Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent: Insights from the shoshonitic high Ba–Sr Montezuma granitoids |
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| Institution: | 1. Universidade Federal de Ouro Preto, Programa de Pós-graduação, Departamento de Geologia, Campus Morro do Cruzeiro, Ouro Preto, MG, CEP 35400-000, Brazil;2. Universidade Federal de Ouro Preto, Departamento de Geologia, Campus Morro do Cruzeiro, Ouro Preto, MG, CEP 35400-000, Brazil;3. Sustain Geologia Ltda, Teresa M. Valadares 503/502, Belo Horizonte, MG, CEP 30575-160, Brazil;4. University of Portsmouth, School of Earth and Environmental Sciences, Burnaby Building, Burnaby Road, Portsmouth, PO1 3QL, UK |
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| Abstract: | New, integrated petrographic, mineral chemistry, whole rock geochemical, zircon and titanite U–Pb 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 São 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 groups. Group I have crystallization ages between ca. 2.15 ?Ga and 2.05 ?Ga and are interpreted as inherited grains. Group II zircon dates vary from 2.04 ?Ga to 1.9 ?Ga and corresponds to the crystallization of the Montezuma granitoids, which were constrained at ca. 2.03 ?Ga by the titanite U–Pb age. Inverse 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 event. Zircon εHf(t) analysis show dominantly positive values for both Group I (?4 to +9) and II (?3 to +8) zircons and TDM2 model ages of 2.7–2.1 ?Ga and 2.5–1.95 ?Ga, respectively. Geochemically, 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 HFSE. Their 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 upwelling. In 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 granitoids. The Córrego Tinguí Complex host rocks are akin to a syn- to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks. The results presented in this study have revealed the occurrence of juvenile rocks, probably related to an island arc environment, that are exotic in relation to the Paleo- to Neoarchean crust from the São Francisco paleocontinent’s core. |
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| Keywords: | Zircon U–Pb-Hf Titanite U–Pb High Ba–Sr Late- to post-collisional São Francisco paleocontinent |
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