HIGH-PRESSURE MAFIC GRANULITES IN THE ALTEROSA SUTURE PALEOZONE (SW OF MINAS GERAIS): PETROGRAPHY AND METAMORPHISM OF METAMAFIC ROCKS BETWEEN THE VARGINHA AND CAMPOS GERAIS SHEAR ZONES

HIGH-PRESSURE MAFIC GRANULITES IN THE ALTEROSA SUTURE PALEOZONE (SW OF MINAS GERAIS)

Abstract

In the southwest of Minas Gerais state, the Alterosa Suture Paleozone separates the Guaxupé Complex from the Barbacena Complex and corresponds to a belt of intensely deformed rocks. In the southernmost portion of this belt, between the Varginha and Campos Gerais shear zones, occur metasediments bearing garnet, kyanite, oligoclase/andesine, orthoclase and rutile, with intercalations of orthogneisses with garnet, amphibole, biotite, clinopyroxene, orthoclase and oligoclase/andesine, in addition to subordinate lenses intercalations of metamafic rocks (amphibolites, mafic granulites and retroeclogites) and metaultramafic rocks. This paper integrates results from petrography and mineral chemistry of mafic granulites that occur in this portion to characterize the metamorphism of these rocks. The mineral associations, textural aspects and mineral chemistry characteristics of mafic granulites indicate a metamorphic peak in high-pressure granulite facies, with garnet + sahlite + andesine/bytownite + quartz + rutile ± meionite paragenesis, developed before the main foliation (Sn). Metamorphic peak paragenesis was progressively superimposed by mineral assemblages from metamorphic re-equilibration in granulite to upper amphibolite facies during Sn development, accompanied by near-isothermal decompression, followed by a decrease in temperature and pressure within the kyanite stability field exhibiting a clockwise metamorphic path.