Formation and destruction of periclase by fluid flow in two contact aureoles

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doi: 10.1007/s004100050312
Authors:Ferry, J. M.; Rumble, D., III
Author Affiliations:Primary:
Johns Hopkins University, Baltimore, MD, United States
Geophysical Laboratory, United States
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 128(4), p.313-334. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1997
Note:In English. 63 refs.; 6 tables, sketch map
Summary:The role of fluid flow in periclase formation in marbles from Beinn an Dubhaich, Skye, and SW Montana, USA, was investigated. Periclase was formed via dolomite = periclase + calcite + CO2, but later replaced by retrograde brucite pseudomorphs. Forsterite is present in many samples. Samples containing brucite all have δ 18O higher than those without, and δ 13C ∼ 1-2 0/00 lower than those without. Fluid XCO2 calculated assuming equilibrium between dolomite, periclase, calcite and fluid were 0.61 for Beinn an Dubhaich and 0.054 for Silver Star, where fluids were more H2O-rich. Brucite and 18O-depleted zones are heterogeneous on the m.-dm. scale, indicating channelization of fluids. Fluids were magmatic in origin and flowed along bedding and lithological contacts. Time-integrated fluid flux (q) was < 500 mol/cm2 rock. In the Beinn an Dubhaich aureole, brucite distribution follows exactly prograde periclase distribution, as later reaction of brucite and calcite with CO2 to produce dolomite and water was insignificant. This process did occur in the Silver Star aureole. Brucite at Silver Star reflects the presence of magnesian beds and not fluid flow geometry, since the distribution of brucite after periclase follows units with high Mg/Ca. Peak metamorphic grade mineralogy alone cannot provide unambiguous information on fluid flow, and details of retrograde processes are essential for correct interpretation. [C.L.H.]
Subsections:Metamorphism: thermal, metasomatic
Subjects:Aureoles; Brucite; Chemical reactions; Contact metamorphism; Fluid phase; Isotopes; Metamorphism; Mineral composition; O-18/O-16; Oxides; Oxygen; P-T conditions; Periclase; Petrography; Retrograde metamorphism; Stable isotopes; Textures; Europe; Great Britain; Hebrides; Highland region Scotland; Inner Hebrides; Inverness-shire Scotland; Isle of Skye; Montana; Scotland; United Kingdom; United States; Western Europe; Beinn an Dubhaich Granite; Silver Star aureole
Abstract Numbers:99M/1006
Record ID:2000042482
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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