An empirical estimate of the diffusion rate of oxygen in diopside

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Authors:Sharp, Z. D.; Jenkin, G. R. T.
Author Affiliations:Primary:
Universite de Lausanne, Institut de Mineralogie, Lausanne, Switzerland
Other:
Scottish Universities Research and Reactor Centre, United Kingdom
Volume Title:Journal of Metamorphic Geology
Source:Journal of Metamorphic Geology, 12(1), p.89-97. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 0263-4929
Publication Date:1994
Note:In English. 58 refs.; illus. incl. 3 tables
Summary:Diopside grains in calcite marble at Cascade Slide in the Adirondack Mts show no oxygen isotope variations as a function of grain size. This provides a limit on the diffusion rate of oxygen in diopside as being of the order of 5.6 times 10-20 cm2/s at 800 degrees C, in agreement with some experimental estimates. The lack of zoning requires that the closure T for diopside is > 750-800 degrees C, even for very small grain sizes. A closed-system, bimineralic diopside-calcite rock must record peak metamorphic T if no retrograde, moderate- to high-T deformation occurred. In a high-T, multi-mineralic lithology, the measured delta18Odiopside value will be identical to the peak-T isotopic composition, regardless of any isotopic modifications that occur in other phases. The Delta18Ocalcite-diopside fractionations preserved in the Cascade Slide samples record maximum T if the minor alteration of the delta18Ocalcite value by a late hydrothermal fluid is factored out of the delta18Ocalcite value. The T estimates are some of the highest obtained in the Adirondacks, highlighting the potential resilience of stable isotope geochemistry to retrograde resetting when appropriate mineral systems are chosen. [R.A.H.]
Subjects:C-13/C-12; Carbon; Chain silicates; Clinopyroxene; Diffusion; Diopside; Facies; Grain size; Granulite facies; Isotope ratios; Isotopes; O-18/O-16; Oxygen; Pyroxene group; Rates; Silicates; Stable isotopes; Adirondack Mountains; New York; United States; Cascade Slide
Abstract Numbers:94M/3352
Record ID:1994006025
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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