| Title | Mafic Heat Sources for Snake River Plain Geothermal Systems |
|---|---|
| Authors | Dennis L. NIELSON, John W. SHERVAIS, Sabodh K. GARG |
| Year | 2017 |
| Conference | Stanford Geothermal Workshop |
| Keywords | basalt, sill complex, heat source, rate of magma supply, thermal modeling |
| Abstract | A large number of hydrothermal systems are powered by mafic magmatic systems. These include systems in the Reykjanes peninsula, Iceland, the Puna District in Hawaii, and mid-ocean ridge spreading centers that represent the largest manifestation of geothermal energy on the planet. For several years, we have been investigating the potential for commercial high-temperature geothermal development in the Snake River Plain in Idaho, a very large basaltic province associated with the Yellowstone mantle plume. Although the province is characterized by high heat flow, we believe that the presence of high-temperature geothermal systems at reasonable drilling depths will require relatively shallow magmatic heat sources. Several studies now relate the geometry of mafic heat sources to the rates of magma supply versus the magnitude of tectonic extension. High extension with respect to magma supply results in feeder dikes and rapid ascent to the surface whereas high magma supply with respect to extension rates produces sills or plutons. Geophysical studies have documented the presence of a 10 km thick mid- to upper-crustal sill complex under the Snake River Plain that is inferred to comprise dozens of individual intrusions. We have proposed that the Graveyard Point Sill, located in western Idaho, is an analog for this complex, and for the buried mafic heat source of the Mountain Home geothermal system. On the basis of field mapping, we estimate that this single high-level intrusive had an average thickness of 100 m and a total volume of about 3 km3. It is estimated that this body was emplaced at a temperature of 1200oC. We will present numerical models to evaluate the cooling history of this intrusive and its potential as a heat source for the Mountain Home geothermal system. |