Carbon isotope exchange during polymetamorphism in the Panamint Mountains, California, USA

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doi: 10.1046/j.1525-1314.1996.05848.x
Authors:Bergfeld, D.; Nabelek, P. I.; Labotka, T. C.
Author Affiliations:Primary:
University of Missouri, Department of Geological Sciences, Columbia, MI, United States
University of Tennessee, United States
Volume Title:Journal of Metamorphic Geology
Source:Journal of Metamorphic Geology, 14(2), p.199-212. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 0263-4929
Publication Date:1996
Note:In English. 46 refs.; illus., incl. 2 plates, 2 tables, geol. sketch maps
Summary:Carbon isotope fractionations between calcite and graphite in this area show the importance of mass-balance on C isotope values in metamorphosed C-bearing minerals while recording thermal conditions during peak regional metamorphism. Interbedded graphitic marbles and graphitic calcareous schists in the Kingston Peak formation define distinct populations on a Δ13C(gr)13C(cc) diagram. The Δ13C values of both graphite and calcite in the marbles are higher than the respective values in the schists. In contrast to graphite-poor calc-silicate systems where C isotope shifts in carbonate minerals are controlled by decarbonation reactions, the Δ13C values in both rock types were controlled by the relative proportions of the C-bearing minerals. The marbles record a peak T of ∼ 531°C of a Jurassic low-P regional metamorphic event above the tremolite isograd; there is much wider T range in the schists. However, there is a T mode at ∼ 435°C, corresponding approximately with the T of the main decarbonation reactions in the schists, suggesting that the C exchange was set by loss of calcite and armouring of graphite by newly formed silicate minerals. Although the modal T also corresponds with the approximate T of the Cretaceous retrograde event, retrograde exchange, for various reasons, is thought less likely. Thus, only the calcite-graphite C isotope fractionations recorded by the marbles demonstrate the high-T conditions of the low-P Jurassic metamorphic event that was associated with the emplacement of granitic plutons to the W of the Panamint mountains. [R.E.S.]
Subjects:C-13; C-13/C-12; Calcite; Carbon; Carbonates; Contact metamorphism; Graphite; High temperature; Isotope ratios; Isotopes; Marbles; Metamorphic rocks; Metamorphism; Native elements; P-T conditions; Petrography; Polymetamorphism; Stable isotopes; Temperature; California; Inyo County California; Panamint Range; United States; Fractionation
Coordinates:N354500 N373000 W1154000 W1184500
Abstract Numbers:96M/4413
Record ID:1996024309
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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