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Published March 14, 2008 | Supplemental Material
Journal Article Open

The Chlorine Isotope Composition of Earth's Mantle

Abstract

Chlorine stable isotope compositions (δ^(37)Cl) of 22 mid-ocean ridge basalts (MORBs) correlate with Cl content. The high-δ^(37)Cl, Cl-rich basalts are highly contaminated by Cl-rich materials (seawater, brines, or altered rocks). The low-δ^(37)Cl, Cl-poor basalts approach the composition of uncontaminated, mantle-derived magmas. Thus, most or all oceanic lavas are contaminated to some extent during their emplacement. MORB-source mantle has δ^(37)Cl ≤ –1.6 per mil (‰), which is significantly lower than that of surface reservoirs (∼ 0‰). This isotopic difference between the surface and deep Earth results from net Cl isotopic fractionation (associated with removal of Cl from the mantle and its return by subduction over Earth history) and/or the addition (to external reservoirs) of a late volatile supply that is ^(37)Cl-enriched.

Additional Information

© 2008 American Association for the Advancement of Science. 26 September 2007; Accepted 1 February 2008. We thank R. Hékinian, A. Jambon, C. Mével, M. Moreira, and F. Pineau for providing most of the samples, as well as A. Bézos, P. Cartigny, J. M. Eiler, F. Guyot, C. H. Langmuir, and M. Moreira for discussion on this work and, together with other reviewers, for their comments on a previous version of this manuscript. M.B. thanks J. M. Eiler and E. M. Stolper at CalTech for their support during the writing of this manuscript. This is IPGP contribution 2342 and CNRS-INSU contribution 408.

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