Skalenie jako wskaźniki fizycznych warunków metamorfizmu

Abstract

FELDSPARS AS INDICES OF PHYSICAL CONDITIONS OF METAMORPHISMSummaryVariation of feldspar composition depending on temperature and pressure was analysed on the basis of experimental data (Figs. 1-4) and results of studies on natural feldspars. The analysis showed that feldspars may be utilized as both geothermometers and pressure indicators. Feldspar barometer works on the principle that anortite content in plagioclase at a given temperature depends on pressure, provided it is not limited by impoverishment of the environment of its formation in Ca. Such plagioclases were marked with symbol Plf in the present paper. The principle of plagioclase barometer may be expressed as follows: the higher is the pressure, the lower is the anortite content in Plf at a given temperature. Two-feldspar barometer makes use of interdependence between temperature and distribution of Na in Or-Pl association - the higher is Or-Plf association situated on a given isotherm from a graph of Na distribution in Or-Plf association vs. temperature (Fig. 1), the higher is the pressure corresponding to it. Feldspar thermometers and barometers can make passible reconstruction of time variation of physical conditions under which a given metamorphic series developed. This is illustrated on the example of gneiss complex of Bialskie Mts and granulite complex of Złote Mts (Polish Sudety Mts). Temperature - plagioclase content Interdependences obtained for those rocks are illustrated in Fig. 5, and order-disorder state of feldspar structure is shown in Figs. 6 and 7.