The terrestrial alteration of saharan shergottites dar al ganid 476 and 489: A case study of weathering in a hot desert environment

Rare earth element (REE) and other selected trace and minor element concentrations were determined in various phases of Dar al Gani 476 and 489, two basaltic shergottites recently found in the Libyan Sahara. Whereas merrillite and feldspathic glass compositions do not seem to have been altered since the fall of these meteorites, olivine and pyroxenes commonly show light REE enrichments, sometimes accompanied by Ce anomalies, that are attributed to terrestrial alteration. Sr and Ba enrichments are also observed. The calcium carbonate that resides in most cracks is essentially devoid of REE but a fine-grained amorphous silicate material that fills some veins and pockets has striking light REE enrichments and elevated P, Sr, and Ba. It is argued that this material, likely to be impact melt, as well as the notoriously light REE-poor olivine and pyroxenes, were preferentially affected by a crustal light REE-rich contaminant. Caution is urged when using whole rock, or even mineral separate, compositional, and isotopic data for hot desert meteorites.