| 镁同位素地球化学研究新进展及其在碳酸岩研究中的应用 |
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| 引用本文： | 陈洁,龚迎莉,陈露,向蜜,田世洪.镁同位素地球化学研究新进展及其在碳酸岩研究中的应用[J].地球科学,2021,46(12):4366-4389. |
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| 作者姓名： | 陈洁 龚迎莉 陈露 向蜜 田世洪 |
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| 作者单位： | 东华理工大学核资源与环境国家重点实验室,江西南昌 330013;清华大学能源与动力工程系,北京 100084;东华理工大学核资源与环境国家重点实验室,江西南昌 330013;自然资源部成矿作用与资源评价重点实验室,中国地质科学院矿产资源研究所,北京 100037 |
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| 基金项目： | 国家自然科学基金41773014江西省“双千计划”创新领军人才长期项目、东华理工大学博士启动基金DHBK2020012高层次人才引进配套经费1410000874 |
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| 摘 要： | 镁（Mg）同位素有3个，24Mg、25Mg和26Mg，其中24Mg和26Mg的相对质量差较大，高达8.33%，这种大的相对质量差使地壳活动或其他地质过程中Mg同位素因化学物理条件的变化而发生明显的同位素质量分馏.目前，自然界可观测到的δ26Mg变化范围为-5.60‰~0.92‰，约6.5‰.镁在低温地球化学过程中分馏显著，而在高温环境下分馏不明显，因而Mg同位素是地质过程的潜在地球化学指标和示踪剂，在低温风化作用、高温部分熔融与岩浆结晶分异、变质作用、板片俯冲及壳幔物质循环、热液蚀变和矿床成因等方面取得重要进展.为此，简要介绍了镁同位素分析方法，系统总结了Mg同位素在地球各储库中的组成与分布特征以及地质作用过程中的镁同位素分馏机理；其次重点介绍了镁同位素近年来在碳酸岩研究中的应用；最后对有关问题进行了探讨，包括幔源岩石低δ26Mg成因解释（与俯冲再循环的碳酸盐岩、洋壳物质有关或与矿物分离结晶有关）和Li-Mg-Ca同位素联合示踪岩浆碳酸岩岩石成因.并对碰撞反应池多接收器电感耦合等离子体质谱仪（Nu Sapphire MC-ICP-MS）分析优势和Li-Mg-Ca等金属同位素联合示踪在稀土元素富集机制的应用进行了展望.
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| 关 键 词： | 镁同位素 分析方法 同位素分馏 联合示踪 碳酸岩 地球化学 |
| 收稿时间： | 2021-06-11 |
New Advances in Magnesium Isotope Geochemistry and Its Application to Carbonatite Rocks |
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| Abstract: | There are three magnesium (Mg) isotopes, 24Mg, 25Mg and 26Mg, among which the relative mass difference of 26Mg and 24Mg is large, up to 8.33%. Such a large relative mass difference can cause significant mass dependent fractionation of Mg isotopes due to the changes of chemical and physical conditions during crustal activities or other geological processes. Variations of δ26Mg in nature are mainly from -5.60‰ to 0.92‰, spanning a limited range of 6.5‰. Mg isotope is a potential geochemical index and tracer for geological processes because Mg fractionates significantly in low-temperature geochemical processes, but not in high-temperature environments. Mg isotopes have made important progress in the fields of low-temperature weathering, high-temperature partial melting and magmatic crystallization differentiation, metamorphism, plate subduction, crust-mantle material recycling, hydrothermal alteration and genesis of deposits. In this paper, the analysis methods of Mg isotopes are briefly introduced firstly. Secondly, the composition and distribution characteristics of Mg isotopes in various reservoirs of the earth and the fractionation mechanism of Mg isotopes in geological processes are systematically summarized. And then, the application of magnesium isotopes in the study of carbonatites in recent years is emphatically introduced. Finally, it discusses the origin of low δ26Mg in mantle-derived rocks (related to carbonate rocks of subduction and recycling, oceanic crust materials or mineral separation crystallization) and trace the petrogenesis of magmatic carbonatites by the combination of Li, Mg and Ca isotopes. At the end of this paper, the advantages of the dual-path collision cell-capable multiple-collector inductively coupled plasma mass spectrometer (Nu Sapphire MC-ICP-MS) and the application of Li-Mg-Ca and other metal isotopes in the enrichment mechanisms of rare earth elements are prospected. |
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