estudio sismico de la corteza iberica norte 3 3 a seismic image of the variscan crust in the hinterland of the nw iberian massif an offshore vertical incidence reflection seismic study with simultaneous on land wide angle recording has been conducted as part of the estudio sismico de la corteza iberica norte escin project

phosphorites co rich mn nodules and fe mn crusts from galicia bank ne atlantic reflections of cenozoic tectonics and paleoceanography a wide variety of marine mineral deposits were recovered from 750 to 1400 m water depths on galicia bank iberian margin mineral deposits include 1 carbonate fluorapatite phosphorite slabs and nodules that replaced limestone and preserved original protolith fabric 2 ferromanganese vernadite crusts with high mn and fe mn fe 1 contents and thick stratabound layers consisting mainly of mn up to 27 mno and fe 15 fe2o3 which impregnated and replaced the phosphorite 3 co rich mn nodules are composed of romanechite and todorokite laminae mn rich layers up to 58 mno contain up to 1 8 co 4 goethite nodules with fe up to 67 fe2o3 have low mn and trace metals we interpret this mineralization paragenesis to be related to major changes in oceanographic and tectonic regimes three phosphatization generations formed hardgrounds dated by 87sr 86sr isotopes as late oligocene early miocene and latest early miocene during the latest early miocene the hardground was fractured and breached due to regional intraplate tectonism which was coeval with a widespread regional erosional unconformity the stratabound layers and co rich manganese nodules were derived from low temperature geothermally driven hydrothermal fluids with fluid conduits along reactivated faults during middle and late miocene the introduction of vigorous deep water flow from the arctic generated growth of hydrogenetic ferromanganese crusts finally growth of diagenetic fe rich nodules late pliocene was promoted by the introduction of hypersaline mediterranean outflow water into the atlantic ocean

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

the hercynian crust in northwestern spain a seismic survey abstract in summer 1982 a network of crustal seismic profiles was established in nw spain with shotpoints at sea and on land some profiles were designed to capture the general features of the crust whereas others were aimed at resolving the detailed structure of specific geological features the interpretation of three profiles aimed at the most important features of the earth s crust in northwest spain is discussed here the crust consists of three layers with compressional velocities of 6 0 6 1 km s 6 2 6 3 km s and 6 7 6 9 km s the thicknesses of these layers vary laterally the average values under the central part of galicia being 13 km 8 km and 10 km the fine structure of the lower crust has still to be determined so far lateral variations in the velocity structure of the lower crust from a constant velocity layer to a gradient layer have been detected along the main profile from ne to sw over a distance of 250 km the moho discontinuity is reached at 30 32 km in the central part of the surveyed area this decreases to 23 27 km to the north and to the west on the basis of pmp amplitudes the moho seems to be rather sharp the pn velocity is close to 8 3 km s which is slightly above the normal value elsewhere in hercynian europe the crustal structure is remarkably similar to other hercynian domains particularly brittany the massif central and the central iberian massif

assessment of bedload equations using data obtained with tracers in two coarse bed mountain streams narcea river basin nw spain abstract this paper evaluates the predictive power of nine bedload equations comparing the results provided by the equations with the bedload rates obtained in a previous field based tracer experiment accomplished in river piguena and river coto two coarse bed streams from nw spain rivers from nw spain draining the northern watershed of the cantabrian mountain range flow into the bay of biscay in a short path 50 60 km in this region they are developed forested catchments featured by fluvial networks with relatively steep slopes single thread sinuous channels and where bed sediment is typically coarse cobble and gravel tagged stones were used to trace bed sediment movement during flood events in river piguena and river coto the two main tributaries of the narcea river basin with the tracer results bedload transport rates between 0 2 and 4 0 kg s were estimated for six flood episodes the tracer based bedload discharges were compared with the bedload rates estimated with the bedload formulae duboys straub schoklitsch meyer peter muller bagbold einstein parker klingeman mclean parker klingeman parker and wilcock crowe our assessment shows that all of the bedload equations tend to overestimate when compared with the tracer based results with the wilcock and crowe 2003 equation the only exception in river piguena we linked these results to the particular geomorphology of coarse bed rivers in humid and forested mountain environments within these rivers armored textures and structural arrangements in the bed are ubiquitous these features together with a low sediment supply coming from upstream forested reaches define a supply limited condition for these channels limiting the potential use of bedload equations the wilcock and crowe 2003 equation introduces complex corrections into the hiding function and this could explain why it performs better

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

effect of unbalanced topography and overloading on coulomb wedge kinematics insights from sandbox modeling 1 this study addresses the effect of variable unbalanced topography and overload on the kinematics of a fold and thrust belt developed within a collisional belt that underwent a subduction polarity reversal event this was done by physical modeling of doubly vergent coulomb wedges using sand as an analogue material during the experimental procedure a preexisting topography was generated by a first phase of subduction in one direction a second phase of subduction was then initiated in the opposite direction simulating a subduction flip an anomalous strong frontal growth for the wedge during the second phase was experimentally shown to be dependent upon surface slope breaks and the critical asymmetrical architecture achieved by the wedge at mature stages of deformation the latter is suggested to be the rule for doubly vergent orogens at steady state even after a subduction flip during the experiments surface processes like syntectonic erosion and sedimentation markedly altered mass transfer within the wedge in particular lowering the surface slope by syntectonic erosion favored cycling between accretion and underthrusting modes by contrast a sudden syntectonic sediment load in the prowedge region promoted prolonged phases of underthrusting retarding accretion of new imbricates at the prowedge toe however at later stages of deformation the prowedge was forced to regain its characteristic minimum critical taper as predicted by theory and did so by the sudden nucleation of long flat thrust units rapidly rebalancing the asymmetry between prowedge and retrowedge regions the experiments suggest that given a fixed critical taper related to time invariant frictional properties along the wedge bounding surfaces deformation does vary within the wedge according to time varying location of normal stress surpluses and unbalanced topography acting on potential failure surfaces these in turn alter the equilibrium between prowedge and retrowedge basal detachments that is here considered to be a major factor controlling the self regulating dynamics of collisional orogens

seismotectonics of the nubia plate compressive margin in the south tyrrhenian region italy clues for subduction inception 1 seismological and structural data are used to constrain the active tectonics of the nubia plate compressive margin in southern italy in this region compressional displacements have resumed at the rear of the maghrebian orogenic wedge since about 700 500 ka and are presently accommodated along a seismic belt in the south tyrrhenian area where a passive margin has developed during late neogene quaternary times earthquake data from the south tyrrhenian belt are analyzed with bayloc a probabilistic nonlinear location method results show that the seismic belt is segmented and involves a series of ne sw and nw se elongated clusters the ne sw clusters are interpreted as high angle reverse fault zones verging toward the southeast whereas the perpendicular clusters are interpreted as possible strike slip fault zones transferring the contractional displacements to advanced segments of the belt in the southeast brittle deformations observed in the quaternary volcanic island of ustica are consistent with the geometry and kinematics of the seismic belt deduced from the seismological data the south tyrrhenian active belt may constitute an early stage of subduction of the tyrrhenian oceanic crust beneath sicily a similar scenario has been hypothesized also for the westward prolongation of the south tyrrhenian belt off the algerian coast by integrating instrumental and historical seismic data with tectonic evidences we infer that the south tyrrhenian belt is probably capable of producing earthquakes with a maximum size close to magnitude 7 the analyzed data suggest a multifault system behavior for the studied compressional belt this inference is important to estimate and mitigate the seismic and tsunamic hazards in such a densely populated region

estimation of surface roughness and stone cover in burnt soils using sar images abstract in many quartzitic slopes in the nw of the iberian peninsula there is a high topsoil stoniness which produces a random surface roughness the surface roughness is one of the control parameters in the signal of synthetic aperture radar sar images in this work we test the use of the sar images for distinguishing and mapping areas with different surface roughness which in this study correspond with areas with different surface stoniness in accordance with the geographic location the relief of the study area and the aims of the project jers and envisat sar images were used the images are characterized by the high view angles between 33 and 42 alternating polarization hh hv vv vh data and ascending and descending passes in order to describe the soil roughness various measuring methods were applied in plot parcels direct measurements of height of clasts and laser scanning and different roughness models were tested the results show that there are relation between sar signal dn and the soil roughness classes dn a b and the b parameter is correlated with the roughness the best fit between roughness model and sar data was found for mean standard deviation rms height of clasts once verified that the correlation between sar signal and surface roughness exists the envisat images were classified into three successive surface roughness classes in order to facilitate the classification principal components analysis were carried out over all polarization bands and the object oriented classification was applied to validate the accuracy of the sar images classification we elaborated by photointerpretation a surface condition map for an area of 10 700 ha the sar classification and photointerpreted map were compared for three classes surface without stones surface with stones low and medium stoniness and total cover of loose clasts the overall coincidence between the maps is about 70 besides large areas located in the northwest of the iberian peninsula suffer soil degradation caused by wildfires and the increase of surface stoniness is one of the effects described in the postfire erosion the influence of wildfires and the associated erosion is particularly important on quartzitic slopes partially covered by coarse grain supported deposits like the ones considered in this study the available data for the area of study suggest the high correlation between the different classes of surface roughness and stoniness obtained from sar imagery and the gradual different status of postfire soil erosion

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

compressional deformation at the ocean continent transition in the ne atlantic local zones of compressional deformation spatially coincident with the ocean continent transition occur in the ne atlantic off western iberia on the northern margin of the bay of biscay and in the southern rockall trough the deformation zones are typically broad oceanward facing monoclines several tens of kilometres in width the amount of shortening is small although the structures may also accommodate some strike slip motion deformation peaked during the mid late eocene in biscay off galicia bank and in rockall trough and in the mid miocene off western iberia these deformation pulses were contemporary with the pyrenean and betic orogenies in western europe and may have resulted from structural reorganizations within the evolving orogens driven by changes in plate motion possible mechanisms which might concentrate deformation at the ocean continent transition include slip within serpentinized peridotite underlying the transitional region and reactivation of a pre existing detachment fault within the thinned continental crust our observations may imply that rifted continental margins when reactivated can develop into new sites of plate subduction

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

crustal structure and evolution of the pyrenean cantabrian belt a review and new interpretations from recent concepts and data this paper provides a synthesis of current data and interpretations on the crustal structure of the pyrenean cantabrian orogenic belt and presents new tectonic models for representative transects the pyrenean orogeny lasted from santonian 84 ma to early miocene times 20 ma and consisted of a spatial and temporal succession of oceanic crust exhumed mantle subduction rift inversion and continental collision processes at the iberia eurasia plate boundary a good coverage by active source vertical incidence and wide angle reflection and passive source receiver functions seismic studies coupled with surface data have led to a reasonable knowledge of the present day crustal architecture of the pyrenean cantabrian belt although questions remain seismic imaging reveals a persistent structure from the central pyrenees to the central cantabrian mountains consisting of a wedge of eurasian lithosphere indented into the thicker iberian plate whose lower crust is detached and plunges northwards into the mantle for the pyrenees a new scheme of relationships between the southern upper crustal thrust sheets and the axial zone is here proposed for the cantabrian belt the depth reached by the n dipping iberian crust and the structure of the margin are also revised the common occurrence of lherzolite bodies in the northern pyrenees and the seismic velocity and potential field record of the bay of biscay indicate that the precursor of the pyrenees was a hyperextended and strongly segmented rift system where narrow domains of exhumed mantle separated the thinned iberian and eurasian continental margins since the albian cenomanian the exhumed mantle in the pyrenean rift was largely covered by a mesozoic sedimentary lid that had locally glided along detachments in triassic evaporites continental margin collision in the pyrenees was preceded by subduction of the exhumed mantle accompanied by the pop up thrust expulsion of the off scraped sedimentary lid above to the west oceanic subduction of the bay of biscay under the north iberian margin is supported by an upper plate thrust wedge gravity and magnetic anomalies and 3d inclined sub crustal reflections however discrepancies remain for the location of continent ocean transitions in the bay of biscay and for the extent of oceanic subduction the plate kinematic evolution during the mesozoic which involves issues as the timing and total amount of opening as well as the role of strike slip drift is also under debate discrepancies arising from first order interpretations of the adjacent oceanic magnetic anomaly record

mesozoic exhumation history and palaeolandscape of the iberian massif in eastern galicia from apatite fission track and u th he data apatite fission track aft and u th he ahe data combined with time temperature inverse modelling reveal the cooling and exhumation history of the iberian massif in eastern galicia since the mesozoic the continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins the data provide constraints on the 107 timescale longevity of a relict paleolandscape aft ages range from 68 to 174 ma with mean track lengths of 10 7 2 6 to 12 6 1 8 m and ahe ages range from 73 to 147 ma fastest exhumation 0 25 km ma occurred during the late jurassic to early cretaceous main episode of rifting in the adjacent western and northern margins exhumation rates have decreased since then and have been approximately one order of magnitude lower across inland galicia the aft data are consistent with early cretaceous movement on post variscan ne trending faults this is coeval with an extensional episode offshore the ahe data in this region indicate less than 1 7 km of denudation in the last 100 ma this low exhumation suggests the attainment of a mature landscape during late cretaceous post rift tectonic stability whose remains are still preserved the low and steady rate of denudation prevailed across inland galicia despite minor n s shortening in the northern margin since 45 ma ago in north galicia rock uplift in response to nw strike slip faulting since early oligocene to early miocene has caused insufficient exhumation 3 km to remove the mesozoic cooling signal recorded by the aft data

testing the influence of far field topographic forcing on subduction initiation at a passive margin abstract despite favourable gravitational instability and ridge push elastic and frictional forces prevent subduction initiation from arising spontaneously at passive margins here we argue that forces arising from large continental topographic gradients are required to initiate subduction at passive margins in order to test this hypothesis we use 2d numerical models to assess the influence of the andean plateau on stress magnitudes and deformation patterns at the brazilian passive margin the numerical results indicate that plateau push in this region is a necessary additional force to initiate subduction as the se brazilian margin currently shows no signs of self sustained subduction we examined geological and geophysical data to determine if the margin is in the preliminary stages of subduction initiation the compiled data indicate that the margin is presently undergoing tectonic inversion which we infer as part of the continental oceanic overthrusting stage of subduction initiation we refer to this early subduction stage as the brazilian stage which is characterized by 10 km deep reverse fault seismicity at the margin recent topographic uplift on the continental side thick continental crust at the margin and bulging on the oceanic side due to loading by the overthrusting continent the combined results of the numerical simulations and passive margin analysis indicate that the se brazilian margin is a prototype candidate for subduction initiation

growth and propagation of buckle folds determined from syntectonic sediments the ubierna fold belt cantabrian mountains n spain abstract the geometry of syntectonic tertiary sediments in the ubierna fold belt can be explained using the buckling folding theory the geometric features of the fold train in the pre orogenic succession also agree with a buckling process each fold grew with progressive and coeval rotation of both limbs although rotation was asymmetric and greater on the forelimb than the backlimb the diachroneity of synrotational sequences progressive unconformities through different folds indicates that fold propagation migrated towards the foreland however the initial folds were tightened during a later deformation stage synchronous with the development of younger folds

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

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

crustal structure of the north iberian continental margin from seismic refraction wide angle reflection profiles abstract the structure and geodynamics of the southern margin of the bay of biscay have been investigated from a set of 11 multichannel seismic reflection profiles recorded also at wide angle offsets in an onshore offshore network of 24 obs obh and 46 land sites this contribution focuses on the analysis of the wide angle reflection refraction data along representative profiles the results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the iberian peninsula offshore the crust has a typical continental structure in the eastern tip of the bay which disappears smoothly towards the nw to reach crustal thickness close to 10 km at the edge of the studied area 45 n 6 w the analysis of the velocity depth profiles altogether with additional information provided by the multichannel seismic data and magnetic surveys led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic typical oceanic crust has not been imaged in the investigated area onshore the new results are in good agreement with previous results and document the indentation of the bay of biscay crust into the iberian crust forcing its subduction to the north the interpreted profiles show that the extent of the southward indentation is not uniform with an alpine root less developed in the central and western sector of the basque cantabrian basin n s to ne sw transfer structures seem to control those variations in the indentation degree

comparison of deep structure along three transects of the western north american continental margin similarities in geology and potential field data that have in the past been noted among the regions of southern alaska southern vancouver island and central california are now seen to be accompanied by similarities in deep crustal structure a number of tectonic elements have been identified in the deep structure along transects in these three regions although not all elements are present along each transect these elements are a an actively subducting oceanic plate and b an overriding continental plate that consists of 1 a cenozoic accretionary prism 2 a mesozoic accretionary prism 3 a backstop to the mesozoic prism 4 a tectonically underplated body of oceanic rocks and 5 a crustal root the mesozoic prism is in some cases an underthrust body type 2a but in other cases forms the principal component of a landward verging tectonic wedge type 2b the technically underplated body of oceanic rocks extends landward from the fault contact between the cenozoic and mesozoic prisms to a point beneath the backstop the crustal root lies beneath the backstop and landward of the underplated body all of these elements are interpreted to be present along the alaskan and vancouver island transects in alaska the underplated body is interpreted to be fragments of the kula plate the same may be true at vancouver island these two transects appear to differ in that in alaska the mesozoic prism in one interpretation is the principal component of a tectonic wedge type 2b whereas at vancouver island it is an underthrust body type 2a along the central california transect active subduction is no longer taking place and the san andreas fault has removed the cenozoic prism from this region of the north american plate on the north american plate i e east of the san andreas fault the mesozoic prism interpreted as the main component of a tectonic wedge type 2b and the backstop to the mesozoic prism are present there is however no clear evidence of tectonically underplated oceanic rocks and the crust is thin no root in both alaska and vancouver island the mesozoic prisms above the underplated bodies experienced low pressure high temperature metamorphism at about the time of tectonic underplating no such metamorphism is currently exposed in california the metamorphism may have been caused by the underplating of young hot oceanic crust or alternatively by subduction of an oceanic ridge the presence of a tectonic wedge type 2b in alaska and california and the absence of such a wedge at vancouver island could arise either from the fact that in the former two locations the mesozoic prisms were more voluminous owing to either more rapid trench sedimentation or more rapid convergence or to the possibility that at the latter location the mesozoic prism was juxtaposed with the backstop primarily by strike slip faulting

influence of dominant wind patterns in a distal region of the nw iberian margin during the last glaciation this work combines planktonic foraminiferal assemblages stable isotope transfer function estimated sea surface paleotemperatures sst and export productivity pexp with sedimentological records from the pc7 core to document paleoclimatic and paleoceanographic changes on a distal region of the nw iberian margin since the last glaciation 87 sr 86 sr indicate that the studied locality mostly received sediments from european ice sheets eis during h5 during the hs and d o stadial events ssts were in general higher than in other cores collected in inner areas of the nw iberian margin the presence and intensification of portugal current probably induced heat transfer to this distal region of the iberian margin our results also suggest the occurrence of high variability in the intensity and wind patterns during the last glaciation in some periods the intensity of northerly winds could have been very strong and contributed to a significant stimulation of ocean productivity in this distal area through the intensification of upwelling in general oceanic productivity decreased during the hs and d o as the presence of cold and less saline water prevented nutrient rich waters from deep levels reaching the surface the high productivity events were bracketed by periods characterized by the highest influence of the azores current eastern branch during which northerly winds and the oceanic productivity should have been weakened supplementary material geochemical and foraminiferal data analysed in this work as well as pearson correlations between the analysed data are available at https doi org 10 6084 m9 figshare c 3931813

subduction related structures in the north iberian margin the oblique convergence of eurasia and iberia since the early cretaceous caused the formation of the pyrenean intracontinental collisional orogen in the east and progressed to continent ocean collision with subduction of the bay of biscay oceanic crust beneath the north iberian margin in the west two deep multichannel seismic profiles iam 12 and escin 4 integrated with gravity modeling and other geological and geophysical data provide the crustal scale architecture of this margin and its tectonic evolution during the convergence the north iberian margin is modeled with a south or south southeast dipping oceanic crust beneath the outer part of the continental shelf mesozoic basins on the shelf were inverted during the tertiary and compressional activity continued until recent times in the escin 4 section while a shallower probably neogene age basin is subjected to active recent erosion in the iam 12 section in the oceanic areas a marginal trough deepens and widens toward the east as a result of the regional east dip of the oceanic basement the accretionary prism increases in size from west to east 18 56 km and its internal structure and morphology varies along strike the prism is buried by postcorivergence sediments in both sections and in the iam 12 section appears to have been active at least during lutetian to burdigalian times the crustal scale structure of the north iberian margin is that of an arrested subduction zone in which a remnant oceanic basin was being consumed near two continental plates that collided obliquely

magnetotelluric signature of the western cantabrian mountains the magnetotelluric signature of the alpine part of the cantabrian mountains was investigated in a n s magnetotelluric profile from the duero basin to the cantabrian shoreline a two dimensional conductivity model was obtained from the joint inversion of tm te modes and the geomagnetic transfer functions a shallow conductor associated with the sediments of the duero basin and three north dipping conductors in the upper and middle crust were detected of the latter one is interpreted as the sole detachment of the cantabrian mountains whereas the others correlate with the cabuerniga and san vicente de la barquera faults this geometry suggests that the cantabrian mountains comprise uplifted variscan basement a comparison with a seismic reflection profile shows a good correlation between these conductors and seismic features the lower crust is characterised by high conductivities

the le danois contourite depositional system interactions between the mediterranean outflow water and the upper cantabrian slope north iberian margin abstract the le danois contourite depositional system cds located in an intraslope basin along the cantabrian margin is unique with respect to the known sedimentary systems along the upper slope of the biscay margin whereas the steep biscay slopes are dominated by downslope processes the le danois cds has been generated by alongslope processes and has a strong potential to contain a record of the neogene palaeoceanography this paper will focus on the onset development and present day functioning of this system with respect to its unique morphological control and the responsible local oceanographic processes new bathymetric and seismic reflection data show that the past and present le danois cds is shaped by the mediterranean outflow water conditioned by seafloor irregularities and two topographic highs the large le danois bank and the smaller vizco high the seismic stratigraphic analysis carried out on the contourite deposits has allowed to identify 3 seismic sequences separated by 3 major regional discontinuities changes in depositional styles the vertical stacking of seismic units and the nature of the discontinuities suggest a correlation with the development of the cadiz cds and well known palaeoceanographic events along the ne atlantic margin the first clues for bottom current deposits are identified in the lower sequence which is developed after tentatively the lower pliocene the drift deposits of both the lower and middle sequences were confined into two palaeobasins within the intraslope basin however from the middle pleistocene revolution 0 9 ma onwards the contouritic deposition is intensified due to the switch to a full glacial mode with 100 ka cyclicity this has allowed the development of the present day depositional and erosive features such as respectively elongated mounded and separated drifts plastered drifts moats and slide scars

the marconi reflection seismic data a view into the eastern part of the bay of biscay abstract seismic data acquisition for the marconi project took place in 2003 in the eastern half of the bay of biscay the overall goal of the multichannel experiment was to collect seismic data to elucidate the structure and evolution of the southern margin of the bay where an along the margin transition between oceanic subduction in the west and continental convergence in the east occurs and its relationship to the pyrenean realm we describe the multichannel experiment and present an interpretation of the abyssal plain sector of the profiles altogether eleven regional seismic reflection profiles were collected with a total length of 1800 km between the longitudes 6 and 2 w and latitudes 43 5 and 46 n the seismic profiles show first images of the thick sedimentary pile that covers the eastern abyssal plain of the bay the interpretation includes three sedimentary sequences separated by unconformities that correspond to the pre syn and post alpine sequences the post orogenic deposits lay unconformably over the previous compressional structures in the eastern part of the bay floored by transitional crust these compressional features are evident in the presence of a young accretionary prism sealed at its first stages of development the overall structure and shape is similar to those of active subduction prisms worldwide but evidencing differences in width and sediment wedge thickness from west to east along the margin buoyancy of the transitional crust and resistance to subduction led to stronger plate coupling towards the east where oceanic crust is absent and may be the main cause for these morphological changes along the east west traverse of the wedge the marconi multichannel deep seismic dataset provides the first estimation of the thickness of the sediment load on the 5000 m deep abyssal plain of bay of biscay where no direct data were available

reply to comment by pedreira et al on reconstruction of the exhumed mantle across the north iberian margin by crustal scale 3 d gravity inversion and geological cross section

the role of tectonic inheritance in the morphostructural evolution of the galicia continental margin and adjacent abyssal plains from digital bathymetric model dbm analysis nw spain the identification of recent major tectonic structures in the galicia continental margin and adjacent abyssal plains was carried out by means of a quantitative analysis of the linear structures having bathymetric expression on the seabed it was possible to identify about 5800 lineaments throughout the entire study area of approximately 271 500 km2 most lineaments are located in the charcot and coruna highs in the western sector of the galicia bank in the area of the marginal platforms and in the northern sector of the margin analysis of the lineament orientations shows a predominant ne sw direction and three relative maximum directions nw se e w and n s the total length of the lineaments identified is over 44 000 km with a mode around 5000 m and an average length of about 7800 m in light of different tectonic studies undertaken in the northwestern margin of the iberian peninsula we establish that the lineaments obtained from analysis of the digital bathymetric model of the galicia continental margin and adjacent abyssal plains would correspond to fracture systems in general the orientation of lineaments corresponds to main faults tectonic structures following the directions of ancient faults that resulted from late stages of the variscan orogeny and mesozoic extension phases related to triassic rifting and upper jurassic to early cretaceous opening of the north atlantic ocean the n s convergence between eurasian and african plates since palaeogene times until the miocene and nw se convergence from neogene to present reactivated the variscan and mesozoic fault systems and related physiography

crustal structure and continent ocean boundary along the galicia continental margin nw iberia insights from combined gravity and seismic interpretation the magma poor rifted continental margin of galicia has an extremely complex structure its formation involved several rifting episodes that occurred ultimately during the early cretaceous near a ridge triple junction which produced a change in the orientation of the main structures in its transition to the north iberia margin in addition there is a superimposed partial tectonic inversion along its northwest and northern border which developed from the late cretaceous to at least oligocene times the present study integrates a large volume of new geophysical information mainly marine gravity data and 2d seismic reflection profiles to provide insights on the formation of this rift system and on the development of its later inversion the combined interpretation and modeling of this data enable the presentation of a new crustal and structural domains map for the whole galicia margin this includes the rift domains related to the extreme thinning of the crust and the lithospheric mantle stretched necking and hyperextension and mantle exhumation hme domains as well as a domain of intense compressional deformation new constraints arise on the origin the deep structure and the characterization of the along and across strike variation of the continent ocean transition of the margin where a progressive change from hyperextension to partial inversion is observed the development of both rifting and later partial tectonic inversion is influenced by the existence of former first order tectonic features most of the tectonic inversion is focused on the hme domain which in some areas of the northwestern margin is completely overprinted by compressional deformation

gravitational potential energy and active deformation in the apennines we use velocity measurements from a network of continuous gps sites spanning the apennines of peninsular italy to test the hypothesis that the active deformation of the region is explained by variations in gravitational potential energy of the lithosphere the simple geometry of the mountain chain allows us to treat the deformation as two dimensional neglecting gradients of velocity along the strike of the chain under this assumption the integral of gravitational potential energy per unit area of the lithosphere gpe in the direction perpendicular to the chain is related by a simple expression to the velocity in the same direction we show that the observed velocities match this expression with an rms misfit of 0 5mm yr this agreement suggests that deformation of the apennines reflects a balance within the mountain chain itself between lateral variations in gpe and the stresses required to deform the lithosphere forces arising from processes external to the belt are not required to explain the observations

seismotectonics of portugal and its adjacent area in the atlantic abstract new elements on the seismicity of portugal and new focal mechanism solutions of earthquakes with epicentres situated off the coast of the portuguese mainland and in the azores region are presented historical seismicity data show that in the territory of the portuguese mainland there are active faults that are responsible for earthquakes that have caused important damage and many casualties however most of the intraplate earthquakes with epicentres situated in the portuguese mainland or near the shore are normally of small magnitude and this renders difficult their interpretation in the light of focal mechanisms a solution for one earthquake with magnitude 5 and epicentre at the nazare submarine canyon is presented southwestwards of cape st vincent there is an important seismic zone responsible for high magnitude earthquakes such as that of 1 november 1755 this zone is situated in the region where the extension of the messejana fault into the ocean joins with the azores gibraltar fault the seismicity of the area situated between the western coast of the portuguese mainland and the azores increases approximately along the 15 w meridian from the latitude of the azores gibraltar fault up to 44 n focal mechanisms of earthquakes with epicentres situated along this line show very similar solutions the interpretation of the focal mechanism solutions of the earthquakes with epicentres situated in the studied area shows that the stress field trends approximately nw se it is assumed that this stress field results from the interaction of the eurasian and african plates however this direction is not maintained in the azores region

crustal transition between continental and oceanic domains along the north iberian margin from wide angle seismic and gravity data deep crustal features of the transition between the north iberian mainland and the bay of biscay are constrained from new wide angle seismic and gravity data velocity depth models are derived from far offset recordings onshore of two n s marine profiles complemented with new refraction data inland and tested against models that fit the gravity anomalies important lateral variations are inferred along the north iberian margin in the western transect a variscan crust is documented from the mainland across the continental shelf and a rapid crustal thinning beneath the slope marks the transition to the oceanic domain the eastern transect shows an outstanding crustal thickening beneath the coastline moho depths around 50 km and a gradual thinning across the shelf differences are related to the v shape of the bay of biscay that causes a w e transition along the margin from a short lived oceanic subduction to continental collision during the tertiary oblique convergence between europe and iberia

the seismogenic zone of the continental crust in northwest iberia and its relation to crustal structure the distribution of seismicity at the western end of the cantabrian mountain range nw iberia reflecting current crustal dynamics is investigated integrating seismically active structures long term structures and the topographic features at the surface the thickness of the seismogenic zone within the continental crust is established in 20 km two crustal domains can be distinguished in the study area in terms of the seismicity pattern the style of alpine structures and the relief the presence of crustal fluids arises as a very likely contributing factor to the excessive thickness of the seismogenic zone in the study area more importantly a switch in tectonic style at the transition between crustal domains in coincidence with the lateral termination of orogenic frontal thrusts is envisaged as involving sufficient stress heterogeneity and amplification to explain the current concentration and characteristic pattern of historical seismicity in the region overall the distribution of seismicity in the crust is sensitive to the type and style of crustal structures

unravelling the architecture and evolution of the inverted multi stage north iberian bay of biscay rift abstract current rift models propose polyphase rift evolutions that develop with the same kinematic framework and accommodate continuous and sequential extension through the stacking of deformation modes several rifted margins show however evidence for multiple and out of sequence rift events which developed within different kinematic frameworks with a complex spatial and temporal evolution in this work we address the problem of multi stage rifting based on the study of the central north iberian margin located at the southern bay of biscay triangular oceanic domain this magma poor rifted margin recorded three major mesozoic rift events and a subsequent alpine compressional reactivation representing a unique setting to study the architecture of multi stage rift systems and the exerted control on subsequent reactivation relying on a dense set of 2d seismic reflection profiles boreholes and published velocity models we map and describe structural domains and major extensional and compressional structures and we construct depth and thickness maps of syn rift units these new maps display the geometry and spatial distribution of major rift basins and bounding structures distinctive scenarios resulting from this tectono stratigraphic approach led us to define three rift systems a first diffuse and widespread triassic system with classical fault bounded half graben basins a second narrow deep and localised late jurassic to barremian transtensional system including laterally confined pull apart basins and a third widely distributed aptian to cenomanian hyperextended system our results show that each rift system controlled the successive extensional events and the subsequent contractional deformation resulting in a complex 3d template deciphering the tectono stratigraphic architecture of such multi stage systems provide key insights on the spatial temporal and thermal evolution of divergent plate boundaries it is likewise indispensable to propose and test kinematic plate deformable models on conjugate rifted margins and to comprehend the implications for their reactivation

seismic signature of variscan and alpine tectonics in nw iberia crustal structure of the cantabrian mountains and duero basin the seismic structure of the crust of the nw iberian peninsula along the cantabrian mountains and their southern foreland the duero basin is investigated from the first data set available from refraction and wide angle reflection profiles the velocity depth distributions obtained along e w and n s transects evidence lateral variations in crustal structure that can be associated to variscan and alpine tectonic episodes the western part of the range toward the variscan hinterland zones as well as the duero basin below the sediments show a crustal structure similar to that of the variscan belt elsewere in europe the total crustal thickness is 30 32 km and three main layers upper middle and lower crust with average velocities 6 0 6 25 and 6 8 km s are resolved some paleozoic structures such as the basal detachment of the cantabrian zone are expressed in the seismic models the crust appears to vary eastward in the external zones the most outstanding feature is a crustal root beneath the highest cantabrian summits where the moho is found at 47 km depth a prominent alpine reworking of the crust in the eastern part of the cantabrian zone is thus revealed and the n s seismic transects delineate a geometry similar to the one found across the central pyrenees in the etude continentale et oceanique par reflexion et refraction sismique ecors profile revealing the importance of the alpine deformations in the northern part of the iberian plate

multiphased tectonic evolution of the central algerian margin from combined wide angle and reflection seismic data off tipaza algeria 1 the origin of the algerian margin remains one of the key questions still discussed in the western mediterranean sea due to the imprecise nature and kinematics of the associated basin during the neogene for the first time the deep structure of the maghrebian margin was explored during the spiral seismic survey in this work we present a n s transect off tipaza west of algiers a place where the margin broadens due to a topographic high khayr al din bank new deep penetration seismic profiles allow us to image the sedimentary sequence in the algerian basin and the crustal structure at the continent ocean boundary modeling of the wide angle data shows thinning of the basement from more than 15km in the continental upper margin to only 5 6km of oceanic type basement in the algerian basin and reveals a very narrow or absent transitional zone analysis of the deep structure of the margin indicates features inherited from its complex evolution 1 an oceanic type crust in the deep basin 2 similarities with margins formed in a transform type setting 3 a progressive deepening of the whole sedimentary cover and the thickening of the plio quaternary sediments at the margin foot coeval with 4 a downward flexure of the basement in the basin these features argue for a multiphased evolution of the margin including 1 an early stage of rifting and or spreading 2 a late transcurrent episode related to the westward migration of the alboran domain and 3 a diffuse plio quaternary compressional reactivation of the margin

seismic structure of the northern continental margin of spain from escin deep seismic profiles abstract by the end of the carboniferous the crust of the continental shelf in northwestern spain was made up of deeply rooted structures related to the variscan collision from permian to triassic times the tectonic setting had changed to mainly extensional and the northern iberian continental margin underwent rifting during late jurassic early cretaceous times along with sea floor spreading and the opening of the bay of biscay until the late cretaceous subsequently the northern iberian margin was active during the north south convergence of eurasia and iberia in the tertiary a multichannel seismic experiment consisting of two profiles one north south escin 4 crossing the platform margin offshore asturias and another escin 3 crossing the platform margin to the northwest of galicia was designed to study the structure of the northern iberian margin the escin 4 stacked section reveals inverted structures in the upper crust within the le danois basin north of the steep continental slope escin 4 shows a thick sedimentary package from 6 to 9 5 s two way travel time twt within this latter package a 40 km long north tapering wedge of inclined mainly south dipping reflections is thought to represent a buried alpine age accretionary prism in the north western part of the escin 3 escin 3 1 stacked section horizontal reflections from 6 5 to 8 5 s correspond to an undisturbed package of sediments lying above oceanic type basement in this part of the line a few kilometres long strong horizontal reflection at 11 2 s within the basement may represent an oceanic moho reflection also a band of reflections dips gently towards the southeast from the base of the gently dipping continental slope the part of escin 3 line that runs parallel to the nw galicia coast escin 3 2 is characterized by bright continuous lower crustal reflections from 8 to 10 s beneath the lower crustal reflectivity a band of strong reflections dips gently toward the southwest from 10 to 13 5 s the part of escin 3 that parallels the northern margin escin 3 3 shows good reflectivity in all levels upper crustal reflections image the sedimentary fill of probable mesozoic to recent basins mid crustal reflectivity is characterized by dipping reflections until 8 s that are probably related to compressional variscan features the lower crustal level shows layered reflections between 8 and 12 s dipping reflections are found below the continental moho

age and regional tectonic and metallogenetic implications of igneous activity and mineralization in the andahuaylas yauri belt of southern peru