Cenozoic tectonic deformation and uplift of the South Tian Shan: Implications from magnetostratigraphy and balanced cross-section restoration of the Kuqa depression

• Magnetostratigraphy and balanced cross-section restoration of the southern Tian Shan
• Age determination of major stratigraphic boundaries in the Kuqa depression
• Total shortening of 13.95 km during the Cenozoic is suggested
• Significant shortening began at 36 Ma, accelerated at 13 Ma, 6.5 Ma especially 2.6 Ma
• Significant deformation and uplift of South Tian Shan at the foregoing stages were argued

The collision of India with Eurasia has caused rejuvenated deformation and uplift of the remote Tian Shan intracontinental orogenic range and has led to deposition of thick Cenozoic sediments in its flank depressions. However, our knowledge when and how the range was deformed and uplifted is still limited. We carried out detailed tectonic investigations, seismostratigraphic analysis and paleomagnetic dating of the thrust-fold belt in the Kuqa depression at the southern Tian Shan flank. Combined with re-interpretation of other magnetostratigraphic results in the depression, we determined ages of major stratigraphic boundaries and constructed and restored the balanced cross-section across the depression. The results show that the total Cenozoic shortening along the cross section in the depression is ~ 13.95 km. Significant shortening began at ~ 36 Ma, accelerated since ~ 13 Ma and further increased two- to three-fold since 6.5 Ma, especially since ~ 2.6 Ma. This shortening process caused the development of the Kuqa thrust-fold system associated with the variation of the sedimentation rate, upward coarsening of sediments and a progressive development of growth strata. We therefore argue that significant deformation and uplift of the South Tian Shan began at ~ 36 Ma, becoming more evident since ~ 13 Ma, and culminating since ~ 6.5 Ma reaching its peak after ~ 2.6 Ma.

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