著者

村田 正文 大上 和良 蟹沢 聰史 永広 昌之

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.21, pp.245-259, 1982-04

被引用文献数

4

---

北上山地における古期花崗岩である氷上花崗岩類と,シルル系川内層は密接な関連をもって分布する。筆者ら(村田ら,1974:OKAMI&MURATA,1975)は,大船渡市日頃市地域の資料に基づき,氷上花崗岩類の少くともその一部"大野型花崗岩"がシルル系川内層の基盤を構成することを指摘してきた。また近年,川村(1980)により気仙郡住田町下有住奥火ノ土で,中井ら(1979MS)により同町上有住八日町で,氷上花崗岩類に属する小岩体とシルル系の不整合関係が指摘された。花崗岩とその上位に重なるシルル系基底部との間に,小規模な滑動面をもづくさやみ沢"と異なり,八日町ではアーコーズ砂岩が,奥火ノ土では,数センチメートル以下のラテライト様泥質岩をへだてて溶結凝灰岩が,何らの破断面もなく直接に花崗岩を覆う。シルル系川内層の基底相の1つである礫質アーコース砂岩は,八日町・奥火ノ土両地区にも発達し,その堆積岩々石学的な検討を行った。八日町地区のものは,日頃市地区のものと類似しアーコース砂岩であるが,奥火ノ土のものは,下位の火山岩・火山砕屑岩々片を含み不純アーコース砂岩である。粒度組成・鉱物組成からみて,日頃市地区のものと同様花崗岩風化物源で,原地性に近い堆積物であることを示している。また,数メートル以下の砂岩中での,粒度・鉱物組成の垂直変化は,その間の風化作用の進行状況を反映している。野沢ら(1975),許(1976),吉田ら(1981MS)によって指摘された,"氷上花崗岩の古生界各層への貫入"についても筆者らの見解を示した。層位学・堆積学的な諸事実により,氷上花崗岩類がシルル系川内層の基盤を構成することは,より一層確実になったことを主張する。

著者

蟹沢 聰史

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.48, no.2, pp.67-75, 1962-08-05 (Released:2008-08-07)

参考文献数

5

---

The Ryoke metamorphic rocks of the Takato district are composed mainly of pelitic and psammitic rocks, with subordinate amounts of basic volcanic rocks and limestone. The grade of metamorphism of the district increases progressively from the northwest to the southeast. Petrofabric analysis has been carried out for biotite, muscovite and quartz in the pelitic schistose hornfelses and gneisses of the district. Biotite and muscovite fabrics are generally determined by the bedding schistosity, and quartz fabrics of the schistose hornfelses show weak symmetry and ac-girdle, while those of the gneisses do not show any symmetrical pattern. When compared with those of the Yanai district belonging to the Ryoke metamorphic belt in southwestern Japan, the fabric diagram mentioned above are less symmetrical. This fact may suggest that the movement during the Ryoke metamorphism was different between the Takato and the Yanai districts.

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

---

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.