MICROSTRUCTURAL DEFECTS IN EXPERIMENTALLY SHOCKED DIOPSIDE - A TEM CHARACTERIZATION

Transmission electron microscopy was used for characterizing the defec t microstructure induced by shock experiments in a single crystal of d iopside. The shock-induced defects found in the crystal can be divided in four distinct types: 1) A high density and pervasive distribution of dislocations in glide configuration (glide systems (100)[001], {110 }[001] and (100)[010]). 2) Mechanical twin lamellae, mostly parallel t o (100), the (001) twin lamellae are less abundant. 3) Straight and na rrow amorphous lamellae parallel to a few planes with low crystallogra phic indices (the (331BAR) lamellae are the most abundant but (221BAR) and (110) lamellae are also present). 4) Heterogeneously distributed tiny molten zones (3 to 20 mum size) which, after cooling, appear as a glass with a chemical composition very close to the one of the origin al diopside. The present TEM study reveals that the defect microstruct ure in shocked diopside consists of a large variety of shock-induced d efects. Especially, the amorphous PDFs which were never observed in st atically deformed diopside seem to be an important characteristic micr ostructural defects in shocked silicate minerals. Although the presenc e of amorphous PDFs is not yet confirmed for naturally shocked clinopy roxene, we strongly suggest that these features can serve as a diagnos tic tool for recognizing impact phenomena on all planetary bodies of o ur solar system.