Activity Ratios of Uranium Isotopes in Volcanic Rocks from Izu-Mariana Island-Arc Volcanoes, Japan

Abstract

The ²³⁴U/²³⁸U activity ratios of 45 products from 6 volcanoes of Izu-Mariana island-arc ranged from 0.96 to 1.04, representing a Gaussian distribution with the average value of 0.997 and the standard deviation of 0.014. The result indicates that ²³⁴U is in radioactive equilibrium with ²³⁸U in the erupting magmas from island-arc volcanoes.