广西大宁岩体和初洞岩体锆石U-Pb年代学及Hf同位素研究
Zircon Geochronology and Hf Isotopes of Daning and Chudong Intrusions, Guangxi Prvince

摘要 利用锆石LA-ICP-MS U-Pb定年, 获得大宁岩体形成年龄为441.1±3.0 Ma, 其包体年龄为439.5±3.6 Ma, 初洞岩体形成年龄为423.5~434.2 Ma。结果表明, 大宁岩体及其包体几乎同期形成, 而初洞岩体是后期的侵入体。Lu-Hf同位素研究结果表明, 大宁岩体及其暗色包体与初洞岩体具有相似的Hf同位素组成, 在εHf(t)–年龄图上落在1440~1960 Ma的老地壳区间, 表明三者的岩浆源区均是早元古代到中元古代地壳, 暗色包体是岩浆早期分离结晶的产物, 而初洞岩体是岩浆结晶分异晚期的产物。
Abstract LA-ICP-MS zircon U-Pb dating for Daning pluton, dark inclusions and Chudong pluton yield the weighted mean 206Pb/238Pb ages of 441.1±3.0 Ma, 439.5±3.6 Ma and 423.5–434.2 Ma, respectively, revealing that Daning pluton and the dark inclusions were formed almost concurrently, while the Daning pluton was intruded by the Chudong pluton. In-situ zircon Lu-Hf isotopic analyses of Daning pluton, dark inclusions and Chudong pluton show same characteristics with negative εHf(t) values, plotted within the revolution areas of the 1440–1960 Ma old continental crust in the age vs. εHf(t) diagrams. The Hf isotopic characteristics indicate that the magmas could be derived from the partial melting of Early Proterozoic to Mesoproterozoic crust materials. The dark inclusions were produced by the fractional crystallization of parental magma. The Chudong pluton was the advanced stage product of the magma crystallization differentiation.