Iron sulfide and metal melt veins in chondritic materials are associated with advanced stages of dynamic shock. The shock-induced residual temperatures liquefy the sulfide component and enable melt distribution. However, the distribution mechanism is not yet fully understood. Capillary forces are proposed as agents of melt distribution; yet, no laboratory experiments were conducted to assess the role that capillary forces play in the redistribution of iron sulfide in post-shock conditions. To investigate this further, we conducted thermal experiments under reducing conditions (N2(g)) using dunitic fragments, suitable chondritic analog materials that were doped with synthesized troilite (stoichiometric exact FeS). We observed extensive iron sulfide (troilite) migration that partially resembles that of ordinary chondrites, without the additional influence of shock pressure-induced fracturing. The iron sulfide melt infiltrated grain boundaries and pre-existing fractures that darkened the analog material pervasively. We also observed that the iron sulfide melt, which mobilized into grain boundaries, got systematically enriched in Ni from the surrounding host olivine. Consequently, FeNi metal fractionated from the melt in several places. Our results indicate that capillary forces majorly contribute to melt migration in the heated post-shock environment.

The hyperarid Atacama Desert is one of the driest and oldest deserts on Earth, rendering it a valuable climate archive. However, unraveling its past climate is particularly challenging and the few studied paleoclimate records of the region reveal strong temporal and spatial variabilities. To enhance our understanding of these dynamics we investigated a sedimentary record in the Yungay valley located in the southern hyperarid Atacama Desert. We employed paleomagnetic and radiocarbon dating, and for the first time for Atacama Desert sediments, a meteoric Be-10/Be-9 based method for determining the depositional age. The respective 4.20 m deep profile comprises a lower alluvial fan deposit with a maximum age of 3.8 +/- 0.8 Ma, and an upper 1.84 m thick clay pan deposit that has accumulated over the last 19 ka. Different proxies including grain size, salt concentration, and elemental composition indicate an aridity increase around 2.3 Ma ago and repeated dry and wet phases during the late Pleistocene and the Holocene. The latter climatic shifts can be assigned to variabilities of the South American Summer Monsoon and El Ni & ntilde;o Southern Oscillation with moisture sources from the Atlantic and the Pacific Ocean, respectively. This study provides deeper insights into the heterogeneous climate of the hyperarid Atacama Desert and underlines the importance of interdisciplinary investigations to decipher climate systems and their effect on potential habitable regions in such an extreme environment.

Introduction: Impactors several tens up to 200 m in size are likely to suffer complete disruption and to produce large airbursts, similarly to the Tunguska event over Russia in 1908 [e.g., 1]. Observations and numerical modeling of medium sized impacts producing large airbursts have shown that such impacts represent an important fraction of extraterrestrial matter accretion to Earth, with Tunguska-like events occurring every 100 to 10,000 years, which is notably more frequent than crater-forming impact events. However, little is known about occurrences of such airburst events in the geological record, principally because of the lack of readily identifiable evidences such as impact craters. Finding residues of such events is thus critical for assessing the complete impact history of the Earth. Here we present the discovery of extraterrestrial particles in the Sør Rondane Mountains, Queen Maud Land, Antarctica, which were produced during a “touchdown” impact event ca. 430 ka ago, when a large airburst vapor jet interacted with the Antarctic ice sheet.Material and Methods: Twenty nine igneous particles were recovered from glacial sediment collected during the 2017-2018 BELAM (Belgian Antarctic Meteorites) expedition that took place in the Sør Rondane Mountains, Queen Maud Land, Antarctica. Glacial sediment was sampled from a flat eroded summit in the Walnumfjellet (WN) area. 10Be exposure age of nearby summits suggest that the first sampled area has been continuously exposed over the last 870 ka [2]. About half the particles are compound spherules consisting of two or more spherules fused together. The petrography and mineralogy of 18 particles were determined at the Royal Belgian Institute of Natural Sciences of Brussels, Belgium. Their major and trace element compositions were determined at the Museum für Naturkunde of Berlin, Germany, and at Florida State University, USA, respectively. Oxygen isotopic compositions were determined by means of secondary ion mass spectrometry at the CRPG of Nancy, France.Results: The mineralogy of the particles consists of olivine and spinel, with minor interstitial glass. On the basis on their internal textures and spinel content, we identify four groups of particles: 1/ the spinel-rich particles (SR; N = 9; ≥19% vol. spinel); 2/ Porphyritic olivine (PO; N = 5;

Meteorite recoveryAsteroid 2024 BX1 was discovered by astronomer K. Sárneczky at 21:48 UTC on 20 January 2024. NASA’s Scout and ESA’s Meerkat impact assessment systems soon identified it as a potential impactor and predicted that it would pass over Nennhausen, ~60 km W of Berlin, Germany, between 00:15 and 00:51 UTC on 21 January. At this time, a fireball was observed by eyewitnesses and recorded by allsky cameras of the European Fireball Network, IMO/All-Sky7, and FRIPON. Bolide analysis and strewn field calculations [1] indicated that strong winds blew the surviving meteorites to the SE, predicting a fall just south of Ribbeck. Starting on 22 January, a systematic search was carried out by scientists and students of MfN, DLR, FU Berlin, TU Berlin, the SETI Institute, and the Arbeitskreis Meteore. The first meteorite, totaling 171 g, was found by meteorite hunters on 25 January just west of Ribbeck. Two students from our team found two smaller meteorites (8.1 and 4.7 g) on 26 January, proving that the strewn field model was correct. Searching continued until 20 March and revealed about 200 reported finds with a total mass of >1770 g.Strewn fieldThe strewn field extends along a ~1 km wide and ~8 km long, WNW-ESW oriented corridor just south of Ribbeck (where meteorites of between 50 and 230 g were found) and Berge and Lietzow (where meteorites 5 km than predicted. The distribution of total mass per kilometer along the strewn field is approximately constant (~230 g/km) until the distribution of small (6 km due to sampling bias or a lack of small masses during fragmentation.Petrography of the Ribbeck aubritesPetrographic observations revealed that Ribbeck is an aubrite, which are rare enstatite achondrites [2–4]. The Ribbeck meteorites are fragmental breccias predominantly composed of up to 1.2-cm-sized, mostly angular, FeO-free, homogeneous enstatite (En99.2Fs0.0Wo0.8), less abundant (~1–11%), up to-1.5-cm sized, homogeneous forsterite (Fo99.9), and highly variable amounts (~1–17%) of sodic feldspar (An2.4Ab95.1Or2.5) set in a fine-grained, comminuted matrix of related material. Less abundant silicates include K-feldspar (An0.1Ab7.0Or92.2) and diopside (En53.5Fs0.1Wo46.4). Opaque phases include Ti-bearing troilite, exotic sulfides such as alabandite, keilite, djerfisherite, oldhamite, caswellsilverite, schöllhornite, and cronusite, Si-bearing (0.7–1.0 wt% Si) and Si-poor (

Several recent petrogenetic models propose that layers of stratiform chromitites in the Bushveld Complex are produced by mechanical separation of chromite from co-existing silicate minerals (e.g., olivine, orthopyroxene, plagioclase) within crystal-rich slurries. One feature in common for the slurry models is that they imply that interstitial liquid in stratiform chromitites solidifies underneath a crystal pile ranging from 20 to 100 m thick. This means that the interstitial liquid would not be able to chemically communicate with the resident melt overlying the crystal pile. Equilibrium crystallization of interstitial melt within chromitites will, therefore, produce interstitial plagioclase with an average Ca/Na ratio similar to that of the interstitial liquid itself, i.e., plagioclase must be evolved in composition (-40-50% An-content). In contrast to this prediction, extensive microprobe data show that interstitial plagioclase in Bushveld chromitites has a rather primitive composition (-60-80% An-content) that is close to that of cumulus plagioclase (-70-80% An-content) from adjacent norites and anorthosites that are produced by fractional crystallization. This implies that interstitial plagioclase is not a product of equilibrium crystallization within a deeply buried chromite-rich pile. Modification of interstitial plagioclase composition by various additional processes (fractional crystallization, selective diffusion, reactive melt flow, etc.) are considered but shown to be inconsistent with field, textural or chemical observations. We conclude that either slurry models for the origin of stratiform chromitites are incorrect and should be abandoned or must be substantially modified to address the issue of the high An-content of interstitial plagioclase in stratiform chromitites.

Micrometeorites originate from the interplanetary dust complex and continuously fall to the Earth's surface in large amounts. About 10 to 20% of micrometeorites are not melted upon reaching the Earth's surface, preserving the primary features and characteristics of the parent material. Consequently, unmelted micrometeorites, together with scoriaceous micrometeorites, an intermediate form between cosmic spherules and unmelted mi-crometeorites, are pivotal in documenting the nature and evolution of interplanetary dust as well as the modi-fications experienced by micrometeorites during atmospheric entry. Based on their petrographic features, here we identified and characterized 64 scoriaceous and unmelted micrometeorites with diameters varying between 90 and 410 & mu;m from fine-grained sediment sampled in the Sor Rondane Mountains of East Antarctica. Based on their size distribution, the micrometeorites from the Sor Rondane Mountains show a clear distinction between unmelted micrometeorites (<300 & mu;m) and cosmic spherules (>400 & mu;m) and imply an accumulation mechanism or exposure history distinct from other collections (e.g., Transantarctic Mountains). Different exposure windows, weathering processes and environmental factors (e.g., snow cover) could affect the size and composition of preserved particles.A selection of the particles (n = 49) was further characterized for geochemical composition and high-precision oxygen isotope ratios to identify potential parent bodies and document their alteration histories. About 63% of the particles, exhibiting both coarse-and fine-grained textures, derive from carbonaceous chondritic precursors. Two particles (-4%) display anomalously 16O-poor isotopic compositions similar to that previously observed for (giant) cosmic spherules and unmelted micrometeorites, classified as "group 4" particles. These particles are thought to originate from an unidentified chondritic parent body located in a specific region of the protoplan-etary disk or may have been characterized by a distinct alteration history, with recent studies linking them to CY carbonaceous chondrites. Only a single fine-grained particle (-2%) can be assigned to ordinary chondritic parentage with confidence. The partially hydrated fine-grained matrix suggests this particle might be consistent with a Semarkona-like parent body. Approximately 10% of the studied particles exhibit extensive evidence for secondary terrestrial weathering with formation of (hydr)oxides during residence in the Antarctic environment, preventing detailed parent body identification. Ten particles (-20%) could not be assigned to a specific parent group due to ambiguous oxygen isotope values. Overall, the parent body statistics from this study agree with those reported for different collections of a similar size fraction. Clear associations between textural groups and parent bodies could not be established. Even though unmelted micrometeorites are generally considered pristine and often do not exhibit any obvious petrographic evidence of terrestrial weathering, the chemical and isotopic data obtained here confirm that alteration can occur at the microscale and any data on unmelted particles from Antarctic subaerial collections should be evaluated with caution.

Non-active molybdenum-rich Ca/Zn glass composite materials (GCM) were prepared on the Vitrification Test Rig (VTR) in the UK. The GCM samples were subjected to Ni and Au ion irradiations to simulate the effects of alpha recoil damage and to determine how the crystallinity characteristics might affect the overall radiation tolerance of high-level wastes (HLW) generated during post-operational clean-out (POCO) operations at the Sellafield nuclear site. The typical crystal phases identified in the GCM were: powellite, ruthenium dioxide, zincochromite, zircon and cerianite. Gadolinium (a proxy for radioactive elements) accumulated mainly in powellite, zircon and cerianite crystals. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and grazing incidence X-ray diffraction (GIXRD) analyses showed that cerianite is a highly radiation-tolerant phase, whereas powellite and zircon became amorphous and swelled considerably after the Ni and Au ion irradiations. This research shows the first evidence of powellite amorphisation under heavy-ion irradiation and suggests that powellite is susceptible to amorphisation by alpha recoils in HLW materials, in contrast to previous findings. The evolution of cooling-related and irradiation-induced microcracks is also described. In HLW glass composite materials, the formation of microcracks is expected in the middle of the canister, where relatively large powellite and zircon crystals appear.

The Bushveld Complex is the largest layered mafic intrusion on earth and also the leading resource for platinum group elements (PGE). There are major gaps in understanding the modal layering and the concentration of PGE into certain layers of the Critical Zone (e.g., the Merensky Reef and the UG2 chromitite), but evidence suggests that hydrous melts and/or fluids played a role. Crystallized melt inclusions with hydrous, Cl-bearing phases occur in both the Merensky Reef and UG2, and both layers also contain interstitial phlogopitic mica. While the existence of late-stage hydrated melts and their effects on phase relations and element redistribution in the cumulate layers have been described, the source of water remains an open question: is it internal, concentrated by fractional crystallization, or is it external? To address this, we analyzed the hydrogen and triple-oxygen isotope composition of interstitial, late-magmatic phlogopite separated from UG2 drillcores at three widely-separated localities. All three localities yielded similar compositions. The triple oxygen isotope values ( Δ ' 17 O 0.5305 ) average -0.06 ± 0.01‰ ( δ 18 O = 5.6 to 6.2‰), which are consistent with previous models of 30–40% contamination of mantle-derived

There is abundant evidence for significant H2O in evolved melts from the platinum-rich UG2 chromitite and the Merensky Reef of the Bushveld Complex (South Africa), but there is no consensus about the source of H2O. We report triple-oxygen and hydrogen isotope ratios of interstitial, late-magmatic phlogopite from three localities of the UG2 layer. The phlogopite yielded 8D values of -43 parts per thousand to -23 parts per thousand, which is >30 parts per thousand higher than previously known from Bushveld rocks and far above the mantle values of similar to-75 parts per thousand. The phlogopite triple-oxygen isotope ratios are the first to be reported for Bushveld rocks, with values of Delta'O-17(0.5305)(O-17 excess relative to the reference line 0.5305) from -0.069 parts per thousand to -0.044 parts per thousand (delta O-18 5.2 parts per thousand-6.2 parts per thousand). The oxygen data support existing models of as much as 30 %-40 % contamination of mantle-derived magmas in the lower to middle crust. However, the high delta D values require a second step of contamination, which we attribute to brines from the marine sediments in the Transvaal Basin at the emplacement level.

The Rum Eastern Layered Intrusion (ELI; Scotland) is an open-system layered intrusion constructed of 16 macro-rhythmic units. Each of the macro-rhythmic units consists of a peridotite base and a troctolite (± gabbro) top, previously attributed to the fractional crystallisation of a single magma batch. This classic paradigm has been challenged, however, with evidence presented for the emplacement of peridotite sills in Units 9, 10, and 14, such as cross-cutting relationships, upward-oriented apophyses, and lateral discontinuities. To test whether the other major peridotites within the ELI represent sills, we have carried out new field, petrographic, and mineral chemical analyses of the peridotites in Units 7, 8 and 9. The peridotites display large- and small-scale cross-cutting relationships with the overlying troctolite, indicative of an intrusive relationship. The peridotites also show large-scale coalescence and lateral spatial discontinuities such that the ELI unit divisions become arbitrary. Harrisite layers and Cr-spinel seams found throughout Units 7, 8, and 9 suggest the peridotites were constructed incrementally via repeated injections of picritic magma. Our observations allow for distinct subtypes of peridotite to be defined, separated by intrusive contacts, allowing for their relative chronology to be determined. Older, poikilitic peridotite, rich in clinopyroxene, is truncated by younger, well-layered peridotite, containing abundant harrisite layers. In addition to the new peridotite subtypes defined in this study, we find strong evidence for laterally oriented metasomatism within clinopyroxene-rich wehrlites at the top of the Unit 8 peridotite. The wehrlites and surrounding peridotites record a complex series of metasomatic reactions that transformed thin picrite sills into clinopyroxene-rich wehrlites without any evidence for the sort of vertical melt movement typically posited in layered intrusions. The observations presented in this study from the ELI cannot be reconciled with the classic magma chamber paradigm and are better explained by the emplacement of composite sills into pre-existing feldspathic cumulate (gabbro or troctolite). The evidence for sill emplacement presented here suggests that the layered complex was constructed by a combination of sill emplacement and metasomatism, forming many of the unusual (often clinopyroxene-rich) lithologies that surround the sills. The broad-scale formation of the layered peridotites via incremental sill emplacement, suggested by the occurrence of upward-oriented apophyses, coalescence, and lateral discontinuity, could be applied to much larger ultramafic intrusions, which might have formed by similar mechanisms.

Small-scale variations in mineral chemistry, textures, and platinum group element (PGE) mineralization were investigated in the Lower and Middle Group chromitite layers LG6, LG6a, MG1, MG2, and MG2 II from vertical drill core profiles at the Thaba mine in the northwestern limb of the Bushveld Complex. We present detailed geochemical profiles of chromite composition and chromite crystal size distribution curves to shed light on the processes of chromite accumulation and textural modification as well as mineralization. Multiple samples within each layer were assayed for PGE concentrations, and the respective platinum group mineral association was determined by mineral liberation analysis (MLA). There is strong evidence for postcumulus changes in the chromitites. The crystal size distribution curves suggest that the primary chromite texture was coarsened by a combination of adcumulus growth and textural equilibration, while compaction of the crystal mush played only a minor role. Mineral compositions were also modified by postcumulus processes, but because of the very high modal amount of chromite and its local preservation in orthopyroxene oikocrysts, that phase retained much primary information. Vertical variations of chromite composition within chromitite layers and from one layer to another do not support the idea of chromite accumulation from crystal-rich slurries or crystal settling from a large magma chamber. Instead, we favor a successive buildup of chromitite layers by repeated injections of relatively thin layers of chromite-saturated magmas, with in situ crystallization occurring at the crystal mush-magma interface. The adcumulus growth of chromite grains to form massive chromitite required addition of Cr to the layers, which we attribute to downward percolation from the overlying magma. The PGE concentrations are elevated in all chromitite layers compared to adjacent silicate rocks and show a systematic increase upward from LG6 (avg 807 ppb Ir + Ru + Rh + Pt + Pd + Au) to MG2 II (avg 2,062 ppb). There are also significant internal variations in all layers, with enrichments at hanging and/or footwalls. The enriched nature of chromitites in PGEs compared to host pyroxenites is a general feature, independent of the layer thickness. The MLA results distinguish two principal groups of PGE mineral associations: the LG6, LG6, and MG1 are dominated by the malanite series, laurite, and PGE sulfarsenides, while the MG2 and MG2 II layers are characterized by laurite and PGE sulfides as well as Pt-Fe-Sn and PGE-Sb-Bi-Pb alloys. Differences in the PGE associations are attributed to postcumulus alteration of the MG2 and MG2 II layer, while the chromitites below, particularly LG6 and LG6a, contain a more pristine association.

The oldest known evidence of large impacts in Early Earth history are Archaean to Palaeoproterozoic impact spherule layers of the Barberton Greenstone Belt in South Africa and the Pilbara craton in Western Australia. Four drill core sections (BH5901, BH5907, BH5911 and BH5949) containing spherule layers were intersected in exploration drilling at Fairview Gold Mine in the northern Barberton Greenstone Belt. Here, we provide a first detailed mineralogical study of these new spherule layer intersections. The spherule layers are densely packed with sand-sized, spherical to ovoid, i.e., in part strongly deformed, "beads". They generally have morphological and textural features similar to other 3.4-3.2 Ga old spherule layers of the Barberton Greenstone Belt. The Fairview spherule layers are stratigraphically positioned at the contact between the silicified volcanic tuff of the uppermost unit of the Onverwacht Group and the lowermost silicidastic rocks of the Fig Tree Group, like the S2 and S4 layers in the southern, and S3 layer in the northern, domain of the greenstone belt. Micro-XRF scanning allowed (i) to distinguish spherule layers from their host rocks by their major element distribution, and (ii) to characterize secondary alteration and micro-deformation features in the SL and host rocks. Ni-Cr spinel, the only primary mineral in evidence in these sections, is not distributed uniformly along a spherule layer intersection, and occurrences can not be stratigraphically correlated between the four layer intersections either. Spinel crystals vary with respect to Ni, Cr, Fe and Zn contents and respective zonation patterns for these elements. Zinc abundances are likely related to post-depositional hydrothermal overprint. The results of this investigation comprising geological, petrographic, semiquantitative micro-X-ray fluorescence spectrometry, and quantitative electron microprobe analysis on spinel support a complex and heterogeneous genetic process that must have taken place during spherule formation in an impact vapor plume and in post-depositional times. The Fairview spherule layers are thought to possibly represent the product of a single impact event. They represent fallout into deep-water conditions, as they lack evidence for reworking or sorting by current or wave action. The heterogeneous Ni-Cr spinet concentrations are similar to what has been reported for spinel occurrences in the S3 layer, but considering the complex tectonic overprint on this lithostratigraphic sequence at the changeover from the Onverwacht to the Fig Tree Group it is not possible to conclude whether or not these spherule layers represent the same impact event.

Two typical mineral textures of the MG 1 chromitite of the Bushveld Complex, South Africa, were observed; one characterised by abundant orthopyroxene oikocrysts, and the other by coarse-grained granular chromitite with only minor amounts of interstitial material. Oikocrysts form elongate clusters of several crystals aligned parallel to the layering, and typically have subhedral, almost chromite-free, core zones containing remnants of olivine. The core zones are surrounded by poikilitic aureoles overgrowing euhedral to subhedral chromite chadacrysts. Chromite grains show no preferred crystal orientation, whereas orthopyroxene grains forming clusters commonly share the same crystallographic orientation. Oikocryst core zones have lower Mg# and higher concentrations of incompatible trace elements compared to their poikilitic aureoles. Core zones are relatively enriched in REE compared to a postulated parental magma (B1) and did not crystallise in equilibrium with the surrounding minerals, whereas the composition of the poikilitic orthopyroxene is consistent with growth from the B1 magma. These observations cannot be explained by the classic cumulus and post-cumulus models of oikocryst formation. Instead, we suggest that the oikocryst core zones in the MG1 chromitite layer formed by peritectic replacement of olivine primocrysts by reaction with an upwards-percolating melt enriched in incompatible trace elements. Poikilitic overgrowth on oikocryst core zones occurred in equilibrium with a basaltic melt of B1 composition near the magma-crystal mush interface. Finally, adcumulus crystallisation followed by grain growth resulted in the surrounding granular chromitite.

Variations of mineral chemistry and whole-rock compositions were studied in detail, at millimetre to centimetre intervals, in two vertical drill core profiles through the platiniferous UG2 chromitite layer in the western and eastern limbs of the Bushveld Complex, South Africa. Analytical methods included electron microprobe and LA-ICP-MS analyses of the main rock-forming minerals, orthopyroxene, plagioclase and interstitial clinopyroxene. One profile was also studied by synchrotronsource XRF. Statistical analysis of crystal size distribution of chromite was also performed at different levels in the chromitite layer and in adjacent silicate rocks. The results provide new evidence for chemical and textural late magmatic re-equilibration in the UG2 layer and in the silicate rocks at the contact zones. The chromite crystal size distributions imply extensive coarsening of that mineral within the main chromitite seam, which has erased any textural evidence of primary deposition features such as recharge or mechanical sorting of crystals, if those features originally existed. The mineral compositions in chromitite differ from those in adjacent silicate rocks, in general agreement with predictions of chemical re-equilibration with evolved, residual melt (the trapped liquid shift effect). In detail, the geochemical data imply, however, that the conventional trapped liquid shift model has shortcomings, due to the effects of material transport driven by chemical gradients between modally contrasting layers of crystal mush undergoing re-equilibration reactions. In the presence of such gradients, selective open-system conditions may hold for alkalis and hydrogen because of their higher diffusion rates in silicate melts. Differential mobility of components in the interstitial melt can also sharpen the original modal layering by causing minerals to crystallise in one layer and dissolve in another. Detailed trace element profiles by synchrotron XRF reveal an uneven vertical distribution of incompatible elements which implies that the permeability of the chromitite layer may have been significant, even at the latest stages of interstitial crystallization.