Structural styles and tectonic significance of Tian Shan foothill fold-thrust belts, northwest China

The Tian Shan orogenic belt in northwestern China has experienced repeated episodes of deformation related to terrane collisions at the southern Asian margin throughout Phanerozoic time. The sedimentary basins flanking the Tian Shan preserve a sedimentary record of uplift and subsidence in the Tian Shan orogenic belt. Previous estimates of shortening across the Tian Shan have been based primarily on the relationship between physiographic relief and crustal thickening. A significant proportion of postulated total shortening is accommodated in the low-lying foreland basins flanking the high Tian Shan. The history and styles of deformation in the Tarim and Junggar sedimentary basins have been investigated through geologic interpretation of eight 1:250,000-scale satellite images and construction of a series of balanced structural cross-sections across the southern Tian Shan foreland.;Inherited structural grain inherited has influenced the structural styles of the northern Tarim craton since Carboniferous time. The Kalpin block preserves a Paleozoic stratigraphic succession unconformably overlain by Cenozoic strata. Neogene compression resulted in uplift and deformation of the Kalpin block and tectonic loading of adjacent depressions. Oblique compressive stresses from the southwest caused west- and east-vergent basement-involved thrusting in the Bachu uplift south of the Kalpin block. With clockwise rotation of the craton, stresses oriented nearly north-south produced south-vergent, basement-involved thrusting of the Kalpin block. Additional shortening was accommodated along south-vergent, imbricate thrusts deforming the sedimentary section. Balanced structural cross-sections indicate up to 50 km of total slip on these faults.;In the Kuqa depression, south-vergent Tian Shan nappes tectonically loaded the crust and created a migrating foredeep filled with clastic rocks derived from the range to the north. The depression preserves a Mesozoic and Cenozoic sedimentary sequence nearly 10 km thick. The sedimentary section is characterized by fault-propagation folding, thrusting, and salt movement. Cross-sections across the depression indicate slip in the sedimentary section totaling some 30 km; overthrusting and underthrusting of Tian Shan nappes accounts for an additional 10 to 20 km.;Shortening in the forelands accounts for up to 25% of the total across the orogenic belt.