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

南卡罗来纳州帕金森大学这项提议的主要目的是记录巴西东南部米纳斯吉拉斯州泛非推覆体高压-超高压变质作用的岩石学特征和构造意义。结晶推覆体是托坎廷斯造山带的组成部分，该造山带沿走向延伸约1000公里，记录了圣弗朗西斯科克拉通和里约拉普拉塔板块之间的新元古代会聚、俯冲和碰撞。将采用的技术包括：[1]石榴石中主要元素和微量元素的X射线成分填图，[2]利用显微拉曼光谱鉴定石榴石和锆石中的包裹体物种，[3]出溶片层的结构和成分特征以及前驱物相组成的整合，[4]锆石带状域的SHRIMP U-Pb年代学。这些研究将得到反应织构和岩石组构的常规分析的补充。在美洲发现的柯石英变质作用不仅影响了当地对巴西-泛非构造格架的研究，而且提供了元古界(约630 Ma)深埋与更好地研究新生代造山类似物之间的对比。这一建议直接针对古代会聚边缘造山作用，提供了目前地表暴露的深埋岩石的关键细节野外、地球化学和地质年代学数据。新获得的630 Ma地体的P-T时间数据将被纳入南美造山带演化的区域地球动力学模型中。

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.