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Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems

Research output: Contribution to journalArticle

  • Michael A. Antonelli
  • Tushar Mittal
  • Anders McCarthy
  • Barbara Tripoli
  • James M. Watkins
  • Donald J. DePaolo
Original languageEnglish
Pages (from-to)20315-20321
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number41
DOIs
DateAccepted/In press - 5 Sep 2019
DatePublished (current) - 8 Oct 2019

Abstract

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2%) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10−3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

    Research areas

  • Ca isotopes, Crystal growth, Magma recharge, Timescales, Volcanic eruptions

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