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SUMMARY:Seismic evidence for melt in the upper mantle - Michael Kendall (U
 niversity of Bristol)
DTSTART:20160610T103000Z
DTEND:20160610T113000Z
UID:TALK66424@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Michael Kendall\,&nbsp\;School of Earth Sciences\, University 
 of Bristol\, UK.  &nbsp\;&nbsp\;<br>(Co-author)  James Hammond\,&nbsp\;Dep
 artment of Earth and Planetary&nbsp\;Sciences\, Birkbeck\, University of L
 ondon\, UK.  &nbsp\;  <br>A range of seismic measurements can be used to m
 ap melt distribution in the deep Earth. These include seismic P- and S-wav
 e velocities derived from tomography\, Vp/Vs ratios obtained from receiver
  functions\, and estimates of seismic anisotropy and attenuation. The most
  obvious melt parameter that seismic data might be sensitive to is volume 
 fraction. However\, in many cases such data are more sensitive to the aspe
 ct ratio of melt inclusions\, which is controlled by the wetting angle. In
  many active regions these observations are readily explained by silicate 
 melt in the upper 100 km of the mantle. While low wavespeeds may be attrib
 uted to thermal effects in tectonically young or actively volcanic regions
 \, in older\, tectonically stable regions low velocity anomalies apparentl
 y persist even past the decay time of any thermal perturbation\, rendering
  such a mechanism implausible. Low volume melts can also reduce wavespeeds
 \, but their buoyancy should drain them upward away from source regions\, 
 preventing significant accumulation if they are able to segregate. Sulfide
 \, ubiquitous as inclusions in lithospheric mantle xenoliths\, forms dense
 \, non&#x2010\;segregating melts at temperatures and volatile fugacities c
 haracteristic of even old lithospheric mantle. Modest amounts of sulfide m
 elt can lead to long-term reductions in seismic wavespeeds in areas of the
  lithosphere and the asthenosphere disturbed by prior melting events that 
 carry and concentrate sulfide.  &nbsp\;  &nbsp\;  &nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
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