Recycled components in mantle plumes deduced from variations in halogens (Cl, Br, I), trace elements and 3He/4He along the Hawaiian‐ Emperor Seamount chain

Halogens are primarily located within surface reservoirs of the Earth; as such they have proven to be effective tracers for the identification of subducted volatiles within the mantle. Subducting lithologies exhibita wide variety of halogen compositions, yet the mantle maintains a fairly uniform signature, suggesting halogens may be homogenised during subduction to the mantle, or during eruption. Here we present halogen (Cl, Br and I), K, noble gas and major and trace element data on olivines from three seamounts along the Hawaiian-Emperor Seamount Chainto determine if the deep mantle source has retained evidence of halogen heterogeneities introduced through subduction. High Ni contents indicate that the Hawaiian-Emperor mantle source contains a recycled oceanic crust component in the form of pyroxenite,which increases from the 46% in the oldest (Detroit) to 70% in the younger seamount (Koko). Detroit seamount retains MORB-like Br/Cl and I/Cl, whilst the Br/Cl and I/Cl of Suiko and Koko seamounts are higher than MORB and similar to altered oceanic crust and dehydrated serpentinite. Helium isotopes show a similar evolution,from MORB-like values at Detroit seamount towards higher values at Suiko and Koko seamounts. The correlation between pyroxenite contributions, Br/Cl, I/Cl and 3He/4He indicates that subducted material has been incorporated into the primordial undegassed Hawaiian mantle plume source.The identification of recycled oceanic crustal signatures in both the trace elements and halogens indicates that subduction and dehydration of altered oceanic crust may exert control on the cycling of volatile elements to the deep mantle.