geometry and regional significance of neoproterozoic cadomian structures of the narcea antiform nw spain the narcea antiform is located at the hinterland to foreland transition of the variscan belt in the nw of the iberian massif it consists of an antiformal stack of fault propagation folds that developed in the hanging wall of allochthonous thrust sheets during the first variscan deformation event in the palaeozoic rocks the neoproterozoic narcea slates formation cropping out in the core of the narcea antiform records a cadomian deformation event that formed large asymmetric nw vergent folds with related axial planar cleavage developed in the lower greenschist facies these folds are truncated by the lower cambrian angular unconformity lower cambrian conglomerates contain pebbles with predepositional microstructures that are widespread in the underlying neoproterozoic rocks the narcea antiform provides valuable information concerning major tectonic cadomian events the large scale near recumbent cadomian folds developed between 560 and 540 ma top to the nw kinematics can be deduced for the cadomian plate convergence transverse to the variscan convergence in present coordinates it was followed shortly afterwards by large displacements along the northern gondwana margin that resulted in its accretion alongside the essentially undeformed neoproterozoic rocks of the central iberian zone before early cambrian times

deciphering the sardic ordovician and variscan deformations in the eastern pyrenees sw europe detailed geological mapping of the la cerdanya area canigo unit eastern pyrenees provides new data characterizing the different structural styles exhibited by cambrian lower ordovician jujols group and upper ordovician successions their unconformable contact related to the sardic phase ranges from 0 paraconformity to 90 angular discordance the jujols group rocks topped by the unconformity are affected by sardic foliation free open folds the pre sardic succession the sardic unconformity and the lower part of the post sardic succession rabassa conglomerate and cava formations are cut and offset by several late ordovician nne ssw trending synsedimentary extensional faults associated with hydrothermal activity which dramatically affected the thickness of the lower part of the upper ordovician succession we relate 1 the mid ordovician sardic uplift and erosion and 2 a mid to late ordovician upward propagating extensional fault system bounding the outline of half grabens subsequently infilled by alluvial deposits to a thermal doming event about 475 450 ma that led to the uplift and stretching of the ordovician lithosphere thermal doming may be caused by mafic magma underplating and responsible for the coeval calc alkaline magmatic activity broadly developed in the eastern pyrenees we discuss the similarities between the mid ordovician sardic unconformity and other early paleozoic unconformities described in neighbouring areas finally we suggest a geodynamic scenario in which a regional scale thermal event was related to the opening of the rheic ocean that led to the drift of avalonia from the sw european margin of gondwana

the initial response of a stratified lake to a surface shear stress laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress the experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress this study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled i e the stratified region of the fluid reaches the surface at the upwind endwall the majority of the experiments use three layer initial density profiles as an approximation to a continuously stratified water column a linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred at this point the wave development ceased and the flows developed via entrainment mechanisms consideration of the energy budget showed that little of the input energy was stored in the system the initial mixing efficiency defined as the ratio of the mean potential energy gained to the energy imparted by the belt never exceeded 30 peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface

numerical comparison of different convergent plate contacts subduction channel and subduction fault summary at convergent plate boundaries the properties of the actual plate contact are important for the overall dynamics convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain we investigate two fundamental physical states of the subduction contact one based on a fault and the other based on a subduction channel using a finite element method we determine the specific signatures of both states of the subduction contact we pay particular attention to the overriding plate in a tectonic setting of converging plates where the subducting plate is freely moving the subduction channel reduces compression relative to the fault model in a land locked basin setting where the relative motion between the far field of the plates is zero the subduction channel model produces tensile stress regime in the overriding plate even though the amount of slab roll back is small the fault model shows a stronger development of slab roll back and a compressive stress regime in the upper plate based on a consistent comparison of fault and channel numerical models we find that the nature of the plate contact is one of the controlling factors in developing or not of backarc extension we conclude that the type of plate contact plays a decisive role in controlling the backarc state of stress to obtain backarc extension roll back is required as an underling geodynamic process but it is not always a sufficient condition

ordovician alluvial fan to marine shelf transition in sw sardinia western mediterranean sea tectonically sardic phase influenced clastic sedimentation abstract a localized lower ordovician early caledonian structural event sardic phase is recorded in sw sardinia by an angular and erosional unconformity faulting and mild folding this event was accompanied by sedimentation of a transgressive clastic unit puddinga beds which is particularly well developed along a major fault system gonnesa fault zone there the puddinga beds range from basal interfingering fans some formed by coarse carbonate and schist clasts others by schist clasts only to fluvio lacustrine mud and gravelly sandstone to coastal muddy and sandy deposits and to fossiliferous restricted marine shelf sediments the existence of the slightly compressive sardic phase in sw sardinia and quasi coeval calc alkaline volcanism and an extensional structural phase sarrabese phase in central east sardinia suggest transcurrent faulting the calc alkaline acid volcanism is also interpreted by some authors to indicate that the rifted basins developed in backarc position the non volcanic sequence of sw sardinia analyzed in this paper was probably formed in basins developed on the northern margin of the gondwanaland craton this sardinian system may be the eastward extension of transcurrent rifts which have also been recently reported from nw spain structural activity has been the predominant control on sedimentation however worldwide recurring low sea level stands may have influenced the sedimentation of the lower part of the puddinga beds and the deglaciation of the saharan ice sheet has contributed to the uppermost ordovician early silurian deepening of the euxinic shelf

origin of the lethal gas burst from lake monoun cameroun abstract on 15 august 1984 a lethal gas burst issued from a submerged 96 m deep crater in lake monoun in cameroun western africa killing 37 people the event was associated with a landslide from the eastern crater rim which slumped into deep water waters below 50 m are anoxic dominated by high fe 2 600 mg l and hco 3 1900 mg l anoxic and supersaturated with siderite which is a major component of the crater floor sediments the unusually high fe 2 levels are attributed to reduction of laterite derived ferric iron gradually brought into the lake as loess and in river input sulfur compounds are below detection limits in both water and gas gases effervescing from depressurized deep waters are dominantly co 2 with minor ch 4 having 13 c of 7 18 and 54 8 per mil respectively bacterial decomposition of organic matter may account for the methane but 14 c of lake water indicates that only 10 of the carbon is modern giving an apparent age of 18 000 years the dominant source of carbon is therefore attributed to long term emission of co 2 as volcanic exhalation from vents within the crater which led to gradual build up of hco 3 in the lake the density stratification of the lake may have been upset by an earthquake and underwater landslide on 15 august which triggered overturn of the lake and caused nucleation of co 2 in the deep water the resultant ebullition of co 2 from deep lake waters led to a gas burst at the surface and locally generated a water wave up to 5 m high people travelling through the gas cloud were asphyxiated presumably from co 2 and suffered skin discoloration from unidentified components

co2 degassing along the san andreas fault parkfield california the fluxes concentrations and carbon isotopic compositions of soil co2 were measured along the parkfield segment of the san andreas fault saf single or double peak co2 flux anomalies 18 g m 2 d 1 were observed along 12 of 16 fault crossing transects at five sites flux anomalies did not coincide with concentration anomalies flux anomalies paralleled the fault trace suggesting zones of high diffusivity permeability one flux anomaly may have been accentuated by a 0 3 mm creep event however values of 13c 23 7 to 21 6 and 14c 110 5 to 111 9 pmc for soil gas co2 are characteristic of co2 of biogenic origin the co2 flux anomalies are therefore consistent with fault related biogenic gas flow and do not yield evidence for degassing of deeply derived co2

internal waves in a small reservoir horizontally distributed temperature time series recorded in the thermocline of a small reservoir during autumn are used to identify both basin scale and higher frequency internal waves stationary and nonstationary spectral analyses are used to identify dominant frequencies the horizontal distribution of data allows a map of the basin scale wave energy to be determined three layer normal mode modeling incorporating damping emulates the basin scale behavior well this provides estimates of velocity shear and hence the internal stability the nonstationary frequency analysis identifies times of high frequency internal wave activity wave periods of 2 10 min this is definitely linked to the basin scale wave driven shear and hence to deceases in stability estimates of dissipation for the thermocline and hypolimnion are 3 10 8 and 6 10 9 m 2 s 3 respectively the inferred variability in the hypolimnetic value is demonstrated

wind induced internal seiches in lake zurich observed and modeled1 during august and september 1978 3 1 current meters and 120 temperature sensors were deployed to record every 10 or 20 min at various depths at 12 moorings with wind speed and direction at three moorings in lake zurich we explore here the baroclinic internal seiche response to wind impulses observed as fluctuations in isotherm depth and current speeds those fluctuations and their energy spectra are compared with the predictions of two models fitted to basin topography and to the observed average thermal structure a two layered variable depth tvd model developed by d j schwab fitted to basin topography and incorporating a two dimensional horizontal grid and c h mortimer s two layered modification of a simpler procedure originally developed for surface seiche calculations by a defant the dominant responses to wind impulses were internal seiches of the first longitudinal mode average period 44 h weaker signals from the second 24 h and third 17 h modes were also seen in spectra of temperature and current fluctuations the models displayed patterns of thermocline displacement and current which in periodicity and structure were closely similar to those observed predictions of the defant model were less precise particularly for current founded on linear theory and neglecting the effects of rotation the models were unable to reproduce two features occasionally seen in the lake motions clockwise or anticlockwise rotation of current direction and internal surges arising when storms induced large amplitude downstrokes of the thermocline at one basin end or the other the lake s internal response was principally dependent on the timing strength and duration of the wind impulse relative to and interacting with internal seiche motions already in progress

the strongly damped baroclinic response to wind in a multibasin reservoir field data and a forced modal based two layer variable cross section model tlvc were used to examine the baroclinic response to wind in a large multibasin reservoir nechako reservoir british columbia canada the tlvc showed that most of the thermocline deflections at the dam could be accounted for by considering the first two basins upstream of the dam knewstubb and natalkuz lakes and that the thermocline deflections were dominated by the first h1 and second h2 horizontal baroclinic modes of the combined basins calibration of the tlvc against the field data showed that the h1 and h2 modes were strongly damped with effectively no free thermocline oscillations this strong damping had two effects high coherence between the wind and thermocline deflections and phase lags between thermocline deflections at different locations the damping in nechako reservoir is stronger than in many lakes and results from both high velocities within the geometric constriction between knewstubb and natalkuz lakes and drag due to submerged trees which cover 30 of the bed our study provides a picture of overdamped baroclinic response and shows how useful information about the baroclinic response in complex bathymetries can be obtained using relatively simple tools such as the tlvc

gas emission from diffuse degassing structures dds of the cameroon volcanic line cvl implications for the prevention of co2 related hazards abstract in the mid 1980s lakes nyos and monoun violently released massive gas mainly magmatic co 2 killing about 1800 people subsequent geochemical surveys and social studies indicate that lakes nyos and monoun event is cyclic in nature and may occur anywhere in the about 37 other volcanic lakes located in the corridor of the cameroon volcanic line cvl this potential threat motivated us to check if alike nyos and monoun the internal dynamic of the other lakes is also controlled by inputs of deep seated derived co 2 and attempt to measure and provide comprehensive insights on the passive gas emission along the cvl this knowledge shall contribute to the prevention of volcanic lake related hazards in cameroon and the refinement of the global carbon cycle we used in situ fixation and dry gas phase sampling methods to determine co 2 origin and the concentration and the accumulation chamber technique to measure diffuse co 2 emission from nine lakes and on soil at nyos valley and mount manenguba caldera the results suggest that although in minor concentrations compared to nyos and monoun ranging from 0 56 mmol kg 1 to 8 75 mmol kg 1 the bottom waters of some lakes also contain measurable magmatic co 2 with 13 c varies from 4 42 to 9 16 vs pdb that finding implies that under certain circumstances e g increase to volcanic and or tectonic activities along the cvl the concerned lakes could develop a nyos type behavioural scheme the diffuse gas emission results indicate that the nine surveyed lakes release approximately 3 69 0 37 kt km 2 yr 1 of co 2 to the atmosphere extrapolation to the approximately 39 volcanic lakes located on the cvl yields an approximate co 2 output of 27 37 0 5 kt km 2 yr 1 representing 0 023 of the global co 2 output from volcanic lakes in addition to the precedent value the gas removal operation in lakes nyos and monoun released approximately 2 52 0 46 10 8 mol km 2 yr 1 co 2 to the atmosphere from january 2001 to march 2013 more than double the per area co 2 released by the yellowstone volcanic system the co 2 emission from soil was estimated to be 4 57 1 30 kt km 2 yr 1 the soil gas geochemistry of the mount manenguba caldera also indicates a dominant magma derived co 2 mean 13 c 8 6 vs vpdb

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

ordovician metagranitoid from the anatolide tauride block northwest turkey geodynamic implications we report a middle ordovician metagranitoid from the northern margin of the anatolide tauride block the basement of which is generally characterized by voluminous latest proterozoic to early cambrian granitoids the ordovician metagranitoid forms an 400 m thick body in the marbles and micaschists of the tavsanli zone the whole sequence was metamorphosed in the blueschist facies during the late cretaceous c 80 ma zircons from the metagranitoid give a middle ordovician pb pb evaporation age of 467 0 4 5 ma interpreted as the age of crystallization of the parent granitic magma the micaschists underlying the metagranitoid yield cambro ordovician 530 450 ma and carboniferous c 310 ma detrital zircon ages indicating that the granitoid is a pre or syn metamorphic tectonic slice the ordovician metagranitoid represents a remnant of the crystalline basement of the anatolide tauride block and provides evidence for ordovician magmatism at the northern margin of gondwana prismatic carboniferous detrital zircons in the micaschists indicate that during the triassic the northern margin of the anatolide tauride block was close to variscan terranes

tectonic evolution of the japanese island arc system abstract growth of the japanese arc system which has mainly taken place along the continental margin of asia since the permian is the result of subduction of the ancient pacific ocean floor backarc basin formation in the tertiary shaped the present day arc configuration the neotectonic regime which is characterized by strong east west compression has been triggered by the eastward motion of the amur plate in the quaternary the tectonic evolution of the japanese arc system includes formation of rock assemblages common in most orogenic belts because the origin and present day tectonics of these assemblages are better defined in the case of the japanese arc system study of the system provides useful insight into orogenesis and continental crust evolution

soil gas geochemistry in relation to eruptive fissures on timanfaya volcano lanzarote island canary islands spain abstract we report herein the first results of an extensive soil gas survey performed on timanfaya volcano on may 2011 soil gas composition at timanfaya volcano indicates a main atmospheric source slightly enriched in co2 and he soil co2 concentration showed a very slight deep contribution of the timanfaya volcanic system with no clear relation to the main eruptive fissures of the studied area the existence of soil helium enrichments in timanfaya indicates a shallow degassing of crustal helium and other possible deeper sources probably form cooling magma bodies at depth the main soil helium enrichments were observed in good agreement with the main eruptive fissures of the 1730 36 eruption with the highest values located at those areas with a higher density of recent eruptive centers indicating an important structural control for the leakage of helium at timanfaya volcano atmospheric air slightly polluted by deep seated helium emissions co2 degassed from a cooling magma body and biogenic co2 might be the most plausible explanation for the existence of soil gas helium is a deep seated gas exhibiting important emission rates along the main eruptive fissure of the 1730 36 eruption of timanfaya volcano

pre mesozoic alpine basements their place in the european paleozoic framework prior to their alpine overprinting most of the pre mesozoic basement areas in alpine orogenic structures shared a complex evolution starting with neoproterozoic sediments that are thought to have received detrital input from both west and east gondwanan cratonic sources a subsequent neoproterozoic cambrian active margin setting at the gondwana margin was followed by a cambrian ordovician rifting period including an ordovician cordillera like active margin setting during the late ordovician and silurian periods the future alpine domains recorded crustal extension along the gondwana margin announcing the future opening of the paleotethys oceanic domain most areas then underwent variscan orogenic events including continental subduction and collisions with avalonian type basement areas along laurussia and the juxtaposition and the duplication of terrane assemblages during strike slip accompanied by contemporaneous crustal shortening and the subduction of paleotethys under laurussia thereafter the final pangea assemblage underwent triassic and jurassic extension followed by tertiary shortening and leading to the buildup of the alpine mountain chain recent plate tectonic reconstructions place the alpine domains in their supposed initial cambrian ordovician positions in the eastern part of the gondwana margin where a stronger interference with the chinese blocks is proposed at least from the ordovician onward for the visean time of the variscan continental collision the distinction of the former tectonic lower plate situation is traceable but becomes blurred through the subsequent oblique subduction of paleotethys under laurussia accompanied by large scale strike slip since the pennsylvanian this global collisional scenario has been replaced by subsequent and ongoing shortening and strike slip under rising geothermal conditions and all of this occurred before all these puzzle elements underwent the complex alpine reorganization

ordovician deformations in the pyrenees new insights into the significance of pre variscan sardic tectonics two deformational events which developed prior to the variscan structures can be characterized in the palaeozoic rocks of the pyrenees a middle ordovician folding event and a late ordovician fracture episode the middle ordovician folding event gives rise to nw se to n s oriented metric to hectometric sized folds without cleavage formation or related metamorphism these folds can account for the deformation and uplift of the pre upper ordovician cambro ordovician sequence and for the formation of the upper ordovician unconformity ordovician folds control the orientation of the variscan main folding phase minor structures fold axes and intersection lineation in the cambro ordovician sediments the late ordovician fracture episode gave rise to normal faults affecting the lower part of the upper ordovician series the basal unconformity and the underlying cambro ordovician metasediments displacement of some of these faults diminishes progressively upwards of the series and tapers off in the upper part of the upper ordovician rocks indicating that the faults became inactive during late ordovician times before deposition of the ashgillian metasediments normal faults can be linked to the upper ordovician volcanic activity which has been extensively described in the pyrenees the aforementioned deformation episodes took place after the early ordovician magmatic event which gave rise to a large volume of plutonic rocks in the pyrenees as in other segments of the european variscides this middle ordovician contractional event separated two extensional events in the pyrenees from early ordovician to silurian times this event prevents us from assuming the existence of a continuous extensional regime through ordovician and silurian times and suggests a more complex evolution of this segment of the northern gondwana margin during the ordovician

from thickening to extension in the variscan belt kinematic evidence from sardinia italy the variscan nappe stack of se sardinia originated as a result of several stages of nappe imbrication during the lower carboniferous phases of the variscan orogeny the crustal shortening caused regional ssw and w directed thrusting greenschist facies metamorphism and open to isoclinal polyphase folding the final stage of shortening produced large scale antiforms and synforms post collisional deformation resulted in inversion of earlier thrusts as normal faults development of low angle normal faults and refolding of earlier foliation and thrust planes by asymmetric folds with subhorizontal axial planes facing directions of these latest folds are directed horizontally outward from the hinge zones of main antiforms suggesting that they cannot be regarded as parasitic folds of the latest thickening phase but instead are the consequence of vertical shortening during gravitational collapse of dome like km scale antiforms leading to denudation of antiformal culminations

the 2002 2003 eruption of stromboli italy evaluation of the volcanic activity by means of continuous monitoring of soil temperature co2 flux and meteorological parameters 1 from december 2002 to july 2003 stromboli volcano was characterized by a new effusive stage of eruption after a period of extraordinary strombolian activity signals recorded in two continuous monitoring stations during the eruption which have already been presented in very recent papers evidenced anomalies in the co2 flux just before the onset of the eruption a more detailed analysis carried out on the data subset acquired during the eruption integrated by daily field observations of the scientific personnel working at the volcanological observatory in stromboli showed that co2 flux and soil temperature are strictly related to volcanic events furthermore the relative minima and maxima of the two parameters showed a strong correlation with wind speed and direction this fact was especially true at the summit station whereas at the coastal sites seasonal and meteorological effects masked the volcanic signal the analysis of the wind data particularly the relationships between wind speed and direction air and soil temperature and local circulation of atmospheric air masses revealed that during the eruption in the summit area of stromboli air movements were not only related to atmospheric circulation but were also significantly affected and in certain cases caused by volcanic activity this conclusion was reached by observing several anomalies such as the discrepancies in the wind direction between the two stations higher air temperatures at the summit site and inversion of direction for wind before and after the reopening of the conduit in a major explosion on 5 april 2003 the relationships found between volcanic activity soil temperatures co2 fluxes and wind speed and direction indicate that soil temperature measurements in an open conduit volcano such as in this case could be used to monitor the level of volcanic activity along with co2 flux furthermore the possible volcanic origin of a peculiar type of air circulation identified in the summit area of stromboli suggests that the separation between volcanic and atmospheric signals might not be obvious requiring monitoring over a wide area rather than a single location

internal waves of the second vertical mode in a stratified lake a time series of measurements of thermal structure and near bottom currents in a stratified lake revealed both first and second vertical mode internal seiching the transition into second mode seiching occurred after first mode waves usually generated by pulses of strong winds died down we describe the major features of the second mode seiche and discuss its effects on mixing in the lake below the thermocline on the basis of calculations of eddy diffusion coefficients there is only weak mixing in the interior of the hypolimnion scaling arguments suggest that mixing at the lake s edges due to motion of the isotherms is not significant despite the larger amplitudes of the second mode seiche the most important mixing region appears to be a turbulent bottom boundary layer driven by seiche currents however resuspension of bottom sediments did not occur probably due to a combination of sediment nature and low current speeds

convective hydrothermal c02 emission from high heat flow regions abstract in addition to volatiles released from volcanoes the flux of co2 to the atmosphere from other sources e g metamorphism and subsurface magmatism represents an important aspect of the global carbon cycle we have obtained a direct estimate of the present day atmospheric co2 flux from convective hydrothermal systems within subaerial seismically active high heat flow regions geothermal systems of the salton trough california u s a and the taupo volcanic zone new zealand provide benchmarks for quantifying convective hydrothermal co2 fluxes from such regions co2 fluxes from the salton trough 109 mol yr 1 and the taupo volcanic zone 8 109 mol yr 1 were computed using data on convective heat flow and the temperatures and co2 concentrations of reservoir fluids the similarity in specific co2 flux 106 mol km 2 yr 1 from these two disparate geologic tectonic settings implies that this flux may be used as a baseline to compute convective hydrothermal co2 emission from other areas of high heat flow if this specific flux is integrated over high heat flow areas of the circum pacific and tethyan belts the total global co2 flux could equal or exceed 1012 mol yr 1 adding this flux to a present day volcanic co2 flux of 4 1012 mol yr 1 the total present day earth degassing flux could balance the amount of co2 consumed by chemical weathering 7 1012 mol yr 1

soil diffuse degassing and thermal energy fluxes from the southern lakki plain nisyros greece two diffuse soil co2 flux surveys from the southern lakki plain show that co2 is mainly released from the hydrothermal explosion craters the correspondence between high co2 fluxes and elevated soil temperatures suggests that a flux of hot hydrothermal fluids ascends towards the surface steam mostly condenses near the surface and the heat given off is conductively transferred to the atmosphere through the soil accompanied by a large co2 flux it was calculated that 68 t d 1 of hydrothermal co2 are released through the total surveyed area of 1 3 km admitting that a steam flux of 2200 t d 1 accompanies this co2 flux the thermal energy released through steam condensation amounts to 58 mw

structural pattern and co2 ch4 degassing of ustica island southern tyrrhenian basin brittle tectonics and ground degassing including fracture field soil gas and exhalation flux analyses of co2 and ch4 were studied at ustica island a pleistocene volcanic complex in the southern tyrrhenian sea the mesoscopic fracture pattern perfectly fits an e w trending left lateral strike slip master fault in agreement with the main morpho structural submarine alignment including ustica island and anchise seamount along the sw ne high angle normal arso fault geological evidence of reactivation with different kinematics left to right lateral displacements was recognised major co2 and ch4 degassing with fluxes up to 93 750 and 20 t km 2 a 1 respectively and soil gas concentrations of 11 3 and 5 7 ppm occur over the arso fault although this fault is mapped just in the sw sector of the island soil gas co2 anomalies point out its clear continuation up to the ne margin of the island these data together with those of previous geophysical and geochemical results from off shore ustica suggest that the arso fault is the local evidence of a more important active gas bearing structure this tectonic feature is interpreted as a reactivation of a preexistent sw ne trend inherited as a second order structure of the e w deep shear zone the reactivation is related to the interplay among different structures of the southern tyrrhenian basin

distribution of linear mesostructures in oblique folded surfaces unravelling superposed ordovician and variscan folds in the pyrenees abstract detailed mapping and structural analysis yielded new data on the geometry of ordovician folds in the pyrenees these folds caused the variscan mainphase folds to develop over non horizontal bedding surfaces in the pre upper ordovician rocks as a result the variscan mainphase fold axes and intersection lineations in these rocks present a wide range of orientations bedding surfaces exhibit a complex pattern in map view making it necessary to reconstruct the structure in 3d computer aided reconstruction tools such as foldplot proved useful for visualizing and reconstructing the geometry of such refolded structures in 3d in the absence of map scale key horizons evidence of superposed folds is provided by detailed mapping of mesostructures this requires a good and continuous outcrop over an extended area since one single fold system can account for a complex distribution of the subsequent intersection lineation as a result a cartographic study and a structural analysis are warranted because the direction of the ordovician folds cannot be established only by the orientation of the l2 mesostructures

change of nappe transport direction during the variscan collisional evolution of central southern sardinia italy abstract the collisional variscan early carboniferous evolution of the greenschist facies metamorphic basement of sardinia is characterized by three deformation phases and two 90 reorientations of shortening direction during the first phase of deformation n s shortening occurred with south facing isoclinal folding south directed nappe emplacement and mylonitization in central and southeastern sardinia and large scale e w striking upright folds in southwestern sardinia emplacement of the barbagia meana sardo gerrei and riu gruppa units took place during this event this deformation phase was followed by e w shortening with w directed emplacement of the sarrabus and arburese units along the villasalto thrust and upright to e dipping large scale n s striking upright folds in southwestern sardinia during the third deformation event the shortening direction again rotated 90 and n s shortening produced kilometer scale antiforms and synforms the most prominent features in the metamorphic basement of sardinia the limbs of the kilometer scale antiforms and synforms are vertically shortened during gravitational collapse with contemporaneous faulting and conjugate shear zone development presence of large scale e w oriented antiforms was therefore critical for the formation of late variscan extensional features such as e w striking low angle normal faulting

tectonic setting of the north gondwana margin during the early ordovician a comparison of the ollo de sapo and famatina magmatic events abstract this paper presents a comparison of compiled geochronological and geochemical data from the ollo de sapo and famatina magmatic events the ollo de sapo magmatic sequence is located in northwest iberia and was emplaced during the early ordovician from 495 to 474 ma the famatina complex is a magmatic sequence located in northern argentina that was emplaced during the early to mid ordovician from 483 to 463 ma these magmatic events are currently interpreted to have been emplaced in different tectonic settings despite both having occurred along the north gondwana margin geochronological data indicates that these magmatic events occurred contemporaneously over at least 9 m y and therefore can provide a snapshot of the northern gondwana margin during the mid ordovician major element data indicates that both magmatic suites are calc alkaline to alkali calcic and trace element and ree data show magmatic signatures that are indistinguishable this study highlights the similarity between the ollo de sapo and the famatina magmatic suites and discusses alternative models for their emplacement based on paleomagnetic and paleobiogeographical data these data indicate that the ollo de sapo was likely emplaced in a subduction zone setting while the famatina magmatic suite may be of parautochthonous origin to gondwana implying that the pampeanan margin may not have been active during the early to mid ordovician

physical properties of turbulent benthic boundary layers generated by internal waves physical properties of active turbulent benthic boundary layers tbbl generated by basin scale internal waves were studied within a northern hemisphere thermally stratified lake a microstructure profiler was used to measure the nature of the turbulence within the tbbls while a series of thermistor chains were used to monitor the thermal structure of the lake it was observed that a wind driven anticlockwise diurnal period vertical mode one kelvin wave generated large scale motions within the water column and that the interactions between this wave and the sloping lakebed induced tbbls a simple model based on potential energy change and boundary shearing was shown to describe the mean tbbl thickness

a plate tectonic scenario for the iapetus and rheic oceans abstract the tectonics dynamics and biogeographic landscape of the early paleozoic were dominated by the opening and expansion of one large ocean the rheic and the diminution to terminal closure of another iapetus an understanding of the evolution of these oceans is thus central to an understanding of the early paleozoic but their chronicle also presents a rich temporal profile of the wilson cycle illustrating continental scale rifting microcontinent formation ocean basin development arc accretion and continent continent collision nevertheless contemporary paleogeographic models of the iapetus and rheic oceans remain mostly schematic or spatiotemporally disjointed which limits their utility and hinders their testing moreover many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios with the specific aim to resolve some of the uncertainties in the evolution of this early paleozoic domain and a broader aim to instigate the application of quantitative kinematic models to the early paleozoic i present a new plate tectonic model for the iapetus and rheic oceans the model has realistic tectonic plates which include oceanic lithosphere that are defined by explicit and rigorously managed plate boundaries the nature and kinematics of which are derived from geological evidence and plate tectonic principles accompanying the presentation and discussion of the plate model an extensive review of the underlying geological and paleogeographic data is also presented

ediacaran to cambrian oceanic rocks of the gondwana margin and their tectonic interpretation in tectonic maps of variscan europe allochthonous pieces of cadomian basement clearly stand out with their predominant metabasic to ultrabasic elements the so called exotic terranes with ophiolites most of these domains are observed in basements of the central iberian allochthone the south armorican domain the nappe structures of the french massif central the saxothuringian zone and the bohemian massif similar relics can be recognized in many alpine basement areas and correlations with supposedly more autochthonous basements such as the ossa morena zone and the central iberian basement can be envisaged all of these relics are thought to represent the interrupted trace of a former continuous or discontinuous structure characterized by the presence of ocean derived proto rheic rock suites these can be interpreted as pieces of former magmatic arcs of ediacaran to cambrian age accreted to the gondwana margin which later were scattered as allochthonous units during the variscan plate tectonic processes the presence of similar rock suites of ordovician age in the alpine realm is explained by the accretion of exotic china derived basements and their collision with the gondwana margin during the opening of the rheic ocean

mid ordovician u pb ages of porphyroids in the peloritan mountains ne sicily palaeogeographical implications for the evolution of the alboran microplate petrographic geochemical and geochronological work on a metavolcanic suite interbedded in a metapelitic sequence of the palaeozoic basement in the peloritan mountains sicily is used to contribute to a better understanding of the pre variscan geodynamic evolution of the former alboran microplate major and trace element data show that the volcanic suite consists of two main groups an intermediate unit of andesites and dacites with volcanic arc affinity and a felsic porphyroid unit of rhyolites with peraluminous composition isotope dilution thermal ionization mass spectrometry u pb analyses for single and multigrain zircon fractions from four samples of the felsic porphyroids yield results that are tightly clustered on or near concordia giving caradoc ages in the range of 456 452 ma the consistent morphological characteristics and oscillatory zoning of the zircons indicate single stage magmatic crystallization xenocrystic zircon grains with ages of 1150 and 2015 ma indicate that these rocks were developed upon a cratonic basement with grenvillian and transamazonian components hence supporting a peri gondwanan origin from the combined evidence we conclude that this portion of the alboran microplate formed as a mid ordovician volcanic arc in a sector of the peri gondwanan terranes that was affected by a tectonothermal caradoc event

rifting and arc related early paleozoic volcanism along the north gondwana margin geochemical and geological evidence from sardinia italy abstractthree series of volcanic rocks accumulated during the cambrian to silurian in the metasediment dominated variscan basement of sardinia they provide a record of the changing geodynamic setting of the north gondwana margin between upper cambrian and earliest silurian a continuous upper cambrian lower ordovician succession of felsic submarine and subaerial rocks dominantly transitional alkaline in character ca 492 480 ma is present throughout the variscan nappes trace element data together with nd isotope data that point to a depleted mantle source indicate an ensialic environment a middle ordovician ca 465 ma calc alkaline bimodal suite restricted to the external variscan nappes overlies the sardic unconformity negative ndi values 3 03 to 5 75 indicate that the suite is a product of arc volcanism from a variably enriched mantle a late ordovician early silurian ca 440 ma volcano sedimentary cycle consists of an alkalic mafic suite in a post caradocian transgressive sequence

energetics and damping of basin scale internal waves in a strongly stratified lake energetics and damping of basin scale internal waves and subsequent near bottom transport processes in lake kinneret were investigated using the modal analysis in a layer stratified irregular basin the theory was extended to include small linear damping and energy budgets and damping rates of five dominant internal waves were extracted by fitting numerically calculated internal waves to isotherm displacements measured by six thermistor chains distributed throughout the lake energy contained in the dominant internal waves 3 gj resulted from a balance between energy input from diurnal winds and dissipation within a day both of which were estimated to be 3 4g j d 21 damping was caused primarily by bottom friction and the damping rates e folding time varied from 1 to 3 d depending on the velocity structure currents induced by the internal waves caused considerable spatial variability of the bottom shear stress and near bottom transport processes such as entrainment rate at the top of the benthic boundary layer and mass transfer at the sediment water interface

multiple early paleozoic volcanic events at the northern gondwana margin u pb age evidence from the southern variscan branch sardinia italy abstract in sardinia one of the southernmost remains of the european variscan belt a crustal section through different gondwanan paleodomains is largely preserved laser ablation icp ms u pb ages on undoubtedly igneous sites of the zircons were determined on the lower palaeozoic volcanic rocks constrained by defined field relationships thus evidencing three subsequent volcanic events i intermediate and felsic 491 7 3 5 ma 479 9 2 1 concordia ages transitional volcanic rocks embedded within a cambro ordovician terrigenous succession that occurs with continuity in external and inner nappes bounded to the top by the sardic unconformity ii this cambrian lower ordovician succession is cut by calc alkalic rhyodacites which yielded a concordia age of 465 4 1 4 ma confirming their pertinence to the huge bimodal mid ordovician arc volcanism commonly interpreted as the widespread marker of the rheic ocean subduction iii alkalic metaepiclastites in the external nappe within the post caradocian transgressive sequence dated at 440 1 7 ma likely related to rifting and collapse of the mid ordovician volcanic arc in the reshaped lower palaeozoic stratigraphy of sardinia the timing of the early steps of the variscan wilson cycle can be inferred

the formation of pangea abstract the making of pangea is the result of large scale amalgamation of continents and micro continents which started at the end of the neoproterozoic with the formation of gondwana as pieces were added to gondwana on its south american antarctica and australia side ribbon like micro continents were detached from its african and south chinese side cadomia in the late neoproterozoic avalonia and hunia in the ordovician galatia in the devonian and cimmeria in the permian cadomia was re accreted to gondwana but the other ribbon continents were accreted to baltica north china laurussia or laurasia finding the origin of these numerous terranes is a major geological challenge recently a global plate tectonic model was developed together with a large geological geodynamic database at the lausanne university covering the last 600 ma of the earth s history special attention was given to the placing of gondwana derived terranes in their original position using all possible constraints we propose here a solution for the variscan terranes another paper deals with the altaids the galatian super terrane was detached from gondwana in the devonian during the opening of paleotethys and was quickly separated into four sub terranes that started to by pass each other the leading terranes collided at the end of the devonian with the hanseatic terrane detached from laurussia in the carboniferous gondwana started to impinge onto the amalgamated terranes creating the variscan chain and the pangean super continent east of spain paleotethys remained opened until the triassic subducting northward under laurasia roll back of the paleotethyan slab triggered the collapse of most of the european variscan orogen which was replaced by series of permian rifts some of them becoming oceanized back arc basins during the triassic major force changes at the pangean plate limits at the end of the triassic provoked its break up through the opening of the proto caribbean central atlantic alpine tethys oceanic seaways

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

seasonal evolution of the basin scale internal wave field in a large stratified lake the response of the water column to varying conditions of stratification and wind forcing was investigated in lake kinneret israel using data collected from thermistor chains and acoustic doppler current profilers during 1997 and 1998 the strong daily sea breeze was found to generate a vertical mode 1 internal kelvin wave and basin scale internal poincarewaves of vertical modes 1 2 and 3 the kelvin wave the dominant component of the internal wave field was responsible for alongshore velocities in the nearshore regions in the upwind nearshore regions velocities were dominated by the forced response to the wind and were cross shore in nature in the lake interior the kelvin wave effect on the horizontal velocity field was minor compared to the higher vertical mode poincarewaves the kelvin wave is shown to exist in resonant and nonforced states with the wind whereas the vertical mode 1 poincarewave energy remained relatively constant despite large variability in the forcing condi tions the energy in the higher mode poincarewaves varied greatly both on daily and seasonal timescales the results demonstrate that the wind energy forces multiple basin scale internal wave modes and that prior motion in the water column must be considered when determining the subsequent internal wave response in periodically forced systems lake kinneret israel has long been an important regional resource providing a substantial supply of drinking water as well as supporting a commercial fishery the monomictic lake is forced daily during the summer by a powerful sea breeze with stratification and wind patterns showing little variation from year to year these factors along with a fa vorable bathymetric pattern combine to make lake kinneret an ideal place for the field investigation of large scale inter nal waves and related phenomena such as the benthic bound ary layer horizontal transport and vertical mixing processes in addition to providing substantial insight into the local pro cesses and hence influencing local management study of the lake also provides fundamental knowledge of the dynam ics of enclosed basins on a geophysical scale during summer the internal rossby radius in lake kin neret is typically one half the basin width hence large scale motion in the lake will be affected by the earth s rotation and basin scale internal waves may be of topographic ross by kelvin or poincareform topographic rossby waves are sub inertial frequency oscillations that exist only in rotating fluids with variable bathymetry mysak et al 1985 stocker and hutter 1987 and these waves result from changes in depth affecting the relative vorticity of fluid elements in the absence of vertical boundaries wavelike solutions to the lin ear inviscid equations of motion for a flat bottomed region of homogeneous fluid with a constant rate of rotation are 1

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

soil efflux and total emission rates of magmatic co2 at the horseshoe lake tree kill mammoth mountain california 1995 1999 abstract we report the results of eight soil co 2 efflux surveys by the closed circulation chamber method at the horseshoe lake tree kill hltk the largest tree kill on mammoth mountain the surveys were undertaken from 1995 to 1999 to constrain total hltk co 2 emissions and to evaluate occasional efflux surveys as a surveillance tool for the tree kills hltk effluxes range from 1 to 10 000 g m 2 day 1 grams co 2 per square meter per day they are not normally distributed station efflux rates can vary by 7 35 during the course of the 8 to 16 h surveys disturbance of the upper 2 cm of ground surface causes effluxes to almost double semivariograms of efflux spatial covariance fit exponential or spherical models they lack nugget effects efflux contour maps and total co 2 emission rates based on exponential spherical and linear kriging models of survey data are nearly identical similar results are also obtained with triangulation models suggesting that the kriging models are not seriously distorted by the lack of normal efflux distributions in addition model estimates of total co 2 emission rates are relatively insensitive to the measurement precision of the efflux rates and to the efflux value used to separate magmatic from forest soil sources of co 2 surveys since 1997 indicate that contrary to earlier speculations a termination of elevated co 2 emissions at the hltk is unlikely anytime soon the hltk co 2 efflux anomaly fluctuated greatly in size and intensity throughout the 1995 1999 surveys but maintained a n s elongation presumably reflecting fault control of co 2 transport from depth total co 2 emission rates also fluctuated greatly ranging from 46 to 136 t day 1 metric tons co 2 per day and averaging 93 t day 1 the large inter survey variations are caused primarily by external meteorological processes operating on time scales of hours to days the externally caused variations can mask significant changes occurring at depth a striking example is the masking of a degassing event generated at depth and detected by a soil gas sensor network in september 1997 while an efflux survey was in progress thus occasional efflux surveys are not an altogether effective surveillance tool for the hltk and making them effective by greatly increasing their frequency may not be practical

spatial structure of the dominant basin scale internal waves in lake kinneret field data and numerical simulations were used to investigate the effects of basin shape continuous stratification and rotation on the three dimensional structure of the dominant natural basin scale internal wave modes in lake kinneret a stratified lake large enough so that the earth s rotation influences the wave motion the structure of the modes was inferred from power spectral density of measured and simulated isotherm vertical displacements and from rotary power spectral density of isopycnal velocities obtained from numerical simulations the shape of the lake at the level of the thermocline in conjunction with the dispersion relationship determines the horizontal configuration of the natural modes the dominant response to wind forcing was an azimuthal and vertical mode 1 kelvin wave with a natural period of 22 6 h that propagated around the entire basin the second most dominant response was a vertical mode 1 wave with a natural period close to 10 5 h and composed of two counter rotating

annual volcanic carbon dioxide emission an estimate from eruption chronologies continuing interest in the effects of carbon dioxide on climate has been promoted by the exponentially increasing anthropogenic production of co2 volcanoes are also a major source of carbon dioxide but their average input to the atmosphere is generally considered minor relative to anthropogenic input this study examines eruption chronologies to determine a new estimate of the volcanic co2 input and to test if temporal fluctuations may be resolved employing representative average values of 2 7 g cm 3 as density of erupted material 0 2 wt percent co2 in the original melt 60 percent degassing during eruption and an average volume of 0 1 km3 for each of the eruptions in the recently published eruption chronology of hirschboeck 1980 a volcanic input of about 1 5 1011 moles co2 yr 1 was determined for the period 1800 1969 the period 1800 1899 had a somewhat lower input than 1900 1969 which could well be related more to completeness of observational data than to a real increase in volcanic co2 this input is well below man s current co2 production of 4 5 1014 moles co2 yr 1