Izvestiya, Atmospheric and Oceanic Physics - The current state of microwave radiometry for remote sensing of the Earth is considered. There are currently some 30 satellite microwave radiometers... 相似文献
Results of the isotope-geochronological studies of the Late Cenozoic magmatism of Caucasus have been considered. The Neogene-Quaternary
volcanic activity is found to have evolved during the last 15 m. y. being most intensive in the Middle-Late Pliocene. Within
separate neovolcanic areas of the Caucasus region, magmatism was of a clearly discrete character when intense eruption periods
interchanged with prolonged (up to several million years) times of quiet conditions. Four stages of young magmatism of the
Caucasus are recognized: the Middle Miocene (15–13 Ma), the Late Miocene (9–5 Ma), the Pliocene (4.5–1.6 Ma), and the Quaternary
(less than 1.5 Ma). However, for certain areas the time limits of these stages were shifted relative to each other and overlap
the whole age range from the mid-Miocene to the end of the Quaternary period. Therefore, within the collision zone, the Neogene-Quaternary
magmatism evolved almost continuously during almost the last 9 m. y., but in the time interval of 13–9 Ma in the Caucasian
segment, volcanic activity was possibly low. No evidence of directed lateral migration of volcanic activity within the entire
Caucasus region was found. At the same time, in the Lesser Caucasus the young magmatism commenced earlier (∼15 Ma), compared
to the Greater Caucasus (∼8 Ma). 相似文献
Energy features of the succession of interrelated tropical cyclones (plural cyclogenesis) in the oceans of the Southern Hemisphere
(the southern part of the Indian Ocean and the southwestern part of the Pacific Ocean) over February 2008 are comprehensively
analyzed on the basis of the method of combining different-scale data of the infrared and radio thermal satellite sounding.
The data of infrared thermal channels of the geostationary Meteosat-7 satellite and the results of reconstruction of integral
water vapor from data of the AMSR-E microwave complex of the Aqua satellite were used. The analysis showed that the region
where water vapor has an increased integral concentration is the most effective channel for pumping the latent heat energy
from the tropics into midlatitudes. Each cyclone captures this region from the tropical zone and retains it throughout the
entire stage of its own evolution with the aid of the jet spiral bridge. The quantitative estimates of the latent energy of
the central equatorial region of water vapor in the intratropical convergence zone (ITCZ) of the Indian and Pacific oceans
were a basically new result, as well as the detection of considerable time variations in the latent heat associated with the
ejection of coherent water-vapor regions into high latitudes by plural cyclogenesis. 相似文献
The Early Paleoproterozoic Monchegorsk Complex is exposed over an area of 550 km2 and comprises two layered mafite-ultramafite intrusions of different age: the Monchegorsk pluton of ultramafic and mafic rocks and the predominantly gabbroid Main Range Massif (also referred to as the Moncha-Chuna-Volch??i Tundras Massif), which are separated by a fault. Both massifs consists of intercalating cumulates (first of all, Ol ± Crt, Ol + Opx ± Crt, Opx, Opx + Pl ± Cpx, and Pl), they were produced by similar melts of siliceous high-Mg series but differ in the stratigraphy of their cumulates: while the Monchegorsk pluton is dominated by ultramafites, the Main Range Massif consists mostly of gabbroids, first of all, of gabbronorites. The complex is accompanied by PGE-Cu-Ni ore mineralization, low-sulfide Pt-Pd mineralization, and chromite mineralization. Judging from geological data and isotopic dates, the Monchegorsk Complex is a long-lived magmatic center, which evolved over a time span of 50 Myr at 2.50?C2.46 Ga. The Main Range Massif is younger and likely truncates the western continuation of the Monchegorsk pluton. The complex is spatially restricted to the zone of the Middle Paleoproterozoic regional Central Kola Fault and is now tectonic collage whose rocks were variably affected by overprinted metamorphism in the course of deformations. These processes most significantly affected rocks along the peripheries of the Monchegorsk pluton in the south. These rocks were completely transformed under greenschist-facies conditions but often preserved their primary textures and structures. The processes overprinted both the marginal portions of the pluton itself and the rocks of its second phase, which are accompanied by economic low-sulfide PGE deposits. The PGE-Cu-Ni ore mineralization of the Monchegorsk Complex is genetically related to two distinct evolutionary episodes with a quiescence period in between:
The emplacement of large layered mafite-ultramafite intrusions at 2.5?C2.45 Ga. Economic deposits of sulfide Cu-Ni ores with subordinate PGE mineralization occur within the Monchegorsk pluton, and the moderate-grade low-sulfide PGE ores are related to its second evolutionary phase (in the foothills of Vuruchuaivench and in the Moroshkovoe Lake, and Southern Sopcha areas). The primary magmatic ore mineralization is predominantly Cu-Fe-Ni sulfide with PGE bismuthides-tellurides.
The Monchegorsk Complex was involved in the zone of the Central Kola Fault at 2.0?C1.9 Ga and was broken in a collage of tectonic blocks. The rocks were sheared along the boundaries of the blocks and were affected by overprinted metamorphism, which proceeded under greenschist-facies conditions in the structures surrounding the Monchegorsk pluton in the south. Thereby the primary PGE-Cu-Ni ore mineralization underwent metamorphic processes was recrystallized with the formation of Pt-Pd arsenides, stannides, antimonides, selenides, etc. This processes was associated with the partial redistribution of PGE with their local accumulation (up to economic concentrations), and the orebodies themselves acquired diffuse outlines. In other words, the second episode was marked by the transformation of the older primary magmatic ore mineralization.
New data on the Akkermanov deposit characterized by specific structure and composition of primary (carbonate) and secondary (manganese oxide) ores are presented. Distribution of mineralization in host rocks and weathering crusts is considered. It is shown that manganiferous carbonate rocks, which host orebodies, formed in a marine basin with well-aerated bottom waters. Oxide ores are mainly composed of crystalline pyrolusite produced by multiple processes of the oxidation of manganese compounds. In this respect, the Akkermanov deposit differs drastically from all manganese deposits developed in Russia and Ukraine. 相似文献
The problem of the Daly Gap is considered for the example of bimodal basalt–trachyte series and their intrusive analogs (layered syenite–gabbro intrusions). It is shown that the gap is not controlled by the processes of crystallization differentiation or liquid immiscibility in intermediate chambers of igneous systems (intrusive chambers) and has a primary nature. We interpret its origin as from the existence of two independent types of melts from the materials of head parts of the same mantle plumes. These are mid-alkali Fe–Ti basalt, products of its adiabatic melting, and trachyte, which is the result of incongruent melting of the material of the upper cool rims of plumes under the influence of fluids percolating from the underlying zone of adiabatic melting.
The Earth and Moon evolved following a similar scenario. The formation of their protocrusts started with upward crystallization
of global magmatic oceans. As a result of this process, easily fusible components accumulated in the course of fractional
crystallization of melt migrating toward the surface. The protocrusts (granitic in the Earth and anorthositic in the Moon)
are retained in ancient continents. The tectonomagmatic activity at the early stage of planet evolution was related to the
ascent of mantle plume of the first generation composed of mantle material depleted due to the formation of protocrusts. The
regions of extension, rise, and denudation were formed in the Earth above the diffluent heads of such superplumes (Archean
granite-greenstone domains and Paleoproterozoic cratons), whereas granulite belts as regions of compression, subsidence, and
sedimentation arose above descending mantle flows. The situation may be described in terms of plume tectonics. Gentle uplifts
and basins (thalassoids) in lunar continents are probable analogues of these structural elements in the Moon. The period of 2.3–2.0 Ga ago was a turning point in the
tectonomagmatic evolution of the Earth, when geochemically enriched Fe-Ti picrites and basalts typical of Phanerozoic within-plate
magmatism became widespread. The environmental setting on the Earth’s surface changed at that time, as well. Plate tectonics,
currently operating on a global scale, started to develop about ∼2 Ga ago. This turn was related to the origination of thermochemical
mantle plumes of the second generation at the interface of the liquid Fe-Ni core and silicate mantle. A similar turning point
in the lunar evolution probably occurred 4.2–3.9 Ga ago and completed with the formation of large depressions (seas) with thinned crust and vigorous basaltic magmatism. Such a sequence of events suggests that qualitatively new material previously
retained in the planets’ cores was involved in tectonomagmatic processes at the middle stage of planetary evolution. This
implies that the considered bodies initially were heterogeneous and were then heated from above to the bottom by propagation
of a thermal wave accompanied by cooling of outer shells. Going through the depleted mantle, this wave generated thermal superplumes
of the first generation. Cores close to the Fe + FeS eutectics in composition were affected by this wave in the last turn.
The melting of the cores resulted in the appearance of thermochemical superplumes and corresponding irreversible rearrangement
of geotectonic processes. 相似文献
A new type of sulfide occurrence related to metasomatically altered brecciated gabbroids has been studied at the Sierra Leone site situated in the axial rift valley of the Mid-Atlantic Ridge (Markov Deep, 6° N). Two associations of plutonic, subvolcanic, and volcanic rocks were dredged: (1) mid-ocean ridge basalts (MORB) and their intrusive analogues and (2) rocks of the silicic Fe-Ti-oxide series with dominating gabbronorites and sporadic trondhjemites. Almost all igneous rocks at the Sierra Leone site are enriched in Pb, Cu, U, Ga, Ta, Nb, Cs, and Rb and depleted in Zr, Th, and Hf. The rocks of the Fe-Ti-oxide series are enriched in Zn, Sn, and Mo and depleted in Ni and Cr. The main ore-bearing zone is situated at the foot of the eastern wall of the deep, where it is hosted in cataclastic hornblende gabbro and gabbronorite of the Fe-Ti-oxide series. Ore mineralization in metasomatically altered rocks is composed of quartz-sulfide and prehnite-sulfide veinlets, disseminated sulfide, and veined copper sulfide ore. The ore consists of pyrite, chalcopyrite, sphalerite, pyrrhotite, bornite, chalcocite, and digenite. The δ34S value of sulfides varies from 3.0 to 15.3‰. At the foot of the eastern wall of the Markov Deep, directly downslope from the ore-bearing zone, loose sediments contain grains of native Cu, Pb, Zn, and Sn and intermetallic compounds (isoferroplatinum, tetraferroplatinum, and brass) apparently derived from the ore. Mineral assemblages of ore-bearing metasomatic rocks and fluid inclusions therein were studied. Ore metasomatism developed under a low oxygen potential within a temperature interval from 400 to 160°C, though initial hydrothermal alteration of rocks proceeded at temperatures of 800–450°C. The temperature of stringer-disseminated ore mineralization is estimated at 170–280°C. The hydrothermal fluids are considered to be of magmatic origin; as the hydrothermal system evolved, they became diluted with seawater that was contained in fractured oceanic crust. The ore matter could have been derived from magmatic fluids that were released from water-saturated melts of the Fe-Ti oxide series during their ascent and leached from host gabbroids in the process of metasomatic alteration. 相似文献