ge11d: connection between seismic observations and...
TRANSCRIPT
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