The Los Pedroches Batholith (Southern Spain): Polyphase Interplay between Shear Zones in Transtension and Setting of Granites

Abstract

The Los Pedroches batholith (LPB) in the Variscan belt of southern Spain is a 200 kilometres long magmatic body which has intruded low-grade metamorphic rocks of the Central Iberian Zone. The LPB is composed of granodiorites, a dyke swarm, and granites emplaced during three successive magmatic events. Field structural data from both the country rocks and the LPB indicate that the northern boundary of the LPB is a transtensional shear zone, the Conquista shear zone, dipping 50° to the NE. This shear zone is sealed by the Cerro Mogabar granite which was emplaced during the last magmatic event. A detailed magnetic susceptibility study, using 2236 oriented samples from 559 stations, of the main part of the batholith yields flat magmatic foliations, and magmatic lineations with a mean east-west trend. The structural, kinematic and magnetic susceptibility data indicate that the emplacement of the LPB was controlled by a crustal scale and dextral transtensional shear zone, parallel to the batholith elongation. The eastern part of the granodiorite takes the shape of a large laccolith prolonged westwards by four NW-SE elongate domes. These contrasted geometries reflect the upwelling of magma through the transtensional zone that vanishes towards the west. Intrusion of dykes along Riedel shears related to the regional transtension took place in a second magmatic event. The main transtensional shear zone is interpreted as a lateral ramp that accommodated the crustal thinning developed in the Central Iberian zone during the collapse of the Iberian Variscan belt.