METAMORPHISM OF CALCAREOUS SEDIMENTS IN THE WATERVILLE-VASSALBORO AREA, SOUTH-CENTRAL MAINE: MINERAL REACTIONS AND GRAPHICAL ANALYSIS.

Abstract

Six isograds were mapped in metacarbonate rocks based on mineral reactions that produce biotite plus chlorite plus calcite; calcic amphibole plus calcic plagioclase; zoisite; microcline plus calcic amphibole; diopside; and scapolite with increasing metamorphic grade. Mineral reactions in the metacarbonate rocks are compared to those in pelitic interbeds at corresponding grades. The calc-silicate isograds are extremely irregular: they do not parallel the pelitic isograds; they form isolated concentric patterns and exhibit minor cross-cutting relationships. Graphical analysis of the isogradic reactions on isobaric T-X prime //c//o//2 diagrams explains the peculiarities of the calc-silicate isograds and indicates that H//2O was introduced into the high-grade metacarbonates. The results of the study indicate that gradients in the fugacities of CO//2 and H//2O existed during metamorphism on both outcrop and regional scales. Refs.