Abstract A minor fraction of meteorites contains xenoliths, that is, clasts that were formed on a different parent body than that of the host lithology. The occurrence of xenoliths is direct evidence for the exchange of material between asteroids, including exchanges between asteroids from the carbonaceous (CC) and non‐carbonaceous (NC) reservoirs. Overall xenolith population statistics may therefore inform us about the dynamical mixing of these two asteroid reservoirs. Xenoliths are also intrinsically interesting because they may sample parent bodies that are not represented in the meteorite collection. In this work, we conducted a critical and exhaustive review of xenoliths described in the literature and performed a new large‐scale search for macroscopic lithic xenoliths. We identify 89 xenolith‐bearing meteorites in the literature, and report 18 new ones. We expand the diversity of known host/xenolith pairs with occurrence that had not been reported before: a CM clast in a L chondrite, a CO3 clast in a eucrite, a pallasite and H clasts in howardites, and two CO‐CM breccias. Based on our observations, we reinterpret a number of previously described xenoliths. In particular, many “CI‐like” xenoliths should rather be classified as ungrouped C1 or C2 chondrite xenoliths. At least a third of xenoliths do not belong to the known meteorite groups, suggesting that they represent a flux of meteoroids different from the present‐day one that is dominated by the products of recent (~<50 Ma) collisions. Although xenoliths are present in only 0.14% of meteorites, the statistics of the total data set of 107 xenolith‐bearing meteorites can be discussed in relation with the asteroid population. Xenoliths are more abundant in the regolith breccias of large asteroids, in agreement with their ability to maintain an old and mature regolith. Chondritic xenoliths represent 95% of xenolith occurrence, in line with a higher number of chondritic asteroids with respect to achondritic ones. Xenoliths from the CC and NC reservoirs are found in host meteorites from both reservoirs, and a majority was implanted at low collisional speed (below about 2 km s −1 ). The low proportion of CC meteorites with NC xenoliths can be related to the fact that the present‐day outer asteroid belt that hosts the majority of CC asteroids is depleted in NC asteroids. The broad agreement between the xenolith population and the present‐day architecture of the asteroid belt, as well as the low collisional speed between CC and NC materials suggest that the implantation of most xenoliths occurred after the main scattering event of the asteroids triggered by the formation of Jupiter a few Myr after the formation of the solar system. Conversely, CV, CK, and CO chondrites contain only xenoliths from a meteorite group of their own meteorite clan suggesting that these intra‐clan xenoliths were implanted while their parent bodies were still orbiting in a narrow range of heliocentric distance, that is, before the main scattering event of the asteroids triggered by the formation of Jupiter. Eventually, a few xenoliths were incorporated in asteroids that were still accreting. Therefore, xenolith implantation seems to have been a universal and protracted phenomenon, active for most of solar system history.
Abstract Public fascination with impact craters often drives bold speculations, but rigorous verification is critical. In southeastern Bavaria, numerous depressions have been proposed to represent impact craters associated with a catastrophic event in Celtic times (between 900 BC and 600 BC)—the so called “Chiemgau Impact.” To date, the evidence presented in support of the proposed Chiemgau Impact has not been independently validated as diagnostic of a confirmed impact event, and this interpretation has been repeatedly challenged in the scientific literature. More recently, numerous newly identified, predominantly small‐scale structures have been presented as further evidence supporting this claim. Many, however, lack precise geographic information, complicating independent verification. We localized and critically examined these structures in the field as well as using publicly available high‐resolution LIDAR data, aerial imagery (historic and recent), and development plans. The majority of these images show structures which are demonstrably anthropogenic, including gravel pits, WWII bomb craters, retention basins, and—most notably—golf course features such as bunkers and ponds. Other depressions correspond to glacial landforms characteristic of the Inn‐Chiemsee foreland. None of the structures examined exhibit characteristics that would support a formation by a cosmic impact. The repeated misinterpretation of recently constructed golf course elements as impact craters highlights a striking lack of methodological rigor and illustrates how extraordinary claims can arise from neglecting simple cross‐checks with publicly available geospatial and planning data and indicates that the postulated impact in Chiemgau belongs to the realm of myths.
Abstract Yamato‐type (CY) carbonaceous chondrites are a group of meteorites that experienced both intense aqueous alteration and subsequent dehydration. They consist of a few CY1 and CY2 samples; however, their nature and genetic relationship remains an issue of debate. Here, we report the detailed petrography and mineralogy of four sections of Dhofar 1988, a newly proposed CY chondrite. We find that Dhofar 1988 is a dimict breccia, containing a CY2‐like host region (~73 area%) and numerous CY1‐like dark clasts (~27 area%). Using Ti‐minerals as a clue, we identified 14 calcium‐aluminum‐rich inclusions (CAIs) (including an Al‐rich chondrule containing CAI material, with most of the CAIs present in the host region, ~1 area%) and only one CAI in dark clasts (~0.04 area%). These CAIs contain a series of Ti‐minerals, including primary perovskite, Ti‐rich fassaite, Ti‐rich hibonite, and probably ilmenite–rutile assemblage, and secondary ilmenite, anatase, rutile, zirconolite (ideal formula CaZrTi 2 O 7 ), and perovskite. Formation of the secondary Ti‐minerals involves: (1) replacement of Ti‐rich fassaite by melilite‐like phase, perovskite, and minor spinel; (2) subsolidus breakdown of potential armalcolite to ilmenite and rutile and minor spinel and zirconolite; (3) alteration of perovskite to ilmenite; (4) alteration of perovskite to anatase; (5) alteration of fassaite to phyllosilicate and ilmenite; and (6) transition from ilmenite to perovskite. They probably formed during pre‐alteration metamorphism (1 and 2), intense aqueous alteration (3–5), and postalteration metamorphism (6), respectively, and reflect the evolution of temperature and water/rock ratio. The similarity between the two components in Dhofar 1988 and the CY1 and CY2 samples indicates that the material from CY1 and CY2 samples was once mixed with each other through collision‐induced mixing or during initial planetesimal accretion.
Abstract Volatile‐rich xenolithic clasts in different meteoritic breccias represent primitive solar system material. Here, we report the mineralogy and organic maturity of C1, C2, and CM‐like clasts present within five polymict ureilites, two polymict eucrites, one howardite, and one CR chondrite. Of all the clasts, the C1s are the most abundant, and the majority have mineralogy and organic maturity similar to the CI chondrites. Two C1 clasts show the least altered polyaromatic organic matter, similar to Bells, Essebi, and a CR chondrite. A few C1 clasts have unique mineralogy with abundant Fe‐rich olivine surrounding magnetite grains. Such clasts show a Raman signature of mild to moderate heating effects related to impact‐shock processing. The Fe‐rich olivine within these clasts formed around magnetite grains from an aqueous fluid at a water/rock ratio of 0.1–0.2, T > 150 °C, and high activity of SiO 2 and Fe. Additionally, the Fe‐rich olivine could have also formed through the reduction of magnetite by H 2 gas and SiO 2 (aq). The CM‐like clasts are found only in the studied HED meteorites and have mineralogy and organic maturity similar to the CM chondrites. Only one CM‐like clast shows unique Raman signatures, either due to thermal effects or the presence of unique organic precursor material. The C2 clasts show similarities with other C2 clasts in CH/CB chondrites. None of the studied clasts show signatures of high degrees of thermal metamorphism like the subtype ≥3.1 chondrites.
Abstract Brachinites and brachinite‐like achondrites record melting processes at more oxidizing conditions than many other achondrite meteorites, attested by relatively Fe‐rich silicate phases. Here, new major‐, trace‐, and highly siderophile‐element (Os, Ir, Ru, Pt, Pd, Re) abundances, as well as Re‐Os and Rb‐Sr isotope data are reported for the brachinite El Medano 395 and for the anomalously apatite‐rich (~1.26% modal) brachinite‐like achondrite Northwest Africa (NWA) 12,532. Both meteorites have Rb‐Sr and Re‐Os isotope systematics that have been significantly affected by terrestrial alteration, reflecting variable addition of Sr and variable loss of Rb and Re. Brachinite‐like achondrite NWA 12532 experienced late addition of metallic phases and apatite on its parent body, having nearly chondritic abundances of Os, Ir, Ru, Pt, and Pd. The apatite in NWA 12532 gives an age of 4491.3 ± 14.1 Ma, overlapping with apatite U‐Pb ages for ordinary chondrites, as well as for other brachinites and brachinite‐like achondrites. This age is significantly younger than available Mn‐Cr ages for brachinite silicate phases. The young U‐Pb ages of brachinites and brachinite‐like achondrites likely reflect significant impact shock resetting events at ~4.43 to 4.49 Ga across the solar system, also recorded in ordinary chondrites. These resetting events may be related to a significant dynamical reorganization at that time.
