Abstract
Peridotites from a ultramafic intrusive in the Sanbagawa metamorphic belt of the Kanto mountains have high iron contents (about 16 weight percent as FeO), which are also reflected on the chemical compositions of constitutent olivines. This iron-rich character may be common in many ultramafic intrusives in the Sanbagawa belt. It is proposed that ultramafic intrusives can be divided into two types; the one is a representative of the upper mantle materials brought in the solid state, and the other is derived from ultramafic magma which is formed by the melting of the mantle materials. Each of the two types of ultramafic intrusives probably has a considerable range in iron content. At present, however, there is no general rule to distinguish these two types from chemistry of rocks and their rock-forming minerals. Some diversity of ultramafic intrusives in their chemical nature among different petrographic provinces is discussed.
