early permian peak metamorphism recorded in u pb system of black slates from the ogcheon metamorphic belt south korea and its tectonic implication abstract we report pb pb whole rock and uraninite chemical th u total pb isochron method chime ages of carbonaceous black slates from the ogcheon metamorphic belt south korea the pb isotopic data of whole rock samples yield 207 pb 206 pb ages of 283 33 and 291 13 ma for two outcrops from the northeastern part of the belt the uraninite chime age is estimated at 283 26 and 281 27 ma for the northeastern and the middle part of the belt respectively all of the above ages are identical within error ranges and represent the timing of peak metamorphism after the late precambrian intraplate rifting on the other hand the 207 pb 206 pb whole rock age for the southwestern part of the belt is estimated at 194 27 ma probably representing the timing of contact thermal metamorphism associated with the intrusion of jurassic granitic plutons rb sr isotopic data of the black slates do not define any meaningful isochron the early permian metamorphic age of this study does not support any tectonic scheme in favor of major tectonometamorphism at either the silurian devonian or the triassic time instead it corroborates the probability that the two zones in the ogcheon belt the ogcheon metamorphic belt and the taebaegsan zone were separated from each other before the development of major structural framework in the former our data do not support an idea that the ogcheon belt corresponds to the continuation of the triassic collision belt in east central china

tracking paleozoic evolution of the south korean peninsula from detrital zircon records implications for the tectonic history of east asia abstract the southern part of the korean peninsula preserves important records of the paleozoic evolutionary history of east asia here we present shrimp u pb ages of detrital zircon grains from paleozoic metasedimentary successions okcheon and joseon supergroups yeoncheon group taean formation and pyeongan supergroup that are incorporated into the major phanerozoic mountain belts okcheon and hongseong imjingang belts in south korea providing new insights for provenances and paleotectonic evolution of the south korean peninsula during paleozoic time the zircon ages from our samples display two distinct spectra patterns in their presence absence of neoproterozoic and or paleozoic populations our results together with the available data from the korean peninsula suggest that 1 the early to middle paleozoic successions in the okcheon belt were deposited in continental margin setting s formed by neoproterozoic intracratonic rifting 2 the middle paleozoic metasedimentary rocks in the imjingang belt can be interpreted as molasse and flysch sediments along an active continental margin 3 the late paleozoic to early triassic taean formation along the western gyeonggi massif represents a syn to post collision deltaic complex of a remnant oceanic basin and 4 the late paleozoic to possibly early triassic pyeongan supergroup in the okcheon belt might represent a wedge top and or foreland basin the spatial and temporal discrepancy between the south korean peninsula and the central china orogenic belt during paleozoic might reflect lateral variations in crustal evolution history along the east asian continental margin during the paleo tethyan ocean closure

monotonic behavior of mississippi river valley silt in triaxial compression the static behavior of mississippi river valley silt was characterized using triaxial compression testing silt specimens especially overconsolidated ones showed dilation behavior there was no unique critical state among specimens with different overconsolidation ratios ocrs with ocrs of 1 2 and 8 the specimens exhibited normal behavior and dilated more as effective consolidation pressure dropped however for an ocr of 4 the specimens showed opposite behavior and dilated more as effective consolidation pressure rose the friction angle of the silt was computed on the basis of several failure criteria and the limiting strain was found to be the best one owing to better consistency and rational results of the friction angle the silt showed a unique behavior compared with sand and clay the critical state line was not parallel to the normal consolidation curve in the e lnp 0 space the stress strain behavior can be normalized by effective consolidation pressure the normalized shear strength of overconsolidated specimens was correlated to that of a normally consolidated specimen using ladd et al s equation with an mvalue of 0 58 for low plasticity silts however the normalized shear strength of overconsolidated silts cannot be related to ocr directly it was indicated that at least the normalized shear strength of a normally consolidated specimen needs to be tested for low plasticity silts to obtain the normalized shear strength of overconsolidated specimen using ladd et al s equation doi 10 1061 asce gt 1943 5606 0000603 2012 american society of civil engineers

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

the shallow magma chamber of stromboli volcano italy in this work we integrate artificial and natural seismic sources data to obtain high resolution images of the shallow inner structure of stromboli volcano overall we used a total of 21 953 p readings from an active seismic experiment and an additional 2731 p and 992 s readings deriving from 269 local events the well defined vp vs and vp vs tomograms have highlighted the following i the region where magma cumulates at shallow depths 2 4 km below sea level bsl forming an elongated ne sw high velocity body vp 6 0 km s and vs 3 5 km s with a very fast velocity core 6 5 vp 7 0 km s of 2 km3 ii the presence of some near vertical pipe like structures characterized by relatively high p velocities values mainly linked to past activity e g strombolicchio and iii a near vertical pipe like volume with high vp vs 1 78 1 85 located beneath to the craters down to 1 0 km bsl overlying a deeper region 1 0 to 3 0 km bsl with low vp vs 1 64 1 69 interpreted as the actual and preferential pathway of magma toward the surface our results demonstrate the importance of combining passive and active seismic data to improve in a tomographic inversion the resolution of the volcanic structures and to discover where magma may be stored

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

effect of depositional method on the undrained response of silty sand the results from a laboratory experimental study on silty sand are presented undrained triaxial compression tests were performed on nevada sand containing nonplastic silt all specimens underwent monotonic loading after isotropic consolidation to 25 kpa various depositional techniques were used to create specimens to compare their stress strain behavior within three separate density ranges and three different silt contents as density increased the effect of the depositional method on the undrained behavior decreased the influence of the depositional method on specimen behavior also was found to increase with silt content particularly at lower densities these findings therefore are of special interest with regard to laboratory testing for the purpose of characterizing liquefaction potential where loose silty sands may be encountered a description and analysis of five different depositional techniques is provided these methods include dry funnel deposition water sedimentation slurry deposition

mineralogy and geochemistry of metalliferous black slates in the okcheon metamorphic belt korea a metamorphic analogue of black shales in the south china block metalliferous black slates which were locally exploited for their low quality coal are distributed in the late proterozoic to paleozoic okcheon metamorphic belt omb of the korean peninsula the mineralogy of the fine matrix is dominated by either quartz ba v mica graphite or quartz ba feldspar graphite polycrystalline submillimeter ellipsoids and elongate lenses aligned along foliations and veinlets are scattered through the fine matrix both ellipsoids and veinlets include many minor minerals containing rare elements titanite apatite allanite rutile polycrase barite uraninite xenotime armenite zircon molybdenite and sphalerite large graphite apatite ellipsoids nodules with widths of several centimeters also occur in the highly carbonaceous black slates goldmanite occurs locally as porphyroblasts the maximum rare element contents are ba 9 7 v 2 04 mo 0 13 u 0 11 cr 0 33 cu 254 ppm ni 479 ppm zn 607 ppm y 255 ppm platinum group element pge au 309 ppb and carbon 57 the occurrence of the black slates and their elemental abundances suggests that most of the rare elements were accumulated from seawater in an oxygen poor environment however the high ba content of the omb black slates indicates some hydrothermal input into an organic rich basin although metamorphism and multiple deformations prevent a direct temporal and spatial correlation metal abundances and a close association with graphite apatite nodules and low quality coal suggest that the omb black slates are metamorphosed analogues of the early cambrian ba v deposits hosted by the black shales in the south china block

neoproterozoic bimodal volcanism in the central ogcheon belt korea age and tectonic implication abstract u pb zircon ages were determined for a metavolcanic rock from the munjuri formation in the central ogcheon belt korea four zircon fractions were analyzed of which three are nearly concordant the data define a discordia with an upper intercept at 755 8 1 3 ma and a lower intercept at 160 19 ma mswd 0 72 the upper intercept age is interpreted to indicate the timing of bimodal volcanism and the lower intercept age is interpreted to reflect jurassic thermal metamorphism this is the first definite evidence supporting the existence of a formation in the ogcheon belt that is at least in part late precambrian nd isotope and trace element geochemistry of the amphibolites and felsic metavolcanics suggests that they originated from a mantle source in a continental rift environment the rift does not appear to have matured enough to develop oceanic crust since rocks indicating deep sea environments are absent the possibility that the ogcheon belt is an extension of the east chinese collision belt as suggested by several authors is not supported by the available evidence

pb and nd isotopic constraints on paleoproterozoic crustal evolution of the northeastern yeongnam massif south korea abstract we report pb isotopic ages and nd isotopic signatures of paleoproterozoic basement rocks from the pyeonghae area northeastern yeongnam massif south korea the pbsl lead step leaching garnet data of the wonnam group precambrian metasediments yield a 207pb 206pb age of 1840 26 ma which can be regarded as the timing of amphibolite to upper amphibolite facies metamorphism and associated garnet growth whole rock data for the pyeonghae gneiss intruding the wonnam group give a 207pb 206pb age of 2093 86 ma denying the possibility of a direct link between the intrusion of the pyeonghae gneiss and the regional metamorphism of the wonnam group our results confirm the significance of the 2 1 ga and 1 8 ga episodes that have been broadly constrained in the yeongnam massif the depleted mantle nd model ages of metasedimentary rocks from the wonnam group 2 63 2 47 ga are slightly younger than those of the pyeonghae gneiss samples 2 71 2 57 ga this nd isotopic signature also precludes a direct derivation of the pyeonghae gneiss from the wonnam group instead implying the presence and involvement of the older probably late archean crustal materials during the 2 1 ga magmatism in the northeastern yeongnam massif compiled pb and nd isotope data from the yeongnam and gyeonggi massifs suggest a similar geologic history for them arguing against the conventional idea that the gyeonggi and yeongnam massifs are separate continental blocks respectively correlated to the south and north china blocks the whole rock pb isotope data of basement rocks from the two massifs form a well defined 207pb 206pb linearity of around 2 0 ga suggesting their common crustal evolution process for the past two billion years a broad coincidence of major tectonic episodes in the two massifs is confirmed by reviewed geochronological data the nd model ages of basement rocks from the two massifs support a probable existence of archean crusts in south korea the nd model ages both archean and proterozoic of the gyeonggi and yeongnam massifs agree with neither those of the north china block predominantly archean nor those of the south china block predominantly proterozoic our compiled isotope data together with recent estimation for the age of the honam shear zone appear to refute the presence of suture zone between the two south korean precambrian massifs which leaves the imjingang belt as the possible suture zone

effect of fines and confining stress on undrained shear strength of silty sands a silty sand is considered as a delicate composite matrix containing a sand grain matrix and a silt matrix large strain undrained shear strength sus data in triaxial compression for a particular host sand mixed with different amounts of nonplastic fines are presented results indicate that the intergranular void ratio es which is the void ratio of the sand grain matrix given by e fc 1 fc where fc is the silt content fraction by weight plays an important role on sus of silty sands at the same void ratio e a silty sand shows low sus compared to that of the host sand however when compared at the same es provided that it is less than the maximum void ratio of the host sand emax hs both the silty sand and the host sand show similar sus that is fairly independent of the initial confining stress when es of the silty sand is in the vicinity of or exceeds emax hs the sus depends on the initial effective confining stress at such loose states sus normalized with respect to the initial con

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

termination of the permo triassic songrim indosinian orogeny in the ogcheon belt south korea occurrence of ca 220 ma post orogenic alkali granites and their tectonic implications abstract the indosinian orogeny is defined in a broad sense as encompassing all the late paleozoic to early mesozoic tectonic events associated with the closure of the eastern parts of the paleo tethys ocean it includes the permo triassic continent continent collision between the north china and south china blocks that generated the qinling dabie sulu orogen containing the largest ultrahigh pressure uhp terrane in the world the korean peninsula situated at the easternmost end of the tethyan tectonic regime was also tectonically influenced by the indosinian orogeny often known as the songrim orogeny in korea the songrim orogeny characterized by intense regional medium to high pressure metamorphism extends from the imjingang belt through the gyeonggi massif to the ogcheon belt it was initiated as early as the early permian period ca 290 ma and peaked in the triassic period ca 255 to 225 ma this paper presents new geochemical and shrimp u pb zircon ages for two alkali granites that postdated the songrim orogeny in the ogcheon belt both granites are contemporaneous 219 3 3 3 ma and 219 6 1 9 ma and are geochemically post orogenic a type granites intruded in an extensional setting subsequent to a major collision the data provide a critical time constraint on the termination of the indosinian orogeny in the korean peninsula despite the absence of an uhp terrane in the korean peninsula similarities in the duration metamorphic characteristics and post orogenic magmatism between the qinling dabie sulu and songrim orogens as parts of the broad indosinian orogenic regime are clearly alike suggesting a genetic linkage in their time space characteristics

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

metamorphic evolution of the northwestern ogcheon metamorphic belt south korea the ogcheon metamorphic belt omb comprises late proterozoic to paleozoic metasedimentary and metavolcanic sequences which are intruded by mesozoic granitoid plutons to delineate the metamorphic evolution of the omb we have investigated mineral parageneses metamorphic reactions and p t conditions of pelitic and mafic schists in the chungju area northwestern part of the omb the regional metamorphic grade increases north westward from biotite to garnet zones although low pressure assemblages have developed in contact aureoles around jurassic granites garnet crystals show chemical zoning typical for prograde metamorphism with decreasing mn and increasing fe and mg from core to rim compositions of amphiboles constituting the common assemblage in the mafic schist are consistent with those of biotite and garnet zones documented in the medium pressure metabasites p t conditions of the garnet zone estimated from garnet biotite garnet chlorite and amphibole plagioclase geothermometers together with garnet plagioclase biotite muscoviterquartz geobarometers are in the range of 5 8 kbar and 520 5908c retrograde p t path based on fluid inclusion studies suggests that the exhumation of the omb has passed through the p trange of 1 3 kbar and 350 5008c following the isochore curves of the co inclusions in conjunction with structural and geochronologic data we conclude 2 that the omb has experienced a polycyclic p t evolution characterized by 1 crustal thickening during the middle paleozoic time and 2 regional retrograde metamorphism in the triassic our result further suggests that the triassic collision belt in east central china does not pass through the omb q 1998 elsevier science b v

spatial variability drained and undrained deviatoric load response geotechnical properties vary in space geostatistical parameters such as the mean the standard deviation and the correlation length are characteristic for each sediment and formation history the effects of spatial variability on the drained and undrained shear response of soils are investigated using numerical parametric studies where multiple realisations are tested for selected geostatistical parameters results show that the mean undrained shear strength decreases as spatial variability and correlation length increase spatial variability prompts strain localisation along neighbouring weak zones under both drained and undrained loading heterogeneous contractive media show internal homogenisation during drained deviatoric loading and the drained shear resistance evolves towards the critical state media with higher variability and longer correlation length require higher strain to attain internal homogenisation anisotropy in spatial correlation causes anisotropy in shear strength an intermediate d

a mist pluviation method for reconstituting silty sand specimens abstract a mist pluviation mp technique was proposed in an effort to develop a practical method for reconstituting silty sand specimens without inducing severe particle segregation the mist pluviation method includes both air and water pluviation processes with the addition of a mist zone that mixes soil particles with water droplets while falling through air the soil and water mixtures have similar particle sizes thus resulting in significantly reduced particle segregation a thin water layer on top of the deposited soil mimics the water deposition process and saturates the soil with little chance for particle segregation the performance of the mp method was evaluated with regard to homogeneity repeatability undrained monotonic compression and cyclic strength of triaxial specimens with various fines contents results have indicated that the mp method can be a promising technique to prepare reconstituted silty sand specimens

pretectonic and posttectonic emplacements of the granitoids in the south central okchon belt south korea implications for the timing of strike slip shearing and thrusting structural analyses of three granitic plutons in the south central okchon belt of the korean peninsula reveal that the baegnok and cheongsan plutons are pretectonic with respect to right lateral strike slip ductile shearing along the cheongsan shear zone and later top to the ese thrusting whereas the boeun pluton is posttectonic with respect to these two deformation events u pb sphene age data from the three plutons indicate that the intrusion ages of the baegnok cheongsan and boeun plutons are 222 7 2 1 ma 216 9 2 2 ma and 171 7 1 4 ma respectively microstructural evidence preserved in deformed rocks from the ne striking cheongsan shear zone and adjacent nne striking thrusts suggests that the right lateral ductile shearing event along the shear zone occurred before the ese directed thrusting since these thrusts crosscut the late triassic early jurassic taedong group we estimate that the thrusts developed at 180 ma during the daebo tectonic event just prior to the intrusion of the boeun pluton we also constrain the age of the cheongsan shear zone at middle late triassic time corresponding to the songrim orogeny so that the shear zone is not related to deformation along the middle jurassic honam shear zone 176 ma the honam shear zone is not a simple tectonic boundary between the okchon belt and the yongnam massif but an anastomosing ductile shear zone not only affecting the okchon belt and the yongnam massif but also crosscutting the boundary between them at a low angle we suggest that the right lateral cheongsan shear zone is a major boundary between the okchon zone and the yongnam massif with paleozoic cover rocks the kyonggi massif and the okchon zone south china block were juxtaposed against the yongnam massif and taebaeksan basin north china block along the cheongsan shear zone during a late stage of the middle triassic songrim orogeny probably related to the late paleozoic early mesozoic collision between the north and south china blocks

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

neoproterozoic bimodal volcanism in the okcheon belt south korea and its comparison with the nanhua rift south china implications for rifting in rodinia abstract a systematic geochemical examination and zircon u pb dating of neoproterozoic bimodal volcanic rocks from the chungju area in the northeast segment of the okcheon metamorphic belt omb south korea allow a comparison with similar rocks from the nanhua rift south china the bimodal metavolcanics of the chungju area comprise the subalkaline to alkaline basalts hereafter mafic metavolcanic rocks and trachytes hereafter felsic metavolcanic rocks the mafic metavolcanic rocks are characterized by light rare earth element lree enriched and humped trace element patterns with moderate depletions in sr and ti and variable but reasonably low end t values between 0 83 and 2 99 these geochemical features are consistent with the area s origin in an ocean island basalt oib mantle source with minor crustal contamination the felsic metavolcanic rocks are characterized by lree enriched patterns with a remarkable negative eu anomaly they display an overall enriched trace element pattern with

extensional deformation along the southern boundary of the gyeonggi massif south korea structural characteristics age constraints and tectonic implications the permo triassic collision of the north and south china blocks caused the development of the dabie sulu orogen in china and songrim orogen in the korean peninsula extension after this collision is known from the dabie sulu orogen but post orogenic extension is not well defined in the korean peninsula extensional deformation along the southern boundary of the gyeonggi massif in korea is characterized by top down to the south ductile shearing and subsequent brittle normal faulting and was predated by regional metamorphism and north vergent contractional deformation extension occurred between 220 and 185 ma based on the ages of pre extensional regional metamorphism and post extensional pluton emplacement 40ar 39ar dating of syn extensional muscovite in quartz mica mylonite yields an age of 187 8 5 6 2 ma in agreement with constraints from structural relationships together with the extensional deformation identified along the northern boundary of the gyeonggi massif 226 ma the extension along the southern boundary is probably related to the exhumation of the massif during late orogenic or post orogenic extension associated with the songrim orogeny of the korean peninsula and forms an important event in the phanerozoic crustal evolution of east asia

characterization of a gold tailings with hypersaline pore fluid a series of samples obtained from adjacent to piezocone penetration test cptu locations within a gold tailings storage facility with hypersaline pore fluid was tested to compare the inferred stat

shrimp u pb ages of detrital zircons in metasedimentary rocks of the central ogcheon fold thrust belt korea evidence for tectonic assembly of paleozoic sedimentary protoliths abstract we analyzed detrital zircons in four metasandstones and two metadiamictites of the central ogcheon metamorphic belt omb in order to provide geochronologic constraints on the time of deposition and protolith age distributions shrimp u pb ages of the newly analyzed zircons range from archean to early paleozoic and their age patterns permit the definition of four lithotectonic slices upper and lower pibanryeong units consisting primarily of quartzite and metasandstone an upper poeun unit of black slate containing early permian plant fossils and a lower poeun unit made up of metasandstone and metadiamictite a quartzite of the upper pibanryeong unit yielded two major zircon age populations at 965 11 ma and 447 5 ma whereas two lower pibanryeong metasandstones show major age concentrations at 2 5 ga 1 0 0 9 ga and 545 535 ma the youngest components of these units suggest maximum ages of sedimentation as late ordovician and early cambrian respectively these upper and lower pibanryeong zircon age distribution patterns are consistent with those of ordovician and devonian sedimentary strata respectively from the south china craton scc on the other hand three samples of the lower poeun unit yielded two distinct age populations at 1 87 ga and 755 7 ma in addition a metadiamictite contains abundant mesoproterozoic zircons with two broad peaks centered at 1 3 and 1 6 ga protolith ages and distribution patterns are profoundly different between the pibanryeong and poeun lithotectonic packages suggesting the presence of a major thrust fault juxtaposing allochthons that are also characterized by large p t contrasts our detrital zircon results for the pibanryeong unit are compatible with derivation from the scc in apparent contrast with the poeun occurrence of early permian plant fossils most likely correlative with the north china craton ncc taken together the suturing of paleozoic metasedimentary terranes in the omb is a product of permo triassic orogeny reflecting collision of the north and south china cratons

cyclic loading response of loose air pluviated fraser river sand for validation of numerical models simulating centrifuge tests cyclic loading response of loose fraser river sand was investigated as input to numerical simulation of centrifuge physical models using constant volume direct simple shear tests conducted with a

strontium isotopic equilibration during metamorphism of tillites from the ogcheon belt south korea the ne sw trending ogcheon belt formed during the mesozoic by deformation and metamorphism of a sedimentary sequence which includes tillite formations of late precambrian or lower palaeozoic age in this study rb sr isotopic data are reported from cm scale sampling of clasts and matrix in these tillites which underwent metamorphism at grades ranging from the biotite zone to the kyanite zone sr isotopic disequilibrium between clasts and matrix persists up to the highest grade but in four out of five rocks the matrix samples approximate to isochrons mswd s 12 the mechanism for this selective isotopic equilibration is considered to be related to the metamorphic reactions in the matrix which were probably accompanied by a substantial fluid flow the matrix isochrons for three of the rocks together with separated white micas from associated schists suggest that metamorphism took place in the trias approximately 200 myr ago metamorphism was followed by slow cooling and biotite closure temperatures were not reached until 190 150 myr these results suggest that where high fluid rock ratios can be demonstrated on independent petrological grounds the analysis of small scale whole rock samples may allow effective rb sr dating of metamorphism

uranium isotopes as a tracer of sources of dissolved solutes in the han river south korea abstract the uranium u content and 234u 238u activity ratio were determined for water samples collected from korea s han river in spring summer and winter 2006 to provide data that might constrain the origin of u isotope fractionation in river water and the link between u isotope systematics in river waters and the lithological nature of the corresponding bedrock the large difference in the major dissolved loads between the two major branches of the han river the north han river nhr and south han river shr is reflected in the contrasting u content and 234u 238u activity ratio between the tributaries low u content 0 08 0 75 nm average 0 34 nm and small 234u 238u activity ratio 1 03 1 22 average 1 09 in the nhr and high u content 0 65 1 98 nm average 1 44 nm and large 234u 238u activity ratio 1 05 1 45 average 1 24 in the shr the large spatial differences in u content and 234u 238u activity ratio are closely related to both lithological differences between the two tributaries and groundwater input the low u content and small 234u 238u activity ratio in the nhr arise mainly from a combination of surface and meteoric weathering of the dominant silicate rocks in this branch and congruent dissolution of already weathered secular equilibrium materials in contrast the high u content and large 234u 238u activity ratio in the shr are ascribed to the dissolution of carbonates and black shales along with significant inputs of deep groundwater

shrimp u pb zircon ages of pyroclastic rocks in the bansong group taebaeksan basin south korea and their implication for the mesozoic tectonics abstract the bansong group daedong supergroup in the korean peninsula has long been considered to be an important time marker for two well known orogenies in that it was deposited after the songnim orogeny permian triassic collision of the north and south china blocks but was deformed during the early to middle jurassic daebo tectonic event here we present a new interpretation on the origin of the bansong group and associated faults on the basis of structural and geochronological data shrimp sensitive high resolution ion microprobe u pb zircon age determination of two felsic pyroclastic rocks from the bansong group formed in the foreland basin of the gongsuweon thrust in the taebaeksan basin yielded ages of 186 3 1 5 and 187 2 1 5 ma respectively indicating the deposition of the bansong group during the late early jurassic inherited zircon component indicates ca 1 9 ga source material for the volcanic rocks agreeing with known basement ages the bansong group represents syntectonic sedimentation during the late early jurassic in a compressional regime during the daebo tectonic event the northeast trending regional folds and thrusts including the deokpori gakdong and gongsuweon thrusts with a southeast vergence developed in the taebaeksan basin this is ascribed to deformation in a continental arc setting due to the northwesterly orthogonal convergence of the izanagi plate on the asiatic margin which occurred immediately after the juxtaposition of the taebaeksan basin against the okcheon basin in the late stage of the songnim orogeny thus the deokpori thrust is not a continental transform fault between the north and south china blocks but an intracontinental thrust that developed after their juxtaposition

crustal development of the hida belt japan evidence from nd sr isotopic and chemical characteristics of igneous and metamorphic rocks abstract chemical and sr nd isotopic investigations were performed on the igneous and metamorphic rocks in the hida belt central japan to clarify their ages and possible sources and to provide constraints on the crustal evolution of the eastern margin of the asian continent igneous rocks of three main stages in the hida belt represented by the late silurian amphibolites first stage the middle carboniferous mafic dikes second stage and the late triassic to early jurassic granite gabbro plutons third stage show alkaline to calc alkaline chemical affinity major and trace element characteristics show that the three stages of igneous rocks were emplaced in a continental margin or continental arc environment the mafic igneous rock suites have relatively high e nd 0 5 to 5 5 and low 87 sr 86 sr 0 7049 to 0 7061 values indicating their origin from upper mantle sources though the third stage granitoids contain recycled crustal components the hida gneisses of clastic origin show two groups of model ages t dm middle proterozoic 1 4 2 2 ga and late proterozoic to early paleozoic 0 55 0 74 ga consistent with geological geochemical and radiometric age data are that the sedimentation and basaltic volcanism occurred in early to middle paleozoic and the protoliths with middle proterozoic model ages are detritals from the proterozoic continental provenances a synthesis of available geological and geochemical data for the basement metamorphic and igneous rocks in eastern asia suggests two possibilities for the paleozoic to early mesozoic history of the hida belt 1 the hida belt was formed at the eastern margin of the north china block with later evolution as a suture zone between the north and south china blocks or 2 it evolved as a part of the east central asian orogenic belt ecaob to the north

tectonometamorphic evolution of the chuncheon amphibolite central gyeonggi massif south korea the chuncheon amphibolite part of the gubongsan group which overlies the yongduri gneiss complex is interlayered with calc silicate rock marble quartzite biotite schist and quartzofeldspathic gneiss in the central gyeonggi massif south korea metamorphic pressures and temperatures estimated from the amphibolite are 5 5 10 6 kbar and 615 714 c these p t conditions are close to those defined by the reaction curve between kyanite and sillimanite and suggest medium pressure type metamorphism of the chuncheon amphibolite for two metapelites intercalated with the amphibolite temperatures are estimated to be 607 699 c consistent with those obtained from the amphibolite on the other hand pressures estimated from these metapelites are significantly different 4 6 kbar and 9 13 kbar when rim and core compositions of garnet are respectively used these p t estimates obtained from the amphibolite and metapelite suggest a nearly isothermal decompression of 3 7 kbar during denudation rapid decompression is likely on the basis of the results of mineral chemistry phase equilibria and geothermobarometer moreover in conjunction with the occurrence of kyanite in the adjacent gyeonggi gneiss complex p t estimates of the chuncheon amphibolite and metapelite suggest a clockwise p t t path this evolutionary path may be related to the amalgamation of continents during the late proterozoic event which corresponds to the jinningian orogeny in the qinling belt of china

drained and undrained strength interpretation for low plasticity silts the engineering behavior of low plasticity silts is more difficult to characterize than is the behavior of clay or sand due to their tendency to dilate during shear establishing a consistent and practically useful failure criterion for low plasticity silts can be very difficult consideration of how the undrained shear strength of silt is related to changes in pore pressure provides a more useful and practical framework for understanding the undrained strengths of these materials and for characterizing undrained strengths for practical purposes using a value of skempton s a as a failure criterion has been found to result in very reasonable values of undrained strength and to reduce scatter in the results as compared to using other criteria using a failure criterion based on an appropriate value of a results in consistent values of su p and tolerably small values of strain at failure for low plasticity dilative silts that pose the greatest problems with respect to definition of failure using

state boundary surface for very loose sand and its practical implications a state boundary surface defines a boundary in stress void ratio space above which no stress state can exist the applicability of the state boundary surface for sand has not gained widespread attention primarily because sand is not generally considered to be a difficult soil from a design point of view apart from liquefaction liquefaction is a phenomenon usually encountered in very loose cohesionless materials an experimental study relating the drained and undrained behavior of very loose saturated sand is presented it is shown that the post peak portion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line the slope of this straight line appears to stay constant for very loose sand there are potentially an infinite number of these lines which form a three dimensional surface in deviator stress effective mean normal stress void ratio space previously published results by various researchers are used to confirm the existe

contrasting plate tectonic styles of the qinling dabie sulu and franciscan metamorphic belts the dabie mountains are part of the 2000 km long qinling dabie sulu suture zone juxtaposing the sino korean and yangtze cratons an eastern extension apparently crosses korea and lies along the japan sea side of honshu as the imjingang and sangun terranes respectively a northeastern segment may be present in sikhote alin russian far east this orogenic belt records late paleozoic ocean floor consumption and the triassic collision of two precambrian continental massifs in east central china coesite and microdiamond inclusions in strong refractory minerals of eclogite facies ultrahigh pressure uhp metamorphic rocks in the dabie sulu area attest to profound subduction of a leading salient of the old cold yangtze craton now recovered through tectonic exhumation and erosion northward increase in intensity of subsolidus recrystallization of the suture complex is analogous to the internal progression in grade of high pressure hp and uhp metamorphism documented in the western alps in both regions subduction of narrow prongs of continental material uhp metamorphism and return toward midcrustal levels of relatively lower density buoyant microcontinental blocks resulted from delamination of these rocks from the descending higher density oceanic crust capped lithospheric plate such salients of continental crust represent an integral structural part of the downgoing slab remain intact and may be dragged to great depths before disengaging and rising differentially as coherent blocks uhp parageneses include trace mineralogic relics requiring peak metamorphic conditions of 700 900 c and 28 35 kbar or more in contrast pacific type hp metamorphic belts as represented by the franciscan complex of western california recrystallized under physical conditions up to 200 500 c 10 3 kbar in this setting voluminous quartzo feldspathic and graywacke debris was carried downward on oceanic crust capped lithosphere choking the subduction zone with incompetent material sited between both plates and strongly adhering to neither this buoyant largely sedimentary complex decoupled at 25 30 km depth and ascended toward the surface in both alpine type intracontinental collision and pacific type underflow light sialic material displaced dense mantle thus the return to midcrustal levels was propelled dominantly by body forces

the effect of allanite inclusions on u pb step leaching ages and sm nd isotope systematics of garnet from the ogcheon metamorphic belt south korea abstract the ogcheon metamorphic belt consists primarily of metasedimentary and metavolcanic rocks that have experienced polyphase tectonometamorphism since the neoproterozoic peak metamorphism reaching up to lower amphibolite facies produced ubiquitous garnet porphyroblasts in pelitic and mafic schists to determine the timing of their formation step leaching experiments were undertaken for five garnet fractions separated from pelitic and quartz hornblende garnet schists the u pb ages from three samples are identical within 2 errors ranging from 291 41 ma to 276 29 ma the quasi linearity of leachates in 238u 206pb and 208pb 206pb diagrams suggests that u and pb are released from a single mineral phase and that minor chemical fractionation between u and pb may have occurred during the leaching experiment deviations of residues and bulk garnet fractions from the linear trend are attributed to partial dissolution of refractory inclusions of detrital zircon th u ratios of leachates are in the range of 3 4 12 much higher than those of pure garnet and suggest the contribution of allanite negative relationships in the sm nd isochron diagram and similar 147sm 144nd ratios between whole rock and garnet corroborate the influence of light rare earth element lree rich allanite on the sm nd isotopic system simple mass balance calculations indicate that only a trace amount 0 35 modal of allanite inclusions should govern the u th pb systematics of garnet petrographic evidence together with the consistency in u pb ages suggests that allanite is a product of prograde metamorphism thus peak metamorphism responsible for the growth of allanite bearing garnet porphyroblasts in the ogcheon metamorphic belt is best estimated to be early permian

monotonic and cyclic liquefaction of very loose sands with high silt content the results from an experimental study on sands with high nonplastic silt content are presented drained and undrained triaxial compression tests undrained cyclic triaxial tests and drained undrained instability tests were performed on specimens of loose nevada sand with 40 silt content the behavior was observed to be somewhat different from previously published tests with sands at lower silt content the greater silt content appears to provide a more volumetrically contractive response throughout the entire stress strain curve however some aspects of the response were similar to sands with lower silt content monotonic undrained tests indicated reverse behavior i e static liquefaction occurred at low confining pressures and increasing dilatant volume change tendency was observed with increasing confining pressure analyzing the results using the concepts of steady state resulted in a unique steady state line only when undrained tests were sheared from the same isotropic compression line when

strength of undisturbed versus reconstituted silt and silty sand specimens the differences in undrained stress strain strength behavior between undisturbed and reconstituted silt and silty sand specimens tested at the same void ratio and initial stress state may be dramatic in all tests reported herein the undisturbed specimens showed dilative and ductile behavior whereas in all but a very few cases the accompanying reconstituted specimens at the same or lower density showed contraction much lower undrained strength and brittle behavior the test series included samples from a natural fluvial silt deposit as well as from silty sand hydraulically placed in a tailings dam when reconstituting specimens for laboratory testing it is not sufficient to only satisfy the criteria of correct density and grain size distribution but somehow the same fabric also must be reproduced otherwise deformation and stability analyses based on the results of reconstituted specimens or on in situ tests calibrated against such results may be misleading most of the reconstituted specimens

flow slide prediction method influence of slope geometry a quasi two dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand the initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation the condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state i e a state in which the undrained response to any quick change in load however small it may be consists of a sudden large increase in pore pressure the metastability of any sand element is predicted as a function of its constitutive properties its location in the slope and the slope geometry the constitutive properties are derived from dry triaxial tests and basically describe the liquefiability brittleness of the sand the metastability criterion for a soil element in a slope is different from that under triaxial loading flow slides observed in large scale

the geology of north korea an overview abstract the korean peninsula kp occupies a junction area of three big tectonic domains that are the paleo central asian orogenic belt paleo tethyan orogenic belt and the western pacific orogenic belt therefore the kp is a key area to understand the northeast asian and even global geotectonic evolution in terms of geological unit division the kp has long been thought to be closely tied with the mainland of china with using collective term the sino korea craton for the north china craton ncc however such correlation suffered from the absence of relevant geological information in north korea nk to bridge this knowledge gap our group carries out a long term collaborative study between the two sides of the kp and china and organized united field investigation in the north korea south korea sk and china as possible this paper introduces general geology in the north korea and simply make comparison with the ncc and south korea these pioneering works culminated in the following summaries 1 the kp comprises three major precambrian massifs i e rangnim gyeonggi and yeongnam massifs the rangnim and gyeonggi massifs are separated by the imjingang structural belt while the gyeonggi and yeongnam massifs are separated by the ogcheon structural belt 2 the basement of the rangnim massif is correlated with that of the ncc the characteristic metamorphic rocks of high temperature high pressure granulite facies including meta sedimentary rocks kondalites and meta sandstones and marbles with 1 9 1 8 ga metamorphic ages occur in the three massifs similar to the ncc 3 the proterozoic rift sedimentary sequences are developed in the ncc and north korea but lower paleoproterozoic strata are rare and neoproterozoic strata are more developed in north korea relative to the ncc 4 two main paleozoic basins within the rangnim massif and within the gyeonggi and yeongnam massifs are the phyongnam basin and taebaeksan basin both of them have a similar paleozoic tectono stratigraphy to the ncc 5 although the nature and tectonic significance of the imjingang belt remains controversial it doesn t show characteristics and natures of collisional orogenic belt 6 the eclogite bearing hongseong complex hsc is located in the southwestern part of the gyeonggi massif in south korea but no similar rock unit has been found in north korea 7 mesozoic igneous rocks are widespread throughout the northern and southern parts of the kp triassic magmatism is related to indosinian orogeny jurassic and cretaceous igneous rocks are different and irregular from those in the ncc on age and spatial temporal distribution this paper also suggests several key and controversial academic issues that are worthwhile to study in the future

ground sampling program at the canlex test sites one of the primary objectives of the canadian liquefaction experiment canlex project was to develop and evaluate undisturbed sampling techniques as part of the overall goal to focus and coordinate canadian geotechnical expertise on the topic of soil liquefaction six sites were selected by the canlex project in an attempt to characterize various deposits of loose sandy soil the sites consisted of a variety of soil deposits including hydraulically placed sand deposits associated with the oil sands industry natural sand deposits in the fraser river delta and hydraulically placed sand deposits associated with the hard rock mining industry at each site a target zone was selected and various methods of ground sampling were performed these included ground freezing and sampling fixed piston tube sampling christensen double tube core sampling large diameter sampling using the laval sampler and sonic rotary vibratory continuous coring ground freezing and sampling was performed at all six sites the

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

influence of silt size and content on liquefaction behavior of sands this study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain controlled monotonic undra

evolution of the qinling orogenic belt detailed field mapping geophysics and geochemistry show that the qinling orogenic belt is a southward vergent tectonic wedge consisting of six regional thrust sheets the lushan luanchun qinling douling wudang and zhuqi thrust sheets these regional thrusts underwent displacement at the end of the mid triassic and the end of the late jurassic due to the collision between the north and south china blocks and subsequent detachment the qinling orogenic belt is thus an indosinian yanshanian collision detachment zone the so called caledonian orogeny in the qinling orogenic belt records a succession of extensional and partial melting events in the continental crust the basic lavas in the lower paleozoic were erupted into rifting zones both in the northern qinling subzone and southern qinling subzone at the same time local melting of the transitional continental crust occurred and resulted in formation of s type granites

phanerozoic polyphase orogenies recorded in the northeastern okcheon belt korea from shrimp u pb detrital zircon and k ar illite geochronologies abstract we present the shrimp u pb detrital zircon and k ar illite 1m d 1m and 2m 1 ages suggesting new insight into the phanerozoic polyphase orogenies preserved in the northeastern okcheon belt korea since the initial basin formation during neoproterozoic rifting through several successive contractional orogens the u pb detrital zircon ages from the early paleozoic strata of the taebaeksan zone suggest a cambrian maximum deposition age and are supported by trilobite and conodont biostratigraphy although the age spectra from two sedimentary groups the yeongwol and taebaek groups show similar continuous distributions from the late paleoproterozoic to early paleozoic ages a grenville age hiatus 1 3 0 9 ga in the continuous stratigraphic sequence from the taebaek group suggests the existence of different peripheral clastic sources along rifted continental margin s in addition we present the k ar illite 1m d 1m ages of the fault gouges which confirm fault formation reactivation during the late cretaceous to early paleogene ca 82 62 ma and the early miocene ca 20 18 ma the 2m 1 illite ages at least those younger than the host rock ages provide episodes of deformation metamorphism and hydrothermal effects related to the tectonic events during the devonian ca 410 ma and permo triassic ca 285 240 ma these results indicate that the northeastern okcheon belt experienced polyphase orogenic events namely the okcheon middle paleozoic songrim late paleozoic to early mesozoic daebo middle mesozoic and bulguksa late mesozoic to early cenozoic orogenies reflecting the phanerozoic tectonic evolution of the korean peninsula along the east asian continental margin

detrital zircon u pb geochronology and tectonic implications of the paleozoic sequences in western south korea abstract the middle paleozoic metasedimentary sequences of the western gyeonggi massif taean formation and wolhyeonri complex imjingang belt and southwestern okcheon belt provide clues to the successive tectonic events that occurred during the evolution of the korean peninsula in this study we present shrimp u pb ages of detrital zircon grains from the metasandstones of the taean formation and yeoncheon group of the imjingang belt and from quartzites in three paleozoic formations of the southwestern okcheon belt the zircon grains from all of the samples yielded similar u pb age spectra of paleoarchean neoarchean to middle paleozoic with a dominant age population within the paleozoic the maximum ages of deposition estimated from the youngest dominant concordant detrital zircons were 431 457 ma for the western gyeonggi massif and imjingang belt and 380 355 ma for the southwestern okcheon belt permian metamorphic zircon overgrowths correlated with subduction prior to the triassic collision were also found middle paleozoic metamorphic zircon overgrowths that can be compared to those of the yunkai wuishan orogenic belt of the cathaysia block were indentified in the wolhyeonri complex the dominant zircon populations of this study and the available data for the korean peninsula compare well with those from the yangtze block cathaysia block and qilian qinling orogenic belt which were located at the northeastern margin of eastern gondwana during the early paleozoic

tectonics of an ultrahigh pressure metamorphic terrane the dabie shan tongbai shan orogen china ultrahigh pressure metamorphic rocks with coesite and diamond form a tectonic slice over 20 km thick called the eclogite zone within the dabie shan complex in the qinling orogen in central china the orogen separates the sino korean block in the north from the yangtze block in the south the dabie shan complex is a composite terrane made up of eclogite facies and amphibolite facies gneiss slices and represents fragments of the lower continental crust of the yangtze block the dabie shan complex is bounded in the south by a triassic foreland fold thrust belt and in the north by a greenschist facies metaclastic unit the foziling group which probably represents the passive continental apron deposits of the yangtze block farther north is a granulite facies gneiss complex the qinling group which has ultramafic slivers and includes the remnants of an island arc with two bounding suture zones north of the qinling group are early paleozoic active margin deposits of the sino korean block the eclogite zone in the dabie shan complex is sandwiched between amphibolite facies gneiss slices dating by sm nd rb sr and ar ar of two eclogite samples from the eclogite zone gives early to middle triassic ages 236 246 ma the initial end values indicate reworking of a 2 11 and 1 55 ga continental crust a himalayan type tectonic evolution is envisaged for the qinling orogen with the creation of a 100 km thick crustal thrust wedge through continuous underplating during the subduction of the yangtze continental lithosphere exhumation of the ultrahigh pressure metamorphic rocks was chiefly achieved by the southward propagation of the thrust planes thereby isostatically uplifting and eroding the earlier deeply subducted parts of the orogen a total of 680 km of southward thrusting in front of dabie shan is inferred based on the abrupt termination of the tanlu fault normal faulting possibly caused by gravitational collapse probably also had a role in the exhumation process

discovery of a c 370 ma granitic gneiss clast from the hwanggangri pebble bearing phyllite in the okcheon metamorphic belt korea abstract the chemical th u total pb isochron method chime of dating was carried out on accessory minerals in samples from the okcheon metamorphic belt in korea dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the hwanggangri formation metamorphic allanite in garnet bearing muscovite chlorite schist of the munjuri formation and polycrase and monazite in post tectonic granite from the hwanggangri area overgrowth of mantles took place at 369 10 ma on c 1750 ma cores of xenotime and monazite in the granitic gneiss allanite occurring in textural equilibrium with peak metamorphic minerals yields a chime age of 246 15 ma that is discriminably older than the polycrase 170 6 ma and monazite 170 3 ma ages of the post tectonic granite these chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c 250 ma from post 370 ma sediments late permian age signatures have also been reported from the precambrian gyeonggi and yeongnam massifs that border the okcheon metamorphic belt and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event

in situ liquefaction resistance of clean sands over a wide density range the paper describes a method of obtaining undisturbed samples of saturated clean sand by freezing it in situ using a single freezer pipe tests have shown that the method can yield high quality samples that retain the density and the undrained cyclic strength of the sand in situ undrained cyclic triaxial tests were run on in situ frozen samples and on samples obtained with conventional tube samplers the liquefaction resistance of the frozen samples of clean sands correlates well with a normalized iv value of the standard penetration test over a wide range of tv values the in situ liquefaction resistance of the clean sands estimated from the results of the undrained cyclic tests on the frozen samples is consistent with a criterion based on field performance data during earthquakes for dense sands the samples obtained with the tube samplers are looser and much weaker than those obtained by the in situ freezing method the reverse is true for very loose sands the correlation between relative density an

correlation between cyclic resistance and shear wave velocity for providence silts as an alternative to a field based liquefaction resistance approach cyclic triaxial tests with bender elements were used to develop a new correlation between cyclic resistance ratio crr and overburden stress corrected shear wave velocity vs1 for two nonplastic silts obtained from providence rhode island samples of natural nonplastic silt were recovered by block sampling and from geotechnical borings split spoon sampling the data show that the correlation is independent of the soils stress history as well as the method used to prepare the silt for cyclic testing the laboratory results indicate that using the existing field based crr vs1 correlations will significantly overestimate the cyclic resistance of the providence silts the strong dependency of the crr vs1 curves on soil type also suggests the necessity of developing silt specific liquefaction resistance curves from laboratory cyclic tests performed on reconstituted samples

implications based on the first shrimp u pb zircon dating on precambrian granitoid rocks in north korea abstract precambrian basement rocks in north korea consist of supracrustals and granitoid rocks of which the former comprise the late archean nangrim group and the paleoproterozoic jungsan and machollyong groups whereas the latter include four major types grey ttg gneisses garnet sillimanite bearing s type granites massive porphyritic granites and hornblende bearing granites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the precambrian history of north korea and its relations to north china shrimp u pb zircon analyses on two grey gneiss samples po501 and k14 reveal that they were emplaced at 2538 14 ma and 2636 49 ma respectively and metamorphosed at 2462 2433 ma these data for the first time confirm the existence of late archean rocks in the korean peninsula moreover one grey gneiss sample k14 contains several zircons with ages of 3 1 3 4 ga suggesting possible middle archean crust in north korea rocks with such ages are widely distributed in north china implying that north china and north korea have similar archean basement one grey gneiss sample r53 yielded a shrimp zircon age of 1933 12 ma indicating that some grey gneisses in north korea formed during the paleoproterozoic two garnet and or sillimanite bearing s type granite samples gave 207 pb 206 pb ages of 1908 31 ma and 1903 49 ma interpreted to reflect the time of metamorphism of the paleoproterozoic jungsan and machollyong groups since these s type granites are considered to be derived from the partial melting of pelitic rocks from these groups the 1 9 ga metamorphic event has also been revealed in paleoproterozoic rocks in south korea and north china shrimp zircon data also show that massive porphyritic monzogranites in north korea evolved over a protracted interval from 1865 ma to 1843 ma similar aged porphyritic monzogranites are also found in north china and south korea and their origin is considered to be related to a post tectonic extensional event of regional extent the last phase of precambrian magmatism recognized in north korea is grenvillian aged represented by the hornblende bearing granite that yields a shrimp zircon age of 1195 4 ma and is considered to be the source rock of the adjacent yushulazi group north china that contains numerous 1 1 1 2 ga old detrital zircons

permo triassic collision subduction zone metamorphism and tectonic exhumation along the east asian continental margin abstractconvergent plate motion at 320 210 ma generated the tongbai dabie sulu east central china imjingang gyeonggi central korea renge suo southwestern japan sikhote alin orogen along the paleo pacific edge of cratonal asia this amalgamated belt reflects collision between the sino korean and yangtze cratons on the sw portion and accretion of outboard oceanic arcs sialic fragments against the ne margin subducted proterozoic paleozoic continental and oceanic crustal complexes underwent high and ultrahigh pressure metamorphism at low to moderate temperatures tectonic slices of sialic crust episodically disengaged from the downgoing plate and driven by buoyancy ascended rapidly to midcrustal levels from depths exceeding 90 200 km after continental collision in east central china plus or minus korea and from 30 50 km after arrival of far traveled oceanic terranes in sw japan and the russian far east on achieving neutral buoyancy and stalling out at 10 20 km depth later doming gravitation

nd isotopic study of upper cambrian conodonts from korea and implications for early paleozoic paleogeography abstract correlation of the korean peninsula with the neighboring south and north china blocks has been one of the most important and long debated issues in east asian tectonics the eastward extension of the chinese collisional belt between the south and north china blocks into the korean peninsula is still in dispute the lower paleozoic sedimentary rocks in south korea the joseon supergroup accumulated in the okcheon belt which has been proposed as the suture zone or the block boundary between the south and north china blocks in korea the joseon supergroup comprises five different lithostratigraphic units and has been proposed to represent two tectonostratigraphic blocks bounded by the honam shear zone hsz in the okcheon belt among them the yeongweol unit in the western part of the hsz is correlated with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed the nd isotopic composition of upper cambrian conodonts from the duwibong and yeongweol units the difference of the nd t values between the upper cambrian duwibong and yeongweol units is about 3 units compared to a wide range of the nd 0 values in the modern oceanic basins this slight difference can be regarded as a variation in a same paleo watermass the nd t values of the two units are consistent with coeval values from north china and this suggests that the duwibong and yeongweol units shared the same oceanic watermass with the north china considering current early paleozoic paleogeographic reconstructions the nd isotopic signatures of north china duwibong and yeongweol units may be independent of laurentia and baltica and thus can be indicative of another unique oceanic watermass in contrast to the previous tectonic interpretations the same paleoceanographic signatures shown by the duwibong and yeongweol units and north china and recent developments suggest that the yeongweol unit in the early paleozoic joseon supergroup is not correlated with south china but correlated with north china and the korean peninsula and north china block may have been included in a larger continental block the sino korean block the collisional belt between the south and north china blocks may not extend into the korean peninsula

is the ogcheon metamorphic belt of korea the eastward continuation of the nanhua basin of china abstract the ogcheon metamorphic belt in central korea has been interpreted to be the eastward extension of the nanhua basin aulacogen of southeast china in this paper comparisons are made between the two regions based on stratigraphic thermal tectonic and other considerations from this comparison correlation of geological events between the nanhua basin and ogcheon metamorphic belt are at best equivocal the closest similarity is the presence in both regions of two major diamictite units of glacial origin and neoproterozoic age 750 690 ma range in china but of controversial origin and uncertain age in korea volcanic rocks in both regions appear to have similar petrological and geochemical traits and are interpreted to be rift related however their ages are different mostly 795 780 ma in the nanhua basin and c 750 ma in central korea so correlation remains uncertain more isotopic data from both regions may shed light on this comparison correlation between other pre carboniferous stratigraphic units in the two regions is hampered by the uncertainty about the stratigraphic age and succession in the ogcheon metamorphic belt stemming mainly from the absence of fossils and the strong tectonic metamorphic overprint both regions appear to have undergone deformation and metamorphism during the middle triassic indosinian songrim in some uncertain way related to the collision between the north and south china plates in the ogcheon metamorphic belt there has been no confirmation of a mid palaeozoic event but in the nanhua basin that event is recorded by stratigraphic and palaeogeographic evidence in the nanhua basin there is no evidence for an early permian metamorphic event that appears on isotopic grounds to have affected the ogcheon metamorphic belt this apparent difference has been interpreted as a result of diachronous deformation during late palaeozoic early mesozoic plate collisions that took place earlier in the east in korea than in the west in china

tracing the precambrian tectonic history of east asia from neoproterozoic sedimentation and magmatism in the korean peninsula abstract the neoproterozoic metasedimentary successions and igneous suites in the central korean peninsula provide important insights into the tectonic evolution of east asia here we report detailed detrital zircon u pb age data from the neoproterozoic metasedimentary successions as well as geochemical data on the early neoproterozoic rift related plutonic rocks our results together with the available data from the central korean peninsula lead to the following inferences 1 regional sedimentation in the early neoproterozoic ca 1000 920 ma as a result of the late paleoproterozoic to early neoproterozoic intracratonic rifting 2 arc magmatism in the southern periphery of the central korean peninsula in the early neoproterozoic ca 913 895 ma and ca 865 770 ma 3 back arc magmatism in the inland area of the central korean peninsula in the early neoproterozoic ca 888 852 ma 4 magmatism and sedimentation in the early neoproterozoic ca 765 720 ma due to early neoproterozoic back arc and intracratonic rifting the early neoproterozoic geological and tectonic events in the central korean peninsula correlate with those in the southeastern part of the north china craton the spatial and temporal similarities and discrepancies in the early neoproterozoic geological records of the sino korean continent mark the tectonic evolution within a continental inland the southeastern part of the north china craton and a continental margin the central korean peninsula

constraints on crust mantle transition zone with pn waveforms a case study of eastern china and southern korean peninsula abstract the seismic velocity structure of the crust mantle transition zone cmtz provides key constraints on crustal dynamics and can be studied with pn wave which propagates horizontally along the moho discontinuity in this study we first explore an effect of velocity gradient structures in the cmtz through synthetic pn waveforms and demonstrate that the shape of pn changes from step like to pulse like when the cmtz becomes from sharp to a gradient velocity structure respectively we then use pn waveforms of the regional earthquakes the july 2012 mw 4 8 earthquake in east china and the september 2016 mw 5 1 earthquake in south korea to examine the cmtz structures to the west and east of the yellow sea and thus to constrain tectonic affinity between the eastern china and southern korean peninsula the pn waveforms from the mw 4 8 event in east china show that the moho in southern yangtze craton is sharp whereas there may be a gradient structure in cmtz with a 6 10 km thickness in northern yangtze craton the pn waveforms from the mw 5 1 event in south korea show that the cmtz in south korea is also sharp similar to the southern yangtze craton observed difference in cmtz structures suggest that sulu orogenic belt may extend along the north of the gyeonggi massif in korea

recurrent rare earth element mineralization in the northwestern okcheon metamorphic belt korea shrimp u th pb geochronology nd isotope geochemistry and tectonic implications abstract rare earth element ree mineralization is hosted within neoproterozoic alkaline metaigneous rocks in the northwestern part of the okcheon metamorphic belt omb a polymetamorphosed fold and thrust belt transecting the paleoproterozoic gyeonggi and yeongnam massifs in the southern korean peninsula the principal carrier phase of rees is allanite allanite grains can be subdivided into several types based on the texture and mineral assemblage including quartz k feldspar biotite britholite apatite fergusonite andradite magnetite zircon titanite and fluorite electron microprobe analysis of allanite clearly distinguishes sample to sample variations in total rees ca al fe and y but the textural varieties from each rock sample do not show marked differences in those elements sensitive high resolution ion microprobe dating of allanite and zircon reveals a complex history of multistage mineralization allanite grains from ree ores yielded late ordovician 444 6 8 0 ma permian to triassic ca 300 220 ma and early jurassic 199 183 ma 208pb 232th ages these multiple age components often coexist in single grains showing slight differences in backscattered electron brightness the ordovician components have distinctly higher th u than the younger domains in the same rock sample the cores and rims of zircon from a syenite hosting ree ore bodies yielded neoproterozoic 858 2 6 3 ma and early jurassic ca 190 ma 206pb 238u ages respectively the early jurassic ages 194 187 ma also obtained from zircon grains from granites taken from dykes occurring close to the ores and a drill core indicate the correspondence between granitic magmatism and ree mineralization the neoproterozoic zircon inheritance weighted mean 853 9 3 8 ma in these granites is in sharp contrast to the dominant paleoproterozoic inherited zircon from the widespread earliest middle jurassic granites enclosing the mineralized zone the geotectonic significance of the late ordovician event recorded in the allanite as well as in detrital zircon from the omb is still unclear but its temporal coincidence with intraplate volcanism and arc related igneous activity respectively reported from the southwestern edge of the adjacent taebaeksan basin and the southwestern gyeonggi massif is noteworthy the following permian triassic and early jurassic mineralization events are probably linked to the continental suturing between the north and south china blocks and subsequent post orogenic magmatism and arc magmatism resulting from the paleo pacific plate subduction respectively sub grain sm nd isotopic analyses of allanite by laser ablation multiple collector icpms yielded initial end values plotting along the nd isotopic evolution path of the neoproterozoic metaigneous rocks indicating that rees originating from the host rock have been recycled during multistage mineralization events the profound differences in inherited zircon ages and nd isotopic compositions between the early and middle jurassic granites may reflect the presence of a major thrust bounded crustal structure beneath the omb

nature and evolution of the cretaceous basins in the eastern margin of eurasia a case study of the gyeongsang basin se korea abstract the gyeongsang basin is the largest among the non marine cretaceous sedimentary basins in korea and japan formed by sinistral strike slip movement induced by the oblique subduction of the paleo pacific plate under the eastern asian continental margin and has an evolutionary history of about sixty million years shrimp and la mc icpms u pb analyses were performed on the detrital zircons separated from the constituent formations of the gyeongsang basin we determined the maximum depositional ages of the four formations based on their ages of the youngest groups as follows 118 0 2 6 ma n 4 for the hasandong formation 108 7 0 8 ma n 11 for the chilgok formation 106 0 0 2 ma n 63 for the silla conglomerate 105 4 0 4 ma n 14 for the haman formation and 99 9 0 7 ma n 5 for the jindong formation belonging to the period from aptian to cenomanian the pre cretaceous detrital zircons of the lower to middle gyeongsang supergroup indicate their derivation from the yeongnam massif and the okcheon metamorphic belt surrounding the gyeongsang basin at around 115 ma as reflected as enhanced proportion of such ages in the detrital zircons and occurrence of farther inland igneous activities the tectonic environment of gyeongsang basin changed to intra arc due to the more active reestablishment of subduction related igneous activity however the upper gyeongsang supergroup has a new age component of the mid permian along with changes in the direction of paleocurrent flowing from the northeast and east indicating sediment supply from sw japan with rocks of that age the changes in the direction of the paleocurrent flow seem to indicate that the center of igneous activity has moved in the direction of the subduction zone to the east as the intensity of igneous activity continued to increase the gyeongsang basin was closed by the filling of the basin by volcanic activity the cretaceous basins of the korean peninsula and southwest japan show similar evolutionary histories suggesting a type model of the creation and the evolution of basin around the continental margin subduction zone creation of sedimentary basin by pull apart or rifting in the backarc region evolution to intra arc basin by the landward progress of subduction related igneous activity and finally the closure of the basin due to the advent of highly enhanced igneous activity

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

linking the sulu uhp belt to the korean peninsula evidence from eclogite precambrian basement and paleozoic sedimentary basins abstract considerable debate on whether and how the sulu orogenic belt extends eastward to the korean peninsula has remained over the past decade new results reported here include the following 1 an eclogite and retrograded eclogite bearing complex hongseong complex is discovered in south korea in which the eclogite occurs as lenses in circa 810 820 ma granitic gneiss shrimp zircon dating of the eclogite yields 230 ma for the metamorphic age and 880 ma for the protolith age 2 the basement of the rangnim gyeonggi and yeongnam massifs have affinities to the basement of the north china block ncb however the gyeonggi massif encloses a minor amount of large or small slabs of the hongseong complex that are similar to the rocks of the sulu belt 3 two main paleozoic basins within the rangnim and gyeonggi massifs have a similar paleozoic tectono stratigraphy to the ncb 4 the imjingang and ogcheon belts do not exhibit any metamorphic characteristics of collisional orogenic belts based on these facts we propose a crustal detachment and thrust model and suggest that the collision belt between the yangtze block yb and ncb sino korea craton is preserved along the western margin of the korean peninsula the lower part of the uhp metamorphosed lithosphere of the yb was subducted under the korean peninsula and not uplifted to the surface the lower crust of the yb the hongseong complex was detached from the subducted lithosphere and thrust over the korean peninsula and inserted into the basement rocks of the gyeonggi massif the upper crust of the yb possibly was detached from the lower crust and overthrusted along the honam and chugaryong shear zones the imjingang and ogcheon belts possibly represent the detached upper crust of yb and their present occurrences are controlled by a mesozoic strike slip shear structure all these detached lower and upper crustal slabs were strongly deformed during the late jurassic and early cretaceous tectonic event leading to their present geological distribution and characteristics

crustal evolution of the gyeonggi massif south korea nd isotopic evidence and implications for continental growths of east asia abstract we investigated the sm nd isotopic characteristics of the gyeonggi massif korea in order to delineate its crustal growth history nd isotopic depleted mantle model ages t dm obtained from 32 new measurements of basement and supracrustal samples and from the literature suggest that the gyeonggi massif is as old as middle archean 3 0 ga and was primarily extracted from the mantle during the late archean 2 9 2 5 ga in addition minor crustal formation occurred during the early proterozoic ca 1 9 1 8 ga late archean early proterozoic crustal growth of the gyeonggi massif is comparable with that of the sino korean or yangtze craton the t dm distribution pattern alone is not sufficient to determine the crustal affinity of the gyeonggi massif with either of the chinese cratons however late proterozoic crustal evolution of the gyeonggi massif appears to favor its tectonic correlation with the yangtze craton

neoproterozoic bimodal magmatism in the cathaysia block of south china and its tectonic significance shrimp u pb zircon age geochemical and sm nd isotopic results are reported for the mamianshan volcanic rocks in the cathaysia block of southeastern south china the mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite with an eruption age of 818 9 ma the basaltic samples are characterized by lree enriched and humped trace element patterns similar to many alkali basalts in continental rifts variablend t values between 3 33 and 4 35 indicate that the primary magma of these basalts was derived from an oib like mantle source and underwent fractional crystallization plus crustal contamination the rhyolitic rocks are highly enriched in th ta nb ree zr hf and y and depleted in sr p eu and ti sharing affinity to a 1 type granites combined with their slightly positive nd t values 0 22 to 0 92 the mamianshan felsic rocks were most likely generated by partial melting of the regional paleoproterozoic mayuan amphibolites the mamianshan bimodal volcanic rocks in the cathaysia block are coeval with the widespread intraplate magmatism around the yangtze block our results support the idea that a coherent south china craton was formed during the ca 1 0 ga sibao orogeny and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath rodinia since ca 825 ma 2004 elsevier b v all rights reserved

a middle ordovician drowning unconformity on the northeastern flank of the okcheon ogcheon belt south korea abstract the maggol limestone of ordovician age was deposited in the taebaeksan taebacksan basin which occupies the northeastern flank of the okcheon ogcheon belt of south korea carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the maggol limestone probably culminated in subaerial exposure of platform carbonates in the early middle ordovician earliest darriwilian elsewhere this subaerial exposure event is manifested as a major paleokarst unconformity at the sauk tippecanoe sequence boundary beneath the middle ordovician succession and its equivalents most in notably north america and north china due to its global extent this paleokarst unconformity has been viewed as a product of second or third order eustatic sea level fall during the early middle ordovician the sauk tippecanoe sequence boundary in south korea however appears to be a discrete marine flooding surface in the upper maggol limestone strata beneath this surface represent by a thinning upward stack of exposure capped tidal flat dominated cycles that are closely associated with multiple occurrences of paleokarst related solution collapse breccias this marine flooding surface is onlapped by a thick succession of thin bedded micritic limestone that is eventually overlain by a middle ordovician condensed section this physical stratigraphic relationship suggest that second and third order eustatic sea level fall may have been significantly tempered by regional tectonic subsidence near the end of maggol deposition the tectonic subsidence is also evidenced by the occurrence of coeval off platform lowstand siliciclastic quartzite lenses as well as debris flow carbonate breccias i e the yemi breccia in the basin with continued tectonic subsidence a subsequent rise in the eustatic cycle caused drowning and deep flooding of the carbonate platform forming a discrete marine flooding surface that may be referred to as a drowning unconformity this tectonic interpretation contrasts notably with the slowly subsiding carbonate platform model for the basin as has been previously suggested thus it is proposed that the taebaeksan basin in the northeastern flank on the okcheon belt evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early middle ordovician

a new concept on tectonic correlation between korea china and japan histories from the late proterozoic to cretaceous abstract the dabie sulu collision belt in china extends to the hongseong odesan belt in korea while the okcheon metamorphic belt in korea is considered as an extension of the nanhua rift within the south china block the hongseong odesan belt divides korea s gyeonggi massif into northern and southern portions the southern gyeonggi massif and the yeongnam massif are correlated with china s yangtze and cathaysia blocks respectively while the northern gyeonggi massif is part of the southern margin of the north china block the southern and northern gyeonggi massifs rifted from the rodinia supercontinent during the neoproterozoic to form the borders of the south china and north china blocks respectively subduction commenced along the southern and eastern borders of the north china block in the ordovician and continued until a triassic collision between the north china and south china blocks while subduction was occurring on the margin of the north china block high p t metamorphic belts and accretionary complexes developed along the inner zone of southwest japan from the ordovician to the permian during the subduction the hida belt in japan grew as a continental margin or continental arc collision between the north and south china blocks began in korea during the permian 290 260 ma and propagated westwards until the late triassic 230 210 ma creating the sinistral tanlu fault in china and the dextral fault in the hida and hida marginal belt in japan phanerozoic subduction and collision along the southern and western borders of the north china block led to formation of the qinling dabie sulu hongseong hida yanji belt

743 17 ma granite clast from jurassic conglomerate kamiaso mino terrane japan the case for south china craton provenance korean gyeonggi block abstract the polymict kamiaso conglomerate mino terrane japan contains jurassic to palaeoproterozoic clasts probably derived from korean basement that lay nearby to the northwest at time of deposition clast k2 broke cleanly into two halves during sampling but the halves were recombined for zircon separation a third of the k2 zircons are colourless euhedral prisms with oscillatory zoning with no inheritance and yielded a shrimp u pb date of 743 17 ma two thirds of k2 zircons are brown oscillatory zoned corroded prisms with a date of 1860 8 ma with inherited cores up to 2460 ma a likely explanation for this could be that clast k2 might have been composite and contained undistinguished 743 ma and 1860 ma granites kamiaso granitic clast k3 igneous zircons gave a date of 179 3 2 1 ma toarcian early jurassic with 2100 2300 ma and 1860 ma inherited cores 740 ma a type magmatism related to the extension and break up of rodinia occurs in both korea gyeonggi block and the main part of the south china craton but is unknown in the sino korean craton thus from recognition of a 743 ma clast the kamiaso detritus was probably derived from the northernmost part of the south china craton in korea

estimating slope of critical state line from cone penetration test an update estimation of density from cone penetration test cpt results is challenging as cone resistance is a function of a number of soil properties particularly compressibility while many of the relev

delayed collapse of cut slopes in stiff clay delayed failure of railway cutting slopes in stiff clays excavated in the nineteenth and early twentieth centuries has been studied for some forty years known failures have generally been deep seated more recently failures have been a problem in the slopes of motorway cuttings and embankments although generally these have been shallow the average operational strength at failure in these slides has been significantly less than the peak strength and progressive failure has been postulated as the probable cause of this progressive failure can now be analysed using advanced numerical techniques a series of coupled finite element analyses have been conducted assuming strain softening soil with properties based on the brown london clay and the results are reported they show that progressive failure is considerable and fully explain the observed field behaviour the delays experienced in the field are also recovered by the analyses progressive failure is generated primarily by the high lateral stresse

structural characteristics of the central ogcheon belt south korea orogen parallel tectonic transport model abstract the rocks in the central ogcheon belt south korea underwent three deformational phases d1 d2 and d3 during the mesozoic era in the study area nw and ne trending geological structures such as thrusts and folds are juxtaposed the nw and ne trending folds deform isoclinal folds f1 with axial planar slaty cleavage s1 and have axial planar crenulation cleavage all of these folds are overprinted by brittle faults d3 it is inferred from field data that the nw and ne trending structures are products of a single deformational phase d2 a very large scale inclined ne vergent isoclinal fold f1 produced an irregular boundary of precambrian basement and a basement promontory which acted as a structural obstacle against subsequent deformational phases during the e vergent phase d2 deformation partitioning occurred due to the irregular block boundary and orogen parallel and orthogonal structures were produced the d3 phase is recognized as large scale e w trending structures including folds and faults thus the structural evolution of the central ogcheon belt is related to the clockwise rotation of the maximum compressive stress axis from ne sw to n s during the mesozoic era this study shows that the shape of colliding boundary is a very important factor in controlling the structural pattern and evolution in the study area

neoproterozoic 900 ma sariwon sills in north korea geochronology geochemistry and implications for the evolution of the south eastern margin of the north china craton article the sariwon sills are distributed in the pyongnam basin at the center of the korean peninsula eastern part of the north china craton these sills are up to 150 m in thickness and up to more than 10 km in length baddeleyite grains separated from a 50 m thick sill give a sims 206 pb 207 pb age of 899 7 ma mswd 0 34 n 14 which is interpreted to be the crystallization age of this sill zircon grains from the same sill gives a lower intercept u pb age of 400 ma which is likely a close estimation of the greenschist facies metamorphism of this sill the sariwon sills are dolerites and have tholeiitic compositions they show enrichment of light rare earth element concentrations la ybn 1 4 2 8 and are slightly depleted in high field strength elements e g nb zr and ti in comparison to neighboring elements on the primitive mantle normalized spidergram the whole rock endt t 900 ma values are around 2 whereas in situ ehft t 900 ma values from zircon grains vary from 25 to 8 they are similar to the coeval sills in other parts of the north china craton e g the chulan sills xu huai basin shandong peninsula and the dalian sills lv da basin liaodong peninsula these sills possibly originated from a depleted mantle source e g asthenosphere rather than from the ancient lithospheric mantle of the north china craton and have experienced significant assimilation of lithospheric materials the strata and sills in the xu huai lv da and pyongnam basins are comparable moreover the three basins are geographically correlatable based on neoproterozoic geographical reconstruction we therefore propose that there is a xu huai lv da pyongnam rift system along the south eastern edge of the north china craton during neoproterozoic 900 ma with the closure of the rift at 400 ma as a result of a continent margin process it is possible that this southeastern margin of the ncc did not face the inland in the configuration of the supercontinent rodinia

liquefaction susceptibility criteria for silts and clays new liquefaction susceptibility criteria for saturated silts and clays are presented that are based on the mechanics of their stress strain behavior and which provide improved guidance for selecting engineering procedures for estimating potential strains and strength loss during seismic loading monotonic and cyclic undrained loading test data for silts and clays show that they transition over a fairly narrow range of plasticity indices pi from soils that behave more fundamentally like sands sand like behavior to soils that behave more fundamentally like clays clay like behavior with the distinction having a direct correspondence to the type of engineering procedures that are best suited to evaluating their seismic behavior it is recommended that the term liquefaction be reserved for describing the development of significant strains or strength loss in fine grained soils exhibiting sand like behavior whereas the term cyclic softening failure be used to describe similar phenomena in fine grained soils exhibiting clay like behavior for practical purposes clay like behavior can be expected for fine grained soils that have pi 7 although a slightly lower transition point for soils with a cl ml classification perhaps pi 5 or 6 would be equally consistent with the available data issues related to the practical application of these criteria are discussed