Ultra-high pressure garnet inclusions in Monastery diamonds

trace element abundance patterns and conditions of origin

R. O. Moore, J. J. Gurney, W. L. Griffin, N. Shimizu

Research output: Contribution to journalArticle

76 Citations (Scopus)

Abstract

Eclogitic diamonds predominate over peridotitic diamonds at Monastery in the approximate ratio 9:1. Two distinct populations of eclogitic garnets are present: a small number (Group A) have compositions similar to those described from diamonds worldwide, while the majority (Group B) host variable amounts of pyroxene in solid solution. Formation pressures for Group B garnets are inferred to range from 68 to 154 kbar (200 to 480 km). The geochemistry of these garnets is discussed and it is concluded that diamonds containing Group B garnet inclusions probably formed in the asthenosphere. It is speculated that they may have crystallised from partial melts within a rising asthenospheric diapir that has underplated onto the lithosphere prior to kimberlite eruption. Alternatively, they may have been sampled by a hot-spot related kimberlite from pre-existing pockets of diamondiferous eclogite over the depth interval indicated by the inclusions (480-150 km). -after Authors

Original languageEnglish
Pages (from-to)213-230
Number of pages18
JournalEuropean Journal of Mineralogy
Volume3
Issue number2
Publication statusPublished - 1991
Externally publishedYes

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