Abstract
Abstract The generation and initial migration of magma produced by crustal anatexis involves partial melting and at least partial separation of melt from residual solid. The generation of anatectic granitic magma is thus governed by the flow of heat, melt and residual solid. A model which couples two-phase flow in porous media and heat flow was developed to simulate the evolution of anatectic melt around a mantle-derived mafic heat source. Results of our modelling suggest that emplacement of a mafic intrusion in the lower crust may result in partial melting of the crustal rocks and, if sufficient porosity is produced by melting, in migration and segregation of the anatectic melt. Segregation of the melt and its residuum was significant in models in which at least 25% melting of the host rock occurred. As an example, our calculations indicated that a 5-km-thick mafic intrusion emplaced in country rocks with an initial temperature of 800°C will create a zone of partial melting 5 km thick above and below the intrusion. In this case migration and segregation of the melt will produce a layer of magma approximately 1 km thick above the intrusion, and an even larger volume of melt below the intrusion. The anatectic magma moves upward by disaggregating the partially melted country rocks which form the roof of the evolving magma chamber. Upward migration by this process is limited to the portion of the crust which is partially melted by heat from the intrusion. The process of melt migration will modify the melt composition by both zone-refining and fractional crystallization in the initial stages of melt accumulation.
Published Version
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