The results of U–Pb isotope dating (LA-ICP-MS) of zircons from metatuffaceous sandstones of the Shidzhatmaz (sample DN223A) and Dolina Narzanov (sample DN224A) Formations within the Bechasyn Zone on the northern slope of the Greater Caucasus are presented. The minimum age estimates for zircons from the studied metatuffaceous sandstones of the Shidzhatmaz and Dolina Narzanov Formations, taking into account the error, are very similar. The weighted mean of the youngest coherent zircon dates from metatuffaceous sandstones of the Dolina Narzanov Formation is 544 ± 5 Ma (based on 5 dates), while that from the Shidzhatmaz Formation metatuffaceous sandstones is 545 ± 5 Ma (based on 6 dates). The weighted mean of the 9 youngest coherent dates of zircons from both samples is 544 ± 4 Ma. The Shidzhatmaz and Dolina Narzanov Formations are assigned to the Upper Riphean on the certified second-generation State Geological Map. Our results reliably constrain the ages of the Shidzhatmaz and Dolina Narzanov Formations not older than the latest Vendian (Ediacaran). The zircons extracted from the metatuffaceous sandstones of both formations are dominated by age groups ranging from 700 to 540 Ma, with distinct frequency peaks at 557 and 630 Ma, which are nearly identical for samples from both formations. This pattern of zircon age distribution is highly typical of clastic rocks from Upper Precambrian and Lower Paleozoic sequences that form tectonic blocks interpreted as Peri-Gondwanan terranes and widespread in Western and Central Europe, on the Atlantic coast of North America, in North Africa, Anatolia, and Arabia. In this context, it is concluded that the metatuffaceous sandstones of the Dolina Narzanov and Shidzhatmaz Formations were most likely formed in close proximity to a large volcanic edifice that developed on the Northern periphery of Gondwana (in Peri-Gondwana) with enhanced magmatic activity occurring at approximately 630 and 557 Ma. The Dolina Narzanov Formation is composed of the erosion products of the upper part of the volcanic edifice, while the structurally overlying Shidzhatmaz Formation is made of the erosion products of its lower part and the basement.
In the paper, the results of a tectonophysical reconstruction of crustal stresses for the Crimea–Black Sea region, which includes both the peninsula itself and seismogenic regions in its immediate vicinity, have been presented. Stress determination has been performed based on seismological data on earthquake focal mechanisms using a modified version of Rebetsky’s cataclastic method. Based on the results of stress reconstruction, it has been possible to identify patterns of stress variation in the fault zone located in the waters along the Southern Coast of Crimea (SSC). It has been shown that stresses favorable for the formation of normal fault earthquakes as discharges currently exist in the vicinity of the source of the strong Yalta earthquake of September 11/12, 1927, with M = 6.8. Therefore, the risk of a repeat strong earthquake similar to the 1927 event has increased in the region. Based on analysis of the patterns of reconstructed stresses in the SCC fault structure, a relation between the stress state of the fault zone at the source of the Yalta earthquake and northwest strike faults located along the coast has been demonstrated. Shear displacements along these faults can be considered as stress generators in the offshore fault zone.
After a significant interruption, precision geodynamic monitoring has resumed at the underground Geophysical Observatory “Protvino” of the IPE RAS. The multichannel data recording system has been completely updated. Remote access to recorded signals in real time is now possible. Tilt recording has begun with the NSh adit tiltmeter. Along with tidal tilt variations, teleseismic events and local effects arising from the passage of seismic waves are being recorded. Anomalous tilt variations of unknown origin have been detected, requiring further investigation. To this end, temperature monitoring has been significantly enhanced. Specially developed precision electronic thermometers are used for this purpose. Special circuit design solutions that minimize induced interference in both the power and signal circuits have allowed the thermometers to achieve a resolution of 0.0004°C.
The occurrence of poloidal Pc4 pulsations was registered on the GOES geostationary satellites during 4 days from October 3 to 6, 2013, which coincided with the growth of electron fluxes with energies >2 MeV, 475 keV. It is hypothesized that Pc4 pulsations excited by energetic protons may participate in the acceleration of electrons to relativistic energies in the Earth’s outer radiation belt.
An analysis of the contemporary geodynamic situation in the Vladikavkaz area is presented, based on long-term GNSS (Global Navigation Satellite System) observations at continuous stations and field sites at the Ossetian geodynamic polygon. Velocity estimates were obtained in two reference frames: the global International Terrestrial Reference Frame (ITRF) and the regional Eurasia-fixed frame (ITRF2014_EURA). In the ITRF, the motion of the region is consistent with the overall motion of the Greater Caucasus in a northeasterly direction at a rate of 27–30 mm/year. The results of velocity profiling in the local reference frame showed a number of oppositely directed kinematic features that define the contemporary geodynamic regime of this area. These results, as well as those from seismological studies, indicate that the city of Vladikavkaz is located in a region with relatively active geodynamic processes.
