Japan Sea, opening history and mechanism: A synthesis Laurent Jolivet, Kensaku Tamaki, Marc Fournier

To cite this version:

Laurent Jolivet, Kensaku Tamaki, Marc Fournier. Japan Sea, opening history and mechanism: A synthesis. Journal of Geophysical Research : Solid Earth, American Geophysical Union, 1994, 99 (B11), pp.22237-22259. ￿10.1029/93JB03463￿. ￿insu-00726737￿

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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. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 99, NO. Bll, PAGES 22,237-22,259, NOVEMBER 10, 1994

Japan Sea, openinghistory and mechanism:A synthesis

Laurent Jolivet D6partementde G6ologie,Ecole Normale Sup6rieure,Paris, France

Kensaku Tamaki OceanResearch Institute, University of Tokyo, Tokyo, Japan

Marc Foumier D6partementde G6ologie,Ecole Normale Sup6rieure, Paris, France

Abstract. The respectivetectonic effects of backarc spreadingand continental collision in Asia are consideredeither as two independentprocesses or asclosely interrelated. Extrusion tectonics assumesthat the openingof the SouthChina Sea and the left-lateralmotion along the Red River fault aregeometrically linked in a pull-apartmanner. This modelis not acceptedby several workersbecause the structurallink betweenthe two processesis not clearlydemonstrated. In the caseof theJapan Sea,, we canshow without ambiguity that back arc opening was controlled by largeintracontinental strike-slip faults which can be easilyunderstood as effects of the India-Asia collisionfar from the indenter.The JapanSea opened in the early Miocenein a broadpull-apart zonebetween two majordextral strike-slip shear zones. The first oneextends from northSakhalin to centralJapan along 2000 km, it hasaccommodated about 400 km of finite displacement. Deformationalong it variesfrom dextraltranspression in the northto dextraltranstension in the south.The secondis betweenKorea and SW Japanand has accommodated a smaller displacementof about200 km. The extensionaldomain in betweenlies in theback arc region of Japan.Distributed stretching of thearc crust resulted in theformation of mostof theJapan Sea, while localizedoceanic spreading at the southerntermination of the easterntranspressional shear zoneshaped the Japan Basin. The firstoceanic crust was formed in a smalltriangle based on the easternshear zone, and spreading propagated westward inside the pull-apartregion. Timing of oceanic crust formation, of formation of the dextral shear zones and of block rotation in between, as well as the internalstructure of the basinsand the geometryof deformationalong the master shearzones are usedto reconstructthe openinghistory. This evolutionis discussedby comparison to othermanifestations of the arc andback arc activity,such as the historyof sedimentationand volcanism.The paperthen suggests that the collisionof India canhave tectonic consequences as far northas Japan and Sakhalin and describes the geometricalrelation of backarc opening there and diffuse extrusion.

Introduction is discussedgenerally in termsof extrusionversus crustal thickeningas a result of the indentationof Asia by India The deformationof Asia (Figures 1 and 2) is viewed (see, for instance, a recent discussionby Dewey et al. commonlyas if the region northof the indenter(Tibetan [1989] or Le Pichon et al. [1992]). The opening of the plateau,Tien Shan)and immediately east of it (Indochina) SouthChina Sea is, for instance,seen by Tapponnieret al. is deformedas a responseto the Himalayancollision only [ 1982] and Peltzer and Tapponnier[ 1988] as the resultof and the back-arc regions along the Sunda and Pacific extrusionof Indochina alone. The merely passiverole of trenchesare deforming as an effect of subductiononly, the subduction zone played in these schemesis very without any link between both. Moreover, most papers unlikely, however,given that large back arc basinsopened dealing with the Cenozoic deformation of the Asian along the eastern border of the Philippine Sea plate continentdescribe it in sucha way that the influenceof the (Shikoku-Parece Vela Basin) as a response to the eastern and southeasternplate boundariesis ignored, particularstress conditions created in the upperplate by althoughit is obviousthat large extensional and strike-slip the subductionof the Pacific plate. Far from the indenter, deformationis concentratedin the back arc regionsof the the most obvious deformation features related to collision Sunda and Pacific subduction trenches. Finite deformation are localized strike-slipshear zones such as the Red River fault or the Altyn Tagh fault. Further away from it, marginalbasins have openedduring the collisionprocess, Copyright1994 by the AmericanGeophysical Union. and one can consider collision as a possible cause for , opening [Tapponnieret al., 1982; Kimura and Tamaki, Papernumber 93JB03463. 1986; Jolivet et al., 1990]. This paper deals with the 0148-0227/94/93JB-03463505.00 openingmechanism of marginalbasins settled onto the

22,237 22,238 JOLIVET ET AL.' JAPAN SEA, OPENING HISTORY AND MECHANISM

EURASIA ß ß

I INDIAI

10'N

ß ß IPRESENTI

colli •

Figure 1. General geodynamicframework of Asia, SoutheastAsia, and the northwestPacific. Fault patterninside Asia after Tapponnieret al. [1982].Doubleopen arrows represent the directionof relative convergenceacross intracontinental thrust zones,open semi-arrowsrepresent the senseof relative motionalong major strike-slipfaults, open single arrows represent relative direction of motionof the subductingplate in subductionzones, and solid divergentarrows representdirection of relative divergenceacross major zonesof extension. margin of the deformingEurasia and showshow back arc thePhilippine Sea plate makes it unlikelythat the opening openingand intracontinental strike-slip faults cooperate to is dueonly to collisionbecause there is a priori no link shapethose basins on the exampleof theJapan Sea. betweenthe internaldeformation of the PhilippineSea Most of the northwestPacific large back arc basins plate and the India-Eurasiainteractions. Pacific subduction opened between the late Oligocene to middle Miocene obviouslyplayed a largerole in theopening, as recognized [Taylor and Karner, 1983;Mrozowski and Hayes, 1979; earlier by most authors working on marginal basins Taylor and Hayes, 1983; Tamaki, 1986; Briais, 1989; [Karig, 1971; Uyedaand Kanarnori,1979; Uyeda, 1986; Chamot-Rookeet al., 1987;Taylor et al., 1990;Rangin et Viallon et al., 1986; Uyeda and McCabe, 1983; Tarnaki al., 1990a, b; Tamaki and Honza, 1991]. Most are now in and Honza, 1991; Honza, 1991]. Analog experiments a closingstage [Tamaki and Honza, 1984;Rangin and performedby $hemenda[1993] showthat trenchroll back Silver, 1991],active back arc spreadingand rifting being and back arc opening during fast convergenceare activeonly alongthe easternmargin of thePhilippine Sea physicallyfeasible. In someconditions, tensional stresses plate in the Mariana trough [Karig et al., 1978; Stern et can be appliedto the upperplate and lead to the opening al., 1984] and Bonin rift [Taylor, 1992], and in the of oceanicbasins above a convergentzone. The geometry Okinawa trough [Wageman et al., 1970; Kimura, 1985; of the East Asian marginalbasins is, however,controlled Letouzeyand Kimura, 1985; $ibuet et al., 1987]. That the by large strike-slipfaults, which can hardlybe relatedto largest basinsopened at almost the sametime from the the subductionprocess only. The Red River fault has,for Sulu Sea to the Kuril basinon the Eurasianmargin, and instance, accommodated some 500 km of left-lateral the Shikoku-PareceVela basin on the easternmargin of displacementduring the South China Sea opening, JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,239

60øE 70øE 80øE 90øE 100øE 110øE 120øE 130øE 140øE

50øN

40øN

30øN

20øN

10øN

Figure 2. Generalbathymetry and topography of Asia andwest Pacific. Contours: 5000, 3000, 1000, 0, -1000, and -3000 are represented.Regions deeper than 3000 meters(oceanic crust in general)in marginal seasare ruled.

according to Tapponnier et al. [1982, 1986, 1990] or flow and basementdepth [TamakL 1988] and the tectonic Peltzer and Tapponnier [ 1988]. Dextral motion is known history of the margins [lijima and Tada, 1990, and also along the marginsof the JapanSea and extends2000 references therein]. It instead contradicts the classical km far from the subductionzone along northeastJapan considerationthat the Japan Sea opened by fast rigid and Sakhalin [Lallemand and Jolivet, 1985; Jolivet and rotations in a bar-door fashion, as deduced from Miyashita, 1985; Jolivet and Huchon, 1989; Jolivet et al., paleomagnetic data (Otofuji and Matsuda [1983], and 1991, 1992; Fournier et al., 1994]. Total dextral offset subsequentpapers). Subsidence history of severalsections was recentlyquantified to a minimum 400 km [Jolivetand insidethe basinand alongthe margins[Ingle, 1992] is also Tamaki, 1992]. CenozoicN-S dextralstrike-slip motion is consistentwith the pull-apart model that we proposed recordedalso in the regionof the North China basin[Chen earlier [Lallemand and Jolivet, 1985; Jolivet et al., 1991]. and Nabelek, 1989]. We discussthis problem based on the exampleof the PresentTectonic Environment of the JapanSea JapanSea, which now provides a well-controlledhistory of riftingand spreading, in termsof geometryand timing. Openingin the JapanSea stoppedsometime in the Geophysicaland geological data that were used until middle Miocene, and a new compressionaltectonic recentlyto constrainthe tectonichistory of theJapan Sea contextwas set about 10 m.y. agoand ultimately led to the gave rise to contradictorymodels, mostly becausehard formationof an incipientsubduction zone inside the basin data concerningthe age of rifting and spreadingwere in the early Quaternary. lacking.It is onlyvery recently that Ocean Drilling Project (ODP) legs127 and 128 broughtinescapable evidence that Compressionand Incipient Closure it openedduring a 10 to 15 m.y. time spanfrom the endof The present-dayNE Japanarc is everywhereunder E-W the Oligocene to the middle Miocene. These results compression(Figure 3), approximatelyparallel to the confirmed some of the earlier conclusions based on heat directionof relativeconvergence between the Eurasiaand 22,240 JOLIVET ET AL.' JAPAN SEA, OPENING HISTORY AND MECHANISM

48øN

YBK

136øE

Figure 3. Present-daytectonic context in the JapanSea region showing the directionof relative convergenceor strike-slip motion along the major zones of deformation.TPF, Tym-Poronaysk fault; HSZ,Hidaka shear zone; YBK, Yamato bank; TB, Tsushimabasin; TF, Tsushimafault; YF, Yangsan fault;PHS, PhilippineSea plate.

Pacific plates [Fukao and Furumoto, 1975; Nakamura, in the subsidencecurves of severalODP and Deep Sea 1983; Nakamura and Uyeda, 1980; Seno, 1985; De Met& Drilling Project (DSDP) drilling sites [Von Huene and 1992]. The arc is currently undergoing uplift, which Lallemand, 1990]. Active crustaldeformation is localized startedsome 5 to 6 m.y. ago [Sugi et al., 1983]. Recent alongthe subductioncontact as well as a N-S trending uplift is recordedalso on the inner wall of the Japantrench narrowzone alongthe easternmargin of the JapanSea JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,241

[Fukao and Furumoto, 1975]. Large-magnitude Dextral Transpression in South Korea compressionalearthquakes frequently occur there, in a Crustal seismic activity is recorded also in the zone where numerousactive reversefaults are recognized TsushimaStrait, and recentactivity is observedalong the [Tamaki and Honza, 1984]. Nakamura [1983] suggested Yangsan fault in South Korea [Jun, 1990]. Strike-slip that this active zone is the southernmost extension of the focal mechanisms with a notable compressional North America-Eurasia plate boundary which extends componenthave beenjcomputed by Jun [1990], who from easternSiberia to Sakhalinand Japan[Chapman and concludes that a NE-SW trending zone of dextral Solomon, 1976]. En 6chelon troughs were further transpressionexists between the Korean peninsulaand interpretedby Nakamura [1983] as a nascentsubduction Japanarc. zone. This hypothesiswas testedkinematically by several authors, first Seno [1977], and then De Mets [1992] with Crustal Structure and Age the NUVEL-1 data set, and it seems to be a viable kinematic solution. Proper oceanic crust is found only in a restricted Further north active seismic deformation is recorded in domain of the Japanbasin, which has a triangularshape Sakhalin.It hasbeen interpreted as the resultof eitherpure with its basealong the easternmargin of the back arc basin E-W compression [Chapman and Solomon, 1976] or [Tarnakiet al., 1992]. Its seismicvelocity structure and the dextral transpression[Savostin et al., 1983; Jolivet et al., recognition of magnetic anomalies ascertainits oceanic 1992; Fournier et al., 1994]. The coexistence of nature [Tarnaki and Kobayashi, 1988]. It roughly compressionaland strike-slip events, the latter being correspondsto the area deeper than 3000 m. Between localized along major reactivated Miocene strike-slip 3000 and 2000 m, stretched arc crust is distributed in the faults suchas the Tym-Poronayskfault (seeFigure 6), and Yamatoand Tsushima basins as well asin the westernpart the observation of recent dextral offset in northernmost of the Japanbasin [Tarnaki,1988; Tokuyarnaet al., 1987]. Sakhalin by Rozhdestvenskyi[1982] led us to conclude The velocity structureof the Yamato basinshows the same that dextral transpressionoccurs. This deformationis part verticalsuperposition as in the nearbyJapan arc exceptfor of a continuoustectonic development which startedin the its thicknessand the absenceof the 6.0 km/s layer. It is Oligocene(see below). much too thick for a normal oceanic crust and has been interpretedas highly stretchedarc crustintruded by mafic dykes and sills [Tokuyamaet al., 1987]. In the middle of Collision of the Izu-Bonin Arc With Central Japan the basin,the Yamato bank again showsthe samestructure The present-dayplate configurationputs the Pacific- as the Japan arc. It is believed to be a rift block left over PhilippineSea-Eurasia triple junctionin the southeastern duringcrustal extension. corner of the Japan arc and the Philippine Sea Tarnaki et al. [1992] also suggested that oceanic Plate/Eurasia(PHSP/EUR) rotationpole is locatedclose to spreadingin the Japanbasin involved a propagationof the the collision zone [Seno, 1977; Ranken et al., 1984; Huchon, 1985]. This situationis fairly recent, and most kinematicreconstructions show the triple junctionmoving alongthe easternmargin of Eurasiafrom southto north and reachingits presentposition in the middle Miocene [Jolivet et al., 1989; Haston and Fuller, 1991; Hall et al., 1993]. In this region,two buoyantfeatures, the Japanand Izu-Bonin arcs meet and collide [Matsuda, 1978; Niitsuma and Akiba, 1985]. The northernmosttip of the Bonin arc Oceanic (Izu peninsula)is being accretedto centralJapan along Crust several thrust contacts. As described by Taira et al. [1989], older collisions occurred since the middle Miocene,in the form of a sequentialaccretion of piecesof the Bonin arc to centralJapan. Compression is recordedin the area north of the collision zone with a fan-shaped patternof stress,which merges to the northwith the E-W compressionof NE Japan[Huchon, 1985]. Large strike- slip faultssuch as the Itoigawa-Shizuokatectonic line are reactivated as sinistral transpressionalwrench, and the thick late Cenozoic sedimentsof the FossaMagna suffer shortening.

Slow Dextral Motion Along the Median TectonicLine Westof thecollision zone, subduction of thePhilippine Seaplate occurs at a slowrate of 2-4 cm/year[Seno, 1977; Figure 4. Simplifiedgeometry of theJapan Sea opening Ranken et al., 1984]. A slight obliquity of the relative after Jolivet and Tarnaki[1992]. Distributedextension and motion vector inducesa partitioningof strain between oceanic spreading with westward propagation pure compressionin the Nankai trenchand a slow dextral accommodatethe southwardmotion of Japan along two motionalong the Median tectonicline [Okada, 1980]. major shearzones. 22,242 JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM

48Ohl

Figure 5. Reconstructionsof thekinematics and tectonic context in theJapan Sea and Sakhalin region in the Miocene after Jolivet and Tamaki [ 1992]. spreadingridge toward the west, based on the geometry of [Tamaki and Kobayashi,1988] or heat flow [Tamaki, magneticanomalies. This is in goodagreement with the 1986],as well asdrilling results show that the Japan Sea generaltriangular shape of theoceanic domain: spreading opened in the early and middle Miocene between25 and has startedearlier in the east where oceanic crust is more 15-12 Ma, as confirmedby tectonicand sedimentation widely distributed. historiesof the basinand its margins[Tamaki, 1988; Most geophysicaldata suchas magneticanomalies Tamakiet al., 1992;Jolivet al., 1991;Ingle, 1992]. JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,243

Miocene Tectonic Environment 55ø.._ The geometryof openingis constrainednot only by 140 ø 145 ø the internal structureof the basinbut also by the tectonic evolution of its margins. As discussedby Jolivet and Tamaki [ 1992], there is a considerabledifference between the eastern narrow strike-slip margin and the southern wide extensional one (Figure 4). As described by Lallernand and Jolivet [1985], Jolivet et al. [1992], and Tamaki et al. [1992], the eastern margin is the southernmostextension of a 2000-kin-long strike-slip shear zone which extends from the northern tip of Sakhalinto centralJapan (Figures 3 and 5). Sakhalinand Hokkaido are locatedalong the transpressionalbranch of the dextral shear zone, which is characterizedby major dislocationssuch as the Tym-Poronayskfault in Sakhalin and the Hidaka shearzone in Hokkaido, as well as by en 6chelon folds and thrusts (Figure 6) [Fournier et al., 1994]. It is relayedto the southat the latitudeof Hokkaido by a transtensionalbranch, which boundsthe JapanSea back arc basin to the east. A second dextral shear zone is found between Korea and Japan in the Tsushima Strait [Sillitoe, 1977]. These two shearzones were active in the late Oligocene (or earlier) until the middle Miocene contemporaneouswith opening in the back arc region [Jolivet et al., 1991]. The shear zone seems to control sedimentdeposition in pull-apart basins in the Tartary 45 ø Strait (H.S. Gnibidenkoet al., unpublisheddata, 1990), or along the easternmargin of the oceanicdomain, or again along the east coast of Korea. The direction of the maximum horizontalprincipal stressduring the Miocene was NE-SW in the whole JapanSea as well as along its margins[Otsuki, 1989; Jolivet and Huchon,1989; Jolivet al., 1992; Charvet et al., 1992]. The general geometryis that of a large pull-apart basin, as suggestedearlier by Lallemand and Jolivet [1985] and Kimura and Tamaki [ 1986]. Formationof en 6chelongrabens along the eastern marginof the JapanSea lastedduring the early Miocene until the middle Miocene (see Figure 8) [Suzuki, 1989; Yamaji, 1989; Amano and Sato, 1989] and was contemporaneouswith dextral shear along the Hidaka ShearZone [Jolivet and Huchon, 1989]. Figure 7 [after Ingle, 1992] shows the timing of subsidencein the JapanSea and alongits margins,based on sedimentationhistory of severaldrill holesaround and inside the basin. It showsthat the history of subsidence started around 30 Ma and lasted until 10 Ma, after which uplift of the marginsis recorded.This timing is in fair agreementwith that deducedfrom the study of brittle deformationin Hokkaidoby Jolivetand Huchon [1989], who showed that E-W compressionreplaced dextral strike-slipshear at the endof themiddle Miocene (Figure 8). The inceptionof compressionoccurred 8 m.y. ago beforecompressional deformation became localized along the easternmargin, leading to the seismicityobserved today.The high rate of subsidenceis alsoin agreement with the pull-apart hypothesis[Ingle, 1992] as is the geometricalrelation between the easternshear zone and the oceanic domain. Figure 6. Main featuresof the dextral shearwhich guide Jolivet and Tamaki [1992] interpret the oceanic the opening of the Japan Sea to the east. Thick lines domainas a largetension gash at the end of a strike-slip representthe strike-slip structures,and thinner lines the shearzone (Figure 4). As the reconstructionswill show present-daycompressional ones. Dotted lines show the below, crustalextension was distributedin the Miocene in main en 6chelon folds in Sakhalin. 22,244 JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM

I Dextral strike-slip and Extension - Compression --,- Incipient Fast spreading Accelerating rifftingand and subsidence, deformation subsidence arc rotation of arc and basin

Thermal subsidence

1

(Ingle, 1992) Average tectonic subsidence/uplift Average total subsidence/uplift

30 25 20 15 10 5 0 Age (Ua) Figure 7. Subsidencecurve in theJapan Sea after Ingle [1992]. a wide area boundedby two dextral shear zones, and Back arc opening was claimed to have been oceanicspreading started in a limited zone next to the contemporaneouswith rotations about vertical axes of the easternshear zone. Lithosphericbreakup was localized Japan arc [Otofuji and Matsuda, 1983, 1984, 1987; where extensionaland strike-slipdeformations coexisted, Otofuji et al., 1985, 1991]. As shownby Figure 9, e.g., where the maximum of strain rates is expected. counterclockwiserotation of NE Japanlasted about as Tamakiet al. [1992] emphasizedthat it mightbe a general long as back arc openingproceeded (see references to the rule that oceanicspreading in back arc basinsstarts along originaldata in Figure9 caption).In SW Japaninstead, strike-slipfaults. clockwise rotation seems instantaneoustoward the end of

Amount of Convergence explosive volcanism volcanism

Sedimentation

Nonm in NE Japan

E-W compression Dextraltranstension (1,2,6,9) Stress and Uplift (12,13) • Riftingeast Japan Sea (4) tectonic history --• Rifting(5) • Blocktilting (6) esitic Aosawa basalts (7) Onland and subaqueaous Bimodal Dacitic tuffs volcanism (8) ..... ,' ,' ,' ,' ,', No volcanism

Volume Onland of ejecta (10) volcanic history FUNAKAWA ONNAGA WA MONZEN Stages (11) I 5 10 15 20 25 30 Age (Ma) Figure 8. Synthesisof the tectonicand volcanicevents in northeastHonshu after (1) Jolivet and Huchon[1989], (2)Jolivet et al. [1990],(3)Nakamura and Uyeda [1980], (4)Suzuki [1989], (5) Yamaji [1989], (6) Amanoand Sato [1989], (7) Tsuchiya[1989], (8) Usuta [1989], (9) Otsuki [1989], (10) Sugimuraet al. [1963],(11) Fujioka[1986], (12) Sugiet al. [1983],and (13) lijima et al. [1990]. JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,245

80 ø

40-- Japan Japan.sea •i:•:i

-40--

-8O I I o 5 lO 15 20 25 30 35 Age (Ma.)

Figure 9. Rotationpath for southwestand northeast Japan and the periodof JapanSea opening versus age compiled from Otofuji et al. [1991], Hayashida et al. [1991], Hayashida [1986], Otofuji and Matsuda [1983], Otofuji and Matsuda [1984], Otofuji and Matsuda [1987], Otofuji et al. [1985], and Tosha and Hamano [1988].

the opening time span. This last observation had led inceptionof compression,after which, acidic explosive Otofuji et al. [1985] to postulatean instantaneousopening volcanism resumed in the form of large-scalecalderas, of the JapanSea by rigid rotationof SW Japanabout 15 until 2 Ma, when the present-day andesitic volcanism Ma. This situation would have led to the formation of started [Usuta, 1989; Yahata, 1989; Ito et al., 1989]. This oceanic crust around 15 Ma in the whole Japan Sea. transition from explosive acidic volcanismto andesitic Recent drilling [Tamaki et al., 1992] showedinstead that volcanismwas interpretedby Jolivet and Tamaki [1992] the basin is everywhere older than the middle Miocene. as an effect of the localization of compressional There is so far no definiteexplanation to this discrepancy, deformation along the eastern margin at 2 Ma: the but it is likely that local rotationsof dominosplayed an compressionalstress field which prevailed before made important part in the story as suggestedby Kanaori the ascent of magma through the upper crust difficult. [1990] and Kodama and Nakayama [ 1993]. Magma had to accumulatein magma chambers,where it could differentiate, and made its way in an explosive Correlations of Arc Volcanism and Tectonics manner, forming large calderas. Once deformation had been localized along the easternmargin, compressional Besides correlations between the subsidence and stress was reduced through the arc, and the ascent of tectonic evolution, a clear contemporaneityof volcanic magma made easier. and tectonicepisodes can be drawn out of an analysisof The volcanicfront migratedduring this evolution,as is offshoreash layers and onland volcanicdeposits [Jolivet well documentedby Ohguchiet al. [1989]. This migration and Tamaki, 1992]. Arc volcanismin Japanexperienced can alsobe explainedin a simpleway in the sametectonic two stagesof activity from the late Oligocene, separated timing. During the opening,the volcanic front migrated by one quiet episodebetween 10 and 7 Ma (Figure 8). first eastward by 200 km with respect to its present This short period is seen in the ash record of numerous position between 30 and 20 Ma, and then came back drilling sitesaround Japan, on the Pacific side as well as progressivelyto its present position, which it reached on the JapanSea sideof the arc. about 12 Ma [Ohguchiet al., 1989]. These displacements The first episode correspondsto the rifting and were interpretedas indicationsof variationsof the slabdip spreadingof the JapanSea. In thelate Oligoceneand early angle throughtime [Tatsumiet al., 1989]. It is, however, Miocene (Green Tuffs period) the volcanicproducts of possibleto interpretit more simply,taking into account extensiveexplosive volcanism are found on land on either the thinning and stretchingof the arc crust during rifting side of the JapanSea. As is true of most back arc basins and spreadingof the JapanSea. If one assumes,contrary [Taylor, 1992], the JapanSea early rift was locatedalong to Tatsumi et al. [1989], a constant dip angle of the the volcanic arc, in a manner similar to the active intraarc subductingslab throughtime, and that the volcanicfront riftingof the Boninarc. The endof the openingis marked correspondsto a constantdepth of the slab,one can then by a distinctiveperiod of basalticvolcanism along the use the displacementof the volcanicfront to estimateto eastern margin (Aosawa Basalts [Tsuchiya, 1989]). A thinning history of the arc, as the distancebetween the period of no volcanic activity is recognized on land trenchand the active volcanicfront at any given time must between 13 and 8 Ma [Cadet and Fujioka, 1980; Usuta, remain constant.As shown by Figure 10, homogeneous 1989]. The timing of offshore ash layers allows us to stretchingof the upperplate crustleads to a displacement shortenthis periodto 2-3 m.y., between7 and 10 Ma. This of the volcanic arc oceanwardwith respectto its previous period correlatesto the transitionbetween opening and position.The distancebetween the two volcanicfronts 22,246 JOLIVET ET AL.' JAPAN SEA, OPENING HISTORY AND MECHANISM

150 km ......

Slabdip angle Slab retreat Extension VF

30 :-•'d •,":'••D-••,"- T ...... Via_• ......

150 km I -- I I VF . Tectonicerosion

150 km

Figure 10. Migrationof thevolcanic front from 30 Ma to thepresent. VF, volcanicfront; T, trench;D, distance between volcanic front and trench; d, distancebetween the 20-Ma and 30-Ma volcanic fronts. Duringthe rifting period, homogeneous stretching of thearc lithosphere is assumed.D is keptconstant throughtime becausethe slab geometryis supposedlyconstant (modified after Jolivet and Tamaki [19921). before and after stretching dependsonly upon finite TectonicHistory extension[•. A displacementoceanward of 200 km, as described in Ohguchi et al. [1989], leads to a finite We now present tectonic reconstructionswhich are homogeneous stretching factor of 1.8, which is a basedon the kinematics described by Jolivet et al. [1991] reasonablevalue comparedto longitudinalvariations of andJolivet and Tamaki[1992] (Figures 1 la to 1lf). The crustalthickness within arcswhere extensionis active, Japanarc is dividedinto severalrigid blockswhich move such as the Bonin arc. The subsequentretreat of the alongtwo masterstrike-slip faults, described above, and volcanic front toward its present position can be rotateabout vertical axes. As suggestedby Jolivetet al. interpretedas the result of tectonicerosion as discussed by [ 1991],the transtensionalregime which prevailed in the VonHuene and Lallemand [ 1989] (Figure 10]. This simple Miocene in the back arc domain favored clockwise explanationdoes not excludethe possibilityof variations rotations,while the transpressionalregime in the north of the slabdip angle,but it showsthat internal deformation insteadfavored counterclockwise rotations. A larger of the arc duringthe rifting episodehas to be takeninto dextralslip is accommodatedalong the eastern shear zone accountas well asdeep-seated phenomenas which are by than along the western one, and the difference is nature more difficult to observe and to test. accommodatedby dextralrotation of southwestJapan. This hypothesisneeds to be tested,and the simplest NortheastJapan also rotates counterclockwise in response way wouldbe to quantifythe amountof late Oligocene to the transpressionalcontext in Hokkaido. When one extensionfrom faults offset. Given the thick late Neogene closesback the oceanic domain of theJapan basin, moving and Quaternarycover of NE Japan,late Oligocene backthe Japan arc toward the north, a smalltriangular deformationmight not be easyto observe.It is verylikely regionremains where oceanic accretion has started. Figure anywaythat duringthe JapanSea rifting, extensionwas 11f showsthe positionbetween 25 and30 Ma (drawnat not localized only in the back arc region, but rather 30 Ma) when we assume the earliest oceanic crust was encompassedthe entire width of the arc until the forearc formed(An 7). The schemeis the following:a wide region,as illustratedby the present-daystructure of the domain of distributed extension accommodates the Bonin arc. transitionbetween two majorstrike-slip shear zones. At JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,247

Figure 11. Reconstructionof the tectonicevolution of the JapanSea. Kinematicsafter Jolivet et al. [1991] and Jolivet and Tamaki [1992]. Numbers in parenthesesare the intervals relevant to the coastlinestaken from Iijima and Tada [1990]. Light shadingrepresents the onshoreregions, white areas anrebelow sealevel. Dark shadingin the JapanSea represents the regionof distributedstretching, and the black area the domain of oceaniccrust. Solid dot representsfreshwater lakes. VF is the volcanic front after Ohguchiet al. [1989]. 22,248 JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM

...... :.:.:.,...

Figure 11. (continued) the junction between the eastern shear zone and the discussedabove. Active oceanicspreading enlarges the domainof distributedextension, high shear strains lead to oceanic domain with a westwardpropagation of the a complete rupture of the lithosphereand formationof spreadingcenter. Distributed extensiondeepens the oceanic crust. The newly formed oceanic ridge then Yamatobasin and the westernextension of theJapan basin localizes most of the relative displacementin the as shownon the subsidencecurves of Ingle [1992]. Two extensionaldomain. Farther west, crustal stretching zones of fresch waters characterize the domains of active accommodatesthe southwardmotion of SW Japan.Note intraarctranstension (west of Tohoku)or pureextension that the formation of oceanic crust occurs at the transition (SW Japan). The Fossa Magna startsto be seen as a betweentranspressional and transtensional regimes. narrow N-S trendingbasin parallel to the major shear Coastlines have been drawn on the reconstructions zones,and separates SW andNE Japan.The arcuateshape basedon the work by Iijima and Tada [1990], who of Japanappears progressively. The outer zonesof SW compiledstratigraphic and sedimentologicaldata in and Japan(Shimanto belt) emergedat this time. Charvetand aroundthe JapanSea. We take from their compilation, Fabbri [1987] attribute this event to compressional only coastlines which are sufficient to illustrate the deformations,which they relateto a collisionevent in the geometry of basins and discuss the first-order early Miocene. In their reconstructions,they use the sedimentologicalhistory in relationto tectonicevents. PhilippineSea plate (PHSP), which carries high standing On the 30 Ma (Figure 1lf) reconstruction,most of the featuressuch as the Palau-Kyushuridge and the Bonin arc Japanarc is abovesea level exceptfor the outerzones of aswell asthe Shikokubasin spreading center as a collider. SW Japan,where an accretionaryprism is beingbuilt in This is in contradiction with the timing of our the proto-Nankaitrench, as well as for the centralpart of reconstructionsof the motion of the PHSP, which lead to a Hokkaido,where coarse clastics fill narrowN-S trending more recent subduction and collision of the PHSP under basinsparallel to the Hidaka shearzone. Freshwater lakes SW Japan.In a recentstudy of thepaleomagnetic rotation are describedon the mainland.Dextral motionalong the of the PHSP, Haston and Fuller [1991] concludedto even two major shear zones was transferred to distributed more recent collisionof the Bonin arc with SW Japan extensionin the Yamatobasin and oceanicspreading in around 10 Ma. If the deformation in Shimanto is not due the Japanbasin. to the collisionof the PHSP, it must involve buoyant Around 20 Ma (Figure 1l e) the Japanand Yamato featurescarried by thePacific plate. basinswere fully separatedand below sea level. The entire About 15 Ma (Figure 1l d) the openingwas almost Hidakashear zone has gone above sea level. Migration of complete.The last incrementsof oceanicspreading are the volcanicfront far eastof its presentposition is takenas recorded,while rotationand strike-slipmotion are still an indicationof distributedrifting withinthe Japanarc, as active.The arc has now reachedits presentshape, and JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,249

most of it is below sealevel with the notableexception of following and see the respectiveroles they played in the the Hidaka shearzone, which remainsan elongatedhigh JapanSea history. ground, and a narrow stripe in SW Japan which is perpendicular to the direction of extension. The N-S- Japan Sea and ContemporaneousOceanic Basins trending Hidaka Mountains are flanked on both sidesby in the West Pacific narrow, shallow marine basins filled with coarse clastic deposits.The shapeof the basinto the eastis controlledby Major back arc basinsof the westernPacific region dextral strike-slip faults [Miyasaka et al., 1986]. The openedin a shorttime spanbracketed between 30 and 10 westernpart of SW Japan,most of the Shimantobelt, is Ma (see the compilationby Park et al. [1990]). Three abovesea level. The present-dayplate configuationof the largebasins are settledin the easternmargin of Asia. The trench-trench-trench(T-T-T) triple junction is established Kuril basin(Figures. 1 and 2) openedbetween 15 and 30 around this time also, and collision of the Bonin arc with Ma, accordingto Kimura and Tamaki [1985], northof the centralJapan begins. At the sametime, the last increments Kuril arc in a triangulardomain with oneside along the of spreadingare recordedin the Shikokubasin. Sakhalin-Hokkaidoshear zone. Its age of openingis The period at 12 Ma (Figure 11c) is when most strike- certainlythe lesswell controlledand is basedmostly on slip motionhas stoppedand will soonbe replacedby E-W thetectonic and sedimentological evolution of itsmargins compressionin NE Japan. The emergeddomain of SW in Japanand Sakhalin,which are very similarto that of Japanhas progressed toward the eastand is startingto the Japan Sea. The South China Sea has been studied in close the FossaMagna. This might be an effect of the greaterdetail andreveals a consistentpattern of magnetic progressiveeastward displacement of theBonin arc during anomalies.The first interpretationsby Taylor and Hayes its collisionwith southernJapan. The westernside of NE [1980, 1983] providedan age of openingbetween 32 and Japanis still below sea level, as is the centralpart of 17 Ma, based on the identification of anomalies 11 to 5d. Hokkaido.Between 10 and2 Ma, a compressionalstress More recently, Briais et al. [1993], basedon a new set of fieldprevailed in NE Japan,and this led to theprogressive data (Figure 12), recognizedanomaly 5c andconcluded uplift of the arc in Honshuand Hokkaido. that the opening occurred between 32 and 15 Ma. At 2-3 Ma (Figure1 lb), only the westernmostpart of Extensionpredated spreading along the southernmargin NE Japanwas belowsea level beforethe inceptionof the of China and startedas early as the Paleocene[Ru and activedeformation zone localized along the eastern margin Pigott, 1986].The SuluSea was recently dated by drilling of the JapanSea. This led to the final uplift of thisnarrow of the early and middle Miocene [Rangin et al., 1990a; stripe in the Recent period. The entire SW and central Rangin and Silver, 1991]. Rangin et al. [1990b] showed Japanhas been uplifted as well, and intraoceanicthrusts that the Sulu Sea was formedinside the marginof Eurasia formed south of the collision zone inside the PHSP. and not as a trappedbasin, as suggestedby Lee and Thesereconstructions, which showgood correlations McCabe [1986]. Oceanicspreading in thesefour large of tectonic,volcanic, and sedimentologicalevents, also basinsthus occurred in the sameperiod on the marginof allow a crudequantification of the dextraldisplacement Eurasia, and was precededby severalmillion years of along the major strike-slip faults. We assumethat the intracontinentalrifting. This observationshows that from south-to-northfinite motionof NE and SW Japanwith the Paleocene to the middle Miocene, the entire eastern respectto Asia between30 and 12 Ma hasbeen entirely margin of Asia was subjected to extensional stress taken up further north along the more localizeddextral conditions. shearzone which runs along Sakhalinand in the Tartar Two large basinsformed in the sameperiod along the Strait. This leads to a finite dextral motion of about 400 eastern border of the PHSP, the Shikoku and Parece Vela km. Given the uncertaintiesof the reconstructions,which basins(Figure 2), which are part of the largestback arc are difficult to quantify,one can reasonably conclude that basin in the world and formed behind the Bonin-Mariana several hundreds of kilometers have been accommodated trenchsystem. Mrozowski and Hayes [1979] recognized along this shearzone, which makesit a first-orderfeature magnetic anomalies 10 to 5d and concluded that the of the finite deformation of Asia. The western shear zone opening occurredbetween 30 and 17 Ma for the Parece in the Tsushima Strait has accommodated a smaller Vela basin.The ageof the Shikokubasin is morecertainly displacementof theorder of 200 km, thedifference being known, based on several drill holes [de Vries Klein and takenup by rotationof SW Japan. Kobayashi, 1980] which reached oceanic crust and We thusconclude with the following scheme:several identification of magnetic anomalies [Shih, 1980; large-scale intracontinentaldextral shear zones run N-S Chamot-Rooke et al., 1987] (also, N. Chamot-Rooke et obliqueto the easternmargin of Asia, whichis subjected al., Magnetic lineation and paleomagnetism in the to back arc extension.Asymmetric back arc spreading Shikoku basin: Implications for the Miocene kinematics occurswhere the dextralshear zones intercept the region of the Philippine Sea plate, submittedto Geophysical of backarc extension and control the geometry of opening, Journal International, 1993; hereinafter referred to as as describedabove. The questionthen is the causeof these submittedmanuscript, 1993). Anomalies7 to 5b suggest dextralshears in easternAsia. Kimura and Tamaki [1986] an openingbetween 27 and 13 Ma (Figure 12). Opening and Jolivet et al. [1990] suggestedearlier that they are started along the paleo-Bonin arc and separatedthe consequences of the India-Asia collision. Back arc present-dayBonin arc and the remnant Palau-Kyushu extension, on the other hand, occurred in the whole ridge. It probablystarted with rifting along the volcanic westernPacific region in the sameperiod, late Oligocene arc, as is seen today in the Bonin arc [Taylor, 1992]. to the middle Miocene.We shalldiscuss separately the Extension and spreading also continue in the Mariana two phenomenas,back arc spreadingand collision,in the trougheast of the PareceVela basin. 22,250 JOLIVET ET AL.' JAPAN SEA, OPENING HISTORY AND MECHANISM

• 6b

•8 9 -'10

12 5c 5c 5e

138

$HIKOKU BASIN SOUTH CHINA SEA (CHAMOT-ROOKE ET AL. 1993) (BRIAIS ET AL. 1993) Figure 12. Magnetic anomaliesin the Shikokubasin and SouthChina Sea (after N. Chamot-Rookeet al., submittedmanuscript, 1993; Briais et al. [ 1993]).

While the Japan Sea, South China Sea, Kuril basin, the Himalayas, the Karakoram-Pamirregion, and Tien and Sulu Sea were in the processof opening,a large back Shanand Alta¾ ranges. These regions of hightopography arc basin was formed along the easternmargin of the are boundedby distinctivelarge-scale structures, such as PHSP. Figure 12 showsthe magneticanomaly pattern of the Altyn-Tagh fault or Longmen Shan thrust zone. the two best surveyedbasins, the Shikoku basin and the Regionsof crustalthinning are the AndamanSea, South South China sea (after N. Chamot-Rooke et al., submitted China Sea, Gulf of Thailand, and Sulu and Celebes Seas. manuscript,1993) [Briais et al., 1993]. Thoughspreading The Ryukyu back arc region (Okinawa basin)extends in startedearlier in the South China Sea, it stoppedat the the East China Sea and the north China grabensand sametime after Anomaly 5c in both basinsand a similar further to the northeast,to the Japanand OkhotskSeas. kinematic reorganizationoccurred by counterclockwise The Baikal rift is the westernmostextensional region. All rotation and segmentationof the ridge aroundAn 6 (20 theserifting eventsstarted during the Paleogeneafter the Ma). The contemporaneity of opening and intimate collision, and those rifts closest tO the thickened crust are evolution of these two basins suggeststhat a common still active (Baikal, North China Gr•bens,Andaman Sea). processcreated extension and spreading.As it affectsthe All but the Okinawabasin are now extinct(Kuril basin)or easternmargins of the Eurasiaplate andPHSP, we believe in a closingstage (South China Sea, JapanSea). Those that this processis not relatedto the India-Asia collision, still active along subductionzones face normal oceanic which would not affect the PHSP. However, the large- lithospherewhich subductsfreely beneaththe western scalestrike-slip shear zones which controlrifting and part of the Sunda arc or beneaththe Ryukyu arc. The spreadingin the JapanSea as well as in the SouthChina South China, Sulu, and Celebes Seas started to close when Sea,if onefollows the modelproposed by Tapponnieret the collisionof Australiawith Indonesiaoccurred [Rangin al. [1982], cannot be simply explainedby back arc et al., 1990], and Japan Sea rifting was reverted to spreading. compressionwhen the Bonin arc collided with central Japan. Japan Sea and the Deformation of the Asian Jolivet et al. [1989] and Rangin et al. [1990b] Continent exploredpreviously the tectonicevolution of the eastern margin of Asia in two sets of reconstructions.The first Variations of crustal thickness in Asia can be showed the entire northwest Pacific region, putting visualizedby the topographicmap of Figure 2. The area emphasison the JapanSea and the PHSP [Jolivet et al., of crustalthickening encompasses the Tibetanplateau and 1989], and showedthe Indonesianregion only crudely. JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,251

......

...... EURASIA i-!:i:i:!:i:i:i:i::' 25 Mo .:.. i.i:i:i::'

.:::::i.i:i:i::'

...... v.v.....v.v.

......

......

......

......

\ x \ I I I I i 70• 80*E •O*E 100'E 110'E I•I•'E I•'E 140'E

Figure 13. Reconstructionof Asia and west Pacific at 25 Ma (early Miocene). See Figure 1 for explainationof symboles.

More precisereconstructions were made by Rangin et al. trenches[Rangin and Silver, 1991]. The motion of major [1990b]. Precise age constraintscame through ODP leg plates around the deformed domain was taken from the 124 in the Sulu and Celebes Seas [Rangin et al., 1990a]. global kinematic data set [Stock and Molnar, 1982], We can use these reconstructionsto obtain a crude image whichprovided a generalframework. Various kinds of of the finite displacementof the easternand southeastern data were used for the reconstructions.The geometryof borders of Asia, with respect to fixed Eurasia. The openingof theSouth China Sea is constrainedby a setof geometry that we obtain can be used to illustrate the well-defined magnetic anomalies, as described above. general evolution of the boundariesof Asia during its Recent data, obtainedby drilling in the Sulu and Celebes collision with India. They certainly are not precise Seas,provided age constraintsfor the openingof these becauseuncertainties on the total displacementalong basins [Rangin et al., 1990a; Silver and Rangin, 1991a; major faults insideAsia are very large. Only the general Ranginand Silver, 1991], but no geometricalbounds. The schemematters for our discussion(Figures 13 and 14). regional geological history of the Philippines and Rangin et al. [1990b] proposedreconstructions of the Indonesia was used as an indicator of where and when Philippinesand Indonesian region from the Eoceneto the extensionor shorteninghad taken place. Rangin et al. Present,describing deformation of the region where the [1990b] attemptedto describethis complexdeformation Pacific, Philippine Sea, Australia, and Eurasian plates with simplekinematics, in which mostmicroplates rotate meet. Complex deformationis distributedover a large about a pole located in the Andaman Sea [Le Pichon, area [Hamilton, 1979], where a numberof marginalbasins 1988], deduced from the magnetic anomaly pattern openedin the Oligoceneand Mioceneand then startedto [Briais, 1989]. closealong subductionzones, such as the Manila or Sulu The southernmargin of the South China Sea moves 22,252 JOLIVET ET AL.' JAPAN SEA, OPENING HISTORY AND MECHANISM

Stable Eurasia ...... NAM ::•.... 50øN OKHOTSK ...... !:!:!:!:!:!:•

.....

40øN

30øN

20øN PHSP '.'•,,

500 km/EU 10øN

India...... OON

1000 km/EU "• '"•, Ma

15 Ma -lOON ß T AUS

70øE 80øE 90øE 100øE 110øE 120øE 130øE 140øE Figure 14. Finitedeformation of theeastern and southeastern border of Asiausing the reconstructions describedin thepaper and crude quantification of thedisplacements. togetherwith Indochinain the reconstructions,following terminationof theRed River fault.Opening stopped about Tapponnier et al. [ 1982], who linked the South China Sea 15 Ma. The Manila trench was formed in the early openingto extrusion,although we take into accountthe Miocene [Cardwell et al., 1980] and the South China Sea actual geometryof opening.The displacementof the progressivelysubducted below the northernPhilippine PHSP is basedon (1) paleomagneticdata which give the arc. The Sulu Sea began to underthrustthe Sulu arc latitudinaldrift and (2) the deformationhistory of the shortlyafter it opened,and the CelebesSea was consumed Philippinearchipelago [Jolivet et al., 1989 andreferences beneath the northern arm of Sulawesi from 15 Ma. therein]. More precise reconstructions using Sinistraltranspressional motion has been active along the paleomagneticdata by Hastonand Fuller [ 1991] andHall Philippinearchipelago from at least20 Ma to the Present, et al. [1993] give a similar clockwise rotation and fast and the present-dayPhilippine trench was formed some5 northward drift between 25 and 10 Ma. Ma ago. Most of the sinistral displacement was Two periodsmay be distinguished:first, whenmost of accommodatedalong the Philippinefault [Cardwellet al., basins opened (reconstructionat 25 Ma) and, second, 1980; Karig et al., 1986; Barrier et al., 1991]. Collision when most began to close while the whole deformed of blocks belonging to the Australian realm started domainbegan to shorten.The changefrom the first to the between 20 and 15 Ma, which is about the time when the secondtook placeat approximatelythe time whenthe first basins started to close. collision of Australia with Indonesia occurred. In the first Reconstructionsof Indonesia and Japan were made period, the SouthChina Sea openedclose to the eastern with a fixed "Eurasia"(North China) addingthe relative JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,253 motion of north China with respect to stable Eurasia to the reconstructions of Indonesia, that some 200 km is a obtain the desired reconstructions.Total displacement reasonablenumber for the total eastward expulsion of along the Tien Shan-Baikal-Stanovoy shear zone is SouthChina with respectto Eurasia. knownonly approximatelybut is probablyfairly small. We can then use these three sets of reconstructions to There is an acutecompatibility problem at thejunction reconstructthe geometryof the easternand southeastern between the N-S trending dextral system and the E-W marginsof Asia from 45 Ma to the Present.Four stages trending left-lateral system south of the North China have been plotted togetherin Figure 14 to show the grabens.The dextral systemreactivates the Cretaceous progressivedisplacement of theborders of Asiain a fixed Tanlu fault [Xu et al., 1987; Chen and Nabelek, 1988], but geographicframe. Stable Eurasia refers to the portionof the active domain does not seem to extend south of the Asia west and north of the Pamir-Tien Shan-Baikal shear Qin Ling ranges,and the Qin Ling fault is not seeneast of zone [Cobbold and Davy, 1988], which bounds the the Tanlu fault. As arguedby Dewey et al. [1989] and Xu deformeddomain. Given the assumptionsdescribed above et al. [1987], the Tanlu fault is not offset by the E-W for the variousreconstructions, Figure 14 showsthe finite trending left-lateral strike-slip system,though its strike deformationof Asia with respectto a fixed Eurasiafrom changesslightly southof the Qin Ling, preventingany 45 Ma to the present.The displacementof India wastaken large eastwardescape of South China with respectto from Besse and Courtillot [1988], who used both the North China. As shown by Mattauer et al. [1985] and magnetic lineation data set of the Indian Ocean, as did Okay and Senggir[1992], the Tanlu fault does not extend Patriat and Achache [1984], and the apparentpolar south of the Dabie Shan, which is the Mesozoic thrust wander path of Eurasia [Besseand Courtillot, 1991] to front of the Qin Ling range. But the left-lateral activity computethe motion of India with respectto Eurasia.For recongnized by Peltzer et al. [1985] is restricted to the Recent time, motion around the pole of De Mets et al. northernpart of the Qin Ling and it does not offset the [1990] was chosen, which takes into account the active Tanlu fault. This fits the palaeostressfield data obtained shorteningin the eastern Indian Ocean. Inception of by Bellier et al. [1988], who suggestedthat left-lateral shorteningwas chosenat 7 Ma, after Leg 116 Shipboard motion occurred only in the Plio-Quaternary. In the ScientificParty [1987], similar to Le Pichon et al. [1992]. Miocene the displacementnorth of the Qin Ling (Wei He Figure 14 shows crude estimates of the total graben)was dextral transtension. displacements of the margins of Asia, 400 km Sucha junction betweentwo large strike-slipsystems southeastwardin the northeast, and 1000 km southward in that do not offset one anotherimplies someblock rotation. the southeast. A shortening of several hundreds of Using a comparison with Davy and Cobbold's [1988] kilometers is seen along the Philippine archipelago experiments, Jolivet et al. [1990] suggestedthat the concommitantlywith the left-lateral motion. easternpart of North China and Japancan be describedas These reconstructions, though unprecise, show a a set of dominosrotating counterclockwise in a major left- drasticchange in the kinematicboundary conditions from lateral shearzone, the displacementbetween the dominos the early Miocene to the Present, from basically free being taken up by dextral motion along the N-S dextral subduction all around eastern and southeastern Asia to strike-slip faults, and a componentof extension being lockedsubduction or collisionat present.This changeled expected,as observedin the JapanSea. to the closingof mostmarginal basins formed during the Large-scale deformation is taken up through a left- early stage.Based on different kinematic hypothesesor lateral shearzone which encompassesthe region from the assumptionson the relationbetween large-scale strike-slip Qin Ling to the Stanovoy and accommodated by faults and marginal basinsopening, one could produce counterclockwise rotation of dominos and dextral motion. different reconstructions, but all would show the same As in the reconstructions, we use a counterclockwise basic first-order observations: (1) distributed extension rotation of 15ø since 25 Ma about a pole located to the andlocalized spreading occurred in southeastAsia during northeastof Lake Baikal, from Savostinet al. [1983] to fit the Paleoceneand early Miocene, (2) back arc extension the extensionaltectonics of Lake Baikal and the partly and spreading was associatedwith large-scale dextral compressionalfield in the Stanovoyrange. This addsan shear zones in NE Asia between two major left-lateral overall eastward displacementof the Korean peninsula shear zones, (3) marginal basins closed during the and Japan region during the dextral shear and Japan Sea progressivenorthward motion of the PHSP along the opening. The total displacementalong the Altyn-Tagh easternmargin of Asia and settlingof the T-T-T triple fault is not known with precision;we assumeda value of junctionin its presentposition in themiddle Miocene and 200 km left-lateral offset in our reconstructions. This as first effects of the collision of Australia around 20 Ma. strike-slipmotion is transferedinto crustalthickening in Note that we have chosento link the openingof the the Nan Shanrange, which is in turn partly transferedinto South China Sea to left-lateral motion along the Red left-lateral strike-slip displacementalong the Qin Ling River fault, as did Tapponnieret al. [1982; 1986], in our fault. Which proportion of the left-lateral motion along reconstructions.This model is not acceptedby all authors the Altyn Tagh fault is transferredinto the Qin Ling fault [Taylor and Hayes, 1983] (also, C. Rangin et al., is a matter of debate [Dewey et al., 1989]. Certainly not Cenozoic tectonics of central and South Vietnam: all displacementcan be found to the east, as a part of the Evidence for superposedtectonic regimes, submittedto eastward displacement of Tibet is taken up along the Tectonophysics,1993; hereinafterreferred to as Rangin et LongmenShan thrust zone. A studyof recentdeformation al., submitted manuscript, 1993) and some prefer to in the Wei He graben(immediately north of the Qin Ling) disconnectthe openingfrom extrusionof Indochina.This also suggeststhat left-lateral slip is smaller there than hypothesis would lead to a slightly different more to the west [Bellier et al., 1988]. We considered, in reconstruction in this region, with a much smaller 22,254 JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM extrusion of Indochina, but it would not affect the total experimentaldevice except for a thinnerlithosphere and a displacementof the southernmargin of the South China larger size experiment.In order to create extensionthe Sea with respectto South China, which is constrainedby rheologywas chosenso that the "lithosphere"tends to magnetic anomalies and is thus independentof any a collapse under its own weight. In the absence of priori model. It would necessitatea large-scaledextral indentation the eastern and southeasternboundaries tend to motion alongthe easternmargin of Vietnam, as postulated move outward and grabens form perpendicular to by Taylor and Hayes [1983] and recentlydescribed from gravitationalspreading. With suchboudary conditions, we field observationsby Rangin et al. (submittedmanuscript, appliedan indentationat variousvelocities. Figure 15 1993) and Huchon et al. [1994]. showsone of the experiments.The basicfeatures are the This dramatic change in kinematic boundary following:(1) extrusionis very diffuseand the extruded conditionsquestions the relevanceof present-daystrain block is internallyseverely deformed as in the numerical rate measurements in Asia to the finite deformation modeling of Housemanand England [1993], (2) the mechanism. Most discussions and models are concerned transtensionaldextral strike-slip shear zones are more with large displacements of several hundreds of preciselydefined thanin the experimentsof Davy and kilometersand openingof large rifts and oceanicbasins, Cobbold [1988] and more numerous,and (3) distributed andtherefore deal with finite deformation.If the boundary extensionis important in the southeasterncomer of the conditionshave changedsignificantly enough to affectthe model and orientated N-S. These first-order results are deformationregime of Asia as a whole, as suggestedby similar to the observations we made above on the real the 20 Ma revolution, then the strain rate measurement object in a first approach.The details seen in this must be used only to discuss the instantaneous experimentdue to its largesize and thin lithosphere reveal deformationof Asia. The reconstructionssuggest that the second-orderdominos along the N-S dextral shearzones length of the so-called free boundary of Asia, where whichrotate clockwise with respectto their surrounding extensionis active, was reducedprogressively through (larger scaledominos which rotate counterclockwisewith time by the northward drift of the PHSP and the respectto stableEurasia). It alsoreveals dextral pull-apart progressivecollision of Australia. This leavesonly small geometriesnext to the northeasternboundary. This portionsof the Eurasianmargin whereback arc opening geometryis similarto that of the JapanSea. We find here takesplace, while it is still activealong the easternmargin a confirmationof the idea developedby Jolivet et al. of the PHSP. If extrusion has occurred, it must be more [1990] with an emphasison the role playedby extensional difficult now than it was in the early Miocene, when the boundaryconditions. whole easternand southeasternboundary was subjectedto extension;therefore the present-dayrates of strike-slip Discussion motion along the major faults cannot be extrapolated easily to the past. This is obvious when consideringthe Severalobservations can be drawnfrom this synthesis, Red River fault, which no longer acts as a left-lateral some of which are readily discerniblefrom a simple guide for extrusion, but was changedto a dextral fault tectonicmap of Asia. (1) The displacementof the outer around 15 Ma. boardof Asia with respectto stableEurasia is apparently larger than the displacementof blocksinside the continent Analog Small-Scale Modeling (1000 km of southwardmotion of the Sundatrench versus 500 km of left-lateraloffset alongthe Red River fault, and Looking for a model which would integrate the this would be even more so without extrusion), (2) the deformation of Asia and the deformationof its margins extensional component of the deformation increases behind subduction zones, Jolivet et al. [1990] used the toward the back arc regions of the Japan and Sunda analogmodels of Davy and CobboM [1988] and Cobbold trenches,and (3) strike-slip faults (Japan) far from the and Davy [1988]. Thosemodels used a "lithosphere"made indenterhave accommodated large displacements, as large of siliconeputty (lower ductile crust)and dry sand(upper as thosealong closerstrike-slip faults (Red River, Altyn brittle crust) floating on glycose syrup (asthenosphere). Tagh). They also had simple kinematic boundary conditions, These observationssuggest that the trench roll-back indentationby a rigid indenter,and a stress-freeboundary, componentof subductionplayed an importantrole in the as in most models considered so far. Most of the deformation of the upper plate. At variance to the deformation was localized in front of the indenter in the assumptionmade by Tapponnieret al. [1982], Tapponnier form of folding and bucklingof the lithosphere,as well as et al. [1986], or Peltzer and Tapponnier [1988] for the along a wide sinistral N-E trending shear zone which South China Sea, we believe that the marginal basinsof connects the northwest corner of the indenter (Pamir SoutheastAsia did not open as "mismatchbasins" whose region) to the eastern boundary. Along this shear zone, openingis forced along strike-slipshear zones as a result large-scaledominos rotate counterclockwisebetween N-S of extrusion, subduction acting only as a passive trendingtranstensional dextral shearzones, which Jolivet boundary, but that they opened as the result of active et al. [1990] compared to the Sakhalin-Hokkaido-Japan extensionin the back arc region,and that their geometryis Sea shear zone. Extrusion is not localized along discrete then controlledby large strike-slipfaults. left-lateral shearzones as in Tapponnieret al. [1982], but The JapanSea and other marginalbasins opened in a distributed.In orderto investigatethe effectof extensional kinematicand dynamiccontext which is no longeractive boundary conditionsalong the easternand southeastern today except along the eastern margin of the PHSP. To margins, we (Fournier et al., unpublishedmanuscript, understandthe mechanismof openingof thosebasins, one 1994) performed new experiments with a similar must consider the kinematic context active in the early JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM 22,255

I Figure 15. Line drawing of an analog experiment of continental collision (M. Fournier et al., unpublishedmanuscript, 1994). The strainpattern is shownby faults observedin the sandlayer. Fold axes are shownby double arrows.Thrust faults are shownby thin lines with triangleson the upthrust side, normal faults by thin lines with barson the downthrownside. Dextral strike-slipfaults are shown by thick lines, and sinistralones by thin lines. The box in the lower left corneris the rigid indenter.The total lengthof the experimentis 1.20 m (from M. Fournieret al., unpublishedmanuscript, 1994).

Miocene, and reconstructionswith their inherent large longerimpinging the easternmargin of the Philippinesand errorsare an essentialstep. A comparisonof the 25 Ma South China, whereas collision of Australia was active in reconstructionand the present-daysituation shows how the south. The stress regime had evolved toward a the evolution of the boundary condition along the different situation, where the easternpart of the Sunda subduction zones and the deformation of Asia may be trench was no longer subjectedto trench roll-back and related. At 25 Ma, trench roll-back was probably active extensionbut insteadto compression.The Ryukyu arc was along all of the Sunda, Japan and Kuril trenches.The now facing a free subductionof the oceaniclithosphere of situation was different along the proto-Philippinefault, the PHSP, and central Japanexperienced the beginningof whereleft-lateral strike-slipwas active and the westerntip the Bonin arc collision. This new situation was of the Bonin arc was moving along the easternmargin of progressivelyintroduced from 20 to 10 Ma. Without the Eurasia. Stress conditions were most likely less trench roll-back along the Sunda trench, SoutheastAsia extensionalalong this boundary.During this period, N-S was no longerdragged southward, a•nd the directionof extension and spreading were active behind the Sunda spreadingconsequently changed in the SouthChina Sea as trenchin the SouthChina Sea, and the regionof Japanwas discussedabove. South China was then dragged toward dragged eastward behind the Pacific subduction.At 15 the east betweentwo more constrainedregions, collisions Ma, the Bonin arc had reachedcentral Japanand was no of Australia, Taiwan, and the Bonin arc. It could escape 22,256 JOLIVET ET AL.: JAPAN SEA, OPENING HISTORY AND MECHANISM betweenthe left-lateral Qin Ling fault and the dextral Red explosive volcanism:Japan trench transect, Initial Rep.Deep River fault, leading to the present situation. Note that SeaDrill. Proj., 1027-1041, 1980. during this complex evolution, back arc spreadingwas Cardwell, R.K., B. L. Isacks, and D. E. Karig, The spatial continuouslyactive behindthe Bonin arc in the Shikoku- distribution of earthquakes,focal mechanismsolutions, and PareceVela basinand the Mariana trough. subducted lithosphere in the Philippine and northern Indonesianislands, in The Tectonicand GeologicEvolution The JapanSea is thusunder the influenceof two large- of Southeast Asian Seas and Islands, Part 1, Geophys. scalephenomena: "classical" back arc spreadingprovided Monogr. Ser., vol. 23, editedby D.E. Hayes,pp. 1-36, AGU, the extensionalcomponent, and internal deformationof Washington,D.C., 1980. Asia due to the collision of India provided the dextral Chamot-Rooke, N., V. Renard, and X. Le Pichon, Magnetic strike-slipcomponent. We have no originalmechanism to anomaliesin the Shikoku basin: A new interpretation,Earth originate extensionother than the one usuallyconsidered Planet. Sci. Lett., 83, 214-223, 1987. after Uyeda and Kanamori [1979]. We only emphasize Chapman,M. C., and S.C. Solomon,North American-Eurasian here that the JapanSea is part of the westernPacific back plate boundaryin northeastAsia, J. Geophys.Res., 81,921- arc basinswhose openingis due to subduction,whatever 930, 1976. the exact mechanism, which is still controversial, as well Charvet, J., and O. Fabbri, Vue g6n6rale sur l'orog6nbse Shimantoet l'6volutiontertiaire du Japonsud-ouest, Bull. $oc. as the result of the internal deformationof Asia duringits Geol. France, 3, 1171-1188, 1987. collision with India. Without collision, the Japan Sea Charvet, J., K. Grimm, J. Griffin, L. Jolivet and A. 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