著者

片田 正人 高橋 一男 藤原 郁夫

出版者

Japan Association of Mineralogical Sciences

雑誌

岩鉱 (ISSN:09149783)

巻号頁・発行日

vol.86, no.3, pp.91-99, 1991-03-05 (Released:2008-03-18)

参考文献数

6

被引用文献数

1 1

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The Himekami pluton is a complex of mafic rocks and their differentiated felsic rocks, which belong to shoshonite rock association. The pluton is devided into three bodies: South pluton, North pluton and Shiroishi pluton. The South pluton, consisting mainly of monzonite, monzogabbro, quartz monzonite and quartz monzodiorite, is classified genetically into four groups of mafic and felsic rocks. Each rock group accompanies a few amounts of xenolithic mass of cumulated, ultramafic rocks and melagabbro. The North pluton is a zoned pluton of quartz monzonite, granite and granodiorite. The Shiroishi pluton is a leucocratic tonalite-granodiorite.

著者

水野 篤行 片田 正人

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.1958, no.39, pp.1-14, 1958-08-28 (Released:2017-07-24)

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The lithological and structural features of the Nishiyatsushiro group in the northwestern area of Southern Fossa Magna are clarified in this paper. 1) The Nishiyatsushiro group, overlain by the Shizukawa and Nishikatsura groups, of upper Miocene or lower Pliocene, comprises 7 formations and 24 members. It is divided into 4 parts, namely, the lower, middle, upper and uppermost parts, each having its own characteristic sedimentary facies and products of igneous activities. 2) The lower part (more than 800m. in thickness) is characterized by a large quantity of basalt and andesite lavas with their pyroclastics; the middle (600 to 4,000m. in thickness) by mudstone with dacite pyroclastics and basalt lavas, the last of which comprises alkaline rocks ; the upper (500 to 3,000m. in thickness) by dacitic rocks and coarse clastic rocks, in which Lepidocyclinabearing limestone beds are intercalated; and the uppermost (more than 1,200m, in thickness) by various clastic rocks, 3) The group is assigned to middle-early Miocene in geologic age. 4) The tectonic movement in the area took place after and also during the formation of the Nishiyatsushiro group, probably with the intrusion of quartz diorite.

著者

西川 一雄 西堀 剛 小早川 隆 但馬 達雄 上嶋 正人 三村 弘二 片田 正人

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.78, no.2, pp.51-64, 1983-02-05 (Released:2008-08-07)

参考文献数

24

被引用文献数

3 4

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The late Cretaceous Koto Rhyolite is divided into two groups according to the succession. Each group forms an igneous cycle. The older group consists of the Kaiwara Welded Tuff and the Hatasho Quartz Porphyry, and their relationship is transitional in the field showing their co-magmatic origin. The Kaiwara Welded Tuff erupted apparently first as vesiculated magma from the top of the magma_??_reservoir followed by the intrusive phase of the Hatasho Quartz Porphyry. There are enrichment of phenocrysts such as quartz and alkali feldspar in the Kaiwara Welded Tuff, whereas plagioclase phenocrysts are more commo in the Hatasho Quartz Porphyry. The K/Rb ratios of the whole rocks are larger in the Hatasho Quartz Porphyry than in the Kaiwara Welded Tuff. The younger group consisting of the Yatsuoyama Pyroclastic Rock and the Inugami Granite Porphyry is also considered to be of co-magmatic origin although obvious intimate relationship of the two units could not be observed in the field. The differences between them in the composition of phenocryst minerals and K/Rb ratio of the whole rocks are similar to and somewhat larger than those between the Kaiwara Welded Tuff and the Hatasho Quartz Porphyry. The Inugami Granite Porphyry of the last igneous activity intruded along the ring faults whose center subsided stepwise and resulted in a double ring dike about 30km across. Thus the Koto Cauldron was composed. Natural remanent magnetism through the Koto Rhyolite suggests a clock-wise movement of the area during its igneous activity.

著者

蟹沢 聰史 片田 正人

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.42, no.4, pp.220-236, 1988-07-25

被引用文献数

8

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The Early Cretaceous igneous activity in the Kitakami Mountains is one of the most important events during the geologic development of Northeast Japan. This activity has been recently discussed as a sequence of the Mesozoic subduction system in the circum-Pacific region. In the present paper, characteristics of the igneous activity of the Kitakami Mountains are reviewed from the viewpoint of petrography and geochemistry. The Early Cretaceous volcanism preceded slightly the plutonism in the district, are closely associated with plutonism and include those of various kinds of rock series, namely calc-alkaline, tholeiitic high-alumina basalt and alkaline, but the relationship among them and their succession is still uncertain. Granitic rocks of the district were divided into six zones, i. e., Zones I, II, III, IV, V and VI; the last one is divided into subzones of VIa and VIb, from their distribution, mode of occurrences and petrography. These zonal arrangements coincide with the geochemical nature of the rocks showing systematic increase of incompatible elements from rocks of Zone I on the Pacific Coast side to those of Zone IV of the western side of North Kitakami Mountains, but the boundary between Zones V, Via and VIb in ths South Kitakami Mountains is complex. The relation of zonal arrangements between the North and South Kitakami is considered to be as follows: Zones I, II and III of the North Kitakami correspond with Zones Via, V and VIb of the South Kitakami respectively. Some granite bodies such as the Tanohata, Miyako, Tono and Orikabe bodies are typical zoned pluton having felsic central facies and ferromagnesian marginal one. Many granitic rocks are closely associated with gabbroic rocks. Gabbroic rocks of Zones I, II and V are small in amount and are usually composed of hornblende gabbro, and sometimes contain olivine which is relatively rich in Fe and coexists with anorthite. On the other hand, gabbroic rocks of Zones III, IV and VIb occupy a larger part of body, and some of them contain alkali-feldspar and biotite coexisting with olivine which is also rich in Fe and coexists with An poor plagioclase. From these characters, it is suggested that the former gabbroic rocks have been crystallized from more hydrous magma than the latter. The rocks of Zone IV are similar to those of shoshonite association. Field evidence, major and trace element geochemistry of granitic and gabbroic rocks of Zones III, IV and Vlb show continuous relationship in different from that of Zones I, II and V. However, the latter is thought to have possibility of cogenetic in origin at deeper part. N-MORB normalized trace element patterns indicate that all the granitic rocks are rich in LILE and depleted in HFSE and show Nb anomaly similar to those of the rocks of island arcs and active continental margins, but patterns of gabbroic rocks are irregular due to difference in modal proportion of minerals.