Russian Journal of Pacific Geology最新文献

From the 1980s to the present, a set of geophysical methods has been implemented in southeast Kamchatka, including the earthquake converted waves method, magnetotelluric sounding, gravimetry, magnetometry, and seismology. Based on a comprehensive interpretation of the data obtained, a geological and geophysical model of the Earth’s crust and upper mantle along the Khodutka Bay–village of Nikolaevka profile was constructed. A genetic relationship has been established between dynamically active areas of the Earth’s crust with gold deposits. A hypothesis has been put forward about the division of a previously single xenoblock into two separate fragments under the action of strike-slip faults along the Nachikinskaya transverse dislocation zone. The southern fragment is represented by the Pribrezhny Terrane. To the west of the terrane is a permeable zone in which modern volcanism has occurred. The intrusion of magma and high-temperature fluids enriched in noble metal solutions into the upper layers of the crust occurs through a magma conduit formed in the palaeosubduction zone.

Abstract

There are five tectonomagmatic stages in the evolution of Magellan Seamount guyots: 1, Late Jurassic–Early Cretaceous (Earliest Cretaceous, ∼160–140 (?) Ma); 2, Early Cretaceous (Late Barremian (?)–Aptian–Albian, ∼127–96 Ma); 3, Late Cretaceous (Late Cenomanian (?)–Turonian–Early Campanian, ∼95–76 Ma); 4, Late Cretaceous (Late Campanian–Maastrichian, ∼74.5–66.0 Ma); 5, Cenozoic, 66–0 Ma. Each of the tectonomagmatic stages corresponds to a specific age complex of volcanic rocks of the Magellan Seamounts. Tectonomagmatic stages have different durations and played different roles in the evolution and formation of the modern structure of Magellan Seamount guyots. Each of the tectonomagmatic stages characterizes a specific geomorphological space of guyots (base, main part of the structure, small complicating overprinted second-order structures). In general, the tectonomagmatic stages in the evolution of the Magellan Seamounts agree well with the stages of the evolution of some other regions of the Pacific Ocean and correspond to the earlier established periods of their tectonomagmatic activation.

The article presents the results of hydrochemical studies of the Nizhne-Shchapinsky (Kipely) carbon dioxide thermal (39°C) springs in 2021. The springs are discharged within the Shchapinsky graben near the active Kizimen volcano. The results include macro- and microcomponent composition, isotopic composition of source water, some free gas components, and dissolved strontium. The results are discussed using previously published and archive data, taking into account the geological and structural position of the area, water–rock interaction, as well as using simple thermochemical calculations in order to explain the rare, but characteristic of the chemical composition of some carbon dioxide waters, predominance of magnesium over calcium. It has been shown that the waters of the Nizhne-Shchapinsky springs are formed as a result of mixing of two components: deeper and more heated sodium chloride water and more surface, less heated water with the composition Mg–Ca–({text{HCO}}_{3}^{ - }), formed due to interaction with carbonate-bearing rocks and CO₂ of igneous origin.

Abstract

In 2020, in the caldera of Uzon volcano (Kamchatka Peninsula), electrical prospecting studies were carried out using the electrotomography method within the eastern thermal field near Shaman geyser. The geoelectric section is divided into three zones according to the level of electrical resistivity: relatively high-resistivity cold zones at the edges and a relatively low-resistivity hot zone in the center. The hot zone, situated at a depth of 5–20 m and hosting the Shaman geyser, is distinguished by anomalously low resistivity (less than 0.5 Ω m), which indicates the highest fracturing and saturation of rocks with fluid. Resistivity monitoring was carried out above the geyser using an Omega-48 electrical tomography station and two cables with lengths of 235 and 47 m. The first cable provided a survey depth of 60 m; the second, ∼12 m. Four phases of the geyser’s operation are distinguished on the difference geoelectric sections, constructed from the monitoring results: filling, outpouring, spouting, and steaming in the form of alternating positive and negative electric field anomalies. The channel to the geyser was found from the results of areal measurements.

Abstract

The paper presents a study of typomorphic characteristics of placer gold from tributaries of the Kengeveem River, Magadan oblast. The placer gold was studied by optical and scanning electron microscopy at the Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences. As a result, the first information on the morphology, internal structure, and chemical composition of placer gold from the southeastern Taigonos Peninsula was obtained. Three mineral types of the gold were determined. The first type is dominant. Its grains are characterized by subore morphology, with weak and medium roundness. Only Au and Ag are present in the composition of native gold, other macrocomponents were not found. The gold fineness is 750‒950‰. Some gold grains bear signs of supergene transformation, which is expressed in the development of high-fineness gold rims and intergranular veins. The second type of the gold is represented by well-rounded plates with a fineness of 980‒990‰. The third type is loose aggregates of secondary high-grade mustard gold. The obtained data allowed us to determine the different transport distances of native gold and to consider the low-sulfide epithermal Au‒Ag mineralization and presumably distal gabbroids as the primary sources of gold.

Abstract

Debris flow activity in the Geysernaya River basin was mapped. Large-scale debris flow processes due to the collapse of fragments of the valley’s left wall were observed in this area three times over the past 40 years. Three independent debris flow areas of the river basin were identified and described: the upper reaches of the river, the Levaya Geysernaya basin; the middle reaches of the river, below the dammed lake that formed in 2014; and the lower downstream part, below the dammed lake that existed in 2007–2014. Debris flow processes are typical of most tributaries of the Geysernaya River. Moreover, debris flows can be aseasonal in the left tributaries, because they are formed under constant heating and active gas–hydrothermal influence within the thermal fields. The landslide dam formed in 2014 is resistant to erosion, and an independent outburst of the dammed lake is unlikely. With further erosion of the 2007 dam and expansion of the breach in the dam body, collapse of its sides and debris flow in the lower part of the Geysernaya River valley should not be ruled out. Risks of rockfall, landslide, and debris flow processes, most likely on the left wall of the valley, should be taken into consideration in planning the development of recreation facilities.

Abstract

The eruption of the unique Taketomi side volcano, located on Atlasov Island in the northern part of the Kuril Island arc, began underwater and ended on land. It happened before people’s eyes and was, in essence, the formation of a new side volcano. The volcano that formed was studied in 1933–1936 by renowned Japanese scientists, and from 1946 to the present, by Soviet and Russian researchers. The Taketomi side volcano continues to amaze with its landscapes and is actively visited by numerous tourists. Unfortunately, there is still no single publication about people who, to one degree or another, have made a significant contribution to the study of this side volcano. This study is the first attempt to talk about them in lapidary form. In addition, available photographs show the destruction of the Taketomi structure starting in the 1950s until 2020, and for the first time, the existing inconsistencies cited in various publications that describe the eruption of this side volcano are noted.

Abstract

The Sloboda Geodynamic Intersection is considered an convergence zone for major segments, aulacogens, faults, and suture zones of the East European Platform. Between 2020 and 2022, researchers of the Geological Faculty of Moscow State University and the Geoelectromagnetic Research Center of Branch of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences (GEMRC IPE RAS) conducted deep magnetotelluric surveys in this region, performed along the Pushkinskiye Gory–Andreapol (PA), Sebezh–Velikiye Luki–Rzhev (SVR), and Ostrov–Ostashkov (OO) profiles. Qualitative analysis of the data made it possible to assess the dimensionality of the studied medium, the total longitudinal conductivity of the sedimentary cover, and the dominant strike of the conductive structures. Quantitative interpretation using 1D, 2D, and 3D inversions resulted in geoelectric models comprising a conductive sedimentary cover and a highly resistive basement. Transcrustal zones of enhanced electrical conductivity interpreted as the southwest extension of the Ilmen–Ladoga anomaly were consistently identified within the depth range of 10–40 km. These conductivity anomalies are attributed to the deep subsidence of heavily tectonized and metamorphosed sedimentary rocks initially saturated with organic and carbonate matter.

Abstract

Authigenic minerals have been studied in Phanerozoic volcanosedimentary deposits in the northern part of the Asian continent–Pacific Ocean transition zone. The following were found: chlorite, mica, corrensite, rectorite, defective chlorite, kaolinite, smectite, calcite, barite, gypsum, epsomite, zeolites, cristobalite, quartz, and goethite. The minerals corrensite and rectorite have significant indicative properties, as do the assemblages corrensite–laumontite, corrensite–epsomite–authigenic calcite and mica–kaolinite–quartz. Such a range of minerals indicates that the thickness of sediments in the studied basins could reach 3–5 km, and their formation temperature could be more than 150°C. The mica–kaolinite assemblage may indicate epicontinental sedimentation conditions associated with coal formation on nearby land, the corrensite–chlorite assemblage may indicate conditions favorable for the evaporation of seawater, and the presence of laumontite in it may indicate periodic calcium supply to the sedimentary basin. The periods of mineral formation, possibly associated with global climatic events, have been identified: 113–120, 110–113, 105–110, 93–95, 72–83, 61–72, 56–61, 33–56 Ma, which can serve as benchmarks to determine sedimentation conditions and the framework for more reliable stratigraphic constructions.

Abstract

The study of the composition of sedimentary formations raises the problem of identifying extraterrestrial matter, in particular, distinguishing cosmic spherules from technogenic and volcanogenic ones. Based on a study of a collection of 482 bulk spherules separated from ferromanganese crusts of the Pacific Ocean floor, it is proposed to use relief forms on spherule surfaces as an additional feature of their origin. The paper describes in detail such relief forms arising as cosmic particles pass through the upper layers of Earth’s atmosphere, and isolation and separation of the Fe–Ni cores from the spherules. The presence of a round hemispherical cavity on the flattened side of the spherule, a depression with concentric circles, or a “button” structure, as the presence of a Fe–Ni core, is sufficient but not necessary evidence for the cosmic origin of a spherule.