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1.
The origin of the crustal conductive layer and the conductivity of supercritical brine（Ⅱ） 总被引：3，自引：0，他引：3
徐常芳 《地震学报(英文版)》1996,(3)
Ｔｈｅｏｒｉｇｉｎｏｆｔｈｅｃｒｕｓｔａｌｃｏｎｄｕｃｔｉｖｅｌａｙｅｒａｎｄｔｈｅｃｏｎｄｕｃｔｉｖｉｔｙｏｆｓｕｐｅｒｃｒｉｔｉｃａｌｂｒｉｎｅ（Ⅱ）ＣＨＡＮＧ－ＦＡＮＧＸＵ（徐常芳）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｌｏｇｙ，ＳｔａｔｅＳｅｉｓｍｏ... 相似文献
2.
Chang-Fang Xu 《地震学报(英文版)》1996,9(2):327-334
This paper is the first one of a series of three papers on the fluid evolution of the crust-upper mantle and the causes of
earthquakes. Their relationship between the deep-seated fluids and the seismic activities are discussed from aspects of their
macoscopic scale, microscopic mechanism and dynamic behaviors in the three papers respectively.
Based on magnetotelluric sounding (MT) measurements conducted by Chinese geophysicists in more than 20 years, the maps of
the upper mantle conductive layer (MCL) with a buried depth of >50 km and the crustal conductive layer (CCL) with a buried
depth of >15 km in the Chinese mainland are presented in this paper. The resistivity structure, the causes of conductive layers
in crust-mantle and the relationships between earthquake distribution and conductive layers are discussed. 相似文献
3.
The earthquake distribution and the resistivity structure in the Chinese mainland（Ⅰ） 总被引：3，自引：0，他引：3
徐常芳 《地震学报(英文版)》1996,(2)
ＴｈｅｅａｒｔｈｑｕａｋｅｄｉｓｔｒｉｂｕｔｉｏｎａｎｄｔｈｅｒｅｓｉｓｔｉｖｉｔｙｓｔｒｕｃｔｕｒｅｉｎｔｈｅＣｈｉｎｅｓｅｍａｉｎｌａｎｄ（Ⅰ）ＣＨＡＮＧ－ＦＡＮＧＸＵ（徐常芳）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｌｏｇｙ，ＳｔａｔｅＳｅｉｓｍｏｌｉｇ... 相似文献
4.
In this paper, we show that supercritical fluids have a greater significance in the generation of pegmatites,and for ore-forming processes related to granites than is usually assumed. We show that the supercritical melt or fluid is a silicate phase in which volatiles; principally H_2O are completely miscible in all proportions at magmatic temperatures and pressures. This phase evolves from felsic melts and changes into hydrothermal fluids, and its unique properties are particularly important in sequestering and concentrating low abundance elements, such as metals. In our past research, we have focused on processes observed at upper crustal levels, however extensive work by us and other researchers have demonstrated that supercritical melt/fluids should be abundant in melting zones at deep-crustal levels too. We propose that these fluids may provide a connecting link between lower and upper crustal magmas,and a highly efficient transport mechanism for usually melt incompatible elements. In this paper, we explore the unique features of this fluid which allow the partitioning of variouselements and compounds, potentially up to extreme levels,and may explain various features both of mineralization and the magmas that produced them. 相似文献
5.
Great strides have been made in understanding the upper part of the crust by in-situ logging in, and laboratory experiments on core recovered from super-deep bore-holes such as the KTB. These boreholes do not extend into the lower crust, and can contribute little to the elucidation of mechanisms that produce the high electrical conductivities that are commonly observed therein by magneto-telluric (MT) methods. Laboratory studies at simulated lower crustal conditions of temperature, pressure and saturation, on electrolyte saturated rocks thought to have been derived from the lower crust, have not been possible up until now due to their experimental difficulty. It is necessary to subject electrolyte-saturated rock samples to independently controlled confining and pore-fluid pressure, which implies that the rock be sleeved in some impermeable but deformable material, that can withstand the very high temperatures required. Metals are the only materials capable of being used, but these cause great difficulties for cell sealing and conductivity measurement. In this paper we describe recent breakthroughs in experimental work, specifically the development of two new types of sophisticated metal/ceramic seal, and a conductivity measurement technique that enables the measurement of saturated rock conductivity in the presence of a highly conducting metallic sleeve. The advances in experimental technique have enabled us to obtain data on the electrical conductivity of brine saturated basic, acidic and graphite-bearing rocks at lower crustal temperatures and raised pressures. These data have facilitated the comparison of MT derived crustal electrical conductivity profiles with profiles obtained from laboratory experiments for the first time. Initial modelling shows a good agreement between laboratory derived and MT derived profiles only if the mid-crust is composed of amphibolite pervaded by aqueous fluids, and the lower crust is composed of granulite that is saturated with aqueous fluids and/or contains interconnected grain surface films of graphite. The experimental data are consistent with a three layer crust consisting of an aqueous fluid saturated acidic uppermost layer, above an aqueous fluid saturated amphibolite mid-crust, and a granulite lowermost crust, which may or may not be saturated with aqueous fluids, but if not, requires the presence of an additional conduction mechanism such as conduction through thin graphite films. 相似文献
6.
Cratons have a long history of evolution. In this paper, applications of the magnetotelluric method used in the study of craton lithosphere over the past 30 years were reviewed, examining case studies of cratons in North America, South America, Asia, Australia, and Africa. The nuclei of the Archean cratons, for example the Kalahari Craton and Rae Craton, are usually characterized by thick and highly resistive lithospheric roots. During or after the formation of the cratons, tectonothermal events, such as collision, mantle plume, and asthenosphere upwelling led to the formation of high-conductivity zones in the craton lithosphere, which could be attributed to the increased hydrogen content (of nominally anhydrous minerals), higher iron content, and formation of graphite films or sulfides along the grain boundary of minerals. These conductive zones are characterized by resistivity discontinuities in craton lithosphere. In particular, the conductive zones include (1) large-scale lithospheric mantle conductors beneath the Slave Craton, Gawler Craton, and central part of North China Craton(Trans-North China Orogen); (2) near-vertical high-conductivity zone associated with the fossil subduction zone beneath the Dharwar Craton and Slave Craton; and (3) regional lateral electrical discontinuities, such as a conductive anomaly under the Bushveld Complex of the Kaapvaal Craton. The eMoho refers to the electrical discontinuity in the crust-mantle boundary. In existing research, this has been detected under the condition of extremely high lithospheric resistivity with only a slight decrease in the lower crust, and in the case of a very thin conductive lower crust or the lack thereof. In the resistivity model, the unique “mushroom-like” lower crust-lithosphere mantle conductor and very thin lower crust layer of the North China Craton may represent lithosphere destruction and/or thinning. We also find that some of the cratons are still not well understood. Therefore, extensive three-dimensional inversion and joint interpretation of geochemical, geophysical, and geologic data are necessary to understand the tectonic evolutionary history of craton lithosphere.
相似文献7.
Introduction More real models are being developed by the modern seismology. As we all know, the earth is not a simple elastic body. Oil and gas reservoir, ground surface, seashore zone, sea bottom layer, etc, are porous solid media with fluids. It has been confirmed that there are two main fluid flow mechanisms in these media (Dvorkin, Nur, 1993), i.e., the Biot flow mechanism (Biot, 1956, 1962) based on the macroscopic property and the Squirt-flow mechanism (Mavko, Nur, 1979) based on the … 相似文献
8.
In this paper, we are concerned with sediment transport models consisting of a shallow water system coupled with the so called Exner equation to describe the evolution of the topography. We show that, for some bedload transport models like the well-known Meyer-Peter and Müller model, the system is hyperbolic and, thus, linearly stable, only under some constraint on the velocity. In practical situations, this condition is hopefully fulfilled. Numerical approximations of such system are often based on a splitting method, solving first shallow water equation on a time step and, updating afterwards the topography. It is shown that this strategy can create spurious/unphysical oscillations which are related to the study of hyperbolicity. Using an upper bound of the largest eigenvector may improve the results although the instabilities cannot be always avoided, e.g. in supercritical regions. 相似文献
9.
The influence of inclusions of fluids, ore minerals, and graphite on the electric conductance of rocks of the consolidated crust is considered by using geoelectric investigations in the Ukraine as an example. The abundance of graphite and fluid inclusions is shown, and the anomalies associated with them are estimated. 相似文献
10.
Biot流动和喷射流动是含流体多孔隙介质中流体流动的两种重要力学机制. 近年来，利用同时处理这两种力学机制的BISQ(Biot-Squirt)模型，弹性波衰减和频散的问题已被广泛研究；然而基于BISQ方程的波场数值模拟尚未见到公开的报道．本文从BISQ方程出发，利用交错网格方法对横向各向同性孔隙介质中不同频率和相界情况，以及双层介质中的弹性波传播进行数值模拟，研究了在同时考虑两种流动机制作用情况下地震波和声波的传播特性及传播过程中出现的各种波动现象． 相似文献
11.
Stress And Seismicity In The Lower Continental Crust: A Challenge To Simple Ductility And Implications For Electrical Conductivity Mechanisms 总被引：4，自引：0，他引：4
F. Simpson 《Surveys in Geophysics》1999,20(3-4):201-227
The lower crust is generally considered to be an aseismic, weak zone where fluid distribution might be governed by textural equilibrium geometries. Saline fluids below the transition from brittle to ductile rheology have been advanced as a joint explanation for deep crustal conductivity and seismic reflectivity, the depth of onset of both phenomena being apparently bounded by isotherms in the 300–450 °C temperature range. Some petrologists, meanwhile, contest that the deep crust should be devoid of extensive fluid networks. This review exposes some geophysical exceptions to the statistical norm suggested by global geophysical data compilations and presents counter-arguments that the lower crust in places may be both dry and strong, that fluids if at all present at such depths may not necessarily be connected and that fluid mobility in the lower crust may be more limited and heterogeneous than commonly assumed.Laboratory data on crustal rocks implies that the transition from brittle to ductile rheology actually occurs over a much broader range of temperatures than 300–450 °C, and the apparent association of deep crustal conductive horizons with a temperature field of 300–450 °C may be interpretable in terms of formation temperatures of graphite, rather than fluids and brittle-ductile transition rheology.High vP/vS ratios from a 6 km thick, seismically layered zone below the Weardale granite, NE England can be explained by underplated mafic material. They are unlikely to be explained by fluids in an area where deep crustal conductance has been shown to be relatively low, unless conventional assumptions regarding deep crustal fluid distribution are inadequate or false.Perusal of the literature reveals that lower crustal seismicity is less seldom than generally appreciated. Interpretation of earthquakes nucleating at lower crustal depths is ambiguous, but in some tectonic regimes may indicate preservation of brittle rheology to the Moho and a lower crust that is predominantly mafic and dry.A better understanding of lower crustal deformation mechanisms and history may provide better insight into deep crustal conductivity mechanisms. Recent rock mechanical experiments suggest that permeability (and thus fluid connectivity) may be decreased by ductile shearing, whereas ductile shearing may aid graphitisation at lower crustal temperatures. If the lower crust in some regions is strong, this may explain the apparent preservation of both extant- and palaeostress orientations in interpretations involving electrical anisotropy. 相似文献
12.
The mixing of seawater/hydrothermal fluid within the large seafloor hydrothermal sulfide deposits plays a key role in the
formation processes of the sulfide deposits. Some issues attract considerable attentions in the study of seafloor hydrothermal
system in recent years, such as the relationships among different types of vent fluids, the characteristics of chemical compositions
and mineral assemblages of the hydrothermal deposits and their governing factors. Combined with the measured data of hydrothermal
fluid in the TAG field, the thermodynamic model of mixing processes of the heated seawater at different temperatures and the
hydrothermal fluid is calculated to understand the precipitation mechanism of anhydrite and the genetic relationships between
the black and white smoker fluids within the TAG mound. The results indicate that the heating of seawater and the mixing of
hydrothermal fluid/seawater are largely responsible for anhydrite precipitation and the temperature of the heated seawater
is not higher than 150°C and the temperature of the end-member hydrothermal fluid is not lower than 400°C. Based on the simulated
results, the evolving patterns of fluids within the TAG deposit are discussed. The mixed fluid of the end-member hydrothermal
fluid and the seawater heated by wall rock undergoes conductive cooling during upflowing within the deposit and forms “White
Smoker” eventually. In addition, the end-member hydrothermal fluid without mixed with seawater, but undergoing conductive
cooling, vents out of the deposit and forms “Black Smoker”.
Supported by China Ocean Mineral Resources Research and Development Association Program (Grant No. DY115-02-1-01) and National
Basic Research Program of China (Grant No. G2000078503) 相似文献
13.
Joint analysis of deep three-dimensional models of the electrical resistivity, seismic velocity, and density of the complex hosting the Sorskoe Cu–Mo deposit (Russia) is carried out aimed at finding geophysical markers characterizing the areas of ore generation, transportation and deposition. The three-dimensional lithology model of the study area is built based on the empirical relationship between the silica content of the rocks and seismic velocities. It is in agreement with geological and geochemical studies provided in this area earlier and could be used as a basis for forecasting locations of the copper–molybdenum ore deposits at depth. A conceptual model of the copper–porphyry complex explaining the mechanisms of ore generation, transportation from the lower to the upper crust and deposition in the upper crust is suggested. In particular, it is supposed that post-magmatic supercritical gas–water ore-bearing fluids are upwelling through the plastic crust due to the sliding of the fluid films along the cleavage planes of the foliated rocks while at the depths of the brittle upper crust this mechanism could be changed by volumetric fluid transportation along the network of large pores and cracks. 相似文献
14.
We consider the methods and results of magnetotelluric sounding in the AMTS and MTS modifications. Audiomagnetotelluric sounding (AMTS) was carried out for the first time in the area of a recent Tolbachik eruption. The results from our analysis of the magnetotelluric parameters show that the geoelectric medium involving a regional fault can be fitted by a 2D inhomogeneous model. The longitudinal and transverse sounding curves were assumed as the leading elements for interpretation. A joint analysis of these curves and of pseudo-sections of impedance phases provides evidence of a geoelectric inhomogeneity in the area where the Naboko Vent is situated. A bimodal inversion of the AMTS curves yielded a geoelectric section that contains a conductive inhomogeneity that is possibly related to a fault that carried fluids up to the ground surface. Along with AMTS, we used MTS curves in a broader range to identify a crustal conductive anomaly at depths of 15–35 km. The data from AMTS, MTS, and other geological and geophysical information were used to develop a conceptual model for the area of study that characterizes a possible origin of the anomalous zones. We obtained approximate estimates of rock porosity in the fault zone that transported magma melts upward into the overlying rocks in the area of the Naboko Vent. 相似文献
15.
Abstract Starting from Euler's equations of motion a nonlinear model for internal waves in fluids is developed by an appropriate scaling and a vertical integration over two layers of different but constant density. The model allows the barotropic and the first baroclinic mode to be calculated. In addition to the nonlinear advective terms dispersion and Coriolis force due to the Earth's rotation are taken into account. The model equations are solved numerically by an implicit finite difference scheme. In this paper we discuss the results for ideal basins: the effects of nonlinear terms, dispersion and Coriolis force, the mechanism of wind forcing, the evolution of Kelvin waves and the corresponding transport of particles and, finally, wave propagation over variable topography. First applications to Lake Constance are shown, but a detailed analysis is deferred to a second paper [Bauer et al. (1994)]. 相似文献
16.
松辽盆地中地壳有一低速-高导层(也称塑性层),中地壳的塑性层与松辽盆地的成因以及盆山耦合系统有关.盆地地幔流体活动有下列表现:(1)高热流、高地温场;(2)深大断裂与火山岩喷溢;(3)碱交代作用(如钠长石化、伊利石化);(4)Mg2 交代作用(如白云石化)等等.地球化学省与地球化学急变带控制了大油气田的分布并显示了盆地发生的壳-幔相互作用.中地壳的低速-高导层不是岩浆岩,而是一充满地幔流体的地质体,它们富含氢、碱金属(K 、Na )、卤素(F-、Cl-)、碳(甲烷、CO、CO2)、氮、硫等.在中地壳的温度压力条件下,在Fe、Ni等催化荆的参与下,H2与CO(CO2)可发生费-托合成烃的反应.实验表明:这个反应不仅可生成气态烃还可生成液态烃,并将发生碳同位素分馏作用.松辽盆地的U形运移模型受到质疑.按照石油无机生成的模型,松辽盆地的深部将会有更多的石油与天然气,庆深气田的发现便是一个明证. 相似文献
17.
Colin Brown 《Surveys in Geophysics》1994,15(2):123-157
This review paper selects key results from electromagnetic induction studies of a variety of distinctive tectonic phenomena in the top 200 km of the Earth. Its main theme is that electromagnetic data are essential for an understanding of tectonism involving partial melting, recycling of large volumes of fluids (CO2 and H2O) and underthrusting of metasedimentary rocks. The wide variety of tectonic regimes in which these processes are known to be important is reflected in the choice of case studies. A discussion of conductivity models for young oceanic lithosphere and asthenosphere is followed by results from induction studies across the S.E. Australian passive margin, the North American active margin, the Ryukyu Island-Arc and the Oregon Cascades continental arc. The importance of partial melting and free fluid movement i apparent in these regions. Terrain accretion and/or continent-continent collisions recorded at palaeosuture zones in Ireland, Germany and Scandinavia have left distinctive conductivity structures. These are often associated with grain-boundary graphite either in weakly-metamorphosed black shales in underthrust sedimentary basins or precipitated from CO2-rich fluids. They are discussed in the context of the evolution of mature continental crust. All of the case studies are based on experiments published since 1989 in which the electromagnetic results have been central to an integrated geophysical and geological interpretation. 相似文献
18.
Wavefields in porous media saturated by two immiscible fluids are simulated in this paper. Based on the sealed system theory,
the medium model considers both the relative motion between the fluids and the solid skeleton and the relaxation mechanisms
of porosity and saturation (capillary pressure). So it accurately simulates the numerical attenuation property of the wavefields
and is much closer to actual earth media in exploration than the equivalent liquid model and the unsaturated porous medium
model on the basis of open system theory. The velocity and attenuation for different wave modes in this medium have been discussed
in previous literature but studies of the complete wave-field have not been reported. In our work, wave equations with the
relaxation mechanisms of capillary pressure and the porosity are derived. Furthermore, the wavefield and its characteristics
are studied using the numerical finite element method. The results show that the slow P3-wave in the non-wetting phase can
be observed clearly in the seismic band. The relaxation of capillary pressure and the porosity greatly affect the displacement
of the non-wetting phase. More specifically, the displacement decreases with increasing relaxation coefficient. 相似文献
19.
E. L. Gégo G. S. Johnson M. Hankins 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(1):47-64
Stochastic techniques, such as Monte Carlo experiments, are more and more frequently used for the study of flow and transport
in heterogeneous aquifers. When the aquifer is composed of distinct hydrofacies, a common way to model heterogeneity is to
first generate equally-possible hydrofacies fields, and then convert these hydrofacies fields into hydraulic conductivity
(K) fields by assigning a single K value to each facies. This technique assumes relative homogeneity of K within each facies
but may not be appropriate for the most conductive facies that often exhibits substantial variability. In this paper, we assessed
the impacts of assigning multiple random K, rather than a uniform K value, to the highly conductive facies on the results
of a flow and transport model. A set of fifty stochastic hydrofacies maps depicting an environment similar to the Snake River
Plain aquifer (SRPA) in south-east Idaho were generated. Simulations demonstrated that a uniform K value, if carefully chosen,
can reasonably reproduce the specific discharges and early particle arrival times produced by multiple K values. Yet, the
results obtained with a uniform K value are dramatically less variable than those obtained with multiple K values. It is therefore
concluded that stochastic simulations with uniform K assigned to the most conductive and variable facies do not necessarily
portray the entire uncertainty in the analyses. 相似文献
20.
Biot流动和喷射流动是含流体多孔隙介质中流体流动的两种重要力学机制,对地震波和声波的传播均产生重要影响. Dvorkin和Nur提出了同时包含Biot流动和喷射流动力学机制的统一的BISQ(Biot-Squirt)模型,基于这一模型,尽管有关弹性波在多孔隙介质中的衰减和频散问题已被广泛研究,然而,基于BISQ波传播方程的波场数值模拟至今仍未见报道. 本文从同时包含两种力学机制的孔隙弹性波方程出发,利用FCT有限差分法对含流体孔隙各向同性介质中的地震波和声波进行了数值模拟,并与基于Biot流动的Biot理论之模拟结果进行比较. 数值模拟结果表明:同时包含Biot流动和喷射流动影响的地震波和声波速度比仅包含Biot流动作用的地震波和声波速度慢,慢P波的衰减比根据Biot理论模拟的慢P波衰减更强. 相似文献