Petrochronology of low-Al metapelites from Southernmost Brasilia Orogen basement: Insights into the role of water-fluxed melting at low T and implications for U-Pb zircon geochronology

The Southernmost Brasilia Orogen surrounds the southern margins of the Sa similar to o Francisco Craton. It exposes a structural window with a WNW-ESE direction formed by the Archean-Paleoproterozoic basement reworked by the Campo do Meio Shear Belt. Using metamorphic modeling, geothermobarometry, and U-Pb dating of zircon and monazite, this study established the pressure-temperature-time (P-T-t) evolution of the Colonia metapelite, one of the main units of the Campo do Meio Shear Belt. This revealed a clockwise path with metamorphic peak conditions at 706 +/- 16 degrees C and 9.7 +/- 0.7 kbar on a staurolite-kyanite-muscovite-garnet-biotite schist, with cooling at-600 degrees C and -6 kbar. Forward metamorphic modeling based on the whole-rock composition of this sample supports partial melting in the staurolite stability field, facilitated by water influx. Water-fluxed anatexis promoted dissolution of detrital zircon grains. These processes, occurring during prograde metamorphism, are influenced by temperature, crystal size-distribution, bulk-rock composition, and the permanence of the rock at the thermal peak. Analysis of the zircon overgrowth zones, which were linked to peak metamorphic conditions, produced an age of 605 +/- 7 Ma. The monazite age of 580 +/- 5 Ma was associated with later syntectonic melt crystallization. The clockwise P-T-t path of the Colonia metapelite is similar to the evolution of Neoproterozoic units from the Southernmost Brasilia Orogen. However, the degree of dissolution in detrital zircon grains restricts accurate evaluation of the possible stratigraphic correlations proposed in the literature.

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Using metamorphic modeling, geothermobarometry, and U-Pb dating, this study analyzed the P-T-t evolution of Colonia metapelite in the Campo do Meio Shear Belt and found similarities with the Neoproterozoic units in the Southernmost Brasilia Orogen. However, the degree of zircon dissolution hampers accurate evaluation of stratigraphic correlations proposed in the literature.