| Title | Clay Mineralogy and Zoning in CSDP Corehole VC-2A: Further Evidence for Collapse of Isotherms in the Valles Caldera |
|---|---|
| Authors | Hulen, Jeffrey B.; Nielson, Dennis L. |
| Year | 1988 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Exploration; USA; New Mexico; Valles Caldera; Hydrothermal Alteration; Mineralization; Geothermometers; Geochemistry; Chemical Analysis |
| 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. |