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

The recycling Factory

Geodynamics Davies (2002) - depth and temperature dependent viscosity viscosity - 2 moving/subducing plates - 1 stationary continent - tracers = geochemical heterogeneity - passive tracers - periodic side boundaries - greyscale = viscosity

Convection Movie Supplemental material movie 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 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

Seismological Snapshots Model by Grand (2002)

Array Seismology: Vespagram Phase-weighted stack Incidence Angle Time

Stacking Stacks - sliding time window (~1s) - select highest amplitude in each time slice time slice - timing – amplitude - slowness Condensing information into one trace time

Stacking Stacks ~ 500 events stacked

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 ~ km (?). - Lumps of recycled crust at this depth? Why just there ? What happens below 200 km ? 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. Statistical description of seismic properties.