interplay between subduction retreat and lateral extrusion tectonics of the western carpathians 1 analysis of brittle microstructures reveals three tertiary deformation events in the western carpathians 1 late paleogene bedding parallel extension 2 oligocene to middle miocene nne ssw compression and ese wnw extension 3 post mid miocene nw se extension these regional deformations applied to crustal blocks in the intra carpathian region resulted from forces which were induced by the coupled plate tectonic processes of subduction retreat beneath the carpathian arc and lateral extrusion from the eastern alps toward the carpathian region material flow from the alps spread toward east and ne guided by sinistral strike slip zones along the ne trending continental margin subduction retreat was terminated by mid miocene soft collision of the inner western carpathians with the european foreland ongoing subduction retreat beneath the eastern carpathians caused post mid miocene back arc extension forming the pannonian basin extension spread into the western carpathians by reactivating the extrusion related strike slip faults as normal faults

recovery of temperature salinity and potential density from ocean reflectivity this work explores a method to recover temperature salinity and potential density of the ocean using acoustic reflectivity data and time and space coincident expendable bathythermographs xbt the acoustically derived vertical frequency 10 hz and the xbt derived vertical frequency 10 hz impedances are summed in the time domain to form impedance profiles temperature t and salinity s are then calculated from impedance using the international thermodynamics equations of seawater gsw teos 10 and an empirical t s relation derived with neural networks and finally potential density is calculated from t and s the main difference between this method and previous inversion works done from real multichannel seismic reflection mcs data recorded in the ocean is that it inverts density and it does not consider this magnitude constant along the profile either in vertical or lateral dimension we successfully test this method on mcs data collected in the gulf of cadiz ne atlantic ocean t s and are inverted with accuracies of tsd 0 1 c ssd 0 09 and sd 0 02kg m 3 inverted temperature anomalies reveal baroclinic thermohaline fronts with intrusions the observations support a mix of thermohaline features created by both double diffusive and isopycnal stirring mechanisms our results show that reflectivity is primarily caused by thermal gradients but acoustic reflectors are not isopycnal in all domains

post collisional tertiary quaternary mafic alkalic magmatism in the carpathian pannonian region a review mafic alkalic volcanism was widespread in the carpathian pannonian region cpr between 11 and 0 2 ma it followed the miocene continental collision of the alcapa and tisia blocks with the european plate as subduction related calc alkaline magmatism was waning several groups of mafic alkalic rocks from different regions within the cpr have been distinguished on the basis of ages and or trace element compositions their trace element and sr nd pb isotope systematics are consistent with derivation from complex mantle source regions which included both depleted asthenosphere and metasomatized lithosphere the mixing of dmm himu emii mantle components within asthenosphere derived magmas indicates variable contamination of the shallow asthenosphere and or thermal boundary layer of the lithosphere by a himu like component prior to and following the introduction of subduction components various mantle sources have been identified lower lithospheric mantle modified by several ancient asthenospheric enrichments source a young asthenospheric plumes with oib like trace element signatures that are either isotopically enriched source b or variably depleted source c old upper asthenosphere heterogeneously contaminated by dm himuemii emi components and slightly influenced by miocene subduction related enrichment source d old upper asthenosphere heterogeneously contaminated by dm himu emii components and significantly influenced by miocene subduction related enrichment source e melt generation was initiated either by i finger like young asthenospheric plumes rising to and heating up the base of the lithosphere below the alcapa block or ii decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs the tisia block d 2004 published by elsevier b v

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

magma flow directions in dikes of the koolau complex oahu determined from magnetic fabric studies we compared the magnetic fabric with the macroscopic surface lineation direction previously assumed to be parallel with magma flow direction for 35 dikes of the koolau complex oahu anisotropy of magnetic susceptibility ams was determined for 530 samples from 59 dikes including a sill and a pluglike intrusive body and two filled lava tubes and statistically significant ams clusters were found in all but five dikes for the 35 lineated dikes the mean maximum ams direction 1 coincides with the macroscopic lineations to within 25 in 18 and to within 15 in eight the ams ellipsoid shape in about half of the samples is prolate cigar shaped and in about half is oblate pancake shaped we interpret the ams to be determined by shape anisotropy of ferromagnetic grains the mean total anisotropy is 2 2 and total anisotropy h ranges from 0 24 to as high as 14 12 the principal ams axes for samples from a dike are tightly grouped on equal area plots and for most of the dikes the minimum ams axes plot near to the pole of the dike our ams measurements enable us to infer absolute magma flow directions for half the dikes studied the maximum ams axes of samples from one side of the dike form a tight cluster on an equal area plot and those from the other side of the dike form another tight cluster the two clusters are close together separated by 10 30 for narrow dikes 100 cm wide and are farther apart 30 60 for wide dikes and are symmetrically disposed on either side of the plane of the dike we infer that these paired clusters are caused by imbrication of nonequant ferromagnetic crystals against each margin of the dike during deposition in a velocity gradient and hence indicate the flow azimuth i e the absolute magma flow direction nearly half of the dikes measured 25 gave paired ams plots in 12 the magma flowed up at low oblique angles 5 30 from the horizontal in five it flowed down at 5 20 in four it flowed horizontally 5 in three it flowed up at a steep angle 50 75 and in one it flowed down at a steep angle the magma flow in general was rarely vertical or horizontal

estimating mixing rates from seismic images of oceanic structure an improved understanding of the spatial distribution of diapycnal mixing in the oceans is the key to elucidating how meridional overturning circulation is closed the challenge is to develop techniques which can be used to determine the variation of diapycnal mixing as a function of space and time throughout the oceanic volume one promising approach exploits seismic reflection imaging of thermohaline structure we have applied spectral analysis techniques to fine structure undulations observed on a seismic transect close to the subantarctic front in the south atlantic ocean 91 horizontal spectra were fitted using a linear combination of a garrett munk tow spectrum for internal waves and a batchelor model for turbulence the fit between theory and observation is excellent and enables us to deduce the spatial variability and context of diapycnal mixing rates which range from 10 5 to 10 3 5m2s 1

potassium rich magmatism in the western outer carpathians magmagenesis in the transitional zone between the european plate and carpathian pannonian region abstract miocene igneous rocks of the western outer carpathians in poland and moravia czech republic were emplaced in a tectonic setting transitional between the european foreland and the carpathian pannonian arc system they form medium to high k calc alkaline suites which are compositionally different to each other and to other calc alkaline sequences in the region geographically and compositionally the moravia rocks can be seen as transitional between the rift related alkaline magmatism of the foreland and the dominantly calc alkaline magmatism of the carpathian pannonian region certain moravia rocks are unusually enriched in incompatible trace elements e g nb 122 ppm and th 31 ppm the primary magmas of both suites were formed in metasomatised lithosphere mantle of the european plate but the enrichment mechanism differed in poland it was by ancient subduction related events whereas in moravia metasomatism was mainly by melts and or fluids from deeper mantle sources partial melting was promoted by impingement of rising asthenosphere on the base of the lithosphere possibly related to reactivation of trans lithospheric nw se trending fault zones

geochemistry and tectonic development of cenozoic magmatism in the carpathian pannonian region this review considers the magmatic processes in the carpathian pannonian region cpr from early miocene to recent times as well as the contemporaneous magmatism at its southern boundary in the dinaride and balkans regions this geodynamic system was controlled by the cretaceous to neogene subduction and collision of africa with eurasia especially by adria that generated the alps to the north the dinaride hellenide belt to the east and caused extrusion collision and inversion tectonics in the cpr this long lived subduction system supplied the mantle lithosphere with various subduction components the cpr contains magmatic rocks of highly diverse compositions calc alkaline k alkalic ultrapotassic and na alkalic all generated in response to complex post collisional tectonic processes these processes formed extensional basins in response to an interplay of compression and extension within two microplates alcapa and tisza dacia competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism mainly as a result of extension and differences in the rheological properties and composition of the lithosphere extension led to disintegration of the microplates that finally developed into two basin systems the pannonian and transylvanian basins the southern border of the cpr is edged by the adria microplate via sava and vardar zones that acted as regional transcurrent tectonic areas during miocene recent times major trace element and isotopic data of post early miocene magmatic rocks from the cpr suggest that subduction components were preserved in the lithospheric mantle after the cretaceous miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere changes in the composition of the mantle through time support geodynamic scenarios of post collision and extension processes linked to the evolution of the main blocks and their boundary relations weak lithospheric blocks i e alcapa and western tisza generated the pannonian basin and the adjacent styrian transdanubian and z rand basins which show high rates of vertical movement accompanied by a range of magmatic compositions strong lithospheric blocks i e dacia were only marginally deformed where strike slip faulting was associated with magmatism and extension at the boundary of adria and tisza dacia strike slip tectonics and core complex extension were associated with small volume miocene magmatism in narrow extensional sedimentary basins or granitoids in core complex detachment systems along older suture zones sava and vardar accommodating the extension in the pannonian basin and afterward pliocene quaternary inversion magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

shallow intrusive directions of sheeted dikes in the troodos ophiolite anisotropy of magnetic susceptibility and structural data sheeted dikes play a central role in the formation of oceanic crust it is commonly assumed that sheeted dikes intrude vertically upward from elongated mid ocean ridge mor magma chambers but there are no direct observational data bearing on this hypothesis this assumption contrasts with the intrusive behavior of subaerial volcanoes where magmas rise into shallow central magma chambers that laterally feed vertically oriented dikes the authors have studied intrusive directions of sheeted dikes in a structural analogue to oceanic crust the troodos ophiolite structural and magnetic fabric data of 65 dikes provide consistent results and suggest a broad distribution of shallow 20 degree to nearly vertical upward magma transport directions these data suggest that horizontal emplacement has to be considered for sheeted dikes at mors implying more centralized mor plumbing systems than previously thought such plumbing systems provide ample opportunity for complex mixing fractionation and contamination of mor lavas in magma chambers and tabular magma storage volumes whether the mor magma supply is linear or centralized also has a fundamental effect on crustal accretion processes and the geometry of hydrothermal convection systems

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

effect of seismic source bandwidth on reflection sections to image water structure 1 the seismic reflection profile is the convolution of the seismic acquisition impulse response and the target impedance contrasts in the ocean these contrasts are mainly determined by the widths and gradients of the temperature transitions between the different water masses hence seismic oceanography profiles are sensitive to the frequency bandwidth of the seismic acquisition system we tested a novel seismic source that allowed us to simultaneously profile the ocean with differing impulse responses we show that frequencies 20 hz are best to delineate large impedance contrasts that occur over a vertical scale of several tens of meters whereas frequencies 80 hz image the boundaries of layers of around 10 m we demonstrate a towed acquisition system that can operate from a research vessel to give a bandwidth from 10 to 120 hz that could if required be modified to provide frequencies up to 200 hz

namurian bentonites in the pennine basin uk origin and magmatic affinities nine namurian clay bands retrieved from boreholes in the northern part of the pennine basin are on the basis of their petrography mineralogy and geochemistry shown to be volcanic in origin and are therefore bentonites the bentonites which have a fragmental texture are normally graded and show rare preservation of shard textures representing vitric tuff deposits that have been altered subsequently to clay dominated horizons crystals are a minor component of the bentonites but biotite in particular is concentrated at the base of the beds a clay mineral assemblage of mixed layer illite smectite with subordinate kaolinite identifies most of the samples as k bentonites but kaolinite dominates two samples that can be classed as tonsteins temporal variation of salinity within the depositional basin is suggested to explain these different clay assemblages the major element geochemistry of the bentonites reflects their clay mineralogy and the compositions of diagenetic minerals present the latter including pyrite carbonates and hydroxyapatite enrichment of the bentonites in some trace elements including ba sr pb cu and ni can be related to the presence of the diagenetic minerals but the extent to which the elements are added from external sources as opposed to being redistributed within the ash is unclear immobile trace element systematics suggest a rhyodacite dacite composition for the original ash and derivation from the collision of plates this being supported by evidence provided by the rare earth elements ree in one group of samples however in another group of samples variations in ree concentrations may be caused by mobility of these elements during alteration the chemistry of the namurian bentonites contrasts markedly with that of the local carboniferous volcanics but is comparable in some respects with one group of westphalian tonsteins although the latter are more rhyolitic in character it is suggested that the namurian bentonites and the westphalian tonsteins of acid affinities originated from volcanic activity associated with a destructive plate margin in the variscan externides and that the observed compositional trend may reflect magma evolution possibly related to the progressive east west closure

petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the guadeloupe archipelago west indies abstract the results of the geotref project presented here aim to develop high enthalpy geothermal energy in fractured reservoirs they focus on active volcanic islands especially the basse terre island guadeloupe archipelago as part of this project we measured several petrophysical properties to better understand how fluids flow in the hydrothermal system provide a set of parameters to modelers and build datasets for future interpretation of well logs the thermo physical rock properties of bulk and grain density porosity permeability compressional wave velocity thermal conductivity and diffusivity specific heat capacity of outcropping volcanic rocks from the guadeloupe archipelago lesser antilles were measured and a dataset was built according to field observations samples were grouped into three lithological classes and then separated by their degree of alteration according to macroscopic aspects and optical microscopy results geochemical data were obtained and magnetic minerals identified by combining anisotropy of magnetic susceptibility and variation of magnetic susceptibility with temperature the lithotypes investigated were lava flows debris flows and pyroclastics gathering ash pumice and scoria deposits for lavas and debris flows three degrees of alteration were defined fresh slightly to moderately altered and highly hydrothermalized only fresh pyroclastics were studied because the altered state was not outcropping typically samples are composed of andesite and belong to tholeiitic and calc alkaline series lava porosity consists of high density cooling joints and vesicles of different shapes whereas pores in debris flows and pyroclastics are located both between and within particles median porosities and permeabilities are clearly distinct for lavas 4 and 6 10 18 m2 debris flows 33 and 4 10 14 m2 and pyroclastics 34 and 8 10 13 m2 the porosity difference implies a thermal conductivity twice to three times higher for lavas 1 68 w m 1 k 1 specific heat capacity of all lithothypes is similar 0 75 0 97 kj kg 1 k 1 advancing hydrothermal alteration removes magnetic minerals and transforms initial rocks the original plagioclases and pyroxenes in neoformed chlorite white micas quartz epidote and clay minerals are replaced this modifies the shape of the pore network furthermore hydrothermal alteration results in a reduction of pore throat diameter it tends to decrease petrophysical differences between lavas and debris flows increasing the porosity and permeability of effusive rocks while the opposite effects are observed for debris flows

ocean temperature and salinity inverted from combined hydrographic and seismic data recently seismic reflection methods have been successfully applied to oceanographic issues here we present a new approach combining xbt and ctd surveys with seismic observations to visualize long sections with a resolution down to a few meters the challenge to a full investigation of mixing processes has been the tremendous span of spatial scales ranging from hundreds of kilometers to centimeters traditional hydrographic observations could only resolve the large scale effects by measuring temperature and salinity profiles at discrete locations typically several kilometers apart whereas dedicated localized measurements allowed investigation of the ocean fine structure at the other end of the spatial spectrum the intermediate scales have in contrast been difficult to observe systematically here we present temperature and salinity data inverted from seismic observations that cover the intermediate scales and provide a new approach to image mesoscale processes and allow the investigation of their dynamics at unprecedented resolution

ocean internal wave spectra inferred from seismic reflection transects 1 internal waves affect many important dynamical processes in the ocean but in situ observations of internal waves are infrequent and spatially sparse here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean seismic images of the norwegian sea water column show reflections that capture snapshots of finestructure displacements due to internal waves horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the garrett munk tow spectrum of oceanic internal wave displacements spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave sloping boundary interactions

quantitative imaging of complex structures from dense wide aperture seismic data by multiscale traveltime and waveform inversions a case study an integrated multiscale seismic imaging flow is applied to dense onshore wideaperture seismic data recorded in a complex geological setting thrust belt an initial p wave velocity macromodel is first developed by first arrival traveltime tomography this model is used as an initial guess for subsequent full waveform tomography which leads to greatly improved spatial resolution of the p wave velocity model however the application of full waveform tomography to the high frequency part of the source bandwidth is difficult due to the non linearity of this kind of method moreover it is computationally expensive at high frequencies since a finitedifference method is used to model the wave propagation hence full waveform tomography was complemented by asymptotic prestack depth migration to process the full source bandwidth and develop a sharp image of the short wavelengths the final traveltime tomography model and two smoothed versions of the final full waveform tomography model were used as a macromodel for the prestack depth migration in this study wide aperture multifold seismic data are used after specific preprocessing of the data 16 frequency components ranging from 5 4 hz to 20 hz were inverted in cascade by the full waveform tomography algorithm the full waveform tomography successfully imaged sw dipping structures previously identified as highresistivity bodies the relevance of the full waveform tomography models is demonstrated locally by comparison with a coincident vertical seismic profiling vsp log available on the profile the prestack depth migrated images inferred from the traveltime and the smoothed full waveform tomography macromodels are shown to be on the whole consistent with the final full waveform tomography model a more detailed analysis based on common image gather computations and local comparison with the vsp log revealed that the most accurate migrated sections are those obtained from the full waveform tomography macromodels a resolution analysis suggests that the asymptotic prestack depth migration successfully migrated the wideaperture components of the data allowing medium wavelengths in addition to the short wavelengths of the structure to be imaged

from the variscan to the alpine orogeny crustal structure of the bohemian massif and the western carpathians in the light of the sudetes 2003 seismic data summary the variscan orogeny is the major middle to late palaeozoic tectonometamorphic event in central europe and the bohemian massif is the largest exposure of rocks deformed during this orogeny the bohemian massif consists of the saxothuringian barrandian and moldanubian units adjacent to this massif in the southeast the western carpathians form an arc shaped mountain range related to the alpine orogeny during the cretaceous to tertiary the complex crustal scale geological structure of the variscan bohemian massif and the western carpathians and especially their contact were analysed in this study employing the data of the sudetes 2003 international seismic refraction experiment the analysed seismic data were acquired along the 740 km long nw se oriented s04 profile that crossed the bohemian massif and the western carpathians before terminating in the pannonian basin the data were interpreted by 2 d trial and error forward modelling of p waves and additional constraints on crustal structure were provided by gravity modelling the complex velocity structure derived in our analysis included low velocities of 5 85 km s 1 at the contact of the saxothuringian and barrandian units that reflect the presence of low density granites there are distinct lateral variations in deep crustal structure in the transition between the bohemian massif and the western carpathians the abrupt change of the crustal thickness in this transition zone may be associated with the pieniny klippen belt a deep seated boundary between the colliding palaeozoic lithospheric plate to the north and the alcapa microplate to the south in the upper crust of this transition low velocities of 4 km s 1 extend to 6 km and represent the sedimentary fill of the carpathian flysch and foredeep that thins towards the foreland this basin is also expressed as a pronounced gravity low the moho in the carpathians reaches a depth of 32 33 km in contrast in the pannonian basin the moho rises to a depth of 25 km which corresponds to the pannonian gravity high

exploring some issues in acoustic full waveform inversion the least squares error measures the difference between observed and modelled seismic data because it suffers from local minima a good initial velocity model is required to avoid convergence to the wrong model when using a gradient based minimization method if a data set mainly contains reflection events it is difficult to update the velocity model with the least squares error because the minimization method easily ends up in the nearest local minimum without ever reaching the global minimum several authors observed that the model could be updated by diving waves requiring a wide angle or large offset data set this full waveform tomography is limited to a maximum depth here we use a linear velocity model to obtain estimates for the maximum depth in addition we investigate how frequencies should be selected if the seismic data are modelled in the frequency domain in the presence of noise the condition to avoid local minima requires more frequencies than needed for sufficient spectral coverage we also considered acoustic inversion of a synthetic marine data set created by an elastic time domain finite difference code this allowed us to validate the estimates made for the linear velocity model the acoustic approximation leads to a number of problems when using long offset data nevertheless we obtained reasonable results the use of a variable density in the acoustic inversion helped to match the data at the expense of accuracy in the inversion result for the density

magnetic properties of a columnar basalt from central mexico the variation of low field magnetic susceptibility with low temperature between 77 k and 300 k observed for a vertical columnar basalt from central mexico shows a rare pattern for continental basalt i e susceptibility decreases with temperature to about 40 70 of room temperature value and then increases up to about 60 100 at 77 k these results combined with other rock magnetic measurements including af and thermal demagnetization irm experiments lowrie fuller tests thermomagnetic analysis and optical and sem observations suggest the presence in the columnar basalt of predominantly single domain and pseudo single domain titanomagnetites with composition around tm60 and a small amount of very fine grained particles

tertiary subduction and slab break off model of the carpathian pannonian region abstract this paper illustrates the application of multidisciplinary data analysis to the carpathian pannonian region and presents a new tertiary development model that incorporates all multidisciplinary parameters during the late cretaceous eocene the future carpathian orogen was part of the larger alpine carpathian orogen formed by the southeastward subduction 135 55 ma of the penninic ocean and the ultimate collision 55 40 ma of the european and adriatic continents the subduction in the alpine region ended by the slab break off of the subducting oceanic lithosphere from the continental one and by the related magmatism 43 24 ma while the eocene alps were under continental collision the eocene remnant carpathian flysch basin rcfb was still subducting the carpathians and eastern parts of the alps started to occupy the region of the present carpathians during the early miocene the oceanic plate underlying the rcfb subducted southwestwards later westwards while the northeastward and eastward migration velocity of the accreting plate boundary decreased through time the slower subduction rate caused a steeper dip of the subducting slab the beginning of the eggenburgian 22 19 ma and following duration of extension in the orogenic hinterland accompanied by the asthenosphere upwelling the onset of the crustally derived volcanism above the risen asthenosphere and the younger mantle derived volcanism progressively less contaminated by the crustal material all contemporaneous with a shortening in the carpathian accretionary wedge the subduction of the rcfb finally led at the end of the early miocene to a collision with the continental margin along the westernmost part of the present carpathian arc the subduction roll back of the subducting slab of the rcfb under the advancing inner carpathians the oblique closure of the basin the progressive change of the subduction to collision from the west to the east along the carpathian arc drove a scissors like break off of the subducting oceanic slab along the west carpathians the break off in the east carpathians was driven by the weight of a subducting oceanic slab and buoyancy of the attached continental slab the break off started in the west of the carpathian arc in the early miocene ran along the arc to its present position in the bend area between the east and south carpathians and separated the oceanic slab that subducted passively under its own weight from the european continental margin the lateral propagation rate of the slab tear decreased with time the break off related volcanism was synchronous with the final stages of the collision

crustal structure of the eastern alps and their foreland seismic model beneath the cel10 alp04 profile and tectonic implications summary the subject of this paper concerns the seismic modelling of the crustal structure in the transition zone from the bohemian massif across the molasse basin and the eastern alps to the southern alps mainly on the territory of austria the cel10 alp04 profile crosses the triple point of the european plate adriatic microplate and the recently identified pannonian fragment the seismic data along the presented profile originate from two large experiments celebration 2000 and alp 2002 the wavefield observed in the eastern alps is more complex than in the bohemian massif strong first arrivals pg are distinct up to 60 90 km offset and are characterized by large variations in apparent velocity and amplitude the contact between the molasse basin and the eastern alps represents a barrier for seismic waves midcrustal reflections pc are usually recorded at short distance intervals 20 50 km and are also characterized by variations in apparent velocity and amplitude the moho reflections are usually strong and well correlated while pn arrivals are only fragmentarily recorded detailed 2 d forward modelling of all refracted post critical and reflected phases identified in the correlation process was undertaken using a ray tracing technique the p wave velocity in the crystalline upper crust of the bohemian massif and molasse basin is about 6 15 km s 1 which is slightly higher than in the alpine area about 6 0 km s 1 below the northern accretionary wedge of the eastern alps low velocity sediments penetrate towards the southwest sw down to about 10 km depth in the middle crust of the alpine part a reflective zone was modelled by a lamellae structure with alternating high and low velocities and thicknesses of about 2 3 km the lower crust in this part of the model is more homogeneous with a velocity of about 6 9 km s 1 in the bohemian massif a high velocity hv body vp 7k m s 1 o f af ew kilometres thickness was delineated in the depth interval 18 23 km the crustal thickness along the cel10 alp04 profile changes from about 42 44 km in the sw alpine part to around 40 km in the central part of the profile molasse basin and 38 40 km in the ne bohemian massif the velocity in the uppermost mantle determined from pn wave traveltimes is about 8k m s 1 along the whole profile the interpretation of the seismic wavefield is supplemented by an existing 3 d p wave velocity model of the area main features derived by 2 d modelling low velocities beneath the accretionary wedge high velocities in the lower crust of the bohemian massif moho topography well correlate with the 3 d model furthermore the 3 d model allows assessing the lateral extent of significant features alongside the cel10 alp04 profile this area is affected by both collision and escape tectonics the high reflectivity zone

waveform preserving processing flow of multichannel seismic reflection data for adjoint state full waveform inversion of ocean thermohaline structure this paper presents a specific data processing flow to be applied to marine multichannel seismic reflection data collected by a streamer in order to use them to perform prestack adjoint waveform inversion of ocean s thermohaline properties the overall goal is to increase the signal to noise ratio snr of the weak reflections generated at the small impedance contrasts within the water layer while preserving the direct wave the processing flow focuses on increasing the snr of the shot gather records by forcing noise amplitudes to fall inside a range of physical plausible values for water layer reflections this processing step is applied in two independent branches of the workflow one dealing with the water layer reflections and the second with the direct wave which are separated by applying a singular value decomposition to test the performance of the processing flow we combine actual noise field recordings with a synthetic seismic data set we apply the proposed data processing flow to quantify differences between noise free and processed record sections and we then compare with the results obtained by applying a butterworth filter bf for offsets smaller than 1500 m the bf processing produces a signal with snr 0 1 the proposed workflow allows to retrieve the seismic signal with 0 1 snr 2 4 for offsets larger than 1500 m the bf processing allows obtaining the snr up to 1 4 while the proposed workflow increases the snr up to 5 we finally demonstrate that the processed data can be used to perform waveform inversion with an accuracy of 0 02 m s

seismic reflection imaging of large amplitude lee waves in the caribbean sea 1 results from the first testing of the r v marcus langseth as a platform for collecting seismic reflection data from the water column of the ocean demonstrate that large amplitude lee waves can be acoustically mapped a seismic profile collected in the caribbean sea offshore costa rica shows disturbances in finestructure which we interpret to be lee waves propagating hundreds of meters vertically through the water column above seafloor ridges waves show vertical displacements of 30 50 m and horizontal wavelengths of 300 3000 m reflector displacement spectra calculated in the region containing the lee waves exceed garrett munk energy levels by up to a factor of 10 at horizontal wavelengths of 300 3000 m suggesting a locally derived source of internal wave energy consistent with our interpretation our results show that it is possible to image large scale lee waves a phenomenon potentially responsible for dissipation and mixing within the ocean

multiscale imaging of complex structures from multifold wide aperture seismic data by frequency domain full waveform tomography application to a thrust belt summary an application of full waveform tomography to dense onshore wide aperture seismic data recorded in a complex geological setting thrust belt is presented the waveform modelling and tomography are implemented in the frequency domain the modelling part is solved with a finite difference method applied to the visco acoustic wave equation the inversion is based on a local gradient method only the p wave velocity is involved in the inversion the inversion is applied iteratively to discrete frequency components by proceeding from low to high frequencies this defines a multiscale imaging in the sense that high wavenumbers are progressively incorporated in images the linearized waveform tomography requires an accurate starting velocity model that has been developed by first arrival traveltime tomography after specific pre processing of the data 16 frequency components ranging between 5 4 and 20 hz were inverted ten iterations were computed per frequency component leading to 160 tomographic models the waveform tomography has successfully imaged southwest dipping structures previously identified from other geophysical data as being associated with high resistivity bodies the relevance of the tomographic images is locally demonstrated by comparison of a velocity depth function extracted from the waveform tomography models with a coincident vertical seismic profiling vsp log available on the profile moreover comparison between observed and synthetic seismograms computed in the starting traveltime and waveform tomography models demonstrates unambiguously that the waveform tomography successfully predicts for wide angle reflections from southwest dipping geological structures this study demonstrates that the combination of first arrival traveltime and frequency domain full waveform tomographies applied to dense wide aperture seismic data is a promising approach to quantitative imaging of complex geological structures indeed wide aperture acquisition geometries offer the opportunity to develop an accurate background velocity model for the subsequent waveform tomography this is critical because the building of the macromodel remains an open question when only near vertical reflection data are considered

imaging meddy finestructure using multichannel seismic reflection data 1 this work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution 10 15 m we present seismic images of three meddies acquired in the gulf of cadiz sw iberian peninsula which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure the seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature t and salinity s data the core region characterized by smooth t and s variations is weakly reflective the double diffusive upper and lower boundaries and the lateral interleaving outer edges characterized by stronger t and s contrasts display strong reflectivity bands these new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans

magnetic fabric and weak deformation in sandstones of accretionary prisms of the flysch and klippen belts of the western carpathians mostly offscraping indicated abstract the magnetic fabric of sandstones in thrust sheets of the flysch belt of the western carpathians is basically sedimentary in origin in minority of specimens slightly affected by deformation which is generally very weak corresponding to the earliest deformation stage and to types i ii in terms of the magnetic fabric classification of the accretionary prisms by pares et al 1999 and aubourg et al 2004 respectively this indicates an absence of the return flow during the subduction process the deformation is weaker in the thrust sheets located at the margins of the flysch belt the danice and silesian thrust sheets in the west and the bile karpaty and oravska magura thrust sheets in the east than in the fore magura raca and bystrica thrust sheets located in the centre of the flysch belt in the danice and silesian thrust sheets the weak deformation reflects their sedimentation on the northern european slope of the flysch belt basin and relatively short transport during their thrusting over the foredeep in the bile karpaty and oravska magura thrust sheets that are located near the subduction zone the weak deformation is explained by assuming early offscraping and frontal accreting of these thrust sheets in the pieniny klippen belt the deformation of the palaeogene sandstones peri klippen palaeogene is stronger than that in the marginal thrust sheets danice silesian bile karpaty and oravska magura thrust sheets of the flysch belt but weaker than that in the central thrust sheets fore magura raca and bystrica thrust sheets of the flysch belt this is in an apparent contradiction with strong macroscopic deformation of mesozoic rocks of the pieniny klippen belt but understandable realizing that the sediments of the peri klippen palaeogene were deformed only during the neoalpine orogenies in palaeogene and neogene after the main deformation late cretaceous in the pieniny klippen belt

ordovician k bentonites in the upper plate active margin of western gondwana famatina ranges stratigraphic and palaeogeographic significance abstract numerous thin bedded tabular pale yellowish clay bands are interlayered with black shales in a biostratigraphically constrained early ordovician volcano sedimentary succession at famatina western argentina this region was part of a fairly continuous upper plate convergent volcanic chain that fringed western gondwana mineralogy on both clay and non clay fractions whole rock chemistry and field observations on these distinctive event beds indicate that they originated as relatively coarse fallout tephras altered first into bentonites and later through burial metamorphism into k bentonites metabentonites these tephras were deposited as single crystals and glassy dust or pumiceous fragments in a restricted subtidal environment the region of famatina has previously been inferred as the source of abundant distal k bentonites recorded in the adjacent lower plate allochthonous precordillera terrane however these k bentonites within the proximal arc site were unknown and rather unexpected since they are generally better preserved like distal deposits associated either with central vent plinian ultraplinian eruptions or with accompanying co ignimbrite ash clouds their chemistry and comparison with those k bentonites in the precordillera allow tracing an evolution from volcanic arcs into continental crust k bentonites described in this paper are much older than those recorded in the adjacent precordillera terrane and seem to be associated with a first eruptive period along western gondwana that has no counterpart in the argentine precordillera suggesting a significant longitudinal separation between these two regions by the early ordovician

field dependence of ac susceptibility in titanomagnetites abstract ac susceptibility measurements as a function of field amplitude hac and of frequency show a strong field dependence for a set of synthetic titanomagnetites fe3 xtixo4 and for certain basalts from the soh 1 hawaiian drill hole and from iceland in phase susceptibility is constant below fields of about 10 100 a m and then increases by as much as a factor of two as hac is increased to 2000 a m both the initial field independent susceptibilities and the field dependence of susceptibility are systematically related to composition initial susceptibility is 3 si for a single crystal sphere of tm0 x 0 and decreases with increasing titanium content field dependence is nearly zero for tm0 and increases systematically to a maximum near tm60 x 0 6 this field dependence can in some cases be mistaken for frequency dependence and lead to incorrect interpretations of magnetic grain size and composition when titanomagnetite is present

the mineralogy and origin of some silurian bentonites welsh borderland u k thirty clay rich horizons from the wenlock and ludlow series of the welsh borderland were analysed to investigate their mineralogy and possible origins two mineralogical assemblages were determined an assemblage of illite smectite and kaolinite of volcanic origin which was associated in many samples with an assemblage of illite and chlorite of detrital origin immobile chemical discriminants zr tio2 versus nb y infer an originally rhyolitic ash composition with a possible temporal progression from the wenlock to ludlow to more differentiated compositions the thin nature of the bentonites and lack of juxtaposed subduction related calc alkaline magmatism suggests that the tuffs were derived from distant explosive eruptions from volcanic centres possibly in ne europe

thermohaline fine structure in an oceanographic front from seismic reflection profiling we present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between the labrador current and the north atlantic current the images show that distinct water masses can be mapped and their internal structure imaged using low frequency acoustic reflections from sound speed contrasts at interfaces across which temperature changes the warm cold front is characterized by east dipping reflections generated by thermohaline intrusions in the uppermost 1000 meters of the ocean our results imply that marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena including thermohaline intrusions internal waves and eddies

magnetic fabric in the umvimeela dyke satellite of the great dyke zimbabwe abstract anisotropy of magnetic susceptibility ams has been determined for 22 locations from the 500 km long gabbroic umvimeela dyke of zimbabwe ams is controlled by the presence of multi domain magnetite grains which appear to have preserved a variety of magnetic fabrics related to magma movement at the time of dike emplacement three locations along the umvimeela dyke have been identified as feeder points at which magma flowed into the dike from below lateral flow away from these points supplied the rest of the dike system the presence of several foci of igneous activity along the umvimeela dyke parallels the development of the neighbouring contemporaneous great dyke layered complex which consists of a line of contiguous subchambers individual feeder points to the umvimeela dyke may be directly related to activity in adjacent subchambers

magnetic fabric and petrology of miocene sub volcanic sills and dykes emplaced into the sw flysch belt of the west carpathians s moravia czech republic and their volcanological and tectonic implications abstract magnetic fabrics were investigated in the sub volcanic bodies occurring within the sw flysch belt of the western carpathians magnetite or low ti titanomagnetite is the principal carrier of the anisotropy of magnetic susceptibility ams in these rocks though various fe ti oxides were also identified in minor amounts the magnetic fabric in almost all sills and dykes is conformable to the shapes of the bodies and no doubt originated through more or less free magma flow that requires relatively open voids to be injected that likely originated in an extensive tectonic regime in an ankaramite sill where the rock creates typical hexagonal columns the magnetic fabric is related rather to the column axes than to the overall shape of the sill the magnetic fabric formation in this sill is controlled by the post emplacement process of the creation of the columns at some studied localities signs of post magmatic middle miocene tectonic deformation are observed in the field the youngest known in the flysch belt as the magnetic fabric is unrelated to those signs we conclude that these young tectonic movements did not penetrate ductilely in the volume of the volcanic body it seems that the strain was focused to thin zones along the faults since it did not change the preferred orientation of magnetic minerals in the rock volume substantially

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

tertiary extension development and extension compression interplay in the west carpathian mountain belt abstract this paper describes palaeostresses calculated from fault striae data the inferred palaeostrain patterns and determines the inter relation of the compression and extension during the tertiary development of the west carpathians the calculated stress and inferred strain patterns for the palaeogene burdigalian indicate that the ancestral west carpathians formed a more or less straight orogenic belt this belt underwent contraction and uplift in its narrow frontal zone stretching along its strike during the paleocene chattian and regional contraction and uplift during the chattian burdigalian the strain stress pattern is similar to the collision related pattern known from the eastern alps for the paleocene burdigalian during the burdigalian tortonian the calculated and inferred west carpathian stress and strain patterns indicate narrow frontal contractional and lateral sinistral transpressional zones in the orogenic front and broad extensional and dextral transtensional zones in the orogenic interior the stress strain pattern is similar to the subduction related pattern known from areas such as the hellenic or sunda banda arcs

fine scale thermohaline ocean structure retrieved with 2 d prestack full waveform inversion of multichannel seismic data application to the gulf of cadiz sw iberia this work demonstrates the feasibility of 2d time domain adjoint state acoustic full waveform inversion fwi to retrieve high resolution models of ocean physical parameters such as sound speed temperature and salinity the proposed method is first described and then applied to pre stack multi channel seismic mcs data acquired in the gulf of cadiz sw iberia in 2007 in the framework of the geophysical oceanography project the inversion strategy flow includes specifically designed data pre conditioning for acoustic noise reduction followed by the inversion of sound speed in the shotgather domain we show that the final sound speed model has a horizontal resolution of 70m which is two orders of magnitude better than that of the initial model constructed with coincident expendable bathy thermograph xbt data and close to the theoretical resolution of o temperature t and salinity s are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local depth dependent t s relation derived from regional conductivity temperature depth ctd measurements of the national oceanic and atmospheric administration noaa database the comparison of the inverted t and s models with xbt and ctd casts deployed simultaneously to the mcs acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0 18oc for temperature and 0 08 psu for salinity the combination of oceanographic and mcs data into a common pseudo automatic inversion scheme allows to quantitatively resolve submeso scale features that ought to be incorporated into larger scale ocean models of oceans structure and circulation this article is protected by copyright all rights reserved

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

characterization of the sub mesoscale energy cascade in the alboran sea thermocline from spectral analysis of high resolution mcs data part of the kinetic energy that maintains ocean circulation cascades down to small scales until it is dissipated through mixing while most steps of this downward energy cascade are well understood an observational gap exists at horizontal scales of 103 101 m that prevents characterizing a key step in the chain the transition from anisotropic internal wave motions to isotropic turbulence here we show that this observational gap can be covered using high resolution multichannel seismic hr mcs data spectral analysis of acoustic reflectors imaged in the alboran sea thermocline shows that this transition is likely caused by shear instabilities in particular we show that the averaged horizontal wavenumber spectra of the reflectors vertical displacements display three subranges that reproduce theoretical spectral slopes of internal waves x 100 m kelvin helmholtz type shear instabilities 100 m x 33 m and turbulence x 33 m indicating that the whole chain of events is occurring continuously and simultaneously in the surveyed area

parallel magnetic fabrics in metamorphic granitoid and sedimentary rocks of the branisko and cierna hora mountains e slovakia and their tectonometamorphic control abstract the magnetic anisotropy of rocks from the branisko and cierna hora mountains west carpathians was investigated and the ferromagnetic and paramagnetic components were separated and found to be roughly coaxial the magnetic fabrics in metamorphic granitoid and sedimentary rocks display very similar patterns of principal susceptibilities metamorphites underwent a polyphase prograde and retrograde metamorphis granitoids were metamorphosed retrogressively and sedimentary rocks suffered a very weak prograde metamorphism retrogressive and progressive alpine metamorphism and the formation of magnetic anisotropy took place simultaneously before during and after the emplacement of the central west carpathian nappes

internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties internal flow structures in columnar jointed basalt from hreppholar iceland ii magnetic anisotropy and rock magnetic properties

modelling of gi gun signatures1 in 1989 a new type of marine seismic source was introduced this new air gun which consists of two air chambers instead of one is called the gi gun the main feature of this gun is that the bubble created by the gun is stabilized by an injection of extra air from the second chamber at a later time this injection mechanism reduces the amplitude of the bubble oscillations which also means that the acoustic signal from a gi gun shot is characterized by a very clean primary pulse followed by very small bubble oscillations a method for calculating the acoustic signal generated by a gi gun is presented based on the solution of a damped kirkwood bethe equation the far field pressure of single gi guns and of arrays of gi guns is calculated it is shown that the optimal values for injection start time and injection period vary with injector volume and gun depth it is also shown that the precision in the firing time for the injector should be of the order of 4 ms while the precision of the injection period should be of the order of 8 ms modelled and measured far field signatures have been compared and the relative error energy is found to be less than 3 5 for all examples

relative contribution of temperature and salinity to ocean acoustic reflectivity 1 marine seismic data display laterally coherent reflectivity from the water column that is attributed to fine scale oceanic layering the amplitude of the different reflections is the expression of acoustic impedance contrasts between neighbouring water masses and therefore water reflectivity maps the ocean s vertical sound speed and density i e temperature and salinity variations here we determine the relative contribution of each parameter by computing the temperature and salinity partial derivatives of sound speed and density and using them to estimate reflection coefficients from a real oceanographic dataset the results show that the mean contribution of density variations is 5 10 while 90 95 is due to sound speed variations on average 80 of reflectivity comes from temperature contrasts salinity contribution averages 20 but it is highly variable and reaches up to 40 in regions prone to diffusive convection such as the top of the mediterranean undercurrent in the gulf of cadiz

single domain particles in rocks and magnetic fabric analysis magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes we have recently demonstrated however in laboratory produced samples that as theoretically expected susceptibility anisotropy is dependent on particle size multidomain particles of magnetite or similar strongly magnetic particles with shape anisotropy exhibit a maximum susceptibility parallel to their easy remanent magnetization axes whereas uniaxial single domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state by demonstrating uniaxial single domain anisotropy characteristics for the first time in a rock specimen we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro or ferrimagnetic particles in rocks in particular apparently foliated rocks can actually be lineated and vice versa moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment

interplay of tectonics and neogene post collisional magmatism in the intracarpathian region abstract distribution of the neogene calc alkaline magmatism of the carpathian arc is directly related in space and time to the kinematics of the two major terranes of the intracarpathian area alcapa tisia getia along the south eastern border of the european plate in the west carpathians and adjacent areas the volcanic activity occurred between 20 11 ma with large volumes of both acidic and intermediate rocks generally distributed randomly sometimes transversally to the orogenic belt and as rare small occurrences along the flysch belt in the east carpathians the volcanic rocks are distributed along the northern margin of the zemplin block the north easternmost part of the alcapa and eastward along the front of the getic block at the contact with european plate between tokaj slanske vihorlat up to northern calimani mountains the magmatism occurred between 14 9 ma and along the calimani harghita chain between 9 0 2 ma the calc alkaline magmatic rocks of the apuseni mountains are located in the interior of the tisia block and occurred between 14 9 ma the generation of the calc alkaline magmatism is considered here as the result of complex interplay between plate roll back and lithospheric detachment tectonic processes and the break off of the subducted plate mostly in a post collisional setting 1 the magmatites of the western carpathians and the pannonian basin were generated in direct relation to subduction roll back processes over the downgoing slab during the period of lateral extrusion and back arc extension in this area characterized by maximum crustal shortening we can infer further delamination processes to explain the generation of magmas 2 the magmatic rocks from the northern sector of the east carpathians tokaj slanske vihorlat up to the northern calimani mountains resulted after subduction roll back processes and an almost simultaneous break off of the descending plate all along the arc segment during main clockwise rotation of the intracarpathian terranes 3 in the eastern sector of the east carpathians calimani up to harghita mountains the magmatic rocks were generated through partial melting of the subducted slab followed by gradual break off of the subducted plate along strike north to south 4 the apuseni mts magmatic activity resulted in transtensional tectonic regime by decompressional melting of lithospheric mantle during the translation and rotation of tisia getia block

element fluxes associated with subduction related magmatism destructive plate margin magmas may be subdivided into two groups on the basis of their rare earth element ree ratios most island arc suites have low ce yb and remarkably restricted isotope ratios of 87 sr 86 sr 0 7033 143 nd 144 nd 0 51302 206 pb 204 pb 18 76 207 pb 204 pb 15 57 and 208 pb 204 pb 38 4 however they also have rb sr 0 03 th u 2 2 and ce yb 8 5 ratios which are significantly less than accepted estimates for the bulk continental crust the high ce yb suites have higher incompatible element contents more restricted heavy ree and much more variable isotope ratios such rocks are found in the aeolian islands grenada indonesia and philippines and their isotope and trace element features have been attributed both to contributions from subducted sediment and or old trace element enriched material in the mantle wedge it is argued that for isotope and trace element models the slab component can usefully be taken to consist of subducted sediment and altered mid ocean ridge basalts since these may contain ca 80 of the water in the subducted slab and the distinctive trace element features of arc magmas are generally attributed to the movement of material in hydrous fluids the isotope data indicate that not more than 15 of the sr and th in an average arc magma were derived from subducted material and that the rest were derived from the mantle wedge the fluxes of elements which cannot be characterized isotopically are more difficult to constrain but for most minor and trace elements the slab derived contribution in arc magmas is too small to have a noticeable effect on the residual slab

magnetic fabric and its significance in the 1400 ma mealy diabase dykes of labrador canada an anistropy of magnetic susceptibility ams study of the relatively fresh mealy diabase dyke swarm indicates a correlation between the ams and the deformational effects in the rocks several ams components were revealed during experimental work on 211 samples that had been heated to 640 c during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields seventeen sites with slight or no deformation have a magnetic fabric composed of two major components the stable component attributed to a primary shape anisotropy has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike n 60 e respectively this configuration is consistent with an origin due to a post emplacement stress field whereby horizontal extension acted on a vertical sheet of partially crystallized magma the orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement the unstable component removed by fields up to 250 mt is attributed to induced domain anisotropy produced by mild tectonic stress during the grenville orogeny the approximate orientation of its principal components as found by the method of substitutional ellipsoids suggests an east west directed maximum stress four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed but which may be largely composed of domain and stress induced anisotropies developed during the grenville orogeny

low field variation of magnetic susceptibility as a tool for magnetic mineralogy of rocks abstract low field variation of magnetic susceptibility was investigated on a collection of several hundreds specimens of various minerals and rocks using the kly 4s kappabridge the measurement is fully automated being executed in 21 distinct fields ranging from 2 to 450 a m in one frequency of 875 hz the measurement is rapid 7 min per specimen so that large collections of specimens can be investigated the results can be processed both graphically and mathematically for the latter processing parameters of two kinds were introduced one characterizes the susceptibility change with field the other one characterizes the field in which the susceptibility no longer obeys the rayleigh law and starts becoming more complex the results were evaluated statistically remarkable differences were revealed between individual minerals and between some rock types for example the field variation of susceptibility of pyrrhotite is in general an order of magnitude larger than that of titanomagnetite the susceptibility increase in pyrrhotite starts at the field an order of magnitude lower than that of titanomagnetite low field variation of susceptibility then appears as an interesting phenomeon that helps in the identification of magnetic minerals and in some cases also in assessing the compositional variation of them