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Title: A stochastic sampling approach to zircon eruption age interpretation

Abstract

The accessory mineral zircon is widely used to constrain the timing of igneous processes such as magma crystallisation or eruption. However, zircon U-Pb ages record zircon crystallisation, which is not an instantaneous process. Zircon saturation calculations link zircon crystallisation, temperature, and melt fraction, allowing for the estimation of zircon crystallisation distributions as a function of time or temperature. Such distributions provide valuable prior information, enabling Bayesian estimates of magma eruption time and allowing for comparison of the relative accuracy of common weighted-mean and youngest-zircon age interpretations with synthetic datasets. We find that both traditional interpretations carry a risk of underestimating the uncertainty in eruption age; a low mean square of weighted deviates (MSWD) does not guarantee the accuracy of weighted-mean interpretations. In the absence of independent confirmation that crystallisation timescale is short relative to analytical uncertainties, a Bayesian approach frequently provides the most accurate results and is least likely to underestimate uncertainty. Finally, since U-Pb zircon studies now routinely resolve geological age dispersion due to increasing analytical precision, such considerations are increasingly critical to future progress in resolving rates and dates of Earth processes.

Authors:
 [1];  [2];  [3]
  1. Berkeley Geochronology Center, Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States). Dept. of Earth and Planetary Science
  2. Princeton Univ., NJ (United States). Dept. of Geosciences
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1488817
Report Number(s):
LLNL-JRNL-738859
Journal ID: ISSN 2410-3403; 892278
Grant/Contract Number:  
AC52-07NA27344; FG02-97ER25308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geochemical Perspectives Letters
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 2410-3403
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; geochronology; Bayesian statistics; zircon age distribution

Citation Formats

Keller, C. B., Schoene, B., and Samperton, K. M. A stochastic sampling approach to zircon eruption age interpretation. United States: N. p., 2018. Web. doi:10.7185/geochemlet.1826.
Keller, C. B., Schoene, B., & Samperton, K. M. A stochastic sampling approach to zircon eruption age interpretation. United States. doi:10.7185/geochemlet.1826.
Keller, C. B., Schoene, B., and Samperton, K. M. Tue . "A stochastic sampling approach to zircon eruption age interpretation". United States. doi:10.7185/geochemlet.1826. https://www.osti.gov/servlets/purl/1488817.
@article{osti_1488817,
title = {A stochastic sampling approach to zircon eruption age interpretation},
author = {Keller, C. B. and Schoene, B. and Samperton, K. M.},
abstractNote = {The accessory mineral zircon is widely used to constrain the timing of igneous processes such as magma crystallisation or eruption. However, zircon U-Pb ages record zircon crystallisation, which is not an instantaneous process. Zircon saturation calculations link zircon crystallisation, temperature, and melt fraction, allowing for the estimation of zircon crystallisation distributions as a function of time or temperature. Such distributions provide valuable prior information, enabling Bayesian estimates of magma eruption time and allowing for comparison of the relative accuracy of common weighted-mean and youngest-zircon age interpretations with synthetic datasets. We find that both traditional interpretations carry a risk of underestimating the uncertainty in eruption age; a low mean square of weighted deviates (MSWD) does not guarantee the accuracy of weighted-mean interpretations. In the absence of independent confirmation that crystallisation timescale is short relative to analytical uncertainties, a Bayesian approach frequently provides the most accurate results and is least likely to underestimate uncertainty. Finally, since U-Pb zircon studies now routinely resolve geological age dispersion due to increasing analytical precision, such considerations are increasingly critical to future progress in resolving rates and dates of Earth processes.},
doi = {10.7185/geochemlet.1826},
journal = {Geochemical Perspectives Letters},
issn = {2410-3403},
number = ,
volume = 8,
place = {United States},
year = {2018},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 7 works
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Figures / Tables:

Figure 1: Figure 1:: Zircon distributions. a: Theoretical and empirical relative zircon crystallization distributions f(tr), scaled from initiation to termination of zircon crystallization. 1: Kinetic model of Watson (1996), based on zirconium diffusion constraints. 2:Thermodynamic model of Keller et al. (2017) using MELTS calculations. 3: Observed zircon crystallization distributions of Samperton etmore » al.(2017), shown as a kernel density estimate for all autocrystic zircons, truncated at +/- 1 kernel bandwidth. b-d: Representative synthetic zircon age datasets for a variety of ∆t/σ at N=10. e: Example dataset with N=100 a ∆t = 1σ; note the range is greater than in c despite lower ∆t. f: Schematic illustration of the three most common volcanic zircon age interpretations.« less

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