光谱学与光谱分析, 2018, 38 (6): 1753, 网络出版: 2018-06-29  

湖南砂矿金刚石中石墨包裹体拉曼光谱原位测定: 形成条件及成因指示

In-Situ Raman Spectroscopy Testing and Genesis of Graphite Inclusions in Alluvial Diamonds from Hunan
作者单位
1 中山大学地球科学与工程学院, 广东省地球动力作用与地质灾害重点实验室, 广东省地质过程与矿产资源探查重点实验室, 广东 广州 510275
2 广州出入境检验检疫局综合技术服务中心珠宝鉴定实验室, 广东 广州 510275
3 国土资源部珠宝玉石首饰管理中心北京珠宝研究所, 北京 100013
摘要
石墨是天然金刚石中最常见的包裹体之一, 按其形成顺序可分为原生、 同生、 次生, 原生/同生与次生石墨包裹体的存在指示了金刚石形成的环境及形成后可能经历的变化。 对湖南沅水流域产出的13粒宝石级-半宝石级砂矿金刚石中的原生/同生石墨包裹体及次生石墨包裹体进行显微激光拉曼光谱的原位测试。 测试显示, 湖南沅水流域金刚石中原生/同生石墨包裹体与次生石墨包裹体的G带与D带拉曼位移均存在漂移, 其中原生/同生石墨包裹体G带的漂移范围为1 591~1 600 cm-1, 次生石墨的漂移范围为1 575~1 588 cm-1, 显示其形成压力较低, 结晶压力变化范围大。 原生/同生石墨漂移程度估算出该区域压力范围为4.01~5.88 GPa, 估算结果与利用橄榄石包裹体拉曼位移估算的源区压力范围基本一致。 该区域内金刚石中原生/同生石墨包裹体的D带拉曼位移在1 350~1 368 cm-1之间, D带与G带的强度比(ID/IG值)值位于0.36~0.82之间, 具有较低有序度结构/结晶程度与橄榄岩型金刚石的高结晶度石墨明显不同指示该区域部分砂矿来源的金刚石的形成深度较浅, 成因与榴辉岩关系更为密切, 形成过程极可能曾位于石墨-金刚石稳定域附近。 研究结果表明, 金刚石石墨包裹体拉曼位移的漂移程度可成为探索金刚石原生源区形成环境的有效方法之一。
Abstract
Graphite is one of the most common inclusion in diamond, it can be divided into protogenetic, syngenetic and epigenetic on the basis of sequence of graphite inclusion formation. The formation environment of the diamond and its late change are indicated by protogenetic/syngenetic and epigenetic graphite. In-situ microscopic laser Raman spectroscopy, we carried out on graphite inclusions in 13 gem-grade and semiprecious alluvial diamonds from the the Yuanjiang Basin in Hunan province(Yangtze Craton). The results showed that the graphite inclusions whether protogenetic/syngenetic or epigenetic Raman shift in position of the G band and D band toward high frequency region and Show low ordered structures and defects. Raman shift of the protogentic/syngenetic graphite G band range from 1 591 to 1 600 cm-1, the shift of the G band of epigenetic graphite is wide rang from 1 575 to 1 588 cm-1, it is thought that forming pressure for diamond in Yuanjiang Basin(Yangtze Craton)is lower and its crystallization pressure have great varying range. We calculated the pressure are rang from 4.01 to 5.88 GPa according to Raman shift of the protogentic/syngenetic graphite G band range. It is consistent with what result of calculation in Raman shift of the olivine in Hunan diamonds, the D band rang from 1 350~1 368 cm-1 andthe G band and D band intensity ofprotogenetic/syngeneticgraphite inclusions of Hunan diamonds between 0.36 to 0.82, it indicatethat those area diamondswereformed depth is shallow and may be formed in a lithospheric mantle containing abundant eclogite. In these cases, the diamonds may have formed diamond-graphite boundary and diamond stability field. The graphite inclusion Raman shift of diamond is one of effective approach to explore the formation environment of the diamond primary area.

马瑛, 王琦, 丘志力, 陆太进, 李榴芬, 陈华, 邓小芹, 薄昊楠. 湖南砂矿金刚石中石墨包裹体拉曼光谱原位测定: 形成条件及成因指示[J]. 光谱学与光谱分析, 2018, 38(6): 1753. MA Ying, WANG Qi, QIU Zhi-li, LU Tai-jin, LI Liu-fen, CHEN Hua, DENG Xiao-qin, BO Hao-nan. In-Situ Raman Spectroscopy Testing and Genesis of Graphite Inclusions in Alluvial Diamonds from Hunan[J]. Spectroscopy and Spectral Analysis, 2018, 38(6): 1753.

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