Mantle Metasomatism and the Kimberlite-Lamprophyre Association: Evidence from an Eclogite Nodule from Roberts Victor Mine, South Africa

Abstract

An eclogite xenolith from the Roberts Victor kimberlite mine in South Africa contains evidence of permeation by a metasomatizing fluid rich in , and possibly FeO*. The metasomatic event severely affected the omphacite within the eclogite, altering its chemistry and leading to partial melting; the garnet was little affected. The combination of partial melt from the pyroxene and the metasomatizing fluid produced a bulk fluid composition that in places crystallized to a lamprophyric material containing microphenocrysts of phlogopite, pargasite, clinopyroxene, analcime, and green spinel in a very fine-grained matrix of 12-14% total alkali oxides and probably alkali feldspar. The secondary material is comparable to that from other eclogites from the Roberts Victor mine. It appears that at least some lamprophyres are derived from the mantle in association with kimberlites.