Zone Of Southwest Japan Research Articles

K-Ar ages of hornblendes from gabbroic rocks in Southwest Japan.

K-Ar age determinations have been carried out on 15 hornblendes from the Yakuno Basic Rocks and their affinities in the Inner Zone of Southwest Japan. Gabbroic rocks from the Yakuno Basic Rocks and those from the Sangun Metamorphic Terrane in eastern Chugoku gave ages ranging from 228 to 275 m.y.; more than half of them are concordant with the geologically estimated age of the rocks. Remaining older ages may indicate either the time of plutonism in Early Permian, which might have been contemporaneous and comagmatic with the basic volcanic activity in the same areas, or the existence of inherited argon in hornblendes. Ages of gabbroic rocks from the Sangun Metamorphic Terrane in northern Kyushu are 296-372m.y., all older than those from eastern Chugoku. Hornblendes from gabbroic rocks in the Nagasaki Metamorphic Terrane gave still older ages of 449-472m.y., suggesting that these rocks may be a part of old basement rocks in the Japanese Islands. Graphical presentation of argon and potassium data indicates that most of the hornblende samples contain no significant amount of excess argon.

Discovery of kyanite from epidote-amphibolite in the Oeyama ultramafic mass,inner zone of southwest Japan

Discovery of kyanite from epidote-amphibolite in the Oeyama ultramafic mass,inner zone of southwest Japan

REGIONAL VARIATION OF MAGNETIC SUSCEPTIBILITY OF THE GRANITIC ROCKS IN JAPAN

Magnetic susceptibility was measured on about 1, 200 granitic rocks collected crossing the major granitic units in Japan. The regional variation in terms of x-value varies greatly from 10 to 3, 000×10-6(emu/g) even within the same granitic unit. The Inner Zone of Southwest Japan, for example, it is very low in the Ryoke foliated granitic rocks associated with high-T/low-P type regional metamorphism, but high in the innermost belt. Thus, a lateral regional variation is obvious. The magnetic susceptibility increases toward the continent-side in the Southwest Japan, while the ocean-side in Northeast Japan of the Kitakami and Abukuma Belts. The magnetic susceptibility increases with increase of a “basicity” in general. Averages of the x-values, granodiorite as the base, of the major granitic units, are as follows: The Outer Zone, SW-Japan (Miocene) •••• 30×10-6emu/g San-in Belt •••• 500 Eastern Chugoku District (late Cretaceous-Paleogene) San-yo Belt •••• 70 Ryoke Belt •••• 30 Abukuma Belt (Cretaceous) •••• 70 Kitakami Belt excluding Kf>Qz series (early Cretaceous) •••• 500 Hida Belt (early Mesozoic) •••• 400 The main constituent of FeO-Fe2O3-TiO2 oxide minerals of the high x-granitic rocks is magnetite; while that of the low ones is ilmenite.

Paleomagnetism of the Paleogene system in the inner zone of Southwest Japan, with special reference to the paleomagneto-chronology

Paleomagnetism of the Paleogene system in the inner zone of Southwest Japan, with special reference to the paleomagneto-chronology

Metamorphism of the Paleozoic Volcanic Rocks in the Inner Zone of Southwest Japan

Metamorphism of the Paleozoic Volcanic Rocks in the Inner Zone of Southwest Japan

GOTLANDIAN STRATIGRAPHY OF THE OUTER ZONE OF SOUTHWEST JAPAN

Many localities of the Gotlandian rocks have been found in the Outer Zone of Southwest Japan since Kobayashi and Iwaya's discovery of Halysites-bearing limestone at Imose, Kochi Prefecture, Shikoku in 1940. However, little has been done in their stratigraphy and paleontology. Here, the writer describes a tentative division of the Gotlandian strata with reference to the Halysitidae. The bed G4, which is composed of thick acidic volcanic and clastic materials, is presumed to be the Gotlandio-Devonian passage bed, and is correlated to the Takainari, Ono and the, lower half of the Nakazato series in the Kitakami mountains, Northeast Honshu, because of the predominance of acidic rocks. The so-called Upper Gotlandian Fukuji formation in Gifu Prefecture, Hida plateau is also brought into comparison. The strong acidic volcanic activities in these Gotlandio-Devonian rocks suggest that the “Oboke sandstone schists” in the lower part of the so-called Sambagawa metamorphic complex of the Sakawa orogenic zone are the ...

Chemical Compositions of Paleozoic Slates :III., Three Areas in the Inner Zone of Southwest Japan

Chemical Compositions of Paleozoic Slates :III., Three Areas in the Inner Zone of Southwest Japan

The Pre-Teritary Crustal-Movements in the Inner Zone of Southwest Japan

The Pre-Teritary Crustal-Movements in the Inner Zone of Southwest Japan