Influence of Overlapping decollements, Syntectonic Sedimentation, and Structural Inheritance in the Evolution of a Contractional System: The Central Kuqa Fold-and-Thrust Belt (Tian Shan Mountains, NW China)

摘要

Contractional deformation in the Kuqa fold-and-thrust belt (southern foreland of the Tian Shan Mountains, NW China) is recorded by well-preserved syntectonic continental sequences. In addition, its structural evolution was strongly controlled by synorogenic salt (Eocene in age) and presalt decollements with varying spatial distribution. We present a balanced and sequentially restored cross section across the central part of this fold-and-thrust belt that provides a new interpretation of the structure beneath the evaporites, in which Paleozoic and Mesozoic strata are deformed by a thrust stack involving (i) a thin-skinned thrust system detached on Triassic-Jurassic coal units and (ii) an ensemble of south-directed basement thrusts. The latter formed from the inversion of Mesozoic extensional faults such as those preserved both in the Tarim foreland basin and beneath the frontal part of the Kuqa fold-and-thrust belt. The constructed section shows a total shortening of 35km from the Late Cretaceous to the present. The restoration depicts a three-stage evolution for the Kuqa fold-and-thrust belt: (i) minor Mesozoic extension, (ii) an early compressional stage (Late Cretaceous to early Miocene) with low shortening and syntectonic sedimentary rates, and (iii) a later compressional stage (late Pliocene-Pleistocene) characterized by a greater and progressively increasing shortening rate and rapid deposition. Our results are discussed in light of previous analogue and numerical modeling studies and demonstrate the control exerted by the interplay between syntectonic sedimentation, the inversion of inherited basement structures, and the nature and extent of Triassic/Jurassic and Eocene decollements.