How sediment promotes narrow rifting: Application to the Gulf of California

If the gravitational stress changes related to crustal thinning are large enough to affect the mode of extension, then sedimentation should also affect that mode. We propose that the weight of sediments reduces the difference in crustal buoyancy forces caused by local crustal thinning, allowing a rift to extend more easily in a narrow rift mode. We examine the effect of deposition of large amounts of nonlocally derived sediment on extensional style using two-dimensional, regional-scale numerical experiments of extending thick continental crust with varied initial thermal conditions, geometries, rheological parameters, and sedimentation properties. Depending on initial model conditions, the onset of rifting in thick continental crust occurs in the narrow rifting, wide rifting, or core complex mode. With continued extension, all cases eventually transition to a narrow rifting mode. For a system in wide rift mode, moderate to fast sedimentation shortens the time needed to transition to a narrow rift. In the Gulf of California, changes in extensional style correlate with sediment thickness, with an earlier transition to narrow rifting in the north versus the south. We compare our model results to the extensional history of the Gulf of California, where sediments may have caused the northern and north central domain of the gulf (Delfin-Tiburon and Guaymas segments) to transition to narrow rifting before the south central domains (Alarcon segment). Citation: Bialas, R. W., and W. R. Buck ( 2009), How sediment promotes narrow rifting: Application to the Gulf of California, Tectonics, 28, TC4014, doi:10.1029/2008TC002394.