Geologia e geocronologia U-Pb (LA-ICPMS) do Domínio Italva na região entre Cantagalo e Itaocara, nordeste do Estado do Rio de Janeiro

Abstract

The Italva Domain represents a tectonic unit which overrides the Costeiro Domain, and was placed there during the Brasiliano tectonic event between 605 and 500 million years ago. In the northen region of Rio de Janeiro State the outcropping units display a belts with NE-SW strike, covering about 430 Km² between the municipalities of Cantagalo and Itaocara. Six units were maped in the area: a) Serra da Prata Unit: homogeneous or banded hornblende biotite gneiss, leucocratic or mesocratic, with mafic lenses and médium graned biotite gneiss interlayered; b) Macuco Unit: homogeneous biotite gneiss, white color, locally with sillimanite and garnet; c) São Joaquim Unit: medium to coarse grained calcitic marble, homogeneous, with graphite and intercalations of amphibolites and rare quartz feldspathic bands; d) Euclidelândia Unit: biotite muscovite orthogneiss, granitic to tonalitic, rich in magnetite and locally with sillimanite, garnet and tourmaline; e) Amphibolites that change from mesocratic to melanocratic, medium to coarse grained locally with clinopyroxene and garnet; f) leucocratic homogeneous (garnet) biotite muscovite granite, locally showing foliation and centimetric feldspar crystals. The klippe Italva is a synformal structure with subparallel flanks and NE axis. The northern contact is with biotite hornblende gneiss of the Rio Negro Complex which have similar petrographic characteristics to the Serra da Prata Unit. The southern contact is with migmatitic sillimanite garnet biotite gneisse of the Costeiro Domain. The mineralogical composition of the units of the Italva Domain, rich in plagioclase and amphibole in addition to the homogeneity in outcrops suggest an igneous protolith especially for units inthe care of the klippe (Serra de Prata and Macuco units). Geochemical data obtained for metabasic rocks of the Italva Domain indicate the predominance of tholeiitic rocks with MORB-like signature and more rarely, calc alkaline island arc basalts. Unpublished geochronological data reveal crystallization ages of ~918 Ma for amphibolite intercalated with marble indicating the limit (a minimum age) for the sedimentation in the Italva Basin. The orthogneisses of the Italva Domain have a crystallization ages of ~860 Ma, ~750 Ma e ~630 Ma with metamorphic events recorded at ~570 Ma. These data suggest that a back arc basin developed in the early stage of subduction since ~918 Ma and remained active until ~ 625 Ma resulting in several pulses of generation of calc alkaline rocks of the Rio Negro Complex.