a new triassic shortening extrusion tectonic model for central eastern asia structural geochronological and paleomagnetic investigations in the xilamulun fault north china abstract at the northern margin of the north china block ncb the xilamulun fault xmf is a key belt to decipher the tectonic evolution of central eastern asia as it records the paleozoic final closure of the paleo asian ocean and localizes a late triassic intracontinental deformation in this study structural analysis 40 ar 39 ar dating and paleomagnetic studies were performed to investigate the kinematics of the xmf and to further discuss its triassic geodynamic significance in the central eastern asia framework after the paleozoic central asian orogenic evolution the structural analyses reveal two phases of ductile deformation the first one d1 which displays n verging and e w trending folds is related to the early paleozoic collisional event between the ncb and the songliao hunshandake block shb the second phase d2 displays a high angle foliation and a pervasive sub horizontal e w stretching lineation with kinematic criteria indicative of dextral strike slip shearing the 40 ar 39 ar dating on mylonitic granite places the main shearing event around 227 209 ma this d2 shearing is coeval with that of the dextral strike slip bayan obo chifeng fault bcf and the chicheng fengning longhua fault to the south which together constitute a dextral shearing fault system on the northern margin of the ncb during the late triassic the paleomagnetic study performed on the middle permian guangxingyuan pluton located between the xmf and bcf documents a local clockwise rotation of this pluton with respect to the ncb and shb our multidisciplinary study suggests an nnw sse shortening and strike slip shearing dominated tectonic setting on the northern margin of the ncb during the late triassic combining the contemporaneous dextral strike slip movements of the xmf and bcf in northern china and the sinistral strike slip movement of east gobi fault egf in southeastern mongolia with the large scale tectonic framework a late triassic nnw sse shortening eastward extrusion tectonic model for central eastern asia is firstly proposed the nnw sse shortening results in the eastward extrusion of the continental wedge bounded by the bcf and egf which is accommodated by the different kinematic patterns of the southern xmf and bcf and northwestern egf bounding faults this shortening extrusion tectonic framework is tentatively interpreted as the result of the far field forces associated with three late triassic lithosphere scale convergences in east asia i northward intracontinental subduction between the ncb and south china block ii collision of the qiangtang block with the qaidam block and iii southward subduction of the mongol okhotsk ocean beneath the mongolia block

effects of nonlinear inertial forces on nearshore currents abstract a perturbation method is developed to investigate the effects of nonlinear inertial forces on breaking wave induced nearshore currents obliquely incident waves are considered and the bottom topography varies periodically in the shoreline direction for simplicity lateral turbulent mixing is ignored numerical examples are given for a specified bottom topography with various angles of incidence and surf zone width the nearshore currents of interest mainly belong to the meandering type when the nonlinear terms are included there appears an advective shift as well as an amplitude reduction in the current pattern

zircon u pb ages of the metamorphic supracrustal rocks of the xinghuadukou group and granitic complexes in the argun massif of the northern great hinggan range ne china and their tectonic implications abstract the basement of the argun massif in the northern great hinggan range consists of the metamorphic supracrustal rocks of the xinghuadukou group and associated granitic complexes the metamorphic supracrustal rocks were previously interpreted as paleoproterozoic while the granitic complexes were considered mesoproterozoic in age this paper presents new zircon la mc icp ms u pb ages of biotite plagioclase leptynite and biotite schist from the xinghuadukou group in the lulin forest area heilongjiang province zircon shrimp u pb ages of biotite plagioclase gneiss from the xinghuadukou group in lulin forest and quartz diorite and monzogranite from the granitic complexes in mohe county heilongjiang province new geochronological data from the three metasedimentary rock samples of the xinghuadukou group can be preliminarily divided into five groups 1 2017 2765 ma 2 1736 1942 ma 3 1359 1610 ma 4 749 1239 ma and 5 448 716 ma except for the zircons of the 448 716 ma group belonging to a metamorphic origin the other age groups had the youngest age of 749 17 ma indicating that the xinghuadukou group formed during the neoproterozoic era at least

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

preliminary paleomagnetic results from the upper carboniferous of uliastai block inner mongolia china paleomagnetic samples from five sites from the upper carboniferous baoligemiao formation of the uliastai block 117 10 e 45 30 n preserve stable normal and reversed magnetizations with mean d 138 3 i 47 8 a95 9 7 k 9 9 irm acquisition and thermal demagnetization of irm indicate that the magnetization in these pyroclastic sediments is predominantly carried by magnetite however higher coercivity minerals contribute to the remnant magnetization as well the pole position 53 4 n 14 8 e derived from these results is near those of sino korea and central mongolia but significantly different from that of siberia suggesting that the uliastai was not a siberian related fragment as traditionally proposed instead the block along with the mongolia and sonid blocks may have moved as a series of north facing arc terranes frontal and remnant arcs of the sino korean continent during the late paleozoic possibly an ancient analogue of the southeast asian archipelago today

alaskan type kedanshan intrusion central inner mongolia china superimposed subduction between the mongol okhotsk and paleo pacific oceans in the jurassic abstract the xing an inner mongolia accretionary belt in the eastern central asian orogenic belt caob was produced by the subduction of three oceanic plates the paleo asian mongol okhotsk and paleo pacific oceanic plates the interactions between these plates remain unclear here we report an alaskan type ultramafic mafic intrusion in the kedanshan area central inner mongolia china the main lithologies of this intrusion include cumulate dunite pyroxene peridotite olivine pyroxenite and cumulate gabbro with late gabbroic anorthositic dykes minerals and whole rock compositional variations display characteristics of an arc cumulate trend alaskan type through fractional crystallization of mg rich and hydrous basaltic magma associated with oceanic subduction zircons from two gabbro samples yield early jurassic ages of 193 6 ma and 179 4 ma respectively we conclude that this ultramafic mafic complex is an accumulated intrusion from an arc related high mg magma chamber above a supra subduction zone considering the ages location and tectonic setting of the complex we suggest that it was most likely generated by melting of a large and triangle shaped mantle wedge during superimposed subduction between the mongol okhotsk and the paleo pacific oceanic plates in the jurassic

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

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

effects of wave rollers and bottom stress on wave setup 1 setup the increase in the mean water level associated with breaking waves observed between the shoreline and about 6 m water depth on an ocean beach is predicted well by a model that includes the effects of wave rollers and the bottom stress owing to the mean flow over the 90 day observational period the measured and modeled setups are correlated squared correlation above 0 59 and agree within about 30 although rollers may affect setup significantly on beaches with large amplitude several meters high sandbars and may be important in predicting the details of the cross shore profile of setup for the data discussed here rollers have only a small effect on the amount of setup conversely bottom stress calculated using eddy viscosity and undertow formulations based on the surface dissipation and assuming that the eddy viscosity is uniform throughout the water column significantly affects setup predictions neglecting bottom stress results in underprediction of the observed setup in all water depths with maximum underprediction near the shoreline where the observed setup is largest

triassic southeastward subduction of north china block to south china block insights from new geological geophysical and geochemical data abstract lithospheric subduction prior to the assembly of the south china and north china blocks is traditionally considered to be directed northward however some critical geological and geochemical data cannot be reconciled with this northward subduction this paper presents new lines of evidence against the traditional models and proposes a new and revolutionary tectonic model to explain the distribution and exhumation of high pressure hp ultrahigh pressure uhp metamorphic rocks of the dabie sulu belt we emphasize the following 1 the triassic tectonic environment of the southern margin of the north china block was passive not active based on the stratigraphy 2 in the southern margin of the north china block no arc magmatism was recorded 3 many paleoproterozoic slices of jiaobei affinity of the jiao liao ji belt in the north china block were located in the triassic sulu orogen 4 many 1 85 ga metamorphic zircons are preserved in the dabie sulu high pressure ultra high pressure hp uhp metamorphic rocks 5 the geometric asymmetry of many structural patterns in the hp uhp slices indicates top to the northwest thrusting during the exhumation of hp uhp slices 6 blueschists occur in the south of the uhp eclogite slices 7 in the eastern segment of the north qinling orogen no components with an affinity of the south china block have been found along the shangdan suture of the qinling orogen has been recorded an apparent northward subduction we consider that the suture is just a lateral subduction zone rather than a major collisional zone along the shangdan suture the rarity of i type plutonism can be attributed to a transform type continental margin the bureya jiamusi khanka block has an affinity to the south china block based on its similarity regarding the paleozoic history of deformation and triassic blueschist metamorphic facies metamorphism the bureya jiamusi khanka block could be the northern extension of the dabie sulu belt and this gigantic belt could be interpreted as an orocline related to the southeastward subduction of the north china block beneath the greater south china block

carboniferous and cretaceous mafic ultramafic massifs in inner mongolia china a shrimp zircon and geochemical study of the previously presumed integral hegenshan ophiolite abstract we present shrimp zircon ages and whole rock geochemical data to identify mafic ultramafic massifs of early carboniferous and early cretaceous ages from northern inner mongolia china the early carboniferous massifs chongenshan xiaobaliang wusnihei comprise predominantly lherzolite and minor gabbroic rocks zircons from a microgabbro e nd t 9 8 and a plagiogranite e nd t 9 yielded weighted mean 206 pb 238 u ages of 354 7 ma and 333 4 ma that we interpret as reflecting the time of zircon and magma crystallization a volcanic breccia resting unconformably on the ultramafic rocks serpentinites has an eruption age of 300 2 ma and provides a younger minimum time limit for the emplacement of the early carboniferous mafic ultramafic massifs in contrast the early cretaceous mafic ultramafic massifs hegenshan chaogenshan consist predominantly of harzburgite a pegmatoid gabbro and a rodingite e nd t 10 6 from the hegenshan massif have magmatic zircon ages of 139 2 ma and 132 7 ma respectively the chaogenshan massif is concentrically zoned with an ultramafic core dominantly harzburgite dunite subordinate lherzolite surrounded by gabbro with minor hornblendite and an outermost volcano sedimentary sequence metabasaltic flows metapelites we dated zircons from a leuocogabbro 125 2 ma e nd t 10 6 a coarse grained gabbro 142 4 ma and a metabasalt 134 2 ma zircon xenocrysts ca 152 492 ma are ubiquitous in these and other associated rocks a coarse grained gabbro and a diabase as in the hegenshan rocks ca 152 468 ma the youngest detrital zircon in outer zone garnet schist i e metapelite has an age of 132 2 ma accordingly we conclude that the northern inner mongolia lherzolite dominant and harzburgite dominant massifs are temporally and genetically unrelated their emplacement is attributed to asthenospheric upwelling and consequent lithospheric extension during periods of orogenic quiescence in the southern central asian orogenic belt

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

laboratory experiment on rip current circulations over a moveable bed drifter measurements 1 this study describes a laboratory experiment on rip current circulations over a moveable bed rip current characteristics over eight contrasting nature like beach morphologies are investigated the seabed varied from reasonably alongshore uniform to strongly alongshore nonuniform with crescentic patterns and bar rip morphologies representative of a full morphological down state sequence the same offshore shore normal waves were generated by the wavemaker for the eight situations with the same mean water level to study the sensitivity of rip current characteristics as a function of the beach morphology only in each case a 30 to 60 min video run was used to track a large number of drifters released within the surf zone results show the presence of classic rip current patterns with counterrotating cells and a relatively narrow offshore directed jet varying from shore normal to strongly skewed wave driven circulations were strongly unstable computed standard deviations of flow intensity and direction provide high resolution information on the spatial variability of rip current instabilities highly pulsating and weakly directionally variable offshore directed flow is observed in the rip neck for well developed bar rip morphologies that turns into a weakly pulsating and highly directional variable rip current flow with decreasing beach alongshore nonuniformity proposing a definition of rip current intensity based on the rip current circulation geometry rip current intensity was found to linearly increase with increasing measure of beach alongshore nonuniformity within both the low energy and moderate energy rip current regimes to date our laboratory experiment provides the first extensive quantitative rip current information during a full down state sequence for a given wave condition

final amalgamation of the central asian orogenic belt in ne china paleo asian ocean closure versus paleo pacific plate subduction a review of the evidence abstract the central asian orogenic belt caob evolved through complex closure of the paleo asian ocean from the neoproterozoic to the late phanerozoic this caused the chinese cratons to collide with eurasia and led to the formation of the world s largest phanerozoic orogenic belt ocean closure commenced in the west and was completed in the east near changchun closure of the paleo asian ocean in ne china was along the solonker xar moron changchun yanji suture and this was likely completed in the late permian although associated activity continued into the triassic there was an overlap in the latest permian early triassic between terminal activity associated with paleo asian ocean closure and the onset of tectonism associated with subduction of the paleo pacific plate this switch in geodynamic setting occurred at 260 250 ma and is reflected by a relaxing of north south directed compression and the onset of east west directed processes related to paleo pacific subduction by the early jurassic events associated with the westward advance of the paleo pacific plate dominated leading to extensive development of i type granites as far inland as the great xing an range from 140 ma the paleo pacific plate retreated eastward resulting in an extensional setting in the early cretaceous the effects of which were enhanced by regional thinning of the lithosphere commonly attributed to delamination throughout this period the eastern asian margin was tectonically complex the north south oriented jiamusi khanka bureya block was rifted away from the eastern margin of the caob in the late triassic but was then re united in the jurassic by westward advancing subduction that affected both the western and eastern margins of the block accretionary complexes continued to evolve in the cretaceous along the whole eastern margin of asia with final accretion of the nadanhada terrane part of the sikhote alin accretionary terrane with the caob at 130 ma followed by the emplacement of s type granites

modeled alongshore circulation and force balances onshore of a submarine canyon alongshore force balances including the role of nonlinear advection in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system delft3d swan the model is calibrated with waves and alongshore flows recorded over a period of 1 5 months at 26 sites along the 1 0 2 5 and 5 0 m depth contours spanning about 2 km of coast field observation based estimates of the alongshore pressure and radiation stress gradients are reproduced well by the model model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation stress gradients and the sum of the nonlinear advective terms and bottom stress with the remaining terms e g wind stress and turbulent mixing being negligible the simulations also indicate that unexplained residuals in previous field based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms which are similar in magnitude to the sum of the forcing pressure and radiations stress gradients and to the bottom stress

new paleomagnetic data from the mongol okhotsk collision zone chita region south central russia implications for paleozoic paleogeography of the mongol okhotsk ocean we present a reconnaissance paleomagnetic study of rocks from several formations of the chita region of south central russia representative location 51 n 116 e within the mongol okhotsk collision zone sections of siltstone and fine grained sandstone dated using fossils as bashkirian to moscovian epochs ussr carboniferous system middle carboniferous early permian late permian and triassic in age were sampled the resulting collection from five stratigraphic sections is a total of 319 oriented samples from 51 sites generally 5 to 10 samples per site were collected sample orientation was determined using both magnetic and sun shadow azimuths all paleomagnetic measurements were completed in the paleomagnetic laboratory at the university of pittsburgh using a 3 component 2g superconducting rock magnetometer srm in a magnetically shielded room thermal demagnetization was completed using between 12 to 20 heating steps up to temperatures of 685 c principal component analysis of the demagnetization data was successful in isolating two characteristic remanent magnetizations the lower unblocking temperature component component a fails the fold test is always of downward directed magnetic inclination and may record the present day earth s pdf magnetic field pdf i 69 4 d 351 8 component a ig 65 1 dg 356 5 95 6 2 n sites 50 the higher unblocking temperature magnetic component b was observed in the triassic bt n 3 late permian blp n 14 early permian bep n 5 and bashkirian to moscovian epochs of the late carboniferous bmc n 8 sections the b component differs significantly from component a and is recorded by sites of both downward and upward directed magnetic inclinations in the late permian and bashkirian to moscovian epoch sections component bmc and blp may represent primary remanent magnetizations the bashkirian to moscovian epochs of the late carboniferous mean paleolatitude is mc 19 9 14 8 and the late permian mean paleolatitude is lp 19 6 14 5 both are similar to that expected from reference paleomagnetic poles from the north china block but significantly different from paleolatitudes calculated using reference poles from the siberian or european plates we interpret the results of this study to suggest that the sampled sections were located near or associated with the north china block during their deposition

implementation and modification of a three dimensional radiation stress formulation for surf zone and rip current applications regional ocean modeling system roms v 3 0 a three dimensional numerical ocean model was previously enhanced for shallow water applications by including wave induced radiation stress forcing provided through coupling to wave propagation models swan ref dif this enhancement made it suitable for surf zone applications as demonstrated using examples of obliquely incident waves on a planar beach and rip current formation in longshore bar trough morphology haas and warner 2009 in this contribution we present an update to the coupled model which implements a wave roller model and also a modified method of the radiation stress term based on mellor 2008 2011a b in press that includes a vertical distribution which better simulates non conservative i e wave breaking processes and appears to be more appropriate for sigma coordinates in very shallow waters where wave breaking conditions dominate the improvements of the modified model are shown through simulations of several cases that include a obliquely incident spectral waves on a planar beach b obliquely incident spectral waves on a natural barred beach duck 94 experiment c alongshore variable offshore wave forcing on a planar beach d alongshore varying bathymetry with constant offshore wave forcing and e nearshore barred morphology with rip channels quantitative and qualitative comparisons to previous analytical numerical laboratory studies and field measurements show that the modified model replicates surf zone recirculation patterns onshore drift at the surface and undertow at the bottom more accurately than previous formulations based on radiation stress haas and warner 2009 the results of the model and test cases are further explored for identifying the forces operating in rip current development and the potential implication for sediment transport and rip channel development also model analysis showed that rip current strength is higher when waves approach at angles of 5 to 10 in comparison to normally incident waves

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

intra oceanic arcs of the paleo asian ocean abstract the paper reviews and integrates geological geochronological geochemical and isotope data from 21 intra oceanic arcs ioa of the paleo asian ocean pao which have been identified in the central asian orogenic belt the world largest accretionary orogeny the data we discuss structural position of intra oceanic arc volcanic rocks in association with back arc terranes and accretionary complexes major periods of intra oceanic arc magmatism and related juvenile crustal growth lithologies of island arc terranes geochemical features and typical ranges of nd isotope values of volcanic rocks four groups of ioas have been recognized neoproterozoic early cambrian early paleozoic middle paleozoic and late paleozoic the neoproterozoic early cambrian or siberian group includes eleven intra oceanic arcs of eastern and western tuva sayan southern siberia russia northern and southwestern mongolia and russian altai the early paleozoic or kazakhstan group includes selety urumbai bozshakol chingiz and baydaulet aqastau arc terranes of the kazakh orocline the middle paleozoic or southern group includes six arc terranes in the tienshan orogen chinese altai east kazakhstan west junggar and southern mongoia only one late paleozoic intra oceanic arc has been reliably identified in the caob bogda in the chinese tienshan probably due to pao shrinking and termination the lithologies of the modern and fossil arcs are similar although the fossil arcs contain more calc alkaline varieties suggesting either their more evolved character or different conditions of magma generation of special importance is identification of back arc basins in old accretionary orogens because boninites may be absent in both modern and fossil ioas the three typical scenarios of back arc formation active margin rifting intra oceanic arc rifting and fore arc rifting were reconstructed in fossil intra oceanic arcs some arcs might be tectonically eroded and or directly subducted into the deep mantle therefore the structural and compositional records of fossil intra oceanic arcs in intracontinental orogens allow us to make only minimal estimations of their geometric length life span and crust thickness

timing and nature of the xinlin xiguitu ocean constraints from ophiolitic gabbros in the northern great xing an range eastern central asian orogenic belt jifeng ophiolitic melange ultramafic rocks meta basalts and gabbros crops out in the northern segment of the great xing an range the eastern segment of the central asian orogenic belt which marks the closure of the xinlin xiguitu ocean associated with the collision between the erguna block and xing an block in order to investigate the formation age and magma source of the jifeng ophiolitic melange the gabbros from newly discovered the jifeng ophiolitic melange are studied with zircon u pb ages whole rock geochemistry and zircon hf isotopes zircon u pb dating from the ophiolitic gabbros yields u pb age of 647 5 3 ma which may represent the formation age of the ophiolitic melange the gabbros display low sio2 tio2 k2o contents high na2o lree contents and indistinctive ree fractionation la yb n 1 97 2 98 it shows an e morb like affinity while the element concentrations of the jifeng samples are lower than that of e morb more importantly nb displays negative anomaly in comparison with th which shows a transitional ssz type ophiolite signature moreover the e hf t values of 647 ma zircons in the gabbros range from 8 4 to 13 4 and the corresponding hf single stage ages t dm1 are between 687 and 902 ma which is obviously older than the crystallization age of 647 ma these geochemical features can be explained as melts from the partial melting of a depleted mantle source meta somatized by fluids derived from a subducted slab accordingly we conclude that the jifeng ophiolitic melange is probably related to transitional ssz type ophiolite and developed in an intra oceanic subduction which indicates that an ocean the xinlin xiguitu ocean existed between the erguna block and xing an block the ocean s formation might be no later than the neoproterozoic 647 ma and it was closed in the late cambrian because of the collision between the erguna block and xing an block

observations of steady longshore currents in the surf zone abstract steady surf zone longshore currents and directional properties of the incident wave field were measured on a beach with nearly straight and parallel depth contours selected data were processed into 64 segments each of 68 2 min duration irregularly spaced throughout an 18 day period a wide variety of incident wave and longshore current conditions were observed the radiation stress spectrum sxy f was estimated from a slope array and two current meters located seaward of the surf zone in many cases the total radiation stress sxyt sxy f f contains important contributions from a wide range of frequencies in a few instances sea and swell approach the beach from different directions quadrants resulting in a new zero sxyt the strong shears and direction reversals of the longshore current that could conceivably occur in this circumstance were not observed an eof decomposition of the mean longshore current pattern shows that most 90 of the current spatial variation in the 64 runs is

the south siberia central mongolia transect abstract studies of geological and geophysical data on the south siberia central mongolia geoscience transect which runs approximately along 100 e show that the asian continent was formed in the phanerozoic by accretion of terranes most of which were microcontinents with precambrian basement suture zones separating the terranes are deformed and deeply eroded magmatic arcs of different widths likewise classified as specific terranes in these sutures magmatic arc rocks are locally associated with fore and back arc basin series most of the oceanic crust has been subducted the observed ophiolite belts are as a rule attributed to the base of oceanic island arcs the fragment of the asian continent traversed by the transect was formed through early middle and late paleozoic stages of accretion

palaeomagnetism and palaeogeography of mongolia in the cretaceous permian and carboniferous preliminary data abstract the paper reports on the results of palaeomagnetic stability tests of oriented samples of lithologically different types of cretaceous permian and carboniferous rocks from northern and southern mongolia the permian andesites and tuffites from three localities barun buren tel tin gol and chulut tsagan del have yielded interesting results groups of normally and reversely polarized andesite tuffs were found even within a single outcrop by means of thermal field demagnetization and multicomponent analysis of the magnetization with a view to the number of samples 177 suitable for analysis and the number of localities 9 the reported palaeomagnetic data should be considered as preliminary the interpreted results indicate a different palaeogeographic evolution of northern and southern mongolia relative to the siberian platform and north china in the permian and carboniferous on the other hand similar apparent polar wander paths for north china lin et al 1985 and the studied regions of northern and southern mongolia indicate similar palaeogeographic evolution in the permian to carboniferous

when did the subduction first initiate in the southern paleo asian ocean new constraints from a cambrian intra oceanic arc system in west junggar nw china abstract we report here a cambrian southward subducting intra oceanic arc system in the southern west junggar nw china where an immature arc occurred initially on ssz type ophiolites and finally evolved into a more mature one the immature arc is dominantly represented by early middle cambrian 510 ma low k tholeiitic felsic rocks whereas the mature arc is characterized by late cambrian 495 ma medium and high k calc alkaline felsic and mafic rocks the ssz type ophiolites show remarkable depletion of nb and ta and contain high cr spinel cr 0 6 resembling these formed in the forearc altogether they record the initiation of subduction and transformation of crust during early subduction of the paleo asian ocean in the southern part of the central asian orogenic belt caob the subduction initiation might occur in the early cambrian 515 ma as constrained by both the ssz type ophiolites 516 ma and the oldest arc plutons 515 509 ma that crosscut the ophiolites the immature felsic plutons have high sio 2 72 wt contents and variable mgo 0 42 1 49 wt and mg values 22 62 crustal anatexis may be responsible for the genesis of those plutons and thus the transformation from oceanic to continental crust these results combined with regional data convincingly indicate that it is one of the oldest intra oceanic arc systems in the southern caob which may mark the initial subduction of the paleo asian ocean in its southern part much later than those reported in the north an archipelago type model is proposed for the evolution of the southern west junggar and has implications for the development of the southern part of the caob

rip currents under obliquely incident wind waves and tidal longshore currents abstract a field experiment on the nature of rip currents was conducted on the dutch coast which differs from previous rip current study sites because it is a wind sea dominated environment with mostly obliquely incident waves and tidally driven longshore currents during the experiment three distinct flow patterns obtained with gps tracked drifter instruments were observed 1 a locally governed circulation cell 2 an offshore current that is deflected shore parallel outside the surf zone and 3 a meandering longshore current the transition from rip currents flow patterns 1 and 2 to meandering longshore currents flow pattern 3 occurred gradually within the tidal cycle with longshore currents prevalent at mid to high tide rip currents at this site appeared at depressions in the surf zone bar and typically occurred when the water level fell below nap equivalent to msl even in the presence of obliquely incident waves and tidally driven longshore currents hindcast simulations of the drifter experiments were performed with the numerical model xbeach and showed good agreement with field observations the model was subsequently used to investigate the influence of tidal water level fluctuations longshore currents and obliquely incident waves on rip currents rip currents were initiated when the water level dropped below a specific threshold with the magnitude of the rip current associated with the water level the strength of the tidal current and its orientation with respect to the incident waves governed the offshore extent and orientation of the rip current in contrast to other studies that suggest that rip currents solely occur under shore normal or slightly oblique waves in this study both observations and numerical model simulations indicate that rip currents can exist under large angles of wave incidence when the rip channel is sufficiently wide and the wave height is small

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

field observations of wave driven setdown and setup wave driven setdown and setup observed for 3 months on a cross shore transect between the shoreline and 5 m water depth on a barred beach are compared with a theoretical balance between cross shore gradients of the mean water level and the wave radiation stress the observed setdown the depression of the mean water level seaward of the surf zone is predicted well when radiation stress gradients are estimated from the observations using linear theory at each location along the transect the observed setdown also agrees with analytical predictions based on offshore wave observations and the assumption of linear dissipationless normally incident waves shoaling on alongshore homogeneous bathymetry the observed setup the superelevation of the mean water level owing to wave breaking is predicted accurately in the outer and middle surf zone but is increasingly underpredicted as the shoreline is approached similar to previous field studies setup at a fixed cross shore location increases with increasing offshore wave height and is sensitive to tidal fluctuations in the local water depth and to bathymetric changes numerical simulations and the observations suggest that setup near the shoreline depends on the bathymetry of the entire surf zone and increases with decreasing surf zone beach slope defined as the ratio of the surf zone averaged water depth to the surf zone width a new empirical formula for shoreline setup on nonplanar beaches incorporates this dependence

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

the middle permian to triassic tectono magmatic system in the southern korean peninsula abstract the permo triassic adakitic magmatism in the southern korean peninsula preserves important tectonomagmatic records along the east asian continental margin in this study we present shrimp la mc icpms u pb zircon ages and hf isotope signature with whole rock geochemical compositions of the middle permian to middle triassic granitoid gneiss granitoid suites and the middle to late triassic plutonic rocks in the southeastern korean peninsula the former yields three age groups of ca 272 263 ma ca 258 251 ma and ca 243 240 ma respectively the latter group yields ca 237 216 ma ages indicating a long term magmatism that lasted from the middle permian to late triassic the granitoid gneiss granitoid suites have chemical compositions similar to high silica adakitic rocks showing high sio2 59 55 73 97 wt na2o 3 55 5 30 wt sr y 30 401 and la ybn 11 173 and low mgo 0 18 1 82 wt y 2 14 ppm and ybn 2 7 these rocks are peraluminous with high ba and sr and show relatively high k2o contents and k2o na2o ratios 0 7 with positive correlation between la ybn vs sr y ratios and high initial sr ratios these features reflect different contribution of the slab derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the middle paleoproterozoic lower crustal basement of the yeongnam massif on the contrary the triassic alkaline magmatism in the yeongnam massif is alternatively interpreted either by a tectonic switch to the extension dominated arc system or by a delamination of an overthickened arc the results from this study offer important evidence for a common subduction accretion system existed between the north and south china cratons and microcontinents between them along margins of the east asian continental blocks with different plate interaction in different locations generating distinct magmatic suites

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

spatial prediction of landslide susceptibility using an adaptive neuro fuzzy inference system combined with frequency ratio generalized additive model and support vector machine techniques abstract the spatial prediction of landslide susceptibility is an important prerequisite for the analysis of landslide hazards and risks in any area this research uses three data mining techniques such as an adaptive neuro fuzzy inference system combined with frequency ratio anfis fr a generalized additive model gam and a support vector machine svm for landslide susceptibility mapping in hanyuan county china in the first step in accordance with a review of the previous literature twelve conditioning factors including slope aspect altitude slope angle topographic wetness index twi plan curvature profile curvature distance to rivers distance to faults distance to roads land use normalized difference vegetation index ndvi and lithology were selected in the second step a collinearity test and correlation analysis between the conditioning factors and landslides were applied in the third step we used three advanced methods namely anfis fr gam and svm for landslide susceptibility modeling subsequently the results of their accuracy were validated using a receiver operating characteristic curve the results showed that all three models have good prediction capabilities while the svm model has the highest prediction rate of 0 875 followed by the anfis fr and gam models with prediction rates of 0 851 and 0 846 respectively thus the landslide susceptibility maps produced in the study area can be applied for management of hazards and risks in landslide prone hanyuan county

neoarchean suprasubduction zone ophiolite discovered from the miyun complex implications for archean paleoproterozoic wilson cycle in the north china craton abstract the north china craton ncc offers a window to archean paleoproterozoic crustal evolution following the amalgamation of microblocks during neoarchean the ncc witnessed another protracted wilson cycle in the paleoproterozoic with subduction accretion collision process here we report a newly identified suprasubduction zone ophiolite suite from the miyun complex in the ncc where a rare and near complete ophiolite succession is preserved including serpentinite lherzolite olivine clinopyroxenite websterite gabbro dolerite diorite monzonite metabasalts and trondhjemite in association with banded iron formation bif the geochemical features of the suite are consistent with those of suprasubduction ophiolite complexes with the mafic and intermediate members displaying island arc tholeiite iat and mid ocean ridge basalt morb affinity zircon grains from lherzolite define three groups of 207pb 206pb weighted mean ages at 2500 12 ma marking the formation age and 2237 47 ma and 1843 30 ma representing subsequent thermal events the majority of zircon grains in olivine clinopyroxenite gabbro and quartz monzonite yield 207pb 206pb weighted mean ages of 2510 19 ma 2495 10 ma and 2486 21 ma respectively those from the trondhjemite show weighted mean age of 2476 9 4 ma the compiled age data from all the rock types in the miyun suite show two distinct age peaks at ca 2486 ma and 1832 ma corresponding to the timing of magma differentiation and subsequent metamorphism the zircon lu hf isotope data display distinct positive hf t values in the range 0 35 7 05 suggesting magma derived from neoarchean to paleoproterozoic depleted mantle juvenile source the zircon tdm ages show a peak at 2670 ma confirming neoarchean components the timing of magma formation in the miyun ophiolite is broadly identical to those of the other rare neoarchean early paleoproterozoic ophiolite suites described from the ncc including those from yishui and zunhua furthermore evidence from the recently reported alaskan type intrusions and arc root mafic ultramafic complexes around miyun complex with ages in the range of 2 4 2 0 ga suggest continued subduction related magmatic processes with final collision in latest paleoproterozoic at around 1 84 ga we propose that following the assembly of ancient microblocks along multiple zones of ocean closure marked by major greenstone belts of 2 6 2 5 ga and high grade metamorphism along the margins of the microblocks during archean paleoproterozoic transition the ncc went through another major wilson cycle from early to late paleoproterozoic involving prolonged subduction accretion and collision of larger crustal blocks and intervening arc complexes leading to final cratonization

a simplified model of rip currents systems around discontinuous submerged barriers although in the last years several numerical models have been shown to be able to reproduce rip currents around discontinuous submerged barriers only few simple methods of practical use are available for estimating main flow parameters like the current intensity and the mean water levels in terms of geometrical barrier and gap dimensions parameters and wave characteristics the aim of this paper is to present a simplified model to be used for an easy estimate of these important rip currents parameters the model which is based on rough simplifications considers the area between the shoreline and the barrier as a reservoir in which water is pumped by breaking short waves across the barrier and from which water flows out at the gap four equations mass and momentum conservation across the barrier free discharge at the gap and balance of water pumped towards the shore and freely flowing offshore are used to derive one single model equation that can be solved for the wave set up and subsequently used for rip current velocity calculation two free parameters appear in this equation which respectively account for energy losses at the gap cv and bed friction the proposed model is validated against available laboratory experiments to show its ability in providing reasonable estimates of the desired parameters that may be considered by engineers adequate at the preliminary design stage of submerged breakwaters and that can be used for evaluating hydrodynamics on barred beaches

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

did the paleo asian ocean between north china block and mongolia block exist during the late paleozoic first paleomagnetic evidence from central eastern inner mongolia china 1 the tectonic evolution of the paleo asian ocean between the north china block ncb and the mongolia block mob is a contentious issue and geodynamic models remain speculative in an effort to puzzle out this controversy a paleomagnetic study was carried out on the silurian to permian formations in central eastern inner mongolia china more than 680 sedimentary and volcanic samples were collected from 86 sites we have established titanium poor magnetite and hematite as the principal magnetic carriers anisotropy of the magnetic susceptibility measurements demonstrate negligible deformation of the majority of study rocks with sedimentary fabrics from primary magnetizations a late devonian and a permian pole are calculated for inner mongolia block imb at 46 8 n 349 1 e dp 14 6 dm 27 3 with n 3 and 48 7 n 3 7 e dp 5 2 dm 9 1 with n 6 respectively two stages of secondary magnetization are also identified probably due to early permian and early cretaceous magmatic events as preliminary results the comparison of our new paleomagnetic poles with available data from ncb mob and siberia indicates that 1 the paleolatitudes of imb ncb and mob are consistent between late devonian and permian suggesting pre late devonian closure of the paleo asian ocean and further evaluation of these three blocks as a single entity and 2 post permian intracontinental deformation was significant and characterized by block rotations which are due to strike slip faulting within the welded ncb imb mob block

paleomagnetic constraints on the paleogeography of the east asian blocks during late paleozoic and early mesozoic times abstract although the axial and dominant geocentric character of the earth s magnetic field means that paleolongitude is indeterminate paleomagnetism is otherwise the only truly quantitative method available to the earth scientist for constraining paleogeography and reconstructing the kinematic evolution of continental blocks during the past half century numerous paleomagnetic results have provided substantial quantitative constraints on the origin and tectonic evolution of the major tectonic divisions now comprising eastern asian in this paper we first assess the available early paleozoic to early cretaceous paleomagnetic results from the south china north china and tarim blocks using internationally recognized reliability criteria we then construct a running mean through a 20 ma window by weighting the poles according to their q factors and fit a spherical spline with smoothing factor of 300 to derive apparent polar wander apw paths for these three major blocks during this early paleozoic to late mesozoic time interval together with late paleozoic to early mesozoic paleomagnetic poles from the qaidam qiangtang lhasa sibumasu indochina and some other smaller blocks terranes of east asia we produce a series of paleogeographic reconstructions for these major blocks and lesser terranes of east asia between mid ordovician and late jurassic times 460 160 ma which although based primarily upon paleomagnetic evidence aim to embrace the geological constraints finally we discuss the current evidence for closure times of the paleo asian mianlue and east paleo tethyan oceans which incorporate fundamental issues concerning the formation of the east asian continental collage and collision with the northern main body of the pangean supercontinent we use the collective evidence to argue that these major paleo oceans had closed by the late triassic and that the east asian sector of the supercontinent had united to become an integral part of pangea by that time 220 ma

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

lagrangian observations of circulation on an embayed beach with headland rip currents abstract this study describes the first comprehensive measurements of nearshore current patterns across the entire extent of an embayed beach bounded by headland rip currents a field experiment at whale beach nsw australia provides valuable insights into i embayment wide spatial and temporal flow behaviour ii rates of cross and alongshore water exchange and iii the influence of geological control by headlands on morphology and circulation lagrangian flow data was obtained using 34 gps drifters with 293 individual deployments over a single ebbing tidal cycle during moderate low energy h s 1 m oblique wave forcing in situ wave and current data and bathymetric data were also collected beach morphology was dominated by a large mid beach rip channel with lesser headland rip channels mean flow rates were 0 6 ms 1 in the mid beach channel and 0 4 ms 1 in the headland channels with the majority of cross shore water volume flux 60 through the central channel a weak alongshore current o 0 1 ms 1 was forced by the oblique offshore wave angle rip current velocities flow variability and rate of surfzone exits by lagrangian drifters increased as water level decreased transient currents on a planar bar along the northern half of the beach with velocity standard deviation up to 0 2 ms 1 were not tidally modulated lagrangian time series were used to differentiate four current regimes rip cell rip head planar bar and offshore low energy zone based on mean velocity velocity variability and degree of tidal modulation an increase in surfzone exit rates by drifters was observed from south upwave to north downwave with exit rates per drifter deployment of 22 at the south headland rip 65 at the mid beach open rip and 80 at the north headland rip the high rate of drifter exits contrasts previous observations on open coast beaches observed flow behaviours are attributed to wave shadowing at the upwave protected end of the beach and longshore currents forced by oblique waves deflected offshore at the downwave headland these field observations are in good agreement with recent numerical modelling a relationship between bathymetric variability and current intensity was determined with cross shore average mean velocity correlating with a parameterisation of bathymetric alongshore non uniformity this study demonstrates that flow behaviour and exchange rates can vary along the length of an embayed beach due to geological control this research has implications for transport of organisms nutrients and pollutants is relevant to beach safety practitioners and can be used in calibration of numerical models

offshore controls on nearshore rip currents 1 the rip current field resulting from the transformation of surface gravity waves over offshore submarine canyons is studied employing a wave transformation model and a wave induced circulation model over observed bathymetry we find that wave height variations associated with undulations in the canyon contours cause rip current circulation cells with alongshore spacing of o 100m even though the nearshore bathymetry displays no variations at these length scales further the predicted rips correspond to observed rip currents during the nearshore canyon experiment ncex motivated by these results we study the relationship between o 100 m scale variations in offshore bathymetric contours and the resulting rip current field in the nearshore to isolate the roles of possible bathymetric features we construct a series of idealized case studies that include site characteristics found at ncex that are conducive of rip current development such as a curved shoreline an offshore submarine canyon and undulations in the canyon contours our results show that the first two components are unable to produce the observed short scale circulation systems while wave refraction over undulations in the canyon walls at length scales of o 100 m provides a sufficient disturbance to generate alongshore wave height variations that drive multiple rip currents for a variety of incident wave conditions rips are not generated when the wave period is short or when the angle of incidence is large analysis of the alongshore momentum balances further demonstrates that the rip current locations are also strongly influenced by inertial effects hence nonlinear processes are important within the rip current circulation cell and we find that nonlinear advective acceleration terms balance a large portion of the driving alongshore gradient in the mean water surface elevation in the vicinity of the rip currents with bottom friction accounting for the remainder away from the rips the balance is between the wave forcing and the pressure gradient outside the surf zone and wave forcing and bottom friction inside the surf zone as expected

provenance analysis of the late paleozoic sedimentary rocks in the xilinhot terrane ne china and their tectonic implications abstract the xilinhot terrane is located in the eastern segment of the central asian orogenic belt in ne china and is a key to a hotly debated issue on the paleozoic tectonic evolution of this giant progenic belt to constrain the tectonic evolution of the xilinhot terrane in the late paleozoic we undertook zircon u pb dating and geochemical analyses of the zhesi and benbatu formations in the suolun and xi ujimqin areas in the xilinhot terrane samples of the benbatu formation yield detrital zircon u pb ages ranging from 2659 ma to 316 ma with four age populations at 2659 1826 ma 1719 963 ma 590 402 ma and 396 316 ma whereas samples from the zhesi formation yield detrital zircon u pb ages ranging from 1967 ma to 250 ma with four age populations at 1967 1278 ma 971 693 ma 561 403 ma and 399 250 ma the age groups of both the benbatu and zhesi formations in the xilinhot terrane are similar to those in other parts of the central asian orogenic belt caob this evidence indicates that the xilinhot terrane is a microcontinent and not an accretionary complex as previously thought furthermore the youngest zircon grains in the benbatu and zhesi formations yield weighted mean 206 pb 238 u ages of 322 12 ma msdw 0 12 n 4 and 257 2 8 ma msdw 1 6 n 8 respectively combined with fossil data our new data suggest that the benbatu and zhesi formations in the xilinhot terrane were possibly deposited at 322 ma and 257 ma respectively based on the provenance of the carboniferous permian sandstones came from the blocks of ne china we speculate that the xilinhot terrane is the western part of the songliao block

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

silurian magmatism on the eastern margin of the erguna block ne china evolution of the northern great xing an range abstract there are few early paleozoic volcanics and mafic rocks in the xing an mongolia orogenic belt in spite of the extensive occurrence of granites caused by a synchronous orogenic event despite the fact that this was a major orogen the properties of the lithosphere and its associated orogenic processes are poorly known in this paper a comprehensive study of u pb zircon ages lu hf isotopes and whole rock elemental analyses was carried out on three intermediate mafic intrusions which were recently identified in the northern great xing an range representative samples of the yikete yalu and xinglong intrusions yielded the weighted mean 206pb 238u ages of 435 1 ma 430 8 ma and 447 4 ma respectively this indicates the presence of silurian intermediate mafic rocks in the region the dioritic rocks exhibit a na rich a calc alkaline affinity and enrichment in liles rb ba k and sr and depletion in hsfes ta ti zr and hf indicating that the yikete dioritic rocks were a mantle wedge that had previously been subjected to metasomatism by fluids and melts related to a subducted oceanic slab and its overlying sediments the gabbroic rocks are tholeiitic in composition with variable mgo 3 14 8 31 and low k2o 0 16 1 0 and tio2 0 25 2 12 contents they are characterized by enrichment of liles depletion of hfses and highly positive zircon ehf t 5 8 to 13 3 values in addition they possess geochemical features of morb with subordinate oib the geochemical features indicate that the gabbroic rocks were derived from an upwelling of asthenospheric mantle that had been into the supra subduction wedge facilitated by subduction rollback before their generation combined with the coeval arc type magmatic rocks widely exposed on the eastern margin of the erguna block we link the generation of the dioritic rocks to the northwestern subduction of the nenjiang oceanic plate during the early paleozoic the generation of the gabbroic rocks might result from rifting of the back arc basin consequently an arc back arc model is proposed to explain the subduction evolution of the nenjiang ocean during the early paleozoic

experimental study of nearshore dynamics on a barred beach with rip channels 1 wave and current measurements are presented from a set of laboratory experiments performed on a fixed barred beach with periodically spaced rip channels using a range of incident wave conditions the data demonstrate that the presence of gaps in otherwise longshore uniform bars dominates the nearshore circulation system for the incident wave conditions considered for example nonzero cross shore flow and the presence of longshore pressure gradients both resulting from the presence of rip channels are not restricted to the immediate vicinity of the channels but instead are found to span almost the entire length of the longshore bars in addition the combination of breaker type and location is the dominant driving mechanism of the nearshore flow and both are found to be strongly influenced by the variable bathymetry and the presence of a strong rip current the depth averaged currents are calculated from the measured velocities assuming conservation of mass across the measurement grid the terms in both the cross shore and longshore momentum balances are calculated and their relative magnitudes are quantified the cross shore balance is shown to be dominated by the cross shore pressure and radiation stress gradients in general agreement with previous results however the rip current is shown to influence the wave breaking and the wave induced setup in the rip channel analysis of the longshore balance shows that the overall strength of the longshore feeder currents is governed by a balance between longshore pressure gradient forcing and an opposing radiation stress gradient in addition the longshore feeder currents show maxima in the bar trough region providing experimental evidence that longshore pressure gradients can shift longshore current maxima shoreward from the bar crest finally since the longshore radiation stress gradient in the surf zone is governed by the amount of wave dissipation on the rip current there exists a positive feedback mechanism whereby a strong rip current can weaken the radiation stress gradient opposing the feeder currents and lead to even stronger feeder currents and rips

rip currents and alongshore flows in single channels dredged in the surf zone to investigate the dynamics of flows near nonuniform bathymetry single channels on average 30 m wide and 1 5 m deep were dredged across the surf zone at five different times and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions in addition circulation was simulated with the numerical modeling system coawst initialized with the observed incident waves and channel bathymetry and with an extended set of wave conditions and channel geometries the simulated flows are consistent with alongshore flows and rip current circulation patterns observed in the surf zone near the offshore directed flows that develop in the channel the dominant terms in modeled momentum balances are wave breaking accelerations pressure gradients advection and the vortex force the balances vary spatially and are sensitive to wave conditions and the channel geometry the observed and modeled maximum offshore directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking wave driven setup across the nonuniform bathymetry a function of wave height and angle water depths in the channel and on the sandbar and a breaking threshold and the breaking wave driven alongshore flow speed the offshore directed flow speed increases with dissipation on the bar and reaches a maximum when the surf zone is saturated set by the vertical scale of the bathymetric variability

nearshore circulation over transverse bar and rip morphology with oblique wave forcing there is a paucity of field data to describe the transition in nearshore circulation between alongshore meandering and rip current systems a combination of in situ current meters and surf zone drifters are used to characterize the nearshore circulation over a transverse bar and rip morphology at pensacola beach florida in the presence of relatively low energy oblique waves current speeds vary in response to the relative wave height ratio hs h which defines the degree and extent of breaking over the shoal in the absence of wave breaking the nearshore circulation was dominated by an alongshore current driven by the oblique waves as waves begin to break across the shoal 0 2 0 5 the meandering current is replaced by an unsteady rip circulation that moves offshore between the shoals before turning alongshore in the direction of wave advance outside the surf zone the increase in wave dissipation is associated with an increase in very low frequency vlf variations in the current speed across the shoal and in the rip channel that caused the circulation to oscillate between an offshore and an alongshore flow the unsteady nature of the nearshore circulation is responsible for 55 of all surf zone exits under these more dissipative conditions in contrast only 29 of the drifters released from the shoal exited the surf zone and bypassed the adjacent shoal with the alongshore meandering current while the currents had a low velocity maximum of 0 4 m s 1 and would not pose a significant hazard to the average swimmer the results of this study suggest that the transverse bar and rip morphology is sufficient to create an alongshore variation in wave dissipation that forces alongshore meandering and low energy rip circulation systems under oblique wave forcing copyright 2013 john wiley sons ltd

ripex observations of a rip current system rip current kinematics and beach morphodynamics were measured for 44 days at sand city monterey bay ca using 15 instruments composed of co located velocity and pressure sensors acoustic doppler current profilers and kinematic gps surveys the morphology consisted of a low tide terrace with incised quasi periodic rip channels representative of transverse bars offshore 17 m depth significant wave height and peak period ranged 0 20 3 0 m and 5 20 s the mean wave direction was consistently near 08 resulting in rip channel morphology which evolved in response to the changing wave characteristics an inverse relationship between sediment accreting on the transverse bar and eroding in the rip channel was found the spatial distribution of sediment is reflected in the background rip current flow field the mean velocity magnitudes within the rip channel transverse bars increased offshore onshore with decreasing tidal elevations and increased with increasing sea swell energy eulerian averaged flows were predominantly shoreward on the transverse bars and seaward within the rip channel throughout the experiment resulting in a persistent cellular circulation except during low wave energy the rip current spacing to the rip channel width was less than or equal to two which suggests that the rip currents are influenced by each other and that no two dimensional bar return flow should be present the vertical velocity profile on the bar indicated that the flow was predominantly shoreward the flow field within the surf zone was depth uniform except for significant shear occurring near the surface owing to stokes drift the wave induced transport hypothesis is evaluated d 2005 elsevier b v all rights reserved

tectonic implications of new zircon u pb ages for the xinghuadukou complex erguna massif northern great xing an range ne china abstract the nature and the timing of formation of the xinghuadukou complex of ne china are important to further our understanding of the precambrian geological evolution of the erguna massif and the eastern segment of the central asian orogenic belt caob here we present the results of zircon u pb dating of a metavolcanic rock and 11 granitoid basement samples collected from the complex we use these data to determine the age and tectonic origin of the complex and to examine the linkages between this complex and the surrounding tectonic domains and older cratonic areas igneous zircons from the metavolcanic rock yield a magmatic age of 850 ma indicating that the supracrustal rocks that represent the original xinghuadukou group formed during the neoproterozoic petrological data and new zircon u pb ages for these samples enabled the identification of multiple stages of granitoid magmatism within different sections of the xinghuadukou group indicating that this group which was originally thought to have formed contemporaneously actually records the emplacement of granitoids at 957 786 479 418 265 and 209 192 ma this result indicates that the xinghuadukou complex records multiple stages of magmatism and contains various neoproterozoic supracrustal components combining the new age data with regional geological data we propose that the erguna massif should be considered part of the mongol domain as it has a close affinity to other blocks that formed part of this domain during the neoproterozoic these data suggest that all of the complexes and terranes within the mongol domain belong to the caob and were finally accreted to the southern margin of the siberian craton in the early paleozoic

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

a mechanism for sandbar straightening by oblique wave incidence 1 breaker bars in the surf zone of sandy beaches generally evolve between straight bars parallel to the shore and meandering crescentic bars associated with intense dangerous currents flowing seaward through rip channels understanding the behavior of such systems is fundamental as they control the entire surf zone dynamics the shape of the coastline and the exchange of floating material with the shoreface although the mechanisms behind the meandering of an originally straight bar have been studied extensively a clear physical explanation on the crescentic bar straightening was missing recent field observations have highlighted that this morphological reset can be due to wave obliquity by using a two dimensional horizontal morphological model we show that the bar straightening by oblique waves occurs because the rip current is both weakened in intensity and shifted downdrift from the channel deepest section the technique employed is useful for the study of other types of bed forms

effect of alongshore nonuniformities on longshore current predictions longshore currents have been primarily modeled by assuming alongshore uniformity in this paper we revisit the problem of nonuniform longshore currents to refocus attention on the importance of accounting for alongshore nonuniformity in longshore current predictions and to provide an analytical estimate of the importance of this nonuniformity we derive a semianalytical solution for the longshore currents that allows for weak alongshore variations in the bottom topography the solution shows that the alongshore pressure gradient induced by alongshore variations in the bottom topography could contribute substantially to the forcing for the longshore currents an example calculation shows that the longshore current could deviate by up to 30 from the mean for a 10 deviation of the bottom topography thus we suggest that in many practical cases it is important to include the alongshore pressure gradient to accurately model longshore currents

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

timing of closure of the eastern mongol okhotsk ocean constraints from u pb and hf isotopic data of detrital zircons from metasediments along the dzhagdy transect abstract the mongol okhotsk belt a major structural element of east asia is probably the youngest orogenic segment within the central asian orogenic belt however the timing of final closure of the mongol okhotsk ocean remains unresolved here we present detrital zircon u pb hf isotopic data and whole rock geochemical data major and trace elements and sm nd isotopes for the metasedimentary rocks from the un ya bom terrane dzhagdy terrane and the eastern part of the tukuringra terrane our new zircon u pb ages suggest that all sedimentary formations along the dzhagdy transect are early mesozoic in age rather than paleozoic as previously thought the detrital zircons from the metasedimentary rocks in the un ya bom terrane the dzhagdy terrane and the eastern part of the tukuringra terrane yielded the youngest concordant ages of 194 4 193 2 and 171 2 ma respectively moreover we note that the so called sedimentary formations of these terranes are not single sedimentary sequences as previously suggested but a set of an olistostrome or tectonic melanges composed of rocks of different ages and origins these sedimentary formations are probably relics of the mongol okhotsk remnant basin that formed in the gaps between the southern margin of the north asian craton and the amur block during their collision the absence of detrital zircons younger than 171 ma in the sedimentary rocks of the mongol okhotsk basin implies that the final closure of this basin could have taken place at the boundary of the early and middle jurassic as a result of the collision or the development of the mongol okhotsk orogenic belt in this region after that the mongol okhotsk belt underwent intense deformation related to within plate strike slip faulting which could be attributed to the late mesozoic rotation of the north asian craton relative to the continental massifs of east asia

geochronology and geochemistry of late pan african intrusive rocks in the jiamusi khanka block ne china petrogenesis and geodynamic implications abstract to constrain the early paleozoic tectonic evolution of the jiamusi khanka block and its relationship to the late pan african event in gondwana we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic intrusive rocks in the jiamusi khanka block ne china la icp ms zircon u pb age data demonstrate that these intrusive rocks were emplaced at three stages during the late pan african event represented by 540 ma syenogranite 515 ma quartz syenite and 500 ma monzogranite and gabbro geochemically the 500 ma gabbros in the jiamusi khanka block have low sio 2 50 26 51 21 wt relatively high mgo 4 08 5 67 wt ni 13 1 14 1 ppm and cr 28 4 56 0 ppm and are slightly enriched in liles e g ba k and lrees and depleted in zr hf nb ta and p the e hf t values of zircons in the gabbro range from 2 6 to 6 4 all these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab in contrast the ca 540 500 ma granites and quartz syenites contain high sio 2 64 49 72 20 wt and low mgo 0 40 0 75 wt cr 1 69 6 88 ppm and ni 1 26 3 26 ppm they have relatively low 176 hf 177 hf ratios of 0 282247 0 282599 with hf two stage model ages of 1173 2280 ma and most of the magmatic zircons have positive e hf t values varying from 0 2 4 8 indicating that these granites and quartz syenites were probably derived from a dominantly paleo mesoproterozoic old crustal source with possible different degrees of addition of juvenile materials according to the geochemical data and global geological investigations we propose that the 541 498 ma intrusive rocks in the jiamusi khanka block formed in a post collisional or post orogenic extensional setting linked to the collapse of a late pan african orogen associated within the gondwana

tectonic units of the early precambrian basement within the north china craton constraints from gravitational and magnetic anomalies abstract the tectonic divisions of the north china craton ncc basement has always been a hot and yet unresolved topic we collected the latest gravity and magnetic data and then used a two dimensional discrete wavelet transform method to decompose the bouguer gravity anomaly of the ncc into the 1st to 8th approximations and details respectively we then compared the dynamic tectonic division schemes with the gravity and magnetic division schemes for the precambrian basement at the end of the neoarchean and archean our results show that the 2nd order detail field of the bouguer gravity anomalies is well consistent with the paleoproterozoic tectonic divisions of the ncc by zhao et al 2005 for it clearly outlines the 3 unit layout of the eastern and western blocks and the central trans north china orogen with some anomalous zones identically trending with the dike swarms faults and volcanic rocks generally produce magnetic anomalies but the main anomalous zones in the magnetic field are merely distributed around the plate boundaries of the ncc it may indicate that the amalgamation of the ncc was mostly completed in the paleoproterozoic the 5th order detail field of bouguer gravity anomalies of the ncc corresponds well with its tectonic division at the end of the neoarchean for it well reflects the general boundaries and axial trends of the archean units these archean units are mainly separated into three paleoproterozoic tectonic units by paleoproterozoic tectonic boundaries respectively the magnetic anomalies within the western and eastern blocks have separately similarities with the trans north china orogen the 6th order detail fields however match well the boundaries of the 10 continental nucleii of the archean ncc but the anomalous distributions in the 6th order detail are also divided by the paleoproterozoic tectonic borders in view of the gravity and magnetic anomalies it further reveals that the ncc basement may have experienced a dynamic evolutionary process from continental nucleation to micro continental amalgamation and to a final unified crystalline basement

field observations of wave setup wave setup is assumed to be a balance between the cross shore convergence of the onshore flux of momentum wave radiation stress sxx in the surfzone and a cross shore pressure gradient oceanic observations between the 2 and 8 m isobaths near duck north carolina provide a test of the wave setup balance without assuming that wave height in the surfzone is proportional to water depth analysis of data from a cross shore array of 11 pressure gauges and 10 sonar altimeters deployed during the fall of 1994 indicates the wave setup balance holds to at least the accuracy of the pressure measurements a few centimeters the correlation between the two terms in the setup balance is 0 93 and the linear regression slope is 1 05 0 19 accurate estimates of the cross shore pressure gradient require density measurements to adjust pressure measurements taken at different depths to the same level the assumption that pressure and bathymetry are linear between the 2 and 8 m isobaths or the more common assumption that the height of normally incident shallow water waves is proportional to the water depth introduces errors of up to 6 cm for the conditions considered here given this assumption 3 5 years of data from pressure gauges in 2 and 8 m of water indicate that the wave setup balance is valid for a wide range of conditions correlation 0 71 and regression slope 0 98 0 08

intracontinental deformation in a frontier of super convergence a perspective on the tectonic milieu of the south china block abstract since mesozoic the south china region has been located at the center of a triangular area surrounded by westward subduction of the pacific plate northward subduction of the india plate beneath the eurasia plate and collision of the north and south china blocks along the central china orogen this region thus marks the frontier of a super convergent regime within the super convergence domain the compressional structures in the center of the south china block are mainly characterized by shortening thrusting and decollement the block underwent inhomogeneous rejuvenation of the pre existing crust and lithospheric structures through reactivation of late stage activities the surface deformation of the xuefeng intracontinental tectonic system within the south china block is possibly derived from intraplate tectonics particularly the distinct magmatism between the west and east limbs of the xuefeng precambrian uplift is a possible response of the rheological structure of the lithosphere the deep structures as revealed from tomographic studies show marked difference of lithosphere architecture between the eastern and western sub blocks of the south china block these data illustrate the long term mosaic of multi block convergence which led to present day inhomogeneity in the continental lithosphere in south china a comparison of the intensive contraction of the south china block with the distinct features of rifting of the north china block brings out the contrasting structural and tectonic signatures developed in the same frontier of one of the largest super convergent systems on the globe during the mesozoic to cenozoic

mean lagrangian flow behavior on an open coast rip channeled beach a new perspective article i nfo the accepted view of rip currents is that they are an efficient mechanism for transporting material out of the surf zone previous rip current campaigns on natural beaches have focused on eulerian measurements with sparse in situ pressure and current meter arrays here for the first time spatially synoptic estimates of rip current flow patterns vorticity and lagrangian transport behavior are measured in the field using a fleet of 30 position tracking surfzone drifters during multiple rip current occurrences on an open coast beach in monterey ca contrary to the classic view shepard et al 1941 the rip current flow field consisted of semi enclosed large scale vortices that retained the drifters and resulted in a high number of lagrangian observations that are temporally and spatially repeated approximately 19 of the drifters deployed in the rip currents exited the surf zone per hour on average during the experiments the observed surf zone retention of drifters is consistent with measurements from different open coast beach rip current systems 14 at meso macrotidal truc vert france and 16 at macrotidal perranporth united kingdom the three hour average cross shore rip current velocity at monterey was 30 cm s with peak time averaged velocities of 40 60 cm s depending on wave and tidal conditions drifters that episodically exited the surf zone were transported approximately 2 surf zone widths offshore at 20 cm s published by elsevier b v

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

modeling of depth induced wave breaking under finite depth wave growth conditions 1 recent studies have shown that the spectral wind wave model swan simulating waves nearshore underestimates wave heights and periods in situations of finite depth wave growth in this study this inaccuracy is addressed through a rescaling of the battjes and janssen 1978 bore based model for depth induced breaking considering both sloping bed surf zone situations and finite depth wave growth conditions it is found that the variation of the model error with the breaker index bj in this formulation differs significantly between the two types of conditions for surf zones clear optimal values are found for the breaker index by contrast under finite depth wave growth conditions model errors asymptotically decrease with increasing values of the breaker index weaker dissipation under both the surf zone and finite depth wave growth conditions optimal calibration settings of bj were found to correlate with the dimensionless depth kpd where kp is the spectral peak wave number and d is the water depth and the local mean wave steepness subsequently a new breaker index based on the local shallow water nonlinearity expressed in terms of the biphase of the self interactions of the spectral peak is proposed implemented in the bore based breaker model of thornton and guza 1983 this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations hence the proposed expression yields a significant improvement in model accuracy over the default battjes and janssen 1978 model for finite depth growth situations while retaining good performance for sloping bed surf zones

palaeomagnetism of east siberian traps and kimberlites two new poles and palaeogeographic reconstructions at about 360 and 250 ma summary we studied basalt sills and dykes and kimberlite pipes from the eastern part of the siberian platform these are spread out over a few hundred kilometres and are divided into two age groups late permian early triassic mir aikhal and olenyek regions and late devonian early carboniferous viluy and markha basins aikhal region the palaeomagnetic poles determined for each sill or dyke are statistically different from each other but averaging all corresponding directions from these sills and dykes with those from kimberlites of different generations yields results with acceptable statistics this is probably due to the averaging out of secular variation and or changes in magnetic polarity the resulting palaeomagnetic poles allow one to reconstruct the palaeopositions of siberia during the two large flood basalt events at about 360 and 250 ma a significant rotation of the siberian platform during the devonian and carboniferous is suggested the new data are in general agreement with some earlier palaeomagnetic poles for the late permian early triassic traps of the tungusska basin and significantly reduce uncertainties for previous late devonian early carboniferous siberian poles which were very scattered together with geological and absolute age data the palaeomagnetic data support the hypothesis that kimberlite magmatism and trap intrusions were both rapid and relatively close in time the 360 ma event is emerging as a magmatic event with considerable extent over the russian and siberian platforms related to incipient continental break up and triple junction formation possibly at or near the time of the frasnian famennian mass extinction

petrogenesis of late paleozoic volcanic rocks from the daheshen formation in central jilin province ne china and its tectonic implications constraints from geochronology geochemistry and sr nd hf isotopes abstract we present geochronological geochemical whole rock sr nd and zircon hf isotopic data for late paleozoic volcanic rocks from the daheshen formation in central jilin province northeastern china and constrain the petrogenesis of the volcanic rocks and late paleozoic tectonic evolution of the northern margin of the northern china craton which is regarded as the eastern segment of the central asian orogenic belt caob lithologically the daheshen formation is composed mainly of rhyolite rhyolitic tuff dacite and andesite with minor basalt the zircons from three rhyolites two dacites one rhyolitic tuff and one basalt are euhedral subhedral display oscillatory zoning and have high th u ratios 0 50 2 28 implying a magmatic origin la icp ms zircon u pb age data indicate that the volcanic rocks from the daheshen formation formed during late carboniferous early permian time 302 299 ma geochemically late paleozoic volcanic rocks have sio 2 52 13 81 77 wt and k 2 o 0 86 6 88 wt belonging to mid k to high k calc alkaline series these rocks are characterized by enrichment in large ion lithophile elements liles and light rare earth elements lrees and depletion in high field strength elements hfses such as nb ta and ti and heavy rare earth elements hrees with affinities to igneous rocks forming in an active continental margin setting all volcanic rocks have depleted nd isotopic compositions e nd t 2 4 to 2 5 for the basalts and 5 8 to 7 1 for the andesites and dacites respectively in situ hf isotopic results of zircon from the rhyolites show that they have e hf t 1 1 to 10 6 all these geochemical features indicate that the andesites dacites and rhyolites likely originated from the partial melting of meso neoproterozoic accreted lower crust hf and nd model ages t dm2 of 1384 662 ma and 1061 800 ma respectively in contrast the basalts were derived from the partial fusion of a depleted lithospheric mantle that had subsequently been metasomatized by subducted slab derived fluids these data along with the regional geological investigations suggest that the generation of late paleozoic volcanic rocks from the daheshen formation was related to southward subduction of the paleo asian oceanic plate beneath the northern margin of the north china craton this also indicates that the paleo asian ocean may have not closed before the early permian

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

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

the role of morphology and wave current interaction at tidal inlets an idealized modeling analysis the outflowing currents from tidal inlets are influenced both by the morphology of the ebb tide shoal and interaction with incident surface gravity waves likewise the propagation and breaking of incident waves are affected by the morphology and the strength and structure of the outflowing current the 3 d coupled ocean atmosphere wave sediment transport coawst modeling system is applied to numerically analyze the interaction between currents waves and bathymetry in idealized inlet configurations the bathymetry is found to be a dominant controlling variable in the absence of an ebb shoal and with weak wave forcing a narrow outflow jet extends seaward with little lateral spreading the presence of an ebb tide shoal produces significant pressure gradients in the region of the outflow resulting in enhanced lateral spreading of the jet incident waves cause lateral spreading and limit the seaward extent of the jet due both to conversion of wave momentum flux and enhanced bottom friction the interaction between the vorticity of the outflow jet and the wave stokes drift is also an important driving force for the lateral spreading of the plume for weak outflows the outflow jet is actually enhanced by strong waves when there is a channel across the bar due to the return current effect for both strong and weak outflows waves increase the alongshore transport in both directions from the inlet due to the wave induced setup over the ebb shoal wave breaking is more influenced by the topography of the ebb shoal than by wave current interaction although strong outflows show intensified breaking at the head of the main channel

mean currents and sediment transport in a rip channel measurements of hydrodynamics and suspended sediment transport were carried out along a cross shore transect in a rip channel a tidally induced threshold for rip flow initiation was found this threshold depended upon the degree of wave energy dissipation and could be identified through a critical value of the ratio of significant wave height to water depth s in the rip neck with normally incident waves rip current velocities were well correlated with velocities predicted from a simple model involving the onshore mass transport in asymmetric breaking waves crossing the bar hydrodynamics and sediment transport were tidally modulated with strong offshore directed rip currents and associated offshore sediment transport due to the mean flow at low tide at high tide when the rip was inactive the tendency was for weak onshore directed mean flows and or oscillatory incident waves transporting smaller amounts of sediment landward the net result was a gradual lowering of the topographic relief along the rip channel with net deposition seaward of the rip outside the surf zone transport was mainly landward due to oscillatory incident waves