REVIEW OF PYROXENE RELATIONS IN TERRESTRIAL ROCKS IN THE LIGHT OF RECENT EXPERIMENTAL WORKS

抄録

Recent experimental works have shown that clinopyroxene of MgSiO₃-FeSiO₃ series has a stability field at high pressures and at temperatures lower than several hundred degrees. But review of the data on natural pyroxenes suggests that pigeonite crystallizes from magmas within its own stability field at temperatures higher than that of orthopyroxene stability. There are also some experimental evidences in favor of the existence of a form of clinopyroxene stable at high temperatures. Crystallization of orthopyroxene and pigeonite from basalt magmas is discussed on the basis of hypothetical phase diagrams of MgSiO₃-FeSiO₃ system and also of (Mg, Fe) SiO₃-Ca (Mg, Fe) Si₂O₆ system. No drastic change is needed for the existing theories on the crystallization of pyroxenes from magmas. It is pointed out that an existence of the stability field of Mg-Fe clinopyroxene at low pressures and low temperatures raises many serious questions which are difficult to answer.