Navegando por Autor "Serrano, Paula"
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Item A-type Medina batholith and post-collisional anatexis in the Araçuaí orogen (SE Brazil).(2018) Serrano, Paula; Soares, Antônio Carlos Pedrosa; Medeiros Júnior, Edgar Batista de; Boa, Tobias Fonte; Araujo, Cristina Santos; Dussin, Ivo Antonio; Queiroga, Gláucia Nascimento; Lana, Cristiano de CarvalhoThe Medina batholith and its host granitic migmatites record intriguing plutonic processes in the northern Araçuaí orogen (SE Brazil). This orogen shows a long lasting (630–480 Ma) succession of granite production events from the earliest pre-collisional plutons to the latest post-collisional intrusions. The Medina batholith includes granite intrusions ascribed to the post-collisional stage. They show high alkali and halogen contents, low CaO (at SiO2=71%:Na2O+K2O=7 to 9%; CaO=1.6%), and high FeOt/(FeOt+MgO) ratios (0.78 to 0.92). The Medina granites are metaluminous to weakly peraluminous, with ASI (molecular ratio Al/(Ca-1.67P+Na_K)) values of 1.76 to 2.07, and have high concentrations of high field strength elements (Zr+Nb+Ce+Y N 700 ppm), as well as high Ga/Al ratios. Accordingly, the Medina intrusions are typical ferroan A-type granites. U\\Pb ages fromzircon (501±2 Ma) and monazite (497±2 Ma) constrain the emplacement timing of theMedina batholith. Surprisingly, all monazite ages from host rocks also cluster around 500Ma, despite their nature and distance from the batholith, suggesting that they would have shared a same thermal process. The studied host rocks are granitic migmatites varying from patch metatexite to nebulitic diatexite, comprising paleosome of foliated sillimanite-garnet-biotite metagranite to gneiss, and non-foliated garnet-cordierite neosome poor to free of biotite. A metatexite (R14) located relatively far from the Medina batholith, and a diatexite (M26) found at the batholith contact were sampled for detailed studies. The paleosome of foliated metagranite (R14A) only shows zircon grains with igneous features and Th/U ratio from1.64 to 0.26. Although the spreading of zircon spots, themain cluster yields a Concordia age at 556±6 Ma, constraining the protolithmagmatic crystallization. A minor cluster furnishes a Concordia age at 499±7 Ma, in agreement with the U\\Pb monazite age at 501±2Ma. Extracted from the same metatexite sample, the non-foliated garnet-cordierite neosome (R14B) shows both igneous and metamorphic zircon domains with Th/U ratios ranging from 1.47 to 0.00. Again, the U\\Pb spots cluster at two distinct Concordia ages (562±3Ma and 499±3Ma). The youngest of them, fitting with themonazite age (495±3Ma), constrains melt crystallization,while the oldest age suggests paleosome inheritance. The nebulitic diatexite (M26) showsmonazite (497±2Ma) and zircon (Th/U=1.7 to 0.0; Concordia ages at 564±2Ma and 507±3Ma) populations similar to themetatexite neosome, alsowith the youngest ages bracketing themelt crystallization process around 500 Ma. Accordingly, all those ages at around 500Ma disclose a partial melting episode coeval with the Medina batholith emplacement. Phase equilibrium modeling on a garnet-cordierite neosome furnished P-T conditions of 750–840 °C at 2.4–3.5 kbar for that post-collisional anatexis. Evidence for such a late thermal event are common in the Araçuaí orogen, even far from the post-collisional batholiths. Thus, a possible major heat source can be envisaged, like a mantle plume triggering crustal anatexis and regional fluid circulation during the gravitational collapse of the Araçuaí orogen.Item Time and isotopic constraints for Early Tonian basaltic magmatism in a large igneous province of the São Francisco – Congo paleocontinent (Macaúbas basin, Southeast Brazil).(2022) Souza, Maria Eugênia Silva de; Martins, Maximiliano de Souza; Queiroga, Gláucia Nascimento; Soares, Antônio Carlos Pedrosa; Dussin, Ivo Antonio; Castro, Marco Paulo de; Serrano, PaulaThe Neoproterozoic Macaúbas basin (southeast Brazil) provides key hints to unravel the history of the São Francisco – Congo paleocontinent before its amalgamation as part of Gondwana. Among the several Proterozoic taphrogenic events and anorogenic igneous episodes documented for the São Francisco – Congo paleocontinent, Early Tonian event has been particularly focused on in the literature owing to the large production of bimodal (felsic-mafic) magmas now found in the Araçuaí (SE Brazil) – West Congo (SW Africa) orogenic system (AWCO) and neighboring cratonic regions. Aiming to examine the stratigraphic relations, timing and isotopic signatures of extensive basaltic magmatism related to the Macaúbas basin, we carried out detailed field, lithochemical, isotope (whole-rock Sm-Nd and Lu-Hf in zircon) geochemistry and zircon U-Pb geochronological studies on the Pedro Lessa suite and Planalto de Minas Formation, located in the central-western Araçuaí orogen. The studied Pedro Lessa suite consists of a series of mafic dikes that crosscut the lowermost units of the Macaúbas Group but not the Planalto de Minas Formation. The Pedro Lessa suite yielded zircon U-Pb ages between 951 ± 54 Ma and 939 ± 7 Ma. The Planalto de Minas Formation comprises volcaniclastic rocks crystallized at 889 ± 10 Ma, and sedimentary rocks with maximum depositional age of 867 ± 10 Ma. The lithochemical and isotopic datasets (Pedro Lessa dikes: εNd(t) = +0.60; εHf(t) = –22.21 to +4.66; Planalto de Minas volcanism: εNd(t) = +0.76 to +0.78; εHf(t) = − 19.27 to +10.03) indicate predominantly continental tholeiite and minor enriched MORB-type mantle magmas with variable amounts of crustal contamination. The (La/Sm)N ratios indicate a theoretical partial melting (1–7%) of the spinel-lherzoite lithospheric zone for the Pedro Lessa suite, and of the spinel-garnet transition zone (3–10%) for the Planalto de Minas metamafic rocks, in accordance with La/Nb and La/Ba ratios. The new and complied isotopic and lithochemical data suggest a time-dependent evolution of magma sources, with lithospheric mantle sources for the Early Tonian dike swarms (Pedro Lessa and correlatives) evolving to predominantly asthenospheric mantle sources for the late basaltic volcanism recorded in the Planalto de Minas Formation. Such an extensive and long-lasting anorogenic magmatism of Early Tonian age (c. 965 – 870 Ma) found in the AWCO and São Francisco – Congo craton likely records more than one extensional event and related aborted continental rifts, altogether driven by the same mantle plume. Although long-lived, this mantle plume acted beneath a strong continental lithosphere so that it was unable to break up the São Francisco – Congo paleocontinent into two completely separated landmasses. Highlighting the main stages of anorogenic magmatism, we also present an updated barcode for the São Francisco – Congo paleocontinent.Item Zircon in emplacement borders of post-collisional plutons compared to country rocks : a study on morphology, internal texture, U–Th–Pb geochronology and Hf isotopes (Araçuaí orogen, SE Brazil).(2020) Araujo, Cristina Santos; Soares, Antônio Carlos Pedrosa; Lana, Cristiano de Carvalho; Dussin, Ivo Antonio; Queiroga, Gláucia Nascimento; Serrano, Paula; Medeiros Júnior, Edgar Batista deZircon is a powerful tool to study the internal evolution of igneous bodies and their interactions with country rocks. At pluton borders, zircon may record the emplacement history from the crystallization onset to deuteric processes, as well as inheritance from country rocks. We present a detailed morphology and internal structure study coupled with isotopic analyses (UeThePb and LueHf) on a great number of zircon grains extracted from samples collected at the borders of three distinct post-collisional intrusions of the Araçuaí orogen: granites from the Arace^ e Pedra Azul and Vitoria plutons, and a tonalite from the Mestre Alvaro pluton. For comparison, we also present mineral and bulk-rock chemistry data from these samples of post-collisional intrusions, as well as zircon UePb-Hf data from their country rocks (the Nova Venecia migmatitic paragneisses and Atal eia granites) and a wide dataset compilation. Zircon saturation geothermometry suggests igneous temperatures above 800 C for pluton borders. Zircon geochronology resulted in crystallization ages for borders of the plutons at 523 ± 2 Ma (Arace^ e Pedra Azul), 505 ± 1 Ma (Vitoria), and 527 ± 2 Ma (Mestre Alvaro). Lu eHf data (Arace^ e Pedra Azul pluton: εHf(t) 18.6 to 23.8, TDM ages from 2.25 to 2.47 Ga; Vitoria pluton: εHf(t) 7.4 to 10.3, TDM ages from 1.58 to 1.71 Ga; Mestre Alvaro pluton: εHf(t) 0.7 to 8.8, TDM ages from 1.27 to 1.66 Ga; Nova Venecia migmatitic paragneiss: εHf(t) þ4.1 to 39.2, TDM ages from 1.20 to 3.47 Ga; and Ataleia granite: εHf(t) 3.2 to 8.1, TDM ages from 1.42 to 1.64 Ga) indicate involvement of country rocks in the petrogenesis of post-collisional intrusions. Together, new and compiled data suggest: i) magma hybridization at high temperature, involving country rocks; ii) rapid growth of zircon crystals probably at rapid cooling rates; and iii) in situ dissolutionerecrystallization and overgrowth processes in zircon crystals in response to interactions with residual (late-stage) melts and/or deuteric fluids.