Late Pliocene-Pleistocene stress field in the Teruel and Jiloca grabens (eastern Spain): contribution of a new method of stress inversion

摘要

Samples of non-striated fracture surfaces within clastic materials of Late Pliocene-Pleistocene age from the Teruel grabens (eastern Spain) have been analysed using a stress inversion method based on observations of slip sense. The results obtained at 21 sites are compared with Late Miocene-Early Pliocene extensional stress tensors previously inferred from striated faults in the same area. The similarity between both sets of stress states suggests that the extensional Miocene-Pliocene stress field essentially continues (with minor changes) into Pliocene-Pleistocene times. The main changes involve (a) the dominant trend of σ_3 trajectories, which evolve from ESE to ENE; (b) the waning of the compressional component caused by Europe-Iberia-Africa convergence; and (c) the progressive trend towards a multidirectional extension regime. Stress deflection caused by large-scale extensional faults as well as switching of σ_2 and σ_3 axes induced by fracture development are common within this stress field. They produce groups of local stress ellipsoids with σ_3 axes orthogonal to each other and either orthogonal or parallel to the faults bounding the grabens. The regional consistency of the new results gives support to the new inversion method and demonstrates its utility in research on young sedimentary rocks, where 'gaps' in palaeostress records may exist due to absence of striated faults.