DOCSLIB.ORG

Chapter 14 Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 14 Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes © 2012 Society of Economic Geologists, Inc. Special Publication 16, pp. 329–360 Chapter 14 Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes CONSTANTINO MPODOZIS† AND PAULA CORNEJO Antofagasta Minerals, Apoquindo 4001, Piso 18, Santiago, Chile Abstract Subduction under South America has been active for the past 550 m.y. but large porphyry copper deposits were essentially emplaced during the Paleocene (60−50 Ma) in southern Peru, and mid-Eocene-early Oligocene (43−32 Ma) and late Miocene-Pliocene (10−6 Ma) in north and central Chile. Although the tectonic setting of the Paleocene porphyry deposits is still poorly understood, those of the northern Chile Eocene- Oligocene belt were emplaced along the margin-parallel Domeyko fault system, where active compressional and/ortranspressional deformation and block rotations took place during the formation of the Bolivian orocline. Eocene-early Oligocene oroclinal bending was a consequence of differential tectonic shortening focused along a mechanically weak zone of the Central Andean crust inherited from the Paleozoic. Deformation occurred during an episode of accelerated westward absolute motion of the South American plate, which coincided with very high rates of oceanic crust production in the eastern Pacific. The slow South American-Farallon conver- gence rates recorded for the Eocene-Oligocene suggest, however, that strong interplate coupling existed dur- ing that time. This permitted the transfer of horizontal stresses and large-scale deformation of the Andean mar- gin, creating a favorable scenario for the generation and emplacement of porphyry copper magmas along the Domeyko fault system. The younger, Miocene-Pliocene porphyry copper deposits of central Chile-Argentina were emplaced in a different setting, after the initiation of compressional deformation within a volcano-tectonic depression (Aban- ico basin) that evolved during another, late Oligocene to early Miocene, period of increased East Pacific oceanic crust production. Nevertheless, in contrast to the Eocene-Oligocene situation in northern Chile, the relatively stationary position of the South American plate compared to the mantle reference frame and weak interplate coupling that permitted rapid subduction, increased volcanism, and overriding plate extension. Tec- tonic inversion of the basin and compressional deformation along with crustal thickening and mountain build- ing began at around 20 m.y. ago as interplate coupling increased when the westward motion of South America accelerated and the Nazca-South America convergence velocity decreased in the mid-Miocene. Compression was accompanied, as during the Eocene-Oligocene in northern Chile, by slab shallowing and increased fore- arc subduction erosion. In both cases, the largely structurally controlled, syn- to post-tectonic porphyry copper deposits are associ- ated with long-lived magmatic systems that were active for more than 10 m.y. In northern Chile, the deposits occur as parts of discrete intrusive clusters that comprise a suite of precursor plutons emplaced during multi- ple events since the Cretaceous. Porphyry copper mineralization is linked to multistage, amphibole-bearing in- trusions of intermediate composition derived from hydrous, oxidized magmas with adakitic geochemical sig- natures. These intrusions appeared when crustal thickness increased to a critical threshold in the course of deformation. Production of magmas with high metal-carrying capacity was fostered as fluids were liberated when amphibole became unstable and was destroyed as the crust thickened. At the same time, source regions within the mantle were contaminated by hydrated fragments of fore-arc continental crust, as the result of en- hanced subduction erosion during peaks of compressional deformation. Introduction Basin and Range extension in the Eocene, far inland from the THE STUDY of the tectonic setting of porphyry copper deposits Pacific margin of North America (Kloppenburgh et al., 2010). is fundamental to understanding their genesis (e.g., Sillitoe, Noncollisional porphyry copper deposit examples in sub- 1998; Kay and Mpodozis, 2001; Cooke et al., 2005; Sillitoe duction-related arc settings include those from the Chagai and Perelló, 2005; Richards, 2009, 2011a; Tosdal et al., 2009). belt in Pakistan, the Laramide porphyry copper province of Some Cenozoic porphyry copper deposits are known to have the western United States and northern Mexico (Lang and Ti- formed during or shortly after continent-continent, conti- tley, 1998; Valencia-Moreno et al., 2007; Perelló et al., 2008) nent-island arc, or island arc-island arc collisions in the Hi- and the Central Andes province, which host some of the malayas-Tibet, the Kerman arc in Iran, and Papua New largest known porphyry copper deposits in the world (Camus, Guinea (Solomon, 1990; Zenqiang et al., 2003; Shaifei et al., 2003; Cooke et al., 2005; Sillitoe and Perelló, 2005). 2009). A Paleozoic example of this type of deposit may be The Andes has long been considered as the type example of Oyu Tolgoi in Mongolia (Perelló et al., 2001). In contrast, a noncollisional orogenic system (e.g., Jordan et al., 1983), other large porphyry deposits such as Bingham Canyon in the where subduction of Pacific oceanic crust beneath South western United States formed during the earliest stages of America has been active for the past 570 m.y. (Cawood, 2005). Nevertheless, the largest porphyry copper deposits are † Corresponding author: e-mail, [email protected] the result of anomalous magmatic systems that developed 329 Downloaded from https://pubs.geoscienceworld.org/books/chapter-pdf/3813036/9781629490410_ch14.pdf by guest on 05 August 2020 330 MPODOZIS AND CORNEJO during short periods at specific locations within the Andean Diverse, yet basically subeconomic, porphyry copper deposits orogen. These include the Paleocene to early Eocene (66−52 formed during these events in northern Chile and along the Ma) and middle Eocene to early Oligocene (43−32 Ma) belts Frontal Cordillera in west-central Argentina (Sillitoe, 1977; in southern Peru and northern Chile, and the late Miocene to Sillitoe and Perelló, 2005; Cornejo et al., 2006; Munizaga et early Pliocene (10−5 Ma) porphyry systems in central Chile al., 2008). and contiguous Argentina (Perelló et al., 2003a; Sillitoe and Perelló, 2005). In this contribution, with emphasis on the Jurassic to Early Eocene Tectonics and Chilean belts, we will try to demonstrate how major Cenozoic Metallogeny of the Central Andes tectonic events along the central Andean convergent margin, After the Triassic rifting event, subduction was reestab- prompted by large-scale reorganizations of the global tectonic lished in northern Chile and southern Peru during the Early system, were the main triggers for the formation of large por- Jurassic when a new magmatic arc developed west of the phyry copper deposits. extinct late Paleozoic arc front. Since then, subduction has proceeded uninterrupted to date. Initial Jurassic to Early Pre-Andean History: Cretaceous arc magmatism occurred under extensional con- From Rodinia Dispersal to Pangea Breakup ditions that permitted the formation of a series of intercon- The western margin of South America underwent mag- nected back-arc basins to the east of the main arc, which were matic and tectonic activity at least since the late Neoprotero- progressively filled with marine and continental sedimentary zoic breakup of Rodinia (800−700 Ma), when the separation strata (Mpodozis and Ramos, 1989, 2008). Transpressional of Laurentia from Gondwana produced the opening of the deformation along the arc axis created the intra-arc Atacama proto-Pacific (Iapetus) ocean (Dalziel, 1997). East-directed fault system in northern Chile (Scheuber and González, subduction of newly formed ancestral Pacific crust below 1999) and was accompanied in the Early Cretaceous by the western Gondwana began at ~570 Ma and was fully active emplacement, in northern Chile, of some porphyry copper along the proto-Andean margin by 485 to 465 Ma (Pankhurst deposits at ~140 to 130 Ma (e.g., Antucoya-Buey Muerto, et al., 1998; Cawood, 2005; Chew et al., 2007). Plate conver- 141−139 Ma; Puntillas-Galenosa, 135−132 Ma; Perelló et al., gence in the Central Andes region during the Ordovician to 2003b; Maksaev et al., 2006, 2010). Fast convergence rates Devonian included the progressive collision and accretion of during the global mid Cretaceous superplume event (Larson, a group of tectonostratigraphic terranes of Laurentian and/or 1991) produced an upsurge in volcanism along the Andean Gondwanan affinities (e.g., Ramos et al., 1986; Astini et al., margin, accompanied by intra-arc extension and transtension 1995) against the western South American margin. Terrane which fostered iron oxide-copper-gold (IOCG)−type mineral- amalgamation contributed to the formation of the accre- ization between 120 and 100 Ma in northern Chile and south- tionary Terra Australis orogen, which extended for more than ern Peru (Marschik and Fontboté, 2001; Sillitoe, 2003; Silli- 18,000 km along the Pacific margin of Gondwana from Aus- toe and Perelló, 2005; Chen et al., 2010). Small, low-grade, tralia to South America (Cawood, 2005). The accretionary gold-rich porphyry copper deposits such as Andacollo (104 stage was followed, in the Central Andes, by the buildup of a Ma), Domeyko-Dos Amigos (108−104 Ma), and Pajonales (97 late Carboniferous to Early Permian (320? -280 Ma) supra- Ma) were emplaced under extensional conditions during
Load more

Recommended publications
  • Uplift, Rupture, and Rollback of the Farallon Slab Reflected in Volcanic
    PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Uplift, rupture, and rollback of the Farallon slab reflected 10.1002/2017JB014517 in volcanic perturbations along the Yellowstone Key Points: adakite hot spot track • Volcanic perturbations in the Cascadia back-arc region are derived from uplift Victor E. Camp1 , Martin E. Ross2, Robert A. Duncan3, and David L. Kimbrough1 and dismemberment of the Farallon slab from ~30 to 20 Ma 1Department of Geological Sciences, San Diego State University, San Diego, California, USA, 2Department of Earth and • Slab uplift and concurrent melting 3 above the Yellowstone plume Environmental Sciences, Northeastern University, Boston, Massachusetts, USA, College of Earth, Ocean, and Atmospheric promoted high-K calc-alkaline Sciences, Oregon State University, Corvallis, Oregon, USA volcanism and adakite generation • Creation of a seismic hole beneath eastern Oregon resulted from thermal Abstract Field, geochemical, and geochronological data show that the southern segment of the ancestral erosion and slab rupture, followed by Cascades arc advanced into the Oregon back-arc region from 30 to 20 Ma. We attribute this event to thermal a period of slab rollback uplift of the Farallon slab by the Yellowstone mantle plume, with heat diffusion, decompression, and the release of volatiles promoting high-K calc-alkaline volcanism throughout the back-arc region. The greatest Supporting Information: • Supporting Information S1 degree of heating is expressed at the surface by a broad ENE-trending zone of adakites and related rocks • Data Set S1 generated by melting of oceanic crust from the Farallon slab. A hiatus in eruptive activity began at ca. • Data Set S2 22–20 Ma but ended abruptly at 16.7 Ma with renewed volcanism from slab rupture occurring in two separate • Data Set S3 regions.
    [Show full text]
  • 0 Master's Thesis the Department of Geosciences And
    Master’s thesis The Department of Geosciences and Geography Physical Geography South American subduction zone processes: Visualizing the spatial relation of earthquakes and volcanism at the subduction zone Nelli Metiäinen May 2019 Thesis instructors: David Whipp Janne Soininen HELSINGIN YLIOPISTO MATEMAATTIS-LUONNONTIETEELLINEN TIEDEKUNTA GEOTIETEIDEN JA MAANTIETEEN LAITOS MAANTIEDE PL 64 (Gustaf Hällströmin katu 2) 00014 Helsingin yliopisto 0 Tiedekunta/Osasto – Fakultet/Sektion – Faculty Laitos – Institution – Department Faculty of Science The Department of Geosciences and Geography Tekijä – Författare – Author Nelli Metiäinen Työn nimi – Arbetets titel – Title South American subduction zone processes: Visualizing the spatial relation of earthquakes and volcanism at the subduction zone Oppiaine – Läroämne – Subject Physical Geography Työn laji – Arbetets art – Level Aika – Datum – Month and year Sivumäärä – Sidoantal – Number of pages Master’s thesis May 2019 82 + appencides Tiivistelmä – Referat – Abstract The South American subduction zone is the best example of an ocean-continent convergent plate margin. It is divided into segments that display different styles of subduction, varying from normal subduction to flat-slab subduction. This difference also effects the distribution of active volcanism. Visualizations are a fast way of transferring large amounts of information to an audience, often in an interest-provoking and easily understandable form. Sharing information as visualizations on the internet and on social media plays a significant role in the transfer of information in modern society. That is why in this study the focus is on producing visualizations of the South American subduction zone and the seismic events and volcanic activities occurring there. By examining the South American subduction zone it may be possible to get new insights about subduction zone processes.
    [Show full text]
  • Cambios Ambientales Pleistoceno-Holocénicos: Ocupación Humana Y Uso De Recursos En La Puna De Atacama (Norte De Chile)
    Estudios Atacameños Nº 11, pp. 7-20 (1994) Cambios ambientales pleistoceno-holocénicos: Ocupación humana y uso de recursos en la Puna de Atacama (norte de Chile) Lautaro Núñez1 y Martin Grosjean2 RESUMEN Las fluctuaciones climático-ambientales en los Andes Centro Sur han jugado un papel importante en las Los datos paleoambientales indican que los recursos de variaciones de la estabilidad ocupacional paleoin- agua, vegetación y fauna de la Puna de Atacama (>4000 dia y arcaica (Lynch 1990; Fernández et al. 1991; m.snm), fueron abundantes durante la última edad glacial y Holoceno Temprano, mientras que las condiciones de aridez Núñez et al. 1993). Esto implica que los cambios en prevalecieron bajo los 3500 m. Los cazadores del Período la disponibilidad de los recursos naturales impactó Arcaico Temprano (ca. 10800 a 8500 AP) estaban adaptados directamente sobre los patrones de subsistencia. a la alta Puna y su piedemonte, a lo largo del desagüe de Especialmente en áreas con alimentos y abasteci- los ríos provenientes de las tierras altas, en donde los re- miento hídrico marginal, los cambios ambientales cursos de diferentes alturas se explotaban óptimamente en forma trashumante dentro de distancias cortas. Los lagos rápidos y drásticos, como los observados durante se restringieron a los niveles actuales y el proceso pedo- la transición Pleistoceno/Holoceno, constituyeron genésico concluyó en la alta Puna. Los recursos naturales fuerzas conductoras primarias en el modo de subsis- decrecieron significativamente durante el Período Arcaico tencia de las ocupaciones de cazadores recolectores Medio (ca. 8500-5000 AP), de manera que las actividades limitadas a recursos altamente fluctuantes.
    [Show full text]
  • Palaeoindian Occupation of the Atacama Desert, Northern Chile
    Palaeoindian occupation of the Atacama Desert, northern Chile MARTIN GROSJEAN,1* LAUTARO NU´ N˜ EZ2 and ISABEL CARTAJENA3 1 National Center of Excellence in Research on Climate (NCCR Climate) and Institute of Geography, University of Bern, Bern, Switzerland 2 Instituto de Investigaciones Arqueolo´gicas y Museo, Universidad Cato´lica del Norte, San Pedro de Atacama, Chile 3 Departamento de Antropologı´a, Universidad de Chile, N˜ un˜oa, Santiago de Chile ABSTRACT: Palaeoindian occupation of the Atacama Desert in northern Chile has been found between 12 600 and 10 200 cal. yr BP. The new site at Salar Punta Negra (24 280S/60 530W/ 2976 m) includes about 1000 classifiable, mostly unifacial artefacts and, uniquely, three different diagnostic types of early projectile points. Two of the Lateglacial/early Holocene projectile types have wide distribution and are known from different geographical areas in South America: the Palaeoindian ‘Fell’ fish-tail point mainly from the southern cone of South America, and the triangular ‘Tuina’ points typical of the Puna of the south-central Andes in northern Chile and northwestern Argentina. In addition, we found a third type, a stemmed point typical for the Salar Punta Negra. Fill- ing a large geographical gap of ‘Fell’ occupation, the site at Salar Punta Negra provides evidence for generally much higher mobility and diversity of early cultures, and supports an Andean-Pacific route for early human exploration of South America to the south through the desert at intermediate alti- tudes. Contemporaneous high-amplitude climatic changes were fundamental preconditions to pro- vide adequate environments and habitats, and to make Palaeoindian hunting-gathering occupation possible in the Atacama Desert.
    [Show full text]
  • Exhumation and Uplift of the Western Main Cordillera Between 33° and 34°5
    6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 273-276 Exhumation and uplift of the western Main Cordillera between 33° and 34°5 Andrés Fock" Reynaldo Charrier 2, Marcelo Fadas 3, Victor Maksaev 4, Mark Fanning 5, & Pamela Alvarez 6 1 Departamento de Geologia, Universidad de Chile, Santiago, Chile ([email protected]); 2 Departamento de Geologia, Universidad de Chile, Santiago, Chile ([email protected]); 3 Departamento de Geologia, Universidad de Chile, Santiago, Chile, and LMTG-IRD, Université Paul Sabatier, Toulouse, France ([email protected]); 4 Departamento de Geologia, Universidad de Chile, Santiago, Chile ([email protected]); 5 Research School of Earth Sciences, Australian National University, Camberra, Australia ([email protected]); 6 SIPETROL, Santiago, Chile ([email protected]) KEYWORDS: Central Chile, Andes, Apatite fission-track ages, Neogene mountain building INTRODUCTION ln this paper we discuss the control of major structures in the exhumation of Cenozoic rocks and surface uplift in the Andean Main Cordillera based on new apatite fission tracks age analysis and the study of geological cross -sections. Fig. 1: Principal morphostructural Units. The box shows de Study Region The study area is segmented in the following N-S oriented morphostructural units (Fig. 1), from west to east: Coastal Cordillera, Central Depression, Western and Eastern Main Cordil1era (WMC and EMC, respectively), and Frontal Cordillera. The Coastal Cordillera consists mainly of volcanic and sedirnentary Mesozoic rocks, the Aptian - Albian Las Chilcas and Maastrichtian La Valle formations and Late Mesozoic intrusive bodies (Sellés and Gana, 2001), which are in contact with Cenozoic rocks through west vergent thrust faults located in the Central Depression and the western border of the WMC.
    [Show full text]
  • Counterclockwise Rotation of Late Eocene – Oligocene Forearc Deposits in Southern Peru and Its Significance for Oroclinal Bend
    Counterclockwise rotation of Late Eocene – Oligocene forearc deposits in southern Peru and its significance for oroclinal bending in the Central Andes Pierrick Roperch, Thierry Sempere, Orlando Macedo, César Arriagada, Michel Fornari, Claudio Tapia, Marcelo Garcia, Carlo Laj To cite this version: Pierrick Roperch, Thierry Sempere, Orlando Macedo, César Arriagada, Michel Fornari, et al.. Coun- terclockwise rotation of Late Eocene – Oligocene forearc deposits in southern Peru and its significance for oroclinal bending in the Central Andes. Tectonics, American Geophysical Union (AGU), 2006, 25 (3), pp.TC3010. 10.1029/2005TC001882. insu-00261209 HAL Id: insu-00261209 https://hal-insu.archives-ouvertes.fr/insu-00261209 Submitted on 29 Jun 2016 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 25, TC3010, doi:10.1029/2005TC001882, 2006 Counterclockwise rotation of late Eocene–Oligocene fore-arc deposits in southern Peru and its significance for oroclinal bending in the central Andes Pierrick Roperch,1,2 Thierry Sempere,3 Orlando Macedo,4 Ce´sar Arriagada,2 Michel Fornari,5 Claudio Tapia,2 Marcelo Garcı´a,6 and Carlo Laj7 Received 6 July 2005; revised 20 February 2006; accepted 14 March 2006; published 1 June 2006.
    [Show full text]
  • Thermal Modelling of the Laramide Orogeny: Testing the £At-Slab Subduction Hypothesis
    Available online at www.sciencedirect.com R Earth and Planetary Science Letters 214 (2003) 619^632 www.elsevier.com/locate/epsl Thermal modelling of the Laramide orogeny: testing the £at-slab subduction hypothesis Joseph M. English a;Ã, Stephen T. Johnston a, Kelin Wang a;b a School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC, Canada V8W 3P6 b Paci¢c Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC, Canada V8L 4B2 Received 1 April 2003; received in revised form 7 July 2003; accepted 16 July 2003 Abstract The Laramide orogeny is the Late Cretaceous to Palaeocene (80^55 Ma) orogenic event that gave rise to the Rocky Mountain fold and thrust belt in Canada, the Laramide block uplifts in the USA, and the Sierra Madre Oriental fold and thrust belt in Mexico. The leading model for driving Laramide orogenesis in the USA is flat-slab subduction, whereby stress coupling of a subhorizontal oceanic slab to the upper plate transmitted stresses eastwards, producing basement-cored block uplifts and arc magmatism in the foreland. The thermal models presented here indicate that arc magma generation at significant distances inboard of the trench ( s 600 km) during flat-slab subduction is problematic; this conclusion is consistent with the coincidence of volcanic gaps and flat-slab subduction at modern convergent margins. Lawsonite eclogite xenoliths erupted through the Colorado Plateau in Oligocene time are inferred to originate from the subducted Farallon slab, and indicate that the Laramide flat-slab subduction zone was characterised by a cold thermal regime.
    [Show full text]
  • Late Mesozoic to Paleogene Stratigraphy of the Salar De Atacama Basin, Antofagasta, Northern Chile: Implications for the Tectonic Evolution of the Central Andes
    Late Mesozoic to Paleogene stratigraphy of the Salar de Atacama Basin, Antofagasta, Northern Chile: Implications for the tectonic evolution of the Central Andes Constantino Mpodozisa,T,Ce´sar Arriagadab, Matilde Bassoc, Pierrick Roperchd, Peter Cobbolde, Martin Reichf aServicio Nacional de Geologı´a y Minerı´a, now at Sipetrol. SA, Santiago, Chile bDepartamento de Geologı´a, Universidad de Chile, Santiago, Chile cServicio Nacional de Geologı´a y Minerı´a, Santiago, Chile dIRD/Dep. de Geologı´a, Universidad de Chile, Santiago, Chile eGe´osciences-Rennes (UMR6118 du CNRS), France fDepartment of Geological Sciences University of Michigan, United States Abstract The Salar de Atacama basin, the largest bpre-AndeanQ basin in Northern Chile, was formed in the early Late Cretaceous as a consequence of the tectonic closure and inversion of the Jurassic–Early Cretaceous Tarapaca´ back arc basin. Inversion led to uplift of the Cordillera de Domeyko (CD), a thick-skinned basement range bounded by a system of reverse faults and blind thrusts with alternating vergence along strike. The almost 6000-m-thick, upper Cretaceous to lower Paleocene sequences (Purilactis Group) infilling the Salar de Atacama basin reflects rapid local subsidence to the east of the CD. Its oldest outcropping unit (Tonel Formation) comprises more than 1000 m of continental red sandstones and evaporites, which began to accumulate as syntectonic growth strata during the initial stages of CD uplift. Tonel strata are capped by almost 3000 m of sandstones and conglomerates of western provenance, representing the sedimentary response to renewed pulses of tectonic shortening, which were deposited in alluvial fan, fluvial and eolian settings together with minor lacustrine mudstone (Purilactis Formation).
    [Show full text]
  • 30564 NMA 23 Degrees South
    chapter 6 Claudio Latorre, Julio L Betancourt, Jason A Rech, Jay Quade, Camille Holmgren, Christa Placzek, Antonio JC Maldonado, Mathias Vuille and Kate Rylander Late Quaternary history of the Atacama Desert Of the major subtropical deserts found in the Southern Hemisphere, the Atacama Desert is the driest. Throughout the Quaternary, the most pervasive climatic infl uence on the desert has been millennial-scale changes in the frequency and seasonality of the scant rainfall, and associated shifts in plant and animal distributions with elevation along the eastern margin of the desert. Over the past six years, we have mapped modern vegetation gradients and developed a number of palaeoenvironmental records, including vegetation histories from fossil rodent middens, groundwater levels from wetland (spring) deposits, and lake levels from shoreline evidence, along a 1200-kilometre transect (16–26°S) in the Atacama Desert. A strength of this palaeoclimate transect has been the ability to apply the same methodologies across broad elevational, latitudinal, climatic, vegetation and hydrological gradients. We are using this transect to reconstruct the histories of key components of the South American tropical (summer) and extratropical (winter) rainfall belts, precisely at those elevations where average annual rainfall wanes to zero. The focus has been on the transition from sparse, shrubby vegetation (known as the prepuna) into absolute desert, an expansive hyperarid terrain that extends from just above the coastal fog zone (approximately 800 metres) to more than 3500 metres in the most arid sectors in the southern Atacama. Our study focuses on rodent middens (cf. Betancourt et al. 1990). These are amalgamations of plant remains (including seeds, fl owers, leaves and wood), bones, insects, feathers and rodent faeces, glued together within a crystallised matrix of rodent urine.
    [Show full text]
  • PDF Linkchapter
    Index Page numbers in italic denote Figures. Page numbers in bold denote Tables. Abanico extensional basin 2, 4, 68, 70, 71, 72, 420 Andacollo Group 132, 133, 134 basin width analogue modelling 4, 84, 95, 99 Andean margin Abanico Formation 39, 40, 71, 163 kinematic model 67–68 accommodation systems tracts 226, 227, 228, 234, thermomechanical model 65, 67 235, 237 Andean Orogen accretionary prism, Choapa Metamorphic Complex development 1, 3 20–21, 25 deformation 1, 3, 4 Aconcagua fold and thrust belt 18, 41, 69, 70, 72, 96, tectonic and surface processes 1, 3 97–98 elevation 3 deformation 74, 76 geodynamics and evolution 3–5 out-of-sequence structures 99–100 tectonic cycles 13–43 Aconcagua mountain 3, 40, 348, 349 uplift and erosion 7–8 landslides 7, 331, 332, 333, 346–365 Andean tectonic cycle 14,29–43 as source of hummocky deposits 360–362 Cretaceous 32–36 TCN 36Cl dating 363 early period 30–35 aeolian deposits, Frontal Cordillera piedmont 299, Jurassic 29–32 302–303 late period 35–43 Aetostreon 206, 207, 209, 212 andesite aggradation 226, 227, 234, 236 Agrio Formation 205, 206, 207, 209, 210 cycles, Frontal Cordillera piedmont 296–300 Chachahue´n Group 214 Agrio fold and thrust belt 215, 216 Neuque´n Basin 161, 162 Agrio Formation 133, 134, 147–148, 203, Angualasto Group 20, 22, 23 205–213, 206 apatite ammonoids 205, 206–211 fission track dating 40, 71, 396, 438 stratigraphy 33, 205–211 (U–Th)/He thermochronology 40, 75, 387–397 Agua de la Mula Member 133, 134, 205, 211, 213 Ar/Ar age Agua de los Burros Fault 424, 435 Abanico Formation
    [Show full text]
  • Crustal Faults in the Chilean Andes: Geological Constraints and Seismic Potential
    Andean Geology 46 (1): 32-65. January, 2019 Andean Geology doi: 10.5027/andgeoV46n1-3067 www.andeangeology.cl Crustal faults in the Chilean Andes: geological constraints and seismic potential *Isabel Santibáñez1, José Cembrano2, Tiaren García-Pérez1, Carlos Costa3, Gonzalo Yáñez2, Carlos Marquardt4, Gloria Arancibia2, Gabriel González5 1 Programa de Doctorado en Ciencias de la Ingeniería, Pontificia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, Macul, Santiago, Chile. [email protected]; [email protected] 2 Departamento de Ingeniería Estructural y Geotécnica, Pontificia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, Macul, Santiago, Chile. [email protected]; [email protected]; [email protected] 3 Departamento de Geología, Universidad de San Luis, Ejercito de Los Andes 950, D5700HHW San Luis, Argentina. [email protected] 4 Departamento de Ingeniería Estructural y Geotécnica y Departamento de Ingeniería de Minería, Pontificia Universidad Católica de Chile. Avda. Vicuña Mackenna 4860, Macul, Santiago, Chile. [email protected] 5 Departamento de Ciencias Geológicas, Universidad Católica del Norte, Angamos 0610, Antofagasta, Chile. [email protected] * Corresponding author: [email protected] ABSTRACT. The Chilean Andes, as a characteristic tectonic and geomorphological region, is a perfect location to unravel the geologic nature of seismic hazards. The Chilean segment of the Nazca-South American subduction zone has experienced mega-earthquakes with Moment Magnitudes (Mw) >8.5 (e.g., Mw 9.5 Valdivia, 1960; Mw 8.8 Maule, 2010) and many large earthquakes with Mw >7.5, both with recurrence times of tens to hundreds of years. By contrast, crustal faults within the overriding South American plate commonly have longer recurrence times (thousands of years) and are known to produce earthquakes with maximum Mw of 7.0 to 7.5.
    [Show full text]
  • Petrology and Geochemistry of Volcanic Rocks Behind the Cenozoic Arc Front in the Andean Cordillera, Central Chile (33°50'S)
    Abanico East Formation: petrology and geochemistry of volcanic rocks behind the Cenozoic arc front in the Andean Cordillera, central Chile (33°50'S) Marcia Muñoz1, Francisco Fuentes1, Mario Vergara1, Luis Aguirre1, Jan Olov Nyström2, Gilbert Féraud3, Alain Demant4 1 Departamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile. [email protected] , [email protected] , [email protected] , [email protected] 2 Swedish Museum of Natural History, SE-10405 Stockholm, Sweden. [email protected] 3 UMR Géosciences Azur, CNRS-UNSA, Université de Nice-Sophia Antipolis, 06108 Nice Cedex 02, France. [email protected] 4 Laboratoire de Pétrologie Magmatique Université Aix-Marseille III, 13397 Marseille Cedex 20, France. [email protected] ABSTRACT The stratigraphy, chemistry and age of rocks assigned to the eastern portion of the Abanico Formation exposed along the El Volcán river valley, Principal Cordillera east of Santiago (30º50'S/70º12'-70º5'W), are reported and discussed. This ca. 3,300 m thick succession is mainly composed of basalts, basaltic andesites and volcaniclastic rocks. 40Ar/39Ar radiometric dates on plagioclase from the lava flows yield Oligocene-lower Miocene ages with a maximum age of 34.3 ±0.4 Ma for the lower part and a plateau age of 21.4±1.0 Ma for the upper part of the succession. The lava flows show calc-alkaline affinities and have chemical characteristics that are typical of arc volcanic rocks erupted in an active continental margin. A temporal chemical evolution in the sequence is indicated by upward increases in concentrations of LILE and LREE elements and LaN/YbN ratios.
    [Show full text]