Journal of Geography 108 (3) Origin of the Mineoka Ophiolite Hiroshi SATO", Hidetsugu TANIGUCHI2), Naoki TAKAHASHI3), Mia Mohammad MOHIUD

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1 Journal of Geography 108 (3) Origin of the Mineoka Ophiolite Hiroshi SATO", Hidetsugu TANIGUCHI2), Naoki TAKAHASHI3), Mia Mohammad MOHIUDDIN4), Naoto HIRANO5) and Yujiro OGAWA6) Abstract Geological, petrological, and biostratigraphical studies of Mineoka ophiolite and related rocks, Hayama and Mineoka Belts, central Japan, were reviewed, and the origin of ophiolite is summarized as follows. 1) Pelagic to hemipelagic sedimentary rocks occur from late Paleocene to middle Miocene. 2) Basaltic rocks in the Hayama Belt are mostly alkali basalts of hotspot origin, whereas those in the Mineoka Belt are mostly tholeiite of mid-ocean ridge origin. 3) Chemical compositions of gabbros and diorites indicate island arc origin. 4) Peridotites are residues after a medium degree of partial melting. These facts arenot consistent with previous ideas that the ophiolite is island arc or back arc originonly. It is concluded that ophiolite is part of the "Mineoka plate" in the Pacific Ocean side,not in the Philippine Sea as previously proposed. Reconstruction of plate motions of the Mineoka plate is proposed, as it was formed at mid-ocean ridge, was subducted by the Pacific plate, and obducted to the Honshu arc during Miocene age after the eastward motion of the triple junction. Key words: Mineoka ophiolite, Hayama and Mineoka Belts, tectonic origin, obduction, Mineoka plate 4) Department of Geology and Mining, University of Rajshahi, Bangladesh 1) Doctoral Program in Geoscience, University of Tsukuba (Present address, Ocean Research Institute, University of Tokyo) 2) Komazawa Univeristy High School 3) Chiba Prefectural Museum and Institute 4) Department of Geology and Mining, University of Rajshahi, Bangladesh (Present address, Geological Survey of Japan) 5) Doctoral Program in Geoscience, University of Tsukuba 6) Institute of Geoscience, Univeristy of Tsukuba

2 Fig. 1 (A) Present plate distributions around the Miura and Boso Peninsulas. (B) Simplified geologic map of the Miura Peninsula (after Yokosuka City Museums 1991). (C) Simplified geologicmap of the Boso Peninsula (after Ogawa et al., 1985; Mohiuddin and Ogawa, 1997).

3 Fig. 2 Stratigraphy of the Miura and Boso Peninsulas (modified after Suzuki et al., 1996). Shaded strata (groups) are associated with and/or contain the ophiolitic rocks.

5 Fig. 3 Distributions of basaltic rocks in the Mineoka Belt, Boso Peninsula, and their chemical compositions ( modified after Taniguchi, 1991). In the Mineoka Belt basaltic rocks have zonal arrangements corresponding to their chemical compositions.

6 Fig. 4 (A) FeO*/MgO-SiO2 diagram of bulk rock compositions of gabbros and diorites in the Mineoka belt. FeO*: total FeO, TH tholeiite series, CA: calc-alkali series (Miyashiro, 1974). Chemical compositions were analyzed with XRF at the Faculty of Science, Kanazawa Univ. by Naoki Takahashi. B) Olivine forsterite (Fo) content against Plagioclase anorthite (An) Discriminations of each tectonic setting are based on the Beard (1986). Chemical compositions were analyzed with EDX at the National Science Museum by Naoki Takahashi.

7 Fig. 5 (A) Degree of partial melting of ultramafic rocks in the Hayama and Mineoka Belts based on bulk rock chemistries. Degree of partial melting is estimated by Ishiwatari (1985). Chemical compositions were analyzed with XRF at the Ocean Research Institute, Univ. Tokyo by Messrs. Satoru Haraguchi and Shinji Kanayama. (B) Chemical compositions of spinel in ultramafic rocks in the Hayamaand Mineoka Belts on Cr#-Mg# diagram. Data of those from the Izu-Ogasawara- Mariana forearc are after Ishii et al. (1992). Chemical compositions were analyzed with EPMA at Chemical Analysis Center, Univ. Tsukuba and Ocean Research Institute, Univ. Tokyo by Hiroshi Sato.

10 Fig. 6 Simplified plate tectonic model showing the Mineoka ophiolite (the Mineoka Plate) and adjacent area, modified after Ogawa et al. (1985). EU, PA, PHS, NNG, and MI are Eurasian, Pacific, Philippine Sea, North New Guinea (Seno and Maruyama, 1984), and Mineoka plates, respectively. WPB, SB, and PVB are West Philippine, Shikoku, and Parece-Vela basins, respectively. T and IZ are Tanzawa and Izu massive, respectively.

11 Arai, S. (1991): The Circum-Izu massif peridotite, central Japan as back-arc mantle fragments of the Izu-Bonin Arc system. In Peters, Tj. et al. eds.: Ophiolite genesis and evolution of the Oceanic lithosphere. Ministry of Petroleum and Minerals, Sultanate of Oman, Arai, S. and Uchida, T. (1978): Highly magnesian dunite from the Mineoka Belt, central Japan. J. Japan. Assoc. Min. Petr. Econ. Geol., 73, Beard, J.S. (1986): Characteristic mineralogy of arc-related cumulate gabbros: Implications for the tectonic setting of gabbroic plutons and for andesite genesis. Geology, 14, Dick, H.J.B. and Bullen, T. (1984): Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contrib. Mineral. Petrol., 86, Fryer, P., Mottl, M., Johnson, L., Haggerty, J., Phipps, S. and Maekawa, H. (1995): Serpentine bodies in the forearcs of western Pacific convergent margins: Origin and associated fluids. In Taylor, B. and Natland, J. eds.: Active margins and marginal basins of the Western Pacific. American Geophysical Union Geophysical Monograph, 88,

Ishii, T., Robinson, P.T., Maekawa, H. and Fiske, R. (1992): Petrological studies of peridotites from Diapiric Serpentinite seamounts in the Izu-Ogasawara-Mariana forearc, Leg 125. In Fryer, P.

12 Ishii, T., Robinson, P.T., Maekawa, H. and Fiske, R. (1992): Petrological studies of peridotites from Diapiric Serpentinite seamounts in the Izu-Ogasawara-Mariana forearc, Leg 125. In Fryer, P., Pearce, J.A., Stokking, L. B. et al. eds.: Proc. ODP, Sci. Results, 125. College Station, TX, island arcs and active continental margins. mer. J. Sci., 274, A Mohiuddin, M.M. (1997): Biostratigraphic and tectonic significance of the Paleogene to early Miocene carbone rocks: Mineoka Tectonic Belt and Kyushu-Palau Ridge. Ph. D. thesis, University of Tsukuba, 160p. Ishiwatari, A. (1985): Igneous petrogenesis of Mohiuddin, M.M. and Ogawa, Y. (1996): Middle the Yakuno ophiolites. Contrib. Mineral. Eocene to early Oligocene planktonic Petrol., 89, foraminifers from the micritic limestone beds of the Heguri area, Mineoka Belt, Boso Peninsula, Japan. J. Geol. Soc. Japan, 102, Mohiuddin, M.M. and Ogawa, Y. (1998a): Early Miocene pelagic sequences in the Mineoka Kanehira, K., Banno, S. and Yui, S. (1975): Belt, Boso Peninsula, Japan. J. Geol. Soc. Awaruite, heazlewoodite, and native copper in Japan, 104, serpentinized peridotite from the Mineoka Mohiuddin, M.M. and Ogawa, Y. (1998b): Late district, southern Boso Peninsula. J. Japan. Paleocene-middle Miocene pelagic sequences Assoc. Min. Petr. Econ. Geol., 70, in the Boso Peninsula, Japan : New light on Kaneoka, I., Takigami, Y., Tonouchi, S., northwest Pacific tectonics. The Island Arc, 7, Furuta, T., Nakamura, Y. and Hirana, M (1981): Pre-Neogene volcanism in the central Moore, G. W. and Fujioka, K. (1980): Age and Japan based on K-Ar and Ar-Ar analysis. origin of dacite boulder conglomerate Abst. IAVCEI Symp., Tokyo and Hakone, anomalously near the Japan trench. In Scientific Party: Init. Repts. DSDP, 56/57. Pt, 2, 166. Washington, D.C., U.S. Govt. Printing Office, Kobayashi, S. and Shoji, T. (1988): Metasomatic process in the formation of rodingite in Boso Peninsula, Chiba, Japan. J. Mineralogy, Petrology and Economic Geology, 83, Harland, W.B., Cox, A.V., Llewellyn, P.G., Pickton, C.A.G., Smith, A.G. and Walters, R. (1982): A geologic time scale. Cambridge Lockwood, J.P. (1971): Sedimentary and Gravity-Slide Emplacement of Serpentinite. Geol. University Press, 131p. Soc. Amer. Bull., 82, Lorand, J. P. (1987): Cu-Fe-Ni-S mineral assemblages in upper-mantle peridotites from the Table Mountain and Blow-Me Down Mountain ophiolite massifs (bay of islands area, Newfoundland): Their relationships with fluids and silicate melts. Lithos, 20, Miyashiro, A. (1974): Volcanic rock series in Ogawa, Y. and Taniguchi, H. (1988): Geology and tectonics of the Miura-Boso Peninsulas and the adjacent area. Modern Geology, 12,

13 Ogawa, Y., Horiuchi, K., Taniguchi, H. and Naka, J. (1985): Collision of the Isu are with Honshu and the effects of oblique subduction in the Miura-Boso Peninsulas. Tectonophysics, 119, Ohara, Y., Kasuga, S. and Ishii, T. (1996): Peridotites from the Parece Vela Rift in the Philippine Sea upper mantle material exposed in an extinct back-arc basin. Proc. Japan Acad., 72, Ser. B, Otsuki, K. (1990): Westward migration of the Izu-Bonin Trench, northward motion of the Philippine Sea Plate, and their relationships to the Cenozoic tectonics of Japanese island rcs. Tectonophysics, 180, a peridotites in the Hayama-Mineoka Belt, central Japan. Geol. Soc. Amer., Spec. Pub. Uchida, T. and Arai, S. (1978): Petrology of Sato, H. and Ogawa, Y. (submitted): Sulfide ultramafic rocks from the Boso Peninsula and minerals in peridotites as tectonic indicators the Miura Peninsula. J. Geol. Soc. Japan, 84, for genesis of ophiolitic rocks: Example from Vacquire, V. and Uyeda, S. (1967): Palaeomagnetism of nine seamounts in the western Pacific and of three volcanoes in Japan. Bull. Earthquake Res. Inst., Univ. Tokyo, 45, Yanagisawa, M., Takigami, Y., Ozima, M. and Seno, T. and Maruyama, S. (1984): Paleogeographic reconstruction and origin of the drilled at site 439, leg 57, Deep Sea Drilling Kaneoka, I. (1980): 40Ari39Ar ages of boulders Philippine Sea. Tectonophysics, 102, Project. In Scientific Party : Init. Repts. DSDP, 56/57. Pt. 2, Washington, D.C., U.S. Govt. Printing Office

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Microsoft Word - 研究者向け案内書.docx E-mail: michio_tagiri220130@nifty.com 1:25,000 505 Ma 3.5 1.5 3.5 1.5 115 117 Ma AKS 510 Ma 119 Ma 1 1970 1924 Minato, 1955; 1972 Kuroda, 1959 119 101 Ma K-Ar 1969 1977 1996 AKS Tagiri et al., 2011 Kuroda