日本地球惑星科学連合2023年大会

講演情報

[E] オンラインポスター発表

セッション記号 S (固体地球科学) » S-GC 固体地球化学

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

2023年5月24日(水) 15:30 〜 17:00 オンラインポスターZoom会場 (3) (オンラインポスター)

コンビーナ:羽生 毅(海洋研究開発機構 海域地震火山部門)、Tomonaga Yama(University of Basel)、角野 浩史(東京大学先端科学技術研究センター)、佐野 有司(高知大学海洋コア総合研究センター)

現地ポスター発表開催日時 (2023/5/23 17:15-18:45)

15:30 〜 17:00

[SGC37-P02] Water and dissolved gas geochemistry of cold CO2-rich springs in Ulleungdo volcano, South Korea

*Wonhee Lee1、Hyunwoo Lee1Heejun Kim1、Jungpyo Hong1,2、Jeonghoon Lee3、Hyejung Jung3Naoto Takahata4Yuji Sano4,5 (1.School of Earth and Environmental Sciences, Seoul National University, Republic of Korea、2.Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan, USA、3.Department of Science Education, Ewha Womans University, Republic of Korea、4.Atmosphere and Ocean Research Institute, University of Tokyo, Japan、5.Center for Advanced Marine Core Research, Kochi University, Japan)


キーワード:Ulleungdo, Cenozoic intraplate volcanism, Volatiles, Stable isotopes

Volatiles are released from deep into the atmosphere through fluids from springs of volcanoes and hydrothermal systems. Thus, chemical and isotope compositions of water and dissolved gases of springs may provide information on the source and evolution of volcanic gases. Ulleungdo, located in South Korea, is a volcanic island formed by Cenozoic intraplate volcanism and is an important site for understanding geological processes of East Asia after the formation of the back-arc basin in the rear of the Japanese arc. Here, we report the first results of water and dissolved gas geochemistry in nine cold springs (T = 9.5 to 22.7 ℃) in Ulleungdo to account for the origin of volatiles and constrain the conditions of the current hydrothermal system for the volcano. In particular, this presentation focuses on six springs with high CO2 content (89.3 to 99.9 vol.%). The collected water and gas samples were analyzed for chemical and stable isotope compositions (e.g., d18O-H2O, dD-H2O, d13C-CO2, and 3He/4He). The dD and d18O values of the spring water samples (-9.0 to -7.6‰ and -51.5 to -41.9‰ vs. V-SMOW, respectively) are plotted parallel to the global and local meteoric water lines, indicating the meteoric origin. The CO2-rich springs are characterized by the Ca-(Na)-HCO3 water type and travertine depositions. Their high total dissolved inorganic carbon (TDIC) contents (28.4 to 579.2 mg/L) and positively correlated cation concentrations imply silicate weathering due to acidic pH possibly caused by the addition of deep-derived CO2-rich fluids. The d13C-CO2 values (-7.3 to -5.1‰ vs. V-PDB) and the 3He/4He ratios (1.40 to 5.87 Ra) of CO2-rich springs indicate the CO2 and He input from deep sources (e.g., mantle) rather than the shallow crust. Interestingly, two N2-rich springs exhibit atmospheric 3He/4He ratios (0.98 to 0.99 Ra), while one spring shows 3He/4He ratios (3.45 to 4.51 Ra) as high as the CO2-rich springs. These high 3He/4He ratios of both spring types fall within the range reported in olivine and clinopyroxene phenocrysts in Ulleungdo basalts (4.5 to 6.0 Ra). In conclusion, this suggests that the spring gases may have originated from the same magma source that formed the volcanic rocks, and magma releasing volatiles still exists beneath Ulleungdo volcano.