Volcanism, structure, and geochronology of Long Valley Caldera, Mono County, California

摘要: Long Valley caldera, a 17- by 32-km elliptical depression on the east front of Sierra Nevada, was formed 0.7 m.y. ago during eruption Bishop tuff. Subsequent intracaldera volcanism included (1) aphyric rhyolite 0.68-0.64 resurgent doming caldera floor, (2) porphyritic hornblende-biotite from centers peripheral to dome at 0.5, 0.3, and 0.1 ago, (3) rhyodacite outer ring fractures 0.2 50,000 yr sequence that apparently records progressive crystallization subjacent chemically zoned magma chamber. Holocene rhyolitic phreatic eruptions suggest residual present in chamber as recently 450 ago. Intracaldera hydrothermal activity began least 0.3 widespread moat; it has since declined due self-sealing near-surface sediments zeolitization, argillization, silicification become localized reactivated northwest-trending Nevada frontal faults tap hot water depth.