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SUMMARY:Magma generation and extraction beneath mid-ocean ridges and ocean
 ic hotspots - Garrett  Ito (University of Hawaii)
DTSTART:20160606T130000Z
DTEND:20160606T134500Z
UID:TALK66356@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Much knowledge about the physics of melt generation and migrat
 ion in the mantle has come from seismic imaging and geodynamic modelling s
 tudies of mid-ocean ridges (MORs) and oceanic hotspots.&nbsp\; Global-scal
 e seismic studies show evidence for incipient\, perhaps volatile rich\, me
 lting starting at depths of ~150 km beneath MORs.&nbsp\; Variations in the
  width of the seismically-imaged melting zone as well as asymmetries in th
 is zone across MORs reveal important influences of mantle flow on melt gen
 eration.&nbsp\; Enhanced temperatures and mantle upwelling rates associate
 d with mantle plumes are especially important in giving rise to local peak
 s in melt generation at hotspots.&nbsp\; The upper-mantle seismic structur
 e of plumes can in some cases (Iceland) be explained by relatively simple 
 models of thermal plume-lithosphere interaction\, in other cases suggests 
 more complex thermochemical convection (Hawaii)\, and in other cases (Gala
 pagos) requires large variations in solid volatile content\, temperature\,
  and/or melt content not explained by current models.&nbsp\; The thermo-me
 chanical process by which melt is extract out of the asthenosphere and ent
 ers the lithosphere is poorly understood\, but the process can evidently a
 lter the isotropic as well as anisotropic seismic wave speeds over substan
 tial volumes of this boundary beneath MORs and hotspots.&nbsp\; Other seis
 mic studies show evidence that the amount of melt that is retained in the 
 mantle increases as spreading rate decreases at slow spreading rates\, thu
 s explaining global trends of crustal thickness at MORs.&nbsp\; Studies al
 so show that more melt is retained in the shallow-most mantle near offsets
  in ridge segments than near centers of ridge segments.&nbsp\; Together\, 
 these findings suggest that the ability of melt to penetrate the asthenosp
 here-lithosphere boundary is impeded by decreases in melt flux\, strain ra
 te\, gradients in mantle temperature or a combination of the three.<br><br
 >Related Links <ul> <li><a target="_blank" rel="nofollow">http://www.soest
 .hawaii.edu/GG/FACULTY/ITO</a>  - Garrett&#39\;s website&nbsp\;</li></ul>
LOCATION:Seminar Room 1\, Newton Institute
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