Tectonics and Petrograpby of the East Ongul Islana, Lutzow-Holm Bukt, Antarctica
スポンサーリンク
概要
- 論文の詳細を見る
The East Ongul Island on the coast of the Lutzow-Holm Bukt, East Antarctica, was investigated from the tectonical and petrographical points of view. The rocks exposed in the island are petrographically classified into the following seven types : 1) Metabasites, 2) Pyroxene gneisses, 3) Hornblende gneisses, 4) Garnet gneisses, 5) Granites, 6) Feldspathic rocks, and 7) Pegmatites. It is verified that the unique structural feature of the island is represented by the isoclinal fold recumbent to the west with the frontal zone in which many small anticlinal as well as synclinal folds occur. The inner core of the main anticline is generally composed of the garnet gneisses with the pyroxene gneisses forming the outer mantle. The hornblende gneisses, which are distributed in front of the recumbent anticline, occur in the same horizon as the pyroxene gneiss, so the former may have been converted from the latter. This is also confirmed by the geological and petrographical observations. Besides, the hornblende gneiss zone coincides with the zone of granite and subsequent microcline pegmatite emplacement. The lineation of the rocks, represented by the undulating foliation, is defined to be a b-lineation parallel to the fold axis, but another lineation with the same character but perpendicular to the fold axis is also found. The fracture systems indicated by the pegmatite and joint patterns were analyzed by tectonic dating. The pegmatite intruded at the earlier folding stage, whereas the joint pattern was formed at the later upwarping stage. The gneisses and granites are classified mainly by the characteristic mafic minerals, and their modes of occurrence as well as the optical mineralogy are described. The optical data of the constituent minerals revealed that there is a tendency that the Fe/Mg ratio of the mafic minerals such as pyroxene, hornblende, biotite and garnet, may increase with acidity of the rocks, from the matabasites to the granites. The anorthite content of plagioclase is restricted within a rather narrow range between 22% and 35% when feldspar coexists with potash-feldspar, although that of plagioclase in metabasite and basic enderbitic pyroxene gneiss free from potash-feldspar ranges widely from 42% to 93%. The triclinicity of the potash-feldspar may become higher in the granite than the gneisses judging from the data of their 2V values. It is probable that the gneisses were formed originally under the condition of a granulite facies in the regional metamorphism. At the same time, the widespread developement of hornblende and biotite in the metabasites and gneisses suggests subsequent changes in temperature and pressure or the presence of water as well as changes in chemical composition which facilitated the mobilization and plastic deformation of the rocks. It is considered that two phases of metamorphism may be detected in the area; the granulite facies at an earlier phase and the amphibolite facies at a later phase. This has been suggested by the investigations not only in other regions of the East Antarctica but also in other Precambrian shields of the world.
- 国立極地研究所の論文
- 1964-12-00
著者
関連論文
- Mode of occurrence, bulk chemical compositions, and mineral textures of ultramafic rocks in the Lutzow-Holm Complex, East Antarctica
- Aluminum silicates in the Prince Olav and Soya Coasts, East Antarctica
- A review of the tectonic and metamorphic history of the region around Lutzow-Holmbunta, East Antarctica (abstract)
- Tectonics and Petrography of the East Ongul Island, Lutzow-Holm Bukt,Antarctica
- Geology and Petrograpby of the Yamato Sanmyaku, East Antarctica
- Petrographic Studies of Potash Feldspar from the Yamato Sanmyaku, EastAntarctica
- Tectonics and Petrograpby of the East Ongul Islana, Lutzow-Holm Bukt, Antarctica
- Tectonic significance of Lutzow-Holmbunka in Gondwanaland reconstruction (abstract)
- Geology and Petrography of the Yamato Sanmyaku, East Antarctica