Mapping a Fossilized Geothermal System in the Fra Cristobal Range of South-central New Mexico

Kyle Gallant, New Mexico Bureau of Geology and Mineral Resources
Veronica Prush, New Mexico Institute of Mining and Technology
Shari Kelley, New Mexico Bureau of Geology and Mineral Resources
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Abstract

Fluid flow along faults is an important process for concentrating minerals, circulating hydrothermal fluids, and reducing local shear stress. However, the record of fluid flow in the geologic past may be indistinct. Fossilized geothermal systems preserved along faults provide an outcrop record of paleo-fluid flow, and mineralization and alteration effects can be used as proxies for past flow paths down-dip and along-strike of faults and adjacent damage zones.

Elevated geotherms in rift settings often result in geothermal systems (active or fossilized), and fluid flow is commonly concentrated along or within rift faults. The Rio Grande rift of Colorado, New Mexico, and northern Mexico is an excellently exposed intracontinental rift. Several uplifts adjacent to or within the Rio Grande rift expose mineralized fault planes meters to kilometers in length. The Fra Cristobal Range in south-central New Mexico is a horst block on the eastern side of the Rio Grande rift with a ~20-kilometer-long mineralized normal fault bounding its eastern margin. Low- and medium-temperature thermochronological datasets collected in the Fra Cristobal Range suggest that cooling occurred ~10-15 Ma; however, structural data suggests that cooling likely occurred >30 Ma. We hypothesize that this discrepancy in cooling between the structural and thermochronological datasets is attributable to high-temperature fluid flow along the fossilized geothermal systems preserved along the basin-bounding fault of the Fra Cristobal Range.

Presented here is a mapping schema for the relict fossilized geothermal system in the Fra Cristobal Range, focused on the mineralization and alteration effects related to high-temperature fluid flow along the fault zone. The mapping here provides insight into the along-strike and down-dip record of fluid flow, which may have caused post-exhumation thermal resetting of thermochronometers in the Fra Cristobal Range.

Session

Societal relevance of structural geology and tectonics