Stages of Paleoarchean to Paleoproterozoic Basic–ultrabasic Magmatism in the Sarmatian Craton

Abstract

The early stages of basic–ultrabasic magmatism in Sarmatia are characterized by the appearance of ultrabasic rocks formed from the mantle with an abnormally high iron content. Therefore, it is important to study them as the source of information about the stages and causes of the activity of the mantle and its possible composition. This magmatism has been recorded in Sarmatia since the beginning of the Eoarchean. The relics of Eo- and Paleoarchean basic and ultrabasic rocks were found in the Dniester–Bug, Kursk, and Azov provinces, which underwent tectonic reconstruction in the Mesoarchean and Paleoproterozoic. Mesoarchean basic–ultrabasic magmatism is manifested in all provinces of Sarmatia and is represented by effusive and intrusive facies. The Mesoarchean greenstone belts composed of komatiites and basalts have been well preserved in the Middle Dnieper province; in other provinces, they are strongly deformed and form narrow linear structures. The Paleoproterozoic endogenous activity in Sarmatia differs from that in other regions in the almost complete absence of magmatism in the period 2.5–2.3 Ga and its significant manifestation 2.1–2.0 Ga. The magmatism in Sarmatia at this stage is similar in the ratios of basic–ultrabasic and granitoid complexes to the magmatism in South Africa but differs from that in Fennoscandia and Canada. The volume of granitoids coeval with basic rocks is larger than the volume of mantle magmatism. The igneous complexes formed 2.1–2.0 Ga in Sarmatia and South Africa are also similar in the presence of norites, the enrichment in Ni and platinum group elements, and the ratio of granitoids and basic–ultrabasic rocks. Magmatic activity (first of all, basic–ultrabasic magmatism in ancient cratons) is not a synchronous phenomenon on a planetary scale and varies greatly in the volume of produced material within the same time intervals. Early Precambrian basic–ultrabasic rocks (volcanics of greenstone belts, intrusions of large igneous provinces, and layered massifs) resulted from plumes, whose derivates formed within the lower and upper mantle and/or the upper mantle and crust, which determined the heterogeneous composition of igneous rocks. The spatial heterogeneity and nonsynchronic occurrence of basic–ultrabasic magmatism might have been due to impact events serving as the triggers of plumes.