Isochron dating methods forummember phpu

Oldest reliable 40Ar/39Ar ages for terrestrial rocks: Barberton Mountain komatiites.

The isotopic abundance of 142Nd in the Juvinas meteorite.

I think I was trying to use scirus.com, which is heavily slanted towards searching the real technical journals (not the Google Scholar isn't). Dewise1, in message 7: My understanding of your OP is that it's basalt in continental plates that are unsuitable for dating because they are too old, which would cause concentrations of the elements you list to be too low.

The SHRIMP is sensitive enough to date each zircon individually, so it is fantastic for rock types were zircon minerals are rare, and in some instances in can date individual zones within a single zircon crystal to give a crystallisation age for each zonation. Thanks for the effort, but more than I was looking for. At the time (or the technology of the time), basalts of any age just didn't have the needed minerals and/or elements in useful concentrations.

Nevertheless, the best plateau age of 3447 Myr is in close agreement with the best komatiite results.

The saddle-shaped form is well known for samples containing excess argon.... The effect of fine crushing on a 40)39 age spectrum, due to 39Ar recoil.

Bulk samples usually have low Rb/Sr ratios, yielding ages of low precision, while separated minerals in many achondrites yield Rb)Sr ages below 4.5 Byr, indicative of disturbance.

The Sm)Nd system in separated minerals from achondrites is more resistant to re-setting, yielding better age estimates.

Nature 202, 171)2Notsu, K., Mabuchi, H., Yoshioka, O., Matsuda, J. Since its establishment, the reversal time-scale has been subject to almost continuous revision, and some landmarks are reviewed here. (1963) on 0 ) 3 Myr-old lavas from California, and by Mc Dougall and Tarling (1964) on 0 ) 3 Myr-old lavas from the Hawaiian islands. used K)Ar dates on sanidine, obsidian, biotite, and whole-rocks, while Mc Dougall and Tarling worked on basalt whole-rocks. Good agreement between the two data sets confirmed that the reversal timescale is due to world-wide changes in the polarity of the Earth’s magnetic field, rather than post-crystallisation alteration phenomena, as had been suggested by some workers.------------------Allegre, C. However, Rb)Sr mineral isochrons are not possible for other achondrites due to later disturbance of the Rb—Sr system. Chondritic meteorites have been readily dated by the Rb)Sr method, but achondrites are more problematical.

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