Reorganization of the Hydrothermal Circulation Pattern at the Long Valley Exploratory Well, CA - Geologic Record and Numerical Simulation
Abstract
The Long Valley Exploratory Well (LVEW), drilled into the resurgent dome at Long Valley Caldera (California) to explore the potential for geothermal power in an active magmatic system, recorded temperatures of only ca. 100° C at 2500 to 3000 m depth. This is well below the range expected above an active magma chamber. Open fissures encountered at 2600 m depth are coated by mm-sized idiomorphic quartz crystals with first and second order growth discontinuities. Specific growth defects indicating rapid crystallization reflect dramatic changes in SiO2 supersaturation. Fluid inclusions contain low salinity (0 to 5 wt-% NaCl equiv.) and low CO2 (<3 mole%) aqueous fluids, with V-L homogenization temperatures of 300 to 350° C, indicating trapping at more than 200° C above the ambient temperatures measured within the borehole today. The inhomogeneous quartz growth and fluid inclusion results reflect dramatic changes in the convective pattern of the hydrothermal system that led to the unexpected low temperatures at depth. Numerical simulations are being carried out to constrain the length and time scales relevant for the reorganization of the circulation pattern, in particular the influence of episodic heat supply by intrusions and changes of permeability related to seismic events.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T22A0895F
- Keywords:
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- 5418 Heat flow;
- 8045 Role of fluids;
- 8424 Hydrothermal systems (8135)