PETROLOGY, GEOCHEMISTRY AND THERMOBAROMETRY OF METAULTRAMAPHIC ROCKS IN THE ITAGUARA SEQUENCE (SOUTH SECTOR OF THE SAO FRANCISCO CRATON): POSSIBLE FRAGMENT OF THE PALEOPROTEROZOIC OCEANIC LITHOSPHERIC MANTLE?

Petrology, geochemistry and thermobarometry of metaultramaphic rocks in the Itaguara Sequence (South sector of the São Francisco Craton): possible fragment of the Paleoproterozoic oceanic lithospheric mantle?

Abstract

The base of ophiolitic sequences contains ultramafic rocks from oceanic lithospheric mantle. When found in continental terrain, these lithotypes show metamorphic processes that are registered in their mineralogy, chemical composition and textures. In the south of the São Francisco craton, between the cities of Itaguara and Crucilândia (Minas Gerais-Brazil), the Itaguara Sequence (SI) is located and it is composed of paleoproterozoic quartzites, schists, banded iron formations, ortho-amphibolites and metaultramafics. This study presents petrographic, geochemical and thermobarometric data from metaultramafic rocks of the Itaguara Sequence. Mineralogically they are composed of serpentine (antigorite), tremolite, talc, chlorite, olivine, spinel, clinopyroxene and opaque minerals, with spinel wehrlite as protolith. Thermometry and lithogeochemistry data respectively point to serpentinization occurred below 500 °C and to similarities with subduction-related paleoproterozoic serpentinites found in the Congo craton. Possibly, the SI metaultramafic rocks were part of an oceanic basin involved in subduction and continental collision processes of the Rhyacian-Orosirian orogenetic event between the Divinópolis and Campo Belo/Bonfim Metamorphic Complexes.