Estructura extensional del sector centro-norte de la Zona Vasco-Cantábrica

Abstract

We study the central part of the Bilbao Anticlinorium located in the north-central sector of the Basque-Cantabrian Zone. The aims of this work are: 1) to determine the tectonic regime in this part of the Basque-Cantabrian Basin, located in the Iberian-Europe boundary during the Mesozoic opening of the Bay of Biscay, and 2) to check the consistency of the tectonic regime with the geometry of the basin. Geological mapping, kinematic analysis of syn-sedimentary faults and geometric analysis of syn-rift units were carried out to achieve these goals. We conclude that this part of the basin was developed mainly under a pure and/or a sinistral-oblique extensional regime, which is in agreement with the geometry of the syn-rift wedges. These stratigraphic units thicken in a NW direction, parallel to the strike of the faults, as a result of lateral variations in fault displacements. This mechanism also explains the development of the SW-oriented axis of subsidence, perpendicular to the strike of the main faults. We rule out that this sector of the Basque-Cantabrian Basin developed primarily as a pull-apart basin, between NW oriented sinistral strike-slip faults, as it has been proposed often in the literature.