Probing Earth’s deep Probing Earth’s deep interior interior using mantle using mantle discontinuities discontinuities Arwen Deuss Arwen Deuss University of Cambridge, UK University of Cambridge, UK also: Jennifer Andrews, Kit Chambers, Simon Redfern, John also: Jennifer Andrews, Kit Chambers, Simon Redfern, John Woodhouse Woodhouse
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Probing Earth’s deep interior using mantle discontinuities Arwen Deuss University of Cambridge, UK also: Jennifer Andrews, Kit Chambers, Simon Redfern,
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Probing Earth’s deep interior Probing Earth’s deep interior using mantle discontinuitiesusing mantle discontinuities
Arwen DeussArwen DeussUniversity of Cambridge, UKUniversity of Cambridge, UK
also: Jennifer Andrews, Kit Chambers, Simon Redfern, John Woodhousealso: Jennifer Andrews, Kit Chambers, Simon Redfern, John Woodhouse
Global tomographyGlobal tomography
Velocity heterogeneity inthe Earth:
* thermal in origin?* also chemical/compositional heterogeneity?* lithosphere/asthenosphere boundary?* what happens in the transition zone?* where do slabs go?Ritsema, van Heijst & Woodhouse (1999)
Mantle discontinuitiesMantle discontinuities
mineral physics
Seismology
seismology
(Deuss & Woodhouse, GRL, 2002)
HistoryHistory
Number of papers per depth, since 1959
QuestionsQuestions
(1) what is the nature of the Lehmann discontinuity(1) what is the nature of the Lehmann discontinuity
at 220 km depth?at 220 km depth?
(2) what happens in the transition zone and(2) what happens in the transition zone and
how much thermal vs. chemical heterogeneity?how much thermal vs. chemical heterogeneity?
(3) are there discontinuities in the lower mantle?(3) are there discontinuities in the lower mantle?
* change in chemical composition?* change in chemical composition?
* change in deformation mechanism?* change in deformation mechanism?
What next? Fresnel zonesWhat next? Fresnel zones
Dahlen, 2003
ConclusionsConclusions
* comparison of seismic observations of mantle * comparison of seismic observations of mantle discontinuities with mineral physics implies significant discontinuities with mineral physics implies significant amount of chemical heterogeneityamount of chemical heterogeneity
* important implications for mantle flow* important implications for mantle flow
* we need to expand to other data types and implement * we need to expand to other data types and implement new techniques (such as finite frequency kernels) to new techniques (such as finite frequency kernels) to further understand the level of heterogeneityfurther understand the level of heterogeneity