Suevites and Tagamites of Zhamanshin Astrobleme: Distribution in the Crater and Petrographic Features

Abstract

The study of impact glasses from the Zhamanshin meteorite crater has a long history extending back to early 1970ies. Most attention is paid to unique impact-related rocks known as zhamanshinites (bombs) and irghizites (lapilli). But, as first shown by V.L. Masaitis, other, more common types of impactites, suevites and massive melts (tagamites), are also present in Zhamanshin. We study the distribution in the crater, structure and composition of these particular rocks using powder X-ray diffraction and scanning electron microscopy. It is shown that all impact glasses from the Zhamanshin crater are genetically related and derive from the impact event, while the observed petrographic differences between them reflect the conditions of their formation. Individual varieties of studied impactites (suevites and tagamites) are spatially separated and, as a rule, do not intersect. This points to the absence of global mixing of the target material as a result of the impact event, as well as to the complex nature of the impactor.