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SUMMARY:The secret life of magma revealed by zoning patterns in volcanic c
 rystals - Prof. Jon Blundy\, Bristol 
DTSTART:20161017T160000Z
DTEND:20161017T170000Z
UID:TALK66871@talks.cam.ac.uk
CONTACT:Alex Lipp
DESCRIPTION:Zoned crystals are ubiquitous in volcanic rocks. Their zoning 
 patterns are hold clues to the magmatic processes that shaped their host r
 ocks. An enduring question is whether this information pertains to kinetic
  process\, changes in intensive variables\, open system behaviour\, or com
 binations thereof. The challenge is to unpick the mute testimony of zoned 
 crystals as an archive of pre-eruptive magmatic processes. This challenge 
 has been lessened by the advent of microbeam techniques capable of high sp
 atial and analytical resolution\, thermodynamic models for plagioclase-mel
 t equilibrium and element partitioning\, and numerical models of intracrys
 talline diffusion. We have developed new models for "uncrystallising" zone
 d plagioclase feldspars from the 1980-86 eruptions of Mount St. Helens vol
 cano in the USA. We have been able to show that individuals crystals recor
 d ascent from 12 to 4 km depth before eruption. The crystal cores are old\
 , and resided in the deeper (12 km) reservoir for more than 10\,000 years.
  In contrast\, the rims whose growth pertains to ascent to shallower depet
 h\, developed in timescales of 3 years or less prior to eventual eruption.
  A picture emerges of a long-lived\, vertically extensive magmatic system 
 that became abruptly destabilised\, probably gravitationally\, shortly bef
 ore eruption.\n\nAll welcome to attend\, free for members of the Sedgwick 
 Club\, £2 for non-members. Refreshments provided!
LOCATION:Harker Room 1\, Department of Earth Sciences
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