Ge11d: Connection between seismic observations and Earth’s average mineralogy

Jennifer M. Jackson

Lecture slides: January 25, 27, and 29, 2010

PREM Earth’s internal divisions

Model A Bullen 1942

PREM Fraction

of MEarth

Region

(km)

Layer Depth

range (km)

(%)

A Crust:

Upper

0-15

0.10 (O)

0.37 (C) Lower 15-24

B Upper

mantle: Uppermost

24-80

10.3

Low-velocity

layer

80-220

220-400

C U.M.:

Transition zones

400-670 670-770

7.5

D Lower

mantle: D’

770-2740 49.2

D” 2740-2890

E Outer core 2890-5140 30.8

F Transition layer

G Inner core 5150-6370 1.7

(Dziewonski & Anderson 1981)

Basic information needed to formulate a mineralogical &

compositional model of Earth’s crust:

Field observations: hand samples

Laboratory measurements: Density (as a function of chemistry)

Wave velocities (as a function of chemistry)

“Mineral Physics” constraints

Solar system constraints

Crustal minerals

D.L. Anderson, New Theory of the Earth (2007) Oceanic crustal minerals

Basic information needed to formulate a mineralogical &

compositional model of Earth’s crust:

Field observations: hand samples

Laboratory measurements:

Density (as a function of chemistry) Wave velocities (as a function of chemistry)

Solar system constraints

D.L. Anderson, New Theory of the Earth (2007)

Average crustal abundance, density, & seismic velocities of major crustal minerals.

Oceanic crustal minerals

D.L. Anderson, New Theory of the Earth (2007)

Density, VP, and VS in rock types found in ophiolite sections (~oceanic crust)

Dunite

Lower, depleted oceanic crust (~20km) “ultramafics”

Upper oceanic crust (~7km)

D.L. Anderson, New Theory of the Earth (2007)

Continental crustal thickness

Density, VP and VS for continental minerals & rocks

D.L. Anderson, New Theory of the Earth (2007)

Density & seismic velocities of major crustal minerals.

Oceanic crustal minerals

PREM (mantle)

Earth’s internal divisions

Model A Bullen 1942

PREM Fraction

of MEarth

Region

(km)

Layer Depth range

(km)

(%)

A Crust:

Upper

0-15

0.10 (O) 0.37 (C)

Lower 15-24

B Upper mantle:

Uppermost

24-80

10.3

Low-velocity

layer

80-220

220-400

C U.M.:

Transition zones

400-670 670-770

7.5

D Lower mantle:

D’ 770-2740 49.2

D” 2740-2890

E Outer core 2890-5140 30.8

F Transition layer

G Inner core 5150-6370 1.7

(Dziewonski & Anderson 1981)

Sources of information about the composition

of Earth’s deep interior

Solar atmosphere analyses

Mineralogy and (isotope) geochemistry:

Meteorites

Mantle xenoliths

Inclusions in diamond

Geophysical observations and modeling:

Seismic body waves, normal-modes, gravity, magnetic field, viscosity, heat flow, …

High-pressure-temperature experiments: elasticity (wave velocities), phase equilibrium, thermodynamic data, calculations, …

Kola borehole: 12.6 km

Understand the structure, dynamics and evolution of

Earth’s interior….

…in terms of the physical, chemical and thermodynamic

properties of minerals under extreme conditions.

“Micro to macro”

Basic information to understand seismic observations:

As a function of P-T-X

Density

Wave velocities

Clausius-Clapeyron

slope: dP/dT = S/ V

Elastic anisotropy

Texture development

Phase Equilibrium Chemistry

“sharpness” of transition interval Solid, melt, or partial melt?

Deep interior behavior?

DAC, mulit-anvil, theory

Upper mantle mineralogy

D.L. Anderson, New Theory of the Earth (2007)

Measurements to determine: wave velocities

Ultrasonic interferometry

crustal and mantle rocks

Brillouin light scattering

crustal and mantle minerals

High-resolution inelastic x-ray scattering

lower mantle & core materials

Measurements to determine: density

Immersion

Determination of mass & volume (density = mass/volume)

Chemical analysis: mass

Diffraction: volume

3 million times atmospheric pressure

Clarity Hardness Conductivity Melting point

1 sq. centimeter

The Boeing 747-200 is ~500 tons

(1 million pounds)

3.6 million times atmospheric pressure = 360 GPa

1/2 million times atmospheric pressure = 50 GPa

The diamond anvil cell

X-rays in

X-rays out

0.5 mm

gasket

rubies

medium surrounding

sample

metal

6 cm

IR laser in

IR laser in

Jackson’s lab, Caltech

6900 6950 7000 7050Wavelength, A

Inte

nsity

0 5 10 15 20 25 30Pressure, GPa

Annealed18.6 GPa

Ambient

Pressure Measurement

Un-annealed

R2 R1

Pressure measurements by ruby fluorescence

Jackson’s lab, Caltech

DAC

Spectrometer

Frost, Elements (2008)

See also D. Anderson, New Theory of the Earth (2007)

Average mineralogy of the deep Earth

90 μm

57Fe sample

Creating high-temperatures in the diamond anvil cell: Novel mineral physics studies

X-ray meV bandwidth, focused

Laser Laser 8μm 30μm

Be-mirror (transparent for x-rays)

SMS signal

Jackson’s lab, Caltech

Advanced Photon Source (APS) Argonne National Laboratory, Chicago, IL

High-resolution X-ray scattering measurements at high-pressures and high-temperatures

Frost, Elements (2008)

Suggested isochemical mineralogy of the Earth’s mantle

Model A Bullen 1942

PREM Fraction

of MEarth

Region

(km)

Layer Depth

range (km)

(%)

A Crust:

Upper

0-15

0.10 (O)

0.37 (C) Lower 15-24

B Upper

mantle: Uppermost

24-80

10.3

Low-velocity

layer

80-220

220-400

C U.M.:

Transition zones

400-670 670-770

7.5

D Lower

mantle: D’

770-2740 49.2

D” 2740-2890

E Outer core 2890-5140 30.8

F Transition layer

G Inner core 5150-6370 1.7

The Lower Mantle

4.6%

6.8%

Compare measurements of aluminous MgSiO3 perovskite compressional (VP) and shear (VS) velocities

with PREM

Jackson et al. (2005)

D.L. Anderson, New Theory of the Earth (2007)

The core-mantle boundary region: D”

VS ~2%

VP <1%

Sound velocities of MgSiO3 post-perovskite:

Determined by Brillouin Spectroscopy Murakami et al. EPSL (2007)

Effect of iron?

Effect of aluminum?

More complicated chemistries and/or phases

Model A Bullen 1942

PREM Fraction

of MEarth

Region

(km)

Layer Depth

range (km)

(%)

A Crust:

Upper

0-15

0.10 (O)

0.37 (C) Lower 15-24

B Upper

mantle: Uppermost

24-80

10.3

Low-velocity

layer

80-220

220-400

C U.M.:

Transition zones

400-670 670-770

7.5

D Lower

mantle: D’

770-2740 49.2

D” 2740-2890

E Outer core 2890-5140 30.8

F Transition layer

G Inner core 5150-6370 1.7

The Core

Densities in the Core

(PREM)

Density deficit of ~3-5% in the outer core

Measured velocities of candidate core materials