start-ver=1.4 cd-journal=joma no-vol=8 cd-vols= no-issue=13 article-no= start-page=eabm1821 end-page= dt-received= dt-revised= dt-accepted= dt-pub-year=2022 dt-pub=20220330 dt-online= en-article= kn-article= en-subject= kn-subject= en-title= kn-title=Viscosity of bridgmanite determined by in situ stress and strain measurements in uniaxial deformation experiments en-subtitle= kn-subtitle= en-abstract= kn-abstract=To understand mantle dynamics, it is important to determine the rheological properties of bridgmanite, the dominant mineral in Earthfs mantle. Nevertheless, experimental data on the viscosity of bridgmanite are quite limited due to experimental difficulties. Here, we report viscosity and deformation mechanism maps of bridgmanite at the uppermost lower mantle conditions obtained through in situ stress-strain measurements of bridgmanite using deformation apparatuses with the Kawai-type cell. Bridgmanite would be the hardest among mantle constituent minerals even under nominally dry conditions in the dislocation creep region, consistent with the observation that the lower mantle is the hardest layer. Deformation mechanism maps of bridgmanite indicate that grain size of bridgmanite and stress conditions at top of the lower mantle would be several millimeters and ~105 Pa to realize viscosity of 1021?22 Pa?s, respectively. This grain size of bridgmanite suggests that the main part of the lower mantle is isolated from the convecting mantle as primordial reservoirs. en-copyright= kn-copyright= en-aut-name=TsujinoNoriyoshi en-aut-sei=Tsujino en-aut-mei=Noriyoshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=YamazakiDaisuke en-aut-sei=Yamazaki en-aut-mei=Daisuke kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=NishiharaYu en-aut-sei=Nishihara en-aut-mei=Yu kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= en-aut-name=YoshinoTakashi en-aut-sei=Yoshino en-aut-mei=Takashi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=4 ORCID= en-aut-name=HigoYuji en-aut-sei=Higo en-aut-mei=Yuji kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=5 ORCID= en-aut-name=TangeYoshinori en-aut-sei=Tange en-aut-mei=Yoshinori kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=6 ORCID= affil-num=1 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=2 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=3 en-affil=Geodynamics Research Center, Ehime University kn-affil= affil-num=4 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=5 en-affil=Japan Synchrotron Radiation Research Institute kn-affil= affil-num=6 en-affil=Japan Synchrotron Radiation Research Institute kn-affil= END start-ver=1.4 cd-journal=joma no-vol=105 cd-vols= no-issue=3 article-no= start-page=319 end-page=324 dt-received= dt-revised= dt-accepted= dt-pub-year=2020 dt-pub=20200501 dt-online= en-article= kn-article= en-subject= kn-subject= en-title=Pressure dependence of Si diffusion in gamma-Fe kn-title=Pressure dependence of Si diffusion in -Fe en-subtitle= kn-subtitle= en-abstract= kn-abstract=The pressure dependence of Si diffusion in -Fe was investigated at pressures of 5?15 GPa and temperatures of 1473?1673 K using the Kawai-type multi-anvil apparatus to estimate the rate of mass transportation for the chemical homogenization of the Earth's inner core and those of small terrestrial planets and large satellites. The obtained diffusion coefficients D were fitted to the equation D = D0 exp[?(E* + PV*)/(RT)], where D0 is a constant, E* is the activation energy, P is the pressure, V* is the activation volume, R is the gas constant, and T is the absolute temperature. The least-squares analysis yielded D0 = 10-1.17}0.54 m2/s, E* = 336 } 16 kJ/mol, and V* = 4.3 } 0.2 cm3/mol. Moreover, the pressure and temperature dependences of diffusion coefficients of Si in -Fe can also be expressed well using homologous temperature scaling, which is expressed as D = D0exp{?g[Tm(P)]/T}, where g is a constant, Tm(P) is the melting temperature at pressure P, and D0 and g are 10-1.0}0.3 m2/s and 22.0 } 0.7, respectively. The present study indicates that even for 1 billion years, the maximum diffusion length of Si under conditions in planetary and satellite cores is less than ?1.2 km. Additionally, the estimated strain of plastic deformation in the Earth's inner core, caused by the Harper?Dorn creep, reaches more than 103 at a stress level of 103?104 Pa, although the inner core might be slightly deformed by other mechanisms. The chemical heterogeneity of the inner core can be reduced only via plastic deformation by the Harper?Dorn creep. en-copyright= kn-copyright= en-aut-name=TsujinoNoriyoshi en-aut-sei=Tsujino en-aut-mei=Noriyoshi kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=1 ORCID= en-aut-name=M?rzaAndreea en-aut-sei=M?rza en-aut-mei=Andreea kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=2 ORCID= en-aut-name=YamazakiDaisuke en-aut-sei=Yamazaki en-aut-mei=Daisuke kn-aut-name= kn-aut-sei= kn-aut-mei= aut-affil-num=3 ORCID= affil-num=1 en-affil=Institute for Planetary Materials, Okayama University kn-affil= affil-num=2 en-affil=Faculty of Geology and Geophysics, University of Bucharest kn-affil= affil-num=3 en-affil=Institute for Planetary Materials, Okayama University kn-affil= en-keyword=-Fe kn-keyword=-Fe en-keyword=silicon diffusion kn-keyword=silicon diffusion en-keyword=high pressure kn-keyword=high pressure en-keyword=planetary core kn-keyword=planetary core END