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Li B.,Beijing University of Technology | Li B.,Key Laboratory of Geo detection of Ministry of Education | Wei W.B.,Beijing University of Technology | Wei W.B.,Key Laboratory of Geo detection of Ministry of Education | And 3 more authors.
Applied Mechanics and Materials | Year: 2014

The cental Asian orogenic belt (CAOB) which between the North China Craton and the Siberian Craton is one of the tectono-metallogenic belts in the world. The central Inner Mongolia belongs to the eastern part of the CAOB, recently a series of research and exploration work has been done in this region. However, no breakthrough has been made in the exploration of metal ore. In order to research current mineralization issues in the eastern part of the CAOB, a long magnetotelluric (MT) profile was acquired across the central part of Inner Mongolia. The profile starts within the DongUjimqinqi in the northwest, goes southeastward across the Chagan Obo-Arongqi fault, the Erenhot-Hegenshan fault, the Xilinhot fault and the Linxi fault, and ends around the Xar Moron fault in the northern part of Chifeng city; the strike direction of most faults is southeast; the faults have direct control effect to the magmation and mineralization of this region. The model of electrical structure along the profile can be divided into two regions: widely distributed low resistivity is the key feature north of Nianzigou; high resistance is the key feature south of Nianzigou. The Chagan Obo-Arongqi fault, the Erenhot-Hegenshan fault and the Xilinhot fault all present as a southeastward dipping conductor, which reflects their overthrusting process; there are many high conductivity areas along the faults in the region. The electrical structure to the south of Nianzigou is expressed as a mushroom shape, which reflects the tectonic origin of magmatic rock in this region. © (2014) Trans Tech Publications, Switzerland. Source

Liu Z.-L.,Beijing University of Technology | Liu Z.-L.,Tianjin Geothermal Exploration and Development Designing Institute | Ye G.-F.,Beijing University of Technology | Ye G.-F.,Key Laboratory of Geo detection of Ministry of Education | And 7 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

In order to study the central-upper crust electrical structure and tectonic features of Hailar Basin, and discuss metallogenic geological srtucture background characteristics and metallogenic environments of Hailar Basin, this paper selected 66 magnetotelluric sounding points in Hailar Basin which is acquired in 2011 of “Comprehensive geophysical survey in the eastern part of China-Mongolia border region” project for line 4 to treatment and research. The magnetotelluric sounding methord via studying the propagation characteristics of natural electromagnetic field in the earth to detect the underground geological structure. The model of lithosphere scale electrical conductivity can be obtained by magnetotelluric sounding methord, and provides a physical basis for the study of deep geological structure. Through analysis and interpretation of 2D inversion results based on magentotelluric sounding profile, knowing that the deep geological structure of the study area is NE-SW trending, and large scale electrical resistivity structures were revealed for the first time. The electrical structure of the middle-upper crust of Hailar Basin is clearly stratified and can generally be divided into four layers, namely the high conductivity layer-high resistivity layer-high conductive layer-high resistivity layer, while the transverse could also be divided into several blocks horizontally. The numerous distributed faults in Hailar Basin's edge and interior divide the Basin itself into alternating structures of uplifts and depressions. It's also found that there are small scale bulges in depression parts, and the electrical structure of each tectonic unit is of distinct features. The lower boundary of high conductivity layer in middle-upper crust of Hailar Basin is generally between 6 and 16 km, which can reach 28 km at the deepest part with little change in thickness, which is about 4~10 km. The lower boundary in uplift and depression areas are largely different. According to the electrical structure model, two new faults of F8 and F9 are inferred, and the fault F9 is of larger scale that cut the basement. The high conductivity layer in middle-upper crust may to some extent control the distribution of oil and gas deposits within the Hailar Basin. It is speculated that the high conductivity layer uplifts is a favorable area for oil and gas exploration. © 2015, Science Press. All right reserved. Source

Dong H.,Beijing University of Technology | Dong H.,Key Laboratory of Geo detection of Ministry of Education | Wei W.-B.,Beijing University of Technology | Wei W.-B.,Key Laboratory of Geo detection of Ministry of Education | And 6 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

An algorithm of three-dimensional (3D) magenetotlluric inversion with topography based on finite difference (FD) method is presented. A staggered-mesh, finite-difference method is utilized for the 3D magnetotelluric numerical simulation with surface topography. Cuboid mesh grid is used for discretization to meet the plane wave assumptions in magnetotelluric forward calculations with topography.Magnetotelluric responses are generated utilizing a topography model of square frustum hill to compare with previous result from finite element method, verifying the correctness and reliability of the forward code. In the inversion part, a 3D inversion scheme with topography is developed based on nonlinear conjugate gradient method.Different conjugate gradient search direction updater β are tested to improve the global convergence. Explicit calculations and storage of the Hessian matrix are avoided. Finally, a series of forward models with topography is established to generate synthetic data, which is inverted by the 3D inversion method with topography. The results are hence compared with the results from 3D MT inversion with no topography implications.The reliability and stability of the three-dimensional inversion is tested. Source

Cui J.,Beijing University of Technology | Cui J.,Key Laboratory of Geo detection of Ministry of Education | Deng M.,Beijing University of Technology | Deng M.,Key Laboratory of Geo detection of Ministry of Education | And 8 more authors.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2014

It is difficult to estimate precise magnetotelluric (MT) impedance tensor in high correlated noise areas. In order to approximate MT impedance tensor, we use remote sites which contain relatively lower correlated noise to compute separation tensor by using Robust least square method. The MT data in three sites which are contaminated by higher and lower correlated noises are processed using signal-noise separation method. The results show that it can separate higher correlated noise and get much smoother apparent resistivity and phase curves than those obtained by using Robust least square method and remote reference method. It is concluded that signal-noise separation method is efficient for much more precise MT impedance tensor. Source

Wei W.B.,Key Laboratory of Geo detection of Ministry of Education | Wei W.B.,State Key Laboratory of Geological Processes and Mineral Resources | Wei W.B.,Beijing University of Technology | Jin S.,Key Laboratory of Geo detection of Ministry of Education | And 9 more authors.
Science China Earth Sciences | Year: 2010

To understand deep lithosphere structure beneath the Qinghai-Tibet Plateau more comprehensively and objectively and to explore important scientific issues, such as characteristics of plateau lithospheric deformation, state of strain, thermal structure, plate (or terrane) movement, and crust-mantle rheology, it is necessary to research the variation of crust-mantle electrical structure in the east-west direction in every geological unit. For this purpose, six super-broadband magnetotelluric (MT) sounding profiles have been completed by INDEPTH-MT Project in the Himalayas-Southern Tibet. Based on the imaging results from the six profiles, three-dimensional electrical conductivity structure of the crust and upper mantle has been analyzed for the research area. The result shows that the high-conductivity layers in the middle and lower crust exist widely in Southern Tibet, which extend discontinuously for more than 1000 km in the east-west direction and become thinner, shallower and more resistive toward the big turning of the Yarlung Zangbo River. The discussion on the rheology of lithosphere in Southern Tibet suggests that the mid-lower crust there is of high electrical conductivity, implying the existence of "partial-melt" and "hot fluid" in the thick crust of Tibet, which make the medium hot, soft, and plastic, or even able to flow. Combining the experimental result of petrophysics and the MT data, we estimate the melting percentage of the crustal material to be up to 5%-14%, which would reduce the viscosity of aplite in the crust to meet the flow condition; but for granite, it is likely not enough to cause such a change in rheology. © Science China Press and Springer-Verlag Berlin Heidelberg 2010. Source

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