Hydrogeochemistry of Hot Springs and the 2018 Mojiang M 5.9 Earthquake-Related Chemical Changes in the Simao Basin, China

The Simao Basin is characterized by strong tectonic activity and frequent seismicity. This study investigated the hydrochemical characteristics of 21 thermal springs in the Simao Basin from 2018 to 2020. In this study period, the 2018 Mojiang M5.9 earthquake caused several hydrochemical changes. The results indicate that the Simao Basin contained saline spring waters, HCO3−-rich spring waters, and SO42−-rich spring waters. In the study area, the water chemistry types were controlled by stratum lithology. Saline springs flowed through red beds and dissolved large amounts of halite, which is a rich source of Cl−and Na+ ions. In the hot spring waters, Ca2+ (Mg2+) and HCO3− were mainly derived from the dissolution of carbonate minerals, gypsum, and anhydrite of Triassic rocks. The higher SO42- content in the hot spring waters was caused by the pyrite present in Ailaoshan metamorphic rocks. The reservoir temperatures (121–289 °C) in the Simao Basin were estimated by the silica-enthalpy mixing model equation and the silica-enthalpy diagram. The hot springs had higher reservoir temperatures (>250 °C) and were mainly located at the edges of the basin. Metamorphic rocks exposed in the region had low permeabilities and these springs was close to nearby deep faults that provided deep heat. In most springs, the concentrations of Ca2+ and HCO3− ions increased obviously before the 2018 Mojiang M5.9 earthquake; however, the concentrations of these ions decreased after the earthquake. The hydrogeochemical variations might be attributed to the vigorous water-rock interactions and the mixing of secondary fluids. The entry of cold shallow groundwater caused changes in the reservoir temperatures of some spring samples.

GEODYNAMICS

The aim of the research presented in this article is to analyze the properties and geological informative value of the anisotropic transformations of gravitational and magnetic fields, which use averaging procedures, including analysis of Andreev-Klushin's method. Anisotropic transformations of potential fields are designed to detect and track elongated anomalies or their chains, caused by deep linear dislocations in the geological section. The study of the anisotropic transformations properties is based on the analysis of their depth characteristics, as well as theoretical and practical experiments. The study applies the analysis method of fault tectonics reflection features in anisotropic anomalies of gravimagnetic fields, in particular, on the example of the South-East of the Ukrainian Carpathians. It is based on the search of morphological signs of manifestation of deep faults and other long structural-tectonic dislocations in gravitational and magnetic anisotropic anomalies. The method also suggests tracing these elements, relying on the comparison of morphology, intensity, size and direction of anisotropic anomalies with published regional tectonic and geological maps. Results. The paper presents definitions and algorithms of such anisotropic transformations as Andreev-Klushin's methods of anticlinal and terrace types, anisotropic averaging and anisotropic difference averaging. The research allowed us to perform study of the geological informative value of anisotropic transformations of potential fields on theoretical and practical examples. It is shown that in the morphology of anisotropic gravitational and magnetic anomalous fields in the south-east of the Ukrainian Carpathians long local anomalies are traced. They are caused by fault tectonics, in particular deep longitudinal and transverse faults, as well as linear complications into sedimentary cover. The analysis of anisotropic anomalous fields reveals a number of characteristic features of large tectonic zones reflecting regional behavior of the foundation surface and deep faults; on its basis fault tectonics schemes of the South-Eastern region of the Ukrainian Carpathians can be constructed. The study traced a significant extension of the foundation of the Eastern European platform from the Maidan's ledge and the Pokutsko-Bukovynian Carpathians under the Folded Carpathians. The definition of a number of anisotropic transformations is given and their properties are considered. The work substantiated geological informative value of the anisotropic transformations morphology of potential fields in the study of the Ukrainian Carpathians and adjacent depressions fault tectonics. The use of anisotropic transformations of potential fields will increase the reliability and detail of tracing deep faults, as well as other linear dislocations both in the foundation and in the sedimentary cover. The study of fault tectonics is an important factor in the successful solution of problems in the search and exploration of areas which are promising for oil and gas deposits.

Revelation of Potentially Seismic Dangerous Tectonic Structures in a View of Modern Geodynamics of the Eastern Caucasus (Azerbaijan)

The stress state of the earth’s crust in the Eastern Caucasus, located in the zone of collision junction of the North Caucasian, South Caucasian, and Central Iranian continental massifs, is a consequence of the inclusion of the Arabian indenter into the buffer structures of the southern framing of Eurasia at the continental stage of alpine tectogenesis. This evidenced from the results of geophysical observations of the structure and seismic-geodynamic activity of the region’s crust. The latter, at the neotectonic stage, was presented as underthrust of the South Caucasian microplate under the southern structures of Eurasia. The analysis and correlation of historical and recent seismic events indicate the confinement of most earthquake foci to the nodes of intersection of active faults with various orientations or to the planes of deep tectonic ruptures and lateral displacements along unstable contacts of material complexes of various competencies. The focal mechanisms of seismic events reveal various rupture types, but in general, the earthquake foci are confined to the nodes of intersection of faults of the general Caucasian and anti-Caucasian directions. Based on the observed weak seismicity, active areas of deep faults were identified, which are accepted as potential source zones.

SEISMICITY of the NORTH-EAST of RUSSIA in 2015

The results of seismic monitoring of the Magadan oblast, the Chukotka Autonomous okrug, and the shelves of the adjacent seas (Okhotsk, Chukchi, Bering, and East Siberian seas) are considered. There were 14 seismic stations working in the region. The new station “Gadlya” was opened on the Okhotsk sea coast. The catalog includes information about 290 earthquakes with energy classes KR=4.4–12.6. As usual, most of them (93 %) are localized in the Kolyma region. The total seismic energy released within the region’s borders was ΣЕ=4.6341012 J. According to the earthquake energy completeness map Кmin built for the region, minimal energy level of earthquakes, Кmin=5.0, is provided at two areas near the Susuman and Magadan stations. The station network can register without omissions the earthquakes with Kmin≥8 at the Okhotsk sea and Kolyma areas, with Kmin≥10.6 in the Chukotka area. In 2015 three earthquakes with intensities I=2–4 by MSK-64 scale were felt in settlements of North East of Russia. The 2015 strongest earthquake occurred on June 1 at 10h53m with KR=12.6 (MPSP=4.9), h=31 km in the Kolyma area. A maximum shaking intensity of I=4 was observed in Omsukchan settlement (∆=132 km). In March 2015 a swarm of 29 weak earthquakes with KR=6.2–9.8 occurred northeast of Talaya settlement. Epicenters of Kolyma area earthquakes were plotted on the tectonic zoning map of the Magadan region. Most earthquakes are confined to the main deep faults oriented in the northeastern and sublatitudinal directions. All hypocenters are located within the Earth's crust. The seismicity level of the North-East of Russia in 2015 according to the “SOUS09” scale was assessed as "background average" for the observation period from 1968 to 2015. Spatially, all earthquakes in the North-East of Russia are traditionally concentrated within the major seismogenic belts – Chersky, North-Okhotsk, and Trans-Beringian.

Calculation of tectonic stresses in the earth’s crust of SouthWestern Uzbekistan

In this article, based on accounting, the interaction of the Earth’s crust blocks is limited by the deep breaks in the form of three-layer panels. The analysis dependences for tectonic pressure on elasticity parameters and the Earth’s crust layers capacity were obtained using the hypothesis of linear changes of deformations on the height of panels and the elasticity for bottom layers of the Earth’s crust. This paper considers the elastic interaction of crustal blocks bounded by deep faults in the form of three-layer panels. Using the hypothesis of linear measurement of deformations along with the height of the board and the elastic limit for the lower layer of the Earth’s crust, calculated dependences for tectonic stresses on the elasticity and thickness of the layers of the Earth’s crust are obtained.

Prospects for exploration of hydrogen fields in riftogene structures of platforms (the case of the Dnieper-Donets Aulacogene)

This paper shows the prospect to find industrial-scale hydrogen accumulations in riftogenic structures of platforms using the example of the Dnieper-Donets Aulacogene, located in the southern part of the East European Platform. Within the Dnieper-Donets Depression, geological and geophysical methods indicate a significant number of deep faults and ring structures of volcanogenic and explosive origin promising increased hydrogen content. Possible locations of the most propitious areas of hydrogen concentration are associated with faults in rift systems and their nearest margins, as well as with explosive and volcanogenic ring structures with signs of modern activation. At a fine-grained level, the prospectivity of the area is determined not only by the specified structural relationship, but also by the set of geophysical characteristics (thermal, seismic, gravity, electrical conductivity, magnetic) and the corresponding geological and hydrogeological parameters. Areas for further more detailed investigations within the Sribne and other ring structures, Southern Near-Edge Fault, Northern Near-Edge Fault were identified based on the data on geological and geophysical materials, satellite images, and field work. We defined high-priority and low-priority territories. Areas for initial investigations using satellite images, gas sampling (hydrogen, helium, methane, etc.), primary geophysical surveys (with evaluation of intermediate reservoirs and cap rocks) were identified. The primary results can be used to plan pilot shallow drilling and wells sampling. The areas for priority deeper drilling and sampling are selected by the sum of results obtained and data comparison. The paper presents the results obtained 30 km east of Kyiv as an example of field assessment of H2 degassing in a local depression. The results show that hydrogen concentrations at depths of 0.45 to 1.5 m are near zero outside the local depression. The maximum values of H2 concentration (up to 3300 ppm 1.5 m deep) are characteristic of the point inside the depression.

Origin of the Multiple-Sourced Cherts in Maokou Carbonates in Sichuan Basin, South China

Cherts have been thought to originate from biosilicification, terrestrial inputs and hydrothermal activity. The study of cherts is helpful in understanding the paleo-ocean environment and tectonic–sedimentary processes. Large amounts of cherts occur widely in the Maokou Formation in the Sichuan Basin, which may be largely connected to the Permian Chert Event (PCE). However, the source of silica and the formation process of cherts remain debated. Here, we analyze the petrographic and geochemical features of the cherts from the Guadalupian Maokou Formation (~268–259 Ma) in six sections in the Sichuan Basin. Two main types of cherts, nodular and bedded, are recognized in the Maokou Formation. The formation of nodular cherts was mainly affected by hydrothermal fluids, whereas the bedded cherts are mainly of biogenetic origin. The Emeishan large igneous province (ELIP) caused the activation of deep faults, accompanied by intense hydrothermal activities. Correspondingly, the cherts of significant hydrothermal origin developed near the active deep faults. The intensified hydrothermal activities may provide extra silica supplies and flourish the silica-secreting organisms by the associated volcanogenic upwellings that facilitated the enrichment of cherts. The study of Maokou cherts can help to record the volcanic- and silicon-related biological activities in the eastern Paleo-Tethys Ocean and can provide significant implications for chert enrichment in analogous settings.

Prospects for diamond potential of the Charo-Sinskaya fault zone

New data on the geological structure of the CharoSinskaya zone of deep faults located on the southern side of the Vilyui syneclise are presented. Based on the processing of the seismic survey results, the deep structure of the territory has been analyzed, and graben-like structures similar to those found near the known kimberlite fi lds of Yakutia have been identifi d. Taking into account the results on the mineralogy of the indicator minerals of kimberlite, a new kimberlite field location is predicted.

Volcanic and fault-fractured ore-controlling structures and minerals of the Azerbaijan part of the Lesser Caucasus

This article is focused on volcanic and fault-fissure ore-controlling structures of the Lesser Caucasus. The territory of the Lesser Caucasus is dissected by many deep tectonicfaults, along which volatile compound sofpostmagmatic products and water vapor migrate from great depths. The presence of numerous tectonic deep faults, which provide hydrodynamic connection of waters of fracturse, and fracture-veins, determines the complex mineralization of the chemical and gas composition of mineral-thermal waters throughout the studied area. The study of volcano-intrusive and fault-fracture ore-controlling structures, volcanogenic formations, petrochemical composition of rocks and associated mineral deposits and mineral-thermal waters of the Azerbaijan part of the Lesser Caucasus is relevant from a scientific and practical points of view. A detailed study of the modern structure of the Lesser Caucasus shows that transverse rupture faults and deep flexures cut through the folded system. Deposits of various minerals, including mineral and thermal waters, are confined to these ruptured faults. The study revealed that the formation and discharge of numerous outcrops of carbonic mineral and thermal waters occurs mainly in fissure systems, in deep tectonic faults. In the Lok-Karabakh zone, most of the sources of the formation of gold-bearing placers belong to the deposits and manifestations of the gold- quartz-low-sulphide formation. Gosha, Kedabek, Karadag, Chovdar, Dagkesemen, Gyzylbulag and less significant deposits and ore occurrences are located in this zone. The Dashkesan ore region is distinguished by the reserves of iron, alunite and cobalt. The Zaylik alunite deposits are world famous in terms of large reserves. Analysis of geological materials confirms that the origin and distribution of deep tectonic faults plays a major role in the formation of geological, including volcanoplutonic, metamorphic processes and associated ore formation. Currently, there are dozens of variously evaluated and explored gold deposits on the territory of the Republic. The bulk of the primary deposits are located in the Lesser Caucasus part of the Republic.

Hydrothermal Ore Genesis in the Sea of Japan

—The Sea of Japan is a tectonically active region with rift-related destruction of the Earth’s crust and numerous volcanic edifices on the seafloor. Since the 1970s, numerous zones with ferromanganese crusts (FMCs) and phosphorite and barite ore occurrences have been discovered during the repeated expeditions of the Pacific Oceanological Institute, Vladivostok. Analysis of the distribution of these ore occurrences showed that all of them are confined to tectonically active zones of the seafloor: submarine volcanoes, tectonic scarps, or fault zones. In some zones, phosphorites occur together with FMCs, and in one zone, together with FMCs and barites. Ferromanganese hydroxides, phosphorites, or barites are found in the pores of basalts composing submarine volcanic edifices in the Sea of Japan. These data indicate that the ore matter in all zones is supplied with postvolcanic gas-hydrothermal fluids or hydrothermal solutions circulating along deep faults during the destruction of the continental crust in the southern and eastern parts of the sea. Thus, ferromanganese, phosphate, and barite ore occurrences in the Sea of Japan are related to low-temperature hydrothermal-sedimentary processes.