The Agoudal (High Atlas Mountains, Morocco) shatter cone conundrum
|Untertitel:||A recent meteorite fall onto the remnant of an impact site|
|Autoren:||Chennaoui Aoudjehane, Hasnaa (Hassan II University, Casablanca) El Kerni, Houda (Hassan II University, Casablanca) Reimold, Wolf Uwe (Museum für Naturkunde Berlin - Leibniz-Institut für Evolutions- und Biodiversitätsforschung) Baratoux, David (Université Paul Sabatier CNRS & IRD UMR 5563) Koeberl, Christian (Naturhistorisches Museum Wien (NHM)) Bouley, Sylvain (Université Paris Sud 11 - UP11) Aoudjehane, Mohamed|
Associations between impact structures and meteorite occurrences are rare and restricted to very young structures. Meteorite fragments are often disrupted in the atmosphere, and in most cases, meteorite falls that have been decelerated by atmospheric drag do not form a crater. Furthermore, meteorites are rapidly weathered. In this context, the finding of shatter cones in Jurassic marly limestone in the same location as a recent (105 ± 40 ka) iron meteorite fall near the village of Agoudal (High Atlas Mountains, Morocco) is enigmatic. The shatter cones are the only piece of evidence of a meteorite impact in the area. The overlap of a meteorite strewn field with the area of occurrence of shatter cones led previous researchers to consider that the meteorite fall was responsible for the formation of shatter cones in the context of formation of one or several small (2) and the strewn field of meteorites are distinct, although they show some overlap. The alleged impact breccia is revealed as calcrete formations. No evidence for a genetic relationship between the shatter cones and the meteorites can be inferred from field observations. The extent of the area where in situ shatter cones and macrodeformation not corresponding to Atlas tectonic deformation are observed suggest that the original diameter of an impact structure could have been between at least 1–3 km. For typical erosion rates in the Atlas region (~0.08 cm yr−1), the period of time required for the erosion of such a structure (1.25–3.75 Ma) is much larger than the age of the meteorite fall. This line of reasoning excludes a genetic link between the shatter cones and the meteorite fall and indicates that the observed shatter cones belong to an ancient impact structure that has been almost entirely eroded.
|Anzahl der Seiten:||22|
|Journal Titel:||Meteoritics and Planetary Science|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1111/maps.12661|