Sodium-rich metasomatism in the upper mantle: Implications of experiments on the pyrolite-Na2O-rich fluid system at 950°C, 20 kbar

K, Na and Ca are the most common elements transported during mantle metasomatism and result in formation of phlogopite (K), amphibole (Na) and clinopyroxene (Ca) by various reactions. This review presents models for this type of metasomatism based on experiments on the pyrolite-K2CO3-H20, pyrolite-Na2CO3-H20 systems and on the pyrolite-CaCO3 system. The addition of K 2 CO3 and Na 2 CO3 lowers the iiquidus of pyrolite providing a low temperature, alkali-rich hydrous melt which may ascend and metasomatize overlying mantle regions. Several reactions are proposed for the formation of phlogopite and amphibole (pargasite-edenite) in these systems. The compositions of amphiboles correspond to those found in metasomatized mantle xenoliths. In contrast, Ca-metasomatism is considered to be mainly an anhydrous process in which orthopyroxene and carbonate react to produce clinopyroxene, olivine and CO2. High pressure liquids in this model system are of carbonatitic composition and this low viscosity melt can ascend converting harzburgite mantle assemblages to olivine-rich wehdite.Based on an inverse experimental approach, moderately high degrees of partial melting of a model metasomatized alkali clinopyroxenite xenolith yield liquids at 30 kb which are very comparable in composition to the lavas enclosing such types of xenoliths.Experimental modelling of mantle metasomatism produces assemblages which are in good agreement with the mineral assemblages and textural relationships found in metasomatized mantle xenoliths from areas such as West Eifel and South-West Uganda.

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Origin of phlogopite-orthopyroxene inclusions in chromites from the Merensky Reef of the Bushveld Complex, South Africa

Ripley

Sarkar

et al. 2005

Contrib Mineral Petrol

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Sodium-rich metasomatism in the upper mantle: Implications of experiments on the pyrolite-Na2O-rich fluid system at 950°C, 20 kbar

Cited by 20 publications

References 33 publications

Recent Developments in Igneous Petrology

Recent Developments in Igneous Petrology

Patent mantle-metasomatism: Inferences based on experimental studies

Origin of phlogopite-orthopyroxene inclusions in chromites from the Merensky Reef of the Bushveld Complex, South Africa

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