Discordia

Figure 11,26 Concordia diagram. (A) Interpretation of straight discordia path as a result of a single episode of Pb loss. (B) Continuous diffusion model of Tilton (1960) applied to world minerals of a = 2800 Ma common age. Reproduced with modifications from G. Faure (1986), Principles of Isotope Geology, 2nd edition, copyright 1986 by John Wiley and Sons, by permission of John Wiley Sons and from Tilton (1960) by permission of the American Geophysical Union.

Figure 5-6 The concordia and an example of discordia for U-Pb dating. The x-axis is The y-axis is ° Pb / U. The...

Another coupled system is the Sm-Nd system, with two Sm isotopes ( Sm and Sm) undergoing ot-decay to become two Nd isotopes ( Nd and Nd). The half-life of Sm is 106 billion years and that of is 103 million years. In principle, the concepts for the U-Pb system (such as concordia and discordia, Nd-Nd isochron) can also be applied to the Sm-Nd system. However, the Sm-Nd coupled system has not found many applications. One reason is that the half-life of " Sm is so short that it is an extinct nuclide. Secondly, the half-lives of Sm and " Sm are very different, by a factor of 1000 (in contrast, the half-lives of and 235 differ only by a factor of 6.3). Hence, the coupled system has found only limited applications to very old rocks, such as meteorites and very old terrestrial rocks. 

Tera-Wasserburg diagram for lunar basalt 14053. The measured data define a discordia line that intersects the -axis at (207 /206 ), = 1.46. The slope of the line, based on two whole-rock samples and a magnetite separate, is -0.88366. The intersection of the discordia line with the concordia curve gives the age of the sample. After Faure and Mensing (2005). 

Martin Woodard Katsuki Yamada Ikeda Sharpless J. Am. Chem. Soc. 1981, 103, 6237. See also Kobayashi Kusakabe Kitano Sato J. Org. Chem. 1988,53, 1586 Kitano Matsumoto Sato Tetrahedron 1988, 44, 4073 Carlier Mungall Schroder Sharpless J. Am. Chem. Soc. 1988, 110, 2978 Discordia Dittmer J. Org. Chem. 1990, 55, 1414. For other examples, see Miyano Lu Viti Sharpless J. Org. Chem. 1985, 50, 4350 Paquette DeRussy Cottrell J. Am. Chem. Soc. 1988, 110, 890 Weidert Geyer Horner Liebigs Ann. Chem. 1989, 533 Katamura Ohkuma Tokunaga Noyori Tetrahedron Assymetry 1990, /, 1 Hayashi Miwata Oguni J Chem. Soc., Perkin Trans. 1 1991, 1167. 

Nicolaou, K.C. Sorensen, E.J. Discordia, R. Hwang, C.-K. Minto, R,E, Bharucha, K.N. Bergman, R.E. Ten-membered ring enediynes with remarkable chemical and biological profiles. Angew. Chem., Int. Ed. Engl. 1992, 31, 1044-1046. 

---