High Regional Heat Flow Research Articles

Late Cenozoic Alkalic Basaltic Magmas in the Western Colorado Plateaus and the Basin and Range Transition Zone, U.S.A., and Their Bearing on Mantle Dynamics

Late Cenozoic volcanism along the eastern margin of the Basin and Range province in northern Arizona and Utah has created a suite of essentially alkalic basaltic lavas similar to those occurring in other regions of recent uplift, extensional tectonism, and high heat flow. The lavas were derived from a series of partial melts of the mantle, modified to varying degrees by polybaric fractionation of olivine and possibly plagioclase and clinopyroxene during ascent to the surface. Basanite and alkali olivine basalt melts originated at depths of at least 65 km and possibly as much as 95 km (20 to 30 kb) by variable but generally small degrees of partial melting. More voluminous hawaiite magmas originated at shallower depths by a somewhat greater degree of partial melting and were more substantially modified by crystal fractionation prior to extrusion. Magmas parental to the lava extrusions became increasingly divergent in composition with time, reflecting a broadening depth interval of partial melting in the mantle. Concurrent eruptive activity and block faulting generally shifted eastward with time at a rate of approximately 1 cm/yr. These time-space-composition variations, in combination with the observed essentially marginal localization of basaltic volcanism for the whole Basin and Range province, are explained in terms of upper mantle dynamics. We envisage upwelling mantle or plume activity beginning sometime in the middle to late Cenozoic in the core area of the Basin and Range province and causing progressive thinning or “erosion” of the lithosphere. Erosion ultimately produced a steep, keellike asthenosphere-lithosphere boundary beneath the Colorado Plateaus and the Basin and Range transition zone. Eastward-flowing mantle peridotite from the core of the plume was throttled against this keel, causing localized shear heating. This heat enhanced partial melting so that sufficient liquid was created to separate from the refractory residuum and to rise to the surface. Diapiric uprise of magma, or partially melted mantle in the uppermost mantle, or injection of a swarm of dikes into the lower crust, might have weakened and attenuated the overlying brittle crust, causing concurrent faulting. Eastward erosion of the keel and site of partial melting as time progressed allowed eruptive and fault activity to also migrate.

High Fluid Potentials in California Coast Ranges and Their Tectonic Significance

High Fluid Potentials in California Coast Ranges and Their Tectonic Significance

Heat flow in the southwestern Pacific

One hundred and fifty-eight new heat-flow measurements in and around the marginal basins of the western Pacific are presented. Most of the measurements were collected in the Melanesian area and show that the region of high heat flow and shallow crustal elevation landward of the island arcs in the western Pacific includes the Fiji plateau and Lau basin. The high heat flow and shallow crustal depth of these two provinces can be accounted for by the recent intrusion of magma by a process similar to that at midocean ridges. The mean heat flow of the south Fiji basin, the Tasman abyssal plain, and the Coral Sea basin are below 1.5 μcal/cm2 sec, and the average depths of these provinces are greater than 4.5 km. These data are compatible with a simple sea-floor-spreading origin for these marginal basins if the process occurred more than 30 m.y. B.P.

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.

Origin and Tectonic Significance of High Fluid Pressures in the California Coast Ranges

Anomalous, high fluid potentials exist within the miogeosynclinal Great Valley and eugeosynclinal Franciscan sequences of Jurassic-Cretaceous age within the Coast Ranges and at depth on the west side of the Central Valley, Calif. These sediments are dominantly mudstones with low fluid transmissibilities. Certain problems exist as to the probable regional distribution of these high fluid potentials. Low-fluid-potential areas such as The Geysers geothermal occurrence are present in the Franciscan of Northern California within a region that generally seems to be characterized by high fluid potentials. These low potential areas are attributed to fracture zones with potential areas are attributed to fracture zones with channel-type flow whose transmissive characteristics greatly exceed those of inter-granular flow. Where the transmissive characteristics of such a fractured zone decrease downwards from the surface, the probable fluid pressures at depth within that fracture are interpreted as being at near-hydrostatic values. Other fractures whose transmissive characteristics decrease upwards from zones with anomalously high fluid pressures are interpreted to have extraordinarily high pressures are interpreted to have extraordinarily high fluid potentials at relatively shallow depths. In both cases, a near static fluid pressure would exist along the fracture. Thus, we conclude that the Franciscan of Northern California probably is characterized regionally by near-lithostatic fluid pressures at depth but that extensive fracture systems probably cause a very erratic distribution of fluid potential zones near the surface. Fracture zones with both low (i. e., near-hydrostatic) and high (i. e., near-lithostatic) fluid potentials probably exist at various depths from the surface. probably exist at various depths from the surface. The Geysers dry steam occurrence is envisioned as a fracture zone that has low fluid potentials by virtue of a decrease of the transmissive characteristics of a fracture system with depth but that happens to be located within a local region of high heat flow possibly caused by the existence at depth of a magma chamber. An abundance of direct fluid pressure measurements within the Great Valley section of the Sacramento Valley demonstrates the existence of such high fluid potentials, but only one such measurement exists within the San Joaquin Valley. The regional chemistry of the waters (membrane-effluent type) within the Tertiary of the San Joaquin, however, suggests that this water has been extruded from a widely distributed series of mudstones and other rocks that are undergoing compaction. The presumed source for this widespread compacting sequence is the underlying Great Valley sediments with their postulated high fluid potentials. potentials. We conclude that the anomalous, high fluid potentials of Tertiary sediments within folds on the west side of the San Joaquin Valley reflect indirectly the presence at depth of high fluid potentials in the underlying Great Valley section. The origin of the folds is attributed to dynamic tectonic compression caused by current deep-seated Bear diapirism of Great Valley mudstones and related rocks that possess near-perfect plastic properties by virtue of their possess near-perfect plastic properties by virtue of their near-lithostatic fluid pressures. The closed gravity minimum over the south end of South Dome-Lost Hills Anticline is postulated as being the result of a diapir of serpentine or similar material. It is postulated that a fault zone, named herein the West Side Fault, probably exists at depth along the west side of the Central Valley. This buried West Side Fault is envisioned as having an intermittent near-surface expression in the form of faults such as the Midland Fault or long linear folds such as the Kettleman folds. The diapirism presumed to be responsible for these folds is postulated as occurring along this fault. postulated as occurring along this fault. JPT P. 13

Effect of a Region of Low Viscosity on Thermal Convection in the Mantle

GEOPHYSICAL and geological studies have revealed a world-wide pattern of tectonic features and have provided increasing evidence of crustal mobility. These have recently been related through the remarkable work of Vine and Matthews and others1,2 on sea floor spreading. There is some indication3 that the rifts which mark the bifurcation line of sea floor spreading are also regions of high heat flow. Regions of low heat flow appear to parallel the rifts at distances of several thousand kilometres.

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.

Experimental determination of the coefficient of heat transfer during hole boring and the re-establishment of the temperature field equilibrium

The results of 7 temperature measurements repeated in bore hole MB-5A have been analyzed, and the character of the disturbance of the natural temperature field during hole boring has been studied. The results make it possible to determine the heat transfer coefficient between the circulating drilling fluid and the surrounding tock. The heat flow in the bore hole is 2.14 ± 0.06 μcal/cm 2 sec, which proves the location of a region of high heat flow in the centre part of the Bohemian Cretaceous.

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.

Terrestrial heat flow in Lake Malawi, Africa

Twenty measurements of heat flow through the floor of deep Lake Malawi (Central Africa) gave values ranging from 0.15 to 2.88 μcal/cm² sec. A systematic areal distribution of the values indicated regions of low heat flow at the northern and southern ends of the lake (average = 0.54 and 0.70 μcal/cm² sec, respectively), separated by a central region of high heat flow (average = 2.30 μcal/cm² sec.). The variability implies local heat sources within a few tens of kilometers of the earth's surface and/or disturbances from the local environment.

Some geophysical implications from gravity and heat flow data

The negative correlation coefficient, −0.82, between Izsak's satellite geoid and Lee and MacDonald's heat flow distribution suggests a correlation between the geoidal undulations and the highs and lows of heat flow, in the sense that depressions on the geoid correlate with regions of high heat flow while rises on the geoid correlate with regions of low heat flow. This implies that the depressions on the geoid are related to hotter and lighter material in the interior of the earth and the rises on the geoid are related to colder and heavier material. Assuming that the density anomaly Δρ, which is responsible for the geoidal undulations, is related to a temperature perturbation ΔT by Δρ/ρ = −αΔT, where α is the coefficient of thermal expansion, and that ΔT is caused by an inhomogeneous distribution of radiogenic heat sources, the location of this distribution of heat sources is found within the outer 100 to 200 km of the mantle, and the corresponding temperature variation has a maximum amplitude of about 100°C. The corresponding fluctuation of radiogenic heat is about ±1 to ±2×10−14 cal/cm3 sec, which implies that the upper mantle contains much stronger heat sources than does peridotite or dunite. An eclogitic upper mantle seems, in this respect, more likely.

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.

Terrestrial heat flow in Japan

Terrestrial heat flow has been determined at 58 localities (39 on land and 19 in the sea) in and around the Japanese Islands. The average values of observed heat flow on land and in the sea are 1.55 × 10−6 and 1.30 × 10−6 cal/cm2 sec, respectively. The out-standing features of the heat-flow distributions are as follows: (a) Regions of high heat flow (Q > 2.0 × 10−6 cal/cm2 sec) exist in the Japan Sea side of the Honshu arc. (b) The region of high heat flow seems to extend, through the Fossa Magna area, down to the Izu-Marianne arc. (c) It is probable that a similar zone of high heat flow exists in the inner side of the Kurile arc. (d) These zones of high heat flow precisely coincide with the zones of the late Cenozoic tectogenesis in the area, (e) Low heat flow (Q < 1.0 × 10−6 cal/cm2 sec) prevails in the Pacific coast side of northeastern Japan and in the oceanic areas directly east of it. (f) The region outside these zones of high and low heat flow has heat flow that is within the range of normal values. Various hypothetical processes, such as the distribution of radio-activity in the crust, upheaval and denudation of the land, subterranean chemical reactions, thermal refraction, and mantle convection, have been examined in order to account for the observed heat-flow distribution. Owing to the uncertainty of assumed quantities, it is difficult to determine which hypothesis should be selected.

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.