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Halogen systematics (Cl, Br, I) in Mid-Ocean Ridge Basalts: A Macquarie Island case study

Citation

Kendrick, MA and Kamenetsky, VS and Phillips, D and Honda, M, Halogen systematics (Cl, Br, I) in Mid-Ocean Ridge Basalts: A Macquarie Island case study, Geochimica et Cosmochimica Acta, 81, (March) pp. 82-93. ISSN 0016-7037 (2012) [Refereed Article]

Copyright Statement

Copyright 2011 Elsevier Ltd.

DOI: doi:10.1016/j.gca.2011.12.004

Abstract

The abundance of halogens (Cl, Br and I) in the Earth's mantle has the potential to provide information about mantle metasomatism and volatile recycling in subduction zones. Basalt melts sample different parts of the Earth's mantle, but few data are available for Br or I in basalt melts, and the relative partitioning behaviour of these elements has not been investigated rigorously. To address these issues, we determined the abundances of Cl, Br and I in enriched Mid-Ocean Ridge Basalt (E-MORB) glasses from Macquarie Island in the southwest Pacific. The Macquarie Island glasses are fairly typical of Pacific MORB with MgO of ∼5.5. to 9wt%, 87Sr/ 86Sr of 0.70257-0.70276, 143Nd/ 144Nd of 0.51300-0.51306 and 3He/ 4He of ∼8Ra. These glasses provide a unique opportunity to investigate halogen partitioning behaviour, because their variable MgO contents and trace element signatures (e.g. La/Sm ∼1.4-7.9) result from different degrees of partial melting and fractional crystallisation. The combined measurement of Br/Cl, I/Cl and K/Cl, together with correlations between Cl and other trace elements, demonstrate that the halogens in the Macquarie Island glasses had a mantle source and were not influenced by seawater contamination. Log-log correlation diagrams indicate that Cl, Br and K were not statistically fractionated during partial melting, crystallisation or degassing of CO 2 from these melts. The behaviour of I is less well constrained and minor fractionation of I/Cl cannot be precluded during multi-stage melting and enrichment processes. The data indicate the mantle source of the Macquarie Island glasses was characterised by K/Cl of 13±4, Br/Cl of (3.7±0.5)×10 -3 and I/Cl of (130±100)×10 -6 (2σ uncertainties; weight ratios). The K/Cl ratio of the Macquarie Island glasses is equivalent to the median of all published MORB data. This suggests the Br/Cl and I/Cl values may also be representative of average MORB mantle values. © 2011 Elsevier Ltd.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and Metamorphic Petrology
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
ID Code:81363
Year Published:2012
Funding Support:Australian Research Council (CE0561595)
Web of Science® Times Cited:32
Deposited By:Centre for Ore Deposit Research - CODES CoE
Deposited On:2012-12-03
Last Modified:2013-04-16
Downloads:0

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