1. Ch 6: Internal Constitution of the Earth

3. Mantle composition

4. Geological background
88 elements found in the Earth's crust -- of these, only 8 make up 98%: oxygen, silicon, aluminum, iron, calcium, magnesium, potassium and sodium
In the whole earth, only 4 elements dominate: iron, oxygen, silicon and magnesium
• These elements go up to make minerals. A mineral is a naturally occurring, inorganic solid with a characteristic chemical composition and a crystalline structure
• Even though there are more than 2500 minerals knows, only nine minerals make up most of the rocks of the Earth's crust -- these are the "rock-forming minerals"

5. The rock-forming minerals
Minerals containing silicon and oxygen are called silicates. These make up more than 95% of the crust. The seven most abundant silicates in the crust are feldspar, quartz, pyroxene, amphibole, mica, clay minerals, and olivine. Olivine and pyroxene are the main constituents of the uppermost mantle.
Most silicates are formed from SiO4 tetrahedra (a silicon atom surrounded by four oxygens) arranged in a variety of ways. Exceptions are quartz and feldspar which are so-called framework silicates. The silicate tetrahedron is exceptionally stable and allows close-packed structures to be formed.

6. Pyrolite composition:

7. Common mantle minerals: Olivine Orthoppyroxene Clinopyroxene Al-phase
DIRECT SAMPLES (Peridotite)
Common mantle minerals:
Olivine
Orthoppyroxene
Clinopyroxene
Al-phase
Spinel
Garnet

9. High pressure experiments

10. Multi-anvil press:

11. Large volume multi anvil cells:
3 orders of magnitude higher than DACs!
Large volume: House probes, synthesize larger specimens, some experiments require large V (e.g. ultrasonic interferometry)
Hydrostatic Pressure: Closer, since squeezing from 8 directions,
But, not easily used with gas pressure medium
Pressures: Top of lower mantle at best with sintered diamonds and synchrotron radiation

12. Diamond anvil cells:

13. Diamond Anvil Cells: Why Diamonds?
Can use: Steel, tungsten carbide, boron carbide,
sapphire, cubic zirconia, sintered diamond,
or single-crystal diamond
Single crystal diamond:
1) Strongest material known
2) Transparent (IR, optical, UV, and X-ray)
3) Non-magnetic insulator: , 

14. Creating Temperature:
3 ways:
1) External heating
2) Internal heating
3) IR Laser Heating

15. Measurement of Pressure
Measuring Material Parameters…
Measurement of Pressure
Ruby Chips Fluorescence Method
Freq. shift of ruby with increasing pressure
Linear to 30 GPa
Calibrated to 100 GPa by Raman Spec.
Calibrated to >200 GPa by Gold
Accurate to 15-20% at 200 GPa
Diffuses with temperature (>700K)
Ruby and Diamond Fluorescence overlap between GPa
KEY: Allows sampling at multiple points in pressure medium

16. T: temperature I: intensity : wavelength Cs: constants : emissivity
Laser heating - use black body radiation
T: temperature
I: intensity
: wavelength
Cs: constants
: emissivity
is wavelength dependent
But dependence not known for many materials! (known for Fe)
Perfect black body:  = 1
Grey body:  < 1

17. In-Situ X-Ray Diffraction
Measuring Material Parameters…
In-Situ X-Ray Diffraction
Provides Crystal Structure, Density and melting points
Synchrotron Radiation provides highly collimated x-ray source
Braggs Law: 2q = angle of diffraction
d = spacing of crystal planes
 = wavelength of X-ray

18. Phase transformations in the upper mantle

24. Structures of minerals

27. Spinel structure (ringwoodite)

31. Undistorted (cubic) perovskite structure

34. Fitting seismic models

35. Matching seismic observations with the pyrolite model:

36. Red=density
Blue=Vc
Green=Vs
Xpv=0.65: “pyrolite”

37. Shock wave data and the core

43. Melting Temperature: Pure Fe
Boehler(1993)
Yoo et al (1993)
Nguyen & Holmes(2009)
Brown & McQueen (1986)
Belonoshko et al (2000
Alfe et al (2002)
Alfe (2009)
Sola & Alfe (2009)
Density jump is accounted when considering compositional convection
Anzellini et al (2013)
(slide courtesy Chris Davies)
CMB
ICB