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白云鄂博矿床基底岩石的年代学研究及其地质意义
引用本文:刘健,李印,凌明星,孙卫东.白云鄂博矿床基底岩石的年代学研究及其地质意义[J].地球化学,2011,40(3):209-222.
作者姓名:刘健  李印  凌明星  孙卫东
作者单位:1. 浙江省第十一地质大队,浙江温州,325006
2. 中国石油天然气管道工程有限公司,河北廊坊,065000
3. 中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州,510640
4. 中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州,510640;中国科学技术大学地球和空间科学学院,安徽合肥,230026
摘    要:白云鄂博裂谷带发育于古老基底之上,并在裂谷带中形成了白云鄂博超大型REE-Nb-Fe矿床.但是由于古老基底在白云鄂博矿区出露较少,研究工作开展不多.本研究对象是华北克拉通北缘白云鄂博地区宽沟断裂东段被第四纪沉积层覆盖的冲沟中的基底片麻岩.主元素特征是,SiO2含量介于47.07%~79.10%之间,低钛,低钙,Al2O...

关 键 词:基底岩石  年龄  白云鄂博  华北克拉通

Chronology and geological significance of the basement rock of the giant Bayan Obo REE-Nb-Fe ore deposit
LIU Jian,LI Yin,LING Ming-xing,SUN Wei-dong.Chronology and geological significance of the basement rock of the giant Bayan Obo REE-Nb-Fe ore deposit[J].Geochimica,2011,40(3):209-222.
Authors:LIU Jian  LI Yin  LING Ming-xing  SUN Wei-dong
Institution:3,4 1.The 11th Geological Team of Zhejiang Province,Wenzhou 325006,China; 2.China Petroleum Pipeline Engineering Corporation,Langfang 065000,China; 3.State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China; 4.School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China
Abstract:The Bayan Obo rift valley zone,the host of the giant Bayan Obo REE-Nb-Fe ore deposit,developed on an old basement.The studied basement rocks were sampled from a newly exposed gully along the Kuangou fault,where the basement rock is covered by Quaternary sediments.These samples have low TiO2 and CaO with varied major elements,e.g.,SiO2 ranges between 47.07%–79.10%,total alkali between 3.35%–7.51%,R-index(σ=(K2O+Na2O)2/(SiO2–43)) between 0.31–13.9,and the A/CNK ratio,1.24–2.65.They are enriched in LILE and LREE,and depleted in HFSE and HREE,with negative Eu anomaly,which implies the basement rocks originated from crustal sources.Protolith recovery diagrams indicate that the samples contain both orthogneiss and paragneiss.Also,the basement is not related to mineralization,based on the geologic and geochemical characteristics.The SIMS zircon U/Pb ages range from 2914±20 to 1946.0±4.4 Ma.Most of the ages distribute on the concordant line,and can be grouped into 3.Most ages are close to 2.0 Ga,which can be divided into 3 subgroups: 1950–2000 Ma,2000–2050 Ma,2050–2100 Ma.The first one most likely represents metamorphic age,as they distribute on the edge of zircons,with low Th/U.The others likely represent formation age of rocks(with a weighted mean of 2029±54 Ma),as they distribute on the mantles or cores of zircon grains,with high Th/U,representing the formation age of the basement.It also gives the upper limit of Bayan Obo group stratum.The other ages also reflects two magmatism events as suggested by high Th/U.These ages provide new constraints on the geologic evolution of the Bayan Obo rift valley zone and the history of North China craton.
Keywords:basement rock  age  Bayan Obo  North China craton
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