Crustal and upper mantle velocity structure in Yunnan, Southwest China

Zhang, Xi; Wang, Yanghua

doi:10.1016/j.tecto.2009.02.009

Cited by 46 publications

(21 citation statements)

References 35 publications

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“…Decoupling between the upper and the middle–lower crusts associated with formation of the decollement is geophysically inferred. Analysis of P ‐wave velocity confirms that surface deformation in the upper crust does not extend to the lower crust because of mechanical decoupling (Flesch et al 2005; Lev et al 2006; Zhang & Wang 2009; Huang et al 2009). The presence of a weak middle–lower crust has also been inferred from magnetotelluric studies in the Simao Basin (Rippe & Unsworth 2010).…”

Section: Discussionmentioning

confidence: 89%

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Kondo

Yamamoto

et al. 2012

Geophysical Journal International

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SUMMARY An active oroclinal bending is discovered in the Shan‐Thai Block to the south of the eastern Himalayan syntaxis. To investigate the evolution of the Simao Arc using palaeomagnetic techniques, the Middle Cretaceous red beds of the Nanxin Formation were sampled at the Zhengwan (22.8°N, 100.9°E) and Dadugang (22.4°N, 101.0°E) localities in the southern Simao Basin. Most of the studied samples revealed the presence of characteristic remnant magnetization with unblocking temperatures around 680 °C. A primary nature for this magnetization is interpreted on the basis of a positive fold and reversal test. Tilt‐corrected mean directions calculated for Zhengwan and Dadugang localities are characterized by large easterly deflected declination; D= 51.8°, I= 47.9°, ks= 45.0, α95= 6.9°, N= 11 and D= 64.1°, I= 48.1°, ks= 36.0, α95= 7.3°, N= 12, respectively. Steep inclination values at both these localities with respect to those expected are in the range previously reported from the Shan‐Thai Block, confirming their southward displacement by 6.2°± 1.7° as part of the Shan‐Thai Block. Combination of the present data (two localities) with those previously reported from Simao Basin (seven localities) reveals a positive palaeomagnetic oroclinal test, indicating that the present‐day arc‐like geometry of the Simao Basin was formed by oroclinal bending. Comparison with recent GPS and structural data suggest that formation of the Simao curvature started after the early Pliocene (after 4 Ma) and continuing until the present. Origin of the Simao Arc is ascribed to southwestward movement of the crustal material across the Ailao Shan‐Red River Fault (around the eastern Himalaya syntaxis), which was formed by westward movement of the decollement with progressive eastward deepening of the Lanping‐Simao Basin. Decoupling between the upper and the middle–lower crusts is a requisite condition for the arc formation on the continent.

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Section: Discussionmentioning

confidence: 89%

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Kondo

Yamamoto

et al. 2012

Geophysical Journal International

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“…Relatively refined crustal structure in Yunnan is revealed by active source wide‐angle reflections profiles and teleseismic receiver functions analysis [ Hu et al , 2005; Langston , 1977b; Owens et al , 1984; J. Wu et al , 2001; Xu et al , 2006]. The crust thickness varies from ∼30 km at Simao to ∼60 km at Zhongdian, and the Moho dips toward the north generally [ Zhang and Wang , 2009]. …”

Section: Introductionmentioning

confidence: 99%

Crustal thickness and average V_p/V_s ratio variations in southwest Yunnan, China, from teleseismic receiver functions

Wang¹,

Wang²,

Mi³

et al. 2010

J. Geophys. Res.

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[1] Recently, many portable broadband three-component seismic stations have been deployed in Yunnan, China. We use teleseismic receiver functions to determine the crustal thickness (H) and the crustal average compressional to shear wave velocity (V p /V s ) ratio (k) variations beneath in southwest Yunnan. By comparing the synthetics generated from dipping Moho models with those from a flat Moho model, it reveals that for the rays traveling along or around the updip direction, the differential arrival times of Ps and multiples generated at the dipping Moho are comparable with those generated at the flat Moho and the result from stacking with these synthetics is a better estimate of model structure. For the synthetics traveling along or around the downdip direction, the differential arrival times of Ps and multiples generated at dipping Moho are smaller than those generated at flat Moho and make the H-k stacking results deviate from the model structure. Thus, the ambiguity induced by dipping Moho can be reduced significantly by only stacking with the rays traveling along or around the updip direction. Applying this technique to 19 stations, we obtained that H ranges from ∼35-42 km and the k ranges from ∼1.66-1.78. From the central Simao basin, H increases northward and northeastward; k increases significantly northeastward across the Ailao Shan-Red River shear zone.

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“…We also discuss the coupling relationship and deformation characteristics of upper‐middle crust and lower crust, through the surface GPS (Niu et al, ; Wang et al, ), focal mechanism solutions (Cui et al, ; Wen et al, ; Zhao et al, ), and seismic anisotropy (Chen, Zhang, Sun, & Badal, ; Sun, Lei, Li, & Zhang, ). The Midu‐Jiangchuan (AA’) and Simao‐Malong (BB’) wide‐angle seismic profiles (Bai & Wang, , ; Zhang & Wang, ) are digitized for examining the quantitative relationships between topographic uplift, horizontal crustal shortening, and crustal thickening.…”

Section: Descriptionmentioning

confidence: 99%

“…Layered P‐wave velocity models (Bai & Wang, , ; Wang, Wang, Mi, et al, ; Zhang & Wang, ), earthquakes, and faults beneath the Midu‐Jiangchuan profile (AA’) and Simao‐Malong profile (BB’). White solid lines are from the observed data, and white dotted lines are estimated data.…”

Section: Descriptionmentioning

confidence: 99%

Surface uplift of the Central Yunnan Plateau since the Pliocene

Jiang

Gong

et al. 2017

Geological Journal

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The Central Yunnan Plateau (CYP) is located in the southeastern end of the Sichuan‐Yunnan rhombic block. CYP is surrounded by the South China Block to the east and the Indo‐China Block to the southwest. Stratigraphy and topography research shows the relative surface uplift of the CYP since the Pliocene. However, the widely accepted model of lower crustal flow is very difficult to fully explain the surface uplift of CYP, with faults and fold structures in the brittle shallow crust. The lower crust thickening led by the lower crustal flow only contributes 34–54% (600–950 m) of the total surface uplift. The wide‐angle seismic profiles and topography analysis show that the CYP surface uplift is predominately a consequence of isostatic compensation due to surface erosion, upper‐middle crustal shortening, and lower crustal thickening. The average isostatic adjustment caused by surface erosion of CYP is about 500 m, which is about 29% of the total surface uplift (1750 m). The GPS station velocities, focal mechanisms, and seismic anisotropy show the strong decoupling relationship between upper‐middle crust and lower crust. In detail, there is a movement with southeast‐directed and clockwise rotation around the Eastern Himalayan syntaxis in the upper‐middle crust, although south‐directed flow in the lower crust. The southeast motion of the upper‐middle crust could be resolved into two portions. The eastward component of upper‐middle crust motion is obstructed by the South China Block in the east. The result is the W‐E direction shortening of upper‐middle crust, shown by the S‐N trending CYP anticlinorium. The W‐E direction shortening of upper‐middle crust contributes 17–37% (300–650 m) of the total surface uplift. In contrast, the southward component of upper‐middle crust motion, shown by the sinistral strike‐slip displacement of the Xiaojiang fault zone, could pass through the Red River fault zone into the Indo‐China Block, where the left‐lateral Dien Bien Phu Fault would be the counterpart. The contribution of upper‐middle crustal shortening in a S‐N direction is very limited. The lower crustal flow could have been playing a prominent role in the growth of the whole southeast margin of the Tibetan Plateau, and the contribution from upper‐middle crustal shortening cannot be ignored in some local areas.

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Crustal and upper mantle velocity structure in Yunnan, Southwest China

Cited by 46 publications

References 35 publications

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Crustal thickness and average V_p/V_s ratio variations in southwest Yunnan, China, from teleseismic receiver functions

Surface uplift of the Central Yunnan Plateau since the Pliocene

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Crustal and upper mantle velocity structure in Yunnan, Southwest China

Cited by 46 publications

References 35 publications

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Oroclinal origin of the Simao Arc in the Shan-Thai Block inferred from the Cretaceous palaeomagnetic data

Crustal thickness and average Vp/Vs ratio variations in southwest Yunnan, China, from teleseismic receiver functions

Surface uplift of the Central Yunnan Plateau since the Pliocene

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Crustal thickness and average V_p/V_s ratio variations in southwest Yunnan, China, from teleseismic receiver functions