basal melting of ross ice shelf from solar heat absorption in an ice front polynya ice ocean interactions at the bases of antarctic ice shelves are rarely observed yet have a profound influence on ice sheet evolution and stability ice sheet models are highly sensitive to assumed ice shelf basal melt rates however there are few direct observations of basal melting or the oceanographic processes that drive it and consequently our understanding of these interactions remains limited here we use in situ observations from the ross ice shelf to examine the oceanographic processes that drive basal ablation of the world s largest ice shelf we show that basal melt rates beneath a thin and structurally important part of the shelf are an order of magnitude higher than the shelf wide average this melting is strongly influenced by a seasonal inflow of solar heated surface water from the adjacent ross sea polynya that downwells into the ice shelf cavity nearly tripling basal melt rates during summer melting driven by this frequently overlooked process is expected to increase with predicted surface warming we infer that solar heat absorbed in ice front polynyas can make an important contribution to the present day mass balance of ice shelves and potentially impact their future stability high melt rates in a key location beneath the ross ice shelf result from a seasonal inflow of water heated in the ross sea polynya according to in situ observations

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

does subduction polarity control metallogeny the mediterranean case the distribution of ore deposit types in different sectors of the circum mediterranean realm that have been affected by subduction processes since the cretaceous varies in space and time sectors involved in w directed subduction sardinia apennines maghrebides internal betics tyrrhenian western eastern carpathians are dominated by relatively low sulphidation epithermal vms deposits orogens formed by ne directed subduction dinarides hellenides pontides anatolides taurides dhpat were initially dominated by pluton related porphyry skarn high sulphidation epithermal associations these distinct metallogenic styles can be related to the systematic tectono magmatic asymmetry of e ne and w directed subduction systems and are analogous to the relationship observed in circum pacific belts exceptions to this simple pattern occurred in the dhpat in the cenozoic when deposit associations typical of both e directed and w directed systems were formed such exceptions are interpreted to reflect superimposition of contrasting subduction trends and inheritance from earlier metallogenic stages apuseni or the interference of subduction processes with subduction unrelated extension hellenides west anatolia

magma evolution and the formation of porphyry cu au ore fluids evidence from silicate and sulfide melt inclusions silicate and sulfide melt inclusions from the andesitic farallon negro volcanic complex in nw argentina were analyzed by laser ablation icpms to track the behavior of cu and au during magma evolution and to identify the processes in the source of fluids responsible for porphyry cu au mineralization at the 600 mt bajo de la alumbrera deposit the combination of silicate and sulfide melt inclusion data with previously published geological and geochemical information indicates that the source of ore metals and water was a mantle derived mafic magma that contained approximately 6 wt h2o and 200 ppm cu this magma and a rhyodacitic magma mixed in an upper crustal magma chamber feeding the volcanic systems and associated subvolcanic intrusions over 2 6 million years generation of the ore fluid from this magma occurred towards the end of this protracted evolution and probably involved six important steps 1 generation of a sulfide melt upon magma mixing in some parts of the magma chamber 2 partitioning of cu and au into the sulfide melt enrichment factor of 10 000 for cu leading to cu and au concentrations of several wt or ppm respectively 3 a change in the tectonic regime from local extension to compression at the end of protracted volcanism 4 intrusion of a dacitic magma stock from the upper part of the layered magma chamber 5 volatile exsolution and resorption of the sulfide melt from the lower and more mafic parts of the magma chamber generating a fluid with a cu au ratio equal to that of the precursor sulfide 6 focused fluid transport and precipitation of the two metals in the porphyry yielding an ore body containing au and cu in the proportions dictated by the magmatic fluid source the cu s ratio in the sulfide melt inclusions requires that approximately 4 000 ppm sulfur is extracted from the andesitic magma upon mixing this exceeds the solubility of sulfide or sulfate in either of the silicate melts and implies an additional source for s the extra sulfur could be added in the form of anhydrite phenocrysts present in the rhyodacitic magma it appears thus that unusually sulfur rich not cu rich magmas are the key to the formation of porphyry type ore deposits our observations imply that dacitic intrusions hosting the porphyry cu au mineralization are not representative of the magma from which the ore fluid exsolved the source of the ore fluid is the underlying more mafic magma and unaltered andesitic dikes emplaced immediately after ore formation are more likely to represent the magma from which the fluids were generated at alumbrera these andesitic dikes carry relicts of the sulfide melt as inclusions in amphibole sulfide inclusions in similar dykes of other less explored magmatic complexes may be used to predict the au cu ratio of potential ore forming fluids and the expected metal ratio in any undiscovered porphyry deposit

near surface environmentally forced changes in the ross ice shelf observed with ambient seismic noise author s chaput j aster r c mcgrath d baker m anthony r e gerstoft p bromirski p nyblade a stephen r a wiens d a das s b stevens l a

west antarctic ice sheet collapse charles r bentley perspectives 21 feb p 1077 1 suggests that a useful estimate of the probability of a west antarctic ice sheet collapse in the next 100 years can be obtained by assuming it to be a random event occurring once every 100 000 years he bases this view on results of a single

catastrophic ice shelf breakup as the source of heinrich event icebergs 1 heinrich layers of the glacial north atlantic record abrupt widespread iceberg rafting of detrital carbonate and other lithic material at the extreme cold culminations of bond climate cycles both internal glaciologic and external climate forcings have been proposed here we suggest an explanation for the iceberg release that encompasses external climate forcing on the basis of a new glaciological process recently witnessed along the antarctic peninsula rapid disintegrations of fringing ice shelves induced by climate controlled meltwater infilling of surface crevasses we postulate that peripheral ice shelves formed along the eastern canadian seaboard during extreme cold conditions would be vulnerable to sudden climate driven disintegration during any climate amelioration ice shelf disintegration then would be the source of heinrich event icebergs

breakup and conditions for stability of the northern larsen ice shelf antarctica the breakup of ice shelves has been widely regarded as an indicator of climate change1 with observations around the antarctic peninsula having shown a pattern of gradual retreat associated with regional atmospheric warming and increased summer melt and fracturing processes2 3 4 5 6 7 8 9 the rapid collapse of the northernmost section of the larsen ice shelf larsen a over a few days in january 1995 indicated that after retreat beyond a critical limit ice shelves may disintegrate rapidly here we use a finite element numerical model that treats ice as a continuum without fracture10 to examine the breakup history2 between 1986 and 1997 of the two northern sections of larsen ice shelf larsen a and larsen b from which we establish stability criteria for ice shelves analysis of various ice shelf configurations reveals characteristic patterns in the strain rates near the ice front which we use to describe the stability of the ice shelf on larsen a only the initial and final ice front configurations show a stable pattern larsen b at present exhibits a stable pattern but if the ice front were to retreat by a further few kilometres it too is likely to enter an irreversible retreat phase

a tutorial on the use of control methods in ice sheet modeling control methods are recommended as an efficient means to estimate undetermined physical parameters and boundary conditions and in so doing to improve the fidelity of a given ice sheet flow model to specific ice sheet velocity observations to accomplish this task the underlying dynamics of the model are inverted this permits model tuning adjustments to be represented explicitly in terms of model observation misfit

ice shelf history from petrographic and foraminiferal evidence northeast antarctic peninsula a detailed record of late pleistocene deglaciation followed by mid holocene ice shelf breakup and late holocene re growth is contained in continental shelf sediments in the northern larsen area northeast antarctic peninsula the zero age of core tops is confirmed by new and published 210pb profiles and 70 accelerator mass spectrometer ams 14c dates on bulk organic carbon define sedimentation rates of 7 6 92 cm ka the varied geology in the local ice drainage basins facilitates the use of ice rafted debris ird provenance in determining the presence or absence of ice shelves all inshore cores contain an interval of non local ird in the post glacial section demonstrating widespread ice shelf breakup in the mid holocene both breakup and re growth may have taken centuries and there are no widespread debris layers associated with breakup cores beyond and up to 30 km inside the historical ice shelf limit exhibit a varied ird provenance throughout the holocene suggesting the maximum ice shelf limit may date only from the little ice age benthic foraminiferal assemblages are related to water masses and position on the continental shelf and have been modified by taphonomic processes nevertheless we discern a deglaciation signal in prince gustav channel of a calcareous spike in predominantly agglutinated assemblages and this is repeated at the time of mid holocene ice shelf breakup the inferred mid holocene warm period occurred later in the northern larsen area than on the west coast of the antarctic peninsula

the origin of ch4 rich fluids in reduced porphyry skarn cu mo au systems abstract although most of the methane on earth is of biogenic origin significant abiogenic methane has been identified in a variety of geological environments moreover the presence of methane has been reported recently in fluid inclusions from a number of reduced porphyry deposits the genesis of this methane however remains poorly understood here we present results of a study of magma exsolved ch4 rich aqueous fluid inclusions in the seleteguole reduced porphyry skarn cu mo au deposit nw china four types of fluid inclusions namely intermediate density two phase aqueous inclusions low density vapor inclusions brine inclusions and aqueous liquid inclusions have been distinguished on the basis of the phases present at room temperature the intermediate density inclusions were trapped as a single phase and contain 3 8 10 4 mol kg ch4 corresponding to an oxygen fugacity between fmq 1 and fmq 0 5 this attests to the remarkably reduced nature of the fluid the 13c value of the ch4 hosted fluid inclusions ranges from 29 4 to 19 1 pdb which distinguishes this methane from biogenic methane indeed the high homogenization temperature of the ch4 rich inclusions 400 c implies that the ch4 was exsolved directly from the magma given the environment in which the magma was likely generated i e at or immediately above a subducting plate we propose that the methane was produced by reactions involving organic matter bearing carbonate rocks in the subduction zone although cu mo and au in most porphyry systems are interpreted to have been transported under oxidizing conditions our results indicate that reduced aqueous liquids and vapors are also capable of transporting appreciable concentrations of these metals

northern larsen ice shelf antarctica further retreat after collapse changes of larsen ice shelf antarctica and the surrounding glaciers after its collapse in 1995 were investigated using satellite radar imagery with emphasis onchanges in the glaciers which previously nourished the ice shelf north of seal nunataks the large glaciers retreated several kilometres inland of the previousgrounding line the velocity field of drygalski glacier the largest glacier in this area was mapped by means of interferograms derived from pairs of ers syntheticaperture radar images from 1995 and 1999 the main part of the glacier showed significant acceleration of flow over these 4 years with an increase of veocity upto three fold at the terminus similar accelerations were observed by means of interferometry on several other grounded glaciers suggesting that the removal ofice shelves could lead to an effect on eustatic sea level for larsen b the northernmost surviving part of larsen ice shelf the retreat of the ice front to october2000 is documented

numerical modelling and data assimilation of the larsen b ice shelf antarctic peninsula in this study the flow and rheology of pre collapse larsen b ice shelf are investigated by using a combination of flow modelling and data assimilation observed shelf velocities from satellite interferometry are used to constrain an ice shelf model by using a data assimilation technique based on the control method in particular the ice rheology field and the velocities at the inland shelf boundary are simultaneously optimized to get a modelled flow and stress field that is consistent with the observed flow the application to the larsen b ice shelf shows that a strong weakening of the ice in the shear zones mostly along the margins is necessary to fit the observed shelf flow this pattern of bands with weak ice is a very robust feature of the inversion whereas the ice rheology within the main shelf body is found to be not well constrained this suggests that these weak zones play a major role in the control of the flow of the larsen b ice shelf and may be the key to understanding the observed pre collapse thinning and acceleration of larsen b regarding the sensitivity of the stress field to rheology the consistency of the model with the observed flow seems crucial for any further analysis such as the application of fracture mechanics or perturbation model experiments

radarsat 1 antarctic mapping project change detection and surface velocity campaign theradarsat 1antarcticmappingproject ramp isacollaboration betweennasaandthecanadianspaceagencytomapantarcticausingsyntheticaperture radar sar the first antarctic mapping mission amm 1 wassuccessfullycompleted in october 1997 data from the acquisition phase of the 1997 campaign have been used to achievetheprimarygoalofproducingthefirsthigh resolutionsarimagemapofantarctica the modified antarctic mapping mission mamm occurredduring thefallof 2000 the acquisition strategy concentrated on collecting highest resolution radarsat 1 data of antarctica s fast glaciers for change detection and feature retracking estimates of surface velocity additionally extensive data were acquired for interferometric analysis over the entire viewable region which extends north of 80 1 s latitude this paper summarizes the goalsand strategybehind mamm it goes onto discuss ice sheet marginchanges observed on several ice shelvesaroundthecontinent margin changesare documentedbycomparing amm 1and mamm datawith earlier datasets including european remote sensing satel lite 1sar imagery landsat imagery the antarctic digital database version1 coastline and declassified intelligence satellite photography analysis reveals a complex pattern of ice margin advance and retreat without indicating any systematic behavior in ice sheet extentabouttheice sheetperimeter

climatically induced retreat and collapse of northern larsen ice shelf antarctic peninsula the areal changes of the northern larsen ite shelf lis antarctic peninsula between march 1986 and march 1997 have been analyzed based on synthetic aperture radar images of the european remote sensing satellites ers 1 and ers 2 and on landsat images this analysis is complemented by data on ice motion and surface mass balance which have been obtained during several field campaigns since the early 1980s after a period of retreat coinciding with atmospheric warming and with decreasing net accumulation at the surface due to melt losses the two northernmost sections of lis disintegrated almost completely within a few days in january 1995 recent observations of the ice shelf section north of jason peninsula which is presently the northernmost section of lis show increased summer melt and intensification of the rifting processes probably causing accelerated retreat of this section in the near future the retreat and the disintegration event of lis indicate high sensitivity of ice shelves to prolonged perturbations of the mass balance

sensitivity of tidewater glaciers to submarine melting governed by plume locations this work was funded by nerc award ne p011365 1 calismo calving laws for ice sheet models to pi benn

the retreat of jones ice shelf antarctic peninsula in recent decades several ice shelves along the antarctic peninsula have diminished in size as a result of climate warming using aerial photographic satellite and survey data we document a similar retreat of jones ice shelf which was another small ice shelf on the west coast of the antarctic peninsula this ice shelf was roughly stable between 1947 and 1969 but in the early 1970s it began to retreat and had completely disappeared by early 2003 jones ice shelf has two ice fronts only a few kilometres apart and its retreat provides a unique opportunity to examine how different ice fronts retreat when subjected to similar climate forcing we mapped the retreat of both the east and west ice fronts of jones ice shelf and found that although individual episodes of retreat may be related to particularly warm summers the overall progress of retreat of the two ice fronts has been rather different this suggests that in this case the course of retreat is controlled by the geometry of the embayment and location of pinning points as well as climatic events

ice shelf disintegration by plate bending and hydro fracture satellite observations and model results of the 2008 wilkins ice shelf break ups abstract satellite remote sensing observations of three break up events in 2008 for the wilkins ice shelf 28 february to 6 march 27 may to 31 may and 28 june to mid july provide unprecedented detail of ice shelf calving during rapid break up the observations reveal that the wilkins break ups occur through a distinctive type of shelf calving which we term disintegration as well as more typical rifting and calving here we focus on the disintegration process which is characterized by repeated rapid fracturing that creates narrow ice edge parallel blocks with subsequent block toppling and fragmentation forming an expanding iceberg and ice rubble mass we use these data to develop and test a model of floating ice plate disintegration in which ice plate bending stresses at the ice front arising from buoyancy forces can lead to runaway calving when free mobile water is available high resolution satellite images and laser altimetry of the first break up event provide details of fracture spacings ice thicknesses and plate bending profiles that agree well with our model predictions we suggest that surface or near surface meltwater is the main pre condition for disintegration and that hydro fracture is the main mechanism brine layers from near waterline brine infiltration can support a similar process but this is less effective unless regional ice stress patterns contribute to the net stress available at the crack tip for fracturing a combination of brine enhanced fracturing and changing internal net extensional stresses was the likely mechanism behind the latter two wilkins events

the aitik cu au ag deposit in northern sweden a product of high salinity fluids the aitik cu au ag deposit is located in northern sweden and is hosted by strongly deformed 1 9 ga svecofennian volcano sedimentary rocks the main copper mineralization which occurs as disseminations and veinlets is hosted by garnet biotite schist subeconomic mineralization in the footwall to the ore is hosted by feldspar biotite amphibole gneiss and porphyritic quartz monzodiorite the deposit has been affected by post mineralization metamorphic and igneous activity fluid inclusions in six samples of copper mineralized quartz veins record the presence of three different fluid populations the main ore was deposited from an aqueous highly saline 31 37 eq wt nacl cacl2 fluid this fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization later bornite deposition took place from a less saline 18 27 eq wt nacl cacl2 aqueous fluid a third fluid composed of almost pure co2 interacted with the copper rich system during a post ore event the aitik cu au ag deposit shares some features with both porphyry type and fe oxide cu au deposits a high calcium content of the ore fluids similar to other cu au deposits in northern scandinavia suggests a contribution to the salinity of the mainly magmatic hydrothermal fluids from evaporitic rocks in stratigraphically lower units

the relationship between the southern hemisphere annular mode and antarctic peninsula summer temperatures analysis of a high resolution model climatology abstract the large regional summer warming on the east coast of the northern antarctic peninsula ap which has taken place since the mid 1960s has previously been proposed to be caused by a trend in the southern hemisphere annular mode sam the authors utilize a high resolution regional atmospheric model climatology 14 km grid spacing to study the mechanisms that determine the response of the near surface temperature to an increase in the sam t sam month to month variations in near surface temperature and surface pressure are well represented by the model it is found that north of 68 s t sam is much larger on the eastern lee side than on the western windward side of the barrier this is because of the enhanced westerly flow of relatively warm air over the barrier which warms and dries further as it descends down the lee slope the downward motion on the eastern side of the barrier causes a decrease in surface mass balance and cloud cover south of 68 s vertical deflection across

strong surface melting preceded collapse of antarctic peninsula ice shelf 1 during the austral summer of 2001 02 melting at the surface of larsen ice shelf in the antarctic peninsula was three times greater than the average of five previous summers this exceptional melt event lasted for three months and was followed by the collapse of larsen b ice shelf during which 3 200 km2 of ice shelf surface was lost the strong melting was caused by a persistent atmospheric circulation anomaly which depleted sea ice concentrations in front of larsen ice shelf and transported warm air to the ice shelf throughout the 2001 02 summer this supports the theory that large meltwater fluxes accelerate the retreat of antarctic peninsula ice shelves

evidence of recent climatic warming on the eastern antarctic peninsula air temperatures at the stations marambio esperanza and matienzo have been analysed to investigate recent climate change on the eastern part of the antarctic peninsula the data are compared with the station orcadas on the south orkney islands the longest record available in antarctica and with faraday on the western coast of the peninsula though the interannual variability is comparatively high and the stations are located in different climatic regimes a pronounced warming trend shows up in all records at marambio a temperature increase of 1 5 c has been observed since the beginning of the record in 1971 this is of similar magnitude as the increase at the station faraday on the west coast with 2 5 c for the longer period since 1945 the steady retreat and collapse of the northern larsen ice shelf coincided with this warming trend of particular importance for the ice shelf mass balance in this region are the summer temperatures which show a statistically significant warming trend at the stations marambio and esperanza the representativity of the summer temperatures of marambio for northern larsen ice shelf is confirmed by intercomparison with the parallel measurements at matienzo which is located on the ice shelf

34 year satellite time series to monitor characteristics extent and dynamics of larsen b ice shelf antarctic peninsula a variety of data are used to investigate larsen b which is at present the northernmost section of the larsen ice shelf recently declassified usargon satellite photographs of 1963 kosmos photographs of 1975 landsat images of 1986 1988 and 1990 ers 1 2 sar images from 1992 to1997 radarsat of 1998 and field surveys are used to analyze the areal extent surface characteristics and dynamic behaviour of this ice shelf sectionover more than three decades visible and radar imagery together with field observations are used synergistically to describe the ice shelf morphology including meltwater features and rifts in contrast to the retreat of the ice shelf sections in the north larsen b advanced steadily from 1963 to early1995 when the area decreased significantly due to a major calving event analysis of different satellite images indicates that melting is proceedingfurther south in coincidence with the regional warming trend in addition fracturing processes and rapid development of new rifts are observed associated with recent acceleration of ice motion close to the front all observations indicate that major calving events should be expected for this iceshelf section in the near future

quantifying vulnerability of antarctic ice shelves to hydrofracture using microwave scattering properties abstract recent ice shelf disintegrations on the antarctic peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture in this study we use active microwave scatterometry in time series to estimate melt season duration and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in antarctic ice shelf firn we demonstrate a physical relationship between melt days and firn ice backscatter using scatterometry and field data from greenland and apply the observed relationship to derive and map a vulnerability index for antarctica s ice shelves the index reveals that some remaining antarctic peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture we also show that the progression of an ice shelf towards vulnerability is affected by many factors such as surface mass balance internal stresses and ice shelf geometry

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

experimental fracture and mechanical properties of antarctic ice preliminary results an experimental study of the fracture mechanics and rheology of ice from the ronne ice shelf antarctica is currently being undertaken the apparent critical stress intensity factor or apparent fracture toughness k q for crack propagation has been measured using a three point bend method for inducing crack growth perpendicular to the axis of cylindrical ice core specimens tensile crack nucleation under applied uniaxial compressive stress has also been evaluated both methods have allowed a profile of ice elastic and fracture properties with depth through the ice shelf to be constructed preliminary results indicate that the measured elastic modulus increases with depth through the firn and upper meteoric ice before reaching a constant value in the deeper dense meteoric and basal marine ice the resistance to fracture as measured by changes in apparent fracture toughness and crack nucleation stress increases with depth right through the firn and meteoric ice layers a simple fracture mechanics model applied to the ronne ice shelf indicates that crevasses form from small surface cracks less than 40 cm deep which quickly grow to depths of 40 60m and then remain stable

the la union au cu prospect camaguey district cuba fluid inclusion and stable isotope evidence for ore forming processes the camaguey district cuba is known for its epithermal precious metal deposits in a cretaceous volcanic arc setting recently the la union prospect was discovered in the southern part of the district containing gold and minor copper mineralization interpreted as porphyry type mineralization is hosted in a 73 0 1 5 ma calc alkaline i type oxidized porphyry quartz diorite intrusive within volcanic and volcaniclastic rocks of the early cretaceous guaimaro formation the porphyry is affected by propy litic alteration and crosscut by a network of quartz and carbonate veinlets and veins chlorite epidote sericite quartz and pyrite are the main minerals in the early veins which are cut by late carbonate and zeolite veins late barite pseudomorphously replaces pyrite gold is associated with pyrite as disseminations in the altered quartz diorite and in the veins occurring as inclusions or filling fractures in pyrite with 4 g t au in bulk samples and up to 900 ppm au in in pyrite fluid inclusion and oxygen isotope data are consistent with a h2o nacl kcl mineralizing fluid derived from the quartz diorite magma and trapped at least at 425 c and 1 2 kbar this primary fluid unmixed into two fluid phases a hypersaline aqueous fluid and a low salinity vapor rich fluid boiling during cooling may have played an important role in metal precipitation pyrite 34 s values for the la union prospect range between 0 71 and 1 31 consistent with a homogeneous magmatic sulfur source the fluids in equilibrium with the mineralized rocks have estimated 18 o values from 8 to 11 8 calculated for a temperature range of 480 505 c the tectonic environment of the la union prospect its high gold and low copper contents the physical chemical characteristics of the mineralizing fluids and the isotopic signature of the alteration minerals and fluids indicate that the la union gold mineralization is similar to the porphyry gold type even though the ore related epidote chlorite alteration can be classified as propylitic and not the classic potassic and or phyllic alteration the low copper contents in the prospect could be due to a mineralizing fluid previously saturated in copper which is indicated by trapped chalcopyrite crystals in high temperature fluid inclusions the low temperature paragenesis represented by carbonate zeolite and barite indicates epithermal overprint the study shows the potential for other gold porphyry type deposits in the cretaceous volcanoplutonic arc of cuba

understanding ice sheet mass balance progress in satellite altimetry and gravimetry satellite remote sensing has come to dominate the measurement of glacier and ice sheet change three independent methods now exist for assessing ice sheet mass balance and we focus on progress in two satellite altimetry icesat and gravimetry grace with improved spatial and temporal sampling and synergy with ice flow measurements both the mechanisms and causes changing mass balance can be investigated we present examples of mass losses due to widespread intensifying glacier dynamic thinning in northwest greenland but local ablation rates in the northeast that are unchanged for decades advances in grace processing reveal greenland net ice sheet mass loss continuing into 2010 at 19530 gt a 1 a similarly negative trend in the gulf of alaska has significant spatial and temporal variation that highlights the importance of intense summer melting here strong summer melt on the antarctic peninsula also precipitated recent ice shelf collapse and prompted rapid dynamic thinning of tributary glaciers at up to 70ma 1 thinning continued for years to decades after collapse and propagated far inland while understanding of the physical mechanisms of change continues to improve estimates of future behaviour and in particular the near future glacial sea level contribution still rely on projections from such observations we introduce the suite of new sensors that will monitor the ice sheets into the future

hydrothermal evolution in the calabona porphyry copper system sardinia italy the path to an uneconomic deposit the calabona porphyry copper system is developed in a small relatively deep seated nearly equal 5 km dacitic intrusion located in northwestern sardinia italy early hydrothermal alteration produced a potassic assemblage in the deep and central parts of the complex and a peripheral propylitic halo sodic alteration was subsequently superimposed on the potassic zone and volumetrically dominant phyllic alteration overprinted the apical parts of the intrusion hypogene copper mineralization chalcopyrite and minor bornite was associated with potassic alteration the earliest fluid that circulated in the calabona porphyry complex had high salinity 40 60 wt nacl equiv and is interpreted to have been exsolved directly from the crystallizing magma however major entrapment of this fluid only occurred after it had cooled to temperatures of about 400 degrees c this fluid was responsible for potassic alteration and for precipitation of chalcopyrite and bornite in thin discontinuous group 1 veins and irregular and widely spaced group 2 veins the average cu grade in the potassic zone is between 0 05 and 0 1 percent the circulation of a lower temperature 270 degrees 330 degrees c ca enriched fluid of meteoric origin in the peripheral parts of the system caused propylitic alteration at an intermediate stage of hydrothermal evolution waters of external origin entered the central parts of the system along a network of late fractures group 3 veins or reopened group 2 veins partial mixing of this meteoric formational water with the high salinity fluid already circulating in the system created a fluid characterized by salinities ranging from 2 to 23 wt percent nacl equiv circulation of this mixed fluid at relatively low fluid rock ratios along a prograde thermal path caused sodic alteration the continuous inflow of meteoric water and the general temperature decrease in the system produced progressively more oxidized and acidic fluids which caused phyllic alteration and intense copper leaching late boiling in the apical parts of the phyllic alteration zone favored deposition of chalcopyrite and bornite but did not add significant copper cu grade 0 03 supergene enrichment led to copper grades higher than those in the phyllic zone 0 07 but not enough to permit mining the very low concentration of cu in the calabona deposits is surprising in view of wall rock alteration style of mineralization and a fluid evolution typical of those of many productive porphyry copper systems we propose that this is mainly a consequence of the raltive deep level of emplacement of the intrusion and the dacitic composition of the magma these factors are interpreted to have combined to retard melt saturation with alkali chlorife enriched fluids until late stages of crystallization which restricted the amount of exsolved fluid and cu extracted form the melt as a result overpressuring in the apical parts of the system was limited the related fracture density was low and the system therefore failed to provide the focus for the mineralizing fluids needed to permit bulk concentration of copper to economic levels further reasons for the uneconomic nature of the calabona porphyry were the lack of multiple intrusive events and the sulfide destructive cu leaching effects of phyllic alteration

deformation and structural evolution of mantle peridotites during exhumation on transform faults a forced transition from ductile to brittle regime abstract the exhumation of peridotite rocks in oceanic transform zones passes by the rheological transition between the ductile and brittle deformation until the complete emplacement in the oceanic lithosphere the sao pedro and sao paulo archipelago spspa in the equatorial atlantic records the deformational products of ductile brittle and the rocks fluid interaction generating specific structures in each domain the deformational stages are related to the transpressional and transtensional geodynamics of sao paulo transform fault firstly during transpression exhumation occurs associated with the ductile domain causing intense mylonitization in temperatures between 700 and 800 c defined by olivine and orthopyroxene recrystallization the interaction with fluids initially originated from the mantle generates amphibole and oxide rich layers marking the passage to a semi brittle deformation the continuation of peridotite exhumation associated with an nw se shortening and transpressional led to a higher availability of hydrothermal fluids as a consequence four serpentinization episodes are recorded which are associated with semi brittle to brittle transition under temperatures between 300 and 400 c finally the complete exhumation and establishment of brittle mechanisms led to carbonatation phase near the surface with temperatures ranging from 300 to 150 c the active nw se tectonic stress generated e w strike slip faults that were filled by carbonates recording the final exhumation stage

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

monstars on glaciers le point isotropique des vitesses de deformation sur un glacier sont de type monstar citronetoile mais les iso lignes autour de lui peuvent etre soit elliptiques soit hyperboliques de plus le glacier contient des points isoles de pur cisaillement

fracture propagation and stability of ice shelves governed by ice shelf heterogeneity tabular iceberg calving and ice shelf retreat occurs after full thickness fractures known as rifts propagate across an ice shelf a quickly evolving rift signals a threat to the stability of larsen c the antarctic peninsula s largest ice shelf here we reveal the influence of ice shelf heterogeneity on the growth of this rift with implications that challenge existing notions of ice shelf stability most of the rift extension has occurred in bursts after overcoming the resistance of suture zones that bind together neighboring glacier inflows we model the stresses in the ice shelf to determine potential rift trajectories calving perturbations to ice flow will likely reach the grounding line the stability of larsen c may hinge on a single suture zone that stabilizes numerous upstream rifts elevated fracture toughness of suture zones may be the most important property that allows ice shelves to modulate antarctica s contribution to sea level rise

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

numerical modelling of the ice sheet in western dronning maud land east antarctica impacts of present past and future climates time dependent ice sheet modelling of a 176 000 km2 area in western dronning maud land east antarctica provided information on the ice sheet s response to six climate change scenarios another experiment was done to study changes in ice thickness flow and basal temperature conditions between the present ice configuration and a simulated maximum palaeo ice sheet the input to the model included new datasets of bed and surface topography compiled for this study the results of the six climate change experiments including a 0 5 c per century global warming scenario show that the ice sheet has a robust behaviour with respect to the different climate changes the maximum change in ice volume was

the role of cooperative iceberg capsize in ice shelf disintegration disintegration of several ice shelves along the antarctic peninsula demonstrates a mechanism that involves the conversion of a contiguous ice shelf into an expanding plume of ice shelf fragments that spreads rapidly across the ocean surface the growth of surface area and energetic expansion are hypothesized to be driven by gravitational potential energy release associated with iceberg capsize and break up here we investigate this process using a water tank filled with plastic icebergs scaled to represent a laboratory analogue of an expanding plume of ice shelf fragments icebergs our experiments suggest that hydrodynamic pressure within the water separating neighbouring icebergs is sufficient to couple the motion when their separation is comparable to the iceberg size this allows one iceberg s capsize to initiate a domino like effect where the entire array will subsequently capsize in the same direction and expand across the water surface our experimental results motivate the suggestion that cooperative iceberg hydrodynamics is a process that enhances the expansion of ice shelf fragment plumes during ice shelf disintegration

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

orthomagmatic origin for the ilkwang cu w breccia pipe deposit southeastern kyongsang basin south korea abstract four distinct types of fluid inclusion are associated with brecciation alteration and mineralization in the ilkwang cu w breccia pipe deposit in the southeastern kyongsang basin south korea the earliest fluid inclusions in igneous quartz have salinities of 35 49 wt nacl equiv and homogenize by halite dissolution this fluid exsolved directly from the melt a co2 bearing fluid 2 4 wt nacl equiv was trapped during the initial stages of brecciation and pressure decrease and later brecciation events and continued decreasing pressure in the magma chamber generated low salinity supercritical fluids that boiled to produce brine 40 48 wt nacl equiv and coexisting vapor 2 13 wt nacl equiv at 343 493 c and 120 400 bars the latest fluid 5 24 wt nacl equiv was trapped during the waning stages of hydrothermal activity the oxygen and hydrogen isotopic compositions of the fluid 18 o smow 9 4 4 8 d smow 45 to 49 of quartz and the sulfur isotopic compositions 34 s cdt 0 3 to 0 9 of sulfide minerals cementing the breccia fragments are consistent with a magmatic origin for the hydrothermal fluids fluid inclusion data and stable isotopic compositions suggest that ilkwang cu w mineralization and alteration are products of orthomagmatic hydrothermal processes that were strongly pipe controlled the various types of fluid inclusions in the ilkwang deposit reflect the evolution from a high pressure to a low pressure magmatic system the evolution to a low pressure stage and concomitant aqueous fluid immiscibility in the ilkwang deposit are major factors in the formation of economic mineralization

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

global teleconnections in response to freshening over the antarctic ocean abstract in this paper coupled ocean atmosphere responses to freshening over the antarctic ocean are investigated in a fully coupled model with a series of sensitivity experiments in the model 1 0 sv 1 sv 106 m3 s 1 of freshwater flux is uniformly imposed over the antarctic ocean for 400 yr while the ocean and atmosphere remain fully coupled both locally and elsewhere the model explicitly demonstrates that a freshening of the antarctic ocean can induce a significant local cooling coupled with an intensification of the westerly winds and expansion of sea ice furthermore the cooling can extend to the entire southern extratropical and tropical oceans coupled with an intensification of southeasterly trades and the equatorial trade winds some modest warm anomalies also occur in the northern extratropical oceans forming a sharp interhemispheric sst contrast a series of sensitivity experiments are conducted to understand the mechanisms responsible for transmitting the southern high latitude cooling

ice shelf changes in pine island bay antarctica 1947 2000 aerial photographs from 1947 and 1966 satellite optical imagery from 1973 and 1980 and interferometric synthetic aperture radar insar data from 1992 1996 and 2000 are employed to detect ice shelf changes in pine island bay antarctica the front position of the fast flowing central ice shelf did not migrate discernibly over the past 50 years new cracks and rifts appeared in the 1990s however that reveal a major weakening of the ice shelf at the grounding line center the ice shelf thinned 21 m in 8 years the northern slow moving ice shelf also shows signs of decay 1 its calving front is retreating at an accelerating rate and 2 the ice shelf is slowly unpinning from its bedrock anchors these changes are taking place in a region well beyond the temperature dependent limit of viability of ice shelves and hence differ from those observed along the antarctica peninsula they are likely due to a change in oceanic forcing not to a change in air temperature one possibility is that the documented intrusion of warm circumpolar deep water on the continental shelf has increased basal melting compared to that required to maintain the ice shelf in a state of mass balance and that this has triggered a general retreat of ice in this sector

spontaneous ice front retreat caused by disintegration of adjacent ice shelf in antarctica abstract antarctic ice discharge constitutes the largest uncertainty in future sea level projections floating ice shelves fringing most of antarctica exert retentive forces onto the ice flow while abrupt ice shelf retreat has been observed it is generally considered a localized phenomenon here we show that the disintegration of an ice shelf may induce the spontaneous retreat of its neighbor as an example we reproduce the spontaneous but gradual retreat of the larsen b ice front as observed after the disintegration of the adjacent larsen a ice shelf we show that the larsen a collapse yields a change in spreading rate in larsen b via their connecting ice channels and thereby causes a retreat of the ice front to its observed position of the year 2000 prior to its collapse this mechanism might be particularly relevant for the role of east antarctica and the antarctic peninsula in future sea level

fluid inclusion evidence for hydrothermal fluid evolution in the darreh zar porphyry copper deposit iran abstract the darreh zar porphyry copper deposit is associated with a quartz monzonitic granodioritic porphyritic stock hosted by an eocene volcanic sedimentary complex in which magmatic hydrothermal fluids were introduced and formed veins and alteration within the deepest quartz rich and chalcopyrite poor group a veins lvhs2 inclusions trapped high salinity high temperature aqueous fluids exsolved directly from a relatively shallow magma 0 5 kbar these late fluids were enriched in nacl and reached halite saturation as a result of the low pressure of magma crystallization and fluid exsolution these fluids extracted cu from the crystallizing melt and transported it to the hydrothermal system as a result of ascent the temperature and pressure of these fluids decreased from 600 to 415 c and approximately 500 315 bars at these conditions k feldspar and biotite were stabilized type a veins were formed at a depth of 1 2 km under conditions of lithostatic pressure and abrupt cooling upon cooling and decompressing the fluid intersected with the liquid vapor field resulting in separation of immiscible liquid and vapor this stage was recorded by formation of lvhs1 lvhs3 and vl inclusions these immiscible fluids formed chalcopyrite pyrite quartz veins with sericitic alteration envelopes b veins under the lithostatic hydrostatic pressure regime at temperatures between 415 and 355 c at 1 3 km below the paleowater table as the fluids ascended copper contents decreased and these fluids were diluted by mixing with the low salinity external fluid therefore pyrite dominated quartz veins were formed in purely hydrostatic conditions in which pressure decreased from 125 bars to 54 bars and temperature decreased from 355 to 298 c during the magmatic hydrothermal evolution the composition and p t regime changed drastically and caused various types of veins and alterations the abundance of chalcopyrite precipitation in group b veins suggests that boiling and cooling were important factors in copper mineralization in darreh zar