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

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

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Acknowledgments

We are grateful for the assistance of Lin Liao, Xiaogen Fan, Biao Bi, Xinwei Chen, Chao Chen, and Dongxu Chen during the field investigation. We received funding from National Natural Science Foundation of China (Grant Nos. 41472181, 41330207, 41102128 and 41072154), the National S&T Major Project (Grant Nos. 2016ZX05008-001 and 2016ZX05003-001), and Fundamental Research Funds for the Central University (Grant No. 2016FZA3007). We are grateful to two anonymous reviewers for their comments that improved the manuscript significantly.

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2016 Higher Education Press and Springer-Verlag Berlin Heidelberg