西准噶尔野鸭沟地区褶皱冲断构造的特征及意义

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

西准噶尔地区的褶皱冲断带多被认为是向东南逆冲的。在东部野鸭沟发育的褶皱冲断构造中识别出顶端指向北西的褶皱组合。褶皱自北西向南东逐渐由直立褶皱转变为斜歪褶皱,最后褶皱北西翼发生倒转而倾向南东,表明它们的极性指向北西;褶皱翼间角也由110°转变为60°左右,显示野鸭沟褶皱自北西向南东变形程度逐渐增强。根据卷入褶皱冲断带最年轻的地层为石炭系,又被307 Ma的闪长岩穿切的事实,认为该褶皱冲断带形成于晚石炭世的顶端指向北西的剪切环境。

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.