New results and major progress in regional geological survey of the Washixie and Altyn Tagh sheets
The metamorphic series originally assigned to the Paleoproterozoic "Altyn Tagh" Group is disintegrated into two parts: metamorphosed supracrustal rocks and metamorphosed plutonic intrusive rocks. According to the rock association and characteristics of deformation and metamorphism, the metamorphosed supracrustal rocks may be subdivided into the Milan Group-complex and Altyn Tagh Group-complex. Isotopic dating suggests that the metamorphosed plutonic intrusive rocks are Meso- to Neoproterozoic in age. A high-pressure metamorphic rock association of granulite, garnet amphibolite and kyanite-garnet-gedrite schist was first found in the central Altyn Tagh block. The p-T-t path of metamorphism indicates that this rock association underwent a dynamic process of rapid subduction-collision and then rapid exhumation (uplift). On the basis of the discovery of the tectonic ophiolitic melange zone and large-scale thrust nappe structure, combined with regional tectonic characteristics, this tectonic units in the survey area have been redefined and a deformation sequence of tectonic features established. It has been preliminarily ascertained that in the survey area there occur at least three-level ancient planation surfaces, which divide the neotectonic movement such as mountain-making movement, geomorphologic changes and water drainage evolution into five phases.