大别山木子店地区细粒二长花岗岩脉的年龄和成因--锆石U-Pb年龄和Hf同位素制约

摘要

This paper presents LA-ICP-MS zircon U-Pb dating and zircon in-situ Hf isotopic analytical results for the Muzidian fine-grained monzogranite dyke in northern Dabie orogenic belt. The dating results show that the granite was formed at 128.9 ± 0.7Ma in Early Cretaceous. Two Paleoproterozoic and Neoproterozoic inherited zircons were found in the granites. The Hf isotopic analytical results show that the zircons εHf(t) values are from-25.1 to-19.2 with the mean of-22.7, and the two-stage Hf model ages (TDM2) generally range from 2115Ma to 2505Ma. TheεHf(t) values of the two inherited zircons are-10.5 and 6.5, with the cor⁃responding TDM2 of 1151Ma and 1709Ma, respectively. The zircon U-Pb dating and in-situ Hf isotopic results indicate that the paren⁃tal magmas of Muzidian fine-grained monzogranite dyke were derived from partial melting of Paleoproterozoic crustal rocks, with some Mesoproterozoic mantle and Archean crustal materials probably making contributions to the source. The Muzidian fine-grained monzogranite dyke is considered to have been formed at the time of tectonic transition from compression to extension during Early Cretaceous in the Dabie orogen.%用LA-ICP-MS技术对北大别木子店地区细粒二长花岗岩脉中的锆石进行原位U-Pb年龄和Hf同位素测定，结果表明，该花岗岩形成于128.9±0.7Ma，为早白垩世岩浆活动的产物，在锆石中发现古元古代和新元古代的锆石核；锆石εHf(t)介于-25.1～-19.2之间，平均值为-22.7，二阶段模式年龄TDM2主要介于2115～2505Ma之间，2个继承锆石分析点分别给出了-10.5和6.5的εHf(t)值，对应的二阶段模式年龄TDM2分别为1151Ma和1709Ma。木子店地区细粒二长花岗岩脉的锆石年龄和Hf同位素特征表明，花岗岩为古元古代古老地壳物质部分熔融形成，岩石源区可能有中元古代地幔物质及太古宙古老地壳物质的贡献，形成于大别造山带从挤压向伸展的转换阶段。