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

Primary source of information about the deep interior structure:

seismological data

Other sources of information, Earth structure and dynamicsGravitational 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 / R2 M

Homogeneous massive sphere: MIF = 0.4

Planet with high-density core: MIF < 0.4

P-wavesJust like sound waves throughair (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 modesGlobal, very low frequency vibrations of the entire Earth

G/r = vs2

K/r = vp2 – 4/3vs

2 = vf2 = F

vf: bulk sound velocity,

F : seismic parameter

Seismic velocities physical properties

Bulk modulus: K (= incompressibility / stiffness)

Shear modulus: G

vs2 = G/r

vp2 = (K + 4/3*G)/r

Bragg's lawpositive interference when nl = 2d sinq

Unit cell V and r as a function of p In-situ high-pT XRD, using high-intensity synchrotron radiation

Angle-dispersive XRDMonochromatic beam, fixed , l variable q

Energy-dispersive XRDPolychromatic (”white”) beam, fixed qd-spacings from the energy peaks

E = hf = hc/l

= l hc/E 2d sinq = nl = 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 FeNi0.1

+ minor Si, O, S

solid FeNi0.1

First-order Earth structurePREM: Preliminary Earth Reference Model

- from seismology (normal modes) and gravity- includes r and p

Mg-pv

Ferro-periclase

garnet

Ca-pvga

garnetfp

FeNiS-metal

Mg-perovskite

BSE-image of subsolidus phase relations, 24 GPa

Simple system Mg2SiO4

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] O3

Garnet: Mg3[8] MgSi[6] Si3

[4] O12

Akomotoite (ilmenite): Mg[6] Si[6] O3

Perovskite: Mg[8] Si[6] O3

System MgSiO3

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 ranion/rcation-ratio

Stixrude and Lithgow-Bertelloni (2011, GJI)

Stixrude and Lithgow-Bertelloni (2011, GJI)pv: Mg-perovskitefp: ferropericlasemw: magnesiowustiteol: olivinewd: wadsleyiterwd: ringwooditest: stishovite

op: orthopyroxenecp: clinopyroxeneak: akimotoitega: garnetcor: 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 ! 2500 - 3800 K ! (DT: 1300K)

Why such a large thermal boundary layer at CMB ?

Density contrast 5500 - 9900 kg/m3

precludes mantle - core mixing

Viscocity of solid rock is quite high, even at very high T near the CMB

peridotite liquid FeNi

T-dependent viscosity models Steinberger and Calderwood (2006, GJI)

CMB

Grand model, Masters and Laske, website

Seismic tomography models Large vS-amplitudes at the top and bottom of the mantle

Montelli et al. (2006, GGG)(finite frequency tomography)

S-wave models 6 depth sections: 900-2800 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)

L2-norm L1-norm

Cluster analysis of 5 tomographic modelsLekic 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: 16-297 Ma

SC

–1%

slow

+2.5% fast

–3%slow

AfricaPacific

Burke & Torsvik, 2004, EPSLTorsvik et al., 2006, GIJBurke et al. 2007, EPSLTorsvik 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 Degree 2

Spherical harmonics modeling

Power spectra Cumulative power spectra

Slab m

odel

Tomog

r.

mod

elsTomographic 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 ( > 300-500 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

vs-gradients

S-wave model

NE part of Pacific LLSVPSamoa quakes, recorded in N-America

S-wave model

Double crossing of thepv-ppv-transition

Large lateral variation Horizontal flow

Lay et al (2006)

Bin 1-3

Mantle flow model

Working model - Earth dynamics

Equatorial section