the avalonian cadomian belt and related peri gondwanan terranes during the past decade it has widely been accepted that the avalonian cadomian belt results from neoproterozoic to early paleozoic andean type orogeny that was active at the northern margin of gondwana the major imprints of this orogeny are recorded by so called perigondwanan terranes which faced open oceans during the neoproterozoic avalonianand cadomian type terranes show significant differences concerning the age of protoliths and the timing of accretion avalonian type terranes developed from ca 1 ga old rocks and were subsequently accreted to the northern margin of west gondwana amazonia cadomian type terranes originated along the african margin by recycling ca 2 ga crust in paleozoic times the avalonian cadomian belt fell into microplates that were detached from gondwana and collided with laurentia or baltica several attempts have been made to reconstruct the neoproterozoic early paleozoic distribution of the peri gondwanan microplates relative to the west african and amazonian cratons however as robust paleomagnetic and other quantitative data are largely lacking these reconstructions are still speculative and need further confirmation the contributions of this special volume provide new data and models which help to improve our knowledge on the avaloniancadomian orogeny the papers are an outcome of the geo 2002 meeting held during october 2002 in w rzburg germany in an invited paper murphy et al compare inferred relationships between peri gondwanan terranes and the northern gondwanan margin with paleomagnetically constrained movements interpreted for the amazonian and west african cratons for the interval ca 800 500 ma the following eight papers deal with cadomian events in the bohemian massif a large number of new isotopic data is presented which helps to constrain the timing of orogenic events the paper by linnemann et al represents new u pb shrimp ages of detrital and inherited zircons from pre variscan rocks of saxo thuringia which reflect a west african provenance for sediments and magmatic rocks based on single zircon pb pb evaporation and shrimp ages combined with major and trace element data and sm nd isotope systematics mingram et al on the other hand suggest a link between saxo thuringia and avalonia they found evidence for at least two discrete magmatic events in the so called red gneisses of the erzgebirge patocka and torch elucidate cadomian sediment provenances of the early paleozoic siliciclastic rocks of the tepl barrandian unit bohemian massif the paper by drost et al presents new u pb shrimp ages for the cambrian volcanics of the tepl barrandian unit and yields constraints on the late neoproterozoic to cambrian geotectonic settings u pb and pb pb ages obtained by mazur et al and by zelazniewicz et al indicate neoproterozoic to cambrian magmatism in different parts of the sudetes bohemian massif teipel et al obtained new u pb shrimp and nd isotopic data which suggest upper vendian and lower ordovician magmatism in the bavarian forest that is part of the moldanubian unit friedl et al derived new u pb zircon ages shrimp and tims from different orthogneisses of the austrian part of the bohemian massif they found evidence for both neoproterozoic and ordovician magmatism in the moldanubian domain the latter is interw d rr institut f r geowissenschaften und lithosph renforschung universit t giessen senckenbergstr 3 35390 giesen germany

uranium 236 as a new oceanic tracer a first depth profile in the japan sea and comparison with caesium 137 we present a feasibility study for using 236u as an oceanic circulation tracer based on depth profiles of 236u and 137cs in the japan east sea the concentration of the predominantly anthropogenic 236u measured with accelerator mass spectrometry ams decreased from 13 3 106 atom kg in surface water to 1 6 0 3 106 atom kg close to the sea floor 2800 m the profile has a smooth trend with depth and concentration values are generally proportional to that of 137cs for the same water samples but with a slightly lower ratio of 137cs 236u below 2000 m the cumulative inventory of dissolved 236u in the water column was estimated to be 13 7 0 9 1012 atom m2 which is similar to the global fallout level 17 8 1012 atom m2 in japan additional analyses of suspended solids ss and bottom sediments yielded negligible amounts of 236u our results suggest that 236u behaves as a conservative nuclide in seawater with potential advantages over other tracers of oceanic circulation

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

topography of the variscan orogen in europe failed not collapsed the variscan orogenic collage consists of three subduction collision systems rheno hercynian saxo thuringian and massif central moldanubian devonian to early carboniferous marine strata are widespread not only in the individual foreland fold and thrust belts but also in post tectonic basins within these foreland belts and on the cadomian crust of peri gondwanan microcontinental fragments which represent the upper plates of the subduction collision zones these marine basins preclude high elevations in the respective areas and also in their neighbourhood widespread late carboniferous intra montane basins with their coal bearing sequences are likewise incompatible with high and dry plateaus while narrow belts with high elevations remain possible along active margins within the orogen comparison of the variscides with the himalaya tibetan plateau is unfounded plausible reasons for the scarcity of high variscan relief include subduction of oceanic and even continental crust subduction erosion orogen parallel extension and most important lithospheric thinning accompanied by high heat flow and magmatism in many areas timing and areal array of magmatism and ht metamorphism are not compatible with a model of tectonic thickening and subsequent gravitational collapse it is suggested instead that lithospheric thinning and heating are due to mantle activities caused by the tethys rift the lower and middle crust were thermally softened and rendered unfit for stacking and isostatic uplift in terms of topography the variscides represent a failed orogen the ht regime also explains the abundance of granitoids and ht lp metamorphic rocks typical of the variscides melting in the ht regime extracted mafic components from variscan and cadomian crust as well as from cadomian metasomatized lithospheric mantle thus mimicking subduction related magmatism the onset of the ht regime at c 340 ma may also have triggered the final ascent of hp uhp felsic metamorphic rocks

extension in compressional orogenic belts the eastern alps extension in the eastern alps encompasses the following 1 extension accompanying simple shear crustal stacking subhorizontal stretching occurs along flat lying foliations and regionally consistent stretching lineations with associated high strains on a local scale stretching results from extrusion of ductile sediments squeezed between rigid basement blocks basement blocks during thrust sheet imbrication the overall geometric effect is crustal thickening 2 classical extensional tectonics extension first occurs as a consequence of accretion and underthrusting of continental and oceanic material and represents gravitational adjustment of an unstable orogenic wedge extension then occurs as a consequence of terminal continental collision and is accommodated by lateral extrusion of crustal of crustal blocks the overall geometric effect is crustal thinning extension is generally oriented subparallel to the strike of the orogen

a first transect of 236u in the north atlantic ocean abstract in this study the first comprehensive dataset of 236u in the north atlantic ocean is presented 236u 238u ratios and 236u concentrations are determined in about 70 seawater samples collected from 9 depth profiles along a transect through the northwest atlantic ocean during the first two legs of the geotraces cruise ga02 in 2010 the cruise track was designed to follow the path of the north atlantic deep water nadw from its formation region to the deep parts of the western atlantic ocean basins our results show that there is a strong north to south and surface to deep ocean gradient spanning a broad range of 236u 238u from 44 15 10 12 to 1477 91 10 12 that correlates well with the distribution of water masses in this region all measured ratios are above the theoretical pre anthropogenic levels of 10 13 to 10 14 showing that the whole transect is dominated by anthropogenic 236u based on the calculated 236u inventories the 236u inputs of global fallout and direct releases from nuclear reprocessing plants could be constrained to a range from 1000 to 1400 kg and from 115 to 250 kg of 236u from the two sources respectively our results show that the 236u 238u atomic ratio can be used as a marker of north atlantic water masses with high ratios 1000 10 12 characterizing northern water masses lsw and dsow and lowest ratios 50 400 10 12 corresponding to the increasing influence of aabw and aaiw

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

evidence for pre orogenic early devonian rifting in the variscan belt stratigraphy and structure of the palaeozoic cover of the mauges unit upper allochthon armorican massif france the palaeozoic sediments from the mauges unit armorican massif france are the best preserved pre orogenic sequences belonging to the upper allochthon two coherent sequences are identified the southern unit ch teaupanne unit represents the cover of the proterozoic basement and consists of ordovician sediments unconformably overlain by emsian carbonates followed by emsian to earliest eifelian immature sandstones the northern unit tombeau leclerc unit consists of an hirnantian to emsian condensed sequence in reverse position that has been thrust over the southern unit the devonian unconformity is interpreted as evidence for an early devonian extension recorded by normal faults affecting both the early devonian limestones and the underlying ordovician series this crustal extension recorded here for the first time is possibly related to the opening of a back arc basin saint georges sur loire associated with the subduction of an ocean located further south galicia brittany massif central ocean

paleomagnetism of upper devonian reefal limestones canning basin western australia two conflicting models have been proposed for the middle paleozoic position of gondwana with respect to euramerica a pole from morocco msissi norite that may be of late devonian age suggests that a broad ocean 3 000 km separated the northern continents from gondwana whereas results from mauritania gneiguira supergroup indicate that this ocean had closed by devonian time detailed thermal and alternating field demagnetization experiments have been carried out on red and gray limestones from seven sites 89 samples in an essentially undeformed late devonian reef complex northern canning basin western australia after minor tilt correction the site mean characteristic directions average 42 7 28 9 declination inclination with k 61 6 and 95 7 8 these results position northwestern australia at 15 s latitude in the late devonian a paleolatitude consistent with the presence of a well developed reefal sequence an early age is inferred for these magnetizations on the basis of the occurrence of mixed polarities and the fact that no post devonian directions for australia resemble the observed declinations and inclinations if the smith and hallam reconstruction for gondwana is used the paleomagnetic pole calculated for the late devonian of western australia agrees with the msissi norite result from morocco and suggests that an ocean still separated gondwana from euramerica in the late devonian the pole measured from the gneiguira supergroup in mauritania may be based on remagnetizations of late paleozoic age the directions determined from canning basin limestones are similar in inclination to but differ by 40 in declination from paleomagnetic results from the upper devonian comerong volcanics lachlan fold belt southeastern australia canning basin samples are from the stable craton and comerong volcanics samples are from the tasman fold belt the discrepancy between the two australian results may be best explained by tectonic rotation of the comerong volcanics locality

a depth profile of uranium 236 in the atlantic ocean abstract in this study the first two oceanic depth profiles of 236u sampled in the western equatorial atlantic ocean are presented the measured 236u 238u ratios decrease from about 10 9 at the surface down to about 10 10 even the lowest ratios measured below 4000 m depth are more than three orders of magnitude above the estimated natural 236u 238u level for the pre anthropogenic ocean this clearly indicates that anthropogenic 236u already has reached the deep atlantic ocean three different conceptual models are applied to identify the relevant processes capable of transporting significant amounts of 236u from the surface into the deep ocean while the vertical transport of particulate u is excluded as a significant source box model calculations suggest that north atlantic deep water production with some minor contribution of 236u from nuclear reprocessing as the most likely source for 236u in the deep western equatorial atlantic ocean our results show that 236u has a large potential as a new conservative and transient tracer in oceanography

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

kaolinite and mixed layer illite smectite in lower cretaceous bentonites from the peace river coalfield british columbia the x ray diffraction analysis of 75 thin volcanic clay bands in the lower cretaceous of the peace river coalfield shows kaolinite and mixed layer illite smectite to be the two clay minerals present kaolinite is dominant in the clay bands tonsteins in the coal bearing gething and gates formations whereas illite smectite is dominant in the clay bands k bentonites in the marine moosebar formation a complete gradation exists between the two clay minerals demonstrating their common volcanic origin volcanic textures are seen in thin section the relationship between clay composition and depositional environment corresponds with the clay stability fields with smectite the precursor of the mixed layer clay the proportion of illite in the latter averages 22 and corresponds with the coal rank the major element analyses mainly reflect the clay composition but with contributions from resistate and diagenetic minerals amongst the trace elements there are those that are both immobile in the alteration pro

eclogites with a short lived granulite facies overprint in the moldanubian zone czech republic petrology geochemistry and diffusion modelling of garnet zoning the petrology and geochemistry of a newly discovered suite of high pressure garnet clinopyroxene bearing rocks from the monotonous series of the moldanubian zone of the bohemian massif southwest czech republic have been investigated three types common eclogites quartz kyanite clino zoisite eclogites and garnet hornblende clinopyroxenites are distinguished by petrography and geochemistry all underwent a significant degree of partial breakdown under granulite and amphibolite facies conditions during exhumation important features include the growth of orthopyroxene in breakdown domains after garnet and omphacite and anorthite spinel corundum exceedingly peraluminous sapphirine replacing kyanite garnet zoning and inclusion patterns support a prograde evolution from low pressures for at least some of the samples the post eclogite stage granulite facies overprint indicates that high temperatures prevailed during exhumation but preservation of zoning in some garnets and the results of diffusion modelling suggest that this overprint took place over a very short time scale the geochemical and petrological results allow characteristic differences to be recognized between these eclogites and metabasites found in other tectonic units of south bohemia and consequently the assigning of all high pressure rocks to a single now disrupted tectonic unit is a gross simplification that seriously misrepresents the tectono metamorphic history of the region

paleozoic evolution of continental crust in the beaujolais lyonnais area northeastern part of the massif central france in the beaujolais lyonnais area of the northeastern massif central accretion of continental and possibly oceanic crustal fragments occurred between cambrian and early carboniferous time three distinct lithotectonic units terranes have been recognized the southern lyonnais unit consists of medium to high grade metamorphics and includes eclogites it formed in the early paleozoic the brevenne unit to the north contains low to medium grade metamorphic mafic and felsic volcanics and subordinate sedimentary rocks which possibly originated during the early paleozoic until devonian time in a sialic back arc environment or along an active continental margin the beaujolais unit is represented by volcanics on the south and predominantly shallow marine clastics and carbonates on the north it developed in a late devonian or early carboniferous ensialic marginal basin the peak of metamorphism in the lyonnais unit hp ht was reached in silurian time subsequent nw se to e w oriented convergence produced mylonitic foliation structural imbrication of the lyonnais basement rocks with the brevenne unit and se vergent folds accompanied by low to medium grade metamorphism late visean to namurian n s to nw se directed n vergent thrusting produced tectonic imbrication of the metamorphic northern brevenne unit with the nonmetamorphic beaujolais unit in the southern brevenne unit and in the lyonnais unit updoming along right lateral high angle normal faults was followed by emplacement of voluminous granitic plutons of crustal origin late carboniferous to early permian crustal thinning in the beaujolais lyonnais area was associated with n s trending left lateral strike slip faults and e w to ne sw trending right lateral strike slip faults basins that developed along these faults contain continental red beds

seismic anisotropy of the french massif central and predisposition of cenozoic rifting and volcanism by variscan suture hidden in the mantle lithosphere 1 we model the structure of the lithosphere its thickness and seismic anisotropy caused mainly by systematic orientation of olivine crystals from spatial variations of p wave delay times and the shear wave splitting observed at a dense network of mobile and permanent stations within the french massif central mc three major lithosphere domains with different seismic anisotropy are distinguished a suture in the deep lithosphere limits the thick lithosphere of the limousin western mc characterized by a consistent anisotropic pattern with high velocities dipping to the west the eastern mc comprising two different domains with a weakened mantle fabric in the south shows the high velocities dipping systematically to the east the suture between the western and eastern mc parallels the major crustal boundary the late variscan sillon houiller transfer fault in the south and the tauve aigueperse fault in the north with an offset of 10 20 km to the east the offset of the crustal and mantle parts of the same suture indicates that the rigid upper crust might be detached from the mantle lithosphere we suggest that the mantle suture hidden beneath an allochthonous crust was reactivated during the cenozoic extension of the weakened and thinned lithosphere in the south of the eastern mc and predestined a space for the major volcanism mont dore cantal the rigid northern domain characterized by a thicker lithosphere with a well preserved mantle fabric reacted to the extension predominantly by rifting e g limagne and roanne grabens

129i anthropogenic budget major sources and sinks data are presented here on the anthropogenic 129i inventory in regions that have been strongly affected by releases from european reprocessing facilities which to the authors knowledge presently account for 90 of the global isotope source in the earth s surface environment the results show that 90 of the isotope inventory occurs in marine waters with the nordic seas and eurasian basin of the arctic ocean containing most of the 129i within the terrestrial environment of europe soils contain the largest part of the isotope inventory however the inventory of the terrestrial system did not provide clues on the most plausible atmospheric source of 129i to europe thus supply from both gaseous and marine releases is proposed the sum of the total inventory in both the marine and terrestrial environments did not match the estimated releases this imbalance is likely to relate to unconstrained inventory estimates for marine basins irish sea english channel and north sea close to the facilities but also to the occurrence of 129i in the biosphere and possible overestimated releases from the nuclear reprocessing facilities there is no doubt that the available data on 129i distribution in the environment are far from representative and further research is urgently needed to construct a comprehensive picture

geochronology of carboniferous permian magmatism in the midland valley of scotland implications for regional tectonomagmatic evolution and the numerical time scale four new u pb isotope dilution thermal ionization mass spectrometry dates from carboniferous igneous rocks of the midland valley of scotland are integrated with 16 recently published 40ar 39ar dates the numerical and stratigraphical ages of the dated samples are compatible to stage level allowing improved intrabasinal and regional correlations early carboniferous extension related volcanism in the midland valley was pulsed with a date of 343 4 1 0 ma from the garleton hills volcanic formation and dates of 334 7 1 7 and 335 2 0 8 ma from the clyde plateau volcanic formation the magmatic pulses are synchronous with synrift phases in the northumberland solway basin volcanism continued in mid to late carboniferous time contemporaneous with dextral strike slip tectonics in contrast to a post rift tectonic setting in northern england after late carboniferous basin inversion tholeiitic magmatism dated at 307 6 4 8 ma provides a maximum westphalian d age for post variscan magmatism and extension dextral transtension across scotland and northern england in the early permian as rift systems developed across nw europe alkaline extension related magmatism resumed in the midland valley from c 298 to 292 ma the improved geochronology provides important data for poorly constrained parts of the numerical carboniferous time scale such as stages within the visean and provides a well controlled tie point that supports a tournaisian visean boundary age of c 345 4 ma

are the oroclines of the variscan belt related to late variscan strike slip tectonics terra nova 23 241 247 2011 abstract early variscan structures and magnetic anomalies delineate four oroclines along the variscan belt the arcs bend the lithostratigraphic zones of the autochthon and the allochthonous terranes which include ophiolites of the rheic suture and units of gondwanan derivation subducted on both sides of the rheic ocean a transcurrent model dominated by right lateral motion explains the genesis and evolution of the oroclines and a simple plate tectonics scenario links late variscan dextral strike slip movements in the variscides to a broad intracontinental shear zone kinematically equivalent to a transform fault terra nova 00 1 7 2011

uplift and late orogenic deformation of the central european variscan belt as revealed by sediment provenance and structural record in the carboniferous foreland basin of western poland the carboniferous foreland basin of western poland contains a coherent succession of late visean through westphalian turbidites derived from a uniform group of sources located within a continental magmatic arc detrital zircon geochronology indicates that two main crustal components were present in the source area of namurian a sediments they represent late devonian and early carboniferous ages respectively the detritus from westphalian d beds is much more diversified and contains admixture of late carboniferous zircons suggesting rapid unroofing of variscan igneous intrusions in the hinterland between namurian a and westphalian d times tectonic repetitions of tens of metres thick fault bounded stratigraphic intervals recorded in several wells provide evidence for compressional regime that occurred in the sw part of the carboniferous basin not earlier than during the westphalian c and produced nw se trending folds concordant with the structural grain of the adjacent ne part of the bohemian massif

epigenetic dolomitization of the přaidoli formation upper silurian the barrandian basin czech republic implications for burial history of lower paleozoic strata stratabound epigenetic dolomite occurs in carbonate facies of the barrandian basin silurian and devonian czech republic the most intense dolomitization is developed in bioclastic calcarenites within the transition between micritic limestone and shaledominated p idoli and lochkov formations deposited on a carbonate slope medium crystalline 100 400 m inclusion rich xenotopic matrix dolomite 18o 4 64 to 3 40 pdb 13c 1 05 to 1 85 pdb which selectively replaced most of the bioclastic precursor is volumetrically the most important dolomite type coarse crystalline saddle dolomite 18o 8 04 to 5 14 pdb 18c 0 49 to 1 49 pdb which precipitated in fractures and vugs within the matrix dolomite represents a later diagenetic dolomitization event in some vugs saddle dolomite coprecipitated with petroleum inclusion rich authigenic quartz crystals and minor sulfides which in turn were post dated by semisolid asphaltic bitumen the interpretation of the dolomitization remains equivocal massive xenotopic dolomite although generally characteristic of a deeper burial setting may have been formed by a recrystallization of an earlier possibly shallow burial dolomite deeper burial recrystallization by reactive basinal pore fluids that presumably migrated through the more permeable upper portion of the p idoli sequence appears as a viable explanation for this dolomitization overprint saddle dolomite cement of the matrix dolomite is interpreted as the last dolomitization event that occurred during deep burial at the depth of the oil window zone the presence of saddle dolomite the fluid inclusion composition of associated quartz crystals and vitrinite paleogeothermometry of adjacent sediments imply diagenetic burial temperatures as high as 160 c although high geothermal gradients in the past or the involvement of hydrothermally influenced basinal fluids can account for these elevated temperatures burial heating beneath approximately 3 km thick sedimentary overburden of presumably post givetian strata no longer preserved in the basin appears to be the most likely interpretation this interpretaion may imply that the magnitude of post variscan erosion in the barrandian area was substantially greater than previously thought

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

accretion and exhumation at a variscan active margin recorded in the saxothuringian flysch the saxothuringian flysch basin on the north flank of the central european variscides was fed and eventually overthrust by the northwestern active margin of the tepla barrandian terrane clast spectra mineral composition and isotopic ages of detrital mica and zircon have been analyzed in order to constrain accretion and exhumation of rocks in the orogenic wedge the earliest clastic sediments preserved are of early famennian age ca 370 ma they are exposed immediately to the nw of the suture and belong to the par autochthon of the foreland besides ultramafic ophiolite material these rocks contain clasts derived from early paleozoic continental slope sediments originally deposited at the nw margin of the saxothuringian basin these findings together with the paleogeographic position of the famennian clastics debris on the northwestern passive margin indicate that the saxothuringian narrow ocean had been closed by that time microprobe analyses of detrital hornblendes suggest derivation from the randamphibolit unit now present in the middle part of the saxothuringian allochthon munchberg nappes detrital zircons of metamorphic rocks formed a little earlier ca 380 ma indicate rapid recycling at the tectonic front the middle part of the flysch sequence ca early to middle visean both in the par autochthon and in the allochthon contains abundant clasts of paleozoic rocks derived from the northwestern slope and rise together with debris of cadomian basement 500 ma granitoids and 380 ma early variscan crystalline rocks all of these source rocks were still available in the youngest part of the flysch c middle to late visean but some clasts record in addition accretion of the northwestern shelf our findings permit deduction of minimum rates of tectonic shortening well in excess of 10 30 mm per year and rates of exhumation of ca 3 mm a and possibly more

metamorphism and microstructures along a high temperature metamorphic field gradient the north eastern boundary of the kralovsky hvozd unit bohemian massif czech republic a metamorphic field gradient has been investigated in the moldanubian zone of the central european variscides encompassing from base to the top a staurolite kyanite zone a muscovite sillimanite zone a k feldspar sillimanite zone and a k feldspar cordierite zone respectively the observed reaction textures in the anatectic metapsammopelites of the higher grade zones are fully compatible with experimental data and petrogenetic grids that are based on fluid absent melting reactions from structural and microstructural observations it can be concluded that the boundary between the kyanite staurolite zone and the muscovite and k feldspar sillimanite zones coincides with an important switch in deformation mechanism s besides minor syn anatectic shearing melt enhanced deformation microstructural criteria point a to a switch in deformation mechanism from rotation recrystallization climb accommodated dislocation creep to prism slip and high temperature fast grain boundary migration in quartz b to the activity of diffusion creep in quartz feldspar layers and c to accommodation of strain by intense shearing in fibrolite biotite layers it is suggested that any combination of these deformation mechanisms will profoundly affect the rheological characteristics of high grade metamorphic rocks and significantly lower rock strength hence the boundary between these zones marks a major rheological barrier in the investigated cross section and probably also in other low to medium pressure high temperature areas at still higher metamorphic grades k feldspar cordierite zone where the rheologically critical melt percentage is reached rock rheology is mainly governed by the melt and other deformation mechanisms are of minor importance in the study area the switch in deformation mechanism s is responsible for large scale strain partitioning and concentration of deformation within the higher temperature hanging wall during top to the s thrusting thus preserving a more complete petrostructural record within the rocks of the footwall including indications for a devonian high to medium pressure medium temperature metamorphic event thrusting is accompanied by diapiric ascent of diatexites of the k feldspar cordierite zone and infolding of the footwall suggesting local crustal overturn in this part of the moldanubian zone

first 236u data from the arctic ocean and use of 236u 238u and 129i 236u as a new dual tracer the first dataset of 236u 238u in the water column of the arctic ocean ao is presented and shows the widest range of ratios reported so far in the open ocean from 5 55 5 to 3840 260 10 12 3840 260 10 12 surface samples and depth profiles were collected during two geotraces expeditions in 2011 2012 and analyzed for the concentrations of 236u and 129i with the aim of investigating whether the combination of 236u 238u and 129i 236u can be used as a new oceanographic tool in the ao results show that the distributions of the 236u 238u and 129i 236u atomic ratios are consistent with the different water masses in the ao high 236u 238u and 129i 236u ratios in the upper water column 2000 10 12 2000 10 12 and 200 respectively illustrate the penetration of atlantic waters aw into the ao lower values were found in pacific waters pw and deep waters of the ao rivers seem to represent a temporally and spatially constrained third anthropogenic source of 236u but more data are needed to confirm this in a simple mixing model the combination of 236u 238u and 129i 236u reveals a high contribution 99 of natural background waters pre nuclear era in the deep and bottom waters of the amerasian basin indicating an apparent water mass renewal time of 1000 years despite the relatively high apparent age of the amerasian basin deep waters this work shows the potential of using the dual tracer approach as a new oceanographic tool in the arctic ocean

bomb fall out 236 u as a global oceanic tracer using an annually resolved coral core anthropogenic 236u t 23 4 my is an emerging isotopic ocean tracer with interesting oceanographic properties but only with recent advances in accelerator mass spectrometry techniques is it now possible to detect the levels from global fall out of nuclear weapons testing across the water column to make full use of this tracer an assessment of its input into the ocean over the past decades is required we captured the bomb pulse of 236u in an annually resolved coral core record from the caribbean sea we thereby establish a concept which gives 236u great advantage the presence of reliable well resolved chronological archives this allows studies of not only the present distribution pattern but gives access to the temporal evolution of 236u in ocean waters over the past decades

hercynian polyphase tectonics in the northeast french massif central the closure of the brevenne devonian dinantian rift field and laboratory structural studies show that the devonian dinantian units of the northeast french massif central experienced a complex and contrasting tectonic metamorphic evolution during the hercynian orogeny the structural analysis of the pre middle visean brevenne violay beaujolais rocks in the loire area shows a polyphase tectonic evolution associated with greenschist to amphibolite facies metamorphism the first event d1 probably occurred in early tournaisian or latest devonian times it is responsible for the flat lying regional foliation and the nw se to n s trending lineation it is well observed in the violay group and corresponds to the nw vergent emplacement of the late devonian units upon their gneissic basement represented by the affoux gneisses the second event d2 is responsible for the ne sw to e w trending lineation to the south d2 deformation is locally reworked by the grand chemin dextral wrench fault around 345 350 ma ago this polyphase deformation is also found in several devonian dinantian areas of the ne massif central but not in morvan this tectonics corresponds to the tournaisian closure by northward thrusting and subsequent intracontinental deformation of the oceanic brevenne violay beaujolais rift which opened in devonian times in a back arc setting

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

diamond and coesite discovered in saxony type granulite solution to the variscan garnet peridotite enigma diamond and coesite were discovered in situ as inclusions in garnet kyanite and zircon in high pressure granulites from northern bohemian massif these continental crustal rocks were therefore subducted to depths of c 140 km which also explains their common association with mantle garnet bearing peridotites models involving crustal thickening for these high pressure granulites need to be significantly modified whole variscan belt with numerous hp granulite occurrences can represent a large ultrahigh pressure terrain

the tracing of riverine u in arctic seawater with very precise 234u 238u measurements abstract the riverine flux of u that enters the deep oceans is not well constrained since the net losses during estuarine mixing are difficult to quantify riverine dissolved u normally has a higher 234 u 238 u activity ratio 234 u 238 u ar than the uniform value that characterizes open ocean seawater and could be used as a tracer of riverine inputs if one could resolve subtle variations in seawater composition using new mass spectrometry techniques we achieve a long term reproducibility 0 3 on 234 u 238 u ar which permits the tracing of riverine u in seawater samples from the arctic a partially restricted basin that is ideal for such a study we find that surface waters from the arctic basins carry elevated 234 u 238 u ar when compared with deep ocean seawater samples from the canada basin have a significant freshwater component and provide evidence that the mackenzie river loses 65 of its u in the mackenzie shelf estuary zone before entering the deeper basin this is in contrast to samples from the makarov basin which provide evidence that all of the freshwater input is derived from the major yenisey river alone despite the proximity of the lena and ob rivers the differing behaviour of u between the mackenzie and yenisey rivers is most likely a consequence of the strong binding of u to dissolved organic matter doc or secondary phases in these rivers the yenisey river appears to transport the majority of the doc through the shelf and into the makarov basin in contrast the mackenzie river appears to lose a significant amount of doc 50 in the estuary shelf zone which may lead to loss of associated u these findings offer a more detailed picture of the fresh riverine water flow patterns in the arctic ocean when compared to other geochemical proxies the non conservative behaviour of u in the mackenzie river through the shelf estuaries has important implications for u input into oceans and the total marine budget

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

accompanying seismic refraction investigations along the profile dekorp 2 north seismic refraction measurements were carried out along the dekorp 2 n reflection line traveltime data have been inverted to velocity depth distributions using x t inversion und ray tracing methods the velocity model shows alternating layers of high and low velocity high velocity values range from 6 0 to 6 6 km s in the upper crust and from 70 to 8 2 km s in the lower crust in low velocity zones velocities do not exceed 6 25 km s the crust mantle boundary lies in about 28 30 km depth correlations exist between the velocity model of refraction seismics and the line drawing section of reflection seismics

reply to w franke on w dorr and g zulauf elevator tectonics and orogenic collapse of a tibetan style plateau in the european variscides the role of the bohemian shear zone in his comments on our paper about variscan elevator tectonics w franke this issue presents several reasons which according to his view would not be compatible with overthickened crust in the tepla barrandian unit during upper devonian lower carboniferous continent continent collision in the following paragraphs we will show that 1 most points addressed by w franke are not relevant for our model of elevator tectonics 2 correlations made by w franke between various crustal blocks of the bohemian massif are not consistent with data and 3 the models presented by w franke are based on assumptions but ignore a complete set of robust data w franke is pointing out that the barrandian paleozoic rocks underwent only minor shortening less than 20 there would be no evidence for major thrust stacking under the paleozoic cover and the diagenetic grade of the devonian rocks would preclude the once former existence of higher structural units these observations would directly contradict the reconstruction of fig 15 of dorr and zulauf 2010 in which the barrandian syncline is shown to occupy the central and upper part of a strongly thickened crust all the facts listed by w franke are correct his conclusions however are wrong the metamorphic grade and the magnitude of upper crustal shortening cannot be used to constrain crustal thickness w franke does not consider that the entire tepla barrandian crustal block was thrust on top of saxothuringian crust during upper devonian continent continent collision this scenario of doubling the crustal thickness has already been emphasized by bues et al 2002 it explains why mantle and lower crust slices occur inside the bohemian shear zone an almost complete oblique crustal section is exposed between stod and the hoher bogen shear zone thrusting of the tepla barrandian crust on top of saxothuringian crust is also shown in the seismic section 9hr and is supported by gravimetric data published recently by guy et al 2011 note that both the seismic and the gravimetric data are fully compatible with the elevator tectonics model of dorr and zulauf 2010 northwest from the moldanubian domain occurs an important gravity high corresponding to the neoproterozoic basement of the tepla barrandian unit limited in the north by southeast dipping reflectors of the tepla suture which is characterized by high density eclogites and ultramafics the footwall of the suture corresponds to lowdensity felsic crust of the saxothuringian basement and underneath the tepla barrandian suprastructure a lowdensity granulite channel was identified the latter coinciding with vertical extrusion of felsic granulites in the eger valley guy et al 2011 the steep boundary between the tepla barrandian and moldanubian zone is interpreted by guy et al 2011 in terms of major vertical elevation of the orogenic lower crust supporting the dorr and zulauf 2010 elevator tectonics model concerning the magnitude of shortening in elevated domains w franke should also consider recent analogs of the tepla barrandian plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows no evidence for significant upper crustal shortening densmore et al 2007 the same holds for the interior parts of the tibetan plateau w franke believes that the amount of crustal thickening can be constrained from the level of erosion he states that w dorr g zulauf institut fur geowissenschaften universitat frankfurt a m altenhoferallee 1 60438 frankfurt germany e mail g zulauf em uni frankfurt de

provenance analysis of the paleozoic sequences of the northern gondwana margin in nw iberia passive margin to variscan collision and orocline development abstract the cantabrian zone of nw iberia preserves a voluminous almost continuous sedimentary sequence that ranges from neoproterozoic to early permian in age its tectonic setting is controversial and recent hypotheses include i passive margin deposition along the northern margin of gondwana or ii an active continental margin or iii a drifting ribbon continent in this paper we present detrital zircon u pb laser ablation age data from 13 samples taken in detrital rocks from the cantabrian zone sequence ranging from early silurian to early permian in depositional age the obtained results together with previously published detrital zircon ages from ediacaran ordovician strata allow a comprehensive analysis of changing provenance through time collectively these data indicate that this portion of iberia was part of the passive margin of gondwana at least from ordovician to late devonian times zircon populations in all samples show strong similarities with the sahara craton and with zircons found in libya suggesting that nw iberia occupied a paleoposition close to those regions of present day northern africa during this time interval changes in provenance in the late devonian are attributed to the onset of the collision between gondwana and laurussia additionally the middle carboniferous to permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the variscan orogeny late devonian to permian samples yield zircon populations that reflect topographic changes produced during the variscan orogeny and development of the lithospheric scale oroclinal buckling

distribution of 236u in the u s geotraces eastern pacific zonal transect and its use as a water mass tracer abstract we report dissolved concentrations of the long lived radioisotope 236u measured in the water column along the 2013 us geotraces eastern pacific zonal transect gp16 this transect followed a 10 15 s line from manta ecuador to papeete haiti french polynesia crossing the southern east pacific rise intercepting one of the largest hydrothermal plumes as well as a productivity gradient which includes the upwelling zone and associated low oxygen waters offshore from peru and the oligotrophic sub tropical gyre accelerator mass spectrometry was used to measure dissolved seawater 236u concentrations as low as 1 103 atom kg 1 which are among the lowest levels reported to date differences in upper water column 236u distributions from east to west are a result of variable contributions from different surface and intermediate waters encountered along the transect the distribution of 236u both in depth and geographically provides complementary information to that obtained from 14c and helium isotopes demonstrating that 236u concentrations are diagnostic in the identification of and contributions from the different deep and bottom water masses encountered along the epzt jenkins et al 2017 for example we observe minimum 236u concentrations along the epzt between 2000 and 3000 m that are consistent with contributions attributed to pacific deep water we also observe increases in 236u below 3000 m at the eastern and western termini of the epzt this is consistent with contributions associated with antarctic bottom water and lower circumpolar deep water our results indicate that 236u may be used in conjunction with 14c and 3he isotopes as an additional tool with which to identify and resolve contributions from different water masses in the pacific ocean this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

the role of the east asian active margin in widespread extensional and strike slip deformation in east asia east asia is a region of widespread deformation dominated by normal and strike slip faults deformation has been interpreted to result from extrusion tectonics related to the india eurasia collision which started in the early eocene in east and se china however deformation started earlier than the collision latest cretaceous to palaeocene suggesting that extrusion tectonics is not the only driving mechanism for east asia deformation it is suggested that the east asian active margin has influenced deformation in east asia significantly along the margin cenozoic back arc extension took place behind several adjoining arcs implying eastward rollback of the subducting slab and collapse of the overriding plate towards the retreating hinge line we show that extension took place along a c 7400 km long stretch of the east asian margin during most of the cenozoic physical models are presented simulating overriding plate collapse and back arc extension the models reproduce important aspects of the strain field in east asia for geometrical and rheological conditions scaled to represent east asia modelling shows that the active margin can be held responsible for deformation in east asia as far west as the baikal rift zone located c 3300 km from the margin

clasts of variscan high grade rocks within upper visean conglomerates constraints on exhumation history from petrology and u pb chronology in this paper u pb zircon monazite and rutile data for crystalline rocks deposited as clasts in the upper visean conglomerates at the eastern margin of the bohemian massif are reported u pb data of spherical zircon from three different granulite clasts yielded a mean age of 339 0 0 7 ma 2 while oval and spherical grains of another granulite pebble define a slightly younger date of 337 1 1 1 ma these ages are interpreted as dating granulite facies metamorphism thermochronology and the derived pressure temperature p t path of the granulite pebbles reflect two stage exhumation of the granulites near to isothermal decompression from at least 44 km to mid crustal depths of around 22 km was followed by a near isobaric cooling stage based on reaction textures and geothermobarometry minimum average exhumation rate corresponds to 2 8 4 3 mm year 1 the extensive medium pressure high temperature overprint on granulite assemblages is dated by u pb in monazite at c 333 ma this thermal event probably has a close link to generation and emplacement of voluminous moldanubian granites including the cordierite granite present in clasts this granite was emplaced at mid crustal levels at 331 3 ma u pb monazite whereas the u pb zircon ages record only a previous magmatic event at c 378 ma eclogites and garnet peridotites normally associated with high pressure granulites are absent in the clasts but exotic subvolcanic and volcanic members of the ultrapotassic igneous rock series durbachites of the bohemian massif have been found in the clasts it is therefore assumed that the clasts deposited in the upper visean conglomerates sampled a structurally higher tectonic unit than the one that corresponds to the present denudation level of the moldanubicum of the bohemian massif the strong medium temperature overprint on granulites dated at c 333 ma is attributed to the relatively small size of the entirely eroded bodies compared with the presently exposed granulites

erratum to early permian pangea b to late permian pangea a earth planet sci lett 215 2003 379 394 a dipartimento di scienze della terra universita di milano via mangiagalli 34 20133 milan italy b lamont doherty earth observatory palisades ny 10964 usa c department of geological sciences rutgers university piscataway nj 08854 usa d dipartimento di scienze geologiche e geotecnologie universita di milano bicocca piazza della scienza 4 20126 milan italy e departement erdwissenschaften eth zentrum ch 8092 zu rich switzerland f department of earth sciences aarhus university aarhus denmark

oroclines of the variscan orogen of iberia paleocurrent analysis and paleogeographic implications abstract coupled structural and paleomagnetic analyses have shown that the northern iberian bend of the variscan orogen referred to as the cantabrian orocline developed by vertical axis rotation of an originally linear orogen however palinspastic restoration of the orocline has proven difficult owing to 1 an unusually great orogenic width of over 700 km and 2 exposure of shallow water strata of the gondwanan margin in the northern and southern portions of the orogen we present paleocurrent data from lower ordovician shallow marine clastic sedimentary rocks across the variscan of northern and central iberia collected to constrain palinspastic restoration of the orogen paleocurrent data were collected from over 50 sites and include cross bed foresets ripple crests and casts as well as rare ball and pillow structures syn sedimentary slump folds and incised channels paleocurrent directions fan around the cantabrian orocline are consistently oriented at a high angle to structural strike and yield a consistent offshore direction outward from the oroclinal core similarly changes in structural strike and paleocurrent direction across central iberia imply the presence of a second more southerly orocline the central iberian orocline that is continuous with but convex in the opposite direction of the cantabrian orocline together the cantabrian and central iberian oroclines define an s shaped pair of continental scale buckle folds palinspastic restoration of the oroclines yields a linear continental margin 1500 km long characterized by consistent offshore paleoflow to the west defining a westerly oceanic domain presumably the rheic ocean and an easterly landward direction presumably gondwana recognition of the southern orocline explains the unusual width of the orogen the geometry of aeromagnetic anomalies attributable to variscan rocks and is consistent with available structural data paleomagnetic declination data and the distribution of correlative paleozoic and older rock sequences including shallow water strata of the gondwanan margin the s geometry of the oroclines is similar to the z geometry of the alaskan oroclines of the north america cordillera suggesting that as in the cordillera the iberian oroclines may record a significant margin parallel translation event

carboniferous tectonics of the variscan basement collage in eastern bavaria and western bohemia the tectonometamorphic units in the variscan basement of eastern bavaria and western bohemia have a long and complex record of large scale continental deformation metamorphism and syn and posttectonic magmatism although there is a large database describing each of the above mentioned phenomena an integrated tectonic synthesis is hard to achieve in this paper we review some of the prominent effects in the carboniferous tectonic evolution which is accountable for much of the deformation regionally extensive low pressure high temperature metamorphism and abnormally intense partial anatexis and plutonism deformation was multistage and its kinematics were dominated by lateral compression transpression and strike slip shearing tectonic units were mostly deformed en masse without operation of large discrete shear zones an exception were the boundary zones of those units that had already cooled to sub greenschist facies temperatures before the onset of carboniferous deformation these boundaries were operated as normal or transtensive faults the large present vertical thickness of the zone of erbendorf vohenstrauss at the ktb drill site is most probably due to a combination of carboniferous block tilting related to the intrusion of the falkenberg granite and cretaceous distributed reverse faulting and imbrication late orogenic plutonism in the bohemian massif led to the emplacement of at least 176 000 km3 of granitoids melt flux through the moldanubian unit may have been as high as 0 2 km m y allowing the estimated volume of granitoids to be segregated by partial anatexis of the continental crust within a time span of approximately 8 8 million years

did the variscides collapse or were they torn apart a quantitative evaluation of the driving forces for postconvergent extension in central europe extension following immediately after the end of convergence caused rapid destruction of the european variscan orogen and resulted in the formation of numerous sedimentary basins and widespread magmatism possible driving forces for this phase of extension i e gravitational collapse of the thickened crust or reorientation of the far field stress regime are assessed quantitatively using a two dimensional thermomechanical finite element modeling approach the initial model setup approximates the geometry and physical properties of a lithosphere scale half profile through the variscan orogen and its foreland various numerical simulations and parameter studies suggest that the gravitational instability of the variscan orogen alone was not sufficient to explain the observed amount and timing of crustal extension tensile plate boundary stresses of the order of 10 mpa superposed on the gravitational forces are required to overcome the finite strength of the crust and restore a uniform crustal thickness in the variscan realm modeling results are constrained by comparison with existing data sets from the central european variscides for example crustal structure seismic reflectivity as well as temporal and spatial distribution of magmatic activity

reconstruction of the 236u input function for the northeast atlantic ocean implications for 129i 236u and 236u 238u based tracer ages a reconstruction of historical discharges of 236u into the northeast atlantic ocean by nuclear installations is presented the nuclear reprocessing facilities sellafield sf great britain gb and la hague lh france and potentially also the nuclear fuel processing installation springfields sp gb represent the main contributors of 236u in the northeast atlantic ocean because data on 236u releases is lacking 236u discharges from sp and sf are estimated based on the u isotopic systematics found in the discharges from lh the resulting reconstruction of 236u releases indicates that until 2013 a total of 95 32 kg of 236u was discharged from sf sp and lh in a second step the reconstructed 236u releases are combined with 129i data from literature and oceanic and atmospheric box models are used to derive the 129i 236u and 236u 238u input functions that for example can be used to calculate tracer ages of atlantic waters in the arctic ocean our conceptual results show that the combination of 129i 236u and 236u 238u generally allows the estimation of tracer ages over the past approximately 25 yr if contributions of 236u from global fallout are considered finally as a proof of concept the new method is applied to calculate tracer ages of arctic ocean surface samples collected in 2011 12 and the results are in good agreement with literature data we conclude that the combination of 129i 236u with 236u 238u in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the north atlantic region this article is protected by copyright all rights reserved