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

[SGC37-16] Halogen and noble gas systematics of mantle xenoliths from the rear-arc regions in Eastern Asia

*角野 浩史¹、小林 真大² (1.東京大学先端科学技術研究センター、2.東京都立産業技術研究センター)

キーワード：ハロゲン、希ガス、マントル捕獲岩、大陸下マントル

Halogens and noble gases are powerful tracers of volatile cycling in subduction zones. We present heavy halogen (Cl, Br, and I) compositions and noble gas isotope compositions of mantle xenoliths from rea-arc regions in Eastern Asia (Ichinomegata, Jeju, Oki, Sikhote-Alin, and Takashima) to discuss the subduction influence in the rear-arc mantle. Halogens in the mantle xenoliths can be explained by mixing among three components: sedimentary pore fluid-like high I/Cl component, high Br/Cl component, and MORB source mantle-like component. The high I/Cl and high Br/Cl halogens are considered to be of subducted origin, and the MORB source mantle-like halogens would be those inherent in the mantle convecting in the rear-arc mantle. While halogens in the wedge mantle beneath volcanic fronts are overwhelmed by subducted halogens, subducted influence is limited in the rear-arc mantle. The halogen/⁴⁰Ar* ratios are intermediate between volcanic fronts and the depleted mantle, indicating that the extent of subduction influence is smaller in rear-arc regions. Halogen/⁴⁰Ar* ratios have the advantage that the ratios are less affected by secondary processes, particularly free from atmospheric contamination. This advantage and the variation of the halogen/⁴⁰Ar* ratios of mantle xenoliths among different geological settings suggest that halogen/⁴⁰Ar* ratios can be used as a reliable proxy of the extent of subduction influence.