closure of the tornquist sea constraints from mona lisa deep seismic reflection data deep seismic reflection profiles west of denmark across the suture between baltica and eastern avalonia reveal weak southward dipping reflectors within the crystalline basement these reflectors are interpreted as thrusts resulting from emplacement of ea

seismic velocity structure of crustal intrusions in the danish basin abstract we image the east and westward extent of a crustal high velocity body the thickness of a layered sequence around the moho at the flank of the body and the uppermost mantle velocity along the 320 km long refraction and wide angle reflection seismic profile estrid 2007 in the danish basin ray tracing modelling of the seismic data reveals a high velocity body 6 7 7 7 km s between 10 and 30 km depth with a lateral extent of at least 110 km it is interpreted as an intrusive body of gabbroic composition moho depth is variable between 30 and 35 km along the profile the crust is thin in a 180 km wide zone approximately below the western part of the intrusive body and further westward in the basin area the pn velocity in the uppermost mantle is relatively low 7 8 km s beneath the thin crust whereas higher pn velocities 8 0 km s are observed outside this zone the pmp reflection is characterized by reverberations ringing in the seismic signal in the zone with low pn velocity by 2d full waveform modelling these reverberations are explained by a layered transition zone around the moho consisting of intermixed crustal and mantle material the layering may be explained by magmatic intrusion along the moho over a lateral distance of 130 km away from the magmatic source which is located in the middle of the intrusive body these intrusive features may be related to extensional transtensional tectonism in the tornquist fan during the late carboniferous and early permian our new findings suggest a minimum volume of the intrusive body in the danish basin of about 60 000 km3 which is 20 000 km3 larger than interpreted from earlier data such a large intrusion must have affected the temperature field substantially and may have initiated the subsidence of the post permian danish norwegian basin

potential field imaging of palaeozoic orogenic structure in northern and central europe abstract the trans european suture zone tesz is the most fundamental lithospheric boundary in europe separating the ancient crust of the fennoscandian shield east european craton from the younger crust of central europe and extending deep into the mantle geophysical potential field images provide an overview of the entire palaeozoic orogenic system of northern and central europe for the first time the tesz is largely concealed by sedimentary basins of permian cenozoic age geological observations are largely restricted to local basement highs and deep boreholes and the coverage of deep seismic surveys is widely spaced despite experiments recently acquired within the europrobe programme by contrast the potential field data offer a relatively detailed coverage of standardised observations throughout the tesz while some features of the images may be sourced in the near surface particularly in the gravity image much of their content reflects the structure of the underlying palaeozoic basement at the scale presented the images highlight the most fundamental features of the crustal structure of the tesz these include the strong contrast between the highly magnetic crust of the east european craton and the less magnetic palaeozoic accreted terranes of central europe the lateral continuity of terranes and their internal structure particularly where arc magmatic complexes are involved and the location and geometry of the terrane boundaries oceanic sutures and strike slip zones that separate them

numerical models of tectonic deformation at the baltica avalonia transition zone during the paleocene phase of inversion abstract predictions from dynamic modelling of the lithospheric deformation are presented for northern europe where several basins underwent inversion during the late cretaceous and early cenozoic and contemporary uplift and erosion of sediments occurred in order to analyse the evolution of the continental lithosphere the equations for the deformation of a continuum are solved numerically under thin sheet assumption for the lithosphere the most important stress sources are assumed to be the late cretaceous alpine tectonics localized rheological heterogeneities can also affect local deformation and stress patterns present day observations available in the studied region and coming from seismic structural interpretations and stress measurements have been used to constrain the model our modelling results show that lateral variation in lithospheric strength below the basin systems in central europe strongly controls the regional deformation and the stress regime furthermore we have demonstrated that the geometry of the boundary between baltica and avalonia together with different rheological characteristics of the two plates had a crucial role on local crustal deformation and faulting regime resulting in the baltica avalonia transition zone from the s n alpine convergence

crustal memory and basin evolution in the central european basin system new insights from a 3d structural model abstract the central european basin system cebs is composed of a series of subbasins the largest of which are 1 the norwegian danish basin 2 the north german basin extending westward into the southern north sea and 3 the polish basin a 3d structural model of the cebs is presented which integrates the thickness of the crust below the permian and five layers representing the permian cenozoic sediments structural interpretations derived from the 3d model and from backstripping are discussed with respect to published seismic data the analysis of structural relationships across the cebs suggests that basin evolution was controlled to a large degree by the presence of major zones of crustal weakness the nw se striking tornquist zone the ringkobing fyn high rfh and the elbe fault system efs provided the borders for the large permo mesozoic basins which developed along axes parallel to these fault systems the tornquist zone as the most prominent of these zones limited the area affected by permian cenozoic subsidence to the north movements along the tornquist zone the margins of the ringkobing fyn high and the elbe fault system could have influenced basin initiation thermal destabilization of the crust between the major nw se striking fault systems however was a second factor controlling the initiation and subsidence in the permo mesozoic basins in the triassic a change of the regional stress field caused the formation of large grabens central graben horn graben gluckstadt graben perpendicular to the tornquist zone the ringkobing fyn high and the elbe fault system the resulting subsidence pattern can be explained by a superposition of declining thermal subsidence and regional extension this led to a dissection of the ringkobing fyn high resulting in offsets of the older nw se elements by the younger n s elements in the late cretaceous the nw se elements were reactivated during compression the direction of which was such that it did not favour inversion of n s elements a distinct change in subsidence controlling factors led to a shift of the main depocentre to the central north sea in the cenozoic in this last phase n s striking structures in the north sea and nw se striking structures in the netherlands are reactivated as subsidence areas which are in line with the direction of present maximum compression the moho topography below the cebs varies over a wide range below the n s trending cenozoic depocentre in the north sea the crust is only 20 km thick compared to about 30 km below the largest part of the cebs the crust is up to 40 km thick below the ringkobing fyn high and up to 45 km along the teisseyre tornquist zone crustal thickness gradients are present across the tornquist zone and across the borders of the ringkobing fyn high but not across the elbe fault system the n s striking structural elements are generally underlain by a thinner crust than the other parts of the cebs the main fault systems in the permian to cenozoic sediment fill of the cebs are located above zones in the deeper crust across which a change in geophysical properties as p wave velocities or gravimetric response is observed this indicates that these structures served as templates in the crustal memory and that the prerift configuration of the continental crust is a major controlling factor for the subsequent basin evolution

birth of a volcanic margin off argentina south atlantic 1 based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off argentina the segment under study is located between 44 s and 41 s we describe in detail the facies of the extrusive basaltic complexes across the margin these include single and multiple inner seaward dipping reflectors sdrs with varying architecture along the margin outer highs and outer sdr wedges a detailed interpretation of a transitional zone between the inner and outer sdr wedges is presented multiple inner sdrs are concentrated at the southern part of the margin segment while in the north only one steeply dipping wedge is present the dip of the inner sdr wedges changes along the margin and we propose subsidence by loading as main cause the transitional zone between the inner and outer sdr wedges becomes narrower toward the north by correlating with magnetic data we conclude that the emplacement of the 30 100 km wide multiple inner sdrs occurred episodically we propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple inner sdrs a scissor like opening of the margin segment resulted in different amounts of stretching along strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes the varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment

regional geological and tectonic structures of the north sea area from potential field modelling the spatial distribution of large scale crustal domains and their boundaries are investigated in the north sea area by combining gravity magnetic and seismic data the north sea is situated on the plates of three continents avalonia laurentia and baltica which collided during the caledonian orogeny in the middle palaeozoic the location and continuation of the collisional sutures are debated we apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures the transformations reveal intrinsic features of crustal transitions between the caledonian plates and their relation to later extensional structures the transformations include the hough transform applied to the gravity field calculation of fractional derivatives and integrals of the gravity and magnetic fields the pseudogravity field and the horizontal gradient field as well as upward continuation the results indicate a fundamental difference between the lithosphere of avalonia laurentia and baltica the location of the mesozoic rift system the central graben and viking graben may have been partly determined by the presence of the sutures between these three plate indicative of extensional reactivation of compressional structures a significant lineament across the entire north sea between scotland and north germany indicates that the lower crust of baltica provenance may extend as far south westward as to this lineament comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties this lineament could represent the suture between lithosphere of caledonian origin avalonia versus lithosphere of precambrian origin baltica in the lower crust and upper mantle if this is the case the lineament is the missing link in the reconstruction of the triple plate collision

seismic and gravity modelling of crustal structure in the central graben north sea observations along mona lisa profile 3 abstract high quality wide angle and deep normal incidence seismic data sets recorded during the mona lisa marine and onshore north sea acquisition for lithospheric seismic analysis experiment have allowed detailed crustal investigations in the area of the central graben and south eastern north sea to be conducted an integrated velocity density model based on a joint inversion of traveltimes and gravity data is presented for the crust and uppermost mantle along mona lisa line 3 which crosses the central graben approximately perpendicular to its strike direction this model shows pronounced crustal thinning and associated moho uplift beneath the deepest part of the central graben in the graben area moho is interpreted to be situated at 25 km depth and the crystalline crust is about a factor of 2 thinner than in the surrounding crustal provinces where moho is interpreted to reach depths between 32 and 36 km maximum thickness of the sedimentary column in the central graben is 10 11 km the mass deficit of the thick sediments is compensated by the moho uplift the modelled moho coincides with the base of lower crustal reflectivity observed in the coincident normal incidence seismic section good overall agreement between the integrated velocity density model and the normal incidence data is observed the migrated deep seismic reflection section recorded to 26 s traveltime contains deep west ward and east ward dipping events symmetric about the deepest part of the central graben these dipping upper mantle reflections may be linked to extensional processes that formed the central graben at least one of the upper mantle dipping reflectors may be a reactivated structure formed originally during caledonian collision

the legacy of the european geotraverse abstract the european geotraverse egt created a 4600 km profile across europe from north cape norway to tunisia not only did this produce the first comprehensive cross section to a depth of 450 km of continental lithosphere covering an eighth of the earth s circumference it covered the geological history of europe from the archaean to the present egt built up a detailed knowledge of the crust and upper mantle of europe by integrating geological and geophysical information in a coherent way continuously along a single profile it illuminated the dramatic contrast between the thickness and complexity of the lithosphere of western europe and that of fennoscandia which remain in isostatic equilibrium and elucidated the multilayered elements of thickened alpine crust and lithosphere and the dynamics of the western mediterranean nine years on the legacy of egt is the platform it provided for major scientific advances that have stemmed from it the greatest being through europrobe projects the pancardi project has discovered the subducted slab beneath the carpathian arc in the process of tearing apart from the lithosphere uralides has discovered the urals orogen is almost perfectly preserved since the palaeozoic and the tesz project has elucidated the complex evolution of the transitional region between the baltic shield and the caledonian and variscan crustal terranes of western europe the scientific advances of egt were matched by its achievement in mobilising an international workforce from every discipline of the earth sciences friendships made in that endeavour are another legacy of egt and many of those who started their research careers in egt are now leading europrobe projects and other collaborative ventures we all owe a great debt to professor stephan mueller who founded and led the european geotraverse and was its enduring inspiration

a new tectonic model for the laurentia avalonia baltica sutures in the north sea a case study along mona lisa profile 3 abstract we present a new model for the lithospheric structure of the transitions between laurentia avalonia and baltica in the north sea northwestern europe based on 2 d potential field modelling of mona lisa profile 3 across the central graben with constraints from seismic p wave velocity models and the crustal normal incidence reflection section along the profile the model shows evidence for the presence of upper and lower palaeozoic sedimentary rocks as well as differences in crustal structure between the palaeo continents laurentia avalonia and baltica our new model together with previous results from transformations of the gravity and magnetic fields demonstrates correlation between crustal magnetic domains along the profile and the terrane affinity of the crust this integrated interpretation indicates that a 150 km wide zone characterized by low grade metamorphosis and oblique thrusting of avalonia crust over baltica lower crust is characteristic for the central north sea area the magnetic susceptibility and the density across the coffee soil fault range from almost zero and 2715 kg m3 in avalonia crust to 0 05 si and 2775 kg m3 in baltica crust the model of mona lisa profile 3 indicates that the transition between avalonia and baltica is located beneath the central graben with a ramp flat ramp geometry our results indicate that the initial rifting of the central graben and the viking graben was controlled by the location of the caledonian collisional suture located at the coffee soil fault and that the deep crustal part of baltica extends further to the west than hitherto believed

seismic model of the crust and upper mantle in the scythian platform the dobre 5 profile across the north western black sea and the crimean peninsula the scythian platform scp with a heterogeneous basement of baikalian variscan cimmerian age is located between the east european craton eec on the north and the crimean caucasus orogenic belt and the black sea bs basin on the south in order to get new constrains on the basin architecture and crustal structure of the scp and a better understanding of the tectonic processes and evolution of the southern margin of the eec during mesozoic and cenozoic time a 630 km long seismic wide angle refraction and reflection warr profile dobre 5 was acquired in 2011 october it crosses in a w e direction the fore dobrudja trough the odessa shelf of the bs and the crimean plain the field acquisition included eight chemical shot points located every 50 km and recorded by 215 stations placed every 2 0 km on the land in addition the offshore data from existing profile 26 placed in the odessa shelf were used the obtained seismic model shows clear lateral segmentation of the crust within the study region on four domains the fore dobrudja domain km 20 160 an offshore domain of the karkinit trough at the odessa shelf of the bs km 160 360 an onshore domain of the central crimean uplift crimean plain km 360 520 and the indolo kuban trough at the kerch peninsula km 520 620 that is the easternmost part of the crimea two contrasting domains of the scp within the central part of the dobre 5 profile the karkinit trough and the central crimean uplift may represent different stages of the scp formation a deep karkinit trough with an underlying high velocity 7 16 km s 1 lower crust body suggests its rifting related origin during early cretaceous time the central crimean uplift represents a thick up to 47 km crustal domain consisting of three layers with velocities 5 8 6 4 6 5 6 6 and 6 7 7 0 km s 1 which could be evidence of this part of the scp originating on the crust of precambrian craton eec the thick heterogeneous basement of the central crimean uplift shows inclusions of granitic bodies associated with magmatic activity related with variscan orogeny within the scp general bending and crustal scale buckling of the central crimean uplift with a wavelength of 230 km could be an effect of the alpine compressional tectonics in the adjacent crimean mountains the extended rifted continental margin of the scp eec at the odessa shelf and buckling uplifted domain of the central crimean uplift affected by compressional tectonics are separated by the n s oriented western crimean fault the crust of the southern margin of the eec is separated from the scp which originated on the eec crust tectonised and reworked during the palaeozoic mesozoic by the crustal fault of w e orientation which corresponds with the golitsyn fault observed at the surface between the eec and the scp the fore dobrudja domain with a thick 10 km heterogeneous basement and two subhorizontal layers in the crystalline crust with velocities 6 2 6 3 and 6 4 6 65 km s 1 differs from the scp crust and its origin could be very similar to that of the trans european suture zone and palaeozoic west european platform

post permian evolution of the central north sea a numerical model abstract a dynamic thermomechanical model is presented for the post permian evolution of the central north sea including the central graben permo carboniferous and jurassic thermal events as well as triassic and jurassic extensional phases and late cretaceous shortening are considered the equations of force balance for a continuum and the transient heat equation are solved using the finite element method the lithosphere responds to applied forces by elastic deformation at low deviatoric stress levels fracture at low temperature and pressure conditions and nonlinear viscous flow at high temperature and pressure a first order rheological strain softening is incorporated to simulate a transition from strong to soft material behaviour such as a change from dislocation creep to diffusion creep seismic refraction and reflection data indicate crustal thinning below the central graben by a factor of 2 while the triassic rifting appears to have been associated with a more distributed deformation pattern the upper jurassic rifting is more localised pure shear extensional models have been advocated to explain this however dipping seismic reflectors in the upper mantle indicate that simple shear could be important the strain softening of the present model allows for modelling of strain localisation during the upper jurassic rifting phase and detailed modelling of moho structures the present model accounts for the main structural and stratigraphic observations in the central north sea furthermore the results indicate that in the part of the central north sea investigated in this paper a pure shear regime in triassic changed into a simple shear dominated regime with mantle shear zones developing during late jurassic extension

palaeozoic terranes and their lithospheric boundaries within the trans european suture zone tesz a review the trans european suture zone tesz is a broad and complex zone of terrane accretion separating ancient lithosphere of the baltic shield and east european craton eec from the younger lithosphere of western and southern europe there is debate about the number of terranes involved and their origins the most significant terrane boundaries originally oceanic sutures are poorly exposed and are defined using faunal provinciality prominent geophysical lineaments may represent sub terrane boundaries within composite terranes the avalonia composite terrane was amalgamated to baltica in latest ician time the provenance of the malopolska and moravo silesian terranes whose neoproterozoic basement is suspect with respect to baltica but with which they nonetheless share faunal affinities is still debated the extent of the variscide rhenohercynian zone defines the southern limit of the early palaeozoic accreted terranes terranes within the bohemian massif exhibit hp metamorphism recording subduction driven collision prior to incorporation in the tesz collage itself associated with a hp event in romania the saxothuringian zone and rheic suture are directly juxtaposed with the eec and the crustal structure of the tesz has been much modified by post palaeozoic tectonism deep seismic reflection data where available show that the oceanic sutures are frequently associated with inclined reflectivity zones irz in the lithospheric mantle here inferred to mark relict subduction zones interpreting the age of subduction is complicated by offset of originally coplanar mantle and crustal segments of the irz resulting from early orogenic lithospheric delamination at the moho interface and or post orogenic reordering processes the mantle irz appear to indicate a n directed polarity for early palaeozoic subduction apparently incompatible with the geological evidence which indicates subduction of the tornquist sea beneath avalonia and a large amount of underthrusting of avalonia by baltica possible explanations for these apparently incompatible observations are evaluated

3 d flexural modelling of the silurian baltic basin abstract the baltic basin bb is situated on the western part of the east european craton eec it was established initially as a passive margin basin in response to the breaking apart of the rodinia megacontinent during the latest precambrian early cambrian times thereafter it has been suggested that the late ordovician silurian basin subsidence was generated by foreland bending of the western margin of the eec as a result of the caledonian convergence and collision of continental plates namely baltica laurentia and eastern avalonia this is based on the regional basin architecture which indicates accelerating subsidence rapid deepening of the basin and significant thickening of the sedimentary succession towards the tornquist teisseyre zone ttz along the southwestern margin of the eec during the silurian however the very broad extent of the silurian bb is not obviously explicable by a model of simple foreland flexure this problem has been investigated by quantitative modelling of caledonian foreland flexure east of the ttz using a 3 d finite difference technique the results are interpreted in terms of their implications for the rheology of the eec and the geometry and temporal evolution of caledonian orogenic loading assuming higher values of effective elastic thickness eet for the eec than for caledonian lithosphere the model results demonstrate that the evolution of the bb cannot be explained by the effects of orogenic loads lying only on the west of the present caledonian deformation front cdf furthermore the inferred shape of the bb deflection is not easily reproduced even allowing lateral changes of eec lithosphere eet rather additional loads east of the cdf and ttz were necessary in order to replicate the shape and amplitude of the bb as a flexural basin these are tentatively interpreted to be dynamic loads related to mantle flow above an eastward dipping silurian subduction zone

the deep structure of the scandes and its relation to tectonic history and present day topography abstract we review the results of the toposcandiadeep project a component of the topoeurope project in which we have studied the crustal and upper mantle structures of southern norway in relation to its high topography the scandinavian mountain chain the scandes is an intracontinental mountain chain at the western edge of the baltic shield and has its southern part located in southern norway the timing as well as the processes causing the formation of the scandes are disputed we bring new geophysical constraints to this issue by providing crustal and mantle seismic models for the area and by integrated modeling of the lithosphere and its potential deformation new maps of moho depth and crustal seismic velocities have been compiled using data from refraction lines p receiver functions and noise cross correlation these results show a thickening of the crust from southwest to northeast and a small crustal root not directly located below the topographic high p s and surface wave tomography infer seismic mantle velocities lower than in normal shield structure with a possible sharp boundary close to the oslo graben these low velocities are imaged in the lithosphere and in the underlying mantle down to the 410 km discontinuity integrated modeling of seismic models and gravity data shows that the low velocities below southern norway are compatible with a change in lithosphere thickness from c 100 km under southern norway to nearly 200 km under southern sweden with possible additional differences in composition the study also indicates that the topography can be isostatically sustained by the density distribution in the crust and lithospheric mantle we argue that the lithospheric lateral variation has been present for at least 300 my and has had a significant influence on the localization of the topography independently of the mechanism for uplift

crustal structure of the mid polish trough beneath the teisseyre tornquist zone seismic profile abstract a new seismic refraction and wide angle reflection experiment in the teisseyre tornquist zone ttz in poland was conducting during july 1993 as an international polish finnish german and swedish co operation the ttz profile running in an se nw direction was exactly located in the central part of the mid polish trough in the zone of maximum subsidence from upper permian to upper cretaceous 19 shot points were placed along the 450 km profile the interval between the shot points was about 25 km 31 explosions 90 to 1000 kg of dynamite were recorded in two deployments using 135 modern three component seismic stations with spacing of the recording sites of about 1 7 km in this area the depth of the consolidated basement with a velocity of about 5 7 5 8 km s is 5 to 12 km deep nevertheless the p wave velocity is very low vp

seismic tomographic interpretation of paleozoic sedimentary sequences in the southeastern north sea seismic wide angle data were recorded to more than 300 km offset from powerful airgun sources during the mona lisa experiments in 1993 and 1995 to determine the seismic velocity structure of the crust and uppermost mantle along three lines in the southeastern north sea with a total length of 850 km we use the first arrivals observed out to an offset of 90 km to obtain high resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust seismic tomographic traveltime inversion reveals 2 8 km thick paleozoic sedimentary sequences with p wave velocities of 4 5 5 2 km s these sedimentary rocks are situated below a mesozoic cenozoic sequence with variable thickness 2 3 km on the basement highs 2 4 km in the horn graben and the north german basin and 6 7 km in the central graben the thicknesses of the paleozoic sedimentary sequences are 3 5 km in the central graben more than 4 km in the horn graben up to 4 km on the basement highs and up to 8 km i

receiver function analysis of the crust and upper mantle from the north german basin to the archaean baltic shield summary two passive seismic experiments have been carried out across the trans european suture zone tesz from northern germany to southern sweden tor and across the proterozoicarchaean suture in finland svekalapko to improve our understanding of the processes involved in the creation of the european continent teleseismic earthquakes recorded by the two networks and stations of the grsn and geofon permanent networks have been used for studies of the crust mantle and upper mantle seismic discontinuities with the receiver function method along the tor network the depth to the moho increases from 30 km at the southern edge of the profile to 40 km at the elbe line between the elbe line and tesz the moho branches off and whereas the deeper branch continues at 40 km depth to the tesz a second branch appears at 30 35 km depth the upper branch descends north of the tesz to below 55 km under the northern end of the tor profile the crustal thickening north of the tesz is accompanied by an increase in average vp vs values appearance of intracrustal conversion zones and north dipping features which we interpret as remnants of the subduction and subsequent collision between avalonia and baltica in southern finland beneath the svekalapko network the moho starts in the south at the depth of 40 45 km plunges to about 65 km depth south of the archaean proterozoic suture this deepening of the moho is coincident with a north dipping intracrustal structure apparently related to the subduction and collision and of the proterozoic and archaean provinces in proterozoic north of the line of the suture the moho rises smoothly to 45 50 km depth in the archaean province along the tor profile 410 and 660 discontinuities were hard to detect however manyfold stacking of receiver functions revealed that the conversions from the two discontinuities arrive more or less according to iasp91 predicted time across the svekalapko network 410 and 660 discontinuities arrive markedly earlier than iasp91 theoretical arrival times in particular north of the archaean proterozoic suture in finland the 410 and 660 km conversions arrive about 2 s earlier indicating about 5 per cent higher average upper mantle velocities and lower temperatures than what iasp91 global model predicts

geophysical constraints on geodynamic processes at convergent margins a global perspective abstract convergent margins being the boundaries between colliding lithospheric plates form the most disastrous areas in the world due to intensive strong seismicity and volcanism we review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure seismicity and geometry of subducting slab we present global maps of free air and bouguer gravity anomalies heat flow seismicity seismic vs anomalies in the upper mantle and plate convergence rate as well as 20 profiles across different convergent margins a global analysis of these data for three types of convergent margins formed by ocean ocean ocean continent and continent continent collisions allows us to recognize the following patterns 1 plate convergence rate depends on the type of convergent margins and it is significantly larger when at least one of the plates is oceanic however the oldest oceanic plate in the pacific ocean has the smallest convergence rate 2 the presence of an oceanic plate is in general required for generation of high magnitude m 8 0 earthquakes and for generating intermediate and deep seismicity along the convergent margins when oceanic slabs subduct beneath a continent a gap in the seismogenic zone exists at depths between ca 250 km and 500 km given that the seismogenic zone terminates at ca 200 km depth in case of continent continent collision we propose oceanic origin of subducting slabs beneath the zagros the pamir and the vrancea zone 3 dip angle of the subducting slab in continent ocean collision does not correlate neither with the age of subducting oceanic slab nor with the convergence rate for ocean ocean subduction clear trends are recognized steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate with slab rotation towards a near vertical dip angle at depths below ca 500 km at very high convergence rate 4 local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs however near isostatic equilibrium may exist in broad zones of distributed deformation such as tibet 5 no systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation magmatic activity crustal faulting horizontal heat transfer and also due to low number of heat flow measurements across many margins 6 low upper mantle vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

segmentation and volcano tectonic characteristics along the sw african continental margin south atlantic as derived from multichannel seismic and potential field data abstract regional seismic reflection and potential field data document the south atlantic s break up history between 39 s and 19 s from the early cretaceous onwards previous maps of distribution of volcanics along the margin showed volcanics along the whole african margin based on extrapolation of data based on previously unpublished marine geophysical data we found the southernmost 460 km long margin segment to be lacking huge volumes of break up related volcanic effusives northwards break up was accompanied by the emplacement of huge volumes of volcanic material prominently featured in seismic sections as huge wedge shaped seaward dipping reflectors sdrs detailed mapping of offsets left and right stepping and variations in structural character of the volcanics reveal the segmentation along and the break up history of the margin several superimposed sdr sequences suggesting episodicity of volcanic emplacement divided by periods of erosion and sedimentation are distinct along southerly lines losing prominence northwards a main outcome of our study is that this passive margin is not continuously of the volcanic type and that the change from a non volcanic to a volcanic margin occurs abruptly we define four distinct first order segments along the 2400 km section of the southwestern african margin covered by our seismic data from south to north these first order segments are magma poor segment i segment ii with enormous sdrs volumes decreasing sdrs volumes in segment iii segment iv again with enormous volcanic output likely influenced by walvis ridge volcanism most important is that there is no systematic increase in the volumes of the effusives towards the tristan da cunha hot spot rather there is an alternating pattern in the sdrs volumes and widths the boundary between the volcanic and magma poor margin segments in the southernmost study area is sharp 10s of km which we propose is reflected in magnetic anomaly data as well we suggest that this variability along the margin is mainly due to a change in stretching rifting character from oblique during the early stages of breakup to conventional seafloor spreading from chron m4 130 ma onwards

seismic evidence of caledonian deformed crust and uppermost mantle structures in the northern part of the trans european suture zone sw baltic sea abstract collisional structures from the closure of the tornquist ocean and subsequent amalgamation of avalonia and baltica during the caledonian orogeny in the northern part of the trans european suture zone tesz in the sw baltic sea are investigated a grid of marine reflection seismic lines was gathered in 1996 during the dekorp basin 96 campaign shooting with an airgun array of 52 l total volume and recording with a digital streamer of up to 2 1 km length the detailed reflection seismic analysis is mainly based on post stack migrated sections of this survey but one profile has also been processed by a pre stack depth migration algorithm the data provides well constrained images of upper crustal reflectivity and lower crustal uppermost mantle reflections in the area of the caledonian suture a reflection pattern is observed with opposing dips in the upper crust and the uppermost mantle detailed analysis of dipping reflections in the upper crust provides evidence for two different sets of reflections which are separated by the o horizon the main decollement of the caledonian deformation complex s dipping reflections beneath the sub permian discontinuity and above the o horizon are interpreted as caledonian thrust structures beneath the o horizon sw dipping reflections in the upper crust are interpreted as ductile shear zones and crustal deformation features that evolved during the sveconorwegian orogeny the caledonian deformation complex is subdivided into 1 s dipping foreland thrusts in the north 2 the s dipping suture itself that shows increased reflectivity and 3 apparently ne dipping downfaulted sedimentary horizons south of the avalonia baltica suture which may have been reactivated during mesozoic normal faulting the reflection moho at 28 35 km depth appears to truncate a n dipping mantle structure which may represent remnant structures from tornquist ocean closure or late collisional compressional shear planes in the upper mantle a contour map of these mantle reflections indicates a consistent northward dip which is steepest where there is strong bending of the caledonian deformation front the thin skinned character of the caledonian deformation complex and the fact that n dipping mantle reflections do not truncate the moho indicate that the baltica crust was not mechanically involved in the caledonian collision and therefore escaped deformation in this area

crustal structure along the egt profile across the tornquist fan interpreted from seismic gravity and magnetic data abstract the tornquist fan is a northwestward widening splay of late carboniferous to early permian fault zones in the danish area which emanates from the teisseyre tornquist zone in the baltic sea it is located over an area of deep sedimentary basins around denmark in the southwestern corner of the former baltica plate this paper presents an integrated model of seismic velocity density and magnetic properties along the egt profile across the tornquist fan between southern sweden and northern germany the model shows distinct features that may be related to the main tectonic events in the area the caledonian crustal suture between baltica and eastern avalonia is interpreted from changes in physical parameters at all crustal levels most noticeable as an abrupt lateral change in seismic velocity in the lowest crust at moho level from 6 9 km s in baltica to only 6 4 km s in eastern avalonia thick sedimentary successions beneath the mesozoic sequence are interpreted as palaeozoic sedimentary rocks which may have been deposited on the southern margin of the baltica plate in a deep caledonian foreland basin and in late carboniferous early permian rifts and extensional basins rift related magmatism is indicated by the presence of zones of high velocity density and magnetic susceptibility as well as strong remanent magnetization thermal subsidence following the emplacement of these bodies may be the origin of regional subsidence of the danish and north german basins of late paleozoic and mesozoic age late cretaceous to early cenozoic inversion of basin structures is detected at the sorgenfrei tornquist zone stz in the transition between shield and basin areas the stz coincides with a pronounced change in crustal thickness and the southwestern edge of a major magmatic intra crustal body significant abrupt changes in moho depth exist along the profile 26 30 km beneath the deep basins ca 35 km beneath the ringkobing fyn basement high and 48 km beneath the baltic shield around the sorgenfrei tornquist inversion zone the basement in the tornquist fan area is of proterozoic age the moho topography indicates strong thinning of the crust during its phanerozoic evolution the model supports the hypothesis that existing tectonic structures and weakness zones are continuously being reactivated during subsequent tectonic activity

seismic images of caledonian lithosphere scale collision structures in the southeastern north sea along mona lisa profile 2 abstract the unexposed suture between baltica and eastern avalonia is imaged by coincident normal incidence reflection and wide angle reflection refraction seismic data of the mona lisa project we present new results of the upper lithospheric seismic structure from the n s striking profile 2 across the caledonian deformation front which represents the crustal collision suture between baltica and eastern avalonia that formed after closure of the tornquist sea during the caledonian orogeny in late ordovician times three different crustal types are identified with great similarities to the nearby profile 1 1 a three layered crust typical of shields to the north 2 a transitional crust suture zone in the central part and 3 a two layered crust of caledonian origin to the south characterized by very low velocities throughout the crust the crustal thickness varies from 38 35 km under the northern margin of the ringkobing fyn high baltica crust to 28 27 km beneath the north german basin in the caledonian crust to the south the suture zone is imaged by s dipping crustal reflections from 1 9 to 10 6 s two way travel time twt over a horizontal distance of 70 km within the transitional crust the reflection suture zone terminates in a 60 km wide reflective lens with velocities of 6 6 6 8 km s in the lowermost crust the reflective lens may be interpreted as a remnant of oceanic or island arc crust that was accreted to the leading edge of baltica during closure of the tornquist sea alternatively the reflective lens may represent an indentor of baltica crust into the avalonian terrane the change in lower crustal reflectivity and the abrupt transition from a three to a two layered crust further south suggest that the trans european fault and the elbe lineament continue into the north sea the upper mantle reflectivity is dominated by bands of strong amplitude s dipping reflections from 13 5 to 21 8 s twt and a weaker band of n dipping reflections from 12 to 16 s twt reversed wide angle refractions and reflections indicate the presence of a s dipping high velocity layer 8 65 8 8 km s in the uppermost mantle the sub moho high velocity layer partially coincides with the strong s dipping normal incidence mantle reflections we propose that the s dipping mantle structure may represent a late caledonian or late carboniferous to early permian mantle shear zone

upper mantle reflectors modelling of seismic wavefield characteristics and tectonic implications summary deep seismic experiments on continental lithosphere generally reveal marked reflectivity from structures in the crust and a significant decrease in reflectivity from the upper mantle however reflected and refracted energy from mantle lithosphere are observed in both near normal incidence and wide angle data the origin of the reflective structures is a matter of debate hypotheses include remnant subduction zones shear zones fluids and seismic anisotropy through analytical and numerical modelling studies including full wavefield modelling we investigate seismic characteristic signatures generated from a variety of geologically plausible models we have found that both upper mantle shear zones of reduced velocity and density and remnant subduction slabs containing high density eclogites may contain sufficient seismic impedance contrasts to normal mantle peridotites to generate near normal incidence reflectivity wide angle energy originates from subduction slabs containing either high or lowvelocity eclogites whereas intermediate velocity eclogites are unlikely to produce significant wide angle phases in general energy of seismic phases originating from upper mantle zones of anomalous seismic velocities and densities is significantly increased if homogeneous zones are replaced by zones of inhomogeneous petrophysical properties resulting from constructive interference maximum wavefield anomalies are generated from sub moho dipping slabs of incomplete transformation of low velocity low density crustal material to high velocity highdensity eclogites localized shear zones generated in mantle peridotite generally do not produce significant wide angle energy only if highly inhomogeneous structures containing material of marked ca 10 per cent velocity and density reduction are present may shear zones be observed in wide angle data analyses of two specific deep seismic data sets mona lisa data from the north sea and babel data from the baltic sea show good agreement between observations and modelling results for dipping remnant subduction slabs containing small scale inhomogeneities associated with incomplete transformation our modelling results improve our possibilities of distinguishing between two often contrasting tectonic interpretations for dipping upper mantle seismic reflectors the remnant subduction and shear zone models

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

pre permian sedimentary basins in the north sea images from reprocessed and pre stack depth migrated mona lisa data pre permian sedimentary basins in the southeastern north sea have been previously interpreted from potential field data but only poorly imaged on seismic sections due to the presence of salt layers and a thick mesozoic and cenozoic cover furthermore potentially low prospectivity for hydrocarbon resources has resulted in sparse penetration of pre permian sediments in the southeastern north sea we present images of large palaeozoic basins obtained through reprocessing and pre stack depth migration of seismic data from the mona lisa project the depth images show in detail the structure of pre permian basins beneath the danish basin and the ringkobing fyn high providing new insights into upper palaeozoic basin formation in the north sea

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

salt diapir downbuilding fast analytical models based on rates of salt supply and sedimentation abstract salt diapir shapes are influenced by the rate of salt supply into the base of the diapir the rate of sedimentation regional slope local deformation around the salt body and regional deformation prior graphical solutions to this complex problem consider only the salt supply and sediment aggradation rate but there are major problems with these existing plots precise computation of diapir shapes using a new fast analytical approach reveals that the shapes shown in previous publications were incorrect rise rate a proxy used for salt supply in previous models was inconsistently defined the fundamental controlling factors used in this study to predict salt diapir shapes are the volumetric rate of salt supply to the base of the diapir and the rate of sediment aggradation these are combined to create predictive charts of salt shapes for both radial and linear geometries we discuss the strengths and limitations intrinsic to our fast analytical models suggesting geological conditions where they may be appropriate simple downbuilding models may not be directly applicable to geological settings that involve subsequent deformation of the sediments or of the salt body however the modified salt downbuilding concept as elaborated in our study can explain many real world situations where the salt body flares or tapers upwards

potential field modelling of the baltica avalonia thor tornquist suture beneath the southern north sea magnetic anomaly maps of the trans european suture zone tesz highlight the contrast between the highly magnetic crust of baltica and the less magnetic terranes to the sw of the suture although the tesz is imaged on gravity maps anomalies related to postcollisional rifting and reactivated rift structures tend to dominate seismic and potential field data have been used to construct 212 d crustal models along three profiles crossing the baltica avalonia suture in the southern north sea sns the first of these models lies along a transect assembled from reflection line geco snst 83 07 and refraction profile eugeno s 2 the other two models are coincident with mona lisa profiles 1 and 2 additional structural information and density information for the cover sequence is available from released wells while magnetic susceptibility values are compatible with values measured from borehole core samples magnetic anomalies related to the suture are interpreted as due to magnetic baltican basement of the ringkobing fyn high dipping sw beneath nonmagnetic avalonian basement underlying the western part of the sns low amplitude long wavelength magnetic anomalies occurring outboard of the suture are interpreted as due to a mid crustal magnetic body possibly a buried magmatic complex this might represent the missing arc related to inferred southward subduction of the tornquist sea or an exotic element emplaced during the collision between avalonia and baltica the present model supports an imbricated structure within baltica as indicated by the latest reprocessing of the mona lisa seismic data

the long term strength of europe and its implications for plate forming processes field based geological studies show that continental deformation preferentially occurs in young tectonic provinces rather than in old cratons this partitioning of deformation suggests that the cratons are stronger than surrounding younger phanerozoic provinces however although archaean and phanerozoic lithosphere differ in their thickness and composition their relative strength is a matter of much debate one proxy of strength is the effective elastic thickness of the lithosphere te unfortunately spatial variations in te are not well understood as different methods yield different results the differences are most apparent in cratons where the bouguer coherence method yields large te values 60 km whereas the free air admittance method yields low values or 1 5 gyr old is much larger mean te 60 km than that of younger lithosphere mean te 30 km we propose that this strength difference reflects changes in lithospheric plate structure thickness geothermal gradient and composition that result from mantle temperature and volatile content decrease through earth s history

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

strain localization due to structural in homogeneities in the central european basin system the large scale crustal deformations observed in the central european basin system cebs are the result of the interplay between several controlling factors among which lateral rheological heterogeneities play a key role we present a finite element integral thin sheet model of stress and strain distribution within the cebs unlike many previous models this study is based on thermo mechanical data to quantify the impact of lateral contrasts on the tectonic deformation elasto plastic material behaviour is used for both the mantle and the crust and the effects of the sedimentary fill are also investigated the consistency of model results is ensured through comparisons with observed data the results resemble the present day dynamics and kinematics when 1 a weak granite like lower crust below the elbe fault system is modelled in contrast to a stronger lower crust in the area extending north of the elbe line throughout the baltic region and 2 a transition domain in the upper mantle is considered between the shallow mantle of the variscan domain and the deep mantle beneath the east european craton eec extending from the elbe line in the south till the tornquist zone the strain localizations observed along these structural contrasts strongly enhance the dominant role played by large structural domains in stiffening the propagation of tectonic deformation and in controlling the basin formation and the evolution in the cebs