Zheng-Yu Long^a,b, Frédéric Moynier^a, Marine Paquet^a,c, James M.D. Day^d, Linru Fang^a, Tu-Han Luu^a, Dimitri Rigoussen^a, Kun-Feng Qiu^b, Jun Deng^b, Christian Koeberl^e
Earth and Planetary Science Letters 118979 Link to Article [https://doi.org/10.1016/j.epsl.2024.118979]
^aIstituto Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 75005 Paris, France
^bFrontiers Science Center for Deep-time Digital Earth, State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing, China
^cCentre de Recherches Pétrographiques et Géochimiques de Nancy, CNRS, Université de Lorraine 15 Rue Notre Dame des Pauvres 54500 Vandoeuvre-lès-Nancy, France
^dScripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093-0244, USA
^eDepartment of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
Copyright Elevier

Evaporation can fractionate elements and their isotopes between the condensed and gas phases. The fractionation of zinc isotopes during impact-induced evaporation can be used to effectively determine the extent of volatile loss. A robust understanding of the Zn isotope system in assessing the volatile loss, however, relies on well-constrained empirical isotopic fractionation factors (α) during evaporation under a range of pressure and temperature conditions. In this study, Zn isotopic data for well-documented impact glasses from six sites (Darwin, Australia; Zhamanshin, Kazakhstan; El’gygytgyn, Russia; Boltysh, Ukraine; Lonar, India; and Ries, Germany) are reported to investigate the extent of Zn isotopic fractionation under conditions of impact-induced evaporation on Earth. Our findings suggest that the initial Zn isotopic composition in terrestrial impact glasses is comparable to that of continental crustal rocks, but this composition becomes progressively heavier as more isotopically light Zn is lost from the impact melt, reaching a maximum δ⁶⁶Zn value of +1.1 ‰. The investigated samples show a statistically significant negative correlation between δ⁶⁶Zn values and Zn contents, especially those from the Darwin crater (R² = 0.90). These samples define an α value of 0.99971 ± 0.00005 (1SE). This α value is consistent with those previously estimated for melt glasses and fused sands (α = 0.9997 to 0.9998) from the Trinity nuclear detonation site, slightly higher than the value estimated from tektites (α = ∼0.998), and notably higher than that theoretically expected for evaporation into a vacuum (α = 0.985 to 0.993). This result highlights the limited fractionation of Zn isotopes during terrestrial impact processes. Moreover, the modelling suggests that the range of α values from 0.9997 to 0.9998 aligns with the observed compositions in lunar mare basalts and products from nuclear detonation, supporting α values close to but not exactly unity for Zn isotopic fractionation during various high-energy impact events. Utilizing the modelled fractionation factor (α = 0.9997), it is possible to reproduce the Zn concentration and isotopic composition of the lunar mare basalts, indicating a loss of about 98 % of the Moon’s initial Zn inventory. Terrestrial impact glasses demonstrate that, under natural impact conditions, stable Zn isotopes can undergo evaporative fractionation to a degree comparable to lunar mare basalts and melted fallout glass and fused sands from nuclear detonation, suggesting an important contribution from impact to the volatile depletion of terrestrial planets.

G. Schmidt^a,b, F. Salvini^b  
Earth and Planetary Science Letters 118974 Link to Article [https://doi.org/10.1016/j.epsl.2024.118974]
^aIstituto di Astrofisica e Planetologia Spaziali (IAPS), INAF, Rome, Italy
^bGeoQuTe Lab, Department of Science, Roma Tre University, Rome, Italy
Copyright Elevier

Load on a planet’s lithosphere can often form a well-defined flexural bulge, including a permanent (or long-lasting) forebulge, which preserves important information on the force of the load and properties of the lithosphere itself. On Pluto, aspects of the outer ice shell (i.e. the lithosphere) have become increasingly ascertainable, as recent work using data from the New Horizons space probe has revealed evidence of ongoing surface cryovolcanism and a subsurface water ocean. However, the precise thickness and elasticity of the ice shell has yet to be fully established. Sputnik Planitia, one of the largest surface features on Pluto, is an elliptical depression that may have formed during an impact event and subsequently infilled with nitrogen ice. It is characterized by a smooth, radially asymmetrical, forebulge which has been retained in places along the border of the depression. However, the proportion of influence on the formation of the forebulge between the impact load and the load induced by the infill remains unknown. Here, we report results from the analysis of the forebulge of Sputnik Planitia to explore the characteristics of the ice shell and the nitrogen infill. By utilizing multiple Converging Monte Carlo (CMC) simulations within the material and environmental parameters of Pluto, the best fit flexure surface was able to replicate the topography of the flexure (including the forebulge) from ten profiles. Results show an ice shell thickness ranging from 65 to 90 km, with an average of 78 km. The density of the ice shell is 50 kg/m³ less than the density of the subsurface water ocean. We demonstrate that if the formation of the forebulge occurs solely from the nitrogen ice infill load, the infill must reach >18 km of thickness. Furthermore, a southeast-northwest central load symmetry may have been produced by an impacting object with a southeast-northwest trajectory.

Kees Erica R. JAWIN^1,2, Timothy J. MCCOY¹, Lisette E. MELENDEZ^1,3, Catherine M. CORRIGAN¹ , Kevin RIGHTER^4,8, and Harold C. CONNOLLY Jr^5,6,7 
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14263]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
²Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC, USA
³Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
⁴NASA Johnson Space Center, Houston, Texas, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁶Department of Geology, School of Earth and Environment, Rowan University, Glassboro, New Jersey, USA
⁷Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA
⁸Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York, USA Sciences

Orbital observations of Bennu revealed a surface covered in boulders that are most similar among meteorites in our collections to aqueously altered carbonaceous chondrites, and initial analyses of the returned Bennu sample have begun to reveal insights into Bennu’s origins. We identified a suite of paired CM2 chondrite meteorites that have a finely layered texture and bear a striking similarity, although at a different scale, to rugged, layered boulders on Bennu. We investigated the nature and potential origin of this layered texture by performing a petrofabric analysis on samples MET 00431, 00434, and 00435. We developed a micro-geospatial mapping framework that is more commonly used for landscape-scale investigations. Our results reveal a pervasive fracture network that exhibits a similar orientation to flattened particles dominated by tochilinite–cronstedtite intergrowths (TCI). We propose that their petrofabrics originated from a low-energy impact on the parent body that occurred after the main period of aqueous alteration halted. The impactdeformed TCI (which formed during earlier aqueous alteration) and generated the fractures. We propose that the sample from Bennu may contain particles with similar layered textures to these meteorites which, if present, would likewise indicate the dominant role of impacts and aqueous alteration on Bennu’s parent body.