Neotectonics of the Altai-Sayan Mountains and reactivation of regional faults controlling seismicity

The formation of mountain system and neotectonic structure of the Altai-Sayan region is regarded to be a result of intercontinental deformations, related to a distant effects of tectonic stress from the Indo-Eurasian collision. Within this tectonic model we carried out the joint analysis of the geology, seismicity data and topographic materials enable to assume that the maximum changes in the relief and seismic activity in the northern part of Central Asia mountain belt are confined to the zones of intersections of the Late Paleozoic regional faults. The intersections and junctions of faults should be considered as one of the most important structural factors that increase the fragmentation of the substrate, affect changes in the local stress field and predetermine the localization of large earthquake foci with a magnitude M≥5. Some regularities were revealed, based on the example of helium and travertine manifestations in the junction zone of the Charysh-Terekta and Kurai regional faults, which can be used as precursors of earthquakes

Shalkar Ophiolite Complex, northern Kazakhstan: structural setting, age, geochemistry and genesis

The Shalkar ophiolite complex consists of a series of tectonic slabs including lavas, a complex of parallel dikes, and a layered complex of gabbros and gabbro-pyroxenites intruded by dikes of plagiogranites. The tectonic slabs are subsided northward and are confined to the base of a large nappe made up of rocks of the Kokchetav microcontinent. The ophiolitcs and fragment of the microcontinent are jointly thrust over the Kokchetav megamelange complex with HP-UHP rocks. It is inferred from the chemical composition and structural position that the Shalkar ophiolites formed under the conditions of suprasubduction zone of extension and occur in the setting of the initial stage of formation of the Stepnyak island arc. The upper age of the ophiolites is 485 ± 6 Ma, as determined for zircons from plagiogranites using the U-Th-Pb SHRIMP method. The age of the Shalkar ophiolites is within 495-485 Ma. This interval is marked by a considerable rearrangement in the subduction zone, which might have been due to the jump of the subduction zone to the hinterland of the Kokchetav microcontinent and to the origin of a zone of extension within its limits with the formation of ophiolites

Deposition in the Kuznetsk Basin, Siberia: Insights into the Permian–Triassic transition and the Mesozoic evolution of Central Asia

This paper describes the Permian–Mesozoic stratigraphy of the Kuznetsk Basin, southern Siberia, which is adjacent to the vast and hydrocarbon-rich West Siberian Basin and on the edge of the Siberian flood basalts. The basin fill is Permian to Cretaceous in age, and is dominated by non-marine siliciclastics up to ∼ 7 km thick. Palaeocurrent indicators show dominant flow to the north/northeast during the Permian to Jurassic. Fourteen lithofacies are grouped in three facies associations: fluvial channel belt, overbank and floodplain/floodplain pond. Coal-bearing Permian siliciclastics are interpreted as meandering river deposits in a foreland basin, with subsidence generated by thrust-sheet loading from at least three basin margins. These sediments pass abruptly but conformably upwards into coal-barren sandstones and conglomerates and siltstones, interpreted as braided river deposits. Two basalt flows occur within the coal-barren succession. A recently-published, precise Ar-Ar age of 250.3 ± 0.7 Ma for the lower of these basalts, < 50 m above the sedimentary transition, suggests that the Permian–Triassic boundary occurs just above this flow. We relate the loss of coal-producing flora and the increase in mean sediment grain size to vegetation loss, in turn triggered by the eruption of the Siberian flood basalts to the north. End-Permian and Lower Triassic(?) strata are overlain by Lower Jurassic fluvial siliciclastics via a gentle angular unconformity. Conglomerates punctuate a sandstone-dominated succession that continues in to the Middle Jurassic. Both the basal unconformity and the rejuvenation in sedimentation may result from intracontinental thrusting at the basin margins and beyond; this thrusting was triggered by orogenies at the Eurasian margin. Lower and mid Cretaceous siliciclastics are poorly exposed and crop out only locally: field relations indicate an angular unconformity at their base. The end-Permian stratigraphy in the Kuznetsk Basin documents the environmental crisis at the time of the Siberian flood basalts, and reinforces the link between these eruptions and climatic and environmental deterioration. The Mesozoic sedimentary record highlights how episodic deformation influenced sediment supply to the West Siberian Basin, and is an example of the record of Eurasian assembly and deformation preserved within the continental interior

Eclogite-Like Metagabbro of the Olkhon Terrane, West Baikal Area

© 2020, Pleiades Publishing, Ltd. Abstract: Eclogite-like rocks of the Olkhon terrane correspond to two types according to the mode of occurrence and mineral compositions, although both types developed after the same type of gabbro of a single complex. The rocks of the first type are composed of garnet, clinopyroxene, pargasite (± scapolite, ± anorthite, ± spinel) and occur as thin veins or patches in the marginal parts of several small gabbro massifs of the Tonta Zone. The garnet is of almandine–pyrope–grossular composition and contains up to 40% of the pyrope end member. The rocks of the second type have been found in the Zamogoi Island in the Maloe More Strait. The island is composed of metasomatically altered gabbro cut by numerous granite and syenite veins. Carbonate and carbonate–silicate rocks compose dismembered veins and veinlets, as well as matrix embedding variably sized fragments of metasomatized gabbro and eclogite-like rocks in the southern part of the island. Based on the mode of occurrence and the presence of calcite–anorthite symplectite in some of the rocks, we suggest that the gabbro was penetrated by carbonate fluid or fluid–melt in a tectonic zone. The zone contains veins of garnet–clinopyroxene composition (varying from monomineralic garnetite to monomineralic pyroxenite) with minor pargasite, zoisite, anorthite, scapolite, and titanite. The garnet of Zamogoi Island has a grossular–almandine composition with a minor andradite concentration (about 10%). The compositions of minerals of the Zamogoi massif differ from the compositions of minerals in Tonta Zone, and the former are much more similar to skarn minerals