Artificial weathering of an ordinary chondrite: Recommendations for the curation of Antarctic meteorites

Abstract

Meteorites are prone to errestrial weathering not only after their fall on the Earth's surface but also during storage in museum collections. To study the susceptibility of this material to weathering, weathering experiments were carried out on polished sections of the H5 chondrite Asuka 10177. The experiments consisted of four 100-days cycles during which temperature and humidity varied on a twelve hours basis. The first alteration cycle consisted of changing the temperature from 15 to 25 °C; the second cycle consisted of modifying both humidity and temperature from 35 to 45% and 15 to 25 °C, respectively; the third cycle consisted of varying the humidity level from 40 to 60%; and the fourth cycle maintained a fixed high humidity of 80%. Weathering products resulting from the experiments were identified and characterized using scanning electron microscopy-energy dispersive spectroscopy and Raman spectroscopy. Such products were not observed at the microscopic scale after the first cycle of alteration. Conversely, products typical of the corrosion of meteoritic FeNi metal were observed during scanning electron microscope surveys after all subsequent cycles. Important increases in the distribution of weathering products on the samples were observed after cycles 2 and 4 but not after cycle 3, suggesting that the combination of temperature and humidity fluctuations or high humidity (>60%) alone is most detrimental to chondritic samples. Chemistry of the weathering products revealed a high degree of FeNi metal corrosion with a limited contribution of troilite corrosion. No clear evidence of mafic silicate alteration was observed after all cycles, suggesting that postretrieval alteration remains limited to FeNi metal and to a lesser extent to troilite.

Dense collection areas and terrestrial alteration of meteorites in the Atacama Desert

“…Within the Atacama chondrites, metal and sulfide grains are the main phases that show significant signs of alteration by terrestrial fluid percolation, suggesting that silicates and calciumaluminum-rich inclusions (CAIs) likely preserve their original O isotopic compositions acquired upon condensation/crystallization. The limited extent of the alteration of silicates and CAIs is also supported by recent weathering experimental results in chondrites (Van Ginneken et al, 2022). Applying a range of temperatures and humidity levels on polished sections of the H5 chondrite Asuka-10177, the experiments revealed extensive weathering of the Fe-Ni metal grains, but only a minor alteration of troilite and no evidence of mafic silicate alteration.…”

“…These variations depend on the distance from the Pacific Ocean, which can generate dense coastal fog and topographic elevation, which controls the precipitation rate among the different morphotectonic units (Boy et al., 2022). Experimental studies show that metal corrosion in OCs is mostly controlled by thermoclastic weathering produced by temperature fluctuations during day/night and high level of humidity (Van Ginneken et al., 2022). Both are common factors in the Atacama Desert, with slightly major level of humidity in CR.…”

The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes

“…(this volume) also found terrestrial sulfates occurring in areas outside the fusion crust within the P30552 section of Winchcombe. Other studies have shown early weathering occurs in meteorites (e.g., Van Ginneken et al., 2022); however, these observations emphasize that terrestrial alteration occurs rapidly and that even meteorites observed to fall are not exempt. It also suggests that fusion crust provides an opportunity to demonstrate the terrestrial origins of alteration products.…”

Fluid mobilization of rare earth elements, Th, and U during the terrestrial alteration of H chondrites

“…According to Mittlefehldt and Lindstrom (1991), melting of ice in Antarctica can trigger sample alteration following chemical leaching as demonstrated by the loss of Ca‐phosphates in eucrites from Antarctic samples, in line with our observations for cracks in Antarctic chondrites. Rain or humidity is known to trigger a similar mechanism in hot deserts (e.g., Al‐Kathiri et al., 2005; van Ginneken et al., 2022). During the residence of meteorites in Antarctica, hot deserts, or anywhere else on the Earth, fluids such as melting ice or rain pass through the interior of a meteorite following any physical weaknesses, cracks, or grain boundaries.…”

“…As falls are usually collected shortly after the fall events, they are in general significantly fresher than finds, as the latter have been subjected to weathering to various degrees during their terrestrial residence (roughly of the order of tens of kyr in most hot deserts and up to a few Myr in Antarctica and Atacama: e.g., Al‐Kathiri et al., 2005; Drouard et al., 2019; Nishiizumi et al., 1989; Zekollari et al., 2019). Terrestrial weathering may change the original mineralogy and chemical compositions of meteorites due to oxidation, hydration, and so on, that is, the alteration to phases that are more stable at the Earth's surface depending on environmental factors such as humidity and temperature (e.g., Bland et al., 2006; Koeberl & Cassidy, 1991; Lee & Bland, 2004; van Ginneken et al., 2022). To evaluate the degree of weathering for finds, two classification systems are commonly applied: the ABC index for Antarctic meteorites and a scale with seven categories from W0 to W6 used mainly for ordinary chondrites (Antarctic Meteorite Newsletter, NASA; Meteorite Newsletter, NIPR; Bland et al., 2006; Gooding, 1989; Wlotzka, 1993).…”