Comment on “Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals”

Wilson, C. J. N.; Morgan, D. J.; Charlier, B. L.; Barker, Simon J.

doi:10.1126/science.aap8429

Cited by 12 publications

(12 citation statements)

References 14 publications

(8 reference statements)

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“…The disequilibrium incorporation of two 'nominally' incom-patible trace elements like P and Al confirms the concerns expressed by a number of recent studies: crystallographic site preference and charge-balancing considerations are criti-cal when interpreting trace-element variations in minerals, particularly in light of disequilibrium processes involv-ing kinetics of crystal growth and diffusion (Spandler and O'Neill 2010;Jollands et al 2014;Zhukova et al 2017;Lynn et al 2018;Tollan et al 2018). As highlighted by the recent debates sparked by vastly differing results for diffusiv-ity of REE in olivine (Cherniak 2010;Spandler and O'Neill 2010) or for differing results for diffusion vs. element cou-pling of Li in zircon (Trail et al 2016;Tang et al 2017;Sliwinski et al 2018), crystal-chemical effects may dictate our ability to use equilibrium and disequilibrium thermo-dynamics to recover the P-T-X-t history of magmas (e.g., Rubin et al 2017;Wilson et al 2017). High disequilibrium P concentrations in the initial growth regions of an olivine lead to different charge-balancing considerations for other nearby non 2 + cations incorporated or diffusing through the octahedral sites.…”

Section: Implications For Element Coupling and Thermometrymentioning

confidence: 99%

Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

Shea

Hammer

Hellebrand

et al. 2019

Contrib Mineral Petrol

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Phosphorus zoning in olivine is receiving considerable attention for its capacity to preserve key information about rates and mechanisms of crystal growth. Its concentration can vary significantly over sub-micron spatial scales and form intricate, snowflake-like patterns that are generally attributed to fast crystal growth. Ostensibly similar aluminum enrichment patterns have also been observed, suggesting comparable incorporation and partitioning behavior for both elements. We perform 1-atm crystallization experiments on a primitive Kīlauea basalt to examine the formation of P and Al zoning as a function of undercooling − ΔT (− ΔT = Tliquidus − Tcrystallization) during olivine growth. After 24 h spent at Tinitial = 1290 °C (10 °C above olivine stability), charges are rapidly cooled to final temperatures Tfinal = 1220-1270 °C, corresponding to undercoolings −ΔT= 10-60 °C (with Tliquidus = 1280 °C). Compositional X-ray maps of experimental olivine reveal that only a small undercool-ing (≤ 25 °C) is required to produce the fine-scale enrichments in P and Al associated with skeletal growth. Concentration profiles indicate that despite qualitatively similar enrichment patterns in olivine, P and Al have contrasting apparent crystal/ melt mass distribution coefficients of = 0.01-1 and = 0.002-0.006. Phosphorus can be enriched by a factor > 40-fold in the same crystal, whereas Al enrichment never exceed factors of 2. Glass in the vicinity of synthetic and natural olivine is usually enriched in Al, but, within analytical uncertainty, not in P. Thus, we find no direct evidence for a compositional boundary layer enriched in P that would suffice to produce P enrichments in natural and synthetic olivine. Numerical models combining growth and diffusion resolve the conditions at which Al-rich boundary layers produce the observed enrichment patterns in olivine. In contrast, the same models fail to reproduce the observed P enrichments, consistent with our observation that P-rich boundary layers are insignificant. If instead, P olivine/melt partitioning is made to depend on growth rate, models adequately reproduce our observations of 40-fold enrichment without boundary layer formation. We surmise that near-partitionless behavior ( close to 1) of P is related to the olivine lattice being perhaps less stiff in accommodating P during rapid crystallization, and/or to enhanced formation of vacancy defects during fast growth. Our results confirm that P is a robust marker of initial rapid growth, but reveal that the undercooling necessary to induce these enrichments is not particularly large. The near-ubiquitous process of magma mixing under volcanoes, for instance, is likely sufficient to induce low-tomoderate degrees of undercooling required for skeletal growth.

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Section: Implications For Element Coupling and Thermometrymentioning

confidence: 99%

Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

Shea

Hammer

Hellebrand

et al. 2019

Contrib Mineral Petrol

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“…Yet large‐ and small‐volume eruptions associated with larger, long‐lived magma systems produce zircon thermometry that records high‐temperature excursions (e.g., Kent & Cooper, ; Szymanowski et al, ), including Kaharoa, which has been proposed as an exemplar of cold magma storage (Rubin et al, , ). However, a method by which to resolve the durations of these reheating events has proven elusive (Barboni et al, ; Kent & Cooper, ; Rubin et al, ; Szymanowski et al, ; Wilson et al, ).…”

Section: Discussionmentioning

confidence: 99%

Repeated Rhyolite Eruption From Heterogeneous Hot Zones Embedded Within a Cool, Shallow Magma Reservoir

2019

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Despite the hazard posed by explosive silicic eruptions, the magma storage conditions and dynamics that precede these events remain controversial. The Laguna del Maule volcanic field, central Chile, is an exceptional example of postglacial (younger than ca. 20,000 years) rhyolite volcanism and sustained unrest driven by a large, shallow, active silicic magma system. New zircon petrochronologic data reveal that compositionally distinct domains developed concurrently within the Laguna del Maule magma reservoir, which produced two episodes of concentrated rhyolitic eruptions at 23–19 and 8–2 ka. Zircon crystallization ages record 160 kyr of magma emplacement resulting in a several hundreds of cubic kilometers reservoir that has been imaged geophysically. The average magma emplacement rate inferred from the zircon geochronology and tomographically defined magma volume is consistent with those required by thermal models to maintain a shallow silicic system. Ti‐in‐zircon temperatures of crystal cores and rims and hiatuses in crystal growth indicates most of this volume persisted in a near‐solidus state. However, consistent patterns of trace element zoning in crystal interiors and crystallization rates derived from a model of diffusion‐limited zircon growth suggest the erupted rhyolite magma batches originated from long‐lived hot zones of extractable mush embedded within the larger, cool reservoir of rigid mush. These contrasting, coeval magma storage conditions obviate a simple hot versus cold storage dichotomy for large silicic magma systems.

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“…Possible charge-balancing behavior of Li with other minor or trace elements in minerals can complicate the interpretation that concentration gradients are solely driven by diffusion (Cooper et al, 2017;Rubin et al, 2017;Tang et al, 2017;Wilson et al, 2017). Some Keanaka¯ ko'i Tephra olivine show clear correlations between Li and P zoning within laser ablation profiles (Supplementary Material, Fig.…”

Section: Element Couplingmentioning

confidence: 99%

Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions

Lynn

Shea

Garcia

et al. 2018

Earth and Planetary Science Letters

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Comment on “Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals”

Abstract: Rubin et al. (Research Report, 16 June 2017, aam8720) proposed that gradients in

Cited by 12 publications

References 14 publications

Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

Phosphorus and aluminum zoning in olivine: contrasting behavior of two nominally incompatible trace elements

Repeated Rhyolite Eruption From Heterogeneous Hot Zones Embedded Within a Cool, Shallow Magma Reservoir

Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions

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