EGU24-6583, updated on 08 Mar 2024
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Petrology and geochemistry of a Cratonic mantle-derived Eclogite Xenolith Suite from the Balmoral Kimberlite, Kimberley Region, South Africa

Jiten Pattnaik1,2 and Fanus Viljoen2
Jiten Pattnaik and Fanus Viljoen
  • 1Department of Earth and Environmental Sciences, Ben Gurion University of the Negev, Be'er Sheva, Israel (
  • 2Department of Geology, University of Johannesburg, Auckland Park Kingsway Campus, Johannesburg, South Africa

This study presents the first comprehensive investigation into the petrography, major and trace element mineral chemistry of a mantle-derived eclogite xenolith suite from the Balmoral kimberlite. Most of the eclogite xenoliths from the Balmoral kimberlite pipe are bimineralic (garnet and clinopyroxene) rocks with a substantial number of corundum-bearing xenoliths also recognised. The bimineralic eclogites are classified into low MgO (<15 wt% MgO) and high MgO (<15 wt% MgO) varieties. Mica with average modal abundances ≤10 vol% is observed as an accessory phase in bimineralic xenoliths. Modal abundances of corundum in corundum-bearing samples range between 1 and 6 vol%. Textures are ambiguous in Balmoral eclogites, while the chemical criteria of McCandless and Gurney (1989) place all of them into Group II. The temperature range of Balmoral eclogites (at an assumed pressure of 50 kbar; Ellis and Green, 1979) is between 1046 and 1311 °C. The low-MgO bimineralic eclogites are characterised by relatively higher temperatures than the high-MgO variety. Corundum-bearing eclogites have the highest equilibration temperatures. Based on calculated temperatures, corundum-bearing eclogites have the highest inferred pressures of equilibration with the high-MgO eclogite variety having the lowest. The reconstructed Balmoral major element bulk compositions are characterised by variations in MgO, CaO and Al2O3 contents, with less variation in FeO contents. Reconstructed major element bulk compositions from bimineralic eclogites coincide with those of tholeiitic basalts, and to a lesser extent, basalts from mid-ocean ridges and oceanic gabbros. Corundum-bearing eclogites are similar to oceanic gabbros in general. The REE pattern of bulk eclogite commonly show humped-shaped REEN patterns. High MgO eclogites have a slight enrichment in the LREEN pattern while low MgO eclogites have enrichment in HREEN patterns. These REEN patterns are broadly comparable to those of oceanic gabbro and MORB. The protolith for these Balmoral eclogite xenoliths is thought to be a once composite oceanic crustal section which underwent partial melting during subduction and/or dehydration and, subsequent metasomatic re-enrichment in incompatible trace elements.

How to cite: Pattnaik, J. and Viljoen, F.: Petrology and geochemistry of a Cratonic mantle-derived Eclogite Xenolith Suite from the Balmoral Kimberlite, Kimberley Region, South Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6583,, 2024.

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