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Subduction-related halogens (Cl, Br and I) and H2O in magmatic glasses from Southwest Pacific Backarc Basins

Citation

Kendrick, MA and Arculus, RJ and Danyushevsky, LV and Kamenetsky, VS and Woodhead, JD and Honda, M, Subduction-related halogens (Cl, Br and I) and H2O in magmatic glasses from Southwest Pacific Backarc Basins, Earth and Planetary Science Letters, 400 pp. 165-176. ISSN 0012-821X (2014) [Refereed Article]

Copyright Statement

Copyright 2014 Elsevier

DOI: doi:10.1016/j.epsl.2014.05.021

Abstract

Submarine magmatic glasses from the Manus, Woodlark, North Fiji and Lau backarc basins in the Southwest Pacific, and VolcanoA on the volcanic front of the Tonga Arc adjacent to the Lau Basin, were investigated to characterise the Cl, Brand I elemental budgets in subduction systems. Inparticular we seek to determine the extent of variability in the Br/Cl and I/Cl ratios of backarc basin basalts (BABB) and evaluate if these ratios could improve constraints on the source of subducted volatile components in backarc basins worldwide. The selected glasses represent variably evolved melts of boninite, basalt, basaltic-andesite, dacite and rhyolite composition and were selected from spreading centres and seamounts located at varying distances from the associated arcs. Ingeneral the strongest subduction signatures (e.g. Ba/Nb of 100–370) occur in the samples closest to the arcs and lower more MORB-like Ba/Nb of <16are found in the more distal samples. The glasses investigated have extremely variable halogen concentrations (e.g. 3–4200ppm Cl), with the highest concentrations in enriched glasses with the most evolved compositions. Asobserved in previous studies, the K/Cl, Br/Cl and I/Cl ratios of glasses from individual settings do not vary as a function of MgO and are considered representative of the magma sources because these ratios are not easily altered by partial melting or fractional crystallisation. Systematic variations in these ratios between basins can therefore be related to mixing of halogens from different sources including: (i)the mantle wedge which has MORB-like Br/Cl and I/Cl; (ii)asubduction-derived slab fluid with estimated salinity of ∼4–10wt%salts and variable I/Cl; and (iii)brines characterised by salinities of 55 ±15wt%salts and Br/Cl slightly higher than seawater, that are sometimes assimilated in crustal magma chambers. The slab fluids enriching the Woodlark Basin, North Fiji Basin and the Fonualei Spreading Centre of the Lau Basin have MORB-like I/Cl and Br/Cl overlapping the lower end of the MORB range, indicating a probable source from dehydration of altered ocean crust (AOC). Incontrast, slab fluids with I/Cl ratios of up to 10 times the MORB value were detected in BABB from Manus Basin, the Valu Fa Ridge and the Tonga Arc, and in these cases the elevated I/Cl ratios are most easily explained by the involvement of fluids released by breakdown of I-rich serpentinites. The data show that slabfluids vary in composition across the Tonga Arc and from north to south in the Lau Basin. However, the compositional range of subducted halogens overlaps with thatof MORB indicating subduction could be a major source of halogens in the Earth’s mantle.

Item Details

Item Type:Refereed Article
Keywords:halogens, chlorine, water, subduction, mantle, backarc basin basalts
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Geochemistry not elsewhere classified
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Danyushevsky, LV (Professor Leonid Danyushevsky)
Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
ID Code:92887
Year Published:2014
Web of Science® Times Cited:14
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2014-06-28
Last Modified:2017-11-02
Downloads:0

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