Some thermal problems associated with magma migration

The mechanisms by which magma migrates from the point in the earth's interior where melting occurs to the earth's surface are poorly understood. In this paper several aspects of this problem are examined. Magma can migrate upward due to its differential buoyancy on the scale of crystalline grains or as large dispairs. Magma transport is an effective means of heat transport. Magma transport at a rate of 0.15 cm/yr is equivalent to a heat flow of 10^-6 cal/cm² s. If magma encounters country rock witha lower melting point the original magma is likely to solidify while melting the country rock. This would be an effective mechanism of purging silicic rocks and incomparable elements from the lower crust. Under some circumstances magma must penetrate up to 100 km or more of cold lithospheric rock. In order for this magma to reach the surface without solidification a heated path must be provided. The heating of this path requires the solidification of some magma. It is estimated that magma penetrates the lithosphere in about 5000 years and that the crack is lined by several hundred meters of frozen basalt.