effects of topography on the curvature of fold and thrust belts during shortening of a 2 layer model of continental lithosphere abstract we have used analogue experiments to investigate the effects of surface topography on the curvature of fold and thrust belts under conditions of 1 initial relief but no erosion and 2 no initial relief but differential erosion sedimentation and transport in experiments where a 2 layer model lithosphere shortened and thickened in front of an advancing straight piston the geometry of the developing thrust wedge was very sensitive to variations in surface topography in models with an initially flat horizontal surface and in the absence of erosion and sedimentation thrusts were straight propagated forwards and nucleated at buckle folds far in front of an advancing piston around an initial topographic high plateau or cone thrusts tended to be arcuate forming salients towards the foreland initial plateaux and cones tended to behave rigidly while arcuate thrust slices formed around them to accommodate differential slip transfer zones developed on both sides of initial highs fault blocks rotated about vertical axes and thrusts moved in oblique slip within transfer zones in models with initially horizontal surfaces which were subject to differential erosion sedimentation and transport thrusts initially were straight but then progressively rotated around non eroded thickened and stronger areas these worked as indenters in front of which new thrusts nucleated at curved buckle folds these thrusts were also curved their apices being in front of the thickened non eroded areas in nature arcuate structural patterns are to be found around the altiplano of the central andes and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high elevations and that differential erosion at the scale of the entire andes may have contributed to oroclinal bending

the 9th generation international geomagnetic reference field summary the international association of geomagnetism and aeronomy has recently released the 9th generation international geomagnetic reference field the latest version of a standard mathematical description of the earth s main magnetic field used widely in studies of the earth s deep interior its crust and its ionosphere and magnetosphere the coefficients were recently finalized at the xxiii general assembly of the international union of geophysics and geodesy held at sapporo in japan in 2003 july the igrf is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world

variability of the 0 3 ma palaeomagnetic field observed from the boring volcanic field of the pacific northwest the boring volcanic field of the pacific northwest usa composed of more than 80 eruptive units ranging in age from 3200 to 60 ka offers a unique possibility to investigate the variability of the quaternary to late neogene palaeomagnetic field to complement previous work on palaeodirections we conducted 240 absolute palaeointensity api experiments with the joint use of the continuous wilson and stepwise thellier coe double heating protocol along with 620 relative palaeointensity rpi experiments based on the pseudo thellier approach we successfully determined absolute estimates for 12 independent eruptive units as well as relative estimates for 47 out of 132 investigated sites we compare these results with the existing database for the last 3 myr and obtain an estimate of the relative variability in palaeointensity on the order of 40 45 per cent as a proxy for palaeosecular variation api and rpi data suggest a possible asymmetry between normal and reverse polarities

a new towed marine vector magnetometer methods and results from a central pacific cruise summary this paper focuses on new instrumental and methodological aspects of the acquisition processing and interpretation of marine magnetic data between two overhauser sensors towed as a longitudinal gradiometer a new fluxgate vector magnetometer was employed a second independent vector magnetometer system operated simultaneously this equipment was used during research cruise so 180 of r v sonne in the central pacific at about 120 w just south of the equator the survey area on the pacific plate is the mirror image to the currently subducting cocos plate off central america the oceanic crust was formed around 23 ma at the east pacific rise when the farallon plate broke up into the cocos and nazca plates the magnetic seafloor anomalies in the survey area strike approximately north south almost parallel to the main field resulting in very low anomaly amplitudes which had hindered detailed anomaly identification so far a new processing scheme was applied to the data which identifies the weak anomalies in the total field and those in the vertical component that as a consequence of the source body geometry have about doubled amplitude the vertical component constrains 2 d modelling much better than the total field alone processed fluxgate total field data are practically identical to the overhauser reference and even provide a reliable gradient when combined with one overhauser although towed vector magnetometers typically provide no independent estimate of yaw we illustrate that a numerical yaw bandpass filtered magnetic heading can provide reasonable estimates of the horizontal field components these component data open additional analysis tools the strike direction of magnetic lineations can be estimated from single profiles by either magnetic boundary strike ellipses in the space domain or by coherences between vertical and horizontal components in the wavenumber domain auto power spectra of the total field provide an approximate depth to the anomaly source or if in obvious contradiction to the bathymetric depth allow the detection of distortions for example by external temporal geomagnetic variations

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

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

using motionally induced electric signals to indirectly measure ocean velocity instrumental and theoretical developments abstract the motion of conductive sea water through the earth s magnetic field generates electromagnetic em fields through a process called motional induction direct measurements of oceanic electric fields can be easily converted to water velocities by application of a first order theory this technique has been shown to obtain high quality velocities through instrumental advances and an accumulation of experience during the past decades em instruments have unique operational considerations and observe for instance vertically averaged horizontal velocity from stationary sensors or vertical profiles of horizontal velocity from expendable probes or autonomous profiling floats the first order theory describes the dominant electromagnetic response in which vertically averaged and vertically varying horizontal velocities are proportional to electric fields and electric currents respectively after discussions of the first order theory and deployment practices operational capabilities are shown through recently published projects that describe stream coordinate velocity structure of the antarctic circumpolar current quickly evolving overflow events in the denmark strait and time development of momentum input into the ocean from a hurricane a detailed analysis of the gulf stream at its separation point from the continental slope serves as a case study for interpreting em measurements including the incorporation of geophysical knowledge of the sediment in addition the first order approximation is tested by the many features at this location that contradict the approximation s underlying assumptions sharp horizontal velocity gradients steep topography and thick and inhomogeneous sediments numerical modeling of this location shows that the first order assumption is accurate to a few percent a few cm s 1 in almost all cases the errors in depth varying velocity are 1 are substantiated by the direct observations and can be corrected by iterative methods though errors in the depth uniform velocity are 1 1 or less in almost all regions of the ocean an error similar to the instrumental accuracy of em instruments

tectonic accretion versus erosion along the southern chile trench oblique subduction and margin segmentation 1 the southernmost tip of south america is an active continental margin where oblique convergence between plates transcurrent motion and tectonic rotation on land make the geodynamic setting more complex than that of the central andes a multichannel seismic data set has been used in conjunction with multibeam and altimetry data to clarify the regional architecture of the continental margin from 50 s to 57 s despite the thick sedimentary section in the trench and the slow plate convergence rate peculiar of typical accretionary margins seismic reflection profiles image widely varying frontal wedge morphologies different rates of accretion a high degree of structural diversity and different modes of continental building offscraping underplating tectonic erosion correlation between structural parameters depth of the decollement level width of the wedge accretionary rates moho depth suggests large scale structural control on margin geometry and structural diversity the transition from tectonic accretion to erosion and general structural variations do not show any gradual trend but rather they occur along oblique structural trends that produce a tectonic segmentation of the margin this is mainly related to tectonic processes on the overriding plate block rotations along strike slip faults while local disturbances on the incoming plate seamounts fracture zones and oceanic fabric relative orientation add further structural complexity altimetry data in conjunction with structural analysis suggest that large scale tectonic variations and structural development are related to trench parallel gravity anomaly variations and ultimately to basal friction on the plate interface strong negative gravity anomalies are associated with sedimentary basins wide wedges and accretionary domains while positive gravity anomalies mainly refer to transverse structural highs and narrow wedges

frontal accretion an internal clock for bivergent wedge deformation and surface uplift 1 we propose a conceptual model of frontal accretion within bivergent wedges which is based on two dimensional sandbox simulations and the analysis of particle displacement fields each frontal accretion cycle consists of a thrust initiation an underthrusting phase and a reactivation phase the location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable therefore the frontal accretion cycle can be considered as an internal clock for wedge scaled deformation and surface uplift we further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle we estimate cycle duration to range between 104 and 105 years which is thus similar to the time frame of climatic cycles the proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic paleoseismologic and geologic estimates of fault slip

evolution of the northeast german basin inferences from a 3d structural model and subsidence analysis abstract a 3d structural model of the northeast german basin was evaluated with special emphasis on its evolution as an intracontinental depression the study includes investigations on subsidence history and structural setting of the basin thickness evolution and calculated tectonic subsidence volumes of permian to quaternary sediments in the northeast german basin indicate that the subsidence history was related to five stages of basin evolution which differ in their subsidence mechanisms for the initial rift phase in the late carboniferous to early permian a dominant thermal event and subordinate horizontal stresses were indicated by thickness variation evolution and by structural evidence the main part of basin subsidence occurred in a nw se oriented basin in the subsequent phase of thermal relaxation with maximum subsidence from early permian rotliegend to middle triassic muschelkalk from middle triassic the thermal subsidence pattern was superposed by further tectonic events in the middle triassic regional extension led to a reconfiguration of the southern part of the basin where new nne ssw trending troughs rheinsberg and gifhorn troughs developed in the jurassic the northwestern part of the basin was uplifted while in the south the keuper subsiding areas continued to sink and nw se trending depressions related to salt margins became important differentiation continued into cretaceous times when regional compression caused uplift of the southeastern part of the basin and basin margins a final subsidence phase occurred in the cenozoic this was accompanied by intensive salt movement recent basin configuration reflects the superposition of structural elements resulting from different evolution stages the main structural characteristics of the basin are 1 a vertical tectonic zonation in a pre zechstein succession which lacks significant internal structures and a strongly deformed post zechstein succession which was decoupled due to the thick zechstein salt and 2 a marked asymmetry of the basin with a shallow northern slope and a steep bounding fault at the southern margin elbe fault system the northwestern part of the basin shows the structural properties of an intracratonic sag basin with persisting subsidence and with minor salt mobilisation in contrast initial structures in the southeastern part are strongly overprinted by younger tectonic events including middle triassic to jurassic extension late cretaceous inversion and late to post cretaceous salt movements tectonic elements that deform the whole sedimentary succession are restricted to the basin s southern eastern and northeastern margins where salt thickness decreases combined volumetric and backstripping investigations show that 2 3 of the total subsidence was induced by the sediment load and 1 3 was caused by tectonics the tectonic subsidence history varies laterally across the basin while tectonic subsidence curves in the northwestern part of the basin show fast subsidence during the permian and early triassic decreasing exponentially with time subsidence curves in the southeastern part indicate repeated tectonic activity however the tectonic subsidence volume created during permian to late triassic is significantly higher than the tectonic subsidence during younger phases of basin history

on the origin of the southern permian basin central europe abstract a detailed study of the structural and stratigraphic evolution of the southern permian basin during latest carboniferous to early jurassic times supported by quantitative subsidence analyses and forward basin modelling for 25 wells leads us to modify the conventional model for the rotliegend zechstein development of this basin the late permian early jurassic tectonic subsidence curves are typical for a permian to early triassic extensional stage that is followed by thermal subsidence however a purely extensional model is extremely problematic because active faulting during this time is minor and generally hard to document using inverse techniques to model the subsidence curves we quantitatively show that a significant component of late permian and triassic tectonic subsidence can be explained by thermal relaxation of early permian lithospheric thinning and by delayed infilling of paleo topographic depressions that developed during the early permian in this interpretation stephanian autunian wrenching resulted in thermal destabilisation of the lithosphere deep fracturing of the crust disruption and erosion of its sedimentary cover and regional uplift of the area of the future southern permian basin upon termination of wrench tectonics and associated volcanism towards the end of the autunian the southern permian basin began to subside in response to thermal contraction of the lithosphere the evolving basin was isolated from the world oceans and had subsided possibly up to some 700 m below their level at the beginning of upper rotliegend sedimentation after catastrophic flooding of this paleo topographic depression at the beginning of the zechstein changing sea level sedimentation and subsidence rates remained essentially in balance although the effects of triassic rifting overprinted parts of the southern permian basin its overall subsidence pattern persisted well into the jurassic in contrast to the remainder of the southern permian basin permian and triassic crustal extension contributed significantly to the subsidence of the polish trough

syntectonic sedimentation controls on the evolution of the southern pyrenean fold and thrust belt inferences from coupled tectonic surface processes models 1 numerous studies in the central pyrenees have provided evidence for a rapid phase of exhumation of this mountain belt during the late eocene 37 30 ma simultaneously the closure of the ebro foreland basin allowed the accumulation of sediments at the southern piedmont which partially covered the fold and thrust belt from late eocene e g when it was still actively deforming to miocene times we aim here at understanding the consequences of such syntectonic sedimentation on the southern pyrenean fold and thrust belt by using a 2 d numerical model that reproduces the development of a thin skinned wedge subject to different modes of sedimentation and erosion the results show contrasting fold and thrust belt behavior when applying aggrading or prograding sedimentation which we link to the critical state of the wedge when the sediments are sourced from the hinterland progradation the thrusting propagates toward the foreland whereas when the sediments aggrade from the basin the thrusting sequence migrates backward this latter mode shows patterns of deformation that compare favorably to the pyrenean thrusting sequence observed during eocene miocene times

the southern margin of the east european craton new results from seismic sounding and potential fields between the north sea and poland abstract the extension of eastern avalonia from britain through the ne german basin into poland is in some sense a virtual structure it is covered almost everywhere by late paleozoic and younger sediments evidence for this terrane is only gathered from geophysical data and age information derived from magmatic rocks during the last two decades much geophysical and geological information has been gathered since the european geotraverse egt which was followed by the babel lt 7 mona lisa dekorp basin 96 and polonaise 97 deep seismic experiments based on seismic lines a remarkable feature has been observed between the north sea and poland north of the elbe line el the lower crust is characterised by high velocities 6 8 7 0 km s a feature which seems to be characteristic for at least a major part of eastern avalonia far eastern avalonia in addition the seismic lines indicate that a wedge of the east european craton eec or baltica continues to the south below the southern permian basin spb a structure which resembles a passive continental margin the observed pattern may either indicate an extension of the baltic crust much farther south than earlier expected or oceanic crust of the tornquist sea trapped during the caledonian collision in either case the data require a reinterpretation of the docking mechanism of eastern avalonia and the elbe odra line eol as well as the elbe fault system together with the intra sudedic faults appear to be related to major changes in the deeper crustal structures separating the east european crust from the paleozoic agglomeration of middle european terranes

modelling the coupling between salt kinematics and subsidence evolution inferences for the miocene evolution of the transylvanian basin large scale diapiric salt movements affect the architecture of sedimentary basins and often prevent the understanding of their mechanics by hiding or distorting subsidence patterns one good example is the evolution of the transylvanian basin which formed during miocene times in an area located in between the rapid slab rollback and continental collision recorded at the exterior of the carpathians and the extension of the neighbouring pannonian basin in the absence of major genetic fault systems quantifying these external tectonic forcing factors requires an accurate reconstruction of subsidence evolution having the advent of a detailed 3d geometrical model of the transylvanian basin we apply a 3d numerical modelling technique that couples salt re distribution and subsidence evolution to quantify and understand the basin kinematics and vertical motions two techniques backward and forward modelling are coupled in order to discriminate between salt migration driven by overburden and the influence of external tectonic forcing factors the results show that salt kinematics was more complex than simple unidirectional migration suggesting the existence of areas with significant subsidence hidden by the inward salt migration and areas with apparent large subsidence that are in reality artefacts of outwards salt migration additionally the results suggest that parts of the basin have been successively affected by in and out ward salt migration events an effect of localising subsidence and overburden furthermore accelerated moments of salt migration took place during the main miocene contraction events recorded at the exterior of the carpathians demonstrating that salt migration is enhanced by intraplate stresses our study also infers that the subsidence of the transylvanian basin is the result of the superposition of the contraction at the exterior of the orogenic chain and the back arc extension

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

computerized tomographic analysis of displacement trajectories and three dimensional fold geometry above oblique thrust ramps computerized tomographic analysis of physical models of fold thrust structures permits nondestructive systematic analysis of variations in displacement trajectories and variations in three dimensional fold geometry as a function of thrust fault geometry the authors studied models in which sand layers with embedded transport parallel marker lines were shortened incrementally up to a maximum of 24 over rigid footwall fault templates these templates simulated a right stepping oblique ramp connecting two ramps perpendicular to the shortening direction in response to movement over the oblique ramp templates overturned folds formed and marker line deflections indicative of out of plane strains developed marker lines within layers originally truncated by fault templates were deflected leftward away from the right stepping oblique ramp during deformation whereas marker lines within sand layers that originally extended across the upper flat of the fault template were deflected in a more radial pattern differences in marker line deflections imply that displacement trajectories within natural thrust sheets may vary as a function of overburden and structural position furthermore their tomographic studies graphically demonstrate that out of plane strain and differential rotation of layers within thrust sheets occur in the vicinity of oblique ramps

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

tectonic evolution of the northeastern south china sea from seismic interpretation 1 we interpret a grid of 2 d seismic reflection profiles to resolve the tectonic evolution of the northeastern south china sea scs identifying two significant postbreakup events t1 and t2 which occurred before the end of the scs opening in the absence of the drilling data in the deep basin we date these two events using the identification of the magnetic anomalies the age of major unconformities at ocean drilling program site 1148 drilled on the northeastern scs margin and the age of basalt samples in the deep scs the tectonic phase t1 is a slight tensional tectonic event which occurred in the deep scs south of the luzon ryukyu transform plate boundary lrtpb it is characterized by oceanic tilted blocks and fan shaped deposits which developed 8 10 myr after the onset of scs seafloor spreading 37 8 ma it corresponds to the first ene wsw to e w change in spreading direction which occurred around chron c10 28 7 ma event t2 is a magmatic phase observed in the deep scs south of the lrtpb it is characterized by the uplift of former spreading features caused by an early miocene 22 ma magmatic phase which is also recorded in north and south central taiwan

vertically averaged velocities in the north atlantic current from field trials of a lagrangian electric field float abstract a subsurface lagrangian float that utilizes motional induction to calculate vertically averaged velocities was tested in the north atlantic current nac taking advantage of existing cruises and infrastructure the electric field float eff is a rafos float with horizontal electrodes that measures its own velocity by rafos tracking and calculates vertically averaged velocities when merged with the electrode system the observations showed depth averaged velocities that were fast in the core of the nac 0 6 0 9 m s 1 and moderate in adjacent recirculations and eddies 0 3 0 4 m s 1 a float at 850 dbar moved at close to the depth averaged velocity while shallower floats followed surface intensified flow on top of the depth averaged motion integral time scales of depth averaged velocity 1 3 1 6 0 4 d are slightly shorter than time scales of float velocity 1 6 2 0 0 3 d while integral length scales of depth averaged water velocity 35 10 km for u 18 6 km for v are slightly shorter than length scales of float motion 53 12 km for u 28 6 km for v velocity spectra of depth averaged velocity show significant variance at inertial periods quantitative and qualitative validation with multiple independent data sets confirms the accuracy of the instrument and sampling strategy in the nac advancing the limited observational knowledge of depth averaged circulation in subpolar regions

modeling of the 3d thermal field in the northeast german basin the regional thermal field of the ne german basin is modeled by a three dimensional finite element approach and is compared to classical one dimensional extrapolations two alternative boundary conditions are assumed at the approximate depth of the moho a constant temperature distribution and a constant heat flow surprisingly both results are almost identical down to approximately 10 km depth based on the models presented the results are due to a complex interaction of different strata and the related regional variability of conductivities in addition the available temperature maps for different depths hurtig et al 1992 indicate a relative high heat flow at the basin margins especially at the southern and eastern boundary the models are able to reproduce the generalized pattern by regarding only a conductive heat flow however because both models are successful at shallow depth we conclude that the current techniques of thermal modeling require improvement even on the theoretical aspects of depth continuation and inversion

style and evolution of salt pillows and related structures in the northern part of the northeast german basin the northern part of the northeast german basin contains a large number of late permian zechstein salt pillows whereas diapiric structures are almost completely absent this lack of diapirs facilitated the study of early stages of salt movement in the basin salt pillows and related structures were investigated in terms of distribution geometry and time of initiation of salt flow within the regional geological context the primary zechstein thickness in the study area was reconstructed to gain more insight into the relationship between the geometry of the salt layer and the style of the salt related structures in this study no clear spatial relationship between the salt structures and basement faults has been found and the location of the salt structures in this area appears to be highly independent of the underlying structural grain the overburden is affected by minor faulting we propose that buckling of the overburden due to regional compression significantly contributed to the initiation of the late jurassic to early cretaceous salt structures in the basin reverse faulting of the gardelegen and haldensleben faults is related to inversion tectonics and exerted a compression on the basin fill during the deformation the late permian salt layer acted as an efficient detachment and led to a marked decoupling of the mesozoic overburden from the underlying pre zechstein rocks

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

multi decadal ingredients of the secular variation of the geomagnetic field insights from long time series of observatory data abstract the temporal evolution of the geomagnetic field is shown on data from 24 observatories with 100 150 years long time series of annual means to be composed of several ingredients which we call the steady the 80 year the 22 year and the 11 year variations the latter is the result of incomplete averaging out in the annual mean of external effects and shows a characteristic 11 year solar cycle related evolution with an amplitude of 10 40 nt in h and z and within 0 05 in d the other three characterize the main field while the steady variation carries the largest part of the main field and is smoothly increasing or decreasing in time the 80 year variation shows changes with amplitudes amounting to several hundred nt in the intensity components h and z and of 0 2 0 7 in declination the 22 year variation changes with much smaller amplitudes of 20 60 nt in h and somewhat larger in z 20 100 nt and of about 0 05 0 15 in d the analysis of the first time derivative of declination for the 24 study observatories showed that the 80 year variation dominated the secular variation in the last 100 years and that the 22 year variation has gotten its importance in defining the time evolution of the first time derivative of declination jerks included since 1960 the external contribution is decisive though in establishing the very short time scale characterizing jerks and to some extent also the amplitude and timing of the jerk the analysis of 400 years long declination time series from three european locations london munich rome resulted in tracing back of the 80 year variation to the 15th century and showed that what we called steady variation based on 150 years of observatory data proves to be only a part of a larger timescale variation when 400 years of data are available according to our results the term jerk loses its presently accepted meaning of sudden change in the temporal evolution of secular variation a more complex concept in describing the secular variation of the main field namely the superposition of several quasi periodic effects corresponding to specific core processes at various time scales should be used instead

a time dependent model of the earth s magnetic field and its secular variation for the period 1980 2000 1 this study presents an investigation and description of the secular variation of the earth s magnetic field between 1980 and 2000 a time dependent model c3fm continuous covariant constrained endpoints field model of the main field and its secular variation between 1980 and 2000 is developed with gauss coefficients expanded in time on a basis of cubic b splines this model is constrained to fit field models from high quality vector measurements of magsat in 1980 and orsted in 2000 and to fit both magnetic observatory and repeat station secular variation estimates for the period in between these secular variation estimates first time derivatives are derived from observatories monthly or annual means and repeat station data in order to reduce the contributions of crustal noise annual and semiannual variation on average the model input consists secular variation estimates of the x y and z components at 130 locations per month treatment of covariance between the different components allows a higher temporal sensitivity of the model due to the exclusion of some external field variation the model is computed up to degree and order 15 the model is a useful extension of the hitherto existing time dependent description of the secular variation gufm which describes the secular variation until 1990 it reveals a short term secular variation on subdecadal timescale and has a higher spatial resolution than previously resolved the model is also valuable to test the frozen flux hypothesis and to link features of the radial field at the core mantle boundary to the geodynamo

can core surface flow models be used to improve the forecast of the earth s main magnetic field 1 geomagnetic main field models used for navigation are updated every 5 years and contain a forecast of the geomagnetic secular variation for the upcoming epoch forecasting secular variation is a difficult task the change of the main magnetic field is thought to be principally due to advection of the field by flow at the surface of the outer core on short timescales and when large length scales are considered with accurate secular variation sv and secular acceleration sa models now available from new satellite missions inverting for the flow and advecting it forward could lead to a more accurate prediction of the main field however this scheme faces two significant challenges the first arises from the truncation of the observable main field at spherical harmonic degree 13 this can however be handled if the true core flow is large scale and has a rapidly decaying energy spectrum the second is that even at a given single epoch the instantaneous sv and sa cannot simultaneously be explained by a steady flow nevertheless we find that it may be feasible to use flow models for an improved temporal extrapolation of the main field a medium term 10 years hindcast of the field using a steady flow model outperforms the usual extrapolation using the presently observed sv and sa on the other hand our accelerated toroidal flow model which explains a larger portion of the observed average sa over the 2000 2005 period fails to improve both the short term and medium term hindcasts of the field this somewhat paradoxical result is related to the occurrence of so called geomagnetic jerks the still poorly known dynamical nature of which remains the main obstacle to improved geomagnetic field forecasts

tectonics of the southern tip of the parece vela basin philippine sea plate we report new geophysical and petrological data collected at the southern tip of the parece vela basin in the philippine sea the parece vela basin which was formed as a backarc basin behind proto mariana arc trench system from late oligocene to middle miocene provides us a good opportunity to study the nature of successive backarc basin formations in the philippine sea and the relationship between are and backarc magmatisms regional bathymetric map derived from satellite altimetry shows that the southern tip of the basin now located just west of the yap arc trench system has unique morphological and tectonic features which include 1 the absence of spreading center or its trace 2 shallow average depth and 3 enigmatic curved structures our newly collected high resolution bathymetric data reveal that the spreading fabric similar to the central parece vela basin exists to the north of 9 degrees 20 n thus it appears that the present day yap arc and backarc region represent the western half of the seafloor that was produced by the early e w and the following ne sw spreading in the northern and central parece vela basin and that the eastern counterpart now lies west of the west mariana ridge unlike the northern parece vela basin there appears to be no evidence for a systematic propagation of spreading center in the southern part instead two rift segments one which extends from the central parece vela basin and the other which lies within the western remnant arc kyushu palau ridge overlap at the southern tip of the basin producing a complex seafloor that includes curvilinear deeps and deformed topographic highs c 2007 elsevier b v all rights reserved

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

transformation of a magmatic arc and an orogenic root during oblique collision and it s consequences for the evolution of the european variscides mid german crystalline rise the architecture of the european variscides has been subdivided by kossmat 1927 into paleogeographically coherent units which are presently interpreted as former plate fragments the mid german crystalline rise mgcr separates two fragments rhenohercynian and saxothuringian belts at the site of an inferred plate boundary and reequilibrated orogenic root the commonly favoured model interprets the mgcr as the magmatic arc on saxothuringian crust above a south dipping subduction zone in upper devonian and carboniferous times data from the mgcr the kinematic evolution of the mid european variscides and first order volume balancing suggest a reinterpretation of this unit which challenges classical views on the mgcr as well as on the subdivision of variscan architecture the mgcr is composed of two rock groups with different tectonic identity a lower carboniferous low pressure high temperature magmatic arc association on lower paleozoic basement rests tectonically on a stack of medium pressuremedium temperature rocks of inferred rhenohercynian origin the latter were tectonically accreted to the base of the overriding plate by tectonic underplating the entire process was controlled by oblique convergence this led to regional partitioning of the plate kinematic vector into contractional domains lower rhenohercynian plate and back arc area of the upper saxothuringian plate bulk heterogeneous plate margin parallel extensional domains mgcr and plate margin parallel wrench domains mgcr boundaries during this process material was continually transferred from the lower plate to the upper plate uplifted and exhumed by net crustal extension the concomitant removal of parts of the former arc and the entire orogenic root necessitates a reappraisal of variscan architecture and evolution

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

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

magmatic activities on the southwest indian ridge between 35 e and 40 e the closest segment to the marion hotspot 1 we conducted geophysical surveys including bathymetry gravity and magnetism within a first order segment of the southwest indian ridge swir between the prince edward and eric simpson fracture zones fzs latitude 35 40 e segment pe in the vicinity of the marion hotspot segment pe includes four orthogonally spreading second order segments pe 1 pe 2 pe 3 and pe 4 and a long oblique axial valley ntd 1 segments pe 1 pe 2 and pe 4 are magmatic whereas segment pe 3 and ntd 1 are characterized by low magmatic activity segment pe 3 is a nascent segment and ntd 1 contains three tiny magmatic sections each low magmatic interval along the axis of segment pe lies between two magmatic segments this segmentation pattern is similar to the swir between the gallieni and melville fzs therefore a strong melt focusing process can be expected different characteristics of second order magmatic segments suggest that the magmatic activity in each segment varies among each other as well as that of the other segments of swir continuous seafloor morphology and isochrons over off axis areas of segment pe 1 and ntd 1 suggest that pe 1 shortened after the c2an chron the v shaped bathymetric structure between segment pe 1 and ntd 1 suggests that the melt supply center has migrated westward this westward melt migration would have reduced magmatic activity at ntd 1 after c2an ridge obliquity may also have reduced magmatic activity geophysical characteristics of second order segments suggest that magmatic activity of segment pe is mainly controlled by a strong melt focusing process and a comparatively low contribution of melt supply from marion hotspot

the petrophysical behaviour of crustal rocks under the influence of fluids abstract fluid phases of different composition have been found to be present ubiquitously in most crustal rocks down to deep levels in the lower crust they are stored either in isolated fluid inclusions within the mineral grains or in open and frequently interconnected cracks and fissures although the porosity of typical basement rocks usually is very small the presence or absence of fluids is found to be of paramount importance for rock strength and stability experiments of the triaxial deformation cell type were performed with two typical basement rocks a monzogranite and a two mica granite at a confining pressure of 55 mpa and deformation rates 10 7 s 1 at temperatures of 80 250 and 300 c respectively the rock samples were pressurized by fluid phases independent of the confining pressure fluids applied were pure h2o ar co2 compared to drained rock samples i e samples in which internal fluids could leave the rock specimen and the sample chamber during the experiment and no fluid pressure could build up the presence of fluids generally caused a strong reduction in rock strength internal fluid pressures up to 65 mpa independent of the fluid contents were controlled externally the mode of failure also changed sigificantly from a simple shear fracture in the fluid absent case to a subaxial multiple splitting mode when fluids were present the deformation style prior to brittle failure in the wet experiments shows a distinct phase of ductile yielding preceding it intergranular creep i e ductile mineral deformation sensu stricto has not been observed at this stage but change in the mineral fabric has been the interpretation of the brittle to ductile transition of rocks in the earth s crust has to take into account these influences exerted by fluid phases

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

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

thrust mechanics in highly overpressured accretionary wedges rapid tectonic loading of wet sediment in accretionary wedges is likely to cause the fluid pressure to rise until it is sufficient to cause dilatant fracturing dewatering of sediment that has been underthrust and accreted beneath the wedge can produce a large steady supply of such highly overpressured fluid dilatant fracturing will create escape routes so the fluid pressure is likely to be buffered at the value required for the transition between shear and oblique tensile dilatant fracture which is slightly in excess of the load pressure if the maximum compression is nearly horizontal this in turn buffers the strength of the wedge at the cohesive strength which is not pressure dependent and will not vary greatly throughout the wedge near the wedge front the strength is likely to be that of the cohesion on existing thrust faults in the wedge the shear resistance on the base of the wedge will also be fairly constant and related to the cohesive strength of the weak sediment layer that acts as the basal detachment these assumptions allow the application of a simple plastic continuum model which successfully predicts the observed gently convex taper of accretionary wedges they also allow the use of a mechanical model for frontal imbrication which predicts the spacing of imbricate thrusts at the front of the wedge from the strength and thickness of the imbricated layer the ramp angle and the factional resistances on the bounding faults and decollement surfaces reconstruction of thrust geometries from seismic data across the makran and other accretionary wedges allows the determination of the geometrical parameters and the thrust imbrication model allows the mechanical parameters to be calculated in terms of an assumed cohesive strength for the incoming sediment layer the calculated values are reasonable and successful forward modelling of the profile of the makran shows that the postulate of a buffered value of fluid pressure in excess of the load pressure is consistent with observation

an unstable kinematic state of the himalayan tectonic wedge evidence from experimental thrust spacing patterns abstract the frontal tectonic wedge in the nw himalayas shows a sequence of imbricate thrusts with increasing spacing in the foreland direction we used analogue model experiments to analyze the thrust pattern in relation to the kinematics of wedge evolution experimental findings reveal two kinematic states of the foreland ward propagation of a wedge unstable state and stable state the unstable state is characterized by continuous vertical growth of the wedge with progressive horizontal contraction on the other hand in the stable state the wedge ceases to grow vertically but propagates laterally in the foreland direction in the experimental runs thrust wedges remained in the unstable state even after large horizontal shortening 50 when the basal friction was high 0 46 our analysis suggests that successive thrusting occurs always with increasing spacing in unstable wedges and the rate of increase is larger for larger basal friction it can maintain uniform spacing only when the wedges turn into the stable state using finite element models we determined the stress distribution in the deforming wedge to find the potential locations of new thrusts in front of a wedge which also show larger spatial distances with increasing vertical thickness of the wedge both physical and numerical models suggest that the tectonic wedge in the nw himalayan frontal belt has evolved in an unstable state

geomagnetic secular variation of bransfield strait western antarctica from analysis of marine crossover data summary tracking the secular variation of the geomagnetic field in the past is severely limited in some cases by factors relating to the remoteness of the sites this is maximal in the antarctic where the remote location and severe climate lead to logistic limitations that make it difficult to keep a continuous record of magnetic field variations from the magnetic information available from historical marine expeditions it is possible to infer this time varying component from the comparison of readings at crossovers this study focuses on this technique discusses the impact of the different error sources and proposes a simple mathematical procedure to infer average secular variation rates the result is validated by comparing it with local data from the arctowski and livingston magnetic observatories sited in the area additionally using a high quality data set from a local area in the neighbourhood of deception island we have detected a systematic distribution in its secular variation this dichotomy has been interpreted in terms of a volcano magnetic signal this fact and the nature of its principal mechanisms are analysed and discussed

structural geometry of the source region for the 2013 mw 6 6 lushan earthquake implication for earthquake hazard assessment along the longmen shan abstract the 2013 mw 6 6 lushan earthquake occurred in the longmen shan fold and thrust belt sichuan province china near the five year anniversary of the devastating 2008 mw 7 8 wenchuan earthquake to define the fault that generated the 2013 earthquake and its relationship with the beichuan fault which ruptured in the wenchuan earthquake we construct several cross sections and a 3d structural model the sections and models reveal that the main shock of the lushan earthquake occurred on a portion of the range front blind thrust rfbt and that the structural geometry of this fault varies along strike the lushan main shock occurred at a location along the strike of the fault where the geologic shortening and total fault slip are greatest a lateral ramp of the rfbt appears to coincide with the northern limit of aftershocks from the lushan earthquake leading to a 75 km seismic gap between the wenchuan earthquake and the 2013 earthquake sequence although both the wenchuan and lushan earthquakes occurred within the longmen shan fold and thrust belt different faults generated the two events based on this structural characterization and analysis of the aftershocks of the wenchuan and lushan earthquakes we suggest that the lushan earthquake may have been triggered by the 2008 rupture but is best considered as an independent event rather than an aftershock of the wenchuan earthquake the rfbt that generated the lushan earthquake is linked to a detachment that extends into the sichuan basin along the triassic evaporite layer the coulomb stress change simulation suggests that other faults linked to this detachment may have been loaded by the 2008 and 2013 earthquake posing the risk of future earthquakes along the longmen shan and in the densely populated sichuan basin

intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central german platform abstract the structural evolution of central europe reflects contrasting tectonic regimes after the variscan orogeny during mesozoic cenozoic time the brittle deformation related to each tectonic regime is localized mainly along major fault zones creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events by contrast fracture patterns in less deformed domains often provide a pristine structural inventory we investigate the brittle deformation of a relatively stable wide area of the central german platform using fault slip data to identify the regional stress fields required to satisfy the data in a non classical approach and in order to avoid local stress variations and misinterpretations the fault slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks direct stress tensor inversion was performed through an iterative refining process and the computed stress tensors were verified using field based observations criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events which begins with a post triassic normal faulting regime with 3 axis trending ne sw the deformation then follows by strike slip and thrust faulting regimes with a change of 1 axis from n s to ne sw supposedly in the late cretaceous two younger events are characterized by cenozoic normal and oblique thrust faulting regimes with nw se trending 3 and 1 axes respectively the fracture patterns of both the cover and basement rocks appear to record the same states of stress

sandstone composition and provenance of the rotliegend of the ne german basin abstract the ne german basin contains an approximately 2 5 km thick rotliegend sedimentary section subdivided into 4 formations these were deposited following the cessation of the late carboniferous early permian volcanic episode and a ca 20 ma period of erosion and non deposition initial deposition was confined to two areas but with increasing thermal subsidence the basin extended to the south petrographic 190 sandstones and geochemical 48 sandstones and mudstones analyses suggested that the sands are quartz rich and are derived largely from cratonic or recycled sources volcanic and sedimentary rock fragments form most of the labile grains the succession was deposited in a relatively stable tectonic environment with sediment input derived largely from the lower and upper palaeozoic strata of the variscan hinterland and the upper carboniferous and lower permian volcanics volcanic input increases with younger stratigraphic units this is interpreted as resulting from the unroofing of a more basic source

a historical declination curve for munich from different data sources abstract long series of geomagnetic field changes are important for studying processes in the earth s core we have compiled 635 historical declination values for southern germany and surrounding areas indirect estimations including the oldest ones from back in the 15th century come from 185 sundials and compasses with declination information and 15 historical maps measurements carried out by monks in the time interval 1668 1854 amount to 122 annual mean values and data related to the orientation of mine shafts contributes by 313 annual values for several locations all these data can be useful to improve historical geomagnetic field models previously compiled german church orientations however are shown to be no reliable sources of the past declination the compiled new declination curve for munich shows general agreement with previously published curves for london and paris and allows to detect geomagnetic jerks with a temporal uncertainty of 10 years more or less regular impulses on a decadal time scale ranging from 30 to 60 years are identified for most of the time interval 1400 2000 but the century from about 1760 to 1860 seems to be devoid of sudden secular variation changes

the legacy of the ne german basin reactivation by compressional buckling in contrast to previously published models for the area the seismic reflection moho is essentially flat beneath the ne german basin along the dekorp deep seismic profile basin 96 this raises the question whether the present structure of the crust and flat moho reflect the initial formation of the basin or modification by more recent processes a 2d flexural model developed for a thin elastic plate is presented together with lithospheric strength profiles calculated along the basin 9601 reflection seismic line the analysis shows a southward decrease of lithospheric strength below the basin with a lithospheric decoupling between the crust and the mantle the modelling supports the hypothesis that the present moho topography is caused by flexural buckling which caused subsidence of the ne german basin during the upper cretaceous early cenozoic inversion event this suggests that the basin is in isostatic disequilibrium and that compressive stresses are required to keep the present basin geometry

magnetic structure of an oceanic core complex at the southernmost central indian ridge analysis of shipboard and deep sea three component magnetometer data 1 we investigated the magnetic structure of an oceanic core complex occ at the southernmost central indian ridge cir near 25 s on the basis of newly collected magnetic and bathymetric data and submersible dives the occ is located off axis on the western flank of the cir and is characterized by typical megamullion morphology with flow line parallel corrugations the occ is similar in size to those found along the mid atlantic ridge mar but the cir occ formed in an estimated 0 8 ma which is slightly shorter than the average time for the formation of occs along the mar the magnetization intensity over the cir occ is quite weak compared to that over adjacent seafloor of the same age mostly gabbroic rocks were recovered from outcrops during submersible dives fault rocks were also recovered from the corrugated surface suggesting that the occ surface represents the plane of a detachment fault although the magnetization intensity is rather low we were able to identify the brunhes matuyama boundary and the jaramillo and olduvai subchrons on and around the occ using vector magnetic analysis over the occ the jaramillo subchron which cannot be recognized from magnetic data acquired at the sea surface was identified using data from a magnetometer attached to a submersible the locus of this subchron is consistent with that observed over the seafloor adjacent to the occ combining the results of magnetic survey and rock sampling we would like to point out the possibility that the gabbroic rocks constituted the occ and preserved seafloor spreading history although there are several interpretations of the low magnetization

ergodicity of the recent geomagnetic field the geomagnetic field is a fundamental property of our planet its study would allow us to understand those processes of earth s interior which act in its outer core and produce the main field knowledge of whether the field is ergodic i e whether time averages correspond to phase space averages is an important question since if this were true it would point out a strong spatio temporal coupling amongst the components of the dynamical system behind the present geomagnetic field generation another consequence would be that many computations usually undertaken with many difficulties in the phase space can be made in the conventional time domain we analyse the temporal behaviour of the deviation between predictive and definitive geomagnetic global models for successive intervals from 1965 to 2010 finding a similar exponential growth with time also going back in time at around 1600 and 1900 by using the gufm1 model confirms the same findings this result corroborates previous chaotic analyses made in a reconstructed phase space from geomagnetic observatory time series confirming the chaotic character of the recent geomagnetic field with no reliable prediction after around 6 years from definitive values and disclosing the potentiality of estimating important entropic quantities of the field by time averages although more tests will be necessary some of our analyses confirm the efforts to improve the representation of the geomagnetic field with more detailed secular variation and acceleration

the elbe fault system in north central europe a basement controlled zone of crustal weakness abstract the elbe fault system efs is a wnw striking zone extending from the southeastern north sea to southwestern poland along the present southern margin of the north german basin and the northern margin of the sudetes mountains although details are still under debate geological and geophysical data reveal that upper crustal deformation along the elbe fault system has taken place repeatedly since late carboniferous times with changing kinematic activity in response to variation in the stress regime in late carboniferous to early permian times the elbe fault system was part of a post variscan wrench fault system and acted as the southern boundary fault during the formation of the permian basins along the trans european suture zone sensu geol mag 134 5 1997 585 the teisseyre tornquist zone ttz most probably provided the northern counterpart in a pull apart scenario at that time further strain localisation took place during late mesozoic transtension when local shear within the elbe fault system caused subsidence and basin formation along and parallel to the fault system the most intense deformation took place along the system during late cretaceous early cenozoic time when the elbe fault system responded to regional compression with up to 4 km of uplift and formation of internal flexural highs compressional deformation continued during early cenozoic time and actually may be ongoing the upper crust of the elbe fault system which itself reacted in a more or less ductile fashion is underlain by a lower crust characterised by low p wave velocities low densities and a weak rheology structural seismic and gravimetric data as well as rheology models support the assumption that a weak stress sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the elbe fault system

the stress regime in a rotliegend reservoir of the northeast german basin in situ stresses have significant impact either positive or negative on the short and long term behaviour of fractured reservoirs the knowledge of the stress conditions are therefore important for planning and utilization of man made geothermal reservoirs the geothermal field gros schonebeck 40 km north of berlin germany belongs to the key sites in the northeastern german basin we present a stress state determination for this lower permian rotliegend reservoir by an integrated approach of 3d structural modelling 3d fault mapping stress ratio definition based on frictional constraints and slip tendency analysis the results indicate stress ratios of the minimum horizontal stress s hmin being equal or increasing 0 55 times the amount of the vertical stress s v s hmin 0 55s v and of the maximum horizontal stress s hmax 0 78 1 00s v in stress regimes from normal to strike slip faulting thus acting stresses in the 4 100 m deep reservoir are s v 100 mpa s hmin 55 mpa and s hmax 78 100 mpa values from hydraulic fracturing support these results various fault sets of the reservoir are characterized in terms of their potential to conduct geothermal fluids based on their slip and dilatation tendency this combined approach can be adopted to any other geothermal site investigation

geomechanical model for the post variscan evolution of the permocarboniferous mesozoic basins in northeast germany abstract the permocarboniferous basins in northeast germany formed on the heterogeneous and eroded parts of the variscan orogene and its deformed northern foreland transtensional tectonic movements and thermal re equilibration lead to medium scale crustal fragmentation fast subsidence rates and regional emplacement of large amounts of mostly acidic volcanics the later basin formation and differentiation was triggered by reversals of the large scale stress field and reactivation of prominent zones of weakness like the elbe fault system and the rhenohercynian saxothuringian boundary that separate different variscan basement domains in the area the geomechanical behaviour of the latter plays an important role for the geodynamic evolution of the medium to large scale structural units which we can observe today in three dimensions on structural maps geophysical recordings and digital models this study concentrates on an area that comprises the southern northeast german basin the saale basin the flechtingen high the harz mountains high and the subhercynian basin the presented data include re evaluations of special geological and structural maps the most recent interpretation of the dekorp basin 9601 seismic profile and observations of exposed rock sections in northeast germany on the basis of different structural inventories and different basement properties we distinguish two structural units to the south and one structural unit to the north of the elbe fault system for each unit we propose a geomechanical model of basin formation and basin inversion and show that the rhenohercynian fold and thrust belt domain is deformed in a thin skinned manner while the mid german crystalline rise domain which is the western part of the saxothuringian zone rather shows a thick skinned deformation pattern the geomechanical model for the unit north to the elbe fault system takes account to the fact that the base of the zechstein beneath the present northeast german basin shows hardly any evidence for brittle deformation which indicates a relative stable basement our geomechanical model suggests that the permocarboniferous deposits may have contributed to the structural stiffness by covering small to medium scale structures of the upper parts of the brittle basement it is further suggested that the pre zechstein successions underneath the present northeast german basin were possibly strengthening during the cretaceous basin inversion which resulted in stress transfer to the long lived master faults as indicated for example by the shape of the salt domes in the vicinity of the latter faults contrary to this post zechstein successions deformed in a different and rather complex way that was strongly biased by intensive salt tectonic movements

magmatic flare up at the carboniferous permian boundary in the ne german basin revealed by shrimp zircon ages shrimp ages of 12 volcanic samples indicate intense magmatic activity to have occurred at the carboniferous permian boundary throughout much of the ne german basin rhyolitic crystal rich samples have been taken from quarries in the halle volcanic complex hvc and in the flechtingen ignimbrite and from drill cores of the kotzen mirow friedland and penkun areas ten samples yielded 206pb 238u ages between 302 and 297 ma 3 ma respectively which indicate that the magmatic activity took place concentrated in a relatively short time span throughout much of the ne german basin two hvc samples have ages of 307 and 294 ma this remarkably synchronous magmatic activity occurred during the initial phase of the basin development considering published volume estimates 48 000 km3 extrusion rates during this time period probably were in the order of 0 01 km3 a 1 implying magma production rates of 0 1 km3 a 1 the calc alkaline sio2 rich volcanic rocks originated from magmas that presumably formed during anatexis and subordinate magma mixing in an intra continental transtensional setting the basaltic magma which must have provided the thermal input into the lower crust probably formed during decompressional melting of lithospheric mantle fertilised by previous magmatic processes the dated volcanic rocks occur in three geotectonic provinces namely the a mid german crystalline rise which forms the northern part of the internal variscides the b external variscides and the variscan foreland which is considered as c eastern avalonia many of the old zircons found in the hvc samples reflect the magmatic activity of the mid german crystalline rise 325 400 ma however cadomian 500 650 ma and older gondwanian elements 1674 2373 ma are also present although the flechtingen and kotzen areas are located within the external variscides it seems more likely that the middle to lower crust that experienced anatexis formed part of the eastern avalonia plate overridden by the variscan front thus the old zircons found in flechtingen 350 and 538 ma and kotzen 345 ma but certainly those present in the penkun drill cores 1483 ma represent eastern avalonia tectonic history the anatectic magmas in the friedland area probably formed partly from baltic crust thrusted below eastern avalonia during the caledonian orogeny among the old zircons from the friedland samples in addition to proterozoic ages 1456 ma we found testimony of caledonian 443 ma and of clearly post caledonian 387 ma magmatism