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921.
Geodynamic characteristics of tectonic extension in the northern margin of South China Sea 总被引:1,自引:0,他引:1
Based on the geothermal and gravitation methods, this paper investigated the rheological and thermal structure of the lithosphere
under the northern margin of South China Sea. The result shows that the temperature of the upper crust is 150–300°C lower
than that of the lower crust, and the viscous coefficient of the upper crust is 2–3 orders of magnitude larger than that of
the lower crust. It reveals that the upper crust is characterized by brittle deformation while the lower crust by ductile
deformation. A channel of lower-viscosity should be formed between the upper and lower crust when the lithosphere is scattered
and spreads out toward ocean from northwest to southeast along the northern margin of South China Sea. And, a brittle deformation
takes place in the upper part of the lithosphere while a ductile deformation takes place in the lower part of the lithosphere
due to different viscous coefficients and temperature. The layered deformation leads the faulted blocks to rotate along the
faulting and the marginal grabens to appear in the northern margin of South China Sea in Cenozoic tectonic expansion. 相似文献
922.
The inertial coupling approach for the momentum transfer at the ocean–atmosphere interface, which is based on the assumption
of a similarity hypothesis in which the ratio between the water and air reference velocities is equal to the square root of
the ratio between the air and water densities, is reviewed using a wave model. In this model, the air and water reference
velocities are identified, respectively, with the spectrally weighted phase velocity of the gravity waves and the Stokes velocity
at the water roughness length, which are evaluated in terms of the dimensionless frequency limits in Toba's equilibrium spectrum.
It is shown that the similarity hypothesis is approximately satisfied by the wave model over the range of wave ages encountered
in typical sea states, and that the predicted values of the dimensionless surface drift velocity, the dimensionless water
reference velocity, and the Charnock constant are in reasonable agreement with observational evidence. The application of
the bulk relationship for the surface shear stress, derived from the inertial coupling hypothesis in general circulation modeling,
is also discussed.
Received: 6 January 2001 / Accepted: 28 June 2001 相似文献
923.
Non-hibernating mammals that live in seasonal and arid environments change their non-shivering thermogenesis (NST) capacity to maintain homeothermy. Metabolic capabilities of animals, such as NST, are considered adaptive plastic traits because they have a broad range of possible phenotypes with different ambient temperatures (i.e. the reaction norm). Consequently, we determined the reaction norm for NST in Octodon degus (Bennett, 1832; mb=189 g) andPhyllotis darwini (Waterhouse, 1837; mb=61 g) from the mesic habitat of central Chile, and inPhyllotis xanthopygus (Waterhouse, 1837; mb=67 g) from the high Andean plains of northern Chile, an arid and seasonal habitat. Octodon degus showed a 22% increase in NST with thermal acclimation, whereas P. xanthopygus showed a 112% increase, and P. darwini showed a 117% increase in NST, being the largest change observed. These results are in agreement with our hypothesis of evolutionary inertia, which states that observed metabolic plasticity in Phyllotis species is consequence of their high Andean origin, in spite of the fact the actual habitat ofP. darwini is the less seasonal central valley of Chile. 相似文献
924.
Abstract Apatite and zircon fission-track (FT) analyses of the Shimanto accretionary complex and its vicinities, southwest Japan, unraveled the episodic material migration of the deep interiors of the accretionary complex. Apatite data with 100°C closure temperature (Te) generally indicate ~10 Ma cooling throughout the Shimanto complex. In contrast, zircon data with 260°C Te exhibit a wide range of apparent ages as a consequence of paleotemperature increase to the zircon partial annealing zone. In the Muroto and Kyushu regions, maximum temperatures tend to have been higher in the northern, older part of the complex, with indistinguishable temperature differences between coherent and melange units adjacent to each other. It thus suggests, along with vitrinite reflectance data, that older accretionary units occurring to the north sustain greater maximum burial during the accretion-burial-exhumation process. Zircon data suggest two cooling episodes: ~70 Ma cooling at widespread localities in the Cretaceous Shimanto Belt and Sambagawa Belt, and ~15 Ma cooling in the central Kii Peninsula. The former is consistent with 40Ar/39Ar cooling ages from the Sambagawa Belt, whereas the latter slightly predates the widespread 10 Ma apatite cooling ages. These data imply that the extensive material migration and exhumation took place in and around the Shimanto complex in Late Cretaceous as well as in Middle Miocene. Considering tectonic factors to control evolution of accretionary complexes, the episodic migration is best explained by accelerated accretion of sediments due to increased sediment influx at the ancient Shimanto trench, probably derived from massive volcano-plutonic complexes contemporaneously placed inland. Available geo- and thermochronologic data suggest that extensive magmatism triggered regional exhumation twice in the past 100 Ma, shedding new light on the cordilleran orogeny and paired metamorphism concepts. 相似文献
925.
本文论述了渍害遥感识别的主要标志,通过土壤热惯量、土壤含水量及土壤温度等渍害相关因子的讨论,阐明了渍害遥感识别的基本原理及几种主委方法。由于渍害涉及诸多因素,本文给出了以地学相关分析为基础的渍害判别模型。本研究表明,用遥感方法研究渍害是切实可行的。 相似文献
926.
雷州半岛硅藻土煅烧中的结构变化 总被引:5,自引:4,他引:5
本文应用X射线衍射、红外光谱、扫描电镜等手段,对广东海康、徐闻的硅藻土在煅烧过程中热结构变化进行了探讨。结构表明,煅烧使硅藻内部矿物的微观结构发生变化而引起形变,主要为SiO2从无序含水的蛋白石转变为有序的方石英晶体。形变温度随其硅藻的种类和杂质不同而各异。本研究为这两地硅藻土的开发提供了科学依据。 相似文献
927.
928.
镜质组反射率与沉积盆地古地温分析 总被引:3,自引:1,他引:3
在地质研究与资源勘探中,特别是针对油气生成、运移和保存有关的地热过程分析,镜质组反射率(R)已被广泛地应用于沉积盆地古地温的确定。本文从R增值的反应动力学、R-古地温-受热时间模拟计算、流体扰动对流型热体系中的R性征及R古地温分析技术扩展等方面,概括地总结讨论了有关应用现状与理论进展。由于沉积有机质构成及其热反应作用的复杂性,过分简单地将R与地温值对应的做法已被否定,代之以地质、地球热力学与反应动力学的综合分析。不同源岩中R增值与热能关系的确定,温度-时间计算方法的改进、异常热背景如对流型热体制的分析以及低成熟与镜质组缺失条件下成熟度参数的R标定等,将是今后急待解决的主要问题。 相似文献
929.
A review of the geochemistry of methane in natural gas hydrate 总被引:7,自引:0,他引:7
Keith A. Kvenvolden 《Organic Geochemistry》1995,23(11-12)
The largest accumulations on Earth of natural gas are in the form of gas hydrate, found mainly offshore in outer continental margin sediment and, to a lesser extent, in polar regions commonly associated with permafrost. Measurements of hydrocarbon gas compositions and of carbon-isotopic compositions of methane from natural gas hydrate samples, collected in subaquatic settings from around the world, suggest that methane guest molecules in the water clathrate structures are mainly derived by the microbial reduction of CO2 from sedimentary organic matter. Typically, these hydrocarbon gases are composed of > 99% methane, with carbon-isotopic compositions (δ13CPDB) ranging from − 57 to − 73‰. In only two regions, the Gulf of Mexico and the Caspian Sea, has mainly thermogenic methane been found in gas hydrate. There, hydrocarbon gases have methane contents ranging from 21 to 97%, with δ13C values ranging from − 29 to − 57‰. At a few locations, where the gas hydrate contains a mixture of microbial and thermal methane, microbial methane is always dominant. Continental gas hydrate, identified in Alaska and Russia, also has hydrocarbon gases composed of > 99% methane, with carbon-isotopic compositions ranging from − 41 to − 49‰. These gas hydrate deposits also contain a mixture of microbial and thermal methane, with thermal methane likely to be dominant. Published by Elsevier Science Ltd 相似文献
930.
华北蓟县元古界长城系串岭沟组岩石的古地磁再研究 总被引:1,自引:0,他引:1
华北蓟县剖面串岭构组5个点37个样品的热退磁再研究成果,获得极位为239.1°E和22.2°N,k=82,A95=8.5°,落在已建立的蓟县元古界的视极移轨迹的常州组极和团山子组极之间连线附近,合理而可信.结果还表明测试的(次)火山岩与沉积岩是准同生的,可用作钻石U-Pb法测年对象. 相似文献