Three studies on Cordilleran foreland basin deposits in the western U.S.A. constitute this dissertation. These studies differ in scale, time and discipline. The first two studies include basin analysis, flexural modeling and detailed stratigraphic analysis of Upper Cretaceous depocenters and strata in the western U.S.A. The third study consists of detrital zircon U-Pb analysis (DZ U-Pb) and thermochronology, both zircon (U-Th)/He and apatite fission track (AFT), of Upper Jurassic to Upper Cretaceous foreland-basin conglomerates and sandstones. Five electronic supplementary files are a part of this dissertation and are available online; these include 3 raw data files (Appendix_A_raw_isopach_data.txt, Appendix_C_DZ_Data.xls, Appendix_C_UPb_apatite.xls), 1 oversized stratigraphic cross section (Appendix_B_figure_5.pdf), and 1 figure containing apatite U-Pb concordia plots (Appendix_C_Concordia.pdf). Appendix A. Subsidence in the retroarc foreland of the North American Cordillera in the western U.S.A. has been the focus of a great deal of research, and its transition from a flexural foreland basin, during the Late Jurassic and Early Cretaceous, to a dynamically subsided basin during the Late Cretaceous has been well documented. However, the exact timing of the flexural to dynamic transition is not well constrained, and the mechanism has been consistently debated. In order to address the timing, I produced new isopach maps from ~130 well log data points that cover much of Utah, Colorado, Wyoming and northern New Mexico, producing in the process, the most detailed isopach maps of the area. These isopach maps span the Turonian to mid-Campanian during the Late Cretaceous (~93–76 Ma). In conjunction with the isopach maps I flexurally modeled the Cordilleran foreland basin to identify when flexure can no longer account for the basin geometry and identified the flexural to dynamic transition to have occurred at 81 Ma. In addition, the dynamic subsidence at 81 Ma is compared to the position of the hypothesized Shatsky Oceanic Plateau and other proposed drivers of dynamic subsidence. I concluded that dynamic subsidence is likely caused by convection over the plunging nose of the Shatsky Oceanic Plateau. Appendix B. The second study is a detailed stratigraphic study of the Upper Cretaceous, (Campanian, ~76 Ma) Sego Sandstone Member of the Mesaverde Group in northwestern Colorado, an area where little research has been done on this formation. Its equivalent in the Book Cliffs area in eastern Utah has been rigorously documented and its distal progradation has been contrastingly interpreted as a result of active tectonism and shortening in the Cordilleran orogenic belt ~250 km to the west and to tectonic quiescence, flexural rebound in the thrust belt and reworking of proximal coarse grained deposits. I documented ~17 km of along depositional dip outcrops of the Sego Sandstone Member north of Rangely, Colorado. This documentation includes measured sections, paleocurrent analysis, a stratigraphic cross section, block diagrams outlining the evolution of environments of deposition through time, and paleogeographic maps correlating northwest Colorado with the Book Cliffs, Utah. The sequence stratigraphy of the Sego Sandstone Member in northwest Colorado is similar to that documented in the Book Cliffs area to the south-southwest, sharing three sequence boundaries. However, flood-tidal delta assemblages between fluvio-deltaic deposits that are present north of Rangely, Colorado are absent from the Book Cliffs area. These flood-tidal-delta assemblages are likely caused by a large scale avulsion event in the Rangely area that did not occur or was not preserved in the Book Cliffs area. In regards to tectonic models that explain distal progradation of the 76 Ma Sego Sandstone Member to be caused by tectonic quiescence and flexural rebound in the thrust belt, the first study shows that at 76 Ma, flexural processes were no longer dominant in the Cordilleran foreland, so it is inappropriate to apply models driven by flexure to the Sego Sandstone Member. Dynamic processes dominated the western U.S.A. during the Campanian, and flexural processes were subordinate. Appendix C. In order to test the tectonic vs. anti-tectonic basin-filling models for distal coarse foreland deposits mentioned above, the third study involves estimating lag times of Upper Jurassic to Upper Cretaceous conglomerates and sandstones in the Cordilleran foreland basin. Measuring lag time requires a good understanding of both the stratigraphic age of a deposit and the thermal history of sedimentary basin. To further constrain depositional age, I present twenty-two new detrital zircon U-Pb (DZ U-Pb) sample analyses, spanning Upper Jurassic to Upper Cretaceous stratigraphy in Utah, Colorado, Wyoming and South Dakota. Source exhumation ages can be measured using thermochronology. To identify a thermochronometer that measures source exhumation in the North America Cordillera, both zircon (U-Th)/He, on eleven samples, and apatite fission track (AFT) thermochronology, on eleven samples was performed. Typically, the youngest cooling age population in detrital thermochronologic analyses is considered to be a source exhumation signal; however, whether or not these apatites are exhumed apatites or derived from young magmatic and volcanic sources has been debated. To test this, I double dated the detrital AFT samples, targeting apatites with a young cooling age, using U-Pb thermochronology. Key findings are that the maximum depositional ages using DZ U-Pb match existing biostratigraphic and geochronologic age controls on basin stratigraphy. AFT is an effective thermochronometer for Lower to Upper Cretaceous foreland stratigraphy and indicates that source material was exhumed from >4–5 km depth in the Cordilleran orogenic belt between 118 and 66 Ma, and zircon (U-Th)/He suggests that it was exhumed from <8–9 km depth. Double dating apatites (with AFT and U-Pb) indicate that volcanic contamination is a significant issue; without having UPb dating of the same apatite grains, one cannot exclude the possibility that the youngest detrital AFT population is contaminated with significant amounts of volcanogenic apatite and does not represent source exhumation. AFT lag-times are 0 to 5 Myr with relatively steady-state to slightly increasing exhumation rates. We compare our data to orogenic wedge dynamics and subsidence histories; all data shows active shortening and rapid exhumation throughout the Cretaceous. Our lag-time measurements indicate exhumation rates of ~.9–>>1 km/Myr.

New and existing U–Pb and 40Ar/39Ar geochronological data, and oxygen and hydrogen stable isotope data, are combined with structural and metamorphic data from Thor–Odin, the southern culmination of the Monashee Complex. This leads to a new interpretation of the timing of deformation and metamorphism. Amphibolites in Thor–Odin with hornblende 40Ar/39Ar dates between ~75–70 and ~51 Ma experienced more 18O- and D-depletion than amphibolites with older dates. The younger dates that were previously interpreted as cooling ages, may have resulted from complete or partial Ar loss in the presence of meteoric fluids that were introduced into the rock during extension. <br><br> Monazite crystals in pelitic schist, quartzite and orthogneiss, which have U–Pb ages younger than 40Ar/39Ar hornblende ages in amphibolite in northwest Thor–Odin, may have grown during tension in the presence of fluids. Titanite, xenotime and zircon dates may be interpreted in the same way. Thus, the U–Pb dates that were previously interpreted as representing peak of metamorphism and the hornblende 40Ar/39Ar dates that were previously interpreted as representing cooling ages, may be interpreted as reflecting meteoric fluid penetration of the crust during regional extension. This implies that the age of the thermal peak of metamorphism is older than ~75–70 Ma. Migmatisation in a basement orthogneiss in Thor–Odin occurred at ~1.8 Ga. Dissolution rims are preserved in zircon between ~1.8 Ga domains and 52 Ma overgrowths. Because growth of new zircon (and possibly other U–Pb accessory phases) did not take place, any geological event that occurred during the ~1.8 Ga to 52 Ma time interval is not recorded. Cordilleran deformation and metamorphism may have taken place within that time interval, e.g. in the Middle Jurassic and/or mid- to Late Cretaceous, the time of Cordilleran deformation and metamorphism in the rocks overlying the Monashee Complex. <br><br> The Joss Mountain orthogneiss, west of the Monashee Complex in the Selkirk Allochthon, is dated at 362 +/– 13 Ma. F3 folding in pelitic schist at Joss Mountain is constrained between ~73 and ~70 Ma. Existing structural, metamorphic and geochronological data in, and close to, the Shuswap Metamorphic Complex in the southern Canadian Cordillera are shown to be consistent with a channel flow model.

The Mount Somers Volcanic Group (MSVG) and Mandamus Igneous Complex (MIC) are the magmatic manifestations of the transition from convergence to extension at the Gondwana margin, which culminated in the separation of New Zealand from Australia and Antarctica. The MIC has been correlated both geochemically and temporally with the Central Marlborough Igneous Province (CMIP). The MSVG and CMIP are located in the Eastern Province of New Zealand. The MSVG is restricted to the Rakaia terrane, whereas the CMIP is restricted to the Pahau terrane. The Rakaia and Pahau terranes are thick accretionary complexes, which were strongly deformed as a result of prolonged subduction at the Gondwana margin. The Pahau terrane is the younger of the two and continued to be deposited and deformed until the abrupt cessation of subduction, which in the Marlborough sedimentary record occurred in the Motuan (100 - 105 Ma). Following the cessation of subduction, after an interval of 2-7 Ma of relative quiescence and subsidence of the Pahau terrane, the MSVG and MIC were erupted/emplaced. The production of MSVG and MIC magmas occurred simultaneously and the activity was of short-lived duration. SHRIMP geochronology yielded crystallisation ages of 97.0 ± 1.5 Ma to 98.0 ± 1.2 Ma from zircons separated from MSVG rhyolites. The SHRIMP ages are within error of the previously published Rb-Sr age for the MIC. The SHRIMP geochronology also confirmed the presence of inherited zircons which yielded ages consistent with their derivation from the Rakaia terrane. Ar-Ar geochronology confirmed the coeval nature of the MSVG and MIC magmatism, but yielded consistently younger ages (94.5 ± 3 Ma for the MSVG and 94.2 ± 1.7 Ma for the MIC). The systematic differences in ages obtained by SHRIMP and Ar-Ar are believed to be method-dependent. The MSVG comprises a calc-alkaline volcanic assemblage, which ranges in composition from basaltic-andesite lavas (SiO₂ = 54.5%) to high-silica rhyolites and ignimbrites (SiO₂ ≤ 78.1%). The MSVG had an original extent of at least 18 000 km². The magmas from the MSVG had high LILE/HFSE, high LILE/REE and moderately high LREE/HFSE which are characteristic of subduction derived magmas. Geochemical modelling suggests that the MSVG magmas were formed from partial melting of a subduction-modified mantle wedge, with high degrees of crustal assimilation. The assimilant had an isotopic composition similar to that of the Rakaia terrane, which is consistent with the geological setting of the MSVG. The MSVG has ⁸⁷Sr/⁸⁶Sri from 0.7055 to 0.7100 and ¹⁴³Nd/¹⁴⁴Ndi from 0.51254 to 0.51230 (ɛNd +0.5 to -4.2), which reflects varying degrees of contamination by Rakaia terrane. Radiogenic isotope modelling suggests that the MSVG end-members were derived from the same parent magma, which evolved through AFC processes from basaltic-andesite to rhyolite. The modelling strongly suggests that assimilation played a lesser role in the petrogenesis of the Malvern Hills magmas than in the petrogenesis of the other units. AFC modelling requires the degree of assimilation to increase as the magmas evolved. Oxygen isotope data are consistent with high degrees of crustal assimilation, and may indicate that the assimilant had higher ¹⁸O characteristics than the Rakaia terrane samples analysed. The MIC is an alkaline suite which ranges in composition from basalt and gabbro to syenite, trachyte and phono-tephrite. The MIC is interpreted to have formed from enriched asthenospheric mantle, with a composition similar to HIMU (²⁰⁶Pb/²⁰⁴Pbi ranges from 19.2 to 20.3). The samples range in isotopic composition from ⁸⁷Sr/⁸⁶Sri = 0.7030 to 0.7036, ¹⁴³Nd/¹⁴⁴Ndi = 0.51275 to 0.51268 (ɛNd +4.6 to +3.3). The range in isotopic composition is due to varying degrees of contamination by Pahau terrane, which reaches a maximum of 25% but in most samples is < 10%. The MIC is contaminated to a much lesser extent than the MSVG which is interpreted to be related to the thinner nature of the Pahau crust in the mid-Cretaceous. The latest phases of activity in the MIC were subjected to lower degrees of contamination which is interpreted to reflect the passage of magmas through pre-existing pathways. The onset of MSVG and CMIP magmatism coincided with the initiation of major rift-related depositional basins, and the eruption of the MSVG is demonstrably associated with normal faulting. The tectonic trigger responsible for the sudden onset of magmatism and rifting in the Eastern Province terranes was the detachment of the previously subducting slab following the cessation of subduction due to the arrival of the Hikurangi Plateau at the margin and the subsequent stalling of the Pacific spreading centre. The capture of the Gondwana margin led to the propogation of extension into the margin by the divergent Pacific plate. The ensuing extension aided the detachment of the subducting slab beneath the Eastern Province terranes. The slab-detachment promoted decompression melting of the sub-lithospheric mantle wedge to produce the MSVG magmas and triggered the ascent of asthenospheric mantle through the slab window, which melted through decompression to produce the CMIP magmatism. The asthenospheric mantle tapped by the slab detachment episode was highly enriched relative to N-MORB and is akin to the similar age HIMU-OIB affinity melts documented from Antarctica and Australia. The short-lived duration of activity is typical of slab-detachment related magmatism which occurs as a passive response to plate reconfiguration. The similarity in geochemistry of the MIC with OIB-affinity igneous centres in Australia and Antarctica implies an enriched mantle domain of large geographical extent. The distribution of relatively small volumes of OIB magmatism is suggestive of a fossil plume component, which was tapped in response to lithospheric extension producing relatively short-lived HIMU magmatism. The same fossil plume component has previously been implicated in the formation of the Cenozoic West Antarctic Rift System and may be responsible for the late Cretaceous magmatism in the Chatham Islands and Tertiary volcanics of the South Island of New Zealand.

In the Pilgangoora Belt of the Pilbara Craton, Australia, the 3517 Ma Coonterunah Group and 3484-3468 Ma Carlindi granitoids underlie the 3458 Ma Warrawoona Group beneath an erosional unconformity, thus providing evidence for ancient emergent continental crust. The basalts either side of the unconformity are remarkably similar, with N-MORB-normalised enrichment factors for LILE, Th, U and LREE greater than those for Ta, Nb, P, Zr, Ti, Y and M-HREE, and initial e(Nd, Hf) compositions which systematically vary with Sm/Nd, Nb/U and Nb/La ratios. Geological and geochemical evidence shows that the Warrawoona Group was erupted onto continental basement, and that these basalts assimilated small amounts of Carlindi granitoid. As the Coonterunah basalts have similar compositions, they probably formed likewise, although they were deposited >60 myr before. Indeed, such a model may be applicable to most other early Pilbara greenstone successions, and so an older continental basement was probably critical for early Pilbara evolution. The geochemical, geological and geophysical characteristics of the Pilbara greenstone successions can be best explained as flood basalt successions deposited onto thin, submerged continental basement. This magmatism was induced by thermal upwelling in the mantle, although the basalts themselves do not have compositions which reflect derivation from an anomalously hot mantle. The Carlindi granitoids probably formed by fusion of young garnet-hornblende-rich sialic crust induced by basaltic volcanism. Early Archaean rocks have Nd-Hf isotope compositions which indicate that the young mantle had differentiated into distinct isotopic domains before 4.0 Ga. Such ancient depletion was associated with an increase of mantle Nb/U ratios to modern values, and hence this event probably reflects the extraction of an amount of continental crust equivalent to its modern mass from the primitive mantle before 3.5 Ga. Thus, a steady-state model of crustal growth is favoured whereby post ~4.0 Ga continental additions have been balanced by recycling back into the mantle, with no net global flux of continental crust at modern subduction zones. It is also proposed that the decoupling of initial e(Nd) and e(Hf) from its typical covariant behaviour was related to the formation of continental crust, perhaps by widespread formation of TTG magmas.

Thesis (M.S.)--Indiana University, 2008. / Department of Earth Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Kathy J. Licht, Andrew P. Barth, R. Jeffery Swope, Gabriel M. Filippelli. Includes vitae. Includes bibliographical references (leaves 182-191).

Este trabalho baseou-se no estudo de xenólitos de rochas metamórficas na região de Piratini e Pinheiro Machado, sudeste do Escudo Sul-rio-grandense. Partindo de estudos de campo, microscopia ótica, geoquímica de elementos maiores e traços e geocronologia U-Pb em zircão, essa associação de rochas gnáissicas, denominada de Gnaisses Piratini, apresenta uma composição intermediária a ácida, predominantemente granodiorítica a tonalítica, subalcalina cálcio-alcalina médio-K, peraluminosa a levemente metaluminosa. Estes dados, juntamente com sua idade magmática de 784 ± 4 Ma, leva esta associação a ser interpretada como originada em um ambiente de arco magmático continental, e metamorfisada em fácies anfibolito em torno de 664 a 688 Ma. Nesta dissertação é apresentado um estado da arte dos estudos publicados sobre os Gnaisses Piratini, além de considerações sobre a importância desta unidade como um embasamento de sua região. Após, é apresentado o artigo denominado “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submetido para publicação no periódico Brazilian Journal of Geology, onde são descritos os dados e interpretações obtidos sobre os Gnaisses Piratini. / This work has based on the study of xenoliths of metamorphic rocks in the region of Piratini and Pinheiro Machado, southeastern Sul-rio-grandense Shield. Through field studies, optical microscopy, geochemistry of major and trace elements and U-Pb zircon geochronology, this association of gneissic rocks, named Piratini Gneisses, features an intermediate to felsic composition, predominantly granodioritic to tonalitic, medium-K calc-alkaline subalkaline, peraluminous to slightly metaluminous. These data, together with the magmatic age of 784 ± 4 Ma lead this rock association to be originated on an active magmatic arc environment, and metamorphosed at around 664 to 688 Ma in amphibolite facies. This dissertation presents a state-of-the-art of studies published about Piratini Gneisses, in addition to considerations about the importance of this unit as a basement of your region. After, it is featured the article entitled “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submitted for publication in the “Brazilian Journal of Geology”, where are described the data and interpretations obtained on the Piratini Gneisses.

Este trabalho baseou-se no estudo de xenólitos de rochas metamórficas na região de Piratini e Pinheiro Machado, sudeste do Escudo Sul-rio-grandense. Partindo de estudos de campo, microscopia ótica, geoquímica de elementos maiores e traços e geocronologia U-Pb em zircão, essa associação de rochas gnáissicas, denominada de Gnaisses Piratini, apresenta uma composição intermediária a ácida, predominantemente granodiorítica a tonalítica, subalcalina cálcio-alcalina médio-K, peraluminosa a levemente metaluminosa. Estes dados, juntamente com sua idade magmática de 784 ± 4 Ma, leva esta associação a ser interpretada como originada em um ambiente de arco magmático continental, e metamorfisada em fácies anfibolito em torno de 664 a 688 Ma. Nesta dissertação é apresentado um estado da arte dos estudos publicados sobre os Gnaisses Piratini, além de considerações sobre a importância desta unidade como um embasamento de sua região. Após, é apresentado o artigo denominado “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submetido para publicação no periódico Brazilian Journal of Geology, onde são descritos os dados e interpretações obtidos sobre os Gnaisses Piratini. / This work has based on the study of xenoliths of metamorphic rocks in the region of Piratini and Pinheiro Machado, southeastern Sul-rio-grandense Shield. Through field studies, optical microscopy, geochemistry of major and trace elements and U-Pb zircon geochronology, this association of gneissic rocks, named Piratini Gneisses, features an intermediate to felsic composition, predominantly granodioritic to tonalitic, medium-K calc-alkaline subalkaline, peraluminous to slightly metaluminous. These data, together with the magmatic age of 784 ± 4 Ma lead this rock association to be originated on an active magmatic arc environment, and metamorphosed at around 664 to 688 Ma in amphibolite facies. This dissertation presents a state-of-the-art of studies published about Piratini Gneisses, in addition to considerations about the importance of this unit as a basement of your region. After, it is featured the article entitled “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submitted for publication in the “Brazilian Journal of Geology”, where are described the data and interpretations obtained on the Piratini Gneisses.

Este trabalho baseou-se no estudo de xenólitos de rochas metamórficas na região de Piratini e Pinheiro Machado, sudeste do Escudo Sul-rio-grandense. Partindo de estudos de campo, microscopia ótica, geoquímica de elementos maiores e traços e geocronologia U-Pb em zircão, essa associação de rochas gnáissicas, denominada de Gnaisses Piratini, apresenta uma composição intermediária a ácida, predominantemente granodiorítica a tonalítica, subalcalina cálcio-alcalina médio-K, peraluminosa a levemente metaluminosa. Estes dados, juntamente com sua idade magmática de 784 ± 4 Ma, leva esta associação a ser interpretada como originada em um ambiente de arco magmático continental, e metamorfisada em fácies anfibolito em torno de 664 a 688 Ma. Nesta dissertação é apresentado um estado da arte dos estudos publicados sobre os Gnaisses Piratini, além de considerações sobre a importância desta unidade como um embasamento de sua região. Após, é apresentado o artigo denominado “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submetido para publicação no periódico Brazilian Journal of Geology, onde são descritos os dados e interpretações obtidos sobre os Gnaisses Piratini. / This work has based on the study of xenoliths of metamorphic rocks in the region of Piratini and Pinheiro Machado, southeastern Sul-rio-grandense Shield. Through field studies, optical microscopy, geochemistry of major and trace elements and U-Pb zircon geochronology, this association of gneissic rocks, named Piratini Gneisses, features an intermediate to felsic composition, predominantly granodioritic to tonalitic, medium-K calc-alkaline subalkaline, peraluminous to slightly metaluminous. These data, together with the magmatic age of 784 ± 4 Ma lead this rock association to be originated on an active magmatic arc environment, and metamorphosed at around 664 to 688 Ma in amphibolite facies. This dissertation presents a state-of-the-art of studies published about Piratini Gneisses, in addition to considerations about the importance of this unit as a basement of your region. After, it is featured the article entitled “Geology of the Piratini Gneisses: medium-K calc-alkaline magmatism of 784 ma (U-Pb SHRIMP) on the southeastern of Dom Feliciano Belt, RS”, submitted for publication in the “Brazilian Journal of Geology”, where are described the data and interpretations obtained on the Piratini Gneisses.

Orientador: Elson Paiva de Oliveira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-05T08:14:55Z (GMT). No. of bitstreams: 1 Nascimento_RosemerydaSilva_D.pdf: 5636781 bytes, checksum: 8732e39c60030622a2ca93f4c6f2c946 (MD5) Previous issue date: 2005 / Resumo: A Faixa Sergipana está localizada na região nordeste do Brasil, entre o Maciço Pernambuco-Alagoas e o Cráton do São Francisco. Na literatura é interpretada como a continuação, na América do Sul, da Faixa Oubanguides, na África, com idade Neoproterózóica (Ciclo Brasiliano/Pan-Africano). O quadro lito-estrutural da região está individualizado em diversos domínios, dentre os quais destaca-se o Domínio Canindé na porção central dessa unidade geotectônica. O Domínio Canindé é constituído por rochas metavulcanossedimentares invadidas por uma suíte gabróica e granitos diversos (Boa Esperança, Lajedinho, Tipo Sítios Novos e Xingo). Sobre este domínio há controvérsia quanto ao provável contexto tectònico dessas rochas, com propostas que vão desde complexo ofiolítico, ambiente intra-continental a seqüência de arco intra-oceânico. Assim este trabalho visa a caracterização geoquímica e temporal do Domínio Canindé, usando técnicas, como o ICP-MS capaz de analisar elementos (Nb, Ta, Th, La,) com elevado poder de interpretação na definição de ambiência tectõoica. Somada as técnicas modernas de geocronologia ( U-Pb em grãos de zircão utilizando SHPJMP) em conjunto com métodos convencionais e integração dos resultados obtidos com as observações das relações de campo. As análises isotópicas Pb-Pb do Domínio Canindé revelaram isócrona de 963±20 Ma para mármores associado com anfibolitos e outros metassedimentos. Os resultados das análises Sm-Nd indicam para os metassedimentos da Unidade Novo Gosto dois conjuntos de idade modelo (Td_m) 1.5 e 1,14 Ga e o anfibolitos entre 1,3-0,8 Ga. Os anfibolitos da Unidade Gentileza apresentam Tdm com valores entre 1,2-0,8 Ga e quartzo-monzodiorito com textura rapakivi desta unidade apresenta Tdm em torno de 0,89 Ga. O sNa\t=o> para as unidades Novo Gosto e Gentileza são dominantemente negativos. Os resultados de análise de SHRIMP em metassedímento da Unidade Novo Gosto revelaram idades de áreas fontes distintas (977-718-679 Ma). A Unidade Gentileza apresenta idade U-Pb (SHRIMP) em torno de 688 = 15 Ma, Granito Lajedinho 634 ± 10 Ma e Suíte Gabróica Canindé em torno de 690 ± 16 Ma. O quartzo-monzodiorito com textura rapakivi da Unidade Gentileza apresenta idade de 684 ± 7,3 Ma (U-Pb em zircão por diluição isotópica). As áreas fontes mais antigas da Unidade Novo Gosto correspondem às rochas do Domínio Poço Redondo e Maciço Pernambuco-Alagoas, enquanto as mais jovens as rochas do próprio Domínio Canindé. As composições isotópicas de Nd e anomalias negativas de Nb e Ta das unidades Novo Gosto e Gentileza, associadas com granitos com caracteríticas químicas anorogênicas, além de diorito com textura rapakivi, sugerem um cenário geotectônico de rifle intra-continental para as rochas do Domínio Canindé, cuja a sedimentação perdurou até o ciclo Brasiliano. / Abstract: The Sergipana belt is located in the northeastern region of Brazil, between the Pernambuco-Alagoas massif and the São Francisco craton. The Sergipana belt has been interpreted as the South American counterpart of the African Neoproterozoic Oubanguides belt, both developed during the Brazilian/PanAfrican cycle. The litho-structural array of the Sergipana belt is composed of several domains, with the Canindé domain that is located in the central part of that geotectonic unity. The Canindé domain comprises of metavolcano-sedimentary rocks that are crosscut by a gabbroic suite and several granite bodies (eg. Boa Esperança, Lajedinho, Sítios Novos and Xingo granites). The tectonic context in which these rocks were formed is controversial. Previous models considered the area as an ophiolitc complex, an intracontinental environment, or alternatively as an island arc. In this work the Canindé domain is characterized in terms of stratigraphy, geochemistry and geochronology. Trace-element contents (eg. Nb, Ta, Th, La) were used in order to define the geotectonic environment. Geo chronologic data were obtained on zircon by U-Pb SHRIMP and other conventional techniques. Pb-Pb isotopic analyses revealed an isochron of 963 ± 20 Ma for marbles associated with amphibolites and metasedimentary rocks. Sm-Nd data of metasedimentary rocks (Novo Gosto unity) indicated model ages (Tdm) of 1.5 Ga and 1.14 Ga. Tdm amphibolites are comprised between 1.3 Ga and 0.8 Ga. Amphibolites from the Gentileza unity have (Tdm) situated in the interval 1.2 and 0.8 Ga. Quartz-mozodiorites displaying rapakivi texture from the Gentileza unity present Tdm ages of ca. 0.89 Ga. The eNd(t=o) values of Novo Gosto and Gentileza unities are dominantly negative. SHRIMP data of Novo Gosto unity indicated different ages for the source rocks (977 Ma, 718 Ma and 679 Ma). U-Pb SHRIMP zircon data of the Gentileza unity and the Lajedinho granite are respectively 688 ± 15 Ma and 634 ± 10 Ma. The Gabbroic Suite Canindé was dated at 690 ± 16 Ma and quatz-monzodiorite rapakivi from the Gentileza unity by U-Pb conventional technique (zircon) revealed age 684 ± 10 Ma. It is suggested that the oldest sources of the Novo Gosto metasediment correspond to rocks from the Poço Redondo domain and the Pernambuco-Alagoas massif, whereas the youngest ones are those from the Canindé domain. Nd isotopic compositions and the negative Nb and Ta anomalies observed in rocks from the Novo Gosto and Gentileza unities associated with the anorogenic character of the granites and with the presence of rapakivi-textured diorites permit to propose that the Canindé domain developed in an intra-continental rift whose sedimentary history lasted until the Braziliano cycle. / Doutorado / Metalogenese / Doutor em Ciências

>Magister Scientiae - MSc / The Sea Point contact, Cape Town, South Africa, exposes the contact between the Neoproterozoic Malmesbury Group metasedimentary rocks of the Pan-African Saldania belt and the intrusive S-type Peninsula Granite of the Neoproterozoic-Paleozoic Cape Granite Suite (CGS). The exposure outcrops over an area of approximately 170 m × 60 m with the northern end of the exposure being characterized by the country rock–microgranite intrusive contact. Heading further south, the outcrop transitions to the main contact zone, which is a predominantly gradational zone marked by sheets of compositionally variable granitic injections (collectively referred to as hybrid granite phases) concordant to the country rock structure, before reaching the main pluton area comprising the voluminous coarse-grained porphyritic granite. Using a combined study incorporating field, structural, geochemical, isotopic and U-Pb geochronological data, the intrusive contact is investigated to determine the construction history of the pluton and delineate possible emplacement mechanisms. The granitic phases, which vary from fine-grained leucocratic, medium-grained porphyritic to coarse-grained porphyritic, are peraluminous, magnesian to ferroan, and alkali-calcic. Based on the linear trends between the whole-rock major and trace element content of the granites vs. maficity (molar Fe + Mg), their initial Sr ratios and εNd(t) values, the granites of the study area are consistent with the currently proposed petrogenetic model for the CGS (e.g. Stevens et al., 2007; Villaros et al., 2009a; Harris & Vogeli, 2010); i.e., they are crustally derived and their chemical variability is controlled primarily by peritectic assemblage entrainment. The fractional crystallization of K-feldspar is identified as the primary mechanism for the local geochemical variability of the granites. The fractionation of K-feldspar as a mechanism of variability was evaluated using binary log-log diagrams of Ba, Sr and Eu and is interpreted to have taken place at levels close to the emplacement site after source entrainment processes. Although there is outcrop evidence, particularly in the main contact zone, to suggest that local assimilation and filter pressing took place, this was not reflected by the whole-rock and isotope geochemistry of the granites. This suggests that these processes are very localized and will need further rigorous testing to ascertain the extent to which they caused variability. Outcrop evidence for assimilation includes gradational country rock-granite contacts and the ductile behaviour of the country rock, whereas the occurrence of K-feldspar megacrysts embedded in the country rock at the main contact zone suggests melt accumulation and escape consistent with the filter pressing mechanism. In the case of the latter, the melt fraction of the granite was easily mobilized and driven out compared to the crystal fraction (K-feldspars) during the emplacement of the granites. Field relationships and the structural interpretation of the Malmesbury Group country rocks and the granites reveal that: (1) the various granites are late syn-tectonic and (2) were emplaced as incrementally assembled, repeated pulses of inclined granitic sheets more or less normal (i.e. at high angles) to the regional NE-SW shortening (D1) of the Malmesbury forearc during the Saldanian orogeny. Given the lack of a controlling shear zone in facilitating granite emplacement in the study area, the pre-existing planar anisotropies (bedding planes and foliations) in the country rock provided preferential pathways for magma emplacement and propagation during deformation. This implies that the tensile strength normal and parallel to the bedding and foliation anisotropy of the country rock was larger than the regional differential stress (σ1 – σ3, with σ1 ≥ σ2 ≥ σ3), allowing for magma emplacement relative to shortening. Sheet propagation is interpreted to have occurred through the balance of the following conditions: (1) density contrasts between host rocks and magmas, (2) the pressure differential along the subvertical fractures/sheets, and (3) the melt pressure equalling the lithostatic pressure to keep the magma pathways open and being sufficiently high such that it exceeds the sum of σ1 and the tensile strength of the rock parallel to σ1. The crystallization ages of the dated granite samples are identical within error and vary between 538.7 ± 3.6 Ma and 542.7 ± 2.9 Ma. They, therefore, cannot prove which granite phase intruded first and which one proceeded and so forth. Field relationships, however, suggests that the microgranites were first to intrude given their fine-grained nature and the localized chilled contacts they show with the country rock. The various coarser-grained and porphyritic phases were next to intrude, with their coarse grain-sizes and lack of chilled margins with the country rock suggesting that the time interval between their successive emplacements was not too long; this prevented the country rock from completely cooling down between each magma batch. Magma stoping and the ductile flow of the host material (owing to highly viscous magma flow) to accommodate granite emplacement are interpreted to be secondary emplacement processes.