| 基于重砂鉴定技术的火山岩锆石精选与测年方法关系探讨 |
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| 引用本文： | 马慧英,孙海清,罗来,马铁球.基于重砂鉴定技术的火山岩锆石精选与测年方法关系探讨[J].华南地质与矿产,2014(3):187-193. |
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| 作者姓名： | 马慧英 孙海清 罗来 马铁球 |
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| 作者单位： | 湖南省地质调查院,湖南长沙410116 |
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| 基金项目： | 国家自然科学基金重点基金资助项目（编号：41030315）;中国地质调查局项目（编号：1212011121108）资助. |
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| 摘 要： | 针对中浅变质沉凝灰岩锆石U-Pb同位素年龄分散幅度较大的现状,在湘中地区碧溪长安组底部凝灰岩几次采集样品测年不成功的情况下再次取样,通过室内重砂样品加工分选等工序,利用立体显微镜和偏光显微镜对锆石进行详细的矿物学特征对比分析,确定样品是否有来自不同时代、不同成因或不同地质背景的锆石。将精选出的锆石进行再次分选,分离成两组样品送往测年,采用LA-ICP-MSU-Pb法测得同沉积期的火山岩岩浆成因锆石年龄751±5 Ma和构造岩浆热事件年龄431.3±4.3 Ma,两组年龄数据与区域地质事实吻合。由此认为对此类样品的锆石进行成因、形态与光学性质等方面的综合分析研究,将混合锆石进行分组,有助于同位素测年数据的有效集中,保证测年数据精度。本文研究表明重砂精细分析鉴定是同位素精准定年的基础。
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| 关 键 词： | 锆石 分期分离 凝灰岩 重砂鉴定技术 |
Application of heavy placer mineral identification for sorting zircons from volcanic rocks to improve geochronology method |
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| MA Hui-Ying,SUN Hai-Qing,LUO Lai,MA Tie-Qiu.Application of heavy placer mineral identification for sorting zircons from volcanic rocks to improve geochronology method[J].Geology and Mineral Resources of South China,2014(3):187-193. |
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| Authors: | MA Hui-Ying SUN Hai-Qing LUO Lai MA Tie-Qiu |
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| Institution: | (Hunan Institute of Geological Survey, Changsha 410116, China) |
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| Abstract: | The current status is that isotopic dating of zircons from low-grade metamorphic tuff is often inaccurate and age scattering range large. The age tests for the initial tuff sampling in Chang＇ an Group bottom in Bixi, central Hunan Province are not successful. Nonetheless, through re-sampling by strictly conducting heavy concentrate sample processing and sorting procedures, and using stereo and polarizing microscopes to make comparative analyses on detailed mineralogical characteristics of zircon, it can discriminate the ages, causes or geological backgrounds of the zircon samples. The selected zircons are sorted again and separated into two phases for dating their ages and this time the LA-ICP-MS zircon U-Pb dating method is used to measure the sedimentary volcanic zircons and yielded age of 751 ± 5 Ma and the magmatic-tectonic thermal event age of 431.3 ±4.3 Ma, which match the regional geological facts. Hence it is proved that comprehensive analyses of the causes, forms and other aspects of the optical properties can identify different zircons from low-grade metamorphic tuff, and the phasing and separating of mixed zircon can help improve effective centralized dating data and ensure the data accuracy. And this shows that fine analysis and identification of zircons on heavy concentrate is the basis of precise isotope dating. |
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| Keywords: | zircon separated on different time initial tuff technology of heavy placer mineral identification |
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