Autor(es)

Westin, Alice ; Tedeschi, Mahyra ; Campos Neto, Mario C. ; Luvizotto, George L. ; Motta, Rafael G. ; Nobre, Augusto G. ; Ando, Romulo A.

• Tipo de documento: Artigo Científico
• Fonte: LITHOS; v. 490-491, p. 22-pg., 2024-12-15.

Resumo

In this contribution, we employed a petrochronological approach to investigate the tectonometamorphic evolution of Al-rich garnet-staurolite and garnet-staurolite-kyanite (biotite- and plagioclase-free) metapelites of the southernmost portion of the Neoproterozoic Brasilia orogen. We have reconstructed the first prograde to peak pressure-temperature-time (P-T-t) paths reported for metamorphic units of the area, by combining petrographic analyses, quantitative compositional mapping of major elements, phase equilibrium modeling, and EPMA Th-U-Pb monazite chemical dating. The metamorphic reactions involved in the prograde metamorphic evolution are discussed, including the effects of garnet fractionation, exhaustion of reactants, and re-equilibration reactions on the major-element composition of garnet porphyroblasts, and their influence on P-T condition estimates. Raman spectroscopy on carbonaceous material (RSCM) thermometry provided insights into the synkinematic retrograde path. A steep prograde path marked by two stages is recorded by the garnet porphyroblasts of garnet-staurolite-muscovite (+/- kyanite) schists: (i) 555-585 degrees C and 0.60-0.90 GPa; (ii) 590-635 degrees C and 1.0-1.4 GPa. Monazite crystals record the prograde to peak path from ca. 630-625 Ma to ca. 605-595 Ma. Matrix graphite crystals suggest post-peak cooling to 400-500 degrees C concurrent with the late stages of development of the main foliation. The reconstructed P-T-t paths indicate an intermediate dT/dP metamorphism, and a burial rate of similar to 0.55 km/Ma, with garnet compositional zoning suggesting that the high-pressure P-T-t path resulted from a single metamorphic event. The corresponding geothermal gradients, and in-situ ages, combined with regional evidence, suggest that peak metamorphic conditions were attained during collisional underthrusting of the continental crust related to the West Gondwana amalgamation. (AU)

• Processo FAPESP: 16/06952-1 - Termo-cronologia aplicada à modelamentos geotectônicos: o caso do Orógeno Brasília Meridional, Brasil
• Beneficiário: Alice Westin Teixeira
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 15/03737-0 - O Cráton Rio de la Plata e o Gondwana Ocidental
• Beneficiário: Miguel Angelo Stipp Basei
• Modalidade de apoio: Auxílio à Pesquisa - Temático