The transformation of feldspars and muscovite to clay minerals in (Ca,Mg)-carbonate bearing hydrothermal media

Abstract

Experimental transformations of feldspars and muscovites following additions of magnesite and dolomite have been studied at PH20 = 1 kbar, T= 20~600~ Formation of layer silicates such as smectite, 7/k (Mg,A1)-serpentine, some mixed-layer phases and other minerals is shown to be a function of the composition of the starting materials, temperature and run duration. It is established that 1 M-and 2 Ml-phlogopites are formed from 1 M-and 2 M 1-muscovites, respectively, under Mg-bearing hydrothermal conditions. Some causes of variations in the composition of 7 A (Mg,A1)-serpentines at elevated temperature as a function of the composition of hydrothermal media are given. These data may be used to explain the main characteristics of clay mineral formation from feldspar-and muscovite-bearing sedimentary rocks during their alteration in postdiagenetic and metasomatic processes.