Petrology of Hayachine ultramafic complex in contact aureole, NE Japan I

primary and metamorphic minerals

Abstract

Hayachine ultramafic complex has been suffered a contact metamorphism. The rocks mainly consist of metamorphic olivine, clinopyroxene, orthopyroxene, serpentine, talc, tremolite, anthophyllite and magnetite. Relict minerals were distinguished from metamorphic minerals. In the northern area of the low metamorphic grade, relict olivine as well as clinopyroxene were found. Chromite is a probable relict mineral appearing throughout the complex. Metamorphic orthopyroxene is found in the area of the highest metamorphic grade, and is enstatite depleted in diopside component. The relict olivines are Fo_89.5-93 and enriched in NiO, whereas the metamorphic olivines in the low grade (up to Fo_96.5) are depleted in NiO. In the high grade area in the south of the complex, the metamorphic olivine (Fo_90-93.5) are enriched in NiO as much as the relict olivine. The metamorphic diopside is extremely poor in Cr₂O₃ and Al₂O₃. The relict diopsides are more enriched in the both elements than the metamorphic ones, but they are less enriched in wollastonite component than the metamorphic ones.