tectonic evolution of the qinling orogenic belt central china new evidence from geochemical zircon u pb geochronology and hf isotopes abstract the qinling orogenic belt qob located between the north china craton ncc and the yangtze craton yzc is composed of the northern qinling belt nqb and the southern qinling belt sqb this study presents new geochemical data zircon u pb ages and hf isotopes from a suite of metamorphic rocks from the kuanping qinling danfeng douling and wuguan groups in the nqb and the sqb our results suggest that the qinling group in the nqb formed in an active continental margin related to the subduction of the songshugou ocean under the southern ncc during grenvillian period the kuanping group in the northern nqb was deposited in the within plate extension basin during late neoproterozoic to early paleozoic the detritus of sedimentary rocks of the kuanping group were mainly sourced from the nqb and subordinately from the basement rocks of the ncc the danfeng group in the southern nqb formed later than 827 ma with the sediments derived mainly from the qinling terrane the nqb witnessed multiphase tectono thermal events from mesoproterozoic to early paleozoic including several magmatic events and the early paleozoic metamorphic event the original douling group in the sqb represents the basement complex of the sqb which is composed of rocks with different formation ages the oldest rock in the complex is represented by 3 0 ga granitic gneiss which underwent at least two periods of metamorphism at 2 5 ga and 0 97 0 91 ga in this study the douling group is redefined as a suite of neoproterozoic 860 750 ma rocks formed in an extensional setting after the subduction of the songshugou ocean the wuguan group in the sqb formed in the middle late neoproterozoic later than 740 ma and was subjected to early paleozoic metamorphism our data indicate that the sqb experienced early neoproterozoic 970 865 ma and early paleozoic 444 ma metamorphism and strong middle neoproterozoic 870 730 ma magmatism the age spectra of zircons from the nqb trace major tectono thermal events at 1462 ma 927 ma and 412 ma which are different from those recorded in the southern ncc and northern yzc suggesting that the nqb had a distinct evolution during mesoproterozoic to early neoproterozoic grenvillian the hf isotopic compositions of zircons from the various rocks suggest that the nqb probably developed on the basement of the southern ncc the rocks in the sqb show zircon age spectra and hf isotope compositions similar to those in the northern yzc suggesting a close affinity we therefore interpret the sqb to have developed on the basement of the northern yzc integrating the new data in this study with those from previous works we propose a new tectonic model for the formation and evolution of the qob during late mesoproterozoic to early paleozoic involving the following major events 1 late mesoproterozoic to early neoproterozoic grenvillian northward subduction of the songshugou ocean 2 early middle neoproterozoic 870 800 ma bidirectional subduction and collision 3 middle neoproterozoic 800 710 ma post collision extension 4 middle late neoproterozoic 710 600 ma within plate extension 5 late neoproterozoic early paleozoic 600 520 ma opening of the shangdan ocean and 6 early paleozoic 520 420 ma subduction collision we thus trace at least two distinct wilson cycles in the qob

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

initiation and displacement of landslide induced by earthquake a study of shaking table model slope test landslide researches often focus on factor of safety critical acceleration and displacement for an earthquake induced landslide the initiation and displacement of the landslide were important factors for definition of failure in this research the shaking table model slope test is adopted for study of slope failure initiation based on analyses of limit equilibrium particle image velocimetry piv analysis and acceleration time history recorded within the model slope based on the analyses landslide initiation could be defined as surface and local movement of the slope slope failure could be defined based on the massive movement of the slope the piv analysis provides good information for identifying both surface movement and massive movement the landslide displacement determined from the slope movement provides consistent results compared to observed displacements

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

the grenvillian songshugou ophiolite in the qinling mountains central china implications for the tectonic evolution of the qinling orogenic belt abstract the qinling mountains in central china mark a gigantic composite orogenic belt with a complex tectonic evolution involving multiple phases of rifting and convergence this belt separates the north china and south china blocks and consists of the south and north qinling terranes separated by the shangdan suture the suture is marked by the grenvillian songshugou ophiolite along the southern margin of the north qinling terrane which is key to understanding the proterozoic tectonic evolution of the belt the ophiolite consists of highly metamorphosed ultramafic and mafic rocks three groups of meta basalts are present group 1 rocks are lree depleted and have a morb compositional affinity their low ta yb ratios 0 12 and display slight enrichment of lree suggesting that the original magmas were derived from a depleted mantle source mixed with some enriched material samples from group 3 are enriched in lree and other incompatible elements ti zr ta nb suggesting derivation from an enriched mantle source possibly a plume all the basalts have high end t 4 2 to 6 9 variable esr t and high 207pb 204pb and 208pb 204pb ratios for given 206pb 204pb ratios these characteristics are compatible with formation at a mid ocean ridge system above an anomalous dupal mantle region the mafic rocks have a sm nd whole rock isochron age of 1030 46 ma the songshugou ophiolite was emplaced onto the southern margin of the north qinling terrane an active continental margin from the meso proterozoic to neo proterozoic

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

isotopic balance of the greenland ice sheet modelled concentrations of water isotopes from 30 000 bp to present abstract polar ice cores contain a complex record of climate and ice flow that can be used to decode climate history interpretation of ice core records requires the flow signature to be either simple or removable when the signature is complex computer modelling can become a powerful aid to interpretation by combining an ice dynamics model with tracer deposition and transport models the stratification of individual tracers can be calculated in this way the time evolving three dimensional chemical stratigraphy can be simulated by linking an ice tracer dynamics model with models of atmosphere and ocean tracer dynamics coupled models of the global geochemical cycling of water isotopes can be developed such models hold promise for an integrated interpretation of the marine and ice core climate records as a first step along this path we apply tracer transport modelling to simulate the temporal and spatial variations of water isotopes in the greenland ice sheet over the past 30 000 years and calculate the influence of greenland ice volume and isotopic chemistry on the isotopic content of the ocean we find that the greenland ice sheet maintained its maximum ice volume from 18 000 to 15 000 bp but was isotopically lightest at 11 000 bp the sea level equivalent of ice volume changes occurring over the past 30 000 years did not exceed 2 1 m and the volume averaged influence on ocean chemistry did not exceed 0 025 for 18 o and 0 20 for d and at the last glacial maximum taken as 21 000 bp these values were respectively 1 9 m for ice volume 0 022 for 18 o and 0 17 for d

a shaking table model test on a rock slope anchored with adaptive anchor cables abstract to determine the load transfer mechanism and dynamic response characteristics of an adaptive anchor cable aac equipped with a mechanical energy dissipation device a shaking table model test was conducted on rock slope test models anchored with a system consisting of several aacs that were fabricated based on a landslide mass in xiangjiapo during the test the strain of the aac structure and the dynamic response of the slope model were monitored to determine the anchoring mechanism of the aac system and the dynamic characteristics of the aac system anchored slope model the sliding sleeve energy dissipation device of the aac automatically adjusted its tension or deformation to allow its deformation to be consistent with that of the rock and earth mass thereby buffering the impact at the instant of the start of seismic loading the constant sliding resistance of the aac determined its working conditions under a certain seismic loading condition when the constant sliding resistance was set excessively high the energy dissipation device was ineffective under the seismic loading when the constant sliding resistance was set too small the aac slid at the instant of the start of seismic loading however when the constant sliding resistance and the sliding distance were set to proper values the aac slid gradually in a stepwise motion and its peak strain was significantly lower the test results can be used as a reference for designing cut slopes in regions of high seismicity and in selecting anti seismic engineering measures for these slopes

ice volume and subglacial topography for western canadian glaciers from mass balance fields thinning rates and a bed stress model abstracta method is described to estimate the thickness of glacier ice using information derived from the measured ice extent surface topography surface mass balance and rate of thinning or thickening of the ice column shear stress beneath an ice column is assumed to be simply related to ice thickness and surface slope as for an inclined slab but this calculation is cast as a linear optimization problem so that a smoothness regularization can be applied assignment of bed stress is based on the flow law for ice and a mass balance calculation but must be preceded by delineation of the ice flow drainage basin validation of the method is accomplished by comparing thickness estimates to the known thickness generated by a numerical ice dynamics model once validated the method is used to estimate the subglacial topography for all glaciers in western canada that lie south of 60 n adding the present ice volume of each glacier gives the estimated total volume as 2320 km3 equivalent to 5 8 mm of sea leve

characteristics of the landslide dams induced by the 2008 wenchuan earthquake and dynamic behavior analysis using large scale shaking table tests abstract the ms 8 0 wenchuan earthquake triggered at least 257 landslide dams more than 300 aftershocks with the magnitudes higher than ms 4 0 occurred after the formation of these landslide dams which might largely influence the structure and soil properties of these dams this paper aims to comprehensively investigate the characteristics of the landslide dams induced by the 2008 wenchuan earthquake and study the dynamic behaviors of the landslide dams under aftershocks using large scale shake table tests first the characteristics of the landslide dams including the distribution geometric parameters stability and longevity mitigation measures and the influence of the aftershocks are proposed then two groups of shaking table tests to simulate the dynamic behaviors of two types of landslide dams under aftershocks are illustrated one with quartz sand contained 10 kaolin dam i and the other with quartz sands all dam ii finally the results of the tests including the acceleration distribution dam deformation and dam breaching process are discussed through this study it is found that the landslide dams caused by high magnitude earthquakes have distinctive characteristics which may largely influence the stability breach process and risks of these dams in the model tests the accelerations are generally higher on the surface of the dams either on the crest or on the both upstream and downstream slopes the dam i was prone to settlement and cracking the aftershocks may not directly trigger the failures of landslide dams but accelerate the overtopping failures by lowering the dam crest with settlement and cracking

stable isotope pattern predicted in surge type glaciers the distribution pattern of stable isotope ratio 18o in cold glaciers ice streams and ice sheets has the potential to reveal past changes in flow rate for example those associated with surges in this study we use a time dependent numerical model of ice flow to establish that each surge creates a stratigraphic horizon across which 18o is discontinuous two plausible relations between glacier geometry and 18o in snowfall allow us to bracket the expected magnitude of this isotopic signal these stratigraphic markers could be located by 18o analysis of a longitudinal series of ice cores or by detailed longitudinal sampling of exposed ice calculations for a model with characteristics resembling those of steele glacier yukon territory showed that at most three stratigraphic markers could be detected at any one time the discontinuities in 18o were as large as 0 8 this is an order of magnitude larger than mass spectrometer precision but comparable to observed background noise at steele glacier

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

landslides triggered by the 20 april 2013 lushan earthquake sichuan province china abstract the 20 april 2013 lushan earthquake with a magnitude of m s 7 0 induced widespread landsliding along the southern segment of the longmen shan fault zone this paper presents a preliminary analysis of the characteristics of these co seismic landslides triggered in an area of 13 323 km 2 a total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the lushan earthquake to facilitate the more detailed analysis on the areal frequency of co seismic landslides as polygons we selected an area of 732 km 2 around the epicenter that had the highest density of co seismic landslides the sizes of the landslides are in general much smaller than those that were triggered by the 2008 wenchuan earthquake the most common types of landslides in the study area were rock falls and shallow disrupted landslides from steep slopes which typically involved the top few meters of weathered bedrock and colluvium in this study the relation between the landslide distribution and five main factors was analyzed fault proximity epicenter proximity peak ground acceleration pga slope angle and lithology our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault and the highest landslide concentration is located within a distance of 5 km regarding the distance to the epicenter the largest landslide density is found at a distance between 5 and 10 km the landslide concentration also increases with increasing slope angle until a maximum for the slope class 45 55 in addition results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co seismic landslides in this study we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution this is in contradiction to what has been reported in other earthquake areas such as the wenchuan area

episodic growth of the gondwana supercontinent from hafnium and oxygen isotopes in zircon it is thought that continental crust existed as early as 150 million years after planetary accretion but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records for example the striking global peaks in juvenile igneous activity 2 7 1 9 and 1 2 gyr ago imply rapid crustal generation in response to the emplacement of mantle super plumes rather than by the continuous process of subduction yet uncertainties persist over whether these age peaks are artefacts of selective preservation and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle these model ages are only meaningful if the host magma lacked a mixed or sedimentary source component but the latter can be diagnosed by oxygen isotopes which are strongly fractionated by rock hydrosphere interactions here we report the first study that integrates hafnium and oxygen isotopes all measured in situ on the same precisely dated detrital zircon grains the data reveal that crust generation in part of gondwana was limited to major pulses at 1 9 and 3 3 gyr ago and that the zircons crystallized during repeated reworking of crust formed at these times the implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts

response of glacier flow and structure to proglacial lake development and climate at fjallsjokull south east iceland over recent decades the number of outlet glaciers terminating in lakes in iceland has increased in line with climate warming the mass balance changes of these lake terminating outlet glaciers are sensitive to rising air temperatures due to altered glacier dynamics and increased surface melt this study aims to better understand the relationship between proglacial lake development climate glacier dynamics and glacier structure at fjallsjokull a large lake terminating outlet glacier in south east iceland we used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016 and a combination of aerial and satellite imagery to map the structural architecture of the glacier s terminus in 1982 1994 and 2011 the temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001 2009 and 2011 our surface velocity and structural datasets revealed the development of localised flow corridors over time which conveyed relatively faster flow towards the glacier s terminus we attribute the overall changes in dynamics and structural architecture at fjallsjokull to rising air temperatures but argue that the spatial complexities are driven by glacier specific factors such as basal topography

fracture propagation as means of rapidly transferring surface meltwater to the base of glaciers 1 propagation of water filled crevasses through glaciers is investigated based on the linear elastic fracture mechanics approach a crevasse will penetrate to the depth where the stress intensity factor at the crevasse tip equals the fracture toughness of glacier ice a crevasse subjected to inflow of water will continue to propagate downward with the propagation speed controlled primarily by the rate of water injection while the far field tensile stress and fracture toughness determine where crevasses can form once initiated the rate of water driven crevasse propagation is nearly independent of these two parameters thus rapid transfer of surface meltwater to the bed of a cold glacier requires abundant ponding at the surface to initiate and sustain full thickness fracturing before refreezing occurs

eclogite origin and timings in the north qinling terrane and their bearing on the amalgamation of the south and north china blocks the amalgamation of south scb and north china blocks ncb along the qinling dabie orogenic belt involved several stages of high pressure hp ultra high pressure uhp metamorphism the new discovery of uhp metamorphic rocks in the north qinling nq terrane can provide valuable information on this process however no precise age for the uhp metamorphism in the nq terrane has been documented yet and thus hinders deciphering of the evolution of the whole qinling dabie sulu orogenic belt this article reports an integrated study of u pb age trace element mineral inclusion and hf isotope composition of zircon from an eclogite a quartz vein and a schist in the nq terrane the zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning high th u and 176lu 177hf ratios pronounced eu anomalies and steep heavy rare earth element hree patterns the zircon cores yield an age of 796 13 ma which is taken as the protolith formation age of the eclogite and implies that the nq terrane may belong to the scb before it collided with the ncb the hf t values vary from 11 3 to 3 2 and corresponding two stage hf model ages are 2402 to 1495 ma suggesting the protolith was derived from an enriched mantle in contrast the metamorphic zircon rims show no zoning or weak zoning very low th u and 176lu 177hf ratios insignificant eu anomalies and flat hree patterns they contain inclusions of garnet omphacite and phengite suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions and their weighted mean 206pb 238u age of 485 9 3 8 ma was interpreted to date the timing of the eclogite facies metamorphism zircon in the quartz vein is characterized by perfect euhedral habit some oscillatory zoning low th u ratios and variable hree contents it yields a weighted mean u pb age of 480 5 2 5 ma which registers the age of fluid activity during exhumation zircon in the schist is mostly detrital and u pb age peaks at c 1950 to 1850 1800 to 1600 1560 to 1460 and 1400 to 1260 ma with an oldest grain of 2517 ma also suggesting that the nq terrane may have an affinity to the scb accordingly the amalgamation between the scb and the ncb is a multistage process that spans c 300 myr which includes the formation of the erlangping intra oceanic arc zone onto the ncb before c 490 ma the c 485 ma crustal subduction and uhp metamorphism of the nq terrane the c 430 ma arc continent collision and granulite facies metamorphism the 420 to 400 ma extension and rifting in relation to the opening of the palaeo tethyan ocean the c 310 ma hp eclogite facies metamorphism of oceanic crust and associated continental basement and the final 250 to 220 ma continental subduction and hp uhp metamorphism

slow surge of trapridge glacier yukon territory canada 1 trapridge glacier a polythermal surge type glacier located in the st elias mountains yukon territory canada passed through a complete surge cycle between 1951 and 2005 air photos 1951 1981 and ground based optical surveys 1969 2005 are used to quantify the modifications in flow and geometry that occurred over this period yearly averaged flow records suggest that the active phase began 1980 and lasted until 2000 the average velocity in the central area of the glacier went from 16 m yr 1 in 1974 to 39 m yr 1 in 1980 it peaked at 42 m yr 1 in 1984 and remained above 25 m yr 1 until 2001 over that interval the flow decelerated by steps in 4 year pulses after a particularly vigorous acceleration in 1997 1999 the glacier gradually slowed to presurge velocities in 2005 the flow was less than 9 m yr 1 digital elevation models are generated by stereographic analysis of air photos for 1951 1970 1972 1977 and 1981 these models are updated annually using ground based survey data and a novel implementation of bayesian kriging over the course of the surge the front of active ice advanced 450 m and the glacier area increased by 10 with an associated thinning of the ice the previous surge of trapridge glacier starting before 1939 and ending before 1951 led to a terminus advance of 1 km comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s and switched to a faster flow mode after 1941 this second phase was never attained in the recent surge probably owing to a lack of mass

tracer transport in the greenland ice sheet constraints on ice cores and glacial history the climate history and dynamics of the greenland ice sheet are studied using a coupled model of the depositional provenance and transport of glacier ice allowing simultaneous prediction of the detailed isotopic stratigraphy of ice cores at all the major greenland sites adopting a novel method for reconstructing the age depth relationship we greatly improve the accuracy of semi lagrangian tracer tracking schemes and can readily incorporate an age dependent ice rheology the larger aim of our study is to impose new constraints on the glacial history of the greenland ice sheet leading sources of uncertainty in the climate and dynamic history are encapsulated in a small number of parameters the temperature and elevation isotopic sensitivities the glacial interglacial precipitation contrast and the effective viscosity of ice in the flow law comparing predicted and observed ice layering at ice core sites we establish plausible ranges for the key model parameters identify climate and dynamic histories that are mutually consistent and recover the past depositional elevation of ice cores to ease interpretation of their climatic records with the coupled three dimensional model of ice dynamics and provenance transport we propose a method to place all the ice core records on a common time scale and use discrepancies to adjust the reconstructed climate history analysis of simulated grip ice layering and borehole temperature profiles confirms that the grip record is sensitive to the dynamic as well as to the climatic history but not enough to strongly limit speculation on the state of the greenland ice sheet during the eemian in contrast our study indicates that the dye 3 and camp century ice cores are extremely sensitive to ice dynamics and greatly constrain eemian ice sheet reconstructions we suggest that the maximum eemian sea level contribution of the ice sheet was in the range of 3 5 4 5 m

conditions for bubble elongation in cold ice sheet ice highly elongated bubbles are sometimes observed in ice sheet ice elongation is favored by rapid ice deformation and opposed by diffusive processes we use simple models to show that vapor transport dominates diffusion except possibly very close to the melting point and that latent heat effects are insignificant elongation is favored by larger bubbles at pore close off but is nearly independent of bubble compression below close off the simple presence of highly elongated bubbles indicates only that a critical ice strain rate has been exceeded for significant time and provides no information on possible disruption of stratigraphic continuity by ice deformation

stability analysis of three dimensional seismic landslides using the rigorous limit equilibrium method abstract in this paper a new method combining the rigorous limit equilibrium method and the pseudo dynamic method is proposed to investigate stability of 3d seismic landslides in which the force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied moreover sinusoidal cosinusoidal wave is applied to simulate earthquake displacement and an amplification factor of peak seismic acceleration is referred to as the amplification of seismic wave when it propagates from the bottom to the top of landslides the pseudo dynamic factor of safety of 3d seismic landslides is determined using trust region reflective iterative algorithm the effects of the parameters of the seismic landslides on the stability are analyzed by the bp neural network algorithm in which a database to investigate the stability of 3d seismic landslides is established in addition the stability of donghekou landslide is studied to verify the accuracy and precision of the present method

structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard hambrey michael murray t glasser n f hubbard a 2005 structure and changing dynamics of a polythermal valley glacier on a centennial timescale midre lovenbreen svalbard journal of geophysical research 110 pp 1 19 rae2008

the meta gabbroic complex of fushui in north qinling orogen a case of syn subduction mafic magmatism abstract sims zircon geochronology and oxygen isotopes as well as la icpms zircon lu hf isotopic analyses were carried out on a suite of rocks from the fushui complex to probe its origin and tectonic significance for the evolution of the qinling group in the north qinling orogenic belt the fushui complex comprises several phases of meta gabbros the dominant rock type is light colored meta gabbro followed by mica bearing and dark colored meta gabbros with abundant dark gabbroic enclaves with different sizes and shapes and occasional occurrence of mica bearing gabbroic pegmatite dikes age determination shows that the magmatic intrusion began at about 500 ma and surged at 490 480 ma with the latest zircon crystallized at about 476 ma this age spectrum is remarkably coeval with the peak metamorphism 500 480 ma of the surrounding qinling group metamorphic rocks dated by zircons from eclogites retrograded eclogites hp mafic granulites and uhp felsic gneisses representing syn subduction mafic magmatism these late cambrian to early ordovician zircons display a slightly enriched hf isotopic feature with a limited range in ehf t 5 to 2 and yield uniform tdm age 1 15 1 38 ga they also show a relatively small variation in 18o 6 69 0 44 2 8 75 0 34 2 much higher than the normal mantle value the isotopic feature suggests that the fushui complex was originally derived from enriched lithospheric mantle which was metasomatized by melts from ancient continental sediments and altered morb basalts the carboniferous zircons dominantly occurring as rims of early ordovician cores display very similar hf tdm ages 1 19 1 27 ga and oxygen isotopes as their counterparts corresponding to their recrystallization at 335 ma during amphibolite facies metamorphism when exhumed our study on the fushui complex together with the recently reported zircon u pb age data on the surrounding hp uhp metamorphic rocks demonstrates that the qinling group preserves a complete cycle of tectonic evolution in an orogenic belt from an oceanic basin spreading and mini continent formation to deep subduction of mini continent and multiple stage exhumations