Field, petrological and isotopic studies of the intrusive complex of San Jacinto Mountain

Abstract

Underlying much of the San Jacinto Mountains is crystalline basement of the Peninsular Ranges Batholith. This batholith is part of the Mesozoic circum-Pacific plutonic belt which includes the batholiths of Peru and Chile in South America, and the Sierra Nevada, Idaho, and Coast Range Batholiths of western North America; it extends for some 1500 kilometres (900 miles) along the spine of the peninsula of Baja California (Fig. 1). An understanding of the genesis of these immense volumes of intermediate to felsic igneous rock is crucial to the study of geologic problems as different as the nature and origin of the continental crust and the origin of many ore deposits. Of this great string of batholiths, only the Peninsular Ranges Batholith has a demonstrated simple emplacement history; north of the international border the batholith was emplaced over a 40 m.y. period from more than 120 m.y. to 80 m.y. ago in a single magmatic episode (Silver and others, 1975, 1979). Such a simple history makes the Peninsular Ranges Batholith an ideal area for both the study of batholith development, and for the testing of assumptions inherent in the application of many modern geochemical techniques.

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