Variation of Moho Depth across Bangong-Nujiang Suture in Central Tibet—Results from Deep Seismic Reflection Data

Lu, Zhanwu; Gao, Rui; Li, Hongqiang; Li, Wenhui; Xiong, Xuejian

doi:10.4236/ijg.2015.68066

Cited by 8 publications

(9 citation statements)

References 43 publications

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“…Curiously, the gently north dipping conductive layer C1 beneath the Himalaya and south Lhasa is also consistent with the lower crustal zone with decreased velocity (blue; Figure 4a). Moreover, resistor R1 in the vicinity of the BNS also overlaps with the region with an apparently “obscure Mohorovicic discontinuity” imaged between ~31.5° and 33°N (Figure 4a), as well as the shallower “unclear” Moho trace near BNS at ~88.5°E revealed by a deep seismic reflection survey (Lu et al, 2015).…”

Section: The 3‐d Inversion Of the Mt Datamentioning

confidence: 81%

Section: Tectonic Scenariosmentioning

confidence: 89%

“…Not affected by the large portion of melts as in southern Lhasa, the lower crust remained stronger and is imaged as a resistive anomaly (R1 in Figure 8c) near the BNS, which also overlaps with the lower crustal high velocity zone revealed by INDEPTH active seismic data (Haines et al, 2003). The lower crust could have experienced partial eclogitization, which formed the obscure Moho imaged near the BNS region (Lu et al, 2015; J. Nabelek, 2009). This is because the velocity difference between a partially eclogitized lower crust and uppermost lithospheric mantle (peridotite) can be insignificant (7.5 and 8.0 km/s for P waves; e.g., Kukkonen et al, 2008) and virtually invisible for most seismic investigations.…”

Section: Discussionmentioning

confidence: 99%

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Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

et al. 2020

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The ongoing India-Asia collision since the Paleogene created the Tibetan Plateau, the most prominent elevated plateau on our planet. This convergence also contributed to the formation of two distinct types of active surface deformation of the plateau, namely, north-south trending normal fault systems and "conjugate" strike-slip fault systems. The tectonics and geodynamic mechanism(s) behind this curious combination are still unclear, despite numerous theories proposed over past decades. Here we present a new three-dimensional, lithospheric-scale, electrical conductivity model with unprecedented resolution of the central part of Tibetan Plateau derived from the SINOPROBE magnetotelluric array data set and discuss its inferences related to this question. Our model reveals contrasting conductivity structures corresponding to the surface deformation patterns, namely, highly conductive lower crustal anomalies beneath the graben systems in the Lhasa and Qiangtang terranes and moderately resistive crustal features in the strike-slip region near Bangong-Nujiang Suture Zone. With the help of experimentally calibrated constraints between conductivity and melt fraction, the conductivity model and the inferred lateral viscosity distribution together suggest a weak lower crust beneath the graben regions, compared to a stronger crustal rheology associated with the strike-slip zone. Here we expand the previously proposed "extensional extrusion" tectonic model in central Tibet to interpret our conductivity model and other geophysical/geodesic observations. The weak rheology under a N-S directed primary stress may have caused the east-west extension of the graben regions, which further aides the eastward extrusion of the conjugate strike-slip zone and eventually shapes the surface deformation of central Tibetan Plateau into its current, complex pattern. Plain Language Summary The collision between the Indian and Asian continents built the Tibetan Plateau, the highest plateau in the world. This active collision also formed distinctly different types of large-scale geological structures on the plateau surface. Among the most important features on the plateau, the origin of the N-S directed normal (or spreading) fault zones in two regions named Lhasa and Qiangtang, and the NW/SE directed slip fault zones between these two regions are still unclear. In order to understand the generation of those structures, we use a geophysical imaging method called magnetotellurics to measure the naturally occurring electromagnetic waves in the earth. We model and analyze these magnetotellurics data to obtain the deep structure beneath those surface structures, using sophisticated computer codes. We find that the two dominant but different types of those structures are most likely due to the different strengths of the deep crust. This strength difference can lead to a mechanical stress contrast, which further builds the distinctly different surface structures. These kinds of deep physical structure differences have not been detected for the area bef...

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Section: The 3‐d Inversion Of the Mt Datamentioning

confidence: 81%

Section: Tectonic Scenariosmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

et al. 2020

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“…The crustal thickness increases from 40 km in the southern Himalayas to 70 km beneath the YZS, reaches a maximum value of 80 km in southern Lhasa, and then decreases to 70 km beneath the BNS. A Moho offset of 5-10 km has been identified beneath the BNS by seismic reflection studies (e.g., Lu et al, 2015). In the Qiangtang terrane, the crustal thickness is ∼65 km (e.g., Kind et al, 2002).…”

Section: Tectonic Settingmentioning

confidence: 99%

Magmatic Underplating Thickening of the Crust of the Southern Tibetan Plateau Inferred From Receiver Function Analysis

Liu

Tian

Liang

et al. 2021

Geophysical Research Letters

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The Tibetan Plateau has been produced by continental convergence between India and Asia since 55 ± 10 Ma (Fielding et al., 1994;Tapponnier et al., 2001). With an average elevation of 4-5 km, the Tibetan crust is twice the thickness of normal continental crust (Zhang, Teng, et al., 2014). However, exactly how the plateau crust thickened by crustal shortening (Dewey & Burke, 1973) or underthrusting (Argand, 1924) is still a matter of debate.Spatial and temporal variations in the crustal thickness based on the whole-rock La/Yb ratios of intrusive rocks indicate that the crust of the Lhasa terrane was thickened by at least 20 km during the Cenozoic (Zhu et al., 2017). However, the late Paleocene-early Eocene volcanic sequence and sedimentary stratigraphic studies suggest that the Lhasa terrane has experienced little deformation since the Indian-Eurasian collision (Yin & Harrison, 2000). Receiver function imaging has shown two positive amplitude bands (doublet) at the base of the crust in the southern Lhasa terrane (

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“…To date, a variety of geophysical studies have been carried out in the Lhasa and Qiangtang terranes, mainly including gravity and magnetism (He et al, 2014) and magnetotellurics (Wei et al, 2001;Unsworth et al, 2005;Zeng et al, 2015;Liang et al, 2018;Sheng et al, 2019;Xue et al, 2021;Jin et al, 2022). Deep seismic Frontiers in Earth Science frontiersin.org reflection detection (Ross et al, 2004;Gao et al, 2013Gao et al, , 2016Lu et al, 2015;Shi et al, 2021) and seismological methods (He et al, 2010;Xu et al, 2011;Shi et al, 2016) have provided essential information for the convergent front of Indian lithosphere, highconductivity and low-velocity material inside the crust. In general, previous geophysical studies have mainly focused on the direct contact zone of continent-continent collisions in the southern Tibetan Plateau.…”

Section: Introductionmentioning

confidence: 99%

Lithospheric electrical structure across the Bangong-Nujiang Suture in northern tibet revealed by magnetotelluric

et al. 2023

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Competing hypotheses have been proposed to explain the subduction polarity of the Bangong-Nujiang Tethyan Ocean and the formation of the high-conductivity anomaly beneath the Qiangtang terrane. However, the lithospheric architecture of the northern Tibetan Plateau is still poorly understood due to inhospitable environments and topography. Therefore, in the winter of 2021, a 440 km long, SN-trending broadband magnetotelluric (MT) profile was recorded in northern Tibet to detect its regional lithospheric structure. The nonlinear conjugate gradients algorithm is conducted to invert the individual TM mode data. A reliable 2D electrical model was obtained by ablation processing and analysis of broadband magnetotelluric data to test the lithospheric electrical structure and dynamics between the northern Lhasa and Qiangtang terranes. The inversion results reveal the lithospheric structure at a depth of 100 km in northern Tibet, which synthesizes geological, geochemical and deep seismic reflection evidence and firmly identifies that the trace of the south-dipping conductor mainly resulted from the southward subduction of the Bangong-Nujiang Tethyan Ocean under the Lhasa terrane and the trace of the north-dipping conductor likely due to the northward subduction of the Bangong-Nujiang Tethyan Ocean under the Qiangtang terrane. In addition, the magnetotelluric profile also images a high-conductivity lithospheric-scale anticline beneath the central Qiangtang terrane, which may correspond to the upwelling of postcollisional magmatism triggered by northward subduction of the Bangong-Nujiang Tethyan Ocean under the Qiangtang terrane, aqueous fluid and/or partial melting.

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Variation of Moho Depth across Bangong-Nujiang Suture in Central Tibet—Results from Deep Seismic Reflection Data

Cited by 8 publications

References 43 publications

Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

Magmatic Underplating Thickening of the Crust of the Southern Tibetan Plateau Inferred From Receiver Function Analysis

Lithospheric electrical structure across the Bangong-Nujiang Suture in northern tibet revealed by magnetotelluric

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