Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-MP Mineralogy & Petrology

[S-MP38] Physics and Chemistry of Minerals

Thu. May 24, 2018 3:30 PM - 5:00 PM A02 (Tokyo Bay Makuhari Hall)

convener:Hiroaki Ohfuji(Geodynamics Research Center, Ehime University), Seiji Kamada(Frontier Research Institute for Interdisciplinary Sciences, Tohoku University), Chairperson:Kamada Seiji(FRIS, Tohoku Univ.)

3:45 PM - 4:00 PM

[SMP38-14] Phase diagram of MgSiO3 in the upper mantle

*Shigeaki Ono1 (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Pyroxene, Upper mantle, Phase diagram

As olivine, pyroxene and garnet are major minerals in the upper mantle, understanding the dynamics and evolution of the mantle requires knowledge of MgSiO3, which is an end-member of pyroxene. Therefore, phase relations in MgSiO3 have been repeatedly investigated by a number of author. We investigated the disputed issue of two phase boundaries (high-pressure clinoenstatite and wadsleyite + stishovite, ringwoodite + stishovite and akimotoite) in MgSiO3, and suggest a revised phase diagram for MgSiO3 based on the obtained data.

We performed the high-pressure experiments using a multi-anvil high-pressure system combined with a synchrotron radiation source made it possible to acquire precise data from samples under high-pressure and high-temperature conditions. Experimental details have been described elsewhere [1,2]. A synthetic gel was used to produce a reactive and homogeneous starting material. The chemical composition of the synthesized gel was MgSiO3.

The reaction boundaries in MgSiO3 were determined over the range of 1150–1450 K. The stability of each phase was determined by observing the powdered X-ray diffraction data and analyzing the recovered samples. The reaction boundary between high-pressure clinoenstatite and wadsleyite + stishovite was found to occur at P (GPa) = 16.1 + 0.0064 x (T-1250) (K). According to our new data, the stability field of wadsleyite and stishovite expands to a low temperature region. The reaction boundary between ringwoodite + stishovite and akimotoite was found to occur at P (GPa) =22.0 - 0.0012 x T (K) [3]. This indicated that the triple point of ringwoodite+stishovite-wadsleyite+stishovite-akimotoite estimated in our study was at ~20 GPa and ~1700 K. The revised phase boundaries reconcile inconsistencies recorded between previous studies regarding the phase relation in MgSiO3

[1] S. Ono et al. (2011) Phys. Chem. Minerals, 38, 735-740.

[2] S. Ono et al. (2013) Phys. Chem. Minerals, 40, 811-816.

[3] S. Ono et al. (2017) Phys. Chem. Minerals, 44, 425-430.