Deformation in Neogene sediments of the Sorbas and Vera Basins (SE Spain): constraints on simple-shear deformation and rigid body rotation along major strike-slip faults

Detailed structural analyses are presented of the Neogene Sorbas Basin adjacent to the E-W striking Gafarillos fault zone and the Vera Basin adjacent to the 020degrees striking Palomares fault zone in southeastern Spain. A stress regime with an E-W oriented subhorizontal maximum principal stress (sigma(1)) existed in pre-Tortonian (> 11.3 Ma) time. A strike-slip regime with NW-SE oriented compression during Tortonian and earliest Messinian time caused dextral displacement along the E-W trending Gafarillos fault of approximately 10 kin. Structural analysis indicates that most displacement took place in the Early Tortonian. Deformational patterns within the adjacent pull apart basin reflect a dextral simple shear-zone of at least 500 in width. Kinematical analysis of folds in the Sorbas Basin suggests, however, that rotational effects are largely caused by rigid-body rotation without much internal deformation. Sinistral strike-slip displacements occurred along the Palomares fault zone under the influence of the same stress-regime. An abrupt change in the orientation of the stress field to N-S directed compression in earliest Messinian time (6.5 Ma) caused the termination of displacements along the Gafarillos fault zone, whereas the 020degrees trending Palomares fault zone continued to accumulate sinistral strike-slip displacements of about 25 kin. Volcanism occurred along splays of the fault zone. A wider shear-zone of a few kilometers width evolved, in which considerable anti-clockwise rotation of folds occurred. Kinematic analysis of these folds shows that these rotational effects are again dominantly rigid-body rotations. Assuming rotations are merely caused by simple-shear deformation overestimates the amounts of strain. A better way to deal with simple-shear deformation is to compare observed shortening caused by folding with the magnitude of rotation of fold-hinges. (C) 2002 Elsevier Science Ltd. All rights reserved.