Pliocene volcanic rocks of the Coso Range, Inyo County, California

Journal Article · Wed Jan 01 00:00:00 EST 1986 · U.S. Geol. Surv., Prof. Pap.; (United States)

OSTI ID:5360678

Novak, S W; Bacon, C R

Major volcanic episodes occurred in the Coso Range at about 6 m.y., 4-2.5 m.y., and later than 1 m.y. Petrographic features, such as quartz xenocrysts in basalt, sieved plagioclase phenocrysts, broad compositional ranges of phenocrysts within single samples, and occurrence of commingled bombs and lava flows, indicate that many of the intermediate-composition rocks formed by mixing of basaltic magma with silicic material. A large volume, highly silicic center near Haiwee Ridge evolved 3.1-2.5 m.y. ago. This system erupted high-silica rhyolite air-fall and ash-flow tuff and in its later stages rhyodacite lava flows. The evolution of the Coso volcanic field, from early basalt to polygenetic intermediate-composition volcanoes to a comparatively large-volume silicic center, is thought to reflect systematic changes in the least principal stress (S/sub 3/) and the related tectonic extension rate. Beginning about 4 m.y. ago, basalt was erupted onto a surface of little relief, ponding in a shallow north-trending basin. Intermediate-composition magma was produced mainly between 3.5 and 3.3 m.y., at a time when S/sub 3/ may have decreased and the extension rate increased. Thus, Pliocene volcanism progressed through a sequence of compositions and eruptive patterns that reflect the transition from tectonic stability to extension.

• OSTI ID: 5360678
• Journal Information: U.S. Geol. Surv., Prof. Pap.; (United States), Vol. 75:1383
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
CALIFORNIA
VOLCANIC REGIONS
GEOLOGIC HISTORY
VOLCANIC ROCKS
PETROGRAPHY
BASALT
COSO HOT SPRINGS
GEOCHEMISTRY
MAGMA
MAGMATISM
MIXING
PLIOCENE EPOCH
SILICATE MINERALS
TECTONICS
CENOZOIC ERA
CHEMISTRY
FEDERAL REGION IX
GEOLOGIC AGES
IGNEOUS ROCKS
MINERALS
NORTH AMERICA
ROCKS
TERTIARY PERIOD
USA
150201* - Geology & Hydrology of Geothermal Systems- USA- (-1989)