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Tracking volatile behaviour in sub-volcanic plumbing systems using apatite and glass: insights into pre-eruptive processes at Campi Flegrei, Italy

Stock, Michael J.; Humphreys, Madeleine C.S.; Smith, Victoria C.; Isaia, Roberto; Brooker, Richard A.; Pyle, David M.

Tracking volatile behaviour in sub-volcanic plumbing systems using apatite and glass: insights into pre-eruptive processes at Campi Flegrei, Italy Thumbnail


Authors

Michael J. Stock

Victoria C. Smith

Roberto Isaia

Richard A. Brooker

David M. Pyle



Abstract

Volatile elements play an important role in many aspects of the physicochemical architecture of sub-volcanic plumbing systems, from the liquid line of descent to the dynamics of magma storage and eruption. However, it remains difficult to constrain the behaviour of magmatic volatiles on short timescales before eruption using established petrologic techniques (e.g. melt inclusions), specifically, in the final days to months of magma storage. This study presents a detailed model of pre-eruptive volatile behaviour in the Campi Flegrei system (Italy), through combined analyses of apatite crystals and glass. The deposits of eight eruptions were examined, covering the full spectrum of melt compositions, eruptive styles and periods of activity at Campi Flegrei in the past 15 kyr. Measured apatite compositions are compared with thermodynamic models that predict the evolution of the crystal compositions during different fractional crystallisation scenarios, including: (i) volatile-undersaturated conditions; (ii) H2O-saturated conditions; (iii) varying P-T conditions. The compositions of clinopyroxene-hosted and biotite-hosted apatite inclusions are consistent with crystallisation under volatile-undersaturated conditions that persisted until late in magmatic evolution. Apatite microphenocrysts show significantly more compositional diversity, interpreted to reflect a mixed cargo of crystals derived from volatile-undersaturated melts at depth and melts which have undergone cooling and degassing in discrete shallow-crustal magma bodies. Apatite microphenocrysts from lavas show some re-equilibration during cooling at the surface. Clinopyroxene-hosted melt inclusions within the samples typically contain 2-4 wt % H2O, indicating that they have been reset during temporary magma storage at 1-3 km depth, similar to the depth of sill emplacement during recent seismic crises at Campi Flegrei. Comparable apatite compositional trends are identified in each explosive eruption analysed, regardless of volume, composition or eruption timing. However, apatites from the different epochs of activity appear to indicate subtle changes in the H2O content of the parental melt feeding the Campi Flegrei system over time. This study demonstrates the potential utility of integrated apatite and glass analysis for investigating pre-eruptive volatile behaviour in apatite-bearing magmas.

Citation

Stock, M. J., Humphreys, M. C., Smith, V. C., Isaia, R., Brooker, R. A., & Pyle, D. M. (2018). Tracking volatile behaviour in sub-volcanic plumbing systems using apatite and glass: insights into pre-eruptive processes at Campi Flegrei, Italy. Journal of Petrology, 59(12), 2463-2492. https://doi.org/10.1093/petrology/egy020

Journal Article Type Article
Acceptance Date Feb 16, 2018
Online Publication Date Mar 27, 2018
Publication Date Dec 31, 2018
Deposit Date Mar 7, 2018
Publicly Available Date Mar 8, 2018
Journal Journal of Petrology
Print ISSN 0022-3530
Electronic ISSN 1460-2415
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 59
Issue 12
Pages 2463-2492
DOI https://doi.org/10.1093/petrology/egy020

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Copyright Statement
© The Author(s) 2018. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.









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