Marins Granite (MG/SP): petrography, geochemistry, geochronology, and geotectonic setting

Abstract

The Marins Granite forms an ellipsoidal body that crops out along the border between So Paulo and Minas Gerais states. It intrudes meta-sedimentary and meta-igneous rocks of Neoproterozoic age, belonging to the Socorro Nappe and Embu Complex, in the interference zone between the Brasilia and Ribeira fold belts. Geochemical analyses indicate a high-K calc-alkaline signature, weakly peraluminous, type I character, poorly differentiated with restricted silica range and similar rare earth element patterns enriched in light rare earth elements. Two lithofacies were defined: (1) Marins facies, predominantly inside the body, isotropic, light gray with inequigranular porphyritic texture containing euhedral to subhedral microcline phenocrysts (< 1 cm), and (2) Mendanha facies, restricted to the border zone of the body, are pinkish with elongated microcline phenocrysts and aligned biotite grains, defining a deformational foliation. Neodymium isotopes point to a crustal signature, revealed by a Nd(0.6) : -10.4. T DM ages indicate a paleoproterozoic source. U-Pb LA-ICPMS ages in zircon yielded concordia crystallization ages of 606.9 1.9 Ma for the Mendanha facies and 603.7 4.8 Ma for the Marins facies. These ages are consistent with the interpretation that the Marins Granite is a late to post-collisional body with respect to the collision of the southern Braslia Belt, also reinforced by the location of the granite in the upper plate (Socorro Nappe), a few tens of kilometers away from the suture. The apparent lack of deformation related to collision in the Ribeira Belt (590 -570 Ma), in the Marins facies, after crystallization of the body, is interpreted as the result of its rheological behavior, more resistant to deformation than the surrounding schists, similar to the behavior of a pre-or syntectonic porphyroblast.