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Shallow magmatic processes revealed by cryptic microantecrysts: a case study from the Taupo Volcanic Zone

Lormand, C.; Zellmer, G.F.; Sakamoto, N.; Ubide, T.; Kilgour, G.; Yurimoto, H.; Palmer, A.; Németh, K.; Iizuka, Y.; Moebis, A.

Shallow magmatic processes revealed by cryptic microantecrysts: a case study from the Taupo Volcanic Zone Thumbnail


Authors

G.F. Zellmer

N. Sakamoto

T. Ubide

G. Kilgour

H. Yurimoto

A. Palmer

K. Németh

Y. Iizuka

A. Moebis



Abstract

Arc magmas typically contain phenocrysts with complex zoning and diverse growth histories. Microlites highlight the same level of intracrystalline variations but require nanoscale resolution which is globally less available. The southern Taupo Volcanic Zone (TVZ), New Zealand, has produced a wide range of explosive eruptions yielding glassy microlite-bearing tephras. Major oxide analyses and textural information reveal that microlite rims are commonly out of equilibrium with the surrounding glass. We mapped microlites and microcrysts at submicron resolution for major and trace element distributions and observed three plagioclase textural patterns: (1) resorption and overgrowth, (2) oscillatory zoning, and (3) normal (sharp) zoning. Pyroxene textures are diverse: (1) resorption and overgrowth, (2) calcium-rich bands, (3) hollow textures, (4) oscillatory zoning, (5) sector zoning, (6) normal zoning and (7) reverse zoning. Microlite chemistry and textures inform processes operating during pre-eruptive magma ascent. They indicate a plumbing system periodically intruded by short-lived sub-aphyric dykes that entrain microantecrysts grown under diverse physico-chemical conditions and stored in rapidly cooled, previously intruded dykes. Changes in temperature gradients between the intrusion and the host rock throughout ascent and repeated magma injections lead to fluctuations in cooling rates and generate local heterogeneities illustrated by the microlite textures and rim compositions. Late-stage degassing occurs at water saturation, forming thin calcic microcryst rims through local partitioning effects. This detailed investigation of textures cryptic to conventional imaging shows that a significant proportion of the micrometre-sized crystal cargo of the TVZ is of antecrystic origin and may not be attributed to late-stage nucleation and growth at the onset of volcanic eruptions, as typically presumed.

Citation

Lormand, C., Zellmer, G., Sakamoto, N., Ubide, T., Kilgour, G., Yurimoto, H., …Moebis, A. (2021). Shallow magmatic processes revealed by cryptic microantecrysts: a case study from the Taupo Volcanic Zone. Contributions to Mineralogy and Petrology, 176, Article 97. https://doi.org/10.1007/s00410-021-01857-7

Journal Article Type Article
Acceptance Date Oct 18, 2021
Online Publication Date Nov 5, 2021
Publication Date 2021
Deposit Date Oct 20, 2021
Publicly Available Date Mar 29, 2024
Journal Contributions to Mineralogy and Petrology
Print ISSN 0010-7999
Electronic ISSN 1432-0967
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 176
Article Number 97
DOI https://doi.org/10.1007/s00410-021-01857-7

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.




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