Steven B Shirey

 
 

Superdeep diamonds are derived from below the continental lithosphere and most likely from the transition zone (670km deep) or the top of the lower mantle. A full understanding of their origins and the compositions of the high pressure mineral phases has potential to revolutionize our understanding of deep mantle circulation.

These sulfides will be analyzed by our team for Re-Os to determine both the age of the diamond, the isotopic composition of the Os and by inference the source of the diamond forming fluids. Another goal will be to understand the role of carbonate melt in diamond and inclusion petrogenesis.  SIMS analysis of volatiles will provide evidence for whether transition zone inclusion minerals are higher in water to understand what constraints are there on the composition and amount of water delivered to the transition zone. The ultimate origin of the carbon in the diamond is of great importance to the igneous carbon cycle.  Whether biogenic carbon, subducted into the mantle, really contributes to diamond formation at these depths can perhaps be answered with  C and where possible, N isotopic analyses.

Typical high pressure phases from superdeep diamonds. Pictures drom Harte, B., Mineralogical Magazine (2010) vol. 74 (2) pp. 189

A new collaboration on superdeep diamonds

Conceptual petrologic model for the diamonds from the Collier 4 kimberlite based on their slicate inclusion compositions and diamond carbon isotopic compositions from Bulanova, G.P. et al.. Contributions to Mineralogy and Petrology, 2010. XXX: p. DOI 10.1007/s00410-010-0490-6.].

Relevant publication