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The application of the Sm-Nd isotope system of scheelite to dating of low-sulfide, quartz-vein hosted Au mineralization is still under discussion. In the present work, new Sm-Nd and Rb-Sr data for scheelite from the giant Muruntau/Myutenbai Au deposit (Kyzylkum, Western Uzbekistan) are discussed. Based on the geological relationship, mineralogical properties, and trace element characteristics, two types of scheelite can be distinguished within the deposit. The first one is represented by early bluish luminescent and weakly coloured scheelite (generation 1) found within strongly deformed flat quartz veins. The apparent isochron defined by this scheelite (351ᆪ Ma) is interpreted as a mixing line. Typically brownish to orange and yellowish luminescent scheelite from steeply dipping veins (generation 2) defines a Sm-Nd isochron age of 279ᆦ Ma ()Nd=-9.5ǂ.3; MSWD: 1.5). No evidence for mixing or disturbance by late alteration were found for these scheelites. This Sm-Nd isochron age agrees with the Rb-Sr and K-Ar age range for wall rock alteration in this deposit reported previously. The age of 280 Ma is interpreted to date the high-grade ore formation in the Muruntau deposit. There are currently no reliable age data available on the magmatic events in the Muruntau region. Probably, there is some overlap in time of the Hercynian gold deposition with the intrusion of lamprophyric dykes. The Nd and Sr isotopic signatures of scheelite define the wall rocks (mainly metasiltstones and metasandstones) as the most probable sources for these elements in scheelite. 相似文献
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G. F. Krymsky P. A. Krivoshapkin V. P. Mamrukova S. K. Gerasimova 《Astronomy Letters》2010,36(8):596-604
The anisotropy of high-energy (∼10 GeV and above) cosmic rays is investigated. A simplified model of the heliosphere constructed
as a basis for the theory of their long-period variations is investigated for applicability to describing the cosmic-ray anisotropy.
This model has been found to need a modification. The necessary changes of the model do not affect the conclusions on the
22-year variations reached on its basis but make it possible to construct a theory of cosmic-ray anisotropy. The theoretical
results on the anisotropy are compared with its long-term observations in a wide energy range performed in Yakutsk. 相似文献
4.
Previously we have reported the detection of a sequence of three particle arrival events at energies above 1019 eV during one day and from a small sky region by two extensive air shower (EAS) arrays. We have shown that the probability of a chance coincidence of the three events is very low and suggested the arrival of a short-lived particle beam at the Earth. Here we refine the energies of the recorded particles and discuss a possible beam formation mechanism that explains the observational results.
相似文献5.
G. F. Krymsky P. A. Krivoshapkin S. K. Gerasimova P. Yu. Gololobov 《Astronomy Letters》2014,40(4):230-233
Long-termobservations of the muon intensity of galactic cosmic rays at the Nagoya (35°10′ N, 136°58′ E) and Yakutsk (62°01′ N, 129°43′ E) stations have revealed amplitude-phase annual and semiannual oscillations of the semidiurnal variation. These oscillations are attributable to the properties of the cosmic-ray anisotropy tensor that result from shielding by the interplanetary magnetic field and solar-wind shear flow. The mentioned tensor is also shown to have a north-south asymmetry. 相似文献
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G. F. Krymsky P. A. Krivoshapkin S. K. Gerasimova P. Yu. Gololobov 《Astronomy Letters》2012,38(9):605-608
The behavior of the cosmic-ray intensity and anisotropy near the neutral sheet of the interplanetary magnetic field has been studied at the sector-boundary crossing times. The detected patterns are indicative of a north-south asymmetry in the interplanetary magnetic field attributable to a systematic shift of its neutral sheet into the southern hemisphere. 相似文献
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G. F. Krymsky P. A. Krivoshapkin S. K. Gerasimova P. Yu. Gololobov V. G. Grigor’ev S. A. Starodubtsev 《Astronomy Letters》2012,38(9):609-612
The previously developed basic theory of the heliospheric modulation of high-energy cosmic rays is generalized to lower energies. Comparison of the theory with the results of long-term observations of cosmic rays in the stratosphere carried out by the group from the Lebedev Institute of Physics inMoscow andMurmansk shows satisfactory agreement. The cosmic rays are shown to behave quite differently when even and odd solar cycles alternate. Possible causes of the anomalously high cosmic-ray intensity recorded during the last solar activity minimum are discussed. 相似文献
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G. F. Krymsky P. A. Krivoshapkin V. P. Mamrukova S. K. Gerasimova 《Geomagnetism and Aeronomy》2006,46(6):708-710
The dependence of cosmic ray north-south anisotropy on the distance of the Earth to the IMF neutral current sheet has been studied. It has been indicated that the value of this anisotropy increases with increasing distance of the current sheet, and the anisotropy direction depends on polarity of the global solar magnetic field and on the sign of the IMF sector. 相似文献
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A. M. Krymsky L. S. Marochnik P. D. Naselsky N. V. Pelikhov 《Astrophysics and Space Science》1978,55(2):325-350
On the basis of the theory set out in Papers I and II (Marochniket al., 1975a, b), the kinetic equations for the spectra of classical and quantum short-wave turbulences have been obtained, taking account of the influence of the latter on the process of cosmological expansion of a homogeneous and, on average, isotropic Universe. The equilibrium and stationary spectra of the turbulence do not change the form of the cosmological solution found in II. The latter change if the spectra are non-stationary, or if the dissipation is taken into account. It is possible that a situation exists in which the primordial short-wave turbulence, having had a significant influence on the early metric, would not be observable at the present time. Quantum turbulence has been studied. Its influence on the metric may be significant only near the Planckian timet
g. 相似文献
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G. F. Krymsky P. A. Krivoshapkin V. P. Mamrukova S. K. Gerasimova 《Astronomy Letters》2009,35(10):696-700
A model of a piston shock produced by a sharp jump in the velocity of the solar wind with a helical magnetic field is suggested
to explain the origin of the Forbush decrease of cosmic rays with a hard energy spectrum at solar activity minimum and, in
some cases, at solar activity maximum. The contact velocity, the compression ratio, the contact position, the ratio of the
magnetic field near the contact to the seed field, the maximum momentum of the particles subjected to modulation, and the
modulation depth for the neutron and muon cosmic ray components have been calculated. The theoretical calculations are compared
with experimental data. 相似文献