Temperatures outside a cooling intrusive sheet

Abstract

Contact temperatures and temperatures in the country rock outside a cooling intrusive sheet are disscussed, taking into account tbe effect of heat of solidification. It is shown that, for calculation of temperatures outside an intrusion, it is adequate to ssume that the magma has a definite melting point stead of a melting range. On this assumption, contact temperatures, and temperatures in the country rock, are discussed with particular refrence to dissimilar rocks. It is shown that the maximum temperatures attained in the country rock vary slowly with distance from the contact: the thin baked contact zones sometimes observed may be explained by pre-heating of the country rock for a short time before solidification commences. The theory is extended to cover the case of intrusion to wet sediments in which heat is absorbed by vaporization of pore-water, and calculated values of the contact temperature for a range of conditions are given. It is found in typical cases that a sheet surrounded by a region of the order of half its thickness in which the country rock is heated in the presence of water vapor and vapor from the solidifying intrusion; beyond this to a distance of the order of the thickness of the sheet the country rock is heated in contact with vaporized pore-water; and beyond this again, it is in contact with heated pore-water only. The effect of movement of pore-water is also discussed approximately. The same theory applies to metamorphic reactions in the country rock, and the coking of coal is briefly discussed as an example.