Composition, P-T parameters, and metasomatic transformations of mafic schists of the Svyatoi Nos Peninsula, Eastern Baikal Area

The paper reports data on rock and mineral compositions from the Svyatonosskaya Formation, which is a continuation of the Ol’khon Series in the northern part of the Svyatoi Nos Peninsula, eastern shore of Lake Baikal. The pyroxene-amphibole-plagioclase schists (metagabbro) are replaced there by the garnet-biotite-quartz assemblage, which was formed, according to the data of various geothermometers and calculations by the THERMOCALC computer program, under conditions corresponding to the transition from the granulite (848–811°C) to high grades of the amphibolite (715–670°C) facies under high pressures (8.7 ±1.6 kbar). In petrogenetic grids, these conditions fall onto the line of the onset of eclogitization. In nature these rocks are a continuation of the Chernorudskaya-Barakchinskaya zone of elevated pressures in the Ol’khon area. The metasomatic rocks were formed simultaneously with strike-slip faulting, when coupled zones of relatively high-(eclogite-like) and low-pressure (quartzite-marble melange) developed at the inflow of SiO₂ and K₂O and the removal of MgO and CaO. Analogous compositional changes in gneisses and schists in tectonic extension zones in Ol’khon Island and neighboring areas occurred during the development of migmatites. The migmatization of the gneisses was likely coupled with the garnetization of mafic schists in high-pressure zones and the formation of eclogite-like rocks replacing marbles. The accompanying graphitization of this block suggests that the metasomatic fluid had a hydrocarbon-hydrogen composition.     

Phlogopite and phlogopite–amphibole parageneses in the lithospheric mantle of the Birekte terrane (Siberian craton)

Mantle xenoliths containing phlogopite and phlogopite–amphibole mineralization from kimberlites of the Kuoika field have been studied. Such xenoliths were found in two series of rocks: magnesian (Mg) pyroxenite–peridotite and Fe-type phlogopite–ilmenite hyperbasite. The ⁴⁰Ar/³⁹Ar phlogopite age (1600–1800 Ma) and Re–Os and oxygen isotope data in rocks and minerals of the first series of rocks allow us to suggest that Phl–Amph metasomatism of the lithospheric mantle under the Birekte block and its accretion to the Siberian craton occurred in the subduction zone. The second series of rocks is comagmatic to potassium ultramafites and mafites, finding in the Siberian Platform. The phlogopite ages (870–850 Ma) from Phl–Ilm ultramafites corresponds to the beginning of the breakup of the supercontinent Rodinia and is close to ancient age datings of the alkaline ultramafic-carbonatite Tomtor massif. Phlogopite from xenoliths with garnet is much younger in age (500–600 Ma).

     

Solar wind variation with the cycle

The cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density, velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics of the solar wind are reviewed with the emphasis on the cycles.     

Climatic trends in temperature,zonal flow,and stationary planetary waves from NCEP/NCAR reanalysis data

A detailed analysis of climatic trends in the longitudinally averaged temperature, zonal wind velocity, and activity of a stationary planetary wave with the zonal wave number 1 (SPW1) is made for January. The results of analysis indicate that marked climatic temperature variations having opposite signs in the low and high latitudes are observed. These variations cause the relevant variations in the intensity and arrangement of maxima of tropospheric jet flows and, thereby, are responsible for changes in SPW1 propagation conditions. SPW1 propagation from the troposphere into the upper atmosphere is calculated with a linearized model by using the distributions of zonal mean flow that are characteristic of the 1960s and the early 21st century. These calculations indicate that, over the past 40 years, the propagation conditions have improved “on average” and the calculated SPW1 amplitude in the stratosphere and mesosphere of the winter hemisphere has increased substantially. Analysis of the amplitudes of the zonal wind velocity for SPW1 that were obtained from the NCEP/NCAR data is consistent with the results of simulation and shows that some enhancement of SPW1 activity in the lower stratosphere has been actually observed in recent years. These variations in the amplitudes are also accompanied by the enhancement of SPW1 interannual variability.     

Deformation of the magnetosphere and the penetration boundary of solar protons before the onset of the main phase of a magnetic storm

The ring current is conventionally considered responsible for the shift of the boundary of solar proton penetration into the inner Earth’s magnetosphere during magnetic storms. The cases of a boundary shift were observed in some works on the dark side before the onset of a magnetic storm, i.e., at positive values of the Dst index. In this work, this type of shift of the penetration boundary is considered in detail with two storms as examples. It is shown that the corresponding distortion of the magnetosphere configuration is induced by an increase in the solar wind pressure during the initial phase of a magnetic storm. The current induced in this case on the magnetopause is closed by a current in the equator plane, which changes the configuration of the dark side of the inner magnetosphere, weakens the magnetic field, and allows solar protons to penetrate the inner magnetosphere. The significant difference in the positions of the penetration boundary and the boundary found from models of the magnetosphere magnetic field can be explained by insufficient consideration of closing currents.     

Orthorhombic lazurite from the Tultui deposit in the Baikal region

A lazurite sample taken from the Tultui deposits in the Baikal region has been studied using petrographic examination, X-ray diffraction, and local X-ray spectroscopy (electron microprobe). It is established that the line of the basic cell in the X-ray diffraction pattern of the orthorhombic lazurite is widened, so the unit-cell parameters should be recalculated from the interlayer distances of the superstructural reflections. The chemical compositions and unit-cell parameters of the lazurites from the Baikal region and the Pamirs are different. Two schemes of the chemical substitutions of atoms in the mineral are assumed: (1) the hauyne cluster [Na₃CaSO₄]³⁺ is replaced with a sodalite cluster [Na₄Cl]³⁺, and (2) two hauyne clusters 2[Na₃CaSO₄]³⁺ are substituted by nosean clusters [Na₄SO₄]⁺ and [Na₄H₂O]⁴⁺ with retention of the total charge. The increase in the Na and Cl contents in the orthorhombic lazurite is accompanied by a decrease in the unit-cell dimensions. Orthorhombic lazurites from the southern Baikal region and the southwestern Pamirs were formed in apocarbonate (apocalciphyre) metasomatic rocks at a lower temperature than pyroxene, afghanite, and cubic lazurite.     

Variability of planetary waves as a signature of possible climatic changes

The long-term variability of stationary and traveling planetary waves in the lower stratosphere has been investigated using the data of NCEP/NCAR reanalysis. The results obtained show that during the last decades winter-mean amplitude of the stationary planetary wave with zonal wave number 1 (SPW1) increases at the higher middle latitudes of the Northern Hemisphere. It has been suggested that the observed increase in the SPW1 amplitude should be accompanied by the growth in the magnitude of the stratospheric vacillations. The analysis of the SPW1 behavior in the NCEP/NCAR data set supports this suggestion and shows a noticeable increase with time in the SPW1 intra-seasonal variability. The amplitudes of the long-period normal atmospheric modes, the so-called 5-, 10- and 16-day waves, diminish. It is supposed that one of the possible reasons for this decrease can be a growth of radiative damping rate caused, for instance, by the increase of CO₂. To investigate a possible climatic change of the middle atmosphere dynamics caused by observed changes in the tropospheric temperature, two sets of runs (using zonally averaged temperature distributions in the troposphere typical for January 1960 and 2000) with the middle and upper atmosphere model (MUAM) have been performed. The results obtained show that on average the calculated amplitude of the SPW1 in the stratosphere increased in 2000 and there is also an increase of its intra-seasonal variability conditioned by nonlinear interaction with the mean flow. This increase in the amplitudes of stratospheric vacillations during the last four decades allows us to suggest that stratospheric dynamics becomes more stochastic.