decomposing of mixed pattern of arsenic using fractal model in gangdese belt tibet china abstract decomposing mixed geochemical patterns is a challenge in geochemical exploration and environmental assessment in this paper the spectrum area technique s a is used to decompose a mixed pattern of arsenic in gangdese belt based on stream sediment data s a is a multifractal model based on power law relationships between area of the set consisting of wave numbers with spectral energy density above s a s on the 2d frequency domain the original spatial distribution map of arsenic obtained by inverse distance weighted idw shows a mixed pattern due to superposition of different geological processes or events and is converted into the frequency domain by means of fourier transformation two components including power spectrum density and phases are obtained the spectrum energy density s and the area a enclosed by the above threshold spectrum energy density is plotted on a log log scale two cutoff values determined by three straight lines define three filters which decompose the original map of arsenic into background anomalous and high frequency noise components the areas with high anomaly of arsenic mainly are located surrounding known cu deposits indicating that arsenic anomalies may be related to cu mineralization

reappraisal of deep seismic reflection profile viii across the pripyat trough two deep 24 s multi channel seismic reflection profiles each 200 km in length were shot across the pripyat trough a late devonian rift basin in belarus in the 1980s by the polessian geophysical expedition of the former soviet union additional post stack processing and migration on one of these profile viii has been applied at uppsala university and allows a re evaluation of the crustal structure of the pripyat trough with particular focus on the deeper parts previous interpretations showed numerous steeply dipping faults extending from the surface to depths of 30 40 km and sometimes penetrating into the mantle which was defined to be located at the top of a reflective zone beginning at about 10 s twt this reflective zone recorded to depths of 16 s twt was interpreted as a mixture of crustal and mantle rocks based on the original stacked section and the further processing the reflective zone is reinterpreted to be reflective lower crust not upper mantle and the moho is identified to be at 45 50 km about 15 s twt the major basin bounding faults appear to be listric at depth and sole into the top of the reflective lower crust rather than be truncated by it the newly interpreted crustal structure is consistent with a model of continental rifting involving brittle failure in a thick upper crustal layer and ductile shear in the lowermost crust with some degree of detachment between crust and mantle within the lower crustal ductile layer

seismic anisotropy and mantle creep in young orogens summary seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere we discuss the origin of anisotropy at various depths and relate it to tectonic stress geotherms and rheology the anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine and may result from ductile deformation dynamic recrystallization or annealing anisotropy beneath young orogens has been measured for the seismic phase pn that propagates in the uppermost mantle this anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event and thus provides information on the process of mountain building whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts pn anisotropy is aligned parallel to the structural axis we interpret this to indicate mountainparallel ductile i e creeping deformation in the uppermost mantle that is a consequence of mountain perpendicular compressive stresses the preferred orientation of the fast axes of some anisotropic minerals such as olivine is known to be in the creep direction a consequence of the anisotropy of strength and viscosity of orientated minerals in order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal escape or extrusion tectonics to the uppermost mantle we present rheological model calculations to support this hypothesis mountain perpendicular horizontal stress determined in the upper crust and mountain parallel seismic anisotropy in the uppermost mantle require a zone of ductile decoupling in the middle or lower crust of young mountain belts examples for stress and mountain parallel pn anisotropy are given for tibet the alpine chains and young mountain ranges in the americas finally we suggest a simple model for initiating mountain parallel creep

reflection diffraction seismic pattern at crustal suture zones seismic reflection profiling across strong dip more than 25 suture zones between different crustal terranes or provinces reveals a distinct seismic reflectivity pattern of dipping reflections and associated diffractions suture zones in areas dominated by thin skinned tectonics do not show this pattern profiles from southern germany deutsches kontinentales reflexionsseismisches programm great britain british institutions reflection profiling syndicate and north america consortium for continental reflection profiling and u s geological survey crossing major sutures are examined with respect to dipping reflections in the upper crust and accompanying diffractions in the lower crust the strong resemblance of seismic patterns suggests a similar origin for these structures

comparison of crustal structure along dss profiles in se fennoscandia summary main features of the crustal structure of the karelian and svecofennian provinces are discussed on the basis of data obtained from deep seismic sounding dss profiles across the se fennoscandian shield the data show that in the ancient karelian province the crust is thinner about 40 km the average velocity is lower about 6 4kms l and the moho boundary is a sharp discontinuity which produces strong reflections the high velocity layer in the lower crust if it exists at all is thin in the younger svecofennian province crustal thickness averages about 45 km with a velocity of 6 6 6 8 km s the reflectivity of the moho is usually weak and a high velocity layer with velocities greater than 7 km s is ubiquitous in the lower crust high velocities in the lower crust and upper mantle are found in deep moho areas beneath the younger granitic intrusions gothian complex and vyborg rapakivi granites the crust is thinner than on average

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

moho depth across the trans european suture zone from p and s receiver functions the mohorovicic discontinuity moho for short which marks the boundary between crust and mantle is the main first order structure within the lithosphere geodynamics and tectonic evolution determine its depth level and properties here we present a map of the moho in central europe across the teisseyre tornquist zone a region for which a number of previous studies are available our results are based on homogeneous and consistent processing of p and s receiver functions for the largest passive seismological data set in this region yet consisting of more than 40 000 receiver functions from almost 500 station besides we also provide new results for the crustal vp vs ratio for the whole area our results are in good agreement with previous more localized receiver function studies as well as with the interpretation of seismic profiles while at the same time resolving a higher level of detail than previous maps covering the area for example regarding the eifel plume region rhine graben and northern alps the close correspondence with the seismic data regarding crustal structure also increases confidence in use of the data in crustal corrections and the imaging of deeper structure for which no independent seismic information is available in addition to the pronounced stepwise transition from crustal thicknesses of 30 km in phanerozoic europe to more than 45 beneath the east european craton we can distinguish other terrane boundaries based on moho depth as well as average crustal v p v s ratio and moho phase amplitudes the terranes with distinct crustal properties span a wide range of ages from palaeoproterozoic in lithuania to cenozoic in the alps reflecting the complex tectonic history of europe crustal thickness and properties in the study area are also markedly influenced by tectonic overprinting for example the formation of the central european basin system and the european cenozoic rift system in the areas affected by cenozoic rifting and volcanism thinning of the crust corresponds to lithospheric updoming reported in recent surface wave and s receiver function studies as expected for thermally induced deformation the same correlation applies for crustal thickening not only across the trans european suture zone but also within the southern part of the bohemian massif

seismic models of the lower lithosphere beneath the southern baltic sea between sweden and poland abstract based on recordings from the northern part of the baltic sea black sea profile and eugeno s profile 4 2 d seismic models have been constructed for a profile across the southwestern part of the east european platform from southern sweden to northern poland the thickness of the crust along the profile varies from 33 to 47 km the moho p wave velocity is 8 0 8 3 km s the uppermost mantle has a fine structure with alternating layers of higher and lower velocities down to a depth of about 120 km three alternating high and low velocity layers have been modelled the velocities vary between 8 2 and 8 7 km s in the high velocity layers and 8 0 and 8 5 km s in the low velocity layers a tendency of the depth of the moho and the depth of the uppermost mantle seismic boundaries to increase towards the southeast is observed

recently formed elastic anisotropy and petrological models for the continental subcrustal lithosphere in southern germany this paper advances new evidence for elastic anisotropy in the continental subcrustal lithosphere in southern germany the range of petrological models compatible with the observed azimuthal variation of seismic p wave velocity is explored the azimuthal distribution of amplitudes of mantle phases and the observed increase of p velocity with depth both indicate a continuation of anisotropy with depth together with an increase of preferred orientation even depletion of the upper mantle in basaltic components as suggested by mantle xenoliths from various parts of germany cannot explain the velocity depth and azimuthal amplitude observations without an increase of anisotropy with depth preferred orientation of olivine is the most likely mechanism for the observed phenomena its fast a axis at the moho level is directed towards n22 5 e the b axis is also required to be horizontal i e the b plane one of the preferred glide planes of olivine is vertical with a strike of n22 5 e therefore this preferred glide plane of olivine practically coincides with the plane of maximum horizontal shear stress deduced from fault plane solutions of earthquakes in western germany this is a strong indication that the preferred orientation of olivine is formed in the recent west european crustal stress field leaking into the upper mantle the distribution of velocities to a depth of at least 50 km requires slight horizontal rotation of the a axis with depth by 10 towards n32 e and a change in the modal composition towards a depletion increasing with depth compatible with the composition of mantle xenoliths from western germany further experiments are needed to substantiate this suggestion which could lead to a better understanding of the interaction of crustal and upper mantle stress strain fields

super deep reflection profiling exploring the continental mantle lid abstract reflections from the continental mantle lithosphere have now been reported from common mid point cmp profiles at numerous sites around the world these reflections include 1 distinct dipping events that appear to originate in the lower crust and continue some distance into the upper mantle 2 kilometer scale discontinuous diffusely distributed or isolated reflections at varying depths 3 continuous sub horizontal reflections tens of kilometers in extent often interpreted as the base of the lithosphere in spite of a wide variation in depth and 4 very deep reflections in the mantle lithosphere 125 km the first category of mantle reflections is most commonly observed in proximity to crustal sutures lending credence to their interpretation as fossil subduction zones isolated discontinuous mantle reflections are by far the most common and though observed in both ancient and modern collisional environments are difficult to interpret due to both their limited extent and a corresponding lack of three dimensional control sub horizontal mantle reflections appear in disparate tectonic environments in at least nine locations worldwide of special note are the various reports of specific reflections at 80 100 km 22 24 s twt in the north sea eastern europe and the urals which suggest a more ubiquitous mantle horizon the deepest events imaged thus far in a controlled source cmp survey are the super deep mantle reflections of the urseis project that have been identified at 135 165 km 35 43 s and 225 km 56 s of the many reported mantle reflections these are the most likely to be associated with the base of the lithosphere although such an interpretation averts the question of why an essentially thermo mechanical transition should be reflective at high frequencies 10 20 hz

deep seismic structure of the earth s crust along the baltic sea profile abstract in summer of 1989 the institute of oceanology of the russian academy of sciences moscow for the first time used a new large volume airgun for deep seismic sounding dss in the baltic sea the experiment was carried out during the 23 rd cruise of r v professor shtockman the wave field analysis showed clear p and s wave arrivals including moho reflections the moho reflections were distinctly observed at distances exceeding 100 km the p waves can be followed to a maximum distance of 368 km two dimensional raytracing modelling of the data revealed a pronounced topography of the moho along the baltic sea profile a depression in the middle of the profile at a depth of 45 km is bounded by 2 3 km steps and uplifts on both sides reflections off a sub moho boundary at a depth of 60 km have also been recorded the upper mantle velocities vary between 7 8 km s under the depression to 8 1 km s to the side of it the crustal p waves velocities define three layers 5 8 6 3 6 3 6 7 and 6 9 7 1 km s all crustal velocity boundaries bend over the moho depression and reach their deepest points in the central part of the profile the velocities in the crust also change laterally reaching their minimum within the central depression the crustal thickness along the profile varies notably between 38 and 45 km a comparison with the fennolora and the babel b profiles indicates that the moho depression found along the baltic sea profile correlates with similar depressions on the other profiles

magmatism and the geodynamics of rifting of the pripyat dnieper donets rift east european platform abstract the distribution of volcanism in the late devonian pripyat dnieper donets rift within the east european platform based upon the results of deep drilling indicates that pre existing basement structures and the major rift bounding faults played an important role in channelling the magmas towards the surface major and trace element and sr nd isotopic studies of the most primitive basic and ultrabasic magmas combined with estimates of the amount of extension 1 1 to 1 3 strongly suggest that magmatism was triggered by the upwelling of a thermally and geochemically anomalous mantle plume from the deep mantle during the late frasnian the peak of the magmatism occurred in the famennian coincident with the maximum amount of lithospheric extension magmatism rifting and domal basement uplife were contemporaneous at several localities within the eep suggesting that the thermal and geodynamic evolution of the platform could have been influenced by a cluster of mantle plumes during the late devonian

seismic velocity structure across the fennoscandia sarmatia suture of the east european craton beneath the eurobridge profile through lithuania and belarus

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

riphean rifting and major palaeoproterozoic crustal boundaries in the basement of the east european craton geology and geophysics abstract the east european craton which occupies the northeastern half of the european continent is characterized by the presence of giant even transcratonic systems of riphean meso to neoproterozoic rifts aulacogens the largest of these riphean rift systems tend to follow the course of palaeoproterozoic sutures and junction zones that subdivide the craton into three crustal segments with autonomous development histories these segments named fennoscandia volgo uralia and sarmatia are marked by distinct t magsat anomalies genetically the intersegment junction zones represent different types of collisional and accretional interaction between the component crustal segments of the craton in accordance with this the riphean rift systems vary in width the presence or absence of moho uplifts and other properties like for instance heat flow values however all of them follow belts of weakly magnetized crust studded with local magnetic maxima due to the presence of mafic rocks associated with the rifting the rift system intersegment junction zone relationships in consequence similarly represent a range of variation and cannot be referred to one single model

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

relationship of late quaternary tectonics and volcanism in the khanarassar active fault zone the armenian upland the syunik rhombus like structure in the khanarassar active dextral fault zone of armenia is a typical pull apart basin formed between terminal parts of two adjacent en echelon fault segments some component of subsidence associated with the faults of the structure is found between the en echelon segments nevertheless the dextral component continues to be predominant even on the boundaries of the pull apart basin the late pleistocene and holocene lava volcanoes of the basin are also associated with those faults that have a component of extension the relative ages of fault displacements and volcanic eruptions have been identified by the mutual correlation of lavas moraines and topographic features and by archaeological and radiocarbon dating according to the interpretation of rupturing and volcanism major earthquakes and volcanic eruptions appear inter related and three pulses of such activity during the earlier and middle holocene have been identified

absolute dating of brittle fault movements late permian and late jurassic extensional fault breccias in western norway 40ar 39ar geochronological and palaeomagnetic dating methods applied to fault breccias in western norway have isolated two brittle reactivation episodes of the syn post caledonian extensional nordfjord sogn detachment these events of latest permian and latest jurassic early cretaceous ages demonstrate temporal relationships between development of chemical remanent magnetism and partial resetting of ar isotopic systems during distinct breccia forming episodes a third event of carboniferous age was also identified in the breccias with the 40ar 39ar technique and is a relict unroofing signature inherited from the fault wall rocks these brittle faults are significant time markers and become relevant to interpretations of offshore seismic data which attempt to place ages on faults that have undergone multiple reactivation episodes

seismic velocities and q factors in the uppermost crust beneath the sveka profile in finland the sveka deep seismic sounding profile in central finland was shot in 1981 to study the crustal structure of the fennoscandian shield in the contact zone between the archaean and svecokarelian provinces apart from p and s waves well developed rayleigh surface waves r waves with periods of 0 5 2 0 s were recorded from all the shot points in the frequency band 0 5 2 5 hz the r waves were clearly observed on the entire 325 km long profile amplitudes of p s and r waves corrected for charge size were used to study the attenuation of waves and q factors from the records of body and r waves the distributions of seismic velocities and quality factors were determined using the dynamic ray tracing method 2 d modelling and the reflectivity method 1 d modelling in the 2 d model of the uppermost crust the p wave velocities vary from 5 8 5 9 km s at the top to 6 2 6 3 km s at a depth of 6 km the velocity ratio solvpvs varies with depth and distance from 1 67 to 1 74 reaching its maximum value of 1 8 2 0 in the uppermost 200 500 m and values of 1 76 1 80 in the uppermost 1 km the quality factors qp and qs vary in the uppermost 1 km from 20 to 120 reaching a higher value of 140 in the marginal zone of the archaean basement in the depth range of 1 2 km q values of 80 400 were found in the depth range 2 6 km q values of 300 800 were found for the svecokarelian province and 200 400 for the archaean the low values of vs and q in the uppermost 1 km are thought to be the result of rock fracturing the crack density was estimated for the uppermost crust along the profile for the sveka profile we found values of 0 35 0 54 in the uppermost 200 m 0 10 0 32 at a depth of 0 2 1 0 km and 0 1 for depths of 1 4 km the comparison of our seismic data with results of theoretical and laboratory investigations implies that the uppermost crustal rocks are saturated the zones of strong attenuation of r waves coincide with faults and schist zones which are well known from surface geology

observation of high frequency teleseismic p n on the long range quartz profile across northern eurasia short period three component recordings of the seismic wave field of peaceful nuclear explosions pnes on long range profiles are used to determine the fine structure of the mantle lithosphere by analyzing the frequency content of the recorded phases and applying different band pass filters to the data it is possible to divide the wave field into two distinctly different constituents low frequency body waves traveling along fermat paths first arrivals and the high frequency teleseismic or long range pn phase traveling with a group velocity of 8 1 km s and accompanied by a long incoherent coda this high frequency teleseismic pn phase is observable from about 750 km where it separates from the faster first arrival to the maximum recording distance of 3145 km it is recorded from shots at different locations and appears to be almost unaffected by the major tectonic feature along the profile the urals the frequency spectrum of this pn phase contains more high frequency energy up to 12 hz than first arrivals that penetrate deeper into the upper mantle the teleseismic high frequency pn arrival has a remarkable coda which is incoherent between closely spaced stations the coda duration is dependent on the component of motion being shortest on the vertical and longest on the transverse component we propose a velocity model that is characterized by a zone extending from the crust mantle boundary to a depth of about 100 km this zone has randomly distributed spatially anisotropic velocity fluctuations we propose that these velocity heterogeneities are stretched in the horizontal direction this zone forms a scattering waveguide that confines the high frequency teleseismic pn there are indications that below this pn waveguide either the scale of the velocity fluctuations or the q factor changes this is expressed in a separation of the teleseismic pn phase from the phase diving deeper into the mantle lithosphere

p and s wave velocity model of the southwestern margin of the precambrian east european craton polonaise 97 profile p3 the large scale seismic experiment polonaise 97 investigated the seismic structure of the crust and the uppermost mantle in the polish region of the trans european suture zone this paper covers the interpretation of seismic data along the 300 km long p3 profile which is located in the precambrian east european craton eec parallel to the teisseyre tornquist zone the recordings were of high quality with seismic energy detectable out to 300 km ovsets the crustal model developed by two dimensional raytracing forward modelling and waveform analysis is characterized by a subhorizontal uniform structure although the boundaries of several large basement features are crossed the crystalline crust consists of three parts the upper middle and lower crust with p wave velocities of 6 1 6 4 km s 6 55 6 7 km s and 7 05 7 15 km s respectively the p m p wave can usually be correlated at distances beginning at about 100 km but it has variable reflection character moho depth increases from 38 km at the nw end of the profile to 44 km at the se end the p n velocity of 8 05 8 1 km s is less than that previously found in neighbouring areas of the eec the v p v s ratio was determined separately for the upper middle and lower crust to be 1 67 and 1 77 respectively following the p n wave another phase with an apparent velocity of about 8 3 km si s interpreted as a weak reflection from a low contrast discontinuity in the uppermost mantle 1999 elsevier science b v all rights reserved

moho topography and lower crustal wide angle reflectivity around the tesz in southern scandinavia and northeastern europe abstract the moho topography is strongly undulating in southern scandinavia and northeastern europe a map of the depth to moho shows similarities between the areas of the teisseyre tornquist zone ttz in poland and the fennoscandian border zone fbz which is partly coinciding with the sorgenfrei tornquist zone stz in denmark the moho is steeply dipping at these zones from a crustal thickness of approximately 32 km in the young palaeozoic platform and basin areas to approximately 45 km in the old precambrian platform and baltic shield the moho reflectivity pmp waveform in the polonaise 97 refraction wide angle seismic data from poland and lithuania is variable ranging from sharp to strongly reverberating signals of up to 2 s duration there is little or no lower crustal wide angle reflectivity in the thick precambrian platform whereas lower crustal reflectivity in the thin palaeozoic platform is strongly reverberating suggesting that the reflective lower crust and upper mantle is a young phenomena from stochastic reflectivity modelling we conclude that alternating high and low velocity layers with average thicknesses of 50 300 m and p wave velocity variations of 3 4 of the background velocity can explain the lower crustal reflectivity sedimentary layering affects the reflectivity of deeper layers significantly and must be considered in reflectivity studies although the reverberations from the deeper crust cannot be explained by the sedimentary layering only the reflective lower crust and upper mantle may correspond to a zone that has been intruded by mafic melts from the mantle during crustal extension and volcanism

crustal structure of the trans european suture zone region along polonaise 97 seismic profile p4 1 the large scale polonaise 97 seismic experiment investigated the velocity structure of the crust and upper mantle in the trans european suture zone tesz region between the precambrian east european craton eec and paleozoic platform that comprises terranes added during the caledonian and variscan orogenies 530 370 and 370 225 ma respectively this experiment included 64 shots recorded by 613 seismic stations during two deployments very good quality data were recorded along five profiles and the longest and most important one p4 is the focus of this paper clear first arrivals and later phases of waves reflected refracted in the crust and moho were interpreted using two dimensional 2 d tomographic inversion and ray tracing techniques the crustal thickness along the profile varies from 30 35 km in the paleozoic platform area to 40 km below and due northeast of the tesz to 43 km in the polish part of the eec and to 50 km in lithuania the paleozoic platform and eec are divided by the polish basin so the upper crustal structure varies considerably in the area of the polish basin the p wave velocity is very low vp 6 1 km s down to depths of 15 20 km indicating that a very thick sedimentary sequence is present we suggest two possible tectonic interpretations of the velocity models 1 baltica indented avalonia obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and 2 a rifted margin of baltica underlies the polish basin this model is similar to other interpretations of seismic profiles recorded in the baltic sea the second model implies that the paleozoic platform solely consists of avalonian lithosphere and the eec of baltica lithosphere it offers a simple explanation of the difference in crustal thickness of the two platforms it also implies that the caledonian and variscan orogenies in this area were relatively soft collisions that left this continental margin largely intact

proterozoic sutures and terranes in the southeastern baltic shield interpreted from babel deep seismic data abstract a hitherto unknown terrane and its bounding sutures have been revealed by a combined study of normal incidence and wide angle seismic data along the babel profile in the baltic sea this intermediate terrane is situated between a northern terrane of svecofennian age and a southwestern terrane of gothian age it is delimited upwards by two low angle and oppositely dipping sutures and occupies mainly middle and lower crustal levels with a width of 300 km at moho level the 1 86 ga suture against the northern terrane is imaged by a prominent almost continuous ne dipping crustal reflection from 3 5 to 14 s twt over 175 km where it downlaps on the moho sub moho velocities change from 8 2 to 7 8 km s 0 2 over less than 25 km a relatively strong ne dipping normal incidence and wide angle reflection at 19 23 s twt indicates that the suture extends into the upper mantle the pervasive ne dipping reflection fabric of the intermediate terrane is interpreted as shear zones that developed during collision and possibly were reactivated by later events high poisson s ratios suggest a mafic composition or high fluid content the 1 86 ga collision was probably succeeded by continental break up and removal of an unknown continent except for the intermediate terrane subsequent formation of an east dipping subduction zone further to the west led to the emplacement of 1 81 1 77 ga old granitoids in the southern part of the transscandinavian igneous belt the 1 65 1 60 ga suture against the southwestern terrane is defined by a semi continuous band of strong sw dipping reflections between 3 and 8 s twt over 65 km which are interpreted as a low angle thrust zone along which gothian crust overrode the intermediate terrane the identification of three individual seismic terranes in the southeastern part of the baltic shield provides new evidence for palaeoproterozoic plate tectonic processes

crustal structure from p and s seismic waves and petrological models of the ukrainian shield presented are the results of reinterpretation of data from deep seismic sounding profiles viii and xxiv located in the central part of the ukrainian shield seismic models of the crustal structure were determined by 1 d and 2 d modelling using refracted and reflected p and s waves velocities of the uppermost crystalline basement vary between 5 8 6 0 km s at the surface and 6 3 6 4 km s at a depth of 5 8 km underlain by a 4 9 km thick low velocity layer the boundary below the low velocity layer is situated at a depth of 10 16 km and characterized by a velocity of 6 25 6 4 km s which increase towards the lower crust reaching up to 6 8 7 3 km s with a gradient of 0 015 0 025 s 1 the moho depth varies greatly from 30 to 56 km and the velocity below moho is 8 1 8 35 km s these results show that the crustal structure is heterogeneous and differentiated apart from a distinct division into the upper and lower crust crustal blocks are observed the deep fracture zones correlate on the surface with faults which are well known from geology a large range in the velocity ratio k p s is observed in the upper crust k is usually from 1 65 to 1 71 the lower crust is characterized by a low gradient and a relatively low value of the s wave velocity with k reaching 1 8 petrologically we interpret the uppermost part of the crust as represented by rocks cropping out at the surface migmatites granitoids gneisses and granites the middle and lower parts of the crust consist of enderbites and metamorphic rocks of granulite facies charnockites the rocks of the lower crust with velocities of 7 2 km s and higher are interpreted as a subfacies of eclogitelike rocks

seismic structure across the caledonian deformation front along mona lisa profile 1 in the southeastern north sea abstract seismic data from the mona lisa marine and onshore north sea acquisition for lithospheric seismic analysis project in the southeastern north sea image the caledonian deformation front cdf which is the collisional suture between baltica to the north and east and avalonia to the south and west the n s trending mona lisa normal incidence reflection profile 1 was recorded to 26 s twt coincident wide angle data were acquired on nine ocean bottom hydrophones and several onshore mobile seismographs along and off the profile the model of compressional seismic velocity shows three different crustal types a a typical three layered shield type crust below the ringkobing fyn high to the north b a highly complex transitional crust in the central part and c a two layered crust of caledonian origin to the south sharp and strong normal incidence and wide angle reflections from moho were recorded south of the caledonian deformation front in contrast to less distinct reflections further north s dipping crustal reflections from 4 to 11 s twt over 70 km horizontal distance terminate at moho and coincide with a change in the seismic velocity structure this indicates northward obduction of avalonian crust non migrated normal incidence seismic sections show crossing weak n dipping and stronger s dipping reflections to 20 s twt from the uppermost mantle we propose a tectonic model where the closure of the tornquist sea took place along a n dipping subduction zone which was later overprinted by a late or post caledonian s dipping shear zone sub moho velocities are 7 8 7 9 km s under 34 35 km thick baltica crust and 8 1 8 3 km s under 25 26 km thick caledonian crust the sub horizontal moho across the caledonian collision zone implies late or post caledonian re equilibration of the seismological moho we interpret the low velocity upper mantle 7 8 8 1 km s to the north as former baltica lower crust in eclogite facies after pressure induced metamorphism as a result of lithospheric flexure during the caledonian orogeny these rocks today appear as upper mantle that was uplifted to their present position during the middle devonian collapse of the north german polish caledonides