A MAP-VIEW RECONSTRUCTION OF THE STRUCTURAL DEVELOPMENT OF THE KUQA FOLD-AND-THRUST BELT, NORTHWESTERN CHINA

The Kuqa fold-and-thrust belt hosts one of the Earth’s most active surface salt structures and features the interactions of thrusting, folding and river erosion processes. Key aspects of the structural development of the range are unresolved. In particular, it is unclear whether the fold-and-thrust belt developed via a forward-propagating series of salt-cored detachment folds which locally nucleated late thrust faults, or if detachment folds developed interspersed with long-lived pre-kinematic salt diapirs that evolved into local salt thrusts. Because it is clear from surface stream patterns that detachment fold development in this region involved significant along-strike propagation, if thrusts nucleated within detachment folds, then surface stream patterns along the thrust culminations may yet record patterns of along-strike fold propagation. In contrast, pre-kinematic diapirs would not involve such propagation, and thus predict no such patterns. In this study, we focus on the best-developed salt thrust system, the Quele salt thrust, as a key test site, and furthermore explore folds along the entire frontal Kuqa fold-and-thrust belt for comparative analysis vs. the Quele salt thrust. Specifically, we integrate an array of fold growth indicators derived from the remotely-sensed surface data, including drainage basin morphometry and deflection of stream network patterns. Our findings suggest that the Quele salt thrust developed from two detachment fold segments which propagated laterally to the east and west, coalesced into a composite anticlinorium, and with continued shortening this anticlinorium broke, thereby becoming the Quele salt thrust. Similar coalescence of fold segments is observed along the remainder of the fold-and-thrust belt. Collectively, our findings indicate that the development of the Kuqa fold-and-thrust belt does not require pre-kinematic diapirs, but is rather controlled by largely forward-propagating detachment fold development with local late nucleation of thrust faults.