| Abstract |
Shatter cones are one of the most accepted field evidence for animpact crater. However, the exact mechanism of formation is stilldebated and several contrasting ideas can be found in the literature.The identification of shatter cones is not straightforward and I willrecall their main characteristics. Several points deserve a particularattention when evaluating models of formation: (1) the shape, notconical but curved, (2) the presence of surface striations, and (2)the direction of apices. Recent ideas (Sagy et al., 2002, 20O4 andBaratoux and Melosh, 2003, Wieland et al., 2006) will be presented.While the enigma remains, it is now clear that shatter cones resultfrom tensile fractures during shock unloading just behind the passageof the shock front and are controlled by rock heterogeneities.Preliminary observations of shatter cones in basalt made during afield campaign in August 2009 in Vargeao and Vista Allegre (Brazil)will be presented at this occasion. |
