1. Neoproterozoic, Mildly Alkaline, Bimodal Volcanism in Southern Brazil: Geological and Geochemical Aspects
- Author
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Evandro Fernandes de Lima, Joaquim Daniel de Liz, Carlos Augusto Sommer, Lauro Valentim Stoll Nardi, and Breno Leitão Waichel
- Subjects
Basalt ,Fractional crystallization (geology) ,Subduction ,Bimodal volcanism ,Magmatism ,Geochemistry ,Silicic ,Geology ,Siliciclastic ,Petrology ,Mantle (geology) - 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 peralu...
- Published
- 2005
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