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Paleoproterozoic juvenile magmatism within the northeastern sector of the Sao Francisco paleocontinent:Insights from the shoshonitic high Ba-Sr Montezuma granitoids

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Geoscience Frontiers 2020年第5期11卷 1821-1840页

作者： Samuel Moreira Bersan Alice Fernanda de Oliveira Costa andre danderfer Francisco Roberio de Abreu Cristiano Lana Glaucia Queiroga Craig Storey Hugo Moreira Universidade Federal de Ouro Preto Programa de Pos-graduacaoDepartamento de GeologiaCampus Morro do CruzeiroOuro PretoMGCEP 35400-000Brazil Universidade Federal de Ouro Preto Departamento de GeologiaCampus Morro do CruzeiroOuro PretoMGCEP 35400-000Brazil Sustain Geologia Ltda Teresa M.Valadares 503/502Belo HorizonteMGCEP 30575-160Brazil University of Portsmouth School of Earth and Environmental SciencesBurnaby BuildingBurnaby RoadPortsmouthPO13QLUK

New,integrated petrographic,mineral chemistry,whole rock geochemical,zircon and titanite UPb geochronology,and zircon Hf isotopic data from the Montezuma granitoids,as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex,provides new insights into the late-to post-collisional evolution of the northeastern Sao Francisco paleocontinent.U-Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca.2.2 Ga to 1.8 Ga and comprise distinct *** I have crystallization ages between ca.2.15 Ga and 2.05 Ga and are interpreted as inherited *** II zircon dates vary from 2.04 Ga to1.9 Ga and corresponds to the crystallization of the Montezuma granitoids,which were constrained at ca.2.03 Ga by the titanite U-Pb *** age zoning is common within the ca.1.8 Ga Group III zircon ages,being related to fluid isotopic re-setting during the Espinhaco rifiting ***εHf(t)analysis show dominantly positive values for both Group I(-4 to+9)andⅡ(-3 to+8)zircons and TDM2 model ages of 2.7-2.1 Ga and 2.5-1.95 Ga,***,the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids,enriched in LILES and LREE,with high to moderate Mg#and depleted in some of the *** lithochemical signature,added to the juvenile signature of both inherited and crystallized zircons,allowed its classification as a shoshonitic high Ba-Sr granitoid related to a late-to post-collisional lithosphere delamination followed by asthenospheric *** this scenario,the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc,being these hybrid magma interpreted as the source of the Montezuma *** Corrego Tingui Complex host rocks are akin to a syn-to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal *** results presented in this study have revealed the occurrence of j

关键词： Zircon U–Pb-Hf Titanite U–Pb High Ba–Sr Late-to post-collisional Sao Francisco paleocontinent

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A perspective on potassic and ultrapotassic rocks:Constraints on the Paleoproterozoic late to post-collisional event in the São Francisco paleocontinent

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Geoscience Frontiers 2022年第5期13卷 242-266页

作者： Samuel Moreira Bersan Andrédanderfer Craig Storey Henrique Bruno Hugo Moreira Francisco Abreu Cristiano Lana Leonardo Gonçalves Isabela Nahas Universidade Federal de Ouro Preto Departamento de GeologiaCampus Morro do CruzeiroOuro PretoMG CEP 35400-000Brazil University of Portsmouth School of the EnvironmentGeography and GeosciencesBurnaby BuildingBurnaby RoadPortsmouth PO13QLUK Tektos Research Group UERJ-Rio de Janeiro State UniversityBrazil Sustain Geologia Belo HorizonteBrazil

The late-to post-collisional stage in orogenic systems is characterized by the coeval existence of bimodal potassic to ultrapotassic magmatic activity related to partial melting of an enriched lithospheric mantle together with crustal derived *** this paper,we present new whole rock geochemical analyses combined with zircon and titanite U–Pb and zircon Hf isotopic data from potassic to ultrapotassic rocks from six plutons that occur within the Archean Itacambira-Monte Azul block(BIMA),to discuss their petrogenesis and the tectonic implications for the São Francisco *** new U–Pb ages range from ca.2.06 Ga to 1.98 Ga and reveal long-lasting potassic magmatism within the BIMA,which is within the late-to-post-collisional stage of the São Francisco paleocontinent *** ultrapotassic rocks are compatible with a fluid-related metasomatized mantle source enriched by previous subduction events,whereas the potassic rocks are bimodal and have a transitional shoshonitic to A-type *** rocks have a hybrid nature,possible related to the mixing between the mafic potassic/ultrapotassic rocks and high temperature crustal melts of the Archean continental *** results also show an increase of within-plate signature towards the younger potassic *** participation of an important Archean crustal component in the genesis of these rocks is highlighted by the common and occasionally abundant occurrence of Archean inherited *** Hf isotopic record shows that most of the zircon inheritance has dominantly subchondriticεHf(t)values,which fits a crustal reworking derivation from a similar Eo-to Paleoarchean precursor ***,the presence of juvenile 2.36 Ga zircon inheritance in an ultrapotassic sample reveal the existence of a hidden reservoir that is somewhat similar to the described for the Mineiro Belt in southern São Francisco paleocontinent.

关键词： Late-to post-collisional Potassic-ultrapotassic rocks U–Pb dating São Francisco paleocontinent Rhyacian-Orosirian orogenic system

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Record of Early Tonian mafic magmatism in the central Espinhaco(Brazil):New insights for break-up of the Neoproterozoic landmass ancestor of Sao Francisco-Congo paleocontinent

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Geoscience Frontiers 2020年第6期11卷 2323-2337页

作者： Helen F.Moreira Andrédanderfer Alice F.O.Costa Samuel M.Bersan Cristiano C.Lana Gláucia N.Queiroga Post Graduate Program of Department of Geology Mine SchoolFederal University of Ouro PretoBrazil Department of Geology Mine SchoolFederal University of Ouro PretoBrazil

Petrological characterization,U-Pb geochronology,Lu-Hf analyses and major and trace element data from mafic intrusions in the Central Espinhaco(central portion of the Brazilian shield)are used here to investigate the geological significance of the Early Neoproterozoic magmatism in the context of the Sao Francisco-Congo *** mafic bodies are represented by medium to coarse-grained metagabbros with plagioclase,amphibole and *** U-Pb isotopic data from two samples yielded weighted mean 206pb/238U ages of 895±3.4 Ma(MSWD=1.7)and 896±2.4 Ma(MSWD=0.64),regarded as the best estimates for the crystallization age of these mafic *** and trace element data(including REEs)show that the gabbros originated from a subalkaline tholeiitic magma,typical of intraplate *** rocks are slightly enriched in LREEs and LILEs and depleted in *** new isotope and geochemical data,along with regional knowledge,indicate that these metagabbros mark the beginning of an important Tonian-age extensional tectonic event of the landmass of which the Sao Francisco-Congo paleocontinent was part(Rodinia supercontinent or Central African block?).We furthermore suggest that these rocks belong to a prominent suite of Tonian-age mafic rocks that mark a diachronic breakup attempt of this landmass which may have occurred from south to north along the Espinhaco mountain range.

关键词： Mafic rocks Espinhaco basin Sao Francisco-Congo paleocontinent Tonian rifting U–Pb geochronology

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