1. Transition Zone Discontinuities
Why focus here?
1. Deeper than “normal” melt sources
2. Very sensitive to changes in temperature and chemistry
“Normal” = Ridge, which has a melt source confined within upper mantle and should not affect TZ discontinuities.  This is a bit of a spoiler for the students for the ridge temperature results in the activity. Can decide you want to keep this in and have them confirm, or take it out and let them investigate. In this sense, TZ discontinuities are used to test temperature beneath ocean islands. (Hotspots? Maybe hot, maybe not.)

2. Transition Zone Phase Transitions
410
520
660
Olivine (α)
Wadsleyite (β)
Perovskite
Ringwoodite (γ)
Wendy Mao posted some nice PowerPoint slides for these phase transitions. They follow this slide.

3. Olivine (Mg,Fe)2SiO4
From Wendy Mao
0-14 GPa
( km)

4. Olivine (Mg,Fe)2SiO4 Wadsleyite 0-14 GPa (0 - 410 km) 14-19 GPa
+ 8% density
From Wendy Mao
0-14 GPa
( km)
14-19 GPa
( km)

5. Wadsleyite Ringwoodite 1 – 140,000 atm (0 - 410 km) 14-19 GPa
+ 2% density
From Wendy Mao
1 – 140,000 atm
( km)
14-19 GPa
( km)
19-24 GPa
( km)

6. + ‘Perovskite’ (Mg,Fe)SiO3 Ringwoodite (Mg,Fe)2SiO4
GPa
( km) +
+ 12% density
From Wendy Mao
Ferropericlase (Mg,Fe)O
19-24 GPa
( km)

7. ‘Perovskite’ ‘Post-Perovskite’ 24-127 GPa (660 - 2740 km)
‘Perovskite’ (Mg,Fe)SiO3
+ 2% density
From Wendy Mao
GPa
( km)
127 GPa-136 GPa
( km)
Discovered in 2004

8. Transition Zone Topography
Left = Standard onion slice picture, Right highlights variations in discontinuity depth (and strength) and the presence of additional discontinuities that may not be global features  Indicates heterogeneity within the Earth, probably for both temperature and composition.

9. Clapeyron Slope
Describes changes in phase transition with temperature and pressure
“Normal” TZ
Thickness
Colder
Warmer

10. Mineralogy: Not Just Olivine
“Garnet”
Component
“Olivine Component”

11. Mineralogy: Not Just Olivine
From

12. Detecting Discontinuities
Triplications
Receiver Functions
ScS
Reverberations SS
Precursors
Seismic methods used to detect discontinuities. Scale is approximate. Star = Earthquake, Squares = Stations (Indicates general geographic region where each method can be detected). Color change of seismic raypath indicates change in wave type (ex. P-wave converts to S beneath the station for Receiver Functions)