都龙-Song Chay穹窿片麻状花岗岩的LA-ICP-MS锆石U-Pb年代学和微区微量元素研究

LA-ICP-MS zircon U-Pb chronology and trace elements study of the Dulong-Song Chay dome gneissic granite

横跨中-越两国的都龙-Song Chay穹隆的核部杂岩发育了混合岩化作用。对穹隆核部的混合片麻岩和浅色花岗岩脉中锆石CL图像、U-Pb年龄和锆石微区微量元素组成的研究表明,锆石发育复杂的内部结构,可分为:继承锆石、深熔锆石、变质增生锆石。锆石核部为原岩继承锆石,一般较明亮且具有最高的Th/U比值,最低的U含量和较高的∑REE、LREE含量,获得的年龄为前寒武纪年龄,代表了混合岩的原岩年龄;深熔锆石具有振荡环带,次高的Th/U比值和最低的∑REE、LREE含量,在混合片麻岩和浅色花岗岩中获得的~(206)Pb/~(238)U年龄分别为(422±6) Ma、(423±6) Ma,代表了都龙-Song Chay穹隆发生深熔作用的时间,与区域上碰撞-岩浆事件时间一致;变质增生锆石产于锆石边部,颜色较暗且不具环带,具有最低的Th/U比值,最高的U含量和较高的∑REE、LREE含量,获得的年龄反映了后期区域变质作用事件。因此,都龙-Song Chay穹隆核部的花岗质杂岩大部分实为前寒武纪地壳物质在加里东期深熔作用的产物,并受到了印支运动的影响。

Dulong-Song Chay dome lies on the border of China and Vietnam,and migmatization developed in its core complex.Study on Cathodoluminescence,U-Pb chronology and trace elements distributions of zircons in migmatitic gneiss and leucogranite show that zircons could be divided into three types:according to their complex internal structure,i.e inherited zircon,anatectic zircon,metamorphic accretive zircon.The cores of zircon are protolith inherited zircons with light color,the highest Th/U ratios,the lowest U contents,higher∑REE and LREE content.The obtained age is Precambrian which represents the age of protolith.The anatectic zircons have oscillatory zoning,with second highest Th/U ratios,the lowest∑REE and LREE contents.The 206Pb/238U ages tested from the migmatitic gneiss and leucogranite are 422±6 Ma and 423±6 Ma respectively,which represent the time when Dulong-Song Chay dome was deeply molten and which were consistent with the time of the regional collision-magma events.Metamorphic and accretive zircons occur in the edges of zircons of dark color and without zoning and the lowest Th/U ratios,highest U contents and the higher∑REE and LREE contents.These obtained ages reflect the influence of later regional metamorphism.We concluded that most of the granitic complex in the core of Dulong-Song Chay dome were anatectic products from Precambrian crustal materials during Caledonian movement and were influenced by Indosinian movement.