初期地球の海水量とその進化: 酸素・水素同位体分析法の開発と解析

早期地球海水量及其演化：氧和氢同位素分析方法的发展和分析

• 批准号: 16K05619
• 负责人: フォリエル ジュリアン
• 金额: $ 2.5万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2016
• 资助国家: 日本
• 起止时间: 2016-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16K05619/
• 关键词: oxygen isotopes; hydrogen isotopes; analytical development; water cycle; Archaean environment; Fluorination; methodology; 数物系科学; 地球惑星科学; 地球宇宙化学; 大気圏; 水圏化学; oxygen isotopes; hydrogen isotopes; analytical development; water cycle; Archaean environment; Fluorination; methodology; 数物系科学; 地球惑星科学; 地球宇宙化学; 大気圏; 水圏化学

We have built a model for the long-term evolution of the hydrogen isotope composition of the surface water, water in the mantle and in crustal rocks (Kurokawa, Foriel et al, 2018). Processes affecting the abundance of water and its H isotopic composition are hydrogen escape (in anoxic atmosphere conditions), water degassing during volcanism and ingassing during subduction, water-rock exchanges during alteration of the seafloor and weathering of the continents.The first output of this modeling is that the modern H isotope composition of seawater requires that in the past, the water cycle was significantly different form the present-day cycle. Either hydrogen escape, regassing from the surface to the mantle, or faster plate tectonics must have occurred in the Archean era and perhaps after. In any case, the amount of water in the early ocean should have been greater than it is now, as was hypothesized in the proposal for this project.However, in order to differentiate which process drove the loss of water from the surface, isotopic composition of the seawater and of the mantle water need to be estimated. This requires analysis of ancient rocks for H isotopes as well as O isotopes as oxygen data can help identify the isotopic signature of the seawater. A method for analyzing O isotopes in silicates was adapted in the lab (Ueno Lab, ELSI/Tokyo Institute of Technology). These measurements could not be completed before the termination of the project, but the method is established and analysis will continue in the Ueno Lab.

我们已经建立了一个模型，用于地表水，地幔和地壳岩石中的水的长期演变（Kurokawa，Foriel等，2018）。影响水及其同位素组成的过程是氢的逃生（在缺氧气氛条件下），在火山和俯冲过程中的水脱水，在俯冲过程中散发，在海底变化期间的水摇滚交换以及这种模型的首次输出是现代的H同步量的循环。氢逃逸，从地面重新升级到地幔，或者更快的板块构造必须发生在大帝时代，也许是之后。无论如何，早期海洋中的水量应该比现在要大，正如该项目的提案中所说的那样。但是，为了区分哪种过程使水从表面损失，海水的同位素组成和地幔水的同位素组成需要估计。这需要分析用于H同位素的古代岩石以及O同位素，因为氧数据可以帮助识别海水的同位素特征。在实验室（ELSI/东京技术研究所Ueno Lab）中，对分析硅酸盐中O同位素的分析方法进行了调整。这些测量值无法在项目终止之前完成，但是该方法已建立，分析将继续在UENO实验室中进行。