The pyroxene-garnet transformation in the earth's mantle

摘要: An investigation of the solid solubility pyroxenes in garnet structures pressure range 0–250 kb and at about 900°C, is described. At 100 kb, enstatite pyrope increases suddenly, resulting formation a composition Mg3(AlMg0.5Si0.5)Si3O12. Analogous relationships are found to exist between calcium-rich garnets. The results imply occurrence type pyroxene-garnet transformation, which garnets characterized by partial 6-fold coordination silicon. transformation accompanied density increase 10%. A variety evidence strongly indicates that these new thermodynamically stable. has also been demonstrated typical eclogite, which, 127 crystallizes an assemblage 95% 5% pyroxene, with mean 3.75 g/cm3. The may be important earth's mantle where it would occur depth 350 km, thus marking beginning transition zone. speculative model presented whereby garnet-pyroxene blocks eclogite sinking through provides mechanism for deep-focus earthquakes.