Behavior of uranium and thorium during evolution of Mesozoic volcanic apparatuses in Transbaykal
As the composition of volcanic rocks changes from intermediate to acidic, their concentrations of radioactive elements increase, in two out of the three volcanoes examined here. The reverse is true of the third volcano. Significant enrichment of uranium develops only in the latest portions of the melt, but thorium is enriched gradually and smoothly. U-Th and SiO2-K correlations are found to be regionally obscure.