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EM- type. 750 ppm H 2 O in source. HIMU wet. HIMU- type. 400 ppm H 2 O in source. EM damp. HIMU d D = -35‰. HIMU wet. MORB. EM damp. MORB. EM d D = -65‰. ( From Dixon et al., 2002, Nature ).

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Presentation Transcript
slide1
EM-

type

750 ppm

H2O in

source

HIMU

wet

HIMU-

type

400 ppm

H2O in

source

EM

damp

HIMU

dD = -35‰

HIMU

wet

MORB

EM

damp

MORB

EM

dD = -65‰

(From Dixon et al., 2002, Nature)

(dD data, ESC-Kingsley et al., 2002; Shona/Discovery-Kingsley et al., in prep.)

slide2
Origin of OIB: An Integrated Approach

Fractionation 1: Water-dominated

fluid/melt metasomatism = source

of arc volcanism

300 km

Fractionation 2: Carbon-dominated

melting of mostly dehydrated slab =

Source of OIB and EMORB

(figure modified from Donnelly et al., 2004)

  • Prefer Model 2 (Donnelly et al., 2004; Cooper et al., 2004)
  • Deeper melting of mostly dehydrated slab related to presence of recycled carbon
  • Melting below 300 km will produce incompatible element enriched incipient melts with positive Nb, Ta anomalies due to breakdown of rutile (Bromily and Redfern, 2008)
slide3
HIMU vs EM
  • Slabs mostly dehydrated (>90%) before deep melting.
  • All OIB and EMORB heavier than or similar to MORB
  • Slab water concentration function of themal structure of slab.
  • EM = HOT SLAB ENDMEMBER
    • Slab more dehydrated (<500 ppm H2O)
    • Slab is slightly isotopically lighter than HIMU (dD -65‰) and similar to MORB
    • Hot slab = more coupling with wedge = more deep subduction erosion of underplated crustal materials = greater sediment contribution
  • HIMU = COOL SLAB ENDMEMBER
    • Slab less dehydrated (1500 ± 500 ppm H2O)
    • Slab is isotopically heavier than EM and MORB (dD -30‰ to -40‰) and similar to wedge values
    • Cool slab = less coupling with wedge = less deep subduction erosion of underplated crustal materials = less sediment signature
  • Addition of a few percent of an incipient melt (carbonatitic to ~kimberlitic) of slab gives incompatible element enriched pattern and estimated mantle volatile concentrations
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