The part of the Pacific covered in this volume contains a wide variety of constructional volcanic features: volcanic rises (Hess Rise), volcanic ridges (Cocos Ridge), large seamount chains (Line Islands, Pratt-Welker chain, the Fieberling Chain, and the Musician seamounts), small chains like those west of the Juan de Fuca Ridge, guyots, and many seamounts that are not members of linear chains but instead are distributed in patchy clusters or small groups or are isolated. In the eastern Pacific, unlike the western and south Pacific, volcanic topography is not dominated by large linear island and seamount chains (Menard, 1964). Instead, the most abundant seamounts of the eastern Pacific are clustered and isolated volcanoes. The purpose of this chapter is to discuss the characteristics, distribution, and origin of the volcanoes and groups of volcanoes in the eastern Pacific exclusive of the Hawaii-Emperor chain, which is discussed else-where (Clague, this volume).
Some of the volcanoes and linear groups of the eastern Pacific are probably of hotspot origin; most probably are not. The origin of many of these not-hotspot volcanoes is probably linked to mid-ocean ridge volcanism, but others may originate on old lithosphere far from active ridge crests. Oceanic volcanoes of non-hotspot character are almost certainly of several types, inasmuch as there are many tectonic environments in which a favorable combination of magma availability and plumbing systems can lead to the formation of volcanoes. These conditions may prevail for a variety of reasons in both near–ridge crest and off-ridge locations. The study of seamount volcanism thus contributes directly to solution of a variety of problems concerning the characteristics, origin, and evolution of oceanic lithosphere.
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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.