作　　者： (代友旭）; (董国臣）; (景国庆）; (李雪峰）; (王鹏）; (和文言）; (周千）;

机构地区： 中国地质大学地球科学与资源学院,北京100083 中国人民武装警察部队黄金第七支队,烟台264000

出　　处： 《岩石学报》 2017年第8期2548-2562,共15页

摘　　要： 位于义敦岛弧南端的中甸弧地区在印支期内发育大规模酸性-中酸性岩浆活动。近年来,前人对该地区做了大量的研究,但主要着眼于侵入岩,对火山岩的研究偏少。本文对分布于滇西北中甸格咱地区的中酸性火山岩进行锆石U-Pb定年、地球化学及Hf同位素分析,2件样品的锆石U-Pb年龄变化于214~212Ma,表明其为晚三叠岩浆活动的产物。岩石Si O2含量为53.37%~63.77%,全碱含量达5.19%~7.16%,为高钾钙碱性系列,富集大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti等高场强元素,具有典型岛弧火山岩特征。所测锆石εHf(t)值介于-0.04~3.06之间,大部分为正值,显示出幔源岩浆特征,相对应的锆石Hf同位素二阶模式年龄为1.05~1.25Ga。综合岩石学、地球化学及构造地质特点认为,格咱火山岩形成于印支期甘孜-理塘洋壳西向俯冲构造背景,其源区为俯冲流体交代的岩石圈地幔,岩浆上升过程经历了壳源沉积物质混染。 Intermediate-acidic magmatism was extensively developed in Zhongdian arc,which is located in the south of Yidun island arc in Indo-Chinese epoch. In recent years,researches have been concentrated on the intrusive rocks in this area while less on the volcanic rocks. This paper focused on the intermediate-acidic volcanic rocks in Gezan of Zhongdian,northwestern Yunnan Province.Zircon U-Pb dating of two samples yield the ages of 214 Ma and 212 Ma,indicating that the volcanic rocks were the productions of Late Triassic magmatic activity. The volcanic rocks have contents of Si O2 from 53. 37% to 63. 77%,alkali（ K2 O ＋ Na2O） of 5. 19% ~7. 16% as K high calc alkaline system. All the samples enrich in large ion lithophile elements and light rare earth elements and deplete in high strength filed elements（ such as Nb,Ta,Ti）,showing characteristics of island-arc volcanic rocks. The εHf（t） values vary from-0. 04 to 3. 06 and are mostly positive,displaying the features of mantle derived magma. The two-stage model ages of these zircons range from 1. 05 Ga to 1. 25 Ga. Based on petrology,geochemistry and regional tectonic background,it is concluded that Gezan volcanic rocks formed in the westward subduction setting of Ganzi-Litang oceanic crust in Indo-Chinese epoch. They were derived from the lithosphere mantle metasomatized by subduction-related fluids and underwent contamination of crustal materials.

关 键 词： 晚三叠世 年代学 地球化学 格咱火山岩 滇西北