adakite like and normal arc magmas distinct fractionation paths in the east serbian segment of the balkan carpathian arc are used to assess petrogenetic and regional geodynamic processes associated with late cretaceous subvolcanic intrusions within the sparsely studied timok magmatic complex tmc and ridanj krepoljin zone rkz of eastern serbia the tmc and rkz form part of the apuseni banat timok srednogorie abts magmatic belt a cu au mineralized calc alkaline magmatic arc related to closure of thetethys ocean that extends through romania serbia and bulgaria in se europe zircon ages based on u pb laser ablation inductively coupled plasma mass spectrometry supplemented by existing isotope dilution thermal ionization mass spectrometry data respectively range from 89 to 79 ma and from 76 to 71 ma for the tmc and rkz this age pattern corresponds to cross arc younging away from the european continent adakite like trace element signatures y 18 ppm are linked with samples that extend across the arc these overlap in space and time with samples that conform to a normal arc differentiation trend we performed energy constrained assimilation fractional crystallization ec afc modeling of sr la nd yb concentrations and sr and nd isotopic data results suggest that the two distinct fractionation trends may be explained in terms of a common mantle derived parental magma but distinct fractionation and assimilation paths in the lower and upper crust petrogenesis of the adakite like magmas is consistent with extensive high pressure amphibole fractionation in the lower crust followed by ascent and plagioclase dominant fractionation and assimilation in the upper crust in contrast normal arc signatures appear to have evolved exclusively via an upper crustal differentiation process overall our interpretation supports mantle wedge melting related to weak extension during progressive rollback of a subducting slab

evolution of volcanism around the eastern sector of mt etna inland and offshore in the structural framework of eastern sicily abstract the authors highlight a new perspective to understanding the volcanism in the mt etna eastern sector inland and offshore based on original studies of the sea floor off the ionian coast of etna by means of various direct surveying methods underwater explorations and indirect ones bathymetric reconstructions using echosounders they also propose a new interpretation of geophysical geochemical and structural surveys carried out over the last two decades results show that eastern etnean sector s volcanism extends as far as the ionian sea to a maximum distance from the coast of probably about 20 km in their opinion the absence of outcropping apparatuses in the lower eastern flank of etna is due to these apparatuses being buried by a large detritic formation chiancone due to the dismantling of the ancient alkaline centres aac localised to the west the authors consider the structures highlighted by the study of the digital elevation model dem of the ionian sea floor and by the multibeam analysis marani et al 2004 from seafloor to deep mantle architecture of the tyrrhenian backarc basin vol 44 mem descr carta geol ital pp 1 2 to be of a volcanic nature this hypothesis opens up a new field of study within the evolution of the eastern etnean edge s volcanism inland and offshore in the last 500 ky and would further confirm the eruptive axes migration from east to west

slabs hotspots cratons and mantle convection revealed from residual seismic tomography in the upper mantle to further investigate the fate of slabs the structure of hotspots and the style of mantle convection we calculate residual tomographic maps in the upper mantle by excluding from the tomography the first order effects of conductive cooling of oceanic plates deep cratonic roots and cooling or partial melting associated with subducted lithosphere no correlation is found between residual tomography in the upper mantle and the 30 130 ma subduction the good correlations between residual tomography in the transition zone 400 650 km and 0 30 ma subduction at spherical harmonic degree l 2 can be explained either by slab accumulation in the transition zone beneath some subduction zones or by the poor lateral resolution of seismic tomography hotspots correlate with the residual tomography in the shallow 100 400 km and the lowermost mantle at degree l 2 however correlations of hotspots and seismic velocities in the middle mantle and correlations between residual tomography at shallow depths and lowermost mantle tomography are poor therefore the connection between residual tomography at shallow depths and seismic tomography in the lowermost mantle is not clear craton distribution correlates with distribution of hotspots and residual topography very well at degree l 6 this might indicate that cratonic roots may affect the locations of upwellings and thus modulate upper mantle convection or that the degree l 6 could be intrinsic in upper mantle convection with cratons and and other near surface features establishing the pattern

the geometry of aleutian subduction three dimensional kinematic flow model we construct a steady state kinematic model of slab flow along the aleutian arc assuming the slab s geometry is known the slab geometry is constrained by local network data where the slab is seismically active and by p wave residual sphere analysis of 11 earthquakes and one nuclear explosion where it is aseismic the slab is approximated by a thin newtonian sheet subducting in a less viscous and incompressible mantle particles enter the trench at known rates of relative plate motion and are required to subduct along the predefined slab geometry for discrete but small 0 1 m y time steps we determine the speed and direction of each slab particle that minimizes dissipation power as the spherical shell oceanic lithosphere deforms to obtain the observed slab shape because the dip of the slab in the central aleutians is steep relative to the radius of curvature of the trench the slab must stretch along arc to obtain its present configuration our kinematic model represents one internally consistent flow that results in the observed geometry furthermore it provides a lower bound on the total amount of internal in plane deformation required by the shape and an estimate of stream lines and of the orientation and spatial distribution of the deformation rate the predicted in plane strain rate field is dominated by along arc extension reaching values as large as 10 15s 1 in the central aleutians and decaying by an order of magnitude to the east and west the slab accumulates an in plane strain of 10 by the time it reaches the depth of the seismicity cutoff along arc variations in both the magnitude and orientation of calculated strain rates are consistent with the spatial distribution of seismic moment release and source mechanism orientations of intermediate depth earthquakes suggesting that in order to understand intermediate focus earthquakes one must consider along arc deformation three dimensional analyses of subduction in a spherical geometry such as the present study are required to model along arc effects relative plate motions along the trench vary from nearly normal in the eastern aleutians to transform farther west coincident with this change the maximum depth of seismicity within the descending slab decreases from 250 to 50 km and active andesitic volcanism ceases the kinematic flow model predicts that the slab subducted obliquely along the central portion of the aleutian arc is transported laterally westward producing cold slab material to a depth of at least 300 km along the entire arc after only 15 m y of subduction the lack of volcanic activity in the western aleutians is apparently related to the lateral transport of the slab perhaps indicating that the slab is dehydrated and incapable of producing the volatiles necessary for arc magmatism the along arc variation in the maximum depth of seismicity can be explained thermally we construct temperature estimates within the slab using a quasi three dimensional finite difference scheme including entrained mantle flow stream lines from the kinematic model and the time history of the age of the subducting lithosphere as a function of position along the trench the theoretical temperature at the seismicity cutoff depth is remarkably close to a constant fraction of the depth dependent mantle solidus along the entire arc this observation is consistent with the hypothesis that seismicity terminates because of the initiation of high temperature steady state creep and provides an explanation for the lack of intermediate focus earthquakes in the western aleutians even though slab material exists there

trench migration and subduction zone geometry seismic tomography results show a large variety in upper mantle structure along convergent plate boundaries we numerically investigate the effect of trench migration on the evolution of a slab with temperature dependent viscosity encountering a viscosity interface we find that subduction zone geometry is sensitive to even small rates 1 cm yr of retrograde motion increase in trench migration rate decreases the dip angle of the slab and its ability to penetrate the lower mantle upon including a background mantle flow it turns out that trench migration relative to the upper mantle flow is more decisive than the absolute plate velocities subduction zone geometry appears to be strongly time dependent we conclude that individual tectonic setting and time dependent slab behaviour can account for many different types of observable subduction zone anomalies our model temperature can adequately account for magnitudes and patterns of seismic anomalies as obtained from seismic tomography

seismic structure of the southern apennines as revealed by waveform modelling of regional surface waves summary we investigate the crust and upper mantle structures beneath the southern apennine mountain chain using three component seismograms from the calabria apenninetyrrhenian subduction collision accretion network cat scan array surface wave waveforms from three moderate sized m w 5 0 regional earthquakes are modelled using multiple frequencies 0 03 0 06 and 0 05 0 2 hz and both forward and linearized inversion algorithms our best fitting shear velocity models clearly reflect the major tectonic units where for example the average seismic structure at depths above 50 km beneath apulia is substantially faster than beneath the apennine mountain chain we identify a prominent low velocity channel under the mountain belt at depths below 25 30 km and a secondary low velocity zone at 6 12 km depth near mt vulture a once active volcano speed variations between love and rayleigh waves provide further constraints on the fabric and dynamic processes our analysis indicates that the crustal low velocity zones are highly anisotropic maximum 14 per cent and allow transversely polarized shear waves to travel faster than vertically polarized shear waves the upper crustal anomaly reveals a layer of highly deformed rocks caused by past collisions and by the active normal faults cutting across the thrust sheets whereas hot mantle upwelling may be responsible for a high temperature partially molten lower crust beneath the southern apennines

seismic velocity and poisson s ratio tomography of the crust beneath east anatolia abstract eastern anatolia is a region in the early stages of continent continent collision and so provides a unique opportunity to study the early development of continental plateau located within the alpine himalayan fold thrust fault belt the anatolian plateau is geologically very complex with over half of the surface area covered with late cenozoic volcanics of diverse composition the plateau is also seismically active and is dissected by numerous seismogenic faults predominantly of strike slip motion in this study we determine 3 d tomographic images of the crust beneath eastern anatolia by inverting a large number of arrival time data of p and s waves from the obtained p and s wave velocity models we estimated the poisson s ratio structures for a more reliable interpretation of the obtained velocity anomalies our tomographic results are generally consistent with the major tectonic features of the region high p and s wave velocity anomalies are recognized near the surface while at deeper crustal layers low seismic wave velocities are widely distributed poisson s ratio exhibits significant structural heterogeneities compared to the imaged velocity structure the seismic activity is intense along highly heterogeneous zones and is closely associated with pre existing faults in the central and western parts of the study area results of the checkerboard resolution test indicate that the imaged anomalies are reliable features down to a depth of about 40 km the low velocity high poisson s ratio zones in the middle to lower crust are consistent with many geophysical observations such as strong sn attenuation low pn and sn velocity and the absence of mantle lid implying the presence of partial melt in the uppermost mantle

olivine spinel transitions experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity the sequence of high pressure phase transitions in olivine is traditionally used as a model for seismic velocity variations in the 200 to 650 km depth interval in a mantle of peridotitic bulk composition it has been proposed that the observed seismic velocity increase at 400 km depth is too sharp and of too small a magnitude to be attributable to the phase change and that the upper mantle must thus be chemically stratified with the 400 km discontinuity being due either to a combination of phase changes in a layer of pyroxene garnet rich piclogite composition or to a chemical boundary between such a piclogite layer and an overlying peridotitic layer using available calorimetric thermoelastic and synthesis data and their associated experimental uncertainties we have derived internally consistent high pressure phase relations for the mg2sio4 fe2sio4 join we find that the divariant transition which is generally regarded as occurring over a broad depth interval for mantle olivine compositions is in fact extremely sharp the seismic discontinuity corresponding to the transition in mg0 9fe0 1 2sio4 should occur over a depth interval isothermal of about 6 km at a depth of approximately 400 km the sharpness of this transition is quite insensitive to uncertainties in the constraining calorimetric thermoelastic and synthesis data in addition we have computed seismic velocity profiles for a model mantle consisting of pure olivine of mg0 9fe0 1 2sio4 composition comparison of these computed profiles to those derived from recent seismic studies indicates that the magnitude of the observed velocity increase at 400 km depth is consistent with a mantle transition zone composed of about 60 70 olivine we conclude that there is no need to infer the existence of pyroxene garnet rich compositions such as eclogite or piclogite in the transition zone since an upper mantle of homogeneous olivine rich peridotitic composition is consistent with the available seismic velocity data

slab temperature and thickness from seismic tomography 1 method and application to tonga delay times of compressional body wave phases from both teleseismic and local events are used to invert for a high resolution p wave velocity model in the tonga subduction zone the images obtained show a high velocity subducting slab with velocity deviations of the order of 3 4 assuming to first order that the positive velocity anomalies within the slab are caused by a temperature effect a theoretical slab temperature model based on the diffusion equation is used to explain velocity anomalies within the tomographic slab temperature differences between the interior of the slab and the ambient mantle are converted to velocity perturbations using the scaling parameter dvp dt 4 8 10 4 km s 1 c 1 for lithosphere material the optimal values for the parameters in the temperature model are found using a nonlinear optimization that compares the integrated velocity anomalies in the tomographic slab region to integral of high velocities in a synthetic slab derived from a temperature model the parameters for slab thickness and mantle potential temperature are not uniquely determined therefore a fixed value for the mantle potential temperature based on laboratory values for the temperature of the spinel to perovskite transition at 660 km is used using 1180 c as the potential temperature the theoretical temperature model gives an optimal slab thickness of 82 km for a region near 29 s in tonga the uncertainty in the thickness is dominated by the uncertainty in the mantle temperature and would be 8 km for an uncertainty of 100 in mantle temperature but nonsystematic errors are less in order to enhance the tomographic result the velocity model is biased towards the theoretical slab model however a posteriori changes made to the tomogram will most likely violate the fit to the delay time data to prevent this the difference between the tomogram and the predicted slab model is projected onto the null space of the inversion to remove components which do not satisfy the seismic data using only null space components to modify the minimum norm solution an enhanced model is obtained which has been biased toward the theoretical solution but has the same data misfit as the minimum norm solution the final image shows a very narrow and continuous slab with maximum velocity anomalies of the order of 6 7 many of the gaps within the slab as well as artifacts around the slab which were present in the minimum norm solution are absent in the biased image

wide angle images of the mediterranean ridge backstop structure the mediterranean ridge is an accretionary wedge consisting of a large pile of tectonically deformed sediments in the past the mediterranean ridge has been interpreted as a prism related to hellenic subduction however geophysical evidence pasiphae cruise 1988 has indicated the presence of a high velocity body southward of the hellenic trench which was subsequently interpreted as an extended continental backstop during the recent imerse project coincident wide angle and normal incidence seismic data were collected over the ridge along the ne sw medriff corridor explora cruise 1994 the objectives of the imerse project were to acquire the seismic observations necessary for a high resolution structural model of the western mediterranean ridge including the structure of the newly interpreted continental backstop here we present the results of recent re modelling of two ship expanding spread seismic refraction data esp 8 and 9 recorded during the pasiphae cruise the modelling of these data has allowed an approximate constraint on the position of the juncture between the mediterranean accretionary complex and its buttress also presented are processing and modelling results of the recently acquired imerse wide angle data travel time modelling of these data has allowed the construction of six multi azimuth velocity depth models these models show the existence of high velocity material at depth p wave velocity 5 km s inferred to be extended backstop and constrain its southward extent all models show the presence of a messinian evaporite layer near the surface the evaporite layer is observed to vary in thickness from 0 to 2 0 km with the existence of local thickening and thinning due to depositional factors tectonism and salt dissolution in addition combined analysis of the wide angle velocity models with coincident seismic reflection and swath bathymetry data indicates that the geometry of the continental backstop varies laterally as a consequence of transform faulting possibly related to the southward rotation of the peloponnesus thrust sheet and backstop emplacement

joint inversion for three dimensional s velocity mantle structure along the tethyan margin abstract for purposes of studying the lateral heterogeneity as well as for ultimately predicting seismograms for this region we construct a new 3 d s velocity model by jointly inverting a variety of different seismic data we jointly invert regional waveforms surface wave group velocity measurements teleseismic s arrival times and crustal thickness estimates from receiver functions refraction lines and gravity surveys these data types have complementary resolving power for crust and mantle structures vertical and lateral variations shallow and deep mantle features local and global structure therefore a joint inversion of these data sets might help unravel the complexity of this tectonically diverse area these measurements are made from a combination of mantle investigation of the deep suture between europe and africa midsea program for array seismic studies of the continental lithosphere passcal geoscope geofon global seismographic network gsn international deployment of accelerometeres ida mednet national networks and local deployments throughout the study region which extends from the western mediterranean region to the hindu kush and encompasses northeastern africa the arabian peninsula the middle east and part of the atlantic ocean for reference we have fitted the waveforms of regional s and rayleigh waves from over 3800 seismograms using partitioned waveform inversion we include over 3000 crustal thickness estimates from receiver functions gravity measurements and refraction profiles we include rayleigh wave group velocities for hundred thousands of paths transecting the region we have over 3000 teleseismic s arrival times measured through cross correlation and over 170000 from picks originally reported to the international seismological centre isc

heat flow in the balearic and tyrrhenian basins western mediterranean we present the results of three detailed heat flow surveys which are used to investigate the variations of heat flow and age of the balearic and tyrrhenian basins in the western mediterranean analysis of 12 measurements within a 10 km radius from 40 01 4 55 e in the balearic abyssal plain shows a mean heat flow of 92 10 mw m 2 after correction for the effects of sedimentation this value agrees well with the predictions of plate cooling and high extension stretching models for crust of the late oligocene age proposed for the basin a similar survey with 18 measurements around 40 16 n 11 19 e in the western tyrrhenian gives a flux of 134 8 mw m 2 while the third survey of 26 measurements in the southern tyrrhenian abyssal plain at 37 17 n 12 58 e yields a slightly higher heat flow of 151 10 mw m 2 these values are within the range predicted by simple plate cooling models for the late miocene ages of the deep tyrrhenian basin thus our observations suggest that although the mode of crustal formation of these deep marginal basins is less well defined than that of the major ocean basins the thermal signature is similar also the trend of increasing heat flow from west to east through the balearic and tyrrhenian basins is in agreement with models of the formation of the western mediterranean behind an eastwardly migrating trench system in all three areas the measured flux shows significant local variability in the two westernmost surveys this can be attributed to the presence of buried high conductivity salt structures but in the third area se tyrrhenian the magnitude of the variations is several times greater than can be attributed to steady state thermal refraction alone instead evidence exists for localized hydrothermal activity linked to the small topographical relief within the survey area

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

nappe stacking resulting from subduction of oceanic and continental lithosphere below greece we quantitatively investigate the relation between nappe stacking and subduction in the aegean region if nappe stacking is the result of the decoupling of upper crustal parts 5 10 km thick from subducting lithosphere then the amount of convergence estimated from balancing the nappe stack provides a lower limit to the amount of convergence accommodated by subduction the balanced nappe stack combined with the estimated amount of completely subducted lithosphere indicates 700 km of jurassic and 2400 km of post jurassic convergence from seismic tomographic images of the underlying mantle we estimate 2100 2500 km of post jurassic convergence we conclude that 1 the imaged slab represents the subducted lithosphere that originally underlay the nappes 2 since the early cretaceous subduction in the aegean has occurred in one single subduction zone and 3 the composition of the original basement of the nappes indicates that at least 900 km of sub upper crust continental lithosphere subducted in the aegean

upper mantle compressional velocity structure beneath the west mediterranean basin p waveforms of regional crustal earthquakes have been modeled to obtain an upper mantle compressional velocity model for the west mediterranean basin data come from long period stations of the world wide standardized seismograph network and broadband stations located in the iberian peninsula synthetic waveforms have first been computed for published velocity models corresponding to different tectonic provinces and obtained with analogous techniques a model that strongly improves the fits to the data is then derived the proposed model is characterized by a 100 km thick lid overlaying a not very pronounced low velocity zone and a 3 discontinuity at 368 km where an increase of the velocity gradient also occurs these features could be explained either as a deflection of the olivine to spinel phase transition regionally detected at about 395 km resulting from the lower temperature produced by the subduction of the african plate or as being due to the presence below 300 km depth of a layer of silicate melt producing a strong reflection from its bottom and a more usual depth for the olivine spinel transition in both cases the occurrence of relatively low velocities beneath 300 km is interpreted as being caused by the presence of melt associated with the northward dipping subduction of the african plate

from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region abstract de jonge m r wortel m j r and spakman w 1993 from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 53 65 the seismic velocity structure of the upper mantle and lithosphere in the mediterranean region is very complex many areas with anomalous p wave velocities can be recognized by means of seismic tomography in view of the complicated tectonic evolution of the peri mediterranean orogens and basins this is not surprising in this study we will show results of a modelling approach we have recently developed to predict this structure in this approach we make a quantitative connection between the tectonic evolution on one hand and the present seismic velocity structure on the other our model predicts the evolution of temperature distributions in the lower lithosphere and upper mantle by simulating the flow of material inferred from a kinematic description of lithosphere scale processes from the modelled present thermal state the endpoint of an evolution we calculate expected seismic velocity anomalies that can be compared with results obtained by seismic tomography thus the method enables us to compare the implications of geological reconstructions describing the past tectonic processes with seismological results for the present structure the predicted mantle models show a good correlation with the tomographic results obtained for the mantle this means we can verify many features present in the tectonic scenarios with the seismologically determined deep structure

large scale mantle convection and the history of subduction a large scale pattern of mantle convention is evident in the shape of the earth s gravity field1 lateral variations in seismic velocity2 3 the distribution of hotspots4 and long wavelength bathv metric anomalies5 paradoxically these signals of mantle convection bear little resemblance to present day plate motions1 4 although they seem to be related to past subduction zone configurations6 here we quantify this relationship by correlating a time integrated history of subduction calculated in the hotspot reference frame for the past 180 myr with regions of the deep mantle inferred from other geophysical observations to be colder than average our results support suggestions6 9 that a direct relationship exists between large scale thermal heterogeneity in the lower mantle and subduction during the cenozoic and mesozoic

the thermal structure of the mediterranean upper mantle a forward modelling approach we develop and present an approach for gaining insight into the thermal structure of the upper mantle in a tectonically active region as a starting point for the analysis we use regional geological reconstructions based on data from surface geology shallow seismics and paleomagnetism for these reconstructions we determine the necessarily associated upper mantle processes such as subduction we then forwardly model the thermal structure of upper mantle corresponding with the geological reconstruction used in this way we obtain an estimate of a very important characteristic the temperature distribution of the upper mantle that is independent from those estimates from the usual deep seismic methods if sufficient detailed information on the seismological structure of the region is available a quantitative test of our modelling results is possible via the temperature dependence of seismic velocities we apply our approach to the mediterranean area for which we will test the reconstruction published by dercourt et al 1986

gravity and aeromagnetic constraints on the extent of cenozoic volcanic rocks within the nefza tabarka region northwestern tunisia bouguer gravity and aeromagnetic data are analyzed to determine the extent of miocene magmatism in the nefza and tabarka regions of northwestern tunisia construction of magnetic intensity and enhanced analytic signal eas maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the nefza and tabarka regions because of the lack of lateral resolution of the eas techniques 3 d magnetic and 2 5 d gravity models were constructed over the anomalies at nefza and tabarka the final models indicate that the maximum depths of the igneous bodies are between 2 5 and 2 7 km with maximum widths between 15 and 22 km the final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust at least 3 km these widths greatly expand the region of known miocene magmatism in northwestern tunisia combined with geochemical and petrological data of the surface volcanic rocks the gravity and magnetic models imply a wider range of miocene volcanic activity in northern tunisia probably related to a subduction zone

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

3 d architecture and plio quaternary evolution of the paola basin insights into the forearc of the tyrrhenian ionian subduction system

underpinning tectonic reconstructions of the western mediterranean region with dynamic slab evolution from 3 d numerical modeling no consensus exists on the tectonic evolution of the western mediterranean since 35 ma three disparate tectonic evolution scenarios are identified each portraying slab rollback as the driving mechanism but with rollback starting from strongly different subduction geometries as a critical test for the validity of each tectonic scenario we employ thermomechanical modeling of the 3 d subduction evolution from each tectonic scenario we configure an initial condition for numerical modeling that mimics the perceived subduction geometry at 35 ma we seek to optimize the fit between observed and predicted slab morphology by varying the nonlinear viscoplastic rheology for mantle slab and continental margins from a wide range of experiments we conclude that a tectonic scenario that starts from nw dipping subduction confined to the balearic margin at 35 ma is successful in predicting present day slab morphology the other two scenarios initial subduction from gibraltar to the baleares and initial subduction under the african margin lead to mantle structure much different from what is tomographically imaged the preferred model predicts slab rotation by more than 180 east west lithosphere tearing along the north african margin and a resulting steep east dipping slab under the gibraltar strait the preferred subduction model also meets the first order temporal constraints corresponding to mid miocene 16 ma thrusting of the kabylides onto the african margin and nearly stalled subduction under the rif gibraltar betic arc since the tortonian 8 ma our modeling also provides constraints on the rheological properties of the mantle and slab and of continental margins in the region

subduction zone seismicity and the thermo mechanical evolution of downgoing lithosphere in this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km with emphasis on the role of temperature and rheology in controlling the deformation of and the seismic energy release in downgoing lithosphere this is done in two steps after a brief review of earlier developments we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth dependent critical valuetcr

on melting of the subducted oceanic crust effects of subduction induced mantle flow abstract based on petrological and geochemical arguments it is possible that arc magma is derived from subducted oceanic crust in this paper regional thermal models have been constructed to study the feasibility of melting cold subducted oceanic crusts at shallow depth i e at depths of about 100 km by a dynamic mantle calculated results suggest that plate subduction will generate an induced flow in the wedge above the subducting slab this current continuously feeds hot mantle material into the corner and onto the slab surface a high temperature thermal environment can be maintained in the vicinity of the wedge corner immediately beneath the over riding plate our regional models further demonstrate quantitatively that production of local melting is possible just about 30 km down dip from the asthenosphere wedge corner additional geological processes such as reasonable amounts of shear heating and minor dehydration which will lower the local melting temperature will further increase the probability of melting a cold subducted oceanic crust at shallow depth

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

back arcs basins and p wave crustal velocity in the ionian and aegean regions tomographic images of the lower crust and uppermost mantle beneath the central mediterranean have been obtained from arrival times of regional earthquakes we find a low velocity belt at about 25 km beneath the hellenic arc a low velocity anomaly at a depth of 40 km extends under the aegean back arc basin high velocities are present at moho depth beneath the ionian sea close to the calabrian and aegean arcs and under the aegean sea the results suggest a close relation between p wave crustal velocity and the subduction systems of the studied area

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

velocity anomalies and spatial distributions of physical properties in horizontally lying slabs beneath the northwestern pacific region abstract we calculated velocity anomalies by constructing thermal structural models of horizontally lying slabs beneath kuriles central japan northern izu bonin and central izu bonin arcs the values of v p and v s anomalies become maximum in the depth range of 100 to 200 km within the slabs reaching 5 to 6 4 for v p anomalies and 7 to 8 5 for v s anomalies the calculated v s anomalies are larger than the v p anomalies and the ratio of the former to the latter is 1 2 to 1 5 within the slab this suggests that v s anomalies are more sensitive to temperature variation than v p anomalies indicating that the existence of the horizontally lying slabs is detectable in more detail by using s wave we also calculated spatial distributions of physical properties in the horizontally lying slabs beneath the four regions in the calculation we assumed that the material of the slabs consists of olivine mg 0 89 fe 0 11 2 sio 4 the estimated values of physical properties within the slabs are larger than those in the surrounding upper mantle except for poisson s ratio while the values within the metastable wedge of olivine become smaller this is most remarkable within the slab beneath the central izu bonin arc due to the lowest temperature among the four regions the horizontally lying slab above the 660 km seismic discontinuity beneath the central izu bonin arc is denser up to 60 kg m 3 and the slab within the metastable wedge of olivine is lighter up to 120 kg m 3 the values of the physical properties except for poisson s ratio decrease with increasing the horizontal distances of the horizontally lying portions of the slabs this is due to thermal assimilation which is largely dependent on moving velocity of the slabs

fault activity and marine terracing in the capo vaticano area southern calabria during the middle late quaternary abstract the capo vaticano peninsula is a structural high bordered by several normal fault segments mainly striking ne sw and wnw ese and belonging to the so called siculo calabrian rift zone both the two fault systems extend in the tyrrhenian offshore and show recent activity in the capo vaticano peninsula six orders of marine terraces with their preserved paleoshorelines and a top surface have been recognised they form a continuous set of morphological elements ascribed to the last seven principal high stands of the eustatic curve occurred from 330 to 60 kyr on the basis of new chronological data available in the recent literature the morphotectonic analysis of the paleoshorelines allowed recognition of a deformation pattern characterised by a northeastward tilting of the area and to quantify the uplift rates moreover vertical slip rates ranging between 0 25 and 2 5 mm yr have been calculated for a wnw ese trending fault segment the coccorino fault in this structural framework the late quaternary uplift of the capo vaticano peninsula can be related to the activity of both the ne sw and wnw ese striking normal fault systems added to the regional component of uplift the recent activity of these structures is also suggested by the 1905 seismic event that occurred offshore of the capo vaticano peninsula

tectonic evolution of the corsica apennines alps region studied by the method of successive approximations paleotectonic and paleogeographic maps are often very complex users find it difficult to evaluate the extent to which the features shown are based on reliable geologic data and it is not generally possible to estimate uncertainties in shapes and positions in the scientific tradition of designing simple models to represent complex reality this study uses systematically simplified palinspastic models to study the tectonic evolution of the central mediterranean the prime constraint is northwestward motion of the african continent toward europe at 7 5 km m y in the first approximation model only unidirectional plate motion is allowed and the model is unable to generate both the alpine and apennine orogenic belts at right angles to each other the second approximation allows rotations it is surprising how well this very simple model with its rigidly restrictive rules reproduces the known evolution of the central mediterranean this agreement allows some optimism that the second approximation is correctly modeling the primary features of the tectonic evolution of the central mediterranean revising the shapes of the tectonic entities in a third approximation would allow the final pattern to mimic even more closely the present tectonic situation in the mediterranean but here the advantages of rigid simplification would start to diminish the first conclusion of the paper is thus that strongly simplified models are useful in tectonic studies and are justified in light of the uncertainties simplified models are used to explore the recently proposed ancient apennine hypothesis in which apennine deformation begins with a reversal of subduction polarity at about 100 90 ma this view contrasts with the standard young apennine hypothesis in which subduction reversal and the onset of apennine orogensis do not occur until 35 30 ma study of the simplified tectonic models leads to the second conclusion of the paper that the ancient apennine hypothesis honors regional constraints as well as the standard view does the simplified modeling suggests specific tests in alpine corsica for choosing between the young apennine and ancient apennine hypotheses

gravity constraints on the structure of the northern margin of tunisia implications on the nature of the northern african plate boundary summary bouguer gravity data were analysed to determine the general crustal and upper mantle structure in northern tunisia residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the tunisian coastline an edge enhancement analysis e g enhanced analytic signals of the short wavelength anomalies suggests a previously unknown east west trending gravity anomaly south of 37 n with source depths of between 3 and 7 km modelling of residual and bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern tunisia 1 thickening of cenozoic and mesozoic sediments north of a strike slip fault or 2 a crustal and uppermantle low density zone interpreted as being crustal material of the remnant subducted african plate the latter result is favoured based on seismic tomographic images of the mediterranean region which implies that subducting material exists under the african coast geological interpretations suggesting that the tell atlas may be a thrust wedge accreted by underplating of the african continental crust and seismic refraction models indicating a thinning of sediments in northern tunisia the east west trending gravity anomalies south of 37 n correspond to an important structural feature that may be related to either a structural boundary e g a transform fault or subduction beneath the african plate

a new finite frequency shear velocity model of the european mediterranean region 1 we invert a global phase anomaly database of intermediate to long period rayleigh waves recently updated with increased coverage in the european mediterranean region on a global scale with a higher resolution parameterization in the region of interest we first compare phase velocity inversions based on ray and finite frequency theory and derive for each a corresponding set of local phase velocity dispersion curves one per model pixel between 35 s to 300 s period effects of the two different theories on the three dimensional upper mantle structure are investigated by inverting each dispersion curve for radial shear velocity profiles the combination of a gradient descent method and a random monte carlo model search provides an estimated shear velocity model with associated uncertainties for depths between 40 km to 400 km while differences between ray theoretical and finite frequency models are small compared to model uncertainty comparisons with independent models favor the finite frequency one

subduction history of the tethyan region derived from seismic tomography and tectonic reconstructions 1 in the mantle underneath the tethyan suture zone large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present day signature of subducted tethyan lithosphere we investigate the mesozoic cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions three different subduction scenarios for the tethyan oceanic lithosphere representative for the available tectonic reconstructions are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late mesozoic next these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images in this analysis we include among others the possible effects of ridge subduction and slab detachment after the cenozoic continental collisions absolute plate motion and slab thickening in the mantle our preferred subduction model comprises the opening of large back arc oceanic basins within the eurasian margin the model points to slab thickening by a factor of 3 in the mantle in which case the estimated volumes allow for active oceanic spreading 1 2 5 cm yr in the tethyan lithosphere during convergence our results further indicate the occurrence of early oligocene slab detachment underneath the northern zagros suture zone followed by both westward and eastward propagation of the slab tear and diachronous eocene to miocene slab detachment below the eastern to western himalayas free sinking rates of the detached material of 2 cm yr in the lower mantle provide the best fit between the tomographic mantle structure and our tethyan subduction model

uppermost mantle velocities and anisotropy beneath europe pn data collected within southern europe and the mediterranean are used to tomographically image variations in both seismic velocity and seismic anisotropy seismic anisotropy is an essential part of the inversion and without it several low velocity features within the uppermost mantle could not be properly imaged the technically active mantle of southern europe has much lower seismic velocities 7 6 8 1 km s than the more stable mantle of the sub african plate of the adriatic sea 8 3 km s however the most dramatic features within europe s uppermost mantle relate to the apennine dinaride and hellenide arcs these arcs all have extremely low 5 amounts of arc parallel anisotropy the tyrrhenian and aegean back arc regions also show low velocities 7 7 7 9 km s but less anisotropy the same may be true for the pannonian basin but the tomography has poorer resolution there a model explaining these observations focuses on subducted water metasomatizing the mantle wedge the addition of water causes melting creates arc volcanism lowers the seismic velocity and enhances the formation of anisotropy due to preferential olivine orientation for collisional arcs of the northern mediterranean arc parallel anisotropy has formed in response to compression across them and extension along them within back arc regions water is no longer a major factor instead convection associated with subduction and back arc extension controls the anisotropy

old sm nd ages for cumulate eucrites and redetermination of the solar system initial 146sm 144sm ratio article i nfo sm 142 nd systematics short lived 146 sm 142 nd and long lived 147 sm 143 nd chronometers have been measured in three cumulate eucrites binda moore county and moama the two major mineral phases plagioclase and pyroxene present in these achondrites are characterized by a wide range of sm nd ratios that allows well resolved sm nd isochrons this group of meteorites thus is suitable to better constrain the initial 146 sm 144 sm ratio of the solar system binda and moore county give concordant ages of 4544 88 and 4542 85 ma respectively with initial 143 nd 144 nd ratios slightly higher to within error of chondritic these ages are in agreement with most of the radiometric ages determined on basaltic eucrites a best estimate for the solar system initial 146 sm 144 sm ratio is obtained using the five point regression line determined for binda the 146 sm 144

core complex related extension of the aegean lithosphere initiated at the eocene oligocene transition 1 core complex related stretching of the aegean lithosphere was accommodated in part by the south cyclades shear zone scsz which outcrops on the islands of ios and thera aegean sea greece this paper reports new microstructurally focused 40ar 39ar geochronology that suggests the scsz initiated just before the time of the eocene oligocene transition at 35 ma therefore it is not only miocene extension that led to the tethyan metamorphic core complexes exposed in the cycladic archipelago it is shown here that pervasive top to the south directed ductile shear took place in the scsz for 5 ma during the early oligocene followed by initiation of overprinting north sense shear zones at the time of the oligocene miocene transition at 25 ma this means that modern core complex related extension in the aegean started much earlier than has been previously recognized and that stretching of the aegean lithosphere took place in a distinctly episodic fashion not in a manner that can be described as continuous or progressive the data also mean that the complementary shear sense geometry of the scsz and the north cyclades shear zone ncsz cannot be interpreted as crustal scale boudinage initiated during crustal extension in miocene time since the opposing sense shear zones operated at distinctly different times the paper illustrates the difficulties involved in systematically determining the age of deformation fabrics using 40ar 39ar geochronology and provides a case study that shows the value of carefully designed step heating experiments on microstructurally controlled samples in samples such as these from complex metamorphic tectonites laser fusion or step heating experiments with relatively few steps would have led to erroneous conclusions

crustal structure beneath the tell and atlas mountains algeria and tunisia through the analysis of gravity data abstract bouguer and isostatic residual gravity anomaly maps were analyzed for the general crustal structure under the tell and atlas mountains of algeria and tunisia two dimensional gravity models and profiles of topography free air and bouguer gravity anomalies were constructed to provide estimates of the crustal thickness and the degree of isostatic compensation the thickest crust 38 40 km was found beneath the saharian atlas in northern algeria whereas under the tunisian atlas it is approximately 34 36 km there is little evidence of crustal thickening due to the formation of the tell mountains large amplitude negative bouguer small amplitude positive free air gravity and small amplitude positive isostatic residual gravity anomalies suggest that saharian and tunisian atlas are partially isostatically compensated with regions of possible overcompensation in algeria the boundary between the saharian and tunisian atlas is characterized by negative isostatic residual anomalies suggesting overcompensation and a thick crustal root however the cause may be low density material in the upper crust the amplitude and width of bouguer gravity anomalies and two dimensional gravity models across the saharian and tunisian atlas indicate that there was a greater amount of crustal shortening in algeria than in tunisia

new insights into the local crust structure of mt etna volcano from seismological and morphotectonic data abstract the reconstruction of the extensional active tectonic structures on the eastern flank of mt etna and of the related earthquakes allowed the analysis of fault parameters for more than 50 episodes of coseismic ground rupture for the last 250 years the calculation of statistical relationships among earthquake magnitude surface rupture length surface fault displacement and their combination was performed moreover we found out that the minimum earthquake magnitude to have ground rupture effect is ca 2 5 we were therefore able to hypothesize a reduced seismogenic layer 5 6 km under the lower eastern flank of the volcano we also analysed structural and marine geology data to find further surface evidences of the volcano dynamics we recognized for the first time a local component of uplift affecting the volcanic domain at least in the last 20 ka with a rate up to 3 5 mm yr that is likely related to a volcanic dome effect coupling the two aspects the seismological one and the morphostructural one of our research we propose a local thinning of the brittle crust in this sector of mt etna the thermal effects of the uprising magma on the rheology of the crust rocks well explain all our observations

surface wave tomography in the european and mediterranean region summary we present a new surface wave tomographic study of the broad european and mediterranean region our goal is to enhance the resolution of previously published group velocity models using new data from european permanent seismic networks and a dense broad band array in northern apennines retreat we measure fundamental mode rayleigh and love wave group velocities from long period seismograms recorded at regional distance between 600 and 7000 km our measurement technique is based on iterative application of multiple filters and phase matched filters we accurately estimate dispersion curves for more than 1500 rayleigh wave and about 850 love wave paths in the period range 35 170 s consistency of measurements is evaluated by comparing ray clusters from sample earthquakes to closely spaced retreat stations in the whole data set measurement errors in group velocity decrease with increasing distance and show to be caused by inaccuracy in the estimate of group arrival time we calculate maps of love and rayleigh group velocity at selected periods by linear tomographic inversion accounting for group arrival time errors and evaluating a posteriori group slowness errors data coverage in this region is not uniform and it is highly influenced by the uneven distribution of earthquakes and seismic stations we therefore build a laterally heterogeneous reference model by inverting a global data set of group velocity derived from the phase velocity library of ekstr

p and s wave upper mantle seismic velocity structure beneath the northern apennines new evidence for the end of subduction orogeny in the geologically young northern apennines is explained by the eastward retreat of a convergence zone in which adriatic lithosphere subducts to the west it is unclear however whether all of the lithosphere or only the lower portion has subducted since 15 ma when the convergence zone lay near corsica we combine teleseismic p and s wave arrival time data from the retreat seismic network 2003 2006 and surrounding permanent stations to estimate tomographic images of the upper mantle structure beneath the northern apennines we image a vertically oriented slab that that extends to only 300 km depth our slab termination is shallower than previous studies but is confirmed by resolution tests furthermore our images resolve the southern edge of the northern apennines slab at 43 n with no deep continuity with any slab segment to the south as earlier proposed our results suggest that only a 300 400 km strip of lithosphere has subducted since 15 ma beneath the northern tyrrhenian sea a length roughly equivalent to the distance from the present day west coast of corsica to the crest of the northern apennines although not a definitive indicator the largely aseismic vertical slab configuration and its limited extent coupled with other volcanic and geophysical indicators suggests the delamination scenario of bird 1979 in which only the lower portion of the continental lithosphere subducts

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

low intra crystalline closure temperatures of cr bearing spinels from the mantle xenoliths of the middle atlas neogene quaternary volcanic field morocco mineralogical evidence of a cooler mantle beneath the west african craton the crystal chemistry of nine cr spinels from lherzolite and harzburgite xenoliths from the middle atlas neogene quaternary volcanic field of morocco have been studied by means of x ray single crystal diffraction and electron microprobe analyses cell edges are usually within the range 8 13 8 14 a but there are three samples with longer a value so that the whole analyzed series is within the range 8 1334 4 8 2021 2 a while the oxygen positional parameter values are very similar ranging between 0 2626 1 and 0 2629 2 for all of them the cation distribution shows that the crystal structure is ordered with almost all divalent cations in the tetrahedral site and trivalent cations in the octahedral site the determined intracrystalline temperatures are in the range 550 750 c that are the lowest values ever found for cr spinels from mantle xenoliths as these are usually higher than 730 c if we consider the behavior of some geotherms from literature the determined temperatures are confined in a depth range of about 20 40 km lithospheric models for the studied area indicate that the lower crust reaches its deepest value in a range between 30 and 40 km consequently we can assume that the studied xenoliths were emplaced at a shallow depth of about 20 30 km just beneath the lower crust where they were disrupted and brought to the surface from the ascending alkaline lavas this assumption is consistent with the concomitant presence of some crustal xenoliths it is important to notice that even in the case of a mantle xenoliths where all the silicates could be heavily altered the presence of one single crystal of cr spinel and the study of its oxygen coordinates u inversion parameters i cr content and calculated closure temperatures can be used to validate the thermal history of the mantle xenoliths the combined approach of structural data intra and inter crystalline temperatures and the literature geophysical data seems to be an interesting tool to assess the pre exhumation history of the mantle xenoliths

the bursa gonen depression nw turkey a complex basin developed on the north anatolian fault in this study we show that the southern branch of the north anatolian fault has been active since late pliocene time and that evidence of activity is supported by geological and seismological data the southern branch of the north anatolian fault consists of four segments from west to east yenice gonen manyas mustafakemalpasa uluabat and bursa these faults delimit the bursa gonen depression with the bandirma mudanya uplift to the north and uludag sularya uplift to the south the bursa gonen depression includes upper pliocene to recent sediments that thicken to the south suggesting a deposition pattern under active fault control study of fault kinematics suggests that the bursa gonen depression started as a small pull apart basin during late pliocene time and then evolved to a large depression the faults delimiting this depression are still active and capable of producing future earthquakes

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

a community benchmark for subduction zone modeling we have developed a suite of benchmarks to facilitate the comparison of numerical models for the dynamics and thermal structure of subduction zones the benchmark cases are based on a thermomechanical approach in which the slab is prescribed kinematically and the wedge flow is computed dynamically we propose various cases to investigate the influence of boundary conditions and rheology on wedge flow and resulting thermal structure a comparison between the codes suggest that accurate modeling of the thermal field requires a good implementation of the velocity discontinuity along the seismogenic zone and high resolution in the thermal boundary layers a minor modification to the boundary conditions of the wedge flow is also necessary to avoid a pressure singularity that exists in analytical solutions of the cornerflow model

multiple resolution surface wave tomography the mediterranean basin summary from a large set of fundamental mode surface wave phase velocity observations we map the transversely isotropic lateral heterogeneities in the upper mantle shear velocity structure we design a multiple resolution inversion procedure which allows us to parametrize any selected region more finely than the rest of the globe we choose as a high resolution region the upper mantle underlying the mediterranean basin we formulate the inverse problem as in a

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

s velocity structure and radial anisotropy in the aegean region from surface wave dispersion summary the lithospheric structure of the aegean region is investigated by analysis of rayleigh wave fundamental mode dispersion measurements isotropic 1 d models for almost 100 two station ray paths across the region display distinct variations in the moho depth and crustal s wave velocities the descending slab of the subducting african plate can be resolved down to 120 km depth beneath the volcanic arc three different regions are distinguished in terms of moho depth 1 the forearc with large crustal thicknesses between 38 and 48 km and an average of 43 km 2 the northern aegean with an average moho depth of 28 km and 3 the southern aegean central volcanic arc i e cyclades and sea of crete with an even thinner crust of around 25 km lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc collocated with pronounced changes in trench and slab geometry as well as published deformation rates s velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the peleponnesus to crete an abrupt change occurs between western and central crete in terms of the visibility of the aegean moho and the seismic structure of the lithospheric mantle wedge an aegean mantle wedge with s velocities above 4 4 km s 1 is only observed to the east of central crete whereas to the west velocities of less than 4 0 km s 1 occur down to the plate contact these low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths a low velocity asthenospheric layer is observed beneath the sea of crete and the cyclades below 40 km depth between the thinned lithosphere above and the slab below the observed radial anisotropy in the northern part of the aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust possibly caused by lateral ductile flow associated with recent lithospheric extension

joint inversion of local regional and teleseismic data for crustal thickness in the eurasia africa plate boundary region summary a new map for the moho discontinuity eam02 in the eurasia africa plate boundary region is presented reliable results have also been obtained for the southern and eastern mediterranean basin the northern african coasts and the eastern atlantic ocean regions only occasionally considered in studies on the mediterranean region the moho topography model is derived from two independent sets of constraints information contained in the fundamental and highermode rayleigh waves obtained from waveform modelling is used to constrain the moho depth between estimates of crustal thickness taken from published reflection and refraction surveys gravity studies and receiver function analysis strong lateral variations in the moho topography have been observed in the mediterranean sea confirming the complex evolution of this plate boundary region in the west the moho discontinuity has been found at 15 20 km depth suggesting extended and at least in some locations oceanic crust while in the east the crust is on average 25 30 km thick there it is interpreted either as mesozoic oceanic or thinned precambrian continental crust covered by thick sedimentary deposits standard continental crust 30 35 km is observed along the eastern part of the northern african coast while to the west a rapid change from a relatively deep moho down to 42 km below the atlas mountain range to the thin crust of the southwestern mediterranean sea has been found the crust beneath the eastern north atlantic ocean can be up to 5 km thicker compared with standard oceanic crust 6 km the crust has been interpreted to be heterogeneous as a consequence of irregular magma supply at the mid atlantic ridge in addition serpentinization of the submoho mantle could contribute to the imaging of apparently anomalous thick oceanic crust in europe the presence of crustal roots 45 km beneath the major mountain belts has been confirmed while thin crust 25 km has been found beneath extensional basins comparing the obtained moho topography and moho depth computed assuming isostatic compensation at 60 km depth shows that most of the mediterranean and eastern atlantic region appears to be in isostatic equilibrium the large positive residuals observed for the eastern mediterranean are likely to be due to overestimating crustal thickness owing to the thick sediment deposits present

shear wave velocity structure of the western part of the mediterranean sea from rayleigh wave analysis the lithospheric structure of the western part of the mediterranean sea is shown by means of s velocity maps for depths ranging from 0 to 35 km determined from rayleigh wave analysis the traces of 55 earthquakes which occurred from 2001 to 2003 in and around the study area have been used to obtain rayleigh wave dispersion these earthquakes were registered by 10 broadband stations located on iberia and the balearic islands the dispersion curves were obtained for periods between 1 and 45 s by digital filtering with a combination of mft and tvf filtering techniques after that all seismic events were grouped in source zones to obtain a dispersion curve for each source station path these dispersion curves were regionalized and after inverted according to the generalized inversion theory to obtain shear wave velocity models for rectangular blocks with a size of 1 1 the shear velocity structure obtained through this procedure is shown in the s velocity maps plotted for several depths these maps show the existence of lateral and vertical heterogeneity in these maps is possible to distinguish several types of crust with an average s wave velocity ranging from 2 6 to 3 9 km s the south balearic basin sbb is more characteristic of oceanic crust than the rest of the western mediterranean region as it is demonstrated by the crustal thickness we also find a similar s wave velocity ranging from 2 6 km s at the surface to 3 2 km s at 10 km depth for the iberian peninsula coast to ibiza island the north balearic basin nbb and mallorca island in the lower crust the shear velocity reaches a value of 3 9 km s the base of the moho is estimated from 15 to 20 km under iberian peninsula coast to ibiza island continues towards nbb and increases to 20 25 km beneath mallorca island while the sbb is characterized by a thinner crust that ranges from 10 to 15 km and a faster velocity a gradual increase in velocity from the north to the south especially in the upper 25 km is obtained for the western part of the mediterranean sea the base of the crust has a shear wave velocity value around of 3 9 km s for the western mediterranean sea area this area is characterized by a thin crust in comparison with the crustal thickness of the eastern mediterranean sea area this thin crust is related with the distensive tectonics that exists in this area the low s wave velocities obtained in the upper mantle might be an indication of a serpentinized mantle the obtained results agree well with the geology and other geophysical results previously obtained the shear velocity generally increases with depth for all paths analyzed in the study area

stress in the descending relic slab beneath the vrancea region romania we examine the effects of viscous flow phase transition and dehydration on the stress field of a relic slab to explain the intermediate depth seismic activity in the vrancea region a 2 d finite element model of a slab gravitationally sinking in the mantle predicts 1 downward extension in the slab as inferred from the stress axes of earthquakes 2 the maximum stress occurring in the depth range of 70 km to 160 km and 3 a very narrow area of the maximum stress the depth distribution of the annual average seismic energy released in earthquakes has a shape similar to that of the depth distribution of the stress in the slab estimations of the cumulative annual seismic moment observed and associated with the volume change due to the basalt eclogite phase changes in the oceanic slab indicate that a pure phase transition model cannot solely explain the intermediate depth earthquakes in the region we consider that one of the realistic mechanisms for triggering these events in the vrancea slab can be the dehydration of rocks which makes fluid assisted faulting possible

tectonic control on the eruptive dynamics at mt etna volcano sicily during the 2001 and 2002 2003 eruptions abstract the eruptive events of the july august 2001 and october 2002 january 2003 at mt etna provide new insights for reconstructing the complex geometry of the feeding system and their relationship to regional tectonics the 2001 eruption took place mainly on the upper southern sector of the volcano the eruption was preceded by a large earthquake swarm for a few days before its onset and accompanied by ground deformation and fracturing the development of surface cracking along with the seismic pattern has allowed us to recognize three distinct eruptive systems the sw ne nnw sse and n s systems which have been simultaneously active such eruptive systems are only the upper portions of a complex feeding system that was fed at the same time by two distinct magmas the sw ne and nnw sse systems connected with the se crater conduit were fed by magma coming from depth whereas the n s system served instead as an ascending pathway for an amphibole bearing magma residing in a shallow reservoir the eruptive activity started again on october 2002 on the ne rift zone where about 20 eruptive vents were aligned between 2500 and 1900 m a s l and on the southern flank from the central crater to the montagnola the onset of eruptive activity was accompanied by a seismic swarm as in the 2001 eruptive event two independent feeding systems formed characterized by distinct magmas the sw ne system controlled the feeding of the northeast rift and was accommodated by left lateral displacement along the wnw ese trending pernicana fault the n s system fed the eruptions on the southern flank moreover the associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano and offshore these two last eruptions indicate that at mt etna the ascent of magma as well as the accommodation of deformation is strongly dominated by local extensional structures that are connected to a regional tectonic regime

one dimensional models of shear wave velocity for the eastern mediterranean obtained from the inversion of rayleigh wave phase velocities and tectonic implications summary on a sw ne profile from the libyan coast towards central turkey phase velocity curves of the fundamental rayleigh mode were measured using a two station method the inversion of phase velocity curves yields 1 d models of shear wave velocity down to approximately 200 km depths that may be interpreted as estimates of average models between neighbouring stations on the profile strong lateral variations in the shear wave velocity structure are imaged along the profile the subducted oceanic african mantle lithosphere is indicated in 1 d models for the region around crete by significantly enlarged shear wave velocities it is also imaged by an average model of the structure between stations on crete and santorini on a path crossing the libyan sea south of crete the resulting model is slower than a model expected for 110 myr old oceanic lithosphere the passive african margin is thus assumed to extend northwards beneath the libyan sea anomalous low shear wave velocities are found for the uppermost mantle beneath central turkey down to a depth of approximately 130 km using two stations on crete the average depth of the oceanic moho within the subducting slab is estimated to be at approximately 50 km beneath crete for this arc parallel path an enlarged standard deviation of the measured phase velocities of approximately 0 2 km s 1 between 10 and 30 mhz is observed that is probably caused by strong lateral heterogeneity related to the subducting slab in addition in this frequency range an anomalous propagation of the fundamental rayleigh mode is detected that is indicated by measured phase velocities that are approximately one standard deviation faster than phase velocities expected from a great circle approximation an average shear wave velocity of approximately 3 5 km s 1 is observed above the oceanic moho in order to explain the recent lithospheric structure of the hellenic subduction zone a tectonic model is assumed for the ne sw striking profile considered it is based on the calculated 1 d models tectonic reconstructions and on a model derived from the metamorphic history of rocks exposed on crete the suggested model summarizes the tectonic development at a lithospheric scale starting in the late cretaceous accretion of crustal material of two microcontinents to eurasia is assumed while continuous subduction of the oceanic lithosphere of different ocean basins and possibly of the mantle lithosphere of the microcontinents resulted in a single slab the length of the oceanic lithosphere that was subducted south of crete is estimated to be not greater than approximately 550 km

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

analysis of the temporal properties of greek aftershock sequences abstract the temporal distribution of aftershock sequences can be analyzed by means of new parameters other than the omori s p value a deep analysis of the temporal properties of six aftershock sequences occurred in greece from 1980 to 1997 has been carried out by means of fractal tools we performed the omori s law the r s and the allan factor analyses in order to estimate the p value of the aftershock rate the hurst exponent h of the interevent time series and the spectral exponent respectively our results show a significant variability of the p value from 0 89 to 1 48 of h from 0 78 to 1 186 and of from 0 49 to 1 44 the variation of the normalized with the threshold magnitude for all the aftershock sequences examined has displayed almost the same decreasing behaviour the temporal fractality of aftershock sequences is primarily due to the power law decay of the aftershock rate

constructing a geodynamic a priori seismic gaps velocity model of upper mantle heterogeneity 1 seismic studies of the deep mantle suffer from the fact that the probing seismic waves must traverse the highly heterogeneous and poorly resolved shallow structure one potential way forward is to develop high resolution models of the crust and upper mantle using other information here we describe the construction of a geodynamic a priori model of some aspects of upper mantle seismic velocity heterogeneity it is based on an equal area tomographic grid and it has been produced at two scales a 1 1 resolution at the equator i e each cell has an approximate dimension of 100 km by 100 km and a 5 5 resolution at the equator both have a constant layer thickness of 100 km currently the model accommodates the subducting lithosphere and global variation in continental crustal thickness and age of oceanic lithosphere the shape of subducting oceanic lithosphere was derived from profiles through seismicity the shape was combined with estimates of plate velocities and age of subducting lithosphere using an analytic solution of the thermal field to define the slab thermal anomaly the temperature perturbation was converted to a slowness 1 velocity perturbation for oceanic lithosphere a plate cooling model was used to convert lithosphere age to slowness perturbation via a temperature perturbation the variation in the thickness of continental crust around a global average formed the third element of the slowness perturbation model this model has already been applied in a high resolution mantle tomographic study of lower mantle heterogeneity

epmantle a 3 d transversely isotropic model of the upper mantle under the european plate summary we present a new 3 d transversely isotropic shear wave velocity model of the european and mediterraneanuppermantleobtainedbyanalysisofsurfacewaves datausedarefundamentalmode rayleigh and love group velocity measurements in the period range 35 170 s taken on seismograms recorded by european stations for regional earthquakes the tomographic inversion to map the 3 d earth structure is split into two steps first we regionalize the group velocity dispersion measurements obtaining distinct geographical group velocity maps at different periods then each local dispersion curve is inverted separately to find the shear wave velocity structure at depth the inversion benefits from using ap rioriinformation from a 3 d global mantle model s20rts and a new detailed european crustal model epcrust to constrain the shallower layers the inversion scheme follows a non linear iterative algorithm by which rayleigh and love group slowness are inverted simultaneously for the best fitting isotropic voigt shear wave speed 2 vsv 1 vsh and radial anisotropy parameter vsh vsv final merging of the vs profiles results in a new higher resolution 3 d model of european upper mantle we find that western europe and mediterranean sea are mainly characterized by relatively low velocities strongly contrasting with the fast roots of the eastern european craton many regional scale structures are also evident in the model thus providing insights into the complex geodynamic framework of the european continent most prominent are the low velocity west mediterranean spreading basins and european cenozoic rift system and seismically fast features connected to subduction of adria microplate hellenic arc and calabrian arc radial anisotropy does not vary very significantly with respect to the prem profile as available data only resolve lateral variations to a limited degree due to trade off with velocity epmantle has the potential to provide a reliable seismological reference for the upper mantle structure in the broad european region

from collisional to rifted basins an example from the southern calabrian arc italy structural interpretation of available geological and geophysical data carried out along a regional transect extending across the southern calabrian arc from the tyrrhenian margins to the ionian off shore demonstrates that a complex interplay between compressional and extensional processes has controlled the evolution of upper miocene pleistocene sedimentary basins developing in this region our data indicate that an upper miocene lower pliocene succession outcropping in the southern calabrian arc represents the infilling of perched basins developed between crystalline basement thrust sheets a similar tectonic pattern characterises the plio pleistocene basins occurring on the frontal part of the arc in the ionian off shore upper pliocene pleistocene sediments outcropping along the tyrrhenian side of the arc reveal that they in fact represent the infilling of extension related basins time space migration of compressional and extensional related sedimentary basins can be explained as the result of different tectonic processes developing on the upper plate as a result of the underplating of the ionian domain beneath the calabrian block in this framework upper miocene lower pliocene and upper pliocene pleistocene perched basins represent therefore fore arc basins developed on the frontal accretionary wedge and or on the hangingwall buttress of the arc during its southeastwards migration late pliocene early pleistocene extensional tectonics occurring along the tyrrhenian side of the arc may indeed be related to accommodation processes which characterised the rear of the wedge to maintain a stable geometry as a result of the underplating of the ionian crust

between scylla and charybdis part 2 the sedimentary dynamics of the ancient early pleistocene messina strait central mediterranean based on its modern analogue abstract the 3 km wide messina strait divides sicily from the italian peninsula representing one of the most impressive examples of tide dominated marine passageway of the central mediterranean sea the tidal hydrodynamics governing the strait results from a semi diurnal phase inversion between two interlinked wider basins i e the tyrrhenian sea to the north and the ionian sea to the south due to the presence of a nodal tidal point in the centre of the strait this condition associated with coastal narrowing causes continuous water exchanges and a local phenomenon of tidal amplification producing collinear tidal currents up to 3 m s 1 in velocity in the point of tidal maxima of the strait centre currents follow bi directional patterns across the strait decelerating towards either opposite peripheries because of the progressive enlargement of the cross sectional areas tides exert a relevant influence on the strait bottom shaping characteristic erosional features governing the main sediment transport routes and promoting the migration of distinctive bedforms the textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions indicating a specific partition of the strait in individual sedimentary zones in the early pleistocene analogous conditions established across the same area and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient messina strait under a similar tidal hydrodynamics the 250 m thick strait fill succession which is magnificently exposed across the two opposite margins i e scylla and charybdis of the modern passageway represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait based on the observation of the modern system in this work which represents the second part of a first article focused on the modern messina strait previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas in particular outcrop analysis allows distinguishing a number of facies associations which are described and interpreted by taking into account the correspondent modern depositional strait setting the results of this study highlight a mutual correlation between the depositional zones detected in the modern messina strait and the individual facies associations recognised in the onshore margins the strait centre zone represented a bedload parting sector in the ancient system this zone which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record is suggested to coincide with a structural palaeo high exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait this tectonic horst symmetrically separated two opposite highly depositional zones to the north and to the south hosting gravel and sand size siliciclastic and bioclastic deposits exhibiting diffuse motifs of large scale tidal cross stratification and a specific vertical facies stacking these characteristic tidal deposits which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait reflect a tidal asymmetry between flood and ebb currents tidal asymmetry is referable to the oceanographic setting observable nowadays in the messina strait and deriving from a marked density driven water mass stratification between the two opposite flows in the ancient system tidal dunes transited down current to highly bioturbated fines including sporadic small scale tidal cross strata representing the distal periphery of the early pleistocene strait here bedforms followed migration pathways not always reflecting mutually evasive net gross sediment transport routes due to local conditions of current rotation occurring during each tidal phase inversion during these stages similar to slack water periods currents were weak enough to allow fine sediments to be settled from suspension reproducing a signature typical of other tide dominated coastal systems e g estuaries tidal flats etc these sedimentary zones of the ancient messina strait were laterally bounded by tectonically active margins where fan deltas clastic aprons and carbonate wedges developed under the constant interplay between mass transport processes and tidal currents the resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho bathymetric features nowadays documented in the correspondent strait margin modern environments these considerations allow deciphering a general palaeo environmental reconstruction of the ancient strait which although suffering of limitations due to a partial preservation of the whole rock record discloses sedimentary processes and depositional environments of the ancient messina strait the process based analysis of this field based case study is crucial in predicting long term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits which are the less understood among the most common tidal depositional systems

crustal structure beneath broad band seismic stations in the mediterranean region summary we have analysed receiver functions to derive simple models for crustal structure below 12 broad band seismological stations from the midsea project and 5 permanent broad band stations in the mediterranean region including northern africa to determine an accurate moho depth we have reduced the trade off between crustal velocities and discontinuity depth using a new grid search method which is an extension of recently published methods to determine crustal thickness in this method the best fitting synthetic receiver function containing both the direct conversion and the reverberated phases is identified on a model grid of varying moho depth and varying poisson s ratio the values we found for moho depth range from around 20 km for intra oceanic islands and extended continental margins to near 45 km in regions where the eurasian and african continents have collided more detailed waveform modelling shows that all receiver functions can be well fit using a 2 or 3 layer model containing a sedimentary layer and or a mid crustal discontinuity on comparing our results with moho maps inferred from interpolated reflection and refraction data we find that for some regions the agreement between our receiver function analysis and existing moho maps is very good while for other regions our observations deviate from the interpolated map values and extend beyond the geographic bounds of these maps

seismological evidence for a delamination process in the lithosphere under the alboran sea summary the continental collision between the african and eurasian plates in the iberian peninsula is solved with a nw se compression with an extensional basin the alboran sea to explain this paradox several models have been proposed including the subduction process of a lithospheric plate in this study a relocation of the seismicity of the area using a jhd algorithm for the period 1950 1995 has been performed which shows a specific hypocentre pattern that is not compatible with plate subduction in addition the direction of the stresses acting in the area has been determined through a comprehensive study of all existing focal mechanisms together with calculations for 19 new earthquakes with sufficient data to determine the focal solution after considering all these data the absence of intermediate shocks in the central part of the alboran basin and the predominantly thrusting mechanisms at the borders of the basin with pressure axes perpendicular to the front we consider a delamination process as a possible mechanism acting in the area

the shear wave velocity structure in the upper mantle beneath eurasia summary we develop an approach that allows us to invert for the mantle velocity structure within a finely parametrized region as a perturbation with respect to a low resolution global tomographic model we implement this technique to investigate the upper mantle structure beneath eurasia and present a new model of shear wave velocity parametrized laterally using spherical splines with 2 9 spacing in eurasia and 11 5 spacing elsewhere the model is obtained from a combined data set of surface wave phase velocities long period waveforms and body wave traveltimes we identify many features as narrow as few hundred kilometres in diameter such as subducting slabs in eastern eurasia and slow velocity anomalies beneath tectonically active regions in contrast to regional studies in which these features have been identified our model encompasses the structure of the entire eurasian continent furthermore including mantleand body wave waveforms helped us constrain structures at depths larger than 250 km which are poorly resolved in earlier models we find that up to 9 per cent faster than average anomalies within the uppermost 200 km of the mantle beneath cratons and some orogenic regions are separated by a sharp gradient zone from deeper 1t o 2 per cent anomalies we speculate that this gradient zone may represent a boundary separating the lithosphere from the continental root which might be compositionally distinct from the overlying lithosphere and remain stable either due to its compositional buoyancy or due to higher viscosity compared with the suboceanic mantle our regional model of anisotropy is not significantly different from the global one

scientific objectives of current and future wegener activities abstract the wegener group has promoted the development of scientific space geodetic activities in the mediterranean and in the european area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research wegener currently has three scientific objectives which are related to plate boundary processes sea level and height changes and postglacial rebound in a full exploitation of the space geodetic techniques namely slr vlbi and gps the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories in the past particularly slr observations within wegener medlas have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the mediterranean with high precision with gps spatially denser site distributions are feasible and in several wegener projects detailed studies of tectonically active areas were possible on the basis of repeated episodic gps observations current projects associated with wegener are successful in separating crustal movements and absolute sea level variations as well as in monitoring postglacial rebound these tasks require high precision height determinations a problem central to all of the present wegener activities in these projects continuously occupied gps sites are of increasing importance time series of heights observed with continuous gps can be determined with a few centimeters rms error thus enabling the reliable estimates of vertical rates over relatively short time intervals regional networks of continuous gps sites are already providing results relevant for example for the study of postglacial rebound the mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes and the wealth of observations acquired in previous wegener projects together with new space geodetic observations will allow the test of geophysical hypotheses linking three dimensional deformations of the earth s surface to the dynamics of the earth s interior in particular it is anticipated that wegener projects will aim at a test of the slab detachment hypothesis the complex investigations on sea level fluctuations presently carried out at basin scale from the strait of gibraltar to the black sea make it possible to study the present and recent past interactions of ocean atmosphere and solid earth as well as to develop appropriate models to assess future aspects

cutting of the european continental lithosphere plasticity theory applied to the present alpine collision presently active european alpine collision has a history of more than 100 myr convergence we investigate the collisional contact problem of an apparently rigid african promontory currently the italy adria block iab steadily penetrating at 1 cm yr over at least the past 45 myr into the deformable european plate we assume that neither continental subduction nor delamination occurs presently in the 300 km wide contact zone enabling use of the indenter indentee approach a key parameter is the aspect ratio h a defined by the width of the deformable foreland over the width of the indenter itself this parameter controls the activation of two fundamentally different modes of deformation 1 classical indentation mode for h a 4 4 described by previous authors and having effect only in a portion of the deformable plate in the vicinity of the indenter and 2 cutting mode for h a 4 4 giving plane strain longitudinal splitting of the entire deformable plate and plastic separation of the two halves we use a matrix operator method to solve for slip lines in the mixed boundary value problem obliquity velocity friction stress of the european alpine case implications are as follows 1 plane stress vertical lithospheric thickening is the first indentation mode of continental collision and 2 for the present ratio of h a 3 deformation is in the cutting mode and slow plane strain intraplate extension rifting is predicted this mode explains the intraplate stress field obtained from borehole and earthquake data considering that the paleoindenter probably has been larger than the iab it is inferred that h a has been below 4 4 since at least the end of the eocene and that consequently the intraplate graben system lower rhine rhine bresse limagne is due to the cutting of the european plate by alpine collision

numerical tests on the seismic visibility of metastable minerals in subduction zones abstract in current views on the origin of deep focus earthquakes the presence of metastable olivine in subducting slabs plays a central role in this study we construct synthetic slab models to investigate the expression of metastable minerals in seismic velocities in particular we investigate the visibility of different slab mineralogy for seismic traveltime studies from forward modeling we construct a range of mineralogical models which include phases with olivine and pyroxene structures differentiation of subducted lithosphere with respect to the surrounding mantle is included and critical temperatures are used to bound the eventual wedge of metastable minerals a case with pure olivine mantle and slab is also considered from the mineralogical slab models we compute seismic p wave velocities including uncertainty bounds due to a variation range in mineralogical composition elastic data and slab temperature as model predictions we compute the traveltime signatures of different slab models by 2 d ray tracing for a number of earthquakes located at the top and bottom side of slabs we infer that upper and lower bounds on computed mineralogy lead to significantly distinct seismic velocities for slabs with equilibrium or metastable mineralogy the predicted traveltime signature including uncertainty bounds of different slab models suggests the possibility to discriminate between metastable and equilibrium slab models models with a pure olivine mineralogy lead to differences in traveltime reaching 1 s the consideration of non olivine phases is thus crucial when looking for a weak seismological signal using forward modeling further we conclude from our results that the traveltime signature of slab mineralogy strongly depends on earthquake position specifically events at the top side of slabs yield significantly different traveltime signatures from events located at the bottom side top side events are most discriminating in traveltimes directly up dip of the slab whereas bottom side events are most discriminating in traveltimes observed directly above the slab i e above the mantle wedge this leads to the important conclusion that highly accurate event locations and accurate knowledge of 3 d structure outside the slab region are prerequisites for studying slab mineralogy with traveltimes

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

p and s velocity anomalies in the upper mantle beneath europe from tomographic inversion of isc data we present a new tomographic model for p and s velocity anomalies beneath europe 30 n 55 n 5 w 40 e extending in depth up to 700 km and constrained by inversion of data from the international seismological center isc catalogue the algorithm uses the traveltimes from events located in the study area recorded by all available worldwide stations as well as times from teleseismic events recorded by european stations the events from the isc catalogue have been relocated and combined into composite events all the traveltimes were corrected for crustal structure using the reference model eucrust 07 the resulting velocity anomalies show similar large scale patterns as observed in previous studies but have a higher resolution which allows detection of some features in more detail for example it is now possible to assess the depth extension of the small slow velocity body beneath the eifel region and eger graben the p and the s model show a good consistency in the uppermost 200 km below most of the european area and in some parts even in the deeper layers e g beneath the apennines and the hellenic arc the new model provides clear images of some principal features which were previously detected in a limited number of studies while the comparison between p and s velocity anomalies provides novel constraints to address on their nature e g the gap in the adriatic plate subducted below the central southern apennines in this paper we pay special attention to testing the reliability of the results the random noise effect is evaluated using a test with independent inversion of two data subsets with odd even events the spatial resolution is estimated using different checkerboard tests furthermore we present a synthetic model with realistic patterns which reproduces after performing forward and inverse modelling the same shape and amplitudes of the anomalies as in the case of the real data inversion in this case the parameters of the model can be used to assess the amplitudes of p and s anomalies that is critical for evaluation of other petrophysical parameters temperature density composition etc in the upper mantle 2009 the authors journal compilation 2009 ras