Contribuição a litogeoquímica das rochas do entorno da Comunidade Santa Elisa, Castanheira, Mato Grosso

Abstract

In the province Rio Negro-Juruena province, south-western Amazon Craton at around Santa Elisa and Castanheira in northeast Mato Grosso, there are three mesoproterozoic magmatic events, Fontanillas and Juara granites of the Rio do Sangue Suite and part of the AMCG suite (anorthosite, mangerite, charnockite and rapakivi granites) and the Rio Branco Granite interpreted as a late intrusion. The petrographic characteristics of the Granite Fontanillas, mesocratic, led to identification of biotite granodiorite to monzogranite, and in Juara and Rio Branco granites, leucocratics, monzogranites predominate and sometimes all are foliated. The major element geochemistry of the content of SiO2 shows intermediate to acidic compositions for Fontanillas and acidic to Juara and Rio Branco. The Fontanillas and Rio Branco granites are the peraluminous and the Juara is metaluminous. In the TAS diagram Fontanillas Granite plots in diorite, granodiorite to granite, from low to high K. The Juara as well as the Rio Branco plots in Granite and with medium K. The Al2O3 contents and sum of CaO + Al2O3 are high in Fontanillas Granite when compared to Juara and Rio Branco granites. REE patterns show enrichment in LREE relative to HREE and negative Eu anomaly in the three granites. The multi-element diagram shows Sr, P and Ti depletion for Fontanillas and Rio Branco granites and Sr and Ti for the Juara, as well as the Nb for all. In the FeOT/(FeOT + MgO) versus Al2O3 / (K2O/Na2O) and FeOT/(FeOT + MgO) versus the Al2O3 diagrams, the Fontanillas is predominantly calc-alkaline to oxidized A type and the Juara and Rio Branco granites plots overlap the calc-alkaline and oxidized A type. The CaO/FeOT + MgO + TiO2) versus Al2O3 and CaO/(FeOT + MgO + TiO2) versus CaO + Al2O3 diagrams show that Fontanillas Granite is mainly of calc-alkaline affinity and the Juara and Rio Branco granites plots overlap the calc-alkaline and alkaline type A fields, and A type alkaline. The Zr/Y and Th/Yb ratio of the three granites range from transitional to calc-alkaline. In contrast, the La/Yb ratio shows transitional to calc-alkaline affinity to Fontanillas and calc-alkaline for Juara and Rio Branco. The Y/Nb ratio greater than 1.2, as well as A2 granite evidenced by ternary diagram Y, Nb and Ce, suggests crustal sources melting in post-collisional tectonic setting for these granites.