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SUMMARY:Resolving the Boundary Layer Paradox: Seismic Clues to the Origin 
 of Lithosphere Discontinuities - Tolulope Olugboji\, University of Rochest
 er
DTSTART:20250618T130000Z
DTEND:20250618T140000Z
UID:TALK231340@talks.cam.ac.uk
CONTACT:Tom Merry
DESCRIPTION:The upper mantle beneath old\, stable continents reveals puzzl
 ing seismic discontinuities within the cold and strong thermal boundary la
 yer. This is unexpected\, as tomographic models depict fast wavespeeds and
  low energy dissipation\, offering no basis for sharp velocity gradients w
 ithin the boundary layer. Resolving this paradox requires explaining the o
 bservations with mechanisms such as metasomatic alteration by volatile-bea
 ring rocks or grain-scale solid-state processes. I present new constraints
  derived from scattered-wave imaging that significantly improve global cov
 erage and depth resolution. Advanced denoising of body-waves reveals a sha
 rp velocity reduction beneath two-thirds of all continents at ~90 ± 20 km
  depth\, best explained by sub-solidus grain-boundary weakening. In some r
 egions\, velocity drops are observed between 120 and 250 km\, while in oth
 ers\, velocity increases occur at ~150 ± 50 km. Across all cases\, upper 
 mantle discontinuities rarely extend beyond the continental heterosphere. 
 Near continental margins and subduction zones\, these features may indicat
 e partial melting\, while rare double discontinuities could reflect melt l
 ayers or tectonic remnants from continental assembly\, paleo-subduction\, 
 or underplating. These findings provide crucial seismic clues for resolvin
 g the paradox of lithosphere discontinuities\, offering new insights into 
 the nature and dynamics of the thermal boundary layer beneath continents
LOCATION:Wolfson Lecture Theatre
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