1,720,968 research outputs found
Testing models for the compositions of chondrites and their components: II. CR chondrites
No full textChondritic ingredients: I. Usual suspects and some oddballs in the Leoville CV3 meteorite
No full textReduced CV3 chondrites are relatively pristine rocks and prime candidates for studies exploring processes that predated planet formation. We closely examined the petrographic features and trace elemental composition of different CV3 constituents in the accretionary breccia Leoville. The petrographic results are presented here. Our sample (2.2 cm2) is not brecciated. The main ingredientabout 65 area%is fine- to coarse-grained ferromagnesian type I chondrules. Minor constituents (in order of 2-D abundance) include refractory inclusions, Al-rich chondrules, and very fine-crystalline clasts of moderately volatile composition. Type II chondrules and metal nuggets occur sporadically. The chondrulematrix ratio is approximately 3:1. Medium- and coarse-grained chondrules exhibit porphyritic textures, probably caused by incomplete melting, and frequent, partial or continuous, recrystallized dust rims. The fine-grained population most likely represents randomly sectioned dust rims. The rim material and some of the medium-grained objects are relatively troilite-rich. Iron-nickel metal is rare. In addition, almost all constituents show strikingly ragged or convoluted outlines. Only a few, rim-less components exhibit smooth contours. Evidence for incomplete melting and the formation of recrystallized or igneous rims in carbonaceous chondrites is well established, suggesting that both processes were widespread events. The observed features in Leoville support this conclusion. In addition, our findings indicate that surface abrasion in a turbulent dust-filled regime may have taken place after the consolidation of dust rims. Alternatively, the irregular, convoluted nature of at least the rimmed chondrules may have been inherent to the dust accretion event and was not erased by subsequent heating.DFG (German Research Foundation) [PA1970/1-1, PA909/2-1, PA909/2-2
The catastrophic break‐up of the ureilite parent body: Modeling constraints on the debris size
No full textAbstract
The ureilite parent body (UPB) was, in all likelihood, completely broken apart when hit by another object early in its history and reassembled into daughter bodies. We here present a study tailored to constrain the dimensions of the impact debris produced in the catastrophic disruption. Using a customized Python code to simulate the thermal evolution of the UPB fragments, we compared the FeO profiles modeled for different depths within those fragments with those measured across the reduction rims in olivines of 12 different ureilites (
n
= 37). Our profile data were fitted to the theoretical cooling profiles determined with a transient thermal model. The results are coherent and consistent with earlier studies and, despite using simplified boundary conditions (fragments described as ideal spheres and maximum radiation), our data provide valuable context on possible cooling pathways of the UPB debris. In detail, we found that the average depths within the given fragments from which our samples of ureilites originated were limited to 0.3–0.4 ± 0.1 m, with only few exceptions (e.g., one highly reduced sample lacked suitable reduction profiles suggesting either a depth of origin of >2 m or shielding of this fragment from rapid cooling, e.g., due to hovering in the center of a relatively dense cloud of debris). In addition, we calculated that the cooling from 1473 to 1100 K of the average fragment at the depth of our samples took no more than 3–4 days, suggesting that the reassembly of the ureilite daughter bodies could have been a very fast process.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Zirconium and hafnium in meteorites
No full textThe ratio of the two refractory trace elements zirconium (Zr) and hafnium (Hf) in meteorites has been proposed to be uniform. The most precise value available is 34.3 +/- 0.2 (1 sigma). It was obtained by isotope dilution ICP-MS applied to 15 chondrites, most of which were carbonaceous chondrites, and six achondrites. We reinvestigated the case and determined Zr/Hf ratios of a broad spectrum of meteoritic samples via laser ablation ICP-MS. Our sample suite comprised 29 chondrites and five achondrites. The main objective of the study was two-fold: we intended to verify the accuracy and precision of a relatively fast and inexpensive sample preparation method combined with expeditious laser ablation ICP-MS techniques. Furthermore, we were looking into the possibility of systematic fine-scale Zr/Hf variations among bulk meteoritic matter of different classes. The applied fusion technique together with laser ablation ICP-MS turned out to be well suited to determine relative refractory trace element abundances. Absolute Zr/Hf ratios yield uncertainties of approximately 4% (1 sigma). As opposed to the most recent findings, we observed variable Zr/Hf ratios in different meteorites ranging from approximately 28 to approximately 38. Our value for Orgueil (CI1) is 34.0 +/- 0.3 (1 sigma). Including literature data, we propose a solar system value of 34.1 +/- 0.3. Our data also suggest that H chondrites tend to exhibit higher Zr/Hf ratios (average of 35.6 +/- 0.5 [1 sigma]) while EL6 chondrites rather show low values (average of 30.8 +/- 0.6 [1 sigma]). In addition to examining Zr/Hf ratios, we also explored the content of refractory major elements in different meteorite groups. Here, we found that EL6 chondrites often show very low Ca/Al ratios. The CI1 value for CaO/Al(2)O(3) is 0.804. EL6 chondrites, however, display ratios as low as approximately 0.3. While the variation in Zr/Hf can be explained by fractional condensation processes in the early solar nebula, the observed low Ca/Al ratios in EL6 chondrites are probably attributable to deficits in oldhamite (CaS).[PA909/2-1]; [PA909/2-2
Testing models for the compositions of chondrites and their components: III. CM chondrites
No full texthttp://dx.doi.org/10.13039/100000104 National Aeronautics and Space Administrationhttp://dx.doi.org/10.13039/501100001659 Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100007522 Muséum National d'Histoire Naturellehttp://dx.doi.org/10.13039/501100008957 National Institute of Polar Researc
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