Vol 11, No 2 (2017)

New data on the chemical and rare-element composition and age of the rocks referred earlier to the Iruney suite of the Kamchatka Isthmus are received. In the recent structure these rocks compose the structural–strata complexes of the nappe-folded Lesnovsky Rise. Radiolarian analysis data substantiate that the deposits belonging to the Ening series and the middle and upper parts of the Iruney suite were formed in a single sedimentation basin in the Campanian time. The discovery of a new occurrence of Prunobrachidae representatives on the Kamchatka Peninsula allows us to draw wide interregional correlations and reconstruct the sedimentation conditions. The studied volcanites relate to different igneous series and were formed in geodynamic conditions of the marginal sea and the volcanic arc. The igneous rocks of the Ening stratum are similar to the N-MOR and OI basalts that were formed within the marginal sea (Iruney Marginal Sea) basin. The Upper Cretaceous formations of the eastern slope of the Sredinny Range were formed within the volcanic rise with the island-arc type of volcanism. The younger Eocene igneous rocks of the neo-autochthon (granites and granodiorites) and the volcanic rocks of the Kinkil suite mark a new orogenic stage of development of the Kamchatka margin.

A detailed study of a relatively well-exposed fragment of the Barabash Formation in the southern part of the Voznesenka terrane is carried out to specify the geodynamic settings of the Permian volcanogenic and volcanogenic-sedimentary complexes in South Primorye. It is established that the basaltic flows juxtaposed in the studied sequence originated from sharply different sources. The geochemical characteristics indicate that the basalts from the sequence base were presumably derived by melting of oceanic lithospheric mantle or asthenosphere, while the source of the overlying basalts was lithospheric mantle reworked by a subduction process. The basalts are subsequently overlain by tuffaceous–terrigenous and terrigenous rocks and limestones with remains of Capitanian (Middle Permian) fauna. Accessory zircons extracted from the tuffaceous–terrigenous rocks yield an U–Pb concordant age of 233.3 ± 3.3 Ma (Middle Triassic Ladinian Stage) for the youngest zircon population. The obtained data lead us to conclude that the Barabash Formation is a tectonostratigraphic rather than stratigraphic unit and may be a fragment of the Triassic accretionary wedge. The obtained data cast doubt on the accepted assignment of this unit to the Voznesenka terrane. It is more logical to include it in the Laoelin–Grodekov terrane, which represents a fragment of the Late Paleozoic active continental margin. This suggests that the boundary between these blocks should be specified and the timing of the final stage of amalgamation of the Laoelin–Grodekov terrane with the terranes of the Bureya–Khanka orogenic belt should be revised.

The paper reports on the AMT (audiomagnetotelluric) sounding results obtained along the Troitskoe–Lidoga–Vanino Profile in the Northern Sikhote-Alin Region. The amplitude curves are analyzed; one- and two-dimensional interpretations are made; and the geoelectrical section down to 5 km depth is constructed and its geological interpretation is given.