Micrometeorites are dust-sized (i.e., 10 to 2000 µm in size) extraterrestrial particles reaching the Earth’s surface [1]. We report the discovery of hundreds of micrometeorites during the 2017-2018 BELAM (Belgian Antarctic Meteorites) expedition that took place in the south to south-east area up to 40 km away from the Belgian Princess Elisabeth Station (71°57Ļ00ļS; 23°20Ļ49ļE). Two types of micrometeorite traps were targeted on the glacially eroded tops of Vengen, Walnumfjellet, Widerøfjellet, Svindland and Smalegga Mountains, consisting of 1/ seven samples of soils that have potentially been exposed for long periods of times (up to several Ma), similarly to samples collected in the Atacama Desert [2] and 2/ five samples of wind catchment areas, such as the base of large boulders or within cracks. The lee-sides of three lateral and supraglacial moraines were also sampled, totalling eleven samples. In all cases, the sampled material, weighing 80 kg, consisted of moderately sorted finegrained rock detritus. Preliminary results suggest that the distribution of micrometeorites varies according to the type of trap, with glacial moraines exhibiting the lowest concentrations, followed by wind-catchment areas and soils from the top of the glacially eroded summits of mountains. Samples exposed on the border of the Sør Rondane Mountains with the Antarctic Plateau exhibit concentrations one order of magnitude greater than in moraines. Similarly to the Larkman Nunatak micrometeorite collection [3], the micrometeorite accumulation mechanism in moraine and wind-catchment areas seems to be mainly controlled by wind. Conversely, direct infall of micrometeorites may contribute significantly as an accumulation mechanism in exposed soil samples, as evidenced by the presence of large micrometeorites (>400 µm in size). Thus, this new collection, comprising various sampling site types, may serve as the basis to understand micrometeorite distribution patterns in Antarctica.
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RBINS Staff Publications 2018
We report the discovery of a pristine chondrule-like object in a scoriaceous meteorite recovered from the Sør Rondane Mountains, East Antarctica. A preliminary study using a JEOL JSM-IT 300 scanning electron microscope, coupled to an energy dispersive spectrometer (SEM-EDS), at the Vrije Universiteit Brussel indicates that i) the chondrulelike object has a minimum diameter size of ~187 µm, which is broadly analoguous to chondrules found in CM, CO, H and EH chondrites [1]; ii) the chondrule-like object displays a radial pyroxene texture and is readily delineated from the surrounding micrometeorite ground mass. This is emphasized by the presence of microscopic olivine and magnetite crystals at the outer edge of the chondrule-like object. This suggests that it served as a nucleation point for crystallization of secondary mineral phases during atmospheric deceleration and heating. Hence, this object likely represents an original feature of the micrometeoroid; iii) the mineralogical content of the chondrule-like object is mainly composed of low-Ca pyroxene with interstitial glass, some smaller nodules of FeNi metal and a local cluster of chromite grains. The surrounding micrometeorite material displays a micro-porphyritic olivine texture which contains a single nodule of Fe sulfide, vesicles, and a number of relict mineral grains that survived atmospheric entry. The latter are predominantly composed of forsterite-rich olivine, although several relict grains of low-Ca pyroxene (i.e., enstatite-rich end-members) are observed as well. The objective of this study is twofold: i) analyze the major element and triple-oxygen isotope composition of the chondrule-like object, and the relict mineral phases to specify the nature of the precursor material, and ii) discuss the overall rarity of chondrules in micrometeorites.
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