Remobilization in the Cratonic Lithosphere Recorded in Polycrystalline Diamond
D. E. Jacob,1*
K. S. Viljoen,2
N. Grassineau,3
E. Jagoutz4
Polycrystalline diamonds (framesites) from the Venetia
kimberlite in South Africa contain silicate minerals whose isotopic and
trace element characteristics document remobilization of older carbon
and silicate components to form the framesites shortly before
kimberlite eruption. Chemical variations within the garnets correlate
with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can
be explained by the interaction of eclogites with a carbonatitic melt,
derived by remobilization of material that had been stored for a
considerable time in the lithosphere. These results indicate more
recent formation of diamonds from older materials within the cratonic
lithosphere.
1 Institut für Geologische
Wissenschaften, Universität Greifswald, F.-L. Jahnstrasse 17a,
D-17487 Greifswald, Germany.
2 DeBeers Geoscience
Center, Post Office Box 82232, Southdale 2135, South Africa.
3 Department of Geology, Royal Holloway University
of London, Egham, Surrey TW20 0EX, UK.
4 Max-Planck
Institut für Chemie, Saarstrasse 23, D-55122 Mainz, Germany.
*
To whom correspondence should be addressed.
