a review of magmatism and deformation history along the ne asian margin from ca 95 to 30 ma transition from the izanagi to pacific plate subduction in the early cenozoic abstract previous plate reconstruction in the paleo pacific domain indicates that the izanagi and pacific plates influenced the ne asian continental margin during the mesozoic and cenozoic respectively however it remains unclear how and when the transition from izanagi to pacific plate subduction occurred because most evidence came from the oceanic crust however the onshore geological records are poorly understood so in order to solve this problem we review recently published data and identify three magmatic episodes a magma gap and four deformation stages from ca 95 to 30 ma margin parallel izanagi pacific ridge subduction is proposed to explain the changing magmatic and deformation signatures and other regional events in the early cenozoic from ca 95 to 65 ma the n or nnw directed subduction of the izanagi plate triggered sinistral shearing along the nne striking faults arc magmas at that time incorporated older crustal materials from ca 65 to 55 ma the nww striking transform faults and ridge segments were subducted developing small slab windows and facilitating the input of juvenile magmas local extension was active above these windows during ca 55 to 45 ma the ridge was totally subducted and a margin wide slab window was opened resulting in an arc magma gap and extension massive asthenosphere upwelling caused the extensive accretion of juvenile materials from ca 45 30 ma the dextral nne trending faults resulted from the w directed subduction of the pacific plate new arc magmas were generated from juvenile materials and thus are isotopically depleted

cretaceous stress field evolution and origin of the jiaolai basin eastern north china abstract the jiaolai basin to the east of the tan lu fault zone tlfz is a cretaceous ne trending basin in eastern north china and has a multi episodic evolution different from other contemporary nw trending en echelon graben systems west to the tlfz the origin of the jiaolai basin three episodes k1l 135 120 ma k2q 120 105 ma k2w 88 65 ma cannot be simply explained by the sinistral displacement of the tlfz at the beginning of the early cretaceous around ca 135 ma the purpose of this paper is to investigate the critical factors e g bounding faults tectonic setting stress field driving the development of the jiaolai basin and constraint its evolution three episodes of two dimensional finite element models were generated in order to determine the roles of the boundary conditions and to reveal the tectonic development of the basin when compared to the calculated maximum horizontal compressive stress hmax trajectories and the observed data along with a comparison between the von mises stress u von and the depocenters of the basin the calculated results can be well proved by the geological evidence both in stress field evolution and in the basin patterns our analysis show that the three episodes of the maximum principle stress trajectories changed from ne sw earlier early cretaceous k1l nne ssw later early cretaceous k1q then e w late cretaceous k2w moreover the results show a good consistency between the u von and the depocenters in the basin through geological cross sections via models we suggest that the origin and evolution of the jiaolai basin were controlled by three episodes of tectonic events i the reactivated bounding faults and the post orogenic extension of the sulu orogen during the earlier early cretaceous ii the lithospheric delamination of the thickened lithosphere during the later early cretaceous and iii the likely far field effects produced by the collision between the kohistan drags arc complex and asia during the late cretaceous the jiaolai basin evolved from extension to pull apart experiencing volcanic activity during the three episodes of the cretaceous

an analysis of apparent polar wander path for southwest japan suggests no relative movement with respect to eurasia during the cretaceous abstract to test the hypothesis that southwest japan was involved in large scale tectonic movement with southward translation as far as 2000 km with respect to eurasia during the cretaceous we examined cretaceous paleomagnetic poles from southwest japan to compare with those from eurasia red and gray sandstone samples from the upper cretaceous onogawa group were collected from twelve sites in the onogawa basin in the western part of southwest japan for paleomagnetic analysis this group formed over the time span in which the proposed tectonic event is hypothesized to have occurred a characteristic remanent magnetization component was isolated from red sandstone at ten sites it is interpreted to be of primary late cretaceous origin the primary directions combined with previously reported data provide a mean direction d 76 8 i 44 6 95 11 1 n 15 and a paleomagnetic pole 24 4 n 202 6 e a95 11 0 for the onogawa area this pole is consistent with other late cretaceous poles from a wide area of southwest japan and a mean late cretaceous pole 28 4 n 202 5 e a95 7 5 n 6 is calculated and regarded as representative of this region the late cretaceous pole together with mid and early cretaceous poles constitutes an apparent polar wander path apwp for southwest japan during the cretaceous after restoration of post cretaceous tectonic rotation each cretaceous pole for southwest japan shows agreement with the coeval poles for eurasia therefore it is unlikely that the previously proposed tectonic model that includes southward translation of southwest japan occurred in the late cretaceous southwest japan is considered to have behaved as a stable part of the eurasian continental margin during the cretaceous

changing stress field in the middle segment of the tan lu fault zone eastern china abstract the tan lu active fault zone is an important tectonic boundary in east china minor structures associated with the fault show that the nature of displacement on the middle segment of the fault zone has changed in consecutive episodes since the cretaceous normal faulting during the cretaceous sinistral strike slip and reverse faulting at the end of the cretaceous or in the early tertiary and dextral strike slip and reverse faulting from the late tertiary to the present the regional orientation of the maximum principal compressive stress based upon the statistical study of minor shear fracture orientation is 6 s52 w in the late tertiary to quaternary this stress field may be related to the collision between india and tibet and the microspreading of the japan sea

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

mesozoic collision extrusion tectonics in eastern asia abstract the eastern part of the asian continent was intensively deformed in early cretaceous time deformation has been interpreted to be related to subduction tectonics along the eastern continental margin we propose an alternative tectonic framework of collision extrusion tectonics resulting from collision of the indochina block with the eurasian continent this event controlled the jurassic to cretaceous tectonic history in eastern asia and the evolution of the subduction zone along the eastern margin of the continent

paleomagnetic evidence for the miocene counter clockwise rotation of northeast japan rifting process of the japan arc paleomagnetic results have been obtained from more than 700 oriented samples in igneous rocks of cretaceous to miocene age from northeast japan the remanent magnetizations of welded tuffs with age between 32 ma and 21 ma old from 17 widely distributed sampling sites in northeast japan are fairly well grouped with a mean ofd 41 2 i 56 5 95 7 2 the remanent magnetization of welded tuffs of 14 ma and 11 ma from 4 sites shows a northerly direction d 11 7 i 60 5 95 15 3 these data imply that northeast japan was apparently subjected to a counter clockwise rotation through 47 14 about a vertical axis on the representative point of northeast japan 141 e 39 n during the past 21 ma comparing with the period of the clockwise rotation of southwest japan the differential rotation between northeast japan and southwest japan is concluded to have occurred concurrently during the period between 21 ma and 12 ma a rifting model of the japan arc is proposed northeast japan rotated counter clockwise through 50 about a northern pivot at 146 e 44 n while southwest japan rotated clockwise through 54 about a southern pivot at 129 e 34 n the differential rotation about different rotation pivots gives rise to the opening of a diamond shaped back arc basin the japan sea

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

late eocene granites in the central sakhalin island russian far east and its implication for evolution of the sakhalin hokkaido orogenic belt abstract the sakhalin hokkaido orogenic belt along the western margin of the okhotsk sea is an important early cenozoic accretionary orogen related to subduction of the paleo pacific oceanic plate in order to study the eocene evolution of this accretionary orogen and related magmatism we carried out zircon u pb dating whole rock elemental and sr nd isotopic analyses on the langeri and val za granitic plutons that intruded the east sakhalin accretionary complex in the central sakhalin island zircon u pb dating results revealed that the langeri and val za plutons were emplaced in the late eocene at 38 36 ma whole rock elemental data indicate that granitoids are mainly peraluminous s type with subordinate i type granites and all granitic samples show arc like geochemical affinity whole rock sr nd isotopic results show consistent low initial 87sr 86sr ratios 0 7042 to 0 7049 positive end t values 1 7 to 3 1 and young nd two stage model ages 611 to 717 ma elemental and isotopic data reveal that granitic rocks of the langeri and val za plutons were generated from remelting of metasediments and amphibolites in the accretionary complex from comprehensive analyses of regional tectonics we concluded that the late eocene granitic rocks were generated in a syn collisional tectonic setting marking the timing for formation of the sakhalin hokkaido orogenic belt the middle late eocene welding of the okhotsk sea plate and the eurasia plate is the most plausible mechanism that caused crustal thickening beneath the sakhalin island and anatexis of metasediments and oceanic crustal materials in the lower crust might be responsible for the formation of late eocene granitic rocks considering the eocene tectonic events in ne asia late paleocene to early eocene subduction of the kula pacific ridge beneath the hokkaido island and eocene initial rift of pull apart basins along strike slip fault system in the hokkaido and sakhalin islands may also contribute to the emplacement of eocene magmatism in the sakhalin hokkaido orogenic belt

the hidaka shear zone hokkaido japan genesis during a right lateral strike slip movement the mesozoic structure of hokkaido which is characterized by a wide spread ophiolite sequence unconformably overlain by a cretaceous flysch sequence is cut by a north south trending metamorphic belt the hidaka belt this contribution aims to demonstrate that the hidaka belt is a wide right lateral strike slip shear zone the movement is contemporaneous with the metamorphism and the magmatism of oligo miocene time

counterclockwise rotation of northeast japan paleomagnetic evidence for regional extent and timing of rotation early to late miocene welded tuffs have been sampled from northeast honshu island and the oshima peninsula of hokkaido island japan for paleomagnetic study characteristic directions with a high unblocking temperature component above 560 c are isolated from 24 sites westerly declinations d 1 91 are identified in welded tuffs older than 17 ma from these areas when combined with previous paleomagnetic data from welded tuffs the early miocene paleomagnetic poles derived from northeast honshu island and the oshima peninsula are statistically identical and indicate that northeast honshu island and the oshima peninsula were subjected to counterclockwise rotation as a single tectonic block these results establish that the rotating block of northeast japan extends north to the oshima peninsula to the latitude 43 n the dimension of this rotating block is of the order of 500 km the paleomagnetic data provide a best curve for the rotation process with the counterclockwise rotation reaching a climax at 15 0 ma and a net amount of rotation of 46 4 the 500 km long northeast japan block was rotated counterclockwise through more than 45 and accompanied a clockwise rotation of the 600 km long southwest japan block at about 15 ma

krill as a central node for iron cycling in the southern ocean 1 in order to establish the potential role of antarctic krill euphausia superba in the recycling of bioactive elements we have quantified the release of iron phosphate and ammonia by these organisms along the antarctic peninsula sector of the southern ocean the experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations as large amounts of this trace element were released by the krill 22 689 nmol fe g dry weight 1 h 1 equivalent to 0 2 to 4 3 nmol fe l 1 d 1 half of this iron release occurred within the first hour of the experiment and differences in iron and phosphate release rates 3 1 to 14 0 mol po43 g dw 1 h 1 seemed to reflect differences in food availability these results identify krill as a major node in iron cycling in the southern ocean potentially influencing iron residence time in the upper water column of this region

deep scientific dives in the japan and kuril trenches abstract in the summer of 1985 during the french japanese kaiko program ten dives to depths of 6000 m in the japan and kuril trenches were made in the newly launched submersible nautile the sites of the dives were selected on the basis of surface geophysical surveys made during the preceding summer involving seabeam mapping geomagnetic and gravimetric measurements and single channel seismic profiling the results of the dives provide new constraints on the geodynamics of these subduction zones in the japan and kuril trenches huge slump scars were observed on the landward slopes of the trenches slumps produce a typical active erosional morphology with vertical or even overhanging cliffs in poorly consolidated material the slump scars allowed us to observe the internal structure of the margin the monoclinal structure on the northern japan trench margin deduced from the seismic profiles and dsdp drilling was confirmed several dives on kashima seamount confirmed that this volcano has recently been split into two parts by a normal fault system comparisons of lithology and paleontology on the two separated parts of the seamount were made deep sea clams colonies were observed from nearly 6000 m up to 5000 m on the landward slopes of the trenches it can be concluded that the whole margin is venting fluids from depths of 2 3 km which is consistent with the indications of overpressure observed in drill sites on the japan trench margin the fluids probably originate by dewatering of the subducting sediments and then migrate to the seafloor

incipient subduction and deduction along the eastern margin of the japan sea the eastern margin of the japan sea has been under convergent tectonics since sometime after the pliocene the suture line is on the ocean continent boundary between the japan yamato basins and the tohoku northeast japan arc incipient subduction and obduction of the oceanic and sub oceanic crust are observed along the suture line with the occurrence of numerous n s trending fault bounded ridges and troughs focal mechanism solutions of several compressional type earthquakes with magnitudes of m 6 9 to 7 7 which have occurred along the zone are consistent with the observation of geological thrust faults the convergent stresses in the japan sea may be due to india eurasia collision and its associated intra plate or inter microplate movements in east asia the eastward movement of the amurian plate causes baikal extension along its western margin and the japan sea convergence along its eastern margin

geology of the idonnappu belt central hokkaido japan evolution of a cretaceous accretionary complex the cretaceous idonnappu belt located along the western hidaka mountains of central hokkaido island in japan records evidence of west to northwest directed underthrusting of oceanic crust the idonnappu fault divides the idonnappu belt into two subbelts the western oku niikappu on subbelt and the eastern koiboku ko subbelt the on subbelt is dominated by a melange facies it includes various thicknesses of pillow basalts bedded radiolarian cherts limestones and greenish siliceous shales all of which are intermixed with a highly sheared shaley matrix that displays a scaly cleavage the ko subbelt is dominated by a thick flysch sequence and alternations of sandstone and shale with thin tectonic melange the stratigraphic sequences within these belts usually young toward the west and display westward vergent structures outcrop to microscopic scale structures in the melange zone of the idonnappu belt however suggest eastward vergence detailed biostratigraphic studies show that structural packages young toward the east ranging in age from lower to upper cretaceous these observations are consistent with an accretionary prism model in which oceanic crust is underthrust toward the west or north west in the middle miocene a change to westward vergence was caused by uplift of the hidaka mountains

microtectonic evidence for eastward ductile shear in the jurassic orogen of sw japan abstract two jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the mesozoic chain of sw japan the first phase was synmetamorphic and took place under hp lt conditions microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from w to e parallel to the stretching and mineral lineation at the regional scale the first phase corresponded to the obduction of the greenschist nappes upon the kurosegawa continent during the second phase the greenschist nappes were sliced leading to an apparent reverse metamorphic zoning the first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear

eocene arc continent collision and crustal consolidation in kamchatka russian far east the age and origin of high grade metamorphic rocks of the sredinnyi range kamchatka have been the subject of a long and controversial debate based on geochronologic data and its association with a collage of accreted oceanic terranes leading interpretations argue that the sredinnyi range metamorphic rocks represent an accreted precambrian or mesozoic microcontinent in this contribution we present new data that indicate that these metamorphic rocks were formed from the cretaceous paleocene sedimentary margin of northeast russia when it was overridden during eocene obduction of the olyutorsky arc a far travelled oceanic island arc our data include new mapping and structural observations along the northern and eastern flanks of the sredinnyi range and shrimp zircon and monazite u th pb age data from 15 key samples these new isotopic data demonstrate that paragneissic units were formed from sediments with depositional ages locally no older than late cretaceous to paleocene furthermore the statistical similarity of zircon u pb grain ages from the kamchatka schist with very low grade turbidite sandstones of the ukelayat and khozgon groups indicate that metasediments of the sredinnyi range are upgraded stratigraphic equivalents of northeast russian marginal strata shrimp u pb ages of zircon overgrowths and metamorphic monazite extracted from migmatite and gneiss indicate that peak metamorphism occurred at 52 ma which is synchronous with the onset of the olyutorsky arc continent collision heating and cooling occurred rapidly at rates approaching 80 c m y rapid heating is attributed to syn collisional subduction related magmatism thermochronology and structural observations indicate that exhumation was due to a combination of ductile and brittle thinning of the crust we speculate that this thinning was caused by diapiric ascent of a low density low viscosity continental material beneath a dense structural lid of the obducted island arc

geodynamics of an early eocene arc continent collision reconstructed from the kamchatka orogenic belt ne russia abstract the principal structures of the central and eastern ranges of the kamchatka orogenic belt were formed during collision of an upper cretaceous lower paleocene island arc with the asian continental margin during the early eocene two major syncollisional tectonic events are recognized westward thrusting of the island arc onto the continental margin and eastward thrusting on the eastern side of the deformed arc accompanied by tectonic accretion of eastward derived slices of oceanic crust both tectonic processes occurred under upper to middle crustal conditions syntectonic high temperature medium pressure metamorphism up to amphibolite and granulite facies affected the units of the arc its oceanic basement and the continental margin synkinematic gabbro plagiogranite intrusions occurred along major decollements of both vergences according to the geodynamic model both of the observed tectonic events i e westward overthrusting of the arc and eastward thrusting at its eastern side represent incremental stages of a single processes that lasted over 7 ma and was initiated by the arc continent collision the first stage corresponds to southeastward continent subduction under the arc which was soon blocked followed by reversal of subduction polarity and the beginning of northwestward oceanic subduction

acoustically inferred zooplankton distribution in relation to hydrography west of the antarctic peninsula abstract the relationship between the distribution of zooplankton especially euphausiids euphausia and thysanoessa spp and hydrographic regimes of the western antarctic peninsula continental shelf in and around marguerite bay was studied as part of the southern ocean globec program surveys were conducted from the rvib n b palmer in austral fall april june and winter july august of 2001 acoustic video and environmental data were collected along 13 transect lines running across the shelf and perpendicular to the western antarctic peninsula coastline between 65 s and 70 s depth stratified net tows conducted at selected locations provided ground truthing for acoustic observations in fall acoustic volume backscattering strength at 120 khz was greatest in the southern reaches of the survey area and inside marguerite bay suggestive of high zooplankton and micronekton biomass in these regions vertically highest backscattering was in the 150 450 m depth range associated with modified circumpolar deep water cdw the two deep troughs that intersect the shelf break were characterized by reduced backscattering similar to levels observed off shelf and indicative of lower zooplankton biomass in recent intrusions of cdw onto the continental shelf estimates of dynamic height suggested that geostrophic circulation likely caused both along and across shelf transport of zooplankton by winter scattering had decreased by an order of magnitude 10 db in the upper 300 m of the water column in most areas and high backscattering levels were found primarily in a deep 300 m scattering layer present close to the bottom the seasonal decrease is potentially explained by advection of zooplankton vertical and horizontal movements and mortality predictions of expected backscattering levels based on net samples suggested that large euphausiids were the dominant source of backscattering only at very particular locations and depths and that copepods siphonophores and pteropods were more important in many locations

a model for estimating cross shore surface transport with application to the new jersey shelf 1 a one dimensional steady state numerical model is developed for estimating cross shore surface transport in shallow waters where the water depth is comparable to boundary layer thickness the model is used to solve a momentum equation which describes the cross shore balance to validate the model acoustic doppler current profiler adcp current data collected during an experiment off the new jersey shelf in the summer of 1996 are used to estimate the cross shore surface transport during that period and then compared with model predictions based on the local wind the success of the model in estimating the cross shore surface transport leads to an improved version of the conventional upwelling index i e the bakun index particularly for coastal areas with wide and shallow shelves such as the east coast of the united states finally the model because of its simplicity is well suited for operational applications where computational resources may be limited

archean protolith and accretion of crust in kamchatka shrimp dating of zircons from sredinny and ganal massifs abstract we used an ion microprobe shrimp rg for u pb dating of individual zircons in high grade metamorphic basements of the felsic sredinny and mafic ganal massifs in kamchatka thirty percent of zircons from paragneisses of the sredinny massif contain archean 2800 2500 ma early proterozoic 1700 2100 ma and late proterozoic 1000 ma detrital cores in addition a broad and almost uninterrupted range of phanerozoic detrital cores 460 175 ma is present with jurassic to lower cretaceous 150 96 ma zircons forming the youngest detrital age group ubiquitous documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand tex

lithospheric contributions to arc magmatism isotope variations along strike in volcanoes of honshu japan major chemical exchange between the crust and mantle occurs in subduction zone environments profoundly affecting the chemical evolution of earth the relative contributions of the subducting slab mantle wedge and arc lithosphere to the generation of island arc magmas and ultimately new continental crust are controversial isotopic data for lavas from a transect of volcanoes in a single arc segment of northern honshu japan have distinct variations coincident with changes in crustal lithology these data imply that the relatively thin crustal lithosphere is an active geochemical filter for all traversing magmas and is responsible for significant modification of primary mantle melts

instantaneous movement of krill swarms in the antarctic circumpolar current antarctic krill are known to have strong swimming capabilities but direct observations of the speed and direction of krill swarm movement within their natural environment are rare we identified and examined 4060 swarms within the main flow of the antarctic circumpolar current scotia sea using a combination of an ek60 echosounder a 153 6 khz acoustic doppler current profiler and ground truthing nets net displacement magnitude m and net angle of deviation d were determined by vector subtraction from the background flow immediately below them values were compared against control data sets in which swarms were absent with greater background flow m became increasingly lower than predicted which suggests that drag influences swarm movement the characteristics of the flow regime influenced swarm behavior given that both m and d varied according to the direction of background flow furthermore multiple regression analysis indicated that swarm area the vicinity of the sea ice edge and salinity had a significant influence on m with levels of displacement being greatest in larger swarms and in low salinity regions close to the ice edge the ice edge is a key environment for antarctic krill and swarm behavior may assist in retaining this location only fluorescence was found to have a significant influence on d with deviations being greatest in regions of highest fluorescence this agrees with laboratory observations of krill turning more frequently within food patches we demonstrate that it is possible to measure instantaneous movement patterns in antarctic krill swarms and at large scales these movements are consistent with current understanding of responses of krill to local stimuli such as sea ice and patches of food swarms of antarctic krill form some of the highest concentrations of animal biomass found in any of the world s ocean reaching densities of up to 2 million tons over an area of 100 km2 nowacek et al 2011 krill swarm

tertiary paleomagnetism of north and south china and a reappraisal of late mesozoic paleomagnetic data from eurasia implications for the cenozoic tectonic history of asia abstract to contribute to the understanding of the cenozoic tectonic history of china and eastern eurasia in general we collected paleomagnetic samples from tertiary rocks in both north and south china our miocene paleomagnetic data for northern china are from four widely separated basalt sections in the inner mongolia autonomous region and shandong province both normal and reversed polarities of the characteristic magnetization are present in the stratigraphie sequence and the mean normal and reversed directions are closely antiparallel to each other the fact that the same characteristic direction was carried by both magnetite and hematite suggests that the hematite was probably formed by auto oxidation processes during primary cooling of the basalts the paleomagnetic data from these four areas also pass a regional generalized fold test the corresponding mean miocene paleomagnetic pole for northern china is longitude 261 6 e latitude 88 3 n a 95 6 4 our early tertiary paleomagnetic results for south china are from two sandstone sections around the city of nanning 22 7 n 108 3 e in guangxi zhuang autonomous region high temperature characteristic directions isolated in 31 samples from five sites pass both tilt and reversal tests the paleomagnetic pole position determined from the five sites lies at longitude 228 0 e latitude 83 6 n a 95 8 5 the tertiary paleomagnetic poles for north and south china are statistically indistinguishable from each other and thus confirm that north and south china were fully assembled at least by the tertiary our new tertiary paleomagnetic data are consistent with the hypothesis that the major continental blocks of north and south china were in the same position as today during the tertiary a critical evaluation and selection of paleomagnetic results from the late jurassic onward for siberia europe and north and south china further corroborate this hypothesis most previously existing jurassic and cretaceous paleomagnetic poles from europe siberia are of uncertain reliability and should not be used for tectonic reconstruction using poles derived from transferring reliable data from other continents we show that the previous paleomagnetic inferences of large eastward displacements between these chinese blocks during the cenozoic are no longer warranted the available paleomagnetic data that meet our acceptance criteria are also of interest concerning the boundary conditions of the propagating extrusion model for asian tectonics additional mesozoic and cenozoic paleomagnetic data from siberia and north and south china are still needed to resolve the smaller second order displacements that appear to characterize the cenozoic tectonic history of this part of asia

late cretaceous cenozoic deformation of northeast asia abstract the plate tectonic paradigm implies rigid plates and narrow plate boundaries in contrast diffuse plate boundaries are common both in the oceans and continents r g gordon annu rev earth planet sci 26 1998 615 642 and their history is difficult to constrain especially in remote tectonically complex areas such as northeast asia m e chapman s c solomon j geophys res 81 1976 921 930 here we show how extensive north atlantic marine magnetic r macnab et al eos 76 1995 449 458 and gravity data d t sandwell w h f smith j geophys res 102 1997 10039 10054 can be used to unravel with tight confidence limits successive periods of deformation over 80 million years along the diffuse continental eurasian north american plate boundary a period of compression in the late cretaceous 14 mm yr in the laptev sea to 20 mm yr in kamchatka led to thrusting in the verkhoyansk mountains and was followed by extension from 68 to 40 ma when 400 km of extension was accommodated by the formation of a series of grabens including the moma rift system since 40 ma time varying compression and transpression along the moma rift system created strike slip faults thrusts and folds at rates up to 6 3 mm yr in the laptev sea region 600 km of extension from latest late cretaceous to present created the laptev sea and lena rift systems the deformation predicted by our model fits most geological features formed in the laptev sea and central northeast asia during late cretaceous cenozoic times the most recent deformation late miocene pliocene is not very well constrained since our model lacks data younger than 11 ma the deformation that occurred in kamchatka reflects a complex tectonic setting and our model s predictions are only tentative

nankai trough and the fossil shikoku ridge results of box 6 kaiko survey abstract seabeam mapping and detailed geophysical surveying have been conducted over the nankai trough where the fossil shikoku ridge is subducted below southwest japan the geometry of the oceanic lithosphere bending under the margin as well as the three dimensional structure of the accretionary prism have thus been determined in detail three 350 trending probably transform faults have been identified in the area of the survey they do not extend further south and appear to be limited to the last phase of spreading within the shikoku basin probably between 15 and 12 ma this last phase of spreading would then have been accompanied by a sharp change in spreading direction from east west to n 350 the two eastern transform faults limit a zone of reduced nankai trench fill of turbidites opposite to the tosa bae embayment this observation suggests that the tosa bae embayment actually results from this reduced supply of trench fill to the imbricate thrusting process the accretionary prism can be divided into three different tectonic provinces separated by continuous mappable thrusts the lower and upper main thrusts surface shortening is limited to the lower accretionary prism south of the upper main thrust umt whereas uplift with possible extension characterizes the prism above the umt deformation due to the relative plate motion mostly affects the lower accretionary prism south of the umt

mesozoic evolution of northeast asia and the collision of the okhotsk microcontinent abstract tectonic models of northeast japan generally involve the progressive subduction of the paleo pacific oceanic crust during the mesozoic and collision of the okhotsk microcontinent at the end of the cretaceous with eurasia however these models are not based on a precise knowledge of the overall structure and succession of deformations in the collision zone our survey leads us to propose structural maps and cross sections of the hokkaido central belt and a tectonic description of each tectonic stage it appears that at the end of the jurassic until the early cretaceous an important event of nappe emplacement occurred we interprete this event as the collision of the okhotsk block with eurasia much earlier than in classical models during this collision the oceanic crust of a marginal basin was obducted with an east vergence and partly metamorphosed contemporaneously with the collision an important volcanism linked with the pacific subduction started and continued during the whole of the cretaceous period the continental margin was affected by strike slip faults running parallel to the margin with a left lateral motion the main fault was the tanlu fault which accommodated the northward movement of the eastern part of the asian continent which led to the closing of an oceanic domain between siberia and the okhotsk block this tectonic scenario ended 70 m y ago contemporaneously with the cessation of the volcanism in the okhotsk uda margal volcanic belt from the eocene to the middle miocene a right lateral strike slip motion along sakhalin and hokkaido gave rise to the hidaka shear zone and finally led to the opening of the sea of japan

an unrecognized major collision of the okhotomorsk block with east asia during the late cretaceous constraints on the plate reorganization of the northwest pacific abstract interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions however the traditional tectonic model for the east asian margin during the mesozoic invoking successive episodes of paleo pacific oceanic subduction does not provide an adequate context for important late cretaceous dynamics across east asia including continental scale orogenic processes significant sinistral strike slip faulting and several others the integration of numerous documented field relations requires a new tectonic model as proposed here the okhotomorsk continental block currently residing below the okhotsk sea in northeast asia was located in the interior of the izanagi plate before the late cretaceous it moved northwestward with the izanagi plate and collided with the south china block at about 100 ma the indentation of the okhotomorsk block within east asia resulted in the formation of a sinistral strike slip fault system in south china formation of a dextral strike slip fault system in north china and regional northwest southeast shortening and orogenic uplift in east asia northeast striking mountain belts over 500 km wide extended from southeast china to southwest japan and south korea the peak metamorphism at about 89 ma of the sanbagawa high pressure metamorphic belt in southwest japan was probably related to the continental subduction of the okhotomorsk block beneath the east asian margin subsequently the north northwestward change of motion direction of the izanagi plate led to the northward movement of the okhotomorsk block along the east asian margin forming a significant sinistral continental transform boundary similar to the san andreas fault system in california sanbagawa metamorphic rocks in southwest japan were rapidly exhumed through the several kilometer wide ductile shear zone at the lower crust and upper mantle level accretionary complexes successively accumulated along the east asian margin during the jurassic early cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike slip fault system the departure of the okhotomorsk block from the northeast striking asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin in the campanian the block collided with the siberian margin in northeast asia at about 77 ma a new oceanic subduction occurred to the south of the okhotomorsk block ending its long distance northward motion based on the new tectonic model the abundant late archean to early proterozoic detrital zircons in the cretaceous sandstones in kamchatka southwest japan and taiwan are interpreted to have been sourced from the okhotomorsk block basement which possibly formed during the late archean and early proterozoic the new model suggests a rapidly northward moving okhotomorsk block at an average speed of 22 5 cm yr during 89 77 ma it is hypothesized that the okhotomorsk east asia collision during 100 89 ma slowed down the northwestward motion of the izanagi plate while slab pull forces produced from the subducting izanagi plate beneath the siberian margin redirected the plate from northwestward to north northwestward motion at about 90 89 ma

the kamuikotan zone in hokkaido japan tectonic mixing of high pressure and low pressure metamorphic rocks in the kamuikotan zone central hokkaido japan two distinct types of metamorphic rocks are tectonically mixed up along with a great quantity of ultramafic rocks one type consists of high pressure metamorphic rocks and the other of low pressure ones the high pressure metamorphic rocks are divided into two categories 1 prograde greenschist to glaucophaneschist facies rocks derived from mudstone sandstone limestone a variety of basic rocks such as pillow and massive lavas hyaloclastite and tuff and radiolarian valanginian to hauterivian chert among which the basic rocks and the chert and occasionally the sandstone occur as incoherent blocks or inclusions enveloped by mudstone 2 retrograde amphibolites with minor metachert and glaucophane calcite rock which are tectonic or exotic blocks enclosed within prograde mudstone or serpentinite or separated from these prograde rocks by faults the k ar ages of the prograde metamorphic rocks 72 107 and 116 ma on phengitic muscovites are younger than those of the retrograde rocks 109 132 135 and 145 ma on muscovites and 120 ma on hornblende the low pressure metamorphic rocks consist of the mafic members of an ophiolite sequence with a capping of radiolarian tithonian chert with the metamorphic grade ranging from the zeolite facies through the greenschist partly actinolite calcic plagioclase facies to the amphibolite partly hornblende granulite facies the low pressure metamorphism has a number of similarities with that described for ocean floor metamorphism the tectonic evolution of such a mixed up zone is discussed in relation to mesozoic plate motion

collision rotation and back arc spreading in the region of the okhotsk and japan seas the india eurasia collision caused extensive deformation in the eurasia continent since late eocene time we propose that back arc spreading in the okhotsk and japan seas was related to the movement of microplates relevant to the india eurasia collision the kuril basin of the okhotsk sea and the basins of the japan sea were formed as back arc basins simultaneously their late oligocene to middle miocene age is constrained by sediment stratigraphy basement depth and heat flow data the movements of two microplates the okhotsk and amuria plates are significant for the tectonics of the okhotsk and japan seas simultaneous retreat of both microplates from trench hinge lines caused back arc spreading in the kuril basin and the japan sea the amuria plate moved north northeastward due to the india eurasia collision this caused pull apart opening of the baikal rift along a transform boundary between the siberia and amuria plates and a collision along the stanovoy range at its northern margin this movement triggered a clockwise rotation of the okhotsk plate with a component of dextral collision between the okhotsk and amuria plates which is well observed along the central zone of the sakhalin hokkaido islands between the two back arc plates the clockwise rotation of the okhotsk plate is suggested by the southwestward fan shaped opening of the kuril basin the kuril basin narrows to the northeast and terminates south of the kamchatka peninsula where a relative rotation pole between the okhotsk and kuril forearc plates is located the kamchatka peninsula was a zone of collision on the other side of the clockwise rotating okhotsk plate during the opening of the kuril basin the sredinny range in the kamchatka peninsula is one of the results of the collision between the okhotsk plate and the forearc plate of the kuril arc the bending of the japanese islands occurred in association with the back arc spreading of the yamato basin of the japan sea

inversion of the erlian basin ne china in the early late cretaceous implications for the collision of the okhotomorsk block with east asia abstract a significant transition in tectonic regime from extension to compression occurred throughout east asia during the mid cretaceous and has stimulated much attention however the timing and driving mechanisms of the transition remain disputed the erlian basin a giant late mesozoic intracontinental petroliferous basin located in the inner mongolia northeast china contains important sedimentary and structural records related to the mid cretaceous compressional event the stratigraphical sedimentological and structural analyses reveal that a nw se compressional inversion occurred in the erlian basin between the depositions of the lower cretaceous saihan and upper cretaceous erlian formations causing intense folding of the saihan formation and underlying strata and the northwestward migration of the depocenters of the erlian formation based on the newly obtained detrital zircon u pb data and previously published paleomagnetism and fossil based ages the saihan and erlian formations are suggested as latest aptian albian and post early cenomanian in age respectively implying that the inversion in the erlian basin occurred in the early late cretaceous cenomanian time apatite fission track thermochronological data record an early late cretaceous cooling exhuming event in the basin corresponding well with the aforementioned sedimentary structural and chronological analyses combining with the tectono sedimentary evolutions of the neighboring basins of the erlian basin we suggest that the early late cretaceous inversional event in the erlian basin and the large scale tectonic transition in east asia shared the common driving mechanism probably resulting from the okhotomorsk block east asia collisional event at about 100 89 ma

low frequency free wave and wind driven motions over a submarine bank abstract this study attempts to isolate the physics peculiar to a submarine bank the particular model is barotropic and contains an infinitely long straight bank within an unbounded ocean basin the low frequency free wave solutions consist of two infinite sets of model analogous to barotropic continental shelf waves one set trapped to each side of the bank in addition a severely distorted double kelvin wave is associated with the net depth difference across the bank inclusion of bottom friction representative of georges bank suggests that only one free wave westward propagating on the south side will have a sufficiently long decay time to be likely to be observed in nature the spatial variation in local spindown time also causes the lines of constant wave phase to be no longer perpendicular to the isobaths steady forward motions are considered for winds which vary slowly in the alongbank direction when the ekman scale depth is the same order as the minimal depth over the bank the primary dri

preliminary phanerozoic polar wander paths for the north and south china blocks polar wander paths for the north and south china blocks suggest that 1 both were parts of gondwana in the palaeozoic 2 the north china block accreted to siberia in the late permian and 3 the south china block accreted to the north china block in the middle triassic to the early jurassic comparison of the polar wander path for the south china block with that for northern eurasia suggests that relative motion of over 4 000 km has occurred between them

is northern honshu a microplate abstract seismic slip vectors along the japan trench the eastern margin of the japan sea and the sagami trough are compared with global relative plate motions rm2 minster and jordan 1978 to test a new hypothesis that northern honshu japan is part of the north american plate this hypothesis also claims that the eastern margin of the japan sea is a nascent convergent plate boundary kobayashi 1983 nakamura 1983 seismic slip vectors along the japan trench are more parallel to the direction of the pacific north american relative motion than that of the pacific eurasian relative motion however the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence seismic slip vectors and rates of shortening along the eastern margin of the japan sea for the past 400 years are also consistent with the relative motion between the north american and eurasian plates calculated there seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south kanto beneath which the philippine sea plate is subducting indicate two major directions one is the relative motion between the north american and philippine sea plates and the other that between the eurasian and philippine sea plates one possible interpretation of this is that the eastern margin of the japan sea may be in an embryonic stage of plate convergence and the jump of the north american eurasian plate boundary from sakhalin central hokkaido to the eastern margin of the japan sea has not yet been accomplished in this case northern honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates behaving as part of either the eurasian or north american plate another possibility is that the seismic slip vectors and crustal deformations in south kanto do not correctly represent the relative motion between plates but represent the stresses due to non rigid behaviors of part of northern honshu

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

crustal scale strike slip deformation in hokkaido northern japan abstract field surveys in hokkaido reveal that the entire tectonic belt in northern japan was a right lateral shear zone from eocene to middle miocene time this zone of deformation can be followed northwards in sakhalin for more than 2000 km and formed at the same time as the opening of the japan sea a thrusting component during the strike slip deformation and later deformation stages led to the uplift of the deep parts of the shear zone exposing a complete section through the upper crust the stress field inferred from the analysis of fault sets is consistent with the non coaxial deformation observed in the deeper ductile parts of the shear zone there is a transition from west to east across the width of the belt 100 km from en echelon folds thrusts and nappes at upper structural levels through the brittle ductile transition with an incipient vertical schistosity into ductile deformation with a vertical foliation and metamorphic recrystallization in the amphibolite facies deep parts of the crust granulites were uplifted and retrogressed during the strike slip movement fault set analysis together with data concerning the direction and sense of nappe emplacement imply that thrusting west of the ductile deformation zone occurred during the strike slip deformation minor flat lying structures coexist with vertical pure strike slip structures this study and previous ones reveal a crustal scale half flower structure with superficial thrusting associated with a deep narrow ductile zone with a high gradient of deformation and temperature

multibeam bathymetric survey and high resolution seismic investigations on the barbados ridge complex eastern caribbean a key to the knowledge and interpretation of an accretionary wedge abstract an important problem of active margin processes is the way accretionary wedges form in response to oceanic crust subduction new data have been obtained along the barbados ridge in front of the lesser antilles tertiary island arc they include high resolution multichannel seismic data and accurate sea beam bathymetric maps both have been used to propose a 3 dimensional interpretation of tectonic and sedimentary processes related to subduction such as oceanic off scraping ductile folding relative uplift and subsidence fore arc basin evolution and mud diapirism they all improved our knowledge of the evolution of accretionary prisms and more specifically of the barbados ridge development in plio quaternary time previous tectonic events are deduced from recently published geological data from barbados and the lesser antilles islands

eastern asia in the cretaceous new paleomagnetic data from south korea and a new look at chinese and japanese data lower cretaceous continental sediments and volcanic rocks have been sampled in the gyeongsang basin south korea a detailed analysis of 160 specimens reveals two stable components of magnetization a postfolding low temperature lt component with normal polarity and a stable high temperature ht component with both normal and reversed polarities the blocking temperature of the ht component ranges from 540 c up to the neel temperature of hematite this component predates the folding of the series and yields a pole at 68 n 205 e a95 6 the prefolding magnetization indicates that south korea stood at a latitude nearly identical to its present day latitude in the lower cretaceous comparison of korean data with revised paleomagnetic data from north and south china and japan shows that all these blocks of eastern asia occupied the same positions in term of latitude and were probably parts of a single craton since at least the lower cretaceous the paleomagnetic directions of the sino korean block show large discrepancies with respect to the expected directions of the stable eurasian siberian block an interpretation involving significant n s motion 1000 km between either north and south china or between north china and siberia appears to contradict geological data a preferred interpretation is that the siberian data are in serious error and that the combined china korea lower cretaceous pole provides a valid estimate for the eurasian plate as a whole

paleomagnetic evidence for the clockwise rotation of southwest japan abstract over 500 oriented samples of felsic rocks of cretaceous to middle miocene age were collected along the go river in the central part of southwest japan in an attempt to detect the process of tectonic rotation of southwest japan from the paleomagnetic view point thermal demagnetization was successful in isolating characteristic directions from the remanent magnetization of samples reliability of the paleomagnetic direction is ascertained through the agreement of directions from different kinds of rocks as well as the presence of both normal and reversed polarities the paleomagnetic results establish that southwest japan began to rotate clockwise through58 14 later than 28 ma and ceased its motion by about 12 ma southwest japan has undergone no detectable north south translation since 28 ma these results imply that southwest japan was rotated about the pivot around 34 n 129 e between 28 ma and 12 ma in association with the opening of the japan sea

late permian early triassic paleogeography of northern japan did pacific microplates accrete to japan extensive and detailed field studies were conducted in the kitakami mountains of northern japan in order to sample permian rocks and to make paleogeographic reconstructions for permian time these field studies demonstrate that large landmasses were present on both sides of the honshu geosyncline during permian time i e on both the pacific ocean and the sea of japan sides these landmasses appear on the basis of sediment studies to have been present during permian mesozoic and paleogene time the paleogeographic reconstructions presented here and papers by other authors show that neither the accretion of microplates from the pacific nor major horizontal movements of the japanese part of tethys occurred in mesozoic time

the pre cretaceous structure of the outer belt of southwest japan abstract based on a study of the island of shikoku a new zonation of the outer belt of the mesozoic chain of japan is proposed from top to bottom the nappe structure consists of 1 1 a superficial nappe composed of a middle jurassic olistostrome thrusted from the north in superficial conditions during the late jurassic early cretaceous second phase 2 2 a nappe of hp mt schists the green schist nappe including reworked ophiolitic debris and radiolarites thrusted in the late jurassic first phase from west to east in ductile and synmetamorphic conditions upon detrital formations interpreted as the mesozoic sedimentary cover of the paleozoic continent of kurosegawa this basement presently outcrops owing to post cretaceous strike slip faults in the kurosegawa zone during the second phase the green schist nappe was sliced into two post metamorphic nappes southwards the sanbosan zone is a late jurassic early cretaceous turbiditic sequence reworking the paleozoic kurosegawa rocks and triassic sediments it is considered as the southern margin of the kurosegawa continent the tangential structure is explained by the subduction of an oceanic area where the materials of the green schist nappe were deposited followed by the continental subduction of the kurosegawa mass responsible for the obduction of the oceanic sequences the main component of the displacement was subparallel to the belt the new zonation is valid for all southwest japan and also extends up to the kitakami massif and western hokkaido in northeast japan