Argon isotope

The possibility that an even larger impact caused the P T extinction received support when Becker and Poreda found that helium and argon atoms were present in the inner cores of some of the fullerenes from the P T boundary sediments (The cover of this book shows a helium atom inside a mol ecule of Ceo) What is special about the fullerene trapped atoms is that the mixtures of both helium and argon isotopes resemble extraterrestrial isotopic mixtures more than earthly ones The He/ He ratio in the P T boundary fullerenes for example is 50 times larger than the natural abundance ratio... 

Megrue, G. H., Distribution and Origin of Helium, Neon, and Argon Isotopes in Apollo 12 Samples by n Situ Analysis with a Laser-Probe Mass Spectrometer, J. Geophys. Res. 76, 4956 (1971). 

Ironically, our current plans call for the reverse linkage of the above enrichment procedures. That is, we shall use an electromagnetic isotope separator to enrich argon isotopes for a mass spectrometry experiment, and we shall enrich radiocarbon via thermal diffusion for improved mini-gas proportional counting. 

Fig. 8.9 (a) A four stage thermal diffusion cascade for argon isotope separation (Modified from Spindel, W. ACS Symp. Ser. 11, 82 (1975)). (b) The thermal diffusion cascade operated by K. Clusius and collaborators at the University of Zurich during the 1950s (Photo credit Archives of the Institute of Physical Chemistry, University of Zurich)... 

Black DC (1972) On the origins of trapped helium, neon and argon isotopic variation in meteorites - II. 

Marty B, Humbert F (1997) Nitrogen and argon isotopes in oceanic basalts. Earth Planet Sd Lett 152 101-112... 

The Apollo missions attempted to take advantage of the Moon s location outside of the Earth s magnetic field to capture solar wind in aluminum collectors. The collectors were deployed for the duration of each mission (from 10 to 45 hours) and provided information on the helium, neon, and argon isotopic compositions in the solar wind. 

Glauconite, being of sedimentary origin, can he used to determine the age of those sediments by evaluating its Ar ratio (potassium-argon isotope ratio). See also Ocean Resources (Mineral). 

From Figure 7.10, we can see that if intense EUV radiation had lasted more than 70 Ma, this would account for the observed Ne isotopic fractionation in the atmosphere relative to solar (SW) Ne, regardless of the amount of the C02 content. Although not shown in Figure 7.10, a fractionation in a pure steam atmosphere is little different from those with the second constituent. Figure 7.10 also shows that the existence of the second major constituent C02 in the steam atmosphere would result in a much larger fractionation effect in the argon isotopic ratio than in the neon isotopic ratio. This calculation is made for an assumed steam atmosphere of 270 bars, which corresponds to the mass of the present ocean. Note that the amount of the prim-... 

Elliot, T., Ballentine, C. X, O Nions, R. K., Ricchiuto, T. (1993) Carbon, helium, neon and argon isotopes in a Po Basin (northern Italy) natural gas field. Chem. Geol., 106, 429-40. 

Hilton, D. R., Hammerschmidt, K., Loock, G., Friedrichsen, H. (1993) Helium and argon isotopic systematics of the central Lau Basin and Valu Fa Ridge Evidence of crustal/mantle interactions in a back-arc basin. Geochim. Cosmochim. Acta, 57, 2819—41. 

Turner, G. (1988) Hydrothermal fluids and argon isotopes in quartz and veins and cherts. Geochim. Cosmochim. Acta, 52, 1443-8. 

Valbracht, P. I, Honda, M., Matsumoto, T., Mattielli, N., McDougall, I., Ragettli, R., Weis, D. (1996) Helium, neon and argon isotope systematics in Kerguelen ultramafic xenoliths Implications for mantle source signatures. Earth Planet. Sci. Lett., 138, 29-38. 

Radioactive ages of rocks Variations of argon isotopic ratios are found within solids because of radioactive decay of 4°K, which also enables the ages of minerals to be determined. This works as follows. Ifrocks solidify with all three I< isotopes present... 

Marty B. and Alle P. (1994) Neon and argon isotopic constraints on Earth-atmosphere evolution. In Noble Gas Geochemistry and Cosmochemistry (ed. J.-l. Matsuda). Terra Scientihc Publishing Company, Tokyo, pp. 191-204. 

Marty B., Tolstikhin I., Kamensky I. F., Nivin V., Balagans-kaya E., and Zimmermann J. L. (1998) Plume-derived rare gases in 380 Ma carbonatites from the Kola region (Russia) and the argon isotopic composition in the deep mantle. Earth Planet. Sci. Lett. 164, 179-192. 

Pickles C. S., Kelley S. P., Reddy S. M., and Wheeler J. (1997) Determination of high spatial resolution argon isotope variations in metamorphic biotites. Geochim. Cosmochim. Acto 61(18), 3809-3833. 

In Antarctica, both paleothermometry and the use of nitrogen and argon isotopes pose some problems. First, the low accumulation that prevails at East Antarctic inland sites such as Vostok... 

Figure 3 Helium and argon isotope compositions of MORE ( Popping Rock from the Atlantic, Shona ridge section, and N. Chile ridge) and selected islands. " °Ar/ Ar ratios vary widely due to variahle amounts of atmospheric...

Overall, argon isotope compositions indicate that the mantle is much more radiogenic than the atmosphere, and this provides an important starting point for degassing history models. It appears that there are variations in " °Ar/ Ar associated with different He/ He ratios in the mantle, although atmospheric contamination of samples has made this difficult to quantify. It appears that the same proportion of " °Ar has been in the atmosphere over the last 380 Ma, although reliable data are required from much earlier to effectively discriminate between different degassing histories (see Section 4.11.4). 

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