Radioisotope analyses of basalt samples from Hawaii, Japan, and Iwo Jima show that: (1)234U and238U are virtually in radioactive equilibrium, (2)230Th exceeds equilibrium values in all these samples, (3)210Pb concentrations range from 10–200% of the equilibrium values and average 30% deficient, and (4)226Ra is probably not in equilibrium with234U.
The source regions of the basalts or magma forming processes are open systems, chemically. The enrichment of some of the uranium-daughter nuclides is insufficient to account for the excess206Pb in volcanic rocks.
The isotopic composition of lead and specific activity of210Pb in sublimates from Showa-shinzan, Japan are also reported.