O versus S and H
O versus CO
concentrations of Iwate glassy melt inclusions. (a) H2O concentrations versus S concentrations of Iwate glassy melt inclusions (black filled circles). The positive correlation is interpreted as a degassing trend of both water and S. For reference, the blue circles are melt inclusions from EPR, Juan de Fuca, and Gakkel ridge basalts (Wanless and Shaw 2012; Shaw et al. 2010). (b) H2O concentrations versus CO2 concentrations of Iwate glassy melt inclusions. The dashed curves are water and CO2 saturation curves (Witham et al. 2012); therefore, they define a depth at which the saturation in these molecules is obtained. Since H2O and CO2 concentrations are minimum concentrations (see text for details), the depth of entrapment is imprecise and at best is a minimum estimate. However, we distinguish two groups of inclusions, one with H2O < 2 wt.% and the other with H2O > 2 wt.%. Both groups can be interpreted as representing two degassing trends. Maybe, this reflects the presence of two distinct magma chambers at two different depths as suggested by other geophysical data (see text for details). Solid line indicates an example of open system degassing trajectory; the dotted line indicates closed system degassing.