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Deciphering variable mantle sources and hydrous inputs to arc magmas in Kamchatka

Iveson, Alexander A.; Humphreys, Madeleine C.S.; Savov, Ivan P.; de Hoog, Jan C.M.; Turner, Stephen J.; Churikova, Tatiana G.; Macpherson, Colin. G.; Mather, Tamsin A.; Gordeychik, Boris N.; Tomanikova, Lubomira; Agostini, Samuele; Hammond, Keiji; Pyle, David M.; Cooper, George F.

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Authors

Ivan P. Savov

Jan C.M. de Hoog

Stephen J. Turner

Tatiana G. Churikova

Tamsin A. Mather

Boris N. Gordeychik

Lubomira Tomanikova

Samuele Agostini

Keiji Hammond

David M. Pyle

George F. Cooper



Abstract

The chemistry of primitive arc rocks provides a window into compositional variability in the mantle wedge, as well as slab-derived inputs to subduction-related magmatism. However, in the long-term cycling of elements between Earth's internal and external reservoirs, a key unknown is the importance of retaining mobile elements within the subduction system, through subduction-related metasomatism of the mantle. To address these questions, we have analysed olivine-hosted melt inclusions and corresponding bulk rocks from the Kamchatka arc. Suites of melt inclusions record evidence for entrapment along melt mixing arrays during assembly of diverse parental magma compositions. Systematic variations in parental magma B/Zr, Nb/Zr, Ce/B, and B are also apparent among the different eruptive centres studied. These element ratios constrain the nature of subduction-related metasomatism and provide evidence for ambient mantle heterogeneity and variable degrees of mantle melting. High Nb/Zr and low B/Zr in back-arc rocks indicate smaller degree melts, lower slab-derived inputs, but relatively enriched mantle compositions. Similarly, small monogenetic eruptive centres located away from the main stratocones also tend to erupt magmas with relatively lower slab contribution and overall smaller melting degrees. Conversely, arc-front compositions reflect greater slab contributions and larger degree melts of a more depleted ambient mantle. Across-arc variations in B (ranging from ca. ‰ in the rear-arc and Sredinny Ridge to ‰ in the Central Kamchatka Depression) are generally consistent with variable addition of an isotopically heavy slab-derived component to a depleted MORB mantle composition. However, individual volcanic centres (e.g. Bakening volcano) show correlations between melt inclusion B and other geochemical indicators (e.g. Cl/K2O, Ce/B) that require mixing between isotopically distinct melt batches that have undergone different extents of crustal evolution and degassing processes. Our results show that while melt inclusion volatile inventories are largely overprinted during shallower melt storage and aggregation, incompatible trace element ratios and B isotope compositions more faithfully trace initial mantle compositions and subduction inputs. Furthermore, we suggest that the signals of compositional heterogeneity generated in the sub-arc mantle by protracted metasomatism during earlier phases of subduction can be preserved during later magma assembly and storage in the crust.

Citation

Iveson, A. A., Humphreys, M. C., Savov, I. P., de Hoog, J. C., Turner, S. J., Churikova, T. G., …Cooper, G. F. (2021). Deciphering variable mantle sources and hydrous inputs to arc magmas in Kamchatka. Earth and Planetary Science Letters, 562, https://doi.org/10.1016/j.epsl.2021.116848

Journal Article Type Article
Acceptance Date Feb 17, 2021
Online Publication Date Mar 1, 2021
Publication Date 2021-05
Deposit Date Mar 3, 2021
Publicly Available Date Mar 28, 2024
Journal Earth and Planetary Science Letters
Print ISSN 0012-821X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 562
DOI https://doi.org/10.1016/j.epsl.2021.116848

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