The role of deformation-assisted by water influx on partial melting of a granite protolith, and its role in the evolution of southwestern Sao Francisco Craton margin, Brazil

The Areado Granite-Migmatite Unit is part of the basement from the Southern Brasilia Orogen at southwestern Sao Francisco Craton margin, outcropping between Alfenas and Areado regions, Minas Gerais State, Brazil. This unit is composed of garnet meta-syenogranite, hornblende-garnet metatexite, and stromatic diatexite with different degrees of partial melting. This study characterizes the garnet meta-syenogranite, its migmatitic counterparts and investigates the different patterns of deformation and partial melting involved to produce the observed migmatites within the unit. The connection between the garnet meta-syenogranite, hornblende-garnet metatexite, and biotite diatexite is inferred from field observations and assemblage of accessory minerals. Petrography associated with modal analysis, structural data, quartz c-axis analysis, zircon U-Pb (LA-MC-ICP-MS and SHRIMP) dating, as well as trace elements chemical analysis in quartz and titanite to determine metamorphic, partial melting, and deformation evolution were used as tools in this investigation. The garnet meta-syenogranite has a crystallization age of 2069.8 +/- 5 Ma. Lower intercepts from zircon indicate a metamorphic and partial melting age between 671 +/- 58 and 657 +/- 40 Ma. Melt crystallization ages are inferred between 622 +/- 7 Ma and 604 +/- 6 Ma. Different rates of partial melt are structurally connected, being higher at the base of the unit, and are related with contrasting amounts of water influx and deformation. The deformation during metamorphism/partial melting was the main cause of the differential aspect of the produced rocks. Quartz c-axis thermometer yielded deformation temperatures of 765-935 degrees C and other pulses occurred between 590 and 715 degrees C, both between 11 and 15 kbar. Those values match the Zr-in-titanite thermobarometer data, which is 670-710 degrees C for low-temperature titanite and 785-815 degrees C for high-temperature crystals. These data indicate that the protolith was generated at a Rhyacian late magmatic stage of the Mineiro Belt and passed by a Neo-proterozoic deformational-metamorphic event of high temperature. (AU)