Experimental study of spinel-garnet phase transition in upper mantle and its significance
Experimental study of spinel-garnet phase transition was carried out using natural mineral and rock specimens from xenolith of mantle rocks in Cenozoic basalt as starting materials. From the result it was found that the condition of spinel Iherzolite-garnet Ihenolite phase transition (T = 1 100°C andP = 1.8–2.0 GPa) is consistent with theP-T equilibrium condition of the five-phase assemblage spinel/garnet Iherzolite in eastern China, suggesting that there may exist a spinel-garnet Iherzolite phase transition zone with the thickness of a few km to several ten km at the depth of 55–70 km in the continental upper mantle of eastern China. The depth of phase transition from spinel pyroxenite to garnet pyroxenite is found to be less than 55 km. Experiment results also show that water promotes metasomatism on one hand but suppresses phase transition on the other. Zoning of mineral composition was also discussed.
Keywordsspinel-garnet phase transition high temperature and high pressure experiment upper mantle of eastern China phase transition zone
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