Japan Geoscience Union Meeting 2025

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S (Solid Earth Sciences ) » S-GC Geochemistry

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

Tue. May 27, 2025 3:30 PM - 5:00 PM 301A (International Conference Hall, Makuhari Messe)

convener:Hirochika Sumino(Research Center for Advanced Science and Technology, The University of Tokyo), Antonio Caracausi(National Institute of Geophysics and Volcanology), Kenji Shimizu(Kochi Institute of Core Research, Japan Agency for Marine-Earth Science and Technology), Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Research Institute for Marine Geodynamics), Chairperson:Kenji Shimizu(Kochi Institute of Core Research, Japan Agency for Marine-Earth Science and Technology), Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Research Institute for Marine Geodynamics), Hirochika Sumino(Research Center for Advanced Science and Technology, The University of Tokyo), Antonio Caracausi(National Institute of Geophysics and Volcanology)

4:15 PM - 4:30 PM

[SGC37-14] Helium, argon and nitrogen systematics in the KR1 segment of the Australian-Antarctic Ridge: Constraints on enriched sources for the Zealandia–Antarctic mantle domain

*Donghwan Kim1,2, Sung-Hyun Park3, Naoto Takahata1, Hyunwoo Lee2 (1.Atmosphere and Ocean Research Institute, University of Tokyo, 2.Seoul National University, 3.Korea Polar Research Institute)

Keywords:Mid-ocean ridge basalt, Australian-Antarctic Ridge, Mantle enrichment, Helium isotopes, Argon isotopes, Nitrogen isotopes

Oceanic volcanism provides valuable insights into various mantle compositions, shaped by recycling processes and mantle convection. This study reports volatiles (He-Ar-N2) in glassy basalts from the KR1 segment of the Australian-Antarctic Ridge (AAR) to elucidate the origin of the enriched components characterizing the Zealandia-Antarctic mantle domain. Helium, argon, and nitrogen isotope compositions in the KR1 segment samples range from 4He/3He = 88,000 to 131,000 (3He/4He = 5.5 to 8.2 Ra, 1 Ra: the 3He/4He ratio in air), 40Ar/36Ar = 297 to 8,970, and δ15N-N2 = -6 to +4 ‰, respectively. Excluding samples affected by isotope fractionation due to post-eruption He diffusive loss, the 4He/3He ratios in KR1 fall between 88,000 to 103,000 (3He/4He = 7.0 and 8.2 Ra). The regional variation of helium isotopes in the KR1 segment suggests the presence of an enriched component with high 4He/3He ratios within the ascending hot mantle. Helium isotopes show a clear correlation with Nd, Pb, and Hf isotopes reported by Park et al. (2019). The time required to generate the differences in 206Pb/204Pb and 4He/3He among the samples is estimated to be approximately 380 to 430 Ma. Samples with high N2/36Ar (>105) and 40Ar*/36Ar (>500) ratios, indicating minimal atmospheric contamination, display δ15N-N2 values ranging from -6 to +1.5 ‰, differing from the depleted MORB mantle (DMM) value of δ15N-N2 = -5 ‰. This indicates the influence of subducted slabs containing heavy nitrogen, distinct from DMM, at least within the KR1 segment. Volcanic systems in the Zealandia-Antarctic mantle domain including KR1, the Balleny Islands, the West Antarctic Rift System, and the Auckland Volcanic Field, show a clear correlation between 4He/3He and lead isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb), indicating a common enriched source. The results of the principal component analysis (PCA) indicate that volcanic systems within the same mantle domain share a common enriched component, distinct from those of the surrounding Pacific Antarctic Ridge (PAR) and Southeast Indian Ridge (SEIR). The common enriched source in the mantle domain is characterized by high 4He/3He ratios and high 206Pb/204Pb ratios, and elevated δ15N values, indicating relatively recent subducted materials (380 to 430 Ma), not ancient subducted materials like HIMU. The common enriched materials may be associated with continuous subduction processes in Zealandia and West Antarctica between 550 and 100 Ma and dispersed by the mantle plume related to the breakup of the Gondwana supercontinent.