Age, petrogenesis and geological significance ofthe Linzizong volcanic successions in the Linzhou basin, southern Tibet: Evidence from zircon U-Pb dates and Hf isotopes

作者：Lee H Y^*; Chung S L; Wang Y B; Zhu D C; Yang J H; Song B; Liu D Y; Wu F Y

来源：Acta Petrologica Sinica, 2007, 23(2): 493-500.

• Linzizong volcanic successions
• Linzhou basin
• Tibet
• zircon
• U-Pb dating
• Hf isotope

In this study a dacitic breccia and a rhyolitic ignimbrite were collected from the bottom layers of the Dianzhong and Nianbo Formations, respectively, in the Linzhou basin, the typical locality of the Linzizong volcanic successions, for zircon U-Pb dating and Hf isotope analysis. The results indicate that the former erupted at 62.5 +/- 1.1 Ma and the latter at 56.4 +/- 1.2 Ma, implying the Linzizong volcanism to have started right after the K/T boundary. Igneous zircons from the Dianzhong and Nianbo samples yield epsilon(Hf) ( T) values of + 9. 0 similar to + 0. 5 and + 11. 0 similar to + 4. 8, respectively, suggesting involvement of the depleted mantle source in the magma generation. These e,,(T) values are corresponding to those of igneous zircons from the coeval Gangdese batholith, thus allowing us to infer a cognate origin related to partial melting of the mantle wedge and associated magma underplating/remelting. However, inherited zircons with Carboniferous ages in the Dianzhong sample have E, ( T) values from -0. 6 to -3.2 and Mesoproterozoic model ages, similar to those of inherited zircons from the Nyainqentanglha granituids, indicating an involvement of ancient crustal materials from the Lhasa terrane in the generation of these volcanical rocks. Based on all above and regional geology, we interpret the Linzizong volcanic successions in the Lhasa terrane, southern Tibet as the products of northward subduction of the Neo-Tethyan oceanic slab and its subsequent breakoff at the early stage of the India-Asia collision.

• 出版日期2007-2
• 单位岩石圈演化国家重点实验室; 中国科学院地质与地球物理研究所; 成都地质矿产研究所; 中国科学院地质与地球物理研究所兰州油气资源研究中心; 中国地质科学院