It is a challenge to make thorough but efficient experimental designs for the coupled mineral dissolution and precipitation studies in a multi-mineral system, because it is difficult to speculate the best experimental...It is a challenge to make thorough but efficient experimental designs for the coupled mineral dissolution and precipitation studies in a multi-mineral system, because it is difficult to speculate the best experimental duration, optimal sampling schedule, effects of different experimental conditions, and how to maximize the experimental outputs prior to the actual experiments. Geochemical modeling is an efficient and effective tool to assist the experimental design by virtually running all scenarios of interest for the studied system and predicting the experimental outcomes. Here we demonstrated an example of geochemical modeling assisted experimental design of coupled labradorite dissolution and calcite and clayey mineral precipitation using multiple isotope tracers. In this study, labradorite(plagioclase) was chosen as the reactant because it is both a major component and one of the most reactive minerals in basalt. Following our isotope doping studies of single minerals in the last ten years, initial solutions in the simulations were doped withmultiple isotopes(e.g., Ca and Si). Geochemical modeling results show that the use of isotope tracers gives us orders of magnitude more sensitivity than the conventional method based on concentrations and allows us to decouple dissolution and precipitation reactions at near-equilibrium condition. The simulations suggest that the precise unidirectional dissolution rates can inform us which rate laws plagioclase dissolution has followed. Calcite precipitation occurred at near-equilibrium and the multiple isotope tracer experiments would provide near-equilibrium precipitation rates, which was a challenge for the conventional concentration-based experiments. In addition, whether the precipitation of clayey phases is the rate-limiting step in some multi-mineral systems will be revealed. Overall, the modeling results of multimineral reaction kinetics will improve the understanding of the coupled dissolution–precipitation in the multi-mineral systems and the quality of geochemical modeling prediction of CO_(2) removal and storage efficacy in the basalt systems.展开更多
大西洋中脊是慢速扩张洋脊的典型代表。本文以大西洋中脊26°S地区脊轴及海山玄武岩代表性样品为研究对象,开展系统的Sr-Nd-Pb-Hf同位素研究,并结合已发表的数据,探讨研究区玄武岩成因及地幔源区性质和演化,旨在为认识地幔不均一性...大西洋中脊是慢速扩张洋脊的典型代表。本文以大西洋中脊26°S地区脊轴及海山玄武岩代表性样品为研究对象,开展系统的Sr-Nd-Pb-Hf同位素研究,并结合已发表的数据,探讨研究区玄武岩成因及地幔源区性质和演化,旨在为认识地幔不均一性和地幔柱-洋脊相互作用方式提供关键证据。样品主-微量元素与Sr-Nd-Pb-Hf同位素分析结果表明,所有样品均显示同位素富集的N-MORB特征。此外,大西洋26°S玄武岩主微量元素和同位素具有较大的变化范围,且同位素之间呈现出良好的相关关系,表明其是亏损软流圈地幔熔融的结果,但有富集组分参与。结合元素和同位素特征以及Sr-Nd-Hf同位素定量模拟结果,富集组分可能为Tristan da Cunha地幔柱残余组分,显示EMⅠ型富集地幔特征。同位素定量模拟结果表明:海山玄武岩地幔源区组成为约90%~95%的亏损组分和10%~5%的富集组分;而脊轴玄武岩地幔源区富集组分较少(<5%)。点位6、7海山玄武岩样品显示高放射成因Pb同位素组成,符合Dupal异常边界条件。定量计算表明,造成其异常的原因可能与EMⅠ型组分参与有关,这与同位素定量模拟结果相吻合。本文研究的同位素不同程度富集N-MORB可能的成因机制为:远端地幔柱-洋脊相互作用,即Tristan da Cunha地幔柱距离洋脊>1000km,地幔柱在运移至大西洋中脊的过程中,岩石圈厚度明显变薄,为减压熔融的发生提供了良好条件,使残余地幔柱物质不相容元素亏损,但同位素组成保留源区富集的特征。地幔柱残余物质到达大西洋中脊下方后,参与洋脊地区减压熔融,最终形成研究区不相容元素亏损且同位素富集的N-MORB。因此,本文研究的同位素富集的N-MORB可能记录了远端柱-脊相互作用和洋脊之下富集地幔柱物质再熔融的过程,为认识地幔不均一性提供了新的岩石学和地球化学证据。因此,地幔柱-洋脊相互作用不仅是E-MORB的可能成因,对理解N-MORB形成也有十分重要的意义。展开更多
基金partially supported by U.S. National Science Foundation grants EAR-2221907partly sponsored by agencies of the United States Government。
文摘It is a challenge to make thorough but efficient experimental designs for the coupled mineral dissolution and precipitation studies in a multi-mineral system, because it is difficult to speculate the best experimental duration, optimal sampling schedule, effects of different experimental conditions, and how to maximize the experimental outputs prior to the actual experiments. Geochemical modeling is an efficient and effective tool to assist the experimental design by virtually running all scenarios of interest for the studied system and predicting the experimental outcomes. Here we demonstrated an example of geochemical modeling assisted experimental design of coupled labradorite dissolution and calcite and clayey mineral precipitation using multiple isotope tracers. In this study, labradorite(plagioclase) was chosen as the reactant because it is both a major component and one of the most reactive minerals in basalt. Following our isotope doping studies of single minerals in the last ten years, initial solutions in the simulations were doped withmultiple isotopes(e.g., Ca and Si). Geochemical modeling results show that the use of isotope tracers gives us orders of magnitude more sensitivity than the conventional method based on concentrations and allows us to decouple dissolution and precipitation reactions at near-equilibrium condition. The simulations suggest that the precise unidirectional dissolution rates can inform us which rate laws plagioclase dissolution has followed. Calcite precipitation occurred at near-equilibrium and the multiple isotope tracer experiments would provide near-equilibrium precipitation rates, which was a challenge for the conventional concentration-based experiments. In addition, whether the precipitation of clayey phases is the rate-limiting step in some multi-mineral systems will be revealed. Overall, the modeling results of multimineral reaction kinetics will improve the understanding of the coupled dissolution–precipitation in the multi-mineral systems and the quality of geochemical modeling prediction of CO_(2) removal and storage efficacy in the basalt systems.
文摘大西洋中脊是慢速扩张洋脊的典型代表。本文以大西洋中脊26°S地区脊轴及海山玄武岩代表性样品为研究对象,开展系统的Sr-Nd-Pb-Hf同位素研究,并结合已发表的数据,探讨研究区玄武岩成因及地幔源区性质和演化,旨在为认识地幔不均一性和地幔柱-洋脊相互作用方式提供关键证据。样品主-微量元素与Sr-Nd-Pb-Hf同位素分析结果表明,所有样品均显示同位素富集的N-MORB特征。此外,大西洋26°S玄武岩主微量元素和同位素具有较大的变化范围,且同位素之间呈现出良好的相关关系,表明其是亏损软流圈地幔熔融的结果,但有富集组分参与。结合元素和同位素特征以及Sr-Nd-Hf同位素定量模拟结果,富集组分可能为Tristan da Cunha地幔柱残余组分,显示EMⅠ型富集地幔特征。同位素定量模拟结果表明:海山玄武岩地幔源区组成为约90%~95%的亏损组分和10%~5%的富集组分;而脊轴玄武岩地幔源区富集组分较少(<5%)。点位6、7海山玄武岩样品显示高放射成因Pb同位素组成,符合Dupal异常边界条件。定量计算表明,造成其异常的原因可能与EMⅠ型组分参与有关,这与同位素定量模拟结果相吻合。本文研究的同位素不同程度富集N-MORB可能的成因机制为:远端地幔柱-洋脊相互作用,即Tristan da Cunha地幔柱距离洋脊>1000km,地幔柱在运移至大西洋中脊的过程中,岩石圈厚度明显变薄,为减压熔融的发生提供了良好条件,使残余地幔柱物质不相容元素亏损,但同位素组成保留源区富集的特征。地幔柱残余物质到达大西洋中脊下方后,参与洋脊地区减压熔融,最终形成研究区不相容元素亏损且同位素富集的N-MORB。因此,本文研究的同位素富集的N-MORB可能记录了远端柱-脊相互作用和洋脊之下富集地幔柱物质再熔融的过程,为认识地幔不均一性提供了新的岩石学和地球化学证据。因此,地幔柱-洋脊相互作用不仅是E-MORB的可能成因,对理解N-MORB形成也有十分重要的意义。
