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SUMMARY: Preservation of H2O heterogeneity in the Icelandic mantle - Simon
  Matthews (University of Cambridge)
DTSTART:20230509T110000Z
DTEND:20230509T120000Z
UID:TALK177023@talks.cam.ac.uk
CONTACT:Oscar Branson
DESCRIPTION:\nIt is well established that the mantle is chemically heterog
 eneous on length scales of 10s of kilometres or less\; a product of recycl
 ing melting residues and subducted lithosphere\, followed by stirring and 
 mixing during vigorous convective cycling. We might also expect these mant
 le components to have distinct H2O concentrations\, determined by their hi
 story of hydrous alteration near Earth’s surface\, devolatilization duri
 ng subduction\, or H2O extraction during melting. However\, the rapid diff
 usion of H+ in mantle minerals acts to dampen or remove this H2O heterogen
 eity during transport from the lower mantle. The persistence of H2O hetero
 geneity can place a lower bound on the length scales of mantle heterogenei
 ty.\n\nSince subaerially erupted lavas lose most of their volatile element
  budget prior to or during eruption\, volatile studies are limited to glas
 ses quenched at high pressures\, their eruption having occurred on the sea
  floor or at the base of glaciers. I will present new H2O\, trace element\
 , and radiogenic isotope analyses\, alongside compiled data\, for glasses 
 erupted on the submarine ridges adjacent to Iceland\, subglacial glasses o
 n Iceland\, and olivine-hosted melt inclusions from 8 primitive Icelandic 
 eruptions. To estimate pre-eruptive volatile concentrations\, we develop m
 ethods for filtering melt inclusion datasets for the effects of H2O degass
 ing and H+ diffusion.\n\nTogether\, the datasets demonstrate pervasive sma
 ll-scale H2O heterogeneity is present throughout the mantle beneath Icelan
 d and the surrounding spreading ridges\, implying small-scale mantle heter
 ogeneities are large enough that H+ diffusion has not eroded their presenc
 e.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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