Abstract Title: Comparing and contrasting extension styles in the Southern Gulf 
of California and the Basin and Range

Abstract Author(s): Sutherland, Fiona (UCSD)-Harding, Alistair (UCSD)-Kent, 
Graham (UCSD)  

Abstract: The Basin and Range and the southern Gulf of California have markedly 
different styles of extension; the former being a wide, asymmetric zone of 
extension and the latter being a narrow, possibly symmetric rift that quickly 
culminated in seafloor spreading. Extension in the Gulf of California began ~12 
Ma; rifting was initiated at the mouth of the Gulf at the now inactive 
Magdalena spreading ridge about 5 Ma. The continental extension seems to have 
been largely accommodated by normal faulting, and seismicity suggests that some 
of these faults remain active. Our dataset consists of a ~880 km transect of 
refraction seismic data spanning the Alarcon Basin with 64 ocean-bottom and 
land seismometers along with ~600 km of multi-channel seismic data. The 
velocity structure of the crust and uppermost mantle derived from the 
refraction data, shows typical oceanic crustal structure bounded on either side 
by slower continental crust with a more complicated velocity structure. The 
rift appears non-volcanic from both the MCS and velocity model and the 
continent-ocean transition is narrow (~20km). Both margins seem to have about 
180 km of extended continental crust, which suggests rift symmetry, but the 
southern margin includes a failed rift, complicating the issue. Moreover, a 
suggested shallowing of the Moho on the northern margin in the velocity model 
could point to another failed rift.