Abstract:

The Tianshan Mountains is characteristic of a typical intracontinental activity. The northern piedmonts consist of three main fold and fault belts, which are mainly faultrelated folds that deformed the strata from the south Junggar Basin. Understanding their Cenozoic Uplift history thus has a bearing on beans on the understanding of the mountain building process and petroleum explorations in Western China in general, and on how deformation has occurred under the influence of the IndiaAsia collision in particular. In order to help decipher the actual structural interpretation of the south Junggar Basin and the styles of deformation, we measured strikes and dips of strata at every spot in detail by the use of 200mlong lining rope or GPS along a 50 km section at the Jinggou River (Xinjiang Province) in the year 2005, and regional field survey for many years after 2005. Along with satellite Landsat ETM (Enhanced Thematic Mapper) and interpretation of 2D, 3D seismic data and well data, we have completed an approximately SNdirected 50kmlong geological section by using the faultrelated fold theories. Our field investigations indicate that the growth strata are present in the north limb of the Anjihai anticlines, and the growth unconformities interpreted by the seismic lines are present in both limbs of the anticline. The growth strata in the south limb of the anticline show us that it was originated in about the Early Miocene, ultimately formed during the Early Quaternary Xiyu Formation(Q1x) and Wusu Group(Q2) and the MiddleLate Quaternary(Q4), which was composed of the deeper faultbend fold, and shallower wedgeshaped backthrust faultbend fold. The Huo’erguosi anticlines was originated in about the Late Miocene, ultimately formed during the MiddleLate Quaternary(Q4), which was composed of the deeper faultbend fold, the middle wedgeshaped backthrust faultbend fold and the shallower faultpropagating fold. It is very clear that an approximately EW 285°striking strikeslip fault was discovered by our regional geological survey and satellite Landsat ETM interpretation. The Fault is located north to the south Junggar boundary thrust fault, formed in the Late Quaternary, which dislocated the Late Quaternary alluvial plains. Based on the times of three main folds, we conclude that the south Junggar fault and fold belt is of a breakback thrust sequence(new thrusts developed in the hangingwall), still being active from the early quaternary to present.

Key words: geological cross section measured on the field, seismic profile, faultrelated folds, strikeslip fault, overstep propagation, multipledeformation