On the estimation of the vertical distribution of radiogenic heat production in the crust

Summary. A differential-difference equation governing the distribution of radiogenic heat in the crust has been obtained. The solution of this equation gives the exponential model of the heat production distribution with the logarithmic decrement as determined in Singh & Negi.     

Red Sea heat flow

Since 1970, the number of heat flow observations in the Red Sea has increased fivefold. A new heat flow map is presented together with a table of observations. The new data confirm that the whole of the Red Sea is associated with high heat flow. The observations within 5 km distance of the deepest water of the axial trough have a mean of 467 mWm^-2 (i.e. about eight times the world mean) and the observations from 50 to 170 km from the axial deep water have a mean of 111 mWm^-2 (i.e. about twice the world mean). The heat flow distribution is thus typical of that associated with an active spreading centre. The observations are difficult to assess and interpret in detail because of the complex sedimentary and tectonic environment. The high heat flow extends at least as far as the Red Sea coasts.     

Heat refraction and heat production in and around granite plutons in north-east England

Summary. Existing surface heat flow determinations in north-east England indicate a difference in thermal structure between the Alston block of the North Pennines and the coastal regions. New heat flow determinations in the Askrigg block and on the coast support the original indications of higher heat flow in the positive blocks, which are underlain by 400 Myr old granites, than in their marginal sedimentary troughs along the present coastline. Although the two blocks are geophysically and geologically similar, surface heat flow in the Alston block is 30mW m^-2 higher than it is in the Askrigg block 50km to its south. Heat flow refraction around high conductivity plutons with high heat production may significantly affect the interpretation of heat flow measurements made on a regional scale but in the present case its effect, if any, is to emphasize the heat flow difference between the two otherwise similar blocks. The chemical differences between the Wensleydale and the Weardale granites – cupolas of the granites underlying the Askrigg and Alston may be representative of the granites as a whole and the blocks respectively – difference in surface heat flows may result from a contrast in radiogenic heat production between the two granites extending to mid-crustal depths.     

Uplift and heat flow following the injection of magmas into the lithosphere

Summary. The thermal effect of a rapid injection of hot magmas into the lower part of the lithosphere is modelled as an increase in heat production through the invaded region. The change in surface heat flow and the uplift resulting from the thermal expansion are determined in three-dimensional axially symmetric geometry: they are expressed as the space time convolutions of a Green's function with the anomalous heat production.
The anomalies with shorter wavelength (compared to the lithospheric thickness) are attenuated. This filtering affects the surface uplift more than the heat flow anomaly; the attenuation effect is larger when only the lower part of the lithosphere is invaded.
The uplift time constant is of the same order as the heat conduction time if the lower lithosphere is invaded by magmas at a moderate rate (i.e. the rate of injection does not exceed the equivalent of 0.1 per cent of the lithospheric volume in 10⁶yr). Fifty per cent of the total uplift takes place in about 80 × 10⁶yr for a lithosphere 100 km thick. The uplift is slightly faster when the whole lithosphere is invaded. The heat flow anomaly is delayed when the lower part of the lithosphere is invaded.
The spatial extent and the timing of the uplift and heat flow anomalies are critical in determining the mechanism's feasibility. Magma injections explain rapid uplifts [> 100 m (10⁶ yr)⁻¹] only if the magma is supplied at a very high rate (i.e. at least 10 per cent of the lithosphere volume per 10⁶yr). It is a feasible mechanism for uplifts that occur over longer periods of time (≊ 30 × 10⁶yr) such as those that seem to have occurred when the African plate came to rest with respect to the mantle.     

Feedbacks of sedimentation on crustal heat flow: New insights from the Vøring Basin,Norwegian Sea

Basement heat flow is one of the key unknowns in sedimentary basin analysis. Its quantification is challenging not in the least due to the various feedback mechanisms between the basin and lithosphere processes. This study explores two main feedbacks, sediment blanketing and thinning of sediments during lithospheric stretching, in a series of synthetic models and a reconstruction case study from the Norwegian Sea. Three types of basin models are used: (1) a newly developed one‐dimensional (1D) forward model, (2) a decompaction/backstripping approach and (3) the commercial basin modelling software TECMOD2D for automated forward basin reconstructions. The blanketing effect of sedimentation is reviewed and systematically studied in a suite of 1D model runs. We find that even for moderate sedimentation rates (0.5 mm year^?1), basement heat flow is depressed by ～25% with respect to the case without sedimentation; for high sedimentation rates (1.5 mm year^?1), basement heat flow is depressed by ～50%. We have further compared different methods for computing sedimentation rates from the presently observed stratigraphy. Here, we find that decompaction/backstripping‐based methods may systematically underestimate sedimentation rates and total subsidence. The reason for this is that sediments are thinned during lithosphere extension in forward basin models while there are not in backstripping/decompaction approaches. The importance of sediment blanketing and differences in modelling approaches is illustrated in a reconstruction case study from the Norwegian Sea. The thermal and structural evolution of a transect across the Vøring Basin has been reconstructed using the backstripping/decompaction approach and TECMOD2D. Computed total subsidence curves differ by up to ～3 km and differences in computed basement heat flows reach up to 50%. These findings show that strong feedbacks exist between basin and lithosphere processes and that resolving them require integrated lithosphere‐scale basin models.     

Insulating effect of coals and organic rich shales: implications for topography-driven fluid flow, heat transport, and genesis of ore deposits in the Arkoma Basin and Ozark Plateau

ABSTRACT Sedimentary rocks rich in organic matter, such as coal and carbonaceous shales, are characterized by remarkably low thermal conductivities in the range of 0.2–1.0 W m^?1 °C^?1, lower by a factor of 2 or more than other common rock types. As a result of this natural insulating effect, temperature gradients in organic rich, fine‐grained sediments may become elevated even with a typical continental basal heat flow of 60 mW m^?2. Underlying rocks will attain higher temperatures and higher thermal maturities than would otherwise occur. A two‐dimensional finite element model of fluid flow and heat transport has been used to study the insulating effect of low thermal conductivity carbonaceous sediments in an uplifted foreland basin. Topography‐driven recharge is assumed to be the major driving force for regional groundwater flow. Our model section cuts through the Arkoma Basin to Ozark Plateau and terminates near the Missouri River, west of St. Louis. Fluid inclusions, organic maturation, and fission track evidence show that large areas of upper Cambrian rocks in southern Missouri have experienced high temperatures (100–140 °C) at shallow depths (< 1.5 km). Low thermal conductivity sediments, such as coal and organic rich mudstone were deposited over the Arkoma Basin and Ozark Plateau, as well as most of the mid‐continent of North America, during the Late Palaeozoic. Much of these Late Palaeozoic sediments were subsequently removed by erosion. Our model results are consistent with high temperatures (100–130 °C) in the groundwater discharge region at shallow depths (< 1.5 km) even with a typical continental basal heat flow of 60 mW m^?2. Higher heat energy retention in basin sediments and underlying basement rocks prior to basin‐scale fluid flow and higher rates of advective heat transport along basal aquifers owing to lower fluid viscosity (more efficient heat transport) contribute to higher temperatures in the discharge region. Thermal insulation by organic rich sediments which traps heat transported by upward fluid advection is the dominant mechanism for elevated temperatures in the discharge region. This suggests localized formation of ore deposits within a basin‐scale fluid flow system may be caused by the juxtaposition of upward fluid discharge with overlying areas of insulating organic rich sediments. The additional temperature increment contributed to underlying rocks by this insulating effect may help to explain anomalous thermal maturity of the Arkoma Basin and Ozark Plateau, reducing the need to call upon excessive burial or high basal heat flow (80–100 mW m^?2) in the past. After subsequent uplift and erosion remove the insulating carbonaceous layer, the model slowly returns to a normal geothermal gradient of about 30 °C km^?1.     

Large-scale gravity profiles across subducted plates

Summary. The mean gravity profiles, across Central and South America and Eurasia, in the direction normal to the subduction zone are deduced from the Gem 10B gravity model. They have a typical shape: a maximum close to the trench, a negative slope towards the interior of the plate over a 3000 km wide distance, usually followed by a local maximum. It is found that large convective cells driven by the heat sink of the sinking slab have an associated gravity signal having such a typical shape. A detailed comparison between observed and theoretical data supports this point of view and thus constrains the possible structure of the convective flow under these plates.     

Speculations on the Thermal and Tectonic History of the Earth

Summary. The connection between the Earth's thermal history and convection in the mantle is exploited to elucidate the early evolution of the Earth. It appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the Earth's history. Only in boundary layers at the surface and at a depth of 650–700 km is conduction likely to be important. The resulting evolution appears to be consistent with geological observations on early Precambrian rocks.
Various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km. The large scale flow is related to the motion of major plates, and must be ordered over distances of more than 5000 km. Its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions. Small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the Earth's surface and to reconcile the geophysical observations with the results of numerical experiments. Though the existence of the small scale flow is at present speculative, various tests of its presence are proposed.     

Erosion and the age dependence of continental heat flow

Summary. Erosion of continental crust has two effects on surface heat flow: a decrease due to the removal of heat-producing elements, and an increase due to the movement of hot rock towards the surface. In an orogenic belt, where erosion may remove tens of kilometres of material, these effects are important over time-spans comparable with the life of the belt as an elevated region.
An expression is derived which relates surface heat flow to time, heat flow through the deep lithosphere, the distribution of heat sources and the amount and time constant of erosion. The variability of crustal processes permits wide ranges of values for these parameters and geologically reasonable parametral combinations can readily be found which satisfy the surface heat flow observations. These combinations can account for the long time-scale of surface heat flow decay, and the influence of erosion on 'reduced' heat flow has important consequences. This approach predicts a relationship between reduced heat flow and age which is close to that observed, and a linear relation between surface heat flow and reduced heat flow similar to that reported by Pollack & Chapman. The intercept on q ₀– A ₀ plots (the reduced heat flow) has a physical meaning which changes with time and should not be interpreted as, for example, the heat flux across the Moho.
We conclude that an important part of the observed variation of surface heat flow with age may be explained by the effects of erosion and the variability of crustal processes. In its range of greatest variation surface heat flow mainly reflects these crustal processes and should not be used to infer directly the thermal development of the subcrustal lithosphere.     

Volume, heat and salt transport by the West Spitsbergen Current

During the summer of 2000 (June-July) 14 CTD and ADCP transects perpendicular to the West Spitsbergen Current and along the western border of the Barents Sea were made. The measurements covered the area between 69° 43'and 80° N and 01° and 20° E. The main purpose was to follow changes in volume, heat and salt content of Atlantic Water (AW) on its way north. The strongest and most stable flow of AW was located along the continental slope where northward flowing currents exceeding 40 cm/sec were measured. A few weaker northward branches were also found to the west of the slope. South-directed currents were recorded between them and eddy-like mesoscale structures were commonly observed. Measured by vessel-mounted acoustic Doppler current profiler (VM-ADCP), the net northward transport of AW volume in the upper 136 m layer decreased from nearly 6 Sv at the southernmost transect to below 1 Sv at a latitude of 78° 50'N. Similarly, heat transport drops from about 173 TW to about 9 TW and relative salt transport (over 34.92 psu) from 980 × 10³ kg/sec to 14 × 10³ kg/sec. Transport in the southern direction prevails at the transect located between 79° 07'and 79° 30'N. The calculated baroclinic geostrophic transport of AW volume, heat and salt in the upper 1000 m layer behaves similarly. East-directed transport dominates at the Barents Sea boundary while westward flow prevails on the western side of the West Spitsbergen Current.     

On the importance of rock thermal conductivity and heat flow density in basin and petroleum system modelling

Basin and petroleum systems are routinely modelled to provide qualitative and quantitative assessments of a hydrocarbon play. The importance of the rock thermal properties and heat flow density in thermal modelling the history of a basin are well-known, but little attention is paid to assumptions of the thermal conductivity, present-day heat flow density and thermal history of basins. Assumed values are often far from measured values when data are available to check parameters, and effective thermal conductivity models prescribed in many basin simulators require improvement. The reconstructed thermal history is often justified by a successful calibration to present-day temperature and vitrinite reflectance data. However, a successful calibration does not guarantee that the reconstruction history is correct. In this paper, we describe the pitfalls in setting the thermal conductivity and heat flow density in basin models and the typical uncertainties in these parameters, and we estimate the consequences by means of a one-dimensional model of the super-deep Tyumen SG-6 well area that benefits from large amounts of reliable input and calibration data. The results show that the entire approach to present-day heat flow evaluations needs to be reassessed. Unreliable heat flow density data along with a lack of measurements of rock thermal properties of cores can undermine the quality of basin and petroleum system modelling.     

起伏地形下黄河流域太阳直接辐射分布式模拟

1 Introduction Directsolarradiation (DSR)isthe key com ponentofthe globalradiation reaching the Earth.For the influence of terrain factors,calculation of DSR quantity of rugged terrain is considerably com plex (Oliphantetal.,2003). The solarradiation quan…     

起伏地形下黄河流域太阳直接辐射分布式模式

基于数字高程模型(DEM)数据和气象站观测资料建立了起伏地形下太阳直接辐射分布式计算模型,模型充分考虑了地形因子(坡向、坡度、地形相互遮蔽)对起伏地形下太阳直接辐射空间分布的影响;以1km×1km分辨率的DEM数据作为地形的综合反映,计算了起伏地形下黄河流域1km×1km分辨率太阳直接辐射的空间分布;深入分析了起伏地形下太阳直接辐射受地理、地形因子影响的变化规律.结果表明受地形起伏和坡向、坡度等局地地形因子的影响,山区年太阳直接辐射量的空间差异比较明显,向阳山坡(偏南坡)的年直接辐射量明显高于背阴山坡(偏北坡).     

Convective and conductive heat transfer in sedimentary basins

In the Earth's crust the temperature is largely controlled by heat conduction. However, under some circumstances, the thermal state is disturbed by advection of heat associated with groundwater flow. The corresponding thermal disturbance depends on the water flow velocity (modulus and direction) and therefore thermal data may be used to constrain the pattern of natural fluid flow. In this paper, some models of thermal disturbance induced by convective heat transfer are presented. They are based on the assumption that the water flow is concentrated in thin permeable structures such as aquifer or fault zones. The steady-state and transient thermal effects associated with such scenarios are computed using a somewhat idealized model which depends on a small number of parameters: flow rate, time, aquifer geometry and thermal parameters of surrounding rocks. In order to extract the conductive and convective components of heat transfer from temperature data and to estimate the corresponding fluid flow rate, it is first necessary to estimate the thermal conductivity field. The problem of the estimation of thermal conductivity in clay-rich rocks, based on laboratory and in-situ measurements, is emphasized. Then a method is proposed for the inversion of temperature data in terms of fluid flow. Vertical and lateral variations of thermal conductivity are taken into account and the fluid flow is assumed to be concentrated on a specified surface (2-D quasi-horizontal pattern). Thermal effects of the flow are simulated by a distribution of surface heat production which can be calculated and then inverted in terms of horizontal fluid flow pattern.     

云南怒江流域泥石流敏感性空间分析

泥石流敏感性空间分析是通过评估诱发泥石流发生的因子,应用空间技术,进行泥石流发生的敏感性分析。本文探讨了GIS技术与敏感性分析的条件概率模型相结合的泥石流敏感性空间分析,并且阐述了GIS空间分析技术在泥石流敏感性制图中特有的优越性。研究区选择在遭受泥石流危害严重的云南怒江流域。用于泥石流敏感性分析评价的主要敏感因子包括地形坡度、岩土体类型、暴雨、河网密度、土地利用、地震动峰值加速度和人类活动。在对这些因子进行了敏感性空间分析的基础上,应用GIS的分析工具对敏感因子集成评价而产生了云南怒江流域泥石流敏感性评价图。泥石流敏感性评价图可以帮助规划者或工程师在土地发展规划中选择最佳建设场所,以减轻泥石流灾害的影响。     

The effects of sedimentation and compaction on oceanic heat flow

Summary. The estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements. In particular, the perturbations associated with sedimentation and surface temperature changes must be taken into account. Analytical solutions can be obtained only for individual, simplified versions of these problems, whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth. A physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment/basement system. These values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time. In addition to variations in sedimentation rate, sediment type, radioactive heat production and surface temperature changes are considered. Heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent. The results also indicate that alterations determined from simple analytical models tend to over-estimate the true perturbation to the flux.     

数字地形模型在濒危动物生境研究中的应用

本文建立了卧龙自然保护区２０００ｋｍ２范围的数字地形模型,并将其应用在濒危珍稀动物大熊猫的生境研究上。通过计算机叠加大熊猫可分布的高度、坡度及竹子分布区域,获得了大熊猫在卧龙自然保护区内的潜在生境区,其比实际的熊猫分布范围大出近一倍,文章还对潜在生境的适宜性进行了划分。     

复杂地形下长江流域太阳总辐射的分布式模拟

利用长江流域气象站1960-2005年的观测资料(包括常规气象站点资料和辐射站点资料)、NOAA-AVHRR遥感数据(反演地表反照率),以1km×1km的数字高程模型(DEM)反映地形状况的主要数据,通过基于DEM数据的起伏地形下天文辐射模型和地形开阔度模型,分别建立了长江流域太阳直接辐射、散射辐射和地形反射辐射分布式模型,实现了长江流域太阳总辐射模拟,并对总辐射模拟结果进行了时空分布规律分析和对其受季节、纬度、地形因子(高度、坡度和坡向等)影响的局部规律分析,以及模拟结果的误差分析和站点验证分析。结果显示:太阳总辐射在季节上受影响的程度依次是春季>冬季>夏季>秋季;随着高度、坡度、纬度的增加,太阳总辐射受坡向影响的程度呈增强趋势,从坡向上看,向阳山坡(偏南坡)对太阳总辐射量明显高于背阴坡(偏北坡)。模拟的平均绝对误差为13.04177MJm^-2,相对误差平均值3.655%,用站点验证方法显示:模拟绝对误差为22.667MJm^-2,相对误差为4.867%。     

Further data on the South-west England heat flow anomaly

Summary. Temperature gradients and thermal conductivities were determined for a number of exploration boreholes in South-west England in order to verify and further delineate the anomalously high heat flow which has been reported. A pattern is emerging of an anomalously high geothermal gradient and heat flow of about 40°C Km⁻¹ and 126 mWm⁻¹ respectively over the Hercynian granite batholith, with normal values adjacent to it. A synthesis of related data indicates that the heat flow anomaly is associated with convection of hydrothermal fluids and although the mechanism is not well understood it may be caused by a combination of above average natural radioactive heat generation coupled with deep, permeable fracture systems within the batholith.     

Thermal properties of sediments in southern Israel: a comprehensive data set for heat flow and geothermal energy studies

To decipher the thermal structure of the sedimentary veneer in southern Israel, new values of thermal conductivity and porosity as well as of the radiogenic heat budget are provided. Thermal conductivity is measured for lithotypes and scaled up for geological formations. The new data are higher than most of the previously measured values, in particular for sandstones and siltstones, whose mean values are 5.0 and 2.9 W m^?1 K^?1. Mean values of the most abundant lithotypes, which are dolomites and limestones, are on the order of 4.1 and 2.7 W m^?1 K^?1, respectively. The total radiogenic heat production of the sedimentary cover varies slightly over southern Israel, due to variable lithology and total sediment thickness, yielding a maximum heat flow on the order of 4 mW m^?2 where the sedimentary section is thickest (ca. 7 km). A temperature prognosis was made by calculating temperature profiles to the top of the crystalline basement at five well locations applying the new thermal‐conductivity data set and three scenarios of surface heat flow (50, 55 and 60 mW m^?2). The calculated temperatures best match with measured drillstem‐test temperatures by using heat‐flow values close to the upper bound of range. Surface heat flow on the order of 55–60 mW m^?2 is supported by a reevaluation of an existing temperature log and the application of thermal conductivity from this study. The temperature prediction for southern Israel shows values of 100–120°C at 3500–4500 m depth, indicating a geothermal potential that can be used for heating as well as electricity production.