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Book Chapter

Shallow-Level Plutonic Complexes in the Eastern Sierra Nevada, California, and Their Tectonic Implications

Richard A. Schweickert
Richard A. Schweickert
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January 01, 1976

Several related sequences of plutonic and metavolcanic rocks of probable Early Jurassic age occur between Lake Tahoe and Mono Lake in the eastern Sierra Nevada and Sweetwater Range, California. The plutons solidified at very shallow levels; some broke through to the surface to erupt compositionally similar pyroclastic rocks and lava flows. In many respects, the more felsic plutons resemble Tertiary epizonal plutons in the Northern Cascade Mountains.

The pre-Cretaceous volcano-plutonic complexes are part of a terrane of shallow-level mafic and felsic intrusions and remnants of metamorphosed sedimentary and volcanic rocks, all of probable Late Triassic to Middle Jurassic age, that extends the length of the Sierra Nevada in eastern California and Nevada. Felsic plutons of this general age typically have seriate textures and are moderately metamorphosed. They form a low-quartz and high-K2O group that is modally and chemically distinct from Upper Jurassic and Cretaceous plutons that occur locally among them and that also form the main expanse of the Sierra Nevada batholith to the west. The extent and arrangement of this terrane suggest that it is part of an Andean-type magmatic arc that developed between Late Triassic and Middle Jurassic time in eastern California and western Nevada, generally east of the site of the second, much larger, magmatic arc that developed mainly in Cretaceous time. Triassic and Jurassic subduction linked to the evolution of this older arc probably occurred in the foothills of the western Sierra Nevada. Later subduction of the Franciscan Complex in the California Coast Ranges was linked to Sierra Nevada plutonic activity that occurred after Middle Jurassic time.

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