SUCCESSIVE GRANITIC MAGMA BATCHES DURING PLUTON EMPLACEMENT - THE CASE OF CABEZA DE ARAYA (SPAIN)

We present a dynamic scenario of granite emplacement in the upper crus t of the pluton of Cabeza de Araya (Extramadura, Spain), based on inte rpretations of gravity data, internal structures and geochemical varia tions. The three-dimensional shape of the pluton is derived from the i nversion of gravity data, and the magma flow structures are obtained b y mapping the rock anisotropy of magnetic susceptibility. The deepest zones of the pluton, which also correspond to vertical lineations, are interpreted as feeder zones from which magma upwelled. These feeders form small, distinct areas connected to the pluton's floor 6 km below the present surface level. We propose that the two main feeders of the pluton represent tension gashes that formed at the base of the brittl e crust and served as conduits for the magma that was ready to be tapp ed. In the southern half of the pluton, granite type A is cross-cut by type B in the magmatic state. These magmas show a continuation in the ir chemistries attributed to progressive differentiation. A fine-grain ed leucocratic granite, more evolved chemically, cross-cuts the surrou nding facies and crops out above the southern feeder zone. It is inter preted as a late magma batch, coming from a different source, that int ruded into the incompletely crystallized surrounding facies. The norma l petrographic zoning of the massif of Cabeza de Araya is therefore vi ewed as a succession of continuous and discontinuous infillings, seque ntially permissive and forceful, of increasingly evolved magma batches into a reservoir that opened at varying rates within the brittle crus t.