著者

伊藤 剛 中村 佳博

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.110, pp.3-16, 2021-09-30 (Released:2021-10-15)

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Jurassic accretionary complex of the Chichibu belt is distributed in the western Akaishi Mountains, central Japan. The Miocene Wada Formation, composed mainly of mudstone with basal conglomerate, is exposed in Minami-Shinano, Iida City, Nagano Prefecture, central Japan. This article reports the occurrences of Permian, Triassic, and Jurassic radiolarians from the Jurassic accretionary complex and Triassic radiolarians from the chert pebbles within the basal conglomerate of the Wada Formation. The chert pebbles are most probably derived from accretionary complex of the Chichibu belt exposed near the distributional area of the Wada Formation. Meanwhile, clasts of Cretaceous-Paleogene chert derived from the Shimanto belt nor metamorphic rock from the Sambagawa belt have never been discovered from the Wada Formation so far. This implies that the Shimanto and Sambagawa belts have not largely exposed in the Miocene in the hinterland of the Wada Formation.

著者

伊藤 剛 中村 佳博

出版者

国立研究開発法人 産業技術総合研究所 地質調査総合センター

雑誌

地質調査研究報告 (ISSN:13464272)

巻号頁・発行日

vol.72, no.4, pp.383-396, 2021-10-13 (Released:2021-10-20)

参考文献数

33

被引用文献数

2 3

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栃木県足利市名草には,足利岩体と呼ばれる黒雲母花崗閃緑岩が分布する.本論では,この黒雲母花崗閃緑岩とその周辺のジュラ紀付加体足尾テレーン構成岩類の記載を行う.黒雲母花崗閃緑岩は,等粒状組織を示す.主要構成鉱物は石英,斜長石,カリ長石,黒雲母である.周辺の足尾テレーンの構成岩類である泥岩やチャートは,黒雲母花崗閃緑岩の貫入によって明瞭な接触変成作用を被り変成泥岩や変成チャートとなっている.また,足利岩体から1.5 km以上離れた地点のチャートから,放散虫化石が得られた.1試料からはPseudoristola sp.やArchaeospongoprunum sp.が得られており,その年代は前期ジュラ紀のプリンスバッキアン期~トアルシアン期前期を示す.また,別の1試料からは,主にジュラ紀から白亜紀に産出する放散虫である閉球状ナッセラリアが得られた.炭質物を多く含む泥質岩を対象に炭質物温度計を利用した変成温度推定を試みたところ,岩体の北縁部と南縁部の2試料からそれぞれ385 °C及び513 °Cの変成温度が得られた.足利岩体の南北で変成温度が大きく異なっており,岩体の貫入角度の違いによる影響が考えられる.また,足利岩体から南西に約1 km離れた試料から291 ± 15 °Cの変成温度が得られたのに対し,足利岩体から北西に1.3 km以上離れた試料からは,より高温の362 ± 16 °Cの変成温度が得られた.地下に伏在する岩体や既に削剥されて現存しない岩体の存在が示唆される.

著者

金木 俊也 中村 佳博 纐纈 佑衣 向吉 秀樹

雑誌

JpGU-AGU Joint Meeting 2020

巻号頁・発行日

2020-03-13

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Carbonaceous material (CM) is widely distributed in sedimentary and metamorphic rocks, and its thermal maturity and crystallinity have been used as an indicator of burial and metamorphic temperature history. The relationship between maturity and temperature history of CM has been documented by various analytical techniques, including X-ray diffraction measurements, vitrinite reflectance measurements, transmission electron microscopy, infrared spectroscopy, and Raman spectroscopy. Among these, Raman spectroscopy is increasingly being used because of its rapidness and usefulness, as well as it is normally non-destructive technique (Henry et al., 2019).A typical Raman spectrum of CM exhibits two distinct peaks of D (around 1350 cm–1) and G bands (around 1580 cm–1) (Tuinstra & Koenig, 1970). Various spectral parameters, which is associated with the thermal maturity of CM, are reported; e.g., intensity ratio and full-width at half maximum (FWHM) of D and G bands. Importantly, there are mainly two types in these spectral parameters: (1) parameters calculated from raw data, or (2) parameters calculated by performing spectral fitting. One of the representative parameters of the latter was proposed by Beyssac et al. (2002). Because it is argued that their R2 ratio (area of G band / area of D1+D2+G bands) is closely related to the CM maturity, numerous studies adopted the R2 ratio as a representative parameter of Raman spectra of CM (e.g., Kouketsu et al., 2014). On the other hand, Henry et al. (2018) suggested that spectral fitting should not be performed because it leads to unnecessary errors, and recommended to focus on the parameters that can be calculated from the raw spectrum without spectral fitting.In the light of these backgrounds, the final goal of this study is to investigate whether spectral fitting of Raman spectra of CM is useful to evaluate its thermal maturity. As a first step toward this purpose, we developed a Python script that automatically perform spectral fitting of Raman spectra of CM. Analytical procedures of the script mainly consist of 5 parts: (i) smoothing by Savitzky-Golay filtering method, (ii) background correction with 1st or 3rd order polynomial function, (iii) normalization, (iv) setting of initial spectral parameters, and (v) non-linear spectral fitting with pseudo-Voigt function. We analyze the published data of Raman spectra of CM by Kouketsu et al. (2014), Mukoyoshi et al. (2018), and Nakamura et al. (2019), and compared the calculated parameters with the reported values of vitrinite reflectance. We will show preliminary results of our attempts in this presentation.