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地球深部真的贫铀钍吗?——来自秦岭造山带加里东期岩浆岩体锆石铀钍含量的讨论
投稿时间:2020-12-08  修订日期:2021-04-30  点此下载全文
引用本文:伍皓,李小刚,吴晨,夏彧,周恳恳,熊国庆,姚雪婷.2021.地球深部真的贫铀钍吗?——来自秦岭造山带加里东期岩浆岩体锆石铀钍含量的讨论[J].地质论评,67(5):1207-1230,[DOI]:.
WU Hao,LI Xiaogang,WU Chen,XIA Yu,ZHOU Kenken,XIONG Guoqing,YAO Xueting.2021.Uranium and thorium elements are loss in the deep inside the earth?——Disscusion from the uranium and thorium contents of zircon minerals from the Caledonian igneous plutons in the Qinling Orogen[J].Geological Review,67(5):1207-1230.
DOI:10.16509/j.georeview.2021.04.306
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作者单位E-mail
伍皓 中国地质调查局成都地质调查中心成都610081 wuhaocgs@sohu.com 
李小刚 重庆科技学院复杂油气田勘探开发重庆市重点实验室重庆401331 xg_lee@cqust.edu.cn 
吴晨 中国科学院青藏高原研究所青藏高原地球系统科学国家重点实验室北京100101  
夏彧 中国地质调查局成都地质调查中心成都610081  
周恳恳 中国地质调查局成都地质调查中心成都610081  
熊国庆 中国地质调查局成都地质调查中心成都610081  
姚雪婷 重庆科技学院复杂油气田勘探开发重庆市重点实验室重庆401331  
基金项目:本文为中国地质调查局二级项目(编号:DD20190122)、重庆市自然科学基金资助项目(编号:cstc2013jcyjA90017、cstc2017jcyjA1300、cstc2020jcyj-msxmX0487)和重庆科技学院大学生科技创新训练计划项目(编号:2019042,2020006)的成果
中文摘要:为尝试利用锆石来初步探索地球内部铀、钍的丰度,通过搜集秦岭造山带加里东期岩浆岩体锆石U-Th-Pb同位素测年文献,掌握了3件超基性岩、52件基性岩、46件中性岩、90件酸性岩,共计191件样品,6979个(铀含量数据3552个,钍含量数据3427个)锆石定年数据。数据分析指示铀和钍在同一类型岩浆岩锆石中含量均相差悬殊,可在不同类型岩浆岩锆石中富集或亏损,不具有从超基性岩到基性岩到中性岩再到酸性岩总体增加的趋势。在所有样品锆石铀、钍平均值2倍以上的45件高富集样品中的34件呈现“局部长期”分布的特征,表现为:10件在451.0~422.1 Ma期间的以OIB型基性、中基性岩为主的样品约29 Ma时间集中产出在南秦岭大巴山地区,岩浆多来自由HIMU,EMII和EMI三个富集地幔端元组分混合而成的复杂地幔区;24件在495.9~413.6 Ma期间的以I型、S-I型酸性岩为主的样品约82 Ma时间集中产出于北秦岭商丹(商南—丹凤)地区,岩浆可来自地幔、壳幔混合和地壳源区。结合华南金属铀(0价)的发现等前人研究成果初步分析认为,加里东期大巴山和商丹地区可能分别存在地幔柱和大陆型热点,地核中大量铀、钍沿地幔柱和大陆型热点上升致使地幔和地壳局部熔体中铀、钍长期富集,其超高含量可能被熔体中锆石结晶部分记录,这一元素迁移过程可能是两区域产出高锆石铀、钍含量样品和商丹地区生成铀矿的主要原因。支持铀、钍可在地核和地幔柱富集的认识。
中文关键词:秦岭造山带  加里东期岩浆岩体  锆石铀、钍含量  地核  地幔柱  大陆型热点
 
Uranium and thorium elements are loss in the deep inside the earth?——Disscusion from the uranium and thorium contents of zircon minerals from the Caledonian igneous plutons in the Qinling Orogen
NameInstitution
WU HaoChengdu Center,China Geological Survey,Chengdu,610081
LI XiaogangChongqing Key Laboratory of Complex Oil & Gas Exploration and Development,Chongqing University of Science & Technology,Chongqing,401331
WU ChenState Key Laboratory of Tibetan Plateau Earth System Science (LATPES),Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing,100101
XIA YuChengdu Center,China Geological Survey,Chengdu,610081
ZHOU KenkenChengdu Center,China Geological Survey,Chengdu,610081
XIONG GuoqingChengdu Center,China Geological Survey,Chengdu,610081
YAO XuetingChongqing Key Laboratory of Complex Oil & Gas Exploration and Development,Chongqing University of Science & Technology,Chongqing,401331
Abstract:In an attempt to use zircon to preliminarily explore the abundance of uranium and thorium in the earth's interior,3 ultramafic samples,52 mafic samples,46 intermediate igneous samples,and 90 acid igneous samples,totaling 191 samples with 6,979 zircon dating data (3,552 for U and 3,427 for Th),were mastered by collecting the U-Th-Pb isotopic dating in the literature invovled about Caledonian igneous zircons from the Qinling Orogen.The data results indicate that the U content in zircon in the same type igneous samples are quite different,as well as the Th,and both can be enriched or loss in different types of magmatic zircons, without the overall increasing trend from ultramafic,mafic,intermediate,to acid rocks.In addition,in all samples,45 highly enriched samples with an average U and Th contents more than 2 times,34 of which exhibit the characteristics of "local long-term" distributions as follows:ten 451.0~422.1 Ma mainly of OIB type mafic and intermediate igneous samples from Daba Shan area of the southern Qiling Orogen,most of which show the magma were derived from mantle magma source of HIMU,EMII and EMI;twenty-four 495.9~413.6 Ma mainly of I-type and S-I type acid igneous samples collected from the northern Qinling Shangdan (Shangnan-Danfeng) area,most of which show the magma were derived from mantle,crust-mantle and crustal source areas.Combined with the discovery of U metal (0 valence) in South China and other previous researches,it is preliminary belived that a mantle plume and a continental hot spot exsit in Daba Shan and Shangdan area during Caledonian period,respectively,and a large amount of U and Th in the earth's core rise along the mantle plume and continental hot spots,resulting in long-term enrichment of U and Th in the local melts of mantle and crust,the ultrahigh contents of which are partly recorded by zircons in the melting,this process of element migration may be the main reason for producing high zircon U and Th samples in these two areas, and the reason for generating U deposits in Shangdan area.Our results possibilily support the hypothesis that U and Th could be enriched both in the core and mantle plumes.
keywords:Qinling orogen  caledonian igneous plutons  uranium and thorium contents in zircon minerals  Earth’s core  mantle plumes  continental hot spots
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