Clay Mineralogy and Zoning in CSDP Corehole VC-2A: Further Evidence for Collapse of Isotherms in the Valles Caldera
- Key words
- Exploration; USA; New Mexico; Valles Caldera; Hydrothermal Alteration; Mineralization; Geothermometers; Geochemistry; Chemical Analysis
- Location
- Valles Caldera, New Mexico; Sulphur Springs, New Mexico
- Conference
- Geothermal Resources Council Transactions
- Year
- 1988
- Session
- Exploration; Geological surveys; Mineralogy; Hydrothermal al
- Language
- English
Abstract
Phyllic alteration in CSDP corehole VC-2A shows that a relatively cool, vapor dominated zone above a depth of 240 m evolved form a high temperature, liquid dominated precursor. Sericite geothermometry indicates that temperatures near 200°C once prevailed near the present surface where temperatures are now below 80°C. Measured temperatures gradually approach but never reach paleotemperatures (212°C vs. approx. 230°C) in a deeper chlorite/sericite zone (163-528 m/TD). Alteration in other Valles boreholes indicates a caldera wide cooling trend similar to that documented for VC-2A. Textural evidence from the VC-2A core shows the phyllic alteration post dated or accompanied the waning stages of resurgent doming (at about 1.12 app. 1 Ma). Collapse of isotherm was probably initiated by bringing of a contemporaneous caldera lake after resurgence was complete.
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