Development of spatial variations in reaction progress during regional metamorphism of micaceous carbonate rocks, Northern new England

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ID: 300883
2006
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Abstract
Progress (ξ) of the infiltration-driven reaction, muscovite + ankerite + quartz + rutile + H2O = biotite + calcite + plagioclase + CO2, which occurred during Barrovian and Buchan regional metamorphism in east-central Vermont and south-central Maine, can vary by a factor of ten or more at all spatial scales down to that of adjacent lithologic layers <1 cm thick. Values of proxies for the activity of CO2 and δ18Ofluid, Ks(6) ≡ [(aphl)(aan)(acal)2]/[(ams)(adol)3(aqtz)2] and δ18OCal, are uniform within error of measurement over distances up to ≈1 m across layering. The conventional explanation of cm- to dm-scale variations in ξ in terms of layer-parallel channeled fluid flow cannot explain the uniformity in the proxies. Observed cm- to dm-scale variations in ξ are better explained by (a) mineral reactants and products that are solid solutions, (b) layer-by-layer variations in the amounts and compositions of minerals prior to reaction, and (c) uniformity of Ks(6) on a spatial scale larger than the scale of variations in ξ during subsequent infiltration and reaction. The m-scale uniformity in Ks(6) and δ18OCal is interpreted as homogenization of aCO2 and δ18Ofluid caused by the combined effects of intergranular diffusion and hydrodynamic dispersion. Reaction progress therefore was driven by the interplay of layer-parallel advection of chemically-reactive H2O-rich fluid at decameter and larger scales and cross-layer transport of CO2 and H2O by diffusion/dispersion at scales of ≈1 m and less. Regardless of whether mineral reactants and products are solid solutions, the geochemical tracer considered, or the mechanism of fluid-rock reaction, the geometry of fluid flow can never be determined at a scale smaller than the one over which the concentration of the tracer is homogenized in the fluid within error of measurement by diffusion and dispersion.
Reference Key
openalex_W2056030294 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Sarah Penniston‐Dorland, John M. Ferry
Journal american journal of science
Year 2006
DOI
10.2475/07.2006.01
URL
https://doi.org/10.2475/07.2006.01
Keywords Keywords not found

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