CERRO PRIETO AND ITS RELATION TO THE GULF OF CALIFORNIA SPREADING CENTERS

The Cerro Prieto geothermal field is located in the Mexicali Valley, B aja California. Tectonically, this northern part of the Gulf of Califo rnia has been classified as a spreading center, within a transitional area of oceanic to continental conditions. Thermal, geologic-tectonic and magnetic evidence has been used to postulate the existence of a he at source in the area that is associated with magmatic processes, simi lar to those that occur in a typical oceanic spreading center. Based o n the petrography and geochemistry of the volcanic rocks obtained duri ng the drilling of the wells in the geothermal field, the rocks were c lassified as: basalts, basalt-andesites, andesites and dacites. The pe trogenetic model of the intrusive volcanic bodies that is proposed for the area of crustal spreading at Cerro Prieto is different from the o ne proposed for a typical oceanic spreading center, as is the case for the spreading centers located in the Gulf of California. This region of continental basaltic magmatism is complex due to: a) chemical compo sition and mineralogy of the mantle source, b) partial melting of the parent magma, c) magma segregation depth, and d) extension of the frac tioned crystallization and the melting processes during the storage of the magma in the upper levels of the magmatic chamber.