Heat flow in the eastern pacific and sea floor spreading

A simple model based on the hypothesis of sea floor spreading can account for the main features of two major high heat flow anomalies in the eastern Pacific; the broad band of high values along the crest of the East Pacific Rise and the large concentration of high values centered on the Galapagos Rift Zone. Using the same model to interpret both the surface shape of the midocean ridges and the heat loss of the entire ridge system, the calculated elevation is found to be comparable, though smaller than, that observed for the ridges and the heat dissipated by crustal production along the axis of the entire ridge system is shown to be approximately 15% of the total heat loss through the oceans.     

Heat flow measured in five holes in eastern and central Slovakia

Five new heat flow values obtained in deep boreholes in the Western Carpathians are presented. Three holes were located in pre-Neogene folded units, the other two holes in Tertiary volcanites. The heat flow values range from 50.7 to 73.3 mW m^?2 with an average value of 65.9 mW m^?2 and they represent very needed information on the geothermal field in an area where heat flow values are still scarce.     

Heat flow,radioactive heat generation,and theoretical tectonics for northwestern Mexico

Nine heat flow values from Baja California and Sonora represent the first determinations of heat flux from Mexico and, in general, justify southerly extensions of the Basin and Range and Southern California thermal provinces of the southwestern United States. Heat flow in northern Baja California is low (0.84 hfu), consistent with known values from the Sierra Nevada Batholith, but a value of 1.23 hfu was recorded in the central area of the peninsula. Seven measurements from Sonora, averaging 2.5 hfu, are similar to Basin and Range values.Reduced heat flow values (q*) have been calculated for Sonora and are interpreted as indicative of a separate Basin and Range thermal subprovince in Mexico. A tectonic model developed for northwestern Mexico attributes the high heat flow of the Basin and Range to behind arc extension associated with the termination of Cenozoic subduction. Opening of the Gulf of California and sea-floor spreading therein has provided a vent for the release of heat accumulated under northwestern Mexico. Thus, the southern portion of the Basin and Range province (in Mexico) appears to be cooling and narrowing and a subprovince of high reduced heat flow is defined east and perhaps southwest of the Gulf of California.     

Review of heat flow data from the eastern Mediterranean region

Heat flow data from the eastern Mediterranean region indicates an extensive area of low heat flow, spreading over the whole basin of the Mediterranean east of Crete (Levantine Sea), Cyprus, and northern Egypt. The average of the marine heat flow measurements in the Levantine Sea is 25.7±8.4 mW/m², and the heat flow on Cyprus is 28.0±8.0 mW/m². The estimated values of heat flow in northern Egypt range from 38.3±7.0 to 49.9±9.3 mW/m², apparently with no consistent trend. To the east, on the coast of Israel, the heat flow values increase, ranging from 36.6±22.4 to 56.7±14.2 mW/m² along a SSE trend. The trend apparently correlates with an increase in crustal thickness, which is about 23 km at the north-west base of the Nile-Delta-cone, and close to 40 km beneath Israel.Contribution No. 157, Department of Geology, Kent State University, Kent, Ohio, USA.     

Heat flow and its coalbed gas effects in the central-south area of the Huaibei coalfield, eastern China

Based on an analysis of the present geo-temperature field and the thermal conductivity (K) of 62 samples from the central-south area of the Huaibei coalfield in eastern China, we calculated the heat flow and plotted its distribution map. The results show that the average heat flow in the research area is about 60 mW/m2. It is different from other major energy basins in the North China Plate, but has close relationship with the regional geology and the deep geological setting. The heat flow is comparatively ...     

Heat flow in Italy

More than fifty heat flow measurements in Italy are examined. The values, corrected only for local influences (when present), are related to the main geological features with the following results: foreland areas, 55±19 mW m^–2, foredeep areas, 45±21 mW m^–2; folded regions and intermountain depressions, 76±29 mW m^–2. In volcanic areas the heat flow rises to in excess of 600 mW m^–2. From a tectonic point of view, these values are consistent with the hypothesis that the Apennine chain is intersected by two arcuate structures: the first from Liguria to Latium is very probably a continental arc, that is an are which occurs within a continent, and the second from Campania to Calabria is very similar from geophysical evidence to the classic island arcs.     

Heat flow and gravity in Czechoslovakia

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Heat flow maps and deep ground water circulation: Examples from Switzerland

The effect of regional and local ground water circulation systems on the Heat Flow Density (HFD) field is demonstrated by two examples from Switzerland, one near St. Gall in an area at the northern border of the Alps, and the other northwest of Zurich along the eastern end of the Jura mountains. Detailed HFD maps of both areas slow pronounced high heat flow zones which are attributed to discharge of subsurface water which has migrated laterally over several 10 km. Seepage velocities on the order of several mm/yr have been calculated. Geothermal information is not available about the infiltration zones where low HFD values are expected. Geochemical and isotopic analysis of water samples from springs and drillholes indicates the recharge zones and demonstrates the effect of extensive regional systems. These results indicate that in regions with significant topographic relief HFD mapping can be seriously biased if drillholes are positioned in valleys which correspond to discharge areas with relatively high HFD, whereas the low heat flow zones remain undetected.     

Heat flow anomalies and their interpretation

More than 10,000 heat flow determinations exist for the earth and the data set is growing steadily at about 450 observations per year. If heat flow is considered as a surface expression of geothermal processes at depth, the analysis of the data set should reveal properties of those thermal processes. They do, but on a variety of scales. For this review heat flow maps are classified by 4 different horizontal scales of 10ⁿ km (n = 1, 2, 3 and 4) and attention is focussed on the interpretation of anomalies which appear with characteristic dimensions of 10^{(n − 1)} km in the respective representations.The largest scale of 10⁴ km encompasses heat flow on a global scale. Global heat loss is 4 × 10¹³ W and the process of sea floor spreading is the principal agent in delivering much of this heat to the surface. Correspondingly, active ocean ridge systems produce the most prominent heat flow anomalies at this scale with characteristic widths of 10³ km. Shields, with similar dimensions, exhibit negative anomalies.The scale of 10³ km includes continent wide displays. Heat flow patterns at this scale mimic tectonic units which have dimensions of a few times 10² km, although the thermal boundaries between these units are sometimes sharp. Heat flow anomalies at this scale also result from plate tectonic processes, and are associated with arc volcanism, back arc basins, hot spot traces, and continental rifting. There are major controversies about the extent to which these surface thermal provinces reflect upper mantle thermal conditions, and also about the origin and evolution of the thermal state of continental lithosphere.Beginning with map dimensions of 10² km thermal anomalies of scale 10¹ km, which have a definite crustal origin, become apparent. The origin may be tectonic, geologic, or hydrologic. Ten kilometers is a common wavelength of topographic relief which drives many groundwater flow systems producing thermal anomalies. The largest recognized continental geothermal systems have thermal anomalies 10¹ km wide and are capable of producing hundreds of megawatts of thermal energy.The smallest scale addressed in this paper is 10¹ km. Worldwide interest in exploiting geothermal systems has been responsible for a recent accumulation of heat flow data on the smallest of scales considered here. The exploration nature of the surveys involve 10's of drillholes and reveal thermal anomalies having widths of 10⁰ km. These are almost certainly connected to surface and subsurface fluid discharge systems which, in spite of their restricted size, are typically delivering 10 MW of heat to the near surface environment.     

Assessing plot-scale impacts of land use on overland flow generation in Central Panama

Land use in Panama has changed dramatically with ongoing deforestation and conversion to cropland and cattle pastures, potentially altering the soil properties that drive the hydrological processes of infiltration and overland flow. We compared plot-scale overland flow generation between hillslopes in forested and actively cattle-grazed watersheds in Central Panama. Soil physical and hydraulic properties, soil moisture and overland flow data were measured along hillslopes of each land-use type. Soil characteristics and rainfall data were input into a simple, 1-D representative model, HYDRUS-1D, to simulate overland flow that we used to make inferences about overland flow response at forest and pasture sites. Runoff ratios (overland flow/rainfall) were generally higher at the pasture site, although no overall trends were observed between rainfall characteristics and runoff ratios across the two land uses at the plot scale. Saturated hydraulic conductivity (K_s) and bulk density were different between the forest and pasture sites (p < 10⁻⁴). Simulating overland flow in HYDRUS-1D produced more outputs similar to the overland flow recorded at the pasture site than the forest site. Results from our study indicate that, at the plot scale, Hortonian overland flow is the main driver for overland flow generation at the pasture site during storms with high-rainfall totals. We infer that the combination of a leaf litter layer and the activation of shallow preferential flow paths resulting in shallow saturation-excess overland flow are likely the main drivers for plot scale overland flow generation at the forest site. Results from this study contribute to the broader understanding of the delivery of freshwater to streams, which will become increasingly important in the tropics considering freshwater resource scarcity and changing storm intensities.     

Heat flow at standard depth

Secular and long-term periodic changes in surface temperature cause perturbations to the geothermal gradient which may be significant to depths of at least 1000 m, and major corrections are required to determine absolute values of heat flow from the Earth's interior. However, detailed climatic models remain contentious and estimates of error in geothermal gradients differ widely. Consequently, regions of anomalous heat flow which could contain geothermal resources may be more easily resolved by measuring relative values at a standard depth (e.g. 100 m) so that all data are subject to similar corrections.Regional heat flow data obtained in existing deep holes show reasonable correlation with values determined at shallow depth. Hence geothermal resources of low enthalpy can be characterised by extrapolating temperatures from relative heat flow data readily obtained from shallow boreholes. Regional control can be provided by casing deep boreholes drilled for other purposes.For routine geothermal exploration, borehole temperatures can be measured using gradient probes with fixed sensor separation (e.g. 5 m), allowing very accurate determinations of the geothermal gradient at a single depth. Values of relative heat flow can then be obtained after determining the thermal resistivity of the corresponding core interval. Sampling errors can be minimised by multiple determinations of thermal conductivity over the complete interval.     

Heat flow and deep temperature in South Portugal

Summary Heat-flow density determinations were made in South Portugal. The region of study covers the Algarve Basin, the South Portuguese Zone, part of the Ossa Morena Zone and part of the Lusitanian Basin.Two sets of data were used to obtain heat-flow density values in this region: 13 determinations were made in boreholes under equilibrium conditions and 4 determinations in oil exploration boreholes.Gravity and aeromagnetic data were used to constrain the interpolation of the heat-flow density isolines in the South Portuguese Zone and part of the Ossa Morena Zone.Seismic data were used to model two-dimensional heat transfer through a vertical cross section located in the South Portuguese Zone.The radiogenic heat source distribution was estimated using a relationship between seismic velocity (V_p) and radiogenic heat production (A).A temperature profile was computed taking into account the effect of temperature on thermal conductivity and on the seismic velocity.Presented at the International Meeting on Terrestrial Heat Flow and the Structure of Lithosphere, Bechyn Castle, Czech Republic, September 2 – 7, 1991.     

Heat flow and heat production in northeast Africa

The analysis of both temperature data and thermal conductivity material from seven deep oil exploration horeholes in northeast Africa has allowed the calculation of a heat flow value in the Somalian Horn (average58 ± 12mW m^?2) and one from the coastal plain of northeast Sudan (average96 ± 19mW m^?2). Heat production measurements of granites from the Sudanese basement indicate a substantial depletion in the radiogenic heat producing elements.The heat flow results complement previous measurements from the Gulf of Aden and the Red Sea and are consistent with the geological and geophysical consensus that these two regions are young proto-oceans formed by the mechanisms of spreading lithospheric plates. The heat production evidence suggests that the lithospheric plate beneath the Sudan coastal plain is approximately 30–50 km thick and underlain by a zone of partial or complete melt.     

Heat flow and thickness of the oceanic lithosphere

Existing thermal models of the oceanic lithosphere predict too sharp an increase of heat flow towards the ridge axis. A new mathematical model of a thickening lithosphere is presented. The temperature distribution is computed by the use of observed surface heat flow as a boundary condition. If observed heat flow values represent flow of heat from the mantle, the model predicts a rather rapid growth of the lithosphere within the first 30 m.y. and a nearly steady state after 100 m.y. Heat flow from the asthenosphere to the lithosphere shows a minimum near the ridge axis, suggesting a down-going convective flow in the asthenosphere at both sides of a spreading center.     

Heat flow and the geothermal potential of Egypt

Preliminary heat flow values ranging from 42 to 175 mW m^–2 have been estimated for Egypt from numerous geothermal gradient determinations with a reasonably good geographical distribution, and a limited number of thermal conductivity determinations. For northern Egypt and the Gulf of Suez, gradients were calculated from oil well bottom hole temperature data; east of the Nile, and at three sites west of the Nile, gradients were calculated from detailed temperature logs in shallow boreholes. With one exception, the heat flow west of the Nile and in northern Egypt is estimated to be low, 40–45 mW m^–2, typical of a Precambrian Platform province. A local high, 175 mW m^–2, is probably due to local oxidational heating or water movement associated with a phosphate mineralized zone. East of the Nile, however, including the Gulf of Suez, elevated heat flow is indicated at several sites, with a high of 175 mW m^–2 measured in a Precambrian granitic gneiss approximately 2 km from the Red Sea coast. These data indicate potential for development of geothermal resources along the Red Sea and Gulf of Suez coasts. Water geochemistry data confirm the high heat flow, but do not indicate any deep hot aquifers. Microearthquake monitoring and gravity data indicate that the high heat flow is associated with the opening of the Red Sea.     

Heat flow on the Pacific-Antarctic Ridge

Twenty-four heat flow measurements are clustered in 5–20 m.y. and 60–80 m.y. old seafloor on the crest and northern flank of the Pacific-Antarctic Ridge. The crestal heat flow stations are characterized by (1) low mean heat flow relative to that predicted by theoretical models, (2) thin sediment cover, and (3) high ratio of standard deviation to mean heat flow, all of which indicate a system dominated by convective heat transfer. The measurements made on older seafloor of the northern flank have (1) mean heat flow equal to the theoretical predictions of conductively-cooling lithospheric plate models, (2) thick sediment cover, and (3) low ratio of standard deviation to mean heat flow. Thus convective loss associated with hydrothermal circulation is not considered to be important in 60–80 m.y. old seafloor on the Pacific-Antarctic Ridge. The pattern of heat flow on this ridge is thus similar to that in the Atlantic, Indian and Pacific Oceans: hydrothermal circulation is dominant on the ridge crest but is suppressed on the flanks, possibly due to a difference in the hydraulic admittance of the sediment between the two regions.     

Heat flow from the earth’s interior depending on inner parameters variations

The approximate equality of heat flows on the land and the ocean; high heat flow values on the middle oceanic ridges; a relationship of heat flow with age of tectogenesis; the extremely low heat flow values are considered as main evidence for any theoretical explanation. The deviation of surface heat flow from its equilibrium value is considered. Computing analysis of high temperature heat transfer coefficients is given. Some aspects of numerical techniques of the thermal history of the Earth are discussed. The influence of sudden and gradual formation of the Earth Crust on the surface heat flow is considered.     

Heat flow and age of the Gulf of Oman

We present the results of twenty heat flow stations in the Gulf of Oman which are used to infer the first reliable age estimates for the basin. A mean surface heat flux of 42.6±3.6 mW m^?2 exhibits no significant regional variation. After correction for thick and rapidly deposited sediments this yields an age of 70 to 100 Ma according to oceanic thermal models. This age is also consistent with the sediment corrected basement depths of 5.5–6.0 km and with formation during the Cretaceous quiet zone. The latter can explain the absence of magnetic sea-floor spreading lineations. Heat flow measurements are also used to confirm the presence of gas hyrdate layers. The measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from “bright spots” seen on seismic reflection profiles.