nappes tectonics of oblique plate convergence and metamorphic evolution related to 140 million years of continuous subduction franciscan complex california this paper presents a new synthesis of franciscan complex tectonics with the emphasis on the pre san andreas fault history of these rocks field relations suggest that the franciscan is characterized by nappe structures that formed during sequential accretion at the trench the presence of these structures along with other field relations including the lack of evidence for large offset of conglomerate suites indicates that strike slip fault systems of large displacement 500 km did not cut the franciscan complex during subduction regional geology and comparisons to modern arc trench systems suggest that strike slip faulting associated with oblique subduction took place inboard east of the franciscan in the vicinity of the magmatic arc the franciscan varies along strike because individual accreted elements packets of trench sediment seamounts etc did not extend the full length of the trench different depths of underplating distribution of post metamorphic faulting and level of erosion pro

focused subaerial erosion during ridge subduction impact on the geomorphology in south central peru data obtained from low temperature thermochronometers such as apatite fission track and u th he are combined with morphometric information extracted from digital elevation models this combination shows several geomorphological effects that are caused by the migration of the nazca ridge along the peruvian coastal margin offshore the depth of the deep sea trench decreases by 1500 m where the nazca ridge collides with the continental south american plate onshore the ridge causes an uplift of at least 800 m in the coastal cordillera this uplift results in a westward shift of the coastline thereby focusing and increasing erosion in the uplifted areas at the trailing edge the shelf subsides and the coastline retreats eastwards producing at least part of the indentation observed between paita and pisco the ridge acts therefore like a wave uplifting the andean margin as it traverses inland and southwards leaving a clear fingerprint on the topographic evolution of the peruvian coastal margin

on the tectonics of the ligurian apennines northern italy four nappes have been recognized in the ligurian apennines in the lavagna nappe very low grade metamorphism is combined with very large originally w facing isoclinal folds in the other nappes no evidence for metamorphism is found and all eutectonic folding was originally e to ne facing tectonic transport along the major nappe contacts was in an e to ne direction a tectonic model is presented which explains the generation of the large originally w facing folds as a result of originally e inclined subduction within a young oceanic basin young oceanic lithosphere maximum age approximately 25 ma subducted beneath oceanic lithosphere with a maximum age of approximately 40 ma under the influence of horizontally oriented compressional forces within the tectonic wedge associated with the subduction originally w facing isoclinal folding and metamorphism occurred decrease and or termination of compression resulted in the cessation of the subduction movements followed by uplift of the region above the subducted plate by means of buoyancy this uplift formed a slope from which sequences slid in an e to ne direction causing e to ne facing folds ultimately detachment and thrusting of gravitational nappes took place by which process rock sequences of oceanic origin have been externally transported to attain ensialic continental domains the triassic early oligocene tectonic events recognized in the ligurian apennines correlate quite well with the events that preceded the collision phase of the alps

the giant ruatoria debris avalanche on the northern hikurangi margin new zealand result of oblique seamount subduction despite convergent margins being unstable systems most reports of huge submarine slope failure have come from oceanic volcanoes and passive margins swath bathymetry and seismic profiles of the northern hikurangi subduction system new zealand show a tapering 65 30 km wide by 65 km deep margin indentation with a giant 3150 630 km3 blocky debris avalanche deposit projecting 40 km out across horizontal trench fill and a debris flow deposit projecting over 100 km slide blocks are well bedded up to 18 km across and 1 2 km high the largest being at the avalanche deposit s leading edge samples dredged from them are mainly miocene shelf calc mudstones similar to those outcropping around the indentation cores from cover beds suggest that failure occurred 170 40 ka possibly synchronously with a major extension collapse in the upper indentation however the northern part of the indentation is much older the steep straight northern wall is close to the direction of plate convergence and probably formed around 2 0 0 16 ma as a large seamount subducted leaving in its wake a deep groove obliquely across the margin and an unstable triangle of fractured rock in the 60 angle between groove and oversteepened margin front the triangle collapsed as a blocky avalanche leaving a scalloped southern wall and probably causing a large tsunami tentative calculations of compacted volumes suggest that the indentation is over 600 km3 larger than the avalanche supporting a two stage origin that includes subduction erosion since failure convergence has carried the deposits 9 km back toward the margin causing internal compression the eventual subduction accretion of the ruatoria avalanche explains the scarcity of such features on active margins and perhaps the nature of olistostromes in fold belts

the association of continental crust rocks with ophiolites in the northern apennines italy implications for the continent ocean transition in the western tethys abstract the late cretaceous sedimentary melanges from the external liguride units of the northern apennines include large slide blocks of ophiolites and lower and upper continental crust rocks representative of a continent ocean transition between the internal liguride oceanic domain and the thinned continental margin of the adria plate the slide blocks preserve a record of the long lived history of rifting which led to opening of the jurassic western tethys basin the external liguride ophiolites consist of 1 undepleted spinel peridoties partly re equilibrated under plagioclase facies conditions which were interpreted as unroofed subcontinental mantle 2 rare gabbroic rocks mainly troctolite to olivine bearing gabbro probably crystallised from n morb magmas and 3 basalts with n to t morb affinity covered by late callovian early oxfordian radiolarian cherts both gabbroic rocks and basalts locally intrude the mantle peridotites and postdate their re equilibration to plagioclase facies conditions the slide blocks of lower continental crust are composed of gabbro derived mafic granulites and felsic granulites the latter include quartzo feldspathic granulites and rare quartz poor to quartz free charnockitic rocks in both mafic and felsic granulites granulite facies re equilibration was followed by a retrograde metamorphic evolution to amphibolite greenschist and subgreenschist facies conditions retrogression is commonly accompanied by deformations progressively changing from plastic to brittle the upper crustal rocks occurring as slide blocks consist of hercynian granitoids with orogenic affinity mainly biotite bearing granodiorites and peraluminous two mica leucogranites locally the granitoids are intruded by basaltic dykes or capped by basaltic flows and radiolarian cherts the granitoids underwent polyphase brittle deformations under subgreenschist facies conditions which predated the basalt emplacement the tectono metamorphic evolution recorded by the slide blocks of the external liguride units started in the late carboniferous early permian about 290 ma with the emplacement at deep crustal levels of the gabbroic protoliths for the mafic granulites the associated felsic granulites likely represent the remnants of the lower continental crust intruded by the gabbro derived granulites mafic and felsic granulites subsequently underwent tectonic exhumation in permo triassic times as testified by the development of granulite to amphibolite facies ductile shear zones the granulites were finally exhumed to shallow levels probably in association with the subcontinental mantle in late triassic middle jurassic times the latter period was most likely characterized by extensive brittle faulting at shallow crustal levels thus giving rise to extensional allochthons formed by stretched slices of granitoids the western tethys opening is finally testified by the basalt intrusion and effusion in the late jurassic followed by deep sea pelagic sedimentation the external liguride crustal stratigraphy can be regarded as a fossil example of the transitional realm at the continent ocean boundary this reconstruction fits well with the available data on the present day continental margins derived from passive lithosphere stretching

petrology and geochemistry of siliciclastic rocks of mixed feldspathic and ophiolitic provenance in the northern apennines italy provenance in clastic sedimentary rocks in the northern apennines is determined by integrated petrographic and geochemical criteria thus mafic poor arkoses in the gottero formation senonian paleocene deposited prior to the alpine orogeny were derived from granitic provenance in the sardinian corsican massif in the gottero formation chemical criteria distinguish between very low input of detrital mafic material and co c and ni added entirely by adsorption on clay minerals post alpine orogeny feldspathic sandstones in the macigno formation mid oligocene lower miocene and cervarola formation lower miocene reflect a more diverse provenance of granitic metamorphic ophiolitic and sedimentary rocks in the apennines and alps the macigno and cervarola rocks are distinguished by serpentine gabbro and diabase fragments and higher chlorite contents than in the gottero rocks chemically the macigno and cervarola rocks contain distinctive signatures expressed in higher mgo co cr and ni contents of the mafic ultramafic detritus a wider range and more scattered cr and ni variation and higher niggli ti for a given niggli al alk content the mgo co cr and ni abundances indicate up to 10 ultramafic ophiolitic detritus in the macigno and cervarola sandstones and up to 17 ophiolitic detritus in associated shales estimated by comparison of mixtures of feldspathic sands with ligurian peridotites up to 10 basaltic ophiolitic detritus in these sediments is suggested by cao and fe2o3 total abundances petrographic data indicate that a major part of the detritus in the macigno and cervarola formations is from alpine granitic basement of calc alkaline granite to tonalite plutons and gneisses but apart from higher ba in macigno and cervarola sandstones than in the gottero sandstones this is difficult to identify chemically the trace elements cr ni ba rb ce la y co cu ga pb and zn generally have positive correlations with niggli al alk a chemical surrogate measure of sheet mineral clays micas and chlorites content whereas sr which is associated with carbonate and feldspar shows negative correlation with al alk an olistostrome unit contains the most weathered detritus but otherwise shows similar chemical variation to the other formations methods to 1 identify separately mafic and ultramafic inputs 2 recognize in shales co cr and ni derived from ophiolitic sources and non ophiolitic sources 3 estimate the minimum mafic ultramafic proportion in a sediment may have general application elsewhere in sedimentary and metasedimentary rocks

on the source of water from the thermomineral springs of lake kinneret israel the chemical and isotopical 18o deuterium composition of the thermomineral water emerging around lake kinneret is shown to be similar to that of the saline water found in deep oil exploration wells in the coastal plain of israel and different from the water found near the dead sea it is suggested that an ancient brine which is filling the deep non flushed aquifers is driven from the south towards the rift valley by a piston action and is mixed with paleo and contemporaneous meteoric water before emerging as thermomineral springs

beach response to shore parallel breakwaters at sea palling norfolk uk abstract the effects of four offshore breakwaters built between 1993 and 1995 at sea palling norfolk uk on beach morphology are discussed the structures were built during the first phase of a multi phase construction programme and are expected to provide long term protection for sea palling and 6000 ha of low lying land against tidal inundation through the provision of a wide beach in front of the existing seawall and dunes the results presented here span all stages of breakwater construction during phase 1 beach level changes were monitored during the period from 1995 to 1999 a geographical information system gis was used to calculate differential surfaces between surveys in order to investigate local patterns of accretion and erosion and to determine volume changes between consecutive surveys additional data collected by the environment agency since 1991 were analysed to investigate beach and bathymetry changes prior to the construction of the breakwaters in association with periodic nourishment programmes the scheme has been locally successful in retaining recharged sediment on the beach but the extent of the salients prevents to a great extent the south eastward littoral drift as a result effects on the beaches both down and up drift of the breakwaters have been considerable the continuing increase in beach volume indicated that by january 1999 equilibrium had not been reached

empirical orthogonal function analysis of shoreline changes behind two different designs of detached breakwaters this paper compares the shoreline responses immediately shoreward of two adjacent schemes of segmented shore parallel rubble mound breakwaters undergoing the same forcing by waves and tides scheme one consists of four longer emergent breakwaters that have produced tidal tombolos in their lee scheme two consists of five shorter lower breakwaters that are submerged at higher tides with salients in the breakwater s lee empirical orthogonal function analysis was used to decompose a video derived shoreline dataset into the dominant modes of shoreline change for both schemes the two schemes showed similar modes of change the primary mode of change for both schemes was the cross shore growth and shrinking of the salients tombolos the secondary mode of change was the longshore movement of the salients tombolos for all modes of change the dominant length scale was dictated by the breakwater dimensions and locations a new manifestation of hydrodynamic parameters is introduced the cumulative integral of the de meaned parameters this parameterisation allowed for meaningful correlation of the temporal eof components with forcing parameters and identification of the important influence of the tide on observed morphodynamic change clear differences were observed between the shoreline responses measured in schemes one and two including differences in bay erosion accretion and the longshore translation of salients tombolos the beaches in scheme two showed behavioural patterns similar to unprotected beaches which were not observable in scheme one it is postulated that these differences are caused both by the different breakwater designs and by variation in longshore sediment supply

melange rheology and seismic style shear displacements in crustal fault zones are accommodated by a range of seismic styles including standard earthquakes non volcanic tremor and continuous and transitory aseismic slip subduction channel shear zones containing highly sheared fluid saturated trench fill sediments intermingled with fragments of oceanic crust are commonly inferred to occur along active subduction megathrusts if this interpretation is correct these plate boundary faults are not discrete planes but may resemble the melange shear zones commonly found in exhumed subduction related rock assemblages melange deformation appears to depend critically on the ratio of competent to incompetent material with shear surfaces localized along lithological contacts or within competent domains while matrix flow accommodates shearing by distributed strain if the style of strain and or displacement accommodation in a melange reflects the partitioning between aseismic and seismic slip the proportion of competent material seems likely to be a significant factor affecting seismic style within subduction channel shear zones and along comparable mixed lithology fault zones

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

recycling of heterogeneous material in the subduction factory evidence from the sedimentary melange of the internal ligurian units italy in the northern apennine italy the internal ligurian units consist of middle late jurassic ophiolites covered by thick sedimentary deposits whose top is represented by the early paleocene bocco shale this formation is characterized by mass transport deposits interlayered with thin bedded siliciclastic turbidites the sedimentological and structural features of these mass transport deposits reveal a long lived history of recycling of heterogeneous material in a subduction setting this history started with the frontal accretion of a fragment of oceanic crust into an accretionary prism whose lower slope was subsequently affected by tectonic erosion and consequent instability leading to the production of mass transport deposits and the transfer of material to the lower plate these mass transport deposits were subsequently underthrust and then again transferred to the base of the accretionary prism by coherent underplating before their exhumation to the surface the bocco shale is thus representative of a subduction setting where both accretionary and erosive events occurred depending on changing boundary conditions the reconstructed history for the bocco shale indicates that the sedimentary and gravitational processes both at the prism front and on the prism slope possibly induced by alternating accretion and erosion events are the most efficient mechanisms of lithological mixing and recycling in subduction margins

beach morphologies induced by breakwaters with different orientations abstract a desired outcome in the construction of a detached emerged breakwater is the formation of an accretionary salient in its lee to augment the beach improve beach amenity and provide an additional buffer from storm waves the extent to which this salient forms and its morphology are strongly controlled by the breakwater geometry with respect to the original shoreline sediment availability and local wave climate the purpose of this paper is to identify how breakwater geometry and orientation of gaps between individual breakwaters alter the direction of waves entering the gaps and change the asymmetry of the salients four distinct breakwater sites along the emilia romagna coastline in northern italy were chosen for a detailed field and desktop study comprising three dimensional topographic and bathymetric surveys sediment sampling lidar flights and historical shoreline mapping the orientations of the shorelines at these four sites range over 43 resulting in different exposures to the dominant waves the oblique orientations of the gaps between individual breakwater segments at three of the four sites effectively create a gap window between breakwaters favoring the exposure of short period waves from the north and diminishing the effect of longer waves from the dominant east salients can be symmetrical despite an acute angle of approach of the dominant deep water waves where refraction is enhanced by offshore topography and breakwaters are parallel to the shore waves approaching normal to the gap window undergo less diffraction due to their shorter length relative to the gap window width and undergo less attenuation by breaking and bottom friction if they are locally generated and have short periods greater breaking wave energy on the gap facing slope of the salient can create shoreline and morphological asymmetry the implication is that breakwater orientations can be designed or altered to selectively dampen or facilitate wave energy to enhance sediment transport in a desired direction provided that breakwaters are not too far offshore and sediment availability is not restricted to affect salient formation adjusting exposure via gap orientation can create morphologies that cannot be inferred from process dominant conditions

the architecture of an incipient oceanic basin a tentative reconstruction of the jurassic liguria piemonte basin along the northern apennines alpine corsica transect in this paper a scenario for the early evolution of the jurassic oceanic liguria piemonte basin is sketched for this purpose four selected examples of ophiolite sequences from the northern apennines and corsica are described and analyzed in the external ligurian units northern apennines the ocean continent transition of the adria plate was characterized by a basement made up of subcontinental mantle and lower continental crust covered by extensional allochthons of upper crust both the basement rocks and the extensional allochthons are cut by basaltic dikes and covered by basalts and pelagic deposits the conjugate ocean continent transition of the corsica margin represented by the balagne nappe corsica was composed of mantle peridotites and gabbros covered by basaltic flows and minor breccias that in addition include continent derived clasts by contrast the innermost i e closest to the ocean preserved area observed in the internal ligurian northern apennines and inzecca corsica units consists of former morphological highs of mantle peridotites and gabbros bordered by small basins where the basement is covered by a volcano sedimentary complex characterized by ophiolitic breccias and cherts interlayered with basaltic flows the overall picture resulting from our reconstructions suggests an asymmetric architecture for the liguria piemonte basin with a central area bounded by two different transition zones toward the continental margins this architecture can be interpreted as the result of a rifting process whose development includes a final stage characterized by passive asymmetric extension of the lithosphere along an east dipping detachment fault system

izu bonin arc subduction under the honshu island japan evidence from geological and seismological aspect abstract the izu bonin intra oceanic arc with 20 35 km thick continental crust is being subducted under the honshu presumably since 17 ma tomographic image clearly demonstrates that the whole izu bonin arc is subducting under the honshu arc geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 ma

recharge and salination processes in the carbonate aquifers in israel limestone and dolostone aquifers play a major role in the water supply system of israel in many cases there are brackish to saline springs at their outlets the source of the saline water and the mechanism of salinization differ from place to place in some cases it is due to mixing with seawater mediterranean or dead sea at the fresh saline water interface while in other cases deepseated brines emerge along regional faults the general policy for reclaiming the fresh component of the water before mixing with the saline component is to try to catch the fresh water as far as possible upstream from the outlet in most cases this is the area where the mixing takes place the main case histories in israel are discussed in this paper

fluid flow during accretion in sediment dominated margins evidence of a high permeability fossil fault zone from the internal ligurian accretionary units of the northern apennines italy abstract we report here a detailed structural study carried out in the internal ligurian units of the northern apennines italy formed during the building of the alpine accretionary complex through subduction of the sediment filled ligure piemontese oceanic basin the deformation mechanisms associated with fluid migration across an accretion related fault zone have been studied through a detailed analysis of different generations of syn tectonic veins hydrofracturing occurred mainly sub parallel to bedding in unlithified to semi lithified sediments transient upward directed fluid injection locally connected the decollement parallel veins through bedding normal hydrofractures of lithified sandstone layers a third vein system comprises fibrous hydrofractures developed on the limbs of accretion related folds crosscutting vein sets and the peculiar features of each identified vein set suggest that deformation was intricately associated with lithification and diagenetic processes dehydration produced fluids transiently injected the lithifying sediments leading to local stress permutations the proposed model provides a ramp flat migration of fluids in which fluid flow is enhanced along high permeability less cohesive layers leading to the development of regional dilated hydrofracture channels like those recognized along the decollement zone of modern margins the more competent layers are truncated by high angle fractures representing the transient connectivity that existed between horizontal conduits

growth of accretionary wedges and pulsed ophiolitic melange formation by successive subduction of trench parallel volcanic elevations fault bounded coherent belts alternating with belts of melanges are common in accretionary wedges and are usually interpreted as a result of imbrication along subduction zone megathrusts using the neoproterozoic early cambrian blovice accretionary complex bac bohemian massif as a case example we present a new model for the origin of alternating belts through the repetition of several cycles of 1 offscraping and deformation of trench fill sediments to form the coherent units interrupted by 2 arrival and subduction of linear trench parallel volcanic elevations the latter process leads to an increase in the wedge taper triggering mass wasting and formation of olistostromes at the same time ophiolitic melanges form by disruption of an upper part of the volcanic ridge and incorporation of the disrupted ocean floor succession into the olistostromes specifically the bac represents a complete section across an accretionary wedge and records three such major pulses of ophiolitic melange formation through subduction of an outboard back arc basin

the rate of flushing as a major factor in determining the chemistry of water in fossil aquifers in southern israel abstract issar a 1981 the rate of flushing as a major factor in determining the chemistry of water in fossil aquifers in southern israel in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 285ndash 296 a parallel trend has been found to exist between the isosalinity lines and the isopiezo metric lines in the fossil aquifers of the nubian sandstones in southern israel and the central sinai the flow pattern in these aquifers determines the rate of mixing between paleo seawater and paleo meteoric water this flowpattern is determined by the spatial relations between the nubian sandstone outcrops in the central sinai and the major fault lines of the dead sea and suez rift valleys a cumulative chemical composite diagram in which 18o stable isotope data were plotted makes it possible to classify the water and to trace the ratios in the mixture

probabilistic modelling of long term beach evolution near segmented shore parallel breakwaters this paper presents a new framework for probabilistic modelling of long term beach evolution in the vicinity of detached breakwaters the study focuses on the key physical processes contributing to beach variability over a range of spatial and temporal scales based on a one line model the framework is enhanced with sophisticated solutions for beach wave structure interaction diffraction together with a treatment of varying tide level the sediment transport rate is calibrated at regional and local levels using data from bespoke field campaigns and site specific coefficients are proposed monte carlo simulation is conducted for long term shoreline simulation under a sequence of time varying sequence of waves currents and tidal levels the results of the monte carlo simulation give an insight into the statistical characteristics of beach behaviour within the defence system in particular regions within the scheme that are relatively stable and those that exhibit greater natural fluctuations are identified

extensional faulting in an intraoceanic subduction complex working hypothesis for the palaeogene of the alps apennine system abstract within the ophiolite complexes exposed in the ligurian alps and apennines nw italy several extensional detachment faults are identified which overprint late cretaceous high pressure metamorphic fabrics developed in an intraoceanic subduction system one of these detachment faults is the sestri voltaggio line which marks an 8 kbar pressure gap between blueschist facies ophiolites and calcareous sediments of the sestri voltaggio zone and underlying eclogite fades ophiolites and metasediments of the voltri massif radiometrie and stratigraphie constraints suggest that extension has occurred during the late paleocene to possibly early eocene from the middle eocene onward compressional tectonics prevailed again resulting in westerly directed imbrications in the ligurian alps and easterly directed folding and thrusting in the ligurian apennines a strong correlation is identified between the africa europe convergence rate and the stability of the accretionary wedge i e the paleocene extension coincides with a period of strongly reduced convergence velocities whilst the middle eocene transition to compressional tectonics concurs with an acceleration of the convergence rate this inferred relation between convergence rate and style of internal deformation matches very closely the results from mechanical models addressing the stability of orogenic wedges with a strain rate dependent rheology and provides the basis for a working hypothesis on the palaeogene evolution of the alps apennine orogenic system

deformation and hydrofracture in a subduction thrust at seismogenic depths the rodeo cove thrust zone marin headlands california we have investigated the fabric and the deformational processes of an exhumed subduction zone thrust active at seismogenic depths the rodeo cove thrust zone which outcrops north of the golden gate bridge of san francisco imbricates two basalt chertsandstone sequences belonging to the marin headlands terrane franciscan complex the thrust outcrop is a 200 m thick complex zone that displays a range of stratal disruption from incipient deformation to a broken formation in the central part of the outcrop dominated by basaltic lithologies where zones of concentration of deformation have been mapped disruption is made by variably dense discrete fault systems synthetic to the main thrust r and p fractures these faults are marked by cataclasites with a shaly matrix that shows a scaly foliation defi ned by chlorite and pumpellyite which also constrain the depth of faulting 8 10 km t 200 250 c within the seismogenic zone the central part of the fault also features the densest system of carbonate fi lled veins veins occur in the broken formation matrix and fragments in both cases parallel to the foliation the veins are either folded truncated or pressure solved along the cleavage cementation and hardening of shear surfaces of the fault core may have caused the distribution as opposed to localization of subsequent slip events the fault core may have developed in basaltic rocks because of their inherently high permeability and propensity to transmit overpressure from deeper levels of the subduction zone our analysis has shown that accretionary deformation is strongly controlled by injection of overpressured fl uids occurring through systems of multiple dilatant fractures grossly parallel to the decollement zone the crosscutting relationships between veining and foliation suggest that fl uid injection is cyclic and consequently that large transient variations in permeability and cohesion may occur the repeated injection of veins parallel to the fault zone may be explained by cyclic changes of the stress or by difference in tensional strength parallel to and perpendicular to the foliation both of which would require extremely high fl uid pressure we interpret the features of the rodeo cove thrust zone as evidence of the seismic cycle and hypothesize a compressional stress fi eld in the interseismic phase and an extensional stress fi eld in the immediately postseismic phase

decadal scale impacts of a segmented shore parallel breakwater system abstract between 1994 and 1997 nine segmented shore parallel rock mound breakwaters were constructed at the meso tidal beach of sea palling on the north sea coast of the uk to provide protection for a low lying hinterland vulnerable to storm surge inundation and a 3 5 km section of sea wall that was in danger of collapse due to low beach levels in this paper we assess the effectiveness of these breakwaters and of the associated beach recharge events in stabilising the beaches both within and around the breakwater system and we examine their impact on the wider littoral drift system we discuss a trapping mechanism whereby sand entering the system as littoral drift is effectively retained at both ends of the system at the northern updrift end the trapping of littoral drift sediments aided by a 1 3 106 m3 sediment recharge designed to remedy severe gap erosion lead to the growth of salients into tidal tombolos effectively changing the x h ratio distance offshore depth on pope and dean s 1986 morphology existence diagram the largest tombolo tombolo 5 is at the updrift end is only inundated during large storm surges and forms a 260 m wide barrier to littoral drift and the alongshore supply of sediment to breakwater beaches in response to a large reduction in littoral drift shorelines in the centre of the system are steadily retreating with some embayment shorelines being closer to the seawall in 2005 than they were pre construction these shorelines have not reached a steady state and further recharge will be needed unless the littoral drift supply can be restored the evidence nearshore morphology sediment starved beaches down drift recharge shoreline change patterns and a simple sediment budget indicates that an estimated 80 of littoral drift sediments are directed offshore at tombolo 5 bypass the breakwaters and downdrift beaches but may return to shore 2 5 km downdrift as a direct result of recharge sea palling makes a less than ideal case for assessing the applicability of micro tidal shoreline response equations to breakwaters in tidal settings the sea palling experience also demonstrates that the use of beach recharge in combination with breakwaters in settings of high littoral drift requires very careful consideration as it has the potential to block littoral drift and starve the local beaches the opposite effect of that intended by both techniques

provenance changes for arenaceous formations of the northern apennines italy a complex pattern of provenances is displayed by 15 formations in the northern apennines composed chiefly of turbidites that were deposited during the alpine orogenesis q f l and qp lv ls values can be used to characterize specific source areas that existed in the apennine region from cretaceous through miocene time whereas sandstone mineralogy can be used to infer plate tectonic setting such an approach must make allowances for both the size of the area studied and the tectonic framework that existed prior to sandstone deposition in an early stage of the compressive phase of the tethys late cretaceous both arkose and litharenite were derived from cratonic blocks whereas volcanic sandstone was derived from uplifted oceanic sediments and lavas sediments recording the main oligo miocene collisional tectonic phases accumulated in two principal tectonic settings 1 intermontane successor basins and 2 foreland basins in the first case individual formations exhibit a wide provenance variability arkosic lithic sandstone recycled orogen volcanic sandstone magmatic arc and arkose were deposited simultaneously in the second case basins filled with thick turbidite sequences composed of arkose and lithic arkose which were supplied by basement rocks uplifted along the edge of the european craton and or by the nascent orogenic belt

accuracy assessment of georectified aerial photographs implications for measuring lateral channel movement in a gis aerial photographs are commonly used to measure planform river channel change we investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number 6 30 and type human versus natural landscape features of ground control points gcps and the order of the transformation polynomial first second and third order affected the spatial accuracy of a typical georectified aerial photograph error was assessed using the root mean square error rmse of the gcps as well as error in 31 independent test points the rmse and the mean and median values of test point errors were relatively insensitive to the number of gcps above eight but the upper range of test point errors showed marked improvement i e the number of extreme errors was reduced as more gcps were used for georectification using more gcps thus improved overall georectification accuracy but this improvement was not indicated by the rmse suggesting that independent test points located in key areas of interest should be used in addition to rsme to evaluate georectification error the order of the transformation polynomial also influenced test point accuracy the second order polynomial function yielded the best result for the terrain of the study area gcp type exerted a less consistent influence on test point accuracy suggesting that although hard edged points e g roof corners are favored as gcps some soft edged points e g trees may be used without adding significant error based upon these results we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately f5 m with 10 chance of greater error the implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them this study demonstrates the importance of using an independent test point analysis in addition to the rsme to evaluate and treat locational error in channel change studies d 2005 published by elsevier b v

salinization and dilution history of ground water discharging into the sea of galilee the dead sea transform israel abstract the mechanism governing salinization of ground water discharging into the sea of galilee in israel has been the subject of debate for several decades because the lake provides 25 of the water consumed annually in israel correct identification of the salt sources is essential for the establishment of suitable water management strategies for the lake and the ground water in the surrounding aquifers existing salinization models were evaluated in light of available and newly acquired data including general chemistry and o h c and cl isotopes based on the chemical and isotopic observations the proposed salt source is an ancient intensively evaporated brine 21 to 33 fold seawater which percolated through the valley formations from a lake which had formed in the rift valley following seawater intrusion during the late miocene low na cl and high br cl values support the extensive evaporation whereas high ca cl and low mg cl values indicate the impact of dolomitization of the carbonate host rock on the residual solution based on radiocarbon and other isotope data the dilution of the original brine occurred in two stages the first took place 30 000 a ago by slightly evaporated fresh to brackish lake water to form the sea of galilee brine the second dilution phase is associated with the current hydrological regime as the sea of galilee brine migrates upward along the rift faults and mixes with the actively circulating fresh ground water to form the saline springs the spatially variable chemical and isotopic features of the saline springs suggest not only differential dilution by fresh meteoric water but also differential percolation timing of the original brine into the tectonically disconnected blocks registering different evaporation stages in the original brine consequently various operations to reduce the brine contribution to the lake may be differentially effective in the various areas

seafloor structural geomorphic evolution of the accretionary frontal wedge in response to seamount subduction poverty indentation new zealand abstract high quality swath bathymetry and seismic reflection data reveal that the steep forearc slope along the northern sector of the obliquely convergent hikurangi subduction zone is characteristic of non accretionary and tectonically eroding continental margins with reduced sediment supply in the trench relative to further south and the presence of subducting seamount relief on the hikurangi plateau these seamounts influence the subduction process and the structurally driven geomorphic development of the over riding margin of the australian plate frontal wedge the origin of the poverty indentation on the inboard trench slope is attributed to multiple seamount impacts over the last c 1 myr period accompanied by canyon incision thrust fault propagation into the trench fill and numerous large scale gravitational collapse structures with multiple debris flow and avalanche deposits ranging in downslope length from a few hundred metres to more than 40 km the indentation is directly offshore of the waipaoa river which is currently estimated to have a high sediment yield into the marine system the poverty canyon stretches 70 km from the continental shelf edge directly offshore from the waipaoa to the trench floor incising into the axis of the indentation the sediment delivered to the margin from the waipaoa catchment and elsewhere during sea level high stands including the holocene has remained largely trapped in a large depocentre on the poverty shelf while during low stand cycles sediment bypassed the shelf to develop a prograding clinoform sequence out onto the upper slope the formation of the indentation and the development of the upper branches of the poverty canyon system has led to the progressive removal of a substantial part of this prograding wedge by mass movements and gully incision sediment has also accumulated in the head of the poverty canyon and episodic mass flows contribute significantly to continued modification of the indentation by driving canyon incision and triggering instability in the adjacent slopes prograding clinoforms lying seaward of active faults beneath the shelf and overlying a buried inactive thrust system beneath the upper slope reveal a history of deformation accompanied by the creation of accommodation space the middle to lower poverty canyon represents a structural transition zone within the indentation coincident with the indentation axis the lower to mid slope south of the canyon conforms more closely to a classic accretionary slope deformation style with a series of east facing thrust propagated asymmetric anticlines separated by early stage slope basins north of the canyon system seamount impact has resulted in frontal tectonic erosion associated with the development of an over steepened lower to mid slope margin fault reactivation and structural inversion and over printing

evidence for precollisional subduction erosion in ancient collisional belts the case of the mid european variscides analysis of the fore arc remnants and suture zone rocks in the european variscides using criteria established for the circum pacific margins geometry sedimentary evolution and style of deformation shows that precollisonal orogenic evolution can also be reconstructed for ancient collisional belts the collision zone of the lower plate thrust belt rhenohercynian zone and the upper plate arc and fore arc remnants saxothuringian zone and saar basin indicate subduction erosion of the upper plate by some 50 km length of upper plate lithosphere prior to collision removal started during early convergence in the famennian ca 365 ma and lasted until the late visean onset of collision ca 330 ma part of this material may have been underplated below the upper plate and has since resurfaced as high pressure rocks contributing to the metamorphic core of the orogen

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

mechanisms of subduction accretion as implied from the broken formations in the apennines italy mesoscale structural analysis of the ligurian broken formations of the northern apennines and the regional occurrence of subduction related structures indicate polyphase folding as the mechanism responsible for progressive disruption the evidence for direct correlation between regionally extensive noncylindrical folds and tectonic disruption has a strong bearing on determining how the ligurian accretionary prism evolved for example the block in matrix structure of the ligurian tectonic melanges is produced through extension developed along fold limbs in a compressive stress field as expected from offscraping and intraprism deformation the model implied by the mesoscale and macroscale analyses of the ligurian tectonic melanges provides one mechanism of accretion reconciling two deformation styles i e stratal disruption and folding commonly seen in ancient accretionary prisms furthermore this model could be relevant in active accretionary prisms especially in the intraprism part where the seismic and drilling data are sparse

large scale melange formation due to seamount subduction an example from the mesozoic accretionary complex in central japan deformation of forearc wedges due to seamount subduction in modern trenches is related to the origin of mesozoic melanges in central japan and a hypothetical model for large scale melange formation due to seamount subduction is proposed recent studies of seamount subduction in modern trenches have revealed that seamounts pass under forearc wedges retaining their approximate original shape but the forearc wedges themselves are swelled in front of subducting seamounts and indented behind them this strongly suggests that forearc wedges are widely disrupted and transformed into large scale melanges that include seamount fragments the mesozoic accretionary complex in the mino terrane of central japan is comprised of large scale melanges including seamount fragments and coherent tectonically stacked sedimentary successions of chert siliceous shale and turbidite in ascending order melanges are widespread in a belt 20 to 40 km wide and about 100 km long and seamount fragments of permian basalts and ree

from seamount accretion to tectonic erosion formation of osa melange and the effects of cocos ridge subduction in southern costa rica 1 the costa rica portion of the middle america trench mat is characterized by active tectonic erosion a process that causes the removal of material from the base of the upper plate as the plate boundary migrates upward offshore studies demonstrate accelerated subduction erosion starting at the miocene pliocene boundary as the result of subduction of thickened galapagos related crust as presently represented by the cocos ridge the subduction of the cocos ridge also caused uplift and exposure of the outer forearc on the osa peninsula which offers a window to explore the tectonic evolution of the area the rocks outcropping on osa peninsula are a middle eocene middle miocene melange dominated by basalt chert and limestone resulting from accretion of seamounts the accretion dominated period of the mat evolution ended at the miocene pliocene boundary when thickened crust a paleo cocos ridge produced at the galapagos hot spot arrived at the trench the thick crust caused uplift and severe tectonic erosion of the accretionary edifice allowing exhumation of the osa melange the change from accretion to erosion caused the outer forearc to be offset along subvertical faults that define small kilometer to tens of kilometers size blocks that are going through differential vertical movements in response to the morphology of the subducting ridge subduction accretion and erosion are two processes that can alternate in time and space or coexist along the same margin so that mass removal can develop on a previously growing margin and completely remove an accretionary prism

subduction of a late cretaceous seamount of the louisville ridge at the tonga trench a model of normal and accelerated tectonic erosion the hotspot generated louisville ridge is a 4000 km chain of seamounts typically 2 2 5 km high and 10 40 km in diameter and an underlying crustal swell 1 5 km high and 100 km wide trending nnw across the southwestern pacific the northwest end of the ridge collides with the north trending tonga trench 26 s which just north of that point is exceptionally deep 10 8 km and lacks both a turbidite wedge and a bordering accretionary complex the collision zone is moving rapidly southward multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2 3 km beneath the lower western trench slope which is interpreted as the flat summit of a subducted guyot motuku of the louisville chain projected eastward the summit plain passes 1 2 km above the trench floor dredging of the nearby inner trench wall recovered uppermost cretaceous maestrichtian oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted louisville seamount the principal effects of hotspot ridge collision with a sediment starved trench are 1 the impacting seamounts are subducted rather than accreted and 2 although some seamount rocks are temporarily accreted the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km m y accelerated tectonic erosion is related to 1 fracturing shearing and general weakening of arc substrate rocks as they are lifted by the swell penetrated by impacting seamounts and left to collapse as the ridge moves away 2 a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell 3 a possible elevation of the subduction decollement to account for the removal of as much as 30 000 km of material from a 400 km sector of the trench in 1 million years and 4 a reduction in supply of arc derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge normal tectonic erosion in the tonga trench is apparently minor and we conclude that the bulk of the 37 000 km of material which fills subducting grabens each million years is arc derived volcanic and pelagic sediment