A major field of inquiry in the earth sciences is the understanding of mechanisms of magma migration and how magma compositions can change as a result of this migration. Areas where this is of importance include the geochemistry of mantle melts and the understanding of how these melts change as they migrate to the surface of the earth. A number of studies have highlighted the importance of melt migration through porous rock as a major control on the geochemistry of both magma and the mantle lithosphere.

In addition, infiltration and reaction in mafic layered intrusions has been recognized as an important mechanism in changing both the mineralogy and composition of primary magmatic phases. In this instance, compaction or interstitial liquid convection can lead to a variety of effects ranging from stratiform mineral and compositional offsets to pipe-like replacement bodies. In a number of cases, these features are associate with platinum-group element mineralization; hence, there is considerable economic interest in these problems as well.

Ongoing studies in numerical models of crystallization and compaction behavior in layered intrusions by our group has lead to a need to incorporate more realistic silicate crystallization behavior. This study will combine a quantitative model for liquid-mineral equilibria with one-dimensional transport equations to develop a program for modeling magmatic reaction-transport phenomenon. We have already written the liquid-mineral equilibria part of the program. It is based on the MELTS software algorithm of Ghiorso and coworkers and includes trace element modeling. Much of this study will involve adding transport equations, both general and compaction-driven. Our main interest in the program is for investigation into compaction-driven magma transport and reaction in layered intrusions.

In addition to the theoretical modeling, we plan parallel field studies of textural, chemical and mineralogical features of the Bushveld complex, South Africa. These field studies will help to constrain and compare results of the numerical models.

The final program is expected to be a useful tool to a broad range of igneous studies. This program will be general enough so users can specify a range of starting compositions (including inhomogeneous host rock compositions). The program will allow calculation of reaction and chromatographic fronts as silicate liquid percolates through a porous solid matrix. In addition, results of this study will include a quantitative investigation into the role of compaction in returning evolved liquid back into the main magma reservoir. This will allow us to evaluate compaction as a significant cause of in situ or boundary layer differentiation in layered intrusions.

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