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

摘要：本项目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（HP-UHPM）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，它沿走向沿着延伸约1000 km，记录了新元古代圣弗朗西斯科克拉通和里奥德拉普拉塔板块之间的会聚、俯冲和碰撞。将应用的技术包括：[1]石榴石中主量和微量元素的X射线成分制图，[2]通过显微拉曼光谱鉴定石榴石和锆石中的包裹体种类，[3]出溶层的结构和成分表征以及前体相成分的整合，[4]锆石带状域的SHRIMP U-Pb年代学。这些研究将得到常规反应结构和岩组分析的补充。在美洲对柯石英级变质作用的观察不仅影响了巴西-泛非构造框架的当地研究，而且还提供了元古代（c. 630 Ma）和更好地研究新生代造山类似物。 这一建议，直接解决古代会聚边缘造山作用，提供了关键的详细领域，地球化学和地质年代学数据的深埋岩石现在暴露在地表。 这630 Ma的新导出的P-T时间数据将被纳入南美洲造山带演化的区域地球动力学模型。

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.