CONTRIBUIÇÃO A ESTRATIGRAFIA DO PRÉ-CAMBRIANO DO LESTE DO ESTADO DE SÃO PAULO E ÁREAS VIZINHAS

Abstract

A stratigraphic revision of the eastern precambrian part of the State of São Paulo (Brazil) and surrounding areas is presented, based on newly available data. The occurrence of the Amparo Group (Middle Precambrian, Transamazonic Cycle), the Pinhal Group (Upper Precambrian, Brazilian Cycle) and the Eleutério and Pouso Alegre Formations (also related to the Brazilian Cycle) are discussed, and redefined. The Amparo Group comprises an essentially metassedimentary sequence belonging to the amphibolite and granulite facies originally, composed of impure clastic sediments, associated with tuffs, basic and subordinately ultrabasic rock. The Pinhal Group incorporates several granitic and migmatitic rocks of which the latter are a result of intrusion of granitic material into the above mentioned rock assemblage of the Amparo Group. The anchi - to low grade metamorphic, Eleutério and Pouso Alegre Formations include the Metamorphic equivalents of arkoses, mudstones and different types of conglomerates and breccias. Geological, geochronologicaì, structural and petrographic data sugest a polymetamorphic evolution for the area under examination, which can be ascribed to the Transarnazonic and Brazilian tectono-thermal cycles of middle and upper precambrian times. Regional studies suggest the prevalence of differently oriented compressive forces related to the older and the younger cycle; to the latter, transcurrent faults of great magnitude are linked. In spite of the improved knowledge on the geology of the area, a clear definition for the basement uppon which the Amparo Group was laid is not thus far possible.