Diamonds from Jagersfontein (South Africa)

messengers from the sublithospheric mantle

Ralf Tappert*, Thomas Stachel, Jeff W. Harris, Karlis Muehlenbachs, Thomas Ludwig, Gerhard P. Brey

*Corresponding author for this work

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

The diamond population from the Jagersfontein kimberlite is characterized by a high abundance of eclogitic, besides peridotitic and a small group of websteritic diamonds. The majority of inclusions indicate that the diamonds are formed in the subcratonic lithospheric mantle. Inclusions of the eclogitic paragenesis, which generally have a wide compositional range, include two groups of eclogitic garnets (high and low Ca) which are also distinct in their rare earth element composition. Within the eclogitic and websteritic suite, diamonds with inclusions of majoritic garnets were found, which provide evidence for their formation within the asthenosphere and transition zone. Unlike the lithospheric garnets all majoritic garnet inclusions show negative Eu-anomalies. A narrow range of isotopically light carbon compositions (δ13C -17 to -24 ‰) of the host diamonds suggests that diamond formation in the sublithospheric mantle is principally different to that in the lithosphere. Direct conversion from graphite in a subducting slab appears to be the main mechanism responsible for diamond formation in this part of the Earth's mantle beneath the Kaapvaal Craton. The peridotitic inclusion suite at Jagersfontein is similar to other diamond deposits on the Kaapvaal Craton and characterized by harzburgitic to low-Ca harzburgitic compositions.

Original languageEnglish
Pages (from-to)505-522
Number of pages18
JournalContributions to Mineralogy and Petrology
Volume150
Issue number5
DOIs
Publication statusPublished - Nov 2005
Externally publishedYes

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