Ratios In Meteorites Research Articles

The S32/S34ratio in troilite from the Bruderheim and Peace River meteorites

During the initial studies of sulphur isotope abundances, MacNamara and Thode [1950] reported that the S32/S34 ratio in meteorites was markedly constant, in contrast to the significant variations found in terrestrial samples. This constancy has been further confirmed [Vinogradov, 1958; Ault and Kulp, 1959; Thode et al., 1961; Shima and Thode, 1961; Jensen and Nakai, 1962]. Within the past four years, fragments of two chondritic meteorite showers, Bruderheim and Peace River, fell and were recovered in Alberta [Folinsbee and Bayrock, 1961, 1964].

Die relativen Produktionsquerschnitte für 3He und 21Ne aus Mg, Si, S und Fe in Steinmeteorite

With various mineral separation methods, including our newly developed technique of specific solvents, we succeeded in separating very pure fractions of metallic iron, troilite, olivine and pyroxene from the Holbrook meteorite. Helium and neon were extracted from those minerals. The measurements allowed a determination of the relativ production rates of 3He and the neon isotopes by cosmic rays in iron, sulphur, magnesium and silicon. The results enable us to calculate the relative production rates of these isotopes in all kinds of meteorites whatever their chemical composition. The ratio of the relative production rates of 21Ne from Mg and Si is 1.8 ± 0.4. Therefore, we can conclude that the variations of the 3He/21Ne ratio in stone meteorites can not be explained by variations in their chemical composition, at least not for the normal chondrites.

The fluorine content of some chondritic meteorites

The fluorine content of four normal chondritic and two carbonaceous chondritic meteorites was determined by nondestructive activation analysis. The range in values is (0.4 - 4)×10-4 gram/gram. Finally, the F19/O18 meteoritic ratio is not in agreement with predictions based on the creation of these nuclides in stars.

Geochemical study of boron isotopes

There has not been a general agreement concerning the isotopic abundance ratio B 11 B 10 of boron in natural minerals. The B 11 B 10 ratios of rocks and sea water which are typical of terrestrial samples are around 4.05 ± 0.05. The B 11 B 10 ratios in meteorites are lower than the terrestrial value.

Sulfur isotopes and the origin of the sulfide deposits of the Bathurst-Newcastle area of northern New Brunswick

The regional geology of the Bathurst-Newcastle area is briefly outlined. There are 2 types of sulfide deposits in the area: a) epigenetic fissure deposits, and b) massive sulfide deposits. Geological evidence can be variously interpreted to suggest a syngenetic, a source bed, or a magmatic hydrothermal origin for the massive sulfide deposits. S 32 /S 34 ratios are presented for more than 300 sulfide samples from the host rocks and sulfide deposits. Four granite bodies are dated by the K-Ar method. Model Pb ages are presented for 5 galena samples. Sulfides disseminated through the black shale and argillites of the host rocks are enriched in S 32 (mean value 22.31) relative to the meteoritic ratio, and broad range of values. S 32 /S 34 ratios for the sulfide deposits fall into 2 distinct groups. In general one group (21.88-22.05) represents the massive sulfide deposits, while the other group (22.18-22.21) represents the fissure deposits. This suggests 2 separate, but probably closely related sources for the S. Granites intrusive into the host rocks of the sulfide deposits have a mean age of 386 + or - 10 m.y. Pb minerals in the sulfide deposits have a mean model Pb age of 370 + or - 20 m.y. Thus the Pb minerals and the granite bodies were emplaced during the same major orogenic event. The sulfide deposits of the Bathurst area have a narrow range of S 32 /S 34 values. Sulfide deposits thought to have a magmatic hydrothermal origin all have a narrow range of S 32 /S 34 values. It therefore seems reasonable that well homogenized magmatic hydrothermal solutions are the most logical source for the sulfide deposits. The homogeneity of the Pb isotope abundance data gives strong independent evidence that the ores are of a magmatic hydrothermal origin. The problem of why the massive sulfide deposit are enriched in S 34 is open for further investigation.

Depth Variation of Tritium and Argon-37 Produced by High-Energy Protons in Iron

The ${\mathrm{H}}^{3}$ produced by 0.16-, 1.0-, 3.0-, and 6.2-Bev protons and the ${\mathrm{A}}^{37}$ by 0.16-, 1.0-, and 6.2-Bev protons in long iron targets is measured as a function of depth. The maximum effective ${\mathrm{H}}^{3}$ cross section is 7.2 mb at 0.16 Bev, 60 mb at 1.0 Bev, 100 mb at 3.0 Bev, and 130 mb at 6.2 Bev. The maximum effective ${\mathrm{A}}^{37}$ cross section is 0.19 mb at 0.16 Bev, 4.7 mb at 1.0 Bev, and 6.7 mb at 6.2 Bev. The depth variation of these isotopes is very energy-dependent. At the higher energies a slight transition effect occurs. At the lower energies there is an exponential decrease with depth. The comparison of these measurements with the depth variation of ${\mathrm{He}}^{3}$ in the Carbo meteorite shows that the cosmic rays that produced the ${\mathrm{He}}^{3}$ in this material were very similar to the protons with 6-Bev energy. The ${\mathrm{H}}^{3}$ to ${\mathrm{A}}^{37}$ ratio is not very energy- or depth-dependent. The ratio is 15 at 1 Bev and 20 at 6.2 Bev. However, for 0.16-Bev protons the ${\mathrm{H}}^{3}$ to ${\mathrm{A}}^{37}$ ratio increases from 40 to 1000 in 4-cm depth. The ${\mathrm{H}}^{3}$ to ${\mathrm{A}}^{37}$ ratio is compared with the ${\mathrm{He}}^{3}$ to ${\mathrm{A}}^{36}$ ratio in four iron meteorites. These are comparable to a remarkable extent with the Bev proton results. The small variation of the ${\mathrm{He}}^{3}$ to ${\mathrm{A}}^{36}$ ratio in meteorites is related to the fact that the ${\mathrm{H}}^{3}$ to ${\mathrm{A}}^{37}$ ratio is not very energy- or depth-sensitive for protons in the Bev range; however, the ${\mathrm{He}}^{3}$ to ${\mathrm{A}}^{36}$ ratio also favors the 6-Bev energy.

Getting Older

THE AGE OF THE EARTH as suggested by a comparison of the ratios in meteorites of two isotopes of lead has been pushed back to 4.5 billion years, which is the earliest date yet obtained by analyzing the elements in the solar system. Studies made with a mass spectrometer at the University of Chicago by H. Brown, M. Inghram, C. Patterson, and G. Tilton on the lead content of meteorites have provided better agreement with astronomical estimates of the earth's age (about four billion years) than has other geophysical evidence. Comparisons of uranium to lead ratios in rocks, for example, have indicated an age no greater than 3.3 billion years. The present results, reported at a recent conference on geophysics and described in the University's publication Reports, depend on the fact that calculable amounts of lead 206 result from the radioactive decay of uranium 238 while larger amounts of lead 207 result from the more rapid decay of uranium 235.