Mapeamento Geológico e Geoquímica dos ortognaisses da região de Castelo (ES), limite entre os Orógenos Araçuaí e Ribeira

Abstract

The Araçuaí and Ribeira Orogens were formed during the amalgamation of Gondwana supercontinent developed in the Upper Neoproterozoic. The limit between them has several questions and to contribute in a way to understand how was the geological evolution in the Orogens connection we present new detailed data of geological mapping, structural geology, petrographic and geochemical analyzes from Castelo region (ES) in the connection Araçuaí/Ribeira. The mapped lithostatigraphic units comprise alluvial sedimentary and talus deposits, intrusive igneous bodies of granite and gabbro, leucogranites, marbles, silimanite-garnet-biotite gneiss and orthogneisses that can vary among hornblende-biotite gneiss and biotite-gneiss. The geochemical analyzes of hornblende –rich orthogneiss allowed the separation into two subgroups as low and high K, the former with typical adakite signature. The leococratic biotite-orthognaisses, on the other hand, were characterized as A- type granitoids. The identification of these rocks present in the northern segment of the Serra Prata arc together with existing data that define them with Tonian and juvenile with mantle contribution, allows the proposal of a new geotectonic model for the study area. Adakites are considered to be the result of partial melting of a young, hot oceanic plate under moderate to high pressures in which garnet was an important stable residue. The occurrence of adakites with A- type granitoids in the final sector of the Serra da Prata arc is interpreted here as the result from a slab window gap, either associated with slab tearing or ridge subduction