A mathematical model describing isotope transport and fractionation during phase convection in the melt-solid system is discussed. The gravity sedimentation of mineral particles within a magmatic chamber accompanied by isotopic exchange and melt displacing upwards is considered. As assumed, mineral crystals are formed near the upper boundary of the chamber and are melted or accumulated in the lower part. Employing oxygen isotopes, it is demonstrated that these conditions may result in a substantial vertical gradient in the isotopic composition of the melt and solid phase. For systems with vertical dimensions of hundreds of meters, the difference between the isotopic composition at the lower and upper boundaries of the system may be tens to hundreds of times greater than the effect of equilibrium isotopic fractionation between coexisting melt and solid. The time period required to reach a notable isotopic heterogeneity is comparable with the characteristic duration of crystallization of large intrusions, that is, about hundreds to thousands of years.
|Number of pages||9|
|Publication status||Published - Mar 1999|