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Abstract: Thermal Regime of the Great Basin and Its Implications for Hydrocarbon Occurrence

John H. Sass, Colin F. Williams

The Great Basin is a province of high average heat flow (92±9 mW m-2), but it contains sub-provinces of both higher and lower heat flow. Higher heat flow (>100 mW m-2) is characteristic of the north-central Great Basin (the Battle Mountain High, BMH) and several smaller areas along its margins. There is also a large area of lower heat flow (<60 mW m-2, the Eureka Low, EL) in the south-central portion of the province. There is hydrologic and thermal evidence that the EL is a shallow (~3 km) hydrologically controlled heat sink associated with interbasin water flow. For example, the temperature profile from a 3.7 km deep hole at Pahute Mesa in the EL indicates low heat flow in the upper 1.5 km and high heat flow in the lowermost ki ometer. On the other hand, seismic and magnetic studies suggest that the heat sink in the EL extends to at least mid-crustal depths. Temperatures in the deeper parts of many basins in the BMH are higher than considered favorable for generation or stability of oil. Paradoxically, temperature-gradients as high as 100°C km-1 and an underlying hydrothermal system are found within the EL in Railroad Valley, the site of the most productive oil-fields in the Great Basin. The heat source driving this hydrothermal system is a combination of local upward flow from the Paleozoic carbonate aquifer and possible thermal input from nearby igneous activity. J. B. Hulen and others have suggested that the Railroad Valley hydrothermal system has enhanced hydrocarbon transport and accelerate maturation. If a hydrothermal system is required for the formation of significant hydrocarbon reservoirs in the EL, then such reservoirs will occur only where groundwater flow the carbonate aquifer is not removing heat from the basins.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada