Rare-earth element geochemistry of banded iron formations and associated amphibolite from the Sargur belts, south India

Abstract

Major and rare-earth elements (REE) of banded iron formations (BIFs) and associated amphibolite from the Sargur belts, the oldest schist belts in the Dharwar craton, were determined by X-ray fluorescence and inductively coupled plasma mass spectrometry (ICP-MS). The chondrite-normalized REE patterns of BIFs are light REE-enriched with a striking positive Eu anomaly, resembling those of modern hydrothermal solutions from the mid-oceanic ridge. Amphibolite is flat and chondritic in the REE plot. The $\text{Al}{}_2\text{O}{}_3\text{TiO}{}_2$ ratio of BIFs is about the same as that of amphibolite and is different from that of terrigenous clastics. These facts suggest that the BIFs were of hydrothermal origin and had a genetic relation to amphibolite, which may have originated from the Archaean mid-oceanic ridge basalt. Subtle negative or no Ce anomaly of BIFs indicates that contemporary seawater was less oxic than today.