Petrografia, litogeoquímica e geologia isotópica do granito pós-colisional Itaoca, Campos dos Goytacazes - RJ

Abstract

The Itaoca Granite is the youngest representative of the post-collisional magmatism stage of the Ribeira Belt. This unit is inserted in Nova Friburgo suite and is located in the city of Campos dos Goytacazes, north of the state of Rio de Janeiro. It is a large plutonic body, intruded in the metasedimentary rocks of the St. Fidelis Group - Oriental terrain. This body is represented mainly by the Serra do Itaoca, and there are smaller bodies mapped in the southern of the area. This unit has been subdivided into three igneous facies, based on textural variations, as follows: porphyritic facies, uneven grained facies and even-grained facies. The transition between these facies occurs concentrically and gradational form. Compositionally are homogeneous rocks, where there is no mineralogical differences occur only variations in the modal share of the minerals that compose them. The unit is basically composed of monzogranites, and also found quartz monzonite and syenogranites. A large amount of xenoliths are found in specific regions of the Serra do Itaoca, which are rich in mica, mafic microgranular and xenoliths of amphibolite. The rocks of the Itaoca Granite belong to the calc-alkaline series are weakly metaluminous to peraluminous, have high levels of potassium and are saturated in silica. The reasons for 87Sr / 86Sr, calculated for 476 million years, the age of crystallization of granite Itaoca, ranging between 0.701 and 0.708, indicating magmatic sources with mantle signature, as well as the petrogenetic's parameter ƐNd ranging from -13.2 to -11 , 4. The proposed model for the origin of Itaoca granite is partial melting of rocks Magmatic Arc Rio Negro, the slab-breaking time of subduction and consequently delamination of the duplicated continental crust. The magma generated lodges in supracrustals of St. Fidelis Group and in the process assimilates of these interlocking, contaminated the primary magma. And the main magmatic differentiation process that worked in the formation of this igneous body was the fractional crystallization assimilation of host rocks