Western Chugoku Research Articles

Iron-titanium oxide minerals of Cretaceous to Paleogene volcanic rocks in western Chugoku district, Southwest Japan. Special reference to manganese content of ilmenites.

Fe-Ti oxide minerals of Cretaceous to Paleogene volcanic rocks in the western Chugoku district, Southwest Japan, have been examined mineralogically by means of electron microprobe. The volcanic rocks are divided into the Cretaceous Kanmon, Shunan, Hikimi, Abu and Paleogene Tamagawa Groups. Magnetite predominates in the volcanic rocks of the Kanmon, some of the Shunan, and Tamagawa Groups, while it is generally absent in those of Hikimi and Abu Groups. Chromian spinel has been found from the basaltic andesites of the Kanmon and Tamagawa Groups. The magnetic susceptibility of whole rock well reflects the above-described difference of the magnetite content, that is, X-value is higher than 50×10-6emu/g for the Kanmon, some of the Shunan and Tamagawa Groups, while it is lower than that for the Hikimi and Abu Groups. Ilmenite is contained in almost all volcanic rocks examined, and its mode of occurrence is classified into three main types; 1) independent type, 2) trellis type, 3) composite type. Manganese least concentrates in the independent type. The difference of the MnO content of ilmenite among the five volcanic groups is far larger than that of the mode of occurrence and it is well distinguished in the FeTiO3-Fe2O3-MnTiO3 triangular diagram. That is, ilmenites from the Paleogene Tamagawa volcanic rocks are higher in MnTiO3 and Fe2O3 molecules than those of the Cretaceous volcanic rocks (e. g., Kanmon, Hikimi and Abu Groups). Ilmenites from the Shunan Group are intermediate between the above-cited two groups of composition. In general, ilmenites from Paleogene volcanic rocks are richer in MnTiO3 and Fe2O3 molecules than Cretaceous ones. Similar tendency in respect to age is observed in ilmenites of plutonic rocks, too. The Mn2+/Fe2+ ratio of ilmenite depends on temperature, Mn/Fe ratio of source magma and fo2. Available data indicate that high M-concentration in ilmenites from Paleogene igneous rocks may be attributable to high fo2, during the formation of ilmenite.

17. Late Mesozoic volcanic activity in the western Chugoku mountainlands(Abstracts of Papers submitted for the Meetings of the Society)

17. Late Mesozoic volcanic activity in the western Chugoku mountainlands(Abstracts of Papers submitted for the Meetings of the Society)

Dike rocks in the Cretaceous Hiroshima granite in Western Chugoku

Several types of dike rock can be found in the Hiroshima granite as follows: dolerite, pyroxene-porphyrite and hornblende-porphyrite, lamprophyre, hornblende-quartz-porphyrite, hornblende-biotite-granite-porphyry, biotite-granite-porphyry, fluidal micro-aplitic rock, coarse-grained quartz-porphyry, granophyre, felsite and felsitic quartz-porphry, plagiophyre, and pitchstone. In the broadly-distributed normal Hiroshima granite these dike rocks have sharp contacts . In the Yashiro granite which is a coarse-grained biotite-granite bearing porphyritic potash-feldspars, the dikes of spessartite and granite-porphyry are often invaded by aplite and quartz veins, and slightly granitized. The genetical history of the Yashiro granite is divided into the stage of magmatic intrusion of main body and later metasomatic replacement. The above-mentioned dikes must have intruded in the later metasomatic stage. The origin of these dikes are quitely unknown, but their original magma would be unrelated with the granite magma.

A Geograhpical Study of Rural Houses in Western Japan

i) In terms of geography, the rural house, especially its roof, is an important key to approach a settlement structure. The roof of a rural house differs from one area to another, as it reflects conditions as well as the specific way of living of the people of an area. It is possible to grasp the typical regional character in the type of roof and arrangement of rooms; also, the dynamic change of life in a rural area, such as pervasion of the use of roof-tiles and the rise and fall of silkworm culture, can be made clear through the roof-type and its change.The present writer chooses the whole Western Japan an object, examines the distribution of several roof-types, and courses of their circulation, and tries to make clear settlement structures as seen through the roofs.ii) Roofing material:More isolated mountain or island villages use more thatched or shingle roofs. Tiled roofs are widely used in industrialized areas; they show the tendency to spread from suburban areas into mountain areas with the development of urbanization and traffic. This tendency will grow stronger in future.Different roof-tiles are used between each area, reflecting local conditions: the tile-guard and the Iwami red tile in the snowy area of the northern parts (although not so wide spread as in the Tohoku and Hokuriku Districts); windbreaks in the seacoast area (especially in the Pacific Coast). Chinese red tiles in Okinawa are interesting as showing foreign influences.To a large extent, roofing material is conditioned by economic backgrounds.iii) Roof-types:Many types can be recognized: the U. and L. roofs, the conical roof and other varieties beside three fundamental types-the “irimoya” (gabled) roof, the “yosemune” (hipped) roof, the “kirizuma” (barge) roof.The “irimoya” roof is spread over the Kinki District north of the median dislocation line, eastern Chugoku, north-western Shikoku.The “yosemune” roof is widely adopted in the Kii Peninsular, western Chugoku, the Shikoku District, and the Kyushu District. It is especially much used along the Pacific Coast.The “kirizuma” roof is popular in the mountain areas of Tajima, Hyogo Pref., and the Yamato Basin. In Tajima, silkworm culture accounts for its popularity. In Yamato, the “kirizuma” style has developed into the so-called “yamatomune” roof.The U. type roof, a variety usually called “kudozukuri”, is centered at the Tsukushi Plain in the North Kyushu District. It is called “U” because it has two projections in the rear.The L. type roof, another variety with one projection in the rear of the house, is found in Kyushu (“kagiya”), in the Kochi Plain (“magariya”), and on the Tamba Plateau (“tsunoya”). Old families often adopt this roof-type.The “futamunezukuri” roof, where the main body of house and the kitchen are separated, is found in Kagoshima down to Nansei Islands. This roof-type is originated in the Micronesian and the Melanesian Islands.The conical roof is found in Okinoerabu and Yoron, the islands situated at the southernmost tip of Japan.iv) As shown here, roofs in Western Japan richly vary in type. They are further varied by the use of different ridge pressings (decorative). The distribution of these roof-types, remarkably correspond with distinctive areas. It further coincide with topographical districts.The mixture of two or more types as well as the transformation of a type is seen where two distributional areas meet. Social changes have at places resulted in changes of roof-type. Adaptation to climatic conditions has also contributed to improving the roof. At defiles and mountain passes, the course of circulation of each roof-type can be traced.