SYNTECTONIC EMPLACEMENT OF THE MALADETA GRANITE (PYRENEES) DEDUCED FROM RELATIONSHIPS BETWEEN HERCYNIAN DEFORMATION AND CONTACT-METAMORPHISM

The relationships between Hercynian deformation and contact metamorphi sm in the aureole of the Aneto unit, a constituent pluton of the Malad eta granite complex (Spanish Pyrenees), provide new data relevant to t he controversy between the syn-and post-tectonic models of emplacement for the Pyrenean granites. The deformation in the Aneto aureole is re lated to two superimposed Hercynian episodes. The first was a 'top to the SW' thrusting which induced SW-verging recumbent folds. The second , which was essentially compressive in the Aneto area, is represented by E-W-trending subvertical cleavage and folds with subhorizontal axes . This second episode can be assigned to the D2 main Hercynian tectoni c event of the Pyrenees. The contact metamorphic assemblages grew duri ng the D2 event and were deformed by it close to the contact. The conc lusion that the pluton was emplaced during D2 is strengthened by the s tructural and kinematic similarities between the magmatic deformation in the southern rim of the pluton and the D2 deformation in the countr y rocks. This syntectonic timing is supported by new geochronological data that conflict with an existing Rb-Sr post-tectonic Permian whole- rock age for the Maladeta granite. More generally, in accordance with some very recent structural and U-Pb zircon studies, our results contr adict the geodynamical models of the Pyrenees which relate the granite intrusions to a late extensional event.