Crustal Structure of the Salton Trough : Constraints from Gravity Modeling.



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The Salton Trough (ST) in the southwestern U.S. is the northward extension of the Gulf of California extensional province. It consists of a series of deep, complex pull-apart structures that formed at different stages of rift evolution. The ST formed as a result of strike-slip motion between the Pacific and North-American plates after Farallon plate subduction ceased and the San Andreas Fault system developed. Pull-apart basins formed at step-overs along the strike-slip faults. Further south, the pull-apart basins evolved into short seafloor spreading segments in the Gulf of California. Different basins within the ST and further south in the Gulf of California are at different stages of evolution. The nature of the underlying crust depends on the stage of evolution of the basin. There is debate on the nature of the crust below the Salton Trough; models range from oceanic crust to highly extended continental crust.

This study uses gravity and magnetic anomaly data to better understand the type of rock that underlies the ST area. These data, in conjunction with supplementary data such as Moho depth from refraction studies, sediment thickness, depth to the lithosphere-asthenosphere boundary, and other geologic data are used to produce 2D gravity models. Moho depth in the study area ranges from 22 – 43 km. The sedimentary layers were modeled with densities of 2.4-2.5 kg/m3 and 2.57-2.9 kg/m3 for other crustal layers, to produce models that reveal a thick sedimentary package (3-5 km) in the Salton Trough area, as well as basaltic igneous intrusions with density 3.0 kg/m3 in the crust.

The models matched for oceanic, continental, and transitional crustal types. However, I propose that the thick sediment package in the basin, the basin’s structure, and the presence of basaltic intrusions indicate that the crust underneath the pull-apart basins of the Salton Trough is of transitional type. Continental rupture has not evolved into a mature spreading ridge.



Salton Trough