Host: Japan Association of Mineralogical Sciences
In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from the low-temperature mush zones (boundary layer fractionation). In this study, the relative role of these two fractionation processes in chemical differentiation of magmas have been examined, using a thermodynamics-based mass balance model. Model calculations show that, in magma chambers located at relatively shallow levels, the magmas evolve principally by homogeneous fractionation. On the other hand, in basaltic magma chambers located at relatively deep levels, boundary layer fractionation can occur effectively depending on the melt water contents.
