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Water-in-olivine magma ascent chronometry: Every crystal is a clock

Newcombe, Megan E. and Plank, Terry and Barth, Anna and Asimow, Paul and Hauri, Erik (2020) Water-in-olivine magma ascent chronometry: Every crystal is a clock. Journal of Volcanology and Geothermal Research, 398 . Art. No. 106872. ISSN 0377-0273. https://resolver.caltech.edu/CaltechAUTHORS:20200406-131646410

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Abstract

The syneruptive decompression rate of basaltic magma in volcanic conduits is thought to be a critical control on eruptive vigor. Recent efforts have constrained decompression rates using models of diffusive water loss from melt embayments, olivine-hosted melt inclusions and clinopyroxene phenocrysts; however, these techniques are difficult to apply because of the rarity of pyroxene crystals or melt embayments suitable for analysis and the complexities associated with modeling water loss from melt inclusions. We have developed a new magma ascent chronometer based on syneruptive diffusive water loss from olivine phenocrysts. We have found water zonation in every olivine phenocryst we have measured, from explosive eruptions of Seguam, Fuego, Kilauea and Cerro Negro volcanoes. The majority of the olivine phenocrysts were polished to expose a central plane normal to the crystallographic ‘b’ axis and volatile concentration profiles were measured along ‘a’ and ‘c’ axes by secondary ion mass spectrometry (SIMS). Profiles are compared to 1D and 3D finite-element models of diffusive water loss from olivine, whose boundaries are in equilibrium with a melt undergoing closed-system degassing. Least-squares fitting of measured water concentration gradients in olivine to a 1D Monte Carlo model produces constraints on magma decompression rates that are in good agreement with independent constraints from melt embayment studies and modeling of water loss from olivine-hosted melt inclusions at Fuego, Seguam, Kilauea, and Cerro Negro. Such agreement confirms the accuracy and sensitivity of the water-in-olivine chronometer over a range of decompression rates (dP/dt) spanning ~2 orders of magnitude (from 0.007 to 0.45 MPa/s). We find that the assumption of a zero-water boundary condition (in which the water concentration at the edges of the olivine phenocrysts is fixed at 0 ppm throughout their ascent) leads to an overestimation of the decompression rate by an order of magnitude compared to the closed-system degassing boundary condition assumed in our model, thereby highlighting the sensitivity of the water-in-olivine chronometer to the host magma degassing path. At Seguam, a wide range of best-fit values of dP/dt is obtained both from the water-in-olivine chronometer (0.04–0.23 MPa/s) and from melt embayments (0.02–0.13 MPa/s). We find systematically higher dP/dt values in the melt embayments that appear to have stalled or crystallized at the shallowest depths. Together, these observations are suggestive of magma acceleration during ascent. A strength of the water-in-olivine chronometer is the prevalence of olivine in mafic to intermediate magmas. This new technique yields many values of dP/dt from a single eruption, providing insight into the diversity of ascent records carried by the crystal cargo and possibly defining changes in dP/dt through time and space. This data density offers a more detailed window into syneruptive conduit processes than has been possible using other techniques for constraining dP/dt. In theory, each crystal is a clock, with the potential to record variable ascent in the conduit, over the course of an eruption, between eruptions, and among volcanic systems.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.jvolgeores.2020.106872DOIArticle
ORCID:
AuthorORCID
Newcombe, Megan E.0000-0002-8450-768X
Asimow, Paul0000-0001-6025-8925
Hauri, Erik0000-0002-7449-4774
Additional Information:© 2020 Published by Elsevier B.V. Received 18 September 2019, Revised 25 March 2020, Accepted 31 March 2020, Available online 4 April 2020.
Funders:
Funding AgencyGrant Number
NSFEAR-1551868
Record Number:CaltechAUTHORS:20200406-131646410
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200406-131646410
Official Citation:Megan E. Newcombe, Terry Plank, Anna Barth, Paul D. Asimow, Erik Hauri, Water-in-olivine magma ascent chronometry: Every crystal is a clock, Journal of Volcanology and Geothermal Research, Volume 398, 2020, 106872, ISSN 0377-0273, https://doi.org/10.1016/j.jvolgeores.2020.106872. (http://www.sciencedirect.com/science/article/pii/S0377027319305153)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102355
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Apr 2020 20:19
Last Modified:21 May 2020 18:32

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