Deformation geometry and timing of the Wupoer thrust belt in the NE Pamir and its tectonic implications

doi:10.1007/s11707-016-0606-z

Front. Earth Sci.

2016, Vol. 10

Issue (4) : 751-760 https://doi.org/10.1007/s11707-016-0606-z

RESEARCH ARTICLE

Deformation geometry and timing of the Wupoer thrust belt in the NE Pamir and its tectonic implications

Xiaogan CHENG^1,²(

),Hanlin CHEN^1,²,Xiubin LIN^1,²,Shufeng YANG^1,²,Shenqiang CHEN^1,²,Fenfen ZHANG^1,²,Kang LI^1,²,Zelin LIU³

¹. School of Earth Sciences, Zhejiang University, Hangzhou 310027, China
². Research Center for Structures in Oil- and Gas-Bearing Basins, Ministry of Education, Hangzhou 310027, China
³. Department of Exploration Geophysics, College of Geophysics and Information Engineering, China University of Petroleum-Beijing, Beijing 102249, China

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Abstract

The Pamir region, located to the northwest of the Tibetan Plateau, provides important information that can aid the understanding of the plateau’s tectonic evolution. Here we present new findings on the deformation geometry and timing of the Wupoer thrust belt at the northeastern margin of Pamir. Field investigations and interpretations of seismic profiles indicate that the eastern portion of the Wupoer thrust belt is dominated by an underlying foreland basin and an overlying piggy-back basin. A regional unconformity occurs between the Pliocene (N₂) and the underlying Miocene (N₁) or Paleogene (Pg) strata associated with two other local unconformities between Lower Pleistocene (Q₁) and N₂ and between Middle Pleistocene (Q_2-4) and Q₁ strata. Results of structural restorations suggest that compressional deformation was initiated during the latest Miocene to earliest Pliocene, contributing a total shortening magnitude of 48.6 km with a total shortening rate of 48.12%, most of which occurred in the period from the latest Miocene to earliest Pliocene. These results, combined with previous studies on the Kongur and Tarshkorgan extensional system, suggest an interesting picture of strong piedmont compressional thrusting activity concurrent with interorogen extensional rifting. Combining these results with previously published work on the lithospheric architecture of the Pamir, we propose that gravitational collapse drove the formation of simultaneous extensional and compressional structures with a weak, ductile middle crustal layer acting as a décollement along which both the extensional and compressional faults merged.

Keywords Pamir Kongur Wupoer gravitational collapse fold-and-thrust belt

Corresponding Author(s): Xiaogan CHENG

Online First Date: 18 September 2016 Issue Date: 04 November 2016

Cite this article:

Xiaogan CHENG,Hanlin CHEN,Xiubin LIN, et al. Deformation geometry and timing of the Wupoer thrust belt in the NE Pamir and its tectonic implications[J]. Front. Earth Sci., 2016, 10(4): 751-760.

URL:

https://academic.hep.com.cn/fesci/EN/10.1007/s11707-016-0606-z
https://academic.hep.com.cn/fesci/EN/Y2016/V10/I4/751

Fig.1 Simplified map of major tectonic domains within the Pamir and simplified geologic map of the Wupoer thrust belt. (a) Tectonic setting and locality of the study area (modified from Robinson et al., 2004 and Cowgill, 2010); (b) Simplified geologic map of the Wupoer thrust belt plotted on a grey-shaded DEM image.

Fig.2 Cenozoic stratigraphic units and lithology in the study area (modified from Yin et al., 2002).

Fig.3 Structural interpretation of seismic profile Section A-A'. The section locality is shown in Fig. 1(b). TWTT: two-way travel time.

Fig.4 Structural interpretation of seismic profile Section B-B'. The section locality is shown in Fig. 1(b).

Fig.5 Field observations of unconformities. (a) Angular unconformity between N₂a and E_2-3b units. (b) Slight angular unconformity between Q₁x and N₂a units. The sites are shown in Fig. 1(b).

Fig.6 Regional geologic section C-C' showing the upper crustal structure in the Wupoer region established from field data and seismic profile B-B'. The section locality is shown in Fig. 1(b).

Fig.7 Structural restoration results of regional section C-C', showing the evolution of deformation structures in the Wupoer region. The section locality is shown in Fig. 1(b).

Fig.8 Two-stage evolution of the NE Pamir. (a) Evolution of the NE Pamir before orogenic gravitational collapse. During this stage, the NE Pamir was bounded by the KYTS to the east and E–W striking folds developed in the NE Pamir. Crustal thickening resulted in the formation of a weak and ductile middle crustal layer. (b) Evolution of the NE Pamir during orogenic gravitational collapse triggered by high gravitational energy imposed by the elevated Pamir. During this stage, N–S striking folds developed between the KNF and MPT. The thrust and normal faults merged along the décollement at the weak, ductile middle crustal layer. The Tarim and Pamir crustal thicknesses and the décollement are adopted from Sipple et al. (2013). KYTS: Kashgar-Yecheng Transfer System; KNF: Kongur normal fault; MPT: main Pamir thrust; PFT: Pamir front thrust/Wupoer thrust.

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