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Geothermobarometry is the science of measuring the previous pressure and temperature history of a metamorphic or intrusive igneous rocks. Geothermobarometry is a combination of ''geobarometry'', where a pressure of mineral formation is resolved, and ''geothermometry'' where a temperature of formation is resolved. ==Methodology== Geothermobarometry relies upon understanding the temperature of the formation of minerals within metamorphic and igneous rocks, and is particularly useful in metamorphic rocks. There are several methods of measuring the temperature or pressure of mineral formation relying on chemical equilibrium between metamorphic minerals or by measuring the chemical composition of individual minerals. Thermobarometry relies upon the fact that mineral pairs/assemblages vary their compositions as a function of temperature and pressure. There are numerous extra factors to consider such as oxygen fugacity and water activity (roughly, the same as concentration). The distribution of component elements between the mineral assemblages is then analysed using an electron microprobe or scanning electron microscope (SEM). Data on the geothermometers and geobarometers is derived from both laboratory studies on artificial mineral assemblages, where minerals are grown at known temperatures and pressures and the chemical equilibrium measured directly, and from calibration using natural systems. For example, one of the best known and most widely applicable geothermometers is the garnet-biotite relationship where the relative proportions of Fe and Mg in garnet and biotite change with increasing temperature, so measurement of the compositions of these minerals to give the Fe-Mg distribution between them allows the temperature of crystallization to be calculated, given some assumptions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Geothermobarometry」の詳細全文を読む スポンサード リンク
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