吉南夹皮沟地区变质侵入岩的锆石U-Pb定年、Lu-Hf同位素分析及其构造意义

Zircon U-Pb dating and Lu-Hf isotope analysis of metamorphic intrusive rocks in the Jiapigou area of southern Jilin Province and their tectonic implications

吉南夹皮沟变质地体作为华北克拉通东北部太古宙基底的重要组成部分,其新太古代到古元古代的构造演化过程一直存在争议。为此,在详细野外地质调查基础上,选择三种代表性变质侵入岩,开展了锆石稀土微量元素、锆石U-Pb定年与Lu-Hf同位素分析工作。结果显示:夹皮沟地区紫苏花岗岩的侵位年龄为2504±8Ma,并记录有2476±13Ma的变质年龄;其锆石Hf模式年龄介于2.82~2.66Ga之间,εHf(t)值介于1.72~5.1之间,反映为新生地壳物质再循环的产物。变辉长岩体(斜长角闪岩)的侵位年龄为2529±14Ma,并记录有2484±23Ma的变质年龄。变基性岩墙(石榴角闪岩)的侵位年龄为2214±18Ma,并记录有1930±16Ma的变质年龄;其岩浆锆石具有异常高的εHf(t)值(7~15),并存在明显的重稀土亏损现象,推测其母岩浆来源于富含石榴石的岩石圈地幔。综合多种信息,认为吉南地区新太古代末期(2.50~2.48Ga)构造热事件受大规模地幔柱活动控制,古元古代中晚期(2.2~1.84Ga)构造热事件可能源于克拉通边缘板块俯冲引起的碰撞造山作用。

The Jiapigou metamorphic terrane is an important part of the Archean basement in the northeast of the North China Craton,whose tectonic evolution from Neoarchean to Paleoproterozoic remains controversy for a long time.Based on detailed field geological investigation,three representative metamorphic intrusive rocks involving charnockite,metagabbro and metabasic dyke in the Jiapigou area were studied on zircon REE,zircon U-Pb chronology and zircon Lu-Hf isotope geochemistry.The results suggest that the emplacement age of charnockite was determined as 2504±8Ma with metamorphic age of 2476±13Ma.Its zirconεHf(t)values are 1.72~5.1 with Hf model ages of 2.82~2.66Ga,indicating that the rock derived from partial melting of juvenile crust.The emplacement age of meta-gabbro(amphibolite)was determined as 2529±14Ma with a metamorphic age of 2484±23Ma.The meta-basic dyke(garnet amphibolite)has an emplacement age of 2195±15Ma and a metamorphic age of 1930±14Ma.The magmatic zircons from the meta-basic dyke show abnormally highεHf(t)values(7~15)and significant depletion of heavy REE,indicating that the parent magma was originated from the garnet-bearing lithospheric mantle.Combining other geological information,it can be concluded that the tectonic thermal event during the Late Neoarchean(2.50~2.48Ga)in the southern Jilin region was dominated by large-scale mantle plume.The middle to late Paleoproterozoic(2.2~1.84Ga)tectonic thermal event was related to collisional orogeny occurred in the edge of the craton.