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Eclogite
in the
upper mantle?
chemical heterogeneities
and
seismology
Sebastian Rost
DEEP 23. Februar 2005
The recycling Factory
Geodynamics
- depth and temperature dependent
viscosity
- 2 moving/subducing plates
- 1 stationary continent
- tracers = geochemical heterogeneity
- passive tracers
- periodic side boundaries
- greyscale = viscosity
Davies (2002)
Convection Movie
Supplemental material movie 1
- 2 oceanic plates – 1 continental plate
- subduction under stationary continent
- migration of subduction zones
- buckling under higher viscosity in lower mantle
- dark – high viscosity light – low viscosity
stiff
runny
Davies (2002)
Passive stirring
Insert supplemental material 2
- tracers throughout the model - orange
- subducted tracers – black
- ULVZ material (20 km) – purple
- 4 time segments: 4, 3, 2 Ga ago – present
- 97 % of tracers processed
Davies (2002)
Heavy tracers
Supplemental material 3
- tracer are slightly heavy
- 2 time segments: early – late
- accumulation of tracers at the bottom
- plumes high in incompatible elements
Davies (2002)
Snapshots
Davies (2002)
Seismological Snapshots
Model by Grand (2002)
Incidence Angle
Array Seismology: Vespagram
Phase-weighted stack
Time
Stacking Stacks
- sliding time window (~1s)
- select highest amplitude in each
time slice
- timing – amplitude - slowness
time
Condensing information into one trace
Stacking Stacks
~ 500 events stacked
Stacking Stacks
Stacking Stacks
Stacking Stacks
PP raypaths
Information about
Reflection point
Single vespagram – Phase weighted stack
Raw seismogram – Beam trace
Scattered PP energy
1-D Earth models
1-D model IASP
1-D model LAMELLAE
Further modelling
Axisymmetric acoustic code – Thomas and Igel (2000)
- Multidomain setup
- Staggered grid
- Acoustic – P-waves only
- Center – cartesian
Thomas et al. (2000)
Conclusions
- PP data shows evidence for scatterers in the upper 200 km of mantle.
- High-frequency data – scatterer size ~10 - 20 km (?).
- Lumps of recycled crust at this depth?
Why just there ?
What happens below 200 km ?
- Array seismology give slowness information.
Better modeling possible.
- Modeling possible by using slowness, timing and amplitude info.
- 1D Lamellae point in the right direction.
- Acoustic wavepropagation will give further clues.
Statistical description of seismic properties.