JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT22] [EE] Interaction and Coevolution of the Core and Mantle in the Earth and Planets

Sat. May 20, 2017 10:45 AM - 12:15 PM A05 (Tokyo Bay Makuhari Hall)

convener:Taku Tsuchiya(Geodynamics Research Center, Ehime University), Hidenori Terasaki(Graduate School of Science, Osaka University), Madhusoodhan Satish-Kumar(Department of Geology, Faculty of Science, Niigata University), Tetsuo Irifune(Geodynamics Research Center, Ehime University), John Hernlund(Earth-Life Science Institute, Tokyo Institute of Technology), Eiji Ohtani(Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University), Chairperson:Tetsuo Irifune(Geodynamics Research Center, Ehime University)

11:30 AM - 11:45 AM

[SIT22-10] Constraints on lowermost mantle structure from core-mantle boundary dynamic topography

★Invited papers

*Frederic Deschamps1, Yves Rogister2, Paul J Tackley3 (1.Academia Sinica, 2.University of Strasbourg, 3.ETH Zurich)

Keywords:Mantle convection, Core-mantle-boundary topography, Mantle structure

Mantle flow induces dynamic topography at the core-mantle boundary (CMB), with distribution and amplitude that depend on details of the flow. To assess whether CMB topography can bring constraints on the deep mantle structure, we calculate the CMB dynamic topography associated with different models of mantle convection, including thermo-chemical and purely thermal models. We investigate the influence of key controlling parameters, more specifically the thermal viscosity ratio (δηT) and, for thermo-chemical models, the chemical density contrast (δρC) and viscosity ratio (δηC) between primordial and regular materials. In purely thermal models, plume clusters induce positive topography with an amplitude that decreases with increasing δηT. In thermo-chemical models with δρC around 100 kg/m3 or more, reservoirs of dense material induce depression in CMB topography, surrounded by a ridge of positive topography. The average depression depth and ridge height increase with increasing δρC and δηC, but decrease with increasing δηT. We find that for purely thermal models or thermo-chemical models with low δρC, 90 kg/m3 and less, the long-wavelength (spherical harmonic degrees up to l = 4) dynamic topography and shear-wave velocity anomalies predicted by thermo-chemical distributions anti-correlate. By contrast, for models with δρC ≥ 100 kg/m3 and δηC > 1, long-wavelength dynamic topography and shear-wave velocity anomalies correlate well. This potentially provides a test to infer the nature, thermal or thermo-chemical, of low shear-wave velocity provinces (LLVSP) observed by global tomographic images. The presence of post-perovskite (pPv), provided that the viscosity of this phase is similar to that of bridgmanite, does not alter these conclusions. If the viscosity of pPv is lower than that of bridgmanite by 2 or 3 orders of magnitude, however, more substantial changes may arise.