Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-GC Geochemistry

[S-GC46] Solid Earth Geochemistry, Cosmochemistry

Tue. May 22, 2018 1:45 PM - 3:15 PM 202 (2F International Conference Hall, Makuhari Messe)

convener:Gen Shimoda(Geological Survey of Japan, AIST), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology), Katsuyuki Yamashita(岡山大学大学院自然科学研究科, 共同), Akira Ishikawa(Department of Earth Science and Astronomy, The University of Tokyo), Chairperson:Wakaki Shigeyuki(JAMSTEC), Yamashita Katsuyuki(岡山大学), Suzuki Katsuhiko(JAMSTEC)

2:15 PM - 2:30 PM

[SGC46-09] Tectonic control on 3He/4He isotopic composition of OIB: an interpretation

*Gen Shimoda1, Tetsu Kogiso2 (1.Geological Survey of Japan, AIST, 2.kyoto Univ.)

Keywords:OIB, mantle, isotope

The isotopic variation of OIB is commonly represented by just four end-member components with extreme isotopic signatures, i.e., DMM, EM1, EM2 and HIMU. In addition to these four end-member components, some researchers have proposed the existence of components with intermediate isotopic compositions between the four end-member components, such as FOZO, C and PHEM mainly based on 3He/4He ratios of OIB and MORB. Namely, Hart et al. (1992) argued that FOZO is derived from the lower mantle, because OIB with FOZO-like isotopic compositions tends to have high 3He/4He ratios. Similarly, Hanan and Graham (1996) proposed component C based on 3He/4He ratios of MORB, i.e., C is situated in isotopic field where MORB arrays converge and 3He/4He ratios of OIB increase. Similarly, Farley et al. (1992) advocated a PHEM component that is characterized by high 3He/4He ratios, FOZO-like Pb isotopic compositions, and Sr-Nd isotopic ratios near that of the bulk Earth.

Although the Pb-Nd-Sr isotopic compositions of these intermediate components may be explained by simple mixing of the four end-member components, high 3He/4He ratios of intermediate reservoirs cannot be explained by mixing of the end-member components because all of end components are inferred to be derived from recycled crustal materials which necessary have low 3He/4He ratios. One explanation that can link a high-3He/4He component and recycled crustal material, whose Pb-Nd-Sr isotopic compositions match to the isotopic composition of intermediate components, is a model in which the lithospheric thickness beneath a hotspot is a major factor in determining the chemical composition of OIB yielded by melting of a heterogeneous source. In this presentation, we will examine effect of thickness of lithosphere beneath a hot spot that should control degree of melting of a heterogeneous magma source to produce Pb-Nd-Sr-He isotopic composition suitable for the intermediate mantle components.