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Book Chapter

Tectonic and magmatic processes on the East Pacific Rise

By
Ken C. Macdonald
Ken C. Macdonald
Department of Geological Sciences and Marine Science Institute, University of California at Santa Barbara, Santa Barbara, California 93106
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Published:
January 01, 1989

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).

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DNAG, Geology of North America

The Eastern Pacific Ocean and Hawaii

E. L. Winterer
E. L. Winterer
Scripps Institution of Oceanography La Jolla, California 92093
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Donald M. Hussong
Donald M. Hussong
University of Hawaii Department of Geology and Geophysics Honolulu, Hawaii 96822
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Robert W. Decker
Robert W. Decker
4087 Silver Bar Road Mariposa, California 95338
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Geological Society of America
Volume
N
ISBN electronic:
9780813754659
Publication date:
January 01, 1989

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