冀东地区含大量始太古代碎屑锆石的太古宙铬云母石英岩再次发现及地质意义  

The geological significance of the rediscovered fuchsite quartzite with abundant Eoarchean detrital zircons in eastern Hebei Province

作　　者：初航[1] 王惠初[1] 荣桂林 常青松[1] 康健丽[1] 靳松 肖志斌[1] 

机构地区：[1]天津地质矿产研究所,天津300170 [2]河北省地质调查院,石家庄050081

出　　处：《科学通报》2016年第20期2299-2308,共10页Chinese Science Bulletin

基　　金：中国地质调查局地质调查项目(12120114076301);国家自然科学基金(41572046)资助

摘　　要：冀东卢龙地区新发现的铬云母石英岩为产自冀东太古宙基底中的巨大透镜体（残块）,构造位置接近元古宙长城系地层与太古宙基底的不整合之下,与冀东曹庄地区铬云母石英岩产状类似.对其年代学研究发现,卢龙地区铬云母石英岩中碎屑锆石年龄范围为3200~3800 Ma,表明铬云母石英岩形成的年代应小于3200 Ma,这与迁安曹庄地区出露的曹庄组铬云母石英岩中碎屑锆石相同.说明这种含有始太古代碎屑锆石的铬云母石英岩在冀东地区可能还有更广泛的分布.此前认为两个地区铬云母石英岩的围岩分别属于两个不同的构造单元（迁西群和滦县群）,但本文新发现的相近年代数据说明这两个岩群可能位于同一构造背景下的同一层位.卢龙地区铬云母石英岩的年代学研究为理解冀东地区太古宙地质构造提供了更多信息.A new fuchsite quartzite block was discovered in Lulong in the east of the Hebei Province. The fuchsite quartzite, structurally contacting with various rocks including metamorphic gabbro, feldspar biotite schist and feldspar quartzite, all together constitute massive lenses enclosed in monzonitic granite that intruded into the Archaean basement. The occurrence of the complex was just below the unconformity between the Proterozoic Changcheng Group and Archaean basement, which is quite similar to the fuchsite quartzite discovered in the adjacent Caozhuang area about 40 km to the west Lulong. The detrital zircons in fuchsite quartzite of Lulong area are light brown, rounded with typical detrital zircon features, demonstrating prominent characteristics of long-distance transportation. Most of the zircon grains were of magmatic origin with oscillation internal belts and high Th/U values, implying a provenance of granitic rocks. The U-Pb ages of the detrital zircon scattered in the range of 3200–3200 Ma, which constrain the maximum deposition age of the fuchsite quartzite should be less than 3200 Ma. The maximum age of single zircon was 3960 Ma, which implies the possible existence of 3900 Ma detrital supracrust in the eastern Hebei Province. The age distribution of the detrital zircons is similar to that of the fuchsite quartzite in Caozhuang Group in Caozhuang, Qian＇an. Considering this similarity of the detrital zircon of fuchsite quartzite from the two different sites, it could be inferred that this kind of fuchsite quartzite with Eoarchean detrital zircons might have a wider distribution in eastern Hebei Province than thought before. In previous studies, the wall rocks of the fuchsite quartzite in the two different regions were assumed belong to two separate structural units： Qianxi Group and Luanxian Group. However the new data in this paper indicate these two complex groups have similar detrital zircon age spectra, which suggests the two groups might locate in the same stratigraphic horizon of the same str

关 键 词：铬云母石英岩 太古宙 卢龙 冀东 

分 类 号：P597.3[天文地球—地球化学]