DEGEO - Departamento de Geologia

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8

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2020 - 20222

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Tem arquivos: SimAssunto: search.filters.subject.Post-collisional magmatism

Resultados da Pesquisa

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    New clues for magma-mixing processes using petrological and geochronological evidence from the Castelo Intrusive Complex, Araçuaí Orogen (SE Brazil).
    (2022) Macêdo, Iago Mateus Lopes de; Geraldes, Mauro César; Marques, Rodson de Abreu; Melo, Marilane Gonzaga de; Tavares, Armando Dias; Martins, Maria Virgínia Alves; Oliveira, Hudson Costa; Rodrigues, Renzo Dias
    Bimodal magmatism was recorded during the post-collisional stage that occurred during the Brasiliano/Pan-African cycle in the Araçuaí Orogen (southeastern Brazil) at ∼500 Ma. The Castelo Intrusive Complex (CIC) is a zoned post-collisional pluton in the orogen and is composed of monzogranites, granodiorites, quartz monzodiorites and diorites. CIC (∼100 km2) was emplaced along a regional lineament during the post-collisional stage of the orogeny and cut pre-collisional granitoids and metasedimentary sequences. In this work, a detailed petrographic study associated with data on U–Pb ages and Hf isotopic compositions of zircons from monzogranites, quartz monzodiorites and leucocratic dikes is presented to detail the geochronology, composition and context of CIC emplacement. Macroscale and microscale records show that several CIC lithotypes demonstrate the direct interaction of contemporaneous felsic and mafic magmas. U–Pb age dating of zircons (by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)) reveal crystallization ages of 486 ± 6 Ma for quartz monzodiorites and 524 ± 5 Ma to 499 ± 4 Ma for monzogranites. The analyzed leucocratic dike at 426 ± 15 Ma represents a late magmatic pulse. Hafnium isotopic data show variable ƐHf(t) values (from −24.05 to +12.7) and depleted mantle model ages (TDM) of 2.71–0.64 Ga, indicating the involvement of distinctly different mantle and crustal sources. At least two crustal sources with different Hf isotope signatures were distinguished (TDM of 2.6–2.4 Ga and ƐHf(t) of −26 to −22; and TDM of 2.2–1.7 Ga and ƐHf(t) of −17 to −8). These results suggest that the rocks in this study were partially derived from Archean and Paleoproterozoic crust. The isotopic data also show TDM model ages ranging from 1.28 to 0.64 Ga, with highly positive ƐHf(t) values (from +1.6 to +12.7). These data suggest the existence of a mantle reservoir source for magma generation and for heat that induced crustal melting during the post-collisional stage of the Araçuaí Orogen.
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    Deciphering the source of multiple U–Pb ages and complex Hf isotope composition in zircon from post-collisional charnockite-granite associations from the Araçuaí orogen (southeastern Brazil).
    (2020) Melo, Marilane Gonzaga de; Lana, Cristiano de Carvalho; Stevens, Gary; Hartwig, Marcos Eduardo; Pimenta, Marcel Sarcinelli; Nalini Júnior, Hermínio Arias
    Giant post-collisional magmatic systems are marked by an intricate diversity of zircon ages and Hf isotopic signatures. Granites and charnockites from such systems are in high contrast with simple isotopic composition of modern granites, which often record no more than one crystallization age. Despite the complexity, the assortment in ages and isotopic compositions can be explored to extract vital information to understand magma histories, isotope fractionation and magma sources. Here we focused on a charnockite-granite association (Barra do Sao ˜ Francisco pluton - BSFP) formed during the post-collisional stage of the Araçuaí orogen (southeastern Brazil). The chemical composition of these rocks points towards a metaluminous to slightly peraluminous character, ferroan and calc-alkalic to alkalic signature. Zircons extracted from the BSFP show a large scatter in the U–Pb age distributions (from 614 to 498 Ma), indicating a complex history of magmatic processes during the wanning stages of the orogeny. Detailed discrimination analysis based on texture, chemistry and U–Pb data established well-defined age groups (groups I to III); each of which reveales a significant part of this post-collisional magmatic evolution (ca. 614-552 Ma, ca. 528-513 Ma and ca. 510-498 Ma). Zircon xenocryst cores of Group I have a broad age distribution (ca. 614-552 Ma) that mirror the age distribution within the magmatic and inherited zircon populations from the country rock (Carlos Chagas batholith). The other two age groups are present in all samples and are interpreted here as antecrysts (Group II: ca. 528-513 Ma) and autocrysts (Group III: ca. 510-498 Ma). All charnockite samples show negative εHf(t) (from − 7.4 to − 0.5) and Calymmian to Ectasian model ages (TDM = 1.58-1.21 Ga), indicating contribution from heterogenous sources. The granites exhibit more negative εHf(t) values (from − 9.3 to − 5.9) and largely older model ages (TDM = 1.68-1.49 Ga), indicating that the charnockite and granite magmas were derived from the different crustal sources. These Hf isotopes data are a robust evidence of different source rocks for these magmas with different water activities. The age of the zircon autocrysts and antecrysts can be interpreted as an evidence for a prolonged pluton assemblage probably combined with slow magma cooling during the post-collisional stage of the Araçuaí orogen.