Composition of the Earth from Ab Initio Mineral

Composition of the Earth from Ab Initio Mineral Physics Taku Tsuchiya Geodynamics Research Center, Ehime University, Japan Dearth-Life Science Institute, Tokyo Institute of Technology, Japan 2016/01/07 ERI, U Tokyo

Chemical composition of Earth’s interior Crust 0 GPa, 300 K UM 24 GPa, 1900 K LM Silicate 136 GPa, 4000 K OC 329 GPa, 5500 K Fe + light elements IC 364 GPa, 6000 K Details still remain unclear!

Seismological reference model PREM (Dziewonski & Anderson 81) Mineral physics: Search for ｌithology which can reproduce the references

Mineralogical model of the upper mantle UM & TZ LM Li & Leibermann (07) Ø UM = Pyrolitic (Peridotite/Basalt ~ 4/1) Ø LM … remain controversial Irifune+ (08)

Ab initio quantum mechanical calculation method • Method to compute electronic structure and chemical bonding nonempirically, based only on fundamental quantum mechanical principles with basic information such as atomic number Density Functional Theory (Hohenberg & Kohn 64; Kohn & Sham 65; Nobel prize in chemistry 98) GRC Parallel Computation Systems

Universal applicability of DFTbond types Valence charge density of some representative Metal [Au (100)] Ionic crystal [Mg. O (100)] Au Covalent crystal [diamond] C Van der Waals crystal [Ar (100)] Ionic + covalent Si. O 2 [Stishovite] Ar O Si

Fundamental tools

Predictability of DFT calculations Mg. Si. O 3 bridgmanite Compression curve Thermodynamics Earth’s lower mantle (e. g. specific heat) 0 GPa Calorimetry Calculation J. Tsuchiya+ (05) JGR Akaogi+ (08) Phys Chem Miner Quite high predictability!!

Structure search by ab initio molecular dynamics Mg. Si. O 3 Bridgmanite Si. O 2 α-Quartz ~700 GPa Mg Si ~130 GPa Tsuchiya+ (04) EPSL O Tsuchiya & Tsuchiya (11) PNAS

Phase diagram LDA GGA LM OC D” D” layer 7. 5 MPa/K iabat Mantle ad 1000 K Murakami+ (04) Bridgmanite Postperovskite ΔPT~10 GPa Valley bottom Hill top ~8 GPa ~250 km Tsuchiya+ (04) EPSL

High-P, T elasticity Method-1: stress-strain (MD) Method-2: energy-strain (LD) Equilibrium structure Relaxation for strained cell Isothermal-adiabatic conversion Elastic wave velocity Polycrystalline average

Elastic wave velocity (Mg. Si. O 3 bridgmanite)

Representative lithology for the lower mantle Chondrite Pyrolite Olivine Pyrolite model agrees best with PREM in the whole LM P range Along an adiabatic T profile with TP =1600 K Blue: Fe 2+-bearing Green：Fe 3+-bearing Red：Fe 3++Al-bearing Wang, Tsuchiya & Hase (15) Nature Geo

Liquid iron alloys in the outer core Fe-Ni + ~10 wt% light elements (O, S, Si, C, H…) (e. g. , Birch 64) outer core CMB ICB TICB = 5000 K PREM P-wave velocity (km/s) Density (g/cm 3) CMB Pressure (GPa) Pure Fe Ø 8~9% denser than PREM Ø Already comparable VP outer core ICB PREM TICB = 5000 K Pressure (GPa) Pozzo+ (13) PRB Ichikawa+ (14) JGR

VP and ρ along adiabat CMB outer core ICB Fe 100 VP: almost T-independent ρ: strongly T-dependent PREM TICB=9000 TICB=7000 TICB=5000

Optimized compositions of binary systems (atomic %) Fe 78 O 22 Fe 82 S 18 Fe 70 H 30 Fe 85 Si 15 Comparable & indistinguishable CMB outer core ICB Further observations Ø Melting points Ø Partitioning Fe 80 C 20 Worse fit required

Core-mantle boundary heat flow (JCMB) Heat flow Arc Subducting slab Thermal boundary layer Global mantle convection Cold region Lattice thermal conductivity t a e H Core Hot region Hot plume qi qj qk=qi+qj+G Ø Mantle convection strength Ø Core cooling rate qj qi qk

Thermal conductivity of the lower mantle z = 660 km 4000 t+ Hot 2500 2000 1500 1000 20 Dekura, Tsuchiya+ (13) Phys Rev Lett Ø Close to the lower bound d 1981) t adiaba anklan h S & n (Brow Cold Pv+Fp 40 60 +2004 T sol pe of T (K) 3000 tite o rid 0) 1 20 Tsuchiy a 3500 e qu i F ( ICMB z = 2890 km of previous estimations Ø ~10% of surface heat flow PPv +Fp Ø Enough to sustain geodynamo 80 100 120 140 P (GPa) 0 5 10 (W m K ) -1 -1 LM 15

Earth’s inner core 5150 km-6370 km depth Enigmatic properties u Anisotropy u Hemispherical asymmetry Hot? Cold? u Layering Stable Fe phase Hcp (ε) Refs: Tanaka+ (97) Creager+ (00) Ishii & Dziewonski (02) etc

Density Co. E ICB Inner core ~3 -5% Pure hcp Fe: M RE Liq . (I ch ika wa +1 4) P Ø ~1. 9% heavier than liquid Fe Ø ~3 -5% heavier than PREM Reasonable agreements with some extrapolations (Dubrovinski+ 00; Dewaele+ 06; etc)

Elastic wave velocity of hcp-Fe Co. E ICB Inner core Ø Velocities of pure iron closer to PREM over 7000 K! light elements Consistent with Sha & Cohen (10) & Martorell+ (13) But 7000 K is too high (> Tmelt)!!! Ø Light elements may enhance discrepancy!

http: //core-mantle. jp/ Leader 2015 FY ~ 2020 FY A 04 Theory & Computation 土屋卓久（愛媛大） A 02 Seismology/ Geomagnetism A 03 田中聡（JAMSTEC） Neutrino Isotope Geophysical observation Core-Manlte Coevolution Geochamical analysis 鈴木勝彦（JAMSTEC） Partitioning S. Kumar （新潟大） A 01 田中宏幸（東京大） Dynamics Structure 芳野極（岡山大） 鈴木昭夫（東北大） High-P experiment 参加機関 東北大 新潟大 東京大 東 大 京都大 大阪大 岡山大 広島大 愛媛大 九州大 JAMSTEC 共同利用 基盤施設 SPring-8 J-PARC KEK Kam. LAND Technique 入舩徹男（愛媛大） 44/45