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Avalanches…. None of this whatsoever has been proven. But that’s what fun about it. …at the CMB. CORE. MANTLE. MANTLE. Richard. A. Muller- hero. http://muller.lbl.gov/. Avalanches at the Core-Mantle Boundary, Geophysical Research Letters , vol 29 pp 41-1 to 41-4 (2002).

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avalanches

Avalanches….

None of this whatsoever has been proven. But that’s what fun about it

at the cmb
…at the CMB

CORE

MANTLE

MANTLE

richard a muller hero http muller lbl gov
Richard. A. Muller- hero.http://muller.lbl.gov/

Avalanches at the Core-Mantle Boundary, Geophysical Research Letters, vol 29 pp 41-1 to 41-4 (2002)

how will they form i hear you say
How will they FORM I hear you say?

Please don’t let Charlie bite my finger…

let it snow let it snow
Let it snow, let it snow…
  • 70% of density change as liquid core solidifies is due to exclusion of lighter element exclusion- leads to convection.
  • Excluded light elements remain in solution and freeze out as they rise (1000oC temp drop I.C to CMB)
  • Light elements fall like snow onto undulating surface of CMB
  • Gathers like snow…how nice…
  • Exceeding the angle of repose will cause slumping, bringing core liquid with it.
  • Only need a few degrees slope.
  • Shear stress causes slumping- oblique impact?
meteor impact
Meteor Impact
  • Must be oblique
  • Consider, for example, a comet with velocity 25 km/sec, radius 5 km
  • ΔΩ = mvR/I
  • If the magnetic field of the core is coupled to entrained Fe in the sediment, sudden acceleration could cause an avalanche.
consequence numero uno
Consequence numerouno
  • Trigger the disturbance of the geodynamo
    • Implications for magnetic reversals
geodynamo
Geodynamo
  • Slumping Heat re-distribution as cool precipitate mixes with hot liquid Fe, cooling the Fe and letting it fall due to density increase.
  • This may disturb large convection cells of the outer core, reduce the overall scale of flow and even change the dipole component.
  • Cells in close association may be also affected, driving an overall shut down of the geodynamo
geodynamo cont
Geodynamo cont…
  • When the convective cells re-establish themselves, there is a 50% chance the magnetic field will reform in the reversed direction.

I’m lost too mate…must be the geodynamo again. Game of chess?

Help. I have absolutely no idea where the hell I am

consequence numero dos
Consequence numero dos
  • Mantle Plume initiation
    • The part of the mantle that lost the ‘sediment’ blanket is exposed to hot Fe and rapidly heated
      • Maybe only from the largest of avalanches (thickness >>100m)
consequence numero dos1
Consequence numero dos
  • Mantle plume initiation
    • Flood Basalts and Kimberlites
slide16
Mantle plume initiation
    • Flood Basalts and Kimberlites

If several avalanches are coupled from an intense impact, could result in separate but simultaneous plumes e.g simultaneous but spatially distant plumes at 61-62Ma (Larson et al. 1999)

a grand unified theory mass extinctions
A grand unified theory- MASS EXTINCTIONS
  • Meteor impacts and flood basalts have long been possible explanations for mass extinctions.
  • Flood basalts almost always seem to post-date the main phase of extinction
  • This would be satisfied by the impact avalanche model

TIME???

Mantle plumes take millions of years to reach the surface- would destroy correlations.

Kimberlite rates- 300km/s?

evidence for linking reversals to impacts
Evidence for linking reversals to impacts
  • Reversal in fall back breccia of 24-km Reis impact crater.
  • No reversal occurs with Chicxulub crater
    • Ooooooooooo…..
    • High iridium suggests impact was vertical (would have been ejected to space if oblique)??
geomagnetic quiet periods
Geomagnetic quiet periods
  • 120-85Ma has no magnetic reversals
  • Linked to mantle plume activity (Larson and Olsen 1991) which created Ontong-Java plateau
  • The LARGEST, yes, the largest, volcanic province on Earth. Alaska, 30Km thick.
multiple avalanches
Multiple avalanches…

Slope recharge after 35Ma

Crater subduction- candidates?

Marine Extinction peak at 120Ma

links to the chandler wobble
Links to the Chandler Wobble?
  • Decadal variations in avalanching
    • Small avalanches more likely and thus common than larger ones