mineral evolution and element mobility during episyenitization dequartzification and albitization in the postkinematic bohus granite southwest sweden abstract the petrography and geochemistry of two subsurface occurrences of pervasively albitized and episyenitized i e dequartzified granite in the central part of the postkinematic sveconorwegian bohus granite in southwestern sweden were studied the altered granite is whitened and consists of an albite microcline framework with a very fine grained interstitial assemblage of illite hematite ankerite anatase textural relations indicate that the initial dissolution of magmatic quartz accompanied by albitization of plagioclase left a vuggy reservoir rock which facilitated fluid penetration and thereby further alteration the subsequent stage is characterized by infilling of vugs by the very fine grained authigenic assemblage and by concomitant alteration of igneous minerals such as magnetite ilmenite and biotite deuteric alteration products of magmatic minerals are affected by these two alteration stages implying that episyenitization occurred widely after emplacement and cooling of the host granite mass balance calculations with reference to adjacent unaffected granite evince mainly si loss and na gain reflecting the observed mineralogical changes the volume decrease is estimated to be 9 owing to compaction accompanying the dequartzification and a slight porosity increase the calculations revealed a slight enrichment in hrees y essentially hosted by xenotime and a thorite xenotime solid solution both exsolved during recrystallization of monazite oxidation of ferrous iron and partial loss of chalcophile elements reflect oxidizing conditions the alteration episode is permo carboniferous and is possibly associated with circulation of oxidizing fluids through the bohus granite

submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

pre grenvillian and grenvillian lithotectonic regions in eastern labrador correlations with the sveconorwegian orogenic belt in sweden the trans labrador batholith groswater bay terrane and lake melville terrane are three major crustal segments located adjacent to or within the grenville province in eastern labrador each crustal segment is a distinct lithotectonic entity displaying contrasts with each other in proportions of rock types structural style and metamorphic imprint together they indicate a unilateral polarity to the region partly reflecting grenvillian tectonism which sliced the region into thrust bound blocks in all three crustal segments an archean or aphebian gneissic basement is inferred onto or adjacent to which ca 1900 1700 ma supracrustal rocks were deposited deformation metamorphism and granitoid pluton emplacement were partly coeval with and partly postdated the supracrustal assemblages in the north tectonothermal effects can be assigned to hudsonian ketilidian orogenesis but their peak was 50 100 ma later farther south post tectonic granitoid plutons and layered mafic intrusions were emplaced at about

disturbed radiometric ages and their bearing on interregional correlations in the sw baltic shield abstract rb sr whole rock and zircon u pb isotopic work is reported from the northern part of the region between the mylonite and protogine zones in the southern baltic shield three age determinations on polymetamorphic gneissic granites were carried out two of these yielded u pb upper intercept ages of 1650 and 1675 ma respectively which is approximately one hundred ma less than expected from the combined field evidence and earlier isotopic age determinations although the new discordias appear well defined various criteria suggest that the u pb isotope system was disturbed thus the rb sr system had been opened but nevertheless the rb sr errorchrones are consistent with the u pb upper intercept ages and an abraded zircon fraction suggests an older age than the unabraded fractions the third u pb age determination resulted in a poorly constrained discordia its upper intercept ranges between 1575 and 1605 ma depending on the number of fractions considered this paper tests a three stage model where the intrusion age is set identical to the 1780 ma intrusion age of the undeformed assumed protolith the first two analysed rocks are consistent with a model suggesting intrusion at 1780 ma followed by partial opening of the isotopic systems early 1200 ma and late 950 ma during the sveconorwegian orogeny an abraded fraction together with the time of the suggested last opening of the system 950 ma ago defines a two point discordia with an upper intercept age of 1745 ma this age is in close agreement with the assumed intrusion age the isotope data from the third gneissic granite cannot be fitted to this simple model it is concluded that the analysed rocks could belong to the granitoids of the transscandinavian igneous belt but if they do they were reworked during the sveconorwegian orogeny as a corollary it follows that the regions separated by the northern part of the protogine zone largely had a common pre sveconorwegain geological history another important implication is that the intrusion ages in the area between the mylonite and protogine zones are older than those of the trans labrador batholith in canada

late quaternary lithofacies provenance and depositional environments 12 30 cal ka north and south of the denmark strait this paper describes the lithofacies and chronology of cores from north and south of the denmark strait for a period when ice sheets flanked both sides of the strait a wide range of sediments have been recovered indicating a complex of depositional processes jm96 1229ggc1 1047 m water depth is from the base of the nw iceland slope at the southern edge of the blosseville basin whereas jm96 1226ggc4 retrieved sediments south of the sill in 1519 m of water additional information is based on jm96 1220ggc2 and 1221ggc2 which were recovered from the upper w iceland slope at 500 m water depth below the latra moraine of possible last glacial maximum age and upslope of jm96 1226 ams 14c dates indicate that jm96 1226 and 1229 span the last 10 to 27 32 ka bp whereas jm96 1220 and 1221 recovered sediments dated between ca 8 and 18 ka bp closely spaced radiocarbon dates on jm96 1229 indicate an erosional hiatus of 7 ky between 12 and 19 cal ka lithofacies descriptions are based on visual descriptions and x radiographs jm96 1229 consists of fine grained sediments sometimes graded with scattered ice rafted debris whereas jm96 1226 consists largely of beds of matrix supported diamicton provenance indicators mass magnetic susceptibility and geochemistry for jm96 1229 support the delivery of sediments from nw iceland but there is a substantial difference in these properties between sediments from the w iceland upper slope and the sediments in jm96 1226 south of the denmark strait this indicates that the diamictons on the floor of the strait did not derive entirely from the iceland ice sheet and adjacent upper slope the general absence of sediments 12 cal ka on the slopes and floor of the denmark strait indicates that denmark strait overflow waters inhibited sediment accumulation during the holocene between ca 12 and 30 cal ka however a combination of more proximal sediment sources ice sheets and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors

canyons and late quaternary sedimentation on the north norwegian margin the presence of erosive canyons on high latitude passive margins is unusual such margins are more normally dominated by subsidence and glacially influenced deposition however ten canyons are identified at the edge of the narrow shelf on the north norwegian margin off the lofoten islands between the traenadjupet and andoya slides on the basis of gloria long range side scan sonar and contemporaneous 3 5 khz profiler data combined with a detailed bathymetry the canyons are located down stream of sediments transported through the lofoten drift and the margin is characterized by an absence of cross shelf troughs canyons are up to 420 m deep u shaped display steep gradients in their upper parts and sediments derived from them have short runout distances onto the continental rise the canyons are estimated to be 20 30 ma old being incised into only thinly covered lithified pre miocene sediments as a response to cenozoic uplift late quaternary sedimentation processes associated with the canyons are inferred to occur during both glacials and interglacials glacial sedimentation is probably in the form of direct subglacial debris input in addition to turbid subglacial meltwater plumes interglacial sedimentation processes are probably dominated by the along shelf transport of sediments by strong ocean currents canyon heads capture sediment from the shelf the remobilization of this coarse material and erosion of the canyons occurs through debris flows and turbidity currents canyon preservation and continued development can be attributed directly to the comparatively low sedimentation rates during full glacial conditions as ice streams located to the north and south produce regional depocentres away from this area of relatively slow flowing ice

did hot high heat producing granites determine the location of the oslo rift abstract the late carboniferous early permian oslo rift formed in apparently cold stable lithosphere of the fennoscandian shield in a tensional stress regime widely documented in northwest europe at that time the rift formed obliquely to older crustal structures that display only limited permian reactivation and although numerical modelling suggests that the present day lithospheric structure would serve to focus tensional stresses in the oslo region the assumption that no lithospheric evolution has occurred since the palaeozoic is by no means obvious here i show that up to 5 km thick regional scale late to post sveconorwegian granites in the vicinity of the oslo rift with heat production rates averaging ca 5 w m3 nearly three times higher than the surrounding sveconorwegian gneisses would have increased the temperature in the lower crust and lithospheric mantle by up to 100 c resulting in significant thermal weakening of the lithosphere in this area given a tensional stress regime weakening by these high heat producing element granites would have made the oslo area a favoured site for passive rifting and may have been a first order parameter locating rifting to this part of the fennoscandian shield the thermo rheological effects of such granites must be considered along with other factors in future models of initial rift mechanisms in the oslo rift and probably in other rifts elsewhere

high grade localized metasomatic alteration of the granitic gneiss surrounding a clinopyroxene rich pegmatoid dyke sondrum stenhuggeriet halmstad sw sweden the sondrum stone quarry halmstad sw sweden exposes a transition from migmatized granitic gneissic country rock into a foliated clinopyroxene free granitic gneiss and then a central pegmatoid dyke dominated by clinopyroxene megacrysts this transition zone represents a fracture controlled fluid alteration zone that developed under conditions of 650 700 degrees c and 790mpa mineral chemical trends in f cl fe ti mn and y are interpreted as documenting a fluid infiltration event associated with the formation of the pegmatoid dyke fluid inclusions from the pegmatoid dyke are co2 dominant whereas in the surrounding country rock they are dominated by h2o nacl cacl2 fluid inclusions from the intermediate foliated clinopyroxene free granitic gneiss are a mixture of the two types the pegmatoid dyke appears to have originated from a high ca activity fe mg enriched fluid rich granitic melt with a co2 component which was emplaced along a tectonic fracture in a regionally migmatized granitic gneiss in the lower crust this was accompanied by limited partial melting of the surrounding granitic gneiss the ca activity of the melt was high enough to allow for the formation of clinopyroxene megacrysts as opposed to orthopyroxene h2o enriched fluids expelled from the crystallizing pegmatoid dyke which retained the majority of the co2 helping to stabilize the clinopyroxene the expelled fluids coarsened and chemically affected the surrounding country rock resulting in trends in the mineral and fluid inclusion chemistry seen today in the foliated and regional granitic gneiss less

the deformation history of the eastern part of the southwest swedish gneiss belt abstract the deformation history of the eastern part of the sw swedish gneiss belt has been investigated regional events more than c 1700 ma are identified as d1 d2 more than c 1400 ma as d3 less than c 1130 ma as d4 and more than c 900 ma as d5 d7 thus the d4 d7 events are considered to be sveconorwegian a common deformation history is suggested for southwestern sweden gradational changes in lithology from west to east are apparently associated with different tectonic styles and intensity of strain the principle deformation of the protogine zone of central sweden is suggested to be d4 the mylonite zone of western sweden appears to have been initiated before d3 the smaland varmland granitoid belt c 1700 ma is geneally considered as early postorogenic in respect to the svecokarelian orogeny because it has been influenced by the d3 event it represents a link between svecokarelian rocks and the sw swedish gneisses

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

marine geophysical evidence for late pleistocene ice sheet extent and recession off northwest ireland abstract multibeam swath bathymetry data collected through the irish national seabed survey provides direct evidence for extensive glaciation of the continental shelf off northwest ireland streamlined subglacial bedforms on the inner shelf record former offshore directed ice flow the major glacial features however consist of well developed nested arcuate moraines which mark the position of former ice sheet margins on the shelf distal to these moraines on the outermost shelf prominent zones of iceberg ploughmarks give way into a well developed system of gullies and canyons which incise the continental slope the large scale nested arcuate moraines record the episodic retreat probably punctuated by minor readvances or oscillations of a lobate grounded ice sheet across this sector of the continental shelf during deglaciation initial retreat from the outer shelf was associated with an episode of ice sheet break up and calving as recorded by extensive zones of iceberg ploughmarks distal to the outermost moraine it is conceivable that this initial phase of retreat could have been driven by rising sea level the data indicate a major reorganisation of the irish ice sheet on the northwest shelf during deglaciation an initial elongate ice sheet configuration extending along the shelf edge changed to a pronounced lobate form during retreat consideration of dated marine stratigraphic records from the wider northwest margin suggests that ice sheet advance to the shelf edge likely occurred at about 29 27 cal ka bp but that retreat from this shelf edge position did not take place until after 24 cal ka bp large scale contrasts in continental margin morphology west of ireland from trough mouth fans in the north to gully canyon systems further to south reflects a combination of factors including spatial variations in sediment flux related to palaeo glaciology

kinematics of a major fan like structure in the eastern part of the sveconorwegian orogen baltic shield south central sweden abstract the n s trending so called protogine zone in the baltic shield of south central sweden is usually considered to mark a tectonic boundary between the rocks of the transscandinavian igneous belt tib in the east and the sveconorwegian orogen in the west detailed structural mapping in the karlskoga kristinehamn area has shown that an anastomosing network of ductile deformation zones with generally n s strike extends ca 40 km east of the traditional protogine zone furthermore the western boundary of this ductile deformation and the tib is not constrained in the kristinehamn area reconnaissance studies indicate that they both extend westwards towards the so called mylonite zone it is suggested that the eastern limit of the sveconorwegian orogen is located some 40 km east of the present boundary and that the protogine zone concept is obsolete the term sveconorwegian frontal deformation zone sfdz is proposed as a more appropriate alternative in southern sweden south of lake vattern and to correspond to a younger set of oblique ductile deformation zones with reverse and right lateral components of movement in the easternmost part of the orogen farther to the north ductile deformation zones older than the sfdz in the karlskoga kristinehamn area display a fan like geometry in an e w cross section with steep westerly dips in the eastern part of the section vertical dips farther west and moderate easterly dips in the western part of the section kinematic analysis indicates that dip slip movements predominate with a consistent top to the east sense of movement across the entire fan like structure in their present orientation deformation zones are characterized by reverse movements in the eastern part and normal movements in the western part of the structure between kristinehamn and the mylonite zone the main foliation is gently dipping to subhorizontal indicating that the regional structure is strongly asymmetric and that the fan like structure occurs close to the foreland of the orogen deformation zones are spaced to semi penetrative in the eastern part of the fan like structure whereas the deformation is more or less penetrative and the tib rocks are transformed to orthogneisses west of kristinehamn this east to west increase in bulk strain is in accordance with an increase in syn deformational metamorphic grade across the structure younger ductile deformation zones belonging to the sfdz are responsible for a major change in orientation of the older deformation zones in the easternmost part of the structure the fan like structure is best explained by models involving the interference of two separate tectonic events deformation occurred after 1 57 ga and prior to deposition of neoproterozoic and younger cover sedimentary rocks it is not yet clear whether the initial phase of deformation early sveconorwegian or older was related to the build up of an imbricate thrust stack in a compressional regime as favoured here or to regional e w extension the younger deformation phase was related to rotation of these older structures into the compressional late sveconorwegian sfdz

linking deformation migmatite formation and zircon u pb geochronology in polymetamorphic orthogneisses sveconorwegian province sweden absolute ages of migmatization in the polymetamorphic parautochthonous basement of the sveconorwegian province sweden have been determined using u pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses migmatite zircon was formed by recrystallization whereas dissolution reprecipitation and neocrystallization were subordinate the recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes it is backscatter electron bright u rich 800 4400 ppm with low th u ratios generally 0 01 0 1 unzoned or oscillatory ghost zoned and occurs as up to 100 m thick rims with transitional contacts to cores of protolith zircon protolith ages of 1686 12 and 1668 11 ma were obtained from moderately resorbed igneous zircon crystals generally th u 0 5 1 5 u 300 ppm in mesosomes protolith zircon is also present as resorbed cores in the leucosomes linkage of folding synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south vergent folding at 976 7 ma at a second locality similar recrystallized zircon rims in leucosome date pre sveconorwegian migmatization at 1425 7 ma an upper age bracket of 1394 12 ma for two overprinting phases of deformation upright folding along gently ssw plunging axes and stretching in ese was set by zircon in a folded metagranitic dyke lower age brackets for these events were set at 952 7 and 946 8 ma by zircon in two crosscutting and undeformed granite pegmatite dykes together with previously published data the present results demonstrate i tectonometamorphic reworking during the hallandian orogenesis at 1 44 1 42 ga resulting in migmatization and formation of a coarse gneissic layering ii sveconorwegian continent continent collision at 0 98 0 96 ga involving a emplacement of an eclogite unit b regional high pressure granulite facies metamorphism c southvergent folding subhorizontal east west stretching and migmatization all of which caused overprint or transposition of older mesoproterozoic and sveconorwegian structures the sveconorwegian migmatization and folding took place during or shortly after the emplacement of sveconorwegian eclogite and is interpreted as a result of north south shortening synchronous with east west extension and unroofing during late stages of the continent continent collision

seismic imaging in the frontal part of the sveconorwegian orogen south western sweden reflection seismic data have been acquired along a 17 km profile in the eastern frontal part of the sveconorwegian orogen south western sweden receiver spacing was 25 m and nominal shot spacing 100 m shots ranging in size from 0 5 to 1 0 kg were fired in 3 m deep shot holes the data image the structure of the upper part of the crust from depths of a few 100 m down to depths of approximately 10 km the profile crosses the central axis of an inferred fan like structure indicated from earlier detailed surface mapping results deformational fabrics within this structure dip approximately 15 40 e in the western part of the profile and 60 80 w in its eastern part the seismic data display a bivergent geometry with the central axis situated approximately 8 km east of a major fault protogine zone in earlier studies surface structural data predict the hinge axis to be located about 3 km farther east despite this discrepancy there is good general agreement with the structure inferred from the surface data the image obtained from the reflection seismic data establishes that the fan like structure is a major upper crustal feature the present data in combination with previous deep seismic data sets exclude a single stage extensional model with an east dipping extensional deformation zone protracting eastwards from the western part of the profile the combined seismic data provide support for a two stage compressional model for the development of the fan like structure with crustal thickening and stacking prior to 955 ma and later compression with a stronger horizontal component of displacement during 930 905 ma the latter gave rise to the development of the complex system of retrogressive deformation zones referred to as the sveconorwegian frontal deformation zone sfdz a tectonic analogy to the grenville front in the eastern part of north america the sfdz dips westwards may become listric at depth and possibly sole in a zone of lower crustal reflectivity west of the present profile the kinematics and geometry of the sfdz suggest that reverse displacements thrusting may be responsible at least in part for the exhumation of the medium to high grade rocks in the western part of the fan like structure both the seismic data and the surface structural geology show many similarities to the grenville front

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

geophysical investigations of a high latitude submarine channel system and associated channel mouth lobe in the lofoten basin polar north atlantic the lofoten basin channel forms one of two major submarine channels on the norwegian margin of the polar north atlantic the channel system connects upslope with the andoya canyon which is the only canyon to cut back across the continental shelf in this region high resolution geophysical records including multibeam swath bathymetric and tobi side scan sonar data show that the distal part of the channel system is braided and connects to a low gradient 0 01 channel mouth lobe on the abyssal plain of the lofoten basin geophysical data indicate that the channel floor is composed of sandy material deposited by turbidity currents these turbidity currents spilled out over the channel sides to deposit acoustically stratified sediment in the channel levees side scan sonar data supplemented by sediment cores indicate that the channel mouth lobe is sandy in composition the lofoten channel and its associated channel mouth lobe is therefore related to turbidity current activity and formation of the system appears to pre date the holocene morphological variation between the upper reaches of the andoya canyon lofoten channel system and the submarine channels of the greenland basin is proposed to relate to differences in the nature of the flows feeding both systems the andoya canyon lofoten channel system bears strong similarities to some mid and low latitude submarine fans with respect to its morphology and architecture

retreat patterns and dynamics of the sentralbankrenna glacial system central barents sea accepted manuscript version published version available at https doi org 10 1016 j quascirev 2017 06 004 accepted manuscript version licensed cc by nc nd 4 0

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

late cenozoic evolution of high gradient trough mouth fans and canyons on the glaciated continental margin offshore troms northern norway paleoclimatic implications and sediment yield trough mouth fans contain information about the evolution of high latitude continental margins including rates of glacial sedimentation and hinterland erosion here the late cenozoic evolution of high gradient trough mouth fans and canyons on the troms margin northern norway is reconstructed paleocanyons were active prior to the quaternary glaciations glaciomarine and glaciofluvial conditions prevailed between ca 2 7 ma and ca 1 5 ma and ice sheets possibly reached the paleo shelf break at least once the minimum average sedimentation rate of this period was 0 22 m k y from ca 1 5 ma to ca 0 7 ma the glaciations intensified and fast flowing ice streams reaching the shelf break were established in the cross shelf troughs subglacial deformation till was deposited at the outer shelf and later reworked by debris flows and turbidity currents the fennoscandian ice sheet started to route much of its ice mass to the north and south of the study area and so the troms margin possibly was a low ice flow sector from this time with a minimum average sedimentation rate of 0 15 m k y during the last ca 0 7 m y ice streams continued to traverse the troughs while sluggish flowing ice prevailed on the banks a minimum average sedimentation rate of 0 14 m k y is estimated for this period the minimum total erosion and erosion rate for the quaternary are 50 140 m and 0 02 0 05 m k y respectively compared with previous studies from other areas this implies up to one order of magnitude variation in average glacial erosion rates along the western sector of the fennoscandian barents sea ice sheets this is interpreted to be due to the size and bedrock composition of the catchment areas and the timing of ice growth and ice sheet dynamics in addition the steep preglacial continental slope promoted high sediment flow velocity for the glacigenic sediments causing much of the debris flows to transform into turbidity currents which efficiently transported sediments across the slope and thereby maintained its steep gradient

dansgaard oeschger events is there a signal off the hudson strait ice stream abstract it is generally accepted that the dramatic heinrich h events were principally sourced from the major hudson strait drainage basin of the laurentide ice sheet but it is not known whether the higher frequency dansgaard oeschger d o events have an imprint on sediments deposited during the inter h intervals in ice proximal slope sediments this paper examines this question by an analysis of data from cores on the se baffin slope because the proxies for heinrich events are so massive in scale we removed the major h events h 1 h 2 and h 4 from the records so as to better examine the structure of data in the intervening hemipelagic sediments the period of interest extends between 15 and 40 cal ka interstadial events 2 8 resolution varies with the proxy to between 210 and 700 yrs per sample in hu87033 009 from the lower slope a total of twelve variables for example 18o mass magnetic susceptibility calcite dolomite ratio number of ird 2 mm show a variety of multi millennial oscillations although not all of the same amplitude nor frequency several parameters show little correlation with the gisp2 18o record however a comparison of cie sediment color l from hu87033 009 and hu97048 007 from the upper slope with the gisp2 oxygen isotope record suggests that a substantial correlation exists between the records such changes might be associated with either detrital carbonate content or foraminiferal concentrations analysis suggests however that the first possibility is correct hence suggestive of a glaciological response of the hudson strait ice stream with d o events in the nw labrador sea the sediment records from around h 3 time 30 cal ka show excursions which might be correlative within this event but its amplitude is not unusual compared to events both before and after this reaffirms the argument that h 3 represents a different glaciological response a significant issue discussed in this paper is the inherent ambiguity of correlating records whose errors in the time domain approach that of a dominating periodicity in this case ca 1 5 kyr

large scale sedimentation on the glacier influenced polar north atlantic margins long range side scan sonar evidence long range side scan sonar gloria imagery of over 600 000 km of the polar north atlantic provides a large scale view of sedimentation patterns on this glacier influenced continental margin high latitude margins are influenced strongly by glacial history and ice dynamics and linked to this the rate of sediment supply extensive glacial fans up to 350 000 km were built up from stacked series of large debris flows transferring sediment down the continental slope the fans were linked with high debris inputs from quaternary glaciers at the mouths of cross shelf troughs and deep fjords where ice was slower moving but still extended to the shelf break large scale slide deposits are observed where ice failed to cross the continental shelf during full glacials the continental slope was sediment starved and submarine channels and smaller slides developed a simple model for large scale sedimentation on the glaciated continental margins of the polar north atlantic is presented

the glacier influenced scoresby sund fan east greenland continental margin evidence from gloria and 3 5 khz records a major submarine fan gradient about 2 offshore of the scoresby sund fjord system is indicated by the crescentic shape of the shelf break gloria long range side scan sonar imagery was obtained over about 20 000 km2 of the fan along with 1000 km of 3 5 khz records three acoustic facies were defined from gloria backscatter signatures and sea floor morphology and sediment acoustic character on 3 5 khz records facies 1 includes a series of acoustically transparent features 0 5 2 km in width elongate downslope with irregular surface topography which are interpreted as debris flows this makes up the bulk of relatively recent sedimentation on the upper fan diamictic sediments in a core support a debris flow origin facies 2 is featureless on gloria images 3 5 khz profiles reveal irregular former sea floor morphology above which is a draping unit 15 m thick this northern region of the fan is a less active area where hemipelagic sediments and limited ice rafted debris overlie older material formed by past debris flow activity the more distal area of the adjacent ocean basin has a flat floor with parallel sub bottom reflectors of facies 3 this facies is probably an area of low energy hemipelagic sedimentation punctuated by occasional ice rafting and turbidity current activity the debris flows interpreted from gloria and 3 5 khz data are basic building blocks in the long term development of the scoresby sund fan glacier influenced fan volume is about 15 000 5000 km3 based on seismic reflection studies during full glacials in east greenland the inland ice sheet advances to fill the scoresby sund fjord system and extends across the shelf to reach the shelf break in some glacial cycles debris flows form in areas of most rapid sediment flux the scoresby sund fan is relatively similar to the storfjorden fan on the eastern polar north atlantic margin but differs from the larger bear island fan in having a steeper fan gradient much smaller debris flows and no large scale slides

late quaternary palaeoenvironment and chronology in the traenadjupet slide area offshore norway the northern mid norwegian continental slope was studied based on high resolution side scan sonar data multibeam bathymetry high resolution and multichannel seismics together with gravity cores sedimentary provinces identified include a partly buried slide on the eastern inner voring plateau an area dominated by glacigenic debris flows south west of the traenadjupet slide the traenadjupet slide and an area of glacimarine sedimentation and a slide scar north east of the traenadjupet slide the traenadjupet slide affected an area of about 14100 km2 and mobilised about 900 km3 of sediments little is known about the areal extent and volume of the older events the glacigenic debris flows and glacimarine sediments were deposited while the fennoscandian ice sheet was at the shelf break during the late weichselian glacial maximum prior to 13 2 14c kyr bp hemipelagic and or contouritic sedimentation prevailed during the holocene period two large slide scars were probably formed sometime prior to or during the late weichselian glacial maximum inner voring plateau and north east of the traenadjupet slide and another during the mid holocene interglacial period immediately prior to 4000 14c kyr bp the traenadjupet slide the two older scars may represent one event or two separate events deposition of poorly permeable glacigenic sediments over high water content fine grained hemipelagic and or contourites may have prevented water escape and increased failure potential thus continental slope areas of episodically high sediment input of glacigenic sediments are prone to failure as illustrated by this study which has identified at least two large slope failures failures have occurred both during glacial maxima periods of climate deterioration and low global eustatic sea level and during interglacials as today with improved climatic conditions and a high global eustatic sea level

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

ice sheets viewed from the ocean the contribution of marine science to understanding modern and past ice sheets over the last two decades marine science aided by technological advances in sediment coring geophysical imaging and remotely operated submersibles has played a major role in the investigation o

high temperature deformation in the basal shear zone of an eclogite bearing fold nappe sveconorwegian orogen sweden ductile shear zones associated with emplacement of high pressure nappes are key features to resolve exhumation mechanisms the eastern segment of the sveconorwegian orogen hosts an eclogite bearing fold nappe whose basal shear zone shows structures associated with emplacement of the eclogite bearing nappe and decompression under high to intermediate pressure granulite and upper amphibolite fades conditions based on detailed structural mapping of a 4 km well exposed section of the basal shear zone we describe two major phases of deformation an early deformation stage d1 formed a penetrative gneissic foliation and tectonic layering including isoclinal folds f1 the sequence was subsequently affected by up to km scale tight south vergent folds f2 with sheared out limbs at the outcrop scale asymmetric f2 folds are commonly s vergent but symmetric folds with different degrees of tightness are also present melt was present at all stages of deformation and the structural relations demonstrate mutual feedback between melt localization and fold formation f2 folds have shallowly e plunging fold axis parallel to a stretching lineation defined by high grade mineral aggregates both constitute prominent structures of the basal shear zone f2 folds are associated with an axial planar fabric s2 defined by upper amphibolite and locally granulite facies mineral assemblages d2 shear structures are associated with top to the east kinematic indicators throughout the section the d1 episode was responsible for emplacement of the eclogite nappe into its present structural position the subsequently developed lineation parallel folds are interpreted to form by general shear where the structures reflect the regional e directed flow of the entire eclogite nappe c 2015 elsevier b v all rights reserved less

geomorphology under ice streams moving from form to process ice streams are integral components of an ice sheet s mass balance and directly impact on sea level their flow is governed by processes at the ice bed interface which create landforms that in turn modulate ice stream dynamics through their influence on bed topography and basal shear stresses thus ice stream geomorphology is critical to understanding and modelling ice streams and ice sheet dynamics this paper reviews developments in our understanding of ice stream geomorphology from an historical perspective with a focus on the extent to which studies of modern and palaeo ice streams have converged to take us from a position of near complete ignorance to a detailed understanding of their bed morphology during the 1970s and 1980s our knowledge was limited and largely gleaned from geophysical investigations of modern ice stream beds in antarctica very few palaeo ice streams had been identified with any confidence during the 1990s however glacial geomorphologists began to recognise their distinctive geomorphology which included distinct patterns of highly elongated mega scale glacial lineations ice stream shear margin moraines and major sedimentary depocentres however studying relict features could say little about the time scales over which this geomorphology evolved and under what glaciological conditions this began to be addressed in the early 2000s through continued efforts to scrutinise modern ice stream beds at higher resolution but our current understanding of how landforms relate to processes remains subject to large uncertainties particularly in relation to the mechanisms and time scales of sediment erosion transport and deposition and how these lead to the growth and decay of subglacial bedforms this represents the next key challenge and will require even closer cooperation between glaciology glacial geomorphology sedimentology and numerical modelling together with more sophisticated methods to quantify and analyse the anticipated growth of geomorphological data from beneath active ice streams

on the origin of large shelf embayments on glaciated margins effects of lateral ice flux variations and glacio dynamics west of svalbard glaciated continental shelves are characterised by large amphitheatre like embayments between prominent cross shelf troughs the integration of swath bathymetry and high resolution seismic data 3d 2d collected across the western svalbard continental margin indicates how such embayments form although their bathymetric expression resembles headwall scarps of submarine slope failures the shelf embayments are the result of the interplay between sediment dynamics and transport underneath fast moving ice streams in the cross shelf troughs and the slower moving parts of the ice sheets on the adjacent shallower shelf banks during full glacial conditions this is supported by 1 the absence of major landslide deposits at their toe 2 continuous prograding shelf deposition and 3 absence of landslide related faulting instead the seismic data suggest a depositional origin of the shelf embayments that is characterised by continuous sediment input at lower rates off a slow moving ice mass in the centre of the embayment which is fringed by the lateral ice stream ridges these findings put into perspective the importance of submarine slope failure on glaciated margins

age tectonic setting and provenance of ostfold marstrand belt supracrustals westward crustal growth of the baltic shield at 1760 ma the ostfold marstrand paragneiss belt is the oldest part of the sw scandinavian domain of the baltic shield in the swedish part of the belt minor mafic volcanics now amphibolites in the metagreywacke dominated stora le marstrand slm supracrustals are chemically similar to primitive modern oceanic arcs or back arc regions a wide compositional range is attributed mainly to fractional crystallisation yielding fe rich andesitic amphibolites diverging lree patterns between different localities are consistent with variations in the degree of partial melting in the source a nine point sm nd errorchron of 1758 78 ma mswd 9 4 for the amphibolites is interpreted to date the volcanism and coeval sedimentation and hence directly dates crustal growth in this part of the baltic shield the exclusion of two pillow lava samples which may have been contaminated yields an isochron with an identical though more precise age an nd value of 4 3 indicates a depleted mantle source similar to that of canada sw u s a s greenland and parts of finland but rather more depleted than that reported hitherto from eastern sweden at the same time nd isotopic data suggest a two component provenance for the slm sediments involving acid derivatives from the mafic volcanics and a continental source similar to the exposed 2 0 1 75 ga old svecofennian crust of eastern sweden with minimal contribution from substantially older crust the mafic volcanism took place during subduction of oceanic crust outboard of the svecofennian part of the baltic shield after substantial addition of 1650 ma old granitoids accretion to the baltic shield possibly took place at 1580 ma

seven million years of glaciation in greenland glacial till glaciomarine diamictites and ice rafted detritus found in marine cores collected off the shore of southeast greenland record multiple late cenozoic glaciations beginning in the late miocene distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast greenland margin glaciers advanced to the sea during several intervals in the pliocene and pleistocene north atlantic glaciation may have nucleated in southern greenland rather than further north because of the high mountains and the high levels of precipitation in this region

asynchronous deposition of ice rafted layers in the nordic seas and north atlantic ocean instabilities in ice stream flow within the north american laurentide ice sheet leading to the periodic release of armadas of icebergs into the north atlantic ocean over the past 60 000 years have produced extensive layers of coarse grained iceberg rafted debris heinrich layers in north atlantic sediments1 2 correlation of these layers with iceberg discharge events from the ice sheets on greenland iceland and scandinavia suggested in previous studies for some heinrich layers and in some areas3 4 5 would imply that ice sheet instability had been synchronous across the north atlantic presumably in response to a common environmental cause here we show a lack of widespread systematic correlations both between ice rafted debris layers in different sediment cores from the nordic seas and between the nordic layers and the north atlantic heinrich layers this suggests that the full glacial nordic ice sheets did not exhibit unstable behaviour coincident with iceberg discharge from the vast hudson bay drainage basin of the laurentide ice sheet6 7 off the hudson strait significant ice sheet discharge of melt water is indicated by size sorted sandy and muddy turbidite sediments different from the poorly sorted debris flows which dominate sedimentation on the margins of the nordic seas8 9 10 together these results suggest that the dynamics of quaternary ice sheets surrounding the nordic seas were different from the outlet glacier draining the hudson bay basin and they provide evidence against a common circum north atlantic mechanism driving the discharge of icebergs

u pb and sm nd dating of high pressure granulite and upper amphibolite facies rocks from sw sweden abstract geochronological data from different radiometric systems on high grade metamorphic rocks in the southwest swedish granulite region southwestern sweden are generally analytically precise but sometimes in conflict with each other age data from seven samples on which a variety of radiometric methods have been applied are presented the age of peak metamorphism is determined by metamorphic zircons from two garnet amphibolites at c 975 ma using the conventional u pb isotope and pb pb evaporation methods titanites from the same type of rocks give ages of c 923 3 ma and 945 2 ma the sm nd data on mafic granulites and garnet amphibolites yield surprisingly young ages between 945 and 900 ma similar to previous sm nd ages these ages are comparable to or even younger than the 40 ar 39 ar hornblende ages that range between 1030 and 930 ma assuming that the sm nd systematics are entirely controlled by volume diffusion the closure temperature of the sm nd system in minerals from these rocks would be comparable to or lower than that of ar diffusion in hornblende i e around 500 c

localized solid state dehydration associated with the varberg charnockite intrusion sw sweden the mineralogy petrology and fluid inclusion chemistry of two charnockite patches within a distance of 4 5 km of the varberg magmatic charnockite intrusion sw sweden are investigated and described utilizing sem empa and fluid inclusion microthermometry garnet clinopyroxene 890 930 degrees c garnet amphibole 600 800 degrees c and garnet biotite 670 860 degrees c fe mg exchange thermometry indicates high temperatures for charnockite patch i compared to relatively lower garnet orthopyroxene garnet amphibole and garnet biotite temperatures of 500 to 600 degrees c for charnockite patch ii plagioclase in the charnockitic patches tends to be more anorthitic and less albitic x an 0 20 x ab 0 76 than in the surrounding regional granitic gneiss x an 0 13 x ab 0 84 replacement antiperthite is commonly found in unrelated plagioclase grains from either patch compared to the regional granitic gneiss where it is relatively rare in either patch k feldspar is considerably less albitic x kfs 0 90 0 92 x ab 0 05 0 10 compared to k feldspar from the regional granitic gneiss it can also be found as micro veins along quartz grain rims both patches are dominated by clinopyroxene as opposed to orthopyroxene garnet biotite and amphibole and in both charnockite patches tend to have lower fe and correspondingly higher mg values compared with garnet biotite and amphibole from the surrounding regional granitic gneiss fluorapatite tends to be relatively enriched in cl and depleted in y ree compared with fluorapatite from the regional granitic gneiss fluid inclusions in charnockite patches i and ii are dominantly carbonic similar to what is seen for the varberg charnockite in addition to quartz relatively high density carbonic inclusions are also preserved in garnet and in fluorapatite it is presumed that pure carbonic fluids must have once coexisted with relic magmatic h2o co2 nacl fluids at peak metamorphic conditions the most likely scenario suggests that charnockite patches i and ii were formed during the later stages of crystallization of the varberg charnockite magmatic body during which copious amounts of co2 rich fluids with a brine cacl2 dominated component were expelled into the country rock via pegmatoid segregations both within and in the immediate surroundings of the charnockite body patch i appears to represent the extension of a pegmatoid segregation whereas patch ii appears to represent fluid induced lower temperature solid state dehydration transport was facilitated via a system of tectonic fissures and fractures generated in the regional migmatized granitic gneiss during its emplacement within the scope of what is known these two charnockite patches fall into the generally observed parameters for localized dehydration zones in general c 2014 elsevier b v all rights reserved less

re advance of the fennoscandian ice sheet during heinrich event 1 abstract five sediment cores bathymetric and 2d seismic reflection data from vestfjorden northern norway were studied in order to constrain the timing and extent of a major ice stream draining the northwestern fennoscandian ice sheet during the last deglaciation 15 10 14 c ka b p the bathymetric and seismic data indicate that vestfjorden traenadjupet was covered by grounded ice reaching the shelf break during the last glacial maximum lgm after the lgm break up and recession towards outer inner vestfjorden at 13 6 14 c ka b p the ice re advanced towards the outer part of vestfjorden prior to 13 1 14 c ka b p this is inferred from glaciomarine sediments overlain by diamicton at the base of the sediment cores interpreted as basal tills and associated contemporaneous build up of grounding zone wedges in the central vestfjorden this sequence of events is coherent with the late weichselian ice sheet dynamics both along the western norwegian continental shelf and in the barents sea possibly indicating a direct response to meltwater injection and accompanied cooling during disruption of the thermohaline circulation associated with heinrich event 1 enhanced supply of suspension load resulted in deposition of laminated sediments at 13 14 c ka b p reflecting the retreat of the ice stream towards the inner fjord in response to global climate amelioration and increased atlantic water inflow two additional ice re advances towards the norwegian coastline are inferred from distinct input of ice rafted debris ird with a typical mineralogical fingerprint derived from neoproterozoic early silurian calcite and dolomite marbles in the ice sheet catchment area thus the re advances may be concurrent with the older dryas 12 2 14 c ka b p skarpnes and younger dryas 10 7 14 c ka b p tromso lyngen cooling events

deep water geomorphology of the glaciated irish margin from high resolution marine geophysical data abstract the continental margin offshore of western ireland offers an opportunity to study the effects of glacial forcing on the morphology and sediment architecture of a mid latitude margin high resolution multibeam bathymetry and backscatter data combined with shallow seismic and tobi deep towed side scan sonar profiles provide the basis for this study and allow a detailed geomorphological interpretation of the northwest irish continental margin several features including submarine mass failures canyon systems and escarpments are identified in the rockall trough for the first time a new physiographic classification of the irish margin is proposed and linked to the impact of glaciations along the margin correlation of the position and dimensions of moraines on the continental shelf with the level of canyon evolution suggests that the sediment and meltwater delivered by the british irish ice sheet played a fundamental role in shaping the margin including the upslope development of some of the canyon systems the glacial influence is also suggested by the variable extent and backscatter signal of sedimentary lobes associated with the canyons these lobes provide an indirect measurement of the amount of glaciogenic sediment delivered by the ice sheet into the rockall trough during the last glacial maximum none of the sedimentary lobes demonstrates notable relief indicating that the amount of glaciogenic sediment delivered by the british irish ice sheet into the rockall trough was limited their southward disappearance suggests a more restricted biis which did not reach the shelf edge south of 54 23 n the various slope styles observed on the irish margin represent snapshots of the progressive stages of slope development for a glacially influenced passive margin and may provide a predictive model for the evolution of other such margins

antarctic palaeo ice streams we review the geomorphological sedimentological and chronological evidence for palaeo ice streams on the continental shelf of antarctica and use this information to investigate basal conditions and processes and to identify factors controlling grounding line retreat a comprehensive circum antarctic inventory of known palaeo ice streams their basal characteristics and minimum ages for their retreat following the last glacial maximum lgm is also provided antarctic palaeo ice streams are identified by a set of diagnostic landforms that nonetheless display considerable spatial variability due to the influence of substrate flow velocity and subglacial processes during the lgm palaeo ice streams extended via bathymetric troughs to the shelf edge of the antarctic peninsula and west antarctica and typically to the mid outer shelf of east antarctica the retreat history of the antarctic ice sheet since the lgm is characterised by considerable asynchroneity with individual ice streams exhibiting different retreat histories this variability allows antarctic palaeo ice streams to be classified into discrete retreat styles and the controls on grounding line retreat to be investigated such analysis highlights the important impact of internal factors on ice stream dynamics such as bed characteristics and slope and drainage basin size whilst grounding line retreat may be triggered and to some extent paced by external atmospheric and oceanic forcing the individual characteristics of each ice stream will modulate the precise timing and rate of retreat through time

geochronology of eclogite facies metamorphism in the sveconorwegian province of sw sweden abstract decompressed eclogites in the sveconorwegian province sw sweden have been dated using u pb geochronology zircons are common as inclusions in garnet and kyanite and other minerals in the decompressed eclogites titanite inclusions are found exclusively in the core of garnets the mineral inclusions and the chemical zoning of the garnets suggest inital growth under prograde amphibolite facies conditions followed by eclogite facies metamorphism and subsequent decompression through the high pressure granulite and upper amphibolite facies the zircon and titanite thus formed prior to the eclogite stage of the p t path the age of the eclogite forming event was determined by ion probe dating of zircon inclusions in garnets the obtained age of 972 14 ma is the maximum age of the eclogitisation the age of the titanite inclusions in garnet is 945 4 ma this age is similar to other u pb ages of titanite in the region which suggest that the titanite has been isotopically reset and that the age reflects cooling the mode of occurrence textural relationships and the chemical homogeneity suggest that the zircons formed from zr released from magmatitic fe ti oxides and possibly amphiboles during breakdown of magmatic minerals at the onset of the sveconorwegian metamorphism spot analyses of complex zircons from a granitic dyke in the eclogite yielded an age of 1403 15 ma for magmatic cores and an age of 963 22 ma for metamorphic rims the older age is a minimum age of the eclogite protolith and correspond to the age of a generation of granites in the region the rim age is within error identical to the age of eclogite metamorphism the eclogite metamorphism in sw sweden is younger than its grenvillian counterparts in scotland canada and usa

submarine slope stability on high latitude glaciated svalbard barents sea margin abstract slope stability is evaluated at two locations on high latitude deep sea fans along the svalbard barents sea margin based on available samples and using an infinite slope analysis the stability evaluation uses the mohr coulomb failure criterion and a semi analytical approach based on gibson s formulation for determining the excess pore pressure build up due to sedimentation the main results are presented in the form of contour plots of slope safety factors in a diagram with axes of time and thickness of deposit the results show that during rapid sedimentation which mostly takes place during periods of maximum glaciation with the ice front located along the shelf edge slope failure will occur with a frequency varying between 95 and 170 years only part of the upper sedimented layer will be mobilised 10 30 m while the remaining thickness 40 70 m will remain at the initial sedimentation site these results may explain why the continental slope is characterised by relatively uniform sediment thickness from upper to lower slope

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

the timing of initiation of fast flowing ice streams during a glacial cycle inferred from glacimarine sedimentation fast flowing ice streams drain huge basins within modern ice sheets and are a mechanism for rapid iceberg production and mass loss some ice streams are known to be unstable and to switch between fast flow and stagnation numerical ice sheet models and geophysical observations of large scale streamlined glacial landforms and large glacier derived sedimentary fans along high latitude continental margins indicate the presence of ice streams in quaternary ice sheets high resolution ams dated sedimentary records from an inter fan area on the svalbard continental margin yield evidence on the timing of initiation of fast glacier flow during a glacial cycle of ice sheet growth and decay sedimentation rates and iceberg rafted debris influx show that debris delivery to the svalbard margin was relatively high during the period of late weichselian ice sheet growth from about 30 000 18 000 yr bp both parameters fell dramatically in inter fan areas when full glacial conditions with ice at the continental shelf edge were established at about 18 000 yr bp this shift is interpreted to mark the initiation of a fast flowing ice stream the convergence of flow from the surrounding ice sheet into this ice stream and the consequent slowing of ice flow and sediment delivery to the inter fan area beyond the ice stream margins this provides a constraint on the timing of icestream initiation during the cycle of ice sheet growth and decay 4 2002 elsevier science b v all rights reserved

crustal insights from gravity and aeromagnetic analysis central north slope alaska aeromagnetic and gravity data are processed and interpreted to reveal deep and shallow information about the crustal structure of the central north slope alaska regional aeromagnetic anomalies primarily reflect deep crustal features regional gravity anomalies are more complex and require detailed analysis we constrain our geophysical models with seismic data and interpretations along two transects including the trans alaska crustal transect combined geophysical analysis reveals a remarkable heterogeneity of the pre mississippian basement in the central north slope pre mississippian basement consists of two distinct geophysical domains to the southwest the basement is dense and highly magnetic this basement is likely mafic and mechanically strong possibly acting as a buttress to basement involvement in brooks range thrusting to the northeast the central north slope basement consists of lower density moderately magnetic rocks with several discrete regions intrusions of more magnetic rocks a conjugate set of geophysical trends northwest southeast and southwest northeast may be a factor in the crustal response to tectonic compression in this domain high resolution gravity and aeromagnetic data where available reflect details of shallow fault and fold structure the maps and profile models in this report should provide useful guidelines and complementary information for regional structural studies particularly in combination with detailed seismic reflection interpretations future challenges include collection of high resolution gravity and aeromagnetic data for the entire north slope as well as additional deep crustal information from seismic drilling and other complementary methods

molybdenite re os dating constrains gravitational collapse of the sveconorwegian orogen sw scandinavia abstract re os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the sveconorwegian orogen in sw scandinavia a 1019 3 ma planar quartz vein defines a minimum age for brittle behaviour in central telemark in rogaland vest agder molybdenite associated with deformed quartz and pegmatite veins formed between 982 3 and 947 3 ma in the amphibolite facies domain three deposits and between 953 3 and 931 3 ma west of the clinopyroxene in isograd two deposits in the vicinity of the 0 93 0 92 ga rogaland anorthosite complex the data constrain the last increment of ductile deformation to be younger than 0 95 and 0 93 ga in these two metamorphic zones respectively molybdenite is the product of an equilibrium between biotite oxide and sulfide minerals and a fluid or hydrated melt phase after the peak of 1 03 0 97 ga regional metamorphism molybdenite precipitation is locally episodic a model for gravitational collapse of the sveconorwegian orogen controlled by lithospheric extension after 0 97 ga is proposed in the west of the orogen the rogaland vest agder sector is interpreted as a large shallow gneiss dome formed slowly in two stages in a warm and structurally weak crust the first stage at 0 96 0 93 ga was associated with intrusion of the post collisional hornblende biotite granite suite the second stage at 0 93 0 92 ga restricted to the southwesternmost area was associated with intrusion of the anorthosite mangerite charnockite suite most of the central part of the orogen was already situated in the brittle upper crust well before 0 97 ga and did not undergo significant exhumation during collapse in the east of the orogen situated against the colder cratonic foreland exhumation of high grade rocks of the eastern segment occurred between 0 97 and 0 95 ga and included preservation of high pressure rocks but no plutonism

quaternary evolution of the northern north sea margin through glacigenic debris flow and contourite deposition the norwegian channel ice stream of the scandinavian ice sheet extended across the northern north sea margin during the mid to late quaternary eroding older sediment from the continental shelf consequently little is known about early quaternary sedimentation on this margin we use two and threedimensional seismic reflection data to investigate changing sediment volumes and sources in the northern north sea through the quaternary the northern north sea basin was infilled during the early quaternary by intercalated glacigenic debris flows and contourites which provide a record of the delivery of glacigenic sediment to the slope and the intensity of north atlantic thermohaline circulation during early quaternary glacial interglacial cycles the infilling of the basin reduced accommodation and led to the deflection of mid to late quaternary sediments into the norwegian sea forming the north sea fan close to the onset of the mid quaternary the south western scandinavian ice sheet margin was drained by an ice stream located beneath maluy plateau 60 km east of the last glacial maximum norwegian channel ice stream the southward flowing norwegian sea bottom water current was directed into the partially filled northern north sea basin during the early quaternary and deflected progressively northwards as the basin became infilled

numerical modeling of the late weichselian svalbard barents sea ice sheet abstract previous reconstructions of the ice cover of the svalbard barents sea region during the late weichselian have ranged from small ice masses on svalbard to complete inundation of the barents shelf region by an ice sheet several kilometers thick we have used a time dependent finite difference numerical model to undertake a new glaciological reconstruction for the svalbard barents sea ice sheet over the last 30 000 yr the numerical model requires environmental forcing functions in the form of air temperature and precipitation and their behavior with respect to altitude together with sea level change and an iceberg calving relation ice buildup on svalbard is calculated to have begun 28 000 yr ago and maximum dimensions were reached by 20 000 yr ago covering svalbard and the northwestern barents sea with a center of mass 1 3 km thick around eastern svalbard decay was complete by about 10 000 yr ago the margin of the modeled ice sheet at its maximum is in good agreement with observed sea floor morphological features but there are discrepancies in timing between the modeled ice sheet decay and i a dated meltwater spike in fram strait and ii the observed rebound curves for svalbard an inverse approach was used to predict ice sheet decay and it was found that increasing the rate of iceberg calving within the model produces a deglaciation some 2000 yr earlier which is compatible with these two independent datasets the reconstruction is also compatible with geological evidence on the isostatic response of bjornoya close to the southern limit of the ice sheet and seismically observed deposits interpreted to be ice proximal facies located in the northwestern barents sea our time dependent model reconstructions of the svalbard barents sea ice sheet indicate ice cover over only the northwestern barents sea during the late weichselian but this does not preclude the presence of ice derived from fennoscandia and the kara sea region elsewhere in the barents sea

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

a seismic study along the east greenland margin from 72 n to 77 n summary around 4370 km of new seismic reflection data collected along the east greenland margin between 71 30 n and 77 n in 2003 provide a first detailed view of the sediment distribution and tectonic features along the east greenland margin after processing and converting the data to depth we correlated odp site 913 stratigraphy into the new seismic network unit gb 2 shows the greatest glacial sediment deposits beneath the east greenland continental shelf this unit is characterized by the beginning of prograding sequences and has according to our stratigraphic correlation a middle miocene age it might have been caused by rapid changes in sea level and or glacial erosion by an early ice sheet or glaciers along the coast a basement high presumably a 360 km long basement structure at 77 n 74 54 n prevents continuous sediment transport from the shelf into the deep sea area in times before 15 myr the origin of this prominent structure remains speculative since no rock sample from this structure is available seaward dipping reflectors at the eastern flank of this structure strongly support that it is a volcanic construction and is most likely emplaced on continental or transitional crust the compilation of sediment thickness provide an insight into the regional sediment distribution in the greenland basin an average sediment thickness of 1 km is observed the north bordering boreas basin has a sediment thickness of 1 8 km close to the greenland fracture zone gfz

morphology sedimentary infill and depositional environments of the early quaternary north sea basin 56 62 n abstract the north sea basin has been subsiding during the quaternary and contains hundreds of metres of fill seismic surveys 170 000 km2 provide new evidence on early quaternary sedimentation from about 2 75 ma to around the brunhes matuyama boundary 0 78 ma we present an informal seismic stratigraphy for the early quaternary of the north sea and calculate sediment volumes for major units early quaternary sediment thickness is 1000 m in the northern basin and 700 m in the central basin total about 40 000 km3 northern north sea basin fill comprises several clinoform units prograding westward over 60 000 km2 architecture of the central basin also comprises clinoforms building from the southeast to the west an acoustically layered and mounded unit unit z was deposited remaining accommodation space was filled with fine grained sediments of two central basin units above these units an upper regional unconformity equivalent uru records a conformable surface with flat lying units that indicate stronger direct glacial influence than on the sediments below on the north sea plateau north of 59 n the upper regional unconformity uru is defined by a shift from westward to eastward dipping seismic reflectors recording a major change in sedimentation with the shetland platform becoming a significant source a model of early quaternary sediment delivery to the north sea shows sources from the scandinavian ice sheet and major european rivers clinoforms prograding west in the northern north sea basin representing glacigenic debris flows indicate an ice sheet on the western scandinavian margin in the central basin sediments are generally fine grained suggesting a distal fluvial or glacifluvial origin from european rivers ploughmarks also demonstrate that icebergs derived from an ice sheet to the north drifted into the central north sea basin by contrast sediments and glacial landforms above the uru provide evidence for the later presence of a grounded ice sheet

the role of the cryosphere in source to sink systems abstract glacial erosion and sediment production are of interest to diverse scientific communities concerned with the interaction of climatic tectonic and surface processes that influence the evolution of orogens and with the climatic signals archived in glacigenic strata we review the current state of knowledge on the generation transfer and accumulation of glacigenic sediment from land to sea we draw from geomorphology marine geology geochronology numerical modeling of surface processes and landscape evolution and experimental and field observations of glacier erosion and deposition and the interaction of ice with its bed and the ocean boundary our primary goal is to examine glacial systems using a holistic source to sink approach with a focus on describing a how glacial motion produces sediment b how the sediments sink record the dynamic nature of glacial systems under different climatic thermal regimes c the challenges in using the sedimentary record to interpret these dynamics in space and time and d the approaches still needed to further our understanding of how ice and associated sediment fluxes respond to climatic and other perturbations the dynamic state of ice i e the ice flux and ice extent is defined differently between the source and sink communities reflecting the challenges of establishing a stratigraphic signal that volumetrically constrains glacigenic sediment production as a function of the ice response to climate advances in marine geophysics have greatly assisted our understanding of mass transfer pathways and of former ice extents as a measure of ice dynamics and have identified the primary depocenters and key lithofacies of glacial sinks sediment fluxes associated with the dynamic state of the ice are best constrained where sediment volumes derived from key lithofacies and seismic reflection isopachs can be temporally partitioned of which there are few examples rather than from discrete point measures of sediment flux that are subject to sediment transfer biases forward numerical modeling of sediment fluxes as a function of ice dynamics agree with observational data at the continental margin scale but finer time space scale ice dynamic models do not yet recreate observed ice extent or flowpaths future source to sink work in glaciated systems should focus on refining empirical relationships between ice velocity and sediment production and expand the application of existing methods to develop sediment volumes and fluxes in known depocenters of former and modern ice streams

lateral shear moraines and lateral marginal moraines of palaeo ice streams abstract an understanding of the nature of sedimentation at ice stream lateral margins is important in reconstructing the dynamics of former ice sheets and modelling the mechanisms by which sediment is transported beneath contemporary ice streams theories of the formation of ice stream lateral moraines islms have hitherto been based on a relatively limited number of terrestrial and marine examples here an inventory of islms is compiled from available studies together with independent analysis of seismic reflection and bathymetric datasets the locations and dimensions of 70 islms alongside a synthesis of their key architectural and geomorphic characteristics are presented two different types of islms are identified type 1 islms are up to 3 5 km wide and 60 m thick they maintain a constant width thickness and cross sectional shape along their length type 1 islms are interpreted and referred to as ice stream lateral shear moraines that form subglacially in the shear zone between ice streams and slower flowing regions of an ice sheet in contrast type 2 islms are up to 50 km wide and 300 m thick they are only identified close to the shelf break in the marine environment type 2 islms exhibit an increase in width and thickness along their length and their distal slopes become steeper in a seaward direction they contain internal dipping reflections that indicate sediment progradation away from the former ice stream type 2 islms are interpreted and referred to as ice stream lateral marginal moraines that were formed at the lateral boundary between ice streams and seafloor terrain that was free of grounded ice we suggest that using bathymetric images and acoustic profiles it is possible to differentiate between ice stream lateral shear moraines and lateral marginal moraines in the geological record this distinction is important for understanding the mechanisms of sediment transfer beneath ice streams and for making inferences about the conditions that existed beyond the lateral ice stream margin at the time of lateral moraine formation slow moving ice beyond lateral shear moraines and ocean water rather than ice beyond lateral marginal moraines

onset and growth of trough mouth fans on the north western barents sea margin implications for the evolution of the barents sea svalbard ice sheet abstract the aim of this study is to discuss the onset and growth of the bellsund hornsund and storfjorden trough mouth fans tmfs on the north western barents sea margin this is done on the basis of a seismo stratigraphic analysis of new 2d seismic reflection profiles and a new correlation between odp site 986 west of spitsbergen and the seismo stratigraphic network in the central part of the western barents sea margin we infer that reflector r4a marks the onset of both the development of the tmfs and the contourite deposition which dominate this part of the margin from this time onward we conclude that these deposits were frequently affected by episodes of small scale mass wasting focused at the mouth of the glacially eroded cross shelf troughs with a new interpolation between the few available constraints we propose an age of about 1 3 ma for the onset of both the development of the tmfs and the contourite deposition thus we hypothesize from our results and from previous studies that the barents sea svalbard ice sheet expanded first beyond the coast north of svalbard later reaching the shelf edge at the mouth of bjornoyrenna and then to storfjorden southern spitsbergen

protolith ages and timing of deformation in the eastern marginal part of the sveconorwegian orogen southwestern sweden abstract u pb zircon and titanite ages from variably metamorphosed igneous rocks in the eastern marginal part of the sveconorwegian orogen eastern segment north of lake vanern sweden suggest that these rocks belong to the younger c 1 71 1 65 ga igneous suite of the c 1 85 1 65 ga transscandinavian igneous belt tib two porphyritic meta granites and one isotropic monzonite yield u pb zircon ages of 1661 27 1674 7 and 1674 7 ma respectively these ages support earlier interpretations that the eastern segment north of lake vanern contains tectonically reworked tib rocks and that there is no major lithological discontinuity either across the sveconorwegian frontal deformation zone or within the eastern segment igneous brown coloured titanites from five samples yield similar u pb ages as the zircons in contrast colourless and oblate shaped titanites from the western penetratively deformed parts of the eastern segment give concordant ages of 976 4 and 956 6 ma further to the east similar titanite from both a penetratively deformed meta granite and a ductile shear zone within a porphyritic quartz monzonite are strongly discordant close to late sveconorwegian lower intercept ages this type of titanite is interpreted to be syntectonic and formed during the upper greenschist east to amphibolite west facies fabric forming event in the eastern segment since the brown igneous titanites and the zircons share a common igneous origin and the single type of metamorphic titanites are either concordant or strongly discordant towards late sveconorwegian intercept ages it is inferred that no major tectonothermal event occurred between the time of tib emplacement and the late sveconorwegian tectonothermal reworking pre sveconorwegian palaeo to mesoproterozoic deformational and metamorphic events gothian which have been inferred west of and further south within the eastern segment appear to be absent in the northern part of this crustal unit

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

uranium lead zircon and titanite ages from the northern portion of the western gneiss region south central norway abstract the geochronologic history of the northern portion of the western gneiss region south central norway has been investigated by u pb analyses of zircon and titanite from various basement units and one supracrustal gneiss a six point four zircon and two titanite discordia line from a migmatite melt pod and its host gneiss astfjord migmatite gneiss defines upper and lower intercept ages of 1659 1 1 8 ma and 393 6 3 6 ma respectively the upper intercept age is interpreted as a time of tonalite emplacement and migmatite formation in the region a seven point three zircon and four titanite discordia line from the ingdal granite gneiss has similar upper and lower intercept ages 1652 9 1 7 ma and 396 1 4 9 ma respectively and the upper intercept age is interpreted as the time of granite crystallization the lower intercept age from both theastfjord migmatite gneiss and the ingdal granite gneiss is interpreted as the time of regional metamorphic resetting and is evidence for caledonian influence in the region titanite from these two gneiss units as well as from other tonalite granite and supracrustal gneisses throughout the western gneiss region displays a remarkably uniform pattern of discordance titanite discordance is variable from 6 to 100 and in general the degree of discordance is proportional to the caledonian metamorphic grade of nearby supracrustal schists episodic diffusional lead loss from titanite during caledonian metamorphism probably caused the discordance pattern but a combined mechanism of mixing and diffusional lead loss cannot be ruled out in any case the seventeen point titanite and zircon discordia line clearly indicates that 1 the bulk of the granitoid terrane in this portion of the western gneiss region was emplaced migmatized and cooled in a short time interval about 1657 ma ago 2 a second short lived thermal event that exceeded the blocking temperature of titanite occurred about 395 ma ago and 3 titanite and zircon in the region were not isotopically disturbed by comparable geologic events in the period from 1657 to 395 ma or at any time after 395 ma

age origin and cooling history of the coronel joao sa pluton bahia brazil received april 2 2002 accepted august 8 2004advance access publication october 22 2004in north east brazil archean and paleoproterozoic cratonic blocksare enclosed within a network of brasiliano age 0 7 0 55ga metasedimentary foldbelts the unfoliated coronel joa o sa grano diorite pluton which contains magmatic epidote and stronglyresorbed clinopyroxene intrudes the sergipano foldbelt zirconsyield a concordant u pb crystallization age of 625 2ma titanite ages are approximately 621ma discordant zircons suggestinheritance from at least two magma sources of ages 2 2ga model calculations based on diffusion parameters andrb sr isotope data from separated minerals indicate that the plutoncooled ata rate of 36 c myr whole rock element compositionsandinitialsr ndisotopic compositionsthat areheterogeneous onalllength scales suggest magma mixing trace element concentrationsand nd isotope data argue against a contribution from a contem poraneous mantle derived magma values of magmatic e

chemical variation in a proterozoic suite of granitoids extending across a mobile belt craton boundary contrary to earlier opinions the southwestern margin of the baltic shield was formed after the svecokarelian orogenic event 2 2 1 8 ga during the initial stages of its formation 1 7 1 6 ga granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield among these granitoids the most important chemical difference is between calc alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic suture the mylonite zone the chemical differences between alkali calcic granites found on both sides of the interorogen boundary proper the protogine zone are less significant as yet a final choice cannot be made between wholly actualistic and non actualistic possibly intracratonic variants of precursory plate tectonic processes

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

paleoceanographic evolution of the sw svalbard margin 76 n since 20 000 14c yr bp abstract two cores from the southwestern shelf and slope of storfjorden svalbard taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera oxygen isotopes and ice rafted debris the results show that over the last 20 000 yr atlantic water has been continuously present on the southwestern svalbard shelf however from 15 000 to 10 000 14c yr bp comprising the heinrich event h1 interval the bolling allerod interstades and the younger dryas stade it flowed as a subsurface water mass below a layer of polar surface water in the benthic environment the shift to interglacial conditions occurred at 10 000 14c yr bp due to the presence of a thin upper layer of polar water surface conditions remained cold until ca 9000 14c yr bp when the warm atlantic water finally appeared at the surface neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of atlantic water its warm core was merely submerged below the cold polar surface water

architecture and sedimentary processes on the mid norwegian continental slope a 2 7 myr record from extensive seismic evidence abstract quaternary architectural evolution and sedimentary processes on the mid norwegian continental slope are investigated using margin wide three and two dimensional seismic datasets of 100 000 km3 sediments delivered to the mid norwegian shelf and slope over the quaternary 75 000 km3 comprise the slope succession the structural high of the voring plateau characterised by initially low 1 2 slope gradients and reduced accommodation space exerted a strong control over the long term architectural evolution of the margin slope sediment fluxes were higher on the voring plateau area increasing up to 32 km3 ka 1 during the middle pleistocene when fast flowing ice streams advanced to the palaeo shelf edge resulted in a more rapid slope progradation on the voring plateau these rates of sediment delivery are high compared to the maximum of 7 km3 ka 1 in the adjacent sectors of the slope characterised by steeper slope 3 5 more available accommodation space and smaller or no palaeo ice streams on the adjacent shelves in addition to the broad scale architectural evolution identification of more than 300 buried slope landforms provides an unprecedented level of detailed process based palaeoenvironmental reconstruction channels dominate the early pleistocene record 2 7 0 8 ma during which glacimarine sedimentation on the slope was influenced by dense bottom water flow and turbidity currents morphologic signature of glacigenic debris flows appear within the middle late pleistocene 0 8 0 ma succession their abundance increases towards late pleistocene marking a decreasing role for channelized turbidity currents and dense water flows this broad scale palaeo environmental shift coincides with the intensification of northern hemispheric glaciations highlighting first order climate control on the sedimentary processes in high latitude continental slopes