【摘要】 幕阜山复式花岗岩基南缘的长庆黑云母花岗岩与其内部Be伟晶岩呈渐变接触关系,为Be伟晶岩的母岩,其成岩时代及同位素特征可指示幕阜山地区黑云母花岗岩阶段的Be成矿时代及成矿物质来源。本次研究对长庆地区的似斑状黑云母二长花岗岩进行了LA-ICP-MS锆石U-Pb定年和Hf同位素组成测试,结果显示,该岩体成岩年龄为(142.9±0.9)Ma,代表了幕阜山复式花岗岩体黑云母花岗岩演化阶段的稀有金属成矿时代,此次成矿为华南地区中生代大规模成岩成矿作用的组成部分;继承锆石核的存在表明区域可能存在古老基底。长庆地区似斑状黑云母二长花岗岩的εHf(t)值主要变化于-9.2～-5.5,二阶段模式年龄主要为1.6～1.8 Ga,与幕阜山岩体不同类型花岗岩的εHf(t)和Hf同位素TDM2相近,暗示它们的源岩具有相似源区特征,为同源岩浆不同演化阶段的产物。此外,长庆似斑状黑云母二长花岗岩的源区物质中还有少量古元古代壳源物质(εHf(t)=-16)和新元古代地层物质加入,反映源区物质的复杂性。结合区域内其他年代学与同位素研究资料,表明幕阜山地区伟晶岩稀有金属成矿作用发生于早白垩世,岩浆连续分异演化过程中伴随着多阶段稀有金属成矿作用,最早在黑云母花岗岩阶段开始出现Be矿化,之后随着岩浆的分异演化程度不断增高,矿化规模越来越大,矿种由单一元素(Be)向综合演化(Be-Nb-Ta-Li)。成矿物质来源方面,幕阜山岩体锆石的TDM2与冷家溪群的锆石Hf同位素二阶段模式年龄的一个峰值(1.7～2.0 Ga)接近,表明二者的源岩在此时同时脱离地幔形成,为幕阜山岩体形成于冷家溪群部分熔融提供了支持,冷家溪群可能为稀有金属成矿提供了主要的物质来源。更多还原

【Abstract】 The Changqing porphyaceous biotite granite in the south margin of Mufushan shows gradual contact with the Be pegmatite inside, which suggests that the granite is the parent rock of the pegmatite. Therefore, the forming age and isotopic compositions of the granite could reveal the epoch and material source of Be mineralization relating to biotite granite in Mufushan. In this research, the LA-ICP-MS was employed for U-Pb dating and Hf isotopic compositions of zircon grains from porphyaceous biotite monzonitic granite in Changqing. The result shows that the forming age of the granite is(142.9±0.9) Ma. This age could be interpreted as the rare metal mineralization age referring to biotite granite of Mufushan composite granite mass, suggesting that the mineralization is part of Mesozoic large-scale diagenesis-mineralization in South China. The inherited core in zircon indicates that there is probably an old base in Mufushan. The εHf(t) and Hf two-stage model age TDM2 of the Changqing granite mainly range from-9.2 to-5.5 and from 1.6 to 1.8 Ga, respectively, corresponding to those of various granites in Mufushan batholith, which suggests these granites, whose source rocks share similar sources, result from homologous magma with different evolution levels. Besides, it also shows that there are also materials derived from Paleoproterozoic crust(εHf(t)=-16) and Neoproterozoic sedimentary strata in the source of the studied granite,regarded as a proof of muti-source. Together with previously published data, it’s indicated that the rare metal mineralization in pegmatite of Mufushan was in Early Cretaceous. During magma evolution, there were multistage rare metal mineralization, starting at Be mineralization connected with biotite granite, and then developing into larger scale and richer minerals(Be-Nb-Ta-Li) as magma evolved. The TDM2 of zircons from Mufushan batholith is close to one of peaks of that of zircons from Lengjiaxi Group(1.7～2.0 Ga), which means their source rocks were separated from the mantle simultaneously. It supports the hypothesis that the Mufushan granitoids were derived from partial melting of Neoproterozoic Lengjiaxi Group, which may provide significant ore-forming source for rare metal mineralization.更多还原