an interannual link between arctic sea ice cover and the north atlantic oscillation this work investigates links between arctic surface variability and the phases of the winter djf north atlantic oscillation nao on interannual time scales the analysis is based on era reanalysis and model data from the ec earth global climate model our study emphasizes a mode of sea ice cover variability that leads the nao index by 1 year the mechanism of this leading is based on persistent surface forcing by quasi stationary meridional thermal gradients associated thermal winds lead a slow adjustment of the pressure in the following winter which in turn feeds back on the propagation of sea ice anomalies the pattern of the sea ice mode leading nao has positive anomalies over key areas of south davis strait labrador sea the barents sea and the laptev ohkostsk seas associated to a high pressure anomaly over the canadian archipelago baffin bay and the laptev east siberian seas these anomalies create a quasi annular quasi steady positive gradient of sea ice anomalies about coastal line when leading the positive nao phase and force a cyclonic vorticity anomaly over the arctic in the following winter during recent decades in spite of slight shifts in the modes spectral properties the same leading mechanism remains valid encouraging actual models appear to reproduce the same mechanism leading model s nao relative to model areas of persistent surface forcing this indicates that the link between sea ice and nao could be exploited as a potential skill source for multi year prediction by addressing the key problem of initializing the phase of the nao ao arctic oscillation

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

characteristic patterns of variability of sea level pressure in the northern hemisphere abstract seasonal and annual mean sea level pressures for the northern hemisphere have been analyzed to determine the dominant modes of interannual and longer period variability using monthly sea level pressure analyses as revised by trenberth and paolino 1980 empirical orthogonal function eof analysis is used to reveal the modes which explain most of the variance for the period 1925 77 in winter kutzbach s 1970 eof 1 for january remains the dominant mode and a closely related pattern dominates all seasons and the annual means although there are differences in detail in each season the dominant mode is basically a high latitude zonal index type pattern with departures in pressure at high latitudes corresponding to anomalies of opposite sign in low latitudes eof 1 is linked to the north atlantic oscillation but the north south fluctuations in mass also occur in the pacific and to a lesser extent elsewhere time series associated with this pattern have highly significant spectral peaks at the

structural mineralogical and petrophysical effects on deep crustal rocks of fluid limited polymetamorphism western gneiss region norway the proterozoic banded granulite facies complex of bardsholmen western gneiss region norway t 815 845 c was locally transformed to eclogite t 455 510 c p 12 kbar and amphibolite facies rocks t 460 c during the caledonian continental collision the granulite complex consists of mafic two pyroxene granulite and leucocratic orthopyroxene garnet bearing layers alternating on a scale from 1 cm to 10 m the granulite facies rocks change to eclogite facies rocks over centimetre scale distances along well defined fluid infiltration fronts the mafic granulite was transformed to omphacite garnet rich eclogites and the leucocratic rocks were converted to quartz phengite rich assemblages with minor garnet and local omphacite melange like lithologies consisting of mafic lenses of eclogite surrounded by felsic material represent an advanced stage in the process of converting deep crust to eclogite facies during amphibolitization this melange like lithology evolves to a rock where amphibolite lenses and layers are surrounded by granitoid gneiss a lithology typical of the western gneiss region the bardsholmen locality illustrates the profound control exerted by fluids on the timing of metamorphism the structural make up and petrophysical properties such as density and rheology of crustal root zones fluid induced metamorphism will therefore exert control on the attributes of orogenic belts such as topography and moho depth and influence the dynamics of collision zones by controlling the time of orogenic collapse and the buoyancy of the subducted crust we suggest that orogens may develop differently depending on the fluid budget

geochemistry of the sunnfjord melange sediment mixing from different sources during obduction of the solund stavfjord ophiolite complex norwegian caledonides

variations in basaltic geochemistry along a propagating rift of the late ordovician marginal basin of the west norwegian caledonides the late ordovician solund stavfjord ophiolite complex in the western norwegian caledonides records a multi stage seafloor spreading history of an iapetus marginal basin and contains three structural domains with distinctive tectonomagmatic evolutionary paths the nne trending domain 1 consisting of high level gabbro sheeted dykes and extrusive rocks is interpreted to represent fossil oceanic crust developed along a spreading centre that propagated northwards into pre existing oceanic crust in the marginal basin dyke swarms at the head of this inferred propagating rift range from primitive high mgo basalts to highly fractionated quartz diorites southwards along strike of domain 1 the abundance of primitive basalts decreases and the proportion of feti basalts increases to become predominant furthest behind the tip of the propagating rift this geochemical evolution is comparable to that of the basalts of modern propagating rifts at the east pacific rise and the galapagos spreading ridge we suggest that the chemical variations of the metabasalts reflect changes in magma supply rates and in the increasing size of magma chamber s along strike of the spreading centres

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

magmatic development and tectonomagmatic models for the solund stavfjord ophiolite complex west norwegian caledonides abstract geochemical variation and different extrusion rates of the late ordovician solund stavfjord ophiolite complex ssoc suggest both open and closed magma chambers closed chambers existed off axis and within a transform fault and are indicated by dykes and pillow lavas that evolved from high mgo basalt to ferrobasalt by fractional crystallization of olivine plagioclase and clinopyroxene hybrid magmas with ferrobasaltic composition represent open magmatic systems and are characterized by frequent eruptions of sheet flows the ssoc is interpreted as representing either a normal or a propagating ridge transform intersection rti the propagating rti model is favoured as it explains both the high frequency of ferrobasalt and uplift of ultramafic rocks to above the sea level which is suggested by detrital ultramafics occurring in an ophiolitic melange

initiation of crustal scale thrusts triggered by metamorphic reactions at depth insights from a comparison between the himalayas and scandinavian caledonides active eclogitization has recently been inferred at depth beneath the himalaya from geophysical observations and the mechanical consequences of eclogitization can be observed in the field in the eroded and extended nappe stack of the scandinavian caledonides there proterozoic metastable granulites and igneous protoliths underwent partial eclogitization during the collision of baltica with laurentia the reaction began in pseudotachylites and veins and eventually formed a connected network of eclogite facies shear zones that localized deformation and weakened the lower crust of baltica during the collision with laurentia all these features can be compared with the seismic activity of the indian lower crust its strength loss beneath the himalayan ranges and its delayed density increase regarding its penetration in the eclogite facies the caledonian bergen arc eclogites and the himalayan ama drime eclogites are both derived from continental crust in both cases these eclogites were formed contemporaneously with the activation of the main thrusts responsible for the construction of the orogenic wedges the main central thrust in the himalayas and the main thrust below the jotun nappe complex in the caledonides the similarities in these two orogens which compare both in size and structure highlight the importance of eclogitization at depth as a mechanism for weakening of the lower crust and for decoupling of the crust and lithospheric mantle in collision zones

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

the evolution of the hornelen basin detachment system western norway implications for the style of late orogenic extension in the southern scandinavian caledonides abstract the geology of the devonian hornelen basin and the surrounding western gneiss region wgr western norway has been examined in detail structural clast provenance and geothermobarometric data have been combined to reconstruct the motion history of part of a major late orogenic extensional shear zone in the southern scandinavian caledonides the nordfjord sogn detachment nsd the nsd in the hornelen basin area is a zone of mylonites 4 6 km thick tectonostratigraphically constrained within the lower and middle allochthons lma and the uppermost part of the wgr it separates eclogite bearing gneisses of the wgr from greenschist and amphibolite facies rocks of the middle and upper allochthons marking a profound metamorphic break and indicating major excision of crustal section kinematic indicators give a consistent top to the west shear sense indicating a reversal of the movement sense of the scandian nappes with the ductile strain being distributed through the entire lma section the wgr was exhumed from depths of up to 100 km in the footwall of the shear zone partly aided by pure shear vertical flattening below the nsd and extension and erosion of the hanging wall the majority of the movements on the nsd in the hornelen basin area occurred under amphibolite facies conditions prior to 410 ma subsequent shear caused limited greenschist retrogression along extensional crenulation cleavages depending on interpretation of mica 40 ar 39 ar ages this lower grade shearing may be due to a continuation of movements or renewal of motion associated with opening of the hornelen basin at about 385 ma the lack of clear evidence of penetrative greenschist facies mylonites in the hornelen area may be due to the faulted omission of tectonites of this grade following scandian a subduction and eclogite facies metamorphism at 425 ma the p t t path of the wgr shows very rapid decompression associated with early slip on the extensional detachment horizons unroofing was initially near isothermal followed by a phase of rapid near isobaric cooling after 410 ma decompression and cooling slowed as slip on the nsd slowed or even ceased by the middle devonian the wgr lay at about 10 15 km depth and the crust had almost returned to isostatic equilibrium at this time a brittle fault splaying from the nsd ramped upwards through the upper allochthon opening a scoop shaped west facing half graben the hornelen basin a further 50 km of heave on the nsd occurred during alluvial infilling of the basin subsequently the basin fill was folded by late devonian n s compression and the basin margins were modified by mesozoic faulting these features are consistent with an orogenic collapse model for southern scandinavia that involves large scale backsliding of the scandinavian caledonides within tectonostratigraphic units by this mechanism the baltic shield could have been efficiently unloaded with tectonic translations producing significant metamorphic breaks within a seemingly preserved tectonostratigraphic sequence the model favours orogenic collapse driven by an external pull rather than internal body forces

cusp latitude magnetic impulse events 3 associated low latitude signatures low latitude magnetic perturbations at san juan puerto rico occurring simultaneously with the set of south pole magnetic impulse events mies discussed by lanzerotti and konik are examined the amplitudes of the magnetic deflections at the times of the mies at south pole and at san juan are compared to the magnetic deflections seen at these two stations during storm sudden commencements sscs at the south pole the authors find the mean deflections in the magnetic h and v components to be larger for the mies than for the sscs at san juan they find the opposite to be true the mean amplitudes of the deflections in the h and v components of the field are much smaller during the mies than for the sscs the interplanetary plasma conditions prevailing at the times of the mies are also examined and contrasted to those found during sscs the authors find that while the mies are characterized by changes in the solar wind dynamic pressure and the noise level the sscs are concurrent with large changes in the dynamic pressure examining the correlations between mie amplitudes and dynamic pressure changes they find no correlation for the mie deflections at the south pole butmore a strong correlation for the concurrent deflections seen at san juan in contrast they find strong correlations between ssc amplitudes and dynamic pressure changes at both the south pole and san juan the authors conclude that the mie signatures at the south pole are not predominantly generated by dynamic pressure fluctuations and that the concurrent ground magnetic signatures at san juan are unrelated to those at the south pole they also examine their data in order to deduce any amplitude dependence upon local time and in particular whether larger ground signatures are found in local morning than in local afternoon they find that for both the sets of mies and sscs the amplitudes of deflections at the south pole exhibit no significant local time pattern 44 refs 9 figs 5 tabs less

oxygen and carbon isotope compositions of carbonates in a prominent lithologically mixed unit in the central south norwegian caledonides a prominent pre scandian lithologically mixed unit in the central south norwegian caledonides contains more than 100 partly carbonated and hydrated metaperidotite bodies and locally fossiliferous detrital serpentinites the lateral consistency of this mixed unit was not fully appreciated in the past therefore parts of the mixed unit along strike were interpreted to belong to several different tectonostratigraphic levels here we present new carbonate stable isotope data that suggest that the carbonates of the mixed unit between bergen and otta re equilibrated at unit wide similar peak metamorphic conditions the isotope compositions are characteristic for this unit and indicate that it represented one single tectonic unit during the scandian orogeny the carbonates in the melange are characterized by a narrow range of 18o smow values between 11 and 15 5 and three groups of 13c pdb values i 1 6 to 0 3 ii 1 8 to 3 9 and iii 6 to 8 6 carbonates of group iii probably were affected by decarbonation or by a fluid containing organic carbon whereas carbonates of group i and ii overlap with 13c values typical for ediacaran silurian marine carbonates and may have retained their initial 13c imprint we suggest that the 18o values re equilibrated with unit wide released metamorphic fluids during scandian metamorphism an outcrop scale homogenisation of the 13c values reflects the local carbon isotope signature of the released metamorphic fluids that circulated channelized through the melange unit

observed linkages between the northern annular mode north atlantic oscillation cloud incidence and cloud radiative forcing the signature of the northern annular mode north atlantic oscillation nam nao in the vertical and horizontal distribution of tropospheric cloudiness is investigated in cloudsat and calipso data from june 2006 to april 2011 during the northern hemisphere winter the positive polarity of the nam nao is marked by increases in zonally averaged cloud incidence north of 60 n decreases between 25 and 50 n and increases in the subtropics the tripolar like anomalies in cloud incidence associated with the nam nao are largest over the north atlantic ocean basin middle east and are physically consistent with the nam nao related anomalies in vertical motion importantly the nam nao related anomalies in tropospheric cloud incidence lead to significant top of atmosphere cloud radiative forcing anomalies that are comparable in amplitude to those associated with the nam nao related temperature anomalies the results provide observational evidence that the most prominent pattern of northern hemisphere climate variability is significantly linked to variations in cloud radiative forcing implications for two way feedback between extratropical dynamics and cloud radiative forcing are discussed

zabargad st john s island an uplifted fragment of sub red sea lithosphere zabargad is a small island located in the red sea about 50 km w of its axis between 23o and 24on the island is not volcanic but probably represents an uplifted block of upper mantle and crustal rocks and yields information on the nature of the underlying lithosphere peridotites are the main rock type consisting of exceptionally fresh spinel lherzolites which equilibrated last at a depth 30 km in the mantle other ultramafic facies some representing rocks which mixed with a basaltic melt fraction and some which underwent metasomatic exchange at depth are also present the peridotite bodies are in tectonic contact with a metamorphic formation consisting of gneissic and amphibolitic rocks similar to those outcropping in the pan african metamorphic basement of eastern egypt peridotites and metamorphic rocks are both crossed by several generations of basaltic dykes the sedimentary zabargad formation of probable cretaceous or palaeocene age consists of alternations of silicified limestones sandstones black shales and phosphoritic lenses and is overlain by evaporites probably of miocene age and by reef limestone units one probably of early pleistocene age the other probably deposited during the last interglacial various formations are affected by localized metasomatic mineralizations recrystallized large gem quality olivine cancrinite scapolite garnierite the uplift of upper mantle ultramafic bodies with fragments of crust which created the island might have occurred in connection with the early stages of development of the rift which preceded the formation of the red sea an alternative explanation that the zabargad peridotites are remnants of a pan african palaeozoic ophiolitic complex is possible but less likely

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

cyclic volcanic stratigraphy in a late ordovician marginal basin west norwegian caledonides the well preserved extrusive sequence of the solund stavfjord ophiolite complex ssoc in the west norwegian caledonides enables reconstruction of the uppermost oceanic crust that developed in a marginal basin basaltic sheet flows pillow lavas and volcanic breccias are the main components of the extrusive sequence and show stratigraphic and structural evidence for a cyclic development the first stage in a volcanic cycle is characterized by high extrusion rates yielding sheet flows commonly with the thickest flow units at the base sequences of sheet flows can be correlated laterally for at least 6 5 km pillow lavas succeed the sheet flows later in a volcanic cycle with progressively smaller pillows forming at decreasing extrusion rates volcanic breccias occur towards the end of a volcanic cycle but may also occur at lower stratigraphie levels they are made generally of pillow breccias and hyaloclastites the extrusive sequence of the ssoc oceanic crust was constructed through seven volcanic cycles that resulted in stratigraphic units with thicknesses ranging from 40 to 225 m this architecture is comparable to sequences in in situ oceanic crust developed along slow to intermediate spreading ridges

superimposed fabrics due to reversal of shear sense an example from the bergen arc shear zone western norway abstract a profile through the upper margin of a large scale ductile shear zone the bergen arc shear zone western norway has been studied in detail within the shear zone asymmetric structures indicate dextral or top to nw movement which is interpreted as representing late or post caledonian extensional tectonics the hanging wall of the shear zone is characterised by kinematic indicators such as shear bands associated with curved or inclined foliation and asymmetric boudins indicating sinistral or top to se movements these are interpreted as related to thrusting during the caledonian orogeny the studied profile shows the progressive overprinting of the sinistral structures by the later dextral shear this first led to a decrease in the obtuse angle between shear bands and the curved inclined foliation subsequently backfolding of asymmetric boudins in quartz veins occurred and a composite cleavage developed from shear bands and associated curved inclined foliation dextral asymmetric extensional shear bands were developed at a later stage when the folded quartz veins had attained tight to isoclinal geometries

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

40ar 39ar muscovite dates from the nappe region of southwestern norway dating extensional deformation in the scandinavian caledonides abstract the caledonian thrust nappes and basal decollement zone above the baltic shield record penetrative caledonian deformation related to ese directed nappe transport and subsequent wnw directed ductile shearing during extensional collapse of the orogen muscovite within proterozoic quartzite conglomerates in the lower bergsdalen nappe that record only ese vergent caledonian deformation display internally concordant 40ar 39ar age spectra which yield plateau ages of 403 ma and 398 ma similar plateau ages 402 and 399 ma were obtained from muscovite from mica schists which record additional penetrative wnw directed shearing suggesting that muscovite intracrystalline argon systems did not cool below appropriate closure temperatures until during or after extensional wnw vergent movements quartz microfabrics indicate that temperatures were higher than those required for argon retention in muscovite until the end of the wnw directed nappe translation extension and that lower temperatures were maintained during subsequent movements along w and nw dipping extensional ductile shear zones the 40ar 39ar muscovite ages are therefore interpreted to post date the extensional wnw directed shearing along the decollement zone and closely date the initiation of w and nw dipping extensional shear zones when compared to the age of contractional deformation the results confirm that extension followed orogenic contraction very shortly after the main scandian orogenic phase

evidence for a fossil transform fault in the solund stavfjord ophiolite complex west norwegian caledonides on the island of tviberg west norway a sheeted dike complex is rotated anticlockwise into parallelism with a zone of strong deformation hosting screens of sheared meta ultramafite incompatible element enriched high level plutonic rocks and two swarms of mafic dikes are intruded into sheared and unsheared meta ultramafites intrusion and sinistral shearing of the high level plutonic rocks and an old swarm of mafic dikes took place contemporaneously with sinistral shearing of the meta ultrabasites these field relationships are interpreted to reflect magmatism within a transform fault and the dike rotation is explained as fault drag along a strike slip zone in the transform a younger swarm of mafic dikes striking at a high angle to the shear zones transects all tectonic structures and may reflect a second phase of magmatism within the transform in fault contact with the transform fault related plutonic rocks and dikes lenses of serpentine diatreme breccias and lenses of sediments composed of mafic and ultramafic detritus are hosted in a phyllonitic matrix comprising basic ultrabasic and continent derived detritus this rock unit is interpreted as an ophiolitic melange and it probably started to form when obduction of the ophiolite nucleated on the transform

timing and kinematics of caledonian thrusting and extensional collapse southern norway evidence from 40ar 39ar thermochronology 40ar 39ar dating methods have been applied to rocks across the caledonian orogen in southwestern norway in the eastern nappe area k feldspar thermochronological modeling microfabric characteristics and conodont color alteration together indicate that temperatures were not above the closure temperature of muscovite for any significant period of time two groups of muscovite and biotite ages from this area 415 408 for most samples with top to the se fabrics and 402 394 for samples with top to the nw fabrics are therefore interpreted as ages of contractional thrusting and extensional hinterland directed nappe translation deformation respectively in the west hinterland peak caledonian temperatures were higher and 40ar 39ar plateau ages are generally interpreted as cooling ages the western basement and lower nappes cooled rapidly through 500 c basement at 404 ma and 350 c basement and lower nappes shortly after i e during extensional top to the nw transport of the orogenic wedge in addition tectonostratigraphically higher nappes in the hinterland show evidence of earlier cooling probably following ordovician orogenic activity prior to the main collisional stage the new 40ar 39ar data conform to kinematic observations that contraction and extension in the caledonian nappe region were sequential and that the change from contraction convergence to extension divergence was quick between 408 and 402 ma

the solund stavfjord ophiolite complex and associated rocks west norwegian caledonides geology geochemistry and tectonic environment

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

provenance information recorded by mineral inclusions in detrital garnet abstract garnet single grain analysis is an often used and well established tool in sedimentary provenance studies especially when metamorphic source rocks are involved so far however solely the geochemical composition of detrital garnets is considered to draw conclusions concerning probable source rocks the gained information is often limited by i geochemical overlap of garnets derived from different lithology and metamorphic grade ii similar probabilities of belonging to more than one source rock type and iii the limitations of discriminating different protolith compositions here we present the first attempt of using mineral inclusions in detrital garnet as a provenance tool we analyzed the inclusions of 300 fine to medium sand sized detrital garnets from two proximal modern sand samples taken in the hp uhp western gneiss region of sw norway all mineral inclusions 2 m were identified by raman spectroscopy showing that i most garnets from hp uhp metamorphic source rocks contain mineral inclusions 2 m ii raman spectroscopy is a very powerful tool to characterize the inclusion types and iii less stable mineral phases like kyanite omphacite diopside enstatite coesite amphibole group and epidote group minerals occur as inclusions in garnet these minerals which are important for provenance studies can thus be preserved in the sedimentary record as long as garnet is stable the combination of inclusion types in garnet and geochemical garnet classification shows that i inclusions well reflect the geological characteristics of the sampled catchments implying that they are useful indicators for hp uhp provenance and ii inclusions in garnet can be used to support and enhance the provenance information obtained by garnet geochemistry

the age and tectonic significance of dolerite dykes in western norway coast parallel dykes in sw norway primarily of permo triassic age have been linked regionally to the early tectonic evolution of the norwegian continental shelf we demonstrate from palaeomagnetic data mean declination 206 1 inclination 30 1 a 95 11 8 that dolerite dykes in the coastal sunnfjord region of western norway and immediately west of the devonian basins are also of permian c 250 270 ma age and not lower or pre devonian as previously advocated the sunnfjord dykes appear to be contemporaneous with dykes from sw norway at sotra 262 6 ma and the oldest dykes from sunnhordland 260 280 ma and geochemical data attest to a transition from sub alkaline to alkaline magmatism at the dawn of the mesozoic the sunnfjord dykes are not simple records of e w extension and magma intrusion but instead represent significant mid late permian time markers within a complex zone of fault activation and rejuvenation late mesozoic cenozoic magnetic overprinting mean declination 348 6 inclination 68 9 a 95 12 and metamorphic alteration documented by these dykes are directly dependent upon proximity to major e w brittle faults south of the hornelen devonian basin hence some motion and related fluid activity do post date dyke intrusion the e w high angle normal or oblique slip faults can be regionally traced offshore to the oygarden fault zone onshore these faults truncate the hornelen low angle detachment which in turn cuts folded d evonian strata these observations along with evidence for permian and late jurassic cretaceous extension from the nearby dalsfjord region demonstrate important reactivation of a late to post caledonian detachment and high angle fault system in western norway

volcanic evolution of oceanic crust in a late ordovician back arc basin the solund stavfjord ophiolite complex west norway 1 the stratigraphy of the well preserved solund stavfjord ophiolite complex in the west norwegian caledonides documents the volcanic evolution of a spreading center in a late ordovician back arc basin basaltic sheet flows pillow lavas and volcanic breccias are the main components of the 470 800 m thick extrusive sequence and are organized stratigraphically in a cyclic manner cyclic units vary in thickness from 5 m to 225 m and are typically composed of basal sheet flows or lava flows with large pillows that are succeeded by flows with progressively smaller pillows and volcanic breccias thick independent breccia units also occur in the stratigraphy in sheet flow dominated parts of the sequence the cyclic units are thicker average 85 m than in pillow dominated parts average 20 m detailed logging of closely spaced profiles 1 km or less apart shows that the proportions of sheet flows pillow lavas and volcanic breccias varies laterally along an axial segment of less than 10 km the volcanic products change from predominantly sheet flows reflecting robust volcanic centers to pillow lavas to volcanic breccias sheet flow dominated volcanic centers seem to be spaced at intervals of 25 30 km and we tentatively interpret their regularity as an expression of volcanic segmentation at an intermediate to fast spreading center observations of modern ocean crust suggest that sheet flows dominate at fast spreading ridges while pillow lavas dominate at slow spreading ridges volcanic breccias are apparently rare in both of these environments these features contrast with the stratigraphy of the solund stavfjord ophiolite complex where the proportion of different volcanic products varies laterally and volcanic breccias are common we emphasize the importance of detailed studies of the volcanic stratigraphy of ophiolites as complements to those of in situ oceanic crust in order to provide a more complete picture of volcanic evolution of oceanic crust in different spreading regimes

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

metamorphism and 40ar 39ar dating of the halaban ophiolite and associated units evidence for two stage orogenesis in the eastern arabian shield the arabian shield has long been recognized as a region where plate tectonic processes have been in action during most of the late proterozoic resulting in the amalgamation of the shield s five constituent terranes along four major suture zones studies thus far carried out on these collisional belts have concentrated on the origin and dating of intermediate to acidic igneous rocks and very little emphasis has been placed on the understanding of metamorphic processes operative during plate convergence the al amar suture separates the afif microplate from the ar rayn block in the easternmost section of the shield among several ophiolite occurrences in this suture the halaban belt is by far the largest and preserves within and around it a record of a number of thermal structural events related to the opening and eventual closure of a supra subduction zone back arc basin that existed in the period 695 680 ma the bimodal nature of 40 ar 39 ar dates from the halaban ophiolite and associated units is indicative of a two stage orogenesis climaxing at 680 and 600 ma instead of the previously proposed model of a single orogenic episode between 670 and 630 ma the first stage 680 ma is believed to be related to basin closure and ophiolite emplacement as the ar rayn island arc collided with the afif microcontinent the second episode 600 ma was the outcome of a major collisional event between the arabian craton and a large continental mass east of the ar rayn block

volatile phase fluxed anatexis of metasediments during late caledonian ophiolite obduction evidence from the sogneskollen granitic complex west norway in the west norwegian caledonides minor granitic sheets were intruded during obduction of the c 443 ma solund stavfjord ophiolite complex the sogneskollen granitic complex is the largest intrusive complex and consists of several minor lenses and one larger lens of granodiorite the sogneskollen granitic complex samples generally have high ba sr and na 2 o very low y values nd 420 ma values c 7 to 10 1 and 87 sr 86 sr 420 ma ratios of 0 70437 0 70705 the ree patterns are strongly hree depleted and la yb n varies from 0 3 to 36 most samples display small positive eu anomalies but those that are most fractionated have small negative anomalies the main part of the sogneskollen granitic complex is a white composite granodiorite which is intruded by a suite of grey biotite granite dykes it is suggested that this and other similar granitic sheets in the area most probably formed by melting of sediments in the presence of a h 2 o bearing volatile phase during obduction of the ophiolite the quartzofeldspathic source sediments most probably contained detritus from long term rb depleted lower continental crust and from an island arc the sediments were deposited in large amounts in the marginal basin now represented by the solund stavfjord ophiolite complex during obduction the sediments were buried beneath the hot overriding ophiolite complex and the associated island arc and yielded granitic magmas during partial melting

divergence in subduction zones and exhumation of high pressure rocks eocene western alps abstract exhumation of high pressure rocks has long remained a controversial issue in the earth sciences in this article we analyze the tectono metamorphic stratigraphic and plate motion constraints from the western alps region providing new insights on exhumation mechanisms and tectonic evolution during the earliest orogenic stages eocene eclogites of the western alps form a 20 25 km wide belt on the upper plate side of the orogen eclogite belt exposed beneath extensional shear zones at the rear of a lower pressure accretionary wedge units of the eclogite belt show the youngest peak pressure assemblages within the subduction zone and experienced superfast tectonic exhumation since 45 40 ma the role of erosion was negligible during the whole of this stage eocene foreland basins remained starved and the massive arrival of axial belt detritus began well after exhumation was completed tectonic reconstructions based on fixed boundaries exhumation models e g channel flow and or implying fast erosion at the surface e g slab breakoff are thus not consistent with geological evidence in the lack of erosion exhumation through the overburden requires divergence within the subduction zone we demonstrate that this was not attained by rollback of the lower plate europe but was instead attained by nneward motion of the upper plate adria africa away from the western alps trench such motion induced localized extension within the weak portion of the upper plate at the rear of the accretionary wedge and allowed tectonic emplacement of the eclogite belt in the upper crust at rates much faster than subduction rates tectonic exhumation ceased in the oligocene when oblique divergence along the western alps traverse changed into oblique convergence the onset of slow erosional unroofing was synchronously recorded by pressure temperature paths in all major tectonic units of the western alps and by arrival of orogenic detritus in sedimentary basins this work demonstrates that divergence between upper plate and trench is a viable mechanism to exhume large and coherent eclogite units in continental subduction zones our exhumation model can be applied to other eclogite belts showing a similar exhumational record including the western gneiss region the dabie sulu and eastern papua new guinea

co2 sequestration and extreme mg depletion in serpentinized peridotite clasts from the devonian solund basin sw norway the conglomerates of the solund devonian basin of sw norway contain numerous locally up to 20 vol peridotitic clasts with concentric mm to 10 cm thick zones of varying red to black color the peridotite clasts show a clear alteration related textural evolution the least altered rocks are partly serpentinized peridotites showing a typical mesh texture with veins of serpentine magnesite and ni rich magnetite surrounding olivine fo91 relicts and its mg depleted clay like alteration product deweylite assemblage in the more advanced ophicarbonate stage the mesh cells contain calcite silica and are surrounded by talc in the final stage quartz calcite and hematite dominate the mineralogy and occur together with minor amounts of chromite talc cr chlorite and cr hydroandradite in tandem with this textural evolution is a decrease in mgo from 40 to 2 5 wt and a cao increase from 1 to 35 wt all peridotite clasts are characterized by high cr and ni concentrations the chemistry and the textural evolution show that the clasts formed by an extreme mg mobilization from the peridotite with development of secondary porosity and subsequent precipitation of calcite mgo removed from the clasts after burial is in part consumed by replacement reactions in the sediment matrix around the clasts where mg free minerals e g almandine are replaced by mg bearing minerals e g talc calculated apparent 87 sr 86 sr ratios of the clasts at 385 ma 0 7124 0 7139 corresponding to the inferred age of sediment deposition and incipient clast alteration indicate interaction with diagenetic basinal fluids we explain the reaction history as a three stage process involving a partial serpentinization of olivine in an oceanic environment b breakdown of olivine relicts to the deweylite assemblage resulting in mobilization of mgo under near surface conditions in a tropical devonian climate and c further mg mobilization and replacement of the deweylite assemblage by calcite and quartz after diagenesis sedimentary basins with abundant weathered peridotite represent potential sites for a permanent co2 storage by formation of calcite in a low temperature environment 2010 elsevier ltd all rights reserved

the sunnfjord melange evidence of silurian ophiolite accretion in the west norwegian caledonides a major composite terrane the sunnfjord melange has been identified in the west norwegian caledonides the rocks of the melange provide a terrane link between the allochthonous continental rocks of the dalsfjord suite with its cover of continental margin deposits and the oceanic terrane of the solund stavfjord ophiolite complex the melange was formed as the ophiolite was emplaced on the the fossiliferous lower to middle silurian continental margin deposits of the herland group this group unconformably overlies older metasedimentary rocks of the hoyvik group and the crystalline basement of the dalsfjord suite a structural style characteristic of thin skinned thrust foldbelts is locally preserved within the herland group on atloy and the thrust foldbelt was developed in the foreland of the continental margin during the ophiolite accretion a u pb zircon age of 443 3 ma from the ophiolite the silurian fossils in the herland group and the identification of the sunnfjord melange as an obduction melange provide the basis for a well constrained model of ophiolite accretion in the scandinavian caledonides

magnetic impulse events and related pc1 bursts observed by the automatic geophysical observatories network in antarctica magnetic field data obtained by fluxgate and search coil magnetometers installed at four automatic geophysical observatories ago pl p2 p3 and p4 and at south pole and mcmurdo in antarctica and at iqaluit on baffin island are used to study the relationship between magnetic impulse events mies and pc1 bursts at high geomagnetic latitudes the spatial scale sizes of mies are determined in the investigation of the sources of these events in the magnetosphere four mie events with simultaneous pc1 bursts are studied contour plots of mie amplitudes show the scale sizes of the examined mies to be 5 to 7 in the magnetic latitude direction and 40 to 60 in the magnetic longitude direction temporal changes of the ionospheric currents calculated from the fluxgate h and d component data indicate that the convection vortices associated with the mies traveled westward and decayed rapidly an important finding is that mie related pc1 bursts were observed at higher latitude pl p4 near 80 and lower latitude p2 p3 near 70 ago stations and south pole station at 74 with different spectral structures although the pc1 spectral power was always a maximum at south pole station these results imply that pc1 bursts are excited not only in the dayside outer magnetosphere but also in the low latitude boundary layer region

origin and significance of intra basement seismic reflections offshore western norway we use 3d seismic data to image a series of enigmatic sw dipping reflection packets within pre mesozoic crystalline basement offshore western norway based on their low angle dip and complex reflection wave train our preferred interpretation is that the reflection packets are the seismic expression of mylonitic zones generated by nappe emplacement during the caledonian orogeny late jurassic faults truncate and offset these reflection packets by several hundred metres suggesting that these faults did not exploit pre existing basement weaknesses our observations suggest that older basement fabrics may not always play a significant role in determining the geometry of later fault systems supplementary materials details of the time depth relationships from wells that have been used to depth convert interpretations s1 a supplementary figure showing an uninterpreted version of the seismic profile presented in fig 2 s2 and a throw v distance plot for fault f1 at the structural levels of the basement reflection and intra basement reflection 1 are available at www geolsoc org uk sup18683

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

occurrence patterns for transient magnetic field signatures at high latitudes impulsive events marked by durations ranging from 5 to 15 min and peak to peak variations in the h component exceeding 40 nt are common in observations by high latitude day side ground magnetometers we survey observations by a global network of high latitude ground magnetometers to distinguish between their proposed causes peak event amplitudes and occurrence rates occur prior to local noon in the range of geomagnetic latitudes from 70 to 76 although most events can be associated with abrupt changes in the interplanetary magnetic field imf orientation few can be associated with abrupt changes in the solar wind dynamic pressure many events can be observed during intervals of steadily northward imf orientation but only a few can be observed during intervals of steadily southward imf orientation we suggest an interpretation of the events in terms of a model in which changes in the imf orientation modulate the fraction of the solar wind pressure applied to the magnetosphere

sm nd dating of seve eclogites norrbotten sweden evidence for early caledonian 505 ma subduction the seve nappes consist of long transported thrust sheets belonging to the upper allochthon within the scandinavian caledonides eclogites from two different megalenses within the seve nappe complex in norrbotten northern sweden have been dated with the sm nd method the two eclogite bearing megalenses have been subjected to different pressure and temperature conditions during the high pressure metamorphism garnet omphacite whole rock from ts2 within the tsakkok lens give an age of 505 18 ma 2 i 0 512231 0 000024 mswd 0 10 garnet and whole rock from ts5 and whole rock ts3 also fall on the above isochron the composite isochron gives an age of 503 18 ma 2 these results are interpreted to date the peak of the high pressure metamorphism 500 630 c and 12 15 kbars for the tsakkok lens the eclogites in the vaimok lens at grapesvarre were subjected to higher pressure and temperature conditions and more extensive reequilibration during the early cooling stages retrograde breakdown reactions accompanied by retrograde zoning of relict garnet seems to be associated with disturbance of the sm nd isotopic systems in contrast a sample with unzoned garnet and well preserved high pressure mineralogy from grapesvarre gives a sm nd garnet omphacite age of 503 14 ma 2 i 0 512010 0 000038 2 the ages for the seve eclogites are significantly older than the sm nd eclogite dates from the western gneiss region of norway wgr suggesting the existence of at least two eclogite forming events in the caledonide orogen the younger event has been related to the main continent continent collision stage of the caledonian orogeny while the older event that led to the production of the norrbotten eclogites must have taken place several hundred kilometres to the north and in a different tectonic setting more oceanward to the wgr it appears that the older event ca 505 ma was restricted to the subduction of dyke intruded sedimentary cover rocks which are thought to represent the rifted edge of the baltic continent

u pb ages of ophiolites and arc related plutons of the norwegian caledonides implications for the development of iapetus u pb zircon ages are reported for four ophiolites and three crosscutting arc related plutons from the norwegian caledonides plagiogranite differentiated from gabbro of the karmoy ophiolite is dated at 493 7 4 ma whereas arc related trondhjemite cutting this ophiolite crystallized at 485 2 ma a crosscutting clinopyroxene phyric gabbro intrusion is dated at 470 9 5 ma by near concordant magmatic titanite sphene and discordant u rich 2903 6677 ppm zircon lower intercepts of 247 68 and 191 70 ma defined by the plagiogranite and clinopyroxene phyric gabbro best fit lines may reflect a real low t alteration rift related event

petrogenesis and significance of late caledonian granitoid magmatism in western norway obduction of the late ordovician solund stavfjord ophiolite complex 443 3 ma west norwegian caledonides involved generation and high level emplacement of granitic and granodioritic dikes and plutons initial 87sr 86sr ratios in the granites are low 0 7042 0 7059 suggesting either a mantle component or a rb poor crustal source initial end end t ranges from 0 8 to 8 8 indicating that the granites represent recycling of old crustal rocks which is supported by precambrian inheritance in zircons from two of the studied granites i argue that the rb sr and the sm nd isotope systems are decoupled in the sense that the sr and the nd isotopes derive their dominant signals from two different sources a mantle source and a crustal source respectively the granites are metaluminous to peraluminous and typically have high sr ba and na2o k2o ratios sio2 contents range from 66 to 74 wt ree abundances are highly variable the la contents range from 80 to 200 times chondrite and are inversely correlated with the contents of sio2 the concentration of nd in the granites decreases asymptotically with decreasing end t suggesting fractional crystallization of accessory phases and assimilation of continental crust this argument is supported by the presence of partly dismembered xenoliths in the granites with end t values that are significantly lower than end t values in the host granite the following models are suggested for the granites when the ophiolite complex obducted an outboard subduction zone approached the continental margin and subduction related magmas accumulated beneath the continental margin and probably intruded the overlying eugeosynclinal deposits the mantle derived magmas most likely evolved to granitoid composition by assimilation of these eugeosynclinal sediments and by fractional crystallization of amphibole feldspar sphene and allanite alternatively but less likely the heat content of the mantle derived magmas caused extensive melting of immature graywackes and calc alkaline volcaniclastic rocks in the deepest portions of the eugeosyncline either way during ascent the compositions of the granitic melts were modified by fractional crystallization of lree rich phases and by assimilation of continental metasediments

thermomechanical modeling of slab eduction 1 plate eduction is a geodynamic process characterized by normal sense coherent motion of previously subducted continental plate this mechanism may occur after slab detachment has separated the negatively buoyant oceanic plate from the positively buoyant orogenic root eduction may therefore be partly responsible for exhumation of high pressure rocks and late orogenic extension we used two dimensional thermomechanical modeling to investigate the main features of the plate eduction model the results show that eduction can lead to the quasi adiabatic decompression of the subducted crust 2 gpa in a timespan of 5 my large localized extensional strain in the former subduction channel flattening of the slab and a topographic uplift associated with extension of the orogen in order to further investigate the forces involved in the eduction process we ran systematic parametric simulations and compared them to analytic plate velocity estimations these experiments showed that eduction is a plausible mechanism as long as the viscosity of the asthenospheric mantle is lower than 1022 pa s while subduction channel viscosity does not exceed 1021 pa s we suggest that eduction can be a viable geodynamic mechanism and discuss its potential role during the orogenic evolution of the norwegian caledonides

tubular textures in pillow lavas from a caledonian west norwegian ophiolite a combined tem la icp ms and stxm study tubular alteration textures mineralized by titanite in glassy rims of pillow lavas from a norwegian ophiolite solund stavfjord ophiolite complex ssoc are described and characterized by a multimethod approach tubular alteration textures mineralized by titanite have been previously proposed to result from bioalteration the microstructure of the titanite and the tubes is investigated using focused ion beam milling in combination with transmission electron microscopy tem and scanning transmission x ray microscopy stxm these indicate an assemblage of submicrometer sized about 500 nm titanite single crystals with no organic film or residue in between the grains in situ u pb radiometric dating of the titanite using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms yielded a metamorphic age of 442 13 ma an isotope dilution thermal ionization mass spectrometric age obtained previously for zircons from the ssoc plutonic rocks yielded a magmatic age of 443 3 ma the overlap in ages indicates that subseafloor metamorphism responsible for titanite formation occurred during seafloor or subseafloor formation of the tubular alteration textures the rare earth element contents of the titanite were determined using la icp ms and chondrite normalized patterns are similar to those of the ssoc volcanics hence these do not reflect hydrothermal or seawater influence the y ho ratio of 20 30 in the titanite is also consistent with an upper mantle derived origin the sum of all of the spatial resolved data reported here neither supports nor refutes a biogenic origin for the tubular textures

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

volcanic rocks in the devonian solund basin western norway large landslides of silurian 439 ma rhyolites abstract the devonian solund basin in sw norway is the only old red sandstone basin in the scandinavian caledonides from which volcanic rocks have been described these rhyolitic lavas yield a concordant id tims u pb zircon age of 439 1 ma early silurian interpreted as dating the crystallization of the rhyolite and are thus too old to be syndepositional with the devonian sedimentary rocks this new age constraint combined with field observations suggests that the volcanic rocks form part of a 30 km 2 landslide of rhyolite granite gabbro and metasedimentary rocks rather than extension related volcanism as previously suggested the landslides show an inverted stratigraphy with respect to the nearby solund stavfjord ophiolite complex and its overlying volcanic arc which was formed immediately prior to obduction of caledonian exotic terranes onto baltica the dated rocks thus appear to record the youngest pre collisional volcanism in the scandinavian caledonides tectonic models involving devonian old red volcanic rocks in the scandinavian caledonides must thus be revised

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

palaeozoic palaeogeography of laurentia and its margins a reassessment of palaeomagnetic data summary the recognition of wide spread remagnetization events during the palaeozoic has greatly added to the problems of reconstructing the palaeozoic drift history of laurentia and in recent years increasing emphasis has been placed on evaluating the relative reliability of palaeomagnetic data in an attempt to overcome some of these difficulties in the light of these developments a revised apparent polar wander apw path has been constructed following a rigorous evaluation of all published palaeozoic palaeomagnetic data from laurentia and its palaeozoic margins i e north america northern britain northern ireland and greenland the use of data from the laurentian margins when corrected for the opening of the north atlantic has resulted in a revision of previously published palaeozoic palaeogeographic reconstructions and these new palaeogeographic reconstructions for laurentia are in good agreement with faunal and lithological data a comparison of this new apw path with other apw paths from avalonia and baltica reveals a very close agreement between all three paths from mid silurian times onwards indicating that the closure of the iapetus ocean and the tornquist sea was essentially complete by this time laurentia occupied equatorial latitudes from cambrian to early silurian times and its drift history was dominated by anti clockwise rotation up to 0 7 ma 1 and low latitudinal drift rates up to 3 cm yr 1 late silurian and early devonian times were characterized by increased rates of anti clockwise rotation up to 1 3 ma 1 and southerly directed latitudinal drift rates up to 13 cm yr 1 of the continent which place laurentia in moderate southerly latitudes 30 40 s by the early devonian these palaeolatitudes are comparable with those from avalonia and baltica for this time indicating that the amalgamation of eurmerica had already taken place by late devonian time laurentia had begun to drift north rates up to 5 cm yr 1 towards equatorial latitudes by mid carboniferous time

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

structural observations adjacent to a large scale extensional detachment zone in the hinterland of the norwegian caledonides abstract structural and lithological observations in a n s traverse across bremangerlandet western norway demonstrate that the region is separated into two plates by the e w striking s dipping ductile brittle vetvika shear zone the vetvika shear zone places caledonian high grade gneisses with a precambrian protolith age of the lower plate in tectonic contact with heterogeneous gneisses of the upper plate the vetvika shear zone is the uppermost part of the nordfjord sogn detachment zone a gently w plunging stretching lineation within the s dipping lower plate augen gneisses is interpreted as having formed within a several kilometers thick ductile w dipping extensional shear zone that has undergone later rotation around an e w axis a highly attenuated sequence of nappes occur structurally on top of a heterogeneous basement and cover quartzite of the upper plate pre caledonian structures are preserved locally in the gneissic upper plate basement the nappes at bremangerlandet are correlated with the caledonian middle and upper allochthons representing baltic suspect and exotic terranes respectively one large and several medium to small scale brittle top to the south extensional faults are superimposed on ductile contractional structures in the upper plate some of the extensional faults merge downward with the vetvika shear zone the contractional structures include e w trending folds and s directed thrusts in the cover quartzite and are superimposed on a pronounced w e stretching lineation conjugate sets of fractures and faults related to e w extension represent the youngest structures in the upper plate the old red sandstones devonian of the hornelen basin rest unconformably on top of extensionally faulted upper plate rocks on bremangerlandet the unconformity is partly faulted at bremanger and truncated by a regionally extensive late brittle fault along the basin margin further east this suggests a long lived tectonic history for the vetvika shear zone and its eastward continuation with movement pre and post dating the filling of the collapse basin possibly as an eastward migration of the break away fault

geochronology of ophiolites of the newfoundland appalachians precise u pb zircon ages 2 errors are reported for four ophiolite complexes from the newfoundland appalachians zircons from trondhjemite from blow me down mountain bay of islands complex give an age of five points those from gabbro from blow me down brook give a minimum 207pb 206pb age of 480 ma one point confirming that this is the age of the main plutonic episode these data refute previously determined latest cambrian u pb zircon and sm nd mineral rock isochron ages of 504 10 and 505 ma for the complex gabbro from the betts cove complex yielded zircon that gives an age of four points this refutes the interpretation of an earlier u pb zircon age of 463 6 ma for a trondhjemite dyke as the age of the ophiolite it was inconsistent with the presence of arenigian graptolites in the overlying snooks arm group two zircon ages from a pegmatitic and medium grained trondhjemite of the annieopsquotch complex are five points and two points zircon from trondhjemite of the pipestone pond c

caledonian compressional and late orogenic extensional deformation in the staveneset area sunnfjord western norway abstract the studied area in western norway constitutes part of the hangingwall of the extensional kvamshesten detachment zone kdz the kdz separates eclogite bearing lower crust from a hangingwall consisting of a precambrian basement cover pair silurian continental margin sediments a silurian obduction melange a late ordovician ophiolite and the devonian kvamshesten basin deposited unconformably on the pre devonian rocks contractional deformation related to ophiolite obduction and to the caledonian scandian orogeny produced a suite of se verging structures developed under greenschist facies conditions as orogenic collapse commenced extensional shear zones were formed in the upper and middle crust re activating contractional shear zones and fabrics the direction of transport on the inherited fabrics was reversed from top to southeast to top to northwest and structures related to the regional extension were superimposed on the contractional structures back folding of the main contractional foliation by asymmetric w vergent folds together with nw and w directed shearing along weak lithologies and semi ductile faulting in the melange are the main structural expressions of early stages of the orogenic collapse in the staveneset area there is apparently no metamorphic break between the contractional fabrics and the earliest extensional structures the extensional structures developed however under progressively more brittle conditions the devonian sediments were deposited upon a sequence of rocks in the upper plate of the kvamshesten detachment that had already undergone significant extensional deformation and tectonic exhumation in the late silurian early devonian the extensional deformation in the upper plate of the western norwegian extensional detachments has up to recently been largely ignored in the discussion of the structural control of the formation of the devonian basins

exhumation of ultrahigh pressure rocks beneath the hornelen segment of the nordfjord sogn detachment zone western norway the nordfjord sogn detachment zone of western norway represents an archetype for crustal scale normal faults that are typically cited as one of the primary mechanisms responsible for the exhumation of ultrahighpressure uhp terranes in this paper we investigate the role of normal sense shear zones with respect to uhp exhumation using structural geology thermobarometry and geochronology of the hornelen segment of the nordfjord sogn detachment zone the hornelen segment of the zone is a 2 6 km thick top w shear zone primarily developed within amphibolite grade allochthonous rocks that juxtaposes the uhp rocks of the western gneiss complex in its footwall with lower grade allochthons and carboniferous devonian basins in its hanging wall new thermobarometry and sm nd garnet geochronology show that these top w fabrics were initiated at lower crustal depths of 30 40 km between 410 ma and 400 ma structural geology and quartz petrofabrics indicate that top w shear was initially relatively evenly distributed across the shear zone and then overprinted by discrete ductile brittle detachment faults at slower strain rates during progressive deformation and exhumation these results require a three stage model for uhp exhumation in which normal sense shear zones exhumed uhp rocks from the base of the crust along initially broad ductile shear zones that were progressively overprinted by discrete ductile brittle structures

ground observations and possible source regions of two types of pc 1 2 micropulsations at very high latitudes we have used 1 year s data from the recently installed magnetometer array for cusp and cleft studies maccs in arctic canada and from two stations of the developing conjugate array of automated geophysical observatories agos in antarctica to study ulf waves in the pc 1 2 100 600 mhz frequency band at cusp and polar cap latitudes 74 80 in this paper we focus on the spectral properties and latitudinal and local time distributions of pc 1 2 events observed during 1994 and use these along with several case studies to infer the source locations of the two major wave types we have observed we found little variation in center band frequency of the pc 1 2 waves we observed but the average event bandwidth was distinctly wider at stations near 80 mlat than at stations near 75 mlat broadband waves with diffuse spectral character dominated at the higher latitudes but their occurrence was confined at most stations to within 4 hours of local magnetic noon waves with narrower bandwidth were much more common in our data set and were the statistically dominant wave type at the lower latitude maccs stations their occurrence was also limited to the dayside but extended both later and more widely in local time than the more broadband waves these multistation observations combined with data from the dmsp imp 8 and geotail satellites suggest the possibility that these two wave types originate in quite different regions near the magnetospheric boundary the more narrowband waves in the subsolar and postnoon equatorial region and the more broadband waves in the high latitude plasma mantle and possibly at the poleward edge of the cusp the cusp itself appears to not be a significant source of pc 1 2 wave activity that can be detected by ground observatories

influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the northern hemisphere winter it has been suggested that the zonal mean stratospheric zonal wind anomalies can propagate downward into the troposphere producing considerable changes on the other hand volcanic aerosols are thought to produce a stronger polar vortex in the winter stratosphere if these suggestions are correct the influence of volcanic eruptions can be expected to produce changes in the northern hemisphere winter troposphere through stratospheric process in the present study this idea is examined by analyzing changes in the january circulation after three recent volcanic eruptions regional features of observed changes in tropospheric temperatures due to volcanic eruptions can be explained by the changes in the propagation of stationary waves associated with dipole type anomalies in the zonal mean zonal winds which are similar to those observed in a previous work on the influence of polar night jet

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

winter north atlantic low cloud anomalies associated with the northern hemisphere annular mode ship observations of low cloud anomalies over the atlantic ocean from jan 1956 through mar 1995 are linearly related to the northern hemisphere annular mode nam and to the corresponding anomalies of surface pressure surface wind and sea surface temperature sst positive nam anomalies are associated with coherent cloud anomaly patterns a band of increased bad weather stratiform cloud along the storm track between 40 n and 50 n positive anomalies of precipitating stratiform and convective clouds together with negative anomalies of fair weather stratiform clouds north of this band and negative anomalies of cumulonimbus with weak increases in fair weather stratiform clouds south of this band near 10 n positive nam anomalies are associated with increased trade winds and increases in both fair weather and bad weather stratiform clouds resulting in an increase of total low cloud amount low cloud anomalies are also related to anomalies in sst and surface wind divergence

ophiolites as faithful records of the oxygen isotope ratio of ancient seawater the solund stavfjord ophiolite complex as a late ordovician example

cretaceous high pressure metamorphism in ne oman and its relationship to subduction and ophiolite nappe emplacement an occurrence of glaucophane bearing schists is reported from near muscat in ne oman in rocks which underlie the upper cretaceous semail ophiolite nappe these blueschists formed by the metamorphism of quartz sandstones shales and basic igneous rocks belong to a pre permian basement in the area metamorphic micas phengites from these rocks have been dated at between 101 and 80 ma k ar ages indicating a mid to late cretaceous age for the high pressure event a syn to late f 1 assemblage of almandine glaucophane phengite in the pelites shows that the peak of metamorphism reached about 400 450 c and 4 8 kbars pressure this was followed by a greenschist facies overprint with the formation of epidote and albite porphyroblasts in the meta igneous rocks and a widespread retrogression to chlorite the high pressure metamorphism is ascribed to the effects of partial subduction of the ne oman continental margin during the initial stages of ophiolite obduction and the subsequent greenschist facies event to uplift of the area during the later stages of emplacement of the nappes

propagating rift tectonics of a caledonian marginal basin multi stage seafloor spreading history of the solund stavfjord ophiolite in western norway abstract the late ordovician solund stavfjord ophiolite in western norway represents a remnant of the iapetus oceanic lithosphere that developed in a caledonian marginal basin the ophiolite contains three structural domains that display distinctively different crustal architecture that reflects the mode and nature of magmatic and tectonic processes operated during the multi stage seafloor spreading evolution of this marginal basin domain i includes from top to bottom an extensive extrusive sequence a transition zone consisting of dike swarms with screens of pillow breccias a sheeted dike complex and plutonic rocks composed mainly of isotropic gabbro and microgabbro extrusive rocks include pillow lavas pillow breccias and massive sheet flows and are locally sheared and mineralized containing epidosites sulfide sulfate deposits fe oxides and anhydrite veins reminiscent of hydrothermal alteration zones on the seafloor along modern mid ocean ridges a fossil lava lake in the northern part of the ophiolite consists of a 65 m thick volcanic sequence composed of a number of separate massive lava units interlayered with pillow lavas and pillow breccia horizons the ne trending sheeted dike complex contains multiple intrusions of metabasaltic dikes with one and two sided chilled margins and displays a network of both dike parallel normal and dike perpendicular oblique slip faults of oceanic origin the dike gabbro boundary is mutually intrusive and represents the root zone of the sheeted dike complex the internal architecture and rock types of domain i are analogous to those of intermediate spreading oceanic crust at modern mid ocean ridge environments the ophiolitic units in domain ii include mainly sheeted dikes and plutonic rocks with a general nw structural grain and are commonly faulted against each other although primary intrusive relations between the sheeted dikes and the gabbros are locally well preserved the exposures of this domain occur only in the northern and southern parts of the ophiolite complex and are separated by the ene trending domain iii in which isotropic to pegmatitic gabbros and dike swarms are plastically deformed along ene striking sinistral shear zones these shear zones which locally include fault slivers of serpentinite intrusions are crosscut by n20 e striking undeformed basaltic dike swarms that contain xenoliths of gabbroic material the nw trending sheeted dike complex in the northern part of domain ii curves into an ene orientation approaching domain iii in the south the anomalous nature of deformed crust in domain iii is interpreted to have developed within an oceanic fracture zone or transform fault boundary ree chemistry of representative extrusive and dike rocks from all three domains indicates n to e morb affinities of their magmas with high th ta ratios that are characteristic of subduction zone environments the magmatic evolution of domain i encompasses closed system fractional crystallization of high mg basaltic magmas in small ephemeral chambers which gradually interconnected to form large chambers in which mixing of primary magmas with more evolved and fractionated magma caused resetting of magma compositions through time the compositional range from high mg basalts to ferrobasalts within domain i is reminiscent of modern propagating rift basalts we interpret the ne trending domain i as a remnant of an intermediate spread rift system that propagated northeastwards in present coordinate system into a pre existing oceanic crust which was developed along the nw trending doomed rift domain ii in the marginal basin the n20 e dikes laterally intruding into the anomalous oceanic crust in domain iii represent the tip of the rift propagator the inferred propagating rift tectonics of the solund stavfjord ophiolite is similar to the evolutionary history of the modern lau back arc basin in the sw pacific and suggests a complex magmatic evolution of the caledonian marginal basin via multi stage seafloor spreading tectonics

the tectonic significance of pre scandian 40ar 39ar phengite cooling ages in the caledonides of western norway pre silurian continental margin deposits in western norway non conformably overlying allochthonous continental orthogneisses retain ordovician 40 ar 39 ar cooling ages for phengites implying either rapid cooling immediately after a late ordovician orogenic event or less likely a slow cooling following an early ordovician or older orogeny the dalsfjord suite hoyvik group basement cover pair are probably a lateral equivalent to late proterozoic sandstones sparagmites covering the jotun nappe gneisses of the middle allochthon in central south norway the hoyvik group underwent polyphase deformation greenschist facies metamorphism t max 40 ar loss probably occurred during subsequent scandian deformation and late to post orogenic extension the hoyvik group rocks were unroofed before the wenlock time 423 428 ma and cooled through the temperature for argon retention in phengite at c 447 4 ma indicating a maximum cooling rate between 14 and 22c ma 1 through ashgill and llandovery times before being subjected to low grade metamorphism during the scandian orogeny rapid pre scandian cooling combined with peak metamorphic conditions of 450c or less may indicate that the dalsfjord hoyvik basement cover pair were avected by an orogenic event during the late ordovician caradoc time the data also suggest that the caledonian margin of baltica may have experienced a more protracted tectonism during the caledonian cycle than previously models focusing on early caledonian and tremadoc or older ophiolite obduction and the scandian continental collision between baltica and laurentia

the gabbro dyke transition zone demonstrated on tviberg solund stavfjord ophiolite complex the transition zone between 100 dykes and high level plutonic rocks of the solund stavfjord ophiolite complex is complex due to the existence of many lithologies with different and variable contact relationships the rocks of the plutonic complex vary in composition from feti basaltic to quartz dioritic and the grain sizes vary from fine to pegmatitic felsic varieties are produced by fractional crystallization of basaltic magma as demonstrated by geochemical evolution and by gradual transition from gabbro to quartz diorite patches of fractionated dioritic rocks may show both gradual and intrusive relationships with the surrounding host gabbro this demonstrates that late stage liquids commonly left the source region and locally intruded the surrounding parent rocks the high level plutonic rocks are thoroughly epidotized and are cut by dykes consisting of granoblastic epidote and quartz the high level plutonic complex is associated with irregular bodies of fine to medium grained plagioclase porphyritic diabase of high mgo content these diabase bodies are intruded by dykes that become progressively more regular in shape the plutonic complex locally shows intrusive relationships with the overlying 100 dyke complex but is itself cut by two dyke swarms the dykes of the first swarm formed while the plutonic complex experienced sinistral shear strain and the dykes are generally less regular and thinner than the dykes of the second swarm this indicates that the dykes of the first swarm intruded while the rocks of the plutonic complex were still hot while the next dyke swarm intruded later when the rock complex was colder dykes of both swarms range in composition from slightly to strongly fractionated suggesting that the magma chambers they were expelled from underwent significant fractionation in between magma replenishment numerous dykes of both swarms carry large quantities of glomeroporphyritic aggregates of plagioclase and altered clinopyroxene indicating that the source area to the dykes very often was a crystal mush

kinematics of post caledonian polyphase brittle faulting in the sunnfjord region western norway abstract structural studies in the sunnfjord region of western norway focused on faulting episodes that post date the major period of early devonian extension clarify the style and prolonged complex evolution of brittle faulting major brittle structures in the region can generally be divided into 1 e w faults and 2 n s fault joint zones with subordinate ne sw and nw se structures in close association with these large scale features four distinct groups populations of mesoscopic faults can be distinguished with basis in common characteristics spatial distribution orientation sense of slip and cross cutting relationships two reference areas the eastern parts of the kvamshesten and hornelen devonian basins feature clear cross cutting relationships of major faults and folds such relations and kinematic patterns of the distinct populations of mesoscopic faults and their relationship to dated fault rocks and dykes form the basis for a four stage history of post early devonian brittle faulting stage 1 is characterised by n s shortening expressed by thrusting and folding related to either late devonian carboniferous transpression or compression stage 2 is characterised by n s shortening and e w extension on conjugate strike slip faults and bisecting normal faults and is probably related to the regional e w folding during progressive shortening stage 3 is characterised by approximate e w extension and is manifested as low angle silicified fault breccias of possible permian age that mainly bound the eastern margin of the devonian basins stage 4 features n s extension on steep e w striking normal faults that possibly relates to a regional late jurassic early cretaceous extensional phase significant throw 500 1000 m on some of the faults emphasise the importance of late devonian and younger faulting indicating that these deformation episodes had a regional extent and therefore also occurred in the neighbouring offshore areas the established four stage fault evolution is examined in the light of known episodes of rejuvenation of faults on the nearby shelf and along the more trondelag fault zone emphasising the importance of movement on master faults with respect to local strain conditions in the sunnfjord region