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曼秀闪长岩体位于景洪县城南东,与著名的南林山岩体呈平行展布,主要由黑云角闪闪长岩、黑云角闪石英闪长岩和石英闪长质碎粒碎斑岩组成。采用LA-ICP-MS法获得了曼秀岩体中闪长岩的四组锆石U-Pb年龄,分别是321±14 Ma、305.7±9.3 Ma、291.3±7.6 Ma和307.4±7.3 Ma,表明曼秀岩体的形成时代在晚石炭—早二叠。全岩微量元素特征表明,岩石中Th、Zr等富集,而Nb、Hf等亏损。具有轻稀土富集特征,δEu=0.73~0.98(平均0.85)呈弱负异常特征,而δCe=0.89~1.06(平均0.95),异常不显著。微量和稀土元素特征显示,曼秀闪长岩体与火山弧花岗岩相似,并向同碰撞花岗岩过渡,说明南澜沧江带在晚石炭—早二叠早期为大洋岛弧俯冲带。
The Meixiu diorite body is located in the south east of Jinghong County, and is distributed in parallel with the famous Nanlin Mountain pluton. It consists of biotite phlogoid, biotite amphibolite and quartz diorite Porphyry composition. The zircon U-Pb dating of four groups of diorite in Manxiu rock body was obtained by LA-ICP-MS method, which are 321 ± 14 Ma, 305.7 ± 9.3 Ma, 291.3 ± 7.6 Ma and 307.4 ± 7.3 Ma, respectively The formation time of Manxiu rock mass lies in Late Carboniferous-Early Permian. The characteristics of trace elements in the whole rock show that Th, Zr, etc. are enriched in the rock, while Nb, Hf, etc. are depleted. With the characteristics of light rare earth enrichment, δEu = 0.73 ~ 0.98 (average 0.85) showed a weak negative anomaly characteristics, and δCe = 0.89 ~ 1.06 (average 0.95), the anomaly was not significant. Trace and rare earth element characteristics show that the Manxutan body is similar to volcanic arc granite and transitions to craton granulite, indicating that the South Lancangjiang belt was an oceanic island arc subduction zone in the early stage of Late Carboniferous-Early Permian.