rise in frequency of surface melting at siple dome through the holocene evidence for increasing marine influence on the climate of west antarctica 1 a new melt layer history from siple dome west antarctica indicates notable late holocene summertime warming visual stratigraphic analyses of the 1004 m ice core identified 62 years with melt layers melting events began around 11 7 ka followed by a period of no melting from 8 8 6 6 ka melt layer frequency increased from 6 6 ka to the present with the 1000 year average melt layer frequency reaching a maximum of 2 at 0 8 ka we use our millennial scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in west antarctic holocene summer climate our calibration suggests the change in melt frequency from 0 to 2 may represent a summer temperature increase of 2 c from the middle to late holocene this temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to east antarctic climate records which show peak warmth in the early holocene followed by stable or decreasing temperature we interpret the rise in melt frequency as evidence of an increasing marine influence on the ross sea sector of west antarctica although the surface elevation of siple dome has not changed greatly the continued lateral retreat of the west antarctic ice sheet from its last glacial maximum configuration across the outer continental shelf and the delayed drawdown in ice thickness from the adjacent coastal marie byrd land region in conjunction with periods of increased cyclogenesis perhaps related to variations in enso would allow a moderated maritime climate to more easily reach west antarctica

densification of polar snow measurements modeling and implications for altimetry density profiles in the upper 10 14 m of snow have been measured along a 500 km traverse across the greenland ice sheet using a neutron scattering technique repeat measurements over periods ranging from a few days to 5 years allow strain rates to be determined as a function of depth very large strain rates are observed in the surface layer of snow over summer periods in the underlying multiyear snow strain rate decreases with decreasing porosity however once this effect has been removed the effect of increasing overburden pressure is counteracted by increasing strength of the material there are fluctuations in strain rate associated with the annual layering which indicate that winter and summer snow have different strengths based on these observations we derive a new densification equation which includes the effect of snow density and snow type and the effect of temperature described by an arrhenius expression with activation energy of the order of 110 kj mol 1 and an exponential prefactor determined simply by the temperature history of the snow for multiyear snow and meteorological conditions that do not vary from year to year our equation reduces to a form similar to the herron and langway equation for first stage densification using the new equation we calculate the sensitivity of compaction rate to short term fluctuations in temperature and accumulation as 0 11 0 20 m a 1 k 1 and 0 33 0 95 m a 1 meters water equivalent 1 respectively and discuss the consequent uncertainty in satellite measurements of the long term elevation trend in this area of the greenland ice sheet

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

geochronological and geochemical constraints on aolunhua porphyry mo cu deposit northeast china and its tectonic significance abstract the aolunhua porphyry mo cu deposit is located in the northern margin of the north china craton ncc and belongs to the northern part of the xilamulun metallogenic belt more than 90 of the mineralization occurs within the aolunhua monzogranite porphyry a small part is hosted within quartz veins that crosscut late permian strata the syenogranite occurring as dikes and cutting through the aolunhua monzogranite porphyry is radially distributed in the mining district zircon u pb ages show that the aolunhua monzogranite porphyry and the post ore syenogranite have concordant 206pb 238u ages of 138 7 1 2 ma and 131 4 2 8 ma respectively based on analyses of major trace elements and hf isotopes the aolunhua porphyry is characterized by high sr low y with high la yb and sr y ratios typical of adakitic granites whereas the post ore syenogranite has lower sr and higher y values showing apparently negative eu anomalies eu 0 26 to 0 31 the hf isotopic composition of the aolunhua porphyry ehf t 3 6 to 9 2 and the post ore syenogranite ehf t 3 6 to 8 7 indicates that both juvenile crustal sources and depleted mantle contributed to their origin the regional geological setting together with the discrepancy of geochemistry between the aolunhua porphyry and the post ore syenogranite probably indicates that they formed in different tectonic regimes the aolunhua porphyry is derived from partial melting of the thickened crust due to underplating of the basaltic magma under the transformation tectonic regime while the post ore syenogranite comes from the crustal root melting during the lithospheric delamination stage under the lithosphere thinning regime of northeast china

depletion of light rare earth elements in felsic magmas contrary to simple generalizations about their behavior light rare earth elements lree do not act as incompatible elements in very felsic magmas in fact lree concentrations typically decrease often drastically during differentiation of such magmas the simplest explanation for this depletion involves the separation of minute easily overlooked quantities of an extremely lree rich accessory mineral either monazite or allanite our data indicate that felsic liquids with 50 ppm lree may be saturated in either of these accessories and that the concentration required for saturation decreases in increasingly felsic liquids this accounts for incompatible behavior of lree even at high concentrations in mafic magmas in contrast to compatible behavior at low concentrations in felsic magmas partitioning of lree into solid rather than liquid has important implications for trace element and nd isotope modeling of crustal anatexis as well as for magma differentiation

assessing a multilayered dynamic firn compaction model for greenland with asiras radar measurements a method to assess firn compaction using data collected with the airborne sar synthetic aperture radar interferometric radar altimeter system asiras is developed for this we develop a dynamical firn compaction model that includes meltwater retention based on the asiras data which show internal layers as annual horizons in the uppermost firn the method relies on inferring the age depth internal layers information from the radar data using a monte carlo inversion technique to tune in parallel both the firn model and the atmospheric forcing parameters temperature and accumulation the model is validated against two firn cores and it is shown that applying both firn densities and age depth information for the inversion gives the most accurate understanding of model biases the method is then applied to a 67 km section of the egig line forced by atmospheric output from a regional climate model using only age depth information in the inversion step the layers traced by the asiras data are modeled with a root mean square error of 9 cm which is within the estimated error of the layer tracing this gives us confidence in applying observed annual layering from firn radar data to assess firn compaction however the study also indicates that our firn model tuning parameters are site dependent and cannot be parameterized by temperature and accumulation alone

chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

greenland snow accumulation estimates from satellite radar scatterometer data data collected by the c band ers 2 wind scatterometer escat the ku band adeos 1 nasa scatterometer nscat and the ku band seawinds on quikscat qscat satellite instruments are used to illustrate spatiotemporal variability in snow accumulation on the greenland ice sheet microwave radar backscatter images of greenland are derived using the scatterometer image reconstruction sir method at 3 day intervals over the periods 1991 1998 and 1996 1997 for escat and nscat respectively the backscatter coefficient normalized to 40 incidence a and gradient in backscatter b in the range 20 60 are compared with historical snow accumulation data and recent measurements made in the program for arctic regional climate assessment parca shallow snow pits empirical relationships derived from these comparisons reveal different exponential relationships between c and ku band a values and dry snow zone mean annual accumulation q frequency difference images between overlapping scatterometer images suggest that c band data are more sensitive to snow layering and buried inhomogeneities whereas ku band data are more sensitive to volume scattering from recently accumulated snow direct comparisons between nscat b values and in situ q measurements show a linear relationship between ln q and b with a negative rank correlation of r 0 8 the root mean square residual in fitting regression line equation ln q 3 08 17 83b to the data is 0 05 m snow water equivalent this simple ku band empirical relationship is exploited to investigate decadal changes in dry snow zone accumulation between seasat 1978 and nscat 1996 additional comparisons between nscat and recent qscat 1999 data reveal significant upslope shifts in the dry snow line along the southwestern flank of the ice sheet recent acceleration in the increase in intensity of scattering is observed in the percolation zone suggesting increased melting between 2000 and 3000 m elevation in the southern half of the ice sheet

spatial and temporal variability in the snowpack of a high arctic ice cap implications for mass change measurements interpretation of ice mass elevation changes observed by satellite altimetry demands quantification of the proportion of elevation change which is attributable to variations in firn densification detailed stratigraphic logging of snowpack structure and density was carried out at 1k m intervals along a 47 km transect on devon ice cap canada in spring pre melt and autumn during after melt 2004 and 2006 to characterize seasonal snowpack variability across the full range of snow facies simultaneous meteorological measurements were gathered spring pre melt snowpacks show low variability over large spatial scales with low magnitude changes in density the end of summer autumn density profiles show high variability in both 2004 and 2006 with vastly different melt regimes generating dissimilar patterns of ice layer formation over the two melt seasons dye tracing experiments from spring to autumn 2006 reveal that vertical and horizontal distribution of meltwater flow within and below the annual snowpack is strongly affected by the pre existing often subtle stratigraphic interfaces in the snowpack rather than its bulk properties strong interannual variability suggests that using a simple relationship between air temperature elevation and snowpack densification to derive mass change from measurements of elevation change across high arctic ice caps may be misguided melt timing and duration are important extrinsic factors governing snowpack densification and ice layer formation in summer rather than averaged air temperatures

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

ore lead and sulphur isotope pattern from the low temperature veins of the catalonian coastal ranges ne spain the lead isotopic composition of galenas from low temperature veins of the catalonian coastal ranges ne spain displays a small but distinct range of values 18 318 206pb 204pb 18 678 15 678 207pb 204pb 15 767 and 38 534 208pb 204pb 39 189 the data define a linear trend in the 208pb 204pb versus 206pb 204pb diagram that can be interpreted in terms of mixing of lead from different reservoirs the lead appears to be derived from a solution that preferentially leached granites of late hercynian age sulphur isotopic compositions of the galenas range from 8 5 to 7 3 but variations in a single deposit are small 1 2 pointing to different sources of sulphur in a 34s versus 206pb 204pb plot no clear correlation trends appear lead isotope data from deposits of similar characteristics situated within the hercynian orogenic belt as the linares la carolina district s spain and the inglesiente sulcis area sardinia show slight differences indicating a source area of similar lead isotopic composition in the ccr and linares la carolina districts the main source of lead is related to the hercynian granites of each area although small contributions from metasediments cannot be ruled out the contribution of lead from metasedimentary rocks is particularly seen in the sardinian hercynian vein type ores

mineralogical and geochemical evidence of weathering in a middle to late pleistocene paleosol sequence in the driftless area of wisconsin paleosols occur in the driftless area of southwestern wisconsin because this area escaped direct pleistocene glaciation allowing long term loess and colluvium accumulation in selected settings the most complete known depositional sequence at oil city wisconsin contains eight lithologic units with five paleosols all with normal remanent magnetism i e 2 cao zr sr and rb sr generally align with the pedological evidence of weathering mineral ratios plagioclase quartz and k feldspar quartz display greater scatter and less certainty in interpretation the paleosols with bt horizons have ratios indicating greater weathering than the modern soil the most weathered paleosol is formed in the unnamed fourth loess unit stratigraphically below the loveland member the stratigraphic position and higher degree of weathering support correlation of the fourth loess with the yarmouth geosol and crowley s ridge silt of the middle mississippi valley geochemical indices by pxrf are more consistent with established lithologic breaks than mineralogy by xrd our results support the use of pxrf for stratigraphic and weathering studies of quaternary sediments

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

geochemistry and sr nd pb hf isotopes of early cretaceous basalts from the great xinggan range ne china implications for their origin and mantle source characteristics abstract late mesozoic volcanism is widespread throughout northeastern china mainly clustering in the great xinggan range where the major period of volcanic eruption was during the early cretaceous the spatial distribution of volcanic rocks shows a nne extending pattern the lithology of mesozoic basaltic rocks in the great xinggan range ranges from trachytic basalts basalts to basaltic andesites on the basis of lithological associations and spatial relationships we divide the basalts into four groups i e tahe genhe zalute and xiwu the early cretaceous volcanism in the great xinggan range is characterized by significant large ion lithophile elements lile and light rare earth elements lree enrichment and high field strength elements hfse depletion with a slightly enriched to depleted nd hf and weakly enriched sr isotopic compositions initial 87sr 86sr 0 7046 0 7079 end t 3 6 to 6 9 and ehf t 8 9 to 4 6 the pb isotopic compositions are also variable with 206pb 204pb 207pb 204pb and 208pb 204pb values of 17 791 18 530 15 477 15 597 and 37 761 38 497 respectively the sr nd pb hf isotopic data indicate that the magmatic sources are heterogeneous showing an enriched to depleted signature of continental lithospheric mantle the magmatic sources of the genhe and zalute groups are characterized by mixing among pm em ii and dm whereas the tahe and xiwu groups derive from enriched lithospheric mantle that had experienced metasomatism by fluids or melts from subducted paleo asian and mongol okhotsk ocean slabs and possible influence of precambrian blocks the late mesozoic volcanic rocks in the great xinggan range resemble those of the cenozoic calc alkaline magmatism in the basin and range province of the united states we therefore suggest that the widespread mesozoic volcanic rocks in the great xinggan range were generated in an extensional tectonic setting

warming glacier melt and surface energy budget from weather station observations in the melville bay region of northwest greenland the glaciers in the melville bay region of northwest greenland have shown a mean retreat since the earliest observations at the beginning of the 20th century the largest steenstrup gletscher has retreated 20 km partly during the period of atmospheric cooling 1940 80 melville bay air temperature observations starting in 1981 indicate a regional change of 0 208 ca 1 this exceeds the warming on the east coast of greenland confirming the west coast to be a region of relatively large change also in a global perspective the largest temperature increase is observed in the winter months 0 3 0 48 ca 1 results from a 4 year 2004 08 net ablation record obtained by an automatic weather station aws near the calving front of steenstrup gletscher show an ablation rate that is relatively low for a low elevation position on the greenland ice sheet 2 4 m ice equivalent per year a first order estimate from positive degree day totals suggests that net ablation has roughly doubled since the 1980s a surface energy and mass balance model is applied to the steenstrup aws data to quantify the energy flux contributions to surface melt solar radiation is the main source for melt energy but due to shortwave radiation penetration into the ice only one third of the melt takes place at the glacier surface nearly two thirds occurs within the upper ice layers

evolution of the lower gangetic plain landforms and soils in west bengal india abstract three major landforms uplands old fluvial deltaic plains and young fluvial plains are identified from the lower gangetic plains of west bengal india on the basis of remote sensing and field studies morphologic quantitative and thermoluminescence studies of soils of the study area have been conducted two types of uplands are recognised upland in the west overlain by red soils autochthonous and allochthonous types and upland in the north barind tract characterised by three topographic levels aspects of the autochthonous upland red soils lower to middle pleistocene age show the ferrugination ferrisol phase of development soils of the old fluvial deltaic plains 6 3 ka and lower level of the barind tract have argillic horizons and exhibit the fersiallitisation phase of development development of ferrugination and fersiallitisation phases was favored due to the pre weathered nature of the parent material soils of the old fluvial deltaic plains barind tract lower level and young fluvial plains show effects of hydromorphism due to waterlogging in the form of segregations of fe mn oxides gleying and chloritisation probably due to ferrolysis in the upper horizons of some of these soils neotectonics seems to have affected development of landforms and soils significantly due to reactivation of some basement faults in the western region some tectonic blocks subsided causing transgression during the early pleistocene and at ca 7 ka subsequent uplift of these blocks caused regressions and development of soils on the exposed landscapes episodic uplift of the barind tract in the northern region may have given rise to three topographic levels some faults confine the courses of the damodar ganga and bhagirathi rivers

penny ice cap cores baffin island canada and the wisconsinan foxe dome connection two states of hudson bay ice cover ice cores from penny ice cap baffin island canada provide continuous holocene records of oxygen isotopic composition 18 o proxy for temperature and atmospheric impurities a time scale was established with the use of altered seasonal variations some volcanic horizons and the age for the end of the wisconsin ice age determined from the grip and gisp2 ice cores there is pre holocene ice near the bed the change in 18 o since the last glacial maximum lgm is at least 12 5 per mil compared with an expected value of 7 per mil suggesting that lgm ice originated at the much higher elevations of the then existing foxe dome and foxe ridge of the laurentide ice sheet the lgm 18 o values suggest thick ice frozen to the bed of hudson bay

geochronology and isotopic geochemistry of the a type granites from the huanggang sn fe deposit southern great hinggan range ne china implication for their origin and tectonic setting abstract the huanggang sn fe deposit inner mongolia is located in southern great hinggan range metallogenic belt la icp ms zircon u pb dating show that the k feldspar granite and granite porphyry in the huanggang mine were formed at 136 7 1 1 ma and 136 8 0 57 ma respectively sr nd pb isotope of the rocks and in situ zircon hf isotopic systematics show that 87 sr 86 sr i values range from 0 70211 to 0 70729 close to the 87 sr 86 sr i of oceanic basalts and lower than those of continental crust the e nd t values and nd model ages t dm vary from 0 8 to 0 9 and 855 to 993 ma respectively the pb isotopic compositions are also variable with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb values of 18 974 26 107 15 554 15 914 and 38 894 39 890 respectively suggesting that the lead is derived from a mixed source the 176 hf 177 hf values range from 0 282744 to 0 282922 with corresponding e hf t values ranging from 1 9 to 18 3 and two stage hf model ages t dm2 of between 561 and 888 ma the isotope composition shows that huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle perhaps contaminated by small amounts of ancient continental crust younger nd hf isotope model ages imply that an important crustal growth event took place in this area during the neoproterozoic integrating our data with previously published results and the late mesozoic regional tectonic setting we conclude that the huanggang granites were generated in an intraplate tectonic magmatic setting asthenospheric mantle upwelling due to lithospheric delamination and magma underplating caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle this resulted in remelting differentiation and a continued evolution of the mafic juvenile crust producing a large quantity of granitic magma the tectonic setting for these processes may be linked to the nnw subduction of the pacific plate izanagi in the mesozoic which affected most of eastern china

paleozoic crustal growth and metallogeny of central asia evidence from magmatic hydrothermal ore systems of central kazakhstan abstract the ore deposit spectrum of central kazakhstan reflects a range of lithospheric magmatism controlled by the polycyclic geodynamic evolution of an active continental margin which develops from back arc oceanic settings volcanic hosted massive sulphide cu au ore deposits to subduction controlled calcalkaline magmatism copper porphyries with subsequent stages of crust differentiation of low degree partial melting and extended intramagmatic fractionation molybdenum porphyries on to continental rifting peralkaline ree zr nb rich systems mesothermal gold deposits mark transcrustal shear zone controlled fluid conduits formed during arc slicing and thermal relaxation in a post orogenic setting the ore deposits characterize successive and spatially overlapping stages of crustal growth and consolidation the general subduction setting of this range of ore deposits is reflected by calc alkaline trends in the associated subalkaline high k felsic rocks with a wide range in silica contents the predominant metal spectrum of au cu and mo indicates relatively oxidized magmatic hydrothermal systems in accordance with the metaluminous i type nature of their igneous host rocks i e oxidized igneous precursor material despite of presumably highly variable ratios of mantle crust components in individual magmatic systems gabbros to leucogranites most rocks have very similar positive initial e nd values of 0 to 5 5 and depleted mantle model ages in the range of 500 800 ma the ubiquitous relatively young mantle extraction age is likely to characterize the lower crust of central kazakhstan this basement is interpreted as back arc oceanic crust that formed behind oceanwards drifting continental margin slivers during the initial stages of the active continental margin evolution of the late precambrian angara baltica supercontinent the early back arc oceanic crust was transformed into the present lower crust during the paleozoic orogenic evolution in which the back arc crust was buried by magmatic arc and sedimentary material and recurrently affected by high grade metamorphism basaltic melt injection underplating and granitic melt extraction anorogenic rift related permian peralkaline riebeckite granites with ree zr nb mineralization have very high positive e nd of 5 to 8 which is probably inherited from young subcrustal lithosphere at the mantle crust boundary that was affected by partial remelting due to asthenospheric upwelling during rifting

formation of the giant chalukou porphyry mo deposit in northern great xing an range ne china partial melting of the juvenile lower crust in intra plate extensional environment abstract the chalukou porphyry mo deposit 2 46 mt 0 087 mo located in the northern great xing an range ne china is the largest mo deposit discovered in china so far the host rocks consist of aplite porphyry granite porphyry and quartz porphyry and are intruded into lower ordovician intermediate felsic volcanic sedimentary rocks and pre ore monzogranite and are cut by post ore feldspar porphyry diorite porphyry and quartz monzonite porphyry here we present the zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data for the pre ore syn ore and post ore intrusive rocks the chalukou ore forming porphyries intruded during 147 148 ma and have high silica alkali rich metaluminous to slightly peraluminous compositions and are oxidized they are enriched in large ion lithophile elements e g k rb u and th light ree and depleted in high field strength elements e g nb p and ti depletions in eu ba sr nb ta p and ti suggest that they have experienced strong fractional crystallization of plagioclase biotite hornblende and accessory minerals the pre ore monzogranite 172 ma also belongs to the high k calc alkaline series highly fractionated ree patterns la yb n 19 6 21 7 high values of sr y 54 69 and la yb 29 32 are adakite like geochemical features the post ore rocks 141 128 ma have similar geochemical characteristics with ore forming porphyries except that quartz monzonite porphyry shows no ba sr negative anomaly all intrusive rocks have relative low initial 87sr 86sr 0 705413 0 707889 and end t values 1 28 to 0 92 positive ehf t values 2 4 to 10 1 and young two stage nd and hf model ages tdm2 nd 863 977 ma tdm2 hf 552 976 ma these geochemical and isotopic data are interpreted to demonstrate that the ore forming porphyries formed by partial melting of the juvenile lower crust caused by underplating of mafic magmas in an intra plate extensional setting the pre ore monzogranite formed by partial melting of thickened lower crust in a collisional setting caused by closure of mongol okhotsk ocean the post ore feldspar porphyry shares a similar magma source with ore forming porphyry but the quartz monzonite porphyry has a relatively deeper magma source region and has not experienced as much fractional crystallization the transformation from middle jurassic compression to late jurassic extension created favorable conditions for the generation and emplacement of the ore forming magma the juvenile lower crust provided the main source of molybdenum for chalukou deposit enrichment of mo by fractional crystallization played an important role in concentrating mo during formation of the chalukou mo deposit the age 147 ma high fluorine and associated pb zn deposits are all different from other major porphyry mo deposits in ne china chalukou is a new mineral deposit type in the great xing an range

local to regional scale variability of annual net accumulation on the greenland ice sheet from parca cores a suite of spatially distributed cores collected under the program for arctic regional climate assessment parca provides an unprecedented opportunity to assess local to regional variability of annual accumulation rates over the greenland ice sheet parca cores are unique in their broad spatial distribution and accurate dating of annual layers using multiple seasonally varying indicators the core data provide 1 a more rigorous evaluation of spatial and temporal variations in accumulation rates 2 critical input to ice sheet mass balance estimates 3 ground truth measurements for satellite observations and climate model based precipitation estimates and 4 important constraints on paleoclimatic interpretations from ice cores multiple closely spaced cores demonstrate that signals of high frequency annual to possibly decadal scale climate variability preserved in the ice sheet are partially masked by glaciological noise two 350 year accumulation histories one from northwest greenland and one from the summit area reveal significant multidecadal variability the regional trends show long periods 60 90 years of strong positive correlation and an equally long period of strong negative correlation since 1940 the trends have been decoupled this spatial variability reflects the strong modulation of greenland precipitation and the climate information it contains by changes in north atlantic atmospheric circulation patterns proxy records from the parca cores document that climate reconstructions from a single core must be interpreted cautiously with application of appropriate filters to reduce local noise and careful extrapolations from local to regional scales richer more robust ice core derived data sets should result from combining multiple more widely spaced cores to produce regional stacked records

signal and noise in four ice core records from the agassiz ice cap ellesmere island canada details of the last millennium for stable isotopes melt and solid conductivity four ice cores and two deep pit auger sequences from the top of the agassiz ice cap have been variously analysed for o18 ecm solid conductivity and ice melt layer stratigraphy the high resolution data are presented on time scales covering about the last 1000 years the 8 time series are compared and the noise examined in terms of snow drifting and wind scouring of winter snow from the higher exposed parts of flow lines the highly scoured 8 records reflect a mixture of summer biased conditions and the amount of winter scoured snow sites away from the ridges and domes are not scoured the signal part of the scoured and unscoured sites is obtained by stacking averaging normalized series the stacked unscoured series of 8 and accumulation are compared to similar stacked series from central greenland for the last century of annual averages the comparison is surprisingly good suggesting that at these resolutions low noise 8 series have some coherence over fairly large distances the percentage melt

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

utilizing portable x ray fluorescence spectrometry for in field investigation of pedogenesis abstract in recent years portable x ray fluorescence pxrf spectrometers have been recognised as an in field tool for soil analyses as they offer rapid real time simultaneous multi element analysis of soil samples with no or minimal sample preparation portable xrf has been used quite extensively to estimate the degree of soil contamination with heavy metals and to measure the concentration of elements in soils that are important for the soil s fertility but more recently it has also been used to calibrate for a range of soil chemical and physical properties to perform digital soil morphometrics however this still relatively new technology also offers an opportunity for soil scientists to investigate processes of pedogenesis in the field which in turn will complement the in field descriptions of soils profoundly here we employed a handheld pxrf spectrometer to investigate the pedogenesis pathways and likely parent materials of three different soil types utilizing elemental concentration data and geochemical indices our study site a property called nowley is situated on the liverpool plains in the spring ridge district on the north west slopes of new south wales australia in one of the most versatile dryland cropping regions of the continent the variation in soil types and parent materials across the property offers an unique opportunity to study the impact of parent materials and topography on soil formation a total of three soil pits were excavated to a depth of 1 0 m to expose the lower b horizons soil pit faces were then scanned at 0 1 m depth increments starting from the top of the soil profile to the lowest b horizon exposed our results show that elemental data acquired in field condition which are affected by sample heterogeneities and soil moisture content are comparable to elemental data acquired in air dried ground condition as geochemical index values show similar trends down the soil profile we found that the use of pxrf is a very effective in field tool to assess pedogenic pathways and parent material origin because of the instant computation of weathering indices and elemental ratios we conclude that pxrf can be applied successfully and readily to study the soil s weathering history and identify processes of soil formation in the field

interannual variability of elevation on the greenland ice sheet effects of firn densification and establishment of a multi century benchmark in order to interpret measurements of ice sheet surface elevation changes in terms of climatic or dynamic trends it is necessary to establish the range of stochastic variability of elevation changes resulting from interannual fluctuations of accumulation rate and firn density the analyses presented here are intended to facilitate such interpretations by defining benchmarks that characterize elevation change variability in central greenland in the current climate and over the past millennium we use a time dependent firn densification model coupled to an ice and heat flow model forced by annual accumulation rate and temperature reconstructions from the greenland ice sheet project ii gisp2 ice core to examine the elevation changes resulting from this climatic forcing from these results effective firn densities are calculated these are factors that convert water equivalent accumulation rate variability to surface elevation variability a current climate benchmark is defined by applying this conversion to van derveen and bolzan s water equivalent statistics and to a 50 year accumulation variability estimate from the gisp2 core elevation change statistics are compiled for the past millennium to define longer term benchmarks which show that multi century variability has been substantially larger than current variability estimated by van der veen and bolzan it is estimated here that the standard deviation of net elevation change over 5 and 10 year intervals has been 0 27 and 0 38 m respectively an approximate method for applying these quantitative results to other dry snow sites in greenland is suggested

towards digital soil morphometrics article i nfo article history digital soil morphometrics is defined as the application of tools and techniques for measuring and quantifying soil profile attributes and deriving continuous depth functions this paper reviews how proximal soil sensing and other tools can be used in soil profile descriptions where techniques and toolkits have not changed in the past decades the application of such tools is compared to standard soil profile descriptions for 11 common attri butes horizons texture color structure moisture mottles consistence carbonates rock fragments pores and roots these attributes are extensively used in soil classification and are indicative of many soil functions there has been progress in distinguishing soil horizons texture and soil color mainly using vis nir gpr and electrical resistivity there is potential for in situ digital morphometrics for all attributes of a soil profile smaller depth increments can be sampled and analyzed and that gives continuous depth functions of soil properties the com bined use of in situ digital morphometrics and continuous depth functions of soil properties may enhance our pedological understanding it will take time before the toolbox of the field pedologists will be digitally enriched but we think that digital soil morphometrics has the potential to complement existing description and analytical methods it may yield new insights in soil horizonation how soils form and how they could be classified published by elsevier b v

the treatment of meltwater retention in mass balance parameterisations of the greenland ice sheet retention of melt water runoff by percolation and or refreezing in the snowpack cannot be neglected when studying the surface mass balance of the greenlandice sheet in this paper we make a detailed comparison of several treatments proposed in the literature to account for this process in large scale mass balanceparameterizations the melt on the greenland ice sheet is calculated with a revised degree day model using updated datasets of surface elevation and precipitationrate on a 5 km grid crucial model parameters are recalibrated by comparing mass balance characteristics with available observations on a regional basis wediscuss the role of meltwater retention in the light of the overall mass balance of the greenland ice sheet and its sensitivity to climatic change and displaypatterns of effective retention fractions for the various methods as a main conclusion it appears that overall results are quite similar for the various models butthat meltwater retention has a large spatial variation not described by the simple treatments using the most comprehensive retention model the sensitivity of therunoff is found to be 0 35 mm deg c of sea level change per year we also present a new map of the different zones facies that characterize the accumulationarea of the greenland ice sheet that is useful for interpreting field data and calibrating satellite observations

early cretaceous highly fractionated i type granites from the northern tengchong block western yunnan sw china petrogenesis and tectonic implications abstract western yunnan an important constituent of the southeastern segment of the east tethyan tectonic domain lies along a transformed orientation from the nww trending himalayan tethyan segment to the northerly trending southeast asian segment however the geodynamical setting of the early cretaceous tectonothermal magmatism along the bangong nujiang lushui luxi ruili belt as the tethyan branch in western yunnan sw china remains controversial the donghe granitoid which is located between the gaoligong and tengliang belts in the northern tengchong block reveals its petrogenesis and its tectonics both of which play a vital role in resolving previous disputes our zircon laser ablation inductively coupled plasma mass spectrometry u pb dating of granites from the donghe batholith yields ages of 119 9 0 9 130 6 2 5 ma these granites display features typical of highly fractionated i type granites high sio 2 contents 71 wt high k contents k 2 o 3 88 5 66 wt calc alkaline character slight peraluminosity a cnk 1 02 1 16 and a highly differentiated index ranging from 83 6 to 95 6 in addition as sio 2 contents increase the rare earth element ree abundances especially heavy ree abundances and ree pattern slopes change gradually but the negative eu anomalies increase sharply while the degree of enrichment in rb th u and pb and depletion in ba nb sr p and ti are enhanced these features indicate that k feldspar plagioclase biotite amphibole apatite sphene garnet and fe ti oxides such as ilmenite play the major role in the fractional crystallization process the high initial 87 sr 86 sr 0 7067 and 0 7079 and negative e nd t values 8 6 to 10 1 with t 2dm ranging from 1 39 to 1 49 ga indicate that the sources were mainly derived from the mature ancient middle to lower crust and minor mantle derived materials the initial 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 462 18 646 15 717 15 735 and 38 699 39 007 respectively signify that some subduction related material such as ocean island volcanic rocks and mature arc primitive rocks may be involved as sources based on an analysis of similar zircon saturated temperature and geochemical characteristics of typical highly fractionated i type granites in se and sw china and consideration of the regional geological setting we suggest that the parent magma may be derived from the ancient middle to lower continental crust and mantle derived basaltic magma these were generated in the setting of a westward subducted lushui luxi ruili llr tethyan oceanic slab where mantle wedge derived sources provided enough heat and material to melt the middle to lower ancient crust taking into account the temporal spatial distributions of early cretaceous magmatic rocks in the region we further suggest the existence of an andean type active continental margin from the lhasa block to the tengchong block along the bangong nujiang llr tethys ocean during the early cretaceous

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

petrogenesis and metallogenic potential of the wulanba granite southern great xing an range ne china constraints from whole rock and apatite geochemistry the wulanba granite consisting of biotite monzogranite and syenogranite is located in the southern part of the great xing an range ne china whole rock major and trace element geochemistry suggests the wulanba granite is a high k shoshonitic slightly peraluminous and highly differentiated i type granite the sr nd hf isotopes indicate that it originated from partial melting of juvenile crust derived from the depleted mantle with a minor input of old crust the relatively young t 2dm and t dm2 ages indicate it was most likely derived from a late neoproterozoic to early palaeozoic source we have demonstrated that the biotite monzogranite is the ore related intrusion of the haobugao zn fe mineralization based on the following geological geochronological and geochemical evidence 1 the chalcopyrite pyrite in the biotite monzogranite and the continuous mineralization of drill core zk2508 2 the consistence of the emplacement age of the biotite monzogranite 141 140 138 ma with the skarn mineralization age 142 ma and 3 the presence of rich ore forming elements fe zn cu in the biotite monzogranite and the similar pb compositions of the sulfides from the haobugao deposit and the biotite monzogranite compared to the barren syenogranite the fertile biotite monzogranite is more oxidized while the edges of the apatite grains in the biotite monzogranite are more oxidized than the centres the average f cl ratio of the fertile biotite monzogranite 123 45 is much higher than that of the barren syenogranite 73 98 we conclude that these differences reflect unique geochemical signatures and the geochemical composition of the apatite can be used to infer the economic potential of granites

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

mass loss of greenland s glaciers and ice caps 2003 2008 revealed from icesat laser altimetry data 1 the recently finalized inventory of greenland s glaciers and ice caps gic allows for the first time to determine the mass changes of the gic separately from the ice sheet using space borne laser altimetry data corrections for firn compaction and density that are based on climatic conditions are applied for the conversion from volume to mass changes the gic which are clearly separable from the icesheet i e have a distinct ice divide or no connection lost 27 9 10 7 gt a 1 or 0 08 0 03 mm a 1 sea level equivalent sle between october 2003 and march 2008 all gic including those with strong but hydrologically separable connections lost 40 9 16 5 gt a 1 0 12 0 05 mm a 1 sle this is a significant fraction 14 or 20 of the reported overall mass loss of greenland and up to 10 of the estimated contribution from the world s gic to sea level rise the loss was highest in southeastern and lowest in northern greenland

high altitude accumulation and preserved climate information in the western pamir observations from the fedchenko glacier accumulation basin the accumulation region of fedchenko glacier represents an extensive snow reservoir in the pamir mountains feeding the longest glacier in central asia observed elevation changes indicate a continuous ice loss in the ablation region of fedchenko glacier since 1928 while the mass balance of the accumulation region is largely unknown in this study we show that accumulation varies considerably in the main accumulation basin with accumulation rates up to 2400 mm w e a 1 in the west decreasing to 1 in the center although the elevation difference is

aerial photographs reveal late 20th century dynamic ice loss in northwestern greenland global warming is predicted to have a profound impact on the greenland ice sheet and its contribution to global sea level rise recent mass loss in the northwest of greenland has been substantial using aerial photographs we produced digital elevation models and extended the time record of recent observed marginal dynamic thinning back to the mid 1980s we reveal two independent dynamic ice loss events on the northwestern greenland ice sheet margin from 1985 to 1993 and 2005 to 2010 which were separated by limited mass changes our results suggest that the ice mass changes in this sector were primarily caused by short lived dynamic ice loss events rather than changes in the surface mass balance this finding challenges predictions about the future response of the greenland ice sheet to increasing global temperatures

insights into the behaviour of s f and cl at santiaguito volcano guatemala from apatite and glass abstract the mineral apatite can incorporate all of the major magmatic volatile species into its structure where melt inclusions are not available magmatic apatite may therefore represent an opportunity to quantify volatile concentrations in the pre eruptive melt we analysed apatites and matrix glasses from andesites and dacites erupted from santiaguito volcano guatemala between the 1920s and 2002 x ray mapping shows complex zoning of sulphur in the apatite grains but typically with sulphur rich cores and sulphur poor rims apatite microphenocrysts are enriched in f and depleted in cl relative to inclusions matrix glasses are dacite to rhyolite and contain low f but up to 2400 ppm cl overall the data are consistent with progressive depletion of cl in the most evolved melts due to crystallisation and degassing in the absence of pristine melt inclusions we used apatite together with published partitioning data to reconstruct the likely volatile contents of the pre eruptive melt and hence estimate long term average gas emissions of so 2 hf and hcl for the ongoing eruption the data indicate time averaged so 2 emissions of up to 157 tonnes day hcl of 74 1382 tonnes day and up to 196 tonnes day hf apatite may provide a useful measure of long term volatile emissions at volcanoes where direct emissions measurements are unavailable or for comparison with intermittent gas sampling methods however significant uncertainty remains regarding volatile distribution coefficients for apatite and their variations with temperature and pressure

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

ice sheet elevation changes caused by variations of the firn compaction rate induced by satellite observed temperature variations 1982 2003 changes in the surface elevation of the greenland and antarctic ice sheets and ice shelves caused by variations in the rate of firn compaction are calculated with a time dependent firn densification model driven by two decades 1982 2003 of satellite observed monthly surface temperatures the model includes the effects of melting and refreezing both the direct changes in density and the subsequent effects on the densification rate as previously shown the temperature dependent rate of densification is largest in summer but changes in winter temperatures also have a significant effect over the last decade climate warming has enhanced the rate of compaction and lowered the average surface elevation of greenland by 1 8 cma 1 and most of west antarctica by 1 9 cma 1 in east antarctica a small cooling raised the average surface elevation by 0 14 cma 1

radiostratigraphy and age structure of the greenland ice sheet 2015 the authors several decades of ice penetrating radar surveys of the greenland and antarctic ice sheets have observed numerous widespread internal reflections analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections here we present a comprehensive deep radiostratigraphy of the greenland ice sheet from airborne deep ice penetrating radar data collected over greenland by the university of kansas between 1993 and 2013 to map this radiostratigraphy efficiently we developed new techniques for predicting reflection slope from the phase recorded by coherent radars when integrated along track these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing core intersecting reflections were dated using synchronized depth age relationships for six deep ice cores additional reflections were dated by matching reflections between transects and by extending reflection inferred depth age relationships using the local effective vertical strain rate the oldest reflections dating to the eemian period are found mostly in the northern part of the ice sheet within the onset regions of several fast flowing outlet glaciers and ice streams reflections typically do not conform to the bed topography disrupted radiostratigraphy is also observed in a region north of the northeast greenland ice stream that is not presently flowing rapidly dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly this radiostratigraphy provides a new constraint on the dynamics and history of the greenland ice sheet

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

a nonsteady state firn densification model for the percolation zone of a glacier 1 a simple steady status firm densification model is modified to account for short term time variations of accumulation rate and surface temperature the temporal surface elevation and mass changes at two sites in the percolation zone of an ice sheet in response to various climate histories are determined it is shown that a straight forward translation of observed short term ice sheet surface elevation variations into mass changes may be completely misleading particularly for the percolation zone of the ice sheet where temperature driven variations of melting refreezing rates have a strong impact on near surface density in the lower percolation zone the mass change associated with a temperature anomaly in respect to the mean climate may for example amount to as little as 10 percent of the observed simultaneous surface elevation change moreover significant surface elevation change may occur even in periods of constant surface climate and consequently unchanged mass balance as a delayed response to previous changes of the local surface climate forcing the model with cyclic temperature variations mimicking fluctuations of west greenland instrumental temperature records during the past hundred years shows that surface elevation may increase by as much as 1 m in 5 years in periods with no mass change at all in the lower percolation zone temperature induced density changes rather than fluctuations of accumulation rate are the dominant cause of short term surface elevation changes in contrast to the situation in the higher percolation zone where short term surface elevation change is dominated by fluctuations of accumulation rate

trace element partitioning between apatite and silicate melts we present new experimental apatite melt trace element partition coefficients for a large number of trace elements cs rb ba la ce pr sm gd lu y sr zr hf nb ta u pb and th the experiments were conducted at pressures of 1 0 gpa and temperatures of 1250 c the rare earth elements la ce pr sm gd and lu y and sr are compatible in apatite whereas the larger lithophile elements cs rb and ba are strongly incompatible other trace elements such as u th and pb have partition coefficients close to unity

improved ice loss estimate of the northwestern greenland ice sheet 1 we estimate ice volume change rates in the northwest greenland drainage basin during 2003 2009 using ice cloud and land elevation satellite icesat laser altimeter data elevation changes are often reported to be largest near the frontal portion of outlet glaciers to improve the volume change estimate we supplement the icesat data with altimeter surveys from nasa s airborne topographic mapper from 2002 to 2010 and nasa s land vegetation and ice sensor from 2010 the airborne data are mainly concentrated along the ice margin and thus have a significant impact on the estimate of the volume change our results show that adding airborne topographic mapper and land vegetation and ice sensor data to the icesat data increases the catchment wide estimate of ice volume loss by 11 mainly due to an improved volume loss estimate along the ice sheet margin furthermore our results show a significant acceleration in mass loss at elevations above 1200m both the improved mass loss estimate along the ice sheet margin and the acceleration at higher elevations have implications for predictions of the elastic adjustment of the lithosphere caused by present day ice mass changes our study shows that the use of icesat data alone to predict elastic uplift rates biases the predicted rates by several millimeters per year at gps locations along the northwestern coast

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

radar response of firn exposed to seasonal percolation validation using cores and fdtd modeling we use ground penetrating radars gprs firn cores and electromagnetic finite difference time domain fdtd numerical modeling to characterize the gpr response to a frozen high arctic firn pack as a result of extensive summertime percolation the firn pack comprises a high fraction of ice layers lenses and vertical glands we show that the gpr response on the firn pack mainly depends on the following 1 the thickness of the ice layers 2 the distance between layers 3 the layer roughness and 4 the presence or absence of elliptical ice lenses using 3 d fdtd modeling we show that the gpr is not sensitive to typical ice glands which implies that the gpr underestimates firn heterogeneity such that firn stratigraphy in percolation and wet snow zones could be incorrectly interpreted as being better preserved than it actually is we find that thin ice layers 0 05 m or multiple thin ice layers give a strong response thicker ice layers typically give a weaker backscatter per unit area mainly due to the lack of interference of the reflections from the upper and lower interfaces but are due to their continuity easily trackable ice layers with a thickness comparable to the gpr wavelength give 180deg phase shifted upper and lower reflections and are in general separated by a band of low gpr response due to the lack of permittivity contrast within the ice layers despite the ice lenses relatively short horizontal correlation length as inferred from cores bands of high amplitude clutter caused by these features can be traced over several kilometers in gpr profiles

improving surface boundary conditions with focus on coupling snow densification and meltwater retention in large scale ice sheet models of greenland snowpack changes during the melt season are often not incorporated in modelling studies of the surface mass balance of the greenland ice sheet densification of snow accelerates when meltwater is present due to percolation and subsequent refreezing and needs to be incorporated in ice sheet models for ablation calculations in this study simple parameterizations to calculate surface melt snow densification and meltwater retention are included as surface boundary conditions in a large scale ice sheet model of greenland coupling the snow densification and meltwater retention processes achieves a separation of volume and mass changes of the surface layer in order to determine the surface melt contribution to runoff experiments for present day conditions show that snow depth at the onset of melt mean annual near surface air temperature and the mean density of the annual snow layer are key factors controlling the quantity and spatial distribution of meltwater runoff above the equilibrium line on the greenland ice sheet

variations of near surface firn density in the lower accumulation area of the greenland ice sheet pâkitsoq west greenland firn density variations have been studied in the lower accumulation area of the greenland ice sheet 1440 1620 m a s l near p kitsoq west greenland the main control on density in the near surface firn layer of 5 10 m thickness is the formation of ice layers by the refreezing of meltwater that reaches depths of 2 4 m below the surface the density variations are described by the ratio of annual surface melt m to the annual accumulation c the ratio m c is about 0 6 at the run off limit at about 1400 m a s l in the study area where refreezing of meltwater transforms snow into impermeable ice the mean density of near surface firn decreases with elevation reflecting a decrease in melt with elevation there is a surprising decrease in firn density at depths of more than about 4 m below the 1991 summer surface which reflects lower melt rates and or higher accumulation in the early 1980s and late 1970s when this firn was passing through the surface layer the formation of such low density firn may have partially contributed to the 1978 85 thickening of the ice sheet observed by satellite radar altimetry near surface firn density is therefore very sensitive to climate change and might be an attractive target for climate monitoring

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

melting of small arctic ice caps observed from ers scatterometer time series 1 time series of active microwave backscatter data from the ers wind scatterometers are used to demonstrate 1 the timing of melt onset can be observed over small ice caps as well as the major ice sheets and multi year sea ice and 2 temporally integrated backscatter reduction r is strongly correlated with total annual positive degree days pdd as measured at four automated weather stations on the surface of the greenland ice sheet the latter is particularly interesting because unlike melt onset r is a measure of melt processes integrated over an entire ablation season both methods work owing to the well known sharp decrease in radar backscatter triggered by the appearance of liquid water in a glacier snowpack melt onset and r are determined for 14 small arctic ice caps from 1992 2000 interannual and regional variability in the timing of melt onset are comparable averaging 33 9 and 38 13 days respectively regional variability in r exceeds interannual variability averaging 906 164 and 309 130 db d respectively the brevity of the derived nine year records limits their statistical testing for trend however their qualitative interpretation suggests that the timing of melt onset is more variable for arctic ice caps than for sea ice and the intensity of summer surface melting increased by about 20 in the 1990s