Geochronological Records of Southern Ribeira Belt (Brazil): New Calibrations for Gondwana History.

Abstract:

The Paranaguá terrane is mainly constituted by an arc-related granitic complex, spread in a large NE-SW elongated stripe, located in Southern Ribeira Belt, Southeastern Brazil. The country rocks of these granites occur as a disrupted folded belt composed of metassedimentary rocks and gneissic-migmatitic rocks in split basement nuclei. The southern part of the Paranaguá Terrane is characterized by high angle tectonics; on the other hand, the northern portion by low angle tectonics. The transcurrent shear zones of Southern Paranaguá Terrane, comprising a sinistral kinematic with oblique component, are marked by the coexistence of strike-slip and down-dip lineations. The thrust shear zones represent a large front collision, located in the Northern Paranaguá Terrane, with north-northwest convergence and oblique components. The transition between these two distinct tectonic styles is given by N-S faults associated with a transpressive regime, with lateral ramp characteristics. Different generations of granite intrusions took place during the magmatic arc development, with petrographic, lithogeochemical and isotopic similarities suggesting emplacement stages during a late collisional event. Older U-Pb zircon ages between 620-610 Ma indicate the presence of a relatively early magmatism associated to the first stages of subduction in southern Paranaguá Terrane. The main magmatic period is characterized by Neoproterozoic records obtained by U-Pb zircon, which give ages between 600-580 Ma. Furthermore, the metamorphic peak of the metassedimentary sequence, with U-Pb monazite age of 599 ± 5 Ma, is quite close to the main magmatic events. In addition, the U-Pb zircon records obtained in crystals rims of deformed granitoids and late leucogranitic veins show ages between 530-480 Ma. This geological context suggests a complex history for Gondwana agglutination, with late stages at Cambro-Ordovician’s Buzios Orogeny.