late carboniferous to permian sedimentation in inner mongolia china and tectonic relationships between north china and siberia a belt of deformed permo carboniferous sedimentary rocks in inner mongolia represents an orogenic zone between the north china and siberian blocks the belt apparently contains accretionary terranes thrust onto the margins of both blocks with scattered ophiolite blueschist suites indicating the consumption of oceanic crust at least slightly older than the age of deformation upper carboniferous to lower permian strata in central inner mongolia show both sedimentological and paleontological differences from middle and upper permian rocks in comparison with pre middle permian rocks younger permian strata 1 contain less laterally extensive limestone and more lensoidal carbonate in clastic sections 2 contain a higher percentage of coarse clastic material 3 grade upward from marine to terrestrial deposits 4 contain fauna indicating more restricted circulation particularly toward the western part of the belt and 5 contain fauna that are consistent with but do not require northward movement

the structure biological activity and biogeochemistry of cryoconite aggregates upon an arctic valley glacier longyearbreen svalbard glacier surfaces support unique microbial food webs dominated by organic and inorganic debris called cryoconite observations from longyearbreen spitsbergen show how these aggregate particles can develop an internal structure following the cementation of mineral grains mostly quartz and dolomite by filamentous microorganisms measurements of carbon and dissolved o2 show that these microorganisms mostly cyanobacteria promote significant rates of photosynthesis average 17 gc g 1 d 1 which assist aggregate growth by increasing the biomass and producing glue like extracellular polymeric substances the primary production takes place not only upon the surface of the aggregates but also just beneath due to the translucence of the quartz particles however since total photosynthesis is matched by respiration average 19 gc g 1 d 1 primary production does not contribute directly to cryoconite accumulation upon the glacier surface the microorganisms therefore influence the surface albedo most by cementing dark particles and organic debris together rather than simply growing over it time lapse photographs show that cryoconite is likely to reside upon the glacier for years as a result of this aggregation these observations therefore show that a better understanding of the relationship between supraglacial debris and ablation upon glaciers requires an appreciation of the biological processes that take place during summer

contemporary rates of chemical denudation and atmospheric co2 sequestration in glacier basins an arctic perspective this paper presents new estimates of solute fluxes from five high arctic glacier basins in svalbard these estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on svalbard and to estimate rates of temporary or transient co2 drawdown we use a solute provenance model to partition solutes into marine aerosol atmospheric and crustal components and to estimate their annual fluxes crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 meq m 2 a 1 for svalbard range 160 560 meq m 2 a 1 which lies within the global range of 94 4200 meq m 2 a 1 for 21 glacier basins in the northern hemisphere and is close to the continental average of 390 meq m 2 a 1 specific annual discharge is the most significant control upon chemical denudation in the glacierized basins and basin lithology is an important secondary control with carbonate rich and basaltic lithologies currently showing the greatest chemical denudation rates estimates of transient co2 drawdown are also directly associated with specific annual discharge and rock type on svalbard transient co2 drawdown lies in the range 110 3000 kg c km 2 a 1 whilst the range is 110 13000 kg c km 2 a 1 for the northern hemisphere glacial data set transient co2 drawdown is therefore usually low in the svalbard basins unless carbonate or basalt rocks are abundant the analysis shows that a large area of uncertainty in the transient co2 drawdown estimates exists due to the non stoichiometric release of solute during silicate hydrolysis silicate hydrolysis is particularly non stoichiometric in basins where the extent of glacierization is high which is most probably an artefact of high flushing rates through ice marginal and subglacial environments where k feldspars are undergoing mechanical comminution copyright 2000 john wiley sons ltd

paleomagnetism of paleozoic and mesozoic sediments from the southern margin of mongol okhotsk ocean far eastern russia 1 this paper presents new data from paleomagnetic investigations of middle paleozoic early middle late devonian early carboniferous and middle jurassic geological units from the amuria block south of the mongol okhotsk suture zone with fold tests for all localities and two polarities for the devonian our new results constrain the evolution of the mongol okhotsk ocean from the devonian to the middle jurassic the corresponding paleopoles lie at 21 6 n 6 3 e dp dm 5 3 10 6 for early devonian 26 3 n 345 3 e dp dm 6 4 12 8 for early middle devonian 24 6 n 12 9 e dp dm 8 7 16 9 for middle late devonian 40 5 n 352 4 e dp dm 9 16 7 for late devonian 39 8 n 31 6 e dp dm 10 15 5 for early carboniferous and 46 n 37 9 e dp dm 9 4 13 4 for middle jurassic the poles confirm that the large paleozoic mongol okhotsk ocean closed during the jurassic ending up in the late jurassic or early cretaceous at the eastern end of the suture zone as originally proposed on geological grounds the new paleomagnetic results exhibit large tectonic rotations about local vertical axes which we interpret as probably arising from both the collision process and left lateral shear movement along the suture zone related to incipient extrusion of amuria due to indentation of india into asia

late paleozoic polar wander path for the tarim platform and its tectonic significance abstract stepwise thermal and a f demagnetizations have been carried out on 518 samples 47 sites from the sishichang section across the akesu area in the tarim basin the results lead to a discussion on some problems concerning the tectonic history of the tarim platform and adjacent blocks during the late paleozoic from the late carboniferous until the early permian the tarim platform collided with the kazakhstan block siberian platform and russian platform no large displacements have occurred between these blocks since the mesozoic however the permian pole position of the tarim platform obviously differs from that for the sino korea platform the difference in paleolatitude between the tarim and sino korea platforms in the permian was about 10 their orientations were also different the paleomagnetic result is in contrast to the geologically accepted idea that the two platforms in question occur as a whole in the late paleozoic

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

late miocene adakites and nb enriched basalts from vizcaino peninsula mexico indicators of east pacific rise subduction below southern baja california a typical slab melt association was emplaced from 11 to 8 ma in the santa clara volcanic field vizcaino peninsula baja california sur it includes adakitic domes and associated pyroclastic flow deposits together with lava flows of niobium enriched basalts the trace element and isotopic sr nd pb signatures of adakites are consistent with melting of altered mid ocean ridge basalts and the sources of the nb enriched basalts contain an enriched mantle wedge component such associations commonly form at depths of 70 80 km during low dip subduction of very young oceanic crust however the santa clara field is relatively close 100 km to the paleotrench which suggests that the genesis of its adakites and nb enriched basalts occurred in a very high thermal regime linked to the subduction of the then active guadalupe spreading center of the east pacific rise our data suggest that the asthenospheric window documented below northern baja california also developed beneath the south of the peninsula during the neogene this hypothesis is consistent with the spatial distribution and the ages of adakites and magnesian andesites from this region

concentration of gold in in situ laterites from mato grosso the gold concentration studied is located in lateritic soils overlying precambrian schists of the cuiaba group in mato grosso brazil the following five horizons may be recognized from bottom to top 1 a gray blue altered schist horizon 2 a red argillaceous alterite 3 a horizon characterized by iron oxihydroxide rich pebbles and quartz fragments in an iron oxihydroxide rich matrix and clays 4 an iron crust and 5 the present soil the most significant gold content is found in the third horizon just below the iron crust according to geological study and morphological observations of the gold particles the gold ore mined today is the result of two combined processes i e the ferrallitic alteration of quartz lodes enclosed in schists and the effect of the red argillaceous alterite which acts as an impervious structure preventing the largest gold grains from migrating downward during their mechanical concentration

seasonal release of anoxic geothermal meltwater from the katla volcanic system at solheimajokull iceland understanding patterns of geothermal and volcanic activity at many of iceland s most active volcanic systems is hampered by thick overlying ice which prevents direct observation and complicates interpretation of geophysical signals katla is a prime example being a large and restless volcanic system covered by the 740 m thick m rdalsjokull ice cap whose eruptions have triggered some of the most powerful known meltwater floods in historical times to shed new light on geothermal and subglacial hydrological processes at katla we have determined the sulphate isotopic composition of a series of glacial meltwater samples discharged from solheimajokull a valley glacier of m rdalsjokull between 2009 and 2012 dual isotopic analysis of 34s and 18o in dissolved sulphate allows identification of source mixing processes and chemical evolution during subglacial meltwater transport strikingly meltwater 18oso4 signatures indicate redox conditions at the glacier bed which are inverse to those normally encountered at arctic and alpine glaciers discharge of reduced anoxic meltwater in summer rather than winter points towards seasonal release of geothermally derived volatile gases we attribute this to headward expansion of the channelized subglacial drainage system during the summer melt season accessing key areas of geothermal activity within the katla caldera volatile release may be further enhanced by unloading of overburden pressure due to snowpack melting in the summer season in winter restriction of subglacial channels to lower elevations effectively seals geothermal fluids and dissolved gases beneath the ice cap with only sporadic release permitted by periodic increases in subglacial water pressure when the subglacial drainage configuration permits access to key geothermal areas sulphate isotopic signatures thereby form sensitive indicators of geothermal activity occurring deep beneath the m rdalsjokull ice cap

geocryological processes linked to high arctic proglacial stream suspended sediment dynamics examples from bylot island nunavut and spitsbergen svalbard recent research has identified differences in processes contributing to suspended sediment concentration ssc dynamics in proglacial streams between high arctic and alpine catchments but does not examine processes explicitly linked to the periglacial environment three glacierized basins were studied austre broggerbreen and midre lov enbreen svalbard 79 n 12 e and glacier b28 unofficially named stagnation glacier bylot island nunavut 73 n 78 w ssc variations were modelled from continuous turbidity discharge and meteorological data throughout the summer months three statistical tools were utilized principal component analysis changepoint analysis and multivariate regression these are shown to be effective in identifying subperiods of distinctive geocryological and glaciofluvial characteristics multivariate regression for the subseasons included autoregressive integrated moving average modelling and showed that ssc variations were related not only to discharge variability but also to fluctuations in energy fluxes the results are interpreted in terms of spatio temporal changes in sediment mobilization and supply associated with changes in the relative importance of fluvial glacial and periglacial processes this evidence supports the notion of important linkages between glacial fluvial and periglacial systems but exemplifies distinct variability between high arctic glaciers copyright 2005 john wiley sons ltd

convective self aggregation and tropical cyclogenesis under the hypohydrostatic rescaling abstractthe behavior of rotating and nonrotating aggregated convection is examined at various horizontal resolutions using the hypohydrostatic or reduced acceleration in the vertical rave rescaling this modification of the equations of motion reduces the scale separation between convective and larger scale motions enabling the simultaneous and explicit representation of both types of flow in a single model without convective parameterization without the rave rescaling a dry bias develops when simulations of nonrotating radiative convective equilibrium are integrated at coarse resolution in domains large enough to permit convective self aggregation the rescaling reduces this dry bias and here it is suggested that the rescaling moistens the troposphere by weakening the amplitude and slowing the group velocity of gravity waves thus reducing the subsidence drying around aggregated convection separate simulations of rotating radiative convective equilibrium exhibit tropical cyclogenesis as horizo

multi year water and surface energy budget of a high latitude polythermal glacier evidence for overwinter water storage in a dynamic subglacial reservoir this paper examines the water budget and surface energy balance of a svalbard glacier midre lovenbreen over a 6 year period 1997 2002 fresh water yields are found to lie between 1 1 and 1 5 m a 1 and reflect variable amounts of glacier ice ablation 0 27 0 15 m a 1 and more consistent amounts of snowmelt and summer precipitation 0 40 0 10 and 0 49 0 12 m respectively between 24 and 36 of the annual runoff is thought to pass through a subglacial drainage system although the site is heavily influenced by stable maritime air masses during the summer surface melting is achieved largely by net shortwave radiation fluxes 74 100 of ablation water budget analysis shows that the annual runoff yields may be strongly influenced by water storage within the glacial system storage can occur over the winter period and force the early development of the subglacial drainage system during the following summer thus annual water fluxes from this glacier cannot be estimated from glacial mass balance data alone and there is a need to assess the implications of overwinter storage for our understanding of glacial dynamics annual fluvial process rates and mixing processes in svalbard s fjords

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

the hydrochemistry of meltwaters draining a polythermal based high arctic glacier south svalbard i the ablation season solute and runoff time series at finsterwalderbreen svalbard provide evidence for considerable basal routing of water and the existence of at least two contrasting subglacial chemical weathering environments the hydrochemistry of a subglacial upwelling provides evidence for a snowmelt fed subglacial reservoir that dominates bulk runoff during recession flow high concentrations of cl and crustal ions high pco2 and ratios of so2 4 so2 4 hco 3 close to 0 5 indicate the passage of snowmelt through a subglacial weathering environment characterized by high rock water ratios prolonged residence times and restricted access to the atmosphere at higher discharges bulk runoff becomes dominated by icemelt from the lower part of the glacier that is conveyed through a chemical weathering environment characterized by low rock water ratios short residence times and free contact with atmospheric gases these observations suggest that icemelt is routed via a hydrological system composed of basal ice marginal englacial and supraglacial components and is directed to the glacier margins by the ice surface slope upwelling water flows relatively independently of icemelt to the terminus via a subglacial drainage system possibly constituting flow through a sediment layer cold basal ice at the terminus forces it to take a subterranean routing in its latter stages the existence of spatially discrete flow paths conveying icemelt and subglacial snowmelt to the terminus may be the norm for polythermal based glaciers on svalbard proglacial mixing of these components to form the bulk meltwaters gives rise to hydrochemical trends that resemble those of warm based glaciers these hydrochemical characteristics of bulk runoff have not been documented on any other glacier on svalbard to date and have significance for understanding interactions between thermal regime and glacier hydrology 1998 john wiley sons ltd

permian gondwana boreal antitropicality with special reference to brachiopod faunas in a reconstructed global permian marine biogeographic framework antitropicality is defined as a biogeographic phenomenon whereby a taxon occurs only in the boreal and gondwanan realms and is lacking completely or nearly so in the intervening palaeoequatorial realm we recognise three types of antitropical distributions bipolar high latitude generally 50 latitude in each hemisphere bitemperate approximately between 30 and 50 latitudes in each hemisphere and a combination of both evidence of permian antitropicality has been reported from almost all major marine invertebrate groups both pelagic or benthic forms and is best known at the generic level although an increasing number of antitropical species have also been recognised antitropicality appears to have occurred throughout most of the permian but its strength varied from stage to stage judging by the number of brachiopod genera shared between the two hemispheres the phenomenon manifests itself most strongly from the sakmarian to the kazanian wordian suggesting a prolonged interval of enhanced biotic interchanges between the gondwanan and boreal realms possible migration pathways and mechanisms are reviewed and discussed among a number of existing scenarios invoked to explain the origin of both modern and geological antitropicality we here present data particularly supporting 1 a south to north stepping stone migratory mechanism via island terranes scattered in the eastern palaeotethys 2 a vicariance model exemplified by the spatio temporal distribution of tomiopsis and 3 a shelf north to south migration along the western coast of the palaeotethys as suggested by sowerbina in addition we also consider dispersal along the western coast of pangea facilitated at times by upwelling systems as an additional migration pathway for intercontinental biotic exchanges during the permian although corroborating data are required at present

generation of oceanic island basalt type volcanism in the western trans mexican volcanic belt by slab rollback asthenosphere infiltration and variable flux melting mantle plumes or decompression melting of a heterogeneous mantle have been proposed to explain oceanic island basalt oib type lavas found in the western trans mexican volcanic belt we show that mantle plumes cannot account for several geologic observations whereas decompression melting is unrealistic given the low extension rate in the volcanic arc on the basis of new geologic and geochemical studies we propose an alternative model that reconciles geologic data plate tectonic history and petrology since 8 5 ma the volcanic front has migrated trenchward 80 km and oib began to be emplaced in the rear half of the arc after a period of stalled subduction of the rivera plate between 7 2 and 4 8 ma as a whole oib accounts for 5 of the total volume of volcanism their trace element signatures require an enriched mantle source akin to the deep asthenosphere but also indicate a minor involvement of a subduction component we propose that during the period of very low convergence at the end of the miocene the leading edge of the rivera slab started to sink into the mantle and continued rolling back until it reached the present dip of 45 the sinking of the slab may have induced small amounts of asthenosphere to flow laterally into the opening mantle wedge from the gulf of california rift on the west and through the subducted rivera cocos plate boundary on the east this mechanism would produce veins of relatively enriched mantle which would be able to produce melts with an oib composition once the flux of fluids released from the subducted slab resumed

evidence for seasonal subglacial outburst events at a polythermal glacier finsterwalderbreen svalbard bulk runoff and meteorological data suggest the occurrence of two meltwater outburst events at finsterwalderbreen svalbard during the 1995 and 1999 melt seasons increased bulk meltwater concentrations of cl during the outbursts indicate the release of snowmelt from storage bulk meltwater hydrochemical data and suspended sediment concentrations suggest that this snowmelt accessed a chemical weathering environment characterized by high rock water ratios and long rock water contact times this is consistent with a subglacial origin the trigger for both the 1995 and 1999 outbursts is believed to be high rates of surface meltwater production and the oversupply of meltwater to areas of the glacier bed that were at the pressure melting point but which were unconnected to the main subglacial drainage network an increase in subglacial water pressure to above the overburden pressure lead to the forcing of a hydrological connection between the expanding subglacial reservoir and the ice marginal channelized system the purging of ice blocks from the glacier during the outbursts may indicate the breach of an ice dam during connection although subglacial meltwater issued continually from the glacier terminus via a subglacial upwelling during both melt seasons field observations showed outburst meltwaters were released solely via an ice marginal channel it is possible that outburst events are a seasonal phenomenon at this glacier and reflect the periodic drainage of meltwaters from the same subglacial reservoir from year to year however the location of this reservoir is uncertain a 100 m high bedrock ridge traverses the glacier 6 5 km from its terminus the overdeepened area up glacier from this is the most probable site for subglacial meltwater accumulation copyright 2001 john wiley sons ltd

comments on petrology of the hegenshan ophiolite and its implication for the tectonic evolution of northern china by t nozaka and y liu earth planet sci lett 202 2002 89 104

dissolved oxygen variations in alpine glacial meltwaters recent models of chemical weathering in alpine glacial meltwaters suggest that sulphide oxidation is a major source of solute in the distributed component of the subglacial hydrological system this reaction requires o2 and may lower dissolved oxygen levels to below saturation with respect to the atmosphere this should result in an inverse association between so72 and dissolved oxygen saturation however measurements of o2 saturation in bulk meltwaters draining the haut glacier d arolla switzerland show that there is a positive association between so42 and o2 saturation the o2 content of glacial meltwaters depends on the initial content of snow and icemelt which may be controlled by the rate of melting and the kinetic balance between o2 losses e g sulphide oxidation microbial respiration and gains e g diffusion of o2 into solution

biogeochemistry and dissolved oxygen dynamics at a subglacial upwelling midtre lovenbreen svalbard there is a growing awareness that biological processes affect solute acquisition in glacial meltwaters an unprecedented high resolution record of dissolved oxygen do in emergent subglacial meltwaters at polythermal midtre lovenbreen svalbard is discussed in conjunction with the major ion chemistry of periodic water samples within the catchment the subglacial outburst increased solutes passing through the proglacial area and was coupled to a seasonal transition in upwelling character from suboxic waters to those with large diurnal fluctuations in the levels of do saturation latterly returning to sustained suboxic runoff during the period of daily variation do correlated positively with discharge and inversely to total dissolved solute concentration consideration of so 4 2 concentrations showed they exceed those achievable with complete consumption of do in saturated supraglacial meltwater and dissolution experiments illustrated protracted abiotic sulphide oxidation remains an unlikely cause similarly relatively elevated ratios of no 3 ci preclude denitrification aiding the catalysis of sulphide oxidation results here tentatively suggest sulphide oxidation is mediated by both aerobic and anoxic biochemical processes and that transition metals are the most likely oxidants bacteria are shown to impart a major control on the ionic composition of subglacial upwelling with variability in the ratio of oxygenated surface meltwaters and suboxic subglacial waters

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

exploring former subglacial hodgson lake antarctica paper i site description geomorphology and limnology at retreating margins of the antarctic ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered this paper presents a site description of one of these lakes hodgson lake situated on southern alexander island west of the antarctic peninsula 72 00 549 s 68 27 708 w first we describe the physical setting of the lake using topographic and geomorphological maps second we determine local ice sheet deglaciation history and the emergence of the lake using cosmogenic isotope dating of glacial erratics cross referenced to optically stimulated luminescence dating of raised lake shoreline deltas formed during ice recession third we describe the physical and chemical limnology including the biological and biogeochemical evidence for life results show that the ice mass over hodgson lake was at least 295 m thick at 13 5 ka and has progressively thinned through the holocene with the lake ice cover reaching an altitude of c 6 5 m above the present lake ice sometime after 4 6 ka thick perennial ice cover persists over the lake today and the waters have remained isolated from the atmosphere with a chemical composition consistent with subglacial melting of catchment ice the lake is ultra oligotrophic with nutrient concentrations within the ranges of those found in the accreted lake ice of subglacial lake vostok total organic carbon and dissolved organic carbon are present but at lower concentrations than typically recorded in continental rain no organisms and no pigments associated with photosynthetic or bacterial activity were detected in the water column using light microscopy and high performance liquid chromatography increases in so4 and cation concentrations at depth and declines in o2 provide some evidence for sulphide oxidation and very minor bacterial demand upon o2 that result in small perhaps undetectable changes in the carbon biogeochemistry however in general the chemical markers of life are inconclusive and abiotic processes such as the diffusion of pore waters into the lake from its benthic sediments are far more likely to be responsible for the increased concentrations of ions at depth the next phases of this research will be to carry out a palaeolimnological study of the lake sediments to see what they can reveal about the history of the lake in its subglacial state and a detailed molecular analysis of the lake water and benthos to determine what forms of life are present combined these studies will test some of the methodologies that will be used to explore deep continental subglacial lakes

solute acquisition in glacial melt waters i fjallsjokull south east iceland bulk melt waters with closed system characteristics l etude de la composition des eaux de surface cations alcalinite sulfates et ph montre des modifications par rapport aux precipitations par l acquisition de substances dissoutes provenant de l alteration et de la dissolution de debris rocheux dans un systeme ouvert aux gaz carbonique atmospherique les eaux resurgentes ont des compositions variables calcite qui peuvent provenir de l eau de surface

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

40ar 39ar and k ar dating on the volcanic rocks in the songliao basin ne china constraints on stratigraphy and basin dynamics precise 40ar 39ar and k ar ages were determined on sanidine and whole rock separates of volcanic rocks in the songliao basin sb the volcanism is characterized by a series of continual and episodic eruptions in the late jurassic 147 157 ma and early cretaceous 113 136 ma a fairly accurate chronostratigraphic column was first established based on those data the volcanic activities happened synchronously with closure of the mongolia okhotsk ocean north to the sb structures of the volcanogenic successions are s dipping or se dipping fault blocks coupled with n dipping or nw dipping major detachment systems distribution of the volcanics revealed by high resolution seismic reflections is neither restricted within nor in agreement with the framework of the overlying sedimentary sequence striking nne this new evidence fits the overlap model proposed in the present paper that formation of the volcanic successions in the sb is related to the subduction of the mongolia okhotsk plate under the mongolia north china block during the jurassic and early cretaceous whereas the overlying sedimentary sequence unconformably on the volcanics is tectonically controlled by the oblique subduction of the pacific plate under the eurasian plate since late aptian in addition the coal bearing epiclastic sediments intercalating the volcanics were deposited at the subduction quiescence episodes when extensional collapse occurred

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

acceleration in thinning rate on western svalbard glaciers 1 geodetic measurements indicate that a number of glaciers in western svalbard ranging in size from 5 1000 km2 are losing mass at an accelerating rate the average thinning rate for midtre lovenbreen the glacier with the best data coverage has increased steadily since 1936 thinning rates for 2003 2005 are more than 4 times the average for the first measurement period 1936 1962 and are significantly greater than presented previously on slakbreen thinning rates for the latest measurement period 1990 2003 are more than 4 times that of the period 1961 1977 thinning of several glaciers along a previously measured airborne lidar profile in wedel jarls land has also increased doubling between the period 1990 1996 and 1996 2002 our results imply an increased sea level contribution from svalbard in addition the mass loss is an important influence on measured rates of rebound on western svalbard and should be factored into analysis of grace results

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment

slab detachment control on mafic volcanic pulse and mantle heterogeneity in central mexico seismic tomography studies and plate reconstructions suggest that the farallon slab broke off shortly before subduction ended off southern baja california however the progress of detachment in time and space and its consequences on the volcanism of central mexico have not so far been considered here i use the neogene geologic record of central mexico to propose a lateral propagation of slab detachment beneath the trans mexican volcanic belt during the late miocene i suggest that the trace of the detachment is expressed by a short 2 3 m y eastward migrating pulse of mafic volcanism that took place from ca 11 5 to ca 6 ma to the north of the pliocene quaternary volcanic arc as hot subslab material flowing into the slab gap produced a transitory thermal anomaly in the mantle wedge slab detachment of the deeper and denser part of the plate was initiated in the southern gulf of california area by the incoming of progressively younger oceanic lithosphere at the paleotrench that produced an increasing coupling between the magdalena microplate and the overriding north american plate the tear in the slab propagated eastward from the gulf of california to the gulf of mexico paralleling the southern mexico trench system the decrease in the rivera north america convergence rate between ca 9 and 7 ma appears to be related to the loss of slab pull after the detachment sparse oceanic island type basalts emplaced since the end of the miocene in the trans mexican volcanic belt are located above a trench parallel slab window between the inferred detachment trace and the leading edge of the present slab which has been detected seismically in this context the occurrence of these unusual intraplate magmas is easily explained by the infiltration of enriched asthenosphere into the subarc mantle

changes in geometry and subglacial drainage of midre lovenbreen svalbard determined from digital elevation models digital elevation models dems of the bed and surface of the polythermal midre lovenbreen svalbard are used to identify changes in glacier geometry between 1977 and 1995 the calculated mean annual mass balance 0 61 m water equivalent w e a 1 is more negative than that derived from field measurements 0 35 m w e a 1 although the error associated with this value 0 7 m a 1 suggests that the difference may be accounted for by errors however similar discrepancies between dem based and field based measurements of mass balance have been reported elsewhere in svalbard although errors may be responsible patterns of surface elevation change may also be explained in terms of patterns of ablation accumulation and dynamics the theoretical structure of the subglacial drainage system is modelled using different assumptions about subglacial water pressure in 1977 and 1995 these reconstructions are compared with the observed positions of proglacial outlet streams decreasing subglacial water pressure results in a decrease in the influence of surface morphology and an increase in the role of the bed topography on drainage routing which generally leads to more dispersed drainage long term changes in the position of proglacial outlet streams occur as a result of changes in glacier geometry but short term changes may also occur in response to early season water pressures controlled by meteorological and hydrological conditions copyright 2003 john wiley sons ltd

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd