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SUMMARY:Five things about the cold forearc mantle wedge - Kelin Wang\, Pac
 ific Geoscience Centre\, Geological Survey of Canada
DTSTART:20201014T150000Z
DTEND:20201014T160000Z
UID:TALK150322@talks.cam.ac.uk
CONTACT:Camilla Penney
DESCRIPTION:*This seminar will be held online. Zoom details will be sent t
 o members of the Earth Sciences department via email. Please contact the o
 rganisers if you are outside the department and would like to attend*\n\nT
 he forearc mantle wedge plays a critical role in the geodynamics of subduc
 tion zones. From five perspectives\, I will highlight its thermal\, petrol
 ogic\, and mechanical states and how it affects megathrust slip behaviour.
  (1) Heat flow data and seismic imaging indicate that the forearc mantle w
 edge is cold\, referred to as the “cold nose”\, in sharp contrast with
  the hot arc-backarc region. With fluids supplied by the dehydrating slab\
 , hydrous minerals form in the ultramafic cold nose. (2) Maintaining the c
 old and stable thermo-petrologic state requires the forearc wedge to be fu
 lly decoupled from the subducting slab and does not participate in mantle 
 wedge flow. This is supported by the lack of seismic anisotropy in the col
 d nose as inferred from local-earthquake shear wave splitting analysis in 
 the Japan Trench subduction zone. (3) The cold state gives rise to high st
 iffness\, affecting postseismic deformation following megathrust earthquak
 es. The mechanical contrast of the cold nose with the rest of the mantle w
 edge is clearly reflected in geodetically observed postseismic uplift betw
 een the cold nose and the volcanic arc. (4) In warm-slab subduction zones\
 , a very high degree of serpentinization of the tip area of the mantle wed
 ge is expected to diminish permeability. The hydrological consequence is i
 nferred to foster a geological condition for episodic tremor and slip (ETS
 ) downdip of\, but separated from\, the megathrust seismognic zone. (5) In
  colder-slab subduction zones\, serpentinite derived from the base of the 
 forearc mantle wedge affects the mechanics of the megathrust fault zone\, 
 resulting in complex seismogenic behaviour downdip of the Moho-megathrust 
 intersection. I will use the 2010 M=8.8 Maule\, Chile\, earthquake as an e
 xample to show how this process may affect coseismic slip\, stress drop\, 
 and aftershock distribution under the specific P/T condition in this area.
 \n\nBackground reading: \nWada & Wang\, Common depth of slab-mantle decoup
 ling: Reconciling diversity and uniformity of subduction zones\, G3\, 2009
 \nWang\, Hu\, He\, Deformation cycles of subduction earthquakes in a visco
 elastic Earth\, Nature\, 2012\nGao & Wang\, Rheological separation of the 
 megathrust\nseismogenic zone and episodic tremor and slip\, Nature\, 2017
LOCATION:ONLINE - Details to be sent by email
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