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UID:2937@gleanreport.com
DTSTART;TZID=Pacific/Auckland:20170630T160000
DTEND;TZID=Pacific/Auckland:20170630T170000
DTSTAMP:20170625T011401Z
URL:https://www.gleanreport.com/events/mike-heap/
SUMMARY:From rock to magma and back again: The evolution of temperature and
  deformation mechanism in conduit margin zones. A seminar by Mike Heap
DESCRIPTION:Abstract: Explosive silicic volcanism is driven by gas overpres
 sure in systems that are inefficient at outgassing. The zone at the margin
  of a volcanic conduit—thought to play an important role in the outgassi
 ng of magma and therefore pore pressure changes and explosivity—is the b
 oundary through which heat is exchanged from the hot magma to the colder c
 ountry rock. Using a simple heat transfer model\, we first show that the i
 sotherm for the glass transition temperature (whereat the glass within the
  groundmass transitions from a glass to an undercooled liquid) moves into 
 the country rock when the magma within the conduit can stay hot\, or into 
 the conduit when the magma is quasi-stagnant and cools (on the centimetric
  scale over days to months). We then explore the influence of a migrating 
 viscous boundary on compactive deformation micromechanisms in the conduit 
 margin zone using high-pressure (effective pressure of 40 MPa)\, high-temp
 erature (up to 800◦C) triaxial deformation experiments on porous andesit
 e. Our experiments show that the micromechanism facilitating compaction in
  andesite is localised cataclastic pore collapse at all temperatures below
  the glass transition of the amorphous groundmass glass Tg (i.e.\, rock). 
 In this regime\, porosity is only reduced within the bands of crushed pore
 s\; the porosity outside the bands remains unchanged. Further\, the streng
 th of andesite is a positive function of temperature below the threshold T
 g due to thermal expansion driven microcrack closure. The micromechanism d
 riving compaction above Tg (i.e.\, magma) is the distributed viscous flow 
 of the melt phase. In this regime\, porosity loss is distributed and is ac
 commodated by the widespread flattening and closure of pores. We find that
  viscous flow is much more efficient at reducing porosity than cataclastic
  pore collapse\, and that it requires stresses much lower than those requi
 red to form bands of crushed pores. Our study therefore highlights that te
 mperature excursions can result in a change in deformation micromechanism 
 that drastically alters the mechanical and hydraulic properties of the mat
 erial within the conduit margin zone\, with possible implications for pore
  pressure augmentation and explosive behaviour.\nAll Welcome\n
CATEGORIES:Wellington
LOCATION: CO304\, Cotton Building\, VUW\, Victoria University of Wellington
 \, Wellington\, New Zealand
GEO:-41.2904017;174.7686615
X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=Victoria University of Well
 ington\, Wellington\, New Zealand;X-APPLE-RADIUS=100;X-TITLE=CO304\, Cotto
 n Building\, VUW:geo:-41.2904017,174.7686615
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