Search

The new results of experimental study of the Na2MgSiO4–Mg2SiO4 section of the SiO2–MgO–Na2O model system at 22–24 GPa and 1600–1900°C are discussed in this paper. An association of Na-bearing ringwoodite (up to 0.42 wt % Na2O) and the phase with the composition Na2MgSiO4 with a cristobalite-type structure was obtained at 22 GPa. Incorporation of Na in ringwoodite occurs through the mechanism Mg2+ → 2/3Na+ + 1/3Si4+ and results in an increase in the cell parameter in relation to that of pure Mg2SiO4 ringwoodite. A paragenesis of Na-bearing bridgmanite (up to 0.67 wt % Na2O), periclase, and anhydrous sodium phase X (Na2Mg2Si2O7) is formed at 23–24 GPa. Based on the data obtained, high-pressure Na–Mg silicates, Na2MgSiO4 and Na2Mg2Si2O7, may be considered as mineralogically probable mantle phases within the locally metasomatized mantle regions, although their finds as inclusions in diamond crystals are unlikely.

Based on the data of atomic modeling, the different schemes of isomorphic incorporation of Cr3+ ions into the crystal structures of CaSiO3 and MgSiO3 were tested in the pressure range of 18–25 GPa and at temperatures of 1873–2223 K. Under these PT parameters, the content of Cr3+ in these structures was estimated quantitatively. The semi-empirical simulation data are in good agreement with the results of experiments.

The relationship between radon and the tectonic activity of faults for two geodynamically active regions of Central Mongolia is shown with account for the influence of individual characteristics of the radon field. As a whole, the radon activity of the faults increases with an increasing contribution of extension to the dynamic environment of their formation, with increasing seismic activity, and near concentrated faults of the late stages of evolution in comparison with the wide zones of fractures at the early stages of the formation of the internal structure. The studied patterns should provide an increase in the efficiency of application of radon surveys in investigation of the seismic hazard of faults in the Earth’s crust.

A weak seismic event with body wave magnitude 2.1 was detected near the epicenter of an underground explosion conducted by the Democratic People’s Republic of Korea (DPRK) on September 9, 2016. The event occurred approximately two days after the test. Using the method of waveform cross-correlation, two array stations of the International Monitoring System (IMS), USRK and KSRS, recorded the arrival of P n waves. At the same time, this event was not recorded during the standard automatic processing at the International Data Center. The location and other characteristics of this weak event indicate that it is likely to have been an aftershock of the preceding explosion. Based on the successful automatic detection and construction of the event, we conducted an extended investigation, which consisted in searching for secondary seismic phases at the nearest stations that do not belong to the International Monitoring System. The final solution, which is based on waveform cross-correlation, includes stations MDJ (China) and SEHB (Republic of Korea), the aftershock epicenter is located at ~2 km northwest of the epicenter of the DPRK test.

Shock waves and impact of the Chelyabinsk Meteorite fragments on the ground initiated various waves in the atmosphere and the earth. Three different sources of seismic and infrasound waves were found by arrival time and azimuth of seismic and infrasound waves recorded by the International Monitoring System.

When examining the peat deposit discovered in Vydrinaya bog, South Baikal region, the authors encountered anomalous Zn and Cu concentrations for highmoors being up to 600–500 ppm on a dry matter basis in the Early Holocene beds (360–440 cm) formed 11 000–8500 years ago. It has been demonstrated that Zn and Cu are present inside the plant cells of peat moss in the form of authigenic sulfide minerals of micron size. Apart from Zn and Cu, native Ag particles (5–7 um) have been encountered in the peat of the Vydrinaya bog at a depth of 390–410 cm; these particles formed inside the organic matter of the plasma membrane of peat moss containing Ca, Al, S, and Cu. This study suggests probable patterns of the formation of zinc sulfides, copper sulfides, and native silver in peat moss. The results obtained indicate that biogenic mineral formation plays a significant role in this system, which is a very important argument in the discussion on the ore genesis, in which physicochemical processes are normally favored, while the role of living matter is quite frequently disregarded.

New data on the elemental composition of the Severnaya Dvina River, the largest one in the White Sea region, are presented. The elemental composition of the river water in May, the period of the snowmelt flood, is similar to the upper layer of the Earth’s continental crust due to the active erosion of the earth material in the catchment area. In August, the period of the summer low water, the impact of biogenic components increases and elevated concentrations of Cd, Sb, Mn, Zn, Pb, and Cu are observed. At other times, no significant pollution by heavy and rare-earth elements is registered.

The composition of the parental melt for the predominant mass of natural diamonds may be determined from concerted mineralogical and experimental data [1]. The study of mineral inclusions in diamonds demonstrates their affiliation to peridotite and eclogite parageneses [2]; i.e., the composition of the diamond crystallization medium is strongly variable. Its component composition may be estimated from inclusions of minerals, quenched melts, and fluids in diamonds. It has become evident that the multicomponent and multiphase parental medium consists of chemically different compounds and phases: oxides, silicates, aluminosilicates, sulfides, phosphates, carbonates, chlorides, metals, water, carbon dioxide, and others. However, the main problem of dominating compound in parental media during the diamond formation is still unclear. The reason is that efficiency of diamond formation for

The majority of diamonds from kimberlite and lamproite pipes were formed within a quite narrow range of 140‐220 km, as evident from calculations of pressures and temperatures for the formation of their silicate inclusions [1]. The upper boundary of this range corresponds to the graphite‐diamond transition in the Earth’s mantle. The lower boundary is limited by the maximal lithosphere thickness that is typical only for the old parts of continents (cratons). Mineral inclusions in ultradeep diamonds comprising majoritic garnet, magnesiowustite, and phases of CaSiO 3 and MgSiO 3 compositions (presumably, with a perovskite structure), as well as tetragonal phase of pyrope-almandine composition (TAPP) [2] are direct samples from mantle depths, which allow us to test models of the Earth’s deep structure based on geophysical and experimental investigations. Of special interest among all the ultrahigh-pressure phases is majoritic garnet, because its composition and parageneses are most indicative for estimation of physicochemical conditions of the formation of deep mineral assemblages. According to the experimental data, pyroxene component starts to dissolve in garnet at a depth of ~250 km, resulting in the increase of Si and Na and the decrease of Al concentrations in this mineral according to the scheme Na + + Si 4+ = Mg 2+ + Al 3+ [3]. Experiments performed for mantle eclogite systems in a wide PT range using a high-pressure multianvil apparatus [4‐8] confirmed the influence of pressure on the composition of garnets (mainly Na admixture and excess Si contents) obtained in experiments (Fig. 1). In our study, we have analyzed the experimental data in the multicomponent Na 2 O–CaO–MgO–FeO–Al 2 O 3 – SiO 2 system and suggested a model of the garnet‐clinopyroxene barometer based on the change of Na concentration in garnet. In the opinion of Haggerty and Sauter [9], jadeiterich pyroxene lamellae in garnet are related to the decomposition of high-pressure Na-bearing garnets. The increase of pressure may lead to the opposite process of pyroxene microlite dissolution in garnet. This fact provides an explanation for the increase in the Si content up to 3.3 f.u. and a decrease in the Al content down to 1.3 f.u., as observed in garnets from the Monastery kimberlite pipe. According to the experimental data, such garnets were formed at a pressure of >10 GPa. Therefore, Na incorporation in garnet may be considered as a result of jadeite dissolution accompanied by Na and Si ingress according to the reaction [1]