Tectonic controls on magmatism in The Geysers--Clear Lake region: Evidence from new geophysical models
- Geological Survey, Denver, CO (United States). Denver Federal Center
- CalEnergy Corp., Ridgecrest, CA (United States)
In order to study magmatism and geothermal systems in the Geysers-Clear Lake region, the authors developed a detailed three-dimensional tomographic velocity model based on local earthquakes. This high-resolution model resolves the velocity structure of the crust in the region to depths of approximately 12 km. The most significant velocity contrasts in The Geysers-Clear Lake region occur in the steam production area, where high velocities are associated with a Quaternary granite pluton, and in the Mount Hannah region, where low velocities occur in a 5-km-thick section of Mesozoic argillites. In addition, a more regional tomographic model was developed using traveltimes from earthquakes covering most of northern California. This regional model sampled the whole crust, but at a lower resolution than the local model. No large silicic magma chamber is noted in either the local or regional tomographic models. A three-dimensional gravity model also has ben developed in the area of the tomographic imaging. The gravity model demonstrates that all density contrasts can be accounted for in the upper 5--7 km of the crust. Two-dimensional magnetotelluric models of data from a regional east-west profile indicate high resistivities associated with the granitic pluton in The Geysers production area and low resistivities in the low-velocity section of Mesozoic argillites near Mount Hannah. No indication of midcrustal magma bodies is present in the magnetotelluric data. The geophysical models, seismicity patterns, distribution of volcanic vents, heat flow, and other data indicate that small, young intrusive bodies that were injected along a northeast trend from The Geysers to Clear Lake probably control the thermal regime.
- Sponsoring Organization:
- USDOE Assistant Secretary for Energy Efficiency and Renewable Energy, Washington, DC (United States); Department of the Interior, Washington, DC (United States)
- DOE Contract Number:
- AC07-94ID13223
- OSTI ID:
- 669934
- Journal Information:
- Geological Society of America, Bulletin, Vol. 110, Issue 9; Other Information: PBD: Sep 1998
- Country of Publication:
- United States
- Language:
- English
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