Multiple fluid pulses in a Samoan harzburgite

Noble gases trapped in fluid inclusions in residual mantle xenoliths from Samoa have a wide range in 4He/40Ar* which anti-correlates with enrichments in non-atmospheric Ar, Ne and Xe isotopes and with the concentration of 40Ar* trapped in the mineral. These correlations cannot be due to post-eruption loss of He from the inclusions, but are likely due to mixing of a He-depleted mantle fluid and an unfractionated, plume-derived, fluid that has entrained significant atmospheric noble gases. Mixing of the two fluids occurred within the mantle or at the base of the Samoan lithosphere. Helium loss at depth is implied.