middle miocene ocean climate transition high resolution oxygen and carbon isotopic records from deep sea drilling project site 588a southwest pacific high resolution stable isotopic records are presented for the epi benthic foraminifer cibicidoides the inferred shallow dwelling planktonic globigerinoides quadrilobatus and the inferred deep dwelling planktonic globoquadrina dehiscens from the middle miocene 16 12 ma of deep sea drilling project site 588a lord howe rise southwest pacific high resolution multiple species oxygen and carbon isotopic data define the timing and character of the well known middle miocene climatic oceanographic transition with a resolution comparable to quaternary records the benthic foraminiferal 18o record is marked by several large fluctuations from 16 to 14 8 ma followed by a series of rapid 50 kyr 18o increases that suggest a new state of the ocean climate system after 14 8 ma the total middle miocene benthic oxygen isotopic increase of 1 2 is largely incorporated in two steps an increase of 0 8 from 14 5 to 14 0 ma and a second increase of 0 7 from 13 45 to 12 45 ma each step is comprised of a series of marked 18o increases indicative of rapid east antarctic ice sheet growth and contemporaneous deepwater cooling a strong covariance of 0 7 between the benthic and deep dwelling planktonic species from 14 5 to 14 0 ma including a rapid increase from 14 1 to 14 05 ma suggests a 0 7 increase in the 18o composition of seawater 18osw because of east antarctic ice sheet growth comparison of the 18o record of gs quadrilobatus suggests that surface waters warmed at this site by 3 c from 14 1 to 13 6 ma carbon isotopic time series for each species generally covary throughout the early to middle miocene interval 16 12 ma confirming that 13c variations in this interval largely represent reservoir changes high resolution 13c data allow improved resolution of the latter five of six 13c maxima within the well known early to middle miocene carbon isotopic excursion the monterey carbon isotopic excursion from 17 0 to 13 5 ma this is useful for global correlation the last of these maxima ends with a 1 decrease centered from 13 9 to 13 7 ma 300 kyr after the 18o increase considered to reflect east antarctic ice growth covariance between benthic 18o and 13c from 16 to 13 8 ma suggests a sensitive relation between global carbon cycling and the ocean climate system prior to 13 8 ma episodic increases in organic carbon burial may have contributed to deep sea benthic 13c maxima and synchronous global cooling the positive relationship ended at 13 8 ma indicative of changing relations between global carbon cycling and the ocean climate system brought on by the increased stability of the east antarctic ice sheet after a major growth phase from 14 5 to 14 0 ma

complete dynamic modeling calibration for the thurwieser rock avalanche italian central alps abstract few rock avalanches have been witnessed and no exact real time description is available the 2 5 m m 3 punta thurwieser rock avalanche september 2004 italian central alps is a unique event for which many quantitative observations have been gathered this is the first case ever of a natural rock avalanche being recorded on video and for which an almost exact value of the total time duration from initial detachment to final deposition is available the landslide travelled over 2 9 km from its source partially in a glacial environment the initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos the mean front velocities along the path have been estimated from the video the final geometry and the characteristics of the deposit have been obtained by gps measurements aerial photos field surveys and laboratory tests a quasi 3d continuum dynamic analysis of the landslide motion has been performed assuming both a voellmy and a frictional rheology in the model dan 3d for the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters together with the final shape and thickness of the deposit and its developing extension the dynamic flow resistance parameters initially calibrated with dan were adopted and validated in dan 3d showing good consistency they are consistent with the existing database for calibrated landslides of similar type and scale flow velocities on the path segment underlain by glacial deposits up to 55 65 m s 1 are more accurately predicted by adopting a frictional rheology up to 50 55 m s 1 with zero pore pressure and a 26 friction angle than by a voellmy rheology up to 40 45 m s 1 both observations and modelling show that glacial ice plays a substantial role in increasing the rock avalanche mobility

eccentricity paced monsoon like system along the northwestern tethyan margin during the valanginian early cretaceous new insights from detrital and nutrient fluxes into the vocontian basin se france high resolution changes in terrigenous and nutrient fluxes into the vocontian basin northwestern tethyan margin were investigated for the late berriasian late valanginian time interval in order to assess the precipitation patterns in the source areas and to evaluate the effect of orbital forcing on the strength of the hydrological cycle in this study new high resolution mineralogical bulk rock and clay fraction and geochemical phosphorus and oxygen isotope data are used from the astronomically calibrated orpierre section for the first time kaolinite detrital and phosphorus accumulation rates kar dar and par are calculated and compared to a set of 547 geochemical and 260 mineralogical published data from other vocontian sections it appears that three regional increases in the kar document three successive humid episodes during the valanginian this is confirmed by contemporaneous increases in dar and partly also in par which highlight higher terrigenous and nutrient fluxes to the vocontian basin during these episodes concomitant decreases in the 18owhole rock signals may reflect higher sea surface temperatures during the early valanginian and the early late valanginian transition the occurrence of the three humid episodes is interpreted to relate to an orbital paced monsoonal circulation pattern through seasonally reversing movements of air mass heat and precipitation over the northwestern tethyan margin in particular based on the correlation between the 405 kyr eccentricity cycles and the kar signal obtained at orpierre an eccentricity influenced monsoonal circulation is proposed as the possible forcing factor behind these climatic patterns the average duration between the climaxes of the three regional wetter episodes is approximately 2 43 myr the wetter and likely also warmer episode at the early late valanginian transition is in step with the onset of the weissert episode in this regard the intensification of monsoonal driven precipitations appears as a possible external forcing factor leading or at least accelerating the important perturbation in the global carbon cycle associated with the weissert episode

recent mass movement processes on the ebro continental slope nw mediterranean abstract mass movement is an important process controlling the sedimentary structure and growth patterns of the ebro continental slope during recent time at least quaternary about 37 of the slope surface is affected by mass movement features which are variable in distribution size and morphology the northern and central sectors are mainly affected by erosive canyons with gullies on their upper courses and massive and chaotic slump bodies on the middle and lower courses the southern sector is mainly affected by large scale slides 10 km and debris flow deposits in the three sectors the slope is also locally affected by small scale slides

zircon petrochronology reveals the temporal link between porphyry systems and the magmatic evolution of their hidden plutonic roots the eocene coroccohuayco deposit peru abstract we present zircon geochronologic la icpms and id tims trace element and hf isotopic evidence for a complex evolution of the plutonic roots of the eocene coroccohuayco porphyry system southern peru la icpms u pb dating has initially been carried out to optimize grain selection for subsequent high precision id tims dating and to characterize crustal assimilation xenocrystic cores this combined in situ and whole grain u pb dating of the same grains has been further exploited to derive a robust temporal interpretation of the complex magmatic system associated with the coroccohuayco porphyry skarn deposit our data reveal that a heterogeneous gabbrodioritic complex was emplaced at ca 40 4 ma and was followed by a nearly 5 ma long magmatic lull until the emplacement of dacitic porphyry stocks and dykes associated with the mineralizing event at ca 35 6 ma however at the sample scale zircons from the porphyries provide insight into a 2 ma long lived hidden magmatism probably at 4 9 km paleodepth prior to porphyry intrusion and mineralization for which no other evidence can be found on the surface today these dates together with zircon trace element analysis and hf isotopes argue for the development of a long lived magmatic system dominated by amphibole fractionation with an increasing amount of crustal assimilation and the development of a large and sustained thermal anomaly the system was probably rejuvenated at an increasing rate from 37 5 to 35 6 ma with injection of fresh and oxidized magma from the lower crust which caused cannibalism and remelting of proto plutons the porphyry intrusions at coroccohuayco were emplaced at the peak thermal conditions of this upper crustal magma chamber which subsequently cooled and expelled ore fluids zircon xenocrysts and hf isotopes in the porphyritic rocks suggest that this large upper crustal system evolved at stratigraphic levels corresponding to triassic sediments similar to the mitu group that may be present below the district using the zircon ce anomaly as a proxy for oxidation state of the magma through time we show that the high oxidation state of the porphyries is not the result of upper crustal processes but is rather controlled by magmatic processes occurring at deeper levels a comparison of our data with available high precision geochronologic data at other porphyry systems suggests that such deposits may form when injection rate volume and heat of their long lived upper crustal magmatic system reach their peaks these features might be diagnostic of a productive deposit

correlating the end triassic mass extinction and flood basalt volcanism at the 100 ka level new high precision u pb geochronology from volcanic ashes shows that the triassic juras sic boundary and end triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the central atlantic mag matic province to 150 ka this narrows the correlation between volcanism and mass extinc tion by an order of magnitude for any such catastrophe in earth history we also show that a concomitant drop and rise in sea level and negative 13 c spike in the very latest triassic occurred locally in 290 ka such rapid sea level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end triassic extinction and potentially driven by central atlantic magmatic province volcanism

a new method integrating high precision u pb geochronology with zircon trace element analysis u pb tims tea increased precision in isotope dilution thermal ionization mass spectrometry id tims u pb geochronology has revealed age complexities in zircon populations that require new tools for understanding how the growth of zircon is related to geologic processes u and pb are routinely separated from other elements in dated minerals by ion exchange separation prior to tims isotope measurement we develop a method in which trace elements in the exact same volume of zircon are redissolved and analyzed using solution nebulization inductively coupled plasma sector field mass spectrometry with matrix matched external liquid calibration using 0 5 ml solution resulting concentrations are between 1 ppt for elements such as ti nb and ta and tens of ppb for zr by analyzing a series of standard solutions zircons and procedural blanks we show that accurate measurements are performed on zr hf y sc and the hree while low concentration elements can be measured accurately to 5 ppt we performed combined u pb id tims geochronology with trace element analysis here called u pb tims tea on zircons from eight volcanic rocks comprising several volcanic systems and one metamorphic sample similar to previous in situ trace element analyses zircon geochemistry is distinct between different samples and records petrogenetic processes such as fractional crystallization assimilation and or magma mixing unique from in situ analysis u pb tims tea can trace geochemical evolution in accessory minerals with adequate age precision to resolve magmatic processes in rocks at least 200 million years old this provides a means to identify auto ante and xenocrystic zircon and lead to more robust age interpretations in id tims u pb geochronology one suite of cretaceous andesitic zircons shows correlations in geochemistry and absolute time that record evolution of a magmatic system over 250 ka prior to eruption future work will combine u pb tims tea with solution isotopic analysis of nd sr and hf and will be applied to a host of datable minerals such as monazite sphene apatite rutile xenotime and baddeleyite these combined tools will provide access to an improved understanding of a wide range of igneous and metamorphic processes as a function of time

experimental zircon melt and zircon garnet trace element partitioning and implications for the geochronology of crustal rocks garnet is the most commonly used mineral in thermobarometry whereas zircon is the most robust chronometer to date high grade metamorphic rocks to provide a basis for correlation of zircon and garnet growth we determined experimentally the trace element partitioningbetweenzircon ahydrousgraniticmeltandgarnetat20kbarand800 1000 cforp y rareearthelements ree zr hf th andu inrespecttomelt zirconpreferentiallyincorporatesallinvestigatedelementsapartfromreewithatomicnumberlowerthansm at this pressure and in the chosen composition the distribution coefficient between zircon and melt d zrn melt for ree increases with increasingatomicnumberofthereeandwithdecreasingtemperature dyb is 20at1000 c butmorethananorderofmagnitude higher at800 c the solubilityofzrinhydrousgraniticmelts buffered by zirconisabouta factoroftwo lower at20kbar than what has been previously established for mid crustal pressures large garnet produced in the experiments allowed determination of garnet melt trace element partitioning d grt melt at temperatures of 800 1000 c conditions relevant for partial melting of crustal rocks there is a systematic increase indree with decreasing temperature zircon contains significantly more heavy ree than garnet at temperatures of 800 850 c zircon garnetpartitioncoefficientsofheavy reedecreasewithincreasingtemperaturefromdlu of12at800 cto 1 4at1000 c middle reepartitioningisclosetounityforthewholeinvestigatedtemperaturerange differentempiricallydetermined zircon garnet partition coefficients from granulites and ultra high temperature granulites can potentially be explained by the experimentallydeterminedchangeofpartitioningasafunctionoftemperature thesedatacanassistinestablishingequilibriumbetween garnetandzirconzonesinnaturalrocks andintheconstructionofdetailedpressure temperature timepathsinhigh grademetamorphic rocks

high resolution insights into episodes of crystallization hydrothermal alteration and remelting in the skaergaard intrusive complex this paper presents a new high precision zircon u pb geochronological view on the crystallization and assembly process of one of the most important and intensely studied intrusive bodies on earth the skaergaard intrusion in east greenland with analytical uncertainties of a few tens of thousands of years we were able to resolve several important events during cooling of this intrusion initial cooling of the shallowly intruded 300 km3 of tholeiitic basaltic magma from liquidus to zircon saturation at 1000 c is recorded by a precise zircon crystallization age of 55 960 0 018 ma of an intercumulus gabbroic pegmatite in the lower portion of the intrusion based on this zircon crystallization age and a published cooling model we estimate the true age of emplacement to be 56 02 ma the last portions of skaergaard appear to crystallize completely 100 ka after emplacement as recorded by abundant 55 91 55 93 ma zircons in the sandwich horizon sh where lower and upper solidification fronts met intrusion of an isotopically distinct new magma batch the 600 m thick basistoppen sill into the solidified upper portion of skaergaard happened at 55 895 0 018 ma suggesting close timing between crystallization of evolved rocks around the sh and intrusion of the basistoppen sill the novel result of this work is the demonstration that zircons in the sh 100 m below the basistoppen contact have a bimodal age distribution with the youngest population of 55 838 0 019 ma postdating intrusion of the basistoppen sill by 57 37 ka oxygen isotope analyses reveal that sh zircons are low and heterogeneous with respect to 18o these results support the proposed conclusion that the sh crystallized twice it was fully crystalline then hydrothermally altered by low 18o surface waters and subsequently partially remelted triggered by heat of the basistoppen sill the low degree partial melt generated during remelting partially migrated upward by intergranular compaction driven flow explaining the existence of the most incompatible trace element rich horizon 100 m above sh as the skaergaard intrusion is also the most classic example of a shallow meteoric hydrothermal system this work documents the alternating processes in a life of an intrusion with periods of hydrothermal cooling heating by new intrusions and related remelting events which cause the generation of low 18o magmas our precise temporal framework for intrusion crystallization also provides constraints for the timing of coeval flood basalt volcanism and its synchronicity with the paleocene eocene thermal maximum

an analysis of the supply process of loose materials to mountainous rivers and gullies as a result of dry debris avalanches a dry debris avalanche will produce different volumes of colluviums or depositions loose materials which can have a significant impact on mountainous rivers or gullies the loose material supply process caused by a debris avalanche is an important issue for understanding secondary disasters that form via the coupling of water flow and loose materials two flumes were designed for laboratory tests of the loose materials supply process to rivers gullies and the related impact factors were analyzed experimental results show that the supply of loose materials is a continuous process that directly relates to the avalanche s mass movement processes the sliding masses with smaller particle sizes are more sensitive to the flume slope and exhibited a longer supply time the time consuming for the debris avalanche travel in the flume decreased with the increasing particle size such as flume b time consuming is decreased 0 2 s when the particle size increased from 1 0 to 20 60 mm landslide volume and flume slope flume a consuming 1 6 2 1 s when flume slope is 29 decreased to consuming 1 3 1 5 s when flume slope is 41 which means the increasing mobility of loose materials the total supply time increased with the increasing landslide volume or decreasing particle size and flume slope an empirical model for the process is presented based on numerous laboratory tests and numerical simulations which can successfully describe the supply process for loose materials to a river gully the supply process of loose materials to mountainous gully from a dry debris avalanche is controlled by the material compositions of sliding masses topographical conditions landslide volume and bed friction where large volume debris avalanches that occur in mountainous river regions are more likely to obstruct the river flow and form a landslide dammed lake

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

a model for the analysis of rapid landslide motion across three dimensional terrain a new numerical model for the dynamic analysis of rapid flow slides debris flows and avalanches has been developed the model is an extension of an earlier algorithm and is implemented using a nu

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

some factors affecting mass front velocity of rapid dry granular flows in a large flume tests were carried out to investigate some propagation mechanisms involved in rapid dry granular flows and to identify factors influencing mass front velocity in a large flume with two slopes by analyzing image records as a step in understanding the behavior of rock avalanches the varied test conditions were gradation and volume of materials shape and initial arrangement of blocks consecutive releases obstacles and bottom roughness flume test results show that the mass front velocity varied with the characteristics and concentration of particles the velocity was high and its fluctuation was also great along the upper slope for the cobbles the velocity increased with the volume for mono materials the composite of cubes and gravel with a large volume displayed a rather lower mobility than the mono material of cubes and of gravel with a small volume the velocity for the composite of cobbles and gravel with a large volume was almost the same as the mono material of cobbles and of gravel with a small volume the velocity also depended on macro and micro topography the velocity decreased by about 25 when the granular flow changed the direction of movement near a concavity for all cases two peak velocities were showed in those cases with a convexity the materials decelerated when it encountered the convexity and then accelerated greatly after they took a ballistic trajectory from the vertex of the convexity and briefly lost contact with the base of the flume the mean velocity along the lower slope reduced by 29 4 due to the resistance of a model forest and increased by 26 2 without matting

mixed carbonate siliciclastic record on the north african margin malta coupling of weathering processes and mid miocene climate we investigated rock outcrops spanning the middle miocene global climate cooling step on the maltese islands in order to reconstruct continental weathering rates and terrigenous fluxes as well as to explore the coupling between these later regional climate and carbonate accumulations sedimentation at this location was dominated during the oligocene and early miocene by a transitional platform to slope carbonates but progressively switched to a clay rich carbonate slope system in the middle miocene around 13 ma an abrupt change toward clay dominated marls occurred and marl deposition persisted until the tortonian ca 12 ma when a shallow water carbonate ramp was reestablished clay mineralogy and bulk rock oxygen isotope analyses suggest that the deposition of the blue clay formation was mainly caused by global climate change and related change in the rate of continental weathering a significant negative correlation r 2 0 65 exists between the carbonate content and the 1 8 o record this combined with the variation of mass accumulation rate of terrigenous material suggests that shorter term periods of globally cooler climate mi events were associated with higher rates of accumulation in continental derived material since during the miocene malta was attached to the north african margin we propose that the observed trends were due to a regional increase in rainfall during cooler periods which consequently increased continental weathering and runoff we further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the miocene thus regional increase in rainfall might have been linked to the northward migration of the intertropical convergence zone itcz

high precision zircon u pb geochronology of astronomically dated volcanic ash beds from the mediterranean miocene several orbitally tuned miocene sedimentary sequences around the mediterranean contain abundant intercalated volcanic ash beds these sequences provide the rare opportunity to directly compare radioisotopic dating methods with independent and accurate deposition ages derived from astrochronology we present a large data set n 16n 16 n 166n 166 of zircon u pb dates obtained by chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims techniques for ash beds from an almost continuous orbitally tuned messinian to langhian 6 2 15 4 ma sedimentary sequence exposed along the adriatic coast south of ancona italy we use this unique data set to evaluate 1 the accuracy of zircon u pb dates 2 the significance of initial intermediate daughter product disequilibria for zircon u pb geochronology of young rocks 3 the effect of prolonged pre eruption zircon crystallization and zircon recycling on u pb derived ash bed deposition ages and 4 discuss the implications for the intercalibration of radioisotope geochronometers and the calibration of the geologic time scale

discrete element modeling of the mass movement and loose material supplying the gully process of a debris avalanche in the bayi gully southwest china abstract the dynamic process of a debris avalanche in mountainous areas is influenced by the landslide volume topographical conditions mass material composition mechanical properties and other factors a good understanding of the mass movement and loose material supplying the gully process is very important for understanding the dynamic properties of debris avalanches three dimensional particle flow code pfc3d was used to simulate a debris avalanche in quaternary deposits at the bayi gully southwest china fortran and autocad were used for the secondary development to display the mass movement process and to quantitatively describe the mass movement and loose material supplying the gully process the simulated results show that after the landslide is initiated the gravitational potential energy is converted into kinetic energy with a variation velocity for the sliding masses two stages exist for the average movement velocity the acceleration stage and the slowdown stage which are influenced by the topographical conditions for the loose materials supplying the gully process the cumulative volume of the sliding masses into the gully gradually increases over the time when the landslide volume is not large enough the increasing landslide volume does not obviously influence the movement process of the sliding masses the travel distance and movement velocity increase with the decreasing numerical parameters and the mass movement process is finished more quickly using low value parameters the deposition area of the sliding masses decreases with the increasing numerical parameters and the corresponding deposition thickness increases the mass movement of the debris avalanche is not only influenced by the mechanical parameters but is also controlled by the topographical conditions

the role of rock fragmentation in the motion of large landslides abstract by considering the implications of the comminution generally associated with very large landslides we arrive at a simple explanation for the remarkably low frictional resistance to motion demonstrated by large intact blockslides e g waikaremoana new zealand volcanic debris avalanches e g socompa chile and large rock avalanches e g falling mountain n z which allows such mass movements to achieve unexpectedly high velocities and long runout distances during rapid grain flow under high direct stress the overall grain motion generates stresses in many force chains that strain individual grains to failure most of the elastic strain energy accumulated in these force chains before failure is returned at failure to the resulting grain fragments resulting in apparent instantaneous pressures of 3q on the surroundings where q is the ambient strength of the previously intact grains gpa these intense pressures support some of the direct force on the shear layer so that the effective intergranular stress in the shear layer is reduced because frictional resistance is proportional to effective stress this reduces the overall frictional resistance to shear the steady state effective stress is that which just allows fragmentation to continue the resistance to motion estimated from this relationship explains to much better than order of magnitude accuracy the reported motions of the large rapid mass movements we also deduce that grain fragmentation can be sustained for sufficiently long to explain the phenomena without reducing the mean grain size by volume in the granular layer to unrealistically small values the presence of pore fluid does not appear to influence the effect of fragmentation dynamics in a major way the proposed mechanism requires further laboratory and simulation studies to reduce its current dependence on limited field data but its success suggests that it is worthwhile investigating further as an explanation for large mass movements in the types of brittle rock in which fragmentation occurs

controls on the size and geometry of landslides insights from discrete element numerical simulations abstract we use numerical two dimensional discrete element method dem to study the controls on the size and geometry of an individual landslide this method allows us to analyze the temporal and spatial evolution of slope failure and landsliding from the intact pre failure slope to the restabilized post failure slope the size of our simulated landslides reflects the amount of disintegrated material available for sliding which is controlled by the peak strength of the slope material and to a lesser degree by the pre failure slope angle the observed size of natural landslides therefore reflects mainly the local natural material strengths we hypothesize that the observed global characteristic landslide size is a result of the limited thickness generally up to a few meters of disintegrated and weathered material that exists on hillslopes poised and ready for sliding the primary controls on the landslide geometry quantified as the ratio of their thickness to length t l prove to be the residual friction angle of the slope material and the original slope angle the t l is observed to be unchanged for a given initial slope angle and independent of the slope material peak strength or the slope height we suggest that the narrow range of observed natural t l is a result of narrow ranges of mechanical properties and initial slope geometries involved in natural slope failure

acigol rhyolite field central anatolia part ii geochemical and isotopic sr nd pb δ18o constraints on volcanism involving two high silica rhyolite suites the acigol rhyolite field erupted the most recent high silica rhyolites within the cappadocian volcanic province of central anatolia turkey it comprises two sequences of domes and pyroclastic rocks with eruption ages of 150 200 ka eastern group and 20 25 ka western group compositionally the eastern rhyolite group lavas are less evolved sio2 74 76 wt whereas the western group has higher silica abundance sio2 77 wt with extremely depleted feldspar compatible trace elements within each group compositional variability is small and 143nd 144nd 0 51257 0 51265 and pb isotope compositions 206pb 204pb 18 87 18 88 207pb 204pb 15 65 15 67 and 208pb 204pb 38 94 38 98 are homogeneous the western group rhyolites have 18o zircon overlapping mantle values 5 7 0 2 whereas eastern group rhyolites are enriched in 18o by 0 5 consistent with a tendency to lower end values by contrast western group rhyolites have markedly more radiogenic 87sr 86sr ratios 0 7065 0 7091 compared to those of the eastern group 0 7059 0 7065 the presence of angular granitic xenoliths and a correlation between hydration based on loss on ignition data and 87sr 86sr in the western lavas however indicates that sr was added during the eruption or post eruption alteration isotope constraints preclude the possibility that the rhyolite magmas formed by partial melting of any known regional crystalline basement rocks basalts and andesites erupted in the periphery of the acigol field are characterised by 87sr 86sr ratios between 0 7040 and 0 7053 143nd 144nd 0 51259 0 51300 206pb 204pb 18 85 18 87 207pb 204pb 15 646 15 655 208pb 204pb 38 90 38 97 the isotopic and trace element data favour an origin of the rhyolites by mixing of basaltic andesitic magmas with minor amounts of crustal melts and followed by extensive fractional crystallization

cenozoic evolution of continental humidity and paleoenvironment deduced from the kaolinite content of oceanic sediments abstract the distribution of detrital kaolinite in cenozoic sediments of the atlantic and west pacific oceans has been used to reconstruct the variations of the continental humidity and associated paleoenvironmental factors five stages have been recognized 1 1 during the late oligocene chattian c 30 m y p21 and np24 increased kaolinite content at every site marked an increase of global humidity 2 2 during the early miocene aquitanian c 20 m y n5 n6 and nn2 nn3 increasing continental aridity is deduced from low kaolinite contents in the atlantic ocean and philippine sea 3 3 during the middle miocene langhian c 14 m y n10 n12 and nn5 nn6 increased kaolinite contents at most of the sites marked a further increase of global humidity which was especially important at low latitudes in africa 4 4 during the late miocene tortonian c 10 m y n16 and nn10 nn11 kaolinite content and inferred continental humidity increased toward high latitudes but decreased toward low latitudes especially off tropical africa where it marked the development of arid conditions 5 5 during the late pliocene piacenzian c 3 m y nn15 nn16 kaolinite content and humidity increased again toward high latitudes while these conditions decreased again toward low latitudes emphasizing the latitudinal climatic zonation periods of increasing humidity show good correlation with the development of polar ice locally volcanism tectonic activity oceanic circulation and migration of lithospheric obliterated the climatic significance of clay mineral associations which therefore express complementary aspects of the continental and marine paleoenvironments

acigol rhyolite field central anatolia part 1 high resolution dating of eruption episodes and zircon growth rates protracted pre eruptive zircon residence is frequently detected in continental rhyolites and can conflict with thermal models indicating briefer magma cooling durations if scaled to erupted volumes here we present combined u th and u th he zircon ages from the acigol rhyolite field central anatolia turkey which is part of a quaternary bimodal volcanic complex unlike other geochronometers this approach dates crystallization and eruption on the same crystals allowing for internal consistency testing despite the overall longevity of acigol rhyolite volcanism and systematic trends of progressive depletion in compatible trace elements and decreasing zircon saturation temperatures we find that zircon crystallized in two brief pulses corresponding to eruptions in the eastern and western part of the field during middle and late pleistocene times respectively for late pleistocene zircon resolvable differences exist between interior average 30 7 0 9 ka 1 error and rim 21 9 1 3 ka crystallization ages these translate into radial crystal growth rates of 10 13 to 10 14 cm s broadly consistent with those constrained by diffusion experiments rim crystallization and u th he eruption ages 24 2 0 4 ka overlap within uncertainty evidence for brief zircon residence at acigol contrasts with many other rhyolite fields suggesting that protracted zircon crystallization in or recycling from long lived crystal mushes is not ubiquitous in continental silicic magma systems instead the span of pre eruptive zircon ages is consistent with autochthonous crystallization in individual small volume magma batches that originated from basaltic precursors

δ18o and marion plateau backstripping combining two approaches to constrain late middle miocene eustatic amplitude d 18 obenthic values from leg 194 ocean drilling program sites 1192 and 1195 drilled on the marion plateau were combined with deep sea values to reconstruct the magnitude range of the late middle miocene sea level fall 13 6 11 4 ma in parallel an estimate for the late middle miocene sea level fall was calculated from the stratigraphic relationship identified during leg 194 and the structural relief of carbonate platforms that form the marion plateau corrections for thermal subsidence induced by late cretaceous rifting flexural sediment loading and sediment compaction were taken into account the response of the lithosphere to sediment loading was considered for a range of effective elastic thicknesses 10 te 40 km by overlapping the sea level range of both the deep sea isotopes and the results from the backstripping analysis we demonstrate that the amplitude of the late middle miocene sea level fall was 45 68 m 56 5 6 11 5 m including an estimate for sea level variation using the d 18 obenthic results from the subtropical marion plateau the range of sea level fall is tightly constrained between 45 and 55 m 50 0 6 5 0 m this result is the first precise quantitative estimate for the amplitude of the late middle miocene eustatic fall that sidesteps the errors inherent in using benthic foraminifera assemblages to predict paleo water depth the estimate also includes an error analysis for the flexural response of the lithosphere to both water and sediment loads our result implies that the extent of ice buildup in the miocene was larger than previously estimated and conversely that the amount of cooling associated with this event was less important

remelting in caldera and rift environments and the genesis of hot recycled rhyolites abstract large and small volume rhyolites are generated in calderas and rift zones inheriting older and isotopically diverse crystal populations from their volcanic predecessors low 18o values in many of these rhyolites suggest that they were derived from the remelting of solid hydrothermally altered by meteoric water protoliths that were once close to the surface but become buried by caldera collapse or rifting these rhyolites persist for millions of years in these environments with little evidence of coeval basalts we present a series of numerical experiments on convective melting of roof rocks by the underplated by near liquidus to superheated silicic melts generated at the base of the chamber by basaltic intrusions in shallow crustal conditions we used a range of temperatures and compositions an appropriate phase diagram with a defined extended eutectic zone appropriate for these environments varied sill thickness viscosity of the boundary layer and considered hydrothermal and lower boundary heat losses the goal was to estimate melting rates and mechanisms define conditions that are required for efficient and rapid remelting in the upper crust quantitatively describe novel details of the dynamics of convecting melting and compare it to the earlier parametric and numerical treatments of roof melting by underplating resolution of numerical experiments allowed us to track mixed thermal and two phase plume like convection in silicic magma with a bulk viscosity of 104 5 105 5 pa s the following results were obtained 1 remarkably fast melting magma generation rates of many meters per year 2 intrinsic inhomogeneities in the roof accelerates convection and melting rates via rapid gravitational settling of refractory blocks and exposing detachment scars to the melting front 3 due to rapid melting hydrothermal heat loss through the roof and conductive heat dissipation through the bottom are less important on melting timescales 4 convective melting is capable of digesting cold roof rocks with high assimilation degrees which are primarily controlled by sill thickness and roof rock temperature thin 10 m sills are able to digest 40 of the initially hot roof rock t 650 c roof rock but 100 m sills achieve the same level of bulk digestion with t 400 c roof rocks the proposed model can explain the origin of hot above 800 850 c crystal poor recycled rhyolites in calderas and rift zones it can also explain the generation of large supervolcanic rhyolite volumes through remelting of their erupted and subvolcanic predecessors on rapid timescales dictated by their zoned and disequilibrium crystalline cargo

experimental study on the structural parameters of an optimized sloping roof grill barrier for the prevention of debris flows in yanmen gully abstract a horizontal permeable retaining structure i e a sloping roof grill barrier is an efficient way to separate water from sediment however the effect of the structural parameters and lateral deposit area on separation efficiency has not been investigated taking yanmen gully as an example this paper first expands the lateral deposit area of the retaining structure and then conducts a series of flume experiments to study the influences of the structural parameters grid spacing and grid inclination degree on the separation efficiency the experimental results indicate that the retention ability of the structure with the optimized lateral deposit area is much higher the grid spacing is the main factor affecting the grain size distribution of the debris flow beyond the barrier and should be higher than the d80 value of grain size distribution of the debris flow the retention capacity is directly proportional to the grid inclination degree while the separation efficiency is inversely proportional to the grid inclination degree the steeper the grid inclination is the smaller the displacement of debris flow particles along the barrier surface is the experimental results are analysed to correlate the barrier length with the structural parameters this paper serves as a reference for the structural design of horizontal permeable barriers

reappraisal of los humeros volcanic complex by new u th zircon and 40ar 39ar dating implications for greater geothermal potential

rates of magma differentiation and emplacement in a ballooning pluton recorded by u pb tims tea adamello batholith italy abstract geochemical structural field and geochronological data have been used to arrive at very different models for the construction of upper crustal batholiths models for pulsed intrusion of small magma batches over long timescales 1 ma versus transfer of larger magma bodies on shorter timescales predict a different thermal metamorphic and rheological state of the crust highlighting the importance of robust time constraints this study focuses on a well characterized upper crustal intrusion the 15 km2 lago della vacca complex lvc adamello batholith n italy previous studies used structural and petrologic data to argue that the lvc was emplaced through pulsed magma injection and in situ expansion or ballooning of a short lived 105 yr magma chamber we test this model using a dense sampling strategy and high precision id tims u pb geochronology of zircon and titanite combined with hafnium isotope and trace element analyses of the same volume of dated mineral u pb tims tea these data show that the marginal mafic pulses of magma crystallized zircon with primitive hf isotopes and negligible eu anomalies during fractional crystallization and ascent through the crust on 10 30 ka timescales subsequent more felsic pulses yield individual zircon dates spanning as much as 200 ka within single handsamples and restrict the total construction time of the lvc to

zircon record of the plutonic volcanic connection and protracted rhyolite melt evolution the potential petrogenetic link between a crystal poor rhyolite the rhyolite canyon tuff and its associated subvolcanic intrusion and crystal rich post caldera lavas from turkey creek arizona usa is examined using zircon chemical abrasion thermal ionization mass spectrometry u pb geochronology and inductively coupled plasma mass spectrometry trace element analyses u pb ages indicate that zircon growth within the rhyolite and the dacite monzonite porphyry magmas was coeval over 300 k y prior to the large eruptive event trends in zircon trace elements hf y dy sm yb eu eu through time in the dacitic monzonitic units and rhyolite reflect melt evolution dominated by crystal fractionation importantly the y dy ratio in zircons in both units remains mostly similar for the first 150 k y of the system s evolution but the dominant population in the rhyolitic unit diverges from that of the dacite monzonite porphyry 150 k y before eruption we interpret this divergence in trace element composition to record the assembly time of the melt rich cap within its intermediate mush zone in the upper crustal reservoir these results are consistent with 1 a connection between plutonic and volcanic realms in the upper crust 2 a protracted time scale for constructing an intermediate mush large enough to hold 500 km 3 of rhyolite and 3 the prolonged extraction of that melt prior to eruption

low δ18o rhyolites from yellowstone magmatic evolution based on analyses of zircons and individual phenocrysts the yellowstone plateau volcanic field is one of the largest centers exchange time to form zoned zircons is between a few hundred and a few thousand years which reflects the residence time of lowo of rhyolitic magmatism on earth major caldera forming eruptions are followed by unusual lowo rhyolites new oxygen isotope magmas after formation and before eruption petrologic and geochemical data from rhyolites belonging to the 2 0 my eruptive history of yellowstone are presented with emphasis on the genesis of lowo magmas erupted after the huckleberry ridge tuff 2 0 ma 2500 km and lava creek tuff 0 6 ma

release of iron from chlorite weathering and links to magnetic enhancement in chinese loess deposits abstract chlorite weathering is potentially useful as an indicator of in situ weathering related to the strength of the east asian summer monsoon in chinese loess deposits the chlorite ratio the integral area ratio of chlorite diffraction peaks at 0 47 nm and 0 7 nm is a new proxy for evaluating the release of free iron from chlorite weathering this ratio was measured using x ray diffraction xrd on the

u pb zircon geochronology of silicic tuffs from the timber mountain oasis valley caldera complex nevada rapid generation of large volume magmas by shallow level remelting large volumes of silicic magma were produced on a very short timescale in the nested caldera complex of the sw nevada volcanic field swnvf voluminous ash flows erupted in two paired events topopah spring ts 1 200 km3 12 8 ma tiva canyon tc 1 000 km3 12 7 ma and rainier mesa rm 1 200 km3 11 6 ma ammonia tanks at 900 km3 11 45 ma all cited ages are previously published 40ar 39ar sanidine ages within each pair eruptions are separated by only 0 1 0 15 my and produced tuffs with contrasting isotopic values these events represent nearly complete evacuation of sheet like magma chambers formed in the extensional basin and range environment we present ion microprobe ages from zircons in the zoned ash flow sheets of ts tc rm and at in conjunction with 18o values of zircons and other phenocrysts which differ dramatically among subsequently erupted units bulk zircons in the low 18o at cycle were earlier determined to exhibit 1 5 core to rim oxygen isotope zoning and high spatial resolution zircon analyses by ion microprobe reveal the presence of older grains that are zoned by 0 5 2 5 the following u pb isochron ages were calculated after correcting for the initial u pb disequilibria at zircon rims 11 7 0 2 ma cores 12 0 0 1 ma pre at rhyolite lava 12 0 0 3 ma rm 12 4 0 3 tc 13 2 0 15 ma ts 13 5 0 2 average zircon crystallization ages calculated from weighted regression or cumulative averaging are older than the ar ar stratigraphy but preserve the comparably short time gaps within each of two major eruption cycles ts tc rm at notably every sample yields average zircon ages that are 0 70 0 35 ma older than the respective ar ar eruption ages the th u ratio of swnvf zircons are 0 4 4 7 higher than typically found in igneous zircons which correlates with elevated th u of the whole rocks 5 16 high th u could be explained if uranium was preferentially removed by hydrothermal solutions or is retained in the protolith during partial melting for low 18o at cycle magmas rim ages from unpolished zircons overlap within analytical uncertainties with the 40ar 39ar eruption age compared to core ages that are on average 0 2 0 3 my older than even the age of the preceding caldera forming eruption of rm tuff this age difference the core to rim oxygen isotope zoning in at zircons and disequilibrium quartz zircon and melt zircon isotopic fractionations suggest that at magma recycled older zircons derived from the rm and older eruptive cycles these results suggest that the low 18o at magmas were generated by melting a hydrothermally altered protolith from the same nested complex that erupted high 18o magmas of the rm cycle only 0 15 my prior to the eruption of the at the largest volume low 18o magma presently known

tracking the evolution of large volume silicic magma reservoirs from assembly to supereruption the most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs the thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style here we combine high precision zircon u pb geochronology trace element analyses of the same mineral grains and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the oligocene fish canyon tuff magma reservoir colorado united states as a function of absolute time systematic compositional variations in u pb dated zircons record 440 k y of magma evolution an early phase of volumetric growth was followed by a period of cooling and crystallization during which the fish canyon magma approached complete solidifi cation subsequent remelting due to underplated andesitic recharge magmas began 219 45 k y prior to eruption and led to the generation of 5000 km3 of eruptible crystal rich 45 vol dacite age equivalent but compositionally different zircons in an andesite enclave from late erupted fish canyon tuff tie the growth and thermal evolution of the upper crustal reservoir to a lower crustal magma processing zone our results demonstrate that the combination of high precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

landslide seismic signal recognition and mobility for an earthquake induced rockslide in tsaoling taiwan abstract landslide seismic signal processing and the newmark s sliding block analysis are used in this research to analyze the initiation time and mobility of the tsaoling rockslide triggered by the 1999 chi chi earthquake in central taiwan a new technique the time frequency spectrum analysis is employed to identify the rockslide initiation and landing times from four real time seismic records of strong ground motion stations the results suggest that higher frequencies ranging from 30 to 70 hz correspond to the rockslide initiation and sliding process which are opposed to the low signal frequency of earthquake the landslide began at 32 5 s the sliding block sped up at 37 5 s and impacted on the opposite riverbank at 76 s on the seismic time record the mobile scenario of tsaoling rockslide induced by chi chi earthquake is simulated using newmark s sliding block analysis the maximum sliding velocity reaches approximately 75 1 m s despite being a simple conceptual model the newmark s sliding block analysis provides consistent results with the real time seismic signal analysis and details of the rockslide kinematics

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

a dynamic model for rainfall induced landslides on natural slopes assessment of landslide hazard often requires a good knowledge of the landslide characteristics and runout mechanics in this paper a quasi three dimensional model using lagrangian finite element method lfem is formulated to reproduce the dynamic runout process caused by landslides a case study of rainfall induced landslide on a natural slope in 1993 in lantau island hong kong is presented voellmy rheology is adopted to characterize the multi dimensional runout behaviour for engineering applications the selection of appropriate rheology and the determination of relevant key parameters associated with the failure mechanisms and runout mechanics are highlighted details of the mathematical formulation particularly with respect to the stability of the numerical scheme and quality control of the mesh are provided the close correlation between the calculation results and the field observations shows that if an appropriate rheological relationship is selected for the simulation a reasonable description of the runout behaviour can be obtained using the present model implications of the potential hazard from natural terrain landslides to downslope development are also discussed used in conjunction with geographical information system gis database the model can also be applied to the preliminary hazard zoning of terrain and land use management in mountainous areas

relative control of paleoceanography climate and eustasy over heterozoan carbonates a perspective from slope sediments of the marion plateau odp leg 194 in this paper we explore the relative control of paleocean ography eustasy and water temperature over the evolution of a car bonate slope system deposited on the marion plateau northeastern australia growth of several carbonate platforms started in the early miocene on this plateau and although they occurred in low latitude subtropical waters they are composed mainly of heterozoan organisms we investigated an upper to distal slope transect drilled during odp leg 194 and located close to the northern marion platform we re constructed mass accumulation rates of carbonate as well as the evo lution in the ratios of carbon and oxygen stable isotopes power spec trum analysis of the carbon isotope record revealed the existence of cycles with main frequencies centered around 409 kyr and 1800 kyr we interpret the 409 kyr cycle as being paced by changes in the ec centricity of the earth orbit and we suggest that the 1800 kyr cycle could be linked to long term eustatic changes finally on the basis of the timing of changes in mass accumulation rates of carbonate we infer that the strength and direction of oceanic currents affected sedimen tation on the marion plateau by shifting depocenters of slope sedi mentation a process probably further modulated by sea level changes we argue that the evolution and demise of the heterozoan carbonate systems present on the marion plateau were controlled mainly by the evolution of strong benthic currents and that eustasy and water tem perature alone did not account for the drowning of the platforms in the mid miocene

the late cenozoic uplift climate change paradox the geologic evidence for worldwide uplift of mountain ranges in the neogene is ambiguous estimates of paleoelevation vary according to whether they are based on the characteristics of fossil floras on the masses and grain sizes of eroded sediments or on calculations of increased thickness of the lithosphere as a result of faulting detrital erosion rates can be increased both by increased relief in the drainage basin and by a change to more seasonal rainfall patterns the geologic record provides no clear answer to the question whether uplift caused the climatic deterioration of the neogene or whether the changing climate affected the erosion system in such a way as to create an illusion of uplift we suggest that the spread of c4 plants in the late miocene may have altered both the erosion and climate systems these changes are responsible for the apparent contradictions between data supporting uplift and those supporting high elevations in the past

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

uranium series accessory crystal dating of magmatic processes complex and protracted crystallization histories over geologic timescales are recorded in accessory minerals e g zircon allanite although magmatic crystallization was traditionally assumed to occur essentially instantaneously for the purposes of interpreting mineral geochronometers with low absolute time resolution for ancient samples it emerged relatively recently that magmatic crystallization can occur over extended durations this discovery arose from applying high spatial resolution accessory mineral dating techniques for uranium series isotopes to young volcanic and cognate plutonic rocks the emerging pattern from these studies is that individual crystals and crystal populations record crystallization episodes lasting from 1 000 to many hundreds of thousands of years accessory mineral dating of volcanic rocks and cognate plutonic xenoliths opens new research avenues for crystal age fingerprinting that correlates pyroclastic deposits lavas and plutonic rocks by using characteristic age dis

age intercalibration of 40ar 39ar sanidine and chemically distinct u pb zircon populations from the alder creek rhyolite quaternary geochronology standard abstract we report results from a 40 ar 39 ar sanidine and ca tims 238 u 206 pb zircon dating study of eruption and crystal residence timescales of the alder creek rhyolite acr california extruded during the cobb mountain normal polarity subchron c1r 2n a 40 ar 39 ar acr sanidine date of 1 1850 0 0016 ma 2 external uncertainty determined relative to the astronomically dated a1 tephra sanidine is interpreted as the acr eruption age this age is supported by ca tims u pb zircon dating guided by la icpms trace element analyses titanium in zircon tizr thermometry and cathodoluminescence cl imaging using these data two compositionally distinct zircon populations were revealed pre acr group b zircon exhibit oscillatory zoning large positive ce and negative eu anomalies high incompatible trace element contents tizr temperatures of 650 c 750 c and th u disequilibrium corrected 238 u 206 pb dates of 1 38 1 24 ma these crystals are interpreted as antecrysts inherited from earlier intrusives in the geysers cobb mountain magma source region acr related group a zircon present as discrete grains and overgrowths on group b zircon display less intense cl with diffuse zoning and have less pronounced positive ce and negative eu anomalies lower incompatible trace element contents higher tizr temperatures that range up to 840 c and significantly younger dates the youngest group a dates yield a weighted mean of 1 1978 0 0046 ma 2 including systematic uncertainties that is interpreted as the mean age of zircon crystallization prior to eruption the 13 5 ka offset between the 40 ar 39 ar and 238 u 206 pb dates can be attributed to zircon magma residence time recognition of a young population of acr zircon is consistent with the 40 ar 39 ar eruption age which coincides with the astronomical age estimate for the cobb mountain subchron determined by correlating the oxygen isotope record of the giant piston core md972143 to the la93 1 1 orbital solution on the basis of independent radio isotopic and orbital forcing results we propose the refined age of 1 1850 0 0016 ma 2 external uncertainty for the quaternary acr 40 ar 39 ar sanidine standard

p and s velocity structure of the yellowstone volcanic field from local earthquake and controlled source tomography the three dimensional p and s velocity from vp vs ratios distribution and improved hypocenters for the yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled source explosions the p velocity model has an rms residual of 0 09 s whereas the vp vs ratio model calculated from 511 earthquakes has an rms residual of 0 29 s high p and s velocities outside the yellowstone caldera represent thermally undisturbed basement and sedimentary rocks a caldera wide 15 decrease from regional p velocities at depths of 6 to 12 km is coincident with a 60 mgal gravity anomaly and is interpreted as a hot subsolidus granitic batholith with a quasi plastic rheology localized 30 reductions from regional seismic velocities and higher vp vs ratios 8 km beneath yellowstone s resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful less than 2 ma silicic volcanism additional low seismic velocities and vp vs ratios and a 20 mgal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt hypocenters relocated with the three dimensional p velocity model show subparallel alignment with nw se trending postcaldera volcanic vents and normal faults northwest of the caldera focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera reflecting thinning and heating of the seismogenic crust

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

kinematics of an alpine retrogressive rockslide in the japanese alps the aresawa rockslide in the japanese alps experienced a partial collapse 5 10 105 m3 in 2004 followed by an accelerated downward movement of the head area rather than stabilization this paper discusses the kinematics of a retrogressive rockslide area and factors promoting slope instability subsequent to the 2004 collapse on the basis of geodetic surveys and meteorological observations from 2006 to 2010 the unstable area covers at least 2 3 104 m2 and consists of five active blocks the main blocks are separated from the stable rock slope by pre existing sackung features that follow the strike of the bedding plane shear zones below these sackung features have developed into slip planes potentially causing the next collapse in particular the propagation of a slip plane causing movement at 70 cm yr 1 in the head area is promoted by bidirectional movement it consists of slow dip slip movement in snow accumulating periods and rapid side slip movement in snow melting and snow free periods both of which occur on the same slip plane this bidirectional movement appears to result from the combination of a loss of lateral support by the 2004 event and the immature state of the slip plane the primary trigger of the acceleration in the unstable area is the stress release by the 2004 collapse in addition the presence of a potential slip plane below the sackung features also promotes slope instability suggesting that sackung features behind a rockslide area may predefine the new head scarp of a forthcoming collapse copyright 2012 john wiley sons ltd

monitoring super volcanoes geophysical and geochemical signals at yellowstone and other large caldera systems earth s largest calderas form as the ground collapses during immense volcanic eruptions when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the earth s crust over a period of days to weeks continuing long after such great eruptions the resulting calderas often exhibit pronounced unrest with frequent earthquakes alternating uplift and subsidence of the ground and considerable heat and mass flux because many active and extinct calderas show evidence for repetition of large eruptions such systems demand detailed scientific study and monitoring two calderas in north america yellowstone wyoming and long valley california are in areas of youthful tectonic complexity scientists strive to understand the signals generated when tectonic volcanic and hydrothermal hot ground water processes intersect one obstacle to accurate forecasting of large volcanic events is humanity s lack of familiarity with the signals leading up to the largest class of volcanic eruptions accordingly it may be difficult to recognize the difference between smaller and larger eruptions to prepare ourselves and society scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

timing and development of the heise volcanic field snake river plain idaho western usa the snake river plain srp developed over the last 16 ma as a bimodal volcanic province in response to the southwest movement of the north american plate over a fixed melting anomaly volcanism along the srp is dominatedby eruptions of explosive high silica rhyolites and represents some of the largest eruptions known basaltic eruptions represent the final stages of volcanism forming a thin cap above voluminous rhyolitic deposits volcanism progressed generally from west to east along the plain episodically in successive volcanic fields comprised of nested caldera complexes with major caldera forming eruptions within a particular field separated by ca 0 5 1 ma similar to and in continuation with the present day yellowstone plateau volcanic field passage of the north american plate over the melting anomaly at a particular point in time and space was accompanied by uplift regional tectonism massive explosive eruptions and caldera subsidence and followed by basaltic volcanism and general subsidence the heise volcanic field in the eastern srp idaho represents an adjacent and slightly older field immediately to the southwest of the yellowstone plateau volcanic field five large volume 0 5 km 3 rhyolitic ignimbrites constitute a time stratigraphic framework of late miocene to early pliocene volcanism for the study region field relations and high precision 4 0 ar 3 9 ar age determinations establish that four of these regional ignimbrites were erupted from the heise volcanic field and form the framework of the heise group these are the blacktail creek tuff 6 62 0 03 ma walcott tuff 6 27 0 04 ma conant creek tuff 5 51 0 13 ma and kilgore tuff 4 45 0 05 ma all errors reported at 2a the fifth widespread ignimbrite in the region is the arbon valley tuff member of the star light formation 10 21 0 03 ma which erupted from a caldera source outside of the heise volcanic field these results establish the conant creek tuff as a distinct and widespread ignimbrite in the heise volcanic field eliminating former confusion resulting from previous discordant k ar and fission track dates new 4 0 ar 3 9 ar determinations when combined with geochemical lithologic geophysical and field data define the volcanic and tectonic history of the heise volcanic field and surrounding areas volcanic units erupted from the heise volcanic field also provide temporal control for tectonic events associated with late cenozoic extension in the snake range and with uplift of the teton range wyoming in the snake range movement of large 0 10 km 3 slide blocks of mississippian limestone exposed 50 km to the east of the heise field occurred between 6 3 and 5 5 ma and may have been catastrophically triggered by the caldera eruption of the 5 51 0 13 ma conant creek tuff this slide block movement of 300 vertical meters indicates that the snake range had significant relief by at least 5 5 ma in jackson hole the distribution of outflow facies of the 4 45 0 05 ma kilgore tuff related to eruption from the kilgore caldera in the heise volcanic field on the eastern srp indicates that the northern teton range was not a significant topographic feature at this time

geochemical and mineralogical characteristics of bauxites darling range western australia abstract the lateritic bauxites of the darling range western australia vary greatly in chemical and mineralogical properties and it shown that this is due partly to the parent materiald ranging from granatic to doleritic rocks gibbsite is the dominant form of al in the friable and duricrust zones goethite is the major fe oxide mineral and is highly al substituted 16 33 mole whereas hematite shows lower al substitution 3 11 mole halloysite and kaolinite are mostly responsible for the reactive silica content of these bauxites maghemite 0 10 and secondary microcrystalline corundum 0 3 5 occur only in duricrust and their abundances are very highly correlated indicating a common origin and they may have been formed during forest fires the abundances of several elements are highly correlated due to the association of these elements within specific minerals such as ti mn and v in residual ilmenite grains the mineralogical and chemical properties of the darling range bauxite deposits are compared with those of other large bauxite deposits in australia and overseas these properties are also related to problems in processing bauxite using the bayer process darling range deposits differ from other australian and many other of the world deposits in that they are low grade 34 5 al2o3 and high in silica 21 sio2 and fe 21 fe2o3 the provision of detailed information on the mineral and chemical constituents of these bauxites has enabled refinery operators to improve the efficiency of the bayer process

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

crustal scale recycling in caldera complexes and rift zones along the yellowstone hotspot track o and hf isotopic evidence in diverse zircons from voluminous rhyolites of the picabo volcanic field idaho abstract rhyolites of the picabo volcanic field 10 4 6 6 ma in eastern idaho are preserved as thick ignimbrites and lavas along the margins of the snake river plain srp and within a deep 3 km borehole near the central axis of the yellowstone hotspot track in this study we present new o and hf isotope data and u pb geochronology for individual zircons o isotope data for major phenocrysts quartz plagioclase and pyroxene whole rock sr and nd isotope ratios and whole rock geochemistry for a suite of picabo rhyolites we synthesize our new datasets with published ar ar geochronology to establish the eruptive framework of the picabo volcanic field and interpret its petrogenetic history in the context of other well studied caldera complexes in the srp caldera complex evolution at picabo began with eruption of the 10 44 0 27 ma u pb tuff of arbon valley tav a chemically zoned and normal 18o 18o magma 7 9 unit with high zoned 87sr 86sri 0 71488 0 72520 and low e nd 0 18 and e hf 0 28 the tav and an associated post caldera lava flow possess the lowest end 0 23 indicating 40 60 derivation from the archean upper crust normal 18o rhyolites were followed by a series of lower 18o eruptions with more typical lower crustal sr nd hf isotope ratios and whole rock chemistry the voluminous 8 25 0 26 ma west pocatello rhyolite has the lowest 18o value 18omelt 3 3 and we correlate it to a 1 000 m thick intracaldera tuff present in the inel 1 borehole with published zircon ages 8 04 8 35 ma and similarly low 18o zircon values the significant 4 5 decrease in magmatic 18o values in picabo rhyolites is accompanied by an increase in zircon 18o heterogeneity from 1 variation in the tav to 5 variation in the late stage low 18o rhyolites a trend similar to what is characteristic of heise and yellowstone and which indicates remelting of variably hydrothermally altered tuffs followed by rapid batch assembly prior to eruption however due to the greater abundance of low 18o rhyolites at picabo the eruptive framework may reflect an intertwined history of caldera collapse and coeval basin and range rifting and hydrothermal alteration we speculate that the source rocks with pre existing low 18o alteration may be related to 1 deeply buried and unexposed older deposits of picabo age or twin falls age low 18o volcanics and or 2 regionally abundant late eocene challis volcanics which were hydrothermally altered near the surface prior to or during peak picabo magmatism basin and range extension specifically the formation of metamorphic core complexes exposed in the region could have facilitated the generation of low 18o magmas by exhuming heated rocks and creating the large water rock ratios necessary for shallow hydrothermal alteration of tectonically rift zones and volcanically calderas buried volcanic rocks these interpretations highlight the major processes by which supereruptive volumes of magma are generated in the srp mechanisms applicable to producing rhyolites worldwide that are facilitated by plume driven volcanism and extensional tectonics

large volume rhyolite genesis in caldera complexes of the snake river plain insights from the kilgore tuff of the heise volcanic field idaho with comparison to yellowstone and bruneau jarbidge rhyolites generation of large volume rhyolites in the shallow crust is an important yet enigmatic process in the snake river plain and worldwide here we present data for voluminous rhyolites from the 6 6 4 5 ma heise volcanic field in eastern idaho heise is arguably the best site to evaluate shallow rhyolite genesis in the snake river plain it is the youngest complete record of caldera cluster volcanism along the yellowstone hotspot track and it culminated with the eruption of the most voluminous low 18 o rhyolite known on earth the 1800 km 3 kilgore tuff 18 o 3 4 such low 18 o values fingerprint meteoric waters and thus the shallow crust new oxygen isotope data for phenocrysts obtained by laser fluorination correspond to a low 18 o magma value of 3 4 0 1 2 standard error for kilgore tuff samples erupted 100 km apart however ion microprobe data for single zircon crystals show significant diversity with 18 o values that range from 1 3 to 6 1 u pb zircon ages mineral chemistry whole rock major and trace element geochemistry sr and nd isotope data and magmatic liquidus temperatures are similar and or overlapping for all studied samples of the kilgore tuff normal 18 o heise tuff units that preceded the kilgore tuff define a temporal compositional trend in trace element concentrations trace element ratios and sr and nd isotope ratios that is consistent with fractional crystallization from a common reservoir whereas low 18 o kilgore cycle units have compositions that define a sharp reversal in the temporal trend back towards the composition of the first normal 18 o heise tuff 6 62 ma blacktail creek tuff the data support derivation of the voluminous low 18 o kilgore tuff from remelting of hydrothermally altered 18 o depleted intracaldera and subvolcanic portions of the blacktail creek tuff single pockets of melt with variable low 18 o values were assembled and homogenized on a caldera wide scale prior to the climactic kilgore tuff eruption and the best record of this process is provided by the 18 o diversity in kilgore tuff zircons temporal trends of oxygen isotopic depletion and recovery in rhyolite eruptions of the heise volcanic field are clearly linked to caldera collapse events and remarkably consistent with trends in the yellowstone plateau volcanic field at heise and yellowstone magmatic 18 o values can be predicted on the basis of cumulative eruptive volumes with a decrease in 18 o by 1 for every 1000 km 3 of erupted rhyolite the kilgore tuff of the heise volcanic field has the same timing magnitude of 18 o depletion and cumulative eruptive volume as the youngest phase of voluminous rhyolitic eruptions in the yellowstone plateau volcanic field indicating that the kilgore tuff may serve as a useful analog for these and perhaps other large volume low 18 o rhyolites on earth

intercalibration of radioisotopic and astrochronologic time scales for the cenomanian turonian boundary interval western interior basin usa we develop an intercalibrated astrochronologic and radioisotopic time scale for the cenomanian turonian boundary ctb interval near the global stratotype section and point in colorado usa where orbitally influenced rhythmic strata host bentonites that contain sanidine and zircon suitable for 40ar 39ar and u pb dating paired 40ar 39ar and u pb ages are determined from four bentonites that span the vascoceras diartianum to pseudaspidoceras flexuosum ammonite biozones utilizing both newly collected material and legacy sanidine samples of j obradovich comparison of the 40ar 39ar and u pb results underscores the strengths and limitations of each system and supports an astronomically calibrated fish canyon sanidine standard age of 28 201 ma the radioisotopic data and published astrochronology are employed to develop a new ctb time scale using two statistical approaches 1 a simple integration that yields a ctb age of 93 89 0 14 ma 2 total radioisotopic uncertainty and 2 a bayesian intercalibration that explicitly accounts for orbital time scale uncertainty and yields a ctb age of 93 90 0 15 ma 95 credible interval total radioisotopic and orbital time scale uncertainty both approaches firmly anchor the floating orbital time scale and the bayesian technique yields astronomically recalibrated radioisotopic ages for individual bentonites with analytical uncertainties at the permil level of resolution and total uncertainties below 2 using our new results the duration between the cenomanian turonian and the cretaceous paleogene boundaries is 27 94 0 16 ma with an uncertainty of less than one half of a long eccentricity cycle

mass movements in peat a formal classification scheme abstract published accounts of peat mass movements throughout the last 500 years reveal common characteristics among the failures however there has been no consistency in the terminology used to describe them given the apparently increasing frequency of peat failures in the british isles and the possibility of more peat failures elsewhere in the world as a consequence of climate change there is a need for a specific classification scheme this paper proposes a scheme that uses clearly defined terms that can be readily applied and reliably used to understand and assess future hazards from peat mass movements the paper begins with a general definition of what should constitute a peat failure then presents a precisely defined classification scheme for peat landslides i e excluding creep using type of peat deposit and failure morphology as the key criteria the new scheme for peat failures is discussed in the context of existing landslide classification systems definitions are provided for bog bursts flow failure of raised bogs bogflows flow failure of blanket bogs bog slides shear failure and sliding of blanket bogs peat slides shear failure at peat mineral interface in blanket bogs peaty debris slides shear failure within mineral substrate beneath blanket bogs and peat flows natural failures of other types of peat deposits including flow failure caused by head loading some practical problems of classifying peat failures are discussed

simulation of tsaoling landslide taiwan based on saint venant equations over general topography the 1999 chi chi earthquake triggered the catastrophic tsaoling landslide in taiwan the geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0 126 km3 and 0 15 km3 respectively the debris material ran over a distance of 1 6 km with 500 m descent in elevation in this paper we use the continuum model of hydraulic flow shaltop2d based on the equations of bouchut and westdickenberg to simulate numerically the landslide dynamics when the mass is moving the flow is assumed hydrostatic with a basal coulomb friction the best fit is obtained using the basal friction angle equal to 6 the only parameter of the simulation uniformly applied in the calculation domain the landslide front reaches the chinshui river valley the foothill of the slope within only about 25 s after initiation and the motion settles in about 113 s the maximum speed is estimated 75 m s the spreading of the deposit agrees well with the field measurement

a kinematic model of the hsiaolin landslide calibrated to the morphology of the landslide deposit abstract this paper presents results of a case study on the hsiaolin catastrophic landslide including its kinematic process and the geometry of deposition based on geomorphologic analysis the landslide initiated in thick multi aged colluvium soils at the headwaters of a small stream upslope of hsiaolin village a 3d discrete element program pfc3d was used to model the kinematic process that led to the landslide and destruction of hsiaolin village the landslide advanced from debris slide to debris avalanche during the kinematic process assuming a friction coefficient of each particle of 0 1 the predicted maximum velocity was about 70 m s a velocity which permits the debris to cross qishanxi stream and deposit on the opposite bank based on simulation results hsiaolin village was inundated in 60 to 65 s after failure initiation and at 112 s after the event the debris avalanche came to rest forming a landslide dam

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

diagenetic implications of stylolitization in pelagic carbonates canterbury basin offshore new zealand abstract stylolites are irregular discontinuity surfaces that are thought to result from localized stress induced dissolution during burial or tectonic compression the genesis of stylolites and the controls on stylolitization are still debated and the interplay between stylolitization generation of carbonate rich fluids diagenetic fluid flow within fractures and matrix cementation and porosity modifications is complex all of these processes have important diagenetic effects potentially altering the intrinsic properties of the host rock with implications for hydrocarbon exploration and water resources in aquifers we investigate the process of stylolitization by a macroscopic petrographic and geochemical study of pressure solution features in eocene to early oligocene limestones in cores from the integrated ocean drilling program iodp hole 317 u1352c canterbury basin the results indicate correlations among stylolite amplitude stylolite density and siliciclastic content of the host rock these relationships are interpreted to suggest that siliciclastic content in carbonate rocks increases heterogeneity which in turn impacts stylolite nucleation moreover the geochemical data support that clay along the stylolite is not authigenic but a relict from impurities in the limestone host rock the statistical approach of stylolite spacing used in this study which is different than previous studies reinforces the model of random occurrence of stylolites in carbonate lithologic units this study shows that local stresses in tectonically passive areas may allow the formation of rare oblique stylolites with peaks perpendicular to the stylolite plane estimation of the amount of limestone dissolved during stylolitization minimum 7 to 12 of the depositional limestone and the volume of sparite in the host rock up to 1 6 of the compacted limestone suggests that the pressure solution fluids cemented the micropores reducing porosity to about 10 from a common porosity of about 40 in mechanically compacted chalk this study thus highlights the importance of microporosity as a sink for burial cements an observation difficult to make in thin section analysis of stylolite infills at site u1352 shows no evidence that the stylolites acted as conduits for diagenetic fluids unless if the fluid was host rock buffered and thus its chemistry indistinguishable from that of the host rock the link between siliciclastic content in carbonate rocks and the spacing and amplitude of stylolites improves understanding of burial compaction processes predicting the morphology and spacing of stylolites in the subsurface can be used to identify baffles to cross stylolite fluid flow or cementation of microporosity influencing heterogeneity of petrophysical properties in subsurface reservoir host rocks

crustal velocity structure across the eastern snake river plain and the yellowstone swell teleseismic receiver functions are used to estimate the crustal structure beneath a 36 station 500 km long nw oriented linear array centered on the eastern snake river plain and crossing the yellowstone hotspot swell 250 km sw of yellowstone structure derived previously for this region from wide angle reflection data is used as an initial model and this structure explains most features observed in our receiver functions based on a combination of forward and inverse modeling our data require several modifications to the initial structure 1 moho depth is 42 km beneath most of the snake river plain shallows to 37 km to either side and thickens abruptly to 47 km beneath sw wyoming 2 a midcrustal layer interpreted previously as a 9 km thick gabbroic sill is flat topped across the entire 90 km width of the snake river plain and 3 a low velocity layer is found beneath and southeast of the snake river plain which probably is partially molten lower most crust using the seismic structure of the crust to estimate the crustal load upon the mantle and assuming local isostasy we calculate that mantle beneath the yellowstone swell is approximately uniformly as buoyant as 12 million year old ocean mantle and more buoyant than the adjacent wyoming mantle by an amount equivalent of 1 5 km of elevation the transition between these regions of greatly different mantle occurs across a major paleozoic boundary that now separates the basin and range from the rocky mountains

the evolution of the samaoding paleolandslide river blocking event at the upstream reaches of the jinsha river tibetan plateau abstract a large number of landslides have occurred in the upstream reaches of the jinsha river tibetan plateau due to the intensity of tectonic movement in the area remote sensing and field investigation indicate that one of them the samaoding paleolandslide previously blocked the river various river blocking phenomena are well preserved including the old landslide dam and deposits fluvial sediments and hydrostatic sandy sediment to better understand the evolution of the samaoding landslide the authors carried out thermoluminescence tl dating and numerical simulations the tl analysis shows that the landslide occurred at 10 6 0 5 ka bp discrete element method dem simulation of the landslide based on landform restoration provided results that are consistent with field observations the simulation indicates that the entire landslide process lasted for 80 s and the sliding mass reached a maximum velocity of 64 m s the landslide formed a landslide dam with a length of 1900 m a width of 600 m and a depth of 200 m the simulation results show that the level of the riverbed at that the time of the landslide was at least 25 m higher than it is today on the combined basis of the simulation results and field observations the authors propose explanation that the following valley evolution sequence occurred after river blocking the landslide dam experienced flood overtopping and then was eroded until it had mostly had been transported away by river flow and the river then rapidly incised the bedrock to form the present day landform based on the field investigations the authors summarize the failure mechanism of steep inclined antidip rockslides and found that tectonics play an important role in the formation of landslide dams or trigger of landslides and the failure of landslide dams in an active tectonic environment of tibetan plateau

synchroneity of major late neogene sea level fluctuations and paleoceanographically controlled changes as recorded by two carbonate platforms shallow water carbonate systems are reliable recorders of sea level fluctuations and changes in ambient seawater conditions drilling results from ocean drilling program odp legs 133 and 166 indicate that the timing of late neogene sedimentary breaks triggered by sea level lowerings is synchronous in the sedimentary successions of the queensland plateau and the great bahama bank this synchrony indicates that these sea level changes were eustatic in origin the carbonate platforms were also affected by contemporary paleoceanographically controlled fluctuations in carbonate production paleoceanographic changes are recorded at 10 7 3 6 and 1 7 2 0 ma at the queensland plateau sea surface temperature shifts are documented by shifts from tropical to temperate carbonates 10 7 ma and vice versa 3 6 ma the modern tropical platform was established at 2 0 1 8 ma at great bahama bank changes were registered in compositional variations of platform derived sediment such as major occurrence of peloids 3 6 ma and higher rates of neritic carbonate input 1 7 ma the synchroneity of these changes attests to the far field effects of modifications in the oceanographic circulation on shallow water low latitude carbonate production

regional trends in clay mineral fluxes to the queensland margin and ties to middle miocene global cooling abstract three odp sites located on the marion plateau northeast australian margin were investigated for clay mineral and bulk mineralogy changes through the early to middle miocene kaolinite to smectite k s ratios as well as mass accumulation rates of clays point to a marked decrease in accumulation of smectite associated with an increase in accumulation of kaolinite starting at 15 6 ma followed by a second increase in accumulation of kaolinite at 13 2 ma both of these increases are correlative to an increase in the calcite to detritus ratio comparison of our record with published precipitation proxies from continental queensland indicates that increases in kaolinite did not correspond to more intense tropical humid conditions but instead to periods of greater aridity three mechanisms are explored to explain the temporal trends in clay on the marion plateau sea level changes changes in oceanic currents and denudation of the australian continent followed by reworking and eolian transport of clays though low mass accumulation rates of kaolinite are compatible with a possible contribution of eolian material after 14 ma when australia became more arid the lateral distribution of kaolinite along slope indicates mainly fluvial input for all clays and thus rules out this mechanism as well as oceanic current transport as the main controls behind clay accumulation on the plateau we propose a model explaining the good correlation between long term sea level fall decrease in smectite accumulation increase in kaolinite accumulation and increase in carbonate input to the distal slope locations we hypothesize that during low sea level and thus periods of drier continental climate in queensland early miocene kaolinite rich lacustrine deposits were being reworked and that the progradation of the heterozoan carbonate platforms towards the basin center favored input of carbonate to the distal slope sites the major find of our study is that increase kaolinite fluxes on the queensland margin during the early and middle miocene did not reflect the establishment of a tropical climate and this stresses that care must be taken when reconstructing australian climate based on deep sea clay records alone

the tsaoling landslide triggered by the chi chi earthquake taiwan insights from a discrete element simulation article i nfo in the village of tsaoling in yunlin county taiwan a major landslide was triggered by the chi chi earthquake in 1999 with more than 125 10 6 m 3 of rock displaced the kinematic behaviour of this landslide is simulated using a 2d discrete element model pfc2d code our numerical model is composed of discs bonded together the initial boundary conditions are applied along the ball wall contacts by using derived velocities integrated from the strong motion data with a duration of 160 s including the peak acceleration near tsaoling the constraints are mainly issued from the final geometry of the landslide including its capacity to cross the river valley and reach a significant elevation on the opposite mountain flank they also result from a variety of geological and hydrological observations including the local levels of material disruption and the location of survivors our modelling thus indicates that a low friction coefficient about 0 15 and a medium strength are required to account for the actual landslide characteristics a self lubrication mechanism probably accounts for the low residual friction our model also suggests that the maximum velocity of sliding reached 50 m s a result that cannot be checked in the absence of actual measurements in addition to friction the strength of sliding block is of special importance because it controlled the possibility for the upper layer fragments to roll and get buried and hence the probability of survival

linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved yellowstone type supervolcanoes the geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations the a d 1815 tambora indonesia eruption perhaps nowhere on earth are deposits of such supereruptions more prominent than in the snake river plain yellowstone plateau srp yp volcanic province northwest united states while magmatic activity at yellowstone is still ongoing the heise volcanic field in eastern idaho represents the youngest complete caldera cycle in the srp yp and thus is particularly instructive for current and future volcanic activity at yellowstone the heise caldera cycle culminated 4 5 ma ago in the eruption of the 1800 km3 kilgore tuff accessory zircons in the kilgore tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity and the vast majority are 18o depleted this suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low 18o meteoric hydrothermal fluids prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir u pb geochronology of isotopically diverse zircons using chemical abrasion isotope dilution thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206pb 238u date of 4 4876 0 0023 ma mswd 1 5 n 24 these zircon crystallization ages are also indistinguishable from the sanidine 40ar 39ar dates and thus zircons crystallized close to eruption this requires that shallow crustal melting assembly of isolated batches into a supervolcanic magma reservoir homogenization and eruption occurred extremely rapidly within the resolution of our geochronology 103 104 yr the crystal scale image of the reservoir configuration with several isolated magma batches is very similar to the reservoir configurations inferred from seismic data at active supervolcanoes the connection of magma batches vertically distributed over several kilometers in the upper crust would cause a substantial increase of buoyancy overpressure providing an eruption trigger mechanism that is the direct consequence of the reservoir assembly process

lake toba volcano magma chamber imaged by ambient seismic noise tomography 1 for the first time ambient noise tomography is used to clearly image the magma chamber beneath lake toba caldera one of the largest quaternary calderas on earth using data from 40 seismic stations deployed between may and october 2008 around lake toba empirical green s functions are extracted from long term cross correlations of continuous records these functions are dominated by rayleigh waves whose group velocities can be measured in the period range from 2 5 to 12 seconds arrival times of these waves are picked for a given period and inverted using 2 d tomography to calculate lateral variations in velocity for the given period this was done for six different periods which all correspond to different sampling depths thus the six 2 d models presented together provide information on velocity variations with depth the results show a low velocity body coincident with the lake toba caldera representing the magma chamber under the volcano the chamber is observed to have a complex 3 d geometry with at least two separate sub chambers underlying the caldera other results include a deep low velocity body possibly another magma chamber south west of the lake with an upper limit of 7 km depth the maximum depth to which this body reaches could not be resolved the sumatra fault marks a velocity contrast but only down to depths not greater than 5 km the reliability of the results was further confirmed by checkerboard recovery tests

zircon petrochronology and 40ar 39ar sanidine dates for the mesa falls tuff crystal scale records of magmatic evolution and the short lifespan of a large yellowstone magma chamber

voluminous low δ18o magmas in the late miocene heise volcanic field idaho implications for the fate of yellowstone hotspot calderas we report oxygen isotope compositions of phenocrysts and u pb ages of zircons in four large caldera forming ignimbrites and post caldera lavas of the heise volcanic field a nested caldera complex in the snake river plain that preceded volcanism in yellowstone early eruption of three normal 18 o voluminous ignimbrites with 18 o quartz 6 4 and 18 o zircon 4 8 started at heise at 6 6 ma and was followed by a 2 3 18 o depletion in the subsequent 4 45 ma kilgore caldera cycle that includes the 1800 km 3 kilgore ignimbrite and post kilgore intracaldera lavas with 18 o quartz 4 3 and 18 o zircon 1 5 the kilgore ignimbrite represents the largest known low 18 o magma in the snake river plain and worldwide the post kilgore low 18 o volcanism likely represents the waning stages of silicic magmatism at heise prior to the reinitiation of normal 18 o silicic volcanism 100 km to the northeast at yellowstone the occurrence of low 18 o magmas at heise and yellowstone hallmarks a mature stage of individual volcanic cycles in each caldera complex sudden shifts in 18 o of silicic magmas erupted from the same nested caldera complexes argue against any inheritance of the low 18 o signature from mantle or crustal sources instead 18 o age trends indicate progressive remelting of low 18 o hydrothermally altered intracaldera rocks of previous eruptions this trend may be generally applicable to older caldera complexes in the snake river plain that are poorly exposed

origin and evolution of silicic magmatism at yellowstone based on ion microprobe analysis of isotopically zoned zircons the origin of large volume yellowstone ignimbrites and smallervolume intra caldera lavas requires shallow remelting of enormous volumes of variably o depleted volcanic and sub volcanic rocks altered by hydrothermal activity zircons provide probes of these processes as they preserve older ages and inherited do values this study presents a high resolution oxygen isotope examination of volcanism at yellowstone using ion microprobe analysis with an average precision of 0 2o and a 10 mm spot size we report 357 analyses of cores and rims of zircons and isotope profiles of 142 single zircons in 11 units that represent majoryellowstone ignimbrites and post caldera lavas many zircons from these samples were previously dated in the same spots by sensitive high resolution ion microprobe shrimp and all zircons were analyzed for oxygen isotope ratios in bulk as a function of grain size by laser fluorination we additionally report oxygen isotope analyses of quartz crystals in three units the results of this work provide the following new observations 1 most zircons from post caldera low do lavas are zoned with higher do values and highly variable u pb ages in the cores that suggest inheritance from pre caldera rocks exposed on the surface 2 many of the higher do zircon cores in these lavas have u pb zircon crystallization ages that postdate caldera formation but pre date the eruption age by 10 20 kyr and represent inheritance of unexposed post caldera sub volcanic units that have do similar to the lava creek tuff 3 young and voluminous 0 25 0 1ma intra caldera lavas which represent the latest volcanic activity atyellowstone contain zircons with both high do and lowdo cores surrounded by an intermediate do rim this implies inheritance of a variety of rocks from high do pre caldera and low do post caldera units followed by residence in a common intermediate do melt prior to eruption 4 major ignimbrites of huckleberry ridge and to a lesser extent the lava creek and mesa falls tuffs contain zoned zircons with lower do zircon cores suggesting that melting and zircon inheritance from the lowdo hydrothermally altered carapace was an important process during formation of these large magma bodies prior to caldera collapse 5 the do zoning in the majority of zircon core rim interfaces is step like rather than smoothly inflected suggesting that processes of solution reprecipitation were more important than intracrystalline oxygen diffusion concave downward zircon crystal size distributions support dissolution of the smaller crystals and growth of rims on larger crystals this study suggests that silicic magmatism atyellowstone proceeded via rapid shallow level remelting of earlier erupted and hydrothermally alteredyellowstone source rocks and that pulses of basaltic magma provided the heat for melting each postcaldera yellowstone lava represents an independent homogenized magma batch that was generated rapidly by remelting of source rocks of various ages and do values the commonly held model of a single large volume super solidus mushy state magma chamber that is periodically reactivated and produces rhyolitic offspring is not supported by our data rather the source rocks for theyellowstone volcanism were cooled below the solidus hydrothermally altered by heated meteoric waters that caused low do values and then remelted in distinct pockets by intrusion of basic magmas each packet of new melt inherited zircons that retained older age and do values this interpretation may have significance for interpreting seismic data for crustal low velocity zones in which magma mush and solidified areas experiencing hydrothermal circulation occur side by side new basalt intrusions into this solidifying batholith are required to form the youngest volcanic rocks that erupted as independent rhyolitic magmas we also suggest that the lava creek tuff

catastrophic detachment and high velocity long runout flow of kolka glacier caucasus mountains russia in 2002 abstract in september 2002 a catastrophic geomorphic event occurred in the caucasus mountains southern russia in which almost the entire mass of kolka glacier detached from its bed accelerated to a very high velocity max 65 80 m s and traveled a total distance of 19 km downstream as a glacier debris flow based on the interpretation of satellite imagery obtained only 8 5 h before the event occurred the analysis of seismograms from nearby seismic stations and subsequent detailed field observations and measurements we suggest that this remarkable event was not a response to impulse loading from a rock avalanche in the mountainside above the glacier or to glacier surging but due entirely to the static and delayed catastrophic response of the kolka glacier to ice and debris loading over a period of months prior to the september 20 detachment we reconstruct the glacier debris flow using field observations in conjunction with the interpretation of seismographs from nearby seismic stations and successfully simulate the behaviour runout velocity and deposition of the post detachment glacier debris flow using a three dimensional analytical model our demonstration of a standing start hypothesis in the 2002 kolka glacier detachment has substantial implications for glacier hazard assessment and risk management strategies in valleys downstream from unstable debris covered glaciers in the mountain regions of the world

mass movement in the himalaya new insights and research directions abstract ongoing studies that relate tectonics to the processes at the surface of earth show that many more sources of information about agents of shallow denudation such as mass movement are required to comprehend the long term erosion that leads to deep denudation over geologic time mass movement in the himalaya is scale dependent from the massive extension of whole mountain ranges gravity tectonics through the sackung failure of single peaks to the smallest slope failures generally denudation of the himalayan orogen begins with slope failure onto glaciers and into river valleys and continues by glacial and fluvial transport the maximum size of stable slopes and mean angles of slope that are produced by these failures are complex and controlled by a variety of factors including mass strength of the rocks stress fields angles of internal friction controlled by rock type cohesion that includes the control of rock temperature bulk unit weight of rock and discontinuities the processes of mass movement in the himalaya have been described many times for the past two centuries recently developments in a variety of fields have been introduced to assess the character of mass movement geomorphometry remote sensing digital elevation models and geographic information system technology are revolutionizing the study of mass movement in the himalaya

dynamic process analysis for the initiation and movement of the donghekou landslide debris flow triggered by the wenchuan earthquake the donghekou landslide debris flow was a remarkable geological disaster triggered by the wenchuan earthquake in 2008 the dynamic process of a rapid landslide debris flow is very complicated and can be divided into two aspects the slope dynamic response of the earthquake and the mass movement and accumulation process a numerical method combined with a finite difference method fdm and discrete element method dem for simulation of landslide debris flow under seismic loading is presented the fdm and dem are coupled through the critical sliding surface initiation time and velocity the dynamic response of the slope is simulated by the finite difference method and critical sliding surface is determined using the earthquake response spectrum method the landslide initiation time and the velocity are determined by time history analysis the mass movement and accumulation process is simulated using the discrete element method simulation results demonstrate that the maximum amplification coefficient of dynamic acceleration for the donghekou slope is approximately 3 909 the initiation time of landslide is approximately 6 0 s and the average initial velocity of the sliding mass is approximately 0 85 m s the failure of the slope is the result of elevation orientated amplification effect and the sliding mass triggered with a small initial velocity the numerical simulated result of the maximum sliding velocity is approximately 66 35 m s and the mass is disintegrated rapidly because of collision and free fall the landslide velocity decreases when the flowing mass reaches a lower slope angle and gradually comes to a stop and the total travel distance is approximately 2400 m c 2013 elsevier ltd all rights reserved

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

evolution of the large landslide induced by typhoon morakot a case study in the butangbunasi river southern taiwan using the discrete element method abstract in 2009 typhoon morakot delivered high intensity rainfall and triggered many sites of large landslide which projected areas were larger than 10 000 m 2 from the satellite image especially in southern taiwan according to dtm analysis the material volume of the large landslide in butangbunasi river was more than four times larger than that of the nearly famous landslide disaster in hsiaolin village nevertheless the different movement of these two large landslides led to different disaster impacts based on literatures and field works the large hsiaolin landslide was a catastrophic landslide which had high velocity and less energy loss in the kinematic process the source area of the large landslide in the butangbunasi river on the other hand was composed of several landslide events and the kinetic energy dissipated when the landslide materials attained to riverbed in sequence in this study we divided the butangbunasi river large landslide into five slope units namely a b c d and e landslide events to recognize the mechanism of the large landslide and the simulation by using the particle flow code 3d pfc3d which is based on the discrete element method provided the kinematic process of the large landslide in the butangbunasi river it is noticed that most of the initial energy dissipated during the movement which the fist happening landslide event counteracted the crash of the follow up events and the residual energy gradually declined by the collision interaction of landslide blocks until the end of the large landslide the result helps to reconstruct the evolution of the large landslide from small scale landslide events and contributes to predict the affected region of the disaster it also reveals that even though the impact of the large landslide is reduced by sequent small scale landslide events there still remain secondary disasters such as landslide dam which show a high potential risk in the river valley and midstream

silicic recharge of multiple rhyolite magmas by basaltic intrusion during the 22 6 ka okareka eruption episode new zealand abstract deposits of the 22 6 ka okareka eruption episode from tarawera volcanic complex record the sequential and simultaneous eruption of three discrete rhyolite magmas following a silicic recharge event related to basaltic intrusion the episode started with basaltic eruption 0 01 km3 magma and rapidly changed to a plinian eruption involving a moderate temperature 750 c cummingtonite bearing rhyolite magma t1 with a volume of 0 3 km3 hybrid basalt rhyolite clasts demonstrate direct basaltic intrusion that helped trigger the eruption crystals shards and lapilli of two other rhyolite magmas then joined the eruption sequence they comprise a cooler 720 c crystal rich biotite hornblende rhyolite magma t2 0 3 km3 and a hotter 780 c crystal poor pyroxene hornblende rhyolite magma t3 4 5 km3 all mid to late stage ash units contain various mixtures of t1 t2 and t3 components with a general increase in abundance of t3 and rapid decline of t1 with time about 4 km3 of t3 magma was extruded as lavas at the end of the episode contrasts in melt composition crystal and volatile contents and temperatures influenced viscosity and miscibility and thus limited pre eruption mixing of the rhyolite magmas the eruption sequence and the restricted direct basaltic intrusion into only one magma t1 is consistent with the rhyolites occupying separate melt pods within a large crystal mush zone melt crystal equilibria and volatile contents in melt inclusions indicate temporary magma storage depths of

limits of hydrosphere lithosphere interaction origin of the lowest known δ18o silicate rock on earth in the paleoproterozoic karelian rift geologic records of earth9s hydrosphere and meteoric precipitation older than 2 ga are rare although they provide insight into the past climate rates of water rock interaction and intensity of plate tectonics here we report and describe in detail the lowest known 18 o 16 to 25 terrestrial silicate rocks on earth found in paleoproterozoic plagiogneisses from the belomorian complex karelia russia geochronologic and oxygen isotopic data on zircons 7 to 26 and monazite 17 5 imply that the protoliths of these rocks were ca 2 5 ga metasediments and metavolcanics that were hydrothermally altered prior to 1 85 ga within an intracontinental rift zone and involved ultralow 18 o 18 o waters outside of polar regions or the interiors of large landmasses provide independent evidence for a moderately glaciated so called slushball earth climate between 2 45 and 2 4 ga in which low or mid latitude mid size continents were covered with glaciers while the ocean remained at least partially unfrozen to allow for intracontinental isotopic distillation in a large temperature gradient in addition to these climatic inferences the data are more readily explained by a depleted 10 seawater reservoir during paleoproterozoic time

the role of crustal melting in the formation of rhyolites constraints from sims oxygen isotope data chon aike province patagonia argentina

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com