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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. Some-times, 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.

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.

Dendritic crystallisation is a key geological pattern-forming mechanism, typical of, and recording information about, rapid crystallization events. In this contribution we report on clinopyroxene (Cpx) dendrites in a basaltic rock fulgurite, which formed due to electrical discharge impacting a basaltic rock. Unusually, these dendrites exhibit a curved morphology. The curved, tapering main dendrite branches are up to 50 µm long, range from 3 µm to 100 nm thickness, and are surrounded by several higher orders of branches, which are also curved. The morphological curvature corresponds to lattice rotation, so branches have consistent elongation directions in crystal coordinates. Total rotation exceeds 180° for some branches, with the highest curvature found being 7° per µm. Such “bent” Cpx dendrites have been observed in experiments (e.g. Hammer et al. 2010), but the mechanism of bending was not previously understood.By combining microstructural observations with crystallographic orientation maps from electron backscatter diffraction analyses of multiple Cpx dendrites, their three-dimensional morphological and crystallographic configuration was reconstructed. Dendrites feature a planar latticework of branches parallel to the Cpx (010) plane. Branches in this plane are elongated either parallel to {001}* (i.e. normal to the (001) plane) or , and exhibit strong and weak lattice curvature, respectively. Sprouting out of this plane are branches parallel to {021}* (originating from {001}* branches) and (originating from branches), both types being weakly curved. Regardless of the crystallographic direction parallel to elongation, all branches exhibit a crystallographic rotation axis parallel to [010] of Cpx. Furthermore, the rotation sense is consistent regardless of elongation direction in crystal or sample coordinates.The crystallographic control on the sense of bending and on the rotation axis indicates that bending is not caused by sample-scale compositional, thermal, or mechanical gradients. Instead, asymmetric compositional and thermal fields around branch tips are responsible for bending, supported by the fact that compositional gradients exist in the glass surrounding dendritic crystals. The specific cause of bending is inferred to be asymmetric distribution of melt supersaturation at branch tips, resulting from unequal growth rates of different facets. Branch-tip morphology alone poorly explains the constant sense of rotation of all branches, as the sense of morphological asymmetry is unlikely to be consistent for all branch types. The [010] rotation axis implies that lattice rotation is accomplished by incorporation of a single sign of [001](100) edge dislocations, with a maximum inferred density of 2*1014 m-2.This work provides new insights into fundamental processes occurring during rapid crystallization of Cpx and other minerals. Furthermore, microstructural observations suggest that higher degree of undercooling correlates with greater lattice curvature. Bent dendrites may thus encode information about spatial variations in the cooling rate and/or undercooling of samples. Finally, the consistent [010] rotation axis is expected to be preserved during recrystallization, offering a potential way to identify curved dendritic growth stages even after recrystallization.References:Hammer et al. (2010), Geology 38:367-370. https://doi.org/10.1130/G30601.1Griffiths et al. (2022), J Petrol, egac125. https://doi.org/10.1093/petrology/egac125This contribution was funded by the Austrian Science Fund (FWF): P 33227-N

We report a huge organic diversity in the Tissint Mars meteorite and the sampling of several mineralogical lithologies, which revealed that the organic molecules were nonuniformly distributed in functionality and abundance. The range of organics in Tissint meteorite were abundant C 3-7 aliphatic branched carboxylic acids and aldehydes, olefins, and polyaromatics with and without heteroatoms in a homologous oxidation structural continuum. Organomagnesium compounds were extremely abundant in olivine macrocrystals and in the melt veins, reflecting specific organo-synsthesis processes in close interaction with the magnesium silicates and temperature stresses, as previously observed. The diverse chemistry and abundance in complex molecules reveal heterogeneity in organic speciation within the minerals grown in the martian mantle and crust that may have evolved over geological time.

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 (weak lattice curvature). Three or more orders of branches are observed in the (010) plane, alternating between {001}* and . Side branches with weak lattice curvature extend sub-perpendicular to the (010) plane, following either {021}* (sprouting from {001}* branches) or (from 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.

The occurrence of shock-induced diamonds in ureilite meteorites is common and is used to constrain the history of the ureilite parent bodies. We have investigated a fragment of the Kenna ureilite by micro-X-ray diffraction, micro-Raman spectroscopy and scanning electron microscopy to characterize its carbon phases. In addition to olivine and pigeonite, within the carbon-bearing areas, we identified microdiamonds (up to about 10 μm in size), nanographite and magnetite. The shock features observed in the silicate minerals and the presence of microdiamonds and nanographite indicate that Kenna underwent a shock event with a peak pressure of at least 15 GPa. Temperatures estimated using a graphite geothermometer are close to 1180 °C. Thus, Kenna is a medium-shocked ureilite, yet it contains microdiamonds, which are typically found in highly shocked carbon-bearing meteorites, instead of the more common nanodiamonds. This can be explained by a relatively long shock event duration (in the order of 4–5 s) and/or by the catalytic effect of Fe-Ni alloys known to favour the crystallization of diamonds. For the first time in a ureilite, carletonmooreite with formula Ni3Si and grain size near 4–7 nm, was found. The presence of nanocrystalline carletonmooreite provides further evidence to support the hypothesis of the catalytic involvement of Fe-Ni bearing phases into the growth process of diamond from graphite during shock events in the ureilite parent body, enabling the formation of micrometer-sized diamond crystals.

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.

The possibility of a "death from above" cause for biotic crises and extinction events is intriguing, to say the least, but such claims must be supported by reliable and reproducible data, not only impact diagnostic criteria, but also accurate and precise radioisotopic ages of the impact structures/events. To date, only one example of such an impact-related global extinction event is confirmed, at the end of the Cretaceous period. Here we present and discuss results of newly obtained Ar-40/Ar-39 data from step heating analysis of impact melt rock samples from the 40 km-in-diameter Puchezh-Katunki impact structure, Russia, which allow us to precisely and accurately date its formation at 195.9 +/- 1.0 Ma (2 sigma; P = 0.10). Based on these new data, we challenge the proposed temporal correlation with as many as five different extinction events (including the end-Triassic mass extinction) that were based on previous age estimations ranging from similar to 164 to 203 Ma. Our new age for the formation of the Puchezh-Katunki impact structure allows us to exclude a relationship between this impact event and a known extinction event. We also show that careful sample preparation and methodology can overcome problems with inherited and trapped Ar-40, issues that are common when dating impact melt rocks. This is supported by Ar-40* diffusion and mixing numerical models showing that the most prominent negative effects in the case of the Puchezh-Katunki impact melt rock samples are caused by hydrothermal alteration and undegassed melt rock domains present in an otherwise homogenized melt rock. Numerical modeling also shows that the Ar-40* from high-Ca inherited crystals or clasts is decoupled from the melt rock during step heating experiments allowing to safely recover a plateau age. Finally, our results highlight the importance of improving the database of ages of impact structures and show that caution should be practiced when suggesting connections between specific impact events and extinction events, especially in the case of poorly dated impact structures. (C) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Hydrothermal activity is a common phenomenon in the wake of impact events, yet identifying and dating impact hydrothermal systems can be challenging. This study provides the first detailed assessment of the effects of shock microstructures and impact-related alteration on the U-Pb systematics and trace elements of titanite (CaTiSiO5), focusing on shocked granite target rocks from the peak ring of the Chicxulub impact structure, Mexico. A > 1 mm long, shock-twinned titanite grain preserves a dense network of irregular microcracks, some of which exploit shock twin interfaces. Secondary microcrystalline anatase and pyrite are heterogeneously distributed along some microcracks. In situ laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICPMS) analysis reveals a mixture of three end-member Pb components. The Pb components are: 1) common Pb, consistent with the Pb isotopic signature of adjacent alkali feldspar; 2) radiogenic Pb accumulated since magmatic crystallization; and 3) a secondary, younger Pb signature due to impact-related complete radiogenic Pb loss. The youngest derived ages define a regression from common Pb that intersects Concordia at 67 ± 4 Ma, in agreement with the established age of 66.04 ± 0.05 Ma for the Chicxulub impact event. Contour maps of LA-MC-ICPMS data reveal that the young ages are spatially restricted to microstructurally-complex domains that correlate with significant depletion in trace elements (REE-Y-Zr-Nb-Mo-Sn-Th) and reduction in magnitude of the Eu/Eu* anomaly. Mapping by time-of-flight secondary ion mass spectrometry (ToF-SIMS) show that patterns of localised element depletion in titanite are spatially related to microcracks, which are enriched in Al. The spatial correlation of ages and trace element abundance is consistent with localised removal of Pb and other trace elements from a pervasive network of fast fluid pathways in fractured domains via a fluid-mediated element transport process associated with the impact event. Here we interpret the 67 ± 4 Ma U-Pb age to represent hydrothermal Pb-loss in the Chicxulub peak ring in the wake of the impact event. These results highlight the potential of our analytical approach using titanite geochronology and geochemistry for dating post-impact hydrothermal activity in impact structures elsewhere.

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.

This study presents a new classification of a ∼100-m-thick crater suevite sequence in the recent International Ocean Discovery Program (IODP)-International Continental Scientific Drilling Program (ICDP) Expedition 364 Hole M0077A drill core to better understand the formation of suevite on top of the Chicxulub peak ring. We provide an extensive data set for this succession that consists of whole-rock major and trace element compositional data (n = 212) and petrographic data supported by digital image analysis. The suevite sequence is subdivided into three units that are distinct in their petrography, geochemistry, and sedimentology, from base to top: the ∼5.6-m-thick non-graded suevite unit, the ∼89-m-thick graded suevite unit, and the ∼3.5-m-thick bedded suevite unit. All of these suevite units have isolated Cretaceous planktic foraminifera within their clastic groundmass, which suggests that marine processes were responsible for the deposition of the entire M0077A suevite sequence. The most likely scenario describes that the first ocean water that reached the northern peak ring region entered through a N-NE gap in the Chicxulub outer rim. We estimate that this ocean water arrived at Site M0077 within 30 minutes after the impact and was relatively poor in rock debris. This water caused intense quench fragmentation when it interacted with the underlying hot impact melt rock, and this resulted in the emplacement of the ∼5.6-m-thick hyaloclastite-like, non-graded suevite unit. In the following hours, the impact structure was flooded by an ocean resurge rich in rock debris, which caused the phreatomagmatic processes to stop and the ∼89-m-thick graded suevite unit to be deposited. We interpret that after the energy of the resurge slowly dissipated, oscillating seiche waves took over the sedimentary regime and formed the ∼3.5-m-thick bedded suevite unit. The final stages of the formation of the impactite sequence (estimated to be

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.

Highly sensitive nondestructive HPGe gamma-ray spectrometry was used for the analysis of the cosmogenic (26Al) and primordial (40K, 238U, and 232Th) radionuclides in the Oued Awlitis 001 and Galb Inal lunar meteorites. The measured 26Al activities were very different (84.0 ± 4.8 dpm/kg vs. 8.4 ± 1.2 dpm/kg, respectively), mainly because of different cosmic-ray exposure ages of the investigated meteorites. The pre-atmospheric radii were 5 ± 1 cm and 11 ± 2 cm, respectively, which would result in total pre-atmospheric masses in the range of 0.7–2.5 kg and 7–23 kg, respectively.

The Kundelungu Plateau in the southeast of the Democratic Republic of the Congo (DRC) hosts numerous kimberlites, but up to now, only 34 bodies have been mapped. Locating these occurrences is hampered by the presence of sand cover on the plateau, a few tens of meters thick. Thus, most of the known pipes occur at the edge of the plateau where erosion has removed most of the sand cover. We report here on the Katuba kimberlite, a volcaniclastic kimberlite typical of a diatreme environment, with xenoliths of peridotite, carbonate, sandstone and shale, and lapilli-like microstructures. U-Pb analysis of perovskites from the Katuba kimberlite provides an age of 23 ± 1.8 Ma for the intrusion. Considering the age of 33 ± 4 Ma for perovskites from the Msipashi kimberlite pipe (also located on the same plateau), this new age suggests that the kimberlite magmatism in the Kundelungu Plateau lasted at least for 10 myr. The emplacement of these kimberlites is coeval with the opening of the Mweru graben, which is part of the East African Rift System (EARS), with structures oriented generally NW-SE and NE-SW. Some copper mineralisations inside the Katanga copperbelt, including those at Dikulushi and Kipushi, are located in similar structures, suggesting that the fluids responsible for the remobilisation of the mineralisation may be related to the kimberlite magmatism. Alternatively, the trigger for both the remobilisation of the mineralisation and the kimberlite magmatism is the tectonism that lead to the opening of the EARS. The upwelling of the asthenosphere or the mantle plume associated with the kimberlite magmatism may have supplied sufficient heat for fluid generation or contributed to the remobilisation of fluids. The location of the Katuba kimberlite along the NW-SE structures that were reactivated during the rifting inducing the opening of the Mweru graben, and which themselves are crosscut by the Luizi impact structure, provides another constraint on the relative age of the Luizi structure, which must be younger than the NW-SE structures and older than the emplacement of the Katuba kimberlite.

The Puchezh-Katunki impact structure, 40–80 km in diameter, located ~400 km northeast of Moscow (Russia), has a poorly constrained age between ~164 and 203 Ma (most commonly quoted as 167 ± 3 Ma). Due to its relatively large size, the Puchezh-Katunki structure has been a prime candidate for discussions on the link between hypervelocity impacts and extinction events. Here, we present new 40Ar/39Ar data from step-heating analysis of five impact melt rock samples that allow us to significantly improve the age range for the formation of the Puchezh-Katunki impact structure to 192–196 Ma. Our results also show that there is not necessarily a simple relationship between the observed petrographic features of an impact melt rock sample and the obtained 40Ar/39Ar age spectra and inverse isochrons. Furthermore, a new palynological investigation of the postimpact crater lake sediments supports an age significantly older than quoted in the literature, i.e., in the interval late Sinemurian to early Pliensbachian, in accordance with the new radioisotopic age estimate presented here. The new age range of the structure is currently the most reliable age estimate of the Puchezh-Katunki impact event. (Less)

The abstract is available here: https://uscholar.univie.ac.at/o:1095789

Four impact structures are known from the Republic of Kazakhstan, most of which have been poorly studied. This includes the Shili impact structure, an ~1.5-km-wide circular feature visible in satellite imagery. It is located in the western part of Kazakhstan, in the Aktobe Region, where the structure is centered at 49°10.5′N and 57°50′E. While the structure was first considered to be a salt diapir, its impact origin was confirmed in 1989 based on the findings of rare shocked quartz grains and a few poorly developed “shatter cones.” In this contribution, we report the results of a field campaign and a detailed petrographic investigation of 15 quartz sandstone samples. We confirm the presence of rare shocked quartz grains with planar fractures (PFs) and planar deformation features (PDFs). The characterization of shocked quartz allows us to not only confirm the impact origin of the structure, but also to estimate a shock pressure of at least 16 GPa (with a local peak-shock pressure of at least 20 GPa) for some of the rocks now outcropping at the surface. Signs of postimpact hydrothermal alteration include the decoration of many of the PDFs and the occurrence of fractures filled with secondary silica in a few samples. The name and some statistics commonly reported for this structure are also discussed. We suggest the structure be referred as “Shili,” after the name of a nearby river and also that of a phytonym. The minimum original diameter of the Shili impact crater is estimated at ~4–5 km based on a minimum central uplift diameter of 1 km. An early Eocene to Pliocene age for the formation of the Shili impact structure is inferred based on stratigraphy.

This volume represents the proceedings of the homonymous international conference on all aspects of impact cratering and planetary science, which was held in October 2019 in Brasília, Brazil. The volume contains a sizable suite of contributions dealing with regional impact records (Australia, Sweden), impact craters and impactites, early Archean impacts and geophysical characteristics of impact structures, shock metamorphic investigations, post-impact hydrothermalism, and structural geology and morphometry of impact structures—on Earth and Mars. Many contributions report results from state-of-the-art investigations, for example, several that are based on electron backscatter diffraction studies, and deal with new potential chronometers and shock barometers (e.g., apatite). Established impact cratering workers and newcomers to the field will appreciate this multifaceted, multidisciplinary collection of impact cratering studies.

The IODP-ICDP Expedition 364 drilling recovered a 829 m core from Hole M0077A, sampling ~600 meters 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 forty-one granitoid samples, i.e., 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 in situ 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 adakites. However, other criteria (such as Al2O3 and MgO contents, Mg#, K2O/Na2O ratios, Ni concentrations, etc.) do not match the adakite definition. In addition, initial 87Sr/86Srt=326 Ma is indicative of an hydrothermal fluid metasomatic event occurring shortly after the granite formation, affecting mainly 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 εNd (t=326 Ma) values range from -4.0 to 3.2 for the samples which were less affected by the hydrothermal overprint and indicate that a minor Grenville basement component may be 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 with the closure of the Rheic ocean associated with the assembly of Pangea. Then, an hydrothermal metasomatic event, possibly related to the initial breakup of Pangea, occurred ca. 50 Myr after the granite crystallization. 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 insight into the Yucatán basement.

On February 28, 2020 at 09:30:32 UTC, a daytime superbolide was observed over southeastern Slovenia and neighbouring countries1. In the following days, three meteorite pieces (469, 203, and 48 grams)2 were recovered nearby the Slovenian city of Novo Mesto by local people. The meteorite was classified as an L5 ordinary chondrite, more or less brecciated and shocked. In this work we reconstruct the trajectory using the available video data which consist of two static security cameras and four dash cameras mounted on cars in motion (Figure 1). We use a new radial distortion method developed by Vida et al. (2021) to accurately model the lens distortion of individual cameras and we determine the position of the vehicles to a precision of several centimetres on every video frame. Figure 1. Map of observer locations and the fireball trajectory (red line). The preliminary trajectory was computed using the lines of sight method and the trajectory uncertainties were computed using the Monte Carlo method (Vida et al., 2020) by adding 3σ noise to the original measurements. The fireball was first observed at a height of 68.7 km and it reached an end height of 17.1 km. The fireball had an entry angle of 47.812° ± 0.096° and an initial velocity of 22.098 ± 0.012 km/s (computed using measurements above 45 km, i.e. before any noticeable deceleration was visible). Figure 2 shows that the average per-station trajectory spatial fit errors were around 100 m (200 m maximum). More observations will be included in a future analysis. Figure 2. Spatial trajectory fit residuals. The Tkon and Senj stations were fixed security cameras, but only Tkon was calibrated on stars. The fireball had the following geocentric radiant (J2000): R.A. 330.920 ± 0.095 deg Dec +2.320 ± 0.098 deg VG 18.991 ± 0.014 km/s LG 333.802 ± 0.093 deg BG +13.319 ± 0.103 deg The computed orbit is: La Sun 338.983613 deg q 0.5679 ± 0.0011 AU a 1.451 ± 0.004 AU e 0.60866 ± 0.0006 i 8.755 ± 0.063 deg peri 82.649 ± 0.184 deg node 338.993041 deg T 1.7473 ± 0.0072 years TJ 4.4156 ± 0.0091 A parent body search returned a match for a few objects, depending on the used D criterion. The Potentially Hazardous Asteroid 2005 OX had the Southworth & Hawkins (1963) DSH criterion value of 0.078, while the Drummond (1981) criterion had close matched for asteroids 2008 DK5 (DD = 0.043), 2004 DF2 (DD = 0.050), and also 2005 OX (DD = 0.058). Possible connection to these objects may be a topic of future work, although these correlations might be spurious as the orbital parameter space is dense in that region. The fireball was bright enough to be picked up by the US government sensors3 which measured a total radiated energy of 11.5×1010 J. Assuming a typical L chondrite bulk density of 3620 kg/m3, we estimate that the meteoroid had an initial mass of 470 kg, corresponding to a diameter of about 0.63 m. We use the energy estimate to scale the observed light curve using the luminous efficiency of Borovička et al. (2020) – it compares well to an empirically derived light curve using a light source of known magnitude (reflection of the Sun from a chromium sphere at various distances). The fireball had one major fragmentation event at the height of 35 km which was picked up by the seismographs in the vicinity. A total of 18 fragments were tracked on the videos after the main fragmentation. The dynamic mass analysis shows that the final mass of the largest fragment was on the order of 10 kg. This rather large fragment has not been found yet – it is possibly buried into the soft ground and ploughed over. The fireball experienced fragmentations at dynamic pressures of 2.5, 3.5, and 10 Mpa, as shown in Figure 3. The peak dynamic pressure is the highest ever measured, after the the Benešov fall (Borovička et al., 1998). Figure 3. Left: Light curve measured on the Sesvete dash cam video. Blue curve is scaled using the CNEOS energy, and the orange curve was derived using the chromium sphere and the original dash camera. Middle: Velocity measurements and the Gritsevich (2007) model fit. Right: Dynamic pressures derived using the velocity fit and the NRL-MSISE00 air density model (Picone et al., 2002). Observed fragmentation points are marked with horizontal lines. The distribution of finds on the ground indicate that these meteorites were not produced at the end height but that some were ejected at several discrete heights above 20 km. Footnotes: 1AMS fireball report: https://fireball.imo.net/members/imo_view/event/2020/1027 2Meteoritical Bulletin Database, entry for Novo Mesto: https://www.lpi.usra.edu/meteor/metbull.php?code=72430 3CNEOS Fireballs: https://cneos.jpl.nasa.gov/fireballs/ References: Borovička et al. (1998). A&A, 334, 713-728. Borovička et al. (2020). AJ, 160(1), 42. Drummond, J. D. (1981). Icarus, 45(3), 545-553. Gritsevich, M. I. (2007). Solar System Research, 41(6), 509-514. Picone et al. (2002). Journal of Geophysical Research: Space Physics, 107(A12), SIA-15. Southworth, R. B., & Hawkins, G. S. (1963). Smithsonian Contributions to Astrophysics, 7, 261-285. Vida et al. (2020). MNRAS, 491(2), 2688-2705. Vida et al. (2021). The Global Meteor Network - Methodology and First Results. Submitted to MNRAS.

Additional information on methods, Figures S1–S3, and Tables S1–S4.

The authors have requested that this preprint be removed from Research Square. This preprint was removed as a condition of publication in a journal.

Drolshagen, E., et al., [Context] In meteor physics, the luminous efficiency τ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. However, a lack of sufficiently accurate verification methods or adequate laboratory tests mean that discussions around this parameter are a subject of controversy. [Aims] In this work, we aim to use meteor data obtained by the Fireball Recovery and InterPlanetary Observation to calculate the luminous efficiencies of the recorded meteors. We also show the limitations of the methods presented herein. [Methods] Deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. These can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. Fragmentation of the meteoroids is not considered within this model. Good measurements of the meteor deceleration are required. [Results] We find τ-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10-6-100 kg. The derived τ-values have a median of τmedian = 2.17%. Most of them are of the order of 0.1-10%. We present how our values are obtained, compare them with data reported in the literature, and discuss several methods. A dependence of τ on the pre-atmospheric velocity of the meteor, ve, is noticeable with a relation of τ = 0.0023 ve2.3. Furthermore, a dependence of τ on the initial meteoroid mass, Me, is found with negative linear behaviour in log-log space: τ = 0.48 Me-0.47. [Conclusions] The higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. Fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. Furthermore, the negative dependence of τ on Me implies that the radiation of smaller meteoroids is more efficient. The results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency.

Funder: European Union‐funded Integrated Activities, Funder: SYNTHESYS, 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.

The practical limitations inherent to human and robotic planetary exploration necessitate the development of specific protocols and methods. This non-standard approach requires testing and validation phases in order to optimise instrumental setups and improve data interpretation; this can occur prior to, during, or even after a mission. Flight instruments, and/or their spare models, may be evaluated using relevant terrestrial materials and/or locations. These materials are called analogues: “analogue sites” for large-scale locations, and “analogue samples” for smaller-scale materials. Depending on the scientific domain, the word “analogue” may carry different meanings but is invariably used to denote objects having compositions and/or physical properties similar to specific extraterrestrial objects. However, due to the variability in composition and properties of natural materials, there are always – inevitably – some differences between the analogue and the object(s) to which it refers. In analogue studies, it is, thus, important to focus on the specific properties that need to be imitated and to consider analogue properties rather than analogue sites or samples alone. Here, we introduce the concept of “functional analogues”. We first make an overview of the different types of analogues and sort them according to their utility. We then describe how different types of functional analogues can be used throughout the timeline of space missions, from the evaluation of different methods in the definition of a mission to understanding the results acquired by probes exploring extraterrestrial bodies. Finally, logical pathways are outlined that facilitate the selection of the best-suited functional analogue(s) according to their intended use and taking into account practical limitations., SCOPUS: ar.j, info:eu-repo/semantics/published

Main-group pallasites (MGPs) are meteorites mainly composed of Fe-Ni metal and olivines, the latter being considered as one of the largest sampling of extraterrestrial mantle material available for study on Earth. We analysed the rare earth element (REE) concentrations of olivines from six MGPs to understand better the processes of formation of their parent mantle. All the investigated samples display very low REE abundances, and enrichments in both light REEs and heavy REEs. We interpret the light REE enrichments as a fingerprint of terrestrial contamination. The least contaminated olivines have higher heavy REE enrichments than those inferred for olivines directly crystallised in a magma ocean. Such enrichments in heavy REEs are possible if the mantle of the MGPs parent body is a residue of partial melting from a chondritic source. Alternatively, re-melting of magma ocean cumulates would explain both the homogeneity of the Ä17O values of MGPs, and the heavy REE enrichments of the olivines.

Sample return missions are among the most exciting space missions, providing both scientifically unique information and an unparalleled mechanism for the inspiring the public. Returned samples allow us to make critical ground truth measurements that can calibrate remote sensing measurements from spacecraft. Some scientific studies can only be done in laboratories rather than remotely or with landed spacecraft. Currently Europe does not have a facility suitable for the curation of returned extra-terrestrial samples. This not only hinders European Space Agency (ESA) missions, but also renders European institutions and Principal Investigators unable to fully participate as equal participants in missions implemented by other countries. The EURO CARES project was the first European attempt to review and evaluate the current state-of-the-art in curatorial practice for sample return missions, and determine the different and necessary steps in order to create a fully functional European Extra-terrestrial Sample Curation Facility to match the ESA requirements.

The meteorite Northwest Africa (NWA) 11962 has been recently classified as a lunar regolith breccia. For the present study, the clasts and the matrix of NWA 11962 have been characterized by optical and electron microscopy along with electron microprobe analyses. The meteorite has a glassy impact melt matrix, which accounts for 35% of the surface area in the thin sections examined, and which contains a very large variety of different lithic clasts, monomineralic clasts, and glass fragments. 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 component in the breccia are gabbroic clasts. The mineral chemistry of the pyroxenes in these gabbroic clasts and the chemistry of various types of glasses 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 relation with the NWA 4472/4485 group of lunar meteorites is discussed.

Funding to GRO from the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant program and the Canadian Space Agency (CSA) Canadian Analogue Research Network and Field Investigation programs is gratefully acknowledged. Part of LF’s work was supported by the Department of Foreign Affairs and International Trade (DFAIT), Government of Canada. The origin of the Stac Fada Member has been debated for decades with several early hypotheses being proposed, but all invoking some connection to volcanic activity. In 2008, the discovery of shocked quartz led to the hypothesis that the Stac Fada Member represents part the continuous ejecta blanket of a meteorite impact crater, the location of which was, and remains, unknown. In this paper, we confirm the presence of shock-metamorphosed and -melted material in the Stac Fada Member; however, we also show that its properties are unlike any other confirmed and well documented proximal impact ejecta deposits on Earth. Instead, the properties of the Stac Fada Member are most similar to the Onaping Formation of the Sudbury impact structure (Canada) and impact melt-bearing breccias from the Chicxulub impact structure (Mexico). We thus propose that, like the Sudbury and Chicxulub deposits, Melt Fuel Coolant Interactions – akin to what occur during phreatomagmatic volcanic eruptions – played a fundamental role in the origin of the Stac Fada Member. We conclude that these rocks are not primary impact ejecta but instead were deposited beyond the extent of the continuous ejecta blanket as high-energy ground-hugging sediment gravity flows. Postprint

Introduction Geochemical evidence for a collision between a large (~10 km) extraterrestrial body and Earth at the end of the Cretaceous, ca. 66 million years ago, and the conclusion that this event was the cause for the global Cretaceous-Paleogene boundary extinction event [1], triggered an intense worldwide search for evidence of other impact events that could be temporally correlated to other extinction events [2, 3]. To date, no convincing links to any other extinction events have been presented [2]. Connecting extinction events with a specific impact event/crater is complicated by the fact that the inventory of terrestrial impact craters remains largely incomplete, due to, e.g., erosion and sedimentary cover. In addition, our understanding of impact diagnostic markers in sedimentary strata is far from complete, especially in the case of target rocks that lack quartz or when dealing with extraterrestrial projectiles with “not so distinctive” geochemical signature, such as achondrites. On top of these considerations, the ages of a large number of the known terrestrial impact structures are poorly constrained. A precise, and most importantly accurate, age for an impact event is crucial when attempting to tie a specific impact event to a biosphere episode recorded in the stratigraphic record. The 40-km-diameter Puchezh-Katunki impact structure [4], located ~400 km northeast of Moscow (Russia), with an estimated age ranging from ~164 to 203 Ma [5, 6], has been discussed as a possible trigger for four different biotic crises (Fig. 1; [7-12]). Here we present new 40Ar/39Ar data on impact melt rock samples from the Vorotilovo Deep Well drill core, retrieved from the center of the Puchezh-Katunki impact structure [4,6]. The new age obtained for the structure provides valuable data regarding relationships between impact events and extinction events in general and specifically the proposed relationship with some Mesozoic extinction/biotic events, and also contributes to the improvement of the age database of terrestrial impact structures. Results and Discussion Laser step-heating of four whole-rock samples of impact melt rock from the Puchezh-Katunki impact structure were run in duplicate (Fig. 1). The samples (V1018, V1144, and V1251) come from the upper parts of the drill core. The new 40Ar/39Ar data allow us to precisely and accurately date the formation of the Puchezh-Katunki impact structure to 195.8 ± 1.0 Ma (2σ; mean square of weighted deviates (MSWD) = 2.0; P = 0.11). This new age makes Puchezh-Katunki one of the most precisely dated impact structures on Earth (2σ relative error: 0.51%). As previously noted, only one global mass extinction has been confirmed to be the direct result of an impact event. The possible relation between impact events and global mass extinctions has been extensively discussed in the literature [2, 3], and lower limits on crater sizes that cause global effects have been debated as well (op.cit.). For example, there is little evidence that the late Eocene impact events (e.g., the Popigai and Chesapeake Bay impact events) have caused any global biotic effects. It is of course possible that less severe, perhaps regional, biotic events have also played an important role in the evolution of life (e.g., [13]). Understanding these events can yield important insights into e.g., the relationship between environmental changes and extinctions (i.e., causality), and how life recovers after such sudden events. Despite not causing global mass extinction, impact events of significant magnitude to cause regional havoc (e.g., resulting in impact craters equivalent to the size of Puchezh-Katunki) will have an impact on life (e.g., [14]) at least on a regional to continent-wide scale, and could possibly have caused both yet undetected biotic events as well as some of the (minor) extinction events that are recognized in the stratigraphic succession. However, since the geological timescale is continuously refined and ages updated, connecting even a well-dated impact structure with an event in the stratigraphic record is by no means straight-forward. Our new age of 195.8 ± 1.0 Ma for the formation of Puchezh-Katunki excludes any relationship with the previously mentioned biotic/extinction events, and clearly illustrates that connecting poorly constrained crater ages with extinction events is troublesome. Therefore, we stress that using poorly constrained or outdated ages leads to erroneous or problematic conclusions (see also e.g., [15, 16]). We also want to emphasize that proving synchronicity between an impact event and a biotic event is not the same thing as proving causality. Fig. 1. Comparison of previous age data with our results from 40Ar/39Ar analyses of Puchezh-Katunki impact melt rocks, with plateau ages and mini-plateau “ages” (2σ errors, all ages in million years). For references to previous age estimates see [5, 6]. For references to environmental/biotic events that have been suggested to possibly be synchronous with the Puchezh-Katunki impact event, see text. Abbreviations: Baj/Bat = Bajocian/Bathonian, Pl/To = Pliensbachian/Toarcian, Si/Pl = Sinemurian/Pliensbachian, Tr = Triassic. Acknowledgements We are very grateful to our late friend and colleague Dr. Svetlana Bogdanova for providing the samples investigated here. SHA is supported by VR (2017-06388). References [1] Alvarez L. W., et al. (1980) Science 208, 1095–1108. [2] French B. M. and Koeberl C. (2010) Earth Sci. Rev. 98, 123–170. [3] Racki G. (2012) Acta Palaeontol. Pol. 57, 681–702. [4] Masaitis V. L. and Naumov M. V. (2020) The Puchezh-Katunki impact crater. Geology and Origin. Springer, 213 p. [5] Mashchak M. S. (1999) In Deep drilling in the Puchezh-Katunki impact structure. VSEGEI-Press. pp. 242–244. [6] Holm-Alwmark S., et al. (2019) Met. Planet. Sci. 54, 1764-1780. [7] Blackburn T. J., et al. (2013) Science 340, 941–945. [8] Cohen K. M., et al. (2013; updated) Episodes 36, 199–204. [9] Sell B., et al. (2014) Earth Planet. Sci. Lett. 408, 48–56. [10] Raup D. M. and Sepkoski J. J. (1986) Science 231, 833–836. [11] Rampino M. R. and Caldeira K. (2015) Mon. Not. R. Astron. Soc. 454, 3480–3484. [12] Rampino M. R. (2020) Earth-Sci. Rev. 201, 102990. [13] Patzkowsky M. E., and Holland S. M. (1993) Geology 21, 619. [14] Toon O. B., et al. (1997) Geophys. 35, 41–78. [15] Jourdan F., et al. (2012) Elements 8, 49–53. [16] Jourdan F., et al. (2009) Earth Planet. Sci. Lett. 286, 1–13.

The Chicxulub impact event generated a long-duration hydrothermal system suitable for microbial life., The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.

Yallalie is a ~12 km diameter circular structure located ~200 km north of Perth, Australia. Previous studies have proposed that the buried structure is a complex impact crater based on geophysical data. Allochthonous breccia exposed near the structure has previously been interpreted as proximal impact ejecta; however, no diagnostic indicators of shock metamorphism have been found. Here we report multiple (27) shocked quartz grains containing planar fractures (PFs) and planar deformation features (PDFs) in the breccia. The PFs occur in up to five sets per grain, while the PDFs occur in up to four sets per grain. Universal stage measurements of all 27 shocked quartz grains confirms that the planar microstructures occur in known crystallographic orientations in quartz corresponding to shock compression from 5 to 20 GPa. Proximity to the buried structure (~4 km) and occurrence of shocked quartz indicates that the breccia represents either primary or reworked ejecta. Ejecta distribution simulated using iSALE hydrocode predicts the same distribution of shock levels at the site as those found in the breccia, which supports a primary ejecta interpretation, although local reworking cannot be excluded. The Yallalie impact event is stratigraphically constrained to have occurred in the interval from 89.8 to 83.6 Ma based on the occurrence of Coniacian clasts in the breccia and undisturbed overlying Santonian to Campanian sedimentary rocks. Yallalie is thus the first confirmed Upper Cretaceous impact structure in Australia.

International audience; Minerals that record high-pressure deformation from meteorite impact are relatively common on Earth; however, minerals that record both high-pressure and high-temperature effects of impact are rare, and they occur mostly in meteorites. Here, we report new occurrences of a type of granular zircon that is the only terrestrial mineral known that uniquely records both high-pressure and high-temperature conditions diagnostic of impact. Granular zircon grains in impact melt rock from the Luizi impact structure (Democratic Republic of the Congo) and in glass from the recently described Pantasma structure (Nicaragua) consist of similar to 1-mu m-sized neoblasts in multiple domains that are systematically oriented such that all (001) poles are approximately orthogonal and coincide with a direction from adjacent domains. The neoblast orientations are produced uniquely by transformation to the high-pressure polymorph reidite and its subsequent reversion to neoblastic zircon at high-temperature conditions, as evidenced by the occurrence of ZrO2. We here refer to such granular grains that preserve orientation evidence for reversion from reidite as "former reidite in granular neoblastic" zircon, or FRIGN zircon, in order to distinguish this type of granular zircon from those that do not record high-pressure conditions. In addition to the localities described here, examples of what can now be classified as FRIGN zircon have been documented at Meteor Crater (Barringer crater, USA), at the Acraman impact structure (Australia), and in Australasian tektites. Occurrences thus span five continents, range in age from Precambrian (ca. 590 Ma) to recent (ca. 49 ka), and serve as a diagnostic indicator of impact metamorphism that may be present throughout much of the geological record. FRIGN zircon further has potential to be found in extraterrestrial samples, where granular zircon has previously been reported.

Axel Wittmann, Aaron J. Cavosie, Nicholas E. Timms, Ludovic Ferriere, Auriol Raed, Cornelia Rasmussen, Catherine Ross, Daniel Stockli, Martin Schmieder, David A. Kring, Jiawei Zhao, Long Xiao, Joanna V. Morgan, Sean P. S. Gulick, and the IODP-ICDP Expedition 364 Scientists

Planar deformation features (PDFs) in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks. They can also be used for estimating average shock pressures that quartz-bearing rocks have been subjected to. Here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of PDF orientations in quartz. These include a comparison between manual and automated methods of indexing PDFs, an evaluation of the new stereographic projection template, and observations regarding the PDF statistics related to the c-axis position and rhombohedral plane symmetry. We further discuss the implications that our findings have for shock barometry studies. Our study shows that the currently used stereographic projection template for indexing PDFs in quartz might induce an overestimation of rhombohedral planes with low Miller-Bravais indices. We suggest, based on a comparison of different shock barometry methods, that a unified method of assigning shock pressures to samples based on PDFs in quartz is necessary to allow comparison of data sets. This method needs to take into account not only the average number of PDF sets/grain but also the number of high Miller-Bravais index planes, both of which are important factors according to our study. Finally, we present a suggestion for such a method (which is valid for nonporous quartz-bearing rock types), which consists of assigning quartz grains into types (A-E) based on the PDF orientation pattern, and then calculation of a mean shock pressure for each sample. (Less)

The shergottite meteorites are ultramafic to mafic igneous rocks whose parental magmas formed from partial melting of the martian mantle. This study reports in-situ laser ablation inductively coupled plasma mass spectrometry analyses for siderophile and chalcophile major and trace elements (i.e., Co, Ni, Cu, As, Se, Ag, Sb, Te, Pb, Bi, and the highly siderophile platinum-group elements, PGE: Os, Ir, Ru, Rh, Pt and Pd) of magmatic Fe-Ni-Cu sulfide assemblages from four shergottite meteorites. They include three geochemically similar incompatible trace element- (ITE-) depleted olivine-phyric shergottites (Yamato-980459, Dar al Gani 476 and Dhofar 019) that presumably formed from similar mantle and magma sources, and one distinctively ITE-enriched basaltic shergottite (Zagami). The sulfides in the shergottites have been variably modified by alteration on Earth and Mars, as well as by impact shock-shock related melting/volatilization during meteorite ejection. However, they inherit and retain their magmatic PGE signatures. The CI chondrite-normalized PGE concentration patterns of sulfides reproduce the whole-rock signatures determined in previous studies. These similarities indicate that sulfides exerted a major control on the PGE during shergottite petrogenesis. However, depletions of Pt (and Ir) in sulfide relative to the other PGE suggest that additional phases such discrete Pt-Fe-Ir alloys have played an important role in the concentration of these elements. These alloys are expected to have enhanced stability in reduced and FeO-rich shergottite magmas, and could be a common feature in martian igneous systems. A Pt-rich PGM was found to occur in a sulfide assemblage in Dhofar 019. However, its origin may be related to impact shock-related sulfide melting and volatilisation during meteorite ejection. In the ITE-depleted olivine-phyric shergottites, positive relationships exist between petrogenetic indicators (e.g., whole-rock Mg-number) and most moderately to strongly siderophile and chalcophile elements in sulfides. These variations extend to incompatible elements like Te and Pd. The whole-rock concentrations of Pd derived from mass-balance calculations decrease by one order of magnitude in the order Y-980459, DaG 476 and Dhofar 019, and broadly overlap the trends in previously published whole-rock analyses. Mantle heterogeneities, and the timing of sulfide saturation as function of mantle melting and/or magma fractionation following ascent from the mantle, may have been the controlling factors of the siderophile and chalcophile element systematics in the analyzed shergottites.

We present a report about the fourth Arab Impact Cratering and Astrogeology Conference (AICAC IV) that took place in Algiers at the USTHB (Universite des Sciences et Technologie Houari Boumedienne, Algiers, Algeria) in the presence of the presidents of the USTHB and Boumerdes Universities, the Director of CRAAG (Centre de Recherche en Astronomie, Astrophysique et Geophysique), and the General Director of the National Administration for Scientific Research (NASR/DGRSDT). This series of conferences aims to promote research interest for impact cratering in the Arab world and beyond, including for instance in African countries. In spite of persistently restraining travel measures to Algeria, the fourth edition held in Algiers was marked by continuous international participation, with participants from seven different countries. This conference focused on presentations of scientific results in the research fields related to planetology, meteorites, and impact craters. In particular, the Algerian impact structures were under the spotlights during both oral and poster sessions. During this conference, the presence of freshly graduated Ph.D. students and new Ph.D. projects related to impact cratering or meteoritic science by a positive sign for the consolidation of research groups in this domain in the Arab world and Africa. Therefore, international cooperation or external support and funding are still needed to ensure the development of this scientific discipline in this part of the world.

A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium-137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium-90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr-90/Cs-137 activity ratio is characteristic for Kyshtym-derived contaminations. Based on the cesium-137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron-rich chemical composition. Mossbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.

The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high-field strength and highly siderophile element (HSE) data, Sr-Nd-Hf-W-Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high-field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars’ tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (187Os/188Os = 0.1289 ± 15 and an ε182W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu-Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm-Nd and Lu-Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre-atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic-ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general.

We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” [CaAl4Si2O11], honoring the U.S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth's mantle. Donwilhelmsite forms in the Earth's mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.