annual net balance of north cascade glaciers 1984 94 annual net balance on eight north cascade glaciers during the 1984 94 period has been determined by measurement of total mass loss from firn and ice melt and of residual snow depth at the end of the summer season overall spatial density of measurement points is 200 points km 2 mean annual balance of north cascade glaciers from 1984 to 1994 has been 0 38 m a 1 the resulting 4 2 m loss in water equivalent thickness is significant since north cascade glaciers have an average thickness of 30 50 m cross correlation of annual net babance for eight glaciers ranges from 0 83 to 0 97 this indicates the mass balances of the eight glaciers have been responding similarly to climate conditions despite their range of topographic and geographic characteristics annual net balance of individual glaciers was correlated with climate records the highest ablation season correlation coefficient is mean may august temperature ranging from 0 63 to 0 84 the highest accumulation season correlation coefficient is total accumulation season precipitation ranging from 0 35 to 0 59

contrasting compositions of mariana trough fallout tephra and mariana island arc volcanics a fractional crystallization link discrete quaternary 400 ka tephra fallout layers mostly 1 cm thick within the siliceous oozes of the central mariana trough at 18 n are characterized by medium k to high k subalkalic volcanic glasses k2o 0 8 3 2 wt with high large ion lithophile elements lile high field strength elements hfse ratios and nb depletion ba la 35 ba zr 3 5 la nb 4 typical for convergent margin volcanic rocks compositional zoning within layers ranges from basaltic to dacitic sio2 48 71 wt mgo 0 7 6 5 wt all layers contain basaltic andesites the tephra layers are interpreted as single explosive eruptive events tapping chemically zoned reservoirs the sources being the mariana arc volcanoes mav due to their proximity 100 400 km and similar element ratios mav ba la 36 7 ba zr 3 5 0 9 the glasses investigated however contrast with the contemporaneous basaltic to dacitic lavas of the mav by being more enriched in tio2 1 2 wt mav 0 8 wt feo 10 wt mav 8 9 wt k2o 1 1 wt mav 0 8 wt and p2o5 0 4 wt mav 0 2 wt semi incompatible trace elements including rare earth elements ree of the basaltic andesitic and dacitic glasses match those of the dacitic mav lavas which became enriched by fractional crystallization moreover the glasses follow a tholeiitic trend of fractionation in contrast to mav transitional trends and have a characteristic p2o5 trend that reaches a maximum of 0 6 wt p2o5 at 57 wt sio2 whereas mav lavas increase linearly in p2o5 from 0 1 to 0 3 wt with increasing silica both explosive and effusive series are interpreted to have evolved in common magma reservoirs by convective fractionation similar parental magmas are suggested to have separated into coexisting si andesitic to dacitic and basaltic melts by in situ crystallization the differentiated melt is interstitial in an apatite saturated crystalline mush of plag px ox ol at the cooler chamber margins in contrast to the less differentiated basaltic to basaltic andesitic magmas which are not yet saturated in apatite and occupy the chamber interior reinjection of interstitial melt into the chamber interior and mixing with larger melt fractions of the interior liquid mixing ratios about 1 8 9 can explain the paradoxical behavior of apatite controlled p and mree variation in the basaltic andesite glasses and their mav dacite like fractionation patterns the process may also account for the exclusively tholeiitic trend of fractionation of the glass shard series but in situ crystallization alone cannot cause their absolute enrichment in semi incompatible elements the newly mixed melt is suggested to form the basaltic end member of the glass shard series however it must have become physically separated from the main mav magma body possibly by density driven convective fractionation in order to allow for further evolution of the contrasting geochemical paths as well as differentiation

forty years of ttg research abstract ttgs tonalite trondhjemite granodiorite are one of the archetypical lithologies of archaean cratons since their original description in the 1970s they have been the subject of many studies and discussions relating to archaean geology in this paper we review the ideas concepts and arguments brought forward in these 40 years and try to address some open questions both old and new the late 1960s and the 1970s mark the appearance of grey gneisses ttg in the scientific literature during this period most work was focused on the identification and description of this suite and the recognition that it is a typical archaean lithology ttgs were already recognised as generated by melting of mafic rocks this was corroborated during the next decade when detailed geochemical ttg studies allowed us to constrain their petrogenesis melting of garnet bearing metamafic rocks and to conclude that they must have been generated by archaean geodynamic processes distinct from their modern counterparts however the geodynamic debate raged for the following 30 years as many distinct tectonic scenarios can be imagined all resulting in the melting of mafic rocks in the garnet stability field the 1990s were dominated by experimental petrology work a wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to ttg liquids whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate from 1990s onwards one of the key questions became the comparison with modern adakites as originally defined these arc lavas are reasonably close equivalents to archaean ttgs pending issues largely revolve around definitions as the name ttg has now been applied to most archaean plutonic rocks whether sodic or potassic irrespective of their hree contents this leads to a large range of petrogenetic and tectonic scenarios a fair number of which may well have operated concurrently but are applicable only to some of the rocks lumped together in the ever broadening ttg bin

recent glacier decline in the kerguelen islands 49 s 69 e derived from modeling field observations and satellite data the retreat of glaciers in the kerguelen islands 49 s 69 e and their associated climatic causes have been analyzed using field data and moderate resolution imaging spectroradiometer modis satellite images to validate a positive degree day pdd model forced by data from local meteorological stations mass balance measurements made during recent field campaigns on the largest glacier of the cook ice cap were compared to data from the early 1970s providing a 40 year view of the differences in the spatial distribution of surface mass balance smb to obtain additional regional data for the validation of our models we analyzed modis images 2000 2012 to determine if our model was capable of reproducing variations in the transient snow line the pdd model correctly simulated the variations in the snow line the spatial variations in the smb and its trend with elevation yet current smb values diverge from their classic linear representation with elevation and stake data at high altitudes now display more negative smb values than expected by analyzing modis albedo we observed that these values are caused by the disappearance of snow and associated feedback on melt rates in addition certain parts of ampere glacier could not be reproduced by the surface energy balance model because of overaccumulation due to wind deposition finally the modis data field data and our models suggest that the acceleration of glacier wastage in kerguelen is due to reduced net accumulation and an associated rise in the snow line since the 1970s

diapiric transfer of melt in kilauea iki lava lake hawaii a quick efficient process of igneous differentiation kilauea iki lava lake formed in 1959 is a large pond of picritic basalt average mgo content 15 34 by weight which has cooled and crystallized as a small self roofed magma chamber repeated drilling of the upper crust of the lake down to its molten core and more recent 1981 drilling through the thermal maximum and part way through the lower crust have made it possible to monitor the differentiation processes in the lake in detail differentiation processes recognized as active in the lake include rather inefficient settling of the larger 2 10 mm olivine phenocrysts formation of segregation veins and formation of diapir like vertical olivine rich bodies all processes which occur in one or more of the other kilauean lava lakes as well in addition most of the central part of kilauea iki has been affected by diapiric melt transfer in this process relatively low density liquid present at 1145 1160 c rose from within the loose crystal mush at the base of the lens of melt and intruded the equivalent thermal horizon at the top of the lens of melt passing through the hotter but denser melt in the core of the lake without mixing the source volume from which the low density liquid was extracted is depleted in tio 2 and other incompatible elements and enriched in feo and cao the upper part of the lake shows the opposite effects the crystalline assemblage present was olivine augite minor plagioclase the crystallinity of both the source and receiving layers was low enough that no obvious textural imprint was left by the transfer process the principal evidence for its occurrence is the chemical zonation of the lake seen in core from depths of 13 to 80 m diapiric melt transfer was active from 1960 to 1971 and has affected most of the central part of the lake from 13 m to at least 80 m the process ran simultaneously with the other three main differentia tion processes but started and stopped independently of the others calculations suggest that between 21 and 42 wt liquid has been extracted from the depleted zone at 56 78 m in the center of the lake making this a very efficient process of chemical differentiation

magmatic fractionation by compositional convection in a sheet like magma body constraints from the nosappumisaki intrusion northern japan the mechanism of fractionation in a sheet like magma body was investigated based on observations from the nosappumisaki intrusion northern japan this is one of a number of late cretaceous shoshonite sills in the nemuro peninsula and has a compound structure comprising a bottom cumulate zone containing 50 vol cumulus crystals and a overlying middle zone free of such cumulus crystals these zones are sandwiched between porphyritic rocks of upper and lower chilled and marginal zones it is inferred that massive crystal settling or flotation from a magma initially laden with 20 vol of crystals primocrysts in a sheet like magma body formed a cumulus pile and an overlying crystal free melt layer after the formation of the compound structure with partial freezing of the upper and lower marginal zones the internal part of the intrusion slowly solidified during this period the melt in the central part of the intrusive sheet underwent fractional crystallization this is shown by patterns of vertical variation in the composition of the interstitial melt the overall patterns are inverted mirrorimage s shaped and s shaped for incompatible and compatible elements respectively the incompatible element abundances show maxima near the bottom of the middle zone which corresponds to the final solidification horizon they show minima in the cumulate zone which suggests discharge of an evolved melt from the crystal pile fractionation is inferred to have taken place via compositional convection without settling of crystals grown after the intrusion event or collapse of the upper boundary layer the melt in the central melt layer descended into the permeable crystal pile counterbalancing discharge of buoyant evolved melt formed by crystallization of the pore melt in the crystal pile this conclusion is based on the following observations 1 there is no accumulation of crystals grown after the intrusion of the magma above the cumulate zone 2 leucocratic pipe like structures which represent relict pathways for the evolved melt are developed in the cumulate zone these structures increase in diameter decrease in number density and increase in abundance of incompatible elements with height 3 cumulus augite in the cumulate zone has ca rich and al poor dissolved rims the extent of dissolution increases with stratigraphic height suggesting downwelling of an h2o rich melt from the overlying melt layer 4 there is no evidence for extensive compaction accompanying pore melt crystallization in the main part of the cumulate zone 5 the initial melt composition estimated from the groundmass of the chilled margin rocks and the average composition of the material interstitial to the primocrysts for the whole sill are statistically identical a mass balance model for compositional convection was constructed to quantify the melt transportation processes model parameters were optimized by fitting the observed vertical variation of the interstitial melt compositions the optimized results suggest that the evolved melts discharged from the crystal pile and rose through the central melt layer as plumes with minor mingling with the surrounding melt the initially formed compound structure is a highly preferential environment for compositional convection

geology and petrogenesis of the edgecumbe volcanic field se alaska the interaction of basalt and sialic crust the edgecumbe volcanic field is a holocene volcanic province located on kruzof island se alaska exposed within the 260 km2 field are basalt andesitic basalt andesite dacite and rhyodacite the rhyodacites were erupted after the basalts and before the andesites the volcanics which are al rich 14 18 wt and lack an iron enrichment trend range from tholeiites 47 wt sio2 through rhyodacites 72 but a compositional gap of approximately 9 wt separates the dacites and rhyodacites initial 87sr 86sr ranges from 0 70297 in the basalts to 0 70440 in a pyroxene andesite 18o increases across the suite 5 8 to 7 9 plagioclase an32 86 is the dominant phenocryst in all but one lava olivine fo58 86 occurs in the basic lavas 53 wt sio2 but is replaced by orthopyroxene en43 73 and clinopyroxene en31wo41 en48wo40 in the more siliceous volcanics in the basalts and rhyodacites plagioclase is weakly zoned but extreme zoning 30 mole an is characteristic of phenocrysts in the intermediate lavas fractionation of the observed phenocryst assemblages could not have produced the more silicous volcanics instead they were generated by partial melting of intrusive basement 87sr 86sr 0 70487 18o 8 7 9 3 by basaltic magma and subsequent assimilation mass balance calculations show the rhyodacites are almost pure partial melt 5 basaltic component whereas the intermediate lavas contain between 30 and 60 partial melt

modelling glacier advances and related climate conditions during the last glaciation cycle in the kuzigun valley tashkurgan catchment on the north west tibetan plateau understanding regional climate during the last glaciation cycle lgc is far from complete for the north western tibetan plateau recent improvements in understanding glacial extents and chronologies in the tashkurgan catchment north west tibetan plateau present an opportunity to estimate the glacial climatic conditions of the lgc here we use a coupled mass balance and ice flow model to reconstruct glacier advances in the kuzigun valley during the lgc and quantify the related climate conditions in the tashkurgan hangdi and kuzigun glacial stages for the region the model results show that the kuzigun valley contained ice volumes of 5 713 0 005 4 874 0 005 and 3 631 0 004 km3 with equilibrium line altitude lowering values of 500 560 and 610 m in the three successive glacial stages respectively by referencing the climatic 18o proxy records we conclude that temperature decreased by 5 8 4 and 140 modern values in the kuzigun hangdi and tashkurgan glacial stages respectively our climatic estimates for the kuzigun stage are generally consistent with previous studies that showed the last glacial maximum climate was 4 9 c colder than today on the tibetan plateau more accurate climate proxies are needed for evaluating our modelled tashkurgan climatic conditions

silicic volcanism at ljosufjoll iceland insights into evolution and eruptive history from ar ar dating abstract ljosufjoll volcano is the largest outcrop of silicic volcanic material in the volcanic snaefellsnes flank non rifting zone of iceland the silicic eruptives range from trachytes to alkaline and peralkaline comenditic rhyolites and show evidence for eruption in both subaerial and subglacial environments thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation the trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar rich trachytic mush with continued fractionation of the interstitial melt producing low ba and sr rhyolite magma ar ar dating of feldspars and matrix glass or holocrystalline groundmass has been carried out on twelve of the units many units have a complex ar isotopic system with many samples showing evidence for inherited 40ar in the form of feldspar xenocrysts the deduced eruption ages span an age range from 650ka the eruptive history of ljosufjoll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried a syenite xenolith was dated at 1 1ma indicating that silicic alkaline magmatism has been occurring at ljosufjoll for over one million years eruptions of silicic material at ljosufjoll appear to be more common during times of rapid climate change and fluctuating ice volume

erosion by an alpine glacier assessing the impact of glaciation on earth s surface requires understanding glacial erosion processes developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice bedrock interface of contemporary glaciers we demonstrate that the glacial erosion rate is proportional to the ice sliding velocity squared by quantifying spatial variations in ice sliding velocity and the erosion rate of a fast flowing alpine glacier the nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation a nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast flowing glaciers it may also explain the wide range of observed glacial erosion rates and in part the impact of glaciation on mountainous landscapes during the past few million years

crystal size distribution in jurassic ferrar flows and sills victoria land antarctica evidence for processes of cooling nucleation and crystallisation jurassic ferrar rocks in victoria land antarctica occur predominantly as basaltic or andesitic flows and sills both show characteristic petrographical and chemical variations which can be related to in situ differentiation processes such characteristics have been investigated at one flow colonnade flow and one sill thumb point sill in the prince albert mountains central victoria land based on a statistical grain size analysis and the application of the crystal size distribution theory a third magma body hiti unit which in previous literature was described as a flow does not show clear similarities to either the flow or sill sill and flow are in situ differentiated with accumulation of silicic residual melt in the latest cooled parts for the flow this part is located in the lower half and for the sill in the upper third of their thickness thumb point sill additionally shows an accumulation zone of olivine in the lower third the position of the residual melt accumulation zone is an indicator for an origin as flow or sill the hiti unit by contrast exhibits only moderate petrographical and chemical variations growth and nucleation rates have been determined using with some modifications the csd theory introduced by marsh 1988 growth rates of plagioclase for the flow vary from 10 11 to 10 10 cm s and are comparable with literature values for basaltic lava lakes on hawaii nucleation rates vary from 10 4 to 10 3 cm 3s 1 which are generally smaller than for hawaiian basalts growth and nucleation rates for the sill cover a large range from 10 13 to 10 11 cm s and 10 9 to 10 3 cm 3s 1 respectively systematic variations of these parameters with vertical position were obtained for the sill with its extensive differentiation history nucleation and growth rates are dependant on the mode of cooling nevertheless small but significant differences between the flow and sill exist growth and nucleation rates of hiti unit 10 12 to 10 11 cm s and 10 6 to 10 5 cm 3s 1 are intermediate between the flow and sill and thus do not allow a distinction of emplacement mode

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

past and future mass balance of ka roimata o hine hukatere franz josef glacier new zealand despite their relatively small total ice volume mid latitude valley glaciers are expected to make a significant contribution to global sea level rise over the next century due to the sensitivity of their mass balance systems to small changes in climate here we use a degree day model to reconstruct the past century of mass balance variation at ka roimata o hine hukatere franz josef glacier new zealand and to predict how mass balance may change over the next century analysis of the relationship between temperature precipitation and mass balance indicates that temperature is a stronger control than precipitation on the mass balance of franz josef glacier the glacier s mass balance relative to its 1986 geometry has decreased at a mean annual rate of 0 02 m a 1 w e between 1894 and 2005 we compare this reduction to observations of terminus advance and retreat of which franz josef glacier has the best record in the southern hemisphere for the years 2000 05 the relative mass balance ranged from 0 75 to 1 50 m a 1 w e with 2000 01 the only year showing a negative mass balance in a regionally downscaled intergovernmental panel on climate change mean warming scenario the annual relative mass balance will continue to decrease at 0 02 m a 1 w e through the next century

temperature and precipitation climate at the equilibrium line altitude of glaciers expressed by the degree day factor for melting snow several authors relate accumulation or precipitation at the glacier equilibrium line altitude ela to summer mean temperature using exponential or power law functions i analyze the accumulation temperature relation at the ela with a degree day model using data from the 1992 paper by a ohmura and others the dataset includes estimates at the ela of winter balance and of winter balance plus summer precipitation which represent respectively low and high estimates of annual accumulation which is seldom measured the ohmura dataset only lists summer mean temperature but i recover monthly temperatures for the whole year for 66 of the glaciers by assuming sinusoidal temperature variation through the year and using annual temperature range from a gridded climatology monthly degree day sums are then estimated from monthly mean temperature and summed to give annual totals so degree day factors for melting snow at the ela are obtained the degree day factors fall close to those reported in the literature for glacier snowmelt with averages of 3 5 1 4 and 4 6 1 4 mm d 1 k 1 for low and high accumulation estimates on the 66 glaciers the degree day model gives a family of accumulation temperature curves that depend upon the annual temperature range representing the contrast between maritime and continental climates

hawaiian basalt and icelandic rhyolite indicators of differentiation and partial melting in spite of the voluminous basaltic volcanism on the island of hawaii rhyolite is not produced iceland on the other hand exhibits common rhyolitic volcanism amounting to some 10 12 of its surface rocks this contrast is investigated using the fundamental igneous processes exhibited by sheet like hawaiian lava lakes and shonkin sag laccolith in montana highly differentiated residual melts normally reside within inwardly advancing solidification fronts and are generally inaccessible to eruptive processes only when a large initial phenocryst population is present from which a thick basal cumulate can rapidly form is it possible to supply highly differentiated melt into the active i e eruptable portion of the magma chamber although there is protracted control of differentiation at hawaii by settling of olivine further differentiation occurs within the solidification fronts only by repeated transport and holding is it possible to differentiate beyond the critical composition of the leading edge of the solidification front 7 mgo and 51 5 sio2 crystal size distributions csds for hawaii and shonkin sag are used to demonstrate the inferred physical and chemical processes of solidification including the kinetics of crystallization

crystal capture sorting and retention in convecting magma the mystery of producing strong compositional diversity among suites of comagmatic igneous rocks is investigated by considering the dynamic evolution of basaltic magma in a sheet like chamber a central conclusion is that inward progressing crystallization produces strong viscosity and temperature gradients that promote convection only near the leading edge of the upper thermal boundary layer convection is apparently confined to an essentially isoviscous isothermal region that hugs the downward growing roof zone strong changes in viscosity with crystallization divide the upper and lower thermal boundary layers into regions of decreasing viscosity and crystallinity n called rigid crust n 0 5 mush 0 5 n 0 25 and suspension n 0 25 the strong increase in viscosity near the mush suspension interface acts as a capture front that overtakes and traps slowly settling crystals initial phenocrysts mostly escape capture but crystals nucleated and grown in the suspension zone can escape only if the capture front slows to a critical rate attainable only in bodies thicker than about 100 m escaping crystals are redistributed and sorted by convection driven by the advance of the capture front itself crystal laden plumes traverse the central hot core of the body and deposit partially resorbed and sorted crystals within the lower suspension zone convection is never vigorous but is part of an overall intimate balance between roofward heat loss rigid crust growth crystallization kinetics and transport and sorting of sinking escaped crystals there is a strong similarity between these processes and those producing both varves and saline pan deposits it is clear that lavas lava lakes and sills are indeed examples of true magma chambers strongly exhibiting certain aspects of this over all process these aspects commonly also characterize the large mafic magmatic bodies because strong compositional changes in the residual melt occur largely outward that is at lower temperatures and higher crystallinities of the capture front which is immobile and mostly within rigid crust the possible range in comagmatic compositions available for eruption anywhere within the active magma is very limited this is in broad agreement with the compositional range observed in basaltic lava lakes sills and plutons like skaergaard the tuning of convection crystallization kinetics and phase equilibria in chambers of this type can produce a variety of textures and layering but not a diversity of compositions

to the origin of icelandic rhyolites insights from partially melted leucocratic xenoliths we have studied glass bearing leucocratic granitic to qz monzonitic crustal xenoliths from the tindfjoll pleistocene volcanic complex sw iceland the xenoliths consist of strongly resorbed relicts of anorthitic plagioclase k rich feldspar and rounded quartz in colorless through pale to dark brown interstitial glass spongy clinopyroxene and or rounded or elongated crystals of orthopyroxene are in subordinate amount magnetite ilmenite zircon apatite allanite and or chevkinite are accessory minerals the xenoliths more likely are relicts of earlier formed partially melted si rich rocks or quartz feldspar rich crystal segregations which suffered latter interaction with hotter and more primitive magma s icelandic lavas are typically low in 18o compared to mantle derived morb like rocks 5 6 0 2 likely due to their interaction with or contamination by the upper crustal rocks affected by rain and glacial melt waters surprisingly many quartz and feldspar crystals and associated colorless to light colored interstitial glasses of the studied xenoliths are not low but high in 18o 5 1 7 2 excluding three dark brown glasses of 4 5 the xenoliths contain abundant low to high 18o 2 4 6 3 young zircons u pb age 0 2 0 27 0 03 ma u th age 0 16 0 07 ma most of them in oxygen isotope equilibrium with interstitial glasses the 18o values 5 6 recorded in the coexisting zircon quartz feldspar and colorless interstitial glass suggest crystallization from melts produced by fusion of crustal rocks altered by seawater also reflecting multiple melting and crystallization events this suggests that normal 18o silicic magmas may not be ultimately produced by crystallization of mafic basaltic magmas instead our new single crystal laser fluorination and ion microprobe o isotope data suggest addition of diverse partial crustal melts probably originated from variously altered and preconditioned crust

glacial advance and stagnation caused by rock avalanches abstract new model results show that a glacier advance caused by deposition of a rock avalanche on the ice will be followed by stagnation of the advanced ice lobe producing distributed hummocky deposits quite different from the single moraine ridges typically dated in paleoclimatic reconstructions we obtain these results using a numerical flow line glacier model with superimposed rock debris in particular our results imply that the single moraine ridge known as the waiho loop of the franz josef glacier new zealand is not the result of an advance triggered by a rock avalanche else there would be a widespread hummocky glacial stagnation deposit associated with it

first cosmogenic 10be constraints on lgm glaciation on new zealand s north island park valley tararua range we report the first direct ages for late quaternary glaciation on the north island of new zealand mt ruapehu the volcanic massif in the north island s centre is currently glaciated and probably sustained glaciers throughout the late quaternary yet no numeric ages have been reported for glacial advances anywhere on the north island here we describe cosmogenic 10be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the tararua range part of the axial ranges of the north island results indicate that a limited valley glaciation occurred culminating in recession at the end of the last glacial coldest period lgcp ca 18 ka this provides an initial age for deglaciation on the north island during the last glacial interglacial transition lgit it appears that glaciation occurred in response to an equilibrium line altitude ela lowering of 1400 m below the present day mean summer freezing level ages for glaciation in the tararua range correspond closely to exposure ages for the last glacial maximum lgm from the lateral moraines of cascade valley in the south island and in cobb valley in northern south island the corollary is that glaciation in the tararua range coincided with the phase of maximum cooling during mis 2 prior to the antarctic cold reversal acr during the lgcp copyright 2008 john wiley sons ltd

the last glacial maximum at 44 s documented by a 10be moraine chronology at lake ohau southern alps of new zealand abstract determining whether glaciers registered the classic last glacial maximum lgm 26 500 19 000 yrs ago coevally between the hemispheres can help to discriminate among hypothesized drivers of ice age climate here we present a record of glacier behavior from the southern alps of new zealand during the local lgm llgm we used 10 be surface exposure dating methods and detailed glacial geomorphologic mapping to produce a robust chronology of well preserved terminal moraines deposited during the llgm near lake ohau on central south island we then used a glaciological model to estimate a llgm glacier snowline and atmospheric temperature from the ohau glacier record seventy three 10 be surface exposure ages place culminations of terminal moraine construction and hence completions of glacier advances to positions outboard of present day lake ohau at 138 600 10 600 yrs 32 520 970 yrs ago 27 400 1300 yrs ago 22 510 660 yrs ago and 18 220 500 yrs ago recessional moraines document glacier recession into the lake ohau trough by 17 690 350 yrs ago exposure of an ice molded bedrock bench located inboard of the innermost llgm moraines by 17 380 510 yrs ago indicates that the ice tongue had receded about 40 of its overall length by that time comparing our chronology with distances of retreat suggests that the ohau glacier terminus receded at a mean net rate of about 77 m yr 1 and its surface lowered by 200 m between 17 690 and 17 380 yrs ago a long term continuation of ice retreat in the ohau glacier catchment is implied by moraine records at the head of irishman stream valley a tributary of the ohau glacier valley the irishman stream cirque glacier advanced to produce a set of lateglacial moraines at 13 000 500 yrs ago implying that the cirque glacier was less extensive prior to that advance we employed a glaciological model fit to these mapped and dated llgm moraines to derive snowline elevations and temperature parameters from the ohau glacier record the modeling experiments indicate that a snowline lowering of 920 50 m and temperature depression of 6 25 0 5 c below modern values allows for the ohau glacier to grow to an equilibrium position within the lgm moraine belt taken together with a glaciological simulation reported from the irishman stream valley snowlines and temperatures increased by at least 520 m and 3 6 c respectively between 18 000 and 13 000 yrs ago climate parameters derived from the ohau glacier reconstruction are similar to those derived from glacier records from patagonia to air temperature indicators from antarctica as well as to sea surface temperature and stratification signatures of the southern ocean we think that the best explanation for the observed southern llgm is that southern winter duration modulated southern ocean sea ice which in turn influenced southern ocean stratification and made the surface ocean cooler orbitally induced cooling of the southern ocean provides an explanation for the llgm in the southern alps having been coincident with the northern lgm we argue further that the global effect of north atlantic stadials led to disturbance of southern ocean stratification southward shifts of the subtropical front and retreat of southern alps glaciers collapse of southern ocean stratification during heinrich stadial 1 along with attendant sea surface warming triggered the onset of the last glacial termination in the southern alps of new zealand

the crustal magma chamber of the katla volcano in south iceland revealed by 2 d seismic undershooting summary results of a 2 d seismic undershooting experiment on the katla central volcano in south iceland are reported large localized traveltime anomalies 0 4 s are observed on an array within the katla caldera the traveltimes are forward modelled using a wavefront tracker developed in appendix a thus non linear effects encountered in traveltime tomography are avoided as well as common problems with ray tracing in the presence of strong lateral heterogeneity an extreme variation in compressional velocity is required to extend over a significant volume in order to model the data the resulting model is not unique but constraints on the allowable range of velocities 2 5 6 0 km s render the basic features well constrained a clear s wave shadow is closely associated with delays in traveltime due to a shallow slow anomaly low amplitude p waves go hand in hand with early arrivals due to thin structural features flanking the slow anomaly the model is interpreted in terms of a magma chamber containing extensively molten rock the magma chamber is shallow with a bottom at a depth of about 1 5 km below sea level 3 0 km below surface and measures about 5 km across the depth of the chamber is roughly at the level of buoyant equilibrium for basaltic melt in the crust owing to poor vertical resolution at shallow depths in the undershooting geometry the top of this shallow magma chamber is not well resolved on the other hand the bottom of the chamber is well resolved the chamber is underlain by rocks of average or high velocity for that depth the magma chamber is a persistent feature big enough 10 km3 to supply magma for large eruptions and to supply heat to permit remelting of hydrated basaltic crust to produce silicic magmas at shallow levels the chamber is fed by magma fracturing from below the model agrees with phenomenological models of magma chambers in iceland based on geological observations and provides a quantification of those models in terms of depth and size on the other hand it is fundamentally different from recent models of magma chambers at mid ocean ridges which may be more akin to the pervasive region of partial melt at depth beneath iceland this underlines the important effect of the icelandic hotspot on tectonics and volcanism in iceland and implies a substantially different crustal and thermal structure in iceland from that of normal mid ocean ridges

alteration and remelting of nascent oceanic crust during continental rupture evidence from zircon geochemistry of rhyolites and xenoliths from the salton trough california abstract rhyolite lavas and xenoliths from the salton sea geothermal field southern california provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust salton buttes rhyolite lavas contain xenoliths that include granophyres fine grained altered rhyolites felsite and amphibole bearing basalts zircon is present in lavas and xenoliths surprisingly even in the basaltic xenoliths where it occurs in plagioclase rich regions interpreted as pockets of crystallized partial melt zircons in the xenoliths are exclusively late pleistocene holocene in age and lack evidence for inheritance u th isochron ages are 20 5 1 2 1 2 ka granophyres 18 3 3 5 3 6 ka felsite 30 1 12 4 14 1 ka and 9 2 6 6 7 0 ka basalts all errors 1 the dominant zircon population in the rhyolite lavas yielded u th ages between 18 and 10 ka with few pre quaternary xenocrysts present 18ozircon values are lower than typical crustal basement values thus ruling out rhyolite genesis by melting of continental crust moreover 18ozircon values are 0 5 1 0 lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid ocean ridge basalt suggesting that basaltic crust and silicic plutons in the subsurface of the salton sea geothermal field isotopically exchanged with meteoric waters this is evidence for deep reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma

evolution of crystal settling in magma chamber convection abstract the motion of negatively buoyant particles embedded within kinematically prescribed convective velocity fields is used to study the evolution of crystal settling in magma chambers we consider the effects of stokesian settling velocity crystal growth aspect ratio of the convective domain and the site of crystal nucleation on mixing and transport of heavy crystals in this system the percentage of particles retained in a convecting fluid is very sensitive to the site of nucleation particles nucleating along the cold roof or within the wall boundary layers are generally not retained as a consequence crystal settling can occur even in rapidly convecting magma chambers equilibrium crystal densities are reached relatively quickly within one overturn and the distribution of particles deposited on the bottom of the chamber is always asymmetric this feature may facilitate the formation of primary sedimentary structures in plutons laboratory experiments using small negatively buoyant spheres in a highly viscous fluid with axisymmetric thermal convection confirm the basic predictions of this model

could iceland be a modern analogue for the earth s early continental crust for the last two decades iceland and other oceanic plateaux have been considered as potential analogues for the formation of the early earth s continental crust this study examines the compositions of silicic rocks from modern oceanic plateaux revealing their differences to archaean continental rock types trondhjemite tonalite granodiorite or ttg and thereby emphasising the contrasted mechanisms and or sources for their respective origins in most oceanic plateaux felsic magmas are thought to be formed by fractional crystallization of basalts in iceland the interaction between mantle plume and the mid atlantic ridge results in an abnormally high geothermal gradient and melting of the hydrated metabasaltic crust however despite the current archaean like high geothermal gradients melting takes place at a shallow depth and is unable to reproduce the ttg trace element signature consequently oceanic plateaux are not suitable environments for the genesis of the archaean continental crust however their subduction could account for the episodic crustal growth which has occurred throughout the earth s history

reconstructing climate from glaciers glaciers offer the potential to reconstruct past climate over timescales from decades to millennia they are found on nearly every continent and at the last glacial maximum glaciers were larger in all regions on earth the physics of glacier climate interaction are relatively well understood and glacier models can be used to reconstruct past climate from geological evidence of past glacier extent this can lead to significant insights regarding past present and future climate for example glacier modeling has demonstrated that the near ubiquitous global pattern of glacier retreat during the last few centuries resulted from a global scale climate warming of 1 c consistent with instrumental data and climate proxy records climate reconstructions from glaciers have also demonstrated that the tropics were colder at the last glacial maximum than was originally inferred from sea surface temperature reconstructions future efforts to reconstruct climate from glaciers may provide new constraints on climat

a distributed surface energy balance model for a small valley glacier i development and testing for haut glacier d arolla valais switzerland this paper describes the development and testing of a distributed surface energy balance model used to calculate rates of surface melting at haut glacier d arolla valais switzerland the model uses a digital elevation model dem of the glacier surface and surrounding topography together with meteorological data collected at a site in front of the glacier to determine hourly or daily totals of the energy balance components and hence of melting over the entire surface of the glacier with a spatial resolutio of 20 m the model can also be used to determine temporal and spatial variations in snow depth snow line position and glacier surface albedo calculations from the model are compared with observations made along the glacier centre line in 1990 and in general the model performs very well the correlation coefficients between calculated and measured snow line elevation albedo and ablation are 0 99 0 85 and 0 81 respectively the main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

crystal size distribution systematics and the determination of magma storage times the 1959 eruption of kilauea volcano hawaii abstract the theory of crystal size distribution csd theory is based on a steady state population balance that monitors the flux of crystals growing into and out of specificed size categories in precipitating solutions the conservation equation describing this balance permits crystal growth and nucleation rates to be determined directly from crystal size distribution data in this investigation it is shown that csd analysis can alternatively be used to calculate the residence time of crystals in the system or in volcanologic terms the magma storage time prior to eruption if the characteristic crystal growth rate can be independently determined or estimated the crystal size data needed for storage time determinations are easily obtained from thin sections of glassy eruption samples and the mathematical calculations are relatively simple analysis of the errors inherent in this new technique predicts storage estimates accurate to within an order of magnitude

generation of rhyolitic melt in an artificial magma implications for fractional crystallization processes in natural magmas abstract a large 1 3 10 7 g artificial mafic melt with a bulk composition similar to an unusually calcic basalt 17 wt cao was produced by in situ heating of soil and subsequently cooled and crystallized the final crystalline assemblage consisted dominantly of acicular diopsidic to hedenbergitic pyroxene and anorthitic feldspar with a subordinate amount of potassic feldspar electron microprobe analyses reveal the presence of a small amount 10 vol of rhyolitic glass 71 sio 2 within the crystalline network this glass is the residual material left after crystallization of pyroxene and feldspar analogous to rhyolitic melt which may be generated from fractional crystallization of a basaltic magma ion microprobe imaging indicates that the rhyolitic glass is generally present in isolated triangular to rectangular shaped interstices left by crystallization of acicular and tabular phases and that the glass is enriched in trace elements such as zr and cs which are incompatible within the crystalline phases no evidence of coalescence or migration of the rhyolitic melt is suggested by glass morphology although these observations were made in an artificial magmatic system analogies to a natural system may be drawn the isolated nature and low abundance of the rhyolitic glass highlights the difficulty of extracting and segregating evolved melts produced by high degrees of crystallization of a primitive parent particularly one characterized by elongated rather than equant crystals the distribution of the rhyolitic glass supports the suggestion that extraction of significant amounts of evolved melts from rocks may require repeated partial melting of crystallized material in order to allow the evolved liquid to physically separate from the parent and also suggests that the geometry of crystals may be an important factor in melt segregation

last glacial maximum climate based on cosmogenic 10be exposure ages and glacier modeling for the head of tashkurgan valley northwest tibetan plateau abstract fully understanding the timing and climate of last glacial maximum lgm is still lack in the head of the tashkurgan valley northwest tibetan plateau tp the recent improvements in cosmogenic 10 be exposure dating and glacier modeling present an opportunity to estimate the lgm climatic conditions in the paper we investigated the moraines and used the 10 be exposure dating on the moraine boulders to constrain the timing of the lgm the kuzigun glacial stage in the head of the tashkurgan valley then we used a coupled mass balance and ice flow model to quantify the paleoclimate from past glacier extents constrained by mapped and dated kuzigun glacial moraines in the area we showed that the glaciers terminated at an elevation of 4100 4200 m asl during the kuzigun glacial stage and the glacial stage occurred during or slightly before 15 23 ka corresponding to the timing of the global lgm the modeled mass balances indicated that present day equilibrium line altitude ela ranges from 5150 to 5250 m asl and lgm ela is between 4550 and 4600 m asl in the area suggesting an ela lowering of 600 m during the lgm model results suggested that the temperature during the lgm in the head of the tashkurgan valley is 5 8 c colder than today considering a 30 70 reduction in precipitation compared to today the paleoclimate estimates are generally consistence with previous studies that showed the lgm climate was colder and drier than today on the tp

timing and configuration of the gongga ii glaciation in the hailuogou valley eastern tibetan plateau a glacier climate modeling method abstract the timing and extent of late quaternary glaciation in the hailuogou valley of eastern tibetan plateau have been extensively studied over past decades debate however exists in the timing of the gongga ii moraine that represents the maximum glaciation in the hailuogou valley furthermore the gongga ii glaciation is not quantitatively reconstructed and what climate conditions could support this maximum glaciation is unknown this study used a glacier climate model driven by data from local weather stations to simulate the gongga ii glacier extent by fitting modeled glaciers to field geological evidence running multiple simulations with different temperature precipitation combinations we inferred the climate scenarios sufficient to generate the gongga ii glacier extent the modeled gongga ii glaciers have an area of 119 km 2 and an average volume of 1 35 10 10 m 3 with an average equilibrium line altitude of 4050 m asl combined with other independent climate reconstructions the glacier climate model simulations suggested that the gongga ii glacial stage most likely occurred in the lgm

explosive silicic volcanism in iceland and the jan mayen area during the last 6 ma sources and timing of major eruptions abstract fifty three major explosive eruptions on iceland and jan mayen island were identified in 0 6 ma old sediments of the north atlantic and arctic oceans by the age and the chemical composition of silicic tephra the depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6 ma and paleoclimatic proxies 18 o ice rafted debris for the last 1 ma major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off rift volcanic zones in iceland and to the jan mayen volcanic system the tholeiitic central volcanoes along the iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4 9 ma they were the source of at least 26 eruptions of dominant rhyolitic magma composition including the late pleistocene explosive eruption of krafla volcano of the eastern rift zone at about 201 ka the central volcanoes along the off rift volcanic zones in iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition with three distinct episodes recorded at 4 6 5 3 3 5 3 6 and 0 1 8 ma the longest and last episode recorded 11 pleistocene major events including the two explosive eruptions of tindfjallajokull volcano thorsmork ca 54 5 ka and katla volcano solheimar ca 11 9 ka of the southeastern transgressive zone eight major explosive eruptions from the jan mayen volcanic system are recorded in terms of the distinctive grain size mineralogy and chemistry of the tephra the tephra contain k rich glasses k 2 o sio 2 0 06 ranging from trachytic to alkali rhyolitic composition their normative trends ab q or and their depleted concentrations of ba eu and heavy ree reflect fractional crystallisation of k feldspar biotite and hornblende in contrast their enrichment in highly incompatible and water mobile trace elements such as rb th nb and ta most likely reflect crustal contamination one late pleistocene tephra from jan mayen was recorded in the marine sequence its age estimated between 617 and 620 ka and its composition support a common source with the borga pumice formation at sor jan in the south of the island

high basal melting rates within high precipitation temperate glaciers the role of basal melting within high precipitation temperate glaciers represents a significant gap in understanding glacier melting processes we use a basal melt equation to calculate geothermal and frictional heat induced basal melt and develop an equation to calculate the rainfall induced basal melt for franz josef glacier new zealand a high precipitation temperate glacier additionally we calculate basal melt due to heat dissipation within water and ice data collated from published information on glacier dynamics and climate station readings show that total basal melt contributes on average similar to 2 50 m a 1 over the lower to mid ablation zone 300 1500 m a s l which is equivalent to 10 of the total ablation for the glacier this indicates that basal melting is an important component of mass balance for high precipitation temperate glaciers

degree day glacier mass balance modelling with applications to glaciers in iceland norway and greenland a degree day glacier mass balance model is applied to three glaciers in iceland norway and greenland for which detailed mass balance measurements are available over a period of several years model results are in good agreement with measured variations in the mass balance with elevation over the time periods considered for each glacier in addition the model explains 60 80 of the year to year variance in the elevation averaged summer season mass balance measurements on the glaciers using a single parameter set for each glacier the increase in ablation on the glaciers due to a warming of 2 c is predicted to range from about 1 m w e year 1 at the highest elevations to about 2 5 m w e year 1 at the lowest elevations predicted changes in the winter balance measured between fixed date are relatively small except at the lowest elevations on the icelandic and norwegian glaciers where the winter balance is significantly reduced equilibrium line altitudes are raised by 200 300 m on the icelandic and norwegian glaciers except at the highest elevations the winter balance of the icelandic and norwegian glaciers is predicted to decrease even if the warming is accompanied by a 10 increase in the precipitation no firm evidence of a climate related variation in the degree day factors or in the temperature lapse rate on the same glacier could be found the model furthermore reproduces large variations in the mass balance with elevation and from year to year on each glacier using the same parameter set we assume therefore that these parameters will not change significantly for the climate scenarios considered here

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

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

chemical stratigraphy iceland research drilling project reydarfjordur eastern iceland major element data are reported for lavas and dikes from a 3 2 km section through the eastern iceland lava pile the section includes a 1 2 km subaerial exposure and a 1 9 km sequence drilled by the iceland research drilling project irdp alteration increases down section although primary magma chemistry may be interpreted from feo al2o3 tio2 p2o5 and to a lesser extent sio2 in addition to immobile trace elements lava compositions range from mgo rich tholeiite to sio2 rich icelandite while dikes range from tholeiite to tholeiitic andesite three stratigraphic divisions based on volcanologic and trace element criteria e g ce yb and zr y are confirmed by major elements upper and lower groups are predominantly basaltic while the middle group includes a high proportion of silicic lavas variation within groups conforms to simple models combining fractional crystallization and accumulation of phenocryst plagioclase during build up of the pile eruptive phases commenced with silica rich magma and frequently terminated with basaltic or intermediate plagioclase cumulates dike chemistry resembles that of upper group lavas and also the nearby breiddalur volcano middle group lavas probably derive from a buried silicic complex while the lower group may represent the flank of a more deeply buried complex chemical stratigrapy is consistent with iterative burial with spreading of lenticular basaltic silicic complexes magma supply fractionation and mixing are considered in the framework of such kinematic models although it is premature to draw direct analogies to the active neogene zone of iceland

b o th isotope systematics in icelandic tephra abstract we report new boron concentrations and isotope compositions measured by ion microprobe on holocene tephra samples from 6 icelandic volcanoes the b concentrations range over almost a factor of 10 from 1 50 0 10 to 13 10 0 10 ppm in basalt and obsidian respectively the highest 11b 16 9 2 2 and 6 1 1 6 measured in rhyolites from the rift related askja and krafla volcanoes in contrast the lowest 11b values 5 3 and 5 2 observed in samples with the some of the highest 18o 4 92 and 5 18 respectively and 230th 232th 1 067 and 1 030 respectively correspond to a normal mantle signature the variations of boron isotope compositions in the icelandic tephra and their negative correlations with both 18o and 230th 232th strongly support the mixing between mantle derived basalts and crustal rhyolites produced from anatexis of hydrothermally altered basaltic crust the low 18o in combination with high 11b values in rhyolite is best explained by the presence of seawater derived b in a hydrothermal fluid that is mostly of meteoric origin

nb depleted andesites from the pacific antarctic rise as analogs for early continental crust sampling of the pacific antarctic rise close to the foundation hotspot in the south pacific reveals that silicic lavas erupt together with basalts on a 130 km long part of this mid oceanic ridge representing the most extensive occurrence of andesites on the submarine spreading system most of these tholeiitic andesites and dacites have negative nb and ta anomalies a signature that has so far been attributed only to subduction related magmas and the continental crust the silicic lavas formed by fractional crystallization from basalts and assimilation of melts from hydrothermally altered amphibolite in the oceanic crust the presence of andesites with negative nb and ta anomalies on the pacific antarctic rise implies that such magmas are not restricted to subduction zones but can form at a plume influenced mid oceanic ridge the andesites and dacites from the pacific antarctic rise may represent analogs to some precambrian volcanic rocks and early continental crust

an approach to modelling the impact of snow drift on glaciation in the cairngorm mountains scotland this paper uses a geographical information system gis to develop a rule based model of the effect of snow drifting on glacier growth in the cairngorm mountains scotland during the younger dryas interval we develop a qualitative model of snow drift that uses a number of simple heuristics to generate a map of relative accumulation at a 50 m resolution over the massif relative susceptibility to snow drifting is then compared for a number of different zones under varying wind directions we conclude that under the conditions tested in our model glaciation of the cairngorms during the younger dryas was confined to the high corries and that the pattern of snow drifting suggested by our model points to dominant southerly winds copyright 1999 john wiley sons ltd

warming and glacier recession in the rakaia valley southern alps of new zealand during heinrich stadial 1 abstract the termination of the last ice age featured a major reconfiguration of earth s climate and cryosphere yet the underlying causes of these massive changes continue to be debated documenting the spatial and temporal variations of atmospheric temperature during deglaciation can help discriminate among potential drivers here we present a 10be surface exposure chronology and glaciological reconstruction of ice recession following the last glacial maximum lgm in the rakaia valley southern alps of new zealand innermost lgm moraines at big ben have an age of 17 840 240 yrs whereas ice marginal moraines or ice molded bedrock surfaces at distances up valley from big ben of 12 5 km lake coleridge 25 km castle hill 28 km double hill 43 km prospect hill and 58 km reischek knob have ages of 17 020 70 yrs 17 100 110 yrs 16 960 370 yrs 16 250 340 yrs and 15 660 160 yrs respectively these results indicate extensive recession of the rakaia glacier which we attribute primarily to the effects of climatic warming in conjunction with geomorphological maps and a glaciological reconstruction for the rakaia valley we use our chronology to infer timing and magnitude of past atmospheric temperature changes compared to an overall temperature rise of 4 65 c between the end of the lgm and the start of the holocene the glacier recession between 17 840 and 15 660 yrs ago is attributable to a net temperature increase of 4 0 c from 6 25 to 2 25 c accounting for 86 of the overall warming approximately 3 75 c 70 of the warming occurred between 17 840 and 16 250 yrs ago with a further 0 75 c 16 increase between 16 250 and 15 660 yrs ago a sustained southward shift of the subtropical front stf south of australia between 17 800 and 16 000 yrs ago coincides with the warming over the rakaia valley and suggests a close link between southern ocean frontal boundary positions and southern mid latitude climate most of the deglacial warming in the southern alps occurred during the early part of heinrich stadial 1 hs1 of the north atlantic region because the stf is associated with the position of the westerly wind belt our findings support the concept that a southward shift of earth s wind belts accompanied the early part of hs1 cooling in the north atlantic leading to warming and deglaciation in southern middle latitudes

the neuquen super basin with more than 6000 m of sedimentary thickness and several superimposed petroleum systems the neuquen basin of argentina has all the elements to be considered a super basin the basin developed during the triassic early jurassic in a rift environment that generated a localized petroleum system continued subsidence during the early jurassic resulted in the first marine ingression los molles formation total organic carbon toc 1 7 this unit matured 120 to 55 m y a before the formation of major structures with the exception of the huincul high a fast marine flooding in a retroarc setting occurred during the latest jurassic early cretaceous at its base lies the vaca muerta formation a 50 to 1000 m thick world class source rock composed by calcareous shales and marls toc 2 9 this unit reached maturity at 95 ma when the only traps available were structures along the huincul high or stratigraphic a new marine ingression occurred during the early cretaceous depositing bituminous shales and marls agrio formation toc 2 5 that matured during the paleogene these superimposed petroleum systems combined with different structural settings gave rise to numerous plays and trapping configurations that resulted in the discovery of 14 billion boe in addition the unconventional potential of the vaca muerta is now being developed with estimated resources of 91 5 tcf and 14 3 billion bbl of oil the neuquen basin has gone through three main phases of development conventional tight and unconventional after a century of production the basin still shows a wide variety of opportunities for both conventional and world class unconventional plays

the graveyard point intrusion an example of extreme differentiation of snake river plain basalt in a shallow crustal pluton the graveyard point intrusion is the only known example of a wellexposed differentiated mafic pluton associated with the late miocene pleistocene magmatism of the western snake river plain srp it is exposed in a 6 km by 4 km area adjacent to the oregon idaho border and exposures range in thickness from 20 to 160 m the thicker parts of the intrusion are strongly differentiated and contain a 25 60 m thick section of well laminated cumulus textured gabbros that grade upward into pegmatoidal ferrogabbro evolved liquids formed sheets of fe rich siliceous granophyre at least two injections of magma are indicated by abrupt discontinuities in the rock and mineral compositions and by the lack of mass balance between the bulk intrusion and its chilled borders the laminated gabbros are interpreted to have formed from a tongue of augite and plagioclase crystals that were carried in with the second pulse of magma following the final emplacement of the intrusion in situ differentiation proceeded through a two stage process the ferrogabbros are explained as interstitial liquids forced out of the crystal mush by compaction and the siliceous granophyres are interpreted to be residual liquids that migrated out of the partly crystallized ferrogabbros in response to the exsolution of volatiles because the geochemical trend inferred for the mafic to intermediate composition liquids in the graveyard point intrusion is similar to the trend for many western snake river plain lavas the pluton may be a good model for shallow sub volcanic magma chambers elsewhere in the srp however some western srp lavas contain anomalously high concentrations of p2o5 which are best explained by mixing within the active crustal mush column or with partial melts of previously formed differentiated mafic intrusions

eruptions from zoned magma chambers summary an appreciation of the positions within a magma chamber from which magma will be erupted can be gained from an understanding of the pattern of magma removal upwardly converging streamlines followed by a fluid escaping from a flat topped reservoir into a cylindrical conduit cause magma from widely separated horizontal and vertical locations in a pre eruption chamber to be simultaneously erupted the volume erupted v is related to the maximum depth tapped r by the equation v 2 9 r 3 large ash flow sheets 100 km 3 may therefore sample magma up to 5 km below the chamber roof analysis of the flow field suggests that about one half of a given sample of erupted magma represents material from the deepest part of the chamber being tapped at the time of eruption many petrographic features of chemically zoned ignimbrites can best be explained by the operation of such a flow field during eruption where a series of sub spherical sampling shells intersect the horizontal layers in the magma chamber to produce heterogeneous ejecta mixed magmas erupted late in some zoned ash flow sequences can originate by tapping across the boundary between silicic and underplating basaltic magmas which coexist in the source chamber rather than by convective mixing prior to eruption flow banding in rhyolites can result from the same fluid dynamic processes

the southern glacial maximum 65 000 years ago and its unfinished termination abstract glacial maxima and their terminations provide key insights into inter hemispheric climate dynamics and the coupling of atmosphere surface and deep ocean hydrology and cryosphere which is fundamental for evaluating the robustness of earth s climate in view of ongoing climate change the last glacial maximum lgm 26 19 ka ago is widely seen as the global cold peak during the last glacial cycle and its transition to the holocene interglacial dubbed termination 1 t1 as the most dramatic climate reorganization during this interval climate records show that over the last 800 ka ice ages peaked and terminated on average every 100 ka 100 ka world however the mechanisms pacing glacial interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood here we show evidence for a full glacial maximum in the southern hemisphere 65 1 2 7 ka ago and its unfinished termination our 10 be chronology combined with a model simulation demonstrates that new zealand s glaciers reached their maximum position of the last glacial cycle during marine isotope stage 4 mis 4 southern ocean and greenhouse gas records indicate coeval peak glacial conditions making the case for the southern glacial maximum about halfway through the last glacial cycle and only 15 ka after the last warm period mis 5a we present the hypothesis that subsequently driven by boreal summer insolation forcing a termination began but remained unfinished possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the north atlantic through heinrich stadial 6 to drive a full termination yet the unfinished termination left behind substantial ice on the northern continents about 50 of the full lgm ice volume and after another 45 ka of cooling and ice sheet growth the earth was at inter hemispheric last glacial maximum configuration when similar orbital forcing hit maximum size northern ice sheets and ushered in t1 and thus the ongoing interglacial this argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the southern hemisphere climate could transition from interglacial to full glacial conditions in about 15 000 years while the northern hemisphere and its continental ice sheets required half a glacial cycle

the recent isla san luis volcanic centre petrology of a rift related volcanic suite in the northern gulf of california mexico abstract isla san luis one of the most recent eruptive centres in the gulf of california presents a complete magma evolution trend from basaltic andesites to rhyolites the less evolved lavas are palagonite tuffs related to surtseyan type activity which characterized the emergent stage of the island subaerial lava flows and later high energy hydromagmatic eruptions are dacites which make up the tuff rings of the southeastern corner of the island rhyolites are the latest erupted products and the development of the younger dome in the centre of the island was preceded by ash and pumice fallout containing quenched bombs with an obsidian crust and a pumiceous core basaltic andesites contain olivine fo87 80 calcium rich plagioclase and sparse clinopyroxene microphenocrysts the typical mineralogy of dacitic and rhyolitic lavas is plagioclase two pyroxenes major and trace elements vary regularly with mgo taken as a differentiation index isla san luis lavas are enriched in lile and depleted in nb ta and ti their characteristics are intermediate between tholeiitic and calc alkaline lavas they are also lree enriched and the la yb n ratios steepen slightly with differentiation such an evolution is better explained by combined fractional crystallization and assimilation processes

glacier velocity and water input variability in a maritime environment franz josef glacier new zealand short term glacier velocity variations typically occur when a water input is accommodated by an increase in the subglacial water pressure although these velocity variations have been well documented on many glaciers few studies have considered them on glaciers where heavy rain and glacier melt occur year round this study investigates the relationship between water inputs and glacier velocity on franz josef glacier new zealand we installed six gnss stations across the lower glacier during austral summer 2010 11 and one station during summer 2012 13 glacier velocity remained elevated at all stations for 7 days following large rain events during diurnal melt events we find velocity variations in the early afternoon 12 00 16 00 at 600 m a s l and in the late evening 20 00 01 00 at 400 m a s l we hypothesize that the late evening velocity variations occurred as an upstream region of high subglacial water pressures and accelerated ice motion propagated downstream this mechanism may also explain the increased longitudinal compression and transverse extension across the lower glacier during speed up events our results indicate that the subglacial drainage system likely decreases in efficiency upstream and that the water input variability can still cause short term velocity variations despite the large year round water inputs

evaluation of lateglacial temperatures in the southern alps of new zealand based on glacier modelling at irishman stream ben ohau range abstract climate proxy records from the middle to high latitude southern hemisphere indicate that a lateglacial 15 000 11 500 years ago climate reversal approximately coeval with the antarctic cold reversal acr interrupted a warming trend during deglaciation in new zealand some palaeoclimate proxy records indicate a cool episode during the acr ca 14 500 12 500 years ago while others do not express a significant change in climate recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers we use a coupled energy balance and ice flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of irishman stream a high elevation catchment in the southern alps first a suite of steady state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well dated lateglacial moraine crests second time dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record steady state experiments using an optimal parameter set demonstrate that the conditions under which the 13 000 year old moraine formed were 2 3 3 2 c colder than present with the range in temperature corresponding to a 20 variance in precipitation relative to the present day this reconstructed climate change relative to the present day corresponds to an equilibrium line altitude of ca 2000 40 m above sea level asl which is ca 400 m lower than present time dependent simulations of glacier length produce ice advance to within 100 m of the 13 000 year old terminal moraine indicating that the chironomid based temperature forcing and moraine record provide consistent information about past climate our results together with other climate proxy reconstructions from pollen records and marine sediment cores support the notion that temperatures during the acr in new zealand were 2 3 c cooler than today

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

climates during late quaternary glacier advances glacier climate modeling in the yingpu valley eastern tibetan plateau abstract the last glacial maximum lgm featured a major cooling of earth s climate after which the climate evolved in the largest reconfiguration of the past 100 ka despite its significance full understanding of the climate history during and since the lgm is still lacking on the eastern tibetan plateau recent improvements in understanding glacial extents and chronologies in the yingpu valley eastern tibetan plateau present an opportunity to estimate the glacial climatic conditions during and since the lgm using a relatively new glacier climate model this study reconstructs glacier advances in the yingpu valley and quantifies the related climate conditions during the lgm lateglacial and late holocene glacial stages the model results show that the yingpu valley contained ice volumes of 1 65 km3 1 03 km3 and 0 29 km3 with equilibrium line altitude ela lowering values of 500 m 410 m and 150 m in the three successive glacial stages respectively by examining other independent paleoclimatic reconstructions it is concluded that the temperature decreased by 4 0 5 9 c 3 4 3 7 c 0 3 0 6 c with the precipitation amounts being 40 80 80 100 and 100 110 of modern values during the lgm lateglacial and late holocene glacial stages respectively the climate estimates for the three glacial stages are generally in agreement with other climatic proxy records on the tibetan plateau and atmospheric circulation modeling results

formation of the waiho loop terminal moraine new zealand we present an analysis of the formation and evolution of the waiho loop terminal moraine recent work has shown that the loop comprises mainly rock avalanche material and suggested its formation was associated with a rock avalanche driven glacier advance new evidence from shallow seismic studies between the range front and the loop suggests i that the presence of a basal trough critically influences glacier behaviour and moraine formation and ii that the volume of the waiho loop is significantly greater than previously thought a one dimensional dynamic ice flow model is used to test two rock avalanche based scenarios for the formation of the loop first that a rock avalanche caused a significant advance of the glacier terminus from a location within the confined mountain valley to the loop and second that the rock avalanche occurred while the glacier was retreating with its terminus close to the position of the loop it is shown that this terminal moraine was not the result of a glacier advance

the response of two icelandic glaciers to climatic warming computed with a degree day glacier mass balance model coupled to a dynamic glacier model a degree day glacier mass balance model is coupled to a dynamic glacier model for temperate glaciers the model is calibrated for two outlet glaciers from the hofsjokull ice cap in central iceland it is forced with a climate scenario that has recently been defined for the nordic countries for the purpose of outlining the hydrological consequences of future greenhouse warming the scenario for iceland specifies a warming rate of 0 25 c per decade in mid summer and 0 35 c per decade in mid winter with a sinusoidal variation through the year the volume of the glaciers is predicted to decrease by approximately 40 over the next century and the glaciers essentially disappear during the next 200 years runoff from the area that is presently covered by the glaciers is predicted to increase by approximately 0 5 m a 1 30 years from now due to the reduction in the volume of the glaciers the runoff increase reaches a flat maximum of 0 5 2 0 m a 1 100 150 years from now and levels off after that the predicted runoff increase leads to a significant increase in the discharge of rivers fed by meltwater from the outlet glaciers of the ice cap and may have important consequences for the operation and planning of hydroelectric power plants in iceland

climate sensitivity of a high precipitation glacier in new zealand the sensitivity of glaciers to climatic change is key information in assessing the response and sea level implications of projected future warming new zealand glaciers are important globally as an example of how maritime glaciers will contribute to sea level rise a spatially distributed energy balance model is applied to brewster glacier new zealand in order to calculate glacier mass balance run off and sensitivity to climate change the model successfully simulates four annual mass balance cycles close to half 52 of the energy available for melt on the glacier is supplied by turbulent heat fluxes with radiation less important except during the winter model sensitivity to temperature change is one of the largest reported on earth at 2 0 m w e a 1 8c 1 in contrast a 50 change in precipitation is required to offset the mass balance change resulting from a 18c temperature change meltwater run off sensitivity is also very high increasing 60 with a 18c warming the extreme sensitivity of mass balance to temperature change suggests that significant ice loss will occur with even moderate climate warming

segregation vesicles gas filter pressing and igneous differentiation some vesicles in certain subaerial flows of basalt and basaltic andesite are partially filled with dark partly glassy segregation material the segregation material has about three times the concentration of k o tio and p o as the associated host rock therefore the segregation materials are inferred to be frozen residual liquids that migrated into the vesicles several possible processes for filling the vesicles are examined within the context of the cooling time implied by heat conduction the preferred process is one in which the residual liquid migrates through a porous and permeable but rigid network of interlocking crystals in response to a pressure gradient generated by vapor saturated crystallization as crystallization proceeds h o is concentrated in the residual liquid and gas this produces a higher pressure in the gas poor matrix than in the vesicles and forces liquid to migrate into the vesicles textural features suggestive of or consistent with the process include 1 vesiculation

last glacial climate reconstruction by exploring glacier sensitivity to climate on the southeastern slope of the western nyaiqentanglha shan tibetan plateau improvements in understanding glacial extents and chronologies for the southeastern slope of the western nyaiqentanglha shan on the tibetan plateau are required to understand regional climate changes during the last glacial cycle a two dimensional numerical model of mass balance based on snow ice melting factors and of ice flow for mountain glaciers is used to assess the glacier sensitivity to climatic change in a catchment of the region the model can reproduce valley glaciers wide tongued glaciers and a coalescing glacier within step temperature lowering and precipitation increasing experiments the model sensitivity experiments also indicate that the dependence of glacier growth on temperature and or precipitation is nonlinear the model results suggest that the valley glaciers respond more sensitively to an imposed climate change than wide tongued and coalescing glaciers guided by field geological evidence of former glacier extent and other independent paleoclimate reconstructions the model is also used to constrain the most realistic multi year mean temperatures to be 2 9 4 6 degrees c and 1 8 2 5 degrees c lower than present in the glacial stages of the last glacial maximum and middle marine oxygen isotope stage 3 respectively

on some fundamentals of igneous petrology the age old process of crystal fractionation leading to the diversity of the igneous rocks and earth itself is an exceedingly well understood chemical process in magmatism and physical chemistry but the broader physical aspects of this and related processes have proven elusive on many fronts especially in its relation to the spatial variations in rock composition texture and macroscopic features like layering magmatic systems be they volcanic dikes sills or plutons are generally analyzed with a problem at hand and an end result in mind the processes invoked to solve these problems which are most often purely chemical are often unique to each problem with few if any general principles emerging that are central to understanding the wider perspective of magmatic processes and problems an attempt is made at the outset to provide a list of inviolate magmatic first principles that are relevant to analyzing most magmatic problems these involve initial conditions critical crystallinity solidification fronts transport and emplacement fluxes phenocrysts xenocrysts primocrysts crystal size layering and crystal sorting thermal convection magmatic processes are physical along with these principles two reference magmatic systems are suggested where the initial conditions and outcome are unequivocal the sudbury impact melt sheet and the hawaiian lava lakes sudbury formed in 5 min by superheated magma crystallized to a near uniform sequence while the tiny lava lakes formed of crystal laden slurries form a highly differentiated layered sequence the major difference is in the initial conditions of formation especially the nature of the input materials the challenge is to construct and analyze magmatic systems i e magma chambers sills dikes and lavas using these reference end members and the suggested principles the hawaiian 500 000 year volcanic record exhibits what can be expected as input materials namely a highly varied output of magma of an overall composition reflecting the abundance of entrained olivine primocrysts the provenance of these crystals is varied and within any single sample the population may be highly heterogeneous in composition from crystal to crystal yet the overall pattern of chemical fractionation is exceedingly regular and well defined if similar inputs go to form large intrusions these systems will undoubtedly be dominated by crystal rich slurries which provide a vast set of physical processes promoting exotic layering and at the same time given the effects of annealing and continued crystal growth a final chemical record adhering to all the time honored effects of crystal fractionation the long assumed initial condition of instantaneously emplaced crystal free magmas cannot reasonably produce the observed rock records

palisades sill origin of the olivine zone by separate magmatic injection rather than gravity settling the still widely cited view of the palisades sill northeastern united states being differentiated largely by vertically directed olivine dominated fractionation is not supported by available structural petrographic and geochemical data rather the sill can be viewed as a sheetlike composite intrusion possibly made up of multiple magma types common to the mesozoic eastern north america magmatic province the famous olivine zone of the palisades sill may have resulted from a separate late intrusion of olivine normative magma and not from gravity controlled olivine accumulation processes pyroxene dominated fractionation accounts for much of the vertical and lateral compositional variations in the palisades sill and other related intrusions from the province

axisymmetric withdrawal and inflow in a density stratified container the axisymmetric withdrawal of fluid from a linearly stratified container is studied over the full parameter range when only buoyancy and inertia are important the flow in the withdrawal layer is influenced by a virtual control point and is not analogous to that observed in the two dimensional withdrawal problem two further flow regimes are shown to exist in which viscous forces are important one in which convection of species is important and a second in which diffusion of species is important theoretical arguments and laboratory experiments are used to show that s q2n v3 is the appropriate flow parameter to differentiate between these possibilities it is also argued that these results may be generalized to describe the features of several related flows axisymmetric drawdown or drawup in withdrawal from a layered density structure axisymmetric inflow into a linearly stratified environment and the axisymmetric spreading of density currents

steady state volcanism paleoeffusion rates and magma system volume inferred from plagioclase crystal size distributions in mafic lavas dome mountain nevada abstract the dome mountain dm lavas located in the moat of the timber mountain caldera of the sw nevada volcanic field cap a thick sequence of welded tuffs massive and bedded tuffs and mafic and rhyolitic lava flows these 10 9 m y old flows comprise a pile of some twenty flows with a total thickness of about 300 m individual flows range in thickness from 3 to 20 m and are characterized by a basal vesicular zone a massive central region and an upper vesicular region containing in most cases cooling fractures the flows dip gently away from the summit of dm a prominent topographic feature of the region with an elevation of 2065 m silica contents range from 48 8 wt at the base of the pile to 59 4 wt at the top although most of the flows are andesitic crystal size distributions csds for plagioclase in these comagmatic lavas have been determined to provide information on magma storage times these times when coupled with phase equilibria can be used to infer cooling rates which are indicative of the relative dimensions of magmatic bodies and the vigor of various magmatic cooling processes most of the csds show no sign of crystal fractionation or accumulation assuming a growth rate of 10 10 cm s calculated mean crystal residence times for most lavas cluster in the range of 1 5 to 4 years two of the lower lavas have residence times in the range of 4 to 9 years the residence times correlate inversely with nucleation density and broadly correlate inversely with silica content high residence time low silica lavas occur at the base of the pile whereas low residence time high silica lavas occur at the top of the pile one interpretation of the residence time data is that the lavas are from an open system of more or less constant residence time but varying spatially in system locations e g a magma chamber in which steady state recharge and eruption may have been reached alternatively these lavas may represent small samples closely spaced in time of a slowly cooling large batch or reservoir of magma the greater residence times associated with the lower flows may indicate the increased amount of time necessary to form the conduit of the magma volcano system by the oldest magma or simply that part of the system with the highest liquidus temperature a minimum volume of 1 4 to 2 5 km 3 for the magma chamber is estimated for the dm system using the estimated residence times in a simplified cooling model of a sheet of aspect ratio r the actual system volume depends on r which is strictly unknown and thus the actual system volume may be much larger e g 200 km 3 a mean paleoeffusion rate of 0 05 km 3 yr is obtained for the lavas by assuming that the residence time of each lava corresponds to the amount of time elapsed since the eruption of the underlying flow

paterae on io a new type of volcanic caldera paterae defined by the international astronomical union as irregular crater s or complex one s with scalloped edges are some of the most prominent topographic features on io paterae on io are unique yet in some aspects they resemble calderas known and studied on earth mars and venus they have steep walls flat floors and arcuate margins and sometimes exhibit nesting all typical of terrestrial and martian basalt shield calderas however they are much larger many are irregular in shape and they typically lack shields their great sizes some 200 km diameter and lack of associated volcanic edifices beg comparison with terrestrial ash flow calderas however there is no convincing evidence on io for the high silica erupted products or dome resurgence associated with this type of caldera ionian paterae seem to be linked with the eruption of large amounts of mafic to ultramafic lavas and colorful sulfur rich materials that cover the floors and sometimes flow great distances away from patera margins they are often angular in shape or are found adjacent to mountains or plateaus indicating tectonic influences on their formation a database of 417 paterae on io measured from images with 3 2 km pixel 1 resolution 80 of its surface reveals that their mean diameter of 41 0 km is close to that for calderas of mars 47 7 km is smaller than that for venus 68 km but dwarfs those for terrestrial basalt shield calderas 6 6 km and ash flow calderas 18 7 km thirteen percent of all paterae are found adjacent to mountains 42 have straight or irregular margins and 8 are found atop low shields abundant smaller paterae with more continuously active lava eruptions are found between 25 s and 25 n latitude whereas fewer and larger paterae are found poleward of these latitudes patera distribution shows peaks at 330 w and 150 w longitude likely related to the direction of greatest tidal massaging by jupiter ionian patera formation may be explained by portions or combinations of models considered for formation of terrestrial calderas yet their unusual characteristics may require new models with a greater role for tectonic processes

crystal size distribution analysis of plagioclase in experimentally decompressed hydrous rhyodacite magma article i nfo this study presents crystal size distributions csd of plagioclase forming during decompression experiments of hydrous rhyodacite magma samples were annealed at 130 mpa subjected to continuous decompression at either 2 mpa h 1 or 0 5 mpa h 1 and then quenched along their respective decompression paths at 20 mpa intervals samples display concave up curved csd plots which result from a combination of two crystal populations those which formed during the anneal period and those which formed during decompression the csds also display a decrease in crystal number density at 3 7 m a size range that is easily resolvable with the imaging strategy employed the downturn at small sizes is presumably due to insufficient compensation for the intersection probability effect in converting 2d measurements to 3d size distributions crystal nucleation and growth rates derived from csds using standard assumptions are compared with values obtained using 2d measurements of bulk crystal populations batch methods csd calculated nucleation rates are substantially low relative to the batch values in fact csd derived volumetric nucleation rates may underestimate actual nucleation rates by up to two orders of magnitude in contrast growth rates from csds are consistently higher than batch rates although plagioclase growth rates are relatively constant during decompression at a given rate the average growth rate in the rapidly decompressed series is approximately five times faster than the crystal growth rate in the slowly decompressed series because crystal growth rate depends on decompression rate csds are incapable of revealing decompression timescales or magma ascent rates without independent knowledge of crystal growth rate published by elsevier b v

on bimodal differentiation by solidification front instability in basaltic magmas part 1 basic mechanics extensive coarse grained silicic lenses are common in the upper portions of large diabase sills lava lakes and gabbroic intrusions these lenses which often contain up to 10 wt more silica than their host rocks record a clear process of bimodal differentiation that may play a fundamental role in generating significant quantities of silicic magma in predominantly basaltic systems the spatial compositional textural and contact relations suggest that these silicic segregations form by infilling of tears formed during gravitational instability of the upper solidification front this process is investigated in some detail by exploring the thermal and mechanical conditions leading to internal failure of the front and segregation formation as the upper solidification front grows inward and thickens the local strength of the developing crystalline network must increase upward through the front sufficiently fast to offset the increasing weight of the front itself this necessary local variation in strength dictates how crystallinity must vary to prevent failure but the actual variation in crystallinity is determined by phase equilibria which in general varies in a fashion that is noncovariant with that required for mechanical stability it is this mismatch that apparently leads to failure and formation of silicic segregations the rate of filling of the tears by porous flow of interstitial melt from below regulates the rate of tear opening and the overall size of the tears is regulated by the local rate of advance of the solidification front segregations therefore thicken downward as the growth of the front slows and then die out altogether with approach of the lower solidification front this process irreversibly introduces siliceous noise into basaltic systems the silicic signal can be enhanced through subsequent reprocessing of the host rock to form volumetrically important masses of silicic magma this process may be fundamental to achieving the strong compositional diversity of the igneous rocks to yielding continental masses and to the differentiation of earth itself

sensitivity of mass balance of five swiss glaciers to temperature changes assessed by tuning a degree day model a degree day model is used to assess the sensitivity of the mass balance of five swiss glaciers to temperature changes the model uses temperature data extrapolated from nearby climate stations and is tuned by varying precipitation to make the model fit the observed distribution of mass balance with altitude once the model is tuned the effect of temperature change is simulated by recalculating the mass balance with the same parameters as before but with a temperature increase of 1 c throughout the year the largest mass balance changes involving increased ablation of 1 m w e a 1 c 1 occur at the snout with a progressively smaller increase with altitude the area averaged sensitivities for the five glaciers are 0 7 to 0 9 m w e a 1 c 1 if annual precipitation also increased by 20 it would partly offset the effect of the 1 c higher temperatures but could not compensate for it