zircon u pb chronology of the jianping complex implications for the precambrian crustal evolution history of the northern margin of north china craton abstract the neoarchean to paleoproterozoic jianping complex in the western liaoning province is an important component of the precambrian basement of the north china craton this region connects the neoarchean fengning chengde complex in the west the neoarchean to paleoproterozoic north chaoyang complex in the northeast and the yixian fuxin archean greenstone belt in the east the precambrian jianping complex is dominantly composed of metamorphosed supracrustal sequence and dioritic to granitoid gneisses tonalite trondhjemite granodiorite ttg here we present results from la icpms zircon u pb isotope dating from the various lithological units in this complex which reveal that the magmatic precursors of the metavolcanic rocks associated with the supracrustal sequence were generated during 2555 2550 ma and up to 2615 ma a major magmatic pulse of dioritic to granitic suite occurred during 2538 to 2495 ma this was followed by ca 2485 ma granulite facies metamorphism and a retrograde event at ca 2450 2401 ma our data also reveal a major charnockite emplacement event in this region at ca 1694 ma integrating our new results with the available geologic and previous geochronological data we identify three major growth stages in the crustal evolution history of the northern margin of the eastern continental block of the north china craton at ca 2550 2495 ma ca 2403 2394 ma and ca 1700 ma the la icp ms zircon data provide new insights on the neoarchean to paleoproterozoic tectonothermal evolution history in the northern margin of the eastern continental block of the north china craton

detrital zircon u pb dating of low grade metamorphic rocks in the sulu uhp belt evidence for overthrusting of the north china craton onto the south china craton during continental subduction the shiqiao pingshang low grade metasedimentary rocks sporadically crop out in the sulu ultrahigh pressure uhp belt in east central china major and trace element data indicate that they were deposited in a passive margin basin probably located at the southern margin of the north china craton sensitive high resolution ion microprobe shrimp u pb dating of detrital zircons from a quartzite sd53 from pingshang and a quartz schist sd54 from shiqiao records ages ranging from 2800 to 1900 ma three age populations are defined at 2660 2500 2350 2150 and 2100 1900 ma with peak ages at 2522 2212 and 2020 ma respectively muscovite ar ar dating of the quartz schist sd54 yields a plateau age of 265 9 1 2 ma these data support the view that the shiqiao pingshang low grade metasedimentary rocks originated from the north china craton and underwent deformation in the permian during subduction of the south china craton yangtze block beneath the north china craton this requires that the low grade metasedimentary rocks were overthrust for several tens of kilometres onto the south china craton explaining why source materials from the north china craton are common in triassic to jurassic sedimentary basins adjacent to the dabie sulu orogenic belt

provenance of meso to neoproterozoic cover sediments at the ming tombs beijing north china craton an integrated study of u pb dating and hf isotopic measurement of detrital zircons and whole rock geochemistry abstract the north china craton ncc was subjected to an extensional regime after the luliang movement at 1 8 ga and then was covered by an extensive meso to neoproterozoic sedimentary succession namely the changcheng jixian and qingbaikou groups in ascending order we report age spectra for detrital zircons and monazites hf isotopic systematics of detrital zircons and whole rock chemical and nd isotopic compositions for sediments from the succession in the ming tombs area beijing one of the typical meso to neoproterozoic areas in the ncc detrital zircons of six sedimentary samples have two distinct age peaks at 2 52 ga and 1 85 ga there are some detrital zircons at 2 4 2 0 ga but none at 2 3 ga and only a few 2 7 ga the detrital zircon age spectra change with time sediments in the lower succession changcheng group and in the upper successions jixian and qinbaikou groups are dominated by significant detrital zircon populations of late neoarchean and late paleoproterozoic ages respectively the 2 5 ga detrital zircons of the changcheng group have ehf 2 5 ga values and tdm hf model ages mainly ranging from 2 to 7 and 2 8 to 2 7 ga respectively detrital monazites of a sample from the jixian group exhibit a major age peak between 1 95 and 1 80 ga with some data between 2 0 and 1 95 ga the sedimentary rocks of the changcheng group are characterized by high k2o contents mostly 7 09 15 20 and insignificant eu anomalies eu eu 0 71 1 16 they have tdm nd model ages ranging from 2 70 to 2 43 ga being older than the tdm nd ages 2 11 and 1 99 ga of sedimentary samples from the qingbaikou group based on a comparison with ages for the early precambrian 1 8 ga basement of the ncc it can be concluded that 1 the sediments of the meso to neoproterozoic cover were undoubtedly derived from the ncc itself or once neighboring terranes 2 variations in the detrital zircon age spectra from the lower to the upper successions reflect provenance evolution in that the lower crustal late paleoproterozoic rocks were exposed at the surface after the upper crustal late neoarchean rocks had already been eroded

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

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

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

late archean sm nd isochron age for mafic ultramafic supracrustal amphibolites from the northeastern sino korean craton china isotopic data published by previous workers document the presence of early archean 3 5 ga metabasaltic enclaves in grey gneisses west of bohai bay eastern hebei province p r c metabasaltic and metakomatiitic amphibolites crop out as lower supracrustal members of the archean section northeast of bohai bay in southern jilin eastern liaoning provinces six analyzed specimens of the latter unit contain more magnesium on analysis averaging approximately 13 vs 7 wt percent mgo but although they exhibit a wider range of ree concentrations they average a similar range of ree abundance patterns la lu 24 7x chondrite as the former 24 9 chondrite new sm nd isotopic and ree analyses combined with available petrologic geologic information indicate that metakomatiitic amphibolites from the sino korean craton northeast of bohai bay are late archean in emplacement age a wholerock sm nd isochron age of 2660 75 2 ma was obtained with nd t 4 4 0 5 as in many parts of the sino korean craton the highly positive nd t value suggests a prior extended history 1 0 ga of depletion of subcontinental mantle sources in some incompatible elements and in lree relative to hree a seventh analyzed sample a mafic inclusion in tonalitic gneiss of unknown age has an unusual chemical composition with strong enrichment in lree sr and zr and severe depletion in ni and cr judging from isotopic data which yield a much younger depleted mantle model age of 1 67 ga it could represent a cognate xenolith in a mid proterozoic tonalitic intrusion shown on present maps as archean in age the protolith might have been an evolved alkali basalt

end permian to mid triassic termination of the accretionary processes of the southern altaids implications for the geodynamic evolution phanerozoic continental growth and metallogeny of central asia the altaids is one of the largest accretionary orogenic collages in the world with the highest rate of phanerozoic continental growth and significant metallogenic importance it is widely accepted that subduction related orogenesis of the altaids started in the late precambrian and gradually migrated southward present coordinates however it is uncertain when and how the building of the altaids was finally completed based on structural geology geochemical geochronological and paleomagnetic data this paper presents late paleozoic to early mesozoic accretionary tectonics of two key areas north xinjiang in the west and inner mongolia in the east together with neighboring mongolia the late paleozoic tectonics of north xinjiang and adjacent areas were characterized by continuous southward accretion along the wide southern active margin of siberia and its final amalgamation with the passive margin of tarim which may have lasted to the end permian to early mid triassic in contrast in inner mongolia and adjacent areas two wide accretionary wedges developed along the southern active margin of siberia and the northern active margin of the north china craton which may have lasted to the mid triassic the final products of the long lived accretionary processes in the southern altaids include late paleozoic to permian arcs late paleozoic to mid triassic accretionary wedges composed of radiolarian cherts pillow lavas and ophiolitic fragments and high pressure ultrahigh pressure metamorphic rocks permian alaskan type zoned mafic ultramafic complexes intruded along some major faults of the tien shan we define a new tarim suture zone immediately north of the tarim craton that is probably now buried below the tien shan as a result of northward subduction of the tarim block in the cenozoic the docking of the tarim and north china cratons against the southern active margin of siberia in the end permian to mid triassic resulted in the final closure of the paleoasian ocean and terminated the accretionary orogenesis of the southern altaids in this part of central asia this complex geodynamic evolution led to formation of giant metal deposits in central asia and to substantial continental growth

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

evaluating the use of the molybdenite re os chronometer in dating gold mineralization evidence from the haigou deposit northeastern china the haigou lode gold deposit 40 tons t at 3 4 g t which is located near the eastern boundary of the central asian orogenic belt and the north china craton is one of the largest gold deposits in northeastern china native gold is intergrown with molybdenite and pyrite in auriferous quartz veins hosted by a monzogranite monzonite stock and locally by proterozoic gneiss thereby offering an excellent opportunity to directly date the mineralizing event uranium pb age determinations for zircon yielded ages for the monzogranite and monzonite of 327 1 1 1 and 329 5 1 0 ma respectively numerous mafic to felsic dikes which are crosscut by ore veins pre ore parallel to these veins possibly synore or crosscut by them post ore were carefully examined and dated their zircon 206pb 238u ages are 318 3 1 0 310 9 1 1 and 134 9 0 4 ma respectively thereby placing the timing of gold mineralization within the relatively large interval of 318 3 1 0 to 134 9 0 4 ma the age of mineralization was determined directly using the re os method applied to molybdenite a total of 19 molybdenite samples separated from auriferous quartz veins yielded widely differing re os model ages of 467 to 155 ma and replicate analyses of individual samples also yielded widely differing ages significantly the wide range is attributable entirely to the results obtained for some coarse grained molybdenite samples and is interpreted to be due to re and os isotope decoupling the considerable spatial re heterogeneity the analytical procedure e g use of small sample aliquots and the post ore deformation nine of the samples which are all fine grained yielded a robust weighted mean model age of 310 3 ma and an isochron age of 309 8 ma thus the molybdenite re os ages are identical within uncertainty to those of the dikes that are parallel to the ore veins indicating that these dikes were emplaced contemporaneously with the ore and that they and the haigou gold mineralization are of late paleozoic age ca 310 ma finally a sericite sample obtained from an auriferous vein returned a 40ar 39ar plateau age of 165 3 1 2 ma which is much younger than the age of the mineralization constrained by re os age determinations of molybdenite this indicates that the 40ar 39ar isotope system was reset by post ore thermal events our new geochronological data provide evidence for late paleozoic gold mineralization in haigou which makes it the oldest known lode gold deposit in the easternmost central asian orogenic belt a finding that has important implications for precious metal mineral exploration in the eastern part of the solonker xar moron changchun yanji suture zone between the central asian orogenic belt and the north china craton this study also indicates that accurate and reproducible molybdenite re os ages representing the true timing of ore deposition need an integrated combination of careful petrography proper sampling procedures sufficiently large analyzed aliquots multiple analyses of individual samples and multiple dating methods

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

geological setting and controls on the development of graphite sillimanite and phosphate mineralization within the jiamusi massif an exotic fragment of gondwanaland located in north eastern china abstract china is the world s biggest producer and exporter of graphite and also possesses the world s largest reserves of crystalline graphite one of the main production areas is in northeastern china around jixi in heilongjiang province where graphite sillimanite and phosphate form in original sedimentary horizons within the mashan group the mashan group is composed of khondalitic metasediments and tectonically interleaved orthogneisses all metamorphosed to granulite facies the peak conditions have been calculated at 800 850 c at 5 3 6 2 kb and the p t t path defines a tight clockwise loop involving simultaneous decrease in temperature and pressure falling to 410 490 c at less than 3 kb this metamorphic event is interpreted as resulting from continent continent collision with emplacement of mantle derived mafic magma and possible delamination at the base of the crust metamorphism has been precisely dated at 500 ma using u pb zircon shrimp techniques it appears likely that this terrane formed part of an originally more extensive orogenic belt of late pan african age rocks of similar age are recorded from east antarctica western australia india and sri lanka suggesting that the mashan group was most likely juxtaposed with these areas within gondwanaland the mechanism by which the mashan group arrived at its present position between the siberian and north china cratons is poorly constrained but it appears likely that along with the north china south china and tarim blocks it underwent a northward drift from an initial location off northern australia to finally dock with the siberian craton in the late permian to late jurassic

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

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield kroner a windley b f badarch g tomurtogoo o hegner e jahn b m gruschka s khain e v demoux a and wingate m t d 2007 accretionary growth and crust formation in the central asian orogenic belt and comparison with the arabian nubian shield in hatcher r d jr carlson m p mcbride j h and martinez catalan j r eds 4 d framework of continental crust geological society of america memoir 200 p 181 209 doi 10 1130 2007 1200 11 for permission to copy contact editing geosociety org 2007 the geological society of america all rights reserved kroner kroener mail uni mainz de windley brian windley btinternet com tomurtogoo igmr magicnet mn hegner hegner lmu de jahn jahn earth sinica edu tw khain khain ginras ru demoux demoux uni mainz de wingate mwingate tsrc uwa edu au

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

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

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

isotopic evidence from the ivrea zone for a hybrid lower crust formed by magmatic underplating the large mafic complex overlying mantle peridotites in the ivrea zone of northern italy originated by underplating of mantle derived magma onto the base of continental crust and may be a unique outcrop of typical mafic lower crust sampled elsewhere only by mafic xenoliths neodymium and strontium isotope data show that the magmas assimilated large and roughly uniform proportions of crustal material the resulting hybrid magmas have the same isotopic signature as and may represent the lower crustal roots of upper crustal hercynian granitoid intrusions

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

depletion of heavy rare earth elements in metamorphic minerals from adirondack anorthosites repartitioning of rare earth elements ree during the grenville granulite facies metamorphism of adirondack anorthosite has produced metamorphic minerals depleted in the heavy ree relative to concentrations predicted by igneous partition coefficients the heavy ree depletion is observed in garnet bearing metamorphosed anorthosites and results from closed system repartitioning of ree among heavy ree rich garnet and other recrystallizing minerals the resulting heavy ree depleted patterns contrast with primary igneous mineral patterns which conform to predictions from igneous partition coefficients whole rock ree patterns of adirondack anorthosites are not affected by the local ree rearrangement anorthosite ree patterns reflect their primary igneous mineralogy and are independent of any secondary metamorphic minerals formed during the grenville metamorphic event consequently the ree did not move more than a few centimetres during the granulite facies metamorphism

the mongol okhotsk belt in mongolia an appraisal of the geodynamic development by the study of sandstone provenance and detrital zircons abstract the mongol okhotsk belt formed in a late stage of jurassic orogeny in the composite central asian orogenic belt the present paper investigates the late palaeozoic mesozoic sandstones associated with the belt in mongolia aimed at reconstructing the time and mode of ocean formation subduction and collision we apply provenance analysis including 1 heavy mineral and sandstone framework grain analysis 2 u pb laser ablation icp ms dating of detrital zircons for identifying contemporaneous volcanic arc activity and the recycling of older crustal material and 3 on dated zircon grains we analyze trace element contents and hf isotopic ratios in order to characterize the rock types in which they crystallized and the magma sources respectively the investigated samples are derived from 1 the adaatsag and doschgol terranes which represent the suture zone 2 the hangai hentei belt to the northwest and 3 the ereendavaa terrane and the middle gobi volcanic belt to the southeast of the suture the latter two are concurrent with the northern and southern margins of the mongol okhotsk ocean tectono stratigraphic arguments suggest that the mongol okhotsk ocean opened during the silurian within the early palaeozoic collage in the suture zone permian syn sedimentary zircon trace element contents confirm mafic rock sources and the mantle involvement in the magmatism epsilon hf t from 13 up to 20 n and s directed bi vergent subduction developed as revealed by contemporaneous zircons 1 along the northern margin hangai hentei from silurian early carboniferous subduction and accretion prevailed epsilon hf t from 3 up to 12 in associated zircons which was re initiated during the permian and 2 the contemporaneous silurian devonian southern margin ereendavaa middle gobi still represented an extensional continental margin showing reworking of neoproterozoic early palaeozoic zircons from the basement it turned into an active continental margin with starting arc magmatism in the carboniferous zircon mean epsilon hf t 5 75

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

primary positive eu anomaly in clinopyroxenes of low crust gabbroic rocks abstract positive eu and sr anomalies have been found in whole rocks and clinopyroxenes as well as feldspars in gabbros of the deep crustal mafic intrusion of the ivrea zone northwestern italy these anomalies are particularly pronounced at one stratigraphie level of the intrusion the upper part of the upper zone of the layered series huz the eu eu ratios range from 19 to 40 in plagioclases and from 3 to 14 in the coexisting clinopyroxenes mass balance calculations show that metamorphic redistribution of eu from plagioclase cannot account for the positive eu anomalies of the clinopyroxenes and that a corresponding anomaly in the parent melt is required speculatively this feature is attributed to mixing of a mantle component with crustal highly polymerized melts deriving from advanced anatexis of granulite facies metasediments the existence in the deep crust of hybrid melts having a positive eu anomaly may be important for the eu balance between the lower and upper crust

geochronology and geochemistry of metamorphic rocks in the jiaobei terrane constraints on its tectonic affinity in the sulu orogen abstract tectonic affinity of tectono lithological units close to ultrahigh pressure metamorphic belt is a key issue for understanding the geodynamics of continental collision this is particularly so for the jiaobei terrane northeast of the dabie sulu orogenic belt in china new data from la icpms zircon u pb dating whole rock elements and nd sr isotopes and mineral o isotopes are presented for metamorphic rocks from this terrane the results place geochronological and geochemical constraints on their protolith nature and metamorphic timing and thus on its tectonic affinity to one of the two triassic collided continents the north and the south china blocks protolith ages for ttg gneiss amphibolite and mafic granulite are 2 7 2 5 and 2 4 ga respectively regional metamorphism took place extensively at 1 76 ga protolith of the ttg gneiss was generated by partial melting of mantle derived rocks at the root of a thickened crust protolith of the amphibolite was probably a product of arc like magmatism protolith of the mafic granulite was derived from a depleted mantle source both of them were locally contaminated by supracrustal materials protoliths of paragneiss and schist in the fenzishan group were mostly derived from supracrustal sources but protolith of amphibolite in the fenzishan group is of mantle derived signature unlike the uhp metaigneous rocks in the dabie sulu orogenic belt that show unusual 18 o depletion the jiaobei metamorphic rocks have basically preserved their original mantle like o isotope compositions in general the nature and timing of geological events recorded in the metamorphic rocks from the jiaobei terrane are comparable with those from the north china block rather than the south china block thus the jiaobei terrane is concluded to have tectonic affinity to the former but behave like a micro continent during the triassic continental collision the 1 76 ga regional metamorphism in the jiaobei terrane is likely related to reworking of the arc continent collisional orogen in the periphery of the north china block rather than the 1 85 ga collision event between the eastern and western north china blocks the present study lends support to the common assumption that the suture boundary between the north and south china blocks in the sulu orogen is located along the wulian yantai fault tectonic mingling along the wulian yantai fault is probably related to subduction erosion during the continental collision

geochronology and isotope geochemistry studies of an epithermal gold deposit in the northern lesser khingan range ne china the gaosongshan example abstract the gaosongshan epithermal gold au deposit is located in the northern margin of the lesser khingan range polymetallic ore belt northeast ne china and contains au resources of more than 23 tons at an average grade of 6 3 g t gold orebodies are mainly hosted in intensely altered volcanic rocks of the lower cretaceous banzifang formation and as exploration has continued gold has also been discovered in extensively altered porphyritic intrusions with the highest au grade of 70 g t however the ages of metallogenesis and related magmatism have not been well constrained yet which have hindered the summary of metallogenic regularities in this study laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating from the granite porphyry yields a weighted mean 206pb 238u age of 101 6 1 2 ma slightly older than the rb sr isotope age of 98 1 6 ma for the auriferous quartz samples indicating that the gaosongshan au mineralization is genetically related to the granite porphyry the fluid d and 18oh2o values vary from 136 to 111 and from 9 3 to 2 5 respectively and the 4he and 40ar isotope compositions range from 15 7 10 9 to 35 5 10 9 cm3 stp g and 13 4 10 7 cm3 to 34 1 10 7 cm3 stp g respectively the obtained isotopic data show that the ore forming fluids were mixtures of magmatic and meteoric water but were dominated by meteoric water the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of ores in the gaosongshan deposit are 17 752 18 856 15 514 15 674 and 38 005 39 921 respectively which are similar to those of the gaosongshan granite porphyry implying that pb and possibly au originated primarily from late early cretaceous magmatic intrusions combining these results with data from previous studies we propose that the gaosongshan au deposit formed in an extensional tectonic setting during the rollback of the paleo pacific oceanic plate in ne china

the tectonic evolution of the changchun yanji suture zone constraints of zircon u pb ages of the yantongshan accretionary complex ne china abstract the changchun yanji suture zone is composed of a sequence of high pressure metamorphic rocks it lies to the southern margin of the jilin heilongjiang high pressure metamorphic belt and separates the jiamusi khanka block to the north from the north china craton in this study to understand the nature of the changchun yanji suture zone we studied four samples in diverse lithology i e two chlorite schists one felsic dike sample and one piemontite schist from the yantongshan complex these rocks have been intensely deformed without preservation of original sedimentary features integrated evidence from high pressure metamorphic minerals and zircon u pb age results suggests that most of the paleozoic strata in this region might be part of a tectonic melange phengite in the piemontite schist contains high si 3 304 based on 11 oxygens indicative of high pressure metamorphism the piemontite schist contains 6 zircon age populations from 2505 40 to 231 10 ma the 22 youngest zircon grains define a weighted mean age of 237 5 ma placing an upper limit on the depositional time of the protolith of the piemontite schist the felsic dike intruded into the metasedimentary rocks gave concordant ages with a weighted mean age of 217 5 ma providing a minimum emplacement age for the yantongshan complex we conclude from these data that the final collision between the jiamusi khanka block and north china craton along the changchun yanji suture zone occurred before the late triassic moreover this closure time is at least 30 myr later than closure along the solonker xar moron suture in the late permian as such we consider that the changchun yanji suture zone was not related to amalgamation of the siberian and north china cratons but was the result of the subduction of the paleo pacific plate

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

collision belt between the khanka block and the north china block in the yanbian region northeast china the pre jurassic geotectonics in northeast china and its adjacent regions are characterized by collision of microcontinental blocks the yanbian region lies between the north china block ncb and the khanka block kb along the dashanzui antu kaishantun collision belt the yanbian pre jurassic fold belt can be divided into two parts one part represents the western margin of the kb which consists of late proterozoic metamorphic basement and a permian active continental margin the other one is located at the eastern margin of the ncb and is composed of proterozoic passive margin deposits where the seluohe and qinglongcun groups are developed and rocks of the permian passive margin collision of these two parts took place along the dashanzui antu kaishantun collision zone during the late permian to early triassic as evidenced by the emplacement of syncollision granites and a type granites in northeast china and adjacent regions a series of microcontinental blocks collided with one other from the end of early paleozoic to the early triassic the collision event that took place in the yanbian region may represent the latest collision event in the paleo asian oceanic domain c 2003 elsevier ltd all rights reserved

upper jurassic microsolenid biostromes of northern and central europe facies and depositional environment abstract microsolenid biostromes are a common and important reef type in many upper jurassic reefal sections comparative study of these biostromes in western europe allows the characterisation of this distinct biostrome type in terms of its taxonomic composition palaeoecology and sedimentary regime the biostromes are characterised by a coral community of relatively low generic diversity being dominated by the microsolenidae family of corals the coral skeletal biovolume is generally high and is overwhelmingly dominated by platy ecomorphotypes sedimentologically these biostromes developed in low energy marl and limestone regimes which were subject to low sedimentation rates and varying degrees of siliciclastic influx in contrast to the coral fauna the associated fauna shows a high generic diversity in particular a rich assemblage of echinoids and bivalves in addition the coral plates provide an ideal habitat for a well developed and strongly polarised encrusting and boring fauna top surfaces show limited post mortem encrustation by serpulids and cementing bivalves and are also bored by lithophagan bivalves the undersides of the plates show a highly developed and diverse cryptic fauna of serpulids thecidean brachiopods bryozoans calcareous sponges and sclerosponges it is concluded that the main control on the development of these biostromes was low light intensities though low energy level and low background sedimentation rates were also important it is suggested that relatively high nutrient levels may have also played a significant role the conditions for microsolenid biostrome development prevail in relatively deep water environments and hence these are the first coral dominated reefal structures to have developed in deeper water shallowing upward sequences the corals in these biostromes have adapted to these conditions by developing a strongly platy growth form but also reducing their growth rates substantially the microsolenids are particularly adapted to these environments in two ways 1 they secreted an extremely porous calcium carbonate skeleton which in environments where calcification rates are slow such as deep water environments is a distinct advantage 2 in response to the limited potential of phototrophy in these environments the microsolenids have developed a pennular septal structure which is suggested to be a means of improving heterotrophic feeding trophic analysis of the reef fauna reveals that the nutrient limitation model developed for present day coral reefs cannot be applied to these biostromes it is demonstrated that the microsolena and the present day agariciid leptoseris show a number of significant morphological and ecological similarities

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

a tectonic transition from closure of the paleo asian οcean to subduction of the paleo pacific plate insights from early mesozoic igneous rocks in eastern jilin province ne china abstract the timing of tectonic transition from the paleo asian oceanic regime to the paleo pacific regime in the easternmost central asian orogenic belt remains controversial to constrain the event we present new zircon u pb ages hf isotopic compositions and whole rock major and trace element data for early mesozoic igneous rocks from eastern jilin province ne china these new ages together with existing age data indicate that early mesozoic magmatism in the kaiyuan yanji area can be subdivided into four stages early triassic ca 250 ma early middle triassic 249 235 ma late triassic 229 208 ma and latest triassic to early jurassic 207 175 ma the early triassic igneous rocks constitute a bimodal igneous rock association that formed in an extensional environment caused by break off of the subducting slab during final closure of the paleo asian ocean the early middle triassic magmatism is dominated by adakitic granitoids whose primary magmas were derived from partial melting of thickened mafic lower crust suggesting that the north china craton and songliao xilinhot block were still undergoing collisional orogenesis at 249 235 ma the late triassic igneous rocks comprise a typical bimodal association of rocks in an e w trending belt formed in a post orogenic extensional environment related to final closure of the paleo asian ocean the latest triassic to early jurassic igneous rocks have calc alkaline characteristics were emplaced as a ne sw trending belt parallel to the eastern margin of eurasia and formed in an active continental margin setting associated with initial subduction of the paleo pacific plate we conclude that the tectonic transition between the paleo asian and the paleo pacific regimes took place during the latest triassic

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

stratigraphic architecture of upper jurassic oxfordian reefs in the northeastern gulf coast u s and the eastern paris basin france abstract the late jurassic was a major period of reef expansion many jurassic reefs are potential hydrocarbon reservoirs but their stratigraphic distribution has been difficult to predict examination of the stratigraphic architecture of oxfordian reefs in the northeast u s gulf coast and the eastern paris basin france affords a comparison of mixed coral algal sponge reefs versus microbial dominated reefs the smackover formation in the northeastern gulf coast contains microbial dominated reefs the smackover represents deposition during a major transgression and reefs occur within late transgressive system tract tst deposits reefs of mixed coral algae and sponges characterize the oxfordian of the eastern paris basin in the ardennes lorraine reefs appear after the maximum flooding event of a stratigraphic sequence and are maintained through the highstand systems tract hst deposition and into the overlying stratigraphic sequence in burgundy reefs occur in association with the maximum flooding event of the upper stratigraphic sequence dominated by platy microsolenids reef growth begins in the tst this interval is traditionally called the lower reef complex more diverse reef growth the upper reef complex continues above the maximum flooding event through the early hst reef growth ceases by deposition of the late hst with the introduction of grainstones and other high energy lithologies all reefs in this examination regardless of biota are associated with maximum flooding events the sequence stratigraphy of the oxfordian reefs in france and the gulf coast provides a framework for studying jurassic reefs of both mixed and microbial dominated assemblages

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

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

the timing of final closure along the changchun yanji suture zone constraints from detrital zircon u pb dating of the triassic dajianggang formation ne china abstract the dajianggang formation is located in the changchun yanji suture zone of central jilin province and unconformably overlies the changchun yanji accretionary complex cyac which is a melange resulting from subduction of the jiamusi khanka block jkb beneath the north china craton ncc la mc icp ms u pb dating of detrital zircon from four samples of the formation yields ages of 2516 to 216 ma zircons with u pb ages at 2516 2501 ma and 1897 1832 ma indicate a provenance from precambrian basement rocks of the ncc the 525 482 ma ages indicate a provenance from metamorphic rocks of late pan african age in the jkb that have a tectonic affinity to the central asian orogenic belt caob zircon grains with ages of 383 314 ma and 275 250 ma were likely derived from the underlying cyac the youngest population has a peak age of ca 225 ma which together with late triassic fossils suggests that deposition of the dajianggang formation was late triassic or younger this result supports the view that the final collision of the jkb and ncc along the changchun yanji suture took place before the late triassic furthermore this closure time is at least 10 20 ma later than closure along the solonker xar moron changchun suture in the late permian we thus establish that the changchun yanji suture is not related to the collision between the siberia craton sc and the ncc but was instead related to the paleo pacific plate subduction consequently the changchun yanji suture is not the eastward extension of the solonker xar moron changchun suture as previously considered but the southern margin of the jilin heilongjiang high pressure metamorphic belt ji hei hp belt and resulted from westward subduction of the paleo pacific ocean thus the late triassic marked the switch in subduction from the paleo asian ocean to the paleo pacific ocean in ne china

geochronology and geochemistry of the dasuji mo deposit in the northern margin of the north china block implications for ore genesis and tectonic setting abstract the dasuji mo deposit is located in the northern margin of the north china block ncb in this paper we present the whole rock major and trace elements and the sr nd isotopic data zircon u pb and hf isotopic data and molybdenite re os data for the units associated with the deposit laser ablation inductively coupled plasma mass spectrometry la icp ms dating of zircons from the granite porphyry yielded an age of 220 3 0 7 ma which was interpreted to be the emplacement age of this intrusion the molybdenite re os dating yielded model ages of 219 9 217 4 ma an isochron age of 222 1 4 7 ma and a weighted mean model age of 218 9 1 6 ma representing the timing of the formation of the mo mineralization the dasuji granite porphyry contains high k calc alkaline and peraluminous rocks and is characterized by relatively high lrees and low hrees depleted ba sr p and ti and negative eu anomalies and are of highly fractionated i type granitoids the whole rock end t and zircon ehf t values for the granite porphyry range from 13 9 to 12 8 and 16 4 to 7 3 respectively indicating that the magma was generated by the partial melting of ancient lower crust materials the dasuji mo deposit may have formed in a post collisional extensional setting

shrimp u pb zircon dating of the wulian complex defining the boundary between the north and south china cratons in the sulu orogenic belt china abstract neoproterozoic metasedimentary and metavolcanic rocks of the wulian group are associated with gneissic granitoids at the northern margin of the sulu uhp belt adjacent to the wulian yantai fault and are collectively referred to as the wulian complex shrimp u pb dating of detrital zircon from the metasedimentary rocks of the wulian group indicates a range in age from 3478 to 625 ma based on zircons 3000 ma with the oldest age being 3339 ma 2700 2400 ma with a peak at 2436 ma 2200 1800 ma with a peak at 2156 ma and at 770 ma these results indicate that deposition of the wulian group was after 770 ma and that some detrital material most likely came from neoproterozoic sources in the south china craton scc shrimp u pb zircon dating of a metavolcanic rock defines a weighted mean 206 pb 238 u age of 761 8 ma which is consistent with other rocks of south china affinity and can be correlated with syn rift magmatism during the breakup of the supercontinent rodinia the wulian group together with neoproterozoic granites of the wulian complex constrains the location of the triassic suture zone between the north china and south china cratons based on our new data the suture must lie north of the wulian complex and is marked by the baichihe yantai fault

microsolenid corals as rock formers in the corallian upper jurassic rocks of england summary microsolena thurmanni koby and m foliosa roniewicz scleractinia are important rock formers in the upper oxfordian stage of upware and to a lesser extent yorkshire

the hulan group its role in the evolution of the central asian orogenic belt of ne china the hulan group of central jilin province northeastern ne china consists of felsic volcanic and sedimentary rocks that underwent sub greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the central asian orogenic belt young nd model ages of 1100 ma obtained in this study do not support earlier models that the hulan group was either rifted from the north china craton to the south or from the jiamusi block to the north since both these blocks have much older nd model ages detrital zircon u pb ages from a meta sedimentary rock of the hulan group define a maximum age of deposition of 287 6 ma not early palaeozoic as previously believed rb sr mineral isochron data indicate that metamorphism of the hulan group occurred at 250 ma this conclusion is further supported by an age of 248 4 ma for the dayushan granite which intruded the hulan group these new isotopic data together with evaluation of the regional geology indicate that final oceanic closure in the chinese segment of the central asian orogenic belt took place in the late permian the hulan area is located along the solonker xra moronchangchun suture that extends from inner mongolia across to central jilin province it is this zone that marks the final ocean closure resulting in the amalgamation of the north china and siberian cratons 2007 elsevier ltd all rights reserved