Japan Geoscience Union Meeting 2022

Presentation information

[E] Oral

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

[S-IT19] Deep Earth Sciences

Sun. May 22, 2022 1:45 PM - 3:15 PM Exhibition Hall Special Setting (2) (Exhibition Hall 8, Makuhari Messe)

convener:Kenji Ohta(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), convener:Kenji Kawai(Department of Earth and Planetary Science, School of Science, University of Tokyo), Tsuyoshi Iizuka(University of Tokyo), convener:Jun Tsuchiya(Geodynamics Research Center, Ehime University), Chairperson:Kenji Ohta(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Jun Tsuchiya(Geodynamics Research Center, Ehime University)

2:00 PM - 2:15 PM

[SIT19-02] Elastic properties of Fe-bearing Akimotoite at mantle conditions: Implications for composition and temperature in the lower mantle transition zone

*Yajie Zhao1, Zhongqing Wu1, Shangqin Hao2, Wenzhong Wang3,4, Xin Deng1, Jian Song1 (1.University of Science and Technology of China, 2.University of California San Diego, 3.University College London, 4.Carnegie Institution for Science)


Keywords:Akimotoite, Pyrolite, Elastic moduli, Temperature heterogeneity, Gaussian distribution

The pyrolite model, which can reproduce the upper-mantle seismic velocity and density profiles, was suggested to have significantly lower velocities and density than seismic models in the lower mantle transition zone (MTZ). This argument has been taken as mineral-physics evidence for a compositionally distinct lower MTZ. However, previous studies only estimated the pyrolite velocities and density along a one-dimension (1D) geotherm and never considered the effect of lateral temperature heterogeneity. Because the majorite-perovskite-akimotoite triple point is close to the normal mantle geotherm in the lower MTZ, the lateral low-temperature anomaly can result in the presence of a significant fraction of akimotoite in pyrolitic lower MTZ. In this study, we reported the elastic properties of Fe-bearing akimotoite based on first-principles calculations. Combining with literature data, we found that the seismic velocities and density of the pyrolite model can match well those in the lower MTZ when the lateral temperature heterogeneity is modeled by a Gaussian distribution with a standard deviation of ∼100 K and an average temperature of dozens of K higher than the triple point of MgSiO3. We suggest that a harzburgite-rich lower MTZ is not required and the whole mantle convection is expected to be more favorable globally.