Isobaric interference correction is essential for the precise in situ Hf isotopic measurement of zircons; however, there is difficulty in doing a proper interference correction for zircons with high ...Yb/Hf ratios. In most of the current models, a model to determine the “natural” Yb isotopic composition is needed to fit the 176 Hf/ 177 Hf ratios of standard zircons to “true” values (measured by solution-MC-ICP-MS or ID-TIMS methods). In this study, solution doping experiments and laser ablation-multi-collector-ICP-mass spectrometry (LA-MC-ICP-MS) studies were performed. Solution doping experiments showed that β Yb and β Yb/ β Hf directly measured from samples can vary greatly with the intensity of Yb, and therefore are not good options for interference corrections. However, ( β Yb/ β Hf) c , which is calculated from samples with high Yb/Hf ratios by fixing the calibrated 176 Hf/ 177 Hf values to the “true” values, is proven to be a reliable approach for Yb interference correction. Therefore, a new isobaric correction model is proposed in this study for the in situ Hf isotopic analysis using the LA-MC-ICP-MS methodology for zircons, especially for those with a high Yb/Hf ratio. With the proposed model, the determination of the “natural” Yb isotopic composition is no longer necessary. In addition, this proposed model shows no discrimination to the Yb/Hf ratios and therefore can be widely used in most laboratories, especially for those with newly set-up instruments. The lower limit of the 180 Hf intensity is ∼1 V by our new model so that meaningful 176 Hf/ 177 Hf ratios and <1.5 ε unit internal errors can be achieved simultaneously. A ∼3 month monitoring for standard zircons showed that the long-term accuracy error is lower than 2 ε units (to referenced values).
This study presents a method for high-precision stable potassium (K) isotope analysis using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) without a collision cell in ...low-resolution mode. The cold plasma technique (RF power of ∼600 W) combined with wet plasma was used to suppress the formation of argon hydrides, which are direct isobaric interference to K ions. The remaining ArH
+
interference was deducted by measurements from the blank acid before and after each measurement. Using this analytical method, precision of better than 0.08‰ (2SD) for
41
K/
39
K could be achieved based on routine measurements of pure K solution during a six-month period. The effects of matrix elements, acid strength, ArH
+
percentage and concentration mismatch on the precision of the K isotope measurement were also evaluated. Mismatches in K concentration (up to 20%) between samples and bracketing standards did not affect the precision and accuracy significantly, whereas the precision and accuracy were very sensitive to mismatches in acid molarity. Thus, the same batch of acid is needed to dissolve samples and bracketing standards. The measured potassium isotopic compositions of international rock standards using the present method agreed well, within analytical precisions, with previously reported values. We believe that this contribution will accelerate the output efficiency of K isotope data and motivate the use of potassium isotopes as potential tracers in geosciences.
A practical method to measure K isotopes with MC-ICP-MS without a collision cell in low-resolution mode.
Lithium (Li) elemental and isotopic compositions of the Jurassic Jingshan leucogranites, including garnet-rich mafic enclaves and wall rock Wuhe gneisses from the southeast margin of North China ...Craton (NCC) were investigated to understand the behavior of Li isotopes during post-collisional magmatism. The Jingshan leucogranites have distinct U-shape REE patterns with Y and REE concentrations significantly lower yet Sr/Y ratios higher than their presumed source rocks, i.e., the Dabie-Sulu gneisses. Trace element modeling of REE and Sr/Y suggests these elemental signatures of the Jingshan leucogranites can be consistently explained by a fluid-present crustal incongruent partial melting: Bt+Qz+Pl+H2O=Grt+melt, leaving mainly Grt+Bt with minor allanite in the residuum. The mafic enclaves show identical Sr-Nd isotopic compositions with their host leucogranites, contrasting with the Wuhe gneiss and the exposed regional lower crust. The garnet-rich mafic enclaves are thus interpreted as entrained residual phases formed by this incongruent partial melting.
The Jingshan leucogranites show relatively high δ7Li values (+4.0‰ to +9.0‰) and low Li concentrations (4.7–11.3ppm) in comparison to published data for worldwide granites. In contrast, the residual enclaves show low δ7Li values (as low as +0.6‰) and high Li concentrations (as high as 118ppm). Garnet separated from residual enclaves is characterized by a narrow range of low δ7Li values (−1.5‰ to −0.1‰) with high Li concentrations from 32.9 to 81.7ppm. By contrast, coexisting quartz shows relatively high δ7Li values (+15.0‰ to +16.6‰) with very low Li concentrations (~1ppm). Biotite from both leucogranite and residual enclaves shows high Li concentrations (195–382ppm) and relatively heavy Li isotope compositions (+3.2‰ to +7.5‰). The Li elemental and isotopic signatures of the residual enclaves can be modeled as a Grt-Bt rich residuum mixed with leucogranite melt in various proportions. This work indicates that the Li isotopic compositions for magmatic rocks that are derived from anatexis of mid to lower crustal gneisses may not be a faithful source indicator as commonly suggested.
•Trace element modelling (REE and Sr/Y) suggests these elemental signatures of the Jingshan leucogranites can be consistently explained by a fluid-present crustal incongruent partial melting: Bt+Qz+Pl+H2O=Grt+melt, leaving mainly Grt+Bt with minor allanite in the residuum.•The Jingshan leucogranites show relatively heavy δ7Li values (+4.0‰ to +9.0‰) and low Li concentrations (4.7-11.3 ppm) in comparison to that for worldwide granites. In contrast, the residual enclaves show light δ7Li values (as low as +0.6‰) and high Li concentrations (as high as 118 ppm).•Garnet separated from residual enclaves spans a narrow range of low δ7Li values (-1.5‰ to -0.1‰) with high Li concentrations from 32.9 to 81.7 ppm.•This work indicates that the Li isotopic compositions for magmatic rocks that are derived from anatexis of mid to lower crust may not be a faithful source indicator as commonly suggested.
Saiga antelope horn and Rhinoceros horn have been used in traditional Chinese medicine for thousands of years. However, due to the protection of wildlife, the application of these rare animal horns ...has been restricted or prohibited. Therefore, water buffalo horn, goat horn, and yak horn have been applied as alternatives to Rhinoceros horn or Saiga antelope horn in a clinic. It is extremely difficult to distinguish normal animal horns in powdered or decocted form, especially identifying related species such as water buffalo horn, yak horn, and cattle horn. In this work, mathematics set and label‐free proteomics analysis were combined for discovering keratin‐derived specific peptide biomarkers. By using mathematics set analysis after nano liquid chromatography‐tandem mass spectrometry‐based proteomics, the selected species‐specific peptides could be used to identify the authenticity of the Saiga antelope horn and goat horn. Furthermore, peptide biomarkers were selected to distinguish related species‐derived horns, water buffalo horn, yak horn, and cattle horn. In total, eight peptide biomarkers were selected and applied for simultaneously distinguishing different horn samples. The present strategy provides a method for peptide biomarkers discovery and also has positive significance for ensuring the quality and efficacy of animal horn‐derived traditional Chinese medicines and their products.
Rationale
The very small mass difference between 41K and 40ArH+ makes the flat, hydride interference‐free peak shoulders very narrow (0.002–0.003 m/z unit), bringing a number of analytical challenges ...when measuring K isotopic compositions by multi‐collector inductively coupled plasma mass spectrometry (MC‐ICP‐MS). In traditional Sequence Run mode, the parameters are loaded every line of the sequence which can introduce tiny drifts of tune parameters and mass peaks. This may occasionally lead to the failure of K isotope measurements when mass drifts exceed 0.002 m/z unit. It is thus essential to keep the tune parameters, especially the magnet current, very stable to achieve high‐precision K isotopic compositions.
Method
We developed a “Continuous‐Acquisition‐Method” (CAM) MC‐ICP‐MS Run mode to improve the stability when determining K isotopes. Two sets of experiments were designed: (a) Stability test: measuring a single pure K solution (viz. NIST‐999c) for ~3 h and comparing the stability of the two run modes; and (b) GSB‐K test: measuring our inhouse pure K standard solution (GSB‐K) in both run modes and comparing the accuracy and precision.
Results
The traditional Sequence Run mode only kept the MC‐ICP‐MS system stable for the first ~1.5 h during the ~3‐h test, with an offset of the mass peaks of ~0.003 m/z unit. The CAM Run mode yielded higher stability during the whole test (~3 h), with a peak shift <0.0004 m/z unit. Measurement of the GSB‐K standard solution in Sequence Run and CAM Run modes gives identical δ41K values when the magnet was kept stable, with the CAM Run mode offering a better precision and keeping the instrument stable for longer time.
Conclusions
The MC‐ICP‐MS CAM Run mode shows higher stability and better precision. It is, therefore, good for high‐precision K isotope measurements.
Magnesium isotopic compositions are reported for twenty‐four international geological reference materials including igneous, metamorphic and sedimentary rocks, as well as phlogopite and serpentine ...minerals. The long‐term reproducibility of Mg isotopic determination, based on 4‐year analyses of olivine and seawater samples, was ≤ 0.07‰ (2s) for δ26Mg and ≤ 0.05‰ (2s) for δ25Mg. Accuracy was tested by analysis of synthetic reference materials down to the quoted long‐term reproducibility. This comprehensive dataset, plus seawater data produced in the same laboratory, serves as a reference for quality assurance and inter‐laboratory comparison of high‐precision Mg isotopic data.
Les compositions isotopiques du magnésium sont fournies pour vingt‐quatre matériaux géologiques de référence internationaux, comprenant des roches ignées, métamorphiques et sédimentaires, ainsi qu'une phlogopite et des serpentines. La reproductibilité à long terme de la détermination isotopique du Mg, basée des analyses sur quatre ans d’échantillons d'olivine et d'eau de mer, était ≤ 0.07% (2s) pour δ26Mg et ≤ 0.05% (2s) pour δ25Mg. La précision a été testée par l'analyse de matériaux de référence synthétiques jusqu’à la reproductibilité à long terme indiquée. Cette base de données complète, ainsi que des données d'eau de mer produites dans le même laboratoire, servent de référence pour l'assurance qualité et la comparaison inter‐laboratoires de haute précision des données isotopiques du Mg.
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•δ7Li values the Carboniferous seawater are reported for the first time.•Carboniferous continental silicate weathering changed from congruent to incongruent.•Hercynian orogeny and ...radiation of tropical forests are key drivers for the LPIA.
The reasons for decreasing atmospheric CO2 concentration in the Carboniferous and initiation of the Late Paleozoic Ice Age (LPIA) are still in debate. To assess the contributions of continental silicate weathering, we obtain lithium isotope composition (δ7Li) of the Carboniferous seawater based on the East Fenghuangshan carbonate section in South China. Original seawater records are recognized after systematic evaluation of diagenetic impacts, showing that seawater δ7Li declined from ∼ 20 ‰ before the late Visean to ∼ 12 ‰ around the Visean-Serpukhovian boundary followed by a gradual rise to ∼ 21 ‰ until the Moscovian. Combined Li-Sr isotopic modeling indicates that decline of seawater δ7Li requires decrease of riverine δ7Li and twofold increase of riverine Li flux, suggesting a transition to more congruent continental silicate weathering regime that likely results from uplift of the Hercynian orogen. High relief due to the Hercynian orogeny exposes fresh rocks for weathering by physical denudation of the thick soil and saprolite cover, which is beneficial for rapid CO2 consumption and probably initiates the LPIA. By contrast, radiation of tropical forests is responsible for the subsequent increase of seawater δ7Li. It turns the weathering regime to a more incongruent one by promoting clay mineral formation. The colonization of plants with deep roots also accelerates the continental weathering, which together with intense photosynthesis, should contribute significantly to keeping low atmospheric CO2 concentration and maintaining the prolonged LPIA. Therefore, we suggest that uplift of the Hercynian orogen and radiation of tropical forests are the key drivers for initiating and maintaining the LPIA.
With advances in analytical precision by multicollector inductively coupled plasma mass spectrometry, K and Mg isotopes are increasingly used as a combined tool in tracing sources and processes in ...geoscientific research. However, reported methods in the literature require at least two column separation procedures during sample purification, which is time-consuming (at least two days). Therefore, a single column procedure could improve efficiencies, and these efforts are necessary to extend the combined application of K and Mg isotopes as geological tracers. In this study, a simple and time-efficient chromatographic procedure was reported, utilizing a single column for quantitative separation of both K and Mg from sample matrices for high-precision isotopic measurement of K and Mg. Using this novel method, the results for international geological standards agreed with published values, verifying the robustness of the procedure. The popularization of this optimized procedure would potentially extend the combined application of K and Mg isotopes in geological studies.
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•A simple one-step KMg column separation method has been developed.•A “Peak-Center” procedure was employed to ensure the stability of the magnet.•The KMg isotopic ratios of rock standards obtained agree well with published data, which ensures the reliability and robustness of the method.
Magnesium isotopic ratios have been used as a natural tracer to study weathering processes and biogeochemical pathways in surficial environments, but few have focused on the mechanisms that control ...Mg isotope fractionation during shale weathering. In this study we focus on understanding Mg isotope fractionation in the Shale Hills catchment in central Pennsylvania. Mg isotope ratios were measured systematically in weathering products, along geochemical pathways of Mg during shale weathering: from bedrock to soils and soil pore water on a planar hillslope, and to sediments, stream water, and groundwater on a valley floor. Significant variations of Mg isotopic values were observed: δ26Mg values (−0.6‰ to −0.1‰) of stream and soil pore waters are about ~0.5‰ to 1‰ lighter than the shale bedrock δ(26Mg values of +0.4‰), consistent with previous observations that lighter Mg isotopes are preferentially released to water during silicate weathering. Dissolution of the carbonate mineral ankerite, depleted in the shallow soils but present in bedrock at greater depths, produced higher Mg2+ concentrations but lower δ26Mg values (−1.1‰) in groundwater, ~1.5‰ lighter than the bedrock. δ26Mg values (+0.2‰ to +0.4‰) of soil samples on the planar hillslope are either similar or up to ~0.2‰ lighter than the bedrock. Hence a heavy Mg isotope reservoir – complementary to the lighter Mg isotopes in soil pore water and stream water – is missing from the residual soils on the hillslope. In addition, soil samples show a slight but systematic decreasing trend in δ26Mg values with increasing weathering duration towards the surface. We suggest that the accumulation of light Mg isotopes in surface soils at Shale Hills is due to a combined effect of i) sequestration of isotopically light Mg from soil water during clay dissolution–precipitation reactions; and ii) loss of isotopically heavy particulate Mg in micron-sized particles from the hillslope as suspended sediments. This latter mechanism is somewhat surprising in that most researchers do not consider physical removal or particles to be a likely mechanism of isotopic fractionation. Stream sediments (δ26Mg values of +0.3‰ to +0.5‰) accumulated on the valley floor are ~0.2‰ heavier than the bedrock, and are thus consistent with that mobile particulates are the heavy Mg isotope reservoir.
Our study provides the first field evidence that changes in clay mineralogy lead to accumulation of lighter Mg isotopes in residual bulk soils. This example also demonstrates that transport of isotopically distinct fine particles from clay-rich systems could be a new and important mechanism to drive the Mg isotope compositions of silicate weathering residuals. This mechanism drives fractionation in an opposite direction as might be expected from previous studies, i.e. residual soils are driven to lighter Mg values and sediments become isotopically heavier.
•Mg isotope fractionation during shale weathering under a temperate climate•Decreasing trend of δ26Mg values in soils with increasing weathering duration•Accumulation of light Mg isotopes in soils by clay mineral transformation•Loss of isotopically heavy particulate Mg from clay-rich systems
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