variscan strain pattern in the paleozoic series at the lizard front southwest england a structural analysis of the devonian sedimentary gramscatho formations south cornwall allows us to specify the variscan strain pattern at the lizard front this deformation is consistent with a nnw verging tangential shear which first induces a synmetamorphic folding phase f1s1 and whose noncoaxial character is emphasized on different scales by the existence of a positive deformation gradient toward narrow shear zones the development of syncleavage noncylindrical folds whose axes tend to be reoriented in the s1 slaty cleavage plane toward a pervasive stretching lineation l1 which trends n160 e and by the existence of nnw verging sheath folds this folding phase evolves finally to tangential structures which induce over the parautochthonous gramscatho formations subhorizontal shear planes bearing strong slickenside lineations trending parallel to l1 lineations which thus represent on a regional scale the tectonic transport trend of allachthonous units migrating northwards the existence of such allochthonous units in the south cornubian area is now well established by the discovery at the lizard front of a paleozoic carboniferous limestone lens wedged under the lizard hornblendeschist the structural evolution of the south cornubian domain is consistent with the scheme of a continental platform progressively implicated in a tangential deformation propagating northward this compression leads in the internal southern zones to an earlier mid upper devonian crustal tangential tectonic which later carboniferous reaches the external domain of england and it expresses in the devono carboniferous cover by a tegumentary tectonic this northward verging tangential pattern is now testified by swat south west approaches traverses profile interpretation

the geochemistry of mafic metavolcanics implications for the origin of the devonian massive sulfide deposits at zlate hory czechoslovakia mafic metavolcanic rocks in the area of the zlate hory massive sulfide deposits are interpreted as convergent plate margin basalts and basaltic andesites metamorphosed to the greenschist facies according to the major and trace element compositions the metabasites exhibit island arc tholeiitic to low k calc alkaline composition

strong and highly variable push of ocean waves on southern ocean sea ice sea ice in the southern ocean has expanded over most of the past 20 y but the decline in sea ice since 2016 has taken experts by surprise this recent evolution highlights the poor performance of numerical models for predicting extent and thickness which is due to our poor understanding of ice dynamics ocean waves are known to play an important role in ice break up and formation in addition as ocean waves decay they cause a stress that pushes the ice in the direction of wave propagation this wave stress could not previously be quantified due to insufficient observations at large scales sentinel 1 synthetic aperture radars sars provide high resolution imagery from which wave height is measured year round encompassing antarctica since 2014 our estimates give an average wave stress that is comparable to the average wind stress acting over 50 km of sea ice we further reveal highly variable half decay distances ranging from 400 m to 700 km and wave stresses from 0 01 to 1 pa we expect that this variability is related to ice properties and possibly different floe sizes and ice thicknesses a strong feedback of waves on sea ice via break up and rafting may be the cause of highly variable sea ice properties

wind drag coefficient over first year sea ice in the bering sea profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the bering sea and used to compute surface wind drag coefficients based upon 138 profiles for near constant ice conditions northeast winds of 3 15 m s 1 and near neutral stability the mean near neutral 10 m drag coefficient was 0 00309 0 00049 this is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice sixty five percent of the variance of this estimate is explained by orientation of the ice floe to the wind an additional 5 of the variance is explained by wind speed dependence provided that diabatic atmospheric stability over the bering sea ice pack is well correlated with low wind speed the significant ice advecting wind stress on the ice is determined from the neutral value of the drag coefficient a function of ice roughness length alone the ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection

on the effective aerodynamic and scalar roughness length of weddell sea ice we study the effective aerodynamic roughness length z0 eff and scalar roughness length for temperature zt eff over different compact sea ice types in the antarctic weddell sea by aircraft measurements during two austral summer seasons z0 eff and zt eff are highly variable in the weddell sea ice area the averaged value of in all main sea ice areas was smaller than the averaged value of the ratio between the two roughness lengths was relatively small for new young sea ice with 2 but the ratio became significantly large for the multiyear pack ice with 227 for the pack ice area with sea ice concentration ranging between 95 to 100 we determined a median 4 1 10 03 m and a median 1 8 10 05 m in the new young sea ice area with sea ice concentration ranging between 98 and 100 we observed a median 10 04 m and a median 2 2 10 04 m these values of and differ from published observations conducted in a pack ice and new young sea ice area in the northern hemisphere such as the arctic most model parameterizations require the roughness lengths as constant values as boundary input parameters our study shows that by using the overline z 0 rm eff and values of this study instead of commonly used sea ice roughness length values the accuracy of parameterized heat and momentum fluxes in the weddell sea ice area can significantly be improved

geochemistry of the start complex greenschists rhenohercynian morb the meta igneous greenschists of the start complex southdevon are composed of a mineralogically uniform but texturally variable actinolite epidote albite assemblage with retrogressed variants containing chlorite muscovite sphene carbonate and oxidized opaque minerals geochemically they represent a suite of relatively primitive tholeiites exhibiting mild differentiation depleted incompatible element abundances and variable light rare earth element depletion patterns comparable to modern basalts from normal spreading ridge segments n morb as the start greenschistsexhibit a number of chemical similarities to the nearby upper palaeozoic lizard ophiolite and morb type clasts within the rhenohercynian zone generally they may also represent local variscan ocean crust which floored smalloceanic basins that separated the old red sandstone continent from the armorican microplate to the south the start complex could thus represent a previously unrecognized oceanic component to the variscan orogenic belt rhenohercynian zone of northwest europe

measurements of turbulence transfer in the near surface layer over the antarctic sea ice surface from april through november in 2016 the surface energy budget over the antarctic sea ice from 8 april 2016 through 26 november 2016 are presented from april to october sensible heat flux sh and subsurface conductive heat flux g were the heat source of surface while latent heat flux le and net radiation flux rn were the heat sink of surface our results showed larger downward sh due to the warmer air in our site and upward le due to the drier air and higher wind speed in our site compared with sheba data however the values of sh in n ice2015 campaign which located at a zone with stronger winds and more advection of heat in the arctic were comparable to our results under clear skies the values of aerodynamic roughness length z0m and scalar roughness length for temperature z0h being 1 9 10 3 m and 3 7 10 5 m were suggested in this study it is found that snow melting might increase z0m our results also indicate that the value of log z0h z0m was related to the stability of stratification in addition several representative parameterization schemes for z0h have been tested and a couple of schemes were found to make a better performance

autumn sea ice thickness ridging and heat flux variability in and adjacent to terra nova bay ross sea antarctica the variability of sea ice thickness and snow depth observed from the r v nathaniel b palmer in late may 1998 in and adjacent to terra nova bay tnb ross sea antarctica is described conductive heat fluxes are estimated on the basis of the observed snow and ice thicknesses there was only 6 areal coverage of open water in tnb and 87 of the areal coverage of unridged ice was 0 3 m thick between the western and eastern margins of tnb there were increases in the area weighted unridged ice thickness 0 05 0 25 m and the areal extent of ridging 2 5 18 5 ridged ice accounted for 44 66 of the total ice mass in tnb and was as vital to thickening the ice cover as it was outside the bay where 30 60 of the total ice mass was contained within the 5 35 of ice that was ridged satellite passive microwave special sensor microwave imager ssm i data show that the extensive ice cover in tnb was normal for this time of year probably because of the blocking effect of thick ridged 100 concentration pack ice outside the bay despite the extensive ice cover in tnb there was an order of magnitude difference in area weighted mean heat flux between the bay and the pack ice for example depending on the choice of bulk snow thermal conductivity value ks 0 14 or 0 31 w m 1 k 1 the heat flux values for unridged ice were 199 or 216 w m 2 in tnb versus 35 or 49 w m 2 on the inbound pack ice leg and 20 or 39 w m 2 on the outbound pack ice leg factoring in the contribution of ridges to the ice thickness distribution decreased the heat flux in the bay and the pack ice by 25 or 36 depending on ks the greatest proportion of the heat flux in tnb occurred through the ice no more than 30 of the heat loss was from open water since the ice conditions observed in tnb were apparently normal for the time of year the heat fluxes also must have been quite normal

geochemical characteristics and comparison of the basic rocks of the lizard complex and the basaltic lavas within the hercynian troughs of sw england the s cornish basaltic rocks constitute a separate chemical province relative to the rest of the sw england hercynian volcanic suites in particular they are characterized by a lower incompatible element abundances b generally lower large ion lithophile high field strength element ratios and c being mildly enriched in the light ree within this province some of the basalts have chemical features akin to incompatible element enriched morb tectonically the s cornish province can be divided into a the s cornish melange zone n lizard roseland area and b the mylor sedimentary trough penwith camborne area both of which contain localized basaltic lavas these basalts are compared with the lizard ophiolite and associated hornblende schists which have compositions ranging from depleted to enriched morb the exotic volcanic megaclasts within the melange zone are not chemically related to the ophiolite and as such do not represent the dismembered volcanic portion of the lizard ophiolite if the lizard ophiolite and the hornblende schists represent different segments of a palaeozoic oceanic area lying to the s the ocean floor type hercynian basalts of s cornwall are interpreted as an abortive attempt to produce oceanic crust in a rifted continental margin during the early devonian

modeling of the influence of sea ice cycle and langmuir circulation on the upper ocean mixed layer depth and freshwater distribution at the west antarctic peninsula

carboniferous submarine volcanism at herbornseelbach lahn dill area germany a 100 m thick sequence of carboniferous submarine dominantly basaltic volcanic rocks at herbornseelbach lahn dill area is subdivided into six units two pillow volcanoes show a characteristic change from basal megapillows up to 5 m across through normal pillows 0 5 to 0 8 m across to a top facies of small pillows 0 5 m across and or breccias of scoriaceous clasts and discontinuous lava stringers sheet flows 0 5 to 4 m thick can be distinguished from sills by asymmetric cooling structures and textures vesicle concentrations near the top basal flow wrinkles and ponding of sediments on irregular flow tops

upper palaeozoic ophiolite generation and obduction in south cornwall the gramscatho flysch sequence of south cornwall including the melanges of the meneage formation and the lizard ophiolite are described in relation to the development of the gramscatho basin the timing and geotectonic evolution of this feature are considered in its regional context within the rhenohercynian zone of northwest europe this zone is interpreted as an intracontinental dextral transform system that developed during the devonian closure of the so called massif central ocean a basin and rise topography is attributed to extension and compression at offsets on major faults e w extension of the gramscatho pull apart basin in middle and upper devonian times is believed to have caused rifting and the development of ocean crust from which the lizard ophiolite was assembled in an oceanic setting at a ridge transform junction the meneage formation was generated as a result of intrabasinal uplift on transcurrent faults a major change of plate motions took place when the massif central ocean finally closed at the end of the devonian and the weak rhenohercynian zone became a site of crustal convergence from which thrust nappes were transported northwards foreland basins were sequentially developed and deformed by thin skinned tectonics as the system advanced northwards during the carboniferous

drag coefficients for winter antarctic pack ice air ice and ice water drag coefficients referenced to 10 m height winds for winter antarctic pack ice based on measurements made from r v polarstern during the winter weddell sea project 1986 wwsp 86 and from r v akademik fedorov during the winter weddell gyre study 1989 wwgs 89 are presented the optimal values of the air ice drag coefficients made from turbulent flux measurements are 1 79 0 06 x 10 exp 3 for wwsp 86 and 1 45 0 09 x 10 exp 3 for wwgs 89 a single ice water drag coefficient for both wwsp 86 and wwgs 89 estimated from periods of ice drift throught to represent free drift conditions is 1 13 0 26 x 10 exp 3 and the ice water turning angle is 18 18 deg it is suggested that for a typical antarctic winter pack ice cover the ice cover reduces the momentum flux from the atmosphere to the ocean by about 33 percent

geochemistry and u pb and 40ar 39ar geochronology of the man of war gneiss lizard complex sw england pre hercynian arc type crust with a sudeten iberian connection the man of war gneiss is a variably deformed meta igneous body that ranges in composition from gabbro to tonalite and comprises part of the basal structural slice of the lizard ophiolite complex sw england u pb dating of zircon demonstrates that the parental magmas crystallized in the earliest ordovician 499t s 3 ma but 40 ar 39 ar step heating analysis of amphiboles suggests that at least the northernmost zone of the gneiss was subjected to an amphibolite grade metamorphic event at c 374 ma probably associated with thrust emplacement of the ophiolite the gneiss exhibits major trace and rare earth element variations in conformity with an origin through partial melting of an amphibolitic source containing hornblende and plagioclase probably with minor garnet and zircon the elemental abundances and variations are characteristic of granitoids formed in supra subduction zone environments a granitoid sill within the adjacent old lizard head series schists previously inferred to be related to the man of war gneiss is trondhjemitic and exhibits higher sio 2 tio 2 and mgo but lower zr v ba and sr contents and therefore is probably not genetically related to the latter the sill may record local melting during ophiolite emplacement the man of war gneiss probably represents a structural inlier of pre hercynian basement incorporated in the hercynian nappes of sw england during nnw directed thrusting we emphasize the geological and geochronological similarities between variably deformed granitoid units of the lizard complex the sudeten massif of southern poland and the allochthonous complexes of northern portugal and nw spain these granitoid rocks may represent dispersed remnants of tremadoc arcs that formed oceanward from the northern margin of gondwana this is further convincing evidence that at this time eastern avalonia was separated from northern gondwana by an ocean basin that may have been connected with the tornquist sea

the kennack gneisses of the lizard complex cornwall england partial melts produced during ophiolite emplacement the kennack gneisses are a series of migmatites and microgranites found at the base of the peridotite of the lizard ophiolite complex the gneisses were derived by metamorphism and anatexis of interbedded sediments and basalts of a lower ophiolite slice during displacement of the complex from the oceanic regime in devonian times anatexis is thought to have taken place at temperatures of 700 800 c and pressures of several kilobars suggesting that heat was supplied locally by the thrusting of a hot peridotite sheet displacement and assembly of the ophiolite slices therefore probably took place not long after formation subsequent emplacement onto the gramscatho beds was after considerable cooling

the effect of observed ice conditions on the drag coefficient in the summer east greenland sea marginal ice zone the summer east greenland sea marginal ice zone is a region characterized by extreme horizontal variations of surface roughness characteristics the surface drag coefficient is found to be correlated with these roughness characteristics in particular ice concentration and ice floe roughness and size the estimates of wind stress and wind speed yield neutral drag coefficients cdn with standard deviations of 2 3 0 8 10 3 for areas with less than 40 ice concentration and 4 0 1 1 10 3 for ice concentrations greater than 70 much of the variation in cdn for a given ice concentration is explained by differences in ice floe size and roughness very small concentrated rough floes that have been affected by wave action produce twice as much wind stress cdn 4 2 0 7 10 3 as relatively large flat floes cdn 2 1 0 6 10 3 and 4 times as much as typical open ocean for a given wind speed and stability the drag coefficients in this region are higher than other marginal ice zones probably a result of the presence of large amounts of multiyear ice floes that extend higher above the ocean surface and create more drag than first year floes

possible lizard derived material in the underlying meneage formation the lizard complex rests tectonically on the meneage formation within the top of the flysch dominated gramscatho group of sediments the meneage formation is a middle to upper devonian sedimentary melange sequence with interbedded rudites the possibility that one or both of these lithologies include lizard derived debris is examined in detail the rudaceous debris is characterized by a range of meta psammitic pelitic and basic lithologies which cannot be matched with a lizard source parts of this suite notably granite gneiss and amphibolitic material are found to be quite different from superficially similar possible lizard source rocks a cratonic source is required the only widespread type of melange phacoid with a possible lizard source is greenstone geochemically these have ocean floor tholeiite affinities gabbro and amphibolite occur within and serpentinite near one particularly large greenstone phacoid however no precise geochemical comparison can be made between greenstones and lizard dykes autochthonous oceanic tholeiites in the gramscatho group sequence and the absence of varied and widespread possible lizard derived material suggest that the lizard complex is an unlikely source for the allochthonous greenstones a separate local development of oceanic crust now no longer exposed and autochthonous volcanics are postulated as more likely sources

a model for the tectonic evolution of south cornwall a stratigraphy for south cornwall is combined with an analysis of the chronology of thrust nappe emplacement the resulting model suggests that northward overthrusting of nappes of flysch and olistostrome ophiolite and continental basement is related to the closure of an oceanic basin in south cornwall involving southward subduction throughout the devonian the subsequent continental collision between the normannian high and part of laurentia occurred in the upper devonian with deformatian continuing until late carboniferous times

roughness variability of sea ice and snow cover thickness profiles in the ross amundsen and bellingshausen seas investigation of top and bottom surface roughness was carried out on snow and ice thickness profiles sampled on 57 floes in the ross amundsen and bellingshausen seas between may and september 1995 an objective classification scheme was used to group the studied sea ice floes according to the degree of deformation they had undergone different roughness criteria and methods were applied to the classified floes roughness variances and other properties such as fractal dimensions derived from fourier spectra depend critically on the deformational history of the floes under consideration the wavelet transform is presented as a new two dimensional method to find dominant structure lengths and at the same time localize them in the studied profiles finally air water and ice surface drag coefficients are calculated from the surface roughness characteristics air drag coefficients ranged between 1 1 and 1 7 103 and increased with increasingly deformed ice

mantle evolution in the variscides of sw england geochemical and isotopic constraints from mafic rocks abstract the geology of sw england has long been interpreted to reflect variscan collisional processes associated with the closure of the rhenohercynian ocean and the formation of pangea the cornish peninsula is composed largely of early devonian to late carboniferous volcanosedimentary successions that were deposited in pre and syn collisional basins and were subsequently metamorphosed and deformed during the variscan orogeny voluminous early permian granitic magmatism cornubian batholith is broadly coeval with the emplacement of ca 280 295 ma lamprophyric dykes and flows although these lamprophyres are well mapped and documented the processes responsible for their genesis and their relationship with regional variscan tectonic events are less understood pre to syn collisional basalts have intra continental alkalic affinities and have ree profiles consistent with derivation from the spinel garnet lherzolite boundary end values for the basalts range from 0 37 to 5 2 and tdm ages from 595 ma to 705 ma the lamprophyres are extremely enriched in light rare earth elements large iron lithophile elements and are depleted in heavy rare earth elements suggesting a deep garnet lherzolite source that was previously metasomatised they display end values ranging from 1 4 to 1 4 initial sr values of ca 0 706 and tdm ages from 671 ma to 1031 ma suggesting that metasomatism occurred in the neoproterozoic lamprophyres and coeval granite batholiths of similar chemistry to those in cornwall occur in other regions of the variscan orogen including iberia and bohemia by using new geochemical and isotopic data to constrain the evolution of the mantle beneath sw england and the processes associated with the formation of these post collisional rocks we may be able to gain a more complete understanding of mantle processes during the waning stages of supercontinent formation

seasonal variations of the antarctic coastal ocean in the vicinity of lutzow holm bay during the period of 1990 1992 year round oceanographic observations were conducted in the vicinity of lutzow holm bay east antarctica it was found that the thickness of the winter water ww layer characterized by a cold fresh oxygen rich water exhibits its maximum in the austral fall typically 500 m and its minimum in the austral summer typically 350 400 m the associated density variation of the water column explains only about one third of the seasonal variations in sea level at the coast which suggests a large seasonal variation in barotropic coastal flow prominent freshening occurs in the ww layer during fall this appears to be caused by the accumulation of ww whose upper portion is freshened in the preceding summer these seasonal variations appear to occur every year we propose that the seasonal variation in the ww layer is mainly caused by the seasonal variation in the wind over the coastal ocean in fall the prevailing easterly wind intensifies which increases the ekman convergence of ww in the coastal ocean while in summer the opposite occurs

sea ice dynamics in the weddell sea simulated with an optimized model the advection of sea ice and associated freshwater salt fluxes in the weddell sea in 1986 and 1987 are investigated with a large scale dynamic thermodynamic sea ice model the model is validated and optimized by comparison of simulated sea ice trajectories with observed drift paths of six buoys deployed on the weddell sea ice the skill of the model is quantified by an error function that measures the deviations of simulated trajectories from observed 30 day sea ice drift a large number of sensitivity studies show how simulated sea ice transports and associated freshwater salt fluxes respond to variations in physical parameterizations the model reproduces the observed ice drift well provided ice dynamics parameters are set to appropriate values optimized values for the drag coefficients and for the ice strength parameter are determined by applying the error function to various sensitivity studies with different parameters the optimized model yields a mean northward sea ice volume export out of the southern weddell sea of 1693 km3 in 1986 and 2339 km3 in 1987 this shows the important role of sea ice transport for the freshwater budget of the weddell sea and gives an indication of its high interannual variability

the emplacement of peridotites and associated oceanic rocks from the lizard complex southwest england upper mantle peridotites and associated oceanic rocks from the lizard complex south west england preserve evidence for a multistage geological history steeply dipping pre emplacement fabrics record high temperature 900 1100 c shearing and exhumation of the mantle peridotites apparently formed during localized ne sw rifting in a pull apart basin setting c 400 390 ma associated oceanic rocks landewednack amphibolites preserve a pre emplacement prograde brown amphibole bearing metamorphic assemblage and steeply dipping fabric thought to have formed as the newly formed oceanic crust was juxtaposed with newly exhumed hot mantle peridotite during ne sw rifting in both the peridotites and landewednack amphibolites steep pre emplacement structures are cross cut by low angle mylonitic fabrics thought to have formed during the initial phases of emplacement of mantle over crustal rocks in a partially intra oceanic setting c 390 375 ma the fabrics in peridotites and amphibolites exhibit retrograde mineral assemblages c 500 800 c with the amphibolites preserving two superimposed assemblages green amphibole titanite and colourless magnesio hornblende respectively that are thought to record progressive down temperature deforma tion during thrusting emplacement related structures in both the basal peridotites and amphibolites consistently dip at low to moderate angles nw with down dip lineations and kinematic indicators showing consistent top to the nw senses of shear syn emplacement magmatism is recorded by intrusions of foliated kennack gneiss anastomosing serpentine filled faults mark many existing low angle contacts between the peridotites and landewednack amphibolites and appear to represent the final lowest temperature 250 c stages of emplacement c 370 ma this study shows that dynamothermal aureoles in ophiolites may preserve evidence for tectonothermal events that pre date thrust emplacement

element mobility associated with meta shear zones within the ben hope amphibolite suite scotland abstract planar sequences of biotite garnet schists enclosed within the orthoamphibolites of the ben hope sill suite of northern scotland are interpreted as the products of synmetamorphic shearing these meta shear zones and adjacent biotite amphibolites contain higher values of k 2 o 1 0 wt rb 35 ppm and ba 400 ppm than the surrounding main series amphibolites accompanying the metasomatic introduction of these elements via hydrous fluids derived from an external metasedimentary source ca mg mn na and sr were either depleted or redistributed in both the meta shear zones and to a lesser degree in the adjacent amphibolites the abundance and interelement relationships of the immobile group of elements tio 2 p 2 o 5 zr y nb light ree do not appear to have been markedly disturbed during metasomatism with the exception of rare and minor y and la enrichment their stability is probably the result of both the specific secondary assemblages that developed in the meta shear zones and the low water rock ratios or fluid throughput however caution is needed in using immobile element abundances to characterize chemically amphibolite facies shear zones in meta basic sequenes

borehole sections through the traboe hornblende schists a cumulate complex overlying the lizard peridotite three borehole sections in the traboe area provide a partial section through a layered basic ultrabasic complex previously referred to as the traboe hornblende schists this complex though dismembered into thrust sheets shows an overall ne dipping stratigraphy with a generalized upward sequence from dunite and pyroxenite to gabbro and anorthosite the bulk composition of the ultramafic rocks is quite different from the dominantly lherzolitic composition of the main lizard peridotite the composition of the basic rocks is also markedly different from that of the landewednack hornblende schists with which they have previously been correlated the deformation and recrystallization of the rocks has been complex and locally intense producing a fine granular fabric in many rock types amphibolitization has affected many rock types to give assemblages dominated by hornblende mineral composition varies with position in the stratigraphic sequence and is consistent with crystallization of the complex from differentiating basic magma pulses

chemical variation in hercynian basalts relative to plate tectonics the geochemistry of hercynian basalts is reviewed with special reference to sw england hercynian basalts have the following chemical features 1 relative enrichment in incompatible elements 2 fractionated rare earth element ree patterns ranging from mild to strongly light ree enriched and 3 generally low large ion lithophile lil high field strength hfs element ratios high and variable alkali contents and k rb ratios are indicative of low grade alteration basalts are predominantly tholeiites although alkali basalts may be developed on some trough margins basalts from different sedimentary troughs within the main hercynian tectonic zones are characterized by specific incompatible element abundances and ratios these variations are interpreted in terms of variable fractional crystallization partial melting and mantle heterogeneity hercynian volcanism was typically bimodal with basic and acid products characterizing the rheno hercynian and saxo thuringian zones activity in the moldanubian zone was more variable with a high proportion of calc alkali andesites two systematic chemical changes throughout the devonian and carboniferous have been recognized with both light heavy ree and lil hfs element ratios increasing with time these features may relate to the introduction of lil enriched fluids derived by dehydration of subducted lithosphere that caused progressive metasomatism of the overlying mantle wedge chemical discrimination of tectonic setting demonstrates that most of the basalts typify the continental intra plate environment although early devonian basalts produced in the initial stages of continent rifting have some of the chemical features of incompatible element enriched oceanic basalts an ensialic back arc basin model underlain by a shallow northward dipping subduction zone provides a possible explanation for the spatial and temporal variation in the hercynian volcanic rocks

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

the southern ocean at the last glacial maximum a strong sink for atmospheric carbon dioxide analysis of satellite ocean color sea surface temperature and sea ice cover data reveals consistent patterns between biological production iron availability and physical forcings in the southern ocean the consistency of these patterns in conjunction with information on physical conditions during the last glacial maximum lgm enables estimates of export production at the lgm the lgm southern ocean experienced increased wind speeds colder sea surface and atmospheric temperatures increased deposition of atmospheric dust and a greatly expanded winter sea ice cover these variations had strong effects on southern ocean ecology and on air sea fluxes of co2 the seasonal ice zone siz was much larger at the lgm 30 million km2 than at present 19 million km2 the antarctic polar front pf likely marked the northern boundary of this expanded siz throughout the southern ocean as it does today in the drake passage region a large northward shift in the position of the pf during glacial times is unlikely due to topographic constraints north of the pf the increased flux of aeolian dust during glacial times altered phytoplankton species composition and increased export production and as a result this region was a stronger sink for atmospheric co2 than in the modern ocean south of the pf interactions between the biota and sea ice strongly influence air sea gas exchange over seasonal timescales the combined influence of melting sea ice and increased aeolian dust flux with its associated iron increased both primary and export production by phytoplankton over daily monthly timescales during austral spring summer resulting in a strong flux of co2 into the ocean heavy ice cover would have minimized air sea gas exchange over much of the rest of the year thus an increased net flux of co2 into the ocean is likely during glacial times even in areas where annual primary production declined we estimate that export production in the southern ocean as a whole was increased by 2 9 3 6 gt c yr 1 at the lgm relative to the modern era altered seasonal sea ice dynamics would further increase the net flux of co2 into the ocean thus the southern ocean was a strong sink for atmospheric co2 and contributed substantially to the lowering of atmospheric co2 levels during the last ice age

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

correlation of the rhenohercynian variscides recent structural and stratigraphical data from the rhenohercynian variscides of belgium germany and south cornwall indicate tectonic continuity within this zone prior to disruption along a late carboniferous dextral transcurrent fault this extends from the bristol channel to the vosges parallel to similar lineaments of variscan age in europe and north america consequently a tectonic model for south cornwall is extrapolated to europe and a plate tectonic setting for the evolution of the north european variscides by the closure of an oceanic basin is discussed

roughness of weddell sea ice and estimates of the air ice drag coefficient the roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water here we report snow surface ice surface and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the weddell sea the roughness for each surface parameterized as the standard deviation of the surface elevation segregates according to whether or not a floe has been deformed deformed ice has greater roughness than undeformed ice regardless of deformational history the underside roughness is almost always greater than the snow surface and ice surface roughnesses which are nearly equal roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k 1 when the wavenumber k is between 0 1 and 3 rad m 1 the snow surface and underside spectra roll off somewhat faster than k 1 and the ice surface spectra roll off somewhat slower than k 1 both top and underside arctic ice roughness spectra on the other hand have been reported to roll off faster than k 2 we speculate that the excess spectral intensity at high wavenumbers in the antarctic ice surface spectra results from the small scale roughness that the ice sheet had on consolidation this excess high wavenumber spectral intensity persists in the ice surface spectra of second year ice evidently once formed the ice surface remains unchanged on the microscale until the entire ice sheet melts with a remote measurement of roughness we should be able to decide whether an ice floe is deformed or undeformed our spectral analysis hints that remote sensing may also be able to differentiate between first year and second year ice from the snow surface spectra we compute a roughness scale that parameterizes the air ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m cdn10 typical cdn10 values are 1 1 1 4 10 3 over undeformed ice and 1 3 1 8 10 3 over deformed ice

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

water drag coefficient of first year sea ice in may 1977 eddy flux measurements of momentum were made with a three component ultrasonic current meter in the oceanic boundary layer under a first year floe of fast sea ice in barrow strait n w t by using eddy correlation methods values of horizontal reynolds stress were computed from each of 20 data runs of about 1 hour duration during which the mean current was reasonably steady a least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1 m water drag coefficient of 1 32 10 3 with a standard deviation of 0 06 10 3 the diameter of the floe was greater than 1 km and its mean thickness was 128 cm with a standard deviation of 4 cm and a maximum deviation of 7 cm

variscan very low grade metamorphism in southwest england a diastathermal and thrust related origin abstract regional metamorphism in the external variscides of southwest england varied from diagenetic level to greenschist facies there is a fundamental difference in the metamorphic character between the northern and southern regions of the area in the north m1 metamorphism is of a sedimentary burial character associated with high heat flow whilst to the south it is related to tectonic burial during thrust thickening processes with lower geothermal gradients this pattern appears to be related to the character of basin development and its subsequent tectonic evolution the northern region has features that accord with a diastathermal extensional origin for the very low grade metamorphism whilst in the southern region the very low grade metamorphism is linked to thrusting as a consequence of variscan compression the tintagel high strain zone presents an anomaly in this regional pattern where an m2 metamorphic phase is attributed to localized d2 thrust stacking along the southern margin of the culm basin there is no extensive overprint of the regional metamorphic pattern by the contact aureoles surrounding the granite plutons of the region however there is a noticeable coincidence between the areas of regional epizone grade and the extent of the geophysically defined subsurface limit of the granite batholith excluding the north devon area this link is attributed largely to the late stage structural up doming of the higher grade areas over the roof of the batholith

variscan oceans ages origins and geodynamic implications inferred from geochemical and radiometric data abstract a review of the magmatic associations providing evidence for the existence of extensional regimes during the palaeozoic evolution of variscan europe is presented the available geochronological data allow recognition of two major rifting events one in the early ordovician and the other in the middle late devonian scarce relicts of ophiolitic complexes indicate that both extensional episodes reached a true ocean spreading stage it is suggested that the variscan belt resulted from a complex two stage collision process through successive suturing in the silurian and the early carboniferous of these oceanic domains the superposition of two distinct opening closure cycles involving geographically separate oceanic basins may partly account for the unusual width of the variscan orogen

dynamical contrasts between pancake and pack ice investigated with a drifting buoy array 1 the motion of pancake ice was investigated using an array of specialised drifting buoys deployed into the advancing ice edge of the weddell sea in april 2000 the buoys remained in the ice as the pancakes consolidated into a coherent ice sheet and the study examined the contrasts in dynamics for equivalent periods before and after consolidation drift velocities were largely determined by the meridional component perpendicular to the ice edge prior to consolidation these showed significantly elevated magnitudes at high frequencies periods shorter than six hours scalar velocities were higher than previously reported values reducing with time and distance from the ice edge the same trends were not evident from in situ wind data derivation of momentum transfer parameters wind factor turning angle was hampered by a lack of reliable wind directions from the outermost buoys however relative motions between buoys were investigated using differential kinematic parameters these displayed high amplitude high frequency oscillations in unconsolidated ice with rms invariant values up to two orders of magnitude higher than normally reported for weddell sea pack ice the values were found to be strongly dependent on sampling interval increasing further at intervals less than one hour in situ winds did not display an equivalent variation suggesting that wind forcing was not responsible and translation under wave action either internal or surface gravity was postulated as the forcing

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

the tectonosedimentary evolution of the northern margin of the carboniferous foreland basin of ne germany abstract the geometry and evolution of the northern margin of the carboniferous foreland basin in ne germany was examined in terms of depositional environments petrographic and geochemical data lower carboniferous units are carbonate rich and predominantly marine by namurian times continental environments are established along the northern basin margin with turbiditic sedimentation persisting in the south the upper carboniferous succession is continental and clastic the sandstones were derived from a quartz rich source located to the north with subordinate sedimentary input basin evolution and the development of a characteristic marine to continental sedimentary succession while being predominantly controlled by flexure induced by the variscan orogen to the south was also influenced by eustatic sea level variations and more localised tectonic movements

contraints on the evolution of the mid german crystalline rise a study of outcrops west of the river rhine several small outcrops along the western rhinegraben escarpment expose rocks which represent the western prolongation of the so called mid german crystalline rise this basement ridge separates the rhenohercynian and saxothuringian zones of the variscan belt of europe and thus marks the boundary between the external and the internal zones the variable rock association includes an orthogneissamphibolite complex weakly deformed low grade sediments devonian and visean and a number of different syn to post orogenic granodioritic to granitic intrusives all crosscut by late lower carboniferous undeformed lamprophyric dikes and unconformable overlain by permian sediments and volcanics

highly depleted oceanic lithosphere in the rheic ocean implications for paleozoic plate reconstructions the rheic ocean formed at ca 500 ma when several peri gondwanan terranes e g avalonia and carolinia drifted from the northern margin of gondwana and were consumed during the late carboniferous collision between laurussia and gondwana a key event in the formation of pangea several mafic complexes ranging in age from ca 400 330 ma preserve many of the lithotectonic and or chemical characteristics of ophiolites they are characterized by anomalously high end values that are typically either between or above the widely accepted model depleted mantle curves these data indicate derivation from a highly depleted hd mantle and imply that i the mantle source of these complexes displays time integrated depletion in nd relative to sm and ii depletion is the result of an earlier melting event in the mantle from which basalt was extracted the extent of mantle depletion indicates that this melting event occurred in the neoproterozoic possibly up to 500 million years before the rheic ocean formed if so the mantle lithosphere that gave rise to the rheic ocean mafic complexes must have been captured from an adjacent older oceanic tract the transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved possible mesozoic cenozoic analogues include the capture of the caribbean plate or the scotia plate from the pacific to the atlantic oceanic realm our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the rheic ocean was consumed by subduction during laurentia gondwana convergence

provenance and depositional environment of rhenohercynian synorogenic greywackes from the giessen nappe germany the giessen nappe of the south eastern rhenish massif can be subdivided into a northern group and southern group of frasnian lower carboniferous greywackes that differ slightly in their sedimentology clast petrography heavy mineral assemblages and bulk geochemistry

atmospheric boundary layer modification drag coefficient and surface heat flux in the antarctic marginal ice zone during a traverse of the antarctic marginal ice zone miz near the greenwich meridian in october 1981 we launched a series of radiosondes along a 150 km track starting at the ice edge since the wind was from the north off the ocean these radiosonde profiles showed profound modification of the atmospheric boundary layer abl as the increasing surface roughness decelerated the flow the primary manifestation of this modification was a lifting of the inversion layer with increasing distance from the ice edge by the induced vertical velocity but there was also a cooling of the stably stratified mixed layer below the inversion and a consequent flux of sensible heat to the surface that averaged over 200 w m2 the magnitude of this flux suggests that atmospheric heat transport plays a significant role in the destruction of ice in the antarctic miz using the rising of the inversion and abl similarity theory we estimated the change in the neutral stability drag coefficient cd across the miz cd increased from its open ocean value 1 2 10 3 at the ice edge to 4 0 10 3 at 80 90 ice concentration we present an equation for this dependence of drag on ice concentration that should be useful for modeling the surface stress in marginal ice zones

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen