An interdisciplinary study of weathering effects in ordinary chondrites from the Acfer region, Algeria

Abstract

— Weathering effects on meteorite finds from the Acfer region were studied by various analytical techniques and in dependence on the depth of sampling. In thin sections of weathered meteorites, weathering effects usually decrease from the outside to the interior of the meteorite. The results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of Fe‐oxyhydroxides. The secondary alteration effects in the noble gases are distributed unevenly throughout the specimens, as seen in the nonsystematic differences observed for the heavy noble gases. Chemical analyses show significant enrichment of Ba and Sr in the outer parts of the weathered samples due to element contamination through aqueous solution. Iron, Ni, and Co are partly flushed from the system as the metal oxidation proceeds. Oxygen isotopes show increases in δ18O and δ17O with increasing terrestrial age. For a set of H3 chondrites, the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms.

KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt

“…Nevertheless, Dho 287A oxygen isotopic data plot on the terrestrial fractionation line, along with other lunar samples, and when considered in conjunction with the Fe to Mn ratios of olivine and pyroxene grains, provide further evidence for the lunar origin of this meteorite and exclude the possibility of it being any unusual HED meteorite. These unusually high d 18 O and d 17 O values for Dho 287A are, however, most likely due to the effects of terrestrial alteration in the hot-desert environment, as has been suggested previously in the case of meteorites from Algeria (Stelzner et al 1999).…”

Authenticating the recovery location of meteorites: The case of Castenaso

“…Moderately to severely altered Saharan L-chondrite finds (≥W2) are depleted in the siderophile elements Ni and Co (0.45-0.88 and 0.021-0.043 wt%, respectively). This feature was also observed in H chondrites from the Acfer region by Stelzner et al (1999), but we show here that it is not present in the European and slightly weathered (≤W1) Saharan finds and in Castenaso. Moderately to severely weathered Saharan L-chondrite finds (≥W2) can be enriched in LREE (La/Sm = 2.1-3.1).…”

Petrology and chemistry of the basaltic shergottite North West Africa 480

“…NWA 480 is an AI-poor ferroan basaltic rock and resembles Zagami or Shergotty. Because hot desert alteration is able to significantly affect the composition of meteorites (e.g., Barrat et al, 1999Barrat et al, , 2001bStelzner et al, 1999;Zipfel et al, 2000;Crozaz and Wadhwa, 2001), the effects of weathering are evaluated here first. The lack ofevidence ofterrestrial alteration is illustrated by the D, Ba and Sr abundances which are sensitive indicators of surface processes: NWA 480 displays a normal ThIU ratio and its Ba and Sr abundances are not outside the trend defined by other unweathered shergottites (Fig.…”