 18.876 15.601 38.537 9 2 E06127 Balsapamba 0.70366 0.51293 5.6 5.8 18.863 15.592 38.510 22 2 E06136 Balsapamba 0.70368 0.51297 6.5 6.7 18.793 15.603 38.502 22 2 E06131a Balsapamba 0.70369 0.51296 6.3 6.5 18.692 15.583 38.358 21 2 E06132 Balsapamba 0.70369 0.51297 6.5 6.7 18.719 15.619 38.457 21 2 E06135 Balsapamba 0.70370 0.51294 6.0 6.1 18.716 15.587 38.361 21 2 E06138 Balsapamba 0.70371 0.51294 6.0 6.1 18.710 15.589 38.396 21 2 E07045 Telimbela 0.70366 0.51297 6.5 6.7 18.879 15.611 38.572 26 2 E06150 Telimbela 0.70371 0.51299 6.8 6.9 18.823 15.617 38.553 21 3 E06153 Telimbela 0.70372 0.51297 6.5 6.7 18.800 15.604 38.500 16 4 E05070 Gaby 0.70422 0.51290 5.1 5.2 18.900 15.587 38.570 20 2 E05078 Gaby 0.70421 0.51289 5.0 5.1 18.760 15.607 38.461 20 2 E05083b Gaby 0.70416 0.51292 5.5 5.7 18.679 15.598 38.436 20 2 E05088 Gaby 0.70440 0.51286 4.4 4.5 18.848 15.603 38.564 20 2 E05090 Gaby/Papa 0.70427 0.51288 4.7 4.9 19.043 15.634 38.706 20 2 Grande E06049 Gaby 0.70420 0.51287 4.5 4.7 18.972 15.642 38.731 20 5 E06052 Gaby 0.70427 0.51289 5.0 5.0 18.889 15.600 38.578 20 5 E07002 Chaucha: Naran- 0.70441 0.51270 1.2 1.3 19.017 15.648 38.781 10 2 jos E07005 Chaucha: Tunas 0.70445 0.51269 1.0 1.1 19.032 15.636 38.761 10 2 E07001 Chaucha: Naran- 0.70430 0.51275 2.2 2.3 18.968 15.617 38.667 15 5 jos E07003 Chaucha: Tunas 0.70430 0.51276 2.4 2.5 19.054 15.677 38.885 15 2 E07008 Chaucha: Tunas 0.70434 0.51274 2.0 2.1 19.012 15.630 38.724 15 2 E06158 Chaucha: Gur-Gur 0.70464 n/a n/a n/a 19.012 15.642 38.764 15 5 E06071 Cangrejos 0.70646 0.51253 -2.2 -2.0 19.067 15.682 38.974 26 2 E05-M4 Cangrejos 0.70546 0.51265 0.2 0.4 19.033 15.660 38.894 26 2 E06069 Cangrejos 0.70541 0.51255 -1.7 -1.5 18.923 15.631 38.745 23 6 E06070 Cangrejos 0.70560 0.51253 -2.1 -1.8 19.055 15.646 38.889 23 6 E06090 Portovelo 0.70549 0.51261 -0.6 -0.4 18.955 15.661 38.823 24 5 E06112 Portovelo 0.70567 0.51263 -0.3 0.0 19.040 15.666 38.922 24 2 E06115 Portovelo 0.70588 0.51266 0.4 0.5 18.988 15.665 38.847 21 5 E06123 Portovelo 0.70474 0.51271 1.4 1.5 18.888 15.643 38.716 21 5 E07023 Zaruma 0.70482 0.51269 1.1 1.2 18.991 15.639 38.791 21 2 E07016 El Mozo 0.70478 0.51267 0.6 0.7 18.949 15.629 38.730 16 2 E07017 El Mozo 0.70488 0.51266 0.4 0.5 18.972 15.669 38.858 16 2 E07020 El Mozo 0.70461 0.51269 1.0 1.1 18.934 15.634 38.735 16 2

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Table 1 (continued) 87 143 206 207 208 Sample Magmatic center Sr Nd εNd εNdin Pb Pb Pb age age 86Sr 144Nd 204Pb 204Pb 204Pb [Ma] ref.* Neogene volcanics E05102 Quimsacocha 0.70455 0.51269 1.0 1.1 18.990 15.642 38.761 7 2 E06020 Quimsacocha 0.70457 0.51270 1.1 1.2 18.999 15.650 38.783 7 2 E05099 Quimsacocha 0.70440 0.51272 1.6 1.7 18.960 15.649 38.744 7 5 E06022 Quimsacocha 0.70430 0.51272 1.6 1.7 18.917 15.582 38.630 7 5 E06157 Saraguro at 0.70476 0.51275 2.1 2.2 n/a n/a n/a 25 7 Chaucha E06166 Saraguro at 0.70707 0.51266 0.4 0.5 19.173 15.690 39.026 25 7 Chaucha E06010 Saraguro at Cani- 0.70443 0.51274 1.9 2.2 n/a n/a n/a 20 7 capa E06012 Saraguro at Cani- 0.70440 n/a n/a n/a 18.975 15.665 38.837 20 7 capa E06082 Saraguro at Por- 0.70534 0.51261 -0.5 -0.4 18.990 15.667 38.871 25 7 tovelo E07013 Tres Chorreras 0.70477 0.51274 2.1 2.3 19.038 15.664 38.858 31 2 Late Cretaceous intrusions E07029 Curiplaya 0.70412 0.51279 2.9 3.6 18.848 15.665 38.744 92 2 E07027 Curiplaya 0.70450 0.51282 3.5 4.3 18.962 15.622 38.781 92 2 E07031 Curiplaya 0.70419 0.51287 4.5 5.1 18.890 15.640 38.680 92 2 E07028 Curiplaya 0.70420 0.51277 2.6 3.4 18.996 15.643 38.833 92 2 Host rocks E05123 Macuchi (?) at 0.70371 0.51298 6.6 6.8 18.550 15.593 38.243 40 5 Junin E06148 Macuchi at Balsa- 0.70402 0.51301 7.2 7.4 n/a n/a n/a 40 5 pamba E06145 Macuchi at Balsa- 0.70535 0.51301 7.2 7.4 n/a n/a n/a 40 5 pamba E06035 CCOP basalt 0.70367 0.51301 7.3 7.5 19.012 15.631 38.768 90 5 *Age references: 1 - MMAJ/JICA 1992; 2 - this study (Chapter 2); 3 - McCourt et al. 1997; 4 - MMAJ/JICA 1991; 5 - estimated from field relationships and regional geology; 6 - this study (Chapter 3); 7 - Hungerbühler et al. (2002) corrections using measured, alteration‐ 206Pb/204Pb < 19.14, 207Pb/204Pb < 15.64; group 3: 87 86 206 204 influenced Rb contents typically affect the εNdinitial > ‐2, Sr/ Sr < 0.7049, Pb/ Pb < 87Sr/86Sr ratio by ±0.0001 or less; this magnitude 19.08, 207Pb/204Pb < 15.70), following a systematic is below the uncertainty range relevant to the across‐arc distribution trend in northern Ecuador discussion in this article, and no significant bias of (Figs. 1, 2; Appendix Tab. A1). The range of iso‐ our interpretations based on differences be‐ topic compositions defined by multiple volcanoes tween measured and initial 87Sr/86Sr ratios is ex‐ in a given group is homogeneous for about 100 pected. km strike length, corresponding to the whole arc segment for which isotopic data is available. Results The least radiogenic Sr‐Pb and most radiogenic Compiled Sr, Nd, and Pb isotopic data allow the Nd compositions common to all three groups cor‐ distinction of three groups of Quaternary volca‐ respond to the isotopic composition of the petro‐ 87 86 logically most primitive samples identified by noes (group 1: εNdinitial = 4‐6, Sr/ Sr = 0.7038‐ 0.7044, 206Pb/204Pb < 19.03, 207Pb/204Pb < 15.60; Chiaradia (2009) and Chiaradia et al. (2009) based 87 86 on isotope and whole rock chemical correlations, group 2: εNdinitial = 3‐6, Sr/ Sr = 0.7040‐0.7043,

103

87 86 207 204 206 204 Figure 2: Diagrams of εNdinitial vs. Sr/ Sr (plus magnified area), Pb/ Pb vs. Pb/ Pb (plus magnified 87 86 206 204 206 204 208 204 206 204 area), Sr/ Sr vs. Pb/ Pb, εNdinitial vs. Pb/ Pb, and Pb/ Pb vs. Pb/ Pb isotopic compositions of Late Tertiary (except for Curiplaya) samples analyzed in this study, and isotopic fields for potential crustal assimilants and NVZ magmas. Orange X marks the isotopic composition of the most primitive melts identi‐ fied by Chiaradia (2009) and Chiaradia et al. (2009), and serves as a proxy for parental melt isotopic compo‐ sitions of Late Tertiary‐Quaternary arc magmas derived from an isotopically broadly homogeneous mantle wedge. Individual Quaternary arc volcanoes (see Fig. 1 for references) span a relatively narrow field in Sr isotopes, and show increased isotopic diversity in Nd and Pb isotopes reflecting an oceanic plateau compo‐ nent as main assimilant for volcanic edifices situated west of the Peltetec fault.

104 suggesting that all magmas originated in an iso‐ tion, their very limited isotopic variability is con‐ topically homogeneous mantle wedge. The iso‐ sistent with assimilation of older (Macuchi?) arc topic arrays defining the three groups are charac‐ intrusive roots with a similar isotopic composition terized by variable increases in radiogenic Sr and (Dungan & Davidson 2004). Unlike Rio Cala melts Pb, and non‐radiogenic Nd components from mi‐ (Chiaradia 2009), granitoid parental melts did not nor (frontal arc, close to the CPPF) to slightly interact with seawater‐altered CCOP lithologies higher (main arc, west of the PF), and significant characterized by high radiogenic Sr values. Fur‐ (rear main arc, east of the PF); 143Nd/144Nd and ther south, the CCOP basalt‐hosted Gaby intru‐ 207Pb/204Pb are the most powerful isotopic dis‐ sive center shows slightly more radiogenic Sr and criminators between the three groups. These iso‐ Pb, and less radiogenic Nd isotopic compositions topic distribution characteristics suggest that than Western Cordillera granitoids to the north, mantle‐derived arc magmas acquire their distinct and overlaps completely with isotopic composi‐ isotopic signatures either by variable degrees of tions of NVZ frontal arc volcanoes. assimilation (or mixing with partial melts) of a Late Tertiary intrusions and volcanic rocks of the crustal component with constant isotopic com‐ southern Ecuadorian Sierra are characterized by position, by assimilation (or mixing with partial variably higher radiogenic Sr and Pb, and lower melts) of crust of different isotopic composition, radiogenic Nd isotopic compositions than West‐ or a combination of both. While Quaternary vol‐ ern Cordillera granitoids. They partly overlap with canoes situated to the west of the PF completely the isotopic compositions of the Cretaceous Tan‐ overlap with the range of isotopic compositions gula batholith and a number of minor Paleogene of the Macuchi Unit (Eocene island‐arc; Fig. 2), intrusions in southern Ecuador, as well as with volcanoes east of the fault are characterized by rear main arc NVZ magmas east of the PF (group significantly more continental crust‐like Sr‐Nd‐Pb 3 above); they consistently plot between poten‐ isotopic compositions. tial assimilant end‐member isotopic compositions Tertiary samples measured in this study (Tab. 1) (CCOP and Eastern Cordillera or Amotape base‐ define homogenous groups in uranogenic and ment; Fig. 2). Several granitoids and volcanics in thorogenic Pb isotope and combined Sr‐Nd‐Pb southern Ecuador completely overlap isotopically isotope plots for given intrusive suites (Fig. 2). with the isotopic compositions of main arc volca‐ Late Tertiary granitoids of the Western Cordillera noes west of the PF in northern Ecuador. This foothills (Apuela‐Junin, Balsapamba‐Telimbela) includes the Mid‐to Late Miocene Chaucha ba‐ are significantly less radiogenic in Sr and Pb, and tholith, Mid‐Miocene Saraguro Group volcanics at more radiogenic in Nd isotopic compositions than Cañicapa, and the Late Miocene Quimsacocha the most primitive Quaternary NVZ samples volcanic center. The El Mozo intrusions, situated 87 86 206 204 (εNdinitial > 5, Sr/ Sr < 0.7038, Pb/ Pb < 18.9, at the limit between the Loja and Alao terranes of 207Pb/204Pb < 15.62); they isotopically overlap Litherland et al. (1994), and Saraguro Group vol‐ with the most primitive Macuchi and Rio Cala canics at Tres Chorreras overlap with this group units (their immediate host rocks), and parts of in Nd and Pb isotopic compositions, but are char‐ the CCOP (the regional basement unit at depth; acterized by a slightly more radiogenic Sr compo‐ Fig. 2). Given the low thickness of the Macuchi sition, although they are still more primitive than Unit (<2.5 km; Kerr et al. 2005) granitoid parental the bulk Earth (Fig. 2). A significant contribution melts likely assimilated primitive CCOP material of Loja (highly radiogenic Sr and Pb) or Alao while they were differentiating at depth. In addi‐

Figure 2 (caption continued from previous page): Quaternary volcanoes define distinct isotopic groups as defined in Fig. 1; Late Tertiary intrusions and volcanics of the southern Ecuadorian Sierra region partly overlap with these com‐ positional groups suggesting assimilation of similar basement units. Isotopic reference fields as follows: CCOP (Mam‐ berti et al. 2003; only Western Cordillera outcrops considered); Rio Cala and Macuchi (Chiaradia 2009); Raspas Com‐ plex (Bosch et al. 2002); Western Cordillera shallow basement (mica schist of Amortegui 2007; single Pichincha xeno‐ lith of Chiaradia et al. 2009); Western Cordillera amphibolites/granulites (amphibolites of Amortegui 2007; Pichincha granulite xenoliths of Chiaradia et; al. 2009) Amotape, Loja, Alao (Pb; Chiaradia et al. 2004a); Alao, Loja, Cretaceous‐ Paleogene intrusions (Sr, Pb; Chiaradia et al. 2004b). Error bars for Pb isotopes (± 2σ) shown in lower right corner; Sr and Nd isotope error bars are below symbol size.

105 (highly radiogenic Pb) basement units is thus homogeneous at this time scale. The latter seems unlikely for parental melts of the El Mozo intru‐ a plausible assumption if related discussions in sions. Rather, along with other southern Sierra the Central Andes are taken into account. Sub‐ intrusions and volcanics, they define an isotopi‐ duction erosion is proposed to have influenced cally homogeneous group suggesting that their the Sr, Nd, and Pb isotopic composition of the parental melts evolved by assimilation processes Central Andean mantle wedge implying a chang‐ of similar crustal basement units. ing source composition through time (Stern & Skewes 2005). However, these isotopic changes The regional distribution of IAD and southern Si‐ in source composition are shown to be mostly erra basement units is relatively, but not com‐ negligible compared to crustal contamination pletely isotopically homogenous, as evidenced by effects, such that the isotopic composition of the a Saraguro Group tuff collected in the Chaucha mantle wedge can be assumed as broadly con‐ area, which shows the most radiogenic Sr and Pb stant during Tertiary‐Quaternary times (Mamani isotopic compositions of the whole dataset. The et al. 2010). latter notion is in agreement with the surface exposure of several metamorphic inliers around While the Ecuadorian margin has been partly Chaucha which might represent Amotape (El Oro) erosive since the Late Miocene collision with the basement fragments (Litherland et al. 1994; Pratt Carnegie Ridge seamount chain (e.g., Sage et al. et al. 1997) implying that a definite northern 2006), the relative stability of the Ecuadorian arc Amotape basement border cannot be accurately position during the Tertiary excludes significant drawn and rather corresponds to a northwards‐ earlier subduction erosion (Chapter 2). Poten‐ extending tectonized zone (Spikings et al. 2005). tially contaminating effects of subduction erosion on the Sr, Nd, and Pb isotopic composition of the Further south, plutons of the Cangrejos‐Zaruma mantle wedge are thus expected to be of a much intrusive belt compositionally extend towards lower magnitude than in parts of the Central An‐ significantly more radiogenic Sr and Pb, and less des (Stern & Skewes 2005). This is confirmed by radiogenic Nd values (εNd <1, 87Sr/86Sr initial studies of Eocene Macuchi arc magmatism >0.7047, 206Pb/204Pb >18.9, 207Pb/204Pb >15.62) (Chiaradia 2009) and Quaternary arc volcanoes suggesting they assimilated continental crust‐ (e.g., Chiaradia et al. 2009) which show that the dominated basement lithologies in the range of mantle wedge below Ecuador represents an iso‐ the El Oro massif south of the Jubones fault. The topically broadly homogeneous reservoir, slightly Late Cretaceous Curiplaya intrusive center, enriched by a sedimentary component, and has hosted by the Celica‐Lancones basin in south‐ not changed systematically in its isotopic compo‐ ernmost Ecuador, compositionally overlaps with sition throughout the Tertiary. Latitudinal mantle the CCOP‐hosted Gaby intrusions in 87Sr/86Sr and wedge Pb isotopic heterogeneity along the South 143Nd/144Nd, but plots at higher radiogenic Pb iso‐ American margin only applies at a larger scale, topic ratios. and Tertiary Ecuadorian arc magmas define a sin‐ gle regression line in uranogenic and thorogenic Discussion Pb diagrams (Chiaradia & Fontboté 2002). This notion is supported by overlapping isotopic Isotopic compositional changes in the ranges for specific groups of NVZ volcanoes in Ecuadorian mantle wedge along‐ northern Ecuador and Late Tertiary granitoids in strike, and from the Late Tertiary to southern and central Ecuador as described above (Fig. 2). the present day We therefore argue that similarities or differ‐ Differences or similarities in the isotopic compo‐ ences in the isotopic composition of Late Tertiary sition of Late Tertiary and Quaternary arc mag‐ arc magmas in the Western Cordillera and the mas in Ecuador can be attributed to the influence southern Ecuadorian Sierra, and Quaternary arc of crustal basement assimilation if the arc magma volcanoes in northern‐central Ecuador are mainly source, i.e., the mantle wedge, stayed isotopically

106 caused by assimilation of specific crustal base‐ low crustal assimilants may be of significantly ment lithologies, additionally influenced by vari‐ more radiogenic isotopic compositions than deep able crustal thickness. Second‐order modulations to mid‐crustal lithologies, and thus may leave a of isotopic ratios originating from variations in distinct isotopic fingerprint on arc magmas (Hil‐ source (mantle wedge) composition cannot be dreth & Moorbath 1988; Dungan & Davidson ruled out, but are not considered as significant at 2004). Consequently, discriminating between the the isotopic scale relevant for the following dis‐ upper and lower crustal contributions to whole‐ cussion. rock isotopic compositions of arc magmas is of major importance to delineate the deep through The role of crustal thickness on iso‐ shallow crustal basement architecture. topic compositions of Tertiary‐ Petrologic studies (e.g., Chiaradia et al. 2009) Quarter‐nary Ecuadorian arc magmas demonstrate that Quaternary NVZ magmas in northern Ecuador mostly evolved in the stability Assimilation of oceanic plateau units may drive fields of garnet and amphibole, and outside the Tertiary‐Quaternary arc magmas in Ecuador to‐ stability field of plagioclase, suggesting that these wards more primitive Sr and Nd isotopic compo‐ magmas dominantly acquired their crustal iso‐ sitions than their mantle wedge‐derived parental topic signatures through polybaric evolution at melts (Chiaradia 2009); assimilation of (partly) lower to mid‐crustal levels, although minor peri‐ continental Eastern Cordillera basement may ods of subsequent shallow crustal magma evolu‐ have the reverse effect, producing complex iso‐ tion do occur for some volcanic centers. Late Ter‐ topic patterns of crust‐magma interaction (Chia‐ tiary arc magmas evolved in an overall thinner radia et al. 2009). A thick crust maximizes the crust than present‐day arc magmas (Jaillard et al. likelihood of crustal contamination of arc mag‐ 2005) and form two distinct groups (Chapter 5): mas (e.g., Hildreth & Moorbath 1988; Annen et the dominant group comprises most granitoids of al. 2006). However, in a vertically heterogeneous the Western Cordillera (Apuela, Junin, Balsa‐ crustal column bulk crustal thickness does not pamba, Telimbela, Gaby, Chaucha), as well as directly scale with a specific contamination signal. volcanic formations (Saraguro Group at Cañicapa Rather, the relative thickness of crustal material and Tres Chorreras; Quimsacocha) in the south‐ of contrasting isotopic composition (here: oce‐ ern‐central Ecuadorian Sierra. REE patterns of anic plateau vs. Eastern Cordillera basement) and this group commonly lack negative Eu anomalies tectonomagmatic controls on the depth of crustal indicating that the parental magmas of these in‐ magma evolution in a given crustal column con‐ trusions and volcanics did not fractionate signifi‐ stitute the dominant control factors for the final cant amounts of plagioclase at shallow crustal isotopic composition of Tertiary‐Quaternary Ec‐ levels (e.g., at <0.4 GPa, corresponding to the uadorian arc magmas. maximum pressure where plagioclase precedes amphibole on the liquidus for water‐rich basaltic‐ At what crustal level did Late Tertiary andesitic melts; Grove et al. 2003). Rather, paren‐ and Quaternary arc magmas acquire tal melts to these intrusions and volcanics seem their isotopic characteristics? to have evolved at deep to mid‐crustal levels without major compositional overprinting by Bulk crustal contamination of evolving arc mag‐ shallow crustal magma evolution (Chapter 5). A mas by assimilation of crustal lithologies or mix‐ second group comprises some intrusions of the ing with crustal partial melts principally occurs in Cangrejos‐Zaruma intrusive belt, the bulk of the hot zones at lower to mid‐crustal levels; shallow Saraguro Group (here: at Portovelo and crustal magma evolution does not involve signifi‐ Chaucha), as well as some minor intrusions at El cant compositional modification of arc magmas Mozo. REE patterns of this group are usually by crustal contamination (or, more general, as‐ characterized by minor‐moderate negative Eu similation and fractional crystallization; AFC) anomalies suggesting that these intrusions and unless large, supra‐solidus magmatic systems volcanics derive from parental magmas which form which need to be sustained by high magma underwent significant plagioclase fractionation at supply rates (Annen et al. 2006). Potential shal‐

107 shallow crustal levels (Chapter 5). Late Tertiary does not directly scale with the absolute depth of arc magmas thus variably acquired their crustal magma evolution, as it can also be affected by isotopic signatures at deep, mid‐, and shallow pressure‐insensitive accessory phase fractiona‐ crustal levels. tion (Chapter 5). Figure 3 shows the Sr, Nd, and Pb isotopic compositions of NVZ volcanic centers Shallow vs. deep to mid‐crustal magma evolution and Late Tertiary samples as a function of Sr/Y can be qualitatively discriminated using the Sr/Y ratios, and Sr isotopic compositions as a function ratio (e.g., Bachmann et al. 2005); in our dataset, of SiO (SiO , Sr, and Y concentrations for Late Sr/Y ratios >30 indicate the absence of pro‐ 2 2 Tertiary samples from Chapter 5). Individual nounced shallow crustal magma evolution in Late groups of Quaternary arc volcanoes identified in Tertiary Ecuadorian arc magmas (Chapter 5). It is the previous section mostly define subparallel important to note, however, that the Sr/Y ratio

87 86 206 204 207 204 87 86 Figure 3: Diagrams of Sr/ Sr, εNdinitial, Pb/ Pb, and Pb/ Pb vs. Sr/Y, and Sr/ Sr vs. SiO2. The Sr/Y ratio serves as a proxy for shallow crustal vs. mid‐ to deep crustal (>30) magma evolution. Arc magmas color‐coded ac‐ cording to the isotopic classification scheme of Figs. 1 and 2, except for southern Ecuadorian Sierra units which are uniformly shown in black. The various groups define broad subparallel isotopic arrays at Sr/Y >30 suggesting that specific groups of arc magmas undergo AFC (assimilation and fractional crystallization) ± mixing processes at deep to mid‐crustal levels involving variable proportions of different basement units. In addition, Late Tertiary arc magmas of the Cangrejos‐Zaruma intrusive belt undergo significant shallow crustal AFC processes and assimilate crustal ma‐ terial characterized by more radiogenic Sr and less radiogenic Nd isotopic compositions than deep to mid‐crustal 87 86 basement units. Distinct crustal AFC trends exist in a Sr/ Sr vs. SiO2 plot, in agreement with the notions above. Sr/Y and SiO2 data from Chapter 5 (Tertiary magmas), and references given in Fig. 1 (NVZ). See text for discussion.

108 isotopic arrays for Sr/Y ratios >30 (the distinction Tectonic implications of Sr‐Nd‐Pb iso‐ between groups 1 and 2 is somewhat ambiguous: 87 86 topic systematics in Late Tertiary and while mostly overlapping in Sr/ Sr and εNdinitial, they systematically differ in 207Pb/204Pb vs. Sr/Y Quaternary arc magmas plots, but the latter difference is close to the ana‐ The isotopic similarities between Quaternary lytical resolution). Parental melts to these arc northern Ecuadorian volcanic centers east of the volcanics thus variably assimilated deep to mid‐ PF and Late Tertiary southern Ecuadorian intru‐ crustal basement lithologies of distinct isotopic sions and volcanics at Sr/Y >30 (Figs. 1‐3) suggest compositions. Magma differentiation by assimila‐ that the isotopic compositions of lower to mid‐ tion of different crustal lithologies is further crustal IAD basement units north and east of the 87 86 demonstrated by an Sr/ Sr vs. SiO2 plot show‐ Jubones fault (Fig. 1) are broadly homogeneous ing distinct crustal AFC trends for various isotopic in along‐arc dimension. In contrast, isotopic data groups (Fig. 3). for the Cangrejos‐Zaruma intrusive belt record As noted above, Quaternary arc volcanoes merge both shallow and deep to mid‐crustal assimilation at a common isotopic composition (Fig. 2) corre‐ of continental crust‐dominated basement litholo‐ sponding to the most primitive magma composi‐ gies (high radiogenic Sr and low radiogenic Nd); tions. This is not directly visible from Figure 3 be‐ the latter data support the notion that the north‐ cause the Sr/Y ratio of mantle‐derived primitive ern limit of deep crustal basement units of the El melts may show a higher variability both across Oro micro‐continental block is bracketed be‐ and along the arc, e.g., due to variable amounts tween the Piñas‐Portovelo and Jubones faults as of mantle wedge fluxing by slab‐derived fluids, significantly more primitive isotopic compositions and different degrees of partial melting (Chiara‐ occur only north of the Jubones fault. dia et al. 2009). Isotopic compositions show a systematic across‐ Western Cordillera granitoids define a further arc distribution in northern Ecuador. In the frame isotopic subgroup at Sr/Y ratios >30;d as note of a basement architecture characterized by jux‐ above, these magmas acquire their crustal iso‐ taposed oceanic and continental basement do‐ topic signatures by assimilation of primitive CCOP mains (as applicable for Ecuador; e.g., Jaillard et units at depth. Late Tertiary intrusions and vol‐ al. 2005) of strongly contrasting isotopic compo‐ canics of southern Ecuador overlap with the iso‐ sitions (compare reference fields in Fig. 2), more topic range defined by arc volcanoes east of the radiogenic Sr and less radiogenic Nd isotopic PF (group 3) at Sr/Y ratios >30, but show more compositions of arc magmas are mainly indicative radiogenic Sr and less radiogenic Nd ratios at Sr/Y of increasing continental signatures imposed on <30 (Fig. 3). Consequently, we infer that the iso‐ evolving magmas by a higher proportion of conti‐ topic characteristics of Late Tertiary magmas in nental versus oceanic basement assimilation in a southern Ecuador partly reflect deep to mid‐ given crustal column. The role of Pb isotopes is crustal assimilation of basement units similar to more difficult to define as oceanic plateau mate‐ rial in Ecuador is characterized by a wide range in arc volcanoes east of the PF in northern Ecuador, 206 204 but they may additionally acquire distinct isotopic Pb/ Pb (Fig. 2) such that the latter isotopic signatures by further shallow crustal magma evo‐ ratio cannot discriminate oceanic vs. continental material on a regional scale; more radiogenic lution. Note that the isotopic composition of the 207 204 El Mozo intrusions is rather primitive (Fig. 2) sug‐ Pb/ Pb compositions, on the other hand, are gesting that, despite showing minor negative Eu indicative of a stronger continental basement anomalies, isotopic contamination of El Mozo signature, but isotopic variations are of such a parental magmas by upper crust material was small scale that they approach the analytical limited such that their lower to mid‐crustal iso‐ resolution limit (Fig. 2). topic signatures were preserved. Figure 4 illustrates a schematic cross section of the Ecuadorian arc at c. 0.5°S based on seismic studies (Guillier et al. 2001; Jaillard et al. 2005). Eastward underthrusting of high‐density oceanic plateau material below the IAD results in east‐

109 ward thickening of the proportion of Eastern diogenic Nd isotopic compositions overlapping Cordillera basement (simplified here as a single with basement units cropping out in the Western unit) relative to oceanic plateau material in a Cordillera (amphibolites of Amortegui 2007; Fig. given crustal column. Consequently, the potential 2). A single Pichincha xenolith detected by role of Cordillera Real basement as an assimilant Chiaradia et al. (2009) has an isotopic composi‐ for NVZ magmas evolving in lower to mid‐crustal tion resembling shallow crustal metapelites of hot zones progressively increases eastwards. This the Western Cordillera (“Western Cordillera shal‐ regional underthrusting of oceanic plateau mate‐ low basement” in Fig. 2; Amortegui 2007). Incor‐ rial below the IAD is mirrored by across‐arc poration of this type of xenolith into Pichincha trends in Sr, Nd, and Pb isotopic compositions of melts might thus have occurred at shallow crustal NVZ arc volcanoes which get progressively more levels. Alternatively, if this xenolith type repre‐ continental in character towards the east (Figs. 1, sents a deep to mid‐crustal lithology, its occur‐ 4). Initial magma differentiation in a hot zone at rence might be reconciled with the generalized the base of the crust (or in the uppermost litho‐ model presented in Figure 4 if non‐vertical spheric mantle) would mostly include oceanic magma ascent along transcrustal fault systems plateau material, whereas subsequent mid‐ such as the CPPF is taken into account. Structur‐ crustal magma processing should progressively ally controlled melt ascent including significant involve increasing amounts of Eastern Cordillera non‐vertical components has been documented basement units. In contrast, parental magmas to elsewhere, e.g., by pluton emplacement along Western Cordillera granitoids were entirely con‐ fault ramps in the Sevier fold‐and‐thrust belt (Ka‐ fined to oceanic plateau material (or arc intrusive lakay et al. 2001). root zones) during their crustal transit such that High‐resolution seismic data imaging crustal arc magmas evolve towards less radiogenic Sr structures are not available in southern Ecuador, and more radiogenic Nd isotopic compositions but a fundamental change in basement architec‐ (compare Fig. 2). Tertiary and NVZ isotopic com‐ ture is implied by a major change in structural positions in northern Ecuador, therefore, are trends from N‐S (central‐northern Ecuador) to E‐ consistent with the crustal structure inferred W (El Oro massif south of the Jubones fault in from seismic studies involving regional under‐ southern Ecuador; Fig. 1), and is further clearly thrusting of oceanic plateau material below the visible in the isotopic compositions of granitoids paleo‐continental margin (Guillier et al. 2001). of the Cangrejos‐Zaruma intrusive belt (see In addition to considering the differing isotopic above). In this area, the western surface trace of characteristics of main arc volcanoes east and the oceanic plateau‐bounding suture zone (the west of the Peltetec fault zone purely as a func‐ CPPF) splays off and intersects the Western Cor‐ tion of a transitional change of deep to mid‐ dillera towards the Gulf of Guayaquil. Instead of crustal, continental versus oceanic basement displaying a transition in isotopic compositions eunits, th presence of different continental (Li‐ across the arc as in northern Ecuador, there therland et al. 1994) or oceanic terrane units seems to be a rather sharp change in Sr, Nd, and (such as a second, pre‐Late Cretaceous oceanic Pb isotopic compositions from the west (Gaby plateau fragment; e.g., Mamberti et al. 2003) intrusions) to the east (Quimsacocha volcano, might further influence the isotopic signature of Chaucha intrusions, Saraguro volcanics) of the arc magmas produced at these volcanoes, al‐ CPPF. This might suggest that, concomitant with though the geometry of their deep to mid‐crustal its change in strike direction, the mid‐ to deep extensions cannot be predicted with the current crustal structure of the suture zone possibly dataset. changes from 35° E‐dipping in northern‐central Ecuador towards a more subvertical orientation Ecuadorian frontal arc volcanoes such as Pichin‐ in southern Ecuador. An alternative interpreta‐ cha are characterized by the presence of crustal tion of the relatively sharp isotopic contrast xenoliths whose high‐grade (granulite) metamor‐ across the CPPF inn souther Ecuador might be the phic character implies a mid‐ to lower crustal ori‐ absence of an additional terrane unit equivalent gin (Chiaradia et al. 2009). Most xenoliths are characterized by low radiogenic Sr and high ra‐

110 to the NVZ basement west of the Peltetec fault zone as discussed above. Based on gravimetric data, Feininger & Seguin (1983) modeled crustal thickness profiles in Ec‐ uador using a strictly vertical dip for the CPPF (their “Romeral” fault), and confined oceanic pla‐ teau material to the west of the CPPF. Conse‐ quently, these authors identified the absence of the IAD in southern Ecuador (with its low‐density volcaniclastic infill) as a major influence on the gravimetric anomaly pattern, and suggested that the crustal thickness in southern Ecuador might exceed the thickness in northern Ecuador. When taking into account a more realistic 35° E dip of the CPPF in northern Ecuador implying regional underthrusting of high‐density oceanic plateau material, highly negative gravity anomalies (down to ‐292 mgal) in the Andean region east of the CPPF might necessitate an even thicker crustal root in northern Ecuador, making it unlikely that the crustal thickness of southern Ecuador gener‐ ally exceeds northern Ecuador (50‐70 km; Guillier et al. 2001). Rather, the crustal thickness of the main Andean root in southern Ecuador might be similar to or slightly thinner than in northern Ec‐ uador, in agreement with data from northern Peru where a maximum crustal thickness of 45 km below the Western Cordillera is inferred (Fu‐ kao et al. 1989).

Figure 4: Schematic crustal cross section of northern 87 86 206 204 Ecuador, and Sr/ Sr, εNdinitial, Pb/ Pb, and 207Pb/204Pb across‐arc distribution trends for NVZ vol‐ canoes, the Apuela batholith and the Junin porphyry intrusions between 1°S to 0.5°N, orthogonally pro‐ jected onto the cross section shown in Fig. 1; same symbol key as in Fig. 3. Crustal section simplified and modified from Jaillard et al. (2005) sketching under‐ thrusting of oceanic plateau units (v pattern) below the paleo‐continental margin (gray). For simplicity, Eastern Cordillera basement is visualized here as a single unit, but in detail consists of multiple meta‐sedimentary and meta‐igneous units possibly representing different ter‐ ranes of both oceanic and continental affinity (Litherland et al. 1994). Orange bars indicate deep to mid‐crustal hot zones where major magma evolution occurs (Fig. 3; Annen et al. 2006), progressively including a higher component of Eastern Cordillera basement towards the east, and most clearly reflected by decreasing εNdinitial, and increasing 207Pb/204Pb across the arc. Note that transcrustal magma ascent might partly be focused along non‐vertical struc‐ tures such as the Chimbo‐Toachi shear zone (CTSZ) and the Calacali‐Pujili‐Pallatanga fault (CPPF), and, possibly, the Peltetec fault (PF), allowing incorporation of crustal xenoliths of continental crust affinity into frontal arc (Pichin‐ cha) magmas. Section not vertically exaggerated.

111 Conclusions Granitoids of the Cangrejos‐Zaruma intrusive belt in southern Ecuador are characterized by highly Late Tertiary‐Quaternary arc magmas in Ecuador radiogenic Sr and Pb, and low radiogenic Nd iso‐ derive from an isotopically broadly homogeneous topic compositions, which have no equivalent in mantle wedge, and acquire variable deep, mid‐, central‐northern Ecuadorian arc magmas. Their and shallow crustal Sr, Nd, and Pb isotopic signa‐ isotopic compositions relate to the mostly shal‐ tures during subsequent magma evolution low crustal assimilation of basement units form‐ stages. These isotopic imprints provide insights ing part of the El Oro block of continental crust into the crustal basement architecture of Ecua‐ affinity, whose concealed northern limit seems to dor’s Western Cordillera, the IAD, and the south‐ be bracketed between the Piñas‐Portovelo and ern Ecuadorian Sierra region. Jubones faults. The Ecuadorian crust in the investigated areas seems to be vertically heterogeneous where the References relative thickness of crustal material of contrast‐ Amortegui, A. E. (2007): Nature et évolution méta‐ ing isotopic composition (oceanic plateau vs. morphique des terrains océaniques en Equateur; Eastern Cordillera basement) and tectonomag‐ conséquences possibles sur la genèse des magmas matic controls on the depth of crustal magma adakitiques. PhD thesis, Université Joseph Fourier; 194 evolution in a given crustal column constitute the p. dominant control factors for the isotopic compo‐ Annen, C., Blundy, J. D., Sparks, R. S. J. (2006): The sition of Ecuadorian arc magmatic products. genesis of intermediate and silicic magmas in deep Eastern Cordillera basement) and tectonomag‐ crustal hot zones. Journal of Petrology 47; 505‐539. matic controls on the depth of crustal magma Barragan, R., Geist, D., Hall, M., Larson, P., Kurz, M. evolution in a given crustal column constitute the (1998): Subduction controls on the compositions of dominant control factors for the isotopic compo‐ lavas from the Ecuadorian Andes. Earth and Planetary sition of Ecuadorian arc magmatic products. Science Letters 154; 153‐166. Crustal imprints on arc magmas are mostly rela‐ tively primitive in Sr and Nd, and highly variable Bosch, D., Gabriele, P., Lapierre, H., Malfere, JL, Jail‐ lard, E. (2002): Geodynamic significance ofe th Raspas in Pb, and define a regionally systematic distribu‐ etamorphic Complex (SW Ecuador): geochemical and tion pattern, consistent with the notion of large‐ isotopic constraints. Tectonophysics 345; 83‐102. scale underthrusting of allochthonous oceanic plateau material below the paleo‐continental Bourdon, E., Eissen, J.‐P., Monzier, M., Robin, C., Mar‐ margin of northern‐central Ecuador as inferred tin, H., Cotton, J., Hall, M. L. (2002): Adakite‐like lavas from Antisana Volcano (Ecuador): evidence for slab from seismic studies (Guillier et al. 2001). With melt metasomatism beneath the Andean Northern increasing distance from the trench, Late Terti‐ Volcanic Zone. Journal of Petrology 43; 199‐217. ary‐Quaternary arc magmas evolve towards pro‐ gressively more radiogenic 87Sr/86Sr and Bourdon, E., Eissen, J.‐P., Gutscher, M.‐A., Monzier, 207Pb/204Pb, and less radiogenic 143Nd/144Nd com‐ M., Hall, M. L., Cotton, J. (2003): Magmatic response to early aseismic ridge subduction: the Ecuadorian positions at deep to mid‐crustal levels. margin case (South America). Earth and Planetary Sci‐ Late Tertiary arc magmas of the southern Ecua‐ ence Letters 205; 123‐138. dorian Sierra east of the CPPF overlap with iso‐ Bryant, J. A., Yogodzinski, G. M., ,Hall, M. L. Lewicki, J. topic compositions of Quaternary arc volcanoes L., Bailey, D. G. (2006): Geochemical constraints on the east of the PF in northern Ecuador suggesting origin of volcanic rocks from the Andean Northern along‐strike continuity of similar deep to mid‐ Volcanic Zone, Ecuador. Journal of Petrology 47; 1147‐ crustal basement units. Similarly, frontal arc vol‐ 1175. canoes in northern Ecuador isotopically overlap Chiaradia, M. (2009): Adakite‐like magmas from frac‐ with the composition of the Gaby intrusive center tional crystallization and melting‐assimilation of mafic in southern Ecuador west of the Bulubulu fault lower crust (Eocene Macuchi arc, Western Cordillera, system (an eastern splay fault of the CPPF). Ecuador). Chemical Geology 265; 468‐487. Chiaradia, M. & Fontboté, L. (2002): Lead isotope sys‐ tematics of Late Cretaceous – Tertiary Andean arc

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114 Appendix: Data tables

Table A1: Whole rock 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions of North‐ ern Volcanic Zone volcanoes

115

Table A1: Whole rock 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb compositions of Northern Volcanic Zone volcanoes Sample Magmatic 87Sr 143Nd εNd 206Pb 207Pb 208Pb latitude ref* center 86Sr 144Nd 204Pb 204Pb 204Pb (projected)

Frontal arc E05001 Pululagua 0.70420 0.51286 4.4 18.889 15.587 38.552 78.60 1 E05003 Pululagua 0.70416 0.51289 4.8 18.868 15.596 38.565 78.60 1 E05007 Pululagua 0.70417 0.51290 5.0 18.906 15.604 38.619 78.60 1 E05008 Pululagua 0.70415 0.51293 5.7 18.912 15.587 38.566 78.60 1 E05042 Pululagua 0.70412 0.51291 5.4 18.933 15.609 38.645 78.60 1 Pul-9 Pululagua 0.70412 0.51291 5.4 18.934 15.605 38.610 78.60 2 Pul-11 Pululagua 0.70414 0.51292 5.5 18.893 15.606 38.562 78.60 2 Pul-4 Pululagua 0.70414 0.51295 6.2 18.921 15.595 38.572 78.60 2 Pul-7 Pululagua 0.70414 0.51289 5.1 18.921 15.596 38.572 78.60 2 E05016 Pichincha 0.70408 0.51287 4.6 18.957 15.575 38.690 78.60 1 E05017 Pichincha 0.70399 0.51286 4.4 19.018 15.589 38.728 78.60 1 E05018 Pichincha 0.70410 0.51287 4.5 18.884 15.596 38.578 78.60 1 E05130 Pichincha 0.70409 0.51293 5.8 18.927 15.596 38.638 78.60 1 E05131 Pichincha 0.70407 0.51286 4.3 18.934 15.597 38.631 78.60 1 E05010 Pichincha 0.70404 0.51290 5.2 19.017 15.593 38.780 78.60 1 E05012 Pichincha 0.70400 0.51289 4.9 18.957 15.575 38.690 78.60 1 E05013 Pichincha 0.70401 0.51287 4.5 18.999 15.577 38.738 78.60 1 E05014 Pichincha 0.70404 0.51292 5.5 18.945 15.589 38.654 78.60 1 E05015 Pichincha 0.70410 0.51289 4.9 18.933 15.582 38.630 78.60 1 PICH 4C Pichincha 0.70404 0.51288 4.7 19.001 15.591 38.723 78.60 3 PICH 9C Pichincha 0.70407 0.51288 4.8 18.984 15.577 38.670 78.60 3 PICH 10 Pichincha 0.70406 0.51289 5.0 19.000 15.584 38.708 78.60 3 Gp-1 Pichincha 0.70395 0.51289 4.9 18.958 15.597 38.698 78.60 2 Ql-12 Quilotoa 0.70403 0.51286 4.4 18.985 15.644 38.750 78.65 2 ATAC 2C Atacazo 0.70420 0.51289 5.0 18.878 15.589 38.521 78.55 3 ATAC 8 Atacazo 0.70422 0.51286 4.4 18.962 15.601 38.627 78.55 3 ATAC 12B Atacazo 0.70434 0.51286 4.4 18.967 15.600 38.604 78.55 3 AT01 Atacazo 0.70419 0.51285 4.1 n/a n/a n/a 78.55 4 8557 At Atacazo 0.70430 0.51289 4.9 n/a n/a n/a 78.55 4 At-02 Atacazo 0.70408 0.51289 5.0 18.933 15.602 38.619 78.55 2 957 g Atacazo 0.70430 0.51288 4.7 n/a n/a n/a 78.55 2 Frontal arc basement xenoliths E05008a Pululagua 0.70415 0.51289 4.9 18.862 15.552 38.473 78.60 1 E05130a Pichincha 0.70392 0.51288 4.8 18.861 15.588 38.587 78.60 1 E05011 Pichincha 0.70686 0.51260 -0.7 18.607 15.651 38.548 78.60 1 E05015a Pichincha 0.70401 0.51290 5.1 18.945 15.611 38.699 78.60 1 Main arc (west of Peltetec fault) Imb-1 Imbabura 0.70408 0.51290 5.2 19.098 15.600 38.770 78.40 2 Imb-3 Imbabura 0.70408 0.51291 5.3 19.099 15.606 38.786 78.40 2 Imb-11 Imbabura 0.70407 0.51293 5.7 19.072 15.611 38.766 78.40 2 Imb-26 Imbabura 0.70412 0.51288 4.7 18.921 15.607 38.614 78.40 2 Imb-28 Imbabura 0.70406 0.51292 5.5 18.953 15.616 38.657 78.40 2 Imb-29 Imbabura 0.70411 0.51289 5.0 18.974 15.629 38.717 78.40 2 Imb-30 Imbabura 0.70420 0.51282 3.7 18.913 15.622 38.677 78.40 2 Imb-36 Imbabura 0.70402 0.51291 5.3 19.123 15.617 38.833 78.40 2

116

Table A1 (continued) Sample Magmatic 87Sr 143Nd εNd 206Pb 207Pb 208Pb latitude ref* center 86Sr 144Nd 204Pb 204Pb 204Pb (projected)

Imb-38 Imbabura 0.70425 0.51282 3.6 18.900 15.630 38.712 78.40 2 Imb-45 Imbabura 0.70402 0.51290 5.1 19.073 15.618 38.784 78.40 2 E05132 Ilalo 0.70414 0.51282 3.5 18.951 15.612 38.695 78.40 1 E05133 Ilalo 0.70409 0.51296 6.2 18.955 15.621 38.717 78.40 1 E05134 Ilalo 0.70405 0.51285 4.0 18.940 15.606 38.647 78.40 1 E05046 Ilalo 0.70406 0.51284 3.9 18.940 15.607 38.652 78.40 1 Il-2 Ilalo 0.70406 0.51286 4.4 n/a n/a n/a 78.40 2 Cx-9 Cotopaxi 0.70414 0.51282 3.7 18.963 15.631 38.710 78.30 2 Cx-10 Cotopaxi 0.70419 0.51284 4.0 18.951 15.637 38.716 78.30 2 Main arc (east of Peltetec fault) CAY56 Cayambe 0.70431 0.51274 2.0 n/a n/a n/a 78.20 5 CAY55B Cayambe 0.70441 0.51274 2.1 n/a n/a n/a 78.20 5 CAY106B Cayambe 0.70442 0.51264 0.0 n/a n/a n/a 78.20 5 CAY107 Cayambe 0.70442 0.51272 1.6 n/a n/a n/a 78.20 5 CAY31 Cayambe 0.70446 0.51273 1.7 n/a n/a n/a 78.20 5 CAY80A Cayambe 0.70451 0.51271 1.3 n/a n/a n/a 78.20 5 CAY78A Cayambe 0.70454 0.51262 -0.4 n/a n/a n/a 78.20 5 CAY168D Cayambe 0.70434 0.51280 3.1 n/a n/a n/a 78.20 5 CAY98 Cayambe 0.70432 0.51280 3.2 n/a n/a n/a 78.20 5 CAY8 Cayambe 0.70432 0.51277 2.5 n/a n/a n/a 78.20 5 CAY179A Cayambe 0.70445 0.51268 0.9 n/a n/a n/a 78.20 5 CAY39 Cayambe 0.70439 0.51276 2.3 n/a n/a n/a 78.20 5 CAY87 Cayambe 0.70443 0.51274 2.1 n/a n/a n/a 78.20 5 CAY44A Cayambe 0.70437 0.51281 3.3 n/a n/a n/a 78.20 5 CAY46B Cayambe 0.70442 0.51277 2.6 n/a n/a n/a 78.20 5 CAY45C Cayambe 0.70408 0.51270 1.3 n/a n/a n/a 78.20 5 ANT 54 Antisana 0.70454 0.51273 1.8 18.895 15.637 38.711 78.20 3 ANT 26 Antisana 0.70441 0.51274 2.0 18.886 15.654 38.758 78.20 3 ANT 29C Antisana 0.70449 0.51275 2.2 18.974 15.691 38.914 78.20 3 ANT8 Antisana 0.70424 0.51276 2.4 n/a n/a n/a 78.20 6 ANT10 Antisana 0.70440 0.51273 1.8 n/a n/a n/a 78.20 6 ANT14C Antisana 0.70440 0.51274 1.9 n/a n/a n/a 78.20 6 ANT28 Antisana 0.70439 0.51275 2.1 n/a n/a n/a 78.20 6 ANT32 Antisana 0.70445 0.51273 1.7 n/a n/a n/a 78.20 6 ANT36 Antisana 0.70431 0.51273 1.9 n/a n/a n/a 78.20 6 ANT37 Antisana 0.70432 0.51275 2.2 n/a n/a n/a 78.20 6 ANT46 Antisana 0.70438 0.51273 1.8 n/a n/a n/a 78.20 6 ANT47 Antisana 0.70437 0.51274 1.9 n/a n/a n/a 78.20 6 ANT60 Antisana 0.70434 0.51273 1.7 n/a n/a n/a 78.20 6 ANT61 Antisana 0.70437 0.51272 1.6 n/a n/a n/a 78.20 6 ANT62 Antisana 0.70426 0.51276 2.4 n/a n/a n/a 78.20 6 3.2An Antisana 0.70421 0.51280 3.1 n/a n/a n/a 78.20 4 HHJ-An Antisana 0.70419 0.51280 3.1 n/a n/a n/a 78.20 4 GS-3 Antisana 0.70420 0.51289 5.0 n/a n/a n/a 78.20 4 3D2 Antisana 0.70424 0.51289 5.0 n/a n/a n/a 78.20 4 3D1 An Antisana 0.70414 0.51285 4.1 18.936 15.618 38.728 78.20 2 2G3T-A Antisana 0.70437 0.51275 2.3 18.924 15.643 38.762 78.20 2 HHV Antisana 0.70416 0.51279 3.1 18.985 15.703 38.978 78.20 2

117

Table A1 (continued) Sample Magmatic 87Sr 143Nd εNd 206Pb 207Pb 208Pb latitude ref* center 86Sr 144Nd 204Pb 204Pb 204Pb (projected)

E05035 Chacana 0.70434 0.51273 1.9 18.979 15.617 38.705 78.15 1 E05137 Chacana 0.70428 0.51277 2.6 18.933 15.625 38.704 78.15 1 E05138 Chacana 0.70427 0.51277 2.6 18.920 15.641 38.762 78.15 1 E05142 Chacana 0.70430 0.51278 2.7 18.880 15.612 38.640 78.15 1 E05143 Chacana 0.70423 0.51276 2.4 18.901 15.633 38.722 78.15 1 E05144 Chacana 0.70423 0.51279 2.9 18.889 15.604 38.631 78.15 1 E05147 Chacana 0.70426 0.51273 1.8 18.912 15.610 38.675 78.15 1 E05141 Chacana 0.70445 0.51270 1.3 18.953 15.602 38.671 78.15 1 E05030 Chacana 0.70409 0.51281 3.3 18.977 15.632 38.781 78.15 1 E05036 Chacana 0.70414 0.51280 3.2 18.911 15.626 38.723 78.15 1 E05135 Chacana 0.70426 0.51275 2.2 18.938 15.639 38.768 78.15 1 E05136 Chacana 0.70419 0.51273 1.8 18.927 15.638 38.769 78.15 1 E05019 Chacana 0.70430 0.51276 2.4 18.897 15.624 38.688 78.15 1 E05021 Chacana 0.70430 0.51274 2.0 18.953 15.646 38.799 78.15 1 E05032 Chacana 0.70427 0.51276 2.5 18.916 15.634 38.743 78.15 1 E05025 Chacana 0.70464 0.51255 -1.8 19.057 15.654 38.872 78.15 1 E05028 Chacana 0.70456 0.51275 2.2 18.933 15.624 38.748 78.15 1 E05139 Chacana 0.70465 0.51269 1.1 19.008 15.650 38.833 78.15 1 E05140 Chacana 0.70465 0.51271 1.4 19.026 15.626 38.763 78.15 1 Ch-3 Chacana 0.70404 0.51284 4.0 18.956 15.613 38.680 78.15 2 Ch-6 Chacana 0.70432 0.51277 2.6 18.983 15.633 38.755 78.15 2 Ch-7 Chacana 0.70423 0.51276 2.5 19.028 15.688 38.947 78.15 2 Ch-8 Chacana 0.70427 0.51280 3.3 18.925 15.646 38.694 78.15 2 Ch-4 Chacana n/a 0.51271 1.5 18.925 15.646 38.775 78.15 2 Ch-5 Chacana 0.70434 0.51278 2.7 18.918 15.632 38.732 78.15 2 Sg-13 Sangay 0.70437 0.51274 2.0 18.816 15.644 38.754 n/a 2 Cl-11 Chalupas 0.70443 0.51274 2.0 18.993 15.668 38.873 78.10 2 *References: 1 - Chiaradia et al. (2009); 2 - Bryant et al. (2006); 3 - Bourdon et al. (2003); 4 - Barragan et al. (1998); 5 - Samaniego et al. (2005); 6 - Bourdon et al. (2002)

118 CHAPTER V ADAKITE‐LIKE FEATURES IN LATE OLIGOCENE TO LATE MIOCENE EC‐ UADORIAN ARC MAGMAS AND THEIR SIGNIFICANCE FOR PORPHYRY‐ RELATED ORE DEPOSITS Abstract This study presents a comprehensive dataset of the geochemical composition of Late Oligocene to Late Miocene intrusions associated in space and time with porphyry‐related ore deposits in Ecuador, supple‐ mented by compositional data on several arc volcanic formations of the same age. Our aim is to describe the spatio‐temporal distribution pattern of adakite‐like geochemical features related to Late Tertiary arc magmatism, and explore its significance for porphyry‐related mineralization in Ecuador. Most investigated intrusions are moderately to highly differentiated hornblende‐ ±biotite‐bearing tonalites, granodiorites, and quartz‐diorites, and often form part of larger Oligocene‐Miocene batholith complexes; arc volcanics represent mostly flows and subordinate tuffs of andesitic and dacitic‐rhyolitic composition. The overall spatio‐temporal distribution of adakite‐like features in Ecuadorian arc magmas is semi‐ systematic; the relative proportion of adakite‐like magmas increases with decreasing age, and is higher in northern‐central than in southern Ecuador. Magmatic centers characterized by (partly) adakite‐like magma‐ tism are mainly hosted by the Western Cordillera and comprise Balsapamba (c. 21 Ma), Apuela‐Junin (13‐6 Ma), Chaucha (c. 10 Ma), and Quimsacocha (7 Ma). High Sr/Y ratios (the commonly used main criteria to signal adakite‐like magma compositions) of Late Tertiary Ecuadorian arc magmas are mainly derived from strong Y (along with heavy REE) depletion of their parental melts at broadly constant Sr contents, and are related to fractionation/restite equilibration effects of amphibole, garnet, and titanite. In Early to Mid‐Miocene Ecuadorian arc magmas, amphibole (± accessory titanite) fractionation/restite equilibration causedc silici melts to evolve towards adakite‐like compositions; combined amphibole and garnet fractionation/restite equilibration is only observed in the Late Miocene Quimsacocha volcanic cen‐ ter, and continues to the present day. While Y depletion by amphibole fractionation/restite equilibration is particularly efficient for silicic melt compositions, garnet fractionation/restite equilibration produces strong Y depletion already in more mafic melt compositions, i.e, during earlier differentiation stages. Significant shallow crustal plagioclase fractionation affects some, but not all Late Tertiary arc magmas in southern Ec‐ uador; it is of minor petrogenetic significance for Miocene intrusions of the Western Cordillera in northern‐ central Ecuador. A preferential association of adakite‐like features with a specific basement lithology can‐ not be observed. Systematic trace element variations (Sr, Y, REE) through time are indicative of progressively increasing high‐ pressure arc magma differentiation from the Late Oligocene to the Late Miocene, either by crustal thicken‐ ing, or/and by the downwards migration of crustal hot zones. However, adakite‐like features are also locally observed in the Early Miocene in a regional petrogenetic setting otherwise dominated by low‐pressure magma evolution. Where porphyry‐related ore deposits are associated with batholith complexes recording multi‐m.y. precur‐ sor magmatism, porphyry emplacement commonly represents a late intrusive event; in that case porphyry parental melts tend to evolve towards more adakite‐like compositions than precursor batholith intrusions indicating downward migration of the focus of crustal magma evolution towards greater depth and/or in‐ creasing water contents in the magmatic system. However, it is important to note that these compositional changes between porphyry and host intrusions mostly reflect broad changes in arc magma composition through time at a regional scale. Systematic compositional changes between porphyry and precursor intru‐

119 sions are not recorded if their relative emplacement age difference is small. The fact that porphyry‐related ore deposits in Ecuador formed throughout the Late Oligocene to Late Miocene (24‐6 Ma) over a large lati‐ tudinal range (c. 0° to 3°30’S) supports the notion that any arc magma of a sufficient volume has the poten‐ tial to form porphyry‐related mineralization. In some cases adakite‐like magmatism may, however, reflect favorable tectonomagmatic preconditioning of porphyry parental melts for subsequent porphyry‐related mineralization.

Introduction Tertiary‐Quaternary adakite‐like Active arc volcanism in the Andean chain, where magmatism in Ecuador the Nazca plate is subducting below the western A main aspect addressed by most studies on pre‐ plate edge of South America, clusters in three sent‐day NVZ volcanism is the mechanism to major zones referred to as Northern, Central, and generate adakite‐like geochemical signatures in Southern Volcanic Zone (NVZ, CZV, and SVZ, re‐ Ecuadorian arc volcanics. Adakite‐like magmatism spectively). These zones are separated by arc is characterized by a specific geochemical compo‐ segments extending along‐arc for several 100 km sition indicative of, amongst others, parental which are characterized by the absence of active melt equilibration with a Y‐ (and heavy rare earth arc volcanism (Fig. 1). Voluminous Tertiary arc element; HREE‐) retentive mineral phase, and magmatic products extend beyond the present‐ absence of significant plagioclase fractionation day NVZ both in along‐ and across‐arc dimension. (see review by Richards & Kerrich 2007, and ref‐ While the geochemical features of Pleistocene‐ erences therein). The term “adakite‐like” was Holocene NVZ volcanism of the Ecuadorian Andes introduced by Richards & Kerrich (2007) for arcs have been extensively studied., (e.g Bourdon et built on thick continental crust such as the Andes al. 2003; Garrison & Davidson 2003; Samaniego to avoid confusion with adakite sensu stricto et al. 2005; Bryant et al. 2006; Garrison et al. which is exclusively defined for island arc settings 2006; Chiaradia et al. 2009a), geochemical data (Defant & Drummond 1990). In this context, the on Tertiary arc magmatism are sparse. Building term "adakite‐like" does not carry any specific on a pilot study by Chiaradia et al. (2004), this petrogenetic implication with respect to the contribution presents new geochemical data for a magma source. In particular, adakite‐like chemi‐ number of Late Tertiary intrusions and volcanic cal features of continental arc rocks are not nec‐ formations of the northern‐central Ecuadorian essarily associated with slab melting as adakites Western Cordillera and the Interandean Sierra sensu stricto potentially are (Richards & Kerrich region of southern Ecuador, representing the 2007). most extensive dataset to date for Tertiary igne‐ ous rocks in the northern Andes. We focus on Generation of adakite‐like geochemical composi‐ investigating the occurrence of adakite‐like fea‐ tions in present‐day NVZ magmas is envisaged tures in Tertiary arc magmas associated with either by slab melting and mantle wedge con‐ porphyry‐related ore deposits, and evaluate their tamination by slab melting of the subducting metallogenetic significance. young (<24 Ma), hot Nazca slab (e.g., Gutscher et al. 2000; Bourdon et al. 2003; Samaniego et al. 2005), or high‐pressure equilibration of arc mag‐ mas at deep to mid‐crustal levels (e.g., Garrison

Figure 1 (next page): Geological map of Tertiary‐Quaternary Ecuadorian arc units and magmatic centers investigated in this study. Inset shows distribution of the Northern (NVZ), Central (CVZ), and Southern Volcanic Zone (SVZ) resulting from subduction of the Nazca plate below South America; gray bars indicate positions of major seamount chains pres‐ ently colliding with the central‐southern American margin (from N to S: Cocos, Carnegie, Nazca, and Juan Fernandez Ridge). Simplified from various references in Chapter 2.

120 121 & Davidson 2003; Garrison et al., 2006; Chiaradia The present study aims to contribute to a better et al. 2009a). Bryant et al. (2006) note the diffi‐ understanding of the spatio‐temporal distribution culty to clearly discriminate these two processes, of adakite‐like magmatism as part of the general and present intra‐mantle wedge partial melting petrogenetic evolution of Oligocene‐Miocene processes in the garnet stability field as an addi‐ Ecuadorian arc magmatism. In particular, we ex‐ tional option. The Late Miocene collision of the plore the metallogenic significance of adakite‐like Carnegie Ridge seamount chain with the northern magmatism for porphyry‐related mineralization Ecuadorian margin is considered to exert a major in Ecuador, as spatial associations of intrusions influence on arc magmatism either by increasing with adakite‐like geochemical features and por‐ the geothermal gradient along the subducting phyry‐related ore deposits have been observed slab surface thus facilitating slab melting (Sama‐ elsewhere (e.g., Thiéblemont et al. 1997). Conse‐ niego et al. 2005), or by potentially affecting far‐ quently, magmatic centers of this study were se‐ field stress and transcrustal magma ascent kinet‐ lected based on their spatial association with ics (Chiaradia et al. 2009a). Seismic studies at the porphyry‐related ore deposits. The widespread Ecuadorian margin demonstrate a continuously occurrence of this ore deposit type in Ecuador subducting Nazca/Farallon slab, subducting at an (Prodeminca 2000) ensures a regionally represen‐ angle of 25‐30° down to at least 150‐200 km tative coverage of Late Tertiary arc magmatism. depth (Guillier et al. 2001) such that earlier sug‐ Parallel geochronologic (Chapters 2, 3) and iso‐ gestions proposing slab melting due to slab flat‐ topic (Chapter 4) studies provide age and base‐ tening in response to Carnegie Ridge subduction ment control, enabling us to calibrate geochemi‐ (e.g., Gutscher et al. 2000; Beate et al. 2001) can cal changes in arc magmatism through time and be excluded. across different crustal basement domains. The occurrence of adakite‐like magmatic features in the Ecuadorian subduction system through Regional geology and geody‐ time is not clearly understood. Beate et al. namic setting (2001), Somers et al. (2005), and Amortegui (2007) demonstrate that adakite‐like rock com‐ The Ecuadorian margin is characterized by the positions already occur in Late Miocene intru‐ typical principal geologic features of a collisional sions and volcanics. Chiaradia et al. (2004) show continental arc comprising a foreland basin‐ that a number of Tertiary, pre‐Late Miocene in‐ hosting back‐arc region, a major orogen, split into trusions and volcanic formations lack adakite‐like the Eastern and Western Cordillera, and a forearc features, and note an apparent mutual exclusivity sliver which undergoes trench‐parallel, dextral of mainly Early to Mid‐Miocene porphyry‐related strike‐slip displacement relative to the continent mineralization and Late Miocene to Holocene as a result of oblique plate convergence between adakite‐like magmatism in Ecuador. Recently, the Nazca plate and South America (Litherland et Chiaradia (2009) presented evidence for adakite‐ al. 1994; Ego et al. 1996). Basement units of the like features of small intrusive bodies of the Eo‐ back‐arc region and the Eastern Cordillera are of cene Macuchi island arc sequence of central‐ Precambrian‐Paleozoic age; they are intruded by northern Ecuador. a voluminous Triassic‐Jurassic arc sequence

Figure 2 (next page): Macro‐photographs (A, G) and micro‐photographs (B‐F, H) illustrating mineralogical features rep‐ resentative for analyzed samples of Late Tertiary magmatic centers in Ecuador. A – hornblende‐ and biotite‐bearing granodiorite with weak sericite‐chlorite alteration (Chaucha batholith). B – plagioclase and hornblende‐phyric dacite with fresh glassy matrix (Quimsacocha). C – plagioclase‐hornblende porphyry with resorbed quartz and weak propylitic alteration (Cangrejos). D – hornblende‐plagioclase porphyry with sodic‐calcic alteration (Gaby). E – hornblende quartz‐ diorite porphyry with potassic alteration (Balsapamba). F – hornblende‐ and biotite‐bearing granodiorite with potassic alteration at Apuela (Cuellaje). G – hornblende granodiorite porphyry at Apuela (Junin) with pervasive potassic altera‐ tion and sericite alteration haloes around quartz‐pyrite veinlets; note that veinlets and their haloes were removed prior to geochemical analysis. H – hornblende granodiorite porphyry at Apuela (Junin) with pervasive potassic, overprinted by phyllic alteration where feldspars are partly replaced by sericite; this type of alteration significantly affects whole‐ rock Sr contents rendering results petrogenetically insignificant; used only for a limited number of Junin porphyry sam‐ ples where other samples were not available. White scale bar is 1 mm for micro‐, and 2 cm for macro‐photographs.

122 123 124 whose roots are exposed in the Eastern Cordillera Miocene, and was accompanied by voluminous (Litherland et al. 1994). The forearc sliver and arc volcanism (Chapter 2; Fig. 1). Western Cordillera basement consist of oceanic Following the Late Cretaceous oceanic plateau plateau fragments accreted to the paleo‐ accretion, oblique Farallon/Nazca‐South America continental margin in the Late Cretaceous and plate convergence characterized the Ecuadorian interpreted to form part of the Colombian‐ margin throughout the Tertiary (Chapter 2). A Caribbean oceanic plateau (CCOP; e.g., Vallejo et major geodynamic event affected the Tertiary al. 2009). Basement units of the Sierra region be‐ subduction system with the fragmentation of the tween the Eastern and Western Cordillera are Farallon plate, followed by initiation of Cocos‐ obscured by NVZ and Tertiary arc volcanic prod‐ Nazca seafloor spreading during the Early Mio‐ ucts; they likely consist of a tectonized mélange cene (Lonsdale 2005; Barckhausen et al. 2008). At of oceanic plateau units and Eastern Cordillera the Colombian‐Ecuadorian margin, this led to a basement where the proportion of the latter change in subducting slab properties from old, progressively increases towards the east (Fein‐ cool (Farallon) to young, hot (Nazca) oceanic inger & Seguin 1983; Litherland et al. 1994; Spik‐ lithosphere; the Farallon‐Nazca plate boundary is ings et al. 2005; Chapter 4). Southwestern Ecua‐ represented by the offshore ENE‐trending Grijal‐ dor additionally contains a rotated micro‐ vas scarp progressively propagating southwards continental block known as the El Oro massif along the margin, and currently intersects the whose basement units are of Eastern Cordillera Ecuadorian trench at 3°S (Lonsdale 2005). petrogenetic affinity (Litherland et al. 1994). Farallon plate motion reconstructions (Somoza Arc magmatism resulting from the subduction of 1998) imply that seamounts formed at the Gala‐ the Farallon plate below South America was ac‐ pagos hotspot during the Late Cretaceous to Mid‐ tive along the Ecuadorian margin until the Late Tertiary did not collide with the Ecuadorian mar‐ Jurassic (Litherland et al. 1994). Except for the gin, situated due east with respect to the hotspot Mid‐Cretaceous Tangula batholith (Hall & Calle in a present‐day global reference frame; instead, 1982) and few minor backarc intrusions (Barra‐ they were subducted at, or docked onto the Pa‐ gan et al. 2005), voluminous Cretaceous arc nama‐Costa Rica margin to the NE (Hoernle et al. magmatism has not been identified in Ecuador 2002). This situation changed fundamentally in suggesting a magmatic lull during that period. the Late Oligocene‐Early Miocene when a major Following oceanic plateau accretion(s), arc mag‐ change in Farallon plate motion prior to its fission matism resumed in the latest Cretaceous, and a in the Early Miocene caused Galapagos‐derived continuous Tertiary arc developed along the seamounts to drift eastwards, resulting in the whole continental margin (Vallejo et al. 2009; collision of the Carnegie Ridge seamount chain Chapter 2). While southern Ecuador is mostly with the Ecuadorian margin in the Late Miocene characterized by continental, subaerial arc mag‐ where it caused minor shallowing of the subduc‐ matism throughout the Tertiary, magmatism in tion angle, and eastward arc migration and broa‐ northern‐central Ecuador started as a submarine dening (Gutscher et al. 1999; Guillier et al. 2001; island arc system represented by the Macuchi Chapters 2, 3). While Gutscher et al. (1999), Unit which was erupted on accreted oceanic pla‐ based on the erroneous assumption of a flat slab teau basement; this arc was juxtaposed land‐ geometry below central Ecuador, proposed a slab wards against a minor subaerial arc system and tear along the projected trace of the Grijalvas progressively matured during the Tertiary, culmi‐ scarp below southern‐central Ecuador, the shal‐ nating in the present‐day NVZ arc magmatism on low (25‐30°) subduction setting below central substantially thickened crust (Guillier et al. 2001; Ecuador inferred from high‐resolution seismic Jailliard et al. 2005; Chiaradia 2009; Chiaradia et studies (Guillier et al. 2001) makes a slab contor‐ al. 2009a). Emplacement of multiple intrusions tion below southern Ecuador a more likely alter‐ along major structures led to the development of native. A slab contortion is also proposed for the batholith‐size intrusive clusters in northern, cen‐ flat‐normal slab transition between northern and tral, and southern Ecuador during the Oligocene‐ central Peru (James & Sacks 1999). The flat slab geometry initiating below northern Peru in the

125

Late Miocene (e.g., James & Sacks 1999) contin‐ Table 2: Hydrothermal alteration-influenced ues northwards into southern Ecuador where compositional variability of exemplary refer- Late Miocene or younger arc magmatism is con‐ ence lithologies sequently not observed (Chapter 2). Elements Remarks Low compositional variation

Sampling and analytical tech‐ SiO2, TiO2, scatter < ±10% for all systems Al2O3 niques Zr, Hf scatter < ±10% for all systems Samples for geochemical analyses were collected Moderate compositional variation from mineral exploration drill cores or outcrop CaO, P2O5 scatter < ±20% for all systems Sr scatter < ±10% for Apuela-Cuellaje, Gaby, exposures of multiple intrusions and volcanic Balsapamba; scatter ~20% (sometimes higher) formations listed in Table 1. Sampling did not fol‐ for Saraguro low a systematic grid pattern but reflects drill Nb, Ta scatter < ±20% for Apuela-Cuellaje, Balsa- core distribution as well as outcrop accessibility pamba, Saraguro; mostly < ±20%, but up to 35% scatter for Gaby and suitability. Sampled Quimsacocha volcanics are all related to a single volcanic caldera, whe‐ Y scatter < ±20% for Gaby; variable (up to 38%) for Apuela-Cuellaje, Balsapamba, Saraguro reas sampling localities for Saraguro Group vol‐ Sc scatter < ±20% for Apuela-Cuellaje, Balsa- canics show a large geographical spread (c. pamba, Saraguro; slightly higher scatter (up to 100 km) comprising three areas (Chaucha, Cañi‐ 26%) for Gaby capa, Portovelo; Fig. 1) to reflect its widespread Th scatter < ±20% for all systems distribution in southern‐central Ecuador. Both V scatter < ±10% for Apuela-Cuellaje, Balsa- intrusive centers and Saraguro Group volcanics pamba, Saraguro; systematic bias at Gaby caused by reference sample composition, oth- integrate magmatic events of up to 10‐15 m.y. erwise scatter at Gaby would be < ±20% (the time span for batholith construction in cen‐ High compositional variation tral and northern Ecuador; Chapter 2). Fe2O3, MgO scatter < ±20% for Apuela-Cuellaje, Balsa- pamba, Saraguro; highly variable scatter for To ensure compositionally representative geo‐ Gaby (up to 52%) chemical analyses, sample quantities typically Na2O scatter < ±10% for Apuela-Cuellaje, Balsa- comprised c. 0.5 or c. 1 kg of material for fine‐ or pamba, Saraguro; highly variable scatter for Gaby coarse‐grained samples, respectively. Lower sample quantities were occasionally obtained for K2O highly variable scatter for all systems drill core samples where sampling material was Cs, Rb, Ba highly variable scatter for all systems; at Gaby correlated with K O (potassic alt.) limited. In areas where rocks were affected by 2 U highly variable scatter for all systems porphyry intrusion‐related hydrothermal sys‐ Cr, Ni highly variable scatter for all systems tems, careful outcrop selection and drill core REE highly variable scatter for all systems; LREE quick‐logging ensured sampling of least altered decoupled and La/Yb ratios potentially inaccu- material for a given alteration facies. Intense rate; coupled behavior within MREE & HREE groups such that Eu/Eu* and Dy/Yb are poten- feldspar‐destructive phyllic and argillic alteration tially accurate was avoided where possible (essentially every‐ Main alteration types for reference centers where isocons where except for some Junin porphyry intru‐ were constructed sions). Pervasively veined material was avoided Apuela potassic, propylitic for sampling, and isolated hydrothermal veins (Cuellaje) and vein alteration haloes were removed by a Balsapamba potassic, propylitic diamond blade disc saw prior to sample process‐ Gaby sodic-calcic, potassic, propylitic ing. Saraguro propylitic

Samples were cleaned with water, crushed using Single-analysis outliers are not noted, but might be significant; a steel jaw crusher, and powdered (<70 μm) us‐ refer to Table A2 (Appendix). Note that feldspar phenocryst- destructive alteration was generally avoided as far as possible, ing an agate disc mill, where each step was fol‐ but is unavoidable for some samples at Junin and Chaucha; Sr lowed by sample splitting into representative scatter is expected to increase for these centers.

126 proportions to reduce the sample quantity for out during the 2006‐2008 period at the Institute subsequent analytical steps. Reconnaissance XRF of Mineralogy and Geochemistry, University of analysis for major and trace elements (10‐15 Lausanne. XRF measurements were done on g/sample) for a total of 139 samples was carried pressed powder pellets or fused glass beads

Figure 3: Isocon plots of representative Tertiary granitoids and volcanics in Ecuador, constructed after Grant (1986) assuming constant concentrations of Al2O3 (the least alteration‐affected major element oxide) between altered and least‐altered reference sample. Elemental scatter outside gray area (± 10% analytical uncertainty) reflects alteration‐ induced compositional variation (± lithologic compositional heterogeneities) of altered samples with respect to a least‐ altered reference sample of the same lithology. Note that displayed isocons correspond to average compositions of all compared lithologies and serve only for illustrative purposes; to quantify alteration effects individual isocons were cal‐ culated for each sample and considered for relative concentrations shown in the Appendix (Tab. A2). Isocon slopes vary according to dehydration‐induced mass loss effects. Alteration acronym key: K – potassic; Na‐Ca – sodic‐calcic; propyl. – propylitic. Feldspar‐destructive phyllic or argillic alteration is expected to increase Sr mobility but was avoided for most samples. See Seedorff et al. (2005) for definitions of alteration assemblages. Refer to Appendix for discussion of alteration effects, and to Table 2 for a summary of expected alteration effects on sample compositions.

127 fluxed with Li2B4O7 using a Philips PW 2400 ana‐ dataset are listed in the Appendix (Tab. A1). lyzer. Data accuracy, precision, and reproducibil‐ Samples are grouped according to localities (in‐ ity were controlled using a number of natural and trusions) and stratigraphic units (volcanics; Tab. synthetic international or in‐house standard ma‐ 1). Considering the constraints on sampling pro‐ terials (BHVO, EMU3.14, QLO, QTW, MFTH‐1, cedures described above, it is important to em‐ NIM‐G, SDC‐1, SY‐2) which were selected accord‐ phasize that samples within single and between ing to sample composition and analytical meas‐ different sample groups are generally not consid‐ urement program. Expected 2σ uncertainties ered as cogenetic. Apart from sharing an overall from repeated standard measurements are 2‐7% similar petrogenesis in terms of Late Oligocene to for major elements and up to 10% for trace ele‐ Late Miocene arc magmatism, their chemical ments. compositions are therefore not systematically related to each other by a single specific petro‐ Combined microscopic analysis and XRF result genetic process (such as magma mixing or AFC, screening served to select only least altered sam‐ i.e., assimilation and fractional crystallization). ples in a given intrusive suite or volcanic forma‐ tion for subsequentr lase ‐ablation inductively‐ coupled plasma mass spectrometry (LA‐ICP‐MS) Rock alteration and element mobility analysis. LA‐ICP‐MS analysis of glass bead frag‐ Depending on their spatial and temporal prox‐ ments recovered from XRF analysis (n = 97) was imity with respect to centers of porphyry‐related carried out at the Institute of Mineralogy and hydrothermal systems, most rocks display vari‐ Geochemistry, University of Lausanne, using a able degrees of high‐ to low‐temperature altera‐ 193 nm Lambda Physik Excimer Laser system as‐ tion comprising potassic, sodic‐calcic or calcic‐ sociated with a Perkin‐Elmer ELAN 6100 DRC sodic, phyllic, (advanced) argillic and propylitic quadrupole ICP mass spectrometer. The Laser alteration assemblages (e.g., Seedorff et al. 2005; system was operated at 10 Hz frequency using Fig. 2). Effects of hydrothermal alteration on rock 140 or 160 mJ output energy and a 120 μm beam chemistry in our dataset are summarized in Table diameter. Background measurement for c. 90 s 2 and Figure 3, and are further discussed in the was followed by 30‐40 s sample ablation with 3‐4 Appendix. ablation pits for each sample. Used internal stan‐ Element mobility and redistribution due to hy‐ dard elements were CaO (for sample CaO >1 drothermal alteration commonly strongly affects wt.%) or Al2O3 (for sample CaO <1 wt.%), refer‐ large ion lithophile elements (LILE), whereas high enced to NIST SRM‐610 and SRM‐612 standard field strength elements (HFSE) are less affected. materials and sample major element composi‐ As shown above (Fig. 3, Tab. 2; see also discus‐ tions measured by XRF. Off‐line data reduction sion in the Appendix) certain LILE (e.g., Cs, Rb, as including automatic spike correction used the well as K as major element) are strongly affected Matlab‐based SILLS codec (Guillong et al. 2008). by hydrothermal alteration and are thus not Trace elements measured by XRF and selected for suited as petrologic tracers, whereas most HFSE data presentation in this study comprise Sr, Y, Pb, and Sr (although a LILE, and often considered as V, Cr, Cu, Zn, and Ga, whereas for all other trace mobile during hydrothermal alteration) tend to elements LA‐ICP‐MS results were preferred. X‐ray stay relatively immobile in our dataset. Light, fluorescence and LA‐ICP‐MS trace element analy‐ mid‐, and heavy rare earth elements (LREE, MREE ses generally agree within error, except for Nb, and HREE, respectively) do not consistently show where a systematic bias of elevated contents for chemically coupled behavior during hydrothermal XRF measurements was detected, and Zr, where alteration, whereas alteration‐induced intra‐ XRF results scattered outside of the expected MREE and HREE scatter appears to be coupled in ±10% analytical error limit. our reference samples (Fig. 3, Tab. 2; Appendix). Consequently, while chondrite‐normalized REE Results distribution patterns can be used for a qualitative Combined whole‐rock XRF and LA‐ICP‐MS major petrogenetic discussion, LREE/HREE ratios such as and trace element compositions of the complete La/Yb are potentially inaccurate; intra‐HREE and MREE/HREE ratios such as Dy/Yb and Sm/Dy, on

128 the other hand, are more likely to reflect petro‐ in several of the investigated magmatic centers genetically significant, rather than alteration‐ though). biased values. We emphasize that these observa‐ tions reflect our sample selection according to Rock petrography alteration mineralogy, and cannot be generalized Geologic features of sampled magmatic centers for other datasets. Throughout this article we are summarized in Table 1. The igneous (as op‐ avoid using any chemical element for petroge‐ posed to alteration‐induced hydrothermal) min‐ netic discussions whose concentration is consid‐ eralogical inventory of most phaneritic intrusive ered as significantly affected by alteration in one rocks comprises plagioclase, hornblende, quartz, of our reference magmatic centers (Tab. 2, Ap‐ and biotite with accessory opaque minerals pendix; some of these elements may be immobile

Figure 4: Rock petrographic classification of Late Tertiary granitoids and volcanics in Ecuador. Upper left: plutonic rock classification by normative quartz‐alkali feldspar‐plagioclase (QAP) proportions (Gillespie & Styles 1999) using projec‐ tion parameters of Le Maitre (1976); due to alteration‐induced Ca depletion, normative albite was used instead of an‐ orthite to calculate the plagioclase component of Junin porphyry intrusions. CIPW norms were calculated assuming Fe2+ = 0.7 ∑ Fe. Upper right: alumina saturation index classification of plutonic rocks (Maniar & Piccoli 1989). Lower left: Total alkali‐silica classification for plutonic and volcanic rocks (Le Bas et al. 1986). Lower right: SiO2 vs. Zr/TiO2 / 10,000 classification for plutonic and volcanic rocks (Winchester & Floyd 1977); note that using Nb/Zr instead of SiO2 as differ‐ entiation index produces systematic inaccuracies for rock classification in our dataset and is therefore not applied.

129 (mostly magnetite), apatite, and zircon; most stant values with increasing SiO2. Second‐order highly differentiated intrusions additionally con‐ scatter of major elements partly reflects hydro‐ tain minor alkali‐feldspar and accessory titanite. thermal alteration (especially for K2O). Most Most of these intrusions mineralogically classify samples seem to classify as low‐K series or strad‐ as tonalite, granodiorite, or quartz‐diorite (Fig. 2). dle the low‐ to medium‐K series border (Fig. 5), In decreasing order of abundance, phenocryst but rock alteration precludes a detailed classifica‐ modes of porphyry intrusions mainly comprise tion. Except for Quimsacocha dacites, all mag‐ plagioclase, ±hornblende, ±quartz, ±biotite, with matic centers plot in the calc‐alkaline field of Mi‐ quartz commonly displaying rounded, resorbed yashiro (1974). The broad similarity of major grain margins. Sampled Quimsacocha andesite element trends displayed by the whole dataset lava flows and dacite domes contain plagioclase suggests that similar processes of magma evolu‐ and hornblende phenocrysts (the latter often tion operate in all investigated Oligocene‐ opacitized), frequently embedded in a glassy, Miocene magmatic centers. non‐devitrified matrix; clinopyroxene occurs as additional phenocryst in andesites. Saraguro vol‐ Trace element contents canics comprise andesitic, dacitic, and rhyolitic Where appropriate, trace element Harker dia‐ flows and subordinate tuffs where main phenoc‐ grams (Figs. 6, 7) are plotted together with the ryst assemblages are plagioclase, ±hornblende, compositional fields of the present‐day NVZ main ±clinopyroxene, plus quartz with accessory zircon and frontal arc (Chiaradia et al. 2009a), and Eo‐ for dacitic‐rhyolitic compositions. cene lavas of the Macuchi Unit (Chiaradia 2009). Chemical classification plots based on normative These references were chosen for increased in‐ mineral proportions of quartz, alkali‐feldspar, and ternal analytical consistency with our dataset as plagioclase (QAP), total alkali versus silica con‐ they were measured in the same laboratory; tents, or ratios of immobile trace elements (Fig. more compositional NVZ data are available (e.g., 4) yield consistent results, with most samples Bourdon et al. 2003; Samaniego et al. 2005; Bry‐ classifying as andesitic to rhyo‐dacitic in composi‐ ant et al. 2006), and mostly overlap with the tion, or as tonalite, granodiorite, or monzogranite given reference fields. in normative QAP proportions. Based on com‐ In primitive mantle‐normalized spidergrams all parison with visually estimated mineral modes, Late Tertiary samples display negative Nb‐Ta the alkali‐feldspar component calculated from anomalies relative to LILE indicative of a slab flu‐ normative mineral proportions in Figure 4 seems id‐metasomatized mantle wedge as the magma to be slightly, and in the case of Zaruma‐ source (Fig. 8). With the exception of few Sara‐ Portovelo samples moderately, overestimated guro Group samples, trace elements incompati‐ due to hydrothermal alteration. Most intrusions ble in basaltic melts (Th, U, Zr, Hf) consistently straddle the metaluminous‐peraluminous border plot below the present‐day main arc, but overlap (with a tendency to plot in the peraluminous with NVZ frontal arc compositions (Fig. 6). Within field) with only Gaby classifying as entirely meta‐ a given Late Tertiary magmatic center, these luminous (Fig. 4). trace elements for the most part either stay con‐ stant or show decreasing contents at SiO2 Major element contents >65 wt.% possibly reflecting the influence of ac‐ Most samples define broadly continuous distribu‐ cessory phase fractionation which only become tion patterns in Harker diagrams (Fig. 5) where stabilized in relatively silicic melts (e.g., Hoskins TiO2, Fe2O3 and CaO steadily decrease with SiO2, et al. 2000). Trace elements compatible in basal‐ i.e., they show gross compatible behavior, tic melts show petrologically correlated behavior whereas K2O and Na2O mainly display incompati‐ with the previous group in that they consistently ble behavior or constant values with increasing plot above, or overlap with, frontal (and main) SiO2. Al2O3 and CaO/Al2O3 distribution trends di‐ arc NVZ magmas; overall, basalt‐compatible trace verge and show either a broad decrease or con‐

130

Figure 5: Major element oxide vs. SiO2 concentrations of investigated samples. Low‐K, medium‐K, and high‐K classifica‐ tion from Gill (1981). Tholeiitic vs. calc‐alkaline dividing line from Miyashiro (1974).

131 element contents (e.g., Y, Yb, Sc) decrease with or hot zone (Hildreth & Moorbath 1988; Annen et increasing SiO2. al. 2006) through differing AFC ± mixing proc‐ esses compared to Oligocene‐Miocene magmas. Strontium generally shows broadly constant con‐ These contrasting magma evolution trends can centrations around 300 ppm for the 55‐65 wt.% be bracketed in time between the Quimsacocha SiO interval and major scatter (100 to 2 volcano (7.1 Ma; Chapter 2), whose composi‐ c. 800 ppm) for more evolved compositions, al‐ tional trend largely mirrors present‐day NVZ though average Sr contents do not shift system‐ magmas, and the Chaucha batholith (14.8 Ma; atically for compositions >65 wt.% SiO if Quim‐ 2 Chapter 2). Younger porphyry intrusions at Junin sacocha is excluded (Fig. 6). With the exception and Chaucha (9.0 and 9.8 Ma; Chapter 2) are too of Quimsacocha, Sr contents of Late Tertiary arc highly differentiated to confidently predict their magmas between 55‐65 wt.% SiO overlap with, 2 compositional behavior in the differentiation in‐ or slightly exceed the upper compositional range terval relevant for NVZ magmas (<65 wt.% SiO ). defined by the less differentiated Macuchi ba‐ 2 salts‐andesites, but consistently plot below both Chondrite‐normalized REE plots (Fig. 8) display main and frontal arc NVZ magmas, although no moderate to strong LREE enrichments over HREE, data for <59 wt.% SiO2 exist for the latter (Fig. 6). except for Gaby, where relatively flat REE pat‐ terns suggest parental magma differentiation was Trace element ratios (Fig. 7) illustrate the signifi‐ not driven by strongly HREE/LREE‐fractionating cance of these general compositional features for mineral phases. Most REE plots lack negative Eu the development of adakite‐like chemical signa‐ anomalies indicative of plagioclase fractionation tures: the majority of Late Tertiary Western Cor‐ (Fig. 8; see also relatively constant Eu/Eu* range dillera granitoids (Apuela‐Junin, Balsapamba‐ at c. 1.0±0.4 in Fig. 7); however, negative Eu Telimbela, Chaucha) qualify as adakite‐like in a anomalies do characterize a number of mainly Sr/Y vs. Y discrimination plot (we do not use the southern Ecuadorian magmatic centers compris‐ additional La/Yb vs. Yb adakite discrimination plot ing Saraguro Group volcanics at Chaucha and Por‐ because of potential LREE/HREE decoupling dur‐ tovelo‐Zaruma (but not at Cañicapa and Tres ing alteration as mentioned above) due to Chorreras), several intrusions of the Cangrejos‐ strongly depleted Y contents (<10 ppm) and de‐ Zaruma intrusive belt (Cangrejos porphyries; in‐ spite only moderately high (mostly sub‐adakite‐ trusions north of Zaruma), and, partly, the Telim‐ like, i.e., <400 ppm) Sr contents. A Sr/Y vs. SiO 2 bela batholith. Positive Eu anomalies (see discus‐ plot demonstrates that most present‐day NVZ sion below for their petrogenetic interpretation) magmas acquire adakite‐like Sr/Y ratios during are displayed by a fraction of Balsapamba batho‐ relatively early differentiation stages, whereas lith samples and the Gur‐Gur porphyry intrusion most Oligocene‐Miocene magmas (excluding at Chaucha. Several magmatic centers are Quimsacocha) only display clear adakite‐like fea‐ strongly depleted in HREE and display concave‐ tures for highly differentiated (>65 wt.% SiO ) 2 upwards HREE patterns typical of amphibole frac‐ compositions (Fig. 7; note, however, that for the tionation. Apuela batholith and Junin porphyries Sr and Sr/Y partly decrease with increasing SiO2 in the 65‐70 Chondrite‐normalized Dy/Yb ratios may be used wt.% SiO2 interval; this might be an alteration as petrologic fingerprints for garnet or amphibole effect). Quimsacocha, in contrast to other Oligo‐ fractionation (leading to strongly increasing or cene‐Miocene magmatic centers, tends to over‐ slightly decreasing trends with increasing SiO2; lap with NVZ magmas, although it is depleted in Y Davidson et al. 2007). Individual Quaternary NVZ with respect to the latter (Figs. 6, 7). These sys‐ volcanic centers show Dy/Yb and Nb/Ta trends tematic differences imply that Oligocene‐ negatively correlated with SiO2 indicative of am‐ Miocene magmas were either derived from a phibole fractionation (Chiaradia et al. 2009a). No source with a different trace element composi‐ such systematic trends can be clearly discerned tion than present‐day main arc NVZ magmas, for Oligocene‐Miocene arc magmas; Nb/Ta ratios or/and that the latter acquired their surplus in Sr are subchondritic and, mostly, sub‐primitive (and other basalt‐incompatible elements) during mantle (Fig. 7). initial stages of basalt differentiation in a MASH

132 Figure 6: Trace element vs. SiO2 concentrations of investigated samples; two columns arranged in order of downwards decreasing trace element incompatibility in basaltic melts. Macuchi reference fields from Chiaradia (2009); NVZ main and frontal arc from Chiaradia et al. (2009a).

133 The lack of systematic Dy/Yb and Nb/Ta distribu‐ their REE patterns, and have SiO2 contents in the tion trends is not surprising given that most sam‐ range of 53‐66 wt.% (except for a single higher ples do not define cogenetic suites, such that dif‐ differentiated Apuela sample). For the most part, ferentiation trends of individual magmatic sys‐ these plutonic and volcanic rocks show relatively tems are not visible, and any long‐term bulk dis‐ flat MREE‐HREE patterns with HREE concentra‐ tribution trends might additionally become tions ≥10x chondrite; slightly fractionated or U‐ blurred by the somewhat contrasting, superpos‐ shaped HREE patterns are rare. All intrusions are ing effects of amphibole and garnet (or other in‐ characterized by high modal proportions of pla‐ tra‐HREE‐fractionating phases; e.g., Davidson et gioclase, and their REE distribution patterns sug‐ al. 2007) fractionation. In contrast, Sm/Dy ratios gest that their parental melts fractionated plagio‐ will increase in response to both amphibole and clase. Although amphibole is present in signifi‐ garnet fractionation and are thus supposed to cant modal proportions in several intrusions, sig‐ show a more homogeneous distribution pattern. nificant amphibole fractionation did not take This is evidenced in Figure 7 where chondrite‐ place. In H2O‐saturated experimental runs of ba‐ normalized Sm/Dy ratios show an overall steady saltic‐andesitic bulk compositions buffered at increase with SiO2, albeit showing pronounced NNO, plagioclase appears earlier on the liquidus variations between different magmatic centers than amphibole only at pressures <0.4 GPa for a given differentiation stage. With few excep‐ (Grove et al. 2003; the maximum pressure might tions, Sr/Y and Sm/Dy show a broad positive cor‐ increase towards higher degrees of melt H2O‐ relation (Fig. 7). undersaturation) suggesting that parental melts of intrusions and volcanics of this group under‐ Rare earth element distribution went a significant evolution step at shallow crus‐ tal levels. Prior to their shallow crustal evolution, patterns deeper parental melt evolution in a MASH/hot Four major groups of variable REE distribution zone mostly did not involve significant amphibole patterns can be distinguished for the Late Terti‐ (or garnet) fractionation. The latter condition ary Ecuadorian intrusions and volcanic rocks in‐ might apply for primitive melt evolution in a hot vestigated in this study (Fig. 8; Tab. 3). These zone at the base of a relatively thin crust (or a groups mainly differ in their ways of HREE frac‐ mid‐crustal hot zone in a thicker crust) where tionation and in the occurrence or absence of H2O‐undersaturated parental melts would mainly negative Eu anomalies. The facts that (1) no Ce crystallize pyroxene instead of amphibole anomalies are observed, and (2) the main vari‐ (Müntener et al. 2001). ability in the REE pattern shape lies in the MREE and HREE instead of the LREE (Fig. 8) have been Group 2: REE patterns without nega‐ used elsewhere to argue for the petrogenetic tive Eu anomalies or strong HREE de‐ significance of REE patterns of altered rocks (Kay pletion et al. 2005). This group comprises variably differentiated (52‐ Group 1: REE patterns characterized 71 wt.% SiO2) intrusions (Gaby, Chaucha, Cangre‐ jos, Zaruma) and Saraguro Group volcanics (at by negative Eu anomalies and without Cañicapa and Tres Chorreras) which neither show strong HREE depletion significant negative Eu anomalies nor strongly This group mainly comprises volcanics and phan‐ depleted HREE contents, although slightly con‐ eritic‐porphyritic intrusions in southern Ecuador cave‐upwards MREE‐HREE patterns can be ob‐ (Cangrejos‐Zaruma intrusive belt, El Mozo, Sara‐ served for some samples. Parental melts of this guro Group at Chaucha and Portovelo). Addition‐ group probably share a similar deep‐ to mid‐ ally, few samples of the Apuela and the Balsa‐ crustal evolutionary history with the previous pamba and Telimbela batholiths share the same group in that parental melt evolution at depth characteristics. Rocks of this group uniformly dis‐ was dominated by pyroxene fractionation, al‐ play minor‐moderate negative Eu anomalies in though it might have included minor amphibole

134

Figure 7: Trace element ratios vs. SiO2 contents of investigated samples. Reference fields as in Fig. 6 where applicable.

135 fractionation in some cases where more hydrous mann et al. 2005) such that small amounts melts were involved (e.g., the Portovelo porphyry of amphibole fractionation, or trace intrusions; Fig. 8). Intra‐HREE fractionation due to amounts of titanite fractionation (Bach‐ garnet fractionation cannot be observed in any of mann et al. 2005; Glazner et al. 2008) both these magmas. In contrast to the previous group, succeed in explaining strong HREE deple‐ the absence of negative Eu anomalies is indica‐ tion. HREE fractionation patterns do not tive of the absence of significant plagioclase frac‐ suggest significant garnet fractiona‐ tionation and thus suggests limited shallow tion/restite equilibration (but see below). crustal open‐system magma evolution. Alterna‐ . Negative D anomalies for titanite or am‐ tively, plagioclase fractionation took place in Eu phibole and the resulting positive Eu ano‐ highly oxidized melts where Eu incompatibility for malies in REE patterns may partly offset va‐ plagioclase increases (e.g., Rollinson 1993). riably (depending on the prevailing fO2) negative Eu anomalies imposed on REE pat‐ Group 3: REE patterns with strong terns by plagioclase fractionation; depend‐ HREE depletion and concave‐upwards ing on P‐T conditions, melt composition, to flat HREE distribution and fO2 an integrated fractionating mineral assemblage consisting of plagioclase + am‐ Significant HREE depletion (<10x chondritic val‐ phibole + trace amounts (<1%) of titanite ues) combined with mostly concave‐upwards or can produce relatively smooth MREE pat‐ minor relatively flat HREE patterns is observed for terns without negative Eu anomalies mainly porphyritic, plus some phaneritic intru‐ (Glazner et al. 2008). Smooth LREE‐MREE sions at Chaucha (Gur‐Gur), Balsapamba‐ patterns, and/or positive Eu anomalies Telimbela, and Apuela‐Junin (Fig. 8). All intrusive (which are probably not attributable to rocks of this group are highly differentiated (64‐ plagioclase accumulation in our samples) 73 wt.% SiO ). In several cases strong HREE frac‐ 2 observed for some intrusions of this group tionation coincides with the development of a illustrate this effect (Fig. 8). Minor plagio‐ minor‐moderate positive Eu anomaly. The latter clase fractionation, although it is not obvi‐ samples are characterized by moderate Sr con‐ ously manifested as negative Eu anomalies tents (300‐400 ppm; see discussion below), and in the REE patterns of this group, thus can‐ petrographic studies indicate that they do not not be ruled out for parental melts of intru‐ represent plagioclase cumulates, although modal sions of this group. However, nas show be‐ proportions of plagioclase are relatively high. low, non‐depleted Sr contents of these While individual mineral phases (e.g., amphibole, samples indicate that plagioclase fractiona‐ titanite, plagioclase, garnet, zircon) impose char‐ tion was not significant. acteristic fractionation signatures on REE pat‐ The absence of concave‐upwards MREE‐HREE terns, their integrated (not necessarily concomi‐ patterns characteristic of amphibole (and ti‐ tant) fractionation effects might in part produce tanite) fractionation for some intrusions might mutual offsets of otherwise typical REE character‐ signal minor additional fractionation/restite istics. This might be of relevance for our dataset, equilibration with a HREE‐fractionating residual and the following considerations apply in this mineral with D < D such as garnet (or zircon), context: Dy Yb prior to, or concomitant with amphibole (or ti‐ . The strong HREE depletion displayed by tanite) fractionation. Alonso‐Perez et al. (2009) samples of this group (and, possibly, their show that garnet and amphibole are both the partly positive Eu anomalies) are indicative first liquidus phases in H2O‐rich andesitic melts at of amphibole and/or titanite fractionation high pressures; their modal proportions vary (or equilibration with a restite bearing from garnet‐dominated (at 1.2 GPa) to amphi‐ these minerals; e.g., Davidson et al. 2007). bole‐dominated (at 0.8 GPa). While both minerals Given the highly differentiated sample drive bulk HREE depletion, their integrated frac‐ compositions, liquid‐amphibole HREE parti‐ tionation effects (or restite equilibration) might tion coefficients will be fairly high (Bach‐

136

Figure 8: C1 chondrite‐normalized REE diagrams and primitive mantle‐normalized spidergrams of investigated samples. Note that LILE scatter in spidergrams is an effect of hydrothermal alteration, such that these elements are of limited petrogenetic relevance. Normalization values from Sun & McDonough (1989)

137

Figure 8 (continued) partly mask their characteristic fingerprints on intra‐HREE fractionation (e.g., Dy/Yb). Group 4: REE patterns with strong HREE depletion and a negative HREE Most parental melts of this group of intrusions are thus inferred to have undergone significant slope amphibole (± minor titanite; see below) frac‐ This group, comprising the Quimsacocha volcanic tionation. Additional effects from integrated, center and some Junin porphyry intrusions, is relatively minor plagioclase or garnet fractiona‐ characterized by significant HREE depletion and tion, as well as from pyroxene fractionation (as steadily decreasing MREE/HREE ratios (Fig. 8). the groups above) may be variably superposed Negative Eu anomalies are not observed. A single on the observed patterns, but do not strongly sample of a Balsapamba porphyry intrusion influence REE distribution characteristics. shows similarly strong HREE fractionation, but displays a minor negative Eu anomaly; it is there‐ fore included in group 1 above, but the following considerations might apply for the deep crustal

138 petrogenesis of this sample. Quimsacocha dacites and Y distributions with petrogenetic constraints show flatter bulk REE patterns than Quimsacocha obtained from REE patterns discussed above. andesites implying that they cannot directly rep‐ resent derivative liquids from andesite differen‐ Strontium contents tiation; dacite REE patterns resemble Quimsaco‐ Despite a lack of negative Eu anomalies in the cha andesites, but both LREE/HREE and intra‐ majority of Late Oligocene to Late Miocene intru‐ HREE fractionation is less pronounced. Junin por‐ sions and volcanics suggesting limited plagioclase phyry intrusions show similar EEintra‐HR frac‐ fractionation, whole‐rock Sr contents are mostly tionation as Quimsacocha dacites, but their relatively low: most samples show Sr contents LREE/HREE fractionation is slightly less pro‐ around the 348 ppm value of the average lower nounced; the latter might be an alteration effect crust of Rudnick & Gao (2003) and <410 ppm (av‐ as these samples often show pervasive phyllic erage andesite of Gill 1981); except for Quimsa‐ alteration, in agreement with the general notion cocha, most samples invariably plot below pre‐ that LREE are more mobile in fluids than HREE sent‐day main arc values at a given SiO2 content, (see above and Appendix). and there is a broad bulk increase in Sr concen‐ The strongly fractionated intra‐HREE patterns trations through time (Fig. 9). These low Sr con‐ combined with moderate‐strong LREE/HREE frac‐ tents might reflect source and/or a crustal tionation observed in this group closely resemble magma differentiation effects. Considering the some Quaternary arc volcanoes such as Young former, the highly variable geodynamic regime at Chacana, whose parental melts are inferred to the northern Andean margin in the Late Tertiary evolve through combined amphibole, clinopyrox‐ makes source controls on the Sr budget of arc ene, and garnet fractionation/restite equilibra‐ magmas by processes operating in the mantle tion (Chiaradia et al. 2009a). These minerals may wedge likely (e.g., variable degrees of mantle be stabilized in variably H2O‐rich melts processed wedge contamination/metasomatization, or par‐ in deep to mid‐crustal hot zones (e.g., at 0.8‐1.2 tial melting). These effects cannot be evaluated in GPa; Alonso‐Perez et al. 2009). The similarities in this study, however, as our dataset mainly com‐ REE characteristics between some present‐day prises highly differentiated samples. In the fol‐ NVZ magmas and the Late Miocene Quimsacocha lowing, we therefore focus on discussing crustal and some Junin porphyry magmas suggest that magma differentiation. they might share a similar petrogenesis. In the latter case, slab melting (Beate et al. 2001) would Mid‐ to shallow crustal magma differentiation not be required to explain intra‐HREE fractiona‐ (inside the stability field of plagioclase) tion (and other adakite‐like geochemical fea‐ Low Sr contents of Late Oligocene to Miocene tures) of the Quimsacocha volcanic center. samples can in part be attributed to shallow crus‐ tal magma differentiation following an initial dif‐ Adakite‐like features of Late Ter‐ ferentiation step from mantle‐derived basaltic to andesitic‐dacitic compositions in deep to mid‐ tiary Ecuadorian arc magmas crustal MASH/hot zones. This is the case for a When discussing adakite‐like features, we focus group of Miocene intrusions and volcanics (group in the following on Sr and Y concentrations and 1 in the previous section) characterized by nega‐ the Sr/Y ratio, the latter often representing the tive Eu anomalies indicative of plagioclase frac‐ most distinctive discrimination criteria for ada‐ tionation. Significant Sr depletion by extended kite‐like magmatism at convergent margins (e.g., mid‐ to shallow crustal plagioclase fractionation Tulloch & Kimborough 2003). Furthermore, for might be considered unlikely for a number of the majority of samples in our dataset (see dis‐ Late Oligocene to Mid‐Miocene magmatic cen‐ cussion above and Appendix) the Sr/Y ratio is ters (group 2 in the previous section) unless melts more robust with respect to hydrothermal altera‐ were highly oxidized such that negative Eu tion than other adakite discrimination criteria anomalies were not produced. The latter is pos‐ (e.g., La/Yb). We correlate our observations on Sr sibly supported by broadly similar Sr contents of groups 1 and 2 at similar degrees of differentia‐

139 tion (Tab. 3) despite significant variations in the of the focus of crustal hot zone magmatism (e.g., magnitude of Eu anomalies. Mamani et al. 2010). Overall, Sr contents of group 3 are slightly higher Crustal basement composition than Sr contents of groups 1 and 2 (Tab. 3). Pla‐ gioclase fractionation hence was probably minor Basement (assimilant) composition represents a in parental melts of group 3 intrusions, as also further potential control factor on arc magma Sr supported by theirE RE patterns (Fig. 8). In addi‐ budgets. Mature arc systems (i.e., the Late Mio‐ tion, if parental melts of these intrusions were cene‐Quaternary Ecuadorian arc) include arc in‐ trusive roots which are already enriched in in‐ H2O‐rich, as suggested by the amphibole imprint on their REE patterns, plagioclase might be anor‐ compatible elements and thus have a higher po‐ thite‐rich. As shown by Blundy & Wood (1991), tential to contaminate arc magmas of a given the plagioclase‐melt partitioning coefficient for Sr starting composition in incompatible elements decreases with increasing molar fractions of an‐ than a less mature arc system (i.e., the Oligocene orthite in plagioclase. Consequently, residual to Early Miocene Ecuadorian arc; Hildreth & melt Sr depletion by (minor) plagioclase frac‐ Moorbath 1988; see also Davidson et al. 1987). tionation would be less pronounced. However, while this could drive bulk incompati‐ ble element enrichment in Late Miocene‐ Of further significance might be the tendency of Quaternary arc magmas, it would not explain se‐ plutonic rocks to be slightly depleted in incom‐ lective Sr enrichment. patible elements with respect to cogenetic vol‐ canic rocks (Bachmann et al. 2007). However, this Strontium contents of CCOP units as potential effect should be more pronounced for more in‐ assimilant are generally low (typically 11‐267 compatible elements such as Th or U (compared ppm Sr; e.g., Mamberti et al. 2003) compared to to Sr incompatibility), opposite to what is ob‐ average lower continental crust values (348 ppm served (Fig. 6). Furthermore, volcanic rocks of the Sr; Rudnick & Gao 2003); in contrast, CCOP whole Saraguro Group have similar low Sr contents as rock Sr contents reported by Allibon et al. (2008) coeval intrusive rocks (Fig. 6) such that a system‐ are heterogeneous and extend to significantly atic compositional difference between volcanic higher values (98‐1123 ppm Sr; possibly in part and plutonic rocks is an unlikely cause for the reflecting alteration‐induced increases), such that observed variations in Sr contents. partial melting and mixing of high‐Sr oceanic pla‐ teau lithologies with mantle‐derived arc magmas Deep to mid‐crustal magma differentiation (out‐ in a lower crustal MASH/hot zone might contrib‐ side the stability field of plagioclase) ute to producing derivative liquids with Sr con‐ tents typical for NVZ volcanics (400 to >800 ppm Melts extracted from a MASH/hot zone at the Sr; e.g., Chiaradia et al. 2009a). base of a thick (c. 50 km) crust variably equili‐ brate with mineral phases of basal crustal litholo‐ Significant Late Miocene eastward arc broaden‐ gies, e.g., pyroxene or garnet granulites; crustal ing (Chapter 2) likely added further lithologies as assimilation or mixing with crustal partial melts of potential assimilants at depth (whose geochemi‐ these lithologies results in elevated melt Sr con‐ cal composition is unconstrained, but might be tents and plagioclase‐diminished crustal residues higher in Sr than oceanic plateau units), and fur‐ where the latter effect increases with crustal ther caused arc magmatism to migrate towards thickness (Hildreth & Moorbath 1988). The over‐ the region of maximum crustal thickness in all crustal thickness in Ecuador during the Oligo‐ across‐arc dimension (Jaillard et al. 2005). There‐ cene‐Miocene was lower than at the present day fore, the Late Miocene arc migration might con‐ (Jaillard et al. 2005) such that the bulk increase in tribute to increased Sr contents of NVZ and Sr concentrations from Late Tertiary to Quater‐ Quimsacocha volcanics, relative to Oligocene to nary arc magmas (Fig. 9) might reflect stepwise or Mid‐Miocene Ecuadorian arc magmas. progressive crustal thickening. Additionally, in‐ creasing high‐pressure magma differentiation could also be envisaged by downwards migration

140 Yttrium contents Differentiation effects causing Y depletion Maximum and minimum Y contents of Late Oli‐ Excluding the Late Miocene Quimsacocha ande‐ gocene‐Miocene arc magmas show a broad de‐ sites, all samples characterized by Y <10 ppm rep‐ crease from 24 to 9 Ma (if the El Mozo intrusions resent silicic intrusions (SiO2 >64 wt.%). Mineral are excluded; Fig. 9). Extreme Y depletion phases whose stability field is extended in silicic (<10 ppm) can be observed for parts of the Early melts, and which are highly compatible for Y Miocene Balsapamba‐Telimbela batholith, and comprise amphibole, zircon, and titanite. As the Mid‐ to Late Miocene Chaucha and Apuela‐ noted above, amphibole (as major mineral phase) Junin batholiths. It includes both phaneritic and as well as zircon ±titanite (accessory phases) porphyritic intrusive rock facies, and correlates were observed in all or at least some of the Late with strong HREE depletion (groups 3 and 4 in Oligocene‐Miocene intrusions. Zircon and titanite previous section). Strong Y depletion furthermore are unlikely to saturate in bulk andesitic melts affects the Late Miocene Quimsacocha volcanic (although they might saturate in local melt pock‐ center. ets; Hoskin et al. 2000). While amphibole is stable in H2O‐rich mafic melts and may, in concert with Yttrium depletion in arc magmas has been corre‐ garnet, drive Y depletion in mafic‐intermediate lated with increasing crustal thickness as the lat‐ melts at deep to mid‐crustal levels (e.g., Richards ter favors the stability of minerals with a strong & Kerrich 2007), its partition coefficient for Y is affinity for Y (in particular, garnet; Hildreth & highly sensitive to melt composition and sharply Moorbath 1988; Richards & Kerrich 2007). The increases in silicic melts (Bachmann et al. 2005). broad correlations of Sr, Y, and Sm/Dy distribu‐ Fractionation (or restite equilibration) of these tion trends through time (Fig. 9) are in agreement minerals thus succeeds in explaining the ob‐ with progressively increasingh hig ‐pressure served restriction of strong Y depletion to highly crustal magma differentiation by crustal thicken‐ differentiated compositions. ing. The latter does not apply for Y‐depleted in‐ trusions at Balsapamba‐Telimbela, however, as To illustrate the petrogenetic significance of am‐ the crustal thickness in the Early Miocene was phibole, zircon, and titanite fractionation, some significantly below the present‐day crustal thick‐ exemplary fractionation trends are displayed in ness in Ecuador (Jaillard et al. 2005). Figure 10. Figure 10a illustrates that, starting at a position typical for a relatively mafic rock compo‐ A possible explanation for these compositional sition in our dataset (285 ppm Sr; 19 ppm Y), the anomalies is a more prominent role of accessory gross Sr/Y vs. Y distribution trend of the investi‐ titanite fractionation which might also occur at gated Late Oligocene‐Miocene intrusions and low pressures (see below). Alternatively, the ir‐ volcanics could be entirely described by progres‐ regular geochemical signature of Balsapamba‐ sive amphibole fractionation using a Damphibole/melt Telimbela might be related to anomalies in the value for andesitic melts (Rollinson 1993). How‐ subducting lithosphere such as oceanic fracture ever, using a constant Damphibole/melt value for an zones. The latter may lead to a locally increased andesitic melt requires unrealistically high F val‐ volatile flux into the mantle wedge giving rise to ues (up to 70%) to explain extremely fractionated unusually H2O‐rich arc magmas where amphibole Sr/Y ratios, and therefore should only apply for and garnet stability is increased (e.g., Rodriguez moderate Y depletion (c. 10‐20 ppm Y; note that et al. 2007). While Kay et al. (2005) note that lo‐ the parental melt composition could also start cal peaks in mantle wedge contamination by within this range and subsequently evolve to‐ subduction erosion may also explain the irregular wards higher Y concentrations by fractionating occurrence of adakite‐like arc magmas, this is solely Y‐incompatible minerals such as plagio‐ rather unlikely for Balsapamba‐Telimbela, as LILE clase). anomalies (parallel to Y and HREE depletion) are not observed, and large‐scale subduction erosion Starting from a position corresponding to a more did not affect the Oligocene‐Miocene Ecuadorian silicic rock composition in our dataset (as proxy margin (Chapter 2). for an evolved intrusive parental melt; 335 ppm Sr; 9 ppm Y), and using D values for dacitic‐

141

Figure 9: Trace element and trace element ratio vs. age diagrams. Age‐trace element distribution patterns show sys‐ tematic increases (Sr, Sm/Dy, Sr/Y) or decreases (Y) in Late Oligocene to Late Miocene arc magmas suggesting progres‐ sively increasing high‐pressure magma differentiation (trends marked by yellow arrows). The latter might be caused by crustal thickening, or by the downwards migration of crustal hot zones. Extreme Y and HREE depletion at Balsapamba is a local, anomalous phenomenon, and produces elevated Sr/Y and Sm/Dy ratios in the Early Miocene. Sr depletion for some Junin porphyry intrusions might be caused by shallow crustal plagioclase fractionation or hydrothermal altera‐ tion. Ages estimated from geochronologic constraints summarized in Chapters 2 and 3. NVZ main and frontal arc data from Chiaradia et al. (2009a). See text for discussion. rhyolitic melts (Bachmann et al. 2005), fractional contributions can be discerned when other trace crystallization of small amounts (<10%) of amphi‐ elements are considered. Fractionating only trace bole, or trace amounts (<1%) of either zircon or amounts (<1%) of zircon from a dacitic‐rhyolitic titanite, reproduces the observed extreme Y de‐ melt results in extreme Zr depletion of derivative pletion. Fractionating subequal amounts of pla‐ liquids, which is not observed in our dataset (Fig. gioclase and amphibole in a dacitic‐rhyolitic melt 6). Although compatible in both minerals, titanite results in Y depletion at constant Sr/Y ratios of is characterized by a much lower D value for Sc derivative liquids and might apply for some Junin than amphibole in silicic melts (6 vs. 45: Bach‐ porphyry intrusions (Fig. 10a), although hydro‐ mann et al. 2005; note that pyroxene, although thermal alteration‐driven Sr depletion is more not observed in these intrusions, is also highly probable to explain the distribution of Junin por‐ compatible for Sc, and its presence in hypothetic phyries in the Sr/Y vs. Y space. parental melts cannot be ruled out, as it is com‐ monly reacted out during late stages of intrusion While amphibole, zircon, and titanite fractiona‐ development to form amphibole or biotite; tion in silicic melts affects Sr/Y vs. Y distribution Bachmann et al. 2007). Therefore, if Sr/Y frac‐ trends in a similar way, their potential individual tionation was mainly driven by amphibole frac‐

142 tionation, it should be accompanied by a propor‐ The petrogenetic significance of Sr/Y tionally higher increase in Sr/Sc (as DSc >> DY for ratios for crustal magma evolution amphibole in silicic melts; Bachmann et al. 2005). In contrast, titanite fractionation‐dominated Strong Y depletion at broadly constant Sr con‐ changes in Sr/Y should have a minor effect on tents in the above‐listed Miocene intrusions im‐ Sr/Sc ratios. Figure 10b shows that small amounts plies that Sr/Y ratios of these intrusions are main‐ (<5%) of combined amphibole‐titanite fractiona‐ ly controlled by Y depletion; Sr/Y ratios may in‐ tion (in 95:5 proportions) closely reproduce the crease towards adakite‐like values (Fig. 7) al‐ compositional Sr/Y vs. Sr/Sc range of mostc silici though Sr contents are often <400 ppm (the min‐ intrusions, although a higher proportion of ti‐ imum Sr content inferred for most adakite‐like tanite with respect to amphibole might be re‐ rocks; e.g., Richard & Kerrich 2007). As outlined quired for some intrusions at Balsapamba‐ Telim‐ above, this is mainly due to silicic melt differen‐ bela. Several Saraguro Group volcanics (at Cañi‐ tiation by amphibole ±titanite fractiona‐ capa) are characterized by high Sr/Sc ratios with‐ tion/restite equilibration, although in some cases out a concomitant strong increase in Sr/Y sug‐ Y depletion is also influenced by garnet fractiona‐ gesting Sr/Sc fractionation there was mainly tion/restite equilibration (REE group 4: Quimsa‐ driven by amphibole (or clinopyroxene) fractiona‐ ncocha, Juni porphyries). tion. The latter is in agreement with the scarcely Adakite‐like geochemical features of modern NVZ reported occurrence of titanite in volcanic rocks magmas in Ecuador have been shown to be (Hoskin et al. 2000). mostly the result of crustal magma evolution We hence suggest that extreme Y (and HREE) de‐ (e.g., Chiaradia et al. 2009a). In the latter case, pletion of Miocene Ecuadorian intrusions was high Sr/Y ratios commonly signal high‐pressure mainly driven by amphibole ±titanite fractiona‐ magma differentiation, whereas low Sr/Y ratios tion in hydrous silicic melts. As noted above, sig‐ indicate upper crustal magmatism at low pres‐ nificant plagioclase fractionation is not observed sures (e.g., Tulloch & Kimbrough 2003; Bachmann for these intrusions (mostly REE group 3), such et al. 2005). High Sr/Y ratios (with a threshold that pronounced magma evolution at shallow value of c. 30‐40) in our dataset are associated crustal levels (<0.4 GPa), where plagioclase is with parental melt evolution without significant stable closer to the liquidus than amphibole, is plagioclase fractionation at shallow crustal levels unlikely (e.g., Grove et al. 2003). Deep crustal as inferred from REE distribution patterns (Tab. 3), and correlate positively with Sm/Dy (Fig. 7). In (e.g., at 1.2 GPa) H2O‐rich magma evolution po‐ tentially involves significant garnet fractionation contrast, Sr/Y ratios <30‐40 pool with low Sm/Dy (Alonso‐Perez et al. 2009), which is mostly not ratios reflecting low‐pressure magma differentia‐ observed. Consequently, parental melts to most tion. Miocene intrusions might have dominantly Increasing magma differentiation pressures result evolved at pressures of c. 0.4‐0.8 GPa where am‐ in an increasing relative proportion of garnet in phibole is the dominant liquidus phase (Alonso‐ an amphibole‐garnet liquidus assemblage for Perez et al. 2009). In contrast, Quimsacocha vol‐ H2O‐rich andesitic melts (Alonso‐Perez et al. canics (and several other samples of REE group 4) 2009). As discussed above, considering variable, share many compositional features with Quater‐ melt composition‐dependent partition coeffi‐ nary NVZ magmas, including a prominent garnet cients, extreme Y depletion by amphibole frac‐ signature in their REE patterns (Fig. 8). Conse‐ tionation only applies to relatively silicic melt quently, Y depletion in these magmas was likely compositions, whereas garnet fractionation may driven by combined amphibole and garnet frac‐ produce strong Y depletion in more mafic melts tionation/restite equilibration, possibly at higher already. Late Miocene (e.g., Quimsacocha) or pressures than inferred for most Miocene intru‐ younger arc magmas evolving by combined am‐ sive centers. phibole‐garnet fractionation/restite equilibration may therefore develop towards adakite‐like Sr/Y ratios at less silicic compositions, i.e., during ear‐

143 lier differentiation stages than pre‐Late Miocene ture (Chapter 4) they are shown in separate dia‐ arc magmas (Fig. 7). grams in Figure 11. Trace element concentrations and ratios used as Southern‐central Ecuadorian Sierra intrusions and proxies for increasing high‐pressure magma dif‐ volcanics (“east of CPPF” in Fig. 11) in the south‐ ferentiation (and further modulated by melt wards projection of the NVZ main arc consistently composition and differentiation effects) in Figure display low radiogenic 87Sr/86Sr values at Sr/Y ra‐ 9 show a north‐south division of associated mag‐ tios >30 (Fig. 11). In contrast, magmas in south‐ matic centers: low‐pressure differentiation is ern Ecuador with a significant shallow crustal dif‐ mainly inferred for southern Ecuador (Portovelo‐ ferentiation step (mainly the Cangrejos‐ Zaruma, Cangrejos, Saraguro), whereas high‐ pressure differentiation mostly applies for north‐ ern‐central Ecuador (Quimsacocha, Apuela‐ Junin). We suggest that this is mainly an effect of the spatio‐temporal distribution of arc magma‐ tism in Ecuador; Mid‐ to Late Miocene arc mag‐ matism in southern Ecuador migrated north‐ wards in response to progressive slab flattening, such that arc magmatic exposures in southern Ecuador are biased towards older arc units and, by inference, an overall thinner crust (Chapter 2). However, regional along‐arc differences might additionally apply, as the potential for tectonic crustal thickening may be higher in northern‐ central Ecuador where the paleo‐continental margin is buttressed against the allochthonous oceanic plateau block (e.g., Jaillard et al. 2005). Isotopic constraints on shallow vs. deep crustal magma evolution Figure 11 shows plots of several radiogenic iso‐ tope ratios (see Chapter 4 for isotope references) vs. Sr/Y ratio s; Paleogene intrusions and volcan‐ ics in central‐southern Ecuador (Chiaradia et al. 2004) are shown for reference. As discussed above, Sr/Y ratios in our dataset may, to some extent, discriminate between dominant magma evolution at shallow (usually Sr/Y <30) or mid‐ to deep crustal levels (Sr/Y >30) if significant amphi‐ Figure 10: Sr/Y vs. Y (A) and Sr/Y vs. Sr/Sc (B) distribu‐ bole ±garnet ±titanite fractionation is involved tions of Late Tertiary Ecuadorian granitoids and volcan‐ which is not always the case (e.g., at Gaby). To ics, with theoretical effects of amphibole, titanite, zir‐ account for the latter we additionally report the con, and plagioclase fractional crystallization (FC) using presence of negative Eu anomalies in the legend partition coefficients of Rollinson (1993) for andesitic melts, and Bachmann et al. (2005) for rhyolitic melts. of Figure 11, indicative of significant shallow Tick marks (small white diamonds) on andesitic melt crustal plagioclase fractionation. As Miocene in‐ amphibole fractional crystallization trend correspond trusions emplaced in the northern‐central Ecua‐ to 10% steps in F values. Fractionation curves for am‐ dorian Western Cordillera show significant iso‐ phibole, titanite, and zircon in silicic melts overlap and topic differences to central‐southern Ecuadorian are simplified as one in the diagram; whole curve Sierra intrusions and volcanics reflecting along‐ range corresponds to c. 10% amphibole, and <1% ti‐ and across‐arc differences in basement architec‐ tanite and zircon FC. See text for discussion.

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145 Zaruma intrusive belt and Saraguro Group volcan‐ tamination in arc magmas is a function of the ics; groups 1±2) extend towards higher 87Sr/86Sr compositional and isotopic leverage of potential values, analogous to the Paleogene intrusions assimilants; open‐system magma differentiation and volcanics of Chiaradia et al. (2004). Plotting at the base of the crust may be reflected by only Sr concentrations instead of the Sr/Y ratio (Fig. subtle changes in isotopic compositions of deriva‐ 11) results in the same distribution pattern where tive liquids if the arc position stays stable over a Sr content of c. 300 ppm corresponds to the geologically long periods of time such that evolv‐ threshold value dividing high and low radiogenic ing arc magmas mainly consume arc intrusive maximum 87Sr/86Sr values. This trend is further roots (e.g., Davidson et al. 1987). This is reflected reflected in a Eu/Eu* vs. 87Sr/86Sr plot (Fig. 11) by relatively constant 87Sr/86Sr values for intru‐ where lower Eu/Eu* values (shallow crustal sions and volcanics with Sr/Y >30 (Fig. 11); only magma evolution) again tend to be associated samples with Sr/Y <30 tend to extend to signifi‐ with higher 87Sr/86Sr. cantly higher 87Sr/86Sr values. Note, however, that primitive isotopic ratios of Late Tertiary Ecuador‐ Isotope‐based discrimination between shallow ian arc magmas do not necessarily reflect assimi‐ and mid‐ to deep crustal magma evolution in lation of arc intrusive roots, but might instead or southern‐central Ecuador becomes slightly more additionally also indicate assimilation of oceanic blurred for 143Nd/144Nd, and significantly more plateau units. The latter is clearly visible for blurred for 207Pb/204Pb (Fig. 11), suggesting that Western Cordillera intrusions which show quasi MASH/hot zone‐hosting units in the mid or lower constant 87Sr/86Sr values, but slight to moderate crust have a higher variability in these isotopic variations in their 143Nd/144Nd and 207Pb/204Pb ra‐ ratios. This is mirrored by systematic across‐arc tios, respectively (Fig. 11). trends in 143Nd/144Nd and 207Pb/204Pb possibly re‐ flecting changes in the mid‐ to deep crustal Petrogenesis of Late Tertiary arc basement architecture and composition (Chapter 4). magmas in Ecuador – summary Western Cordillera intrusions (“west of CPPF” in Building on the constraints and caveats pre‐ Fig. 11) do not display systematic isotopic differ‐ sented in the preceding sections, we combined ences for samples with or without negative Eu the available petrologic evidence to qualitatively anomalies and thus, by inference, with or without estimate at which crustal levels Late Oligocene to significant shallow crustal magma evolution. The Miocene Ecuadorian arc magmas acquired their absence of systematic isotopic offsets might indi‐ geochemical and isotopic characteristics (Tab. 3). cate a vertically relatively homogeneous isotopic Variable parental magma evolutionary paths are composition of the crust below the Western Cor‐ reflected by systematic compositional and iso‐ dillera, in agreement with tectonic constraints topic differences in Late Tertiary arc magmatic (e.g., Vallejo et al. 2009). There is a small differ‐ products and allow the distinction of four major ence, however, between the isotopic composi‐ groups. These comprise distinct differentiation tions of the Gaby intrusive center and Western processes in lower to mid‐crustal hot zones, as Cordillera granitoids situated further north well as variable shallow crustal overprinting, and (slightly more radiogenic Sr and less radiogenic are schematically sketched in Figure 12. Nd at Gaby; Fig. 11) potentially indicating along‐ (1) Most intrusions and volcanics characterized arc isotopic differences of oceanic plateau units. by a significant shallow crustal magma evolution Overall, the isotopic compositions of Late Tertiary stage occur in southern‐central Ecuador (Sara‐ intrusions and volcanics in southern Ecuador guro Group volcanics and the Cangrejos‐Zaruma clearly reflect polybaric magma evolution at low‐ intrusive belt) and have Early to Mid‐Miocene er to mid‐, and, variably, upper crustal levels. Up‐ ages (Chapter 2). These lithologies show minor‐ per and lower crustal units of the Western Cordil‐ moderate negative Eu anomalies and variable, lera seem to be of similar isotopic composition relatively high Y and HREE contents (11‐25 ppm Y, such that isotopes fail to illustrate polybaric evo‐ Tab. 3; note, though, that most of these values lution stages there. The visibility of crustal con‐ still qualify as adakite‐like), variable Sr contents

146 Figure 11: Radiogenic Sr, Nd, and Pb isotopic composition vs. Sr/Y (plus Sr and Eu/Eu*) distribution of Late Tertiary Ec‐ uadorian granitoids and volcanics. Plots are divided according to different upper crustal compositions (continental vs. oceanic, i.e., east vs. west of the Calacali‐Pallatanga‐Pujili fault zone, respectively) to better resolve isotopic variations. As discussed in the text, the Sr/Y ratio serves as a proxy to discriminate lower vs. upper crust‐dominated magma evolu‐ tion (threshold value for our dataset = c. 30). Paleogene intrusions and volcanics of Chiaradia et al. (2004) are shown for reference; they consistently overlap with distribution trends of Late Tertiary magmas where significant shallow crustal magma evolution is inferred suggesting a broadly similar petrogenesis. See text for discussion.

147 (228‐459 ppm), and Sr/Y ratios in the range of 13‐ gested by the isotopic compositions of some Late 32. Their composition is consistent with H2O‐ Tertiary magmas (mainly the Cangrejos‐Zaruma undersaturated parental melt evolution at basal intrusive belt), which are significantly more ra‐ to mid‐crustal levels of a relatively thin to mod‐ diogenic than any known isotopic composition of erately thick arc crust in the Late Oligocene to present‐day NVZ magmas (compare Chapter 4), Early Miocene where pyroxene constitutes the in agreement with the inferred continental dominant liquidus phase (e.g., Müntener et al. basement domains of the southern Ecuadorian El 2001), followed by shallow crustal‐dominated Oro block (Litherland et al. 1994). magma evolution involving significant plagioclase (3) A third group of Miocene intrusions, mainly fractionation. While their REE patterns mostly do hosted by the Western Cordillera and its western not show any prominent MREE‐HREE fractiona‐ foothills in northern‐central Ecuador, is charac‐ tion, limited magma evolution under influence of terized by strong Y and HREE depletion (mostly a Y‐fractionating mineral is required to explain with concave‐upwards HREE patterns) and con‐ the variable degrees of Y depletion prior to, or sistently displays either minor‐moderate positive concomitant with plagioclase fractionation. Eu anomalies, or smooth Sm‐Eu‐Gd transitions, (2) A second group of intrusions and volcanics in indicative of amphibole ±titanite fractiona‐ southern Ecuador overlaps with the previous tion/restite equilibration without significant pla‐ group in time and space (often forming part of gioclase or garnet fractionation. Strontium con‐ the same integrated intrusive center), and their tents are in the 300‐600 ppm range. Depending main difference to the previous group is the ab‐ on the degree of Y depletion, Sr/Y ratios range sence of negative Eu anomalies in their REE dis‐ from 31 up to 282 (Tab. 3) and thus qualify as tribution patterns, suggesting the lack of signifi‐ adakite‐like (Fig. 7), although Sr contents are cant shallow crustal plagioclase fractionation, or, mostly below the threshold for adakite‐like com‐ alternatively, indicating highly oxidized melts positions (<400 ppm). Strong Y depletion by am‐ where plagioclase fractionation did not result in phibole ±titanite fractionation occurs in silicic negative Eu anomalies. The lower to mid‐crustal melts where titanite may be stable (Hoskin et al. petrogenesis of these magmas is similar to the 2000) and DY values of amphibole increase sig‐ previous group. At roughly constant Sr and nificantly (e. g., Bachmann et al. 2005). slightly lower Y contents, Sr/Y ratios of this group Crystallization experiments on hydrous andesitic are slightly higher than in the previous group melts show that amphibole is the dominant liq‐ (Tab. 3). uidus phase at moderate crustal depth (e.g., at The integrated vertical magma evolution of these 0.8 GPa corresponding to c. 25 km depth; Alonso‐ groups (1 and 2) is clearly recognizable in Perez et al. 2009). A change from pyroxene‐ to 87Sr/86Sr, and to a lesser extent in 143Nd/144Nd iso‐ amphibole‐dominated magma evolution at depth topic compositions (Fig. 11), and supports the (groups 1 and 2 vs. 3) is commonly associated principal notion of Chiaradia et al. (2009a) that with increasing hot zone depth (e.g., Kay & Mpo‐ isotopic differences between Tertiary and Qua‐ dozis 2002). Additionally, amphibole becomes ternary NVZ magmas (in northern‐central Ecua‐ destabilized towards lower melt H2O contents at dor) are partly controlled by the crustal depth of a given temperature and pressure (e.g., magma evolution. Additionally, our regionally Müntener et al. 2001; Alonso‐Perez et al. 2009). more representative dataset of Late Tertiary Consequently, in addition to reflecting an in‐ magmas allows us to refine this conclusion in two crease in hot zone depth (by crustal thickening or points: (1) the Miocene magma evolution in by downward shifting of the hot zone position(s) southern‐central Ecuador does not always in‐ from mid‐ towards deep crustal levels), the clude significant shallow crustal magma differen‐ change from pyroxene‐ to amphibole‐dominated tiation, although it is common; and (2) the iso‐ magma differentiation between the two arc seg‐ topic composition of the mid‐ to upper (and ments might also be related to overall higher lower?) crust might be regionally heterogeneous melt H2O contents. Whereas crustal thickening and thus can further modulate the observed iso‐ can be considered as a regional‐scale effect, vari‐ topic distribution patterns. The latter is sug‐ ations in melt H2O contents could also apply at a

148

Figure 12: Schematic illustration of transcrustal petrogenesis of Late Oligocene to Mid‐Miocene (left) and Late Miocene to Quaternary (right) Ecuadorian arc magmas. Arc magmas in both periods are generally processed in lower to mid‐ crustal MASH/hot zones (orange bars); crustal thickness, hot zone depth, and melt water contents control the lower crustal petrogenesis in each case and may variably include amphibole ± garnet (± titanite) fractionation or restite equilibration, respectively. Involvement of a subsequent shallow crustal magma evolution step (characterized by pla‐ gioclase fractionation) may depend on multiple regional‐local factors such as magma supply rate and crustal heat anomalies (during batholith construction), or stress field. Adakite‐like arc magmas form by high‐pressure crustal differ‐ entiation of H2O‐rich magmas without subsequent significant low‐pressure differentiation. Additional variations may be caused by compositional changes of mantle wedge‐derived melts invading lower crustal hot zones, in particular since the Late Miocene. The indicated Late Oligocene to Mid‐Miocene crustal thickness is only a rough estimate; the present‐ day 50 ‐70 km thickness is constrained by seismic studies (Guillier et al. 2001). See text for further discussion. rather local scale (e.g., Rodriguez et al. 2007). the lower to mid‐crustal petrogenesis for paren‐ This might partly explain the contrasting lower to tal melts of a given magmatic center. mid‐crustal magmatic evolution at Gaby and (4) A last group comprises Late Miocene intru‐ Balsapamba, where only the latter involves sig‐ sions and volcanics (Junin porphyries and Quim‐ nificant amphibole fractionation or restite equili‐ sacocha) which are characterized by strong HREE bration. Both intrusive systems share a number depletion and negative HREE slopes indicating of similar features which include age (c. 20 Ma; combined amphibole and garnet fractiona‐ Chapter 2), a frontal arc position hosted by the tion/restite equilibration during their petroge‐ same basement lithology (oceanic plateau), and netic evolution (e.g., H O‐rich melts processed in moderately‐highly differentiated compositions 2 a mid‐crustal hot zone at 0.8 GPa; Alonso‐Perez (SiO c. 61‐68 wt.%) where plagioclase and horn‐ 2 et al. 2009). Strontium contents are high at blende constitute the main phenocrysts; these Quimsacocha (448‐858 ppm), but low at Junin broad similarities suggest that local (in addition (<336 ppm), the latter probably influenced by to regional) factors can exert a major control on hydrothermal alteration. Negative Eu anomalies

149 are not present suggesting the absence of signifi‐ cant shallow crustal plagioclase fractionation sub‐ sequent to MASH/hot zone processing of Late Miocene arc magmas. The petrogenetic evolution of Late Miocene arc magmas (group 4) resembles several present‐day NVZ volcanic centers where Chiaradia et al. (2009a) propose that bulk arc compression caus‐ es their parental melts to evolve at deep crustal levels of a thick crust; a similar mechanism might apply to Late Miocene arc magmas in northern‐ central Ecuador. However, while Chiaradia et al. (2009a) propose collision of the Carnegie Ridge with the Ecuadorian margin as the cause for bulk margin compression, the latter can only apply for arc magmas <8 Ma, the maximum age of the in‐ ception of Carnegie Ridge collision (Chapter 3). Furthermore, initial ridge collision took place in northern Ecuador; the ridge axis then progres‐ sively swept southwards along the margin (Chap‐ ter 3). Carnegie Ridge subduction thus cannot have affected the far‐field stress regime of the central Ecuadorian arc in the Late Miocene such that alternative causes of compression are neces‐ sary to explain, for example, pronounced deep crustal magma evolution at the 7 Ma Quimsaco‐ cha volcanic center in central Ecuador. The latter could be related to local compression in a region‐ ally restraining bend structural setting associated with oblique plate convergence at the Ecuadorian margin (Chapter 2). Alternatively, compression might not always be required to cause pro‐ nounced magma evolution at mid‐ to deep crustal levels.

Figure 13: Sr/Y vs. Y distribution of Late Tertiary por‐ phyry intrusions and spatially associated host intrusive units in Ecuador. Except for the Cangrejos porphyry intrusions, all porphyries lack petrogenetic evidence for shallow crustal plagioclase fractionation. Amphi‐ bole ±titanite ±garnet fractionation/restite equilibra‐ tion at mid‐crustal levels drives some porphyry paren‐ tal melts towards adakite‐like compositions. Mid‐ crustal magma evolution towards the end of magmatic cycles of batholith construction seems to represent a metallogenically favorable environment whereas intense shallow crustal magmatism during batholith peak assembly may be less favorable to form and preserve porphyry‐related mineralization. Overall, the occurrence of adakite‐like features in porphyry intrusions follows the regional compositional characteristics of arc magmatism at a given time. If present, trace element compositional differences between porphyries and associated host intrusions are associated with regional arc magmatic trends through time. Intrusive ages from Chapters 2 and 3, and references therein. See text for further discussion.

150

Significance of adakite‐like fea‐ sociated precursor intrusions in Sr/Y vs. Y dia‐ grams for all five major porphyry systems (Junin, tures for Late Oligocene to Late Balsapamba‐Telimbela, Chaucha, Gaby, Cangre‐ Miocene porphyry‐related min‐ jos) investigated in this study (Fig. 13). Porphyry stocks at Junin, Balsapamba‐Telimbela, and eralization in Ecuador Chaucha are characterized by adakite‐like signa‐ A spatial association of adakite‐like magma com‐ tures, whereas Gaby and Cangrejos are not (Fig. positions and porphyry‐related mineralization has 13). At the individual deposit scale, the occur‐ been observed in a number of studies of circum‐ rence of adakite‐like magmatism seems to be Pacific subduction‐related ore deposits (e.g., broadly temporally controlled (see Chapters 2 Thiéblemont et al. 1997; see Richards & Kerrich and 3 for age references): there is a shift towards 2007 for a comprehensive summary and an adakite‐like magma compositions at Junin (from evaluation of metallogenic implications). Petro‐ >15 Ma to 13‐6 Ma; note that Sr contents of genetic controls for the development of adakite‐ Junin porphyries might have been lowered by like features in Late Tertiary Ecuadorian arc hydrothermal alteration such that these intru‐ magmas have been discussed above and com‐ sions would originally plot at higher Sr/Y ratios), prise a combination of regional‐scale (hot zone at Telimbela (from c. 26 Ma to 20 Ma), and at depth, total crustal thickness) to local‐scale (melt Chaucha (from 15 to 10 Ma). In contrast, no sys‐ tematic shifts are recorded at Gaby and Cangre‐ H2O contents, differentiation effects in silicic magmas including accessory phases) factors. As jos (always low Sr/Y) and Balsapamba (always noted above, adakite‐like features (Sr/Y ratios high Sr/Y) where the intrusive evolution spans a >30‐40) in our dataset indicate the absence of relatively short time range of <2 m.y. (note that extensive shallow crustal plagioclase fractiona‐ Balsapamba batholith growth comprises a signifi‐ tion, and the fractionation (or restite equilibra‐ cantly longer time span, but geochemical data for tion) of amphibole ±garnet ±titanite at higher older intrusive pulses are not available). pressure or at relatively high melt H2O contents. The distribution of adakite‐ like features of Late As such, the above‐mentioned observation of Tertiary porphyry systems along the Ecuadorian adakite‐like magmatism associated with por‐ margin demonstrates that porphyry‐related min‐ phyry‐related mineralization would imply that eralization is not exclusively associated with a pronounced deep to mid‐crustal H2O‐rich melt specific geochemical signature or a specific path equilibration with mainly amphibole, and the ab‐ of crustal magma evolution in Ecuador; any arc sence of a pronounced shallow crustal magma magma may potentially form porphyry‐related evolution step generated favorable conditions for mineralization in a favorable tectonomagmatic subsequent porphyry‐related mineralization from setting. The spatiotemporal distribution of ada‐ fluids exsolved from these melts at somewhat kite‐like features in Ecuadorian porphyry intru‐ shallower depth. The latter has been demon‐ sions largely reflects regional temporal trends in strated at the Late Miocene‐Pliocene Tampakan arc magma geochemistry. In addition, the con‐ porphyry Cu/epithermal high sulfidation Cu‐Au trasting chemical signatures (adakite‐like vs. non‐ ore deposit district (Mindanao, Philippines) adakitic) do not show any first‐order basement where parental melt evolution involves pro‐ control, as intrusions and porphyry systems of nounced amphibole fractionation at moderate both groups are mainly hosted by oceanic pla‐ crustal depth (0.5‐0.6 GPa) whereupon the melt teau units or Tertiary arc volcanics and granitoids. becomes enriched in H2O (and Cl); the latter re‐ Only the Cangrejos igneous complex and the as‐ sults in earlier, i.e., higher pressure volatile satu‐ sociated porphyry system show isotopic evidence ration of subsequently ascending melt batches of significant magma contamination by continen‐ where exsolved fluids are highly saline and Cu‐ tal crust (Chapter 4). There are a number of rich (Rohrlach & Loucks 2005). broadly applicable systematic distribution criteria To test the significance of this association for Late between the various porphyry systems: Tertiary Ecuadorian porphyry systems, we plotted . If Balsapamba‐Telimbela is excluded, Sr/Y the compositions of porphyry intrusions and as‐ ratios tend to become broadly higher with

151 decreasing intrusive age on a regional scale underrepresentation of long‐lived shallow crustal (influencing the age distribution systemat‐ magmatic systems directly associated with por‐ ics at the deposit scale as noted above). phyry intrusions might relate to (1) lower H2O solubilities of melts stalled at lower pressures . Porphyry systems in Figure 13 are arranged such that less parental melt preconditioning by from north to south; bulk Sr/Y ratios of volatile enrichment takes place; for a given melt porphyry intrusions tend to become higher volume, the overall potential volume of exsolved towards the north. If the anomalous occur‐ fluid focused in space and time, and thus the size rence of adakite‐like features at Balsa‐ of the porphyry‐related hydrothermal system, pamba‐Telimbela is excluded, however, the would then decrease; (2) volatile loss to the sur‐ north‐south trend corresponds to a pro‐ face by volcanism, and fluid dissipation instead of gressively increasing age distribution, con‐ focused flow; (3) destruction of shallow crustal sistent with the previous point. mineralization by later intrusive pulses. As such, . Except for Cangrejos, porphyry intrusions adakite‐like compositions of porphyry intrusions lack negative Eu anomalies indicating the might signal favorable tectonomagmatic precon‐ absence of significant shallow crustal pla‐ ditioning of porphyry parental melts for subse‐ gioclase fractionation. quent intrusion‐related mineralization. . All porphyry systems characterized by high The observed mutual exclusivity of Cu‐Mo and Sr/Y ratios (Junin, Balsapamba, Telimbela, Au‐Cu porphyry systems with or without adakite‐ Chaucha) represent Cu‐Mo porphyry de‐ like magma compositions, respectively, may be posits (Prodeminca 2000), whereas Au‐Cu an apparent one, as adakite‐like features are as‐ porphyry systems (Gaby, Cangrejos) show sociated with Au‐Cu or Cu‐Au por‐ low Sr/Y ratios. phyry/epithermal mineralization elsewhere (e.g., The geochemical composition of most porphyry Rohrlach & Loucks 2005; Chiaradia et al., 2009b). intrusions points to the absence of significant However, it t migh indicate that deep to mid‐ shallow crustal magma evolution of their parental crustal magma evolution and the inferred con‐ melts; where porphyry intrusions are associated comitant volatile enrichment (and its bearing on with larger intrusive complexes, porphyry em‐ the relative timing of volatile saturation and fluid placement is late with respect to batholith con‐ exsolution depth) of porphyry parental melts may struction (Chapters 2, 3). Peaking of the latter is be particularly important for the Cu‐Mo budget commonly associated with high magma supply of a given porphyry system, whereas additional rates and might have allowed establishment of factors influence its Au budget. The significance large shallow crustal magma chambers involving of magma chemistry for the total tonnage of a major plagioclase fractionation (e.g., Bachmann given ore deposit in Ecuador cannot be accurately et al. 2005, 2007). Dwindling magma supply rates evaluated as the Late Tertiary porphyry systems might eventually cause a downwards collapse of are variably deeply eroded such that their current the focus of magmatism towards greater depth tonnage does not necessarily reflect the initial (pressure) where amphibole is stable closer to deposit size (Prodeminca 2000). the liquidus than plagioclase (e.g., Grove et al. 2003); magma subsequently intruding into the Conclusions shallow crust cools rapidly below its solidus with‐ The overall spatio‐temporal distribution of ada‐ out significant further differentiation (e.g., Annen kite‐like features in Late Tertiary Ecuadorian arc et al. 2006). As discussed by Rohrlach & Loucks magmas is semi‐systematic; magmatic centers (2005), progressive melt volatile enrichment by characterized by (partly) adakite‐like magmatism magma evolution (and replenishment) at moder‐ are mainly hosted by the Western Cordillera in ate pressure favorably influences fluid exsolution northern‐central Ecuador and comprise Balsa‐ kinetics (and pressure‐dependent melt‐fluid par‐ pamba (c. 21 Ma), Apuela‐Junin (13‐6 Ma), Chau‐ titioning of Cl as a major Cu complexing agent) of cha (c. 10 Ma), and Quimsacocha (7 Ma). Adakite‐ subsequently ascending melt batches with re‐ like features (high Sr/Y) of Late Tertiary Ecuador‐ spect to porphyry‐related mineralization. The

152 ian arc magmas are mainly due to strong Y and porphyry parental melts to evolve towards ada‐ heavy REE depletion of their parental melts at kite‐like compositions (e.g., at Junin and Chau‐ broadly constant Sr contents, and are related to cha) indicative of downward migration of the fo‐ fractionation/restite equilibration effects of am‐ cus of crustal magma evolution towards greater phibole, garnet, and titanite. depth and/or increasing melt H2O contents. While this may reflect favorable tectono‐ In the Early to Mid‐Miocene, amphibole (± acces‐ magmatic preconditioning of porphyry parental sory titanite) is the most important mineral phase melts, it is important to note that these composi‐ for controlling Y and HREE depletion in silicic arc tional changes are of a regional arc magmatic magmas and thus their evolution towards ada‐ scale, and broadly controlled by the relative age kite‐like features in Ecuador, either by fractiona‐ difference between porphyry and host intrusions. tion, or equilibration with an amphibole‐bearing Systematic compositional changes between por‐ restite. The onset of Y and heavy REE depletion phyry and precursor intrusions are not recorded by garnet fractionation/restite equilibration (in if the time difference between their respective concert with amphibole) seems to be restricted emplacement events is small (<2 m.y.). In the lat‐ to the Late Miocene and continues to the present ter case, magmas may be both of adakite‐like day. While strong Y depletion by amphibole frac‐ (Balsapamba) or non‐adakitic affinity (Gaby, Can‐ tionation/restite equilibration is particularly effi‐ grejos). The fact that porphyry‐related minerali‐ cient in silicic melts, Y depletion by garnet frac‐ zation in Ecuador spans the whole Late Oligocene tionation/restite equilibration is also efficient in to Late Miocene (24‐6 Ma) over a large latitudinal mafic melts and allows Late Miocene and range (c. 0° to 3°30’S) supports the notion that younger arc magmas to acquire adakite‐like com‐ any arc magma of a sufficient volume has the po‐ positions already at somewhat earlier differentia‐ tential to form porphyry‐related mineralization. tion stages than Late Oligocene to Mid‐Miocene Porphyry‐related ore deposits in Ecuador may magmas. Shallow crustal plagioclase fractionation comprise multiple intrusive phases (Chapters 2, affects some, but not all Late Tertiary arc mag‐ 3), eand mor detailed studies are necessary to mas in southern Ecuador; it is of minor petroge‐ better resolve individual deposit‐scale geochemi‐ netic significance for Miocene intrusions of the cal trends and their significance for mineraliza‐ Western Cordillera in northern‐central Ecuador. A tion. preferential association of adakite‐like features with a specific basement lithology cannot be ob‐ served. Systematic trace element variations (Sr, Y, REE) References through time are indicative of progressively in‐ Allibon, J., Monjoie, P., Lapierre, H., Jaillard, E., Bussy, creasing high‐pressure crustal magma differentia‐ F., Bosch, D., Senebier, F. (2008): The contribution of tion. While increasing crustal thickness favorably the young Cretaceous Caribbean Oceanic Plateau to influences the occurrence of adakite‐like fea‐ the genesis of late Cretaceous arc magmatism in the tures, the latter are further modulated by a set of Cordillera Occidental of Ecuador. Journal of South parameters which dynamically control mineral American Earth Sciences 26; 355‐368. stabilities and mineral‐melt partitioning coeffi‐ Alonso‐Perez, R., Müntener, O., Ulmer, P. (2009): Ig‐ cients. These include magma evolution depth neous garnet and amphibole fractionation in the roots (pressure) in a given crustal column and melt of island arcs: experimental constraints on andesitic composition, the latter comprising the degree of liquids. Contributions to Mineralogy and Petrology differentiation and melt H2O contents; these ad‐ 157; 541‐558. ditional controls may operate at a regional or lo‐ Amortegui, A. E. (2007): Nature et évolution méta‐ cal scale. morphique des terrains océaniques en Equateur; con‐ séquences possibles sur la genèse des magmas adaki‐ For porphyry‐related ore deposits where multi‐ tiques. PhD thesis, Université Joseph Fourier; 194 p. m.y. precursor magmatism occurs at the same site, and porphyry emplacement represents the Annen, C., Blundy, J. D., Sparks, R. S. J. (2006): The last major intrusive event, we note a tendency of genesis of intermediate and silicic magmas in deep crustal hot zones. Journal of Petrology 47; 505‐539.

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156 2005). Therefore, for a study of geochemical fea‐ Appendix I – Rock alteration and tures of rocks subject to hydrothermal alteration element mobility in porphyry‐ such as ours it is useful to first evaluate element mobility during hydrothermal alteration stages related hydrothermal systems and the resulting changes in rock geochemistry to Porphyry‐related ore deposits typically comprise define the degree to which elements can be used multiple intrusive bodies of variable geometry as reliable tracers for petrogenetic processes. such as cylindrical stocks (commonly <1 km di‐ While it is generally accepted that the group of ameter, but several km in length), dikes, or large ion lithophile elements (LILE) and, to a less‐ domes (Seedorff et al. 2005). The intrusive bodies er extent, light rare earth elements (LREE), are act as focal points for the flow of metal‐bearing readily transportable by fluids, whereas high field magmatic fluids exsolved from aa magm chamber strength elements (HFSE) and mid to heavy rare situated at greater depth (Sillitoe 1973). These earth elements (M/HREEE) tend to be fluid‐ fluids generate hydrothermal alteration of vari‐ immobile, detailed geochemical studies of al‐ able intensity both inside the porphyry body and tered rocks show that HFSE and M/HREE can also in a significantly larger aureole surrounding the be mobilized to significant extents under certain intrusion. Fluid evolution by fluid ascent, cooling, conditions (e.g., Lesher et al. 1985; Fulignati et al. mixing with external (mainly meteoric) fluids and 1999; Polat & Hofmann 2003; Verma et al. 2005; fluid‐wall rock equilibration dictates its chemical Shikazono et al. 2008). character and the resulting type of hydrothermal We tested the compositional scatter caused by alteration (Seedorff et al. 2005). Typical altera‐ hydrothermal alteration for a number of litholo‐ tion zones associated with porphyry Cu deposits gies where multiple samples of the same lithol‐ comprise sodic‐calcic and potassic alteration at ogy are available (Apuela‐Cuellaje, Balsapamba depth, giving way to phyllic and argillic alteration and Gaby intrusions; Saraguro volcanics at Por‐ at higher or more distant levels, and grading into tovelo) by calculating isocons based on least‐ propylitic alteration in the peripheral parts of the altered samples of each lithology (Grant 1986). At porphyry system. Fluid phase separation into co‐ Gaby, samples comprise two different porphyry existing vapor and brine phases additionally re‐ intrusions which are compositionally indistin‐ sults in concomitant advanced argillic alteration guishable, such that they may be treated as one by the ascending vapor in the uppermost part of for evaluating alteration‐induced compositional the porphyry system. Similar alteration zones ex‐ changes. Isocon slopes are calculated from Al2O3 ist in epithermal deposits. A collapse of the fluid contents of least‐altered versus altered samples, flow pattern driven by decreasing temperatures as this oxide consistently shows constant con‐ and fluid supply rates can promote overprinting tents irrespective of style and intensity of altera‐ of the different alteration types. For a compre‐ tion, attesting to its immobile nature. We limit hensive summary on mineral assemblages asso‐ isocon calculations to major element oxides and a ciated with these different types of alteration see number of trace elements serving as important Seedorff et al. (2005). tracers for certain petrogenetic processes. Some Hydrothermal alteration produces metasomatic mineralogical features of variably altered samples changes of magmatic rock compositions (e.g., are exemplified in Fig. 2; isocon plots are shown Ulrich & Heinrich 2002). As hydrothermal altera‐ in Fig. 3, and a complete overview table where tion is inevitable in a porphyry environment, the relative, isocon‐based compositional changes sampling for our study focused on “least altered are quantified can be found in Table A2. samples” which are supposed to be closest to Compositional scatter between samples of a original magmatic compositions. In this context, given lithology only becomes statistically signifi‐ this term has a relative meaning, depending on cant at relative differences exceeding 10% corre‐ the local alteration style and intensity, such that sponding to the analytical precision of trace ele‐ alteration‐induced compositional changes in ment analysis. To account for the intense altera‐ samples labeled as “least‐altered” cannot neces‐ tion typically associated with porphyry systems, sarily be predicted with confidence (Giffkins et al. we double this value and define a 20% relative

157 scatter in element contents of the same lithology Giffkins, C., Herrmann, W., Large, R. (2005): Altered as acceptable, while regarding elements consis‐ volcanic rocks: a guide to description and interpreta‐ tently showing higher scatter as unreliable to tion. Centre for Ore Deposit Research Publication, characterize magmatic processes. Using this clas‐ University of Tasmania; 275 p. sification scheme, we find the element behavior Grant, J. A. (1986): The isocon diagram – a simple solu‐ patterns listed in Table 2 which we assume as tion to Gresens' equation for metasomatic alteration. representative for our whole dataset. Elements Economic Geology 81; 1976‐1982. of the LILE (Cs, Rb, Ba, K) and REE (especially Lesher, C. M., Goodwin, A. M., Campbell, I. H., Gorton, LREE) groups show alteration‐induced scatter M. P. (1986): Trace‐element geochemistry of ore‐ beyond acceptable means and are thus inappro‐ associated and barren, felsic metavolcanic rocks in the priate to constrain petrogenetic processes. This Superior Province, Canada. Canadian Journal of Earth inhibits usage of crustal contamination‐sensitive Sciences 23; 222‐237. incompatible element ratios such as Rb/K, as well Polat, A. & Hofmann, A. W. (2003): Alteration and as La/Yb as an overall indicator of REE fractiona‐ geochemical patterns in the 3.7‐3.8 Ga Isua green‐ tion. stone belt, West Greenland. Precambrian Research 126; 197‐218. Strontium, though part of the LILE group, shows acceptable scatter and its concentrations are Seedorff, E., and seven others (2005): Porphyry depos‐ its: characteristics and origin of hypogene features. therefore considered as petrogenetically signifi‐ th cant. The relative immobility of Sr in most sam‐ Economic Geology 100 Anniversary Volume; 251‐ 298. ples is likely an effect of avoiding intense feldspar phenocryst‐destructive alteration types during Shikazono, N. and six others (2008): Geochemical be‐ sampling, although potential alteration of small haviour of rare earth elements in hydrothermally al‐ feldspar crystals in the submicroscopic porphyry tered rocks of the Kuroko mining area, Japan. Journal matrix cannot be evaluated. Biotite constitutes a of Geochemical Exploration 98; 65‐79. dominant mineral in potassic alteration assem‐ Sillitoe, R. H. (1973): The tops and bottoms of por‐ blages in Ecuador; substitution of biotite‐hosted phyry copper deposits. Economic Geology 68;9 79 ‐ interstitial‐site K with Rb, Cs and Ba, but not Sr 815. (Deer et al. 1992) is consistent with the inferred Ulrich, T. & Heinrich, C. A. (2002): Geology and altera‐ high mobility of these elements compared to the tion geochemistry of the porphyry Cu‐Au deposit at relative immobility of Sr in our samples. Chemi‐ Bajo de la Alumbrera, Argentina. Economic Geology cally correlated behavior of MREE and HREE in 97; 1865‐1888. altered rocks suggests that element ratios based Verma, S. P., Torres‐Alvarado, I. S., Satir, M., Dobson, on these groups (e.g., Sm/Dy, Dy/Yb) are rela‐ P. F. (2005): Hydrothermal alteration effects in geo‐ tively non‐susceptible to alteration. Several major chemistry dan Sr, Nd, Pb, and O isotopes of magmas elements and the HFSE show only minor to mod‐ from the Los Azufres geothermal field (Mexico): a sta‐ erate variations for rocks affected by the various tistical approach. Geochemical Journal 39; 141‐163. alteration types listed in Table 2, such that their concentrations in hydrothermally altered rocks largely reflect magmatic processes. References Deer, W. A., Howie, R. A., Zussman, J. (1993): An in‐ troduction to the rock‐forming minerals. Pera‐ son/Prentice Hall, Harlow, England; 696 p. Fulignati, P., Gioncada, A., Sbrana, A. (1999): Rare‐ earth element (REE) behaviour in the alteration facies of the active magmatic‐hydrothermal system of Vul‐ cano (Aeolian Islands, Italy). Journal of Volcanology and Geothermal Research 88; 325‐342.

158 Appendix II – Data tables

Table A1 (next 15 pages): Concentrations of major and trace elements of Late Tertiary magmatic centers. Analyzed elements not described/discussed in Chapter 5 (mostly metals and S) are listed at the end of the table. Analyses of several basement units, xenoliths, and the Late Cretaceous Curiplaya porphyry in‐ trusions which were carried out in the frame of this PhD project are shown for comparison, but are not discussed in the text.

Mineral abbreviations used throughout Table A1: qtz ‐ quartz, plag ‐ plagioclase, fsp ‐ feldspar, hbl ‐ horn‐ blende. Other abbreviations: CCOP ‐ Caribbean‐Colombian oceanic plateau; XRF analysis: Rho. ‐ Rhodes pro‐ gram; tr. ‐ standarde trac element program. All analyses performed at the University of Lausanne.

Tab. A2: Relative changes in concentration compared to least‐altered reference sample concentration calculated from Grant (1986); isocon constructed assuming constant mass of Al2O3

159

Table A1 (continued) Sample Method E05129 E06209 E07034 E06200 E06202 E06205A E06206A E06206B Location Apuela batholith at Junin Apuela batholith at Cuellaje

Lithology granodiorite granodiorite qtz-diorite granodiorite granodiorite granodiorite granodiorite granodiorite

SiO2 XRF 69.52 68.27 64.38 66.22 65.69 66.49 66.67 68.12 TiO2 XRF 0.41 0.41 0.54 0.41 0.44 0.40 0.43 0.39 Al2O3 XRF 14.87 15.57 16.31 16.58 16.55 16.21 16.10 15.43 Fe2O3 XRF 3.82 4.37 5.97 3.60 3.73 3.63 3.81 3.39 MnO XRF 0.02 0.04 0.04 0.04 0.05 0.06 0.06 0.05 MgO XRF 1.58 1.70 2.31 1.69 1.89 1.86 1.85 1.62 CaO XRF 1.67 3.07 3.46 3.99 4.37 4.26 4.14 3.60 Na2O XRF 3.05 3.52 3.10 4.42 4.44 4.50 4.49 4.42 K2O XRF 3.34 2.53 1.97 1.46 1.50 1.71 1.55 1.69 P2O5 XRF 0.10 0.10 0.13 0.14 0.14 0.13 0.14 0.13 LOI XRF 1.21 0.81 0.98 1.19 0.51 0.38 0.32 0.30 Total XRF 99.6 100.4 99.2 99.7 99.3 99.6 99.6 99.2 Nb ICP-MS 2.6 2.4 2.5 2.6 Ta ICP-MS 0.22 0.16 0.14 0.15 Zr ICP-MS 104 79 71 82 Y XRF-Rho. 14 14 14 5.9 7.5 6.9 7.1 7.4 Hf ICP-MS 3.0 2.1 2.0 2.2 Cs ICP-MS 3.7 1.8 1.2 1.0 Rb ICP-MS 50 29 25 28 Ba ICP-MS 211 1406 479 654 Sr XRF-Rho. 246 289 331 563 577 549 555 489 Pb XRF-Rho. <2 4 3 <2 2 4 3 4 U ICP-MS 1.7 1.0 0.78 0.84 Th ICP-MS 3.9 1.7 1.5 2.3 La ICP-MS 13 8.5 9.1 11 Ce ICP-MS 25 17 18 20 Pr ICP-MS 2.9 2.0 2.2 2.4 Nd ICP-MS 12 9.0 9.7 10 Sm ICP-MS 2.6 1.9 1.9 2.0 Eu ICP-MS 0.61 0.55 0.53 0.60 Gd ICP-MS 2.2 1.5 1.5 2.0 Tb ICP-MS 0.36 0.17 0.21 0.25 Dy ICP-MS 2.1 0.91 1.31 1.2 Ho ICP-MS 0.39 0.19 0.24 0.22 Er ICP-MS 1.4 0.47 0.69 0.74 Tm ICP-MS 0.22 0.06 0.09 0.10 Yb ICP-MS 1.3 0.52 0.62 0.82 Lu ICP-MS 0.23 0.09 0.10 0.09 Sc ICP-MS 15 8 9 9 V XRF-Rho. 84 87 126 81 84 70 81 69 Cr XRF-Rho. 18 22 29 27 28 26 40 30 Co ICP-MS 12 8.5 9.8 9.5 Ni ICP-MS 11 13 18 16 Cu XRF-tr. 176 12 191 36 8 2 63 10 Zn XRF-Rho. 28 29 46 38 38 47 54 52 Ga XRF-Rho. 14 15 18 18 18 19 19 18 As XRF-tr. <3 4 4 <3 <3 <3 4 4 Mo ICP-MS 2.1 0.47 0.36 0.31 Ag ICP-MS 0.27 <0.10 <0.06 0.08 Sn ICP-MS 1.9 0.84 Sb ICP-MS 1.0 0.32 0.16 0.17 W ICP-MS 1.1 3.0 S XRF-tr. <3 12 288 329 23 107 104 8

160

Table A1 (continued) Sample E05120 E05127 E06183 E06211 E07032 E06186 E06197 E07035 E06127 E06130 Location Junin porphyry intrusions Balsapamba ba- tholith Lithology granodioritic granodioritic granodioritic granodioritic granodioritic fsp-qtz fsp-qtz porphyritic tonalite tonalite porphyry porphyry porphyry porphyry porphyry porpyhry porphyry microdiorite

SiO2 69.30 70.45 69.13 68.66 70.36 70.84 70.22 67.16 67.53 67.54 TiO2 0.23 0.24 0.22 0.33 0.25 0.24 0.20 0.43 0.39 0.38

Al2O3 16.26 15.94 16.70 16.33 16.54 16.01 17.02 16.75 16.53 16.48 Fe2O3 1.32 1.74 2.35 2.93 2.32 2.09 1.92 3.31 3.77 4.01 MnO 0.00 0.02 0.01 0.02 0.02 0.02 0.00 0.03 0.05 0.05 MgO 0.51 0.76 0.82 1.15 0.74 0.72 0.65 1.25 1.52 1.52 CaO 0.17 0.72 0.21 0.39 0.43 0.45 0.10 2.28 4.72 4.67 Na2O 3.39 5.69 4.00 4.67 5.07 5.61 2.80 3.63 3.89 3.83

K2O 5.77 2.91 3.39 3.99 3.44 2.74 5.15 2.85 1.05 1.17 P2O5 0.09 0.10 0.02 0.12 0.10 0.09 0.06 0.13 0.12 0.11 LOI 1.24 0.95 2.33 1.39 1.00 1.32 1.80 1.42 0.41 0.29 Total 98.3 99.5 99.2 100.0 100.3 100.1 99.9 99.2 100.0 100.0 Nb 0.7 1.7 1.8 1.4 1.8 0.7 1.7 2.7 2.0 Ta 0.06 0.13 0.10 0.09 0.12 0.04 0.08 0.22 0.13 Zr 50 68 74 63 71 53 65 61 51 Y 2.4 3.9 6.1 4.4 3.9 4.1 2.4 4.3 6.5 6.9 Hf 1.4 1.9 1.8 1.6 2.0 1.5 1.9 1.7 1.6 Cs 0.4 1.4 0.9 0.9 0.7 0.3 2.6 1.5 1.1 Rb 46 40 51 44 38 55 36 19 18 Ba 620 636 624 836 543 376 1346 222 290 Sr 129 336 210 218 297 298 87 291 402 396 Pb <2 <2 <2 <2 2 3 <2 3 3 3 U 0.46 0.70 0.88 0.51 0.48 0.45 0.38 0.40 0.58 Th 0.34 0.82 0.98 0.75 0.95 0.55 0.57 1.1 1.3 La 1.8 5.9 8.1 6.7 7.2 2.6 6.7 7.5 7.5 Ce 3.9 12 17 14 15 4.9 14 15 15 Pr 0.5 1.6 2.0 1.7 1.8 0.6 1.8 1.8 1.7 Nd 2.2 7.1 8.7 7.4 8.0 2.3 8.6 7.8 8.0 Sm 0.34 1.4 1.9 1.3 1.3 0.51 1.7 1.7 1.9 Eu 0.13 0.35 0.63 0.38 0.49 0.13 0.47 0.56 0.60 Gd 0.36 1.4 1.2 1.1 1.2 0.33 1.4 1.4 1.4 Tb 0.04 0.15 0.16 0.13 0.14 0.05 0.11 0.19 0.26 Dy 0.35 0.81 0.71 0.70 0.82 0.26 0.82 1.1 1.1 Ho 0.07 0.19 0.14 0.11 0.13 0.06 0.14 0.23 0.20 Er 0.16 0.41 0.36 0.26 0.36 0.19 0.38 0.62 0.69 Tm 0.04 0.07 0.04 0.05 0.04 0.04 0.06 0.09 0.09 Yb 0.18 0.43 0.24 0.41 0.48 0.24 0.33 0.59 0.65 Lu 0.02 0.06 0.05 0.05 0.06 0.06 0.04 0.09 0.10 Sc 2 5 5 4 5 3 6 8 8 V 36 46 37 56 40 43 50 80 68 65 Cr <2 7 7 5 5 6 3 16 12 15 Co 1.3 3.1 6.5 4.5 6.5 4.9 6.7 5.6 Ni 1.3 4.4 6.9 2.7 5.3 2.4 6.1 6.5 5.2 Cu 3536 357 370 617 127 291 775 22 62 20 Zn 20 26 28 86 22 29 12 41 38 39 Ga 18 17 18 18 18 18 20 20 17 17 As 3 <3 19 6 3 18 5 5 <3 3 Mo 64 6.3 2.0 0.54 1.2 7.7 0.35 1.3 0.45 Ag 0.43 0.38 0.23 0.15 0.22 0.16 <0.09 <0.10 <0.12 Sn 1.7 1.9 Sb 0.32 0.47 0.52 0.28 0.62 0.42 0.67 <0.12 <0.08 W 8.5 4.0 4.8 6.9 10 0.35 0.48 S 1025 22 5 458 35 938 568 88 222 82

161

Table A1 (continued) Sample E06140 E06144A E06136 E06139 E06138 E06131A E06132 E06135 E06141 E06134 Balsapamba batholith Balsapamba porphyry intrusions

Lithology tonalite tonalite tonalite tonalite qtz-diorite qtz-diorite qtz-diorite qtz-diorite qtz-diorite qtz-diorite porphyry porphyry porphyry porphyry porphyry

SiO2 66.26 65.68 67.65 67.85 62.02 66.06 65.62 65.63 65.85 57.63 TiO2 0.39 0.41 0.46 0.46 0.65 0.43 0.42 0.43 0.43 0.64

Al2O3 15.80 16.31 16.99 16.77 18.46 16.05 16.46 16.45 16.10 17.84 Fe2O3 3.97 4.49 2.37 2.91 3.96 5.18 4.48 5.70 5.61 7.23 MnO 0.06 0.07 0.05 0.05 0.07 0.08 0.06 0.06 0.05 0.06 MgO 1.62 1.65 2.02 1.75 3.24 2.04 1.98 2.01 2.00 3.15 CaO 4.59 5.00 4.68 4.60 4.46 4.94 4.67 4.68 4.64 5.14 Na2O 3.84 3.81 3.78 3.80 4.02 3.42 3.52 3.39 3.31 3.12

K2O 1.74 1.16 1.29 1.21 2.09 1.23 1.46 1.32 1.27 1.98 P2O5 0.10 0.11 0.12 0.05 0.07 0.10 0.11 0.10 0.10 0.13 LOI 0.15 0.41 0.72 0.41 0.84 0.44 0.49 0.60 0.70 2.76 Total 98.5 99.1 100.1 99.9 99.9 100.0 99.3 100.4 100.0 99.7 Nb 2.1 2.1 2.1 2.3 2.2 2.1 1.2 Ta 0.17 0.14 0.17 0.22 0.18 0.19 0.06 Zr 65 48 57 56 59 55 45 Y 8.6 7.5 3.5 1.4 2.4 11 8.0 8.7 9.0 11 Hf 1.7 1.4 1.7 1.7 1.7 1.6 1.3 Cs 1.3 2.2 1.8 2.6 2.5 1.9 2.2 Rb 22 39 24 28 31 27 40 Ba 282 287 262 243 202 202 213 Sr 355 379 393 395 348 333 348 340 335 344 Pb 4 4 3 2 3 <2 3 3 2 3 U 0.29 0.29 0.67 0.92 0.98 0.89 0.46 Th 0.99 0.33 1.3 1.5 1.6 1.3 0.52 La 3.5 2.0 6.3 8.3 5.3 5.5 4.9 Ce 6.6 4.0 13 17 10 10 11 Pr 0.8 0.5 1.8 2.1 1.3 1.2 1.4 Nd 3.5 2.2 7.4 8.2 5.0 5.0 7.4 Sm 0.84 0.44 1.8 1.6 1.1 0.97 2.1 Eu 0.44 0.39 0.51 0.53 0.50 0.40 0.60 Gd 0.81 0.34 1.6 1.0 1.1 1.1 2.2 Tb 0.11 0.07 0.27 0.18 0.20 0.16 0.36 Dy 0.67 0.38 1.8 1.2 1.2 1.2 1.8 Ho 0.12 0.08 0.33 0.24 0.30 0.28 0.34 Er 0.33 0.26 1.1 0.78 0.85 0.89 0.89 Tm 0.06 0.04 0.15 0.11 0.15 0.14 0.13 Yb 0.36 0.32 0.96 0.81 0.98 0.98 0.77 Lu 0.07 0.05 0.18 0.14 0.15 0.18 0.11 Sc 11 19 13 12 13 12 14 V 66 75 79 73 138 98 109 100 97 189 Cr 13 15 19 20 21 14 14 16 14 21 Co 3.0 6.6 5.9 5.8 24 Ni 5.7 9.0 11 9.9 9.6 8.2 13 Cu 5 12 9 8 69 40 23 24 27 658 Zn 40 48 38 45 54 55 58 60 45 49 Ga 17 18 16 17 17 16 17 16 17 19 As <3 <3 <3 <3 <3 4 <3 <3 <3 3 Mo <0.30 1.4 0.97 0.85 0.39 0.40 1.4 Ag <0.10 <0.10 <0.08 0.20 <0.11 <0.10 <0.10 Sn Sb 0.13 <0.08 0.11 0.19 0.22 0.13 0.18 W 0.47 0.84 0.38 0.78 0.78 0.67 0.56 S 123 128 14 257 1162 61 105 66 79 11392

162

Table A1 (continued) Sample E07044 E07045 E06150 E06149 E06153 E05070 E05072 E05073 E05076 E05078 Telimbela batholith Telimbela Gaby porphyry intrusions porphyry intrusion Lithology tonalite tonalite qtz mi- qtz mi- qtz-diorite hbl-plag hbl-plag plag-hbl hbl por- hbl por- crodiorite crodiorite porphyry porphyry porphyry porphyry phyry phyry

SiO2 64.62 65.23 57.34 52.96 64.48 63.85 62.09 62.63 64.00 62.90 TiO2 0.55 0.50 0.72 0.81 0.49 0.52 0.52 0.51 0.54 0.53

Al2O3 16.16 16.37 17.58 18.03 16.47 16.56 16.66 16.26 17.34 16.24 Fe2O3 5.35 5.14 7.96 9.10 4.68 3.67 6.16 5.27 2.70 5.27 MnO 0.10 0.07 0.14 0.12 0.08 0.06 0.06 0.06 0.05 0.07 MgO 2.28 2.24 3.86 4.70 2.02 2.79 2.85 2.83 2.67 2.93 CaO 4.74 5.25 7.26 3.87 5.42 7.34 6.71 7.17 6.70 7.26 Na2O 3.36 3.59 3.60 3.18 3.88 3.94 3.78 3.84 5.20 3.87

K2O 1.94 0.52 0.82 2.79 1.02 0.18 0.55 0.23 0.19 0.17 P2O5 0.11 0.11 0.13 0.15 0.12 0.11 0.11 0.11 0.12 0.11 LOI 0.90 1.04 0.69 3.36 0.72 0.66 0.30 0.61 1.04 0.48 Total 100.1 100.1 100.1 99.1 99.4 99.7 99.8 99.5 100.6 99.8 Nb 4.2 2.5 2.2 1.8 1.8 2.2 2.1 2.1 Ta 0.29 0.15 0.13 0.09 0.17 0.18 0.17 0.18 Zr 113 107 55 41 68 65 65 66 Y 18 17 13 15 7.4 14 14 15 14 15 Hf 4.5 2.8 1.5 1.3 1.9 1.8 1.8 1.8 Cs 0.9 0.7 2.5 18 3.1 0.4 0.4 0.3 Rb 53 9 13 78 18 3 4 2 Ba 593 199 202 212 147 136 164 134 Sr 309 349 400 321 393 309 302 300 256 297 Pb 13 4 3 <2 3 2 2 2 <2 2 U 1.8 0.90 0.27 0.24 0.56 0.42 0.44 0.46 Th 4.4 2.5 0.52 0.20 0.88 1.1 1.1 1.1 La 16 10 4.9 4.7 4.3 4.5 4.1 5.1 Ce 34 21 12 11 10 11 10 12 Pr 4.3 2.6 1.4 1.4 1.4 1.4 1.4 1.6 Nd 19 13 7.5 7.7 6.0 6.5 7.1 6.7 Sm 4.8 2.6 2.0 2.0 1.2 1.7 1.8 1.9 Eu 1.2 0.69 0.59 0.65 0.51 0.64 0.65 0.58 Gd 4.8 2.8 2.3 2.4 1.4 1.8 2.0 1.8 Tb 0.75 0.45 0.38 0.42 0.19 0.29 0.35 0.32 Dy 4.6 2.8 2.2 2.5 1.3 2.2 2.3 2.3 Ho 0.88 0.54 0.45 0.54 0.25 0.46 0.50 0.50 Er 2.8 1.7 1.3 1.6 0.66 1.40 1.5 1.5 Tm 0.39 0.26 0.18 0.20 0.11 0.21 0.23 0.21 Yb 2.7 1.8 1.2 1.5 0.67 1.53 1.6 1.6 Lu 0.39 0.29 0.18 0.20 0.10 0.22 0.25 0.24 Sc 23 13 20 23 11 21 22 21 V 104 88 187 248 114 118 136 136 74 171 Cr 24 25 36 44 28 29 33 29 30 30 Co 19 9.9 21 26 9.7 9.3 10 10 Ni 20 12 22 23 16 8.9 8.2 9.6 Cu 31 8 69 1857 25 98 89 154 36 187 Zn 62 101 74 84 44 32 29 32 26 35 Ga 17 17 19 21 18 16 17 16 15 16 As 4 5 5 105 4 <3 <3 <3 5 <3 Mo 3.4 0.27 0.98 80 70 3.7 5.1 14 Ag 0.22 0.09 <0.15 0.42 0.18 <0.17 0.29 0.27 Sn 2.4 1.8 Sb 0.68 0.80 0.15 0.33 0.22 0.67 0.78 0.61 W 0.51 0.62 4.2 1.5 1.4 1.1 S 851 143 114 5627 729 1358 216 3785 561 713

163

Table A1 (continued) Sample E05083a E05083b E05086 E05088 E06033 E06041 E06046 E06048 E06050 E06051 E06053 Gaby porphyry intrusions

Lithology plag-hbl plag-hbl plag-hbl plag-hbl plag-hbl plag-hbl hbl-plag hbl-plag plag-hbl plag plag porphyry porphyry porphyry porphyry porphyry porphyry porphyry porphyry porphyry porphyry porphyry + enclave

SiO2 60.49 61.08 61.19 61.22 60.80 61.60 61.07 62.72 62.80 61.59 60.67

TiO2 0.54 0.53 0.55 0.53 0.54 0.55 0.53 0.52 0.55 0.53 0.57 Al2O3 16.52 16.69 17.05 17.21 17.18 17.16 16.71 16.56 16.54 16.84 16.47

Fe2O3 7.51 7.09 6.64 6.55 6.52 5.43 6.53 5.21 3.33 5.45 6.71 MnO 0.07 0.07 0.14 0.15 0.14 0.08 0.06 0.06 0.05 0.04 0.06 MgO 2.57 2.61 2.38 2.34 2.35 2.30 2.77 2.69 2.96 2.76 3.00 CaO 6.71 6.76 6.62 6.84 6.77 6.70 6.58 7.19 8.08 7.31 7.09

Na2O 4.10 4.19 3.27 3.31 3.16 3.98 3.60 3.92 3.81 3.45 3.39 K2O 0.30 0.33 0.60 0.67 0.61 0.22 0.71 0.25 0.35 0.60 0.63

P2O5 0.11 0.10 0.13 0.13 0.11 0.12 0.10 0.10 0.10 0.10 0.11 LOI 0.66 0.66 0.90 1.04 1.28 1.05 0.39 0.52 0.51 0.45 0.43 Total 99.6 100.1 99.5 100.0 99.5 99.2 99.1 99.8 99.1 99.1 99.1 Nb 2.4 2.4 2.8 2.8 2.0 2.3 2.3 Ta 0.18 0.16 0.19 0.19 0.12 0.17 0.16 Zr 65 65 73 71 67 69 66 Y 12 12 17 16 16 17 14 15 15 14 16 Hf 1.8 1.8 1.9 1.8 1.8 1.8 1.8 Cs 0.3 0.3 0.6 0.6 0.4 1.1 1.4 Rb 5 6 9 11 2 14 16 Ba 96 93 425 413 125 178 147 Sr 279 283 307 308 310 292 290 293 304 294 287 Pb 3 5 4 4 5 <2 <2 <2 <2 <2 <2 U 0.42 0.44 0.44 0.42 0.63 0.94 0.77 Th 0.98 0.91 1.0 1.0 1.2 1.2 1.1 La 4.7 5.4 6.8 6.6 3.6 12 6.2 Ce 11 12 14 14 10 20 12 Pr 1.5 1.6 1.9 2.1 1.4 2.3 1.6 Nd 6.9 7.8 8.6 8.0 8.4 8.5 6.6 Sm 1.8 1.7 2.1 2.0 2.5 1.7 1.8 Eu 0.62 0.65 0.76 0.66 0.74 0.53 0.58 Gd 2.3 2.3 2.4 2.3 2.6 1.6 1.7 Tb 0.31 0.30 0.38 0.37 0.40 0.28 0.32 Dy 2.0 2.0 2.7 2.6 2.3 2.0 2.1 Ho 0.41 0.39 0.52 0.55 0.52 0.44 0.45 Er 1.2 1.2 1.7 1.7 1.4 1.4 1.4 Tm 0.16 0.17 0.25 0.23 0.23 0.20 0.22 Yb 1.1 1.2 1.8 1.5 1.6 1.5 1.6 Lu 0.20 0.17 0.27 0.29 0.23 0.25 0.25 Sc 18 18 20 20 17 20 21 V 129 129 116 112 116 115 139 133 132 142 156 Cr 31 29 24 24 24 17 29 28 40 23 62 Co 7.8 8.3 13 8.3 14 10 Ni 7.9 8.7 6.1 4.6 9.8 13 11 Cu 72 128 24 21 19 479 155 440 79 822 113 Zn 32 34 82 89 83 48 30 40 28 29 30 Ga 17 17 17 17 17 17 18 17 17 18 18 As <3 7 <3 6 4 5 4 5 <3 <3 <3 Mo 3.8 13 0.97 0.56 1.3 17 5.1 Ag 0.39 0.21 <0.12 <0.12 0.33 0.38 0.16 Sn Sb 1.2 0.85 1.3 0.95 0.69 0.39 0.50 W 2.1 1.8 0.46 0.39 0.74 1.0 1.6 S 2632 2612 169 49 160 3003 1107 1918 292 1765 1906

164

Table A1 (continued) Sample E05090 E06044 E06042 E06043 E06049 E06052 E06054 E06055 E06056 Gaby/Papa Grande Gaby/Papa Grande tonalite porphyry intrusions

Lithology hbl-plag plag(-hbl) tonalite tonalite tonalite tonalite tonalite tonalite tonalite porphyry porphyry

SiO2 61.63 62.08 61.26 63.00 65.27 62.51 61.84 61.90 60.21 TiO2 0.52 0.50 0.54 0.51 0.43 0.52 0.56 0.56 0.62

Al2O3 16.87 16.27 15.96 16.11 15.74 16.22 16.33 16.49 16.33 Fe2O3 6.43 6.36 6.30 5.77 5.21 5.77 5.07 5.25 6.68 MnO 0.17 0.12 0.07 0.07 0.08 0.06 0.05 0.05 0.07 MgO 2.84 2.81 3.09 2.65 2.16 2.62 2.83 2.65 2.93 CaO 7.97 7.58 6.17 6.13 5.26 6.73 7.34 7.15 7.25 Na2O 2.18 1.95 3.46 3.80 3.55 3.77 3.55 3.44 3.95

K2O 0.18 0.38 0.71 0.69 1.02 0.52 0.35 0.51 0.28 P2O5 0.11 0.09 0.10 0.10 0.09 0.09 0.11 0.10 0.11 LOI 1.25 1.26 1.47 0.43 0.69 0.47 1.02 0.93 0.77 Total 100.2 99.4 99.1 99.3 99.5 99.3 99.1 99.1 99.2 Nb 2.5 2.5 2.7 Ta 0.14 0.21 0.18 Zr 70 69 75 Y 13 12 13 13 12 16 15 15 17 Hf 1.5 1.9 2.1 Cs 0.8 1.3 0.8 Rb 3 22 10 Ba 75 453 245 Sr 309 299 255 283 254 282 293 299 294 Pb 4 3 <2 <2 <2 2 <2 <2 <2 U 0.48 1.2 0.52 Th 1.1 2.8 1.6 La 6.3 7.2 6.3 Ce 14 14 13 Pr 1.5 1.4 1.7 Nd 7.4 6.9 6.8 Sm 1.6 1.6 1.9 Eu 0.53 0.48 0.56 Gd 1.7 1.2 2.3 Tb 0.29 0.29 0.34 Dy 1.9 1.7 2.4 Ho 0.33 0.35 0.52 Er 1.2 1.1 1.6 Tm 0.15 0.16 0.22 Yb 1.6 1.2 1.8 Lu 0.19 0.18 0.27 Sc 16 13 20 V 129 128 147 121 101 125 140 148 162 Cr 35 36 35 29 23 33 24 33 22 Co 16 11 11 Ni 10 6.5 9.4 Cu 35 31 336 101 54 166 2302 1095 775 Zn 73 49 39 46 43 34 43 42 37 Ga 18 17 17 16 16 16 17 17 18 As 5 7 <3 4 <3 <3 <3 <3 4 Mo 0.30 0.91 5.32 Ag <0.17 0.16 0.21 Sn Sb 6.2 0.48 0.53 W 1.5 2.3 1.3 S 611 289 8228 94 1977 1769 6691 8838 3256

165

Table A1 (continued) Sample E07002 E07005 E06179 E06181 E07001 E07003 E07008 E06158 E05092 E05093 Chaucha porphyry intrusions Chaucha batholith Quimsacocha (Gur-Gur/Tunas) dacite domes Lithology dacitic dacitic granodiorite granodiorite tonalite tonalite tonalite qtz-diorite dacite dacite porphyry porphyry porphyry porphyry

SiO2 64.49 68.40 73.26 73.41 64.74 68.65 65.39 67.87 69.63 69.19 TiO2 0.59 0.42 0.19 0.21 0.46 0.49 0.50 0.37 0.35 0.34

Al2O3 17.57 16.55 14.86 15.10 16.57 16.65 17.41 16.45 16.58 16.37 Fe2O3 5.20 2.99 1.05 1.13 5.18 3.10 4.77 4.30 2.09 2.17 MnO 0.04 0.04 0.04 0.03 0.05 0.04 0.04 0.04 0.02 0.02 MgO 1.51 1.23 0.77 0.92 1.96 2.09 2.20 1.53 0.25 0.64 CaO 4.89 3.34 3.38 3.30 5.04 4.04 4.22 3.79 2.74 3.50 Na2O 3.94 4.16 4.35 4.11 2.78 3.20 3.17 3.43 4.26 4.64

K2O 1.20 1.75 0.44 0.41 1.23 1.11 1.38 0.51 1.95 1.80 P2O5 0.19 0.13 0.07 0.02 0.11 0.10 0.12 0.09 0.12 0.13 LOI 0.33 1.29 1.34 1.47 1.80 0.82 0.85 1.64 1.20 0.95 Total 100.0 100.3 99.8 100.1 99.9 100.3 100.1 100.0 99.2 99.8 Nb 3.2 3.4 2.1 2.0 3.5 2.7 3.3 2.3 2.9 Ta 0.21 0.22 0.31 0.30 0.27 0.19 0.26 0.22 0.21 Zr 122 92 59 64 81 77 86 63 107 Y 8.3 7.2 4.6 1.7 13 12 13 7.8 4.8 5.1 Hf 3.1 2.5 2.2 2.4 2.9 2.3 2.3 1.8 2.9 Cs 2.1 1.8 1.5 2.0 2.2 1.1 2.2 2.9 0.5 Rb 40 37 10 10 44 42 52 16 34 Ba 407 198 189 170 359 686 251 291 876 Sr 611 492 329 307 409 336 356 416 466 858 Pb 4 7 5 4 9 5 5 5 13 10 U 0.58 1.6 1.8 1.6 2.7 1.1 2.2 0.90 0.82 Th 1.3 5.0 11 10.9 6.5 2.4 7.8 2.6 2.4 La 12 8.0 5.3 3.6 13 12 10 5.6 16 Ce 25 18 9.4 5.5 27 25 21 11 29 Pr 3.1 2.2 0.9 0.5 3.1 3.1 2.5 1.3 3.6 Nd 13 9.4 4.3 1.7 13 13 9.8 5.1 14 Sm 2.9 2.1 0.94 0.28 2.8 2.3 2.1 1.2 2.5 Eu 0.92 0.64 0.47 0.41 0.75 0.54 0.63 0.44 0.63 Gd 2.6 2.0 0.63 0.33 2.7 1.9 2.5 1.1 1.3 Tb 0.33 0.35 0.11 0.03 0.41 0.24 0.33 0.17 0.15 Dy 1.5 1.9 0.78 0.20 2.2 1.3 2.2 1.1 0.79 Ho 0.31 0.40 0.10 0.06 0.46 0.23 0.40 0.21 0.14 Er 0.69 1.1 0.45 0.22 1.3 0.51 1.2 0.61 0.43 Tm 0.12 0.19 0.06 0.02 0.18 0.10 0.16 0.10 0.05 Yb 0.74 1.3 0.54 0.25 1.4 0.64 1.3 0.66 0.37 Lu 0.12 0.21 0.11 0.04 0.21 0.09 0.20 0.11 0.04 Sc 9 12 5 5 12 7 12 8 5 V 79 62 41 23 89 90 111 75 36 33 Cr 5 11 7 7 18 16 18 13 4 3 Co 4.3 8.7 1.5 1.9 8.2 6.4 8.0 2.4 2.3 Ni 2.0 7.6 4.4 5.2 8.5 4.0 9.8 8.6 1.9 Cu 19 34 542 190 9 386 818 826 14 20 Zn 43 38 40 35 55 48 56 87 136 59 Ga 22 20 15 15 17 17 19 17 20 20 As 4 5 4 <3 4 6 <3 3 <3 <3 Mo 0.61 5.9 2.2 2.7 0.84 0.34 2.3 1.1 0.68 Ag 0.16 0.12 0.23 <0.23 0.11 <0.08 0.41 0.32 <0.08 Sn 1.1 1.7 1.2 0.95 1.7 Sb 0.12 0.14 <0.30 0.66 <0.12 0.67 0.12 2.1 0.31 W 3.6 3.3 8.9 0.21 S 478 123 658 371 11838 273 1460 954 <3 <3

166

Table A1 (continued) Sample E05094 E05102 E05115 E06017 E06018 E06019 E06020 E05098 E05099 E05114 E06022 Quimsacocha dacite domes Quimsacocha andesite flows (+subvolcanics?) Lithology dacite dacite dacite dacite dacite dacite dacite microdiorite microdiorite andesite andesite

SiO2 69.49 69.32 70.33 68.97 69.76 68.67 67.42 62.44 61.60 62.80 61.59 TiO2 0.34 0.37 0.36 0.35 0.36 0.38 0.34 0.68 0.70 0.68 0.77

Al2O3 16.43 16.40 16.49 17.11 16.59 16.92 16.28 17.35 17.25 17.43 17.81 Fe2O3 2.16 2.30 2.14 2.38 2.42 2.44 2.17 4.74 4.76 4.63 5.15 MnO 0.03 0.02 0.02 0.02 0.03 0.02 0.04 0.09 0.08 0.08 0.05 MgO 0.56 0.23 0.22 0.18 0.15 0.18 0.64 1.87 2.06 2.23 1.98 CaO 3.39 2.84 2.66 2.53 2.65 3.05 3.37 5.56 5.26 5.21 5.82 Na2O 4.67 4.39 4.28 3.96 4.08 4.55 4.84 4.06 3.68 4.02 4.53

K2O 1.81 1.94 2.04 1.99 2.03 1.82 1.57 1.46 1.29 1.41 1.15 P2O5 0.13 0.12 0.12 0.07 0.10 0.12 0.12 0.17 0.17 0.17 0.17 LOI 0.75 1.10 1.17 1.71 1.21 0.97 2.46 1.19 1.97 1.13 0.42 Total 99.8 99.0 99.8 99.3 99.4 99.1 99.3 99.6 98.8 99.8 99.4 Nb 3.0 2.8 3.1 2.8 2.4 2.5 2.4 2.3 Ta 0.19 0.17 0.18 0.17 0.14 0.14 0.11 0.13 Zr 111 115 108 103 98 90 88 84 Y 4.1 5.7 5.1 4.6 5.0 5.0 4.7 7.8 7.4 7.4 11 Hf 2.8 3.2 2.7 2.9 2.6 2.5 2.4 2.2 Cs 0.7 1.3 0.6 1.4 0.5 0.4 0.4 0.6 Rb 38 42 32 26 31 25 30 20 Ba 888 984 794 692 666 693 683 481 Sr 605 489 457 448 463 556 649 594 578 586 696 Pb 11 12 13 15 15 13 12 10 9 9 6 U 0.89 0.97 0.83 0.69 0.89 0.63 0.67 0.52 Th 3.3 2.7 2.2 1.9 2.4 2.0 2.0 1.5 La 28 17 15 15 14 14 14 13 Ce 49 33 28 30 27 27 28 23 Pr 5.8 3.7 3.6 3.8 3.3 2.9 2.9 3.2 Nd 21 15 14 15 14 13 13 14 Sm 3.1 2.3 2.4 2.4 2.6 2.6 2.4 3.0 Eu 0.70 0.54 0.63 0.73 0.81 0.63 0.85 0.82 Gd 1.7 1.5 1.6 1.6 2.1 2.2 2.3 2.4 Tb 0.18 0.16 0.17 0.17 0.25 0.24 0.24 0.32 Dy 0.91 0.81 0.81 0.83 1.2 1.1 1.3 1.8 Ho 0.17 0.16 0.17 0.16 0.24 0.23 0.25 0.29 Er 0.42 0.46 0.36 0.38 0.71 0.59 0.69 0.90 Tm 0.07 0.04 0.06 0.04 0.10 0.07 0.09 0.14 Yb 0.37 0.38 0.28 0.39 0.67 0.49 0.44 0.78 Lu 0.07 0.05 0.06 0.05 0.10 0.06 0.09 0.14 Sc 5 5 5 5 11 11 10 12 V 35 35 39 32 35 38 37 127 128 125 146 Cr 2 4 4 3 4 4 4 53 12 128 19 Co 2.3 3.1 3.0 3.2 11 11 10 11 Ni 2.5 1.5 2.7 3.0 5.2 4.3 5.1 7.7 Cu 20 10 12 19 18 21 17 23 31 19 39 Zn 56 85 84 62 64 63 79 81 126 93 95 Ga 20 21 21 22 21 22 21 21 21 20 23 As 5 3 5 <3 6 3 5 6 <3 <3 3 Mo 0.84 0.44 0.29 1.0 1.2 0.43 0.55 1.4 Ag 0.15 0.20 0.17 0.18 0.24 <0.15 <0.18 0.18 Sn 1.1 Sb 0.30 0.25 0.32 0.52 0.36 <0.24 0.39 0.46 W 0.20 0.87 0.54 0.25 0.18 0.25 0.19 S <3 <3 <3 <3 <3 <3 9 9 32 10 <3

167

Table A1 (continued) Sample E06157 E06166 E06172 E06004 E06009 E06010 E06011 E06012 E06015 Saraguro Group at Chaucha Saraguro Group at Canicapa

Lithology andesite andesite andesite dacite (sub- dacite dacite dacite dacite andesite volcanic?) (flow) (flow) (subvol- (subvol- flow canic?) canic?)

SiO2 57.16 65.79 61.36 69.86 70.59 70.07 69.37 68.69 62.03 TiO2 0.67 0.57 0.64 0.26 0.27 0.30 0.30 0.30 0.53

Al2O3 18.49 15.62 16.74 14.75 15.23 15.28 15.17 15.60 16.52 Fe2O3 7.88 5.15 6.76 2.36 2.47 2.73 2.76 2.85 5.27 MnO 0.18 0.07 0.04 0.07 0.08 0.07 0.13 0.06 0.11 MgO 3.00 2.26 3.20 0.86 0.67 0.81 1.06 1.02 2.15 CaO 7.88 4.70 4.97 2.83 2.58 2.53 3.14 2.94 5.22 Na2O 2.62 2.30 2.37 3.65 3.96 3.96 3.62 3.81 3.38

K2O 0.75 1.64 1.59 2.41 2.33 2.37 2.20 2.28 1.70 P2O5 0.14 0.13 0.12 0.10 0.12 0.13 0.13 0.13 0.14 LOI 0.60 1.14 1.56 2.03 0.98 0.92 1.30 1.45 2.25 Total 99.4 99.4 99.4 99.2 99.3 99.2 99.2 99.1 99.3 Nb 2.8 5.7 4.7 6.0 5.9 6.0 5.1 Ta 0.22 0.48 0.35 0.53 0.46 0.47 0.38 Zr 72 131 117 94 100 100 87 Y 20 20 19 15 13 12 12 12 15 Hf 2.0 3.5 3.0 2.4 2.5 2.4 2.3 Cs 1.7 5.4 9.4 1.8 2.8 2.6 0.5 Rb 20 67 70 45 42 45 36 Ba 220 534 266 723 682 702 526 Sr 395 320 270 289 340 329 417 401 424 Pb 8 2 <2 14 15 15 15 16 5 U 0.72 2.7 1.3 1.7 1.9 1.8 1.7 Th 1.8 8.1 4.2 5.3 5.4 5.5 4.9 La 7.2 17 10 17 16 17 15 Ce 15 33 21 30 30 31 28 Pr 2.0 4.0 2.6 3.3 3.4 3.5 3.3 Nd 9.4 15 11 13 13 12 13 Sm 2.5 3.4 2.8 2.4 2.1 2.5 2.5 Eu 0.77 0.80 0.67 0.68 0.61 0.59 0.72 Gd 2.8 3.32 3.12 2.2 1.9 1.6 2.5 Tb 0.43 0.47 0.40 0.28 0.26 0.30 0.35 Dy 3.0 3.1 3.1 1.7 1.8 1.9 2.3 Ho 0.66 0.63 0.64 0.35 0.36 0.35 0.46 Er 1.9 2.0 1.8 0.96 1.0 1.0 1.3 Tm 0.27 0.27 0.28 0.15 0.16 0.16 0.19 Yb 1.88 1.8 1.9 1.1 1.2 1.2 1.2 Lu 0.33 0.31 0.29 0.18 0.17 0.20 0.21 Sc 23 16 22 5 5 6 11 V 156 122 138 26 22 27 25 26 95 Cr 10 25 30 2 5 9 <2 <2 10 Co 6.4 12 12 3.5 3.7 3.6 11 Ni 9.5 17 19 3.0 2.2 <1.5 5.6 Cu 49 1082 508 8 6 11 7 7 13 Zn 93 101 48 47 49 57 55 42 54 Ga 19 17 19 15 16 16 15 17 18 As 3 5 4 4 5 4 5 5 4 Mo 0.67 14 2.7 0.90 0.81 0.86 0.75 Ag 0.05 0.59 0.24 0.15 <0.10 <0.15 0.12 Sn Sb 0.23 0.25 0.84 0.38 0.28 0.59 0.12 W 0.36 0.89 2.1 0.89 0.56 0.82 0.34 S 454 1664 308 3 10 <3 11 <3 70

168

Table A1 (continued) Sample E06074 E06075 E06081 E06082 E06083A E06083B E06084 E06086 E06117 E06118 E06120 Saraguro Group at Portovelo

Lithology andesite andesite andesite andesite andesite andesite andesite andesite andesite andesite andesite

SiO2 57.82 59.30 58.85 57.35 58.48 59.37 59.11 58.40 56.13 55.09 57.96 TiO2 0.72 0.70 0.70 0.70 0.71 0.69 0.69 0.71 0.94 0.83 0.73

Al2O3 16.27 16.34 16.16 16.24 16.07 15.81 16.03 15.97 19.17 19.49 16.39 Fe2O3 7.25 6.82 6.70 7.05 6.40 6.38 6.44 6.49 6.94 8.13 6.96 MnO 0.16 0.13 0.17 0.21 0.14 0.14 0.26 0.14 0.19 0.16 0.16 MgO 3.58 3.52 3.52 3.92 3.96 2.97 3.35 3.74 3.89 4.77 3.47 CaO 7.05 6.60 6.67 6.49 6.06 7.26 5.59 5.24 6.68 6.00 6.19 Na2O 2.52 2.62 2.50 2.67 2.51 2.66 2.61 3.27 2.50 2.78 2.36

K2O 1.54 1.62 1.48 1.21 1.24 0.88 2.08 1.71 0.44 0.96 2.10 P2O5 0.11 0.11 0.11 0.11 0.12 0.12 0.12 0.11 0.17 0.15 0.12 LOI 2.08 1.69 2.32 3.50 3.40 2.74 3.01 3.35 2.14 1.64 2.84 Total 99.1 99.5 99.2 99.5 99.1 99.0 99.3 99.1 99.2 100.0 99.3 Nb 4.1 3.8 4.0 Ta 0.25 0.24 0.25 Zr 122 107 113 Y 19 19 20 19 20 20 20 19 21 15 20 Hf 3.3 3.0 2.9 Cs 1.4 2.1 5.2 Rb 29 31 62 Ba 677 456 552 Sr 284 284 344 299 274 310 280 347 309 350 256 Pb 8 18 17 4 8 15 4 7 21 43 10 U 1.8 1.4 1.5 Th 5.6 4.8 4.8 La 13 12 13 Ce 28 25 26 Pr 3.3 3.0 2.9 Nd 14 13 13 Sm 3.4 3.1 2.8 Eu 0.72 0.78 0.76 Gd 3.2 3.2 3.1 Tb 0.53 0.49 0.48 Dy 3.4 3.4 2.9 Ho 0.64 0.63 0.63 Er 2.1 2.1 1.7 Tm 0.30 0.25 0.25 Yb 2.1 1.9 1.7 Lu 0.29 0.30 0.28 Sc 21 23 22 V 159 145 146 152 146 142 139 140 123 142 163 Cr 44 40 46 47 46 41 39 54 44 44 87 Co 19 17 17 Ni 19 13 17 Cu 33 31 32 26 51 11 26 30 39 25 27 Zn 71 68 124 106 128 94 104 92 152 140 79 Ga 19 19 18 18 17 18 18 17 21 23 18 As 7 7 8 6 15 22 13 20 14 <3 4 Mo 2.0 1.1 1.7 Ag 0.48 0.24 0.17 Sn Sb 3.8 1.9 1.7 W 1.2 0.76 0.98 S 286 134 521 1806 1722 2498 178 2050 5618 1093 65

169

Table A1 (continued)

Sample E07013 E06068 E06071 E05-M4 E05-M10 E06067 E06069 E06070 E06088 E06089 Saraguro Cangrejos host intrusive Cangrejos porphyry intrusions Zaruma-Portovelo Group at 3 porphyry intrusions Chorreras complex Lithology granodioritic diorite diorite qtz- plag-hbl plag-hbl plag-hbl plag-hbl qtz-diorite qtz-diorite porphyry diorite porphyry porphyry porphyry (qtz eyes) porphyry porphyry porphyry

SiO2 60.41 52.22 55.88 61.59 64.01 61.51 64.89 64.40 65.33 66.27 TiO2 0.47 0.66 0.38 0.60 0.55 0.63 0.52 0.49 0.41 0.39

Al2O3 16.37 16.07 15.29 16.25 16.29 16.55 15.76 16.50 15.35 15.04 Fe2O3 5.85 7.20 6.35 6.97 4.91 5.25 4.11 4.51 3.93 3.71 MnO 0.06 0.13 0.10 0.04 0.03 0.03 0.06 0.03 0.08 0.07 MgO 1.91 7.94 7.53 2.73 2.70 2.97 2.53 2.47 1.96 1.76 CaO 3.83 11.60 9.49 5.93 5.06 5.47 6.81 5.08 3.57 3.98 Na2O 2.14 1.75 2.15 3.27 2.86 2.89 3.22 2.96 2.61 2.88

K2O 3.61 0.48 0.86 1.30 1.62 1.73 0.20 1.50 3.36 2.60 P2O5 0.13 0.08 0.02 0.13 0.12 0.12 0.10 0.10 0.09 0.09 LOI 4.47 1.02 1.04 1.20 1.47 2.03 0.94 1.37 3.52 3.26 Total 99.3 99.2 99.1 100.0 99.6 99.2 99.1 99.4 100.2 100.1 Nb 3.0 4.8 5.0 4.1 4.8 4.9 5.1 4.7 Ta 0.21 0.29 0.35 0.24 0.29 0.36 0.40 0.32 Zr 86 41 54 118 128 118 115 113 Y 10 18 14 17 19 22 23 17 13 12 Hf 2.0 1.3 1.6 2.9 3.0 3.0 3.0 3.0 Cs 19 0.5 0.6 0.9 1.8 0.9 0.1 1.6 Rb 109 12 26 45 63 62 3 50 Ba 584 67 94 254 281 339 108 242 Sr 210 239 229 302 285 317 308 298 201 275 Pb 3 6 5 12 5 8 7 4 10 11 U 1.3 0.63 0.71 0.87 1.7 1.2 1.4 1.5 Th 2.4 1.8 2.7 2.8 5.1 3.2 4.4 4.6 La 9 6 7 9 19 19 9.3 17 Ce 19 14 17 23 38 39 22 35 Pr 2.2 2.0 2.1 3.0 4.3 4.8 3.0 4.1 Nd 9.3 9.1 9.8 13 18 20 14 16 Sm 2.1 2.5 2.1 3.2 3.9 4.4 3.2 3.3 Eu 0.67 0.77 0.72 0.75 0.83 0.92 0.75 0.79 Gd 1.8 2.6 2.4 3.2 3.6 4.4 3.3 2.6 Tb 0.31 0.44 0.37 0.43 0.49 0.58 0.53 0.43 Dy 1.6 3.0 2.4 2.9 3.2 4.0 3.5 2.9 Ho 0.35 0.61 0.50 0.55 0.67 0.76 0.74 0.57 Er 1.1 1.9 1.3 1.7 1.8 2.1 2.2 1.5 Tm 0.18 0.25 0.22 0.19 0.27 0.30 0.33 0.25 Yb 1.1 1.6 1.3 1.3 1.8 1.9 2.0 1.7 Lu 0.16 0.27 0.20 0.24 0.25 0.28 0.32 0.25 Sc 10 45 34 16 16 20 17 15 V 75 190 154 117 102 120 95 92 70 65 Cr 9 260 103 37 42 40 34 35 19 28 Co 4.2 30 19 12 3.7 14 9.0 2.9 Ni 4.7 56 32 13 12 18 12 15 Cu 143 327 550 388 7 483 1028 8 18 13 Zn 51 101 66 48 82 49 70 72 59 53 Ga 18 16 16 18 17 18 17 19 16 15 As 10 <3 <3 6 4 6 7 <3 8 4 Mo 3.0 0.95 13 1.3 0.34 3.0 4.5 0.43 Ag 0.33 0.37 0.80 0.18 <0.14 0.38 0.34 0.64 Sn 1.3 2.3 3.2 Sb 19 0.50 0.37 1.4 0.38 2.7 0.42 0.45 W 9.4 1.4 0.98 0.98 1.9 S 168 944 928 279 <3 484 2229 16 69 21

170

Table A1 (continued) Sample E06072 E06073 E06090 E06092 E06112 E06115 E06123 E07023 E06114 E06124 Zaruma-Portovelo porphyry intrusions Zaruma-Portovelo phaneritic intrusions

Lithology qtz-diorite qtz-diorite qtz-diorite qtz-diorite plag-hbl granodiorite diorite diorite qtz-diorite diorite porphyry porphyry porphyry porphyry porphyry porphyry

SiO2 64.79 65.76 64.44 64.67 63.36 65.86 55.24 60.46 62.76 57.47

TiO2 0.40 0.41 0.45 0.42 0.52 0.51 0.73 0.67 0.47 0.70 Al2O3 15.29 15.86 15.97 15.75 16.55 15.56 18.79 17.41 14.52 16.11

Fe2O3 3.97 4.16 4.39 4.23 5.05 4.15 7.61 6.42 4.20 7.28 MnO 0.08 0.07 0.09 0.08 0.09 0.11 0.13 0.10 0.08 0.14 MgO 2.00 2.12 2.19 2.13 2.57 2.18 4.37 3.00 1.86 4.60 CaO 4.17 1.42 4.34 4.53 2.94 4.83 8.50 5.60 3.33 4.74

Na2O 3.13 3.83 3.45 2.96 4.42 1.83 2.98 2.98 2.35 2.27 K2O 2.18 3.70 2.06 2.37 2.47 3.46 0.55 1.56 2.60 1.84

P2O5 0.09 0.09 0.09 0.09 0.11 0.10 0.11 0.12 0.09 0.13 LOI 2.92 1.83 2.54 2.90 2.09 1.18 0.95 1.25 7.90 3.77 Total 99.0 99.3 100.0 100.1 100.2 99.8 100.0 99.6 100.2 99.1 Nb 3.8 3.7 3.8 3.7 4.3 2.6 3.8 Ta 0.33 0.31 0.33 0.26 0.32 0.17 0.24 Zr 91 85 92 100 127 66 108 Y 13 12 12 12 14 17 14 19 19 18 Hf 2.6 2.6 2.5 2.6 3.5 1.9 3.1 Cs 3.4 2.8 3.4 4.6 2.7 1.4 4.5 Rb 59 64 75 82 80 14 51 Ba 586 520 573 518 868 239 463 Sr 313 293 309 291 313 228 372 329 308 228 Pb 12 9 14 12 29 26 6 22 20 14 U 1.9 2.1 2.1 1.8 2.4 0.62 1.4 Th 6.8 6.5 6.8 4.8 7.8 1.7 4.9 La 13 13 14 13 14 6.9 11 Ce 25 25 27 25 29 16 24 Pr 2.7 2.6 2.7 2.7 3.4 1.9 3.0 Nd 11 11 11 13 14 8.7 13 Sm 2.1 2.0 2.1 2.5 3.1 2.4 3.2 Eu 0.67 0.59 0.61 0.67 0.83 0.74 0.72 Gd 2.2 1.8 2.0 2.4 3.1 2.5 3.4 Tb 0.29 0.30 0.29 0.34 0.40 0.39 0.52 Dy 1.9 1.9 2.0 2.3 2.5 2.5 3.2 Ho 0.41 0.40 0.37 0.48 0.54 0.47 0.61 Er 1.2 1.2 1.2 1.4 1.6 1.4 1.8 Tm 0.18 0.16 0.18 0.21 0.23 0.21 0.28 Yb 1.1 1.2 1.2 1.3 1.8 1.4 1.7 Lu 0.21 0.20 0.21 0.22 0.28 0.20 0.26 Sc 11 12 12 15 14 26 19 V 68 76 80 76 98 100 182 121 91 158 Cr 20 25 112 67 35 28 34 26 27 90 Co 9.1 11 11 13 9.0 23 15 Ni 8.3 12 11 15 8.1 16 13 Cu 18 13 17 17 21 38 68 9 25 25 Zn 55 52 64 56 155 83 82 98 65 92 Ga 16 16 16 16 17 16 20 18 16 17 As 6 7 7 10 13 13 <3 11 11 16 Mo 0.91 1.0 0.99 1.5 1.5 0.90 0.93 Ag 0.37 <0.12 0.19 0.51 0.50 0.23 0.39 Sn 1.3 Sb 1.3 1.5 1.5 4.4 3.5 0.56 2.4 W 1.1 1.4 1.6 2.2 2.0 0.66 S 11 <3 14 41 47 562 963 173 2148 4411

171

Table A1 (continued) Sample E07016 E07017 E07020 E07026 E07029 E07027 E07031 E07028 El Mozo intrusions Curiplaya intrusions

Lithology dioritic dioritic plag-hbl plag-hbl microdiorite qtz dioritic hbl-plag plag porphyry porphyry porphyry porphyry porphyry porphyry porphyry (Celica flow?!)

SiO2 62.40 62.41 61.31 64.73 50.59 62.18 63.17 56.18

TiO2 0.58 0.57 0.56 0.31 0.86 0.51 0.64 0.69 Al2O3 16.83 17.53 17.02 14.72 17.30 16.48 16.10 17.49

Fe2O3 6.99 6.46 6.01 3.21 8.77 4.98 5.35 7.25 MnO 0.17 0.24 0.13 0.25 0.19 0.14 0.11 0.18 MgO 3.50 2.79 2.48 0.98 3.95 2.76 2.11 2.82 CaO 1.93 3.74 5.67 4.96 7.91 2.18 5.60 5.81

Na2O 2.15 2.56 2.81 1.87 3.35 5.43 3.97 4.79 K2O 0.91 1.22 1.70 2.46 0.38 1.78 0.44 0.48

P2O5 0.14 0.14 0.16 0.11 0.23 0.17 0.17 0.23 LOI 3.72 2.54 1.19 6.43 5.89 2.44 1.65 3.24 Total 99.3 100.2 99.0 100.0 99.4 99.1 99.3 99.2 Nb 4.6 5.0 5.2 3.0 2.1 2.5 1.9 3.0 Ta 0.32 0.41 0.41 0.17 0.14 0.12 0.09 0.14 Zr 85 87 91 89 53 65 85 76 Y 16 19 25 13 18 15 18 21 Hf 2.3 2.3 2.5 2.4 1.5 1.9 2.3 2.1 Cs 10.0 7.2 1.5 3.0 1.8 0.8 0.4 2.1 Rb 28 28 45 60 9 34 5 9 Ba 249 552 558 1233 277 1267 387 293 Sr 197 316 459 142 516 637 432 193 Pb 8 29 10 16 12 4 4 9 U 1.9 2.0 2.0 1.3 0.77 0.75 0.33 1.0 Th 5.2 5.4 5.4 5.7 2.8 2.5 1.3 3.4 La 15 16 20 18 13 14 7 17 Ce 30 31 32 34 27 30 17 36 Pr 3.5 3.5 4.1 3.7 3.4 3.7 2.3 4.4 Nd 14 15 17 15 16 16 12 19 Sm 3.0 3.4 3.7 2.9 3.7 3.3 2.8 4.1 Eu 0.83 0.93 1.1 0.75 1.1 0.99 0.94 1.4 Gd 2.6 3.2 3.9 2.2 3.4 2.8 3.2 3.9 Tb 0.45 0.49 0.52 0.30 0.48 0.40 0.51 0.53 Dy 2.6 3.0 3.5 1.8 3.0 2.5 2.9 3.4 Ho 0.47 0.59 0.71 0.37 0.53 0.44 0.62 0.66 Er 1.5 1.9 2.3 1.2 1.9 1.5 1.7 2.0 Tm 0.25 0.24 0.35 0.17 0.23 0.20 0.22 0.28 Yb 1.5 2.0 2.0 1.2 1.8 1.5 1.9 1.9 Lu 0.24 0.27 0.37 0.21 0.27 0.21 0.27 0.30 Sc 15 16 15 6 18 11 10 16 V 98 105 94 43 195 79 64 102 Cr 17 341 13 <2 9 13 8 5 Co 6.0 13 11 5.4 20 8.9 6.9 17 Ni 4.5 5.5 5.1 1.4 7.7 5.2 2.1 5.7 Cu <2 7 15 20 8 20 147 55 Zn 193 233 53 160 77 51 38 57 Ga 18 18 18 15 18 17 18 19 As <3 4 5 <3 <3 13 5 10 Mo 1.1 1.2 0.67 0.64 0.31 0.26 <0.20 0.50 Ag 0.15 0.33 0.14 0.16 <0.07 0.09 0.14 0.12 Sn 1.2 1.3 1.5 1.0 1.0 1.1 2.2 0.99 Sb <0.12 0.21 <0.14 3.9 1.5 3.0 0.61 0.92 W S 503 6359 179 105 390 168 216 373

172

Table A1 (continued) Sample E05122 E05123 E06148 E06145 E07040 E07042 E07043 E06144B Basement units

Lithology Macuchi subvolcanic at Macuchi basalt at Macuchi subvolcanic at Echeandia xenolith in Junin Balsapamba Balsapamba tonalite (Macu- chi?)

SiO2 64.66 63.95 50.77 52.81 49.45 56.04 57.72 49.02

TiO2 0.64 0.59 0.93 0.94 0.93 0.72 0.75 0.72 Al2O3 15.66 16.63 17.45 17.42 21.23 17.54 17.25 16.37

Fe2O3 3.22 5.44 11.27 10.71 9.10 10.61 7.71 16.82 MnO 0.02 0.05 0.29 0.58 0.19 0.27 0.13 0.28 MgO 2.40 2.87 5.42 4.54 4.97 5.35 3.89 4.58 CaO 0.20 1.21 9.17 6.90 7.95 1.33 7.48 6.86

Na2O 1.74 2.67 3.17 3.89 2.51 4.87 2.93 3.97 K2O 7.49 3.84 0.98 1.34 0.12 0.16 1.45 0.97

P2O5 0.13 0.21 0.17 0.24 0.14 0.09 0.13 0.14 LOI 1.19 2.14 0.35 0.51 2.55 3.14 -0.04 0.13 Total 97.4 99.6 100.0 99.9 99.1 100.1 99.4 99.9 Nb 3.0 1.0 1.0 1.0 0.6 1.6 Ta 0.15 0.05 0.06 0.06 0.06 0.13 Zr 106 66 66 44 34 88 Y 25 20 25 25 16 25 18 34 Hf 3.2 2.2 2.0 1.2 1.0 2.6 Cs 2.3 0.9 1.7 0.2 0.2 2.5 Rb 66 13 27 2 2 32 Ba 262 120 544 134 34 268 Sr 56 199 318 616 288 108 374 332 Pb <2 <2 <2 9 5 4 6 8 U 2.4 0.42 0.23 0.22 0.18 0.87 Th 5.0 0.83 0.81 0.63 0.36 1.9 La 11 5.0 5.3 4.1 2.9 6.3 Ce 23 12 12 10 8 15 Pr 2.9 2.0 1.9 1.5 1.2 2.2 Nd 14 9.6 10 7.9 6.1 11 Sm 3.0 2.6 2.7 2.6 2.1 3.0 Eu 0.62 0.83 0.90 0.89 0.75 0.77 Gd 3.1 3.9 3.8 2.8 3.2 3.2 Tb 0.51 0.57 0.59 0.39 0.55 0.51 Dy 3.2 4.1 4.1 2.7 3.7 3.0 Ho 0.69 0.90 0.88 0.59 0.81 0.60 Er 2.1 2.5 2.5 1.8 2.4 1.7 Tm 0.27 0.38 0.36 0.20 0.29 0.28 Yb 1.9 2.5 2.6 1.6 2.0 1.8 Lu 0.32 0.40 0.43 0.26 0.30 0.28 Sc 14 49 47 33 30 25 V 169 150 386 337 313 288 175 309 Cr 51 37 49 51 38 78 38 162 Co 12 33 29 21 14 20 Ni 18 17 26 22 5.2 22 Cu 3864 346 678 43 64 338 97 14 Zn 30 61 124 140 143 135 66 113 Ga 18 18 19 17 20 17 19 24 As <3 <3 <3 3 5 <3 8 5 Mo 41 0.67 0.63 0.30 0.32 1.7 Ag 0.21 <0.12 0.12 <0.12 0.14 0.10 Sn 1.81 1.5 1.6 Sb 0.17 0.44 0.28 0.59 0.34 0.79 W 5.5 0.35 0.44 S 1290 459 564 94 2437 5711 145 263

173

Table A1 (continued) Sample E06213 E06035 E06036 Basement units

Lithology Rio Cala CCOP basalt at Gaby subvolc. at Junin

SiO2 53.53 50.65 49.73

TiO2 1.08 2.01 2.11 Al2O3 18.05 13.07 13.20

Fe2O3 8.39 14.86 15.55 MnO 0.06 0.21 0.17 MgO 7.52 5.36 6.36 CaO 0.30 9.71 8.50

Na2O 0.41 1.60 1.62 K2O 7.00 0.15 0.13

P2O5 0.11 0.16 0.17 LOI 2.56 1.39 1.71 Total 99.1 99.2 99.3 Nb 3.1 5.8 Ta 0.18 0.35 Zr 60 97 Y 18 36 40 Hf 2.1 2.9 Cs 4.8 0.2 Rb 120 2 Ba 162 70 Sr 25 105 80 Pb <2 <2 <2 U 1.6 0.15 Th 1.6 0.50 La 7.0 5.8 Ce 16 15 Pr 2.1 2.0 Nd 9.8 12 Sm 2.5 3.7 Eu 0.55 1.3 Gd 3.0 5.6 Tb 0.45 0.85 Dy 3.0 5.9 Ho 0.62 1.2 Er 1.8 3.8 Tm 0.24 0.54 Yb 1.7 3.7 Lu 0.28 0.57 Sc 35 44 V 241 482 489 Cr 335 84 69 Co 28 38 Ni 94 55 Cu 1515 159 145 Zn 64 175 154 Ga 21 20 21 As <3 5 6 Mo 5.9 0.80 Ag 0.16 0.24 Sn 1.7 Sb 0.70 1.6 W 0.43 S 295 1663 1020

174

Tab. A2: Relative changes in concentration compared to least-altered reference sample concentration calculated from Grant (1986); isocon constructed assuming constant mass of Al2O3

Sample Magmatic Lithology Alteration SiO2 TiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O P2O5 center

E06200* Junin-Cuellaje granodiorite propy 66.22 0.41 16.58 3.60 1.69 3.99 4.42 1.46 0.14 E06202 Junin-Cuellaje granodiorite K + propy -1% 6% 4% 12% 10% 1% 3% 1% E06206A Junin-Cuellaje granodiorite K 4% 6% 9% 13% 7% 5% 10% 4% E06205A Junin-Cuellaje granodiorite K 3% -2% 3% 13% 9% 4% 20% -4% E06206B Junin-Cuellaje granodiorite K 11% 1% 1% 3% -3% 7% 25% 1%

E06135* Balsapamba qtz-diorite por. K + propy 65.63 0.43 16.45 5.70 2.01 4.68 3.39 1.32 0.10 E06131A Balsapamba qtz-diorite por. K + propy 3% 3% -7% 4% 8% 4% -4% 3% E06132 Balsapamba qtz-diorite por. K + propy 0% -2% -21% -1% 0% 4% 11% 10% E06141 Balsapamba qtz-diorite por. K + propy 3% 2% 1% 2% 1% 0% -2% 2%

E05078* Gaby hbl por. Na-Ca 62.90 0.53 16.24 5.27 2.93 7.26 3.87 0.17 0.11 E05070 Gaby hbl-plag por. Na-Ca 0% -4% -32% -6% -1% 0% 4% -2% E05073 Gaby plag-hbl por. Na-Ca -1% -4% 0% -3% -1% -1% 35% 0% E05083a Gaby plag-hbl por. Na-Ca -5% 0% 40% -14% -9% 4% 73% -2% E05083b Gaby plag-hbl por. Na-Ca -5% -3% 31% -13% -10% 5% 89% -12% E05086 Gaby plag-hbl por. Na-Ca -7% 0% 20% -23% -13% -20% 240% 12% E05088 Gaby plag-hbl por. propy -8% -4% 17% -25% -11% -19% 275% 11% E06048 Gaby hbl-plag por. Na-Ca -2% -4% -3% -10% -3% -1% 44% -11% E06051 Gaby plag por. K -6% -4% 0% -9% -3% -14% 240% -12% E06053 Gaby plag por. K -5% 6% 25% 1% -4% -14% 266% -1%

E05090 Gaby hbl-plag por. Na-Ca/propy -6% -4% 17% -6% 6% -46% 1% -4%

E05072 Gaby hbl-plag por. Na-Ca/propy -4% -4% 14% -5% -10% -5% 216% -2% E05076 Gaby hbl por. Na-Ca -5% -3% -52% -14% -14% 26% 4% 2% E06033 Gaby plag-hbl por. propy -9% -3% 17% -24% -12% -23% 242% -6% E06041 Gaby plag-hbl por. propy -7% -1% -3% -26% -13% -3% 22% 3% K + Na-Ca E06046 Gaby hbl-plag por. -6% -3% 20% -8% -12% -10% 306% -12% K + Na-Ca E06050 Gaby plag-hbl por. -2% 2% -38% -1% 9% -3% 102% -11% Na-Ca/propy E06044 Gaby plag(-hbl) por. -1% -5% 20% -4% 4% -50% 121% -19%

E06081* Portovelo andesite propy 58.85 0.70 16.16 6.70 3.52 6.67 2.50 1.48 0.11 E06082 Portovelo andesite propy -3% 0% 5% 11% -3% 6% -19% -2% propy (weak) E06120 Portovelo andesite -3% 2% 2% -3% -9% -7% 39% 7% E06074 Portovelo andesite propy -2% 2% 8% 1% 5% 0% 3% 0% E06075 Portovelo andesite propy 0% -2% 1% -1% -2% 4% 8% 0% propy (strong) E06083A Portovelo andesite 0% 2% -4% 13% -9% 1% -16% 9% propy (strong) E06083B Portovelo andesite 3% 0% -3% -14% 11% 9% -40% 11% E06084 Portovelo andesite propy 1% -1% -3% -4% -16% 5% 42% 9% Portovelo andesite propy E06086 0% 3% -2% 8% -21% 32% 17% 0%

Abbreviation key minerals: qtz - quartz, hbl - hornblende, plag - plagioclase; alteration: propy - propylitic, K - potassic, Na-Ca - sodic- calcic (cf. Seedorff et al. 2005); por – porphyry intrusion. * reference sample where concentration is given in wt.% (major element oxides) and ppm (trace elements)

175

Tab. A2 (continued)

Nb Ta Zr Y Hf Cs Rb Ba Sr U Th Sample

E06200* 2.4 0.2 78.8 5.9 2.1 1.8 29.5 1406 563 1.0 1.7 E06202 5% -8% -9% 27% -3% -31% -14% -66% 3% -23% -13% E06206A 11% -1% 7% 24% 9% -43% -4% -52% 2% -15% 35% E06205A 20% 0% E06206B 35% -7%

E06135* 2.2 0.2 59.0 8.7 1.7 2.5 30.7 202 340 1.0 1.6 E06131A -3% -6% -1% 26% 1% -23% -21% 33% 0% -30% -13% E06132 2% 18% -5% -8% -2% 4% -8% 20% 2% -7% -3% E06141 -7% 5% -5% 6% -4% -20% -12% 2% 1% -8% -13%

E05078* 2.1 0.2 66.2 14.6 1.8 0.3 2.0 134 297 0.5 1.1 E05070 0% -3% -4% -7% 3% 22% 30% -1% 2% -10% -5% E05073 -1% -5% -3% 1% 4% 13% 99% 22% 1% -3% 2% E05083a 9% -1% -3% -18% -1% 3% 122% -30% -8% -10% -14% E05083b 10% -15% -5% -17% -1% 7% 196% -33% -7% -7% -20% E05086 25% 2% 4% 9% 5% 74% 325% 201% -2% -8% -11% E05088 21% 3% 1% 5% -5% 94% 415% 190% -2% -14% -13% E06048 -10% -35% 0% 1% 0% 9% 18% -9% -3% 36% 3% E06051 5% -11% 0% -6% -3% 232% 569% 28% -5% 99% 5% E06053 4% -14% -2% 5% 2% 344% 671% 8% -5% 66% 2% E05090 10% -23% 1% -15% -20% 153% 67% -46% 0% 0% -4% E05072 -7% -1% E05076 -13% -19% E06033 4% -1% E06041 10% -7% E06046 -7% -5% E06050 -2% 0% E06044 -17% 0%

E06081* 4.1 0.3 121.8 19.7 3.3 1.4 28.5 677 344 1.8 5.6 E06082 -7% -6% -12% -7% -8% 46% 10% -33% -13% -21% -16% E06120 -3% -1% -9% -2% -14% 259% 115% -20% -27% -18% -17% E06074 -2% -18% E06075 -4% -18% E06083A 1% -20% E06083B 4% -8% E06084 1% -18% E06086 -1% 2%

176

Tab. A2 (continued)

La Nd Sm Eu Gd Dy Yb Sc V Cr Ni Sample

E06200* 8.5 9.0 1.9 0.5 1.5 0.9 0.5 7.9 81 27 13.3 E06202 7% 8% -1% -2% -3% 43% 20% 10% 4% 4% 32% E06206A 31% 18% 8% 13% 40% 40% 62% 20% 3% 53% 26% E06205A -12% -1% E06206B -8% 19%

E06135* 5.3 5.0 1.1 0.5 1.1 1.2 1.0 12.5 100 16 9.6 E06131A 23% 52% 64% 4% 47% 49% 1% 8% 0% -10% 16% E06132 58% 64% 46% 7% -7% -6% -17% -5% 9% -13% 3% E06141 6% 2% -12% -19% 4% 1% 2% 2% -1% -11% -13%

E05078* 5.1 6.7 1.9 0.6 1.8 2.3 1.6 21.3 171 30 9.6 E05070 -12% -4% -13% 8% -4% -9% -4% -2% -32% -5% -8% E05073 -19% 6% -5% 11% 8% -1% 5% 1% -21% -3% -14% E05083a -9% 1% -6% 5% 21% -14% -30% -15% -26% 2% -18% E05083b 3% 14% -15% 8% 22% -16% -22% -18% -27% -6% -12% E05086 26% 23% 6% 24% 21% 8% 12% -12% -35% -24% -40% E05088 22% 13% -3% 6% 20% 6% -11% -13% -38% -24% -54% E06048 -30% 24% 30% 24% 37% -2% -2% -21% -24% -8% 0% E06051 121% 22% -16% -13% -17% -20% -5% -8% -20% -26% 29% E06053 20% -2% -8% -2% -11% -12% 2% -5% -10% 104% 18% E05090 19% 6% -21% -12% -10% -21% -3% -26% -27% 12% 1% E05072 -22% 7% E05076 -59% -6% E06033 -36% -24% E06041 -36% -46% E06046 -21% -6% E06050 -24% 31% E06044 -25% 20%

E06081* 13.3 13.8 3.4 0.7 3.2 3.4 2.1 20.9 146 46 19.4 E06082 -12% -8% -9% 7% -1% -1% -10% 8% 4% 2% -31% E06120 -7% -6% -19% 4% -6% -18% -20% 4% 10% 87% -13% E06074 8% -5% E06075 -2% -14% E06083A 1% 1% E06083B -1% -9% E06084 -4% -15% E06086 -3% 19%

177 178 CHAPTER VI GENERAL CONCLUSIONS AND OUTLOOK

Late Miocene led to the eastward migration of Conclusions arc magmatic activity in northern Ecuador. The main objective of this thesis was to explore Chapter 3 demonstrates that porphyry‐related the mutual relationships of geodynamic envi‐ ore deposits in Ecuador formed throughout the ronment, the geochemical features of arc mag‐ Miocene (and latest Oligocene) and follow the matism, and porphyry‐related ore deposit forma‐ general distribution of arc magmatism in space tion in Ecuador at a regional scale. Organized in and time. These ore deposits share many charac‐ four principal chapters, I describe and discuss teristics with, and may be regarded as the north‐ new geochronologic data on arc magmatism ern extension of the central‐northern Peruvian (Chapter 2) and porphyry‐related hydrothermal Miocene metallogenic belt of major economic systems in Ecuador (Chapter 3), as well as on the importance. Ore deposits are often located close isotopic (Chapter 4) and major and trace element to regional structures where focused upper geochemical composition (Chapter 5) of Late Ter‐ crustal magma ascent is suggested by the occur‐ tiary porphyry‐related arc magmas. The geody‐ rence of batholith‐scale intrusive clusters. Por‐ namic evolution of the Panama basin and the Ec‐ phyry‐related ore deposits tend to form towards uadorian margin as known from published data is the final stages of batholith assembly. referenced where appropriate, and supple‐ Suitable exposure (in particular, the lack of mented by a recalculation of the most recent set younger volcanic cover sequences in the Mid‐ to of available Farallon/Nazca‐South America plate Late Miocene flat slab region of southern Ecua‐ convergence parameters for central Ecuador dor) and preservation levels are key factors in (Chapter 2), a discussion of the oblique subduc‐ controlling the outcropping parts of porphyry tion system of Ecuador and its implications for systems and their total tonnages (compare, for crustal strain partitioning (Appendix of Chapter example,e th deeply eroded western foothills of 2), and an updated estimate of the collisional tim‐ the Western Cordillera where locally only the ing of the Carnegie Ridge seamount chain with roots of porphyry systems are preserved, and the the Ecuadorian margin (Chapter 3). bulk of the porphyry Cu mineralization has often As shown in Chapter 2, the regional distribution been eroded). A first‐order spatio‐temporal cor‐ pattern of Tertiary arc magmatism in Ecuador relation between ore deposit formation and shows a strong dependency on crustal structures seamount chain subduction, as proposed by (often reactivated suture zones) and eslab dip, th some authors for the central and southern An‐ latter probably influenced by the subduction of des, is not observed in Ecuador. However, by its buoyant oceanic features such as the Inca pla‐ influence on slab dip (with a potential lag time of teau (southern Ecuador‐northern Peru) and the several m.y.), the subduction of buoyant oceanic Carnegie Ridge seamount chain (northern Ecua‐ features may strongly influence the outcrop pat‐ dor). An arc magmatic flare‐up event comprising tern of arc magmatism, and thus the exposure widespread ignimbrite eruption and batholith and preservation levels of older porphyry‐related construction occurred in the Late Oligocene to ore deposits. Early Miocene and coincides in time with an ac‐ Pronounced crustal evolution of Tertiary arc celeration of Farallon/Nazca‐South America con‐ magmas can be demonstrated by systematically vergence rates. Mid‐ to Late Miocene slab flat‐ changing isotopic (Sr, Nd, Pb) compositions tening progressively shut down arc magmatism in across the arc, reflecting variable basement units the southern Ecuadorian (and northern Peruvian) at depth (Chapter 4). Entirely oceanic basement arc segment, and moderate slab shallowing in the

179 domains host both Au‐Cu and Cu‐Mo porphyry optimum exposure and preservation conditions systems suggesting that crustal basement com‐ for Miocene porphyry‐related ore deposits in position does not control the type of mineraliza‐ southern Ecuador (and northern Peru). tion encountered in a given porphyry system in From a regional mineral exploration point of Ecuador. view, the following major conclusions apply for As discussed in Chapter 5, trace element compo‐ Ecuador: sitions of Ecuadorian arc magmas change sys‐ . Miocene intrusive rocks in Ecuador are inti‐ tematically through time suggesting progressive mately associated with porphyry‐related ore crustal thickening, downwards migration of the deposits at structurally favorable sites. focus of crustal magma evolution (i.e., hot zones), or a combination of both. Moreover, local factors . The cluster of southern Ecuadorian porphyry‐ such as different melt water contents may influ‐ related ore deposits can be regarded as the ence variations in trace element trends through northward extension of the Miocene metal‐ time. Additional variations in the magma source logenic belt of northern‐central Peru. The composition (e.g., with thee chang from Farallon belt is possibly continuous towards Colombia. to Nazca seafloor subduction at the Ecuadorian . A special geodynamic setting (e.g., ridge sub‐ trench during the Miocene) are possible, but can‐ duction) facilitating slab flattening and a not be evaluated with the current dataset of shutdown of arc magmatism may create fa‐ mostly highly differentiated compositions. With vorable exposure conditions for porphyry‐ few exceptions, Late Tertiary Ecuadorian arc related ore deposits formed earlier. This is magmas are mainly non‐adakitic until the Late the case for Miocene ore deposits in south‐ Miocene when adakite‐like signatures are ob‐ ern Ecuador where Late Miocene slab flatten‐ served frequently on a regional scale, a trend that ing occurred. dominates until the present day. . Miocene porphyry‐related ore deposits in Chapter 5 shows that, for the most part, the geo‐ Ecuador are not preferentially associated chemical signatures of porphyry intrusions, in with intrusions of special (in particular, ada‐ particular adakite‐like features, are similar to the kite‐like) geochemical compositions. Por‐ regional geochemical characteristics of arc mag‐ phyry parental melts are not petrogenetically matism for a given period of time. Distinct geo‐ related to slab melting, and thus do not re‐ chemical signatures of porphyry intrusions with quire a special geodynamic setting to form, respect to spatially associated phaneritic intru‐ although the latter may strongly influence sions are occasionally observed. In the latter the exposure conditions of porphyry‐related case, however, there is a time gap of several m.y. mineralization as noted above. between mineralizing porphyry intrusion and phaneritic pluton emplacement, and the change in geochemical composition through time occurs Outlook on a regional scale. These observations suggest This thesis was designed to discuss the metal‐ that parental melts of Tertiary porphyry‐related logenic and petrogenetic evolution of multiple ore deposits in Ecuador are related to ordinary arc segments for which available literature data arc magmatism; they are not associated with a are very sparse. Consequently, the conclusions of distinctive petrogenetic source process such as this work have to be rather general, and several slab melting requiring a special geodynamic envi‐ problematic issues arise; each of these was partly ronment. This agrees well with multiple studies addressed in the discussion of the appropriate which have shown that adakite‐like features of chapter(s) of this thesis, but will briefly be re‐ active Ecuadorian arc volcanoes are the product addressed in the following, combined with a gen‐ of crustal magma evolution, rather than being eral outlook for future work directions. Three of exclusively related to a specific petrogenetic the main issues are: source process such as slab melting. As noted (1) The regional aspect of the subject of this thesis above, however, the post‐porphyry establish‐ implies that, in addition to newly acquired data ment of a flat slab segment may locally create

180 within the frame of this PhD project, literature necessarily be equivalent to (or representative data had to be taken into account for various dis‐ of) the general evolution of Tertiary arc magma‐ cussions (in particular with respect to the spatio‐ tism for which very limited reliable data exist. temporal distribution of arc magmatism). Are Thus, although present‐day Northern Volcanic geochronologic data used from the literature ro‐ Zone (NVZ) geochemical data are used for com‐ bust at a scale significant for this work? parative purposes in Chapter 5, the discussed systematic differences between NVZ and earlier The lack of robust geochronologic data in Ecua‐ Tertiary magmatism might in part be due to in‐ dor often necessitated the consideration of pub‐ complete coverage of the latter, in particular as lished ages based on the potentially disturbed K‐ porphyry‐related intrusions were often of highly Ar isotopic system for the purpose of a regional differentiated compositions. discussion of arc magmatism. Where robust geo‐ chronologic data were available for the same Sampling at a given deposit site was not carried lithology, existing K‐Ar data show broadly (on a out using a systematic grid, but instead was con‐ multi‐m.y. scale) similar ages. All K‐Ar ages used trolled by outcrop and drill core accessibility, al‐ in this thesis were screened carefully and a sys‐ though an attempt was made to include all rele‐ tematic disturbance was not detected; single po‐ vant lithologies in the sampling campaign. As tentially disturbed K‐Ar ages were excluded from knowledge of the individual ore deposit geology the database (Appendix Chapter 2). A systematic at the time of sampling, depending on the devel‐ age bias and resulting significant inaccuracies in opment stage of a given deposit, was highly vari‐ the ndiscussio (especially of Chapter 2) are thus able, it is further possible that sampling was unlikely, although they cannot be entirely ruled somewhat biased and not all lithologies were in‐ out. Future geologic studies in Ecuador aiming at cluded (this applies to both geochemistry and constructing a regionally extensive and robust geochronology). Hence, the number of samples geochronologic framework, both of Tertiary and for geochemical analysis for a given ore deposit older lithologies, would be highly desirable and does not reflect the volume of a particular lithol‐ seem scientifically and economically justified, ogy. Samples chosen for geochronologic analysis given the geologic complexity and metallogenic provide snapshots of the temporal evolution of potential of the country. the magmatic‐hydrothermal system, but do not cover its complete history, especially when mul‐ (2) How representative (in terms of space‐time tiple porphyry intrusions are present. This issue distribution and geochemical composition) is the complicates comparing ages obtained from dif‐ regional sampling approach of this study for Ec‐ ferent isotopic systems (e.g., U‐Pb zircon vs. Re‐ uadorian arc magmatism on a regional scale, and Os molybdenite). More extensive studies of some for individual ore deposits on a local scale? of these ore deposits may only prove useful once This thesis does not comprehensively assess the outcrop accessibility improves, and significant geochemical evolution of Tertiary arc magma‐ progress in project development on behalf of the tism. Instead, it focuses on intrusive suites asso‐ concession holder has been made. ciated with the major porphyry‐related ore de‐ (3) What is the significance of the observed geo‐ posits known during the early planning stages of chemical trends? this PhD project (2005‐2007). Several major batholiths (such as Portachuela in southern Ecua‐ I attempt to statistically evaluate hydrothermal dor) which are partly associated with Tertiary alteration‐induced element mobility in Chapter 5 porphyry‐related mineralization (e.g., the Rio beyond the generic "LILE are mobile, HFSE are Blanco porphyry at the Peruvian‐Ecuadorian bor‐ immobile" scheme by using isocon plots where der) had to be excluded completely due to diffi‐ possible. The results of this exercise are some‐ cult field logistics; arc volcanics were generally what discouraging as most elements (including not sampled except on few occasions where they HFSE such as Y, Nb, and Ta) may be variably mo‐ are spatially associated with epithermal minerali‐ bile, and scatter within a given lithology often zation. Consequently, the trace element vs. time exceeds the expected 10% relative error as in‐ distribution trends shown in Chapter 5 may not ferred from analytical precision. Although some

181 elements, in particular Sr, do not seem to be sig‐ nificantly affected by alteration in three out of four isocon plots shown in Chapter 5, the as‐ sumption that these isocon plots are representa‐ tive for the whole dataset cannot be proven. However, individual trace elements and trace element ratios mostly show correlated behavior where expected (e.g., amphibole fractionation causes increasing Sm/Yb and decreasing Y, both of which is observed in the dataset on a regional scale), and trace element distributions through time are consistent with the conclusions pre‐ sented in Chapter 5 (cf. synthesis above). There‐ fore, while alteration has undoubtedly affected trace element concentrations in most samples to a significant extent, broad regional trends seem to hold some petrogenetic relevance. Further‐ more, as (according to isocon plots) both Sr and Y are only moderately mobile in most cases, I ex‐ pect that a genuine distinction of adakite‐like vs. non‐adakitic features of porphyry and phaneritic intrusions is possible (with the exception of the Junin porphyry system where strong phyllic al‐ teration caused massive feldspar replacement by sericite, and measured Sr contents probably do not approximate fresh rock values). For future works, high‐resolution geochemical studies at the deposit scale might allow quantify‐ ing petrogenetic trends for suites of cogenetic samples, and to better account for alteration ef‐ fects by more detailed mineralogical studies (e.g., electron microprobe analysis of igneous and al‐ teration mineral compositions) which may be used as a reference for regional studies under comparable conditions in a given arc segment. As most investigated porphyry systems comprise multiple intrusive phases, such a high‐resolution study would ideally be coupled with more de‐ tailed geochronologic work based on a solid field campaign which should also include local‐ regional structural studies. The latter is of major importance when evaluating geodynamic changes and their feedback on arc magmatism as it might help unraveling the transitions from in‐ ferred regional to observed local stress field variations, and the potential implications for crustal magma evolution and emplacement.

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