Chinese Science Bulletin 2004 Vol. 49 No. 161736-1740 Zircon V-Pb SHRIMP dating of the Yematan batholith in Dulan, North Qaidam, NW China WU Cailai 1 , YANG Jingsui 1 , Joseph L. Wooden 2 , SHI Rendeng 1 , CHEN Songyong 1 , Anders Meibom 2 & Chris Mattinson 2 1. Key Laboratory for Continental Dynamics of MLR, Institute of Geol- ogy, Chinese Academy of Geological Sciences, Beijing 100037, China; 2. Department of Geological and Environmental Sciences, Stanford University, CA9430S, USA Correspondence should be addressed to Wu Cailai (e-mail: wucailai@ ccsd.org.cn) Abstract The Yematan batholith crops out over 120 km 2 in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. It consists of granodiorite, monzogranite and biotite granite and forms an irregular intrusion into Neoproterozoic gneiss that has undergone Caledonian UHP metamorphism. Zircons from the Yematan granodiorite yield a SHRIMP U-Pb age of 397±3 Ma. These granitic rocks have geochemi- cal characteristics intermediate between 1- and S-type gran- ites, and are post-collisional. We suggest that the Yematan granitic rocks were formed during the last exhumation event of the North Qaidam UHP belt. Keywords: Yematan batholith, zircon V-Pb SHRIMP dating, VHP belt of North Qaidam. DOl: lO.1360/03wd0347 Since the discovery of eclogite blocks in Proterozoic gneiss near Yuka River in Da Qaidam[l], many such bodies have been found in Luliangshan, Xitieshan, Dulan, and in the North Qaidarn and Altyn Mountains. All of these ec- logites have similar compositions and similar SHRIMP U-Pb ages of 445-500 Ma, and are believed to have been metamorphosed under pressures greater than 28 kb[I-3]. Hence, they represent part of an Early Paleozoic ultrahigh pressure (UHP) belt trending E-W for more than 350 km through North Qaidam[4---6]. The UHP nature of this belt has been confirmed by the discovery of coesite inclusions in zircons from gneiss in the vicinity of Dulan[5] (Fig. 1). Although these gneisses are considered to be Proterozoic, Xu et al. [7] reported 39Ar- 40Ar plateau ages of 402±2 Ma for muscovite from the Dulan granitic gneiss. The gneisses have been intruded by numerous granitic bodies and the relationship between them is not clear. Both the age of the granites and their relationship to the UHP metamorphic rocks need to be established. This paper at- lIIIII] Ordovician-Silurian Eclogite [2S] Sample location (()(Q'1 . fT:Tl UHP metamorphlc belt I.:b....:.:Y Diorite DUHPTerrain Im ++ ++ Granite +++ Fault 98' 38° Skm 1736 Fig. 1. Geological sketch map of the Yematan granite near Dulan (revised after the 1 : 200000 Dulan geological map). Chinese Science Bulletin Vol. 49 No. 16 August 2004