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1.
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.  相似文献   

2.
The Red Sea is a modern example of continental fragmentation and incipient ocean formation. Heat flow data have been collected from eastern Egypt to provide information relating to the mode and mechanism of Red Sea opening. Preliminary heat flow data, including new data reported here, are now available from twenty-five sites in eastern Egypt and one site in western Sinai. A pattern of low to normal heat flow (35–55 mW m−2) inland with high heat flow (75–100 mW m−2) in a zone within 30 to 40 km of the coast is indicated.Moderately high heat flow (around 70 mW m−2) is indicated for the Gulf of Suez. The coastal zone thermal anomaly appears continuous with high heat flow previously reported for the Red Sea shelf. Heat production data indicate that the coastal thermal anomaly is not primarily related to crustal radiogenic heat production. The effects of rapid erosion may contribute to the anomaly, but are not thought to be the primary cause of the anomaly. If the anomaly is caused by lateral conduction from hot, extended, offshore lithosphere, the extension must have been active for the last 30 Ma or so, and a minimum of 100% extension is indicated. Alternatively, the anomaly is primarily caused by high mantle heat flow causing lithospheric thinning, centred beneath the Red Sea. The Red Sea is probably underlain by dominantly basic crust, formed either by intrusion into attenuated continental crust or sea-floor spreading, and for most purposes the crust formed in these two modes of extension may be essentially indistinguishable. Fission-track ages from eastern Egypt indicate that uplift started prior to, or at latest at the time of initial Red Sea opening, and this result, together with thermo-mechanical considerations, suggests an active asthenospheric upwelling beneath the Red Sea and high temperature in the lithosphere prior to extension.  相似文献   

3.
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   

4.
Crustal and lithospheric thicknesses of the southeastern Mediterranean Basin region were determined using 3D Bouguer and elevation data analysis. The model is based on the assumption of local isostatic equilibrium. The calculated regional and residual Bouguer anomaly maps were employed for highlighting both deep and shallow structures. Generally, the regional field in the area under study is considered to be mainly influenced by the density contrast between the crust and upper mantle. Use of the gravity and topographic data with earthquake focal depths has improved both the geometry and the density distribution in the 3-D calculated profiles. The oceanic-continental boundary, the basement relief, Moho depth and lithosphere-asthenosphere boundary maps were estimated. The results point to the occurrence of thick continental crust areas with a thickness of approximately 32 km in northern Egypt. Below the coastal regions, the thickness of crust decreases abruptly (transition zone). An inverse correlation between sediment and crustal thicknesses shows up from the study. Furthermore, our density model reveals the existence of a continental crustal zone below the Eratosthenes Seamount block. Nevertheless, the crustal type beneath the Levantine basin is typically oceanic; this is covered by sedimentary sequences more than 14 km thick. The modeled Moho map shows a depth of 28–30 km below Cyprus and a depth of 26–28 km beneath the south Florence Rise in the northern west. However, the Moho lies at a constant shallow depth of 22–24 km below the Levantine Basin, which indicates thinning of the crust beneath this region. The Moho map reveals also a maximum depth of about 33–35 km beneath both the northern Egypt and northern Sinai, both of which are of the continental crust. The resulting mantle density anomalies suggest important variations of the lithosphere-asthenosphere boundary (LAB) topography, indicating prominent lithospheric mantle thinning beneath south Cyprus (LAB ~90 km depth), followed by thickening beneath the Eratosthenes seamount, Florence Rise, Levantine Basin and reaching to maximum thickness below Cyprian Arc (LAB ~115–120 km depth), and further followed by thinning in the north African margin plate and north Sinai subplate (LAB ~90–95 km depth). According to our density model profiles, we find that almost all earthquakes in the study area occurred along the western and central segments of the Cyprian arc while they almost disappear along the eastern segment. The active subduction zone in the Cyprian Arc is associated with large negative anomalies due to its low velocity upper mantle zone, which might be an indication of a serpentinized mantle. This means that collision between Cyprus and the Eratosthenes Seamount block is marked by seismic activity. Additionally, this block is in the process of dynamically subsiding, breaking-up and being underthrusted beneath Cyprus to the north and thrusted onto the Levantine Basin to the south.  相似文献   

5.
The aeromagnetic values over the study region are relatively uniform except for a few anomalies in the northeastern and southwestern areas. Analyses of aeromagnetic data were performed in NW Turkey, in order to have a look into the subsurface regional thermal structure of the region. For this purpose, power spectra, reduced to pole (RTP), and band-pass filtered anomalies were produced using geophysical techniques. Band-pass filtered data were produced from the RTP aeromagnetic anomalies to isolate near surface and undesired deep effects. Based on the aeromagnetic data interpretation, the thickness of the magnetized crust, named the Curie Point Depth (CPD), in the study area lies between 9.7 and 20.3 km. The CPD estimates in the Thrace region of Turkey indicate two shallow CPD (SCPD1 and SCPD2) zones (the Istranca Massif and the Saros Graben area). The deep CPD are located within the Thrace Basin with sediment thickness of about 9 km. The corresponding heat flow map prepared from the averaged thermal conductivities and thermal gradients from the CPD reveals the existence of one low heat flow zone (75 mW/m2) over the center of Thrace Basin, and two high heat flow zones over the Istranca Masif (100–125 mW/m2) in the northern side and Saros Graben (125–135 mW/m2) areas in the southern side of the Thrace Basin.  相似文献   

6.
In southern British Columbia the terrestrial heat flow is low (44 mW m–2) to the west of the Coast Plutonic Complex (CPC), average in CPC (50–60 mW m–2),and high to the east(80–90 mW m–2). The average heat flow in CPC and the low heat generation (less than 1 W m–3) indicate that a relatively large amount of heat flows upwards into the crust which is generally quite cool. Until two million years ago the Explorer plate underthrust this part of the American plate, carrying crustal material into the mantle. Melted crustal rocks have produced the inland Pemberton and Garibaldi volcanic belts in the CPC.Meager Mountain, a volcanic complex in the CPC 150 km north of Vancouver, is a possible geothermal energy resource. It is the product of intermittent activity over a period of 4 My, the most recent eruption being the Bridge River Ash 2440 y B.P. The original explosive eruption produced extensive fracturing in the granitic basement, and a basal explosion breccia from the surface of a cold brittle crust. This breccia may be a geothermal reservoir. Other volcanic complexes in the CPC have a similar potential for geothermal energy.Earth Physics Contribution No. 704.  相似文献   

7.
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   

8.
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   

9.
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10.
Rayleigh wave group velocity data from paths crossing the Levantine Sea are presented. We have derived a suite of models for the crustal structure of the Levantine Sea for extreme values of data errors and of the data corrections which were applied in order to account for lateral heterogeneity.We conclude that models with a crustal thickness less than 30 km are not consistent with the data. Our preferred models are characterized by a crustal thickness of 35–40 km. These results and the presence of an extremely thick sedimentary sequence point to a passive continental margin type of structure underlying the Levantine Sea. Additional data from the path Sicily-Jerusalem suggest that this type of structure is representative of the whole of the eastern Mediterranean (Levantine Sea and Ionian Sea).  相似文献   

11.
Large variations in terrestrial heat flow from 21 to 209 mW/m2 have been observed over the North Island, New Zealand. This is generally in good agreement with the pattern of existing geological and geophysical observations. A high heat flow zone with a value of 92 ±3 mW/m2, which corresponds to melting temperatures near the base of the crust, is delineated in the northern part of the Taranaki Basin. In the rest of the island, heat flow appears to be low to normal, but some isolated high values are also found. Observed results are interpreted in terms of crust and mantle structure in a region of plate subduction.  相似文献   

12.
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   

13.
Based on the data of geo-temperature and thermophysical parameters of rocks in the Kuqa Depression and the Tabei Uplift, northern flank of the Tarim Basin, in terms of the analytical solution of 1-D heat transfer equation, the thermal structure of the lithosphere under this region is determined. Our results show that the average surface heat flow of the northern flank of the Tarim Basin is 45 mW/m2, and the mantle heat flow is between 20 and 23 mW/m2; the temperature at crust-mantle boundary (Moho) ranges from 514℃ to 603℃ and the thermal lithosphere where the heat conduction dominates is 138-182 km thick. Furthermore, in combination with the P wave velocity structure resulting from the deep seismic sounding profile across this region and rheological modeling, we have studied the local composition of the lithosphere and its rheological profile, as well as the strength distribution. We find that the rheological stratification of the lithosphere in this region is apparent. The lowermost of the lower crust is ductile; however,the uppermost of the mantle and the upper and middle parts of the crust are both brittle layers,which is typically the so-called sandwich-like structure. Lithospheric strength is also characterized by the lateral variation, and the uplift region is stronger than the depression region. The lithospheric strength of the northem flank of the Tarim Basin decreases gradually from south to north; the Kuqa Depression has the lowest strength and the south of the Tabei Uplift is strongest.The total lithospheric strength of this region is 4.77× 1012-5.03 × 1013 N/m under extension, and 6.5 × 1012-9.4× 1013 N/m under compression. The lithospheric brittle-ductile transition depth is between 20 km and 33 km. In conclusion, the lithosphere of the northern flank of the Tarim Basin is relatively cold with higher strength, so it behaves rigidly and deforms as a whole, which is also supported by the seismic activity in this region. This rigidity of the Tarim lithosphere makes it little deform interior, but only into flexure under the sedimentation and tectonic loading associated with the rapid uplift of the Tianshan at its northern margin during the Indian-Eurasian continental collision following the Late Eocene. Finally, the influences of factors, such as heat flow, temperature,crustal thickness, and especially basin sediment thickness, on the lithospheric strength are discussed here.  相似文献   

14.
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   

15.
Summary The surface thermal flux of the continental margins of the northwestern Mediterranean Sea is interpreted on the basis of a 1-D instantaneous pure shear stretching model of the lithosphere in terms of three components: the background heat flowing out from the asthenosphere (38 mW m–2), the transient contribution depending on the rift age and extension amount (35 mW m–2 at the most), and the contribution due to the radiogenic elements of the lithosphere. The radiogenic component is estimated at the continental margins of the Ligurian-Provençal basin and Valencia trough, and in the surrounding mainland areas by means of available data of surface heat generation from Variscan Corsica, Maures-Estérel and the Central Massif along with a geophysical-petrological relationship between heat production and seismic velocity. The lithosphere radiogenic heat contribution ql decreases with the thinning factor according to the exponential law: ql() = a exp(-b), in which factor b is greater for that part of the lithosphere below the uppermost 10 km. Considering also the heat generated by radioactive isotopes in sediments, the stable Variscan lithosphere produces an average thermal flux of 30 mW m–2 which decreases by about one half where the lithosphere is thinned by one third. Although the surface heat generation is 2·1 – 3·3 µW m–3 in the Maures-Estérel massif — excepting small outcrops of dioritic rocks with lower heat production — and 1·8 µW m–3 for most of Corsica, the radiogenic heating within the lithosphere for such areas is nearly the same and does not explain the higher heat flux of the Corsica margin. This asymmetric thermal pattern with surface heat flux which is 10 – 15 mW m–2 higher than predictions is probably of upper mantle origin, or can be ascribed to penetrative magmatism.  相似文献   

16.
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   

17.
Continental shield regions are normally characterized by low-to-moderate mantle heat flow. Archaean Dharwar craton of the Indian continental shield also follows the similar global pattern. However, some recent studies have inferred significantly higher mantle heat flow for the Proterozoic northern block of Southern Granulite Terrain (SGT) in the immediate vicinity of the Dharwar craton by assuming that the radiogenic elements depleted exposed granulites constitute the 45-km-thick crust. In this study, we use four-layered model of the crustal structure revealed by integrated geophysical studies along a geo-transect in this region to estimate the mantle heat flow. The results indicate that: (i) the mantle heat flow of the northern block of SGT is 17 ± 2 mW/m2, supporting the global pattern, and (ii) the lateral variability of 10–12 mW/m2 in the surface heat flow within the block is of crustal origin. In terms of temperature, the Moho beneath the eastern Salem–Namakkal region appears to be at 80–100 °C higher temperature than that beneath the western Avinashi region.  相似文献   

18.
Heat flow values from some additional locations in the Cenozoic Cambay Basin have been determined. Together with the previously published data, they show that the heat flow is moderate (55–67 mW/m′) in the southern part of the basin towards Broach and Ankleswar, and that there is a clear trend of high heat flow (75–93 mW/m2; range of average values for six different, widely separated, locations) in a part of the basin located north of the Mahisagan river between Cambay and Mehsana along a stretch of about 140 km. Conductive steady state geotherms, calculated using observed high surface heat flow values and appropriate models show, beneath the Cambay-Mehsana area, a large degree of melting in the lower crust and upper mantle, which is not suggested by the existing geodata. Considering this aspect and taking into account the existence of a normal crust about 37 km thick below the Cambay-Tarapur and Ahmedabad-Mehsana blocks (as obtained from deep seismic soundings), it has been inferred that the heat flow anomaly is due to transient thermal perturbations introduced from tectonic activity in the form of magmatic intrusions. A careful analysis of heat flow, gravity and other related geodata point out and support the possibility of a Miocene/Pliocene basic intrusive body at a depth of around 10 km under the Cambay-Mehsana area. Further, the consistent trend of the thermal and gravity fields indicates thinning of the postulated intrusive body from Cambay towards Mehsana.  相似文献   

19.
Twenty-five new heat flow measurements made in the Gulf of California are presented. All the values except two at the mouth of the Gulf and two in the Sal si Puedes basin are high. The values ranged from 2.0 to greater than 10 μcal/cm2 sec (82 to > 420 mW/m2) with eight values greater than 5.2 (210 mW/m2). Due to high rates of sedimentation throughout the Gulf, the actual heat flow, in many cases, may be up to 25% greater than that recorded.Most of the heat flow stations are concentrated in the Farallon and Guaymas basins and show a marked increase towards the central deeps, where new crust is believed to be forming. The heat flow values in the Farallon basin show a sharp peak 10–15 km southeast of the central depression while those in the Guaymas basin peak in the depression.The heat flow profiles across the Guaymas and Farallon basins are remarkably similar to those observed on other well sedimented spreading centers such as the northern portion of the Explorer trough. Thus they may provide evidence that the crust is being created by an axially symmetric intrusion process with a major loss of heat due to hydrothermal circulation. The absence of magnetic anomalies in the Gulf has been attributed to the supposed presence of large grains in the intruded basalt. Large grains form by the slow cooling of the basalt under a layer of sediment. Prominent magnetic anomalies have been observed on the northern portion of the Explorer trough. Observational data suggest that the thermal processes at this ridge axis and the center of the Farallon basin are identical. We suggest that further careful study is needed in the Gulf before the slow cooling model is accepted as an explanation for the attenuation of the magnetic anomalies.  相似文献   

20.
An attempt is made to obtain a combined geophysical model along two regional profiles: Black Sea— White Sea and Russian Platform—French Central Massif. The process of the model construction had the following stages: 1. The relation between seismic velocity (Vp, km/s) and density (σ, g/cm3) in crustal rocks was determined from seismic profiles and observed gravity fields employing the trial and error method. 2. Relations between heat production HP (μW/m3), velocity and density were established from heat flow data and crustal models of old platforms where the mantle heat flow HFM is supposed to be constant. The HFM value was also determined to 11 ± 5 mW/m2. 3. A petrological model of the old platform crust is proposed from the velocity-density models and the observed heat flow. It includes 10–12 km of acid rocks, 15–20 km of basic/metamorphic rocks and 7–10 km of basic ones. 4. Calculation of the crustal gravity effects; its substraction from the observed field gave the mantle gravity anomalies. Extensively negative anomalies have been found in the southern part of Eastern Europe (50–70 mgal) and in Western Europe (up to 200 mgal). They correlate with high heat flow and lower velocity in the uppermost mantle. 5. A polymorphic advection mechanism for deep tectonic processes was proposed as a thermal model of the upper mantle. Deep matter in active regions is assumed to be transported (advected) upwards under the crust and in its place the relatively cold material of the uppermost mantle descends. The resulting temperature distribution depends on the type of endogeneous regime, on the age and size of geostructure. Polymorphic transitions were also taken into account.  相似文献   

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