Effect of 3-D fault geometry on synextensional sedimentation around a Miocene metamorphic core complex, eastern California–western Arizona, USA

Abstract Mid-Miocene sedimentation across the highly extended Colorado River extensional corridor (CREC) demonstrates how the 3-D geometry and evolution of the regional detachment fault system and overlying listric normal and oblique-slip faults controlled the age, distribution, and fill of coeval supradetachment basins. Basin development followed a temporal evolution in the regional slip direction (NE), with minimal, oldest, siliciclastic sedimentation in the breakaway region (SW) and younger deposits farther northeast, all in the hanging wall of the detachment fault system. The thickest (≤2.5 km) and longest-lived deposition was focused in the center of the CREC, adjacent to the Chemehuevi core complex. Proximal alluvial fan deposition dominated, with lesser distal fan, braidplain, and lacustrine sedimentation. Megabreccia, or rock avalanche, deposits are locally abundant. Syntectonic basins were small (less than a few kilometers across) and isolated from each other, hosting locally derived debris and rapid vertical and lateral facies changes. Basin location, shape, and depositional history were determined by the geometry of the corrugated detachment fault below, permitting thick accumulations in troughs parallel to regional extension (SW-NE). Displacement on listric normal faults in the detachment system hanging wall created elongate half-graben basins perpendicular to regional extension (NW-SE). Drag on oblique-slip faults bordering tilted hanging wall blocks created accommodation space and folded and displaced strata during and after deposition. Depocenters moved as faulting continued. New 40Ar/39Ar ages on interbedded volcanic deposits show sedimentation occurred between ca. 16 Ma and 14 Ma. 3-D analysis of these early synrift supradetachment basins contributes to understanding strata buried deep below nonvolcanic passive continental margins.