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The Characteristics and Tectonic Implications of Electrical Structure in the Crust and Mantle from the Northeastern Margin of the Tibetan Plateau (Dajing) to South China (Quanzhou)

Author: ZhangFan
Tutor: WeiWenBo
School: Chinese Geology University (Beijing)
Course: Geophysics
Keywords: Northeastern margin of the Tibetan Plateau Eastern margin of the TibetanPlateau South China Magnetotellurics Electrical structure
CLC: P631.4
Type: PhD thesis
Year: 2013
Downloads: 54
Quote: 0
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Abstract


Under the auspices of the SinoProbe-02-04, a long magnetotelluric profile whichis longer than2000km was acquired from the town of Dajing in the northeasternmargin of the Tibetan Plateau to the city of Quanzhou in South China. Many methodshave been used during the magnetotelluric data processing such as the robustestimation, the remote reference method and the editing of the power spectrum in orderto acquire the high quality magnetotelluric data. The effects of the ocean coast onmagnetotelluric data have been studied by three-dimensional electromagnetic forwardmodeling. The qualitative analyses of the electrical structure along the profile havebeen done by analyzing many parameters such as Swift skewness, Bahr skewness,phase tensor, magnetic induction vector, and direction of strike. Dimensionalityanalysis has shown a good two-dimensional character along the profile. Subsurfaceelectrical structure has been obtained through nonlinear conjugate gradients algorithmfor two-dimensional magnetotelluric inversion.The electrical resistivity model along the profile indicates that the electricalstructure in eastern Tibetan Plateau is characterized by four distinct layers in verticaldirection and block division in horizontal direction. The electrical properties betweeneastern Tibetan Plateau and South China are quite different. The electrical resistivity ishigh in South China. The electrical structure in South China is characterized by blockdivision in horizontal direction and distinct layering partially in vertical direction.There are the high-conductivity layers in the middle and lower crust in easternTibetan Plateau. The distribution of the high-conductivity layers in different blocks isbased on different formation processes. The high-conductivity layers in the crust underQilian block are likely due to the existence of saline fluids. The high-conductivitylayers in the crust under West Qinling orogeny and Songpan-Ganzi block are likelydue to the existence of partial melts and saline fluids.The granitic rocks are the main components of the continental crust in Cathaysiablock. There might be tectono-magmatism in the crust in western Cathaysia block due to continental intraplate deformations. Both upsurge of heat mantle materials andcontinental rifting might result in partial melts in the crust in central Cathaysia block.Delivery of thermal energy and interaction between crust and mantle in easternCathaysia block might be induced in the stage that Pacific plate subducted to theEurasian continent.The Longmenshan fault in the electrical resistivity model along the profilepresents the overthrusting between the eastern margin of the Tibetan Plateau and theYangtze block. The conductive layer in the range of mid to upper crust marks thedetachment surface under the Longmenshan nappe structure. The boundary betweenthe conductive Tibetan Plateau and the resistive Yangtze block has been shown belowthe conductive layer. The relationship between eastern Tibetan Plateau and Yangtzeblock might reflects the uplift mechanism of eastern Tibet Plateau.

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