高圧下におけるマントルカンラン岩の部分融解と玄武岩マグマの成因 : ダイアモンド粒を用いた融解実験の応用
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Melting experiments on mantle peridotites have been carried out at pressures between 5 and 30 kbar using diamond aggregates method as part of the Scientific Research on Priority Areas "Role of magmas in the evolution of the Earth". The compositional variations of partial melts were determined as function of pressure, temperature and melt fraction for two spinel lherzolites (HK 66 and KLB 1) and a garnet lherzolite (PHN 1611). In the melting of lherzolite PHN 1611, there is a sharp break in the temperature-melt fraction curve at about 20% melt fraction at pressures lower than 15 kbar, indicating that melting proceeds to about 20% with a small increase of temperature at relatively shallow levels in the manlte. The compositions of melts formed by batch partial melting of these lherzolites at about 10 kbar are close to those of primitive MORB; however, the CaO contents are distinclty lower and fractionation of small amounts of olivine is necessary to produce primitive MORB magmas. It is also suggested that if Mg# of the source peridotite is less than 89, primitive MORB magmas can be formed at about 10 kbar either by partial melting of or reequilibration with surrounding peridotites followed by small degrees of olivine fractionation, whereas if the Mg# is greater than 90, MORB mgmas can only be formed by larger degrees of olivine fractionation of magmas generated at pressures greater than 20 kbar. Stepwise fractional melting of a lherzolite was also performed along an adiabat in the pressure range from 20 to 5kbar. The results indicate that the total amount of melt produced by stepwise fractional melting is significantly smaller than that formed by batch melting for an identical adiabat, suggesting that a higher mantle potential temperature is needed to produce the oceanic crust with the same thickness if fractional melting dominates beneath the mid-oceanic ridges. Nearly perfect fractional melting of a mantle peridotite was also carried out using a larger amount of diamond aggregates to understand compositional changes of residual peridotite and melts by such fractional melting.
- 特定非営利活動法人日本火山学会の論文
- 1997-04-25
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関連論文
- マントルの融解とマグマの成因--実験室で中央海嶺玄武岩マグマを再現する
- 高圧下におけるマントルカンラン岩の部分融解と玄武岩マグマの成因 : ダイアモンド粒を用いた融解実験の応用
- わが国の大学における惑星科学の将来