O SISTEMA ORÓS-JAGUARIBE NO CEARÁ, NE DO BRASIL

Abstract

The Oros-Jaguaribe System is a peculiar geotectonic unit in the Borborema Province (NE Brazil) framework. It contains two linear mobile belts, whose evolution began c.a. 1.9 Ga ago, overlying an older basement characterized by high amphibolite metamorphism and tangential tectonics. In contrast with its basement, the System contains essentially metavolcano-sedimentary sequences intruded by acid and basic magmatic rocks metamorphosed under low greenschist to granulite facies and displays a strike-slip deformation pattern of brasiliano age (c.a 600 Ma). The metasediments are essentially pelitic with important intercalation of semi-mature lenticular quartzite, carbonatic quartzite, calcsilicate rocks and calcitic/dolomitic/magnesitic marbles. The Oros Belt exhibitsan inverted distribution: volume and extension of detritic sediments, essentially quartzite, decrease south-westward, whereas carbonates, essentially calcitic marbles, show a significant increase. These ones become more, magnesitic north-eastward by a differentiation chemical process (elimination of Ca that precipitate as calcic, calci-magnesitic carbonates or sulfates). These relationships are consistent with a paralic/deltaic system. The acid metaplutonic and metavolcanic rocks are dominantly alkaline or sub-alkaline, characteristic of an intracratonic setting.The lithologic association and distribution of the metasediments (essentially the basal ones) are shelf type, preceding rift stage, which is associated with an intense magmatism.