THE TURFAN DEPRESSION OF THE WESTERN TURFAN BASIN, NORTHWEST CHINA - ASPECTS OF SUBSIDENCE AND RELATION TO LATERAL ESCAPE TECTONICS

During the Oligocene, lateral escape tectonics caused by India's colli sion with Eurasia started to affect the western part of the Turf an ba sin, and the Turfan depression was initiated. The depression's subside nce can be explained within the context of lateral escape tectonics. O f interest is that contractional as well as synchronous dilatational t ectonics combined to lower the land surface below mean sea level. In t he course of lateral escape, transpressional loading from the north an d ESE-directed escape of the western part of the Turf an basin rook pl ace and continue today (Cunningham et al., 1996). In the western part of the Turf an basin, ongoing extension is a result of relative differ ences in lateral escape velocities-relatively ''slow'' escape in the n orth as a result of restraining bends, and relatively ''fast'' escape in the south. The northern margin of the Turf an depression is affecte d by contractional deformation, but at the same time the depression al so is located in a domain of extensional faulting. Strike-slip tectoni cs play a key role in the formation of the Earth's deep depressions, w hich occur along transtensile segments of important lateral shear zone s. In the case of the Turf an depression, this is nor exactly true. Ho wever, strike-slip motion along the boundaries of the Turf an basin ar e the controlling factors for the formation of the Turfan depression.