West Gondwana orogenies and Pangaea break-up

Abstract

Through the joint use of apatite fission tracks (AFT) and (U–Th)/He analysis in apatite (AHe) and zircon (ZHe), we evaluate the thermotectonic evolution of the Sul-Rio-Grandense Shield (SRGS), southernmost Mantiqueira Province, Brazil. Formed during the assembly of West Gondwana (Neoproterozoic), the shield comprises four tectonostratigraphic terranes separated by regional faults and shear zones. The central and eastern terranes present Mesozoic AFT ages, whereas the western terrane ages are mostly late Paleozoic. AHe ages show considerable dispersion, although most are Mesozoic. ZHe ages from the east are early Permian, whereas the west presents Devonian ages. Inverse thermal modelling indicates a Devonian to Carboniferous cooling phase in the west, time correlated with orogenies occurring at the SW margin of Gondwana, which affected the regional geodynamics and are possibly linked to limited uplift of the shield. From the Permian to Jurassic a major cooling phase took place in the SRGS, probably related to lithosphere thinning and uplift preceding the South Atlantic rifting. Samples closer to the Atlantic coast suggest a subtle reheating after this event, provisionally linked to a geothermal disturbance related to ocean opening and associated magmatism. A final post-Paleocene cooling phase towards surface conditions affected the entire SRGS.