Heat flow and lithospheric thermal regime in the Northeast German Basin

New values of surface heat flow are reported for 13 deep borehole locations in the Northeast German Basin (NEGB) ranging from 68 to 91 mW m^− 2 with a mean of 77 ± 3 mW m^− 2. The values are derived from continuous temperature logs, measured thermal conductivity, and log-derived radiogenic heat production. The heat-flow values are supposed free of effects from surface palaeoclimatic temperature variations, from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow. Two-D numerical lithospheric thermal models are developed for a 500 km section along the DEKORP-BASIN 9601 deep seismic line across the basin with a north-eastward extension across the Tornquist Zone. A detailed conceptual model of crustal structure and composition, thermal conductivity, and heat production distribution is developed. Different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow. The best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the NEGB. This estimate is corroborated by seismological studies and somewhat less than typical for stabilized Phanerozoic lithosphere. Modelled Moho temperatures in the basin are about 800 °C; heat flow from the mantle is about 35 to 40 mW m^− 2. In the southernmost part of the section, beneath the Harz Mountains, higher Moho temperatures up to 900 to 1000 °C are shown. While the relatively high level of surface heat flow in the NEGB obviously is of longer wave length and related to lithosphere thickness, changes in crustal structure and composition are responsible for short-wave-length anomalies.     

Heat flow and thermal modeling of the Yinggehai Basin, South China Sea

Geothermal gradients are estimated to vary from 31 to 43 °C/km in the Yinggehai Basin based on 99 temperature data sets compiled from oil well data. Thirty-seven thermal conductivity measurements on core samples were made and the effects of porosity and water saturation were corrected. Thermal conductivities of mudstone and sandstone range from 1.2 to 2.7 W/m K, with a mean of 2.0±0.5 W/m K after approximate correction. Heat flow at six sites in the Yinggehai Basin range from 69 to 86 mW/m², with a mean value of 79±7 mW/m². Thick sediments and high sedimentation rates resulted in a considerable radiogenic contribution, but also depressed the heat flow. Measurements indicate the radiogenic heat production in the sediment is 1.28 μW/m³, which contributes 20% to the surface heat flow. After subtracting radiogenic heat contribution of the sediment, and sedimentation correction, the average basal heat flow from basement is about 86 mW/m².Three stages of extension are recognized in the subsidence history, and a kinematic model is used to study the thermal evolution of the basin since the Cenozoic era. Model results show that the peak value of basal heat flow was getting higher and higher through the Cenozoic. The maximum basal heat flow increased from 65 mW/m² in the first stage to 75 mW/m² in the second stage, and then 90 mW/m² in the third stage. The present temperature field of the lithosphere of the Yinggehai Basin, which is still transient, is the result of the multistage extension, but was primarily associated with the Pliocene extension.     

Heat flow, heat production and fission track data from the Hercynian basement around the Provençal Basin (Western Mediterranean)

In the complex structural framework of the Western Mediterranean. Hercynian areas are expected to be thermally preserved from the recent tectonic evolution. The thermal regime of these areas is studied using heat flow, heat production and fission track data. The surface heat flow is significantly higher in Corsica (76 ± 10 mW m⁻²) than in the Maures and Estérel (58 ± 2 mW m⁻²). Neither heat production nor erosion subsequent to the Alpine orogeny in Corsica can explain such a difference. It is suggested that a deep thermal source related to the asymmetric evolution of the Provençal basin could explain the higher heat flow in Corsica. A model of thermal structure based on the present day thermal regime of the Maures and Estérei is proposed for the stable Hercynian crust in this area. The mantle heat flow is 20–25 mW m⁻² and the temperature at Moho level is 375–500°C, depending on the thermal parameter distribution with depth.     

Water movement within lac du bonnet batholith as revealed by detailed thermal studies of three closely-spaced boreholes

Successive temperature logs have been obtained over a period of two years in three closely-spaced boreholes in the Lac du Bonnet batholith of the Superior Province of the Canadian Shield. Two of the boreholes, of depth 450 m and 830 m, intersect a dipping fracture zone at 435–450 m. In both holes water is flowing from near the surface to the fracture zone at approximately 1.5–1.9·10⁻⁵ m³ s⁻¹, the flow being inferred from analysis of the temperature logs. Below 25 m, temperatures in these two holes are 0.22–0.28 K lower than those in the third, 145 m, hole.The temperature data have been combined with over 200 thermal conductivity measurements on core samples to produce heat flow values. In the deepest hole heat flow above the fracture zone is 16% higher than that below the zone. This indicates that water is flowing up the fracture zone. The flow rate is approximately 0.3 g s⁻¹ m⁻¹, and the flow has existed for thousands of years.Observation of thermal effects of water flow in massive, relatively unfractured plutons in a region having little topographic relief causes one to be concerned about the reliability of heat flow values measured in similar environments.The regional heat flow is taken to be 50 mW m⁻² after correction for glaciation effects. The average value of 24 determinations of radioactive heat generation in granitic core samples is 5.23 ± 1.11 μW m⁻³, which is more than three times higher than expected for such a heat flow in the Superior Province. This implies that the layer of high radioactive heat generation is thin, being not more than 4 km and probably about 1.3 km thick.     

Contribution to the thermal regime of the Provençal Basin based on Flumed heat flow surveys and previous investigations

We present original heat flow determinations carried out during the Flumed surveys by the CEPM along three transects of the Provençal Basin (Gulf of Lions-West Sardinia; Toulon-Ajaccio; Nice-Calvi). A total of 121 thermal gradients and 37 conductivities are examined together with previous heat flow determinations along depth sections based on previous geophysical investigations. The mean observed heat flows are clearly shown to increase from NW to SE along the profiles (expect for the Toulon-Calvi transect, where results are ambiguous). The observed heat flow increases from 55–65 mW m⁻² (Gulf of Lions) to 85 ± 14 mW m⁻² (West Sardinia) and from 55–65 mW m⁻² (Var Basin) to 103–108 mW m⁻² (lower Corsican margin), suggesting an asymmetrical distribution of the observed heat flow. We examine whether this asymmetry could be caused by thermal refraction above salt structures or by any other superficial cause (sedimentation, topography, etc.) and conclude that an asymmetrical distribution of the subcrustal heat flow is probably the cause of this thermal regime. The elevated heat flows observed to the east in the abyssal plain, corrected for sedimentation, cannot be accounted for by the standard age/heat flow relations established for oceanic or attenuated continental lithosphere. The geodynamic significance of this speculative subcrustal origin remains poorly constrained, but could be related to post-rifting magmatic activity. Further investigations are necessary to elucidate the apparent high local variability of the heat flow on the upper margin of the Gulf of Lions and on the Provençal margin of the Ligurian Sea.     

The variability of heat flow both regional and with depth in southern Alberta, Canada: Effect of groundwater flow?

Detailed studies of terrestrial heat flow in southern and central Alberta estimated on the basis of an order of magnitude larger data base than ever used before (33653 bottom-hole temperature data from 18711 wells) and thermal conductivity values based on detailed rock studies and measured rock conductivities show significant regional and local variations and variations with depth. Heat flow values were estimated for each 3 × 3 township/range area (28.8 × 28.8 km). A difference in heat flow exists between Paleozoic and Mesozoic strata. Generally lower heat flow values are observed in the strata above the Paleozoic erosional surface (20–75 mW m⁻²). Much higher values are estimated for the Younger Paleozoic formations, with large local and regional variations between 40 and 100 mW m⁻².Average heat flow values based on heat flow determinations below and above the Paleozoic surface that agree within 20% show an increase from values less than 40 mW m⁻² in southern and southwestern Alberta to values as high as 70 mW m⁻² in central Alberta. The predominance of regional downward groundwater flows in Mesozoic strata seem to be responsible for the generally observed heat flow increase with depth.The results show that the basin heat flow pattern is influenced by water movement and even careful detailed heat flow measurements will not give correct values of background steady-state heat flow within the sedimentary strata.     

Thermal and mechanical structure of the central Iberian Peninsula lithosphere

The central Iberian Peninsula (Spain) is made up of three main tectonic units: a mountain range, the Spanish Central System and two Tertiary basins (those of the rivers Duero and Tajo). These units are the result of widespread foreland deformation of the Iberian plate interior in response to Alpine convergence of European and African plates. The present study was designed to investigate thermal structure and rheological stratification in this region of central Spain. Surface heat flow has been described to range from 80 to 60 mW m⁻². Highest surface heat flow values correspond to the Central System and northern part of the Tajo Basin. The relationship between elevation and thermal state was used to construct a one-dimensional thermal model. Mantle heat flow drops from 34 mW m⁻² (Duero Basin) to 27 mW m⁻² (Tajo Basin), and increases with diminishing surface heat flow. Strength predictions made by extrapolating experimental data indicate varying rheological stratification throughout the area. In general, in compression, ductile fields predominate in the middle and lower crusts and lithospheric mantle. Brittle behaviour is restricted to the first 8 km of the upper crust and to a thin layer at the top of the middle crust. In tension, brittle layers are slightly more extended, while the lower crust and lithospheric mantle remain ductile in the case of a wet peridotite composition. Discontinuities in brittle and ductile layer thickness determine lateral rheological anisotropy. Tectonic units roughly correspond to rheological domains. Brittle layers reach their maximum thickness beneath the Duero Basin and are of least thickness under the Tajo Basin, especially its northern area. Estimated total lithospheric strength shows a range from 2.5×10¹² to 8×10¹² N m⁻¹ in compression, and from 1.3×10¹² to 1.6×10¹² N m⁻¹ in tension. Highest values were estimated for the Duero Basin.Depth versus frequency of earthquakes correlates well with strength predictions. Earthquake foci concentrate mainly in the upper crust, showing a peak close to maximum strength depth. Most earthquakes occur in the southern margin of the Central System and southeast Tajo Basin. Seismicity is related to major faults, some bounding rheological domains. The Duero Basin is a relative quiescence zone characterised by higher total lithospheric strength than the remaining units.     

New heat flow data from the immediate vicinity of the Kola super-deep borehole: Vertical variation in heat flow confirmed and attributed to advection

We present new heat flow values and other geothermal data in the upper crystalline crust in the immediate vicinity of the 12.4-km deep Kola super-deep borehole, NW Russia. Our results show a systematic vertical increase in geothermal gradient and heat flow density as deep as we could measure (1.6 km). Our results confirm earlier results on vertical heat flow trends of in the uppermost part of the Kola super-deep hole, and imply that the thermal regime is not in steady-state conductive conditions. In an area of 3-km × 5-km measurements were performed in 1–2-km deep boreholes surrounding the Kola super-deep hole and on core samples from these holes. Temperature logs are available from 36 holes. Core data exists from 23 boreholes with a total length of 11.5 km at a vertical resolution of 10 m. We carried out a very detailed study on thermal conductivity with regard to anisotropy, inhomogeneity and temperature dependence. Tensor components of thermal conductivity were determined on 1375 core samples from 21 boreholes in 3400 measurements. Additionally, we measured specific heat capacity, heat generation rate, density, porosity, and permeability on selected subsets of core samples. Heat flow from 19 boreholes varies between 31 and 45 mW m⁻² with an average value of 38 mW m⁻². In most boreholes the vertical heat flow profiles show a considerable variation with depth. This is consistent with observations in the upper part of the Kola super-deep borehole. We conclude that this variation is not caused by technical operations but reflects a natural process. It is considered to be due to a combination of advective, structural and paleoclimatic effects. Preliminary 3-D numerical modeling of heat and flow in the study area provides an indication of relative contributions of each of these factors: advective heat transfer turns out to have a major influence on the vertical variation of heat flow, although transient changes in surface temperature may also cause a significant variation. Heterogeneity of the rocks in the study area is less important.     

Burial and thermal history of the West Bashkirian sedimentary basins

The GALO system is applied to the numerical reconstruction of burial and thermal histories of the West Bashkirian lithosphere from the Riphean to the present. An analysis of the variation in tectonic subsidence of the basin during its development is utilized to estimate approximately the mantle heat flow variations. Our variant of basin evolution suggests that after cooling in the Early Riphean, the rather weak thermal reactivations have not led to considerable heating of the lithosphere in the study region. Surface heat flow decreased from relatively high values in the Early Riphean (60–70 mW/m² in the eastern area and 40–50 mW/m² in the western part) to present-day values of 32–40 mW/m². In spite of the relatively low temperature regime of the basin as a whole, a syn-rifting deposition of more than 10 km of limestone, shale and sandstone in the Riphean resulted in rather high temperatures (180–190 °C) at the base of present-day sedimentary blanket in the eastern area. In agreement with the observed data, computed present-day heat flow through the sediment surface increases slightly from 32 to 34 mW/m² near the west boundary of the region to 42 mW/m² near the boundary of the Ural Foldbelt, whereas the heat flow through the basement surface decreases slightly from 28–32 to 24–26 mW/m² in the same direction. The mantle heat flow is only 11.3–12.7 mW/m², which is considerable lower than mean heat flow of the Russian Platform (16–18 mW/m²) and comparable with the low heat flow of Precambrian shields.     

Geothermal regime and Jurassic source rock maturity of the Junggar basin, northwest China

We analyze the thermal gradient distribution of the Junggar basin based on oil-test and well-logging temperature data. The basin-wide average thermal gradient in the depth interval of 0–4000 m is 22.6 °C/km, which is lower than other sedimentary basins in China. We report 21 measured terrestrial heat flow values based on detailed thermal conductivity data and systematical steady-state temperature data. These values vary from 27.0 to 54.1 mW/m² with a mean of 41.8 ± 7.8 mW/m². The Junggar basin appears to be a cool basin in terms of its thermal regime. The heat flow distribution within the basin shows the following characteristics. (1) The heat flow decreases from the Luliang Uplift to the Southern Depression; (2) relatively high heat flow values over 50 mW/m² are confined to the northern part of the Eastern Uplift and the adjacent parts of the Eastern Luliang Uplift and Central Depression; (3) The lowest heat flow of smaller than 35 mW/m² occurs in the southern parts of the basin. This low thermal regime of the Junggar basin is consistent with the geodynamic setting, the extrusion of plates around the basin, the considerably thick crust, the dense lithospheric mantle, the relatively stable continental basement of the basin, low heat generation and underground water flow of the basin. The heat flow of this basin is of great significance to oil exploration and hydrocarbon resource assessment, because it bears directly on issues of petroleum source-rock maturation. Almost all oil fields are limited to the areas of higher heat flows. The relatively low heat flow values in the Junggar basin will deepen the maturity threshold, making the deep-seated widespread Permian and Jurassic source rocks in the Junggar basin favorable for oil and gas generation. In addition, the maturity evolution of the Lower Jurassic Badaowan Group (J_1b) and Middle Jurassic Xishanyao Group (J_2x) were calculated based on the thermal data and burial depth. The maturity of the Jurassic source rocks of the Central Depression and Southern Depression increases with depth. The source rocks only reached an early maturity with a R₀ of 0.5–0.7% in the Wulungu Depression, the Luliang Uplift and the Western Uplift, whereas they did not enter the maturity window (R₀ < 0.5%) in the Eastern Uplift of the basin. This maturity evolution will provide information of source kitchen for the Jurassic exploration.     

Absence of a regional surface thermal high in the Baikal rift; new insights from detailed contouring of heat flow anomalies

Heat flow in active tectonic zones as the Baikal rift is a crucial parameter for evaluating deep anomalous structures and lithosphere evolution. Based on the interpretation of the existing datasets, the Baikal rift has been characterized in the past by either high heat flow, or moderately elevated heat flow, or even lacking a surface heat flow anomaly. We made an attempt to better constrain the geothermal picture by a detailed offshore contouring survey of known anomalies, and to estimate the importance of observed heat flow anomalies within the regional surface heat output. A total of about 200 new and close-spaced heat flow measurements were obtained in several selected study areas in the North Baikal Basin. With an outrigged and a violin-bow designed thermoprobe of 2–3-m length, both the sediment temperature and thermal conductivity were measured. The new data show at all investigated sites that the large heat flow highs are limited to local heat flow anomalies. The maximum measured heat flow reaches values of 300–35000 mW/m², but the extent of the anomalies is not larger than 2 to 4 km in diameter. Aside of these local anomalies, heat flow variations are restricted to near background values of 50–70 mW/m², except in the uplifted Academician zone. The extent of the local anomalies excludes a conductive source, and therefore heat transport by fluids must be considered. In a conceptual model where all bottom floor heat flow anomalies are the result of upflowing fluids along a conduit, an extra heat output of 20 MW (including advection) is estimated for all known anomalies in the North Baikal Basin. Relative to a basal heat flow of 55–65 mW/m², these estimations suggest an extra heat output in the northern Lake Baikal of only 5%, corresponding to a regional heat flow increase of 3 mW/m². The source of this heat can be fully attributed to a regional heat redistribution by topographically driven ground water flow. Thus, the surface heat flow is not expected to bear a signal of deeper lithospheric thermal anomalies that can be separated from heat flow typical for orogenically altered crust (40–70 mW/m²). The new insights on the geothermal signature in the Baikal rift once more show that continental rifting is not by default characterized by high heat flow.     

Terrestrial heat flow around the aseismic front of the Japanese Island Arc

Very few data on heat flow are available in the area around the aseismic front of the Japanese Islands. In order to remedy this situation, measurements of the terrestrial heat flow were made at three locations in the eastern part of Fukushima Prefecture, northeastern Honshu, Japan. The observed values of heat flow were 37 mW/m² (0.88 μcal/cm²·s) at Soma, 52 mW/m² (1.25 μcal/cm²·s) at Kashima and 19 mW/m² (0.46 μcal/cm²·s) at Naraha, respectively. These data partially fill the gaps in the terrestrial heat flow data on land in northeastern Honshu, Japan. These values are considerably lower than the average heat flow over the world, but agree well with the previous estimation for the area.     

江汉盆地当阳复向斜当深3井热史恢复及其油气勘探意义

江汉盆地当阳复向斜当深3井实测地温剖面和样品热导率测试结果表明:其现今地温梯度为20～24℃/km,热流值为56mW/m²,体现了盆地发育于扬子稳定陆块的大地构造属性。基于7个磷灰石裂变径迹样品和大量镜质体反射率古温标数据进行的热史恢复表明,盆地构造—热演化经历了前印支期的低热流(50～60mW/m²)和小剥蚀量(50～200m),印支期的高热流(约80mW/m²)及燕山期与喜马拉雅期的低热流(50～60mW/m²)与大剥蚀量(1100～2400m)的不同演化阶段,反映了盆地和区域构造演化过程的阶段性。受沉积剥蚀及盆地构造—热演化的控制,生油岩系的生烃阶段与过程具有多期次的特征。     

Geothermal investigations in the Bohus granite area in southwestern Sweden

Heat generation and heat flow were determined for the Bohus granite massif in western Sweden. This is the start of a major program concerning geothermal energy in Sweden. Neutron activation analyses, temperature measurements, thermal conductivity measurements have been carried out. As was expected the result, 76 mW m⁻², shows that even old Precambrian shields locally exhibit much higher values than normal.     

Heat flow and heat generation in the Churchill Province of the Canadian Shield, and their palaeotectonic significance

Six new heat flow determinations are presented for Proterozoic mobile belts of the Churchill Province of the Canadian Shield, an area that was affected by several stages of the Hudsonian orogenic sequence (1.9-1.6 Ga ago). With other, previously published, values the mean of eight determinations considered reliable and representative and corrected for the effects of Pleistocene glaciation is 44 ± 7 mW m⁻². Heat generation measurements have also been made; values range from 0.1–1.04 μW m⁻³.A linear relation between heat flow and heat production is apparent. The heat flow axis intercept is 37 mW m⁻², and the scale depth is 11 km, compared with 28 mW m⁻² and 13.6 km for the Archaean Superior Province. Approximately 20% of the Churchill heat flow appears to be derived from radioactive decay in the upper crust, compared with 30% for the Superior Province and shields as a whole. The observations imply that the heat flow-heat production relation for the Churchill Province should be written as Q = Q_c + Q_e + A₀b where Q_c is equivalent to the reduced heat flow for the Archaean terrain, b is similar for the two, and Q_e is an additional component of heat flow in the Proterozoic mobile belts of the Churchill Province.A speculative tectonic model is presented. It is suggested that rifting along two axes of an original craton, which had lateral variations in near surface radiogenic element concentration, followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments, led to widespread redistribution of radioactive elements into the reactivated inter-rift crustal block. One result would be that crustal temperatures are higher in that part of the Churchill Province than in the Superior.     

Geothermal investigations in the Upper Vindhyan sedimentary rocks of Shivpuri area,central India

Heat flow has been determined by combining temperature measurements in 7 boreholes with thermal conductivity measurements in the Upper Vindhyan sedimentary rocks of Shivpuri area, central India. The boreholes are distributed at 5 sites within an area of 15 × 10 km²; their depths range from 174 to 268 m. Geothermal gradients estimated from borehole temperature profiles vary from 8.0–12.7 mK m⁻¹ in the sandstone-rich formations to 25.5–27.5 mK m⁻¹ in the shale-rich formations, consistent with the contrast in thermal conductivities of the two rock types. Heat flow in the area ranges between 45 and 61 mW m⁻², with a mean of 52±6 mW m⁻². The heat flow values are similar to the >50 mW m⁻² heat flow observed in other parts of the northern Indian shield. The heat flow determinations represent the steady-state heat flow because, the thermal transients associated with the initial rifting, convergence and sedimentation in the basin as well as the more recent Deccan volcanism that affected the region to the south of the basin would have decayed, and therefore, the heat flow is in equilibrium with the radiogenic heat production of the crust and the heat flow from the mantle. The present study reports the heat flow measurements from the western part of the Vindhyan basin and provides heat flow information for the Bundhelkhand craton for the first time. Radioelement (Th, U and K) abundances have been measured both in the sedimentary rocks exposed in the area as well as in the underlying basement granite-gneiss of Bundelkhand massif exposed in the adjacent area. Radioactive heat production, estimated from those abundances, indicate mean values of 0.3 μW m⁻³ for sandstone with inter-bands of shale and siltstone, 0.25 μW m⁻³ for sandstone with inter-bands siltstone, 0.6 μW m⁻³ for quartzose sandstone, and 2.7 μW m⁻³ for the basement granitoids. With a total sedimentary thickness not exceeding a few hundred metres in the area, the heat production of the sedimentary cover would be insignificant. The radioactive heat contribution from the basement granitoids in the upper crust is expected to be large, and together with the heat flow component from the mantle, would control the crustal thermal structure in the region.     

Present Terrestrial Heat Flow Measurements of the Geothermal Fields in the Chagan Sag of the YingenEjinaqi Basin,Inner Mongolia,China

Owing to the lack o f terrestrial heat flow data, studying lithospheric thermal structure and geodynamics of the Yingen-Ejinaqi Basin in Inner Mongolia is limited. In this paper, the terrestrial heat flow o f the Chagan sag in the YingenEjinaqi Basin were calculated by 193 system steady-state temperature measurements of 4 wells, and newly measuring 62 rock thermal conductivity and 20 heat production rate data on basis o f the original 107 rock thermal conductivity and 70 heat production data. The results show that the average thermal conductivity and heat production rate are 2.11 ±0.28 W/(m.K) and2.42±0.25 nW/m~3 in the Lower Cretaceous o f the Chagan sag. The average geothermal gradient from the Lower Suhongtu 2 Formation to the Suhongtu 1 Fonnation is 37.6 °C/km, and that o f the Bayingebi 2 Formation is 27.4 °C/km. Meanwhile, the average terrestrial heat flow in the Chagan sag is 70.6 mW/m~2. On the above results, it is clear that there is an obvious negative correlation between the thermal conductivity o f the stratum and its geothermal gradient. Moreover, it reveals that there is a geothermal state between tectonically stable and active areas. This work may provide geothermal parameters for further research o f lithospheric thermal structure and geodynamics in the Chagan sag.     

Numerical modelling of the thermal evolution of the northwestern Dniepr–Donets Basin (Ukraine)

The Dniepr–Donets Basin (DDB) is a Late Devonian rift structure located within the East-European Craton. Numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin.The numerical models suggest that heat flow was relatively high during Late Carboniferous and/or Permian times. The relatively high heat flow is probably related to an Early Permian re-activation of tectonic activity. Reconstructed Early Permian heat flow values along the axial zone of the rift are about 60 mW/m² and increase to 90 mW/m² along the northern basin margin. These values are higher than those expected from tectonic models considering a single Late Devonian rifting phase. The calibration data are not sensitive to variations in the Devonian/Carboniferous heat flow. Therefore, the models do not allow deciding whether heat flows remained high after the Devonian rifting, or whether the reconstructed Permian heat flows represent a separate heating event.Analysis of the vitrinite reflectance data suggest that the northeastern Dniepr–Donets Basin is characterised by a low Mesozoic heat flow (30–35 mW/m²), whereas the present-day heat flow is about 45 mW/m².     

Thermal properties and coal rank in rocks and coal seams of the southern Sydney Basin,new South Wales: A palaeogeothermal explanation of coalification

Measurements of thermal conductivity on 106 disc specimens of rocks from 275 m of the Permian to Triassic section of the Southern Coalfield of the southern Sydney Basin have been carried out in an effort to explain a high rank gradient in the Permian coals. The samples came from six diamond drill holes north and west of Wollongong, although one hole only provided specimens of a syenitic sill (n = 17, mean thermal conductivity = 2.36 W/m°K, s.d. 0.03). When combined with previously published data on chip specimens, with which there is good agreement, from a further four drill holes the mean thermal conductivity for the late Permian and early Triassic sandstones and shales is 3.20 W/m°K.Heat generation by Permian volcanic rocks below the coal measures (from about 1 to 3 μW/m³), and by basement granitic rocks, appears to be consistent with previously reported heat flow for the southern Sydney Basin (about 80 mW/m²). This heat flow is a relatively high value for the east coast of Australia. Younger (Mesozoic and Tertiary) intrusive and extrusive igneous rocks produce local coal-rank anomalies, but do not appear to have any regional effect.The rank of coals above the Permian volcanic rocks appears to be little affected by the presence of the igneous rocks and the coal-rank decreases towards the major area of vulcanicity. Organic matter in sedimentary rocks interbedded with the volcanic rocks is of relatively high rank but it appears that these thermal effects do not extend more than about 100 m above the base of the coal measures. The area of high rank north and northwest of Wollongong seems likely to be a regional effect associated with a combination of high heat generation in basement and the Permian rocks, and high heat flow from the basement. Greater cover on the coal measures, together with an increase in the proportion of rocks of relatively low thermal conductivity in the cover, may also influence the rank in the Permian coal.     

Tectono-thermal evolution of the Reed Bank Basin,Southern South China Sea

The Reed Bank Basin in the southern margin of the South China Sea is considered to be a Cenozoic rifted basin. Tectono-thermal history is widely thought to be important to understand tectonics as well as oil and gas potential of basin. In order to investigate the Cenozoic tectono-thermal history of the Reed Bank Basin, we carried out thermal modeling on one drill well and 22 pseudo-wells using the multi-stage finite stretching model. Two stages of rifting during the time periods of ∼65.5–40.4 Ma and ∼40.4–28.4 Ma can be recognized from the tectonic subsidence rates, and there are two phases of heating corresponding to the rifting. The reconstructed average basal paleo-heat flow values at the end of the rifting events are ∼60 and ∼66.3 mW/m², respectively. Following the heating periods, this basin has undergone a persistent thermal attenuation phase since ∼28.4 Ma and the basal heat flow cooled down to ∼57.8–63.5 mW/m² at present. In combination with the radiogenic heat production of the sedimentary sequences, the surface heat flow of the Reed Bank Basin ranges from ∼60.4 to ∼69.9 mW/m².