Chlorine isotopic composition

Although GC-C-IRMS systems that can measure the chlorine isotopic composition of individual chlorinated hydrocarbons are currently unavailable, it is clear that chlorine isotope analysis is also a useful technique to consider for study [614,677,678]. Measurement of chlorine stable isotope ratios in natural samples such as rocks and waters has become routine [626,679,680], but few measurements of chlorine isotopes in chlorinated aliphatic hydrocarbons have been reported [614]. A chlorine isotope effect was found in ferf-butyl chloride [681], demonstrating that 37Cl is more strongly bound to carbon than is 35Cl. Significant differences in the <5i7Cl values of some atmospheric chlorinated... 

Chlorine isotope compositions vary by up to 15%o (Chapter 7 Stewart and Spivack 2004). These large variations in Cl isotope compositions are found in marine environments, including mid-ocean ridge basalts, seafloor and hydrothermal alteration products, and sedimentary pore... 

Skulan JL, Beard BL, Johnson CM (2002) Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(III) and hematite. Geochim Cosmochim Acta 66 2995-3015 Stewart MA, Spivack AJ (2004) The stable-chlorine isotope compositions of natural and anthropogenic materials. Rev Mineral Geochem 55 231-254... 

The Stable-Chlorine Isotope Compositions of Natural and Anthropogenic Materials... 

Variations in chlorine isotopic composition are expressed as a per mil (%o) difference (5 Cl) in a measured Cl/ Cl ratio (R) relative to the measured seawater chloride ratio (Standard Mean Ocean Chloride, SMOC),... 

RESULTS AND IMPLICATIONS OF THE STABLE-CHLORINE ISOTOPIC COMPOSITION OF GEOLOGIC AND ANTHROPOGENIC MATERIALS... 

Figure 1. Stable-chlorine isotopic composition of meteorites, igneous and metamorphic rocks and minerals reported as 8 Cl relative to Cl/ Cl in Standard Mean Ocean Chloride (SMOC) represented by die vertical dashed line at 0 %o. Data from Magenheim et al. (1994), Magenheim et al. (1995), Bridges et al. (2001), Eggenkamp and Koster van Groos (1997), Boudreau et al. (1997), Willmore et al. (2002), Musashi et al. (1998), Markl et al. (1997), Eggenkamp and Schuiling(1995). Filled symbols are E-MORB and gray boxes represent preliminary data of E-MORB from Stewart (2000).

Layered intrusions. Chlorine isotope studies of the Stillwater Complex of Montana, USA (e.g., Stewart et al. 1996 Boudreau et al. 1997), and the Bushveld Complex in the Republic of South Africa (e.g., Willmore et al. 2002) show that both intrusions are anomalously rich in chlorine (e.g., Boudreau et al. 1986 Willmore et al. 2000), but that, their chlorine-isotopic compositions are distinct from one another (Fig. 1). The 8 Cl values of Stillwater samples range from -0.93%o to 0.27%o with all but one value below 0.1 %o (Fig. 1). In contrast the... 

The 8 C1 values of oxidized ore minerals reported by Eggenkamp and Schuiling (1995) are nearly all enriched in Cl ranging from -0.05%o to 5.96%o (Fig. 1). The distinctly positive values in some of these ore minerals led these authors to suggest that if chlorine-isotopic composition of the ore deposits was reflected in waters draining them, then the water compositions may be employed as a tool for economic exploration. 

Seawater and marine pore fluids. As discussed above, the chlorine isotopic composition of modem seawater does not vary measurably. This is not surprising in light of its long residence hme (approximately 90 million years) and its conservative behavior in the water column. In contrast, marine pore fluids have been demonstrated to vary considerably. There is also the likelihood that hydrothermal fluids may be fractionated as a result of exchange with mineral phases, as phase separation under marine hydrothermal conditions does not appear to lead to measurable fractionation (e.g., Magenheim et al. 1995). However, to date no stable-chlorine isotopic compositions of marine hydrothermal fluids have been reported in the literature. 

Sedimentary basins and oil flelds. Despite their similarity with seawater chlorine-isotopic composition, enough variability between fluids exists locally (and the precision of the analytical method is fine enough) to distinguish the sources of chloride contributing to... 

Ransom B, Spivack AJ, Kastner M (1995) Stable Cl isotopes in subduction-zone pore waters implications for fluid-rock reactions and the cycling of chlorine. Geology 23 715-718 Reddy CM, Heraty LJ, Holt BD, Sturchio NC, Eglinton XI, Drenzek NJ, Xu L, Lake JL, Maruya KA (2000) Stable chlorine isotopic compositions of aroclors and aroclor- contaminated sediments. Env Sci Tech 34(13) 2866-2870... 

Volpe C, Wahlen M, Spivack AJ (1998) Chlorine isotopic composition of marine aerosols Implications for the release of reactive chlorine and HCl cycling rates. Geophys Res Lett 25(20) 3831-3834 Volpe CM (1998) Stable Chlorine Isotope Variations in the Atmosphere. PhD Dissertation, University of California, San Diego, San Diego, California... 

Wahrenberger C, Eastoe CJ, Seward TM, Dietrich V (1997) Stable chlorine isotope composition of volcanic gas condensates, y" Annual Goldschmidt Conf 213... 

Chlorine is the major anion in surface- and mantle-derived fluids. It is the most abundant anion in hydrothermal solutions and is the dominant metal complexing agent in ore forming environments (Banks et al. 2000). Despite its variable occurrence, chlorine isotope variations in natural waters conunonly are small and close to the chlorine isotope composition of the ocean. This is also true for chlorine from fluid inclusions in hydrothermal minerals which indicate no significant differences between different types of ore deposits such as Mississippi-Valley and Porphyry Copper type deposits (Eastoe et al. 1989 Eastoe and Guilbert 1992). 

A summary of the observed natural chlorine isotope variations is presented in Fig. 2.23. Ransom et al. (1995) gave a natural variation range in chlorine isotope composition of about 15%c with subduction zone pore waters having S Cl values as low as —8%c whereas minerals in which Cl substitutes OH have 5 Cl values as high as 7%c. 

Bonifacie M, Jendrzejewski N, Agiinier P, Humler E, Coleman M, Javoy M (2008) The chlorine isotope composition of the Earth,s mantle. Science 319 1518-1520 Borthwick J, Harmon RS (1982) A note regarding CIF3 as an alternative to BrFs for oxygen isotope analysis. Geochim Cosmochim Acta 46 1665-1668 Bottcher ME (1996) and C/ C fractionation during the reaction of carbonates with... 

A plot of chlorine isotopic composition versus depth shows a few additional aspects of the data from two shield environments (Figure 11(a)). Canadian saline waters generally occur at depths below 500 m. Saline or brackish waters are not commonly found in shallow Canadian Shield systems (Frape and Fritz, 1987). Both the Canadian and the Fennoscandian data show a considerable variation in isotopic signature for any particular depth. If the data points were coded for specific sites, there would still be no discernible trends with depth. Finally, some Fennoscandian samples appear to approach the signature of the Baltic Sea, similar to that for the... 

Chlorine Cl has only two stable isotopes, Cl and Cl. Its isotopic composition is determined relative to the standard, namely chlorine isotope composition of sea water (SMOC, abundance ratio 0.324). Therefore, the value 6 C1 in the ocean is 0%o, and changes in the natural waters of -2%o to +l%o, but sometimes up to 8%o (Kharaka et al, 2003). 

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