Abstract: Magnitude and Timing of Cenozoic Exhumation of the Western Kunlun Thrust Belt, Northwestern China

The western Kunlun thrust belt defines the southern boundary of the Tarim basin, the largest known onshore frontier basin. The foreland basin of the thrust belt experienced more than 8 km of post-Oligocene subsidence, and despite promising Chinese results, it is unclear whether the basin contains economic petroleum reserves, partly due to our poor understanding of the history of basin subsidence. The Kezieryigeer fault is the primary structural boundary forming the southern margin of the foreland basin. The hanging wall of the fault contains garnet-muscovite schists that were thrust over unmetamorphosed Permo-Triassic (?) to Eocene (?) siliciclastics. The footwall of the Kezieryigeer fault is composed of folded Paleozoic sediments, as well as a 10-30 km wide belt of fault-propagation folds which developed synchronously with foreland-basin sedimentation. While it appears the Kezieryigeer fault played a role in driving Tertiary foreland basin subsidence, the time at which thrust loading began, and the rate at which it occurred have previously been poorly constrained. Reconnaissance {40}Ar / {39}Ar analyses of biotites and muscovites collected along a 9-km long transect through the hangingwall of the Kezieryigeer fault have yielded total gas ages of 370 to 350 Ma. Muscovite age spectra indicate that Cenozoic slip on the fault did not perturb the argon systematics. Cenozoic slip on the fault thus appears to have occurred (1) very recently, or (2) at slow rates, or (3) for a short duration. Apatite fission track analyses currently under way will further constrain the timing, rate, and magnitude of exhumation of the Kezieryigeer hangingwall. 

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid