STRUCTURAL DEFORMATION OF THE PROTEROZOIC ALONG HORSE RACING MOUNTAINS,KURUKTAG

The study area is located at the northeastern margin of Tarim basin. Structural analysis reveals that the complex structural deformation formed at different phases. The present structural framework is mainly composed of a western Horse Racing Mountains (HRM) along-bedding detachment ductile deformation zone, Yonghong Mountains nappe and western HRM-Yonghong Mountains dome-basin. The detachment zone occurs within the Xinditag Group of the Paleo-Proterozoic and the Changcheng System of the Middle Proterozoic. The nappe is composed of the Xinditag Group and thrust over a structural basin composed of the Changcheng System. The dome-basin structure influences not only the Changcheng era but also the underlying Xinditage Group. The three structural elements have a close temporal and dimensional relationship. The ductile deformation zone is involved into the dome-basin structure thrust over by the nappe which has the same folding and overlapping structures as the ductile zone and syncline structures corresponding with the main phase of folding structure of the dome-basin structure. Three phases of tectonic movements are thus determined during the Middle Proterozoic. The first phase happened at the early Middle Proterozoic during which large scale along-bedding detachment ductile deformation developed at central depth due to EW-trending extension. The deformation of this phase has features of plastic deformation and multi-layer structures. The second phase occurred at the end of Changcheng Era during which EW-trending tight folds (locally overturned) were developed at shallow depth due to N-S compression. The deformation of this phase influences the earlier ductile deformation. The Yonghong Mountains nappe with overlapping structures formed at shallow depth during the latest phase of folding due to northward thrusting along weak zone of the Xinditage Group. The third phase took place at the end of the Jixian Era during which NS-trending open folds formed by EW-trending compression caused by relaxation of NS-trending intense compression. The HRM-Yonghong Mountains dome-basin formed in a framework of multiphase deformation and resulted from overlapping of earlier structures.