Gravity and Thermal Models of the Twin Peaks Magma System, West-Central Utah

Abstract

Gravity, heat flow, surface geology, and geochemistry have been integrated to evaluation geothermal potential of a site of late Tertiary silicic volcanism at Twin Peaks, Utah. Volcanism began in the area with the extrusion of the Coyote Hills rhyolite 2.74 +/- .1 m.y. ago, and was resumed, after .2 m.y. of quiescence, with extrusion of a complex sequence of domes and flows that lasted until 2.35 +/- .07 m.y. ago. Residual gravity in the Twin Peaks area is characterized by a roughly circular and broad 7 mgal gravity low possibly related to a body approximated by a three dimensional vertical cylinder with a roof at a depth of 3 km, ad radius about 6 km, and a thickness of 2.25-3.5 km. Simple conductive thermal models predict a maximum anomalous heat flow of 175 mW/m2 at the surface, 90,000 years after emplacement of the intrusions. Model prediction of negligible residual heat flow at the present is consistent with measured heat flow of 96mW/m2 at Twin Peaks, which is indistinguishable from background Basin and Range heat flow.