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SUMMARY:Reactive melt migration and the evolution of mid-ocean ridge basal
 t - C. Johan Lissenberg\, Cardiff University
DTSTART:20101130T163000Z
DTEND:20101130T173000Z
UID:TALK20670@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Mid-ocean ridge basalt (MORB) is the most abundant magma on Ea
 rth. It is generated beneath mid-ocean ridges by decompression melting of 
 upwelling mantle\, and\, following processing in lower crustal magma chamb
 ers\, erupted onto the seafloor. For more then four decades igneous petrol
 ogists and geochemists have relied upon MORB as their major window into th
 e mantle\, deriving its composition\, melting processes and melt migration
  mechanisms from the erupted lavas. However\, this approach assumes that m
 odification of melts in crustal magma chambers occurs exclusively by fract
 ional crystallisation\, and can thus be easily corrected for.\nData from a
 n extensive suite of lower crustal rocks from Hess Deep (equatorial Pacifi
 c Ocean) demonstrate that melts do not simply evolve by fractional crystal
 lisation. The gabbros crystallised from melts that underwent extensive rea
 ctive porous flow\, which modified both their major- and trace element com
 position. The degree to which this reactive signature is present increases
  up section throughout the lower crust\, suggesting that it occurs on a cr
 ustal scale. Thus\, magma in the lower oceanic crust evolves by a combinat
 ion of fractional crystallisation and melt-rock reaction. If a reactive si
 gnature is present in MORB\, this requires a reassessment of its use as a 
 messenger from the mantle.
LOCATION:Tilley Lecture Theater\, Department of Earth Sciences
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