Structural Geology and Tectonic Significance of Foreland Thrust Belts, Tarim and Junggar Basins, Northwest China

Cleavy L. McKnight, Jinchi Chu, Alan R. Carroll, Marc S. Hendrix, Xiaomin Wang, Stephan A. Graham, Yun Hai Liang, Zuo Xun Wang, Xuchang Xiao

Mapping of regional structural trends in northwestern China from Landsat MSS images and field investigation of local structure and stratigraphy provide new information on the deformational styles and tectonic history of the margins of the Tarim and Junggar basins adjacent to the Tian Shan, the mountain range which separates the two large sedimentary basins.

The Kalpin uplift, located on the northwestern margin of the Tarim basin, is characterized by a series of thin, southeast-vergent thrust plates modified by tear (strike-slip) faults. Each thrust plate repeats a sedimentary sequence consisting of upper Proterozoic through Permian shallow marine to nonmarine carbonates and clastics. Mesozoic rocks are not present in the uplift, but Tertiary rocks as young as Neogene are affected by the deformation. The most basinward thrust sheet abuts the Bachu uplift, an older structural feature trending almost perpendicular to the thrusts. Sedimentary rocks as old as late Proterozoic are exposed in the Bachu uplift, which apparently represents a west-vergent Late Silurian to Early Devonian thrust belt. An unconformable Silurian-Devonian contact, the resence of Devonian red beds, and another unconformable contact separating Devonian from Upper Carboniferous strata support the interpretation of a middle Paleozoic deformational event. Another unconformity, at the Carboniferous-Permian boundary, apparently coincides with the time of collision of the Tarim craton with the southern margin of central Asia.

The Shihezi fold trend, located in the southern Junggar basin, consists of three lines of surface anticlines trending parallel to the axis of the Urumqi foredeep. A thick sequence of Mesozoic and Cenozoic nonmarine sedimentary rocks accumulated in the growing foredeep. Mesozoic and Paleogene strata are deformed in the southern foldbelt, with Jurassic rocks forming the cores of these thrusted anticlines. The Qigu oil field is located in this southern belt. Deformed Neogene and Quaternary strata are exposed in the thrusted anticlines of the middle and northern foldbelts. The Dushanzi oil field is located in the northern belt.

The episodic development of compressional structures in northwestern China documents the accretion of a number of tectonic units to the growing southern margin of central Asia through time. The most recent structural deformation is related to stresses produced by the continued northward motion of the Indian plate.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.