Abstract

Several features on the Cocos plate appear to be anomalous or of unclear origin. Specifically, the eastern extension of the Orozco Fracture Zone near lat 15°N has a northeast trend, which differs significantly from the nearly east-west motion of the Pacific and Cocos plates. Moreover, the Tehuantepec Ridge has a similar northeast strike and separates the deep Guatemala Basin on its southeast side from shallower crust to the northwest.

The origin of these features can be adequately described by a small change in Cocos-Pacific plate motion and a 20° reorientation of the East Pacific Rise. This reorientation is strongly substantiated by a “fanning” of magnetic anomaly lineations over the Cocos plate between the Orozco Fracture Zone and the Tehuantepec Ridge. The reconstruction assumes that the Tehuantepec Ridge is a relict fracture zone; this interpretation is supported by recent gravity models across the ridge. The Guatemala Basin is the result of older crust formed prior to a ridge-axis jump (Clipperton Ridge to East Pacific Rise) and the reorientation of the East Pacific Rise.

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