Evidências de metamorfismo de alta pressão na faixa de dobramentos Pajeú – Paraíba, Província Borborema, nordeste do Brasil: petrografia e química mineral de rochas metamáficas

Abstract

Metamafic rocks occur as concordant lenses in a sequence of migmatites - orthogneisses of probably paleoproterozoic age. Petrographic and mineral chemistry investigations on metamafic rocks from Itatuba - Itabaiana, the Pajeú-Paraíba Belt of the Borborema Province, are reported. The presence of Mg- Ca-rich garnet, amphibole with Fe-edenite composition as coronas on the garnet grains and tschermakitic amphiboles in the symplectitic intergrowths with plagioclase around clinopyroxene suggest that the studied rocks were metamorphosed under high pressure conditions and that they were reequilibrated during a retrograde metamorphic path successively under temperature and pressure conditions of granulitic, amphibolitic and greenschist facies. In spite of the lack of omphacitic pyroxene in the studied rocks, the texture of the rocks and field relationships suggest the occurrence of a metamorphic event under eclogitic conditions. The studied rocks may mark a continental Paleoproterozoic suture zone in the Transversal Zone Domain of the Borborema Province.