No 1 (2019)

The structure and peculiarities of the tectonic evolution of Precambrian terraines included into the structure of Paleozoids in different parts of the Central Asian orogenic belt are reviewed, types and comparative characteristics of Precambrian terraines are provided. We throw light on two types of Precambrian terrains structure: essentially juvenile Neoproterozoic crust (1); Mezo- and Early Neoproterozoic crust formed due to reworking of Early Precambrian formations (2). Terrains with juvenile Neoproterozioc crust, located in the Central and Eastern parts of the Central Asian orogenic belt, were generated in the oceanic sector of the Earth. Their formation was connected to the Early- and Late Neoproterozoic cycles of tectogenesis up to 200 Ma each cycle. Terrains with Mezo- and Early Neoproterozoic crust, found mainly in the West of the Central Asian orogenic belt, generated in the continental sector of the Earth during the Neoproterozoic, their evolution occurred mainly in the intracontinental environments. In the evolution all of considered terrains in the interval 800–700 Ma, an event associated with rift zones formation and intraplate magmatism was revealed, it coincided with the supercontinent Rodinia split. The conducted research allow to connect formation history of the Precambrian terrains of the Central Asian orogenic belt with the processes took place in the edge of the Syberia-Tarim part of the supercontinent Rodinia and the adjacent sector of the paleo-ocean.

Research of genesis of hydrocarbon accumulations located within pre-Cenozoic basement of the South China Sea shelf (Vietnam) presented. Formation of hydrocarbon deposits is confined to the protrusive massifs of granites that have undergone structural and tectonic processing at the stage of prototectonics and postmagmatic tectonics. The totality of post-structure-forming processes led to a change in the viscosity properties of rocks, to their tectonic and material heterogeneity and stratification and, as a consequence, to vertical and lateral redistribution in space with the formation of granite protrusions. The mechanisms of formation of voids and oil and gas traps within the protrusions are considered. Based on the similarity of the geochemical characteristics and biomarker parameters of the oils and organic matter in the Oligocene-Miocene sediments and in the basement rocks, a conclusion has been made about the organic nature of the oils in the basement of the shelf of the South China Sea (Vietnam). Possible mechanisms of migration and accumulation of hydrocarbons in basement rocks are considered. It is confirmed that the formation of hydrocarbon deposits occurred due to lateral and downward migration of hydrocarbons through the contact area from the Oligocene-Miocene source rocks into crystalline massifs — into voids and increased fracture zone in the protrusions.

Vendian and Permian-Triassic plagiogranite magmatism is distinguished for Ust’-Belsky and Algansky terranes of West-Koryak fold system. U–Pb zircon ages from Vendian and Permian-Triassic plagiogranites are 556 ± 3 Ma (SIMS), 538 ± 7 Ma (LA–ICP–MS) and 235 ± 2 Ma (SIMS) consequently. It is revealed, that Vendian and Permian-Triassic plagiogranites are mainly low-K and low-Al. Sr–Nd isotopy and rare-earth element patterns allow supposing their formation by partial melting of primarily mantle substrate or by fractional crystallization of basic magma. Vendian plagiogranites formed within active margin in ensimatic island arc simultaneously with deposition of lower part of volcanic-sedimentary complex of Otrozhninskaya slice. We suggest the Permian-Triassic plagiogranites were being formed within the limits of Ust’-Belsky segment of Koni-Taigonos arc during partial melting of melanocratic ophiolite material build up as fragments in accretionary structure of that arc or by fractional crystallization of basic magmas melted from the similar substrate.