Disequilibrium of the 238U series in basalt

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.