Evolution of the Barkol Basin, eastern Tian Shan, and its geodynamic background

The Barkol Basin (BB) is an intramontane basin in the easternmost Tian Shan, Northwest China. We reconstructed the tectonic evolution of the BB based on an investigation of its stratigraphy and faults, and we differentiated the basin infill into Quaternary sediments and the Oligocene–Miocene Taoshuyuanzi Formation by combining field observations and geophysical data with borehole data. We used detrital zircon U–Pb dating and palaeo-currents to decipher the provenance of the lower Jurassic Badaowan Formation, which contains the only Mesozoic sediments throughout the easternmost Tian Shan. The results demonstrate that the BB and Harlik Range constitute the main sources. Furthermore, we found that the Taoshuyuanzi Formation unconformably overlies the Palaeozoic basement in the basin, indicating that the BB formed during the Oligocene–Miocene. Based on Magnetotelluric (MT) and seismic profiles, this formation was deposited under the control of basin-bounded faults. According to the field investigation, the boundary faults of the basin were recognized as sinistral strike-slip normal faults. Additionally, remote sensing and electron spin resonance (ESR) data provided valuable information on the Quaternary proluvial fan divisions, which suggest a multi-stage tectonic evolution of the basin during the Quaternary. The Mesozoic–Cenozoic basin evolution in the easternmost Tian Shan was divided into four phases based on an integrated analysis of the stratigraphy and structures of the Santanghu Basin and the Turpan-Hami Basin: (1) from the Late Triassic to the Early-Middle Jurassic, tectonic subsidence dominated the Santanghu Basin and Turpan-Hami Basin; (2) during the Late Jurassic-Eocene, the episodic uplift of the Tian Shan Mountains constricted the Turpan-Hami Basin and the Santanghu Basin; (3) during the Oligocene–Miocene, the BB formed as a subsidence basin controlled by sinistral strike-slip normal faults, and the basins filled with thick layers of clastic rocks; and (4) during the Pliocene–Quaternary, the eastern BB uplifted, and the basins deformed. In conjunction with previous research, the dynamic background of the formation of the BB was presumably related to the clockwise rotation of the Tarim Block to the south and the strong left-lateral movement of the Gobi-Tian Shan fault system.