ABSTRACT

Neutron activation analysis of uranium, thorium and potassium has been. made on St. Paul's rocks of possible oceanic mantle origin. Results of analysis showed that average values of WISEMAN's “challengerite” are (15.8 ± 0.5) × 10^-8 gU/g, (34.5 ± 1.0) × 10^-8 gTh/g and (3100 ± 60) × 10^-6 gK/g, giving a rate of heat production of ca. 300 × 10^-16 cal/cm³·sec. This value agrees with the rate expected for the pyrolitic oceanic upper mantle. Other types of St. Paul's rocks, such as “owenites”, “paulites” and “questites” were shown to contain these elements comparable in amount with peridotite nodules. The Th/U ratio of these rocks, however, is unusually low.