microstructural deformation record of an orogen parallel extension in the vepor unit west carpathians abstract deformation microstructures of quartzo feldspathic rocks have been used to analyse the orogen parallel stretching of the vepor unit in the west carpathians during cretaceous convergence this process occurs contemporaneously with the burial of the vepor basement related to the overthrusting palaeozoic volcano sedimentary sequences of the gemer unit the microstructures develop along a metamorphic gradient indicating an increase of pressure and temperature towards the structural footwall the recrystallization of quartz occurs in the field of subgrain rotation recrystallization sgr while the plagioclase and k feldspar disintegrate into a neocrystallized muscovite albite matrix palaeopiezometry of the recrystallized quartz in conjunction with p t estimates yield strain rates of 9 10 12 to 6 10 14 s 1 depending on temperature 380 480 c and choice of piezometer and flow law calibration strain analysis of the recrystallized quartz aggregates and quartz texture analysis indicate an overprint of the variscan magmatic and high grade fabrics by a cretaceous plane strain deformation resulting in vertical shortening and horizontal orogen parallel east west stretching spatial distribution and conflicting sense of shear of the asymmetrical quartz lattice preferred orientation patterns indicate that the large scale pure shear deformation of the vepor unit is locally accommodated by simple shear zones observed metamorphic gradients across the vepor unit are interpreted to result from later large scale folding and heterogeneous exhumation of the orogen parallel deformation fabric

promotion of graphite formation by tectonic stress a laboratory experiment summary graphitization of less ordered hexagonal carbon was studied under in situ pressure and temperature conditions on anthracite black shale and a synthetic calcite anthracite mixture at upper greenschist facies conditions anthracite exhibited a continuous loss of volatiles in the temperature range from 100 cu p to850 c 9 9 weight per cent at 450 c as detected by differential thermal analysis dta and thermo gravimetry tg energy dispersive x ray diffraction edx revealed a broad amorphous 002 graphite reflection while after p t treatment nearly perfect crystallized graphitic carbon was detected the electrical conductivity was measured at the same time in the frequency range from 0 7 up to 100 khz as a function of time the bulk resistivity was decreased by about three orders in magnitude at constant pressure and temperature conditions 0 7 gpa 450 c while the complex response exhibited a continuous decrease of the imaginary part of the impedance quasi metallic conduction now dominated the charge transport application of pressure strain temperature and time caused an increase in ordering and the degree of interconnection of the formerly randomly oriented carbon sheets the experimental results are an approach towards the explanation of the abundant occurrence of crystalline graphite observed in overthrusts and nappe structures which are distinguished by high conductivity structures

passive and active margin history of the northern tatricum western carpathians slovakia the tatricum an upper crustal thrust sheet of the central western carpathians comprises pre alpine crystalline basement and a late paleozoic mesozoic sedimentary cover the sedimentary record indicates gradual subsidence during the triassic early jurassic initial rifting a jurassic early cretaceous extensional tectonic regime with episodic rifting events and thermal subsidence periods and middle cretaceous overall flexural subsidence in front of the orogenic wedge prograding from the hinterland passive rifting led to the separation of the central carpathian realm from the north european platform a passive margin rimmed by peripheral half graben was formed along the northern tatric edge facing the vahic south penninic oceanic domain the passive versus active margin inversion occurred during the senonian when the vahic ocean began to be consumed southwards below the tatricum it is argued that passive to active margin conversion is an integral part of the general shortening polarity of the western carpathians during the mesozoic that lacks features of an independent wilson cycle an attempt is presented to explain all the crustal deformation by one principal driving force the south eastward slab pull generated by the subduction of the meliatic triassic jurassic tethys oceanic lithosphere followed by the subcrustal subduction of the continental mantle lithosphere

mt and reflection an essential combination summary at many localities in the world there have been coincident comprehensive electromagnetic em studies and seismic reflection profiles conducted unfortunately over many more regions the seismic reflection images are interpreted without the constraints afforded by electrical conductivity information this paper is an attempt to convince the reader that a collocated magnetotelluric mt study should in almost every case be made wherever a seismic reflection survey is undertaken examples are shown from six studies in which the em results aided the geological tectonic interpretations of the seismic sections also difficulties with the mt technique are discussed and the interpretations of conducting zones within the lower crust are examined finally a generalised model is proposed for the continental crust that may account for both the reflectivity and conductivity of the zone at the top of the lower crust

mid cretaceous primitive alkaline magmatism in the northern calcareous alps significance for austroalpine geodynamics basanitic dykes local name ehrwaldite occur over a distance of at least fifty kilometres in a narrow east west trending zone within the lechtal nappe of the northern calcareous alps the dykes crosscut mesozoic sedimentary strata up to the lower cretaceous the sedimentary rocks show contact metamorphism in the immediate vicinity of the dykes the ehrwaldites vary in mineral content from olivine fo 91 87 titanian augite basanites to basanites containing also kaersutite titanian biotite and zeolites minor phases are titanian magnetite picotite llmenite carbonate and sulfides mantle derived xenoliths and xenocrysts form up to five percent of the rock bulk chemical analyses show the typical characteristics of nepheline basanites ne 11 17 wt mg number 74 78 and demonstrate that the ehrwaldites are primitive mantle derived melts trace element contents of the dykes are in excellent agreement with those for basanites and olivine nephelinites from tertiary and quaternary european provinces the same is true for the isotope characteristics of the dykes with average initial esr and end values of 8 2 and 4 7 respectively these data demonstrate similarities in the mantle source rocks and in the melting characteristics with european alkaline rocks and thus similarities in the european subcontinental mantle at different localities for the last 100 ma these data are in clear contrast with the value for the penninic suboceanic mantle geochemical constraints and piston cylinder experiments indicate a depth of origin of 80 kilometres at temperatures of at least 1250 c for the ehrwaldites potassium argon bulk rock data of petrographically different samples of the dykes from different localities yield consistent ages around 100 ma upper albian after emplacement the ehrwaldites underwent conditions of the zone of diagenesis with temperatures around 120 c which the late magmatic zeolites survived

are some of the deep crustal conductive features found in sw iberia caused by graphite abstract recent results obtained from two dimensional inversion of magnetotelluric mt data acquired in sw iberia reveal high conductive features at the middle lower levels of the crust the top of these anomalous structures correlates very well with the depth 10 13 km of an important seismic interface that has been interpreted as a regional detachment horizon very shallow and relatively narrow conductors in the ossa morena zone appear to correspond to small scale fluid deposited graphite systems in the preorogenic metasedimentary sequences some of the midcrustal conductors can be ascribed to graphite bearing thrust zones the formation of graphite with variable crystallinity being a consequence of variscan shearing processes deep seated conductors are tentatively interpreted as a result of relatively continuous highly crystalline grain boundary graphite films presumably preserved in basement granulite rocks assuming that graphite occurs as interconnected films calculations indicate that a fraction of 0 006 0 02 of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of mt models the role of graphite on the thermal behaviour of the crust is also discussed the results show that low contents of graphite do not significantly change the thermal behaviour of earth materials

an audio magnetotelluric investigation of the otjiwarongo and katima mulilo regions namibia abstractas an additional opportunistic component to the southern african magnetotelluric experiment natural source audio magnetotelluric amt data were acquired during phase iv to investigate the local scale electric conductivity subsurface structure in the otjiwarongo and katima mulilo regions namibia as an aid in locating the installation points for high voltage direct current earth electrodes the study showed that the shallow subsurface of areas containing one measurement site in the otjiwarongo region and three sites in the katima mulilo region have appropriate high conductivities for the optimal placement of the earth electrodes both of the amt surveys are situated close to the edge of the orogenic neo proterozoic damara mobile belt dmb previous studies all suggest the existence of a highly conductive midcrustal zone which correlates well with the spatial location of the dmb two dimensional inverse modeling of the otjiwarongo amt data confirms the existence of the high conductive zone at m

late to post variscan deformation phases and palaeostresses in the ktb pilot research well bohemian massif germany abstract brittle faults and veins are very widespread in the crystalline rocks of the northern oberpfalz particularly in the 4000 m deep kontinentale tiefbohrung ktb pilot well in the late variscan late carboniferous subvertical tension gashes were formed under ne sw extension a genetic relationship between the vein development and late phase magmatic activity of the late variscan granites is obvious subsequently but still during the late carboniferous graphite enriched reverse faults developed under e w and ne sw compression in the deeper part of the ktb pilot hole these faults were formed within the brittle ductile transition regime of the paragneisses since during the late variscan the geothermal gradient was remarkably elevated the brittle ductile regime was situated at a relatively high crustal level where cataclasis crystal plasticity and diffusion controlled deformation mechanisms were active simultaneously in post variscan time probably during the cretaceous a further generation of reverse faults developed in addition to subhorizontal tension gashes and minor strike slip faults during these events the temperature was much lower compared with the conditions during the late variscan deformations the reverse faults evolved primarily under n s compression which is probably related to the cretaceous subduction and collision events of the alpine orogeny further to the south the youngest normal faults are probably connected to the subsidence of the nearby eger graben which evolved during the neogene uplift of the investigated area the stress data derived by using faults and striations from surface outcrops and from several oriented core intervals from the ktb pilot well display weak depth dependent variations although the deformation was polyphase the inversion method has proved to be a suitable mode for determining reliable palaeostress data however if the brittle ductile transition regime or broad shear zones are reached the data become more and more invalid

late glacial to holocene transition in northern spain deduced from land snail shelly accumulations abstract shells of the helicid cepaea nemoralis were studied using taphonomic isotopic and morphometric measurements to estimate late glacial holocene 12 1 6 3 cal ka bp environmental conditions in northern spain higher taphonomic alteration among holocene shells suggests lower sedimentation rates or higher shell destruction rates than during glacial conditions shells preserved the aragonitic composition despite differing degree of skeleton damage shell 13 c values were 10 3 1 1 8 2 2 3 and 7 3 1 6 for modern holocene and late glacial individuals respectively higher 13 c values during the late glacial and some holocene periods imply higher water stress of c 3 plants and or higher limestone contribution than today intrashell 13 c values were higher during juvenile stages suggesting higher limestone ingestion to promote shell growth shell 18 o values were 1 1 0 7 0 9 0 8 and 0 1 0 7 for modern holocene and late glacial specimens respectively a snail flux balance model suggests that during 12 1 10 9 cal ka bp conditions were drier and became wetter at 8 4 6 3 cal ka bp and today intrashell 18 o profiles reveal that glacial individuals experienced more extreme seasonality than interglacial shells despite possible larger hibernation periods shell size correlated positively with 18 o values suggesting that growth rates and ultimate adult size of c nemoralis may respond to climate fluctuation in northern spain

trapping of aqueous fluids in the deep crust free aqueous fluids in the deep ductile crust have residence times there which are very short in geological terms if not consumed by retrograde metamorphic reactions they empty very rapidly upwards this can be shown by applying the theory of magma percolation in a ductile host to the problem of aqueous fluid percolation below the brittle ductile transition thermal activation of ductility is strong enough to facilitate the rapid evolution of porosity and consequently allow rapid fluid transport in the cooler crust above the brittle ductile transition however this mechanism vanishes as a consequence fluid overpressures resulting from the accumulation of fluid in the transition zone must induce hydraulic fracturing rather than pore inflation in regions of horizontally compressive regional stress the commonest situation in stable continental crust these fractures will be horizontal aqueous fluids rising through or liberated from the lower crust will therefore probably accumulate at least initially at the brittle ductile transition in horizontally extensive reservoirs with high horizontal permeability but low vertical permeability

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells

robust smooth magnetotelluric transfer functions jimmy c larsen randall l mackie 2 adele man e l l a adolfo fiordelisi4 and shirley rieven2 pacific marine environmental laboratory national oceanic and atmospheric administration 7600 sand point way ne seattle wa 981 15 0070 usa wassachusetts institute of technology 42 carleton street cambridge m a 02142 usa cnr international institute for geothermal research piazza soljerino 2 pisa 56126 italy enel esplorazione mineraria via andrea pisano 120 pisa 56122 italy

magnetotelluric measurements across the sorgenfrei tornquist zone in southern sweden and denmark the results of a magnetotelluric experiment across the sorgenfrei tornquist zone stz in the southwestern part of the baltic shield are presented the stz marks the border between the proterozoic

optimization of signal to noise ratio in dc soundings geoelectric dc sounding methods are usually limited to electrode spacings smaller than 1 km which restrict the depth of investigation to only several hundreds of meters greater depths of investigation require both a larger electrode spacing and motor generator driven transmitters in order to increase the depth of investigation into the middle crust the distance between transmitter and receiver dipole must be increased up to 100 km as well instead of a schlumberger electrode configuration we use a dipole dipole electrode arrangement which avoids cable connections of several tens of kilometers it takes less logistics in the field and requires less precautions to control the cable circuits however the electric field of a grounded dipole decays by the power of 3 even if a strong current source with a power of 30 kw is employed at distances beyond 10 km the amplitude of the transmitted dc signal becomes considerably smaller than the naturally inductive field and cultural noise here we present a technique which resolves the transmitted dc signal at sites up to 60 km apart using an electric dipole source the suggested technique removes the inductive part in the time series and therefore reduces the noise level it requires applying the magnetotelluric technique before and or after the geoelectrical sounding both the magnetic and electric variational fields are recorded during geoelectrical sounding if the magnetotelluric transfer function is obtained at a site then the natural inductive electric field can be predicted which in turn is used to remove the inductive electrical part from the receiver dipole record

revealing the electrical properties of a gneiss dome using three dimensional magnetotellurics burial and exhumation cycles associated with faulting in central anatolia turkey abstract the nigde massif is a small scale exhumed lithospheric entity in central anatolia formed as a result of metamorphism driven by crustal thickening and migmatization its thermal and structural history records two burial and unroofing episodes induced by oblique tectonics related to an adjacent wrench zone of the ecemis fault to show the complex tectonic history of the events of this area its electrical resistivity structure was determined using three dimensional magnetotellurics forty seven high quality soundings within a frequency range of 320 hz 5000 s were utilized for this purpose the dimensionality of the data was investigated via phase tensor analyses and induction vectors a hydrothermal system that might be related to mt hasan was delineated as a widespread conductive zone in addition interpretation of the electrical resistivity models found a rheology seismicity relationship in the study area the nigde massif was depicted as a highly resistive dome like anomaly bounded by low angle detachment faults as indicated by the resistivity contrast between the massif and the adjacent features the lower boundary of the massif is defined by a resistive to conductive transition situated at 25 30 km depth beneath this transition a widespread low resistivity zone was interpreted as a partially melting lower crust this crustal feature is connected to a shallower anomaly beneath the ecemis fault zone which may infer the ascension of fluids that may be contributing to earthquake generation seismicity along the ecemis fault is overtly heterogeneous in that it tends to form a step approaching south along the fault where the lower crustal conductor is absent relevance between the seismicity and resistivity pattern denotes the presence of a fault configuration that is necessary for the yo yo tectonics

a magnetotelluric study of the damara belt in namibia 1 regional scale conductivity anomalies abstract the namibian margin is dominated by the late proterozoic to early cambrian fold belts of the damara orogen which wrap around and separate the congo and kalahari cratons this mosaic of relatively soft fold belts and hard cratons apparently controlled the path for the opening of the south atlantic in the early cretaceous the continents split along the coast parallel fold belts of the damara orogen while the inland fold belt damara belt was effected by extension and widespread igneous intrusion but never developed to the rift stage this paper is concerned with the interpretation of magnetotelluric mt data along a 200 km nw se profile across the damara belt in nw namibia the regional two dimensional electrical resistivity model and the induction vector data exhibit three distinctive zones i a generally very resistive upper crust which is typical for the granites and metasediments of the damara belt ii two subvertical conductors in upper to mid crustal levels which correlate with major tectonic zone boundaries and iii a highly conductive middle to lower crust in the southern part of the profile the geometry of the conductive structures could reflect a regional shear system in which upper crustal listric faults pass into a detachment zone in the middle crust we interpret the high electrical conductivity in terms of graphite or other forms of mineralization enrichment along the shear planes this zone of crustal weakness may have originated in pre damara times and had probably experienced several episodes of crustal reactivation before the intrusion of basaltic dike swarms during the cretaceous rifting and magmatism associated with the opening of the south atlantic

evidence from borehole samples for the role of accessory minerals in lower crustal conductivity the high electrical conductivity of the lower continental crust as inferred from geophysical measurements1 has defied a simple explanation both pore saturating brines2 and interconnected carbon films3 5 have been proposed as conducting pathways but their relative importance remains uncertain and may vary from place to place6 so far attempts to address this question in the laboratory have had to rely on samples of metamorphic rock collected from surface exposures7 10 although these rocks almost certainly originated in the lower crust chemical alteration during their transport to and residence at the surface is likely to have affected their conducting properties here we report conductivity data for pristine crustal rocks recovered from depths of up to 4 6 km in the ktb boreholes in southern germany our results show that the electrical conductivity of accessory phases such as fe ti oxides and sulphides can enhance or even surpass the high conductivity produced by saline fluids

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

transition from convergence to escape field evidence from the west carpathians abstract the tertiary deformation of the west carpathians occurred during northeast directed convergence of the european and apulian plates and was complicated by space constraints imposed by orogen advance palaeostress fields computed from fault slip data and structural interpretation of known gravimetric magnetic seismic palaeomagnetic lithostratigraphic sedimentological fission track and borehole data indicate that during deformation the orogen consisted of both frontal thrust stacking zones and internal extensional trans tensional zones synthesis of available data indicates that the episodes of tectonism in litho tectonic units were both time and plate position related and were caused by conditions which varied in different areas ranging from the foreland to back arc region in each time period discrete deformation phases record the transition from convergent to tectonic escape tectonisrn principal horizontal stress trajectories were approximately co linear with the plate convergence vectors prior to escape the onset of escape conditions is indicated by 1 clockwise rotation of palaeostress orientations during the time of known escape in the eastern alps and 2 the cessation of thrusting of the flysch belt nappes onto the neogene foredeep in the westernmost part of the west carpathians tectonic escape along strike slip faults subparallel to the collision suture zone began in early badenian time in the west carpathians various regions along the orogenic belt were affected by escape that became progressively younger towards the east this agrees with the observations of various authors that the final phase of thrusting towards the european platform became younger to the east along the west carpathian arc in addition palaeostress trajectory patterns for various periods are similar to those modelled by a rigid block indenting a viscous half space an attempt is made to complete the mosaic of information on the cenozoic evolution of the alpine carpathian pannonian area which in the models given by ratschbacher royden horvath bergerat and others is based on extrapolated data the object is to detail the timing and complexity of the local time and plate position related mechanisms in the context of the entire orogen in order to update previous rather simplified models

the impact of dansgaard oeschger cycles on the loessic environment and malacofauna of nussloch germany during the upper weichselian abstract a loess sequence has been sampled continuously at high resolution in nussloch rhine valley germany for malacological and grain size analyses between ca 34 and 20 ka molluscan abundance and richness percentage in hygrophilous species and grain size index show cyclical variations related to the lithological loess gley alternation major molluscan abundance maxima were triggered by temperature increases through an enhancement of the reproduction cycle whereas cyclical richness fluctuations and percentage in hygrophilous species reflect variations in local humidity and changes in the environmental mosaic malacological parameters allow the distinction of four environmental phases organised in cyclical successions correlated with most of the loess gley doublets the correlation of the grain size index of the nussloch loess sequence with the dust content of the grip ice core demonstrates the synchronicity of major molluscan abundance maxima and 18 o increases characterising temperature increases during dansgaard oeschger interstades a schematic model is proposed to link the north atlantic dansgaard oeschger climatic oscillations with local environmental changes indicated by both malacofauna and pedostratigraphy this malacological study of the nussloch loess sequence thus provides new information about the response of terrestrial loessic palaeoenvironments to millennial timescale climatic fluctuations during the upper weichselian marine isotope stage 2 mis 2 and end of mis 3

building and exhumation of the western carpathians new constraints from sequentially restored balanced cross sections integrated with low temperature thermochronometry western carpathian orogeny has been the subject of intense scientific debate due to the occurrence of enigmatic features leading several authors to provide contrasting geological models in this paper a new interpretation for the tectonic evolution of the western carpathians is provided based on i an analysis of the stratigraphy of the mesozoic tertiary successions across the thrust belt domains ii a reappraisal of the stratigraphy and sedimentology of the tectonic melange i e the so called pieniny klippen belt marking the suture between the inner and outer carpathians and iii the construction of a series of balanced and restored cross sections validated by 2d forward modeling our analysis provides a robust correlation of the stratigraphy from the outer to the inner carpathians independently of the occurrence of oceanic lithosphere in the area and allows for the reinterpretation of the tectonic relationships among the inner carpathians the outer carpathians and the pieniny klippen belt and the exhumation mechanisms affecting this orogenic belt in order to constrain the evolution during the last 20 ma our model also integrates previously published and new apatite fission track and apatite u th sm he data these latter indicate a middle late miocene exhumation of the pieniny klippen belt in this study the recent regional uplift of the pieniny klippen belt is described for the first time using a 2d kinematic model for the tectonic evolution of the western carpathians

a 400 km long piggyback basin upper aptian lower cenomanian in the eastern alps piggyback basins ori and friend 1984 comprise sedimentary basins that formed on active thrust sheets based on basin geometry and depositional systems two end member types of piggyback or thrust top basins have been distinguished type 1 basins are deep water basins that occur mainly as elongated synsedimentary deforming troughs in the footwall of thrusts in the early stages of orogenic wedge development and under lled foreland basins e g ori and friend 1984 lash 1990 type 2 piggyback basins are terrestrial to shallow marine intramontane basins that are formed predominantly during late orogenic stages e g ori and friend 1984 nijman 1998 this paper describes the geometry and evolution of an early deepmarine piggyback trough that formed on the cretaceous orogenic wedge of the eastern alps and the western carpathians the narrow basin extended over a considerable horizontal distance as suggested by similarities in stratigraphy and the timing of deformation the basin characterized a signi cant stage in the cretaceous evolution of the austroalpine northern boundary

palaeomagnetic results from the fold and thrust belt of the western carpathians an overview the western carpathians are separated into an outer and inner carpathians both comprising several nappe systems by the extremely narrow and highly deformed pieniny klippen belt the main phase of deformation and thrusting took place during the late cretaceous in the inner carpathians at the end of cretaceous paleocene in the pieniny klippen belt and in the miocene in the outer carpathians in this paper a large amount of palaeomagnetic results of different quality available from several nappe stacks and from overstep sequences were reviewed and interpreted in terms of tectonics the data suggest that all three main units participated in two phases of anticlockwise rotation starting at 18 5 ma that is the outer carpathian nappes in front of the already consolidated alpine carpathian pannonian block became accreted to the block late cretaceous nappe transport neogene uplift of core mountains and possibly oroclinal bending of pre oligocene age can account for important differences in pre cenozoic palaeomagnetic declinations most of them exhibit less or no anticlockwise rotation suggested by the overstep sequences implying pre cenozoic clockwise rotations of variable angles

comparison of geoelectrical tectonic models for suture zones in the western u s a and eastern europe are black shales a possible source of high conductivities abstract large scale geoelectrical anomalies have been mapped with geomagnetic depth sounding gds and magnetotelluric mt surveys in the carpathian mountains region these anomalies are associated with the zone of closure between stable europe and a complex of microplates in front of the converging african plate the zone of closure or suture zone is largely occupied by an extensive deformed flysch belt the models derived to fit the observed geoelectrical data are useful in the study of other suture zones and carpathian structures have been compared with areas currently being studied in the western cordillera of the u s a models derived for a smaller scale suture zone mapped in western washington state have features that are similar to the carpathian models the geoelectrical models for both the carpathian and washington anomalies require dipping conductive slabs of 1 5 m material that extends to depths 20 km in both instances there is evidence that these materials may merge with lower crustal mantle conductors along the down dip margins of the slab the main conductive units are interpreted to be sedimentary rocks that have been partially subducted due to collisional processes heat flow is low in both regions and it is difficult to explain fully the deep conduction mechanisms however evidence suggests that the conduction at depth may include electronic conduction in sulfide mineral or carbon films as well as ionic conduction in fluids or partial melt

why is the electrical resistivity around the ktb hole so low the low resistivity anomaly close to the ktb borehole coincides with both a self potential and a static magnetic anomaly if this coincidence is not accidental it may yield information about the conditions required for the existence of low resistivity anomalies in the deeper crust a possible answer to the question in the title of this paper is that the oxygen fugacity in the crust around the ktb hole must be low enough to stabilize graphite on a grain boundary scale this could partially explain the extremely low resistivities of the graphitized cataclastic zones the formation of magnetic pyrrhotite from 250 to 4000 m deep and the large self potential anomaly the latter requires a large vertical gradient of the oxygen fugacity and a continuous graphitic conductor through this gradient zone

seismic reflectors conductivity water and stress in the continental crust the uppermost 10 15 km of the earth s continental crust differs in several geophysical properties from the lower crust the upper crust is electrically resistive seismically transparent contains nearly all intracontinental earthquake hypocentres and responds to stress elastically with brittle fracture the lower crust is electrically conductive contains many seismic reflectors is aseismic and shows ductile response to stress i show here that the characteristics of both regions can be explained if the entire crust contains saline water in separated cavities in the compressively stressed rocks of the upper crust but in the lower crust forming an interconnected film on the crystal surfaces the model may apply principally to technically active parts of the continental crust beneath shields the lower crust may be dry

the western carpathians interaction of hercynian and alpine processes abstract the complicated structural and rheologic properties of western carpathian lithosphere reflect the complex geodynamic history of the carpathian orogen based on critical analysis of earlier models new interpolation of existing geophysical data and results of integrated modelling a new map of the lithosphere thickness for the carpathian pannonian region has been constructed the map allows for the distinction of a frontal orogen collision zone in the ne from increased lithosphere thickness as well as a zone of oblique collision with the bohemian massif in the west where lithosphere is not significantly thickened the moho discontinuity beneath the western carpathian hinterland danube and east slovak basins as defined by deep reflection seismic profiling is relatively shallow this probably reflects recent crustal extension related to oblique collision between the european plate and the alcapa block and an increase of the asthenospheric updoming from the middle miocene onward crustal thickness reflects the combined effects of deep seated orogenic processes and mantle thermal evolution beneath the pannonian basin system in this study we focus particularly the structures of 1 the late alpine collision and neogene back arc basin development including deep seated contacts between colliding plates a zone of slab detachment the compressional accretionary wedge of the outer western carpathian flysch belt and extensional structures produced by subduction rollback and asthenosphere upwelling 2 early alpine structures related to cretaceous thrust stacking including subhorizontal reflection packages interpreted as multi generational extensional structures the underplated intra penninic oravic continental ribbon and ophiolite traces of the meliatic oceanic suture and 3 north dipping reflectors interpreted as remnant hercynian lithotectonic fragments with opposed vergency to the subducted alpine units

magnetotelluric and geomagnetic modelling reveals zones of very high electrical conductivity in the upper crust of central java abstract we present results of two and three dimensional modelling of magnetotelluric and geomagnetic data from central java indonesia we adopt a hypothesis testing approach where we examine the influence of individual structural elements of competing models on the total model responses the models show that ocean anomalies do not overwhelm the signal due to strong electrical conductivity anomalies within java these highly conducting regions with resistivities of below 1 m are located in the central and northern parts of the island fitting of the geomagnetic data requires that the innermost parts of both regions consist of material with extremely low resistivity 0 2 m young sediments tephra and their alteration products can be responsible for some of the low resistivity regions at shallow depths the two zones of extremely high conductivity however are best explained as consequences of geothermal activity in the vicinity of active volcanism mt merapi in central java and by fluid or graphite enrichment along shear zones in northern java subduction zone related processes in a depth range of 70 400 km cannot be resolved because the highly conductive regions at shallow depths effectively screen deeper structures

the evolution of the meliata hallstatt ocean and its significance for the early evolution of the eastern alps and western carpathians abstract the evolution of the meliata hallstatt ocean and of its southern and northern margin in the inner western carpathians are described the main rifting began during the pelsonian and the sea floor spreading ended at the beginning of the middle carnian contemporaneously with the raibl event the subduction began in the latest triassic and the final closing of the ocean accompanied by uplift of the adjacent marginal areas was dated as basal oxfordian remnants of the oceanic suboceanic sequence occur in two tectonic positions 1 obducted nappes that contain mostly as tectonic melanges the whole middle triassic to middle jurassic sequence including large bodies of dismembered ophiolites of ladinian to early carnian age 2 evaporite melanges at the base of nappes that are derived from the northern margin of the ocean these evaporite melanges consist of late permian evaporitic matrix and blocks of a dismembered ladinian to lower carnian ophiolitic sequence in the inner western carpathians both the northern and southern marginal sequences of the meliata hallstatt ocean and the transitions into the carbonate platforms are present in different nappes the southern marginal development is characterized by middle carnian distal clastic raibl beds and by middle jurassic rhyolithic volcanism both missing in the northern marginal development because the subduction related middle jurassic volcanism contemporaneous with the turbidites in the southern meliaticum is restricted to the marginal area south of the meliata hallstatt ocean southward directed subduction is indicated to the south on the adjacent carbonate platform a jurassic basin with aalenian to bajocian ophiolites opened this may be a back arc basin in the eastern alps only the northern marginal zone and the adjacent carbonate platform are preserved but parts of the dismembered ophiolites in the haselgebirge may be of ladinian to late carnian age like in evaporitic melanges in the same tectonic position in the inner western carpathians the final closing of the meliata hallstatt ocean is indicated by the abrupt end of the turbiditic sedimentntation in the oceanic suboceanic domain and by uplift in the marginal areas where lower oxfordian radiolarites are overlain by shallow water upper oxfordian to tithonian or neocomian limestones silica nappe hallstatt nappes with the evidence of the final closing of the meliata hallstatt ocean near the middle late jurassic boundary the cimmerian orogenesis in the genetic sense of engor 1984 1985 is now also proven in the inner western carpathians and in the eastern alps a continuation of the meliata hallstatt ocean into the pontide paleotethys cimmerian ocean sensu kozur 1990 through the transylbanian oceanic domain and the strandzha unit is assumed a connecction with the vardar ocean is impossible because in the vardar zone no triassic ophiolites or basic volcanics are present and the ophiolites have jurassic age

the north american central plains conductivity anomaly and its correlation with gravity magnetic seismic and heat flow data in saskatchewan canada abstract the north american central plains conductivity anomaly nacp lies virtually in its entirety within the trans hudson orogen accordingly should these two features prove to be contemporaneous then the geometrical relationship between these two is of foremost importance to any evolutionary tectonic model proposed to explain the collision of the superior and churchill provinces in the hudsonian and a model that does not include a mechanism for the generation of this anomaly is obviously untenable in order to map better the trend of the nacp in the province of saskatchewan canada two magnetotelluric mt profiles were conducted over the nacp previously defined by magnetometer arrays and profiles data from these two profiles along with an earlier mt profile just north of the u s canadian border suggest that the nacp is not a continuous feature but rather that it exhibits a definite break at latitude 51 n other geophysical evidence examined herein is concordant with this characteristic if a second mt anomaly mapped to the northwest of this break is in fact a manifestation of the same geological structure then one possible interpretation is of a major nw se trending sinistral fault in the deep crust previously undetected with a movement of some 100 150 km along strike the mt data from the southernmost profile after correction for static shift are modelled in a 2d manner and it is shown that the nacp is consistent with an arcuate structure in vertical section of high conductivity 2 s m 1 beginning at a depth of 10 km centred on 103 w dipping down to the west reaching possibly the base of the crust it is also shown that such an arcuate shape in section can explain an observed gravity high of 40 mgal such high conductivities cannot be explained in terms of connected fluids as it would require implausibly high porosities 12 20 a comprehensive interpretation of all the geophysical data would have to account for the observed characteristics of the anomalous region which are high electrical conductivity positive density contrast no magnetization and high heat flow in the basement in terms of a single causative body one possible explanation is presented in terms of a zone of lithospheric weakness along which was emplaced low density differentia from a mantle derived body an alternative explanation could be the phase transformation of obducted material into eclogite or serpentinite however difficulties exist with both of these explanations and further data are required

the stratification and taphonomy of shells in calcareous soils implications for land snail analysis in archaeology abstract the ecological interpretation of land snails from buried soils has depended on the assumption that assemblages are age stratified and not seriously distorted by differential destruction the temporal and ecological resolutions of assemblages are determined by taphonomic processes controlling the incorporation mixing and subsequent destruction of shells in the soil this paper describes those soil processes affecting snail assemblages in britain and attempts to quantify their effects it is concluded that except in certain restricted circumstances the temporal and ecological resolutions of land snail assemblages in buried soils are poor

the case for metamorphic base metal mineralization pyrite chemical cu and s isotope data from the cu zn deposit at kupferberg in bavaria germany the stratiform cu zn sulfide deposit at kupferberg in germany represents bavaria s largest historic base metal producer the deposit is hosted by early paleozoic volcano sedimentary strata at the margin of a high grade allochthonous metamorphic complex the present paper reports on the first cu and s isotope data as well as trace element analyses of pyrite from this unusual deposit the new data point to syn orogenic mineralization that was driven by metamorphic fluids during nappe emplacement primary cu ore occurs as texturally late chalcopyrite within stratiform laminated pyrite in black shale in two different tectonostratigraphic units of very low and low metamorphic grade respectively that were juxtaposed during the variscan orogeny trace element contents of different pyrite types suggest the presence of at least one hydrothermal pyrite generation mean co ni 35 with the other pyrite types being syn sedimentary early diagenetic mean co ni 3 7 copper isotope analyses yielded a narrow 65cu range of 0 26 to 0 36 for all ore types suggesting a hypogene origin for the principal chalcopyrite mineralization the ore lenses in the two different tectonostratigraphic units differ with regard to their 34s values but little difference exists between poorly and strongly mineralized domains within a given locality a genetic model is proposed in which syn sedimentary early diagenetic pyrite with subordinate chalcopyrite and sphalerite formed in black shale beds in the two different stratigraphic units followed by late tectonic strata internal hydrothermal mobilization of fe cu and zn during syn orogenic thrusting which concentrated especially cu to ore grade in agreement with this model cu distribution in stream sediments in this region shows distinct enrichments bound to the margin of the allochthonous complex thus kupferberg can be considered a rare example of a syn orogenic cu deposit with the cu probably being derived from syn sedimentary early diagenetic pyrite contained in early paleozoic shale units

immobility of reduced carbon along grain boundaries in dunite carbon 14 radiotracer experiments at 10 kbar 1 gpa and 1000 1200 c reveal that due to low diffusivity or low solubility or both carbon is immobile in the grain boundary regions of natural dunite within the resolution of the beta track mapping technique grain boundary diffusion of carbon from a pure graphite source is not detectable in experiments of up to 10 days duration at 1200 c even though measurable volume diffusion profiles are generated at these conditions d 3 4 10 10 cm s in agreement with previous estimates the documented immobility of carbon in dunite grain boundaries precludes development of a continuous carbon film by diffusion from an initially localized source if such a film is the cause of the mantle high conductivity layer it probably originated by a process involving fluid co co2 infiltration and subsequent reduction

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

electrical resistivity tomography to investigate geological structures of the earth s upper crust it is important to have detailed knowledge of the electrical properties of the earth s crust in order to recognize geological structures and to understand tectonic processes in the area surrounding the german continental deep drilling project ktb we have used dc dipole dipole soundings to investigate the electrical conductivity distribution down to a depth of several kilometres we have adapted the electrical resistivity tomography ert technique a well established near surface method to large scale experiments independent transmitting and receiving units were used to realize the concept of simultaneous multichannel registration of the scalar electrical potential at 44 dipoles the measured data yielded apparent resistivities which were inverted to a 2d resistivity model ranging from the surface down to a depth of 4 km two highly conductive structures with steep inclination were detected they are expected to be major fault zones embedded in a metamorphic body the rather low resistivity 10 m can be explained by the existence of graphitic minerals and or electrolytic fluids

comparison of geoelectric and seismic reflection models of the zambezi valley basins northern zimbabwe the mana pools and lower zambezi karoo sedimentary basins lie within the zambezi mobile belt in northern zimbabwe the subsurface apparent resistivities measured at both locations are extremely low magnetotelluric mt data along a profile across part of the lower zambezi basin have been inverted using rapid relaxation inversion smith booker 1991 to find the minimum structure needed to fit the data and compare with an earlier forward model the resistivity models of both the mana pools and the lower zambezi basins are then compared with their structure revealed from seismic reflection data the resistivity structure of the mana pools basin is well modelled as a series of different resistivity layers whose boundaries are defined by the seismic data however the resistivity structure of the lower zambezi basin cannot be matched easily to the seismic structure additional structure with no seismic expression is required there is a conductive feature in the two basins in the upper karoo sandstone layer that extends below the seismic basement beneath the lower zambezi basin this indicates that the conductors may represent different types of features in the two basins consistent with their proposed different tectonic origins a resistive unit is present within the sediments in the lower zambezi basin that may represent intercalated basalt dykes giving an anisotropic mt response it has been suggested that there might be similar thin basalt layers within the sediments of the mana pools basin but these could not be resolved by mt methods the low resistivity of the basement particularly beneath the lower zambezi basin is remarkable and may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation the presence of the lower zambezi basin conductor at depths greater than the seismic basement is consistent with observations to the west in the adjacent damara mobile belt where similar conductors have been seen in regions with no sedimentary cover

lower cretaceous carbonate platform facies western carpathians abstract two principal belts with urgonian carbonate platform sedimentation evolved during the barremian early albian in the western carpathians the northern grew on an accretionary belt in the convergence zone between the external and internal units the limestones here contain rich ophiolite detritus the other belt formed on the tatric ridge in both belts carbonate platforms were subsequently destroyed only slope sediments clastic fan sediments and calciturbidites are preserved in the studied successions

electromagnetic imaging of variscan crustal structures in sw iberia the role of interconnected graphite abstract the western part of the iberian peninsula iberian massif is the best exposed fragment of the variscan orogen in europe its southern half was generated by an oblique collision between three continental terranes belonging to the margins of laurassia avalonia the south portuguese zone spz and gondwana the ossa morena zone omz and the central iberian zone ciz the boundaries between them are considered to be suture zones a 200 km long magnetotelluric profile across the three variscan terranes was done in a nne direction approximately perpendicular to the main tectonic features the results of two dimensional inversion of the mt dataset reveal high conductivity zones coinciding with the transitions spz omz and omz ciz these conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime a high conductivity layer extending along the whole omz was found at a depth of 15 25 km the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile the high conductivity was interpreted as caused by the precambrian serie negra graphite rich rocks carbon and oxygen x ray mapping with electron microprobe on polished sections of serie negra samples from omz revealed the presence of interconnected graphite which supports the hypothesis that graphite is determinant for the high conductivity two graphite types which help to record the geological evolution were identified graphite accumulations in the schistosity surfaces produced by folding and metamorphism and metallic films of graphite developed along late faults the conductive layer shows blobs of higher conductivity suggesting macro anisotropy additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity given that the detachment level is located within the serie negra several high resistivity features were found in the upper crust related to devonian and carboniferous successions and probably to some unexposed plutons in the spz and the palaeozoic series of omz plus some granitic intrusions in the ciz a high resistivity zone extending to the whole crust is correlated with extensive late variscan granite intrusions

compositional variability of pleistocene land snail assemblages preserved in a cinder cone volcano from tenerife canary islands abstract a pleistocene land snail rich scoria sequence was studied to determine if it was influenced by taphonomic bias climate change or both using a multifaceted approach that combines taphonomic ecological body size and stable isotope data shell assemblages were sampled from two layers units a and b in a cinder cone volcano of southern tenerife canary islands dated to the glacial interval mis 8 299 302 ka the two units differed in taphonomy species composition and abundance with the upper unit b showing higher diversity abundance and lower alteration than the lower unit a larger bodied species dominated unit a and were better preserved than smaller species these mismatches likely resulted from physical differences in the sediment matrix surrounding fossils with larger scoria grains of unit a enhancing destruction rates and thus favoring preservation of larger more durable taxa than smaller scoria grains of unit b comparisons with modern assemblages from the coastal scrub the plant biome in which the pleistocene site currently resides indicates that no modern analogue exists for these fossil assemblages within this biome shell oxygen isotope values reveal that the local climate was colder wetter during mis 8 than at present which also may explain variations in species composition through time these data suggest that both taphonomic and climatic factors appear to have induced temporal variations in taxonomic composition but it is difficult to determine which of these has more significantly influenced the observed results

terrestrial environments during mis 11 evidence from the palaeolithic site at west stow suffolk uk abstract multidisciplinary investigations of the sequence at beeches pit west stow suffolk uk have a direct bearing the age of the hoxnian interglacial and its correlation with the continental holsteinian and with the global marine record at this site glacial deposits till and outwash gravels referable to the anglian lowestoft formation fill a subglacial channel cut in chalk bedrock above these glacial deposits a series of interglacial sediments occurs consisting of limnic tufaceous and colluvial silts lacking pollen but rich in shells ostracods and vertebrates lower palaeolithic flint artefacts of acheulian character have also been recovered including refitting examples charred material is abundant at certain horizons and many of the bones have been burned several discrete areas of burnt sediment are interpreted as hearths the molluscan fauna comprises some 78 taxa and includes species of considerable zoogeographical and biostratigraphical importance the land snail assemblage from the tufa consists of woodland taxa with no modern analogue including species that are either extinct e g zonitoides sepultus or which no longer live in britain e g platyla polita p similis neniatlanta pauli this is also the type locality of retinella lyrodiscus skertchlyi which belongs to a subgenus of zonitid land snail now living only on the canary islands there are indications from this fauna the lyrodiscus biome that the climate was wetter and perhaps warmer than the present day the vertebrate fauna is also noteworthy with species of open habitats such as rabbit oryctolagus cf cuniculus and of closed forest such as squirrel sciurus sp and garden dormouse eliomys quercinus present at different times the occurrence of southern thermophiles such as aesculapian snake zamenis longissimus indicates temperatures warmer than those of eastern england today the upper levels include much material reworked from the interglacial sediments although there is clear faunal evidence for climatic deterioration both the molluscan and vertebrate faunas suggest correlation of the interglacial sediments with the hoxnian uranium series dates from the tufa 455 ka bp tl dates from burnt flints 414 30 ka bp and a range of amino acid racemization data all support correlation of this interglacial with mis 11 however four osl dates from sand beneath the interglacial sequence yield a mean age of 261 31 ka bp far younger than all other age determinations and far younger than implied by the biostratigraphy archaeologically the site is unusual in showing prolonged human occupation within closed deciduous forest and evidence for controlled use of fire in a lower palaeolithic context biostratigraphical correlations with other lower palaeolithic sites support the suggestion that acheulian and clactonian industries both occurred in southern britain during the same substage of the hoxnian although not necessarily at precisely the same time the characteristics of the mis 11 interglacial in britain are discussed in the light of evidence from beeches pit and elsewhere

discussion of olistostromes of the pieniny klippen belt northern carpathians d plasienka j michalik j sotak r aubrecht comment in their recent paper golonka et al 2015 described the cretaceous and palaeogene olistostromes and other types of mass transport deposits occurring within the pieniny klippen belt pkb of the western carpathians after a short introduction into the olistostrome concept and an overall description of the pkb structure the authors presented their views on the composition and evolution of the pkb with olistostromes as the leading phenomenon although novel in some aspects the model they present is largely oversimplified and partly erroneous in our opinion in the following we shall comment on the several most disputable statements and interpretations offered in the discussed paper

very high electrical conductivity beneath the munchberg gneiss area in southern germany implications for horizontal transport along shear planes summary new magnetotelluric data from the munchberg gneiss complex in southern germany reveal a zone of extremely high electrical conductivity 1 d modelling of the data is justified in the period range 0 01 to 10 s at least three layers are required to explain the steepness of the apparent resistivity curves and the best fitting models comprise four layers with successively higher conductivities the layers of highest conductivity at depths between 2 2 and 3 6 km correlate with pronounced bands of high seismic reflectivity profile dekorp 85 4n the munchberg complex is today widely recognized as a tectonic klippe consisting of rocks whose metamorphic and stratigraphic order is inverted rather than overturned the material was transported into its present position by predominantly horizontal tectonic forces along shear zones we interpret the high conductivity and high reflectivity as remnants of this transport process

a late glacial colluvial sequence at watcombe bottom ventnor isle of wight england in a dry valley near ventnor isle of wight thick subaerial slope deposits of devensian late glacial age overlie the chalk the deposits are crudely stratified chalk muds and rubble produced by frost shattering and moved downslope by the release of water from melting snow fields and frozen ground a laterally extensive humic horizon of a rendzina soil occurs within the sequence clearly reflecting a period of relative slope stability in places this horizon divides and its upper surface appears to have been disturbed possibly by cryoturbation micromorphological and other analyses confirm the pedogenic origin of this humic horizon but also demonstrate the occurrence of pedological features both above and below it the humic horizon therefore is not a buried soil in the strictest sense but is part of a vertical sequence representing a single complex soil with transported accretionary and welded components molluscan analyses reveal that the sequence can be divided into four local mollusc zones showing a progressive increase in faunal diversity throughout the profile this succession is broadly similar to other late glacial sequences described from south east england minute fragments of charcoal from the lower part of the humic horizon have yielded an ams date of 11690 120 vr bp demonstrating formation during the allerod phase of the late glacial interstadial this humic horizon is correlated provisionally with the pitstone soil even though existing dates from its type site in buckinghamshire are somewhat younger

palaeotectonic reconstruction of the central alpine mediterranean belt for the neogene abstract the structural patterns of the central alpine mediterranean belt ranging from the eastern balearic sea to the western aegean sea have been reconstructed for 10 and 20 ma b p they have been obtained in the frame of the africa europe convergence through a step by step rigid plastic reconstruction using available geological and palaeomagnetic data all domains outlined in the present situation are shown in the palaeotectonic reconstructions while the structural pattern at 10 ma b p is similar to that of the present except for the tyrrhenian region that at 20 ma b p differs from it in most areas the well known adriatic promontory of the african plate is recognizable in both pictures and at 20 ma its original boundaries are revealed as strongly deformed flysch belts the adriatic promontory was broken up in the early or middle miocene into two microplates of comparable sizes the norther one is the adriatic microplate s s which suffered counter clockwise rotation by 20 relative to africa around the alpine apenninic whirl centre the southern one is the apulian microplate first outlined in the present work including the south apenninic and the apulian s s south of the gargano peninsula platforms which suffered no rotations relative to africa but which moved towards the northeast of it the primary reason for the break up of the adriatic promontory was most probably the opening of the balearic ligurian sea since 10 ma the adriatic and apulian microplates were again integral with africa or perhaps they moved towards the west relative to africa pushed by the turkish microplate the orogeny in the area discussed is mostly linked with collisional processes on the boundaries of the adriatic apulian unit

new paleomagnetic results from the upper cretaceous red marls of the pieniny klippen belt western carpathians evidence for general ccw rotation and implications for the origin of the structural arc formation abstract the pieniny klippen belt pkb is a narrow arcuate structure separating the central and outer western carpathians formed during several cenozoic deformational stages the primary aim of this study was to obtain paleomagnetic constraints for the mechanism of formation of the arc we investigate albian santonian red pelagic marls from 14 localities distributed along a strike length of ca 400 km ams measurements reveal a pattern characteristic of weakly deformed sedimentary rocks and magnetic lineations do not correlate with the general strike of the pkb paleomagnetic analysis revealed well defined hematite based ancient magnetization components at 13 localities which are dated using fold and inclination tests a within locality fold test is negative for two localities exhibiting large ccw rotations of similar magnitude situated at the two ends of the pkb remanences of pre folding age were documented for 11 localities with an overall mean paleomagnetic direction of d 311 i 53 and 95 11 the indicated general ccw rotation most probably took place during the miocene together with western central and outer carpathians paleolatitudes for the pkb indicate a considerable separation from the southern margin of stable europe leaving space for coordinated rotation a paleomagnetic oroclinal test involving all localities with primary magnetizations was negative when localities with monoclinal steep dips are omitted due to possible declination bias the overall mean paleomagentic direction does not change significantly but correlation is observed between the general trend of the pkb and the paleomagnetic declinations thus we conclude that the present shape of the arc can be partly due to oroclinal bending this must have happened before oligocene since paleomagnetic declinations for neighboring paleogene basins in the central and outer western carpathians reveal a uniform ccw rotation of ca 50 magnitude irrespective of the position of the localities in relation to the carpathian arc

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

subducted continental margin imaged i n the carpathians of czechoslovakia deep seismic reflection data across the frontal part of the carpathian arc image subducted european continental crust beneath the thick accretionary wedge of the neogene west carpathian arc the upper continental crust of the lower plate is depressed with high curvature to a depth off about 25 km below the arc but the corresponding moho appears to be nearly horizontal flow within the lower crust may account for strain mismatch between the two parts of the subductiog continent although the subdued relief on the moho may partly have evolved after subduction ceased perhaps owing to a gabbro eclogite phase change in a mafic lower crust

inverse ductile thinning via lower crustal flow and fold induced doming in the west carpathian eo alpine collisional wedge 1 continental core complexes are generally interpreted to result from extensional doming due to gravity driven upflow of lower crust in contrast the vepor dome is characterized by the lack of inverted density profile and relatively cold metamorphic field gradient which precludes an activation of rayleigh taylor instability instead the crustal structure of the vepor unit is marked by dense and weak metapelitic lower crust and light and strong granitoid upper crust inherited from variscan nappe stacking it is shown that the cretaceous eo alpine tectonic evolution of the vepor dome is controlled by the dynamics of two neighboring mechanically strong continental blocks i e the overthrusting of the suprastructural gemer unit from the south and the underthrusting of the fatric basement from the north structural metamorphic and geochronological data from the vepor unit imply two main phases of the convergent process 1 lower cretaceous crustal thickening due to overthrusting and internal deformation of the gemer unit together with upper crustal folding in the vepor unit led to the progressive development of the orogenic front parallel pressure gradient the instantaneous response of the lower crustal and low viscosity metapelites led to an along strike lower crustal flow accompanied by prograde barrovian type metamorphism 2 as the south vergent underthrusting of the fatric basement propagated to greater depths during the upper cretaceous the convergent process switched from top driven to bottom driven and the exhumation of the lower crust occurred via polyharmonic folding overall doming of the vepor unit induced upper crustal detachment faulting and eastward unroofing of the dome

pre oceanic rifting in the alps abstract a review of mesozoic mainly earliest jurassic to mid jurassic rifting in the western and central alps normal faults with throws up to a few kilometers are moderately inclined and involve rotation of crustal blocks the amount of stretching and thinning of the crust by jurassic rifting is discussed the rifting 200 165 m y pre dates the opening of the alpine oceans by spreading and transform movements 165 110 m y

40ar 39ar dating of the inner carpathians variscan basement and alpine mylonitic overprinting abstract the 40ar 39ar dating method has been applied to mylonitic rocks from the carpathian mountains these are variscan metamorphic and magmatic rocks that were overprinted during the alpine orogeny the inner western carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike slip and normal faulting resulting in the formation of mylonitic rocks precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of alpine events such as the pre gosauian phase during the turonian 90 ma the 40ar 39ar method allows to define the age of the ancient variscan basement and the ages of the alpine overprinting in the high and low tatras mineral ages of around 340 350 ma are yielded by gneisses micaschists and amphibolites providing a younger limit for the variscan metamorphism the emplacement cooling of the variscan granites is defined between 305 and 335 ma these rocks are overprinted by several alpine tectonothermal events the major events are dated at 65 and 86 88 ma during which the mylonites were generated an older event around 140 ma earlier defined by the rb sr method is now confirmed by the 40ar 39ar method dating of phengites extracted from high pressure metamorphic triassic rocks from the kosice area yields new data for the age of this event at 155 ma