Recovering P–T–t paths from ultra-high temperature (UHT) felsic orthogneiss: An example from the Southern Brasília Orogen, Brazil
نویسندگان
چکیده
Mineral assemblages that are diagnostic of ultrahigh-temperature (>900 °C) metamorphism generally restricted to Mg- and Al-rich rocks. However, in many metamorphic terrains such compositions do not occur, the rocks dominated by orthogneisses typically contain high-variance mineral particular pressure–temperature (P–T) conditions. Here we use whole-rock chemistry, thermodynamic phase equilibrium modelling, zircon U–Pb–Hf isotopic data constrain P–T–time history granulites from Socorro-Guaxupé Nappe Southern Brasília Orogen. These occur as part a stack Neoproterozoic nappes were assembled during formation West Gondwana. Based on peak assemblage garnet-bearing felsic granulite (ortho- clinopyroxene, garnet, K-feldspar, plagioclase, quartz, ilmenite, silicate melt) records pressures around 11.5 kbar temperatures ~1000 °C, consistent with high-Al content orthopyroxene. The retrograde path small decrease pressure 9 marked orthopyroxene replacing garnet exsolution magnetite ilmenite followed near-isobaric cooling led development coronas hornblende pyroxene due crystallization last vestiges melt. Zircon cores yielding U–Pb ages ca. 625 Ma interpreted dating close-to-peak conditions high-temperature metamorphism. In one sample, rims ‘soccer ball’ neoblasts both have high U contents yield 615 Ma, mark onset melt crystallization. two other samples, low-U zircons grains 600–595 date end reveal protracted regional event which lower crust remained at granulite-facies for least 30 Myr collision assembly
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ژورنال
عنوان ژورنال: Precambrian Research
سال: 2021
ISSN: ['1872-7433', '0301-9268']
DOI: https://doi.org/10.1016/j.precamres.2021.106222