heterogeneous strain associated with normal faulting evidence of mass transfer by pressure solution associated with fault displacement abstract in a well stratified flysch in the french pyrenees the offset of layers along a fault zone provide good data of relative displacement it is shown that the fault surface is composed of three right stepping fractures that opened tensile bridges along small left stepping fractures translation on the fault zone is parallel to the fault surface the displacement vector field shows that the movement between the two blocks was not a rigid body translation and that deformation in the hanging wall is greater than that in the foot wall volume loss within the rock is compensated by volume increase close to the fault surface calcite dissolution and reprecipitation by pressure solution is indicated by the occurrence of stylolites and numerous calcite filled veins around the fault calcite dissolution is more important in the hanging wall especially in layers where the calcite content is close to 60 both cathodoluminescence observations and rare earths element patterns are in favour of calcite in veins and dominos coming from units adjacent to the fault there is no evidence that some calcite coming from farther distance could have entered in the system

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

galicia bank ocean continent transition zone new seismic reflection constraints abstract the west iberia continental margin is a type locale for magma poor rifting and studies there have been instrumental in changing the classical view of the ocean continent transition oct from a discrete boundary juxtaposing continental and oceanic crust into a more complicated zone of varying width that can include exhumed mantle this study examines two new seismic lines in the galicia bank area extending west of the peridotite ridge showing high resolution images of five new ridges these ridges could be hyperextended continental crust exhumed continental mantle or rough ultra slow spreading oceanic crust there are no tilted fault blocks with pre syn rift stratigraphy that would indicate continental crust there are also no faults indicating mid ocean spreading with seismic layer stratigraphy indicating normal oceanic crust the ridges have no coherent internal seismic structure and some resemble the topographic profile of the peridotite ridge therefore it is likely the western ridges are also mainly composed of serpentinized mantle these western ridges are also similar to small oceanic core complexes observed along the active part of the mid atlantic ridge which also contain exhumed serpentinized mantle this implies that there is a gradual transition within our study area from continental extension to seafloor spreading exhumation of continental mantle results in the formation of peridotite ridges then transitions to episodic volcanism which produces local thin basaltic crust and exhumation of oceanic core complexes asymmetric processes during initial rifting and spreading result in contrasting structures on the two resulting margins

structure and development of the southeast newfoundland continental passive margin derived from screech transect 3 new seismic reflection data from the grand banks of newfoundland and the newfoundland basin add to the growing knowledge of the composition structure and history of this nonvolcanic margin geophysical imaging is now approaching the extent of that done previously on the conjugate margin along iberia providing a valuable database for the development of rifting models two parallel profiles over the shelf platform image deep crustal fabric representing precambrian or possibly appalachian deformation as well asmesozoic extension progressively more intense extension of continental crust is imaged oceanwards without the highly reflective detachments frequently seen on profiles off galicia a landward dipping event l is imaged sporadically and appears to be analogous to a similar event on the iberian iam9 profile the transition zone is probably exposed serpentinized mantle as interpreted off the iberian margin although there appears to be a difference in the character of ridge development and reflectivity the distinctive u reflection identified previously at the base of the newfoundland basin deep water sedimentary section and recently identified as one or more thin basalt sills is imaged on newly presented profiles that connect previously published profiles scr3 and scr2 showing that u is highly regular and continuous except where interrupted by basement highs u is also seen to have a major impact on the ability to image underlying basement a full transect beginning over completely unextended continental crust through to oceanic crust has provided a data set from which estimates of extension and the pre rifting location of the present continental edge can be made two estimates were obtained 85 km based on faulting and 120 km based on crustal thickness

ploughing the deep sea floor bottom trawling is a fishing technique whereby heavy nets and gear scrape along the sea bed and is shown here to disturb sediment fluxes and modify the sea floor morphology over large spatial scales the direct impact of bottom trawling on local fish populations has received much attention but trawling also affects other aspects of the ocean environment this paper shows that bottom trawling a commercial practice in which heavy nets and gear are dragged along the ocean floor induces sediment reworking and erosion causing the gradient of the sea floor to become smoother over time this reduces the morphological complexity of deep sea environments the authors draw parallels between the effects of bottom trawling at sea and intensive agriculture on land with the important difference that on land ploughing takes place once or twice a year whereas at sea bottom trawling can be a frequent occurrence bottom trawling is a non selective commercial fishing technique whereby heavy nets and gear are pulled along the sea floor the direct impact of this technique on fish populations1 2 and benthic communities3 4 has received much attention but trawling can also modify the physical properties of seafloor sediments water sediment chemical exchanges and sediment fluxes5 6 most of the studies addressing the physical disturbances of trawl gear on the seabed have been undertaken in coastal and shelf environments7 8 however where the capacity of trawling to modify the seafloor morphology coexists with high energy natural processes driving sediment erosion transport and deposition9 here we show that on upper continental slopes the reworking of the deep sea floor by trawling gradually modifies the shape of the submarine landscape over large spatial scales we found that trawling induced sediment displacement and removal from fishing grounds causes the morphology of the deep sea floor to become smoother over time reducing its original complexity as shown by high resolution seafloor relief maps our results suggest that in recent decades following the industrialization of fishing fleets bottom trawling has become an important driver of deep seascape evolution given the global dimension of this type of fishery we anticipate that the morphology of the upper continental slope in many parts of the world s oceans could be altered by intensive bottom trawling producing comparable effects on the deep sea floor to those generated by agricultural ploughing on land

ocean continent boundary in the iberia abyssal plain from multichannel seismic data abstract the ocean continent boundary of the west iberia margin is marked by a basement ridge trending n s four segments of this ridge are recognized each of them being progressively offset westward from 40 n to 43 n because the setting and seismic character of the ridge in the iberia abyssal plain are similar to those of the galicia margin ridge which is made of serpentinized peridotite we think that the southern segments of the ridge are also made of the same mantle material the segmentation of the ridge suggests that the northward propagation of the continental break up during the north atlantic opening in early cretaceous times was discontinuous each segment possibly corresponding to a propagation step east of the ridge the basement of the whole iberia abyssal plain consists of highly thinned continental crust locally resting on a seismic reflector that resembles the s reflector previously recognized off galicia by analogy with the galicia margin we propose that the tilted crustal blocks lay on serpentinized peridotite derived from the upper mantle the s reflector corresponding to the contact between crustal rocks and serpentinite

deformation processes at the down dip limit of the seismogenic zone the example of shimanto accretionary complex in order to constrain deformation processes close to the brittle ductile transition in seismogenic zone we have carried out a microstructural study in the shimanto accretionary complex japan the fossil equivalent of modern nankai accretionary prisms the hyuga tectonic melange was sheared along the plate interface at mean temperatures of 245 c 30 c as estimated by raman spectroscopy of carbonaceous material rscm it contains strongly elongated quartz ribbons characterized by very high fluid inclusions density as well as micro veins of quartz both fluid inclusion planes and micro veins are preferentially developed orthogonal to the stretching direction furthermore crystallographic preferred orientation cpo of quartz c axes in the ribbons has maxima parallel to the stretching direction recrystallization to a small grain size is restricted to rare deformation bands cutting across the ribbons in such recrystallized quartz domains cpo of quartz c axes are orthogonal to foliation plane the evolution of deformation micro processes with increasing temperature can be further analyzed using the foliated morotsuka a slightly higher grade metamorphic unit 342 30 c by rscm from the shimanto accretionary complex in this unit in contrast to hyuga tectonic melange recrystallization of quartz veins is penetrative cpo of quartz c axes is concentrated perpendicularly to foliation plane these variations in microstructures and quartz crystallographic fabric reflect a change in the dominant deformation mechanism with increasing temperatures above 300 c dislocation creep is dominant and results in intense quartz dynamic recrystallization in contrast below 300 c quartz plasticity is not totally activated and pressure solution is the major deformation process responsible for quartz ribbons growth in addition the geometry of the quartz ribbons with respect to the phyllosilicate rich shear zones shows that bulk rheology is controlled by quartz behavior consequently below 300 c the application of quartz pressure solution laws based on realistic geometry derived from hyuga microstructures results in strongly lowering the overall strength of the plate interface with respect to the classical brittle envelop

the ocean continent boundary off the western continental margin of iberia crustal structure west of galicia bank a seismic refraction transect across the galicia bank continental margin shows that the original continental crust thins westward from 17 to 2 km immediately east of a margin parallel peridotite ridge pr immediately west of the pr oceanic crust is only 2 5 3 5 km thick but farther west oceanward it thickens to 7 km the pr caps a similar to 60 km wide lens shaped serpentinized peridotite body underlying both thinned continental and thin oceanic crust when superimposed on a reflection time version of the velocity model the s reflector is clearly intracrustal at its east end westward s cuts down to lower crustal levels eventually coinciding with the top of the serpentinized peridotite lens original crust mantle boundary these observations render almost impossible the seafloor exposure of the pr by s acting as a top to the west detachment fault numerical models of melting and borehole subsidence information constrain our rifting model the easternmost continental crust experienced a total stretching factor of 4 3 most likely in two stages it probably occurred over similar to 25 m y with the highest fate of stretching at the beginning of the main earlier rift phase valanginian 141 135 ma the 3 4 7 km thick continental crust depending on whether serpentinized peridotite is assigned to crust or mantle which may include melt products requires stretching factors 6 more than 11 7 and a rift duration of more than 25 13 m y the thin oceanic crust immediately west of the pr is explained by conductive cooling of the mantle during the long prebreakup stretching phase which temporarily caused reduced melting immediately after breakup

understanding fine grained river sediment dispersal on continental margins studies of fine grained sediment dispersal in the marine environment have documented diversity in the behavior of depositional systems on continental margins with different oceanographic conditions and morphologies based on the pattern and nature of sediment accumulation for twenty three case studies we propose there are five basic types of dispersal systems and these are related to river wave tide and margin characteristics data suggest that the type of dispersal system on any margin can be predicted with knowledge of sediment load mean significant wave height tidal range and continental shelf width at a river mouth and from these a hierarchical decision tree is developed analysis of the dispersal system type of more than 100 river mouths reveals that proximal accumulation dominated pad and marine dispersal dominated mdd systems are most abundant but estuarine accumulation dominated ead systems also are anticipated to be numerous globally research quantifying marine sediment dynamics in these system types is needed although less common the size and nature of subaqueous delta clinoform sdc and canyon captured cc systems also warrant future attention to their study strong correlations between physical characteristics i e significant wave height and tidal range and the depth and distance to the nearest maximum shelf depocenter provide evidence that in reality a continuum exists between the system types the process related partitioning of sediment in the five different types of marine dispersal systems has important implications for understanding the stratigraphic record and the cycling of carbon

crustal structure and magmatism of north atlantic continental margins enormous variations exist along rifted margins of the north atlantic in the magmatic activity that accompanied continental breakup the north atlantic margins exhibit a full range of magmatic behaviour one end of the spectrum commonly termed volcanic margins is found in the northern north atlantic off greenland norway and northwest britain where huge volumes of igneous rock were added to the continental crust as it rifted and the adjacent oceanic crust is considerably thicker than normal the other end of the spectrum so called non volcanic margins occurs further south off france and spain where only minor volcanism accompanied rifting and the oceanic crust immediately adjacent to the continental margin is thinner than normal oceanic crust results from seismic profiles are used to determine the volume and distribution of igneous crust accumulated as the continents broke up and seafloor spreading commenced the volume of melt produced during rifting is controlled mainly by the temperature of the underlying asthenospheric mantle and by the amount and rate of decompression as it rises beneath stretching and thinning lithosphere large quantities of igneous rock were produced as the continents broke up to form the north atlantic where the newly initiated iceland plume brought abnormally hot mantle beneath the rift much smaller quantities of melt were produced further south where mantle temperatures were normal during rifting the distribution of igneous rocks across the continental margin and the adjacent oceanic crust is controlled by the rate at which melt is produced and by the ease with which it can intrude laterally in the crust where the rate of stretching is very slow and the rifting is spread over many millions or even tens of millions of years as is common during the initial stages of rifting then the rising asthenospheric mantle has time to cool by conduction heat is lost from the asthenospheric mantle both vertically into the overlying water layer and laterally into the colder wedges of continental lithosphere on either side of the rifted region as a consequence of the reduced mantle temperatures considerably less partial melting occurs in the slowly rising asthenospheric mantle than in mantle which rises rapidly beneath rifts this explains the abnormally thin oceanic crust found adjacent to the non volcanic rifted continental margins in the north atlantic as the new ocean widens the spreading centre becomes isolated from the continental margins on either side by newly formed warm oceanic lithosphere and the rate of rifting generally increases the oceanic crust then attains its equilibrium thickness as conductive heat loss from the rising asthenospheric mantle reduces and all the melt formed by decompression of the mantle solidifies close to the spreading axis basaltic melts can intrude continental crust far more easily than oceanic crust basaltic dykes may extend many hundreds of kilometres away from the magma source beneath continental rifts this redistributes melt laterally towards the continent in both volcanic and to a lesser extent in non volcanic margins and may be a contributory factor in leaving unusually thin crust in the first formed ocean immediately adjacent to some rifted margins it also allows melt formed under volcanic rifts to migrate large distances laterally as is seen in the rockall area northwest of britain

effect of commercial trawling on the deep sedimentation in a mediterranean submarine canyon abstract in order to study sediment accumulation rates in the palamos submarine canyon northwestern mediterranean during the last century three sediment cores were extracted from the canyon axis at depths of 450 1200 and 1750 m respectively where instrumented moorings were previously located estimated sedimentation rates based on 210 pb and 137 cs profiles suggest that the contemporary trends of sediment transfer and accumulation in the canyon may be different from secular trends during the seventies a two fold increase of the sediment accumulation rate took place at the 1750 m depth site this change has been associated to trawling activities and is attributed to the rapid technical development that the local trawling fleet underwent during the seventies the surroundings and rims of submarine canyons are frequently targeted by commercial trawling fisheries an activity that may enhance the input of resuspended particles into canyons and eventually trigger sediment gravity flows our results suggest that the effects of trawling over the dynamics of the seafloor may extend further and deeper from the fishing grounds eventually extending to bathyal depths hence the anthropogenic influence on the sedimentary budget of some deep submarine environments may be more important than previously thought

a kinematic analysis incorporating incremental strain data for the frontal pennine zones of the western french alps abstract an incremental and finite strain study of the zones adjacent to the frontal pennine thrust fpt has been undertaken using syntectonic fibres taken from veins pyrite type pressure shadows and similar fringes from around pebbles in conglomeratic rocks the resultant strain data together with detailed mapping of local deformational geometries and regional trends has shown that the pennine zones show a more complex structural history than previously envisaged the structural analysis divides the pennine zones into two regions north and south of creve tete the southern termination of the valais basin the zones to the south of creve tete mont fut valbuche nielard and aiguille d arves show an essentially piggy back thrust sequence directed towards the foreland in which the elongation of the strain ellipse initially parallels the transport direction wnw but finally rotates to become sub parallel to the tectonic strike nne ssw the structures of the valais zone to the north of creve tete are more complex with both n and wnw verging folds thrusts and strike slip faults here the long axis of the strain ellipse appears initially to parallel the tectonic strike ne sw this is followed by a rotation into the late transport direction wnw this localised alternation between strike and transport parallelism is problematic specific examples of strike parallel extension may be explained in terms of radial transport buttressing against earlier extensional structures strike slip motion and or stretching over lateral culmination walls the major division in fibre pattern north and south of creve tete however is best explained as being a function of compartmentalization of deformation styles between adjacent areas models which invoke a dominant deformation mechanism e g thrust tectonics along the entirety of the alpine chain thus need to be rethought similarly the recognition of widespread strike parallel extension suggests that two dimensional balanced section techniques are simplistic giving only minimum shortening estimates in a single direction and thus failing to reflect the true situation

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

deep structure in the vicinity of the ocean continent transition zone under the southern iberia abyssal plain we present results from a seismic and magnetic study of acoustic basement beneath the southern iberia abyssal plain an ocean continent transition zone oct characterized by subdued basement relief and weak magnetization lies seaward of thinned continental crust its western edge is a region with isochron parallel ridges and generally higher basement magnetizations the width of the oct decreases to the north the seaward change in basement morphology coincides with changes in seismic velocity structure but in both regions anomalously high velocities at shallow depths within acoustic basement suggest that the oct consists largely of serpentinized peridotite our magnetic and seismic data support the hypothesis of exhumed upper mantle more than that of ultraslow sea floor spreading for the origin of the oct

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

the role of pressure solution and intermicrolithon slip in the development of disjunctive cleavage domains a study from helvick head in the irish variscides the offset of sedimentary laminae bedding surfaces veins and other passive markers across disjunctive cleavage domains has commonly been attributed solely to pressure solution a detailed study of disjunctive cleavage within siltstones and sandstones from helvick head co waterford on the eastern margin of the irish variscides indicates that the cleavage domains were initially formed by pressure solution processes however the study also revealed features which cannot be explained by pressure solution alone the cleavage domains represent planes of weakness within otherwise relatively homogeneous rock during fold tightening they were rotated out of parallelism with the principal xy plane of the finite strain ellipsoid thus enabling shear movement between the microlithons it is considered that this intermicrolithon slip caused a rotation of the elongate quartz grains within the cleavage domains resulting in an asymmetry of their long axes with respect to the cleavage domain margin grain microfracturing and occasionally slickensides on cleavage surfaces intermicrolithon slip is unlikely to be a localized phenomenon but is probably widespread throughout the irish variscides and other orogenic belts

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

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

trawling induced daily sediment resuspension in the flank of a mediterranean submarine canyon abstract commercial bottom trawling is one of the anthropogenic activities causing the biggest impact on the seafloor due to its recurrence and global distribution in particular trawling has been proposed as a major driver of sediment dynamics at depths below the reach of storm waves but the issue is at present poorly documented with direct observations this paper analyses changes in water turbidity in a tributary valley of the la fonera palamos submarine canyon whose flanks are routinely exploited by a local trawling fleet down to depths of 800 m a string of turbidimeters was deployed at 980 m water depth inside the tributary for two consecutive years 2010 2011 the second year an adcp profiled the currents 80 m above the seafloor the results illustrate that near bottom water turbidity at the study site is heavily dominated both in its magnitude and temporal patterns by trawling induced sediment resuspension at the fishing ground resuspended sediments are channelised along the tributary in the form of sediment gravity flows being recorded only during working days and working hours of the trawling fleet these sediment gravity flows generate turbid plumes that extend to at least 100 m above the bottom reaching suspended sediment concentrations up to 236 mg l 1 close to the seafloor 5 m above bottom a few hours after the end of daily trawling activities water turbidity progressively decreases but resuspended particles remain in suspension for several hours developing bottom and intermediate nepheloid layers that reach background levels 2 mg l 1 before trawling activities resume the presence of these nepheloid layers was recorded in a ctd turbidimeter transect conducted across the fishing ground a few hours after the end of a working day these results highlight that deep bottom trawling can effectively replace natural processes as the main driving force of sediment resuspension on continental slope regions and generate increased near bottom water turbidity that propagates from fishing grounds to wider and deeper areas via sediment gravity flows and nepheloid layer development

increasing sediment accumulation rates in la fonera palamos submarine canyon axis and their relationship with bottom trawling activities previous studies conducted in la fonera palamos submarine canyon nw mediterranean found that trawling activities along the canyon flanks cause resuspension and transport of sediments toward the canyon axis 210pb chronology supported by 137cs dating applied to a sediment core collected at 1750 m in 2002 suggested a doubling of the sediment accumulation rate since the 1970s coincident with the rapid industrialization of the local trawling fleet the same canyon area has been revisited a decade later and new data are consistent with a sedimentary regime shift during the 1970s and also suggest that the accumulation rate during the last decade could be greater than expected approaching 2 4 cm yr 1 compared to 0 25 cm yr 1 pre 1970s these results support the hypothesis that commercial bottom trawling can substantially affect sediment dynamics and budgets on continental margins eventually initiating the formation of anthropogenic depocenters in submarine canyon environments

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

shear structures and microstructures in micaschists the variscan cevennes duplex french massif central abstract structural microstructural and quartz c axis orientations have been investigated in shear zones within the cevennes micaschist series southeastern french massif central these shear zones define a hinterland dipping duplex formed during crustal thickening they are characterised by superposed cleavages a well defined stretching lineation isoclinal folds shear planes and abundant quartz lenses these shear zones were formed under p t metamorphic conditions of ca 500 c and 450 mpa the dominant deformation mechanism was dissolution crystallisation fluid circulation responsible for element transfer was limited in space and dissolved silicate minerals are now found in the quartz lenses study of the syntectonic quartz lenses suggests fluid overpressure that has favoured brittle behaviour of the rock and formation of quartz lenses at different stages of the shearing event quartz lenses have accentuated the initial anisotropy of the micaschists and have strongly enhanced folding boudinage and the development of shear zones these deformation criteria for shear zone recognition can be applied in understanding the structure and significance of monotonous micaschist series in orogenic belts

insight into the nature of the ocean continent transition off west iberia from a deep multichannel seismic reflection profile a high quality multichannel seismic reflection profile across the west iberia margin confirms the existence of a 130 km wide transition zone between tilted continental fault blocks and unequivocal oceanic crust the zone is characterized by a 1 0 2 5 km thick seismically unreflective upper basement layer lying over reflective basement that contains major landward dipping reflectors that mostly truncate against the base of the upper layer and penetrate to depths of 10 19 km below the basement surface and minor seaward dipping reflectors moho reflections are absent in this zone we suggest that the unreflective layer represents tectonically exposed upper mantle that has undergone extensive serpentinization enhanced by vigorous seawater circulation about 40 km farther north the transition zone narrows to 35 km and the unreflective layer is less continuous and widespread

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

numerical modeling of bottom trawling induced sediment transport and accumulation in la fonera submarine canyon northwestern mediterranean sea bottom trawling leads to recurrent sediment resuspension events over fishing grounds recent studies have shown how bottom trawling can drive seascape reshaping at large spatial scales and enhance sediment transport in submarine canyons which subsequently impacts deep sea ecosystems present knowledge on the transfer and accumulation of sediment flows triggered by bottom trawling is based on localized and infrequent measurements whilst a more complete picture of the process is needed the present work focuses on the modeling of sediment transport and accumulation resulting from trawling activities in la fonera submarine canyon northwestern mediterranean sea thus contributing to an improved assessment of trawling impacts based on mooring data within a canyon gully we use an inverse model to retrieve the unknown time series of resuspension due to trawling over the fishing grounds this resuspension is later used as forcing for the direct problem we simulate trawling induced flows through the canyon and provide a 3d visualization of potential trawling impacts on sediment dynamics including the identification of the propagation patterns of sediments resuspended by trawling flows coming from shallower fishing grounds are funneled through canyon flank gullies towards the canyon axis with part of the resuspended sediment reaching the continental rise out of the canyon across the open continental slope trawling induced sediment flows promote sediment accumulation beyond the canyon mouth given the wide geographical distribution of bottom trawling our results have far reaching implications that go much beyond la fonera submarine canyon our study represents a starting point for the assessment of the sedimentary impact of bottom trawling in deep continental margins

a deep seismic investigation of the flemish cap margin implications for the origin of deep reflectivity and evidence for asymmetric break up between newfoundland and iberia summary seismic reflection and refraction data were acquired along the southeast margin of flemish cap at a position conjugate to drilling and geophysical surveys across the galicia bank margin the data document first order asymmetry during final break up between newfoundland and iberia an abrupt necking profile of continental crust observed off flemish cap contrasts strongly with gradual tapering on the conjugate margin there is no evidence beneath flemish cap for a final phase of continental extension that resulted in thin continental crust underlain by a strong s like reflection which indicates that this mode of extension occurred only on the galicia bank margin compelling evidence for a broad zone of exhumed mantle or for peridotite ridges is also lacking along the flemish cap margin instead anomalously thin 3 4 km thick oceanic crust is observed this crust is highly tectonized and broken up by high angle normal faulting the thin crust and rift structures that resemble the abandoned spreading centre in the labrador sea suggest that initial seafloor spreading was affected by processes observed in present day ultra slow spreading environments landwards flemish cap is underlain by a highly reflective lower crust the reflectivity most likely originates from older palaeozoic orogenic structures that are unrelated to extension and break up tectonics

interlayer material transport during layer normal shortening part i the model to analyse mass transfer during deformation the case is considered of a multilayer experiencing a layer normal shortening that is volume constant on the scale of many layers strain rate is homogeneously distributed on the layer scale if diffusion is absent when transport of matter between the layers occurs strain rate and dilatation rate are found to vary with distance from the contacts between layers an instantaneous model for differentiation is developed on the assumption that the sole driving force for diffusion is the difference in the hydrostatic component of stress caused by flow of theologically contrasting layers physical properties incorporated in the model are viscosity mobility of the migrating component m and a factor for an isotropy in removal or addition of material each is found to influence flow behaviour and diffusion to a degree depending on scale the magnitude of the characteristic diffusion length b 2 0 m where 0 is the specific volume of the diffusing component is essential in this respect mass removal and mass addition contribute significantly to deformation of relatively thin layers in thick layers beyond about six times the characteristic diffusion length away from a contact deformation proceeds as in the absence of diffusion the theory further predicts a dynamically maintained stable layer thickness to which thicker and thinner layers converge during prolonged deformation the question how periodically layered gneiss may develop by deformation of directionless igneous rock is discussed in the light of this conclusion

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

influence of grain boundary structural evolution on pressure solution creep rates intergranular pressure solution is a well known rock deformation mechanism in wet regions of the upper crust and has been widely studied especially in the framework of compaction of granular materials such as reservoir sandstones and fault rocks several analytical models exist that describe compaction creep by stress induced mass transport and the parameters involved are relatively well constrained by laboratory experiments while these models are capable of predicting compaction behavior observed at relatively high porosities they often overestimate compaction rates at porosities below 20 by up to several orders of magnitude this suggests that the microphysical processes operating at low porosities are different and are not captured well by existing models the implication is that available models cannot be extrapolated to describe compaction of sediments and fault rocks to the low porosities often reached under natural conditions to address this problem we propose a new thermodynamic model that describes the decline of pressure solution rates within individual grain contacts as a result of time averaged growth of asperities or islands and associated constriction of the grain boundary diffusion path here termed grain boundary evolution the resulting constitutive equations for single grain grain contacts are then combined and solved semianalytically the compaction rates predicted by the model are compared with those measured in high strain compaction experiments on wet granular halite a significant reduction in compaction rate is predicted when grain boundary evolution is considered which compares favorably with the experimental compaction data

rheology of the plate interface dissolution precipitation creep in high pressure metamorphic rocks abstract subduction zone models invoke deformation to be concentrated along the plate interface in a region of particularly low temperature geophysical observations do not provide constraints on temperature stress and deformation patterns with desired resolution in contrast the record of high pressure metamorphic rocks exhumed from subduction zones provides details on p t history deformation mechanisms and stress state albeit not readily correlated with the former dynamic situation on larger scale here we review available information on dissolution precipitation creep dpc in high pressure metamorphic rocks which if representative for subduction zones in general can pose constraints on conditions rheology and flow patterns along the plate interface the key observations and conclusions are that 1 deformation is typically highly inhomogeneous and localized into shear zones 2 stresses are generally too low to drive crystal plastic deformation 3 microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism 4 an aqueous fluid at quasi lithostatic pressure is available throughout allowing for tensile fracturing and crack healing or sealing 5 low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity and 6 contribution of shear heating to the thermal budget of subduction zones should be moderate the dominant deformation mechanism dpc is reviewed in some detail including experimental and theoretical approaches various examples of dpc in high pressure metamorphic rocks are illustrated emphasizing the role of interphase boundaries as sites of dissolution rheology governed by dpc is proposed to control interplate coupling and development of a subduction channel with return flow being a likely candidate for rapid exhumation of high pressure metamorphic rocks

dehydration related deformation during regional metamorphism nw sardinia italy the relationship between deformation and dehydration has been investigated in hercynian regionally metamorphosed rocks exposed on nw sardinia two episodes of prograde mineral growth m1 m2 involving dehydration are recognized growth of chlorite phengite porphyroblasts at anchizone metamorphic conditions contemporaneous with the first phase of deformation d1 and growth of biotite from chlorite and phengite coincident with the second phase of deformation d2 deformation during both episodes of dehydration is characterized by penetrative axial planar foliations defined by well developed phyllosilicate preferred orientations quantified by xrd textural goniometry tight to isoclinal similar folds interlimb angles 40 low strain similar folds and minor brittle deformation systematic variations in macrofold interlimb angles with respect to the timing of mineral growth indicate that enhanced shortening c 80 occurred during dehydration microfabrics show that the onset of dehydration is associated with the transition from a crenulation cleavage to a penetrative foliation the presence of axial planar hydrofractures that formed coevally with dehydration and fabric development requires that supralithostatic fluid pressures and low differential stresses c 20 mpa accompanied dehydration these features demonstrate a connection between the timing of dehydration and the style of deformation

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

application of the critical coulomb wedge theory to hyper extended magma poor rifted margins the critical coulomb wedge theory ccwt has been extensively used in compressional tectonics to resolve the shape of orogenic or accretionary prisms while it is less applied to extensional and gravitational wedges despite the fact that it can be described by the same equation in particular the hyper extended domain at magma poor rifted margins forming the oceanward termination of extended continental crust satisfies the three main requirements of the ccwt 1 it presents a wedge shape 2 the rocks forming the wedge are completely brittle frictional and 3 the base of the wedge corresponds to a low friction decollement however hyper extended margins present a fully frictional behaviour only for a very thin crust therefore this study is limited to the termination of hyper extended continental crust which deforms in the latest stage of continental rifting in this paper we define a method to measure the surface slope and the basal deep of this wedge that we apply to 17 hyper extended magma poor rifted margins in order to compare the results to the values predicted by the ccwt because conjugate pairs of hyper extended magma poor rifted margins are commonly asymmetric due to detachment faulting the wedges in the upper and lower plate margins corresponding respectively to the hanging wall and footwall of the detachment system are different while the stress field in the upper plate wedge corresponds to a tectonic extensional wedge the one in the lower plate matches that of a gravity extensional wedge using typical frictional properties of phyllosilicates e g clays and serpentine the shape of the hyper extended wedges can be resolved by the ccwt using consistent fluid overpressures our results show that all lower plate margins are gravitationally stable and therefore have a close to critical shape whereas the tectonic extensional wedges at upper plate margins are critical sub or sup critical due to the detachment initial angle and the duration of the tectonic activity in this paper we discuss the geometry and structural evolution of the most distal parts of hyper extended continental margins and the formation of extensional allochthons during hyper extension using the ccwt theory

volume loss and deformation around conjugate fractures comparison between a natural example and analogue experiments abstract in well stratified sedimentary rocks measurement of the bedding offsets along fractures gives a value for the relative displacement at each location to restore the undeformed geometry of the layers the offset along each fracture must be cancelled restoration of the geometry enables the location of places where shortening is concentrated to be established namely at the fracture intersection and at fracture tips slow displacement during deformation is demonstrated by the growth of fibres on the fault surfaces pressure solution inside the layers is responsible for the internal strain with associated volume loss this mechanism is compatible with low strain rates giving aseismic displacements along the fractures to model rock rheology dominated by pressure solution a viscous material paraffin wax has been employed in the analogue model volume loss in nature is represented by area changes during the analogue experiments in the experiments shortening is concentrated around the fractures in exactly the same geometrical positions as in nature when the amount of displacement is different on each of the two fractures one of the fractures is observed to offset its conjugate fracture when this is the case relative timing of displacement along conjugate fractures cannot be determined without ambiguity from the observation of fracture offsets

deformation by solution deposition and re equilibration of fluid inclusions in crystals depending on temperature internal pressure and stress abstract changes of shape and density of fluid inclusions in crystals were demonstrated when these crystals were subjected to temperatures and internal pressures greater than those of their growth experimental relations have been established between the rate of length change of the inclusions and the different parameters of the experiment nature of the crystal temperature and internal pressure state of stress on the crystal geometric characters of the inclusion length width orientation of the inclusion with respect to the optical axes of host mineral it is essentially the effect of the variation of surface energy with the curvature around the cavity which causes a mass transfer of the host crystal by diffusion through the fluid under pressure the rate of length change is limited by the rate of dissolution at the median part of elongate inclusions this change of shape and density is known to occur in naturally deformed crystals an example of such a behaviour is given which allowed us to use the inclusions as markers of the conditions of temperature and pressure subsequent to the growth of crystal

generation of evenly spaced pressure solution seams during late diagenesis a kinetic theory stylolites and pressure solution seams can form during diagenesis of rocks subjected to stress through a feedback involving texture and pore fluid solute concentration this feedback destabilizes the state of uniform texture represented here only by porosity for simplicity a mathematical kinetic model that includes pressure solution diffusion and reprecipitation predicts the spontaneous generation even in initially uniform rocks of regions alternatingly in space more and less soluble a region that becomes more soluble also becomes simultaneously more porous the kinetic theory predicts that stylolites can form at roughly constant spacings this agrees with many field and petrographic observations bedding planes between beds that have initially different texture are shown by the theory to be the focus of a porosity instability that can lead to the formation of a stylolite and to the generation of more stylolites within each bed this prediction agrees with the observation that many stylolites have developed at bedding planes

variations in heat flow across the goban spur and galicia bank continental margins we present the results of 44 new heat flow stations which were taken in 1984 and 1989 in profiles across the goban spur and galicia bank continental margins nw atlantic ocean simple extensional models indicate that the heat flow across both these early cretaceous rifted margins should increase from values of 45 50 mw m2 over oceanic crust to 65 80 mw m2 on the continents the rate of this increase should help to constrain the mechanism simple versus pure shear by which the upper more radiogenic continental crust is thinned measurements across goban spur increase from values of 40 45 mw m2 over oceanic crust to 50 55 mw m2 near the continental shelf they follow the predicted trend for pure shear rifting but only if the value of upper crustal radiogenic heating is low 1 2 mu w m3 otherwise they would require the upper crust to thin more rapidly than the total crustal thickness as with a lower plate simple shear margin measurements across galicia bank show a very different pattern with similar values over oceanic crust but much lower values 30 35 mw m2 nearer land this is difficult to reconcile with any simple single rifting event but is more compatible with an origin as a pure shear or lower plate rather than upper plate margin we also note that oceanic values of heat flow require asthenospheric temperatures 100 degrees c lower than normal for both margins this indicates that the triple junction in existence between these margin segments during the breakup of iberia europe and north america was not the site of a major mantle plume

accumulation rates of major constituents of hemipelagic sediments in the deep alboran sea a centennial perspective of sedimentary dynamics the accumulation rates of sediment and major constituents in three different geographic areas of the alboran sea have been assessed by means of 210pb and 137cs concentration profiles mixing is present in the top layer of the sedimentary column with mixing coefficients estimated to range from 0 2 to 15 cm2 yr 1 overall apparent sedimentation rates for the last 100 years range from 0 014 to 0 182 g cm 2 yr 1 and show a tendency to decrease with distance to the coast and water column depth however specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation particularly noticeable are the feeding role of submarine canyons the trapping effect of slope terraces and the isolation caused by ridges sediment accumulation induced by turbiditic flows is also observed north of the almeria oran area excess 210pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas this is also evidenced by comparison of bottom sediment with the sediment trap data available from the malaga area we estimate that the particle advective input below 30 m above the bottom accounts for as much as 50 70 of the material that is ultimately deposited onto the sea floor the greater abundance of lithogenic material in the malaga zone 80 reflects its larger input in the western alboran sea conversely carbonate contents increase from less than 20 in this area to about 30 in the almeria oran zone reflecting the lesser importance of the dilution by lithogenic components biogenic silica was only detected in some surface samples and no significant preservation was observed below the eh boundary abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the alboran sea higher in the western part due to the presence of the western alboran gyre however near bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area finally from comparisons with sediment trap data the degradation of organic matter has been estimated to be approximately 30 40 of what reaches the bottom

nature of the s reflector beneath the galicia banks rifted margin preliminary results from prestack depth migration beneath the tilted fault blocks of the galicia rifted margin a bright reflection termed s has been interpreted as the master detachment fault controlling the extension of the margin however on time migrated sections s appears to be locally offset by the steep faults of the upper section we investigate the true geometry of s and its relation to the overlying faults through iterative prestack depth migration we conclude that it is not significantly offset by the faults which instead appear to stop abruptly at s thus we interpret s as the master detachment and consider its role during extension

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

spatial distribution of sedimentation rate increases in blanes canyon caused by technification of bottom trawling fleet abstract a detailed study of 15 sediment cores from blanes canyon and its immediate surroundings nw mediterranean sea was conducted to compare historic sedimentation rates and evaluate the possible impact of bottom trawling intensification on the sedimentary regimes over the past 50 years the canyon axis and flanks as well as the adjacent open slope were sampled at water depths ranging from 300 m to 2200 m grain size dry bulk density and 210pb concentration profiles were measured to assess possible changes in sedimentation rates over the last century and their temporal and spatial relationship to bottom trawling effort sedimentation rates in the upper canyon axis 900 1200 m had the highest rates of 0 9 2 1 cm yr 1 quantified since the 1970s farther downcanyon sedimentation rates increased two to five times after the 1970s from 0 1 0 2 cm yr 1 to 0 2 0 8 cm yr 1 which coincides with a rapid growth of the total engine power of the fishing fleet operating in the study area the enhanced sedimentation rates occur downslope of the main fishing grounds and decrease downcanyon as the distance from trawling grounds increases these results highlight the ability of bottom trawling to resuspend bottom sediments leading to net erosion of the canyon rims and flanks in turn large volumes of sediment are advected towards the canyon s interior ultimately increasing sediment deposition along the canyon axis natural sedimentation rates at similar along canyon distance from shore in the untrawled continental slope 900 1500 m and in the lower canyon axis 1500 2200 m are comparable 0 08 0 20 cm yr 1 suggesting distance from coastal sediment sources as the main control on regional sedimentation in deeper parts of the margin while submarine canyons have been regarded as preferential cross margin conduits for sediment dispersal they can also potentially function as modern depocenters for trawling induced sedimentation

quantitative subsidence analysis of the mesozoic evolution of the lusitanian basin western iberian margin abstract quantitative subsidence analysis of 26 wells in the lusitanian basin provides new constraints on the western iberian mesozoic passive margin development backstripped tectonic subsidence curves show a three fold subdivision of vertical motions from late triassic onward continental rifting was initiated during the late triassic and early jurassic from middle jurassic onward a distinct different behaviour is expressed in the subsidence curves for the north and the south lusitanian basin during the middle jurassic the south lusitanian basin records a stretching episode with stretching factors of about 1 08 while the north lusitanian basin typically has a middle jurassic hiatus this different development is also expressed in the late jurassic and early cretaceous sedimentary sequence when both the north and south lusitanian basin are subjected to another stretching episode with a more pronounced development of the southern than of the northern part of the basin the stretching factors for this last phase are about 1 03 for the northern part and 1 08 for the southern part of the area this north south difference during the middle jurassic to early cretaceous for which the transition roughly coincides with the location of the nazare fault zone is probably a result of differences in pre rift crustal composition or thickness late cretaceous sediments are mostly absent in the analysed wells in the southern part of the basin the absence of the cretaceous record is a consequence of erosion due to cenozoic inversion of the basin the generally low estimates for stretching factors suggest that the analysed eastern part of the lusitanian basin forms the distal part of the mid cretaceous continental breakup a comparison with subsidence curves of neighbouring basins of iberia reflects general patterns in mesozoic basin development and confirms the generally held view that the extension leading to continental breakup migrated from south to north during the middle jurassic to early cretaceous in west iberia

structure and rifting evolution of the northern newfoundland basin from erable multichannel seismic reflection profiles across the southeastern margin of flemish cap we present the results from processing and interpreting five lines from the 1992 erable multichannel seismic reflection experiment extending from the southeastern margin of flemish cap into the northern newfoundland basin these profiles reveal significant along strike variations in the rifting styles experienced by flemish cap in the southwest a 100 km wide transition zone is identified between thinned continental crust and thin oceanic crust similar to the conjugate galicia bank and iberian margins this transition zone contains a section of deep basement adjacent to a series of shallower ridges and is interpreted as exhumed serpentinized mantle along strike towards the northeast this transition zone pinches out completely within 100 km and is replaced by thin oceanic crust directly adjacent to thinned continental crust by interpreting nearby seismic profiles and profiles on the conjugate margins using the same classification criteria we construct regional maps of the distribution of crustal domains on both sides of the north atlantic these maps reveal significant variations in rifting style on the conjugate margins and along strike of each margin and also highlight the role of ancient transfer zones in compartmentalizing these rifting variations into four distinct regions we propose that the limited localization of shallow topographically high serpentinized peridotite ridges on the newfoundland iberia and flemish cap galicia bank conjugate margins was directly related to an increase in the rate of extension following the separation of flemish cap and galicia bank which exhumed deeper less serpentinized mantle

kinematic behaviour of an interface and competence contrast analogue models with different degrees of bonding between deformable inclusions and their matrix abstract in a system composed of a ductile matrix with a particle included in it the deformation of the matrix the displacement field and the rotation and the deformation of the block are related to the viscosity ratio between block and matrix and also to the degree of bonding between the matrix and the block in this paper belemnites from the lower lias of the alps provide a natural example of moderately deformed objects included in a slaty matrix they are compared with analogue models made of paraffin in which a long block of a more competent paraffin is included depending on the degree of bonding between matrix and object the same block appears to be deformable or quite rigid with a high degree of bonding the strain refraction observed corresponds to the viscosity ratio between the block and the matrix when the degree of bonding is weak the block is quite undeformed its rotation is great and the deviation of the strain in the matrix is analogous to that observed around a fault the kinematic conditions appear to have a greater effect on the finite strain than the viscosity ratio of the materials

estimation of volume changes by comparative chemical analyses in heterogeneously deformed rocks folds with mass transfer abstract this paper presents a method for calculating the volume change between the various sectors of the same heterogeneously deformed layer fold shear zone by comparing the chemical composition of deformed sectors with that of a reference sector the principle consists of considering some minerals as being insoluble illite chlorite and passively concentrated in deformed zones because of the loss of more soluble minerals quartz calcite dolomite by pressure solution simple observations can be used to test the validity of the assumptions required to calculate volume change in the analysis of a slaty matrix around a ptygmatic fold a map of values is drawn and these values are shown to be compatible with the general strain pattern for several limb hinge pairs of straight limbed folds the relations between volume change elongation parallel to limb layering l l o and the angle between limb and hinge are determined the influence of various parameters such as temperature pressure initial composition and structure of the rock on these relations is also pointed out

large sediment waves over the gulf of roses upper continental slope nw mediterranean recently acquired swath bathymetry and seismic datasets on the gulf of roses continental slope revealed the presence of large sediment waves that have developed between 200 and 400 m water depth geometric parameters were computed from the multibeam dataset and the obtained results showed mean sediment wave lengths of 2000 m and maximum heights of 60 m the analysis of seismic profiles showed the general architecture of the late quaternary deposits over the gulf of roses outer shelf and slope the outer continental shelf is characterized by morphological erosional features affecting the upper part of the most recent seismic unit over the continental slope five main unconformity bounded seismic units are differentiated with sediment waves developed in all of them the sediment waves observed over the continental slope are presumably generated by bottom currents intensified during major dense shelf water cascading events flowing downslope at an oblique angle with respect to the main bathymetry

azimuthal seismic anisotropy in a zone of exhumed continental mantle west iberia margin summary p wave azimuthal seismic anisotropy of the uppermost mantle has been shown to indicate directions of extension both recent and fossil in oceanic and continental settings we have determined the p wave anisotropy of a zone of exhumed continental mantle beneath the southern iberia abyssal plain as a possible indication of the initial direction of separation of iberia from north america in a region where there are no magnetic lineations or fracture zone lineations adjacent to the margin with which to constrain this direction over 10 000 airgun shots were recorded by 11 ocean bottom seismometers hydrophones from which 24 900 arrivals that had traversed unaltered weakly serpentinized upper mantle were picked complete 360 azimuthal coverage was attained between the shots and receivers for ranges up to 55 km p wave raypaths through the zone of exhumed continental mantle were ray traced through a velocity model that incorporated the 3 d relief of the seabed and acoustic basement time residuals with respect to this model were fitted using an azimuthally dependent function small anisotropy 7 per cent with a fast direction of 143 was determined to exist between 3 1 and 6 7 km below the top of the basement although the fast direction suggests that the post breakup mantle stretching between iberia and north america was northwest southeast this hypothesis is hard to reconcile with other observations instead we conclude that motion along concave downward faults during the exhumation of the upper mantle could have been sufficient to change an initially roughly east west margin normal fast direction to the 143 azimuth observed today the degree of serpentinization was estimated to decrease from 20 to 0 per cent between 3 and 7 km depth into the basement in the zone of exhumed continental mantle the degree of upper mantle anisotropy is similar to that observed in other oceanic and continental settings where similar degrees of serpentinization are inferred from mean p wave velocities

rock matrix structures in a zone influenced by a stylolite abstract a stylolitic structure is one of the visible manifestations of the pressure solution process in a rock the stylolitic process zone as defined in previous studies on both sides of a stylolite is studied by sem the chosen samples concern tectonic stylolites within a high porosity limestone 16 without tension gashes this zone corresponds to a local increase of porosity and comprises a large number of stylolitic joints showing a decreasing size from the macroscopic structure to simple contact between two grains two hypotheses are presented for the stylolite formation 1 the macroscopic stylolite is the result of the coalescence of earlier minor pressure solution structures 2 small stylolites nucleate gradually from a major stylolite joint the mass transfer can be realized either by diffusion between particles or by seepage through previously undescribed process zone fractures the mass deposition can be localized in the porous volume and the microcracks without requiring any additional tectonic openings including tension gashes the rock deformation is therefore limited to shortening parallel to 1 without normal extension

experimental pressure solution deposition on quartz grains the crucial effect of the nature of the fluid abstract experimental deformation by pressure solution was performed on an aggregate of small grains subjected to deviatoric stress 50 mpa for a long time several weeks or months at relatively high temperature and pressure in contact with various fluids air water 0 1 to 1 n naoh for quartz water and 5 nh 4 cl for calcite the change in shape of the grains by solution deposition depended on the duration of the experiment with the same fluid and on the concentration of the solid in solution with the same duration but various fluids significant shape changes were obtained for quartz grains but only with both long duration and very good solvents 1 n naoh by comparison with previously obtained results on the change of shape of fluid inclusions where the kinetics of dissolution was the rate controlling process the limiting process of the deformation of the quartz grains was inferred to be the rate of diffusion along grain boundaries saturated with trapped fluid

seasonal fluctuations of deep megabenthos finding evidence of standing stock accumulation in a flux rich continental slope abstract throughout the deep oceans diversity in the benthos peaks at intermediate slope depths in the western mediterranean lower slope an accumulation of biomass but not diversity at depths of 1200 1350 m has been observed however the precise causes of this biomass peak are unknown we examined the patterns of megafauna benthic biomass in the catalan sea open slope from 900 to 1750 m depth expanding the results in the context of the whole continental margin sampling was carried out by combining an otter trawl maireta system otms and an agassiz trawl during four different seasons in 2008 2009 at the same time current speed temperature and salinity were obtained year round by means of near bottom deployed sensors current meters and temperature conductivity sensors total biomass followed an inverted u shaped pattern peaking at depths of 1050 1350 m range related ecological forcings between shallower and deeper species may have caused this biomass accumulation at intermediate slope depths we also report on the seasonal variations of biomass in the studied depth range identifying a dynamic zone above 1000 m depth where populations of highly mobile species perform year round migrations throughout the slope and a more static region below 1000 m i e the twilight zone end with substantially less inter annual variations the arrival of new western mediterranean deep water from the deep basin to the lower slope in march may may have driven the accumulation of biomass at 900 and 1050 m depth over the same period in addition an adjacent submarine canyon was sampled with the same procedures to characterize its benthic megafauna community analyses revealed higher diversity but not biomass inside the canyon than in the adjacent open slope and a significantly different assemblage composition between the two habitats these results strengthen the concept of submarine canyons as hotspots of biodiversity and underline the importance of their conservation as diversity repositories

tectonosedimentary evolution of the deep iberia newfoundland margins evidence for a complex breakup history most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins both of which underwent only small amounts of crustal thinning in this paper we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended deep iberia newfoundland margins our results show that continental breakup is a complex process distributed in time and space on the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension during a first phase dated as tithonian to barremian 145 128 ma deformation is related to exhumation of mantle rocks basins become younger oceanward and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries a second phase dated as latest aptian 112 ma overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs the observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins

structural comparison of archetypal atlantic rifted margins a review of observations and concepts abstract in this study we compare three pairs of conjugate rifted margins that are often referred to as archetypes of rift systems despite numerous differences a remarkable first order structural similarity appears between the magma poor iberia newfoundland the magma rich mid norway east greenland and the sediment rich angola brazil rifted margins typical is the seaward arrangement of distinct domains proximal necking distal and outer that each present specific comparable structural characteristics our study also suggests that magma rich systems may go through a stage of hyper extension indicating that extreme crustal thinning does not preclude a magmatic breakup in this contribution we clarify the definition of a number of terms introduced recently in rifted margin studies we review the major features constitutive of these key referenced systems discuss their similarities and differences and examine how the related deformation modes develop in the life cycle of a rift that goes to seafloor spreading we conclude that the distinct domains observed in the margin architecture represent distinct stages in the evolution of rifted margin independently of their later evolution into magma poor or magma rich environments

distribution ecology and taphonomy of the organism trace scolicia in northeast atlantic deep sea sediments abstract the organism burrow scolicia was studied in deep sea sediment cores from several regions of the northeast atlantic including the iceland faeroe ridge rockall plateau and reykjanes ridge the data comprised sedimentological and physical measurements and x ray radiographs scolicia generally can be observed only in radiographs grain size and sorting of sediments control the distribution of the echinoids that produce scolicia if developed under optimum ecological conditions in well sorted coarse silts to fine sands scolicia dominates the biogenic structures with its very characteristic ichnofabrics its distribution pattern is influenced mainly by bottom currents sedimentation rate and the faunal association indirectly a dependence on water depth also seems to exist the preservation and recognition of scolicia in lithified sediments needs special conditions these include restricted competition by organisms of the deeper burrowing tiers its generation within the optimum sediment grain size or its production at the sand silt mud interface

metamorphic control of the magnetic mineralogy of black shales in the swiss alps toward the use of magnetic isogrades abstract the magnetic susceptibility of the helvetic jurassic black shales sampled around the aar and gothard massifs in the swiss alps is due to iron bearing silicates magnetite or pyrrhotite it exhibits a clear correlation with the alpine metamorphism from zeolite to amphibolite facies it firstly decreases due to the breakdown of original magnetite then sharply increases when pyrite is transformed into magnetic pyrrhotite using numerous field measurements of the susceptibility it was possible to carry out a fast and precise mapping of the pyrrhotite in isograde which appears to correspond closely to the stilpnomelane out isograde the matrix susceptibility obtained by means of high field measurements with a cryogenic magnetometer is due to iron bearing silicates and shows only smooth variations with metamorphism both monoclinic and hexagonal pyrrhotites are observed in the high grade area

seismic constraints on the three dimensional geometry of low angle intracrustal reflectors in the southern iberia abyssal plain several lines of evidence suggest that simple shear rifting of the continental crust in the form of low angle detachment faulting occurred during the final stages of continental breakup between west iberia and the grand banks the primary evidence for such faulting is the occurrence of low angle high amplitude reflectors within the basement adjacent to the ocean continent transition zone here we present a series of intersecting depth migrated seismic reflection profiles that image one such reflector the h reflector located on the southern edge of galicia bank h lies beneath several boreholes drilled during odp legs 149 and 173 in a region where the oceanward extent of extended continental crust steps at least 150 km westward from its location in the southern iberia abyssal plain to its location off the relatively shallow galicia bank in our profiles h appears to define a surface that extends over a region of at least 200 km2 and that dips down 19 to the north towards galicia bank the profiles show that a close affinity exists between h and the most seaward continental crust based on geophysical data and odp drilling results we infer that the basement above h is composed of continental crust deformed by extensional faults into a series of wedge shaped blocks and thin slivers these basement wedges have a complex 3 d geometry h rises to the basement surface on a number of the seismic profiles and appears to define locally the oceanward extent of continental fault blocks

tectonic implications of exposure of lower continental crust beneath the iberia abyssal plain northeast atlantic ocean geophysical evidence we present new seismic data from a basement high beneath the southern iberia abyssal plain that appears from the latest ocean drilling program odp results and indirectly from various seismic observations to consist of lower continental crustal material this is a unique opportunity to use seismic profiles and other geophysical evidence to investigate the tectonic process which led to the exhumation of these rocks we infer that the lower crust was exhumed at the seafloor and then uplifted toward the end of rifting our results lead to the following new observations low angle detachment faults previously reported along the east west lusigal 12 profile across the southern iberia abyssal plain penetrate both the 3 10 km thick continental crust and unusually the uppermost mantle processing of new multichannel seismic reflection profiles across the basement high on which odp sites 900 1067 and 1068 are located reveals that the high is bounded by a previously unsuspected steep landward dipping normal fault on its east flank basement cores from the above odp sites also reveal that the high is not capped by the previously predicted early syn rift sediment but by rocks from the lower continental crust these unexpected observations are incorporated into a new tectonic model of the development of this part of the west iberia margin which is also consistent with other geophysical observations a novel feature of this model is the proposal that the seaward edge of the continental crust is thinned to 3 6 km by a currently poorly understood process the model implies three stages of deformation 1 lithospheric extension principally by symmetric pure shear which leads to a 10 km thick crust in which the lower crust is largely absent over the axial zone and the crust mantle boundary forms a shear zone 2 further thinning and then dissection of the most distal continental crust by seaward dipping low angle normal faults 3 inception of a high angle landward dipping normal fault that offsets the tectonized crust mantle boundary and uplifts the lower crust to the crest of the basement high on which odp sites 900 1067 and 1068 were drilled

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

exhumed upper mantle within the ocean continent transition on the northern west iberia margin evidence from prestack depth migration and total tectonic subsidence analyses 1 the west iberia continental margin contains an enigmatic north south ridge of serpentinized peridotite located within the ocean continent transition we used prestack depth migration and total tectonic subsidence analysis to constrain the basement type adjacent to the ridge in order to learn more about its emplacement prestack depth migration was performed on segments of the nine east west lines from the iberia seismic experiment ise 97 and total tectonic subsidence analyses were performed on the depth sections the seismic data and subsidence analyses are consistent with exhumed upper mantle occurring immediately landward of the ridge suggesting that the ridge is located within a broad zone of exhumed mantle that has been serpentinized the subsidence analyses also provide minimum bounds on the thickness of the serpentinized layer which extends from the zone of exhumed mantle landward under thinned continental crust exhumed upper mantle has previously been identified in the wider ocean continent transition to the south in the southern iberia abyssal plain and we conclude that similar but narrower exposures occur to the north in the galicia bank area while upper mantle appears to have been tectonically exhumed along all the ise 97 lines it does not always form a distinct basement ridge there is no well defined ridge on three seismic profiles in the middle of the ise 97 survey where it is well developed the peridotite ridge parallels a deeply penetrating west dipping normal fault and the three middle lines appear to represent a transfer zone where this normal fault is not well developed

relationships between strike slip movement and fold trends in thin skinned tectonics analogue models abstract in thin skinned tectonics a sediment cover has been sheared off from an underlying basement in many cases such detachments are located in salt horizons during deformation faults and narrow anticlinal folds can develop in the cover analogue models show that fold axis patterns are related to the compression direction and to the position and shape of the faults in each model a multilayer made of paraffin wax and grease represents the cover sliding over a rigid basement made of plexiglass in each of the three experiments a fault is cut before deformation this fault may be located 1 in the basement 2 in the cover with a limited length or 3 in the cover with an unlimited length the fold axis patterns are very heterogeneous around a limited length fault in the multilayer where the fold axes deviation can reach 90 around the fault tips they are quite homogeneous around an unlimited length fault irrespective of its location an unlimited length fault mainly induces a slight deviation of the fold axes due to strike slip movement the detachment horizon reduces the transmission of stresses from the basement and in such cases the final deformation is very sensitive to local heterogeneities inside the overriding multilayer