Charnoquitóides do maciço de Várzea Alegre: um novo exemplo do magmatismo Ca-alcalino de alto K no arco magmático do Espírito Santo

Abstract

CHARNOCKITIC ROCKS OF THE VA RZEA ALEGRE MASSIF: A NEW EXAMPLE OF THE HIGH K CA-ALKALIC MAGMATISM IN THE MAGMATIC ARC OF THE ESPIRITO SANTO The Varzea Alegre intrusive massif is situated in the central portion of the Espirito Santo State. It is an example of the late to post tectonic magmatism related to the onset of a magmatic are developed during the late-Brasiliano episode. It comprises an inner domain of gabbros, diorites, quartz-diorites and granites completely surrounded by a large ring of charnockitic rocks. The lithotypes found in that ring were chemically classified as opdalites, jotunites, quartz mangerites and enderbites (opx-quartz diorites). They show aporphyritic texture with feldspars and quartz megacrysts set in a medium to coarse grained matrix. The geochemical characteristics of these rocks are typical of a calc-alkalic magmatism enriched in LIL and HFS elements (mainly Ba, K, REE, Zr, P and Nb). Using compatible versus incompatible elements variation diagrams it is possible to sugest that fractional crystalization and magma mixing were the principal mechanisms in the evolution of the suite. The high contents in such incompatible elements point towards a mantelic contribution associated with crustal contamination for the genesis of the rocks.