observed degree day factors and their spatial variation on glaciers in western china the degree day factor ddf is an important parameter for the degree day model which is a widely used method for ice and snowmelt computation spatial variations of the ddf greatly affect the accuracy of snow and ice melt modelling this study analyzes the spatial variability of ddfs obtained from observed glaciers in different regions of western china the results clearly show that the ddf for a single glacier is subject to significant small scale variations and the factor for maritime glaciers is higher than that for subcontinental and extremely continental glaciers in western china the factors increase gradually from northwest to southeast in general the regional patterns of ddfs are detectable on the glaciers due to the unique climatic environment and heat budget of the tibetan plateau and surrounding regions low ddfs can be expected for cold dry areas whereas high ddfs can be expected for warm wet areas in western china depending on spatial variation of the characteristics of ddfs and the meteorological data we can provide gridded degree day models for non monitored glaciers to reconstruct gridded historical glacier mass balance series in western china

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

alpine and pacific styles of phanerozoic mountain building subduction zone petrogenesis of continental crust a broad continuum exists between two distinct end member types of mountain building alpine type orogenic belts develop during subduction of an ocean basin between two continental blocks resulting in collision they are characterized by an imbricate sequence of oceanward verging nappes some alpine belts exhibit superimposed late stage backthrusting sediments are chiefly platform carbonates and siliciclastics in some cases associated with minor amounts of bimodal volcanics pre existing granitic gneisses and related continental rocks constitute an autochthonous parautochthonous basement metamorphism of deeply subducted portions of the orogen ranges from relatively high pressure hp to ultrahigh pressure uhp calcalkaline volcanic plutonic rocks are rare and have peraluminous s type bulk compositions in contrast pacific type orogens develop within and landward from long sustained oceanic subduction zones they consist of an outboard oceanic trench accretionary prism and an inboard continental margin island arc the oceanic assemblage consists of first cycle in part melanged volcaniclastics and minor but widespread cherts deep water carbonates intimately mixed with disaggregated ophiolites the section recrystallized under hp conditions recumbent fold vergence is oceanward a massive slightly older to coeval calcalkaline arc is sited landward from the trench complex on the stable non subducted plate it consists of abundant dominantly intermediate metaluminous i type volcanics resting on old crust both assemblages are thrown into open folds intruded by comagmatic i type granitoids and metamorphosed locally to regionally under high t low p conditions in the subduction channel of collisional and outboard circumpacific terranes combined extension above and subduction below allows buoyancy driven ascent of ductile thin aspect ratio slices of hp uhp complexes to midcrustal levels where most closely approached neutral buoyancy exposure of rising sheets caused by erosion and gravitational collapse results in moderate amounts of sedimentary debris because exhumed sialic slivers are of modest volume at massive sialic buildups associated with convergent plate cusps syntaxes tectonic aneurysms may help transport hp uhp complexes from mid to upper crustal levels the closure of relatively small ocean basins that typify many intracratonic suture zones provides only limited production of intermediate and silicic melts so volcanic plutonic belts are poorly developed in alpine orogens compared with circumpacific convergent plate junctions generation of a calcalkaline arc mainly depends on volatile evolution at the depth of magma generation phase equilibrium studies show that under typical subduction zone p t trajectories clinoamphibole ca al hydrous silicates constitute the major hydroxyl bearing phases in deep seated metamorphic rocks of morb composition other hydrous minerals are of minor abundance ca and na clinoamphiboles dehydrate at pressures of above approximately 2 gpa but low temperature devolatilization may be delayed by pressure overstepping thus metabasaltic blueschists and amphibolites expel h2o at melt generation depths and commonly achieve stable eclogitic assemblages partly serpentinized mantle beneath the oceanic crust dehydrates at roughly comparable conditions for reasonable subduction zone geothermal gradients however white micas biotites remain stable to pressures 3 gpa accordingly attending descent to depths of 100 km mica rich quartzofeldspathic lithologies that constitute much of the continental crust fail to evolve substantial amounts of h2o and transform incompletely to stable eclogite facies assemblages underflow of amphibolitized oceanic lithosphere thus generates most of the deep seated volatile flux and the consequent partial melting to produce the calcalkaline suite along and above a subduction zone where large volumes of micaceous intermediate and felsic crustal materials are carried down to great depths volatile flux severely diminishes thus continental collision in general does not produce a volcanic plutonic arc whereas in contrast the long continued contemporaneous underflow of oceanic lithosphere does

mesozoic transpression transtension subduction and metallogenesis in northern and central california middle paleozoic to middle jurassic terrane assemblies in the klamaths and sierran foothills consist of mafic ultramafic complexes fine grained terrigenous strata derived from previously accreted continental margin belts sutured oceanic terranes reflect c 230 myr of margin parallel slip involving chiefly transtension and transpression quartzofeldspathic clastic rocks and blueschists eclogites are very rare little devolatilization occurred at magmagenic depths hence coeval hydrothermal ore deposits and granitoids are uncommon in contrast nearly head on cretaceous subduction of the farallon plate generated the massive klamath sierra nevada volcanic plutonic arc reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone immature great valley forearc and franciscan trench deposits shed from the arc record c 70 myr of rapid crustal growth au bearing solutions rising from magmagenic depths exsolved from plutons and expelled from heated wall rocks were mobilized attending arc construction precipitation of gold bearing quartz veins occurred where h2o co2 bearing fluids encountered major geochemical discontinuities in the wall rocks

projections of glacier change in the altai mountains under twenty first century climate scenarios we project glacier surface mass balances of the altai mountains over the period 2006 2100 for the representative concentration pathway rcp 4 5 and rcp8 5 scenarios using daily near surface air temperature and precipitation from 12 global climate models in combination with a surface mass balance model the results indicate that the altai glaciers will undergo sustained mass loss throughout the 21st for both rcps and reveal the future fate of glaciers of different sizes by 2100 glacier area in the region will shrink by 26 10 for rcp4 5 while it will shrink by 60 15 for rcp8 5 according to our simulations most disappearing glaciers are located in the western part of the altai mountains for rcp4 5 all glaciers disappearing in the twenty first century have a present day size smaller than 5 0 km2 while for rcp8 5 an additional 7 of glaciers in the initial size class of 5 0 10 0 km2 also vanish we project different trends in the total meltwater discharge of the region for the two rcps which does not peak before 2100 with important consequences for regional water availability particular for the semi arid and arid regions this further highlights the potential implications of change in the altai glaciers on regional hydrology and environment

volcanic and hydrothermal processes in submarine calderas the kulo lasi example sw pacific abstract the study area is located at the transition between the northern end of the tonga trench and the north fiji fracture zone where tectonic movements are reputed to be the fastest in the world to the southeast of futuna island a broad area of volcanism occurs within a region characterized by a change in the tectonic fabric between a ne sw oriented volcanic graben and the n s oriented alofi ridge in 2010 the active volcano kulo lasi which represents the most recent volcanic episode in the futuna area was discovered in the center of this extensive volcanic zone kulo lasi is a 20 km diameter shield volcano that rises 400 m above the seafloor it is composed of basaltic to trachy andesitic lava with no obvious geochemical affinity with the tonga subduction that occurs 500 km to the east the central caldera is 5 km in diameter and 300 m deep and is located at a water depth of 1500 m diving operations with the submersible nautile and high resolution auv mapping have revealed the presence of numerous active and inactive hydrothermal fields on the floor and the walls of the caldera four tectono volcanic stages can be distinguished at kulo lasi caldera in stage 1 the shield volcano is built annular reverse faults develop at the summit and control circulation of water rock dominated hydrothermal fluids and high temperature alteration of rocks along the nascent normal faults mixing of hydrothermal fluids with seawater is favored along normal superficial faults leading to the formation of low temperature fe mn mineralization at the summit of the volcano during stage 2 the caldera collapse gradually revealing outcrops of the altered and mineralized zones formed during stage 1 as the magma chamber cools and collapses less heat is available as a result medium to low temperature

a grenvillian arc on the margin of amazonia evidence from the southern oaxacan complex southern mexico abstract the rocks in the southern oaxacan complex of mexico form part of the basement of oaxaquia a terrane that underlies most of eastern mexico they have undergone granulite facies metamorphism at 1 ga that was initially overprinted by lower amphibolite facies metamorphism accompanied by extensive hydration and then by greenschist facies metamorphism geochemical data indicate that protoliths include volcanic arc lavas and sediments intruded by a rift related granite the metavolcanic rocks have sio2 ranging between 55 and 72 are typically enriched in highly incompatible elements such as ba rb and light rare earth elements and are accompanied by relative depletion of nb and ti characteristic of subduction related magmas the granite has sio2 ranging between 67 and 70 is enriched in strongly incompatible elements and depleted in nb and ti indicative of either a crustal source or a subduction related tectonic setting concordant u pb analyses of single zircons from this granite yield an age of 1117 4 and 988 5 ma interpreted as the age of intrusion and the time of peak granulite facies metamorphism respectively combined with published information from other parts of mexico these data indicate that oaxaquia was a juvenile arc metamorphosed during a relatively young grenvillian metamorphism at 990 ma similar characteristics may also be found in the andean massifs of colombia and in the appalachian terranes carolina piedmont and avalon of amazonian provenance this suggests that oaxaquia may also have lain adjacent to northwestern amazonia at 1 ga a location that may allow neoproterozoic subduction as the origin of the hydrous lower amphibolite facies metamorphism it would also provide a proximal source for low grade to unmetamorphosed 1 ga and neoproterozoic igneous boulders in northern oaxaquia and 1000 900 ma detrital zircons in neoproterozoic and paleozoic sedimentary rocks in avalonia and iberia

petrogenesis of a voluminous quaternary adakitic volcano the case of baru volcano the origin of adakite magmas remains controversial because initially the term adakite had petrogenetic significance implying an origin by direct melting of the eclogitized subducting oceanic crust many models have been produced for their origin and until now there has not been a straightforward method to discriminate between these models in a given adakite suite here we use detailed chronological and geochemical studies of selected adakitic edifices that allows for the determination of the magmatic output rate parameter qe which has been correlated with the rates of magma generation deep within subduction zones by providing temporal and eruption rate estimates we provide constraints on the possible petrogenetic processes involved in the generation of adakite like signatures adakite magmas derived from the melting of the subducting slab should be volumetrically insignificant when compared to the adakite like magmas produced by typical arc magma generation processes in this study we use this observation and the extraordinary stratigraphic exposure from miocene to present in an adakitic volcano in panama and to study the temporal and chemical variation in erupted magmas to estimate rates of magma generation detailed chemical and geochronological analyses of baru volcano indicate that the volcanic edifice was constructed in its entirety during the quaternary and magmas display adakite like features such as steep rare earth elements patterns pronounced depletions in the heavy rare earth elements low y high sr and high sr y the magmatic output rates qe that we have calculated show that compared to other typical adakitic volcanoes most of the volcanic edifice of baru volcano was constructed extremely rapidly 213 k a and in time frames that are similar to typical arc volcanoes the observed chemical and mineralogical variation coupled with the high magma production rates indicate that baru volcano is more representative of a typical arc volcano than a small volume melt of the subducting oceanic crust the technique we outline may have broader application in determining the petrogenetic conditions of other adakite suites

field and geochemical characteristics of mesoarchean to neoarchean volcanic rocks in the storo greenstone belt sw greenland evidence for accretion of intra oceanic volcanic arcs abstract the storo greenstone belt southern west greenland consists of thrust imbricated slices of mesoarchean 3060 ma and neoarchean ca 2800 ma mafic to ultramafic volcanic rocks volcaniclastic sediments and gabbro anorthosite associations the belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600 ma the contacts between the mesoarchean and neoarchean volcanic rocks and surrounding eoarchean to neoarchean tonalite trondhjemite granodiorite ttg gneisses are tectonic and typically bounded by high grade mylonites regardless of age the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition near flat to slightly enriched light rare earth element lree patterns la smcn 0 91 1 48 relatively flat to slightly depleted heavy ree hree gd ybcn 1 0 1 28 and pronounced negative nb ta anomalies nb nb 0 34 0 73 on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow

geochemistry of metamorphosed volcanic rocks in the neoarchean qingyuan greenstone belt north china craton implications for geodynamic evolution and vms mineralization abstract the qingyuan greenstone belt qgb situated in the northeastern section of the north china craton ncc is considered to be the unique metallogenic province in china that hosts both banded iron formations bifs and volcanogenic massive sulfide vms deposits traditionally the qgb is divided into the hunbei and hunnan terranes separated by the hunhe fault and grouped into the lower shipengzi middle hongtoushan and upper nantianmen formations which have undergone amphibolite to granulite facies metamorphism exposed supracrustal rocks are composed of plagioclase amphibolite and biotite plagioclase gneiss with minor amounts of bif marble and schist in this study detailed field and petrographic observations lithogeochemical u pb geochronological as well as whole rock sm nd isotope analyses were conducted on the metamorphosed mafic and felsic volcanic rocks i e plagioclase amphibolite and biotite plagioclase gneiss respectively in the qgb in order to discuss implications for tectonic evolution and comitant vms mineralization the supracrustal rocks of both hunbei and hunnan regions were formed synchronously from 2 57 to 2 53 ga and then had undergone 2 52 2 48 ga regional metamorphism specifically the lower section of the shipengzi formation is composed dominantly of transitional tholeiitic basalts with negative nb anomalies suggesting that they were likely generated by partial melting of a mantle source that was previously altered by variable amounts of slab derived fluids or melts in contrast the lithologic assemblages grade upward into interlayered bimodal volcanic rocks i e n morb type tholeiitic basalts and fi to fii type dacites of transitional to calc alkalic affinities representing a change in tectonic regime related to subduction from compression to extension among them all the basalts are characterized by consistently positive initial nd compositions end t 2 7 to 3 4 further indicate a depleted mantle source whereas those dacites possess negative to positive initial nd values end t 4 6 to 3 0 suggesting they were formed by partial melting of depleted mafic source likely lower mafic crust and accompanied with variable addition of old crustal material significantly vms deposits are genetically linked to this extensional event and closely associated with the fii type dacites that were generated by higher melting degree at high temperature conditions and shallow crustal level likely 10 15 km in all geochemical features e g negative nb anomalies and end value together with contamination from continental crusts for tholeiitic mafic rocks and inherited zircons from these volcanic rocks imply a continental arc setting where the qgb was evolved

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

time variable ice loss in asian high mountains from satellite gravimetry abstract substantial amount of glacial ice is considered to be melting in the asian high mountains gravimetry by grace satellite during 2003 2009 suggests the average ice loss rate in this region of 47 12 gigaton gt yr 1 equivalent to 0 13 0 04 mm yr 1 sea level rise this is twice as fast as the average rate over 40 years before the studied period and agrees with the global tendency of accelerating glacial loss such ice loss rate varies both in time and space mass loss in himalaya is slightly decelerating while those in northwestern glaciers show clear acceleration uncertainty still remains in the groundwater decline in northern india and proportion of almost isostatic e g tectonic uplift and non isostatic e g glacial isostatic adjustment portions in the current uplift rate of the tibetan plateau if gravity increase associated with ongoing glacial isostatic adjustment partially canceled the negative gravity trend the corrected ice loss rate could reach 61 gt yr 1

ancient and modern subduction zone contributions to the mantle sources of lavas from the lassen region of california inferred from lu hf isotopic systematics hafnium isotopic compositions have been determined on a suite of introduction calc alkaline and high alumina olivine tholeiitic lavas from the the geochemical and isotopic variability of mantle wedge lassen region of california and are used in conjunction with peridotites beneath continental volcanic arcs is poorly previously published mineralogical geochemical and isotopic data constrained this is a result of the fact that most of what to constrain their petrogenesis positive correlation between hf is known about the geochemistry of the mantle wedge is values and geochemical indices of the modern subduction component inferred from the composition of basaltic arc lavas which indicates that the isotopic compositions of the calc alkaline lavas although derived from the wedge are affected by variable record addition of radiogenic hf from the subducted slab however contributions from the subducting slab and continental the addition of the modern subduction component increases the hf crust e g gill 1981 tatsumi et al 1986 hawkesworth values of most calc alkaline lavas by 0 5 units over estimates of et al 1993 1994 despite these limitations there is non subduction enriched peridotites of the mantle wedge the lu hf significant evidence to suggest that mantle wedge periisotopic systematics of the lassen lavas suggest that the calc alkaline dotites are heterogeneous in composition and mineralogy magmas have equilibrated with garnet at some point in their history for example it has been postulated that the compositions whereas the tholeiitic magmas have not these observations require of mantle peridotites beneath the cascade arc vary from the two lava types to be derived from different sources the isotopic compositions that are similar to sources for mid ocean variability of the lassen lavas cannot be produced by mixing mantle ridge basalt morb hawaiian ocean island basalt sources inferred to be present in the eastern central pacific and oib and high alumina olivine tholeiites haot from western usa with a modern subduction component instead the the basin and range province hughes 1990 leeman isotopic variability is consistent with mixing of a depleted mantle et al 1990 bacon et al 1997 borg et al 1997 clynne source a more fertile mantle source enriched by an ancient subduction borg 1997 the restite mineralogy of the source component and a modern subduction component regions for cascade magmas is poorly constrained as well for example experiments conducted by baker et al 1994 found that calc alkaline basalts from the mt shasta region of california did not have garnet on their liquidus and reiners et al 2000 were able to model

wet and dry basalt magma evolution at torishima volcano izu bonin arc japan the possible role of phengite in the downgoing slab the arc front volcanoes of sumisu 31 58n 1408e andtorishima 30 58n 140 38e in the central izu bonin arc are similar in size and rise as relatively isolated edifices from the seafloor together they provide valuable along arc information about magma generation processes the volcanoes have erupted low k basalts originating from both wet and dry parental basaltic magmas low zr basalts and high zr basalts respectively based on models involving fluid immobile incompatible element ratios la sm the parental basalts appear to result from different degrees of partial melting of the same source mantle 20 and 10 for wet and dry basalt magmas respectively assuming that the wet basalts contain greater abundances of slab derived components than their dry counterparts geochemical comparison of these two basalt types permits the identification of the specific elements involved in fluid transport from the subducting slab using an extensive set of new geochemical data fromtorishima where the top of the downgoing slab is about 100 km deep we find that cs pb and sr are variably enriched in the low zr basalts which cannot be accounted for by fractional crystallization or by differences in the degree of mantle melting these elements are interpreted to be selectively concentrated in slab derived metasomatic fluids variations in k high field strength element and rare earth element concentrations are readily explained by variations in the degree of melting between the lowand high zr basalts these elements are not contained in the slab derived fluids rb and ba exhibit variable behaviour in the low zr basalts ranging from immobile similar to k to mildly enriched in some low zr basalts we suggest that the k rich mica phengite plays an important role in determining the composition of fluids released from the downgoing slab in arcfront settings where slab depth is 100 km phengite is stable and the fluids released from the slab contain little k in back arc settings however where the slab is at 100 140 km depth phengite is unstable and k rich fluids are released we conclude that cross arc variations in the k content of arc basalts are probably related to differing compositions of released fluids or melts rather than the widely held view that such variations are controlled by the degree of partial melting

glacier runoff and its impact in a highly glacierized catchment in the southeastern tibetan plateau past and future trends we investigate past and future trends in glacier runoff and the associated hydrological impacts on river runoff in the hailuogou catchment a highly glacierized catchment with extensive debris cover in the southeastern tibetan plateau using a catchment scale glacio hydrological model past trends in various runoff components of the catchment indicate that glacier runoff has been a large component of total runoff contributing similar to 53 4 of total runoff during the period 1952 2013 future changes in runoff calculated using the outputs of ten global climate models for representative concentration pathway rcp 4 5 and rcp8 5 reveal that glacier runoff plays different roles in the water supply of the catchment for the two rcps and the discrepancies between the two rcps increase in the second half of this century leading to a considerable difference in the hydrological regime of the catchment in particular changes are more remarkable under rcp8 5 under which all glaciers are projected to retreat dramatically and total runoff to decrease slightly by the end of this century an experimental analysis in which no debris cover is assumed on glacier ablation zones indicates that excess meltwater from the debris covered area provides an 8 1 increase in total runoff relative to the no debris assumption case

glaciological conditions in seven contrasting regions estimated with the degree day model we apply the degree day model to seven glacial regions that offer contrasting conditions and are well documented in the world glacier inventory the regions are axel heiberg island in arctic canada svalbard northern scandinavia southern norway the alps the caucasus and new zealand we estimate the average equilibrium line altitude ela for each half degree latitude longitude grid square from the median elevations of glaciers within the square and we extrapolate temperature from the uea cru climate research unit of the university of east anglia gridded climatology using the degree day model we calculate annual accumulation at the ela equal to ablation at the ela and other quantities like summer mean temperature length of melt season balance gradients and the sensitivity of mass balance to temperature and or precipitation changes glaciers can be characterized on a scale from cold dry axel heiberg island to warm wet new zealand corresponding to the contrast between maritime and continental climates mass balance sensitivities to temperature and or precipitation changes are relatively small for dry cold climate and relatively high for warm wet climate we could extend the approach to other glacier regions but we note that there are large areas for which ela data are not available as they are still not covered by the world glacier inventory

meteorological controls on glacier mass balance in high asia the aim of this study is to investigate spatial and temporal variations of meteorological variables known to control glacier mass balance processes and to demonstrate their relevance in high asia the study uses the ncep ncar reanalysis database us national centers for environmental prediction and us national center for atmospheric research which is global and continuous since 1 january 1948 a positive degree day pdd model of annual glacier wide summer surface balance bs uses upper air temperatures at ncep ncar gridpoints near each of six glaciers between 40 and 458 n and between 71 and 878 e and two others near 508 n 878 e model error ranged between 0 19 and 0 41 m w e comparable with the observational accuracy of bs sensitivity to temperature change dbs dt ranges between 0 5 and 0 2 m w e a 1 8c 1 for these glaciers

pge mineralization in andesite explosive breccias associated with the poperechny iron manganese deposit lesser khingan far east russia whole rock geochemical 190pt 4he isotopic and mineralogical evidence abstract we report in this paper an unusual occurrence of platinum group minerals in evolved explosive breccia associated with the poperechny iron manganese deposit lesser khingan range far east russia pgms in andesite breccia are represented by fe pt solid solutions 85 and pgm mostly os ir ru solid solutions sulfides and sulfarsenides 15 textural and compositional variations in pgm assemblages suggest that pt fe and os ir ru solid solutions as well as erlichmanite laurite series sulfides were formed during high temperature fractionation of mantle derived mafic parental melt similar to alaskan type complexes and were entrained in the evolved andesitic melt during its emplacement in the crust pd pt plumbostannide and copper gold solid solutions reflect late magmatic re crystallization and metasomatism early cretaceous 125 ma age of ferroplatinum in the explosive breccia suggests that pgm bearing ultramafic material could have been sampled during regional slab window tectonics related to the late mesozoic subduction of izanagi plate along southern margin of the north asian continent

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

petrology and geochemistry of early permian volcanic rocks in south tian shan nw china implications for the tectonic evolution and phanerozoic continental growth situated in the southwest of the central asian orogenic belt caob the south tian shan sts block is a key area for understanding the final accretion of the caob a suite of volcanic rocks interbedded with continental sediments from the xiaotikanlike formation lies along the southwestern edge of the tian shan orogen laser ablation inductively coupled plasma mass spectrometer u pb dating provided a crystallization age of 295 0 2 8 ma mswd 1 3 suggesting an early permian magmatic event the volcanic rocks show a variable composition with dominant rhyolites and dacites subordinate basaltic andesites and few basalts the felsic rocks are enriched in k and exhibit remarkably negative anomalies in ba sr eu p and ti these anomalies associated with their high negative nd t values and old nd model ages suggest that they are most likely sourced from ancient lower crustal rocks the mafic rocks are characterized by high mg cr ni contents negative nb ta anomalies and pronounced enrichment in light rare earth elements as well as mild enrichment in large ion lithophile elements the mafic rocks are thus inferred to derive from enriched subcontinental lithospheric mantle the petrographic and geochemical characteristics of the xiaotikanlike formation volcanic rocks indicate that they were generated under a post collisional regime therefore the final collision between the tarim craton and the kazakhstan yili terrane took place before early permian most probably at late carboniferous differing from other tectonic units of the caob the recycling of ancient lithospheric crust played a significant role in the continental growth of the sts block

role of cryptic amphibole crystallization in magma differentiation at hudson volcano southern volcanic zone chile hudson volcano chile is the southern most stratovolcano of the andean southern volcanic zone and has produced some of the largest holocene eruptions in south america there have been at least 12 recorded holocene explosive events at hudson with the 6700 years bp 3600 years bp and 1991 eruptions the largest of these hudson volcano has consistently discharged magmas of similar trachyandesitic and trachydacitic composition with comparable anhydrous phenocryst assemblages and pre eruptive temperatures and oxygen fugacities pre eruptive storage conditions for the three largest holocene events have been estimated using mineral geothermometry melt inclusion volatile contents and comparisons to analogous high pressure experiments throughout the holocene storage of the trachyandesitic magmas occurred at depths between 0 2 and 2 7 km at approximately 972 c 25 and log fo2 10 33 10 24 0 2 one log unit above the nno buffer with between 1 and 3 wt h2o in the melt pre eruptive storage of the trachydacitic magma occurred between 1 1 and 2 0 km at 942 c 26 and log fo2 10 68 0 2 with 2 5 wt h2o in the melt the evolved trachyandesitic and trachydacitic magmas can be derived from a basaltic parent primarily via fractional crystallization entrapment pressures estimated from plagioclase hosted melt inclusions suggest relatively shallow levels of crystallization however trace element data e g dy yb ratio trends suggests amphibole played an important role in the differentiation of the hudson magmas and this fractionation is likely to have occurred at depths 6 km the absence of a garnet signal in the hudson trace element data the potential staging point for differentiation of parental mafic magmas i e 20 km e g annen et al in j petrol 47 3 505 539 2006 and the inferred amphibolite facies 24 km e g rudnick and fountain in rev geophys 33 267 309 1995 combine to place some constraint on the lower limit of depth of differentiation i e 20 24 km these constraints suggest that differentiation of mantle derived magmas occurred at upper mid to lower crustal levels and involved a hydrous mineral assemblage that included amphibole and generated a basaltic to basaltic andesitic composition similar to the magma discharged during the first phase of the 1991 eruption continued fractionation at this depth resulted in the formation of the trachyandesitic and trachydacitic compositions these more evolved magmas ascended and stalled in the shallow crust as suggested by the pressures of entrapment obtained from the melt inclusions the decrease in pressure that accompanied ascent combined with the potential heating of the magma body through decompression induced crystallization would cause the magma to cross out of the amphibole stability field further shallow crystallization involved an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the hudson suite

regional differences in response of flow in glacier fed himalayan rivers to climatic warming river flow from glacierized areas in the himalaya is influenced both by intra annual variations in precipitation and energy availability and by longer term changes in storage of water as glacier ice high specific discharge from ice melt often dominates flow for considerable distances downstream particularly where other sources of runoff are limited providing a major water resource should himalayan glaciers continue to retreat rapidly water shortages might be widespread within a few decades however given the difference in climate between the drier western and monsoonal eastern ends of the region future warming is unlikely to affect river flow uniformly throughout a simple temperature index based hydro glaciological model in which glacier dimensions are allowed to decline through time has been developed with a view to assessing in data sparse areas by how much and when climate warming will reduce himalayan glacier dimensions and affect downstream river flows two glaciers having the same initial geometries were located one each in the headwaters of two identical nests of hypothetical catchments representing contrasting climates in the west and east of the region the hypothetical catchments were nested such that percentage ice cover declined with increasing basin area model parameters were validated against available but limited mass balance and river flow measurements the model was applied for 150 years from an arbitrary start date 1990 first with standard period 1961 1990 climate data and then with application of a 0 06 c year 1 transient climatic warming scenario under this warming scenario himalayan rivers fed by large glaciers descending through considerable elevation range will respond in a broadly similar manner except that summer snowfall in the east will suppress the rate of initial flow increase delay peak discharge and postpone eventual disappearance of the ice impacts of declining glacier area on river flow will be greater in smaller and more highly glacierized basins in both the west and east and in the west where precipitation is scarce for considerable distances downstream copyright 2006 john wiley sons ltd

regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data 1 very few global scale ice volume estimates are available for mountain glaciers and ice caps although such estimates are crucial for any attempts to project their contribution to sea level rise in the future we present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from 123 000 glaciers from a recently extended world glacier inventory we compute glacier volumes and their sea level equivalent sle for 19 glacierized regions containing all mountain glaciers and ice caps on earth on the basis of total glacierized area of 741 103 68 103 km2 we estimate a total ice volume of 241 103 29 103 km3 corresponding to 0 60 0 07 m sle of which 32 is due to glaciers in greenland and antarctica apart from the ice sheets however our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried i e antarctica north america greenland and patagonia this emphasizes the need for more volume observations especially of large glaciers and a more complete world glacier inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps

a more complete version of the world glacier inventory the world glacier inventory wgi was conceived half a century ago as an activity to be completed during the international geophysical year 1957 58 it consisted until very recently of nearly 70 000 glacier records covering slightly less than one quarter of the glacier ice outside the ice sheets a complete wgi must be a compromise if it is to be available and usable soon a more complete version called wgi xf is available and usable now and contains records for just over 131 000 glaciers and nearly half of the global extent of ice the additional glaciers come mainly from the assimilation of existing inventories but also from rescuing inventories that have been lost and from new inventories in canada and the subantarctic in wgi xf the xf stands for extended format flagging the fact that wgi xf conforms to a set of explicit specifications which enhance usefulness by eliminating low level inconsistencies two important features are nominal glaciers and glacier complexes a nominal glacier of which there are about 5000 in wgi xf is one about which little is known other than its existence and approximate location a glacier complex is one or more contiguous glaciers this term embodies the idea which is not new that inventories can be preliminary based upon vector outlines which await subdivision by trained glaciologists many regional studies have found that measurements of changes in single glaciers require accurate work and painstaking quality control wgi xf is not assuredly reliable as a source for such detailed work but there are several other subjects in which less detail would be a price worth paying for more complete coverage incomplete information about the dates of imagery and maps is a hindrance to analysis and the recovery of dates from metadata should have high priority

the origin and compositions of mesoarchean oceanic crust evidence from the 3075 ma ivisaartoq greenstone belt sw greenland the mesoarchean ca 3075 ma ivisaartoq greenstone belt contains well preserved primary magmatic structures such as pillow lavas volcanic breccias and clinopyroxene cumulate layers picrites despite the isoclinal folding and amphibolite facies metamorphism the belt also includes variably deformed gabbroic to dioritic dykes and sills actinolite schists and serpentinites the ivisaartoq rocks underwent at least two stages of post magmatic metamorphic alteration including seafloor hydrothermal alteration and syn to post tectonic calc silicate metasomatism between 3075 and 2961 ma these alteration processes resulted in the mobilization of many major and trace elements the trace element characteristics of the least altered rocks are consistent with a supra subduction zone geodynamic setting and shallow mantle sources on the basis of geological similarities between the ivisaartoq greenstone belt and phanerozoic forearc ophiolites and intra oceanic island arcs we suggest that the ivisaartoq greenstone belt represents a relic of dismembered mesoarchean supra subduction zone oceanic crust this crust might originally have been composed of a lower layer of leucogabbros and anorthosites and an upper layer of pillow lavas picritic flows gabbroic to dioritic dykes and sills and dunitic to wehrlitic sills the sm nd and u pb isotope systems have been disturbed in strongly altered actinolite schists in addition the u pb isotope system in pillow basalts appears to have been partially open during seafloor hydrothermal alteration gabbros and diorites have the least disturbed pb isotopic compositions in contrast the sm nd isotope system appears to have remained relatively undisturbed in picrites pillow lavas gabbros and diorites as a group picrites have more depleted initial nd isotopic signatures end 4 23 to 4 97 than pillow lavas gabbros and diorites end 0 30 to 3 04 consistent with a variably depleted heterogeneous mantle source in some areas gabbros include up to 15 cm long white inclusions xenoliths these inclusions are composed primarily 90 of ca rich plagioclase and are interpreted as anorthositic cumulates brought to the surface by upwelling gabbroic magmas the anorthositic cumulates have significantly higher initial end 4 8 to 6 0 values than the surrounding gabbroic matrix 2 3 to 2 8 consistent with different mantle sources for the two rock types

low sea level rise projections from mountain glaciers and icecaps under global warming the mean sea level has been projected to rise in the 21st century as a result of global warming such projections of sea level change depend on estimated future greenhouse emissions and on differing models but model average results from a mid range scenario a1b suggests a 0 387 m rise by 2100 refs 1 2 the largest contributions to sea level rise are estimated to come from thermal expansion 0 288 m and the melting of mountain glaciers and icecaps 0 106 m with smaller inputs from greenland 0 024 m and antarctica 0 074 m here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise excluding those in greenland and antarctica we provide the first separate assessment of melt contributions from mountain glaciers and icecaps as well as an improved treatment of volume shrinkage we find that icecaps melt more slowly than mountain glaciers whose area declines rapidly in the 21st century making glaciers a limiting source for ice melt using two climate models we project sea level rise due to melting of mountain glaciers and icecaps to be 0 046 and 0 051 m by 2100 about half that of previous projections

crustal assimilation in the burnt lake metavolcanics grenville province southeastern ontario and its tectonic significance three intimately interbedded suites of volcanic rocks are identified geochemically in the burnt lake area of the belmont domain in the central metasedimentary belt and their petrogenesis is evaluated the burnt lake back arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back arc basins formed in continental crust the burnt lake continental tholeiitic suite comprises basalts and andesites similar in trace element composition to continental tholeiitic sequences the burnt lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts rare earth element models suggest that the burnt lake back arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5 partial melting of an amphibole bearing depleted mantle enriched in light rare earth elements by a subduction component the modelling also suggests that t

paleoproterozoic arc magmatism imposed on an older backarc basin implications for the tectonic evolution of the trans hudson orogen canada compositional data from 72 granitoids and associated mafic rocks in the paleoproterozoic kisseynew domain trans hudson orogen canada were used to evaluate the tectonic setting of magma generation between 1840 and 1820 ma these data thus provide insights into the development of the trans hudson orogen just prior to amphibolite grade metamorphism and the final stages of continental collision the granitoid rocks are hornblende or orthopyroxene bearing medium to high k calc alkalic and weakly peraluminous the trends on harker variation diagrams are consistent with crystal fractionation processes although the range in values is related to the temporal and spatial distribution of samples the extent of lree light rare earth element enrichment increases with increasing sio 2 as does variability in hree heavy rare earth element fractionation and magnitude of eu anomalies most samples have gd yb n 10 suite ia although five have gd yb n 17 24 suggesting the presence of garnet residua suite ib the range in rock types calc alkalic character and negative nb and ti anomalies are all characteristic of arc environments magma generation within the trans hudson orogen including the kisseynew domain between 1 84 and 1 82 ga was related to interaction between the sask craton and the flin flon glennie complex a decrease in subduction angle likely resulted from northward directed subduction of more buoyant crust with associated changes in thermal conditions leading to melting over a wide area most magmas formed in a slab dehydration dominated regime although localized slab melts may have been generated ultimately subduction ceased and the slab foundered into the mantle potentially resulting in the generation of alkalic and potassic magmas within the rae and hearne cratons

patagonia icefield melting observed by gravity recovery and climate experiment grace 1 using recently released reprocessed gravity solutions from the gravity recovery and climate experiment grace we estimate the ice loss rate for the patagonia icefield pif of south america for the period april 2002 through december 2006 after postglacial rebound and hydrological effects are corrected the estimated rate is 27 9 11 km 3 year equivalent to an average loss of 1 6 m year ice thickness change if evenly distributed over the entire pif area the estimated contribution to global sea level rise is 0 078 0 031 mm year this is an independent confirmation of relatively large melting rate estimates from earlier studies employing topographic and cartographic data

southern patagonia s perito moreno glacier lake argentino and santa cruz river hydrological system an overview summary an overview of the hydrological data from patagonia s perito moreno glacier lake argentino and santa cruz river system reinforces our previous assertion that the el nino southern oscillation enso and the antarctic oscillation aao are teleconnected with the rupture sequence when the glacier s snout harmonically dams during certain interannual periods the rico branch of lake argentino it is clear however that the incidence of interannual climatic anomalies is not uniform in time and appears embedded in decadal or quasi bidecadal periods of relative damming inactivity the use of nonparametric tests shows that there are no significant positive trends in the river s annual discharge with the only exception of the yearly snowmelt ice melt periods september october when riverine flow appears to increase with statistical significance the question of the glacier s stability looks like a complex multivariate process although we do not rule out the occasional role of enso aao a longer hydrological data series i e 100 years would prove useful in casting some light on this intriguing process surely accounting for the glacier s response time

geochemistry isotope systematics and petrogenesis of the volcanic rocks in the zhongtiao mountain an alternative interpretation for the evolution of the southern margin of the north china craton abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton which are composed primarily of basaltic andesites and andesites with minor dacites and dacitic rhyolites the basaltic andesites and andesites from the xiong er volcanic rocks in the zhongtiao mountain show consistent nd t la nb and th nb values irrespectively of sio 2 which preclude significant crustal contamination during ascent both of these volcanic rocks share similar incompatible ratios e g la sm zr nb la nb indicating that the basaltic andesites and andesites originated from the same source the basaltic andesites are characterized by high mg number 45 55 precluding the possibility of their derivation from the melting of the lower crust variable ti eu zr sm and nb la ratios for the basaltic andesites with higher partial melting degree suggest that amphiboles remained as residues in the magma source indicating that the xiong er volcanic rocks were derived from hydrous magma non radiogenic nd isotopes for the xiong er volcanic rocks are inherited from a mantle source which had been enriched by the subduction related crustal recycling during archean to paleoproterozoic time basaltic andesites show hfse enrichments especially nb 4 7 ppm and high fe ti contents comparable with nb enriched basalts suggesting that the xiong er volcanic rocks were derived from a metasomatized mantle source similar to that of nb enriched basalts therefore the mantle source of the xiong er volcanic rocks in the zhongtiao mountain has been enriched in fe ti oxides and hfse by equilibrium reactions with the slab melts during late archean and paleoproterozoic subduction processes as evidenced by nd isotopes in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative anomalies on the nb ta ti similar to arc related volcanic rocks produced by the hydrous melting of the metasomatized mantle wedge in the paleo mesoproterozoic the xiong er volcanic rocks in the zhongtiao mountain were produced by the slab dehydration induced melting of an existing metasomatized mantle source and the fluids from the slab dehydration introduced significant lile and lree to the source masking its inherent hfse enriched characteristics the arc related characteristics of the xiong er volcanic rocks in the zhongtiao mountain suggest the xiong er volcanic belt constructs a subduction zone along the southern margin of the north china craton in the paleo mesoproterozoic implying that the craton may have recorded the outbuilding history of the columbia supercontinent during paleo mesoproterozoic time

petrological and geochemical characterization of proterozoic ophiolitic melange nellore khammam schist belt se india abstract the ophiolitic melange occurs close to a major fault within the metavolcanics of kanigiri area in the western margin of the khammam nellore schist belt andhra pradesh india the unique feature of kanigiri melange is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust the ophiolitic melange is composed mainly of blocks of variably deformed and metamorphosed pillow basalts serpentinized ultramafic rocks meta gabbros cherts and pelagic sediments in a pervasive scaly argillite matrix the melange has a tectonic contact with a granite intrusion and numerous thrust faults cut across the melange exposures primary magmatic features such as drainage cavities in pillow basalts magmatic layering in gabbros and clinopyroxene cumulates in ultramafic rocks are well preserved in low strain domains mafic components enclosed in the melange are characterized by low pressure secondary mineral assemblages retrograded from amphibolite down to greenschist facies as commonly observed in subducted and exhumed orogens all amphiboles in the studied fragments are calcic and cluster in the range from winchite actinolite to hornblende amphibole compositions are characterized by al 2 o 3 2 4 13 8 feo 5 13 k 2 o 0 04 0 7 and x mg 0 67 0 77 the metabasalt and wherlite samples exhibit light rare earth element lree enriched patterns and negative high field strength element hfse zr and ti consistent with a suprasubduction zone geodynamic setting a notable feature of both metabasalt and wherlite samples is their pronounced negative ce anomaly and a positive eu anomaly as observed in a number of modern island arc suites as the petrological features and the geochemical characteristics of the remnant fragments we analyzed in this study are reminiscent of their phanerozoic ophiolite counterparts we suggest that these rocks were derived from a proterozoic oceanic plate belonging to a suprasubduction ophiolite assemblage subduction zone geochemical signatures and ophiolite like crustal lithologies in the study region are consistent with the accretion of juvenile oceanic fragments to the pre existing continental blocks through a forearc continent collision

the physical basis of glacier volume area scaling ice volumes are known for only a few of the roughly 160 000 glaciers worldwide but are important components of many climate and sea level studies which require water flux estimates a scaling analysis of the mass and momentum conservation equations shows that glacier volumes can be related by a power law to more easily observed glacier surface areas the relationship requires four closure choices for the scaling behavior of glacier widths slopes side drag and mass balance reasonable closures predict a volume area scaling exponent which is consistent with observations giving a physical and practical basis for estimating ice volumes glacier volume is insensitive to perturbations in the mass balance scaling but changes in average accumulation area ratios reflect significant changes in the scaling of both mass balance and ice volume

petrogenetic and geodynamic origin of the neoarchean dore lake complex abitibi subprovince superior province canada the neoarchean ca 2728 ma anorthosite bearing dore lake complex in the northeastern abitibi subprovince quebec was emplaced into an association of intra oceanic tholeiitic basalts and gabbros known as the obatogamau formation the obatogamau formation constitutes the lower part of the roy group which is composed of two cycles of tholeiitic to calc alkaline volcanic and volcaniclastic rocks siliciclastic and chemical sedimentary rocks and layered mafic to ultramafic sills in this study we report major and trace element results and nd sr pb and o isotope data for anorthosites leucogabbros gabbros and mafic dykes from the dore lake complex and spatially associated basalts and gabbros of the obatogamau formation to assess their petrogenetic origin and geodynamic setting field and petrographic observations indicate that the dore lake complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions resulting in widespread epidotization 20 40 and chloritization 10 40 of many rock types plagioclase recrystallized mainly to anorthite and albite endmembers erasing intermediate compositions metamorphic alteration also led to the mobilization of many elements e g lile and transition metals and to significant disturbance of the rb sr and u pb isotope systems resulting in 1935 150 and 3326 270 ma errorchron ages respectively the sm nd isotope system was less disturbed yielding an errorchron age of 2624 160 ma on many binary major and trace element diagrams the least altered anorthosites and leucogabbros and the gabbros and mafic dykes of the dore lake complex plot in separate fields signifying the presence of two distinct magma types in the complex the gabbros and mafic dykes in the dore lake complex share the geochemical characteristics of tholeiitic basalts and gabbros in the obatogamau formation suggesting a possible genetic link between the two rock associations initial end 2 6 to 5 0 and 18o 6 1 to 7 9 values for the dore lake complex and gabbros of the obatogamau formation end 2 8 to 4 0 18o 7 3 to 8 0 are consistent with depleted mantle sources all rock types in the dore lake complex and the roy group share the trace element characteristics of modern arc magmas suggesting a suprasubduction zone setting for these two lithological associations on the basis of regional geology and geochemical data we suggest that the dore lake complex and the obatogamau formation represent a dismembered fragment of a suture zone like many phanerozoic ophiolites resulting from closure of a back arc basin between 2703 and 2690 ma

plume and arc magmatism in the abitibi subprovince implications for the origin of archean continental lithospheric mantle abstract based on eclogitic mantle xenoliths that appear to be the residue of slab melts it is commonly argued that the formation of distinctive lithospheric keels beneath archean cratons occurred by the tectonic accretion of oceanic crust these models are complicated by evident buoyancy of the keels the varied compositions of the mantle xenolith suite as a whole and a compositional constraint that a large portion of the keels originated in mantle plume melting events resolution of these issues is complicated by the long development history of most cratons 100 s of m y and the multiple cycles of magmatism they represent in contrast the single 50 m y period of arc volcanism in the abitibi subprovince and the immediate onset of orogeny and craton stabilisation avoids many of these uncertainties chemical and isotopic data demonstrate that syn volcanic to syn tectonic adakitic abitibi granitoids were derived via slab melting deep seismic reflection profiles image singular slab like features along the moho these are interpreted as the remnants of oceanic slabs emplaced and torn during orogeny nonetheless their presence directly contradicts subcretion models of keel formation because they occupy regions that should correspond to the top of an earlier formed subcreted keel post adakite shoshonitic granitoids and lamprophyres also attest to the presence of a metasomatised mantle wedge throughout the entire period of abitibi arc magmatism diamond bearing lamprophyres in the abitibi and adjacent wawa subprovince are compositionally equivalent to paleoproterozoic diamondiferous rocks and characteristic of adakite generating shallow subduction rather than evidence of pre existing sub cratonic keels abitibi mantle plume and subduction related volcanism also demonstrates the continuous presence of shallow asthenospheric mantle beneath the belt over a 50 m y period komatiites and then boninites erupted along the central part of the belt halfway through its evolution and rifted arc style volcanism dominated the belt within a few m y of orogeny none of these events are consistent with the development of a progressively thickened continental lithospheric keel the geodynamic evolution of the abitibi belt demonstrates a fact recognised in some xenolith studies the characteristic association of deep keels and archean cratons was not developed gradually during greenstone belt volcanism rather it was initiated by the coupling of shallow imbricated plume and arc related crust with the buoyant residue of mantle plume melting that rose from depths of 80 km to 400 km subduction was active along the southern and eastern margin of the superior province craton before and after ascent of the abitibi plume renewal of subduction in the abitibi as marked by the occurrence of the 2716 ma boninitic volcanic suite delayed the ascent of the deep keel and its coupling to the composite crust final ascent of the plume residue occurred following orogeny and slab loss and may have included entrainment of fragmented slab residue into the rising diapir the coupling of shallow crust and deep keel occurred soon after and the keel s presence beneath the subprovince is recognised by phanerozoic diamond deposits xenolith chemistry and geophysical data

effect of summer accumulation on glacier mass balance on the tibetan plateau revealed by mass balance model the characteristics and sensitivities of a cold based glacier on the tibetan plateau where the summer monsoon provides most of the mass input to glaciers are discussed using an energy balance model incorporating the process of water refreezing the model accurately represents the observational results related to the mass balance of xiao dongkemadi glacier on the central plateau during 1992 93 our data revealed that the mass balance of cold glaciers cannot simply be described by the surface mass heat balances because about 20 of infiltrated water is refrozen and thus does not run off from the glacier model calculations demonstrate that glaciers in an arid environment can maintain their mass since the monsoon provides precipitation during the melting season snowfall in summer keeps surface albedo high and largely restrains ablation nevertheless the calculations also make clear that glaciers on the plateau are more vulnerable than those of other regions because of summer accumulation in the monsoon climate warming would cause not only a decrease in accumulation but also a drastic increase in ablation in combination with surface albedo lowering therefore although glaciers on and around the plateau can be sustained by summer accumulation they are more vulnerable to warming than winter accumulation type glaciers

origin of low k intermediate lavas at nekoma volcano ne honshu arc japan geochemical constraints for lower crustal melts at lower crustal depths beneath the frontal arc is suggested by extremely low k basaltic andesite to andesite lavas at nekoma geophysical observations these observations further support lowervolcano situated in the frontal volcanic zone of the ne honshu crustal melting beneath nekoma as the origin of the intermediate arc were produced from melts that originated in the lower crust low k lavas multiple incompatible trace element model calculations suggest that extremely low k basalt found in the same arc is a natural analog for the source composition however fractional crystallization magma mixing and crustal contamination models of primary lowk basalt cannot reproduce the nekoma chemical composition

geochemical characteristics of the rio verde complex central hispaniola implications for the paleotectonic reconstruction of the lower cretaceous caribbean island arc abstract new geochronological trace element and sr nd isotope data for metabasalts dolerites and amphibolites from the rio verde complex central hispaniola are integrated with existing geochemical data for mafic volcanic rocks and metamorphic derivatives from the los ranchos amina and maimon formations giving new insights into magma petrogenesis and paleotectonic reconstruction of the lower cretaceous caribbean island arc back arc system u pb and 40ar 39ar age data show that the rio verde complex protoliths were in part coeval with volcanic rocks of the los ranchos formation upper aptian to lower albian the geochemical data establish the existence of gradients in trace element parameters nb yb th yb zr yb zr ba and normalized ti sm y and yb abundances and nd isotope compositions from throughout hispaniola which reflect differences in the degree of mantle wedge depletion and contributions from the subducting slab the rio verde complex mafic rocks and some mafic sills and dykes intruding in the loma caribe peridotite have a transitional iat to n morb geochemistry and a weak subduction related signature and are interpreted to form in a rifted arc or evolving back arc basin setting the los ranchos amina and maimon formations volcanic rocks have arc like characteristics and represent magmatism in the volcanic front trace element and nd isotope modeling reproduce observed data trends from arc to back arc and suggest that the variations in several geochemical parameters observed in a sw direction across the caribbean subduction system can be explained from the progressively lower subduction flux into a progressively less depleted mantle source the low nb contents and high end i values in both arc and back arc mafic rocks imply however the absence of a significant lower cretaceous plume enriched component in order to explain these observations a model of proto caribbean oceanic lithosphere subducting to the sw at least in the 120 110 ma interval is proposed to cause the observed magmatic variations in the lower cretaceous caribbean island arc back arc system in this context arc rifting and initial sea floor spreading to form the rio verde complex protoliths occurred in the back arc setting of this primitive island arc built on the ne edge of the caribbean plate

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

mass balance of glaciers other than the ice sheets small glaciers appear to have been at equilibrium or shrinking very slightly during 1961 90 according to analysis of an essentially compl ete set of published measurements simple calculations give an average annual mass balance of 195 59 mm a 1 water equivalent but this is too low because of systema tic errors eglect of internal accumulation is respon sible for some tens of millime ters of under esti mate uneven spatial coverage with fewer measurements where mass balances are less negative accounts for about 50 mm a 1 of underestimate this figure derives from spatial interpolati on based on global data on ice extent and on an analysis of correlations between balance time series the eorrelogram shows exponential decay the scale length being about 600 km the largest bias is due to a newly detec ted dependence of mass balance on glacier size among the 231 measured glaciers many arc small and belong to a restricted size range in which balance is negativ e but much of the small glacier extent is accounted for by larger glac iers in a size range where balance is indisti ngui shable from zero correct ing for this size bias increases the average balance to 35 89 mm a i inspection of time series for 1940 95 251 glaciers shows that mass balance was least negative during the 1960s and has varied in broad agreementvith northern hemisphere temperature anomalies smaller small glaciers a 16 km2 appear to be more sensitive than larger small glaciers to changes in thermal forci ng the small glaci er contribution to sea level rise implied by this asse ssment is only 0 06 0 32 mm a i consistent with glaciers in general mak i ng little or no contri bution to sea level change during 1961 90

catchment scale reconstruction of glacier mass balance using observations and global climate data case study of the hailuogou catchment south eastern tibetan plateau summary debris covered glaciers are common in the tibetan plateau where ablation zones are mantled in a supraglacial debris cover that influences glacier mass balance runoff and response to climate change by affecting the melt rate of the underlying ice the impact of debris cover has not yet been taken into account in regional or global scale assessments of glacier mass balances and freshwater resources by using physically based numerical models here a surface energy mass balance model that accounts for the significance of debris cover and its effect on the ice melt rate is applied to reconstruct the glacier mass balance of hailuogou catchment which is located in the south eastern tibetan plateau and contains three debris covered and four debris free monsoonal maritime glaciers according to our calculations the glaciers in hailuogou catchment show a mean annual balance of 0 42 m water equivalent w e per year for a total mass loss of 24 3 m w e over the period 1952 2009 a comparison of summer temperature and precipitation mass balance equilibrium line altitude ela relations indicates that the glaciers in the catchment are much more sensitive to temperature change than to precipitation change in the last 20 yrs increasing summer temperature is the main cause of rapid wasting of the glacier mass in the catchment meanwhile the presence of supraglacial debris markedly accelerates glacier mass loss resulting in the unstable termini of debris covered glaciers in hailuogou catchment this highlights the importance of debris cover for understanding glacier mass balance and hydrology in the tibetan plateau

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

analysis of scaling methods in deriving future volume evolutions of valley glaciers volume area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea level rise we analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one dimensional ice flow model the model is calibrated for six glaciers nigardsbreen rhonegletscher south cascade glacier sofiyskiy glacier midre lovenbreen and abramov glacier volume evolutions forced by different hypothetical mass balance perturbations are compared with those obtained from volume area v a volume length v l and volume area length v a l scaling results show that the scaling methods mostly underestimate the volume losses predicted by the ice flow model up to 47 for v a scaling and up to 18 for v l scaling by the end of the 100 year simulation period in general v l scaling produces closer simulations of volume evolutions derived from the ice flow model suggesting that v l scaling may be a better approach for deriving volume projections than v a scaling sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants yielding both over and underestimates however when normalized by initial volume volume evolutions are relatively insensitive to the choice of scaling constants especially in the v l scaling the 100 year volume projections differ within 10 of initial volume when the v a scaling exponent commonly assumed 1 375 is varied by 30 to 45 0 95 2 00 and the v l scaling exponent q 2 2 is varied by 30 to 45 q 1 52 3 20 this is encouraging for the use of scaling methods in glacier volume projections particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

paleozoic granitic magmatism and tectonic evolution of the south altun block nw china constraints from zircon u pb dating and lu hf isotope geochemistry abstract the south altun orogenic belt saob consisting of the south altun block sab and the south altun continental block sacb is one of several important orogenic belts in nw china numerous granite bodies are widely distributed in the sab however the petrogenesis and tectonic environment of these granites and their relationships to those of the sacb central altun continental block cacb north altun block nab qilian block qlb and north qaidam block nqb remain unclear in this investigation we selected the sab granites for detailed study and explore the petrogenesis employing bulk rock geochemistry zircon u pb dating and hf isotopic analysis zircon u pb la icp ms dating of the granites from the sab identified seven spatially distinct paleozoic plutonic suites a yigan 352 343 ma b baiganhu 448 444 ma c west mangya 444 435 ma d aketishan 265 ma e chaishuigou 406 ma f changchungou 469 ma and g north mangya 462 ma based on previous research combined with our new u pb dating and bulk rock geochemical investigations in the sab we identdified six distinct episodes of granitoid emplacement episodes 1 and 2 quartz diorite granodiorite monzogranite with i type affinities and ages of 503 497 ma and 483 458 ma respectively episode 3 granodiorite monzogranite syenogranite with i and s type affinities and an age of 456 432 ma episode 4 monzogranite syenogranite alkali feldspar granite with a type affinities and an age of 424 385 ma episode 5 granodiorite monzogranite with s type affinities and an age of 352 338 ma and episode 6 quartz diorite monzogranite syenogranite with i type affinities and an age of 265 264 ma zircon lu hf isotope analyses from various episodes show that ehf t values are positive in most cases but negative for a small number of inherited xenocrystic zircons source rocks were mainly juvenile crust evidently mixed with minor ancient continental material based on our new results integrated with regional geological data we conclude that episodes 1 and 2 granitic magma generations were related to the subduction of oceanic crust episode 3 to post collisional partial melting episode 4 to the isostatic adjustment of orogenic blocks after plate suturing episode 5 to petrotectonic thickening of the altun crust and episode 6 to altun fault transcurrent slip attending kunlun paleo tethys subduction

the mafic layered complex of the kabye massif north togo and north benin evidence of a pan african granulitic continental arc root abstract between the predominantly neoarchean paleoproterozoic west african craton wac and the saharian metacraton smc the dahomeyides suture zone represents a valuable witness of continental amalgamation during pan african times in the kabye massif northern togo and northern benin mainly granulitic metagabbros associated with al rich kyanite and garnet bearing felsic dykes are exposed as tectonic lenses within the pre pan african gneisses of the smc new geochemical data suggest that the high grade rocks granulites in the kabye massif originated in a mature continental arc setting afc calculations constrain the amount of contamination of mantle wedge derived magmas by crustal metasediments to about 10 reconstruction of initial magmatic stratigraphy has been carried out using cipw norms for cumulitic sequences within the massif indicating a normal igneous polarity from west to east published geochemical signatures along the pan african suture zone of the dahomeyides in ghana togo and benin constrain the origin of mafic granulitic and eclogitic complexes a distinction is made between bodies with mainly morb signatures originated from the subducted wac plate passive margin and those with magmatic arc signatures originated from the over riding plate mantle wedge this suggests that the closure of the oceanic domain between the wac and the smc from 640 to 610 ma was mainly accommodated by oceanic subduction beneath the active continental margin before pan african collision

archaean crustal growth processes in southern west greenland and the southern superior province geodynamic and magmatic constraints abstract eo to mesoarchaean greenstone belts e g 3800 3700 ma isua c 3075 ma ivisaartoq 3071 ma qussuk occur within orthogneisses of the southern west greenland craton greenstone belts are composed mainly of metavolcanic rocks with minor ultramafic and sedimentary schists compositionally volcanic rocks are dominantly tholeiitic basalts boninites and picrites with minor intermediate to felsic volcanic rocks these greenstone belts appear to have formed in convergent margin geodynamic settings detailed field observations contrasting ages and metamorphic and structural histories suggest that this craton was assembled in several accretionary tectonothermal events involving accretion of arcs back arcs forearcs and continental fragments by horizontal tectonics the superior province of canada was also built by the amalgamation of oceanic and continental fragments ranging in age from 3700 to 2650 ma during five discrete tectonothermal events over 40 ma between 2720 and 2680 ma the neoarchaean 2750 2670 ma wawa greenstone belts are composed of tectonically juxtaposed fragments of oceanic plateaux oceanic island arcs back arcs and siliciclastic trench turbidites following juxtaposition these diverse lithologies were collectively intruded by syn to post kinematic granitoids with subduction zone geochemical signatures oceanic island arc lavas are easily distinguished from oceanic plateau counterparts because they possess positively fractionated rare earth element la sm cn 1 and gd yb cn 1 and high field strength element depleted nb th pm pm c 1000 km scale subduction accretion complex that formed along an intra oceanic convergent plate margin during trenchward migration of the magmatic arc axis several first order geological observations on archaean greenstone belts of sw greenland and the superior province suggest that phanerozoic style plate tectonic models can provide an elegant explanation for their structural lithological metamorphic and geochemical characteristics

mountain glaciers and ice caps around antarctica make a large sea level rise contribution the intergovernmental panel on climate change ipcc estimates that the sum of all contributions to sea level rise for the period 1961 2004 was 1 1 0 5 mm a 1 leaving 0 7

deceleration in the earth s oblateness 1 for over three decades satellite laser ranging slr has recorded the global nature of the long wavelength mass change within the earth system analysis of the most recent time series of 30 day slr based estimates of earth s dynamical oblateness characterized by the gravitational degree 2 zonal spherical harmonic j2 indicates that the long term variation of j2 appears to be more quadratic than linear in nature the superposition of a quadratic and an 18 6 year variation leads to the unknown decadal variation reported by cheng and tapley 2004 although the primary trend is expected to be linear due to global isostatic adjustment there is an evident deceleration j 2 18 1 10 13 yr2 in the rate of the decrease in j2 during the last few decades likely due to changes in the rate of the global mass redistribution from melting of the glaciers and ice sheets as well as mass changes in the atmosphere and ocean

the potential for sea level rise new estimates from glacier and ice cap area and volume distributions projections of sea level rise from mountain glaciers and ice caps for the next century and beyond should be based on an assessment of the ice available for melting projections to date are based on all regions except greenland and antarctica the latter are considered separately by the ipcc yet no sound estimates for the appropriate volume of ice and its potential for sea level rise are evident in the literature an ice cap data set is compiled allowing the separate treatment of glacier area coverage data glacier inventory data are comprehensive enough in some regions to allow the estimation of glacier size distributions the differences in the distributions are related to a metric of the regional topographic variability allowing glacier size distributions to be estimated on a 1 latitude longitude grid of cells containing glaciers appropriate volume area scaling for glaciers and for ice caps gives global estimates of glacier and ice cap volumes by size class this leads to an estimate of the total ice volume of 0 087 0 010 106 km3 and a sea level rise equivalent of 0 241 0 026 m the glaciers and ice caps contribute 41 and 59 to these estimates respectively these values are based on data sets compiled during several decades mainly in the second half of the 20th century we compare our results to published results that include the glaciers and icecaps at the margins of the greenland and antarctic ice sheets

neoarchean seafloor hydrothermal metamorphism of basalts in the zanhuang ophiolitic melange north china craton abstract epidosites are suggested to form in up flow zones located at the base of ore forming oceanic hydrothermal systems and are commonly preserved in ophiolitic sequences however occurrences of epidosites in archean tectonic melanges are rarely documented in this study we report the presence of late neoarchean epidosites in the zanhuang ophiolitic melange in the north china craton using meter scale litho structural and petrologic analysis zircon u pb dating major and trace element and oxygen and strontium isotopic geochemistry field studies show that the epidosites are mainly preserved as the cores of meta pillow lavas and are distributed as blocks in different matrices within the tectonic melange the pillow rims are used as protolith to estimate the element mobility during the alteration process the epidosites display strong depletion in na2o 0 01 0 27 wt mgo 0 43 3 01 wt depletion in large ion lithophile elements lile e g rb ba cs u and transition metals e g co sc cu ni zn and show enrichment of cao 13 35 21 0 wt sr and pb the high field strength elements hfse e g zr hf ta th of epidosites are varied but rare earth elements ree are unchanged the amphibolitic pillow rims are characterized by enrichment of lile flat heavy rare earth elements hree patterns and depletion in hfse with negative ti anomalies and positive pb and ba anomalies oxygen and strontium isotopic ratios of epidosites are 5 0 8 6 and 0 70284 0 70551 respectively both of which are greater than those of fresh basalts the major and trace elements oxygen and strontium isotopic values and extensive element migration indicate that the protolith was altered by a submarine hydrothermal system in the absence of continental influence magmatic zircons from two samples of epidosites yield 207pb 206pb ages of 2512 13 ma mswd 0 51 and 2542 13 ma mswd 1 4 confirming that the epidosites were generated at ca 2 51 2 54 ga based on geochemical data and field observations we suggest that the protolith of the epidosites formed in an arc related tectonic setting during the late neoarchean this study shows that hydrothermal activity operating in the late neoarchean was similar to that of the modern ocean floor

the geochemical nature of the igneous rocks of the sharbot lake domain central metasedimentary belt ontario two bimodal mafic silicic suites of igneous rocks the sharbot lake volcanic rocks and the lavant igneous complex are identified geochemically in the sharbot lake domain of the central metasedimentary belt in ontario and their genesis and thermotectonic environment are evaluated the sharbot lake volcanic rocks comprise a series of basalts characterized by light rare earth element lree depletion and relatively high concentrations of fe2o3 tio2 mno v and y together with rhyolites and silicic pyroclastic rocks they are intruded by rocks of the lavant igneous complex which comprises tholeiitic gabbros characterized by lree enrichment and low concentrations of fe2o3 tio2 mno v and y and granitoid rocks the trace element signatures of the mafic rocks of the sharbot lake volcanic sequences are most like those of back arc tholeiitic basalts and those of the lavant igneous complex are comparable to those of low k tholeiitic basalt suites the trace element signatures of the silicic rocks ass

early jurassic and late cretaceous granites in the tongka micro block central tibet implications for the evolution of the bangong nujiang ocean abstract the tongka micro block located in the eastern section of the bangong nujiang suture and characterized by mesozoic granitoids and high grade metamorphic rocks holds the key to the evolution of the bangong nujiang ocean bno here we present a systematic petrologic geochemical zircon u pb hf and whole rock sr nd pb isotopic investigation on six new granitoids in tongka the results suggest these granitoids yielded two stages of crystallization 171 177 ma and 74 ma and two stages of metamorphism 201 215 ma and 170 175 ma combined with the existing work within bns the magmatism along the bns can be divided into five stages stage 1 240 250 ma stage 2 200 230 ma stage 3 150 190 ma stage 4 100 135 ma and stage 5 73 100 ma both the early jurassic and late cretaceous tongka granitoids in this study are high k calc alkaline series with enrichments in large ion lithophile elements e g cs rb and k and depletions of large ion lithophile elements e g nb ta and ti the variable ehf t values 17 3 to 7 6 end t values 12 08 to 11 15 and ancient tdm2 1 48 2 00 ga for the early jurassic granitoids and weakly negative ehf t values 6 3 to 1 5 end t values 8 75 to 8 60 and old tdm2 ages 1 07 1 33 ga for the late cretaceous granitoids suggest that they are both mainly derived from the melting of ancient crust with minor mantle material input however the formation of the early jurassic and late cretaceous granitoids in tongka is related to different tectonic settings roll back after the tongka micro block subducted beneath the southern qiangtang subterrane and extension collapse after the tongka micro block collided with the northern lhasa subterrane the initial subduction of the bno may start from 190 ma and the collision between the lhasa and qiangtang terranes may continute to the latest cretaceous

a sand wave field in the entrance to bahia blanca estuary argentina abstract sand waves in the mouth of the bahia bllanca estuary show differences in wavelength crestlength and crest shape characteristics between two sectors of the field these differences may be explained by assuming that the residual ebboriented currents are stronger in the southern sector crest bifurcations on the centerline are suggestive of intermediate energy conditions and the development of secondary flows oblique to the main current direction the large lee slopes and the presence of megaripple fans are indicative of flow separation a condition seldom mentioned for subtidal sand waves boundaries of the sand wave field may be controlled by the thickness of the surficial sand layer rapid reduction of the water depth as produced by a large marginal shoal and variations in grain size an average migration rate of 33 m yr 1 was calculated from repeated bathymetric surveys assuming that sand waves preserve shape and size the established net sediment flux over the crests is 0 025 cm3 cm 1 s 1 current measurements made during four individual tidal cycles yielded a net bedload sediment transport of 0 048 cm3 cm 1 s 1

oldest lamproites from peninsular india track the onset of paleoproterozoic plume induced rifting and the birth of large igneous province abstract potassic and ultrapotassic magmatism from deep lithospheric sources in intra cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of large igneous provinces lips triggered by mantle plumes here we report for the first time precise zircon u pb age data from a suite of lamproites in the bastar craton of central india that mark the onset of paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major lip events during the precambrian evolution of the indian shield the lamproites from the nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile apatite and zircon the rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite geochemical features of the lamproites correlate with their counterparts in peninsular india and other similar suites elsewhere in the world related to rift settings and also indicate oib like magma source the associated syenite shows subduction related features possibly generated in a post collisional setting magmatic zircon grains with high th u ratios in the syenite from the nuapada lamproite form a coherent group with an upper intercept age of 2473 8 ma representing the timing of emplacement of the magma zircon grains in three lamproite samples yield four distinct age groups at ca 2 4 ga 2 2 ga 2 0 ga and 0 8 ga the 2 4 ga group corresponds to xenocrysts entrained from the syenite whereas the 2 2 ga group is considered to represent the timing of emplacement of the lamproites the ca 2 0 ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern bastar and the adjacent dharwar cratons a few young zircon grains in the syenite and lamproites show a range of early to middle neoproterozoic ages from 879 to 651 ma corresponding to younger thermal event s as also represented by granitic veins cutting across these rocks and extensive silicification zircon lu hf isotope data suggest magma derivation from a refertilized paleo mesoarchean sub continental lithospheric mantle or oib type sources the differences in hf isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale a combination of the features from geochemical and zircon hf isotope data is consistent with asthenosphere lithosphere interaction during the lamproite magma evolution the timing of lamproite emplacement in central india correlates with the global 2 2 ga record of lips we link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction accretion history prior to the neoarchean cratonization as well as the thermal blanket effect of the earth s oldest supercontinent pulsating plumes and continued rifting generated voluminous dyke swarms across the bastar and dharwar cratons forming part of a major global rifting and lip event

using glacier area ratio to quantify effects of melt water on runoff summary twenty four headwater catchments with varying glacier area ratios gars in the eastern and central tian shan mountains were simulated by the glacier enhanced soil and water assessment tool swat model from 1961 to 2007 the mean catchment gar ranges between 0 7 and 44 8 with a mean of 8 6 through synthetic analysis of the glacio hydrological processes simulation results of the catchments it was found that the gar is an effective index that can be used to interpret quantitatively the varying influences of glaciers on runoff across catchments among the twenty four catchments the ratio of glacier melt contribution rgmc to runoff varies between 3 5 and 67 5 with a mean of 24 0 the ratio of ice melt contribution rimc between 1 4 and 35 8 with a mean of 10 5 the ratio of ice melt in glacier melt between 33 4 and 59 1 with a mean of 43 4 the runoff coefficient rc between 0 24 and 0 90 with a mean of 0 52 and the coefficient of variation cv of runoff between 0 10 and 0 29 with a mean of 0 18 based on synthetic analysis it was found that 1 power functions fit the relations between rgmc rimc rc and cv and gar with high certainty 2 the cv decreases with increasing gar while others increase and 3 these power functions change sensitively with gar when gar is less than 10 implicating that a small change in gar may cause remarkable changes in rgmc rimc rc and cv in the less glacierized catchments

subduction related metasomatic mantle source in the eastern central asian orogenic belt evidence from amphibolites in the xilingol complex inner mongolia china abstract the central asian orogenic belt caob formed mainly in the paleozoic due to the closure of the paleo asian oceanic basins and accompanying prolonged accretion of pelagic sediments oceanic crust magmatic arcs and precambrian terranes the timing of subduction accretion processes and closure of the paleo asian ocean has long been controversial and is addressed in a geochemical and isotopic investigation of mafic rocks which can yield important insight into the geodynamics of subduction zone environments the xilingol complex located on the northern subduction accretion zone of the caob mainly comprises strongly deformed quartzo feldspathic gneisses with intercalated lenticular or quasi lamellar amphibolite bodies an integrated study of the petrology geochemistry and geochronology of a suite of amphibolites from the complex constrains the nature of the mantle source and the tectono metamorphic events in the belt the protoliths of these amphibolites are gabbros and gabbroic diorites that intruded at ca 340 321 ma with positive ehf t values ranging from 2 89 to 12 98 their t dm1 model ages range from 455 to 855 ma and peak at 617 ma suggesting that these mafic rocks are derived from a depleted continental lithospheric mantle the primitive magma was generated by variable degrees of partial melting of spinel bearing peridotites fractionation of olivine clinopyroxene and hornblende has played a dominant role during magma differentiation with little or no crustal contamination the mafic rocks are derived from a late neoproterozoic depleted mantle source that was subsequently enriched by melts affected by slab derived fluids and sediments or melts with a sedimentary source rock the carboniferous mafic rocks in the northern accretionary zone of the caob record a regional extensional event after the early paleozoic subduction of the paleo asian ocean both addition of mantle derived magmas and recycling of oceanic crust played key roles in significant late carboniferous ca 340 309 ma vertical crustal growth in the caob amphibolite facies metamorphism p 0 34 0 52 gpa t 675 708 c affected these mafic rocks in the xilingol complex at ca 306 296 ma which may be related to the crustal thickening by northward subduction of a forearc oceanic crust beneath the southern margin of the south mongolian microcontinent the final formation of the solonker zone may have lasted until ca 228 ma

eocene volcanism in the buck creek basin central british columbia canada transition from arc to extensional volcanism abstract the eocene buck creek volcanic complex central british columbia canada is a part of the challis kamloops volcanic province that extends from yukon across british columbia to the northern united states running approximately parallel to the margin of the north american continent the complex is associated with the formation of a fault bounded basin controlled by strike slip faults the volcanic rocks were emplaced during two short lived

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

late ediacaran 605 580 ma post collisional alkaline magmatism in the arabian nubian shield a case study of serbal ring shaped intrusion southern sinai egypt abstract the serbal pluton is a late neoproterozoic 605 580 ma post collisional a type granites in southern sinai egypt northernmost arabian nubian shield ans it is characterized by discontinuous ring shaped outcrops dislocated by later faulting the pluton intrudes late neoproterozoic metamorphic and high k calc alkaline rocks the serbal pluton mostly comprises an outer zone of alkali feldspar granite surrounding a core of peralkaline granite gradational and sharp contacts in the serbal granites suggest that they were emplaced with a very short time interval still before complete crystallization of the earlier batch serbal granites are highly evolved 75 98 78 52 wt sio2 and display the typical geochemical characteristics of post collisional a type granites namely high sio2 na2o k2o feo mgo ga al zr nb ga and y and low cao mgo ba and sr they are rich in ree and have extreme eu negative anomalies eu eu 0 01 0 23 the chemical characteristics indicate that the peralkaline granite shares many features of granites with the tetrad ree effect the serbal pluton evolved through fractional crystallization of a parental magma derived through partial melting of a juvenile crustal protolith that had been extracted from a source having mantle geochemical and isotopic characteristics the crystallization temperatures using fe ti oxides of the serbal granites point to their formation at high temperatures up to 650 850 c at a shallow depth of emplacement

global scale modeling of glacier mass balances for water resources assessments glacier mass changes between 1948 and 2006 abstract glaciers play an important role for freshwater resources but in global scale freshwater assessments their impact on river flows has not yet been taken into account as a first step we developed a global glacier model that can be coupled to global land surface and hydrological models with a spatial resolution of 0 5 by 0 5 the glacier model hyoga computes glacier mass balance by a simple degree day approach for 50 m sub grid elevation bands modeling all glaciers within a grid cell as one glacier the model is tuned individually for each grid cell against observed glacier mass balance data hyoga is able to compute glacier mass balances reasonably well even those of summer accumulation type glaciers still model uncertainty is high which is among other reasons due to the uncertainty of global data sets of temperature and precipitation which do not represent well the climatic situation at glacier sites we developed a 59 yr 1948 2006 time series of global glacier mass balance and glacier area by driving hyoga with daily near surface atmospheric data according to our computations most glaciers have lost mass during the study period compared to estimates derived from a rather small number of observed glacier mass balances hyoga computes larger glacier mass losses in asia europe canadian arctic islands and svalbard in accordance with the estimates average annual mass losses have increased strongly after 1990 as compared to the 30 yrs before the sea level equivalent of the melt water from glaciers is 0 76 mm yr water equivalent after 1990 as compared to only 0 34 mm yr water equivalent before we computed an acceleration of glacier mass losses after 1990 for all world regions except south america where the number of gauge observations of precipitation is very small after 1980

geochemistry of anorthositic differentiated sills in the archean 2970 ma fiskenaesset complex sw greenland implications for parental magma compositions geodynamic setting and secular heat flow in arcs abstract the fiskenaesset complex sw greenland is one of the best preserved layered archean intrusions in the world consisting of an association of ca 550 meter thick anorthosite leucogabbro gabbro and ultramafic rocks dunite peridotite pyroxenite and hornblendite despite poly phase deformation and amphibolite to granulite facies metamorphism primary cumulate textures and igneous layering are well preserved in the complex this study reports new major and trace element data for three variably thick 1 to 5 m differentiated dunite through peridotite pyroxenite gabbro leucogabbro to anorthosite sequences sequences 1 2 and 3 in the sinarssuk area of the fiskenaesset region on several variation diagrams samples from these sequences plot along a well defined liquid line of descent consistent with in situ fractional crystallization the average chemical compositions of these sequences are used to constrain their approximate parental magma compositions petrographic observations and geochemical data suggest that sequences 2 and 3 solidified from evolved magmas that underwent olivine fractionation prior to their intrusion in contrast sequence 1 appears to have been derived from a near primary parental magma sio2 43 wt mgo 20 wt al2o3 16 wt cao 9 3 wt ni 840 ppm mg number 80 the trace element patterns of this parental magma are comparable to those of phanerozoic boninites consistent with a supra subduction zone geodynamic setting if the relative thickness of ultramafic layers the sum of dunite peridotite and pyroxenite layers in differentiated sequences is taken as an analog for the original complex emplaced into archean oceanic crust the fiskenaesset complex might have had a minimum thickness of 1000 m with a 500 m thick ultramafic unit at the bottom the thickness of the ultramafic unit in the preserved complex is less than 50 m suggesting that more than 90 of the original ultramafic unit was either delaminated and recycled back into the mantle as a residual cumulate or was destroyed during thrusting and ttg intrusion both the fiskenaesset complex and associated tholeiitic basalts display similar th nb lree patterns and plot along the same differentiation trend on zr versus incompatible trace element diagrams suggesting a possible petrogenetic link between the two suites of rocks however basalts do not display the same differentiation trend as the complex on several major and trace element diagrams in addition basalts and parental magma to the complex do not plot along the same fractionation line on al2o3 tio2 versus incompatible trace element diagrams implying that the fiskenaesset layered intrusive rocks were not derived from tholeiitic basalts through fractional crystallization as previously thought accordingly we infer that the fiskenaesset complex and spatially associated basalts were derived from different mantle sources parental magmas to the fiskenaesset complex originated from a mantle source that was metasomatized by highly aluminous slab derived melts layered anorthosite complexes are mostly restricted to the archean and typically associated with tonalite trondhjemite granodiorite ttg gneisses the petrogenesis of both suites appears to have been controlled mainly by slab melting endorsing independent evidence for a secular change from slab dominated melting to wedge dominated melting in arc magmatism at the end of the archean reflecting higher geothermal gradients in archean arcs than post archean counterparts