The Guitiriz granite, Variscan belt of northern Spain: extension-controlled emplacement of magma during tectonic escape

The Ollo de Sapo domain of the northern part of the Variscan belt of Spain, contains Precambrian and Ordovician metamorphic rocks intruded by the Guitiriz granite. The domain is bounded by two NS transcurrent shear zones. Detailed structural and anisotropy of magnetic susceptibility studies of the Guitiriz pluton reveal a syntectonic emplacement, relative to movement on the two NS trending bounding shear zones, characterized by: (1) development of NS trending structural and magnetic fabrics: (2) concordant structures in granites and country rocks; and (3) development of shear zones along the east and west granite margins. Gravity data show two roots trending 110°E extending down to 4.5 km from an otherwise thin (< 3 km), slab-like body. The Guitiriz pluton was emplaced in a magma chamber developed by local NS extension induced by an overall E-W shortening. The proposed emplacement model involves the northwards tectonic escape of a crustal wedge — the Ollo de Sapo Domain — bounded by two shear zones acting as conjugate strike-slip zones.