Abstract
Neoproterozoic magmatism in southern Brazil is associated with translithospheric shear belts and strike-slip basins in a post-collisional setting related to the last stages of the Brasiliano—Pan African orogenic cycle. It evolved from an association of high-K calc-alkaline, leucocratic peraluminous and continental tholeiitic magmas, to shoshonitic, and eventually to sodic mildly alkaline series. Bimodal volcanism in the last group was coeval with subaerial siliciclastic sedimentation in all post-collisional basins preserved in the region. Three magmatic associations were identified in the bimodal volcanism: (1) low-Ti basalts and rhyolites; (2) high-Ti basalts and rhyolites; and (3) high-Nb rhyolites and basalts. Basic parental magmas were produced from sources related to EM1-type mantle previously modified by Brasiliano subduction, whereas silicic high- and low-Ti rocks were probably produced through fractional crystallization. Significant crustal contamination was recognized only in some slightly peraluminous rhyolites with low contents of HFS elements. High-Nb rhyolites, the youngest volcanic rocks, probably reflect the participation of asthenospheric components in the source, and mark the last magmatic event related to the Brasiliano-Pan African orogenic cycle in southern Brazil.
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