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江西相山铀矿田燕山期岩浆活动的多阶段性及其意义
投稿时间:2018-04-22  修订日期:2018-08-13  点此下载全文
引用本文:彭中用,陈卫锋,毛玉锋,方启春,唐湘生,凌洪飞.2018.江西相山铀矿田燕山期岩浆活动的多阶段性及其意义[J].地质论评,64(6):1413-1437,[DOI]:.
PENG Zhongyong,CHEN Weifeng,MAO Yufeng,FANG Qichun,TANG Xiangsheng,LING Hongfei.2018.Multiple Episodes of the Yanshanian Magmatism in Xiangshan Uranium Ore-field, Jiangxi[J].Geological Review,64(6):1413-1437.
DOI:
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作者单位E-mail
彭中用 1)内生金属矿床成矿机制研究国家重点实验室南京大学南京210023 pengzhongyong0502@foxmail.com 
陈卫锋 1)内生金属矿床成矿机制研究国家重点实验室南京大学南京210023 chenwf@nju.edu.cn 
毛玉锋 2)核工业270 研究所, 江西南昌330200  
方启春 2)核工业270 研究所, 江西南昌330200  
唐湘生 2)核工业270 研究所, 江西南昌330200  
凌洪飞 1)内生金属矿床成矿机制研究国家重点实验室南京大学南京210023 hfling@nju.edu.cn 
基金项目:本文为国家重点研发计划“深地资源勘查开采”专项(编号:2017YFC0602601)和核工业地质局科研项目(编号:201631)的成果。
中文摘要:相山铀矿田是我国最大的火山岩型铀矿田,区域内主要出露有碎斑熔岩、流纹英安岩、花岗斑岩等火山岩—潜火山岩。前人对这三种岩浆岩进行了较为详尽的年代学研究。近年来随着相山西部深部钻探的开展,发现钻孔中由上至下出现‘碎斑熔岩—流纹英安岩—碎斑熔岩’的现象,现有的年代学结果还不能给予合理的解释。为此,我们对相山西部典型钻孔中的上下两层碎斑熔岩及其间的流纹英安岩,以及相山北部和西部钻孔中的三个花岗斑岩样品进行了详细的年代学研究,结果显示,流纹英安岩的锆石206Pb/238 U加权平均年龄为139.7±1.0Ma,碎斑熔岩(上层)的加权平均年龄为135.3±0.9Ma,碎斑熔岩(下层)的加权平均年龄为129.9±0.9Ma,不同地点的三个花岗斑岩样品的加权平均年龄分别为125.4±1.0Ma, 134.4±1.3Ma,148.8±2.3Ma,结合上下两层碎斑熔岩的镜下特征,认为下层碎斑熔岩是在上层碎斑熔岩形成后沿流纹英安岩之下的凝灰岩接触面超浅层侵入形成,从而在剖面上显示出“上老下新”的特征。这些结果表明相山燕山期岩浆活动持续时间较长(长达约24Ma),为成矿有利因素,而不是前人认为的相山燕山期岩浆活动是一次短暂而集中的活动。对相山火山—侵入杂岩锆石的Hf同位素研究表明,各岩石样品的锆石εHf(t)值相近,分布在-10.6~-4.9之间,锆石的Hf模式年龄TDM2介于1478~1844Ma之间,本研究认为相山火山—侵入杂岩体可能起源于相山深部中元古代岩地壳所衍生的基底副变质岩部分熔融。
中文关键词:碎斑熔岩,锆石U- Pb年龄,岩浆活动,多阶段性,江西相山
 
Multiple Episodes of the Yanshanian Magmatism in Xiangshan Uranium Ore-field, Jiangxi
NameInstitution
PENG Zhongyong1)State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University,Nanjing, 210023
CHEN Weifeng1)State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University,Nanjing, 210023
MAO Yufeng2)The No. 270 Institute of Nuclear Industry, Nanchang, 330200
FANG Qichun2)The No. 270 Institute of Nuclear Industry, Nanchang, 330200
TANG Xiangsheng2)The No. 270 Institute of Nuclear Industry, Nanchang, 330200
LING Hongfei1)State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University,Nanjing, 210023
Abstract:Objectives: The Xiangshan uranium deposit is the largest volcanic type uranium deposit found in China so far. The Xiangshan volcanic—intrusive complex is composed of rhyodacitic lava, porphyroclastic lava and granitic porphyry. The Xiangshan volcanic—intrusive complex has been previously studied in detail on its petrography, mineralogy, lithochemistry and geochronology. In recent years, with progress in deep drilling in the western Xiangshan area, appearance of porphyroclastic lava — rhyodacite —porphyroclastic lava downward in drilling cores has been found. Previous geochronological study results could not explain this phenomenon. Methods:In this study, we collected samples from the upper and lower layers of porphyroclastic lavas and the rhyodacite in between in the western part of the Xiangshan complex, and from three granitic porphyry dikes in the western and northern Xiangshan area. U- Pb age and Hf isotope of zircon havebeen conducted on these samples by LA- ICP- MS and LA- MC- ICP- MS analysis, respectively. Results:The zircon dating results show that age of the rhyodacite is 139.7±1.0Ma, ages of the upper and lower layer of porphyroclastic lava are 135.3±0.9Ma and 129.9±0.9Ma, respectively. The three granite porphyry dikes from different locations have various ages of 125.4±1.0Ma, 134.4±1.3Ma, 148.8±2.3Ma, respectively. The results zircon Hf isotope compositions of this study show that various rocks of the Xiangshan volcanic—intrusive complex have similar zircon εHf(t)values ranging from -4.9 to -10.6, and Hf isotope two stage model ages between 1478 and 1844Ma. Conclusions:It can be concluded that the Xiangshan volcanic—intrusive complex may have been formed by magmas originated from partial melting mainly of basement para- metamorphic rocks that was derived from the crust differentiated from the mantle in the Mesoproterozoic era.Combined with the photomicrograph of both the upper and lower porphyroclastic lavas, we propose a formation model in that the lower porphyroclastic lava was formed later than the upper porphyroclastic lava,and the lower porphyroclastic lava was actually a kind of ultra- shallow intrusive rock intruding along with the tuff below the rhyodacite. These results show that the magmatism in the Xiangshan was active for a long period (about 24Ma) rather than a short and concentrative magmatic activity thought by previous researchers, which was an important factor favorable for uranium mineralization.
keywords:Xiangshan uranium deposit  porphyroclastic lava  zircon U-Pb age  magmatic activities  multiple episodes
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