Características geoquímicas de los enclaves en las granodioritas de Cangas de Morrazo-Moaña (provincia de Pontevedra)

Resumo

Between the localities of Cangas de Morrazo-Moaña there is a remarkable outcrop of biotitic leucocratic granites with a great number of dark microgranular enclaves rich in plagioclase and corresponding to various different generations. The use of diagrams AFM, De La Roche diagram R^Rj and Peacock's diagram, as well as the contents of trace elements, show the subalkaline character of the series, making it perfectly different from the classical calc-alkaline and tholeiitic series. The rocks have some characteristics which make them similar to rocks with calcalkaline tendencies at the continental edges, but they present the peculiarity of a high content of K, that is to say, they have a certain shoshonitic tendency. Starting from the acceptance of some hypotesis and observing the inter-elemental variation of the V, Cr, Ba, Rb and Sr enclaves, various genetic posibilities are discussed and the conclusion is inferred that there provably exists a double process of diferentiation and mixing of acid and basic magma. In the same way, a source area of pyrigarnitic and granulitic rock for the basic rocks of the area is proposed.