华北克拉通古老物质记录——焦作地区太古宙变质岩的锆石SHRIMP U-Pb定年和LA-MC-ICPMS Hf同位素分析  

Ancient Material Records in the North China Craton:SHRIMP U-Pb Dating and LA-MC-ICPMS Hf analysis of zircons from Archean Metamorphic Rocks in the Jiaozou Area,Henan

作　　者：殷小艳[1] 周红英[2] 刘敦一[3,4] 高林志 董春艳[3,4] 万渝生[3,4] 

机构地区：[1]中国地质科学院,北京100037 [2]中国地质调查局天津地质矿产研究所,天津300170 [3]中国地质科学地质研究所,北京100037 [4]北京离子探针中心,北京100037

出　　处：《地质论评》2015年第1期183-194,共12页Geological Review

基　　金：中国地质调查局项目(编号12120114021301;12120113013700;1212010811033)的成果

摘　　要：本文报道了华北克拉通中部焦作地区太古宙变质岩的锆石U-Pb定年和Hf同位素分析结果。二云钾长片麻岩的碎屑锆石和变质锆石年龄分别为3.3~3.4 Ga和2.47±0.02 Ga,碎屑锆石的ε_(Hf)(3.40Ga)和t_(DM2(CC))。值分别为-2.4^+13.9和2.89~3.84 Ga,变质锆石的ε_(Hf)(2.47Ga)和t_(DM2(CC))值分别为-18.8^-6.4和3.38~4.13 Ma。黑云角闪片麻岩中只存在变质锆石,年龄为2.49±0.01 Ga,变质锆石的ε_(Hf)(2.49Ga)和t_(DM2(CC))值分别为~15.0^-3.8和3.23~3.91 Ga。结合地球化学和前人研究成果,可得出如下结论:①碎屑物质来自以3.4 Ga花岗质岩浆岩为主的物源区,物源区岩石具有相当的规模,是壳幔混合作用的产物,形成过程中有更古老(始太古代)陆壳物质参与;②岩石遭受约2.5 Ga强烈构造热事件作用,深熔作用导致花岗质脉体形成;③可把变质碎屑沉积岩形成(沉积)时代限制在2.5~3.3 Ga之间;④变质锆石的Hf同位索组成与核部锆石的十分类似,变质增生边主要形成于核部锆石的溶解—再沉淀作用。We present an integrated study of zircon U-Pb dating and O--Hf isotopic analysis on metamorphic rocks in the Jiaozuo area, Henan, central North China Craton. A two-mica K-feldspar gneiss sample contains 3.3 ~ 3.4 Ga detrital zircon and 2.47± 0.02 Ga metamorphic zircon. The detrital zircon has enf （3.40Ga） and tDM2（CC） ranging from -2.4 to 13.9 and 2.89 to 3.84 Ga, respectively; whereas the metamorphic zircon has enf （2.47Ga） and tDM（CC） ranging from -18.8 to -6.4 and 3.38 to 4.13 Ga, respectively. A biotite hornblende gneiss sample only contains metamorphic zircon with an age of 2.49 ±0. 01 Ga and 8nf（2.49Ga） of -15.0 to - 3.8 and tDM2（Cc） of 3.23 to 3.91 Ga. Combined with geochemical data and early studies, some conclusions can be drawn as follows. （ 1 ） Detrital sediments were derived from a source region where 3.4 Ga granitoidic rocks widely occurred, formed as a result of mixture of mantle and crustal material ; （2） the sedimentary rocks underwent a strong tectono--thermal event at the end of the Neoarchean （ ~ 2.5 Ga）, with anatexis resulting in the formation of granite veins ; （ 3 ） the formation （deposition） time of the metasedimentary rocks can be limited to between 2.5 ~ 3.3 Ga; （4） metamorphic zircon is similar in Hf isotope composition to the detrital zircon, suggesting that the overgrowth rims were formed through the dissolution--reprecipitation of zircon cores.

关 键 词：古太古代 变质沉积岩 SHRIMP定年 Hf同位素 华北克拉通 

分 类 号：P597.3[天文地球—地球化学] P588.3[天文地球—地质学]