辽东弓长岭—岫岩地区古元古界辽河群变沉积岩的物源及构造背景

Provenance and Tectonic Setting of the Paleoproterozoic Metasedimentary Rocks from the Liaohe Group in Gongchangling-Xiuyan Area,East Liaoning Province

辽东弓长岭—岫岩地区位于胶—辽—吉造山带东段,区内发育厚层古元古代变质沉积岩系,本文对这些变质沉积岩进行了岩相学和U-Pb年代学等方面的研究。岩相学特征显示这些岩石变质程度普遍偏低,多为绿片岩相变质条件,未发现高级特征变质矿物。岩石中主要矿物颗粒为石英,其中北辽河群碳酸盐矿物较为发育。根据辽东弓长岭岫岩地区古元古代变沉积岩碎屑锆石阴极发光(CL)图像,这些锆石普遍具有清晰的振荡环带和较高的Th/U值(>0.3),表明其原岩来自岩浆岩。结合LA-ICPMS U-Pb年代学,得到里尔峪组、高家峪组、大石桥组和盖县组碎屑锆石分别呈现出2159、2500、2189/2530和2044/2197Ma的年龄峰值,表明其沉积物来源于古元古代花岗质岩石和相邻的太古宙杂岩。结合前人资料,本文认为南、北辽河岩群形成于相同的环境并经历了相同的构造演化过程,古元古代弧-陆碰撞模式可能更适用于胶—辽—吉造山带的构造演化。

Gongchangling-Xiuyan area is located in the eastern part of the Jiao-Liao-Ji orogenic belt,where thick layers of the Paleoproterozoic metasedimentary rocks are developed.We studied on these metamorphic sedimentary rocks in petrography and zircon U-Pb chronology.The petrographic characteristics show that the metamorphic degree of these rocks is low,overall greenschist facies metamorphism with no highly metamorphosed minerals formed.Quartz is the main mineral in the rocks,and carbonate minerals are common in the North Liaohe Group.The distinct oscillatory zoning and high Th/U ratios(>0.3)of detrital zircons in the Paleoproterozoic metasedimentary rock suggest these zircons are of magmatic origin.Combining the data of U-Pb geochronology,we found that detrital zircons from the Li’eryu,Gaojiayu,Dashiqiao and Gaixian Formations yield age peaks at 2159 Ma,2500Ma,2189/2530Ma,and 2044/2197Ma,respectively,indicating that their sediments are from the Liao-Ji Paleoproterozoic granitoids and the adjacent Archean complex.Combining the data of previous researches,We considered that the South and North Liaohe Groups formed in the same tectonic setting and underwent the same evolution process.Therefore,the Paleoproterozoic arc-continent collision model may be more applicable to interpret the evolution of the Jiao-Liao-Ji orogenic belt.