Isotopic Composition Of Chlorine Research Articles

Multiple reservoirs of volatiles in the Moon revealed by the isotopic composition of chlorine in lunar basalts

The isotopes of chlorine (37Cl and 35Cl) are highly fractionated in lunar samples compared to most other Solar System materials. Recently, the chlorine isotope signatures of lunar rocks have been attributed to large-scale degassing processes that occurred during the existence of a magma ocean. In this study we investigated how well a suite of lunar basalts, most of which have not previously been analyzed, conform to previous models. The Cl isotope compositions (δ37Cl (‰) = [(37Cl/35Clsample/37Cl/35ClSMOC) − 1] × 1000, where SMOC refers to standard mean ocean chloride) recorded range from ∼+7 to +14‰ (Apollo 15), +10 to +19‰ (Apollo 12), +9 to +15‰ (70017), +4 to +8‰ (MIL 05035), and +15 to +22‰ (Kalahari 009). The Cl isotopic data from the present study support the mixing trends previously reported by Boyce et al. (2015) and Barnes et al. (2016), as the Cl isotopic composition of apatites are positively correlated with bulk-rock incompatible trace element abundances in the low-Ti basalts, inclusive of low-Ti and KREEP basalts. This trend has been interpreted as evidence that incompatible trace elements, including Cl, were concentrated in the urKREEP residual liquid of the lunar magma ocean, rather than the mantle cumulates, and that urKREEP Cl had a highly fractionated isotopic composition. The source regions for the basalts were thus created by variable mixing between the mantle (Cl-poor and relatively unfractionated) and urKREEP. The high-Ti basalts show much more variability in measured Cl isotope ratios and scatter around the trend formed by the low-Ti basalts. Most of the data for lunar meteorites also fits the mixing of volatiles in their sources, but Kalahari 009, which is highly depleted in incompatible trace elements, contains apatites with heavily fractionated Cl isotopic compositions. Given that Kalahari 009 is one of the oldest lunar basalts and ought to have been derived from very early-formed mantle cumulates, a heavy Cl isotopic signature is likely not related to its mantle source, but more likely to magmatic or secondary alteration processes, perhaps via impact-driven vapor metasomatism of the lunar crust.

Strong impact of ion filtration on the isotopic composition of chlorine in young clay-rich oceanic sediment pore fluids

A collection of 34 pore fluids from young clay-rich sedimentary piles of the Shikoku basin on the Philippine oceanic plate at the front of the Nankai subduction zone, southeast of Japan, were analyzed for their chloride content and chlorine stable isotope composition (35Cl and 37Cl, reported as δ37Cl). These pore fluids are samples from IODP Sites C0011 and C0012, which penetrate deeper than 500 meters below the seafloor. At both sites, the δ37Cl values display a regular decrease with depth from about 0‰ (seawater value) at the seafloor to −8.5 and −6.5‰ respectively in hydrogeologically isolated, low permeability, sediment levels. At some depths, local deviations of up to 6‰ in δ37Cl interrupt the overall decreasing trends. They may be interpreted as the injection of external fluids into the sedimentary piles as a result of sedimentary levels with higher permeability. At the bottom of the sedimentary piles, the injected fluids, probably originating from the altered oceanic crust, systematically have δ37Cl values closer to seawater. Literature data indicate the display of downward trends of decreasing δ37Cl values of the pore fluids in many other young clay-rich sedimentary piles (Nankai Trough and the Japan Trench accretionary prisms, Black Ridge and Juan de Fuca Ridge flank). Here, we use conservation equations to demonstrate that these δ37Cl depth profiles can be modeled using the effect of the compaction of growing clay–rich sedimentary piles on the water and chlorides (including 35Cl and 37Cl isotopes). This modeling shows that a small isotope fractionation of chlorine isotopes, α37Cl/35Clexpulsed fluid-residual fluid, in the range of 1.006 to 1.001, may explain the observed negative δ37Cl chlorides at the bottom of the sedimentary piles. The complementary positive δ37Cl chlorides must accumulate at the top but are very likely erased by dilution with seawater chlorides across the seafloor interface. This range of chlorine isotope fractionation values is in agreement with the theory of ion filtration of Phillips and Bentley (1987) in which the mobility of chlorides through semi-permeable clay membrane is determined by ion repulsion. Based on this study, we show that young pore fluids in clay-rich sediments of the oceanic crust are 37Cl-depleted chloride reservoirs. They might be the source of 37Cl-depleted chloride fluids advected at mud volcanoes on the seafloor but do not seem to contribute largely to subduction zone magmatic, tectonic, metamorphic products where no such 37Cl-depleted chlorine is documented. This in turn is a strong argument to propose that most of the clay-rich sediment’s pore waters are released back into the ocean rather than subducted.

Chlorine isotope residual salt analysis: A new tool to investigate formation waters from core analyses

This article presents the first results of chlorine residual salt analysis (Cl-RSA), a new technique that allows investigation of the isotopic composition of chlorine in oil-field waters from core analysis. As water evaporates, the residual salts precipitate in the pores of a core. Unlike the routinely used strontium isotope residual salt analysis (Sr-RSA) technique, which determines the composition of a trace element (strontium), the Cl-RSA technique allows the determination of the isotopic composition and origin of one of the most abundant anions in natural waters. The results show that combining the 37Cl of two successive leachates of a core sample leads to an isotopic composition that is representative of pore water. The reproducibility of the method applied to sandstone samples is considered to be 0.05. The Cl-RSA technique was tested on two wells from the Elgin area (North Sea, United Kingdom). The 37Cl results in formation waters range from 1.03 to 0.57, with an overall increase with depth. These results have been compared to the 87Sr/86Sr ratios of pore waters determined in the same wells using the Sr-RSA technique. The similarity of form between the 37Cl and 87Sr/86Sr profiles with depth confirms that residual salts permit a reliable investigation of the chlorine isotopic composition from core analysis. As with the Sr-RSA technique, Cl-RSA could be used to test the isotopic homogeneity of a sample and to assess the compartmentalization of oil fields and reservoirs. This technique could provide key information regarding the origin of the salinity and its evolution during the reservoirs' filling, as well as help in the monitoring during field production.

A secondary isotopic reference material of chlorine from selected seawater

A secondary isotopic reference material of chlorine as NaCl collected from a sea water, located at 4°18′N, 161°08′E and collected on October 22, 1994, was prepared using ion exchange technique. The δ 37Cl of an NaCl product named ISL 354 was measured to be −0.39±0.05‰ (2 σ) related to NIST SRM 975, an isotopic standard reference material with an absolute 37Cl/ 35Cl ratio of 0.31977. No contamination or isotopic fractionation was observed due to a complete recovery of chlorine and the avoidance of chemical reagents during preparation of ISL 354 from selected seawater. The isotopic composition of chlorine in ISL 354 does not change on long-term storage. So ISL 354 can be used as a secondary isotopic reference material of chlorine.

Variations in isotopic compositions of chlorine in evaporation-controlled salt lake brines of Qaidam Basin, China

The variations in the isotopic compositions of chlorine in evaporation-controlled saline lake brines were determined by using an improved procedure for precise measurement of chlorine isotopes based on Cs2Cl+ ion by thermal ionization mass spectrometry. The results showed that variation in δ37 Cl values in these evaporation-controlled brines are attributable to evaporation of brine accompanied by the deposition of saline minerals. The isotopic fractionation of chlorine between the deposited saline mineral and the co-existing brine caused the variation of δ37 Cl values in the brine. In general the isotopic fractionation of chlorine in nature indicates enrichment of37Cl in the solid phase relative to35Cl. The reverse isotopic fractionation of chlorine in which35Cl is enriched in the solid phase, was observed to some extent during quick deposition under laboratory conditions as well as in nature. The mechanism of isotopic fractionation of chlorine during evaporation deposition was studied.

Chlorine isotopic geochemistry of salt lakes in the Qaidam Basin, China

The isotopic compositions of chlorine in salt lake brine coexisting with halite, oil-field water and river water from the Qaidam Basin (Qinghai, China) have been examined using high-precision measurement of chlorine isotopes based on thermal ionization mass spectrometry of the Cs 2Cl + ion. δ 37Cl values vary from −2.05 to +2.94‰, with average values of +2.94‰ for hot spring water, +1.35‰ for river water, −0.38‰ for oil-field brine, −0.40‰ for saline water and −0.63‰ for salt lake brine. The preliminary results show isotopic fractionation of chlorine in salt lake brine during salt precipitation. The variation of the δ 37Cl value in these salt lakes is mainly associated with brine evaporation and halite precipitation and with the hydrochemistry of the input water. The chlorine isotopic composition may reflect the degree of evaporation of the salt lake brine and may be used to distinguish brines that are in equilibrium with precipitating salts and brines that have dissolved earlier evaporates.

Isotopic compositions of chlorine in brine and saline minerals

The above results indicate that37Cl/35 C1 ratios in saline minerals are higher than those in brine due to chlorine isotopic fractionation during evaporation.37Cl/35 C1 ratios of salt lakes brine reflect the change in hydrochemical condition. The chlorine isotopic composition of saline mineral is associated with environment. Therefore, chlorine isotope may be used to trace evolution of salt lakes and the environment.

Stable chlorine isotopic composition of marine aerosol particles in the western Atlantic Ocean

The isotopic composition of chlorine sampled from the atmosphere has been measured for the first time. Eight aerosol samples collected on bulk filters at Bermuda are enriched in 37Cl relative to sea water. Stable chlorine isotopic compositions are reported in units of per mil as δ37Cl which is defined as 1000 × [(Rsample/Rsea water) ‐ 1] where R is the ratio of 37Cl to 35Cl. The δ37Cl of the aerosols range from +0.42 to +2.53 per mil and strongly correlate with chlorine deficit (based upon sea salt sodium) and non‐sea salt sulfate. The data trend is consistent with the fractional distillation (loss) of HCl from an acidified aerosol governed by a fractionation factor of 0.9972. Subsequent experiments support the hypothesis that HCl evaporation was most likely the primary mechanism of chlorine volatilization in the sampled aerosols. Furthermore, the data indicate that marine aerosols perturbed by anthropogenic NOx and SO2 are an important source of isotopically light chlorine in the free troposphere.

Multiphoton spectroscopy of Rydberg states of tetrachloroethylene

Spectroscopic studies of two-photon resonant vibronic bands of the (π,np) and (π,nf) Rydberg series of jet-cooled C2Cl4 are reported. Polarization ratio measurements for each transition and comparisons of experimental and calculated chlorine isotope shifts permitted the unambiguous assignment of vibronic band structure. Ab initio self-consistent field calculations of the harmonic frequencies for the optimized ground state geometry of C2Cl4 were performed for each of the seven isotopic chlorine compositions to assist interpretation of the isotope shift measurements. The 4p-Rydberg bands are quite weak and strongly perturbed, suggestive of localized Rydberg–valence state configuration mixing. The nf-Rydberg series provides a measurement of the first ionization potential for C2Cl4 of 75 216±5 cm−1 in good agreement with previous measurements. Mass analysis of ion fragmentation patterns reveals a multiphoton ladder switching excitation mechanism.

A comparative molecular dynamics and neutron scattering study of the liquid mixture carbon tetrachloride/carbon disulphide

Neutron diffraction studies on the equimolar liquid mixture CCl4/CS2 with three different isotopic chlorine compositions (99·35 per cent, 75·77 per cent—natural composition—1·79 per cent of 35Cl; the complementary isotope is 37Cl) were carried out under ambient conditions. The data were corrected for back-ground, absorption, multiple scattering and inelastic effects (Placzek correction) and then were normalized to absolute differential cross-section by comparison with vanadium standard. The absolute coherent distinct differential cross-section was separated into intramolecular and intermolecular contributions. A molecular dynamics simulation with 500 molecules was performed. The interaction between molecules was described by a five-centre and a three-centre Lennard-Jones potential for CCl4 and CS2 respectively. For the cross interactions the Lorentz-Berthelot mixing rule was used. An algorithm based on the quaternion method was adapted to this two-component system. Intermolecular pair correlation function...

Dynamics of molten alkali halides: LiCl and DCl

The authors have measured the inelastic neutron scattering spectra of three samples of molten 7LiCl with different isotopic chlorine compositions, and of one sample of molten KCl, using the time-of-flight spectrometer IN6 at the Institut Laue-Langevin. It is observed that the main peak in the total dynamical structure factor for LiCl is sharply peaked in both Q and omega directions, while that for KCl is much weaker and broader. The spectra for LiCl show evidence for two types of collective mode with characteristic energies of 10-20 and 40-50 meV. Using the differences between the samples, it is possible to show that appropriate pairs of dynamical variables for these modes are m+, -m- (low energies) and q+, -q- (high energies), whereas in molten CsCl the variables have been shown to be m+, m- and q+, q-. They propose that for the alkali chlorides (where the ionic radius ratio r+/r-<1) the former variables are appropriate when m+<m-, and the latter when m+>m-. There is a crossover between the variables, resulting in strong-mode coupling, when m+=m-. The data for KCl are consistent with this proposition.

Structure Factors of Molten CsCl at LowQ

Abstract The structure factors for three samples of molten CsCl with different isotopic chlorine compositions have been measured accurately in the region 0.2 > Q > 3.0 A−1 using the D1B diffractometer at the Institut Laue Langevin. A rise in the measured structure factors for Q > 0.5 A−1 is explained as being due to inelastic scattering from overdamped acoustic modes.

Inelastic neutron scattering studies of collective modes in molten CsCl

The authors have measured the inelastic neutron scattering spectra of three samples of molten CsCl with different isotopic chlorine compositions (including the naturally occurring one) using an incident wavelength of 4.1 AA, and also of molten CsCl with natural Cl using 1.08 AA. The experiments were performed on the time-of-flight spectrometers IN6 and IN4 at the Institut Laue-Langevin. By a first-order subtraction they have substantially separated the contributions from mass (acoustic mode) and charge (optic mode) current correlations. A quasi-dispersion curve has been derived from the positions of the peaks in these functions. The acoustic and optic branches are well separated in energy over the measured region (1 AA-1<Q<4 AA-1) with relatively flat dispersion. The modes are strongly overdamped and although the energy of the low-Q optic mode corresponds to the crystal LO there is no evidence of a side peak in Sqq(Q, omega ). Thus the observed optic mode is not propagating, even at the lowest values of Q. Indeed the IN4 measurements show that Sqq(Q, omega ) is very broad (full width 18 meV) at low Q while Smm(Q, omega ) is much narrower. Small maxima in the widths of ST(Q, omega ) at Q approximately=1.7 AA-1 indicate the possible existence of a soft acoustic mode. Classical de Gennes narrowing may be observed at Q approximately=2.0 AA-1, corresponding to a change in diffusion mechanism. The statistical accuracy of the spectra was too low and the differences between scattering lengths too small to enable a second-order separation to be made using results from all three samples.

The observation of longitudinal optic vibrational modes in molten rubidium chloride

The authors have measured the inelastic scattering spectra of two samples of molten RbCl with different isotopic chlorine compositions using the IN6 time-of-flight spectrometer at the Institut Laue-Langevin in Grenoble. By a first-order subtraction they have substantially separated the contributions from the longitudinal mass-mass (acoustic-type mode) and charge-charge (optic-type mode) current-current correlation functions. Over the accessible Q range these have the form of single broad peaks, with the mass peaks being approximately twice as wide and half as high as the charge peaks. A quasidispersion curve has been derived from the peak positions and comparisons have been made with the low-temperature crystalline state.

Mass Spectrometric Isotopic Analysis of Chlorine by the Surface-Ionization Method

Stable isotopes of chlorine are often used as tracers in the study of the chemical reactions of chlorine and its compounds. In these studies, as well as in the control of processes for separation of chlorine isotopes, one needs methods for precise determination of the isotopic composition of chlorine.

The Isotopic Composition and the Atomic Weight of Chlorine in Meteorites

HARKINS and Stone, in a letter under the above title in NATURE of September 19, state that they have found the atomic weight of meteoritic chlorine identical with that of chlorine as found on earth, within the limits of their experimental error. The question of the constancy of isotopic composition of chlorine has already proved of interest to several investigators, and one may recall the work of Curie in 1921 and of Gleditsch and others in 1922 and 1923, on the chlorine from certain ancient minerals. Their results are now confirmed by Harkins and Stone.