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Abstract. This study presents a novel analysis of two hailstones collected in central Argentina to provide insights into the size distribution, composition, and potential sources of non-soluble particles within hailstones. Using this new method, non-soluble particles are trapped beneath a thin layer of polyvinyl resin and analyzed with Confocal Laser and Scanning Electron Microscopy combined with Energy-Dispersive Spectroscopy, preserving their in-situ location and physical characteristics. The study characterized these particles' distribution, shape, and size and identified their elemental composition, which is used to interpret possible source regions. Particles ranged in diameter from 1.2 to 256.0 microns, with the largest found in hailstone embryos. Agglomerated mineral and organic particles dominated the elemental composition, followed by organics and quartz, and were present throughout the hailstones. Agglomerated salt particles detected in one sample were traced to a nearby salt lake, while copper chloride and zinc chloride particles found in the second sample were potentially associated with agrochemicals commonly used for pest control and fertilizer, including in Argentina. Various local and regional land-use types, including shrublands, mixed vegetation, croplands, and urban areas, were linked to specific types of particles. This study, therefore, highlights the regional influence of various land use types on hail formation and growth, pointing to the potential impacts of natural and anthropogenic factors on hailstone composition. 

Metallic glass thin films (MGTFs) are a recently developed class of alloy coatings with potential applications ranging from biomedical devices to electrical components. Their tribological performance in service conditions is dictated by MGTF bulk composition but can be limited by the native oxide surface that inevitably forms upon exposure to atmosphere. Surface oxidation, thickness, and composition of ZrCuNiAl MGTFs were characterized using a combination of X-ray photoelectron microscopy (XPS) and electron probe microanalysis (EPMA). MGTF samples with nominal thicknesses of 50, 500, and 1500 nm were sputtered onto Si and SiN wafer substrates within a high vacuum deposition chamber and their amorphicity was confirmed by X-ray diffraction. XPS depth profiling identified the thin film composition and showed that the surface oxide was dominated by a mixed layer of mostly ZrO2, a little oxidized Al, and some metallic Zr. EPMA X-ray intensities were acquired as a function of beam energy to excite characteristic X-rays from different depths of the MGTFs and reconstructed using open-source thin film analysis software BadgerFilm, to determine the composition and thickness of sample layers. EPMA results constrain the composition to be Zr54Cu29Al10Ni7 within 0.7 at. % variation and total thicknesses to be 49, 470, and 1546 nm. Using the oxide composition identified from XPS depth profiling as an input for BadgerFilm analysis, EPMA results indicate the surface oxidation layer on each of the thin film samples was 6.5 ± 1.1 nm thick and uniform across a 0.25 mm region of the film. 

Abstract Clinopyroxene is a rock-forming mineral that commonly hosts melt inclusions in mafic to intermediate composition volcanic and plutonic rocks. It is highly resistant to alteration compared to other co-existing phenocrysts such as plagioclase. Several recent studies have 40Ar/39Ar dated clinopyroxene in Neoproterozoic to Miocene basalts and dolerites. To assess the viability of the technique at the youngest end of the geologic time scale, we performed 40Ar/39Ar incremental heating experiments on clinopyroxene-hosted melt inclusions from a variety of mafic lithologies and tectonic settings. Most samples produced precise plateau ages including several Quaternary basalts to andesites as young as 0.6 Ma. All data are indistinguishable from new and/or published 40Ar/39Ar ages on groundmass or plagioclase from the same samples. The source of potassium (K) and resulting 40Ar* within clinopyroxene has been debated, but thus far has only been inferred based on 40Ar/39Ar data. Using electron probe microanalysis (EPMA) we show that there is negligible K in the clinopyroxene host, but substantial K (e.g., 1–4 wt%) in trapped melt inclusions and minor amounts in plagioclase inclusions. Thus, melt inclusions, which are common in phenocrysts in basaltic magmas, can be used to obtain accurate and precise 40Ar/39Ar ages for difficult-to-date volcanic and plutonic rocks from the Precambrian to the Pleistocene. 

Mocho-Choshuenco volcano (39.9°S, 72.0°W) produced ∼75 explosive eruptions following retreat of the >1.5-km-thick Patagonian Ice Sheet associated with the local Last Glacial Maximum (LGM, from 35 to 18 ka). Here, we extend this record of volcanic evolution to include pre- and syn-LGM lavas that erupted during the Pleistocene. We establish a long-term chronology of magmatic and volcanic evolution and evaluate the relationship between volcanism and loading/unloading of the Patagonian Ice Sheet via twenty-four 40Ar/39Ar and two 3He age determinations integrated with stratigraphy and whole-rock compositions of lava flows and glass compositions of tephra. Our findings reveal that the edifice is much younger than previously thought and preserves 106 km3 of eruptive products, of which 50% were emplaced immediately following the end of the penultimate glaciation and 20% after the end of the LGM. A period of volcanic inactivity between 37 and 26 ka, when glaciers expanded, was followed by the eruption of incompatible element-rich basaltic andesites. Several of these syn-LGM lavas dated between 26 and 16 ka, which crop out at 1500−1700 m above sea level, show ice contact features that are consistent with emplacement against a 1400- to 1600-m-thick Patagonian Ice Sheet. Small volume dacitic eruptions and two explosive rhyolitic eruptions dominate the volcanic output from 18 to 8 ka, when the Patagonian Ice Sheet began to retreat rapidly. We hypothesize that increased lithostatic loading as the Patagonian Ice Sheet grew prohibited dike propagation, thus stalling the ascent of magma, promoting growth of at least three discrete magma reservoirs, and enhancing minor crustal assimilation to generate incompatible element-rich basaltic andesitic to dacitic magmas that erupted between 26 and 17 ka. From an adjacent reservoir, incompatible element-poor dacites erupted from 17 to 12 ka. These lava flows were followed by the caldera-forming eruption at 11.5 ka of 5.3 km3 of rhyolite from a deeper reservoir atop which a silicic melt lens had formed and expanded. Subsequent eruptions of oxidized dacitic magmas from the Choshuenco cone from 11.5 to 8 ka were followed by andesitic to dacitic eruptions at the more southerly Mocho cone, as well as small flank vent eruptions of basaltic andesite at 2.5 and 0.5 ka. This complex history reflects a multi-reservoir plumbing system beneath Mocho-Choshuenco, which is characterized by depths of magma storage, oxidation states, and trace element compositions that vary over short periods of time (<2 k.y.). 

Abstract. This paper introduces an innovative microscopy analysis methodology to preserve in situ non-soluble particles within hailstones using a protective porous plastic coating, overcoming previous limitations related to melting the hailstone sample. The method is composed of two techniques: trapping non-soluble particles beneath a plastic coat using the adapted sublimation technique and then analyzing the particles individually with confocal laser scanning microscopy (CLSM) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS). CLSM provides insights into physical attributes like particle size and surface topography, enhancing our understanding of ice nucleation. SEM–EDS complement CLSM by offering detailed information on individual particle elemental chemistry, enabling classification based on composition. Strategies to reduce background noise from glass substrates during EDS spectral analysis are proposed. By combining powerful, high-resolution microscopy techniques, this methodology provides valuable data on hailstone composition and properties. This information can give insights into hail developmental processes by enhancing our understanding of the role of atmospheric particles.