¹V. E. Hamilton et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70176]
¹Southwest Research Institute, Boulder, Colorado, USA
Published by arrangement with John Wiley & Sons

Remote spectroscopy is used to characterize the mineralogy and infer the history of planetary bodies. Carbonaceous asteroids, such as B-type (101955) Bennu, represent the earliest stages of planet formation. B types have a blue (negative) spectral slope and comprise <5% of asteroids. Samples from Bennu returned by the OSIRIS-REx spacecraft complement remote observations of this rare population. We show here, using laboratory spectra that are directly comparable to spacecraft data, that OSIRIS-REx accurately determined Bennu’s dust content and most of its surface composition. However, spectra of the asteroid exhibit stronger water absorptions than those of bulk samples, possibly due to hydrous, Mg-rich phosphate or solar wind implantation at Bennu’s uppermost surface. Bennu samples spectrally resemble the most aqueously altered carbonaceous meteorites and samples of (162173) Ryugu, indicating similarly pervasive aqueous alteration. However, one carbon-enriched Bennu stone does not appear to have a spectral analog among Ryugu samples or meteorites. Our findings demonstrate the leverage obtained using a wide range of wavelengths and that sample analysis anchors the interpretations of remote sensing, leading to more robust characterization of planetary surface composition and evolution.

¹Raiza R. Quintero,²Aaron J. Cavosie,³Noreen J. Evans,³Bradley J. McDonald,⁴Sanna Alwmark,²Nicholas E. Timms,⁵Malcolm P. Roberts,⁶Jayson Meyers
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70154]
¹Department of Geology, University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico
²Space Science and Technology Centre, School of Earth and Planetary Science, Curtin University, Perth, Western Australia,Australia
³John de Laeter Centre, Curtin University, Perth, Western Australia, Australia
⁴Department of Geology, Lund University, Lund, Sweden
⁵Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Crawley, Western Australia,Australia
⁶Resource Potentials LTD PTY, Osborne Park, Western Australia, Australia
Published by arrangement with John Wiley & Sons

The Ora Banda structure in Western Australia is situated within an Archean greenstone terrane known for orogenic gold deposits. It is defined by concentric gravity anomalies up to 4 km in diameter, and gravity and passive seismic data indicate the presence of a central uplift and annular trough. Shatter cones were found in surface samples and drill core during gold exploration. Breccia samples from drill core in the annular trough contain shocked quartz and glass with a projectile component. Planar deformation features (PDFs) were found in 17 quartz grains from suevite, and are oriented along crystallographic orientations typical for shock metamorphism, including $$ and $$, recording shock pressures from 15 to 20 GPa. Analysis of glass in suevite by EMPA and LA-ICP-MS shows the composition is basaltic andesite (avg = 54 wt% SiO₂), with major oxide compositions reflecting mixing of local Archean greenstone target rocks. Average abundances of Ni (2640 ppm), Co (205 ppm), Ir (290 ppb), and other PGEs (Rh, Pd, Pt) in the glass are significantly higher than mafic and ultramafic target rock lithologies and are interpreted to be meteoritic in origin, with Cr-Ir abundances indicating an iron projectile. Previous palynological analysis of crater fill sediments overlying the breccias indicates the impact event was likely Early Cretaceous or older. The Ora Banda structure offers insights into the cratering process near the simple-to-complex size transition, including the first documented occurrence of well-preserved “Ries-type” suevite described from Australia. In addition, Ora Banda represents one of the oldest known sites with strong geochemical evidence for an iron meteorite projectile and is one of few confirmed impact structures formed in an Archean greenstone terrane.