Origem e evolução do complexo granitoide neoarqueano de vila Jussara: implicações para a evolução crustal da província Carajás

Abstract

New information on the geology, combined with the acquisition of geochemical and isotopic data (U-Pb, Hf and Nd) from the Vila Jussara Suite, are presented in order to discuss a petrogenetic model for the Neoarchean granitoids of the Carajás Province. This suite appears as a series of coalescing plutons with sigmoidal and elongated shapes, in the E-W direction, which follow the regional trend. The central areas of the plutons are slightly deformed, while the marginal portions have a mylonitic appearance and are delimited by sinistral shear zones belonging to the transcurrent system of the Itacaiúnas Shear Belt. These granitoids present a broad compositional spectrum, with four individualized lithotypes: (i) biotite-hornblende serial monzogranite, which is subdivided into oxidized and reduced types; (ii) biotitehornblende tonalite; (iii) biotite monzogranite; and (iv) porphyritic granite (hornblende biotite monzogranite/granodiorite). The geochronological data U-Pb and Pb-Pb in zircon provided an age of crystallization of 2.74 Ga for the granitic and porphyritic granite varieties, and for the biotite-hornblende tonalite variety, an age of 2.76 Ga. The isotopic data of Nd and Hf suggest that the magmas of the Vila Jussara suite are not juveniles [εNd (-3.5 to 1.5) and εHf (-1.2 to 3.5)] and were derived from rocks of Mesoarchean age (TDM > 3.0 Ga). The petrogenetic model adopted to generate the primary magmas of this suite admits as source rock the Mesoarchean granulites from the Ouro Verde area of the Canaã dos Carajás subdomain. Field relationships, geochemical and isotopic data suggest that the granitoids that make up the Vila Jussara Suite are not formed from a single parental magma, but by multiple magma injections generating extensive hybridization. Its magmas were placed along pre-existing structures under a transtensional tectonic regime dominated by pure shear in a post-collisional syntectonic context.