Melting and dissolution kinetics: Application to partial melting and dissolution of xenoliths

Kinetics of melting and dissolution (rates and textures) in magmatic systems is reviewed and applied to partial melting and dissolution of xenoliths. Special attention is paid to melting/dissolution of solid solution crystals, in which characteristic cloudy textures are formed, and diffusion of elements in the crystals plays an important role due to compositional change of the crystals. Based on the above discussion, model calculations are made for xenolith digestion using the haplogabbro system (diopside‐plagioclase). Xenolith digestion can proceed by partial melting of the xenolith itself as well as dissolution. In this case, xenolith size is not important. The digestion rates suggest that many xenoliths could survive only if they were incorporated into a host basaltic magma just prior to eruption. Natural partial melting found in a spinel lherzolite xenolith from Kilbourne Hole, New Mexico, is also examined with additional heating experiments. It is concluded that spongy clinopyroxene in the spinel lherzolite was formed by “partial dissolution,” reaction between clinopyroxene and partial melt, during partial melting at depth for a short run duration (a month or less). Both the model calculations and the heating experiments show that even mafic to ultramafic xenoliths can easily undergo partial melting or react with basaltic melts, and many xenoliths found in basaltic rocks could be incorporated into the basalts just prior to eruptions.