This dissertation investigates the evolution of continental orogenic systems in Central Asia during and between pre-collisional plate convergence (Cordilleran-style orogenesis), syn-collisional plate convergence (collisional orogenesis), and post-collisional tectonic processes within the scope of closing Paleo-Asian and Tethyan ocean basins. A brief introductory chapter outlines the scope and context of the research. Appendix A focuses on the Late Paleozoic closure of the Turkestan ocean basin and subsequent collision between the Karakum–Tarim and Kazakh–Kyrgyz terranes in the South Tian Shan, within the scope of the final amalgamation of the Mesoproterozoic–Permian Central Asian Orogenic Belt. Appendix B focuses on late Cenozoic syn-collisional exhumation of gneiss domes in the India–Asia collision, which is a component of the Triassic–recent Alpine–Himalayan orogenic belt. Abstracts of the results are provided in the respective appendices.

Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the Pampean flat-slab segment, have been gained by utilising a range of petrological, geochronological and geochemical techniques. These techniques have been applied to a suite of Late Cretaceous (~73 Ma) to Late Miocene (~6 Ma) intrusive (granitoids) and extrusive (basalts to rhyolites) arc rocks collected from an east - west transect across the Andean Cordillera. The oxygen and hafnium isotopic composition of the accessory mineral zircon allows mantle-derived melts contaminated with older, upper continental crustal to be identified. Boron isotopic compositions of melt inclusions, combined with concentrations of certain incompatible trace elements, can be used to assess the source and influence of fluids derived from subducting material on the melt source region. The southern Central Andes provides a particularly interesting area to study these processes as the thickness of the continental crust has increased significantly over the course of the Cenozoic (from ~35 km to >50 km) and the angle of the subducting Nazca plate has shallowed since ~18 Ma, causing the position of the volcanic arc to migrate to the east. In order to unravel the complexities involved with constraining the contributions to arc magmas at an active continental margin, a range of geochronological, geochemical, and geothermobarometric techniques, including high resolution, micro-analysis of mineral phases and melt inclusions, have been applied. High resolution, U-Pb dating of magmatic zircon has improved regional stratigraphy in the Pampean flat-slab segment (between ~29 and 32 °S) and provided an accurate temporal constraint for geochemical and geothermobarometric data. The results of in-situ O and Lu-Hf isotope analysis of zircon show both distinct temporal and spatial variations across the Andean arc. The observed isotopic variability is attributed to variable contamination of mantle-derived melts with distinct Andean basement terranes, which vary east – west in composition and age. ‘Mantle-like’ δ18O(zircon) values, juvenile initial ƐHf(zircon) values and a lack of inherited, xenocrystic zircon cores, suggests the Late Cretaceous (~73 Ma) to Eocene (~39 Ma) plutons located in the Principal Cordillera of Chile, experienced very little interaction with the upper continental crust. Amphibole – plagioclase geothermobarometry indicates these calc-alkaline granitoids, which form extensive north – south trending belts, were emplaced at shallow depths in the crust (~4 – 5 km). Therefore the Late Cretaceous to Late Eocene is interpreted as a period of significant upper crustal growth. The isotopic variability in the Late Oligocene (~26 Ma) to Late Miocene (~6 Ma) arc magmatic rocks demonstrates that during thickening of the continental crust and migration of the Andean arc to the east, arc magmas assimilated Late Paleozoic to Early Mesozoic basement. In addition, arc magmas erupted/emplaced in the Argentinean Precordillera (i.e. farthest east from the trench) assimilated a Grenville-aged (~ 1330 – 1030 Ma) basement. The youngest arc magmas (~6 Ma) erupted in the Frontal Cordillera also show evidence for the assimilation of this ancient basement terrane, potentially signalling under-thrusting beneath the Frontal Cordillera. Overall, the later part of the Cenozoic represents a period of crustal reworking. Boron concentrations and isotope ratios measured in pyroxene hosted melt inclusions and for the first time in zircon hosted melt inclusions, are higher than the values expected for the mantle wedge and show significant variations with time. The source of the Paleocene (~61 Ma) arc magmas were influenced by fluids primarily derived from altered oceanic crust. Lower δ11B values and boron concentrations obtained for Oligocene (25 – 23 Ma) arc magmatic rocks reflects a diminished influence of slab-derived fluids reflecting a greater depth to the top of the slab. Fluids derived from serpentinite influenced the source of the arc magmas after ~19.5 Ma. This has been linked with the intersection of the Juan Fernández Ridge, a volcanic seamount chain associated with hydrated and serpentinised oceanic lithosphere.

Este estudo foca no Complexo Várzea do Capivarita (CVC), localizado no sul da Província da Mantiqueira (PM), Brasil. A fim de investigar a evolução geológica do CVC, uma abordagem multi-disciplinar foi utilizada, incluindo geologia de campo, geologia estrutural, petrografia, geoquímica de elementos maiores e traços, isótopos de Sr-Nd e geocronologia U-Pb em zircão (LA-MC-ICP-MS e SHRIMP). O complexo compreende uma variedade de orto- e paragnaisses de composição e idade diversa. Volumes subordinados de sienitos sintectônicos também perfazem o CVC. A deformação é particionada em zonas de cisalhamento do tipo thrust (D1) e transcorrentes (D2), o que sugere tectônica transpressiva. O arcabouço estrutural descrito é possivelmente relacionado a um evento colisional oblíquo. Os estudos petrológicos e geocronológicos enfatizaram os ortognaisses do CVC a fim de avaliar as fontes magmáticas e paleo-ambientes envolvidos. Idades de cristalização obtidas nos domínios de zircão com zonação tipicamente ígnea variaram entre 780 e 790 Ma. Por sua vez, idades entre 640 - 650 Ma foram obtidas em sobrecrescimentos de zircão, sendo interpretadas como o registro da idade do metamorfismo de alto grau e fusão parcial associada. Os dados geocronológicos apresentados também indicaram que ambos os regimes cinemáticos foram contemporâneos, oferecendo, dessa forma, evidencia adicional para a hipótese de colisão oblíqua. Os ortognaisses do Complexo têm composição tonalítica a granítica e são rochas calcioalcalinas meta- a peraluminosas, com razões elevadas de 87Sr/86Sr (i) variando de 0.71628 a 0.72509 e valores εNd (790) entre -7.19 a -10.06. Sua composição e padrões de elementos traços sugerem que representem um magmatismo de arco maduro continental. O magmatismo registrado no CVC é compatível com outras sequências de arco de ca. 800 Ma, incluindo parte das metavulcânicas ácidas do Complexo Metamórfico Porongos (CMP) e os ortognaisses do Cerro Bori, Uruguai. Todas essas associações têm assinatura típica de orógenos acrescionários, contendo idade TDM Meso a Paleoproterozóica, além de forte evidência da participação de proscessos de assimilação crustal/ contaminação. Desta forma, o conjunto de dados apresentados permite interpretar essas associações como parte do mesmo magmatismo, ou pelo menos como fragmentos de arcos magmáticos similares. As assinaturas Sr-Nd e geoquímica sugere que ao menos parte das metavulcânicas do CMP represente os protólitos dos ortognaisses de alto grau inclusos no CVC. Adicionalmente, as evidencias isotópicas também apontam similaridade entre as rochas sedimentares de ambas as unidades, sugerindo que o CVC e o PMC são, ao menos em parte, expressões do mesmo contexto, onde a atividade magmática e sedimentar ocorreu em um mesmo ambiente de arco continental. A corroboração desta premissa é o objetivo principal de estudos de proveniência em andamento, cujos resultados prévios apontam para o caráter vulcano-sedimentar dos metapelitos do CVC e sua relação co-genética com os ortognaisses do CVC. Os dados isotópico Sr-Nd sugerem que os protólitos dos ortognaisses foram gerados por processos de assimilação crustal associados à cristalização fracionada. O modelamento binário (binary mixing model) realizado indica que o magmatismo estudado teria se originado de fontes mantélicas do tipo EM II. Uma seqüência paleoproterozóica de rochas TTG pertencente ao Complexo Arroio dos Ratos (CAR) é possivelmente o principal contaminante crustal assimilado. Em conjunto com as idades de herança descritas no CVC em ca. 2.0 Ga é sugerido que a fusão crustal que gerou o magmatismo do CVC em ca. 790-780 Ma foi predominantemente similar ao CAR. / This study focuses in the Várzea do Capivarita Complex (VCC), exposed in the southern part of the Neoproterozoic Mantiqueira Province (PM), Brazil. To investigate the evolutionary processes that lead the VCC construction, a multidisciplinary approach is taken, which includes field and structural geology, petrography, major and trace-element geochemistry, Sr-Nd isotope and U-Pb zircon geochronology by LA-MC-ICP-MS and SHRIMP. The complex comprises a compositional and age variety of ortho- and paragneisses tectonically interleaved during a high grade event. Subordinate volumes of syntectonic syenites are also part of CVC. The VCC deformation is partitioned into thrusting (D1) and transcurrent (D2) shear zones, suggestive of transpressive tectonics. This structural framework is possibly related to an oblique collision event. Petrological and goechronological studies emphasize the VCC orthogneisses in order to evaluate magmatic sources and related paleo-environments. Igneous crystallization ages obtained in the typical magmatic domains presenting oscillatory zoning in zircons vary between 780 and 790 Ma. Zircon overgrowths have ages mostly in the 650 – 640 Ma range and are interpreted to record the timing of high-grade metamorphism and associated partial melting. Geochronological data presented also indicates that boths kinematic regimes are contemporaneous, offering, therefore, further evidence for the oblique collisional event hypothesis. The VCC ortogneisses comprise tonalitic to granitic compositions and are metaluminous to peraluminous, calc-alkaline rocks, with high 87Sr/86Sr (i) ratios from 0.71628 to 0.72509 and εNd (790) values from -7.19 to -10.06. Their geochemical composition and trace-element patterns are compatible with a continental mature arc. VCC magmatism is correlated with other ca. 800 Ma arc sequences from southern PM, including part of the Porongos Metamorphic Complex (PMC) metavolcanic rocks and the orthogneisses from Cerro Bori, Uruguay. All these associations show signatures typical of accretionary orogens, TDM and Meso to Paleoproteroic inheritance ages, and present strong evidences of crustal assimilation/contamination. Thus, these sequences may be interpreted as part of the same magmatism, or at least as fragments of similar magmatic arcs. Geochemical and Sr-Nd signatures suggest that at least part of the PMC metavolcanic rocks may represent the protoliths of the VCC high grade orthogneisses. This, together with the isotope evidence of similarity between the sedimentary fractions of both unities, suggest that the VCC and PMC are, at least in part, expressions of the same context, wherein the magmatic and sedimentary activity occurred in a single continental arc environment. The corroboration of this premise is the main goal of provenience studies in prep, which previous results points to the volcano-sedimentary character of part of the VCC metapelites and its co-genetic relation with the VCC orthogneisses. Sr-Nd isotope data suggest that the orthogneiss protoliths were generated by crustal assimilation processes associated with fractional crystallization. Binary mixing models indicate that the VCC magmatism originates from evolved EM II mantle sources. A Paleoproterozoic TTG association (ca. 2.0 Ga) from the Arroio dos Ratos Complex (ARC) seems to be the main crustal contaminant assimilated. Together with the small inheritance contribution at ca. 2.0, this suggests that the melted crust at ca. 790-800 Ma was predominantly like ARC.

Thesis (M.S.)--Indiana University, 2009. / Title from screen (viewed on February 2, 2010). Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Andrew P. Barth, Gabriel M. Filippelli, Kathy Licht. Includes vitae. Includes bibliographical references (leaves 102-110).

The purpose of this study is to investigate the origin, source characteristics, evolution petrogenesis and emplacement mechanisms of Beypazari-Oymaaga&ccedil / granitoids. These granitoids are intruded into a metamorphic basement and nonconformably overlain by Neogene clastic rocks. Field work, petrographical and geochemical studies are carried out to determine the petrologic features and tectonic setting of the granitoid body. The Beypazari-Oymaaga&ccedil / pluton is a composite pluton with its host batholith, enclaves, aplite dykes and a pegmatite. The batholith is generally composed of quartz, K-feldspar, plagioclase and hornblende. Field observations and petrographic investigations indicate that the host batholith has granodiorite composition and shows distinct differences in the abundances of quartz, amphibole minerals (e.g., hornblende) and of enclaves. The samples taken from TavuktaSi Tepe contain relatively less amphibole and enclaves but more quartz. Compared with them, samples from the rest of the batholith have relatively abundant amphibole, K-feldspar megacrysts, and enclaves but less quartz. Enclaves derived from magma mixing/mingling processes are dioritic in composition. Geochemical data obtained from whole rock analyses show that the pluton is shallowly emplaced and has calc-alkaline, metaluminous to peraluminous chemistry. It is characterized by enrichments in LIL and LREE, especially in K, Rb and Th. Although, there is a distinct petrographic variation in the batholith, the geochemical characteristics are uniform throughout the pluton. The Oymaaga&ccedil / Granitoids which have I-type identity are typical representatives of magmatic arc environment. The present study suggests that the possible source of magma is the upper crust and can be compared with the coeval volcanism in Galatean Volcanic Arc.

Este estudo foca no Complexo Várzea do Capivarita (CVC), localizado no sul da Província da Mantiqueira (PM), Brasil. A fim de investigar a evolução geológica do CVC, uma abordagem multi-disciplinar foi utilizada, incluindo geologia de campo, geologia estrutural, petrografia, geoquímica de elementos maiores e traços, isótopos de Sr-Nd e geocronologia U-Pb em zircão (LA-MC-ICP-MS e SHRIMP). O complexo compreende uma variedade de orto- e paragnaisses de composição e idade diversa. Volumes subordinados de sienitos sintectônicos também perfazem o CVC. A deformação é particionada em zonas de cisalhamento do tipo thrust (D1) e transcorrentes (D2), o que sugere tectônica transpressiva. O arcabouço estrutural descrito é possivelmente relacionado a um evento colisional oblíquo. Os estudos petrológicos e geocronológicos enfatizaram os ortognaisses do CVC a fim de avaliar as fontes magmáticas e paleo-ambientes envolvidos. Idades de cristalização obtidas nos domínios de zircão com zonação tipicamente ígnea variaram entre 780 e 790 Ma. Por sua vez, idades entre 640 - 650 Ma foram obtidas em sobrecrescimentos de zircão, sendo interpretadas como o registro da idade do metamorfismo de alto grau e fusão parcial associada. Os dados geocronológicos apresentados também indicaram que ambos os regimes cinemáticos foram contemporâneos, oferecendo, dessa forma, evidencia adicional para a hipótese de colisão oblíqua. Os ortognaisses do Complexo têm composição tonalítica a granítica e são rochas calcioalcalinas meta- a peraluminosas, com razões elevadas de 87Sr/86Sr (i) variando de 0.71628 a 0.72509 e valores εNd (790) entre -7.19 a -10.06. Sua composição e padrões de elementos traços sugerem que representem um magmatismo de arco maduro continental. O magmatismo registrado no CVC é compatível com outras sequências de arco de ca. 800 Ma, incluindo parte das metavulcânicas ácidas do Complexo Metamórfico Porongos (CMP) e os ortognaisses do Cerro Bori, Uruguai. Todas essas associações têm assinatura típica de orógenos acrescionários, contendo idade TDM Meso a Paleoproterozóica, além de forte evidência da participação de proscessos de assimilação crustal/ contaminação. Desta forma, o conjunto de dados apresentados permite interpretar essas associações como parte do mesmo magmatismo, ou pelo menos como fragmentos de arcos magmáticos similares. As assinaturas Sr-Nd e geoquímica sugere que ao menos parte das metavulcânicas do CMP represente os protólitos dos ortognaisses de alto grau inclusos no CVC. Adicionalmente, as evidencias isotópicas também apontam similaridade entre as rochas sedimentares de ambas as unidades, sugerindo que o CVC e o PMC são, ao menos em parte, expressões do mesmo contexto, onde a atividade magmática e sedimentar ocorreu em um mesmo ambiente de arco continental. A corroboração desta premissa é o objetivo principal de estudos de proveniência em andamento, cujos resultados prévios apontam para o caráter vulcano-sedimentar dos metapelitos do CVC e sua relação co-genética com os ortognaisses do CVC. Os dados isotópico Sr-Nd sugerem que os protólitos dos ortognaisses foram gerados por processos de assimilação crustal associados à cristalização fracionada. O modelamento binário (binary mixing model) realizado indica que o magmatismo estudado teria se originado de fontes mantélicas do tipo EM II. Uma seqüência paleoproterozóica de rochas TTG pertencente ao Complexo Arroio dos Ratos (CAR) é possivelmente o principal contaminante crustal assimilado. Em conjunto com as idades de herança descritas no CVC em ca. 2.0 Ga é sugerido que a fusão crustal que gerou o magmatismo do CVC em ca. 790-780 Ma foi predominantemente similar ao CAR. / This study focuses in the Várzea do Capivarita Complex (VCC), exposed in the southern part of the Neoproterozoic Mantiqueira Province (PM), Brazil. To investigate the evolutionary processes that lead the VCC construction, a multidisciplinary approach is taken, which includes field and structural geology, petrography, major and trace-element geochemistry, Sr-Nd isotope and U-Pb zircon geochronology by LA-MC-ICP-MS and SHRIMP. The complex comprises a compositional and age variety of ortho- and paragneisses tectonically interleaved during a high grade event. Subordinate volumes of syntectonic syenites are also part of CVC. The VCC deformation is partitioned into thrusting (D1) and transcurrent (D2) shear zones, suggestive of transpressive tectonics. This structural framework is possibly related to an oblique collision event. Petrological and goechronological studies emphasize the VCC orthogneisses in order to evaluate magmatic sources and related paleo-environments. Igneous crystallization ages obtained in the typical magmatic domains presenting oscillatory zoning in zircons vary between 780 and 790 Ma. Zircon overgrowths have ages mostly in the 650 – 640 Ma range and are interpreted to record the timing of high-grade metamorphism and associated partial melting. Geochronological data presented also indicates that boths kinematic regimes are contemporaneous, offering, therefore, further evidence for the oblique collisional event hypothesis. The VCC ortogneisses comprise tonalitic to granitic compositions and are metaluminous to peraluminous, calc-alkaline rocks, with high 87Sr/86Sr (i) ratios from 0.71628 to 0.72509 and εNd (790) values from -7.19 to -10.06. Their geochemical composition and trace-element patterns are compatible with a continental mature arc. VCC magmatism is correlated with other ca. 800 Ma arc sequences from southern PM, including part of the Porongos Metamorphic Complex (PMC) metavolcanic rocks and the orthogneisses from Cerro Bori, Uruguay. All these associations show signatures typical of accretionary orogens, TDM and Meso to Paleoproteroic inheritance ages, and present strong evidences of crustal assimilation/contamination. Thus, these sequences may be interpreted as part of the same magmatism, or at least as fragments of similar magmatic arcs. Geochemical and Sr-Nd signatures suggest that at least part of the PMC metavolcanic rocks may represent the protoliths of the VCC high grade orthogneisses. This, together with the isotope evidence of similarity between the sedimentary fractions of both unities, suggest that the VCC and PMC are, at least in part, expressions of the same context, wherein the magmatic and sedimentary activity occurred in a single continental arc environment. The corroboration of this premise is the main goal of provenience studies in prep, which previous results points to the volcano-sedimentary character of part of the VCC metapelites and its co-genetic relation with the VCC orthogneisses. Sr-Nd isotope data suggest that the orthogneiss protoliths were generated by crustal assimilation processes associated with fractional crystallization. Binary mixing models indicate that the VCC magmatism originates from evolved EM II mantle sources. A Paleoproterozoic TTG association (ca. 2.0 Ga) from the Arroio dos Ratos Complex (ARC) seems to be the main crustal contaminant assimilated. Together with the small inheritance contribution at ca. 2.0, this suggests that the melted crust at ca. 790-800 Ma was predominantly like ARC.

Este estudo foca no Complexo Várzea do Capivarita (CVC), localizado no sul da Província da Mantiqueira (PM), Brasil. A fim de investigar a evolução geológica do CVC, uma abordagem multi-disciplinar foi utilizada, incluindo geologia de campo, geologia estrutural, petrografia, geoquímica de elementos maiores e traços, isótopos de Sr-Nd e geocronologia U-Pb em zircão (LA-MC-ICP-MS e SHRIMP). O complexo compreende uma variedade de orto- e paragnaisses de composição e idade diversa. Volumes subordinados de sienitos sintectônicos também perfazem o CVC. A deformação é particionada em zonas de cisalhamento do tipo thrust (D1) e transcorrentes (D2), o que sugere tectônica transpressiva. O arcabouço estrutural descrito é possivelmente relacionado a um evento colisional oblíquo. Os estudos petrológicos e geocronológicos enfatizaram os ortognaisses do CVC a fim de avaliar as fontes magmáticas e paleo-ambientes envolvidos. Idades de cristalização obtidas nos domínios de zircão com zonação tipicamente ígnea variaram entre 780 e 790 Ma. Por sua vez, idades entre 640 - 650 Ma foram obtidas em sobrecrescimentos de zircão, sendo interpretadas como o registro da idade do metamorfismo de alto grau e fusão parcial associada. Os dados geocronológicos apresentados também indicaram que ambos os regimes cinemáticos foram contemporâneos, oferecendo, dessa forma, evidencia adicional para a hipótese de colisão oblíqua. Os ortognaisses do Complexo têm composição tonalítica a granítica e são rochas calcioalcalinas meta- a peraluminosas, com razões elevadas de 87Sr/86Sr (i) variando de 0.71628 a 0.72509 e valores εNd (790) entre -7.19 a -10.06. Sua composição e padrões de elementos traços sugerem que representem um magmatismo de arco maduro continental. O magmatismo registrado no CVC é compatível com outras sequências de arco de ca. 800 Ma, incluindo parte das metavulcânicas ácidas do Complexo Metamórfico Porongos (CMP) e os ortognaisses do Cerro Bori, Uruguai. Todas essas associações têm assinatura típica de orógenos acrescionários, contendo idade TDM Meso a Paleoproterozóica, além de forte evidência da participação de proscessos de assimilação crustal/ contaminação. Desta forma, o conjunto de dados apresentados permite interpretar essas associações como parte do mesmo magmatismo, ou pelo menos como fragmentos de arcos magmáticos similares. As assinaturas Sr-Nd e geoquímica sugere que ao menos parte das metavulcânicas do CMP represente os protólitos dos ortognaisses de alto grau inclusos no CVC. Adicionalmente, as evidencias isotópicas também apontam similaridade entre as rochas sedimentares de ambas as unidades, sugerindo que o CVC e o PMC são, ao menos em parte, expressões do mesmo contexto, onde a atividade magmática e sedimentar ocorreu em um mesmo ambiente de arco continental. A corroboração desta premissa é o objetivo principal de estudos de proveniência em andamento, cujos resultados prévios apontam para o caráter vulcano-sedimentar dos metapelitos do CVC e sua relação co-genética com os ortognaisses do CVC. Os dados isotópico Sr-Nd sugerem que os protólitos dos ortognaisses foram gerados por processos de assimilação crustal associados à cristalização fracionada. O modelamento binário (binary mixing model) realizado indica que o magmatismo estudado teria se originado de fontes mantélicas do tipo EM II. Uma seqüência paleoproterozóica de rochas TTG pertencente ao Complexo Arroio dos Ratos (CAR) é possivelmente o principal contaminante crustal assimilado. Em conjunto com as idades de herança descritas no CVC em ca. 2.0 Ga é sugerido que a fusão crustal que gerou o magmatismo do CVC em ca. 790-780 Ma foi predominantemente similar ao CAR. / This study focuses in the Várzea do Capivarita Complex (VCC), exposed in the southern part of the Neoproterozoic Mantiqueira Province (PM), Brazil. To investigate the evolutionary processes that lead the VCC construction, a multidisciplinary approach is taken, which includes field and structural geology, petrography, major and trace-element geochemistry, Sr-Nd isotope and U-Pb zircon geochronology by LA-MC-ICP-MS and SHRIMP. The complex comprises a compositional and age variety of ortho- and paragneisses tectonically interleaved during a high grade event. Subordinate volumes of syntectonic syenites are also part of CVC. The VCC deformation is partitioned into thrusting (D1) and transcurrent (D2) shear zones, suggestive of transpressive tectonics. This structural framework is possibly related to an oblique collision event. Petrological and goechronological studies emphasize the VCC orthogneisses in order to evaluate magmatic sources and related paleo-environments. Igneous crystallization ages obtained in the typical magmatic domains presenting oscillatory zoning in zircons vary between 780 and 790 Ma. Zircon overgrowths have ages mostly in the 650 – 640 Ma range and are interpreted to record the timing of high-grade metamorphism and associated partial melting. Geochronological data presented also indicates that boths kinematic regimes are contemporaneous, offering, therefore, further evidence for the oblique collisional event hypothesis. The VCC ortogneisses comprise tonalitic to granitic compositions and are metaluminous to peraluminous, calc-alkaline rocks, with high 87Sr/86Sr (i) ratios from 0.71628 to 0.72509 and εNd (790) values from -7.19 to -10.06. Their geochemical composition and trace-element patterns are compatible with a continental mature arc. VCC magmatism is correlated with other ca. 800 Ma arc sequences from southern PM, including part of the Porongos Metamorphic Complex (PMC) metavolcanic rocks and the orthogneisses from Cerro Bori, Uruguay. All these associations show signatures typical of accretionary orogens, TDM and Meso to Paleoproteroic inheritance ages, and present strong evidences of crustal assimilation/contamination. Thus, these sequences may be interpreted as part of the same magmatism, or at least as fragments of similar magmatic arcs. Geochemical and Sr-Nd signatures suggest that at least part of the PMC metavolcanic rocks may represent the protoliths of the VCC high grade orthogneisses. This, together with the isotope evidence of similarity between the sedimentary fractions of both unities, suggest that the VCC and PMC are, at least in part, expressions of the same context, wherein the magmatic and sedimentary activity occurred in a single continental arc environment. The corroboration of this premise is the main goal of provenience studies in prep, which previous results points to the volcano-sedimentary character of part of the VCC metapelites and its co-genetic relation with the VCC orthogneisses. Sr-Nd isotope data suggest that the orthogneiss protoliths were generated by crustal assimilation processes associated with fractional crystallization. Binary mixing models indicate that the VCC magmatism originates from evolved EM II mantle sources. A Paleoproterozoic TTG association (ca. 2.0 Ga) from the Arroio dos Ratos Complex (ARC) seems to be the main crustal contaminant assimilated. Together with the small inheritance contribution at ca. 2.0, this suggests that the melted crust at ca. 790-800 Ma was predominantly like ARC.

The Andean Southern Volcanic Zone (SVZ) is a vast and complex continental arc that has been studied extensively to provide an understanding of arc-magma genesis, the origin and chemical evolution of the continental crust, and geochemical compositions of volcanic products. The present study focuses on distinguishing the magma/sub-arc crustal interaction of eruptive products from the Azufre-Planchon-Peteroa (APP 35°15’S) volcanic center and other major centers in the Central SVZ (CSVZ 37°S - 42°S), Transitional SVZ (TSVZ 34.3-37.0°S), and Northern SVZ (NSVZ 33°S - 34°30’S). New Hf and Nd isotopic and trace element data for SVZ centers are consistent with former studies that these magmas experienced variable depths of crystal fractionation, and that crustal assimilation is restricted to the lower crustal depths with an apparent role of garnet. Thermobarometric calculations applied to magma compositions constrain the depth of magma separation from mantle sources in all segments of the SVZ to(70-90 km). Magmatic separation at the APP complex occurs at an average depth of ~50 km which is confined to the mantle lithosphere and the base of the crust suggesting localized thermal abrasion both reservoirs. Thermobarometric calculations indicate that CSVZ primary magmas arise from a similar average depth of (~54 km) which confines magma separation to the asthenospheric mantle. The northwards along-arc Sr-Nd-Hf isotopic data and LREE enrichment accompanied with HREE depletion of SVZ mafic magmas correlates well with northward increasing crustal thickness and decreasing primary melt separation from mantle source regions indicating an increased involvement of lower crustal components in SVZ magma petrogenesis. The study concludes that the development of mature subduction zones over millions of years of continuous magmatism requires that mafic arc derived melts stagnate at lower crustal levels due to density similarities and emplace at lower crustal depths. Basaltic underplating creates localized hot zone environments below major magmatic centers. These regions of high temperature/partial melting, and equilibration with underplated mafic rocks provides the mechanism that controls trace element and isotopic variability of primary magmas of the TSVZ and NSVZ from their baseline CSVZ-like precursors.

Indiana University-Purdue University Indianapolis (IUPUI) / The objectives of this study are, generally, to analyze and understand internal processes that produce melts in an oceanic-continental subduction setting; and, specifically, to understand the assembly of a Cretaceous magmatic arc pluton (Palms pluton), including the timing of melt emplacement(s) and melt evolution from the source. SiO2 concentrations vary from ~ 69-76 % by weight. Whole rock trace element concentrations vary up to 7 times. Zircon analysis shows a minimum age difference in the pluton of 3 my, if considering the uncertainties of the oldest and youngest samples. According to the model made from the HEAT program, this is approximately six times longer than the estimated crystallization time of one batch of melt with the same physical properties as the Palms pluton. Two distinct sources, perceived from chemical analysis of premagmatic zircons, are found throughout the pluton. REE compositional patterns show a hybridization of Proterozoic and Mesozoic sources in some, but not all, Palms pluton granites. This data suggests that the pluton formed from multiple intrusions and the Proterozoic source remained relatively consistent throughout the pluton’s assembly with few additions of younger Mesozoic source material.