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SUMMARY:The signal of mantle heterogeneity in Icelandic basalts - Dr John 
 MacLennan (Earth Sciences\, Cambridge)
DTSTART:20081201T160000Z
DTEND:20081201T170000Z
UID:TALK14292@talks.cam.ac.uk
CONTACT:11283
DESCRIPTION:The chemistry of basaltic melts contains information about the
  nature of their mantle source regions\, in particular their composition\,
  temperature and flow rate. Such information places key constraints upon o
 ur understanding of mantle convection. However\, the models used to link b
 asalt compositions to mantle properties contain a number of key assumption
 s regarding the lengthscales of mantle heterogeneity\, and the role of mag
 matic processes as a filter for the mantle signal. Melt inclusions which a
 re trapped within olivines growing deep in the magmatic system provide a r
 ecord of the evolution of melt compositions and can be used to understand 
 the role of this magmatic filter. New results from Iceland indicate that t
 he mantle is extremely heterogeneous on lengthscales of <100 km. As melts 
 rise towards the surface they mix. This mixing destroys some of the initia
 l heterogeneity. Some of the mixing takes place in mantle channels. More m
 ixing takes place during convection in lower-crustal magma chambers. The r
 elative rates of mixing and cooling may be used to better understand both 
 the relationship between mantle source and basalt compositions and the flu
 id dynamics of magma chambers.\n\n\nReferences:\n\nMeyzen\, C. et al.\, Is
 otopic portrayal of the Earth's upper mantle flow field\, Nature\, 447\, 1
 069-1074\, 2007.\n\nMaclennan\, J.\, Lead isotope variability in olivine-h
 osted melt inclusions from Iceland\, Geochimica et Cosmochimica Acta\, 72\
 , 4159-4176\, 2008.\n\nMaclennan\, J.\, Concurrent mixing and cooling of m
 elts under Iceland\, Journal of Petrology\, doi:10.1093/petrology/egn052\,
  2008.\n\n
LOCATION:Harker 2 lecture room\, Department of Earth Sciences\, Downing Si
 te
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