Fold-and-thrust structure in Yeyagou area, western Junggar, China and its implication.

The fold-and-thrust structure in western Junggar was mostly regarded as southeast directed. The fold-and-thrust belt in Yeyagou, located at east part of the western Junggar, however, is developed as top-to-NW assemblage. The characteristics of folds in this belt, from NW to SE, developed from upright fold to reclined fold to overturned fold, whose northwest limb was overturned. Their interlimb angle changes from 110° to nearly 60°, which indicates a progressive deformation from SE to NW, or a gradually increasing deformation from NW to SE. Furthermore, the youngest stratum involved in the folds is formerly defined Early Carboniferous Tailegula Formation featured by tuffaceous sandstone. The fold-and-thrust structure is cross-cut by diorite dated from 307Ma. All of these facts indicate that the folds were generated by top-to-NW shear during Late Carboniferous.