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521.
Peculiarities of the ice situation in the Sea of Azov and the Kerch Strait during the cold winter of 2005/06 are considered using a set of satellite images in the visible range, accumulated at the Southern Research Institute of Marine Fisheries and Oceanography (in Kerch). The ice conditions of the water area over the last years are examined and compared to the climatic data. 相似文献
522.
523.
Yu. A. Mikhailova N. G. Konopleva V. N. Yakovenchuk G. Yu. Ivanyuk Yu. P. Men’shikov Ya. A. Pakhomovsky 《Geology of Ore Deposits》2007,49(7):590-598
Five minerals of the corundum group have been identified in the Khibiny pluton with certainty. Corundum proper and karelianite occur only in hornfels after volcanic and sedimentary rocks. Xenoliths of hornfels mark the ring faults that bound foidalite within the field of foyaite. Hematite occurs in hydrothermally altered nepheline syenite and crosscutting hydrothermal veins related to the ring faults. Minerals of the ilmenite-pyrophanite series are present in all rocks of the pluton, including veins. Accessory ilmenite in foyaite varies from the manganese variety and pyrophanite in the inner and outer parts of the pluton to manganese-free ilmenite in zone of the Main Ring Fault. In xenoliths of volcanic rocks and alkaline ultramafic rocks, ilmenite is enriched in magnesium. The zoning in distribution of the above-mentioned minerals and the character of variation in their compositions from margins of the pluton to its center are consistent with the petrochemical zoning formed as a result of foyaite alteration of near ring faults. 相似文献
524.
Bruce D. Johnson Mark A. Barry Bernard P. Boudreau Peter A. Jumars Kelly M. Dorgan 《Geo-Marine Letters》2012,32(1):39-48
This study reports the first in situ measurements of tensile fracture toughness, K
IC, of soft, surficial, cohesive marine sediments. A newly developed probe continuously measures the stress required to cause
tensile failure in sediments to depths of up to 1 m. Probe measurements are in agreement with standard laboratory methods
of K
IC measurements in both potter’s clay and natural sediments. The data comprise in situ depth profiles from three field sites
in Nova Scotia, Canada. Measured K
IC at two muddy sites (median grain size of 23–50 μm) range from near zero at the sediment surface to >1,800 Pa m1/2 at 0.2 m depth. These profiles also appear to identify the bioturbated/mixed depth. K
IC for a sandy site (>90% sand) is an order of magnitude lower than for the muddy sediments, and reflects the lack of cohesion/adhesion.
A comparison of K
IC, median grain size, and porosity in muddy sediments indicates that consolidation increases fracture strength, whereas inclusion
of sand causes weakening; thus, sand-bearing layers can be easily identified in K
IC profiles. K
IC and vane-measured shear strength correlate strongly, which suggests that the vane measurements should perhaps be interpreted
as shear fracture toughness, rather than shear strength. Comparison of in situ probe-measured values with K
IC of soils and gelatin shows that sediments have a K
IC range intermediate between denser compacted soils and softer, elastic gelatin. 相似文献
525.
根据白云鄂博赋矿白云石大理岩的岩石学特征及地质产状将其分为两类:粗粒和细粒白云石大理岩.它们的氧、碳和锶同位素及微量元素地球化学特征显然有别于分布在宽沟背斜以北典型的沉积石灰岩和白云岩,而和幢源火成碳酸岩十分相似.与矿床进行对比研究说明,成矿流体和矿质主要起源于碳酸岩浆的分异作用,其放射性成因同位素和微量元素保持了地但指纹,而氧和碳同位素组成却向壳源方向漂移,证实碳酸岩浆侵位过程中受大陆地壳的混染作用非常微弱,但是由碳酸岩浆活动所引起的成矿热液体系中却有一定的地表水混人认为白云鄂博REE-Nb-Fe超大型矿床的成因应归属于火成碳酸岩型矿床. 相似文献
526.
Anton P. Roex Andreas Späth Robert E. Zartman 《Contributions to Mineralogy and Petrology》2001,142(1):89-106
Geochemical data are reported for samples from the flanks and floor of the southern Kenya Rift Valley in the Lake Magadi area, and from two central volcanoes located within the rift valley. Rift lavas include samples of Singaraini and Ol Tepesi basalts on the eastern flank, Kirikiti basalts from the western flank, and plateau trachytes from the rift valley floor. Central volcano samples are from Ol Esayeiti and Lenderut located on the eastern flank. The rift basalts are mildly ne-normative, moderately evolved (Mg#=0.39-0.62) alkali basalts and show an overall range in differentiation. Incompatible trace element abundances are moderately elevated (Nb=17-51; Zr=93-274; La=17-55 ppm) and show strongly coherent variations and constant inter-element ratios (e.g. Zr/Nb=4.2-5.5; Nb/Ta=17.5ǂ.4; (La/Sm)n=7.3ǃ.1); isotope ratios are restricted in range (87Sr/86Sr=0.70393-0.70436; 143Nd/144Nd=0.51272-0.51280; 206Pb/204Pb=19.87-19.92; 207Pb/204Pb=15.68-15.70; 208Pb/204Pb=39.56-39.71). Central volcano lavas are more alkaline in character and include basanite (Ol Esayeiti; Mg# >60) and hawaiite to benmoreite (Lenderut; Mg#=0.48-0.38). Incompatible element ratio are similar to those of the rift basalts, although the chondrite normalised REE patterns are steeper (La/Sm)n=17.4ǃ.2). 87Sr/86Sr (0.70358, 0.70391), 143Nd/144Nd (0.51280, 0.51267), 206Pb/204Pb (19.96,20.17), 207Pb/204Pb (15.66,15.76) and 208Pb/204Pb (39.80,40.00) ratios of Ol Esayeiti basanites are similar to the rift basalts, whereas the Lenderut lavas have unusually low143Nd/144Nd (0.512388-0.512453) ratios for their 87Sr/86Sr (0.70370-0.70481) ratios, and distinctly less radiogenic and variable Pb isotope compositions (206Pb/204Pb=17.93-19.01; 207Pb/204Pb=15.43-15.58; 208Pb/204Pb=37.91-39.14). An integrated model is developed in which the geochemical signature of the lavas is attributed to variable degrees of melting to depths within the garnet stability field, and in the presence of residual amphibole. The stability fields of these phases in P-T space indicates that the lavas must have formed within the sub-continental lithosphere rather than within the underlying ambient asthenosphere or a rising mantle plume. The subcontinental lithospheric mantle must therefore extend to a depth of at least 75 km beneath the Lake Magadi area, which contrasts with recent gravity models for the area, which infer that lithospheric mantle is absent beneath this section of the southern Kenya Rift. 相似文献
527.
A major difficulty in remote sensing is handling the many data from sensors aboard aircraft and satellites. In this paper we identify an optimal procedure for sampling remotely sensed data before their storage or on their retrieval. The procedure depends on spatial correlation in the scene and uses kriging to estimate values that have been lost. An example in which data from an airborne multispectral scanner could be diminished to only about one tenth without serious loss of precision illustrates the method. 相似文献
528.
529.
The common-ray approximation eliminates problems with ray tracing through S-wave singularities and also considerably simplifies
the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation
from the common reference ray. These travel-time errors can deteriorate the coupling-ray-theory solution at high frequencies.
It is thus of principal importance for numerical applications to estimate the errors due to the common-ray approximation applied.
The anisotropic-common-ray approximation of the coupling ray theory is more accurate than the isotropic-common-ray approximation.
We derive the equations for estimating the travel-time errors due to the anisotropic-common-ray (and also isotropic-common-ray)
approximation of the coupling ray theory. The errors of the common-ray approximations are calculated along the anisotropic
common rays in smooth velocity models without interfaces. The derivation is based on the general equations for the second-order
perturbations of travel time. 相似文献
530.
The partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments. For the elements Na, Zn, Se, Sr, Cd, Sn, Sb, Cs, Ba, Hg, Th and Pa (group I) constant distribution coefficients (Kd) were found after a few days of equilibration, whereas the elements Be, Mn, Co and Fe (group II) showed an increasing Kd over the whole time of observation of 108 days. The time dependence of Kd is described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements). The reaction rate constants are compared to Mn oxidation rates and to adsorption rate constants derived from in situ measurements of the disequilibrium as available from literature. 相似文献