A LABORATORY STUDY OF MELT MIGRATION

Melt migration experiments have been carried out to investigate the dependence of permeability on melt fraction and on orthopyroxene content for partly molten aggregates of olivine plus basalt and olivine-orthopyroxene plus basalt. Melt migration couples, formed between discs of olivine or olivine with 20 vol % orthopyroxene plus ca. 8 vol % basalt and discs with either ca. 2 vol % or 0 vol % basalt, were heated at 1250-degrees-C and 300 MPa for 6-32 h. The resulting melt migration profiles, which developed in response to capillary forces, were analysed in terms of coupled differential equations describing melt migration via porous flow through a deformable matrix (compaction theory). For the experiments in which melt was initially present in both the source and the sink, the melt migration profiles could be fit equally well with a permeability proportional to the melt fraction to the first, second or third power. For the experiments in which the sink initially was melt-free a best fit to the melt migration profiles could be obtained with a permeability that is linearly proportional to melt fraction. The melt migration profiles for samples in which the sink disc contained olivine plus 20 vol % orthopyroxene were essentially identical to those for samples in which the sink contained only olivine, even though at least some of the triple junctions in the former samples were not wetted by the melt phase.