Thematic Article Paleogeographic Maps of the Japanese Islands: Plate Tectonic Synthesis from 750 Ma to the Present

The Island Arc (1997) 6, 121-142

Thematic Article Paleogeographic maps of the Japanese Islands: Plate tectonic synthesis from 750 Ma to the present

SHIGENORI MARUYAMA,'YUKIO ISOZAKI,' GAKU KIMURA2 AND MASARUTERABAYASH13 'Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan, 2Department of Earth Sciences, CIAS, Osaka Prefecture University, Sakai, Osaka 593, Japan, 3Department of Earth Sciences, Kagawa University, Takamatsu, Kagawa 760, Japan

Abstract A series of paleogeographic maps of the Japanese Islands, from their birth at ca 750-700 Ma to the present, is newly compiled from the viewpoint of plate tectonics. This series consists of 20 maps that cover all of the major events in the geotectonic evolution of Japan. These include the birth of Japan at the rifted continental margin of the Yangtze craton (ca 750-700 Ma), the tectonic inversion of the continental margin from passive to active (ca 500 Ma), the Paleozoic accretionary growth incorporating fragments from seamounts and oceanic plateaux (ca 480-250 Ma), the collision between Sino-Korea and Yangtze (250-210 Ma), the Mesozoic to Cenozoic accretionary growth (210 Ma-present) including the formation of the Cretaceous paired metamorphic belts (90 Ma), and the Miocene back-arc opening of the Japan Sea that separated Japan as an island arc (25-15 Ma).

Key words: back arc, collision, Japan, Pacific Ocean, paleogeography, rifted margin, subduction, supercontinent, superplume, Yangtze.

INTRODUCTION Continents collide to assemble a supercontinent, for the tectonic evolution of Japan (Isozaki 1996; and a supercontinent breaks up to create new Maruyama 1997), presented here is a newly re- oceans. As precisely predicted by Tuzo Wilson vised version of paleogeographic maps of Japan (1966) nearly three decades ago, recent studies and surroundings. Since the first attempt by suggest that the Earth has been involved in this Maruyama & Sen0 (1986), a series of paleogeo- business at least several times since the late graphic maps of Japan and East Asia explained in Archean (Hoffman 1991; Dalziel 1992). The Japa- terms of plate tectonics has been compiled by nese Islands originated from one such rifted conti- several workers (Taira et al. 1989; Maruyama et nental margin approx. 750-700 million years ago, al. 1989; Isozaki et al. 1990). Remarkable when the Yangtze (South China) craton rifted progress in the studies of on-land accretionary apart from the Neoproterozoic supercontinent complexes during the last decade, however, re- Rodinia to open a new superocean, the paleo- quires a drastic re-drafting of previous versions. Pacific. Since the tectonic inversion from a passive New lines of evidence, particularly from ancient continental margin to an active margin at ca accretionary complexes, constrain the spatio- 450 Ma, proto-Japan has grown asymmetrically temporal dimensions of ancient subducted oceanic oceanward for nearly 400 km across-arc in 450 plates and timings of various tectonic events. million years, through successive subduction from This map series includes 20 sheets (Figs 1-20) the Pacific side. It was in the Miocene that proto- that cover all major tectonic events in Japan from Japan converted to an island arc isolated from its birth at ca 750 Ma to the present. The pre- mainland Asia. Triassic paleogeographic maps are prepared in a In harmony with the abovementioned scenario global scale (Figs 1-7) in order to explain the long-distance journey of proto-Japan with the Accepted for publication December 1996. Yangtze block from the southern hemisphere, 122 S. Maruyama et al. across the equator, until its merge into the mid- namely, India, Congo and Kalahari, may be a part latitude part of Asia in the Early Mesozoic. It is of the supercontinent. noteworthy that Asia hardly represents a reference Underneath Rodinia, a huge mantle upwelling tectonic framework for the earlier evolution of called the Pacific Superplume (Maruyama 1994) Japan because the Yangtze and other continental developed which broke up the supercontinent at ca blocks amalgamated to form Asia mainly in the 750-600 Ma. The position of the plume center was early Mesozoic, at ca 250-200 Ma (Maruyama et somewhere in the domain of Siberia + South al. 1989), that is, long after the birth of proto- China, Australia + Antarctica, and Laurentia. A Japan at ca 750-700 Ma. On the other hand, more few associated plumes may have been present, but localized maps and schematic cross-sections of they have not yet been clearly documented. The Japan and its vicinity are provided for the Jurassic dike swarms along the expected rifted margins by and later stages (Figs 8-20) in order to depict the separation of Laurentia and Australia have detailed geotectonic features. been dated that ca 750-700 Ma (Park et al. 1995). The Proterozoic and Early Paleozoic paleogeo- The continental rifting and related sedimentation graphic reconstruction of major continents is com- started at ca 750 Ma along the western margin of piled from Scotese & McKerrow (1990), Hoffman Laurentia (Hoffman 1991), the Yangtze Craton (Li (1991), Dalziel (1992), Powell et al. (1993), Li et et al. 1995), eastern Australia (Powell et al. al. (1995), and Jurdy et al. (1995). The post- 1993), and probably Antarctica (Dalziel 1992). 180 Ma relative plate motions in the Pacific domain are based on the works by Engebretson et al. VENDIAN, 600 Ma (1985), Sen0 & Maruyama (1984) and Maruyama & Sen0 (1986). The distribution of major sedimen- The birth of the Pacific Ocean, as a surface manifes- tary basins in China and Japan is adopted from tation of the mantle upwelling, and its subsequent Wang et al. (1985) and Minato et al. (1965). For enlargement reduced the space of the unnamed further details on the Phanerozoic tectonics of previous superocean where the next super- Japan, refer to other articles in this special the- continent, Gondwana, was formed at 530 Ma matic issue. Although there are unsettled discus- (Fig. 2). A series of 700-600 Ma events, initiated by sions and debates over various tectonic events from continental rifting through the formation of the pas- different perspectives in Japan, references for the sive continental margin and ended by the formation present map compilation are limited to those sup- of oceanic lithosphere, are documented well around ported by clear evidence. In the following, we the Pacific rim; for example, the western margin of describe each map from the origin of Japan at ca North America (Isozaki & Maruyama 1992), South- 750 Ma to the present. west Japan (Isozaki & Maruyama 1991), eastern Australia, and Antarctica (Dalziel 1992). The South China block was situated between PALEOGEOGRAPHIC MAPS eastern Australia and western Canada (Laurentia), LATE PROTEROZOIC, 750-700 Ma as evidenced by stratigraphic similarities between East Gondwana and Laurentia (Li et al. 1995). The Supercontinent Rodinia (McMenamin & McMe- northwesternmost part of Southwest Japan, that namin 1990) was present in the southern hemi- is, the Oki Island in the Japan Sea and the north- sphere where most major continents were con- ernmost margin of Southwest Japan, was a part of nected, except West Africa and/or Amazonia South China, and was rifted by the Pacific Super- (Fig. 1). The presence of Rodinia in the southern plume to form a passive continental margin and hemisphere is derived from paleomagnetic evidence contiguous oceanic lithosphere (the 0-eyama ophi- in North America (Dickinson 1981) and East Gond- olite; Ishiwatari 1989; Isozaki & Maruyama 1991). wanaland (Powell et al. 1993). The paleogeographic map for 750-700 Ma is largely based on EARLY CAMBRIAN, 540 Ma the reconstruction by Hoffman (1991) and Dalziel (1992), although a considerable discrepancy is As an inevitable result of the rapid and continuous present between them. All of the major continents growth of the Pacific Ocean, the previous unnamed around the present Pacific, that is, North America, superocean was consumed to form a superconti- South America, East Asia, Australia and Antarc- nent, Gondwana, on the opposite side of the Earth tica, once formed a supercontinent in the center of at 530 Ma, beyond the rotation pole of the propa- the present Pacific Ocean. The other continents, gating Pacific ridge into the previously existing Paleogeographic maps of Japan 123 continent (Fig. 3). Several microcontinents and a Pacific orogenic belts: for example, the 467- number of immature island arcs in the oceanic 482 Ma Grenrock blueschists in Australia (Fukui et domain were present in northern Africa and Saudi al. 1995), the 439-451 Ma Skookum Gulch blue- Arabia in the latest Proterozoic-Cambrian, but schists in the Klamath Mountains, North America they were amalgamated by collision and accretion (Cotkin et al. 1992), the ca 450 Ma high-P/T during the Pan-African orogeny (Gass 198 1). West schists in Japan (Isozaki & Maruyama 1991), and and East Gondwana were first amalgamated by the eclogites in Antarctica (Peacock & Goodge 1995). collision of the Baltica, Amazonia, West Africa and For details, see the review by Maruyama et al. Congo Cratons, and by the collision of Kalahari, (1996). These blueschist ages give the minimum Antarctica, Australia, South China, Tarim and age of subduction. The initiation of subduction North China, respectively. Slightly after those must have been earlier than this age, but it is not collisions, West Gondwana collided with East yet clarified by the presence of an accretionary Gondwana to form the Mozambique collisional complex older than 480 Ma; we tentatively put the orogenic belt, the suture of which runs currently value at ca 500 Ma in this paper. along the eastern margin of Africa (Hoffman 1991; The southern part of the Iapetus Ocean closed at Dalziel 1992). a later stage than the northern part by the collision of Africa during the middle Paleozoic, at ca 400- 350 Ma. By this event the southern Appalachian LATE CAMBRIAN, 500 Ma and European Hercynian, including the Bohemian Massif, the Massif Central, Ile de Groix, the Galicia The Iapetus Ocean opened some time between 570 and the Hercynide basement rocks in the Penninic and 520 Ma (Dalziel et al. 1994), by the propagat- nappe of the Alpides were formed (see the recent ing ridge into the Baltica-Amazonia connection summary of blueschist and eclogite of the Euro- from the equatorial paleo-Pacific Ocean, then pean Hercynides and Alpides by Maruyama et al. branched into two segments, one between Lauren- 1996). tia and South America, and the other between The Yangtze craton, including the Japan seg- Baltica and Laurentia. Laurentia has been sepa- ment, was present off Australia, and has developed rated from large Gondwana, through the anticlock- as an active continental margin by the continuous wise rotation at some time between 550 and subduction of oceanic plate. It may be an isolated 480 Ma with respect to Gondwana (Jurdy et al. continental mass in the paleo-Pacific Ocean, or a 1995; Pickering & Smith 1995; Fig. 4). The U-Pb part of Gondwana, although rifted and separated zircon and baddeleyite ages of ca 615 Ma of the from mainland Gondwana at 700-600 Ma. Long Range dike in southeastern Labrador, at the northeastern corner of Canada, may mark the rift timing of the opening of the Iapetus Ocean (Kamo EARLY DEVONIAN, 400 Ma et al. 1989). The Iapetus Ocean thus was closed After the consumption of the oceanic domain be- first to the north between Laurentia and Baltica by tween Baltica and Laurentia, the Iapetus Ocean 450 Ma, with the resultant formation of the colli- between Laurentia and South America still re- sional Caledonide ultrahigh-pressure (UHP) oro- mained, and the subduction of the Iapetus plate genic belt between Baltica and Laurentia (Gee underneath Laurentia continued (Fig. 6). The final 1978; Smith 1984). closure of the Iapetus Ocean was completed by the Yangtze was floated and isolated from East collision of Africa at 350 Ma. Gondwana in the paleo-Pacific Ocean, somehow The Yangtze cratonic landmass has developed an close to the Australian part of Gondwana, but active continental margin and formed an accretion- away from Sino-Korea, at this stage until 350 Ma, ary complex, exhumed a high-PIT schist belt, and as suggested by stratigraphic and paleontological generated the calc-alkaline volcano-plutonism differences (Wang et al. 1985; Kato 1990; Cocks & along the trench. The Yangtze craton moved to the Fortey 1990). east. The Indochina block, Sino-Korea, the Tarim craton, the Kazakhstan block, and Siberia were all EARLY ORDOVICIAN. 480 Ma scattered in the wide ocean (Scotese & McKerrow 1990). The well known Paleozoic faunal provinci- Subduction of oceanic plates in the Pacific domain ality, as typically observed for th? Cambro- started at slightly after 530 Ma (Fig. 5); evidence Ordovician (Burrett 1973), was due mainly to the comes from blueschist ages around the circum- geographic isolation of continents. 124 S. Maruyama et al. LATE CARBONIFEROUS, 300 Ma thalassa. At - 320-300 Ma, the mid-oceanic ridge between the Farallon Plate and the unnamed oce- The continuous subduction of oceanic plates from anic plate subducted along this margin, exhuming the paleo-Pacific Ocean proceeded along the west- a high-P/T metamorphosed accretionary complex ern margin of Gondwana (Fig. 7). The consuming (the 300 Ma Renge schists). In addition, a coeval plate boundary extends further southwards to east- granite batholith belt developed beneath the volca- wards along East Gondwana, namely, from the nic arc along the Yangtze continental margin. southern tip of Africa, through Antarctica to the eastern margin of Australia. The Andean-type oro- EARLY PERMIAN. 280 Ma genesis prevailed along the continental margin. In western Panthalassa, Sino-Korea was moving in Sino-Korea was in a mid-latitude area, while Sibe- the low- to mid-latitude areas, while Yangtze was ria stayed in a high latitude, leaving the ample located far south of it, also in low-latitude Pan- Mongolian seaway sandwiched between two sub- thalassa (Scotese & McKerrow 1990). Both Sino- duction zones like the modern Mollucca Sea Korea and Yangtze were located within the Eu- (Hamilton 1979; Fig. 8). Yangtze was moving roamerican floristic province that was distinct northward but was still in a low-latitude area north either from the northerly Angara province, or from of the equator (Lin et al. 1985). A subduction zone the southerly Gondwana province (Kimura 1987). existed along the southern margin of Sino-Korea, A cold superplume developed in the central part which had been consuming the sea floor of the of present Eurasia at 300 Ma. Since then, all paleo-Tethyan seaway. There was an ample dis- continental plates changed their direction of move- tance between the two blocks, enough to retain ment towards Asia, because of the presence of independent faunal provinces (Nakazawa 1991). single down-welling mantle convection into the The geometry of the southern Sino-Korean margin lower mantle (Maruyama 1994). The scattered was not linear but was characterized by a promon- continental landmasses in the Early-Middle Paleo- tory and re-entrant that probably reflect the an- zoic oceanic domain, such as Baltica, the Kaza- cient rifting pattern. khstan Block (composed of the latest Proterozoic There was another active subduction zone along microcontinents and immature oceanic island arcs), the southern margin of Yangtze. The oceanic plate Siberia, Tarim, Indochina, the Bureya block and that interacted with Yangtze then was probably the Yangtze including proto-Japan, moved to the cold Farallon Plate, which featured the Carboniferous superplume, and formed a composite continent Akiyoshi-Sawadani seamount chain or swarm. called Laurasia in 300-200 Ma (Burrett 1974; These seamounts were capped by the mid-Carboni- Klimez 1983; Miyashiro 1981; Maruyama et al. ferous to mid-Permian reef limestone, with marine 1989). The collision of the Kazakhstan block with fauna of Australian and Tethyan (southern hemi- Baltica formed the Uralides collisional orogen sphere and/or low-latitude) affinity (Kanmera & (Hamilton 1970; Zonenshain et al. 1985); the Nishi 1983; Kanmera et al. 1990; Kato 1990). collision of the Kazakhstan block with Siberia Somewhere in the southern Pacific or Panthalassa, formed the Altai-Sayan fold belt; the collision of a mantle plume has created a huge oceanic plateau. the Kazakhstan Block with Tarim formed the Tien- shan orogenic belt; the collisions and amalgam- EARLIEST TRIASSIC. 250 Ma ation of Sino-Korea, the Bureya block, and the Indochina block completed during the Triassic- Yangtze collided against Sino-Korea, closing the Jurassic. Through the late Paleozoic-Triassic ex- paleo-Tethys seaway in between as a result of the tensive collision in Asia, Pangea was born as a subduction along the southern margin of Sino- supercontinent. The late Paleozoic floristic prov- Korea (Maruyama et al. 1989; Fig. 9). The sutur- inces, Angara, Cathaysia, and Euroamerica in the ing started at ca 250 Ma in the form of a promon- northern hemisphere, disappeared after the amal- tory collision in the Dabie region that probably gamation of Laurasia (Chaloner & Lacey 1973; corresponds to the protruding part of the ancient Asama 1985; Kimura 1987). rifted continental margin. From 250 to 230 Ma, Along the southern (Cathaysian) margin of the the collision suture propagated both northeastward Yangtze block, an arc-trench system developed, and southwestward, destroying the seaway in a consuming an unnamed oceanic plate through sub- zipper-closing manner. After 230 Ma, the promon- duction. Proto-Japan was located somewhere in the tory collision site turned into an exhumation zone eastern part of this Yangtze margin facing Pan- of ultrahigh-pressure (UHP) metamorphic rocks Paleogeographic maps of Japan 125 (Wang et al. 1989; Liou et al. 1994). The medium- gered the exhumation of the Sangun high-PIT pressure-type Hida (-Unazuki) and Hitachi- schists and the formation of a coeval granitic belt Takanuki metamorphic belts in Japan correspond in Southwest Japan. to the eastern extension of the UHP belt along this Brackish to shallow-marine sedimentary basins suture (Sohma et al. 1990). Sino-Korea and Sibe- developed sporadically in Southwest Japan, in ria also moved closer, narrowing the Mongolian which Middle Triassic-Early Jurassic terrigenous seaway in between through subductions on both clastics (e.g. Mine, Kochigatani, Toyora, and Ku- sides. ruma Groups) accumulated unconformably over the The subduction zone along the southern margin Permian Akiyoshi accretionary complex. The fauna of Yangtze continued to interact with the Farallon and flora suggest their strong link to South China Plate, forming the Akiyoshi and Maizuru accretion- (Kimura 1987; Hayami 1990). ary complexes of ca 260 Ma (Kanmera et al. 1990). Numerous fragments of the Carboniferous MIDDLE JURASSIC, 180 Ma Akiyoshi-Sawadani seamount chain or swarm capped by a reef was accreted to the Yangtze According to Engebretson et al. (1985), the Izan- margin. Following these, the Permian Maizuru agi Plate had continued to subduct orthogonally oceanic plateau collided and subducted beneath the beneath Asia at a rate of 4.7 cm/year, forming the Yangtze margin, accreting the Yakuno ophiolite extensive Jurassic accretionary complex all the complex (Ishiwatari et al. 1990). The mid-oceanic way along the Asian margin from the Philippines ridge between the Farallon and Izanagi Plates was to Primorye (Fig. 11). The accretionary complex subducting beneath the Yangtze margin, shifting consists mainly of terrigenous clastics derived from the trench-trench-ridge-type (TTR) triple junction the Qinling-Dabie suture zone, and also of oceanic northeastward. This along-arc movement of the rocks originated from the Izanagi Plate. The frag- triple junction resulted in a northeastward shift of ments from the Izanagi Plate include the Permian the exhumation front of a high-P/T schist belt and reef limestone and pedestal oceanic island basalt a coupled batholith belt in the southwestern exten- (OIB) greenstones of the Akasaka-Kuzuu sea- sion of the arc-trench system. mount swarm and Carboniferous-Early Jurassic deep-sea cherts (Sano 1988; Isozaki et al. 1990; & LATE TRIASSIC, 210 Ma Matsuda Isozaki 1991). The granite batholith belt (Daebo-Funatsu gran- The collision and suturing between Sino-Korea and ite suites in Korea and Japan) was formed through Yangtze annihilated the in-between seaway and the opening of a slab widow by ridge subduction, continental margins on both sides by ca 230 Ma which apparently followed the northeastward mi- (Fig. 10). In the central portion of the Qinling- gration of the TTR triple junction. Note the colli- Dabie suture where the initial promontory collision sion complex in the Hida Belt that is intruded by occurred, the UHP metamorphic rocks were tecton- this granite batholith. ically exhumed (Maruyama et al. 1994; Okay et al. 1993). The event accompanied a localized uplift LATE JURASSIC, 150 Ma and erosion along the suture, and consequently produced abundant terrigenous clastics that were The Izanagi-Kula Plate changed its velocity vector driven along the suture northeastward to form a at 140 Ma; that is, accelerated the rate to 30.0 cm/ huge delta in front of the ocean. Note the location year and changed direction clockwise to the north of the proto-Hida belt on the eastern extension of (Fig. 12). Consequently, the subduction of the the suture (Sohma et al. 1990). Izanagi Plate along Asia became oblique; nonethe- Along the southern margin of this amalgamated less, the formation of the Late Jurassic-earliest continental block, the continuous subduction Cretaceous (Mino-Tanba-Chichibu) accretionary formed an accretionary complex (of the Mino- complexes along the Asian margin continued in the Tanba-Chichibu belt), using terrigenous clastics proto-Japan and proto-Ryukyu segments (Wakita from the suture zone that bypassed the delta. The 1988; Matsuoka 1992). This high-speed subduction subduction process involved the mid-oceanic ridge generated an extensive volcano-plutonic belt along between the Farallon and Izanagi Plates at ca the southern margin of Asia, in particular the 220-180 Ma. The oblique subduction of this ridge Yenshanian domain of South China. On the other resulted in a northeastward shift of a TTR triple hand, the northern extension of this convergent junction along the subduction zone, and this trig- plate boundary changed into a transform boundary, 126 S. Maruyanza et al.

Fig. 1 Late Proterozoic (750-700Ma)

Fig. 2

Fig. 1 Reconstruction of the Late Proterozoic supercontinent Rodinia at ca 750-700 Ma. La, Laurentia; EA, East Antarctica, Au, Australia; Yg, Yangtze (South China), Si, Siberia; Ba, Baltica; Am, Amazonia; WA, Western Africa; Ka, Kalahari; Co, Congo; In, India Note the location of the Pacific Superplume that rifted apart major continental blocks and created the proto-Pacific Ocean. Proto-Japan was born from a rifted margin of Yangtze. Fig. 2 Distribution of the rifted continental blocks after the breakout of Rodinia (Vendian, ca 600 Ma). SK, Sino-Korea; T, Tarim. Note the wide opening of the Pacific Ocean by the propagating ridge into Rodinia. Another ridge penetrated into Rodinia to open the lapetus Ocean. Yangtze, with proto-Japan, was rifted and detached from its former neighbor, Australia. Puleogeogruphic maps of Jupan 127 Fig. 3 Early Cambrian (540 Ma)

Fig. 4

Fig. 3 Reconstruction of the Early Cambrian supercontinent Gondwana at ca 540 Ma. Collisional sutures developed at ca 530 Ma that united most of the continental fragments are called the Pan-African orogenic belts (colored in pink). South America and Africa became stabilized in this event. Proto-Japan, within Yangtze, was located close to Australia and faced the Pacific Ocean, but was clearly isolated from mainland Gondwana. The position of Laurentia and Baltica, and the suture location and timing between East and West Gondwana are highly controversial, due to the two contrasting reconstructions that were proposed by Hoffman (1991) and Oalziel (1992). Fig. 4 Distribution of the rifted continental blocks after the breakout of Gondwana in the Late Cambrian (ca 500 Ma). The opening of the lapetus Ocean separated Laurentia and Baltica from the Gondwana elements. The final closure of the Mozambique Ocean occurred between East and West Gondwana (colored in red). Proto-Japan, together with Yangtze, was located somewhere close to Australia. In response to the further opening of the lapetus Ocean, the initial subduction started around the Pacific Ocean. K, Kazakhstan; T, Tarim. 128 S. Maruyarna et al.

Fig. 5

Fig. 6

Fig. 5 Distribution of the continental blocks in the Early Ordovician, ca 480 Ma The subduction of the Pacific seafloor occurred at almost all of the continental margin around the Pacific Note that proto-Japan in Yangtze still remained almost at the same corner of Australia since the Cambrian, but it was enrolled for the first time into a subduction regime Fig. 6 Distribution of the continental blocks in the Early Devonian. ca400 Ma Following the collisional closure of the seaway between Laurentia and Baltica that formed Laurasia (Caledonian orogenic belts colored in red) the remnant segments of the lapetus Ocean were also narrowed by successive subduction Yangtre moved to the north of Australia and became isolated in the Pacific Sino-Korea was also isolated from other continental blocks and belonged to an independent faunal movince Fig. 7

Fig. 8

Fig. 7 Distribution of the continental blocks in the Late Carboniferous, ca 300 Ma Several continental blocks including Yangtze, Sino-Korea, Tarim and Indochina, moved northward from the southern hemisphere because a large-scale cold superplume (colored in purple) developed and dragged the blocks In addition, other continental blocks in modern Asia, such as Siberia and Kazakhstan, were also dragged to the same domain On the other hand, the closure of the lapetus Ocean was completed along the Hercynian/Appalachian orogenic belt (colored in red), and the merge of Gondwana and Laurasia consequently formed the supercontinent Pangea Fig. 8 Paleogeographic map of the Early Permian Japan at ca 280 Ma The modern coastlines of East Asia are shown in dotted lines for reference. Dark yellow, land, blue. sea, green, seamount and oceanic plateau, red, granite batholith belt; light yellow, mid-oceanic ridge. This color key is used in Figs 8-20 Sino-Korea and Yangtre moved northward to merge with Siberia. closing seaways among these blocks. Their mutual isolation resulted in the development of three distinct floristic provinces, namely, Northern Cathaysia, Southern Cathaysia, and Angara tlora, respectively Proto-Japan was on the southeastern continental margin of Yangtze and faced the Pacific Ocean (or Panthalassa) The Carboniferous Akiyoshi-Sawadani seamount chain capped by reef limestone was approaching the Proto-Japan margin of Yangtze driven by the subduction of the Farallon Plate 130 S. Maruyama et al.

Fig. 9

Fig. 10

Fig. 9 Paleogeographic map of earliest Triassic Japan at ca 250 Ma. Yangtze started to collide against Sino-Korea from the Dabie Promontory, closing the paleo-Tethyan seaway. The collision suture developed along the Qinling-Dabie Mountains in central China. The Mongolian seaway between Sino-Korea and Siberia also narrowed through double-vergent subduction on both sides. Along the southern margin of Yangtze, the active subduction of the Farallon Plate formed the Late Permian Akiyoshi accretionary complex (colored in light pink), incorporating fragments from the subducted Akiyoshi-Sawadani seamount chain and the Permian Maizuru oceanic plateau. Fig. 10 Paleogeographic map of Late Triassic Japan at ca 210 Ma. The Mongolian seaway between Siberia and Sino-Korea was mostly closed and a delta was formed in the eastern terminal of the suture. Note the Qinling-Dabie suture between Sino-Korea and Yangtze that exhumed the ultrahigh-pressure metamorphic rocks (UHP) from the diamond depth. Abundant terrigenous clastics were transported along the suture, and finally brought to a deep-sea fan formed at the trench along the Pacific Ocean. Owing to the abundant supply of clastics from the suture, the accretion along the Yangtze margin revived and constructed the Late Triassic-Early Jurassic accretionary complex of the Mino-Tanba-Chichibu belt, Southwest Japan. As the triple junction moved northeastward, the young and buoyant Farallon and lzanagi Plates subducted. tectonically exhuming the high-P/T Sangun metamorphic rocks (BS) and generating a granite batholith belt beneath the coeval volcanic arc. Paleogeographic maps of Japan 131

Fig. 11

Fig. 12

Fig. 11 Paleogeographic map of Early Jurassic Japan at ca 180 Ma Note the active subduction of the lzanagi Plate beneath amalgamated Asia that constructed a huge accretionary wedge of the Mino-Tanba Chichibu belt along the Pacific margin Components of the accretionary complex include terrigenous clastics from the gigantic deep-sea fan developed at the mouth of the suture and fragments of the Permian Akasaka-Kuzuu seamount swarm The subduction generated the Jurassic granite batholith belt along East Asia that includes the Funatsu suite in Southwest Japan and the Daebo suite in Korea Fig. 12 Paleogeographic map of Late Jurassic Japan at ca 150 Ma The subduction-controlled tectonic regime persisted to form an accretionary complex and arc-related granite belt The huge Mikabu oceanic plateau that developed on the lzanagi Plate was approaching proto-Japan 132 S. Mcrruyarna et al.

Fig. 13

Fig. 14

Fig 13 Paleogeographic map of Early Cretaceous Japan at ca 120 Ma The relative plate motion of the lzanagi Plate with respect to Asia changed to highly oblique and the continental margin changed its tectonic regime from the long-lasting orthogonal convergence to transpression or transform Consequently the accretion and arc-related igneous activity apparently became minimized Fig. 14 Paleogeographic map of Late Cretaceous Japan at ca 90 Ma The orthogonal convergence between Asia and oceanic plates in the Pacific Ocean revived and a convergence in a very high-speed mode appeared Note that the subduction reactivated the formation of a huge accretionary wedge of the Shimanto Belt Southwest Japan The passage of the Kula/Pacific mid-oceanic ridge along the Asian margin created the along-arc pair of high-P/T schists and a granite belt namely the Sanbagawa belt and the Ryoke belt in Southwest Japan A series of fore-arc sedimentary basins (the Onogawa lzumi Groups in Southwest Japan) developed between the Cretaceous high P/T schist belt and the granite belt A small domain in the northeastern Pacific called the Okhotsk became isolated by the oceanward jump of the subduction zone I’aleogeogmphic maps uf Japan 133

Fig. 15

Fig. 16

Fig 15 Paleogeographic map of Japan in the Paleocene ca 60 Ma After the passage of the Kula/Pacific Ridge the Pacific Plate came into full contact with proto Japan for the first time The subduction of the Pacific Plate beneath Asia continued, forming minor amounts of the accretionary complex and coeval volcanic arc The remnant part of the old Mongolian seaway finally closed to form the easterrl Stanovoy Range Fig. 16 Paleogeographic map of Eocene Japan at ca 40 Ma Asia suffered from an extensional tectonic regime on a regional scale which involved sporadic domal uplift and basin formation This extensional regime was induced by hot superplume activity beneath East Asia In the oceanic domain one of the transform faults in the western margin of the Pacific Plate turned into a west-dipping subduction zone giving birth to the Philippine Sea Plate and the proto-lzu-Bonin Arc 134 S. Maruyama et al.

Fig. 17

Fig. 18

Fig. 17 Paleogeographic map of Miocene Japan at ca 25 Ma. Japan became an island arc. The activity of the sub-Asia superplume peaked, accelerating the rifting in several major basins in East Asia, such as the Japan Sea, the Baikal Rift, the Kuril Basin and Bohai Basin in northern China. Bimodal volcanism characterized the initial phase of rift-related basin formation. Fig. 18 Paleogeographic map of the Late Miocene Japanese Islands at ca 15 Ma. The back-arc basins in East Asia reached their full extent, generating several across-arc strike-slip faults. In contrast to the back-arc extension, the fore-arc of the Japanese islands suffered from a local contraction that tectonically juxtaposed the Ryoke granites and the Sanbagawa high-P/T schists by the subhorizontal paleo-Median Tectonic Line (paleo-MTL) in Southwest Japan. Note that another back-arc basin opened in the Philippine Sea Plate, in which the proto-lzu-Bonin Arc split the Kyushu-Palau Ridge and created the Shikoku-Parece Vela Basin. The subduction of the young and hot Philippine Sea Plate generated slab melting along the subduction zone. Paleogeographic maps of Japan 135

Fig. 19

Fig. 20

Fig. 19 Paleogeographic map of the Pliocene Japanese Islands at ca 5 Ma. The back-arc basins opened during the Miocene, namely, the Japan Sea and the South China Sea, were already turned into a contraction regime. The subduction of the Philippine Sea Plate beneath Asia accompanied the collision/subduction of the lzu-Bonin Arc against the Southwest Japan Arc in central Japan. This indented an orocline or syntaxis in the pre-existing orogenic edifice and accreted fragments of the lzu-Bonin Arc crust. A fore-arc sliver was formed in the Kuril Arc by the oblique subduction of the Pacific Plate. Fig. 20 Tectonic map of the modern Japanese Islands. Japan is currently located on four distinct plates; namely, the Eurasia, Okhotsk (North America), Philippine Sea, and Pacific Plates Three active arc-trench systems develop in Southwest Japan-Ryukyu, Northeast Japan, and Izu-Bonin. The oblique subduction of the Philippine Sea Plate generated fore-arc slivers along the Southwest Japan-Ryukyu Arc. Note that the linear neo-Median Tectonic Line (neo-MTL) cutting the low-angle paleo-MTL corresponds to the landward margin of the fore-arc sliver in Southwest Japan. Another back-arc basin, the Okinawa Trough, is opening in the Ryukyus with hydrothermal activity. The question of whether the Okhotsk Plate recently became independent from the North America Plate is still debated. 136 S. Maruyama et al. thus no accretion occurred in the Hokkaido and basins, respectively. Around the end of the Jurassic Sakhalin segments. A small piece of oceanic do- period, a southward thrusting started to move the main remained between Asia and Siberia. Hida belt as an allochthonous nappe from the The prominent Mikabu (-Sanbosan-Sorachi) primary suture zone to and over Yangtze with the oceanic plateau was formed in the southern Pacific Late Paleozoic and Mesozoic accretionary complexes and moved northwestward to approach the active (Sohma & Kunugiza 1993). trench (Kimura et al. 1994). This plateau represents a piece of the triplet plateaux (together with LATE CRETACEOUS, 90 Ma the Shatzky Rise on the Pacific Plate and the Carib- bean plateau on the Farallon Plate) created by the The plate motion of the Izanagi changed again Pacific Superplume activity. The fragments of this from strike-slip mode to a high-speed orthogonal plateau were incorporated into the Early Creta- subduction beneath Asia (23.8 cm/year; Fig. 14). ceous accretionary complex of the southern Chich- The small remnant sea between Siberia and Asia ibu and Sanbagawa belts in Southwest Japan and finally disappeared and the resultant suture in the the Early Cretaceous Sorachi complex in Hokkaido. Stanovoy Range was formed. In Northeast Asia, Shallow marine to brackish sedimentary basins the Okhotsk Block composed of plateau-like oce- sporadically appeared in the south-central part of anic crust became an independent plate as a result Asia. The fore-arc basins along the southern con- of a trench jump, and it began to converge beneath tinental margin of Asia (e.g. Torinosu-type basins the Siberia margin with the paleo-Kuril Arc. in Japan) were washed by the warm water and The subduction of the young and hot Izanagi- were occupied by the Tethyan fauna. In contrast, Kula Plate beneath Asia generated a remarkable inland basins that developed on the north of the igneous activity along the continental arc (Taka- Qinling-Dabie suture (e.g. Tetori-type basins in hashi 1983). By virtue of the shallow subduction Japan) are characterized by the cold-water Boreal angle, slab melting may have occurred in the fauna (Kobayashi 1941). The latter basins were deeper part of the subduction zone to produce a linked to the remnant oceanic domain of the Mon- huge felsic magma reservoir. The formation of the golian seaway to the north. wide granitic batholith belt in Japan triggered the uplift and erosion in the fore-arc region, and the EARLY CRETACEOUS. 120 Ma terrigenous clastics were delivered to the adjacent trench. The abundant supply of trench-filling clas- The rapid northward movement of the Izanagi tics resulted in the growth of a huge wedge of the plate (20.7 cm/year) continued and the resultant Late Cretaceous accretionary complex in the Shi- highly oblique subduction beneath Asia (Fig. 13) manto Belt (Taira et al. 1988). terminated the formation of accretionary complex The mid-oceanic ridge between the Izanagi-Kula along the Japan margin. Instead, a transform and Pacific Plates subducted beneath Asia, causing margin appeared between Asia and the Izanagi the TTR triple junction to migrate to the northeast Plate. Development of relevant sinistral strike-slip (Uyeda & Miyashiro 1974). Along with the passage tectonics is suggested for the inland part of Asia, of the triple junction along the trench off Japan, for example, the Tan-Lu fault in northern China. the Sanbagawa high-PIT schists were tectonically Likewise for the Japan segment, similar tectonics exhumed to shallower levels of the fore-arc crust are suggested, but there is no direct evidence for between 90 and 60Ma. The buoyancy of young the Early Cretaceous strike-slip faulting in the oceanic plate is regarded as the main driving force fore-arc domain. of the tectonic exhumation of high-PIT units, and Shallow marine to brackish sedimentary basins the exhumation front consequently migrated along developed over Asia, and the faunal contrast be- the continental margin following the triple junc- tween the Boreal type and Tethyan type was clear tion. During the oceanward tectonic exhumation of among the basins in Japan (Kobayashi 1941). The the high-P/T nappe, an extensional tectonic regime former fauna is restricted to the basins linked to the appeared on the hanging wall over the exhumed cold water to the north, while the latter character- high-P/T nappe, and this created a fore-arc basin izes the fore-arc basins along the southern continen- quickly filled up by clastics from the volcanic arc tal margin of Asia which were washed by the warm (the Onogawa-Izumi Group in Southwest Japan). Pacific water. The Lower Cretaceous Tetori Group in The subduction of the mid-oceanic ridge opened the Hida belt and the Ryoseki Group in the Chichibu up a slab window beneath the fore arc of Asia, belt, Southwest Japan, represent these contrasting melting the wedge mantle and older arc crust Puleogeogruphic maps of Jupun 137 beneath the fore arc. Together with the along-arc After long-lasting stability since its amalgam- migration of the triple junction, a certain amount ation in the early Mesozoic, the continental interior of S-type granite was added to the Late Cretaceous of Asia started to suffer from an extensional tec- batholith belt along the eastern continental margin tonic regime, and many rifted basins developed in a (Nakajima et ul. 1990; Kinoshita 1995). The shal- regional scale. This regional extension in East Asia lower part of the crust composed of the Permian was probably associated with a domal uplift of the and Jurassic accretionary complexes (Akiyoshi, crust induced by an uprising hot plume from the Maizuru, Sangun and Mino-Tanba-Chichibu belts deep mantle. The inland rifted basins are charac- in Southwest Japan) were penetrated and covered terized mostly by non-marine sediments, while by the Late Cretaceous felsic volcano-plutonic those in Japan accumulated fluvial to shallow- rocks (Nohi rhyolite), and changed into the low- marine sediments with coal seams. Owing to the P/T type regional metamorphic rocks of the Ryoke erosion originated from the regional doming in the belt, Southwest Japan. The Sanbagawa high-P/T mid-continent, the abundant elastic supply to the and coeval Ryoke low-PIT metamorphic belts trench revived the growth of the accretionary com- formed Late Cretaceous paired metamorphic belts plex along the subduction margin and formed the (Miyashiro 1961), although they were primarily Tertiary wedge of the Shimanto belt (Nishi 1988). separated for - 100-200 km from each other and juxtaposed side by side through later tectonics MIOCENE, 25 Ma (Uyeda & Miyashiro 1974). The subduction-related tectonics continued along PALEOCENE. 60 Ma the Asian margin, involving the Pacific and the Philippine Sea Plates (Fig. 17). The Philippine Sea After the passage of the Kula/Pacific Ridge, the Plate widened quickly by arc splitting associated Asian continental margin experienced subduction with the opening of a young intra-arc (or back-arc) of a very young oceanic plate; namely, the Pacific basin; that is, the Shikoku Basin in which rifting Plate (Fig. 15). In addition to the heat directly propagated from the north. The Izu-Bonin Arc from the slab window opened between the Kula became more mature (Seno & Maruyama 1984). and Pacific Plates, the buoyant subduction of the Within the Asian continental plate, on the other young and hot Pacific Plate accumulated enough hand, several large-scale rift zones appeared, for heat to generate abundant magmas beneath the example, the Japan Sea, Bohai Basin, and Baikal fore-arc domain. The shallow-angle subduction Rift. The rift axes trend in a northeast-southwest may have caused slab melting of the Pacific plate direction, roughly parallel to the major plate per se rather than melting of the wedge mantle boundary. The activity of the mantle plume be- beneath the arc. The wide batholith belt developed neath Asia since the Eocene attenuated continental along the continental margin, and the arc crust of crust in several areas, and formed rift-basins un- Japan widened and thickened considerably. derlain directly by oceanic crusts. As the triple junction moved along Asia, how- The smaller sedimentary basins in Japan that ever, the elastic supply to the trench decreased to developed during the initial rifting stage are often suppress the growth of the accretionary complex called ‘green tuff basins’ because they are filled up for a certain duration, or to start tectonic erosion mostly with light green altered rhyolitic-andesitic of the Cretaceous accretionary complex (von Huene volcanics interbedded with terrigenous elastics. & Lallemand 1990). These basins are characterized by bimodal volcanism, the Kuroko-type massive sulfide deposits, EOCENE, 40 Ma and basin margin breccia associated with abut unconformity. The subduction of the Pacific Plate beneath Asia continued, although its convergence rate dropped LATE MIOCENE, 15 Ma to lower than before (Fig. 16). Along the western margin of the Pacific Plate, an ancient transform The Philippine Sea and Pacific Plates continuously fault changed into a new subduction zone, creating subducted beneath the Eurasian Plate (Fig. 18). a rudimentary arc (proto-Izu-Bonin) and a smaller The Philippine Sea Plate grew larger as the three but independent oceanic plate (the Philippine Sea back-arc basins opened one after another by the Plate) that subducted beneath Asia (Seno & trench-retreat along the Izu-Bonin Arc. As the Maruyama 1984). plate underlying the Shikoku-Parece Vela Basin 138 S. Maruyama et al. was young and hot, its buoyant subduction beneath young Philippine Sea Plate, while Northeast Japan Asia triggered slab melting in the depth of the was subducted by the older Pacific Plate (Fig. 19). subduction zone along Southwest Japan and gen- The collision/subduction of the Izu-Bonin island erated the unique late Miocene gabbro/granite in- arc in the eastern margin of the Philippine Sea truded into the Paleogene accretionary complex. Plate added a remarkable feature in the pre- On the Eurasia continental plate, on the other existing orogenic structure of Southwest Japan. hand, plume-induced rifting and back-arc opening The buoyant subduction of the Izu-Bonin arc crust occurred in several areas to expose oceanic crust indented into Southwest Japan Arc to form an with a spreading ridge, such as in Japan Sea, the orocline (or syntaxis) concave to the south (Taira et Kuril Basin, and South China Sea. The Japan Sea al. 1989). The oblique subduction of the Pacific opened with the clockwise rotation of Southwest Plate generated a westward-moving fore-arc sliver Japan coupled with the anticlockwise rotation of along the Kuril Arc (Kimura 1985) that accompa- Northeast Japan (Otofuji 1996), and this changed nied a strike-slip dislocation along the continent the continental arc into an island arc. As the side and compressional regime on its moving front opening of Japan Sea occurred from an anastomos- in the Hidaka mountain. ing multiple rift system, smaller continental frag- The Eurasia continental plate became fragments were scattered in this back-arc basin, for mented into several independent smaller plates, example, the Yamato-tai bank (Jolivert et al. probably as a part of the tectonic reorganization of 1994). Major tectonic boundaries along the west- Asia by the collision and indentation of India into ern and eastern margin of the Japan Sea were central Asia (Tapponier et al. 1982). defined by north-south-trending strike-slip faults with dextral and sinistral offsets along the western PRESENT, 0 Ma and eastern margins of the back-arc basin, respectively (Yoon & Chough 1995). Consequently, all the The Japanese Islands sit on four distinct plates at pre-existing orogenic components in Japan were present; two oceanic plates of the Pacific and isolated from the mainland Asia. Philippine Sea plus two continental plates of Eur- The tectonic juxtaposition of the Cretaceous asia and Okhotsk (or North America). Three sub- paired metamorphic belts in Southwest Japan oc- duction zones and one collisional zone with two curred as a by-product of this regional doming/ triple junctions divide these four plates (Fig. 20). uplift in the continental interior. The extension All of them are characterized by remarkable seis- tectonics probably developed a subhorizontal de- micity and the former three generate active volca- tachment surface within the Asian continental nic chains. The subduction of the Pacific Plate crust, and this fault dislocated the Ryoke low-P/T beneath the Philippines Sea Plate is adding crustal type metamorphic belt (and granite belt) ocean- materials to the Izu-Bonin arc, although accretion ward from the volcanic front to the near-trench site at the trench is inconspicuous. The subduction of where the Sanbagawa high-P/T metamorphic belt the Philippine Sea Plate beneath Southwest Japan occurred (Isozaki & Maruyama 1991; Isozaki is constructing a huge accretionary wedge along 1996). This subhorizontal boundary fault between the Nankai Trough (trench), while that of the the contrasting metamorphic belts, called the Pacific plate beneath Northeast Japan is destroying paleo-Median Tectonic Line (paleo-MTL) in South- the pre-existing accretionary wedge by subduction west Japan, apparently shortened the primary Cre- erosion. A compressional tectonic regime exists taceous arc-trench distance. This secondary modi- between the Eurasia and North America Plates, fication of the primary orogenic structure severely generating a high mountain range along the plate hit Northeast Japan also, where a series of left- boundary in central Japan and seismic activity not lateral strike-slip faults chopped older geologic related to the Pacific subduction. units into several slivers. The facies change in The oblique subduction of the Philippine Sea sediments suggests that the extension tectonics Plate beneath Southwest Japan generated a west- rapidly drowned the rifted intra-arc basins (Yamaji ward moving fore-arc sliver in Southwest Japan 1990). (Isozaki 1989; Kuramoto & Konishi 1989). Its northern margin is a linear right-lateral strike-slip PLIOCENE, 5 Ma fault called the neo-Median Tectonic Line (MTL) that clearly cuts the older low-angle paleo-MTL The Philippine Sea Plate reached its maximum (Isozaki & Maruyama 1991; Yamakita et al. 1995). size. Southwest Japan was subducted by the very Another back-arc basin is now spreading in the Paleogeographic maps of Japan 139 Okinawa Trough that propagates to the north BURRETT C. F. 1973. Ordovician biogeography and toward central Kyushu, splitting the modern continental drift. Paleogeography, Paleoclimatology, Southwest Japan Arc (Kimura et al. 1988). The Paleoecolog y 13, 16 1-2 0 1. 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L. 1992. precision chronology became available for the de- Early Paleozoic blueschist from the Schist of Skoo- scription of various major tectonic events in the kum Gulch, eastern Klamath Mountains, Northern evolution of the Japanese Islands. In particular, California. Journal of Geology 100, 323-38. remarkable innovations occurred in microfossil bio- DALZIEL I. W. D. 1992. Antarctica: A tale of two chronology and in various geochronologic dating supercontinents? Annual Review of Earth and Plan- methods for ancient accretionary complexes. In etary Sciences 20, 501-26. DALZIEL I. W. D., DALLA SALDA L. H. & GAHAGANL. particular, these schemes demonstrated detailed M. 1994. Paleozoic Laurentia-Gondwana interaction timings of plate interactions and time-space di- and origin of the Appalachian-Andean mountain sys- mensions of the ancient oceanic plates already tem. Geological Society of America Bulletin 106, subducted or lost. 243-52. 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