Eclogite in the upper mantle? chemical heterogeneities andseismology Sebastian Rost DEEP 23. Februar 2005.

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.