CENOZOIC BASIN EVOLUTION, STRUCTURAL STYLES OF THE QAIDAM AND AN ESTIMATE OF DENUDATION IN ADJACENT MOUNTAIN SYSTEMS, NORTHEAST QINGHAI—TIBETAN PLATEAU

Qaidam basin is located at northeast Qinghai—Xizang (Tibet) plateau, and surrounded by east Kunlun, south Qilian and Altun mountain systems. The purpose of this paper is to study the Cenozoic basin evolutionary stages, structural styles of the Qaidam, and the denudation in adjacent mountain systems through seismic profile interpretation and complemented by field observation. The Qaidam basin has experienced two tectonic stages of Paleogene—early Miocene (65～12Ma) and late Miocene—present (12～0Ma). The former is characterized by differential uplift of the mountains and subsidence of the basin, and the latter by intense compression, wrench, thrusting and folding. The compressional structural styles are mainly distributed in the Circle Hero—Range Depression of southwest Qaidam, such as Nanyishan, Youquanzi, Younan, Youshashan anticline belts and thrust faults. The wrench structural styles of the northern Qaidam include en echelon uplifts (fault—block outcrops) such as Seshitengshan, Luliangshan, Xitieshan and Eimnikshan, which are mainly composed of pre\|Sinian and Paleozoic rocks; en echelon anticlines such as Lenghu—Nanbaxian belts; and en echelon depressions such as Kunteyi, Senan and Yibei depressions, which are mainly composed of Mesozoic and Cenozoic rocks.