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1.
Heat flow values of 33–58 mW m–2 were found for the Transylvanian Depression, 45–57 mW m–2 for the crystalline nucleus of the Eastern Carpathians, and 70–120 mW m–2 for the Neogene volcanic area. Temperature-depth profile and some geophysical implications of the low values for the Transylvanian Depression are discussed, rendering evident clear-cut differences between this tectonic unit and other Noegene depressions. The heat flow values for the other two investigated tectonic units are usual ones for areas of their age.A preliminary map of the heat flow distribution over the Romanian territory is presented and its relation to other geophysical fields is discussed. A positive correlation was found between gravity and heat flow, and a negative one between crustal thickness and heat flow. A general conclusion could be drawn that the heat flow distribution over the Romanian territory seems to be governed by processes taking place in the upper mantle, rather than by the radioactive decay within the crust.  相似文献   

2.
Sixty new measurements together with published heat flow data in the South Atlantic between 20°S and 35°S latitude have been analyzed. Heat flux is greater through the eastern Mid-Atlantic Ridge flank and basin than their counterparts on the west but the standard deviation or spatial variation is greater on the west, contrary to expectation based on sediment thickness. The variance in the data indicates that this asymmetry in mean heat flux is statistically significant at 87% confidence level. A pair of ridge-flank minima appear in a composite trans-Atlantic profile of heat flux versus sea-floor age, suggesting hydrothermal circulation in the young oceanic crust. The Walvis Ridge has a mean excess heat flux of 28 mW m?2 (0.7 μcal cm?2 sec?1) above the surrounding Cape and Angola Basins, and decreases along the ridge towards the northeast. Consistent with the apparent asymmetric distribution in the South Atlantic, it is also significantly higher than that of the Rio Grande Rise. We hypothesize that the trend and larger mean heat flux of the Walvis Ridge is best explained by a hot-spot origin, perhaps combined with higher radioactivity in the crust. However, the morphologic and heat flow differences between the Walvis Ridge and Rio Grande Rise suggest that these features have different geologic histories.  相似文献   

3.
Heat flow values were calculated from direct measurements of temperature and thermal conductivity at thirteen sites in the Arkansas-Missouri Ozark Plateau region. These thirteen values are augmented by 101 estimates of heat flow, based on thermal conductivity measurements and temperature gradients extrapolated from bottom-hole temperatures. The regional heat flow profile ranges from 9 mW m−2 to over 80 mW m−2, but at least two distinct thermal regimes have been identified. Seven new heat flow determinations are combined with three previously published values for the St. Francois Mountains (SFM), a Precambrian exposure of granitic and rhyolitic basement rocks, average 47 mW m−2. Radioactive heat production of 76 samples of the exposed rocks in the SFM averages 2.4 μW m−2 and a typical continental basement contribution of 14 mW m−2 is implied. Conversely, the sedimentary rock sequence of the plateau is characterized by an anomalously low heat flow, averaging approximately 27 mW m−2. Groundwater transmissivity values that are based on data from 153 wells in deep regional aquifers demonstrate an inverse relationship to the observed heat flow patterns. The areas of high transmissivity that correspond to areas of low total heat flux suggest that the non-conservative vertical heat flow within the Ozark sedimentary sequence can be attributed to the effects of groundwater flow.  相似文献   

4.
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.  相似文献   

5.
We have obtained a suite of 42 closely spaced, acoustically navigated, heat flow measurements on well-sedimented crust of anomaly M0 age (109 Ma) in the northwest Atlantic Ocean (25°N, 68°W; 950 km south of Bermuda). The mean and standard deviation of the values obtained are 1.13 HFU (μcal/cm2 s) (47.3 mW/m2) and 0.05 HFU (2.1 mW/m2), respectively. Some of the variability is accounted for by refractive effects of the basement topography. Drill core data and our modelling suggest that the thermal conductivity contrast between sediments and basement rocks in this region is less than a factor of 1.6. The mean heat flow is close to the 1.1 HFU (46 mW/m2) predicted by both the plate and boundary layer cooling models of the oceanic lithosphere. This is the first detailed comparison with theoretical cooling models on old Atlantic Ocean crust. Since the difference in surface heat flow (0.15 HFU) predicted by the two cooling models for the oldest observed oceanic lithosphere (180 Ma) is also not much larger than the range of uncertainty in our observations, discrimination between the two models on the basis of surface heat flow data alone may prove difficult.  相似文献   

6.
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.  相似文献   

7.
The eastern Pontides orogenic belt is one of the most complex geodynamic settings in the Alpine–Himalayan belt due to the lack of systematical geological and geophysical data. In this study, 1D crustal structure and P-wave velocity distribution obtained from gravity modeling and seismological data in the area has been used for the development of the thermal model of the eastern Pontides orogenic belt. The computed temperature-depth profiles suggest a temperature of 590?±?60°C at a Moho depth of 35?km indicates the presence of a brittle-ductile transition zone. This temperature value might be related to water in the subducted crust of the Tethys oceanic lithosphere. The Curie temperature depth value of 29?km, which may correspond to the crustal magma chambers, is found 5–7?km below the Moho depth. Surface heat flow density values vary from 66.5 and 104.7?mW?m?2. High mantle heat flow density value of 48?mW?m?2 is obtained for the area should be related to melting of the lithospheric mantle caused by upwelling of asthenosphere.  相似文献   

8.
The results of seismic measurements along the deep seismic sounding profile VII and terrestrial heat flow measurements used for construction of heat generation models for the crust in the Paleozoic Platform region, the Sudetic Mountains (Variscan Internides) and the European Precambrian Platform show considerable differences in mantle heat flow and temperatures. At the base of the crust variations from 440–510°C in the models of Precambrian Platform to 700–820°C for the Paleozoic Platform and the Variscan Internides (Sudets) are found. These differences are associated with considerable mantle heat flow variations.The calculated models show mantle heat flow of about 8.4–12.6 mW m–2 for the Precambrian Platform and 31 mW m–2 to 40.2 mW m–2 for Paleozoic orogenic areas. The heat flow contribution originating from crustal radioactivity is almost the same for the different tectonic units (from 33.5 mW m–2 to 37.6 mW m–2). Considerable physical differences in the lower crust and upper mantle between the Precambrian Platform and the adjacent areas, produced by lateral temperature variations, could be expected. On the basis of carbon ratio data it can be concluded that the Carboniferous paleogeothermal gradient was much lower in the Precambrian Platform area than in the Paleozoic Platform region.  相似文献   

9.
On the evolution of the geothermal regime of the North China Basin   总被引：1，自引：0，他引：1  
Recent heat flow and regional geothermal studies indicate that the North China Basin is characterized by relatively high heat flow compared with most stable areas in other parts of the world, but lower heat flow than most active tectonic areas. Measured heat flow values range from 61 to 74 mW m−2. The temperature at a depth of 2000 m is generally in the range 75 to 85°C, but sometimes is 90°C or higher. The geothermal gradient in Cenozoic sediments is in the range 30 to 40°C/km for most of the area. The calculated temperature at the Moho is 560 and 640°C for surface heat flow values of 63 and 71 mW m−2, respectively. These thermal data are consistent with other geophysical observations for the North China Basin. Relatively high heat flow in this area is related to Late Cretaceous-Paleogene rifting as described in this paper.  相似文献   

10.
Application of the silica geothermometer to over 70,000 non-thermal groundwaters from the United States has shown that there is a correlation between the average silica geotemperatures for a region (T SiO2 in °C) and the known regional heat flow (q in mW m?2) of the form: 1 $$TSiO_2 = mq + b$$ wherem andb are constants determined to be 0.67°C m2 mW?1 and 13.2°C respectively. The physical significance of ‘b’ is the mean annual air temperature. The slope ‘m’ is related to the minimum average depth to which the groundwaters may circulate. This minimum depth is estimated to be between 1.4 and 2.0 km depending on the rock type. A preliminary heat flow map based on equation (1) is presented using theT SiO2 for new estimates of regional heat flow where conventional data are lacking. Anomalously high localT SiO2 values indicate potential geothermal areas.  相似文献   

11.
The Chinese Continental Scientific Drilling (CCSD) project is located at the Sulu ultrahigh-pressure metamorphic (UHPM) belt. It offers a unique opportunity for studying the radiogenic heat production of both shallower and deeper rocks. Based on the concentrations of radiogenic elements U, Th and K on 349 samples from main hole of CCSD (CCSD MH), pilot holes and exposures, we determined radiogenic heat productions of all major rock types in the Sulu UHPM belt. Results show the mean values of orthogneiss and paragneiss are respectively 1.65 ± 0.81 and 1.24 ± 0.61 µW m? 3. Due to different composition and grade of retrogressive metamorphism, the eclogites display significant scatter in radiogenic heat production, ranging from 0.01 to 2.85 µW m? 3, with a mean of 0.44 ± 0.55 µW m? 3. The radiogenic heat production in ultramafic rocks also varies within a large range of 0.02 to 1.76 µW m? 3, and the average turns out to be 0.18 ± 0.31 µW m? 3. Based on the measurements and crustal petrologic model, the vertical distribution model of heat production in Sulu crust is established. The resulting mean heat production (0.76 µW m? 3) contributes 24 mW m? 2 to the surface heat flow. 1-D thermal model indicates that the temperature at the Moho reaches above 750 °C, and the thermal thickness of the lithosphere is ~ 75 km, in good agreement with the geophysical results. The high teat flow (~ 75 mW m? 2) together with thin lithosphere presents strong support for the extension events during the late Cretaceous and Cenozoic.  相似文献   

12.
A heat flow isoline map is presented. Low and relatively constant heat flow has been observed in the old shield areas of the East European Platform (25–40 mW/m2). Increased heat flow (>50 mW/m2) has been found in the Dniepr-Donetz depression. The area south of the East European Platform is characterized by highly variable heat flow (55–100 mW/m2). Some geophysical implications are discussed.  相似文献   

13.
A standard core analysis technique has been modified to estimate porosities from measurements on rock fragments. For the range of rocks tested, chip-determined fractional porosities were within ±0.025 of the values measured on solid-core samples. This has enabled thermal conductivity measurements on rock fragments to be corrected for the effect of porosity, yielding agreement with conductivity determinations on solid core generally to better than ± 10%. The application of this is illustrated by the determination of heat flow in a 300-m borehole in western Cyprus (latitude 34°54′N, longitude 32°34′E, elevation 82 m). A decrease in temperature gradient with depth is almost completely compensated for by increasing thermal conductivity, and the best value for heat flow at this site is 23 ± 4 mW m?2.  相似文献   

14.
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.  相似文献   

15.
Regional groundwater flow in deep aquifers adds advective components to the surface heat flow over extensive areas within the Great Plains province. The regional groundwater flow is driven by topographically controlled piezometric surfaces for confined aquifers that recharge either at high elevations on the western edge of the province or from subcrop contacts. The aquifers discharge at lower elevations to the east. The assymetrical geometry for the Denver and Kennedy Basins is such that the surface areas of aquifer recharge are small compared to the areas of discharge. Consequently, positive advective heat flow occurs over most of the province. The advective component of heat flow in the Denver Basin is on the order of 15 mW m−2 along a zone about 50 km wide that parallels the structure contours of the Dakota aquifer on the eastern margin of the Basin. The advective component of heat flow in the Kennedy Basin is on the order of 20 mW m−2 and occurs over an extensive area that coincides with the discharge areas of the Madison (Mississippian) and Dakota (Cretaceous) aquifers. Groundwater flow in Paleozoic and Mesozoic aquifers in the Williston Basin causes thermal anomalies that are seen in geothermal gradient data and in oil well temperature data. The pervasive nature of advective heat flow components in the Great Plains tends to mask the heat flow structure of the crust, and only heat flow data from holes drilled into the crystalline basement can be used for tectonic heat flow studies.  相似文献   

16.
The tectonic stresses can significantly affect the propagation of a magma-filled crack. It has been pointed out that the rheological boundaries control the emplacement of magmas through the effect of stress. However, it has not been clarified how the role of rheological boundaries depends on the regional tectonic and thermal states. We have evaluated the role of rheological boundaries under various tectonic and thermal conditions and found that the level of magma emplacement may jump according to the changes in the tectonic force or the surface heat flow. The stress profiles were estimated by a simple model of lithospheric deformation. We employed a three-layer model of the lithosphere; the upper crust, the lower crust and the upper mantle have different rheological properties. A constant horizontal force is applied to the lithosphere, and the horizontal strain is assumed to be independent of depth. When realistic tectonic forces (>1011 N/m) are applied, the rheological boundaries mainly control the emplacement of magma. The emplacement is expected at the MOHO, the upper–lower crust boundary, and the brittle–ductile boundary. For lower tectonic forces (<1011 N/m), the tectonic stress no longer plays an important role in the emplacement of magmas. When the tectonic stress controls the emplacement, the roles of rheological boundaries strongly depend on the surface heat flow. When the surface heat flow is relatively high (>80 mW/m2), the stress in the mantle is quite low and the MOHO cannot trap ascending magmas. For relatively low heat flow (<80 mW/m2), on the other hand, the MOHO acts as a magma trap, and the upper–lower crust boundary acts as a magma trap only when the magma supply rate is sufficiently high. Our results suggest that the emplacement depth can change responding to the change in the tectonic force and/or that in the surface heat flow. This may provide us a key to understand the relation between the evolution of a volcanic region and its tectonic and/or thermal history.  相似文献   

17.
Heat flows were determined at 12 sites in four distinct areas between longitude 77° and 80°W in eastern Panama and northwestern Colombia. Evidently, most of the region is underlain by mafic oceanic crust so that the crustal radiogenic component of heat flow is very small (～ 0.1 μcal cm?2 sec?1). Low heat-flow values (～ 0.7 μcal cm?2 sec?1) in northwestern Colombia may reflect thermal transients associated with shallow subduction. The normal values (～ 1) at about 78°W are consistent with the mean heat flow from the western Caribbean and the Gulf of Mexico. At 80°W, a fairly high value of 1.8 may define the easterly limit of thermal transients due to Cenozoic volcanic activity in Central America.  相似文献   

18.
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.  相似文献   

19.
Summary The results of geothermal research carried out in South Siberia (West-Siberian and Siberian Platforms, Altai-Sayan folded area and the Baikalian arched uplift zone) were employed to calculate the Earth's crustal temperatures. It is shown that temperature is a function of the heat flow value. The maps of the surface heat flow and the temperatures at the Moho discontinuity are presented and characteristic temperature-depth profiles were compiled for specific tectonic areas. The West-Siberian and Siberian Platforms, as well as the Altai-Sayan folded region are characterized by rather low heat flow, 42–50mW m –2 (1.0–1.2 µcal/cm 2 s), and low temperatures at the Moho boundary.400–500 °C. The thermal conditions in the area of Lake Baikal are extreme, the heat flow reaches here100–142 mW m –2 (2.4–3.4 µcal/cm 2 s), and the temperature at the crust's bottom may exceed1000 °C. The Moho-surface according to our calculations is nonisothermal.  相似文献   

20.
The analyzing data on stratigraphic temperature measurement, thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93 °C/100 m, and the average heat flow value is 61.78 mW/m2, which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.  相似文献   

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