Stability of Hornblende and a Model for the Low Velocity Zone

Abstract

There have been many discussions, but few experiments, related to the occurrence and stability of hornblende in the upper mantle. We have obtained evidence relating to hornblende stability in experiments which extend the phase relationships for calc–alkaline rock series (gabbro–tonalite–granite) to upper mantle pressures, in the presence of excess water, and these experiments have a bearing on the proposals that some intermediate rocks are derived by melting in the upper mantle. They complement other experiments dealing with dry rocks, or with rocks in the presence of water with P_(H_2O) < P_(load) (ref. 4).

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