Geology and tectonic history of the Gulf of California
The Gulf of California, or Sea of Cortez, is an arm of the Pacific 100 to 150 km wide between the Mexican mainland and the 1,200-km-long peninsula of Baja California. The gulf waters flood part of a structural depression that was formed by detachment and oblique separation of the peninsula from the continent, and is occupied by the Pacific-North America plate boundary. The gulf structural province, defined as the complex trough left in the wake of the northwest-drifting peninsula, extends beyond the hydrographic limits of the gulf. In the south, the continental margin conjugate to the rifted tip of Baja California is in the vicinity of the Tres Marias Islands, well outside the gulf proper. Marine geologic and geophysical data across the East Pacific Rise in this "mouth of the gulf' region are reviewed because they prove to be critical for determining the initiation and tectonic evolution of the entire province. At the northern "head of the gulf," the delta of the Colorado River has extended across the structural depression and isolated the Salton Trough, part of the gulf province now exposed as dry land (except for the artificial Salton Sea), though much of it is below sea level. The Colorado delta is bisected by the Untied States-Mexico border; the gulf north of the "midriff islands," which congest it near lat 29°N, is politically part of the internal waters of Mexico, and the remainder is within the exclusive economic zone of Mexico.
Figures & Tables
The Eastern Pacific Ocean and Hawaii
This new synthesis includes a section on plate kinematics, documenting the basis for a new interpretation of the magnetic anomaly patterns. It also includes: six chapters on various aspects of tectonics, petrologic characteristics, and hydrothermal processes of active ridges from the Galapagos Rift to the Juan de Fuca Ridge; a section on mid-plate volcanism, including the Hawaii-Emperor chain; five chapters on various aspects of northeastern Pacific sedimentary regimes; and nine chapters on the geology of the Pacific continental margin from the Aleutians to Guatemala, seen from the perspective of marine geology. Three separate oversize plates illustrate the bathymetry of the northeast Pacific; two more on the same base show distribution of sediment samples and types and magnetic anomaly data and tectonic interpretations; and others include a synthesis of the geology and bathymetry of the Hawaiian Islands, details of bathymetry along parts of the East Pacific Rise, and a major seismic profile across the Pacific margin of Guatemala.