Geochemistry and age of ultrahigh pressure metamorphic rocks from the Kokchetav massif (Northern Kazakhstan)     

V. S. Shatsky  E. Jagoutz  N. V. Sobolev  O. A. Kozmenko  V. S. Parkhomenko  M. Troesch 《Contributions to Mineralogy and Petrology》1999,137(3):185-205

Isotopic and geochemical data of the Zerenda series metamorphic rocks from the Kokchetav massif are reported. Some of these rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism (P > 40 kbar, T = 900–1000 °C). The diamond-bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks. The REE patterns range from LREE depleted to slightly LREE enriched [chondrite normalized (La/Yb)_N– 0.1–5.4] with a negative Eu anomaly. They are depleted in incompatible elements (e.g. Sr, Ba, U, Th) with respect to the upper crust. In contrast non-diamondiferous rocks of the Zerenda series exhibit normal crustal geochemistry. All rocks of the Zerenda series have very radiogenic lead isotopes. The measured μ values (²³⁸U/²⁰⁴Pb) compared with those calculated for the interval between crust formation and ultrahigh pressure (UHP) metamorphism suggest a decrease by factors of up to 200 during the UHP metamorphism. The Sm-Nd mineral isochrons from the diamond-bearing rocks and other rock types of the Zerenda series give a Middle Cambrian (524–535 Ma) age of metamorphism. The Nd model ages show that crust formation occurred about 2.3 Ga ago. Significant fractionation of Sm and Nd and loss of incompatible elements may be due to partial melting of the protoliths. The Ar-Ar age determinations of secondary biotite and muscovite from the diamond-bearing rocks yield an age of 517 ± 5 Ma. This cooling age requires a short time interval between UHP metamorphism and uplift to a crustal level. Ultrahigh pressure metamorphism might be a significant source of Pb for the mantle. We propose that the radiogenic Pb of the oceanic array is the contamination traces of numerous UHP events. Beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using Nd isotopes. We compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the Sm-Nd system during very high grade metamorphic events. Received: 14 August 1998 / Accepted: 1 June 1999  相似文献   

Pulsations of the Free Oscillations of the Earth in an Hourly Period Range     

G. A. Sobolev  N. A. Zakrzhevskaya  K. N. Akatova 《Izvestiya Physics of the Solid Earth》2018,54(3):393-405

The records from 161 identical broadband seismic stations located in different regions of the world after the strong earthquakes off Sumatra Island on December 26, 2004 with magnitude M = 9.1, in Chile on February 27, 2010 with M = 8.8, and the Tohoku earthquake in Japan on March 11, 2011 with M = 9.0 are studied. Oscillations with a period of ~11 h are analyzed. They are observed as pulsations in the free radial oscillations of the Earth lasting more than one week. The stations located a few hundred kilometers apart from each other demonstrate identical records. As the distance between the stations becomes larger, the structure of the records becomes different. At interstation distances of about 3800 km, the records at the stations have opposite phases, and at distances of ~7600 km, the phases coincide. This is reflected in the spatial structure of the areas of the positive and negative phases of the oscillations on the Earth’s surface. This structure recurs at the same time instant after the three considered earthquakes, which indicates that this effect is independent of the properties of the sources. The spatial positions of the areas of positive and negative phases are also not correlated to the geological conditions in the vicinity of the stations which are located both in the subduction zone and within the platform. The structure of the pulsations and their spatial distribution differ from the variations of the Earth’s tides.  相似文献   

Effect of Magnetic Storms on Low-Frequency Seismic Noise     

Sobolev  G. A.  Zakrzhevskaya  N. A.  Migunov  I. N.  Sobolev  D. G.  Boiko  A. N. 《Izvestiya Physics of the Solid Earth》2020,56(3):291-315

Izvestiya, Physics of the Solid Earth - Abstract—The response of seismic noise in the minute range of periods to the strong magnetic storms is studied. The noise is analyzed from the records...  相似文献   

Polarization of the light of quasars     

V. M. Loskutov  V. V. Sobolev 《Astrophysics》1985,23(2):545-553

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The Stark effect in stellar flares     

V. V. Sobolev  V. P. Grinin 《Astrophysics》1995,38(1):15-21

The formation of the Stark wings of hydrogen lines is considered on the basis of theoretical models of flares in type UV Cetus stars. It is shown that, under certain conditions (depending on the power of the beam of charged particles and their energy spectrum), very broad wings may be formed, extending 20 and more angstroms from the center of the line. Observations of such wings may provide valuable information concerning the energy spectra of the particles inducing the flare.Translated from Astrofizika, Vol. 38, No. 1, pp. 33–44, January–March, 1995.  相似文献   

Composition of the Siberian cratonic mantle: evidence from Udachnaya peridotite xenoliths   总被引：31，自引：0，他引：31  

F. R. Boyd  N. P. Pokhilenko  D. G. Pearson  S. A. Mertzman  N. V. Sobolev  L. W. Finger 《Contributions to Mineralogy and Petrology》1997,128(2-3):228-246

Bulk compositions and mineral analyses for forty-one, large, garnet- and spinel-facies peridotite xenoliths from the Udachnaya kimberlite in the central Siberian platform have many similarities to those of well-studied peridotites from the Kaapvaal craton in southern Africa. Coarse Mg-rich lherzolites and harzburgites with equilibration temperatures below 1000 °C are abundant and are believed to form the principal rock type in the Siberian lithosphere. The low-temperature Udachnaya peridotites have an average mg number [Mg/(Mg+Fe)] of 92.6 with a wide dispersion in modal enstatite, ranging to over 40 wt%. High-temperature peridotites are relatively richer in Fe and Ti and are commonly deformed, with porphyroclastic or mosaic-porphyroclastic textures, some of the latter having fluidized enstatite. The Udachnaya peridotites have experienced late-stage metasomatism before, during and after eruption. Garnets and pyroxenes in many of the high-temperature rocks are zoned, probably by reaction with melt prior to eruption. Virtually all the peridotites contain secondary diopside, inhomogeneous on a micron scale, that mantles primary orthopyroxene. It is believed to have crystallized along with lesser amounts of intergranular calcite and monticellite during eruption. Bulk analyses for total Fe in many specimens are higher than whole-rock Fe calculated from the electron probe analyses and the modes. The magnitude of the difference between the two measurements of total Fe correlates with loss-on-ignition, suggesting that Fe has been introduced during serpentinization following eruption. These late metasomatic processes have thus affected some major as well minor and trace element compositions. The similarities in bulk composition of peridotites from Udachnaya and the Kaapvaal are evidence of a common origin. Low-temperature cratonic peridotites differ from oceanic peridotites in having higher mg numbers (>92) and in having relatively high but wide-ranging modal enstatite (Mg/Si = 1.06–1.49 weight fraction). The Udachnaya low-temperature peridotites have an inverse correlation between FeO (calculated from the probe analyses and modes) and SiO₂. This correlation is also present in the Kaapvaal data but is complicated by a greater range in fertility that produces a positive variation of Fe with Si. A negative trend for Fe/Si can be seen within a portion of the Kaapvaal data, that for low-Ca harzburgites, in which the variation in fertility is restricted. The negative trends for Fe/Si can be interpreted as a consequence of either segregation of olivine and orthopyroxene by metamorphic differentiation or partial sorting during cumulate formation. Received: 18 June 1996  / Accepted: 11 February 1997  相似文献   

The Origins of Yakutian Eclogite Xenoliths   总被引：2，自引：2，他引：2       下载免费PDF全文

Snyder  Gregory A.; Taylor  Lawrence A.; Crozaz  Ghislaine; Halliday  Alex N.; Beard  Brian L.; Sobolev  Vladimir N.; Sobolev  Nikolai V. 《Journal of Petrology》1997,38(1):85-113

Owing to the association with diamonds, eclogite xenoliths havereceived disproportionate attention given their low abundancein kimberlites. Several hypotheses have been advanced for theorigin of eclogite xenoliths, from the subduction and high-pressuremelting of oceanic crust, to cumulates and liquids derived fromthe upper mantle. We have amassed a comprehensive data set,including major- and trace-element mineral chemistry, carbonisotopes in diamonds, and Rb–Sr, Sm–Nd, Re–Os,and oxygen isotopes in ultrapure mineral and whole-rock splitsfrom eclogites of the Udachnaya kimberlite pipe, Yakutia, Russia.Furthermore, eclogites from two other Yakutian kimberlite pipes,Mir and Obnazhennaya, have been studied in detail and offercontrasting images of eclogite protoliths. Relative to eclogitesfrom southern Africa and other Yakutian localities, Udachnayaeclogites are notable in the absence of chemical zoning in mineralgrains, as well as the degree of light rare earth element (LREE)depletion and unradiogenic Sr; lack of significant oxygen, sulfur,and carbon isotopic variation relative to the mantle; and intermineralradiogenic isotopic equilibration. Several of these eclogitescould be derived from ancient, recycled, oceanic crust, butmany others exhibit no evidence for an oceanic crustal protolith.The apparent lack of stable-isotope variation in the Udachnayaeclogites could be due to the antiquity of the samples and consequentlack of deep oceanic and biogenically diverse environments atthat time. Those eclogites that are interpreted to be non-recycledhave compositions characteristic of Group A eclogites from otherlocalities that also have been interpreted as being directlyfrom the mantle. At least two separate and diverse isotopicreservoirs are suggested by Nd isotopic whole-rock reconstructions.Most samples were derived from typical depleted mantle. However,two groups of three samples each indicate both enriched mantleand possible ultra-depleted mantle present beneath Yakutia duringthe late Archean and early Proterozoic. The vast majority ofeclogites studied from the Obnazhennaya pipe also exhibit characteristicsof Group A eclogites and are probably derived directly fromthe mantle. However, the eclogites from the Mir kimberlite aremore typical of other eclogites world-wide and show convincingevidence of a recycled, oceanic crustal affinity. We concurwith the late Ted Ringwood that eclogites can be formed in avariety of ways, both within the mantle and from oceanic crustalresidues. KEY WORDS: diamonds; eclogite xenoliths; isotopic composition; REE; Yakutia  相似文献   

Composition of a carbonatitic melt in equilibrium with lherzolite at 5.5–6.3 GPa and 1350°C     

A. N. Kruk  A. G. Sokol  D. A. Chebotarev  Yu. A. Palyanov  N. V. Sobolev 《Doklady Earth Sciences》2016,467(1):303-307

Generation of ultra-alkaline melts by the interaction of lherzolite with cardonatites of various genesis was simulated at the P–T parameters typical of the base of the subcratonic lithosphere. Experiments with a duration of 150 h were performed at 5.5 and 6.3 GPa and 1350°C. The concentrations of CaO and MgO in melts are buffered by the phases of peridotite, and the concentrations of alkalis and FeO depend on the composition of the starting carbonatite. Melts are characterized by a low (<7 wt %) concentration of SiO₂ and Ca# from 0.40 to 0.47. It is demonstrated that only high-Mg groups of carbonatitic inclusions in fibrous diamonds have a composition close to that of carbonatitic melts in equilibrium with lherzolite. Most likely, the formation of kimberlite-like melts relatively enriched in SiO₂ requires an additional source of heat from mantle plumes and probably H₂O fluid.  相似文献   

Graphite and diamond formation via the interaction of iron carbide and Fe,Ni-sulfide under mantle <Emphasis Type="Italic">P–T</Emphasis> parameters     

Yu. V. Bataleva  Yu. N. Palyanov  Yu. M. Borzdov  N. V. Sobolev 《Doklady Earth Sciences》2016,471(1):1144-1148

Experimental research in the Fe₃C–(Fe,Ni)S system was carried out. The objective of the investigation was to model the reactions of carbide–sulfide interaction related to graphite (diamond) formation in reduced lithosphere mantle domains. T ≤ 1200°C is the formation temperature of the Ni-cohenite + graphite assemblage coexisting with two immiscible melts such as sulfide (Fe₆₀–Ni₃–S₃₇)_L and metal–sulfide (Fe₇₁–Ni₇–S₂₁–C₁)_L containing dissolved carbon. Т ≥ 1300°C is the generation temperature of a unified melt such as (Fe₈₀–Ni₆–S₁₀–C₄)_L characterized by graphite crystallization and diamond growth. The extraction of carbide carbon during the interaction with the sulfide melt can be considered as one of the potential mechanisms of graphite and diamond formation in the reduced mantle.  相似文献   

Peculiarities of the composition of volatile components in picroilmenites from Yakutian kimberlites of various ages (by gas chromatography—mass spectrometry)     

A. A. Tomilenko  T. A. Bul’bak  L. N. Pokhilenko  D. V. Kuzmin  N. V. Sobolev 《Doklady Earth Sciences》2016,469(1):690-694

The composition of volatile components in picroilmenites from Yakutian kimberlitic pipes of various ages (the Olivinovaya, Malokuonapskaya, and Udachnaya–East pipes) was studied for the first time by means of gas chromatography–mass spectrometry (GC-MS). It was shown that picroilmenites and olivines from same kimberlitic pipes contained volatile components of close composition, whereas these components were quite different in these minerals from different pipes. These features point to a common source and represent the specificity of the magma chamber formed under the pronounced influence of hydrocarbons with their derivates, as well as nitrogen-, chlorine-, and sulfur-containing compounds. The fraction of hydrocarbons and derivates in the composition of volatile matter is as high as 99%, including 9.7% of chlorine- and fluorinecontaining compounds.  相似文献