Geologia e petrografia do Grupo Alto Jauru, na região da Fazenda Retiro, SW do Cráton Amazônico : evidências de um prisma acrescionário estateriano

Abstract

The Rondoniana-San Ignácio Province, southwestern portion of the Amazonian Craton, is marked by a complex amalgam of terrains from different ages and sources. The basement of one Jauru Terrain consists of metavolcano-sedimentary rocks and intrusive acidic, basic and ultrabasic. The metavolcano-sedimentary rocks has been commonly called Alto Jauru Group. Geologic mapping, petrography, geochronology and structural analysis performed on Retiro Farm region, north of the Araputanga city, SW of Mato Grosso state, reveal that this Group consists of biotite-muscovite-quartz schists, chlorite-biotite-muscovite schists, garnet-cordierite-biotite schist and staurolite-andalusite-biotite schist, garnet-sillimanite associated with biotite-gneiss, biotite gneiss, amphibolite and muscovite granite. The petrography and structural relationships indicate that these rocks were affected by two deformational events Dn and Dn+1, Sn associated with the foliation (schistosity and gneissic banding) and Sn+1 (crenulation cleavage), and three metamorphic events: first metamorphic event (M1), the contemporary Sn lower greenschist facies, the second (M2) associated with Sn+1 phase greenschist to amphibolite facies, and the third thermal event (M3) hornblende hornfels facies. The crystallization age of the biotite gneiss obtained by the method U/Pb (SHRIMP) zircon is 1819 ± 6.7 Ma. The interpretation of these data suggest that the rocks of the Alto Jauru Group are part of a accretionary prism formed in Statherian.