A bright fireball was seen at 4:46 a.m. CET on November 19, 2020, over Austria, and also eye witnessed in Italy and Germany. The resulting Kindberg meteorite was the fifth well‐approved meteorite fall in Austria, and all rocks represent ordinary chondrites. One specimen of Kindberg, measuring 233.08 g, was recovered on July 4, 2021, largely covered by a dark brownish fusion crust. The meteorite is an L6 ordinary chondrite (OC) breccia; Kindberg's highly equilibrated type 6 character is also supported by the large‐sized plagioclase grains (An 9‐12 ; with grains >100 μm) and the homogeneous compositions of olivine (Fa 24.4±0.4 ) and low‐Ca pyroxene (Fs 20.6±0.3 ). The meteorite shows remarkable shock effects in the form of easily visible dark shock veins cross‐cutting the bulk rock. The olivine in Kindberg is dominated by grains with undulous extinction or planar fractures, indicating a weakly shocked (S3 [C‐S3]) chondritic rock. Close to the shock veins, olivine can also show mosaicism. In addition, wadsleyite, a high‐pressure polymorph of olivine, was identified by Raman and IR spectroscopy. Wadsleyite, sometimes in paragenesis with maskelynite and locally part of an intergrowth with majorite and perhaps ringwoodite, was found within and close to the veins. The occurrence of high‐pressure phases of olivine and maskelynite in a weakly shocked bulk rock clearly indicates their formation at relatively low equilibrium shock pressures of <20 GPa (S3/S4 transition). Equilibrium shock pressures consistent with those experienced by bulk rocks shocked to S5 (>30–35 GPa) and S6 (>45 GPa; S5/S6 transition) are not required to form high‐pressure polymorphs of olivine. The L‐chondrite classification is confirmed by O isotope data. The bulk chemical composition also supports L‐group membership.

On the night of June 22, 1931 at 4 h 30 min, a fireball was seen in the vicinity of Malotas, Argentina. During the atmospheric trajectory (southwest to northeast), it experienced several fragmentation events. After the fall, a piece was given to Professor Juan A. Olsacher (National University of Cordoba City, Argentina), who collected some further pieces. One of those samples was officially classified as an H5 ordinary chondrite termed Malotas. The present work focuses on the study of another two pieces rediscovered recently in the Museo de Mineralogia y Geologia Dr. Alfred Stelzner in Cordoba City, Argentina. The first piece turned out to be an achondritic meteorite termed Malotas (b). Petrographic features, chemical composition, and oxygen isotopes point to a monomict basaltic eucrite belonging to the Stannern-trend chemical subgroup of eucrites. The occurrence of anorthitic plagioclase veins in clinopyroxene, veinlet apatite, irregularshaped pockets of silica and troilite and porous silica signal metasomatism and thermal annealing before a late thermal event took place after brecciation. The latter was possibly recorded in the nominal U/Th-He-4 ages of 1.2-3.4 Ga detected in this work, whereas nominal K-Ar gas retention ages are within the range 3.5-4.2 Ga and may have escaped late thermal modifications. The second piece is classified as an L5 chondrite. The different cosmic ray exposure ages of 3, similar to 50, and 27 Ma determined for the H5 and L5 chondrites and the eucrite samples, respectively, might signal a common fall as a result of the breakup of a polymict meteoroid.

Some basaltic eucrites and basaltic lithologies in howardites derived from the asteroid 4 Vesta exhibit unusual secondary veinlet textures consisting mostly of fayalitic olivine and Fe‐enrichments within pyroxenes. Recent studies discussed the formation of these Fe‐rich phases either by interaction with a vapor and/or liquid phase (metasomatism), or by a high‐temperature melting process. We therefore performed a series of heating and hydrothermal experiments with liquids of different compositions on natural pyroxene crystals (augite and orthopyroxene) to evaluate these contrasting hypotheses. The results of the heating experiments show that incongruent melting of pyroxenes at about 1070 °C causes textures that are very similar to those observed in the meteorites. We conclude that a part of the natural secondary veins might be explained by heating processes at similar temperatures. The hydrothermal experiments with aqueous liquids of different Fe‐enriched compositions clearly indicate ion exchange reactions resulting in partial Fe‐enrichments of the pyroxene. Interestingly, these Fe‐enrichments occurred independent of the Fe content of the liquid, which can be explained by an internal origin of Fe from the pyroxenes. In one hydrothermal experiment of augite with Fe‐oxalate solution, deposition of fayalitic olivine was observed. From our experimental observations, we conclude that aqueous liquids are plausible candidates for explaining the deposition of Fe‐enrichments and fayalitic olivine inside the fractures of pyroxene. However, we cannot rule out a high‐temperature melting process slightly above the peritectic point of pyroxene to explain a fraction of observed secondary Fe‐enrichments.

Shock amorphization of plagioclase, from partial to complete, has been used to evaluate the degree of shock in meteorites. Important information on the shock amplitude can be derived from the measurement of the refractive index in plagioclase, either from mineral separates or in petrographic thin sections. However, this technique is time‐consuming, and associated sample preparations are considered destructive and are not always possible for precious and rare meteorite samples. In addition, plagioclase amorphization is commonly inhomogeneous at the sample scale and a statistically meaningful number of grains must be considered. Here, we apply several nondestructive spectroscopic techniques, such as Raman spectroscopy, photoluminescence, and cathodoluminescence, to plagioclase experimentally shocked at 28 GP a, and thus in the transition regime between crystalline plagioclase and fully amorphous material. Most of the plagioclase was transformed into diaplectic glass at 28 GP a, yet some grains exhibit heterogeneously distributed crystalline domains. This confirms that intrinsic and extrinsic factors lead to local variations in the intensity of the shock pressure within individual plagioclase crystals of homogeneous composition. The amorphization of plagioclase can qualitatively (and potentially also quantitatively) be investigated by spectroscopic techniques, highlighting such local variations in the shock efficiency.

We report on the petrography and mineralogy of five Yamato polymict eucrites to better constrain the formation and alteration of crustal material on differentiated asteroids. Each sample consists of different lithic clasts that altogether form four dominant textures and therefore appear to originate from closely related petrological areas within Vesta ' s crust. The textures range from subophitic to brecciated, porphyritic, and quench-textured, that differ from section to section. Comparison with literature data for these samples is therefore difficult, which stresses that polymict eucrites are extremely complex in their petrography and investigation of only one thick section may not be representative for the host rock. We also show that sample Y-793548 consists of more than one lithic unit and must therefore be classified as polymict instead of monomict. The variety and nature of lithic textures in the investigated Yamato meteorites indicate shock events, intense post-magmatic thermal annealing, and secondary alteration. These postmagmatic features occur in different intensities, varying from clast to clast or among coexisting mineral fragments on a small, local scale. Several clasts within the eucrites studied have been modified by late-stage alteration processes that caused deposition of Fe-rich olivine and Fe enrichment along cracks crosscutting pyroxene crystals. However, formation of these secondary phases seems to be independent of the degree of thermal metamorphism observed within every type of clast, which would support a late-stage metasomatism model for their formation.

Meteorite fusion crusts are quenched melt layers formed during meteoroid atmospheric entry, mostly preserved as coating on the meteorite surface. Antarctic ureilite Asuka (A) 09368 and H chondrites A 09004 and A 09502 exhibit well preserved thick fusion crusts, characterized by extensive olivine crystallization. As olivine is one of the major components of most meteorites and its petrologic behavior is well constrained, it can be roughly considered as representative for the bulk meteorite. Thus, in this work, the evolution of olivine in fusion crusts of the above-listed selected samples is investigated. The different shape and chemistry of olivine crystallized in the fusion crust, both as overgrown rim on relic olivine clasts and as new crystals, suggest a general temperature and cooling rate gradient. The occurrence of reverse and oscillatory zoning in individual olivine grains within the fusion crust suggests complex redox reactions. Overall, the investigated fusion crusts exhibit a general oxidation of the relatively reduced initial material. However, evidence of local reduction is preserved. Reduction is likely triggered by the presence of carbon in the ureilite or by overheating during the atmospheric entry. Constraining these processes provides a potential analog for interpreting features observed in cosmic spherules and micrometeorites and for calibrating experiments and numerical models on the formation of fusion crusts.

The timing of the wane in heavy meteorite bombardment of the inner planets is debated. Its timing determines the onset of crustal conditions consistently below the thermal and shock pressure limits for microbiota survival, and so bounds the occurrence of conditions that allow planets to be habitable. Here we determine this timing for Mars by examining the metamorphic histories of the oldest known Martian minerals, 4.476–4.429-Gyr-old zircon and baddeleyite grains in meteorites derived from the southern highlands. We use electron microscopy and atom probe tomography to show that none of these grains were exposed to the life-limiting shock pressure of 78 GPa. 97% of the grains exhibit weak-to-no shock metamorphic features and no thermal overprints from shock-induced melting. By contrast, about 80% of the studied grains from bombarded crust on Earth and the Moon show such features. The giant impact proposed to have created Mars’ hemispheric dichotomy must, therefore, have taken place more than 4.48 Gyr ago, with no later cataclysmic bombardments. Considering thermal habitability models, we conclude that portions of Mars’ crust reached habitable pressures and temperatures by 4.2 Gyr ago, the onset of the Martian ‘wet’ period, about 0.5 Gyr earlier than the earliest known record of life on Earth. Early abiogenesis by 4.2 Gyr ago, is now tenable for both planets. The oldest known minerals from Mars have no strong shock features, indicating early cessation of giant impacts there, according to microanalysis of zircon and baddeleyite grains in meteorites.

The enriched basaltic (martian) shergottite Ksar Ghilane (KG) 002, discovered in 2010, is exceptionally rich in coexisting but discrete apatite and merrillite crystals. It has been selected to better constrain the formation conditions and post-crystallization processes, and thus the evolution of martian rocks based on Ca-phosphates. A petrological, chemical, chronological and microstructural approach using a series of high-spatial resolution techniques including Raman spectroscopy, electron microscopy (SEM, EPMA, CL-imaging) and secondary ion mass spectrometry (SIMS) analysis has been applied to a representative number of Ca-phosphate grains. Analytical results for apatite and merrillite reveal: (i) zoning in F, Cl, Br and I concentrations, (ii) elevated Cl concentrations in the range of similar to 11,900-35,300 mu g/g and halogen ratios, i.e., Cl/Br and Cl/I, as well as stable chlorine isotope composition, reported as delta Cl-37 values rel. to Standard Mean Ocean Chloride (SMOC, defined as 0 parts per thousand) with a value of +0.67 +/- 0.14 parts per thousand (1 sigma), distinguishing KG 002 phosphates from that of other enriched and depleted shergottites. The halogen and heavier delta Cl-37 record indicate a slightly higher degree of similar to 3.5% assimilation of Cl-rich and isotopically heavier crustal reservoir on Mars when compared to other enriched shergottites. (iii) Structural investigations together with the chemical and petrological context of the grains confirm the occurrence of hydroxyl-poor merrillite, indicate weak if any alteration effects induced by metamictization, only minor structural modifications due to shock metamorphism, and absence of replacement reactions. Therefore, igneous crystallization of Ca-phosphates from a fractionated, hydrous and ferrous mantle source, rich in volatiles including the halogens and Na and lithophile rare earth-elements, and absence of interaction with crustal fluids/brines of the sample is deduced. (iv) The Pb isotopic composition of six apatite and three merrillite grains is highly unradiogenic and the U-238-Pb-206 record yields a phosphate crystallization time at 395 +/- 240 Ma (2 sigma), which is similar to those of other enriched shergottites. (C) 2018 Elsevier Ltd. All rights reserved.

1Department of Lithospheric Research, University of Vienna, Vienna, Austria, 2Analytical, Environmental, and Geo-Chemistry (AMGC) Vrije Universiteit Brussel (VUB), Brussels, Belgium, 3University of Potsdam, Potsdam-Golm, Germany, 4Aeronautics and Aerospace Department, von Karman Institute of Fluid Dynamics (VKI), Sint-Genesius-Rode, Belgium, 5Department of Materials and Chemistry, VUB, Brussels, Belgium, 6School of Science and Technology, University of Camerino, Camerino, Italy, 7ESRF, Grenoble, France, 8National Institute of Polar Research (NIPR), Tachikawa, Japan, 9Natural History Museum (NHM), Vienna, Austria, 10Laboratoire G-Time (Geochimie: Traçage Isotopique, Mineral, et Èlementaire), Université Libre de Bruxelles, Brussels, Belgium.

The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm-Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The pc-values (U-238/Pb-204) obtained for these two different stages of Pb growth are mu(1) of 1.8 and a range of mu(2) from 1.4-4.7, respectively. The mu(1)-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial mu-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sr-i, gamma Os-187, epsilon Nd-143, and epsilon Hf-176), the second stage mantle evolution range in observed mantle mu-values display excellent linear correlations (r(2) > 0.85) and represent a spectrum of Martian mantle mixing-end members (depleted, intermediate, enriched). (C) 2017 Elsevier B.V. All rights reserved.

Zircon is a ubiquitous and highly refractory accessory phase in terrestrial rocks, and occurs in some extraterrestrial materials where its internal microstructure carries useful information on formation environments. We present a first step in comparing the internal zoning characteristics (i.e., chemical microstructures and degree of radiation damage) of some of the oldest known zircon grains derived from large differentiated asteroids, Mars and the early Earth spanning the time interval 4.55 Ga (eucrite) to 4.38 Ga (Earth). Electron microscopy (EPMA, SEM-CL, EBSD), Raman spectroscopy (nu(3)(SiO4)), and photoluminescence (Dy3+) reveal a mix of ubiquitous and distinct characteristics in zircon from these different planetary sources. In the eucrite sample suite, representing a wide range of thermal and shock metamorphic conditions, igneous zoning features such as planar growth banding and sector zoning are often preserved but commonly modified by thermal metamorphism to produce rounded, sub-to anhedral grains sometimes with metamorphic rims. In contrast, the subhedral to anhedral crystal clasts in two samples of martian regolith breccia exhibit simple igneous zonation (e.g., concentric U, Th, and Yb zoning) and/or mineral inclusions. Secondary rounding or fracturing of martian zircon can be explained by re-deposition through surface processes that differ from the billions of years of hydrous crustal metamorphic and erosion effects seen in a Jack Hills detrital zircon. Annealing history does not appear to be a clear discriminating property between different sources, as all zircon populations have Raman characteristics and reconstructed alpha doses indicating recovery of crystallinity at some point after formation. Down-shifted nu(3)(SiO4) band positions may, however, distinguish martian grains and some eucrite zircon. At this point, the most promising suite of Solar System provenance discriminants includes internal zoning styles, specific Raman spectral properties, and chronological constraints.

The hydrophilic nature of halogens makes these elements ideal for probing potential hydrous geologic processes. Generally, in magmatic settings the stable isotopes of Cl may fractionate when H is in low concentrations and little fractionation occurs when the H concentration is high. We determined the Cl isotope composition and halogen content (F, Cl, Br, and I) of apatite and merrillite in seven basaltic eucrites, which are meteorites linked to the asteroid 4-Vesta, by using secondary ion mass spectrometry. We compare our halogen results with H isotope data, existing bulk rock concentrations, and petrologic models. The inferred Cl isotope composition of eucrites from this study, expressed in standard δ37Cl notation, which ranges from −3.8 to 7.7‰, correlates with the bulk major- and trace-element content, e.g., the Cl isotope composition positively correlates with Mg and Sc, while Cl isotope composition negatively correlates with K, V, and Cr. Here we suggest that eucrites preserve evidence of a degassing magma ocean as evidenced by the decreasing bulk rock K content with increasing δ37Cl. If the eucrite parent body, 4-Vesta, accreted with a negative δ37Cl of −3.8±1.1‰, at least some parts of the solar nebula would have been isotopically light compared to most estimates of the Earth, which on average is close to 0‰.