Beamlet transforms and their application to geophysical data processing

The paper describes algorithms of data processing using methods of wavelet analysis. The main integral transforms of 2-D data based on ideas of multiscale analysis and the Radon transform are examined. The latter belongs to the class of beamlet transforms. They are briefly characterized and their application is illustrated by simple geophysical examples.     

A nonstationary model of the thermal regime of axial zones of mid-ocean ridges: Formation of crustal and mantle magma chambers

A nonstationary model of spreading with periodic intrusions of a molten material into an axial zone of a mid-ocean ridge (MOR) is applied to numerical analysis of the thermal state in MOR axial zones and the formation of crustal and mantle magma chambers in them. The model satisfactorily explains the positions, dimensions, and shapes of magma chambers, as well as variations in these parameters depending on the spreading rate, temperature, and composition of crustal and mantle rocks. The release and absorption of the latent heat of rock melting, hydrothermal heating of the crust, and variations in the solidus and liquidus temperatures of crustal and mantle rocks as a function of their composition are factors controlling the shape and position of crustal magma chambers.     

Kinematics and characteristic features of the morphostructural segmentation of the Knipovich Ridge

The rift zone??s relief, the spreading kinematics, and the experimental modeling of the Knipovich Ridge??s formation were analyzed. Its rift zone is formed in a transtension environment. Faulting is predominant in its northern part, while strike-slip is characteristic for the south. A system of short extension basins connected by deep strike-slip U-shaped troughs is observed in the south. A system of volcanic rises connected by short shallow basins is observed in the north. The rift valley is V-shaped. According to the experimental modeling data, these extension kinematics provide the formation of short extension basins connected by strike-slips and transtension faults. Their length and orientation depend on the spreading obliquity of each segment.     

Analysis of molybdenum,tungsten, and vanadium in surface water of the Atlantic Ocean using solid phase extraction with 8-hydroxyquinoline and ICP MS determination

An analytical technique is proposed to determine ultratrace concentrations of Mo, V, and W found in seawater using mass spectrometry with inductively coupled plasma (ICP MS) after preliminary concentration by solid-phase extraction of metal complexes with 8-hydroxyquinoline (8-HQ) on C18 octadecyl silica. The technique utilizes 150 mL of a water sample. A preconcentration factor 50 is obtained. The detection limits are 0.25 nmol/kg, 0.041 nmol/kg, and 5 pmol/kg for Mo, V, and W, respectively. Dissolved Mo, V, and Wconcentrations in surface seawater from Atlantic Ocean transect were determined. The concentrations ranges along the transect were: 91–108 nmol/kg for Mo, 28–35 nmol/kg for V, and 55–75 pmol/kg for W. The Mo/W ratio varied from 1300 to 1800.     

Physical Modeling of Structure Formation at the Early Stages of the Iberia–Newfoundland Separation

Oceanology - The features of structure formation on the adjacent margins of Iberia and Newfoundland are considered based on an analysis of geological and geophysical data and physical modeling....     

Comparison of measurements of electromagnetic induction in the magnetosphere of Venus with laboratory simulations

Analysis of Venera 9 and 10 data suggest a comingled excitation of the ionosphere of Venus by the time dependent component of the interplanetary magnetic field, upon which may be super-imposed a contribution from the interplanetary electric field. The inductive contributions correspond respectively to generation of eddy currents and to unipolar induction, i.e., the TE and TM modes of classical electromagnetism. The former is suggested when the interplanetary magnetic field exhibits significant changes in intensity or orientation, but could also have contributions from fluctuations in plasma pressure expressed through the frozen-in field. Since the TM mode depends upon E=v _c ×B, the TM mode can also have an unsteady component. The magnetic field measured near Venus by Venera 9 and 10 is considered within this framework and with respect to laboratory simulation using both conducting and insulated (but internally conducting) spheres.     

Rare elements and Nd and Sr isotopic composition in micronodules from the Brazil Basin,Atlantic Ocean

The Sr isotope stratigraphy of the biogenic apatite was used to determine the age of pelagic sediments in the Brazil Basin (Station 1541) that contain ferromanganese micronodules, nodules, and coatings on the weathered volcanic rocks. The age of sediments at horizons 0–5 and 86–90 cm was estimated at 24.1 ± 0.2 Ma and 24.8 ± 0.2 Ma, respectively. The average sedimentation rate in the Late Oligocene was about 13 mm/ka. The hydrogenous Fe–Mn nodule on the sediment surface with the Mn/Fe value of 1.05–1.95 was formed at a rate of 1.2–2.4 mm/Ma, which is 1000 times lower than the growth rate of buried nodule (Mn/Fe 0.4) at depth of 83 cm. Diagenesis provoked changes in the mineral composition of the buried nodule (asbolane-buserite partially replaced by goethite), leading to the loss of a part of Mn, Ni, Li, and Tl but accumulation of trace elements linked with iron oxyhydroxides (Ce, Th, Be, As, and V) were retained. The composition of manganese micronodules at two studied depths in sediments evolved in the course of two stages of ore formation: related to the oxic and suboxic diagenesis. The Sr isotopic composition in manganese micronodules from both horizons do not differ from that of dissolved Sr in the ocean water. The ¹⁴³Nd/¹⁴⁴Nd ratio, which reflects the Nd isotopic composition in the paleocean during the micronodule formation, varies in manganese micronodules from different horizons and is constant in different size fractions.     

Asymmetry of plasma fluxes at Mars. ASPERA-3 observations and hybrid simulations

The asymmetry of fluxes of solar wind and planetary ions is studied by using the ASPERA-3 observations onboard the Mars Express spacecraft in February 2004 to March 2006. Due to the small scale of the Martian magnetosphere and its induced origin, the flow pattern near Mars is sensitive to the directions of the interplanetary magnetic and electric (-V×B) fields. Asymmetry of the magnetic field draping produces an asymmetry in plasma flows in the plane containing the IMF. The crustal magnetic fields on Mars also influence the flow pattern. Scavenging of planetary ions is less efficient in the regions of strong crustal magnetization and therefore the escape fluxes of planetary ions in the southern hemisphere are smaller. The results of the observations are compared to simulations based on a 3D hybrid model with several ion species.     

Geochemistry and genesis of Fe-Mn mineralization in island arcs in the west Pacific Ocean

This paper presents materials on the chemical and mineralogical composition of Fe-Mn mineralization in island arcs (Kurile, Nampo, Mariana, New Britain, New Hebrides, and Kermadec) in the western part of the Pacific Ocean. The mineralization was proved to be of hydrothermal and/or hydrogenic genesis. The former is produced by hydrothermal Fe and Mn oxi-hydroxides that cement volcanic-terrigenous material in sediments. Some Fe oxi-hydroxides can be derived via the halmyrolysis of volcaniclastic material. Crusts of this stage are characterized by fairly low concentrations of trace and rare elements, and their REE composition is inherited from the volcanic-terrigenous material. The minerals of the Mn oxi-hydroxides are todorokite and “Ca-birnessite.” The Mn/Fe ratio increases away from the discharge sites of the hydrothermal solutions. The hydrogenic Fe-Mn crusts are characterized by high concentrations of trace and minor elements of both the Mn group (Co, Ni, Tl, and Mo) and the Fe group (REE, Y, and Th). The hydrogenic crusts consist of Fe-vernadite and Mn-feroxyhyte. Some of the hydrothermal crusts originally had a hydrothermal genesis. The first data were obtained on crust B30-72-10 from the Macauley Seamount in the Kermadec island arc, which contained anomalously high concentrations of Co (2587 ppm) and other Mn-related trace elements in the absence of hydrogeneous Fe oxi-hydroxides.