Applicability of La-Ce systematics to planetary samples
Ce isotopic compositions in several terrestrial and extraterrestrial materials were determined in order to investigate the applicability of using Ce as an isotopic tracer to geological processes. Owing to the low abundances of 138 La and 138 Ce in nature, our measurements of 138 Ce/ 140 Ce ratios of natural samples have relatively large (>0.02%) errors, and the variations in Ce-isotope ratios were barely resolved. A tenuous anticorrelation was observed between ε Ce and ε Nd for terrestrial basalts and granites, indicating that with some improvement in analytical techniques the Ce isotopic composition may prove useful as a tracer for geological processes. A very low ε Ce predicted from the Ce anomaly in the REE pattern of the Khohar L3 chondrite (Nakamura and Masuda, 1973) was not observed in this study, indicating that the Ce anomaly may be caused by terrestrial contamination or alteration. A low ε Ce estimated for the source of Nakhla is consistent with our previous estimate (Nakamura et al., 1982) of a LREE depleted source.