AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Compression Salt Tectonics and Synkinematic Strata Record in the Western Kuqa Foreland Basin, Southern Tian Shan
(1) Geosciences, Zhejian University, Hangzhou, China.
(2) Department of Geosciences, Western Petroleum University, CHENDU, China.
(3) Tarim Oilfield Company, Petro China, Korla, China.
The synkinematic strata of the Kuqa foreland basin record a rich history of the Tian Shan reactivation during the Cenozoic era. Here, we present new constraints on the deformation time in the southern Tian Shan area, based on an analysis of interactions between tectonics and sedimentation in the western Kuqa basin. Integrating surface geology, well data and a grid of seismic reflection profiles, we constructed six balanced cross sections of the basin.
Our balanced profiles show that the Qiulitage fold belt on the southern edge of the Kuqa basin developed thin-skinned compression salt tectonics. These tectonics have been influenced by two factors: (1) several pre-existing diapirs that developed in the western Kuqa basin. These were initiated soon after the Kumugeliemu salt deposition and had different growth histories, localizing the contraction strain of later shortening. If a diapir had a short development time and was overlain by a thick overburden, it was likely to evolve into a salt dome, comprising 3000-7000 m of allochthonous salt. Conversely, if a diapir was overlain by a thin overburden, it was more likely to form a salt nappe, with the northern flank of the diapir thrust over its southern flank. (2) The distal pinch-out of Kumugeliemu salt located at the Qiulitage fold belt, which resulted in an increase in frictional resistance, was prone to allochthonous salt accumulation.
The synkinematic strata (6-8 km thick) of the Kuqa basin indicate that since the regeneration of the Tian Shan, the shortening deformation of the western Kuqa basin accumulated mainly in the hinterland until the early Miocene. Then, compression stress spread simultaneously southwards to the Dawanqi anticline, the Qiulitage fold belt and the southernmost blind detachment fold at the end of Miocene. The western Kuqa basin has ~23 km of shortening displacements. We assume that ~9 km of them were consumed from the end of the Miocene (5.2/5.8 Ma) to the early Pleistocene (2.58 Ma), and another ~14 km have been absorbed since then. Thus, we obtain a ~3.4/2.8 mm/yr average shortening from 5.2/5.8 Ma to 2.58 Ma, and a ~5.4 mm/yr average shortening rate since 2.58 Ma. Therefore, we suggest that the modern Tian Shan has experienced at least two accelerated events, beginning in the late Miocene/early Pliocene and early Pleistocene, respectively.