The Chlorine Isotope Composition of Earth's Mantle
M. Bonifacie,1,2
N. Jendrzejewski,1
P. Agrinier,1
E. Humler,3,4
M. Coleman,5,6
M. Javoy1
Chlorine stable isotope compositions (
37Cl) of 22 mid-ocean ridge basalts (MORBs) correlate with Cl content. The high-37Cl, Cl-rich basalts are highly contaminated by Cl-rich materials (seawater, brines, or altered rocks). The low-37Cl, 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 37Cl 
–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 37Cl-enriched.
1 Equipe de Physico-Chimie des Fluides, Géologiques, Institut de Physique du Globe de Paris (IPGP) and Université Paris, Diderot (UPD), CNRS-INSU–Unité Mixte de Recherche (UMR) 7154, 75251 Paris Cedex 05, France.
2 Division of Geological and Planetary Sciences, California Institute of Technology (CalTech), Pasadena, CA 91125, USA.
3 Equipe de Géosciences Marines, IPGP, CNRS-INSU-UMR 7154, 75251 Paris Cedex 05, France.
4 Laboratoire de Planétologie et Géodynamique, Université de Nantes, CNRS UMR 6112, 44322 Nantes Cedex 3, France.
5 School of Human and Environmental Sciences, University of Reading, RG6 6AB, UK.
6 Jet Propulsion Laboratory, CalTech, Pasadena, CA 91109, USA.
*To whom correspondence should be addressed. E-mail: bonifaci{at}gps.caltech.edu
