BULLETIN Discovery of eclogite at northern margin of Qaidam Basin, NW China YANG Jingsui, XU Zhiqin, LI Haibing, WU Cailai, CUI Junwen, ZHANG Jianxin & CHEN Wen Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China Abstract Eclogite was first discovered at the northern margin of the Qaidam Basin in this study. It oc- curs as pods in the gneiss sequence of Middle to Upper Proterozoic age and is mainly composed of gar- net, omphacite, phengite and rutile. The garnets contain 44 % -62 % of almandine, 15 % -33 % of grossular and 12%-30 % of pyrope molecules, and the omphacites contain 40%-46% of jadeite. Applying garnet-clinopyroxene thermometry and jadeite geobarometry, the peak conditions of eclogite facies metamorphism occurred at about (722 k 123)C and at the pressure of up to c. 22 x 10' Pa. Keywords: eclogite, high-pressure metamorphism, Da Qaidam, Qinghai-Xizang Plateau. THE coecite-bearing eclogite and ultra-high pressure metamorphism in the Dabie and Sulu areas in East China have been attracting great attention of the geoscientists in the world since they were recognized in 198711'21. Eclogite and high-pressure metamorphism have also been reported from the Altyn Tagh and Tianshan ~ o u n t a i n s ' ~ ' ~ ] , NW China in recent years. During the field season of Sino-French collaboration of 1996 we found that eclogites occur at the northern margin of the Qaidam Basin. All these discoveries make us reconsider the tectonic framework of NW China as well as of East China. Chinese Science Bulletin Vol .43 No. 20 October 1998