THE MALADETA GRANITE POLYDIAPIR, SPANISH PYRENEES - A DETAILED MAGNETOSTRUCTURAL STUDY

The Maladeta granitic complex (Spanish Central Pyrenees) has been subj ected to a detailed magnetostructural study, through the systematic me asurement of magnetic susceptibility and anisotropy of magnetic suscep tibility at 253 regularly spaced sampling sites. Due to the dominant p aramagnetic property of the granites, a first-order correlation can be derived between the susceptibility magnitude and the bulk-rock iron c ontent, hence the petrographic nature of the rock. The Maladeta comple x is shown to be composed of four principal juxtaposed plutons, each o ne being normally zoned, i.e. becoming more basic towards the peripher y. The largest pluton, namely the Colomers unit, is itself made of a n umber of sub-plutons due to distinct but more-or-less coeval batches o f magmas. The various magnetic data, complemented by field and microst ructural observations, allow us to propose that the Maladeta polydiapi r probably exploited NE- and SE-trending openings of the brittle crust for its emplacement, that accompanied or just preceded a SW-verging c ompressive event. A later N-S compression marked by inverse dextral, a nd E-W-trending shears, is preferably attributed to late Variscan rath er than to Alpine tectonics.