Abundances of the fourteen rare-earth elements, scandium, and yttrium in meteoritic and terrestrial matter

Abstract

Abundances and isotopic ratios have been determined for the fourteen rare-earth elements (REE) (Pm excluded) plus Sc and Y by neutron-activation analysis in nineteen meteorites and in three terrestrial specimens. The meteorites investigated included eleven chondrites (1 carbonaceous, 2 pigeonitic, 2 hypersthenic, 3 bronzitic and 3 enstatitic), two calcium-rich and three calcium-poor achondrites, one mesosiderite and two iron meteorites; the terrestrial specimens included a fresh volcanic basalt, and a deep-seated peridotitic and an eclogitic specimen. The absolute abundance of a typical REE (La) in bronzitic and hypersthenic chondrites was found to be 0.34 p.p.m. Relative REE, Sc and Y distributions were identical in the five different chondrite categories. On an absolute basis, the REE, Sc, and Y per 10 6 Si atoms varied monotonically over the chondrite spectrum i.e. from carbonaceous through enstatitic meteorites. Meteoritic isotopic abundances of the sensitive Yb 168/Yb 174 ratio agreed to within ±5 per cent of the terrestrial abundance ratios. Absolute REE abundances in the two calcium-rich achondrites, Nuevo Laredo and Pasamonte, were from 10 to 12 times greater than the average chondritic values. No REE fractionation was found in these achondrites; however, Sc was fractionated by a factor of ~2 relative to the REE. Fractionation of the REE, Sc and Y was found in all three calcium-poor achondrites, Johnstown, Shalka and Norton County, relative to the chondritic meteorites. Absolute REE, Sc and Y abundances varied from ~0.05 to ~0.5 times the comparable values in chondrites. Eu has been depleted in Johnstown and Norton County by ~3—4 times. Th has been depleted in Johnstown to the same degree as La. No REE and Y fractionation was found in the mesosiderite, Estherville; however, Sc has been fractionated. Absolute REE abundances in the two Fe meteorites were ~10 −4 times the REE abundances in chondrites. In one iron, the REE may have been fractionated. Absolute REE. Sc and Y abundances in the uneroded Kilauea Iki-22 basalt, peridotitic and eclogitic specimens were from 30 to 10 times greater than the abundances in chondrites. Compared with chondrites, the light REE have been enriched by factors of up to 5, which agrees with the enrichments of the light REE in terrestrial sediments and igneous rocks, etc. Theoretical calculations of expected REE abundances by Clayton et al. agree well with the present chondritic REE values. For convenience, a description of the detailed procedure for the REE, Sc and Y determinations (now in current use at this Laboratory) has been relegated to the Appendix.