A reappraisal of seafloor spreading lineations in the Gulf of California: Implications for the transfer of Baja California to the Pacific plate and estimates of Pacific-North America motion

An analysis of seafloor spreading lineations in the southern Gulf of California demonstrates that divergence of the Baja peninsula from North America since 3.6 Ma has been significantly slower than Pacific-North America (PA-NA) motion estimated solely from closures of global plate circuits. This discrepancy remains unchanged or increases with modifications to the plate circuits and kinematic data used to predict PA-NA motion, suggesting that it arises from the probably-incorrect assumption that Baja California has been rigidly coupled to the Pacific plate since 3.6 Ma. A similar to 15% increase in seafloor spreading rates in the southern Gulf after similar to 1 Ma could have been caused by a transfer of motion along faults west of Baja California to the modern-day plate boundary, or alternatively could indicate a recent speedup in PA-NA motion. Both interpretations imply that PA-NA motion is now 4+/-2 mm yi(-1) (2 sigma) faster than predicted by the 3.16-Myr-average NUVEL-1A model.