Petrographic and microtextural analyses were done on the thin section of an impactite from the Jacek Siemiątkowski Collection of Meteorites (ING PAN OB Wrocław). Two types of textures, crystalline and glassy are distinguishable. In each of them, mineral and rock fragments are deformed in different way and to various degree. One can distinguish: biotite kink bands, irregularly fractured quartz grains, twins of feldspar crystals. Moreover there are visible textures such as planar deformation features in quartz and feldspar grains, diaplectic and polymineral – lechatelierytic glasses. All the observed textures may testify the origin of the rock. The slightly deformed fragments and strongly deformed ones developed during the compression phase of the crater formation at different distance from a projectile and the crater centre. This event was followed by excavation of deformed material and its redeposition in the crater filling. The rock was recrystallised afterwards, which is inferred from the presence of the decorated PDFs and subgrains in some dynamically recrystallised quartz grains.
The Terny structure is an example of the highly denuded astrobleme, formed in crystalline target rocks of the Ukrainian Shield. Primarily, its impactites were discovered in two mines of iron ore, Pervomaysk and Annovsk, established in jaspilite and magnetite deposits. The Terny impactites are characterised by examples of various breccias, including a ferrugineous one and suevite, and melt rock (tagamite). Quartz of low birefringence, multidirectional PDFs in quartz, isotropic glassy quartz and glass globules evidence an impact influence on rocks. Clasts of melt/glassy quartz were partly brecciated or changed into clay minerals. Clasts of metamorphosed rocks in matrix of breccia are angular or rounded. Their sharp or diffuse contacts with matrix prove the influence of a unidirectional factor on the formation of breccia.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.