reconstruction of northeast asian deformation integrated with western pacific plate subduction since 200 ma abstract the configuration and kinematics of continental deformation and its marginal plate tectonics on the earth s surface are intrinsic manifestations of plate mantle coupling the complex interactions of plate boundary forces result in plate motions that are dominated by slab pull and ridge push forces and the effects of mantle drag these interactions also result in continental deformation with a complex basin mountain architecture and evolution the kinematics and evolution of the western pacific subduction and northeast asian continental margin deformation represent a first order tectonic process whose nature and chronology remains controversial this paper implements a deep time reconstruction of the western pacific subduction continental accretion or collision and basin mountain deformation in northeast asia since 200 ma based on a newly revised global plate model we use gplates software to examine strain recovery geological and seismic tomography constraints for the western pacific plate subduction and sequentially backward rotations of deforming features the results indicate a nw se oriented shortening from 200 to 137 ma a nww see oriented extension from 136 to 101 ma a nearly n s oriented extension and uplift with a short term nww see oriented compressional inversion in northeast china from 100 to 67 ma and a nw se and nearly n s oriented extension from 66 ma to the present day the western pacific oceanic plate subducted forward under east asia along mudanjiang honshu island during the jurassic and the trenches retreated to the sikhote alin north shimanto and south shimanto zones from ca 137 128 ma ca 130 90 ma and in ca 60 ma respectively our time dependent analysis of plate motion and continental deformation coupling suggests that the multi plate convergent motion and ocean continent convergent orogeny were induced by advance subduction during the jurassic and earliest cretaceous our analysis also indicates that intra continent rifting and back arc extension were triggered by trench retreat during the cretaceous and that the subduction of the oceanic ridge and arc were triggered by trench retreat during the cenozoic therefore reconstructing the history of plate motion and subduction and tracing the geological and deformation records in continents play a significant role in revealing the effects of complex plate motions and the interactions of plate boundary forces on plate mantle coupling and plate motion intracontinental deformation coupling

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

new shrimp u pb zircon ages from the heilongjiang high pressure belt constraints on the mesozoic evolution of ne china the heilongjiang complex is a high pressure accretionary belt composed mainly of serpentinite glaucophane bearing metabasalt epidote glaucophane albite schist greenschist marble two mica schist muscovite albite schist quartz schist and quartzite chert located along the suture zone separating the jiamusi and songliao blocks in ne china shrimp u pb zircon analyses of two samples of granitic gneiss from yilan that are interleaved with the heilongjiang complex record diverse protolith ages that are consistent with derivation from regional permian granitoids 263 7 ma and the adjacent mashan complex 492 6 ma indicating tectonic incorporation of older granitic components into the accretionary complex the age of the basaltic protolith of two samples of glaucophane albite schist from yilan is 245 ma and is slightly younger than the protolith age of two samples of amphibole schist from mudanjiang located about 200 km south of yilan that define weighted mean 206pb 238u ages of 257 4 and 257 5 ma all four samples contain a few older inherited zircon grains and also show the effects of an isotopic disturbance at 200 to 190 ma most likely related to the subsequent high pressure metamorphism the timing of which has been determined in previous studies the basaltic rocks record rifting and ocean development from 260 to 210 ma based on previous studies in which both e morb and oib protolith signatures were identified detrital zircons in two samples of mica schist from mudanjiang show distinct populations at 700 ma 500 to 450 ma 350 to 213 ma peak at 255 ma 290 to 200 ma and 200 ma all except the youngest ages can be matched with rocks from the older components of the jiamusi block and with other areas in the central asia orogenic belt caob supporting the view that the jiamusi block was most likely the eastern segment of the caob prior to rifting the youngest concordant magmatic detrital grain with an age of 207 3 ma defines the maximum age of sedimentation this also limits the timing of high pressure metamorphism in the heilongjiang complex to post late triassic consistent with argon data obtained in previous studies final closure between the jiamusi and songliao blocks took place in the latest triassic early jurassic with the two blocks accreted as a result of pacific ocean subduction this suggests that the heilongjiang complex records the time when north south closure of the caob in china gave way to westward movement related to the pacific ocean subduction which has dominated the tectonics of ne china and far east russia since that time

two types of neoarchean basalts from qingyuan greenstone belt north china craton petrogenesis and tectonic implications abstract geochronological geochemical and isotopic studies were carried out on the basalts from the qingyuan greenstone belt to understand the petrogenesis of the basalts and the mantle source characteristics providing insights into neoarchean geodynamic evolution of the north china craton the qingyuan greenstone belt is analogous to the typical barberton type greenstone belt in lithological units u pb isotopic dating using the la icp ms method on zircons from the basalts and the associated andesite reveals that they erupted at 2510 2545 ma and were subjected to subsequent 2486 2491 ma metamorphism the basalts are high fe tholeiitic showing coherently positive end t and ehf t values the geochemical and isotopic studies strongly imply that they experienced significant fractional crystallization and minor no crustal contamination during magma evolution on the basis of chondrite normalized ree patterns the basalts can be further divided into two types viz the enriched and the depleted the enriched basalts are abundant in lree and rees contents depleted in hfses nb zr ti endowed with arc like geochemical peculiarities modeling reveals that the parent magma of the enriched basalts has been derived from 70 to the depleted basalts the basalts from the neoarchean qingyuan greenstone belt witness the episode of the vertical growth of continental crust at ca 2 5 ga combined with other geological considerations a large archean mantle plume model is favored to account for the generation of the late neoarchean basalts from qingyuan greenstone belt in the eastern block north china craton

signature of the agulhas current in high resolution satellite derived wind fields abstract 5 years of systematic envisat advanced synthetic aperture radar asar acquisitions and 8 years of observations from the jason 2 altimeter are used to investigate the signature of the agulhas current on high resolution between 1 and 5 km satellite derived winds the satellite wind observations are analysed together with co located ocean current sea surface temperature sst and significant wave height information satellite derived winds cannot be considered current relative over the agulhas current sar and altimeter winds increase in magnitude over the agulhas current in all up down and cross current wind conditions with contributions from both the ocean surface current and sst when winds blow against the current strong accelerations in satellite winds are observed at the agulhas current s inshore front with the strongest winds observed 10 km offshore from the location of maximum sst gradient the strong sst gradient appears to drive a thermal wind with a magnitude of about 1 m s and which intensifies abates the predominant alongfront winds at the agulhas current s northern wall the sar dataset shows abnormally high increases in wind speeds during up current conditions in comparisons to the jason 2 derived winds we argue that these differences are caused by the inability of the cmod type algorithms to taken into account the wave field and provide accurate wind speed estimates in conditions where wave height exceed the expected value for a given wind speed our analysis suggests that wave current interactions in regions of strong current shear produce enhanced sea surface roughness signatures and lead to artificially high estimates of sar derived wind speeds there is future potential in using high resolution sar imagery to map strong ocean current fronts and thus improve our ability to monitor ocean surface currents from space

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

mesozoic radiolarian biostratigraphy of japan and collage tectonics along the eastern continental margin of asia abstract jurassic accretionary complexes mainly composed of carboniferous to permian limestone associated with greenstone triassic bedded chert jurassic siliceous shale and clastic rocks form the basement rocks of japan the stratigraphy of these complexes has recently been analysed utilizing radiolarian fossils resulting in the discovery that japan comprises a collage of disrupted terranes international co operative works reveal that lithologically and biostratigraphically similar terranes are distributed in northeast china nadanhada terrane and sikhote alin ussr khabarovsk terrane paleomagnetic studies demonstrate that prior to opening of the sea of japan the japanese islands were located much closer to the eastern margin of the asian continent where the nadanhada and khaborovsk terranes are now exposed features of the mino terrane in central japan are characteristic of these terranes which originally formed along the continental margin of east asia seamounts covered by fossiliferous limestone formed during the carboniferous to permian at low latitudes the seamounts drifted towards a continental margin together with upper paleozoic sediments triassic bedded chert and lower jurassic siliceous shale which accumulated around them upper paleozoic triassic and lower jurassic formations were accreted to the eastern continental margin which was a large tectonic collage developed as the chinese mainland during the late triassic enormous amounts of clastic detritus were deposited in sedimentary basins where jumbling and telescoping of pelagic sediments took place in a complicated fashion producing a melange the provenance of clastic detritus within the mino terrane is interpreted as a platform on which permian and carboniferous calcareous sediments containing diagenetic lutecite and orthoquartzite formations were widespread these formations covered a precambrian metamorphic and granodioritic basement similar to that seen in the south china region accretion culminated in the earliest cretaceous and the large disrupted terrane which had developed was transpressed northwards along the eastern margin of the continent during this period of dispersal the original terrane was sheared fragmented and separated into many smaller terranes some of which were transported to the sikhote alin region by the late cretaceous the most recent dispersal occurred during the opening of the sea of japan which is closely related to the latest movement of the pacific plate studies of radiolarian micropaleontology and the significance of these fossils to the resolution of the biostratigraphy and the tectonic history of japan are reviewed the results of biostratigraphic analyses are discussed in relation to the mesozoic tectonics of east asia

allochthonous oceanic basalts within the mesozoic accretionary complex of alexander island antarctica remnants of proto pacific oceanic crust the mesozoic lemay group accretionary complex of alexander island antarctica contains thrust bound slices of accreted ocean floor ocean islands and seamounts they represent fragments of proto pacific oceanic crust of which only a tiny remnant the phoenix plate remains off northern antarctic peninsula they therefore provide an excellent opportunity to sample the ancient oceanic crust that formerly occupied the southern pacific ocean all the basalts experienced sea floor and subduction accretion metamorphism ranging from zeolite to transitional blueschist facies on the basis of rare arth and other immobile trace element characteristics the basalts are divided into depleted morb n morb e morb and tholeiitic and alkaline oib oceanic basalts occur within two rock associations on alexander island basalt volcaniclastite chert and basalt volcaniclastite tuff the basalt volcaniclastite chert rock association is dominated by pillow lavas which have light ree depleted n morb geochemical characteristics and is interpreted as representing ocean floor formed at spreading centres locally sills of tholeiitic oib intrude the sequence the basalt volcaniclastite tuff rock association exposed in the lully foothills was formed in shallow water during the early jurassic it is geochemically varied consisting of basalts with n morb e morb and tholeiitic oib characteristics the association is interpreted to have been formed on a large seamount or ocean island

influence of hegenshan heihe suture on evolution of late mesozoic extensional structures in wunite depression erlian basin inner mongolia china we integrate previous work on the hegenshan heihe suture with our interpretation of geomagnetic anomaly and seismic reflection data to investigate the role of the hegenshan heihe suture in the evolution of late mesozoic extensional structures in the wunite depression of the erlian basin sags in the wunite depression present as ne50 trending in the western sector n0 ne30 trending in the central sector and ne45 trending in the eastern sector our results highlight the importance of the pre existing hegenshan heihe suture in the evolution of the late mesozoic rift system and reveal the following details 1 the ne50 extent sags in the western sector are controlled by the c ne50 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time resulted in a further vertical and horizontal extension of major border faults 2 the n0 ne30 extent sags in the central sector are influenced by the c ne75 trending suture the sinistral strike slip component of the reactivated suture during early cretaceous time resulted in a strike rotation of major border faults from nee trending following the suture to nne trending 3 because of strike slip deformation which resulted from the deformation of the reactivated suture accrued in major border faults light dip slip deformation led to less vertical offset 4 the ne45 trending sags in the eastern sector are controlled by the c ne45 trending suture moreover the extensional deformation of the reactivated suture during early cretaceous time facilitated a further vertical and horizontal prolongation of major border faults

transformation from paleo asian ocean closure to paleo pacific subduction new constraints from granitoids in the eastern jilin heilongjiang belt ne china abstract the eastern jilin heilongjiang belt ejhb of ne china is a unique orogen that underwent two stages of evolution within the tectonic regimes of the paleo asian and paleo pacific oceans 158 available zircon u pb ages including 26 ages obtained during the present study and 132 ages from the literature were compiled and analyzed for the mesozoic and cenozoic granitoids from the ejhb and the adjacent russian sikhote alin orogenic belt saob to examine the temporal spatial distribution of the granitoids and to constrain the tectonic evolution of the east asian continental margin five stages of granitic magmatism can be identified early triassic 251 240 ma late triassic 228 215 ma latest triassic to middle jurassic 213 158 ma early cretaceous 131 105 ma and late cretaceous to paleocene 95 56 ma the early triassic granitoids are restricted to the yanbian region along the changchun yanji suture and show geochemical characteristics of magmas from a thickened lower crust source probably due to the final collision of the combined ne china blocks with the north china craton the late triassic granitoids with features of a type granites represent post collisional magmatic activities that were related to post orogenic extension marking the end of the tectonic evolution of the paleo asian ocean the latest triassic to paleocene granitoids with calc alkaline characteristics were ne trending emplaced along the ejhb and saob and young towards the coastal region and represent continental marginal arc magmas that were associated with the northwestwards subduction of the paleo pacific plate two periods of magmatic quiescence 158 131 and 105 95 ma correspond to changes in the subduction direction of the paleo pacific plate from oblique relative to the continental margin to subparallel taking all this into account we conclude that 1 the final closure of the paleo asian ocean occurred along the changchun yanji suture during the early triassic 2 the onset of the subduction of the paleo pacific plate beneath the east asian continental margin probably took place during the latest triassic ca 215 ma 3 changes in the drifting direction of the paleo pacific plate were responsible for the intermittent magmatic activities and 4 roll back of the subducted plate resulted in the oceanwards migration of the magmatic arc and large scale back arc extension throughout ne china during the early cretaceous

zircon hf o isotopic constraints on the origin of late mesozoic felsic volcanic rocks from the great xing an range ne china abstract the voluminous late mesozoic magmatism was related to extensive re melting of juvenile materials that were added to the central east asia continent in phanerozoic time the most favoured magma generation mechanism of late mesozoic magmas is partial melting of underplated lower crust that had radiogenic hf nd isotopic characteristics but this mechanism faces difficulties when interpreting other isotopic data the tectonic environment controlling the generation of the late mesozoic felsic magmas is also in dispute in this study we obtained new u pb ages and geochemical and isotopic data of representative jurassic 154 4 1 5 ma and cretaceous 140 2 1 5 ma felsic volcanic samples the jurassic sample has inherited zircon cores of permian age with depleted mantle like ehf t of 7 4 8 5 which is in contrast with those of the magmatic zircons ehf t 2 4 0 7 whereas the inherited cores and the magmatic zircons have identical mantle like 18o composition ranges 4 25 5 29 and 4 69 5 54 respectively these hf o isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited permian zircon core this mechanism is manifested by the eruption of jurassic alkaline basalts originated from an enriched mantle source the cretaceous sample has high ehf t of 7 0 10 5 suggesting re melting of a mafic magma derived from a depleted mantle source however the sub mantle zircon 18o values 3 70 4 58 suggest the depleted mantle derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level therefore the cretaceous felsic magma if not all could be generated by re melting of down dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration the two processes enriched mantle contribution and supracrustal juvenile material re melting are new generation mechanisms of the late mesozoic magmas from central east asia rift settings may have controlled these processes throughout crustal and mantle levels

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

the late paleozoic to mesozoic evolution of the eastern margin of the central asian orogenic belt in china abstract the north east central asian orogenic belt caob in china records terminal closure of the paleo asian ocean in the mid to late permian along the solonker xar moron changchun suture this marks the end of the overall northward movement of the chinese blocks from a peri gondwana position toward siberia and a switch in tectonic processes to those dominated by activity associated with the paleo pacific plate to the east four distinct changes in tectonic regime can be recognised here in the late paleozoic to early mesozoic i north south compression resulted in orogenesis and gave way to post collisional extension at 260 250 ma with the emplacement of a type granites ii almost coeval with this there was an the onset of east west extension from 250 to 225 ma along the extreme eastern margin of the caob when a seaway opened between the songliao and jiamusi khanka blocks iii the onset of westerly directed compression associated with subduction of the paleo pacific plate from 210 ma resulted in re amalgamation of the jiamusi khanka block with the caob by 190 180 ma and the massive generation of jurassic i type granitoids throughout the region finally iv a change to east west extension from 140 ma onward resulted from roll back of the paleo pacific plate this latter event was accompanied by the emplacement of s type granitoids and the development of sedimentary basins and core complexes it also accompanied a more widespread thinning or delamination of the lithosphere across most of north east china during the cretaceous

southern ocean contributions to glacial interglacial changes of atmospheric pco2 an assessment of carbon isotope records in diatoms eleven new antarctic records of diatom bound 13corg show significantly lighter values during the last glacial maximum than during the holocene with a general trend of increasing depletions southward of the modern antarctic polar front mapf in contrast glacial diatoms from cores farther north of the mapf show 13corg values which are 1 heavier than during the holocene likely causes for the low glacial 13corg in antarctic diatoms are higher co2 aq lower growth rates and changes in diatom abundance or size taken at face value the glacial depletions of 13corg suggest that antarctic surface waters south of the mapf might have been a source of atmospheric pco2 during the glacial period alternatively the glacial depletions might have been caused by either a relatively small decrease in growth rates or changes in the abundance of the two dominant diatom species or their average cell size interpretations of the subantarctic records are complicated by similar uncertainties

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

early paleozoic metamorphic rocks of the erguna block in the great xing an range ne china evidence for the timing of magmatic and metamorphic events and their tectonic implications abstract the erguna block is a crustal unit located along the eastern margin of the central asian orogenic belt caob in the far north of china it contains a variety of khondalitic rocks that include sillimanite and garnet bearing gneiss biotite plagioclase gneiss and carbonate in association with hornblende plagioclase gneiss and a variety of granitic orthogneisses these rocks are collectively referred to as the mohe complex and make up the basement rocks in this poorly exposed terrane four samples were analyzed for this study including two samples of biotite plagioclase gneiss one sample of garnet sillimanite gneiss and a sample of hornblende plagioclase gneiss all samples provide evidence of metamorphism in the form of discrete zircon grains or metamorphic rims around detrital cores and they record remarkably consistent 206 pb 238 u ages between 495 2 ma and 497 6 ma detrital zircon cores with oscillatory zoning from the two biotite plagioclase gneiss samples yield magmatic ages that range from 608 8 ma to 1015 12 ma whereas those in the garnet sillimanite gneiss range from 678 8 to 1373 17 ma these results establish that a range of meso to neoproterozoic magmatic rocks were present in the source area and contributed to the sedimentary protoliths the youngest zircon core with an age of 608 8 ma limits the maximum possible age of deposition indicating that the rocks of the mohe complex cannot be late archean to early proterozoic as previously considered the 500 ma age for the granulite facies metamorphic event in the mohe complex is identical to that recorded in the mashan complex of the jiamusi block and the hutou complex of the khanka block 1000 km to the south southeast implying that an extensive early paleozoic khondalite belt extended across much of the eastern caob rocks of similar age and metamorphic grade have also been recorded from the sayang baikal orogen along the southern margin of the siberia craton 1000 km to the west it is unclear at present whether these two belts are directly related but whatever the relationship it is evident that extensive tracts of khondalitic rocks were present in the eastern caob they were subsequently affected by high grade metamorphism in the early paleozoic forming collisional accretionary terranes that were accreted during the late pan african global event

changes in dip of subducted slabs at depth petrological and geochronological evidence from hp uhp rocks tianshan nw china article high resolution seismic imaging has previously revealed sudden changes in the dip of subducted oceanic plates this kinking feature is crucial because in many subduction zones it is thought to coincide with the disappearance of the low velocity layers associated with subducted oceanic crust in this study we present petrological evidence for this phenomenon derived from oceanic blueschist and eclogite facies rocks from the chinese tianshan the investigated samples span a large range of peak metamorphic conditions with temperatures between 330 and 580 c at 1 5 to 2 3 gpa such variable peak metamorphic conditions together with the intimate interlayering of high and ultrahigh pressure rocks have also been reported from other tianshan localities these observations suggest that the rocks were derived from varying depths within the subduction zone and then juxtaposed during exhumation in the subduction channel multi point lu hf isochrons from four high pressure rocks yield consistent garnet growth ages of 313 12 315 8 2 9 313 9 4 8 and 315 2 1 6 ma these inconjunctionwiththe 311 maclusterof published 40

geochronology and geochemistry of the heilongjiang complex and the granitoids from the lesser xing an zhangguangcai range implications for the late paleozoic mesozoic tectonics of eastern ne china abstract an integrated study on two subduction related units the heilongjiang complex and magmatic rocks in the lesser xing an zhangguangcai range was carried out to explore the paleozoic to early mesozoic tectonic framework of the eastern northeast china with a focus on the jiamusi block the heilongjiang complex which is considered as the suture between the jiamusi and songliao blocks is composed of blueschist amphibolite and ultramafic rocks the blueschist from the yilan area shows geochemical features similar to oib and has a 206pb 238u age of 288 2 ma which is interpreted as the crystallization age of protolith formed in an ocean island setting in contrast amphibolite from the xiachengzi area shows geochemical features similar to n morb zircons in this amphibolite show magmatic character and yield a 206pb 238u age of 248 4 ma which is interpreted as the protolith age calcic amphiboles in the amphibolite give a 40ar 39ar plateau age of 195 3 ma which is interpreted as the metamorphic age of the heilongjiang complex magmatic rocks in the lesser xing an zhangguangcai range mostly belong to i type granites that were formed in an active continental margin setting zircon u pb ages of these granites range from 200 ma to 174 ma with a westward younging trend shown as two groups of emplacing ages of 200 ma in the east and 180 ma in the west our new data support an early occurrence likely since the early permian of a large ocean namely the mudanjiang ocean in the area whose subduction resulted in the metamorphic unit the heilongjiang complex and the magmatic unit the lesser xing an zhangguangcai range in the jurassic

geodynamic evolution of flat slab subduction of paleo pacific plate constraints from jurassic adakitic lavas in the hailar basin ne china

paleozoic to mesozoic micro block tectonics in the eastern central asian orogenic belt insights from magnetic and gravity anomalies abstract the ne china region involves a complex accretionary belt formed by multiple stages of assembly of micro blocks from the paleozoic to mesozoic the tectonics of which provides important clues on the evolution of the east asian continental margin with a view to evaluating the micro block evolution in ne china we used gravity and magnetic methods to analyze the geophysical characteristics of the micro blocks and their boundaries combining with regional geology paleomagnetism and paleontology we reconstructed the micro block assembly history in the eastern central asian orogenic belt five paleozoic to mesozoic micro blocks are recognized in ne china the erguna xing an songnen jiamusi and nadanhada and their boundaries show significant differences in gravity and magnetic fields the boundary between the erguna block eb and the xing an block xb shows as a continuous tectonic line in the gravity field whereas the one between the xb and the songnen block sb exhibits a rather discrete but strong magnetic anomaly belt the boundary between the sb and the jiamusi block jb is characterized by both distinct gravity and magnetic anomalies the nadanhada micro block nmb appears as an independent micro block in the fourth order detail field of the bouguer gravity anomaly where it shows as a short axis or circinate structure in this anomaly field the paleozoic to mesozoic tectonic evolution of these micro blocks in ne china is closely related to five sutures in the eastern central asian orogenic belt the xinlin xiguitu suture was first formed at 500 ma leading to the assembly of the eb and the xb the heihe hegenshan suture was formed at 320 290 ma marking the amalgamation of the xb and the sb the mudanjiang yilan suture was formed at 200 ma marking the collision of the jb and the sb the paleo asian ocean closed during 250 230 ma in a scissor style the subduction of the paleo pacific ocean was initiated at 200 ma based on the deep structural architecture imaged from gravity and magnetic anomalies we propose an evolutionary model of the micro blocks in the ne china which provides important insights into the tectonic evolution of the ne china region during the paleozoic to mesozoic

petrogenesis of early middle jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china implications for the extent of spatial temporal overprinting of the mongol okhotsk and paleo pacific tectonic regimes abstract the mesozoic tectonic evolution of ne china was controlled mainly by the mongol okhotsk and paleo pacific tectonic regimes however the extent of the spatial and temporal overprinting of these two regimes is poorly understood here we report new zircon la icp ms u pb dating and geochemical analyses of jurassic intrusive rocks in northern liaoning and central jilin provinces northeast china to discuss their petrogenesis and outline the extent of spatial and temporal overprinting of these two tectonic regimes dating results indicate that jurassic magmatism occurred in two stages during the early ca 175 ma and middle jurassic 170 163 ma these rocks represent two stage typical bimodal igneous rock associations composed mainly of olivine gabbro gabbro and gneissic granitoids the early and middle jurassic gabbros have low rare earth element ree abundances positive eu anomalies depletion in high field strength elements hfses and positive ehf t values 4 0 to 10 3 except for one value of 17 8 suggesting that the primary magma was derived from partial melting of depleted lithospheric mantle metasomatized by subducted slab derived fluids the early jurassic monzogranite exhibit high ree abundances 195 201 ppm weak negative eu anomalies eu 0 63 0 64 and negative ehf t values 11 9 to 8 2 suggesting a primary magma that was derived from partial melting of lower continental crust of the ncc the middle jurassic granodiorites are enriched in light rees lrees and large ion lithophile elements liles and are depleted in heavy rees hrees and hfses as well as high sr y 29 132 and la yb n 15 44 ratios in addition the middle jurassic granitoids near or within the ncc exhibit negative ehf t values 18 9 to 0 2 whereas those within the xing an mongolia orogenic belt xmob have generally positive ehf t values 0 6 to 6 4 suggesting their origin from partial melting of thickened ancient ncc and newly accreted continental crust of the xmob respectively the above findings combined with regional geologic data suggest that the early jurassic bimodal igneous rocks formed in an extensional tectonic environment related to subduction of the paleo pacific plate beneath the eurasian continent the middle jurassic bimodal igneous rocks possibly formed in an extensional environment related to the collapse of a thickened region of the lower crust after closure of the mongol okhotsk ocean

the mesozoic accretionary complex in northeast china evidence for the accretion history of paleo pacific subduction abstract the mesozoic accretionary complex in northeast china which mainly consists of the jilin heilongjiang high pressure hp metamorphic belt and the nadanhada accretionary complex are the key area to understand the paleo pacific subduction accretion the jilin heilongjiang hp belt is a hp metamorphic zone between the jiamusi and songliao blocks and consists of the heilongjiang blueschist belt and the zhangguangcai complex previously published and our new geochronological data indicate that the collision between the jiamusi and songliao blocks along the jilin heilongjiang hp belt occurred between 210 and 180 ma suggesting that the jilin heilongjiang hp belt is an important unit for characterizing the geodynamic switch from the north south closure of the central asian orogenic belt to the onset of westward accretion related to subduction of paleo pacific plate in the latest triassic to early jurassic early permian igneous rocks with arc affinity in the eastern margin of the jiamusi block are more likely related to the mongol okhotsk subduction rather than the paleo pacific subduction or the collision between the jiamusi and khanka blocks as previously considered the nadanhada accretionary complex lies to the east of the jiamusi block and is composed of the yuejinshan and raohe complexes compilation of published geochronological data indicate that the yuejinshan complex was probably formed between 210 ma and 180 ma similar to ages for the jilin heilongjiang hp belt along the western margin of the jiamusi khanka block the raohe complex was formed later in the late jurassic to early cretaceous 170 137 ma likely more related to the subduction accretion of paleo pacific plate the final accretion in the target area took place in the early cretaceous 137 130 ma

provenance of cretaceous trench slope sediments from the mesozoic wandashan orogen ne china implications for determining ancient drainage systems and tectonics of the paleo pacific the wandashan orogen of ne china is a typical accretionary orogen related to paleo pacific subduction the raohe complex as a major part of the orogen consists of mid triassic to mid jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial sourced clastic trench slope sediments sensitive high resolution ion microprobe u pb dating and la mc icpms hf isotopic analysis of detrital zircons from the terrestrial sourced yongfuqiao formation sandstone show that most zircons are phanerozoic 90 140 150 ma 10 180 220 ma 25 240 270 ma 15 300 360 ma 15 391 395 ma 3 and 450 540 ma 20 whereas 10 are precambrian in age about 90 of the zircons have ehf t values ranging from 11 1 to 12 8 this suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the central asian orogenic belt and the jiamusi block the age of the yongfuqiao formation is constrained to the earliest cretaceous which represents the accretion time of the mid triassic to mid jurassic oceanic complexes when compared with the mino complex in japan and the tananao complex in taiwan three different provenances are identified suggesting three ancient drainage systems which transported sediments from ne china north china and south china to the paleo pacific subduction accretion system

formation of hp lt rocks and their tectonic implications in the western tianshan orogen nw china geochemical and age constraints the western tianshan high pressure low temperature metamorphic belt in northwestern china formed within a paleozoic accretionary wedge on the south side of the yili central tianshan plate it comprises various lithologies including mafic metavolcanic rocks metavolcaniclastic rocks metagreywacke marble and serpentinite the metavolcanics comprise eclogite omphacitite epidosite and blueschist the trace and rare earth element characteristics of these rocks indicate morb to oib affinities suggesting a seamount like setting for the protoliths of these rocks the end value of the eclogite 8 9 indicates that the protolith was derived from a long term depleted mantle i e an n morb source supporting the trace and rare earth element characteristics of these samples sm nd isochron dating of 343 44 ma omp gln grt wr and an age of 346 3 ma grt gln were determined using an eclogite boudin within blueschist a well defined 40ar 39ar plateau age of 344 1 ma was obtained for crossite from an omphacite phengite bearing blueschist and is concordant with the sm nd isochron age for the eclogite suggesting that neither argon loss nor excess argon affected the crossite a well defined 40ar 39ar plateau age of 331 2 ma was determined for phengite from the same sample the high pressure metamorphic rocks were formed by the b type subduction of a paleozoic south tianshan ocean about 344 ma ago they were however exhumed to higher crustal levels during the collision of the tarim and yili central tianshan plates about 331 ma ago similar to an alpine type tectonic regime

detrital zircons from phanerozoic rocks of the songliao block ne china evidence and tectonic implications abstract rocks that crop out in the northern part of the songliao block are mainly consist of high grade metamorphic gneiss paleozoic strata and mesozoic granites they are essentially similar to rocks reported from beneath the songliao basin that occupies the majority of the songliao block four samples of paleozoic metasedimentary rocks from tieli in the north eastern part of the songliao block yield detrital zircon u pb ages ranging from 2690 to 501 ma with four age populations at 2071 2690 ma with a peak at 2585 ma 1776 1997 ma with a peak at 1890 ma 719 991 ma with a peak at 800 ma and 501 592 ma with a peak at 518 ma these are similar to age populations in other parts of the central asian orogenic belt caob although sediments from the songliao block contain more abundant archean and proterozoic detrital zircons than the neighboring jiamusi khanka block to the east and xing an block to the west this may indicate that rocks of this age comprise a minor component of the songliao block the pan african zircon ages from the songliao block taken together with 500 ma magmatic and high grade metamorphic zircons obtained from the nearby erguna xing an and jiamusi khanka blocks indicate that pan african events affected all blocks of the caob in ne china this suggests that these blocks not only share a common basement but that they had a common history an extensive late pan african 500 ma orogenic terrane thus occupies much of the caob in ne china

pan african metamorphic and magmatic rocks of the khanka massif ne china further evidence regarding their affinity the khanka massif is a crustal block located along the eastern margin of the central asian orogenic belt caob and bordered to the east by late jurassic early cretaceous circum pacific accretionary complexes of the eastern asian continental margin it consists of graphite sillimanite and cordierite bearing gneisses carbonates and felsic paragneisses in association with various orthogneisses metamorphic zircons from a sillimanite gneiss from the hutou complex yield a weighted mean 206 pb 238 u age of 490 4 ma whereas detrital zircons from the same sample give ages from 934 610 ma magmatic zircon cores in two garnet bearing granite gneiss samples also collected from the hutou complex yield weighted mean 206 pb 238 u ages of 522 5 ma and 515 8 ma whereas their metamorphic rims record 206 pb 238 u ages of 510 500 ma these data indicate that the hutou complex in the khanka massif records early palaeozoic magmatic and metamorphic events identical in age to those in the mashan complex of the jiamusi massif to the west the older zircon populations in the sillimanite gneiss indicate derivation from neoproterozoic sources as do similar rocks in the jiamusi massif these data confirm that the khanka massif has a close affinity with other major components of the caob to the west of the dun mi fault based on these results and previously published data the khanka massif is therefore confirmed as having formed a single crustal entity with the jiamusi and possibly the bureya massif since neoproterozoic time

accretion subduction erosion and tectonic extrusion during late paleozoic to mesozoic orogenesis in ne china abstract the high pressure heilongjiang complex records a long and complicated evolution from the late paleozoic to mesozoic in ne china which is still subject to controversy in this paper we present a new detailed study including structural geochemical and geochronological analyses ar ar dating on metamorphic minerals u pb sims dating on zircons two main periods of oceanward accretionary growth are identified between 305 ma and 195 ma and around 112 101 ma these periods of accretionary growth were associated with the emplacement of voluminous magmatism slab roll back with continental back arc extension and growth of a forearc accretionary prism between these periods of accretionary growth a major phase of regional subduction erosion took place between 195 ma and 142 ma at the eastern edge of the songliao block the main effects of this subduction erosion phase were that regional jurassic early cretaceous extrusion overlapped with mesozoic accretion and erosion in ne china which disturbed the initial orogenic architecture with a review of relevant zircon ages of this accretionary orogen we unravel the complicated geodynamic history of accretion subduction erosion and tectonic extrusion that shaped ne china from the late paleozoic to mesozoic

long lived melting of ancient lower crust of the north china craton in response to paleo pacific plate subduction recorded by adakitic rhyolite abstract magmatism in eastern china in response to paleo pacific plate subduction during the mesozoic was complex and it is unclear how and when exactly the magmas formed via thinning and partial destruction of the continental lithosphere to better understand this magmatism we report the results of a geochronological and geochemical study of early cretaceous adakitic rhyolite erupted at 125 4 2 2 ma in the xintaimen area within the eastern north china craton ncc in situ zircon u pb dating shows that this adakitic rhyolite records a long 70 myrs and complicated period of magmatism with concordant 206 pb 238 u ages from 193 ma to 117 ma the enriched bulk rock sr nd isotopic compositions of the xintaimen adakitic rhyolite as well as the enriched zircon hf and o isotopic compositions indicate that the magmas parental to the adakitic rhyolite were derived from partial melting of the paleoproterozoic mafic lower crust heated by mafic melts derived from the mantle during the paleo pacific plate subduction a minor older basement component is indicated by the presence of captured neoarchean to early paleoproterozoic zircons the mesozoic zircons have restricted hf and o isotopic compositions irrespective of their ages suggesting that they formed from similar sources at similar melting conditions the xintaimen adakitic rhyolite offers an independent line of evidence that the ancient lower crust of eastern china underwent a long period 70 myrs of destruction melting or remelting from 193 to 120 ma related to the subduction of the paleo pacific plate beneath eastern china

the emplacement time of the hegenshan ophiolite constraints from the unconformably overlying paleozoic strata abstract controversy has long surrounded the emplacement time of the hegenshan ophiolite that is considered to mark a suture zone called the hegenshan heihe suture resulting from the closure of a back arc basin in the paleo asian ocean the hegenshan ophiolite in the xiaobaliang area is unconformably overlain by a sequence of paleozoic strata called the zhesi formation that consists of conglomerate sandstone siltstone and limestone some of which contain permian marine fossils of brachiopods therefore the ages of these paleozoic strata can be used to constrain the emplacement time of the hegenshan ophiolite four samples of the zhesi formation collected in the xiaobaliang area yield the detrital zircon u pb ages of 285 272 ma with the peak at 279 ma 315 288 ma with a peak at 300 ma 320 358 ma with a peak at 336 ma and 406 3 ma of which the 280 and 300 ma age groups are remarkably similar to the ages of latest carboniferous early permian gegenaobao dashizai formation or a type granites which formed under a post collisional setting however the age groups of 320 to 358 ma with a peak at 336 ma show the features of mafic ultramafic zircons in cl image most likely derived from local mafic ultramafic rocks of the hegenshan ophiolite in the xiaobaliang area which is supported by the fact of the ophiolite unconformably overlain by the middle permian zhesi formation therefore we propose that the emplacement time of the hegenshan ophiolite must have happened at some time before the middle permian 280 ma most likely between 300 and 335 ma not in the silurian devonian or mesozoic as previously considered

late jurassic to early early cretaceous tectonic nature on the ne asian continental margin constraints from mesozoic accretionary complexes abstract it is widely accepted that subduction of the paleo pacific plate beneath eurasia began in the early mesozoic however the tectonic nature and processes of the ne asian continental margin in the late jurassic to early early cretaceous remain unclear in this contribution lithological provenance and metamorphic deformation data are used to constrain the formation of mesozoic accretionary complexes ac along the ne asian continental margin and determine the tectonic relationship between the ne asian continental margin and the paleo pacific plate in the late jurassic to early early cretaceous the mesozoic ac formed during the late jurassic including the raohe ac in ne china the khabarovsk samarka and taukha acs in the russian far east and the mino tamba ac in japan and early cretaceous including the shimanto ac in japan and the kiselevka manoma ac in the russian far east the jurassic ac underwent a complex evolution including the formation of seamounts middle late jurassic terrigenous clastic sedimentation adjacent to the trench collision of seamounts with eurasia northward migration of the ac early early cretaceous terrigenous clastic sedimentation a second period of accretion and final emplacement the earliest mesozoic ac arrived at the trench at ca 195 ma combined with the occurrence of early mesozoic calc alkaline igneous rocks along the ne asian continental margin we suggest that subduction of the paleo pacific plate beneath eurasia began in the early jurassic jurassic ac in japan was affected by a regional high p t metamorphic event at 160 ma which might have been related to subduction collision of seamounts with eurasia at the trench ages and hf isotopic compositions of detrital zircon grains from the middle upper jurassic and cretaceous ac sandstones together with paleontological and paleomagnetic data indicate that jurassic clastic sediments were sourced mainly from the south china block scb whereas the lower cretaceous sandstones were sourced from the eastern central asian orogenic belt caob the inferred northward migration of jurassic ac in the late jurassic to early early cretaceous indicates that the boundary between the ne asian continental margin and the paleo pacific plate was characterized by strike slip tectonics at this time likely due to a small angle of obliquity in the subduction of the paleo pacific plate beneath eurasia in the late early cretaceous westward subduction of the paleo pacific plate beneath eurasia resulted in the emplacement of the raohe and khabarovsk acs at 137 130 ma and the formation of acs in the russian far east and japan

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

paleo pacific subduction accretion evidence from geochemical and u pb zircon dating of the nadanhada accretionary complex ne china the nadanhada terrane located along the eastern margin of eurasia contains a typical accretionary complex related to paleo pacific plate subduction accretion the yuejinshan complex is the first stage accretion complex that consists of meta clastic rocks and metamafic ultramafic rocks whereas the raohe complex forms the main parts of the terrane and consists of limestone bedded chert and mafic ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta sedimentary rocks geochemical data indicate that the yuejinshan metabasalts have normal mid ocean ridge basalt n morb affinity whereas the raohe basaltic pillow lavas have an affinity to ocean island basalts oib sensitive high resolution ion microprobe shrimp u pb zircon analyses of gabbro in the raohe complex yield a weighted mean 206pb 238u zircon age of 216 5 ma whereas two samples of granite intruded into the complex yield weighted mean 206pb 238u zircon ages of 128 2 and 129 2 ma laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon analyses of basaltic pillow lava in the raohe complex define a weighted mean age of 167 1 ma two sandstone samples in the raohe complex record younger concordant zircon weighted mean ages of 167 17 and 137 3 ma these new data support the view that accretion of the raohe complex was between 170 and 137 ma and that final emplacement of the raohe complex took place at 137 130 ma the accretion of the yuejinshan complex probably occurred between the 210 and 180 ma suggesting that paleo pacific plate subduction was initiated in the late triassic to early jurassic

late mesozoic and cenozoic tectono thermal history and geodynamic implications of the great xing an range ne china abstract the mesozoic cenozoic tectonics of northeastern china involves complex multistage interaction of different tectonic domains and has long been controversial the tectono thermal evolutionary history recorded by the widespread outcropped granitoids in the great xing an range gxr may provide significant constraints on the tectonics illuminating the deep geodynamic process here we present new low temperature thermochronology data from the gxr and thus reconstruct the detailed thermal history zircon fission track dating yielded a group of central ages ranging from 80 4 to 185 10 ma while apatite fission track ages range from 55 3 to 75 5 ma the modeled time temperature paths of all the samples reveal two relatively rapid cooling events at 100 60 ma and 50 0 ma and one intervening reheating episode at 60 50 ma the initial uplift exhumation and induced cooling events which represent strong orogenic activity are related mainly to closure of the mongol okhotsk ocean in the north and were subsequently influenced by the paleo pacific plate subduction in the east the evolution of the basin mountain system consisting of the songliao basin and gxr as well as the accretion metamorphism and magmatism at the northeast asian continental margin are all dominated or indirectly influenced by the paleo pacific subduction this indicates that the paleo pacific subduction had affected the evolution of the gxr to the west since the jurassic the significant reheating episode during the late paleocene to eocene may be related to the heat flux derived from asthenosphere upwelling and igneous activity

petrogenesis and tectonic implications of the mesozoic granitoid intrusions in the eastern liaoning peninsula ne china abstract mesozoic magmatic rocks are widely distributed in the eastern region of the north china craton ncc providing important information for understanding the mesozoic tectonic regimes in this area this paper reports newly obtained geological geochemical and zircon u pb lu hf isotope data for the xiaoheishan daheishan intrusion xdi and the yanghezhen dayingzhen intrusion ydi newly identified from precambrian metamorphic basement range in the eastern liaoning peninsula and provides a case study demonstrating that the petrogenesis of granitoid rocks was closely related to the tectonic regimes the middle late jurassic xdi granitoids commonly have the adakite like geochemical characteristics and their primary magma was derived from the partial melting of mafic rocks and neoarchean tonalites in the thickened lower crust the early cretaceous ydi granitoid rocks generally show diversified geochemical characteristics and their primary magma was generated by the partial melting of paleoproterozoic metagreywackes and neoarchean tonalites in the lower crust with minor addition of mantle derived magma these differences indicate that the granitoid magmatism in the eastern liaoning peninsula has occurred a significant variation during the jurassic to cretaceous the variation of late mesozoic granitoid magmatism may be responses to the regional tectonic transition from compression to extension in the eastern liaoning peninsula which is induced by the geodynamic regime of the paleo pacific plate from low angle subduction to slab rollback

mesozoic terrane accretion in northeast china sikhote alin and japan regions abstract the nadanhada range in northeast china is composed of upper paleozoic limestone greenstone middle to late triassic bedded chert and middle jurassic siliceous shale these rocks are enclosed in post middle jurassic clastic rocks the lithologic association ages radiolarian assemblages and geologic structure of the nadanhada range are very similar to those of the tamba mino ashio terrane in southwest japan this indicates that the nadanhada range is the northern extension of the tamba mino ashio terrane mesozoic tectonostratigraphic terranes identified in northeast china sikhote alin and southwest japan are the khanka terrane a micro continent composed of precambrian metamorhic rocks and paleozoic to mesozoic sedimentary and volcanic covers the nadanhada western sikhote alin terrane a disrupted terrane composed of upper paleozoic to jurassic sedimentary rocks the eastern sikhote alin terrane a terrane composed mainly of early cretaceous clastics the tetyukhe terrane a disrupted terrane composed of upper paleozoic to early cretaceous sedimentary rocks the hida terrane a continent type stratigraphic terrane composed of precambrian and upper paleozoic basement covered with jurassic to cretaceous coarse clastics and the tamba mino ashio terrane a disrupted terrane composed of upper paleozoic to earliest cretaceous sedimentary rocks accretionary history of these terranes is discussed on the basis of paleomagnetic and paleobiogeographic data

zircon u pb and lu hf isotope study of the neoproterozoic haizhou group in the sulu orogen provenance and tectonic implications abstract the neoproterozoic haizhou group crops out sporadically in the sulu orogen in east central china it is divided into the jinping and yuntai formations and consists of quartzite quartz schist marble and graphite and apatite bearing sequences major and trace element data for quartz schist from the two formations indicate that these rocks have a greywacke protolith and have been deposited during strong tectonic activity la icpms u pb dating of detrital zircon yields ages of 635 to 1074 ma for three samples from the jinping formation and 611 to 943 ma for two samples from the yuntai formation more than 78 of the detrital zircons from the two formations have u pb ages grouped between 700 and 890 ma with two clusters peaking at 758 ma and 828 ma respectively this indicates that their provenance is magmatic rocks of neoproterozoic age that have a tectonic affinity to the south china block scb a few older zircon populations with peak u pb ages at 943 and 1074 ma are also present a younger population shows peaks at 661 and 611 ma this suggests that deposition of the haizhou group was later than 611 ma rather than during the mesoproterozoic as previously thought zircon lu hf isotope data collected from the same u pb sites show negative ehf t values of 22 8 to 7 4 and hf model ages of 2341 to 3100 ma this indicates that the neoproterozoic magmatic rocks were derived from reworking of ancient paleoproterozoic to archean crust the results support the contention that the haizhou group is similar to the wulian group at the northwestern edge of the sulu orogen both having a scb affinity but that the penglai group does not belong to the scb because of the absence of neoproterozoic ages this lends support to the conclusion that the triassic suture between the north china and south china blocks is located along the baichihe yantai fault which lies north of the wulian complex and south of the jiaobei terrane thus the wulian yantai fault is not the suture zone as is traditionally proposed

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

geochemistry of 1 9 ga morb and oib like basalts from the amisk collage flin flon belt canada evidence for an intra oceanic origin subaqueously erupted basalts that occur in kilometre scale allochthons within the 1 9 ga flin flon belt canada appear to have been generated at oceanic ridges and possibly oceanic plateaus remote from archean cratons the ocean floor basalts fall into two categories 1 n type resembling n morbs and mariana type back arc basin basalts depleted to flat ree patterns high zrnb variable thnb and initial nd 3 3 to 5 4 2 e type resembling transitional and plume morbs slightly enriched ree patterns lower zrnb initial nd 3 1 to 4 5 in the largest and best studied allochthon the elbow athapapuskow assemblage mixing between depleted n morb and enriched oib sources or melts coupled with variable addition of a subduction lile component can explain the chemical variations in the basalts zircon u pb dates of 1904 ma for a syn volcanic diabase sill and 1901 6 5 ma for a gabbro peridotite cumulate complex demonstrate that crystallization of the ocean floor basalts overlapped with in part eruption of the tectonically juxtaposed 1 90 1 88 ga arc volcanic rocks the elbow athapapuskow allochthon is interpreted as back arc basin crust that developed simultaneously with flin flon arc magmatism subaerially erupted basalts that chemically resemble tholeiitic oibs 8 14 mgo relative hree depletion initial nd 2 2 to 3 4 occur in tectonic contact with the elbow athapapuskow assemblage the oibs may have been generated by deeper garnet residue melting of enriched mantle tapped during extension in the elbow athapapuskow back arc basin and were possibly erupted onto a remnant arc deeper mantle melting is also indicated by the presence of the lree enriched oceanic plateau like basalts of the sandy bay assemblage the back arc 01b and plateau volcanic assemblages were jux taposed against ca 1 9 ga arc assemblages in a philippines like intraoceanic accretionary complex by 1 87 ga

u pb ages of zircons from mesozoic intrusive rocks in the yanbian area jilin province ne china transition of the paleo asian oceanic regime to the circum pacific tectonic regime abstract geology in the yanbian area ne china is a key to understanding the relationship between the paleo pacific tectonic regime and the older paleo asian oceanic regime especially the transition between the regimes during the mesozoic a compilation of 131 u pb zircon ages including 18 obtained in the present study shows that the late paleozoic to mesozoic magmatism in the yanbian area took place from 285 to 105 ma mainly 205 160 ma and that there was a peak of activity at 175 ma and a hiatus from the late jurassic to early cretaceous 150 130 ma provisionally we subdivide the magmatic activity into four dominant stages middle permian to middle triassic 280 240 ma late triassic 230 205 ma early to middle jurassic 205 160 ma and early cretaceous 130 105 ma middle permian intrusive rocks including pyroxenite gabbro diorite granodiorite tonalite and monzogranite are interpreted to have been emplaced along an andean style continental margin in association with the subduction of the paleo asian oceanic plate the late permian middle triassic intrusive rocks are mainly quartz monzonite monzogranite and syenogranite and are considered to have been the result of syn orogenic post collisional activities the late triassic magmatism involved not only the emplacement of mafic ultramafic intrusive rocks but also coeval i and a type granitoids indicating an extensional environment after the final closure of the paleo asian ocean since the jurassic the tectonic setting has been dominated by subduction of the paleo pacific oceanic plate previously published data for the yanbian area and age data from surrounding regions show that the entire region from the yanbian area to the korean peninsula and the japanese islands experienced peaks in igneous activities that ranged from 200 to 165 ma during the jurassic and 120 to 110 ma and 90 to 65 ma during the cretaceous the jurassic intrusive rocks were emplaced mainly in the west and cretaceous intrusive rocks in the east in other words there is a southeastwards younging of mesozoic intrusive rocks that appears to have been closely associated with the evolution of the paleo pacific ocean taking all this into account we conclude that the transition from the paleo asian oceanic regime to the circum pacific tectonic regime took place during the late triassic to early jurassic

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

on the occurrence trace element geochemistry and crystallization history of zircon from in situ ocean lithosphere we characterize the textural and geochemical features of ocean crustal zircon recovered from plagiogranite evolved gabbro and metamorphosed ultramafic host rocks collected along present day slow and ultraslow spreading mid ocean ridges mors the geochemistry of 267 zircon grains was measured by sensitive high resolution ion microprobe reverse geometry at the usgs stanford ion microprobe facility three types of zircon are recognized based on texture and geochemistry most ocean crustal zircons resemble young magmatic zircon from other crustal settings occurring as pristine colorless euhedral type 1 or subhedral to anhedral type 2 grains in these grains hf and most trace elements vary systematically with ti typically becoming enriched with falling ti in zircon temperature ti in zircon temperatures range from 1 040 to 660 c corrected for a tio2 0 7 a sio2 1 0 pressure 2 kbar intra sample variation is typically 60 150 c decreasing ti correlates with enrichment in hf to 2 wt while additional hf enrichment occurs at relatively constant temperature trends between ti and u y ree and eu eu exhibit a similar inflection which may denote the onset of eutectic crystallization the inflection is well defined by zircons from plagiogranite and implies solidus temperatures of 680 740 c a third type of zircon is defined as being porous and colored with chaotic cl zoning and occurs in 25 of rock samples studied these features along with high measured la cl s ca and fe and low sm la n ratios are suggestive of interaction with aqueous fluids non porous luminescent cl overgrowth rims on porous grains record uniform temperatures averaging 615 26 c 2sd n 7 implying zircon formation below the wet granite solidus and under water saturated conditions zircon geochemistry reflects in part source region elevated hree coupled with low u concentrations allow effective discrimination of 80 of zircon formed at modern mors from zircon in continental crust the geochemistry and textural observations reported here serve as an important database for comparison with detrital xenocrystic and metamorphosed mafic rock hosted zircon populations to evaluate provenance

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

a 1300 km late pan african metamorphic belt in ne china new evidence from the xing an block and its tectonic implications abstract the xing an block is one of several fault bounded crustal units in northern china located along the southeastern margin of the central asian orogenic belt caob and includes the great xing an range the basement rocks constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and felsic paragneiss named the xinghuadukou complex la icp ms zircon u pb dating of a sillimanite gneiss from hanjiayuan indicates high grade metamorphism occurred at 496 3 ma with several older detrital zircon grains with ages extending from 678 8 to 1373 17 ma a sample of hornblende plagioclase gneiss from the northern part of the xinghuadukou complex yields a metamorphic age of 496 7 ma whereas igneous zircon core ages range from 601 15 to 1637 23 ma another sample of hornblende plagioclase gneiss from farther south in the xinghuadukou complex yields a metamorphic age of 495 5 ma and magmatic core ages of 546 4 ma these data indicate that high grade metamorphism occurred at 500 ma and that several earlier magmatic events are recorded in the area including some in the neoproterozoic these new age data together with other recent data obtained from the erguna songliao jiamusi and khanka blocks establish a 1300 km pan african khondalite belt along the southern margin of the caob

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

accreted terranes in the northern part of the philippine archipelago the philippine archipelago consists of a complex array of ophiolites continental fragments and island arc elements that can be identified as accreted terranes similar to those increasingly recognized as components of orogenic zones the northern philippines including luzon mindoro and nearby smaller islands can be divided into at least six of these tectonic elements from west to east across central luzon there are the neogene accretionary prism of the west luzon arc the eocene zambales ophiolite the cretaceous angat ophiolite and a late cretaceous early paleogene volcanic arc built on an older metamorphic basement this arc terrane is repeated by offset along the philippine fault to the south the western luzon terranes are juxtaposed against the metamorphic basement block of mindoro which itself is colliding with the north palawan microcontinental fragment the ophiolites appear to have originated in back arc basins rather than in oceanic plateaus and the metamorphic belts have protoliths indicating deformation along active margins perhaps deep within accretionary prisms the philippine terranes are interpreted as fragments that originated within the complex pacific eurasian plate boundary rather than as intra pacific basin units these terranes have been assembling at least since the oligocene by strike slip and convergent displacements strike slip displacement either along transcurrent faults or as a component of convergence played a very important if not dominant role in this assembly most terranes identified in the northern philippine appear to be plate fragments with attached crust and upper mantle their characteristics contrast with those usually interpreted for terranes in the north american cordillera where near orthogonal convergence and shallow dipping terrane sutures are favored

two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton petrogenesis and tectonic implications abstract mafic dyke swarms constitute a common occurrence within the cratonic provinces in the world since the archean proterozoic boundary and their geneses harbor critical information for facilitating regional tectonic and supercontinental reconstruction this zircon u pb dating and geochemical study documents two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton ncc the haicheng suite hcs with an emplacement age of ca 2125 ma from the liaodong peninsula and the guohua suite ghs with an age of ca 1816 ma from the western liaoning terrane the hcs meta gabbros are tholeiitic in composition with an sio 2 range from 46 to 52 modest enrichment in light rare earth elements lree and depletion in high field strength elements hfse and possess radiogenic whole rock nd nd t 1 91 to 4 21 and zircon hf hf t 4 02 to 8 48 isotopic compositions these features endow the hcs with a juvenile subduction fluid metasomatized lithospheric mantle source by contrast the ghs exhibits a meta gabbroic to dioritic composition and a transitional character from tholeiitic to calc alkali with variably enriched lrees and more evolved isotopic signatures nd t 0 20 to 5 82 zircon hf t 0 09 to 4 91 than the hcs while the relatively intact high fe gabbroic samples are supposed to represent partial melts from a fertile cratonic sub continental lithospheric mantle source in the garnet spinel stability field the low fe dioritic ones tend to bear the imprints of subsequent assimilation and fractional crystallization process apart from making an important contribution to the present archive of the paleoproterozoic mafic dyke swarms in the ncc the present two mafic magmatic suites witnessed a shift in tectonic setting from a subduction related continental arc environment to a post orogenic extensional regime synthesizing two suites with coeval felsic igneous episodes as well as concomitant episodic metamorphic events in the jiao liao ji belt leads to the characterization of a possible divergent double subduction system in the eastern ncc during the time span of ca 2 2 1 80 ga synchronized beating of episodic magmatic and metamorphic pulses in the constituent mobile belts of the ncc carries further implication of attesting to the ubiquity and importance of divergent double subduction system in the cratonic amalgamation and its incorporation within the supercontinent columbia

zircon u pb hf isotopes bulk rock geochemistry and petrogenesis of middle to late triassic i type granitoids in the xing an block northeast china implications for early mesozoic tectonic evolution of the central great xing an range abstract we report zircon u pb age data hf isotopes and bulk rock geochemical data for the middle to late triassic granitoids in the taerqi chabaqi kutihe region within the xing an block of the central great xing an range northeast china euhedral to subhedral zircon grains were extracted from the nine representative granitoids these zircons exhibit oscillatory zoning typical of a magmatic origin the zircon u pb determinations on the monzogranite syenogranite and quartz diorite samples yielded ages between 244 ma and 206 ma which essentially suggests that the magmatism in the xing an block occurred during the middle to late triassic period geochemically these granitoids have sio2 62 97 76 31 wt a cnk 1 03 1 51 and k2o na2o 0 40 2 39 we infer that they belong to high k calc alkaline series and are peraluminous i type granites in nature the major and trace element systematics indicate that these granitoids have different origins among them the 244 ma syenogranite of taerqi and the 230 206 ma monzogranite and syenogranite of kutihe were probably generated from partial melting of pre existing juvenile arc type rocks in a relatively shallow crustal level the 210 ma quartz diorite of chabaqi likely originated from the hybridization between a depleted mantle component and the juvenile subducted oceanic crustal materials that were buried to depths of the middle to lower continental crust the 212 ma monzogranite and syenogranite of kutihe were probably generated from the partial melting of miscellaneous lower crustal materials at high pressure conditions by combining these new data with regional geological data we conclude that the early mesozoic evolution of the central great xing an range was governed by two superimposed tectonic regimes i e 1 post orogenic extension due to slab break off after the closure of the paleo asian oceanic basin along the hegenshan heihe suture belt and 2 back arc extension associated with the southward subduction of mongol okhotsk oceanic plate

detrital zircon u pb geochronology and stratigraphy of the cretaceous sanjiang basin in ne china provenance record of an abrupt tectonic switch in the mode and nature of the ne asian continental margin evolution abstract the age spectra obtained from 505 spots of detrital zircon u pb ages of five representative sandstone samples from the sanjiang basin in ne china point to a significant change in its provenance during the coniacian santonian the predominant detrital source for the sanjiang basin during the early cretaceous was the zhangguangcai range magmatic belt and jiamusi block along its western and southern periphery whereas it changed in the late cretaceous to its eastern periphery the timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin the time interval of non deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early cretaceous and a contractional deformation episode in the late cretaceous the sanjiang basin evolved during this time window from a backarc to a foreland basin the migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late cretaceous marked the onset of regional scale shortening and surface uplift in the upper plate of a flat or very shallow dipping subduction zone the stratigraphic record the detrital source and geochronology of the basinal strata and the internal structure of the sanjiang basin present therefore an important record of a tectonic switch in the nature of continental margin evolution of northeast asia during the late mesozoic

record of permian early triassic continental arc magmatism in the western margin of the jiamusi block ne china petrogenesis and implications for paleo pacific subduction in this paper we report zircon u pb ages hf isotopes and whole rock geochemical data for the permian to early triassic granitoids from the western margin of the jiamusi block wjb ne china the intermediate to felsic sio2 59 67 74 04 wt granitoids belong to calc alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative nb ta and ti anomalies revealing typical continental magmatic arc geochemical signatures the zircon u pb determinations on the granodiorite monzogranite syenogranite and quartz diorite samples yielded ages between ca 275 245 ma which together with the published coeval intrusive rocks indicates that permian to early triassic continental arc magmatism occurred extensively in the wjb the low and mainly negative zircon e hf t values between 7 6 and 1 6 and the zircon hf model ages of 1 2 1 8 ga which are significantly older than their crystallization ages suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components the geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting assimilation storage and homogenization i e a mashed zone at the base of paleo to mesoproterozoic continental crust where large portions of igneous rocks and minor clay poor sediments involved in the source region in combination with regional geological data we argue that the jiamusi block was unlikely the rifted segment of the songliao block and two possible geodynamical models were proposed to interpret the formation of the ca 275 245 ma granitoids in the wjb in the context of permian global plate reconstruction we suggest that paleo pacific plate subduction was initiated in the permian to early triassic beneath the jiamusi block and even whole eastern ne china