東中国および近畿地域の後期中生代〜古第三紀花こう岩類中のＦｅ‐Ｔｉ酸化鉱物

Abstract

Petrographic descriptions and electron microprobe analyses of Fe-Ti oxides are presented for 182 specimens from the late Mesozoic to early Tertiary granitic rocks in eastern Chugoku and Kinki districts of Southwest Japan. Fe-Ti oxides in the granitoids of the Inbi and Namariyama Intrusives are dominated by magnetite, whereas the Ryoke and Hiroshima Intrusives are occupied by ilmenite with some exceptions, i.e., gabbroic rocks of the Ryoke Intrusives are considered to belong to the magnetite series, and many granitic rocks from northern part of the Hiroshima Intrusives are occupied by the magnetite series. The modal content of Fe-Ti oxides is lowest in the Ryoke Intrusives, while highest in the Inbi Intrusives. The most evident difference in the ilmenite chemistry among the five Intrusives is the content of hematite molecule which is highest in the granites of the Namariyama Intrusives, while lowest in those of the Ryoke Intrusives. The amount of Mn in ilmenite tends to increase as the host rock SiO2 content increases. The ulvöspinel content of magnetite is distinctly lower in the Ryoke and Inbi Intrusives than in the Hiroshima and Namariyama Intrusives.