¹Giovanna Serventi, ²Cristian Carli
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.018]
¹Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Viale delle Scienze 157/A Parma 43124, Italy
²IAPS-Inaf, Viale Fosso del Cavaliere Tor Vergata, Roma, 00133 Italy
Copyright Elsevier

The lunar surface consists of a regolith layer that covers the underlying bedrocks, and is generally characterized by particulates

The coarsest sizes of the regolith are chemically and mineralogically similar, while the finest fractions are more feldspathic, probably due to easier fracturing of plagioclase than mafic minerals.

Due to the more feldspathic nature of the very fine lunar soils, in this paper, we quantitatively investigate the influence of very fine (

(1) fine sizes act principally on reflectance and on spectral contrast (with the former increasing and the latter decreasing); (2) very fine plagioclase has a blue slope in the Near Infrared and very shallow 1250 nm band depth, close to zero; (3) consequently, the plagioclase band is always shallower than mafic bands; (4) in mixtures with olivine, the composite band center always shows the typical olivine value, differently from coarser mixtures; and (5) mafic materials have a blue slope in the Short Wavelength Infrared Region, a more V-shaped 1µm pyroxene absorption and the 1µm mafic band centers are shifted by ca. 40 nm vs. coarse sizes, reflecting a different weight within the crystal field absorption of the mafic component in very fine size. We also evidenced that a coarse plagioclase could be overestimated, while a very fine one could be underestimated if compared with the 63-125µm size.

¹Pierrick Roperch, ²Jérôme Gattacceca, ³Millarca Valenzuela, ²Bertrand Devouard, ⁴Jean-Pierre Lorand, ⁵Cesar Arriagada, ²Pierre Rochette,^6,7Claudio Latorre, ⁸Pierre Beck
Earth and Planetary Science Letters 469, 15-26 Link to Article [http://doi.org/10.1016/j.epsl.2017.04.009]
¹Géosciences Rennes, CNRS–INSU, Université de Rennes 1, Rennes, France
²CNRS, Aix Marseille Univ., IRD, Coll France, CEREGE, Aix-en-Provence, France
³Instituto de Astrofísica, P. Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
⁴Laboratoire de Planétologie et Géodynamique, CNRS UMR 6112, Université de Nantes, 2 Rue la Houssinière, 44322, Nantes, France
⁵Departamento de Geología, Facultad de Ciencas Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
⁶Centro UC del Desierto de Atacama and Departamento de Ecología, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
⁷Institute of Ecology & Biodiversity (IEB), Santiago, Chile
⁸Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414, Rue de la Piscine, Domaine Universitaire, 38400 St-Martin d’Hères, France
Copyright Elsevier

We describe extended occurrences of unusual silicate glass surface layers from the Atacama Desert (Chile). These glasses, found near the town of Pica at four localities separated by up to 70 km, are neither fulgurites, nor volcanic glasses, nor metallurgical slags related to anthropic activity, but show close similarities to other glasses that have been previously attributed to large airbursts created by meteoroids entering the Earth’s atmosphere. The glasses are restricted to specific Late Pleistocene terrains: paleo-wetlands and soils rich in organic matter with SiO2-rich plant remains, salts and carbonates. 14C dating and paleomagnetic data indicate that the glasses were formed during at least two distinct periods. This rules out the hypothesis of a single large airburst as the cause of surface melting. Instead, burning of organic-rich soils in dried-out grassy wetlands during climate oscillations between wet and dry periods can account for the formation of the Pica glasses. Large oases did indeed form in the hyperarid Atacama Desert due to elevated groundwater tables and increased surface discharge during the Central Andean Pluvial Event (roughly coeval with the Mystery interval and Younger Dryas). Finally, we discuss the implications of our results for the other surface glasses previously attributed to extraterrestrial events.