Structural material complexes in the Late Cenozoic Udokan lava plateau: Patterns of distribution and rock associations

We provide a new scheme to classify Late Cenozoic volcanic rocks in the Udokan lava plateau based on isotope datings of rocks derived during the last 15 years. The scheme distinguishes five structural-material complexes (SMCs): Middle Miocene, Late Miocene, Early/Middle Pliocene, Late Pliocene, and Quaternary. Each SMC has its ejecta of central-type eruptions and subvolcanic emplacement episodes that classify themselves into individual rock complexes, while the ejecta of mass fissure effusions from three SMCs (the Late Miocene, the Early/Middle Pliocene, and the Late Pliocene) can be lumped into three stratigraphic series. Each series includes three suites, with the middle position (in the series section) being occupied by suites composed of basaltic melt differentiates.     

Late Cenozoic Volcanism of the Vitim Depression and Its Correlation with the Vitim Lava Plateau (Western Transbaikalia) according to K–Ar Geochronology

New data on the geology, age, and composition of the Late Cenozoic volcanic rocks of the Vitim Depression, a satellite of the Vitim Lava Plateau (VLP), have been obtained. Two-stage volcanic activity has been revealed. In the Middle Miocene (14–13 Ma), a basalt and trachybasalt (hawaiite) lava covers were formed. In the Pleistocene (1.6–0.7 Ma), basanite erupted from scoria cones. Both stages of volcanism were coeval to similar pulses of volcanism within the VLP. However, unlike the latter, there were no Pliocene and Late Miocene eruptions within the Vitim Depression. Additionally, the Vitim Depression basalts have depleted geochemical characteristics comparative to those of the VLP. These features of the Vitim Depression volcanics imply their autonomous formation, whereas the synchroneity of the initial and final stages of volcanism in the depression and in the VLP reflects the existence of a common regulating mechanism of igneous activity.     

On the Jurassic volcanism and on volcanoes in the Shadoron Basin,eastern Transbaikalia

We present new data on the stratigraphy, volcanism, and K–Ar ages of Jurassic features in the Shadoron Basin. Two phases of volcanic eruptions have been identified, a Middle Jurassic and a Late Jurassic, which are separated by a pre-Oxfordian phase of tectogenesis. We show that the Jurassic volcanism in the area of study occurred through fissure vents and mostly evolved in subaqueous conditions.     

Sources of Magmas and Conditions of Rock Formation in the Late Cenozoic Udokan Volcanic Plateau

Doklady Earth Sciences - 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...     

Formation conditions of the ore-bearing lithium-fluoride granites of the Shumilov tungsten deposit,central Transbaikalia

Silicate melt inclusions were studied in the quartz phenocrysts from the Li-F granite porphyry of the Shumilov Massif, which are considered to be the sources of ore-bearing fluids of the Shumilov tungsten deposit. The estimated water content in the granite melt was 2.1–7.6 wt %, at a water pressure in the magmatic chamber of 3.1–5.2 kbar. It was concluded that the fluid-magmatic systems of the Shumilov and Spokoinoe tungsten deposits were formed at similar physicochemical conditions.     

The stages and distribution areas of the late Cenozoic volcanism in the Udokan Range in Transbaikalia based on geochronologic studies

New K-Ar datings of Cenozoic volcanic rocks sampled in the Udokan Range lava plateau are presented and compared with the known geochronologic dates for similar rocks. On the basis of these data, periodization of volcanic eruptions and regionalization of the plateau by the distribution of volcanism of different ages are suggested.