The Journal of Petrology, Volume 38, Issue 12: December 1997.

Successive granitic magma batches during pluton emplacement: the case of Cabeza de Araya (Spain)

JL Vigneresse^1,* and JL Bouchez²

¹Cregu, BP 23, and ENS Geologie, BP3, F-54501 Vandoeuvre/Nancy Cedex, France, ²Petrophysique, Universite Paul-Sabatier and UMR CNRS No. 5563, 38 rue des 36-Ponts, F-31400 Toulouse Cedex, France, ^*Corresponding author e-mail: cregu.cnrs-nancy.fr

We present a dynamic scenario of granite emplacement in the upper crust for the pluton of Cabeza de Araya (Extramadura, Spain), based on interpretations of gravity data, internal structures and geochemical variations. The three-dimensional shape of the pluton is derived from the inversion of gravity data, and the magma flow structures are obtained by 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 brittle crust and served as conduits for the magma that was ready to be tapped. In the southern half of the pluton, granite type A is cross-cut by type B in the magmatic state. These magmas show a continuum in their chemistries attributed to progressive differentiation. A fine-grained leucocratic granite, more evolved chemically cross-cuts the surrounding facies and crops out above the southern feeder zone. It is interpreted as a late magma batch, coming from a different source that intruded into the incompletely crystallized surrounding facies. The normal petrographic zoning of the massif of Cabeza de Araya is therefore viewed as a succession of continuous and discontinuous infillings, sequentially permissive and forceful, of increasingly evolved magma batches into a reservoir that opened at varying rates within the brittle crust.

Key words: granite; gravity; magma emplacement; magnetic structures; petrographic zoning

Pages 1767-1776