Structural Analysis of Capané Metagranite, Porongos Complex, Cachoeira do Sul, RS

Abstract

The structural analysis and the contact relationships between the Capané Metagranite (CM) and the Neoproterozoic metavocanosedimentary rocks of Porongos Complex (PC) is discussed based on detailed geological mapping integrated with microtectonic analysis. The study area is located in the south central region of the state of Rio Grande do Sul, in the Capané Antiform, a regional structure dipping to SW. These units were intensively deformed and metamorphosed during the post-collisional phase of the Dom Feliciano Belt at the end of the Brasiliano Cycle (600-560 Ma). The Capané Metagranite, positioned on the west flank of the antiform is a milonitic aegirine pertite granite with locally preserved medium equigranular hipydiomorphic texture and well developed milonitic foliation (Sm). The body presents an elongated shape and agrees with the S2 foliation of the pelitic schists and the metavolcanic rocks. The Sm has NNE direction and plunges on average 30º to WNW, and the stretch lineation (Lx) has a low angle dip (<10º) to SSW. The microstructures observed are typical of medium grade mylonites, equivalent to the condition of metasedimentary host rocks. The kinematic indicators as SC pairs and asymmetric porphyroclasts suggest top-to S-SW sense of movement. The mylonitization is linked to the activation of NE-oriented oblique shear zones during compressional deformation related to the final stages of the evolution of Dom Feliciano Belt.