About the lithospheric structure of central Tibet, based on seismic data from the INDEPTH III profile

Meißner, R.; Tilmann, Frederik; Haines, Seth S.

doi:10.1016/j.tecto.2003.11.007

Cited by 53 publications

(38 citation statements)

References 60 publications

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“…The passage of lower crustal flow is probably located in the low velocity zone in lower crust . These results have the similar implications to those of many other geophysical measurements [29,44,45,48,49] carried out in the Tibetan Plateau. They constitute the deep environment of lower crustal flow existence.…”

Section: Discussionsupporting

confidence: 88%

S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

Wang

Lou

Lü

et al. 2008

Sci. China Ser. D-Earth Sci.

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A teleseismic profile consisting of 26 stations was deployed along 30°N latitude in the eastern Tibetan Plateau. By use of the inversion of P-wave receiver function, the S-wave velocity structures at depth from surface to 80 km beneath the profile have been determined. The inversion results reveal that there is significant lateral variation of the crustal structure between the tectonic blocks on the profile. From Linzhi north of the eastern Himalayan Syntaxis, the crust is gradually thickened in NE direction; the crustal thickness reaches to the maximum value (~72 km) at the Bangong-Nujiang suture, and then decreased to 65 km in the Qiangtang block, to 57-64 km in the Bayan Har block, and to 40-45 km in the Sichuan Basin. The eastern segment of the teleseismic profile (to the east of Batang) coincides geographically with the Zhubalong-Zizhong deep seismic sounding profile carried out in 2000, and the S-wave velocity structure determined from receiver functions is consistent with the P-wave velocity structure obtained by deep seismic sounding in respect of the depths of Moho and major crustal interfaces. In the Qiangtang and the Bayan Har blocks, the lower velocity layer is widespread in the lower crust (at depth of 30-60 km) along the profile, while there is a normal velocity distribution in lower crust in the Sichuan Basin. On an average, the crustal velocity ratio (Poisson ratio) in tectonic blocks on the profile is 1.73 (σ = 0.247) in the Lhasa block, 1.78 (σ = 0.269) in the Banggong-Nujiang suture, 1.80 (σ = 0.275) in the Qiangtang block, 1.86 (σ = 0.294) in the Bayan Har blocks, and 1.77 (σ = 0.265) in the Yangtze block, respectively. The Qiangtang and the Bayan Har blocks are characterized by lower S-wave velocity anomaly in lower crust, complicated Moho transition, and higher crustal Poisson ratio, indicating that there is a hot and weak medium in lower crust. These are considered as the deep environment of lower crustal flow in the eastern Tibetan Plateau. Flowage of the ductile material in lower crust may be attributable to the variation of the gravitational potential energy in upper crust from higher on the plateau to lower off plateau. eastern Tibetan Plateau, crustal and upper mantle's structure, teleseismic receiver function, lower crustal flowApplication of broadband seismic observation is one of the most marked advances in seismology. The high quality data recorded in broadband seismographs are used to study the deep media of the earth in several ways. Nowadays, it has become one of key techniques for exploring the parameters of the earth's structure and material physical property, such as velocity structure, Poisson

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Section: Discussionsupporting

confidence: 88%

S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

Wang

Lou

Lü

et al. 2008

Sci. China Ser. D-Earth Sci.

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“…These coincident south‐to‐north changes have been interpreted by a number of investigators to mark the northern limit of relatively old, cold Indian mantle lithosphere thrust beneath Tibet during Tertiary time (summarized by Owens and Zandt [1997]). There are also crustal differences on either side of the BNS, with seismically faster crust to the south compared to the north [ Mechie et al , 2004; Meissner et al , 2004]. …”

Section: Banggong‐nujiang Suture: Geological Settingmentioning

confidence: 99%

“…These first‐order features are evident in both RLM2DI and RRI final models, though their forms are different due to the different spatial smoothing approaches used in the two algorithms. This rapid change in resistivity occurs at the same location as a dramatic change of seismic polarization anisotropy (Figure 3), from <0.5 s to the south to >1.5 s to the north [ Huang et al , 2000], and a subvertical, low‐velocity anomaly to midcrustal (∼30 km) depths [ Haines et al , 2003; Mechie et al , 2004; Meissner et al , 2004]. …”

Section: Data Inversionmentioning

confidence: 99%

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

et al. 2005

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[1] Magnetotelluric data from a 150-km-long profile crossing the Banggong-Nujiang suture (BNS), central Tibet, acquired as part of the International Deep Profiling of Tibet and the Himalaya (INDEPTH) project, have been examined for crustal and upper mantle structure. Strike and dimensionality analyses demonstrate that regional-scale electrical structures are two-dimensional and oriented approximately parallel to surface geological strike. As seen elsewhere in Tibet, the double thickness crust is generally characterized by resistive upper crust (hundreds to thousands of ohm meters) overlying conductive middle and lower crust (tens to hundreds of ohm meters), but in detail, there are lateral variations at all levels. Regionally, a northward transition from thick ($45 km) to thin ($15 km) resistive upper crust coincides with (1) the surface trace of the BNS, (2) a prominent strand of the Karakorum-Jiali fault system, (3) northward decrease in upper mantle seismic velocities and increase in attenuation, and (4) pronounced northward onset of seismic polarization anisotropy. The latter two seismological features have been taken to mark the northern limit of Indian mantle lithosphere thrust beneath southern Tibet. On the basis of our electrical model, we speculate that (1) the resistive upper crustal root beneath the Neogene Lunpola and Duba basins was produced by crustal shortening localized along the northern edge of the Lhasa terrane; (2) the low midcrustal resistivity beneath the BNS reflects enhanced Neogene melting and/or metamorphic dewatering of relatively fertile subduction zone complex rocks; (3) observed steep upper crustal low-resistivity anomalies are produced by hydrothermal fluids within active faults localized within and adjacent to the BNS; and (4) these strike-slip and extensional fault arrays are surface manifestations of lithosphere-penetrating shear localized along the northern edge of the underthrust Indian plate.

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“…A high geothermal gradient can reduce shear-wave velocity and may cause partial melting in the crust. Many studies revealed that partial melting exists in the crust beneath the Tibetan plateau, for example, in the middle crust beneath southern Tibet (Nelson et al, 1996;Unsworth et al, 2005) and in the middle-lower crust and upper mantle beneath northern Tibet (Wei et al, 2001;Meissner et al, 2004). In the southeastern Tibetan plateau, a high large-scale Poisson's ratio (0.22-0.32) was observed, suggesting heterogeneity in crustal composition and the existence of partial melting (Xu et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

3D Shear‐Wave Velocity Structure beneath the Southeastern Tibetan Plateau from Ambient Noise

Zheng¹,

Zhao²,

Zhou³

et al. 2015

Bulletin of the Seismological Society of America

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We perform high-resolution 3D shear-wave structures of the crust and upper mantle using continuous wave data recorded at 170 stations from national and regional networks in the southeastern Tibetan plateau. First, empirical Green's functions are obtained between all the possible station pairs. Then Rayleigh-wave group velocity and phase velocity dispersion curves are retrieved using the frequency-time analysis method. The Rayleigh-wave group velocity images at periods from 8 to 50 s and phase velocity images at periods from 8 to 40 s are inverted on a 1°× 1°grid. Finally, the 1D shear-wave structure beneath each grid and the 3D shear-wave velocity structure are acquired by linear interpolation. Our results indicate that low-velocity layers (LVLs) are ubiquitous in the middle-lower crust beneath the southeastern Tibetan plateau but vary in depth (20-35 km), thickness (5-20 km), and strength (5.4%-10.8% velocity reduction) in different blocks. The 3D geometry of the LVLs is complex and cannot be interpreted as a model with a uniform flow channel. The shear velocity in the Chuandian block is unevenly distributed, indicating that the block is inhomogeneous. The 12 May 2008 Wenchuan and 20 April 2013 Lushan earthquake sequences (M s ≥ 3:0) all occurred in the crustal layers in which LVLs are inhibited by the strong Sichuan basin and in which the topography and crustal thickness vary sharply. This formed the earthquake preparation environment of the two earthquakes. The Ningnan-Qiaojia pull-apart region is characterized by low shear-wave velocity in the shallow crust, which agrees well with the sedimentary features of the upper crust. A relatively high velocity is observed in the central part of the low-velocity Sichuan basin in the shallow layers, indicating the basement beneath the Sichuan basin may be uplifted around the central part of the basin.

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About the lithospheric structure of central Tibet, based on seismic data from the INDEPTH III profile

Cited by 53 publications

References 60 publications

S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

S-wave crustal and upper mantle’s velocity structure in the eastern Tibetan Plateau — Deep environment of lower crustal flow

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

3D Shear‐Wave Velocity Structure beneath the Southeastern Tibetan Plateau from Ambient Noise

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