Volcanogenic massive sulfide deposits of ophiolite associations

Volcanogenic massive sulfide deposits in ophiolite complexes are usually attributed to the Cyprus type. They associate with basaltic volcanics that are formed in mid-ocean or back-arc spreading centers and much less frequently in intra-plate settings. The deposits are characterized by copper or copper-zinc ores that are enriched in Ni, Co, and in places Mn and As, but are very poor in Pb and demonstrate a low to moderate content of Ag and Au. Typically, the deposits are low to very low in ore and metal reserves. Cyprus-type deposits were irregularly distributed during geological history. The most ancient of them were formed in the Neoproterozoic, while the bulk of the deposits are Ordovician or Cretaceous in age. Their possible Paleoproterozoic analogues can be found in the Svecofennian belt (Outokumpu ore district), while modern ones are confined to the Explorer and Endeavour Ridges and southern segment of the Juan de Fuca Ridge.     

Hydroextrusion as a possible mechanism for the ascent of diapirs,domes, and mantle plumes

A possible mechanism of the ascent of material within the Earth’s crust and mantle is the mechanism of hydroextrusion, i.e., the effect of squeezing of material under excess pressure. The major factors that predetermine the high plasticity of the material and its ability to produce hydroextrusions are high lithostatic pressures and temperatures. The phenomenon of hydroextrusion can be most clearly illustrated by the example of the origin of salt diapirs. The driving force of hydroextrusions of material in the crust and mantle is excess pressure, which can result from lateral differences between the densities of rocks (as is the case during the development of salt diapirs) and phase transitions associated with a volume increase. When the material of the upper mantle undergoes partial melting with the derivation of basaltic melts at depths of 60–100 km, excess pressures reach 80 MPa, whereas the plasticity limit of 20% melted rocks is no higher than 5 MPa. As a result, the partially molten material is forced from the melting region toward zones with lower lithostatic pressures. A local temperature increase in the transitional zones in the Earth’s mantle at positive dP/dT values of the phase transitions also gives rise to excess pressures, whose values can range from 100 to 800 MPa at a 0.5–3.0% volume change and which can be the driving force during the origin of mantle plumes. Original Russian Text ? V.N. Anfilogov, Yu.V. Khachai, 2006, published in Geokhimiya, 2006, No. 8, pp. 873–878.     

Distinct metamorphic evolution of alternating silica-saturated and silica-deficient microdomains within garnet in ultrahigh-temperature granulites: An example from Sri Lanka

Here we report the occurrence of garnet porphyroblasts that have overgrown alternating silica-saturated and silica deficient microdomains via different mineral reactions. The samples were collected from ultrahigh-temperature (UHT) metapelites in the Highland Complex, Sri Lanka. In some of the metapelites, garnet crystals have cores formed via a dehydration reaction, which had taken place at silica-saturated microdomains and mantle to rim areas formed via a dehydration reaction at silica-deficient microdomains. In contrast, some other garnets in the same rock cores had formed via a dehydration reaction which occurred at silica-deficient microdomains while mantle to rim areas formed via a dehydration reaction at silica-saturated microdomains. Based on the textural observations, we conclude that the studied garnets have grown across different effective bulk compositional microdomains during the prograde evolution. These microdomains could represent heterogeneous compositional layers (paleobedding/laminations) in the precursor sediments or differentiated crenulation cleavages that existed during prograde metamorphism. UHT metamorphism associated with strong ductile deformation, metamorphic differentiation and crystallization of locally produced melt may have obliterated the evidence for such microdomains in the matrix. The lack of significant compositional zoning in garnet probably due to self-diffusion during UHT metamorphism had left mineral inclusions as the sole evidence for earlier microdomains with contrasting chemistry.     

The neotectonics and geodynamics of the Lower Oka Region (East European Craton)

The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone.     

Dispersion characteristics of low-latitude whistlers

The effect of ions on whistler dispersion characteristics has been studied. It is shown that the significant changes in the dispersion characteristics of low-latitude whistlers are brought about by the presence of ions. The dispersions for Nainital (geomagnetic lat. 19°1'N) and Gulmarg (geomagnetic lat. 24°10'N) are found to peak around 800 Hz. The short whistler sonograms recorded at Nainital and Gulmarg have been analysed, using the complete dispersion equation and the effect of ions has been shown. At higher frequencies the dispersion is found to decrease steadily and becomes independent of ions. Some examples of short whistlers have been found whose characteristics do not conform to the general trend of low-latitude whistlers, and, on the other hand, these whistlers show a constant dispersion unaffected by ions up to a fairly low frequency and thereafter decrease sharply at lower frequencies.     

Lunar Gravity-Assist Maneuver As a Way of Reducing the Orbit Amplitude in the Spectrum–Röntgen–Gamma Project

Spectrum–Röntgen–Gamma (SRG) is a space observatory designed to observe astrophysical objects in the X-ray range of the electromagnetic spectrum. SRG is planned to be launched in 2019 by a Proton-M launch vehicle with a DM3 upper stage. The spacecraft will be delivered to an orbit around the Sun–Earth collinear libration point L2 located at a distance of ~1.5 million km from the Earth. Although the SRG launch scheme has already been determined at present, in this paper we consider an alternative spacecraft transfer scenario using a lunar gravity-assist maneuver. The proposed scenario allows a oneimpulse transfer from a low Earth orbit to a small-amplitude orbit around the libration point to be performed while fulfilling the technical constraints and the scientific requirements of the mission.     

Formalization of assessing radioactive waste burial site seismic regime parameters from seismological and geological data

A model is proposed that shows the relation of the block structure of the crust and earthquake sources (Sadovskii, 1979; Rodionov, 1979, 1984, 1994; Bugaev, 1999, 2011, 2014, 2015). The model can formalize how to assess the prediction of seismic regime parameters depending on the elastic limit and conditions and rate of deformation of the Earth’s crust. The spent nuclear fuel repository site in Olkiluoto (Finland) and a site in the area of the Krasnoyarsk Mining and Chemical Combine are considered as examples. It is demonstrated that the parameters of the prediction graphs limit the location of the points of magnitude repeatability graphs calculated for a site based on samples of earthquakes in the area according to different authors. This makes it possible to recommend predictive assessment of seismic regime parameters for stability monitoring of the seismic regime and safety analysis of a geological environment’s insulation properties for waste sites from the results of seismological monitoring and high-precision observations of modern movements of the Earth’s crust.