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The Minami-osumi granite and the granites from Amami-oshima were analyzed for strontium and rubidium by the isotope dilution method. The ages calculated from the slopes on the isochron diagram are (64...±11) m.y. with an initial strontium 87/86 ratio of 0.7071±0.0002 for the Minami-osumi granite and (105±27) m.y. with an initial strontium 87/86 ratio of 0.7065±0.0002 for the granites from Amami-oshima. An order of the differences between the whole rock ages and the K-Ar ages on biotite is about 50 m.y. These whole rocks ages represent the oldest limit of the time of differentiation of these granitic magmas. Relatively high initial strontium ratios of these granites along with other lines of evidence are assumed to suggest the the existence of older rocks in the source region of these granites.続きを見る
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Mendeley出力
21_01_p163