active layer thickness in north central alaska systematic sampling scale and spatial autocorrelation active layer thickness was determined in late august 1995 and 1996 at 100 m intervals over seven 1 km 2 grids in the arctic coastal plain and arctic foothills physiographic provinces of northern alaska collectively the sampled areas integrate the range of regional terrain soil and vegetation characteristics in this region spatial autocorrelation analysis indicates that patterns of active layer thickness are governed closely by topographic detail acting through near surface hydrology on the coastal plain maximum variability occurs at scales involving hundreds of meters and patterns were similar in the two years substantially less spatial structure and interannual correspondence were found within the foothill sites where high variability occurs over smaller distances the divergence in patterns of thaw depth between the two provinces reflects the scale of local terrain features which predetermines the effectiveness of fixed sampling intervals exploratory analysis should be performed to ascertain the scale s of maximum variability within representative areas prior to selection of sampling intervals and development of long term monitoring programs

zircons reveal magma fluxes in the earth s crust magma fluxes regulate the planetary thermal budget the growth of continents and the frequency and magnitude of volcanic eruptions and play a part in the genesis and size of magmatic ore deposits however because a large fraction of the magma produced on the earth does not erupt at the surface determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large scale geological processes here we show that age distributions of zircons a mineral often present in crustal magmatic rocks in combination with thermal modelling provide an accurate means of retrieving magma fluxes the characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the earth s crust our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems analysis of existing age population data sets using our method suggests that porphyry type deposits plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes we anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions and to determine the main factors controlling the distribution of resources on our planet

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

dolomitization of miocene carbonates gulf of suez egypt abstract miocene reef and platform carbonates exposed along the red sea coast at gebel abu shaar and west gemsa are entirely dolostone while exhibiting all the textures and fabrics of a metastable suite of carbonate sediments that has undergone meteoric diagenesis the microfabrics of former mg calcite fibrous marine cements and bioclasts and calcite particles are well preserved and commonly mimetically replaced originally aragonitic components typically illustrate little to no microfabric retention or are leached yielding moldic to vuggy porosity dolomite cement and replacement crystals have inclusion rich or dissolved cores and relatively inclusion free rims most crystals are anhedral and many have an irregular microtopography generated by leaching of crystal surfaces carbon and oxygen isotope values vary widely many samples have the low positive values characteristic of marine precipitates but others are depleted in 13c and 180 reaching minimum 13c and 18o values of 8 9 and 8 0 0 pdb respectively the origin of these dolostones can be explained by two hypotheses the first is dolomitization of a partially stabilized or unaltered mg calcite and aragonite sediment in a zone of mixed freshwater and seawater following dolomite formation the progressive lowering of sea level and resultant freshening of the mixing zone caused leaching of dolomite crystal cores and corrosion of crystal faces the second hypothesis invokes two dolomitization events an earlier pervasive dolomitization by marine or hypersaline waters followed by recrystallization in meteoric or hydrothermal fluids and then selective dissolution both hypotheses are consistent with the geologic setting of these sediments but the pervasive nature of the dolostone favors the recrystallization hypothesis vadose calcite cement ferric oxide hydroxide crusts and secondary evaporite cement are the latest precipitates although they occlude only a minor amount of primary and secondary porosity

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

spatial and temporal variations in active layer thawing and their implication on runoff generation in peat covered permafrost terrain 1 the distribution of frost table depths on a peat covered permafrost slope was examined in a discontinuous permafrost region in northern canada over 4 consecutive years at a variety of spatial scales to elucidate the role of active layer development on runoff generation frost table depths were highly variable over relatively short distances 0 25 1 m and the spatial variability was strongly correlated to soil moisture distribution which was partly influenced by lateral flow converging to frost table depressions on an interannual basis thaw rates were temporally correlated to air temperature and the amount of precipitation input simple simulations show that lateral subsurface flow is governed by the frost table topography having spatially variable storage that has to be filled before water can spill over to generate flow downslope in a similar manner that bedrock topography controls subsurface flow however unlike the bedrock surface the frost table is variable with time and strongly influenced by the heat transfer involving water therefore it is important to understand the feedback between thawing and subsurface water flow and to properly represent the feedback in hydrological models of permafrost regions

construction of a pluton evidence from an exposed cross section of the searchlight pluton eldorado mountains nevada a top to bottom cross section of the searchlight pluton is exposed in a large tilt block in the colorado river extensional corridor of southern nevada hornblende barometry and geologic relations indicate that the pluton was about 10 km thick extending from approximately 3 to 13 km depth the pluton is stratified with about 2 km of fine grained quartz monzonite below the roof 2 km of granite in the center and 6 km of coarser more mafic quartz monzonite at the bottom the lower unit has a pronounced magmatic foliation that was subhorizontal prior to tilting contacts between the units are gradational over a few centimeters to about 20 m geometry field relations and elemental and isotopic data suggest that the three units mark the terminal stages of evolution of magma that filled a very thick magma chamber the upper unit formed as a solidification front that migrated downward from the roof and the middle unit granite and the lower unit represent complementary segregated melt and crystal rich cumulate thus the dominant part of the pluton appears to have solidified in monotonic fashion from more or less uniform magma that was compositionally similar to the upper unit the basal quartz monzonite and the lower part of the granite enclose widely scattered synplutonic hornblende gabbro and diorite pods that range from centimeter to kilometer scale these rocks are commonly fine grained and formed as quenched mafic melts they are isotopically distinct from the main sequence and represent discrete injections into the magma chamber the mafic magmas were contaminated by but did not strongly affect the main sequence magma the nd and sr isotopic compositions of the main sequence magma are intermediate between those of regional crust and enriched mantle derived basalts like those represented by the mafic pods this suggests that the principal magma was a hybrid with about 60 mantle component and thus the pluton represents both addition to and internal reorganization of the crust

water chemistry and caco3 dissolution in the saline part of an open flow mixing zone coastal yucatan peninsula mexico along the caribbean coast of the yucatan peninsula brackish ground water mixed fresh water and sea water is channeled through upper pleistocene limestone via fracture controlled caverns in caves cenotes and caletas at xcaret yalku and tancah this open flow coastal mixing zone comprises three major layers 1 an upper dilute zone of gradually increasing salinity with depth slow mixing 2 a thin intermediate zone of rapidly increasing salinity with depth rapid mixing and 3 a lower saline zone of gradually increasing salinity with depth the intermediate layer occurs at different absolute salinities at different localities and it generally corresponds to the level of a notch apparently related to dissolution in the wall rock of the caverns chemical composition of the mixed ground water is consistent with that predicted from theoretical conservative mixing of fresh water and sea water end members sampled in the yucatan coastal region inorganic c alkalinity mg ca and sr ca and 18o and 13c of the mixed water give no indication of dissolution or precipitation of cac03 as the ground water flows rapidly seaward field and petrographic observations however show that aragonite is preferentially dissolving throughout the modern mixing zone and in particular in the saline portion comparison of saturation indices to calculated mixing curves shows that the coastal mixing zone of the eastern yucatan peninsula is undersaturated with respect to cac03 over a wide range of salinity including mixtures of as much as 95 sea water for aragonite and 90 sea water for calcite supersaturation with respect to stoichiometric dolomite is maintained over the whole range of salinities but super saturation with respect to calcian dolomite ca57mg43 can be confined to high salinity mixtures depending on the thermodynamic data base used in calculations these data suggest that 1 dissolution of coastal limestone can take place in the sea water dominated portion of the mixing zone and 2 the mixing zone model for dolomitization can be extended to much higher salinities than is indicated by the widely accepted dorag model

diagenesis of neogene delta front patch reefs alteration of coastal siliciclastic influenced carbonates from humid equatorial regions abstract this study offers insights into the diagenetic alteration of coastal carbonates that formed coevally with nearly continuous siliciclastic influx in a humid equatorial setting a multi disciplinary petrographic cathodoluminescent stable isotope trace element and major element investigation allowed characterization of diagenetic features paragenetic sequencing and an interpretation of diagenetic environments from neogene patch reefs of the samarinda region mahakam delta borneo se asia marine cements are absent from the patch reefs with grain micritization the only marine diagenetic feature recognized the predominant diagenetic feature within the patch reefs is pervasive neomorphic stabilization and cementation of aragonite reef components to calcite that pre dates all compaction features meteoric aquifer flow derived from the adjacent landmass is inferred as the main parent diagenetic fluid since 18o v pdb values of calcite cements of 3 6 to 11 7 are consistent with precipitation from se asian freshwater and inconsistent with a wholly marine origin late stage fracturing cementation and chemical compaction are relatively minor features and attest to a changing paleohydrologic and diagenetic environment evidence for a shallow to moderate burial diagenetic regime for these later features are maximum temperature of 53 c and burial depths 1000 m inferred from stable isotope values of calcite and late dolomite cements dolomite crystal fabrics the onset depth of stylolite or dissolution seam formation and regional geothermal gradients the humid tropical environment and ever wet conditions on the island of borneo together with rapid cenozoic uplift likely led to paleoaquifer flow with fluids focused through adjacent deltaic units into the reef carbonates in these coastal carbonates from the humid samarinda region continental groundwater flow has resulted in pervasive stabilization and calcitization features rare in arid or temperate counterparts

the chemistry of river lake systems in the context of permafrost occurrence mongolia valley of the lakes part i analysis of ion and trace metal concentrations abstract this study provides a description of water chemistry in river lake systems located in central mongolia at the borderline of permafrost occurrence the analysis involved water samples collected from two river lake systems baydrag river boon tsagaan lake system and shargalyuut tuyn rivers orog lake system in the water samples ions and trace elements were detected and quantified additionally the parameters of ph electrical conductivity sec total dissolved solids tds and total organic carbon toc were determined principal component analysis pca was performed on the sample results water chemistry is mostly influenced by geochemical and hydrometeorological processes permafrost thawing could increase the concentration of nitrogen nh4 no3 as well as na and ca2 cl and so42 however it may also be an effect of other factors such as livestock farming seasonal drying out of lakes e g lake orog may also influence water chemistry by deflation of evaporites from exposed lake beds and at the same time with lower concentration of chemical compounds in water the pca shows that water samples can be divided into two groups the first group contains lake samples where water chemistry is shaped by prevailing evaporation processes whereas the second includes samples from rivers and springs water chemistry of the latter is predominantly influenced by geochemical and hydro meteorological processes

quantum magmatism magmatic compositional gaps generated by melt crystal dynamics compositional gaps are common in volcanic series worldwide the pervasive generation of compositional gaps influences the mechanical and thermal properties of the crust and holds clues on how our planet differentiates we have explored potential mechanisms to generate these gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs we show that gaps are inherent to crystal fractionation for all compositions as crystal liquid separation takes place most efficiently within a crystallinity window of 50 70 vol crystals the probability of melt extraction from a crystal residue in a cooling magma chamber is highest in this crystallinity window due to 1 enhanced melt segregation in the absence of chamber wide convection 2 buffering by latent heat of crystallization and 3 diminished chamber wall thermal gradients this mechanical control of igneous distillation is likely to have played a dominant role in the formation of the compositionally layered earth9s crust by allowing multiple and overlapping intrusive episodes of relatively discrete or quantized composition that become more silicic upward

stable isotopic and geochemical characteristics of groundwater in kherlen river basin a semi arid region in eastern mongolia summary inorganic solute ion concentrations and stable isotopes of oxygen and hydrogen in groundwater river water and precipitation were investigated to gain insight into the groundwater recharge process in the kherlen river basin a semi arid region in eastern mongolia the solute constituents in the river water main stream were of ca hco3 type spatially invariant and low in concentration groundwater in the upstream region was also characterized by a ca hco3 type though all ion concentrations were higher than in the river water on the other hand the chemical composition of the groundwater in the midstream region southern and eastern was spatially variable and the na mg2 cl and hco 3 concentrations were considerably higher than in the river water and upstream groundwater the stable isotopic compositions showed an evaporation effect on the groundwater and river water as well as an altitude effect in the precipitation and river water preferential recharge by relatively large rainfall events is thought to have caused the depleted isotopic ratio in the groundwater in the dry regions the stable isotope chemical and hydrological data suggest that the main stream water of the kherlen river is recharged by precipitation that falls in a headwater region at an altitude of more than 1650 m and that the interaction between the groundwater and river water is not dominant in the midstream and downstream regions of the river basin

mineralogical evidence for fractionation processes in the himalayan leucogranites of the ramba dome southern tibet abstract himalayan leucogranites provide some of the best examples in the world of highly felsic and strongly peraluminous granites and they have been paid special attention with regard to investigating the evolution of continental crust here we describe our mineralogical investigations of a late miocene leucogranite complex within the ramba dome of the tethyan himalaya belt that have helped us decipher the petrogenesis of these high silica peraluminous granites the ramba leucogranites range from two mica granites biotite muscovite to muscovite leucogranites muscovite garnet tourmaline with the two mica granites constituting the main part of the pluton and the muscovite leucogranites commonly occurring as late stage dikes that are located within the pluton or invaded the country rocks variations in the mineral assemblages of the two types of leucogranite are associated with systematic changes in bulk rock geochemistry and the distinctive mineralogical features demonstrate a genetic relationship between the two types of leucogranite that involved fractional crystallization with the muscovite leucogranites being more evolved than the two mica granites chemical data for the minerals in the two mica granites record a long period of differentiation during which a normal granitic melt developed into a highly evolved magmatic system with high flux components e g h2o f b in contrast the mineralogical data for the muscovite leucogranites record the crystallization of a very late residual melt i e a volatile rich highly fluid melt according to recent studies of differentiation processes in silicic magma reservoirs we can interpret the ramba leucogranites as having undergone a high degree of differentiation by in situ fractional crystallization in a crystal mush environment the two mica granites represent a congealed crystal mush that was composed of cumulate crystals and a trapped interstitial liquid and the muscovite leucogranites represent the almost pure liquid that was extracted from the crystal mush modeling using the trace elements sr and ba shows that the extraction probably occurred when the crystallinity of the mush was 59 64 at least for the most evolved muscovite leucogranite sample the two mica granite corresponds to a residual crystal mush that had a terminal porosity of 20 26 filled with a trapped interstitial liquid collectively fractional crystallization can account for the geological mineralogical petrological and geochemical variations between the two types of leucogranite this work highlights the important role of crystal fractionation in the generation of himalayan leucogranites

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

compaction of igneous cumulates when initially deposited mafic igneous cumulates consist of a solid matrix of mineral phases plus 50 60 interstitial liquid due to its greater density the matrix compacts squeezing the interstitial liquid upward a numerical fluid mechanical model of this process indicates that if the cumulate deposition rate is constant compaction occurs in one of two distinct models for rapid deposition the system is permeability controlled with compaction occurring only at the base of the cumulate pile for slowly deposited cumulates an additional compaction zone that is partially viscosity controlled develops at the top of the pile if the extent of compaction and thickness of this zone are known for a real system the model can be used to estimate the permeability and effective viscosity of the compacting cumulates such calculations yield a permeability of 1 5 times 10 3 a 2 f 3 1 f 2 for olivine cumulates in the muskox intrusion reliable viscosity estimates await an empirical law relating ma

a decision tree classification for low lying complex land cover types within the zone of discontinuous permafrost abstract this study presents a decision tree dt approach to classifying heterogeneous land cover types within a northern watershed located in the zone of discontinuous permafrost using airborne lidar and high resolution spectral datasets results are compared with a more typically applied supervised classification increasing errors in discharge resulting from an inaccurate classification are quantified using a distributed hydrological model the hierarchical classification was accurate between 88 and 97 of the validation sub area whereas the parallelepiped classification was accurate between 38 and 74 of the same area despite overall accuracy of 91 kappa 0 91 topographical derivatives were best able to explain variations in land cover types 82 to 96 whilst spectral and vegetation structural derivatives were less accurate when compared with field measurements the hierarchical classification of plateau edges adjacent to a fen was within 2 m of measured 60 of the time whilst this occurred only 40 of the time when using a spectral classification when examining the impacts of land cover classification accuracy on modelled discharge we find that the length of the hydrological response unit defined by the classification and subject to varying levels of errors was linearly related to discharge m 3 such that an increase in permafrost plateau area would increase discharge by 26 of the total the methodology presented in this paper clarifies previous classification and modelling studies using landsat and ikonos data for the same basin this study greatly improves upon past classifications in the same area furthers our understanding of the distribution of connected bogs and fens as conveyors of water to the basin outlet within the watershed and current spatial extents of rapidly thawing permafrost plateaus which are critical for better understanding the impacts of climate change on these northern environments

rates of magma transfer in the crust insights into magma reservoir recharge and pluton growth plutons have long been viewed as crystallized remnants of large magma reservoirs a concept now challenged by high precision geochronological data coupled with thermal models similarly the classical view of silicic eruptions fed by long lived magma reservoirs that slowly differentiate between mafic recharges is being questioned by petrological and geophysical studies in both cases a key and yet unresolved issue is the rate of magma transfer in the crust here we use thermal analysis of magma transport to calculate the minimum rate of magma transfer through dikes we find that unless the crust is exceptionally hot the recharge of magma reservoirs requires a magma supply rate of at least 0 01 km 3 yr much higher than the long term growth rate of plutons which demonstrates unequivocally that igneous bodies must grow incrementally this analysis argues also that magma reservoirs are short lived and erupt rapidly after being recharged by already differentiated magma these findings have significant implications for the monitoring of dormant volcanic systems and our ability to interpret geodetic surface signals related to incipient eruptions

seasonal patterns of coupled flow in the active layer at three sites in northwest north america vertical arrays of temperature and electric potential probes were installed in the upper soil at sites along the mackenzie river valley and on the north slope of alaska time series were obtained at subdiurnal frequencies throughout the year in the active layer and upper permafrost if the data acquisition system is properly configured the time series can be used to infer soil physiochemical processes the electric potential develops primarily in response to soil water solute concentration gradients in the soil column and is a crude surrogate of the soil water electrolytic conductivity summer precipitation can cause rapid penetration of the thaw front when percolating rainwater warmed at the ground surface carries sensible heat downward to the thawing front rates of warming at depth occur significantly faster than those typical of conductive heat transfer in early winter as the freezing front penetrates downward toward the permafrost table ions are excluded from the ice and concentrated in the intermediate unfrozen zone nearly instantaneous warming of the active layer is triggered by spring snowmelt at happy valley in northern alaska temperatures at the 29 cm depth rise from 7 to 3 c in 1 h for several hours during this event the temperature at 29 cm is warmer than that at regions both above and below producing a strong thermal inversion time series of electric potential or a surrogate derived from electric potential suggest rapid transport of meltwater from the snowpack to depth probably through soil cracks serial events hasten active layer warming by 1 2 weeks

threshold relations in subsurface stormflow 2 the fill and spill hypothesis analysis of subsurface stormflow from 147 storms at the 20 m long trench in the panola mountain research watershed by tromp van meerveld and mcdonnell 2006a showed that there was a distinct 55 mm precipitation threshold for significant subsurface stormflow production this second paper in the series investigates the processes responsible for this threshold response we installed a dense spatial array of maximum rise crest stage gauges and recording wells on the hillslope and studied the temporal and spatial patterns of transient saturation at the soil bedrock interface and its relation to subsurface stormflow measured at the trench face results show that while transient groundwater developed on parts of the hillslope during events smaller than 55 mm it was not until more than 55 mm of rain fell before bedrock depressions on the hillslope were filled water spilled over microtopographic relief in the bedrock surface and the subsurface saturated areas became connected to the trench when connectivity was achieved the instantaneous subsurface stormflow rate increased more than fivefold compared to before the subsurface saturated areas were connected to the trench face total subsurface stormflow was more than 75 times larger when connectivity was achieved compared to when connectivity was not achieved the fill and spill hypothesis presented in this paper is a process explanation for the observed threshold behavior of tromp van meerveld and mcdonnell 2006a thereby linking patterns and processes

the process of winter streamflow generation in a subarctic precambrian shield catchment there have been widespread increases in winter streamflow across the circumpolar north since the mid to late 1900s however the physical processes that result in winter runoff generation are not well understood the objective of this research was to determine the runoff generation processes and pathways of cold season streamflow and to compare and contrast them with those of spring freshet in a subarctic canadian shield study catchment in which winter streamflow regime changes have been documented traditional hydrometric methods were used in conjunction with modelling and hydrochemistry to estimate runoff sources and pathways results suggest that while runoff generation processes do not necessarily differ between spring and winter runoff events the timing at which pre event and event water contributes does differ furthermore the periods in which certain runoff pathways activate and deactivate are different runoff during the spring freshet is dominated by pre event water that has not been exposed to the subsurface in contrast and most notably isotopic chemistry reveals that 72 of high cold season streamflow is from new precipitation in precambrian shield regions or in other landscapes where there may be a large fraction of lakes late autumn rainfall can increase lake levels and in turn storage to ample volumes that can provide high amounts of winter runoff where autumn rainfall has been increasing precipitation and surface water should be considered as a source of enhanced winter streamflow in these types of landscapes these results have implications for how widespread environmental changes in the circumpolar north especially those of aquatic chemistry and permafrost thaw should be interpreted and predicted 2013 her majesty the queen in right of canada hydrological processes 2013 john wiley sons ltd

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

tertiary volcanism during extension in the andean foothills of central chile 33 15 33 45 s this lithologic and geochemical study treats two tertiary volcanic formations in the andean foothills of central chile deposited during and after an inferred culmination of crustal attenuation the abanico and farellones formations which are described in their type localities just east of santiago formed from volcanic arcs in continental basins during the oligocene and early miocene respectively aphyric basic lavas of tholeiitic affinity acid pyroclastic rocks and lacustrine deposits constitute the 3100 m thick abanico formation the overlying 2100 m thick farellones formation consists of calc alkaline lavas basalts absent with thick pyroclastic deposits at the base both formations have nd sr isotope signatures within the mantle array the abanico rocks end 5 7 plot closer to n morb normal mid oceanic ridge basalt than the farellones rocks end 3 9 to 5 1 the ree rare earth element patterns indicate greater depth to the mantle source and a smaller degree of partial melting with time the abanico lavas segregated within the stability field of spinel whereas the lavas of the upper farellones member show residual garnet in their source geochemical changes with time are systematic the greatest contrast is between the middle and upper farellones members in 1 2 m y e g for basaltic andesites la yb increases from 4 3 abanico to 5 6 6 0 and 11 6 lower middle and upper farellones members the bimodal composition of the abanico formation and the lower farellones member indicates that volcanism took place during episodes of extensional conditions extension with subsidence is independently shown by the burial metamorphic pattern voluminous pyroclastic flows structural relationships and other evidence suggest recurrent caldera collapse the first extensional episode ended with contraction and folding of the abanico rocks and the second episode resulted in uplift of the lower and middle farellones members followed by a more passive tectonic regime sequences showing many similarities with the abanico and farellones formations occur along the andean foothills of chile they decrease in age from late cretaceous paleocene at 23 s to early miocene late miocene at 35 s and might be explained by oblique subduction of oceanic ridge

the chemistry of river lake systems in the context of permafrost occurrence mongolia valley of the lakes part ii spatial trends and possible sources of organic composition abstract the chemistry of river lake systems located in central mongolia near the southern border of permafrost occurrence has not been well studied the main aim of this paper is to summarize patterns in water chemistry in supply springs rivers and lakes in relation to permafrost occurrence as well as other natural and anthropogenic impacts the analyses involved water samples taken from two river lake systems the baydrag river boon tsagaan lake system and the shargalyuut tuyn rivers orog lake system total organic carbon toc and polycyclic aromatic hydrocarbons pahs were detected and quantified other organic compounds such as organic halogen compounds phthalates and higher alkanes were also noted the main factors which influence differences in toc concentrations in the water bodies involve permafrost occurrence mainly because compounds are released during active layer degradation in the upper reach of the tuyn river and by intensive livestock farming in river valleys and in the vicinity of lakes in relation to the concentrations of pahs high variability between samples 300 ng l 1 indicates the influence of thermal water and local geology structures e g volcanic and sedimentary deposits as well as accumulation of suspended matter in lakes transported during rapid surface runoff events the monitoring of toc as well as individual pahs is particularly important to future environmental studies as they may potentially reflect the degradation of the environment therefore monitoring in the valley of the lakes should be continued particularly in the light of the anticipated permafrost degradation in the 21st century in order to collect more data and be able to anticipate the response of river lake water chemistry to changes in permafrost occurrence

subsurface drainage from hummock covered hillslopes in the arctic tundra in the arctic tundra subsurface drainage occurs predominantly through the saturated zone within the layer of peat that mantles the hillslopes in plan view the peat cover is fragmented into a network of channels due to the presence of mineral earth hummocks in cross section the physical and hydraulic properties of the peat vary with depth and the water transmission characteristics e g hydraulic conductivity of the upper profile differ distinctly from those of the lower water flow through the peat is laminar therefore the friction factor f and the reynolds number nr are inversely related average values for the coefficientc of the relation f a c nr vary from 300 near the surface to 14 500 at depth this large difference in c confirms that the larger diameter soil pores of the living vegetation and lightly decomposed peat near the surface offer much less resistance to water motion than the finer grained peat deeper in the profile also the variability suggests that subsurface drainage is strongly affected by the position and thickness of the saturated zone within the peat matrix a first approximation for a model or simulation of the flow regime may consider a peat profile with depth varying resistance properties in respect to subsurface flow q 2000 elsevier science b v all rights reserved

the carbonate system in hypersaline solutions alkalinity and caco3 solubility of evaporated seawater changes in total alkalinity and in ph during the evaporation of seawater in the laboratory were studied for an evaporation range extending between 1 1 and 26 as defined by the concentration ratio of mg in the evaporated sample relative to mean ocean water the evaporation experiments were performed with and without suspended aragonite the results of the two experimental sets define an alkalinity field for evaporated marine derived brines data from naturally formed marine brines fall within the experimental field deviations therefrom can be explained by changes in alkalinity unrelated to caco precipitation dissolution reactions

melt segregation structures in granitic plutons when melt fraction increases beyond a critical value migmatites behave as magmas conversely when melt fraction decreases crystallizing magmas form solid framework mushes and behave as solids the richness in preserved mesoscopic melt segregation structures in migmatites is not matched by melt segregation structures in granitic bodies this paper identifies melt segregation structures in granites and compares them to structures in migmatites the rarity of segregation structures in granites is a consequence of the solid framework mush allowing for cryptic melt extraction from its pores the relatively short duration of solidification of the mush and the fragile nature of the solid framework identifying segregation features in granitoids at outcrop scale provides the basis for understanding the physical processes that lead to chemical and mineralogical differentiation in granitic magmas

constraints on the origin of zonation of the granite complexes in the fichtelgebirge germany and czech republic evidence from a gravity and geochemical study compositional zoning of granitic plutons is a common feature but the spatial variation of zoning is rarely studied in detail it is suggested that important additional information can emerge if the compositional zoning is regarded with relation to the root zones i e with the granite shape at depth a combined geochemical and gravity investigation was performed on the hercynian fichtelgebirge granites which are composed of an older intrusive complex oic and younger intrusive complex yic the oic and yic are distinct from each other with respect to magma origin differentiation pattern shape of the granite complexes at depth and the zonation pattern in relation to the root zone the oic shows normal compositional zoning whereas the yic both reverse yic 1 and normal zoning yic 2 the general zonation pattern of the oic and the yic is the result of a combination of multiple injections of single magma batches and in situ differentiation during magma emplacement in addition to the general zonation pattern local zonation in individual granite bodies of the yic was caused by sidewall crystallisation producing a less differentiated marginal facies g2 and a more differentiated core facies g3 and g4 it is suggested that the complex zonation patterns of the fichtelgebirge granite complexes reflect interactions between the rate of magma output which is partly governed by their rheological properties and the rate of deformation which provides the room for the magma to be emplaced

hydrometeorological triggers of periglacial debris flows in the zermatt valley switzerland since 1864 1 the triggering of debris flows depends on a critical combination of available unconsolidated material and water supply in periglacial environments debris flows are generally triggered by liquefaction of loose material in a channel or by progressive erosion during a large release of water here we link an unusually dense and highly resolved database on periglacial debris flows with meteorological records dating back to ad 1864 to reconstruct 150 yr of rainstorms that triggered debris flows at high elevation sites source area elevations ranging from 2000 to 4545 m a s l in the swiss alps analysis is based on a tree ring derived frequency series of debris flows from eight torrents as well as on daily records from three meteorological stations and runoff data from four river gauging stations results show that the debris flow season at these high altitude sites now is much longer may to october than it used to be in the late nineteenth century when activity was limited to june september debris flows early in the season are generally triggered by lower rainstorm totals 20 mm day than those occurring later in the season because early season snowmelt adds considerable amounts of water to the system and therefore facilitates debris flow formation debris flows in may june july and august are triggered primarily by short duration high intensity rainstorms local thunderstorms whereas late season september october debris flows are commonly related to longer lasting advective rainstorms

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses

numerical analysis of seawater circulation in carbonate platforms ii the dynamic interaction between geothermal and brine reflux circulation density driven seawater circulation may occur in carbonate platforms due to geothermal heating and or reflux of water of elevated salinity in geothermal circulation lateral contrasts in temperature between seawater and platform groundwa ters warmed by the geothermal heat flux result in upward convective flow with colder seawater drawn into the platform at depth with reflux circulation platform top waters concentrated by evaporation flow downward displacing less dense underlying ground waters we have used a variable density groundwater flow model to examine the pattern magnitude and interaction of these two different circulation mechanisms for mesosaline platform top waters 50 and brines concentrated up to saturation with respect to gypsum 150 and halite 246 geothermal circulation most active around the platform margin becomes restricted and eventually shut off by reflux of brines from the platform interior towards the margin the persistence of geothermal circulation is dependent on the rate of brine reflux which is proportional to the concentration of platform top brines and also critically dependent on the magnitude and distribution of permeability low permeability evaporites can severely restrict reflux whereas high permeability units in hydraulic continuity enhance brine transport reduction in permeability with depth and anisotropy of permeability kv kh focuses flow laterally in the shallow subsurface 1 km resulting in a horizontally elongated brine plume aquifer porosity and dispersivity are relatively minor controls on reflux platform brines can entrain surficial seawater when brine generating conditions cease but the platform top remains submerged a variant of reflux we term latent reflux brines concentrated up to gypsum saturation have relatively long residence times of at least 100 times the duration of the reflux event they thus represent a long term control on post reflux groundwater circulation and conse quently on the rates and spatial patterns of shallow burial diagenesis such as dolomiti zation

the role of soil pipes as a slope runoff mechanism subarctic yukon canada pipeflow in subarctic slopes provides a preferential runoff mechanism that bypasses the soil matrix rapidly conveying water to the stream extensive soil piping occurs in the central wolf creek basin yukon at the interface of the organic and mineral horizons flow in these pipes are ephemeral transmitting water only when the water table is within or above the zone where pipes occur during snowmelt pipeflow began several days after the onset of surface runoff pipeflow contribution increased until ground thaw lowered the water tables leaving matrix flow within the organic layer as the dominant mode of runoff pipeflow accounted for 21 of runoff during the 15 day melt period of 1997 following melt pipeflow recurred only during two intense summer rainstorms each yielding different pipeflow response characteristics during melt pipeflow closely followed the daily snowmelt cycles and responded earlier than the integrated slope runoff in the summer pipeflow hydrographs rose and fell much quicker than direct storm runoff from the entire slope which was dominated by fast matrix flow within the organic layer pipeflow contributing areas were relatively small but their extent changed with hillslope wetness analysis revealed that the manning flow formula can be combined with contributing areas to simulate pipeflow discharges unlike temperate environments where frozen ground is not a factor the frost table position significantly controls the position of the phreatic surface and must be considered in any models of pipeflow in permafrost slopes

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

a sensitivity study of factors influencing warm thin permafrost in the swiss alps alpine permafrost distribution is controlled by a great number of climatic topographic and soil specific factors including snow cover which plays a major role in this study a one dimensional finite element numerical model was developed to analyze the influence of individual snow specific and climatic factors on the ground thermal regime the results indicate that the most important factor is snow depth snow depths below the threshold value of 0 6 m lack sufficient insulation to prevent low atmospheric temperatures from cooling the soil the date of first winter snow insulation and variations in mean annual air temperature maat are also shown to be important delays in early winter snow insulation and in summer snow disappearance are shown to be of approximately equal significance to the ground thermal conditions numerical modelling also indicates that the duration of effective thermal resistance of snow cover governs the slope of the linear dependency between maat and mean annual ground surface temperatures magst consequently the most direct effect of a long term rise in air temperatures on ground temperatures is predicted under a thin snow cover with early snowmelt in spring and or where a large change in the date of total snowmelt occurs in response to atmospheric warming

identifying the crystal graveyards remaining after large silicic eruptions abstract the formation of crystal poor high silica rhyolite via extraction of interstitial melt from an upper crustal mush predicts the complementary formation of large amounts of typically unerupted silicic cumulates however identification of these cumulates remains controversial one hindrance to our ability to identify them is a lack of clear predictions for complementary chemical signatures between extracted melts and their residues to address this discrepancy we present a generalized geochemical model tracking the evolution of trace elements in a magma reservoir concurrently experiencing crystallization and extraction of interstitial melt our method uses a numerical solution rather than analytical thereby allowing for various dependencies between crystallinity partition coefficients for variably compatible and or incompatible elements and melt extraction efficiency results reveal unambiguous fractionation signatures for the extracted melts while those signatures are muted for their cumulate counterparts our model is first applied to a well constrained example searchlight pluton usa and provides a good fit to geochemical data we then extrapolate our results to understanding the relationship between volcanic and plutonic silicic suites on a global scale utilizing the navdat database to identify crystal accumulation or depletion signatures for each suite we suggest that many large granitoids are indeed silicic cumulates although their crystal accumulation signature is expected to be subtle

paleoclimatic controls on sedimentation diagenesis and reservoir quality lessons from miocene carbonates miocene carbonates worldwide were deposited in a wide range of paleogeographic and tectonic settings and form important reservoirs in several regions the reservoir quality of these carbonates appears to have been primarily controlled by the prevailing paleoclimate which exerted a major control on both the depositional patterns and diagenetic pathways two end members are discussed here 1 humid oceanic tropical subtropical settings and 2 arid land locked temperate subtropical settings in humid oceanic tropical subtropical settings e g miocene of southeast asia a warming trend paralleled by generally rising sea level allowed thick coral reefs and skeletal banks to develop most of which are seismically resolvable these carbonates typically represent several stages or cycles of development largely third order separated by discontinuities in platform growth with episodic subaerial exposure development of economic reservoirs is mainly related to relative sea level falls and associated meteoric diagenesis trends and patterns of reservoir distribution can be predicted within a sequence stratigraphic framework basal transgressive carbonates are mostly tight because of their relatively fine grained textures intense compaction and isolation from meteoric water influence best reservoir quality is commonly developed beneath subaerial unconformities in highstand buildups where effects of meteoric water leaching and karstification are most intense in contrast in arid land locked subtropical temperate settings unfavorable environmental conditions caused by periodically increased salinity and probably relatively low temperature restricted the full growth of carbonate buildups as a result relatively thin and narrow fringing coral reefs with small poorly developed lagoons in rhodalgal ramps are the most common facies type in the upper miocene of the mediterranean and the middle miocene of the gulf of suez and red sea whereas the lower miocene of the middle east is characterized by low energy shallow shelfal and lagoonal carbonates under arid climatic conditions recharge of fresh groundwaters is limited thus minimizing meteoric dissolution and cementation during subaerial exposure instead sea level fall and lowstand ommonly resulted in extensive evaporitic conditions hypersaline brines originated within evaporitic basins or lagoons were the main cause of the pervasive dolomitization leaching of metastable skeletal grains and generation of moldic vuggy and intercrystalline porosity often associated with these arid land locked carbonates is the widespread anhydrite cement that precipitated over a wide range of burial depths porosity distribution in these carbonates thus depends not only on the original depositional fabrics but more importantly on the degree to which the porosity occluding anhydrite cement was dissolved or the low permeability carbonates were fractured these miocene examples illustrate the contrasting diagenetic patterns and reservoir styles controlled by paleoclimatic and paleoceanographic trends and demonstrate the importance of the often overlooked hypersaline diagenesis in arid land locked subtropical temperate settings the development of exploration and production strategies for carbonates that were deposited in different climatic settings should acknowledge and use these fundamentally different styles of diagenesis and reservoir characteristics

hillslope runoff from an ice cored peat plateau in a discontinuous permafrost basin northwest territories canada peat plateaus are important landscape features of many high boreal wetland dominated drainage basins raised up to 2 m above the surrounding landscape and underlain by permafrost these forested peatlands provide meltwater drainage to the surrounding wetlands and to basin runoff understanding the factors that control the volume and timing of runoff from peat plateaus is the essential first step towards developing methods of accurately predicting basin runoff from wetland dominated basins in the region of discontinuous permafrost as well as understanding the basin response to hydrological changes brought on by the thermal degradation and thaw of permafrost peatlands in this study a water balance approach and the dupuit forchheimer equation were used to quantify sub surface runoff from a forested peat plateau at scotty creek a small 152 km2 wetland dominated discontinuous permafrost basin in northwest territories canada these two computations yielded similar results in both years of study 2004 2005 and showed that runoff accounted for approximately half of the moisture loss from the peat plateau most of which occurred in response to snowmelt inputs the melt of ground ice was also a significant source of water during the study periods which was largely detained in soil storage soil moisture conditions prior to soil freezing were a major factor controlling the volume of runoff from the hillslope sub surface drainage rates declined dramatically after the snowmelt runoff period when the majority of water inputs went to soil storage and evapotranspiration the minimal lag between rain events and hydrograph response in both years suggests that much of the runoff produced from rain events is rapidly transported to the adjacent wetlands these results give insight into how current climate warming predictions for northern latitudes could affect the hydrological response of forested peat plateaus and the basins which they occupy copyright 2008 john wiley sons ltd

distribution of porosity and permeability in platform dolomites insight from the permian of west texas saller and henderson 1998 presented an article concerning porosity and permeability variations in two west texas oil fields north riley and south cowden fields these fields occur within dolomitized permian platform carbonates near the basinward shelf edge of the central basin platform a paleogeographic element that influenced permian deposition in west texas their carefully documented study outlines several anomalous aspects concerning porosity distribution they noted in particular that porosity distribution is not strictly facies dependent but that porosity tends to increase in a basinward direction they suggested that porosity developed largely during dolomitization by the action of hypersaline evaporative fluids that flowed downdip in a basinward direction during the permian these brines were generated in restricted shelf interior lagoons and moved downdip parallel with bedding in a shallow reflux type of hydrologic system driven by subsurface fluid density differences in the permian clear fork and grayburg formations as shown here in figure 1 see figure 18 in saller and henderson 1998 figure 1 part a shows the scenario proposed by saller and henderson 1998 for porosity creation dolomitization and dolomite cementation of the permian clear fork and grayburg formations of west texas they suggested that macrodissolution of calcium carbonate occurred contemporaneously with dolomitization and dolomite cementation this process of brine backreaction however would cause a net increase of porosity in the shelf interior the opposite of what is observed part b shows a two stage scenario proposed here to circumvent the problem of limestone macrodissolution by shelf interior brines that must have been initially in approximate bulk equilibrium with calcium carbonate the first stage records dolomitization by replacement of limestone with little macrodissolution in stage two evaporative shelf interior brines may have evolved in equilibrium with dolomite only and became undersaturated with calcite and aragonite reflux migration of these brines downdip may

gas driven filter pressing in magmas most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less the buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization and this process of gas driven filter pressing assists the crystallization differentiation of magmas for gas driven filter pressing to be effective the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt these conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs gas driven filter pressing thereby adds fractionated melt to magma bodies gas driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons this process could also account for the production of voluminous crystal poor rhyolites

origin of the silicic volcanic rocks of the early permian panjal traps kashmir india abstract the panjal traps of kashmir india represent a significant outpouring of mafic and silicic volcanic rocks during the early permian and are synchronous with the opening of the neotethys ocean previous studies have suggested that the silicic volcanic rocks are derived by differentiation of mafic magmas dacites and rhyolites collected from the lower portions of the volcanic pile near pampore kashmir are peraluminous anck 1 0 in composition their calculated whole rock i sr values are variable i sr 0 69307 to 0 71825 and indicate open system behavior of either rb or sr or both whereas their nd isotope compositions end t 8 6 to 8 9 are nearly uniform the end t values and trace element th nb pm 4 nb u 8 ratios suggest the rocks are derived partially or wholly from the crust least squares and melts modeling indicate that the likely source of the silicic rocks is the middle crust rather than the lower or upper crust furthermore the silicic panjal traps have trace element compositions similar to some felsic volcanic rocks and a type granitic rocks from other large igneous provinces e g karoo parana and camp the paleoproterozoic t dm ages t dm 1836 to 1937 ma indicate that the rocks were likely derived from an ancient crustal source which experienced multiple episodes of recycling in contrast to silicic volcanic rocks from other lips the silicic panjal traps are unusual in that they did not involve mantle source material the heat required to melt the crust was likely due to the continuous injection of contemporaneous basaltic magmas which formed the majority of the mafic panjal traps

subsurface flow velocities in a hillslope with lateral preferential flow 1 our understanding of hillslope subsurface flow relies on assumptions about how storm characteristics affect the hillslope runoff response experiments in hillslopes dominated by preferential flow features often show that runoff is dynamic and is affected by antecedent conditions rainfall conditions and position of the slope we applied tracers to a hillslope under natural and steady state flow boundary conditions to determine the relationship between lateral tracer velocities and various hillslope lengths and storm indicators tracer velocities were similar to the fastest velocities measured in other similar experiments the velocities were dependent on the boundary conditions and slope length and the subsurface flow velocity was most closely related to the 1 h rainfall intensity unlike some studies there was little correlation between our measured flow velocities and storm volume or antecedent conditions we attributed this to the hillslope characteristics and the relatively consistent wet antecedent conditions during the experiments this experiment showed that the connectivity of the hillslope preferential flow network is an important factor governing the average subsurface flow velocity

hydrology of subarctic canadian shield soil filled valleys the canadian shield landscape includes bedrock uplands and valleys infilled with soil a site near yellowknife in subarctic canada was studied to elucidate the hydrological behaviour of soil filled valleys a suite of hydrological processes was found to be important in the studied valley including snowmelt and rainfall ground frost development evaporation infiltration lateral inflow from adjacent uplands and surface and subsurface flows valley storage requirements during snowmelt are met by local meltwater infiltration but lateral inflows in the summer are needed to satisfy the storage before runoff can be generated from the valley the valleys perform three functions of collecting vertical and lateral water inputs retaining and losing the water held in storage and transferring water down the valley and generating local outflow unlike channel flows in humid areas runoff from the upper valley has to meet the storage demands of the lower valley segments often causing seepage loss along flow paths to render the flows intermittent a fill and spill runoff system is proposed in which the valley physiography results in a series of segments with varying storage conditions as water is supplied to the valley each segment has to be filled until its storage threshold for runoff is exceeded then subsurface or surface flows will be generated but these flows may be arrested to furnish water to satisfy the storage requirements of the segments downstream such a flow system applies also to other valleys in the shield environment

slope runoff processes and flow generation in a subarctic subalpine catchment hillslope runoff was studied in a subarctic subalpine environment to improve understanding of runoff generation processes and the mechanisms whereby water moves from hillslopes to the stream runoff characteristics of four hillslopes were examined between 1997 and 1999 each with distinct soils frost topography and vegetation lateral fluxes were confined to hillslopes with porous organic soils overlying less permeable mineral substrates setting up a two layer flow system whereby most drainage occurs as quickflow in the porous organic layer as matrix flow and or as preferential flow in pipes rills and interconnected surface depressions during snowmelt meltwater infiltrated and percolated the porous frozen organic layers with little resistance percolation ceased at the organic mineral interface due to the impermeable nature of frozen mineral soils forming a perched saturated zone and initiating runoff snowmelt runoff was greater on slopes with greater snow water equivalent and reduced organic layer thickness in summer runoff was greatest on slopes where wet conditions were sustained by inflow stormflow hydrographs responded rapidly to rainfall while exhibiting extended recessions compared with temperate regions where sustained inflow occurred the recession limb showed two segments to reflect different source areas of stormflow production recession analysis was used to quantify contributing areas which were highly variable and controlled largely by hillslope wetness and organic layer properties results indicate that the concept of variable source area for runoff generation applies to subarctic subalpine catchments

the role of permafrost and seasonal frost in the hydrology of northern wetlands in north america abstract wetlands are a common landscape feature in the arctic subarctic and north temperate zones of north america in all three zones the occurrnce of seasonal frost results in similar surface water processes in the early spring for example surface ice and snow generally melt before the soil frost thaws causing melt water to flow into depressions over the land surface and at times across low topographic divides however evapotranspiration and ground water movement differ among the three climatic zones because they are more affected by permafrost than seasonal frost the water source for plants in the arctic is restricted to the small volume of subsurface water lying above the permafrost although this is also true in the subarctic where permafrost exists where it does not plants may receive and possibly reflect more regional ground water sources where permafrost exists the interaction of wetlands with subsurface water is largely restricted to shallow local flow systems but where permafrost is absent in parts of the subarctic and all of the temperature zone wetlands may have a complex interaction with ground water flow systems of all magnitudes

influence of microtopography on active layer thaw depths in qilian mountain northeastern tibetan plateau climate warming over the tibetan plateau has been thickening the active layer the most significant indicator of the permafrost system this study evaluates the influence of microtopography on active layer thaw depth in recent years at eboling basin of the eastern qilian mountain northeastern tibetan plateau thaw depths were measured at microtopographic levels in 2012 2013 and 2014 respectively watershed scale sampling was used to estimate the influence of various morphologies on the active layer while a second sampling scheme to examine the variations in the frost table height along six short transects a third sampling scheme used spatial autocorrelation analysis in a regular grid at 10 10 m intervals the results documented that microtopography elevation microrelief surface configuration and slope played a pivotal role on the active layer thickness of mountainous permafrost in the study area active layer became thinner in depressions which was contrary to most of arctic sites spatial autocorrelation analysis elucidated that the dominant topographic factors controlled the changes of active layer thickness these factors exerted the majority of control over the spatial variations of the active layer the results can help researchers or engineers to roughly estimate the probable influence of micromorphology on the changes in thickness of the active layer in mountainous permafrost regions in the tibetan plateau

paleoreef maps evaluation of a comprehensive database on phanerozoic reefs to get a better understanding of controls on reef development through time we created a comprehensive database on phanerozoic reefs the database currently comprises 2470 reefs and contains information about geographic position paleoposition age reef type dimensions environmental setting paleontological and petrographical features and reservoir quality of each buildup reef data were analyzed in two qualitatively different ways the first type of analysis was by visualization of paleogeographic reef distribution maps five examples late devonian early permian late triassic late jurassic middle miocene are presented to show the potential of paleoreef maps for paleogeographic and paleoclimatological reconstructions the second type of analysis was a numerical processing of coded reef characteristics to realize major trends in reef evolution and properties of reef carbonates the analysis of paleolatitudinal reef distributions through time shows pronounced asymmetries in some time slices probably related to climatic asymmetries rather than controlled by plate tectonic evolution alone the dominance of particular reef builders through time suggests that there are seven cycles of phanerozoic reef development first curves for the phanerozoic distribution of bioerosion in reefs bathymetric setting and debris potential of reefs are presented the observed pattern in the temporal and spatial distribution of reefs with reservoir quality may assist in hydrocarbon exploration statistical tests on the dependencies of reefal reservoir quality suggest that large size high debris potential low paleolatitude high amount of marine aragonite cement and a platform shelf edge setting favor reservoir quality reefal reservoirs are significantly enhanced in times of high evaporite sedimentation elevated burial of organic carbon low oceanic crust production low atmospheric co2 content and cool paleoclimate as well as when they are present in aragonite oceans

slope hydrology as influenced by thawing of the active layer resolute n w t high arctic slopes have a shallow active layer that thaws unevenly during summer the result is often a lack of agreement between the configuration of the frost table and the surface topography and this has effects on the slope hydrology 1 areas with a shallow frost table favour surface runoff but areas with a deeper frost table require a thick zone of saturation to generate surface flow uneven thaw depths then cause alternating seepage and re emergence of water down a slope 2 the configuration of the frost table is highly dynamic causing day to day changes in water storage capacity in the active layer 3 a frost table with local depressions can pond up groundwater which may be rapidly released when part of the frozen sill is breached by continual thawing 4 the topographical drainage divide may not correspond with the subsurface drainage divide as defined by the frost table thus allowing groundwater to drain laterally across topographical boundaries these findings show that a knowledge of

tracing variability of run off generation in mountainous permafrost of semi arid north eastern mongolia the headwaters of mountainous discontinuous permafrost regions in north eastern mongolia are important water resources for the semi arid country but little is known about hydrological processes there run off generation on south facing slopes which are devoid of permafrost has so far been neglected and is totally unknown for areas that have been affected by recent forest fires to fill this knowledge gap the present study applied artificial tracers on a steppe vegetated south facing and on two north facing slopes burned and unburned combined sprinkling and dye tracer experiments were used to visualize processes of infiltration and water fluxes in the unsaturated zone on the unburned north facing slope rapid and widespread infiltration through a wet organic layer was observed down to the permafrost on the burned profile rapid infiltration occurred through a combusted organic and underlying mineral layer stained water seeped out at the bottom of both profiles suggesting a general tendency to subsurface stormflow ssf ongoing ssf could directly be studied 24 h after a high intensity rainfall event on a 55 m hillslope section in the burned forest measurements of water temperature proved the role of the permafrost layer as a base horizon for ssf repeated tracer injections allowed direct insights into ssf dynamics a first injection suggested rather slow dispersive subsurface flow paths whereas 18 h later a second injection traced a more preferential flow system with 20 times quicker flow velocities we speculate that these pronounced ssf dynamics are limited to burned slopes where a thermally insulating organic layer is absent on three south facing soil profiles the applied tracer remained in the uppermost 5 cm of a silt rich mineral soil horizon no signs of preferential infiltration could be found which suggested reduced biological activity under a harsh dry and cold climate instead direct observations distributed tracers and charcoal samples provided evidence for the occurrence of overland flow copyright 2014 john wiley sons ltd

high silica granites terminal porosity and crystal settling in shallow magma chambers abstract high silica 70 wt sio2 granites hsgs are important carriers of highly incompatible elements thus understanding their origin is relevant to understanding how the composition of the continental crust evolves we examined a large scale geochemical study of plutons in the peninsular ranges batholith in southern california usa to better understand the petrogenetic relationships between hsgs and the batholith using highly incompatible and compatible elements we show that hsgs represent residual liquids within a felsic 69 72 wt sio2 magmatic crystal mush at crystal fractions of 50 60 and residual liquid fractions of 40 50 trace element systematics show that separation of the hsg liquid from the crystal mush is inefficient such that no more than 70 80 of the hsg is fully extracted and the remaining greater than 20 30 remains trapped in cumulate mush we find little evidence of more efficient liquid crystal segregation which suggests that compaction induced segregation may be too slow to be important on a large scale instead the terminal porosity of 20 30 coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension 0 74 which may indicate that crystal settling perhaps in the form of hindered settling drives segregation of viscous silicic melts and crystals unlike compaction settling operates on timescales of 1 10 ky fast enough to generate large volumes of hsg and complementary cumulates with trapped melt before magma chambers freeze many felsic plutons may thus be cumulates but because of trapped melt they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent the approach here using a combination of highly incompatible and compatible elements provides a way of identifying and quantifying trapped melt fractions finally we show that hsgs appear to form only in the shallow crust

dolomitizing seas in evaporitic basins a model for pervasive dolomitization of upper miocene reefal carbonates in the western mediterranean petrographic stratigraphic and stable isotopic data from a dolomitized upper miocene reef complex on mallorca spain coupled with the presence of extensive messinian subtidal evaporite deposits throughout the western mediterranean suggests that messinian evaporitic brines were responsible for dolomitization thermodynamic reaction path modeling was undertaken to more rigorously and quantitatively demonstrate the dolomitizing potential of this evaporitic system these calculations provide maximum amounts of dissolution or precipitation moles l to maintain a specified fluid rock equilibrium significant amounts of dolomite can be created when brines ar concentrated by evaporation prior to reaction with calcite heavy stable isotopes of mallorcan dolomites are consistent with an evaporitic origin however lighter stable isotopes do not preclude this model calculations show that mixing evolved brines with unaltered seawater or continental waters produces a suite of fluids with much greater dolomitization potential than seawater and oxygen isotope signatures approaching those of seawater this evaporitic basin model serves as one hypothesis for the many dolomitized upper miocene reef complexes around the western mediterranean and may be applicable to many older phanerozoic carbonates associated with basinal evaporites

salinity reflux and dolomitization of southern australian slope sediments the importance of low carbonate saturation levels anomalously saline waters in ocean drilling program holes 1127 1129 1130 1131 and 1132 which penetrate southern australian slope sediments and isotopic analyses of large benthic foraminifera from southern australian continental shelf sediments indicate that pleistocene holocene meso haline salinity reflux is occurring along the southern australian margin ongoing dolomite formation is observed in slope sediments associated with marine waters commonly exceeding 50 salinity a well flushed zone at the top of all holes contains pore waters with normal marine trace element contents alkalinities and ph values dolomite precipitation occurs directly below the well flushed zone in two phases phase 1 is a nucleation stage associated with waters of relatively low ph ca 7 caused by oxidation of h2s diffusing upward from below this dolomite precipitates in sediments 80 m below the sea floor phase 2 dolomite grows on dolomite cores precipitated during phase 1 phase 2 dolomite has d 13 c values similar to those of the surrounding bulk carbonate and high sr values relative to phase 1 dolomite consistent with having formed in waters affected by aragonite and calcite dissolution the nucleation stage in this model phase 1 challenges the more commonly accepted paradigm that inhibition of dolomitization by sea water is overcome by effectively increasing the saturation state of dolomite in sea water

brine mixing in the middle devonian of western canada and its possible significance to regional dolomitization abstract the desiccation that most large evaporite basins experienced in their history created large elevation heads these heads must have induced flows of ground or formation waters into the evaporite basins the consequences of such groundwater flows are believed to be 1 provision of the necessary hydrodynamic drive to allow dolomitization of carbonates beneath and adjacent to the evaporite basin and 2 the formation of anomalously distributed evaporites in the basin adjacent to sites of groundwater inflow sites where the groundwaters mixed with marine derived brines such brine mixing may also have been responsible for depleting the marine derived brines of their contained sulfate so explaining later development of sulfate impoverished potash deposits anomalous developments of anhydrite surrounding older carbonate buildups in the distal parts of the middle devonian elk point basin of western canada may represent such products of brine mixing and provide evidence of dolomitization of underlying lower palaeozoic and devonian carbonates coevally with the filling of the evaporite basin regional dolomitization in the williston basin is stratigraphically confined beneath the middle prairie evaporite suggesting a genetic link between the dolomitization and evaporite deposition dolomitization by refluxing brines generated in the evaporite basin appears unlikely because of the presence of an aquitard at the base of the evaporite succession developments of laminar and pisolitic carbonates adjacent to the carbonate buildups are believed to indicate the former presence of subaerial springs that carried calcium rich groundwaters into the evaporite basin anhydrite envelopes around the buildups are interpreted to be reaction products that formed when calcium bearing spring waters mixed with sulfate rich but calcium depleted marine brines the calcium in the spring waters is believed to have entered the groundwaters as a by product of the dolomitization of carbonates underlying the evaporite basin precipitation of gypsum now anhydrite as a consequence of brine mixing must have depleted the sulfate content of the marine derived brines it is possible that the sulfate depleted potash deposits in the prairie evaporite originate by this mechanism on the other hand the stratigraphic position of these deposits lends little support for this hypothesis

skeletal aragonite dissolution from hypersaline seawater a hypothesis abstract hypersaline seawater has often been invoked as a mechanism to explain the pervasive dolomitization of ancient platform carbonates but its potential in causing skeletal aragonite dissolution of these carbonates has rarely been investigated previous experimental and theoretical studies have demonstrated that hypersaline seawater is undersaturated with respect to aragonite when evaporation reaches a certain degree it is contended here that similar undersaturation could also have occurred in ancient evaporitic seas geological evidence from the miocene carbonates of se spain gulf of suez red sea and iraq suggests that this may have been the case despite differences in their geological settings these carbonates have common diagenetic features including 1 widespread dissolution of skeletal aragonite with little or no calcite cementation and 2 pervasive dolomitization dolomite occurs as both a replacement of mg calcite and mouldic pore filling cement the association of the dolomites with evaporites their relatively heavy oxygen isotopic values and widespread distribution suggest a hypersaline seawater origin of these dolomites petrographic data indicate that skeletal aragonite was dissolved during dolomitization because the aragonite fossil moulds contain dolomite cements but no pre dolomitization calcite cements implying that the dolomitizing fluids hypersaline seawater were probably undersaturated with respect to aragonite the dissolved calcium may have been subsequently incorporated into the dolomite this may help to explain the lack of calcite cementation despite the extensive skeletal aragonite dissolution

zoning and exsolution in alkali feldspars from laacher see volcano western germany constraints on temperature history prior to eruption compositional zoning and exsolution patterns of alkali feldspars in carbonatite bearing cognate syenites from the 6 3 km3 d r e phonolitic laacher see tephra lst deposit in western germany 12 9 ka are reported these rocks represent the cooler outer portion and crystal rich products of a cooling magma reservoir at upper crustal levels major and trace element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt trace element differences measured by la icp ms are in accordance with silicate carbonate unmixing across the core rim boundary we extracted gray scale profiles from multiple accumulations of back scattered electron images gray scales directly represent k na ratios owing to low concentrations of ba and sr 30 ppm diffusion gradients are modeled to solve for temperature using known pre eruptive u th zircon ages 0 20 ky of each sample schmitt et al j petrol 51 1053 1085 2010 estimated temperatures range from 630 c to 670 c for the exsolution boundaries a diffusive homogenization model is constrained by the solvus temperature of 712 725 c and gives short time scales of only 15 50 days based on our results we present a model for the temperature time history of these rocks the model also constrains the thermal variation across the cooling crystal rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates the cooling carapace and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir

palaeoecological evidence for early aragonite dissolution in ancient calcite seas it has been proposed that shallow carbonate seas of upper ordovician and jurassic ages precipitated calcite as the primary calcium carbonate phase1 3 unlike such settings today it is expected that such seas were undersaturated with respect to the more soluble aragonite so that aragonitic invertebrate skeletons would have tended to dissolve here we describe examples in which this seems to have been the case our evidence consists of submarine cemented horizons in which aragonite fossils have been dissolved out to leave open moulds the walls of the moulds are encrusted by contemporaneous organisms confirming the early timing of the aragonite dissolution

silicic volcanism triggered by increased denudation rates in the quaternary andean arc of central chile between 33 50 34 30 s abstract in central chile 33 50 34 30 s the quaternary arc records a distinctive episode of silicic volcanism sio2 70 wt that occurred during latest pleistocene 0 1 1 ma this episode is recorded in several eroded and inactive arc centers distributed mostly along the highest summits of the andes in the same region covered by the modern arc centers we report new data including field observations petrography whole rock chemical and sr nd isotopic analyses mineral chemistry and geochronology for the quaternary andean arc in the region with emphasis in the latest pleistocene units 0 1 1 ma the silicic episode that the latter units represent constitutes a singularity in the common compositions that characterize in the long term this arc segment as it is preceded and followed by basaltic andesite andesite dacite suite compositions in addition it occurs coevally with a period of increased denudation resulting from the major uplift event of the andean orogen in the area geologic field markers supported by thermobarometric estimations indicate conservative estimates of denudation of 1 5 km during this period in the area which in turn accounts for a significant pressure decrease at upper crustal levels that must have affected the shallow reservoirs that fed the arc volcanoes for evaluating this thermodynamic numerical simulations have been run at different pressure conditions in order to describe for such magmatic systems the evolution in terms of major element composition degree of crystallinity and volatile content with the temperature decrease overall results show that the compositional spectra defined by this arc segment can be reproduced by low pressure

comparing magnetic and magmatic fabrics to constrain the magma flow record in la gloria pluton central chile abstract this contribution illustrates a case study of a pluton la gloria pluton lgp where magnetic and magmatic fabrics are locally decoupled we compare the magmatic fabric with the available magnetic fabric data to explore their abilities and elucidate the magma flow record of lgp results indicate that magnetic controlled by multi domain magnetite and magmatic fabrics are generally consistent throughout lgp foliations define an axisymmetric pattern that gradually changes from vertical near lateral margins to less steep in the pluton interior whereas lineations are subhorizontal following the elongation direction of the pluton however samples at the pluton center show marked differences between both fabrics magnetic fabrics indicate subhorizontal magnetic lineations and foliations and magmatic fabrics indicate subvertical lineations and foliations both magnetic and magmatic fabrics are interpreted to record strain caused by magma flow during thermal convection and lateral magma propagation at the transition between low and high crystallinity stages we suggest that fabrics acquisition and consistency were determined by shear conditions pure simple shear rates ratio and the orientation of the magma flow direction with respect to a rigid boundary critical crystalline region of the pluton magmatic fabric differs at the center of the pluton because pure shear is dominant and ascendant flows are orthogonal to the horizontal rigid boundary lgp represents a whole scale partly molten magma reservoir where both thermal convection and lateral propagation of the magma are recorded simultaneously this study highlights the importance of characterizing both fabrics to properly interpret magma flow recorded in plutons

compositional zonation of the shallow la gloria pluton central chile by late stage extraction redistribution of residual melts by channelization numerical modeling abstract the origin of highly evolved magmas e g rhyolites has been a long standing controversy in earth sciences they are commonly thought to be generated in the upper crust by melt extraction from mush zones but due to the rapid cooling of magma reservoirs in such shallow and typically cold environments high magma emplacement rates of intermediate magmas are thought to be necessary to maintain large silicic mushes above the solidus long enough for the high sio2 melts extraction to occur late stage redistribution of interstitial melts i e heat and mass by channels dikes within those mushes has been invoked as a mechanism to preserve silicic mushes above their solidi for longer periods i e delaying their final crystallization but the nature of this process and its implications on plutons zonation are still poorly understood here using time dependent numerical modeling we study the feasibility of late stage interstitial melt extraction redistribution by channels dikes from a crystalline mush our model accounts for magma fluid dynamics extraction of residual melts and thermal evolution of the crystallizing magma system and its hosting rocks considering the thermal effect of the redistributing material the model was applied to explain the anatomy of the well documented la gloria pluton lgp central chile which exhibits increasing contents of sio2 and abundant leucocratic dikes toward the margins interpreted as trapped residual melts generated elsewhere in the magma chamber our results suggest that favorable conditions for extracting late stage residual melts are reached at temperatures of 750 c 60 vol crystallinity at least for compositions similar to lgp dikes simulations correspond to 30 kyr of reservoir cooling when the concentric compositional zonation of lgp is reproduced after a short period of extraction

on the longevity of large upper crustal silicic magma reservoirs understanding the processes involved in the formation and maturation of upper crustal magma reservoirs ultimately sourcing the largest volcanic eruptions on earth is one of the most fundamental aspects of volcanology while such reservoirs are known to assemble incrementally over extended periods of time debate persists regarding the time scales of melt preservation in the cold upper crust if rapid cooling individually freezes incoming replenishing intrusions accumulations of eruptible magma are impossible precluding the construction of voluminous volcanic reservoirs for all but the highest magma emplacement rates recent numerical thermal models have been used to assess the viability of upper crustal silicic magma survival and have suggested that supervolcanic reservoirs must form on geologically short time scales with anomalously high injection rates and subsist only ephemerally making their long term evolution less predictable motivated by geological observations suggesting the contrary we have improved upon these models by incorporating two fundamental features of natural systems not previously considered 1 a nonlinear crystallization temperature relationship adapted for upper crustal silicic magmas and 2 a temperature dependent thermal conductivity we demonstrate that the incorporation of both of these properties can allow an upper crustal reservoir to remain above its solidus for hundreds of thousands of years when fed by magma fluxes typical of large magmatic provinces while the crystallization temperature path plays the most significant role in maintaining a large pool of eruptible magma the incorporation of temperature dependent thermal properties significantly extends the lifetime of such reservoirs furthermore while deeper emplacement levels e g 10 km depth can both extend magma survival and increase melt availability we show that a 5 km depth can also provide an adequate magma storage environment these results provide strong support for long lived upper crustal mushes as a staging ground for accumulation of highly eruptible crystal poor silicic magmas and further assert the evolutionary link between volcanic and plutonic systems

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

a comparison of simplified methods for routing topographically driven subsurface flow a series of numerical experiments are used to evaluate the accuracy of two approaches for modeling topographically driven subsurface flow suitable for inclusion in spatially distributed hydrologic models the first is an explicit grid cell by grid cell approach and the second is a statistical dynamic method widely used in topmodel both approaches were compared with analytical solutions to the kinematic wave equation for flow down an inclined plane of constant slope using a power law transmissivity function the hillslope discharge and water table profiles simulated by the explicit method were in good agreement with the analytic solution in all test cases the statistical dynamic method converged on the correct steady state solution but failed to reproduce accurately transient conditions the two algorithms were then compared using a 30 m dem representation of the mahantango pa basin and hourly precipitation measured at the site the agreement in discharge between the two methods improved with increasing soil thickness surface conductivity and power law exponent however the percent root mean squared difference rmsd in hourly discharge was above 20 percent in all cases the statistical dynamic model was then calibrated to discharge simulated by the explicit method calibration was most effective for soils with low power law exponents generally producing discharge hydrographs in closemore agreement for soils with linear transmissivity profiles however even under these conditions there are large discrepancies between local water table depths simulated by the two models the level of agreement is best during dry conditions and decreases during wetter conditions as the number of cells with surface soil saturation increases less

geochronology of mesozoic cenozoic magmatism in central chile lat 31 36 s abstract radioisotope dates indicate magmatism in central chile lat 32 36 s has been episodic and migratory throughout mesozoic and cenozoic time dated plutonic and metaplutonic rocks appear to cluster into the following age groups 1 415 380 m y 2 310 270 m y 3 230 170 m y 4 170 140 m y 5 120 80 m y 6 63 56 m y and 7 24 7 m y rocks of meso and cenozoic age are distributed in remarkably well defined parallel linear belts which trend n s and are older away from the central andean cordillera this pattern suggests that the continental margin has increased in width by as much as 200 km in the last 200 m y by the emplacement of successive plutonic belts volcanic strata of lower middle jurassic age 7000 m and early cretaceous age 7000 13000 m occur on the west side of the present coastal cordillera and on both flanks of the andean cordillera these rocks mainly andesites rhyolites and volcano clastic sediments are intercalated with fossil bearing marine sediments which provide age control up until the final emergence of the andean cordillera in late cretaceous time k ar dates indicate this continental volcanism continued through the late cretaceous then ceased during the period between 60 and 30 m y this hiatus in volcanism coincides with the absence of plutonic rocks in this age range in the central andean cordillera volcanism began again about 25 m y ago and has persisted with variable intensity to the present post oligocene volcanic strata are generally nearly conformable above late cretaceous volcanic strata and miocene regional folding has deformed the entire stratigraphic sequence into broad n s trending folds volcanic strata younger than 4 m y are undeformed the presently active chain of strato volcanoes appears to be less than 500 000 years old and west of older extinct volcanoes 1 2 m y old suggesting a westward shift of the volcanic are during the pleistocene

generation of high silica rhyolite a nd sr and o isotopic study of sierra la primavera mexican neovolcanic belt high silica rhyolites of the sierra la primavera a late pleistocene center near guadalajara are extremely sr poor 0 3 1 3 ppm yet with one exception values of 87sr 86sri are relatively low at 0 7041 0 7048 values of 143nd 144nd for all the rhyolites are within errors identical to a basalt at 0 5129 these surprisingly primitive values along with feldspar 18o of 6 6 are consistent with an origin by fractional crystallization of mantle derived basalt however absence of the large volume of associated intermediate rocks that would be expected if the 40 km3 of erupted rhyolite were produced mainly by fractional crystallization suggests alternative processes involving partial melting of mesozoic or tertiary mafic intrusive rocks or lower crustal metamorphic equivalents the latter interpretation is preferred especially in light of comparative data for other north american cenozoic high silica rhyolites isotopic compositions correlate with basement age but generally lie between values for associated basalts and the underlying crust nearly all can be interpreted as containing both a young mantle derived component and a crustal component probably derived by partial melting at intermediate to deep levels of the crust no matter what the proportions of mantle and crust derived material in parental magmas the extremely low concentrations of sr and ba in the high silica rhyolites require extensive fractional crystallization of feldspar rich assemblages after parental liquids attain rhyolitic compositions

the response 1958 1997 of permafrost and near surface ground temperatures to forest fire takhini river valley southern yukon territory forest fires in permafrost areas often modify ground surface conditions causing deepening of the active layer and thawing of near surface permafrost takhini river valley lies in the discontinuous permafrost zone of southern yukon territory the valley floor is covered by glaciolacustrine deposits which are locally ice rich in 1958 extensive forest fires burned most of the vegetation and the soil organic horizon in the valley but 50 km west of whitehorse 1 km2 of spruce forest adjacent to the alaska highway escaped burning permafrost beneath this stand of trees is in equilibrium with surface conditions the active layer is 1 4 m thick the base of permafrost is at 18 5 m the annual mean temperature at the top of permafrost 1 5 m is 0 8 c and the temperature gradient in permafrost is constant with depth at burned sites nearby there has been little regeneration of forest vegetation since the fire and long term permafrost degradation has occurred at one burned site the permafrost table is mor

field and model constraints on silicic melt segregation by compaction hindered settling the role of water and its effect on latent heat release to investigate how large volumes of silicic melts segregate to form granitic plutons we conducted a case study of a zoned pluton in which sio 2 increases from intermediate 69 wt to highly silicic compositions 74 wt toward the contact with metasedimentary wallrock in the outer 25 m of the pluton all other major minor and trace elements vary systematically with sio 2 and indicate that outward increasing sio 2 is due to a decrease in mafic elements and minerals whole rock oxygen isotopes and elemental variation diagrams do not support mixing with wallrock as an explanation for the si rich boundary layer instead mafic enclaves which are common in the pluton also decrease in abundance in the outer 25 m of the pluton suggesting a mechanical origin for the si rich boundary layer the coupling of mechanical and geochemical boundary layers combined with geochemical modeling indicate that the silica rich enclave poor boundary layer formed by hindered settling or compaction of a crystal rich crystal fractions 60 magmatic mush segregation of melts at high crystal fraction is known to be a slow process however petrography and zr based thermometry indicate that the residual si rich liquids were water saturated water decreases melt viscosity which helps expulsion but equally importantly water also delays much of the latent heat release to late in the thermal and crystallization history of a cooling magma we show that the higher the water content the longer the time interval over which a magma chamber resides at the stage when water saturated high silica liquids form allowing sufficient time for exfiltration of silicic liquids before the magma body freezes

late stage magma flow in a shallow felsic reservoir merging the anisotropy of magnetic susceptibility record with numerical simulations in la gloria pluton central chile 1 la gloria pluton is a 10 myr old epizonal intrusion located in the southern andes we present anisotropy of magnetic susceptibility data that indicate a magnetic fabric that is mainly oblate we find that lineations are weak and have a n nw trend with a nearly horizontal dip while foliations are more pronounced have nw trends and have dips that vary from vertical at the walls of the intrusion to horizontal at the center and under the roof of the chamber to interpret these magmatic fabrics we developed a time dependent 2 d magmatic fluid dynamic numerical simulation our model is calibrated with melts and accounts for the coupled processes of cooling crystallization and degassing of a magma chamber simulations indicate that the resulting convective flow pattern in the crystallizing reservoir is consistent with the magnetic fabric which is largely produced in the shear zone between the convecting liquid dominated core and the growing solidification fronts adjacent to the walls the magnetic fabric records the last increment of strain induced by convective magmatic flow in the cooling reservoir during crystallization at the rheological magma locking point along solidification fronts despite the small size of the pluton the core of the chamber remains thermally insulated from the colder host rocks surviving up to 20 kyr above the solidus which allows enough time for the extraction of residual leucogranitic melt and partial late magmatic reactive recrystallization the results of the simulations are also consistent with the previously determined compositional and mineralogical zonation patterns in the pluton

the parona chaotic complex a puzzling record of the messinian late miocene events in monferrato nw italy the parona chaotic complex pcc from monferrato nw italy is a melange composed of carbonate cemented blocks floating in a matrix of weakly consolidated mud breccias it forms a minor 1 km2 chaotic sedimentary body enclosed in a larger messinian melange that rests unconformably on older deposits and is followed again unconformably by pliocene sediments three main facies have been recognized in the blocks a bioclastic rudstones and coquinoid grainstones of early messinian age composed of oligotypic assemblages of gastropods and the brackish water bivalve cerastoderma mixed with shallow water marine biota mollusks corallinae algae benthic foraminifers echinoid fragments rare ahermatypic corals these sediments record shallow water carbonate sedimentation with episodic brackish incursions and show a peculiar diagenetic overprint selective dissolution of aragonitic grains and early dolomitic cements b monogenic breccias composed of clasts of coquinoid grainstones floating in a dolomitic microcrystalline matrix c polygenic conglomerates composed of rounded clasts of pre messinian pelagic sediments of lower messinian bioclastic carbonates and of messinian evaporitic carbonates finally a few blocks of strongly cemented micritic limestones interpreted as methane derived carbonates for the geochemical signature of the carbonate phases strongly depleted in 13c are present the matrix enclosing the blocks is a mud breccia containing centimeter sized clasts of marly sediments micropaleontological analyses have shown that lower messinian and upper tortonian planktic foraminifers are mixed with lower miocene oligocene and eocene forms the pcc results from complex processes involving 1 deposition of the peculiar sediments preserved in the blocks and 2 their dismemberment and mixing as for the depositional history composition of the blocks has allowed to sketch the following evolution a deposition of bioclastic rudstones and coquinoid grainstones that are interpreted as lower messinian carbonate platform deposits for their strong compositional and diagenetical similarity with the lower messinian carbonates cropping out in the mediterranean region the monferrato bioclastic sediments are the northernmost example of messinian shallow water carbonates yet known b deposition of monogenic breccias they formed during the evaporitic phase of the messinian that was accompanied by a relative sea level drop and by erosion of the previously deposited coquinas depositional and diagenetical processes during the evaporitic phase are also recorded by clasts of evaporitic carbonates in the polygenic conglomerates c deposition of polygenic conglomerates that are interpreted as upper messinian post evaporitic fan delta facies resulting from an important erosional phase after deposition this succession was dismembered in the blocks forming the present day melange geometry stratigraphic relationships and internal characteristics of the pcc point to an origin related to gravity driven phenomena triggered by tectonics however the faunal mixing in the mud breccias and the occurrence of blocks of methane derived carbonates suggest that mud diapirism also played a role for the genesis of the pcc this latter mechanism which has been poorly considered until now could also have been effective in the genesis of messinian chaotic deposits that extensively crop out in nw italy