Mineral assemblages in different samples of metamorphosed argillaceous carbonate rock, collected from a single, large outcrop in south-central Maine, record differences in the chemical potentials of CO2 and H2O between samples during metamorphism. Because all samples contain graphite and pyrrhotite of constant composition, differences in the chemical potentials of O2, H2, CH4, and H2S existed as well. Thermodynamic analysis of the mineral assemblages indicates that maximum chemical potential differences were on the order of 100 calories. Maximum differences in the chemical potentials of FeO, MgO, K2O, A12O3, and CaO between samples are of approximately the same magnitude. The differences in chemical potentials of CO2 and H2O between beds, however, correspond to a difference of only a few hundredths XCO2 in the composition of a CO2-H2O fluid in equilibrium with the samples. Maximum gradients in the chemical potentials of CO2 and H2O during metamorphism at the outcrop were 5-6 cal/m in magnitude.

Differences in chemical potentials of CO2 and H2O can be mapped in three dimensions in the outcrop, and they exhibit an extremely regular pattern. With the exception of one sample, there are no detectable differences in chemical potentials parallel to bedding and schistosity (which have identical orientations in the outcrop). All other differences occur between different beds. The mapped differences in chemical potentials can be used to quantitatively estimate upper bounds on mass transfer of CO2 and H2O during metamorphism at the outcrop. The estimated upper bounds on mass transfer are consistent with (but do not require) a model of channelized fluid transfer during metamorphism in which fluid transfer primarily occurs in directions parallel to bedding and schistosity.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.