MICROESTRUTURAS E RELAÇÕES METAMORFISMO-DEFORMAÇÃO DO GRUPO SÃO ROQUE NA FAIXA ENTRE O PICO DO JARAGUÁ E A SERRA DOS CRISTAIS - SP

Abstract

Microstructural studies of rocks belonging to the Sâo Roque Group in an area of about 376 km 2 between Pico do Jaragua (Municipality of Sao Paulo) and Serra dos Cristrais (Municipality of Jundiai) have permitted to recognize their patterns of defornation and metamorphism as a part of a work devoted to the structural analysls of the Sao Roque Group. Three phases of folding affected the metamorphic rocks as determined from characteristics of fold styles, nature of axial-plane foliations, and the interference patterns observable in both outcrops and maps. The relationship between deformation and metamorphism could be recognized with the study of microstructures. The F 1 phase was accompanied by the fornation of axial-plane slaty cleavage or schistosity related to tight folds and it was followed by the regional metamorphic peak under post-kinematic conditions. During this peak porphyroblasts of opaque minerals, gamet, staurclite and sillimanite were developed. This main metamorphic event continued, at least for the staurolite, into the beginning of the second folding episode. The F 2 phase generated a persistent crenulaticn cleavage, frequently both microscopic and of the zonal type, in axial-plane position of the folds are ubiquitous and occur in ali scales, Differentiated banding and some recryatallization of biotite around opaque minerals occurred during this phase. The third folding phase, F 3 , created more spaced crenulation cleavage not of the zonal type so common in the F 2 previous phase. The F 3 phase, which was more intense in the southem part of the area, generated large folds and undulations in regional structures.