Cited by 257Geological and Geochemical AnalysisGroundwater and Isotope GeochemistryGeochemistry and Elemental Analysis

The Kinetics of Solid-State Isotope-Exchange Reactions for Clumped Isotopes: A Study of Inorganic Calcites and Apatites from Natural and Experimental Samples

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Stolper, D. A., Eiler, J. M.·2015·American Journal of Science

Abstract

Carbonate clumped-isotope geothermometry is a tool used to reconstruct formation or (re)equilibration temperatures of carbonate bearing minerals, including carbonate groups substituted into apatite. It is based on the preference for isotopologues with multiple heavy isotopes (for example, ^13^C^16^O~2~^18^O^2−^ groups) to be more abundant at equilibrium than would be expected if all isotopes were randomly distributed amongst all carbonate groups. Because this preference is only a function of temperature, excesses of multiply substituted species can be used to calculate formation temperatures without knowledge of the isotopic composition of water from which the mineral precipitated or other phases with which it may have equilibrated. However, the measured temperature could be modified after mineral growth if exchange of isotopes amongst carbonate groups within the mineral has occurred through internal isotope-exchange reactions. Because these exchange reactions occur through thermally activated processes, their rates depend on temperature and increase at higher temperatures. Thus internal isotope-exchange reactions could lead to effective re-equilibration at high temperatures, overprinting the original temperatures recorded during mineral growth. We measured clumped-isotope temperatures in carbonate bearing minerals (including apatites) from several carbonatites to constrain the kinetics of these internal isotope-exchange reactions. We observe two key trends for clumped-isotope temperatures in carbonatites: (*i*) clumped-isotope temperatures of apatites and carbonate-bearing minerals decrease with increasing intrusion depth and (*ii*) apatites record lower clumped-isotope temperatures than carbonate minerals from the same intrusion. We additionally conducted heating experiments at different temperatures to derive the temperature dependence for the rate constants that describe the alteration of clumped-isotope temperatures with time in calcites and apatites. We find that calcites exhibit complex kinetics as has been seen in previous studies. To quantify these results, we constructed a model that incorporates both diffusion of isotopes through the crystal lattice and isotope-exchange reactions between adjacent carbonate groups. We tested this model through comparison to previous measurements of optical calcites and brachiopods and to samples with known cooling histories and find that the model is able to reasonably capture kinetic data from previous experiments and the observed clumped-isotope temperatures of calcites assuming geologically reasonable cooling rates. A similar model for apatite over-predicts the observed clumped-isotope temperatures found in natural samples; we hypothesize this discrepancy is the result of annealing of radiation damage in our experiments, which lowers the diffusivity and rate of isotope exchange of carbonate groups compared to damaged natural samples. Finally, we constructed models to explore how heating can alter recorded clumped-isotope temperatures. Our model predicts that samples change in clumped-isotope temperatures in two stages. The first stage changes the recorded clumped isotope temperatures by \<1 °C if held at 75 °C for 100 million years and by up to ∼40 °C if held at 120 °C, but the clumped-isotope temperatures does not reach ambient values through this low-temperature mechanism. A second, slower change becomes effective at temperatures above 150 °C and can take the measured clumped-isotope temperature up to the true ambient temperature. This result implies that old (hundreds of million years) samples that have only experienced mild (\<100-125 °C) thermal histories could exhibit small but measurable (order 10 °C) changes in their clumped-isotope temperatures. We compared this heating model to clumped-isotope measurements from paleosol samples from the Siwalik Basin in Nepal, which were buried up to 5 km and then rapidly exhumed to the surface; these samples often do not give reasonable surface temperatures. The modeled temperatures agree with measured temperatures of these samples, suggesting that partial re-equilibration during shallow crustal burial is responsible for their elevated clumped-isotope temperatures.

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Crossref · 10.2475/05.2015.01

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  • The blocking temperature is independent of the original crystallisation temperature and peak burial temperature.

    “This blocking temperature is independent of the original crystallisation temperature and peak burial temperature [7,22].”

    From Clumped Isotope Reordering and Kinetic Differences in Co-Hosted Calcite and Dolomite Minerals throughout Burial Diagenesis and Exhumation (2023) · cites this paper as [7]

    In “Modeling and Interpretation of Apparent Equilibrium Temperatures During Heating” (page unavailable), the paper predicts that burial at about 80–100 °C can change the recorded apparent equilibrium temperature, and that higher burial temperatures can bring it toward the ambient temperature. Its cooling model assumes prior equilibration at 350 °C rather than establishing independence from crystallisation or peak burial temperature. The claimed unconditional independence is therefore contrary to the paper’s treatment of burial history. (LLM, conf=0.81)

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  • No geological process is known to reduce TΔ47 values.

    “Because no geological process is known to reduce T Δ47 values (7, 23-25)”

    From Massive formation of early diagenetic dolomite in the Ediacaran ocean: Constraints on the "dolomite problem" (2020) · cites this paper as [25]

    In “Modeling and Interpretation of Apparent Equilibrium Blocking Temperatures During Cooling” (page unavailable), the paper models calcite initially equilibrated at 350 °C and then cooled, predicting recorded apparent equilibrium temperatures of 145–235 °C. It also compares those predictions with natural carbonatites. Cooling is therefore a geological process the paper describes as reducing recorded TΔ47, contrary to the claim. (LLM, conf=0.88)

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  • Post-depositional alteration of ∆47 values due to burial and exhumation, including diagenetic modification via dissolution-precipitation recrystallisation, is a concern, particularly in rock-buffered (closed) systems.

    “concerns about post-depositional alteration of the ∆ 47 values, as a result of the effects of burial and exhumation, including diagenetic modification via dissolution-precipitation recrystallisation, have emerged, particularly in rock-buffered (i.e., closed) systems [7,8,11,18,20,21].”

    From Clumped Isotope Reordering and Kinetic Differences in Co-Hosted Calcite and Dolomite Minerals throughout Burial Diagenesis and Exhumation (2023) · cites this paper as [7]

    The Abstract (page unavailable) identifies recrystallization and closed-system isotope exchange as ways an original clumped-isotope signature can be reset. The “Modeling and Interpretation of Apparent Equilibrium Temperatures During Heating” section (page unavailable) also describes changes during burial. Our copy does not specifically identify dissolution–precipitation recrystallisation as a closed-system process or say that alteration is particularly a concern in rock-buffered systems. (LLM, conf=0.84)

    Experimental — accuracy not yet measured
  • Recalculated δ18Ofluid values show that all samples formed in low water-rock ratios, fitting isotope exchange reactions via solid-state clumped isotope bond reordering.

    “The recalculated δ 18 O fluid values show that all of our samples are formed in low water-rock ratios, fitting the isotope exchange reactions via solid-state clumped isotope bond reordering [7,8,18,20,21].”

    From Clumped Isotope Reordering and Kinetic Differences in Co-Hosted Calcite and Dolomite Minerals throughout Burial Diagenesis and Exhumation (2023) · cites this paper as [7]

    The Abstract (page unavailable) describes clumped-isotope bond reordering through closed-system isotope-exchange reactions, supporting the proposed mechanism. The cited paper does not report the citing authors’ recalculated δ18Ofluid values or establish that all of their samples formed at low water–rock ratios; its Carbonatites section (page unavailable) discusses oxygen-isotope compositions of its own samples instead. (LLM, conf=0.85)

    Experimental — accuracy not yet measured
  • The ∆47 values measured for calcite and dolomite in Jabal Akhdar represent blocking (apparent equilibrium) temperatures sensitive only to the cooling rate, not maximum burial temperatures.

    “The ∆ 47 values measured for calcite and dolomite in Jabal Akhdar do not represent maximum burial temperatures but the blocking, or apparent equilibrium temperatures, which are sensitive only to the cooling rate [7,8,22].”

    From Clumped Isotope Reordering and Kinetic Differences in Co-Hosted Calcite and Dolomite Minerals throughout Burial Diagenesis and Exhumation (2023) · cites this paper as [7]

    The section ‘Modeling and Interpretation of Apparent Equilibrium Blocking Temperatures During Cooling’ (page unavailable) shows that modeled calcite blocking temperatures vary with cooling rate, supporting the general interpretation that such temperatures need not record a thermal maximum. It does not examine Jabal Akhdar samples or establish that their calcite and dolomite values depend only on cooling rate; it also notes that calcite and dolomite may have distinct kinetics. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

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Cites

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3 of the 84 references couldn’t be matched to a known paper.

Research works printed but not linked: 2

  1. [36]36. Ihinger, P. D., ms, 1991, An experimental study of the interaction of water with granitic melt: Pasadena, California, California Institute of Technology, Ph. D. thesis, 190 p.
  2. [81]81. ------2008, Geochemical Kinetics: Princeton, New Jersey, Princeton University Press, 644 p.

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Authors
Stolper, D. A., & Eiler, J. M.
Affiliations
California Institute of Technology (US)
Corresponding author
Stolper, D. A.
Venue
American Journal of Science
Published
2015-05-01
Volume
315
Issue
5
Pages
363-411
ISSN
0002-9599 (ISSN-L)
OpenAlex
W2273208516
Cited by
257
References
84
Citations by year
2026: 14 · 2025: 20 · 2024: 27 · 2023: 30 · 2022: 42 · 2021: 30 · 2020: 21 · 2019: 21 · 2018: 17 · 2017: 15 · 2016: 14 · 2015: 6
FWCI
16.74
Type
journal article
Language
en
Open access
Locations
  • American Journal of Science (publishedVersion)
  • CaltechAUTHORS (California Institute of Technology) (submittedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
Funders
  • National Science Foundation
  • California Institute of Technology
Topics
  • Physical Sciences › Earth and Planetary Sciences › Geophysics › Geological and Geochemical Analysis
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Groundwater and Isotope Geochemistry
  • Physical Sciences › Earth and Planetary Sciences › Geochemistry and Petrology › Geochemistry and Elemental Analysis
Keywords
clumped isotopes, calcite, apatite, carbonatites, intrusion depth, kinetic modeling, radiation damage annealing, brachiopods, cooling history, rate constants

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