Keywords:Subduction zone, Kermadec Arc, Kibblewhite Volcano, SO-255, Olivine-hosted melt inclusion
During R/V SONNE expedition SO-255 mafic basaltic to magnesian andesitic lavas containing melt inclusion hosting forsteritic olivines (Fo90.3–92.4) were recovered from Kibblewhite Volcano, southern Kermadec Arc. The re-homogenized melt inclusions have compositions similar to primitive basalt (49.6–52.0 wt.% SiO2; 12.7–15.9 wt.% MgO). Their CaO/Al2O3 values, however, range from 0.9 to 1.6, which cannot be explained by melting of lherzolite. Moreover, CaO/Al2O3 values in the melt inclusions correlate negatively with Ni contents of their host olivines suggesting that the high CaO/Al2O3 values result from interaction between mafic melts and subarc lithospheric mantle. Prior to the interaction the mafic magma must have had high Ni contents and low CaO/Al2O3 values, thus they crystallized high Ni olivines trapping low CaO/Al2O3 melt inclusions. During the interaction the olivines crystallized from the mafic magmas and its latent heat assimilated pyroxenes from the surrounding lithospheric mantle. This assimilation of pyroxenes allowed the Ni content of the melt to decrease and CaO/Al2O3 to increase while buffering the the Mg-number of the mafic magmas during the ascent. Thus, magmas during and after the interaction could crystallize low Ni olivines bearing high CaO/Al2O3 melt inclusions.