The proposed work is to produce a high resolution image of the upper mantle velocity anomalies for a large area of the Gulf of California/Baja region. These images will define the extent of the subducted slab beneath the Baja California Peninsula and define where the mantle is upwelling beneath the Gulf of California. This region is of high interest to the MARGINS community and results from the study will be relevant to those studying the spatial and temporal variations in volcanism in the Gulf of California, and those trying to understand the tectonic history of Baja California. Broader Impacts The broader impacts include support of a graduate student and involvement of an undergraduate during the summer months. The results will be of interest to a broad community of geologists and geophysicists.
undertaken between researchers at Brown University and the University of Rhode Island was to onstruct a three-dimensional, high- resolution model of the shear-velocity structure of the crust and upper mantle beneath the Gulf of California Extensional Province (GEP) and neighboring Baja California. We hoped to image remnants of the subducted Farallon plate, search for evidence of lithospheric delamination beneath the Peninsular Range batholith, estimate thickness of the lithosphere, map regions of melt production in the upper mantle, and extend models of crustal thickness variations to areas that are not imaged by seismic refraction or receiver function studies. Overall, these observations will help us understand the processes involving in magma generation and rifting Baja California from the rest of the continent. Our proposed study addresses three of the overarching themes of the Rupturing Continental Lithosphere initiative of MARGINS by mapping variations in crustal thickness that have evolved through lithospheric stretching and spreading; by mapping apparent thickness of the mantle component of the lithosphere, including the subducted fragments of the oceanic lithosphere that were intimately involved in the rupture initiation process; and by imaging regions of anomalously low shear velocity in the mantle that correspond to probable regions of magma generation. The project found numerous what are thought to be stalled subducting lithospheric fragments along the western coast of North America from the southern tip of Baja California into northern California. The magma generation process in the Gulf of California has enlighted the full geoscience community on how oceanic crust is created and the forces at play near Mid-Ocean Spreading centers. We have also developed methods of representing 3D a-priori models built from vast geological and geophycisal data sets to advance towards a well-constrained 3D model much faster than beginning with a simple 1D model. Moreover, a number of earthquakes in the Gulf of California region were shown to have ruptured along strike past the end of the known fault trace indicating a continued extensional regime in the Gulf and a lengthening of the fault traces.
