The subduction of marine carbonates and carbonated oceanic crust to the Earth’s interior and the return of recycled carbon to the surface via volcanism may play a pivotal role in governing Earth’s atmosphere, climat...The subduction of marine carbonates and carbonated oceanic crust to the Earth’s interior and the return of recycled carbon to the surface via volcanism may play a pivotal role in governing Earth’s atmosphere, climate, and biosphere over geologic time. Identifying recycled marine carbonates and evaluating their fluxes in Earth’s mantle are essential in order to obtain a complete understanding of the global deep carbon cycle (DCC). Here, we review recent advances in tracing the DCC using stable isotopes of divalent metals such as calcium (Ca), magnesium (Mg), and zinc (Zn). The three isotope systematics show great capability as tracers due to appreciable isotope differences between marine carbonate and the terrestrial mantle. Recent studies have observed anomalies of Ca, Mg, and Zn isotopes in basalts worldwide, which have been interpreted as evidence for the recycling of carbonates into the mantle, even into the mantle transition zone (410–660 km). Nevertheless, considerable challenges in determining the DCC remain because other processes can potentially fractionate isotopes in the same direction as expected for carbonate recycling;these processes include partial melting, recycling of carbonated eclogite, separation of metals and carbon, and diffusion. Discriminating between these effects has become a key issue in the study of the DCC and must be considered when interpreting any isotope anomaly of mantle-derived rocks. An ongoing evaluation on the plausibility of potential mechanisms and possible solutions for these challenges is discussed in detail in this work. Based on a comprehensive evaluation, we conclude that the large-scale Mg and Zn isotope anomalies of the Eastern China basalts were produced by recycling of Mg- and Zn-rich carbonates into their mantle source.展开更多
Mg是构成牙齿重要组分,其含量和同位素组成可记录居民生活地域、饮食习惯以及口腔健康信息等重要信息。本研究建立了高精度多接收等离子质谱(MC-ICP-MS)测定牙齿中Mg同位素方法。牙齿样品经微波消解仪消解,后采用AG50W-X8阳离子树脂分...Mg是构成牙齿重要组分,其含量和同位素组成可记录居民生活地域、饮食习惯以及口腔健康信息等重要信息。本研究建立了高精度多接收等离子质谱(MC-ICP-MS)测定牙齿中Mg同位素方法。牙齿样品经微波消解仪消解,后采用AG50W-X8阳离子树脂分离溶液中的Mg元素,以1 mol/L HNO_3为介质上柱,40 m L1 mol/L HNO_3洗脱Na^+等杂质离子,再以30 m L 1 mol/L HNO_3收集Mg元素,60 m L 1 mol/L HNO_3洗去其它杂质,蒸干Mg收集液。MC-ICP-MS进行Mg同位素组成测定。MC-ICP-MS仪器自身的质量分馏利用"样品-标准"交叉技术("Sample-standard"bracketing technique)解决。实验结果表明,利用AG50W-X8阳离子树脂,可在保证Mg回收率的情况下,将牙齿样品中的Mg和其它基质元素彻底分离,且不造成同位素分馏。采用此方法对现代人离体牙牙釉质中Mg同位素进行分离测定,牙齿的δ^(26)Mg在较大的范围变化(!1.38‰~4.59‰)。本方法为利用人牙齿中Mg同位素研究Mg的暴露水平、环境污染等信息提供重要的实验和理论依据。展开更多
榴辉岩中单斜辉石和石榴子石之间显著的镁同位素平衡分馏,使其成为一种具有潜力的高精度地质温度计。为此,本文选取文献中已报道的来自西南天山洋壳冷俯冲造山带、大别-苏鲁陆壳碰撞造山带和南非卡普瓦尔克拉通三种构造环境中的64对单...榴辉岩中单斜辉石和石榴子石之间显著的镁同位素平衡分馏,使其成为一种具有潜力的高精度地质温度计。为此,本文选取文献中已报道的来自西南天山洋壳冷俯冲造山带、大别-苏鲁陆壳碰撞造山带和南非卡普瓦尔克拉通三种构造环境中的64对单斜辉石-石榴子石矿物对镁同位素数据,利用δ26MgCpx-δ26MgGrt图解筛选出50对达到镁同位素平衡分馏的数据,采用Huang et al.(2013)通过第一性原理计算和Wang et al.(2012)、Li et al.(2016)分别通过经验估计得出的镁同位素温度计计算榴辉岩的峰期温度,并与前人研究结果进行对比。通过分析计算结果,发现对于造山带榴辉岩,Huang et al.(2013)的温度计计算结果与前人通过传统温度计和相平衡模拟研究结果较一致,较好地重现了榴辉岩的峰期温度,而Wang et al.(2012)和Li et al.(2016)的温度计计算结果明显低于前人获得的峰期温度;对于克拉通榴辉岩,三种镁同位素温度计的计算结果与前人通过传统温度计获得的研究结果大多数相差在50℃以上,很可能是早期退变质过程中镁同位素在高温条件下再平衡导致的,这表明三种镁同位素温度计均不适用于克拉通榴辉岩。同时,基于这些榴辉岩样品数据,本文利用经验估计的方法进行校准,得到了新的单斜辉石-石榴子石镁同位素公式Δ26MgCpx-Grt=1.11×10^6/[T(K)]2(R2=0.92)。此外,本文也对单斜辉石-石榴子石镁同位素地质温度计的应用前景及应用时应当注意的问题进行了简单的探讨。展开更多
基金the National Nature Science Foundation of China (41730214 and 41622303)the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB18030603).
文摘The subduction of marine carbonates and carbonated oceanic crust to the Earth’s interior and the return of recycled carbon to the surface via volcanism may play a pivotal role in governing Earth’s atmosphere, climate, and biosphere over geologic time. Identifying recycled marine carbonates and evaluating their fluxes in Earth’s mantle are essential in order to obtain a complete understanding of the global deep carbon cycle (DCC). Here, we review recent advances in tracing the DCC using stable isotopes of divalent metals such as calcium (Ca), magnesium (Mg), and zinc (Zn). The three isotope systematics show great capability as tracers due to appreciable isotope differences between marine carbonate and the terrestrial mantle. Recent studies have observed anomalies of Ca, Mg, and Zn isotopes in basalts worldwide, which have been interpreted as evidence for the recycling of carbonates into the mantle, even into the mantle transition zone (410–660 km). Nevertheless, considerable challenges in determining the DCC remain because other processes can potentially fractionate isotopes in the same direction as expected for carbonate recycling;these processes include partial melting, recycling of carbonated eclogite, separation of metals and carbon, and diffusion. Discriminating between these effects has become a key issue in the study of the DCC and must be considered when interpreting any isotope anomaly of mantle-derived rocks. An ongoing evaluation on the plausibility of potential mechanisms and possible solutions for these challenges is discussed in detail in this work. Based on a comprehensive evaluation, we conclude that the large-scale Mg and Zn isotope anomalies of the Eastern China basalts were produced by recycling of Mg- and Zn-rich carbonates into their mantle source.
文摘Mg是构成牙齿重要组分,其含量和同位素组成可记录居民生活地域、饮食习惯以及口腔健康信息等重要信息。本研究建立了高精度多接收等离子质谱(MC-ICP-MS)测定牙齿中Mg同位素方法。牙齿样品经微波消解仪消解,后采用AG50W-X8阳离子树脂分离溶液中的Mg元素,以1 mol/L HNO_3为介质上柱,40 m L1 mol/L HNO_3洗脱Na^+等杂质离子,再以30 m L 1 mol/L HNO_3收集Mg元素,60 m L 1 mol/L HNO_3洗去其它杂质,蒸干Mg收集液。MC-ICP-MS进行Mg同位素组成测定。MC-ICP-MS仪器自身的质量分馏利用"样品-标准"交叉技术("Sample-standard"bracketing technique)解决。实验结果表明,利用AG50W-X8阳离子树脂,可在保证Mg回收率的情况下,将牙齿样品中的Mg和其它基质元素彻底分离,且不造成同位素分馏。采用此方法对现代人离体牙牙釉质中Mg同位素进行分离测定,牙齿的δ^(26)Mg在较大的范围变化(!1.38‰~4.59‰)。本方法为利用人牙齿中Mg同位素研究Mg的暴露水平、环境污染等信息提供重要的实验和理论依据。
文摘榴辉岩中单斜辉石和石榴子石之间显著的镁同位素平衡分馏,使其成为一种具有潜力的高精度地质温度计。为此,本文选取文献中已报道的来自西南天山洋壳冷俯冲造山带、大别-苏鲁陆壳碰撞造山带和南非卡普瓦尔克拉通三种构造环境中的64对单斜辉石-石榴子石矿物对镁同位素数据,利用δ26MgCpx-δ26MgGrt图解筛选出50对达到镁同位素平衡分馏的数据,采用Huang et al.(2013)通过第一性原理计算和Wang et al.(2012)、Li et al.(2016)分别通过经验估计得出的镁同位素温度计计算榴辉岩的峰期温度,并与前人研究结果进行对比。通过分析计算结果,发现对于造山带榴辉岩,Huang et al.(2013)的温度计计算结果与前人通过传统温度计和相平衡模拟研究结果较一致,较好地重现了榴辉岩的峰期温度,而Wang et al.(2012)和Li et al.(2016)的温度计计算结果明显低于前人获得的峰期温度;对于克拉通榴辉岩,三种镁同位素温度计的计算结果与前人通过传统温度计获得的研究结果大多数相差在50℃以上,很可能是早期退变质过程中镁同位素在高温条件下再平衡导致的,这表明三种镁同位素温度计均不适用于克拉通榴辉岩。同时,基于这些榴辉岩样品数据,本文利用经验估计的方法进行校准,得到了新的单斜辉石-石榴子石镁同位素公式Δ26MgCpx-Grt=1.11×10^6/[T(K)]2(R2=0.92)。此外,本文也对单斜辉石-石榴子石镁同位素地质温度计的应用前景及应用时应当注意的问题进行了简单的探讨。
