Циркон как источник генетической информации в верхнерифейских терригенных отложениях Южного Тимана

Abstract

Zircon is an important source of genetic information. The purpose of the research is a detailed study, identification of diagnostic features, and determination of the evolution of the composition of zircon, which will make it possible to establish the sources of clastic material and the conditions for the formation of the paleontologically mute terrigenous Dzhezhim Formation on the Dzhzhimparma Rise (Southern Timan). The article presents the results of the study of zircon from the Upper Proterozoic metasedimentary deposits of the South Timan by Raman spectroscopy. According to morphological features, chemical composition, internal structure and degree of crystallinity, four types of zircon have been distinguished. The Raman spectra of all morphological types of the studied mineral was surveyed. A comparative analysis of the Raman characteristics showed that the first type is characterized by the highest degree of crystallinity, the third type is characterized by the minimum, and the second type occupies an intermediate position. The fourth type is a unique highphosphorus zircon, the nature of its spectra reflects the presence of Y, P, REE, and other impurity elements, and also indicates its metamictization as a result of radiation damage to the structure. Morphological features, differences in the chemical composition and characteristics of the Raman spectra of the distinguished types of zircon indicate the difference in the sources from which they entered the sedimentary rock. The source of type I zircon could be felsic igneous rocks. Type II and III zircons are probably of metamorphogenic origin. The formation of the modern composition and appearance of zircons of the fourth type, the formation of which is associated with a high-temperature magmatic source, is due to multiphase transformations in hydrothermal-metamorphic and epigenetic processes. We believe that type IV zircons have the longest history of existence. This is evidenced by their high metamict, i.e., the destruction of the crystal lattice under the action of U and Th radiation, which depends on their number and the age of zircon grains. It is known that the age of zircon of the Dzhezhim Formation is pre-Upper Riphean; during its existence, the mineral was repeatedly subjected to various external influences that changed the parameters of its crystal structure.