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SUMMARY:Under the volcano: geological fieldwork in East Greenland - Dr Mar
 ian Holness\, Department of Earth Sciences\, University of Cambridge
DTSTART:20130211T173000Z
DTEND:20130211T183000Z
UID:TALK38544@talks.cam.ac.uk
CONTACT:Beverley Larner
DESCRIPTION:\nVolcano behaviour is controlled by the composition of the er
 upted magma – for example\, magmas containing a lot of water tend to eru
 pt explosively while drier magmas are erupted in a more effusive (and less
  hazardous) manner. The composition of erupted magma is determined by proc
 esses that occur in the plumbing system underneath the volcano. The most i
 mportant of these processes is the separation of crystals from the remaini
 ng liquid\, driven essentially by gravity. Removing early-formed crystals 
 changes the composition of the remaining liquid\, known as fractionation. 
 While we can examine the end result of fractionation by looking at the eru
 pted magmas\, the best approach to understanding the spatial relationships
  between crystals and liquid in fractionating systems is to look at the de
 eply-eroded remains of ancient sub-volcanic magma chambers. \n\nThe Skaerg
 aard Intrusion of East Greenland formed about 60 million years ago. It is 
 a body of basaltic magma 10 km across and 4 km deep that filled a space in
  the Earth’s crust formed during extension related to the opening of the
  North Atlantic. Unusually\, this batch of magma was then left entirely un
 disturbed\, allowing it to crystallise progressively inwards from the wall
 s\, floor and roof. The fully-solidified intrusion is now very well-expose
 d by erosion\, with continuous outcrop through the magmatic stratigraphy. 
 Since its discovery in 1933 it has become one of the world’s best natura
 l laboratories for the study of magma fractionation. Its importance has in
 creased recently with the discovery of commercially viable quantities of g
 old and platinum-group elements. Field observations coupled with laborator
 y analysis of selected rock samples allow us to trace the progress of frac
 tionation\, work out the behaviour of a crystal mushy layer forming on its
  vertical walls and begin to understand the complexities of a km-scale dyn
 amic crystallising system.\n
LOCATION:Bristol-Myers-Squibb Lecture theatre\, Department of Chemistry
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