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Transforms of the eastern central Pacific

By
Paul J. Fox
Paul J. Fox
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David G. Gallo
David G. Gallo
Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882
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Published:
January 01, 1989

The regional maps of the northern Pacific Basin by Menard and Dietz (1952) established that offsets in the California margin, first documented by Murray (1939) and Shepard and Emery (1941), could be traced westward as bands of grossly irregular topography for more than 2,000 km. Typically these swaths of disturbed terrain separated regions of different depths and were made up of troughs, ridges, escarpments, and seamounts. This distinctive terrain was called a fracture zone, and continued reconnaissance mapping efforts by Menard and colleagues identified a family of subparallel fracture zones that could be traced as lineaments for thousands of kilometers (Menard, 1955; Menard and Fisher, 1958). The straightness of these fractures, their continuity along strike, and the fact that they separated terrain of contrasting depths as well as distinctive and correlatable north-south-trending magnetic anomalies (Mason, 1958; Vacquier and others, 1961) suggested that fracture zones were the product of faulting, with the dominant displacement having been horizontal.

The recognition of a world-girdling and seismically active Mid-Oceanic Ridge system established that this feature was the major morphotectonic element of the ocean basins (Ewing and Heezen, 1956; Heezen, 1957). Models of ridge formation proposed that the ridge axis was the site of extension, stretching, and volcanism (Heezen, 1960; Menard, 1960; Hess, 1962). The long, straight scars of the fracture zones that frequently offset the axis of the Mid-Oceanic Ridge were thought to be large strike-slip faults that broke the ridge into large blocks with differential motion taking place along the length of the fault. Wilson (1965) proposed that major faults, orogenic belts, trenches, and the Mid-Oceanic Ridge were not isolated features but are part of a continuous network of mobile belts that encircle the Earth. In this model, the portion of a fracture zone that links the extensional regions of the two offset ridge axes was called a transform fault. The key prediction of the model was that the relative motion along the transform would be opposite to that predicted if the ridge axis was offset along a transcurrent fault. The kinematic character of fracture zones was established when first-motion studies of earthquakes along several ridge-transform-ridge plate boundaries were shown to have motions in agreement with Wilson’s model (Sykes, 1967).

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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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