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Back in my geology school days in the mid to late 70's, my understanding was that basaltic rocks were unsuitable for radiometric dating. This is because concentrations of elements such as Uranium (U), Rubidium (Rb), and Potassium (K) are too low in such mafic rocks. So, the question is, how are these basaltic rock datings done? Moose Professor, geology, Whatsamatta UEvolution - Changes in the environment, caused by the interactions of the components of the environment."Do not meddle in the affairs of cats, for they are subtle and will piss on your computer." - Bruce Graham"The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness." - John Kenneth Galbraith"Yesterday on Fox News, commentator Glenn Beck said that he believes President Obama is a racist. Combined with Google Site Search I come up with: The first accurate measurement of meteorite initial ratios was made by Papanastassiou et al. These differ from chondritic meteorites in showing evidence of differentiation after their accretion from the solar nebula. 231Pa and 230Th chronology of mid-ocean ridge basalts.
However, the good agreement between the Sm–Nd and Pb–Pb dates has served the important function of confirming the 147Sm half-life of 106 Byr. Nd isotope ratios are affected by the choice of normalising factor for mass fractionation. One example is a dating study on the Deccan basalts (Allegre et al., 1999). 1, the isochron gave a precise age of 65.6 " 0.3 Myr, in excellent agreement with previous K–Ar and Ar–Ar ages averaging 64.5 " 1.5 Myr. Chronology and chemical history of the parent body of basaltic achondrites studied by the 87Rb)87Sr method.
The Ar)Ar dating technique was found to be particularly useful for dating small whole-rock samples of lunar material, especially fine-grained mare basalts. 10.20 shows a typical release pattern (Turner and Cadogan, 1974), attributed to 8% radiogenic Ar loss from K-rich sites with low Ar retentivity. Dashed profile = analysed rock chip of a lunar mare basalt.
However, other samples showed either a sharp decrease in apparent age in the high-temperature fractions, or, particularly in fine-grained rocks, a progressive decrease in apparent age over most of the gas release. Age and Ca/K spectrum for two runs on a basaltic komatiite showing evidence of inherited Ar during low- and high-temperature emission from high Ca/K domains. Solid profile = similar sample activated after fine powdering. One of the most important applications of the K)Ar method has been to calibrate the magnetic reversal time-scale defined by sea floor magnetic anomaly ‘stripes’.
Possible effects of 39Ar recoil in 40Ar/39Ar dating. Additionally, this technique could sometimes give spurious results if zircons with a complex crystallisation history (ie zoned zircons) were not identified and removed from the sample set. Comments about other messages: Jon F, in message 3, just overwhelmed me.
Obviously collecting enough zircon from mafic materials was often very difficult. All hail the mighty SHRIMP (Sensitive High Resolution Ion Microprobe).