refined timing and kinematics for baltica avalonia convergence based on the sedimentary record of a foreland basin the caledonian foreland basin of poland onlaps the sw slope of the east european craton and is elongated in a nw sw direction along the margin of the baltica palaeocontinent the base of the synorogenic clastic wedge rises in age from llandovery to ludlow between nw and se poland respectively as the initial influx of orogen derived detritus can be unequivocally identified this diachronism documents a southeastward migration of the basin depocentre parallel to the present day caledonian deformation front our best fit plate model shows an oblique collision of baltica and avalonia the latter initially indenting the baltica margin in the nw afterwards baltica was progressively underthrust beneath avalonia towards the se in response to the oblique soft mode closure of the tornquist ocean the final deformation event within the caledonian foreland took place in the earliest devonian as a far field effect of sinistral orogen parallel displacements along the iapetus suture this article is protected by copyright all rights reserved

magnetic anomaly pattern of central europe abstract the magnetic anomalies represented on our map of central europe reflect the geological units and these anomalies are tentatively correlated with known geological structures in scandinavia strong magnetic anomalies caused by crystalline rocks of the east european platform have been observed their southern boundary corresponds to the elbe line the border between the mobile part of the east european platform and the dutch german platform here only some broader anomalies can be found and are caused by a magnetic basement magnetization m 2 a m under a 12 15 km thick layer of sediments a southern margin of the dutch german platform can be assumed along the w e northern german line which is marked by local magnetic anomalies younger magmatic events are presumed to be the sources of these anomalies the rhenohercynian is located south of the dutch german platform small ne striking anomalies indicate a weak magnetic basement m 0 35 a m a magnetic relief varying between 9 and 15 km is obtained by relief calculations west of the rhenohercynian anomalies of relatively strong amplitudes prevail these correspond to the brabant massif the eastern boundary of which presumably influences the tectonically controlled anomalies of erkelenz and lingen there is no magnetic indication of a continuation of the brabant massif into the rhenohercynian the mid german crystalline rise and the saxothuringian zone of the variscan belt are situated south of the rhenohercynian both areas show strong magnetic anomalies the southwestern border forms an arch around the brabant massif and ends at the paris basin anomaly this magnetic zone finds its equivalent in a magnetic belt the donau anomaly which can be followed to the massif central in the southwest this is located in the middle of the moldanubian which is characterized by a relatively undisturbed magnetic field the strong anomalies in the saxothuringian and donau magnetic belts point to an accumulation of magmatic rocks these might be fragments of oceanic crust or ophiolites marking previous subduction or obduction zones another explanation may be the intrusion of predominantly basic material during former crustal thinning or stretching with the exception of the saxothuringian and donau anomaly magnetic belts there is no indication of oceanic crust in the magnetic anomaly map

permo carboniferous magmatism of the northeast german basin abstract variscan continent continent collision in central europe was followed by a period of syn to late tectonic magmatism involving the extrusion of large volumes of permosilesian age volcanic rocks particularly in the northeast german basin the volcanic suite up to ca 2000 m thick comprises rhyolites acid and basic andesites and tholeiitic and alkali basalts tectono geochemical analysis in conjunction with volume calculations and petrography reveals changes in volcanic activity over time a total of five eruptive stages are recognised beginning in the stephanian and extending up into the upper rotliegend permian these include the stephanian late carboniferous andesite pre ignimbrite stage i lower rotliegend permian age explosive ignimbrite stage ii post ignimbrite stage iii late rhyolite stage iv and upper rotliegend permian age late basalt stage v in addition several volcanic centres including at least two large caldera like structures are recognised the total calculated volume for the northeast german basin volcanics is ca 48 000 km3 comprising rhyolitic rocks and ignimbrites ca 70 andesitic rocks ca 26 and basalts with cogenetic dolerites ca 4 regional variations in composition and geochemistry are related to diverse crust mantle regimes which correlate with differing positions relative to the heterogeneous basement of the variscan foredeep or within the rhenohercynian orogenic zone the crustal thickening and increasing generation depth of the mafic magmas from north to south may reflect the presence of a pre existing subduction influenced basaltic magma source

the southern border of baltica a review of the present state of knowledge abstract the southern border of baltica was for many years drawn along the nw part of the tornquist zone this important boundary between segments of the pre cadomian east european and the palaeozoic west european platforms is now redefined on the basis of geophysical and well data most probably it runs south of the ringkobing fyn high in denmark the transects bornholm rugen and scania holstein are used to discuss its position and tectonic character two main interpretations are possible in model 1 the boundary coincides with a steep fracture zone the jylland mon fault that forms the northern front of the caledonian folded lower palaeozoic in the southern forefield of baltica because of significant differences in the tectonical lithological and thickness development on both sides of this fault it is interpreted as the northern boundary of a caledonian terrane rugen pomorze terrane accreted to and locally overthrusted onto baltica at early devonian times the south adjoining area between this terrane and the northern front of the mid european variscides is thought to represent a mosaic of predominantly cadomian terranes probably with intervening caledonian folded complexes this mosaic of terranes is assumed to have been amalgamated to a north german superterrane during late caledonian diastrophism at the latest in model 2 the boundary is 50 km south of the caledonian front it coincides with the buried trans european fault that has been documented by deep seismic sounding in this model the caledonian deformed complexes south of the ringkobing fyn high are interpreted as nappe structures of a lower palaeozoic marginal belt thrusted onto the southern edge of baltica hence it follows that the area to the north of the mid european variscides is most probably built up of the internal parts of a north german polish caledonide orogen

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

constraints on the kinematics of post orogenic extension imposed by stretching lineations in the aegean region abstract new kinematic data from shear zones of tertiary age in the metamorphosed basement of the aegean region in combination with published kinematic lithological and palaeomagnetic data have enabled us to determine a detailed kinematic evolution of the region during post orogenic extension in the aegean three distinct stages are recognised firstly extension of both the western and eastern aegean started in the late oligocene early miocene 36 25 ma ago initially in an 023 direction stage two started shortly after this with the division of the aegean crust into the west aegean block a coupled assemblage of small blocks bound on its northwestern and southeastern margins by the scutari pec line and mid cycladic lineament fracture zones respectively between 25 ma and 3 ma the west aegean block underwent 30 clockwise rotation whilst the eastern aegean underwent on average 19 anticlockwise rotation rotation of the west aegean block as a semi coherent block was aided by the relative coolness of the block compared to the warmer eastern aegean region as the crust thinned and rotated the nw se trending faults which characterise the west aegean block were cross cut by e w trending faults in the latest miocene pliocene the thermal front migrated westwards into the west aegean block and the mid cycladic lineament ceased activity the final kinematic stage marked the start of the subdivision of the west aegean block into two portions in the pliocene the southeastern portion nw cycladic area coupled with the sw cycladic area to form a central aegean block that started to translate southwest the northern and western portion rotated a further 10 15 clockwise whilst the southeastern rim rotated anticlockwise these data demonstrate that aegean post orogenic extension is not dominated by a single block rotation or radial spreading event but is characterised by the sequential formation and reformation of lithospheric scale blocks that have developed in response to large scale partitioning of rotational strain

palaeogeographic significance of mid silurian palaeomagnetic results from southern britain major revision of the apparent polar wander path for eastern avalonia summary wenlock c 430 ma lavas from the east mendips inlier southern briain are characterized by either single component magnetizations type 1 or a more complex system of three magnetization components type 2 during stepwise thermal demagnetization the type of demagnetization behaviour is related to changes in magnetic petrology within the lava pile the lower and intermediate unblocking temperature components of type 2 represent magnetic overprints of tertiary recent and hercynian mid carboniferous origin respectively the primary nature of the high unblocking temperature magnetization component types 1 and 2 dec 095 c inc 24 ag5 8 8 is demonstrated by positive agglomerate tests conversely an overlying upper old red sandstone sequence did not provide primary magnetizations the magnetic signature is governed by syn tectonic hercynian remagnetizations the primary silurian data demonstrate that the east mendips inlier experienced considerable clockwise rotation probably of the order of 80 prior to partial remagnetization during hercynian deformation and folding the silurian palaeopole vgp 13 n 271 e dp dm 5 9 cannot therefore be used for apparent polar wander path construction nevertheless the palaeolatitude estimate 13 f 5s suggests that southern britain eastern avalonia was at comparable mid silurian latitudes to baltica and northern britain 10 20 s both the iapetus ocean and tornquist sea therefore which separated southern britain from laurentia and baltica respectively in ordovician times were closed by wenlock time as ordovician and silurian palaeomagnetic data from baltica and eastern avalonia now record a comparable northwards translation from high southerly to near equatorial latitudes during this time we postulate pre wenlock collision of these blocks to form balonia baltica eastern avalonia a new apparent polar wander path for eastern avalonia constructed on the basis of this palaeogeographic model is presented

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

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

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

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

segmentation of the hellenides recorded by pliocene initiation of clockwise block rotation in central greece abstract new paleomagnetic data from early miocene to pliocene terrestrial sedimentary and volcanic rocks in central greece constrain the history of vertical axis rotation along the central part of the western limb of the aegean arc the present day pattern of rapid block rotation within a broad zone of distributed deformation linking the right lateral north anatolian and kephalonia continental transform faults initiated after early pliocene time resulting in a uniform clockwise rotation of 24 3 6 5 over a region 250 km long and 150 km wide encompassing central greece and the western cycladic archipelago because the published paleomagnetic dataset requires clockwise rotations of 50 in western greece after 17 ma while our measurements resolve no vertical axis rotation of central greece between 15 ma and post early pliocene time a large part of the clockwise rotation of western greece must have occurred during the main period of contraction within the external thrust belt of the ionian zone between 17 and 15 ma pliocene initiation of rapid clockwise rotation in central and western greece reflects the development of the north anatolia kephalonia fault system within the previously extended aegean sea region possibly in response to entry of dense oceanic lithosphere of the ionian sea into the hellenic subduction zone and consequent accelerated slab rollback the development of the aegean geometric arc therefore occurred in two short duration pulses characterized by rapid rotation and strong regional deformation

a seismic velocity model for the sw baltic sea derived from basin 96 refraction seismic data abstract within the basin 96 project basin analysis and seismic investigation in north germany 1996 a marine survey gathered seismic data in the southwest baltic sea to study the caledonian collisional zone between baltica to the north and avalonia to the south additionally the airgun pulses have been observed by several land stations special attention was paid to record good quality data on rugen island aiming at linking offshore and land seismic wide angle observations therefore a complex geophone array the star of rugen was designed to enhance the signal quality the star of rugen data and other onshore observations in ne germany and on bornholm an island in the baltic sea have been used for p wave velocity modelling important structures of the transition zone from palaeozoic western europe to the precambrian baltic shield are imaged in the resulting three dimensional velocity model a pronounced basement high north of rugen island indicates the location of the caledonian deformation front cdf velocities also reflect other prominent features such as the ronne graben a pull apart structure of the tornquist zone and the basement outcrops around bornholm island in the investigated area the moho depth varies between 27 and 33 km a high velocity layer in the lower crust below the ne german mainland may indicate genetic relations to baltica the structural continuity however is disturbed by a velocity decrease in an area north of the cdf sporadic but strong reflections from the upper mantle below the cdf seem to be consistent with the reflection seismic data dekorp basin research group 1999 geology 27 1 55 58

introduction geological and geophysical studies in the trans european suture zone the trans european suture zone tesz is the boundary between ancient precambrian lithosphere of the east european craton eec and the younger lithosphere beneath the latest neoproterozoic palaeozoic mobile belts of western europe the former is characterized by a thick crust c 45 km low heat flow and a tectono thermal age of about 3000 to 800 ma the latter by a thinner crust c 30 km higher heat flow and a tectonothermal age of 560 to 290 ma these contrasting types of crust were juxtaposed during the caledonian and variscan orogenic episodes the crystalline basement of the tesz is largely concealed by sedimentary basins controlled by the reactivation of structures within the suture zone during permian mesozoic extension and cenozoic inversion the pre permian evolution of the craton and the mobile belts and the location of the sutures is inferred from isolated outcrops hundreds of boreholes and geophysical evidence existing seismic data demonstrates that the tesz is rather narrow and has an expression at all levels of the lithosphere and deep into the asthenosphere teleseismic studies have demonstrated that the differences in the velocity structure of the asthenospheric and lithospheric mantle across the tesz persist to depths of c 400 km zielhus nolet 1994

the rugen caledonides northeast germany borehole evidence from the isle of rugen and geophysical data from the adjacent baltic sea suggest a caledonian deformation front that caused nne directed thrusting on the east european platform it is thought to mark a caledonian suture zone which was reactivated in syn to post variscan events to form the romio mon fault zone

partitioned waveform inversion and two dimensional structure under the network of autonomously recording seismographs nonlinear optimization methods are very effective in finding models that predict optimal waveform fits to observed seismograms provided the number of model parameters is small to reduce the size of the large scale two or three dimensional seismic modelling problem path integrals over seismic velocities may be defined as model parameters instead of the seismic velocities themselves this partitions the large scale optimization problem into a number of independent small scale problems and reduces the computational effort by several orders of magnitude the path integral parameters are transformed such that their correlation matrix becomes diagonal a linear inversion performs the mapping from the space of path integral parameters into the model space of seismic velocities and makes backus gilbert resolution analysis possible the method has been applied to body wave and surface wave data from the broadband portable network of autonomously recording seismographs nars in western europe using a surface wave ray approximation to generate synthetics by mode summation waveforms were fitted for frequencies as high as 50 mhz variations in s velocity as large as 6 1 have been established with a vertical resolution of 100 150 km and a horizontal resolution as small as 400 km in parts of the model although a low velocity layer is present under the southern part of the nars array such layer is very weak or absent north of the paris basin horizontal velocity gradients are well resolved down to 400 km depth

the deep structure of northern england and the iapetus suture zone from birps deep seismic reflection profiles the nec deep seismic reflection profile images structures in the lower crust which represent the iapetus suture zone beneath southern scotland and northern england on the basis of reflectivity characteristics of the lower crust and reflection moho we recognize four different crustal zones which correspond to four crustal terrane types midland valley zone a a sub continental subduction complex zone b lake district zone c and midland platform zone d the junctions between each of these zones are interpreted as being tectonic a and b originate from the northern continental margin of the iapetus ocean and are separated from c and d which are derived from a southern continent by strong northerly dipping reflections between approximately 15 and 30 km deep in the crust the structure responsible for these reflections does not displace the reflection moho north of the ab cd junction the base of zone b and base of the reflective crust is marked by a pair of parallel reflectors persistent for a horizontal length of about 55 km these reflectors are interpreted as the top and bottom of a slice of remnant oceanic crust at their northerly limit the deepest of the two parallel reflectors transects the moho to a depth of 6 7 km into the uppermost mantle we suggest that their termination delimits the northerly extent of a decollement or shear zone at the present continental moho the shear zone was active during the late stages of caledonian collision when mantle originally from beneath the southern continent underthrust old and newly created crust of the collision zone

geochemistry tectonic setting and metamorphism of mid triassic volcanic rocks of greece abstract mid triassic volcanic rocks are preserved in about eight localities in the nappes of the external hellenides and are also widespread in the pelagonian zone of central greece most have suffered low grade metamorphism immobile trace elements from 35 samples 80 major element analyses and pyroxene analyses show that these rocks are the product of an eastward dipping subduction zone the subducted ocean was perhaps analogous to the pennine zone of the alps the othris and pindos ophiolites are probably contemporaneous products of related back arc extension metamorphic mineral assemblages in volcanic rocks of the phyllite series of the external hellenides indicate high pressure low temperature conditions probably related to a second subduction that occurred prior to the main phase of hellenide nappe emplacement in the miocene

geophysical characteristics of the tornquist fan area northwest trans european suture zone indication of late carboniferous to early permian dextral transtension

reflection seismic constraints on paleozoic crustal structure and moho beneath the ne german basin abstract a 330 km long ne sw trending seismic transect across the ne german basin combined with a 75 km long perpendicular cross line in the basin centre reveals the structure of this intracontinental basin between the stable precambrian baltic shield and the weaker mid european variscides the combination of high fold vibroseis and low fold explosive seismic profiling images both upper and lower crustal structures in detail distinct faults related to a rift stage are not observed below the permian sedimentary basin but there is evidence of lower crustal thinning a moho pattern less reflective below the basin centre than at the margins may be related to magmatic underplating the rather flat lying moho dips slightly towards the basin margins structures further north suggest a southern extent of baltica below the ne german basin the caledonian accretionary wedge may be outlined by sw dipping mid crustal reflectors beneath the basin

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

slab top dips resolved by teleseismic converted waves in the hellenic subduction zone the variations of the arrival times and polarities with backazimuth and distance of teleseismic p to s converted waves at interfaces bounding the slab crust under the upper plate mantle are used to constrain the depth dip angle and azimuth of the slab of the hellenic subduction zone a grid search is designed to estimate the model parameters dip values of 16 18 with an azimuth of 20 to 40 are thus derived at 3 sites aligned over 50 km along the eastern coast of peloponnesus they are consistent with the variation from 54 to 61 km of the slab top depths constrained below each receiver north of the gulfs of corinth and evvia a similar depth for the top of the slab is found at a distance from the subduction at least 100 km larger this suggests flatter subduction of a different slab segment such a variation in slab attitude at depth across the region from south of the eastern gulf of corinth to north of evvia is a candidate for the control of the recent or active localized crustal thinning of the upper plate we documented in earlier work and of the surface deformation

miocene detachment in crete and exhumation p t t paths of high pressure metamorphic rocks a major problem posed by the geology of crete is the horizontal contact of an upper unit without miocene metamorphism onto a metamorphosed lower one with early miocene high pressure low temperature hp lt parageneses this very sharp contact is roughly parallel to the major oligo miocene thrust planes which were reactivated as a large scale detachment which allowed exhumation of high pressure units we describe the extensional deformation and the metamorphic evolution of the lower plate most first order deformation features relate to the retrogression from high pressure to low pressure conditions a n s pervasive stretching is observed everywhere often associated with a top to the north sense of shear the extreme variation of thickness of the phyllite quartzite nappe upper part of the lower plate is probably the result of large scale boudinage similar to the one seen in large outcrops the most important observation is the systematic occurrence of fresh carpholite immediately below the base of the tripolitza nappe except in northwestern crete where a late extensional shear zone is present deeper in the nappe pile carpholite is systematically retrograded this observation reveals a drastically different pt history for the upper part of the phyllite quartzite nappe it also suggests that the late extensional shear zone found along the northern side of crete cuts inside the metamorphic structure and brings the nonmetamorphosed tripolitza nappe directly in contact with the deeper parts of the phyllite quartzite nappe pt t paths suggest a fast temperature decrease in the top of the phyllite quartzite during retrogression and hence during the top to the north shear the deeper part of the phyllite quartzite nappe shows a low temperature regime throughout but its pt path includes an isothermal decompression in the first stage we produce a tentative map of domains having experienced similar pt trajectories during decompression the overall cool regime is related to the continuous underthrusting of cola continental units during exhumation isothermal decompression observed in the core of the phyllite quartzite nappe implies fast exhumation during extension and the faster cooling of the upper part is related to a continuous displacement toward the north of a cooler unit during exhumation single grain 39ar 40ar ages obtained on phengites 15 25 ma in various structural sites are in good agreement with these conclusions and with the geological context suggesting that underthrusting of cold units at the front the accretionnary complex occurred contemporaneously with unroofing below a north dipping detachment near the top of the wedge the age of this detachment is bracketed between the end of the high pressure event 20 ma and the deposition of the breccia early to middle miocene in the neogene basins

crustal structure along the central segment of the egt from seismic refraction studies abstract the seismic refraction line between the gulf of genova and the baltic sea was carried out in 1986 as part of the european geotraverse egt 86 the central segment of the egt also known as eugemi european geotraverse middle part has a total length of 825 km and runs from the northern margin of the alps to the baltic sea traversing mainly the variscan mountain area of western germany the p wave data of nine shotpoints were interpreted in detail and a two dimensional p velocity model of the crust was developed between the molasse basin and the southern end of the north german basin for the north german basin the data quality justifies only the construction of a simplified model the internal crustal structure is quite complex in the upper crust of the moldanubian and saxothuringian zones of the variscan orogen the velocities are lower than in the rhenohercynian area the velocity of 6 0 km s representing consolidated seismic basement is reached at depths of as much as 10 12 km northern margin of alps and north german basin and of only 3 km under the mid german crystalline rise mid crustal velocities range from 5 8 to 6 1 km s forming weak velocity reversals in some parts in the lower crust velocities as low as 6 2 km s are seen near the alps in contrast to velocities between 6 8 and 7 2 km s in the exposed variscan orogen north of shotpoint e between hannover and the river elbe the velocity of the lower crust is about 6 4 km s north of the elbe line it increases abruptly to 6 9 km s the crust mantle boundary rises from 34 km depth under the northern margin of the alps to 29 km under the swabian jura under the variscan orogen to the north the crustal thickness varies only slightly around an average depth of about 29 1 k but drops to about 30 km under the north german basin between the elbe line and the ringkobing fyn high the moho rises to a depth of about 26 km and the data indicate at least one fault like step of 1 km before the crust thickens toward the basement high the velocities in the uppermost mantle show considerable variation the highest velocity of 8 4 km s is observed beneath the saxothuringian zone and the lowest values of 7 8 7 9 km s are recorded under the hessen depression

rapid exhumation of high pressure metamorphic rocks in kythera peloponnese greece revealed by apatite u th he thermochronology abstractapatite u th he and apatite fission track cooling ages from high pressure hp metamorphic rocks in the south aegean forearc along the kythera strait kythera and southeastern peloponnese suggest rapid exhumation during middle to late miocene times hp rocks from the kythera strait exhibit two perpendicular extensional structures samples with arc normal or arc parallel extensional fabrics yielded apatite u th he cooling ages of 8 10 ma the more precise u th he ages are consistent with previously reported apatite and zircon fission track ages obtained from the same rock units the less precise but still accurate fission track data provided a reference for u th he dating on relatively young uranium poor apatites the combined data therefore precisely and accurately constrain the exhumation history of hp rocks and indicate that localized arc parallel extension in the kythera strait was active for an 5 m yr interval during the regional arc expansion

uplift related retrogression history of aragonite marbles in western crete greece in the low grade high pressure 400 c 10 kbar metamorphic phyllite quartzite unit of western crete widespread occurrences of aragonite marbles have been discovered recently a sedimentary precursor is proved by relic structures bedding fossils partial or complete transformation of aragonite into calcite is ubiquitous compositional and microstructural features reflect the metamorphic history 1 the high pressure stage is documented by aragonite that is chemically characterized by incorporation of variable amounts of sr and the lack of mg the most sr rich aragonite has about 9 wt sro xsrarag 0 09 a compositional zoning observed in some aragonite crystals may be due to the prograde divariant calcite aragonite transformation in the system caco3 srco3 because the parent rocks probably were sr poor calcite limestones one can speculate that strontium has been supplied from an external source under high pressure conditions 2 during uplift calcite replacing aragonite did not equilibrate with unreplaced aragonite disequilibrium is indicated by highly variable compositions of calcite crystals that show topotactic relations to the host aragonite the calcite compositions range from that of the host aragonite sr rich and mg free to mg bearing and sr poor 3 calcite that recrystallized during retrogression is generally sr poor mean value ofxsr 0 005 mg bearing xmg 0 010 and chemically homogeneous because practically no sr remains in the calcite an interaction with a fluid phase is indicated in fine grained calcite marbles rich in solid organic matter microstructural features indicative of former aragonite may be present 4 the last stage of retrogression is documented by the appearance of radiating aragonite in veins and nodules this aragonite which shows neither deformation nor retrogression was probably formed metastably in a near surface environment

some aspects of the late and post variscan development of the northwestern german basin abstract the crust of northern germany can be subdivided into three provinces that are evident by differences in crustal density seismic velocity reflectivity magnetic characteristics thermal history and electric conductivity these provinces are limited by the elbe river and the northern foothills of the mittelgebirge during the pre and post variscan evolution the tectonic setting of northern germany has changed repeatedly each of the three recognized basement provinces differs in the timing of basement consolidation caledonian variscan the sequence of basin development during permian mesozoic and cenozoic times and the timing and intensity of magmatic activity permian cretaceous cenozoic

cenozoic thermal evolution of the central sierra nevada california from uth he thermochronometry apatite u th he cooling ages are reported for igneous apatite samples from the central sierra nevada and compared to published apatite fission track ages and track length data from the same mineral separates helium ages are youngest at low elevations and increase systematically toward higher elevations ranging from 43 to 84 ma at yosemite valley 32 to 74 ma at kings river canyon and 23 to 75 ma at mt whitney helium ages from high elevation samples are generally concordant with corresponding fission track ages while lower elevation helium ages are substantially younger cooling histories inferred from present laboratory derived fission track annealing and helium diffusion models do not match well suggesting that either helium diffusion rates or fission track annealing rates are miscalibrated at temperatures below about 60 c for geologic exposure periods unlike the fission track results the helium data do not indicate a very low geothermal gradient in the sierra nevada during early to middle tertiary time

caledonian and proterozoic terrane accretion in the southwest baltic sea abstract a marine seismic reflection survey was carried out in 1996 by dekorp potsdam and bgr hannover in the sw baltic sea several tectonic lineaments were crossed nearly perpendicularly for example the caledonian deformation front which is assumed to mark the northern boundary of the terrane avalonia which accreted to baltica ca 400 ma here a bivergent collision is clearly observed confirming early ideas from the babel survey the ne dipping reflections in the uppermost mantle are interpreted as signs of the subducted tornquist ocean a similar tectonic style of compression and indentation is observed in the proterozoic crust northeast of bornholm where in addition a remarkable crustal thickening and a strong increase of reflection power is observed the three dekorp lines in this area provide a certain three dimensional control and allows extension of similar observations from the babel line a southward this proterozoic terrane accretion seems to be connected to major tectonic lineaments in southern sweden either to the gothian thrust or the sveconorwegian front

middle miocene graben development in crete and its possible relation to large scale detachment faults in the southern aegean the linkage between the development of south facing cretan graben and large scale detachment faulting in the southern aegean is unknown widespread serravallian deposits in the ierapetra graben of crete supply constraints to middle miocene graben development in the southern aegean the ierapetra graben and by inference the cretan graben in general were hitherto believed to have formed as a result of sinistral transpression during n s shortening we argue that the formation of the cretan graben is due to n s extension the south dipping n s extending kritsa normal fault served as the master fault controlling graben development in the ierapetra graben the kritsa normal fault is either an antithetic fault related to the top n cretan detachment or a synthetic fault associated with the top s ios detachment the overall geometry and timing relationships lead us to favour a connection with the ios detachment which in turn implies a large scale displacement on the ios detachment

thermal effects of scanning electron microscopy on he diffusion in apatite implications for uth he dating abstract in order to investigate potential diffusive loss of he from apatites during sem analysis we performed 1 single grain u th he dating for 47 durango apatite fragments from th he ages are internally consistent within their errors and indistinguishable from the reported 40ar 39ar ages of 31 44 0 18 2 ma and the apatite u th he ages of 31 02 1 01 ma standard deviation mcdowell et al 2005 the results from the electron matter interaction simulation suggest that temperature rise t temperature increase during electron bombardment peaks within a very thin layer at the outermost of the hypothetical apatite grain and falls below 50 k within a depth of 0 3 m from the surface based on the simulated t profile combined with available he diffusion parameters the fractional loss of he fhe was calculated for different apatite grain dimensions the numerical simulation supports that the he loss from apatite grains of typical physical dimensions is negligible th he ages for sem treated apatites as well as diffusion simulation using the electron matter interaction model indicate that sem spot analysis or extensive chemical mapping prior to apatite u th he dating does not cause any meaningful diffusive he loss for most of the apatite samples

an integrated study of the ne german basin abstract the ne german basin is part of the southern permian basin south of the transeuropean suture zone tesz here we report an attempt to integrate a variety of geological and geophysical data in order to reveal the present day deep crustal structure of the ne german basin special focus is taken on detailed geological information available reflection seismic data wide angle refraction seismic data and gravity data based on this integrative approach a concise crustal model is developed which can be subject to further evaluation furthermore it is shown that the ne german basin is an outstanding feature quite different from classical basin types as the moho is flat below the basin neither a simple shear nor a pure shear extension model can be applied instead a thick high velocity lower crustal layer is present below the basin centre this high velocity lower crust is also observed in the western part of the basin and can be taken as characteristic for east avalonia results of gravity modelling indicate the presence of a high density lower crust thus supporting the wide angle data furthermore changes in crustal structure can be derived from changes in reflectivity pattern and from the gravimetric signature along the elbe fault system indicating the presence of different crustal domains north and south of the fault system an elastic plate model where the forces applied are the sediment load a vertical load at the southern margin accounting for the harz moutains and a nne ssw directed compression indicates a buckling of the crust during late cretaceous to tertiary inversion however the correlation between the observed crustal structure and the tectonic events that have affected the area remains a subject of discussion a permian thermal event affected the upper mantle and the lower crust and therefore may have modified the crustal memory with regard to caledonian and variscan events additional tectonic events affected the area during the mesozoic in conclusion it remains an open question whether the high velocity and high density lower crustal structure represents a remnant of east avalonia whether it is related to the formation of the permo triassic basin or is the cumulative result of a series of events during the palaeozoic and mesozoic

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

major crustal features between the harz mountains and the baltic shield derived from receiver functions major crustal features between the harz mountains and the baltic shield derived from receiver functions

high resolution seismic analysis of the coastal mecklenburg bay north german basin the pre alpine evolution the pre alpine structural and geological evolution in the northern part of the north german basin have been revealed on the basis of a very dense reflection seismic profile grid the study area is situated in the coastal mecklenburg bay germany part of the southwestern baltic sea from the central part of the north german basin to the northern basin margin in the grimmen high area a series of high resolution maps show the evolution from the base zechstein to the lower jurassic we present a map of basement faults affecting the pre zechstein the pre alpine structural evolution of the region has been determined from digital mapping of post permian key horizons traced on the processed seismic time sections the geological evolution of the north german basin can be separated into four distinct periods in the rerik study area during late permian and early triassic evaporites and clastics were deposited salt movement was initiated after the deposition of the middle triassic muschelkalk salt pillows which were previously unmapped in the study area are responsible for the creation of smaller subsidence centers and angular unconformities in the late triassic keuper especially in the vicinity of the fault bounded grimmen high in this area partly lower jurassic sediments overlie the keuper unconformably the change from extension to compression in the regional stress field remobilized the salt leading to a major unconformity marked at the base of the late cretaceous

strike slip tectonics within the sw baltic sea and its relationship to the inversion of the mid polish trough evidence from high resolution seismic data abstract the sw baltic sea occupies an area where crustal scale regional tectonic zones of different age merge and overlap creating a complex tectonic pattern this pattern influenced the evolution of the mesozoic sedimentary basin in this area we present an interpretation of new high resolution seismic data from the sw baltic sea which provided new information both on modes of the late cretaceous inversion of this part of the danish polish mesozoic basin system as well as on relationship between tectonic processes and syn tectonic depositional systems within the bornholm darlowo fault zone located between the koszalin fault and christianso block both strike slip and reverse faulting took place during the inversion related activity the faulting was related to reactivation of extensional pre permian fault system syn tectonic sedimentary features include a prominent generally s and se directed progradational depositional system with the major source area provided by uplifted basement blocks in particular by the bornholm block sediment progradation was enhanced by downfaulting along a strike slip fault zone and related expansion of accommodation space closer to the christianso block some syn tectonic deposition also took place and resulted in subtle thickness changes within the hinge zones of inversion related growth folds lack of significant sediment supply from the inverted and uplifted offshore part of the mid polish trough suggests that in this area nw se located marginal trough parallel to the inversion axis of the mid polish trough did not form and that uplifted bornholm block played by far more prominent role for development of syn inversion depositional successions

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

nizuse a deep seismic reflection line in north eastern germany out of a dense network of seismic reflection lines for hydrocarbon exploration in the north east german basin several lines were recorded to 12 s twt to obtain information about the structure of the crust and the crust mantle transition one of these profiles is presented here this stretches for 110 km in a nne direction between neustrelitz and the island of usedom it reaches from the external variscides in the south across the north german massif into the rugen pomorze terrane in the baltic sea below cenozoic mesozoic paleozoic cover with clear reflections down to base zechstein the reflectivity varies considerably with depth and also laterally the paleozoic and precambrian sediments and basement are generally void of reflections but the lower crust and the moho show strong reflections to the north the reflectivity decreases and the moho depth increases to beyond the bottom of the record section at 12 s there are no direct indications for deep reaching faults such as the trans european fault in the north the north german massif acted as a ramp towards the variscan orogeny similar to the london brabant massif further west

post cranial remains of coelurosaurs dinosauria theropoda from the late jurassic of tanzania small theropod post cranial material from tendaguru tanzania the only known late jurassic theropod locality in the southern hemisphere is reviewed material originally described as coelurosaurs includes at least one taxon of basal tetanuran and one taxon of small abelisauroid together with the abelisauroid elaphrosaurus and the presence of a larger ceratosaur in tendaguru this material indicates that ceratosaurs were an important faunal element of late jurassic east african theropod faunas one bone furthermore shares derived characters with the holotype of the poorly known middle jurassic australian theropod ozraptor and allows the identification of the latter as the oldest known abelisauroid thus indicating an early divergence of ceratosaurids and abelisauroids within ceratosaurs abelisauroids might have originated in gondwana and represent important faunal elements of cretaceous gondwanan theropod faunas in general

caledonian deformation upon southwest baltica and its tectonic implications alternatives and consequences the continuation of the basement of the southwestern baltic shield toward the sw is of major interest for the caledonian evolution in the southwestern baltic sea and northern germany a reinterpretation of various marine seismic data suggests a reconsideration of the caledonian collision pattern the sorgenfrei tornquist zone forming the northwestern extension of the tornquist zone is regarded as the northeasterly boundary fault and the elbe lineament is regarded as the southwestern limit of an area which suffered from the docking of east avalonia to baltica it shows many northwestsoutheast striking structures anomalies and fault patterns from our studies two alternative models emerge one which considers the caledonian deformation front as the northeastern limit of east avalonia and a zone of major transpression collision and subduction of the tornquist sea another model considers the elbe lineament in schleswig holstein nw germany as a major dextral strike slip fault which is interpreted as the northeasterly limit of east avalonia and the southwest boundary of the baltic shield along the elbe lineament the tornquist sea plus rotating avalonia were displaced to the northwest a large part of the area to be studied might have developed into a passive margin toward the upper ordovician a decision which of the two models is to be prefered has to be the major goal of future geophysical experiments

crustal structure at the trans european suture zone in northwest poland based on gravity data a new gravity model of the crustal structure of the trans european suture zone in the northwestern poland has been constructed the bouguer anomaly map obtained after stripping off the three dimensional gravity effect of the sedimentary cover down to the zechstein formations is characterized by a 50 mgal gravity anomaly we have assumed that the short wavelength components derive from upper crustal intrusions and the long wavelength components reflect crustal thickness and lateral heterogeneity which are strongly supported by the new seismic data along the lt 7 geotraverse quantitative modelling of gravity data along three profiles crossing the area indicate the presence of anomalous masses within the lower palaeozoic sequence mainly along the teisseyre tornquist zone two of the profiles crossing the long wavelength stripped gravity high suggest the existence of a zone of 35 km crust above a dense upper mantle along the teisseyre tornquist zone the extent of the zone can be determined based on the bouguer anomalies interpretation

deep seismic expression of an ancient plate boundary in europe seismological results on the structure of the upper mantle below europe reveal a marked contrast in seismic properties between precambrian and younger parts of europe the precambrian craton in eastern europe is characterized by high shear wave velocities which can be explained by low temperatures the transition to low seismic velocities below phanerozoic europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers despite the long and complex tectonic history of the plate boundary zone the transition is remarkably sharp which rules out any significant lateral transport of asthenospheric material across the suture zone

interpreting data dispersion and inverted dates in apatite u th he and fission track datasets an example from the us midcontinent abstract new apatite u th he ahe and apatite fission track aft data were acquired for cratonic basement samples from an 80 m span of drillcore in northeastern kansas the short depth interval over which the samples were collected indicates that they should have undergone thermal histories that would be indistinguishable using low temperature thermochronometry techniques individual ahe dates from four samples range from 99 to 464 ma three samples yield dates 300 ma higher eu 39 113 ppm and substantial data dispersion uncorrelated with eu and grain size these apatites have strong and variable eu zonation aft dates for five samples range from 242 to 291 ma the sample with the highest eu apatites and oldest ahe dates yields the youngest aft results these results are inverted with ahe dates distinctly older than the corresponding aft date we explore both the causes of data dispersion and the overall compatibility of this cratonic dataset we find that geologically reasonable thermal histories can 1 explain the distribution of the moderate eu ahe data when accounting for the influence of radiation damage grain size and eu zonation on apatite he diffusivity 2 reproduce the observed dispersion in the high eu ahe data when using a viable range of eu zonation and grain size and 3 explain the aft data for the same samples the ahe and aft data are mutually consistent and viable thermal histories successfully predict the observed pattern of older ahe than aft dates for the high eu apatites together these results suggest that appropriately accounting for the known controls on apatite he diffusivity can explain the observed dispersion and inverted ahe and aft results in some thermochronometry datasets a range of ahe dates should be especially common in cratonic data because small differences in apatite he diffusivity are amplified by the thermal histories that typify cratonic settings we use these results to develop some guidelines for interpreting dispersed ahe datasets first date eu and date grain size correlations should be evaluated and if these patterns occur they can be used to better resolve the thermal history second for samples that yield inexplicably large dispersion of ahe dates uncorrelated with eu and crystal size the appropriate strategy is either to reject these samples from the suite used for thermal history interpretation or to acquire additional data to help decipher the significance of the age distribution

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

deep structure of the earth s crust in the contact zone of the palaeozoic and precambrian platforms in poland tornquist teisseyre zone abstract one of the major tectonic problems in europe concerns the southwest margin of the east european platform in the region of the so called polish danish trough in general this margin is assumed to be the tornquist teisseyre t t line running approximately from northwest to southeast in this part of europe determination of deep crustal structure of the contact zone between the precambrian platform and the palaeozoic platform was the main aim of the deep seismic sounding dss programme in poland in 1965 1982 deep seismic soundings of the earth s crust have been made in the t t line zone along nine profiles with a total length of about 2600 km the results of deep seismic soundings have shown that the crust in the marginal zone of the east european platform has highly anomalous properties the width of this zone ranges from 50 km in northwest poland to about 90 km in southeast poland the crustal thickness of the palaeozoic platform in poland is 30 35 km and of the precambrian platform 42 47 km while in the t t tectonic zone it varies from 50 to 55 km above the moho boundary in the t t zone at a depth of 40 45 km there is a seismic discontinuity with p wave velocities of 7 5 7 7 km s boundary velocities mean velocities and stratification of the earth s crust vary distinctly along the t t zone there are also observed high gravimetric and magnetic anomalies in the t t zone the t t tectonic zone determined in this manner is a deep tectonic trough with rift properties the deep fractures delineating the t t tectonic zone are of fundamental importance for the localization of the plate edge of the precambrian platform of eastern europe in the light of dss results the northeastern margin of the t t tectonic zone is a former plate boundary of the east european platform

the trans european fault a critical reassessment abstract new deep seismic pro les in the southern baltic region have failed to image the trans european fault evidence for this structure of suggested pre cadomian age is critically re examined localized geophysical anomalies are present but these cannot be correlated with known structuralfeatures of the region based on the inconclusive evidence for this structure we would therefore pro pose that the term trans european fault should not be used in the future and that to avoid confu sion authors use local names for local structures author for correspondence tmc gfz potsdam de stzcdftefdanishbasinrfh eugemi aelnorthgermanmassif nizu sebasin 9601pq2 9 1 4 13 25 berthelsen 1984eugeno s working group 1988horst flueh borngen 1994krauss 1994franke 1993 0 100 km 12345 i pq2 9pq2 9 3 3 loss 1 70h2 1 90k5 1 88g14 1 86pud 1 86rn 2 67gst 1 73rn 4 64 r u g enusedom 0 30 km figure 1 map showing the main structural features and thelocations of the deep seismic surveys in the region the vari ous trends of the trans european fault are also indicated 1 pozarski brochwicz lewinski tomczyk 1982 buttermed caledonian deformation front berthelsen 1984 babel working group 1993 mona lisa workinggroup 1997 2 eugeno s working group 1988 3 horst flueh borngen 1994 4 krauss 1994 5 franke 1993 inset map shows the locations of wells mentioned inthe text key cdf caledonian deformation front el elbe lineament rfh ringkobing fyn high stz sorgenfrei tornquist zone tef trans european fault