[S-IT15] 地球深部科学 - 核・マントルの相互作用と共進化

[SIT15-04] Imaging paleoslabs and inferring the Clapeyron slope and heat flow in D′′ beneath the northern Pacific based on high-resolution inversion of seismic waveforms for 3-D transversely isotropic structure

★Invited Papers

*鈴木 裕輝¹、河合 研志²、ゲラー ロバート² (1.東京工業大学 理学院 地球惑星科学系、2.東京大学 大学院理学系研究科 地球惑星科学専攻)

キーワード：波形インバージョン、異方性、マントル最深部、沈み込みスラブ、熱流量、相転移

We conduct waveform inversion to infer high-resolution 3-D models of the S-velocity perturbation δVs and the anisotropy parameter δξ in the lowermost 400 km of the mantle beneath the northern Pacific. Our inferred models show three prominent features: (i) a widespread high-δVs layer with ~100 km thickness that exists ~250 km above the core-mantle boundary (CMB), which could be due to a bridgmanite to post-perovskite phase transition related to the D″ discontinuity; (ii) distinct high-δVs anomalies with positive δξ that continue from 100 km to more than 400 km above the CMB, which could be the subducted Izanagi, Farallon, and Telkhinia paleoslabs; (iii) a vertically continuous low-δVs anomaly with negative δξ at the edge of the subducted slab, which we interpret as an upwelling plume induced by sinking of paleoslabs. Based on the δVs gradient as a function of depth for the inferred 3-D Vs structure, we infer the Clapeyron slope of the post-perovskite phase transition in the lowermost mantle beneath the northern Pacific to be 10.2±1.3 MPa/K. Assuming that the δVs anomaly can be attributed to the effects of temperature and a bridgmanite to post-perovskite phase transition, we infer a regional average heat flux of ~90 mW/m², which falls within the global heat flux range suggested by previous studies. We infer a maximum heat flux of ~150 mW/m² beneath the central Bering Sea, where the 3-D seismic velocity model shows that a subducted cold paleoslab makes contact with the CMB.