Andesite magmas from NW Rota-1 volcano, Mariana arc

Abstract

NW Rota-1 volcano is an active submarine volcano in the Southern Seamount Province of the Mariana arc. Using JAMSTEC's ROV, a total of 42 rock samples were collected from the summit region (531-1080 mbsl) and near the base (1474-2260 mbsl) of the volcano. These lavas are medium-K basalts and andesites with 51.5-58.2 wt% SiO2. We note, that lavas ranging from 54-57 wt% SiO2 are conspicuously absent and that most lavas tend to cluster at 52 and 57 wt% SiO2. In constrast, melt inclusions trapped within olivine grains from the same lavas span a much wider range (48.7 to 56.9 wt% SiO2) and show a continuous range (i.e., no gaps). Here we explore why this difference is observed and evaluate whether melt inclusions record primary andesite melt compositions.