SPECULATIVE PROPAGATING RIFT SUBDUCTION ZONE INTERACTIONS WITH POSSIBLE CONSEQUENCES FOR CONTINENTAL-MARGIN EVOLUTION

As rifts propagate through oceanic plates, they must occasionally inte rsect subduction zones, unless subduction-related stresses are suffici ent to terminate propagation. If propagators do reach subduction zones , there are possible consequences for continental margin evolution, de pending on the geometry of propagation. For example, if the left-offse t propagators that approached the western North American continental m argin reached the Farallon-North America subduction zone and continued to propagate down the subducting Farallon plate, they would have tran sferred already-subducted Farallon lithosphere to the Pacific plate. B asal shear stresses between the resulting northwest moving parts of th e subducted slab and the overriding continent could have led to riftin g of the continental margin. The intersections of the only two left-of fset propagators that appear to have reached this margin correlate spa tially and possibly temporally with the initiation of the two most uni que Neogene geologic structures of the western North American continen tal margin, the Gulf of California and the Transverse Ranges, suggesti ng a possible causal relationship.