Geologia, petrografia, geocronologia e geoquímica do Granito Anorogênico Seringa, Província Mineral de Carajás, SSE do Pará

Abstract

The Seringa Granite, with 2250 km2 of outcropping area represents the biggest anorogenic batholith of Carajás Mineral Province. It is intrusive in Archean units of the Rio Maria Granite-Greenstone Terrane, located in the southeastern of the Amazonian craton. The Seringa Granite is formed by two great petrographic groups: A) monzogranites rocks, represented by biotiteamphibole coarse-grained monzogranite, amphibole-biotite coarse-grained monzogranite; B) syenogranites rocks, represented by, porphiritic amphibole-biotite syenogranite, heterogranular leucosyenogranite, leucomicrosyenogranite, and heterogranular amphibole-biotite syenogranite. It’s formed essentially by quartz, alkali feldspar and plagioclase. Biotite and amphibole are varietal minerals and zircon, apatite, opaque, and allanyte the accessories minerals. The magnetic susceptibility (MS) data of Seringa Granite identified four populations with different magnetic characteristics, in which the highest values of MS are related to the less evolved facies and the lowest values to the syenogranitic facies, mainly leucogranites. Magnetite, ilmenite, apatite, zircon, epidote, fluorite, monazite and xenotime are accessory phases identified in Seringa Granite. The textural analysis of their oxides has distinguished five forms of ilmenite: trellis, sandwich, composite internal/external, patch and individual. Textural features suggest that titanomagnetite and individual and composite ilmenite crystallized in early magmatic stage. The Ilmenite was destabilized and partially replaced by titanite still in the magmatic stage. During the subsolidus stage, titanomagnetite was transformed by oxidation-exsolution in intergrowths of almost pure magnetite and ilmenite (sandwich, patch, and trellis ilmenite). We can infer that oxygen fugacity conditions (fO2) that prevailed during the formation of Seringa massive were possibly below the NNO buffer, but higher than the FMQ buffer. The Seringa Granite showed Pb-Pb zircon age of 1895±1 Ga, considered its crystallization age, and coincident with the other anorogenic plutons of the CMP. It is subalkaline, metaluminous to peraluminous, display K2O/Na2O ratios between 1 and 2 and FeOt/(FeOt +MgO) between 0.86 and 0.97. The patterns of REE show increase in negative europium anomalies from the less evolved facies to the more evolved facies. In these sense, it is enriched in light REE parallel to the impoverishment of heavy REE. It shows geochemical affinities with within-plate granites, ferroan granites, of the A2-subtype and oxided A-type granites. The field relations, and the petrographic and geochemistry aspects not indicate that the Seringa Granite evolved through a unique process of fractional crystallization. The Seringa Granite display more petrographic, geochemistry and magnetic susceptibility similarities with the suite Serra dos Carajás rocks, been included in that important granitoid suite.