Conditions of Rock Formation and Magma Sources of the Late Cenozoic Udokan Volcanic Plateau

Abstract

The Udokan volcanic plateau (UVP), like other areas of the Late Cenozoic volcanic province of Central Asia, formed in the interval from the Middle Miocene to the Pleistocene. Its products have high alkalinity and vary in composition from alkaline picrobasalts and basanites to alkaline trachytes. Compositional changes were controlled by two differentiation trends, which corresponded to different conditions of the original magmas generation. Rocks with low SiO2 contents (45 wt. %) were formed from melts of low melting degrees that arose under conditions of elevated pressures and temperatures. Formation of rocks corresponding to the composition range 45–61 wt. %. % SiO2 was associated with the differentiation of basalt melts, which arose at shallower depths and at lower temperatures. The geochemical characteristics of the UVP basaltoids make them similar to OIB-type basalts. They are also close in Sr, Nd, and Pb isotopic composition, corresponding to the parameters of a moderately depleted mantle, which is close to the composition of oceanic basalt sources corresponding to the mantle of deep mantle plumes. The corresponding mantle component is present in the sources of other volcanic regions of the Late Cenozoic intraplate volcanic province of Central Asia, which indicates the involvement of the lower mantle plume in the formation of these regions.