Contribución al estudio de los diques Camptoníticos heteromorfos con subfacies ocelares y de diatrema asociadas. Sierra de la Paramera de Ávila

Resum

The alkaline lamprophyres of the central part of Sistema Central Español, intruding NS deep fractures, are camptonitic in composition. The, locally show heteromorphism, with ocelli and diatreme facies, all along their strike (Dike of Sierra de la Paramera. Fig.1). In this paper we present a contribution to the mineralogical and petrographic aspects of these facies. The lamprophyres with feldespatic ocelli could be due to inmiscibility phenomena between the alkaline basic magma and a differentiated, usually volatile-rich, fraction of it, trapped after the violent escape of part of it (diatreme facies). In fact, both of these facies, ocelli and diatreme, are spatially related. Carbonate ocelli, which can appear in anyone of the different camptonitic dikes, could be explained as segregations of residual liquid into vesicles and veins. The camptonitic magma in diatreme facies is extraordinarily contaminated with xenolithic material, dragged on the ascent of magma from low crust (granulitic in character), up to present levels of emplacement, which are of granite type. All these breccia facies are strongly transformed by alteration and low grade metamorphism, which affect not only foreign material but also the camptonitic "matrix", in a general process of hydrothermalism, likely related to the same magmatic fluidization mechanism of the diatreme genesis.