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Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea

Humphreys, M.C.S.; Zhang, J.; Cooper, G.F.; Macpherson, C.G.; Ottley, C.J.

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Authors

J. Zhang

G.F. Cooper

C.G. Macpherson

C.J. Ottley



Abstract

Volcanism is the surface expression of magma intrusion, crystallization, assimilation and hybridization processes operating throughout the crust over a range of time periods. Many magmas, including those erupted at subduction zones, have complex textures that reflect these processes. Here, we use textural and geochemical characteristics of calcic amphiboles to help identify multiple ingredients of subduction zone magmatism at Mt Lamington volcano, Papua New Guinea. Our approach uses existing trace element partitioning schemes to calculate the compositions of amphibole equilibrium melts (AEMs). The AEM compositions show that Mt Lamington andesites and plutonic enclaves are dominated by fractionation of amphibole + plagioclase + biotite, with assimilation of plagioclase and zircon. Magnesiohastingsite crystals in the andesite and diktytaxitic mafic enclaves reflect multiple episodes of recharge by more primitive, geochemically variable melts. The andesite also contains clots with rounded grains and melt on grain boundaries. These features indicate slow crystallization, and the retention of melt films could significantly enhance the potential for remobilization of crystals by infiltrating melts or during magma mixing. Variations in crystallization conditions could thus significantly affect the mush microstructure. We suggest that this could result in a significant bias of the volcanic record towards the preferential incorporation of more slowly cooled plutonic material from the lower crust or from more thermally mature plumbing systems.

Citation

Humphreys, M., Zhang, J., Cooper, G., Macpherson, C., & Ottley, C. (2019). Identifying the ingredients of hydrous arc magmas: insights from Mt Lamington, Papua New Guinea. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 377(2139), Article 20180018. https://doi.org/10.1098/rsta.2018.0018

Journal Article Type Article
Acceptance Date Jul 30, 2018
Online Publication Date Jan 7, 2019
Publication Date Feb 28, 2019
Deposit Date Jul 30, 2018
Publicly Available Date Mar 29, 2024
Journal Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences.
Print ISSN 1364-503X
Electronic ISSN 1471-2962
Publisher The Royal Society
Peer Reviewed Peer Reviewed
Volume 377
Issue 2139
Article Number 20180018
DOI https://doi.org/10.1098/rsta.2018.0018

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