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Franciscan Complex, Coast Range ophiolite and Great Valley sequence: Pacheco Pass to Del Puerto Canyon, California

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Abstract

This field trip covers part of the Diablo Range and adjacent San Joaquin Valley of central California (Fig. 1 ). The core of the range is made up of rocks of the Franciscan Complex, flanked by Coast Range ophiolite (CRO) and Great Valley sequence (GVS). The Franciscan Complex in this area consists of deformed and metamorphosed sedimentary and volcanic rocks containing fossils of Late Jurassic to Late Cretaceous age. These rocks are believed to represent an accretionary wedge that was subducted to depths of 12-20 mi (20-30 km). The Middle to Late Jurassic CRO represents a slab of oceanic upper mantle and crust that was trapped between the Sierran magmatic arc and the Franciscan trench. The Upper Jurassic to Upper Cretaceous GVS is a thick accumulation of mudstone, sandstone, and con- glomerate that was deposited on the ophiolite in a forearc-basin setting. The objectives of this field trip are to examine good exposures of these three major units in order to better understand their sedimentary, igneous, and metamorphic histories, to examine some of the major faults bounding the units, and to gain an understanding of the tectonic history of this portion of the Coast Ranges.

Publication type Book chapter
Publication Subtype Book Chapter
Title Franciscan Complex, Coast Range ophiolite and Great Valley sequence: Pacheco Pass to Del Puerto Canyon, California
Year Published 1991
Language English
Publisher California Department of Conservation, Division of Mines and Geology
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 16 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Geologic excursions in northern California: San Francisco to the Sierra Nevada
First page 85
Last page 100
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