华北克拉通～2.7Ga的BIF:来自莱州-昌邑地区含铁建造的年代学证据  

Identification of - 2. 7Ga BIF in North China Craton： Evidence from geochronology of iron-bearing formation in Laizhou-Changyi area, Jiaobei terrane.

作　　者：王惠初 康健丽 任云伟 初航 陆松年[1] 肖志斌 

机构地区：[1]中国地质调查局天津地质调查中心,天津300170

出　　处：《岩石学报》2015年第10期2991-3011,共21页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(1212011120154;12120114034201);国家自然科学基金重点项目(41430210)联合资助

摘　　要：越来越多的研究资料显示～2.7Ga是华北克拉通陆壳生长的一个重要阶段,但缺少同时期的世界主要克拉通上广泛发育的BIF铁矿。胶北莱州-昌邑地区的BIF铁矿赋存在原划分的粉子山群小宋组含铁建造中,含铁建造的岩石组合主要为黑云斜长变粒岩、斜长角闪岩、含石榴黑云片岩夹角闪磁铁石英岩,磁铁浅粒岩。岩石地球化学分析显示,斜长角闪岩具有岛弧玄武岩的地球化学特点,变质酸性火山岩具有埃达克质岩的地球化学特点,故推测莱州-昌邑地区的含铁建造形成于与岛弧相关的构造环境,而与粉子山群形成的裂谷构造背景无关。锆石同位素年代学研究表明,含铁建造中变质酸性火山岩（埃达克质火山岩）的岩浆结晶年龄为2726±10Ma,在变质泥砂岩中获得了～2.73Ga和～2.9Ga两组碎屑锆石U-Pb年龄,并缺少新太古代晚期（～2.5Ga）的构造岩浆热事件信息;在斜长角闪岩中获得的变质锆石年龄为～1850Ma,并有〉2.68Ga的继承或捕获锆石年龄信息;因此推断莱州-昌邑地区的BIF铁建造有可能形成于新太古代早期（～2.7Ga）,而在新太古代晚期（～2.5Ga）则处于相对稳定的构造背景。含铁建造被～2.17Ga的二长花岗岩侵入,并共同卷入胶北古元古代晚期（～1.85Ga）的变质变形作用改造。莱州-昌邑地区含铁建造的岩石组合和锆石年龄信息与胶北地块栖霞地区比较有所不同,这可能揭示出胶北地块在新太古代早期（～2.7Ga）构造环境差异和古板块构造演化的重要信息。Abundant previous studies show the Early Neoarchean （ --- 2.7Ga） is an important continental crust growth period within the North China Craton. However,--2.7Ga banded iron formation （BIF）, which were well developed as huge iron deposits in other major cratons worldwide, has not yet been identified within the North China Craton. The BIF iron deposit occurred in the Xiaosong Formation of Laizhou-Changyi area, Jiaobei terrane, is commonly considered as the bottom layer of the Paleoproterozoic Fenzishan Group. As previous and present studies, the iron-bearing assemblage within the Xiaosong Formation consists mainly of biotite- plagioclase leptite, amphibolites, garnet-bearing biotite schist with thin layers of hornblende-magnetite quartzite and magnetite-bearing leucoleptite. Geochemical data reveal that the amphibolite and meta-acidic volcanic rock show protolith characteristics of island arc basalt and adakitic rock, respectively. These features imply that the iron-bearing formation in Laizhou-Changyi area was likely generated within an island-arc setting similar to the modern regime, but distinguished from the rift environment of Paleoproterozoic Fenzishan Group. Geochronological data display that the magmatic zircons from a meta-acidic volcanic rock （biotite-plagioclase leptite） sample present a protolith age of -2726- 10Ma. In contrast, detrital zircons separated from a metamorphic sandstone sample show two major inherited age peaks of --2. 73Ga and - 2. 9Ga, and zircons from an amphibolite sample record a meaningful --1850Ma metamorphic age with a few 〉 2. 68Ga ages recorded in inherited or captured zircons. However, three samples mentioned above are lack of a record of --2. 5Ga tectonic-thermal event as the basement of the Jiaobei terrane. In combination with the zircon U-Pb ages, rock association and geochemical features, it is inferred that the BIF in Laizhou-Changyi area was formed at the Early Neoarchean （ -2. 7Ga）, and subsequently kept in a relatively stable tectonic environment at Late

关 键 词：~2.7Ga条带状铁建造 新太古代早期 锆石U-PB年龄 胶北 华北克拉通 

分 类 号：P597.3[天文地球—地球化学] P618.31[天文地球—地质学]