Tectonic and magmatic processes on the East Pacific Rise
The East Pacific Rise was discovered during the famous Challenger expedition in 1875 on its passage from Tahiti to Valparaiso (Murray, 1895), and was investigated by marine geologists in 1904 aboard the RV Albatross (Agassiz, 1906) and in 1928 aboard the RV Carnegie (Soule, 1944). The original soundings were laborious, with hemp ropes used to dredge and sound. Later, wire rope was used, and the major advance to echo sounders was made aboard Carnegie, although these early measurements were often inaccurate (Menard, 1964). Referred to as the “Albatross Plateau” and the “Easter Island Ridge” during the early years of exploration (e.g., Ewing and Heezen, 1956; Menard, 1960), the East Pacific Rise (EPR) acquired its present name during the mid-1950s (H. W. Menard, 1960, personal communication, 1985).
During the 1950s and 1960s, evidence was gathered that indicated that the EPR was a major bathymetric structure extending from the Gulf of California at least as far south as the Eltanin Fracture Zone in the Pacific, and that it was tectonically and volcanically active (Menard, 1960). Heat-flow measurements showed that the flux of heat was considerably higher than the average of the ocean basins (Von Herzen, 1959; Von Herzen and Uyeda, 1963); fresh, young pillow basalts were dredged from the EPR axis (Engel and Engel, 1964); seismic activity was found to be discontinuous but high (Gutenberg and Richter, 1954); and enormous fracture zone escarpments were mapped that intersected its axis at a high angle (Menard, 1955,1964). The greatest enigma at the time was the highly linear magnetic anomaly pattern measured by Mason and Raff (1961), which was later used to show that the EPR was part of a major spreading center system of mid-ocean ridges (Vine and Matthews, 1963).
Figures & Tables
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.