Crustal thickness variations in the margins of the Gulf of California from receiver functions
Receiver functions (RFs) from teleseismic events recorded by the NARS-Baja array were used to map crustal thickness in the continental margins of the Gulf of California, a newly forming ocean basin. Although the upper crust is known to have split apart simultaneously along the entire length of the Gulf, little is known about the behaviour of the lower crust in this region. 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. The thinner crust is associated with the eastern Peninsular Ranges batholith (PRB). Crustal thickness is uncorrelated with topography in the PRB and the Moho is not flat, suggesting mantle compensation by a weaker than normal mantle based on seismological evidence. The approximately W–E shallowing in Moho depths is significant with extremes in crustal thickness of ∼21 and 37 km. Similar results have been obtained at the northern end of the Gulf by Lewis et al., who proposed a mechanism of lower crustal flow associated with rifting in the Gulf Extensional Province for thinning of the crust. Based on the amount of pre-Pliocene extension possible in the continental margins, if the lower crust did thin in concert with the upper crust, it is possible that the crust was thinned during the early stages of rifting before the opening of the ocean basin. In this case, we suggest that when breakup occurred, the lower crust in the margins of the Gulf was still behaving ductilely. Alternatively, the lower crust may have thinned after the Gulf opened. The implications of these mechanisms are discussed.
© 2007 The Authors. Journal compilation © 2007 RAS. Accepted 2007 February 16. Received 2006 December 22; in original form 2006 November 28. We thank Gene Ichinose and Harold Magistrale for providing us with the results from Ichinose et al. (1996) and Lewis et al. (2001), respectively, and Victoria Langenheim for providing the magnetic potential results from Langenheim & Jachens (2003). Supported by NSF grants EAR-0111650. Contribution no. 8974, Division of Geological and Planetary Sciences, California Institute of Technology. Partial funding for X. Pérez-Campos from UNAM-PAPIIT grants IX1210004 and IN119505–3.
Published - PERgji07.pdf