岩石鉱物鉱床学会誌
Online ISSN : 1883-0765
Print ISSN : 0021-4825
ISSN-L : 0021-4825
79 巻, 5 号
選択された号の論文の3件中1~3を表示しています
  • 野外の産状と岩石学的性質
    小木曽 勝弥
    1984 年 79 巻 5 号 p. 187-199
    発行日: 1984/05/05
    公開日: 2008/08/07
    ジャーナル フリー
    The basic metamorphic rocks of the Miho area are divided into meta-diabase and gabbroic rocks. The meta-diabase, finer-grained basic rocks characterized by granoblastic texture, is widely distributed as small masses sporadically scattered in this area, and the gabbroic rocks are exposed in limited zone around Mts. Suisho-zan and Jo-yama. The gabbroic rocks can be classified petrographically into ten rock-types, cortlandite, allivalite, anorthositic gabbro, gabbroic anothosite, olivine bearing hornblende eucrite, hornblende eucrite, hornblende gabbro, quartz gabbro, olivine bearing pyroxene dolerite, and pyroxene dolerite. The last two rock-types are chilled facies of the gabbroic rocks. In the gabbroic rocks layered structure is recognized in the field. From the field and petrographical observations and the chemical characters of the constituent minerals, it is concluded that these gabbroic rocks have been formed through crystallization differentiation of basic magma and emplaced as a layered intrusion.
    Petrological characteristics of the cortlandites scattered throughout the Ryoke metamorphic belt were reviewed. There is some local variations and a difference between the cortlandites from the Chubu (especially in the north) and ones from the Kinki-Setouchi districts. The cortlandites from the Chubu district contain clinopyroxene and chromium-bearing spinel, but the cortlandites from the Kinki-Setouchi districts do not contain these minerals. Mg/(Fe+Mg) ratio of the constituent minerals and the An content in plagioclase of the cortlandites from the Chubu district are higher than those of Kinki-Setouchi districts.
  • 特に不透明鉱物について
    根建 心具, 大貫 仁, 吉田 武義, 田切 美智雄
    1984 年 79 巻 5 号 p. 200-213
    発行日: 1984/05/05
    公開日: 2008/08/07
    ジャーナル フリー
    An ultramafic-mafic plutonic complex at Mt. izuishi can be divided into the following three emplaced units.
    Unit I: Dunite, wehrlite and olivine clinopyroxenite (serpentinized).
    Unit II: Hornblende gabbro and clinopyroxene hornblende gabbro with or without orthopyroxene.
    Unit III: Hornblende gabbro.
    Unit IV: Biotite-hornblende diorite.
    Some small-scale iron ore deposits are embedded mainly in Unit I. Bulk chemical analyses are presented for twenty-one rocks and two iron ores (magnetitites).
    All the constituents of the complex have been thermally metamorphosed owing to the emplacement of Cretaceous granitic rocks, and therefore their original petrographic chracteristics are not well preserved. However, a most plausible explanation of the origin of the com-plex is a hypothesis of successive injections differentiating from a basaltic magma.
    Microprobe data are presented for olivines and oxide minerals in uitramafic rocks and ironores, and for oxide and sulfide minerals in mafic rocks. At the contact with the granitic mass the equilibrium temperature of contact metamorphism, based on the olivine-spinel geothermometer, can be assumed to be 650-700°C. At a distance from the contact, the compositions of coexisting magnetite and ilmentie in representative mafic rocks indicate consistently temperature and oxygen fugacity of about 550°C and 10-20 bars. The magnetite+ilmenite+pyrite+pyrrhotite and magnetite+ilmenite+pyrite assemblages in mafic rocks also give approximate values of fo2=10-19 and fs2=10-3 bars at 550°C for metamorphic conditions.
  • 山口 尚志
    1984 年 79 巻 5 号 p. 214-232
    発行日: 1984/05/05
    公開日: 2008/08/07
    ジャーナル フリー
    武尊火山において,マグマ溜りにおける結晶の晶出順は次のようである。液のシリカ量が 53.5 から 57%の間では,かんらん石,シソ輝石,普通輝石,斜長石,磁鉄鉱が共存する。シリカ量が 57% を越すとかんらん石は液と反応して消え,少なくともシリカ量 70% まで他の 4 種の鉱物が連続的に晶出する。
    計算による斜長石の晶出量にしめる割合と,斑晶モードにおける斜長石の割合の比較によって,多くの岩石において斜長石の濃縮が推定される。
    石基のシリカ量増加に伴ない,石基輝石は,普通輝石+ピジョン輝石→ピジョン輝石→ピジョン輝石+シソ輝石→シソ輝石と変化する。
    武尊火山マグマの分化経路は,日本の他のソレアイト質マグマのそれと比較して,ノルムディオプサイド量がやや少なく,石基シリカ量 65%以上で石基シソ輝石が出現する点が異なる。
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