geomorphological evidence for jokulhlaups from kverkfjoll volcano iceland abstract jokulhlaups glacial outburst floods are known to have drained along the jokulsa a fjollum river in iceland during the holocene however little is known about their number age source and flow characteristics this paper provides detailed geomorphological evidence for jokulhlaups that have routed from the kverkfjoll ice margin and hence into the jokulsa a fjollum erosional evidence of jokulhlaups from kverkfjoll includes gorges cataracts spillways subaerial lava steps and valley wide scoured surfaces depositional evidence includes wash limits boulder bars cataract fill mounds terraces slackwater deposits and outwash fans some of these landforms have been documented previously in association with jokulhlaups however subaerial lava surfaces that have been scoured of the upper clinker gorges within pillow hyaloclastite ridges gorges between pillow hyaloclastite ridges and subaerial lava flows subaerial lava lobe steps cataract fill mounds and boulder run ups are previously undocumented in the literature these landforms may therefore be diagnostic of jokulhlaups within an active volcanic rifting landscape the nature and spatial distribution of these landforms and their stratigraphic association with other landforms suggest that there have been at least two jokulhlaups through kverkfjallarani the biskupsfell eruption occurred between these two jokulhlaups kverkfjallarani jokulhlaups were very strongly influenced by topography geology and interevent processes that together determined the quantity and nature of sediment availability such controls have resulted in jokulhlaups that were probably fluidal turbulent and supercritical over large areas of the anastomosing channel bed kverkfjallarani jokulhlaups would have had highly variable hydraulic properties both spatially and temporally the knowledge of flow characteristics that can be gained from jokulhlaup impacts has implications for recognising jokulhlaups in the rock record and for hazard analysis and mitigation within similar landscapes and upon other glaciated volcanoes

stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

middle and late quaternary glacial lake outburst floods drainage diversions and reorganization of fluvial systems in northwestern eurasia abstract the middle and late pleistocene glaciations of northern eurasia had a great impact on the evolution of the modern drainage system this paper presents a review and synthesis on the palaeogeography of glacial lakes their drainage and impact on the re organization of the drainage systems during the last two glacial interglacial cycles we will focus on four regions 1 northern central europe and fennoscandia 2 the central part of the east european plain 3 the west siberian plain and 4 the aral caspian black sea area the main findings of the last decade s include the improved chronology of some major river system formation and of meltwater overflows across the continental drainage divides major drainage systems of the north central and west central part of the east european plain upper volga upper dnieper formed due to overspill of glacial lakes in late mis 6 with a partial re organization upper dnieper in mis 2 the aral caspian black sea cascade acted as a sink for glacial meltwater from the north the major meltwater yield to the aral and caspian seas occurred in mis 6 and late mis 5 in mis 2 the meltwater delivery via the volga valley into the caspian sea was low and therefore had only a minor influence on the sea level considerable meltwater discharge to the black sea through the dnieper river system occurred around the maximal stage of the mis 2 glaciation and ceased very quickly after the onset of deglaciation

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

glaciohydraulic supercooling in iceland we present evidence of glaciohydraulic supercooling under jokulhlaup and ablation dominated conditions from two temperate icelandic glaciers observations show that freezing of sediment laden meltwater leads to intraglacial debris entrainment during normal and extreme hydrologic regimes intraglacial frazil ice propagation under normal ablation dominated conditions can trap copious volumes of sediment which forms anomalously thick sections of debris rich ice glaciohydraulic supercooling plays an important role in intraglacial debris entrainment and should be given more attention in models of basal ice development extreme jokulhlaup conditions can result in significant intraglacial sediment accretion by supercooling which may explain the concentration of englacial sediments deposited in heinrich layers in the north atlantic during the last glaciation

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

age geodynamic setting and mantle enrichment processes of a k rich intrusion from the meissen massif northern bohemian massif and implications for related occurrences from the mid european hercynian the plutonic complex of the meissen massif northern margin of the bohemian massif comprises dioritic to mainly monzonitic and granitic rocks the diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series the chemical signatures of less crustally contaminated diorites are similar to arc related shoshonitic rocks derived from continental lithospheric mantle clm sources previously enriched by subduction of altered oceanic crust laser step heating 40ar 39ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329 1 1 4 to 330 4 1 4 ma and from 330 4 2 1 to 330 6 1 8 ma respectively these cooling ages are indistinguishable from sensitive highresolution ion microprobe shrimp 238u 206pb intrusion ages measured on magmatic zircon rims from the monzonite nasdala et al submitted this shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent saxonian erzgebirge by approximately 20 ma the shoshonitic magmas intruded during strike slip tectonism along the elbe valley zone the enrichment of their mantle sources may be of upper devonian lower carboniferous age or older intrusions of shoshonitic to ultra potassic k rich rocks during the upper visean namurian are widespread in the moldanubian zone based on similar ages and structural relationships a similar post collisional setting to the meissen shoshonitic rocks can be demonstrated most of these occurrences cut high grade nappe units which were subducted during the upper devonian lower carboniferous in contrast to the meissen massif at least the ultra potassic members of the central and the south bohemian batholiths were derived from clm sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material despite the similar post collisional geodynamic setting of the k rich intrusions different enrichment processes generated mid european hercynian clm sources with heterogeneous major and trace element and isotopic signatures

boron in granitic magmas stability of tourmaline in equilibrium with biotite and cordierite experiments at 750 c 200 mpa h2o a h2o 1 and fo2 ni nio established that the equilibrium among tourmaline biotite cordierite and melt spinel aluminosilicate or corundum occurs with 2 wt b2o3 in strongly peraluminous melt with an aluminosity measured by the parameter asi of 1 2 the experiments demonstrate the relationship of tourmaline stability to the activity product of the tourmaline components boron and aluminum which are inversely related to one another tourmaline is unstable in metaluminous to mildly peraluminous melts asi 2 wt b2o3 in their bulk magmas

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice ii theory simple theory supports field observations lawson and others 1998 that subglacial water flow out of overdeepenings can cause accretion of layered debris bearing ice to the bases of glaciers the large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths if that flow ascends a sufficiently steep slope out of an overdeepening the water will supercool as the pressure melting point rises and basal ice accretion will occur diurnal occasional or annual fluctuations in water discharge will cause variations in accretion rate debris content of accreted ice or subsequent diagenesis producing layers under appropriate conditions net accretion of debris bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget

paleohydraulic reconstruction of the largest glacial lake missoula draining s glacial lake missoula glm was the source of earth s largest known peak flood discharges onto the channeled scabland northwestern united states the original studies of glm were based on geomorphological mapping of lake sediments and shorelines more recently studies have emphasized the computational fluid dynamics of downstream megaflood routing and characteristics in the channeled scabland and adjacent areas however actual details of the lake draining processes glm have received little scientific attention in this paper we employ two dimensional hydraulic modelling to understand the paleoflow conditions for different scenarios of draining glm at its highest stands values are calculated for three glm drainage hydrographs 2 6 13 17 10 6 m 3 s 1 that previous studies had estimated for outlet flows consistent with regional mapping and with the original interpretation of fluvial geomorphology by other studies the modelling shows that lake silt sequences in the gorges of glm must postdate the most highly energetic outburst events from the lake this is because the flows generated in the lake by megaflood outflows are sufficiently energetic to erode any accumulated silt deposits in contrast the gravels underlying the silts in these zones include boulder sized clasts largescale cross stratification and 70e100 m high bars forms all of which indicate very high energy flood flow conditions the modelling also shows that the paleohydraulic conditions which developed in the lake basin during the largest megaflood outflows would be capable of accounting for the observed bedrock scour at rainbow lake pass various high eddy deposits eddy bars of flood gravel in gorges and the giant ripple marks subaqueous gravel dunes that were classically described in the 1940s previous studies interpreted the glacial lake silt rhythmites and related deposits such as the ninemile section as evidence for numerous fillings and drainings of glm our modelling suggests that these inferred events must have been relatively low in energy and magnitude relative to the earlier outburst s that emplaced the flood gravels subaqueous gravel dunes and scabland like erosion surfaces

late collisional granites in the variscan erzgebirge germany the late collisional erzgebirge granites 325 318 ma were introduction emplaced at shallow crustal levels in the variscan metamorphic the erzgebirge is a ne sw trending antiformal structure basement shortly after large scale extension caused by orogenic exposing variscan crystalline basement rocks at the northcollapse these granites comprise mildly peraluminous transitional ern margin of the bohemian massif the region is famous i s types and strongly peraluminous s type rocks which can be among economic geologists for its extensive and highly subdivided into three major groups low f biotite granites low f variable metallic ore deposits which have been mined two mica granites and high f high p2o5 li mica granites the since the middle ages e g stemprok seltmann 1994 highest degree of differentiation is reached in the li mica granites tischendorf forster 1994 and for the classic studies which exhibit strongly elevated concentrations of p f li rb cs in the fields of economic geology mining and metallurgy ta sn w and u but very low ti mg co ni sr ba y zr chemistry and mineralogy e g werner 1791 breithaupt hf th and rare earth elements crystal melt fractionation is the 1849 agricola 1974 dominant process controlling the bulk composition of all groups of as in many of the other variscan provinces in central granites however metasomatic processes involving late stage residual europe granitic rocks make up a large proportion of the melts and high t orthomagmatic fluids became increasingly more exposed rocks in the erzgebirge and a great variety of important in highly evolved units and have modified the abundances compositional and textural types occur fig 1 knowof mobile elements p f li rb cs ba sr in the li mica ledge of the processes involved in the generation and granites particularly isotopic and geochemical characteristics suggest evolution of these silicic magmas is essential for underthat the three granite groups cannot be derived from a common standing heat and mass transport during the variscan precursor magma their discrete compositions are source related orogeny and also for the formation of metallic ore and are attributed to melting of quartzo feldspathic and pelitic deposits several lines of evidence indicate that early crustal lithologies in different proportions granites are common in high temperature sn w deposits are associated with the the central european variscides but the erzgebirge is unusual for emplacement of highly evolved volatile rich granitic the predominance of evolved li mica granites associated with melts tischendorf 1986 forster tischendorf 1992 economically important sn w and u deposits the abundance of stemprok 1993 the role of the granites in formation of li mica granites is attributed to a combination of favourable factors later permian u pb zn and younger ore mineralization 1 low degrees of anatectic melting of crustal protoliths 2 wide f ba is controversial but good evidence exists that the distribution of fertile lithologies rich in large ion lithophile elements vein type u deposits owe their uranium to leaching from and ore elements 3 extended magmatic differentiation by crystal the uraninite rich granites e g tischendorf forster melt fractionation and subsequent autometasomatism 1994

the composition of a primary granite derived ore fluid from s w england determined by fluid inclusion analysis abstract electrolyte concentrations in aqueous fluid inclusions in quartz from a high temperature hydrothermal rock have been measured for 15 elements by an improved crush leach procedure the primary hydrothermal fluid was dominated by nacl and has been shown by previous studies to have been about 3 m with respect to cl on this basis the molar concentrations include fe 0 21 mn 0 06 and zn 0 02 and the fluid is interpreted as parental to some of the s w england ore bodies

integration of lidar and cropmark remote sensing for the study of fluvial and anthropogenic landforms in the brenta bacchiglione alluvial plain ne italy the geomorphological study of alluvial plains takes great advantage from the integration of detailed altimetry with high resolution images especially in the lower relief sectors like those in the distal plain of the brenta and bacchiglione rivers near the city of padua mean slope 1 0 8 the lidar data which were specifically acquired for this research riegl lms q560 mean density 7 points m2 overall area 123 km2 were classified and interpolated in order to map fluvial and anthropogenic landforms the acquisition was carried out in a moment of minimal vegetation luxuriance march 2011 in order to minimize ground cover the dem z accuracy 5 10 cm was processed and analyzed in integration with high resolution oblique and vertical multispectral vis ir and panchromatic aerial images these latter were acquired during the summer crop season with the aim of maximizing the detection of vegetation response to different soils sediments and landforms cropmarks a detailed field survey was conducted with soil observation hand augerings and description of stratigraphic sections in pits in order to validate the remote sensing interpretations the detailed topography allowed the identification and mapping of low rise interfluves and scarps 1 2 m paleochannels scroll bars and crevasse splays the reconstruction of a precise ground surface in the narrow medieval streets detailed the morphology of the multi stratified archeological mound in the historical center of padua the remote sensing of cropmarks is the most appropriate method to complete the mapping of the numerous fluvial forms that have little or no topographic expression being too small i e minor crevasse channels and splays and or flattened by anthropogenic activity mainly plowing lidar intensity permitted a precise mapping of lgm deposits that have shown peculiar reflectivity related to specific soil characteristics i e presence of calcic horizons in well drained elevated position high resolution images and lidar dem allow the analysis of this largely anthropized low plain environment at cell size scale of 0 5 1 m i e approximating the original complexity of the alluvial sedimentary environment the results bring advances in the comprehension of the last glacial maximum and holocene evolution of the brenta bacchiglione plain the large scale mapping of paleohydrographic features led to the recognition of different fluvial styles adopted by the brenta river i braided to wandering paleochannels 100 300 m wide in fine sediment dominated fluvioglacial lgm distal alluvial plain ii meandering up to 3 5 single channels 50 100 m wide with evidence of lateral migration in early and middle holocene channel belts and iii low to medium sinuosity 1 15 1 5 single channels with vertical aggradation associated with ridges and widespread crevasse channels and splays during the middle holocene the derived maps provide significant support to land and urban planning e g in the definition of appropriate geotechnical analysis the estimation of buried archeological deposits in the city center and the assessment of flooding hazard

metallogeny of tin in central thailand a genetic concept tin mineralization in central thailand is associated with granitic rocks of the thai burmese border range western group granitic intrusions east of bangkok and near the kampuchea border eastern group have no tin fractional crystallization is the fundamental petrogenetic process that controls the evolution of both groups of granites the tin bearing alkali feldspar aplogranites of the western group display an extreme degree of differentiation that has no petrological equivalent in the eastern group these aplogranites are the product of a combination of magmatic fractionation primary tin enrichment trend modified by fluid interaction the latter process is responsible for a secondary geochemical tin deficiency that is balanced by redistribution of tin in fracture systems i e tin mineralization the pattern of tin depletion in the aplogranites provides an indication of the tin potential in a given ore forming system

internal structures and dating of complex zircons from meissen massif monzonites saxony abstract u pb zircon ages were determined for accessory zircons from two monzonites from the meissen massif northern bohemian massif germany by shrimp ion microprobe bse and cl imaging revealed that the monzonite zircons showing oscillatory growth zoning often contain inherited cores raman microprobe measurements showed that zoned rims u 277 1426 ppm th 144 910 ppm are slightly disordered to moderately metamict whereas cores have a wide spectrum of structural states from well crystallized to highly metamict the radionuclide u th content of cores varies from a few hundred to more than 20 000 ppm shrimp ion probe measurements on zoned rims interpreted as zircon growth during crystallization of the monzonite magma gave concordant carboniferous 206 pb 238 u ages of 326 6 ma monzonite from leuben and 330 5 ma monzonite from heidenschanze 95 confidence respectively these ages are consistent with recently published 40 ar 39 ar ages of 329 1 2 8 to 330 4 2 8 ma 2 on amphiboles from the same rocks in contrast shrimp measurements on cores range from slightly discordant proterozoic relic ages in low u and th cores to highly discordant data in the most metamict cores previously obtained 207 pb 206 pb ages single zircon evaporation technique in the range 340 16 to 357 16 ma 1 are probably mixed ages between magmatic and inherited zircon components the u pb ages of the monzonite zircons postdate the upper devonian lower carboniferous subduction and collision events in the area by about 20 ma due to their shoshonitic chemical signature which is typical of rocks from destructive plate boundary settings the meissen massif monzonites might be interpreted as originating during these 350 ma events and the earlier 207 pb 206 pb ages appeared to confirm this interpretation however both the 40 ar 39 ar ages and our current results show that only the enrichment of the lithospheric mantle source but not the monzonite intrusion itself was directly related to these events the monzonite intrusion itself took place 330 ma ago in the framework of strike slip tectonics in the elbe valley zone widely occurring zircon cores are indicative of crustal contamination of the magma causing considerable modification of chemical signatures trace element content of the monzonites

behavior of li and its isotopes during serpentinization of oceanic peridotites analyses of li and li isotopes in serpentinized peridotites have been performed using thermo ionisation mass spectrometry tims and secondary ion mass spectrometry sims techniques on samples collected from the southwest indian ridge swir in the bulk samples li concentrations range from 0 6 to 8 2 ppm while whole rock 6li values range from 2 9 to 14 in situ analyses display a greater range in both li concentration 0 1 19 5 ppm and li isotopic composition 27 to 19 with the serpentinized portions having higher li concentrations than the associated relict phases these variations may reflect changes in li partitioning and isotopic fractionation between serpentine and fluid with temperature and water rock ratio they may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization as the serpentine forms by interaction with a circulating fluid it preferentially removes 6li causing the li in the fluid to become isotopically heavier the isotopic composition of the initial hydrothermal fluid is dominated by basalt derived li which easily overwhelms the very low li content originally present in seawater as this fluid circulates through ultramafic rocks it induces the formation of serpentine that incorporates this mantle derived li hence li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves li recycling within this crust consequently li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid these results imply that serpentinized peridotites are probably only a minor sink of oceanic li

freshwater megaflood sedimentation what can we learn about generic processes abstract there is growing recognition that sedimentary deposits related to high energy large scale freshwater floods are widespread across the continents and in the main can be related to quaternary outbreak flows from ice dammed lakes such deposits may also occur in the neogene and earlier recognition of these megaflood deposits is hindered by the lack of well conditioned stratigraphic models of depositional successions however descriptions of successions from many locations often exhibit commonalities when compared carefully thus the primary purpose of this paper is to examine and condense the published stratigraphic and sedimentological evidence so as to identify the key signatures of megaflood successions the deposits often are the only record of a flood and so the secondary purpose is to interpret the sedimentary sequences in order to recreate the behaviour of floods through single and multiple events finally some pointers are provided as to those areas of sedimentological research that might be profitably explored in more depth to improve understanding of megaflood dynamics a key characteristic of megaflood deposits is the apparent massive appearance of single units which on closer inspection usually are amalgamated layers of similar grain size distribution individual beds and sets of beds are commonly near horizontal planar and laterally extensive successions evidently are not channelized and extensivity is indicative of simultaneous and coherent deposition over large areas localised large scale clinoforms or smaller scale cross beds are common associated with bar front or dune progradation respectively but otherwise extensivity implies that cross cutting erosional contacts notably steeply inclined examples and small scale scours are not common except immediately around large isolated clasts such as dropstones and ice blocks a common vertical stack of sequences in any one succession consists of 1 basal thick coarse parallel bedded units 2 large scale clinoforms 3 horizontally bedded thin laminated units 4 ripple and dune cross beds 5 silt beds and 6 succession capping debris flow deposits in some cases such a succession usually is indicative of a single cycle of waxing and waning flood flow generally dominated by high concentration suspension deposition onto plane beds the high power allows the transport of fine gravel and coarse sand in suspension leading upon deposition to relatively coarse beds from suspension fall out clay and silt is generally sparse or absent being transported further down the system at the scale of the hydrograph the successions indicate that flows initially accelerate and then decelerate with significant shorter period flow pulses also evident in the sedimentary signatures in parallel bedded sequences primarily during waxing flows bedload transport often was ineffective in sorting sediment due to the high rates of deposition from the highly sediment charged waters resulting in diffuse accretion surfaces at each location similar sequence stacks are common leading to the impression of rhythmic deposition from pulsing flow including from repetitive series of floods although often composed of coarse grains many sequence stacks excluding any debris flows are not dissimilar to turbidity flow sequences the bouma sequence in particular although there is limited experimental evidence for turbidity currents associated with high energy freshwater flows theory does not preclude the deposition of similar sedimentary motifs from high concentration flows such that an analogy between some megaflood sedimentary beds and turbidites is not unreasonable despite considerable variation in megaflood sedimentary successions commonalities occur which are indicative of similar processes of deposition from high energy floods at geographically different locations the changes in style of deposition throughout a succession provide clues as to the nature of the flood flows and this information could be used to improve estimates of flood hydrograph behaviour however hypotheses linking deposit characteristics to flow dynamics are currently ill conditioned and often poorly tested the majority of published studies describe the coarser scale stratigraphy with only passing reference to the fine scale structure of individual beds closer attention to lamination styles particle orientation and syn depositional deformation structures for example should provide information on the flow mechanics at the time of bed deposition thus better consideration of the sedimentology of megaflood deposit beds will lead to better understanding of the controlling hydraulics and should result in better models of flood deposition

time transgressive tunnel valley formation indicated by infill sediment structure north sea the role of glaciohydraulic supercooling structure and lithology of the infill sediments from 16 subglacial buried tunnel valleys of pleistocene age in the north sea were analyzed using 3d seismic data and geophysical log data from five hydrocarbon exploration wells the infill sediments are characterized by three seismic facies facies i the volumetrically most important and structurally most distinct is composed of clinoform reflections downlapping axially up valley up ice facies ii is composed of near horizontal continuous and well layered reflections onlapping the clinoform reflections and the valley walls and facies iii is composed of clinoform reflections downlapping axially down valley down ice a model of formation of this sediment architecture is proposed in which valley incision and infill are causally linked it is proposed that facies i is related to glaciohydraulic supercooling of subglacial meltwater in the distal parts of tunnel valleys the valleys formed time transgressively during ice retreat whereby sediment eroded further up ice was re deposited along adverse subglacial slopes of the valleys close to the ice margin the formation of facies ii and iii is related to the deposition in proglacial basins during final deglaciation copyright 2008 john wiley sons ltd

boron recycling in the continental crust of the central andes from the palaeozoic to mesozoic nw argentina whole rock chemical composition and 11b 10b isotope ratios in tourmaline was investigated to study the geochemical recycling of boron during the evolution of the andean basement from the palaeozoic to mesozoic in the basement cambrian to ordovician high grade paragneisses migmatites and orthogneisses the eocambrian puncoviscana formation and paleozoic mesozoic granitoid igneous rocks whole rock b contents are generally below 100 ppm but b contents of 1 wt are found in cogenetic aplite and pegmatite dikes and in tourmaline quartz rocks in the metasedimentary rocks no systematic variation in b content because of metamorphic grade and no correlation of b with other incompatible elements are apparent tourmalines from the high grade metamorphic basement yield 11b values ranging from 11 2 to 6 8 and isotope fractionation during migmatisation was small metamorphic tourmalines from the puncoviscana formation have 11b values between 6 3 and 5 8 the calculated corrected for fractionation 11b values of 6 to 2 for the sedimentary protolith of the metamorphic basement indicate a continental b source with subordinate marine input tourmalines from palaeozoic and mesozoic granitoids display an identical range of 11b values from 12 to 5 3 and indicate a similarly homogeneous b source throughout time tourmalines from pegmatites and tourmaline quartz rocks record the average 11b values of the parental granitic magma we assume that b in the palaeozoic and mesozoic granitoids is derived from the local metamorphic basement supporting the hypothesis that recycling of the lower palaeozoic crust is the dominant process in granitic magma formation from palaeozoic to mesozoic

lithium abundance and isotope systematics of forearc serpentinites conical seamount mariana forearc insights into the mechanics of slab mantle exchange during subduction 1 variable lithium contents and contrasting li isotopic signatures are evident in the serpentininite muds and clasts extruded at conical seamount in the mariana forearc the muds have high li contents compared to mantle values 3 7 ppm and a mean 7li value of 6 the clasts are generally lower in li and 7li varies from 6 to 10 with higher 7li correlating broadly to higher lithium contents the diverse 7li in the serpentinite clasts suggests li exchanges between mantle rocks and evolving slab derived fluids from different depths producing a subarc mantle that is zoned in terms of li abundances and 7li mariana forearc li isotopic signatures reach values as high as those reported in mariana arc lavas but neither mariana lavas nor lavas from other mature arcs show the variability observed in the serpentinites although elevated serpentinite li contents indicate forearc releases of li large differences in 7li are not evident in the slab outputs at forearc versus arc depths in the marianas despite evidence for changes in other alkaline species e g ba sr k it is thus possible that the li sampled by mariana arc volcanoes is in large part li which was released in the forearc and transported in the mantle via convection to arc depths as has been proposed to explain b isotopic variations straub and layne 2002 the uniform 7li signatures observed in mature volcanic arcs tomascak et al 2002 are consistent with higher overall fluxes of slab fluids which generate larger melting anomalies including both modified and nonmodified mantle wedge domains high or low 7li in lavas from anomalous arcs e g panama tomascak et al 2000 may indicate that the volumes of mantle sampled in these magmatic events are smaller and thus more likely to reflect the signatures of hydrated plums e g allegre and turcotte 1986 phipps morgan and morgan 1999 with extremely high or low 7li

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

tourmaline geochemistry and δ11b variations as a guide to fluid rock interaction in the habachtal emerald deposit tauern window austria tourmalines from the habachtal emerald deposit in the eastern alps formed together with emerald in a ductile shear zone during blackwall metasomatism between pelitic country rocks and a serpentinite body electron microprobe and secondary ion mass spectrometric sims analyses provide a record of chemical and b isotope variations in tourmalines which represent an idealized profile from metapelites into the blackwall sequence of biotite and chlorite schists tourmaline is intermediate schorl dravite in the country rock and become increasingly dravitic in the blackwall zones while f and cr contents increase and al drops metasomatic tourmaline from blackwall zones is typically zoned optically and chemically with rim compositions rich in mg ti ca and f compared with the cores the total range in 11b values is 13 8 to 5 1 and the within sample variations are typically 3 5 both of these ranges are beyond the reach of closed system fractionation at the estimated 500 550 c conditions of formation and at least two boron components with contrasting isotopic composition are indicated a key observation from tourmaline core analyses is a systematic shift in 11b from the country rock 14 to 10 to the inner blackwall zones 9 to 5 we suggest that two separate fluids were channeled and partially mixed in the habachtal shear zone during blackwall alteration and tourmaline emerald mineralization a regional metamorphic fluid carried isotopically light boron as observed in the metapelite country rocks the other fluid is derived from the serpentinite association and has isotopically heavier boron typical for morb or altered oceanic crust

melt biotite 11b 10b isotopic fractionation and the boron local environment in the structure of volcanic glasses abstract this paper is focused on the role of boron coordination in determining the 11b 10b isotopic fractionation between melt glass and biotite at magmatic temperatures for this purpose three evolved volcanic rocks from roccastrada mt amiata and mt cimini belonging to the neogene quaternary magmatism of central italy were studied in these samples the measured boron biotite glass partition coefficient ranges between 0 004 and 0 011 indicating that boron behaves as an incompatible element during biotite crystallization the 11b magic angle spinning nuclear magnetic resonance nmr spectra reveal the presence of trigonal bo3 2 units tetrahedral bo4 2 sites and three coordinated bo2 2o species containing one nonbridging oxygen the relative contributions of these different boron sites were estimated by spectral deconvolution and it was observed that the fraction of trigonally coordinated boron decreases with increasing k2o concentration in the glass the 11b 10b isotopic fractionation between biotite and melt glass was observed to be large even at magmatic temperatures and was found to be 1 0066 roccastrada sample 1 00535 mt amiata sample and 1 00279 mt cimini sample fractionation is mostly related to the relative amount of trigonal and tetrahedral boron sites in the glass network rather than to other processes including the speciation of hydrous species in the glass structure the measured values are significantly higher than the calculated ones obtained using the reduced partition function ratios rpfrs for b oh 3 and b oh 4 as reported by kakihana et al 1977 and the abundance of trigonal and tetrahedral boron obtained by 11b nmr spectra furthermore a nonlinear relationship is observed between the percentage of bo4 in the glass structure and the measured 1000ln suggesting that the approximation of monomeric b oh 3 and b oh 4 species contributions through ideal mixing in calculating the rpfrs in polyanions oi et al 1989 probably does not apply to silicate glasses the large b isotopic fractionation measured between glass and biotite and its dependence on the boron coordination in the glass are a limitation to the use of 11b in the mineral to characterize magmas nonetheless the high incompatible behavior of boron in the most common magmatic minerals rules out that fractional crystallization significantly modified the b isotopic composition of the melt

modelling hyperconcentrated flow in the yellow river a large amount of the total sediment load in the chinese yellow river is transported during hyperconcentrated floods these floods are characterized by very high suspended sediment concentrations and rapid morphological changes with alternating sedimentation and erosion in the main channel and persistent sedimentation on the floodplain however the physical mechanisms driving these hyperconcentrated floods are still poorly understood numerical modelling experiments of these floods reveal that sedimentation is largely caused by large vertical concentration gradients both in the channel during the rising stage of the flood as well as on the floodplains during a later stage of the flood these vertical concentration gradients are large because the turbulent mixing rates are reduced by the increased sediment induced density gradients resulting in a positive feedback mechanism that produces high deposition rates erosion prevails when the sediment is largely held in suspension due to hindered settling and is strengthened by the reduced wetted cross section caused by massive sedimentation on the floodplain observed patterns of erosion and sedimentation during these floods can be qualitatively reproduced with a numerical model in which sediment induced density effects and hindered settling are included copyright 2009 john wiley sons ltd

constraints on melting and magma production in the crust major intrusions of granitic rocks are found in several tectonic settings and in all cases crustal melts may contribute to the volumes of granitic magma high grade metamorphism and partial melting of the crust take place predominantly under fluid absent conditions we present a model for calculating the amounts of melt that may be formed by fluid absent breakdown of micas and amphiboles in common crustal rock types pelitic quartzofeldspathic intermediate and mafic melt proportions depend mainly on the kind of source rock the pressure at which melting takes place the temperature and the hydrous mineral h2o content of the source as a consequence of the pressure dependence of water solubility in silicate melts any given source rock will produce more melt by a given fluid absent reaction at lower pressure at a given pressure higher temperature reactions can produce more melt from a given source rock based on a survey of the compositions of common rock types we show that the amounts of melt can vary from 50vol thus crustal rocks vary widely in their fertility as magma sources depending on the types and amounts of hydrous phases they contain in general muscovite breakdown in pelites will yield only small quantities of melt and lead to migmatite formation biotite breakdown in pelites occurs at higher temperature and because most high grade pelites below granulite grade are biotite rich can yield up to about 50 vol of granitoid melt rocks of intermediate composition and hornblende rich mafic rocks are potentially highly fertile magma sources also provided that the high temperatures necessary for biotite and hornblende breakdown are realized pyroxene rich mafic rocks and quartzofeldspathic rocks are much less potentially fertile data suggest that mechanisms exist for the efficient segregation of melt and restite in systems with 30and probably 20vol melt the pressure temperature history of a region can greatly influence crustal source fertility through its control over the occurrence of subsolidus dehydration and melting equilibria

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

granite related paleoproterozoic serrinha gold deposit southern amazonia brazil hydrothermal alteration fluid inclusion and stable isotope constraints on genesis and evolution the serrinha gold deposit in the juruena teles pires gold province is spatially and genetically related to the hydrothermal alteration of the i type calc alkaline 1872 12 ma matupa monzogranite in the south central amazonian craton the mineralized areas are characterized by intense hydrothermal alteration of the monzogranite comprising incipient autometasomatism k silicate sodic mn chlorite phyllic carbonate and microcline alteration with partial overprinting of the early alteration by later stages a distal barren propylitic zone is interpreted from drill core the gold mineralization is disseminated in the most altered samples and genetically related to mn chlorite k silicate and phyllic hydrothermal alteration types hydrothermal magnetite and rutile are ubiquitous within pyrite the early serrinha gold mineralization stage is characterized by ag poor gold included in pyrite au ag 7 15 associated with pyrrhotite cubanite and galena the fluids interpreted to be associated with this early auriferous stage were found only in quartz from the mn chlorite alteration and are typically saline 45 57 wt nacl equiv and high temperature 375 and 480 c h2o nacl kcl fluids entrapped at pressures of at least 1 3 kbars the late stage gold mineralization which is coeval with the phyllic alteration occurs either as isolated gold grains or as fracture fillings and or inclusions within pyrite associated with tetradymite galena tsumoite bite hessite ag2te and aikinite pbcubis3 gold grains associated with this late stage are richer in ag au ag 2 5 data from chlorite geothermometry and aqueous carbonic and saline nacl kcl fluid inclusions associated with this second auriferous event indicate p t conditions of 1 5 to 2 4 kbars and 293 to 365 c the occurrence of lower temperature coeval aqueous aqueous carbonic and carbonic fluid inclusions with no postentrapment modification in the k silicate assemblage partially overprinted by phyllic alteration and in phyllic assemblages suggests that fluid immiscibility and or mixing with meteoric water occurred in the hydrothermal system h2o nacl cacl2 fluids contemporaneous with carbonate and late microcline alteration which postdated gold mineralization were entrapped at lower temperatures 172 200 c calculated 18o and d values are 8 2 and 37 per mil respectively for the early saline fluids in equilibrium with the mn chlorite assemblage and 1 7 to 4 7 and 20 to 15 per mil for the late fluids in equilibrium with the phyllic assemblage these data in conjunction with fluid inclusion results suggest that early fluids exsolved from granitic melts and later mixed with meteoric water gold is interpreted to have been initially transported from the crystallizing magma as chlorine complexes in a hot saline acidic and oxidized fluid decrease in temperature during fluid ascent immiscibility or ph increase is interpreted to have caused gold precipitation subsequent dilution of the saline fluid could have been responsible for the deposition of late gold in pyrite fractures based on field petrological mineralogical fluid inclusion and isotopic evidence we propose that serrinha is a typical proximal intrusion related gold deposit similar to porphyry style gold deposits

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

significant li isotope fractionation in geochemically evolved rare element bearing pegmatites from the little nahanni pegmatite group nwt canada abstract lithium isotope signatures of whole rock pegmatite samples and mineral separates from the rare element bearing little nahanni pegmatite group nwt and whole rock samples from nearby granitic intrusions were measured correlation of the li isotopic values from the pegmatite dikes with whole rock trace element geochemistry mineralogy and primary textural evidence reflect mechanisms of li isotopic fractionation during pegmatite formation the heavier 7 li signatures within the broad range measured from whole rock lnpg samples 0 94 to 11 36 are related to the consolidation of the final 15 melt fraction of a volatile rich peraluminous magma in the late stages of magmatic fractionation rock forming minerals quartz albite spodumene and mica display 7 li signatures that indicate consolidation of the dikes under variable non equilibrium conditions lithium isotope signatures of relatively cool highly evolved peraluminous magmas reflect the build up of fluxes e g h 2 o and f and provide a qualitative assessment of the state of mineral melt chemical equilibrium

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

sedimentary record of a late saalian jokulhlaup case study in siedlątkow outcrop central poland abstract the aim of the research conducted in an outcrop of late saalian sediments in siedl tkow central poland was to reconstruct extreme meltwater flows during a jokulhlaup on the basis of the geological record a combination of field and laboratory lithological methods was used which included lithofacies analysis analyses of grain size distribution shape and roundness of gravelly clasts examination of sediments made it possible to recognise palaeohydrological sedimentation and deformation processes during and immediately after the flood in particular the simultaneous operation of water flows in four paths in the immediate foreland of the ice front was reconstructed mechanisms of transport and sedimentation of deposits were determined characteristic features of the analysed jokulhlaup deposits include erosional and deformational contact with the substrate a high content of very coarse sediments poorly sorted with predominant massive clast supported gravels and boulders the presence of rip up clasts inverse grading in the lower part of the profile normal grading in the upper part and similarities in clast shape and roundness and the ratio of local rocks to northern origin rocks when compared to the surrounding saalian till the documented features allow for the following phases of jokulhlaup to be distinguished initial rising high stage and waning stage during the reconstructed event hyperconcentrated flow was dominant whereas fluvial flow and debris flow were of lesser importance the release of meltwater in the marginal part of the ice sheet came from the depression of the kolo basin to the north of the analysed sites complex deformation processes which occurred in the flood deposits and their substratum were also interpreted the analysed jokulhlaup event resembles some minor glacial floods in the ice contact zone of present day icelandic glaciers further research in marginal zones of pleistocene ice sheets should account for their occurrence as the analysed example indicates that jokulhlaups might have had considerable influence on the course of sedimentation processes in the marginal zones of ice lobes of pleistocene ice sheets as well as in the marginal valleys and sandars

lithofacies variations within sandur deposits the role of runoff regime flow dynamics and sediment supply characteristics abstract the icelandic sandur plains have for long acted as classic sites for models of braided river behaviour and of associated lithofacies assemblages however many of the icelandic sandurs are subject to repeated catastrophic flood events or jokulhlaups which are likely to have played a significant role in sandur construction established lithofacies models based on the icelandic sandurs have failed to take account of the varying runoff regimes which characterise the different sandur environments in addition sediment inputs to sandur channel systems are highly variable fluctuating in response both to varying runoff patterns and to advance and retreat of the source glacier that affect sediment availability within the proglacial zone this paper describes the main lithofacies types and vertical profiles that characterize the sandurs of south iceland and demonstrates that they can largely be attributed to extreme runoff events with few deposits typical of braided river facies occurring within the sedimentary record a preliminary qualitative model is developed that allows interpretation and prediction of vertical lithofacies profiles derived from glacial outwash in terms of i the drainage mechanism which in turn controls the dominant runoff population ii sediment availability and iii the spatial variability in flow dynamics

lithium isotopic systematics of granites and pegmatites from the black hills south dakota to study li isotopic fractionation during granite differentiation and late stage pegmatite evolution li isotopic compositions and concentrations have been measured for the s type harney peak granite the spatially associated tin mountain pegmatite and possible metasedimentary source rocks in the black hills south dakota the harney peak granite is isotopically heterogeneous with 7 li varying from 3 1 to 6 6 the 7 li values of proterozoic metasedimentary rocks that are possible sources of the harney peak granite range from 3 1 to 2 5 and overlap with post archean shales and the harney peak granite for the granite suite there is no correlation between 7 li and elements indicative of degrees of granite differentiation sio2 li rb etc the li isotopic composition of the harney peak granite therefore appears to res ect the source composition minerals from the zoned tin mountain pegmatite have extremely high li contents and heavier li isotopic compositions than the granite or surrounding black hills metasedimentary rocks the heavier compositions may res ect li isotopic fractionation resulting from extensive crystal melt fractionation lithium concentrations decrease in the order spodumene 3 7 wt muscovite 0 2 to 2 0 wt plagioclase 100 1100 ppm quartz 30 140 ppm plagioclase muscovite and spodumene in all zones display a relatively narrow range in 7 li of 7 9 to 11 4 in contrast quartz is isotopically heavier and more variable 14 7 to 21 3 with 7 li showing an inverse correlation with li concentration this correlation res ects the mixing of isotopically heavy li in quartz and lighter li in s uid inclusions as documented by s uid inclusion compositions

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

lithium and boron in late orogenic granites isotopic fingerprints for the source of crustal melts abstract geochemically diverse late and post variscan granites of the erzgebirge vogtland the saxon granulite massif and thuringia germany formed by anatectic melting of palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks the compositional diversity of the least evolved of these granites is largely inherited from the protoliths we present li and b isotopic data of these granites and compare them with the isotopic composition of their protoliths to investigate whether i there exist systematic differences in the li and b isotopic composition among different granite types and ii li and b isotopic compositions provide information on the granite sources complementary to information from the isotopic composition of sr nd and pb and the trace element signatures low f biotite and two mica granite types have flat upper continental crust ucc normalized trace element pattern with variable enrichments in li rb cs sn and w and depletions in sr ba and eu these signatures are least pronounced for the niederbobritzsch biotite granite which has the largest contribution of mafic material and most pronounced for the two mica granites the granites show a relatively narrow range of 7li values 3 0 to 0 5 and a broad range of 11b values 13 4 to 20 1 the 11b values are lower in rocks with distinctly higher contents of li rb cs and sn the high 11b of the niederbobritzsch granite may be explained by the melting of former altered oceanic crust in its source relative to ucc intermediate f to high f low p granites show strong depletions in sr ba eu as well as zr and hf strong enrichments in li rb and cs as well as nb sn ta and w and ree pattern with stronger enrichments for hree than for lree these granites show narrow ranges of 7li 2 0 to 1 6 and 11b values 14 7 to 9 1 reflecting the smaller variability of the li and b isotopic composition in their source lithologies the anomalously high 7li value 14 7 of one granite sample burgberg which is similar to 7li values of its wall rocks up to 14 5 may indicate late magmatic fluid rock interaction with external wall rock derived fluids because of the small compositional range of most source lithologies the li and b isotopic variation in the granites is also small indicating that the isotopic composition of li and b does not represent a particularly sensitive source tracer with the exception of source lithologies characterized by extreme 7li or 11b values

outburst flooding and the initiation of ice stream surges in response to climatic cooling a hypothesis abstract outburst flooding from subglacial reservoirs and associated surging of ice streams are caused by processes following climatic cooling that produce ice shelf grounding on proglacial sills trapping subglacial water according to an hypothesis presented here glaciers often advance into proglacial water bodies cooling may allow ice shelf formation and advance causing grounding on a proglacial sill trapping subglacial water ice shelf freeze on to the sill and development of a local reversal in ice air surface slope over the sill then are likely allowing ice thickening and water overpressurization if basal thawing then occurs as is likely an outburst flood and a surge may be triggered these processes may have been involved in heinrich events generation of antarctic subglacial lakes and meltwater scouring of some regions

extreme chemical heterogeneity of granite derived hydrothermal fluids an example from inclusions in a single crystal of miarolitic quartz magma derived fluids are important in geologic processes e g metal sequestration and ore deposition but are intrinsically transient samples of magmatic fluids represented by fluid inclusions in a single zoned quartz crystal from a miarolitic cavity within a porphyritic leucogranite hosting the industrialnoe tin deposit northeastern russia were studied by using modern in situ analytical methods laser raman spectroscopy proton induced x ray emission the fluid inclusions are either dominated by vapor or by complex multiphase brines the inclusions within a given trapping plane have similar phase relationships however there are significant variations between inclusions in different healed fractures phase and chemical compositions of individual brine inclusions demonstrate significant compositional heterogeneity in terms of absolute element concentrations and ratios of high temperature magmatic fluids accumulated in the miarolitic cavity this finding suggests that fluids leaving a crystallizing magma may have variable initial compositions that are subsequently modified by reactions with the rocks while the fluid is in transit to a miarolitic cavity as well as by processes in the cavity such as mixing crystallization and boiling the inferred chemical diversity and fractionation of granite derived fluids at near magmatic conditions imply that fluids entering a cooler hydrothermal system are extremely complex and their metallogenic signature may differ from that of related ore deposits

lithium isotope fractionation during continental weathering processes a comprehensive understanding of lithium isotope fractionation during terrestrial weathering is necessary in order to use lithium isotopes to trace chemical cycles climatic changes and igneous processes this study investigates lithium isotope fractionation in two laboratory experiments and by analyses of natural basalt weathering products partial dissolution of basalts in the laboratory does not result in fractionation of lithium isotopes but similar dissolution of a granite sample causes significant fractionation this may reflect dissolution of secondary minerals from the granite or differences in the li isotope composition of primary minerals in this more evolved igneous rock significant li isotope fractionation was also observed during sorption onto mineral surfaces in the laboratory although this was highly dependent on sample mineralogy no fractionation accompanies the outer sphere physisorption of li to smectite surfaces some fractionation accompanies sorption onto ferrihydrite and significant fractionation with 0 986 is seen during inner sphere chemisorption to gibbsite surfaces repeat experiments with varying amounts of sorption demonstrate that li remains in an exchangeable site on the gibbsite surface the extent of fractionation onto gibbsite observed in this study 13 is about half that required in order for clay surface removal to balance the ocean li isotope budget isotopic fractionation of li was found to occur on a 300 yr timescale in both cold and warm natural environments a minimally altered rock surface from iceland was found to be two lighter in 7li than the sample interior probably due to the preferential incorporation of 6li in clay or oxide rich alteration products on the sample surface soil samples from hawaii also demonstrate li fractionation during weathering in this environment rainwater 7li 10 contributes a significant flux of isotopically heavy li to the developing soil despite this soils have similar li isotope compositions to the primary basalt 7li 4 indicating that 6li is preferentially retained during weathering this conclusion is supported by isotopically heavy river water on hawaii 7li 22 and by the correlation between li concentration and 7li in the soil the lab and field based measurements of this study clearly demonstrate that lithium fractionates during weathering potentially providing information about the weathering environment now and in the past