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1.
Yu. A. Shukolyukov O. V. Yakubovich B. M. Gorokhovskii S. I. Korneev I. A. Cherkashin 《Doklady Earth Sciences》2011,441(1):1579-1582
A new method of determining the age of native platinum based on alpha-radioactivity of one of its natural isotopes 190Pt is proposed. Due to a special form of occurrence of radiogenic helium in the crystal lattice of native metals as a helium
cluster-bubbles, the stability of 190Pt-4He of the isotope system is extremely high in the natural environment. To check the efficiency of the proposed 190Pt-4He method of isotope geochronology, six independent mineral aggregates of native platinum from chromite-bearing dunites of
the southern part of platinum-bearing zonal Galmoenan dunite-cllinopyroxenite-gabbro plutonic complex (Koryak-Kamchatka belt,
Russia) were analyzed. The age calculated by the tangent of the 190Pt-4He isochrone slope angle equals 69.5 ± 4.9 mln years. The obtained age value coincides with the results of isotope datings,
which were made previously by different methods of isotope geochronology. 相似文献
2.
S.V.S. Murty P.S. Goel D.Vu. Minh Yu.A. Shukolyukov 《Geochimica et cosmochimica acta》1983,47(6):1061-1068
Total nitrogen, measured by neutron activation analysis, is highly enriched in residues from iron meteorites obtained by dissolution of the metal in dilute H2SO4, relative to the bulk value. On the average, the residues, representing 3% mass, contain 22% of total N. Group IA has more dissolved N than IIIA. Lithium and Ir show a distribution pattern parallel to N. Total Xe has been measured in several residues and its isotopic composition is, similar to atmospheric Xe for mass numbers 131 to 136 but not for 124Xe and 126Xe which are strongly depleted in the non-magnetic residues. It is suggested that iron meteorites have trapped in their micro-inclusions, some pre-solar nebular matter which is isotopically heterogeneous. 相似文献
3.
M Wadhwa A Shukolyukov G.W Lugmair D.W Mittlefehldt 《Geochimica et cosmochimica acta》2003,67(24):5047-5069
We report here the results of a study of trace element microdistributions and 53Mn-53Cr systematics in several basaltic and orthopyroxenitic clasts from the Vaca Muerta mesosiderite. Ion microprobe analyses of selected trace and minor element abundances in minerals of the silicate clasts indicate that, following igneous crystallization, these clasts underwent extensive metamorphic equilibration that resulted in intra- and inter-grain redistribution of elements. There is also evidence in the elemental microdistributions that these clasts were subsequently affected to varying degrees by alteration resulting from redox reactions involving the indigenous silicates and externally derived reducing agents (such as phosphorus, derived from the mesosiderite metal) at the time of metal-silicate mixing. Furthermore, our results suggest that the varying degrees of alteration by redox reactions recorded in the different clasts were most likely facilitated by different degrees of remelting induced by heating during the metal-silicate mixing event. After taking into account the effects of these postmagmatic secondary processes, comparison of the trace and minor element concentrations and distributions in minerals of basaltic and orthopyroxenitic clasts with those of noncumulate eucrites and diogenites, respectively, suggests that the primary igneous petrogenesis, including parent magma and source compositions, of Vaca Muerta silicates were similar to those of achondritic meteorites of the Howardite-Eucrite-Diogenite (HED) association. Internal 53Mn-53Cr isochrons obtained for two basaltic (pebble 16 and 4679) and two orthopyroxenitic (4659 and 4670) clasts show that chromium isotopes are equilibrated within each clast. Nevertheless, just as for noncumulate eucrites and diogenites, 53Cr excesses in whole-rock samples of the basaltic clasts (∼1.01 ε in pebble 16; ∼1.07 ε in 4679) are significantly higher than in the orthopyroxene-rich clasts (∼0.62 ε in 4659; ∼0.53 ε in 4670). As in the case of the HED parent body, this suggests that Mn/Cr fractionation in the parent body of the Vaca Muerta silicate clasts occurred very early in the history of the solar system, when 53Mn was still extant. However, the slope of the 53Mn-53Cr isochron defined by the whole-rock samples of Vaca Muerta clasts (corresponding to a 53Mn/55Mn ratio of 3.3 ± 0.6 × 10−6) is distinctly lower than that defined by the HED whole-rock samples (corresponding to a 53Mn/55Mn ratio of 4.7 ± 0.5 × 10−6), indicating that the global Mn/Cr fractionation event that established mantle source reservoirs on the parent body of the Vaca Muerta silicate clasts occurred ∼2 Ma after a similar event on the HED parent body. 相似文献
4.
Two examined fragments of the Kaidun meteorite principally differ in the concentrations of isotopes of noble gases and are very heterogeneous in terms of the isotopic composition of the gases. Because these fragments belong to two basically different types of meteoritic material (EL and CR chondrites), these characteristics of noble gases could be caused by differences in the cosmochemical histories of the fragments before their incorporation into the parent asteroid. As follows from the escape kinetics of all gases, atoms of trapped and cosmogenic noble gases are contained mostly in the structures of two carrier minerals in the samples. The concentrations and proportions of the concentrations of various primary noble gases in the examined fragments of Kaidun are obviously unusual compared to data on most currently known EL and CR meteorites. In contrast to EL and CR meteorites, which contain the primary component of mostly solar provenance, the elemental ratios and isotopic composition of Ne and He in the fragments of Kaidun correspond to those typical of the primary components of A and Q planetary gases. This testifies to the unique conditions under which the bulk of the noble gases were trapped from the early protoplanetary nebula. The apparent cosmic-ray age of both of the Kaidun fragments calculated based on cosmogenic isotopes from 3He to 126Xe varies from 0.027 to 246 Ma as a result of the escape of much cosmogenic isotopes at relatively low temperatures. The extrapolated cosmic-ray age of the Kaidun meteorite, calculated from the concentrations of cosmogenic isotopes of noble gases, is as old as a few billion years, which suggests that the material of the Kaidun meteorite could be irradiated for billions of years when residing in an unusual parent body. 相似文献
5.
The isotopic composition of the noble gases of the new Martian meteorite, the Dhofar 019 shergottite, found in the desert in the territory of the Sultanate of Oman on January 24, 2001, was investigated. Stepwise thermal annealing with isotopic analysis of each of the noble-gas temperature fractions was employed to determine the component composition. The concentration of the trapped noble gases in the new Martian meteorite Dhofar 019 is relatively high, although it lies within the range of concentrations in known SNC meteorites. A characteristic feature of all the trapped noble gases is the presence of two main components: a low-temperature, probably terrestrial atmospheric, component, trapped during the weathering of the meteorite on Earth, and a high-temperature trapped Martian component. Owing to the different ratios of the quantities of the two components, the trapped neon, argon, krypton, and xenon differ markedly in the kinetics of their release. The isotopic composition of the noble gases varies accordingly. The trapped xenon was found to contain two Martian components. One of them, with typical ratios of 129Xe/132Xe and 132Xe/84Kr, is representative of xenon and krypton of the Martian atmosphere; the other, of gases of the Martian mantle. Variations of the isotopic compositions of helium, neon, and argon (and also, to a lesser extent, of krypton and xenon) during the thermal annealing of the Dhofar 019 meteorite clearly point to a large proportion of cosmogenic as well as trapped components. The concentration of cosmogenic neon and argon in the meteorite is unusually high. This corresponds to a maximum exposure age among other SNC meteorites: 20 million years. Estimates of the potassium–argon age (gas-retention age) yielded the figure of 560 million years, which is within the range of values obtained for SNC meteorites by other authors, who used the rubidium–strontium and the potassium–argon technique. 相似文献
6.
S. S. Assonov I. A. Franchi C. T. Pillinger A. S. Semenova Yu. A. Shukolyukov A. B. Verchovsky A. N. Iassevitch 《Meteoritics & planetary science》2002,37(1):27-48
Abstract— Fines, microbreccias and agglutinates from the Luna 16 mature regolith 1635 and fines from the immature/submature Luna 24 regolith have been analysed for N and argon isotopes in order to understand the origin of isotopically distinct N released at different temperatures. All high‐resolution runs reveal a similarity in the release of 36Ar, 40Ar and N over a wide temperature interval. The similarity in the 40Ar and 36Ar releases and the near coincidence in the 1635 agglutinates implies that the implanted species were redistributed and homogenised during regolith processing such that, regardless of the huge difference in ion implantation energy between solar 36Ar and non‐solar 40Ar, their present distribution and their release temperatures are now essentially equal. A small amount of 40Ar released in the lower temperature steps with elevated 40Ar/36Ar is considered to be trapped after reworking. While such mixing and homogenisation may also be expected for N components of different origins, to date all known stepped runs regularly demonstrate a reproducible variation in δ15N, suggesting no homogenisation. We consider regolith N to be a mixture of several components trapped at different times, and some nitrogen that was not involved in the reworking. Relatively heavy N released around 500 °C appears to be the most pure form of the component trapped after reworking, probably from accreted meteoritic matter. Middle‐temperature isotopically lighter N appears to be a mixture of solar and non‐solar N largely homogenised, and therefore solar N can not be seen in its pure form. Bulk δ15N as well as formally deconvoluted δ15N thermal profiles imply that the non‐solar N has a variable δ15N value. Several non‐solar N sources are considered with their input resulting in increasing regolith δ15N with time. Because N from meteorites and interplanetary dust particles appear to be dominant, a mechanism is required to reduce the C/N ratio typical of meteoritic matter to that approaching the low value observed in the lunar regolith. Preferential loss of methane appears to be a viable explanation, following generation either by proton sputtering or in reducing vapour plumes. 相似文献
7.
O. V. Yakubovich Yu. A. Shukolyukov A. B. Kotov M. Brauns A. V. Samsonov A. N. Komarov S. Z. Yakovleva E. B. Sal’nikova B. M. Gorokhovskii 《Petrology》2014,22(5):429-437
In this paper, we consider the application of the U-Th-He method of isotope geochronology for native gold dating. It was shown that inclusions of uranium- and thorium-bearing minerals, including rare earth element phosphates, are one of the main form of uranium and thorium occurrence and, consequently, the main source of radiogenic helium in native gold. Since these inclusions are submicrometer-sized, the radiogenic helium formed in them is not accumulated but implanted in the structure of native gold, which suggests its good preservation over billions of years. This suggestion was experimentally supported by the investigation of the kinetics of radiogenic helium release from native gold. The first results of the U-Th-He dating of native gold from the Pedrolampi (central Karelia) and Witwatersrand (South Africa) deposits are in adequate agreement with available independent geochronological data. This allows us to consider native gold as a U-Th-He mineral geochronometer for the direct dating of ore-forming processes. 相似文献
8.
9.
Yu. A. Shukolyukov O. V. Yakubovich A. G. Mochalov A. B. Kotov E. B. Sal’nikova S. Z. Yakovleva S. I. Korneev B. M. Gorokhovskii 《Petrology》2012,20(6):491-505
A new method of isotope geochronology was proposed for dating native platinum minerals on the basis of the ??-decay of the natural isotope 190Pt. The analysis of the thermal desorption of helium in the crystal lattice of native metals, including platinum, allowed us to predict a very high thermal stability (retentivity) of radiogenic 4He in native platinum minerals up to their melting temperatures. In order to validate the proposed 190Pt-4He method, direct isotopic dating was performed for isoferroplatinum from the Galmoenan dunite-clinopyroxenite and Kondyor alkaline ultramafic massifs. The results of dating obtained by this method for primary ore platinum from the Galmoenan Massif (70 ± 5 Ma) are consistent with geological observations and mean Sm-Nd and Rb-Sr isotopic age estimates. The 190Pt-4He age obtained for placer isoferroplatinum from the Kondyor Massif (112 ± 7 Ma) also agrees with geological observations and is close to the K-Ar and Rb-Sr ages of koswites (phlogopite-magnetite pyroxenites, gabbros, nepheline syenites, and metasomatic rocks after dunites). Our experimental data demonstrated that the 190Pt-4He method is a promising tool for dating native platinum minerals. 相似文献
10.
Yu. A. Shukolyukov O. V. Yakubovich S. Z. Yakovleva E. B. Sal’nikova A. B. Kotov E. Yu. Rytsk 《Petrology》2012,20(1):1-20
It was shown that the behavior of 4He in native and technical metals is very similar owing to the symmetric and stable electron shells of its atoms, which cannot
gain electrons from other atoms or donate their own electrons to metal atoms in a crystal lattice. Therefore, they rapidly
migrate toward grain boundaries and dislocations, where they are released as vesicles or He clusters. It was found that the
thermal desorption of radiogenic He occurring in the crystal lattice of native metals as gas clusters requires activation
energies of 100 and even 180 kcal/mol up to the attainment of the melting temperature of the metal. The frequency factor is
several orders of magnitude higher than the limiting value k
0 ∼ 1013 s−1 for the migration of single atoms in the crystal lattice. Near the melting temperature and tens-hundreds degrees above it,
the character of the thermal desorption of radiogenic 4He changes fundamentally. The migration is strongly accelerated, and sharp narrow peaks appear on the kinetic curves of thermal
desorption. A similar phenomenon was observed during the annealing of technical metals and is known as the burst-effect. The
destruction of the crystal structure results in the disappearance of helium clusters (vesicles). At the very high temperature,
He migrates as individual atoms relatively rapidly from the melt. The activation energy for He thermal desorption and the
pre-exponential frequency factor acquire values characteristic of ordinary migration. Such peculiarities of radiogenic He
provide unique opportunities for its preservation in the structure of gold and other native metals below their melting temperatures.
The rapid advances of (U-Th)/He geochronology is still hampered by the experimentally established extremely heterogeneous
distribution of U, He, and, probably, Th in the structure of gold and other natural metals. This difficulty can be circumvented
by the development of a method for the determination of the contents of all the mentioned chemical elements in a single aliquot
from each sample. 相似文献