Devonian swarms of dolerite dykes in the northeastern Siberian craton and their relation to the Vilyui plume

Abstract

Recently, many researchers have started to pay attention to the study of large dike belts. This is explained by the fact that such belts mark extended faults in the lithosphere and, thus, both play an indic� ative role in defining epochs of important lithospheric reorganizations and serve as reference points in paleo� geodynamic reconstructions, which serve as a basis for recent metallogenic and prognostic concepts and reconstructing past deepseated geodynamic pro� cesses. Like many others structures, the Siberian Craton was subjected to many reorganizations during its life. Its lithosphere was stabilized in the Paleoproterozoic approximately 1.9 Ga ago (1). During its subsequent history, the craton was repeatedly involved in different continental agglomerations (for example, during the formation of Rodinia) and then separated from them during destruction of supercontinents. The corre� sponding events are reflected in differentage dike swarms. The Late Riphean dike belts that appeared during the breakup of Rodinia and indicate at least a Late Riphean age of the southern boundary of the cra� ton are best known among them. Significant swarms and clusters of dykes were also formed in the Middle Paleozoic. Powerful eruptions of Siberian Trap with the formation of a spacious system of sills and dykes occurred at the Permian-Triassic transition, and kim� berlites of a new generation intruded the northeastern part of the craton in the Late Mesozoic One of the most impressive systems of dike swarms was formed in the eastern part of the Siberian Craton during the Devonian. Its development accompanied the formation of the Vilyui rift system. In the opinion of (2), this process crowned the breakup of the conti� nent and formed its eastern boundary. An important feature of this rift system is the radial distribution of its main structural elements, dike swarms included. Such a position and structural features of the rift system allowed its formation to be related to destructive pro� cesses above the mantle plume (3), the center of which was located in the area overlain in the presentday structure by the foreland of the Mesozoic Verkhoyansk fold-thrust belt. In compliance with data on the distribution of gra� bens and dike swarms, the plume head at the base of the rift system should be 1500 km across. The follow� ing questions naturally arise: what mantle substrate was involved in the plume formation and to what extent was the latter uniform in different areas of the giant asthenospheric lens above the plume? Our previ� ous studies of igneous rocks, dykes included, in the southwestern part of the Vilyui rift system (Vilyui rift proper) revealed the main geochemical and isotopic- geochemical parameters of their mantle sources (4).