The Late Jurassic Oblique Collisional Orogen of SW Japan. New Structural Data and Synthesis Michel Faure, Martial Caridroit, Jacques Charvet

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The Late Jurassic Oblique Collisional Orogen of SW Japan. New Structural Data and Synthesis Michel Faure, Martial Caridroit, Jacques Charvet The Late Jurassic oblique collisional orogen of SW Japan. New structural data and synthesis Michel Faure, Martial Caridroit, Jacques Charvet To cite this version: Michel Faure, Martial Caridroit, Jacques Charvet. The Late Jurassic oblique collisional orogen of SW Japan. New structural data and synthesis. Tectonics, American Geophysical Union (AGU), 1986, 5 (7), pp.1089-114. 10.1029/TC005i007p01089. insu-00716159 HAL Id: insu-00716159 https://hal-insu.archives-ouvertes.fr/insu-00716159 Submitted on 10 Jul 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 5, NO. 7, PAGES 1089-1114, DECEMBER1986 THE LATE JURASSIC OBLIQUE COLLISIONAL OROGEN OF SW JAPAN. NEW STRUCTURAL DATA AND SYNTHESIS Michel Faure, Martial Caridroit, and Jacques Charvet DSpartement des Sciences de la Terre, Universit8 d'OrlSans, France Abstract. The structural high pressure (HP) metamorphics (the configuration of SW Japan mainly reflects Sangun schists), the Permian Maizuru a late Jurassic-early Cretaceous orogeny. olistostrome, and the dismembered The region is divided into an inner belt Paleozoic Yakuno ophiolites. In the and an outer belt, on the Japan sea and northern part of SW Japan, the Tanba zone Pacific ocean sides respectively, by a is in faulted contact with the circum- strike-slip fault, the Median Tectonic Hida and the Hida zones. The former is Line (MTL). Both consist of a series of interpreted as the equivalent of the Oga stacked nappes. The inner belt is divided and Sangun-Maizuru nappes of the Chugoku into a Jurassic olistostrome known as the domain crushed by post Cretaceous Tanba zone and a hinterland area tectonics. The latter consists of comprising continental Triassic-Jurassic Paleozoic high temperature (HT) sediments. The Tanba zone is sliced into metamorphic rocks and late Triassic-early two units: a lower one with late Jurassic Jurassic granite, locally mylonitized and matrix and Triassic-early Jurassic covered by early Jurassic sandstone. The radiolarite olistoliths, tectonically outer belt is formed by a superficial overthrust by an upper unit comprising an nappe similar to the Tanba zone thrust olistostrome with middle Jurassic matrix upon a "deep domain" characterized by a and blocks which include late Paleozoic synmetamorphic ductile deformation. The limestone, basic lava, and radiolarite. "deep domain" is divided into a lower The Tanba zone is overthrust by a unit, the Oboke unit formed by Paleozoic nappe complex derived from the continental derived arenites and a Green hinterland. The basal sole of the nappe Schist nappe consisting of oceanic corresponds to a peculiar unit called the sediments and resedimented ophiolites.The ultra-Tanba zone. In the Chugoku area, Green Schist nappe overthrusts the Oboke the hinterland is divided into an upper unit under synmetamorphic conditions with nappe: the Oga nappe, formed by Permo- an eastward displacement. The two belts Carboniferous limestone and Permian are separated by the Ryoke zone which clastic rocks and a lower one: the corresponds to the southern part of the Sangun-Maizuru nappe, formed by Paleozoic Tanba zone affected by a Cretaceous HT metamorphism and sharply cut by the MTL. Copyright 1986 A geodynamic model is proposed for the by the American Geophysical Union. Jurassic orogeny of SW Japan assuming that the evolution of the inner and outer Paper number 6T0398. belts are linked. In the Late Triassic- 0278-7407 / 86 / 006T-0398510. O0 Early Jurassic SW Japan is an active 1090 Faure et al.: Late Jurassic Orogenof SWJapan NEt JAPAN SW JAPAN CENTRAl, :akami kuma Hida circumHida Z Kanto //Sangun f .Maizuru Z. Itoigawa - Oga nbaZ. Shizuoka F. Superficial Nappe reen Schist Nappe Oboke Unit Kurosegawa. Sanbosan Z. 200 km Shimanto Z. Fig. 1. Structural map of Japan, except Hokkaido,with emphasis on the late Jurassic structure.The distinctions between SW, Central, and NE Japan are Tertiary divisions due to the Tanakura and the Itoigawa-Shizuoka faults. plate margin. The upper plate or South of Japan such as the opening of the Japan China block consisted of the hinterland Sea, the collision of the Izu peninsula, and the Tanba belt, a forearc basin; the and the present plate tectonic framework, lower plate consisted of an oceanic area it cannot be used to describe older and the South Japan continent. The basic deformations responsible for the mechanism of the orogeny is ascribed to progressive development of the present the oblique subduction and collision of Japanese Islands since Paleozoic times. the South Japan continent. It is now a widely accepted fact that the pre-Miocene structure of Japan is a INTRODUCTION result of three main orogenic cycles bounded by regional unconformities (e.g., The Japanese Islands can be divided Kobayashi, 1941; Kimura, 1973; Tanaka and into three domains by means of Cretaceous Nozawa, 1977). From youngest to oldest and younger faults (Figure 1), namely : they are: (1) NE Japan north of the Tanakura fault, 1. A Paleogene cycle or Shimanto (2) Central Japan between the Tanakura and orogeny responsible for the deformation Itoigawa-Shizuoka faults, (3) SW Japan of the outermost zone of SW Japan (the south of the Itoigawa-Shizuoka fault. Shimanto zone), for the reworking by This last domain is also divided by a brittle, superficial and local reverse large strike-slip fault, the Median faults of the older zones and for a Tectonic Line, into an inner belt on the calca!kaline magmatism related to the Japan Sea side and an outer belt on the subduction of an oceanic plate under the Pacific Ocean side. However, though this islands. geographic division can be used to 2. A Mesozoic cycle equivalent to the explain the Miocene and younger features early stage of the Sakawa orogeny of T. Faure et al.: Late Jurassic Orogen of SW Japan 1091 Kobayashi (1941). It begins in the late considered in this paper are: (1) the Triassic and ends in the middle Tanba zone and (2) the hinterland Cretaceous when the nappe structures are including all the other zones except the sealed in the outer belt by shallow-water Ryoke zone. This last one is considered Neocomian deposits and in the inner belt separately, since the post-Jurassic by middle to late Cretaceous acidic deformation and magmatism are by far volcanism or continental Cretaceous predominant. Inside the hinterland there deposits or are intruded by late is a distinction between the Chugoku Cretaceous-Paleogene granitoids. The domain on one hand and the Hida-circum- deformation related to this cycle reaches Hida domain on the other hand. This its climax in late Jurassic-early distinction is due merely to present Cretaceous times with the emplacement of geographic conditions, since their large nappes. It corresponds chrono- relationships are hidden under the Japan logically to the Daebo orogeny of Korea Sea. In the following the geology of the (e.g., Reedman and Um, 1975) and the Tanba zone, Chugoku domain, and Hida- early Yenshan deformations in China circum-Hida domain is described with (e.g., Klimetz, 1983). emphasis on Jurassic structure. 3. A late Paleozoic-early Triassic cycle or Akiyoshi orogeny (Kobayashi, The Tanba zone 1941) that very little is known about, since it is largely reworked by the early The Tanba zone is the largest one of Yenshan orogeny. SW Japan (Figures 1 and 2) well developed When considering the early Yenshan around Kyoto, i.e., the Tanba area sensu orogeny, the inner-outer division must stricto and North of Nagoya, i.e., the not be equated with the inner-outer Mino area. Recent sedimentological distinction of the alpine fold belt of studies and discoveries of radiolaria Europe where the inner belt is fossils in siliceous pelite, chert, and characterized by intensely deformed mudstone (e.g. Yao, 1972; Tanba Belt metamorphic rocks and the outer belt by Research Group, 1979; Mizutani et al., more superficial tectonics. The inner- 1981) show the importance of the outer division of SW Japan will be used olistostrome phenomenon. The Tanba zone here as it is a convenient division. should be now considered as an area of The early Yenshan orogeny is not Jurassic chaotic sedimentation. restricted to SW Japan. The Kanto area of Turbidites, diamictites, and Central Japan (Figure 1, Kimura, 1973; olistostromes are conspicuous facies in Tanaka and Nozawa, 1977; Guidi et al., the zone, and almost all of the 1984) is very similar in stratigraphy and radiolarian chert, limestone, and basic structure to the outer belt of SW Japan. volcanic are olistoliths. Local but In NE Japan also, the Kitakami and precise biostratigraphic studies suggest Abukuma massifs can be compared with the the existence of nappes, for instance, in Sanbosan zone, the Kurosegawa zone and the Kyoto area and up to the Japan sea the Green Schist nappe of SW Japan (Figures 2 and 3; Imoto et al., 1981; (Figure 1, Kimura et al., 1975; Faure, Ishiga, 1983; Caridroit et al., 1984, 1985a). 1985) or North of Nagoya(Kano, 1979) and This paper aims to present a new and perhaps south of the circum-Hida zone comprehensive structural map of the (Adachi and Kojima 1983). Jurassic orogen of Southwest Japan, based As the Kyoto area is the best known, on a detailed description of selected key it is given here as an example. There, areas and a synthesis of previous works. the lowermost unit observed in the core It then attempts to gather all the of the anticlines consists of an available data into a new geodynamic olistostrome whose siliceous siltstone model.
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