Gravity and thermal models for the Twin Peaks Silicic Volcanic Center, southwestern Utah

Abstract

Gravity, heat flow, and surface geology observations have been used as constraints for a thermal model of a late Tertiary silicic volcanic center at Twin Peaks, Utah. Silicic volcanism began in the area with the extrusion of the Coyote Hills rhyolite 2.74 ± 0.1 m.y. ago, followed by the Cudahy Mine obsidian, felsite, and volcanoclastics, and finally by a complex sequence of domes and flows that lasted until 2.3 ± 0.1 m.y. ago. Basalt sequences span the time 2.5 to 0.9 m.y. Terrain‐corrected Bouguer gravity anomalies at Twin Peaks are shaped by three features of varying characteristic dimensions: (1) a major north‐northeast trending −30 mGal gravity trough roughly 40 km wide caused by a thick sequence of Cenozoic sediments in the Black Rock Desert Valley, (2) a local roughly circular −7 mGal gravity low, 26 km across, probably related to an intrusive body in the basement, and (3) a series of narrow positive anomalies up to +10 mGal produced by the major Twin Peaks volcanic domes. The intrusive bodies have been modeled as three‐dimensional vertical cylinders; the total volume of intrusive material is estimated to be about 500 km3. Simple thermal models, assuming conductive heat transfer and using geometrical constraints from the gravity results, predict that a negligible thermal anomaly should exist 1 m.y. after emplacement of the intrusion. This prediction is consistent with an average heat flow of 96 mW m−2 for the area, not significantly different from eastern Basin and Range values elsewhere. Magmatic longevity of this system, 2.7 to 2.3 m.y. for silicic volcanism or 2.5 to 0.9 m.y. for basaltic volcanism, does not seem to prolong the cooling of this system substantially beyond that predicted by conductive cooling.