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Proceedings of the International Symposia on Geoscience Resources and Environments of Asian Terranes (GREAT 2008), 4th IGCP 516,and 5th APSEG; November 24-26, 2008, Bangkok, Thailand Occurrence of Quartzarenite (Orthoquartzite) Clasts from Japanese Islands
and Its Significance; Paleogeography Before the Opening of the Sea of
Japan (Preliminary report)
Ken-ichiro Hisada1*, Yuri Nukariya1, Yuko Ito2 and Kosei Komuro1
1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan2. JTB Tokyo Metropolitan Corp. Shinbashi, Tokyo 105-0004, Japan* Corresponding author e-mail: hisadak@geol.tsukuba.ac.jp Abstract
The conglomerate including quartzarenite (orthoquartzite) clasts occurs at the various places in Japan. In this paper,
Tetori, Muro and Soma clasts were examined using optical and cathodoluminescence microscopes. Based on the
paleogeography of Paleo-Japan before the opening of the Sea of Japan, the relationships between the clasts and
their provenance were examined.
Keywords: Quartzarenite, Orthoquartzite, Cathodoluminescence, Provenance, Japanese Islands
1. Introduction
northeastern Japan (Okami and Kano, 1982).
Orthoquartzite represents intense chemical weather- In this paper, we try to make comparison between ing of original minerals other than quartz, considerable quartzarenite clasts and source rocks using cathodolumi- transport and washing action before final accumulation nescence microscope and we elucidate the provenance and stable conditions of deposition (Bates and Jackson eds., 1987). It is well known that the sand may experi-ence more than one cycle of sedimentation before 2. Occurrence of Quartzarenite Clasts from
final accumulation, and orthoquartzite characterizes Japanese Islands
products at the peneplanation stage of diastrophism. The occurrence of quartzite arenite clasts is mostly Orthoquartzite has been used for 95 or more percent of pebbles and sometimes cobbles, and rarely boulders. detrital quartz fraction in sands or sandstones. However, In considering the geologic development of the Japanese the term “orthoquartzite” comes to cause some confu- Islands, it is likely that the source of quartzarenite clasts sion and other terms were needed. Most acceptable is found in various places must be Precambrian basement the term quartzarenite proposed by Gilbert (1954). In rocks underneath the Japanese Islands (e.g. Tokuoka, this paper, we use the term “quartzarenite”.
1970). The accretionary complex theory has been ac- In Japan, as the basement rocks problem of the cepted since 1980’s among Japanese geologists. Thus Japanese Islands, the quartzarenite clasts in the clastic the oldest rocks were dated as the Ordovician for the rocks were highlighted in the 1970’s, when the geosynclinal ophiolitic rocks and we have to reconsider the source of model was extensively accepted and widely prevailing the quartzarenite pebbles and cobbles. Also the opening among Japanese geologists. The quartzarenite clasts of the Sea of Japan occurred at around 15 Ma abruptly have been discovered in various places in the Japanese and rapidly, and that is, it is manifest that the Japanese Islands since 1967 (Figure 1). They are usual y well Islands were located along the easternmost edge of the rounded and most of them are grayish white or light Asian continent and were a part of it. Thus, the source gray in color and some have reddish or purplish tint. rocks of the quartzarenite clasts must be considered It has been believed that there was no opportunity to in the tectonic framework of the continent rather than form quartzarenite in and around the Japanese Islands which was developed as the typical mobile belt. Thus, In this paper, we studied the major occurrence we have to seek their provenance in the area outside localities of quartzarenite clasts; Tetori, Muro and Soma the Japanese Islands or the underlying and unknown areas. The fol owings are brief stratigraphic description basement rocks. Later, the probable source rocks for the quartzarenite clasts were found in the Soma area, Proceedings of the International Symposia on Geoscience Resources and Environments of Asian Terranes (GREAT 2008), 4th IGCP 516,and 5th APSEG; November 24-26, 2008, Bangkok, Thailand 2.1 Tetori Clasts (Yamasaki et al., 2003)
3. Cathodoluminescence Study

Recently the cathodoluminescence microscope has been used for various subject of the sedimentol-ogy (e.g. Götte and Richter, 2006). With the aid of a technical y improved cathodoluminescence microscope that enables the study of low luminescent minerals, six classes of monocrystal ine former high-quartz are distin-guished and used as a guide to provenance (Matter and Ramseyer, 1985). Furthermore, cathodoluminescence enables detrital grains to be distinguished from syntaxial overgrowths in well cemented sandstones so that the original grain size and roundness parameters can be determined (Matter and Ramseyer, 1985).
Yamagami et al. (2003) proposed three types of quartzarenite clasts (Tetori clasts) col ected from the Tetori Group based on polarization-microscope and cathodoluminescence observation of quartzarenite; Types I, II and III. Type I is composed mainly of detrital quartz grains and rarely contains feldspar ones. Under the cathodoluminescence microscope, the luminescence of quartz grains presents light blue, pale blue and so on, and their origin is assigned to large-scaled plutons. Type II is characterized by the presence of sericite. Although the bluish luminescence is stil observed in the central part of quartz grains, the brownish one can Figure 1. Occurrence of quartzite clasts from Japanese Island be also detectable in its surrounding part. This may be (modified from Tokuoka and Okami, 1979) caused by early recrystallization of quartz grains. Type The Tetori clasts were collected from the Jurassic III is represented by the brownish luminescence of the to Early Cretaceous Tetori Group in the Tetori area. unified quartz “grains” and secondary cements. This The Tetori Group yields abundantly quartzarenite suggests that the recrystallization of quartz grains has pervaded extensively. The differences of types I, II and clasts from arkosic sandstone matrix. The diameter I I are due to the degree of diagenetic recrystal ization of clasts ranges from a few centimeters up to 30 cm. They are well rounded and are accompanied with other clasts of sandstone, granite, chert, granite 4. Results and Provenance
4.1 Tetori clasts
We examined 18 thin sections of quartzarenite 2.2 Muro Clasts (Tokuoka and Bessho, 1980)
clasts, and obtained the following data; Types I (7 thin The Muro clasts were col ected from the Eocene sections), Type I (3) and Type I I (2) and quartzose arenite to Oligocene Muro Group in the Muro area. The Muro (5) and others (1). Also quartzarenite from the Cambrian Group yields rarely quartzarenite clasts from greywacke. Jangsan and Ordovician Dongjeom formations in the The diameter of clasts is usual y less than 5 cm. The Okcheon belt, South Korea are investigated. Both for- accompanying clasts are sandstone, chert, granite and The red and blue components of the RGB value under the cathodoluminescence microscopy are most 2.3 Soma Clasts (Okami, 1969)
important in cathodoluminescence images of quartz The Soma clasts were col ected from the Jurassic because the green component commonly remains Somanakamura Group in the Soma area. The So- constant. We compared the Tetori clasts of Type I manakamura Group yields sporadical y quartzarenite with the Jangsan and Dongjeom quartzarenites using clasts from arkosic sandstone matrix. There also occur R/(R+B)*100 ratio. As a result, some of Tetori clasts clasts of acidic volcanics, chert, granite and others. The resemble the Jangsan quartzarenite. This suggests quartzarenite clasts are wel rounded, less than 6 cm in that Tetori clasts were brought from the Okcheon belt and/or its equivalent. This conclusion is supported by Kim et al. (2007) who studied textural y and geochemi-cally quartzarenite clasts from North China, Korea and Tetori clasts.
Proceedings of the International Symposia on Geoscience Resources and Environments of Asian Terranes (GREAT 2008), 4th IGCP 516,and 5th APSEG; November 24-26, 2008, Bangkok, Thailand 4.2 Muro Clasts
References
The Muro clasts are characterized by the frequent Bates, R.L.and Jackson, J.A. eds., 1987, Glossary of presence of quartz grain with dust ring. Secondary Geology (third Edition). 788pp. American Geological overgrowth of quartz, which is shown clearly by dust rings around worn grains, is common. In our preliminary Gilbert C.M., 1954, Petrography, (Wil iams, H. eds.) 406 observation, there is a tendency that the Muro clasts are less recrystal ized than the Tetori clasts. Usual y Götte, T. and Richter, D.K., 2006, Cathodolumines- the original shape of quartz grain is visible in the Muro cence characterization of quartz particles in mature clasts, and they are characteristical y wel rounded. arenites. Sedimentology, 53, 1347-1359.
Also it is noteworthy that the presence of medium type Kim,Yongin, Lee, Yong Il and Hisada, K., 2007, Prov- between Types I and II occur frequently in the Muro enance of quartzarenite clasts in the Tetori Group clasts. Therefore, it seems to be less similar between (Middle Jurassic to Early Cretaceous), Japan: Tetori and Muro clasts and recycle process from Tetori Paleogeographic implications. Jour. Asian Earth to Muro might not happen to these clasts.
Matter, A. and Ramseyer, K. 1985, Cathodoluminescence 4.3 Soma Clasts
microscopy as a tool for provenance studies of The Soma clasts are also divided tentatively into sandstones. In: Provenance of arenites (Ed. G-G. three types; types, A, B and C. In type A, shape of quartz Zuffa), 1st edn, 191-212. Reidel Publishing Co., grain remains clearly, whereas it is faintly visible and invisible in types B and C, respectively. These three are Okami, K. and Kano, H., 1982, The provenance of the almost correlatable to the Types I, II and III. However, it orthoquartzite pebbles occurred in the eastern has been pointed out that the Marumori metamorphic terrain of the Abukuma Plateau, Northeast Japan. rocks, which are now exposed about 30 km north of Mem. Geol. Soc. Japan, no. 21, 231-243. * it, could be source rocks for these quartzarenite clasts Okami, K., Masuyama, H. and Mori, T., 1976, Exotic in the Somanakamura Group (Okami and Kano, 1982). pebbles in the eastern terrain of the Abukuma Pla- Actually, arenaceous schist (quartzite) of the Marumori teau, Northeast Japan (part 1)-the conglomerate of metamorphic rocks consists exclusively of wel -rounded the Jurassic Somanakamura Group. Jour. Geolo. quartz grains. The same texture is also observed in the type A clasts. Accordingly, the Soma clasts were prob- Tokuoka, T., 1970, Orthoquartzitic Gravels in the Pa- ably derived from the near provenance. The Marumori leogene Muro Group, Southwest Japan. Mem. metamorphic rocks and the Somanakamura Group are Fac. Sci., Kyoto Univ., Ser. Geol. & Mineral., 37, Yamakita and Otoh (2000) envisaged the paleo- Tokuoka, T. and Bessho, T., 1980, Re-examination of the geographic maps in the middle Cretaceous and Paleo- exotic clasts of orthoquartzite from the Paleogene gene, paying special attention to large-scale lateral-slip Muro Group, Southwest Japan. Earth Science, faulting; Kurosegawa Fault System (KFS) and Median Fault System (MFS). According to their scenario, the Tokuoka, T. and Okami, T., 1979, Orthoquartzite Class Abukuma terrane moved to north by KFS lateral-slip and the Problem on the Basement Rocks of the on a large scale. In the Jurassic time and earlier, the Japanese Islands. Memorial Volume of Prof. H. Abukuma terrane might be located in the peripheral part of South China. That is, the Marumori metamorphism Yamagami, Y. Shimura, R., Hisada, K. and Komuro, K., might occur there. We need more information on the 2003, Cathodoluminescence microscope observa- tion of orthoquartzite clasts from the Tetori Group. Mem. Fukui Pref. Dinosaur Mus., 2, 161-169. * 5. Concluding Remarks
Yamakita, S. and Otoh, S., 2000, Cretaceous rear- We examined the quartzarenite clasts petrographi- rangement processes of pre-Cretaceous geologic cal y from the three major locations in Japan. The Tetori units of the Japanese Islands by MTL-Kurosegawa clasts were probably derived from the Okcheon belt left-lateral strike-slip fault system. Mem.Geol. Soc. and/or its equivalent. This scheme can be accepted in more ease way if we consider the Paleo-Japan before the opening of the Sea of Japan. Moreover the Soma clasts might be endemic products within the exotic Abukuma terrane. Our data on the provenance for Muro clasts are insufficient yet.

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