2 P

勿 Shin .i r o M izutani and Akira Yao R a d io la ria n s a n d terran es： M esozoic geology of Japan

Nobodv can understand the geology, of Japan R a diolarian biostratigraphy of the w itn o u t tn e Icn o w te a t e o f r a tl io ia r ta ii m o s tr a tt u a 一 Paleozoic to M esozoic group p n v ana th e co ncep t of terra ties. Iti th e P a st aeca tle , considerable research has been carried out oii ra- R adjolarian biostratigraphic research and age assignment by mean diolarian fossils, pai-ticulailv those in the basem ent of rads w ere not done successfully until the 1970s. O ur know ledge (A rads has im proved greatly , how ever, in the past decade, w hich i } rocKs of r ateozoic m ul M esol-oic ages. I tie rcsults show n by several leading papers such as those w ritten by N akasek indicate that Jurassic f})rm atiotis are w idespread and N ishim ura (1979) on L ate T riassic rads, Y ao and others （19801‘ and that they constitute at? accrettonarv com plex. on M iddle Triassic to M iddle Jurassic rads, M izutam and other- (198 1) on M iddle to Late Jurassic rads, and Ishiga and Im oto 门98U ， A fter estab lish itu , a n ew series of ra d io la ria n lo ssit on P erm ian rad s. ,,ones, w e have reexam ined the stratigraph), i)t the M esozoic rad i o la rian assem blage zones w ere set up tirst by Y a, basem ew rocks and have recognized inanY tectono- and others (1980) in chert-clastic sequences that w ere assigned to th, M id dle T riassic to M id d le Jurassic on the basis o f co no do nts aric stratigraphic terranes iii介Japanese Islands. Dis- stratigraphic relationships. Subsequently. m any assem blage zone-, cusson on the tectonc nistory, of the Mesozoic ter- have been proposed, though locally, that range in age from Perm iaii to C retaceous. Integrating these data w ith their ow n observations ranes s exten e尹 to that o easternAsa，reaton M atsuoka and Y ao (1986) established the Jurassic rad zones a, to accret on a na d sp ersio n p rocesses . defi ned by biohorizons. A t present, the rad zones in Japanese late C arboniferous to Jurassic tim e are com piled as show n in figure I ．0 11 these zones, the Jurassic ones are correlated broadly w ith the rad zones of the A tlantic O cean, M editerranean 'Iethys. and N orth A m er ican regions (Y ao , 1990). A ccording to the latest report of the O ceaii D rilling Program (O D P), the rad zones of late M iddle Jurassic tu earliest C retaceou s tim e in the cen tral w estern P acifi c O cean fl oo f correspond w ell to those of the Japanese Islands. In tr o d u c tio n System atic investigations of "Paleozoic" st ra t ig raphy and the age assignm ents based on our rad scale indicate that chert or siliceou} shale in the "Paleozoic" group com m only contains rads ot Perm ian T he Paleozoic：。Mesozoic group of rocks underlies。major part of T riassic, or Jurassic ages. T he occurrences of these rads suggest that the Japanese Islands, and it has been investigated stratigraphically the group is a m 6lange com plex that is com posed principally ot a since the 19th century, chiefl y on the basis of fusulinaceans and C arboniferous to Perm ian greenstone and lim estone (seam ount) fa- m acrofossils. In contrast to this school of biostratigraphy, studies of cies; a C arboniferous to Perm ian shale and chert (pelagic) facies; and radiolarians (rads), particularly using the scanning electron m icro- a Triassic bedded chert, Jurassic chert and siliceous shale (som etim e· scope, w ere undertaken in the 1970s and becam e w idely popular carrying m anganese carbonate nodules), and Jurassic elastic facies in thereafter. In fact, of m ore than 400 papers published on rads in w hich granite-bearing conglom erate is intercalated sporadically. Japan since 1926, m ore than 80 percent appeared in the 1980s. T hese papers, w ritten m ainly by enthusiastic young geologists, have offered startling new evidence for the geologic age of the "P aleozoic" group . T he m ost noticeable papers present the findings of Jurassic rads from M esozoic terranes of the Japanese "Paleozoic" provinces, and it has been dem onstrated that the "Pale- ozoic" group actually form s a M esozoic m elange com plex. Isla n d s It used to be believed that palcogeographic reconstructi o n c ould be m ade by collecting paleoenvironm ental data and by com piling W e have reviewed and reexamined all the classic data in order t( them according to their ages and sim ilarities. H ow ever, the new ly present the w hole tectonic history of the Japanese Islands, w here w e obtained age data have revealed that adjoining geologic units have recognized m any disparate terranes as show n in fi gure 2. TheN bounded by a significant discontinuity have different geologic histo- are m etam orphic terranes (H icla, "Sangun," S anbagaw a, and A bu- ries. T he terrane concept has been accepted, and the term is used now kum a), Paleozoic terranes com posed m ainly of Paleozoic folded especially by the geologists w ho have been w orking in the "Paleozo- form ations (A kiyoshi and South K itakam i), an early M esozoic ter- ic" provinces. rane (M aizuru), m 6lange and disrupted terranes (M inot C hichibu. T hus, the g e o logy of the Japanese Islands prior to the opening of and N orth K itakam i), a m uch younger terrane of an accretionar\ the Sea of Japan is discussed here in term s of collage tectonics on the com plex (Shim anto), and the C enozoic terrane of Izu. O ur discu eastern continental m argin of A sia in M esozoic tim e. sions extend to intraterrane features and to interteff ane relationships

Episodes, Vol. 14, no. 3 R a diolaria n 4 F ig ure L - L ate C arboniferous to J urassic radiolarian fossils Assem blag e zone and their assem blage zones in the Japanese Islands. (1) P prim itiva Pseudodietyom itra prim itiva M atsuoka and Yao. (2) P arvicin- gula m ashitaensis M izutani. (3) G ongylothorax sakaw aeusis T yaoi M atsuoka. (4) D ictyom itrella(?) kam oensis M izutani and K ido. G . s a k a w a e n s is - (5) U num a echinatus Ichikaw a and Y ao. (6) H suum hisuiky- 0 S . n a ra d a n ie n s is 1}1 oense Isozaki and M atsuda. (7) M esosaturnalis hexogonus (Yao). (8) Parashutim sim plum Yao. (9) Canoptum triassicum 一 G u e x e lla n u d a ta E -2 5 乏 Yao. (10) T riassocam pe nova Yao. (11) Y eharaia elegans N a- 琳加，‘，．l，公．’么 U n u m a e c h in a tu s kaseko and N ishim ura. (12) T riassocam pe dew everi N akaseko S ‘ ⋯ and N ishim ura. (13) N coalbaillella ornithoform is Takem ura V H. hisuikyoense 淤﹃斌︸ 〔J 睡零舆哭 滚赴 比 琳内 and N akaseko. (14) F ollicucullus scholasticus O rm iston and ,m a 甸kt’ P （？）grande 针介公︸ B abcock. (15) Pseudoalbaillella u 4orm a H oldsworth and n 游蘸 幼 W 0 瞬 以鱿 ． J ones. Scale bar equals 0.1 m m . A bbreviations: C , C arbonifer- ， 从 hexag onus 粉引 俗色‘ 汗 行 ous; E , E arly; M , M id dle; L , L ate. In Jurassic and Triassic 卜 e lk h o rn e n s is 册豁 定 书少 ages: T . yaoi, T ricolocapsa yaoi; S. naradaniensis, Sti- n 怡 吹 Lij l E卜 (?) 洪盆 d SP. C 粉口 chocapsa naradaniensis; P .(刀grande, Parahsuum (即grande, 住卜 护 T . elkhornensis, T rillus elkhornensis; E ., E ucyrtidiellum ; K , B～ k u ru s u e n s is '.泛 ﹂ K atrom a; A . com p actum , A rchaeospongoprunum com pac- o} jParahsuumaff tum . In P erm ian and C arboniferous ages: N ., N eoalbaillella; 1 Io n g Ic o n Ic u m F ., F ollicucullus; P ., Pseudoalbailiella; A ., A lbaillella. C a nop tum 蕊 0 ﹄ tria s s ic u m sliced and interleaved together. Som e of the fragm entary units in this ｜ 一 乏专 suture zone can be correlated w ith those of the A kiyoshi and "San- 5 ｜ Tria sso cam p e 5 ﹄ n o v a ,-}7 ' ｛ gun" terranes. ＜ ｜ 嘿 叶弓 盆咬‘ Th e A kiy o sh i terrane is com posed principally of C arboniferous － Tria sso cam p e 匡 比 to Perm ian lim estone and underlying greenstone plus Perm ian chert ｜ d e w e v e ri 二娘命暴！ 卜 and shale; all of these are deform ed severely and are overlain uncon- ：候斌释 A . co m p actu m 耀 form ably by slightly deform ed, Triassic, coal-bearing form ations. 乏 6心只 6 田 份 T he Paleozoic group in the A kiyoshi terrane represents an older 诵兮 攀啼壑 N 吟沟街舞缪 一 accretionary com plex that was related to the collision and disruption o rn ith o fo rm is 心、 一 of ancient seam ounts, w hich w ere associated w ith the surrounding N o p tim a 一 pelagic chert and shale during latest Perm ian tim e. Th e A kiyoshi 厂 s c h o la s tic . . 书颧 terrane itself has undergone no intense m etam orphism , w hereas the "Sangun" and Sanbagaw a terranes are m etam orphic terranes that are 2 里水姗 ｜ 厂 m o n a c a n th u s ＜ com posed com m only of m etam orphic rocks of greenschist to blue- 险 尸 － schist facies. Isotopic ages of the "Sangun" m etam orphic rocks re- 乏 ｜ 一 globosa ｜ P veal that three m etam orphic events are detectable or that the terrane 匡 lon gta ne nsis － m ay w ell be com posed of three subterranes; the m etam orphic events 山 卜 A 0－ 1 s in u a ta are supposed to be of C arboniferous to Perm ian, T riassic, and (or) 一 P Jurassic ages. O n the other hand, the isotopic ages of the m etam or- scalprata 蕊 饭 phic rocks of the Sanbagaw a terrane range from 128 to 50 M a and 山 I R lo m e n ta ria cluster in the interval from 1 10 to 60 M a.

P fi-fo rm a The C hichibu terrane is another m 6la n g e and disrupted terrane

7 ＿ that extends m uch of the length of the Japanese Islands on the Pacific P b u lb o sa side. It is som etim es divided into tw o subterranes, N orth C hichibu 1 4 一1 5 u ｝一I P nodosa 6 .8 - 1 3 and South C hichibu, betw een w hich the K urosegaw a terrane is sliced in a fragmentary fashion (these subterranes and the Kurosegawa tcrrane are so sm all in size that they are not shown in fig. 2). A s has been pointed out by Saito and H ashim oto (1982 ) , th e The H ida terrane, for exam ple, consists of a granitic, polym eta - So uth K itaka m i terrane is an e xo tic alloch th on ou s m ass. It co n sists of m orphosed basem ent com plex ranging in age presum ably from the a successive sequence, though bounded by num erous unconform ities, Precam brian to the T riassic, and it is overlain unconform ably by a that is com posed of Silurian shallow -sea carbonate, D evonian acidic Jurassic to C retaceous cIastic sequence. It is juxtaposed w ith the volcanic rocks, C arboniferous shallow -sea carbonate (interrupted by M ino terrane of a m 6lange com plex, w hich is com posed of a Jurassic late C arboniferous folding), Perm ian shallow -sea carbonate overlain radiolarite, a T riassic bedded chert, and a Perm ian greenstone- by coarse clastic deposits, and M esozoic clastic deposits of a shelf lim estone m ass that is associated w ith coeval shale and chert, all facies. A ll these form ations are sim ilar to those of the K urosegaw a enclosed in Jurassic to Low er C retaceous clastic deposits. T hese tw o te rra n e - terranes, the H ida and M ino, w ere stitched together by U pper C reta- T he N orth K itakam i terrane, chiefl y a Jurassic m dlange com - ceous to low er Paleogene rhyolite effusive rocks. B etw een the H ida plex, has m any traits in com m on w ith the M ino terrane or w ith the and M ino terranes, a suture zone exists as a narrow tectonic belt, in C hichibu terrane of southw estern Japan. T he N orth K itakam i terrane w hich irregular blocks of varying sizes (serpentinite, greenschist, and is bounded on the south by a narrow suture zone, w here an ophiolitic blueschist associated w ith m etam orphosed ophiolitic rocks, m iddle to com plex is found to occur together w ith sheared slivers derived from upper Paleozoic lim estone, clastic rocks, and volcanic rocks) are the N orth K itakam i and the So u th K itakam i terran es. T he A bu ku m a

Septem ber 1991 2 1 5

翻 霎H ida ．3 3ngurf 姗 麒 N orth K itakam i 40*N A kiyos hi 翻 溯 姗S o uth K itaka m l 黝 翻M aizuru Abukuma I M in o

X X

声 X X X X X% )} . 夔 36!N

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舅 S a nba ga w a 朋姗 C hichlbu 32'N 口 S him anto ｝ F igure 2 . - M ajor terranes of the Japanese 翻 lZ u Islands (m odified and redraw n on the basis of 132*E 13 6'E 142*E the terrane m ap of I chikawa, 1990). terrane to the sou th and so uthw est of the N orth and So u th K itak am i rude of approxim ately 33' N . In addition, the presence of lutecite in terranes is com posed of m etam orphic rocks that probably w ere de- a Perm ian lim esto ne b lo ck th at is em bed ded w ith in the Ju rassic rived from a Jurassic sedim entary com plex. m 6lange com plex of the M ino terrane suggests that the block proba- bly w as derived from the current southern C hina region. because no lutecite has been reported elsew here so far, except in a platform region of southern C hina (H attori, 1989). M esozoic tectonic history of the eastern T errane accretio n s are inferred to h a v e o ccu rred in the so uth- continental m argin of A sia eastern peripheral zone of A sia after the form ation of a collage of Triassic age in the m ain part of eastern A sia (fi g. 3). Perm ian A long this trend of biostratig raphic studies in Japan,。reconnais- seam ounts and T riassic bedded chert form ations, both com ing from sance survey has been carried out on the A sian continent as w ell. T he the equatorial region, assem bled together w ith the pelitic sedim ents N adanhada area, located in the northeastern part of C hina, is one of Jurassic age, and all w ere enclosed w ithin the coarse clastic such exam ple w here the geology w as reexam ined by using rads and sedim ents derived from an older continental region. It is highly terrane analysis (K ojim a, 1989). T his w ork has disclosed that the probable that the ophiolites in the suture zones betw een m ajor ter- N adanhada terrane is identical to the M ino terrane in all aspects. T he ranes of the Japanese Islands represent an ancient oceanic crust that com parative studies indicate that the N adanhada and M ino terranes existed at the tim e of accretion. A ll terranes of Jurassic to Cretaceous once form ed a single large terrane prior to the opening of the Sea of age in the collage zone w ere transpressed, dispersed, and displaced Japan. B y referring to the terrane m ap of C hina, w e conclude that the along the m argin up to northeastern C hina and the Sikhote-A lin eastern m argin of A sia form ed a collage zone of terranes in Jurassic region of the U SSR , so the prevailing m ovem ent had to be of a to C re taceou s tim e. sinistral sense. M ost of the terranes w ere sliced and fragm ented In order to dis c u ss the process by w hich these terranes w ere during this period, and strike-slip m ovem ents took place in a conti- accreted, dispersed , and positioned finally at their current locations, nental region and w ithin the collage zones. M etam orphism w as the follow ing tw o palcom agnetic investigations are w orthy of note. closely related to this tectonic history, as the accretion in Late Shibuya and Sasajim a (1986) determ ined, after m aking a thorough Jurassic to E arly C retaceous tim e and the transpression in the ensuing exam ination of the folded Triassic bedded chert of the M ino terrane, tim e are, above all, responsible for the form ation of the m etam orphic that the rock w as m agnetized originally in the equatorial region. Z . te rra n e s . Zheng (w ritten com m unication , 199 1) reported that the U pper Juras- A fte r ex tensive acidic m agm atism of Late C retaceous to early sic an d L ow er C retaceou s siltsto n es an d sh ales in the N ad an had a T ertiary tim e in the continental m argin, rift ing occurred w ithin the R ange have paleornagnetic inclinations corresponding to a paleolati- collage zone. This is represented by N eogene andesitic volcanogenic

Episodes, Vol. 14, no. 3 216

Publication University, OsakaCity Japan, Osaka, Japan: of terranes 翻 羹 口 E . 50 Programme 224, Correlation Project Geological of International Cretaceous-Paleogene· 1-12.p. collage of dispersed of collage Tamba. the in radiolarians Permian Some 1980, N., Imoto, and H., Ishiga, terranes ． 尹 v.34,(Chikyu Kagaku), Science Earth Japan: Southwest District, p. 333一45.p. ·：· 霭Sikhote- China, Northeast in accretion terrane Mesozoic 1989, KojimaS., accretion zone accretion N.0}}P Alin and Japan Palaeogeography, Palaeoclimatology, regions: Palaeoecology, v. 69, p. 213-232. p. 69, v. Palaeoecology, 尸aleozoic-Triassic 、 zonation radiolarian Aproposed newly 1986, A., Yao,and A., Matsuoka, for the Jurassic for ofthe v.Japan: Jurassic Marine 11,Micropaleontology, collage ，： 91-106.p. 0 ． 凡 ． ． ． － － ⋯ ⋯ S.,Kido, Y., Okamura,K., M.,Wakita, Adachi, S二Hattori,I., Mizutani, 二1\'81-k1CVJ Mino the in formations Jurassic 1981, S., Kojima, and I., Kawaguchi, area, central Japan: Proceedings of the Japan Academy, v. 57, series Academy,57, v. Japan the of Proceedings Japan: central area, ． ． ⋯ ⋯ 0 ⋯ 30*N 194-199.p. B, Mizutani, S., Shao, J., and Zhang, Q.L., 1990, The Nadanhada terrane in Nadanhadaterrane The 1990, Q.L., Zhang, and J., Shao, S., Mizutani, ． ⋯ 0 relation to Mesozoic tectonics on continental margins of East Asia: East ofmargins on continental Mesozoictectonics to relation Acta Geologica Sinica, v. 3, p. 15-29.p. 3, v. Sinica, Geologica Acta Nakaseko, K., and Nishimura, A., 1979, Upper Triassic Radiolaria from Radiolaria Triassic Upper A.,1979, Nishimura, andK., Nakaseko, Southwest Japan: Osaka, Japan, Science Report of College of Generalof College of Report Science Japan, Osaka, Japan: Southwest 20*N．。．。．尹澳 罗代 61-109.p. 28, v. University, Osaka Education, Saito, Y., Saito, and Hashimoto,M.,An region: 1982, South Kitakarni

． ⋯ TECTONIC 87, v. Research, Geophysical of Journal Japan: in terrane allochthonous

． 吧 ． ． ⋯ EVENT 3691-3696.p. Shibuya, H., and Sasajima, S., 1986, Paleomagnetism of red cherts: Acase cherts: red of Paleomagnetism 1986, S., Sasajima, and H., Shibuya, study in the Inuyama area, central Japan: Journal ofGeophysical Journal Japan: central Inuyamathe inarea, study ． J‘ ． 岛Neogene 二 仙‘ ． 14105-14116.p. 91, v. Research, extension K., in Ichikawa, radiolarians, andYao, Jurassic A., 1990,Triassic Mizutani, S., Hara, I., Hada, S，andHada, Pre-Cretaceous I., Hara,eds., A., Yao,S., Mizutani, OP 14, OP Publication University, OsakaCity Japan, Osaka, Japan: of terranes 产Cretaceous-Paleogenetranslation Programme 224, Correlation Project Geological of International p. 329-345. p. Yao, A., Matsuda, T., and Isozaki, Y., 1980, Triassic and Jurassic Y., Triassic 1980, Yao, A.,T.,and Matsuda,Isozaki, 00 from ofthe InuyamaJapan: Journal central radiolarians area, 、 龟Jurassic-Cretaceousaccretion 135-154．口 p. 23, v. University, City Osaka Geosciences, 、

Dr.born Shinjiro Mizutani, in 1932, is Professor of Geology at the at Geology of Professor is 1932, Figure 3. -Brief summary of the tectonic history of the Mesozoic the of history tectonic the summary-Briefof 3. Figure Department ofSciences, Earth terranes of the Japanese Islands (modified and redrawn onandredrawnthe (modified Islands Japanese the of terranes 464-01,Nagoya NagoyaUniversity, basis of the map by Mizutani and others, 1990). Solid heavy line heavy Solid 1990). others, and Mizutani by map the of basis con- activities Hisresearch Japan. shows the structural trend of the Jurassic accretionary complexes accretionary Jurassic the of trend structural the shows and Paleozoic of geology the cern (Mino and Nadanhada terranes on the Sea of Japan side and Japanside Seaof onand (Minothe Nadanhada terranes of petrology the and groups Mesozoic Chichibu and North Kitakami terranes and their southern equiva- southern their and terranes Kitakami Northand Chichibu and chert as such rocks sedimentary lent on the Pac沙Ocean side). Dashed heavy line shows a connec-ashows Pac沙Oceanline theheavyDashed on lent side). hedecade, past the In graywacke. tion of corresponding terminations of the trend that was displaced was that trend the of terminations corresponding of tion has been involved in research exclusively勿movement. Cenozoic biostratigra- radiolartan on projects phy, terrane analysis, and Mesozoic and analysis, terrane phy, rocks, generally called Green Tuff, that commonly are found in thein found commonly are that Tuff, Green called generally rocks, Asia. eastern of history tectonic Sea of Japan side of the Japanese Islands. This event stands for an for stands event This Islands. Japanese the of side Japan of Sea incipient stage of extension in the island-arc formation and wasand formation island-arc the in extension of stage incipient theto Yaoappointed wasAkira Dr. followed by the opening of the Sea of Japan.of Sea the of opening the by followed OsakaGeosciences, of Department City University, Japan, in 1973. He 1973. in Japan, University, City obtained his doctorate加m samehis the obtained university in 1983妙 in radiolar- doinguniversity References Mes- the on work biostratigraphic ian Hattori, 1., 1989, Length-slow chalcedony in sedimentary rocks of theof rocks sedimentary in chalcedony Length-slow 1989, 1., Hattori, south- of complex sedimentary ozoic Mesozoic allochthonous terrane in central Japan and its use for tectonic for use its and Japan central in terrane allochthonous Mesozoic he Japan.haswestern Recently, synthesis, in Hein, J.R., and Obradovic, J., eds., Siliceous deposits Siliceous eds., J., andObradovic, J.R., Hein, in synthesis, paleontological himse扩to the devoted of the Tethys and Pacific regions: New regions: of theTethysandYork, Pacific Springer-Verlag, ra- Mesozoicand Paleozoic of study diolarians and to geohistorical re- andgeohistorical to diolarians p. 201-215. p. search on the eastern continental Ichikawa, K., 1990, Pre-Cretaceous tcrranes of Japan, in Ichikawa, K., Ichikawa, in Japan, of tcrranes Pre-Cretaceous K., 1990, Ichikawa, Mizutani, S., Hara, I., Hada, S., and Yao, A., eds., Pre-Cretaceous eds., Yao,A., and S., Hada, I., Hara, S., Mizutani, Asia.of margin

September 1991 September