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SUMMARY:Insights into the mineralogy of the lower mantle using comparisons
  between global seismic tomography and geodynamic models [Rescheduled to o
 nline] - Dr. Paula Koelemeijer\, Royal Holloway
DTSTART:20200527T110000Z
DTEND:20200527T120000Z
UID:TALK142024@talks.cam.ac.uk
CONTACT:Camilla Penney
DESCRIPTION:*This seminar will be held online. Details will be sent to the
  Earth Sciences and Bullard mailing lists. If you are not in Earth Science
 s but would like to attend\, please contact the talk organisers.*\n\nGloba
 l tomography models routinely image seismic velocities at depth in the man
 tle. However\, interpretations of these seismic velocities are not unique 
 due to competing effects of temperature\, composition and phase transition
 s. One way to still obtain insights into the structure of the mantle is by
  comparing seismic tomography models to predictions based on geodynamic mo
 dels of mantle convection. These models serve to provide a reasonable temp
 erature distribution\, while the effects of different compositions can be 
 investigated through hypothesis testing of particular scenarios. One impor
 tant aspect to take into account in such comparisons is the limited resolu
 tion of global tomography models.\n\nIn my tomographic-geodynamic comparis
 ons I focus on the mid and the lowermost mantle\, where tomographic models
  consistently find a negative correlation between shear-wave velocity (Vs)
  and bulk sound velocity (Vc) variations. As temperature effects are expec
 ted to have a similar effect on these velocities\, this observation has lo
 ng served as argument for large-scale compositional variations. I will sho
 w instead that the phase transition from bridgmanite to post-perovskite ha
 s a stronger influence on the Vs-Vc correlations and can serve as a possib
 le explanation in the deep mantle. However\, the onset of the negative cor
 relation occurs at shallower depths (~1800 km)\, which is not reproduced b
 y either thermal or thermochemical models with post-perovskite. I hypothes
 ise that the iron spin transition in ferropericlase\, which has a strong e
 ffect on Vc\, can resolve this mid mantle discrepancy. Although ferroperic
 lase only forms ~20 % of the Earth’s mantle\, I will use new first princ
 iples calculations for the mixed spin state to show that this spin transit
 ion effect can be observed in global tomography and leads to an improved f
 it to seismic tomography.
LOCATION:ONLINE - Details to be sent by email
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