华北克拉通南缘太华群铁山庙铁矿床沉积时代的约束-锆石U-Pb定年及Hf同位素证据  

Depositional Time of the Tieshanmiao Iron Ore Deposit in the Taihua Complex,Southern Margin of the North China Craton:Constraint from Zircon U-Pb Dating and Hf Isotope Evidence

作　　者：孟洁 李厚民[2] 李立兴[2] 李洁茹 

机构地区：[1]地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083 [2]国土资源部成矿作用与资源评价重点实验室,中国地质科学院矿产资源研究所,北京100037 [3]中国地质大学长城学院,河北保定071000

出　　处：《地质学报》2018年第1期125-141,共17页Acta Geologica Sinica

基　　金：本文为国家自然科学基金项目(编号41672078)和国地质科学院矿产资源研究所基本科研业务费(编号K1410)资助的成果.

摘　　要：华北克拉通南缘舞阳地区分布有大型铁矿床,赋存于早前寒武纪的太华群变质岩系中。铁山庙铁矿床在舞阳铁矿区分布广泛,大小矿体包括经山寺、冷岗、铁山庙、铁古坑以及岗庙刘等,产出层位为铁山庙组。近年来对铁山庙铁矿床的研究程度较高,不少学者认为其为Superior BIF型铁矿床,但是对于铁山庙铁矿床原始沉积年龄显见报道。本文通过选取穿切铁古坑铁矿体的混合岩化钾长花岗岩以及矿体顶板围岩辉石黑云斜长片麻岩为研究对象,利用SHRIMP锆石U-Pb定年以及原位Hf同位素测试分析技术,以此来约束铁山庙铁矿床沉积时代的上限和下限。结果显示,两个样品中的锆石均记录了两组年龄数据,且在误差范围内明显具有一致性。较老一组^(207)Pb/^(206)Pb年龄为2463~2478Ma,较新一组为1918~1961Ma。此外,混合岩化花岗岩中较老锆石的ε_(Hf)(t)变化范围为-6.96^-12.83,较新锆石的ε_(Hf)(t)为-7.19^-15.75,两类锆石的ε_(Hf)(t)值变化范围相似,说明较老锆石为继承锆石,其年龄可能代表源区岩石的形成时代,而较新锆石为变质锆石,代表深熔作用锆石发生重结晶作用的时间,即混合岩化花岗岩的形成时代;辉石黑云斜长片麻岩中较老一组锆石的ε_(Hf)(t)值为-0.55~2.75,较新一组锆石的ε_(Hf)(t)为-5^-10.06,两类锆石的ε_(Hf)(t)值差别很明显,较老一组锆石是碎屑锆石,其年龄可以约束原岩沉积的最大年龄,而较新一组锆石为变质增生成因,其年龄代表了岩石经历的一期变质事件。综合分析,铁山庙铁矿床的沉积时代可以约束在2.46~1.96Ga之间,很可能在2.3Ga左右,之后于~1.96Ga经历了强烈的区域变质作用。The Wuyang area in the southern margin of the North China Craton （NCC） hosts several large-sized iron deposits, which occur mainly in the early-Precambrian Taihua Complex. The Tieshanmiao iron ore deposit covers most of the Wuyang area, with various sized orebodies distributed mainly in Jingshansi, Lenggang, Tieshanmiao, Tiegukeng and Gangmiaoliu. The Tieshanmiao Formation is major ore-hosting strata. Recently, a large amount of study has been carried out for the Tieshanmiao iron ore deposit, and many workers believe that it belongs to Superior BIF-type iron deposit. But there has been no report about the primary sedimentary age of the Tieshanmiao iron deposit. In this study, migmatitic granite cutting through Tiegukeng orebody and clinopyroxene-biotite-plagioclase gneiss from the roof rock of the orebody were collected to constrain the upper and lower limits of metallogenic deposition time using SHRIMP zircon U-Pb dating and in-situ Hf isotope techonolgy. The results reveal that the zircons of the two samples record two groups of age data, with the error ranges being in consistency. The 207 pb/206 Pb age of the old group is 2463-2478 Ma, and that of the new group 1918-1961 Ma. Besides, the era（t） ranges from --6.96 to --12.83 in the old zircons, and from --7.19 to --15.75 in the new ones, of the migmatitic granite, two of which show consistent ranges, indicating that the old zircons belong to inherited genetic type, and the new ones to metamorphic genetic types. The old ages possibly represent the formation time of the source rock, and the new ages indicate the metamorphic recrystallization time during anataxis process, meaning the age of the formation time of the migmatitic granite. In the clinopyroxene-biotite- plagioclase-gneiss, the εHf（t） value ranges between --0.55 and 2.75 in the old zircons and between --5 and --10.06 in the new zircons. Both of the εHe（t） values differ distinctly, with the age of old detrital zircons constraining the maximum age of protolith rock and the age of new met

关 键 词：舞阳铁山庙铁矿 太华群 SHRIMP锆石U-PB定年 原位锆石Hf同位素 年代学研究 

分 类 号：P618.31[天文地球—矿床学]