Age and chemical composition of volcanic rocks and minerals from the Vityaz Ridge

This paper reports results of geological studies carried out during two marine expeditions of R/VAkademik M.A. Lavrent'ev (Cruises 37 and 41) in 2005 and 2006 at the underwater Vityaz Ridge. Dredging has yielded various rocks from the basement and sedimentary cover of the ridge within three polygons. On the basis of radioisotope age determinations, petrochemical, and paleontological data all the rocks have been subdivided into the following complexes: volcanic rock of Paleocene, Eocene, Late Oligocene, Middle Miocene, and Pliocene-Pleistocene; volcanogenic-sedimentary rocks of Late Cretaceous - Early Paleocene, Paleogene (undifferentiated), Oligocene - Early Miocene, and Pliocene-Pleistocene. Determinations of age and chemical composition of the rocks have enabled to specify formation conditions of the complexes and to trace geological evolution of the Vityaz Ridge. Presence of young Pliocene-Pleistocene volcanites allows to conclude about the modern tectono-magmatic activity of the central part of the Pacific slope of the Kuril Islands.

K-Ar age determination of Paleozoic rock samples from northern Victoria Land, Antarctica

K-Ar ages of 82 slate and schist (white-mica-rich whole rock) samples are reported for Late Precambrian-Early Ordovician metamorphic rocks of the Wilson, Bowers and Robertson Bay terranes of northern Victoria Land. These are amalgamated in two vertical sections along composite NE-SW horizontal profiles across (1) Oates Coast in the north, and (2) Terra Nova Bay area in the south. The ages are in the range 328-517 Ma. Both profiles show some age variation with altitude, but more importantly, they define an inverted wedge shaped pattern, reflecting a "pop-up" strucure. This is oriented NW-SE at the eastern margin of the Wilson terrane, and the edges coincide with the Exiles and Wilson Thrusts which cross the region. Ages inside the "pop-up" structure are younger, ca. 460-480 Ma, than those along its eastern and western flanks, ca. 490-520 Ma. The K-Ar age patterns thus demonstrate a late Ross Orogenic age (ca. 460 Ma) for this structure, which may be associated with assembly of the Wilson and Bowers terranes.

K-Ag age of volcanites from underwater rises of the Sea of Okhotsk and the Sea of Japan

New K-Ar datings of Meso-Cenozoic volcanites from the Sea of Japan and the Sea of Okhotsk were obtained. They enabled to reason age of different volcanic complexes. Basalts from volcanic edifices of the Sea of Japan Basin were determined as Middle Miocene - Pliocene (13.1-4.5 Ma) in age, which correlates well with geological evolution of the Sea of Japan. New datings for basalts from the continental slope of the South Primorye (11.1 Ma) confirm their age being similar to volcanites from Neogene basalt plateaus of the South Primorye; they are very similar not only in age but also in mineral and chemical compositions. Datings for rocks from the andesite series of the Northern Yamato Rise (24.7, 21.5 Ma) show that they are coeval with volcanites of the trachyandesite complex; this allows to combine them into one Oligocene - Early Miocene complex. In the Sea of Okhotsk datings of volcanite samples from three complexes were obtained: Cretaceous, Paleogene, and Pliocene-Pleistocene. Cretaceous magmatic rocks make part of basements of large rises in the Sea of Okhotsk, and Paleogene and Pliocene - Pleistocene complexes illustrate stages of Cenozoic tectono-magmatic activation of the region.

Composition and age of igneous rocks from the Vityaz Ridge

Results of geological research carried out by V.I. Il'ichev Pacific Oceanological Institute (Far East Division of the Russian Academy of Sciences) and P.P. Shirshov Institute of Oceanology (Russian Academy of Sciences) on the submarine Vityaz Ridge during Cruise 37 of R/V Akademik Lavrentyev in 2005 are discussed. Various rocks composing the basement and the sedimentary cover of the ridge were dredged in three areas. Based on isotope geochronology, petrogeochemical, petrographic, and paleontological data and comparison with similar rocks available from the adjacent land and the Sea of Okhotsk, they are subdivided into several age complexes. Late Cretaceous, Eocene, Late Oligocene, Miocene, and Pliocene-Pleistocene complexes are defined among igneous rocks, while volcanogenic-sedimentary rocks are united into Late Cretaceous - Early Paleocene (Late Campanian - Danian), undivided Paleogene (Paleocene-Eocene?), Oligocene - Early Miocene, and Pliocene-Pleistocene complexes. Obtained data on age and formation settings of the defined complexes allowed to reconstruct geological evolution of the central Pacific slope of the Kurile Island arc.