Surface Formations in the Weathering Crusts of Carbonatites: Implication for the Genesis of Unique Rare Metal Ores in the Tomtor Deposit,Russia

Lithology and Mineral Resources - A comparative analysis of the composition and structure of the surface facies of carbonatite weathering crusts (profiles) in the Chuktukon (Russia) and Seis Lagos...     

Digitization of Astronegatives of the Pulkovo Glass Library: Positions of Saturn’s Major Satellites in the Period 1972–1982 in the Gaia DR2 System

Solar System Research - We present the results of the re-reduction of Pulkovo photographic plates with images of Saturn’s major satellites in the Gaia DR2 catalog system (169 plates, 3007...     

Structure and thickness of the Earth’s crust in the northeastern part of the Indian Ocean

A digital database on the seismostratigraphy of the oceanic crust of the northeastern part of the Indian Ocean is compiled. In the first layer of the crust, the interval seismic wave velocities are 3.02 ± 0.16 km/s; in the second layer, they equal to 5.31 ± 0.27 km/s; and, in the third layer, the values are 6.46 ± 0.30 km/s. The bottom of the third seismic layer is represented by mantle rocks with an average velocity of 8.10 ± 0.16 km/s. Schemes of the distribution of the thicknesses of the second and third layers of the oceanic crust, of the total thickness of the crust, of the surface of the basement, and of the Mohorovicic discontinuity for the area considered are presented. The schemes compiled allow one to update and complement the ideas about the configuration of the major tectonic structures of the area.     

The structure of the Falkland Basin’s lithosphere

The peculiarities of the crustal structure within the Falkland Basin have been discussed. Maps of the free-air and Bouguer (2.3 g/cm³) gravity anomalies and their transforms have been made. The complex analysis of the anomalous gravity field has allowed us to confirm the continental origin of the crust. The zoning of the crust has been performed. The crust is thinned and is enriched in basic and ultrabasic intrusions. A map demonstrating the distribution of the faults within the studied water area has been made. A conclusion has been reached about the leading role played by tension processes throughout the evolution of the crust within the studied water area.     

Low-temperature chemical processes of the formation of ore manganese minerals of ferromanganese deposits of the ocean

Doklady Earth Sciences -     

Practical predictability of the standardized precipitation index on monthly and seasonal timescales

The SL-AV global semi-Lagrangian model of Hydrometcenter of Russia is used for considering the issues of practical predictability of the Standardized Precipitation Index (SPI) recommended by WMO. The index values are computed using the actual data (observations and reanalysis) taken as a reference and the forecast (hindcast) data interpolated to the stations (236 stations on the CIS territory). The analysis of practical predictability is based on diagnostic verification as well as on the model verification measures recommended by WMO. The statistically significant useful signal was detected on monthly and seasonal integration intervals. No useful information is found for the second- and third-month forecasts. A case study for the Republic of Kazakhstan (July 1989) demonstrates the dependence of forecast skill on the atmospheric circulation patterns. It is revealed that in the case of meridional atmospheric circulation forms the model resolution increases and, in some cases, not only moderate but also severe drought can be predicted.     

Biogeochemical characteristics of dominant gastropod species from the stony littoral of southern Baikal

The trace element composition of dominant gastropod species from the littoral of southern Baikal was investigated. Both different mollusk species and their parts (shells and soft tissues) show specific trace element characteristics. The highest Sr and Ba contents were observed in Maackia herderiana. The highest Zn, Cu, and Cd and lowest Pb contents were detected in Megalovalvata baicalensis. Choanomphalus sp. shows high Mn and Ti and very low Sr, Cu, and Cd contents. Most of Cu, Zn, and Cd and a considerable fraction of Rb, Pb, Mo, Sc, Ce, W, Ga, Y, and Th are incorporated in the gastropod bodies. The maximum concentration of U is also characteristic of the body tissues. The foot tissues of Maackia herderiana and Megalovalvata baicalensis are depleted in the majority of elements compared with their bodies. Sr and Ba are prevalent in the mollusk shells, where high Mn contents were also detected. A close relationship was observed between the chemical compositions of the gastropods, stony substrate, and bottom water. Group concentration of trace elements is common in the species investigated. Relative to the bottom water layer, the gastropod species concentrate Ti, Mn, La, Co, Y, and V and show similarly low extraction of U, W, Mo, and Cs. Compared with the bottom sediments, the mollusks accumulate Sr. In addition, Maackia herderiana and Megalovalvata baicalensis accumulate Cd and Zn. Megalovalvata baicalensis is distinguished by the ability to concentrate Cu. The following sequence is formed by the gastropods with respect to their capacity to accumulate Cd, Zn, and Cu: Megalovalvata baicalensis > Maackia herderiana > Choanomphalus sp.     

Os isotope systematics of komatiitic basalts from the Vetreny belt, Baltic Shield: evidence for a chondritic source of the 2.45 Ga plume

The Vetreny belt in the southeast Baltic Shield is a large volcano-sedimentary basin containing a 4- to 8-km-thick sequence of basaltic to komatiitic lavas, which were erupted ~2.45 Ga ago in a continental rift setting during the interaction of a mantle plume and the Archean continental crust of the Karelian granite-greenstone terrane. Re-Os isotope data for olivine cumulate samples and chromite separates from Victoria's lava lake and Golets flow 3 define isochrons with ages of 2387ᇍ and 2432ᆶ Ma, respectively. These ages are in good agreement with the previously reported, and new, Nd-Pb and U-Pb zircon ages. These data, coupled with the evidence for immobile behavior of the Re and Os, indicate that the Re-Os system remained closed since the lava eruption. The weighted average initial %¹⁸⁷Os values range between -0.43ǂ.10 for Golets flow 3 and -0.07ǂ.13 for the lava lake. A single chromite separate from Golets flow 1 has a %¹⁸⁷Os(T) of -0.06ǂ.15. Nd-Pb isotope and lithophile trace element data for the Vetreny belt komatiitic basalts were used to monitor the effect of crustal contamination on the Os isotope system and to estimate the initial Os isotope composition of the Vetreny plume source to be approximately chondritic with a %¹⁸⁷Os(T) of -0.9. This implies that the mantle source evolved with a long-term nearly chondritic Re/Os ratio. The data provide further evidence that, by the end of the late Archean, the Earth's upper mantle was well homogenized with respect to the highly siderophile elements, added during the accretion of a late veneer, on a time scale of ~1 Ga.