Eclogite Eclogite in thein the

upper mantle?upper mantle?

chemical heterogeneitieschemical heterogeneitiesandand

seismologyseismology

Sebastian RostSebastian RostDEEP 23. Februar 2005DEEP 23. Februar 2005

The recycling FactoryThe recycling Factory

GeodynamicsGeodynamics

Davies (2002)Davies (2002)

- depth and temperature dependentdepth and temperature dependent

viscosityviscosity

- 2 moving/subducing plates- 2 moving/subducing plates

- 1 stationary continent- 1 stationary continent

- tracers = geochemical heterogeneity- tracers = geochemical heterogeneity

- passive tracerspassive tracers

- periodic side boundariesperiodic side boundaries

- greyscale = viscositygreyscale = viscosity

Convection MovieConvection Movie

Supplemental material movie 1

- 2 oceanic plates – 1 continental plate2 oceanic plates – 1 continental plate- subduction under stationary continentsubduction under stationary continent- migration of subduction zonesmigration of subduction zones- buckling under higher viscosity in lower mantlebuckling under higher viscosity in lower mantle- dark – high viscosity light – low viscositydark – high viscosity light – low viscosity stiff runnystiff runny

Davies (2002)Davies (2002)

Passive stirringPassive stirring

Insert supplemental material 2

- tracers throughout the model - orangetracers throughout the model - orange- subducted tracers – blacksubducted tracers – black- ULVZ material (20 km) – purpleULVZ material (20 km) – purple- 4 time segments: 4, 3, 2 Ga ago – present4 time segments: 4, 3, 2 Ga ago – present- 97 % of tracers processed97 % of tracers processed

Davies (2002)Davies (2002)

Heavy tracersHeavy tracers

Supplemental material 3

- tracer are slightly heavytracer are slightly heavy- 2 time segments: early – late2 time segments: early – late- accumulation of tracers at the bottomaccumulation of tracers at the bottom- plumes high in incompatible elementsplumes high in incompatible elements

Davies (2002)Davies (2002)

SnapshotsSnapshots

Davies (2002)Davies (2002)

Seismological SnapshotsSeismological Snapshots

Model by Grand (2002)Model by Grand (2002)

Array Seismology: VespagramArray Seismology: Vespagram

Phase-weighted stackPhase-weighted stack

Inci

denc

e A

ngle

Inci

denc

e A

ngle

TimeTime

Stacking StacksStacking Stacks

- sliding time window (~1s)sliding time window (~1s)- select highest amplitude in each select highest amplitude in each time slicetime slice- timing – amplitude - slownesstiming – amplitude - slowness

Condensing information into one traceCondensing information into one tracetime

Stacking StacksStacking Stacks

~ 500 events stacked~ 500 events stacked

Stacking StacksStacking Stacks

Stacking StacksStacking Stacks

Stacking StacksStacking Stacks

PP raypathsPP raypaths

Information aboutInformation aboutReflection pointReflection point

Single vespagram – Phase weighted stackSingle vespagram – Phase weighted stack

Raw seismogram – Beam traceRaw seismogram – Beam trace

Scattered PP energyScattered PP energy

1-D Earth models1-D Earth models

1-D model IASP1-D model IASP

1-D model LAMELLAE1-D model LAMELLAE

Further modellingFurther modelling

Axisymmetric acoustic code – Thomas and Igel (2000)Axisymmetric acoustic code – Thomas and Igel (2000)

- Multidomain setupMultidomain setup

- Staggered gridStaggered grid

- Acoustic – P-waves onlyAcoustic – P-waves only

- Center – cartesian Center – cartesian Thomas et al. (2000)Thomas et al. (2000)

ConclusionsConclusions

- PP data shows evidence for scatterers in the upper 200 km of mantle.PP data shows evidence for scatterers in the upper 200 km of mantle.

- High-frequency data – scatterer size ~10 - 20 km (?).High-frequency data – scatterer size ~10 - 20 km (?).

- Lumps of recycled crust at this depth?Lumps of recycled crust at this depth?

Why just there ? Why just there ? What happens below 200 km ?What happens below 200 km ?

- Array seismology give slowness information.Array seismology give slowness information.

Better modeling possible.Better modeling possible.

- Modeling possible by using slowness, timing and amplitude info.Modeling possible by using slowness, timing and amplitude info.

- 1D Lamellae point in the right direction.1D Lamellae point in the right direction.

- Acoustic wavepropagation will give further clues.Acoustic wavepropagation will give further clues.

Statistical description of seismic properties.Statistical description of seismic properties.