CRATER GEOLOGY

CRATER GEOLOGY

Meteoroid impacts on this planet have formed many impact craters, the contact speeds varying from terminal velocity to hypervelocities. The extreme pressures and temperatures at hypervelocity impacts have caused shock metamorphic effects on the target rocks. The breccia and pseudotachylite found at the “outskirts” of impact structures could be explained by naturalistic means (tectonic, volcanic, sedimentary – other than impact), but taken together they strongly suggest evidence for an impact. These findings would suggest that further investigation to gather evidence of in impact may be warranted. Therefore, crater identification cannot rely soly on the discovery of breccias, there must be other impact evidence (IE shatter cones and/or planar deformation features) before the structure is identified as impact related. Shatter cones have been detected in many impact structures and are widely regarded as a diagnostic macroscopic (can be seen with the naked eye) recognition feature for impact. They are a dead give-away for the amateur crater hunter (like me) to confirm that the structure being explored is the result of an impact (if a LARGE man-made explosion can be eliminated). In many cases, the initial discovery of shatter cones has spurred successful searches for other shock effects.