a continental drift flipbook abstract forty six miniature plate tectonic reconstructions are presented that can be assembled into a flipbook that illustrates the movement of the continents since the late precambrian 750 m yr ago six principal lines of evidence have been used to reconstruct the past positions of the continents 1 linear magnetic anomalies produced by sea floor spreading 2 paleomagnetism 3 hotspot tracks and large igneous provinces 4 the tectonic fabric of the ocean floor mapped by satellite altimetry 5 lithologic indicators of climate e g coals salt deposits tillites and 6 the geologic record of plate tectonic history i discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time

two dimensional magnetotelluric modelling of the kos island geothermal region greece abstract the magnetotelluric mt method in the period range 0 075 42 s was applied to determine the electrical structure

paleozoic plate dynamics current plate motions can be accounted for by a balance of active forces slab pull ridge push and for continental plates trench suction with drag beneath the plate as a resistive force if we assume that the same forces have acted through time we can reconstruct plate motions from the geometry of past plate boundaries paleozoic reconstructions are made with paleomagnetic tectonic climatic and biogeographic data as no ocean floor remains paleomap reconstructions are used to estimate past plate speeds and to test simple dynami cal models in order to determine which ranges of forces best accounts for the observations over the last 600 m y plate speeds averaged over 40 to 100 m y intervals show considerable variation gondwana s speed oscillates from 20 to 60 km m y over a long timescale 200 400 m y with considerable noise superposed over the paleozoic era motions for large continental regions average 28 krn m y force balance models based on present day observations suggest that continental regions without a large attached slab would move 30 mrn yr the opening and closing of the ocean between laurentia and gondwana 560 400 ma is used to test dynamical models and the parameter values assumed in the late precambrian laurentia rifted away from gondwana in the earliest cambrian it was near 40os by late cambrian and ordovician it had moved to the equator during the silurian and devonian laurentia reversed direction and later collided with gondwana at 40os in a model of the forces acting on the plates slab pull ridge push and trench suction are assumed to balance plate drag only certain ranges of ridge push and trench parameters can model both the opening and subsequent closing of the ocean the dynamic models with parameter values inferred from present rates bracket the rates required by the reconstructions

preliminary magnetotelluric studies along the hellenic volcanic arc implications for the collision between the african plate and the aegea microplate abstract from middle upper miocene time to the present the african plate has subducted under the so called aegea microplate a prominent feature of this continental collision is the past and present volcanic activity along the hellenic volcanic arc hva which is sited 200 km behind the frontal compressional region since 1986 several magnetotelluric mt surveys have been undertaken along the hva and particularly on the islands of milos kos and nisyros to determine their subsurface electrical structure the derived electrical models have indicated very low resistivities less than 30 m for the uppermost 10 km which have been related to known i e milos and nisyros or potential i e kos geothermal anomalies evaluation of the existing electrical models and subsequent 1d modelling of the broadband mt data has revealed some deeper greater than 10 km depth electrical features of the lithosphere below the hva study of the azimuths of the major axes of the rotated impedance ellipses and the parkinson induction arrows in the period range 10 2 10 4 s has led to their association with the subduction and extensional processes taking place in the aegean the mt results are in agreement with the observed gravity values magnetic anomalies and the results from geotectonic deep seismic refraction and seismological studies finally proposal for the future study of the deep electrical structure of the aegean is presented

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

lateritized tephric palaeosols from central patagonia argentina a southern high latitude archive of palaeogene global greenhouse conditions palaeosols of the koluel kaike formation a red colour banded pyroclastic succession from southern argentina constitute a proxy for eocene climate changes reticulated and vertically elongated ferric mottles along with iron and manganese nodules are the most significant climate indicators which originated by alternating cycles of waterlogging and drying conditions causing fe mn mobilization and fixation clay minerals vary from a kaolinite smectite suite in the lower and middle sections to a smectite kaolinite one in the upper part high concentrations of iron oxides hydroxides and kaolinite lack of exchangeable bases absence of carbonate cement presence of ironstone and redness of hue in most of the palaeosols suggest intense chemical weathering related to leaching and lateritization processes five pedotypes ordered in a stratigraphic sense were identified strongly developed red to orange chornk fragiaquult and kapenk plinthaquult pedotypes display argillic horizons abundant ferric nodules and slickensides they are dominant in the lower and middle sections and formed in seasonal humid and megathermic tropical conditions with a mean annual precipitation of 1200 to 1300 mm and a mean annual temperature of 15 c weakly developed less structured ornek vitrand and polnek placaquand pedotypes occur in the middle and upper sections and originated in sub humid and mesic megathermic conditions with a mean annual precipitation around 1000 mm and a mean annual temperature around 12 c the brownish soorsh argialboll pedotype exhibits a granular structure and is present at the uppermost part of the unit it developed in sub humid semi arid and mesic conditions with a mean annual precipitation of 600 to 700 mm and a mean annual temperature around 10 c this pedotype succession and clay mineral distribution indicates a decrease in chemical weathering and degree of soil development with time koluel kaike palaeosols from central patagonia are some of the first continental non palaeobiological data linked to the early palaeogene global warming in south america they show an especially close relationship with the early eocene climatic optimum and the following long term cooling and drying initiated by middle to late eocene time

permian oolitic carbonates from the baoshan block in western yunnan china and their paleoclimatic and paleogeographic significance marine carbonate ooids are environment sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions this paper describes permian ooids from the baoshan block in western yunnan china in order to offer a new means to refine the uncertain paleogeographic details of this gondwana derived block four major types of ooids micritic ooids compound ooids leached ooids and half moon ooids are documented from the hewanjie formation in the northern and the shazipo formation in the southern baoshan block these ooids are dated via biostratigraphic analysis to be wordian early wuchiapingian and signify an ameliorated shallow marine temperature for the guadalupian strata of the baoshan block results of this study coupled with literature data reveal diachronous debut of permian ooids among the gondwana derived blocks mostly sakmarian in central taurides of turkey central iran central pamir and karakorum block versus wordian capitanian in baoshan block peninsular thailand and south qiangtang in contrast asselian sakmarian strata of baoshan block as well as peninsular thailand and south qiangtang are characterized by glaciomarine diamictites these observations suggest that the baoshan block was probably situated at a considerably higher paleolatitude under distinct influence of gondwana glaciation during the asselian sakmarian than those blocks yielding sakmarian ooids moreover marine ooids are virtually absent nearby the equator within the permian tethys similar to the modern situation the baoshan block is accordingly interpreted to drift to warm water southern mid latitudes during the wordian capitanian and remain to the south of central iran karakorum block and south china which were equatorially located in the capitanian

geochemistry of campanian maastrichtian brachiopods from the rordal 1 core denmark differential responses to environmental change and diagenesis abstract past marine environmental conditions can be reconstructed from geochemical signatures of both benthic and planktic organisms and particularly brachiopods have been extensively used for this purpose however it is seldom possible to investigate the links between environmental conditions and shell geochemistry in monospecific records over extended periods of time here we present geochemical data from the 100 m thick brachiopod rich upper campanian upper maastrichtian chalk 73 8 68 6 ma of the rordal 1 drill core northern denmark two species that lived attached to small substrate argyrotheca bronnii roemer and gisilina jasmundi steinich and one secondarily free living species magas chitoniformis schlotheim have been studied for element concentrations as well as c and o isotope signatures each species has a unique chemical signature with m chitoniformis showing lowest mg and mn concentrations a bronnii the highest mn concentrations and g jasmundi the highest sr concentrations all three species display decreasing mg ca ratios throughout the studied interval and distinct mn enrichments in the campanian maastrichtian boundary cmb interval in the campanian part of the succession the three species are slightly enriched in 13 c median 13 c values of 0 0 to 0 5 and 18 o median 18 o values of 0 3 to 0 6 with respect to coeval chalk in the course of the maastrichtian the two attached species acquire progressively lighter isotopic compositions with a bronnii reaching 13 c and 18 o values 1 0 lower than coeval chalk the secondarily free living species m chitoniformis on the other hand becomes isotopically heavier and reaches 13 c and 18 o enrichments of 1 0 at the top of the core the observed differences between the species illustrate species specific signatures of biomineralisation diagenesis and response to environmental change this geochemical complexity illustrates that a comprehensive geochemistry based picture of the late cretaceous chalk sea can only be painted using detailed multi species and multi proxy datasets

constraining assembly time of some blocks on eastern margin of pangea using permo triassic non marine tetrapod records abstract the supercontinent pangea was mainly formed during the permian but when it reached maximum land is unsure because the configuration of the east asian blocks during the permo triassic is still highly debated fossil tetrapods provide one of the best calibrations to the time of connection between continents but the data of permo triassic tetrapods have rarely been applied in the previous reconstructions here we review the oldest records of non marine tetrapods on the east asia blocks and use them to discuss the timing of connection between continents during the permian and triassic the distribution of seymouriamorpha shows the kazakhstanian was connected to the baltica by land from the cisuralian the diverse dashankou fauna indicates that the alxa block amalgamated to pangea at least in the guadalupian older than 266 ma the questionable footprints and late permian dicynodont assemblage from the north china show the north china craton may have been connected to the main part of pangea from the guadalupian and became part of pangea at least by 256 ma the late permian laotian tetrapods support the hypothesis that the south china block already collided with the north china and the indochina blocks by the end of the permian and there was a land route for the migration of non marine tetrapods

making ends meet in gondwana retracing the transforms of the indian ocean and reconnecting continental shear zones interpretation of the detailed patterns of ocean floor transforms revealed by satellite altimetry enables the creation of the indian ocean to be described quantitatively as four consecutive plate tectonic regimes separated at 200 136 89 and 43 ma each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre existing plates regain their pre regime integrity progressive elimination of the indian ocean demonstrable as a smooth computer animation http www kartoweb itc nl gondwana leads to a refined re assembly of the continental fragments of central gondwana that is substantiated by new geological data a sequence of euler interval poles that describes the dispersal of the gondwana fragments time calibrated against available magnetic anomaly data is given the model requires a mid cretaceous position for india s southern tip about 1000 km south of madagascar prior to india s rapid northward migration

comment on a global review of the late mississippian carboniferous gigantoproductus brachiopoda faunas and their paleogeographical paleoecological and paleoclimatic implications by l qiao and s shen palaeogeography palaeoclimatology palaeoecology 420 2015 128 137 abstract some palaeontological data necessary to make global scale conclusions on fossils distribution may be difficult to access because of their publication in non english and or local scientific media the presence of several alternative plate tectonic reconstructions is another serious challenge for making such conclusions the article by qiao and shen 2015 discusses the global spatio temporal distribution of the mississippian brachiopod genus gigantoproductus according to literature sources missed by the authors its occurrence in central kazakhstan southern kazakhstan and north siberia challenges the idea of restriction of this genus to only the palaeotethys moreover it seems gigantoproductus migrated quickly within the middle visean from the moscow basin where it originated to north siberia the use of plate tectonic reconstructions different from that preferred by qiao and shen 2015 suggests that the position of kazakhstan and siberia in lower latitudes explains well the presence of gigantoproductus in these regions additionally the importance of the rhenohercynian ocean and its remnants for the global dispersal of this genus should be considered

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

subduction and accretionary tectonics of the east kunlun orogen western segment of the central china orogenic system abstract the kunlun orogen is generally divided into the east kunlun orogenic belt e kob and the west kunlun orogenic belt w kob by the altyn tagh fault the e kob forms part of the western segment of the central china orogenic system ccos and is considered to have formed by the collision between the qaidam block and qiangtang or bayanhar terrane as a consequence of the closure of the kunlun ocean branch of the paleo tethyan ocean based on a compilation recently published high quality data this contribution provides an overview of the composition nature and ages of the principal tectonic elements including ophiolitic melanges and related volcanic rocks intrusive plutons and sedimentary cover sequences in the e kob according to multiple lines of evidence from these tectonic elements we proposed herewith a paleozoic triassic subduction and accretionary tectonic model to interpret the spatiotemporal tectonic framework plate subduction polarity and tectonic processes from accretion to collision of the e kob three main ophiolitic melange zones are identified in the e kob from north to south they are the qimantagh xiangride ophiolitic melange zone qxm the aqikekulehu kunzhong ophiolitic melange zone akm and the muztagh buqingshan anemaqen ophiolitic melange zone mbam according to these ophiolitic melange zones the e kob is divided into four major tectonic units the north qimantagh belt the central kunlun belt the south kunlun belt and the bayanhar terrane based on several lines of evidence from geology geochemistry and geochronology the south kunlun belt is interpreted as a paleozoic to triassic fore arc and accretionary complex related to northward subduction of the kunlun ocean during the ordovician triassic time the akm mabm and the south kunlun belt constitute a wide accretionary complex along the kunlun suture zone that marks final closure of the major paleo tethyan ocean while the qxm represents the best expression of another suture that records final closure of the qimantagh back arc basin the central kunlun belt as a long lived island arc terrane from ordovician to triassic times rifted from the qaidam block due to the spreading of the qimantagh back arc basin during the period of ca 485 425 ma taken into all the geological geochemical and geochronological lines of evidence together a trench arc back arc basin tectonic system in the e kob was built up and evolved into a protracted and long lived northward subduction and accretion along the kunlun suture during paleozoic and triassic time

sedimentologic and stratigraphic constraints on the orientation of the late triassic northern indian passive continental margin abstract the orientation and distribution of the northern indian passive continental margin basin during different epochs constrained the geometric characteristics of the hyperextended northern indian edge greater india traditional paleogeographic reconstructions envisage the late triassic northern indian passive continental margin as e w trending whereas paleomagnetic data support an 55 counterclockwise rotation during northward drifting this case study of upper triassic units from the northern indian margin based on facies analysis sandstone petrography heavy mineral assemblages u pb detrital zircon geochronology and stratigraphic correlation from the zanskar range to southern tibet provides new constraints and suggests that the northern indian passive continental margin might have been n s trending in the late triassic given the dominance of quartz sandstones with zircon tourmaline and rutile indicating a provenance from continental blocks and the recycling of older quartz rich sandstones and detrital zircon age spectra characterized by a neoproterozoic detrital zircon u pb age peak 921 13 ma the upper triassic sandstones widespread along the tethyan himalayas may have been partly derived from the eastern ghats mobile belt in eastern india and the rayner orogen in eastern antarctica the upper triassic quartzite series comprises feldspatho quartzose to pure quartzose sandstones with intercalated bioclastic oosparites deposited in backshore foreshore and shoreface coastal environments without considering the subsequent counterclockwise rotation of india the consistent pattern of the upper triassic bidirectional e w paleocurrent observed throughout the himalaya suggests that the paleoshoreline was striking near n s approximately perpendicular to the regional orientation of the northern indian margin progressive eastward thickening of the sandstone layers and eastward younging of the quartzite series suggest diachronous sedimentation such stratal patterns and the strike of the late triassic paleoshoreline were attributed to the neo tethys transgression from the zanskar range to southern tibet

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

3 d structure of the lithosphere in the aegean region summary p wave traveltime residuals from about 300 local and 400 teleseismic earthquakes recorded by the athens seismological network were used to study the structure of the lithosphere in the aegean region teleseismic data included readings from local stations which do not routinely report to the isc the large values of the residuals up to f3 s and their variation with azimuth and epicentral distance indicate significant velocity heterogeneity in the upper mantle p wave traveltime residuals were inverted simultaneously for both local and teleseismic earthquakes tomographic results which are best resolved at lithospheric depths reveal a heterogeneous lithosphere down to a depth of 100km or so a high velocity anomaly is found dipping at an average of 45 to the ne away from the hellenic trench and supports the hypothesis of subduction due to a cooler descending slab of oceanic composition an area of low velocities is observed at depths less than 80 km in the aegean back arc corresponding well with observed high heat flow values in the area in contrast an area of relatively higher velocity anomalies is resolved in the lithosphere underlying the sea of crete the tectonic structure of the crust and upper mantle in the eastern mediterranean area results from the complex interaction of several different geodynamic processes not all of which can be described by simple plate tectonic models at present the eurasian and african plates are converging at a rate of about lcmyr in an approximately n s direction minster jordan 1978 with the latter descending

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

geoelectric investigation of the hellenic subduction zone using long period magnetotelluric data abstract the strongest evidence up to date for a subduction zone in the hellenic region is a clearly identified wadati benioff zone below the central aegean sea to a maximum depth of 180 km alternative seismic tomography models suggest that subduction process continues deeper than the wadati benioff zone to a maximum depth of at least 600 km so far the lack of deep electrical studies in the region impeded scientists from imposing other control factors than seismic to the proposed models for the hellenic subduction zone hsz a long period magnetotelluric lmt study was carried out in the southern part of the greek mainland to study the deep electrical characteristics of the hsz and examine whether prominent modelled features correlate with structures identified by the seismic methods the study comprised collection processing and modelling of magnetotelluric mt data in the period range 100 10000 s from ten sites located along a 250 km ne sw trending profile the dimensionality of the data was examined at a pre modelling stage and it was found that they do not exhibit three dimensional 3 d features the latter enabled to construct both one dimensional 1 d and two dimensional 2 d models the proposed geoelectric model for hsz was based on 2 d modelling since it had better maximum depth resolution of about 400 km and revealed structures not detected by 1 d modelling attempts the model structure which was related to the african and euro asian lithosphere is relatively resistive 800 m and has an average thickness of 150 170 km although the bottom of the lithosphere is adequately resolved the wadati benioff zone that delineates the top of the subducting lithospheric slab is not identified by any electrical feature the modelled structure associated with the subducting part of the african lithosphere penetrates a relatively conductive

the milos geothermal field modelling and interpretation of electromagnetic induction studies abstract the magnetotelluric mt technique in the period range 10 2 to 10 4 s has been applied to determine the electrical structure of the geothermal field of milos island greece data from 39 stations have been processed using standard tensorial techniques and the data have been found to be nearly one dimensional 1d up to 10 s several 1d modelling techniques have been applied to the processed data sets subsequent two dimensional 2d finite difference modelling has revealed some deeper electrical features the 1d and 2d electrical models are in agreement with the existing geothermal model on milos within the uppermost 200 m the resistivity can be

a model for iapetan rifting of laurentia based on neoproterozoic dikes and related rocks geologic evidence of the neoproterozoic rifting of laurentia during breakup of rodinia is recorded in basement massifs of the cratonic margin by dike swarms volcanic and plutonic rocks and rift related clastic sedimentary sequences the spatial and temporal distribution of these geologic features varies both within and between the massifs but preserves evidence concerning the timing and nature of rifting the most salient features include 1 a rift related magmatic event recorded in the french broad massif and the southern and central shenandoah massif that is distinctly older than that recorded in the northern shenandoah massif and northward 2 felsic volcanic centers at the north ends of both french broad and shenandoah massifs accompanied by dike swarms 3 differences in volume between massifs of cover sequence volcanic rocks and rift related clastic rocks and 4 wnw orientation of the grenville dike swarm in contrast to the predominately ne orientation of other neo proterozoic dikes previously proposed rifting mechanisms to explain these features include rift transform and plume triple junction systems the rift transform system best explains features 1 2 and 3 listed here and we propose that it represents the dominant rifting mechanism for most of the laurentian margin to explain feature 4 as well as magmatic ages and geochemical trends in the northern appalachians we propose that a plume triple junction system evolved into the rift transform system a ca 600 ma mantle plume centered east of the sutton mountains generated the radial dike swarm of the adirondack massif and the grenville dike swarm and a collocated triple junction generated the northern part of the rift transform system an eastern branch of this system produced the long range dike swarm in newfoundland and a subsequent western branch produced the ca 554 ma tibbit hill volcanics and the ca 550 ma rift related magmatism of newfoundland mwr206 20 page 1

magnetotelluric measurements on the methana peninsula greece modelling and interpretation abstract as a first deep geophysical survey thirteen magnetotelluric and magnetovariation soundings in the period range of 0 0085 6000 s have been carried out in the methana peninsula and trizina area greece which form the western part of the active hellenic volcanic arc data have been processed using robust techniques and further analysed using decomposition methods in order to find the regional azimuth by using the smooth inverse of smith and booker j geophys res 96 3905 3922 1991 the 2 d modelling has resolved a low resistivity area 100 m parkinson induction arrows also at the range 0 01 0 1 s point towards the centre of the peninsula the conductivity anomaly is interpreted as being connected with the volcanic history of methana as a cooler remnant of former magmatic activity the contrast with the much higher resistivities suggested at depths 5 km is discussed in terms of fluid mobility limitation of the mt method and extensional processes in the southern aegean

the effect of global warming and global cooling on the distribution of the latest permian climate zones abstract the end permian biotic crisis is commonly associated with rapid and severe climatic changes these climatic changes are commonly suggested to have originated from solid earth carbon degassing leading to global warming but aerosol and ash induced cooling induced by lava degassing has been suggested as well the application of an earth system model of intermediate complexity has enabled a visualisation of the major climatic shifts on the supercontinent pangaea caused by rapid temperature changes due to changed radiative properties from greenhouse gases the reconstructed reference climate was validated by latest permian climate indicative sediments to investigate the possible climatic shifts from a set of 22 reconstructions which varied with temperature a minimum global annual mean temperature of 18 2 c for the late permian climate prior to the climatic perturbation event was determined starting from this pre event setup global warming and global cooling scenarios were simulated the response of the end permian climate system to temperature increase and decrease show marked differences while global cooling is followed by major climatic changes in the high latitudes and replacement of boreal biomes by tundra and polar frost the changes during global warming are less pronounced with only locally increasing aridity compensated by humidisation in other regions the different behaviour of the climatic belts under warm and cold conditions is accompanied by different climate sensitivities caused by different strength of the snow cover albedo feedback thus changes in the energy balance of the latest permian surface troposphere system have a 30 higher perturbation potential during cold climate conditions than during warmhouse conditions therefore substantial global cooling resulting in coldhouse climate conditions and an annual global mean temperature below 18 c is more efficient in perturbing the earth palaeoclimate during the end permian warmhouse the results suggest that global cooling mechanisms as injection of sulphur aerosols and ash particles from the siberian traps large igneous province into the late permian palaeoatmosphere have a higher climate perturbation potential than a warming due to carbon greenhouse gases with a similar magnitude of radiative forcing

tectonic fabric map of the ocean basins from satellite altimetry data abstract satellite altimetry data provide a new source of information on the bathymetry of the ocean floor the tectonic fabric of the oceans i e the arrangement of fracture zones ridges volcanic plateaus and trenches is revealed by changes in the horizontal gravity gradient as recorded by satellite altimetry measurements seasat and geosat altimetry data have been analyzed and a global map of the horizontal gravity gradient has been produced that can be used to identify a variety of marine tectonic features the uniformity of the satellite coverage provides greater resolution and continuity than maps based solely on ship track data this map is also the first global map to incorporate the results of the geosat mission and as a result new tectonic features are revealed at high southerly latitudes this map permits the extension of many tectonic features well beyond what was previously known for instance various fracture zones such as the ascension tasman and udintsev fracture zones can be extended much closer to adjacent coninental margins the tectonic fabric map also reveals many features that have not been previously mapped these features include extinct ridges minor fracture zone lineations and seamounts in several areas especially across aseismic plateaus or along the margins of the continents the map displays broad gravity anomalies whose origin may be related to basement structures

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified

modeling the early paleozoic long term climatic trend the early paleozoic climate has been described as warm and equable however recent data based on conodont oxygen isotopic composition reveal a large long cooling trend through the ordovician followed by an abrupt cooling during the late ordovician glaciation this long term climate change is associated with a major radiation in the earth life history nonetheless the driving mechanisms for this cooling trend remain unknown carbon dioxide consumption by the weathering of fresh rocks from volcanic arcs has recently been suggested as a possible driver for this climate change however the impact of the plate motion context has not been explored yet although it might have a major impact on atmospheric co 2 levels simulations with a climate model coupled to a biogeochemical model geoclim show that the atmospheric co 2 decreased from more than 20 pal 5600 ppmv in the furongian down to approximately 10 pal 2800 ppmv in the llandovery before rising again in the early devonian we suggest that changes in geography and exposure of fresh volcanic rocks on continents are required to explain the large co 2 drawdown that led to the onset of cooler to glacial conditions from the middle ordovician to the llandovery the weathering of fresh volcanic rocks is itself responsible for 33 of the late ordovician atmospheric co 2 decrease the rest being related to the continent motion through the intertropical convergence zone itcz mean annual continental temperature falls by 3 c in the early ordovician reaching 13 5 c during the glacial interval and rises to 16 c in the early devonian

the earliest species of burlingia walcott 1908 trilobita from south china biostratigraphical and palaeogeographical significance burlingia balangensis sp nov from the lower cambrian of south china represents the earliest species of this genus and suggests that the genus may have originated in south china a revision of the genus shows that b primitiva and b obscura can be used in order to indentify the base of the cambrian stage 5 when other trilobites are absent because their last appearance datum lad coincides with the first appearance datum fad of oryctocephalus indicus available palaeogeographic and palaeoclimatic models suggest five major palaeocurrents during cambrian times which could control the migration patterns of the burlingia clade from south china to baltica