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SUMMARY:Relamination\, delamination and tadpole zones: Formation of lower 
 continental crust by density sorting of buoyant arc lavas and plutons - Pe
 ter Kelemen\, Lamont Doherty Earth Observatory
DTSTART:20160419T150000Z
DTEND:20160419T160000Z
UID:TALK65667@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Relamination\, delamination and tadpole zones: Formation of lo
 wer continental crust by density sorting of buoyant arc lavas and plutons\
 n\nPeter Kelemen\, Mark Behn & Brad Hacker\n\nKelemen & Behn\, Nature Geos
 ci 2016: Volcanic arc magmas generated above subduction zones have geochem
 ical compositions that are similar to continental crust\, implying that ar
 c magmatic processes played a central role in generating continental crust
 . Yet the deep crust within volcanic arcs has a very different composition
  from crust at similar depths beneath the continents. It is therefore uncl
 ear how arc crust is transformed into continental crust. The densest parts
  of arc lower crust may delaminate and become recycled into the underlying
  mantle. However\, even after delamination\, arc lower crust still has sig
 nificantly different trace element contents from continental lower crust. 
 We suggest that it is not delamination that determines the composition of 
 continental crust\, but relamination. In our conceptual model\, buoyant ma
 gmatic rocks generated at arcs are subducted. Then\, upon heating at depth
 \, they ascend and are relaminated at the base of the overlying crust. A r
 eview of the average compositions of buoyant magmatic rocks — lavas and 
 plutons — sampled from the Aleutians\, Izu–Bonin–Marianas\, Kohistan
  and Talkeetna arcs reveals that they fall within the range of estimated m
 ajor and trace elements in lower continental crust. Relamination may thus 
 provide an efficient process for generating lower continental crust.\n\nKe
 lemen\, Behn & Hacker\, in progress: A hybrid process incorporating aspect
 s of both relamination and delamination may also play an important role. D
 uring "subduction erosion”\, forearc crust may be thrust to Moho depths 
 beneath arcs\, where it undergoes undergoes density sorting once it is hea
 ted to temperatures where viscous\, gravitational instabilities become pos
 sible on geologically relevant time scales.
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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