Fold segment linkage and lateral propagation along the Qiulitage anticline, South Tianshan, NW China

Abstract

The east-west trending Qiulitage anticline is one of the most active elements of the Kuqa fold-and-thrust belt located along the southern margin of the Tianshan Mountains. Subsurface data and the well-preserved tectonic geomorphology provide a natural laboratory for exploring the detailed spatio-temporal evolutionary processes of a “mature fold”. We present a study of fluvial/alluvial terraces which passively record the progressive deformation of active folds across the rapidly uplifting Qiulitage anticline. The vertical incision and lateral erosion rates of the Kezile river derived from 10Be exposure dating are ~1.3–2.0 mm/a and >1.3 mm/a, respectively, while those of the Bositankelake River, located near the central part of the fold, are only ~0.8 ± 0.04 mm/a and <0.8 ± 0.04 mm/a, respectively. This difference indicates that the lateral propagation rate of active fold increases gradually away from its central peak to its tip. In the meanwhile, a comprehensive analysis of stratigraphy, landforms, dominant faults at depth, and inherited drainage patterns reveal that the eastern segment of the Qiulitage anticline initially develop from the linkage of two smaller fold, i.e. the Kuqadawu anticline and the East Qiulitage anticline, and subsequently this fold assemblage has propagated eastward. Although there is an apparent topographic-relief transfer relationship between the eastern segment of the Qiulitage anticline and the adjacent Yaken anticline, a long-term spatio-temporal variation in surficial erosion may have accentuated this relationship by significantly reducing the elevation of the Qiulitage anticline near its central peak.