Petrology of the Woods Mountains volcanic center, San Bernardino County, California
Thesis/Dissertation
·
OSTI ID:6904460
The main purpose of this study is to investigate magma chamber processes through a petrological study of a large, newly examined silicic volcanic center. A characterization of the volcanic center was obtained through a combination of detailed mapping, petrography, analyses of bulk major and trace elements, and microprobe analyses of phenocryst phases. Cooperative studies were undertaken which included geophysical surveys of the center, Nd-Sm and Rb-Sr isotopic systematics and K-Ar dating of the rocks. The volcanic center began at 16.4 mybp with the incremental extrusion of ca 10 km/sup 3/ of dominantly mildly peraluminous dacitic and rhyolitic magma. At 15.5 mybp 870 km/sup 3/ of metaluminous to mildly peraluminous, dominantly rhyolitic pyroclastic flows were extruded, causing the formation of a 10 km diameter caldera. This was followed from 15.5 my to 14.8 my by the incremental, intracaldera extrusion of ca 10 km/sup 3/ of metaluminous to mildly peralkaline, high silica rhyolite magma. A model of magma chamber evolution is presented as follows: (1) a thermal pulse into the base of the crust initiated partial melting of a garnet-biotite gneiss at ca 17 mybp; (2) anatectic pockets of melt of dacitic composition intruded into the upper crust; (3) an increased flux of magma at 16 mybp resulted in the formation of a large magma chamber that evolved a cap of rhyolitic magma by a fractional crystallization within counter buoyant boundary layers; (4) a decay of input into the chamber occurred soon afterward, however chemical potential gradients induced by the rapid extrusion of a large part of the rhyolitic cupola resulted in strong volatile-complex diffusion, forming a thin cap of mildly peralkaline rhyolitic magma.
- Research Organization:
- California Univ., Los Angeles (USA)
- OSTI ID:
- 6904460
- Country of Publication:
- United States
- Language:
- English
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