Triassic Volcaniclastic and Igneous Rocks of the Pronchishchev Ridge (East Siberia, Arctic): Composition, Structure, Genesis, and Age

—Petrographic and geochemical studies of igneous and volcaniclastic rocks of the middle part of the Pronchishchev Ridge and the Terpei lowland provided new data on their composition and structure. The subdivision of the Permian–Lower Triassic strata enclosing igneous and volcaniclastic bodies has been clarified by lithological/stratigraphic methods. The Lower Triassic Ulakhan-Yuryakh, Chekanovsky, Ystanakh, and Pastakh formations have been traced for the first time in the ridge area. It is shown that the studied dolerite body and adjacent breccias in the field of middle–upper Permian rocks are part of the volcanic pipe. The tuffite sandy gritstones in the field of Lower Triassic rocks are parts of an eroded tephra ring around this diatreme. The localization of tuffite bodies in the area of the Ystanakh Formation makes it possible to date the pipe at the beginning of the late Olenekian. The obtained 40Ar/39Ar dates for the dolerites of the volcanic pipe and one of the dikes of the Pronchishchev dike belt indicate the repeated tectonomagmatic activity in the studied area in the Triassic.