Probe into Structural Deoformation in the Joint Part between Altun and Qilian Mountains Based on Gravitational Characteristcs

In the joint part between Altun and Qilian mountains,four kinds of gravitational fields and its related structural deformation were marked out based on 6 newly completed 1:200000 grvitational map The dense NEE gravitational step zone implies the Altun fault zone,which is characterized by left strike-slip with an obduction feature,is a fault zone composed of swell and sagreflected by higher gravitation and lower gravitation together with which shear,compression and tensional stress fields coexist but principally shows shear;in addition,compression and tension also can be seenhere and there.In the west section of Qilian orogenic belt,the higher gravitation as well as lower gravitation stret chin alternant arcs show it selfa tectonic pattern of nappe-extrusion,obduction-superimposition,and basin-mountain coupling,and are related to basin-mountain coupling.It is estimated that the minimum displacements of Xiangm aoshan and Daxueshan are respectively 140km and 120km.The gentle and widegravitational fields of Dunhuang basin and Suhai basin imply their weaker deformations.