Seismic structure of the southern Gulf of California from Los Cabos block to the East Pacific Rise

Multichannel reflection and coincident wide-angle seismic data collected during the 2002 Premier Experiment, Sea of Cortez, Addressing the Development of Oblique Rifting (PESCADOR) experiment provide the most detailed seismic structure to date of the southern Gulf of California. Multichannel seismic (MCS) data were recorded with a 6-km-long streamer, 480-channel, aboard the R/V Maurice Ewing, and wide-angle data was recorded by 19 instruments spaced every similar to 12 km along the transect. The MCS and wide-angle data reveal the seismic structure across the continent-ocean transition of the rifted margin. Typical continental and oceanic crust are separated by a similar to 75-km-wide zone of extended continental crust dominated by block-faulted basement. Little lateral variation in crustal thicknesses and seismic velocities is observed in the oceanic crust, suggesting a constant rate of magmatic productivity since seafloor spreading began. Oceanic crustal thickness and mean crustal velocities suggest normal mantle temperature (1300 degrees C) and passive mantle upwelling at the early stages of seafloor spreading. The crustal thickness, width of extended continental crust, and predicted temperature conditions all indicate a narrow rift mode of extension. On the basis of upper and lower crust stretching factors, an excess of lower crust was found in the extended continental crust. Total extension along transect 5W is estimated to be similar to 35 km. Following crustal extension, new oceanic crust similar to 6.4-km-thick was formed at a rate of similar to 48 mm a(-1) to accommodate plate separation