pliocene uplift of the eastern iberian margin inferences from quantitative modelling of the valencia trough we present the results of quantitative modelling of subsidence in the valencia trough and associated uplift in the catalan coastal ranges and the balearic islands basement subsidence moho depth and gravity anomalies are calculated for different effective elastic thicknesses eet and durations of rifting along two profiles constrained by recently collected multichannel seismic and gravity data the tectonic evolution of the catalan coastal ranges cannot be explained with traditional two layer lithospheric stretching models for the valencia trough but is consistent with a thermomechanical model invoking lithospheric necking combined with a late stage uplift event the modelling of the topography of the balearic islands suggests an interaction of extension in the valencia trough with extension in the south balearic basin our study supports a rifting model with low values for the flexural rigidity an intermediate level of necking and one finite duration stretching event propagating from the northeast towards the southwestern part of the valencia trough the modelling provides constraints on the magnitude of a large scale pliocene uplift of the eastern margin of the iberian peninsula

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

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

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

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

tethys atlantic interaction along the iberia africa plate boundary the betic rif orogenic system abstract initial se dipping slow subduction of the ligurian tethys lithosphere beneath africa from late cretaceous to middle oligocene twisting to a later faster e dipping subduction of the subcrustal lithosphere is proposed as an efficient geodynamic mechanism to structure the arcuate betic rif orogenic system this new subduction related geodynamic scenario is supported by a kinematic model constrained by well dated plate reconstructions tectonic sedimentary and metamorphic data sets the slow initial se dipping subduction of the ligurian tethys realm beneath the malaguide upper plate unit is sufficient to subduct alpujarride and nevado filabride rocks to few tens of kilometers of depth in middle eocene times the shift from se to e dipping subduction during latest oligocene early miocene was possibly caused by both the inherited geometry of the highly segmented ligurian tethys domain and by the fast roll back of the subducted lithospheric slab the early miocene rather synchronous multiple crustal and subcrustal processes comprising the collision along the betic front the exhumation of the hp lt metamorphic complexes the opening of the alboran basin its flooring by hp alpujarride rocks and subsequent ht imprint can be explained by the fast nw and w directed roll back of the ligurian tethys subcrustal lithospheric slab the w retreat of the ligurian tethys lithosphere in middle late miocene times could partly explain the initiation of its lateral tear and consequent subcrustal processes from latest miocene onward the betic rif system evolved under both the northerly push of africa resulting in tightening at crustal and subcrustal levels and by the distinct current dynamics of the steep lithospheric slab the sw directed scape of the rif fold belt is one of the most striking evidences linked to the recent evolution of the squeezed betic rif system between africa and iberia

temporal changes in coda q 1 and b value due to the static stress change associated with the 1995 hyogo ken nanbu earthquake the seismicity in the tamba region northeast of the hyogo ken nanbu earthquake in japan january 17 1995 mjma 7 2 increased significantly following this earthquake this increase suggests that the static stress change due to a large earthquake causes a change in the crustal condition or dynamics in order to reveal the changes quantitatively we investigate the temporal variation in coda q l and b value in the tamba region we analyze the waveform data of many shallow microearthquakes m 1 5 3 0 in the region recorded in a period from 1987 to 1996 coda q 1 is estimated in 10 frequency bands in a range of 1 5 24 hz based on the single isotropic scattering model at frequencies between 1 5 and 4 0 hz the temporal variation in coda q 1 shows significant correlation with the occurrence of the hyogo ken nanbu earthquake coda q l increases after the event a variation in b value whose sign is opposite to that of coda q 1 is recognized the fracture dimensions of microearthquakes that contribute to the variation in b value are estimated to be 400 m this scale length is consistent with the characteristic scale length of scatterer 300 600 m which contributes effectively to a temporal variation in coda q 1 the crustal activity in the tamba region is possibly controlled by the heterogeneity with dominant scale of 102 m the stress sensitivity of the coda q 1 change is estimated to be 10 mpa 1 this value is an order of magnitude larger than the stress sensitivity of seismic velocity reported before

thermochronology constraints for the propagation sequence of the south pyrenean basement thrust system france spain 1 in this work we combined apatite fission track and biotite k feldspar 40ar 39ar ages with tectonic data in the west central part of the axial zone of the pyrenees we discuss the exhumation ages and rates of the neouvielle bordere louron and bielsa variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the pyrenean orogenic prism the 40ar 39ar ages on k feldspars from the neouvielle massif sample nv7 seem to indicate tectonic movements on the eaux chaudes thrust during the early middle eocene fission track results suggest that the exhumation of the neouvielle massif occurred around 35 ma and exhumation of the bordere louron massif around 32 ma in relation to thrusting on the gavarnie thrust the bielsa massif was exhumed from around 19 ma by out of sequence movements on the bielsa thrust we thus show that whereas most of the pyrenean basement thrust faults here the eaux chaudes gavarnie and guarga thrusts were active in sequence toward the southern foreland from the early eocene to the earliest miocene some of them here the bielsa thrust were activated out of sequence in the hinterland later than the generally accepted aquitanian age for the end of the pyrenean compression finally the apatite fission track modeling indicate a last cooling episode starting around 5 ma which is most certainly related to the pliocene reexcavation of the southern and northern flanks of the pyrenees

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

retro wedge foreland basin evolution along the ecors line eastern pyrenees france the eastern aquitaine basin and north pyrenean zone show many characteristics of retro wedge models however they differ significantly in that slow subsidence and low deformation continued throughout orogenesis so that growth and steady state phases cannot be distinguished we show that the eastern pyrenees record two clear phases of convergence and probably never attained steady state analysis of the aquitaine retro foreland basin along the ariege ecors deep seismic line eastern french pyrenees integrates a new litho and chronostratigraphy subsidence analysis low temperature thermochronology data new interpretations of seismic lines and a balanced cross section within an overall regression two shallowing up cycles latest santonian danian thanetian oligocene record slow tectonic subsidence of the eastern aquitaine basin separated by a quiet period continuing thick skinned shortening was low to moderate the early marine basin generated by loading of the weak extended margin was supplied axially from an unknown eastern edifice while the young pyrenean orogeny to the south remained submerged during the quiet period of ultra slow subsidence no basin migration and negligible sediment supply continental conditions characterized the eastern orogen the second marine transgression was quickly followed by continental conditions the basin was supplied by the now emerging pyrenean orogen and continued to subside until miocene time

regional scale cretaceous albitization in the pyrenees evidence from in situ u th pb dating of monazite titanite and zircon abstract albitization is a common metasomatic process active in various geodynamic contexts in the northern pyrenees there are several occurrences of albitites but until now only one occurrence has been dated 117 ma ar ar dating this paper presents new u th pb ages for several albitite occurrences throughout the pyrenees to test whether they are contemporaneous and if so to specify the regional extent of the albitization event ages obtained from large euhedral titanite and monazite grains from distinct albitites are 110 8 and 98 2 ma respectively the zircon u th pb isotopic system did not record this cretaceous metasomatic event even when grains were selected in metasomatically zr enriched rocks or in hydrothermal structures millimetre sized veins cross cutting granitoids we argue that the total time span of 20 ma recorded by albitites corresponds to a long lived hydrothermal system that was active during the rotation of iberia around europe along the north pyrenean fault because albitization and talc mineralization have the same spatial and temporal distribution in the pyrenees we argue that these two metasomatic phenomena are two independent records of this single regional scale long lived hydrothermal system

the western alps from the jurassic to oligocene spatio temporal constraints and evolutionary reconstructions abstract despite extensive research in the last 150 years the regional tectonic reconstruction of the western alps has remained controversial the curved orogenic belt consists of several ribbon like continental terranes sesia austroalpine internal crystalline massifs brianconnais which are separated by two or more ophiolitic sutures piemonte valais antrona lanzo canavese high pressure hp metamorphism of each terrane occurred during distinct orogenic episodes at 65 ma in the sesia austroalpine at 45 ma in the piemonte zone and at 35 ma in the internal crystalline massifs it is suggested that these events reflect individual accretionary episodes which together with kinematic indicators and the speed and direction of plate motions provide constraints for the discussed reconstruction model the model involves a prolonged orogenic history that took place during relative convergence of europe and adria here considered as a promontory of the african plate the first accretionary event involved the sesia austroalpine terrane final closure of the piemonte ocean occurred during the eocene 45 ma and involved ultra high pressure uhp metamorphism of the piemonte oceanic crust incorporation of the brianconnais terrane in the accretionary wedge occurred thereafter possibly during or after subduction of the valais ocean in the late eocene 45 35 ma this subduction was terminated at ca 35 ma when the internal crystalline massifs i e the assumed internal parts of the brianconnais terrane were buried into great depths and underwent hp and uhp metamorphism

integrated prestack depth migration of vertical seismic profile and surface seismic data from the rocky mountain foothills of southern alberta canada we have developed an anisotropic prestack depth migration code that can migrate either vertical seismic profile vsp or surface seismic data we use this migration code in a new method for integrated vsp and surface seismic depth imaging instead of splicing the vsp image into the section derived from surface seismic data we use the same migration algorithm and a single velocity model to migrate both data sets to a common output grid we then scale and sum the two images to yield one integrated depth migrated section after testing this method on synthetic surface seismic and vsp data we applied it to field data from a 2d surface seismic line and a multioffset vsp from the rocky mountain foothills of southern alberta canada our results show that the resulting integrated image exhibits significant improvement over that obtained from a the migration of either data set alone or b the conventional splicing approach the integrated image uses the broader frequency bandwidth of the vsp data to provide

in situ la icp ms u pb titanite dating of na ca metasomatism in orogenic belts the north pyrenean example in the pyrenees in association with the rotation of the iberian plate around europe during the mid cretaceous a na ca metasomatism is recognized as a complementary record of the hydrothermal activity that led to na metasomatism albitization and talc chlorite mineralization it affected metasedimentary rocks as well as hercynian granites in situ laser ablation icp ms u pb analyses of titanite grains formed in albitites during metasomatism date the na ca metasomatism between 110 and 92 ma the temperature of the na ca metasomatism is estimated to be approximately 550 c both the time constraints and temperature estimates suggest that the na ca metasomatism is related to the low p high t north pyrenean metamorphism

foreland basin subsidence driven by topographic growth versus plate subduction the subsidence of foreland basins is classically thought to accelerate with time however a synthesis of data from numerous foreland basins recognizes a wide range of signals and rates our analysis investigates the influence of two broadly ubiquitous controlling factors 1 the upward and outward growth of mountain topography and 2 the subduction velocity of the underthrust lithosphere these two factors have contrasting subsidence signals the former tends to be slow and decelerates while the latter is more rapid and accelerates the geodynamic setting of a foreland basin determines the degrees to which these components dominate the final signal of tectonically induced subsidence in small collisional mountain ranges the common asymmetry of subduction defines a pro and a retro foreland basin based on model experiments and the synthesized data we demonstrate that pro foreland basins exhibit short lived usually 0 05 km m y 1 accelerating subsidence histories recording only a portion of the orogenic history of the mountain range type examples are the carpathian foredeep and the north alpine foreland basin in contrast retro foreland basins are characterized by relatively slow 0 05 km m y 1 protracted usually 40 m y subsidence that records the majority of the orogenic history a good example is the aquitaine foreland basin retro arc foreland basins such as the alberta basin appear comparable to collisional retro foreland basins examples where there is more protracted subsidence appear to record greater evidence of episodic loading and unloading as the topography of the range grows or shrinks in response to the balance between crustal thickening and erosion rates

thermal control on the modes of crustal thinning leading to mantle exhumation insights from the cretaceous pyrenean hot paleomargins the pre rift mesozoic sequences of the cretaceous passive margins fossilized in the north pyrenean zone npz are characterized by high temperature deformation in relation with thinning of the continental basement our compilation of chronological and geological data confirms a clear correlation between the distribution of the highest paleotemperatures in the pre rift sedimentary cover and the loci of extreme crustal stretching geological evidences such as the occurrence of peridotite bodies directly underlying metamorphic pre rift sediments indicate an early attenuation of the rifted continental crust this leads us to propose a mechanism of rifting involving boudinage of the continental crust the lateral extraction of the paleozoic basement occurred under the pre rift cover that is decoupled on the triassic clays and evaporates the thermal conditions allowing coeval ductile deformation of the crust and of the pre rift sediments leaded to the widening of basins devoid of large faulted blocks we discuss the implications on the origin and significance of the granulites and the relations between flysch deposition and high temperature metamorphism of the pre rift sediments in the npz albian cenomanian flysch sequences were deposited synchronously with the syn metamorphic ductile deformation of the pre rift sequences since the base of the flysch deposits also recorded locally the high temperature tectonic event we propose an original mechanism for the evolution of the basins involving continuous deformation of the pre rift metamorphic sediments at the scale of the pyrenean domain our results suggest a strong lateral variability in the tectonic style of passive margins in direct link with their thermic pattern

preorogenic exhumation of the north pyrenean agly massif eastern pyrenees france 1 the pyrenees north of the north pyrenean fault display a complex structure involving a succession of peridotite massifs basement massifs and mid cretaceous to late cretaceous basins located in a narrow domain which was affected by a mid cretaceous preorogenic high temperature low pressure metamorphism the late cretaceous basins were interpreted either as pull apart basins formed during transcurrent motion of iberia relative to eurasia or as remnants of a larger extensional basin recent models support that peridotite massifs result from the exhumation of the mantle during this preorogenic event the northern boundary of the agly basement massif shows evidence of ductile deformation of the basal formations of the agly sedimentary cover macroscopic and microscopic kinematics indicators consistent with asymmetry of crystallographic fabrics suggest normal sense of shear and thus suggest detachment at least partial of the mesozoic cover from its basement triassic to early cretaceous limestones are mylonitic and consistently shows a foliation a ns to ne trending lineation shear criteria suggesting top to the north shearing and locally boudinage at the microscopic scale mylonites are characterized by a very fine grain size frequently 10 m they contain larger partially recrystallized calcite parent grains and undeformed quartz grains with calcite fringes crystallized in pressure shadows in these mylonites calcite systematically shows a weak but well defined crystallographic preferred orientations suggesting ht dislocation creep combined to diffusion creep and possibly grain boundary sliding in the finest fraction of the mylonites paleotemperatures determined using raman spectrometry suggest synkinematic temperature conditions in the range 340 390 c in good agreement with observed microstructures and calcite cpo the mylonitic fabric in mesozoic limestones is folded by ew trending pyrenean folds north of the agly basement massif attesting that this fabric formed before the pyrenean orogeny these data consistently support preorogenic extension under medium temperature conditions of the northern agly massif and likely of the massif itself since simultaneously 100 ma a mid cretaceous basin opened south of the basement massif we suggest a model of preorogenic exhumation of the agly massif in response to the regional extension associated to the rotation of iberia this model may explain the exhumation of the north pyrenean massifs during a single preorogenic event that allowed the opening of extensional basins and the exhumation of the lithospheric mantle all these structures being subsequently reworked during the pyrenean orogeny

quantification and restoration of extensional deformation along the western iberia and newfoundland rifted margins 1 many recent papers describe the structure of the iberia and newfoundland rifted margins however none of them propose kinematic restorations of the complete rift system to quantify the amount of extension necessary to exhume mantle and initiate seafloor spreading in our study we use two pairs of cross sections considered as conjugate lines one across the galicia bank flemish cap and the other across the southern iberia abyssal plain flemish pass both transects have been imaged by reflection and refraction seismic methods and have been drilled during ocean drilling program legs 103 149 173 and 210 drilling penetrated parts of the rift stratigraphy and the underlying basement the cross sections can therefore be considered as the best documented conjugate transects across present day hyperextended magma poor rifted margins the aim of this paper is threefold 1 provide a detailed description of the crustal architecture of the two conjugate sections 2 define the extensional structures and their ages and 3 quantify the amount of strain and strain rate accommodated along these lines this paper proposes a quantitative description of extension along the iberia newfoundland rift system and discusses the limitations and problems in quantifying extensional deformation along hyperextended rifted margins

hydrophone vsp imaging at a shallow site we evaluated the capabilities of vertical seismic profiling vsp for imaging the complex heterogeneous unconsolidated sedimentary structures at a shallow site we deployed a 24 level hydrophone array with 0 5 m level spacing down a preexisting poly vinyl chloride pvc cased well data acquisition time was quick only 15 multioffset shot points using a hammer on plate source were needed to acquire reflection data between the water table at 3 m and the bedrock at 35 m to produce a depth section image this image extended 9 m from the receiver well yielding resolutions between fresh water bearing sands and impermeable muds and clays of better than 1 m depth accuracy of the image was confirmed by good correlation with cone penetrometer logs we used conventional wavefield separation and vsp cdp mapping techniques to image the data tube waves created by seismic arrivals at cross sectional area changes in the borehole fluid column were the primary source of coherent noise in the data the tube wave arriv

reduced time migration of transmitted ps waves we develop the novel theory of transmitted ps migration and show that ps transmitted arrivals in a gulf of mexico vertical seismic profile vsp data set can be migrated to accurately image a salt sheet even though the receiver array is below the transmitting boundary we also show that migrating transmitted arrivals is effective in illuminating the base of an orebody invisible to pp reflections in general interfaces that bisect wavepath propagation i e the source and receiver are on opposite sides of the interface and therefore invisible to pp reflections can be imaged by migration of ps transmitted waves these results suggest that migration of ps transmitted waves opens new opportunities in imaging nearly vertical impedance boundaries that are typically invisible to conventional reflection imaging of crosswell and vsp data we also present a new interferometric method denoted as reduced time migration which uses the arrival time difference between the direct p wave and subsequent events to incre

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

cretaceous albitization and dequartzification of hercynian peraluminous granite in the salvezines massif french pyrenees abstract the salvezines massif in northern french pyrenees has undergone extensive albitization the massif consists of gneisses and a leucogranite hosted in paleozoic sediments schists and carbonates the leucogranite was emplaced at the end of the hercynian orogeny the granite underwent monazite fractionation during magmatic stages which induced lowering of ree and th contents in the most evolved rocks hydrothermal alteration during late magmatic stages is also identified through the development of a tetrad effect in the ree patterns of the granite and through the fractionation of ratios like zr hf out of the charac charge radius controlled range the granite underwent partial to complete sub solidus albitization progressive metasomatic overprint induced metasomatic replacement of feldspars into albite and dissolution of quartz episyenitization together with new albite formation hydrothermal muscovite with a sheaf like structure sometimes crystallised in albitites inherited muscovites from magmatic stage and newly formed muscovites from albitites have distinct chemical compositions with the latter being much more phengitic the initial peraluminous chemistry of the leucogranite was lost during albitization and composition evolved towards a pure albite one a cnk 1 albitization induced gains in na and al and losses in si and k leaching of ree and u is also identified during albitization as well as the non charac behaviour of some elements 18o values of quartz and muscovite in albitized granites are in the magmatic range about 12 and 9 5 respectively feldspars acquired high 18o values during albitization up to 15 muscovite grains from albitites have higher 18o values than inherited ones and tend towards isotopic equilibrium with albite the albitizing fluids have interacted with high 18o rocks probably local carbonates prior to alter granite muscovites inherited from magmatic stages display very characteristic disturbed 39ar 40ar age spectra with saddle shapes when a muscovite associated with albitization provided a plateau age at 117 5 ma for this alteration event albitization in the salvezines massif just preceded the regional talc chlorite hydrothermal mineralization both events might then represent two outward signs of a huge hydrothermal system at the time of the rotation of the iberian plate around europe the north pyrenean metamorphism is identified by 39ar 40ar analyses at ca or younger than 100 ma

high resolution imaging of the pyrenees and massif central from the data of the pyrope and iberarray portable array deployments the lithospheric structures beneath the pyrenees which holds the key to settle long standing controversies regarding the opening of the bay of biscay and the formation of the pyrenees are still poorly known the temporary pyrope and iberarray experiments have recently filled a strong deficit of seismological stations in this part of western europe offering a new and unique opportunity to image crustal and mantle structures with unprecedented resolution here we report the results of the first tomographic study of the pyrenees relying on this rich data set the important aspects of our tomographic study are the precision of both absolute and relative traveltime measurements obtained by a nonlinear simulated annealing waveform fit and the detailed crustal model that has been constructed to compute accurate crustal corrections beneath the massif central the most prominent feature is a widespread slow anomaly that reflects a strong thermal anomaly resulting from the thinning of the lithosphere and upwelling of the asthenosphere our tomographic images clearly exclude scenarios involving subduction of oceanic lithosphere beneath the pyrenees in contrast they reveal the segmentation of lithospheric structures mainly by two major lithospheric faults the toulouse fault in the central pyrenees and the pamplona fault in the western pyrenees these inherited hercynian faults were reactivated during the cretaceous rifting of the aquitaine and iberian margins and during the cenozoic alpine convergence therefore the pyrenees can be seen as resulting from the tectonic inversion of a segmented continental rift that was buried by subduction beneath the european plate

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

mantle exhumation crustal denudation and gravity tectonics during cretaceous rifting in the pyrenean realm sw europe insights from the geological setting of the lherzolite bodies 1 the pyrenean peridotites lherzolites form numerous small bodies of subcontinental mantle a few meters to 3 km across exposed within the narrow north pyrenean zone npz of mesozoic sediments paralleling the north pyrenean fault recent studies have shown that mantle exhumation occurred along the future npz during the formation of the albian cenomanian pyrenean basins in relation with detachment tectonics this paper reviews the geological setting of the pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the bearn region only two types of geological settings have to be distinguished among the pyrenean ultramafic bodies in the first type sedimented type or s type the lherzolites occur as clasts of various sizes ranging from millimetric grains to hectometric olistoliths within monogenic or polymictic debris flow deposits of cretaceous age reworking mesozoic sediments in dominant proportions as observed around the lherz body in the second type tectonic type or t type the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed triassic rocks and have fault contacts with units of deformed jurassic and lower cretaceous sediments belonging to the cover of the npz these deformed mesozoic formations are not older that the aptian early albian they are unconformably overlain by the albian cenomanian flysch formations and have experienced high temperature low pressure mid cretaceous metamorphism at variable grades such a tectonic setting characterizes most of the lherzolite bodies exposed in the western pyrenees these geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the mesozoic cover in the preorogenic evolution of the pyrenean realm in the light of such evidence a simple model of basin development can be inferred involving extreme thinning of the crust and mantle uprising along a major detachment fault we demonstrate coeval development of a crust mantle detachment fault and generalized gravitational sliding of the mesozoic cover along low angle faults involving triassic salt deposits as a tectonic sole this model accounts for the basic characteristics of the precollisional rift evolution in the pyrenean realm

thrust sequences in the eastern spanish pyrenees detailed mapping of the south pyrenean zone in the eastern spanish pyrenees shows that a great number of alpine thrusts affect the basement and the cover the geometry of the thrust structures and their propagation sequence can be interpreted from balanced sections the folding dies out downwards from the higher thrust sheets to the lower ones and demonstrates a piggy back thrusting sequence these thrusts form a duplex the sole thrust of this duplex is the vallfogona thrust the roof thrust is rooted somewhere within the axial zone the thrusts climb southwards from the axial zone basement up into tertiary cover sediments these thrusts have been folded so that they now dip to the south and form the southern side of the axial zone antiformal stack locally smaller antiformal stacks developed and produced strong folds in the higher thrust sheets the south pyrenean zone studied is equivalent to the gavarnie nappe and the connection between them below the detached south pyrenean central unit may be the nogueres zone

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

gravity anomaly map of the pyrenean region and a comparison of the deep geological structure of the western and eastern pyrenees abstract a gravity anomaly map based on over 13 000 observations accurately delineates the major features of the pyrenean region an extensive gravity anomaly low in the south of the region appears to result from crustal thickening associated with the pyrenean mountain building episode several large positive gravity anomalies are apparent in the north pyrenean zone in the centre and west of the mountain chain but are absent in the east the interpretation of a series of gravity anomaly profiles along the pyrenees has been controlled by existing geophysical data the interpretations confirm the cause of the southern gravity anomaly low as thickened iberian crust and demonstrate as shown by previous seismic investigations that the transition to much thinner european crust is quite abrupt the sources of the positive anomalies in the north pyrenean zone are bodies in the upper crust with densities too high to be explained in terms of crustal materials these are interpreted as segments of upper mantle that originated in transtensional n s separation across the north pyrenean fault and were emplaced at shallow levels by thrusting during pyrenean orogenesis this is the first time that evidence has been presented for the presence of such mantle bodies in the pyrenees it is suggested that their absence in the east is caused by less extension between iberia and europe in this region during the transform motion between them prior to orogenesis allowing only limited ascent of deep material the greater extension in the west would have allowed the ascent of upper mantle into the space between iberia and europe which would have been further elevated during the thrusting associated with pyrenean orogenesis

considerations for high resolution vsp imaging vertical seismic profiling vsp data can complement surface seismic data where higher resolution is desired or necessary to fully understand a reservoir vsp data typically provide greater resolution because of the inherently smaller fresnel zone and because the bandwidth is usually wider than comparable surface seismic data high fidelity images are required for effective reservoir monitoring also special situations exist such as attempting to image beneath salt or volcanics where vsp data can potentially yield superior results because the seismic energy travels through the distorting overburden only once

evaluating balanced section restoration with thermochronology data a case study from the central pyrenees we present a new method that can be used to quantitatively evaluate the consistency between balanced section restorations and thermochronological data sets from orogenic belts we have applied our method to a crustal scale area balanced cross section restoration along a profile in the central pyrenees this restoration is well constrained and supported by a wide variety of geological and geophysical data moreover an extensive thermochronological data set has been collected independently in the area we use the structural kinematic software 2d move to constrain a set of velocity fields that describes the kinematics of the central pyrenees using these velocity fields as input for the thermokinematic code pecube we derive predictions of the thermal history and a range of thermochronometric ages for the modeled area we find that the kinematic history of the belt as inferred from section balancing is in good agreement with the published thermochronological data high temperature zircon fission track and k feldspar ar ar data constrain the thermal structure of the belt as well as the timing of underplating low temperature apatite fission track and u th he data require late synorogenic sedimentary burial of the southern flank of the pyrenees between late eocene 40 ma to late miocene 9 ma times consistent with previous studies and imply that no such burial occurred on the northern flank

asymmetric growth of the pyrenees revealed through measurement and modeling of orogenic fluxes orogenic asymmetry is ubiquitous in terms of topography structure and metamorphism but the relative influences of climate and tectonics in determining such asymmetry remain contentious this study demonstrates that for the case of the european pyrenees orogenic asymmetry is not defined by inherited structural asymmetry nor by orographic asymmetry of precipitation but is the simple consequence of the inherent tectonic growth of a doubly vergent orogen the pyrenees record approximately 60 myr of upper crustal accretion erosion and sedimentation that developed from late cretaceous to early miocene times approximately 165 km of plate convergence was accommodated by four phases of orogenic growth that can be summarized in terms of their generic orogenic development as follows 1 early inversion of passive margin extensional faults initiating the pro wedge 2 growth by a combination of frontal accretion and underplating to the pro wedge symmetrical and steady record of erosion and foreland basin sedimentation 3 cessation of pro wedge frontal accretion with propagation of the retro wedge deformation front 4 accelerated growth of pro wedge antiformal stack induced by underplating accelerated erosion over antiformal stack and increase in sediment discharge to pro foreland basin stabilization of outer pro wedge by sediment blanketing discrete element model experiments are used to explore the natural tendency of the system towards asymmetry model output demonstrates that during active frontal accretion to the pro wedge of an orogen the maxima in erosional denudation is offset towards the pro wedge relative to the maximum depths of exhumation this asymmetry is fundamentally driven by the progressive reduction in advection velocities of material within the orogen from the pro wedge into the retro wedge hence for an efficient erosional regime a dynamic coupling between erosion and structural uplift of the pro wedge will reduce activity of the retro wedge and hence drive asymmetry in terms of low temperature thermochronometry erosion and sedimentation the models also demonstrate the tendency for pro wedge growth through frontal accretion to slow however the cessation of frontal accretion as recorded by the south pyrenean thrust belt phases 3 and 4 requires additional forcing it is proposed that the thick wedge top sedimentation recorded at this time increased taper angles and hence stabilized the wedge accretionary influx into the orogen at this time was accomplished through underplating these processes governing asymmetry do not require a spatially variable climate or a laterally heterogeneous underthrust plate

seismic imaging in the krafla high temperature geothermal field ne iceland using zero and far offset vertical seismic profiling vsp data abstract among geothermal exploration methods active surface seismic methods have played only a minor role to date especially in high temperature volcanic systems reflection seismic data often reveal poor delineation of volcanic features due to the internal heterogeneity of volcanic sequences to enhance the vertical resolution one possibility is the application of downhole seismic methods like vertical seismic profiling vsp a test experiment was carried out in the krafla high temperature geothermal field ne iceland to assess the ability of vsp to image subsurface structures such as fractures zones of high permeability magmatic bodies and zones of supercritical fluids and steam logging in such hostile environments is technical challenging in many aspects but mainly due to the high temperature impact on the downhole electronic components of the measuring equipment this requires a thorough pre examination and implementation of the measurement especially to avoid delays and tool failures this paper presents results of zero and far offset vsp data from the k 18 borehole from within the krafla caldera which reveal good correlation with the surrounding lithology the raw three component seismic data display a good signal to noise ratio and dominant signal frequencies between 20 and 40 hz down to c 2200 m depth for air gun and explosive sources respectively a zero offset source comparison was also conducted to assess the use of different impulsive sources for future vsp surveys in similar settings by applying a standard vsp processing we identified stratigraphic boundaries between lavas hyaloclastites and intrusions which are in good agreement with existing well data for the zero offset vsp both p and s wave velocity models were calculated and a depth converted corridor stack was determined in addition multicomponent kirchhoff depth migration and fresnel volume migration were tested around the borehole the 3d results are promising but the specific shape and lateral extent of the reflectors could not be determined due to the restriction to only two sources and the insufficient spatial coverage aperture our study demonstrates that vertical seismic profiles can clearly detect variations in the subsurface volcanic stratigraphy in high temperature geothermal fields a more detailed reservoir characterization can be achieved by further data integration enhanced survey design including more source positions and improved processing and imaging techniques such as full waveform inversion

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget