Rare earths in oceanic basalts

Abstract

Rare-earth relative abundance distribution patterns barely altered from that characteristic of chondritic meteorites have been found in three basalts from the mid-Atlantic ridge and in one from the experimental Mohole. Lanthanum has been depleted to about half its normal chondritic relative abundance in all four specimens, and Ce and Pr have been depleted by 10 to 15 per cent in the ridge basalts. Absolute rare-earth concentrations are 10 to 16 times those of chondritic meteorites and are comparable to those of calcium-rich achondrites. It is probable that the whole-earth lanthanide distribution is identical with the chondritic pattern. The presence of this pattern in terrestrial, chondritic, and achondritic matter is chemical evidence in support of the hypothesis that bodies in the solar system derived from a homogeneous source. No time or mechanism for rare-earth enrichment of the basalts or of the calcium-rich achondrites over chondritic matter is indicated, but mechanisms which would fractionate the rare-earth group may be ruled out.