Evidence of upper-mantle processes related to continental rifting versus oceanic crust in the Gulf of California

S U M M A R Y Receiver functions from teleseismic events, recorded by stations around the Gulf of California, are used to map the upper-mantle seismic discontinuities. We observe a mean transition zone thickness comparable to the global average for most of the region. A low-velocity layer is detected above the 410 discontinuity that varies in thickness along the Gulf of California. The 660 discontinuity shows complex waveforms south of latitude 30◦N as a result of the phase change of garnet to perovskite. Within the transition zone, a complex behaviour of the receiver functions is observed mainly at the southern end of the Gulf. The north–south variations of this zone are likely associated with a slab window at the northern Gulf, resulting from the cessation of subduction of the Farallon plate 12 Ma, and the subduction of the Guadalupe and Magdalena microplates at the southern end, resulting in a hydrated upper mantle. Our results suggest that change in rifting styles occurring along the Gulf of California mirrors deeper processes in the upper mantle.