Kink-bands as indicators of shock-wave propagation direction: Results from experimental impact cratering on gneiss

Abstract

Microscopic kink-bands in platy minerals are a common occurrence at impact craters. The geometry of kink-bands formed in biotite due to an impact cratering experiment on Maggia gneiss was analyzed to see if they might be utilized to deduce the shock wave propagation direction. Here, we investigated the kink-bands in a vertical profile just below the impact point. The intensity of kinking decreases from top to bottom, indicating higher strains near the crater floor. The high asymmetry of kink-bands indicates their formation due to dynamic deformation. We used three methods, viz., the kink-band triangle plot, the contraction-neutral-extension (P-B-T) axes method, and the rotational optimization, to determine the principal stress directions. The shock-wave propagation directions can be deduced from σ1 orientation. All three approaches indicate a top-bottom orientation of the σ1 (maximum principal stress direction), which matches the σ1 orientation during the experiment. Furthermore, we examined the left and right oblique profiles to verify the relationship of kink-band orientations with the variation in angles between the point source and the foliations. The kink-bands in all the profiles show geometric relationship to σ1. Therefore, the present study underlines the ability of kink bands as a potential indicator of shock-wave propagation directions.