| Research Abstract |
The aims of this project are to determine the phase equilibrium of a kimberlite composition, which is thought to be close to a primary kimberlite magma composition, and to examine chemical and stable isotopic characteristics of several kimberlites occurring in North American. The results of this study are summarized as following.
1. High pressure experiments (10-40 kb,100-1500 C) on an aphanitic kimberlite composition from the Wesselton Mine, South Africa, indicate that this kimberlite composition could be equilibrated with a mineral assemblage of olivine, clinopyroxene, spinel, calcite, and perovskite at upper mantle conditions. Monticellite occurs at relatively lower pressures while clinopyroxene stability is limited at higher pressures. The untipathy of monticellite and clinopyoxene in the experiments may be used to explain the incompatibility of these phases in kimberlites. Kimberlite magmas could be partial melts derived calcite-bearing upper mantle material of deverse mineralogy.
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2. Micaceous ultramafic dikes of Jurassic age from Picton and Varty Lake, Ontario, Canada, consist mineralogically of olivine-phlogopite-calcite-serpentine-spinel. The dikes exhibit pronounced enrichments of light rare earth elements combined relatively high CO2. Calcite in the dikes is a primary magmatic phases, from textural relations and C-isotopic compositions. The dikes are hypabyssal facies kimberlite. 3. Barium-rich phlogopite occurs in a mantle derived xenolith incorporated into the Upper Canada Mine Kimberlite, Ontario. The phlogopite is characterized by high BaO (up to 4.3 wt.%) with a high Mg, Na, and low Ti. The chemical characteristics of the phlogopite suggest that the mica has been formed by mantle metasomatism involving Ba- and alkali-rich, Ti-poor hydrous fluids. A range of Ba/K in mantle derived phlogopites is comparable with that in the continental alkali volcanic rocks and in the mantle derived xenoliths, suggesting that phlogopite may be a principal reservoir for Ba in the upper mantle. Less
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