O COMPLEXO METAMÓRFICO CAMPO BELO (CRÁTON SÃO FRANCISCO MERIDIONAL): UNIDADES LITODÊMICAS E EVOLUÇÃO TECTÔNICA

Abstract

The Campo Belo Metamorphic Complex in the study area is constituted by gneissic, amphibolitic and metaultramafic rocks intruded by gabbronorites, granitoids and gabbros. Scattered records of quartzitic rocks are locally found. These petrographic types were grouped in seven lithodemic units, named as follows: 1) Gneissic Unit, 2) Amphibolitic Unit, 3) Metaultramafic Unit, 4) Quartzitic Unit, 5) Gabbronoritic Unit, 6) Granitoid Unit (is.), and 7) Gabbroic Unit. The Gneissic Unit constitutes the regional crystalline basement and acted as host rock (or basement?) for the other lithodemic units. The Amphibolitic Unit presents petrologic evidences that suggest an isobaric cooling history and, as well as the Gneissic Unit, it contains modal hypersthene. Metamorphic characteristics of the granulite facies are also recognized in the rocks of the Metaultramafic and Quartzitic Units; similarly to what happened with the rocks of the Gneissic and Amphibolitic Units, the rocks were retrometamorphosed to the amphibolite and later to the greenschist facies. The Gabbronoritic, Granitic (s.l.) a nd Gabbroic Units, once presenting paragenetic assemblages characteristic of the greenschist facies only, were emplaced in the crust after the tectonothermal events that generated the paragenetic sequences of the granulite and amphibolite facies. This duality, regarding the metamorphic grade intensity, would in part express the complex evolutionary history of the area, which would be related to the occurrence of magmatic (Mesoand Neoarchean) and epeirogenic events after the Neoarchean.