oceanic plateau formation by seafloor spreading implied by tamu massif magnetic anomalies tamu massif is an immense mesozoic submarine volcano the main edifice of the shatsky rise oceanic plateau it is located at a spreading ridge triple junction but considered to be a shield volcano formed by effusive volcanism from an emerging mantle plume however it is unclear how tamu massif eruptions interacted with the spreading ridges which are enormous linear volcanoes themselves here we create a magnetic anomaly map for tamu massif which can provide clues about crustal formation for tamu massif we find dominantly linear magnetic field anomalies caused by crustal blocks of opposite magnetic polarity this pattern suggests that tamu massif is not a shield volcano but was emplaced by voluminous focused ridge volcanism if the magma source at the shatsky rise was a plume it was closely connected to and controlled by seafloor spreading by implication even the largest oceanic plateau edifices can be formed by seafloor spreading we suggest that the widely accepted analogy between continental flood basalts and oceanic plateaus requires reconsideration the shatsky rise oceanic plateau formed by spreading ridge volcanism according to analyses of linear magnetic anomalies over the tamu massif submarine volcano

double flood basalts and plume head separation at the 660 kilometer discontinuity several of the world s flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years these double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle this detached plume head eventually triggers the first flood basalt event the remaining conduit forms a new plume head which causes the second eruptive event the second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head in general agreement with observations regarding double flood basalts

early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

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

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

a numerical study of a mesoscale convective system during toga coare part ii organization in part i the authors presented a successful numerical simulation of the life cycle of a warm pool mesoscale convective system mcs that occurred on 15 december 1992 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment in this study the simulation results of part i are diagnosed to investigate the organization of the mcs and the convective onsets that occurred during the growing and mature stages of the mcs during the life cycle of the mcs four convective onsets occur in the presence of large scale ascent convective available potential energy cape and surface potential temperature drop off sptd it is found that the first convective onset is caused by the existence of upward motion cape and sptd in the model initial conditions the second convective onset is regulated by the favorable occurrence of sptd the third and fourth convective onsets arise from the development of upward motion associated with the westward propagation of the quasi 2day wave the four mesoscale precipitation features clustered together to form the mcs in response to the evolution of the vertical motion field the organization of the mcs is characterized by the presence of a midtropospheric mesovortex situated near the position of the first convective onset analysis of the relative vorticity rv budget indicates that the mesovortex originates and intensifies largely from vortex stretching induced by deep convective heating a decrease in rv above below the mesovortex arises because of the combined effects of the tilting and horizontal advection terms the tilting stretching and solenoidal terms our results suggest that the mesovortex played little role in the subsequent onsets i e second third and fourth and that other warm pool mcss occurring near the transequatorial flow are likely to be associated with mesovortices

early evolution of vertical vorticity in a numerically simulated idealized convective line the generation and organization of mesoscale convective vortices mcvs is a recurring theme in midlatitude and tropical meteorology during the warm season in this work a simulation of a finite length idealized convective line in a westerly shear environment is investigated in the absence of ambient vertical vorticity an asymmetry in average vertical vorticity forms rapidly at early times in the present simulation this study focuses on the formation and organization of vertical vorticity at these early simulation times previous simulations suggest that tilting of either ambient or storm generated horizontal vorticity is the primary mechanism responsible for the formation organization and maintenance of mcvs this study confirms recent work regarding the generation of vertical vorticity at early times in the simulation a lagrangian budget analysis of the vertical vorticity equation however shows that vorticity convergence becomes a comparable and at times dominant mechanism for the enhancement and long term organization of vertical vorticity early in the simulation despite differences in the initial ambient horizontal vorticity hodograph and convective available potential energy the lagrangian budget analysis in the present midlatitude case is consistent with the lagrangian budget results of a previous tropical squall line simulation the study of idealized convective lines in midlatitude environmental conditions therefore provide valuable insight into understanding vertical vorticity production in tropical squall lines and their potential relevance to tropical cyclogenesis

multiscale interactions in the life cycle of a tropical cyclone simulated in a global cloud system resolving model part ii system scale and mesoscale processes abstract the life cycle of tropical storm isobel was simulated reasonably well in the nonhydrostatic icosahedral atmospheric model nicam a global cloud system resolving model the evolution of the large scale circulation and the storm scale structure change was discussed in part i both the mesoscale and system scale processes in the life cycle of the simulated isobel are documented in this paper in the preconditioned favorable environment over the java sea mesoscale convective vortices model mcvs developed in the mesoscale convective systems mcss and convective towers with cyclonic potential vorticity pv anomalies throughout the troposphere model vortical hot towers vhts appeared in the model mcvs multiple model vhts strengthened cyclonic pv in the interior of the model mcv and led to the formation of an upright monolithic pv core at the center of the concentric mcv primary vortex enhancement as the monolithic pv core with a warm core developed near the circulation center the intensif

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

comment on chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt by y h park s j doh and d suk summary a recent paper published in geophysical journal international reports that the late palaeozoic to early mesozoic sedimentary rocks in the northeastern okcheon belt of korea were remagnetized during the late cretaceous to early tertiary and argues that the remagnetization was triggered by fluids travelling more than 800 km from the subducting slab of the kula pacific plates based on available geological data however we suggest that the remagnetization was caused by thermal effects of a late cretaceous pluton intruding the sedimentary rocks and or associated short range hydrothermal fluids rather than by long range fluids

paleomagnetic results from the lower mesozoic daedong supergroup in the gyeonggi block korean peninsula an eastern extension of the south china block abstract lower mesozoic lake deposits in the daedong supergroup of the gyeonggi block were collected at 38 sites for paleomagnetic study a remanent magnetization component with unblocking temperatures of 635 660 c component a was isolated from four sites the directions of this component with both normal and reversed polarities yielded positive fold and reversal tests at the 95 confidence level component a is interpreted to be of primary origin of late triassic time the mean direction of component a d 82 2 i 23 1 with 95 4 1 together with previously reported primary directions yields a pole representative for the gyeonggi block at 31 9 n 220 2 e a 95 12 7 the paleomagnetic pole shows good agreement with that for the south china block suggesting that the gyeonggi block has been part of the south china block the gyeonggi block as the eastern part of the south china block is regarded to have thrust to its position at the present korean peninsula during the collision between the north and south china blocks

structure of a midtropospheric vortex induced by a mesoscale convective system on 9 june 1988 a mesoscale 200 km diameter convectively generated vortex mcv passed through the colorado wind profiling network the generating convective system which was too small to meet maddox s mesoscale convective complex criteria developed beneath a high amplitude mid and upper level ridge axis profiler winds obtained within the stratiform region of the convective system and near the center of the ensuing mcv form the basis of this study with the addition of satellite including rapid scan images and conventional and doppler radar data this vortex was well observed over its entire life cycle the slowly moving vortex was observed by the flagler 50 mhz profiler for more than 16 h for a portion of this period the circulation was quasi steady hence the spatial structure of the vortex was depicted by timeto space conversion of the profiler data the results show a strong coherent circulation with maximum tangential speeds greater than 16 m s21 at 6 km above mean sea level msl and at radii of 50 70 km corresponding relative vorticity was more than three times as large as the local coriolis parameter the long duration and the apparent dominance of vorticity over divergence suggest that the flow in the vortex was in a quasi balanced state hence the temperature perturbation necessary to support the tangential velocity distribution was computed assuming gradient balance in the radial direction the resulting estimated temperature structure showed a warm core with a magnitude of 2 38c at 7 3 km msl and a cold core below 6 3 km msl the associated potential vorticity pv structure at the vortex center consisted of a lens of high pv with a maximum at 6 3 km msl and relative minima above and below this height

ontong java and kerguelen plateaux cretaceous icelands together with iceland the two giant oceanic plateaux ontong java in the western pacific and kerguelen broken ridge in the indian ocean are accumulations of mafic igneous rock which were not formed by normal seafloor spreading we compare published geochronological crustal structure and subsidence results with tectonic fabric highlighted in new satellite derived free air gravity data from the three igneous provinces and conclude that existing evidence weighs lightly against the ontong java and kerguelen plateaux originating at a seafloor spreading centre

intersections of remanence small circles new tools to improve data processing and interpretation in palaeomagnetism summary intersections of remanence small circles are increasingly used in palaeomagnetism to determine the palaeofield direction from synfolding remanences the approach small circle intersection sci method presupposes that remanence small circles from sites tilted to different directions intersect in a common point which is assumed to represent the palaeofield direction the sci method is not restricted to synfolding remanences it can be applied also to derive the palaeofield direction from pre folding remanences in addition to tilt correction and as a cross check for fold tests however the sci method has specific requirements and does not work in all cases the suitability of data sets and reliability of palaeofield estimates have to be assessed carefully and always against the background of local geology this paper examines the occurrence and distribution of sci as a tool of judgement first a data set is most suitable and a palaeofield estimate by sci most reliable when most of the theoretically possible intersections are realized and in addition clearly grouping in a narrow region second the small circles that greatly determine the result of sci are identified by the highest number of intersections they have with the others these criteria allow a systematic investigation of sci estimates upon stability and dependencies moreover scis can be an indicator of irregular unexpected tectonic settings when the intersections disperse strongly although significant bedding strike differences are given relative rotations or other unexpected displacements are likely to have occurred if so the sci estimate will be invalid and probably biased however also fisher mean calculation and most fold tests will be affected in this case the scis can help to separate the data into subsets valid for fisher statistics and sci methods the other possibility is to use tentative reconstructions to infer the true sequence of tilts and rotations and correct the data adequately

contribution of induced magnetization to magnetization of seamounts a fundamental assumption in modelling seamount magnetic anomalies is that the contribution of induced magnetization is negligible the general consistency of seamount and non seamount palaeopoles scarcity of poles skewed toward the present field direction and the high ratio of remanent to induced magnetization koenigsberger ratio of many oceanic basalts have been cited as evidence supporting this assumption1 2 recent discussions concerning the dominance of normally magnetized seamounts have focused attention on the possible role of viscous and induced magnetization in seamount anomalies3 6 here we determine natural remanent magnetization initial volume susceptibility and the koenigsberger ratio for more than 2 000 samples from a subaerially exposed seamount section on la palma canary islands table 1 by contrast to results from the oceanic crust and ophiolites these data indicate that a variety of rock types are potential magnetic sources the significant induced component of intrusives underscores the importance of the lithological distribution in determining the character of seamount magnetic anomalies the la palma data together with a plausible lithological distribution indicate that induced magnetization may account for one sixth of seamount magnetization

jurassic cretaceous boundary age and mid ocean ridge type mantle source for shatsky rise basalt sills cored in lowermost berriasian sediments on shatsky rise in the northwest pacific yield a mean 4 0 ar 3 9 ar incremental heating age of 144 6 0 8 ma providing a minimum estimate on the age of the jurassic cretaceous boundary the largest part of the rise was emplaced at rates similar to those of several continental flood basalts the rise formed at an oceanic triple junction and the sills as well as lavas from two dredge sites exhibit an ocean ridge type nd pb sr isotope signature this signature is provisionally consistent with either a perisphere or meteorite impact model but is not predicted by the plume head model of plateau formation however no model can yet be rejected given the very sparse sampling of shatsky rise

extreme rainfall and flooding from orographic thunderstorms in the central appalachians 1 the central appalachian region has experienced some of the largest rainfall accumulations in the world at time intervals less than 6 h including the 18 july 1942 smethport pennsylvania storm that produced 780 mm in less than 5 h the envelope curve of central appalachian flood peaks at small drainage areas less than 1000 km2 is dominated by orographic thunderstorm systems like the smethport storm orographic thunderstorm systems that have produced catastrophic flooding in the central appalachians are examined through observational and numerical model analyses using the weather research and forecasting wrf model analyses suggest that the frequency of catastrophic flooding varies over the central appalachian region and that small scale variation may be linked to the role of complex terrain in altering thunderstorm dynamics catastrophic flooding along the western margin of the central appalachians is dominated by four storms that occurred on 18 19 july 1889 1942 1977 and 1996 which were associated with warm season extratropical systems and were characterized by rapidly moving storm elements in complex terrain along the eastern margin and interior of the central appalachians catastrophic flooding is linked to four terrain locked orographic convective systems that occurred 17 18 june 1949 18 19 august 1969 27 june 1995 and 11 august 2003 wrf model simulations of the little river storm june 1949 rapidan storm june 1995 smethport storm 18 july 1942 and redbank storm 18 19 july 1996 are used to characterize ingredients of catastrophic rainstorms in the central appalachians

mesoscale convective complexes and persistent elongated convective systems over the united states during 1992 and 1993 abstract large long lived convective systems over the united states in 1992 and 1993 have been classified according to physical characteristics observed in satellite imagery as quasi circular mesoscale convective complex mcc or elongated persistent elongated convective system pecs and cataloged the catalog includes the time of initiation maximum extent termination duration area of the 52 c cloud shield at the time of maximum extent significant weather associated with each occurrence and tracks of the 52 c cloud shield centroid both mcc and pecs favored nocturnal development and on average lasted about 12 h in both 1992 and 1993 pecs produced 52 c cloud shield areas of greater extent and occurred more frequently compared with mccs the mean position of initiation for pecs in 1992 and 1993 followed a seasonal shift similar to the climatological seasonal shift for mcc occurrences but was displaced eastward of the mean position of mcc initiation in 1992 and 1993 the spatial distribution

relative paleointensity stack during the last 250 kyr in the northwest pacific 1 we have conducted a paleomagnetic study of 10 sediment cores recovered from the northwest pacific the purpose is to establish a regional paleointensity stack during the last 250 kyrs nopapis 250 for global coverage of paleointensity data as well as a regional reference for paleointensity assisted stratigraphy in the studied cores reductive dissolution of magnetite appears to have occurred mainly in glacial periods such horizons accompany large decreases in s ratio s 0 3t 1 irm 0 3t sirm 2 as low as 0 90 the sediments are also intercalated by frequent volcanic ash layers prerequisites for reliable relative paleointensity estimation are not satisfied at these horizons we rejected unsuitable data by quantitative criteria based on s ratio and saturation isothermal remanent magnetization sirm and constructed the nopapis 250 curve from the remaining data in the construction of the curve we chose irm as a normalizer because acquisitions of anhysteretic remanent magnetization arm are considered to be influenced by magnetic interactions among magnetic grains in the northwest pacific sediments relative intensity variation of the nopapis 250 gives a standard deviation that is 33 of the average if the normal distribution is assumed the nopapis 250 curve generally shows similar variation patterns compared with other high resolution records reported from other regions many paleointensity lows are recognized in common six out of the nine lows can be correlated with reported excursions in literature

early triassic palaeomagnetic results from the ryeongnam block korean peninsula the eastern extension of the north china block greenish sandstones in the early triassic nogam formation of the ryeongnam block korean peninsula were collected at 23 sites for palaeomagnetic study a high temperature magnetization component with unblocking temperatures of 670 690 c was isolated from seven sites and yielded a positive fold test at the 95 per cent confidence level the high temperature component is interpreted to be of primary origin because the folding age is middle triassic the early triassic palaeomagnetic direction for the ryeongnam block after tilt correction is d 347 1 i 23 8 95 5 5 the palaeomagnetic pole 62 5 n 336 8 e a95 4 7 shows good agreement with the coeval pole for the north china block suggesting that the ryeongnam block has been part of the north china block at least since early triassic times a tectonic history of the korean peninsula includes obduction of the eastern part of the south china block onto the central part of the korean peninsula in the permian with the ryeongnam block geographically isolated from the main part of the north china block collision of the north and south china blocks commenced initially at the korean peninsula and suturing of the two blocks progressed westwards

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

rapid formation of the shatsky rise oceanic plateau inferred from its magnetic anomaly shatsky rise in the northwest pacific ocean is probably the oldest extant oceanic plateau and as with most such features its origin is uncertain both oceanic plateaus and continental flood basalts are thought to be formed by rapid voluminous eruptions that occur when the head of a newly born mantle plume ascends to the base of the lithosphere1 3 high eruption rates have been estimated for flood basalts for example 1 5km3 yr 1 for the deccan traps2 from dating of lava flows but the inaccessibility of oceanic plateaus makes it necessary to extrapolate dating information from a small number of samples and sites4 here we estimate the eruption rate of shatsky rise by a method that is indirect but has the virtue of sampling the entire volume of the plateau above the surrounding sea floor the main southern part of the plateau has a positive magnetic anomaly corresponding to a reversed geomagnetic polarity at the time of eruption using age constraints to identify the longest period of reversed polarity during which the plateau could have formed we estimate that 2 106 km3 of material erupted at a minimum rate of 1 7km3 yr 1 this issomewhat less than the rate of 8 22 km3 yr 1 estimated for the ontong java plateau4 but still represents a massive eruption consistent with the plume head hypothesis

magnetic anomaly map of ori massif and its implications for oceanic plateau formation abstract many oceanic plateaus have been emplaced at or adjacent to mid ocean ridges to explain plateau volume and thickened crust compared to normal oceanic crust hotspot ridge interaction is commonly assumed but the manner of interaction remains unclear the shatsky rise oceanic plateau is a large volcanic mountain that formed at a triple junction during late jurassic and early cretaceous time recent drilling and seismic investigations suggest that the intermediate edifice in the rise ori massif is a central volcano paradoxically magnetic lineations were traced across parts of ori massif implying formation at a spreading ridge in this study we examined magnetic anomalies over and around ori massif to obtain insights about the formation of this volcanic edifice magnetic data from 21 cruises were corrected combined and gridded to construct a magnetic anomaly map forward and inverse magnetic modeling was done to investigate the magnetic structure of ori massif the results imply that this large volcanic edifice is predominantly characterized by linear magnetic anomalies resulting from alternating normal and reversed polarity magnetization blocks analogous to magnetic anomalies recorded by spreading ridges this magnetic structure is not expected for a central volcano that was built by long runout lava flows implying that ori massif eruptions must have been constrained near the ridge axis magnetic bights on the north and south boundaries of ori massif imply that it was bracketed by triple junctions indicating complex ridge tectonics during the formation of shatsky rise the surprising finding that ori massif is traversed by coherent linear magnetic anomalies indicates that oceanic plateaus can record seafloor spreading magnetic anomalies despite large crustal thickness other oceanic plateaus also record linear magnetic anomalies implying a link between divergent plate boundaries and oceanic plateau volcanism

timing of the north south china collision from new middle to late mesozoic paleomagnetic data from the north china block we collected paleomagnetic samples from 43 sites of middle and upper jurassic and cretaceous rocks along a 250 km wide east west trending belt located north of the suture between the north and south china blocks in each case laboratory treatment isolates dual polarity antipodal magnetizations that are demonstrably pre folding the paleomagnetic poles show very good coherence with coeval poles from other localities from the north china block ncb suggesting the apparent polar wander path apwp from the ncb is not distorted by post middle jurassic local vertical axis block rotations a comparison of the ncb apwp with that from the south china block suggests that collision continued after the early jurassic and ended no later than the late jurassic a cusp in the ncb apwp coincides with a marked angular unconformity that separates middle jurassic from upper jurassic and younger sediments together these observations indicate that the scissor like collision and associated deformation ceased at the middle to late jurassic boundary 159 ma the time of rapid 1 ma relative angular velocity between the two plates 225 to 190 ma coincides with a peak in u pb and ar ar dates obtained from metamorphic rocks in the suture the combined late jurassic and cretaceous paleomagnetic data from both blocks suggest that the united china plate traveled 2000 km north relative to eurasia during the late jurassic before docking in the cretaceous this younger collision event is also marked by a cusp on the cretaceous part of the eurasian apwp

copper nickel rich amalgamated ferromanganese crust nodule deposits from shatsky rise nw pacific 1 a unique set of ferromanganese crusts and nodules collected from shatsky rise sr nw pacific were analyzed for mineralogical and chemical compositions and dated using be isotopes and cobalt chronometry the composition of these midlatitude deep water deposits is markedly different from northwest equatorial pacific pcz crusts where most studies have been conducted crusts and nodules on sr formed in close proximity and some nodule deposits were cemented and overgrown by crusts forming amalgamated deposits the deep water sr crusts are high in cu li and th and low in co te and tl concentrations compared to pcz crusts thorium concentrations ppm are especially striking with a high of 152 mean 56 compared to pcz crusts mean 11 the deep water sr crusts show a diagenetic chemical signal but not a diagenetic mineralogy which together constrain the redox conditions to early oxic diagenesis diagenetic input to crusts is rare but unequivocal in these deep water crusts copper ni and li are strongly enriched in sr deep water deposits but only in layers older than about 3 4 ma diagenetic reactions in the sediment and dissolution of biogenic calcite in the water column are the likely sources of these metals the highest concentrations of li are in crust layers that formed near the calcite compensation depth the onset of ni cu and li enrichment in the middle miocene and cessation at about 3 4 ma were accompanied by changes in the deep water environment especially composition and flow rates of water masses and location of the carbonate compensation depth

paleomagnetic results from triassic sections in the ordos basin north china abstract continental triassic sediments with good fossil control have been sampled in two thick sections hancheng 35 5 n 110 2 e and tongchuan 35 2 n 109 1 e from the southern margin of the ordos basin shaanxi province china detailed analysis of 633 samples coming from 69 sites has been carried out with progressive alternating field and or thermal demagnetization most sites display a low unblocking temperature component up to 200 400 c which is undistinguishable from the present earth field pef direction and a characteristic component with higher unblocking temperature with both normal and reversed polarity which differs from the pef and later mesozoic paleomagnetic directions the pole position from the lower triassic part of the hancheng section is at 61 9 n 348 3 e a 95 3 8 n 16 sites the directions of the characteristic magnetization of the middle triassic sites from the tongchuan section pass the fold test and are consistent with those from middle triassic sites of the hancheng section giving a mean paleopole at 59 8 n 359 9 e a 95 4 0 n 17 sites the late triassic sites from the tongchuan section yield a pole at 62 3 n 7 7 e a 95 3 8 n 11 sites the early triassic pole from the ordos basin is consistent with poles obtained from shanxi province a late permian to late triassic apparent polar wander path of the north china block ncb is proposed it is found that poles from the ncb and from the two adjacent blocks south china block and siberia were widely separated until at least the end of the triassic pointing to major motion between the blocks probably during the jurassic at the end of the triassic the two chinese blocks were already at similar latitudes but still were to undergo a 78 28 relative rotation both were some 38 4 to the south of siberia calculated for a reference point at 45 n 115 e on the ncb siberia boundary

the lower cretaceous reference pole for north china and its tectonic implications summary a palaeomagnetic study of lower cretaceous continental sediments from the south southwestern part of the ordos basin north china block ncb has been carried out stepwise thermal demagnetization was used to isolate magnetic components the low temperature component is generally removed between 200 c and 350 c and corresponds to the earth s present field direction a hightemperature component of magnetization with two polarities was defined from 10 sites with d 16 4 i 50 5 k 50 8 ugs 6 8 the corresponding pole position is located at 75 8 n 208 7 e d 6 lo d 9 1 this lower cretaceous pole compares well with the hairpin loop of the eurasian synthetic apw path besse courtillot 1991 that is inferred from the north american eurasian african and indian plates the available late mesozoic palaeomagnetic data from the ncb and adjacent south china block scb are reviewed comparison of these data suggests important intraplate deformation the area to the east of the tancheng lujiang fault may have undergone local clockwise post cretaceous rotations of 10 29 relative to the stable western craton of the ncb the data also indicate that no palaeomagnetically significant eastward movement of the scb with respect to the ncb and eurasia occurred after the cretaceous

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

paleomagnetotectonics of east asia in the proto tethys ocean abstract seven paleomagnetic poles are obtained from early ordovician late carboniferous permo triassic jurassic early cretaceous miocene and quaternary rocks in korea these poles define the apparent polar wander path for the southern part of korean peninsula the comparisons of apwps from the north china block yangtze block and korea reveals that the east asia is comprised of two blocks the north sino korean and south sino korean which were parts of gondwana during the paleozoic time the north sino korean block was migrated northwards in late permian and accreted with laurasia in triassic time during middle late triassic time the north sino korean block collided with the south sino korean and subsequently divided into two the western part of the north sino korean block suffered counter clockwise rotation while the eastern part rotated clockwise until jurassic time complicated shear senses of the early mesozoic fault systems in east asia are well matched by this scenario

mesoscale features associated with tropical cyclone formations in the western north pacific abstract the mesoscale features of 124 tropical cyclone formations in the western north pacific ocean during 1999 2004 are investigated through large scale analyses satellite infrared brightness temperature tb and quick scatterometer quikscat oceanic wind data based on low level wind flow and surge direction the formation cases are classified into six synoptic patterns easterly wave ew northeasterly flow ne coexistence of northeasterly and southwesterly flow ne sw southwesterly flow sw monsoon confluence mc and monsoon shear ms then the general convection characteristics and mesoscale convective system mcs activities associated with these formation cases are studied under this classification scheme convection processes in the ew cases are distinguished from the monsoon related formations in that the convection is less deep and closer to the formation center five characteristic temporal evolutions of the deep convection are identified i single convection event ii two co

genesis of hurricane julia 2010 within an african easterly wave low level vortices and upper level warming abstractwhile a robust theoretical framework for tropical cyclogenesis tcg within african easterly waves aews has recently been developed little work explores the development of low level meso scale vortices llvs and a meso scale surface low in relation to deep convection and upper tropospheric warming in this study the development of an llv into hurricane julia 2010 is shown through a high resolution model simulation with the finest grid size of 1 km the results presented expand upon the connections between llvs and the aew presented in previous studies while demonstrating the importance of upper tropospheric warming for tcg it is found that the significant intensification phase of hurricane julia is triggered by the pronounced upper tropospheric warming associated with organized deep convection the warming is able to intensify and expand during tcg owing to formation of a storm scale outflow beyond the rossby radius of deformation results confirm previous ideas by demonstrating that th

palaeomagnetism of cretaceous pacific seamounts summary the palaeomagnetism of cretaceous pacific seamounts as deduced from their magnetic anomalies is reviewed results from 35 seamounts are reported here for the first time of these 35 results 15 are of high enough quality to be useful this has resulted in a considerable increase in the available information concerning the palaeomagnetism of the pacific plate using only the most reliable results we calculate a palaeomagnetic pole for the upper cretaceous at 58 north 350 east with a 95 per cent cone of confidence of only 5 this pole is considerably more accurate than the one previously reported and is farther to the west the previously reported difference between the mean pole position from seamounts close to japan and the mean pole position from seamounts close to hawaii is not real although one group of seamounts close to japan gives an anomalous pole position several mechanisms have been suggested whereby errors might be introduced in the determinations of pole positions from seamounts no error is introduced in the pole position because of the restricted extent of surveys and the consequent inaccuracy in the determination of the regional field the demagnetization effect which can produce differences between the observed direction of magnetization and the direction of the magnetizing field in an elongated body is unimportant for seamounts the new pole position is sufficiently accurate for use in many types of calculations in which it is desired to locate the pacific plate with respect to the earth s spin axis

high unblocking temperature haematite magnetizations of late palaeozoic red beds from the okcheon zone southern part of the korean peninsula summary the late carboniferous and permo triassic red beds of the pyeongan supergroup in the okcheon zone southern part of the korean peninsula were found to contain three components of remanence these components which are resolved by thermal demagnetization are characterized by high hhc for late carboniferous and hhpc for permotriassic intermediate hm and low hi unblocking temperatures as the maximum unblocking temperature spectra of the hhc hhpt component often overlapped the hm spectra above 680 c 3 o to 5 c steps were needed above 670 c to resolve the hhc hhpt component magnetization the tilt corrected mean direction of the hhc component red beds is d 255 5 i 2 4 a 20 8 and that of the hhpt component is d 271 9 i 33 4 c 16 5 the precisions of mean directions of hhc and hhpt components improve after tilt correction and allow the directions to be distinguished from each another this indicates that both hhc and hhpt component magnetizations were acquired during or shortly after the deposition of the red beds according to micropetrographic observations the haematite in the red beds can be divided into three types detrital specularite a non detrital specularite b and pigmental haematite c type a grains are tens of micrometres in size and many of them are martite the remanent magnetization of type a is possibly depositional remanent magnetization drm post drm or chemical remanent magnetization crm acquired close to the deposition time whereas that of types b and c is of crm origin acquired during and after folding respectively the time of folding is well established as a triassic to jurassic event we believe that the remanent magnetization carried by type a grains is primary and is correlated to hhc or hhpt component magnetization

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part ii roles of vortex merger and ambient potential vorticity abstract in this study the roles of merging midlevel mesoscale convective vortices mcvs and convectively generated potential vorticity pv patches embedded in the intertropical convergence zone itcz in determining tropical cyclogenesis are examined by calculating pv and absolute vorticity budgets with a cloud resolving simulation of tropical storm eugene 2005 results show that the vortex merger occurs as the gradual capture of small scale pv patches within a slow drifting mcv by another fast moving mcv thus concentrating high pv near the merger s circulation center with its peak amplitude located slightly above the melting level the merging phase is characterized by sharp increases in surface heat fluxes low level convergence latent heat release and upward motion lower tropospheric pv surface pressure falls and growth of cyclonic vorticity from the bottom upward melting and freezing appear to affect markedly the vertical structures of diabatic heating convergence absolute vorticity

genesis of typhoon chanchu 2006 from a westerly wind burst associated with the mjo part ii roles of deep convection in tropical transition abstractin this study the life cycles of a series of four major mesoscale convective systems mcss during genesis and their roles in transforming a vertically tilted vortex associated with a westerly wind burst hereafter the wwb vortex into typhoon chanchu 2006 are examined using 11 day cloud resolving simulations presented in part i it is found that the tilted wwb vortex at early stages is characterized by an elevated cold core layer about 200 hpa thick below and a weak warm column above with large vertical wind shear across the layer which extends over a horizontal distance of about 450 km between the vortex s 400 and 900 hpa centers during the final two days of the genesis process the upper level warm column increases in depth and intensity as a result of the absorption of convectively generated vortices cgvs including a mesoscale convective vortex mcv causing more rapid amplification of cyclonic vorticity in the middle than the lower troposphere the commencement of sustained intens

tectonic elements with south china affinity in the korean peninsula new early jurassic palaeomagnetic data summary early jurassic sandstones and shales were collected at 14 sites from the kimpo area in the western part of the korean peninsula for a palaeomagnetic study a characteristic remanent magnetization component which passes the fold test was isolated from seven sites this characteristic component is interpreted to be of primary early jurassic origin because the folding age is middle late jurassic the primary directions together with previously reported ones provide a mean direction d 38 1 i 39 7 95 3 8 11 sites and a palaeomagnetic pole 54 1 n 230 2 e a95 4 1 for the kimpo area this palaeomagnetic pole shows good agreement with the coeval poles for the south china block and is significantly removed from that for the north china block suggesting that the kimpo area has been part of the south china block since at least early jurassic times the kimpo area constitutes a part of the imjingang belt which is palaeontologically allocated to the south china block in its origin while all precambrian tectonic blocks that compose the basement of the korean peninsula are interpreted to be of north china origin we conclude that the imjingang belt including the kimpo area is a tectonic extension of the south china block on the korean peninsula the south china elements were obducted onto the north china block at the site of the present korean peninsula during the collision event of the north and south china blocks and hence the korean peninsula is composed of areas with both north and south china affinities

magnetization of the pacific ocean lithosphere deduced from magsat data magsat anomalies over the pacific ocean are related to volcanic plateaus and the edge effect of the pacific cretaceous quiet zone pcqz four prominent plateaus shatsky rise the mid pacific mountains hess rise and manihiki plateau are considered in this study the major lateral magnetization contrasts associated with these plateaus are considered to arise from the topographic swells and the crustal roots with root thicknesses estimated from topography using an airy isostatic model shatsky rise and the mid pacific mountains are older than the cretaceous quiet period and their natural remanent magnetization nrm is not a significant component of the magnetization contrasts that cause the magsat anomalies associated with these plateaus their magnetic properties are characterized by effective magnetic susceptibility contrasts of 0 07 0 01 s i per unit volume averaged over their topographic swells and crustal roots equivalent to 0 04 if averaged over the entire crustal thicknesses swell plus root plus intervening layer this value agrees well with the estimates of previous investigators for these plateaus and for similar plateaus in other oceans two plateaus of cretaceous quiet period age within the pcqz hess rise and manihiki plateau have origins similar to those of shatsky rise and the mid pacific mountains and they probably have similar effective susceptibility contrasts but they may also carry cretaceous quiet period nrm magnetic anomalies due to hess rise and manihiki plateau calculated from the effective susceptibility contrast deduced for shatsky rise and the mid pacific mountains are substantially larger than the observed magsat anomalies of these plateaus there are also magsat anomalies over parts of the pacific where no plateaus exist some of these anomalies are demonstrated as probably due to a contrast in nrm between the pcqz and its surroundings the total remanent magnetization contrast magnetization contrast in amperes per meter times thickness in meters equivalent to the dipole moment per unit area of the pcqz is 14 000 20 000 amperes 30 which cannot be simply explained by the absolute values of remanent magnetization predicted by conventional models of oceanic crustal magnetic properties modelling of the cretaceous quiet zones in the northern atlantic indicates a similar total remanent magnetization contrast these results may be explained by including uppermost mantle remanent magnetization with an intensity of about 1 2 a m 1 if magnetization persists to a depth of 7 below the seismic moho i e down to the depth of the crustal roots of the plateaus including nrm in the uppermost mantle of the pcqz also serves to reduce the calculated amplitude of the hess rise and manihiki plateau magsat anomalies if the nrm of the crustal roots is less than the nrm of the surrounding uppermost mantle on this basis the estimated intensity of nrm in the uppermost 7 km of the pcqz mantle is 1 3 a m 1 in very good agreement with the intensity estimated from the pcqz edge effect anomalies these estimates of uppermost mantle nrm are probably a maximum limit recognizing that other sources may also contribute to the total remanent magnetization contrasts of the cretaceous quiet zones

bathymetry of shatsky rise northwest pacific ocean implications for ocean plateau development at a triple junction oceanic plateaus are large igneous edifices thought to have been created by nascent mantle plumes but owing to sparse data their origins remain uncertain understanding plateau evolution is important because they are significant ocean features and may provide clues about mantle plume dynamics we constructed a bathymetry map of shatsky rise a large pacific plateau combining multibeam and wide beam echosounder data from 87 cruises and u s navy multibeam contours the rise consists of three large isolated volcanic edifices massifs surrounded by nearly normal lithosphere a linear volcanic ridge and a group of about 80 scattered seamounts massif flank slopes are typically gentle 1 5 and often parallel magnetic lineations or fracture zones the slope angles imply effusive volcanism similar to flood basalts whereas the rise shape suggests formation near the pacific izanagi farallon triple junction with modification of volcano flanks by spreading ridge tectonics edifice sizes and inferred ages imply a trend of decreasing volume and age from southwest to northeast furthermore gaps between massifs suggest episodic volcanism existing data are broadly consistent with the plume head hypothesis wherein the largest edifice formed by massive plume head eruptions the ridge formed from the plume tail and the two massifs in between represent a transition seamounts east of the rise are morphologically distinct which suggests that they may have been formed by a different source or mechanism than shatsky rise proper

recent advances in the cretaceous stratigraphy of korea abstract a subrounded accidental zircon grain from a rhyolite sample of the oknyobong formation has shown an u pb chime isochron age 187 ma implying its derivation from a jurassic felsic igneous rock such a lower limit of the geologic age of the oknyobong formation combined with its pre kyongsang upper limit constrains that the oknyobong formation belongs to the jasong synthem late jurassic early early cretaceous typified in north korea the jaeryonggang movement terminated the deposition of the jasong synthem and caused a shift of the depocenter from north korea to the kyongsang basin southeast korea the cretaceous paleocene kyongsang supergroup of the kyongsang basin is the stratotype of the kyongsang synthem an unconformity bounded unit in the korean peninsula the unconformity at the base of the yuchon volcanic group is a local expression of the interregionally recognizable mid albian tectonism it subdivides the kyongsang synthem into the lower kyongsang subsynthem barremian early albian and the upper kyongsang subsynthem late albian paleocene the latter is unconformably overlain by eocene and younger strata the late permian to early jurassic radiolarian fossils from the chert pebbles of the kumidong and the kisadong conglomerates of the aptian early albian hayang group of the kyongsang basin are equivalent with those of the cherts that constitute the jurassic accretionary prisms in japan the provenance of the chert pebbles in the kyongsang basin bimodal volcanisms throughout the history of the kyongsang basin is exemplified by the felsic kusandong tuff erupted abruptly and briefly in the late aptian when semi coeval volcanisms were of intermediate and mafic compositions the mean paleomagnetic direction shown by the kusandong tuff is in good agreement with the early cretaceous directions known from north china south china and siberia blocks

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part ii inertially stable warm core vortex and the mesoscale convective complex abstract a mesoscale warm core vortex associated with the mesoscale convective complex mcc that produced the 1977 johnstown flood is examined using a three dimensional nested grid model simulation of the flood episode in the simulation the vortex plays a key role in determining the evolution of the mcc a squall line and the distribution of heavy precipitation the vortex has a space scale of 100 200 km in diameter and a time scale of more than 18 hours its low pressure center extends from the midtroposphere down to the surface and its maximum vorticity occurs between 850 and 700 mb a pool of cool moist downdraft air develops in the surface to the 850 mb layer beneath the warm core while a cold dome forms in the vicinity of the tropopause above the warm core following forcing from repeated deep convection prior to model initial time the vortex is initiated by mesoscale ascent associated with a traveling meso scale wave genesis takes place in a nearly saturated slightly conditionally unstabl

the early tertiary chemical remagnetization in the bakjisan syncline korea its geotectonic implications the bakjisan syncline is located in the northwestern part of the taebaeksan basin korea new paleomagnetic data for the upper carboniferous lower triassic pyeongan supergroup from the pyeongchang area on the west limb of the bakjisan syncline have been obtained and synthesized and compared with previous data from the jeongseon area on the east limb of the syncline a total of 350 specimens were collected from 21 sites to clarify the relationship between the spatial distribution of remagnetized areas and the thrust system in the taebaeksan basin the characteristic remanent magnetization chrm isolated from all samples was a remagnetized component acquired after tilting of the strata and carried by various magnetic minerals magnetite hematite and pyrrhotite from rock magnetic studies electron microscope observations and xrd analyses the pervasive remagnetization is interpreted to be associated mainly with a fluid mediated chemical remanent magnetization crm this is consistent with the results of previous work in adjacent areas the paleomagnetic pole position 88 3 e 83 9 n a95 4 9 from the pyeongan supergroup in the bakjisan syncline indicates that the timing of the remagnetization event is early tertiary times i e paleocene to eocene by comparison with reliable paleopoles from the korean peninsula early tertiary crms are also reported from previous studies of an adjacent region within the northwestern part of the taebaeksan basin in contrast a primary remanent magnetization was reported in the southeastern part of the taebaeksan basin this implies that the major thrust system the gakdong thrust which separates the two regions has caused them to experience substantially different geologic histories since deposition of the strata since many thrusts with ns trend are observed in the northwestern part of the taebaeksan basin compared with the southeastern region it appears that the remagnetizing fluids pervasively penetrated the northwestern part of the basin by utilizing the already well developed thrust system

development and nondevelopment of binary mesoscale vortices into tropical cyclones in idealized numerical experiments abstractthe evolution of two symmetric midlevel mesoscale vortices situated above a warm ocean is examined with a basic cloud resolving model idealized numerical experiments provide insight into how the evolution may vary with the initial vortex separation distance d and other parameters that influence the time scale for an isolated vortex to begin rapid intensification the latter parameters include the ambient middle tropospheric relative humidity rh and the initial midlevel wind speed of each vortex at relatively low rh there exists an interval of d where binary midlevel vortex interaction prevents tropical cyclone formation while tropical cyclones generally develop at high rh similar values of d can delay the process if the vortices are initially weak prevention or inhibition of tropical cyclone formation occurs in association with the outward expulsion of lower tropospheric potential vorticity anomalies as the two vortices merge in the middle troposphere it is proposed that the primary mecha

nonuniform magnetization of seamounts a least squares approach residual total magnetic field anomalies relative to the best fitting uniform magnetization models are large and spatially coherent over three small tertiary seamounts on the cocos plate furthermore the paleomagnetic parameters determined from the uniform magnetization models in some cases disagree significantly with those predicted from models of absolute motion for the cocos plate inversion of the sea surface magnetic anomaly using a least squares procedure which allows magnetization to vary among different sections of each seamount shows clear polarity reversals in two of the seamounts studied the reversed zones constitute about 10 of the seamount volume for the third seamount the nonuniform magnetization solution more correctly determines the paleomagnetic inclination and declination for the only section of the dipolar anomaly not obscured by a magnetic lineation traversing the area the polarities indicated in the least squares solutions were confirmed by magnetic gradiometer measurements from the submersible alvin for all three seamounts the paleomagnetic latitudes and or rotation angles in the nonuniform magnetization solutions changed appreciably by as much as 20 to agree better with plate motion models the nonuniform magnetization models reveal that growth rates for such volcanoes approach 1000 km3 ma with the final phase of volcanism consisting of summit as opposed to flank eruptions the largest of the three volcanoes formed off ridge on lithosphere at least 0 5 ma old and may have remained active for 1 ma hydrothermal activity apparently persists at least 0 7 ma after the last major phase of volcanism

hydrothermal fluid controlled remagnetization of sedimentary rocks in korea tectonic importance of pervasive tertiary remagnetization abstract in order to better understand the tectonic environment of the korean peninsula since cretaceous a paleomagnetic study was carried out on the jinan basin located in southwestern korea from the demagnetization of 597 samples we found that remanence is carried by pyrrhotite and or magnetite black siltstone and hematite red siltstone which is a common magnetic mineral assemblage of the rocks remagnetized in early tertiary in korea all the rock units recorded identical ancient geomagnetic field directions in particular paleodirections were better clustered in geographic coordinates indicating a secondary origin the presence of abundant silicates as inclusions within fe oxides and fe sulfides confirms the authigenic origin of the magnetic carriers precipitated by fluid mediated chemical processes compilation of the korean cretaceous and tertiary poles indicates that the jinan basin was remagnetized in the early tertiary age in addition comparison of the korean cretaceous and tertiary poles with those from adjacent major terrains including china and siberia reveals that a dominant feature of tectonic motions in korea was a vertical axis rotation sense of vertical axis rotation was time dependent with clear distinction between clockwise rotation in cretaceous and counter clockwise rotation in early tertiary such differences in the mode of vertical axis rotation might be caused by the activities of basin bounding strike slip faults in korea possibly driven by the changes of subduction regime of the kula pacific plate in early tertiary

chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt summary palaeomagnetic and rock magnetic investigations have been carried out for the upper carboniferous lower triassic pyeongan supergroup exposed in the jeongseon area in eastern south korea a total of 302 independently oriented core samples were drilled from 24 sites for the study the mean direction in stratigraphic coordinates d i 345 3 38 4 k 4 8 95 18 2 is more dispersed than the mean direction in geographic coordinates d i 354 9 61 5 k 58 0 95 4 7 and the stepwise untilting of the characteristic remanent magnetization chrm reveals a maximum value of k at 0 per cent untilting furthermore authigenic magnetic mineral grains accompanied with altered clays are identified by electron microscope observations these results collectively imply that the chrms of this study were acquired by the formation of authigenic magnetic minerals after tilting of the strata the palaeomagnetic pole position 97 3 e 82 4 n a95 6 8 of the pyeongan supergroup calculated from the site mean directions of the chrms in geographic coordinates is close to those of the late cretaceous and tertiary periods of the korean peninsula the presence of many hydrothermal vein deposits reportedly formed between 94 and 73 ma near the study area and the evidence for extensive alteration of clay minerals under the influence of fluids shown in the x ray diffraction study strongly suggest that the chemical remanent magnetization was acquired by a fluid mediated process during the late cretaceous early tertiary considering the different remagnetization timing of several areas in the ogcheon fold belt which extends from ne to sw diagonally across the korean peninsula it is interpreted that the fluids and magmatism associated with this remagnetization originated from the subduction of the kula pacific plates under the eurasian plate during the cretaceous period the fluids might have migrated northward or northeastward through the fault systems within the ogcheon fold belt

subsidence and growth of pacific cretaceous plateaus abstract the ontong java manihiki and shatsky oceanic plateaus are among the earth s largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes we investigate this hypothesis by using sediment descriptions of deep sea drilling project dsdp and ocean drilling program odp drill cores to constrain plateau subsidence histories which reflect mantle thermal and crustal accretionary processes we find that total plateau subsidence is comparable to that expected of normal seafloor but less than predictions of thermal models of hotspot affected lithosphere if crustal emplacement was rapid then uncertainties in paleo water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes comparable to the sources of modern day hotspots such as hawaii and iceland rapid emplacement over a plume head of high temperature and volume however is difficult to reconcile with the subsidence reconstructions an alternative possibility that reconciles low subsidence over a high temperature high volume plume source is a scenario in which plateau subsidence is the superposition of 1 subsidence due to the cooling of the plume source and 2 uplift due to prolonged crustal growth in the form of magmatic underplating this prolonged crustal growth and uplift scenario may explain the low and thus submarine relief during plume initiation the late stage eruptions found on ontong java 90 ma and manihiki 70 ma a large portion of the high seismic velocity lower crust and the widespread normal faults observed throughout and along the margins of the three plateaus such late stage underplating may have occurred continuously or in discrete stages over 30 m y and implies lower magmatic fluxes than previously estimated

jurassic and triassic paleomagnetism of south korea middle to late jurassic samples have been collected from granitic rocks in three geological subdivisions of south korea from north to south kyonggi massif okchon folded belt and ryongnam massif triassic samples granites and sediments were collected in the ryongnam massif and its border area with the okchon folded belt the jurassic declinations of the two massifs are northeasterly mean d i 39 6 57 6 n 7 sites k 31 95 11 1 whereas the intervening okchon folded belt reveals northwesterly jurassic declinations d i 337 5 47 n 7 sites k 32 95 10 8 reversed polarity directions are rare but have been observed in three localities the widespread occurrence of similar directions in a given province argues against major tectonic tilting of the granites two sites in jurassic sediments provide additional structural control we interpret the direction difference between the okchon belt and the adjacent massifs as due to left lateral shear in an actively deforming continental margin during the late jurassic early cretaceous daebo orogeny the triassic directions from the ryongnam massif and its border area are east northeasterly d i 62 9 35 7 n 5 k 27 95 15 with the sediments showing normal and reversed polarities comparisons with jurassic and triassic paleomagnetic results from adjacent blocks in asia eurasia north korea north and south china are hampered by a paucity of reliable paleopoles what seems clear however is that north and south china and the major part of korea yield jurassic and younger paleopoles that are to first approximation similar the exception is formed by the results from the okchon folded belt the aggregate of the china and korea blocks yields mean paleopoles for this interval that are different from those published for eurasia but this may be due to imperfections in the eurasian reference poles for the triassic the directions and paleopoles of the china blocks and the ryongnam massif of south korea are dissimilar resulting in interpretations of the area in terms of relative motions mainly rotations

a mesovortex within a near equatorial mesoscale convective system during toga coare abstract airborne doppler radar observations are used to investigate the internal structure of a midlevel mesovortex that developed within the rear part of the stratiform precipitation region of a mature to decaying mesoscale convective system this system composed of several convective elements occurred on 13 december 1992 on the eastern side of the intensive flux array of the tropical ocean global atmosphere coupled ocean atmosphere response experiment near the equator 2 s the mesovortex contained several features that were previously observed in other tropical and midlatitude systems radar observations show that the closed wind circulation at midlevels had a horizontal dimension of 150 km and was coincident with a marked rear inflow at the central rear of the stratiform region where a notch pattern clearly identified the rear dry air intrusion it was associated with positive vertical vorticity anticyclonic for the southern hemisphere and could be classified as a cooling induced vortex maxi

global gravity bathymetry and the distribution of submarine volcanism through space and time 1 the seafloor is characterized by numerous seamounts and oceanic islands which are mainly volcanic in origin relatively few of these features 0 1 however have been dated and so little is known about their tectonic setting one parameter that is sensitive to whether a seamount formed on near or far from a mid ocean ridge is the elastic thickness te which is a proxy for the long term strength of the lithosphere most previous studies are based on using the bathymetry to calculate the gravity anomaly for different values of te and then comparing the calculated and observed gravity anomaly the problem with such an approach is that bathymetry data are usually limited to single beam echo sounder data acquired along a ship track and these data are too sparse to define seamount shape we therefore use the satellite derived gravity anomaly to predict the bathymetry for different values of te by comparing the predicted bathymetry to actual shipboard soundings in the vicinity of each locality in the wessel global seamount database we have obtained 9758 te estimates from a wide range of submarine volcanic features in the pacific indian and atlantic oceans comparisons where there are previous estimates show that bathymetric prediction is a robust way to estimate te and its upper and lower bounds te at sites where there is both a sample and crustal age show considerable scatter however and there is no simple relationship between te and age nevertheless we are able to tentatively assign a tectonic setting to each te estimate the most striking results are in the pacific ocean where a broad swath of on ridge volcanism extends from the foundation seamounts and ducie island easter island ridge in the southeast across the equator to the shatsky and hess rises in the northwest interspersed among the on ridge volcanism are flank ridge and off ridge features the indian and atlantic oceans also show a mix of tectonic settings off ridge volcanism dominates in the eastern north atlantic and northeast indian oceans while flank ridge volcanism dominates the northeastern indian and western south atlantic oceans we have been unable to assign the flank ridge and off ridge estimates an age but the on ridge estimates generally reflect we believe the age of the underlying oceanic crust we estimate the volume of on ridge volcanism to be 1 1 106 km3 which implies a mean seamount addition rate of 0 007 km3 yr 1 rates appear to have varied through geological time reaching their peak during the late early cretaceous and then declining to the present day

convection over the pacific warm pool in relation to the atmospheric kelvin rossby wave abstract deep convection over the western tropical pacific warm pool is analyzed in terms of its relation to the atmospheric kelvin rossby wave which dominates the large scale flow during the austral summer the study uses doppler radar data collected by aircraft and ship radars during different time periods in the tropical ocean global atmosphere coupled ocean atmosphere response experiment to characterize the mesoscale circulations of organized convective cloud systems occurring throughout the season the study focuses on convection in two contrasting phases of the wave the westerly onset region just west of the point within the wave where low level easterlies change to westerlies and the strong westerly region or westerly wind burst lying between the large scale counterrotating gyres of the kelvin rossby wave in the westerly onset region the zonal wind component had midlevel easterlies overlying low level westerlies in the strong westerly region a deep layer of westerlies extended from the

tectonic evolution of the northern pacific plate and pacific farallon izanagi triple junction in the late jurassic and early cretaceous m21 m10 abstract magnetic lineations in the northwestern pacific near the shatsky plateau were interpreted to trace the tectonic history of the northern pacific plate from the time of anomalies m21 to m10 at m22 time the pacific farallon izanagi p f i triple junction was located southwest of the plateau and migrating north northwest with respect to the pacific plate shortly thereafter the stress field acting on the three plates changed significantly and the pacific lzanagi ridge reacted by pivoting 24 clockwise from m21 to m19 time several ridge propagation events occurred while the ridge adjusted to the new spreading regime to the east of the m22 location of the junction it appears that this reorganization triggered a series of at least three ridge jumps along the pacific farallon ridge the geometry of magnetic isochron m21 suggests that several triple junctions existed simultaneously during the reorganization bordering one or more microplates differences in the spreading rate of the japanese magnetic lineations north of the plateau imply that one microplate which we call the shatsky microplate existed until about m15 m13 time it was probably captured by either the farallon or the izanagi plate and subsequently destroyed by subduction after m15 the p f i triple junction was reformed on seafloor that is now beneath the shatsky plateau the junction drifted generally northeast either in a ridge ridge ridge or in a ridge fault fault configuration perhaps alternating between the two from m11 m10 time the stress field on the three plates changed again and the pacific farallon ridge southeast of the plateau reoriented 15 clockwise at this time the p f i junction assumed a ridge ridge ridge geometry at the northeast end of the plateau

geoid height versus topography for oceanic plateaus and swells oceanic plateaus and swells are a major component of the seafloor topography yet they remain among the most poorly understood features this is especially true of the oceanic plateaus which show large variations in crustal thickness to determine the depth and mode of compensation for 53 of the largest plateaus and swells we analyzed the relationship between geoid height and topography in polygonal areas containing each feature both geoid height and topography were first band pass filtered 400 km i 4000 km to isolate the signal associated with local compensation from flexural and deep mantle signals the ratio of geoid height to topography was then determined by fitting a straight line to the data except for nine of the smaller features there is a high correlation between geoid height and topography that is positive in accordance with airy and thermal compensation models eighteen features have high geoid topography ratios that cannot be explained by the airy compensation model of crustal thickening these features thermal swells are partially supported by thermal buoyancy forces in the lower half of the lithosphere the ratios are highest for active hot spot swells and decay with the thermal age of the swell to values consistent with airy compensation of the enduring volcanic edifice the remaining features plateaus have lower geoid topography ratios in agreement with the airy compensation model those plateaus with average height greater than 4 km are thought to be continental fragments the shorter plateaus tend to be volcanic features modified continental plateaus presumably small fragments of extended and intruded continental margin crust cluster around heights of n3 km overlapping the range associated with oceanic plateaus since the origin of many plateaus is poorly understood this global geoid topography analysis provides a new technique for comparing the deep structure of oceanic plateaus and swells

plateaux ancient and modern geochemical and sedimentological perspectives on archaean oceanic magmatism unequivocal examples of oceanic plateaux older than about 2 1 ga have yet to be identified from the geological record the most likely explanation for this is the partial dismemberment of ancient plateaux at convergent plate margins and their subsequent juxtaposition in accretionary complexes with arc volcanic sedimentary and plutonic rocks a review of cretaceous plateaux in the eastern indian ocean suggests that certain geochemical isotopic criteria e g positive nb anomalies relative to primitive mantle employed by petrologists to identify modern oceanic plateau lavas are of little practical use in distinguishing ancient plateau lavas from arc and volcanic rifted margin basalts the extreme chemical and isotopic heterogeneity of indian ocean plateaux together with large variations in area and volume suggest that these edifices represent one extreme of a spectrum of oceanic plateau compositions the other extreme represented by iceland and ontong java is characterised by relatively homogeneous melt compositions reflecting steady state melting conditions and the absence of a continental lithosphere contaminant to plateau magmas crustal thickness and compositional estimates for archaean oceanic plateaux using the mckenzie bickle method give a mean thickness of 43 km and mean mgo content of 19 wt archaean plateaux were thus compositionally distinct from surrounding ocean floor basaltic komatiite and notably more magnesian than plateaux such as iceland mean for tertiary basalts 6 3 wt mgo and ontong java mean for core samples 6 9 wt mgo by analogy with cretaceous tertiary ultramafic complexes in western colombia the deeper portions of these plateaux may have consisted of noritic rocks underlain by iherzolite pyroxenite gabbronorite and dunite the general absence of such rocks in archaean terrains suggests that these portions of plateaux are only rarely preserved the search for remnants of ancient oceanic plateaux has identified examples of archaean submarine lavas in the canadian shield 2 7 ga southern abitibi belt superior province and kaapvaal craton of southern africa 3 5 3 3 ga barberton and pietersberg belts chemical and isotopic data suggest that komatiite tholeiite units from these areas were derived by partial melting of a plume or asthenospheric mantle source but do not distinguish adequately the tectonic environment rifted continental margin ocean floor oceanic plateau in which these rocks were erupted however the uplift histories of these putative plateau fragments as recorded in sediments bounding and intercalated with the komatiite basalt sequences appear to be broadly comparable to those of the best documented phanerozoic oceanic plateaux although further stratigraphical investigations of presumed plateaux ancient and modern are required to test this hypothesis we believe that the sedimentary record offers the best evidence yet for the formation of oceanic plateaux as far back as the mid archaean 3 5 ga

mesoscale observations of the genesis of hurricane dolly 1996 abstract recent numerical studies of tropical cyclone genesis suggest a new paradigm for how the surface vortex is established based on a highly nonaxisymmetric mechanism involving the interaction of low level cyclonic circulations generated by deep cumulonimbus convection a reexamination of mesoscale observations during the genesis of hurricane guillermo 1991 confirms the presence of multiple cyclonic circulations more recently airborne doppler radar wind observations during the genesis of atlantic hurricane dolly 1996 also reveal multiple lower to middle tropospheric mesoscale cyclonic circulations during sequential 15 20 min compositing periods a particularly well organized but initially weak mean tangential wind of 7 m s 1 low level cyclonic vortex embedded within the pre dolly tropical disturbance is observed coincident with deep vertically penetrating cumulonimbus convection the earliest observations of this vortex show the peak circulation near 2 km height with a mean diameter of 30 4

clockwise rotation of the korean peninsula with respect to the north china block inferred from an improved early triassic palaeomagnetic pole for the ryeongnam block summary in order to detect a possible clockwise rotation of the korean peninsula with respect to the north china block early triassic rocks in the ryeongnam block korean peninsula have been restudied sandstones in the nogam formation were collected at four sites for palaeomagnetic study a high temperature magnetization component with an unblocking temperature of 690 c is isolated from all sites and yields a positive fold test at the 95 per cent confidence level this high temperature component is interpreted to be of primary origin because folding is middle triassic in age the primary directions together with previously reported ones give a new early triassic mean direction d 347 4 i 23 8 95 5 1 and corresponding palaeomagnetic pole 62 6 n 336 1 e a95 4 2 for the ryeongnam block this improved early triassic pole for the ryeongnam block is located to the west of the coeval poles for the north china block it is therefore concluded that the ryeongnam block underwent clockwise rotation of 10 15 with respect to the north china block because the amount of rotation observed in the present study is comparable with rotations observed in cretaceous results from the ryeongnam block and in the triassic cretaceous results from other blocks in the korean peninsula the whole of the korean peninsula appears to have been subjected to clockwise rotation in tertiary times

development of an intense warm core mesoscale vortex associated with the 8 may 2009 super derecho convective event abstractin this study the dynamical processes contributing to warm core meso scale vortex formation associated with the 8 may 2009 super derecho are examined utilizing two complementary quasi lagrangian approaches a circulation budget and backward trajectory analyses applied to a fortuitous numerical simulation of the event warm core meso scale vortex formation occurs in a deeply moist potentially stable environment that is conducive to the development of near surface rotation and is somewhat atypical compared to known derecho supporting environments air parcels in the vicinity of the developing vortex primarily originate near the surface in the streamwise vorticity rich environment associated with the vertical wind shear of the low level jet immediately to the east of the eastward moving system cyclonic vertical vorticity is generated along inflowing air parcels primarily by the ascent induced tilting of streamwise vorticity and amplified primarily by ascent induced vortex tube stretching de

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

paleomagnetism of the lesotho basalt southern africa paleomagnetic study of four sections from middle jurassic karoo lava located in lesotho and south africa yielded a new paleomagnetic pole for africa with coordinates 71 6 n 273 5 e a95 3 7 k 33 n 47 paleosecular variation estimated as the angular standard deviation of vgps distribution is 14 1 2 4 1 8 which is considerably lower than expected for this time interval and latitudinal band preliminary paleointensity results indicate a low field intensity during the acquisition of the magnetization this new result tends to support a possible correlation between secular variation and dipole intensity when the lower to middle jurassic paleomagnetic data set for africa is considered a difference of 13 9 8 7 of arc is found to exist between the mean northwest and south african poles furthermore while the northwest african pole is in very good agreement with the lower to middle jurassic north american pole whichever set of rotation parameters is used to close the north atlantic ocean the south african pole falls some 12 15 of arc apart as intraplate deformation models developed to achieve tighter fit of west gondwana prior to the opening of the south atlantic fail to account fully for the difference between northwest and south african poles the pre cretaceous apparent polar wander path for africa has to be considered with caution

formative stage of a long lived mesoscale vortex observed by airborne doppler radar abstract the formative stage of a long lived mesoscale cyclonic vortex was captured by the noaa p 3 aircraft as it investigated a developing mesoscale convective system mcs near the southeastern coast of taiwan on 16 june 1987 during the taiwan area mesoscale experiment the supporting environment of the mesovortex was characterized by an exceptionally moist atmosphere and moderate ambient vertical shear through a deep layer from the near surface to 6 km with much weaker shear and winds aloft in addition a pronounced low level mesoscale shear convergence zone which resulted from the interaction of southeasterly flow with northeasterly flow confined to the near coast region existed in the vicinity of the observed mesovortex composite three dimensional wind fields derived via pseudo dual doppler synthesis show the vortex had a horizontal diameter expanding from 40 km to 70 km in the lower to midtroposphere respectively and exhibited considerable tilt through this layer contrary to previously d

origin of intraplate volcanoes from guyot heights and oceanic paleodepth the height of a guyot as measured from the surrounding regional sea floor to the vol cano s slope break records the water depth at the time the guyot submerged thus guyot heights may be used as indicators of the paleodepth of the surrounding ocean floor we compile data on the heights of 68 intraplate guyots and atolls in the pacific ocean as well as 46 volcanic islands in the pacific atlantic and indian oceans we find that guyot heights generally increase with the age of the lithosphere upon which they werc cmplaced although therc is a large amount of scattcr in nearly all cases seamount height and thus seafloor paleodepth is less than expzcted of normal seafloor these results suggest that most of the volcanoes in this study formed on anomalously shallow seafloor consistent with formation at hotspots to characterize thermal anomalies associ ated with these hotspot swells we model guyot heights by calculating the isostatic uplift predicted for normal lithosphere that has been partly reheated and is underlain by anomalously hot mantle this model is able to explain the anomalous water depth at most of the seamounts with hotspot thermal anomalies of 100 30o0c the heights of a few volcanic chains however are not anomalously low suggesting that these volcanoes are not associated with hotspots in addition the observed trend of hawaiian emperor guyot heights as well as the subdued morphology and gravity signature of the oldest emperor seamounts supports our hypothesis that cretaceous age meiji seamount may have formed on or near a spreading center

mesoscale convective vortices observed during bamex part i kinematic and thermodynamic structure abstract five cases of mesoscale convective vortices mcvs are described from observations collected during the bow echo and mcv experiment bamex over the central united states during the period from 20 may to 6 july 2003 in the present paper the kinematic and thermodynamic structure of each vortex and its environment are emphasized data consist of bamex dropsondes the national oceanic and atmospheric administration profiler network and national weather service soundings in addition weather surveillance radar 1988 doppler observations documented the signatures of nascent mcvs within nocturnal convection systems as well as the spatial pattern of convection within mcvs during the following day the vertical structure of each vortex was highly dependent on the vertical shear and the presence of upper tropospheric cyclonic vorticity anomalies in strong shear a pronounced downshear tilt of the vortex was evident but with the presence of an upper tropospheric trough the tilt was upshear in the upp

magnetic lineations within shatsky rise northwest pacific ocean implications for hot spot triple junction interaction and oceanic plateau formation oceanic plateaus are major ocean features yet their origins and development are poorly understood many are huge piles of basalt and it is widely accepted that mantle plumes are their source perhaps from eruptions of the voluminous head of an emerging plume shatsky rise is a basaltic plateau that formed during a period of geomagnetic reversals unlike many mid cretaceous plateaus so magnetic data can help us understand its tectonic history in this study we analyzed magnetic anomaly data from 131 cruises over and around shatsky rise and constructed a magnetic lineation chart for tectonic interpretation a significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs indicating nearly normal lithosphere and between large volcanic edifices many lineations form bights near the rise axis and show former locations of the pacific izanagi farallon triple junction they indicate that the junction was in a ridge ridge ridge rrr configuration and closely followed the rise axis from chron m20 146 ma to chron m4 127 ma lineation and bight geometries indicate that the triple junction jumped northeastward at least nine times often apparently in response to volcanic activity from the mantle plume some jumps however appear related to ridge reorientations numerous features within the rise are parallel to lineations or lineation offsets implying that the plateau formed near the triple junction and was modified by ridge faulting most of our observations support the hypothesis that shatsky rise was formed by a mantle plume that captured a triple junction

baroclinic transition of a long lived mesoscale convective vortex abstract the period 5 15 june 2003 during the field phase of the bow echo and mesoscale convective vortex mcv experiment bamex was noteworthy for the wide variety of mesoscale convective systems mcss that occurred of particular interest was a long lived mcv that formed in the trailing stratiform region of an mcs over west texas at 0600 utc 10 june this mcv was noteworthy for its i longevity as it can be tracked from 0600 utc 10 june to 1200 utc 14 june ii development of a surface cyclonic circulation and attendant 2 to 4 hpa sea level pressure perturbation iii ability to retrigger convection and produce widespread rains over several diurnal heating cycles and iv transition into a baroclinic surface cyclone with distinct frontal features baroclinic transition defined here as the acquisition of surface fronts occurred as the mcv interacted with a remnant cold front left behind by a predecessor extratropical cyclone over the great lakes region although the mcv developed well def

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

palaeomagnetism of the upper palaeozoic lower mesozoic pyongan supergroup korea a phanerozoic link with the north china block summary the upper carboniferous lower triassic pyongan supergroup is exposed in an e w trending syncline comprising the samcheok coalfield in eastern south korea it borders the southern margin of a ne sw trending okcheon zone of upper jurassic lower cretaceous deformation daebo orogeny although a recent field overprint widely recorded in korean rocks is represented here an ancient field component structure is recovered from the red bed facies in this supergroup by detailed thermal demagnetization a prominent upper jurassic cretaceous overprint is widespread diz 56 1 54 8 ags 9 6 palaeopole at 200 4 e 46 7 n and records the magnetic effect of the daebo orogeny within the okcheon belt it is post deformational in origin and appears to have been confined mainly to the cretaceous normal superchron it has been rotated clockwise since these times in common with the main synclinal axis as a consequence of dextral movements along the tan lu fault system components predating this deformation are recovered from the lower triassic diz 1 1 19 4 ags 18 2 palaeopole at 306 1 e 63 2 n permian diz 358 3 11 5 c 6 3 palaeopole at 311 9 e 58 7 n and upper carboniferous diz 34l u 9 2 mgs 7 2 palaeopole at 335 7 e 44 6 n sediments second order small circle dispersions of site palaeopoles record unaccommodated tectonic rotations and are largest in the oldest beds below an upper carboniferouslower permian unconformity however the presence of reversals probably acquired before and after the carboniferous permian reversed superchron defines ancient field axes and identifies an upper carboniferous lower triassic apw path this path correlates with the contemporaneous path from the north china block and is removed from the path from the south china block agreement with north china is enhanced when these results are corrected for the rotation indicated by the cretaceous overprint we therefore identify a first order correlation between the korean peninsula and north china at least since upper palaeozoic times establishment of and movements along the tan lu fault system since mesozoic times have not obscured this palaeomagnetic correlation

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

balanced and unbalanced circulations in a primitive equation simulation of a midlatitude mcc part i the numerical simulation abstract a midlatitude mesoscale convective complex mcc which occurred over the central united states on 23 24 june 1985 was simulated using the regional atmospheric modeling system rams the multiply nested grid simulation agreed reasonably well with surface upper air and satellite observations and ground based radar plots the simulated mcc had a typical structure consisting of a leading line of vigorous convection and a trailing region of less intense stratiform rainfall several other characteristic mcc circulations were also simulated a divergent cold pool in the lower troposphere midlevel convergence coupled with a relatively cool descending rear inflow jet and relatively warm updraft structure and a cold divergent anticyclone in the tropopause region early in the mcc simulation a mesoscale convectively induced vortex mcv formed on the eastern edge of the convective line while frequently associated with mccs and other mesoscale convective systems mcss mcvs are more typically repo

genesis of typhoon nari 2001 from a mesoscale convective system 1 in this study the origin and genesis of typhoon nari 2001 as well as its erratic looping track are examined using large scale analysis satellite observations and a 4 day nested cloud resolving simulation with the finest grid size of 1 33 km observational analysis reveals that nari could be traced 5 days back to a diurnally varying mesoscale convective system with growing cyclonic vorticity and relative humidity in the lower troposphere and that it evolved from a mesoscale convective vortex mcv as moving over a warm ocean under the influence of a subtropical high a weak westerly baroclinic disturbance an approaching and departing typhoon danas to the east and the kuroshio current results show that the model reproduces the genesis final intensity looping track and the general convective activity of nari during the 4 day period it also captures two deep subvortices at the eye eyewall interface that are similar to those previously observed a few spiral rainbands and a midget storm size associated with nari s relatively dry and stable environment we find that 1 continuous convective overturning within the mcv stretches the low level vorticity and moistens a deep mesoscale column that are both favorable for genesis 2 nari s genesis does not occur until after the passage of the baroclinic disturbance 3 convective asymmetry induces a smaller sized vortex circulation from the preexisting mcv 4 the vortex vortex interaction with danas leads to nari s looping track and temporal weakening and 5 midlevel convergence associated with the subtropical high and danas accounts for the generation of a nearly upright eyewall

reply to comment by y park and j h ree on chemical remagnetization of the upper carboniferous lower triassic pyeongan supergroup in the jeongseon area korea fluid migration through the ogcheon fold belt summary in their comment park ree have raised several points against the interpretation by park et al and argued that the remagnetization in the jeongseon area was caused by the thermal effects of a late cretaceous pluton and or associated short range hydrothermal fluids rather than by long range fluids advocated by us we disagree with most points raised by park ree and we make a case that these are invalid because of what we believe is incorrect geologic evidence hence our model that the fluids causing the chemical remagnetization might migrate through the fault system within the ogcheon fold belt is the most plausible scenario we recognize that our model needs to be tested in a future study and we welcome new interpretations for or against our model based on reliable geologic or geophysical data