Pull-apart Basins and Sheared Margins: Insights from Geodynamic and Gravity Modeling

Rediet Abera and Jolante van Wijk

Pull-apart basins are strike-slip fault system controlled extensional sedimentary basins with a significant economic and tectonic importance, yet their formation has not been studied in as much detail as orthogonal rifts and rifted margins. The basins form deep depressions between two sub-parallel strike-slip fault segments, dip-slip or transfer faults bound the basin ends. The shape, size and structure of a pull-apart basin depend upon the segmented geometry of the master strike-slip fault system. After continent rupture, the sheared margins (such as Gulf of California) show large variation in structure over short distances along strike that are possibly inherited from the continental rift stage.

We use the general purpose finite element package Abaqus to study the formation of pull-apart basins. Our 3D models show how the shape and structure of the continental pull-apart basins depend on the geometry of the strike-slip discontinuity. In addition, the models show that a situation favorable for continental breakup develops when the segments of the strike-slip faults overlap and tensional stresses rotate to become perpendicular to the strike of the master faults. Based on these and previous modeling results and observations, we propose a new schematic evolutionary model for sheared margin formation. Gravity models of the Gulf of California margins and basins are developed to study the continent-ocean transition, thickness of the sediment layer, and crustal structure. Our crustal models differ from earlier (seismic) works. Conjugate margins are found to be asymmetric. The models constrained the oceanic crustal thickness and northward extent of oceanic crust.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013