DOCSLIB.ORG

Lithospheric Loss in the Andean Convergent Margin During the Triassic: Geochemical Evidence from Igneous Rocks of Northern Chile (24°30’ – 30°00’S)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lithospheric Loss in the Andean Convergent Margin During the Triassic: Geochemical Evidence from Igneous Rocks of Northern Chile (24°30’ – 30°00’S) O EOL GIC G A D D A E D C E I H C I L E O S F u n 2 d 6 la serena octubre 2015 ada en 19 Lithospheric loss in the Andean convergent margin during the Triassic: geochemical evidence from igneous rocks of northern Chile (24°30’ – 30°00’S). Verónica Oliveros*, Paulina Vásquez, Christian Creixell, Javiera González, Mauricio Espinoza, Friedrich Lucassen and Mihai. N. Ducea. Departamento Ciencias de la Tierra, Universidad de Concepción, Edmundo Larenas 129, Concepción, Chile Servicio Nacional de Geología y Minería, A. Santa María 0140, Providencia, Santiago, Chile. Isotope Geochemistry Laboratory, GEOMAR, Universität Bremen, Germany. Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA. Universitatea Bucuresti, Facultatea de Geologie Geofizica, Strada N. Balcescu Nr 1, Bucuresti, Romania *Contact email: [email protected] Abstract. Several volcanic, volcano-sedimentary and continental basins in western Argentina and Chile during plutonic units cropping out in northern Chile between 24°30’ the Late Permian to Triassic period, supported the idea of and 30°S have been characterized petrographically and arrested subduction (Franzese and Spalleti, 2001; Kleiman geochemically. More than 50 new geochemical and isotopic and Japas, 2009). By the other hand, recent studies results from these units are presented and compared to proposed margin-parallel transpressional deformation of previous published data for Late Paleozoic to Late Jurassic the margin during the Triassic, associated to oblique igneous rocks. We propose that the continental margin subduction (Kato and Godoy, 2015). The lack of a underwent significant lithospheric loss, in a continuous recognizable chain of igneous units that could represent the subduction setting, at some time during the Permian to the Permian to Triassic magmatic arc is also seen as an Triassic. Delamination of the lithospheric roots of the Paleozoic arc is a likely process to account for the evidence of this proposed tectonic setting. geochemical evolution of the magmas in the studied time frame, although stretching of the continental plate, without In this work we present new geochemical and isotopic data significant crustal growth due to arc magmatism or for volcanic and plutonic rocks of more than 10 geological sedimentary accretion is also a plausible scenario. The units ranging in age from Carboniferous to Early Jurassic, westwards shift of the magmatic arc, located at the that crop out in the Coastal Cordillera, Precordillera or Principal Cordillera during the Carboniferous to the Early- Principal Cordillera of northern Chile between 24°30’ and Middle Triassic, to the present-day Coastal Cordillera could 30°S. These data are compared to a compilation of more have taken place at ca. 210 Ma. than 460 sets of geochemical results published from rocks of Carboniferous to Late Jurassic in age, cropping out Keywords: Triassic, subduction, magmatism, mainly in Chile but also in Argentina between 18° and geochemistry. 40°S. Our results allow us to propose a model of significant lithospheric loss in the proto-Andean margin during the Triassic. This process would have taken place 1 Introduction after a major orogenic event in the Permian, without the interruption of the subduction of oceanic lithosphere under Crustal growth at the present-day western portion of the the South-American plate, as revealed by the dominant South-American continental plate margin has been calk-alkaline affinities of the Palaeozoic and Mesozoic dominated by terrane accretion and subduction throughout igneous rocks that compose the present-day Andean the Phanerozoic eon. For the Andean region, whereas the forearc in northern Chile. existence of a subduction setting during the Late Palaeozoic and from the Early Jurassic until now has been relatively well proven, the nature of the margin evolution 2 Methods, Samples, Results from Late Permian to Late Triassic has been more difficult to determine. Several authors have proposed geodynamic changes in this time frame, particularly the interruption in Fifty-five samples of volcanic, subvolcanic and plutonic the subduction due to either terrane accretion (Mpodozis rocks from Carboniferous to Early Jurassic units were and Kay, 1992) or extensional forces driven by Pangea’s collected for petrographical and geochemical analysis. The breakup (Uliana et al. 1989). The existence of voluminous studied units in the Coastal Cordillera correspond to the acid explosive magmatism during the Permian (the Llano de Chocolate Beds, the Canto del Agua, Agua Chica Choiyoi group) after a regional scale orogenic event (San and Cifuncho Fms and related subvolcanic bodies; as well Rafael orogenic phase) along with the development of as Permian, Middle Triassic and Upper Triassic plutons. several hundred kilometers-long, NNW-SSE oriented, The studied units in the Precordillera and Principal 864 AT 1 GeoloGía ReGional y Geodinámica andina Cordillera correspond to the Los Tilos and Guanaco Sonso samples, specifically three samples of the Norian-Rhaetian sequences, the La Totora, San Félix, Quebrada del Salitre, La Totora Fm., have transitional to alkaline affinities Sierra de Varas, Cerro Guanaco La Tabla and Algarrobal and/or plot in the whithin plate or oceanic island fields of formations and related subvolcanic bodies, and the Guanta, the discrimination diagrams (Fig. 1b), but the remaining Chollay, Colorado and Punta del Viento plutonic samples fall within, or very close to, the volcanic arc complexes and related dykes. Whole-rock major and trace basalts of continental arc granites fields(Fig. 1b,c). This element composition were obtained through XRF and ICP- pattern is confirmed when the analysed samples are MS for all samples, along with Sr-Nd-Pb isotopic ratio compared to the whole database. measured by TIMS. An interesting feature of the igneous rocks from Late The petrography of the volcanic and subvolcanic rocks Paleozoic to Triassic is their systematic shifts in specific indicates that they range from basalts to rhyolite, but the geochemical parameters that are linked to the extent of most abundant lithologies are dacites. Basalts and basaltic- lithospheric involvement in the magma sources. Thus, andesites occur mainly in the Upper Triassic units (La LaN/YbN ratios of the studied samples decrease from 4.0 at Totora, upper San Félix, Agua Chica, Sierra de Varas, ca. 300 Ma to 3.0 at ca. 250 Ma and to 1.5 at ca. 200 Ma, Guanaco Sonso and Quebrada del Salitre formations). although the younger group has a large dispersion between They have only porphyritic textures, with plagioclase, 1.0 and 3.0 (Fig. 1d). A similar pattern is observed for the clinopyroxene, hornblende and quartz as the main whole dataset including previous published data (Fig. 1d). phenocrysts. Groundmass is often largely altered and This shift suggests that crust over the magmatic arc consists of variable amounts of plagioclase, quartz, k- became thinner from the Carboniferous to the Early feldspar, undetermined mafics and Fe-Ti oxides. Plutonic Jurassic. However, other key ratios that represent proxies rocks range from quartz granodiorite and tonalite to to crustal thickness, such as Sr/Y (Chapman et al, in press) granite, with few gabbros occurring in the principal do not follow a decreasing pattern form the Carboniferous cordillera at ~30°S. to the Jurassic but rather the opposite. The geochemical results indicate that the majority of the The loss of the crustal or lithospheric signal in the studied volcanic and plutonic rocks have calk-alkaline Paleozoic to Mesozoic Andean magmas is also evidenced affinities (Fig. 1a). The trend is observed either in the by their isotopic composition. Nd isotopes are a more major and highly mobile element contents or in the trace reliable proxy to the lithospheric component of arc and more refractory HFS (high field strength) elements. magmas than Sr or Pb since their ratios are little affected There is a consistent enrichment in LILE (large ion by low grade metamorphism or hydrothermal alteration, lithophile elements) over HFSE and marked Nb-Ta troughs which is very common in Andean rocks. The εNd in all the studied samples. REE (rare earth elements) parameter also decreases with time from Carboniferous to patterns vary from very steep to flat with a systematic Jurassic, a trend that is observed either for the set of decreasing in the LaN/YbN and LaN/SmN ratios from the studied samples or the whole database (Fig. 1e). This Carboniferous to the Lower Jurassic samples (Fig. 2d). would imply a tectonic evolution that involved loss of lithosphere and crustal thinning at some time by the end The isotopic composition of the rocks is variable, initial the Paleozoic and beginning of the Mesozoic era. 87Sr/86Sr ranges between 0.696 and 0.712 with over 95% of Delamination or foundering of the arc roots is a process the samples in between 0.701 and 0.709. Abnormal low that can account for this lithospheric loss.. This is a initial ratios are interpreted as extreme Rb loss due to plausible explanation taking into account that a major alteration. Initial 143Nd/144Nd ranges between 0.511848 and trigger for this process is a previous crustal thickening, as 0.512518 with over 95% of the samples in between has been proposed for the Carboniferous-Early Permian, 0.512470 and 0.512060 and initial εNd ranging between associated to the San Rafael Orogeny. Another likely +4.00 and -4.72. The isotopic composition of lead is less scenario is the stretching of the lithosphere. For both cases, variable, ranging between 18.67 and 18.33, 15.76 and regional Frontal cordillera geology (28°-29° S) suggest 15.53 and 38.91 and 36.55, for 206Pb/204Pb, 207Pb/204Pb and major tectonic changes took place during the Early 208Pb/204Pb respectively. Triassic, with evidences of extensional tectonics as voluminous emplacement of mafic dike swarms at 240-230 Ma, onset of extensional basins (San Félix basin) and large 3 Discussion exhumation of basement and Early-Middle Triassic plutons, covered by Late Triassic sequences, coeval with 3.1 Magmatic sources and their evolution from extensional or transtensional deformation.
Load more

Recommended publications
  • Structure, Petrography and Geochemistry EARTH SCIENCES
    EARTH SCIENCES RESEARCH JOURNAL GEOLOGY Earth Sci. Res. J. Vol. 24, No. 2 (June, 2020): 121-132 The Choiyoi Group in the Cordón del Plata range, western Argentina: structure, petrography and geochemistry Amancay Martinez1, Adrian Gallardo1,2, Laura Giambiagi3, Laura Tobares1 1San Luis National University, FCFMyN, Department of Geology, San Luis, Argentina 2CONICET (Argentina National Scientific and Technical Research Council), San Luis, Argentina. 3IANIGLA-CONICET CCT Mendoza. Adrián Ruiz Leal s/n, Parque San Martín. (5500). Mendoza, Argentina. * Corresponding author: [email protected] ABSTRACT Keywords: Choiyoi Group; magmatism; petrography; The Choiyoi Group from the Permo-Triassic, is one of the most conspicuous volcano-sedimentary suites of southern geochemistry; Gondwana; Argentina. South America, considered critical to understand the geological evolution of the western margins of Gondwana. In this regard, petrography, geochemistry, and structural data were examined to better elucidate the physical character and emplacement conditions of the unit in the Cordón del Plata range, within the Frontal Cordillera of Mendoza, Argentina. The site is representative of the magmatism and deformation through different Andean cycles. Results of the study indicate three facies of increasing felsic composition upwards. Mafic units consist of basalts, andesite and andesitic breccias at the base of the sequence. Felsic rocks such as rhyodacites, granites and welded tuffs are predominant above. The fault zone of La Polcura – La Manga is the most prominent structural feature in the region, which presumably controlled the emplacement of breccias and ignimbrites within the middle and upper members. These compositional variations suggest a magma evolution from subduction to a rifting environment after the San Rafael orogeny in the Late Palaeozoic.
    [Show full text]
  • Basement Composition and Basin Geometry Controls on Upper-Crustal Deformation in the Southern Central Andes (30–36° S)
    Geol. Mag.: page 1 of 17 c Cambridge University Press 2016 1 doi:10.1017/S0016756816000364 Basement composition and basin geometry controls on upper-crustal deformation in the Southern Central Andes (30–36° S) ∗ ∗ ∗ JOSÉ F. MESCUA †, LAURA GIAMBIAGI , MATÍAS BARRIONUEVO , ∗ ∗ ANDRÉS TASSARA‡, DIEGO MARDONEZ , MANUELA MAZZITELLI ∗ & ANA LOSSADA ∗ Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Centro Científico Tecnológico Mendoza, CONICET. Av. Ruiz leal s/n Parque General San Martín, Mendoza (5500) Argentina ‡Departamento de Ciencias de la Tierra, Universidad de Concepción, Victor Lamas 1290, Barrio Universitario, Concepción, Casilla 160-C, Chile (Received 13 December 2015; accepted 5 April 2016) Abstract – Deformation and uplift in the Andes are a result of the subduction of the Nazca plate below South America. The deformation shows variations in structural style and shortening along and across the strike of the orogen, as a result of the dynamics of the subduction system and the features of the upper plate. In this work, we analyse the development of thin-skinned and thick-skinned fold and thrust belts in the Southern Central Andes (30–36° S). The pre-Andean history of the area determined the formation of different basement domains with distinct lithological compositions, as a result of terrane accretions during Palaeozoic time, the development of a widespread Permo-Triassic magmatic province and long-lasting arc activity. Basin development during Palaeozoic and Mesozoic times produced thick sedimentary successions in different parts of the study area. Based on estimations of strength for the different basement and sedimentary rocks, calculated using geophysical estimates of rock physical properties, we propose that the contrast in strength between basement and cover is the main control on structural style (thin- v.
    [Show full text]
  • Geodynamics of Late Carboniferous–Early Permian Forearc in North Chile (28°30′–29°30′S)
    Research Article Journal of the Geological Society Published Online First doi:10.1144/jgs2016-010 Geodynamics of Late Carboniferous–Early Permian forearc in north Chile (28°30′–29°30′S) C. Creixell1*, V. Oliveros2, P. Vásquez1, J. Navarro3, D. Vallejos2, X. Valin2, E. Godoy4 & M. N. Ducea5,6 1 Servicio Nacional de Geología y Minería, Avenida Santa María 0104, Providencia, Santiago, Chile 2 Departamento Ciencias de la Tierra, Universidad de Concepción, Barrio Universitario s/n, Concepción, Chile 3 Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile 4 Tehema Consultores Geológicos, Virginia Subercaseaux 4100, Pirque, Santiago, Chile 5 Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA 6 Universitatea Bucaresti, Facultatea de Geologie Geofizica, Strada N. Balcescu Nr 1, Bucuresti, Romania * Correspondence: [email protected] Abstract: A large section of the Late Palaeozoic forearc is exposed along the coastal ranges of north–central Chile (28°–29° 30′S). This is characterized by three lithotectonic units: (1) the Punta de Choros Metamorphic Complex (basal accretion series), composed mostly of micaschists and metabasites; (2) the Chañaral Epimetamorphic Complex (frontal accretion series), formed by metaturbidites and metasediments; (3) the Llano del Chocolate Beds (forearc basin deposits), composed of a sedimentary sequence of clastic sedimentary rocks with minor limestones and acidic volcanic rocks. Within the basal accretion series, two distinctive blocks of garnet-bearing schists with amphibolite-facies metamorphism have been preserved, recording early stages of the subduction system. The stratigraphic record and the U–Pb dating of igneous (291–318 Ma) and detrital zircons (maximal deposition ages between 273 and 292 Ma) in the forearc basin deposits, coupled with 40Ar/39Ar ages for metamorphic rocks (319–280 Ma), indicate that forearc sedimentation was broadly contemporaneous with metamorphism and exhumation of the basal accretion series.
    [Show full text]
  • This Article Appeared in a Journal Published by Elsevier. the Attached Copy Is Furnished to the Author for Internal Non-Commerci
    This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Gondwana Research 20 (2011) 782–797 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr Paleomagnetism and rock magnetism of the Neoproterozoic Itajaí Basin of the Rio de la Plata craton (Brazil): Cambrian to Cretaceous widespread remagnetizations of South America E. Font a,⁎, C.F. Ponte Neto b,1, M. Ernesto b a Instituo Dom Luiz, Universidade de Lisboa, Campo Grande,1749-016, Lisbon, Portugal b Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil article info abstract Article history: A detailed rock magnetic and paleomagnetic study was performed on samples from the Neoproterozoic Itajaí Received 8 July 2010 Basin in the state of Santa Catarina, Brazil, in order to better constrain the paleogeographic evolution of the Rio Received in revised form 27 April 2011 de la Plata craton between 600 and 550 Ma. However, rock magnetic properties typical of remagnetized rocks Accepted 28 April 2011 and negative response in the fold test indicated that these rocks carried a secondary chemical remanent Available online 6 May 2011 magnetization.
    [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]
  • View Lithospheric Evolution of the Pre- and Early Andean Convergent Margin, Chile
    Gondwana Research 80 (2020) 202–227 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr GR Focus Review Lithospheric evolution of the Pre- and Early Andean convergent margin, Chile Verónica Oliveros a,⁎, Paulina Vásquez b, Christian Creixell b, Friedrich Lucassen c, Mihai N. Ducea d,e, Isabella Ciocca a, Javiera González a, Mauricio Espinoza a, Esteban Salazar b, Felipe Coloma b, Simone A. Kasemann c a Departamento Ciencias de la Tierra, Universidad de Concepción, Casilla 160-C, Concepción, Chile b Servicio Nacional de Geología y Minería, Av. Santa María 104, Santiago, Chile c Faculty of Geosciences and MARUM-Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, 28359 Bremen, Germany d Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA e Faculty of Geology and Geophysics, University of Bucharest, 010041 Bucharest, Romania article info abstract Article history: The proto-Andean and Early Andean evolution of the southwestern Gondwana margin comprises three stages Received 29 March 2019 that differ in their magmatic evolution and deformational style: the Gondwana cycle (~330–280 Ma), the Pre- Received in revised form 20 November 2019 Andean stage (~280–210 Ma) and the Early Andean Cycle (210–100 Ma). These stages have been traditionally Accepted 30 November 2019 interpreted as the upper crustal response to changes in the tectonic setting which include: Cordilleran-style con- Available online 10 December 2019 tinental arc (Gondwana cycle), orogenic collapse and possibly slab break-off that led to continental rifting and Editor: M. Santosh extensive crustal melting (Pre-Andean stage), and subsequent subduction re-initiation in oceanic arc-style con- text (Early Andean cycle).
    [Show full text]
  • The Veladero High-Sulfidation Epithermal Au-Ag Deposit
    THE VELADERO HIGH-SULFIDATION EPITHERMAL AU-AG DEPOSIT, ARGENTINA: VOLCANIC STRATIGRAPHY, ALTERATION, MINERALIZATION, AND QUARTZ PARAGENESIS by Elizabeth A. Holley A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology). Golden, Colorado Date _________________ Signed:___________________________ Elizabeth A. Holley Signed:___________________________ Dr. Thomas Monecke Thesis Advisor Golden, Colorado Date _________________ Signed:___________________________ Dr. J. D. Humphrey Associate Professor and Head Department of Geology and Geological Engineering ii ABSTRACT The Veladero Au-Ag high-sulfidation epithermal deposit is located in the El Indio-Pasuca belt in Argentina. Veladero is an oxidized deposit that contained reserves of 12.2 Moz of Au and 226.2 Moz of Ag at the end of 2008. Ore is primarily hosted in silicified breccias. The volcanic package at Veladero is a coalescing complex of domes, diatremes, and hydrothermal breccia bodies, mantled by a thick apron of volcaniclastic deposits. These units are inferred to be of Cerro de las Tórtolas age (16.0 ± 0.2 to 14.9 ± 0.7 Ma) at Amable in the southern part of the Veladero area, and Vacas Heladas age (12.7 ± 0.9 to 11.0 ± 0.2 Ma) at Filo Federico in the northern part of Veladero. Emplacement of hydrothermal breccia units was accompanied or shortly followed by multiple pulses of magmatic-hydrothermal and alternating jarosite alteration from about 15.4 to 8.9 Ma. Alunite and jarosite 40Ar-39Ar ages and U-Pb zircon ages of crosscutting dikes restrict mineralization at Amable to the period from 15.4 to 12.14 0.11 Ma, probably commencing closer to 12.7 Ma.
    [Show full text]
  • South American Triassic Events (245-200 Mya)
    Topics South American n General Triassic Paleogeography Triassic Events (245- n Overview of events that occurred in SA in the Triassic and early Jurassic 200 mya) ¨ General geological layout Kristin Sturtevant n Main volcanic component of the Triassic n Late Triassic sediment deposition n Contrast to NA during this time period Triassic Paleogeography Cont’d n Pangea assembled, stable through most of time period, slowly “cracking” apart by late Triassic n Cracking creates a gap between Laurasia and Gondwana n Climate in this time is warm, and semi-arid to arid Overview Cont’d n Late Paleozoic subduction caused unstable crustal thickening along western coast n Strike-slip faulting along coast causing n Triassic volcanism a result of ending detachment, rifts fill with marine and fluvial convergence and intercontinental extension sediments ¨ Choiyoi group ¨ Ischigualasto Formation n Some subduction farther south along the coast, n During passive margin, sediment deposition in but most of continent in a passive margin by basins adjacent to margin mid -late Triassic n Subduction begins again in the mid Jurassic, forming a new magmatic arc 1 n Terranes from Paleozoic Choiyoi Group ¨ Pampean n Lower and Upper Members ¨ Lower-andesite, dacite ¨ Precordillera ¨ Upper-rhyolite ¨ Primary and frontal cordilleras n Characteristics n Accrentionary wedge from ¨ Pre-rift volcanics Paleozoic subduction ¨ Volcanic plutons and magmatic arcs n Volcanism from back arc ¨ Form igneous provinces basins and beginning ¨ Calc-alkaline extension n Crustal source
    [Show full text]
  • Support for an Atype Pangea Reconstruction from Highfidelity Late
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, B12114, doi:10.1029/2011JB008495, 2011 Support for an “A-type” Pangea reconstruction from high-fidelity Late Permian and Early to Middle Triassic paleomagnetic data from Argentina Mathew Domeier,1 Rob Van der Voo,1,2 Renata N. Tomezzoli,3 Eric Tohver,4 Bart W. H. Hendriks,5 Trond H. Torsvik,2,5,6,7 Haroldo Vizan,3 and Ada Dominguez1 Received 29 April 2011; revised 21 September 2011; accepted 18 October 2011; published 31 December 2011. [1] A major disparity is observed between the late Paleozoic-early Mesozoic apparent polar wander paths (APWPs) of Laurussia and Gondwana when the landmasses are re-assembled in a conventional “A-type” Pangea. This discrepancy has endured from the earliest paleomagnetic reconstructions of the supercontinent, and has prompted discussions of non-dipole paleomagnetic fields and alternative paleogeographic models. Here we report on a joint paleomagnetic-geochronologic study of Late Permian and Early to Middle Triassic volcanic and volcaniclastic rocks from Argentina, which demonstrates support for an A-type model, without requiring modification to the geocentric axial dipole hypothesis. New SHRIMP U-Pb and 40Ar-39Ar isotopic dating has reinforced the inferred age of the sequences, which we estimate at 264 Ma (Upper Choiyoi Group) and 245 Ma (Puesto Viejo Group). Field-stability tests demonstrate that the volcanic rocks are carrying early/primary magnetizations, which yield paleopoles: 73.7°S, 315.6°E, A95: 4.1°, N: 40 (Upper Choiyoi) and 76.7°S, 312.4°E, A95: 7.3°, N: 14 (Puesto Viejo). A comprehensive magnetic fabric analysis is used to evaluate structural restorations and to correct for magnetization anisotropy.
    [Show full text]
  • The Mejillonia Suspect Terrane (Northern Chile): Late Triassic Fast
    Gondwana Research 25 (2014) 1272–1286 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr The Mejillonia suspect terrane (Northern Chile): Late Triassic fast burial and metamorphism of sediments in a magmatic arc environment extending into the Early Jurassic C. Casquet a,⁎, F. Hervé b,c, R.J. Pankhurst d, E. Baldo e, M. Calderón f, C.M. Fanning g, C.W. Rapela h, J. Dahlquist e a Departamento de Petrología y Geoquímica, Universidad Complutense — Instituto de Geociencias (UCM, CSIC), 28040 Madrid, Spain b Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile c Escuela de Ciencias de la Tierra, Universidad Andres Bello, Sazie 2315, Santiago, Chile d Visiting Research Associate, British Geological Survey, Keyworth, Nottingham NG12 5GG, United Kingdom e CICTERRA-CONICET-UNC, Av. Vélez Sarsfield 1611, Pab. Geol., X5016CGA Córdoba, Argentina f Servicio Nacional de Geología y Minería, Santa Maria 0104, Santiago, Chile g Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia h Centro de Investigaciones Geológicas (CONICET-UNLP), 1900 La Plata, Argentina article info abstract Article history: The Mejillonia terrane, named after the Mejillones Peninsula (northern Chile), has been traditionally consid- Received 14 March 2013 ered an early Paleozoic block of metamorphic and igneous rocks displaced along the northern Andean margin Received in revised form 7 May 2013 in the Mesozoic. However, U–Pb SHRIMP zircon dating of metasedimentary and igneous rocks shows that the Accepted 14 May 2013 sedimentary protoliths were Triassic, and that metamorphism and magmatism took place in the Late Triassic Available online 10 June 2013 (Norian).
    [Show full text]
  • Andean Flat-Slab Subduction Through Time
    Andean flat-slab subduction through time VICTOR A. RAMOS & ANDRE´ S FOLGUERA* Laboratorio de Tecto´nica Andina, Universidad de Buenos Aires – CONICET *Corresponding author (e-mail: [email protected]) Abstract: The analysis of magmatic distribution, basin formation, tectonic evolution and structural styles of different segments of the Andes shows that most of the Andes have experienced a stage of flat subduction. Evidence is presented here for a wide range of regions throughout the Andes, including the three present flat-slab segments (Pampean, Peruvian, Bucaramanga), three incipient flat-slab segments (‘Carnegie’, Guan˜acos, ‘Tehuantepec’), three older and no longer active Cenozoic flat-slab segments (Altiplano, Puna, Payenia), and an inferred Palaeozoic flat- slab segment (Early Permian ‘San Rafael’). Based on the present characteristics of the Pampean flat slab, combined with the Peruvian and Bucaramanga segments, a pattern of geological processes can be attributed to slab shallowing and steepening. This pattern permits recognition of other older Cenozoic subhorizontal subduction zones throughout the Andes. Based on crustal thickness, two different settings of slab steepening are proposed. Slab steepening under thick crust leads to dela- mination, basaltic underplating, lower crustal melting, extension and widespread rhyolitic volcan- ism, as seen in the caldera formation and huge ignimbritic fields of the Altiplano and Puna segments. On the other hand, when steepening affects thin crust, extension and extensive within-plate basaltic flows reach the surface, forming large volcanic provinces, such as Payenia in the southern Andes. This last case has very limited crustal melt along the axial part of the Andean roots, which shows incipient delamination.
    [Show full text]
  • Early Permian Arc-Related Volcanism and Sedimentation at the Western Margin of Gondwana: Insight from the Choiyoi Group Lower Section
    Geoscience Frontiers 7 (2016) 715e731 HOSTED BY Contents lists available at ScienceDirect China University of Geosciences (Beijing) Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Research paper Early Permian arc-related volcanism and sedimentation at the western margin of Gondwana: Insight from the Choiyoi Group lower section Leonardo Strazzere, Daniel A. Gregori*, Leonardo Benedini CONICET and Cátedra de Geología Argentina, Departamento de Geología, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina article info abstract Article history: Permian sedimentary and basic to intermediate volcanic rocks assigned to the Conglomerado del Río Received 4 January 2015 Blanco and Portezuelo del Cenizo Formation, lower part of the Choiyoi Group, crop out between the Received in revised form Cordon del Plata, Cordillera Frontal and Precordillera of Mendoza Province, Argentina. The sedimentary 7 August 2015 rocks are represented by six lithofacies grouped in three facies associations. They were deposited by Accepted 31 August 2015 mantled and gravitational flows modified by high-energy fluvial currents that evolved to low-energy Available online 19 October 2015 fluvial and lacustrine environments. They constitute the Conglomerado del Río Blanco, which cover unconformably marine Carboniferous sequences. Five volcanic and volcaniclastic facies make up the Keywords: fi Choiyoi group lower section beginning of volcanic activity. The rst volcanic event in the Portezuelo del Cenizo is basaltic to andesitic fl fl fl Conglomerado del Río Blanco lava- ows emplaced in the anks of volcanoes. Lava collapse produced thick block and ash ows. Cordillera Frontal Interbedding in the intermediate volcanic rocks, there are dacites of different geochemical signature, Argentina which indicate that the development of acidic volcanism was coetaneous with the first volcanic activity.
    [Show full text]