Quantification of growth and lateral propagation of the Kashi anticline, southwest Chinese Tian Shan

The Kashi anticline is a north vergent, asymmetric, doubly plunging detachment fold located in the SW Tian Shan foreland. We combine structural, magnetostratigraphic, and topographic data to define the fold's lateral propagation, surface uplift, and concomitant exhumation. Two new magnetostratigraphic sections indicate that the fold began growing at ∼1.4 Ma and by 1.07 Ma, deformation had propagated eastward ∼13 km at an average rate of ∼40 km/Myr. Subsequently, propagation rates increased at least twofold, until the fold reached >60 km in length by 0.8 ± 0.3 Ma. Since then, eastward fold propagation slowed to ∼15 km/Myr, and the eastern 15–25% of the fold remains buried in the rapidly aggrading foreland. The structure and topography of the emergent fold support interpretations of fold growth in three stages: initial symmetric lateral growth both east and west to a total length of ∼30 km followed by, first, rapid and, then, slower eastward lengthening to 72 ± 10 km total length. Shortening rates as high as 1.9 −0.2 +0.3 mm/yr characterize the western part of the fold but decrease toward the east. Significant dissection of the emergent fold does not occur until topographic relief is sufficient (∼200 m) to permit stripping of protective conglomerates from across the fold's upper surface. As differential rock uplift continues following breaching of the conglomerate, ∼75% of the rock raised above local base level is subsequently eroded at rates as high as 2.4 km/Myr. Despite extensive erosion, the modern fold topography mimics spatial patterns of both long‐term shortening and variations in rock uplift.