HR: 11:05h
AN: S31H-04    [PDF]
TI: The Telltale Moho and Novel Views of the Crust and Upper Mantle in the Gulf of California
AU: * Persaud, P
EM: ppersaud@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: P\'{e}rez-Campos, X
EM: xyoli@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Clayton, R W
EM: clay@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: One of the outstanding questions about the Gulf of California remains: what is the composition of the crust; more specifically, is there any continental crust beneath the thick sedimentary layer in the Gulf or is it all new oceanic crust. An answer to this question places bounds on the strength and the mechanical behavior of this actively extending region and may help explain the curious lack of seafloor spreading despite 300 km of upper crustal separation over the last 6 myrs. We use receiver functions (RFs) from teleseismic events recorded by the NARS-Baja array to map crustal thickness in the margins of this newly forming ocean basin and use these results to constrain the amount of continental crust within the Gulf. The RFs show clear P-to-S wave conversions from the Moho beneath the stations. The delay times between the direct P and P-to-S waves indicate thinner crust closer to the Gulf along the entire Baja California peninsula. This approximately W-E shallowing in Moho depths is significant with extremes in crustal thickness of ${\sim}$~20 and 40 km. A similar trend on the opposite side of the rift may be established with better spatial data coverage. Similar results have, however, been obtained at the northern end of the peninsula by previous workers, who proposed a mechanism of lower crustal flow associated with rifting in the Gulf Extensional Province for thinning of the crust. We also interpret the Gulf-ward thinning of the crust as related to ductile flow in the lower crust during the early stages of rifting and further suggest that the amount of lower continental crust within the Gulf itself is significant. Besides the conversion from the Moho, a number of interesting lithospheric features above and below the Moho are also prominent in the RFs. These may be an indication of isotropic dipping layers or anisotropic layers. In addition, we observed P-to-S conversions from the 410 and 660 upper mantle discontinuities and were able to map these features over a wide area. In contrast to the 660, which is relatively flat lying and continuous, there is evidence of some topography associated with the 410 discontinuity.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8109 Continental tectonics--extensional (0905)
SC: Seismology [S]
MN: 2003 Fall Meeting