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Petrogenetic relationships of the Pliocene Barker Pass volcanic debris-avalanche deposits in northern Sierra Nevada, California
McLain, William Guthrie
McLain, William Guthrie
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2023-12-18
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Abstract
he Pliocene Barker Pass volcanic debris-avalanche deposits unconformably overly Cretaceous and older rocks in the northern Sierra Nevada in California. Basaltic to dacitic megablocks associated with these deposits are believed to derived from the same source volcano and erupted from a single catastrophic eruption. Geochemical data reveals a distinct compositional gap in SiO2 between basaltic andesites and high-silica andesites and dacites suggesting magma mixing as a primary magmatic mechanism. Additional petrographic evidence and plots of compatible and incompatible trace element data further supports this. Distinctive blue-grey to white, holocrystalline high-silica andesites and dacites show very similar trace-element contents and are inferred to be associated from a single igneous unit. A megablock composed of basaltic volcaniclastic material underlain by high-silica andesite/dacite forms a deformed laccolith-like structure suggesting the high-silica andesites/dacites represent one or more hypabyssal bodies intruded into the source volcano, which may have caused large-scale failure.
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Geology
Volcanic debris-avalanche
Ancestral Cascade arc
Volcanic debris-avalanche
Ancestral Cascade arc
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Geological Sciences