THE FEATURE AND FORMATION MECHANISM OF ARCIFORM THRUST-NAPPE STRUCTURE ZONE OF THE SOUTHERN NINGXIA

The southern Ningxia's arciform structure zone, extending 150~300km, consists of four great arcuate thrust-nappe structural belts with a convex toward the northeast.Every belt is composed of many thrust sheets and back margin fault basin.They formed typical basin-range structures.Since Yanshanian movement because of movenent and convection of upper mantle substance took place intracrust substance lateral movement, detachment along the layer surface of incompetent, forming thrust-nappe on the front margin while extensional gliding and tensional fault depression on the back margin, accompanied with that the crust was thicker or thinner, at the end the basin-range structure were formed.