Laser Ablation Multi-collector Inductively Coupled Plasma Mass Spectrometry Research Articles

Sr ISOTOPES BY LA-MC-ICP-MS PROCEDURES COUPLED WITH THE MACS3 REFERENCE MATERIAL IN A CORAL SAMPLE: A RECORD OF ENVIRONMENTAL CHANGES

The main aim of this work is to demonstrate that the Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tool for the analysis of strontium (Sr) isotopes in corals. This work discusses certification strategies for Sr isotopes determination, using reference material (RM) analyses and the results treatment based on detailed data acquired in biological materials, a coral sample. To obtain reliable results, it is essential to properly adjust the mass spectrometer and laser ablation system. Adjusting the equipment to its maximum intensity does not always result in correct 87Sr/86Sr ratios. Therefore, the optimization of the mass spectrometer was performed using the reference material NIST SRM-987 (solution) and adjusting the correct Sr isotope ratio to the reference material (USGS MACS3 and NIST-612, solids) before each analytical session. The protocol applied the solid reference material USGS MACS3 with an isotopic ratio 87Sr/86Sr of 0.72000. The values obtained for this RM varied between 0.7012 and 0.7014, with a correction factor calculated between 0.990 and 0.988. In order to account for potential drifts in the mass spectrometer during an analytical session, the application of bracketing correction and the use of the most convenient reference material are suggested. The analytical uncertainty of Sr data obtained by LA-MC-ICP-MS is comparable to studies carried out on other carbonate materials. The results of ablation techniques are reproducible within the analytical error, which implies that this technique produces robust results when applied to coral carbonates. In addition, several comparative measurements of different reference materials (e.g. USGS MACS3 and NIST 612) and the comparison of the 87Sr/86Sr ratios highlight the robustness of the method. The results along the coral growth axes showed a decrease in the 87Sr/86Sr ratio from the inner to the outer layer of the coral (from 0.70920 to 0.70627), which indicate variations in the availability of particulate matter during the coral growth, probably related to local marine environmental changes.

A Practical Procedure for Analysis of Lead Isotopes in Bivalve Shells Using Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS).

Lead, like other trace elements, is incorporated in the growing bands of bivalve shells. The chemicals stored into the shells can provide valuable information about seawater conditions during the period of shell formation. In this study, we present a practical approach to determine Pb isotopic signatures in bivalve shells as a tool for evaluating lead pollution in coastal waters. To demonstrate the applicability of the method, Pb isotopic fingerprinting in bivalve shell layers were investigated using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Lead isotope ratios (208Pb/206Pb and 206Pb/207Pb) were measured along distinct sections of the maximum growth axis of the shells. Calibration and quantification of Pb isotopes were performed using NIST 612 as reference material. Our results demonstrated that Pb isotope ratios in the shells ranged from 1.143 to 1.201 for 206Pb/207Pb and from 2.061 to 2.161 for 208Pb/206Pb. The isotopic signatures recorded in the sample shells correspond to similar ranges of Pb signatures reported for marine sediments from the same study area. In general, this work shows that LA-MC-ICP-MS is a suitable technique for determining spatially resolved lead isotopic signatures in bivalve shells and that it can be used to estimate the origin of Pb pollution in aquatic environments.

Improved in situ analysis of lead isotopes in low-Pb melt inclusions using laser ablation-multi-collector-inductively coupled plasma-mass spectrometry.

In situ Pb isotope analyses of tiny melt inclusions using laser ablation-multi-collector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) are crucial for exploring the origins of mafic lavas. However, quantitative use of this technique with low-Pb (<10ppm) melt inclusions is difficult due to their low 204 Pb content and 204 Hg interference. Pb isotopic ratios of various reference glasses and olivine-hosted melt inclusions were determined using LA-MC-ICP-MS. Multiple ion counters were used to simultaneously determine signal intensities of all Pb isotopes and 202 Hg. An Hg signal-removal smoothing device reduced its signal in the gas blank by >80%. Instrumental mass bias was corrected using the standard-sample bracketing method. With 24-90 μm diameter laser spots, 2-4Hz repetition rates, and 2.5-4J cm-2 energy fluence, the analytical precisions of 20x Pb/204 Pb ratios (x = 6, 7, 8) for standards BHVO-2G, ML3B-G, NIST 614, NKT-1G, T1-G, GOR132-G, and StHs6/80-G were <1.0% (2RSD) when 208 Pb signals >100 000 cps. The Wangjiadashan melt inclusions have 206 Pb/204 Pb = 17.14-18.44, 207 Pb/204 Pb = 15.28-15.66, and 208 Pb/204 Pb = 37.12-38.68. The described method improves the precision and accuracy of in situ Pb isotope analysis in low-Pb melt inclusions using LA-MC-ICP-MS. The Pb isotopic compositions of the Wangjiadashan melt inclusions indicate the coexistence of LoMu and EMII+young HIMU components in the mantle source of weakly alkaline basalts.

Laser ablation inductively coupled plasma mass spectrometry analysis of isotopically heterogeneous uranium materials

A reliable and accurate laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) method was developed for analysis of inhomogeneous samples containing uranium particles or aggregates of various enrichments. For the method development, a mixed solid standard was prepared using 1% and 3% 235U enriched certified reference materials. After screening and localization of the particles of interest, the U isotopic composition was analysed for a 5-µm sample spot determining accurately and precisely the various constituents. Besides the LA-MC-ICP-MS, the standard was also measured by large-geometry secondary ion mass spectrometry (LG-SIMS) for additional verification.

In-run measuring 177Hf16O/177Hf as a routine technique for in-situ Hf isotopic compositions analysis in zirconium-bearing minerals by laser ablation MC-ICP-MS

Problems with REE oxide interferences during in-situ Hf isotope analysis in zirconium-bearing minerals can give rise to inaccuracies in the obtained dataset. In this study, we present an in-run 177Hf16O/177Hf measurement protocol pertaining to in-situ Hf isotope analysis by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) as a routine method, allowing for a robust real-time method of monitoring the oxide formation rates and offering a method to monitor REE oxide interferences (e.g., Gd and Dy). For this purpose, we set up a static data collection mode to measure Hf isotopes and 177Hf16O signals concurrently in-run. By analyzing zirconium-bearing minerals characterized with a broad range of Dy/Hf and Gd/Hf ratios (e.g., zircon: typically, 0.0001–0.022 for Dy/Hf and 0.00002–0.013 for Gd/Hf; zirconolite: typically, >0.2 for Dy/Hf and > 0.4 for Gd/Hf; eudialyte: typically, >0.1 for Dy/Hf and > 0.1 for Gd/Hf), influences of oxide formation rate on 176Hf/177Hf ratios are investigated via the present in-run method. The level of oxide formation during the analysis is found to impact the measurement accuracy, especially for samples with higher REE/Hf ratios. Therefore, it is imperative that oxide ratios should be routinely monitored for daily in-situ Hf isotope analysis along with oxide formation rates. In addition, based on results of the present work, a higher REE/Hf zircon, like SA02 zircon, is strongly recommended as the primary refence material for routine in-situ analysis of Hf isotopic compositions in zircons to carefully test the accuracy of analysis for zircons.

Lead isotope analysis of Meroitic period glass from Nubia with LA‐MC‐ICP‐MS

AbstractAnalytical studies of glass found at sites in Nubia (ancient Sudan) have shown the variety of glass present during ancient times. This study examines Meroitic period (c.350 bce–350 ce) glass from Nubia: here categorized as low‐lead and high‐lead. The lead (Pb) isotopes of 13 of the high‐lead sealing‐wax red and low‐lead translucent blue, translucent blue/green, colourless and red samples from the sites of Faras, Gabati and Meroe are examined by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) analysis to suggest an Eastern Mediterranean source for the lead due to their overlap with Egyptian and Levantine vitreous and non‐vitreous objects and five Turkish and Greek ore sources.

Testing the advantages of simultaneous in-situ Sm[sbnd]Nd, U[sbnd]Pb and elemental analysis of igneous monazite for petrochronological studies. An example from the late Archean, Penzance granite, Western Australia

Monazite has the ability to incorporate a broad range of trace elements (TE), including SmNd, in addition to being a reliable UPb geochronometer. Nonetheless, many current isotopic tracer studies mostly focus on laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) Hf-in-zircon or whole rock isotope dilution SmNd. The conditions necessary to produce reliable Nd-isotopic data from whole rock analyses (i.e. absence of weathering and alteration) restricts the number of samples suitable for this type of study. Conversely, accessory phases such as monazite, apatite, allanite, epidote and titanite are more resistant to weathering and alteration and have a greater chance of preserving their original Nd-isotopic signature.The Archean Penzance granite, in the Yilgarn Craton, Western Australia, is a relatively unweathered high field strength elements (HFSE)-enriched granite that is associated with the Teutonic Bore volcanic-hosted massive sulfide (VHMS) Camp. Here we compare newly acquired LA split-stream (SS)-MC-ICPMS analyses in monazite from the Penzance granite to previously collected whole rock Nd-isotopes, SHRIMP ages in zircon and monazite and Hf-in-zircon of a specific outcrop. The ƐNd0 of monazite from the Penzance granite have a weighted mean value of +1.6 ± 0.2 both for the values calculated from the SHRIMP single population age and from individual LASS dates. This value is the same within uncertainty to the whole-rock ƐNd0 value of +1.99 ± 0.39, whereas ƐHf0 show similar juvenile values with mean value of +2.2 ± 0.5 (2 SE).These findings complement previous studies that argue that monazite has the potential to provide reliable time constrained isotopic and chemical data, which are comparable to, and at times superior than, Hf-in-zircon and whole-rock Nd-isotopes. Additionally, because monazite can record TE signatures that can be used to retrieve petrological information, this study proposes a LASS-MC-ICPMS routine that achieves simultaneous SmNd isotopes, U/Th-Pb dating and TE analyses in monazite, allowing for further petrological information to be obtained from a single analytical routine. This study also assesses the precision and accuracy in UPb ages in monazite reference materials, when additional masses are measured in the same routine. The application of the routine presented here facilitates the use of monazite as isotopic tracer in petrological and sedimentary studies.

Apatite U-Pb Thermochronology: A Review

The temperature sensitivity of the U-Pb apatite system (350–570 °C) makes it a powerful tool to study thermal histories in the deeper crust. Recent studies have exploited diffusive Pb loss from apatite crystals to generate t-T paths between ~350–570 °C, by comparing apatite U-Pb ID-TIMS (isotope dilution-thermal ionisation mass spectrometry) dates with grain size or by LA-MC-ICP-MS (laser ablation-multicollector-inductively coupled plasma-mass spectrometry) age depth profiling/traverses of apatite crystals, and assuming the effective diffusion domain is the entire crystal. The key assumptions of apatite U-Pb thermochronology are discussed including (i) that Pb has been lost by Fickian diffusion, (ii) can experimental apatite Pb diffusion parameters be extrapolated down temperature to geological settings and (iii) are apatite grain boundaries open (i.e., is Pb lost to an infinite reservoir). Particular emphasis is placed on detecting fluid-mediated remobilisation of Pb, which invalidates assumption (i). The highly diverse and rock-type specific nature of apatite trace-element chemistry is very useful in this regard—metasomatic and low-grade metamorphic apatite can be easily distinguished from sub-categories of igneous rocks and high-grade metamorphic apatite. This enables reprecipitated domains to be identified geochemically and linked with petrographic observations. Other challenges in apatite U-Pb thermochronology are also discussed. An appropriate choice of initial Pb composition is critical, while U zoning remains an issue for inverse modelling of single crystal ID-TIMS dates, and LA-ICP-MS age traverses need to be integrated with U zoning information. A recommended apatite U-Pb thermochronology protocol for LA-MC-ICP-MS age depth profiling/traverses of apatite crystals and linked to petrographic and trace element information is presented.

Understanding pre- and syn-orogenic tectonic evolution in western Himalaya through age and petrogenesis of Palaeozoic and Cenozoic granites from upper structural levels of Bhagirathi Valley, NW India

AbstractThe Himalaya is characterized by the presence of both pre-Himalayan Palaeozoic and syn-Himalayan Cenozoic granitic bodies, which can help unravel the pre- to syn-collisional geodynamics of this orogen. In the Bhagirathi Valley of Western Himalaya, such granites and the Tethyan Himalayan Sequence (THS) hosting them are bound to the south by the top-to-the-N extensional Jhala Normal Fault (JNF) and low-grade metapelite of the THS to its north. The THS is intruded by a set of leucocratic dykes concordant to the JNF. Zircon U–Pb laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) geochronology of the THS and one leucocratic dyke reveals that the two rocks have a strikingly similar age distribution, with a common and most prominent age peak at ~1000 Ma. To the north of the THS lies Bhaironghati Granite, a Palaeozoic two-mica granite, which shows a crystallization age of 512.28 ± 1.58 Ma. Our geochemical analysis indicates that it is a product of pre-Himalayan Palaeozoic magmatism owing to extensional tectonics in a back-arc or rift setting following the assembly of Gondwana (500–530 Ma). The Cenozoic Gangotri Leucogranite lies to the north of Bhaironghati Granite, and U–Pb dating of zircon from this leucogranite gives a crystallization age of 21.73 ± 0.11 Ma. Our geochemical studies suggest that the Gangotri Leucogranite is a product of muscovite-dehydration melting of the lower crust owing to flexural bending in relation to steepening of the subducted Indian plate. The leucocratic dykes are highly refracted parts of the Gangotri Leucogranite that migrated and emplaced along extensional fault zones related to the JNF and scavenged zircon from the host THS during crystallization.

Review of techniques, challenges, and new developments for calcium isotope ratio measurements

Calcium isotope meaurements apply to problems spanning the ‘cosmos to benthos.’ Fractionation, source mixing, radioactive decay, and nucleosynthetic processes cause variations in Ca isotope ratios, which can be measured using different types of mass spectrometers. Early measurements employed thermal ionization mass spectrometry (TIMS), which continues to be the most common and precise reference technique. An increasing number of studies use multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). Both TIMS and MC-ICPMS can yield high-quality data for δ44/40Ca and δ44/42Ca, respectively, but wide ranges in precision exist. Sample size requirements are lower for TIMS, but MC-ICPMS offers faster throughput. Both techniques require purifying Ca by ion-exchange chromatography when analyzing samples with complex matrices. In-situ techniques, like laser ablation MC-ICPMS (LA-MC-ICPMS) and secondary ion mass spectrometry (SIMS), do not require purification. In-situ techniques provide high spatial resolution, but LA-MC-ICPMS and (nano)-SIMS suffer from relatively poor precision compared to TIMS and MC-ICPMS, and the methods lack well-characterized standards, which are essential for comparing datasets.The past few years have seen advances in Ca purification techniques, including automated methods that accelerate sample throughput. The next generation of Ca purification techniques should focus on complete purification and quantitative separation of low-Ca samples. Application of collision-cell technology for suppressing Ar-related molecular isobaric interferences will improve quantification of 40Ca using certain MC-ICPMS models. Similarly, development of new amplifier technology will foster high-precision Faraday cup measurements of low abundance Ca isotopes. Adopting common reference materials, including newly developed standards with complex matrices, would signficantly aid inter-laboratory comparisons, method development, and data compilation efforts. In general, at least two widely-used standards should be measured along with unknown samples to confirm data quality, as well as improve utilization of published Ca isotope datasets by a broader community.

An Improved In Situ Zircon U‐Pb Dating Method at High Spatial Resolution (≤ 10 μm Spot) by LA‐MC‐ICP‐MS and its Application

In situ small‐spot U‐Pb geochronology is essential for measuring zircon crystals containing micrometre‐scale heterogeneities, abundant inclusions, inevitable cracks and narrow growth zones, all of which are especially common in metamorphic zircons. We present a high spatial resolution (≤ 10 μm diameter) laser ablation‐multi‐collector‐inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) U‐Pb dating method using a Nu Plasma II mass spectrometer coupled with a GeoLas HD laser ablation system, which is capable of analysing zircon crystals with a wide range of U contents through two analytical modes (mixed‐mode for 10 μm ablation and IC‐mode for 5 μm ablation). We examined Pb/U down‐hole fractionation (DHF) as a function of different laser settings under small‐spot ablation, and how it controls the accuracy and precision of U‐Pb ages of zircon reference materials. After DHF correction using Iolite software (version 3.71), five measurement sessions (with different laser fluence and/or laser pulse settings) for the two analytical modes yielded accurate and precise U‐Pb ages for four zircon reference materials (Plešovice, 91500, GJ‐1 and Temora‐2). Further determinations of U‐Pb ages of three metamorphic zircon samples (~ 14 to 2000 Ma) from the Himalaya, North China Craton and North Qaidam were conducted, the results of which confirm the effectiveness and feasibility of this small‐spot ablation method for natural zircons with multiple growth zones.

Mass fractionation of Rb and Sr isotopes during laser ablation-multicollector-ICPMS: in situ observation and correction

BackgroundOne of the most critical issues concerning in situ mass spectrometry lies in accounting for elements and molecules that overlap target isotopes of analytical interest in a sample. This study traced the instrumental mass fractionation of Rb and Sr isotopes during laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) to obtain reliable 87Sr/86Sr ratios for high-Rb/Sr samples.FindingsIn the LA-MC-ICPMS analysis, Kr interferences were corrected using Ar and He gas blanks measured without ablating material. Contributions from doubly charged Er and Yb ions were corrected using the intensities of half masses and isotopic compositions reported in the literature. After Kr correction, the calculated 166Er2+ intensity of NIST SRM 610 approached the measured intensity at mass 83, and the 173Yb2+/171Yb2+ ratio agreed with the recommended value within error ranges. Kr- and REE2+-stripped peak intensities were further corrected for Rb interference. Use of the Sr mass bias factor for the calculation of measured 87Rb/85Rb yielded 87Sr/86Sr ratios consistent with the recommended and expected values for low-Rb/Sr materials, such as NIST SRM 616, modern shark teeth, and plagioclase collected from Jeju Island, but failed to account for the 87Rb interference from high-Rb/Sr materials including NIST SRM 610 and SRM 612. We calculated in situ mass bias factor of Rb from the known 87Sr/86Sr ratios of the standards and observed a correlation between Rb and Sr mass fractionation, which allowed inference of the Rb bias from the standard run. Reliable 87Sr/86Sr and 85Rb/86Sr ratios were obtained for SRM 610 and SRM 612 using the inferred mass bias factor of Rb calculated by the standard bracketing method.ConclusionsThis study revealed that Rb and Sr isotopes behave differently during LA-MC-ICPMS and suggests the potential usefulness of the standard bracketing method for measuring the Rb–Sr isotopic compositions of high-Rb/Sr materials.

Simultaneous determination of mass-dependent Mg isotopic variations and radiogenic 26Mg by laser ablation-MC-ICP-MS and implications for the formation of chondrules

Improvements in our understanding of the formation of chondrules requires a better knowledge of the thermal histories and the nature of their solid precursors. We present an in situ nanosecond laser ablation multi-collector inductively-coupled-plasma mass-spectrometry (LA-MC-ICP-MS) technique to measure simultaneously mass-dependent Mg isotopic fractionations and radiogenic 26Mg in chondritic components, thus allowing us to investigate within a chronological framework the thermal processes redistributing Mg in chondrules and their precursors. The internal 26Al-26Mg isochrons provide initial 26Al/27Al ratios from 5.46 (±0.38) × 10−5 to 6.14 (±0.92) × 10−5 for amoeboid olivine aggregates (AOAs) and Ca-, Al-rich inclusions (CAIs), and from 0.16 (±0.08) × 10−5 to 1.87 (±0.92) × 10−5 for chondrules from Allende and Leoville chondrites, which are consistent with the previously reported values. The combination of these values with up to 2.5‰ variation of the 25Mg/24Mg ratio within the studied chondrules shows that: (i) AOAs and the precursors of chondrules were likely formed via condensation of rapid-cooling gas reservoirs, and (ii) Mg stable isotopes are probably at disequilibrium between olivines and mesostases in some chondrules, likely due to Mg loss by vaporization during chondrule formation. We use these new observations to propose that Mg isotopes can likely serve as a tracer for the thermal histories of chondrules. We present here a scenario taking into account Mg loss by vaporization from chondrule melt and Mg gain into the melt by olivine dissolution. The existing Mg isotopic observations in chondrule melts and olivines can be explained in a scenario with a homogeneous distribution of Mg isotopes and initial 26Al in the accretion disk, provided that chondrule precursors have been heated up to sufficiently high peak temperatures (up to 2123 K) and stayed above 1800 K for several tens of minutes to allow for significant Mg evaporation. These conditions are most consistent with a shock wave model for the origin of chondrules.

Evidence of Paleoproterozoic phosphogenesis in the Salvador-Curaçá Orogen (Tanque Novo-Ipirá Complex), northeastern São Francisco Craton, Brazil

Abstract This paper analyzes mineralogical, geochemical, and geochronological aspects, along with the effect of hydrothermal/metasomatic overprints, to identify the presence of primary phosphate as well as depositional and paleoenvironmental conditions in marble and calcsilicate sequences recrystallized under transitional amphibolite-granulite metamorphic conditions in the Tanque Novo-Ipira Complex within the Salvador-Curaca Orogen, northeastern Sao Francisco Craton, state of Bahia, Brazil. Petrographic studies have identified up to 10 vol.% disseminated apatite and whole-rock P2O5 contents up to 3.2 wt.%. Post-depositional events affected the lithofacies to varying degrees. Late hydrothermalism did not modify the rare earth element and yttrium (REEY) patterns considerably. When normalized to Post-Archean Australian Shale (PAAS), these lithofacies are marked by flat pattern REEY, true negative Ce anomalies, and positive Y and Gd. The highly variable Eu anomalies were inherited from the source composition but may have been affected by interaction with fluids. U-Pb LA-ICP-MS (laser ablation multicollector inductively coupled plasma mass spectrometry) ages indicate a maximum depositional age of 2128 Ga, as well as Paleoproterozoic and Neoarchean sources. Samples with anomalous phosphorus show Y/Ho ratios >30 and Ce/Ce* anomalies between 0.53 and 1.0 with an average of 0.70, suggesting a sub-oxic environment for phosphate precipitation.

Natural Clinopyroxene Reference Materials for in situ Sr Isotopic Analysis via LA-MC-ICP-MS.

Clinopyroxene is a major host mineral for lithophile elements in the mantle lithosphere, and therefore, its origin is vital for constraints on mantle evolution and melt generation. In situ Sr isotopic measurement of clinopyroxene has been available since the recent development of laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) in the 2000s. Therefore, there is an increasing demand for natural clinopyroxene reference materials for Sr isotope microanalysis. In this contribution, we present six natural clinopyroxene reference materials from South Africa (JJG1424) and China (YY09-47, YY09-04, YY09-24, YY12-01, and YY12-02) for Sr isotope microanalysis. The Sr content of these clinopyroxenes ranges from 50 to 340 μg g−1, which covers most natural clinopyroxene compositions. Homogeneity of these potential reference materials were investigated and evaluated in detail over a 2-year period using 193-nm nanosecond and 257-nm femtosecond laser systems coupled to either a Neptune or Neptune Plus MC-ICP-MS. Additionally, the major and trace element of these clinopyroxenes were examined by electron probe microanalyzer (EPMA) as well as solution and laser ICP-MS. The in situ 87Sr/86Sr values obtained for the six natural clinopyroxene reference materials agree well with data obtained using the thermal ionization mass spectrometer (TIMS) method. The Sr isotopic stability and homogeneity of these clinopyroxenes make them potential reference materials for in situ Sr microanalysis to correct instrumental fractionation or as quality control materials for analytical sessions. The new Sr isotope data provided here might be beneficial for microbeam analysis in the geochemical community.

Simultaneous lead isotope ratio and gold-lead-bismuth concentration analysis of silver by laser ablation MC-ICP-MS

A new approach is presented for the simultaneous analysis of lead isotope ratios and gold, lead, and bismuth concentrations in metallic silver using nanosecond laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Corrections for both isotope and concentration analyses are performed using an in-house matrix matched silver reference material RM3834. Accuracy and external reproducibility are demonstrated by repeat analyses of a further seven silver reference materials all characterised by solution (MC)-ICP-MS approaches. Typical internal precisions, expressed as two relative standard errors (S.E.) of the mean of the cycles comprising one analysis, are <0.5% for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, and <0.03% for 207Pb/206Pb and 208Pb/206Pb. External reproducibilities, based on repeat analyses over a 10 month period and expressed as two relative standard deviations (S.D.) of the mean, are <0.4% for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb and <0.2% for 207Pb/206Pb and 208Pb/206Pb. Internal precisions and external reproducibilities of gold, lead and bismuth concentration analyses are typically <25%. Data are consistent with solution-based approaches. Methods are further demonstrated through analyses of a set of Islamic silver dirhams from the mint of al-Muhammadiyya, highlighting their applicability to geochemical studies of archaeological artefacts.

Baseline bioavailable strontium and oxygen isotope mapping of the Adelaide Region, South Australia

Strontium and oxygen isotopes provide a useful method for provenancing bioapaties, such as teeth and bone. In order for this approach to be successful, regional baseline bioavailable isotope data are required; however, few databases are currently available in Australia. This study measured stable oxygen and bioavailable strontium isotope ratios from low mobility fauna sampled from the major geological and physiographic provinces in Adelaide, South Australia in order to create a database for this region.Bioavailable strontium isotope ratios (87Sr/86Sr) obtained from the predominantly siliciclastic metasediments of the Neoproterozoic Adelaide Geosyncline have a range of 0.7122 ± 0.0001 to 0.7202 ± 0.0001. Cainozoic samples (dominantly terrestrial fluvial/lacustrine and marine carbonate sediments) from the Adelaide Plains have values in the range of 0.7098 ± 0.0002 to 0.7121 ± 0.0001. Samples from the alluvial fan sediments near the Eden-Burnside Fault at the boundary between these regions have values of 0.7131 ± 0.0001 to 0.7143 ± 0.0001. Stable oxygen isotope results range from − 9.5 to − 4.5‰ δ18OC (VPDB) and do not appear to vary systematically based on elevation, temperature, rainfall or humidity.These results demonstrate that strontium isotopes are potentially a useful tool for provenance studies within the Adelaide area. Oxygen is probably a more appropriate tool for discriminating seasonality rather than location within the study region.This research also suggests that rats are better suited for mapping strontium isoscapes than koalas, and that, while (non-systematic) offsets appear to exist between laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) and thermal ionisation mass spectrometry (TIMS) data, this effect is considerably less than the variation between geological provenances in the region.

Technical note: Single-shell &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;11&amp;lt;/sup&amp;gt;B analysis of &amp;lt;i&amp;gt;Cibicidoides wuellerstorfi&amp;lt;/i&amp;gt; using femtosecond laser ablation MC-ICPMS and secondary ion mass spectrometry

Abstract. The boron isotopic composition (δ11B) of benthic foraminifera provides a valuable tool to reconstruct past deep-water pH. As the abundance of monospecific species might be limited in sediments, microanalytical techniques can help to overcome this problem, but such studies on benthic foraminiferal δ11B are sparse. In addition, microanalytics provide information on the distribution of δ11B at high spatial resolution to increase the knowledge of biomineralization processes, for example. For this study, we investigated the intra- and inter-shell δ11B variability of the epibenthic species Cibicidoides wuellerstorfi, which is widely used in paleoceanography, by secondary ion mass spectrometry (SIMS) and femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). While the average δ11B values obtained from these different techniques agree remarkably well with bulk solution values to within ±0.1 ‰, a relatively large intra-shell variability was observed. Based on multiple measurements within single shells, the SIMS and LA data suggest median variations of 4.8 ‰ and 1.3 ‰ (2σ), respectively, while the larger spread for SIMS is attributed to the smaller volume of calcite being analyzed in each run. When analytical uncertainties and volume-dependent differences in δ11B variations are taken into account for these methods, the intra-shell variability is estimated to be on the order of ∼3 ‰ and ∼0.4 ‰ (2σ) on a ∼20 and 100 µm scale, respectively. In comparison, the δ11B variability between shells exhibits a total range of ∼3 ‰ for both techniques, suggesting that several shells need to be analyzed for accurate mean δ11B values. Based on a simple resampling method, we conclude that ∼12 shells of C. wuellerstorfi must be analyzed using LA-MC-ICPMS to obtain an accurate average value within ±0.5 ‰ (2σ) to resolve pH variations of ∼0.1. Based on our findings, we suggest preferring the conventional bulk solution MC-ICPMS over the in situ methods for paleo-pH studies, for example. However, SIMS and LA provide powerful tools for high-resolution paleoreconstructions, or for investigating ontogenetic trends in δ11B.

In situ Mg isotope measurements of biogenic carbonates using laser ablation multi-collector inductively coupled plasma mass spectrometry: A new tool to understand biomineralisation.

Magnesium is one of the most abundant elements in the earth's crust and in seawater. Fractionation of its stable isotopes has been shown to be a useful indicator of many geological, chemical, and biological processes. For example, biogenic carbonates display an ~5‰ range of δ26 Mg values, which is attributed to variable degrees of biological control on Mg ions during biomineralisation. Understanding this biological control is essential for developing proxies based on biogenic carbonates. In this work, we present a new approach of measuring Mg isotopes in biogenic carbonates using Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS). Our results show that this microanalytical approach provides relatively fast, high spatial resolution (<0.2 μm) measurements with high precision and accuracy down to 0.2‰ (2SE). To achieve high levels of precision and accuracy, baseline interferences need to be monitored and a carbonate standard with a relatively low trace metal composition similar to biogenic carbonates should be used. We also demonstrate that the matrix effect on Mg isotopes in carbonates with low Fe and Mn is limited to less than 0.2‰ fractionation under different laser parameters and low oxide condition (<0.3% ThO/Th). Our newly developed LA-MC-ICPMS method and its applications to biogenic carbonates show significant advantages provided by the microanalytical approach in understanding complex processes of biomineralisation in marine calcifiers.

Using 87Sr/86Sr LA-MC-ICP-MS Transects within Modern and Ancient Calcite Crystals to Determine Fluid Flow Events in Deep Granite Fractures

The strontium isotope signature (87Sr/86Sr) of calcite precipitated in rock fractures and faults is a frequently used tool to trace paleofluid flow. However, bedrock fracture networks, such as in Precambrian cratons, have often undergone multiple fracture reactivations resulting in complex sequences of fracture mineral infillings. This includes numerous discrete calcite crystal overgrowths. Conventional 87Sr/86Sr analysis of dissolved bulk samples of such crystals is not feasible as they will result in mixed signatures of several growth zonations. In addition, the zonations are too fine-grained for sub-sampling using micro-drilling. Here, we apply high spatial resolution 87Sr/86Sr spot analysis (80 µm) in transects through zoned calcite crystals in deep Paleoproterozoic granitoid fractures using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to trace discrete signs of paleofluid flow events. We compare the outermost calcite growth zone with 87Sr/86Sr values of the present-day groundwater sampled in the same boreholes to distinguish potential modern precipitates. We then connect our results to previously reported radiometric dating and C and O isotope signatures to understand the temporal history and physicochemical evolution of fluid flow within the fractures. Comparisons of modern calcite precipitated in a borehole over a period of 17 years with modern waters prove the concept of using 87Sr/86Sr as a marker for fluid origin in this environment and for how 87Sr/86Sr changed during marine water infiltration. Intermittent calcite precipitation over very long time spans is indicated in calcite of the currently open fractures, showing an evolution of 87Sr/86Sr from ~0.705–0.707—a population dated to ~1.43 billion years—to crystal overgrowth values at ~0.715–0.717 that overlap with the present-day groundwater values. This shows that high spatial resolution Sr isotope analysis of fine-scaled growth zonation within single calcite crystals is applicable for tracing episodic fluid flow in fracture networks.