Geochemical characteristics of the Late-Cretaceous dacite in Coqen, western Gangdese batholith,Tibet
Wang Wei1,2, Zeng Lingsen3, Liu Jing4, Xiao Ping4, Gao Li'e3
1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101;
2. University of Chinese Academy of Sciences, Beijing 100049;
3. State Key Laboratory of Continental Tectoincs and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037;
4. Institute of Geology, China Earthquake Administration, Beijing 100029
Field investigations and zircon SHRIMP U-Pb dating show that a suite of dacite formed at Late Cretaceous(88.5±1.2 Ma) occurred in the southeast of Coqen,western Gangdese Batholith,Tibet.This suite of volcanic rocks is characterized by trace element geochemistry similar to those formed in the arc environment.Geochmical and isotopic data indicate that they are Ⅰ-type igneous rocks and have experienced high degrees of plagioclase fractional crystallization.As compared to those intrusive rocks of similar ages,this suite of rocks represents highly evolved magmas drieved from partial melting of deep crustal mafic rocks and is characterized by elevated Rb/Sr but lower Sr/Y ratios.Our new data as well as those from the literature further indicate that the Lhasa terrane had experinecd extensive magmatism at 90～85 Ma due to northward subduction the Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane.