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, while the western mostly late Palaeozoic. AHe ages show considerable dispersion, although most are Mesozoic. ZHe ages from the east are early Permian, while 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 Permian to Jurassic a major cooling phase took place in the SRGS, likely 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-Palaeocene cooling phase towards surface conditions affected the entire SRGS.

Supplementary material: final inverse thermal model of each sample is available at: https://doi.org/10.6084/m9.figshare.c.4579547

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