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The role of volatile transport by diffusion and dispersion in driving biotite-forming reactions during regional metamorphism of the Gile Mountain Formation, Vermont

John M. Ferry
The role of volatile transport by diffusion and dispersion in driving biotite-forming reactions during regional metamorphism of the Gile Mountain Formation, Vermont
American Mineralogist (August 2007) 92 (8-9): 1288-1302

Abstract

Infiltration-driven decarbonation reactions produced biotite in pelites and psammites but not in micaceous carbonate rocks in the biotite zone during metamorphism. In one large exposure, the amount of biotite varies greatly in rocks that retain reactants of biotite-forming reactions (0.01-1.10 mol/L in pelites; 0.15-0.53 mol/L in psammites; 0 in carbonates). Conventionally, the variations are interpreted as reactive fluid flow in chemically isolated channels that correspond to individual metasedimentary layers. Measured values of lnQ (sub s) for the equilibria: KAl (sub 3) Si (sub 3) O (sub 10) (OH) (sub 2) + 3 CaMg(CO (sub 3) ) (sub 2) + 2 SiO (sub 2) = KMg (sub 3) AlSi (sub 3) O (sub 10) (OH) (sub 2) + CaAl (sub 2) Si (sub 2) O (sub 8) + 2 CaCO (sub 3) + 4 CO (sub 2) and 3 KAl (sub 3) Si (sub 3) O (sub 10) (OH) (sub 2) + Mg (sub 5) Al (sub 2) Si (sub 3) O (sub 10) (OH) (sub 8) + 4 CaMg(CO (sub 3) ) (sub 2) + 5 SiO (sub 2) = 3 KMg (sub 3) AlSi (sub 3) O (sub 10) (OH) (sub 2) + 4 CaAl (sub 2) Si (sub 2) O (sub 8) + 8 CO (sub 2) + 4 H (sub 2) O are uniform within error of measurement in all analyzed samples (-1.67+ or -0.08, MSWD = 0.89, and -4.17+ or -0.26, MSWD = 0.52, respectively). The uniformity in Q (sub s) values is explained by homogenization of the activities of CO (sub 2) and H (sub 2) O by diffusion and dispersion over a distance >70 m across layering during metamorphism. The uniformity in Q (sub s) is inconsistent with the conventional interpretation of differences in the abundance of biotite. The differences are better explained in terms of layer-by-layer variations in the amounts and compositions of minerals prior to reaction. Measured progress of the biotite-forming reactions is reproduced by mass-balance calculations that consider different initial amounts and compositions of reactant minerals in different samples but the same or nearly the same value of Q (sub s) at the end of reaction. Mass transport of volatiles both by advection and by diffusion and dispersion are essential controls on the progress of infiltration-driven reactions.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 92
Serial Issue: 8-9
Title: The role of volatile transport by diffusion and dispersion in driving biotite-forming reactions during regional metamorphism of the Gile Mountain Formation, Vermont
Author(s): Ferry, John M.
Affiliation: Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD, United States
Pages: 1288-1302
Published: 200708
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 57
Accession Number: 2007-101935
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, sketch map
N43°45'00" - N43°45'00", W72°30'00" - W72°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200744
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