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Lithium isotope ratios play a key role in tracing weathering processes within the context of paleoclimatologic research. Therefore, accurate and precise determination of the isotopic composition of Li is required for a large variety of complex geological samples with widely different Li contents. This technical note describes the extension and fine-tuning of the existing cation exchange chromatographic procedures for isolation of Li to whole-rock carbonate and clay matrices prior to its isotopic analysis via multi-collector ICP-mass spectrometry. The method developed permits the isolation of ≥20 ng amounts of Li from carbonates and clays, by using a 25 cm long cylindrical column loaded with 8 and 2 mL of AG-50W-X8 cation exchange resin, respectively. A 0.5 M HCl solution is used as eluent. Li recoveries ≥99% were achieved and isotopic analysis using 10–20 ng of isolated Li resulted in accurate and precise δ7Li values – external precision (2SE) of 0.2‰ (N = 15). The analytical procedures developed allow Li isotope ratios to be investigated in parallel in both the clay and carbonate fractions of a geological sample within the context of paleoclimatological research. [ABSTRACT FROM AUTHOR]

Boron isotopic analysis is of interest in many research fields and for a large variety of sample types. Accurate and precise determination of boron isotope ratios using multi-collector ICP-mass spectrometry or thermal ionization mass spectrometry requires isolation of the target element prior to isotopic analysis, which is accomplished using either ion exchange chromatography or microsublimation. This study systematically compares the two methods in terms of B recovery, procedural blank, matrix removal efficiency, accuracy and precision of the resulting δ11B values as measured using multi-collector ICP-mass spectrometry, as well as labor intensiveness and costs. For this purpose, four types of sample matrices, i.e. 20 g L-1 Ca aqueous solution, seawater, digests of spinach (100 g L-1) and silicate glass (10 g L-1), were stripped from their original B content and spiked with δ11B of known isotopic composition and were then subjected to both sample preparation methods and subsequent isotopic analysis of the purified B fraction via multi-collector ICP-mass spectrometry. For both methods, the highest (quantitative) B recoveries were obtained for Ca-rich aqueous solution and seawater. For spinach, accurate d B values were obtained after ion exchange chromatography. However, microsublimation was plagued by isotope fractionation, resulting in large offsets (~8%) between the experimental results and the corresponding reference values. For glass, B recovery was incomplete, nevertheless the absence of fractionation rendered both sample preparation methods suitable. Overall, in the absence of isotope fractionation, microsublimation appears advantageous in terms of procedural blanks, matrix removal efficiency, precision (2 s) on δ11B values, labor intensiveness and costs. [ABSTRACT FROM AUTHOR]

Introduction: The geological record contains scarce evidence for airbursts, the most common type of hypervelocity impact events. During airbursts, impactors of 50 to 150 m in size are fragmented and vaporized during atmospheric entry, as exemplified by the Tunguska and Chelyabinsk events [1]. In recent years, meteoritic debris resulting from such low-altitude airbursts has been found on various locations across Antarctica (cf. summary in [2]). Fine-grained (<100 μm) particles recovered from Miller Butte (Northern Victoria Land), Dome Concordia (C), and Dome Fuji (F) were likely produced by a Tunguska-like event 481 ka ago [2]. More recently, larger (~100 to 500 μm) extraterrestrial spherical and spherulitic particles correlated to similar particles in the Dome C and Dome F ice cores, dated to ca. 430 ka, have been recovered from sedimentary deposits near the Walnumfjellet (WN) summit in the Sør Rondane Mts., East Antarctica (S72°07'11", E24°12'30"). The unique properties of the recovered particles attest to an unusual type of touchdown event, likely intermediate between an airburst and a crater-forming impact, during which a high-velocity vapor jet produced by the disruption of a projectile reached the Antarctic ice sheet [2]. Using additional petrographic, geochemical, and isotopic data, we refine the nature of the impactor, the location of the touchdown, and thermodynamic conditions under which the vapor jet interacted with the Antarctic ice. Samples and methods: The studied particles were extracted from glacial sediment on top of WN during the 2017-2018 BELAM (Belgian Antarctic Meteorites) expedition. Igneous spherical to spherulitic particles exhibiting unusual structures and textures were extracted from the deposits. The nature of the extracted particles was confirmed using scanning electron microscopy (SEM) at the VUB. The most pristine particles were selected for further chemical and isotopic analysis. For Cr and Ti isotopic analysis, 75 particles were combined, digested, and processed using established procedures [3]. For Mg, Fe, and K isotopic analysis, 22 particles were digested together, after which the target elements were isolated and the isotopic measurement performed according to [4,5]. In total, 9 particles were prepared for bulk oxygen isotope analysis following [6]. Results were obtained for 2 particles, while 7 other particles are being processed. Δ17O values were calculated using the linearized format with λ = 0.5247 [7]. Results: The combined particles yield a e54Cr value of 1.57±0.15 and e50Ti value of 1.59±0.25 (2SE), while d25MgDSM-3 is -0.11±0.04 ‰ (2SD) and d56FeIRMM524-A is 0.23±0.10 ‰ (2SD). Two particles show d18O values of -43.7 to -39.7 ±0.4‰ and D17O values of -0.19 to -0.17 ±0.04‰ (2SD). Discussion and conclusions: A touchdown airburst scenario for the WN particles is proposed mainly based on their unique petrologic features (incl. spinel chemistry) and oxygen isotope ratios [2]. The d18O values fall close to those of Antarctic inland ice, while the D17O values are all below the terrestrial fractionation line (TFL), both at the bulk scale and for individual phases [2]. The negative D17O value for the WN particles likely results from mixing of Antarctic ice and/or air to a precursor composition with an even lower D17O. This implies a carbonaceous chondritic impactor rather than an ordinary chondrite body. The measured e54Cr and e50Ti values overlap with CR-type or CItype carbonaceous chondrites, although the latter type can likely be excluded based on the negative D17O. Such composition is supported by the d25Mg value [8], while the d56Fe value is distinct from those reported for chondrites [9], probably due to thermal processing or oxidation in the touchdown plume. Recent spectral analysis by NASA's OSIRIS-REx spacecraft revealed that asteroid (101955) Bennu may be comprised of CR1(-like) material [10]. If confirmed after sample-return, these particles would highlight the importance of (CR-type) carbonaceous chondritic materials among Near-Earth asteroids. The effects of airburst and touchdown events remain poorly studied to date. However, if such a touchdown impact event occurs above a densely populated area, it would be a major hazard resulting in millions of casualties and damage over distances of up to hundreds of kilometers [2]. [ABSTRACT FROM AUTHOR]

Abstract New Sr-Nd-Hf-Pb isotope data for volcanic rocks from the peninsula of Methana (South Aegean Active Volcanic Arc, Greece) show a wide variation, and more 'enriched' isotopic signatures (e.g. elevated 87Sr/86Sr at 0.705–0.709) than those of other active Aegean volcanic centres, all located on thinner crust. The data set is best explained by polybaric AFC processes, with contaminants similar to country rocks and xenoliths, showing moderately high 87Sr/86Sr ratios, and with isotopically more evolved lower crust, similar to the pre-Alpine Ios basement. Pb isotope ratios show some minor influence of assimilation of fluid-altered volcanic cumulates. Intermediate lava domes with mafic enclaves were formed during periods of compression, whereas an extensional period saw the deposition of explosive products of bimodal composition, with the more felsic deposits showing the most pronounced influence of crustal assimilation. The latter likely represent stalled magmas from an earlier compressional period, which were remobilised and flushed out by ascending mafic magmas during extension. Recognition of these volcanological, geochemical and isotopic characteristics of deposits associated with extensional tectonics in a modern arc will enable us to use these criteria to infer paleo-tectonics from older volcanic deposits. Highlights • Volcanic products from Methana (Greece) show large isotopic variation. • Isotopic signature and eruption style document tectonic regime. • Greatest isotopic variation and explosive deposits during extension. • Magma mixing responsible for isotopic arrays. [ABSTRACT FROM AUTHOR]

This paper discusses Sr-Nd-Sb isotopic analysis of Late Bronze Age glass to investigate the origin and nature of the mineral raw materials used in early glass making. Sr–Nd isotopic analysis characterizes the flux and silica component of the glass raw material mixture. This technique has been successfully applied to separate Egyptian from Mesopotamian glass signatures, also identifying the use of at least two distinct flux-silica mixtures in Mesopotamian glass making. Sb isotopic analysis is presented as a novel technique to examine the raw material used to opacify the earliest glass. It is demonstrated that Egyptian and Mesopotamian glass factories likely used an identical source of Sb, possibly originating from the Caucasus. This suggests a steady supply and long distance exchange or trade of this material during the Late Bronze Age. [ABSTRACT FROM AUTHOR]