Cenozoic volcanic geology and probable age of inception of basin-range faulting in the southeasternmost Chocolate Mountains, California

Journal Article · Wed Feb 01 00:00:00 EST 1978 · Geol. Soc. Am., Bull.; (United States)

DOI:https://doi.org/10.1130/0016-7606(1978)89<251:CVGAPA>2.0.CO;2· OSTI ID:5637780

Crowe, B M

A complex sequence of Oligocene-age volcanic and volcaniclastic rocks form a major volcanic center in the Picacho area of the southeasternmost Chocolate Mountains, Imperial County, California. Basal-volcanic rocks consist of lava flows and flow breccia of trachybasalt, pyroxene rhyodacite, and pyroxene dacite (32 My old). These volcanic rocks locally overlie fanglomerate and rest unconformably on pre-Cenozoic basement rocks. South and southeast of a prominent arcuate fault zone in the central part of the area, the rhyolite ignimbrite (26 My old) forms a major ash-flow sheet. In the southwestern part of the Picacho area the rhyolite ignimbrite interfingers with and is overlain by dacite flows and laharic breccia. The rhyolite ignimbrite and the dacite of Picacho Peak are overlapped by lava flows and breccia of pyroxene andesite (25 My old) that locally rest on pre-Cenozoic basement rocks. The volcanic rocks of the Picacho area form a slightly bimodal volcanic suite consisting chiefly of silicic volcanic rocks with subordinate andesite. Late Miocene augite-olivine basalt is most similar in major-element abundances to transitional alkali-olivine basalt of the Basin and Range province. Normal separation faults in the Picacho area trend northwest and north parallel to major linear mountain ranges in the region. The areal distribution of the 26-My-old rhyolite ignimbrite and the local presence of megabreccia and fanglomerate flanking probable paleohighs suggest that the ignimbrite was erupted over irregular topography controlled by northwest- and north-trending probable basin-range faults. These relations date the inception of faulting in southeasternmost California at pre-26 and probably pre-32 My ago. A transition of basaltic volcanism in the area is dated at 13 My ago. 9 figures, 2 tables.

• Research Organization: Los Alamos Scientific Lab., NM
• OSTI ID: 5637780
• Journal Information: Geol. Soc. Am., Bull.; (United States), Vol. 89
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
GEOLOGIC FAULTS
PETROLOGY
STRATIGRAPHY
VOLCANIC ROCKS
AGE ESTIMATION
GEOCHEMISTRY
CENOZOIC ERA
EXPERIMENTAL DATA
GEOLOGY
ISOLATED VALUES
LAVA
MAPS
CHEMISTRY
DATA
DATA FORMS
GEOLOGIC AGES
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
INFORMATION
NORTH AMERICA
NUMERICAL DATA
ROCKS
USA
WESTERN REGION
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