Transition from subduction to Post-Collisional Paleoproterozoic magmatism in the Correntina erosive window of the north São Francisco craton: Evidence for mantle source and slab breakoff from alkaline magmatism by U-Pb, Nd-Sr radiometric and geochemistry data

Abstract

The interaction of multiple sources during convergent setting generates a wide compositional diversity of magmas, sometimes with initial mafic components. Subduction zones produce extensive magmatism, derived from several reservoirs at different depths. New and published geologic data were used here to constrain the tectonomagmatic evolution in the northwestern São Francisco craton. The study area comprises the Correntina Window and Guanambi batholith, where a suite of calc-alkaline rocks was dated at 2.18–2.11 Ga. This suite has metaluminous to peraluminous compositions and chemical characteristics typical of a calc-alkaline series produced through slab melting. The age-corrected Sr-Nd isotope compositions are similar to those of MORB (ƐNd(T): −4 to +4; Sr/Sri: 0.701–0.706), consistent with an origin in a moderately juvenile subduction setting and variable crustal input. This convergent process progressively enriched the subcontinental mantle. The available geologic data indicate that peak metamorphism interpreted to reflect crustal thickening in a convergent regime occurred between 2.11 and 2.05 Ga, and was associated with regional-scale granulitization and migmatization. At the end of this period, a second suite of alkaline rocks was emplaced at ~2.05 Ga in the northwestern São Francisco craton. The petrochemical features indicate a shoshonitic affinity with high compatible element contents, metaluminous to peralkaline compositions, and enriched isotopic compositions (ƐNd(T): −7 to −6 and Sr/Sri: 0.706–0.707), indicating derivation from enriched ultramafic sources. This suite is derived from enriched lithospheric mantle components, with contributions from slab-derived fluids, and possibly asthenospheric mantle. This voluminous magmatism was likely triggered by slab breakoff, which can cause asthenospheric upwelling and accelerated the tectonic transition from convergence to decompression. These processes induced melting of mantle components that were emplaced along transtensional zones and generated the present-day tectonic architecture in the NW São Francisco craton.