¹A. Nathues,¹M. Hoffmann,²N. Schmedemann,¹R. Sarkar,³G. Thangjam,¹K. Mengel,¹J. Hernandez,²H. Hiesinger,²J. H. Pasckert
Nature Communications 13, 927 Link to Article [DOIhttps://doi.org/10.1038/s41467-022-28570-8]
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077, Goettingen, Germany
²Institut für Planetologie, WWU Münster, Münster, Germany
³School of Earth and Planetary Sciences, National Institute of Science Education and Research, NISER, HBNI, Bhubaneswar, India

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹E.Bruschini,¹C.Carli,^1,2A.C.Buellet,³M.Vincendon,¹F.Capaccioni,¹M.Ferrari,^4,5F.Vetere,⁶A.Secchiari,⁷D.Perugini,⁶A.Montanini
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2022.114950]
¹Institute for Space Astrophysics and Planetology – INAF, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
²AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, F-91191 Gif-sur-Yvette, France
³Institut d’Astrophysique Spatiale, Bâtiment 121, Université Paris-Saclay, CNRS, Orsay, France,
⁴Institute of Mineralogy, Leibniz Universität Hannover, Callinstrasse 3, 30167 Hannover, Germany
⁵Dipartimento di Ingegneria & Geologia (InGeO), Università G. D’Annunzio di Chieti-Pescara, Via dei Vestini 31, 66100 Chieti, Italy
⁶Dept. of Chemistry, Life Sciences and Environmental Sustainability University of Parma, Parco Area delle Scienze 157/a, 43124 Parma, Italy
⁷University of Perugia, Department of Physics and Geology Piazza Università, 06100 Perugia, Italy
Copyright Elsevier

We report the VNIR (350–2500 nm) reflectance spectra of a suite of silicic samples mixed with graphite. We used three end-member materials with different chemical composition in order to have a comprehensive understanding of the effect of opaque minerals on reflectance spectra of silicic rocks. To decouple the effect of granulometry and graphite content on reflectance properties, we first measured the reflectance spectra for each end member at different grainsizes (between ⁓20 to 250 μm). Three selected grainsizes for each end-member were then mixed with graphite in the graphite/end-member weight ratio 1 to 5%. For each spectrum we evaluated the main band parameters (position, area, depth). Moreover, we also proposed and discussed the use of an additional parameter, the band centroid. Our results confirm that graphite mixed with silicate materials reduces albedo and decreases the spectral slopes and the spectral contrast of the mixtures. We discussed the subtle interplay between grain size, graphite content and chemical composition of the mixtures. We showed how graphite decreases the spectral slopes of the graphite-silicate mixtures proportionally to iron content (albedo) of the mixtures: low iron (bright) materials are more sensitive to spectral slope variation (decrease) as a function of graphite content. Finally we show how spectral slope influences the measured band parameters.

¹Christian Koeberl et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.02.021]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
Copyright Elsevier

The presence of tektite-like glasses from a geographically restricted area in Belize (Central America) has been known for several decades. We comprehensively studied 18 such Belize glasses by a variety of petrographic and geochemical methods, including major and trace element analysis, radiogenic isotopic composition (Rb-Sr, Sm-Nd, and Re-Os), water content, oxidation state, and cosmogenic radionuclides. The aims were to determine their compositional variation, their mode of formation and possible source rocks, and their relation to known tektites, and to search for evidence of an extraterrestrial component.

In terms of petrography, the samples are similar to tektites from the four “classical” strewn fields, with the presence of lechatelierites, schlieren, and vesicles; these are also widely accepted indicators of an impact origin. No close similarities to volcanic glasses are evident. Water contents are very low, and iron oxidation states are mostly reduced, in both cases similar to observations for other tektites. The geochemical and isotopic data presented, such as Cr, Co and Ni elemental abundances and interelement ratios, as well as trace element patterns are typical for local and regional volcanics from the active Central American Arc. Particular similarities to material comparable to volcanic rocks from Honduras or Guatemala are noted. This is confirmed by Sr-Nd isotope signatures of the Belize glasses, showing close similarities to Central American volcanics in general, and Honduran and Guatemalan volcanic, in particular. Osmium concentrations and 187Os/188Os ratios are comparable to arc volcanics from world-wide locations, but – in a few of the samples – elevated Ir concentrations, near-chondritic Pt/Ir and 187Os/188Os ratios can also be interpreted with the admixture of a minor meteoritic component to some of the Belize samples. 10Be concentrations are consistent with values typical of both, young or deeply buried soils and with values for Central American volcanics, which carry subducted 10Be.

Geochemical data clearly indicate a source different from that of the Australasian tektites. Both isotope data sets for the Belize glasses indicate a close relationship to local arc lavas, especially those from Guatemala and Honduras, suggesting that the glasses were not deposited very far from their source. The main evidence that the Belize glasses are of impact origin are their petrographic characteristics and low water content. The evidence from 10Be is consistent with, but does not require, a model of formation for the Belize glasses by an impact on loosely consolidated surface sediments exposed to rain. A probable meteoritic component is low and heterogeneously distributed.