Sphene: Uranium-Lead Ages

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Science  29 Mar 1968:
Vol. 159, Issue 3822, pp. 1458-1461
DOI: 10.1126/science.159.3822.1458


Uranium-lead ages were measured on 14 samples of sphene from rocks aged from 1000 to 2750 x 106 years. All samples gave concordant or nearly concordant ages, the maximum difference between the Pb206-U238 and Pb207-Pb206 ages being 10 percent. Sphene has more concordant ages than has the coexisting zircon in each of seven rocks in which they were compared. Sphene sometimes has greater ages than does coexisting biotite, although in two metamorphic rocks, in which metamorphism was sufficiently intense to cause redistribution of radiogenic strontium-87 between various mineral phases, sphene dates the time of metamorphism rather than of original crystallization of the rocks.