Devolatilization of metabasic rocks during greenschist-amphibolite facies metamorphism

Abstract

The production of large volumes of fluid from metabasic rocks, particularly in greenstone terranes heated across the greenschist-amphibolite facies transition, is widely accepted yet poorly characterized. The presence of carbonate minerals in such rocks, commonly as a consequence of sea-floor alteration, has a strong influence, via fluid-rock buffering, on the mineral equilibria evolution and fluid composition. Mineral equilibria modelling of metabasic rocks in the system Na2O-CaO-FeO-MgO-Al2O3- SiO2-CO2-H2O (NCaFMASCH) is used to constrain the stability of common metabasic assemblages. Calculated buffering paths on T-XCO2 pseudosections, illustrate the evolution of greenstone terranes durin..