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SUMMARY:Melt-induced weakening of the lithosphere: theory\, numerical impl
 ementation and geodynamic implications - Taras Gerya (ETH Zürich)
DTSTART:20160606T151500Z
DTEND:20160606T160000Z
UID:TALK66359@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Melt-induced weakening can play critical role for enabling lit
 hospheric  deformation in the areas of intense mantle-derived magmatism\, 
 such as mid-ocean  ridges\, rift zones and hot spots. It implies significa
 nt reduction in the  long-term strength of the deforming lithosphere subje
 cted to frequent rapid melt  percolation episodes along planar\, sharply l
 ocalized zones (dykes). Mechanical  energy dissipation balance shows that 
 the long-term effective strength of the  melt-weakened lithosphere is a st
 rain-averaged rather than a time-averaged  quantity. Its magnitude is main
 ly defined by the ratio between melt pressure and  lithostatic pressure al
 ong rapidly propagating dykes\, which control most of the  visco-plastic l
 ithospheric deformation. We implemented governing equations for  melt-bear
 ing deforming visco-elasto-plastic lithosphere based on staggered  finite 
 difference and marker in cell techniques. We then quantified the  lithosph
 eric strength by performing 2D numerical experiments on long-term  lithosp
 heric deformation assisted by frequent short-term dyke propagation  episod
 es. The experiments showed that the lithospheric strength can be as low as
   few MPa and is critically dependent on the availability of mantle-derive
 d melt  for enabling frequent episodes of dyke propagation. Viscous-plasti
 c deformation  is localized along propagating weak dykes whereas bulk of t
 he lithosphere only  deforms elastically and is subjected to large deviato
 ric stresses. Thus\, the low  strength of the melt-weakened lithosphere is
  associated with high  volume-averaged deviatoric stress. Possible geodyna
 mic implications include (1)  establishing of a global tectono-magmatic pl
 ume-lid tectonics regime in the  Archean Earth and modern Venus as well as
  (2) enabling of plume-induced  subduction initiation that triggered globa
 l modern-style plate tectonics on  Earth.
LOCATION:Seminar Room 1\, Newton Institute
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