The Bossoroca Complex, São Gabriel Terrane, Dom Feliciano Belt, southernmost Brazil: U Pb geochronology and tectonic implications for the neoproterozoic São Gabriel Arc

• DOI: 10.1016/j.jsames.2016.04.006
• Publication Date: 2016-04-30T22:09:16Z
• Authors: Mauricio Lemos Gu...; Ruy Paulo Philipp; Miguel Angelo Sti...
• Keywords: Geochronology; Orogeny; Back-arc basin; Continental arc

Abstract U Pb LA-ICPMS geochronological analyses were carried out on zircon grains from metavolcanic rocks of the Bossoroca Complex and for one ash tuff of the Acampamento Velho Formation of the Camaqua Basin, in order to understand the evolution of the Neoproterozoic Sao Gabriel magmatic arc. A total of 42 analyses of igneous zircon grains were performed in three samples. The results yielded U Pb ages of 767.2 ± 2.9 Ma for the metavolcanic agglomerate (BOS-02); 765 ± 10 Ma for the metacrystal tuff (BOS-03) and 565.8 ± 4.8 Ma for the ash tuff (BOS-04). The Orogenic Cycle in Brazil is characterized by a set of orogenic belts consisting of petrotectonic associations juxtaposed by two collisional events that occurred at the end of the Neoproterozoic. In southern Brazil this orogeny formed the Dom Feliciano Belt, a unit composed of associations of rocks developed during two major orogenic events called Sao Gabriel (900–680 Ma) and Dom Feliciano (650–540 Ma). The main Sao Gabriel associations are tectonically juxtaposed as elongated strips according to the N20–30°E direction, bounded by ductile shear zones. The Bossoroca Complex comprises predominantly metavolcano-sedimentary rocks, characterized by medium-K calc-alkaline association generated in a cordillera-type magmatic arc. The volcanism occurred in sub-aerial environment, developing deposits generated by flow, resurgence and fall, sporadically interrupted by subaqueous epiclastic deposits, suggesting an arc related basin. The Sao Gabriel Terrane contains the petrotectonic units that represent the closure of the Charrua Ocean associated to the subduction period of the Brasiliano Orogenic Cycle in the Sul-rio-grandense Shield.