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Eclogite in the upper mantle? chemical heterogeneities and seismology

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

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Eclogite in the upper mantle? chemical heterogeneities and seismology

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  1. Eclogite in the upper mantle? chemical heterogeneities and seismology Sebastian Rost DEEP 23. Februar 2005

  2. The recycling Factory

  3. 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)

  4. 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)

  5. 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)

  6. 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)

  7. Snapshots Davies (2002)

  8. Seismological Snapshots Model by Grand (2002)

  9. Array Seismology: Vespagram Incidence Angle Phase-weighted stack Time

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

  11. Stacking Stacks ~ 500 events stacked

  12. Stacking Stacks

  13. Stacking Stacks

  14. Stacking Stacks

  15. PP raypaths Information about Reflection point

  16. Single vespagram – Phase weighted stack

  17. Raw seismogram – Beam trace

  18. Scattered PP energy

  19. 1-D Earth models

  20. 1-D model IASP

  21. 1-D model LAMELLAE

  22. Further modelling Axisymmetric acoustic code – Thomas and Igel (2000) • Multidomain setup • Staggered grid • Acoustic – P-waves only • Center – cartesian Thomas et al. (2000)

  23. 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.

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