Where dark-colored limestone is "bleached" to white, the composition of metamorphic fluids can be constrained. Dark-blue limestone layers that have a carbon phase comprising 0.04 ±0.02 wt% of the rock were bleached during contact metamorphism by a neighboring quartz monzonite. Fluids responsible for the bleaching must have been >90% water, on the basis of graphite-C-O-H fluid interactions.
Mathematical modeling indicates that diffusion of a water-rich fluid through pores or along fluid films on grain edges could complete the observed bleaching, if it is assumed that the diffusion coefficient of water is greater than 10-15.
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