Crustal Structure at the Northeast Side of the Pamirs

Zhang, Xian‐Kang; Zhao, Jun‐Hong; Zhang, Chengke; Ren, Qingwen; Nie, Wen-Ying; Cheng, Shuang‐Xi; Pan, Suli; Tang, Zhou-Qiong

doi:10.1002/cjg2.283

Cited by 38 publications

(40 citation statements)

References 3 publications

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“…A deep seismic reflection profile has imaged a detachment interface stretching northward from somewhere near the basement of the Tarim Basin. The imaged detachment fault is hypothesized to cut through the whole crust down to Moho under the southern flank of the western Tianshan Mountains [35] . An underthrusting of the Tarim basement over this detachment fault is estimated at rates as far as 12-13 mm/a by the elastic dislocation modeling of GPS velocities.…”

Section: Discussionmentioning

confidence: 99%

The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

Yang

Wang

2008

Sci. China Ser. D-Earth Sci.

150

127

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Based on GPS measurements conducted from 1992 to 2006, we present the current crustal movement velocity field for approximately 400 sites in the Tianshan Mountains and their adjacent areas, and estimate slip rates on the major faults using a 2-D elastic dislocation model. Our studies show slip rates within the range of 1-4 mm/a on the NW-SE trending strike-slip faults (such as Talas-Fergana fault) in the Tianshan Mountains. We also found the slip rates on the approximately WE-SN trending gently-dipping detachment fault vary from 10-13 mm/a for the southwest Tianshan Mountains to 2-5 mm/a for the eastern Tianshan Mountains, and to 6-12 mm/a for the Kyrgrz Tianshan. The GPS velocity field reveals that the total convergence is not uniformly distributed across the Tianshan Mountains, with 80%-90% of the N-S shortening absorbed along the southern and northern edges, and relatively little deformation accommodated within the interior. This first-order feature of strain pattern is explained best by underthrusting of adjacent blocks beneath the Tianshan Mountains along a basal detachment fault. We found the occurrence of historical M7-8 earthquakes somewhere in the locked ramp that connects the creeping and locking segments of the detachment, thereby resulting in elastic strain concentration and accumulation around it. The elastic strain confined in the upper crustal layer above the detachment ultimately releases through infrequent great earthquakes in the Tianshan Mountains, resulting in considerable folding and faulting at their margins. The Tianshan Mountains propagated outward and rose progressively as a wedge-shaped block. Tianshan Mountains, GPS, slip rates, tectonic deformationThe Tianshan orogenic belt has experienced multi-stage upheavals in its long-term tectonic evolution. Subject to the far-field effects of the India-Eurasia collision, pre-existing structures in the Tianshan Mountains have been reactivated with mountain building reconstruction in the last ~10 Ma. The total crustal shortening across the belt exceeds 200 km [1][2][3][4] in Cenozoic times. As a result, numerous active faults and fold-fault belts are distributed over the Tianshan area, such as the E-W trending north verging Tuotegongbaizi-Arpaleike thrust and the Maidan-Alatongke thrust parallel to the southern edge of the Tianshan Mountains, to the west, as well as the NW-SE trending Talas-Fergana fault with predominantly right-lateral strike slip motion. These major tectonic structures and others elsewhere, on which intensive faulting occurred presumably with high level of seismicity, play an important role in accommodating convergence deformation and mountain building.The crustal shortening rate along the longitude of 74°-76°E is ~20 mm/a [5][6][7] inferred from recent GPS measurements, accounting for about half of the total relative India-Eurasia plate convergence rate of 45 mm/a [8] . Earlier workers showed that the present-day compression deformation is accommodated primarily by

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Section: Discussionmentioning

confidence: 99%

The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

Yang

Wang

2008

Sci. China Ser. D-Earth Sci.

150

127

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“…Meanwhile, Chinese scholars published also many valuable results about geophysical explorations in the Tianshan Mountains in China [4,[13][14][15][16][17][18][19][20][21][22] .…”

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confidence: 99%

Shear wave velocity structure of the crust and upper mantle underneath the tianshan orogenic belt

Liu

Chen

et al. 2007

SCI CHINA SER D

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a passive broadband seismic array consisting of 60 stations was deployed over the Tianshan orogenic belt by State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration. Among them, 51 stations make up an about 500-km-long profile across the Tianshan Mountains from Kuytun to Kuqa. The receiver function profile and S-wave velocity structure of the crust and upper mantle down to 100 km deep are obtained by using the receiver function method (Liu et al. 1996, 2000). The main results can be summarized as follows: (1) A clear mountain root does not exist beneath the Tianshan Mountains, and the crust-mantle boundaries underneath the stations mostly have transitional structures. This implies that the material differentiation between the crust and mantle is not yet accomplished and the orogenic process is still going on. (2) The crust beneath the Tianshan Mountains has laterally blocked structures in direction perpendicular to the mountain strike, and the crust-mantle boundary has a clear dislocation structure. Both of them correspond to each other. (3) The offsets of the Moho discontinuity are highly correlated to the tectonic borders on the surface and that corresponding to the frontal southern Tianshan fault reaches to 14 km. This manifests that large vertical divergent movement took place between different blocks. This supports the discontinuous model of the Tianshan orogeny, and the Tarim block subduction is restricted only to the southern side of the South Tianshan. (4) Inside the upper and middle crust of the Tianshan Mountains exist several low-velocity bodies correlated with high seismicity located on the mountain-basin jointures on both sides of the mountain and between different blocks, and the low-velocity bodies on the mountain-basin jointures are inclined obviously to the mountain. This implies that the low-velocity bodies may be correlated closely to the thrust and subduction of the basins on both sides of the mountain, the splicing of adjacent blocks and the fast uplift of the Tianshan Mountains. nonlinear inversion, receiver function, S-wave velocity, crust and upper mantle, Tianshan orogenic belt

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“…The interval velocity decreases at different depths, and the average velocity of the crust there is 0.2-0.3 km/s less than that in surrounding stable massifs of northeastern margin (Eudos, Sichuan, and Tarim basins), especially the velocity difference of mid and lower crust is 0.3-0.6 km/s [9,16,17]. It implicates the reformed features in northeastern margin of Tibetan Plateau.…”

Section: -D Crust Structure and Discussion In Zoigê Basin And Its Sumentioning

confidence: 94%

“…In general, stable velocity of the crystalline basement (about 6.0 km/s) appears in stable continental massifs and Craton blocks, and strong velocity contrast is formed between Precambrian magmatic crystalline layers or metamorphic complex layers and low velocity sediments of surface (generally the velocity is less than 5.0 km/s). The North China, Yangtze and Tarim craton blocks of Chinese Oldland have this kind of crystalline basement structure [9,16,17]. The basement structure of Zoigê basin is particular, and the density and velocity of Triassic bedrocks in Zoigê basin are so high that they correspond to the density of the upper crust in Taihang and Yanshan Mountains (2.64-2.73 g/cm 3 ) in North China and to the density of the upper crust beneath the crystalline basement in Tianshan Mountains (2.63-2.71 g/cm 3 ) [17,18].…”

Section: Basement Structure In Zoigê Basin and Its Surrounding Foldedmentioning

confidence: 99%

Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts

Jia

Zhang

Zhao

et al. 2009

Sci. China Earth Sci.

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Songpan-Garze massif is located at the turning position of tectonics from the nearly west-east direction to the nearly north-south direction in the northeastern margin of Tibetan Plateau, with Zoigê basin in the centre of the massif. In this paper, we build a crustal structure model of Zoigê basin and its surrounding folded orogenic belts using the deep seismic sounding data in this region. We also discuss structures and properties of the basement in Zoigê basin, tectonic relations between Zoigê upland basin and its surrounding folded orogenic belts, crustal deformation and thickening in the northeastern margin of Tibetan Plateau, and decoupling and relaxing processes in the crust. The results indicate that a special "Mesozoic basement" is formed of Triassic rocks with high density (2.65-2.75 g/cm 3 ) and high velocity (5.6 km/s) in Zoigê basin. Songpan-Garze tectonic massif was transformed into two types of tectonic units with different crustal structures, i.e., relatively stable Zoigê upland basin and active folded orogenic belts around the basin, in the course of the crustal material of Tibetan Plateau flowing eastward and obstructed by surrounding stable blocks. The thickening of the crust in the northeastern margin of Tibetan Plateau mainly occurred in the mid and lower crust, and the structure characterized by low velocities and multiple reflectors obviously appears in the folded orogenic belts around Zoigê basin. It implies that the mid and lower crust underwent a strong tectonic deformation in the folded orogenic areas. The thickness of the crust is about 50 km in Zoigê basin and the folded orogenic belts at the both southern and northern sides of Zoigê basin. The "Mountain root" cannot be identified. It is inferred that during the later orogenic period the eastwards flowing deep materials moved clockwise along the relatively relaxing southern side around the eastern tectonic knot under the obstructing of surrounding rigid massifs, and it resulted in the strong stretching action of the folded orogenic belts around Zoigê basin.Zoigê basin, folded orogenic belt, deep seismic sounding, basement structure, crustal structure and tectonics Citation:Jia S X, Zhang X K, Zhao J R, et al. Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts.

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Crustal Structure at the Northeast Side of the Pamirs

Cited by 38 publications

References 3 publications

The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

The deformation pattern and fault rate in the Tianshan Mountains inferred from GPS observations

Shear wave velocity structure of the crust and upper mantle underneath the tianshan orogenic belt

Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts

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