著者

金沢 康夫 中嶋 輝允 高木 哲一

出版者

The Society of Resource Geology

雑誌

資源地質 (ISSN:09182454)

巻号頁・発行日

vol.49, no.3, pp.203-216, 1999-12-31 (Released:2009-06-12)

参考文献数

35

被引用文献数

2

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Recent geoscientific data and models for ore geneses of the Bayan Obo REE-Nb-Fe deposits, Inner Mongolia, China were reviewed. The rift system developed in the northern margin of the Sino-Korean massif during the Early-Middle Proterozoic era made a favorite tectonic setting for the depositions of Bayan Obo Group and the ore deposits. A variety of veins and dykes around the deposits occur in the footwall clastic rocks and the basement of migmatites. K-metasomatism and brecciation of hanging H9 shale indicate that the shale could serve as a sealing cap-rock for the deposits (DREW et al., 1992). Data of isotope ages from Sm-Nd, La-Ba, Rb-Sr, Th-Pb, Ar-Ar, and Re-Os methods suggest that there are at least three metallogenic periods: (1) 1, 700 - 1, 260 Ma (Middle Proterozoic); (2) 555 - 370 Ma (Caledonian); and (3) 343 - 298 Ma (Hercynian). In the three periods the first one is of the most important (BAI et al., 1996). C, O and S isotopic compositions together with mineral chemistry and field observations of the H8 dolostone and ore minerals indicate the following possibilities: (1) The dolostone belongs to normal sedimentary carbonate rocks and is not a magmatic carbonatite. (2) The original iron (hematite) ore bodies were formed syngenetically before REE-Nb mineralization. (3) The hydrothermal fluids with an alkaline-carbonatite chemistry were derived from the upper mantle, and printed the REE-Nb mineralization over the original iron bodies. The process of the above (2) and (3) is considered as a composite process of both crustal and mantle source mineralization (CAO et al., 1995). Many geochemical data and field observations are consistent with the composite model for the origins of the Bayan Obo deposit.

著者

田村 糸子 水野 清秀 宇都宮 正志 中嶋 輝允 山崎 晴雄

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.125, no.1, pp.23-39, 2019-01-15 (Released:2019-04-15)

参考文献数

116

被引用文献数

9 12

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房総半島に分布する上総層群は,層厚3000mに達する下部~中部更新統の前弧海盆堆積物である.古くから多くの層序学的研究が行われ,日本の海成更新統の模式層序である.また500層を超える多くのテフラが挟在され,上部の笠森層から下部の黄和田層まで詳細なテフラ層序が確立されている.多数の広域テフラ対比も報告され,日本列島の更新世テフラ編年上,重要である.本論では,現在までに明らかにされた上総層群の広域テフラをまとめ,約0.4Ma~2Ma間の20層を超える広域テフラを示した.そして黄和田層中のテフラ層序に関して,ダブルカウントや上下逆転などの問題点を指摘した.また報告の少なかった上総層群下部の大原層,浪花層,勝浦層において,新たに多数の細粒ガラス質テフラを記載し広域対比を検討した.その結果,Bnd2-O1(2.1Ma),Fup-KW2(2.2Ma)の2層の広域テフラを新たに見出した.これらのテフラ対比から,上総層群基底の堆積年代が2.3Maを遡る可能性を示した.