Geoelectric Structure of Lithosphere Beneath Eastern North China: Features of Thinned Lithosphere from Magnetotelluric Soundings

Wei, Wenbo; Ye, Gaofeng; Jin, Sheng; Deng, Ming; Jing, Jianen; Zhang, Peng; Xiaobin, Lin; Shi, Song; Tang, Baoshan; Qu, Shuanzhu; Chen, Kai; Yang, Hongwei; Li, Guoqiang

doi:10.1016/s1872-5791(08)60055-x

Cited by 47 publications

(24 citation statements)

References 1 publication

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“…Such variations could be well explained by lower crustal clinopyroxene with minor amounts of water, e.g., a few tens to hundreds of ppm H 2 O (depending on temperature), in the 600–1000°C range, without contributions from other conductive materials such as hydrous fluids, melts or graphite films (note that clinopyroxene in the lower crust generally contains some water, typically a few hundreds to >1000 ppm [ Yang et al , 2008a]). MT profile surveys in north China found a highly conductive layer of ∼0.04 to 0.2 S/m in the depth range of 20–40 km beneath the Hengshan Mountain [ Wei et al , 2008]. If this layer extended northeast to the adjacent Hannuoba region (the distance between these two areas is <100 km), given that the temperature at such depths is mostly ∼850 to 950°C according to geothermal gradient established by both xenolith samples and surface heat flow [ Menzies et al , 1993; Griffin et al , 1998; Chen et al , 2001; Yang et al , 2008a; Zhou et al , 2002], the corresponding H 2 O content of clinopyroxene in the regional lower crust is ∼200 to 1600 ppm (in this case, the highest H 2 O value corresponds to the highest conductivity and low temperature at 850°C, and it is only ∼850 ppm at 950°C).…”

Section: Discussionmentioning

confidence: 99%

Effect of water on the electrical conductivity of lower crustal clinopyroxene

et al. 2011

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[1] The electrical conductivity of lower crustal clinopyroxene was measured at 6-12 kbar, 250-1000°C, and Ni-NiO buffer conditions. The dependence of electrical conductivity on water content was studied using both natural and preannealed samples separated from a fresh xenolith granulite, with water contents from 0 to 375 ppm. An end-loaded piston cylinder apparatus and a Solarton-1260 Impedance/Gain Phase Analyzer were used in the study over a frequency range of 0.01-10 6 Hz to obtain the complex impedance spectra. The results show that the influence of pressure is very weak relative to temperature and water content and that two distinct mechanisms with different activation enthalpies dominate electrical conduction under dry and wet conditions. For the dry sample, the activation enthalpy is ∼102 kJ/mol and the main charge carriers are small polarons, i.e., hopping of electron holes between ferrous and ferric irons. For wet samples, the electrical conductivity is significantly enhanced with an activation enthalpy of ∼70 kJ/mol and the charge carriers are likely to be protons. Under hydrous conditions, the activation enthalpies are nearly independent of water content and the conductivity is a function of water content with an exponent of ∼1. As a major constituent of granulites with >60% modal volume in some regions, clinopyroxene containing minor amounts of water may contribute significantly to the high electrical conductivity in the lower crust, especially under stable continental regions.

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Section: Discussionmentioning

confidence: 99%

Effect of water on the electrical conductivity of lower crustal clinopyroxene

et al. 2011

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“…Previous studies on the NW-trending magnetotelluric (MT) profile through the Fuping region (Yingxian-Fuping-Shanghe profile, HBMT01; Figure 14A and C in revealed that the current thickness of the lithosphere beneath the northern TM is about 70 km. A decoupling phenomenon has been identified between the lower crust and the sublithospheric mantle region (Wei et al 2008). The Fuping terrain, particularly our study area where the Mapeng Pluton and the Xishimen gold deposit are located, occurs at the boundary of the strongly thinned Eastern Block of the NCC (Kusky and Li 2003;Santosh 2010;Guo et al 2013).…”

Section: Link Between Metallogenesis and Magmatismmentioning

confidence: 79%

Stable isotopes and noble gases in the Xishimen gold deposit, central North China Craton: metallogeny associated with lithospheric thinning and crust–mantle interaction

Santosh

2013

International Geology Review

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Quartz-vein type gold mineralization at Xishimen is a recently discovered gold deposit in the central North China Craton. More than 50 auriferous quartz veins occur in this region within a NNW-SSE-trending fault zone 4600 m in length and 3-10 m wide. Wall rocks are mainly Precambrian tonalite-trondhjemite-granodiorite (TTG) gneisses and associated supracrustals, modified by K-feldspathization and pyrite-phyllic hydrothermal alteration. Based on detailed field and petrographic studies, we identify five episodes of mineralization: pyrite-phyllic stage (I), coarse-grained pyrite-milky white quartz stage (II), fine-grained smoky grey quartz-pyrite stage (III), fine-grained smoky grey quartz-polymetallic sulphide stage (IV), and quartz-carbonate stage (V). We present results of δ 34 S analysis of sulphide minerals from the different stages which show tightly clustered values in the range of -1.0‰ to 2.1‰, close to those of mantle and meteorite sulphur. Lead isotopic ratios of pyrite from the early to main stages also show restricted ranges with 206 Pb/ 204 Pb of 16.289-17.286, 207 Pb/ 204 Pb of 15.217-15.453, 208 Pb/ 204 Pb of 37.012-38.232, implying lower crustal input. 3 He/ 4 He and 40 Ar/ 36 Ar ratios of fluid trapped in pyrite are 0.68 Ra to 1.20 Ra (where Ra is the 3 He/ 4He ratio of air = 1.4 × 10 −6 ) and 540.9-1065, respectively. 3 He and 4 Ar concentrations vary from 10.05 to 18.5 (10 −7 cm 3 STP/g) and 6.15 to 17.4 (10 −7 cm 3 STP/g), respectively, with calculated mantle helium ranging from 8.47% to 14.96% (average 11.01%). δ 18 O Q and δ 18 D Q values of quartz range from 8.0‰ to 13.2‰ and -101.9‰ to -70.5‰, respectively, with calculated δ 18 O W values of the mineralizing fluid ranging from 1.11‰ to 5.72‰, suggesting the mixing of magmatic aqueous fluid with meteoric water during gold precipitation. We correlate the mixed crust-mantle signature of the ore-forming sources to magmatism and metallogeny associated with Mesozoic inhomogeneous lithosphere thinning in the central North China Craton.

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“…Its remarkable sign is the obvious reduction of the thickness of lithosphere to the east of Taihang mountain. Not only the thickness of lithospheric mantle has reduced, but also crustal thickness has been considerably reduced (Wang, 2006;Xu, 2007;Jia et al, 2005;Chen et al, 2010;Wei et al, 2008;Zhu et al, 2012;Ge et al, 2011;Duan et al, 2015). The continuous tectonic movement, uplifting of Taihang mountain, and new tectonic activities continue to intensify the continuous deposition of a thick Cenozoic formation in the piedmont basin, and a large-scale depression basin is formed.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

High Resolution Velocity Structure of the North China Craton Basement by Blasting Seismic Wave—results From Dafeng–baotou Refraction Profile

Zhao

Liu

Duan

et al. 2017

Chinese J of Geophysics

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Due to the high density of observation points and shots, we obtained the 21‐shot seismic data with high signal‐to‐noise ratio along the 1334 km long Dafeng‐Baotou profile. On the basis of the analysis of the Pg wave phase characteristics, we processed the data by the inversion method and constructed the fine structure of the basement, revealing the discrepancy of basement structure in different tectonic blocks. The basement depth of Northern Jiangsu basin is 4.5∼9.0 km and that of Jiangsu‐Shandong uplift is 1.5∼2.0 km. Strong fluctuations of the burial depth and velocity structure may be considered as the seismologic manifestation of the collision and extrusion between North China and the Yangtze plate. The basement of Western Shandong uplift area shows the feature of shallow burial depth, high speed and stable structure, while the Pg wave characteristics in the North China basin are lagged travel time, low apparent velocity, basement depth from 7.0 km to 10.0 km, and the local fluctuations in the velocity structure and basement interface. Lots of phenomena above reveal that this area is a large‐scale basement depression zone with thick Cenozoic sediment. Moreover, in different tectonic units of the basin, the tectonic pattern of local basement patch and coexistence of depression and uplift shows obvious tectonic characteristics, such as remarkable Cenozoic sedimentary activities, significant velocity and thickness changes and the unstable structure. Taihang mountain piedmont fault and Liaolan fault are significant seismologic features. On both sides of these two faults, the velocity structure shows intensive lateral heterogeneity, and the basement interfaces collapse as cliff. This study reveals that the Taihang mountain piedmont fault is an important tectonic zone in North China. Its complexity is not only reflected in different landforms and strata on its two sides, but also reflected in the significant differences among the basement depth, velocity structure, the crust and even the mantle lithospheric structures. To the east of Taihang mountain, the important symbol is large scale crustal and lithospheric thinning, which result in the obvious differences and strong lateral heterogeneity of the basement structure, the crust and even the lithosphere structures between the western and eastern North China Craton destruction

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Geoelectric Structure of Lithosphere Beneath Eastern North China: Features of Thinned Lithosphere from Magnetotelluric Soundings

Cited by 47 publications

References 1 publication

Effect of water on the electrical conductivity of lower crustal clinopyroxene

Effect of water on the electrical conductivity of lower crustal clinopyroxene

Stable isotopes and noble gases in the Xishimen gold deposit, central North China Craton: metallogeny associated with lithospheric thinning and crust–mantle interaction

High Resolution Velocity Structure of the North China Craton Basement by Blasting Seismic Wave—results From Dafeng–baotou Refraction Profile

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