Multiple Growth Episodes or Prolonged Formation of Diamonds? Inferences from Infrared Absorption Data

Abstract

The infrared characteristics of 21 sulphide inclusion-bearing diamonds from Finsch Mine, 1 sulphide inclusion-bearing diamond from Udachnaya and 18 silicate inclusion-bearing diamonds from Premier were examined and modelled to investigate the complexity of diamond genesis. Internal heterogeneities in N-abundance and aggregation state within individual diamonds at Finsch range from 5 to 336 at.ppm and 2--60 % of B-defects, respectively. The Udachnaya diamond 3648 displays a steep decrease from the core to the rim of N-abundance from 482 to 10 at.ppm. Nitrogen aggregation state describes the same trend with value of 86 %B in the core down to 14 %B in the rim. Internal variations in N-abundance and aggregation state within diamonds from Premier are 93--654 at.ppm and of 7--62 %B, respectively. These variations reflect more likely multiple growth episodes of diamond at distinct ages rather than steady changes in temperature conditions during prolonged diamond growth. Modelling of infrared characteristics indicates that some diamonds have experienced distinct growth episodes over extended time periods with estimates up to 2,387 {\textpm} 931 Ma. There are implications for dating studies, indicating that isochron ages may be flawed as there appears to be no single formation age for a single diamond. N-abundance and aggregation state mapping by FTIR provide the opportunity to constrain diamond growth history for selecting diamonds for dating.