Russian Journal of Pacific Geology最新文献

The latest geological and geophysical information on the Zeya-Bureya sedimentary basin (Russia, Far East) is summarized. Based on drilling data from corehole and deep wells and 2D and 3D CDPM seismic data, taking into account the integrated interpretation of gravity and magnetic survey data and geological survey materials, a map was compiled for the surface of the pre-Mesozoic basement of the sedimentary basin, as well as structural maps for the top of the Cretaceous formations. The maps reflect a series of rift grabens and uplifts identified by the authors on seismic time sections during their reinterpretation. The method of compiling maps is given. A geological map of sediments overlying the pre-Mesozoic basement of the Zeya-Bureya sedimentary basin and a tectonic map of the sedimentary cover were compiled. During tectonic zoning of the sedimentary cover, the classification of tectonic elements was adopted that is widely used in the tectonic zoning of oil and gas regions, proposed by V.D. Nalivkin and updated at the Trofimuk Institute of Oil and Gas Geology and Geophysics, Siberian Branch, Russian Academy of Sciences (INGG SB RAS). As a result of tectonic zoning in the basin, the Inner Region and the Outer Belt were identified, and the tectonic elements complicating them were characterized. A characteristic feature of the Outer Belt is the presence of large intermediate structures: monoclines and mega- and mesomonoclines. Conversely, the Inner region of the basin is characterized by the presence of a large negative structure, complicated by smaller positive and negative elements. The main stages of the formation and development of the sedimentary cover of the Zeya-Bureya sedimentary basin are identified and described: rifting, early syneclise, late syneclise, and neotectonic.

Abstract

The paper presents the results of comprehensive (microprobe, paleomagnetic and magnetic) studies on peats from the Tyapka peat section (Russian Far East). Radiocarbon dating placed the start of peat formation at ∼11.7 ky B.P. The principle carriers of magnetization were found to be magnetite, to a lesser extent hematite and, possibly, greigite. The relative paleointensity values obtained through calculations are in good agreement with the literature data. Intervals with negative inclinations of the magnetization vector were identified in peats, which most likely correspond to geomagnetic excursions in the Holocene. The research constrained the duration of the geomagnetic excursions, as well as the geomagnetic field intensity behavior not typical for such variations.

Abstract

The article demonstrates the possibility of joint interpretation of seismic, density, magnetic, and geoelectric models of the deep structure of the lithosphere along the Spassk-Dalniy–Zerkalnaya Bay geotraverse. Seismic and density boundaries form the main structural framework of the integrated model of the lithosphere. Magnetic heterogeneities map the elements associated with magmatism. The electrical model reflects the most recent processes of matter redistribution. The resulting integrated geophysical model demonstrated that for the identified terranes on the surface and most of the faults separating them, the structural style is well expressed only within the upper and middle parts of the crust to a depth of 10–20 km. The lithosphere of the Khanka superterrane retains its structure both in the crust and mantle. Structures of the crust and upper mantle of the Sikhote-Alin orogenic belt are different and associated with each other through highly conductive areas and zones.

Abstract

The paper presents the results of retrospective and tectonophysical analysis of the Tokachi-Oki earthquake source area on the September 25, 2003 (M_w = 8.3). Particular attention is paid to the Hidaka tectonic belt, the structures of which were affected by the Tokachi-Oki earthquake. The load–unload response ratio (LURR) method was applied at sufficient spatial (a square with a side of about 400 km) and temporal (continuous 20-year period) intervals to consider the results reliable. The forerunners of the Tokachi-Oki earthquake on the September 25, 2003, were revealed (on average, two years before the seismic event), which strictly determined the earthquake location. The data obtained with The method of cataclastic analysis (MCA), together with LURR data, made it possible to establish the stages of instability development in the Hidaka collision zone. The Hidaka tectonic belt became outlined by destruction zones (mainly horizontal compression) from 1997 to 2003 (up to the Tokachi-Oki earthquake). LURR anomalies were detected along the belt a couple of years before the earthquake. The prediction of the Tokachi-Oki earthquake by the LURR method is one of the most reliable in our practice.

Abstract

For the first time, high-alumina mineral assemblages including rare minerals of the rhönite–kuratite series were found in postcaldera lava flows of the Kudryavy and Menshiy Brat volcanoes (Kuril Islands). These lava flows consist of olivine-bearing basalts and andesite-basalts of the calc-alkaline series. Partially crystallized olivine-hosted melt inclusions in these rocks contain high-alumina daughter phases. Residual glass with up to 25 wt % Al₂O₃, Al-pyroxenes, and spinel with minerals of the rhönite subgroup were identified. The rhönite–kuratite series minerals are characterized by strong variations in Al, Fe²⁺, Fe³⁺, Mg, Si, as well as very low Ti, which makes it possible to call it a low-Ti Fe²⁺ analogue of rhönite with the formula (Ca,Mg,Na)₄(Mg,Fe,Fe, Al,Ti,Mn)₁₂O₄[Si_8.2Al_3.8O₃₆]—(Ca,Na,Mg)₄(Fe,Mg,Al,Fe,Ti)₁₂O₄[Si_6.78Al_5.22O₃₆]. It is assumed that high-alumina daughter phases form in olivine-hosted inclusions via water accumulation in trapped melts during crystallization of the host olivine on the walls of melt inclusions. Water-rich melts can inhibit early crystallization of plagioclase, which promotes enrichment of the residual melt in Al₂O₃.

Abstract

Structural-density modeling of the Earth’s crust carried out using a deep seismic sounding profile previously tested along the western shelf of Sakhalin Island offered a clearer view of the layered block structure of the main tectonic faults and their system within the crust of the region, which accumulate a large number of strong crustal earthquakes. The density structures of the resulting model were compared with geological data on the adjacent territory of Sakhalin Island. Our structural-density model made it possible to separate volcanic blocks and blocks of basified sialic crust and to trace the submarine prolongation of the largest geological complexes of the western margin of Sakhalin Island to the shelf. A spatial correlation between seismic events and some tectonic faults is observed.

Abstract

In this study, we calculated the seismic intensity for the Baikal–Olekma section of the Baikal–Amur Railway based on data on seismicity on the northeastern flank of the Baikal Rift Zone in 1985–2021. During the analysis of earthquakes with an epicentral intensity higher than 4 (1484 events), we selected 270 earthquakes with Ms = 2.1–6.6, whose calculated intensity exceeded 4 points directly on the railway track from the total number of the recorded seismic events (more than 150 000 earthquakes with M ≥ 1.0). The highest intensity values (8–9) were obtained for large earthquakes close to the Baikal–Olekma section of the Baikal–Amur Railway (Δ < 10 km, Ms = 6.1–6.2). A recurrence interval of such seismic events along the considered section of the railway is 20–60 years. The data are agree well with the macroseismic data available, which confirms the correctness of the results. At the same time, macroseismic effects from strong (Ms ≥ 6.6) but remote earthquakes (Δ = 360–1000 km) were found to have no significant impact on the Baikal–Olekma section of the Baikal–Amur Railway. The calculated values of intensity and recurrence intervals of earthquakes should be taken into account when designing, constructing, and operating industrial and civil infrastructure within the study area.

Abstract

The traditional craft villages in Vietnam in general and in Bac Ninh province in particular have been exposing many negative impacts on the environment. The heavy metal-rich wastes from the metal recycling casting craft villages in the field of metal recycling and metal casting are causing severe heavy metal pollution not only to the air, soils, and sediments but also to the groundwater resources. In Da Hoi iron recycling craft village in Chau Khe ward, Tu Son town, Bac Ninh province, Vietnam, the Holocene aquifer is exposed to the Ngu Huyen Khe River’s sediments contaminated with heavy metals Lead, Cadmium, Nickel, and Zinc. Freundlich isotherm parameters of the Holocene aquifer have been selected for finite element modeling of heavy metal transport with high temporal and spatial varying retardation factors to get reliable quantitative heavy metals’ distribution in depth and time. Initial and boundary conditions have been augmented to be established. The retardation factors of the advection and dispersion transport in the Holocene aquifer for heavy metals Pb, Zn, Cd, and Ni are very highly none-linear and very much varying in time and space: 8.7–66.4 for Pb, 2.0–12 for Zn, 1.7–4.8 for Cd and 1.1–5.9 for Ni. The results of the numerical modeling show that heavy metal transport in the Holocene aquifer is very fast and the entire aquifer thickness has equilibrium aquifer formation and aquifer water heavy concentrations after around 2–2.5 years for Cd and Ni, around 4 years for Zn and around 27 years for Pb. The heavy metals’ fluxes from the Holocene aquifer to the Pleistocene aquifer are maximal and more or less constant from the equilibrium time and would cause severe contamination of the Pleistocene aquifer.

Abstract

New data favor the view previously substantiated by geological, geochemical and isotopic data that the orebodies of the Belogorskoe deposit are the Triassic erosion products of the laterite weathering crust after gabbroids, which were metamorphosed and partially regenerated in the Late Cretaceous–Paleogene. The source for the formation of the Belogorskoe deposit was shown to be the products of exogenic destruction of rocks, the isotopic and geochemical characteristics of which are close to those of Cambrian gabbroids of the Vladimiro-Aleksandrovsky massif (southern part of the Okrainsko-Sergeevsky terrane). It has been found that the Belogorskoe deposit consists of rocks and ores, the primary (magmatic) REE distribution in which was variably modified as a result of interaction between sediments (protoliths) and seawater (presumably during the Late Jurassic–Early Cretaceous accretion), as well as between their metamorphosed analogues and hydrothermal solutions (in the Late Cretaceous–Paleogene). The influence of gabbroids (as a source of material) on the chemical and mineral composition of the Belogorskoe deposit agrees with the data reported in a paper on the enrichment of orebodies in such elements as Fe and Mn characteristic of ultramafic rocks and the presence of Au–Ag–Pd–Pt, Ni–Co, and Bi mineralization in them. The orebodies of the Belogorskoe deposit contain accessory minerals and mineral varieties that are rare in nature and poorly studied. They include an unusually Th-rich variety of zircon, baddeleyite, gudmundite, a large group of bismuth compounds, including Bi₂Te, (Ag,Pb)BiS₂, as well as coloradoite, lafossaite, sanbornite, perovskite, and the compound InPO₄. There is also a large group of rare and unusual noble metal compounds: copper gold, platinum gold, jonassonite, disordered solid solutions of Cu, Ag and Au (Au-based), Pt–Pd, Pt–Ag intermetallides, and other rare minerals and mineral varieties.

Abstract

The relationships of ore districts, clusters, and fields with hierarchal subordinate central-type structures of three taxonomic levels are established from an analysis of the 3D distributions of contrast density in the crust of South Sikhote-Alin. The possible occurrence depth of fluid-magmatic sources of ore mineralization is determined from the coincidence of ore mineralization halos with the projections of deep density heterogeneities: Sn (2–6 km), Sn–polymetallic (4–12 km), polymetallic (6–20 km), and Au–W (14–24 km). The spatial location of central-type structures and related ore mineralization halos coincides with viscous shear zones, which exhibit sagging of the upper crustal level (Samarka Terrane, Kavalerovo district, and Soboliny ore cluster) and the displacement of contours of density heterogeneities in various deep sections (Dalnegorsk district). The deep boundaries of ancient continental crust and Mesozoic island-arc wedges, which are underthrust beneath accretionary–fold complexes, are determined. The combination of these structures is characterized by evident features of a transform strike-slip fault.