Subduction control on the curie isotherm around the Pacific-North America plate boundary in northwestern Mexico (Gulf of California). Preliminary results

Abstract

Spectral analysis of NAMAG magnetic data enabled us to estimate depths to the Curie isotherm along the Pacific-North America plate boundary. The estimated depths for the Gulf of California, and southern Baja California peninsula, correlate quite well with the depths to the Moho available from previous studies based on receiver function, and seismic refraction. In northernmost Baja California, and southwestern USA no correlation is observed between depths to the Curie isotherm and depths to the mantle obtained from receiver function analysis. Depths to the Curie isotherm are shallower. Along the coastal plains of Sonora and Sinaloa, differences between receiver function based Mantle depths and Curie depths are equally large. However, there is more consistency with depths established by seismic refraction studies. Four zones with shallow Curie isotherm are identified in southern Gulf of California (GS1, GS2, GS3, and GS4). GS1 is located at the Gulf of California mouth. The Alarcón rise is located between GS1 and GS2. Pescaderos Basin is located northwest of GS2. GS3 stretches from the Carmen Basin to the Farallón Basin. GS4 extends from Tiburón Island up to northern Guaymas Basin. Northernmost shallow Curie depth zone (GN1) comprises Upper and Lower Delfín Basins, as well as the Consag and Wagner Basins. A northern prolongation also covers Pinacate Volcanic center. The southern shallow Curie isotherm zones are associated with lithospheric-asthenospheric material upwelling zones. GN1 also includes a convective component related to the younger magmatism of the Pinacate Volcanic Field.Deeper Curie depths are found at southern Baja California peninsula, interpreted as associated with thicker continental or stretched crust. It is possible that the crust is underlain or underplated by magnetic oceanic crust as suggested by satellite magnetic anomalies centered at the Magdalena shelf. A contrasting pattern features northern Baja California: deep Curie zones to the west contrasting with relative shallower Curie isotherm areas to the east. The prolongation towards the peninsula of the extinct Shirley transform fracture zone roughly separates the two domains observed along the peninsula, and suggests that the Curie isotherm along the peninsula is controlled by differences subduction of the Guadalupe and Magdalena microplates. Major differences pointed out between northern and southern Gulf of California might indicate that subduction also played a key role at the beginning of the opening of the Gulf of California, however, currently, the Curie pattern is controlled by the rifting processes (shallow Curie zones correlating quite well with the rift basins and the lithosphere-asthenosphere upwelling material).