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Title: Tectonic implications of space-time patterns of Cenozoic volcanism in the Palo Verde Mountain volcanic field, southeastern California

Variations in Cenozoic volcanism in the western United States are believed to correlate closely with changes in tectonic setting. A transition in volcanic association from calc-alkaline to fundamentally basaltic volcanism and subsequent crustal extension, appears to have coincided temporally with the initial collision of the East Pacific Rise with the continental margin trench off western North America, between 28 and 25 Ma. The volcanic stratigraphy of the Palo Verde Mountain volcanic field is broadly similar to other volcanic centers in southeastern California and can be divided into tripartite regional stratigraphy. A basal sequence of andesitic to rhyolitic lava flows, plugs, domes, and extensive pyroclastic deposits rests unconformably on pre-Cenozoic basement rocks. The basal sequence is intruded by cogenetic Cenozoic plutonic rocks and overlain by basaltic to rhyolitic lava flows, dikes, and a second widespread assemblage of pyroclastic deposits, cumulatively referred to as the silicic sequence. The youngest volcanic rocks of the field include olivine basalt flows and breccia which occur at scattered localities in the Palo Verde Mountains. The age, stratigraphy, and chemistry of the intermediate and basaltic composition volcanic rocks broadly supports previously cited volcanic-tectonic models, if modified to incorporate modern plate reconstruction theory. This modification results in amore » southeast migration of the transition to basaltic volcanism to southeastern California occurring significantly later in time than the previously cited ages of transition. Moreover, this southeast migration of the volcanic transition is coincident with the inception of Basin and Range faulting and the initiation of movement on the San Andreas fault south of the Transverse Ranges, corresponding to the southward migration of the Pacific-Cocos Ridge.« less
Authors:
Publication Date:
OSTI Identifier:
5424519
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: Thesis (Ph. D.)
Publisher:
Univ. of California,Davis, CA
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CALIFORNIA; PLATE TECTONICS; CENOZOIC ERA; STRATIGRAPHY; VOLCANISM; FEDERAL REGION IX; GEOLOGIC AGES; GEOLOGY; NORTH AMERICA; TECTONICS; USA 580201* -- Geophysics-- Seismology & Tectonics-- (1980-1989)