Trachytic Melt Inclusions Hosted In Clinopyroxene Offer A Glimpse Into Samoan Em2-Endmember Melts

We present major and trace element data on clinopyroxene-hosted, glassy melt inclusions (MIs) from a highly enriched (high Sr-87/Sr-86 = 0.71856) lava (ALIA-D115-18) from the Samoan hot spot. Following correction for post-entrapment crystallization, the MIs are trachytic (62.6-65.4 wt% SiO2, 1.5-3.0 wt% MgO, and 7.2-10.6 wt% total alkalis (Na2O + K2O)) ALIA-D115 lavas dredged off the submarine flanks of Savai'i Island, western Samoa have previously been suggested to exhibit binary endmember magma mixing between a mafic, low Sr-87/Sr-86 magma and an evolved, high Sr-87/Sr-86 magma (the Enriched Mantle 2 endmember; EM2). In major and trace element space, these ALIA-D115 lavas form a mixing trend between more primitive Samoan shield lavas and the MIs of this study, suggesting the MIs could represent the EM2-derived mixing endmember. Recent efforts to constrain the EM2 mixing endmember composition shows remarkable overlap with the MI compositions, supporting the argument they could represent the Sr-87/Sr-86 mixing endmember to the ALIA-D115 lavas and are derived from the EM2 endmember. Additionally, one melt inclusion contains Fo(73) olivines not in equilibrium with the trachytic melt, suggesting the melt interacted with a mafic magma prior to entrapment within host clinopyroxene. Projecting the ALIA-D115 mixing trend in Sr-87/Sr-86 versus SiO2 and K2O space shows that the trend intersects an average MI composition at Sr-87/Sr-86 values of similar to 0.725, thereby offering a window into more extreme compositions associated with the EM2 endmember.