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Brazilian Journal of Geology

Print version ISSN 2317-4889On-line version ISSN 2317-4692

Abstract

BICALHO, Victor; REMUS, Marcus Vinicius Dorneles; RIZZARDO, Rafael  and  DANI, Norberto. Geochemistry, metamorphic evolution and tectonic significance of metabasites from Caçapava do Sul, southern Brazil. Braz. J. Geol. [online]. 2019, vol.49, n.2, e20180039.  Epub Apr 29, 2019. ISSN 2317-4889.  http://dx.doi.org/10.1590/2317-4889201920180039.

This paper proposes the generation and closure of a proto-ocean and formation of an island arc in the Neoproterozoic Passo Feio Metamorphic Complex (PFMC), Caçapava do Sul region, southern Brazil. The PFMC, São Gabriel Terrane, consists of a Neoproterozoic supracrustal metavolcano-sedimentary sequence intruded by the Caçapava Granite. The study uses petrography, whole-rock geochemistry and mineral chemistry to identify the geochemical affinity and tectonic environment of the amphibolites contained in PFMC, the basalts and pillow lavas of Arroio Mudador Formation and dikes intruded in nearby volcanogenic rocks of Hilário Formation. The applied methods allow the metamorphic facies classification of ­prehnite-pumpellyite for the basalts and pillow lavas, greenschist for the dikes and lower amphibolite for the amphibolites. The discriminant diagrams indicate from tholeiitic to alkaline affinities for the Hilário Formation dikes. The basalts, pillow lavas and amphibolites have basaltic to basaltic-andesite composition and predominant tholeiitic affinity, interpreted as derived of the same protolith. The geotectonic diagrams mostly indicate volcanic arc basalts. The proposed evolution model starts with a proto-ocean opening through the Bossoroca Arc rifting around 760Ma, where an island arc is formed (PFMC rocks), precipitation of carbonates and marls, subsequent closure, two metamorphism events and the Caçapava Granite intrusion around 562 Ma.

Keywords : Metabasites; Passo Feio Complex; geochemistry; petrography; metamorphic evolution.

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