Crystallization ages of the basic intrusive Ediacaran magmatism in the southeastern Dom Feliciano Belt, southernmost Brazil: Implications in the belt geodynamic evolution

摘要

The participation of mantle-derived magmas, especially hydrous basaltic liquids, in the evolution of granitic belts in both orogenic and post-collisional environments is crucial to evaluate both mantle and crustal evolution, as well as the material transference processes between these two reservoirs. Besides, this transition in the geodynamic context creates specific conditions, promoting the generation of voluminous magmatism. The Dom Feliciano Belt is a mobile belt in southernmost Brazil, generated during the Brasiliano-Pan-African Orogeny. It comprises an eastern unit, the Pelotas Terrane, essentially formed by Cryogenian and Ediacaran granitoids, with minor dioritic and gabbroic rocks in the southeast of the area. This paper presents geochronological studies to determine the crystallization ages (zircon U-Pb SHRIMP) of the most representative bodies of two associations of basic rocks, the Passo da Fabiana Gabbros (PFG), and the Alto Alegre Diorite (AAD). Besides, two granites in the PFG region were analyzed (zircon U-Pb LA-ICP-MS) to evaluate its emplacement, when compared to those of the basic magmas. The results show that PFG yield a crystallization age of 591.2 +/- 3.5 Ma (MSWD = 1.3), while the AAD presented a crystallization age of 562 +/- 3.7 Ma (MSWD = 0.73). In the PFG region, a biotite monzogranite, included in the Cerro Grande Suite, yielded an age of 612 +/- 1 Ma (MSWD = 0.00083), and a leucosyenogranite of the Dom Feliciano Suite, showed crystallization age of 588 +/- 2 Ma (MSWD = 0.00037). Considering the tectonic context of the Dom Feliciano Belt, it is necessary to highlight that an important mantle component, responsible for the generation of water-rich high-alumina calc-alkaline basaltic liquids, was involved in the belt late evolution (590-560 Ma). In this period, the belt was already in post-collisional settings, in a geodynamic context where compressive tensions were cessing, followed by an extensional regime. These conditions enabled mantlepartial melting, which was responsible for the basic rocks generation, with deep regional structures controlling its evolution and emplacement.