Heat flow in the western United States

Abstract

Between 1962 and late 1970, subsurface temperature measurements were attempted at more than a thousand drilling sites in the western United States. Temperatures from over 150 boreholes at about 100 distinct sites were suitable for estimates of the vertical geothermal flux. These results more than double the data from the western United States and confirm that heat flow is variable but generally high in this region. Within the over-all pattern of high heat flow, there are several distinct geographical regions, each occupying several hundred square kilometers, characterized by low-to-normal heat flow. Normal values were measured in the Pacific northwestern coastal region and the northwestern Columbia Plateaus. Additional results confirm the previously reported trend of very low heat flow in the western Sierra Nevada, increasing to normal near the crest of the range. The present work also confirms that heat flow is high in the northern and southern Rocky Mountains and somewhat lower in the central Rockies. The north-central part of the Colorado Plateau is a region of normal heat flow with higher values near its eastern border with the southern Rockies. The Basin and Range province as a whole is characterized by high heat flow that extends to within 10 to 20 km of the eastern scarp of the Sierra Nevada. The abrupt thermal transition between the Sierra Nevada and the Basin and Range province may occur partly in the Sierra Nevada physiographic province. Between Las Vegas and Eureka, Nevada, there. is a large previously undetected zone of low-to-normal heat flow that is most probably the result of a systematic, regional water circulation to depths of a few kilometers. North of this zone, there is an area of several hundred square kilometers characterized by heat flows of 2.5 HFU (gcal/cm • see) or greater. In central California and adjoining western Nevada, a preliminary contour map suggests a heat-flow pattern with alignment parallel to the strike of the major geologic structures. Since radioactivity was first discovered, the heat flowing from the earth's deep interior has been considered an important constraint on geophysical and geochemical models of the earth. Until fairly recently, however, the measurement of heat flow on land was accorded a low priority compared with other geophysical measurements, so much so that Birch [1954] could report only three reliable measurements for the whole of the United States, and only a dozen or so independent regional determinations (attributable largely to E. C. Bullard and his colleagues) for all the continents. During the late 1950's and 1960's, the early efforts of Francis Birch in the United States, J. C. Jaeger in Australia, and A.D. Misener in Canada, among others, were followed up by these workers, their colleagues, and their students, with the result that the number of reports of reliable heat-flow data from continents is approaching one thousand. Roy et al. [1968b] recently summarized the work of almost a decade by Birch and his students in the conterminous United States....

Relation between alternations of uplift and subsidence revealed by Late Cenozoic fluvial sequences and physical properties of the continental crust

“…We take this as an estimate of the depth of the base of the mobile lower-crustal layer, irrespective of whether it is underlain by a layer of mafic underplating rather than the Moho. The surface heat-flow around Grand Junction is known from several boreholes (e.g., Sass et _ al., 1971) and was reported as 66-69 mW_m -2 by Eggleston & Reiter (1984) would require less radioactive heat production in the upper crust to achieve equivalent agreement. The thermal state of the crust in this region is thus consistent with the model prediction of W i .…”

Alteration and vein mineralization, Schwartzwalder uranium deposit, Front Range, Colorado

“…Furthermore, contemporaneous igneous activity in the Colorado mineral belt, some as close as 16 km to the west (Taylor, 1975), implies addition of heat to the upper crust as well as an increased thermal gradient in the lower crust to produce the magmas (Simmons and Hedge, 1978). A similar situation exists in northern Nevada, where a deep crustal magma is responsible for thermal gradients of up to 64.3°C/km over a relatively large surface area (Sass et al, 1971). As a result, the 63-64 m.y.…”

Reuse of abandoned oil and gas wells for geothermal energy production

“…Sass et al (1984) North Santa Barbara are coastal regions characterized by medium to high heat flows and countless abandoned oil and gas wells (Table 2). Sass et al (1971;1994) The previously mentioned counties were characterized by medium to high crustal heat flows, but other California counties still host vast numbers of abandoned wells and low-medium heat flows (50 to 75 mW/m 2 ) as shown in Table 2 …”