云开变质杂岩新元古代深熔作用：混合岩锆石U-Pb年代学证据

Neoproterozoic Anatexis of the Yunkai Metamorphic Complex:Evidence from U-Pb Geochronology of Zircon in Migmatite

为确定云开地块前寒武纪变质基底(云开变质杂岩)的混合岩化作用时间,对天堂山岩群中混合岩的基体和脉体进行了锆石LA-MC-ICP-MS U-Pb定年研究。结果表明,混合岩基体的原岩年龄为1086±24Ma;混合岩脉体锆石变质增生边的同位素年龄为852.6±8.8Ma,这代表了深熔(混合岩化)作用的年龄。上述年龄证明云开地区存在中元古代的变质基底和新元古代的深熔事件,该事件与区域上四堡运动的时间基本一致,说明其可能为扬子板块与华夏板块发生拼合作用的地质记录。

In order to determine the migmatization time of the Precambrian metamorphic basement（the Yunkai metamor-phic complex）of the Yunkai terrain,a study of LA-MC-ICP-MS U-Pb dating of zircon in matrixes and felsic veins of mig-matites from the Tiantangshan Group.Results show that the inherited magmatic cores of zircon grains from the matrix of migmatite have oscillatory zoning and yield a U-Pb age of 1086 ±24Ma,representing the protolith age,whereas the metamprohic rims of zircon grains from the felsic vein of migmatite yield an age of 852.6±8.8Ma,representing the timing of the anatexis（migmatization）.These results imply that there is a Mesoproterozoic metamorphic basement with a Neoprot-erozoic anatexis event in the Yunkai area.The timing of this anatexis event is consistent with that of the Sibao Movement. Therefore,we conclude that the timing of the anataxis could be an important geological record for the amalgamation of the Yangtze and Cathaysian blocks.