INTEGRATED AND COMPARATIVE GEOPHYSICAL STUDIES OF CRUSTAL STRUCTURE OF PULL-APART BASINS: THE SALTON TROUGH AND DEATH VALLEY, CALIFORNIA REGIONS

We are constructing new crustal scale models of two unique pull apart basins, the Salton Trougth (ST) of south west California, which is inferred to be an incipient ocean basin, and Death Valley (DV) to the east of the ST, which is a highly extended continental basin. We are using receiver functions, controlled source seismic, gravity and magnetic data. The preliminary model suggests the Moho is 21 km deep south of the Salton Sea and deepens to 33 Km in the western region of the ST, while in the DV it is 26 km deep in the central part and deepens to 32 km on either sides. One significant difference between the two areas is the density of the lower crust, which is 2950 kg/m3 for the ST and 2750 kg/m3 for the DV. Sedimentary rocks and metamorphosed sedimentary rocks in the DV are thick and reach a depth of 15 km, while in the ST the depth of sedimentary rocks and metamorphosed sedimentary rocks is 8-9 km. Magnetic anomaly sources are shallow in both regions; unlike the ST the anomalies in DV show higher amplitudes (= 420 nT), compared to 250 nT in the ST. Magnetic profile of the DV shows undulation all over the region especially in the south western part. This is an indication of very shallow basement in the area. Magnetic profiles of the ST are almost flat. The ST has one of the highest seismicity and deformation rates in the southern California the relation plate motion is 50 mm/yr. Right lateral shear strain in the DV is 12 mm/yr, together with 10 mm/yr E-W extension. Heat flow is high in the ST and reaches > 200 mW/m2 in the Imperial Valley area southern of Salton Sea. Heat flow measurement for the DV are in progress, but expected to be less than the ST.