comparative stratigraphy and subsidence history of mesozoic rift basins of north atlantic mesozoic rift basins around the north atlantic all possess many of the following upper jurassic to lower cretaceous oxfordian to albian stratigraphic elements 1 an early oxfordian hiatus 2 backfill deposits in upper jurassic paleovalleys 3 multiple tithonian transgressive regressive sequences 4 early berriasian regressive sequences 5 a sub valanginian unconformity overlain by coarse siliciclastic sandstones and conglomerates 6 valanginian to hauterivian fining upward sequences 7 condensed barremian sequences and 8 prominent aptian unconformities more local features include abrupt kimmeridgian deepening lusitanian basin portugal albian deepening cantabrian and aquitaine basins northern spain and southern france and late albian early cenom nian source rejuvenation cantabrian basin northern iberia decompaction and backstripping of sediments from well and outcrop sections in six basins also reveal broad similarities in trends of rates of apparent basement subsidence relatively high rates 50 100 m m y characterize onset of rift phases in the triassic and the kimmeridgian locally in the lusitanian basin of portugal kimmeridgian rates reach about 250 m m y in the cantabrian and aquitaine basins a third phase of rapid subsidence characterizes the aptian albian interval after the main phase of continental breakup around iberia this phase may be due to transtensional stresses as iberia continued to rotate relative to europe tensional intraplate stresses or gravity driven partial collapse of the new continental marg n the north atlantic mesozoic basins share many features because they had a common origin controlled by intracontinental rifting and subsequent separation of europe and north america pulses of extension generally are reflected in the stratigraphy of all of the basins superimposed on this record are the effects of eustatic sea level variations the main difference between the canadian jeanne d arc basin and iberian basins is the significantly greater early and middle jurassic basement subsidence rate in the former about 40 m m y vs 0 10 m m y this difference may result from prolonged extension on the canadian side perhaps due to northward transfer of shear stress from left lateral transform motion between the grand banks and northwestern africa

coupled ice shelf ocean modeling and complex grounding line retreat from a seabed ridge recent observations and modeling work have shown a complex mechanical coupling between antarctica s floating ice shelves and the adjacent grounded ice sheet a prime example is pine island glacier west antarctica which has a strong negative mass balance caused by a recent increase in ocean induced melting of its ice shelf the mass loss coincides with the retreat of the grounding line from a seabed ridge on which it was at least partly grounded until the 1970s at present it is unclear what has caused the onset of this retreat and how feedback mechanisms between the ocean and ice shelf geometry have influenced the ice dynamics to address these questions we present the first results from an offline coupling between a state of the art shallow ice flow model with grounding line resolving capabilities and a three dimensional ocean general circulation model with a static implementation of the ice shelf a series of idealized experiments simulate the retreat from a seabed ridge in response to changes in the ocean forcing and we show that the retreat becomes irreversible after 20 years of warm ocean conditions a comparison to experiments with a simple depth dependent melt rate parameterization demonstrates that such parameterizations are unable to capture the details of the retreat process and they overestimate mass loss by more than 40 over a 50 year timescale

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

thermal imprint of rift related processes in orogens as recorded in the pyrenees 19 the extent to which heat recorded in orogens reflects thermal conditions inherited from 20 previous rift related processes is still debated and poorly documented as a case study we 21 examine the mauleon basin in the north western pyrenees that experienced both extreme 22 crustal thinning and tectonic inversion within a period of 30 myrs to constrain the time 23 temperature history of the basin in such a scenario we provide new detrital zircon fission 24 track and u th sm he thermochronology data the role of rift related processes in 25 subsequent collision is captured by inverse modeling of our thermochronological data using 26 relationships between zircon u th sm he ages and uranium content combined with 27 thermo kinematic models of a rift orogen cycle we show that the basin recorded significant 28 heating at about 100 ma characterized by high geothermal gradients 80 c km our 29 thermo kinematic modeling and geological constraints support the view that subcontinental 30 lithospheric mantle was exhumed at that time below the mauleon basin such a high 31 geothermal gradient lasted 30 myr after onset of convergence at 83 ma and was relaxed 32 during the collision phase from 50 ma this study suggests that heat needed for ductile 33 shortening during convergence is primarily inherited from extension rather than being only 34 related to tectonic and or sedimentary burial this should have strong implications on tectonic 35 reconstructions in many collision belts that resulted from inversion of hyper extended rift 36 basins

interaction between prerift salt and detachment faulting in hyperextended rift systems the example of the parentis and mauleon basins bay of biscay and western pyrenees prerift salt layers associated with extensional detachment faults exhuming mantle and deeper crustal rocks at the sea floor are observed in the parentis and arzacq mauleon basins located at the eastern termination of the bay of biscay how detachment faults interact with salt in hyperextended rift systems is yet little understood based on field observations and drill hole and seismic data we propose a new model to explain the interaction between salt tectonics and extensional detachment systems we demonstrate that the presence of a thick prerift salt layer in an area undergoing extreme crustal thinning can control the geometry and evolution of rift systems and obscure the rift related structures in the underlying basement during an initial stage of rifting prerift salt layers act as a decoupling horizon between sub and suprasalt units and hinder crustal detachment faults to cut through the salt layers and form breakaways at the sea floor as a consequence they sole out along the ductile salt layer and no subsalt material can be exhumed to the sea floor thus sub and suprasalt layers deform by different deformation modes which makes that detachment fault difficult to identify on seismic images in a later stage when salt has migrated and thinned out sub and suprasalt layers can locally couple and detachment faults can be exposed at the surface resulting in windows of exhumed basement surrounded by extensional allochthons formed by suprasalt sedimentary units

the deep seismic reflection marconi 3 profile role of extensional mesozoic structure during the pyrenean contractional deformation at the eastern part of the bay of biscay abstract the new marconi 3 deep seismic profile allows recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution it denotes that the easternmost part of the bay of biscay consists of a thick wedge of uppermost cretaceous to cenozoic synorogenic sediments lying unconformably on the top of a thinned continental crust with the mesozoic parentis basin to the north and the coeval landes high to the south the parentis basin appears as a major half graben bounded southwards by a north dipping planar fault it is filled by a thick sequence of jurassic upper cretaceous carbonates affected by salt domes and squeezed diapirs made up of triassic evaporites and mudstones these salt tectonic structures also affect the overlying uppermost cretaceous to lower miocene synorogenic deposits which are folded upon these structures the landes high includes a thin pre upper cretaceous cover tilted to the south in the basque shelf it is deformed by a basement involving thrust wedge emplaced during the late eocene miocene that constitutes the north pyrenean contractional front geometric relationships and thickness variations depict that this overall structure results from the following mesozoic extensional stage which includes a late jurassic late aptian syn rift stage in which the parentis basin formed and an albian early late cretaceous post rift stage in which diapirs of triassic evaporites grew close to this major fault compressive deformational stage coeval to the pyrenean orogeny which led to 1 the development of a latest cretaceous up to middle miocene foreland basin and 2 from late eocene the formation of a basement involving thrust wedge in the innermost foreland basin the squeezing of the diapiric structures formed previously in the parentis basin and later middle miocene the partial inversion of some pre existent faults located in the southern parentis basin margin this geodynamic evolution together with the structure of the area evidences that the extensional structure resulting from the opening of the bay of biscay played an important role both in the location of the north pyrenean front and in the north pyrenean foreland contractional deformation features specially the lack of significant inversion structures in the parentis basin despite that it belongs to a severely thinned crustal area before the alpine compression denotes that the mesozoic landes high acted as an important buffer for the propagation of the pyrenean contractional deformation to the north this deformational buffer was active until early miocene and probably vanished afterwards during the last stages of pyrenean orogen development when some basement faults reactivated in the parentis basin

integrated seismic studies of the baltic shield using data in the gulf of bothnia region in the autumn of 1989 a co operative experiment involving 12 research institutions in northwestern europe collected 2268 km of deep seismic reflection profiles in the gulf of bothnia and the baltic

pulsating subsidence during a rift episode stratigraphic and tectonic consequences aptian albian northern spain backstripping analysis has been carried out on nine outcrop sections of the basque cantabrian aptian and albian of northern spain which consist of shallow water marine deposits up to 7000 m thick it reveals four main pulses of common accelerated subsidence i early aptian ii early albian iii lower late albian and iv uppermost late albian separated by tectonic quiescent intervals tectonic subsidence rates of 70 m myr 1 for the aptian and 101 m myr 1 for the albian were recorded sopuerta section the calculated stretching factor referred to a pre rift continental crust of 35 km is bs 1 32 and represents approximately 8 5 km of crustal thinning points of change towards lesser subsidence rate in the curves are correlated with major unconformities in the sections in the basque cantabrian basin and in boreal europe suggesting geodynamic changes related with the opening of bay of biscay minor variations of spreading direction and intensity are proposed to explain the subsidence pulses

flow of the brunt ice shelf antarctica derived from landsat images 1974 85 satellite images recorded in 1973 1974 and 1985 of the brunt ice shelf are compared there are sufficient identifiable features moving with the ice shelf to show flow patterns over an area of 10000 km 2 velocities vary from 500 m a i in the west near the dawson lambton ice stream to 1300 m a i in the east within the stancomb wills ice stream

consequences of foreland basin development on thinned continental lithosphere application to the aquitaine basin sw france abstract we present an analysis of the consequences of foreland basin development on thinned continental lithosphere inherited from pre orogenic phases of extension bathymetry at the transition from pre orogenic extensional basin to foreland basin and compaction of pre orogenic sediments contribute to the accommodation space for foreland basin sediments and thrust loads in addition the extension induced transient thermal state of the lithosphere results in ongoing thermal subsidence and a flexural rigidity which changes through time quantitative modelling of the phase of extension and the foreland basin stage of the aquitaine basin southern france shows that the inherited transient thermal state of the lithosphere contributes significantly to 1 the total foreland basin depth and width 2 the post compressional subsidence history and 3 the cratonward onlap pattern accounting for the thermo mechanical effects of pre orogenic extension significantly reduces the estimates of both the flexural rigidity 30 43 for the aquitaine basin and the required topographic or thrust load 40 for the aquitaine basin at foreland basins emplacement of thrust loads below sea level as expected in a pre orogenic extensional basin setting further reduces the required topographic load this sheds light on the wide range of flexural rigidity values reported for continental lithosphere from foreland basin modelling studies and explains in many instances the inferred hidden load or subsurface load in flexural modelling studies at foreland basins the present study has shown that pre orogenic extension phases significantly affect the record of vertical motion and the stratigraphy of the aquitaine basin and is probably important for foreland basin evolution in general

subsidence of the paris basin we discuss the main results of a systematic quantitative analysis of the subsidence of the paris basin made on 100 wells backstripping techniques with decompaction as well as sea level and water depth corrections are used to derive tectonic subsidence curves in the absence of water and sediment loading assuming local as well as regional compensation a best fitting sea level variations curve is derived for the deepest central part on the basis of the resulting tectonic subsidence curve the adopted amplitude of the regression since upper cretaceous is 330 m the spatial and temporal distribution of tectonic subsidence is reconstructed and discussed it is shown that rigidity of the lithosphere with an adopted 50 km flexural parameter plays a significant role these results are then quantitatively interpreted in terms of the lithospheric stretching model this interpretation is reasonable provided it is made in terms of volumetric subsidence over the whole basin because of the thermal conduction and the rigidity low pass filtering effects the subsidence can be explained if the axial zone was thinned during permo triassic by a factor of about 1 3 with respect to the adjacent lithosphere it is shown that either the initial altitude was more than 500 m above sea level or the lower part of the lithosphere was lost at the beginning of the permo triassic phase of extension resulting in a rapid uplift of several hundreds of meters the similarity of the permo triassic initiating extensional phase with active continental rifting is shown

role of rift structural inheritance in orogeny highlighted by the western pyrenees case study abstract it is commonly accepted that many orogens form by contractional reactivation of earlier continental rifts or rifted margins therefore to better understand orogenesis it is important to also understand how rift domains and their associated structures are incorporated into orogens we investigate the role of rift structural inheritance during orogeny using the western pyrenees as a case study to achieve our aim we use a kinematic forward lithosphere deformation model rifter to produce flexural isostatically compensated as well as balanced cross sections showing the structural and stratigraphic development of both the rift and orogenic stages of the western pyrenees the cross section produced extends from the northern to the southern foreland basins and crosses the mauleon arzacq basin our modelling results show how rift domains and their faults are sequentially reactivated and incorporated into the present day western pyrenees architecture based on the results from our case study we identify a sequence of tectonic stages separated by critical events that record the transition between different tectonic styles by which lithosphere is deformed the pre orogenic extensional stage is characterized by a hyper extended rift system that eventually led to exhumed mantle this constitutes the pre orogenic template the subsequent contractional tectonics consists of two stages i the inversion of the hyper extended rift system reactivating extensional structures and ii the crustal shortening of the southern proximal rift domain results of the western pyrenees case study may be used to understand the development of other alpine type collisional systems involving the sequential reactivation and inversion of former hyper extended rift systems

rift tectonics on the passive continental margin off galicia spain abstract new migrated multichannel seismic profiles on the starved passive continental margin off galicia spain illustrate the tectonic style of the early cretaceous rifting event which preceded the separation of iberia and north america the main episode of rifting was preceded by other tensional episodes probably of earliest cretaceous and late jurassic age listric faulting associated with rifting was accompanied by large scale mass movements from the crests of the tilted blocks two subaerial erosional surfaces are visible one of late jurassic or earliest cretaceous age was affected by the final faulting episode the other was synchronous with the main phase of rifting and is present only on the upper part of the margin because the central trough was under deep water the significance of a ridge near the ocean continent boundary where altered lherzolite has been dredged and cored is discussed below the tilted blocks which include the basement rocks the seismic horizon s is visible as on the armorican margin its significance is also discussed

recording marine airgun shots at offsets between 300 and 700 km this paper demonstrates that under favorable conditions by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up

subsidence history and continental margin evolution of the western pyrenean and basque basins abstract we have studied cretaceous sedimentary sequences of four sedimentary basins along the european and north iberian continental margins of the western pyrenean realm and the basque basin the depression intermediaire sare vera basin and ulzama basin in the western pyrenees and the zumaya basin along the southern margin of the bay of biscay the formation of these basins was largely due to upper cretaceous sinistral strike slip tectonics during iberian plate motion resulting in wrench basins oblique slip and pull apart basins a detailed biostratigraphic framework and paleobathymetric calculations based on sedimentologic and benthic foraminiferal data were used to construct decompacted and backstripped subsidence history curves for each basin from these curves two major changes in subsidence history are apparent 1 increased subsidence since late albian and 2 decrease in subsidence and or initial uplift since early campanian these changes are closely related to plate tectonic events namely spreading in the bay of biscay followed by european iberian plate convergence

tide induced lateral movement of brunt ice shelf antarctica 1 accurate position data show that brunt ice shelf has an irregular three dimensional motion driven by the ocean tide a 30 day gps record from halley station shows not only the expected vertical tidal displacement but also a significant variation in horizontal velocity the maximum forward velocity occurs about four hours before the maximum tidal height a phase relationship that suggests ocean currents may be responsible however values of ice water friction coefficients needed to make this explanation plausible appear to be too high to be physically reasonable alternative explanations invoke interactions between the ice shelf and a grounded area at the ice front our findings suggest that significant errors might result if these motions are ignored when interpreting double difference satellite sar interferograms where the common assumption is that the horizontal velocity of an ice shelf has no tidal dependence

estimates of upper crustal heterogeneity in the baltic shield from seismic scattering and borehole logs abstract constraints on small scale heterogeneity in the upper crust of the baltic shield were obtained from stochastic modelling of a variety of seismic data from the babel and siljan ring surveys a non linear least squares inversion scheme was applied to wavefield fluctuations in seismic reflections to obtain statistical parameters of the medium through which the wave energy propagated the reflections are from dolerite sills intruded at depths of 6 12 km into the palaeoproterozoic upper crust of the central baltic shield analysis of the babel data set reveals that the upper crust is a weakly scattering stochastic medium with velocities characterised by an exponential autocorrelation function with a correlation length of 150 50 m and rms velocity perturbation of 1 5 0 5 further inversions show that most of the scattering occurs within the upper few kilometres of the crust analysis of the sijan seismic data set reveals heterogeneity with length scales of 210 50 m and a velocity perturbation of about 1 0 the autocovariance and power spectrum of the sonic log and studies of frequency dependent q in vsp data from the gravberg 1 borehole give consistent estimates of basement heterogeneity the upper crust in this region is characterised by a correlation distance of 35 5 m and rms velocity perturbation of 4 6 in the uppermost 1 2 km of crust associated with near surface fracturing and a correlation distance of 140 50 m and rms velocity perturbation of 1 5 0 5 in the uppermost 6 8 km associated with compositional heterogeneity

large scale ice flow over a viscous basal sediment theory and application to ice stream b antarctica recent seismic studies of ice stream b antarctica and field analysis of mid latitude glacial deposits suggest that deformable basal sediments e g water saturated till are important in determining ice sheet flow if the ratio of till viscosity to effective ice viscosity is small vertical shear associated with horizontal flow is confined to the deforming bed alone ice flow over a deformable bed is thus akin to that of floating ice shelves because ice shelves flow over inviscid seawater for some antarctic ice streams and possibly for portions of the late wisconsin ice sheets in north america and eurasia basal drag associated with deforming basal sediment does not induce significant vertical gradients of horizontal velocity instead basal drag affects the flow as if it were a horizontal body force balanced by longitudinal and transverse deviatoric stress gradients comparison of the observed flow of ice stream b to finite element simulations incorporating a viscous basal till suggest that a simple till theology is sufficient to explain the current velocity profile these simulations also highlight the importance of horizontal deviatoric stress in regions where driving stress and basal stress do not locally balance while bed deformation is critical to ice stream existence sensitivity tests suggest that ice shelf back pressure is still a crucial control affecting ice stream response to atmospheric and oceanic climate

five decades of strong temporal variability in the flow of brunt ice shelf antarctica data showing velocity changes on the brunt ice shelf bis antarctica over the last 55 years are presented and analysed during this period no large scale calving events took place and the ice shelf gradually grew in size ice flow velocities however fluctuated greatly increasing twofold between 1970 and 2000 then decreasing again to previous levels by 2012 after which velocities started to increase yet again in the observational period velocity changes in the order of 10 a 1 have commonly been observed and currently velocities are increasing at this rate by modelling the ice flow numerically we explore potential causes for the observed changes in velocity we find that a loss of mechanical contact between the bis and the mcdonald ice rumples following a local calving event in 1971 would explain both the increase and the subsequent decrease in ice velocities other explanations involving enlargement of observed rift structures are discounted as the effects on ice flow are found to be too small and the spatial pattern of velocity change inconsistent with data the most recent phase of acceleration remains unexplained but may potentially be related to a recent re activation of a known rift structure within the bis

scaling of fault displacements from the badajoz cordoba shear zone sw spain faulting occurs over a large range of scale parts of which are sampled by various techniques e g microscopy outcrop measurement mapping seismic reflection and other forms of remote sensing use of a single technique to measure displacement or strain will not sample faults at all scales and hence will give a biased estimate in order to assess this bias a knowledge of the distribution over all scales is needed many samples of fault displacement appear to follow a power law distribution with departures which can be attributed to sampling effects the number of faults with a displacement u is given by n u cu d the power law distribution of displacement is consistent with similar distributions of other fault parameters and earthquake magnitudes when sampling along a line e g a bedding trace on a map or section a self similar fault population would have d 1 whereas self affine geometries yield d 1 displacement and extension are dominated by small faults when d 1 and by large faults when d 1 when sampling over areas or volumes these critical values are 2 and 3 respectively a set of strike slip faults from the badajoz cordoba shear zone spain were sampled at two different scales using 1 50000 maps and outcrop measurements displacement ranges over 6 orders of magnitude these and other fault populations typically have d ranging from 0 6 to 1 5 the power law relationship may be integrated to yield estimates of the displacement or extension for faults which lie beyond the resolution of the sampling system for example a knowledge of d allows the extension measured on a map or seismic section to be corrected for faults whose displacement is below the resolution of the survey based on an overall estimate of d 0 9 for the badajoz cordoba data only some 40 of the extension would be recorded by map scale faults a corrected extension of 41 along the shear zone is estimated which if typical for the entire 300 km zone represents some 87 km of along strike extension thus work suggests that significant displacement occurs on faults which are too small to be interpreted from conventional seismic profiles and geological maps

the tectono sedimentary evolution of a hyper extended rift basin the example of the arzacq mauleon rift system western pyrenees sw france in this paper we present a sedimentary and structural analysis that together with maps sections and new ar ar data enable to describe the tectono sedimentary evolution of the mauleon hyper extended rift basin exposed in the w pyrenees hyper extension processes that ultimately resulted in exhuming mantle rocks are the result of the subsequent development of two diachronous detachment systems related to two evolutional stages of rifting an initial late aptian early albian crustal thinning phase is first recorded by the development of a crustal necking zone controlled by the north vergent southern mauleon detachment system during a subsequent exhumation phase active faulting migrates to the north with the emplacement of the northern mauleon detachment system that exhumed north section thinned continental crust and mantle rocks this diachronous crustal thinning and exhumation processes are also recorded by the diachronous deposition of syn tectonic sedimentary tracts above the two supra detachment sub basins syn tectonic sedimentary tracts record the progressive exhumation of footwall rocks along detachment systems tectonic migration from the southern to the northern mauleon detachment system is recorded by the coeval deposition of sag deposits above the necking zone basin and of syn tectonic tracts above exhumed rocks north section located on a hanging wall situation related to the mauleon hyper extension structures the arzacq basin also records a major crustal thinning phase as shown by its subsidence evolution so as by deep seismic images the absence of major top basement structures and its overall sag morphology suggest that crustal thinning processes occurred by decoupled extension of lower crustal levels contrasting with the southern mauleon detachment system reconciling observations from the mauleon and arzacq basins we finally propose in this paper that they were the result of one and the same asymmetric crustal thinning and exhumation processes where extension is accommodated into the upper crust in the mauleon basin lower plate basin and relayed in ductile lower crust below the arzacq basin upper plate basin

representation of sharp rifts and faults mechanics in modeling ice shelf flow dynamics application to brunt stancomb wills ice shelf antarctica ice shelves play a major role in buttressing ice sheet flow into the ocean hence the importance of accurate numerical modeling of their stress regime commonly used ice flow models assume a continuous medium and are therefore complicated by the presence of rupture features crevasses rifts and faults that significantly affect the overall flow patterns here we apply contact mechanics and penalty methods to develop a new ice shelf flow model that captures the impact of rifts and faults on the rheology and stress distribution of ice shelves the model achieves a best fit solution to satellite observations of ice shelf velocities to infer the following 1 a spatial distribution of contact and friction points along detected faults and rifts 2 a more realistic spatial pattern of ice shelf rheology and 3 a better representation of the stress balance in the immediate vicinity of faults and rifts thus applying the model to the brunt stancomb wills ice shelf antarctica we quantify the state of friction inside faults and the opening rates of rifts and obtain an ice shelf rheology that remains relatively constant everywhere else on the ice shelf we further demonstrate that better stress representation has widespread application in examining aspects affecting ice shelf structure and dynamics including the extent of ice melange in rifts and the change in fracture configurations all are major applications for better insight into the important question of ice shelf stability

coupling of ice shelf melting and buttressing is a key process in ice sheets dynamics 1 increase in ice shelf melting is generally presumed to have triggered recent coastal ice sheet thinning using a full stokes finite element model which includes a proper description of the grounding line dynamics we investigate the impact of melting below ice shelves we argue that the influence of ice shelf melting on the ice sheet dynamics induces a complex response and the first naive view that melting inevitably leads to loss of grounded ice is erroneous we demonstrate that melting acts directly on the magnitude of the buttressing force by modifying both the area experiencing lateral resistance and the ice shelf velocity indicating that the decrease of back stress imposed by the ice shelf is the prevailing cause of inland dynamical thinning we further show that feedback from melting and buttressing forces can lead to nontrivial results as an increase in the average melt rate may lead to inland ice thickening and grounding line advance

amount of extension on small faults an example from the viking graben extension estimates based on palinspastic restoration of only the largest faults in a deformed terrane may be significantly deficient due to neglect of small faults i e unsampled faults most of which have smaller displacements than do sampled faults small faults individually account for little extension but there may be large numbers of them the cumulative extension on small faults can be calculated from the fractal size distributions of fault displacements independent extension estimates support the inference from fault population statistics that small faults account for significant amounts of extension for example restorations of mesozoic faults interpreted from seismic reflection profiles across the viking graben in the north sea yield extension estimates that are only 40 75 of independent estimates the fractal size distribution of fault displacements in the viking graben is consistent with the hypothesis that the remaining 25 60 of extension resulted from displacements on small faults

a comparative modeling study of the brunt ice shelf stancomb wills ice tongue system east antarctica two diagnostic dynamic thermodynamic ice shelf models are applied to the brunt ice shelf stancomb wills ice tongue system located off caird coast coats land antarctica the brunt ice shelf stancomb wilis ice tongue system is characterized as a thin unbounded ice shelf with an atypical and highly heterogeneous structure in contrast to other ice shelves a composite mass of icebergs that calved at the grounding line and were then locked within fast sea ice exists between the fast moving stancomb wills ice stream and the slow moving brunt ice shelf we simulate the present flow regime of the ice shelf that results from the ice thickness distribution and the inflow at the grounding line with two different models and compare the model results with feature tracking and insar flow velocities we then incorporate two observed features a rift and a shear margin into the models with two different approaches and demonstrate the effects of variations in numerical values for the shear strength and viscosity in these zones on the simulated velocity field a major result is that both kinds of implementation of the rifts lead to similar effects on the entire velocity field while there are discrepancies in the vicinity of the rifts

extreme crustal thinning in the bay of biscay and the western pyrenees from observations to modeling recent observations and models of continental rifting in magma poor environments have led to the concept of multiphase stages of lithospheric extension in these concepts it is shown that extreme crustal thinning of the crust predates exhumation of lower crustal and subcontinental mantle rocks during final rifting the bay of biscay is a v shaped ocean basin that opened in aptian albian time in front of this propagating ocean several rift basins formed that show evidence for extreme crustal thinning and locally also mantle exhumation the parentis arzacq mauleon and cantabrian basins in this paper we propose based on geological and geophysical observations and using numerical modeling a model that can explain the extreme crustal thinning observed in the arzacq mauleon and parentis basins our results show that rifting in the bay of biscay was initiated by distributed oblique stretching latest jurassic to early aptian before it underwent an more orthogonal asymmetric thinning and exhumation phase from late aptian to albian time these last two stages of deformation are similar to those observed in orthogonal rift systems we show that thinning is accomplished by the formation of a semibrittle shear zone that allows for the transfer of middle to lower crustal material from the side of the rift collocated with the hanging wall to the side of the rift collocated with the footwall of the detachment system the main difference with an orthogonal rift system appears to be generated by the formation of flower structures during the distributed oblique phase and the capacity of localizing the deformation in the subsequent stages these oblique slip faults form very steep normal faults that induce the development of strongly localized compartmentalized and asymmetric rift basins in the case of the parentis and arzacq mauleon basins these strike slip faults separate upper plate sag basins to the north from lower plate sag basins to the south while the northern sag basins do not show any evidence for exhumation the southern ones are more complex and floored by detachment faults as indicated by the occurrence of syntectonic and posttectonic sediments onlapping directly onto exhumed lower crustal and mantle rocks

origin of the permian triassic iberian basin central eastern spain abstract the iberian basin was an intracratonic rift basin in central eastern spain developed since early permian times the basin boundary faults were normal listric faults controlling an asymmetric extension propagating northeast with time hercynian or older lineaments controlled the orientation of the iberian basin and extension was accommodated basically in the hanging wall block by the formation of secondary grabens and a central high the basin was related with the coeval ebro catalan and cuenca mancha basins and their connections are discussed subsidence curves show that the early permian early jurassic period of extension can be subdivided into three rifting episodes and a flexural one extension factor increases from 1 17 in the northwest to 1 29 near the mediterranean coast the increasing extension rate was accommodated by transfer faults trending nne ssw more important in the levante area the rift evolution is intermittent and seems to reflect distinct stress fields the collapse of the late hercynian orogen and related increased heat flux extension and rifting is the most probable origin of the iberian basin and related basins the origin of the catalan and the valencia prebetic basins is related to the southwards migration of the hesse burgundy rift along the eastern margin of the iberian microplate

fortnightly variations in the flow velocity of rutford ice stream west antarctica ice sheets like that of antarctica lose much of their ice via fast flowing ice streams hilmar gudmundsson has monitored the flow in one such stream the rutford ice stream in west antarctica over a period of two months the findings are a surprise surface flow velocities here fluctuate by as much as 20 over a period of two weeks perhaps under the influence of the spring neap fortnightly tidal cycle although the mechanism that couples these tides to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate monitoring of the flow of an ice sheet in antarctica finds that the surface velocity oscillates by as much as 20 per cent every two weeks the spring to neap tidal cycle seems to be the cause although the mechanism through which these tides couple to ice flow has yet to be elucidated these observations caution against the use of velocity measurements over limited periods to infer long term changes in flow rate most of the ice lost from the antarctic ice sheet passes through a few fast flowing and highly dynamic ice streams1 quantifying temporal variations in flow in these ice streams and understanding their causes is a prerequisite for estimating the potential contribution of the antarctic ice sheet to global sea level change2 3 here i show that surface velocities on a major west antarctic ice stream rutford ice stream vary periodically by about 20 per cent every two weeks as a result of tidal forcing tidally induced motion on ice streams has previously been thought to be limited to diurnal or even shorter term variations4 5 6 7 8 9 the existence of strong fortnightly variations in flow demonstrates the potential pitfalls of using repeated velocity measurements over intervals of days to infer long term change

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

instantaneous antarctic ice sheet mass loss driven by thinning ice shelves abstract recent observations show that the rate at which the antarctic ice sheet ais is contributing to sea level rise is increasing increasing ice ocean heat exchange has the potential to induce substantial mass loss through the melting of its ice shelves lack of data and limitations in modelling however have made it challenging to quantify the importance of ocean induced changes in ice shelf thickness as a driver for ongoing mass loss here we use a numerical ice sheet model in combination with satellite observations of ice shelf thinning from 1994 to 2017 to quantify instantaneous changes in ice flow across all ais grounding lines resulting from changes in ice shelf buttressing alone our process based predictions are in good agreement with observed spatial patterns of ice loss providing support for the notion that a significant portion of the current ice loss of the ais is ocean driven and caused by a reduction in ice shelf buttressing

statistical inversion of controlled source seismic data using parabolic wave scattering theory summary statistical parameters describing heterogeneity in the proterozoic basement of the baltic shield were estimated from controlled source seismic data using a statistical inversion based on the theory of wave propagation through random media wprm derived from the parabolic wave approximation synthetic plane wave seismograms generated from models of random media show consistency with wprm theory for forward propagation in the weak scattering regime whilst for two way propagation a discrepancy exists that is due to contamination of the primary wave by backscattered energy inverse modelling of the real seismic data suggests that the upper crust to depths of 15 km can be characterized subject to the range of spatial resolution of the method by a medium with an exponential spatial autocorrelation function an rms velocity fluctuation of 1 5 0 5 per cent and a correlation length of 150 50 m further inversions show that scattering is predominantly occurring in the uppermost 2 km of crust where rms velocity fluctuation is 3 6 per cent although values of correlation distance are well constrained by these inversions there is a trade off between thickness of scattering layer and rms velocity perturbation estimates with both being relatively poorly resolved the higher near surface heterogeneity is interpreted to arise from fractures in the basement rocks that close under lithostatic pressure for depths greater than 2 3 km

seismic identification of basement reflectors the bagdad reflection sequence in the basin and range province colorado plateau transition zone arizona although seismic reflection profiling has contributed greatly to our knowledge of the crust and upper mantle it is often difficult to unambiguously identify the geologic origin of reflections this is particularly true of intrabasement reflectors whose geometry and origin we need to know in order to understand tectonic processes operating in the crust we present synthetic seismogram modeling of recently collected p and s wave seismic reflection data which suggests that the intrabasement bagdad reflectors in west central arizona are intrusive mafic sheets the identification is based on the determination of the phase positive polarity and amplitudes of the reflected arrivals if the bagdad reflectors are cenozoic age mafic sheets they may be the product of rapid intrusion into an area of weak extension where the principal stresses are approximately equal

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

comparison between the galicia and aquitaine margins abstract there is a great similarity between the galicia margin and the aquitaine margin i e the aquitaine basin and the north pyrenean zone in particular the timing of the rifting as well as the resulting structures exposure of perodotite tilted fault blocks normal and transverse faults half grabens are practically the same this comparison leads to the interpretation that the northern side of the pyrenean fold belt is inherited from the mesozoic deep passive margin of europe the cenozoic thrust sheets and reverse faults of the northern pyrenees zone are tentatively interpreted as former rift structures tilted blocks and listric faults which were removed during the convergence of the iberian and european plates during the paleocene and eocene

the sampling of fault populations in dolerite sills of central sweden and implications for resolution of seismic data abstract geological mapping of faults affecting dolerite sills was carried out along the baltic coast in central sweden and scaling relationships for the faults analysed in order to assess the seismic imaging of the sills the sills are 250 400 m thick and dip at low angle

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

accelerating flow of the brunt ice shelf antarctica des determinations de points effectuees a la station halley british antartic survey sur le brunt ice shelf sont examinees pour la periode de 1968 a 1982 elles revelent une vitesse dirigee a l ouest d environ 400 m a 1 croissant a plus de 700 m a 1 vers la fin de la periode les donnees sont bien representees par deux lignes droites la premiere de 1968 a 1971 a une pente de 430 m a 1 conformement a ce qu a trouve thomas 1973 pour la periode anterieure a 1968 la seconde de 1972 a 1982 a une pente de 740 m a 1 c est a dire une importante augmentation continue pendant ces dix annees

roles of marine ice rheology and fracture in the flow and stability of the brunt stancomb wills ice shelf marine ice sometimes as part of an ice melange significantly affects ice shelf flow and ice fracture the highly heterogeneous structure of the brunt stancomb wills ice shelf bsw system in the east weddell sea offers a rare setting for uncovering the difference in rheology between meteoric and marine ice here we use data assimilation to infer the rheology of the brunt stancomb wills ice shelf by an inverse control method that combines interferometric synthetic aperture radar measurements with numerical modeling we then apply the inferred rheology to support the hypothesis attributing the observed 1970s ice shelf flow acceleration to a change in the stiffness of the ice melange area connecting brunt proper with stancomb wills and to examine the consequences of frontal rift propagation we conclude that while the brunt stancomb wills system is currently not susceptible to extreme fragmentation similar to that of the larsen b ice shelf in 2002 our inverse and forward modeling results emphasize its vulnerability to destabilization by relatively rapid changes in the ice melange properties resulting from the interaction of its marine ice component with ocean water or by the further propagation of a frontal rift copyright 2009 by the american geophysical union

dynamic thinning of glaciers on the southern antarctic peninsula growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice especially if it is resting on bedrock below sea level much of the southern antarctic peninsula satisfies this condition and also possesses a bed slope that deepens inland such ice sheet geometry is potentially unstable we use satellite altimetry and gravity observations to show that a major portion of the region has since 2009 destabilized ice mass loss of the marine terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of 56 8 gigatons per year constituting a major fraction of antarctica s contribution to rising sea level the widespread simultaneous nature of the acceleration in the absence of a persistent atmospheric forcing points to an oceanic driving mechanism

evidence for early proterozoic plate tectonics from seismic reflection profiles in the baltic shield plate tectonics provides the linking framework for all tectonic and magmatic activity seen today but it is not known when plate tectonics first developed on earth new deep seismic reflection and

geoelectric studies and conductivity structures of the eastern and northern parts of the baltic shield abstract large resistive regions ideally having a horizontal size of about 200 km are needed to study reliably the conductivity distribution of the lower crust of the baltic scandinavian shield by deep electromagnetic em methods the overburden of the shield consists of quaternary sediments and is thin with a low conductance this makes the shield favourable for em studies the numerous conductive zones e g schist belts in the uppermost crust however require careful two dimensional modelling in order to obtain reliable electrical cross sections of the earth s crust electromagnetic methods magnetometer array studies and magnetotelluric profiling have proven to be a useful tool in studies of the lithospheric geophysics of the shield the crust of the finnish and soviet baltic shield can be divided into geoelectrically different blocks in central finland the blocks are surrounded by narrow highly conductive band like formations they are located in the middle crust and their upper surface often occurs in the 6 10 km region the resisitivities are typically 5 10 m the greatest anomalous crustal regions have a conductance of more than 20 000 s the lower crust is very conductive in most parts of the shield two dimensional models of long magnetotelluric profiles indicate the great variety and complexity of the geoelectric structure of the crust

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

characterizing and identifying structural domains at rifted continental margins application to the bay of biscay margins and its western pyrenean fossil remnants we use the bay of biscay and western pyrenees as a natural laboratory to develop and apply an approach to characterize and identify distinctive rifted margin domains in offshore and onshore settings the bay of biscay and western pyrenees offer access to seismically imaged drilled and exposed parts of one and the same hyperextended rift system offshore we use gravity inversion and flexural backstripping techniques combined with seismic interpretation to provide estimates of accommodation space crustal thickness and lithosphere thinning onshore we focus on key outcrops of the former rift domain to describe the nature of sediment and basement rocks and of their interface this qualitative and quantitative characterization provides diagnostic elements for the identification of five distinct structural domains at magma poor rifted margins and their fossil analogues proximal necking hyperthinned exhumed mantle and oceanic domains this new approach can be used to reconcile offshore and onshore observations and to aid interpretation when only local observations are available onshore remnants can be placed in an offshore rifted margin context enabling the prediction of first order crustal architecture for the interpretation of offshore seismic reflection sections geological insights into rift structures and basement nature can be suggested based on onshore analogies

thermal evolution of a hyperextended rift basin mauleon basin western pyrenees onshore and offshore geological and geophysical observations and numerical modeling have greatly improved the conceptual understanding of magma poor rifted margins however critical questions remain concerning the thermal evolution of the prerift to synrift phases of thinning ending with the formation of hyperextended crust and mantle exhumation in the western pyrenees the mauleon basin preserves the structural and stratigraphic record of cretaceous extension exhumation and sedimentation of the proximal to distal margin development pyrenean shortening uplifted basement and overlying sedimentary basins without pervasive shortening or reheating making the mauleon basin an ideal locality to study the temporal and thermal evolution of magma poor hyperextended rift systems through coupling bedrock and detrital zircon u th he thermochronometric data from transects characterizing different structural rifting domains these new data indicate the basin was heated during early rifting to 180 c with geothermal gradients of 80 100 c km the proximal margin recorded rift related exhumation cooling at ca 98 ma whereas the distal margin remained 180 c until the onset of paleocene pyrenean shortening lithospheric scale numerical modeling shows high geothermal gradients 80 c km and synrift sediments 180 c can be reached early in rift evolution via heat advection by lithospheric depth dependent thinning and blanketing caused by the lower thermal conductivity of synrift sediments mauleon basin thermochronometric data and numerical modeling illustrate that reheating of basement and synrift strata might play an important role and should be considered in the future development of conceptual and numerical models for hyperextended magma poor continental rifted margins

remote sensing of ice motion in antarctica a review abstract the antarctic ice sheet holds 91 of the global ice mass making it the biggest potential contributor to global sea level rise in order to evaluate the ice sheet s present and future response to global climate change detailed information about spatial and temporal ice mass dynamics is required while ice sheet surface mass balance can be estimated from regional climate models ice discharge is often determined from spaceborne measurements of ice thickness and ice motion at selected flux gates the retrieval of ice motion is not only critical for analysing the rate of ice transport into the ocean but also for investigating the spatial and temporal pattern or the driving forcings of antarctic ice flow dynamics this study provides a comprehensive review of state of the art spaceborne ice velocity measurements in antarctica based on 201 scientific papers published over the last three decades our analysis revealed a dominant interest in local and regional scale investigations yet the launch of the ers 1 2 and radarsat 1 sar satellites in the 1990s dramatically increased data coverage over the antarctic continent and enabled the first circum antarctic velocity product to be published in the late 2000s in recent years the improved imaging capabilities of landsat 8 led to a shift towards using mainly optical satellite data and enabled great advances in circum antarctic velocity mapping data from the currently operating sentinel 1 2 missions was applied in fewer studies but will play a crucial role in future ice motion studies e g as part of esa cci projects in addition we found a growing interest in high temporal resolution velocity change analyses based on the reviewed studies we moreover summarized the highly dynamic and locally variable flow pattern over the antarctic continent being in accordance with varying local and regional driving mechanisms despite the great advances in spaceborne ice velocity mapping in antarctica we report some major drawbacks and discuss future challenges and requirements to start with our study uncovered strong variations regarding the spatial availability of investigations while we found an aggregation of studies over selected glaciers we report a major lack of studies in all three antarctic sectors additionally many velocity datasets were created with strongly heterogeneous output parameters and were provided at coarse temporal resolution or at point based measurement locations only future studies should consequently aim at creating more uniform ice motion products at defined spatial and temporal coverage and resolution standards and at analysing particularly the least studied glaciers

the mesozoic tertiary evolution of the aquitaine basin the aquitaine basin situated in southwest france with an area of about 60 000 km 2 has the form of a triangle which opens towards the atlantic bay of biscay and is limited to the north by the hercynian basement of brittany and the massif central and to the south by the pyrenean tertiary orogenic belt beneath the tertiary sequence 2 km thick and which outcrops over much of the basin a mesozoic series up to 10 km thick rests generally on a tectonized hercynian basement but locally it covers narrow nw se trending post orogenic trenches of stephano permian age the mesozoic history can be subdivided into four major structural sedimentary episodes 1 during a triassic taphrogenic phase a continental evaporitic complex developed with associated basic magmatism 2 throughout the jurassic a vast lagoonal platform developed initially lower lias as a thick evaporitic sequence followed by a uniform shale carbonate unit indicating a relative structural stability 3 the end of the jurassic and the lower cretaceous saw a fragmentation of this platform due to an interplay between the iberian and european tectonic plates resulting in an ensemble of strongly subsident sub basins 4 during the upper cretaceous and until the end of the neogene the evolution of the aquitaine basin was influenced by the pyrenean orogenic phase with the development towards the south of a trench infilled by flysch which from the upper eocene is succeeded by a thick post orogenic molasse complex the main hydrocarbon objectives in the basin are situated in the jurassic platform e g the lacq giant gas field and the cretaceous sub basins e g the cazaux and parentis oil fields to date production has been about 4 times 10 7 m 3 of oil and about 15 times 10 10 m 3 of gas since the first gas discovery st marcet in 1939

deep crustal seismic reflection profiling across two major tectonic zones in southern sweden abstract a seismic reflection profile has been shot in varmland southwestern sweden across two major tectonic zones the protogine zone and the mylonite zone the crustal bedrock units separated by the tectonic zones are clearly distinguished in the seismic profile by changes in the reflection character in the upper 5 6 km the protogine zone is represented by a 15 20 km wide band of dipping structures the mylonite zone dips too steeply to be seen directly and a lack of clear reflectors at depth makes a continuation down through the crust hypothetical in the uppermost 5 6 km between the two tectonic zones stronger and more continuous reflections can be seen and are interpreted as being connected with hyperite intrusions which have been mapped at the surface the lower crust shows generally little reflectivity with only short and weak reflectors an exception occurs at mid crustal depths where a number of clearly recognizable bands of reflected energy are suggested to be major shear zones formed during sveconorwegian grenvillian thrusting towards the east a slight increase in reflectivity in the depth range 42 48 km correlates well with the moho depth determined from refraction seismic studies the possible relationships between data acquisition parameters and the observed scarcity and low strength of reflections from the deeper crust have been considered in some detail it is shown that the use of 28 hz single geophones instead of 10 hz geophone strings along a major part of the profile did not reduce the signal to noise ratio for deep reflections however the varying source characteristics in combination with the different quality of the recordings made computation of the residual static corrections difficult which may have resulted in a partly destructive stacking of seismic traces in this way the low reflectivity of the deeper crust in this area is further brought out in the stacked seismic sections

a new kinematic model for iberia further palaeomagnetic and isotopic age evidence abstract palaeomagnetic results and k ar age data from the algarve igneous province have uncovered three ancient relative field components it is inferred that the principal magnetization of the monchique complex with a mean direction of d 42 i 181 95 4 5 was acquired at around the time of the pluton s emplacement some 72 2 ma ago a second magmatic pulse affected the region at 68 2 ma leaving behind a relative field component of d 42 i 341 95 1 7 furthermore an overprinted magnetization characterized by shallow inclination and somewhat smeared northwesterly southeasterly declination most likely originates from the lower tertiary the new palaeomagnetic data are seen in conjunction with previously published upper cretaceous results from the sintra and sines intrusive complexes the resulting database gives entirely new perspectives for evaluating the plate tectonic history of the peninsula in upper cretaceous lower tertiary time a two phase rotation of the iberian micro plate an anticlockwise one of 40 followed by a clockwise one of 70 is clearly in evidence the net clockwise rotation provided a major impetus for the compressive deformation in the pyrenees and the bay of biscay and led to extensive remagnetization of older rock formations in the northern regions of iberia previous palaeomagnetic conclusions in favour of a single anticlockwise rotation of 35 supposed to be directly connected with the formation of the bay of biscay appear to be artefacts which stem from an incorrectly adopted palaeomagnetic reference frame

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

crustal structure of the fennoscandian shield a traveltime interpretation of the long range fennolora seismic refraction profile abstract the 1979 fennoscandian long range project fennolora was aimed at the determination of the detailed structure in the earth s mantle down to a depth of about 400 km observation distances reached almost 2000 km within scandinavia between shotpoints off the north cape and the southern coast of sweden to achieve an unbiased regarding the upper mantle structure a careful crustal survey was carried out along the entire profile at the same time beneath the fennoscandian shield i e the central section of the profile the crust is characterized by quite a smooth increase in p wave velocity down to the moho which lies at a depth of about 50 km in the southern half of the shield and at about 45 km further north the mean crustal velocity is 6 6 6 7 km s at the base of the crust the velocity increases gradually from about 7 km s to 8 0 8 4 km s in a 5 10 km thick crust mantle transition zone both in the south and in the north the relatively homogeneous crust of the baltic shield borders on areas with a more differentiated velocity structure first order discontinuities at shallower depth characterize the crust mantle boundary near the southeastern tip of sweden 38 km and under the caledonides in the north 43 km

role of structural inheritance and salt tectonics in the formation of pseudosymmetric continental rifts on the european margin of the hyperextended mauleon basin early cretaceous arzacq and tartas basins abstract arzacq and tartas were two cretaceous basins developing in the bay of biscay as secondary depocentres in the larger aquitaine basin they belong to an albian rift system where recent studies have stressed the role of simple shear thinning on the genesis of regional asymmetric basins however the two basins differ from recent models in having a pseudo symmetric morphology here we address the early cretaceous tectono sedimentary evolution of the arzacq and tartas rift basins and the lithospheric processes associated with their genesis these basins did not suffer major brittle deformation during rifting stage but nevertheless record a major change in their configuration between the aptian and the albian the arzacq basin shifted from a symmetric to a slightly asymmetric configuration this change was controlled by gravity sliding of the pre rift sedimentary cover in the eastern arzacq basin moving its depocenter south and by salt diapirism in the western arzacq basin moving its depocenter north several inherited paleozoic structures were reactivated as transfer zones and appear to be responsible for this depocenter shift the emplacement of salt diapirs at same time regionally limiting gravity sliding the tartas basin maintained a symmetric regime throughout the early cretaceous except along the barlanes transfer zone where the lussagnet salt diapir originated two drivers of subsidence are thus envisaged in the arzacq basin a neocomian aptian crustal thinning stage followed by reactivation of paleozoic faults in albian time accompanied by salt diapirism and gravity cover sliding the mauleon north pyrenean basin and its north adjacent tartas and arzacq basins thus formed part of a series of rift basins that progressed in maturity southward from a simple sag basin tartas to a slightly asymmetric basin aborted detachment arzacq to a hyperthinned basin mauleon our results offer new insights on the role of 1 structural inheritance in partitioning extensional strain 2 transfer zones as able to influence the sedimentary record of basins during crustal thinning and 3 pre rift salt decollements as able to separate the structural styles of sub and supra salt successions

scaling systematics of fault sizes on a large scale range fault map abstract a large scale high quality fault map was produced for an intensively mined area of the u k south yorkshire coalfield this database has been used to investigate both the scaling properties of fault systems and the robustness of techniques for the prediction of sub resolution faulting the mapped area is 87 km 2 and contains 2257 individual fault traces with on average one throw reading available for every 82 m of fault trace recorded throw values range from 10 cm to 180 m and fault trace lengths from 10 m to 12 km two sets of normal faults nw and ne striking are present together with local wnw striking dextral strike slip zones size populations are power law over at least 2 5 orders of magnitude and the exponents of the throw maximum throw and fault trace length population curves are interrelated and taking into account the effects of resolution on trace length populations are internally consistent derivatives of the primary map reproduce resolutions typical of offshore seismics and illustrate the limitations of seismic data power law fault size distributions provide a basis for sub seismic fault prediction for this data set a fault throw resolution of better than 10 m would be required to provide an accurate prediction of the throw population down to ca 0 6m

fault populations and their relationship to the scaling of surface roughness the relationship between the scaling properties of faulted geological surfaces and parameters describing the underlying fault population are investigated using simulations of a dip slip faulted surface analysis of multiple simulations of sections through the surface allowed the construction of a statistical relationship between the parameters defining the fault population and the fractal dimension of the surface the results indicate a direct if complex relationship between the fault population and the scaling of the surface roughness the main determining factor is the displacement distribution with spacing and dip having only a minor contribution this relationship is tested against examples from the moray firth scotland and the central indian ocean

the influence of the evolution of the pyrenees on adjacent basins abstract important thicknesses of syn and post orogenic sediments are observed in the southern part of the aquitaine basin and in the north of the ebro basin their deposition cannot be explained only as a result of the extensional history of the early cretaceous thus the influence of the compression associated with the pyrenees formation upon the subsidence of these basins is studied europe and iberia are considered to behave as two semi infinite elastic plates the evolution through time of the sedimentary thicknesses is explained by the deflections of these two plates induced not only by the topographic load of the pyrenees but also by additional forces 10 12 n m that may have their origin in the formation of a cold lithospheric root during the shortening a series of calculations is presented for an approximately north south profile across the aquitaine basin the pyrenees and the ebro basin a good fit for the shape of the basins and the gravity anomalies was obtained with flexural rigidities of 1 5 10 23 nm for the northern plate and the outer part of the southern plate and 1 4 10 21 nm for the inner part of the southern plate

the nappe des marbres unit of the basque cantabrian basin the tectono thermal evolution of a fossil hyperextended rift basin the architecture of the pyrenean cantabrian belt results from the inversion of a series of former cretaceous rift basins a ht lp metamorphic event dated at 105 to 85 ma ago is commonly associated with an albo cenomanian episode of hyperextension of the continental crust this metamorphism is well known in the eastern basque cantabrian basin within the nappe des marbres unit nmu that is preserved from intense compressional deformation during the pyrenean orogeny based on a structural study at the scale of the eastern basque cantabrian basin bcb and on a dense sampling for trscm estimates with the rscm method raman spectrometry on carbonaceous material we show following results 1 the nmu has recorded two major phases of deformation related to a localized extensional ductile foliation s1 during the cretaceous rifting and later by the regional n s shortening recorded by a regional cleavage s2 observed only in shale sediments 2 the nmu is affected by early salt tectonics related to several diapirs and salt walls fed by the upper triassic evaporitic layer 3 the nmu recorded maximum temperatures exceeding 550 c which represent some of the highest temperatures along the pyrenees these new data demonstrate that there is no e w lateral metamorphic gradient across the belt and that hyperextension rifting occurred consistently within a high thermal regime 4 metamorphic isograds are oblique in respect of the main structures suggesting that the metamorphic event postdates most of the early salt related deformations prior to or coeval with early stages of rifting as it represents one of the best preserved example of pre orogenic hyperextended basin the eastern bcb record may be used regionally to better understand the rift to orogen evolution of the pyrenean internal metamorphic zone but also more generally as an analog of salt bearing hyper extended rift record

novel type of crust produced during continental rifting a normal oceanic crust cannot be generated after continental crust splitting of rifts filled by a thick pile of young sediments the magma released by the rising mantle is trapped mainly in these sediments as basalts sills and plugs the sediments are themselves metamorphosed by the heat flux from the underlying mantle a metasedimentary crust is formed in direct contact with an abnormal mantle vp 7 5 km s l produced by partial serpentinization

nonlinear interaction between ocean tides and the larsen c ice shelf system 1 we report on three gps records of flow of the larsen c ice shelf spanning 2 months to 2 years variations in speed are evident at periods from a few hours to 182 days including semi diurnal diurnal and 14 76 days at fortnightly periods the ice shelf varies by 10 from its long term speed but at diurnal timescales it is up to 100 a nonlinear relationship between ocean tides and velocity is required to explain the observed variations in flow as an initial examination we model flow as a non linear function of basal shear stress including tidal perturbations in the ice shelf grounding zone and show that the major features of the observations are reproduced notably the long period signal largely absent from the vertical tidal signal alternative explanations are discussed these observations demonstrate that the ice shelf system is highly sensitive to relatively modest changes in forcing at its boundaries

implications of new upb zircon chronology to early proterozoic crustal accretion in northern sweden abstract u pb ages ranging from 1 89 to 1 78 ga are reported for zircon populations formed during major magmatic events in the proterozoic development of northern sweden the studied area includes parts of the continental and the marine svecokarelian domains of the baltic shield the ages record crustal accretion and reactivation off the margin of an exposed archaean craton and show that magmatism was broadly coeval throughout the entire north swedish portion of the svecokarelian province irrespective of regions involved a detailed chronostratigraphy is presented for the skellefte district of northern sweden and comparisons are made with the evolution in other parts of the svecokarelian province two main magmatic phases commencing at 1 89 and 1 79 ga ago are recognized the first represents large scale volcanism and plutonism which in the skellefte district was characterized by the introduction of mainly mantle derived magmas or by magmas formed from rocks with short crustal residence time in the vicinity of the archaean craton some distance to the north the crust generating processes included the mobilization of archaean sources and appear to have continued until c 1 85 ga ago a relatively long period of consolidation and denudation separates this magmatic phase from the one at c 1 79 ga ago the generation of these later migmatite associated granites in the svecokarelian province coincided in time and was possibly associated with those processes which gave rise to the initial plutonism in the neighbouring transscandinavian granite porphyry belt