23. A Model for the Upper MantZe, with Special Reference to the Origin of Rock Magma
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A sharp increase of Poisson's ratio in the upper mantle has beenattributed to the large increase of actual temperature. Possible temperature distribution was calculated on assuming that the upper mantle is mainly composed of eclogite. In the subcontinental upper mantle, actual temperature is believed to be close to the melting point of eclogite between a depth of 120 and 250 km which coincides with the depth of the low velocity zone. The author proposed that the low velocity zone is starred with oblate spheroidal molten pockets. The elastic ratio at normal temperature and pressure, 0oo, has been calculated for the upper mantle, in which the elastic ratio increases from 40(km/s)2 to 50(km/s)2 implying a gradual variation of constituent mineral assemblage with depth. From the considerations of mean atomic weight, density, velocity as well as elastic ratio, the author suggests that the upper mantle is mainly composed of olivine, pyroxene, garnet(pyrope) or even jadeite. Hence, eclogite or garnet peridotite will be the most favourable material in the upper mantle, the basaltic magma being the product of partial melting of these materials originating from the low velocity zone.Upper mantleにおけるPoisson比の増加率から,eclogiteのmelting curveをもとにして温度分布を計算しなおした.φに圧力と温度の補正を行つて,各深さについて常温常圧における値を計算し,程々の珪酸塩および酸化物のそれと比較した.現に縦波速度,平均原子量などを考慮して次の結論を得た.1) elogiteモデルによる温度は深さ120-220kmでecloeriteの融点に近接する.
- 1964-12-25
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