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Shukolyukov, A.

Publications and source records attributed to Shukolyukov, A..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Manganese-Chromium Isotope Systematics of Ivuna, Kainsaz and Other Carbonaceous Chondrites

We have shown earlier that the bulk samples of carbonaceous chondrites [CC] reveal excesses in both Cr-53 (Cr-53*) and Cr-54 (Cr-54*) as compared to the terrestrial standard value. The Cr-53/52 ratios in bulk samples of Orgueil (CI), Murray (CM), Allende (CV), and the Bencubbin/CH-like meteorite Hammadah Al Hambra 237 (HH237) are correlated with the respective Mn/Cr ratios. In contrast to CC, HH237 is characterized by a deficit of Cr-53 (-0.15 +/- 0.10(epsilon)) at a low Mn/Cr ratio of 0.07. The HH237 data point, however, falls on the CC line. Here we report new Mn-53 - Cr-53 results for the CC Kainsaz (CO) and Ivuna (CI).

Shukolyukov, A.↗
NASA NTRS2000

Early Archean Spherule Beds-Confirmation of Impact Origin

The oldest record of major impact events on Earth may be a number of early Archean (3.5 to 3.2 Ga) spherule beds that have been identified in the Barberton Greenstone Belt, South Africa. Several field, petrographic, and geochemical criteria distinguish these beds from typical volcanic and clastic sediments. These criteria include the wide geographic distribution of two beds in a variety of depositional environments, the presence of relict quench textures, absence of juvenile volcaniclastic debris within the beds, and extreme enrichment of Ir and other platinum group elements (PGE) as compared to surrounding sediments. Some researchers, however, argued for a terrestrial origin for spherule bed formation, possibly related to volcanism and gold mineralization.

Shukolyukov, A.↗
NASA NTRS1993

Fe-60 in eucrites

Additional evidence for the existence in the early solar system of live Fe-60 has been found in the basaltic achondrite Juvinas. The relative abundance of Fe-60/Fe-56 of about 4 x 10 exp -10 at the time of meteorite solidification is one order of magnitude lower than that previously observed for the eucrite Chervony Kut. This difference corresponds to an about 4.7 Ma time interval between closure of the Fe-60-Ni-60 isotopic system in the two meteorites. The factor two higher initial Ni-60/Ni-58 ratio in Juvinas is consistent with this time difference and a common bulk Fe/Ni ratio in the two meteorites. Using the Fe-60-Ni-60 isotope system as a chronometer various models for the evolution of the eucrite parent body of different degrees of complexity are discussed. Regardless of the detailed differences between these models a short time interval of only a few million years between planetary differentiation and basaltic crust formation is indicated.

Shukolyukov, A.↗
NASA NTRS1993

Live Iron-60 in the early solar system

Isotopic analyses of nickel in samples from the differentiated meteorite Chervony Kut revealed the presence of relative excesses of Ni-60 ranging from 2.4 up to 50 parts per 10 exp 4. These isotopic excesses are from the decay of the now extinct short-lived nuclide Fe-60 and provide clear evidence for the existence of Fe-60 over large scales in the early solar system. Not only was Fe-60 present at the time of melting and differentiation (that is, Fe-Ni fractionation) of the parent body of Chervony Kut but also later at the time when basaltic magma solidified at or near the surface of the planetesimal. The inferred abundance of Fe-60 suggests that its decay alone could have provided sufficient heat to melt small (diameters of several hundred kilometers) planetary bodies shortly after their accretion.

Shukolyukov, A.↗
NASA NTRS1993

FE-60 and the evolution of eucrites

We have recently presented evidence for the existence of live Fe-60 in the early solar system. This evidence comes from observations of 2.4 to 50 epsilon unit (1 part in 10(exp 4)) relative excesses of Ni-60 measured in samples from the eucrite Chervony Kut (CK). These isotopic excesses have been produced by the decay of the short-lived radionuclide Fe-60 (T(sub 1/2) = 1.5 Ma). Because CK originates from a planetesimal which was totally molten and its high Fe/Ni ratio is due to a planet-wide Fe-Ni fractionation during metal-silicate segregation, the presence of the Fe-60 decay product indicates the large scale abundance of Fe-60 in the early solar system and its presence during differentiation of this planetesimal. The observed variable Ni-60 excesses in different bulk samples and mineral separates from CK can only be understood if some Fe-60 was still alive at the time when basaltic magma had solidified on the eucrite parent body. The lack of a correlation between Ni-60 and the respective Fe/Ni ratios in different mineral fractions from CK indicates a metamorphic remobilization of Ni after essentially all Fe-60 has decayed. However, Ni-60 from three bulk samples from different locations within the meteorite appears to correlate reasonably well with the respective Fe/Ni ratios. If we regard this correlation as an isochron then its slope yields a Fe-60/Fe-56 ratio f (3.9 +/- 0.6) x 10(exp -9) and an initial Ni-60 of 3.2 plus or minus 0.9 epsilon units at the time of crystallization of CK. Estimates based on these values and a approximately 10 Ma time interval between CK solidification and formation of the earliest condensates in the solar system followed by rapid accretion of planetary bodies indicate that the decay of Fe-60 could produce sufficient heat to melt these planetesimals. If Al-26 was present on a planetary scale as Fe-60 and at abundances close to values observed in Allende inclusions then melting of small early formed planets is inevitable. As an attempt to further explore the Fe-60/Ni-60 isotope system as an early solar system chronometer we studied another noncumulate eucrite, Juvinas (JUV) (sample USNM 1051), which belongs to the same subgroup as CK.

Shukolyukov, A.↗