¹Priscille Cuvillier,^2,3Noël Chaumard,¹Hugues Leroux,^2,4,5Brigitte Zanda,^2,4Roger H. Hewins¹Damien Jacob,⁶Bertrand Devouard
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13032]
¹Unité Matériaux et Transformations, Université Lille 1 and CNRS, Villeneuve d’Ascq, France
²Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Université, Muséum National d’Histoire Naturelle, UPMC Université Paris 06, IRD & CNRS, Paris, France
³WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
⁵Institut de Mécanique Céleste et de Calcul des Ephémérides, Observatoire de Paris, Paris Cedex, France
⁶Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Aix en Provence, France
Published by arrangemenr with John Wiley & Sons

We conducted a transmission electron microscope study of the exsolution microstructures of Ca-rich pyroxenes in type I chondrules from the Paris CM and Renazzo CR carbonaceous chondrites in order to provide better constraints on the cooling history of type I chondrules. Our study shows a high variability of composition in the augite grains at a submicrometer scale, reflecting nonequilibrium crystallization. The microstructure is closely related to the local composition and is thus variable inside augite grains. For compositions inside the pyroxene miscibility gap, with a wollastonite (Wo) content typically below 40 mole%, the augite grains contain abundant exsolution lamellae on (001). For grain areas with composition close to Wo₄₀, a modulated texture on (100) and (001) is the dominant microstructure, while areas with compositions higher than Wo₄₀ do not show any exsolution microstructure development. To estimate the cooling rate, we used the spacing of the exsolution lamellae on (001), for which the growth is diffusion controlled and thus sensitive to the cooling rate. Despite the relatively homogeneous microstructures of augite grains with Wo < 35 mole%, our study of four chondrules suggests a range of cooling rates from ~10 to ~1000 °C h⁻¹, within the temperature interval 1200–1350 °C. These cooling rates are comparable to those of type II chondrules, i.e., 1–1000 °C h⁻¹. We conclude that the formation of type I and II chondrules in the proto-solar nebula was the result of a common mechanism.

¹Tomasz Brachaniec
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13035]
¹Department of Geochemisty, Mineralogy and Petrography, Faculty of Earth Sciences, University of Silesia, Sosnowiec, Poland
Published by arrangement wit John Wiley & Sons

Reworking and redeposition of tektites is a highly complex and multistage geological process including many factors. A tumbling experiment was therefore undertaken with the aim of estimating a distance of transport that such moldavites can withstand. Though the experiment probably did not accurately mimic natural conditions, our results proved that moldavites can withstand considerable transport only over a distance of a few kilometers. Observed abrasion of tektites was significant in the early stage of experimental transport; the rate of abrasion decreased correlatively with increasing distance of transport as usual. Overall, given the results obtained from this experimental study and their state of preservation described in the literature, it is very likely that Polish tektites were reworked and redeposited by rivers from the Sudetes Mountains. Based on the paleoreconstruction of river flows, it can be assumed that the Polish tektites originated from two independent sediment supply areas.

^1,2Mona Weyrauch,¹Marian Horstmann,¹Addi Bischoff
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13025]
¹Institut für Planetologie, Universität Münster, Münster, Germany
²Institut für Mineralogie, Universität Hannover, Hannover, Germany
Published by arrangement with John Wiley & Sons

In this study, the metal and sulfide compositions of 45 enstatite chondrites were analyzed to determine possible mineral-chemical trends correlated with the petrologic type. Data for 35 additional samples were taken from the literature. Considering the data from this huge number of different E chondrite samples (80 in total), none of the trends previously described in the literature could be clearly confirmed. Also, among the opaque phases of enstatite chondrites, no other “new” correlations between mineral chemistry and the petrologic type were found. However, major differences in the sulfide and metal chemistry became obvious. Specifically, a certain number of chondrites in the EH and the EL groups have Cr in troilite above 2 wt%, Fe in niningerite or alabandite above 20 wt%, and lack abundant daubréelite. Differences were also found for Ni concentrations in kamacite. Thus, we propose a system for classifying E chondrites by defining four major subgroups: EHa, ELa, EHb, and ELb. All subgroups show full petrologic sequences that are similar to each other. This observation, in combination with the differences in sulfide and metal chemistry, suggests an origin of the samples from different parent bodies. Considering the anomalous E chondrite samples that neither fit in the previous classification scheme nor in the new one described here, the samples investigated in this study require at least eight different parent bodies.