Ge11d: Connection between seismic observations and...
Transcript of Ge11d: Connection between seismic observations and...
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Ge11d: Connection between seismic observations and Earth’s average mineralogy
Jennifer M. Jackson
Lecture slides: January 25, 27, and 29, 2010
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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)
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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
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Crustal minerals
D.L. Anderson, New Theory of the Earth (2007) Oceanic crustal minerals
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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
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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)
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D.L. Anderson, New Theory of the Earth (2007)
Continental crustal thickness
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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
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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)
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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
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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”
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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
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Upper mantle mineralogy
D.L. Anderson, New Theory of the Earth (2007)
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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
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3 million times atmospheric pressure
Clarity Hardness Conductivity Melting point
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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
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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
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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
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Frost, Elements (2008)
See also D. Anderson, New Theory of the Earth (2007)
Average mineralogy of the deep Earth
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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
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Advanced Photon Source (APS) Argonne National Laboratory, Chicago, IL
High-resolution X-ray scattering measurements at high-pressures and high-temperatures
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Frost, Elements (2008)
Suggested isochemical mineralogy of the Earth’s mantle
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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%
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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)
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The core-mantle boundary region: D”
VS ~2%
VP <1%
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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
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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
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Densities in the Core
(PREM)
Density deficit of ~3-5% in the outer core
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Measured velocities of candidate core materials