[S-GC37] Volatiles in the Earth - from Surface to Deep Mantle

[SGC37-P11] The volatiles and hydrogen isotopes of high ³He/⁴He submarine volcanic glass and melt inclusions from Hawaii characterized the water in the deep and primordial Earth

*清水 健二¹、牛久保 孝行¹、兼岡 一郎² (1.海洋研究開発機構　高知コア研究所、2.東京大学　地震研究所)

キーワード：ハワイ、水素同位体比、メルト包有物

The origin of water in the Earth is a first-class enigma that has been approached from various terrestrial and extraterrestrial samples. We used 11 volcanic glasses with high ³He/⁴He ratios (15-30 Ra; Ra denotes ³He/⁴He ratio of the atmosphere) recovered from the deep seafloor (2300-5500 m depth) near Hawaii Island using the deep-sea manned submersible SHINKAI6500 (Kaneoka et al.., 2002, AGU Monograph 128, p373-). We measured the volatile concentrations (H₂O, CO₂, F, Cl, and S) and hydrogen isotopes in these volcanic glasses and their melt inclusions by IMS-1280HR at Kochi Institute, JAMSTEC. We found low δD values (D/H ratio expressed as a deviation from standard mean ocean water) of –129 ± 6 ‰, and correlations between δD and ³He/⁴He, H₂O/F, and 1/H₂O in glasses and melt inclusions, including mid-ocean ridge basaltic (MORB) samples of previous studies. These relations suggest the potential for the mixing of depleted upper mantle and deep primordial mantle components. The δD of the deep primordial mantle is estimated to be -160‰ at the lowest, consistent with recently reported values for enstatite chondrites (Piani et al., 2020, Science, v369, p1110-). The results of this study suggest that the primordial water in Earth may be similar to that in enstatite chondrites, supporting recent hypotheses about the origin of Earth's water. This study provides new insights into the composition of the deep mantle and the early history of Earth's volatile inventory.