グリーンストン帯に"原始マントル"をたずねて : 西オーストラリア巡検記

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From 4 to 13 August '77, the pre-Congress excursion (40 A) of the 25th International Geological Congress was made in the route from Perth to Kalgoorlie-Norseman across the major Archaean Yilgarn Block. The excursion, at first, examined Archaean granulites, charnockites, gneisses and post-kinematic granites in the Southwestern Province in the Block. However, the greater parts of the progamm were spent for the study in the typical-greenstone belt sequences consisting of, in the ascending order, ultramafic and mafic volcanic members, felsic volcanic and pyroclastic complex, and clastic metasediments including polymict conglomerates in the Eastern Goldfields Province. Above all our greatest matter of interest was the famous "spinifex" textured ultramafic lava, komatiite, which may have been considered to be the supracrustal equivalent of the primodial mantle rock. The specimens clearly showing the quench texture were collected from the Serpentine Bay of the Hannans Lake, 15km south of Kalgoorlie, and were thinsectioned and photographed (Plate II). The chemical affinity of komatiites to the assumed primodial mantle rocks including 'pyrolite' model by RINGWOOD (1966) as well as GORAI's models (1973) calculated from carbonaceous chondrites is apparent as illustrated in Fig. 4. Besides a granitoid pebble from the Kurrawang conglomerate belonging to the uppermost sequence of the Greenstone belt was examined microscopically (Fig. 5). It is a striking fact that the pebble is much alike to the granitoid pebbles commonly found in the Permian Usuginu conglomerates (KANO, 1973) in Japan especially in its trondhjemitic composition. Lastly we are very much grateful to Drs. R. A. BINNS and I. R. WILLIAMS, the leaders, for their kind arrangement and guidance through the excursion.
地学団体研究会の論文
1977-09-25

グリーンストン帯に"原始マントル"をたずねて : 西オーストラリア巡検記

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