Lithospheric mantle beneath the south-eastern Siberian craton: petrology of peridotite xenoliths in basalts from the Tokinsky Stanovik

We provide petrographic, major and trace element data for over 30 spinel peridotite xenoliths from the Tokinsky Stanovik (Tok) volcanic field on the Aldan shield to characterize the lithospheric mantle beneath the south-eastern margin of the Siberian craton, which formed in the Mesoproterozoic. High equilibration temperatures (870–1,010°C) of the xenoliths and the absence of garnet-bearing peridotites indicate a much thinner lithosphere than in the central craton. Most common among the xenoliths are clinopyroxene-poor lherzolites and harzburgites with Al₂O₃ and CaO contents nearly as low as in refractory xenoliths from kimberlite pipes (Mir, Udachnaya) in the central and northern Siberian craton. By contrast, the Tok peridotites have higher FeO, lower Mg-numbers and lower modal orthopyroxene and are apparently formed by shallow partial melting (3 GPa). Nearly all Tok xenoliths yield petrographic and chemical evidence for metasomatism: accessory phlogopite, amphibole, phosphates, feldspar and Ti-rich oxides, very high Na₂O (2–3.1%) in clinopyroxene, LREE enrichments in whole-rocks.Electronic Supplementary Material Supplementary material is available for this article at     

Impacts of frontal stability and topography on cross-shelf exchange in the Northern Gulf of Mexico

The shelfbreak wintertime thermal front in the Northeastern Gulf of Mexico often exhibits meandering, eddy formation and warm-water intrusion. A high level of frontal variability plays an essential role in exchange processes across the shelf. This study examines the impacts of local frontal instability and bottom topography on turbulent heat exchange across the front using the results of two numerical models. Analysis of a series of numerical experiments reveals that the flow is baroclinically unstable. Predicted frontal instability contributes significantly to cross-frontal exchange and accounts for about 35% of the total eddy heat flux. Onshore eddy heat flux has the highest intensity at the frontal position. In addition, eddy activity and heat flux are sensitive to variation of bottom topography. For topographic features and frontal characteristics that are typical of the area, bottom steepness enhances the flux and is nearly proportional to the cross-frontal heat exchange. The study attempts to explain physical mechanisms that drive frontal circulation in the area and to quantify heat transport across the shelf. Estimated heat fluxes can provide important information for climate and ecosystem modeling of the Mississippi Bight.     

Mass, Heat and Salt Balances in the Eastern Barents Sea Obtained by Inversion of Hydrographic Section Data

Standard hydrological section data, collected in the eastern Barents Sea in September 1997, have been analyzed using a variational data assimilation technique. This method allows us to obtain temperature, salinity and velocity fields that are consistent with observations and dynamically balanced within the framework of a steady-state model describing large-scale nearly geostrophic circulation. Error bars of the optimized fields are computed by explicit inversion of the Hessian matrix. The optimized velocity field is in agreement with independent velocity observations derived from surface drifter trajectories in the southwestern part of the Barents Sea. Optimized fields provide the following estimates of integral characteristics of the circulation in the region: i) the North Cape current transport is 2.12 ± 0.25 Sv; ii) the Karskie Vorota Strait throughflow is 0.7 ± 0.06 Sv; iii) heat flux with Atlantic water is 4.7 ± 0.16⋅10¹¹ W; iv) salt import from the Atlantic Ocean is 7.41 ± 0.46⋅10³ kg/s. The imbalance of the heat budget in the eastern part of the Barents Sea indicates the presence of statistically insignificant surface heat fluxes which are less than 1 W/m². This revised version was published online in July 2006 with corrections to the Cover Date.     

Formation particularities of hypergene ferromanganese nodules: Far East Russia and Vietnam

Ferromanganese nodules (pisolites) form accumulations in basal layers of Pliocene-Quaternary clayey sections of Far East Russia and Vietnam. They are composed of minerals that are in common for both these regions (authigenic vernadite, feroxyhyte, goethite, halloysite, and terrigenous quartz) and minerals that are characteristic of either the northern (authigenic hollandite, lithiophorite, and bernessite) or southern (authigenic alumophorite, lepidocrocite, ferrihydrite, gibbsite, and terrigenous ilmenite) regions. Pisolites are considered to be microbial colonies with Mn and Fe oxides frequently forming biomorphs. The growth of the colonies was accompanied by dying off and mineralization of microorganisms successively from the central toward the peripheral parts of the nodules. The formation of metalliferous pisolites was linked to the oxidizing geochemical barrier developed at the interface between compact sedimentary clays and the underlying porous readily permeable weathered products of basalts.     

The terminal Permian in European Russia: Vyaznikovian Horizon,Nedubrovo Member,and Permian–Triassic boundary

The comprehensive analysis of the data obtained on terrestrial vertebrata, ostracods, entomologic fauna, megaflora, and microflora in deposits of the Vyaznikovian Horizon and Nedubrovo Member, as well as the paleomagnetic data measured in enclosing rocks, confirms heterogeneity of these deposits. Accordingly, it is necessary to distinguish these two stratons in the terminal Permian of the East European Platform. The combined sequence of Triassic–Permian boundary deposits in the Moscow Syneclise, which is considered to be the most complete sequence in the East European Platform, is as follows (from bottom upward): Vyatkian deposits; Vyaznikovian Horizon, including Sokovka and Zhukovo members; Nedubrovo Member (Upper Permian); Astashikha and Ryabi members of the Vokhmian Horizon (Lower Triassic). None of the sequences of Permian–Triassic boundary deposits known in the area of study characterizes this sequence in full volume. In the north, the Triassic deposits are underlain by the Nedubrovo Member; in the south (the Klyazma River basin), the sections are underlain by the Vyaznikovian Horizon. The Permian–Triassic boundary adopted in the General Stratigraphic Scale of Russia for continental deposits of the East European platform (the lower boundary of the Astashikha Member) is more ancient than the one adopted in the International Stratigraphic Chart. The same geological situation is observed in the German Basin and other localities where Triassic continental deposits are developed. The ways of solving this problem are discussed in this article.     

Tectonic position and preliminary data on geological manifestations of the 2011–2012 Tyva earthquakes

The preliminary data on the tectonic position and seismological manifestations of the strong Tyva earthquakes that occurred on December 27, 2011 and February 26, 2012 are reported. The seismic ruptures are studied. The earthquake source structure in the earth’s depths is considered.     

ROY—A multiscale magnetospheric mission

The scientific rationale of the ROY multi-satellite mission addresses multiscale investigations of plasma processes in the key magnetospheric regions with strong plasma gradients, turbulence and magnetic field annihilation in the range from electron inertial length to MHD scales.The main scientific aims of ROY mission include explorations of:

(a)

turbulence on a non-uniform background as a keystone for transport processes;

(b)

structures and jets in plasma flows associated with anomalously large concentration of kinetic energy; their impact on the energy balance and boundary formation;

(c)

transport barriers: plasma separation and mixing, Alfvenic collapse of magnetic field lines and turbulent dissipation of kinetic energy;

(d)

self-organized versus forced reconnection of magnetic field lines;

(e)

collisionless shocks, plasma discontinuities and associated particle acceleration processes.

In the case of autonomous operation, 4 mobile spacecrafts of about 200 kg mass with 60 kg payload equipped with electro-reactive plasma engines will provide 3D measurements at the scales of 100-10000 km and simultaneous 1D measurements at the scales 10-1000 km. The latter smaller scales will be scanned with the use of radio-tomography (phase-shift density measurements within the cone composed of 1 emitting and 3 receiving spacecrafts).We also discuss different opportunities for extra measurement points inside the ROY mission for simultaneous measurements at up to 3 scales for the common international fleet.Combined influence of intermittent turbulence and reconnection on the geomagnetic tail and on the nonlinear dynamics of boundary layers will be explored in situ with fast techniques including particle devices under development, providing plasma moments down to 30 ms resolution.We propose different options for joint measurements in conjunction with the SCOPE and other missions:

•

simultaneous sampling of low- and high-latitudes magnetopause, bow shock and geomagnetic tail at the same local time;

•

tracing of magnetosheath streamlines from the bow shock to near-Earth geomagnetic tail;

•

passing “through” the SCOPE on the inbound orbit leg;

•

common measurements (with SCOPE and other equatorial spacecraft) at distances of ∼ few thousand km for durations of ∼several hours per orbit.

The orbit options and scientific payload of possible common interest are discussed in this work, including FREGAT cargo opportunities for extra payload launching and the “Swarm” campaigns with ejection of nano- and pico-satellites.