- journal_title：Geology
- Contributor：Ralf Tappert ; Thomas Stachel ; Jeff W. Harris ; Karlis Muehlenbachs ; Thomas Ludwig ; Gerhard P. Brey
- Publisher：Geological Society of America
- Date：2005-
- Format：text/html
- Language：en
- Identifier：10.1130/G21637.1
- journal_abbrev：Geology
- issn：0091-7613
- volume：33
- issue：7
- firstpage：565
Inclusions of majoritic garnet in diamonds from the Jagersfontein kimberlite formed at unusually great depths of ∼250 to >500 km in the asthenosphere and transition zone. The original host rocks were derived from a much shallower, basaltic (eclogitic) source. The presence of negative Eu anomalies in all majoritic garnets requires a crustal origin, thereby linking these very deep diamond sources to subducting oceanic crust. The carbon isotope values (δ13C) of the host diamonds fall within a narrow range at ∼−20‰, which is fundamentally different from the broad range (−24‰ to −2‰) and bimodal distribution of carbon isotopes of Jagersfontein diamonds that formed in the shallower lithosphere. This indicates that majoritic garnet-bearing diamonds at Jagersfontein inherited their light carbon isotopic composition directly from organic matter contained in a subducting slab. These diamonds were likely formed by direct conversion from graphite, well within the diamond stability field.