Helium, argon and carbon isotopic compositions in diamonds and their implications in mantle evolution

Abstract

Helium and argon isotopic data of diamonds suggest that the mantle where diamonds crystallised has remained almost a closed system for most of the Earth's history. The 3 He/4 He — 3 He evolution diagram implies that at least two diamonds studied are nearly as old as the Earth. Carbon isotopic compositions of the stones studied varied from -3.3 to -29.7 %o, while older diamonds show less deviation from the generally considered average δ13 C for diamonds. © 1985, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.