Cenozoic deformation of the Kalpin fold-and-thrust belt, southern Chinese Tian Shan: New insights from low-T thermochronology and sandbox modeling

The Kalpin fold-and-thrust belt (FTB) was active during the Cenozoic and accommodated crustal shortening between the Tian Shan and Tarim Basin. To constrain the timing of thrusting in the Yimugantawu and Kepingtag thrust sheets from north to south in the central area of the Kalpin FTB, we performed apatite fission track (AFT) and apatite (U-Th)/He (AHe) dating, as well as sandbox experiments. The AFT central ages of the Yimugantawu and Kepingtag thrust sheets range from 93.0 to 148.7 Ma. Single grain AHe ages of the Kepingtag thrust sheet (10.7–27.1 Ma) are younger than those of the Yimugantawu thrust sheet (15.1–82.5 Ma), indicating a southward propagation of the Cenozoic deformation. Combined inverse and forward thermal modeling suggest that the Yimugantawu and Kepingtag thrust sheets underwent initial cooling and deformation at 25–20 Ma and 15–10 Ma, respectively. The sandbox experiments also suggest that the Yimugantawu thrust sheet underwent deformation before the Kepingtag thrust sheet was activated, confirming the sequence revealed by low-T thermochronology. This study provides new insights into the timing of deformation at the northern margin of the Tarim Basin, which can significantly enhance understanding of the tectonic evolution of Central Asia.