Nadine Mattielli

High‐precision isotopic characterization of USGS reference materials by TIMS and MC‐ICP‐MS

The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of the isotopic (Sr, Nd, and Pb) compositions and concentrations of a broad compositional range of U.S. Geological Survey (USGS) reference materials, including basalt (BCR-1, 2; BHVO-1, 2), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2), granodiorite (GSP-2), and granite (G-2, 3). USGS rock reference materials are geochemically well characterized, but there is neither a systematic methodology nor a database for radiogenic isotopic compositions, even for the widely used BCR-1. This investigation represents the first comprehensive, systematic analysis of the isotopic composition and concentration of USGS reference materials and provides an important database for the isotopic community. In addition, the range of equipment at the PCIGR, including a Nu Instruments Plasma MC-ICP-MS, a Thermo Finnigan Triton TIMS, and a Thermo Finnigan Element2 HR-ICP-MS, permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the TIMS and MC-ICP-MS methods (e.g., Nd isotopic compositions). For each of the reference materials, 5 to 10 complete replicate analyses provide coherent isotopic results, all with external precision below 30 ppm (2 SD) for Sr and Nd isotopic compositions (27 and 24 ppm for TIMS and MC-ICP-MS, respectively). Our results also show that the first- and second-generation USGS reference materials have homogeneous Sr and Nd isotopic compositions. Nd isotopic compositions by MC-ICP-MS and TIMS agree to within 15 ppm for all reference materials. Interlaboratory MC-ICP-MS comparisons show excellent agreement for Pb isotopic compositions; however, the reproducibility is not as good as for Sr and Nd. A careful, sequential leaching experiment of three first- and second-generation reference materials (BCR, BHVO, AGV) indicates that the heterogeneity in Pb isotopic compositions, and concentrations, could be directly related to contamination by the steel (mortar/pestle) used to process the materials. Contamination also accounts for the high concentrations of certain other trace elements (e.g., Li, Mo, Cd, Sn, Sb, W) in various USGS reference materials.

Cogenetic silica-rich and carbonate-rich melts trapped in mantle minerals in Kerguelen ultramafic xenoliths: Implications for metasomatism in the oceanic upper mantle

In an attempt to characterize metasomatic agents for the oceanic upper mantle, we have undertaken a study of melt and fluid inclusions trapped in metasomatized peridotite nodules (anhydrous spinel lherzolites and harzburgites) from the Kerguelen Islands (southern Indian Ocean). These xenoliths contain three types of genetically related inclusions hosted by olivine, clinopyroxene and orthopyroxene. These are silicate melt inclusions, carbonate-rich inclusions and CO2 fluid inclusions. These inclusions are secondary in nature and form trails along fracture planes in the sheared peridotites. Heating experiments conducted on silicate melt inclusions give an estimation of the entrapment temperatures ( ≈ 1250°C) and indicate that there is no genetic relationship between the inclusions and their host minerals. The chemical composition of the silicate melt inclusions is characterized by normative quartz and feldspar components, with SiO2 ≈ 60wt%, Al2O3 ≈ 20wt%, Na2O and K2O each ≈ 4–5wt%, FeO and MgO 1000 ppm, H2O ⩾ 1.2%, and oversaturation of the melt with CO2. The trace element signature is characterized by LREE enrichment, negative HFSE (Ti and Zr) anomalies and a TiZr value of 17. The trapped melt has crystallized the following minerals: K-rich amphibole (kaersutite), diopside, rutile, ilmenite and carbonate (magnesite). Carbonate-rich inclusions, interpreted as trapped carbonate melt, have crystallized calcite. The carbonate-rich inclusions are often physically connected with the silicate melt inclusions, indicating the former existence of a homogeneous melt which later unmixed into two separate melts. Cogenetic relationships between CO2 inclusions and both carbonate melt inclusions and silicate melt inclusions yield a minimum trapping pressure for all types of inclusions of 12.5 kbar at 1250°C, corresponding to upper mantle depths. Based on their daughter mineral types, their chemical composition and high volatile element contents, the silicate-carbonate melt inclusions trapped in the ultrabasic xenoliths of the Kerguelen Islands are interpreted as small amounts of a metasomatic melt phase. These melt inclusions cannot result from melting of the anhydrous peridotite assemblages in which they have been trapped. They must represent an exotic, migrating metasomatic melt phase in the oceanic lithosphere below the Kerguelen Islands.

Helium, neon and argon isotope systematics in Kerguelen ultramafic xenoliths: implications for mantle source signatures

New noble gas data are presented for ultramafic mantle xenoliths, occurring in 10–20 Ma old volcanics from the Kerguelen Archipelago. Fusion results indicate that neon is isotopically primitive, whereas helium shows considerable isotopic variations, tending towards more radiogenic values. These fusion results of mantle xenoliths are the first report of a difference between helium and neon isotope systematics, which in most other studies show correlated isotope systematics [1–4]. Helium isotopic compositions obtained by crushing the same xenoliths yield values which are identical to or slightly lower than the theoretical values predicted by the neon data. Comparison of helium with mantle neon and argon reveals that the samples have experienced considerable helium loss, making the helium isotope systematics of the xenoliths prone to secondary disturbances. Caution is clearly required when interpreting helium isotopic compositions of mantle-derived samples, particularly in cases where helium abundances are low (also cf. [5]); combined noble gas studies provide a means of evaluating the helium isotopic signature in such cases. Our neon fusion results, together with helium and neon obtained by crushing, preserve evidence for a primitive mantle component in these Kerguelen xenoliths. This primitive component in the Kerguelen xenoliths may have been metasomatically introduced from the Kerguelen plume into upper mantle peridotite by CO2-rich, silica-rich melts, now represented by cogenetic melt and fluid inclusions in the xenoliths [6].

Anthropogenic impacts in North Poland over the last 1300 years - a record of Pb, Zn, Cu, Ni and S in an ombrotrophic peat bog.

Lead pollution history over Northern Poland was reconstructed for the last ca. 1300 years using the elemental and Pb isotope geochemistry of a dated Polish peat bog. The data show that Polish Pb-Zn ores and coal were the main sources of Pb, other heavy metals and S over Northern Poland up until the industrial revolution. After review of the potential mobility of each element, most of the historical interpretation was based on Pb and Pb isotopes, the other chemical elements (Zn, Cu, Ni, S) being considered secondary indicators of pollution. During the last century, leaded gasoline also contributed to anthropogenic Pb pollution over Poland. Coal and Pb-Zn ores, however, remained important sources of pollution in Eastern European countries during the last 50 years, as demonstrated by a high (206)Pb/(207)Pb ratio (1.153) relative to that of Western Europe (ca. 1.10). The Pb data for the last century were also in good agreement with modelled Pb inventories over Poland and the Baltic region.

High-accuracy determination of iron in seawater by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using nitrilotriacetic acid chelating resin for pre-concentration and matrix separation.

In the present paper we describe a robust and simple method to measure dissolved iron (DFe) concentrations in seawater down to <0.1 nmol L(-1) level, by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using a (54)Fe spike and measuring the (57)Fe/(54)Fe ratio. The method provides for a pre-concentration step (100:1) by micro-columns filled with the resin NTA Superflow of 50 mL seawater samples acidified to pH 1.9. NTA Superflow is demonstrated to quantitatively extract Fe from acidified seawater samples at this pH. Blanks are kept low (grand mean 0.045+/-0.020 nmol L(-1), n=21, 3 x S.D. limit of detection per session 0.020-0.069 nmol L(-1) range), as no buffer is required to adjust the sample pH for optimal extraction, and no other reagents are needed than ultrapure nitric acid, 12 mM H(2)O(2), and acidified (pH 1.9) ultra-high purity (UHP) water. We measured SAFe (sampling and analysis of Fe) reference seawater samples Surface-1 (0.097+/-0.043 nmol L(-1)) and Deep-2 (0.91+/-0.17 nmol L(-1)) and obtained results that were in excellent agreement with their DFe consensus values: 0.118+/-0.028 nmol L(-1) (n=7) for Surface-1 and 0.932+/-0.059 nmol L(-1) (n=9) for Deep-2. We also present a vertical DFe profile from the western Weddell Sea collected during the Ice Station Polarstern (ISPOL) ice drift experiment (ANT XXII-2, RV Polarstern) in November 2004-January 2005. The profile shows near-surface DFe concentrations of approximately 0.6 nmol L(-1) and bottom water enrichment up to 23 nmol L(-1) DFe.

Volcano- and climate-driven changes in atmospheric dust sources and fluxes since the Late Glacial in Central Europe

Atmospheric dusts are an important part of the global climate system, and play an important role in the marine and terrestrial bio- geochemical cycles of major and trace nutrient elements. A peat bog record of atmospheric deposition shows considerable variation in dust deposition during the past 15 k.y., with abrupt changes in fluxes at 12, 9.2, 8.4, 7.2, and 6 cal. kyr B.P. Using Nd isotopes and rare earth elements, it is possible to clearly distinguish between volcanic inputs and those driven by climate change, such as the long-term aridification of the Sahara and regional erosion due to forest clearing and soil cultivation activities. Our results indicate that a major dust event in North Africa and Europe preceded the 8.2 kyr B.P. cold event by 200 yr. This dust event may have played an active role in the following climate cooling of the 8.2 kyr B.P. event. Nd isotope evidence also indicates a relatively slow change in dust regime over Europe from 7 to 5 kyr B.P. due to Sahara expansion. These fi ndings show that the inorganic fraction in high-resolution peat records can provide remarkably sensitive indicators of dust load and sources. Our study supports the priority to better identify the impact of dust loading during the Holocene in terms of direct and indirect impacts on environmental and climate changes.

Iron isotopic fractionation in industrial emissions and urban aerosols

A study on tropospheric aerosols involving Fe particles with an industrial origin is tackled here. Aerosols were collected at the largest exhausts of a major European steel metallurgy plant and around its near urban environment. A combination of bulk and individual particle analysis performed by SEM-EDX provides the chemical composition of Fe-bearing aerosols emitted within the factory process (hematite, magnetite and agglomerates of these oxides with sylvite (KCl), calcite (CaCO(3)) and graphite carbon). Fe isotopic compositions of those emissions fall within the range (0.08 per thousand<delta(56)Fe<+0.80 per thousand) of enriched ores processed by the manufacturer (-0.16 per thousand<delta(56)Fe<+1.19 per thousand). No significant evolution of Fe fractionation during steelworks processes is observed. At the industrial source, Fe is mainly present as oxide particles, to some extent in 3-4mum aggregates. In the close urban area, 5km away from the steel plant, individual particle analysis of collected aerosols presents, in addition to the industrial particle type, aluminosilicates and related natural particles (gypsum, quartz, calcite and reacted sea salt). The Fe isotopic composition (delta(56)Fe=0.14+/-0.11 per thousand) measured in the close urban environment of the steel metallurgy plant appears coherent with an external mixing of industrial and continental Fe-containing tropospheric aerosols, as evidenced by individual particle chemical analysis. Our isotopic data provide a first estimation of an anthropogenic source term as part of the study of photochemically promoted dissolution processes and related Fe fractionations in tropospheric aerosols.

Kerguelen basic and ultrabasic xenoliths: Evidence for long-lived Kerguelen hotspot activity

Abstract The xenoliths from the Southeast Province of the Kerguelen Archipelago derived from the lower crust or the upper mantle, can contribute to define the characteristics of the mantle sources below Kerguelen and improve the constraints on the formation of the Kerguelen Islands and plateau. Our petrographic, geochemical and isotopic (Sr, Nd and Pb) study focuses on peridotites (Type Iα: harzburgite/clinopyroxene-poor Iherzolite and Type Iβ: dunite), 2-pyroxenes-spinel bearing ultrabasic and basic xenoliths [Type IIa: clinopyroxene-rich Iherzolite, wehrlite, (± olivine ± plagioclase) websterite, (± garnet ± sapphirine) metagabbro and anorthosite] and ilmenite metagabbros (Type IIc). The large ranges of isotopic ratios for the xenoliths reflect different degrees of interaction between a depleted MORB-type component, quite abundant in the Type II xenoliths, and the Kerguelen plume, distinctly predominant in the Type I xenoliths. Type I peridotites are residues of a previous partial melting event of the Kerguelen plume; residues that subsequently interacted with a percolating alkaline melt. 2-pyroxenes-spinel bearing ultrabasic and basic xenoliths (Type IIa) and ilmenite metagabbroic xenoliths (Type IIc) are deep cumulates crystallized from tholeiitic magmas. The isotopic results for the xenoliths strengthen the hypothesis of an oceanic origin for the Kerguelen Islands and refute the existence of pieces of old continental crust beneath the Islands and the northern part of the Kerguelen Plateau. They also confirm the importance of plume-spreading ridge interactions throughout the history of the Kerguelen plume. The isotopic and geochemical characteristics of the Type IIa and IIc xenoliths are consistent with the hypothesis of an Iceland-type setting for the northern part of the Kerguelen Plateau. The results for the Type I xenoliths on the other hand suggest a similarity between the Hawaii-type midplate volcanic structure and that of Kerguelen Islands. The isotopic data suggest that the Kerguelen xenoliths were formed recently (≤ 45 Ma), and thus support the hypothesis of the formation of the Plateau by the arrival of the plume at the base of the lithosphere (~ 115 Ma ago). The Plateau would have grown through several pulses of plume activity (~ 115, ~ 80, ~ 40 Ma), while the geotectonic environment changed with time (from a ridge-centered position to the present intraplate position). The occurrence of deep Type IIa and IIc xenoliths can explain the crustal thickening and provides evidence for the growth of oceanic plateaus by vertical accretion.

Isotopic fractionation of Zn in tomato plants suggests the role of root exudates on Zn uptake

AimsPhytosiderophore-chelated Zn can be absorbed in grasses. Root exudates of dicotyledonous plants can mobilize soil Zn but it is unclear how this affects Zn bioavailability. Stable Zn isotope shifts can indicate exudate-facilitated Zn uptake, since complexation of Zn2+ by organic ligands in solution yields a small, but detectable, enrichment of the heavy Zn isotope due to thermodynamic fractionation.MethodsTomato seedlings were grown in resin-buffered nutrient solution in which free Zn2+ concentrations are buffered, in a factorial design of two Zn levels and two solution volumes. The latter factor allowed altering the exudate concentrations in the solution. Dissolved Cu concentrations in the resin buffered system were used as a sensitive index of metal mobilization resulting from root activity. In addition, seedlings were grown in Zn deficient soil with and without Zn addition.ResultsThe dissolved Cu concentration increased with Zn deficiency and was highest at the lowest solution volume, suggesting metal mobilization by root exudates. At low Zn supply, Zn in the plant was enriched in heavy Zn (66Zn) and this was most pronounced at small solution volume. Similarly, Zn deficiency in soil enriched tomato shoot Zn with heavy isotope in this plant.InterpretationZinc deficiency increases the contribution of Zn-exudate complexes, which are enriched in the heavy isotope compared to the free ion, to Zn uptake by transporting Zn from the bulk solution or soil to the roots where they likely dissociate and release Zn2+.

Calcined bone provides a reliable substrate for strontium isotope ratios as shown by an enrichment experiment

RATIONALE Strontium isotopes ((87) Sr/(86) Sr) are used in archaeological and forensic science as markers of residence or mobility because they reflect the local geological substrate. Currently, tooth enamel is considered to be the most reliable tissue, but it rarely survives heating so that in cremations only calcined bone fragments survive. We set out to test the proposition that calcined bone might prove resistant to diagenesis, given its relatively high crystallinity, as the ability to measure in vivo (87) Sr/(86) Sr from calcined bone would greatly extend application to places and periods in which cremation was the dominant mortuary practice, or where unburned bone and enamel do not survive. METHODS Tooth enamel and calcined bone samples were exposed to a (87) Sr-spiked solution for up to 1 year. Samples were removed after various intervals, and attempts were made to remove the contamination using acetic acid washes and ultrasonication. (87) Sr/(86) Sr was measured before and after pre-treatment on a Nu Plasma multi-collector induced coupled plasma mass spectrometer using NBS987 as a standard. RESULTS The strontium isotopic ratios of all samples immersed in the spiked solution were strongly modified showing that significant amounts of strontium had been adsorbed or incorporated. After pre-treatment the enamel samples still contained significant amounts of (87) Sr-enriched contamination while the calcined bone fragments did not. CONCLUSIONS The results of the artificial enrichment experiment demonstrate that calcined bone is more resistant to post-mortem exchange than tooth enamel, and that in vivo strontium isotopic ratios are retained in calcined bone.