examining geodetic glacier mass balance in the eastern pamir transition zone glaciers in the eastern pamir have reportedly been gaining mass during recent decades even though glaciers in most other regions in high mountain asia have been in recession questions still remain about whether the trend is strengthening or weakening and how far the positive balances extend into the eastern pamir to address these gaps we use three different digital elevation models to reconstruct glacier surface elevation changes over two periods 2000 09 and 2000 15 16 we characterize the eastern pamir as a zone of transition from positive to negative mass balance with the boundary lying at the northern end of kongur tagh and find that glaciers situated at higher elevations are those with the most positive balances most 67 of 55 glaciers displayed a net mass gain since the 21st century this led to an increasing regional geodetic glacier mass balance from 0 06 0 16 m w e a 1 in 2000 09 to 0 06 0 04 m w e a 1 in 2000 15 16 surge type glaciers which are prevalent in the eastern pamir showed fluctuations in mass balance on an individual scale during and after surges but no statistical difference compared to non surge type glaciers when aggregated across the region

characterizing the surge behavior of alakesayi glacier in the west kunlun shan northwestern tibetan plateau from remote sensing data between 2013 and 2018

rutile solubility in albite h2o and na2si3o7 h2o at high temperatures and pressures by in situ synchrotron radiation micro xrf abstract rutile is an important mineral host for high field strength elements so its solubility in geologic fluids at high pressure and temperature plays an important role in the crustal and mantle processes that control the terrestrial cycling of these elements however experimental measurements of rutile solubility are in conflict by a factor of more than 100 at most studied conditions we performed new measurements of rutile solubility in h 2 o albite and h 2 o na 2 si 3 o 7 ns3 fluids by in situ synchrotron radiation x ray fluorescence spectroscopy using modified bassett type hydrothermal diamond anvil cells minimum detection limits were 1 9 and 2 3 ppm ti by weight for the two cells three albite h 2 o experiments at starting bulk compositions of 2 7 6 7 and 10 3 wt albite involved spectral acquisition at rutile saturation in the presence of albite crystals melt or a single homogeneous fluid phase after accounting for the additional phases corrected fluid compositions were 0 6 to 7 5 wt dissolved silicate over the run conditions at 2 7 wt albite rutile dissolution rate was slow and steady state was not achieved at 600 800 c however at higher dissolved albite contents constant solubility with time was observed rutile solubilities in the presence of a single fluid phase at 700 c 0 79 gpa 5 4 wt albite and at 800 c 1 10 gpa 6 7 wt albite were 37 2 and 156 6 ppm respectively these data agree with results acquired using hydrothermal piston cylinder methods with long run times and suppression of new crystal growth but not with data derived from visual observation in hydrothermal diamond anvil cells this discrepancy is likely due to lack of equilibrium in the latter approach two experiments in 10 and 30 wt ns3 at 660 800 c 0 5 0 1 gpa show extreme concentration dependent enhancement of rutile solubility to 4500 ppm the data indicate a strong positive correlation between rutile solubility and na al because na k al is likely to be greater than unity in aqueous fluids at high pressure and temperature due to incongruent dissolution of albite and micas the increase in rutile solubility along the albite ns3 join points to the possibility of significant ti transport by silicate bearing aqueous fluids in the lower crust and upper mantle

in situ elemental and sr isotope characteristics of magmatic to hydrothermal minerals from the black mountain porphyry deposit baguio district philippines at the black mountain porphyry cu au deposit in the baguio district northern luzon philippines pre and synmineralized rocks preserve magmatic and hydrothermal minerals e g plagioclase amphibole titanite and epidote spanning the complete paragenesis of the deposit strontium isotope values in early crystallized plagioclase phenocrysts from all felsic porphyries can be divided into two types the type i plagioclase crystals show relatively homogeneous sr isotope values 0 7035 0 7038 1 0 0001 indicating crystallization from a relatively stable and long lived felsic magma chamber the type ii plagioclase grains have a wider range of sr isotope compositions 0 7032 0 7039 1 0 0001 indicating mafic and or felsic magma recharge in magmatic titanite nb ta values are higher than those in the whole rock while zr hf and y ho values are lower in hydrothermal titanite and epidote the ratios are similar to those in the whole rock these patterns reflect crystallization effects imposed during the magmatic stage but an absence of differentiation during the hydrothermal stage the consistent gradual decrease in total rare earth element y zr and u contents in both hydrothermal titanite and epidote from early to late stages indicates the effect of hydrothermal fluid evolution with decreasing temperature the variation of 87sr 86sr values in magmatic amphibole plagioclase and hydrothermal epidote in felsic and mafic rocks indicates the addition of mafic magma derived fluid into the felsic magma derived fluid one extra source of fluid probably derived from wall rock limestone was required to generate the highly radiogenic 87sr 86sr values of some epidote 0 7038 0 7053 thus in situ elemental and sr isotope variation in minerals from different paragenetic stages can be used to interpret formation process and source for both magmas and hydrothermal fluids

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

metamorphosed soils as stratigraphic indicators in deformed terranes an example from the eastern alps amphibolite facies schists of anomalously high aluminum and iron content occur along a major unconformity in the tauern window austria their stratigraphic position is consistent with a weathering or paleosol origin for the protolith this interpretation is supported by geochemical data previous paleosol studies have concentrated on their significance as paleoenvironmental indicators the use of the tauern window schists for this purpose is precluded by their metamorphic grade and degree of deformation however these and other similar metasoils can serve as valuable field indicators in structurally complicated areas

topographic parameterization in continental hydrology a study in scale digital elevation models dems are useful and popular tools from which topographic parameters can be quickly and efficiently extracted for various hydrologic applications dems coupled with automated methods for extracting topographic information provide a powerful means of parameterizing hydrologic models over a wide range of scales however choosing appropriate dem scales for particular hydrologic modelling applications is limited by a lack of understanding of the effects of scale and grid resolution on land surface representation the scale effects of aggregation on square grid dems of two continental scale basins are examined base dems of the mackenzie and missouri river basins are extracted from the hydro1k dem of north america successively coarser grids of 2 4 8 64 km were generated from the base dems using simple linear averaging topaz topographic parameterization was applied to the base and aggregated dems using constant critical source area and minimum source channel length values to extract topographic variables at varying scales or resolutions the effects of changing dem resolution are examined by considering changes in the spatial distribution and statistical properties of selected topographic variables of hydrological importance the effects of increasing grid size on basin and drainage network delineation and derived topographic variables tends to be non linear in particular changes in overall basin extent and drainage network configuration make it impractical to apply a simple scaling function to estimate variable values for fine resolution dems from those derived from coarse resolution dems results also suggest the resolution to which a dem can be reduced by aggregation and still provide useful topographic information for continental scale hydrologic modelling is that at which the mean hydraulic slope falls to approximately 1 in this study that generally occurred at a resolution of about 10 km

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

fractal techniques and the surface roughness of talus slopes linear plots of log n against log g where n is the number of steps of length g to span a transit are conventionally used as evidence that geomorphic surfaces are self similar fractals i e the surfaces have a constant fractal dimension in this study 42 transits on talus slope surfaces in niagara and letchworth gorges western new york are investigated to ascertain whether they are self similar log n log g plots which r2 values in excess of 0 99 suggest are linear are found upon more rigorous testing to be curvilinear it is concluded that the talus slope surfaces are not self similar and that log n log g plots are relatively insensitive to departures from self similarity the curvilinearity of the log n log g plots is explained with the aid of a randomized square wave model of the talus slope surfaces this model is used to extend the range of measurement beyond that which was possible in the empirical analysis the negative of the gradient of the log n log g relation at a point is the fractal dimension d measurements made upon the randomized square wave model indicate that the relation between d and scale of measurement has an asymmetrical wave shape with a peak i e maximum d where the scale of measurement is equal to the characteristic scale of roughness in other words the value of d for a surface is not absolute but depends on the scale of measurement relative to the scale of roughness linear regression analysis reveals that at the scale of measurement employed in this study d is positively correlated with particle size this is because the values of d fall on the right hand tail of the wave shaped relation between d and scale of measurement transects normal to the direction of slope are found to have higher values of d than profiles parallel to the direction of slope and this is explained in terms of particle orientation shape and juxtaposition because d varies continuously with scale of measurement there are considerable difficulties in using it to characterize and compare the surface roughness of talus slopes generalizing from talus slopes to other ground surfaces it is evident that to the extent that any natural ground surface has a characteristic scale of roughness it will depart from self similarity and d should be used with caution in quantifying the roughness of the surface geomorphologists are therefore urged to be more rigorous in their testing of self similarity before employing d to characterize surface roughness

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

diffusion induced fractionation of niobium and tantalum during continental crust formation differentiation of the earth into its major spheres crust mantle and core has proceeded dominantly through magmatic processes involving melting and melt separation models that describe these differentiation processes are guided by elemental abundances in the different reservoirs elements are fractionated between coexisting phases during partial melting and geochemical models are generally based on the fundamental assumption that trace element equilibrium is established between the partial melts and the restitic minerals the element pair niobium and tantalum is key to the distinction of different melting regimes involved in crustal differentiation but equilibrium partition models have largely failed to reproduce the nb ta patterns observed in nature posing a long standing geochemical conundrum here we demonstrate that kinetic fractionation of nb and ta by diffusion may have produced the low nb ta observed in the continental crust on the basis of the diffusivities of nb and ta in rutile tio2 determined experimentally in this study we conclude that equilibrium cannot be expected for the natural range of grain sizes temperatures and time scales involved in partial melting of crustal rocks instead the observed fractionation of the geochemical twins nb and ta in the silicate earth most likely proceeds by partial as opposed to complete equilibration of rutile and melt hence the assumption of bulk equilibrium during partial melting for the processes of crustal differentiation may not be justified as is demonstrated here for nb ta the concept presented here is based on kinetic fractionation melting and explains the observed low nb ta ratio of the continental crust

enhanced mass transfer through short circuit diffusion growth of garnet reaction rims at eclogite facies conditions in the monte rosa area northern italy the assemblage garnet phengite quartz was formed in polymetamorphic metapelites from pre existing biotite and plagioclase during an eclogite facies alpine metamorphic overprint while phengite nucleated within plagioclase garnet formed 10 to 20 m wide continuous rims along the original biotite plagioclase interphase boundaries garnet formation involved diffusion of ca fe and mg bearing species across the growing rims the garnet rims show an overall asymmetric compositional zoning and distinct nanometer scale chemical patterns across grain boundaries within the garnet polycrystal the compositional patterns resulted from the interplay of diffusion along grain and interphase boundaries and volume diffusion individual garnet crystals are separated by low angle grain boundaries which are predominantly oriented perpendicular to the reaction rim giving rise to an overall palisade microstructure grain boundaries contain arrays of closely spaced channels about 2 nm wide which are filled with an amorphous phase these channels represent direct links between the garnet biotite and garnet plagioclase reaction fronts and provide pathways for fast diffusion from numerical simulation of the observed chemical patterns diffusion of ca and fe is inferred to have been 5 6 orders of magnitude faster within grain boundaries than through the interior of garnet grains although the amorphous grain boundary phase only takes up a small fraction 2 5 per mil of the total volume of the garnet polycrystal short circuit diffusion along grain boundaries contributed substantially to material transfer across the growing garnet rim despite the presence of fast pathways bulk diffusion was too slow to allow for chemical equilibration of the phases involved in garnet rim formation even on a micrometer scale relying on published garnet volume diffusion data d gb where gb grain boundary is estimated to be on the order of 10 19 20 m 2 s at the estimated reaction conditions of 650 c and 12 5 kbar where d gb ca is slower than d gb fe by a factor of ten

the morphology of the reaction front of the dissolution precipitation reaction rutile wollastonite titanite in time series experiments at 600 c 400 mpa fluid assisted mass transport reactions by dissolution precipitation where a precursor mineral reacts with a fluid play an important role in metamorphism and metasomatism we investigated titanite growth on rutile in time series experiments between one and 107 days at constant p t conditions of 600 c and 400 mpa in the system tio 2 cao sio 2 na 2 o hcl h 2 o a two capsule assemblage allows for transport of ca and si from dissolving wollastonite to dissolving rutile the ti source in a nacl bearing aqueous fluid according to the general reaction casio 3 tio 2 catisio 5 complete overgrowth of rutile by titanite occurred after just one day of experiment fine grained lozenge shaped titanite crystals of short time runs up to 14 days reorganize to larger predominantly prismatic crystals after 14 days after investigation by scanning electron microscopy the titanite overgrowth was removed from the rutile by hydrofluoric acid to provide a three dimensional view of the dissolution reaction front on the rutile surface the morphology of the rutile surface is dominated by humps or ridges beneath the central region of a titanite crystal and valleys at the grain boundaries between adjacent titanite crystals the dissolution pattern on the rutile surface mimics the titanite overgrowth and changes with changing grain size and shape of the titanite with longer run times the preferred dissolution of rutile in the valleys is clearly linked to the position of the titanite grain boundaries which served as pathways for fluid assisted element transport rutile titanite and titanite titanite boundaries show a significant porosity in transmission electron microscopy images of foils prepared by focused ion beam milling the large scale dissolution pattern on the rutile surface is independent of the crystallographic orientation of the rutile and entirely dominated by the arrangement of titanite crystals in the overgrowth dissolution features on a scale smaller than 1 m are dominated by stepwise dissolution and etch pits following the crystallographic orientation of the rutile similar observations were made in experiments with an additional al source although these experiments result in a different overgrowth pattern i e an exposed rutile surface is always present and solitary titanite crystals are accompanied by partial overgrowths quantitative characterization of the surface morphology by white light interference microscopy demonstrates that with increasing grain size of titanite dissolution of rutile is strongly enhanced at the titanite grain boundaries natural examples of titanite overgrowths on rutile show the same relations between element pathways arrangement of titanite crystals and 3d dissolution pattern on rutile as in the experimental systems we conclude that the transport of ti away from the rutile and of ca si into the reaction rim occurred in a grain boundary fluid the composition of which must have been strongly different from the composition of the bulk fluid in the experiment as well as in the natural system the reaction progress depends on the availability of a fluid and relicts of rutile in titanite indicate restricted availability of fluid in the natural system e g a fluid pulse that was consumed by the reactions the reaction examined here can serve as a proxy for other reactions of the conversion of oxide minerals e g spinel or corundum into silicates

fast glacier flow ice streams surging and tidewater glaciers fast flowing glaciers are unusual but important jakobshavns glacier in western greenland illustrates this point figure 1 considered to be the world s fastest glacier its maximum observed flow rate measured in midsummer near the floating terminus is 8360 m yr 1 lingle et al 1981 except for a tidal influence near the terminus the flow is believed to be fairly steady bindschadler 1984

multispectral imaging contributions to global land ice measurements from space global land ice measurements from space glims is an international consortium established to acquire satellite images of the world s glaciers analyse them for glacier extent and changes and assess change data for causes and implications for people and the environment although glims is making use of multiple remote sensing systems aster advanced spaceborne thermal emission and reflection radiometer is optimized for many needed observations including mapping of glacier boundaries and material facies and tracking of surface dynamics such as flow vector fields and supraglacial lake development software development by glims is geared toward mapping clean ice and debris covered glaciers terrain classification emphasizing snow ice water and admixtures of ice with rock debris multitemporal change analysis visualization of images and derived data and interpretation and archiving of derived data a global glacier database has been designed at the national snow and ice data center nsidc boulder colorado parameters are compatible with and expanded from those of the world glacier inventory wgi these technology efforts are summarized here but will be presented in detail elsewhere our presentation here pertains to one broad question how can aster and other satellite multispectral data be used to map monitor and characterize the state and dynamics of glaciers and to understand their responses to 20th and 21st century climate change our sampled results are not yet glaciologically or climatically representative our early results while indicating complexity are generally consistent with the glaciology community s conclusion that climate change is spurring glacier responses around the world mainly retreat whether individual glaciers are advancing or retreating the aggregate average of glacier change must be climatic in origin as nonclimatic variations average out we have discerned regional spatial patterns in glaciological response behavior these patterns are best attributed to climate change variability and to regional differences in glacier size and response times in many cases glacier length changes under represent the magnitude of glacier ablation because thinning sometimes without immediate length changes is also important an expanded systematic uniform analysis of many more glaciers is needed to isolate the glacier response components due to climatic and nonclimatic perturbations to produce quantitative measures of regional variation in glacier changes and to predict future regional glacier trends relevant to water resources glaciological hazards and global sea level this comprehensive assessment to be completed in stages is expected to lend a critically needed filter to identify successful climate models that explain recent glacier changes and change patterns and hence are apt to describe future changes and to eliminate unsuccessful models

very low solubility of rutile in h2o at high pressure and temperature and its implications for ti mobility in subduction zones the solubility of rutile in h2o has been measured at 1000 1100 c 1 2 gpa the data indicate that solubility is very low over the investigated range with a maximum of 4 7 millimol kg h2o at 1100 c 2 gpa the data were fit with the equation log m ti 4 892 10470 t 0 1923 p where m ti is ti molality t is in kelvins and p in gpa when compared to previous results the new data indicate substantially lower solubility opposite pressure dependence and thermodynamic properties of the reaction rutile tio2 aq that are now consistent with other oxide hydrolysis reactions calculations of ti transport during mantle metasomatism by h2o in subduction zone environments predict much lower ti mobility at all conditions these results offer strong support for models of ti retention in eclogites during slab devolatilization and require that examples of significant ti mass transfer be explained by complexing agents in solution most likely aluminosilicate complexes

heterogeneity in karakoram glacier surges many karakoram glaciers periodically undergo surges during which large volumes of ice and debris are rapidly transported downglacier usually at a rate of 1 2 orders of magnitude greater than during quiescence here we identify eight recent surges in the region and map their surface velocities using cross correlation feature tracking on optical satellite imagery in total we present 44 surface velocity data sets which show that karakoram surges are generally short lived lasting between 3 and 5 years in most cases and have rapid buildup and relaxation phases often lasting less than a year peak velocities of up to 2 km a 1 are reached during summer months and the surges tend to diminish during winter months otherwise they do not follow a clearly identifiable pattern in two of the surges the peak velocity travels down ice through time as a wave which we interpret as a surge front three other surges are characterized by high velocities that occur simultaneously across the entire glacier surface and acceleration and deceleration are close to monotonic there is also no consistent seasonal control on surge initiation or termination we suggest that the differing styles of surge can be partly accounted for by individual glacier configurations and that while some characteristics of karakoram surges are akin to thermally controlled surges elsewhere e g svalbard the dominant surge mechanism remains unclear we thus propose that these surges represent a spectrum of flow instabilities and the processes controlling their evolution may vary on a glacier by glacier basis

u pb systematics and trace element characteristics in titanite from a high pressure mafic granulite abstract simultaneous acquisition of u pb isotope ratios and trace element abundances across titanite crystals formed in an anatectic high pressure granulite using la icp ms split stream analysis has enabled evaluation of titanite compositional systematics and intracrystalline variability during growth and residence in high temperature melt present environments although the titanite studied here have a comparatively low initial pb pb 0 component pb 0 pb the pb 0 is highly radiogenic relative to model crustal values indicating inheritance from u bearing accessory minerals consumed in the melt titanite forming reactions additionally titanite crystals typically exhibit core rim decreases in pb 0 pb as defined by 204 pb 206 pb calculated 206 pb 0 206 pb t and uncorrected 206 pb 238 u spot date profiles near the margins this is clearly dominated by local u enrichment but in the uniformly low u interiors outwardly decreasing pb 0 pb appears to reflect decreasing pb 0 concentrations during growth the positive correlation among pb 0 and sr concentrations in crystal interiors over length scales of hundreds of micrometers is consistent with each having experienced similarly small degrees of diffusional relaxation given the high crystallization temperatures 800 c and likely slow cooling rates 5 c our data support slow pb diffusivity in titanite even at high temperature conditions as has been proposed in a number of recent studies along the outer 50 100 m u th zr and ree concentrations are variably elevated relative to the crystal interiors with profiles taking one of two forms 1 sharply increasing to highest concentrations inboard from the crystal edge and decreasing again to lower values near the crystal edge or 2 gradually increasing to highest concentrations nearest the crystal edge high contrast bse imaging shows that the former profiles are associated with 1 2 m wide bright bands surrounding polygonal subgrains that tend to be developed where titanite is or formerly was in contact with matrix feldspar i e crystallized melt and are inferred to represent trace element enriched dissolution precipitation reaction fronts the latter profiles are associated with diffuse locally wispy brightness gradients adjacent to resorbed crystal boundaries subgrain boundaries or thicker bright bands formed in contact with matrix hornblende crystals and are interpreted as regions of enhanced element mobility potentially resulting from the development of local micro porosity pathways at some point in the recrystallization process

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

redistribution of hfse elements during rutile replacement by titanite titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon we investigated an amphibolite sample from the tromso eclogite facies terrain in northern norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite patchy compositional zoning of al ti and f in titanite relates to the presence of a fluid with variable ti al and or f during its growth laser ablation icp ms and electron microprobe data for high field strength elements hfse nb zr ta and hf of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal 8 mm and a systematic decrease towards uniform hfse contents in the large core hfse contents of smaller rutile grains 0 5 mm and rutile inclusions 100 m in the titanite overgrowth are similar or higher than in the rims of large rutile crystals element profiles from the rim inward demonstrate that hfse enrichment in rutile is controlled by diffusion hfse ratios in diffusion altered rutile show systematic variations compared with the uniform core composition of the large rutile modelling of zr and nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems variations of hfse contents in the newly formed titanite show no systematic spatial distribution hfse ratios in titanite and the rims of rutile are different indicating different solid fluid distribution coefficients in these minerals element fractionation by diffusion into the relict rutile and during fluid mediated growth of new titanite could substantially change the hfse budget of these minerals and could affect their use for geochemical tracing and other applications such as zr based geothermobarometry

quantitative methods for analyzing the roughness of the seafloor the bathymetry of the world ocean has been mapped using a variety of acoustic sounding instruments and traditional contouring methods prior to this study relatively few quantitative studies have been focused on the detailed morphology of the seafloor the work of most investigators has generally dealt with the analysis of seafloor relief without regard to spatial frequency or concern for obvious morphologic anisotropies a brief review of previous work is presented and is accompanied by an identification of the specific applications and limitations of those approaches the availability of more precise digital sounding data coupled with the development of higher resolution sonar mapping instruments e g deeptow seamarc now make it possible to investigate quantitatively many important aspects of seafloor relief and the geological processes responsible for its formation typical bathymetric contour maps represent a low frequency deterministic model of the seafloor to describe the higher frequency variability or roughness of the seafloor requires the development of an appropriate statistical method for generating a valid stochastic model new methods are developed herein which allow valid statistical models of the variability of oceanic depths to be derived from existing digital bathymetric soundings the smooth contoured surface often preserved as a geographic grid of depths when supplemented by such a roughness model can provide an essentially complete statistical description of the relief statistical models of seafloor roughness are also valuable tools for predicting acoustic scattering and bottom loss and in addition contain a wealth of information for more comprehensive interpretations of deep sea relief forming geological processes to allow the variability of depths to be described as a function of scale spatial frequency the amplitude spectrum is employed as the fundamental statistic underlying the model since the validity of the amplitude spectrum depends upon the assumption of a statistically stationary sample space a computer algorithm operating in the spatial domain was developed which delineates geographic provinces of limited statistical heterogeneity within each of these provinces a spectral model is derived by fitting the amplitude estimates with one or two two parameter power law functions using specialized regression techniques the distribution of resultant model parameters is examined for a large test area adjacent to the coast of oregon 42 45 n 130 124 w which includes several contrasting geologic environments the distribution of roughness corresponds generally with the various physiographic provinces observed in the region within some provinces additional complexities are apparent in the roughness model which cannot be inferred by simply studying the bathymetry these patterns are related to a variety of geological processes operating in the region such as the convergence of the continental margin and the presence of a propagating rift on the northern gorda rise in contrast a very large area of the continental margin off the east coast of the united states was found to have in common a single distinct amplitude spectrum this amplitude spectrum is almost identical to that found from the tufts abyssal plain region off the west coast of the united states spectra from both of these areas can be clearly separated into two straight line segments of different slope the two segments of these spectra are interpreted as reflecting two dominant relief forming processes the higher frequency band representing a sedimentary regime and the lower frequency band representing an underlying tectonic volcanogenic regime in many cases the calculated roughness statistics are not constant for data collected along different ship track directions this is due to the anisotropic nature of the seafloor relief a simple model is developed which describes the roughness statistics as a function of azimuth the parameters of this model quantify the anistropy of the seafloor allowing insight into the directionality of the corresponding relief forming processes and the physical meaning of the derived model statistical parameters finally the model is used to successfully predict the roughness of a surface at scales much smaller than those resolvable by surface sonar systems the model regression line derived from a hull mounted sonar is compared to data from deep towed sonars and bottom photographs the amplitude of roughness is predicted to within half an order of magnitude over five decades of spatial frequency and this prediction capability can probably be improved even further the stochastic models presented also demonstrate the potential for closely approximating the full two dimensional nature of some areas of the seafloor with only four statistical parameters these parameters can be estimated from random ship track data given a sufficient number of tracks and range of headings

small scale transport of trace elements nb and cr during growth of titanite an experimental study at 600 c 0 4 gpa trace element distribution in titanite overgrowths on rutile has been investigated experimentally at 600 c 400 mpa and fo2 near ninio buffer compositionally homogenous cr or nb doped synthetic rutile single crystals or nb containing natural rutile crystals were the source of cr nb and ti to synthesize titanite using the double capsule technique all element exchange with the source of si ca and al occurred via a nacl h2o fluid titanite forms quickly and exclusively around the rutile crystals the titanite overgrowth separates rutile from the bulk fluid and all elements from rutile dissolution have to pass through the titanite rim trace element concentrations in titanite show a considerable scatter in experiments with and without al although the average concentrations of cr or nb of titanite around compositionally homogeneous synthetic rutile approach the expected values for closed system conditions variability of al with cr or nb in the titanite is not correlated the al zoning is irregular and patchy and also the distribution of trace elements does not show systematic trends in the spatial distribution in experiments using zoned natural rutile the concentrations of nb in titanite are related to the nb zoning in rutile but the contents also vary unsystematically under the controlled conditions of the experiment the explanation for the strongly irregular spatial distribution is most likely due to variations in elemental concentrations during transport from the rutile along the titanite grain boundaries the transport pathway is complex because grain boundary migration is important during titanite growth such irregular element distribution is also found in a natural sample of titanite overgrowth on rutile from an eclogite with retrograde overprint in the amphibolite facies transport of ti and trace elements was focused on grain boundaries and shielded from the rutile as a source of these elements we conclude that this type of zoning is not related to changes in p t or composition in an open system but solely controlled by transport in and through the titanite rim

grenvillian age decompression of eclogites in the glenelg attadale inlier nw scotland the glenelg attadale inlier is the largest basement inlier within the caledonian moine nappe of nw scotland in the eastern part of the inlier amphibolite facies retrogression of the eclogites is associated with tectonic fabrics and p t estimates indicate significant decompression c 20 km previous sm nd mineral whole rock dates indicated that peak eclogite facies metamorphism occurred around c 1 08 ga which was correlated with the grenvillian orogeny however the middle ree enrichment of the analysed garnets suggests the influence of apatite inclusions it is therefore likely that the interpretation of the c 1 08 ga age is complex possibly reflecting re equilibration at lower temperatures sampled eclogites contain zircon in a number of distinct textural forms that are mainly associated with pargasite and plagioclase and are part of the retrograde amphibolite facies assemblages titanite extensively replaces rutile and is clearly associated with the retrograde amphibolite facies event a second textural type of titanite forms anhedral grains with plagioclase and pargasite which is developed where the retrograde amphibolite facies assemblage overprints the eclogite mineralogy u pb dating has yielded the following ages zircon age of 995 8 ma and variably discordant rutile ages between 416 and 480 ma u pb and pb pb isochrons on titanite and plagioclase quartz separates yielded ages of 971 65 ma and 945 57 ma respectively in agreement with the zircon age analysed zircons and titanites are texturally part of the amphibolite facies assemblage the new zircon age demonstrates that amphibolite facies metamorphism during exhumation occurred at 995 8 ma the titanites could have closed with respect to pb at this time or alternatively at some time between c 1000 and 900 ma these data clearly demonstrate that parts of the scottish basement underwent major thick skinned tectonics during the grenvillian orogeny rutile is part of the eclogite facies paragenesis and yet has young ages these data are best explained by reheating producing near total pb loss related to emplacement of the late to post tectonic ratagain granite complex at c 425 ma at the end of the caledonian orogeny

ti al zoning of experimentally grown titanite in the system cao al2o3 tio2 sio2 nacl h2o f evidence for small scale fluid heterogeneity chemical zoning according to the substitution al oh f ti o is a common phenomenon in natural titanite and can be used to reconstruct its growth conditions we synthesized titanite which has a zoning pattern similar to that found in natural titanite that grew at the expense of rutile visible in element distribution maps as a patchy irregular pattern run conditions in the system cao al 2 o 3 tio 2 sio 2 nacl h 2 o caf 2 were 600 c 0 4 gpa 1 to 107 days duration natural rutile crystals were placed in a perforated pt tube within an outer au capsule containing wollastonite al 2 o 3 optionally powdered caf 2 and a nacl brine to simulate conditions where rutile is transformed into titanite by a hydrous ca si al f fluid driven by a chemical potential gradient between inner and outer capsule spontaneous nucleation of titanite is restricted to a small number of crystals on the rutile surface in the inner capsule growth proceeds from sparse isolated titanite crystals after 1 day to assemblages of several 100 m large crystals in a reaction rim in the long time runs titanite is strongly zoned in al ti and shows up to 0 5 al per formula unit pfu in experiments containing f without f substitution is limited to 0 25 al pfu the range of the ti al exchange is already large in short run times and the same heterogeneity is observed in long time runs the al ti distribution with and without f in compositional domains up to several tens of micrometers is patchy and irregular no relation of the zoning with time core rim or preferred growth directions was observed in the case of fluid mediated growth mineral growth zoning represents a disequilibrium at supersaturated conditions the concentration of ti in the fluid is likely the limiting factor for titanite growth considering the low solubility compared to that of al ca and si titanium is not transported in significant amounts into the outer capsule indicating low mobility in contrast to al ca and si which are transported into the inner capsule assuming buffered al concentration from dissolution of the al source we speculate that the ti al of the fluid at the precipitation site was controlled by the local ti concentration which varies over the distance from the rutile surface to the growing titanite crystal and produces the irregular patchy zoning

how much do we really know about glacier surging some of the ideas about glacier surging are considered mainly but not entirely in the light of observations of temperate glaciers in alaska u s a made within the last 15 years climate has an influence on surge recurrence interval climate and weather also affect surge initiation termination and magnitude regional studies lead to the speculation that subglacial till plays a key role in surging and it has been found under all surge type glaciers studied so far including black rapids and variegated glaciers alaska in most of the glaciers studied till deformation processes dominate the motion in quiescence the linked cavity model of surge triggering and rapid motion is not consistent with these observations but the limited coverage of the observations does not rule it out under parts of the glaciers studied the till observations in alaska raise old questions about the interaction between till and the hydraulic systems of temperate glaciers the role of stored water which observations show to be active even in winter on black rapids glacier is noted

automatically derived catchment boundaries and channel networks and their hydrological applications abstract a method of generating drainage networks and catchment boundaries from gridded ground elevation data a digital terrain model is presented the method includes an algorithm for coping with localised low points in the data the paper suggests two objective ways of comparing the conventionally mapped with the automatically generated drainage network emphasis is placed on the way that this approach is capable of benefiting a variety of hydrological applications in particular the automatic estimation of flow statistics from catchment characteristics

mountain glacier velocity variation during a retreat advance cycle quantified using sub pixel analysis of aster images coverage of ice velocities in the central part of the southern alps new zealand is obtained from feature tracking using repeat optical imagery in 2002 and 2006 precise orthorectifica tion co registration and correlation is carried out using the freely available software cosi corr this analysis combined with short times between image acquisitions has enabled velocities to be captured even in the accumulation areas where velocities are lowest and surface features ephemeral the results indicate large velocities for mountain glaciers i e up to 5md 1 as well as dynamic changes in some glaciers that have occurred between 2002 and 2006 for the steep and more responsive fox and franz josef glaciers the speed increased at the glacier snout during the advance period while the low angled and debris covered tasman glacier showed no measurable velocity change velocity increases on the steeper glaciers are the result of an observed thickening and steepening of the glacier tongues as they moved from a retreat phase in 2002 to an advance phase in 2006 this contrasting behaviour is consistent with historic terminus position changes the steeper glaciers have undergone several advance retreat cycles during the observation period 1894 to present while the low angled glacier showed little terminus response until retreat resulting from the accelerating growth of a proglacial lake commenced in 1983

an algorithm for treating flat areas and depressions in digital elevation models using linear interpolation 1 digital elevation model dem data are essential to hydrological applications and have been widely used to calculate a variety of useful topographic characteristics e g slope flow direction flow accumulation area stream channel network topographic index and others except for slope none of the other topographic characteristics can be calculated until the flow direction at each pixel within a dem is determined however flow direction cannot be accurately calculated until depressions and flat areas within a dem have been rectified this is a routine problem in hydrologic modeling because virtually all dems contain flat and sink pixels both real and artifactual that if left untreated will prevent accurate simulation of hydrologic flow paths although a number of algorithms are available for rectifying flat and sink pixels in dem data treatment of flat areas and depressions and calculation of flow direction remain problematic for reasons of complexity and uncertainty a new algorithm that effectively rectifies flat and sink pixels was developed and tested the approach is to use linear interpolation between low elevation grid cells on the edge of each flat area or depression defined as outlets and higher elevation grid cells on the opposite side defined as inflow pixels the implementation requires an iterative solution to accommodate the irregular geometry of flat areas or depressions and exceptions that arise linear interpolation across flat areas or depressions provides a natural way to scale elevation adjustments based on the vertical scale of the surrounding topography thereby avoiding the addition or subtraction of arbitrary small numbers that we regard as a disadvantage in some prior techniques tests for two virtual terrains and one real terrain show that our algorithm effectively rectifies flat areas and depressions even in low relief terrain and produces realistic patterns of flow accumulation and extracted channel networks

topographic signatures in aquarius radiometer and scatterometer response theory suggests that topography large scale roughness will affect thermal emission at l band and could impact remote sensing of surface parameters such as soil moisture from space evidence is presented here for the existence of effects due to topography using data from the l band radiometers and scatterometer aboard the recently launched aquarius the correlation with the slope standard deviation at the topographic scale is presented for data over north africa and australia in the case of the radiometer brightness temperature is observed to increase at horizontal polarization and decrease at vertical polarization in the case of the scatterometer an increase with topographic roughness is observed for both polarizations the presence of the scatterometer provides an independent verification that the behavior observed is due to topography and the observations are consistent with predictions based on monte carlo simulations

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

anticlockwise evolution of ultrahigh temperature granulites within continental collision zone in southern india abstract we report three new localities of corundum and sapphirine bearing hyper aluminous mg rich and silica poor ultrahigh temperature granulites formed during late neoproterozoic cambrian times within the palghat cauvery shear zone system in southern india from petrologic characteristics mineral chemistry and petrogenetic grid considerations the peak metamorphic conditions of these rocks are inferred to lie around 950 1000 c as suggested by al in orthopyroxene thermometer at pressures above 10 kbar as indicated by the equilibrium orthopyroxene sillimanite gedrite quartz assemblage these rocks preserve several remarkable reaction textures the most prominent among which is the triple corona of spinel sapphirine cordierite on corundum with the whole textural assembly embedded within the matrix of gedrite suggesting the reaction ged crn spl spr crd the formation of sapphirine sillimanite assemblage symplectite associated with relict corundum and porphyroblasitc cordierite is explained by the reaction crd crn spr sil the association of sapphirine cordierite symplectite with gedrite sillimanite assemblage as well as with aluminosilicate boundaries indicates the gedrite consuming reaction ged sil spr crd extensive growth of sapphirine cordierite observed on the rim of gedrite porphyroblasts with spinel occurring as relict inclusions within the sapphirine indicates the reaction ged spl spr crd the pressure temperature p t path defined from the observed mineral assemblages and reaction texture is characterized by anticlockwise trajectory with a prograde segment of initial heating and subsequent deep burial followed by retrograde near isothermal decompression such an anticlockwise trajectory is being reported for the first time from southern india and has important tectonic implications since these rocks were developed at the leading edge of the crustal block that was involved in collisional orogeny and subsequent extension during the final phase of assembly of the gondwana supercontinent we propose that the rocks were subjected to deep subduction and rapid exhumation and the extreme thermal conditions were attained either through input from underplated mantle derived magmas or convective thinning or detachment of the lithospheric thermal boundary layer during or after crustal thickening

extremely high solubility of rutile in chloride and fluoride bearing metamorphic fluids an experimental investigation rutile tio 2 is an important high field strength element sequestering phase and thus understanding its solubility in metamorphic fluids is important if we are to understand terrestrial trace element cycling titanium is often assumed to be fluid immobile and previous experimental data suggest that rutile has very low solubility in h 2 o however fluids in high temperature metamorphic rocks are known to be more complex in composition the solubility of rutile in chloride and fluoride rich hydrous fluids was determined experimentally at 0 5 gpa and high temperatures the experimental results indicate much higher rutile solubility in brines compared to pure h 2 o in chloride brines solubility was 2 4 times higher than in h 2 o and in fluoride brines solubility was elevated 20 100 times the results imply that titanium may be much more mobile in metamorphic fluids than previously anticipated as solubility is critically dependent on fluid chemistry we also present a possible mechanism for rutile precipitation in metamorphic veins due to a change in fluid chemistry following the precipitation of halogen rich minerals such as apatite

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

comparison of slope estimates from low resolution dems scaling issues and a fractal method for their solution five different algorithms for calculating slope from digital elevation models dems have been compared from regional to global scales though different methods produce different results the most significant outcome is that slope varies inversely with the dem grid size thus slopes estimated from coarse resolution data can be considered to produce significant underestimates of the true slope a fractal theory is adapted to solve this problem the variogram technique for the definition of fractal parameters is demonstrated to provide a relationship between slope and the spatial resolution of measurement the variation of fractal parameters is discussed at various scales and a model is developed to estimate the high resolution slope based on the coarse resolution dem by using fractal parameters the fractal parameters are estimated from the standard deviation of elevation in a 3 3 window of the dem to account for local variability in the surface standard deviation of elevation is found to be the most invariant property of different scale dems of the same area the model is validated using different resolution dems in southern spain and it is used to estimate the high resolution slope values at global scales based on a coarse resolution dem the slopes estimated using the technique outlined are a significant improvement on those estimated directly from the coarse resolution data slopes estimated in this way allow the more effective use of available coarse resolution data in regional and global scale modelling studies copyright 1999 john wiley sons ltd

element and sr isotope signatures of titanite as indicator of variable fluid composition in hydrated eclogite abstract the trace element signature sr common pb u th ree and hfse of titanite gives important information about the formation process of metamorphic titanite we investigated titanite from different textural positions of a strongly retrogressed eclogite from the tromso norway high p area it shows characteristic titanite rims around partially absorbed rutile interpreted as grown during retrogression and hydration of the high p assemblage the titanite rims around rutile are polycrystalline and in contact with the plagioclase amphibole matrix large idioblastic single crystal titanite grew in veins without relics of precursor rutile compositional zoning of al ti f in titanite of both textural positions is irregular and not related to core or rim position in the crystals there is no evidence for systematic growth sequences or diffusion reflecting changing p t conditions or systematic changes of fluid composition trace element patterns of titanite la icp ms data however show systematic variations in the coupling and decoupling behaviour of strongly fluid mobile sr u moderately fluid mobile ree and little fluid mobile nb ta zr hf elements the trace element signatures of titanite from the two different fabric positions reflect contrasting characteristic fluid compositions single crystal titanite equilibrated with fluid that was channelled in the vein polycrystalline titanite on rutile records the composition of a fluid that had migrated along grain boundaries in the amphibole plagioclase matrix fluid from the matrix also contributed to the geochemical signature of vein titanite whereas influence of fluid from the vein on the composition of polycrystalline titanite in the matrix is not evident 87sr 86sr isotope ratios of the different titanite types support the inference from trace elements of spatially and temporally variable fluid sources