The primary goal of this project is to determine both the prevalence and magnitude of protactinium-uranium fractionation in volcanic rocks, so that the igneous processes causing the fractionation can be identified and temporally constrained. The secondary goal is to produce, purify, and calibrate an isotope- dilution spike for Nb, and to develop the analytic methods to make isotope dilution thermal ionization mass spectrometry (ID- TIMS) measurements of Nb in geologic materials. A third goal assumes that protactinium and niobium have chemical properties so similar that Nb may be considered a stable analog of Pa. This hypothesis will be tested by analyzing young volcanic rock samples for Nb as well as Pa, Th and U.
