Li Isotope Ratios Research Articles

Geofluid behavior prior to the 2018 Hokkaido Eastern Iburi earthquake: insights from groundwater geochemistry

A notable decrease of groundwater Na/K ratios was observed several months before the 2018 Hokkaido Eastern Iburi earthquake (M6.7) at a site approximately 20 km west of the earthquake’s epicenter. To investigate the cause of the decreased Na/K ratios, we analyzed groundwater samples (commercially bottled drinking water) to assess the contribution of deep-derived fluids using Li and Sr isotopic ratios, which are reliable indicators of deep fluid contributions. No pronounced changes in the 7Li/6Li and 87Sr/86Sr ratios were observed; thus, the pre-earthquake decrease of groundwater Na/K ratios did not result from the input of deep-derived fluids. The pre-earthquake decrease in the Na/K ratio observed in this study may instead be related to CO2 influx into the aquifer. The CO2 may have leaked from carbon dioxide capture and storage (CCS), because CCS was in operation near the epicenter of the 2018 Hokkaido Eastern Iburi earthquake. Decreases of the Na/K ratios and increases of the CO2 concentrations in groundwater have been reported before other large earthquakes; thus, CO2 influx into groundwater may be a common phenomenon preceding earthquakes.

The effect of diffusion on lithium isotope ratios in Icelandic basalts

In recent years, diffusion has gained increasing recognition as an important process for explaining the lithium (Li) isotope ratios (δ7Li) of magmatic systems. However, the role of diffusion in explaining the variability of mantle-derived basalts has not yet been investigated in detail. We have measured δ7Li values in a comprehensive suite of fresh, subglacial Icelandic basalt glasses and observe a wide range of values from 2.4‰ to 7.3‰, the largest range in Li isotope compositions identified at any ocean island. We find that δ7Li values do not correlate with lithophile element tracers, but do correlate with 3He/4He. One possibility is that the high diffusivities of both Li and He permit fractionation of Li isotope compositions that couple it to 3He/4He, and decouple it from other, slower-diffusing lithophile tracers. In this study, we explore this idea and model diffusive processes in crystal mushes and mantle melt channels, both with and without melt transport. Our modelling indicates that large (>3‰) fractionation of Li isotope compositions from MORB-like values can be generated by diffusion and that the coupling of Li isotope ratios and 3He/4He signatures can occur as a consequence of diffusive interactions within mantle melt channels. This suggests that the Li isotope compositions of melts cannot be used as a straightforward passive tracer of mantle heterogeneity, because they can be fractionated during magmatic processes. In contrast, we find that diffusive fractionation of 3He/4He is small (∼1 Ra) next to the variability in Icelandic basalts (∼8 to ∼35 Ra). Diffusive fractionation of Li isotope ratios should be most pronounced at OIB localities whose mantle melts have a wide range of [Li], such as Hawaii and Iceland. Although a mantle source can contain Li isotope heterogeneities as a result of crustal recycling, we show that a mantle that is homogenous in Li isotope composition can still generate melts that have variable δ7Li values via diffusion processes.The same diffusion models can also be applied to other stable isotope systems such as H, Mg, Ca, and Fe. Indeed our models show that diffusion during magmatic transport within the mantle may be a significant source of “noise” in the δ7Li, δD, and possibly δ26Mg isotopic systems.

Petrogenesis of Mesozoic pegmatites in the Dahongliutan Li-mineralized belt (Western Kunlun, NW China)

The genesis of pegmatite and the associated Li-mineralization mechanism remain debated. The intimate temporal-spatial relationship between the pegmatites in the Dahongliutan Li-mineralized belt (incl. #509 Daoban and Akshay Li-poor pegmatites, and Akshay Li-rich pegmatite) and the Dahongliutan granite pluton allows us to discuss the origin of pegmatite and the Li-mineralization mechanism by conducting detailed geochemical and geochronological investigations on the two rock units in the Western Kunlun orogen (NW China). The Li-poor pegmatites in the Dahongliutan Li-mineralized belt exhibit similar or much lower Li, Rb, and Cs compared to the adjacent granite, and their εNd(t) values (-8.7–-10.0) are significantly lower than those of the granite (-7.5–-8.1) as well. However, the Akshay Li-rich pegmatite shows extremely high Li, Rb, Nb, Ta, and initial Sr isotopic ratios (0.7223–0.7227, obtained from apatite), in contrast to the Dahongliutan granite (ISr = 0.7108–0.7157). The whole-rock δ7Li values of the Dahongliutan granite, pegmatites, and the wall-rock Bayanharshan Group metapelite are + 0.76–+5.67 ‰, +0.8–+14.4 ‰, and −4.2–+2.8 ‰, respectively. Zircon and cassiterite U-Pb dating yielded 206Pb/238U ages of 216 ± 2 Ma and 195 ± 2 Ma for the #509 Daoban Li-poor pegmatite and Akshay Li-rich pegmatite, respectively. Modeling of trace elements and Li isotopes suggests that the pegmatites in the Dahongliutan Li-mineralized belt did not originate from fractional crystallization of granitic magma. Instead, they may have formed through direct anatexis under amphibolite-facies conditions. Abundant Li-rich claystone, occasionally accompanied by evaporite, may exist in the magma source of the Li-rich pegmatite, which is the key factor controlling pegmatitic Li mineralization.

Lithium Isotope Determination in Spodumene by fs‐LA‐MC‐ICP‐MS with Non‐Matrix‐Matched Calibration: Insights into ICP Operating Conditions and Data Evaluation

Lithium isotope measurement in spodumene by femtosecond LA‐MC‐ICP‐MS was investigated and the influence of plasma operating conditions and data reduction strategy on accuracy and precision was studied. It was found that “hot” plasma conditions led to an unstable baseline signal and substantial variations in the Li isotope ratios. By adding a constant amount of water to the carrier gas, a stable baseline was achieved and isotope ratios became reproducible and were consistent with data from solution‐based MC‐ICP‐MS. The resulting biases were within ± 0.51‰ and the reproducibility was better than 0.09‰. Comparison of Li isotope ratios resulting from different data evaluation schemes showed that the mean of the transient intensity ratios, integration of the entire or a user‐defined period of the ion signals resulted in good agreement with solution‐based data, while linear regression underestimated the Li isotope ratios. It was also found that “cool” plasma operation produced a stable baseline signal, but the Li isotope results were biased by up to ‐4.3%, irrespective of water introduction and the data evaluation scheme. With the optimised “hot‐wet” conditions, the Li isotope ratios in eleven spodumene materials were determined which successfully allowed distinguishing regional deposits and partially veins of the available samples.

Li isotope ratios of spring fluids as an effective tracer of slab-derived subducted sources across the Costa Rica forearc

Abstract Spring waters from across the Costa Rica margin were analyzed for their Li and He isotope compositions to determine the utility of Li isotopes as a tracer of volatile sources in subduction zones. Li isotope ratios systematically decrease with increasing depth to the subducting slab: averaging +15.0‰ ± 9.2‰ in the outer forearc (<40 km to the slab), +9.3‰ ± 4.3‰ in the forearc (40–80 km to the slab), and +5.8‰ ± 2.8‰ in the arc (>80 km to the slab). In contrast, air-corrected 3He/4He values (reported relative to the ratio in air, RA) range from 0.4 to 7.5 RA and increase from predominantly crustal values near the trench to mantle values in the arc. Together, these data support progressive devolatilization of the subducting plate with slab-derived Li components sourced from shallowly expelled pore fluids in the outer forearc, sedimentary and/or altered oceanic crust contributing to the forearc, and limited slab input beneath the arc.

New Trends in Separation Techniques of Lithium Isotopes: A Review of Chemical Separation Methods.

In terms of isotopic technologies, it is essential to be able to produce materials with an enriched isotopic abundance (i.e., a compound isotopic labelled with 2H, 13C, 6Li, 18O or 37Cl), which is one that differs from natural abundance. The isotopic-labelled compounds can be used to study different natural processes (like compounds labelled with 2H, 13C, or 18O), or they can be used to produce other isotopes as in the case of 6Li, which can be used to produce 3H, or to produce LiH that acts like a protection shield against fast neutrons. At the same time, 7Li isotope can be used as a pH controller in nuclear reactors. The COLEX process, which is currently the only technology available to produce 6Li at industrial scale, has environmental drawbacks due to generation of Hg waste and vapours. Therefore, there is a need for new eco-friendly technologies for separation of 6Li. The separation factor of 6Li/7Li with chemical extraction methods in two liquid phases using crown ethers is comparable to that of COLEX method, but has the disadvantages of low distribution coefficient of Li and the loss of crown ethers during the extraction. Electrochemical separation of lithium isotopes through the difference in migration rates between 6Li and 7Li is one of the green and promising alternatives for the separation of lithium isotopes, but this methodology requires complicated experimental setup and optimisation. Displacement chromatography methods like ion exchange in different experimental configurations have been also applied to enrich 6Li with promising results. Besides separation methods, there is also a need for development of new analysis methods (ICP-MS, MC-ICP-MS, TIMS) for reliable determination of Li isotope ratios upon enrichment. Considering all the above-mentioned facts, this paper will try to emphasize the current trends in separation techniques of lithium isotopes by exposing all the chemical separation and spectrometric analysis methods, and highlighting their advantages and disadvantages.

Lithium isotope fractionation during the weathering of granite: Responses to pH

The weathering of silicate rock is a major sink of atmospheric CO2 in the global carbon cycle and thus controls global climate change. Lithium (Li) isotopes are considered to be a sensitive proxy to trace the continental weathering, but factors controlling the fractionation behaviors of Li isotopes during chemical weathering of granite have not been addressed explicitly. Here, we present new Li isotope data of bulk samples, primary minerals, and secondary minerals from a granite weathering profile in South China to constrain the mechanisms of Li isotope fractionation during chemical weathering. The bulk samples of weathering products have relatively negative τLiTiO2 values ranging from −6.0% to −73.8% and δ7Li values ranging from −11.4‰ to +2.4‰. From the bottom to the top of the weathering profile, the pH gradually decreases (from 9.54 to 4.88). With decreasing pH, the Li concentrations of the weathered saprolites gradually decrease, while the δ7Li values of the saprolites decrease first and then increase. Li concentrations and Li isotope compositions of the constituent minerals vary considerably. Interestingly, Li isotope ratios of both the bulk samples and minerals show two distinct fractionation behaviors during chemical weathering under different pH conditions. The heavy isotope (7Li) is preferentially released into the liquid phase under basic and weakly acidic pH conditions and the light isotope (6Li) is preferentially released into the liquid phase under acidic pH conditions. This finding helps to explain the inconsistent fractionation behaviors of Li isotopes between laboratory experiments and field studies. The influence of pH on Li isotope fractionation during silicate weathering implies that the evolution of oceanic pH over geological time scales may partly account for the variations in oceanic Li isotope compositions.

Lithium and strontium isotopic systematics in the Nalenggele River catchment of Qaidam basin, China: Quantifying contributions to lithium brines and deciphering lithium behavior in hydrological processes

The salt lakes fed by the Nalenggele River in the Qaidam Basin, located on the northeastern Qinghai Tibetan Plateau (QTP), are major brine lithium reservoirs in China. The quantitative identifications of the Li sources and their dynamic behavior shed light on the formation mechanism of the brine Li deposits in closed-basin of arid regions. This study presents Li and Sr isotope ratios (δ7Li, 87Sr/86Sr) and other hydrogeochemical parameters for river waters, springs, spring river waters, shallow groundwaters, surface brines, and intercrystalline brines around the Nalenggele River Basin (NRB) and its adjacent small watersheds. The results indicate that the Nalenggele River water is a mixing product of hot springs and regional surface meltwater, and the source of dissolved Li in the NRB is mainly supplied by the hot springs. With multi-tracer models, it is confirmed that around 84.9 %−93.4 % of dissolved Li is provided by the Li-rich hot spring waters, which account for only 3–5 % of the total water input. Furthermore, the dissolved Li in the streams of different hydrological regions shows various isotopic fractionation behavior. In general, the lower average δ7Li values (average of +5.6 ‰) with more enriched Li with respect to Na in the waters of the piedmont Gobi region indicates a significant additional input of dissolved Li from bedrock and sediments. The second-stage alluvial fan of the NRB produces 7Li enrichments and Li-depleted waters (compared with Na), which can be explained by the adsorption of clay or Fe (Mn) oxide phases that fractionate Li isotopes. The highest average δ7Li values (+12.76 ‰) are observed when Li is not adsorbed by the scarce fine clastic sediments in the hypersaline environment of the salt lake region. It can be concluded that the continuous halite precipitation during the brine evolution not only causes the abnormal enrichment of Li in the brine (compared with Na) but also continuously sequesters the 6Li from the brines, resulting in a significant 7Li enrichment. Overall, these findings advance the understanding of the lithium sources of Li-rich brines and its enrichment and metallogenic process during water migration in hyper-arid regions and have crucial indicative significance for lithium cycling under a strong evaporation environment.

Extreme lithium isotope fractionation in quartz from the Stewart pegmatite

Pegmatites are magmatic bodies consisting of centimeter to meter sized crystals and can sometimes be a source for critical economic resources such as lithium (Li). Determining the chemistry and kinetics involved in pegmatite formation may be important for understanding the element enrichment process. Here, we analyzed the Li isotope compositions of quartz crystals from the Stewart pegmatite in southern California, USA. We find large Li isotopic fractionations: >40‰ between different crystals and >20‰ from core to rim in a single crystal. Two mechanisms for these extreme fractionations were considered: rapid crystal growth rate and Rayleigh fractionation. We find that although rapid crystal growth rate (1–10 m/day) can explain elemental variations, rapid growth alone is unable to explain the most extreme isotopic fractionations. Rayleigh fractionation can account for the largest isotopic fractionations if 96–99.9% of the Li is removed from the system through crystallization of lepidolite and spodumene, but alone cannot explain the observed elemental variability in the quartz. We thus suggest that both processes operated. Trace element enrichments may be more sensitive to growth rate while Li isotope ratios may be more sensitive to changes in the isotopic composition of the pegmatitic fluids during crystallization of the quartz.

Three-dimensional structure and sources of groundwater masses beneath the Osaka Plain, Southwest Japan

Study regionQuaternary tectonic basin beneath the Osaka Plain, Southwest Japan Study focusGroundwaters of different sources were categorized by the cluster analysis, using six components; Cl–, alkalinity, Na+ and Ca2+, δ18O and δ2H, and the following characterization by the relationships between δ18O and δ2H and among Cl–, B and Li concentrations, and Li isotopic ratios. Then, three-dimensional mapping was applied to visualize the distribution of the categorized groundwater masses in the whole basin. New hydrological insights for the regionThe sources of groundwater was categorized into two freshwater and three saline water end-members; 1) modern local meteoric water in the aquifers to depths of 300 m beneath the plain and surrounding mountains, 2) fossil freshwater that is more depleted in δ18O and δ2H and enriched in alkalinity than the other, 3) modern seawater recharged since the last submergence appearing in mostly to depths of 300 m beneath the plain, 4) fossil seawater probably recharged before the last submergence remaining in the base of the basin, and 5) deep-seated Arima-type brine, appearing along perimeter active faults at the northern and southern boundaries of the plain. The method used here successfully visualize the different groundwater masses and will be applicable to evaluate the sustainability of groundwater resources in the similar hydrogeological settings such as coastal plains of Asian countries.

Swift Weathering Response on Floodplains During the Paleocene‐Eocene Thermal Maximum

AbstractSilicate weathering is thought to increase and offset the rapid, massive input of CO2 into the atmosphere and ocean during the Paleocene‐Eocene Thermal Maximum (PETM), but few nonmarine records have been used to quantify this. We probe changes in silicate weathering intensity by measuring Li isotope ratios of bedrock and ancient floodplain deposits spanning the PETM in the Bighorn Basin, Wyoming (USA). Our results reveal a rapid increase in silicate weathering intensity during the PETM that remained high during at least the initial stage of climate recovery. Additionally, we determine that soils that formed farthest from ancient river channels underwent larger weathering changes than near‐channel soils. Alongside increased temperatures and pCO2, the simplest explanation for this response relates to increased seasonal fluctuations in water table height in the floodplain that promote dissolution and precipitation reactions. These findings newly demonstrate that weathering on floodplains, like mountain hillslopes, responds to climate change.

Accurate lithium isotopic analysis of twenty geological reference materials by multi-collector inductively coupled plasma mass spectrometry

The lithium (Li) isotopes can be used to track the evolution of continental silicate weathering, which has an important role in maintaining Earth's long-term climate stability. At present, complex separation procedures and analytical mass bias restrict the accurate determination of Li isotopic compositions in various geological samples with different Li concentrations and matrix/Li ratios. Here, an optimization of dual-column chromatography achieves high Li recovery, low procedural blank, and low Na/Li ratio (< 1) after purification, allowing the acquisition of high precision Li isotope ratios by a Nu Plasma 3 multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In order to evaluate the accuracy of new method, the δ7Li values of BHVO-2, BCR-2, AGV-2, JG-2, RGM-2, SGR-1b, GSR-6, GSR-12, and seawater, are repeatedly analyzed more than 3 times each and are consistent with the published data within the uncertainty. The long-term external reproducibility of δ7Li based on L-SVEC and IRMM-016 pure solutions is about ±0.2‰ (2SD), and is suitable for analysis of geological samples. These results suggest that new dual-column method is reproducible and reliable. We also report ten new reference materials including two USGS rocks (SDC-1: 1.8 ± 0.4‰; W-2a: 2.9 ± 0.3‰), four soils (GSS-3: 1.3 ± 0.2‰; GSS-4: −5.1 ± 0.4‰; GSS-6: −1.9 ± 0.3‰; GSS-8: 0.4 ± 0.3‰), and four stream sediments (GSD-6: −1.0 ± 0.4‰; GSD-11: 1.1 ± 0.3‰; GSD-12: 1.8 ± 0.2‰; GSD-14: 1.6 ± 0.4‰), all previously analyzed for K isotopes. There is significantly fractionation of Li and K isotopes during silicate weathering. Compared to the K isotopes, Li isotopes have more promising as an isotope tool for weathering due to its larger fractionation and its abiotic property.

The lithium isotope response to the variable weathering of soils in Iceland

This study has analysed Li isotopes ratios from well-studied soil and pore water profiles from Iceland that have the same parent material but have experienced different degrees of chemical weathering. Thus, from least to most weathered, we have analysed vitrosols (V), gleyic andosols (GA), brown andosols (BA), Histosols (H) and Histic Andosols (HA). Although the most weathered H and HA soils have the highest content in clay-sized material, they have the least fractionated δ7Lipore water values. In contrast, the least weathered GA and BA pore waters are most fractionated for Li isotopes. Given that Li isotope ratios are fractionated by clay mineral formation, this appears counter-intuitive. A single trend for all samples of δ7Li as a function of Li/Na ratios suggests that they are all controlled by a process with a single fractionation factor, in this case likely the formation of poorly-crystalline allophane, which dominates in the “least weathered” soils. This rapidly forming secondary mineral dominates Li isotope fractionation over more slowly-forming crystalline clays. The fractionation along a single path shows that the key process here in controlling the Li isotope ratio of surface waters is the degree of Li uptake by secondary minerals. This does not necessarily correspond to the amount of clay minerals present in the soil, but to the amount of clay minerals that are being newly formed in a single passage of the pore water through the soil, or are in equilibrium with soil solutions at the time of sampling.

Lithium Isotopic Ratios by Single‐Collector ICP‐SFMS: A Critical Evaluation Using Reference Materials

We deployed a procedure to measure Li isotope ratios on a single‐collector sector field inductively coupled plasma mass spectrometer (ICP‐SFMS) operated with a desolvation system and a high‐sensitivity skimmer cone. Under optimised instrumental acquisition conditions, chromatographically separated analyte solutions containing 1 ng g−1 of Li provided adequate sensitivity using analogue mode detection for both isotopes, without adverse memory effect. Unprecedented for this isotopic system, we estimated the expanded uncertainty (U; k = 2) associated with the obtained δ7Li values to validate the procedure. Were considered as potential contributors to the combined uncertainty estimation (uc) the measurement intermediate precision, sample digestion and homogeneity, chromatographic separation, procedural blanks and homogeneity of the bracketing measurement standard (IRMM‐016). The estimated U was on average (from results obtained with reference materials) 1.2‰ (k = 2). This is about twice the intermediate measurement precision (2s) of our data, highlighting the importance of evaluating other measurement uncertainty sources. The δ7Li values obtained for nineteen silicate rocks and one natural water agree with published values. We also provide the first δ7Li = (1.7 ± 1.2; 0.7)‰ (mean value ± U (k = 2); intermediate precision (2s); n = 13) for basalt RM BRP‐1.

The Influence of Weathering, Water Sources, and Hydrological Cycles on Lithium Isotopic Compositions in River Water and Groundwater of the Ganges–Brahmaputra–Meghna River System in Bangladesh

The silicate weathering of continental rocks plays a vital role in determining ocean chemistry and global climate. Spatiotemporal variations in the Li isotope ratio (δ7Li) of terrestrial waters can be used to identify regimes of current and past weathering processes. Here we examine: 1) monthly dissolved δ7Li variation in the Ganges River’s lower reaches; and 2) the spatiotemporal variation of river water of the Brahmaputra, Meghna rivers, and groundwater in Bangladesh. From the beginning to maximum flood discharges of the rainy season (i.e., from June to September), Li concentrations and δ7Li in the Ganges River show remarkable changes, with a large influence from Himalayan sources. However, most Li discharge across the rainy season is at steady-state and strongly influenced by the secondary mineral formation in the low-altitude floodplain. Secondary mineral formation strongly influences the Meghna River’s Li isotopic composition along with fractionation lines similar to the Ganges River. A geothermal input is an additional Li source for the Brahmaputra River. For groundwater samples shallower than ∼60 m depth, both δ7Li and Li/Na are highly scattered regardless of the sampling region, suggesting the variable extent of fractionation. For deep groundwater (70–310 m) with a longer residence time (3,000 to 20,000 years), the lower δ7Li values indicate more congruent weathering. These results suggest that Li isotope fractionation in rivers and groundwater depends on the timescale of water-mineral interaction, which plays an essential role in determining the isotopic signature of terrestrial Li inputs to the ocean.

The evolution of lithium isotope signatures in fluids draining actively weathering hillslopes

The stable isotopes of lithium (Li) serve as a robust proxy of silicate weathering. The fate and transport of these isotopes in the dissolved load of major rivers have been characterized to infer changes in both contemporary weathering regimes and paleo-conditions. In this contribution, we deconvolve this integrated signal into the individual processes that fractionate Li at the inception of silicate weathering by directly measuring Li isotope ratios of waters (δ7Li) transiting through a rapidly eroding first-order hillslope. We use these data to develop a multicomponent reactive transport framework, which shows that net dissolution of weathered material generates light δ7Li signatures (as low as −9.2‰) in the shallow portion of the vadose zone. An increase in δ7Li deeper into the vadose zone (as much as +18‰) reflects an increasing contribution of secondary mineral formation. Below the water table, congruent weathering occurs and imparts elevated cation concentrations and bedrock δ7Li. Silicate weathering continues within the saturated zone as groundwater travels downslope (δ7Li = +13 to + 24‰) to the stream. The stream signatures (δ7Li = +28 to +29‰) reflect the terminus of this network of silicate weathering reactions and the relative magnitude of each contributing process (e.g., transitions in secondary mineral formation, dissolution of weathered material). We show that fluid progressing through the weathering profile of this first-order hillslope is distinguished by a sequence of characteristic Li isotope signatures, which can be reproduced in a forward, process-based model framework. This model development offers an improved quantitative basis for the use of metal(loid) stable isotopes in disentangling catchment-scale chemical weathering fluxes.

Investigation of nitrogen addition, position effect and mismatch intensity effect in Li isotopic analysis by nanosecond laser ablation multi-collector inductively coupled plasma mass spectrometry

The accurate calibration of Li isotope ratio analysis was implemented by a simple and easy-to-operate sample-standard bracketing (SSB) calibration method using nanosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (ns-LA-MC-ICP-MS). The method requires stable instrumental conditions to ensure similar or same mass bias for the sample and the bracketing standard. To stabilize the instrumental conditions and reduce the matrix effect, N2 was added at 4 ml min−1 into the central gas, at a cost of 35–42% reduction in intensity of 7Li. Additionally, to reduce the mass bias difference between the sample and the bracketing standard, their positions in the ablation cell and intensity mismatch effect were also evaluated. An offset of up to 5‰ in δ7Li was observed if the sample and standard were too far apart in the laser ablation cell, and our study demonstrated that the position effect was effectively reduced/eliminated when the sample and standard were placed close to each other, or a volume-optional and low-memory (VOLM) cell was applied for analysis. Furthermore, the intensity mismatch effect was evaluated by changing three laser ablation parameters (spot size, energy and repetition rate). To reduce the intensity mismatch effect, Li content of the selected standard should be close to that of sample, and the Li intensity of sample and standard should be matched by adjusting laser repetition rate. According to the investigation of the above influencing factors on the Li isotope ratio measurements, we can optimize an effective analytical scheme of Li isotope for more geological materials using ns-LA-MC-ICP-MS.

Lithium isotope signatures of weathering in the hyper-arid climate of the western Tibetan Plateau

This study of Lithium (Li) isotopes in surface waters and sediments in the catchment of Lake Bangong and the Upper Indus on the western Tibetan Plateau aims to identify processes that control Li isotope variations during weathering under a cold and hyper-arid climate. Additionally, Li isotope ratios in the Yarlung Tsangpo – Brahmaputra River were investigated. The lake and river sediments of Lake Bangong catchment display remarkable low δ7Li values between −4.7‰ and −0.6‰ relative to L-SVEC. Li isotopes in river bed sediments correlate with weathering intensity tracers such as the chemical index of alteration (CIA), K/(Na + K), or Na/Ti, and δ7Li values decrease continuously within the sediment cascade. These observations cannot be explained by mixing of different lithologies but reflects increasing intensity of weathering. The hyper-arid climate on the western plateau results in considerably long sediment residence times, which allows for overcoming the limitation of water availability on chemical weathering reactions. Samples from the Lake Bangong basins display low δ7Li values between +8.1‰ and +11.1‰. The major inflows have dissolved δ7Li values of +6.1‰ and +8.9‰. High Li/Na ratios in the stream waters indicate some contribution of hydrothermal Li. However, low δ7Li values in surface waters result from impeded silicate weathering processes in the thin soils. The samples from Indus headwaters and Yarlung Tsangpo provide evidence for low δ7Li all over the western and southern Tibetan Plateau. Using data of the Bangong Co, the Indus headwaters, and Yarlung Tsangpo, as well as published data from the northeastern plateau, we explore what controls Li isotope variation across the Tibetan plateau. Mass balance calculations suggest that similar proportions of dissolved Li and particulate Li are exported by river water and sediments on the western plateau. In contrast, high δ7Li values around +17‰ of the dissolved load in rivers on the northeastern Tibetan Plateau reflect a particulate Li export flux that is about five times higher than the export flux of dissolved Li. There is no first-order control by silicate weathering rates. The δ7Li differences largely follow the precipitation gradient across the Tibetan Plateau, which results in high net-incorporation of Li into clays on the northeastern but limits soil formation on the western Tibetan Plateau and, therefore limited, processing of lithium in the weathering zone.

Quantifying the impact of recovery during chromatographic purification on the accuracy of lithium isotopic determination by multi-collector inductively coupled plasma mass spectrometry.

Lithium (Li) isotopes have increasingly been applied as tracers in Earth and planetary sciences and their effectiveness relies upon accurate and precise Li isotopic data. Nowadays, multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) combined with chromatographic purification is the most common strategy for obtaining Li isotopic ratios in natural samples, with a long-term internal precision better than 0.3‰ in most laboratories. However, there is a large discrepancy in the Li isotopic compositions of the same reference materials determined by MC-ICP-MS among international laboratories (e.g. ca 3.5‰ difference for measurements of homogeneous seawater), which has been attributed to insufficient recovery of Li during chromatographic purification. Despite this recognition, the exact impact of Li recovery during purification on Li isotopic determinations by MC-ICP-MS has never been quantified. We employed a normal distribution function to model Li elution curves and quantified the Li isotopic fractionation resulting from Li recovery during chromatographic purification. Furthermore, we compared the calculated and measured relative recovery (R) with the Li isotopic ratios determined by ICP-MS to validate our theoretical calculation. The theoretical calculations showed that R should be higher than 99.8% in order to avoid observable Li isotopic fractionation during chromatographic purification at IEECAS. This idea is further supported by the better long-term external precisions for data with R≥ 99.8% compared with previous values of 99.5% ≤R< 99.8%. Our results indicated that the large differences in the reported Li isotopic ratios for homogeneous seawater among international laboratories are probably attributable to Li isotopic fractionation occurring during ion exchange chromatography. Our theoretical calculation via R is the first quantitative and convenient approach for monitoring Li isotopic fractionation during sample purification, ensuring that R≥ 99.8% can avoid observable Li isotopic fractionation during purification, which will improve the accuracy of Li isotopic measurements by MC-ICP-MS and the comparability among laboratories.

Further Characterization of the BB Zircon via SIMS and MC-ICP-MS for Li, O, and Hf Isotopic Compositions

In this contribution, we report the results for the characterization of the BB zircon, a newly developed zircon reference material from Sri Lanka, via secondary ion mass spectrometry (SIMS) and multiple-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The focus of this work was to further investigate the applicability of the BB zircon as a reference material for micro-beam analysis, including Li, O, and Hf isotopes. The SIMS analyses reveal that BB zircon is characterized by significant localized variations in Li concentration and isotopic ratio, which makes it unsuitable as a lithium isotope reference material. The SIMS-determined δ18O values are 13.81‰ ± 0.39‰ (2SD, BB16) and 13.61‰ ± 0.40‰ (2SD, BB40), which, combined with previous studies, indicates that there is no evidence of conspicuous O isotope heterogeneity within individual BB zircon megacrysts. The mean 176Hf/177Hf ratio of BB16 determined by solution MC-ICP-MS is 0.281669 ± 0.000012 (2SD, n = 29) indistinguishable from results achieved by laser ablation (LA)-MC-ICP-MS. Based on the SIMS and MC-ICP-MS data, BB zircon is proposed as a reference material for the O isotope and Hf isotope determination.