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Carbonates, as secondary minerals found in CM chondrites, have been widely employed for reconstructing the composition of the fluids from which they precipitated. They also offer valuable insights into the hydrothermal evolution of their parent bodies. In this study, we demonstrate that high‐resolution cathodoluminescence (HR‐CL) analyses of calcites derived from the brecciated Cold Bokkeveld CM2 chondrite can effectively reveal subtle compositional features and intricate zoning patterns. We have identified two distinct types of cathodoluminescence (CL) centers: a blue emission band (approximately 375–425 nm), associated with intrinsic structural defects, and a lower energy orange extrinsic emission (around 620 ± 10 nm), indicating the presence of Mn cations. These compositional variations enable discrimination between the calcite grain types previously designated as T1 and T2 in studies of CM chondrites. T1 calcites exhibit variable CL and peripheral Mn enrichments, consistently surrounded by a rim composed of Fe‐S‐rich serpentine–tochilinite assemblage. Conversely, T2 calcites display homogeneous CL and more abundant lattice defects. These polycrystalline aggregates of calcite grains, devoid of serpentine, contain Fe‐Ni sulfide inclusions and directly interface with the matrix. We propose that changes in the Mn content of calcite (indicated by the intensity of orange CL emission) are influenced by variations in redox potential (Eh) and pH of the fluid phase. This proposed hydrothermal evolution establishes a parallel between terrestrial serpentinization followed by carbonation processes and the aqueous alteration of CM chondrites, warranting further exploration and investigation of this intriguing similarity. [ABSTRACT FROM AUTHOR]

The discovery of the Ischgl meteorite unfolded in a captivating manner. In June 1976, a pristine meteorite stone weighing approximately 1 kg, fully covered with a fresh black fusion crust, was collected on a mountain road in the high‐altitude Alpine environment. The recovery took place while clearing the remnants of a snow avalanche, 2 km northwest of the town of Ischgl in Austria. Subsequent to its retrieval, the specimen remained tucked away in the finder's private residence without undergoing any scientific examination or identification until 2008, when it was brought to the University of Innsbruck. Upon evaluation, the sample was classified as a well‐preserved LL6 chondrite, with a W0 weathering grade, implying a relatively short time between the meteorite fall and its retrieval. To investigate the potential connection between the Ischgl meteorite and a recorded fireball event, we have reviewed all documented fireballs ever photographed by German fireball camera stations. This examination led us to identify the fireball EN241170 observed in Germany by 10 different European Network stations on the night of November 23/24, 1970, as the most likely candidate. We employed state‐of‐the‐art techniques to reconstruct the fireball's trajectory and to reproduce both its luminous and dark flight phases in detail. We find that the determined strewn field and the generated heat map closely align with the recovery location of the Ischgl meteorite. Furthermore, the measured radionuclide data reported here indicate that the pre‐atmospheric size of the Ischgl meteoroid is consistent with the mass estimate inferred from our deceleration analysis along the trajectory. Our findings strongly support the conclusion that the Ischgl meteorite originated from the EN241170 fireball, effectively establishing it as a confirmed meteorite fall. This discovery enables to determine, along with the physical properties, also the heliocentric orbit and cosmic history of the Ischgl meteorite. [ABSTRACT FROM AUTHOR]

Diogenites, which are part of the howardite–eucrite–diogenite (HED) group, are considered to represent rocks from the lower crust and mantle of a differentiated planetary body, likely the asteroid 4 Vesta. The Northwest Africa 12973 (NWA 12973) meteorite was classified as an anomalous diogenite due to the occurrence of a vesiculated layer. This work reports on the petrographic and geochemical study of two fragments of this meteorite, aiming to better constrain the origin of the vesiculated layer. Whereas the interior of NWA 12973 (here called host) presents the typical characteristics of an olivine diogenite, that is, coarse‐grained pyroxene, olivine ribbons, chromite, and accessory phases, the vesiculated layer presents a fine‐grained pyroxene groundmass with local rounded relics of olivine and interstitial chromite and metal, and is characterized by abundant large vesicles. The contact between the vesiculated layer and the host is sharply defined. The composition of individual minerals does not show any significant differences between the host and the vesiculated layer, suggesting in situ melting. Geothermobarometry indicates a slightly higher crystallization temperature at lower pressure for the vesiculated layer, consistent with melting and crystallization under lower crustal conditions upon exhumation. The trigger for the local melting was likely a large impact event, which was responsible for adiabatic decompression in the central area or deep faulting and frictional melting. [ABSTRACT FROM AUTHOR]

Understanding dendritic crystallization is key to obtaining petrological information about rapid crystallization events. Clinopyroxene dendrites from a basaltic rock fulgurite from Nagpur, India, exhibit curved branches with corresponding lattice rotation that exceeds 180° for some branches. This paper combines crystallographic orientation mapping with microstructural observations and compositional information to determine the dendrites' 3-D morphology and their bending mechanism. Dendrites exhibit a network of branches in the (010) plane, following either {001}* (normal to {001} planes, strong lattice curvature) or < 10–1 > (weak lattice curvature). Three or more orders of branches are observed in the (010) plane, alternating between {001}* and < 10–1>. Side branches with weak lattice curvature extend sub-perpendicular to the (010) plane, following either {021}* (sprouting from {001}* branches) or < 12–1 > (from <10–1 > branches) and defining curved 'ribbons' containing their respective central branch. All branches rotate about [010], with a consistent rotation sense regardless of elongation direction in sample or crystal coordinates. Bending must therefore be caused by local asymmetric thermal and compositional fields in the melt, generated by dendritic growth itself, not by sample-scale compositional, thermal or mechanical gradients. The most likely cause of bending is asymmetric distribution of melt supersaturation around branch tips, related to unequal growth rates perpendicular to different facets. Lattice rotation is inferred to occur via preferential incorporation of high densities of [001] (100) edge dislocations of one sign. High inferred dislocation densities imply that the preservation of bent dendrites requires rapid quenching. Higher inferred degree of undercooling (based on microstructural observations) correlates with greater lattice curvature. Bent dendrites can thus potentially be used to deliver information about spatial variations in degree of undercooling and place limits on the history of a sample after dendritic crystallization. Finally, finding lattice rotation exclusively about [010] is a new criterion to identify cryptic dendritic growth stages in euhedral crystals. [ABSTRACT FROM AUTHOR]

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6–(Ca)M2(Al)M1(AlSi) TO6–(⎕)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields (if any) and synthesis pathways, considered together with textural constraints, have different implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences casts a new light on many previous conclusions about the shock histories preserved in particular meteorites. [ABSTRACT FROM AUTHOR]

The Nova Colinas structure is an approximately 7 km wide, nearly circular feature centered at 07°09′33″S/46°06′30″W in Nova Colinas municipality in southwestern Maranhão State, Brazil. The area has been investigated for 40 yr and it has been suggested repeatedly that the structure could be of impact origin—without proof having been furnished. Magnetic anomaly maps depict the structure clearly with a strong, positive magnetic anomaly over the apparent rim zone. The central area is characterized by significant positive K and Th radiometric anomalies. Fieldwork showed that the structure has annular features along the outside and some prominent, structurally dissected hills in the interior. Thirty‐three arenite samples were collected for petrographic analysis, mostly from within the structure. Microdeformation, in the form of cataclasis; concussion fractures related to compaction, and presence of planar fractures, feather features, and planar deformation features in quartz are reported. Three samples with a multitude of quartz grains with these microdeformations were analyzed by universal stage to determine the crystallographic orientations of planar fractures and planar deformation features. The results provide robust evidence that these microdeformation features represent shock metamorphism, with low (approximately 5–10 GPa) to moderate (10–16 and 10–20 GPa) shock levels. Thus, the Nova Colinas structure is now confirmed as a bona fide meteorite impact structure. The structure is moderately eroded, as shown by the absence of stronger shock deformation. The still limited available structural geological field evidence, paired with remote sensing and geophysical data, indicates that the innermost part of the structure may have a sizable remnant of a central uplift. The Nova Colinas impact age is only poorly constrained from stratigraphic inference to an upper limit of about 200–250 Ma. [ABSTRACT FROM AUTHOR]

The hydrogen emission from meteors is assumed to originate mainly from the meteoroid composition, making it a potential tracer of H2O molecules and organic compounds. H α line was previously detected in individual fireballs, but its variation in a larger meteor data set and dependence on the dynamical origin and physical properties have not yet been studied. Here, we investigate the relative intensity of H α within 304 meteor spectra observed by the AMOS (All-sky Meteor Orbit System) network. We demonstrate that H α emission is favoured in faster meteors (vi > > 30 km s−1) which form the high-temperature spectral component. H α was found to be a characteristic spectral feature of cometary meteoroids with ∼92 per cent of all meteoroids with detected H α originating from Halley-type and long-period orbits. Our results suggest that hydrogen is being depleted from meteoroids with lower perihelion distances (q < 0.4 au). No asteroidal meteoroids with detected H emission were found. However, using spectral data from simulated ablation of different meteorite types, we show that H emission from asteroidal materials can occur, and apparently correlates with their water and organic matter content. Strongest H emission was detected from carbonaceous chondrites (CM and CV) and achondrites (ureilite and aubrite), while it was lacking in most ordinary chondrites. The detection of H α in asteroidal meteoroids could be used to identify meteoroids of carbonaceous or achondritic composition. Overall, our results suggest that H α emission correlates with the emission of other volatiles (Na and CN) and presents a suitable tracer of water and organic matter in meteoroids. [ABSTRACT FROM AUTHOR]

The formation and shock history of ureilite meteorites, a relatively abundant type of primitive achondrites, has been debated for decades. For this purpose, the characterization of carbon phases can provide further information on diamond and graphite formation in ureilites, shedding light on the origin and history of this meteorite group. In this work, we present X‑ray diffraction and micro-Raman spectroscopy analyses performed on diamond and graphite occurring in the ureilite Yamato 74123 (Y-74123). The results show that nano- and microdiamonds coexist with nanographite aggregates. This, together with the shock-deformation features observed in olivine, such as mosaicism and planar fractures, suggest that diamond grains formed by a shock event (≥15 GPa) on the ureilitic parent body (UPB). Our results on Y-74123 are consistent with those obtained on the NWA 7983 ureilite and further support the hypothesis that the simultaneous formation of nano- and microdiamonds with the assistance of a Fe-Ni melt catalysis may be related to the heterogeneous propagation and local scattering of the shock wave. Graphite geothermometry revealed an average recorded temperature (Tmax) of 1314 °C (±120 °C) in agreement with previously estimated crystallization temperatures reported for graphite in Almahata Sitta ureilite. [ABSTRACT FROM AUTHOR]

Tin Bider is a 6‐km‐diameter complex impact structure, the largest one recognized in Algeria. The crater was excavated in Cretaceous sedimentary rocks composed of, from the base to the top, Albian sandstones, Cenomanian clays, Cenomanian‐Turonian limestones, undifferentiated Coniacian to Maastrichtian clays and limestones. The age of the impact event is poorly constrained to <66 Ma by stratigraphy, the youngest geological unit affected by the event being the ~66 Myr old Maastrichtian limestones. Albian sandstones outcrop in the central sector of the structure and represent the only occurrence at outcrop of this geological unit in the structure. Here we report on a detailed petrographic analysis of eight Albian sandstone samples that were searched for shock‐metamorphic features. We confirm the presence of rare shocked quartz grains with planar deformation features (PDFs) and report on their crystallographic orientations as determined using the universal stage microscope. PDFs oriented parallel to the π{101¯2} and ω{101¯3} orientations are the most abundant ones. For the first time in impactites from Tin Bider, PDFs with basal (0001) orientation, corresponding to amorphized mechanical Brazil twins, are reported. Our results indicate that locally the peak shock pressure was of at least 20 GPa, but much lower in average for the investigated samples. [ABSTRACT FROM AUTHOR]

Natural glass occurs on Earth in different geological contexts, mainly as volcanic glass, fulgurites, and impact glass. All these different types of glasses are predominantly composed of silica with variable amounts of impurities, especially the alkalis, and differ in their water content due to their mode of formation. Distinguishing between different types of glasses, on Earth and also on the Moon and on other planetary bodies, can be challenging. This is particularly true for glasses of impact and volcanic origin. Because glass is often used for the determination of the age of geological events, even if out of geological context, as well as to derive pressure and temperature constraints, or to evaluate the volatile contents of magmas and their source regions, we rely on methods that can unambiguously distinguish between the different types of glasses. We used the case of the Cali glass, found in an extended area close to the city of Cali in western Colombia, which was previously suggested to be of impact or volcanic origin, to show that, using a multimethod approach (i.e., combining macroscopic observations, chemical and isotopic data, and H2O content), it is possible to distinguish between different formation modes. A suite of Cali glass samples was analyzed using electron microprobe, instrumental neutron activation analysis, thermal ionization mass spectrometry, and Fourier-transform infrared spectroscopy, allowing us to definitively exclude an impact origin and instead classify these glasses as a rhyolitic volcanic glass (obsidian). Our results suggest that other "unusual glass occurrences" that are claimed, but not convincingly proven, to be of impact origin should be reexamined using the same methodology as that applied here. [ABSTRACT FROM AUTHOR]

The IODP‐ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ˜600 m of near continuous crystalline basement within the peak ring of the Chicxulub impact structure. The bulk of the basement consists of pervasively deformed, fractured, and shocked granite. Detailed geochemical investigations of 41 granitoid samples, that is, major and trace element contents, and Sr–Nd isotopic ratios are presented here, providing a broad overview of the composition of the granitic crystalline basement. Mainly granite but also granite clasts (in impact melt rock), granite breccias, and aplite were analyzed, yielding relatively homogeneous compositions between all samples. The granite is part of the high‐K, calc‐alkaline metaluminous series. Additionally, they are characterized by high Sr/Y and (La/Yb)N ratios, and low Y and Yb contents, which are typical for adakitic rocks. However, other criteria (such as Al2O3 and MgO contents, Mg#, K2O/Na2O ratio, Ni concentrations, etc.) do not match the adakite definition. Rubidium–Sr errorchron and initial 87Sr/86Srt=326Ma suggest that a hydrothermal fluid metasomatic event occurred shortly after the granite formation, in addition to the postimpact alteration, which mainly affected samples crosscut by shear fractures or in contact with aplite, where the fluid circulation was enhanced, and would have preferentially affected fluid‐mobile element concentrations. The initial (ɛNd)t=326Ma values range from −4.0 to 3.2 and indicate that a minor Grenville basement component may have been involved in the granite genesis. Our results are consistent with previous studies, further supporting that the cored granite unit intruded the Maya block during the Carboniferous, in an arc setting with crustal melting related to the closure of the Rheic Ocean associated with the assembly of Pangea. The granite was likely affected by two distinct hydrothermal alteration events, both influencing the granite chemistry: (1) a hydrothermal metasomatic event, possibly related to the first stages of Pangea breakup, which occurred approximately 50 Myr after the granite crystallization, and (2) the postimpact hydrothermal alteration linked to a long‐lived hydrothermal system within the Chicxulub structure. Importantly, the granites sampled in Hole M0077A are unique in composition when compared to granite or gneiss clasts from other drill cores recovered from the Chicxulub impact structure. This marks them as valuable lithologies that provide new insights into the Yucatán basement. [ABSTRACT FROM AUTHOR]

Northwest Africa (NWA) 11962 is a lunar regolith breccia composed of a wide range of different clasts. The lunar origin of this meteorite is confirmed by oxygen isotope analysis and the Fe/Mn ratio in pyroxene and olivine. In the present study, the clasts and the matrix of NWA 11962 are characterized by optical and electron microscopy along with electron microprobe analyses and micro‐Raman spectroscopy. The meteorite has a glassy impact melt matrix, which accounts for 35% of the surface area in the two thin sections examined, and which contains a very large variety of different lithic clasts, monomineralic clasts, and glass fragments. The presence of volcanic and impact‐related glass spherules led to the classification of this meteorite as a regolith breccia. Lithic clasts include numerous fragments of quartz monzogabbro and lunar felsite, which are quite rare lithologies in the lunar alkali suite. However, the most abundant components in the breccia are gabbroic clasts. The mineral chemistry of the pyroxenes in the gabbroic clasts and the chemistry of various types of glass fragments in the breccia indicate an origin of the regolith from an area with low‐Ti to high‐Ti mare basalt volcanism. In addition to the peculiar petrographic characteristics of NWA 11962, the possible pairing relationships with other lunar meteorites are discussed. [ABSTRACT FROM AUTHOR]

The geochemistry and textures of phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained. We assessed phosphorus‐bearing minerals in the three lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques. The majority of studied phosphate grains appear intergrown with olivine. However, microtextures of phosphates (apatite [Ca5(PO4)3(OH,Cl,F)] and merrillite [Ca9NaMg(PO4)7]) are extremely variable within and between the differently shocked lithologies investigated. We observe continuously strained as well as recrystallized strain‐free merrillite populations. Grains with strain‐free subdomains are present only in the more intensely shocked dark lithology, indicating that phosphate growth predates the development of primary shock‐metamorphic features. Complete melting of portions of the meteorite is recorded by the shock‐melt lithology, which contains a population of phosphorus‐rich olivine grains. The response of phosphorus‐bearing minerals to shock is therefore hugely variable throughout this monomict impact breccia. We propose a paragenetic history for P‐bearing phases in Chelyabinsk involving initial phosphate growth via P‐rich olivine replacement, followed by phosphate deformation during an early impact event. This event was also responsible for the local development of shock melt that lacks phosphate grains and instead contains P‐enriched olivine. We generalize our findings to propose a new classification scheme for Phosphorus‐Olivine‐Assemblages (Type I–III POAs). We highlight how POAs can be used to trace radiogenic metamorphism and shock metamorphic events that together span the entire geological history of chondritic asteroids. [ABSTRACT FROM AUTHOR]

This article describes a novel high frame rate emission spectroscopy setup developed for measurements in high enthalpy flow fields. The optical setup and the associated hardware arrangements are described in detail followed by test case data to demonstrate the capability of recording spectral images at 1 kHz frame rate. The new system is based on a classical Czerny–Turner spectrograph but with a particular setup for high frame rate detection using a Generation II intensifier coupled with a high-speed camera. The high frame rate spectral images acquired enable, for the first time, investigation of the spatial distribution and temporal tracking and evolution of molten droplets of an ablating sample. In this paper, an example is shown from ablating meteorite samples tested in a high enthalpy plasma flow field corresponding to a flight scenario at an altitude of 80 km. This new instrumental configuration allows emission spectroscopic analysis of transient phenomena simulated in the high enthalpy ground test facilities with kHz resolution. The particular feature of this system is the ability to measure very faint spectral lines at high temporal and spatial resolution. [ABSTRACT FROM AUTHOR]

Shocked quartz and feldspar grains commonly exhibit planar microstructures, such as planar fractures, planar deformation features, and possibly microtwins, which are considered to have formed by shock metamorphism. Their orientation and frequency are typically reported to be randomly distributed across a sample. The goal of this study is to investigate whether such microstructures are completely random within a given sample, or whether their orientation might also retain information on the direction of the local shock wave propagation. For this work, we selected samples of shatter cones, which were cut normal to the striated surface and the striation direction, from three impact structures (Keurusselkä, Finland, and Charlevoix and Manicouagan, Canada). These samples show different stages of pre‐impact tectonic deformation. Additionally, we investigated several shocked granite samples, selected at different depths along the drill core recovered during the joint IODP‐ICDP Chicxulub Expedition 364 (Mexico). In this case, thin sections were cut along two orthogonal directions, one parallel and one normal to the drill core axis. All the results refer to optical microscopy and universal‐stage analyses performed on petrographic thin sections. Our results show that such shock‐related microstructures do have a preferred orientation, but also that relating their orientation with the possible shock wave propagation is quite challenging and potentially impossible. This is largely due to the lack of dedicated experiments to provide a key to interpret the observed preferred orientation and to the lack of information on postimpact orientation modifications, especially in the case of the drill core samples. [ABSTRACT FROM AUTHOR]