Analysis of Current Movements and Deformations of the Earth’s Crust in Fennoscandia from GNSS Data

Izvestiya, Physics of the Solid Earth - Abstract—An analysis of the displacement rates of GNSS points indicates that the values of current deformations gradually decrease from the center of...     

Rb-Sr and U-Pb systematics of metasedimentary carbonate rocks: The Paleoproterozoic Kuetsjarvi Formation of the Pechenga Greenstone Belt, Kola Peninsula

The Rb-Sr and U-Pb systematics have been studied in the metasedimentary carbonate rocks from the Paleoproterozoic Kuetsjarvi Formation. Samples were taken from the borehole drilled in the northern zone of the Pechenga Greenstone Belt in the northwestern Kola Peninsula. The carbonate section of the formation is made up of three units (from the bottom to top): (I) dolomite (68 m), (II) calcareous-dolomite (9 m), and (III) clayey calcareous (1 m) ones. Dolomites (Mg/Ca = 0.55–0.61) from the lowermost unit I contain 70.3–111 ppm Sr. Initial ⁸⁷Sr/⁸⁶Sr ratio in them varies within 0.70560–0.70623 and characterizes the primary continental-lacustrine carbonate sediments. Calcareous dolomites (Mg/Ca = 0.39–0.59) and dolomitic limestones of units II and III (Mg/Ca = 0.02–0.36) are enriched in Sr (285–745 and 550–1750 ppm, respectively). Initial ⁸⁷Sr/⁸⁶Sr ratios in these rocks (0.70406–0.70486 and 0.70407–0.70431, respectively) fall within the range typical of the Jatulian seawater, which indicates that the carbonate sediments of two upper units were formed in an open marine basin. Study of dolomites from unit I showed that the Svecofennian metamorphism more significantly affected the U-Pb systems of carbonate rocks as compared to their Rb-Sr systems. In the ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram, most data points corresponding to the carbonate constituent of dolomites define isochron with an age of 1900 ± 25 Ma (MSWD = 0.5). The same samples define a positive correlation in the ²⁰⁸Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb plot. Since sedimentary carbonates usually do not contain Th, this correlation points to secondary enrichment of the studied dolomites in Th or thorogenic ²⁰⁸Pb. Hence, the obtained Pb-Pb dating can be regarded as the age of the Svecofennian metamorphic event. Three samples from dolomites of unit I lack any disturbance of the initial U-Th-Pb systematics, but their trend in the ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram deviates from the 1900 Ma isochron. Based on these samples, the model U-Pb premetamorphic age of the Kuetsjarvi carbonate sediments is 2075–2100 Ma. This interval is consistent with the age range of the Lomagundi-Jatulian event, which was responsible for the formation of carbonate sediments with high positive δ¹³C values.     

Identifying induced variations in the seismic regime by the methods of nonlinear dynamics

The nonlinear analysis of the data on seismicity in the areas where the underground rocks were affected by the injection of fluids, blasting works, and vibrations shows that the technogenous impacts increase the regularity of the seismic regime. The effects of the man-made actions manifest themselves in the formation of stable states characterized by the finite fractal dimension of the attractor and the small dimension of the embedding space. In order to explain the increase in the regularity of the seismic process, we consider the model of motion in the fault zones which is described by the two-parameter friction law. The presence of the stable states paves the way for both forecasting the induced seismic activity and developing the technologies for the controlled forcing of the seismic regime.     

Instrumental geophysical monitoring in the territory of northern Caucasus

Because of the activation of natural hazardous processes in the Caucasus, including the sudden Kolka-Karmadon rock-ice slide on September 20, 2002, the integrated observation system (Karmadon parametric test area) was organized at the end of 2003. The purpose of its operation is the instrumental investigation of hazardous natural and anthropogenic geological processes in the mountain areas.     

Mössbauer characteristics,mineralogy and isotopic age (Rb-Sr,K-Ar) of Upper Riphean glauconites from the UK Formation,the southern Urals

Comprehensive mineralogical analysis, Mössbauer spectroscopy and isotopic-geochronological study have been carried out for globular phyllosilicates (GPS) of glauconite group from the Uk Formation, the second one below the top of the Upper Riphean stratotype in the southern Urals. Glauconites have been sampled in the Kurtaza and Kulmas sections remote from each other in the Alatau anticlinorium that corresponds to western facies zone of the Bashkirian meganticlinorium. As is shown, size and density monomineral fractions of globules are represented by Al-glauconite according to established structural formula. The isotopic (Rb-Sr and K-Ar) dating of glauconites from the Uk Formation is performed for the first time along with computer simulation of cation arrangements in their crystal lattice and comparison of the results obtained with data of Mössbauer spectroscopy. It has been assumed by simulation that origin and transformation of the Rb-Sr and K-Ar systems in glauconite are concurrent to stages in structural evolution of this mineral, which have been controlled by geological and geochemical events in the history of sedimentary successions. The approach has been aimed at recognition of stratigraphically meaningful isotopic dates corresponding to the glauconite formation at the stage of the early diagenesis close to sedimentation time and the “rejuvenated” dates characterizing ages of subsequent geological events. The comparison of simulated cation arrangements with data of Mössbauer spectroscopy shows that the Rb-Sr (663 ± 9 Ma) and K-Ar (669 ± 16 Ma) dates established for glauconites correspond to the time of early diagenesis in their host sediments, being suitable for age assessment of the Uk Formation. The dates obtained are of interregional and wider significance, as they must be taken into consideration when constructing the general curve of Sr isotope variations in the Late Riphean oceans.