Thermodynamic regime of greenstone metamorphism of basic volcanic rocks after experimental data

Abstract

The stability fields of laumontite, prehnite, pumpellyite, zoisite, and tremolite-bearing assemblages were experimentally examined in the CaO–MgO–Al2O3–SiO2–H2O–CO2 system. The influence of the Fe content on the shift of the upper stability boundary towards both lower temperature and [Formula: see text] equilibrium values is shown for pumpellyite. The runs for some dehydration–carbonatization reactions in the complex H2O–CO2–NaCl fluid have revealed a decrease in the [Formula: see text] equilibrium values for even low salt content. The zeolite, prehnite–pumpellyite, and greenschist facies limits are plotted in the schematic [Formula: see text] diagram, and their possible Pfl limits are discussed. For examined P–T conditions of greenschist to amphibolite facies transition the absence of the compositional gap between tremolite and Ca-hornblende is found.