Diamond formation and source carbonation: mineral associations in diamonds from Namibia

Leost, I., Stachel, T., Brey, G.P., Harris, J.W. and Ryabchikov, I.D. (2003) Diamond formation and source carbonation: mineral associations in diamonds from Namibia. Contributions to Mineralogy and Petrology, 145, pp. 15-24. (doi: 10.1007/s00410-003-0442-5)

Abstract

Mineral inclusions in diamonds from Namibia document a range of mantle sources, including eclogitic, websteritic and peridotitic parageneses. Based on unusual textural features a group of inclusions showing websteritic, peridotitic and transitional chemical features is assigned to an 'undetermined suite' (12% of the studied diamonds). The mutual characteristic of this group is the occurrence of lamellar intergrowths of clinopyroxene and orthopyroxene. In addition, the 'undetermined suite' is associated with a number of uncommon phases: in one diamond MgCO3 is enclosed by clinopyroxene. Other minerals that form touching inclusions with the pyroxene lamellae are (1) a SiO2 phase observed in three diamonds, together with CaCO3 in one of them, (2) phlogopite and a Cr-rich 'titanate' (probably lindsleyite). The inclusions document a metamorphic path of decreasing pressures and temperatures after entrapment in diamond. First, homogeneous low-Ca clinopyroxenes were entrapped at high temperatures. They subsequently exsolved orthopyroxene and probably also SiO2 (coesite) on cooling along a P,T trajectory that did not allow garnet to be exsolved as well. Phlogopite, carbonates and LIMA phases are the result of overprint of a peridotitic source rock by a carbon-rich agent. The resulting unusual, olivine-free mineral association and the host diamonds are interpreted as products of extensive carbonation of the peridotite.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Harris, Dr Jeff
• Authors: Leost, I., Stachel, T., Brey, G.P., Harris, J.W., and Ryabchikov, I.D.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Contributions to Mineralogy and Petrology
• Journal Abbr.: Contrib Mineral Petr
• Publisher: Springer-Verlag
• ISSN: 0010-7999
• ISSN (Online): 1432-0967