甘孜-理塘蛇绿混杂岩带晚三叠世洋岛型岩石组合识别及其对甘孜-理塘洋盆构造演化的制约  

Identification of the Late Triassic oceanic island rock assemblages in the Ganzi-Litang ophiolite mélange belt and its constraints on the tectonic evolution of the Ganzi-Litang oceanic basin

作　　者：严松涛 吴青松 朱利东[2] 李虎 代雪健 秦蒙 YAN Songtao;WU Qingsong;ZHU Lidong;LI Hu;DAI Xuejian;QIN Meng(Civil-Military Integration Center,China Geological Survey,Chengdu 610036,Sichuan,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,Sichuan,China)

机构地区：[1]中国地质调查局军民融合地质调查中心,四川成都610036 [2]成都理工大学沉积地质研究院,四川成都610059

出　　处：《地质通报》2023年第10期1684-1695,共12页Geological Bulletin of China

基　　金：中国地质调查局项目《四川甘孜州通宵、博美、下莫坝、下坝幅15万地质矿产综合调查》(编号:DD2016008014)。

摘　　要：甘孜-理塘蛇绿混杂岩带位于特提斯构造域东段,为西南“三江”多岛弧盆系的重要组成部分,具有完整的沟-弧-盆体系。以理塘地区拉扎嘎山一带下坝岩组洋岛型“玄武岩+碳酸盐岩”岩石组合为研究对象,开展岩石学、地球化学和锆石U-Pb测年分析,为甘孜-理塘洋晚三叠世洋陆格局的恢复重建提供新的证据。岩石地球化学分析结果表明,样品SiO_(2)含量为42.16%~48.32%,TiO_(2)为2.81%~3.75%,稀土元素总量为164.51×10^(-6)~414.40×10^(-6),轻稀土元素较重稀土元素富集,(La/Yb)_(N)值为9.35~34.31,明显富集Rb、Ba、Th、U、K等大离子亲石元素,以及Nb、Ta、Zr、Ti等高场强元素,玄武岩的稀土元素配分曲线和微量元素蛛网图与典型洋岛型玄武岩(OIB)相似。锆石U-Pb测年表明,洋岛型玄武岩形成于211 Ma。这些资料进一步表明,晚三叠世甘孜-理塘洋盆存在洋岛环境,同时,也为甘孜-理塘洋盆晚三叠世处于俯冲消减阶段的认识提供了新的证据。The Ganzi-Litang ophiolite mélange belt is located in the eastern Tethys domain.It is an important part of the Sanjiang(Nujiang River,Lancangjiang River and Jinshajiang River)archipelagic arc-basin system in Southwest China,with a complete trench-arc-basin system.The petrological,geochemical and zircon U-Pb dating analyses of the oceanic island-type"basalt+carbonate"rock assemblage in the Xiaba Formation from the Lazaga Mountain in the Litang area are carried out to provide new evidence for the reconstruction of the Late Triassic ocean-continent configuration of the Ganzi-Litang Ocean.Geochemical analyses show that the SiO_(2)content of the basalts is 42.16%~48.32%,and the TiO_(2)content is 2.81%~3.75%.The total rare earth elemnt(ΣREE)ranges from 164.51×10^(-6)to 414.40×10^(-6),and the light rare earth elements are more enriched than the heavy rare earth elements[(La/Yb)_(N)=9.35~34.31],and are obviously enriched in lithophile elements such as Rb,Ba,Th,U,K,and high field strength elements such as Nb,Ta,Zr,Ti,etc.The REE distribution curve and trace element spider patterns of the basalts are similar to typical oceanic island basalt(OIB).The zircon U-Pb dating indicates that oceanic-island basalts were formed at 211 Ma.These data further indicate that an oceanic island environment existed in the Ganzi-Litang Ocean during the Late Triassic,and also provide new evidence for understanding that the Ganzi-Litang Ocean was in the subduction stage during the Late Triassic.

关 键 词：西南三江 甘孜-理塘 蛇绿混杂岩带 洋岛型岩石组合 地球化学 年代学 地质调查工程 

分 类 号：P534.51[天文地球—古生物学与地层学] P597.3[天文地球—地质学]