low to medium pressure variscan metamorphism in galicia nw spain evolution of a kyanite bearing synform and associated bounding antiformal domains

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

paleoceanography of the barents sea during the holocene 1 we measured the oxygen isotopic composition of planktonic and benthic foraminifera in three cores collected at key positions to reconstruct the paleoceanography of the barents sea core asv 880 on the path of the northern branch of atlantic water inflowing from the arctic ocean core asv 1200 in the central basin near the polar front and core asv 1157 in the main area of brine formation modern seawater 18o measurements show that far from the coast 18o variations are linearly linked to the salinity changes associated with sea ice melting the foraminifer 18o records are dated by 14c measurements performed on mollusk shells and they provide a detailed reconstruction of the paleoceanographic evolution of the barents sea during the holocene four main steps were recognized the terminal phase of the deglaciation with melting of the main glaciers which were located on the surrounding continent and islands the short thermal optimum from 7 8 ka b p to 6 8 ka b p a cold mid holocene phase with a large reduction of the inflow of atlantic water and the inception of the modern hydrological pattern by 4 7 ka b p brine water formation was active during the whole holocene the paleoclimatic evolution of the barents sea was driven by both high latitude summer insolation and the intensity of the atlantic water inflow

comparison study of the modern ostracod associations in the kara and laptev seas ecological aspects recent ostracod assemblages were investigated from coretop sediment samples collected in the eastern kara sea from water depths down to 300 m a total of 45 species were identified 27 of them were reported for the kara sea for the first time the kara sea data were compared with our results on the distribution of ostracods in the eastern laptev sea the spatial distribution of recent taxa and the ecological groupings demonstrate a clear relation to dominant environmental factors which range from estuarine to full marine conditions four assemblages related to average summer bottom water salinities were established 1 a freshwater assemblage from the inner estuaries of the ob and yenisei rivers with salinities less than 2 and from thermokarst lagoons of the southern laptev sea coast with strong salinization in winter 2 a brackishwater assemblage of the outer estuaries of the ob and yenisei rivers with salinities up to 26 3 a mixed euryhaline marine assemblage dominated by euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana from the inner shelf river affected zone of the kara and laptev seas where salinities range between 26 and 32 4 a taxonomically diverse marine assemblage dominated by shallow water marine taxa from the northern parts of the kara and laptev shelves and upper continental slope with stable bottom environments and a salinity higher than 32 abundant euryhaline species found at greater water depths are identified as part of an ice rafted assemblage they are possibly entrained into the newly formed fast ice during autumn storms and freeze up period and then transported to the distal open sea areas during summer

history of ice rafting and water mass evolution at the northern siberian continental margin laptev sea during late glacial and holocene times the late glacial and holocene history of environmental changes in the western laptev sea is reconstructed on the basis of continuous records of ice rafted debris ird and atlantic water indicative subpolar planktic foraminifers and benthic foraminifer cassidulina neoteretis from the two ams14c dated sediment cores one from the upper continental slope and another from the khatanga paleoriver valley on the outer shelf since seasonal sea ice cover is a permanent feature in this high arctic region the prominent ird rich intervals in the oldest 15 4 ka and youngest 7 2 ka sediment units are attributed to iceberg rafting rock types like phyllites are used as indicators of sediment material supplied by icebergs from local ice caps of the severnaya zemlya archipelago authigenic concretions of vivianite and rhodochrosite found in the basal ird rich core section on the slope point to strong water stratification likely caused by meltwater inputs the oldest late glacial ird peaks provide evidence for iceberg production by the local ice caps on severnaya zemlya subsequent meltwater influence is tentatively related to the freshwater release from a retreating barents kara ice sheet in the northeastern kara sea already prior to 15 4 ka atlantic derived waters intermittently reached the western laptev sea continental slope probably facilitated by upwelling in coastal polynyas while subsurface atlantic derived waters were constantly present at the continental slope between 15 4 and 12 ka the disappearance of c neoteretis together with reduced abundance of subpolar planktic foraminifers after 12 ka suggests establishment of a freshened shelf water mass on the flooded outer shelf which affected the water mass structure on the continental slope after 7 ka climate cooling and enhanced atlantic derived water inflow caused re growth of ice caps on severnaya zemlya leading to a recurrence of ird peaks of this renewed ird input are centered at 7 2 6 4 5 4 3 and 2 ka implying that this millennial scale variability in the ird input might be related to an overregional changes in atmospheric circulation patterns

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

tracing crustal evolution in the nw iberian peninsula through the rbsr and upb systematics of palaeozoic granitoids a review abstract the abundant granitoids in the palaeozoic basement of the northwestern iberian peninsula include 470 440 ma old suites early middle ordovician now present as orthogneisses and several variscan suites the age data presently available suggest that the latter have been generated in three separate time intervals 330 320 ma ago late visean early namurian 310 300 ma ago westphalian and 290 280 ma ago late stephanian autunian rb sr whole rock and u pb zircon systematics along with field and chemical evidence testify to the generation of the early and late palaeozoic granitoids from lower palaeozoic and precambrian maximum age 1 7 1 6 ga sedimentary sequences respectively the source rocks contained zircons derived from a late archaean early proterozoic continental crust that probably underlies the whole of western europe although for the greater part modified beyond recognition by younger crustal reworking

anchor ice seabed freezing and sediment dynamics in shallow arctic seas diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze up storms in the alaskan beaufort sea these related bottom types were found to be continuous from shore to 2 m depth and spotty to 4 5 m depth spotty anchor ice occurred as pillow shaped crystal aggregates on buried slabs of frozen sand surrounded by unfrozen sand considerations of required conditions for ice bonding and anchor ice growth allows regional extrapolation and suggests the possibility of anchor ice growth out to 20 m depth the estimated maximum depth of supercooling during fall storms anchor ice and seabed freezing apparently do not develop during a calm freeze up because of the abrupt growth of anchor ice during a freezing storm and its release soon after formation of a surface ice cover this ice type has not been documented before the concretelike nature of frozen bottom where present should prohibit sediment transport by any conceivable wave or current regime during the freezing storm but elsewhere particularly where the bonded crust is broken by grounded ice anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

lateglacial and early holocene climatic oscillations on the western svalbard margin european arctic abstract a multi proxy sediment core record on the continental margin off western svalbard european arctic reflects large climatic and oceanographic oscillations at the lateglacial early holocene transition based on studies of planktonic foraminifera their stable oxygen and carbon isotopic composition and ice rafted debris we have reconstructed the last 14 cal ka bp the period 14 13 5 cal ka bp was characterized by highly unstable climatic conditions short lived episodes of warming alternated with meltwater pulses and enhanced iceberg rafting this period correlates to a regional warming of the northern north atlantic an overall decrease in meltwater took place during the deglaciation 14 10 8 cal ka bp the late younger dryas and subsequent transition into the early holocene is characterized by a reduced flux of planktonic foraminifera and increased iceberg rafting a major warming took place from 10 8 to 9 7 cal ka bp the influence of meltwater ceased and the flux of warm atlantic water increased from 9 7 to 8 8 cal ka bp the western svalbard margin surface waters were significantly warmer than today this warm period the thermal maximum was followed by an abrupt cooling at 8 8 cal ka bp caused by an increased influence of arctic water from the arctic ocean the results document that the european arctic was very sensitive to climatic and oceanographic changes at the end of the last glacial and during the holocene

radiometric constraints on hydrothermal circulation in cooling granite plutons improved precision of radiometric dating of ore deposits can provide information about the thermal history of hydrothermal circulation in cooling plutons in jales a hercynian porphyritic two mica granite and pre ordovician mica schists are cut and intensely altered by the campo gold quartz vein the unaltered granite must be younger than 320 6 ma and gives mica rb sr ages of 308 5 2 4 1 ma muscovite and 294 5 1 1 ma biotite alteration muscovites from the granite give a weighted mean rb sr age of 308 1 1 5 ma and a mean 39ar 40ar age of 300 7 2 8 ma alteration muscovites from the mica schists give similar 39ar 40ar ages averaging 303 0 2 8 ma the results suggest that circulation of the campo mineralising fluids took place no more than 2 4 ma after the granite cooled through the muscovite rb sr closure temperature about 500 c and that subsequent cooling to biotite closure at about 300 c took place at less than 14 c ma the mean cooling rate following emplacement was 15 to 25 c ma the most detailed comparable published data for the cornubian ore field imply much faster cooling rates

geochemical studies in the drainage basin of the rio vouga portugal abstract the hydrothermal waters in the vouzela region portugal have a temperature of 68 c and are characterized by a high content of f li b bicarbonate sulphate and silica ninety three water samples including two hydrothermal waters were analyzed for major and trace elements in order to investigate the genesis of the hydrothermal water in the vouzela region two older hercynian granites are exposed the abas granite and the sao pedro do sul granite the abas granite is intersected by the ribama fault albitization is ubiquitous other alteration effects are tourmalinization k feldspathization and muscovitization these processes and the associated sn w deposits were induced by the intrusion of the younger viseu granite in the present situation rainwater penetrates into the abas granite especially via the ribama fault and the greisenization zone it becomes part of a hydrothermal system leaches li f b and silica and rises via the termas fault in the hydrothermal springs of termas de sao pedro do sul geothermal equilibrium calculations yield a temperature of 205 10 c for the thermal reservoir the percentage of mixing with cold groundwater near the surface in the circulation system is estimated at 73 the circulation system is possibly maintained by the heat generated by the decay of u th k and their daughter products elements which are encountered in extremely high concentrations in the sao pedro do sul granite

holocene paleoceanography and glacial history of the west spitsbergen area euro arctic margin two sediment cores from the west spitsbergen area euro arctic margin md99 2304 and md99 2305 have been investigated for paleoceanographic proxies including benthic and planktonic foraminifera benthic foraminiferal stable isotopes and ice rafted debris core md99 2304 is located on the upper continental margin reflecting variations in the influx of atlantic water in the west spitsbergen current core md99 2305 is located in van mijenfjord picturing variations in tidewater glacier activity as well as fjordocean circulation changes surface water warmer than today was present on the margin as soon as the van mijenfjord was deglaciated by 11 200 cal years bp relatively warm water invaded the fjord bottom almost immediately after the deglaciation a relatively warm early holocene was followedby an abrupt cooling at 8800 cal years bp on the continental margin another cooling in the fjord record 8000 4000 cal years bp is documented by an increase in ice rafted debris and an increase in benthic foraminiferal d 18 o the ird record indicates that central spitsbergen never was completely deglaciated during the holocene relatively cool andstable cond itions similar to the present were establishedabout 4000 cal years bp

late archaean early proterozoic source ages of zircons in rocks from the paleozoic orogen of western galicia nw spain abstract u pb data are reported for nine suites of zircons and three monazites from the paleozoic orogen in western galicia nw spain one paragneiss and six orthogneisses from the early paleozoic basement and two carboniferous ca 310 ma old intrusions of two mica granite new whole rock rb sr analyses along with earlier data indicate an age of ca 470 440 ma ordovician for the emplacement of the granitic precursors of the orthogneisses monazite from the paragneiss also yields an u pb age of ca 470 ma for all nine investigated suites of zircons the u pb systematics signal the presence of a minor proportion of precambrian zircon the zircon data from two orthogneisses and the paragneiss display roughly linear arrays with upper intercepts between about 3 0 ga and 2 0 ga and lower intercepts between ca 480 and 460 ma the former are interpreted as approaching the age of the old zircon component and the latter as reflecting either the time of crystallization of new zircons from the magma orthogneisses or the time of radiogenic lead loss from the old zircons paragneiss the suites of zircons from all other investigated orthogneisses suffered isotopic disturbance posterior to the granite emplacement 470 440 ma ago in most cases leading to false discordias without geochronological significance similarly the zircons of the two investigated two mica granites do not produce meaningful discordias because of post paleozoic disturbance the monazite u pb systems of the latter granites indicate sub recent lead loss from the high initial 87 sr 86 sr ratios an involvement of precambrian continental crust material is evident in the generation of the early paleozoic suite of granites while the zircon u pb data give evidence of the presence of about 3 0 2 0 ga old late archaean early proterozoic components in the source material zircons from the oldest sedimentary rocks in the area now present as catazonal paragneisses and a likely source for the granites likewise reveal a provenance age of 3 0 2 0 ga the late archaean early proterozoic source rocks in western galicia probably formed part of an archaean continental crust underlying much of western europe but mostly modified beyond recognition by younger events

stable isotope constraints on the origin of kaolin deposits from variscan granitoids of galicia nw spain abstract kaolinite rich fractions of 18 o from 16 5 to 22 4 and in d from 99 to 40 these widely spread values question a single crystallization process as no statistically significant overall correlation between 18 o and d can be obtained the analytical spread is such that 11 of the 43 analyzed separates plot below the kaolinite weathering line and one at the line separating the supergene from hypogene evolution field noteworthy for this wide scatter is the fact that some separated size fractions especially from ramon fazouro deposit contain also up to 65 halloysite as well as varied amounts of contaminating minerals generally considered as relicts from parental igneous rocks such as quartz illite muscovite and feldspars however the addition of these minerals does not appear to significantly bias the isotopic data of the 18 o and d values with a best fit line d 8 75 18 o 248 r 0 896 n 5 95 rather similar to the kaolinite weathering line of d 7 5 18 o 220 however the overall spread of values and particularly those for coarser material together with occurrences of halloysite strongly suggest that higher temperature process es also occurred kaolinite and also likely halloysite crystallized from waters whose 18 o values were of meteoric signature from about 5 to 1 at temperatures ranging from about 20 c to 50 c the higher crystallization temperatures especially at the sedimentary lendo deposit imply fluids at higher temperatures than during a climatic controlled weathering process probably of a low temperate hydrothermal character with a fluid isotopically close to meteoric origin however interaction with fluids at higher temperatures and with higher 18 o cannot be ruled out because the relatively wide ranges of kaolin 18 o and d values are difficult to reconcile with a narrow range of 18 o and d for the interacting parental fluids the most likely scenario for the kaolinite and halloysite precipitation is then a two stage process of interaction with meteoric waters at close earth surface temperature but with one of the two episodes occurring at temperatures slightly above those of weathering processes even under tropical conditions there is no compelling evidence for an episode of significantly high temperature such as in most hydrothermal fluid rock interactions but a low temperature episode of about 50 c cannot be ruled out unequivocally especially for the

erratum to severnaya zemlya arctic russia a nucleation area for kara sea ice sheets during the middle to late quaternary quaternary science reviews 25 21 22 2006 2894 2936 abstract quaternary glacial stratigraphy and relative sea level changes reveal at least four expansions of the kara sea ice sheet over the severnaya zemlya archipelago at 79 n in the russian arctic as indicated from tills interbedded with marine sediments exposed in stratigraphic superposition and from raised beach sequences that occur at altitudes up to 140 m a s l chronologic control is provided by ams 14c electron spin resonance green stimulated luminescence and aspartic acid geochronology major glaciations followed by deglaciation and marine inundation occurred during mis 10 9 mis 8 7 mis 6 5e and mis 5d 3 the mis 6 5e event associated with the high marine limit implies ice sheet thickness of 2000 m only 200 km from the deep arctic ocean consistent with published evidence of ice grounding at 1000 m water depth in the central arctic ocean till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively suggesting wet based ice cap advance followed by cold based regional ice sheet expansion local ice caps over highland sites along the perimeter of the shallow kara sea including the byrranga mountains appear to have repeatedly fostered initiation of a large kara sea ice sheet with exception of the last glacial maximum mis 2 when kara sea ice did not impact severnaya zemlya and barely graced northernmost taymyr peninsula

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

rb sr evidence for the presence of ordovician gsranites in the deformed basement of the badajoz cordoba belt sw spain a rb sr whole rock investigation of suites of samples from two orthogneiss bodies in the almendralejo area of the oporto portalegre badajoz cordoba belt points to an ordovician age for the granitic magmatism about 470 ma for the almendralejo gneiss peralkaline metagranite and about 425 ma for the ribera del fresno gneiss leucocratic subaluminous metagranite both with high initial87sr 86sr ratios this points to a post ordovician hercynian age for the metamorphism and tectonic deformation that affected the area including the gneisses and rules out the alleged cadomian or even older age

provenance and paleodrainage patterns of upper jurassic and lower cretaceous synrift sandstones in the flemish pass basin offshore newfoundland east coast of canada upper jurassic to lower cretaceous synrift sandstones from two industry exploratory wells in the flemish pass basin were studied for provenance using heavy mineral proxies these sandstones were deposited during the north atlantic rifting stage at which time rifting intensified between iberia and the grand banks several heavy mineral methods were used including in situ u pb geochronology and morphological and chemical analysis of detrital zircons chemical discrimination of detrital tourmalines and heavy mineral ratios clastic bed load material entering the northern flemish pass basin during the tithonian to berriasian was connected to transport systems reaching west as far as 400 to 500 km 249 311 mi source areas to the west included igneous rocks and associated cover sequences of the avalon zone as well as the magmatic rocks metasedimentary rocks and associated cover sequences present in the central mobile belt the eastward directed input of bed load material into the basin is considered to have resulted in the concentration of sandstone units along its western margin with deteriorating reservoir grade toward the east given the regional extent of drainage systems it is likely that similar constraints apply to equivalent sandstones in the adjacent east orphan basin by the valanginian barremian paleodrainage orientations had switched and bed load material began to enter the flemish pass basin from more proximal areas to the southeast with the avalon zone basement overall no evidence exists to support sediment sourcing from the iberian margin or the flemish cap galicia bank continental fragment to the east and material from these areas is instead interpreted to have been shed into the incipient atlantic ocean or bay of biscay also no evidence exists to support sourcing from grenville basement farther to the west implying that a drainage divide may have existed somewhere between central and western newfoundland west of which material was presumably being transported to the south or southwest

a 275 year ice core record from akademii nauk ice cap severnaya zemlya russian arctic between 1999 and 2001 a 724 m long ice core was drilled on akademii nauk the largest glacier on severnaya zemlya russian arctic the drilling site is located near the summit the core is characterized by high melt layer content the melt layers are caused by melting and even by rain during the summer we present high resolution data of density electrical conductivity dielectrical profiling stable water isotopes and melt layer content for the upper 136 m 120 m w e of the ice core the dating by isotopic cycles and electrical conductivity peak identification suggests that this core section covers approximately the past 275 years singularities of volcanogenic and anthropogenic origin provide well defined additional time markers long term temperatures inferred from 12 year running mean averages of d 18 o reach their lowest level in the entire record around 1790 thereafter the d 18 o values indicate a continuously increasing mean temperature on the akademii nauk ice cap until 1935 interrupted only by minor cooling episodes the 20th century is found to be the warmest period in this record

geochemistry of white micas from portuguese tin and tungsten deposits abstract magmatic muscovite of hercynian s type granite muscovite of greisenized granite muscovite of selvages at quartz vein schist contacts and muscovite within the vein of the portuguese w sn deposit from panasqueira are distinguished mainly by trace element contents and there is a tendency for log f h 2 o f hf to increase in this sequence several correlations were found between major elements of these muscovites and of muscovites of hypothermal quartz veins of the sn deposit from montezinho the sn w deposit from argozelo and the w deposit from borralha northern portugal f content of muscovite depends on unit cell parameter b si mg fe2 fe3 alvi and oh sn content of muscovite seems to depend on its celadonite content and is carried by fluorine sn correlates positively with mg fe2 fe3 and f in muscovites from each deposit but a positive correlation between sn and cs was found in hydrothermal muscovites from all deposits the contents of both elements may be guides of sn and w mineralizations w is generally less abundant than sn in muscovite and was probably transported by water as tungstic acid or wo2 4 the muscovite of quartz veins from different deposits can be distinguished by major and trace element contents the muscovites of w quartz veins crystallized at greater log f h 2 o f hf than the muscovite of sn sn w and w sn quartz veins muscovite is also abundant in schists bordering quartz veins and has more distinct major and trace element contents than those of white mica of regional metamorphism and of hydrothermal muscovite of selvages along the vein schist contact it also crystallized at different log f h 2 o f hf

evolution of a kyanite bearing belt within a ht lp orogen the case of nw variscan iberia kyanite replaces andalusite in a belt of ordovician and silurian pelitic rocks that form a narrow synform pinched between high grade antiforms in nw variscan iberia kyanite occurs across the belt in al rich black pelites in assemblages i kyanite chloritoid chlorite muscovite and ii kyanite staurolite chlorite muscovite in i kyanite occurs in the matrix and in kyanite muscovite aggregates that pseudomorph earlier andalusite porphyroblasts the aggregates are found across the belt and can still be recognized in assemblage ii and even in iii andalusite staurolite biotite muscovite this latter being a hornfelsic silurian schist where kyanite is relic and staurolite occurs in the matrix and is resorbed inside new massive pleochroic andalusite kfmash and mnkfmash pseudosections have been constructed using thermocalc for al rich and al poorer compositions from the belt chloritoid zoning in al rich rocks containing assemblage i plus chloritoid chlorite thermometry complemented with garnet chlorite thermometry in al poorer lithologies mean that the path is one of increasing pressure and temperature conditions prior to assemblage i with earlier andalusite stable are those of the andalusite chloritoid chlorite field as testified by chloritoid enclosed in andalusite porphyroblast rims the passage from assemblage i to ii implies a prograde path within the kyanite field assemblage iii represents peak conditions indicating a prograde staurolite consuming reaction across a kfmash field leading eventually to a locally found andalusite biotite muscovite hornfels the lowest pressure stages are recorded by cordierite biotite in al poor pelites garnet bearing mnkfmash assemblages in al poorer pelites record conditions similar to assemblages ii and iii the replacement of andalusite by kyanite in assemblage i is attributed to downdragging of andalusite bearing rocks into a synform as testified by the strained andalusite porphyroblasts affected by a subvertical crenulation cleavage prograde metamorphism in the eastern contact of the belt is due to heat transferred to the belt from the ascending high grade antiform across the vivero fault

late glacial and holocene paleoceanography and sedimentary environments in the st anna trough eurasian arctic ocean margin based on stratigraphical analysis of twelve sediment cores from the saint anna trough we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the holocene detailed analysis of benthic and planktic foraminiferal fauna stable oxygen and carbon isotope analysis lithostratigraphy and radiocarbon dates are used to reconstruct the following evolution after the deglaciation of the saint anna trough 13 300 yr b p until 9500 yr b p the environment was mainly characterised by low biogenic production carbonate dissolution and deposition of proximal to distal glaciomarine sediments intervals with high abundance of the benthic foraminifer cassidulina teretis may indicate influx of atlantic water at bottom the transition into the present interglacial started at 9500 yr b p reflected by increased production of foraminifera and bivalves after 8000 yr b p there was a marked drop in planktic 18o followed by a rise in planktic foraminifera and subsequently an increase of c teretis these paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in nordic seas the early holocene warming of the saint anna trough were delayed by ca 2000 years relative to the northeast nordic seas early holocene sedimentation rates were relatively high 100 cm 1000 yr declining drastically after 8000 yr b p 50 cm 1000 yr this was presumably caused by reduction in winnowing and or riverine input

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

non glacial paleoenvironments and the extent of weichselian ice sheets on severnaya zemlya russian high arctic abstract the extent of the barents kara sea ice sheet northern europe and russia during the last glacial maximum lgm in marine isotope stage mis 2 is controversial especially along the southern and northeastern russian high arctic margins we conducted a multi disciplinary study of various organic and mineral fractions obtaining chronologies with 14 c and luminescence dating methods on a 10 5 m long core from changeable lake 4 km from the vavilov ice cap on severnaya zemlya the numeric ages indicate that the last glaciation at this site occurred during or prior to mis 5d 4 early middle weichselian deglaciation was followed by a marine transgression which affected the changeable lake basin after the regression the basin dried up in late middle weichselian time ca 25 40 ka reworked marine sediments were deposited in a saline water body during the late weichselian mis 2 the basin was not affected by glaciation and lacustrine sediments were formed which reflect cold and arid climate conditions during the termination of the pleistocene and into the holocene warmer and wetter climate conditions than before led to a higher sediment input thus our chronology demonstrates that the northeastern margin of the lgm barents kara sea ice sheet did not reach the changeable lake basin this result supports a modest model of the lgm ice sheet in northern europe determined from numeric ice sheet modelling and geological investigations

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

lithogeochemical studies of aureoles around the panasqueira tin tungsten deposit portugal multi element lithogeochemical surveys of aureoles surrounding tin tungsten bearing quartz vein systems have been utilized infrequently in exploring for these deposits at panasqueira beira beixa portugal a wrich quartz vein mineralization occurs in the beira schists surrounding a greisenized cupola and offers a suitable test case for such lithogeochemical studies therefore shale samples were collected at a density of about 6 samples per km2 pronounced anomalies of tin and tungsten have been detected in these samples together with those of other elements coeval with the mineralizing processes

tectonic evolution of the careon ophiolite northwest spain a remnant of oceanic lithosphere in the variscan belt abstract analysis of the careon unit in the ordenes complex northwest iberian massif has supplied relevant data concerning the existence of a paleozoic oceanic lithosphere probably related to the rheic realm and the early subduction related events that were obscured along much of the variscan belt by subsequent collision tectonics the ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse grained and pegmatitic gabbros an early devonian zircon age documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10

changes in the flow of atlantic water into the arctic ocean since the last deglaciation evidence from the northern svalbard continental margin 80 n 1 the svalbard archipelago is located in the high arctic 76 80 n within the northernmost reach of the west spitsbergen current which is the continuation of the north atlantic current in this specific setting close to the polar front even small variations in the current system are expected to give large and distinct signals in paleoceanographic parameters thus the svalbard area is ideal for monitoring the past history of the inflow of atlantic water to the arctic ocean we have studied sediment core np94 51 taken outside the mouth of the hinlopen strait on the northern svalbard shelf the paleoceanographic development of the last deglaciation and the holocene has been reconstructed using benthic and planktonic foraminifera oxygen isotopes and ice rafted detritus the results show that the first strong subsurface inflow of atlantic water to the arctic ocean after the last glacial maximum commenced at 12 6 14c kyr b p circa 15 000 calendar cal years b p during the bolling allerod interstadial during the younger dryas polar conditions prevailed at the surface with extensive sea ice cover and the inflow of atlantic derived water was generally diminished the inflow of more saline but still cold atlantic water was relatively strong during the early holocene and caused intensified seasonal biological productivity the atlantic water inflow declined gradually during the mid holocene between 4500 and 1100 cal years b p the inflow was very weak and the bottom waters over the northern svalbard margin were cold and of lower salinity during the last 1000 years climatic conditions improved such that the subsurface inflow of atlantic derived water increased however the surface waters were still cold

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

arctic warming through the fram strait oceanic heat transport from 3 years of measurements we present estimates of volume and heat transport through fram strait for the period 1997 to 2000 from data of moored instruments full depth volume transports at 78 55 n were in the order of 10 sv both northwards and southwards with an annual mean net transport between 2 and 4 sv to the south the temperature of the northward flow of atlantic water had a strong seasonality with a minimum in winter nevertheless the northward heat transport was highest in winter caused by the winter maximum of northward volume transport during the three years of observation the heat transport in the west spitsbergen current increased from 28 to 46 tw as a result of both increased speed and temperature in contrast to the west spitsbergen current the volume and heat transport of east greenland current remained fairly constant an integration over a subsection of the east greenland current showed similar values of volume transport to that obtained by measurements in the 1980s foldvik et al 1988 the southward heat transport through modified atlantic water weakened slightly between 1997 and 1999 despite increased temperatures

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

diachronous variscan tectonothermal activity in the nw iberian massif evidence from 40ar 39ar dating of regional fabrics abstract multigrain concentrates of hornblende and muscovite together with whole rock slate phyllite samples have been dated 27 analyses using 40ar 39ar incremental release methods along a systematic traverse across the various lithotectonic structural elements which comprise northwestern sectors of the variscan iberian massif hornblende concentrates from amphibolites in the allochthonous ordenes complex yield plateau isotope correlation ages of 425 ma and 377 ma muscovite concentrates and whole rock slate phyllite from this and the cabo ortegal complex yield plateau ages which range from 367 ma to 295 ma analyses of similar material from the relative autochthon yield plateau ages between 359 ma and 275 ma muscovite concentrates from three late to post kinematic granitic stocks yield plateau ages between 309 ma and 274 ma at least seven of the 40ar 39ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystalline argon systems associated with emplacement of proximal granitic stocks the remaining analyses may be used to constrain the local age of various variscan tectonothermal events the oldest fabric ages are recorded in allochthonous units whereas the youngest fabric ages occur along the boundary between internal and external zones middle devonian ages are recorded in the allochthon and suggest a chronological continuity with deformational events in the relative autochthon where variscan deformation initiated in the upper devonian and diachronously prograded eastward the first deformational events recorded in the limit within the internal and external zones occured ca 20 25 ma later lower namurian variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge however the entire orogen remained tectonically active with different structural features forming at different times and at different places an average propagation rate of ca 5 km m y is suggested by consideration of a 20 25 ma difference in correlative fabric ages and present separations

structural and kinematic analysis of the corredoiras detachment evidence for early variscan synconvergent extension in the ordenes complex nw spain an important detachment is described in the allochthonous ordenes complex in the nw iberian massif and its meaning is related to the kinematics of contemporaneous convergent structures the corredoiras detachment cd separates a hangingwall unit characterised by a medium pressure metamorphic gradient from a footwall high pressure and high temperature unit and an underlying ophiolitic unit an associated ductile shear zone nearly 2000 m thick developed in the lower part of the hangingwall unit where the corredoiras orthogneiss a lower ordovician metagranite was progressively transformed into augengneisses mylonitic and ultramylonitic gneisses the attitude of the stretching and mineral lineation in the mylonites varies due to late refolding at map scale but the sense of movement can be estimated being roughly top to the se according to crosscutting relationships the cd developed subsequent to the thrusting of the high pressure high temperature unit onto the ophiolitic unit and prior to younger extensional detachments upright folding and strike slip tectonics the geometric relationships of the cd with the previous structures in the footwall unit the subtractive character of the metamorphic gap between its hangingwall and footwall and the available isotopic data suggest that the cd is an early variscan ductile extensional detachment the movement of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative autochthon

a multiproxy reconstruction of the evolution of deep and surface waters in the subarctic nordic seas over the last 30 000yr on the basis of various lithological mircopaleontological and isotopic proxy records covering the last 30 000 calendar years cal kyr the paleoenvironmental evolution of the deep and surface water circulation in the subarctic nordic seas was reconstructed for a climate interval characterized by intensive ice sheet growth and subsequent decay on the surrounding land masses the data reveal considerable temporal changes in the type of thermohaline circulation open water convection prevailed in the early record providing moisture for the fennoscandian barents ice sheets to grow until they reached the shelf break at 26 cal kyr and started to deliver high amounts of ice rafted debris ird into the ocean via melting icebergs low epibenthic 18o values and small sized subpolar foraminifera observed after 26 cal kyr may implicate that advection of atlantic water into the nordic seas occurred at the subsurface until 15 cal kyr although modern like surface and deep water conditions first developed at 13 5 cal kyr thermohaline circulation remained unstable switching between a subsurface and surface advection of atlantic water until 10 cal kyr when ird deposition and major input of meltwater ceased during this time two depletions in epibenthic 13c are recognized just before and after the younger dryas indicating a notable reduction in convectional processes despite an intermittent cooling at 8 cal kyr warmest surface conditions existed in the central nordic seas between 10 and 6 cal kyr however already after 7 cal kyr the present day situation gradually evolved verified by a strong water mass exchange with the arctic ocean and an intensifying deep convection as well as surface temperature decrease in the central nordic seas this process led to the development of the modern distribution of water masses and associated oceanographic fronts after 5 cal kyr and eventually to today s steep east west surface temperature gradient the time discrepancy between intensive vertical convection after 5 cal kyr but warmest surface temperatures already between 10 and 6 cal kyr strongly implicates that widespread postglacial surface warming in the nordic seas was not directly linked to the rates in deep water formation

advection of atlantic water to the western and northern svalbard shelf since 17 500 cal yr bp abstract the changes in flow and character of the warm atlantic water through the last 17 500 cal yr are reconstructed from the distribution of benthic foraminifera species planktonic and benthic foraminifera abundances stable oxygen isotopes and lithology in two cores from the western and northern shelf of svalbard the results show almost continuous presence of atlantic water at the shelf areas since 14 500 cal yr bp the bolling and allerod intervals stand out as periods of highest bottom waters temperatures the strong inflow of saline but chilled atlantic water during the early holocene was followed by cooling and freshening of the bottom waters during the mid and late holocene the two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of atlantic water recorded further south in the nordic seas the early holocene warming was not just an effect of higher solar insolation but was also due to increased heat flux from the stronger atlantic water inflow driven by wind force and or thermohaline circulation

21ne versus 10be and 26al exposure ages of fluvial terraces the influence of crustal ne in quartz abstract the accuracy of 21 ne surface exposure ages depends critically on the correction for a trapped ne component commonly the amount of cosmogenic ne used to calculate 21 ne exposure ages is considered to be the ne excess relative to a trapped component of atmospheric composition 21 ne 20 ne 0 00296 here we document a trapped ne component in quartz samples from a series of river terraces at the northern margin of tibet hetzel et al nature 417 2002 428 432 which has a non atmospheric 21 ne 20 ne ratio varying from 0 00299 to 0 00398 vacuum crushing of amalgamated samples each derived from 30 80 quartz clasts revealed that the non atmospheric trapped component is present in fluid inclusions it has probably been incorporated into the quartz crystals during their growth in veins at low grade metamorphic conditions only if the amount of cosmogenic 21 ne is determined relative to this trapped component are the calculated 21 ne exposure ages consistent with the relative ages of the tectonically induced terraces and in agreement with independent 10 be and 26 al exposure ages of the fluvial terraces a significant in situ production of nucleogenic 21 ne by the reaction 18 o n 21 ne in the paleozoic quartz minerals is ruled out by extremely low u contents of the order of 1 5 ppb all ages have been corrected for an inherited cosmogenic component that results from cosmic ray exposure during erosion of the host rock and transport of the clasts to the terraces the origin of the trapped component from crustal fluids is supported by high 40 ar 36 ar ratios of 2000 6000 and slightly elevated 136 xe 132 xe ratios relative to air which can be explained by radioactive decay of 40 k and spontaneous fission of u in the crust

deep drilling of glaciers in eurasian arctic as a source of paleoclimatic records abstract results of the deep drilling 80 100 m of eurasian arctic glaciers svalbard severnaya zemlya and franz josef land from the middle of the 1970s to the end of the 1990s have been discussed all spectra of the techniques used for ice core and borehole studies results of ice core dating and major paleoclimatic conclusions have been analyzed particular emphasis has been placed on the problem of accuracy and comparison of dates suggested by different authors new integrated time scale for eurasian arctic glaciers based on the ice core dating of vetreniy ice cap graham bell island and franz josef land which covers the last 700 800 years has been developed methods and results of the new paleo temperature reconstructions have been analyzed

characterization and timing of the different types of fluids present in the barren and ore veins of the w sn deposit of panasqueira central portugal the panasqueira w sn deposit is the largest quartz vein type deposit of the iberian peninsula and the most important wolframite deposit in western europe the ore veins are almost exclusively sub horizontal besides ore bearing sub horizontal veins the panasqueira mine also contains barren quartz veins there are essentially two generations of barren quartz quartz contemporaneous with the earliest regional metamorphism qi and recrystallized quartz contemporaneous with the thermal metamorphism related to the granite intrusion qii fluid inclusion studies microthermometry and raman were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore bearing quartz qiii fluid inclusion data indicate that the barren and ore bearing quartz fluids are dominantly aqueous 93 to 98 mol h2o with a nearly constant bulk salinity 8 to 12 wt eq nacl with the quantity of volatile component determined by raman spectrometry higher in qiii but never greater than 5 mol however the co2 ch4 n2 ratio is different for each type of quartz volatiles are dominated by ch4 10 to 96 mol zch4 and or n2 3 to 87 mol zn2 in the barren quartz and by co2 60 to 73 mol zco2 in ore bearing quartz the bulk chemical composition of the fluids in qiii is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization where na k ca and hco3 cl so4 a dispersion in th 226 to 350 c found in qiii together with a variation in the degree of filling 0 5 to 0 7 and with the consequent variation of fluid densities 0 70 to 0 79 may result from changes in the fluid pressure regime below lithostatic pressure suggesting vein filling related to tectonic events

u pb ages of zircons from meta igneous and meta sedimentary rocks of the sierra de guadarrama implications for the central iberian crustal evolution u pb data of zircons from various gneisses of the eastern sierra de guadarrama central spain make it possible to reconstruct the pre hercynian and hercynian history of this area 1 upper intercept ages 2400 ma for meta igneous and 2000 ma for meta sedimentary rocks of discordias defined by data of anhedral zircon fractions document the existence of early proterozoic crust 2 lower intercept minimum ages of anhedral zircon fractions show radiogenic lead loss at about 540 ma due to a thermal event leading to volcanism and emplacement of granitoid rocks into precambrian crust growth of euhedral zircons is possibly related to this event 3 lower intercept minimum ages of about 380 ma defined by anhedral zircon fractions in meta sedimentary rocks prove an early hercynian event according to present knowledge on the metamorphism in the sierra de guadarrama this event could be explained in terms of a barrow type medium pressure metamorphism the inferred cadomian igneous event relates the geological history of central spain with that of western africa to the south and brittany to the north furthermore similarities of the crustal evolution in the area studied and other internal zones of the hercynian belt moldanubian zone french central massiv are confirmed the early hercynian event for the first time affected all the rocks of the area together the pre hercynian evolution of the two complexes is different and the present association of the basement rocks may be explained by thrusting or in terms of early hercynian nappe transport

a holocene record of changing arctic ocean ice drift analogous to the effects of the arctic oscillation 1 the arctic oscillation ao controls the configuration of the transpolar drift tpd if thicker ice from the beaufort gyre were exported the volume of fresh water sea ice in the nordic seas would significantly increase decreasing the formation of north atlantic deep water this would cool large parts of the northern hemisphere and affect global climate therefore in order to understand how the global climate system functions it is imperative to know how the tpd changed over the last millennium or more the provenance of grains in a sediment core located near the confluence of the tpd and the beaufort gyre provides a direct proxy for changes in seaice drift owing to these circulation systems the core has more than 200 cm of holocene sediment with intervals dominated by grains from the russian shelves alternating with intervals of abundant grains from north american sources grains matched to russian shelves indicate that the tpd was shifted toward north america similar to what occurs during a more positive phase of the ao this condition alternated with intervals where few grains matched to russian sources presumably because the tpd was restricted to the russian half of the arctic far from the core site during the last 1300 years increased influx of russian grains occurred approximately every 50 150 years this fluctuation might represent the long term oscillation of the ao which modulates the same tpd shift today

meta igneous origin of hercynian peraluminous granites in n w french massif central implications for crustal history reconstructions seventy samples of hercynian peraluminous granites gueret millevaches and saint sylvestre massifs and metamorphic units of the limousin area were analysed for rb sr and sm nd the source rocks of the peraluminous granites can be found in the metamorphic rocks of limousin among them meta igneous rocks were largely predominent over meta sedimentary rocks in the source of the three granites millevaches and gueret granites were generated by the partial melting of rocks comprising meta volcanics and meta sediments whereas the saint sylvestre granite was produced exclusively by the melting of late precambrian granites this leads to confusing t dm nd values the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites which leads to dramatic fractionation in sm nd ratios the data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates late precambrian time seems however to have been a period of extensive crustal generation in western europe

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma