郯庐断裂带南段早白垩世镁铁质岩墙成因及其地质意义  

Petrogenesis and geological significance of Early Cretaceous mafic dyke in the southern segment of Tan‑Lu fault zone

作　　者：钱涛 牛漫兰[1] 李晨[1] 吴齐[1] 苑潇宇 李秀财[1] 王磊 Qian Tao;Niu Manlan;Li Chen;Wu Qi;Yuan Xiaoyu;Li Xiucai;Wang Lei(School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009)

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009

出　　处：《地质科学》2023年第3期837-863,共27页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:41772228,41172201)资助。

摘　　要：地壳再循环物质交代岩石圈地幔形成不均质的地幔源区,其衍生的镁铁质岩浆岩为揭示地幔演化及壳-幔相互作用提供了重要信息。本文对郯庐断裂带内张八岭隆起南段肥东地区镁铁质岩中的锆石进行LA-ICP-MS定年,获得年龄集中在127~122 Ma。镁铁质岩样品中SiO_(2)含量为51.33%~54.01%,Mg#值为52.6~70.0,并具有富钠、富碱(σ=2.46~4.22)的特征,属于亚碱性和高钾钙碱性系列。镁铁质岩样品均富集大离子亲石元素(LILEs,如Ba、Pb、K),相对亏损高场强元素(HFSEs,包括Nb、Ta、Ti等),表现为弧型地球化学特征。锆石Hf-O同位素研究获得极负的εHf(t)值(-23.4~-21.2)和略高的δ18O值(5.49‰~6.01‰),与新元古代斜长角闪岩同位素组成显示出一致的演化趋势和相似的分布特征。因此,早白垩世镁铁质岩墙富集的同位素特征主要继承于新元古代(~800 Ma)岩石圈地幔;在郯庐断裂带伸展背景下,由古老岩石圈地幔发生减压熔融形成。The heterogeneous mantle sources are generally caused by involvements of crustal recycling material into lithospheric mantle.The mafic magmatic rocks derived from heterogeneous mantle sources can provide important information for revealing mantle evolution and crust‑mantle interaction.In this paper,we conducted new LA‑ICP‑MS dating of zircon in mafic rocks from the Feidong area of the southern section of the Zhangbaling uplift of the Tan‑Lu fault zone,and obtained ages concentrated in the range of 127 Ma to 122 Ma.These samples show SiO2 contents of 51.33%to 54.01%and Mg#values of 52.6 to 70.0,with Na‑rich and alkali‑rich(σ=2.46 to 4.22),belonging to the subalkaline and high‑K cal‑alkaline series.These mafic rocks are enriched in large‑ionic lithophile elements(LILEs,such as Ba,Pb,and K)and relatively depleted in high‑field strength elements(HFSEs,including Nb,Ta,Ti,etc.),exhibiting arc‑like geochemical characteristics.Zircon Hf‑O isotopic compositions show extremely negativeεHf(t)values(-23.4 to-21.2)and slightly higherδ18O values(5.49‰ to 6.01‰),showing a consistent evolutionary trend and similar distribution characteristics with the isotopic composition of the Neoproterozoic plagioclase amphibolite.Therefore,the enriched isotopic characteristics of these mafic dykes in the Early Cretaceous were mainly inherited from the lithospheric mantle in the Neoproterozoic(~800 Ma),caused by the decompression melting of the ancient lithospheric mantle during the extension of Tan‑Lu fault zone.

关 键 词：郯庐断裂带 早白垩世 镁铁质岩墙 岩石成因 地幔源区 

分 类 号：P534.53[天文地球—古生物学与地层学] P588.1[天文地球—地质学] P59