Petrografia, geoquímica e geocronologia dos metagabros da região de Xambioá-Araguanã-TO.

Abstract

Several mafic and ultramafic bodies associated with other rocks are incased in the supracrustal sequence in the sector north of the Araguaia belt, and have been treated generically as amphibolites in literature. In the present study the bodies are focused that occur in an important area of exposition, located on Xambioá-Araguanã regions in the northwest of the Tocantins state. The bodies are emplaced in the metassedimentar rocks of the Estrondo Group and Archean gneissic rocks of the basement of the Araguaia belt. These bodies are represented by metagabbro, metadiabase and amphibolite with the indistinct presence in these two main litotypes of scapolite and hornblend as metamorphic minerals, the scapolite decreases to the measure that increases the amount of garnet. The metamorphic paragenesis identified in the metagabbros show Hb + Scp + Grt + Ti ± Qtz + (Pl An44-50 and Cpx, as original igneous minerals) and in amphibolites, Hb+ Pl ± Scp ± Grt ± Ky. Geochemical data demonstrate that the metamafic rocks of the different bodies exhibit homogeneity in their composition as far as in the most different samples. Using various discriminates geochemistry diagrams show the nature of original igneous rocks is transitional toleitic basalts series, and their geochemical signatures is comparable to P-MORB or OIB. This indicates the involvement of fertile mantle sources in the magma generation of the gabbros studied. The geochronological studies carried by U-Pb method (LA-ICP-MS) supplied an interval of 804 ± 35 to 878 ± 22 Ma, considered as minimum age of emplaced of the gabbros, in the Neoproterozoic.