冀北单塔子杂岩的地质学和锆石U-Pb年代学

Geology and Zircon U-Pb Isotopic Chronology of Dantazi Complex, Northern Hebei Province

冀北单塔子杂岩位于华北克拉通北缘中段隆化-赤城断裂以南,主要由高角闪岩相-麻粒岩相变质的英云闪长质、奥长花岗质、花岗闪长质片麻岩(TTG岩套)和铁镁质二辉麻粒岩、辉石斜长角闪岩、石榴石斜长变粒岩、石榴石夕线石黑云母片岩及少量的大理岩等表壳岩残留体组成。详细的SHRIMP和LA-ICPMS锆石U-Pb同位素地质年代学研究表明,冀北单塔子杂岩的形成主要经历了7个演化阶段:(1)2600～2530Ma之间形成了单塔子杂岩中英云闪长质和奥长花岗质片麻岩的围岩,其中一部分铁镁质表壳岩,即铁镁质二辉麻粒岩,可能为英云闪长质—奥长花岗质岩浆的源岩;(2)2517～2505Ma主要为英云闪长质岩浆的侵位结晶阶段;(3)2494～2473Ma,奥长花岗质片麻岩侵位结晶;(4)2427～2404Ma,发生了早期麻粒岩相变形变质作用和深溶混合岩化作用,使这一杂岩经历了强烈的改造;(5)～1859Ma,铁镁质岩浆侵位,形成一些铁镁质岩株和岩脉;(6)～1834Ma到1793Ma,单塔子杂岩经历了最强烈的变质作用改造,形成了晚期麻粒岩相变质作用;(7)～1730Ma经历了强烈的流体活动,使得一些锆石发生了流体交代和改造。但是总体上单塔子杂岩没有经历～300Ma的古生代的变质作用。

The Dantazi complex in northern Hebei province, located in the middle segment of northern margin of the North China Craton, consists of the tonalitic, trondhjemitic and granodioritic gneisses （TTG） metamorphosed in high amphibolite facies to granulite facies, and a supracrustal rock association of mafic two-pyroxene granulites, clinopyroxene amphibolites, garnet plagioclase fine-grained gneisses, garnet sillimanite biotite schists and minor marbles. Detailed studies in SHRIMP and LA-ICPMS zircon U-Pb isotopic chronology reveal that the Dantazi complex experienced seven stages of evolution： （1） 2 600-2 530 Ma, the formation of the country rocks of the TTG gneisses, including some mafic supracrustal rocks that might be sources of the TTG magma; （2） 2 517-2 505 Ma, tonalitic magma emplaced and. crystallized; （3） 2 494-2 473 Ma, trondhjemitic magma emplaced and crystallized; （4） 2 427-2 404 Ma, the plutonic and supracrustal lithological associations in the complex were metamorphosed and deformed in high amphibolite facies to granulite facies （earlier stage） and reworked; （5） -1 859 Ma, mafic magma emplaced, forming some mafic dykes and stocks; （6） -1 834 Ma to 1 793 Ma, the Datazi complex experienced an intensive regional metamorphism in granulite facies （later stage）; （7） -1 730 Ma, the complex was altered by intensive activation of geological fluids. However, there is no -300 Ma Paleozoic age record in all the samples analyzed for zircon U-Pb isotopic chronology, suggesting that the Dantazi complex did not experience the Paleozoic metamorphism.