Research Articles (English)
The records of distant strong earthquakes, obtained by way of a dense linear network of seismic stations in the Severomuysk segment of the Baikal rift system, revealed a complex layered-block structure of the Earth’s crust and subcrustal mantle using the longitudinal receiving function. The distribution of cross-wave velocities indicates that the properties of the blocks that make up the Severomuysk Earth’s crust differ. The western vergence of these blocks and the stratification of the lower part of the Earth’s crust confirm the accretion-collision origin of the uplift. The intensity of the collision effect on the Earth’s crust of the region is explained by the location of the Severomuysk segment on the thinned inclined edge of the Siberian Craton. A convincing correlation was found between the focal depths of earthquakes in 2015 and contrasting velocity heterogeneities in the upper part of the Earth’s crust of the Muyakan depression.
The collision between the Indian and Asian plates uplifted the Himalayan- Tibetan Plateau, thickening and expanding the crust. It is a scientific mystery of global concern as how the two continents collide and how the continent-continent collision deforms the continent. Deep seismic reflection profile detection is one of the most effective ways to unlock this scientific mystery. For more than 20 years using this technology, we have detected fine structures of the thick crust of the Tibetan plateau after overcoming technical bottlenecks to access the lower crust and Moho thus revealing the continental collision processes. This paper systematically summarizes the deep behaviors of the India-Asia collision and subduction beneath the Tibetan Plateau, from south to north, east to west and further into the hinterland of the plateau. The Indian crust undergoes underthrusting beneath the Himalayan orogenic belt on the southern margin of the plateau. Meanwhile, the lithosphere of the Alxa block in the Asian plate subducts southward beneath the Qilian Mountain in the north of the plateau, driving the northward overthrusting of the Qilian crust. Additionally, the Tarim and West Kunlun blocks undergo face-to-face collision in the northwestern margin of the plateau. In the easternmost part of the plateau, the Longriba fault, instead of the Longmen Shan fault zone, marks the western margin of the Yangtze block. It is also seismically evidenced that the Moho geometry in the plateau’s hinterland appears thin and flat, indicating lithospheric collapse and extrusion. Multiple deep reflection profiles revealed the collisional behavior under the Yalung-Zangbo suture zone and longitudinal variation in subducting geometry of the Indian crust from west to the east. In the middle of the suture zone, it shows a decoupling between the upper and lower crusts of the Indian plate, where the upper crust undergoes a northward overthrusting while the lower one experiences a northward underthrusting. It is also seismically evidenced a down-and southward crustal duplexing of the subducting Indian crust thickening the northern Himalayas, leaving over a thinning subducting lower crust of the Indian slab. The subduction front of the Indian crust collides with the lower crust of the Asian plate at the mantle depth. A near-vertical collision boundary is seen between the Gangdese batholith and the Tethyan Himalayas, where the Gangdese batholith shows almost transparent weak reflections in the lower crust with localized bright spot reflection that indicates partial melting. Additionally, the near-flat Moho geometry implies an extensional tectonic environment of the southern margin of the Asian plate.
The Earth's surface is a complex system involving mutual interactions of its many components, including mountains, rivers, forests, farmlands, lakes and grasses. The interaction and mutual feedback of chemical elements in Earths surface layer can drive changes in chemical elemental distribution patterns. In this study, we evaluated the mechanisms and interactions driving the distribution patterns of macroelements, probiotics, halogens and heavy metals in soils in Southwest China, based on a systematic geochemical land-quality survey at a scale of 1250000. The results showed that the parent material determines the natural state of chemical elements in land resources. Epigenetic geochemical dynamics reshapes the distribution patterns of chemical elements in top soil; biogeochemical processes drive the evolutionary trends of land quality; and human activities, such as mining, disrupt the natural evolution of chemical elemental distribution patterns. The establishment of an epigenetic geochemical dynamics theory allows the construction of a framework for understanding the Earths surface layer and promoting technological innovations for the comprehensive geochemical investigation of land resources.
The Yoko-Dovyren layered dunite-troctolite-gabbro massif is located in a folded frame of the South Siberian Craton (North Baikal region, Russia). The massif structure has been studied in detail in the thickest central part. The base of the section is composed of plagioclase peridotites of the endocontact, turning into the main stratigraphic sequence of five zones corresponding to changes in cumulus associations (from bottom to top): dunite → troctolite → olivine gabbro → olivine gabbronorite → quartz gabbronorites and pigeonite-containing gabbro. Among the mineral resources of the massif are sulfide copper-nickel ores, rocks with low-sulfide mineralization of platinum group elements and other mineralization, and chromitites. In addition, the massif contains various types of nonmetallic raw materials, including boron mineralization, diopside, and magnesium silicate rocks. These include dunites, wehrlites and troctolites, which are of high quality. They are promising for obtaining building materials (cements, concretes, asphalt concretes and building ceramics). The solution to this issue is important from the point of view of the integrated use of mineral raw materials in the development of mineral deposits, which allows for establishing environmentally safe mining works.
Nephrite has been used in Eastern Siberia historically as one of the most popular minerals since the Neolithic. The use of nephrite was facilitated by the numerous rich deposits of the stone near the area of Lake Baikal. In Siberia, nephrites come in different colors depending on the genesis of the deposits. There are two fundamentally different genetic types of the stone: apohyperbasite and apocarbonate. Nephrite turned out to be a very good benchmark for reconstructing the development of civilizations over several millennia. The practical role of nephrite in the lives of ancient societies of North Asia and in modern scientific researches has been shown. In this contribution, we discuss the possible ways the natural properties of nephrite can create artistic and artistic-industrial products. We also show the differences between real works of art and serial design products from nephrite.
Gypsum (CaSO4·2H2O) as the most common and abundant secondary mineral in diverse types of mine tailings potentially plays important roles in the stability and bioavailability of heavy metal(loid)s, including As. Understanding on the behavior of As in gypsum-rich mine tailings and development of effective strategies for remediating related As contamination all require knowledge about the speciation and uptake mechanisms of this metalloid in the dominant mineral. However, quantitative determination of arsenic speciation and uptake mechanisms in gypsum-rich mine tailings at trace levels is analytically challenging. In this contribution, we use combined inductively coupled plasma mass spectrometry (ICP-MS), X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy to quantitatively determine structural incorporation and surface adsorption of arsenate in synthetic gypsum. Gypsum coprecipitated from aqueous solutions containing 0.02 M sodium hydrogen arsenate heptahydrate (Na2HAsO4·7H2O) at ambient conditions has As contents increasing from 57 ppm at pH=2 to 67470 and 53980 ppm at pH=12 and 14, respectively. Synchrotron As K-edge XANES and powder EPR spectra confirm that arsenate is the dominant species in coprecipitated gypsum. Specifically, As K-edge XANES spectra exhibit systematic variations in post-edge features as a function of pH, consistent with structure-bound arsenate at pH from 2 to 7.5 but different uptake mechanisms at pH from 9 to 14. Similarly, arsenic contents estimated from the structure-bound [AsO3]2- radical in powder EPR spectra are in agreement with those determined from ICP-MS analyses for gypsum synthesized at pH from 2 to 7.5, but show large discrepancies for the pH=9, 12 and 14 samples, indicative of a large fraction of non-structure-bound As at high pH. The marked pH dependence of arsenate uptake mechanisms in gypsum has important implications for both understanding the roles of this material in mine tailings and developing its optimal applications for remediation of arsenic contamination in aqueous environments. In addition, the radiation-induced [AsO3]2- radical in gypsum with a diagnostic peak at g=~2.33 is potentially useful for EPR/ESR dating and retrospective dosimetry.
The Baranevskoye gold-silver deposit occurs within the caldera of the Balkhach volcano in the south-east part of the Central Kamchatka mining district. The host rocks are andesite, basalt of Miocene-Pliocene age. The hydrothermal alteration varies as a function of depth and is subdivided into deepest quartize zone, intermediate zones of quartz-sericite(alunite)-pyrite-Fe-Ti-oxides and quartz-sericite-illite-pyrite associations, and shallow quartz-adularia-hydromica-clay-carbonate zone. Mineralogical study reveals three major stages of mineralization. The early stage is present by a highly disseminated copper-rich mineralization with main ore minerals of chalcopyrite, bornite, tennantite-tetrahedrite, and rare gold occurring in the Rzhavaya vein. Tennantite-tetrahedrite series is represented by two end-members of tennantite and tetrahedrite with tetrahedrite preponderating. Later stages are characterized by advanced Au-Ag mineralization containing gold, pyrite, chalcopyrite, sphalerite, galena, tellurides, and sulfosalts. The early Cu-rich mineralization (stage I) is designated as an intermediated state, followed by later low-sulfidation Au-Ag mineralization (stages II and III). Gold was constantly deposited through from Stage I to Stage III. Crystalline gold was also found in void-space in the altered host rocks. Early gold is relatively Ag-rich with Au content of about 59-65% compared to later gold of Stage II and III (Au 64-72%). Fluid inclusion microthermometry shows homogenization temperatures between 190-280 ℃ for the Central vein, 190-240 ℃ for the Rzhavaya vein and 230-310 ℃ for the quartz of the altered host rocks associated with crystalline gold. Low salinity of the fluid inclusions (0.9-2.4 wt.% NaCl eq.) suggests an influx of the meteoric waters. Based on mineralogical and fluid inclusions data the physicochemical conditions of the ore formation are discussed.
Halogens such as Cl and Br as geochemical tracers for constraining the sources and evolution of magmatic, metamorphic and hydrothermal systems require knowledge about their structural environments in both rock-forming minerals and coexisting melts/fluids. However, structural studies of Br in rock-forming minerals are challenging due to its exceedingly low concentrations that are not amendable to most structural techniques. In this study, we have conducted the first structural investigation of Br as a trace constituent in selected Cl-rich rock-forming minerals by use of combined 81Br magic angle spin nuclear magnetic resonance (MAS NMR) spectroscopy and Br K-edge synchrotron X-ray absorption spectroscopy (XAS). The whiteline positions of the Br K-edge X-ray absorption near-edge structure (XANES) spectra vary systematically with the coordination numbers of the Cl atoms, except for that in boracite. Similarly, fittings of extended X-ray absorption fine structure (EXAFS) data support the substitution of Br- for Cl-, with significant local expansions. However, the local structural environment of Br in boracite from EXAFS fittings differs from this of the three-coordinated Cl atom in this mineral but is similar to that of the octahedrally coordinated Br in cubic Mg3B7O13Br, suggesting a domain segregation even at the trace level. These local structural data provide new insights into the Br/Cl behavior in geological systems.
The spatial position of the western boundary of the Amur plate within the territory of Mongolia is still not clear; active fault tectonics and the stress state of the Earth’s crust along it have been poorly studied. Within three regions along this border—the Hangay-Khentiy tectonic saddle, the Burgut block (Orhon-Tola interfluve) and the Selenga block, which includes the Selenga depression and the Buren-Nuruu uplift, studies of active faults were carried out using space imagery interpretation, relief analysis, geological structural data and reconstruction of tectonic paleostresses from tectonic fracturing and displacement along with fractures data. It is shown that active faults inherit ancient structural heterogeneities of the Paleozoic and Mesozoic ages. The faults do not form a single zone along the plate boundary, but form clusters. Their kinematics depend on the strike: sublatitudinal faults are left-lateral strike-slip faults with an obligatory reverse component; NW-strike faults are reverse faults or thrusts, most often with a right-lateral strike-slip component; submeridional faults are right-lateral strike-slip faults; and NE-strike faults are normal faults. The activation of fault structures localized in the Selenga depression and in the eastern part of the Hangay began in the Pliocene. Revers and strike-slip faults are not conformal to the Pliocene, and often to the Pleistocene relief, which indicates a younger, Late Pleistocene, age of their activation. Reconstructions of the stress-strain state of the last stage of deformation in zones of active faults, using tectonic fracturing and displacements along fractures, indicate the predominance of compression and strike-slip conditions with the N-NE and NE direction of the axis of maximum compression. Only within the Selenga depression is the prevalence of stress tensors of extension and strike-slip types with the NW strike of the axis of minimum compression noted. To the south, a local area with a predominance of the extension regime is located within the Eastern Hangay (Orhon graben). It is concluded that the activation of faults in the central part of Mongolia at the Pleistocene-Holocene stage, as well as modern seismicity, are mainly controlled by additional horizontal compression in the NE direction associated with the process of convergence of Hindustan and Eurasia. An additional factor that allows the implementation of strike-slip deformations in the crust of the study area and explains the divergent movements in the Baikal Rift, as well as the SE movement of the Amur plate, is the impact on the base of the lithosphere of the asthenospheric flow in the SE direction. The boundary between the Amur plate and the Mongolian block in the tectonic structure is expressed fragmentarily and represents the marginal part of the deformation zone covering the whole of Western Mongolia.
It has been widely recognized that the separation of the African and South American continents is caused by the South Atlantic breakup. The South Atlantic region is highly relevant to the development of the continental drift hypothesis. The driving force behind continental drift, however, has been in debate ever since the hypothesis was proposed. Therefore, quantitative analysis of the forces driving plate movement in the process of Atlantic breakup is particularly important. Here, we analyzed two deep seismic reflection survey profiles located on either side of the South Atlantic, in passive continental margin basins, and estimated the Moho dip angle of the African continent on the basis of tectonic geological interpretation. We then calculated the magnitude of crustal gravitational slip shear force along the Moho to explain the dynamic mechanism of African continent movement in the process of Atlantic breakup. We demonstrated that the African continental crust can produce a strong gravitational slip force on the inclined interface formed by mantle upwelling, and the shear force is greater in the south than in the middle part of the crust. According to our analysis, the continental crust can drift continuously by continuous hot mantle upwelling and gravitational slide. This model can reasonably explain the genetic mechanism for the many linear continental fragments in the Atlantic Ocean, and it can also provide an internal reason for why the South Atlantic today is wider in the south than it is in the middle. Based on this model we reconstructed the tectonic evolutionary history of the South Atlantic breakup process. This research established a new dynamic model of plate motion and provided more accurate constraint for understanding the driving force behind plate movement.
