An experimental study of hornblende stability and compositional variability in amphibolite.

Abstract

Compositional trends for amphibole in a rock of a single bulk composition were experimentally verified and the upper thermal stability of hornblende in a mid-ocean ridge olivine tholeiite, whose bulk composition is representative of many amphibolites, was experimentally calibrated. The chemical variability of hornblende, clinopyroxene, orthopyroxene, plagioclase, and Fe-Ti oxides relative to T, P, fO2, and the subsolidus phase equilibria of the olivine tholeiite are discussed in detail and applied to interpretation of the development of amphibolite and granulite facies. Tables showing results of hydrothermal experiments and electron microprobe analyses of smectite are appended.M.S.