¹J. Gattacceca et al. (>10)
Meteoritics & Planetary Science (in Press)
Open Access Link to Article [DOI: 10.1111/maps.70233]
¹CEREGE, CNRS, Aix-Marseille Univ, IRD, INRAE, Aix-en-Provence, France

Published by arrangement with John Wiley & Sons

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.

¹Robert Huber, ²Hans Lauterbach, ³Robert Darga
Meteoritics & Planetary Science (in Press) Open Access Link to Article [DOI: 10.1111/maps.70255]
¹MARUM—Center for Marine Environmental Sciences, Universität Bremen, Bremen, Germany
²Independent Researcher, Traunreut, Germany
³MammutMuseum Siegsdorf, Siegsdorf, Germany

Published by arrangement with John Wiley & Sons

Public fascination with impact craters often drives bold speculations, but rigorousverification is critical. In southeastern Bavaria, numerous depressions have been proposed torepresent impact craters associated with a catastrophic event in Celtic times (between 900 BCand 600 BC)—the so called “Chiemgau Impact.” To date, the evidence presented in supportof the proposed Chiemgau Impact has not been independently validated as diagnostic of aconfirmed impact event, and this interpretation has been repeatedly challenged in thescientific literature. More recently, numerous newly identified, predominantly small-scalestructures have been presented as further evidence supporting this claim. Many, however,lack precise geographic information, complicating independent verification. We localized andcritically examined these structures in the field as well as using publicly availablehigh-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 coursefeatures such as bunkers and ponds. Other depressions correspond to glacial landformscharacteristic of the Inn-Chiemsee foreland. None of the structures examined exhibitcharacteristics that would support a formation by a cosmic impact. The repeatedmisinterpretation of recently constructed golf course elements as impact craters highlights astriking lack of methodological rigor and illustrates how extraordinary claims can arise fromneglecting simple cross-checks with publicly available geospatial and planning data andindicates that the postulated impact in Chiemgau belongs to the realm of myths.

^1,2Subhasmita Swain, ³Enrico Mugnaioli, ³Anna Musolino, ⁴Markus Patzek, ^5,6Beda Hofmann, ^1,2,7Surya Snata Rout
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.70245]
¹School of Earth and Planetary Sciences, National Institute of Science Education and Research (NISER), Jatni, Khurda, India
²Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, India
³Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
⁴Institut für Planetologie, University of Münster, Münster, Germany
⁵Institute of Geology, University of Bern, Bern, Switzerland
⁶Natural History Museum Bern, Bern, Switzerland
⁷Centre for Interdisciplinary Sciences (CIS), National Institute of Science Education and Research (NISER), Jatni, Khurda, India

Published by arrangement with John Wiley & Sons

Volatile-rich xenolithic clasts in different meteoritic breccias represent primitivesolar system material. Here, we report the mineralogy and organic maturity of C1, C2, andCM-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 majorityhave mineralogy and organic maturity similar to the CI chondrites. Two C1 clasts show theleast altered polyaromatic organic matter, similar to Bells, Essebi, and a CR chondrite.A few C1 clasts have unique mineralogy with abundant Fe-rich olivine surroundingmagnetite grains. Such clasts show a Raman signature of mild to moderate heating effectsrelated to impact-shock processing. The Fe-rich olivine within these clasts formed aroundmagnetite grains from an aqueous fluid at a water/rock ratio of 0.1–0.2, T > 150 °C, andhigh activity of SiO 2 and Fe. Additionally, the Fe-rich olivine could have also formedthrough the reduction of magnetite by H 2 gas and SiO 2 (aq). The CM-like clasts are foundonly in the studied HED meteorites and have mineralogy and organic maturity similar to theCM chondrites. Only one CM-like clast shows unique Raman signatures, either due tothermal effects or the presence of unique organic precursor material. The C2 clasts showsimilarities with other C2 clasts in CH/CB chondrites. None of the studied clasts showsignatures of high degrees of thermal metamorphism like the subtype ≥3.1 chondrites.

^1,2Robert W. Nicklas, ^3,4Aratz Beranoaguirre, ²Dylan M. Seal, ⁵James M. D. Day, ²Ethan F. Baxter, ⁶Anthony B. Love
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.70254]
¹Lunar and Planetary Institute, USRA, Houston, Texas, USA
²Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
³Institut für Geowissenschaften, Goethe-Universität Frankfurt, Frankfurt am Main, Germany
⁴Frankfurt Isotope and Element Research Center (FIERCE), Goethe-Universität Frankfurt, Frankfurt am Main, Germany
⁵Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
⁶Department of Geological and Environmental Sciences, Appalachian State University, Boone, North Carolina, USA

Published by arrangement with John Wiley & Sons

Brachinites and brachinite-like achondrites record melting processes at moreoxidizing conditions than many other achondrite meteorites, attested by relatively Fe-richsilicate 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 ElMedano 395 and for the anomalously apatite-rich (~1.26% modal) brachinite-like achondriteNorthwest Africa (NWA) 12,532. Both meteorites have Rb-Sr and Re-Os isotope systematicsthat have been significantly affected by terrestrial alteration, reflecting variable addition of Srand variable loss of Rb and Re. Brachinite-like achondrite NWA 12532 experienced lateaddition of metallic phases and apatite on its parent body, having nearly chondriticabundances of Os, Ir, Ru, Pt, and Pd. The apatite in NWA 12532 gives an age of4491.3 14.1 Ma, overlapping with apatite U-Pb ages for ordinary chondrites, as well asfor other brachinites and brachinite-like achondrites. This age is significantly younger thanavailable Mn-Cr ages for brachinite silicate phases. The young U-Pb ages of brachinites andbrachinite-like achondrites likely reflect significant impact shock resetting events at ~4.43 to4.49 Ga across the solar system, also recorded in ordinary chondrites. These resetting eventsmay be related to a significant dynamical reorganization at that time.