Regional Heat Flow Research Articles

Heat flow in the western United States

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 (μcal/cm2 sec) 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.

Gravity anomalies and crustal shortening in the eastern Mediterranean

Crustal shortening of the ocean floor in the eastern Mediterranean is recognized by a marked thickening of the sedimentary layer seaward of the Hellenic and Calabrian island arcs. Steep gradients and large negative free-air anomalies in the gravity field along with a highly uniform, low regional heat flow are manifestations of the thickened crust. Bodies of recently deformed sediment in and seaward of the Hellenic Trough reveal the style, polarity, and dynamics of the thickening mechanism. A linear buried anticlinal structure, inferred from analysis of surface ship gravity profiles, may mark the site of contemporary intrabasinal underthrusting. The distribution of earthquakes beneath the Mediterranean Ridge supports the interpretation that the Anaximander, Ptolomy, and Strabo Mountains are features comparable to large basement nappes. Cyprus is one such structure, offset to the south, where the oceanic crust and part of the upper mantle have been involved in the décollement.

Heat flow in Korea

Twelve new heat flow measurements in South Korea are reported. Excluding one anomalous value, the average heat flow in South Korea was found to be 1.5 · 10 −6 cal./cm 2·sec which is equal to the world's average. In the area characterized by Tertiary volcanism, high heat flow was observed. The high heat flow region is considered to be a part of the high heat flow region extending from the Japan Sea side of the Japanese islands. The transition from high heat flow to normal or low heat flow occurs rather sharply. It may indicate that the source causing high heat flow lies at fairly shallow depth or that an unexpectedly effective heat transfer mechanism exists.

Heat-flow determinations in the northwestern United States

Eleven new heat-flow determinations in the northwestern United States, based on data from twenty-one drill holes and two mine shafts, together with previously available data, suggest a heat-flow pattern similar to that observed in the southwestern United States. In particular the high heat flow found in the Basin and Range province, about 2.0 μcal/cm2 sec, is characteristic of the Northern Rocky Mountains province and possibly the Columbia Plateaus as well. This region of high heat flow is referred to in this paper as the Cordilleran thermal anomaly zone. Most of central Wyoming, central Montana, and western Washington may have normal heat flow. A heat-flow determination in the Black Hills is high. The Northern Rocky Mountains and Basin and Range provinces have similar regional heat flow, crustal structure, upper mantle Pn velocity, and Cenozoic geologic history. Thus, tectonic schemes that emphasize the Basin and Range province as a unique area on the North American continent must be reevaluated.

Heat flow and surface radioactivity in the Quirke Lake Syncline near Elliot Lake, Ontario, Canada

Heat flow was measured in seven diamond-drilled holes, ranging in depth from 300 to 900 m, in the Quirke Lake Syncline (82° 30′ W, 46° 30′ N, mean elevation 370 m), Values for individual holes vary from 1.20 to 1.40 with a mean of 1.32 ± 0.02 μcal/cm2s, and no systematic variation was detected within the 50 km2 area studied. Radiometric measurements with a portable, three-channel, gamma-ray spectrometer show a downward concentration (stratigraphically) of Th, U, and K within the lower part of the syncline, with mean concentrations of 12.7 ppm, 3.3 ppm, and 1.9%, respectively. These data yield an average rate of heat production of 4.5 heat generation units (1 hgu = 10−13 cal/cm3s). Taking account of the ore zones, the mean heat production from the syncline is about 6 hgu. Corrections for structural effects and heat production from the ore result in a value of 1.2 for the regional heat flow. This is within the range of other shield values, although somewhat higher than the average for the Canadian Shield. The high value is readily explained if the observed mean surface radioactivity persists to a depth of 7 to 10 km.

Heat flow inside the Island Arcs of the northwestern Pacific

A large region of high heat flow has recently been discovered in the northwest Pacific. The area extends from the Sea of Okhotsk in the north to the Philippine Sea in the south and may continue as far as the Fiji plateau. Two possible sources of the extra heat are volcanic intrusion into the crust and dissipative shear heating in the mantle. There are fundamental objections to both explanations, and, therefore, the origin of the high regional heat flow remains unknown. The high temperature gradient is of geological importance, since the crustal temperatures are sufficiently high to cause metamorphism.

Heat flow and surface radioactivity measurements in the Precambrian shield of Western Australia

A borehole for heat flow measurement has been drilled in a region of high radioactivity granitic rocks in the Archaean shield of Western Australia. Most previous shield heat flow determinations have been in low radioactivity basic and ultrabasic rocks which constitute less than 20% of the shield surface rocks. The heat flow of 1.23 μcal/cm 2sec measured in the granitic rocks is significantly higher than most previous shield values but is still much lower than the heat flows measured in the younger areas of eastern Australia. Two new measurements on the shield in basic and ultrabasic rocks give heat flows of 0.82 and 0.69. The mean surface radioactive element heat production in the Western Australian shield is found to be similar to that of the high heat flow regions of eastern Australia. This suggests that the radioactivity is concentrated in a very thin surface layer in the shield crust. The high radioactivity surface layer is probably largely absent in shield regions of basic and ultrabasic rocks where very low heat flows have been measured. Crustal radioactive element and temperature profiles have been estimated for the shield and for a high heat flow area.

Use of Boundary Sources in Problems of Heat Conduction

A method is presented for solving problems of one-dimensional heat flow in regions with plane, spherical, or cylindrical boundaries. It is based on the physical concept of a uniform continuous-source distribution on the boundary, whose strength varies with time in such a way as to meet the prescribed boundary condition. Examples of the method are given, including the solution for the temperature in a half-space with an initial steady gradient of temperature and the boundary condition (∂T/∂x) − w(∂T/∂t) − hT = − hθ.

Terrestrial heat flow in Japan

Terrestrial heat flow, Q=K×ΔT/ΔZ cal/cm2 sec has been determined at 51 localities (39 on land and 12 in the sea) in and around the Japanese Islands. The average values of observed heat flow in land and sea are 1.53µ cal/cm2sec and 1.48µcal/cm2sec respectively. These value do not differ greatly from the world’s averages. The outstanding features of the heat flow distribution are as follows:a) High heat flow region (Q>2.0µcal/cm2sec) exists in the Inner Zone of the Honshu Arc. This region of high heat flow is more distinct in the northeastern Japan than in the southwestern Japan.b) The High heat flow region seems to extend, through the Fossa Magna area, down to the Izu-Mariana Arc.c) It is also probable that a similar high heat flow zone exists in the inner side of the Kurile Arc.d) These zones of high heat flow precisely coincide with the zones of the Cenozoic orogeny in the area concerned.e) Far off the coast of the northeastern Japan, the area at about 150° E may be a high heat flow region.f) Low heat flow (Q<1.0µcal/cm2sec) prevails in the Pacific coast side of the northeastern Japan and in the oceanic area directly east of it, including the area of the Japan Trench.g) The region bounded by the above mentioned high and low heat flow regions has heat flow which is more or less normal. Based on these measurements, a « steady state ” temperature distribution in the crust has been calculated for each of the above regions of high, low and intermediate heat flow, and it was found that there is a large temperature differences between the bottom of the crust of the high and low heat flow regions: the temperature at the Moho boundary in the high heat flow regions should be as high as some 800∼1000°C (d=27 km), whereas that under the low heat flow region should be only about 200°C (d=23 km). The high general temperature at the Moho under the high heat flow region seems to favor a production of magma in the upper mantle. Calculated Moho temperatures disfavor the hypothesis that the Moho boundary is due to phase transition.

A region of uniform heat flow in the North Atlantic : Reitzel, J., 1963. J. Geophys. Res., 68 (18): 5191–5196

A region of uniform heat flow in the North Atlantic : Reitzel, J., 1963. J. Geophys. Res., 68 (18): 5191–5196

Terrestrial Heat Flow in Japan

Results of terrestrial heat flow measurements so far made in Japan are briefly reviewed. As seen in the figure 1 in the text, it has been established that the heat flow distribution is quite distinct in and around Japan. On the whole, the high heat flow region coincides with the Cenozoic volcanic region in the area, i. e. the Japan Sea side of the Honshu arc and the low heat flow regions lie on the Pacific Ocean side. The pattern of heat flow distribution seems to have important bearings with many other geological and geophysical aspects of the Japanese islands. A tentative picture of the state under Japanese area is presented based on the mantle connection hypothesis.

A region of uniform heat flow in the North Atlantic

Heat flow was determined at sixteen stations regularly spaced over a region of the North American basin between Bermuda and the Bahama Banks. The results show a remarkable uniformity of heat flow in this area, which measures about 800 by 900 km. The mean heat flow at the sixteen stations is 1.14 μcal/cm2 sec, with a standard deviation of 0.06. When allowance is made for experimental errors the actual standard deviation of heat flow in the region is estimated to be only 4½ per cent. Another measurement made at the southern edge of this area, near the Puerto Rico trench, showed a heat flow of 1.76 μcal/cm2 sec, while three measurements made a few hundred km to the northwest, close to the continental slope, gave values of 117, 0.94, and 0.81 μcal/cm2 sec.

Heat flow through the eastern Pacific ocean floor

A total of 194 new measurements of heat flow through the eastern Pacific Ocean floor are presented. They range in value from essentially zero to 8.04×10−6 cal/cm2 sec. The crest of the east Pacific rise is systematically associated with high values, a strip 200 to 300 km wide at the crest having an average heat flow of about 3×10−6 cal/cm2 sec. Within this strip, the highest values occur in two narrower zones which appear to be approximately parallel and symmetrically oriented to the crest. The source of the high heat flow in each of these zones is probably a region of unusually high temperature a few tens of kilometers wide located about 10 km beneath the ocean floor. One-fourth of all the measurements gave low heat-flow values (≤0.80×10−6 cal/cm2 sec). Two approximately equidimensional regions near the equator and to each side of the rise show generally low heat-flow values. These regions are 2 to 4×10−6 km2 in area, and their average heat flows are about half the normal oceanic value of 1.2 to 1.4×10−6 cal/cm2 sec. In other areas, many of the isolated low heat-flow values are correlated with flat topography which suggests an effect of the local environment; these values are presumably not representative of the regional geothermal heat flow. The systematically distributed variations suggest an origin associated with large-scale thermal convection in the mantle.

Heat Flow and Sonic Microstreaming

Measurements are being made to determine solid-to-liquid heat flow in the presence of sonically induced microstreaming near the interface. The microstreaming is induced by an air bubble vibrating near the region of heat flow. The air bubble is placed by means of a micropipette on the bottom of a clear plastic chamber containing the liquid. A 2-kc piston vibrator operated at low amplitudes a few centimeters above the bubble causes the bubble to become a strong source of sonic microstreaming. Imbedded in the plastic on which the bubble sits, and concentric with the bubble, is a thin multilayered annulus, the top of which is flush with the surface of the plastic. For a typical annulus the too layer is copper foil, the second is constantan; the bottom layer is a thermistor wafer through which current can be sent to produce a desired amount of heating. The thermal emf developed at the copper-constantan junction can be measured. Thus we have a source of known heat flow and known surface temperature. Investigations have been carried out in which heat flow was measured as a function of sonic amplitude, the surface temperature of the annulus being kept constant. The results indicate that, when the sonic amplitude A is small, the heat flow H varies linearly with A. This linear relationship between H and A is in agreement with the predictions of a simplified theory. At higher amplitudes the bubble may move about erratically, so that consistent readings are difficult to obtain. (Supported in part by the U. S. Air Force Office of Scientific Research.)

Heat-Flow Values from the South-Eastern Pacific

Prior to these new measurements, twenty-five heat-fiow values from the Pacific Ocean Basin and eight from the Atlantic have been published1. The surprising fact brought out by these measurements is the approximate equality of average heat flow of the oceanic and continental areas, about 1 × 10−6 cal./cm.2 sec. This result was unexpected on the basis of values of radioactivity indicated for typical continental and oceanic crustal rocks existing near the Earth's surface. It has usually been assumed that most of the surface heat flow in continental regions must originate in the relatively thick and radioactive continental crust. Under the oceans, nearly all the average heat flow must come from the mantle beneath the relatively thin oceanic crust.