| Abstract: | Abstract— Ilafegh 013 is a slightly weathered, type-3 ordinary chondrite that is unusual in that it is highly shocked. Olivine grains in chondrules were studied in detail by transmission electron microscopy (TEM) to characterize the dislocations, fractures and recrystallization textures. Only c dislocations, in the (010) glide plane, seem to be activated by the shock wave. Fractures are more numerous in the TEM than at the scale of the optical microscope. They can be divided into two groups: (a) Open fractures with injections of molten metal, sulphide, and in some cases, phases containing Ca, Al, Na and K. (b) Very straight and narrow cracks parallel to {130} planes without injected material and consisting of imperfectly relaxed subgrain boundaries composed of two families of dislocations (Burgers vectors a and c ). Both types of dislocations are roughly in screw orientation (i.e., the subgrain boundaries have a pronounced twist character). It is suggested that they formed during the shock in order to relax stresses around shear fractures (fractures with displacements of their walls parallel to the fracture plane). Recrystallization occurs in areas where the dislocation density is high. Since diaplectic glass was not detected, it is suggested that recrystallization resulted from the large elastic energy of the lattice defects stored in the deformed crystals. |
