Geochemistry and Petrology of the Jequie Granulitic Complex (Brazil): An Archean Basement Complex

Abstract

The Jequie granulitic complex is part of the extensive high-grade metamorphic terrain located within the Sao Francisco craton of northeastern Brazil. Some Jequie rocks appear to have been formed in the middle Archean (~3.1 Ga) from preexisting sialic crust_ The dominant mineral composition of these rocks is quartz-microcline-plagioclase-hypcrstene and occurs over an extensive area (~2,000 km2). Scattered enTichment of normal granites with many minor elements (e.g. Rb, Y, Zr, Nb, Ba, REE), and the non-depletion of other elements (e.g. Cs, U), normally considered mobile during granulite facies metamorphism, must lead either to the reconsideration of regional metasomatism subsequent to granulite facies metamorphism, or at least raise some doubts about common wisdom concerning the distribution of heat-producing elements at depth. The region includes large-scale thrust structures, which could play a part in influencing high-level emplacement of the rocks and their regional metasomatism and structures.