Dissolution of pyroxene in garnet at ultrahigh pressures produces supersilicie garnet with the coupled substitutions of Si^Ⅵ + M^Ⅵ= A^Ⅵ + A^Ⅵ and Si^Ⅵ + Na^Ⅷ=A^Ⅵ + M^Ⅷ,which are enhanced by rising pressure. Th...Dissolution of pyroxene in garnet at ultrahigh pressures produces supersilicie garnet with the coupled substitutions of Si^Ⅵ + M^Ⅵ= A^Ⅵ + A^Ⅵ and Si^Ⅵ + Na^Ⅷ=A^Ⅵ + M^Ⅷ,which are enhanced by rising pressure. The supersilicic garnet and exsolution of pyroxene, rutile, apatite and quartz in garnet during decompression were found in natural rocks,pointing to the importance in studying mantle-derived rocks and ultrahigh pressure metamorphism related to plate deep subduction. Ti, P, K and H2O enters garnet via the substitutions of Ti = Si, P^Ⅵ+Na^Ⅷ = Si^Ⅵ+ CaⅧ, Si^Ⅵ+K^Ⅷ = AI^Ⅵ+M^Ⅷ, and [(OH)4]^4- = [SiO4]^4- or [4H]^4+ = Si^4+ respectively. The possible entering of Eskola pyroxene component M0.5AlSi2O6 in clinopyroxene, together with the common pyroxene component M2Si2O6, into garnet can lead to the presence of the substitution of Si^Ⅵ + 0.5□^Ⅷ= A^Ⅵ + 0.5M^Ⅷ in garnet structure, which plays a key role in the exsolution of rntile, apatite and quartz in garnet. Two new breakdown reactions are thus proposed on the basis of the new coupled substitution, which can be regarded as a theoretical model for the exsolntion of the 3 minerals in garnet. The real exsolution may be a combination of several breakdown reactions.展开更多
文摘Dissolution of pyroxene in garnet at ultrahigh pressures produces supersilicie garnet with the coupled substitutions of Si^Ⅵ + M^Ⅵ= A^Ⅵ + A^Ⅵ and Si^Ⅵ + Na^Ⅷ=A^Ⅵ + M^Ⅷ,which are enhanced by rising pressure. The supersilicic garnet and exsolution of pyroxene, rutile, apatite and quartz in garnet during decompression were found in natural rocks,pointing to the importance in studying mantle-derived rocks and ultrahigh pressure metamorphism related to plate deep subduction. Ti, P, K and H2O enters garnet via the substitutions of Ti = Si, P^Ⅵ+Na^Ⅷ = Si^Ⅵ+ CaⅧ, Si^Ⅵ+K^Ⅷ = AI^Ⅵ+M^Ⅷ, and [(OH)4]^4- = [SiO4]^4- or [4H]^4+ = Si^4+ respectively. The possible entering of Eskola pyroxene component M0.5AlSi2O6 in clinopyroxene, together with the common pyroxene component M2Si2O6, into garnet can lead to the presence of the substitution of Si^Ⅵ + 0.5□^Ⅷ= A^Ⅵ + 0.5M^Ⅷ in garnet structure, which plays a key role in the exsolution of rntile, apatite and quartz in garnet. Two new breakdown reactions are thus proposed on the basis of the new coupled substitution, which can be regarded as a theoretical model for the exsolntion of the 3 minerals in garnet. The real exsolution may be a combination of several breakdown reactions.
