黑龙江穆棱新生代玄武岩锆石巨晶的微量元素及Hf同位素研究

Major and trace element and Hf isotopes were reported for zircon megacrysts from the alluvium of Tertiary alkali basalts at Muling in the Heilongjiang Province, which, together with the Cenozoic basalts at Dunhua and Wangqing in the Jilin Province and Jingpowu and Mudanjiang in the Heilongiiang Province, are distributed along the middle-northern section of Dunhua-Mishan fault-the northern branch of Tanlu fault between Xing-Meng Orogen Belt and Pacific subduction zone. Generally, the zircons have clear surface melting feature and display transitional features compared with igneous or metamorphic zircons. Electronic microprobe analysis shows that they have an average Zr/Hf ratio of 150 with the maximum of 217 which is the highest value among the Cenozoic basalt-related megacryst zircons in the eastern China. They have same origin because of their similar trace element compositions, such as distinct positive Ce anomalies, enrichment in HREEs and HFSEs, most Hf/Y ratios of less than 10, Th/U ratios less than 1 with one exception, and Yb/Sm ratios of 21 - 59. They have a range of ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.283105 to 0.283151 with ε_Hf values ranging from + 11.8 to + 13.4, similar to those from other locations in East China, e. g. Wenchang in the Hainan Province, Mingxi in the Fujian Province, and Changle in the Shandong Province. The Hf isotopic characteristics of depleted mantle origin, combining with other major and trace element features, indicate that Muleng Cenozoic basalt-related megacryst zircons may be developed during Phanerozoic metasomatism in upper mantle related to lithospheric thinning or replacement at Muling in the Heilongjiang Province.