THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS
Distinguished Lecture Tour

Abstract: New Global Tectonics Related to West Coast Structure

By

Mason L. Hill
Esso Production Research Company

A current review of evidence, patterns and history of sea-floor spreading in the NE Pacific; a summary of the character and history of the San Andreas System of deformation; and some geologic implications of their relationships to a worldwide tectonic scheme.

The NE trending E Pacific Rise enters the Gulf of California from the Pacific Ocean. The essentially contemporaneous and parallel Gordo and Juan de Fuca ridges lie off the coasts of Northern California and Oregon. According to the New Global Tectonics, the SE trending San Andreas zone is a transform fault which connects these two segments of the World Rift System. Furthermore, according to the rigid-plate concept, the adjoining oceanic and continental blocks are moving away from these oceanic ridges, and post each other along the San Andreas, in NW and SE directions. On the other hand, according to the new concepts, a portion of the sea-floor magnetic pattern and the NE Pacific fracture zones (transform faults) indicate an earlier (10-30 million years ago) N-S oceanic ridge trend accompanied by E-W crustal extension. However, since the present crustal dynamics typified by the San Andreas System of deformation has been operative for a much longer time (at least 80 and possible for more than 135 million years), some doubt is cast on the interpretation of the San Andreas as a geologically young transform fault. These and other contrasting geophysical data and interpretations from the oceans tested against geologic data and interpretations from the continents serve to emphasize tectonic discrepancies. This approach, versus searching for data and interpretations which tend to confirm the New Global Tectonics, may best stimulate both continental-based geologists and ocean-based geophysicists to obtain critical information leading to the true world tectonics.

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