¹N. G. Rudraswami,¹D. Fernandes,¹M. Pandey
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13574]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa, 403004 India
Published by arrangement with John Wiley & Sons

Micrometeorites (MMs) are extraterrestrial dust particles, in the size range of tens of µm to mm, recovered from the Earth’s surface primarily from deep‐sea sediments, Antarctica, and also from space. The present collection of MMs (>50 µm) obtained by melting ~50 t of ice near the Maitri station, Antarctica, has allowed us to investigate the abundance and properties of the particles by an unbiased collection technique. The collection reveals a large quantity of extraterrestrial material in the ~80−140 µm size range. Previous collections have shown an abundance of particles at diameter ~200 µm, which is in contrast to our findings. This can either be explained by movement of material within the ice or a recent influx of smaller particles. The smaller particles (<80 µm) typically undergo atmospheric entry heating, contrary to earlier observations, which have suggested that they reach the Earth’s surface unmelted. Chondrules and refractory inclusions are rare in the collected MMs indicating that their contribution is only a small percentage. The Maitri station collection does not have a well‐constrained ice accumulation rate and terrestrial age. Nevertheless, based on matching the previous well‐documented flux calculation of Antarctica, we suggest a slow ice accumulation rate of <1.0 g cm−2 yr−1 near Maitri station.

¹Jean‐Guillaume Feignon,²Ludovic FerriÈre,³Hugues Leroux,¹Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13570]
¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
²Natural History Museum, Burgring 7, A‐1010 Vienna, Austria
³Univ‐Lille, CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et transformations, 59655 Villeneuve d’Ascq, France
Published by arrangement with John Wiley & Sons

Planar deformation features (PDFs) in quartz are a commonly used and well‐documented indicator of shock metamorphism in terrestrial rocks. The measurement of PDF orientations provides constraints on the shock pressure experienced by a rock sample. A total of 963 PDF sets were measured in 352 quartz grains in 11 granite samples from the basement of the Chicxulub impact structure’s peak ring (IODP‐ICDP Expedition 364 drill core), with the aim to quantify the shock pressure distribution and a possible decay of the recorded shock pressure with depth, in the attempt to better constrain shock wave propagation and attenuation within a peak ring. The investigated quartz grains are highly shocked (99.8% are shocked), with an average of 2.8 PDF sets per grain; this is significantly higher than in all previously investigated drill cores recovered from Chicxulub and also for most K‐Pg boundary samples (for which shocked quartz data are available). PDF orientations are roughly homogenous from a sample to another sample and mainly parallel to {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00013} and {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00024} orientations (these two orientations representing on average 68.6% of the total), then to {10urn:x-wiley:10869379:media:maps13570:maps13570-math-00032} orientation, known to form at higher shock pressure. Our shock pressure estimates are within a narrow range, between ~16 and 18 GPa, with a slight shock attenuation with increasing depth in the drill core. The relatively high shock pressure estimates, coupled with the rare occurrence of basal PDFs, i.e., parallel to the (0001) orientation, suggest that the granite basement in the peak ring could be one of the sources of the shocked quartz grains found in the most distal K‐Pg boundary sites.