Mineral physics and seismic constraints on Earth’s structure and dynamics Earth stucture, mineralogy, elasticity

Primary source of information about the deep interior structure: seismological data Other sources of information, Earth structure and dynamics Gravitational field Magnetic field Heat flow, dynamic topography and geoid Plate movements Cosmochemistry and geochemistry High pressure mineralogy and mineral physics: experimental – computational

Other planets: No seismology (except rudimentary Moon seismology) Planetary mass distribution: determined via simple flyby Moment of inertia factor (MIF) MIF = I / R 2 M Homogeneous massive sphere: MIF = 0.4 Planet with high-density core: MIF < 0.4

P-waves Just like sound waves through air (pressure waves) S-waves

P-wave S-wave

Lay & Garnero (2011, Ann Rev Earth Plan Sci) Seismic phases generated by a 562 km deep source in PREM 1D Reference Earth Model of Dziewonski and Anderson (1981) Travel time curves. Dashed and dotted curves are upward-radiated P- and S- wave surface reflections (e.g. pPdiff and sPdiff)

Normal modes Global, very low frequency vibrations of the entire Earth

G/  = v s 2 K/  = v p 2 – 4/3v s 2 = v   =  v  : bulk sound velocity,   : seismic parameter Seismic velocities  physical properties Bulk modulus: K (= incompressibility / stiffness) Shear modulus: G v s 2 = G/  v p 2 = (K   G) 

Bragg's law positive interference when n = 2d sin  Unit cell V and  as a function of p In-situ high-pT XRD, using high- intensity synchrotron radiation Angle-dispersive XRD Monochromatic beam, fixed  variable  Energy-dispersive XRD Polychromatic (”white”) beam, fixed  d-spacings from the energy peaks E  hf  hc/  hc/E 2d sin   n  nhc/E gasket

Dziewonski & Anderson (1981, PEPI) 4082 citations, May 28, 2013 ol ga px wd rw ga bm fp Ca-pv pbm fp Ca-pv liquid FeNi minor Si, O, S solid FeNi 0.1 First-order Earth structure PREM : Preliminary Earth Reference Model - from seismology (normal modes) and gravity - includes  and p

Mg-pv Ferro- periclase garnet Ca-pv ga garnet fp FeNiS-metal Mg-perovskite BSE-image of subsolidus phase relations, 24 GPa

Simple system Mg 2 SiO 4 Best one-component analogue to peridotite Phase relations UM, TZ, LM: Modified from Fei & Bertka (1999, Geochem. Soc. Spec. Publ. 6)

Pyroxene: Mg [6] Si [4] O 3 Garnet: Mg 3 [8] MgSi [6] Si 3 [4] O 12 Akomotoite (ilmenite): Mg [6] Si [6] O 3 Perovskite: Mg [8] Si [6] O 3 System MgSiO 3 Modified from Fei & Bertka (1999, Geochem. Soc. Spec. Publ. 6) High-p crystal chemistry - without coordination number (CN) increase: high-p (or low-T) phase transitions: often decreasing symmetry - CN-increase is common for high-p phase transitions Explanation: large anions are more compressible than small cations → reduced r anion /r cation -ratio

Stixrude and Lithgow-Bertelloni (2011, GJI)

pv: Mg-perovskite fp: ferropericlase mw: magnesiowustite ol: olivine wd: wadsleyite rwd: ringwoodite st: stishovite op: orthopyroxene cp: clinopyroxene ak: akimotoite ga: garnet cor: corundum

First-order constraints on temperature Inner-outer core boundary at 330 GPa / 5150 km: melting temperature of FeNi 660 km discontinuity: Reaction rwd = pv+fp at 24 GPa (endothermic transition - small drop in adiabat) Location of mantle adiabat: below solidi of peridotite and basalt Location of outer core adiabat: above solidus of FeNi (+ Si, O, S) CMB: extreme thermal boundary layer ! K ! (  T: 1300K)

Why such a large thermal boundary layer at CMB ? Density contrast kg/m 3 precludes mantle - core mixing Viscocity of solid rock is quite high, even at very high T near the CMB peridotiteliquid FeNi T-dependent viscosity models Steinberger and Calderwood (2006, GJI) CMB

Grand model, Masters and Laske, website Seismic tomography models Large v S -amplitudes at the top and bottom of the mantle

Montelli et al. (2006, GGG) (finite frequency tomography) S-wave models 6 depth sections: km

Two large anti-podal, slow provinces - LLSVP Africa – Pacific (near equator - 180º apart) S-wave models, lowermost mantle (D”-zone) The degree-2 velocity anomalies, recognized >30 years ago, coincide with the residual geoid e.g. Dziewonsky et al. (1977, JGR), Dziewonski & Anderson (1984, Am Sci) Dziewonski et al. (2010, EPSL)

Dziewonski et al. (2010, EPSL) L 2 -norm L 1 -norm Cluster analysis of 5 tomographic models Lekic et al. (2012, EPSL) Seismic tomography, D" Note the plume locations: many/most along the LLSVP-margins

Paleogeographic relocation Clustering near periphery of LLSVPs - long-term stability - dense and hot (thermo-chemical piles) Large igneous provinces (LIPs) - age span: Ma SC –1% slow +2.5% fast –3% slow Africa Pacific Burke & Torsvik, 2004, EPSL Torsvik et al., 2006, GIJ Burke et al. 2007, EPSL Torsvik et al. 2008, EPSL SC

Comparison of seismic tomography (LLSVPs) and slab-sinking model at 2800 km depth Dziewonski et al. (2010, EPSL) Lithgow-Bertelloni & Richards (1998, Rev. Geophys.) Degree 2 Spherical harmonics modeling Power spectra Cumulative power spectra Slab model Tomogr. models Tomographic models Slab model Tentative conclusions 1. The observed degree-2 pattern is only partly reproduced by calculated slab-accumulation 2. The LM-structure may thus be old ( > Ma)

Hawaii Iceland Montelli et al. (2006, GGG): Finite frequency seismic tomography

Red crosses: deep plumes (Montelli et al.) Black crosses: other plumes Large lateral v s -gradients

S-wave model NE part of Pacific LLSVP Samoa quakes, recorded in N-America S-wave model Double crossing of the pv-ppv-transition Large lateral variation  Horizontal flow Lay et al (2006) Bin 1-3 Mantle flow model

Working model - Earth dynamics Equatorial section