ABSTRACT: 3-D Block Rotation in the West Transverse Ranges: the Key to Structure History and Basin Development

Oona Scotti, Amos Nur

Block rotation is widespread in regions of distributed shear. As rigid block-faulted domains rotate, gaps open up along their boundaries and sedimentary basins may develop. The evolution and the geometry of these basins is controlled by the slip history of the faults that bound them. To unravel their history, a three-dimensional (3-D) model was developed that combines the kinematics of block rotation with the mechanics of faulting.

As an example, we present a 3-D computer simulation for the history of rotation of the west Transverse Ranges domain, southern California. A set of preexisting faults, striking north-northeast, is allowed to slip and rotate in accordance with known friction criteria. Rotation is assumed to occur in the strike-slip stress regime. The principal stress axes are assumed fixed in the present-day orientation throughout the deformation. Therefore, as faults slip and blocks rotate, the sense of motion along the faults changes. This simulation predicts, in agreement with the observations, an initial period of normal motion along the reactivated faults. Upon fault slip and block rotation the same faults go through a phase of strike slip. With further slip and rotation they eventually become the east-west-striking oblique reverse faults that characterize the present-day tectonics of this domain.

The model shows that a single set of faults can experience both dip-slip and strike-slip motion throughout its deformation history within a strike-slip stress regime. It is not necessary to appeal to complex and arbitrary changes in the orientation of the stress field. Only by combining a 3-D block rotation model with structural and paleomagnetic data may it be possible to unravel the complex tectonics of distributed deformation and basin evolution.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990