deep structure of the bohemian massif from phase velocities of rayleigh and love waves phase velocities of rayleigh and love waves have been measured between the broadband seismic stations khc kasperske hory south bohemia and ksp ksi z lower silesia a profile that nearly coincides with the interactional dss profile vii the data for both wave types were separately inverted into models of shear wave velocity versus depth novotn s model khks 82 1 for the dss profile vii was used as a start model while the crustal section of novotn s model is compatible with both of our data sets our rayleigh wave data require smaller shear wave velocities on the average by 0 24 km s in the top 180 km of the mantle the average difference between novotn s model and our love wave model in that depth range is only 0 06 km s if our identification of the observed love waves as the fundamental mode is correct this result indicates the presence of polarization anisotropy in the uppermost mantle

provenance of jurassic accretionary complex mino terrane inner zone of south west japan implications for palaeogeography of eastern asia provenance and tectonic history of the jurassic accretionary complex mino terrane located in the inner zone of south west japan were studied using sandstone framework composition and mudrock geochemistry modal analysis of sandstones shows that the tectonic setting of the source area for the studied mino terrane clastic rocks was uplifted basement largely dominated by high grade metamorphic terrain composed of quartz and feldspar especially plagioclase the textural and mineralogical immaturity extent of alkali and alkaline earth element leaching low chemical index of alteration values and depleted rare earth element ree contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity factor analysis revealed that grain size effects governed compositional heterogeneity in the studied sediments provenance of the sediments is interpreted as being plagioclase enriched felsic basement rock such as granodiorite within a continental margin and evolved arc tectonic setting rather than active volcanic arc lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and or erosion of arc volcanics and exposure of basement considering the previous studies on palaeogeography and palaeocurrent reconstruction the north eastern part of the yeongnam massif in the korean peninsula is interpreted as the most probable source area for the studied turbidites the results of mixing calculation for mino terrane sediments suggest that precambrian leucocratic granite and the basement rock of the cretaceous gyeongsang basin shed large amounts of sediments to the mino trench whilst precambrian granitic gneiss and the triassic pluton supplied lesser amounts the results of this study reveal that although active subduction accretion processes were occurring the mino trench was bordered by continental basement rocks this knowledge contributes to enhanced understanding of the jurassic palaeogeography of the east asia continental margin

upper mantle structure under western europe from fundamental and higher mode surface waves using the nars array summary a generalized inversion of a new data set consisting of surface wave phase velocities and sn traveltimes has resulted in a new shear velocity and density model for the west european platform wepl 2 the surface wave phase velocity data set consists of fundamental and higher mode mode 1 6 measurements from 25 to 70mhz using the network of autonomously recording stations nars array which was specifically designed for higher mode surface wave measurements the sn traveltime data set consists of isc readings for selected european events major features of wepl 2 are a high velocity lid of 80 140 km depth underlain by a pronounced low velocity zone between 160 and 220 km depth the transition zone 400 650 km depth is characterized by high shear velocities with respect to prem the density shows a positive gradient from 60 to 140 km depth followed by an approximately constant value down to 400 km depth a model for the baltic shield scsh 2 is obtained by combination of nolet s 1977 higher mode phase velocity data set for western europe including the baltic shield and the present phase velocities for the platform this shield model shows an absence of the low velocity layer and low shear velocities in the top of the transition layer with respect to wepl 2 density although less well resolved shows lower values for the shield structure between 200 and 350 km depth

rapid changes in the level of kluane lake in yukon territory over the last millennium the level of kluane lake the largest lake in yukon territory was lower than at present during most of the holocene the lake rose rapidly in the late seventeenth century to a level 12 m above present drowning forest and stranding driftwood on a conspicuous high stand beach remnants of which are preserved at the south end of the lake kluane lake fell back to near its present level by the end of the eighteenth century and has fluctuated within a range of about 3 m over the last 50 yr the primary control on historic fluctuations in lake level is the discharge of slims river the largest source of water to the lake we use tree ring and radiocarbon ages stratigraphy and sub bottom acoustic data to evaluate two explanations for the dramatic changes in the level of kluane lake our data support the hypothesis of hugh bostock who suggested in 1969 that the maximum little ice age advance of kaskawulsh glacier deposited large amounts of sediment in the slims river valley and established the present course of slims river into kluane lake bostock argued that these events caused the lake to rise and eventually overflow to the north the overflowing waters incised the duke river fan at the north end of kluane lake and lowered the lake to its present level this study highlights the potentially dramatic impacts of climate change on regional hydrology during the little ice age in glacierised mountains

eoarchean paleoproterozoic zircon inheritance in japanese permo triassic granites unazuki area hida metamorphic complex unearthing more old crust and identifying source terrranes abstract u pb zircon geochronology of two permo triassic granites samples ot 52 and ot 272 with ages of 229 8 ma and 256 2 ma respectively in the unazuki area hida metamorphic belt southwest japan revealed the presence of eoarchean to paleoproterozoic inheritance inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions in ot 52 dark in cl low th u zircon domains have a mean 207pb 206pb age of 1940 17 ma which is consistent with an age of 1937 6 ma for anatexis in the precambrian busan gneiss complex in korea eoarchaean inherited zircons with 207pb 206pb ages from ca 3750 to 3550 ma are common in ot 272 but are few in ot 52 suggesting a source from rocks with affinities to those in the anshan area in the northeast china part of the north china craton on the other hand a hida metamorphic belt metasedimentary gneiss into which the granites were intruded contains ca 1840 1130 580 360 285 and 250 ma zircons sano et al 2000 these ages suggest that the unazuki mesozoic granites did not originate from proximal hida metamorphic complex rocks but instead from unrelated rocks obscured at depth the predominance of eoarchean to paleoproterozoic age components and the marked lack of 900 700 ma components suggest that the source was the extended fringe of the north china craton rather than from yangtze craton crust the mesozoic evolution of japan and its linkages to northeast asia are discussed in the context of these results

mid paleozoic arc granitoids in sw japan with neoproterozoic xenocrysts from south china new zircon u pb ages by la icp ms abstract the kurosegawa belt in sw japan preserves fragments of early middle paleozoic granitoids traditionally called the mitaki igneous rocks and previously dated ca 470 435 ma by several isotope analyses such as rb sr k ar and u pb together with high grade metamorphic rocks and silurian strata in a narrow belt however the timing of the oldest arc related plutonism in japan is constrained by laser ablation inductively coupled plasma mass spectrometry la icp ms u pb ages of zircon from mitaki granitoids in 3 areas in sw japan i e kyushu shikoku and kii peninsula weighted mean u pb ages of these zircons are 431 8 3 9 for a granodiorite from the mt mitaki area in shikoku 444 1 5 8 ma for a granodiorite from kuraoka area in central kyushu and 444 5 7 6 ma for a quartzdiorite from the nabaenohana area in western kii peninsula respectively these ages confirm that the mitaki igneous rocks have ca 445 435 ma late ordovician to mid silurian ages they are some of the oldest subduction related plutonic rocks in sw japan particularly noteworthy is a tonalite from the nabaenohana area which has a unique spectrum of zircon u pb ages with distinct 3 clusters ca 700 500 ma neoproterozoic cambrian ca 1350 830 ma meo neoproterozoic and ca 3230 1560 ma paleoarchean mesoproterozoic of the 44 dated zircon grains the youngest possibly xenocrystic grains are ca 500 ma older zircon grains with ages 500 ma range up to 3230 ma and are interpreted as inherited xenocrysts in the tonalite the mitaki igneous rocks are interpreted to have been derived by melting of post 500 ma terrigenous sedimentary rocks that yielded a unique tonalitic s type granitoid magma from the presence of abundant 1350 700 ma meso to neoproterozoic zircon grains in the tonalite we conclude that during the early paleozoic proto japan was located close to the cathaysian margin of south china

seismic anisotropy of the pacific ocean inferred from long period surface waves dispersion abstract the dispersion of surface rayleigh and love waves in the period range 40 300 s along a large number of paths allows the estimation of both the azimuthal anisotropy and the shear wave polarization anisotropy the regional dispersion is determined taking into account simultaneously its dependence with age and an azimuthal factor the pacific ocean has been divided into 5 regions for rayleigh waves and into 3 regions for love waves this partition discriminates the regions of extreme age which show a fast variation of dispersion with age from the regions of intermediate age where the variation is weak a variation of 2 of rayleigh wave group velocity with the azimuth of the path measured with respect to the direction of spreading is displayed up to very long period on the contrary the azimuthal anisotropy for love waves is difficult to resolve for rayleigh waves the present day direction of plate motion seems to agree best with the direction of maximum velocity on the other hand the isotropic inversion of the regional dispersion curves indicates except for young regions a discrepancy between rayleigh wave and love wave models with this hypothesis sh velocities are higher than sv velocities for the regions older than 23 ma down to a depth of 300 km which is indicative of the presence of polarization anisotropy the latter very weak for the young part of the ocean increases with age and reaches 7 for the oldest region

late holocene activity of sherman and sheridan glaciers prince william sound alaska abstract two adjacent glaciers in the chugach mountains of south central alaska have markedly different histories on decadal to perhaps centennial timescales sheridan glacier has advanced and retreated hundreds of metres during the latest holocene its recent fluctuations have markedly altered local base level of sherman river which drains sherman glacier and flows into sheridan lake sheridan glacier advanced to its greatest extent during the little ice age raising base level of sherman river and inducing aggradation there of up to 17 m of sediment retreat of sheridan glacier formed a series of lakes that have coalesced as lower lake outlets have become available base level of sherman river has dropped resulting in the evacuation of substantial volumes of sediment from sherman river valley in about 2000 the terminus of sheridan glacier began to disintegrate retreat accelerated dramatically in 2010 by 2016 the glacier had retreated an average of 600 m from its 2010 terminus although some areas retreated up to 1 9 km and others did not retreat at all meanwhile sherman glacier continued a slow advance initiated by a rock avalanche that blanketed much of its ablation area in the 1964 alaska earthquake

density versus depth models from multimode surface waves multimode love and rayleigh wave data related to the pacific ocean and to north america are inverted using two sets of parameters 1 the isotropic p and s velocities plus the density and 2 five elastic parameters describing a transversely isotropic medium plus the density it is found that the assumption of isotropy leads to very unrealistic upper mantle models while much more realistic models are obtained under the assumption of transverse isotropy the lateral variations in density between the pacific ocean and north america are then less than 1 5 and in both regions a large density gradient is well resolved at a depth near 360 km

mapping the lithosphere asthenosphere boundary through changes in surface wave anisotropy abstract the alignment of olivine crystals is considered as the dominant source of seismic anisotropy in the subcrustal lithosphere and asthenosphere different components of large scale anisotropy can be traced in depth distributions of the radial and azimuthal anisotropy of surface waves we propose a global model of the lithosphere asthenosphere boundary lab as a transition between a frozen in anisotropy in the lithosphere to anisotropy in the sublithospheric mantle related to the present day flow due to different orientations of velocity maxima in the anisotropic subcrustal lithosphere and the asthenosphere the velocity contrast related to the lab can increase in particular directions because of their long wavelengths and horizontal propagation surface waves suffer from poor lateral resolution however surface waves with various wavelengths allow us to map gross features of the lab with a good vertical resolution we estimate depths to the lab to be between 200 and 250 km for the precambrian shields and platforms around 100 km for the phanerozoic continental regions and 40 70 km beneath oceans from the world wide depth distribution of the radial and azimuthal anisotropy of surface waves

recent volume and area changes of kaskawulsh glacier yukon canada recent surface elevation changes of kaskawulsh glacier yukon canada are quantified by comparing an air photo derived dem from 1977 and airborne lidar measurements from 1995 2000 and 2007 surface area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007 combined these measurements provide some of the first detailed records of volume change of a large yukon glacier between 1977 and 2007 kaskawulsh glacier underwent a decrease in area of 1 53 and a decrease in volume of 3 27 5 94 km 3 w e the terminus also retreated by 655 m over the period 1956 2007 there was relatively minor volume change over the period 1977 95 0 01 km 3 w e a 1 while over the periods 1995 2000 and 2000 07 volume losses occurred at a relatively constant rate of 0 51 and 0 50 km 3 a 1 w e respectively since 1995 thinning has been prominent throughout the ablation zone while relative stability and even slight thickening has occurred in the accumulation zone these findings are similar to those recently observed at other nearby alaskan glaciers

the continental rift system of the rhinegraben structure physical properties and dynamical processes abstract the geophysical investigation of the continental rift system of the rhinegraben by various methods has progressed to such a stage that details of structure physical properties and seismic activity and relations between these features can be recognised differences in the nature of the crust mantle boundary inside and outside the graben proper seem to be a typical property of continental rifts asymmetries of structure seismic activity temperature in the crust and physical properties in the lithosphere are an important clue to the understanding of rift dynamics these asymmetries indicate that the formation of the rift cannot be explained by the updoming of an asthenolith alone but that taphrogenesis took place in the foreland of the continent continent collision in the alpine mediterranean zone a number of future key experiments is proposed

polarization anisotropy and fine scale structure of the eurasian upper mantle we have observed shear wave splitting with tsh tsv tsv up to 1 5 on long period records of multiply reflected s waves bottoming in the upper mantle beneath the russian and siberian platforms the dispersion of love and rayleigh waves over these paths shows discrepancies of comparable or larger magnitude with respect to smooth isotropic si structures consistent with a model of the uppermost mantle having significant apparent vertical anisotropy although the splitting and dispersion data can be fit by smooth anisotropic sa models we have investigated the apparent anisotropy associated with fine scale rough structure beneath stable eurasia we fit the data with a rough isotropic ri model having an rms shear velocity fluctuation that varies from 14 in the uppermost mantle to zero at 400 km depth these fluctuations are larger than the variation in isotropically averaged parameters expected for even a diverse assemblage of upper mantle ultrabasic rocks which we take to be evidence for some sort of intrinsic local anisotropy

isotropic and anisotropic pn velocity inversion of regional earthquake traveltimes underneath germany summary this paper investigates the uppermost mantle velocity beneath germany using regional earthquake traveltime data 2149 pn traveltimes corresponding to 220 events recorded at 70 stations covering the region of 47 n 52 n latitude 5 e 15 e longitude result in a satisfactory ray path distribution three methods with increasing degree of complexity are used to analyse the pn traveltime data a straight line fit the classical time term method and a modified time term method including azimuthal anisotropy first from the straight line fit to the data set an average pn velocity of 7 98 km s 1 is inferred second the classical time term method yields a mean uppermost mantle velocity of 7 99 km s 1 the most important feature in this analysis is the azimuth dependent pattern of the residuals indicating some evidence of velocity anisotropy in the upper mantle the time term method achieves about 55 per cent variance reduction relative to the straight line fit third two modified anisotropic time term methods provide an average pn velocity of 8 09 km s 1 with a further data variance reduction of 64 and 20 per cent relative to the straight line fit and the classical time term method respectively the estimated anisotropy level is about 3 5 4 per cent with maximum and minimum velocities of 8 24 8 27 km s 1 and 7 95 km s 1 our estimated maximum velocity direction of n25 e coincides with those of previous anisotropic studies on the uppermost mantle in this region based on seismic refraction data the results from the present study thus support the idea that pn wave anisotropy is a large scale lithospheric feature over much of central europe

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

azimuthally anisotropic model of the oceanic upper mantle abstract a mixed form of forward and backward modelings of azimuthally anisotropic oceanic upper mantle is attempted for a data set of surface wave velocities of periods 30 100 s one of the basic configurations of the anisotropy postulated in the lid and lvz is axial symmetry of elastic properties with a horizontal axis parallel to the spreading direction as found in ultramafic rocks from ophiolite complexes of the bay of islands and oman basic features of the resulting model are a thin lithosphere of 45 km a decrease of s wave velocities and an increase of p wave velocities and of partial melting dislocation relaxation with depth in the lvz this single model explains the overall features of anisotropy observations in the pacific ocean p n velocity anisotropy sh sv anisotropy and azimuthal anisotropy of surface waves and scs polarization anisotropy this fact leads us to a conclusion that the ultramafic rocks from the ophiolite complexes can explain the seismic properties of the oceanic lid and lvz

triassic 40ar 39ar ages from the sakaigawa unit kii peninsula japan implications for possible merger of the central asian orogenic belt with large scale tectonic systems of the east asian margin the 218 4 0 4 228 8 0 9 and 231 9 0 7 ma 40ar 39ar laser probe pseudo plateau ages 2 49 63 39ar release of very low grade meta pelitic whole rocks from the sakaigawa unit date high p t metamorphism we argue that this event occurred in a subduction accretion complex not along the east asian continental margin but on the pacific side of the proto japan superterrane proto japan was a permian magmatic arc presently dispersed in the japanese islands which also contained older subduction accretion complexes the arc system was fringing but not yet part of the eurasian continent the middle to late triassic high p t tectono metamorphic event was partly coeval with proto japan s collision with proto eurasia along the southward extension of the central asian orogenic belt causing the main metamorphism in the hida oki terrane it is possible that this system continued via the cathaysia block china to indochina the late permian to middle triassic indosinian event might stem from docking of pacific derived terranes with southeast asia s continental margin the concept of the proto japan superterrane implies that the qinling dabie sulu suture zone joined the central asian orogenic belt to the east of the north china craton and did not continue to japan as commonly assumed

detrital record of mountain building provenance of jurassic foreland basin to the dabie mountains 1 the huangshi foreland basin developed on the southern margin of the dabie mountains as a result of tectonic loading during triassic collisional suturing between the north china and south china cratons modal and detrital zircon data for jurassic samples within the basin suggest a multicomponent source with input from both the south china craton and dabie orogen samples are predominantly quartz arenites derived on the basis of framework compositions from a recycled orogen source detrital zircons range in age from archean to triassic with a dominant component in the late paleoproterozoic between 1 9 1 7 ga and subsidiary components at 2 6 2 2 ga 0 8 0 7 ga 0 5 0 4 ga and 0 33 0 2 ga age data integrated with cathodoluminescence and trace element data for the zircons indicate that the archean and proterozoic detritus was derived from igneous and metamorphic sources that overlap with time equivalent pulses of such activity within the south china craton phanerozoic zircon ages overlap the times of the ordovician carboniferous and triassic high pressure metamorphism in the dabie mountains the provenance record integrated with paleocurrent and regional relations enables a paleogeographic reconstruction in which the huangshi basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the south china craton and was also fed by short south flowing tributaries supplying some detritus from the evolving dabie orogen the dominance of cratonic derived detritus within the provenance record of the huangshi basin contrasts with that of the hefei foreland basin that lies to the north of the dabie mountains which is dominated by neoproterozoic mesozoic detritus derived directly from the dabie mountains and lacks any significant older paleoproterozoic or archean components easterly extensions of the dabie sulu collisional suture and of the resultant huangshi basin occur in korea and japan over an along strike length of some 2000 km

seismic structure of the upper mantle beneath the western philippine sea abstract we investigate the seismic structure of the western philippine sea using two sets of seismological observations scs reverberations which provide the layering framework for a regional upper mantle model and observations of frequency dependent phase delays for direct s waves surface reflected phases ss ss sss and surface waves r1 g1 which constrain the velocity and anisotropy structure within the layers the combined data set comprising 17 discontinuity amplitudes and layer travel times from the scs reverberation stack and more than 1000 frequency dependent phase delays was inverted for a path averaged radially anisotropic model mineralogical estimates of the bulk sound velocity and density are incorporated as complementary constraints the final model phb3 is characterized by a 11 5 km thick crust an anisotropic lid bounded by a sharp negative g discontinuity at 89 km an anisotropic low velocity layer extending to 166 km a subjacent high gradient region and transition zone discontinuities at depths of 408 km 520 km and 664 km the lid is slower than in a comparable model for the tonga hawaii corridor pa5 but also significantly thicker requiring a compositional variation between the two regions we explore the hypothesis that the thickness of the oceanic lid is controlled by the melting depth at the spreading centers during crust formation and that the thicker crust and lid in the philippine sea results from deeper melting owing to a higher potential temperature and perhaps a higher water content in the upper mantle

flow switching and water piracy between rutford ice stream and carlson inlet west antarctica rutford ice stream and carlson inlet are neighbouring glaciers in west antarctica rutford ice stream flows at speeds greater than 350m a 1 whereas carlson inlet which has some similar dimensions and supports a similar driving stress flows 10 50 times slower we discuss a range of observations concerning carlson inlet and conclude that there is good indirect evidence that it is a relict ice stream which ceased streaming more than 240 years bp but sufficiently recently that its surface morphology basal water content and basal morphology still retain characteristics produced by streaming an analysis of expected subglacial drainage pathways indicates that carlson inlet is not streaming because it is currently starved of subglacial water which is currently directed beneath rutford ice stream this current state of water piracy by rutford ice stream is however sensitive to minor thickness changes on the ice streams a similar to 120 m 4 thickening of rutford ice stream would divert almost all the subglacial water in the system towards carlson inlet and could reactivate its flow the result highlights the importance of subglacial drainage in controlling ice stream evolution and the requirement for ice sheet models to couple ice flow with subglacial drainage

upper mantle seismic anisotropy and lithospheric decoupling the lithosphere underlying stable continental shield regions is thought to extend to a depth of 200 km compressional wave velocity models derived from a recent approximately ns refraction profile in northern australia include a pronounced high velocity zone at a depth of around 200 250 km conventional petrological interpretations in terms of mineralogical or compositional changes cannot readily explain this feature calculated velocities for the garnet pyrolite model using a derived geotherm fit the velocities above and below this high velocity zone but cannot account for the high velocity 8 6 km s 1 zone itself this feature is explained in terms of velocity anisotropy which might reflect mechanical decoupling of the continental lithosphere from the underlying mantle

lithospheric thickness and velocity anisotropy seismological and geothermal aspects abstract we compare inferences of regional variations in the lithospheric thickness in central europe based on three types of observations seismologically determined thicknesses derived from representative p wave residuals agree in most regions both with the magnetotelluric inferences of depths of the top of a layer of increased electrical conductivity and with the geothermally based calculations that allow inferences of the lithospheric thickness from surface heat flow data the seismological definition of the lithosphere as a high velocity layer overlying the low velocity zone in the upper mantle seems to be close to the geothermal concept in which the lithospheric base is defined by temperatures near partial melting decreasing the seismic velocities and increasing the electrical conductivity interpretations of seismic data used for constraining geothermal models of the deep lithosphere assume velocity variations to reflect mainly changes in the mineral composition however recent observations of large scale seismic anisotropy show clearly that in the subcrustal lithosphere velocity variations due to anisotropy caused by preferred orientations of olivine crystals can be much larger than the velocity variations caused by temperature or compositional changes

recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern germany this paper advances new evidence for elastic anisotropy in the continental subcrustal lithosphere in southern germany the range of petrological models compatible with the observed azimuthal variation of seismic p wave velocity is explored the azimuthal distribution of amplitudes of mantle phases and the observed increase of p velocity with depth both indicate a continuation of anisotropy with depth together with an increase of preferred orientation even depletion of the upper mantle in basaltic components as suggested by mantle xenoliths from various parts of germany cannot explain the velocity depth and azimuthal amplitude observations without an increase of anisotropy with depth preferred orientation of olivine is the most likely mechanism for the observed phenomena its fast a axis at the moho level is directed towards n22 5 e the b axis is also required to be horizontal i e the b plane one of the preferred glide planes of olivine is vertical with a strike of n22 5 e therefore this preferred glide plane of olivine practically coincides with the plane of maximum horizontal shear stress deduced from fault plane solutions of earthquakes in western germany this is a strong indication that the preferred orientation of olivine is formed in the recent west european crustal stress field leaking into the upper mantle the distribution of velocities to a depth of at least 50 km requires slight horizontal rotation of the a axis with depth by 10 towards n32 e and a change in the modal composition towards a depletion increasing with depth compatible with the composition of mantle xenoliths from western germany further experiments are needed to substantiate this suggestion which could lead to a better understanding of the interaction of crustal and upper mantle stress strain fields

neotectonics and tree mortality in a forest ecosystem of the negro basin geomorphic evidence of contemporary seismicity in the intracratonic brazilian amazonia abstract neotectonic activity was increasingly recorded over the amazonian lowlands even during historical times of a few tens of centuries however detailed analyses linking structures and styles of deformation are still few considering the large dimension of the region such events in a relatively recent time are expected to have caused conspicuous impacts on amazonian ecosystems and forest disturbance changes in topography and hydrology by fracturing faulting and folding during either subsidence or uplifting are direct effects on landscape that leave marks on the structure of the current forest such as tree mortality and community succession two rectangular elbow like shaped wetlands from the left margin of the middle negro river valley in northwestern amazonia were attributed to neotectonics remote sensing imagery was applied to test this hypothesis and also provide a tectonic model that can explain deformation dynamics in this area the studied wetlands and adjacent river systems display various morphostructural anomalies compatible with a tectonic control as well as lineaments paralleling main nw and ne trending regional structures the geomorphic analysis led to suggest that the wetlands are depressions formed by nw and ne trending master boundary faults of horizontal displacements intercepted by various subsidiary faults transtensional strike slip regime is recorded by both left and right lateral faults with the wetlands corresponding to subsiding areas owned to conjugate strike slip faults habitat fragmentation and other ecological processes promoted by tectonic deformation would have impacted the overlying forest canopy by changing its structure due to tree mortality the complex compartmentalization imposed by active tectonics would have exposed the ground to contrasting hydrological conditions which controlled the rate of tree mortality within the wetlands we pose that the tectonic disturbance and associated tree mortality documented in the middle negro river evidence contemporary seismicity within the intracratonic brazilian amazonia

planform geometry and relief characterization of drainage networks in high relief environments an analysis of chilean andean basins abstract drainage network types give indications of the landscape evolution processes and the lithologic and structural conditions that produced them moreover drainage network attributes affect the hydrologic response of basins several network types have been identified through visual inspection and more recently through quantitative methods developed and applied primarily on relatively low relief regions these methods have not been tested in high relief environments where other factors can control network evolution and other network types may exist in this work we study the occurrence of network types in high relief environments and their potential identification through quantitative classification methods we analyze 29 high relief basins in the chilean andean region after exploring the contextual properties geological climatic and landcover of these networks we calculate several metrics describing their horizontal and vertical attributes and benchmark them against those for network types in low relief regions results show that the high relief networks have three different types herringbone barbed and high relief pinnate which differ in terms of their contextual properties as well as their horizontal and vertical attributes classification trees built using only vertical attributes have accuracies of 93 and 84 when differentiating among the high and low relief networks respectively furthermore an overall accuracy of 91 is reached when classifying the entire set of high and low relief networks with a combination of vertical and horizontal attributes overall we conclude that classification of drainage patterns through vertical and horizontal attributes is feasible and more accurate than with horizontal attributes alone

glacial and fluvial erosion in the dolpo basin western nepal abstract the landscape of western nepal has been dramatically shaped by tectonics and by both glacial and fluvial erosion here we investigate the modern geomorphic and glacial features of the dolpo basin in northern mid western nepal we analyze attributes such as glacier size slope aspect and toe head and peak elevation for 446 glaciers within and around the basin determining their relationship with basin features such as lithology slope and precipitation glaciers reflect lithology and precipitation but glacier size is strongly correlated with base level and slope our data suggest that low slope glaciers with high base level i e those that flow onto the tibetan plateau are forced to grow large because they exist at or above the equilibrium line altitude glaciers within the basin particularly in the western part can become dismembered on steep slopes an effect only partly offset by precipitation the spatial variability in regional slope and presence of a wind gap along the northern basin border suggest recent capture of the dolpo basin a plateau like morphology would have thus once extended at least 45 km southward the southward opening of the basin allowed precipitation to enter forming glaciers along the western end of the northern basin border larger glaciers resulting from high base level pushed the ridge southward over time through headward erosion our study suggests dramatic landscape reorganization in western nepal consistent with other recent studies suggesting a more extensive proto tibet

holocene incisions and flood activities of the keriya river nw margin of the tibetan plateau abstract fluvial terraces are common in the tectonically active western kunlun mountains wklm region northwestern margin of the tibetan plateau and incision of rivers since 5 ka was attributed to the accelerated uplift of the wklm however it is difficult to evaluate their tectonic or climatic origin without detailed chronology in this study optically stimulated luminescence osl dating was applied to fluvial flood and aeolian sediments on five lowest fluvial terraces 49 m in total along the keriya river and the 21 osl ages from 11 samples revealed the incision processes since the mid holocene especially the fast incision 3 5 0 ka 10 9 mm a during the late holocene this was supported by the climatic background i e increased precipitation from the westerlies and meltwater from frequent glacial advance retreat events as a response to the climatic changes large scale floods were frequent as well e g at 3 5 2 6 0 87 and 0 25 ka which were crucial for the fast incisions on the filling gravels additionally the flood also caused the river s further extension into the taklamakan desert and controlled the evolution of oases in the desert including ancient cities and cultures consequently we suggest that climatic change was important for the incision and formation of cut in fill terraces along the keriya river during the holocene and influences from other factors including surface uplift should not be ignored but were difficult to be evaluated

the lithosphere asthenosphere boundary and cratonic lithospheric layering beneath australia from sp wave imaging sp and ps scattered wave receiver functions were calculated for nineteen stations across australia and the island of tasmania in order to image the lithosphere asthenosphere boundary and layering within the lithosphere within phanerozoic eastern australia and the eastern margin of the south australia craton prominent sp phases from a negative velocity contrast were found at depths of 61 11 km to 131 9 km consistent with the lithosphere asthenosphere boundary depth range from surface wave tomography these phases imply significant velocity drops over depth ranges of 30 40 km or less and thus cannot be explained by a lithosphere asthenosphere boundary that is controlled by temperature alone rather they imply that the asthenosphere is hydrated with respect to a drier depleted lithosphere or contains a small amount of partial melt the shallowest sp phases have the largest amplitudes and occur in regions with the most recent voluminous volcanism strengthening the link to partial melt at the base of the lithosphere in contrast no significant negative sp phases were found at the base of the thick cratonic lithosphere at the stations in central and western australia implying that the cratonic lithosphere asthenosphere velocity gradient is distributed over more than 50 70 km in depth this gradient may be purely thermal in origin although gradational changes in composition or melt content cannot be ruled out a negative sp phase was observed at depths of 69 8 km to 85 14 km at stations in central and western australia indicating the presence of a drop in velocity internal to the lithosphere this interface within the lithosphere may be a relic of cratonic mantle formation or the result of alteration by melt and metasomatism

variation with age of anisotropy under oceans from great circle surface waves global great circle measurements of regionalized mantle love wave phase velocities are interpreted in terms of regional models the same study had been made by j j leveque 1980 for rayleigh waves and the resulting models for the two oceanic regions of different ages are used as a basis for comparison the observed love wave dispersion cannot be explained with these models if isotropic the models obtained by inversion of love wave data are compared with the models mentioned the discrepancy appearing in the 250km depth range between the velocities h and v of respectively sh and sv waves is indicative of polarization anisotropy moreover we put forward a significant variation from young to old oceans the difference between h and v is of the order of 1 for the former compared to 3 for the latter this variation can bring information about the behaviour of upper mantle materials in connection with the motion of oceanic plates

seismic observations of large scale deformation at the bottom of fast moving plates abstract we present a new tomographic model of azimuthal anisotropy in the upper mantle dr2012 and discuss in details the geodynamical causes of this anisotropy our model improves upon dkp2005 seismic model debayle et al 2005 through a larger dataset expanded by a factor 3 7 and a new approach which allows us to better extract fundamental and higher mode information our results confirm that on average azimuthal anisotropy is only significant in the uppermost 200 250 km of the upper mantle where it decreases regularly with depth we do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates slow oceanic plates or continents the anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity it peaks in the asthenosphere around 150 km depth it is very weak for plate velocities smaller than 3 cm yr 1 increases significantly between 3 and 5 cm yr 1 and saturates for plate velocities larger than 5 cm yr 1 plate scale present day deformation is remarkably well and uniformly recorded beneath the fastest moving plates india coco nazca australia philippine sea and pacific plates beneath slower plates plate motion parallel anisotropy is only observed locally which suggests that the mantle flow below these plates is not controlled by the lithospheric motion a minimum plate velocity of around 4 cm yr 1 is necessary for a plate to organize the flow in its underlying asthenosphere the correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak a better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age the transition between frozen in and active anisotropy occurs across the typical age isotherm that defines the bottom of the thermal lithosphere around 1100 c under fast continents mostly under australia and india the present day velocity orients also the anisotropy in a depth range around 150 200 km depth which is not deeper than what is observed under oceans

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

paleoproterozoic orogeny in south korea evidence from sm nd and pb step leaching garnet ages of precambrian basement rocks abstract geology and tectonics of the korean peninsula have been considered to be closely associated with those of the adjacent chinese continent although phanerozoic connections between the two areas have been reasonably well worked out precambrian ones are less well established we obtained sm nd and u pb garnet ages of 12 metamorphic rocks from widely separated parts of the gyeonggi and yeongnam massifs in south korea to better understand their precambrian history the two massifs consist of late archean to paleoproterozoic basement rocks and meso to neoproterozoic supracrustal rocks previous studies have shown that the two massifs experienced upper amphibolite to granulite facies metamorphism of medium pressure type with clockwise p t time paths suggesting that the two massifs may represent remnants of a collisional orogen pb pb and u pb garnet ages give two distinct age groups ten paleoproterozoic 1989 34 to 1835 56 ma ages of basement rocks from the two massifs and one late permian 265 8 ma age of a supracrustal rock from the gyeonggi massif that corroborates previous estimates of permo triassic 298 245 ma metamorphic age for the supracrustal rocks on the other hand sm nd garnet ages are less precise and display a wide range of ages from 2257 to 413 ma for the basement rocks when we compare the sm nd and pb pb ages from the same sample the sm nd age is similar to or younger than the pb pb age suggesting that the blocking temperature of the sm nd garnet system may be lower than that of the u pb system 800 c we interpret the pb pb and u pb ages as representing the timing of metamorphic garnet growth since the blocking temperature of the u pb garnet system is similar to or higher than the metamorphic temperature of the analyzed samples apparently the younger metamorphism possibly associated with the permo triassic collision between the north and south china cratons was not strong enough to reset the older metamorphic age similar paleoproterozoic metamorphic ages for basement rocks of the two massifs suggest that they may have come from the same precambrian terrane the metamorphic ages of the basement rocks of south korea agree very well with those of the central zone orogenic belt in the north china craton suggesting a possible correlation between the two terranes

application of inventory data for estimating characteristics of and regional climate change effects on mountain glaciers a pilot study with the european alps a parameterization scheme using simple algorithms for unmeasured glaciers is being applied to glacier inventory data to estimate the basic glaciological characteristics of the inventoried ice bodies and simulate potential climate change effects on mountain glaciers for past and potential climate scenarios glacier changes for assumed mass balance changes are calculated as step functions between steady state conditions for time intervals that approximately correspond to the characteristic dynamic response time a few decades of the glaciers in order to test the procedure a pilot study was carried out in the european alps where detailed glacier inventories had been compiled around the mid 1970s total glacier volume in the alps is estimated at about 130 km3 for the mid 1970s strongly negative mass balances are likely to have caused a loss of about 10 20 of this total volume during the decade 1980 90 backward calculation of glacier length changes using a mean annual mass balance of 0 25m w e a 1 since the end of the little ice age around 1850 ad gives considerable scatter but satisfactory overall results as compared with long term observations the total loss of alpine surface ice mass since 1850 can be estimated at about half the original value an acceleration of this development with annual mass losses of around 1 m a 1 or more as anticipated from ipcc scenario a for the coming century could eliminate major parts of the presently existing alpine ice volume within decades

contribution of alaskan glaciers to sea level rise derived from satellite imagery over the last 50 years retreating glaciers and ice caps gic contributed 0 5 mm yr to sea level rises slr and one third is believed to originate from ice masses bordering the gulf of alaska however these estimates of ice wastage in alaska are based on methods that measure a limited number of glaciers and extrapolate the results to estimate ice loss for the many thousands of others how these methods capture the complex pattern of decadal elevation changes at the scale of individual glacier and mountain range is unclear here combining a comprehensive glacier inventory with elevation changes derived from sequential digital elevation models dems we found that between 1962 and 2006 alaskan glaciers lost 41 9 8 6 km 3 yr water equivalent w e and contributed 0 12 0 02 mm yr to slr our ice loss is 34 lower than previous estimates reasons for our lower values include the higher spatial resolution of our glacier inventory and the reduction of ice thinning under debris and at the glacier margins which were not resolved in earlier work estimates of mass loss from gic in other mountain regions could be subject to similar revisions

provenance of cretaceous trench slope sediments from the mesozoic wandashan orogen ne china implications for determining ancient drainage systems and tectonics of the paleo pacific the wandashan orogen of ne china is a typical accretionary orogen related to paleo pacific subduction the raohe complex as a major part of the orogen consists of mid triassic to mid jurassic radiolarian chert and intraoceanic igneous rocks in an accretionary prism overlain by weakly sheared terrestrial sourced clastic trench slope sediments sensitive high resolution ion microprobe u pb dating and la mc icpms hf isotopic analysis of detrital zircons from the terrestrial sourced yongfuqiao formation sandstone show that most zircons are phanerozoic 90 140 150 ma 10 180 220 ma 25 240 270 ma 15 300 360 ma 15 391 395 ma 3 and 450 540 ma 20 whereas 10 are precambrian in age about 90 of the zircons have ehf t values ranging from 11 1 to 12 8 this suggests that the major provenance of the trench slope sediments was from the adjacent eastern segment of the central asian orogenic belt and the jiamusi block the age of the yongfuqiao formation is constrained to the earliest cretaceous which represents the accretion time of the mid triassic to mid jurassic oceanic complexes when compared with the mino complex in japan and the tananao complex in taiwan three different provenances are identified suggesting three ancient drainage systems which transported sediments from ne china north china and south china to the paleo pacific subduction accretion system

inversion of multimode surface wave data evidence for sub lithospheric anisotropy summary multiparameter inversions of multimode dispersion data are performed for two large regions the pacific ocean and north america anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry two fundamental questions are studied in detail 1 how to make the inverted models consistent when using different sets of parameters 2 what is the significance of transversely isotropic inversion for the actual earth s structure it is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data the models we have obtained are discussed in the light of these investigations considering an olivine rich upper mantle we make a tentative interpretation of these models in terms of preferred orientation of the a axis of the crystals in one fixed horizontal direction

quantifying the erosional impact of a continental scale drainage capture in the duero basin northwest iberia formerly closed drainage basins provide exceptional settings for quantifying fluvial incision and landscape dissection at different time scales endorheic basins trap all the sediment eroded within the watershed which allows estimates of post basin opening erosion patterns the duero basin was a former closed basin and is presently drained by the duero river into the atlantic ocean during the cenozoic the basin experienced a long endorheic period marked by the formation of continental carbonates and evaporites the retrogressive erosion of the atlantic drainage coming from the portuguese coast subsequently captured the internal drainage and significant fluvial dissection occurred presently the basin contains a relatively well preserved sedimentary fill gridding and surface fitting in this paper provide the first attempt to reconstruct the surface of the top of the former endorheic sedimentary sequence to quantify the erosional impact of the basin opening at least 2251 524 km3 of sediment was removed from the formerly closed basin following the start of exorheism this volume represents a mean basin surface lowering of 65 13 m erosion estimates and landscape dissection patterns are consistent with geologic evidence of progressive establishment of an outward drainage system

the formation and impact of landslide dams state of the art abstract the blocking of river courses by mass movements is very common in mountainous areas with deep and narrow valleys landslide dams may pose serious threats to people and their livelihoods downstream in the case of abrupt dam failure since the publication of benchmark reviews of costa and schuster 1988 and korup 2002 there is a growing number of studies focusing on the formation stability and short term impacts of landslide dams this review combines the insights of all these studies builds on current concepts of landslide dams and suggests ways to unify terminologies and classifications we furthermore present a new worldwide database compiled from literature data it contains 410 landslide dams 1 million m3 in volume that were formed since 1900 since these have the most complete data entries these data show that dam longevity is among other factors correlated with the type of landslide forming the dam those formed by rock debris avalanches and rockslides have longest lifespans however the influence of landslide type or material on dam longevity decreases with time after dam formation to ensure consistency in the next database generation we suggest guidelines for data collection to provide a solid basis for evaluating dam stability and governing factors a preliminary classification matrix for landslide dam stability that combines topographic setting and the internal structure of the dam body is another outcome of our review furthermore an evaluation of the various geomorphic stability indices proposed in the literature regarding their suitability and limitations in assessing dam formation and stability shows that they predict the probability of dam formation reasonably well but that their application to longevity estimates requires further assessment the geomorphic impacts of landslide dams in the short medium and long term are summarized and illustrated with key examples finally for a better understanding of the factors controlling dam stability we recommend to 1 include dam composition and sedimentary structures in future case studies 2 maintain and update the worldwide database for sound statistical analyses 3 refine landslide dam stability indices and test them for different landslide types and 4 study hazard cascades related to multiple dams in one watershed for long term landscape evolution studies we suggest to 5 quantify terrestrial sediment flux related to landslide dams 6 detect ancient landslide dams in river profiles and 7 further exploit the sediment archives in former impoundment areas

provenance of trench fill deposits of the jurassic chichibu accretionary complex southwest japan abstract this study constrains the provenance of the trench fill turbidite sandstones of the jurassic accretionary complex chichibu accretionary complex in southwest japan using detrital zircon u pb ages data zircons from all sites six sites yielded mainly precambrian and permian jurassic ages the precambrian zircons were derived from the north china block whereas the permian jurassic zircons were derived from igneous rocks in and around the korean peninsula the percentage of precambrian zircons ranged from 39 9 to 52 9 average 45 5 of the total and that of the permian jurassic zircons ranged from 46 5 to 57 6 average 52 6 thus during the jurassic an equal number of zircons was continuously supplied from in and around the korean peninsula and the north china block into a trench on the eastern margin of the asian continent the percentage of permian and triassic zircons gradually decreased over time whereas the percentage of jurassic zircons gradually increased these changes likely reflected the igneous activity in and around the korean peninsula during the jurassic these results indicate that the turbidite sandstones of the jurassic accretionary complex in southwest japan comprise detritus from not only the north china block but also the igneous activity in and around the korean peninsula therefore the jurassic accretionary complex in southwest japan was likely formed near the north china block

river piracy and drainage basin reorganization led by climate driven glacier retreat river piracy the diversion of the headwaters of one stream into another one can dramatically change the routing of water and sediment with a profound effect on landscape evolution stream piracy has been investigated in glacial environments but so far it has mainly been studied over quaternary or longer timescales here we document how retreat of kaskawulsh glacier one of canada s largest glaciers abruptly and radically altered the regional drainage pattern in spring 2016 we use a combination of hydrological measurements and drone generated digital elevation models to show that in late may 2016 meltwater from the glacier was re routed from discharge in a northward direction into the bering sea to southward into the pacific ocean based on satellite image analysis and a signal to noise ratio as a metric of glacier retreat we conclude that this instance of river piracy was due to post industrial climate change rapid regional drainage reorganizations of this type can have profound downstream impacts on ecosystems sediment and carbon budgets and downstream communities that rely on a stable and sustained discharge we suggest that the planforms of slims and kaskawulsh rivers will adjust in response to altered flows and the future kaskawulsh watershed will extend into the now abandoned headwaters of slims river and eventually capture the kluane lake drainage river piracy the diversion of one stream s headwaters into another has occurred on long timescales an analysis of streamflow and digital elevation models documents river re routing in response to glacier retreat in yukon canada in may 2016

anisotropy of the asthenosphere the higher mode data of the pacific revisited surface wave data previously used by the authors to constrain upper mantle anisotropy in the pacific ocean are re examined after an error was found in the calculations of the love wave phase velocities sub lithospheric anisotropy is still required by the corrected data but it extends to shallower depth than we originally proposed using different parameterizations of the upper mantle we present strong evidence that the bottom of the anisotropic layer has been reached around 250 km in the pacific beneath north america no revision of our data is required and anisotropy could extend to around 400 km depth our results are in agreement with an upper mantle anisotropy due to preferred orientation of olivine crystals in an overall horizontal shear strain parallel to the present day plate motion we suggest that this preferred orientation of the crystals mainly occurs within the upper mantle low velocity layer

late jurassic to early early cretaceous tectonic nature on the ne asian continental margin constraints from mesozoic accretionary complexes abstract it is widely accepted that subduction of the paleo pacific plate beneath eurasia began in the early mesozoic however the tectonic nature and processes of the ne asian continental margin in the late jurassic to early early cretaceous remain unclear in this contribution lithological provenance and metamorphic deformation data are used to constrain the formation of mesozoic accretionary complexes ac along the ne asian continental margin and determine the tectonic relationship between the ne asian continental margin and the paleo pacific plate in the late jurassic to early early cretaceous the mesozoic ac formed during the late jurassic including the raohe ac in ne china the khabarovsk samarka and taukha acs in the russian far east and the mino tamba ac in japan and early cretaceous including the shimanto ac in japan and the kiselevka manoma ac in the russian far east the jurassic ac underwent a complex evolution including the formation of seamounts middle late jurassic terrigenous clastic sedimentation adjacent to the trench collision of seamounts with eurasia northward migration of the ac early early cretaceous terrigenous clastic sedimentation a second period of accretion and final emplacement the earliest mesozoic ac arrived at the trench at ca 195 ma combined with the occurrence of early mesozoic calc alkaline igneous rocks along the ne asian continental margin we suggest that subduction of the paleo pacific plate beneath eurasia began in the early jurassic jurassic ac in japan was affected by a regional high p t metamorphic event at 160 ma which might have been related to subduction collision of seamounts with eurasia at the trench ages and hf isotopic compositions of detrital zircon grains from the middle upper jurassic and cretaceous ac sandstones together with paleontological and paleomagnetic data indicate that jurassic clastic sediments were sourced mainly from the south china block scb whereas the lower cretaceous sandstones were sourced from the eastern central asian orogenic belt caob the inferred northward migration of jurassic ac in the late jurassic to early early cretaceous indicates that the boundary between the ne asian continental margin and the paleo pacific plate was characterized by strike slip tectonics at this time likely due to a small angle of obliquity in the subduction of the paleo pacific plate beneath eurasia in the late early cretaceous westward subduction of the paleo pacific plate beneath eurasia resulted in the emplacement of the raohe and khabarovsk acs at 137 130 ma and the formation of acs in the russian far east and japan

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

provenance diversification within an arc trench system induced by batholith development the cretaceous japan case by comparing detrital zircon u pb age spectra of coeval fore arc and back intra arc basin sandstones we identified the overall distributary pattern of terrigenous clastic material within the cretaceous arc system of sw japan abundant proterozoic c 1500 2500 ma detrital grains from the interior of east asia are present in the cretaceous intra arc basin however after a barrier mountain range formed during batholith emplacement proterozoic clastics were rarely transported into the fore arc domain episodic batholith formation in pacific type orogens likely played a major role in controlling terrigenous supply routes between coeval back arc and fore arc domains the cretaceous orogen in japan thus provides a good template for analysing the tectono sedimentary development of other arc related basins

global tomography from rayleigh and love wave dispersion effect of ray path bending summary a large data set of fundamental mode rayleigh and love wave phases has been employed for global tomographic inversions these data represent observations of the first arriving surface waves r1 and l1 from approximately 850 seismic events with about 10 observations of dispersion per event the inversion for laterally varying depth dependent structure is performed in several steps at discrete periods from 111s 250s for love waves and from 111s 200s for rayleigh waves we first determine simultaneously the global distribution of phase velocity anomaly and the relocations of the seismic events each phase velocity distribution is then corrected for laterally varying moho depth and bathymetry followed by inversion for 3 d earth structure in the depth range 0 240 km in order to lie within the limits of ray theory we restrict all model perturbations to a degree 0 16 spherical harmonic expansion a second order scattering ray path correction is included in the inversions the phase velocity perturbations show a high correlation with surface tectonics at shorter periods comparison of inversions shows that those performed without the ray path correction exhibit a complicated pattern of fast and slow velocity bias the only common feature in the patterns of bias with respect to period or wave type is that fast velocity bias is concentrated in regions of large structural gradient the amplitude pattern of the depth dependent model has pronounced peaks in the intervals 0 70 km and 140 210 km the deeper peak is associated with lateral variations in asthenosphere structure we derive new estimates for the spherically averaged phase velocities of the fundamental mode rayleigh and love waves the spherically averaged phase velocities are decreased by about 0 1 per cent by including the ray path correction these phase velocity dispersions can be simultaneously fit well with an isotropic model either with or without the ray path correction but particularly well when the ray path correction is included in both cases a pronounced low velocity zone of the global extent is required in the depth range 120 190 km

three dimensional seismic models of the earth s mantle accurate models of the distribution of elastic heterogeneity in the earth s mantle are important in many areas of geophysics the purpose of this paper is to characterize and compare quantitatively a set of recent three dimensional models of the elastic structure of the earth to assess their similarities and differences and to analyze their fit to one class of data in order to highlight fruitful directions for future research the aspherical models considered are the following m84c woodhouse and dziewonski 1984 lo2 56 dziewonski 1984 mdlsh tanimoto 1990a sh 10c 17 masters et al 1992 and s12 wm13 su et al 1994 through much of the discussion m84c and lo2 56 are combined into a single whole mantle model m84c lo2 56 the fit of each model to previously tabulated even degree normal mode structure coefficients taken from smith and masters 1989a and ritzwoller et al 1988 for multiplets along the normal mode fundamental and first second and fifth overtone branches is also presented rather than concentrating on detailed comparisons of specific features of the models analyses of these models are general and statistical in nature in particular we focus on a comparison of the amplitude and the radial and geographical distribution of heterogeneity in each model and how variations in each affect the fit to the normal mode observations in general the results of the comparisons between the models are encouraging especially with respect to the geographical distribution of heterogeneity and in the fit to the normal mode data sensitive to the upper mantle and lowermost lower mantle there remain however significant discrepancies in amplitude and in the radial distribution of heterogeneity especially near the top of the upper mantle and near the top of the lower mantle the confident use of these models to constrain compositional and dynamical information about the mantle will await the resolution of these discrepancies the factors that may be responsible for the differences in the models and or for the misfit between the observed and predicted normal mode data are divided into two types intrinsic or procedural and extrinsic or structural we discuss only three extrinsic factors at length here including errors in the reference crustal models unmodeled topography on discontinuities in the interior of the mantle and errors in the assumed relationships between shear s and compressional p heterogeneity

upper mantle cross section from tonga to newfoundland a record section of long period u s and canadian observations of multibounce sh waves from a tonga event is used to study lateral variation in the upper mantle source to receiver distances range from 81 to 131 with triplication patterns apparent in s4 for the western north america stations and s5 for the more distant stations a corresponding synthetic section explaining the timing separation and waveform distortions for the various multiple s phases was derived by forward modeling initial trial models consisted of connecting existing pure path models assuming atl old atlantic as an analog for the old pacific tna for the western portion of the united states and sna for the shield portion of north america isovelocity depth contours were constructed to connect these models and corresponding synthetics were computed following a modified wkbj method lateral heterogeneity is found to exist in the upper 350 km of the pacific ocean region and can be modeled reasonably well with a high velocity lid vs 4 7 km s which thickens with increasing oceanic crustal age at the expense of the underlying low velocity zone velocities in the upper 200 km of the older southwest pacific are found to be up to 6 faster than those at comparable depths in the younger tectonic region near western north america the best fitting model indicates that the upper mantle structure of the old pacific is similar to that of the old atlantic although perhaps slightly slower

u pb geochronology and ree geochemistry of zircons from palaeoproterozoic paragneiss clasts in the mesozoic kamiaso conglomerate central japan evidence for an archean provenance abstract sensitive high resolution ion microprobe shrimp u pb analyses of zircons from a pelitic gneiss clast from the jurassic kamiaso conglomerate in central japan show that most grains are 1850 1950 ma but six are 2400 ma including a very old one 3254 14 ma the shrimp data give chronological evidence for previously unrecognized igneous activity from 1850 to 1950 ma the existence of archean zircons allows us to consider the evolutionary history of the archean crust in eastern asia chondrite normalized ree patterns of the individual zircons determined by shrimp show that the 2400 3250 ma zircons have large positive ce and small negative eu anomalies whereas the 1850 1950 ma zircons have small positive ce and significantly negative eu anomalies these differences in the ree abundances for the 2400 3250 and 1850 1950 ma zircons may reflect the composition of the melt that produced the zircons and reveal the possibility of a geological constraint on the origin of kamiaso zircons

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

a three dimensional crustal model of southwest germany derived from seismic refraction data abstract from densely covered seismic refraction data obtained in 1978 urach experiment and 1984 schwarzer zollern wald experiment and from seismic reflection data and results from previous refraction investigations a three dimensional crustal model of southwest germany was derived travel time and amplitude information of seismic refraction data were interpreted with two dimensional forward modeling ray tracing to calculate two crustal cross sections in southwest germany these results fill a gap in the existing data and enabled the construction of a detailed three dimensional crustal model while seismically the upper crust is laterally homogeneous 5 9 6 0 km s throughout the area the middle and lower crust show pronounced lateral variations in thickness velocity and reflectivity the moho is a flat surface at a relatively shallow depth 25 26 km we classify the middle and lower crust of southwest germany into two characteristic crustal types type i consists of a mid crustal low velocity zone 5 4 5 8 km s overlying a thick 10 km high velocity 6 6 6 8 km s lower crust type ii has no prominent mid crustal low velocity zone and a thin

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

azimuthal anisotropy in the earth from observations of sks at geoscope and nars broadband stations abstract we have analyzed observations of low frequency sks waves recorded on horizontal components at several broadband stations of the geoscope and nars arrays splitting of sks is consistently observed and in good agreement with a hypothesis of azimuthal anisotropy due to transverse anisotropy with a horizontal axis in the upper mantle beneath the receivers we have designed an inversion method which takes advantage of observations made simultaneously at different azimuths and which permits us to obtain estimates of the direction of fast axis of anisotropy as well as the time delay between the orthogonal quasi shear waves in general the directions of fast velocity obtained both for stations around the atlantic and around the pacific appear to be related to directions of past and present plate motions

regional dispersion of first order overtone rayleigh waves summary records of the first rayleigh overtone in the 70 110s period range following deep subduction zone events are analysed through standard surface wave techniques to retrieve dispersion characteristics in the oceanic environment our data are in general agreement with published models obtained from regionalization of fundamental rayleigh wave paths a general increase in phase velocity with age is observed with a somewhat smaller effect on group velocities continental and trench area data are processed through a regionalization scheme indicating that the difference between average continental and oceanic velocities both phase and group is about 0 2 km s l at periods of the order of 95 s an investigation of a set of simple models allowing structural heterogeneities between oceans and continents down to variable depth suggests that they probably do not extend past the bottom of the asthenosphere 250 km

evolution of the mesozoic yuljeon basin in south korea and its tectonic implication abstract the mesozoic yuljeon basin yb is a small scale non marine sedimentary basin in the northeastern part of the gyeonggi massif in the korean peninsula the yb consists of two lithostratigraphic units the munamdong and yuljeon formations based on an integrated study of stratigraphy structural geology geochronology and geochemistry major episodes of the yb have been investigated in the late triassic after 227 ma the yb was formed in a tectonic setting wherein crust was extended and uplifted which resulted in deposition of the munamdong formation in the latest early jurassic circa 180 ma the yuljeon formation was deposited in association with volcanic activity in a continental magmatic arc setting on entering the middle jurassic circa 174 ma extension in the yb stopped and then basin inversion occurred due to contractional deformation the middle jurassic thermal pulse in the area generated various scale igneous rocks and induced hydrothermal circulations which created suitable conditions for fault activity with help of fluid pressure this study demonstrates that the yb formed with sedimentation in a post collisional extensional setting related to the songrim orogeny and then it was enlarged with volcanic related sedimentation in a continental arc setting related to the daebo orogeny and lastly it was followed by basin inversion with arc magmatism in the same continental arc setting reflecting the temporal and spatial changes in regional tectonics moreover the general provenance characteristics for the early mesozoic strata in the eastern north china block gyeonggi massif of south korea and southwest japan can be geochronologically correlated the sedimentary rocks record the distinctive tectonothermal histories of east asia such as the middle paleoproterozoic orogens in the eastern north china block the permo triassic continental collision between north and south china blocks and the subduction of paleo pacific plate during the mesozoic

long period love wave overtone data in north america and the pacific ocean new evidence for upper mantle anisotropy abstract two tonga trench earthquakes recorded in north america on wwssn long period instruments have been processed by making use of spatial analysis techniques to retrieve the phase velocities of love wave modes dispersion data up to the third overtone at periods longer than 30 s have been obtained for two broad areas the pacific ocean and north america it is found that the observed love wave phase velocities are not in agreement with the values predicted from the previously published models inferred from rayleigh wave data phase velocity discrepancies as large as 3 4 in the pacific ocean and 2 in north america are observed up to the second overtone preliminary direct computations which have been performed in the framework of transversely isotropic models with the axis of symmetry oriented vertically suggest that the cause for this departure from isotropy probably extends to depths 200 km

the nature and cause of polarization anomalies of surface waves crossing northern and central eurasia summary results of a pilot experiment preliminary to a systematic study of surface wave polarization across eurasia are presented long period fundamental rayleigh and love waves recorded by the broad band seismic stations kiv kislovodsk and obn obninsk of the iris ida network deployed in the former soviet union fsu were analysed from 14 events to the north east east and south east of these stations in search of particle motion anomalies using a technique called frequency time polarization analysis ftpan all anomalies indicate deviations of wave propagation paths to the north relative to the great circle paths polarization anomalies at obn are uniformly small 5 significant frequency dependent polarization anomalies 5 20 are found for rayleigh and love waves arriving at kiv from teleseismic events at a wide range of backazimuths 26 103 polarization measurements are repeatable both for a number of nearly degenerate events and for reciprocal paths and vary smoothly and continuously as epicentral location is moved consequently such measurements are robust and can provide useful structural information the systematics of the frequency dependence of the polarization anomalies as epicentral position is moved from north to south display sensitivity to structures at a number of length scales results from synthetic experiments using coupled normal mode and gaussian beam synthetics reveal that 1 recently constructed long wavelength aspherical models produce polarization anomalies that are significantly smaller 5 at kiv but of the same sign negative as the observed anomalies and 2 the frequency dependence of the observed anomalies must result from a combination of structures of differing wavelengths with scale lengths ranging from regional to global thus polarization measurements provide new information about currently unmodelled structures a model that fits the polarization anomalies observed at kiv includes a regional scale low velocity feature near to kiv in order to fit the large magnitude short period polarization anomalies and a smaller magnitude continent scale increase in upper mantle velocities and or the reduction of crustal thickness from south to north in central eurasia in order to fit the broad band longer period anomalies the small scale low velocity feature is a model of the sedimentary basin of the sub caspian depression we conclude that measurements of polarization anomalies can be obtained accurately that they are reproducible that they contain currently unmodelled information and that they should prove to be useful in combination with velocity and amplitude information in future tomographic inversions especially to help focus global scale models to regional wavelengths

three dimensional radial anisotropic structure of the north american upper mantle from inversion of surface waveform data summary seismic anisotropy provides insight into palaeo and recent deformation processes and there fore mantle dynamics in a first step towards a model for the north american upper mantle with anisotropy characterized by a symmetry axis of arbitrary orientation aimed at filling the gap between global tomography and sks splitting studies we inverted long period waveform data simultaneously for perturbations in the isotropic s velocity structure and the anisotropic parameter v 2 sh v2 in the framework of normal mode asymptotic coupling theory nact the resulting 2 d broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental and higher mode surface waves at the same time to ensure high quality of the retrieved regional upper mantle structure accurate crustal cor rections are essential here we follow an approach which goes beyond the linear perturbation approximation and split the correction into a linear and non linear part the inverted data set consists of more than 40 000 high quality three component fundamental and overtone sur face waveforms recorded at broad band seismic stations in north america from teleseismic events and provides a fairly homogeneous path and azimuthal coverage the isotropic part of our tomographic model shares the large scale features of previous regional studies for north america we confirm the pronounced difference in the isotropic velocity structure between the western active tectonic region and the central eastern stable shield as well as the presence of subducted material juan de fuca and farallon plate at transition zone depths the new regional 3 d radial anisotropic model indicates the presence of two distinct anisotropic layers beneath the cratonic part of the north american continent a deep asthenospheric layer con sistent with present day mantle flow and a shallower lithospheric layer possibly a record of ancient tectonic events

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

saying goodbye to glaciers global glacier volume is shrinking this loss of earth s land ice is of international concern rising seas to which melting ice is a key contributor are expected to displace millions of people within the lifetime of many of today s children but the problems of glacier loss do not stop at sea level rise glaciers are also crucial water sources integral parts of earth s air and water circulation systems nutrient and shelter suppliers for flora and fauna and unique landscapes for contemplation or exploration

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

coarse sediment dynamics in a large glaciated river system holocene history and storage dynamics dictate contemporary climate sensitivity the gravel bedded white river drains a 1279 km2 basin in washington state with lowlands sculpted by continental glaciation and headwaters on an actively glaciated stratovolcano chronic aggradation along an alluvial fan near the river s mouth has progressively reduced flood conveyance in order to better understand how forecasted climate change may influence coarse sediment delivery and aggradation rates in this lowland depositional setting we assessed the contemporary delivery and routing of coarse sediment through the watershed this assessment was based on a rich set of topographic sedimentologic and hydrologic data from the past century with a focus on repeat high resolution topographic surveys from the past decade we found that most of the lower river s contemporary bed load flux originates from persistent erosion of alluvial deposits in the lower watershed this erosion is a response to a drop in local base level caused by a major avulsion across the fan in 1906 and then augmented by subsequent dredging the 1906 avulsion and modern disequilibrium valley profiles reflect landscape conditioning by continental glaciation and a massive mid holocene lahar in the proglacial headwaters infrequent large sediment pulses have accomplished most of the observed coarse sediment export with exported material blanketing downstream valley floors during typical floods transported bed material is largely sourced from erosion of these valley floor deposits throughout the watershed we observe decadal scale coarse sediment dynamics strongly related to the filling or emptying of valley scale sediment storage over 102 104 yr time scales often in response to major disturbances that either emplace large deposits or influence their redistribution paraglacial responses in large watersheds are suggested to be inherently complicated and punctuated as a result of internal landform interactions and stochastic threshold dependent events we argue in combination that holocene disturbance storage dynamics and human flow modification make coarse sediment fluxes in the lower white river relatively insensitive to decadal climate variability results highlight the degree to which river sensitivity to contemporary disturbance climatic or otherwise may be contingent on local and idiosyncratic watershed histories underscoring the need to unpack those histories while demonstrating the utility of watershed scale high resolution topography toward that end

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

climate change river redirected glaciers and ice sheets are retreating in response to climate warming an analysis of drainage patterns of a huge glacier in yukon canada shows that glacier retreat has led to a drastic change in the destination of its meltwater in spring 2016

anisotropic gradients in the upper mantle pn amplitudes in some widely spaced sets of orthogonal marine refraction lines on young oceanic crust are greater in the fast direction than in the slow direction this is inconsistent with the predicted amplitude behavior for simple head waves but can be explained by an increase in anisotropy with depth it appears that these gradients are due to increasing olivine crystal orientation although changes in the relative abundance of two anisotropic minerals without variable tectonization could also account for the observations depth variation of tectonization most probably indicates very high temperature gradients at the moho this would imply a substantial amount of convective heat transport in the whole oceanic crust near mid ocean rises

3800 to 2500 ma crustal evolution in the anshan area of liaoning province northeastern china shrimp u pb zircon geochronology has revealed several generations of granitoids and gneisses from the anshan area of northeastern china two samples of the baijiafen granite sensu lato 3804 5 and 3812 4 ma chentaigou granite 3306 13 ma lishan granite 3142 7 ma east and west anshan granites 3001 4 and 2994 8 ma tiejiashan granite 2962 4 and 2964 6 ma and qidashan granite 2475 ma the 3800 ma baijiafen granite consists of banded migmatitic trondhjemitic gneisses and forms only a small part of the area nonetheless they are the oldest known rocks in asia and are one of very few locations in the world where rocks of this antiquity have been found the younger suites are predominantly granite sensu stricto in composition and although foliated they have not been transformed into banded gneisses nd isotopic data suggest that the 3800 ma granites were produced at least in part by remelting of very ancient lree enriched sources perhaps like the exposed remnants of the 3800 ma rocks the chentaigou supracrustals contain layered mafic and ultramafic rocks banded iron formation bif and siliceous layered rocks of probable volcanogenic origin a sample of the latter has yielded a concordant u pb zircon age of 3362 5 ma interpreted as the age of deposition a trondhjemitic sheet cutting these rocks has yielded a u pb zircon age of 3342 6 ma the chentaigou supracrustals are the oldest recognised in the area younger supracrustal sequences collectively known as the anshan group contains the main economic bif units in the area bif is intruded by the 2475 ma qidashan granite indicating that the anshan group is archaean or earliest proterozoic in age

quaternary drainage evolution of the datong river qilian mountains northeastern tibetan plateau china abstract drainage basins are useful recorders of tectonics and climate the datong river which drains the qilian mountains china is one of the most elongated river basins of the world how this unusual basin configuration was established remains unknown despite this area being ideal for assessing the controlling effects of tectonics and climate on the drainage evolution in this study we reconstruct the history of the drainage evolution of the datong river using integrated provenance methods u pb dating heavy mineral and gravel compositions and river terrace dating the drainage system of the modern datong river began to form at 1100 ka and the drainage basin was limited to the area of the lower modern datong river since then it has gradually extended through headward erosion the river channelized into the menyuan basin between 620 ka and 420 ka and it captured the upper datong river between 130 ka and 60 ka we suggest that the rapid uplift of the qilian mountains disrupted and longitudinally deflected the transverse rivers over the past 1100 ka additionally intensified precipitation and glacial meltwater enhanced the river incision and captured the middle and upper datong river during 620 420 ka and 130 60 ka respectively this model shows that the direction of drainage pattern evolution is controlled by tectonics and that the timing of drainage reorganization is controlled by climate change in the active fold thrust belt

seismic anisotropy within the uppermost mantle of southern germany summary this paper presents an updated interpretation of seismic anisotropy within the uppermost mantle of southern germany the dense network of reversed and crossing refraction profiles in this area made it possible to observe almost 900 traveltimes of the p phase that could be effectively used in a time term analysis to determine horizontal velocity distribution immediately below the moho for 12 crossing profiles amplitude ratios of the p phase compared to the dominant crustal phase were utilized to resolve azimuthally dependent velocity gradients with depth a p wave anisotropy of 3 4 per cent in a horizontal plane immediately below the moho at a depth of 30 km increasing to 11 per cent at a depth of 40 km was determined for the axis of the highest velocity of about 8 03 kms at a depth of 30 km a direction of n31 e was obtained the azimuthal dependence of the observed p amplitude is explained by an azimuth dependent sub moho velocity gradient decreasing from 0 06 s in the fast direction to 0 s in the slow direction of horizontal p wave velocity from the seismic results in this study a petrological model suggesting a change of modal composition and percentage of oriented olivine with depth was derived

early proterozoic granulites in central korea tectonic correlation with chinese cratons abstract a coherent granulite complex has been discovered in the central part of the korean peninsula formerly regarded as the eastern imjingang belt this granulite complex hwacheon granulite complex hgc experienced two cycles of tectonometamorphic events the first event corresponded to crustal thickening followed by peak granulite facies metamorphism and associated partial melting the quasi isobaric cooling path suggested by the occurrences of secondary garnet mantling orthopyroxene and secondary kyanite in mafic and pelitic granulites respectively indicates substantial residence time at midcrustal levels prior to exhumation of the hgc the timing of peak metamorphism was dated from the unzoned overgrowth rims on zircons in a migmatitic granulite at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra