Sources of Magmas and Conditions of Rock Formation in the Late Cenozoic Udokan Volcanic Plateau
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OLOGY
Sources of Magmas and Conditions of Rock Formation in the Late Cenozoic Udokan Volcanic Plateau Academician V. V. Yarmolyuka,*, V. M. Savatenkovb, F. M. Stupaka, and E. A. Kudryashovaa Received May 1, 2020; revised May 4, 2020; accepted May 6, 2020
Abstract—The Udokan volcanic plateau differs from other volcanic regions of the Late Cenozoic volcanic province of East Asia in the high alkalinity of volcanic rocks, their potassium specialization, and rock composition, varying from melaleucytitis and melanephelinites to alkaline trachytes. The presence of alkalinesalic rocks in volcanic associations makes it unique to the province. The reasons that determined the unique magmatism of the Udokan plateau are considered. The data of geochemical and isotopic studies have shown that the moderately enriched magma of the mantle plume served as a melt source in the region. The initial melts were formed under conditions of garnet stability at low degrees of melting. This contributed to their enrichment in alkalis and other incompatible elements that is especially characteristic of ultramafic rocks. It is established that fractionation processes controlled the distribution of the trace elements in the rocks of volcanic associations. Deep differentiation of the magmas to alkaline trachytes occurred in the peripheral magma chambers. Here, magmas interacted with intracrustal waters, which led to a change in their oxygen isotopic composition. It is shown that contamination did not play a decisive role in the formation of lava plateau rocks. Keywords: Late Cenozoic volcanic province, Udokan lava plateau, volcanism, isotopic and geochemical sources of magmatism, mantle melting, crystallization differentiation DOI: 10.1134/S1028334X20070223
A large volcanic province appeared in the Late Cenozoic in East Asia [1]. A series of volcanic regions composed primarily of mafic rocks stands out in its structure. Felsic volcanics are an exception in the structure of the province. They were identified in the structure of two volcanic regions, Changbaishan, located in the eastern part of the province, and Udokan tending to its northwestern margin. These differences indicate the special conditions of origin and evolution of the magmatism within these regions, which remain insufficiently studied. Based on the isotopic (Sr, Nd, Pb) and geochemical data, we estimated the compositions of the initial melts of the Udokan volcanic region (or the volcanic plateau), the conditions of their formation and evolution in time, and the causes, which led to their deep differentiation. The Udokan volcanic plateau is located on the northwestern flank of the Baikal rift zone, covering an a Institute
of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Moscow, 119017 Russia b Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, 199034 Russia *e-mail: [email protected]
area of about 3000 km2 [2, 3]. It stands out against the general background of the volcanic province by the l
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