Geophysical Evidence of the Olivine-spinel Transition Hypothesis in the Earth's Mantle

Abstract

Assuming olivine-spinel transition of Mg2SiO4 at the depth of 400 km in the earth, the difference in free energy between sub-stances composing the upper and lower mantle is estimated. The difference obtained here is approximately the same as that deduced by Ringwood from experimental results. The influence of the transition on the electrical conductivity is also studied. The steep increase of the electrical conductivity at the depth as inferred from the studies of geomagnetic variations seems to be justified by the transition hypothesis.最近Ringwoodは,Ni2GeO4-Mg2SiO4固溶体を調べ,地球中間層内に於てMg2Si04がオリビンスピネル転移を起すことが可能であることを推論した.彼の研究によれば,転移に伴なう自由エネルギーの変化は1,500℃に於て70,000±10,000Joule/mole,密度変化は約11%,スピネルMg2SiO4の格子常数は7.99Åとなる