Evolution in plate tectonics; The Juan de Fuca Ridge
The boundary between the Pacific and Juan de Fuca Plates in the northeast Pacific Ocean is marked by a series of spreading centers (Fig. 1) and their connecting fracture zones (transform faults). The longest (490 km) of these, the Juan de Fuca Ridge, is bounded on the south by the Blanco Fracture Zone and on the north by the Sovanco Fracture Zone. Despite its relatively small size compared to other mid-ocean ridges, the Juan de Fuca has played a historic role in the development of plate tectonics, and is still one of the most intensively studied spreading centers in the world. The Juan de Fuca Plate, lying east of the ridge system, forms an actively convergent margin with the North American Plate. The Juan de Fuca spreading center is composed of a series of at least six ridge segments, 50 to 150 km long, which although generally spreading at a total opening rate of 6 cm/yr, display a remarkable diversity of ridge-axis morphology.
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.