Gas Source Mass Spectrometry Research Articles

Amazarkan gold deposit: conditions of formation, sources of ore substance (Eastern Transbaikalia)

Relevance. The need to clarify the sources and conditions of formation of gold mineralisation of the Amarzakan gold deposit. The characteristic feature of the deposit is the spatial combination of gold mineralisation and small intrusions of the middle and basic composition of the Amudzhikan complex. Aim. Determination of physico-chemical conditions and nature of the source of the ore substance of the Amazarkan deposit. Methods. ICP-MS method and standard chemical analysis were used to determine the elemental composition of rocks. Sulfur isotope composition of sulfides was obtained using gas-source mass-spectrometry and fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and by FTIR spectroscopy at the Centre for Collective Use of Multi-element and Isotope Studies of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The oxygen isotope composition was determined at the Geological Institute of the Siberian Branch of the Russian Academy of Sciences (Ulan-Ude) using the MIR 10-30 laser heating system with a 100-watt CO2 laser and a wavelength of 10.6 µm in the infrared region in the presence of BrF5 reagent. Results. The authors have established the spatial confinement of ore zones to Mesozoic dikes of the Amudzhikan complex (J2-3). The Eu/Sm and Eu/Eu* ratios in the dikes indicate fractionation of magmatic melts in the sources at the level of the lower continental crust and low degree of their differentiation. The character of REE distribution in the rocks of dikes of the Amudzhikan complex is similar to the distribution of REE in the ores of the deposit. Eu/Sm–Eu/Eu* figurative points of compositions of ore veins and granodiorites of the Amudzhikan complex form a single trend. Dykes of the Amuzhikan complex are characterized by increased Au content from 0.026 to 1.171 g/t. These data suggest a paragenetic link between Au mineralization and rocks of the Amudzhikan complex. Ore veins of productive stages of ore formation were formed at temperatures ranging from 125 to 410°C. The calculated S and O isotopic composition of the ore-forming fluid in equilibrium with pyrite and quartz, as well as the Co/Ni>1 ratio in the ores indicate the presence of a magmatic component in its composition.

Quantitative reconstruction of a single super rainstorm using daily resolved δ18O of land snail shells

A “once-in-a-millennium” super rainstorm battered Zhengzhou, central China, from 07/17/2021 to 07/22/2021 (named “7.20” Zhengzhou rainstorm). It killed 398 people and caused billions of dollars in damage. A pressing question is whether rainstorms of this intensity can be effectively documented by geological archives to understand better their historical variabilities beyond the range of meteorological data. Here, four land snail shells were collected from Zhengzhou, and weekly to daily resolved snail shell δ18O records from June to September of 2021 were obtained by gas-source mass spectrometry and secondary ion mass spectrometry. The daily resolved records show a dramatic negative shift between 06/18/2021 and 09/18/2021, which has been attributed to the “7.20” Zhengzhou rainstorm. Moreover, the measured amplitude of this shift is consistent with the theoretical value estimated from the flux balance model and instrumental data for the “7.20” Zhengzhou rainstorm. Our results suggest that the ultra-high resolution δ18O of land snail shells have the potential to reconstruct local synoptic scale rainstorms quantitatively, and thus fossil snail shells in sedimentary strata can be valuable material for investigating the historical variability of local rainstorms under different climate backgrounds.

Evaluating the multiple sulfur isotope signature of Eoarchean rocks from the Isua Supracrustal Belt (Southwest-Greenland) by MC-ICP-MS: Volcanic nutrient sources for early life.

On the anoxic Archean Earth, prior to the onset of oxidative weathering, electron acceptors were relatively scarce, perhaps limiting microbial productivity. An important metabolite may have been sulfate produced during the photolysis of volcanogenic SO2 gas. Multiple sulfur isotope data can be used to track this sulfur source, and indeed this record indicates SO2 photolysis dating back to at least 3.7 Ga, that is, as far back as proposed evidence of life on Earth. However, measurements of multiple sulfur isotopes in some key strata from that time can be challenging due to low sulfur concentrations. Some studies have overcome this challenge with NanoSIMS or optimized gas-source mass spectrometry techniques, but those instruments are not readily accessible. Here, we applied an aqua regia leaching protocol to extract small amounts of sulfur from whole rocks for analyses of multiple sulfur isotopes by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Measurements of standards and replicates demonstrate good precision and accuracy. We applied this technique to meta-sedimentary rocks with putative biosignatures from the Eoarchean Isua Supracrustal Belt (ISB, >3.7 Ga) and found positive ∆33S (1.40-1.80‰) in four meta-turbidites and negative ∆33S (-0.80‰ and -0.66‰) in two meta-carbonates. Two meta-basalts do not display significant mass-independent fractionation (MIF, -0.01‰ and 0.16‰). Insitu Re-Os dating on a molybdenite vein hosted in the meta-turbidites identifies an early ca. 3.7 Ga hydrothermal phase, and insitu Rb-Sr dating of micas in the meta-carbonates suggests metamorphism affected the rocks at ca. 2.2 and 1.7 Ga. We discuss alteration mechanisms and conclude that there is most likely a primary MIF-bearing phase in these meta-sediments. Our new method is therefore a useful addition to the geochemical toolbox, and it confirms that organisms at that time, if present, may indeed have been fed by volcanic nutrients.

Triple oxygen isotopes of modern terrestrial mammalian tooth enamel – New implications for paleoenvironmental and physiological research

Triple oxygen isotope ratios (17O/16O, 18O/16O) of bioapatite (apatite, carbonate) of mammals can be used for paleo-CO2 reconstruction, as climate proxies, and for physiological studies. Key to this approach is that mammals incorporate atmospheric molecular oxygen with a marked 17O anomaly. Here, we report new apatite tooth enamel triple oxygen isotope data of a large set of terrestrial mammals (0.002 ≤ body mass ≤ 6000 kg) from different habitats. The triple oxygen isotope ratios were measured by means of laser fluorination in combination with gas source mass spectrometry. For samples from different species and climatic regions, a negative correlation between body mass and 17O anomaly is observed. Implications for using triple oxygen isotope ratios of terrestrial mammalian tooth enamel as paleo-CO2, climate, and physiology proxy are discussed.

A New Method for Silicon Triple Isotope Analysis With Application to Siliceous Sponge Spicules

AbstractMultiple isotope ratios of elements disclose information on the fractionation mechanism that cannot be obtained from a single isotope ratio alone. We describe a laser fluorination technique in combination with gas source mass spectrometry for the measurement of triple Si isotope ratios with high precision that allows resolving ppm‐level variability in triple silicon isotope ratios (29Si/28Si, 30Si/28Si) Δ‘29Si due to purely mass‐dependent fractionation in Si isotopes. We demonstrate how the triple silicon isotope ratios can be used to characterize different mass‐dependent processes that fractionate silicon isotopes. We report new data on reference materials (NBS‐28 [RM8546], Diatomite, BigBatch) and on siliceous sponges. Our triple silicon isotope data resolve that kinetic fractionation, possibly related to breaking Si(OH)4 molecules, causes the low δ30Si of sponges. The data further suggest that the cause for fractionation may be the same for the groups of Demospongiae, Homoscleromorpha, and Hexactinellida and that triple silicon isotope ratios of sponges have potential as seawater silicon isotope proxy.

Comparison of δ13 C analyses of individual foraminifer (Orbulina universa) shells by secondary ion mass spectrometry and gas source mass spectrometry.

The use of secondary ion mass spectrometry (SIMS) to perform micrometer-scale in situ carbon isotope (δ13 C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole-shell δ13 C values measured by gas source mass spectrometry (GSMS). Paired SIMS and GSMS δ13 C values measured from final chamber fragments of the same shell of the planktic foraminifer Orbulina universa are compared. The SIMS-GSMS δ13 C differences (Δ13 CSIMS-GSMS ) were determined via paired analysis of hydrogen peroxide-cleaned fragments of modern cultured specimens and of fossil specimens from deep-sea sediments that were either untreated, sonicated, and cleaned with hydrogen peroxide or vacuum roasted. After treatment, fragments were analyzed by a CAMECA IMS 1280 SIMS instrument and either a ThermoScientific MAT-253 or a Fisons Optima isotope ratio mass spectrometer (GSMS). Paired analyses of cleaned fragments of cultured specimens (n = 7) yield no SIMS-GSMS δ13 C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ13 CSIMS-GSMS values of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS-GSMS δ13 C difference. The noted Δ13 CSIMS-GSMS values are most likely due to matrix effects causing sample-standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~105 times smaller than that analyzed by GSMS; hence, the extent to which these Δ13 CSIMS-GSMS values represent differences in analyte or instrument factors remains unclear.

Secondary controls on the stratigraphic signature of the carbon isotope excursion marking the Paleocene-Eocene thermal maximum at Ocean Drilling Program Site 1135

The negative carbon isotope excursion (CIE) associated with an ancient global warming event referred to as the Paleocene Eocene thermal maximum (PETM, ca. 56 Ma) is commonly observed to have a smaller magnitude in marine records than in terrestrial records. This disparity has been attributed to secondary mechanisms that either attenuate or amplify the CIE magnitude in marine and terrestrial records, respectively. Here we investigate the effects of carbonate diagenesis and sediment mixing on the stratigraphic signature of the CIE in a PETM record recovered at Ocean Drilling Program (ODP) Site 1135 in the southern Indian Ocean. Comparison of parallel planktic foraminifer δ13C records constructed with two different analytical techniques – conventional gas source mass spectrometry (GSMS) measurements of individual whole shells versus in-situ microanalyses on subdomains inside individual foraminifer shells using secondary ion mass spectrometry (SIMS) – shows that both the δ13CGSMS and δ13CSIMS records capture the CIE. However, the δ13CSIMS records yield excursion magnitudes (acarininids = 5.3‰, morozovellids = 3.9‰) that are ~1.6‰ larger than in the whole-shell δ13CGSMS records. Patterns of intrashell δ13C variation delineated by the in-situ SIMS microanalyses indicate that the smaller CIE magnitude registered by δ13CGSMS records is chiefly due to incorporation of diagenetic calcite overgrowths by GSMS analyses of whole foraminifer shells. We also find that many foraminifer shells are infilled with fine-fraction carbonate (nannofossils) and posit that incorporation of non-CIE nannofossils into these infillings further bias whole-shell GSMS δ13C measurements toward more positive values over the CIE interval. We propose that 5.3‰ is the best estimate of the CIE in this deep-sea record, a near match to the average CIE magnitude published for terrestrial PETM records.

Stable-isotope ratios (δ18O and δD) in a firn core from West Antarctica.

A 22.48 m long ice core (BR-IC-4) was collected in the West Antarctic Ice Sheet (at 83°58'59.4" S, 80°07'01.4" W, 1,295 m above the sea level) during the Austral summer of 2004-2005, as a contribution to the International Trans-Antarctic Expedition program. The isotopic composition (δD and δ18O) of 599 samples, corresponding to the upper 12.98 m of the ice core, was determined by gas source mass spectrometry and cavity ring-down spectroscopy. Relative dating was based on the isotopic ratios and major ions (MS-, Na+, nssSO4 2-) and trace elements (Na, S, Sr) concentrations. The record covers approximately 13 years - from 1990 to 2003. The mean accumulation rate of 0.48 ± 0.09 m water equivalent per year (m eq H2O a1) is relatively high for the geographical area and possibly results from snowdrifting from near areas, as attested by ice glaze surfaces in other sites in the region. The stable isotope δD content varies between -367.90‰ and 256.30‰ (mean -314.42 ± 19.01‰); and δ18O ranges from -44.96‰ to 35.08‰ (mean -39.95 ± 2.05‰). Deuterium excess values (mean 3.70 ± 1.54‰) indicate episodic intense oceanic evaporation and high relative humidity in the moisture sources.

COM-1 and Hongcheon: New monazite reference materials for the microspot analysis of oxygen isotopic composition

BackgroundMonazite, a moderately common light rare earth element (LREE) and thorium phosphate mineral, has chemical, age, and isotopic characteristics that are useful in the investigation of the origin and evolution of crustal melts and fluid-rock interactions. Multiple stages of growth and partial recrystallization commonly observed in monazite inevitably require microspot chemical and isotopic analyses, for which well-characterized reference materials are essential to correct instrumental biases. In this study, we introduce new monazite reference materials COM-1 and Hongcheon for the use in the microspot analysis of oxygen isotopic composition.FindingsCOM-1 and Hongcheon were derived from a late Mesoproterozoic (~ 1080 Ma) pegmatite dyke in Colorado, USA, and a Late Triassic (~ 230 Ma) carbonatite-hosted REE ore in central Korea, respectively. The COM-1 monazite has much higher levels of Th (8.77 ± 0.56 wt.%), Si (0.82 ± 0.07 wt.%) and lower REE contents (total REE = 49.5 ± 1.2 wt.%) than does the Hongcheon monazite (Th, 0.23 ± 0.11 wt.%; Si, < 0.1 wt.%; total REE, 59.9 ± 0.7 wt.%). Their oxygen isotopic compositions (δ18OVSMOW) were determined by gas-source mass spectrometry with laser fluorination (COM-1, 6.67 ± 0.08‰; Hongcheon-1, 6.60 ± 0.02‰; Hongcheon-2, 6.08 ± 0.07‰). Oxygen isotope measurements performed by a Cameca IMS1300-HR3 ion probe showed a strong linear dependence (R2 = 0.99) of the instrumental mass fractionation on the total REE contents.ConclusionsWe characterized chemical and oxygen isotopic compositions of COM-1 and Hongcheon monazites. Their internal homogeneity in oxygen isotopic composition and chemical difference provide an efficient tool for calibrating instrumental mass fractionation occurring during secondary ion mass spectrometry analyses.

Certification of a Natural Silicon Reference Material with SI‐Traceable Isotopic Composition

Silicon (Si) is the second most abundant element in the continental crust. Studies have illustrated that silicon isotopes have a potential to be tracers in the biogeochemical silica cycle. This paper details a developed method for the production and certification of a new Si reference material with natural‐like isotopic composition using a fully calibrated multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). To correct for the mass bias effect, three blend solutions were gravimetrically prepared with isotopically enriched 28Si, 29Si and 30Si materials. Homogeneity and stability tests were performed, and no significant influences were found. Uncertainties of property values were evaluated, and the traceability to the International System of Units (SI) was established. The developed certified reference material (GBW04503) is a silicon powder (≈ 300 mesh) with high purity (≈ 0.999 99 kg kg−1), which can be used in silicon isotopic measurement to support validation of analytical procedures and/or quality control of gas source mass spectrometry (GS‐MS) or MC‐ICP‐MS. The certified isotope amount ratios of n(29Si)/n(28Si) and n(30Si)/n(28Si) are 0.050291(12) mol mol−1 and 0.033397(16) mol mol−1, respectively, (k = 2), and the certified isotope amount fractions of silicon are 92.2776(20)% (28Si), 4.6407(10) % (29Si) and 3.0818(14)% (30Si) (k = 2). Meanwhile, the delta value of δ30/28SiNBS 28 = 1.679(17)‰ was obtained (k = 2).

SIMS oxygen isotope matrix effects in silicate glasses: Quantifying the role of chemical composition

Instrumental mass fractionation (IMF) associated with Secondary Ion Mass Spectrometry (SIMS) measurements of oxygen isotope compositions in silicate glasses was studied using a set of 27 synthesized glasses spanning a compositionally broad range of six major oxides: SiO2, TiO2, Al2O3, total FeO (FeOt), MgO and CaO. The impact of chemical composition on the IMF values was investigated using a Cameca 1280-HR during a single SIMS analytical session operated under constant instrumental conditions. The data measured were compared with the δ18O values obtained by laser fluorination gas source mass-spectrometry (LF). The offset between the δ18O(LF) and δ18O(SIMS) was found to reach up to 5‰. Our data document that SIMS oxygen isotope matrix effects in silicate glasses strongly depend on the chemical composition of silicate glasses, here the cation‑oxygen bond strength was found to have a strong influence on the IMF value. We tested a variety of models based on single oxide contents and various composition-dependent parameters, but none were fully satisfactory for predicting IMF. Neither mean atomic mass nor NBO/T (the ratio of non-bridging oxygens per tetrahedrally coordinated cation) show a strong correlation with the IMF values (R2 of 0.45 and 0.46, respectively). Among the single oxides, only the model based on the SiO2 content is useful for prediction of the IMF in silicate glasses, but this model has a large standard error (1σ = ± 0.90‰) and was also found to break down for glasses with high Na and K contents. We propose an empirical model based on the correlation of six major element oxides that shows a strong correlation with IMF (R2 = 0.98, 1σ = ± 0.40‰). This model describes the experimental data with uncertainties that are roughly a factor of two better than the correction methods proposed in earlier studies. We also investigated using the correlation between IMF and isotope I-18O index, which describes the correlation between atomic bond strength and relative oxygen isotope enrichment in silicate substances (R2 = 0.87). Although our efforts provide refinements to the SIMS determination of δ18O in natural silicate glasses, truly accurate IMF corrections will need further refinements related to the impact of alkali elements.

Inter‐laboratory Characterisation of Apatite Reference Materials for Chlorine Isotope Analysis

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with &gt; 0.5 % m/m Cl and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.

A comparison of sulfur isotope measurements of geologic materials by inductively coupled plasma and gas source mass spectrometry

Sulfur isotope measurements by multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) require up to one hundred times less sulfur than traditional measurements via elemental analyzer isotope ratio mass spectrometry (EA-IRMS). Here, we report an improved MC-ICP-MS protocol for measuring δ34S values in different natural samples, specifically, calcium-sulfate minerals, carbonate associated sulfate, and dissolved sulfate in water. Sample preparation and subsequent anion exchange chromatography quantitatively recovers sulfur as sulfate. However, for samples with high and complex anion budgets, such as meteoric water, a stronger retention of sulfate on the anion exchange resin is observed relative to samples that contain sulfur as pure sulfate such as calcium-sulfate minerals and carbonate associated sulfate. An extended elution scheme with HNO3 is therefore required to achieve full recovery of sulfur, and thus accurate and reproducible δ34S values for the different materials investigated. Sulfur isotope measurements were performed on a Neptune Plus MC-ICP-MS coupled to an Apex-Ω desolvator, resulting in a “dry” plasma, negligible level of isobaric interferences, a sensitivity of >40 V ppm−1 sulfur, and a precision of 0.2‰ (2 S.D.) for δ34S for as little as 70 ng sulfur of a pure sulfate solution. The accuracy of the procedure was tested against duplicate δ34S EA-IRMS measurements for eleven different geologic samples. The EA-IRMS and MC-ICPMS values generally agree well within analytical uncertainty. However, procedural blank levels are on the order of a few tens of nanogram sulfur, and are thus the main limiting factor for accurate low-level sulfur isotope measurements with MC-ICP-MS.

The chlorine isotope composition of iron meteorites: Evidence for the Cl isotope composition of the solar nebula and implications for extensive devolatilization during planet formation

AbstractThe bulk chlorine concentrations and isotopic compositions of a suite of non‐carbonaceous (NC) and carbonaceous (CC) iron meteorites were measured using gas source mass spectrometry. The δ37Cl values of magmatic irons range from −7.2 to 18.0‰ versus standard mean ocean chloride and are unrelated to their chlorine concentrations, which range from 0.3 to 161 ppm. Nonmagmatic IAB irons are comparatively Cl‐rich containing &gt;161 ppm with δ37Cl values ranging from −6.1 to −3.2‰. The anomalously high and low δ37Cl values are inconsistent with a terrestrial source, and as Cl contents in magmatic irons are largely consistent with derivation from a chondrite‐like silicate complement, we suggest that Cl is indigenous to iron meteorites. Two NC irons, Cape York and Gibeon, have high cooling rates with anomalously high δ37Cl values of 13.4 and 18.0‰. We interpret these high isotopic compositions to result from Cl degassing during the disruption of their parent bodies, consistent with their low volatile contents (Ga, Ge, Ag). As no relevant mechanisms in iron meteorite parent bodies are expected to decrease δ37Cl values, whereas volatilization is known to increase δ37Cl values by the preferential loss of light isotopes, we interpret the low isotope values of &lt;−5‰ and down to −7.2‰ to most closely represent the primordial isotopic composition of Cl in the solar nebula. Similar conclusions have been derived from low δ37Cl values down to −6, and −3.8‰ measured in Martian and Vestan meteorites, respectively. These low δ37Cl values are in contrast to those of chondrites which average around 0‰ previously explained by the incorporation of isotopically heavy HCl clathrate into chondrite parent bodies. The poor retention of low δ37Cl values in many differentiated planetary materials suggest that extensive devolatilization occurred during planet formation, which can explain Earth's high δ37Cl value by the loss of approximately 60% of the initial Cl content.

Encyclopedia of Geochemistry

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Position-specific hydrogen isotope equilibrium in propane

Intramolecular isotope distributions can constrain source attribution, mechanisms of formation and destruction, and temperature-time histories of molecules. In this study, we explore the D/H fractionation between central (CH2) and terminal (CH3) positions of propane (C3H8)—a percent level component of natural gases. The temperature dependence of position-specific D/H fractionation of propane could potentially work as a geo-thermometer for natural gas systems, and a forensic identifier of specific thermogenic sources of atmospheric or aquatic emissions. Moreover, kinetically controlled departures from temperature dependent equilibrium might constrain mechanisms of thermogenic production, or provide indicators of biological or photochemical destruction. We developed a method to measure position-specific D/H differences of propane with high-resolution gas source mass spectrometry. We performed laboratory exchange experiments to study the exchange rates for both terminal and central positions, and used catalysts to drive the hydrogen isotope distribution of propane to thermodynamic equilibrium. Experimental results demonstrate that D/H exchange between propane and water happens easily in the presence of either Pd catalyst or Ni catalyst. Exchange rates are similar between the two positions catalyzed by Pd. However, the central position exchanges 2.2 times faster than the terminal position in the presence of Ni catalyst. At 200 °C in the presence of Pd catalyst, the e-folding time of propane-water exchange is 20 days and of homogeneous exchange (i.e., equilibrium between central and terminal positions) is 28 min. An equilibrated (bracketed and time-invariant) intramolecular hydrogen isotope distribution was attained for propane at three temperatures, 30 °C, 100 °C and 200 °C; these data serve as an initial experimental calibration of a new position-specific thermometer with a temperature sensitivity of 0.25‰ per °C at 100 °C. We use this calibration to test the validity of prior published theoretical predictions. Comparison of data with models suggest the most sophisticated of these discrepant models (Webb and Miller, 2014) is most accurate; this conclusion implies that there is a combined experimental and theoretical foundation for an ‘absolute reference frame’ for position-specific H isotope analysis of propane, following principles previously used for clumped isotope analysis of CO2, CH4 and O2 (Eiler and Schauble, 2004; Yeung et al., 2014; Stolper et al., 2014).

Comparison of δ18O analyses on individual planktic foraminifer (Orbulina universa) shells by SIMS and gas-source mass spectrometry

Abstract The oxygen isotope (δ18O) compositions of final chamber fragments of individual shells of the planktic foraminifer Orbulina universa were measured in situ via secondary ion mass spectrometry (SIMS) and by traditional gas-source mass spectrometry (GSMS) entailing acid digestion of sampled calcite. The paired SIMS-GSMS analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core (Holocene) as well as shells grown in laboratory culture. Multiple iterations of SIMS-GSMS analyses were conducted on final chamber fragments treated with a variety of cleaning protocols. The series of paired analyses yielded an average SIMS-GSMS δ18O offset (Δ18OSIMS-GSMS) of −0.9 ± 0.1‰ (±2 SE). The volume of material analyzed in 10-μm SIMS spots is ~105 times smaller than that analyzed by GSMS; hence, the extent to which these Δ18OSIMS-GSMS values represent real differences in analyte vs. instrumental factors remains unclear. Possible contributing factors to the SIMS-GSMS δ18O difference include sample-standard mismatch by SIMS, differences in standardization of SIMS and GSMS, and non-calcite contaminants in samples. Although the two datasets are consistently offset, SIMS values reproduce inter-shell δ18O variability delineated by shell fragment GSMS values. This strong positive covariance proved useful for bringing the two datasets into agreement (i.e. Δ18OSIMS-GSMS = 0), and confirms that SIMS-based foraminifer δ18O values record changes in calcification temperature and/or δ18O of seawater. Whether shells of foraminifer taxa with differing microcrystalline structures, chemical composition, and/or preservation histories register a similar Δ18OSIMS-GSMS value is a subject of ongoing testing.

Evaluating baddeleyite oxygen isotope analysis by secondary ion mass spectrometry (SIMS)

Two baddeleyite megacrysts were evaluated as potential reference materials (RMs) for SIMS oxygen isotope analysis, and utilized to understand and calibrate instrumental mass fractionation (IMF). A baddeleyite crystal (S0045) from the Phalaborwa carbonatite, South Africa has a mean δ18OVSMOW = +4.6 ± 0.3‰ (range 0.75‰) measured using laser fluorination gas source mass spectrometry (LF-GMS) and one (S0069) from the Mogok metamorphic belt, Myanmar has δ18OVSMOW = +22.2 ± 0.4‰ (range 0.89‰). SIMS standardization utilizing these inherently heterogeneous RMs is possible by analyzing a number of crystal fragments and utilizing one of them lying at the median of the range. Metamictization, lattice orientation, and chemical composition do not appear to be significant (<0.5‰) variables in matrix matching of RMs and unknowns. Propagation of errors while utilizing the imperfect RMs results in 10 μm diameter spot uncertainties of about ±0.3‰ (2σ).SIMS oxygen isotope analysis of co-crystalline zircon and baddeleyite from the 2.2 Ga Duck Lake sill (DLS) in the Northwest Territories, Canada, yield predominant δ18OVSMOW modes of +6.0‰ and +3.2‰, respectively. This difference is consistent with preserving high-temperature isotopic equilibrium between zircon and baddeleyite. DLS baddeleyite δ18O data as a whole are negatively skewed (to 0.0‰), and interpreted to reflect low temperature, open-system behaviour. Zircon δ18O are less affected, but also show hints of the same influences of secondary alteration and oxygen isotope exchange.

Secondary Ion Mass Spectrometry Analyses of Diamond and Moissanite in Ophiolite

The Cameca 1280‐HR large geometry SIMS instrument is a highly versatile analytical tool which can support a broad range of geochemical applications. Research using the Potsdam 1280 instrument focuses primarily on isotope ratio determinations in geomaterials. Optimized measurement protocols have already been established for δ18O determinations in zircon, and we are also working towards routine oxygen isotope determinations for quartz, calcite, mica, apatite and titanite. The primary challenge in developing such measurement systems are the identification and characterization of suitable reference materials (RMs), and this is made particularly challenging due to the matrix dependent ion yields of the SIMS ion source.Here we wish to report our progress towards establishing new analytical protocols for the determination of δ13C in both diamond and moissanite. In the case of diamond, our facility possesses three natural RMs with which we are able to produce data with a typical analytical repeatability of ∼0.15 ‰ (1sd). An inter‐comparison of our three diamond RMs demonstrates an overall data quality of better than 0.5‰ in terms of systematic offset between the various materials characterized using gas source mass spectrometry (Palot et al., 2012). A single such δ13C determination in diamond requires 80 s of data acquisition and involves a test portion mass of ∼400 pg of material. In‐house diamond reference materials for δ15N calibration allow us to measure this isotopic system to a total analytical uncertainty of ± 1.6 ‰ (1sd) at nitrogen concentrations reaching down to 250 μg/g. Due to the relatively low abundance of nitrogen in diamonds, such isotope ratio determinations require around 9 minutes of data collection.With respect to δ13C determinations in moissanite, we use a kimberlitic SiC as calibrant (Mathez et al., 1995), on which we achieve a repeatability of ∼0.2 ‰ (1sd) on a ∼350 pg test portion mass. Total data acquisition time for such measurements is 80 s. We are currently in the process of developing a second moissanite RM based on a synthetic, coarse‐grained powder. We will also investigate this new material for its δ30Si characteristics.

Non-Traditional Stable Isotopes: Retrospective and Prospective

Traditional stable isotope geochemistry involves isotopes of light elements such as H, C, N, O, and S, which are measured predominantly by gas-source mass spectrometry (Valley et al. 1986; Valley and Cole 2001). Even though Li isotope geochemistry was developed in 1980s based on thermal ionization mass spectrometry (TIMS) (Chan 1987), the real flourish of so-called non-traditional stable isotope geochemistry was made possible by the development of multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) (Halliday et al. 1995; Marechal et al. 1999). Since then, isotopes of both light (e.g., Li, Mg) and heavy (e.g., Tl, U) elements have been routinely measured at a precision that is high enough to resolve natural variations (Fig. 1). The publication of RIMG volume 55 ( Geochemistry of Non-Traditional Stable Isotopes ) in 2004 was the first extensive review of Non-Traditional Stable Isotopes summarizing the advances in the field up to 2003 (Johnson et al. 2004). When compared to traditional stable isotopes, the non-traditional stable isotopes have several distinctive geochemical features: 1) as many of these elements are trace elements, their concentrations vary widely in different geological reservoirs; 2) these elements range from highly volatile (e.g., Zn and K) to refractory (e.g., Ca and Ti); 3) many of these elements are redox-sensitive; 4) many of them are biologically active; 5) the bonding environments, especially for the metal elements, are different from those of H, C, N, O and S; and finally, 6) many of these elements have high atomic numbers and more than two stable isotopes. These features make the different elements susceptible to different fractionation mechanisms, and by extension, make them unique tracers of different cosmochemical, geological and biological processes, as highlighted throughout this volume. Figure 1 Non-traditional stable isotope systems covered in this volume. Figure 2 The terrestrial isotopic variation vs. the relative mass difference for non-traditional …