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( From Dixon et al., 2002, Nature )

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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( From Dixon et al., 2002, Nature )

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  1. 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.)

  2. 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)

  3. 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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