Rare Earth Element Geochemistry of the Munnar Carbonatite, Central Kerala

Abstract

Rare earth element abundance in carbonatite associated with the 740 Ma old alkaline complex of Munnar is reported. High values of La (up to 232 ppm) and Ce (up to 261 ppm), moderate Sm (upto 11 ppm), with low Tb (up to 1.1 ppm), Yb (upto 3 ppm) and Lu (up to 0.6 ppm) are observed, comparable with similar values for carbonatites from other regions. The chondrite normalised patterns exhibit a steep slope from LREE to HREE, with (La/Lu)_cn ranging upto 191. A genetic model involving CO₂ degassing from the mantIe and ion exchange reactions with deep crustal rocks is envisaged, with the carbonatites probably representing a late immiscible fraction that separated from a polymerized alkali silicate melt. REE geochemistry of the carbonatite substantiates the view of a Late Precambrian alkaline magmatic regime in this part of the Indian Shield.