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Rhyolite thermobarometry and the shallowing of the magma reservoir, Coso volcanic field, California

Journal of Petrology

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Abstract

The compositionally bimodal Pleistocene Coso volcanic field is located at the western margin of the Basin and Range province ~ 60 km north of the Garlock fault. Thirty-nine nearly aphyric high-silica rhyolite domes were emplaced in the past million years: one at 1 Ma from a transient magma reservoir, one at ~ 0.6 Ma, and the rest since ~ 0.3 Ma. Over the past 0.6 My, the depth from which the rhyolites erupted has decreased and their temperatures have become slightly higher. Pre-eruptive conditions of the rhyolite magmas, calculated from phenocryst compositions using the two-oxide thermometer and the Al-in-hornblende barometer, ranged from 740??C and 270 MPa (2.7 kbar; ~ 10 km depth) for the ~ 0.6 Ma magma, to 770??C and 140 MPa (1.4 kbar; ~ 5.5 km) for the youngest (~ 0.04 Ma) magma. Results are consistent with either a single rhyolitic reservoir moving upward through the crust, or a series of successively shallower reservoirs. As the reservoir has become closer to the surface, eruptions have become both more frequent and more voluminous.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Rhyolite thermobarometry and the shallowing of the magma reservoir, Coso volcanic field, California
Series title:
Journal of Petrology
Volume
41
Issue:
1
Year Published:
2000
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
149
Last page:
174
Number of Pages:
26