Japan Geoscience Union Meeting 2023

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-GC Geochemistry

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

Tue. May 23, 2023 3:30 PM - 5:00 PM 303 (International Conference Hall, Makuhari Messe)

convener:Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Research Institute for Marine Geodynamics), Yama Tomonaga(University of Basel), Hirochika Sumino(Research Center for Advanced Science and Technology, The University of Tokyo), Yuji Sano(Center for Advanced Marine Core Research, Kochi University ), Chairperson:Yuji Sano(Center for Advanced Marine Core Research, Kochi University), Takeshi Hanyu(Japan Agency for Marine-Earth Science and Technology, Research Institute for Marine Geodynamics)

4:45 PM - 5:00 PM

[SGC37-11] Identification of multiple components of noble gas isotopes in backarc lithospheric mantle

*Lena Yokokura1, Hirochika Sumino2, Takeshi Kuritani1, Yuuki Hagiwara3, Junji Yamamoto4 (1.Hokkaido University, 2.The University of Tokyo, 3.Japan Agency for Marine-Earth Science and Technology, 4.Kyusyu University)

Keywords:mantle xenolith, noble gas isotope ratio, fluid inclusion

I investigated isotope ratios of noble gases (3He/4He and 40Ar/36Ar) extracted by laser microprobe methods for upper mantle-derived xenoliths collected from northeast China. The heterogeneous noble gas isotope ratios (ex. 6.45–0.14 Ra) obtained from the mantle xenoliths by crushing method may reflect local metasomatism induced by multi-components with various origins. Observation of inclusions would be effective in investigating the cause of the heterogeneity of noble gas isotope ratios extracted from the xenoliths by crushing method. On the basis of shape and chemical composition, the inclusions were classified into three types. I performed quantitative verification of the correlation between 3He/4He and area ratio of three types of inclusions on the polished surface of ten olivine grains in each sample. As a result, it is calculated that type (3) inclusions with negative crystal shape have a relatively high 3He/4He, and types (1) and (2) inclusions may have a relatively low 3He/4He. In order to verify the speculation and to determine the 40Ar/36Ar for each type of the inclusions, I applied laser spot analysis of noble gas isotopes for type (2) and type (3) inclusions. The type (2) inclusions showed relatively low 3He/4He and atmospheric 40Ar/36Ar. In contrast, type (3) inclusions showed relatively high 3He/4He and 40Ar/36Ar, which were almost typical of SCLM values. The atmospheric 40Ar/36Ar and relatively low 3He/4He. The type (2) inclusions are composed of melt inclusions. Considering the growth stage of inclusion form, type (2) inclusions would be vestiges of melt infiltrated to the upper mantle beneath northeast China later than type (3) inclusions, whose shape represents a matured stage. Taking the tectonic setting of the studied area into account, the coexistence of the inclusions with different noble gas isotopic compositions indicates that the upper mantle with SCLM-like noble gas isotopic compositions was infiltrated by the melt associated with slab-related components.