geodynamic framework of large unique uranium orebelts in southeast russia and east mongolia abstract some of the largest uranium orebelts and deposits of asia occur in southeast russia and east mongolia in russia the elkon and streltsovka belts are located in the aldan south yakutia and urulyungui southeast trans baikal area districts covering a distance of more than 1200 km the superlarge dornod deposit occurs in the north choibalsan district of east mongolia ca 300 km to the southwest of streltsovka these uranium occurrences are distributed in the central aldan and kerulen argun cratonic domains separated by the selenga stanovoi yenisei trans baikal and mongol okhotsk orogenic belts a synthesis of the characteristics and the timing of mineralization suggest that all of these occurrences were generated synchronously seismic tomography data show that these deposits are mostly located above the frontal part of a stagnant oceanic slab we envisage that slab dehydration and influx of fluids into the asthenospheric mantle and their subsequent interaction with the lithosphere aided the localization of these unique scale uranium concentrations

hydrogeochemical and isotope evidence of groundwater evolution and recharge in minqin basin northwest china a hydrochemical investigation was conducted in the minqin basin to identify the groundwater evolution and recharge in the aquifer the mbr cl ratio is strongly depleted average 0 000451 compared with sea water 0 0035 indicating an evaporite origin the ionic ration plot saturation index si and chloro alkaline indices cai suggest that the dissolution of halite the glauberite gypsum dolomite and calcite determine na cl ca2 mg2 so42 and hco3 chemistry but other processes such as na exchange for ca2 and mg2 and calcite precipitation also contribute to the water composition the 6180 and 62 h in precipitation near the study area are linearly correlated similar to that for the world meteoric water line wmwl with an equation of delta h 2 7 49 delta o 18 5 11 r 2 0 97 according to radiocarbon residence time estimates the deep groundwater is approximatety 40 ka old and was recharged during a period when the climate was wetter and colder the radiocarbon content of shallow groundwater shows a clear evolution along the groundwater flow path from the beginning of the groundwater flow path to similar to 31 km the radiocarbon values are 73 6 pmc whereas beyond this point the values are 42 9 pmc based on radiocarbon content the shallow groundwater is older than 1 ka and represents pataeowaters mixed with a limited quality of modern recharge the rain fed groundwater direct recharge was estimated by chloride mass balance cmb method to range from 1 55 to 1 64 mm yr 1 with a mean value of 1 6 mm yr 1 this value represents about 1 5 of local rainfall the direct recharge volumes is about 0 666 x 10 8 m 3 yr 1 indirect recharge volumes by the surface water is about 0 945 x 10 8 m 3 yr 1 the total natural recharge in the minqin basin is 1 6 x 10 8 m 3 yr 1 whereas the groundwater abstraction has reached 11 6 x 10 8 m 3 yr 1 far exceeding the groundwater natural recharge c 2006 elsevier b v all rights reserved

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

paleovolcanic necks and extrusions indicators of large uranium orebelts in the territories joining russia mongolia and china abstract the large ore clusters and uranium deposits detected in southeast russia eastern transbaikal region eastern mongolia and northern china constitutes a large area specialised in u with a wide range of geological and mineral ore types amongst various types of uranium ore hydrothermal deposits related to volcanic rocks infiltration deposits of uranium sandstone and polygenous mineralisation in leucogranites represent main commercial interest large uranium clusters are located on the outer side and peripheral parts of the great xing an volcano plutonic belt as well as in the framing taphrogenic depressions the clusters formation timed to late mesozoic i k geodynamic processes deep geodynamics allowed the fluid flows of asthenosphere which were concentrating around the periphery of the slab stagnated in the transition mantle zone to penetrate into the above lithosphere and earth s crust with formation of pockets of magma and ore bearing volcano tectonic depressions eventually therefore the presence of igneous stocks extrusions and volcanic necks within the volcano plutonic belts and depressions can be indicative of mineral potential of the area

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

a record from lake cardiel of climate change in southern south america southern south america the only continental land mass lying between 38 s and the antarctic circle presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid latitude wind and pressure belts in the bulk of this region patagonia are many hydrographically closed lakes which despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1 2 have escaped detailed study using sedimentary and geomorphic evidence together with 14c dating we present here a detailed lake level record for lake cardiel fig 1 the highest level of the past 21 000 years occurred at about 9 780 bp reminiscent of tropical lakes rather than those in northern mid latitudes1 2 the lake cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in patagonia

the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile the geomorphology and sedimentology of the tempanos moraine at laguna san rafael chile journal of quaternary science 21 0 pp 1 15 sponsorship nerc rono ner b s 2002 00282

accelerating shrinkage of patagonian glaciers from the little ice age ad 1870 to 2011 davies b j glasser n f 2012 accelerating shrinkage of patagonian glaciers from the little ice age similar to ad 1870 to 2011 journal of glaciology 58 212 1063 1084

evidence of early holocene glacial advances in southern south america from cosmogenic surface exposure dating cosmogenic nuclide surface exposure dating reveals that glaciers in southern south america 46 s advanced at ca 8 5 and 6 2 ka likely as a result of a northward migration of the southern westerlies that caused an increase in precipitation and or a decrease in temperature at this latitude the older advance precedes the currently accepted initiation of holocene glacial activity in southern south america by 3000 yr both of these advances are temporally synchronous with holocene climate oscillations that occurred in greenland and the rest of the world if there are causal links between these events then rapid climate changes appear to be either externally forced e g solar variability or are rapidly propagated around the globe e g atmospheric processes

younger dryas and early holocene age glacier advances in patagonia reliable dating of southern hemisphere glacier fluctuations since the last glacial maximum lgm is crucial to resolving debates about millennial scale climate change here we present be 10 dates f

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

climate change during the last deglaciation in antarctica greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators in this work rapid climate change events in the northern and southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores high resolution glaciochemical series covering the period 10 000 to 16 000 years ago from a central greenland ice core and a new site in east antarctica display similar variability these findings suggest that rapid climate change events occur more frequently in antarctica than previously demonstrated

groundwater dynamics and arsenic contamination in bangladesh although arsenic contaminated groundwater in bangladesh is a serious health issue little is known about the complex transient patterns of groundwater flow that flush solutes from aquifers and carry solutes into the subsurface hydrologic modeling results for our field site in the munshiganj district indicate that groundwater flow is vigorous flushing the aquifer over time scales of decades to a century and also transporting solute loads into the aquifer with recharge from ponds rivers and rice fields the combined hydrologic and biogeochemical results from our field site imply that the biogeochemistry of the aquifer system may not be in steady state and that the net effect of competing processes could either increase or decrease arsenic concentrations over the next decades modeling results suggest that irrigation has greatly changed the location timing and chemical content of recharge to the aquifer flushing water through the system more quickly and also cycling large fluxes of water through rice fields during the dry season that could mobilize arsenic from oxides in near surface sediments furthermore the hydrologic model reveals that ponds many of which have been excavated over the last 50 years now provide much of the groundwater recharge these ponds receive most of the waste from the villages and thus provide another potential source of organic carbon to the groundwater system

holocene glacier fluctuations a global overview of glacier advances and retreats grouped by regions and by millennia for the holocene is compiled from previous studies the reconstructions of glacier fluctuations are based on 1 mapping and dating moraines defined by 14 c tcn osl lichenometry and tree rings discontinuous records time series and 2 sediments from proglacial lakes and speleothems continuous records time series using 189 continuous and discontinuous time series the long term trends and centennial fluctuations of glaciers were compared to trends in the recession of northern and mountain tree lines and with orbital solar and volcanic studies to examine the likely forcing factors that drove the changes recorded a general trend of increasing glacier size from the earlyemid holocene to the late holocene in the extra tropical areas of the northern hemisphere nh is related to overall summer temperature forced by orbitally controlled insolation the glaciers in new zealand and in the tropical andes also appear to follow the orbital trend i e they were decreasing from the early holocene to the present in contrast glacier fluctuations in some monsoonal areas of asia and southern south america generally did not follow the orbital trends but fluctuated at a higher frequency possibly triggered by distinct teleconnections patterns during the neoglacial advances clustered at 4 4e4 2 ka 3 8e3 4 ka 3 3e2 8 ka 2 6 ka 2 3e2 1 ka 1 5e1 4 ka 1 2e1 0 ka 0 7e0 5 ka corresponding to general cooling periods in the north atlantic some of these episodes coincide with multidecadal periods of low solar activity but it is unclear what mechanism might link small changes in irradiance to widespread glacier fluctuations explosive volcanism may have played a role in some periods of glacier advances such as around 1 7e1 6 ka coinciding with the taupo volcanic eruption at 232 5 ce but the record of explosive volcanism is poorly known through the holocene the compilation of ages suggests that there is no single mechanism driving glacier fluctuations on a global scale multidecadal variations of solar and volcanic activity supported by positive feedbacks in the climate system may have played a critical role in holocene glaciation but further research on such linkages is needed the rate and the global character of glacier retreat in the 20th through early 21st centuries appears unusual in the context of holocene glaciation though the retreating glaciers in most parts of the northern hemisphere are still larger today than they were in the early and or mid holocene the current retreat

recharge in karst and dune elements of a semi arid landscape as indicated by natural isotopes and chloride abstract the rates and mechanisms of local recharge in a semi arid environment have been investigated beneath two major landscape settings in the murray basin in south australia these were calcrete flats with sinkholes and sand dunes in adjacent landscape settings five minor settings were investigated and identified as undisturbed calcrete primary older sinkholes secondary younger sinkholes sand dunes with native vegetation and sand dunes with introduced pasture data from a limited series of boreholes were interpreted to suggest that recharge varied from in excess of 100 mm yr 1 for secondary sinkholes to less than 0 1 mm yr 1 beneath sand dunes with native vegetation the data suggest that recharge under sand dunes has increased by more than two orders of magnitude following clearing of the native vegetation 50 yr ago as 90 of an area of 10 000 km2 has been cleared this clearing has ensured that inflow of saline groundwater to the adjacent river murray will increase and in view of the amount of salt stored in both the unsaturated and saturated zones will continue for a very long time at sites where the inferred recharge is lowest profiles of the chloride concentration of soil water are consistent with the hypothesis that there is in excess of 50 000 yr recharge stored in the thick unsaturated zone some evidence for changes in recharge rate over this time scale is seen

chronology of bathymetric variations of the pueyrredon posadas salitroso lacustrine system during the late pleistocene to early holocene abstract the pueyrredon posadas salitroso lacustrine system pps ls is located in the andean patagonia region of argentina 47 22 28 s 71 55 34 w and represents a series of lakes formed as glaciers retreated during the late pleistocene and early holocene these lakes began as proglacial lakes and later evolved into periglacial lakes this research presents the chronological evolution of the pps ls bathymetric variations based on the analysis of stratigraphic profiles surveyed at different locations and the dates obtained from lake sediments four paleogeographic sketches representing the chronological evolution of the pps ls between 23 580 bp and 5208 bp have been developed based on the integration of these data

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

isotopic and trace element constraints on the origin and evolution of saline groundwaters from central missouri na ca cl groundwaters with salinities of 1 to 30 discharge from natural springs and artesian wells in mississippian carbonates and ordovician sandstones and carbonates in central missouri carbonate saturation and quartz supersaturation are maintained throughout the salinity range major and trace element and isotopic variations in the waters are used to place constraints on models for rock water interaction and regional hydrology the groundwaters have d values that range from 108 to 45 and 18 o values that range from 14 7 to 6 5 smow these data lie approximately along the meteoric water line ranging from values similar to local recharge in missouri to significantly lower values that are similar to 18 o and d for meteoric recharge in high altitude and high latitude regions of north america the more saline samples have the lowest 18 o and d contents a trend that is opposite to that observed in most other studies of saline waters the h o isotopic correlation and the range in salinity and several major and trace element concentrations in central missouri groundwaters are readily explained by a saline dilute water mixing model 87sr 86sr ratios for the groundwaters range from 0 7155 to 0 7161 these values are significantly higher than previously published values for 1 estimates of 87 sr 86 sr in phanerozoic seawater 0 7068 0 7092 and 2 carbonates of the mississippian burlington keokuk fm 0 7075 0 7105 through which some of the waters migrate as they pass to the surface nd 0 values in the groundwaters range from 10 9 to 8 1 and 147 sm 144 nd ratios range from 0 108 to 0 128 these values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the burlington keokuk fm mean nd 0 7 8 0 8 1 mean 147 sm 144 nd 0 141 the h o sr and nd isotopic data and the results of model calculations preclude 1 models involving the modification of ancient seawater for the origin of the saline waters and 2 extensive interaction between the groundwaters and their host carbonates the waters apparently acquired their 18 o and d values as meteoric recharge and their 87sr 86sr and rare earth element signatures from extraformational crustal sources high 87 sr 86 sr low nd 0 low 147sm 144nd and largely preserved these isotopic signatures during subsequent migration through the carbonates chemical exchange via rock water interaction is required for isotopic exchange to occur therefore the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock water interaction and hence preserve the extraformational isotopic signatures in the waters the integration of geochemical isotopic and hydrologic data on a local and regional scale suggests a history for the central missouri groundwaters involving 1 meteoric recharge in the front range of colorado 2 dissolution of permian halite in the subsurface of kansas 3 interaction with predominantly silicate mineral assemblages in paleozoic strata and possibly precambrian basement with aquisition of crustal sr and ree signatures 4 dilution and migration to shallow aquifer levels in central missouri and 5 mixing with local meteoric recharge through mississippian carbonates with no significant change of the isotopic signatures acquired in stage 3

evidence from the rio bayo valley on the extent of the north patagonian icefield during the late pleistocene holocene transition abstract this paper presents data on the extent of the north patagonian icefield during the late pleistocene holocene transition using cosmogenic nuclide exposure age and optically stimulated luminescence dating we describe geomorphological and geochronological evidence for glacier extent in one of the major valleys surrounding the north patagonian icefield the rio bayo valley geomorphological mapping provides evidence for the existence of two types of former ice masses in this area i a large outlet glacier of the north patagonian icefield which occupied the main rio bayo valley and ii a number of small glaciers that developed in cirques on the slopes of the mountains surrounding the valley cosmogenic nuclide exposure age dating of two erratic boulders on the floor of the rio bayo valley indicate that the outlet glacier of the icefield withdrew from the rio bayo valley after 10 900 1000 yr the mean of two boulders dated to 11 400 900 yr and 10 500 800 yr single grain optically stimulated luminescence osl dating of an ice contact landform constructed against this glacier indicates that this ice mass remained in the valley until at least 9700 700 yr the agreement between the two independent dating techniques osl and cosmogenic nuclide exposure age dating increases our confidence in these age estimates a date obtained from a boulder on a cirque moraine above the main valley indicates that glaciers advanced in cirques surrounding the icefield some time around 12 500 900 yr this evidence for an expanded north patagonian icefield between 10 900 1000 yr and 9700 700 yr implies cold climatic conditions dominated at this time

patagonian glacier response during the late glacial holocene transition whether cooling occurred in the southern hemisphere during the younger dryas yd is key to understanding mechanisms of millennial climate change although southern hemisphere records do not reveal a distinct climate reversal during the late glacial period many mountain glaciers readvanced we show that the puerto bandera moraine 50 s which records a readvance of the southern patagonian icefield spi formed at or shortly after the end of the yd the exposure age 10 8 0 5 thousand years ago is contemporaneous with the highest shoreline of lago cardiel 49 s which records peak precipitation east of the andes since 13 thousand years ago absent similar moraines west of the andes these data indicate an spi response to increased amounts of easterly sourced precipitation reflecting changes in the southern westerly circulation rather than regional cooling

high frequency holocene glacier fluctuations in new zealand differ from the northern signature understanding the timings of interhemispheric climate changes during the holocene along with their causes remains a major problem of climate science here we present a high resolution 10be chronology of glacier fluctuations in new zealand s southern alps over the past 7000 years including at least five events during the last millennium the extents of glacier advances decreased from the middle to the late holocene in contrast with the northern hemisphere pattern several glacier advances occurred in new zealand during classic northern warm periods these findings point to the importance of regional driving and or amplifying mechanisms we suggest that atmospheric circulation changes in the southwest pacific were one important factor in forcing high frequency holocene glacier fluctuations in new zealand

a geodynamic perspective of world class gold deposits in east asia abstract the world class gold ore districts of south east russia and north east china are located above the frontal and peripheral regions of subducted oceanic lithosphere accumulated as stagnant slabs in the mantle transition zone generated by paleo pacific plate subduction the highly productive ore systems of the aldan south yakutiya baley transbaikalia and zhao ye jiaodong metallogenic belts which are widely separated in space but formed at the same time are associated with similar mechanisms of huge magma flare ups in the middle jurassic early cretaceous driven by deep mantle processes their common features and crust mantle interaction signature offer important clues to mantle dynamics rooted along the periphery of the subducted slabs in a mega convergent zone in east asia

southern patagonian glacial chronology for the last glacial period and implications for southern ocean climate the magellan region of southern south america is in a unique setting at 50 s on the equatorial side of the antarctic frontal zone to record in detail terrestrial glacial to interglacial events a 10be chronology shows growth and millennial fluctuations of a patagonian ice sheet between 25 and 17 6 17 0 cal ka in the strait of magellan the maximum ice margin position is dated to 24 6 0 9 ka and other moraine ages are 18 5 1 8 and 17 6 0 2 ka mean 1 standard deviation in bahia inutil dated moraine ages are 20 4 1 2 and 17 3 0 8 ka the chronology of the local last glacial maximum lgm reveals a record of atmospheric cooling that was broadly in phase with changes in southern ocean conditions such as sea ice fluctuations and surface water characteristics published modeling results indicate that a decline in temperature of 6 c and slight drying over southernmost patagonia could simulate the growth and sustained presence of an ice sheet to the mapped lgm limit the terrestrial record in southern patagonia and marine records in adjacent oceans indicate mean northward movement of the antarctic frontal zone which caused the last southern south american ice age the antarctic frontal zone at present lies only 3 5 to the south some significant changes in the magellan region occurred in step with north atlantic region and the northern hemisphere for example the overall time span of the last glaciation and the timing of maximum ice extent were similar between the hemispheres despite maximum local summer insolation intensity in southern south america other characteristics of the southern patagonian glacial history differ from the north atlantic region specifically an out of phase relationship during deglaciation which is more similar to that of southern ocean and antarctic records

latest pleistocene and holocene glacial events in the colonia valley northern patagonia icefield southern chile the northern patagonia icefield npi is the primary glaciated terrain worldwide at its latitude 46 5 47 5 s and constraining its glacial history provides unique information for reconstructing southern hemisphere paleoclimate the colonia glacier is the largest outlet glacier draining the eastern npi ages were determined using dendrochronology lichenometry radiocarbon cosmogenic 10be and optically stimulated luminescence dated moraines in the colonia valley defined advances at 13 2 0 95 11 0 0 47 and 4 96 0 21 ka with the last being the first constraint on the onset of neoglaciation for the eastern npi from a directly dated landform dating in the tributary cachet valley which contains an ice dammed lake during periods of colonia glacier expansion defined an advance at ca 2 95 0 21 ka periods of advancement at 810 49 cal a bp and 245 13 cal a bp and retreat during the intervening periods recent colonia glacier thinning which began in the late 1800s opened a lower elevation outlet channel for lago cachet dos in ca 1960 our data provide the most comprehensive set of latest pleistocene and holocene ages for a single npi outlet glacier and expand previously developed npi glacial chronologies

impact of irrigation with as rich groundwater on soil and crops a geochemical case study in west bengal delta plain india abstract the distribution of as was explored in soils and crops in order to investigate the influence of irrigation with as rich groundwater on the soil plant system and to determine its impact on the environment and human health the study was carried out in an intensively cultivated agricultural area of the bengal delta plain west bengal india soils plants and irrigation water from adjacent rice and wheat fields were analysed for as and other elements irrigation water has concentrations of up to 780 g l 1 as in the study area rice and wheat grains are not contaminated by as about 0 3 and 0 7 mg kg 1 respectively but concentrations in rice roots were found to be 169 178 mg kg 1 as which is more than 20 times higher than value of 7 7 mg kg 1 measured at the uncontaminated reference site this high content is due to an fe rich plaque which coats the rice roots a significant increase of as concentration was registered also in the stems of the rice plants irrigated with as rich groundwater 6 55 7 06 relative to 0 36 mg kg 1 as in the reference plant arsenic concentration in the uppermost soil layers of the rice paddy field 38 mg kg 1 was found to be roughly twice as high as in the soil of the less intensively watered wheat field 18 mg kg 1 and more than 5 times higher than in the soil of a rice paddy irrigated with uncontaminated water 7 mg kg 1 in both soil sections as contents decreased downwards to 11 mg kg 1 at 100 110 cm depth approaching the background value of 5 10 mg kg 1 measured in an unaffected reference area sequential extraction experiments show that most of the mobile as in soils is bound to fe oxides though no tight correlation was found between fe and as in the bulk soil samples these experiments coupled with synchrotron radiation xrf analysis of single soil particles from the rice paddy also indicates that additional to the mobile fraction a substantial part of as is immobilized in chiefly fe bearing silicates in rice soil some as was also found in the sulphide bearing phase of the extraction

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

middle cambrian to permian subduction related accretionary orogenesis of northern xinjiang nw china implications for the tectonic evolution of central asia abstract middle cambrian to permian subduction related records are widely distributed in northern xinjiang which can be grouped into the chinese altay east junggar eastern tien shan west junggar yili and tarim domains by integrating paleogeographic and geological data we suppose that the chinese altay east junggar eastern tien shan domain was more closely located to siberia while the west junggar and yili domains occupied an intermediate position near the kazakhstan block in the early paleozoic paleoasian ocean distribution of andean type magmatic arcs island arcs accretionary wedges ophiolitic slices and or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences the tarim domain was on the opposite side of the early paleozoic paleoasian ocean remaining passive margin these tectonic units drifted northwards and approached the southern active margin of the siberian craton in the late paleozoic leading to termination of the paleoasian ocean and formation of a complicated orogenic collage between siberian craton and the tarim block between the end permian and triassic these multiple accretion processes significantly contributed to the lateral growth of central asia

holocene glacier fluctuations in patagonia are modulated by summer insolation intensity and paced by southern annular mode like variability abstract alpine glaciers are sensitive indicators of changes in climate and their ubiquity in mountainous regions make them valuable proxies for terrestrial climate reconstructions worldwide however the timing and extent of glacier change across the south american mid latitudes through the holocene are still poorly constrained relative to their counterparts in the northern hemisphere here we report a new 10be surface exposure based chronology of moraines recording a series of progressively less extensive glacier advances of glaciar torre argentina 49 3 s 73 0 w since the last glacial maximum with expansions culminating at 17 600 900 13 500 500 9700 400 6900 200 6100 300 4500 200 and 530 60 yr bp the declining magnitude of holocene glacier expansions parallels a gradual rise in local summer insolation intensity during the holocene while individual advances occurred during inferred negative southern annular mode sam like states at centennial to millennial timescales these observations suggest that i summer insolation intensity modulated antiphased trends in glacier extent in the polar hemispheres during the holocene and that ii centennial scale sam like temperature and precipitation anomalies paced glacier fluctuations throughout patagonia given the persistence of the inferred sam like anomalies throughout the holocene the modern measured trend towards positive sam index conditions could mark the onset of a fundamental shift in the climate of the southern hemisphere midlatitudes that warrants consideration in projections of future climate

geodynamics of late mesozoic pge au and u mineralization in the aldan shield north asian craton abstract late mesozoic pge au and u mineralization in the precambrian aldan shield constitutes important ore deposits on the southern margin of the siberian craton here we provide an overview of the salient characteristics of these ore deposits and evaluate their regional geodynamic setting geological geophysical and geochronological data on the distribution and timing of the ultramafic and alkaline magmatism in the aldan shield and the associated late jurassic early cretaceous pge au and u mineralization correlate with the convergence in the asia pacific zone during the late mesozoic the multistage magmatism and ore formation can be traced along the perimeter of the subducted slab now stagnant at the mantle transition zone the flanks of which coincide with paleo transform faults slab dehydration is considered to have transferred source metals through plume conduits resulting in the formation of productive ore magmatic systems

influence of irrigation practices on arsenic mobilization evidence from isotope composition and cl br ratios in groundwater from datong basin northern china environment isotopes 18o and 2h and cl br ratios in groundwater have been used to trace groundwater recharge and geochemical processes for arsenic contamination in datong basin the arsenic concentrations of groundwater samples ranged from 0 4 to 434 9 g l with the average of 51 2 g l which exceeded china s drinking water standard 10 g l all the groundwater samples are plotted on or close to the meteoric water line of the 18o vs 2h plot indicating their meteoric origin the relationship between 18o values and cl br ratios and cl concentrations demonstrate that leaching and mixing are the dominant processes affecting the distribution of high arsenic groundwater in this area the observed non linearity in the trend between 18o and arsenic concentration is due to combined effects of mixing and leaching the similarity of the trend in cl br ratios and 18o values for high arsenic groundwater demonstrate that extensive leaching of irrigation return and salt flushing water flow could be the dominant process driving arsenic mobilization in the groundwater system moreover the long term irrigation practice can cause the drastic change of the biogeochemical and redox condition of in the aquifer system which in turn promotes the mobilization of arsenic therefore groundwater pumping for irrigation in this area of waterborne endemic arsenic poisoning should be under strict control to protect groundwater quality in this area

the last glacial holocene transition in southern chile warming at the last glacial termination in the north atlantic region was interrupted by a period of renewed glacial activity during the younger dryas chronozone ydc the underlying mechanism of this cooling remains elusive but hypotheses turn on whether it was a global or a north atlantic phenomenon chronological sedimentological and palaeoecological records from sediments of small lakes in oceanic southern chile demonstrate that there was no ydc cooling in southern chile it is therefore likely that there was little or no cooling in southern pacific surface waters and hence that ydc cooling in the north atlantic was a regional rather than global phenomenon

gold deposits and gold metallogeny of far east russia abstract the russian far east or far east russia fer is host to a huge gold endowment and has produced more than 6500 t of gold since the 1860s much of this gold has come from several mining districts aldan upper amur lower amur okhotsk allakh yun yana kolyma priokhotie omolon and chukotka these districts include several gold deposits mostly of orogenic and epithermal nature as well as large and very large alluvial placer deposits the main gold districts are of late mesozoic age but there are also three districts aldan omolon and southern primorie with pre mesozoic gold ores and three districts kamchatka sakhalin south kurile and lower amur with gold ores of cenozoic age this review paper attempts to marshal on the regional scale all available data aiming to provide a framework for generating and testing new ideas on the gold deposits of fer the focus is on 1 gold metallogeny 2 details of key gold deposits and 3 relationship between gold ore forming processes metamorphic processes and granitoid intrusions in different geodynamic settings the largest gold metallogenic belts in fer were formed in the late mesozoic namely in the late jurassic yana kolyma early cretaceous eastern flank of mongol okhotsk aldan oloy chukotka okhotsk koryak and late cretaceous sikhote alin the mesozoic era was also the time when most of the gold hosting orogens were formed paleozoic mesozoic and cenozoic orogens resulted from the interaction between the pacific oceanic plates with the siberian craton and the north china craton these orogens are products of diverse geodynamic settings and can be divided into four types 1 collisional e g yana kolyma 2 accretionary or uncompleted collisional e g okhotsk koryak or kamchatka 3 combined collisional and transform margin mongol okhotsk and 4 active transform margin sikhote alin the first two types are typical of north east russia whereas the third and fourth types are in the southern part of fer the late cretaceous okhotsk chukotka and east sikhote alin gold provinces are associated with continental margin magmatic arcs and are post accretionary post orogenic comparison of lode gold deposits from different geodynamic settings reveals specific features in metallogeny of the late mesozoic orogens at the southern and eastern margins of the siberian craton yana kolyma collisional orogen okhotsk koryak accretionary orogen and mongol okhotsk transform margin orogen these orogens possess different metal associations the yana kolyma belt contains au sn w and cu pb zn lode deposits the late jurassic transbaikalian sector of the mongol okhotsk orogen contains au mo pb zn sn ta nb w hg sb lode deposits whereas early cretaceous au cu mo hg sb lode deposits are present in the amur sector finally the okhotsk koryak orogen hosts au cu mo cu w bi ag co bi as and be sn li w deposits of early cretaceous age epithermal gold deposits occur in two different geodynamic settings 1 island arcs kamchatka kurile islands and magmatic belts at active continental margins omolon okhotsk chukotka and eastern sikhote alin and 2 rift related magmatism linked with orogenic events and strike slip kinematics such as transform like continental margin settings aldan and upper amur in the mongol okhotsk orogen mineralogic geochemical and isotope systematics indicate a metamorphic magmatic origin of hydrothermal plutonic systems in collisional settings yana kolyma okhotsk koryak and oloy chukotka orogens and active continental margin okhotsk chukotka and east sikhote alin settings with source contributions from the lower crust and mantle the mongol okhotsk and sikhote alin orogens are of transform fault related origin and suggest a source of the ore forming fluids mostly from the mantle

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

the glacial geomorphology and pleistocene history of south america between 38 s and 56 s abstract this paper presents new mapping of the glacial geomorphology of southern south america between latitudes 38 s and 56 s approximately the area covered by the former patagonian ice sheets glacial geomorphological features including glacial lineations moraines meltwater channels trimlines sandur and cirques were mapped from remotely sensed images landsat 7 etm pan sharpened landsat 7 and aster the landform record indicates that the patagonian ice sheets consisted of 66 main outlet glaciers together with numerous local cirque glaciers and independent ice domes in the surrounding mountains in the northern part of the mapped area in the chilean lake district 38 42 s large piedmont glaciers developed on the western side of the andes and the maximum positions of these outlet glaciers are in general marked by arcuate terminal moraines to the east of the andes between 38 s and 42 s outlet glaciers were more restricted in extent and formed alpine style valley glaciers along the eastern flank of the andes south of 45 s a series of large fast flowing outlet glaciers drained the ice sheet the location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes west of the andes at this latitude there is geomorphological evidence for an independent ice cap close to sea level on the taitao peninsula the age of this ice cap is unclear but it may represent evidence of glacier growth during the antarctic cold reversal and or younger dryas chronozone maximum glacier positions are difficult to determine along much of the western side of the andes south of 42 s because of the limited land there and it is assumed that most of these glaciers had marine termini in the south east of the mapped area in the fuegan andes cordillera darwin the landform record provides evidence of ice sheet initiation by adding published dates for glacier advances from the literature we present maps of pre last glacial maximum lgm glacier extent lgm extent and the positions of other large mapped moraines younger than lgm in age a number of large moraines occur within the known lgm limits the age of these moraines is unknown but since many of them lie well outside the established maximum neoglacial positions the possibility that they reflect a return to glacial climates during the younger dryas chronozone or antarctic cold reversal cannot be discounted

cosmogenic nuclide exposure ages for moraines in the lago san martin valley argentina at several times during the quaternary a major eastward flowing outlet glacier of the former patagonian ice sheet occupied the lago san martin valley in argentina 49 s 72 w we present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide 10be exposure ages n 10 of boulders on moraines and lake shorelines there are five prominent moraine belts in the lago san martin valley associated with extensive sandar glaciofluvial outwash plains and former lake shorelines cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14 3 1 7 ka 22 4 2 3 ka 34 4 3 4 ka to 37 6 3 4 ka and possibly 60 3 5 ka and 99 11 ka 1 these dated glacier advances differ from published chronologies from the lago san martin valley based on 14c age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges the moraine boulder ages also point to possible pre lgm glacial advances during the last glacial cycle and a key observation from our data is that the lgm glaciers were probably less extensive in the lago san martin valley than previously thought

deglacial holocene environmental changes at the pacific entrance of the strait of magellan abstract we show environmental and nitrogen cycle changes between 13 and 2 5 kyr bp from the latest deglaciation to the holocene based on biogeochemical records in a sediment core from the pacific entrance of the strait of magellan organic carbon total nitrogen and c 37 alkenone contents were low during 13 9 kyr bp but increased rapidly at 8 kyr bp the relative contribution of tetra unsaturated c 37 alkenone used as a salinity proxy suggests low salinity during 13 9 kyr bp changing to high salinity at 8 kyr bp planktic foraminifer data showed that globigerina bulloides was more abundant during the deglacial early holocene than in the mid late holocene whereas abundances of neogloboquadrina pachyderma showed the opposite pattern this evidence plus biogenic opal data suggest that sea level rose surface waters were relatively stratified and in situ productivity was low except for organisms with opal tests from 13 to 9 kyr bp bulk 15 n values were high 9 11 relative to present day values during the deglacial early holocene with consistently lower values 7 after 8 kyr bp these relatively high 15 n values most likely reflect increased nutrient utilization in the southern ocean which resulted in high 15 n water being advected to the patagonian fjords although local denitrification caused by the delivery of copious terrestrial materials and organic matter to the ocean cannot be ruled out by 8 kyr bp continental influences and surface stratification were reduced and characteristic holocene conditions were established with increased influence of southern ocean water in the western strait of magellan sea surface temperatures showed millennial scale changes during the deglaciation and early holocene with relatively warm temperatures 11 12 c corresponding to the antarctic counterpart of the younger dryas cooling event of the northern hemisphere the longer term pattern 10 kyr time scale in alkenone derived sea surface temperatures generally follows orbital changes in insolation during austral spring suggesting a controlling influence of austral spring insolation on southern patagonian climate

mobility of arsenic in west bengal aquifers conducting low and high groundwater arsenic part i comparative hydrochemical and hydrogeological characteristics abstract the present study demonstrates the importance of hydrogeochemical characteristics groundwater flow and recharge of an aquifer in the release of as to groundwater the study area 20 km 2 is located in chakdaha block nadia district west bengal which hosts groundwaters of variable as content the spatial distribution pattern of as is patchy with areas containing groundwater that is high in as 200 g l 1 found in close vicinity to low as 1 groundwaters within 100 m the concentration of groundwater as is found to decrease with depth in addition the data shows that there is no conspicuous relationship between high groundwater as concentration and high groundwater abstraction although the central cone of depression has enlarged over 2 a and is extending towards the se of the study area the river hooghly which forms the nw boundary of the study site shows dual behaviour effluent and influent during pre and post monsoon periods respectively complicating the site hydrogeology the observed groundwater flow lines tend to be deflected away from the high as portion of the aquifer indicating that groundwater movement is very sluggish in the as rich area this leads to a high residence time for this groundwater package prolonging sediment water interaction and hence facilitating groundwater as release

early and mid holocene age for the tempanos moraines laguna san rafael patagonian chile data about the nature and timing of holocene events from the southern hemisphere especially in southern south america are required to provide insight into the extent and nature of past climate change in a region where land based records are restricted here we present the first use of single grain optically stimulated luminescence osl dating of a moraine sequence recording glacial advance along the western side of the patagonian icefields dates from the tempanos moraines at laguna san rafael lsr show that the san rafael glacier srg advanced to maximum holocene positions during the period 9 3 to 9 7 ka and at 5 7 ka outwash lying beneath the moraine in its northern portion dated to 7 7 ka indicates that the glacier front was also advanced at this time since these advances span both the regional early holocene warm dry phase 11 5 ka to 7 8 ka and the subsequent cooling and rise in precipitation in the mid late holocene since 6 6 ka we infer that the advances of the srg are not simply climate driven but that the glacier has also probably responded strongly to non climatic stimuli such as internal ice dynamics and the transition between calving and non calving many westwards flowing glaciers in patagonia were probably calving during much of the late pleistocene and holocene so we conclude that establishing robust glacial chronologies where climatic and non climatic factors cannot be distinguished is likely to remain a challenge

stagnant slab a review a stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above across or below the 660 km discontinuity this phenomenon has now been widely recognized beneath subduction zones around the circum pacific and in the mediterranean collaboration of seismic and electromagnetic observations mineral physics measurements and geodynamic modeling has begun to provide a consistent picture of stagnant slab

variations in sediment yield over the advance and retreat of a calving glacier laguna san rafael north patagonian icefield abstract bathymetric and sub bottom acoustic data were collected in laguna san rafael chile to determine sediment yields during the little ice age advance and subsequent retreat of san rafael glacier the sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance retreat cycle sediment yields from san rafael glacier averaged 2 7 107 m3 a since the end of the little ice age circa ad 1898 corresponding to average basin wide erosion rates of 23 9 mm a the highest erosion rates 68 23 mm a occurred at the start of the retreat phase and have since been steadily decreasing erosion rates were much lower during glacial advance averaging at most 7 mm a than during retreat such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today the detailed sub bottom information of a proglacial lagoon yields important clues as to the timing of erosion deposition and transfer of glacigenic sediments from orogens to the continental shelves and the influence of glacier dynamics on this process

genesis of arsenic fluoride enriched soda water a case study at datong northern china abstract the high as and f groundwaters from datong basin are mostly soda waters with a na cl so4 meq ratio greater than unity as and f up to 1550 g l and 10 4 mg l respectively and with ph between 7 6 and 9 1 geochemical modeling indicates that the waters are oversaturated with respect to calcite and clay minerals such as kaolinite and undersaturated with respect to primary rock forming minerals such as anorthite and albite the water chemistry also is affected by evapotranspiration the degree of evaporative enrichment is up to 85 in terms of cl results of the hydrogeochemical studies indicate that the occurrence of soda water at datong is the result of incongruent dissolution of aluminosilicates at one stage of their interaction with groundwater when the water is oversaturated with respect to calcite and evapotranspiration related salt accumulation is not too strong studying the genesis of soda waters provides new insights into mechanism of as and f enrichment in the aquifer system due to caf2 solubility control and oh f exchange reactions f can be enriched in soda water and the high ph condition of soda water favors as desorption from oxyhydroxide surfaces thereby increasing the concentration of as in the aqueous phase

characteristics of tide water calving at glaciar san rafael chile glacial calving is a poorly understood process this study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at glaciar san rafael chile near the terminus of the glacier surface speeds average 17 m d 1 in summer and calving is profuse and continual the size location and characteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992 together with meteorological bathymetric and oceanographic data mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 mm 3 d 1 mean annual calving speed and calving flux are about 4500 m a 1 and 2 0 km 3 a 1 respectively this calving speed is higher than that predicted by the established empirical relationship between tide water calving speed and water depth this is surprising given the low salinity of laguna san rafael and that fresh water calving speeds are commonly much lower than those in tide water daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables but tidal stage may have some control over the timing of large submarine calving events submarine calving produced the largest bergs however the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

glaciar leon chilean patagonia late holocene chronology and geomorphology harrison s glasser n f winchester v haresign e warren c duller g a t bailey r ivy ochs s jansson k kubik p 2008 glaciar leon chilean patagonia late holocene chronology and geomorphology the holocene 18 4 pp 643 652 sponsorship nerc university of st andrews american alpine club british geomorphological research group dudley stamp memorial trust royal scottish geographical society quaternary research association carnegie trust for the universities of scotland

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified