Petrotectonic Evolution of High-Pressure and Suspected Ultrahigh Pressure Granulites and Eclogites in Neoproterozoic Nappes of South-East Brazil

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AbstractEAR-0125867ParkinsonUniversity of South CarolinaThe primary objective of this proposal is to document the petrological characteristics and tectonic significance of high- to ultrahigh-pressure metamorphism (HP-UHPM) of Pan-African nappes in Minas Gerais State, southeast Brazil. The crystalline nappes are components of the Tocantins orogen, which extends along strike for around 1000 km, and records Neoproterozoic convergence, subduction and collision between the Sao Francisco craton and Rio de la Plata plate. Techniques to be applied will include: [1] X-ray compositional mapping of major and trace elements in garnets, [2] identification of inclusion species in garnet and zircon by micro-Raman spectroscopy, [3] textural and compositional characterization of exsolution lamellae and integration of precursor phase compositions, [4] SHRIMP U-Pb geochronology of zircon zonal domains. These studies will be complemented by conventional analyses of reaction textures and petrofabrics. The observation of coesite-grade metamorphism in the Americas not only impacts local studies of the Brasiliano-Pan African tectonic framework, but also provides a comparison between deep burial in the Proterozoic (at c. 630 Ma) and better studied Cainozoic orogenic analogues. This proposal, which addresses directly ancient convergent margin orogenesis, provides critical detail field, geochemical, and geochronological data of deeply buried rocks now exposed at the surface. The newly derived P-T-time data for this 630 Ma terrane will be incorporated into regional geodynamic models for the evolution of the South American orogen.