Application of 2D magnetotelluric methods in a geological complex area, Xinjiang, China

Xiao, Qibin; Cai, Xinping; Liang, Guanghe; Xu, X.; Zhang, Baolin

doi:10.1016/j.jappgeo.2011.06.007

Cited by 15 publications

(10 citation statements)

References 38 publications

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“…The NLCG code described by Rodi and Mackie [] was used for the 2D inversions. This inversion code shows stable convergence in practical applications [ Xiao et al , ].…”

Section: D and 3d Electrical Structuresmentioning

confidence: 99%

Eastern termination of the Altyn Tagh Fault, western China: Constraints from a magnetotelluric survey

et al. 2015

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The left-lateral Altyn Tagh Fault forms the northern boundary of the Tibetan Plateau. The strike-slip rate of the active Altyn Tagh Fault decreases northeastward and reduces close to zero as it passes north of the Qilian Shan. This geometry raises controversies on whether and how the fault terminates or extends further east. To address these controversies, wide-band magnetotelluric data were collected along four profiles across the Altyn Tagh Fault ranging from 135 to 261 km in length. All four profiles are located in the foreland of the Qilian Shan Ranges and are oriented perpendicular to the inferred fault zone that could be the continuation of Altyn Tagh Fault. Both the two-dimensional and three-dimensional electrical resistivity models derived from our magnetotelluric data show that the Hexi Corridor crust is generally of low resistivity, whereas the crust of the Huahai-Jinta basin is, in general, of high resistivity with a local and isolated low-resistivity anomaly within the mid-lower crust. The generally high-resistivity crust of the Huahai-Jinta basin may be rheologically unfavorable for the Altyn Tagh Fault passing through the basin toward the northeast. The entirely different electrical structure between the Hexi Corridor and its northern neighbors indicates the existence of a tectonic boundary that coincides with the Altyn Tagh Fault in the west and reverse faults in the east. The two-dimensional electrical conductivity models suggest that the Altyn Tagh Fault transfers from a single fault in the west to a branching set of mainly dip-slip faults in the east.

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“…The NLCG code described by Rodi and Mackie [] was used for the 2D inversions. This inversion code shows stable convergence in practical applications [ Xiao et al , ].…”

Section: D and 3d Electrical Structuresmentioning

confidence: 99%

Eastern termination of the Altyn Tagh Fault, western China: Constraints from a magnetotelluric survey

et al. 2015

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“…High conductivity anomalies are widely distributed in the middle to lower crust and upper mantle, and there are various causes of these anomalies in different regions (Xiao et al, 2007(Xiao et al, , 2011Pape et al, 2015;Novella et al, 2017). Hence, it is crucial to comprehensively measure the electrical conductivities of minerals and rocks that are distributed in the deep Earth.…”

Section: Introductionmentioning

confidence: 99%

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

Dai

Sun

et al. 2018

Solid Earth

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Abstract. The electrical conductivity of gneiss samples with different chemical compositions (W A = Na 2 O + K 2 O + CaO = 7.12, 7.27 and 7.64 % weight percent) was measured using a complex impedance spectroscopic technique at 623-1073 K and 1.5 GPa and a frequency range of 10 −1 to 10 6 Hz. Simultaneously, a pressure effect on the electrical conductivity was also determined for the W A = 7.12 % gneiss. The results indicated that the gneiss conductivities markedly increase with total alkali and calcium ion content. The sample conductivity and temperature conform to an Arrhenius relationship within a certain temperature range. The influence of pressure on gneiss conductivity is weaker than temperature, although conductivity still increases with pressure. According to various ranges of activation enthalpy (0.35-0.52 and 0.76-0.87 eV) at 1.5 GPa, two main conduction mechanisms are suggested that dominate the electrical conductivity of gneiss: impurity conduction in the lower-temperature region and ionic conduction (charge carriers are K + , Na + and Ca 2+ ) in the higher-temperature region. The electrical conductivity of gneiss with various chemical compositions cannot be used to interpret the high conductivity anomalies in the Dabie-Sulu ultrahigh-pressure metamorphic belt. However, the conductivity-depth profiles for gneiss may provide an important constraint on the interpretation of field magnetotelluric conductivity results in the regional metamorphic belt.

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“…Where AMT signal levels are low, e.g., in the dead band at $ 800-3000 Hz (Garcia and Jones 2002), the controlled-source audiomagnetotelluric method (CSAMT, f = 1-10000 Hz, Zonge and Hughes 1991) is routinely applied. Consequently, MT methods have a long-standing history in the investigation of mineral deposits (Strangway et al 1973;Meju 2002;Jones 2017) with field cases reported from, for instance, copper, gold, lead, silver and zinc deposits (Kellett et al 1993;Garcia Juanatey et al 2013a, b;Hübert et al 2013;Hu et al 2013), copper, gold and iron deposits (Heinson et al 2006), copper and iron deposits (Chouteau et al 1997;Jones and Garcia 2003), copper, iron and zinc deposits (Basokur et al 1997), copper, lead and zinc deposits (Sasaki et al 1992;Bastani et al 2009), copper and nickel deposits (Lakanen 1986;Livelybrooks et al 1996;Jones et al 1997;Balch et al 1998;Stevens and McNeice 1998;Zhang et al 1998;Watts and Balch 2000;King 2007;Xiao et al 2011;Varentsov et al 2013; Le et al 2016a), copper, silver and zinc deposits (Gordon 2007), gold deposits (Jones et al 1997;Liu et al 2006;Howe et al 2014;Takam Takougang et al 2015;Hübert et al 2016;Le et al 2016b), and uranium deposits (Leppin and Goldak 2005;Tuncer et al 2006;Farquharson and Craven 2009;Goldak et al 2010;…”

Section: Mt Methods In Exploring Deep Ore Depositsmentioning

confidence: 99%

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

Kalscheuer

Juhojuntti

Vaittinen³

2017

Surv Geophys

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A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $ 300-1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and elect...

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Application of 2D magnetotelluric methods in a geological complex area, Xinjiang, China

Cited by 15 publications

References 38 publications

Eastern termination of the Altyn Tagh Fault, western China: Constraints from a magnetotelluric survey

Eastern termination of the Altyn Tagh Fault, western China: Constraints from a magnetotelluric survey

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

Two-Dimensional Magnetotelluric Modelling of Ore Deposits: Improvements in Model Constraints by Inclusion of Borehole Measurements

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