The project aims to quantify metamorphic and tectonic processes recorded in the Embu Terrane, a major segment of the southern Ribeira Belt, in order to refine reconstructions of the tectonic evolution of the belt. The nature and evolution of the Ribeira Belt are contentious, mainly due to a lack of robust geochronological data, resulting in poorly constrained tectonic models. These models include those based on a Wilson cycle of oceans opening and closing, multiple collisional events, sometimes dominated by exotic and suspect terrane accretion, lateral escape tectonics following oblique collision, and intracontinental settings. These models have important implications to reconstruction the Gondwana and Rodinia supercontinents. Recently obtained zircon U/Pb age data indicate that the Embu Terrane is composed of a Tonian (970-850 Ma) metasedimentary rock succession inferred to have accumulated at the margin of Rodinia, while metamorphic zircon overgrowths indicates an important tectonic event occurred between 820 and 790 Ma. The nature and tectonic setting of this Tonian orogenic event, including the determination of thermal and baric regimes, the thermochronological evolution and tectonic setting of coeval magmatism, have not been investigated and form the focus of this proposal. In particular, this project aims to investigate this Tonian tectonic event by: (1) in situ U/Pb dating of metamorphic minerals with distinct closure temperatures (zircon, monazite, titanite, apatite) coupled with determination of their trace element characteristics; (2) Rb/Sr dating of metamorphic biotite and muscovite; and, (3) determination of trace element and Lu/Hf isotope characteristics of igneous zircons from Tonian granites (ca. 800-770 Ma) and metabasites (ca. 900 Ma). Data from the metamorphic minerals and igneous zircons will be used to constrain robust pressure-temperature-time (P-T-t) paths and the tectonic setting of the Tonian magmatic events, respectively. Most of the data will be acquired in thin sections (already available) using a LA-ICP-MS in the Monash Isotopia Facility at Monash University. The Lu/Hf isotopic geochemistry data will be obtained in available zircon concentrate mounts that were previously used to SHRIMP U/Pb geochronology.
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