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91.
A New Model for Heat Flow in Extensional Basins: Estimating Radiogenic Heat Production 总被引:1,自引:0,他引:1
Radiogenic heat production (RHP) represents a significant fraction of surface heat flow, both on cratons and in sedimentary basins. RHP within continental crust—especially the upper crust—is high. RHP at any depth within the crust can be estimated as a function of crustal age. Mantle RHP, in contrast, is always low, contributing at most 1 to 2 mW/m2 to total heat flow. Radiogenic heat from any noncrystalline basement that may be present also contributes to total heat flow. RHP from metamorphic rocks is similar to or slightly lower than that from their precursor sedimentary rocks. When extension of the lithosphere occurs—as for example during rifting—the radiogenic contribution of each layer of the lithosphere and noncrystalline basement diminishes in direct proportion to the degree of extension of that layer. Lithospheric RHP today is somewhat less than in the distant past, as a result of radioactive decay. In modeling, RHP can be varied through time by considering the half lives of uranium, thorium, and potassium, and the proportional contribution of each of those elements to total RHP from basement. RHP from sedimentary rocks ranges from low for most evaporites to high for some shales, especially those rich in organic matter. The contribution to total heat flow of radiogenic heat from sediments depends strongly on total sediment thickness, and thus differs through time as subsidence and basin filling occur. RHP can be high for thick clastic sections. RHP in sediments can be calculated using ordinary or spectral gamma-ray logs, or it can be estimated from the lithology. 相似文献
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Global heat budget, plate tectonics and climatic change 总被引:1,自引:0,他引:1
For the past 2000 Ma, the temperature of the Earth's surface has fluctuated around a mean similar to that of today, although individual locations have undergone long-term changes of ∼30°C at different times in different places. Water bodies absorb at least five times as much solar radiation as land surfaces, and ocean currents transport the excess heat absorbed in the tropics towards the poles. Changes in the distribution of land and sea due to plate tectonics explain the major temperature fluctuations (>25°C) around the globe in the last 350 Ma, and are first-order controls. Large-scale changes in ocean currents and thermohaline circulations are probably second-order controls (15–25°C). The Milankovitch orbital cycles are third-order controls producing variations in air temperature of the order of 10°C, while massive volcanic eruptions and changes in carbon dioxide are amongst the fourth-order controls producing minor perturbations (<5°C). The major climatic fluctuations are continuous but regional in effect and not global. Extraterrestrial factors may not cause major changes in climate when viewed from a geological perspective. 相似文献
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热害矿井巷道温度场分布规律研究 总被引:8,自引:0,他引:8
为解决深部开采带来的热害问题,基于地质学和热力学理论,建立了热害矿井巷道温度场的数学模型,研究了巷道内部温度场随埋深和通风热速的变化规律。计算结果表明,巷道温度场对埋深的敏感度要高于风速、温度随埋深的增加而呈阶段性递增。控制入口温度是解决矿井热害的关键。以上结论为矿井热害的综合治理提供了重要依据。 相似文献
97.
Velocity structure of uppermost mantle beneath North China from Pn tomography and its implications 总被引:1,自引:0,他引:1
20301 Pn arrival time data are collected from the seismological bulletins of both national and regional seismic networks. Pn travel time residuals are tomographically inverted for the Pn velocity structure of uppermost mantle beneath North China. The result indicates that the average Pn velocity in North China is 7.92 km/s, and the velocity varies laterally from ?0.21 to +0.29 km/s around the average. The approximately NNE trending high and low velocity regions arrange alternatively west-eastward. From west to east we can see high velocity in the middle Ordos region, the Shanxi graben low, the Jizhong depression high, the west Shandong uplift and Bohai Sea low, and the high velocity region to the east of the Tanlu fault. In the southern boundary zone of the North China block, except for the high velocity in the Qingling Mountains region, the velocity is generally lower than the average. Obvious velocity anisotropy is seen in the Datong Cenozoic volcanic region, with the fast velocity direction in NNE-SSW. Notable velocity anisotropy is also seen around the Bay of Bohai Sea, and the fast velocity directions seem to show a rotation pattern, possibly indicating a flow-like deformation in the uppermost mantle there. The Pn velocity variations show a reversed correlation with the Earth's heat flow. The low Pn velocity regions generally show high heat flow, e.g., the Shanxi graben and Bohai Sea region. While the high Pn velocity regions usually manifest low heat flow, e.g., the region of Jizhong depression. This indicates that the Pn velocity variation in the study region is mainly aroused by the regional temperature difference in the uppermost mantle. Strong earthquakes in the crust tend to occur in the region with the abnormal low Pn velocity, or in the transition zone between high and low Pn velocity regions. The earthquakes in the low velocity region are shallower, while that in the transition zone are deeper. 相似文献
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探讨了在地图投影的最小二乘二元多项式拟合中参考点的分布对拟合误差的影响,提出了一种基于矩阵的秩亏的方法来判断参考点是否在指定次数的二元多项式空间的代数曲线上,并导出在极小范数最小二乘意义下的拟合多项式的误差估计式,公式表明拟合误差和参考点的最小二乘误差无关。 相似文献