The Bazar shear zone (NW Spain): Microstructural and Time-of-Flight neutron diffraction analysis

Juan Gómez Barreiro, and José Ramón Martínez Catalán

Unraveling the kinematic and rheological evolution of tectonic contacts it is crucial to understand mass distributions across an orogen. Reactivation of structures is common and might lead to the misunderstanding of the structural evolution. As a consequence, unequivocal determination of the shear sense is required in major contacts. Besides, the interpretation of deformative linear fabrics as transport direction is always a controversial task. The Bazar Shear Zone (BSZ) represents a major regional contact between two allochthonous units in the Ordenes complex (NW Spain), the metagabbroic Monte Castelo unit, with magmatic arc affinities above, and the Bazar ophiolite, below. Previous regional works interpreted the contact as a top-to-the E thrust related to the formation of the Variscan tectonic pile. New crystallographic preferred orientation or texture (TOF-neutron diffraction) and shape fabric data in mylonitic amphibolites suggest that the BSZ recorded a different flow direction, with a top-to-the S shearing. Microstructural analysis suggests a complex interaction of frictional and viscous mechanisms within the shear zone that is compatible with the prevalence of dissolution-precipitation creep. Mechanical and regional implications are discussed.