The kinetics of metamorphism of the Staroe Boriskino C2 chondrite heated at 450°C in an inert atmosphere of helium flow was investigated. After being heated at 450°C during 160 minutes one specimen was moreover heated for 10 minutes at 500°C. The phase distribution was determined by means of Mössbauer spectroscopy, X-ray diffraction analysis, and electron probe microanalysis.The material changes rapidly (1–2 minutes). As a result of dehydration, the iron of the phyllosilicate is oxidized, the charge compensation being realized through the removal of iron and magnesium cations with the formation of magnetite and forsterite. Upon 10 minutes additional heating at 500°C iron appears in the olivine structure, the degree of iron oxidation declines, and magnetite disappears. Possible trends of change of C2 chondrite material are:
Geomagnetism and Aeronomy - The features of the geomagnetic effect of the approach of an interplanetary magnetic cloud to the Earth’s magnetosphere during the recovery phase of a strong... 相似文献
Izvestiya, Atmospheric and Oceanic Physics - The study of mesoscale eddies provides an understanding of entire systems of interconnected oceanic characteristics. Mesoscale eddies have their own... 相似文献
We have constructed and analyzed the 1896-year-long tree-ring chronology for the territory of the Altai Republic. The chronology was based on wood of live trees and remains of trunks of Siberian larch (Larix sibirica Ledeb.) from the upper timberline (2300 m) of the Dzhelo river valley. The chronology agrees well with palaeoclimatic data and reflects the main climatic changes in the northern hemisphere for the last two millennia: an extraordinary decrease in increment after the year 536, ??mean secular warming??, the ??Little Ice Age??, and current warming. By calculating the response function between the tree-ring chronology for the Dzhelo and data from weather stations, it was possible to reconstruct the series of June?CJuly air temperature variability for the last 1500 years. The chronology can be used in dating archaeological wood, i.e. in determining the calendar time at which archaeological monuments were constructed. 相似文献
A model is studied which claims to describe the effects of air pressure variations on the outflow of radon into the atmosphere from loose deposits that are treated as a porous medium having the gas dynamic properties described by Darcy’s law. It is shown that the model results are in satisfactory agreement with the experimental data acquired from a network for monitoring subsoil radon in the Petropavlovsk-Kamchatskii Geodynamic Site in 1997–2006. A technique has been developed for estimating the Darcy coefficient based on radon concentration data in loose deposits at various depths. 相似文献
A new type of high-latitude magnetic bays is revealed at geomagnetic latitudes higher than 71°, called ??polar substorms.?? It is shown that polar substorms differ from both classical substorms and high-latitude geomagnetic disturbances of the type of polar boundary intensifications (PBIs). While classical substorms start at latitudes below 67° and then expand poleward, polar substorms start almost simultaneously in the evening-night polar region of the oval. In contrast to PBIs, accompanied by auroral streamers expanding southward, polar substorms are accompanied by auroral arcs quickly traveling northward. It is shown that polar substorms are observed before midnight (20?C22 MLT) under weak geomagnetic activity (Kp ?? 2) during the late recovery phase of a magnetic storm. It is shown that a typical feature of polar substorms is the simultaneous excitation of highly intensive Pi2 and Pi3 geomagnetic pulsations at high latitudes, which exceed the typical amplitude of these pulsations at auroral latitudes by more than an order of magnitude. The duration of pulsations is determined by the substorm duration, and their amplitude decreases sharply at geomagnetic latitudes below ??71°. It is suggested that pulsations reflect fluctuations in ionospheric currents connected with polar substorms. 相似文献
Geomagnetism and Aeronomy - The development of two supersubstorms (i.e., very intense substorms with an amplitude of more than 2000 nT) recorded in the main phase of two consecutive strong magnetic... 相似文献
An analysis of sampled 1-s observational data on geomagnetic pulsations within the Pc3 range on the INTERMAGNET network of near-equatorial and low-latitude observatories spaced over longitude during the initial phase of a moderate magnetic storm (April 5–7, 2010) was carried out for the first time. The obtained results were compared with magnetic observations at the low-latitude Chambon-la-Foret (CLF) and subauroral Kerguelen (PAF) observatories, as well as with observations at six Australian observatories located at low and middle latitudes. Two time intervals were studied in detail: the sudden commencement (SC) of the storm and the onset of the great global substorm. In the first interval, maximal amplitudes of near-equatorial pulsations were observed in the near-noon sector; in the second interval, in the near-midnight sector. The dynamics of the spectral structure of Pc3 pulsations in the considered events was shown to be different in spite of the fact that in both cases an amplification of waves was observed in two close spectral bands of the Pc3 spectrum: ～20–30 and ～30–40 mHz. The considered Pc3 pulsations were characterized by very small azimuthal wavenumbers (0.5 and less). Possible generation mechanisms for the observed Pc3 pulsations are discussed. 相似文献
Most abyssal basalt can be divided into two groups based on major and minor element compositions of the glassy rinds of pillow lavas. Crystal differentiation models cannot relate one group to the other. Instead, depth of partial melting may exert the primary control. The first group (MORB-1) is characterized by low TiO2 and Na2O and higher MgO, and is derived from a primary melt originating from the spinel peridotite facies. The higher TiO2-NaO2 group (MORB-2) appears to have been derived from the lower-pressure (shallower depth) plagioclase peridotite facies. Mössbauer spectra show that MORB-1 is from a mantle source region with lower oxidation states (between the QFM and NNO buffers) than for MORB-2 (around the NNO buffer). 相似文献
