Diamonds from Jagersfontein (South Africa): messengers from the sublithospheric mantle |
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| Authors: | Email author" target="_blank">Ralf?TappertEmail author Thomas?Stachel Jeff?W?Harris Karlis?Muehlenbachs Thomas?Ludwig Gerhard?P?Brey |
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| Institution: | 1.Department of Earth and Atmospheric Sciences,University of Alberta,Edmonton,Canada;2.Division of Earth Sciences,University of Glasgow,Glasgow,UK;3.Institut für Mineralogie,Ruprecht Karls Universit?t,Heidelberg,Germany;4.Institut für Mineralogie,J.W. Goethe Universit?t,Frankfurt,Germany |
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| 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. |
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