Fold structure and its origin in Dapinggou area, eastern Altun Mountains

Dapinggou area of eastern Altun Mountains, is situated in the clamping area between NE-trending Altun strike-slip fault and EW-trending northern Altyn Mountains margin fault. There outcropping a series of volcano-sedimentary rocks of Zhuoabulake Formation. Among which, grayish black silt mudstone, as a deputy to the sedimentary rocks, outcrops about 3～5km in width, while there outcropping only about 1km in width in Kaladawan area only 20km eastern of the Dapinggou area. In this paper, after a detailed geological survey and investigation of the sedimentary rock section by means of minor fold analysis and discriminant analysis of the relation of the bedding and axial-place cleavage of fold, the authors for the first time take an attempt to restore the outline of fold structure in the Dapinggou area. Then the authors analysis the origin of the fold structure and consider that the basic condation for forming Dapinggou fold structure are the competent bed of the Proterozoic carbonatite southern of the Kaladaban-Akedaban fault, the rigid block of the Archeozoic crystalline basement northern of the EW-trending northern Altyn Mountains margin fault, the plastic strata of the grayish black silt mudstone of Zhuoabulake Formation and the strinkage to the east of the cover strata of the Binggou granite masscausing from the uplift of the granite mass. And the authors also believe that the direct cause is lateral compression in the western end of the sedimentary rock of Zhuoabulake Formation result from sinistral strike slip of the NEE-trending Zhuoabulake fault in the regional SN-trending compressive stress field.