云南中甸地区翁水晚三叠世火山岩地球化学特征及其构造意义

“三江”构造带中甸弧北部的印支期岩浆活动目前尚无正式的研究报道.本文的岩石学及年代学的研究表明,中甸弧北部的翁水地区存在印支期中酸性岩浆活动,锆石U-Pb定年结果显示这些火山岩在211.1±1.5Ma喷发,与该地区的印支期火山岩与斑岩矿床的成矿斑岩的形成时代一致.翁水安山岩岩石地球化学特征显示其以中性的安山岩为主,具有亏损Nb、Ta、Ti等高场强元素的典型岛弧岩浆成分特征.与同一构造单元内中句弧南部的烂泥塘-浪都安山岩进行主、微量元素的对比研究发现,两者均具有正常岛弧火山岩的成分组成特征.结合其形成时代和构造背景,初步认为中甸弧北部的翁水和南部的烂泥塘-浪都安山岩以及该区域的成矿斑岩很可能形成于同一构造-岩浆事件,都是甘孜-理塘洋晚三叠世俯冲作用的岩浆产物.

The geochemical characteristics of Late-Triassic volcanic rocks from Wengshui in Zhongdian area, Yunnan and tectonic significant

It has not been reported at present of arc magmatic activities for Late Triassic in northern zhongdian arc of Sanjiang tectonic belt. Our petrological and chronological researches show that the intermediate-acid magmatic activity of Indosinian developed in Wengshui areas of Zhongdian arc; zircon U-Pb dating indicates that the volcanic rocks in Wengshui area were erupted at 211.1±1.5Ma, which is similar to ages of other Indosinian volcanic rocks and ore-bearing porphyric rocks in southern Zhongdian area. The Wengshui volcanic rocks mainly consist of andesites and show depletion of high field strength elements such as Nb, Ta, Ti similar to arc volcanic rocks. Compared with Lannitang-Langdu andesites from southern area of Zhongdian arc, the both clearly show compositional signature of an arc volcanic rock. Combining their age and tectonic background, we conclude that Wengshui andesites, Lannitang-Langdu andesites and ore-bearing porphyric rocks from Zhongdian area were most likely formed by a same tectono-magmatic event, which were generated by westward subduction of the Ganzi-Litang in Late-Triassic.