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SUMMARY:Observational constraints on mantle melt transport - John MacLenna
 n (University of Cambridge)
DTSTART:20160215T143000Z
DTEND:20160215T153000Z
UID:TALK64706@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:The review paper of Kelemen et al. (1997) summarised the key o
 bservations used to develop a model of rapid melt extraction in porous cha
 nnels. Many subsequent observations have been acquired with the aim of ref
 ining estimates of the timescales of melt extraction from the mantle. Neve
 rtheless\, substantial uncertainty remains concerning how these observatio
 ns can be used to characterise variation in melt transport velocities unde
 r basaltic volcanoes at spreading ridges and ocean islands. Uranium series
  disequilibria indicate that melt transport rates are almost certainly >1 
 m yr-1 and probably >50 m yr-1. An alternative method for estimating melt 
 transport rates is based upon the observational record of the response of 
 magmatism to loading and unloading of a mantle melting region. Such loadin
 g cycles may be generated by with glaciation and sea-level change. It is w
 ell-established that the record of volcanic productivity in certain region
 s of Iceland is strongly influenced by variations in the load from glaciat
 ion of the island. The minimal time-lag between deglaciation and a burst i
 n volcanic productivity indicates that melt transport is rapid (>50 m yr-1
 ). More recent analyses of seafloor morphology and temporal variation in h
 ydrothermal activity at submerged mid-ocean ridges have made a tentative l
 ink between sea-level fall during glacial growth and increased magmatic ac
 tivity during glacial terminations. This link can only work if melt extrac
 tion rates are <5 m yr-1. Further modelling work is required to investigat
 e this link and to establish if a single physical framework can be used to
  reconcile the observations from Iceland with those from the submerged mid
 -ocean ridges.<br><span><br>A number of models of melt extraction have bee
 n developed in order to understand the emergence of rapid channelized melt
  flow. One promising research direction is the study of the behaviour of m
 antle where fusible heterogeneities sit in a more refractory matrix.</span
 >
LOCATION:Seminar Room 1\, Newton Institute
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