Kinematic characterization of a NNE-trending transcurrent shear zone, marked in the evolution of its syntectonic granitic magmatism in the region of Camboriu, SC

Abstract

The Corre-mar Granite (GCM) is located in the region of Itapema-Camboriu, Santa Catarina, Brazil, in the northeastern part of Dom Feliciano Belt. A subvertical NNE-trending shear zone controls its emplacement, and a subvertical S-C fabric is generated with sinistral shear sense. The S-planes (magmatic) strike NE-SW and are marked mainly by the orientation of feldspar crystals and xenoliths, while the C-planes (shearing), strike NNE-SSW, marked by mineral stretching, tails of asymmetric recrystallization in feldspars, and inflection of the structures previously oriented along S. Low-temperature deformation zones parallel to the GCM local C-foliation, best developed near the contacts with the host rocks, do not extend more than a few meters into the country rocks. The GCM bodies have a systematic variation in thickness, where wider zones show the least developed foliations. Microstructures indicative of progressive deformation under decreasing temperature are represented by chessboard-pattern subgrains in quartz, and granoblastic K-feldspar grains. These are overprinted by lower temperature microstructures, such as fine-grained recrystallized quartz, frequently by bulging, sealing of fractures in larger K-feldspar grains by the finely recrystallized matrix, and neoformation of fine grains around the feldspar crystals. The integration of structural and petrological data indicate that the GCM was positioned when the NNE-trending shear zone was active, and its geometry indicates an opening component along the NE direction, typical of transtensional regimes. The transtensional structure is compatible with its positioning in a low-strain zone of the Southern Brazilian Shear Belt, situated between the higher strain zones represented by the Major Gercino and Itajai shear zones, both active in the post-collisional stages of Brasiliano Cycle in southern Brazil.