Abstract
The area is located at the northern boundary of the Guaxupé Complex, which corresponds to the northern domain of the Socorro-Guaxupé Nappe, in the Southern Brasília Orogen, close to the Varginha Shear Zone. This study integrates petrography, mineral chemistry, optimized geothermobarometry, and trace elements thermometry data, aiming to define and characterize the metamorphic conditions and the P-T path of the granulitic rocks from the northern portion of the Guaxupé Complex. In the area, the Guaxupé Complex consists predominantly of ortho-derived rocks represented by granulitic gneisses (orthopyroxene gneisses) of felsic to mafic composition with clinopyroxene, garnet, amphibole, biotite, and rare rutile. The calculated pressure and temperature conditions record metamorphic peak around 1,078°C and 14.8 kbar, compatible with ultra-high temperature metamorphism conditions, marked by grt + cpx + opx + pl ± qtz ± rt mineral assemblages, and granulite facies re-equilibration in the sillimanite stability field at P-T conditions of 930 to 800°C and 13.5 to 11.0 kbar. The results are compatible with deeper portions of the lower crust involved in a continental collision and suggest a clockwise P-T path, typical of crustal thickening zones, followed by near-isothermal decompression during tectonic exhumation.
Highlights
Orogens record tectono-metamorphic processes that affected continental crust rocks at convergent plate boundaries
Ultra-high temperature (UHT) metamorphism is a subdivision of granulite facies metamorphism and is defined as crustal metamorphism at temperatures above 900°C and pressures not exceeding the sillimanite stability field (Harley 1998, 2008, 2016, Brown 2007, Kelsey and Hand 2015)
Petrographic and mineral chemistry analyses were performed at the Department of Petrology and Metallogeny (DPM) laboratories of the Institute of Geosciences and Exact Sciences (Instituto de Geociências e Ciências Exatas – IGCE), Universidade Estadual Paulista “Júlio de Mesquita Filho” (Unesp), Rio Claro Campus
Summary
Orogens record tectono-metamorphic processes that affected continental crust rocks at convergent plate boundaries. UHT metamorphism provides evidence that tectonic processes may operate under extreme thermal conditions. Identifying and obtaining accurate quantitative P-T conditions and P-T metamorphic history of rocks that attained extreme conditions is crucial to provide valuable insights into the tectono-metamorphic settings, tectonic processes in Supplementary data Supplementary data associated with this article can be found in the online version: Supplementary Table. UHT granulitic terranes and implications for crust evolution (Harley 1998, 2004, 2008, 2016, Brown 2007, Kelsey 2008, Kelsey and Hand 2015). Identify the metamorphic peak conditions of UHT granulitic terranes is potentially hampered by the application of conventional element exchange geothermobarometry, due to diffusional resetting during cooling, significantly modifying their compositions (Moraes et al 2015, Pape et al 2016)
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