the carbon stable isotope biogeochemistry of streams taylor valley antarctica abstract the mcmurdo dry valleys region of antarctica is the largest ice free region on the continent this study reports the first c stable isotope measurements for dissolved inorganic c present in ephemeral streams in four dry valleys that flow for four to twelve weeks during the austral summer one of these valleys taylor valley has been the focus of the mcmurdo dry valleys long term ecological research mcm lter program since 1993 within taylor valley numerous ephemeral streams deliver water to three perennially ice covered closed basin lakes lake fryxell lake hoare and lake bonney the onyx river in the wright valley the longest river in antarctica flows for 40 km from the wright lower glacier and lake brownworth at the foot of the glacier to lake vanda streamflow in the mcmurdo dry valley streams is produced primarily from glacial melt as there is no overland flow however hyporheic zone exchange can be a major hydrogeochemical process in these streams depending on landscape position these streams vary in gradient channel substrate biomass abundance and hyporheic zone extent this study sampled streams from taylor wright garwood and miers valleys and conducted diurnal sampling of two streams of different character in taylor valley in addition transect sampling was undertaken of the onyx river in wright valley the 13 c pdb values from these streams span a range of greater than 14 from 9 4 to 5 1 with the majority of samples falling between 3 and 2 suggesting that the c stable isotope composition of dissolved c in mcmurdo dry valley streams is largely inorganic in character because there are no vascular plants on this landscape and no groundwater input to these streams atmospheric exchange is the dominant control on 13 c dic

the geochemical fingerprints of different tectonomagmatic environments using hygromagmatophile element abundances of tholeiitic basalts and basaltic andesites abstract using hygromagmatophile element abundances normalized to primordial mantle composition it is possible to discriminate between the tectonic settings of tholeiitic basalts and basaltic andesites 47 0 53 5 sio2 based on field and chemical evidence data from provinces or grouped localities have been compiled in order to establish chemical reference data sets for ocean island continental ocean ridge and floor subduction zone and back arc environments the disturbing effects of crustal contamination and hydrothermal alteration on the hygromagmatophile h element patterns are of minor significance in the recognition of plate tectonic settings on the basis of the data sets magmas from a number of ambiguous tectonic settings have been recognized using their h element patterns attention is directed to problems concerning rifting and drifting related basalts in an apparent continental setting and to the origin of ophiolite complexes using available data the pillow lavas of the troodos ophiolite complex cyprus are recognized as basalts erupted in a subduction zone environment

paleogene igneous underplating and subsidence anomalies in the rockall faeroe shetland area abstract crustal thickening caused by igneous underplating related to continental break up in the northeast atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many mesozoic basins in the northwest european area in this study we examine a set of commercial wells in the rockall faeroe shetland region and calculate tectonic subsidence histories the rate of post rift basement subsidence during the cretaceous cenozoic determined from backstripping calculations always implies a higher degree of extension than the total basement subsidence assuming uniform extension furthermore the size of this discrepancy increases northward along the rockall trough and westwards in the northern north sea towards scotland we interpret this depth anomaly to reflect the effect of igneous underplating rethickening the crust following mesozoic and cenozoic extension late paleocene extension is identified in subsidence reconstructions throughout the west of britain area and is greatest in the rockall trough assuming that the underplating is gabbroic in composition the subsidence depth anomalies indicate a regional pattern of 2 3 km underplated between the erris trough and porcupine basin increasing to 4 5 km in the west lewis basin and hebrides shelf area in the faeroe shetland basin underplating is 1 0 1 5 km in the east and increases to 4 5 km in the west the data support the hypothesis of a major asthenospheric thermal anomaly centered under the faeroes in the paleocene dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 ma implying rapid emplacement of the mantle anomaly the intrusion of gabbroic bodies to the base of the crust in the late paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region however thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models suggesting that underplating was a gradual process achieved through the accretion of several small rapidly cooled bodies

seismic stratigraphic analysis of the cenozoic sediments in the nw faroe shetland basin implications for inherited structural control of sediment distribution abstract the post basalt strata in the faroese area have been investigated based on interpretation of 2d and 3d reflection seismic data the post basalt package is divided into 5 units which have led to the constructions of 6 structural maps and 5 thickness maps within the 5 units 12 prograding sediment bodies have been identified based on the interpretation it is possible to obtain an overview during time of the location of depocentres and direction of prograding units within eocene time the depocentre was placed in the central part of the basin and the sediment influx was mostly from south and southwest during oligocene pliocene time the sediment influx was from north and northwest and the depocentre had moved in a westward direction closer to the faroe platform area emplacement of the cenozoic sediments in the faroese sector of the faroe shetland basin is controlled by thermal subsidence of the basin and local uplift of sediment source areas reactivation of older paleozoic and mesozoic structural elements seem to control the sediment path way and restrict the depositional areas various structural elements being re activated at different times caused considerable structural complexity understanding the older structural elements and their control on sedimentation is a potential tool for understanding deviations from normal thermal subsidence and for predicting the prospectivity in the post basalt succession in the faroe shetland basin

widespread palaeocene volcanism around the northern north atlantic and labrador sea evidence for a large hot early plume head abstract voluminous volcanism took place west of greenland and northwest of the british isles in the palaeocene 6 7 ma before the start of sea floor spreading in the northern north atlantic very hot picritic magmas were produced simultaneously in such widely separated areas that they could not all have been above the central stem of the same mantle plume a single large plume head with temperatures of c 1500 c over a diameter of c 2000 km can explain the observations if surface volcanic activity took place only where the lithosphere was thin the presence of picrites does not indicate proximity to the plume stem

upb geochronology of the central ribeira belt brazil and implications for the evolution of the brazilian orogeny abstract the ribeira belt in southeastern brazil was generated during the brazilian orogeny the south american equivalent of the pan african orogeny 700 450 ma the central sector of the belt is characterised by a series of northwest vergent crustal scale thrust stacks emplaced under amphibolite grade conditions major shear zones separate four lithotectonic domains andrel ndia to the northwest juiz de fora paraiba and coastal domains analyses of zircon monazite and titanite from a variety of rock types from the four domains lead to the following conclusions all domains record an important tectono thermal event at 590 565 ma represented by partial melting granitoid intrusion and remobilisation of older basement gneisses and corresponding to thrusting and development of dextral shear zones also recorded are older metamorphic ages 611 604 ma of unknown significance only the paraiba and coastal domains in the south record a younger metamorphic event m2 at 535 520 ma most likely associated with another episode of thrusting and shear zone development the absence of m2 metamorphism in the andrel ndia and juiz de fora domains can be explained by post 535 520 ma emplacement of the paraiba domain late to post tectonic activity is represented by 503 492 ma metamorphism precursors of the basement gneisses are 2185 2134 ma old rocks generated during the transamazonian orogeny some of which contain a significant archean component with minimum ages of 2981 2846 ma the ages presented above define specific metamorphic events for the brazilian orogeny for the first time in southeastern brazil in addition together with previously published data they indicate that the basement rocks found in the allochthonous domains of the central ribeira belt represent an extension of the units present in the southern sao francisco craton and indicate that the foreland was more extensive than the presently defined craton

k ar and 39ar 40ar whole rock dating of zeolite facies metamorphosed flood basalts the upper paleocene basalts of the faroe islands ne atlantic

trans atlantic correlation of the palaeogene volcanic successions in the faeroe islands and east greenland before continental break up in the ne atlantic the faeroe islands and central east greenland were within a distance of 100 120 km chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous palaeogene flood basalts in the faeroe islands and in the nansen fjord area in east greenland show very similar basalt compositions and evolution patterns with time the faeroes lower basalt formation and the equivalent nansen fjord formation in east greenland form a pre break up succession overlain by a sediment horizon a syn break up succession consists of the faeroes middle and upper basalt formations and the equivalent milne land formation in east greenland in which five intervals can be correlated with a compositional evolution from ti rich magnesian basalts and picrites at the base to a dominance of morb like low ti basalts at the top the successions were generated in the same mantle melting column beneath a thinning continent with a rift zone that eventually ruptured the continent the evolution pattern is very similar to that seen on the se greenland margin but spreading according to the palmason model of 1973 was not yet established the pre and syn break up successions formed volcanic megasystems stretching across the rift zone with areal extents of 70 000 and 220 000 km 2 and volumes of 120 000 and 250 000 km 3 rocks from the pre and syn break up successions can be discriminated based on a simple major element plot the overlying succession was 3 3 5 km thick in e greenland but was thin or absent in the faeroes the energy source for the melting appears to have been concentrated on the greenland side

geochemistry of late palaeocene and early eocene tephras from the north sea basin the late palaeocene to early eocene balder and sele formations of the north sea basin contain over 200 air fall water lain tephras these occur over the entire north sea area extending onshore into denmark nw germany the netherlands and se england they have also been recorded in the bay of biscay and goban spur areas of the ne atlantic and offshore mid norway results from cores drilled in two widely separated areas of the north sea have been integrated with earlier work on the northern north sea and danish sequences to demonstrate that the stratigraphic and geochemical development of the tephra sequence is regionally consistent this indicates that a single source or group of sources was responsible rather than a number of geographically separated intrabasinal volcanoes for which little geophysical evidence can be found the sequence comprises a lower group of sporadic thin tephras of variable composition including tholeiitic alkalic trachytic trachyandesitic and peralkaline varieties and an upper group of thicker more abundant tephras almost exclusively of fe ti tholeiitic composition general thickness trends and geochemical evidence indicates that the source volcanoes lay on the proto greenland scotland ridge with the tephras showing several features that ally them to the early palaeogene faeroe greenland igneous province the reasons behind the highly explosive nature of the basaltic magmatism remain enigmatic

3d seismic imaging of the shallow plumbing system beneath the ben nevis monogenetic volcanic field faroe shetland basin seismic reflection data allow for the 3d imaging of monogenetic edifices and their corresponding plumbing systems this is a powerful tool in understanding how monogenetic volcanoes are fed and how pre existing crustal structures can act as the primary influence on their spatial and temporal distribution this study examines the structure and lithology of host rock as an influence on edifice alignment and provides insight into the structure of shallow sub volcanic monogenetic plumbing systems the anticlinal ben nevis structure located in the northerly extent of the faroe shetland basin ne atlantic margin was uplifted during the late cretaceous and early paleocene by the emplacement of a laccolith and a series of branching sills fed by a central conduit seismic data reveal that multiple intrusions migrated up the flanks of the ben nevis structure after its formation c 58 4 ma kettla equivalent and fed a series of scoria cones and submarine volcanic cones these monogenetic edifices are distributed around the crest of the ben nevis structure the edifices are fed from a complex network of sills and transgressive sheets involving lateral magma migration of tens of kilometres before extrusion at the surface this work highlights the importance of underlying basin structures in influencing the sites and development of subaerial monogenetic fields and the importance of lateral magma flow within volcanic systems supplementary materials the results of the statistical alignment analysis of the monogenetic edifices are available at https doi org 10 6084 m9 figshare c 3662809

the structure of the faeroe shetland trough from integrated deep seismic and potential field modelling in the faeroe shetland trough thick basaltic lava units make it difficult to image underlying structure with conventional seismic profiles we have therefore used potential field modelling to estimate crustal structure along the fast deep seismic line and other regional transects we introduce the additional constraints of crustal isostasy to gravity models and the observations of the polarity of magnetic remanence within the lava pile to magnetic models the crustal stretching factor ranges up to 3 along the fast traverse and our model also suggests that a sedimentary section with a thickness of up to 3 4 km is present beneath a c 2 km basalt layer on the faeroese shelf

crustal structure beneath the faroe islands from teleseismic receiver functions we use teleseismic receiver function analysis to constrain the crustal structure beneath the faroe islands on the northwest european volcanic continental margin a cluster of 45 broad band seismometers on the glyvursnes peninsula streymoy island recorded 10 teleseismic events ranging in magnitude from 6 1 to 8 0 during july december 2003 receiver functions show a clear ps peak for the first time in this region the depth of the converting boundary is estimated as 29 32 km using forward and inverse modelling and thickness versus vp vs ratio stacking techniques modelling experiments suggest that this estimate may represent the conversion from a region of high velocity lower crust rather than the crust mantle transition at the moho the best fit modelling results were achieved with a gradational high velocity region at least 6 km thick in the lower crust this is interpreted as due to the emplacement of sills into pre existing continental crust rather than the simple underplating of a block of high velocity igneous material at its base

assessment of diel chemical and isotopic techniques to investigate biogeochemical cycles in the upper klamath river oregon usa abstract the upper klamath river experiences a cyanobacterial algal bloom and poor water quality during the summer diel chemical and isotopic techniques have been employed in order to investigate the rates of biogeochemical processes four diel measurements of field parameters temperature ph dissolved oxygen concentrations and alkalinity and stable isotope compositions dissolved oxygen 18 o and dissolved inorganic carbon 13 c have been performed between june 2007 and august 2008 significant diel variations of ph dissolved oxygen do concentration and do 18 o were observed due to varying rates of primary productivity vs respiration vs gas exchange with air diel cycles are generally similar to those previously observed in river systems although there are also differences compared to previous studies in large part these different diel signatures are the result of the low turbulence of the upper klamath river observed changes in the diel signatures vs sampling date reflect the evolution of the status of the algal bloom over the course of the summer results indicate the potential utility of applying diel chemical and stable isotope techniques to investigate the rates of biogeochemical cycles in slow moving rivers lakes and reservoirs but also illustrate the increased complexity of stable isotope dynamics in these low turbulence systems compared to well mixed aquatic systems

diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions and in a mesocosm experiment abstract rates of diel 24 h biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts daily changes in the rates of biogeochemical processes have more recently been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the 18o composition of dissolved molecular oxygen 18o do and the 13c composition of dissolved inorganic carbon 13c dic across five montana usa rivers investigated over a 4 year period a mesocosm experiment showed the same behavior in 18o do and 13c dic as seen in riverine settings across light and dark periods a cross plot of 18o do and 13c dic from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air water gas exchange the amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in 18o do and 13c dic is presented this relationship between trophic status with 18o do 13c dic and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters

surface interpolation within a continental flood basalt province an example from the palaeogene faroe islands basalt group abstract the faroe islands basalt group fibg is a continental flood basalt province with four proven lithohorizons that have abundant spot height data the spline interpolation method was used to construct spatial surfaces for the lithohorizons the resultant surfaces conform to dip and strike estimates that were previously modelled by hand and confirm the methods reliability the surfaces should be used as guides only but can be quickly and easily updated as new information becomes available the surfaces have been used for a variety of different tasks for example obtaining gross thickness estimates producing isopach maps and constructing geological cross sections an additional benefit of the spatial surfaces is the ability to constrain disparate observations in a stratigraphic framework which will be particularly important for future studies attempting to understand for example the temporal and spatial development of continental flood basalt volcanism the spline interpolation method applied in this study can be equally used for other stratigraphic horizons e g chemohorizon chronohorizon biohorizon and in other continental flood basalt provinces e g deccan traps columbia river basalt group

regional distribution of volcanism within the north atlantic igneous province an overview of the distribution of volcanic facies units was compiled over the north atlantic region the new maps establish the pattern of volcanism associated with breakup and the initiation of seafloor spreading over the main part of the north atlantic igneous province naip the maps include new analysis of the faroe shetlands region that allows for a consistent volcanic facies map to be constructed over the entire eastern margin of the north atlantic for the first time a key result is that the various conjugate margin segments show a number of asymmetric patterns that are interpreted to result in part from pre existing crustal and lithospheric structures the compilation further shows that while the lateral extent of volcanism extends equally far to the south of the iceland hot spot as it does to the north the volume of material emplaced to the south is nearly double of that to the north this suggests that a possible southward deflection of the iceland mantle plume is a long lived phenomenon originating during or shortly after impact of the plume

p wave velocity distribution in basalt flows of the enni formation in the faroe islands from refraction seismic analysis the main objective of this work is to establish the applicability of shallow surfaceseismic traveltime tomography in basalt covered areas a densely sampled 1300 m long surface seismic profile acquired as part of the seifaba project in 2003 japsen et al 2006 at glyvursnes in the faroe islands served as the basis to evaluate the performance of the tomographic method in basalt covered areas the profile is centred at a 700 m deep well vp vs and density logs a zero offset vsp downhole geophone recordings and geological mapping in the area provided good means of control theinversionwasperformedwithfacilitiesofthewideanglereflection refraction profiling program package ditmar et al 1999 we tested many inversion sequences while varying the inversion parameters modelled traveltimes were verified by fullwaveform modelling typically an inversion sequence consists in several iterations that proceed until a satisfactory solution is reached however in the present case with high velocity contrasts in the subsurface we obtained the best result with two iterations first obtaining a smooth starting model with small traveltime residuals by inverting with a high smoothing constraint and then inverting with the lowest possible smoothing constraint to allow the inversion to have the full benefit of the traveltime residuals the tomogram gives usable velocity information for the near surface geology in the area but fails to reproduce the expected velocity distribution of the layered basalt flows based on the analysis of the tomogram and geological mapping in the area a model was defined that correctly models first arrivals from both surface seismic data and downhole geophone data

the role of palaeocene magmatism in the tectonic evolution of the sea of the hebrides basin implications for basin evolution on the nw seaboard

neogene seismic facies and deep water gateways in the faeroe bank area ne atlantic abstract interpretation of sedimentary structures on high resolution multichannel sleeve gun seismic records has been used to illustrate changes in the neogene deep water flow regime around the bill bailey bank at the southern end of the faeroe shetland channel the main part of the norwegian sea overflow water nsow turns into the faeroe bank channel leaving the faeroe bank channel the nsow forms an erosive flow along the southern part of the faeroe platform where the basalt is outcropping it is indicated that part of the overflow waters continues to the northwest entering the n atlantic basin to the west of the faeroe rockall plateau intermittent overflow of nsow occurs via the wyville thomson ridge complex between the bill bailey bank and faeroe bank sedimentary structures seen on the seismic profiles indicate the existence of a former nsow pathway which was active until presumably the late pliocene along the southern rise of the bill bailey bank the seismic profiles indicate that deep water flow was still active in the late quaternary which presumably can be related to intermittent overflow of the wyville thomson ridge complex

tracing dissolved o2 and dissolved inorganic carbon stable isotope dynamics in the nyack aquifer middle fork flathead river montana usa abstract the geochemistry and microbiology of shallow groundwater aquifers is greatly influenced by the concentration of dissolved oxygen gas do however the mechanisms that consume do in groundwater e g biotic or abiotic are often ambiguous the use of stable isotopes of molecular o 2 18 o do in conjunction with stable isotopes of dissolved inorganic carbon 13 c dic has potential to discriminate between the various mechanisms causing do depletion in subsurface waters here we report the results of spatial and seasonal changes in 18 o do and 13 c dic at the nyack floodplain aquifer along the middle fork of the flathead river near west glacier montana usa over a short well constrained flow path 100 m near a main recharge zone of the floodplain the 18 o do consistently increased as do concentrations decreased with distance from the recharge source concurrently dic concentrations increased and 13 c dic values decreased these observations are explained by community respiration coupled with dissolution of calcite from cobbles in the aquifer matrix when these results are compared to data from wells distributed over the entire floodplain several km a much less predictable relationship was observed between do concentration and 18 o do many wells with low do concentrations e g 1 or 4 mg l 1 had anomalously low 18 o do values e g 2 may be contributed to the aquifer by diffusion from the vadose zone and by advection from the river recharge calculations presented here suggest that diffusion across a narrow air water interface can contribute isotopically light 18 o do to the saturated zone possible contributions of light 18 o do from other processes such as isotopic exchange and radial oxygen loss from plant roots in or near the water table are compared and evaluated

age of tertiary volcanic rocks on the west greenland continental margin volcanic evolution and event correlation to other parts of the north atlantic igneous province radiometric ages for undated parts of the volcanic succession and intrusions in west greenland were obtained by the 40ar 39ar incremental heating method acceptable crystallization ages were obtained for 27 samples combined with published results the new data provide a volcanic stratigraphy correlatable throughout the nuussuaq basin the thick onshore volcanic pile consists of four widespread formations 62 5 61 ma picrites vaigat formation 61 60 ma depleted basalts malig t formation and the hellefisk 1 well 60 58 ma less depleted basalts svartenhuk formation and 56 54 ma enriched basalts naqerloq formation two local successions comprise 53 5 ma alkali basalts erqua formation and 38 7 ma transitional basalts talerua member a central volcano developed on ubekendt ejland leading to the sarq ta qaq gabbro granophyre intrusion at 57 55 ma pre break up volcanism took place further south as early as 64 63 ma the offshore volcanic succession most probably comprises the known onshore succession plus some younger lavas the change in spreading direction near the paleocene eocene boundary took place west of the nuussuaq basin c 56 2 ma some tectonomagmatic events are correlatable across the entire north atlantic igneous province a quiescent 58 56 ma period correlates with similar periods in east greenland and the faroes and the naqerloq formation is coeval with the eocene basalts in east greenland the paleocene and eocene tholeiitic basalts are distinguishable chemically in early eocene time mantle typical of the iceland plume seems to have extended beneath the whole west greenland margin as well as the central east greenland margin

imaging igneous rocks on the north atlantic rifted continental margin summary extruded basalt flows with thicknesses of several kilometres occur ubiquitously along the rifted continental margins of the northern north atlantic their total volume exceeds 1 million km 3 and may reach several million cubic kilometres intruded igneous rock comprising the complementary melt fraction to that extruded at the surface should exist in the lower crust with a volume at least as large as that of the extrusive basalts to image the extrusive and intrusive igneous rocks on the continental margin near the faroe islands in 2002 we shot a 375 km long deep penetration seismic profile across the margin using 85 ocean bottom seismometers for wide angle acquisition and shot a separate reflection profile using a 12 km streamer for optimal imaging by using large airgun sources tuned to produce low frequency energy we were able to constrain the seismic velocity structure of the whole crust we imaged not only layering and structure within the extrusive basalts but also lower crustal intrusions on the continent ocean transition cot combination of good velocity control on the lower crust together with direct imaging of the extrusive basalts enables us to constrain the volumes of extrusive and intrusive igneous rocks produced near the faroe islands to be 340 420 and 560 780 km 3 per kilometre along strike respectively the cot marked both by high velocity intrusions and lower crustal layering is surprisingly narrow with only 50 km separating unstretched continental crust from fully oceanic crust in contrast the extruded basalts flow up to 150 km landward at the paleo surface

the e greenland rifted continental margin an examination of the coastal flexure the structure of the e greenland coastal flexure a major structure developed during continental break up is interpreted on the basis of field observations an earlier model which involves normal inland dipping antithetic faulting and seaward rotation of fault blocks is confirmed and amplified this model requires that regional dips are very much less than dips measured on bedding planes thus leading to considerably reduced thicknesses for the tertiary volcanic succession in e greenland detailed mapping confirms the validity of these thickness estimates and leads to the conclusion that the volcanic extrusion rate was similar to that of present day iceland thus obviating the need for special mechanisms of magma generation comparable structures occur in other regions of continental break up and voluminous basalt discharge and it is suggested that the flexure developed by collapse of the attenuated crust subsequent to the massive extrusion of plateau basalts

early opening history of the north atlantic i structure and origin of the faeroe shetland escarpment summary marine geophysical surveys show that the escarpment is the buried feather edge of a thick pile of flood basalts of early eocene age overlying a thinner more widespread layer of basalts of late palaeocene age the escarpment does not therefore define the continent ocean boundary in the southern norwegian sea but instead marks the contemporary shoreline separating terrestrially erupted basalt flows in the north from a restricted shallow water shelf to the south the basalts overlie 5 6 km of mesozoic sediments which have completely buried a large conical flat topped seamount of similar dimensions to anton dohrn and rosemary bank we call this newly postulated body the brendan seamount the mesozoic sediments are at least as old as early cretaceous in age therefore precluding the possibility that the mid cretaceous seafloor spreading episode supposed by some to have created the rockall trough could have also created the thin crust inferred to underlie the faeroe shetland trough and mbre basin

how natural remanent magnetization of basaltic units can dominate the reduced to pole magnetic value a case study from the faroe islands abstract early attempts to utilize magnetic data to understand the volcanic and subvolcanic succession on the faroese continental shelf have shown that conventional interpretation and modelling of magnetic data from this area leads to ambiguous results interpretation of the aeromagnetic data on the faroese continental shelf shows that some previously identified basement highs coincide with reduced to pole magnetic highs whereas others coincide with negative or mixed magnetic features similarly igneous centres are characterized by different polarity magnetic anomalies palaeomagnetic analysis of the onshore volcanic succession has demonstrated that the thermoremanent magnetization of the basaltic lavas is stronger than the induced magnetism and both reversely and normally magnetized units are present we have tested this with 2 d profile modelling using the palaeomagnetic information to correlate high amplitude magnetic anomalies with basalt successions containing changes in magnetic polarity this approach has enabled us to map the termination of the differently magnetized units offshore and thereby extend the mapping of the faroe island basalt group on the faroese platform and into adjacent areas

crustal growth through successive arc magmatism reconnaissance u pb shrimp data from the northeastern superior province canada abstract north of the la grande subprovince in northern quebec the superior province is dominated by plutonic rocks of the bienville subprovince and minto block which have been further subdivided into domains on the basis of reconnaissance geological mapping and geochronology and projected along strike using aeromagnetic anomalies to test the validity of the extrapolations u pb ages were obtained through shrimp analyses of zircon from 18 small archival samples selected from a suite of 2000 specimens collected during a helicopter reconnaissance survey conducted in the 1960s the results reveal a history of successive arc magmatism between 3 07 and 2 70 ga followed by metamorphism emplacement of crustally derived granites 2 702 2 685 ga and late hydrothermal events ca 2 65 ga in the northeastern minto block the douglas harbour domain previously extrapolated from dated localities to the northeast is substantiated through an age of 2 87 ga the older tonalitic crust is punctured by 2 734 2 725 ga granodioritic plutons of the leaf river suite that locally carry 3 01 ga inherited zircon the northern utsalik domain is made up of pyroxene and hornblende bearing leaf river plutons with consistent 2 725 2 723 ga ages and local inheritance of 2 82 and 2 77 ga however the southern extension of utsalik domain contains pyroxene bearing granodiorites both older 2 762 ga and younger 2 692 ga than the leaf river suite a tonalitic rock from the southern goudalie domain with an age of 2 833 ga supports a linkage to 2 84 2 83 ga units of the qalluviartuuq domain along strike to the north tikkerutuk domain represents a north trending 50 km wide calc alkaline magmatic arc with ages between 2 71 and 2 70 ga that extends southward into the bienville subprovince on the basis of aeromagnetic anomalies and geochronology zircon inheritance ages indicate that the tikkerutuk arc was built upon antecedent arcs of 2 84 2 77 and 2 725 ga the inukjuak domain in the west consists mainly of granite dated in one locality at 2 72 ga

generation and polybaric differentiation of east greenland early tertiary flood basalts major element trace element isotope and petrographic studies of magma diverentiation mantle melting the basal volcanics in the kangerdlugssuaq fjord region of the east greenland margin provide constraints on the generation and subsequent diverentiation and contamination histories of magmas during the early stage of continental rifting creating the north atlantic ocean basin most primitive lavas of the succession are introduction shown to have accumulated olivine corrections for crystal ac the distinctive geochemical features of continental flood cumulation yield estimates for erupted primitive liquids with mgo basalts cfbs are strongly controlled by the composition contents between 9 and 13 wt the occurrence of suspended and structure of the continental lithosphere and underfo88 olivine phenocrysts further requires the existence of parental lying mantle significant controversy remains concerning magmas with mgo contents up to 17 wt and feo contents up the balance of contributions from the lithosphere and to 14 wt quantitative modeling of fractionation indicates the mantle and the mechanisms by which the various that kangerdlugssuaq magmas primarily diverentiated at moderate source components contribute to basalt petrogenesis pressures 8 kbar to form dunitic and wehrlitic cumulates at how are basalt compositions influenced by generation depths of 25 km evolved east greenland flood basalts from the in anomalous regions in the deep mantle plumes by scoresby sund region record a more complex fractionation history interaction between rising magmas and the continental involving olivine clinopyroxene fractionation in the lower crust lithospheric mantle and by contamination with conas found for the lower basalts followed by olivine plagioclase tinental crust how are the diverentiation con clinopyroxene fractionation at shallow crustal levels cor tamination magma mixing and storage histories of cfbs relations between sio2 incompatible elements and sr nd isotopic controlled by the structure of the continental lithosphere ratios for the lower basalts are consistent with bulk assimilation and how do the thermal and chemical features of the of up to 15 20 archean leucogneiss with unradiogenic sr and mantle and the extensional history of the continental nd isotopic ratios characteristic of lewisian type lower crust lithosphere avect mantle melting and compositions of comparisons between inferred magma types for lower basalts and primary liquids estimated primary liquids from elsewhere in the north atlantic these questions are best addressed in the context of show complex relationships among feo mgo tio2 contents a geologically and geochemically well constrained cfb and cao al2o3 ratios that relate to regional and temporal changes province such as the north atlantic tertiary province in mantle temperatures lithospheric thickness and involvement of separation of east greenland from northern europe in at least two end member mantle sources we postulate that the the early tertiary at 60 myr ago was accompanied by lower basalts of east greenland were derived from iron poor voluminous volcanic activity the blosseville coast of mantle depleted by prior melt extraction and distinct from morb east greenland extending from kangerdlugssuaq fjord source mantle that was enriched in tio2 and lrees by a to scoresby sund fig 1 contains spectacularly exposed metasomatic event shortly before early tertiary magmatism we sections of lavas these sections begin at the basal contact associate this depleted mantle source with the ancestral iceland of the lavas with underlying cretaceous tertiary sediments and archean basement and continue to the plume anomaly

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

the habit and origin of siderite spherules in the eocene coal bearing prestfjall formation faroe islands abstract siderite spherules are described and chemically analysed from two localities holi i helli section and rokhagi coal mine within the coal bearing prestfjall formation the formation marks a significant hiatus in the eruption of lava flows of the paleogene faroe islands basalt group and shortly follows the paleocene eocene thermal maximum the spherules are chemically pure although feco 3 80 6 99 2 mol shows a marked substitution for mnco 3 0 1 13 9 mol the low concentrations of mgco 3 0 0 0 4 mol and the lack of associated sulphide minerals e g pyrite confirm the freshwater lake environment affinity of the formation the siderite spherules from the holi i helli section contain significantly higher concentrations of mnco 3 3 may also account for the abundance of siderite spherules formed by the split crystal process in the holi i helli section whereas prefect spherules consisting of individual crystals growing concentrically around a cryptocrystalline centre are dominant from the rokhagi coal mine

integrated wide angle and near vertical subbasalt study using large aperture seismic data from the faeroe shetland region acquiring large aperture seismic data 38 km maximum offset along a profile crossing the faeroe shetland basin in the north atlantic enables us to use wide angle reflections and refractions in addition to conventional streamer data 0 6 km for subbasalt imaging the wideangle results are complemented and confirmed by images obtained from the conventional near vertical offset range traveltime tomography applied to the wide angle data shows a low velocity layer 3 5 4 5 km s underneath southeastward thinning lava flows suggesting a 2 5 3 0 km thick sedimentary layer the velocity model obtained from traveltime tomography is used to migrate wide angle reflections from large offsets that arrive ahead of the water wave cone the migrated image shows base basalt and sub basalt reflections that are locally coincident with the tomographic boundaries application of a new multiple suppression technique and controlled stacking of the conventional streamer data produces seismic sections consistent with the wide angle results prestack depth migration of the near vertical offsets shows a continuous base basalt reflection and a clearly defined termination of the basalt flows

new paleomagnetic pole and magnetostratigraphy of faroe islands flood volcanics north atlantic igneous province abstract a paleomagnetic sampling was carried out along four sections altogether 86 lava flows 548 samples in the north atlantic igneous province outcropping in faroe islands denmark the four polarity zones in the 700 m thick exposed part of the faroes lower formation can be correlated with the geomagnetic polarity time scale as c26n c25r c25n c24r the seven lava flows erupted during c25n indicate a very low eruption rate in the upper part of the faroes lower formation of 1 70 kyr the faroes middle and upper formations composite thickness 2300 m are all reversely magnetized corresponding to c24r the eruption rate at the onset of middle formation volcanism was very high as evidenced by several thick lava sequences recording essentially spot readings of the paleomagnetic field the shift in eruption rate between the faroes lower and middle formations and evidence that onset of the faroes middle formation volcanism took place in c24r are of particular importance placing onset of middle formation volcanism in close temporal relation to north atlantic continental break up and the late paleocene thermal maximum after grouping flows recording the same field directions we obtained 43 independent readings of the paleomagnetic field yielding a paleomagnetic pole with coordinates 71 4 n 154 7 e a95 6 0 k 14 n 43 age 55 58 ma the pole is supported by a positive reversal test paleosecular variation estimated as the angular standard deviation of the virtual geomagnetic pole distribution 21 7 3 9 2 8 is close to expected for the given age and paleolatitude our new faroes paleomagnetic pole is statistically different from the majority of previously published poles from the british and faroes igneous provinces and we suggest that these older data should be used with care

episodic volcanism during break up of the north atlantic evidence from the east greenland plateau basalts abstract the lower tertiary upper paleocene lower eocene plateau basalts in the scoresby sund region of east greenland formed during three distinct magmatic episodes the activity of the first episode was centred in the present inland areas to the northwest and produced a voluminous regional basalt sequence lower sequence the activity of the second episode was centred to the southeast offshore the present atlantic coast and this also produced a voluminous regional basalt sequence upper sequence the third episode was centred on the atlantic coast and gave rise to a dense coastal dyke swarm and local lavas which are now only locally preserved by downfaulting the lavas are all tholeiitic basalts after an initial phase the two regional lava sequences of the first and second episodes show a similar vertical compositional zonation pattern a thin lower formation with variable composition is followed by a thick uniform formation which shows systematic compositional change with height from tio2 rich feti basalts to tio2 poor basalts and ending with a reversal to tio2 rich basalts each of these cyclic patterns apparently resulted from a temporary rifting episode and much of the compositional variation found can be explained by magma development in open magma chambers the dykes and lavas of the third episode of activity have chemical affinities to ocean floor basalts and their tio2 p2o5 ratios indicate formation at a spreading ridge centre the pattern of two failed rifting episodes and one event that produced oceanic crust can be correlated with stages in the complicated initiation of seafloor spreading in the region and the volcanism itself is closely related to this process

the stratigraphy and structure of the faroese continental margin this paper presents a summary of the stratigraphy and structure of the faroese region as the faroese area is mostly covered by volcanic material the nature of the pre volcanic geology remains largely unproven seismic refraction data provide some indications of the distribution of crystalline basement which probably comprises archaean rocks with the overlying cover composed predominantly of upper mesozoic cretaceous and cenozoic strata the cenozoic succession is dominated by the syn break up faroe islands basalt group which crops out on the faroe islands where it is up to 6 6 km thick and shelf areas post break up sediments are preserved in the adjacent deep water basins including the faroe shetland basin seismic interpretation of the post volcanic strata shows that almost every sub basin in the faroe shetland basin has been affected by structural inversion particularly during the miocene these effects are also observed on the faroe platform the munkagrunnur ridge and the fugloy ridge where interpretation of low gravity anomalies suggests a large scale fold pattern the structure of the iceland faroe ridge which borders the nw part of the faroe area remains ambiguous the generally thick crust together with the absence of well defined seawards dipping reflectors may indicate that much of it is underlain by continental material

influence of diel biogeochemical cycles on carbonate equilibrium in a karst river abstract variations in temperature photosynthesis and respiration force diel variations in ph and dissolved co 2 concentrations of surface streams possibly controlling carbonate equilibrium between river water and carbonate stream beds diel cycles of water chemistry and 13 c of dissolved inorganic carbon dic were measured to assess how biogeochemical processes affect dissolution and precipitation of calcite and thus channel development in ichetucknee river a large spring fed river discharge 6 m 3 s flowing over carbonate karst terrain in north central florida usa samples were collected at a 4 h sampling interval during two one week periods and at a 1 h interval during a single 24 h period simultaneously temperature ph dissolved oxygen do and no 3 concentrations were measured using in situ sensors at 15 min or 1 h intervals ca 2 dic and no 3 concentrations decreased during the day and increased at night causing diel changes of in stream specific conductivity these changes were inversely related to diel changes in ph pco 2 and do concentrations this work shows that photosynthesis and respiration of subaquatic vegetation are the dominant processes influencing in stream diel variation during the day a simultaneous increase of 13 c dic and decrease in dic indicates that photosynthesis was the primary control on dic concentrations calcite saturation indices ranged from 0 to 0 5 with the highest value in daylight as a result of co 2 consumption causing carbonate precipitation the water remained saturated with respect to calcite at night and 13 c dic values decreased indicating that co 2 production from ecosystem respiration was the dominant process affecting dic concentrations but was insufficient to induce significant carbonate dissolution at night outgassing maintained in stream dic concentrations lower than the supersaturated dic springs source but a drop in 13 c dic indicates that ecosystem respiration had a dominant influence over outgassing although co 2 outgassing occurs it is shown to be a minor component of the dic mass balance while carbonate precipitation represents 88 of dic loss these results indicate that in stream biological processes influence carbonate mineral diagenesis in large clear water rivers

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

ambient noise tomography reveals basalt and sub basalt velocity structure beneath the faroe islands north atlantic abstract ambient noise tomography is applied to seismic data recorded by a portable array of seismographs deployed throughout the faroe islands in an effort to illuminate basalt sequences of the north atlantic igneous province as well as underlying sedimentary layers and precambrian basement rayleigh wave empirical green s functions between all station pairs are extracted from the data via cross correlation of long term recordings with phase weighted stacking implemented to boost signal to noise ratio dispersion analysis is applied to extract inter station group travel times in the period range 0 5 15 s followed by inversion for period dependent group velocity maps subsequent inversion for 3 d shear wave velocity reveals the presence of significant lateral heterogeneity up to 25 in the crust main features of the final model include i a near surface low velocity layer interpreted to be the malinstindur formation which comprises subaerial compound lava flows with a weathered upper surface ii a sharp velocity increase at the base of the malinstindur formation which may mark a transition to the underlying beinisvor formation a thick laterally extensive layer of subaerial basalt sheet lobes iii a low velocity layer at 2 5 7 0 km depth beneath the beinisvor formation which is consistent with hyaloclastites of the lopra formation iv an upper basement layer between depths of 5 9 km and characterized by s wave velocities of approximately 3 2 km s consistent with low grade metamorphosed sedimentary rocks v a high velocity basement with s wave velocities in excess of 3 6 km s this likely reflects the presence of a crystalline mid lower crust of archaean continental origin compared to previous interpretations of the geological structure beneath the faroe islands our new results point to a more structurally complex and laterally heterogeneous crust and provide constraints which may help to understand how continental fragments are rifted from the margins of newly forming ocean basins

early cenozoic saucer shaped sills of the faroe islands an example of intrusive styles in basaltic lava piles abstract the early cenozoic igneous activity of the north atlantic igneous province that generated widespread sill complexes in sedimentary basins at the nw european margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the faroe islands the faroe island basalt group comprises seven formations with a total thickness of about 6 5 km of which four major formations are built up of tholeiitic lava flows each being several hundred metres thick and three thinner formations are mostly built up of volcaniclastic lithologies each being a few metres to a few tens of metres thick the largest sills are exposed as partly saucer shaped bodies in the three uppermost formations where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows numerous subvertical and moderately inclined dykes ranging in thickness from c 0 5 to c 4 0 m intersect the areas affected by sill intrusion but only inclined dykes or sheets have been positively identified as sill feeders locally controlled rotations of least principal stress axes 3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions

morphologies and emplacement mechanisms of the lava flows of the faroe islands basalt group faroe islands ne atlantic ocean the palaeogene faroe islands basalt group fibg comprises three eruptive sequences or formations all emplaced into a subaerial environment during the development of the extensive continental flood basalt province that stretches from east greenland through the faroe islands and into the faroe shetland basin the beinisvor formation having a tabular classic facies architecture is composed of a sequence of simple flows each comprising a single sheet lobe the beinisvor formation is overlain by the distinctly contrasting malinstindur formation that has a compound braided facies architecture the enni formation occurs at the top of the sequence and consists of a mixture of simple and compound flows with tabular classic and compound braided facies architectures respectively surface and internal characteristics of the sheet lobes of the beinisvor and enni formations indicate emplacement through inflation which is more obvious for the tube fed compound flows of the malinstindur and enni formations the difference between the simple and compound flow sequences of the fibg is most likely linked to the manner in which the lava was supplied during the eruption and the eruptive style of the volcanic system the sheet lobes were erupted over laterally extensive areas from fissure systems which had a continuous supply of lava which contrasts with the tube fed compound flows which were erupted in a gradual piecemeal manner from point sourced low shield volcanoes with limited areal extents

volcanic ash deposits of early eocene age from the rockall trough the stratigraphy of the rockall trough fig 1 has proved difficult to elucidate because a mantle of recent sediments usually prevents piston corers and dredges from sampling older accumulations although a seismic stratigraphy has been erected1 2 considerable uncertainty surrounds the history of sedimentation and consequently the petroleum potential of the region the upper 500 1 000 m of the succession are clearly cenozoic deposits whose distribution has been strongly influenced by movements of norwegian sea overflow water1 deeper in the section major current controlled accumulations are absent a feature observed elsewhere in the atlantic1 in view of the paucity of samples from these older deposits3 we report here the recovery of sediments that were laid down in the northern rockall trough before polar waters radically changed the depositional regime the sediments record a period of explosive volcanicity during the early eocene in the vicinity of the wyville thomson ridge

pan african rifting and orogenesis in southern to equatorial africa and eastern brazil abstract the upper proterozoic pan african belts of africa and brasiliano belts of south america are assumed to have evolved from an elaborate system of continental rifts which formed on the west gondwana continent 1100 1000 ma ago reviews of the damara belt kaoko belt gariep belt saldania belt west congolian belt lufilian arc and zambezi belt of southern and equatorial africa and the ribeira mantiqueira belt of brazil show the applicability of the continental rifting model to all these belts strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the west congolian belt as traditionally described is incomplete and has to be supplemented by the mayumbian belt and a rift structure situated farther to the west the lufilian arc is assumed to have evolved from two rift structures separated from each other by the later domes region the golfe du katanga which branches off northeastwards from the lufilian arc is interpreted as an aulacogen shaba aulacogen the pan african brasiliano rift system is comparable to the mesozoic arctic north atlantic rift system with regard to size and distribution of rifts ocean floor spreading and opening of a proto south atlantic ocean most probably occurred along a main line of rifting situated between the west coast of africa and eastern brazil the wedge like ocean may have terminated at the sao francisco congo cratonic bridge between northeastern brazil and gabon cameroon there is no evidence of ocean floor spreading in the zambezi belt the lufilian arc and the traditional west congolian belt which are arranged along another major line of rifting closure of the pan african brasiliano rift system took place during two successive orogenic episodes the zambezi belt lufilian arc and west congolian belt underwent their main orogenic deformation with prevailing ene and wsw oriented tectonic transportation directions during the katangan episode at 900 750 ma the transcontinental sinistral mwembeshi shear zone adjusted opposite movement directions in the zambezi belt and lufilian arc and at its western prolongation concurrently supported opening of the khomas trough in the southern damara belt the proto south atlantic ocean still opening during the katangan episode was gradually closed during the damaran episode at 750 500 ma closure proceeded from north to south and was accompanied by northwest directed subduction underneath the brazilian plate and southeast directed tectonic transportation in the kaoko damara and gariep belts in the previously formed west congolian belt lufilian arc and zambezi belt a second deformation phase characterized by strike slip faulting and local emplacement of nappes occurred during this episode

neoproterozoic granulite facies metamorphism and coeval granitic magmatism in the brasilia belt central brazil regional implications of new shrimp u pb and sm nd data abstract new shrimp u pb zircon ages combined with sm nd isotopic characteristics of granulites and associated granitic rocks of the anapolis itaucu complex in the central southern part of the brasilia belt are presented and discussed in this study igneous crystallization ages obtained in zircon grains of orthogranulite and granites vary between 760 and 650 ma growth of new zircon at ca 650 640 ma dates the high grade metamorphism zircon cores from paragranulites and granites give u pb ages between 2 0 and 0 8 ga tdm model ages of the granulitic rocks fall into two age intervals 2 3 1 9 and 1 7 1 4 ga end t values are negative varying between 9 29 and 1 42 shrimp u pb ages of zircon cores indicate that the granulite sedimentary protoliths were deposited after 800 ma ago contradicting previous models which assigned paleoproterozoic or archean ages for these rocks their nd isotopic signature indicate that paleoproterozoic sources within the sao francisco craton as well as younger sources such as the goias magmatic arc contributed to the sediment infilling of the former basin the intrusive granites display nd model age pattern similar to that of the granulitic rocks with most tdm model ages ranging between 1 45 and 1 2 ga end t values are between 2 61 and 7 96 indicative of assimilation of older material by the original magma shrimp u pb data for the granite intrusions indicate that granitoids metamorphosed under amphibolite facies show strong inheritance between 2 1 and 0 8 ga and magmatic metamorphic age at ca 660 650 ma the syn granulite facies granitoid ana 1 gave magmatic and metamorphic ages of ca 650 ma without any discernible inheritance the growth of new zircon occurred at the same time of the high grade metamorphism probably related with the collision event between the goias magmatic arc to the west southwest and the sao francisco craton to the east the data suggest that the anapolis itaucu complex instead of representing the ancient sialic basement of the supracrustal rock units of the brasilia belt constitutes a neoproterozoic high grade metamorphic complex related with the evolution of the brasiliano orogen

crustal structure beneath the faroe islands and the faroe iceland ridge abstract we have mapped the transition from the continental faroe block the faroe islands and surrounding shelf to the thickened oceanic crust of the faroe iceland ridge in the north atlantic using the results of a detailed sea to land seismic profile with wide angle to normal incidence recordings of explosive and airgun shots fired at sea along the faroe iceland ridge interpretation of all available seismic and gravity data indicates that this aseismic ridge is composed of 30 3 km thick oceanic crust with a gradual transition to ancient continental crust from 100 to 40 km northwest of the faroe islands close to the shelf edge this confirms that the crust beneath the faroe islands which may be up to 46 km thick comprises continental material in agreement with previous seismic and geochemical results results suggest that the upper 5 2 0 7 km of the faroe crust consists of tertiary basalts generated during continental breakup overlying the continental crust beneath the lower crust where seismic constraint is poor may exhibit high seismic velocities 7 1 7 6 km s 1 which we attribute to underplating or intrusion by mafic melts during continental breakup in the early tertiary

palaeogene peraluminous magmatism crustal melting and continental breakup the erlend complex faeroe shetland basin ne atlantic well 209 3 1 located close to the centre of the tertiary erlend complex north of the shetland isles contains an unusual volcanic sequence in which thick basalts of n to t type morb affinity overlie highly peraluminous cordierite bearing dacites the dacites from the erlend complex are almost identical in terms of their petrography and major element trace element and isotope geochemistry to those of dacites from two previously described localities in the north atlantic and indicate the formation of the dacites by anatexis of aluminous upper crustal sediments which were probably pelitic in character the discovery of graphite in the erlend dacites suggests that carbonaceous shales may be implicated as parent material the geological settings of the erlend volcanic sequence and the other examples in the rockall trough and on the voring plateau correspond to intra continental pre break up rift systems underlain by thinned continental crust occurring close to the continental margin a possible petrogenesis for the dacites involves the partial melting of upper crustal sediments as a result of the extensive contemporaneous basic magmatism documented to have occurred within a wide area of the north atlantic continental margins during the initial stages of continental break up this mechanism suggests that the observed volcanic sequence may be more common than is obvious from the present very limited drilling evidence

large scale magmatic pulses drive plant ecosystem dynamics the 6 6 km gross thickness of the palaeogene lava field of the faroe islands basalt group was erupted in the initial phases of north atlantic rifting thin interlava sedimentary rocks yield palynofloras that vary in composition and diversity with the duration of the interlava period long term trends in plant ecological succession occur within the record each reflecting initially rapid and subsequently slowing eruption tempo tio 2 and mgo plots derived from the basalt lava flows show corresponding fractionation trends these link melt column processes to vegetation ecosystem dynamics via controls on eruption tempo thermal support and substrate disturbance supplementary material further data are available at www geolsoc org uk sup18538

diel patterns of algae and water quality constituents in the san joaquin river california usa abstract the san joaquin river sjr is a hypereutrophic river that contributes to hypoxia in the downstream stockton deep water ship channel oxidizable materials in the form of algal biomass from upstream sources contribute to the hypoxic conditions especially from july to october our earlier work demonstrated the existence of strong chlorophyll a diel cycles which complicated the calculation of algal loads for the watershed scale monitoring program necessary to address the total maximum daily load tmdl for dissolved oxygen do the purpose of this study was to determine if diel patterns existed for other water quality constituents and to determine the role of algal growth dynamics in driving these diel changes studies conducted between 30 june and 15 october 2004 evaluated temporal changes for several water quality constituents over four 48 h studies at two sites along the mainstem of the sjr strong diel 24 h patterns were observed for chlorophyll a and pheophytin a algal pigments temperature do ph dissolved inorganic nitrogen din nh4 n no3 n soluble reactive phosphorus srp and volatile suspended solids vss patterns of din and srp were inverse of those observed for algal pigments temperature do ph and vss the observed diel patterns of algal pigments and temperature were greater in the beginning of the summer june july and diminished by the end of summer september october due to the decreased photoperiod within a 24 h period the fluctuations observed in algal pigments and nutrients suggest that growth of algae during daylight hours and depletion at night are largely responsible for the observed diel patterns due to the observed diel variability in these water quality constituents the samples collected for tmdl programs may not be representative unless samples are collected at the daily mean for a system

determining magma flow in sills dykes and laccoliths and their implications for sill emplacement mechanisms three dimensional seismic data from the faeroe shetland basin provides detailed information on the relationships between sills dykes laccoliths and contemporaneous volcanic activity the data shows that sills are predominantly concave upwards being complete or partial versions of radially or bilaterally symmetrical forms that possess flat inner saucers connected to a flat outer rim by a steeply inclined sheet such morphologies are only partially modified by pre existing faults sills can be sourced from dykes or the steep climbing portions of deeper sills both sills and dykes can provide magma to overlying volcanic fissures and sills can be shown to feed shallow laccoliths magma flow patterns as revealed by opacity rendering suggest that sills propagate upwards and outwards away from the magma feeder as an individual sill can consist of several leaves emplaced at different stratigraphic levels and as a sill or dyke can provide magma to volcanic fissures other sills and laccoliths the data suggests that neutral buoyancy concepts may not provide a complete explanation for the mechanism and level of sill emplacement instead the data suggests that the presence of lithological contrasts particularly ductile horizons such as overpressured shales may permit sill formation at any level below the neutrally buoyant level

onshore evidence for progressive changes in rifting directions during continental break up in the ne atlantic abstract current models for the palaeogene aged continental break up in the north atlantic invoke a nw se extension vector throughout the rift to drift process accommodated by margin parallel normal faults and margin oblique strike slip transfer zones however palaeogene and younger faults in the faroe islands provide evidence for a progressive anticlockwise rotation in extension vectors immediately prior to and following north atlantic break up six deformation stages are recognized 1 east west to ne sw extension accommodated by dip slip north south and nw se trending faults 2 continued ne sw extension accommodated by nw se and nne ssw oriented dykes 3 north south extension accommodated by ene wsw and ese wnw conjugate dykes 4 crustal extrusion involving both east west shortening and further north south extension along ene wsw dextral and ese wnw sinistral conjugate strike slip faults 5 during the final stages of rifting the regional extension vector became nw se and was accommodated predominantly by slip along ne sw dextral oblique slip faults 6 pre existing structures were locally reactivated as tensional and extensional shear features characterized by the entrainment of clastic material along fault planes the present study reveals a distinct period of margin parallel extension immediately prior to break up that is not accounted for by existing models illustrating the importance of conducting field based studies to validate otherwise widely accepted margin scale models worldwide

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

evolution of polycyclic basement complexes in the aracuai orogen based on u pb shrimp data implications for brazil africa links in paleoproterozoic time paleoproterozoic basement of the aracuaorogen is composed of amphibolite and granulite facies orthogneiss units known as mantiqueira and juiz de fora complexes six u pb shrimp crystallization ages for the mantiqueira complex range from 2137 19 to 2041 7 ma studied samples are characterized by the abundance of inherited archean zircon grains tdm model ages ranging from 2 9 to 3 2 ga and strongly negative end t 9t o 13 gneiss protholits were mainly generated by partial melting of older continental material and the mantiqueira complex is related to active margin and syn collisional magmatism high grade gneiss samples of the juiz de fora complex yields crystallization ages of 2119 16 and 2084 13 and inherited zircon grains are absent this plutonic unit much probably evolved within an oceanic magmatic arc setting or on a very stretched continental crust the mantiqueira and juiz de fora complexes together with the kimezian basement of the west congo belt were parts of a paleoproterozoic orogenic system disrupted and deeply reworked during the evolution of the aracuacongo orogen neoproterozoic metamorphic overprint is dated at ca 590 574 ma 2007 elsevier b v all rights reserved

kinematic evolution of the aracuai west congo orogen in brazil and africa nutcracker tectonics during the neoproterozoic assembly of gondwana abstract the neoproterozoic aracuai west congo a wc orogen is one of many brasiliano pan african orogens that developed during the assembly of west gondwana this orogen was split apart in mesozoic time due to opening of the south atlantic the aracuai orogen now underlies eastern brazil whereas the west congo belt fringes central africa s atlantic coast significantly at the time it formed the a wc orogen was bounded on the west north and east by the sao francisco congo craton a crustal block that had the shape of a lopsided upside down u thus the orogen was partially confined during tectonism in that it occupied an enclave surrounded on three sides by cratonic crust formation of the a wc orogen resulted in kinematically complex deformation substantial crustal shortening and production of a large volume of magma how such features could develop in this particular setting has long been a mystery our field studies in the aracuai orogen together with published data on the west congo belt characterize the kinematic picture of the a wc orogen and lead to a tectonic model that addresses its evolution in our model the a wc orogen formed in response to closure of the macaubas basin this basin was underlain by oceanic crust in the south but tapered northward into a continental rift which terminated against the cratonic bridge linking the eastern and western arms of the sao francisco congo craton closure occurred when the western arm now the sao francisco craton rotated counterclockwise towards the eastern arm now the congo craton this closure may have been driven by collision of the paranapanema amazonian and kalahari cratons against the external margins of the sao francisco congo craton rather than by slab pull associated with subduction of the macaubas basin s floor thus the process of forming the a wc orogen resembled the process of crushing of a nut between two arms of a nutcracker such nutcracker tectonics led to a series of kinematically distinct deformation stages initially internal portions of the orogen flowed northwards then substantial crustal thickening occurred in the orogen s interior and the deformation front migrated outwards producing thrust belts that overlapped the internal margins of the craton with continued closure space in the enclave became restricted and the orogen s interior underwent lateral escape to the south late stage extensional collapse triggered both production of late to post collisional granites and exhumation of high grade rocks from mid crustal levels

the granulite facies rocks of the northern segment of the ribeira belt eastern minas gerais se brazil abstract granulite rocks are exposed in eastern minas gerais brazil its early neoproterozoic evolution is characterised by a history of an active continental margin including the accretion of suspect terranes the manhuacu terrane is one of those which is represented by a granitic continental plutonic arc and terrigeneous metasediments reflecting a continental margin a metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavolcanic and metaplutonic mafic rocks was interpreted as an extensive tectonic segment with suspect development in a back arc setting fragments of a volcanic arc are identified and interpreted as an evidence for a probable island arc domain the granulites occur as massive rocks as well as high grade gneisses and show lithological structural and metamorphic attributes consistent with their host belt type in the western portion granulites derived from sedimentary protoliths have been deposited deformed and metamorphosed together with the mafic intrusions and as well as with their crystallization regional uplift exposed these rocks probably immediately after the metamorphism in these belts the metamorphic grade is not uniform especially where uplifting has exposed oblique cross sections over the granulitic rocks geothermobarometric calculations indicate that the granulites has been generated under t conditions between 800 and 990 50 c and from medium 4 8 kb to relatively high 10 0 kb pressures

geochemistry water balance and stable isotopes of a clean pit lake at an abandoned tungsten mine montana usa abstract the calvert mine is a small tungsten rich scheelite skarn deposit in a remote mountainous region of southwest montana usa the open pit mine closed in the 1970s and subsequently flooded to form a pit lake that is roughly conical in shape 30 m deep and 120 m in diameter with no surface inlet or outlet the lake is holomictic with a groundwater flow through hydrology and an estimated residence time of 2 5 5 y water isotopes show that the lake is at an approximate steady state with respect to water balance and has experienced 30 evaporation the lake has a near neutral ph exceptional clarity and extremely low concentrations of nutrients sulfate and most metals including tungsten manganese concentrations are slightly elevated and increase with depth towards the sediment water interface despite seasonally anoxic conditions in the deep water dissolved fe concentrations are orders of magnitude lower than mn suggesting that insufficient organic carbon is present in the sediment of this oligotrophic lake to drive bacterial fe reduction based on stable isotope fingerprinting diffuse seepage that enters a nearby headwater stream at the base of a large waste rock pile can be directly linked to the partially evaporated pit lake however this seepage has neutral ph and low metal concentrations and poses no threats to the environment stable isotopes of dissolved inorganic carbon dic and dissolved oxygen do are used to track the relative importance of photosynthesis and respiration with depth in summer a zone of high productivity exists near the base of the chemocline releasing do that is isotopically light respiration exceeds photosynthesis below the secchi depth which causes do concentrations to approach zero towards the bottom of the lake in winter thick ice and snow cover prohibits photosynthesis however because of the low nutrient content most of the volume of the lake remains oxic through the winter overall the calvert lake is a good example of a pit lake formed from metal mining that has excellent water quality which is a result of its favorable geology paucity of sulfide minerals and hydrology flow through lake with short residence time in a temperate climate

the cretaceous opening of the northeast atlantic abstract a continuous rift system from the rockall trough through the faeroe shetland channel and the more and voring basins up to the tromso and bear island basins is inferred to have developed during the cretaceous oceanic crust was generated in its southern part but its width presumably decreases toward the northeast and probably ends in the more basin this rift spreading system requires a clockwise rotation of greenland and the rockall plateau during the cretaceous around a rotation pole at its northern end at about 74 n 21 e north of the pole of rotation crustal shortening must have occurred this compression is interpreted to have taken place on west spitsbergen the orogeny there is reinterpreted as 1 1 a cretaceous folding phase 2 2 a phase of overthrusting at the paleocene eocene boundary and 3 3 an extensional faulting phase during the oligocene this plate tectonic model can resolve a series of problems in the northeast atlantic region the connection of the caledonian fronts of scotland and greenland can be easily established the northern ends of the west shetland basin and the north sea graben the unusual depth of the more and voring basins the marked obliqueness of structural trends between the northeast greenland shelf and the norwegian shelf the fact that the western hammerfest basin was intersected by a younger north south trending graben which formed the deep tromso basin all these enigmatic observations can be explained by the cretaceous rift system

archean and paleoproterozoic crust of the sao francisco craton bahia brazil geodynamic features abstract recent geological geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the sao francisco craton in bahia the oldest is the gaviao block in the wsw part of the studied area and comprises granitic granodioritic and migmatitic continental crust including remnants of 3 4 ga ttgs which are amongst the oldest rocks in south america and are associated with archean greenstone belts the youngest segment is exposed in the itabuna salvador curaca belt which extends from se bahia along the atlantic coast to salvador then northwards into ne bahia it is mainly composed of a low k calc alkaline plutonic suite and also contains strips of intercalated metasediments and ocean floor back arc basin gabbro and basalt in the ssw part of the area the jequie block comprises granulitic migmatites with inclusions of supracrustal rocks intruded by many charnockite plutons in the ne the serrinha block is composed of orthogneisses and migmatites which form the basement for paleoproterozoic greenstone belts during the paleoproterozoic transamazonian cycle these four crustal segments collided resulting in the formation of an important mountain belt the regional metamorphism resulting from the crustal thickening associated with the collision occurred at around 2 0 ga major mineralizations were formed during the evolution of the four archean blocks and also during and after the paleoproterozoic collision

coupled control of land uses and aquatic biological processes on the diurnal hydrochemical variations in the five ponds at the shawan karst test site china implications for the carbonate weathering related carbon sink abstract high resolution hydrochemical data from five spring fed ponds are presented to demonstrate the effect of different land uses and aquatic biological processes on the carbon cycle at a karst analog test site the results show that hydrochemical parameters including ph and the concentrations of hco 3 ca 2 no 3 partial pressures of co 2 p co 2 and dissolved o 2 do as well as carbon isotopic compositions 13 c of hco 3 in the pond water all displayed distinct diurnal variations while those of the spring water itself were rather stable the coupled dynamic behaviors of p co 2 do and no 3 indicate a significant influence from the metabolism of submerged plants in the ponds in the afternoon when photosynthesis is the strongest the p co 2 of the five pond waters was lower even than that of the ambient atmosphere demonstrating the existence of a biological carbon pumping bcp effect similar to that in the oceans it was determined that in october autumn the bcp fluxes in the five spring fed ponds were 156 51 t c km 2 a 1 in p1 pond 1 adjoining a bare rock shore 239 83 t c km 2 a 1 in p2 adjoining uncultivated soil 414 139 t c km 2 a 1 in p3 adjoining land cultivated with corn 493 165 t c km 2 a 1 in p4 adjoining grassland and 399 124 t c km 2 a 1 of p5 adjoining brushland indicating the potentially significant role of aquatic photosynthesis in stabilizing the carbonate weathering related carbon sink in addition by comparing the dic concentrations and fluxes of dic transformed into autochthonous organic matter aoc in the five ponds the so called dic fertilization effect was found in which more aoc is produced in pond waters with higher concentrations of dic this implies that the carbon cycle driven by aquatic biological processes can be regulated by changing land use and cover the latter determining the dic concentrations further the rock weathering related carbon sink is underestimated if one only considers the dic component in surface waters instead of both dic and aoc

a refraction seismic transect from the faroe islands to the hatton rockall basin 1 the crustal structure of the faroe rockall plateau was studied by a 790 km long refraction seismic transect consisting of two intersecting lines the air gun shot spacing was 200 m and the signals were recorded by 77 ocean bottom seismometers a p wave velocity model was developed from forward and inverse modeling of the wide angle seismic data and incorporation of coincident multichannel reflection seismic data continental crust with velocities ranging from 5 6 to 6 8 km s can be traced from the faroe islands across the banks to the sw of the faroes and into the hatton rockall basin the thickness of the subvolcanic crust is up to 25 km on the banks but is as little as 8 km in the channels between the banks the thinning in the channels may be related to nw trending shear zones extending from major lineaments in ne rockall trough basalt layers are found along the entire transect with a total thickness of up to 4 km two layers with velocities of 4 9 5 2 and 5 3 5 6 km s are thought to represent paleogene flood basalts that can be correlated from the faroe islands to george bligh bank close to george bligh bank an 80 km wide and up to 9 km thick body with velocities of 6 5 km s is interpreted as intrusion a 5 km thick high velocity lower crustal layer 7 3 km s extends from the area of the intrusion into the northern hatton rockall basin at the northern flank of lousy bank the transition zone to oceanic crust was encountered

petrogenesis of the orthogneisses of the mantiqueira complex central ribeira belt se brazil an archaean to palaeoproterozoic basement unit reworked during the pan african orogeny abstract the occidental terrane of the central segment of the brasiliano pan african ribeira belt comprises two crustal scale thrust sheets andrel ndia and juiz de fora domains taken as reworked neoproterozoic products of the sao francisco cratonic margins pre 1 8 ga orthogneisses and associated rocks of the mantiqueira complex comprise the basement for rocks of the andrel ndia depositional cycle within the andrel ndia tectonic domain geochemical data indicate that the mantiqueira complex comprises rocks that can be grouped as follows intermediate to acid calc alkaline rocks and a transitional basaltic series on the basis of quantitative analysis of the lithogeochemical data these lithotypes cannot be related statistical and or petrological criteria made it possible to define suites and or groups within each one of those units and to constrain petrogenetic models based mostly on their ree data simple least square regression analysis indicates that the basic rocks are unlikely to constitute a single suite themselves the results of the geochemical modelling presented in this work suggest that crustal partial melting rather than fractional crystallisation is the most likely petrogenetic process associated with the rocks of the mantiqueira complex the partial melting processes might have taken place under oxidising conditions typical of tectonic settings associated with the generation of calc alkaline rocks

mantle thermal structure and active upwelling during continental breakup in the north atlantic seismic reflection and refraction data acquired on four transects spanning the southeast greenland rifted margin and greenland iceland ridge gir provide new constraints on mantle thermal structure and melting processes during continental breakup in the north atlantic maximum igneous crustal thickness varies along the margin from s 30 km in the near hotspot zone 6 500 km from the hotspot track to v18 km in the distal zone 500 1100 km magmatic productivity on summed conjugate margins of the north atlantic decreases through time from 1800 300 to 600 50 km 3 km ma in the near hotspot zone and from 700 200 to 300 50 km 3 km ma in the distal zone comparison of our data with the british faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist joint consideration of crustal thickness and mean crustal seismic velocity suggests that along margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature the thermal anomaly vt at breakup was modest v100 125 c varied little along the margin and transient data along the gir indicate that the potential temperature anomaly 125 50 c and upwelling ratio v4 times passive of the iceland hotspot have remained roughly constant since 56 ma our results are consistent with a plume impact model in which 1 a plume of radius v300 km and vt of v125 c impacted the margin around 61 ma and delivered warm material to distal portions of the margin 2 at breakup 56 ma the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin and 3 by 45 ma both the remaining plume head and the distal warm layer were exhausted with excess magmatism thereafter largely confined to a narrow 6 200 km radius zone immediately above the iceland plume stem alternatively the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre existing thermal anomaly unrelated to the plume fl 2001 elsevier science b v all rights reserved

zircon inheritance in diatexite granodiorites and its consequence on geochronology a case study in lusatia and the erzgebirge saxo thuringia eastern germany abstract we used detailed investigations of zircon morphology and internal structures for the interpretation of zircon age data of diatexite migmatites the fine and medium grained varieties of cadomian granodiorites from lusatia and the erzgebirge are interpreted on the base of their geological geochemical and isotope characteristics as well as zircon populations as migmatites where no segregation of melt from residuum occurred whereas coarse grained varieties contain a large proportion of new formed zircons with a limited age range 540 530 ma most zircons in medium and especially fine grained granodiorites seem to be inherited from their source rock with only a small proportion of new zircon material in form of rare single grains or overgrowths therefore we consider mean evaporation zircon ages from these rocks as mixed ages consequently the formerly inferred age span of magmatic activity from 587 17 to 542 9 ma and the interpretation of three successive magmatic episodes kroner et al geol rundsch 83 1994 357 reported values of 585 563 and 542 ma have to be reconsidered as a mixture of two successive magmatic events i the late cadomian event about 540 530 ma that formed the granodiorites and ii a former magmatic event about 580 570 ma in the source indicated by inherited zircons

tertiary compressional structures on the faroe rockall plateau in relation to northeast atlantic ridge push and alpine foreland stresses abstract a number of compressional anticlinal structures are identified in the western and northern part of the faroe rockall plateau these structures occur on that part of the faroe rockall plateau which was above sea level during the latest phase of paleocene plateau basalt extrusion three post basalt compressional phases have affected the plateau most of the compressional structures in the northern part of the plateau are related to ne sw to ene wsw oriented stress which we date to late paleocene early eocene the oligocene phase is interpreted as resulting from n s directed compressional stress which also mainly affected the compressional structures on the northern part of the plateau compressional stress from the northwest seemed to affect the whole of the faroe rockall plateau and we suggest it to be of miocene age it is proposed that during the late paleocene early eocene phase of compression local structure and anomalously oriented gravitational ridge push from the now extinct aegir axis contributed to a local ne sw compressional stress system the two later deformation phases were apparently connected to the regional northwest european stress system with small local modifications