COMPRESSIONAL GRANITE-EMPLACEMENT MODEL - STRUCTURAL AND MAGNETIC STUDY OF THE TRIVES MASSIF (NW SPAIN)

The Trives granodiorite is a syntectonically emplaced pluton belonging to the great Manzaneda batholith, which has intruded into the gneisse s of the Ollo de Sapo Formation (northern part of the Iberian Variscan belt) during Carboniferous times. Combined metamorphic, petrofabric, structural and anisotropy of magnetic susceptibility studies reveal th at interactions between regional metamorphism, deformation and magmati sm played the main role in strain partitioning in and around the empla cing Trives pluton. Low-dipping S-C structures carrying N140 degrees E -trending stretching lineations exist in both the roof-pendants which contain sillimanite bearing gneisses and in the subjacent granodiorite s which are located in the central areas of the Trives pluton, whereas subvertical shear zones but with the same stretching lineation orient ations are found along the pluton margins. At deeper levels of the Tri ves granodiorite, there are fabrics which are related to the crystalli zation of magma at the emplacement level. In these rocks, magnetic fol iations are mainly steeply dipping and magnetic lineations are N140 de grees E-trending. The anisotropy of magnetic susceptibility data here is consistent with field-observed macroscopic structures. Samples show ing solid-state deformation display magnetic foliations and lineations subparallel to C-planes and their macroscopic stretching lineations, respectively. The foliations and lineations of magmatic origin are cha racterized by lower degrees of anisotropy. Structural maps of magmatic and solid-state deformation structures suggest that the emplacement o f the Trives pluton was controlled by D-3-deformational structures, N1 40 degrees E-trending transcurrent shear zones and crustal detachments , which developed in response to a NE-SW compressional stress field. ( C) 1998 Elsevier Science B.V. All rights reserved.