TECTONIC REVERSE OF MESOZOIC AT THE WESTERN FOOT OF HELAN MOUNTAIN AND ITS MEANING

The comprehensive analysis of fractures and bedding structures in the Xiaosongshan fault indicates that,a huge tectonic reverse took place after the Late Jurassic and the Xiaosongshan ‘nappe' structure developed at the western foot of the northern part Helan Mountain is actually a slipping structure.The sedimentary feature and the basaltic environment prove that,the region is a continental rift slope.Therefore,the(massive) compressive stress in EW direction did not exist in the Early Mesozoic.Fold deformation as well as bedding shear is the result of local structural deformation caused by the slipping structure,which is obviously contractive to the typical EW trend thrusting in the west of Ordos block and should be paid attention to in research.