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1.
2.
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   

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.
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   

5.
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   

6.
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   

7.
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   

8.
Summary The radiogenic heat production of rock samples from boreholes in the Bohemian Massif has been calculated from gamma-radiometric determinations of Th, U and K contents. The results, in general, fit the heat flow distribution on the territory of Czechoslovakia[1]. The values of heat production are in the range from 1.1µW m3 in the eastern part to 4.4µW m3 in the north-western part of the Bohemian Massif.  相似文献   

9.
Summary Temperature and conductivity measurements show, that in the Southern part of Transdanubia (the part of Hungary which lies Westwards from Danube) the heat flow is about 2–2.4·10–6 cal/cm2 sec. Eastward from the Danube, in the Hungarian Plain estimates are even higher, and vary between 2.3·10–6 and 2.8·10–6 cgs. The gradient of temperature is everywhere quite high, 5.0 resp. 5.8·10–4 deg. C/cm on the average. Thus, at a depth of 1000 m, the virgin rock temperature is about 60–70 deg. C, at 2000 m about 110–130 deg. C.  相似文献   

10.
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   

11.
Summary The temperature-depth distribution was calculated to a depth of 70 km along the 520 km long Taratashskiy refraction profile crossing the Ural Mts., approximately along latitude 56°N. The steady-state model was solved numerically using the finite-difference method, the vertical distribution of heat production was derived from the observed seismic velocities. It was shown that at the Moho boundary, the mantle heat flow varied between 10 and 25 mWm–2, and the Moho temperature amounted to 300–550°C for the two versions studied.  相似文献   

12.
Summary The geothermal gradient in the Carpathian Basin lies between 40–70 C/km. According to careful measurements in shafts the value of terrestrial heat flow in the southern part of Hungary is (2.055–3.066)·10–6 cal/cm2 sec. These measurements are believed the first ever attempted in continental Europe. Systematic heat flow measurement are being extended to other part of this country.  相似文献   

13.
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   

14.
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.  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.
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   

17.
The surface heat flow in the interior of Archean cratons is typically about 40 mW m−2 while that in Proterozoic and younger terrains surrounding them is generally considerably higher. The eighty-four heat flow observations from southern Africa provide an excellent example of this contrast in surface heat flow, showing a difference of some 25 mW m−2 between the Archean craton and younger peripheral units. We investigate two possible contributions to this contrast: (1) a shallow mechanism, essentially geochemical, comprising a difference in crustal heat production between the two terrains, and (2) a deeper mechanism, essentially geodynamical, arising from the existence of a lithospheric root beneath the Archean craton which diverts heat away from the craton into the thinner surrounding lithosphere. A finite element numerical model which explores the interplay between these two mechanisms suggests that a range of combinations of differences in crustal heat production and lithospheric thickness can lead to the contrast in surface heat flow observed in southern Africa. Additional constraints derived from seismological observations of cratonic roots, the correlation of surface heat flow and surface heat production, petrological estimates of the mean heat production in continental crust and constraints on upper mantle temperatures help narrow the range of acceptable models. Successful models suggest that a cratonic root beneath southern Africa extends to depths of 200–400 km. A root in this thickness range can divert enough heat to account for 50–100% of the observed contrast in surface heat flow, the remainder being due to a difference in crustal heat production between the craton and the surrounding mobile belts in the range of zero to 0.35 μW m−3.  相似文献   

18.
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   

19.
We propose a thermal model of the subducting Ionian microplate. The slab sinks in an isothermal mantle, and for the boundary conditions we take into account the relation between the maximum depth of seismicity and the thermal parameter Lth of the slab, which is a product of the age of the subducted lithosphere and the vertical component of the convergence rate. The surface heat-flux dataset of the Ionian Sea is reviewed, and a convective geotherm is calculated in its undeformed part for a surface heat flux of 42 mW m–2, an adiabatic gradient of 0.6 mK m–1, a mantle kinematic viscosity of 1017 m2 s–1 and an asthenosphere potential temperature of 1300°C. The calculated temperature-depth distribution compared to the mantle melting temperature indicates the decoupling limit between lithosphere and asthenosphere occurs at a depth of 105 km and a temperature of 1260°C. A 70–km thick mechanical boundary layer is found. By considering that the maximum depth of the seismic events within the slab is 600 km, a Lth of 4725 km is inferred. For a subduction rate equal to the spreading rate, the corresponding assimilation and cooling times of the microplate are about 7 and 90 Myr, respectively. The thermal model assumes that the mantle flow above the slab is parallel and equal to the subducting plate velocity of 6 cm yr–1, and ignores the heat conduction down the slab dip. The critical temperature, above which the subduced lithosphere cannot sustain the stress necessary to produce seismicity, is determined from the thermal conditions governing the rheology of the plate. The minimum potential temperature at the depth of the deepest earthquake in the slab is 730°C.  相似文献   

20.
We present a set of 39 new determinations of heat flow and radiogenic heat production for several different geological environments in the State of New Hampshire (U.S.A.). With the extensive data set now available for the state, the linear relation of heat flow and heat production appears as a very useful generalization for the study of the heat flow field of a geological province. Our measurements indicate that the vertical distribution of radiogenic heat production is similar in plutonic and metasedimentary rocks. Our data are compatible with the linear relationship established earlier by F. Birch and his co-workers in 1968. Young granites are markedly enriched in radioactive elements and those which do not outcrop are revealed by anomalies in the general relation of heat flow versus radioactivity.Heat flow is high for plutons by low elsewhere. The mean heat flow through metasedimentary formations is 1.15 μcal/cm2 s (48 mW/m2), a value near the mean heat flow for old cratons. The lowest heat flow measured is 0.76 μcal/cm2 s (32 mW/m2) for a unit poor in radioactivity. The heat flow field grades smoothly into the low heat flow regions of the Canadian Shield.The New Hampshire region is in thermal equilibrium: its heat flow is in secular equilibrium with the heat generated by crustal sources and that supplied from the mantle. In this area, the thermal perturbations due to orogenic events decrease below the detection level in less than 200–275 Ma. The thickness of the layer which is thermally affected during continent-continent collision-type orogenies cannot be greater than about 190 km.  相似文献   

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