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Open AccessArticle

Two-Stage Origin of K-Enrichment in Ultrapotassic Magmatism Simulated by Melting of Experimentally Metasomatized Mantle

1
ARC Centre of Excellence of Core to Crust Fluid Systems and Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
2
Institute für Geowissenschaften, Johannes Gutenberg Universität, 55099 Mainz, Germany
3
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 10083, China
4
Faculty of Mining and Geology, University Belgrade, Đušina 7, 11000 Belgrade, Serbia
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(1), 41; https://doi.org/10.3390/min10010041
Received: 17 November 2019 / Revised: 18 December 2019 / Accepted: 27 December 2019 / Published: 31 December 2019
The generation of strongly potassic melts in the mantle requires the presence of phlogopite in the melting assemblage, while isotopic and trace element analyses of ultrapotassic rocks frequently indicate the involvement of subducted crustal lithologies in the source. However, phlogopite-free experiments that focus on melting of sedimentary rocks and subsequent hybridization with mantle rocks at pressures of 1–3 GPa have not successfully produced melts with K2O >5 wt%–6 wt%, while ultrapotassic igneous rocks reach up to 12 wt% K2O. Accordingly, a two-stage process that enriches K2O and increases K/Na in intermediary assemblages in the source prior to ultrapotassic magmatism seems likely. Here, we simulate this two-stage formation of ultrapotassic magmas using an experimental approach that involves re-melting of parts of an experimental product in a second experiment. In the first stage, reaction experiments containing layered sediment and dunite produced a modally metasomatized reaction zone at the border of a depleted peridotite. For the second-stage experiment, the metasomatized dunite was separated from the residue of the sedimentary rock and transferred to a smaller capsule, and melts were produced with 8 wt%–8.5 wt% K2O and K/Na of 6–7. This is the first time that extremely K-enriched ultrapotassic melts have been generated experimentally from sediments at low pressure applicable to a post-collisional setting. View Full-Text
Keywords: lamproites; high-pressure experiments; ultrapotassic; K-enrichment; subduction zones lamproites; high-pressure experiments; ultrapotassic; K-enrichment; subduction zones
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Förster, M.W.; Buhre, S.; Xu, B.; Prelević, D.; Mertz-Kraus, R.; Foley, S.F. Two-Stage Origin of K-Enrichment in Ultrapotassic Magmatism Simulated by Melting of Experimentally Metasomatized Mantle. Minerals 2020, 10, 41.

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