Geological Thermometry

the aggregate of methods for determining the temperature of solidification of magma, formation of various ore deposits, crystallization of individual minerals, and so on. Thermometric research may be conducted using methods of geological and mineralogical thermometry.

Among the methods of geological thermometry are the direct measurement of the temperature of lavas, gas fumaroles, and liquid thermal springs; the comparison of experimental data on the melting of rock with the degree of metamorphism and fusion of xenoliths in intrusions; indirect estimates of the temperature of magma by the degree of coal coking in areas of contacts with intrusive rocks; and estimates based on study of equilibrium phase relationships in intrusive and metamorphic rocks and on direct measurements of tne temperatures of exogenic geological processes on the earth’s surface (salt deposition, weathering, and so on).

The methods of mineralogical thermometry consist in the study of minerals as indicators of possible temperatures and in the study of remains of mineral-forming mediums that have been preserved in minerals as gaseous-liquid and solidified inclusions. Methods based on use of the actual minerals include the mineralographic method, taking into account the dependence on temperature of the morphological-crystallographic characteristics of mineral formations, the habit of minerals, and the peculiarities of their concretion; the experimental-physical method, using the physical properties of minerals (polymorphic transition temperature, melting point, dissociation and decomposition temperatures, and colors and thermoluminescence of minerals) and indirect characteristics relating to the temperatures of mineral formation, based on data concerning the decomposition temperatures of the primary solid solutions; and the geochemical method, based on the quantitative study of the dependence on temperature of the type of distribution of components of minerals existing together in equilibrium (Kullerud and Earth thermometers), as well as on the relationship between temperature and the isotopic compositions of certain elements.