Secular Trends in Rare Earth Element Patterns of Precambrian Iron-Formations from India and Greenland

Abstract

Rare earth element (REE) analysis have been carried out by neutron activation on samples of iron-formation from southern India and from West Greenland. The investigated iron-formations range in age from about 1800 m. y. to more than 3000 m. y. The different iron-formations have undergone very diffeferent metamorphic histories, from the virtually unmetamorphosed iron-formation in West Greenland, through amphibolite to granulite facies metamorphism in southern India.

The results clearly demonstrate that europium anomalies cannot be used as indicators for oxygen contents of the Precambrian atmosphere. A secular trend has been established in the Precambrian iron-formations, whereby the oldest iron-formations display only slight fractionation of light REE relative to heavy REE, and this fractionas tion increases with decreasing age of the iron-formations.