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

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

groundwater flow fields in infinite slopes this technical note presents an analytical description of all posssible groundwater flow fields in infinite slopes these flow fields may have any spatial orientation and may be affected by hydraulic anisotropy and heterogeneity but they may produce pore pressures or seepage forces that vary only in the co ordinate direction normal to the slope surface an equation is presented that together with its specialized forms define hydraulic gradients and hence determine pore pressure distributions and seepage forces in infinite slopes the practical ramifications of this equation are discussed

potential for landsliding dependence on hyetograph characteristics 1 this paper examines the effect of hyetograph shape on the potential for landsliding in soil mantled landscapes an existing pore pressure response model iverson 2000 is used to study the effects of unsteady rainfall infiltration in hillslopes and the effect of slope and convergent topography is expressed using a steady state model of slope parallel subsurface flow slope stability is assessed using an infinite slope analysis this theoretical framework is coupled with simple hyetograph models and to intensity duration frequency functions to determine the return period of landslide triggering rainfall results also show that hyetographs with a peak at the end of a rainfall event have a stronger destabilizing effect than hyetographs with a constant rainfall or with a peak at the beginning of a storm thus the variability of hyetograph shapes adds uncertainty to the assessment of landsliding triggered by rainfall

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

plan curvature and landslide probability in regions dominated by earth flows and earth slides damaging landslides in the appalachian plateau and scattered regions within the midcontinent of north america highlight the need for landslide hazard mapping and a better understanding of the geomorphic development of landslide terrains the plateau and midcontinent have the necessary ingredients for landslides including sufficient relief steep slope gradients pennsylvanian and permian cyclothems that weather into fine grained soils containing considerable clay and adequate precipitation one commonly used parameter in landslide hazard analysis that is in need of further investigation is plan curvature plan curvature is the curvature of the hillside in a horizontal plane or the curvature of the contours on a topographic map hillsides can be subdivided into regions of concave outward plan curvature called hollows convex outward plan curvature called noses and straight contours called planar regions statistical analysis of plan curvature and landslide datasets indicate that hillsides with planar plan curvature have the highest probability for landslides in regions dominated by earth flows and earth slides in clayey soils ch and cl the probability of landslides decreases as the hillsides become more concave or convex hollows have a slightly higher probability for landslides than noses in hollows landslide material converges into the narrow region at the base of the slope the convergence combined with the cohesive nature of fine grained soils creates a buttressing effect that slows soil movement and increases the stability of the hillside within the hollow statistical approaches that attempt to determine landslide hazard need to account for the complex relationship between plan curvature type of landslide and landslide susceptibility

geochemistry and petrogenesis of the fiskenaesset anorthosite complex southern west greenland nature of the parent magma abstract the petrogenesis of the fiskenaesset anorthosite body has been investigated using major and trace element data for a large range of rock types from each zone of the complex the chemistry of these ultramafic to anorthositic cumulates is interpreted in terms of crystal fractionation of a parental trace element impoverished tholeiitic magma involving crystallisation of the cumulus phases olivine orthopyroxene clinopyroxene and dominant plagioclase feldspar amphibole appears not to have been a significant cumulus phase at any stage of crystallisation of the body the abundant amphibole found in the rocks of the complex being produced by primary intercumulus crystallisation supplemented by secondary metamorphic recrystallisation similarly magnetite is unlikely to have been a significant early cumulus phase although together with chromite it crystallised as a cumulus phase at high stratigraphic levels in the complex the metamorphism appears to be largely isochemical although sub solidus metamorphic re equilibration of the ree can be demonstrated on a grain size scale the spatial and temporal association between the anorthosite complex and the bordering metavolcanic amphibolites is matched by a strong similarity between the observed trace element chemistry of the amphibolites and the trace element chemistry of calculated successive liquids for the complex this is taken to suggest a genetic relationship between the evolution of the anorthosite complex and enclosing amphibolites the presence of trace element impoverished amphibolites which are not cumulates with trace element abundances comparable to those of the suggested parental liquid to the anorthosite complex is used to derive a major element composition for the primary fiskenasset magma this composition approximates a moderately aluminous tholeiitic basalt which may have been generated by hydrous fusion of previously depleted mantle this primary magma underwent crystal fractionation under low pressure conditions allowing the development of extensive plagioclase cumulates the fiskenaesset anorthosite and similar bodies cannot represent a cumulate residue complementary to the enclosing voluminous tonalitic gneisses which have a calc alkaline chemistry controlled by high pressure crystal liquid fractionation rather the association between the cumulate layered complex and bordering supracrustal sequence may imply an ancient ocean crust analogue for the development of this component of archaean high grade terrains it is suggested that slices of such archaean ocean floor may be emplaced laterally into the base of the continental crust during subduction of oceanic lithosphere at cordilleran type continental margins

transient deterministic shallow landslide modeling requirements for susceptibility and hazard assessments in a gis framework abstract application of transient deterministic shallow landslide models over broad regions for hazard and susceptibility assessments requires information on rainfall topography and the distribution and properties of hillside materials we survey techniques for generating the spatial and temporal input data for such models and present an example using a transient deterministic model that combines an analytic solution to assess the pore pressure response to rainfall infiltration with an infinite slope stability calculation pore pressures and factors of safety are computed on a cell by cell basis and can be displayed or manipulated in a grid based gis input data are high resolution 1 8 m topographic information derived from lidar data and simple descriptions of initial pore pressure distribution and boundary conditions for a study area north of seattle washington rainfall information is taken from a previously defined empirical rainfall intensity duration threshold and material strength and hydraulic properties were measured both in the field and laboratory results are tested by comparison with a shallow landslide inventory comparison of results with those from static infinite slope stability analyses assuming fixed water table heights shows that the spatial prediction of shallow landslide susceptibility is improved using the transient analyses moreover results can be depicted in terms of the rainfall intensity and duration known to trigger shallow landslides in the study area

smnd age of the fisken sset anorthosite complex west greenland abstract the fisken sset anorthosite complex of southern west greenland is a sheet like layered igneous body which has been fragmented by granitoid intrusions multiply deformed and folded metamorphosed as high as granulite facies and in some places retrogressed to lower amphibolite or greenschist facies in some localities however such as at majorqap qa va some 20 km inland from the coast these effects are minimal here metamorphic grade reached only amphibolite facies with no apparent retrogression igneous textures and structures are spectacularly preserved detailed stratigraphic sequences have been established and in some samples primary mineralogy remains we report a sm nd isotopic study on samples from this locality attempting to constrain the age of crystallization of the fisken sset complex this complex represents a useful marker unit with which the age relationships of surrounding units may be compared a five point isochron including data for whole rock samples of anorthosite metagabbro metaperidotite and separates of calcic plagioclase and mafic matrix from a coarse megacrystic leucogabbro corresponds to an age of 2 86 0 05 ga mswd 2 5 with initial end of 2 9 0 4 the sm nd age is significantly older than previous pb pb whole rock ages of the complex but is sufficiently close to the 2 8 ga high grade metamorphic event which affected the area to cause partial resetting of the sm nd system to be considered however based on the integrity of the whole rock sm nd isotopic system in similar anorthositic complexes of higher metamorphic grade and the apparent preservation of magmatic ree patterns in the analysed plagioclase megacryst and coexisting mafic matrix we conclude that 2 86 0 05 ga represents the time of crystallization of the fisken sset complex this would imply a relatively short time interval on the order of 70 ma during which anorthosite formation tonalite emplacement and high grade metamorphism took place and this must be accounted for in any tectonic model for late archean events in southern west greenland in any case the positive end value of the fisken sset complex requires that it was derived from a source with long term depletion in light ree these results add to the increasing body of data indicating the widespread presence of depleted mantle sources during the archean

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

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

flume tests to study the initiation of huge debris flows after the wenchuan earthquake in s w china abstract in the wenchuan area in the southwest of china a huge amount of loose co seismic landslide material was deposited on slopes during the wenchuan earthquake of may 2008 these loose deposits formed the source material for rainfall induced debris flows or shallow landslides in the years after the earthquake on august 13 2010 about 20 large debris flows were triggered by heavy rainfall in the area around the epicenter of the wenchuan earthquake field reconnaissance revealed that the initiation of these post earthquake debris flows was closely related to severe erosion of the loose deposits flume tests were carried out to study the initiation mechanism of these post earthquake debris flows and the related influencing factors the flume was instrumented with ten combination sets of suction and pore pressure sensors these sensors were accompanied by tdr probes to measure the soil water content the flume has a length of 2 5 m and a width of 1 5 m a series of 26 tests was conducted to study the influence of slope gradient and discharge on the initiation mechanism and scale of the debris flows the amount of debris flow discharge was obtained by collecting the washed out deposits every 20 s the experimental results showed that the initiation mechanism of debris flows for gentle slopes and steep slopes was different on steeper slope incision by run off water was very rapid initiating directly the start of a debris flow the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls damming and breaching leading to a rapid widening of the erosion channel at gentler slopes less intensive run off incision caused an accumulation of material down slope which after saturation failed as shallow slides transform in a second stage into debris flows it was demonstrated that the slope was the dominant factor in controlling the scale of the debris flows while the effect of discharge on erosion and the size of the debris flows was less clear

combined roles of saturated permeability and rainfall characteristics on surficial failure of homogeneous soil slope abstract both rainfall characteristics rainfall intensity and duration and saturated permeability of soil may influence the type and mechanism of surficial slope failures in general the failures can be initiated by two mechanisms i e loss of matric suction through propagation of wetting front and rise of water table up to date there are still no clear indicators to identify the dominant parameters that control the type of failure for these shallow landslides this paper investigates the hydraulic responses of soils to the variations of rainfall characteristics and soil permeability through numerical analyses the results showed that the hydraulic responses to rainfall for a homogeneous infinite slope underlain by an impermeable layer can be divided into two stages 1 the propagation of wetting front and 2 the rise of water table based on these hydraulic responses the type and mechanism of failures were deduced from the analytical analyses both the rainfall characteristics and saturated permeability were found to be predominant in controlling the hydraulic responses of soil and hence the occurrence time depth of failure plane and type of surficial slope failures

long term investigations on the pore pressure regime in saturated and unsaturated sloping soils abstract pore pressure changes play a major role in the stability of natural slopes whose safety factor value is usually much smaller than that generally accepted in any other geotechnical problem correct assessment of potential seasonal pore pressure distributions is therefore a crucial issue in slope stability analysis based on long term monitoring of some natural slopes this paper compares the pore pressure distribution recorded in saturated fine grained deposits and in shallow unsaturated granular covers both monitored in southern italy in spite of the expected differences the soils display some common features in particular from december to mid may wet period in all examined cases the pore water pressures are quite constant over a monthly scale thus an essentially steady state pore pressure condition establishes it is in this phase which is characterised by an essentially downward flux that the safety factor drops to its lowest yearly value finally a simplified method is adopted to model the steady state pore pressure during the wet period and to calculate the average rain infiltration in equilibrium with the steady state condition the results thereby obtained are compared with the findings of an advanced approach based on the hydrological balance

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

comment on geochemistry and petrogenesis of the fiskenaesset anorthosite complex southern west greenland nature of the parent magma by b l weaver j tarney and b windley abstract evidence that ree have been metamorphically redistributed between plagioclase feldspar and mafic minerals as suggested by weaver et al 1981 is not forthcoming from the six fiskenaesset rocks used in the study ree patterns of the separated feldspars and of two rocks containing small modal amounts of mafic minerals are consistent with a light ree enriched magma during the formation of the fiskenaesset complex

assessment of shallow landsliding by using a physically based model of hillslope stability a model for the simulation of shallow landsliding triggered by heavy rainstorms is analysed and discussed the model is applied in two mountainous catchments in the dolomites eastern italian alps the cordon catchment 5 km2 and the vauz catchment 1 9 km2 where field surveys provided a description of hydraulic and geotechnical properties of soils and an inventory of landslide scars is available the stability mapping procedure which is similar to that proposed by montgomery and dietrich 1994 water resources research30 1153 combines steady state hydrologic concepts with the infinite slope stability model the model provides an estimate of the spatial distribution of the critical rainfall which is the minimum steady state rainfall predicted to cause instability the comparison of the landslides observed in the study basins with model predictions shows that the distribution of critical rainfall obtained from the model provides a surrogate for failure initiation probability as a function of topographic location copyright 2002 john wiley sons ltd language en

a review on the huoqiu banded iron formation bif southeast margin of the north china craton genesis of iron deposits and implications for exploration abstract the huoqiu iron ore field in northwest anhui province is located in the north china craton ncc as a large banded iron formation bif iron ore field ore bodies occur in a middle high grade of neoarchean metamorphic formation forming a banded silicon iron series from north to south the main ore bodies can be divided into two sub belts from bottom to upper layers i e the a b ore belt consisting of leptynite schist magnetite quartz formation and the d ore belt consisting of schist marble hematite quartz formation based on a dataset from geological settings geophysical and geochemical exploration ore forming conditions and structural analysis of the iron deposit we discuss structural types sedimentary environments deep tectonic and ore controlling factors as well as characteristics and distribution of this colossal bif ore field in the huoqiu region using la icp ms techniques we obtained the oldest u pb age of ca 2 7 ga for plagioclase amphibolite as its original rock and 1 8 ga for magmatic granite in the huoqiu group the hf isotopes of zircon were also determined resulting in the oldest hf model age of 3 5 ga geochemical data indicate that the protolithes of amphibolites belong to a series of subalkaline rocks with enrichments of large ion lithophile elements and depletions of high field strength elements which are typical volcanic arc rocks the amphibolites have low k 2 o concentrations with low ratios of ti v 22 7 to 25 9 averaging 24 5 similar to island arc tholeiite this suggests that the iron deposit and bif are of the superior type in the huoqiu region