MULTIPLE FLUID PULSES IN A SAMOAN HARZBURGITE

Noble gases trapped in fluid inclusions in residual mantle xenoliths f rom Samoa have a wide range in He-4/Ar-40 which anti-correlates with enrichments in non-atmospheric Ar, Ne and Xe isotopes and with the con centration of Ar-40 trapped in the mineral. These correlations cannot be due to post-eruption loss of He from the inclusions, but are likel y due to mixing of a He-depleted mantle fluid and an unfractionated, p lume-derived, fluid that has entrained significant atmospheric noble g ases. Mixing of the two fluids occurred within the mantle or at the ba se of the Samoan lithosphere. Helium loss at depth is implied. (C) 199 8 Elsevier Science B.V. All rights reserved.