Title: The chemistry of clinopyroxenes and garnets of eclogite and peridotite xenoliths from the Roberts Victor mine, South Africa
Abstract: The eclogite xenoliths from the Roberts Victor pipe may be divided into two groups. The first group consists of coarse grained, subhedral to rounded garnets in a matrix of anhedral to interstitial clinopyroxene, and they may be subdivided on the basis of their mineralogy into kyanite and rutile-bearing eclogites. The second group consists of irregular, anhedral garnet and clinopyroxene with a tightly interlocking fabric. The garnets of the first group have greater contents of pyrope, and, for equivalent diopside: jadeite ratios, the clinopyroxenes have a greater enstatite-ferrosilite content than those of the second group. In addition, both the garnets and clinopyroxenes of the first group have greater K2O and Cr2O3 and lower CaO contents than those of the second group. FeO and MnO are higher in the clinopyroxenes, and MgO, NiO, Li2O and Na2O higher in the garnets, of the first than the second group. Both groups appear to have formed at similar pressures, but distribution coefficients indicate equilibrium over a range of temperatures. Experimental data indicate that at pressures in the eclogite stability field, mafic liquids that precipitate crystals of eclogite mineralogy can also recrystallize to the same bimineralic assemblage. It is interpreted that the second group of eclogites are the sets of liquids, and that the first group of eclogites are the sets of crystals that have formed as the result of fractional crystallization in a high pressure magma chamber.
Publication Year: 1970
Publication Date: 1970-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 211
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