17:15 〜 18:45
[SIT14-P18] 波形インバージョンによる中米下D"領域の3次元鉛直軸対称異方性構造推定
The D″ region, the lowermost several hundred km mantle region immediately above the core-mantle boundary (CMB), is the thermal boundary layer (TBL) and one of the major regions governing mantle convection. This region, especially beneath the subduction zones, is important to understand the dynamics of the mantle since thermally and chemically distinct slab materials can interact with the TBL and disturb the temperature, chemical composition, and mantle flow.
Central America is one of the typical subduction zones where the paleo-Farallon and the present Cocos plate have been subducted beneath the western margin of the Pangea since 250 million years ago (Müller et al. 2016). Borgeaud et al. (2017) inferred the three-dimensional S-velocity structure in the D″ region beneath Central America, applying the waveform inversion method to the transverse component data. They imaged the paleoslabs having just reached the CMB beneath Central America and Venezuela and eastwardly upwelling hot material continuous to chemically distinct denser material between slabs immediately above the CMB.
To verify the above images, we conduct the waveform inversion of transverse and radial components for the anisotropic S-velocity structure beneath Central America. We infer the isotropic S-velocity and anisotropic parameters (ξ). Various tests show good resolution for both parameters from 400 to 100 km above the CMB. Based on recent results from theoretical mineral physics and deformation experiments, we interpret our model as follows: (i) paleo-Farallon slab flows horizontally from 400 to 200 km above the CMB and descends vertically from 200 to 100 km above the CMB. (ii) chemically distinct denser material moves vertically from 400 to 200 km above the CMB and horizontally from 200 to 100 km above the CMB. These direction changes indicate that horizontally flowing subduction slabs may run into the denser material and change their direction to vertically descending.
Central America is one of the typical subduction zones where the paleo-Farallon and the present Cocos plate have been subducted beneath the western margin of the Pangea since 250 million years ago (Müller et al. 2016). Borgeaud et al. (2017) inferred the three-dimensional S-velocity structure in the D″ region beneath Central America, applying the waveform inversion method to the transverse component data. They imaged the paleoslabs having just reached the CMB beneath Central America and Venezuela and eastwardly upwelling hot material continuous to chemically distinct denser material between slabs immediately above the CMB.
To verify the above images, we conduct the waveform inversion of transverse and radial components for the anisotropic S-velocity structure beneath Central America. We infer the isotropic S-velocity and anisotropic parameters (ξ). Various tests show good resolution for both parameters from 400 to 100 km above the CMB. Based on recent results from theoretical mineral physics and deformation experiments, we interpret our model as follows: (i) paleo-Farallon slab flows horizontally from 400 to 200 km above the CMB and descends vertically from 200 to 100 km above the CMB. (ii) chemically distinct denser material moves vertically from 400 to 200 km above the CMB and horizontally from 200 to 100 km above the CMB. These direction changes indicate that horizontally flowing subduction slabs may run into the denser material and change their direction to vertically descending.