Dielectric relaxation in oil-bearing clayey rocks

The dielectric properties of the bentonite–oil–salt solution mixtures with different water and oil saturation were experimentally studied in the frequency range of 10 kHz to 4 GHz at 25–60 °C. It has been established that besides the region of the Debye water relaxation, there are two more relaxation regions resulting from the interfacial interaction of the mixture components in this frequency range. To describe the dielectric permittivity and equivalent conductivity of the mixture, a spectroscopic model taking into account the multifrequency relaxation is proposed. The dependence of the model parameters on the water saturation and temperatures of the samples has been determined. The experimental data are compared with the modeling results, and the error of prediction for the dielectric permittivity and conductivity of mixture is estimated using the proposed model.     

Mineralogical–Geochemical Features of Ice-Rafted Sediments in Some Arctic Regions

The quantitative mineral composition estimated using the Rietveld method and some geochemical features are considered for bulk samples of the ice-rafted sediments (IRS) from some Arctic regions. Layer silicates in the studied samples vary from ~20 to ~50%. They are dominated by micas and their decomposition products (illite and likely some part of smectites) at significant contents of kaolinite, chlorite, and transformation/decomposition products of the latter. A significant content of illite and muscovite among layer silicates in most IRS samples suggests that sources of the sedimentary material were mainly mineralogically similar to modern bottom sediments of the East Siberian and Chukchi seas, as well as presumably sediments of the eastern Laptev Sea. It is suggested that a significant kaolinite fraction in IRS samples from the North Pole area can be caused by the influx of ice-rafted fine-grained sedimentary material from the Beaufort or Chukchi seas, where kaolinite is supplied from the Bering Sea. Positions of IRS data points in the (La/Yb)_N–Eu/Eu*, (La/Yb)_N–(Eu/Sm)_N, and (La/Yb)_N–Th diagrams show that the studied samples contain variable proportions of erosion products of both mafic and felsic magmatic rocks and/or sufficiently mature sedimentary rocks. This conclusion is confirmed by localization of IRS data points in the Th/Co–La, Si/Al–Ce, and Si/Al–Sr diagrams.     

Crustal structure and properties of Archean cratons of Gondwanaland: similarity and difference

This is a synopsis of available data the on crustal structure and properties of thirteen Archean cratons of Gondwanaland (the cratons of Africa, Australia, Antarctica, South America, and the Indian subcontinent). The data include estimates of surface area, rock age and lithology, Moho depth, thickness of lithosphere and sediments, as well as elevations, all summarized in a table. The cratons differ in size from 0.05 x 10⁶ km² (Napier craton) to 4 x 10⁶ km² (Congo craton) and span almost the entire Archean period from 3.8 to 2.5 Ga. Sediments are mostly thin, though reach 7 km in the Congo and West African cratons. Elevations above sea level are from 0 to 2 km; some relatively highland cratons (Kaapvaal, Zimbabwe, and Tanzanian) rise to more than 1 km. On the basis of regional seismic data, the Moho map for cratons has been improved. The Moho diagrams for each craton are constructed. The analysis of the available new data shows that the average Moho depth varies from 33 to 44 km: Pilbara (33 km), Grunehogna (35 km), Sao Francisco (36 km), Yilgarn (37 km), Dharwar (38 km), Tanzanian (39 km), Zimbabwe (39 km), Kaapvaal (40 km), Gawler (40 km), Napier (40 km), West Africa (40 km), Congo (42 km), and Amazon (44 km) cratons. The Moho depth within the cratons is less uniform than it was assumed before: from 28 to 52 km. The new results differ significantly from the earlier inference of a relatively flat Moho geometry beneath Archean cratons. According to the new data, early and middle Archean undeformed crust is characterized by a shallow Moho depth (28-38 km), while late Archean or deformed crust may be as thick as 52 km.     

Non-recurrent geomagnetic disturbances from high-speed streams

It is shown that at any phase of solar activity cycle the Earth is circumflown mainly by high-speed solar wind streams (M-streams). The attention is called to the fact that M-streams cause not only the wellknown recurrent geomagnetic disturbances (at the declining phase of solar cycle) but also numerous nonrecurrent disturbances (at all the other phases). The intensity and duration of a typical non-recurrent M-disturbance are less than those of a recurrent one.     

Kp index correlations with solar-wind parameters during the first and second stages of a recurrent geomagnetic storm

The dependence of geomagnetic activity during a recurrent magnetic storm on the solar-wind magnetic field and plasma parameters has been studied. According to variations of solar-wind magnetic field strength B, a recurrent magnetic storm is divided into two stages: the first proceeding during the peak of B, and the second proceeding after the return of B to quiet level. The K_p index vs solar-wind parameters scattering diagrams for stages I and II differ significantly. In particular, the random scattering for stage I is much larger than for stage II. It was found that for stage I the K_p index correlates with B, with the sign and value of northsouth field component B_z and with the magnitude ΔB of field fluctuations, the situation being similar to that during sporadic magnetic storms, though the scale of the event is smaller. For stage II, the K_p index does not correlate with B, but strongly correlates with ΔB and weaker—with B_z. So geomagnetic activity at stage II is supported mainly by solar-wind magnetic field fluctuations. The dependence of the K_p index on plasma parameters (concentration of protons n, bulk velocity v and temperature T) is weak for both stages.     

Peculiarities of distribution and transformation of water in the Keret’ River tidal estuary

Presented are the results of the study of the processes of interaction between the river and sea water in the estuary of the Keret’ River flowing into the White Sea. The studies were carried out using the georadar method which enables one to register the boundary between fresh and salt water with the high spatial and temporal resolution. The use of this method helped to determine the boundaries of the area of distribution of fresh water in the estuary during different phases of the tidal cycle and to reveal the typical fluctuations of the boundary between fresh and salt water manifested at different values of river runoff and weather conditions.     

Phase relations and formation of sodium-rich majoritic garnet in the system Mg3Al2Si3O12–Na2MgSi5O12 at 7.0 and 8.5 GPa

The pseudo-binary system Mg₃Al₂Si₃O₁₂–Na₂MgSi₅O₁₂ modelling the sodium-bearing garnet solid solutions has been studied at 7 and 8.5 GPa and 1,500–1,950°C. The Na-bearing garnet is a liquidus phase of the system up to 60 mol% Na₂MgSi₅O₁₂ (NaGrt). At higher content of NaGrt in the system, enstatite (up to ∼80 mol%) and then coesite are observed as liquidus phases. Our experiments provided evidence for a stable sodium incorporation in garnet (0.3–0.6 wt% Na₂O) and its control by temperature and pressure. The highest sodium contents were obtained in experiments at P = 8.5 GPa. Near the liquidus (T = 1,840°C), the equilibrium concentration of Na₂O in garnet is 0.7–0.8 wt% (∼6 mol% Na₂MgSi₅O₁₂). With the temperature decrease, Na concentration in Grt increases, and the maximal Na₂MgSi₅O₁₂ content of ∼12 mol% (1.52 wt% Na₂O) is gained at the solidus of the system (T = 1,760°С). The data obtained show that most of natural diamonds, with inclusions of Na-bearing garnets usually containing <0.4 wt% Na₂O, could be formed from sodium-rich melts at pressures lower than 7 GPa. Majoritic garnets with higher sodium concentrations (>1 wt% Na₂O) may crystallize at a pressure range of 7.0–8.5 GPa. However the upper pressure limit for the formation of naturally occurring Na-bearing garnets is restricted by the eclogite/garnetite bulk composition.