Hydrogen Isotopic Evolution of Earth's Seawater

2016 Fiscal Year Final Research Report

• Project/Area Number: 26287125
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Partial Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Ueno Yuichiro 東京工業大学, 理学院, 准教授 (90422542)
• Co-Investigator(Kenkyū-buntansha): 玄田 英典 東京工業大学, 地球生命研究所, 特任准教授 (90456260)
• Co-Investigator(Renkei-kenkyūsha): SHIBUYA Takazo 国立研究開発法人海洋研究開発機構, 深海・地殻内生物圏研究分野, 研究員 (00512906)
• Research Collaborator: FORIEL Julien 東京工業大学, 地球生命研究所, 特任助教
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 水素同位体 / 海水の起源

Outline of Final Research Achievements

Hydrogen isotopic compositions of Archean basalts were determined by TCEA-IRMS technique. The analysis of more than 200 samples from 3.2 Ga Cleaverville Formation showed that dD values of hydrous minerals are clearly correlated with metamorphic grade which reflect ocean-floor metamorphism at that time based on metamorphic mineral assemblages. Also, the dD values are correlated with water content of the basaltic rocks as observed in modern seafloor basalts. These observations all indicate that hydrous minerals in the Cleaverville basalts preserve the isotopic composition of Archean seawater. The estimated dD value of the 3.2 billion-years-old seawater is -21±5‰, indicating deuterium content of Earth's seawater increased through the history of the Earth, potentially owing to hydrogen escape into space. Furthermore, we found igneous amphibole from the most D-depleted sample, suggesting not only Archean seawater but also Archean mantle was depleted in deuterium.

Free Research Field

安定同位体地球化学