the mid norwegian margin a discussion of crustal lineaments mafic intrusions and remnants of the caledonian root by 3d density modelling and structural interpretation the high density lower crustal body lcb on the mid norwegian margin is almost universally interpreted to represent magmatically underplated material added to the crust during early tertiary opening of the ne atlantic the thickness of the lcb is uneven and its distribution along the margin is sharply limited by margin perpendicular lineaments three dimensional density modelling constrained by petrophysical and seismic data was performed to investigate the expression of the various lineaments bivrost jan mayen gleipne etc in the crustal architecture with and without the lcb the bivrost lineament separating the voring and lofoten margin segments is clearly expressed and so is arguably a lineament in the sw voring margin notably most of the lineaments can be interpreted as offshore prolongations of major onshore detachments stemming from late caledonian orogenic collapse an alternative interpretation of the lcb is thus that it represents high grade metamorphic rocks remnant from the caledonian root determining the nature of the lcb has profound effects for the volume estimate of magmatic rocks in the north atlantic igneous province and consequently also for the degree of crustal thinning and heat flow

backthrusting in accretionary wedges backthrusting of the rear of the accretionary wedge arcward over the rocks of the forearc basin is a common aspect of accretionary tectonics an older assumption that backstops of accretionary wedges dip back toward the arc and that accreted material is emplaced below such backstops is contradicted by observations from many active forearcs that indicate 1 backthrusting is common 2 forearc basins are nearly ubiquitous associates of accretionary wedges and 3 forearc basement where imaged appears to diverge from the sedimentary package dipping under the wedge while the overlying sediments are often lifted up against it backthrusting may be favored where relief is high between the crest of the wedge and the surface of the forearc basin because the relief must be supported by shear stress along the backthrust we find ratios of lt lb averaging 2 64 0 8 where lt is the horizontal distance from the crest of the wedge to the front of the toe and lb is the distance from the crest of the wedge to the surface projection of the backthrust this ratio is predicted to increase with total convergence and with sedimentation because the toe undergoes higher deformation rates than the backthrust and sedimentation in the trench favors outbuilding of the toe whereas sedimentation in the forearc basin tends to cancel the gravitational component of the driving stress for the backthrust

the dynamics of motion of the south american plate observations of the intraplate stress field as compiled and evaluated in the context of the world stress map project can be compared with stress modelling results to increase our understanding of the dynamics of motion of the lithospheric plates in this paper we investigate the driving and resistive plate tectonic forces acting on the south american plate in order to establish a detailed basis for future stress modelling our basic assumption is that the plate is in mechanical equilibrium that is the net torque of the forces acting on the plate vanishes the complexity of the forces exerted along the margins of the south american plate requires the dynamical analysis to be performed step wise incorporating the forces which are expected to be of major importance a first order model is defined the effect of additional plate boundary forces is subsequently examined in terms of superpositions onto the first order model with the first order model the relation between three resistive forces and shear stress on the base of the lithosphere is derived the ridge push force driving the motion of the south american plate can be quantified independently and is included in the calculations as a known quantity solutions are obtained using four different determinations of the euler vector of absolute motion of the south american plate which is taken to define the orientation of the basal shear stress the results demonstrate that the concept of a basal shear stress actively driving plate motion cannot be discarded on the basis of a dynamical analysis further with the assumption that basal drag is entirely concentrated below the continental pan of the lithosphere estimates of the maximum amount of continental basal shear resistance are derived evaluation of an alternative model for the south american plate excluding the northernmost pan of the andes demonstrates the significance of the resistive force exerted on the south american plate due to convergence with the caribbean plate it is to be expected that comparison of theoretical distributions of intraplate stress computed on the basis of the present dynamical analysis with observations of the actual state of stress will further constrain the range of feasible force models

seismic evidence for blind thrusting of the northwestern flank of the venezuelan andes surface geology and seismic and well data from the northwestern flank of the venezuelan andes indicate overthrusting of andean basement rocks toward the adjacent maracaibo basin along a blind thrust fault the frontal monocline is interpreted as the forelimb of a northwestward verging fault related fold deformed over a crustal scale ramp the andean block has been thrust 20 km to the northwest and uplifted 10 km on a ramp that dips about 20o 30 o southeastward the thrust fault ramps up through crystalline basement rocks to a decollement horizon within the shaly units of the cretaceous colon mito juan formations backthrusts in the monocline produce a wedge geometry and reduce the amount of blind slip required on the decollement northwest of the andes the rigid andean uplift was caused by northwest southeast compressive tectonic forces related to the convergence of the caribbean plate the panama volcanic arc and northwestern south america the thick up to 6 km molasse deposits accumulated in the foredeep basin indicate that the venezuelan andes started to rise as early as the early miocene however a late miocene intramolasse unconformity marks the beginning of the formation of the monocline and the greatest uplift the crustal scale fault related fold model may explain structural features seen in other areas of basement involved foreland deformation the regional geologic setting of the area can be described as a mountain front adjacent to a foredeep basin the mountain front represents a precambrian paleozoic igneous metamorphic complex partially covered with sediments of mesozoic and cenozoic ages the foredeep is an asymmetric structural basin that contains up to 12 km of sedimentary section the early miocene to pleistocene molasse deposits up to 6 km in thickness dominate the sedimentary section the oldest sedimentary rocks that crop out in the mountain front are jurassic red beds which are unconformably overlain by a cretaceous sequence up to 2 km in thickness from early cretaceous to middle eocene sediments were deposited in an extensive passive continental margin setting figure 3 coarse clastic sediments of the rio negro formation bioclastic carbonates of the apon formation and siliciclastic sediments of the aguardiente formation were deposited first in the initial stage of the cretaceous transgressive event limestones calcareous shales and black shales of the capacho and la luna formations represent anoxic facies deposited during the maximum marine transgressiolof late cretaceous cenomanian campanian age regression began in the latest cretaceous maestrichtian with marine deposition of the shaly colon formation and the sandier mito juan formation this

estimating regional coral reef calcium carbonate production from remotely sensed seafloor maps carbonate production on coral reefs is responsible for the provision of beach sands for the maintenance of seawater chemical balances and for the growth of reef structure and associated habitat complexity key carbonate producers including hard coral crustose coralline algae foraminiferal sand and halimeda were mapped from satellite imagery spatial resolution 2 5 m mean overall accuracy 81 and an upscaling model was applied to estimate carbonate production a sensitivity analysis was conducted to evaluate the influence of employing different calcification rates for live coral on the upscaling model contemporary coral reef carbonate production for the 21 reef platforms of the capricorn bunker group southern great barrier reef is estimated to be between 489 000 and 659 000 t per year based on seawater chemistry community composition calcification rates and reef structural complexity rugosity the upscaling model was relatively insensitive to different parameterisations of live coral calcification employed probably due to live coral being a relatively minor contributor by area approximately 18 of total reef area throughout the study region this suggests regional scale seafloor characteristics such as percentage of area dominated by substrates prone to dissolution e g coral rubble have a strong bearing on calcium carbonate production and need to be given greater consideration the upscaling framework presented provides a new method for quantifying regional carbonate production that could be applied globally and provides a valuable baseline against which future changes to carbonate production in this region can be assessed

an advanced photogrammetric method to measure surface roughness application to volcanic terrains in the piton de la fournaise reunion island abstract we present a rapid in situ photogrammetric method to characterize surface roughness by taking overlapping photographs of a scene the method uses a single digital camera to create a high resolution digital terrain model pixel size of 1 32 mm by means of a free open source stereovision software it is based on an auto calibration process which calculates the 3d geometry of the images and an efficient multi image correlation algorithm the method is successfully applied to four different volcanic surfaces namely a a lava flows pahoehoe lava flows slabby pahoehoe lava flows and lapilli deposits these surfaces were sampled in the piton de la fournaise volcano reunion island in october 2011 and displayed various terrain roughnesses our in situ measurements allow deriving digital terrain models that reproduce the millimeter scale height variations of the surfaces over about 12 m 2 five parameters characterizing surface topography are derived along unidirectional profiles the root mean square height the correlation length l c the ratio z s 2 l c the tortuosity index and the fractal dimension d anisotropy in the surface roughness has been first investigated using 1 m long profiles circularly arranged around a central point the results show that l c z s and d effectively catch preferential directions in the structure of bare surfaces secondly we studied the variation of these parameters as a function of the profile length by drawing random profiles from 1 to 12 m in length we verified that and l c increase with the profile length and therefore are not appropriate to characterize surface roughness variation we conclude that z s and d are better suited to extract roughness information for multiple eruptive terrains with complex surface texture

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

first gps baseline results from the north andes the casa uno gps global positioning system experiment january february 1988 has provided the first epoch baseline measurements for the study of plate motions and crustal deformation in and around the north andes two dimensional horizontal baseline repeatabilities are as good as 5 parts in 108 for short baselines 100 1000 km and better than 3 parts in 108 for long baselines 1000 km vertical repeatabilities are typically 4 6 cm with a weak dependence on baseline length the expected rate of plate convergence across the colombia trench is 6 8 cm yr which should be detectable by the repeat experiment planned for 1991 expected deformation rates within the north andes are of the order of 1 cm yr which may be detectable with the 1991 experiment

implications of the north and south panama thrust belts for the origin of the panama orocline high resolution imaging of the north nptb and south panama thrust belts using the seamarc ii seafloor mapping system and digital seismic reflection profiling provides an excellent data base with which to determine the kinematics of oroclinal deformation of panama remarkable continuity of structural orientations over 300 km along the nptb argues for widespread uniformity in direction of thrusting between panama and the caribbean plate westward decrease in the width and height of the accretionary wedge indicates a westward decrease in the total amount of convergence two major cross faults cut the wedge in its eastern part forming two minor blocks with different relative motions with respect to the caribbean frontal thrust orientations change across these faults major faults have been proposed to cut the isthmus of panama but simple cross isthmus faulting alone cannot explain the orientations of the major thrusts of the nptb bending of a flexible beam can explain much of the observed structure both directions and rates though the scale of the orocline precludes considering this as an elastic phenomenon plastic deformation of panama may be a useful mechanical explanation at least for eastern panama but consideration of plastic slip lines must include the northern andes as well changing from more rigid blocklike offsets on faults in western panama to a continuum of strain in eastern panama may be the best explanation for observations at present

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

vp vs ratio along the voring margin ne atlantic derived from obs data implications on lithology and stress field a total of 13 regional ocean bottom seismograph obs profiles with an accumulated length of 2207 km acquired on the voring margin ne atlantic have been travel time modelled with regards to s waves the vp vs ratios are found to decrease with depth through the tertiary layers which is attributed to increased compaction and consolidation of the rocks the vp vs ratio in the intra campanian to mid campanian layer 1 75 1 8 in the central voring basin is significantly lower than for the layers above and beneath suggesting higher sand shale ratio this layer was confirmed by drilling to represent a layer of sandstone this mid cretaceous anomaly is also present in the northern voring basin as well as on the southern lofoten margin further north the vp vs ratio in the extrusive rocks on the voring plateau is estimated to be 1 85 conformable with mafic basaltic rocks landward of the continent ocean transition cot the vp vs ratio in the layer beneath the volcanics is estimated to be 1 67 1 75 these low values suggest that this layer represents sedimentary rocks and that the sand shale ratio might be relatively high here the vp vs ratio in the crystalline basement is estimated to be 1 67 1 75 in the basin and on the landward part of the voring plateau indicating the presence of granitic granodioritic continental crust in the lower crust the vp vs ratio in the basin decreases uniformly from southwest to northeast from 1 85 1 9 to 1 68 1 73 suggesting a gradual change from mafic gabbroic to felsic granodioritic lower crust significant 3 5 azimuthal s wave anisotropy is observed for several sedimentary layers as well as in the lower crust all these observations can be explained by invoking the presence of liquid filled microcracks aligned vertically along the direction of the present day maximum compressive stress nw se

compositional and metamorphic controls on velocity and reflectivity in the continental crust an example from the grenville province of eastern quebec we present velocity and density data for a suite of gabbros and metagabbros over a range of metamorphic grades from subgreenschist to the eclogite facies most of these rocks have a mesocratic protolith with overlapping bulk chemistry ranges providing an opportunity to investigate the systematics of mineralogy and physical properties across a wide range of metamorphic grades with minimal compositional variation in addition more mafic gabbros in the eclogite facies were also investigated in order to take into account variations in the extent of transformation of gabbro to eclogite controlled by bulk chemistry the physical properties data are used as the basis for a first order crustal model composed of granitic anorthositic and gabbroic components the objective of constructing the crustal model is to evaluate the relative contribution of compositional variation and metamorphism to the velocity density and reflectivity structure of the continental crust the model suggests that in the upper crust if fracture porosity is neglected composition dominates the velocity and density structure while in the middle and lower crust composition and metamorphism play equally important roles simulations designed to predict potential reflection coefficient size distributions for the various bulk chemistries and mineralogies in the crustal model indicate step increases in the potential for large reflection coefficients that are dominantly controlled by metamorphic grade step increases in reflectivity are predicted between the lower and upper amphibolite facies and between incompletely and completely eclogitized metagabbros in the eclogite facies we also consider several alternative mixing models which account for the effects of one of the three lithologic components occurring as isolated bodies rather than perfectly mixed with the other two components these models indicate a reduction of the potential for large reflection coefficients by as much as 50 emphasizing the importance of the degree of mixing for crustal reflectivity

crustal structure of the lofoten continental margin off northern norway from ocean bottom seismographic studies summary in 1988 an extensive geophysical experiment was performed on the lofoten passive continental margin which was formed by the continental break up between greenland and northern norway at 58 ma the geological units of the outer lofoten margin are characterized by seaward dipping reflectors sdrs and landward flood basalt which extends up to 100 km landwards of sdrs in this study we obtain the p wave velocity structure beneath the lofoten basin the sdrs and the landward flood basalt by use of ocean bottom seismograph refraction profiling and we also discuss the formation of the northern norwegian passive continental margin in the lofoten basin the crust is of oceanic type consisting of sedimentary layers oceanic laver 2 4 9 5 5 km s 1 layer 3a 6 3 6 8 km s 1 and layer 3b 7 0 7 1 km s 1 beneath the sdrs the crustal layers are identical to those of the lofoten basin but the thickness of the lower crust which represents the same velocity as layer 3b increases to 5 km towards the continent side and a high velocity lower crustal layer 7 3 km s 1 is formed at the base of the crust the ocean continent transition zone is situated between the landward side of the sdrs and the northward continuation of the voring plateau escarpment in this region the velocity of the lower crust gradually decreases and approaches the lower crustal velocity beneath the lofoten islands 6 8 km s 1 the model also indicates that the high velocity layer disappears in this region comparing our model with the crustal structure on the voring margin it is clear that the lower crustal body 7 km s 1 thickens southwards along the northern norwegian continental margin recent results from petrological and geophysical studies of the generation of the oceanic crust have shown that increasing the temperature of the upwelling asthenospheric material increases the thickness of the oceanic crust we interpret this as that the oceanic crust in the southern area in the voring lofoten margin was generated by hotter material than that of the northern area

the geodynamics of lithospheric extension lithospheric extension is a fundamental plate tectonic process controlling the collapse of mountain belts the break up of continents and the formation of new oceanic basins this review summarises major advances on understanding a the nature of the ocean continent transition b the origin and evolution of detachment faults c the dynamic strength of continental lithosphere during extension and d the role of magmatism during extension major steps have been made in mapping out the complexities of the ocean continent transition zone particularly in magma poor rifted margins where extensional structures are not masked by voluminous magmatism the role of detachment faulting during rifting seems to be crucial and explains observations on depth dependent stretching of the lithosphere despite new insights into the dynamic behaviour of the lithosphere its rheological response remains a major uncertainty in modelling the evolution of extensional systems likewise the multiple roles that basaltic magmatism may have in modifying extension remain a key question future insights into the global behaviour of extensional systems will be gained by constraining lithospheric rheology through integrating structural evolution and magmatism in the field geodetic measurements of active extension thermochronology seismic surveys and drilling programs 2008 elsevier b v all rights reserved

evidence from the rare earth element record of mantle melting for cooling of the tertiary iceland plume widespread flood basalt volcanism and continental rifting in the northeast atlantic in the early tertiary period 55 myr ago have been linked to the mantle plume now residing beneath iceland1 2 3 4 5 although much is known about the present day iceland plume6 7 8 9 its thermal structure composition and position in the early tertiary period remain unresolved estimates of its temperature for example range from 1 600 c in some plume models3 to 1 500 c based on the volume and composition of basaltic crust10 11 12 several recent studies4 have emphasized similarities in the thermal and chemical structure of the tertiary and present day plumes to argue for stability of the mantle anomaly whereas others12 13 relate variations in basalt volumes and compositions to changes in plume flux moreover some authors1 2 13 have assumed that the plume was rift centred for its entire history whereas others argue that it became ridge centred only after plate separation14 15 here we report compositional data for 6 000 metres of flood basalts erupted in east greenland close to the inferred plume axis that we use to constrain the tertiary plume structure rare earth element systematics place limits on the pressures and extents of mantle melting and show that the mantle was initially moderately hot 1 500 c but that its temperature declined during flood volcanism these observations are difficult to reconcile with current plume head models and call for important lithospheric control5 10 16 17 18 on actively upwelling mantle along the rifted margin

magma transport through the crust via interconnected sill complexes three dimensional seismic data from the volcanic margin offshore norway have been used to map the complex three dimensional geometry of two major sill complexes these data show that the complexes consist of bowl shaped or inclined sheetlike discordant sills that intersect with one another over a vertical distance of 8 12 km and transect basement and sedimentary rocks of the middle to upper crust using a simple graphical technique we demonstrate the interconnectedness of the sill complex and hence the maximum time for sill emplacement we show that sills are interconnected by junctions occurring systematically at the lowest points of the overlying sills and hence that the sill complex could have acted as a single throughgoing magmatic plumbing system transporting mafic melts from mid lower crustal depths to near surface based on this imaging of the magmatic plumbing system we conclude that sills can form viable and efficient conduits for crustal magma transport in volcanic margins and may play a role in feeding large extrusive complexes

measuring coral reef terrain roughness using structure from motion close range photogrammetry our understanding of earth surface processes is rapidly advancing as new remote sensing technologies such as lidar and close range digital photogrammetry become more accessible and affordable a very high spatial resolution digital terrain model dtm and orthophoto mosaic mm scale were produced using close range digital photogrammetry based on structure from motion sfm algorithms for a 250 m transect along a shallow coral reef flat on heron reef great barrier reef the precise terrain data were used to characterise surface roughness a critical factor affecting ecological and physical processes on the reef three roughness parameters namely the root mean square height tortuosity or rugosity and fractal dimension were derived and compared in order to asses which one better characterises reef flat roughness the typical relief across the shallow reef flat was 0 1 m with a maximum value of 0 42 m coral reef terrain roughness as characterised by the three chosen parameters generally increased towards the middle of the transect where live coral covers most of the reef flat and decreases towards the edges of the transect the fractal dimension values ranging from 2 2 to 2 59 best characterised reef roughness as evidenced by a closer agreement with the distribution of known coral benthic substrates this is the first study quantifying scale independent roughness of a coral reef at benthic and biotope patch levels cm m the readily available and cost effective methods presented are highly appropriate for data collection processing and analysis to generate very high spatial resolution dtms and orthophoto mosaics of shallow and energetic coral reefs

the crustal structure of central east greenland results from combined land sea seismic refraction experiments summary we present results from the first combined marine land seismic refraction survey in the area of the east greenland caledonides together with gravimetric measurements the seismic and gravimetric models show a consistent picture of the crustal structures in the western area which is part of the caledonian mountains of east greenland crystalline rocks with p wave velocities of about 5 5 km s 1 occur at the surface seismic velocities increase continuously with depth and reach values of 6 6 km s 1 at 12 km the total thickness of the crust as revealed by the seismic measurements reaches high values of up to 48 km in the southwestern part of the region 28 w gravity data which also cover the region west of the seismic lines indicate a possible further increase of the crustal thickness these high values raise questions about whether they represent a caledonide crustal root which would stand in strong contrast to the findings in the caledonian areas of europe or whether the crustal thickening represents a pre caledonian structure and is affine rather to the older regions west of the caledonides and adjacent to the greenland inland ice towards the east crustal thickness decreases rapidly it reaches a minimum of 22 km under the late palaeozoic mesozoic sedimentary basin of jameson land the crustal thinning is the result of the stretching of east greenland which was produced by a general extensional tectonic regime and the collapse of the caledonian mountain chain from devonian time onwards in the area of transition from thick to thin crust the seismic data indicate a layered structure at the moho this region is interpreted as a zone of extensive intrusion or underplating during the rifting in the tertiary

extension discrepancy at north atlantic nonvolcanic rifted margins depth dependent stretching or unrecognized faulting rifted margins show an apparent discrepancy between the amount of extension measurable from faults and the amount of crustal or lithospheric thinning determined from wide angle data or subsidence this extension discrepancy has been interpreted in terms of depth dependent stretching in which the upper crust is extended and thinned far less than the rest of the lithosphere here i show that at those nonvolcanic margins where the velocity structure is well known the upper and lower crust appear to thin equally toward the margin implying that the discrepancy is not due to depth dependent stretching but more likely due to unrecognized polyphase and top basement faulting

deep seismic and geochemical constraints on the nature of rift induced magmatism during breakup of the north atlantic abstract the deep crustal structure of the norwegian and east greenland conjugate passive margins has been investigated with two ship multichannel reflection and refraction techniques in the region from the iceland faeroe ridge to the greenland fracture zone the data demonstrate the presence of thick 15 20 km igneous crust that was emplaced along the conjugate margins during the initiation of seafloor spreading seaward dipping units comprise the uppermost 3 6 km of the thick crust the thickness of igneous crust diminishes seaward with oceanic layer 2 approaching normal thickness nearer to the margin than does oceanic layer 3 wide angle reflection techniques used in conjunction with expanded spread profiling reveal deep moho reflections beneath 20 km thick oceanic crust that continue seaward into the ocean basin margins that have experienced unusually prolific magmatic activity during breakup have been termed volcanic to distinguish them from non volcanic margins that have evolved into accreting plate boundaries without excessive volcanism the origin of volcanic margins cannot be determined from seismically derived crustal thicknesses alone however thermal and chemical properties of the mantle source may be revealed in the compositions of magmatic products emplaced within volcanic passive margins a combined investigation of crustal structure and associated basalt composition could better resolve processes that result in volcanic passive margins on the voring plateau of the norwegian margin seismic lines coincide with dsdp leg 38 drill sites whole rock major element abundances in the freshest basalts are compatible with moderate extents of partial melting of mantle much like that believed to underlie modern mid ocean ridge systems and would be expected to result in the emplacement of oceanic crust about 9 2 km thick this is about the thickness of oceanic crust located seaward of the dipping basaltic units off the hatton more and voring plateau margins and 10 km south of iceland on the reykjanes ridge these results together with regional heat flow depth gravity and geoid anomalies suggest that the mantle beneath this region has experienced a moderate long lived temperature increase compared to mantle beneath normal ocean basins the much greater thicknesses of igneous crust adjacent to the margins do not appear to reflect an unusually hot flux associated with their construction since this would lead to much greater extents of partial melting than are inferred from the basalt geochemistry evidently the difference between volcanic and non volcanic margins is not simply proximity to a hot spot instead we suggest that the magmatism is closely related to the continental rifting phase tectonism resulting in an abrupt transition from continental to oceanic lithosphere may induce small scale convection that results in the circulation of a greater amount of mantle material into the pressure temperature field where partial melting begins than would occur through passive upwelling alone initial crustal thicknesses are enhanced as a result of the convective partial melting crustal thickness is expected to diminish as this secondary convection slows but the degree of partial melting of the source should not change dramatically

magma productivity and early seafloor spreading rate correlation on the northern voring margin norway constraints on mantle melting abstract continental rifting at the voring margin off mid norway was initiated during the earliest eocene 54 ma and large volumes of magmatic rocks were emplaced during and after continental breakup in 2003 a marine survey collecting ocean bottom seismometer single channel reflection and magnetic data was conducted on the norwegian margin to constrain continental breakup and early seafloor spreading processes the profile described here crosses the northern part of the voring plateau and the crustal velocity model was constructed through a combination of ray tracing and forward gravity modeling the latter corrected for the thermal effects remaining from the seafloor spreading we found a maximum igneous crustal thickness of 18 km decreasing to 6 5 km over the first 6 m y after continental breakup both the volume and the duration of excess magmatism are about twice as large as that of the more margin south of the east jan mayen fracture zone which offsets the two margin segments by 170 km a similar reduction in magmatism occurs to the north over an along margin distance of 150 km to the lofoten margin but without a margin offset both the geochemical data and the mean p wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the voring margin the mean p wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production 2 m y after breakup the magnetic data were used to derive plate half spreading rates for the northern voring margin which are very similar to that obtained at the more margin there is a strong correlation between magma productivity and early plate spreading rate suggesting a common cause a model for the breakup related magmatism should be able to explain this correlation but also the magma production peak at breakup the along margin magmatic segmentation and the active mantle upwelling proposed end member hypotheses comprise elevated upper mantle temperatures caused by a hot mantle plume or edge driven small scale convection fluxing mantle rocks through the melt zone edge driven convection does not easily explain these observations but a mantle plume model in which buoyant plume material flows laterally to pond in the rift topography at the base of the lithosphere close to breakup time is promising when the continents break apart the hot and buoyant plume material can flow up into the rift zone from surrounding areas as the rift transits to drift and the excess temperature of this material will then cause excess magmatism which dies off as the rift restricted material is spent the buoyancy of the plume material may in addition cause active upwelling which can increase the melting furthermore and also increase the force on the plate boundaries to enhance plate spreading rate this conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading and thus correlate

basin modeling of late cretaceous mio pliocene petroleum system of the deep water eastern colombian basin and south caribbean deformed belt abstract previous interpretation of 2d and 3d seismic reflection data have shown widespread direct hydrocarbon indicators from deep water successions of the eastern colombian basin ecb and adjacent south caribbean deformed belt scdb that suggest the presence of an extensive but poorly defined petroleum system we integrate rock eval analysis seismic interpretation and 1d 2d thermal and basin modeling to better understand the origin of gas chimneys and bright spots identified in the ecb our dataset consists of 36 rock eval samples of coniacian to santonian source rocks from the dsdp well sites 153 151 and 146 located in the beata ridge tied to a 270 km long composite 2d seismic line covering the ecb rock eval analyses reveal intervals of immature source rocks containing 1 kerogen types ii and iii 2 an average toc of 3 17 with a maximum toc of 11 4 3 an average hi of 241 and 4 an average oi of 124 seismic interpretation reveals 1 wedging of post coniacian organic rich successions from the beata ridge 35 73 m towards the ecb 500 1700 m 2 late cretaceous to eocene slow sedimentation rate of 38 m my followed by faster oligocene to recent sedimentation rate of 149 m my from the magdalena river and 3 late oligocene to recent thrusting and propagation of the scdb thermal and basin modeling show 1 mature source rocks in the scdb and ecb 2 miocene to pliocene reservoir and seal rocks related to deltaic and turbiditic sandstone and mass transport deposits of the magdalena fan 3 trap formation since the late oligocene related to thrust front structures compaction folds and stratigraphic traps 4 hydrocarbon expulsion since pliocene times 5 vertical and lateral migration in the scdb and vertical up dip migration in the ecb and 6 hydrocarbon accumulation and preservation may be affected by remobilization due to biodegradation and trap breaching

microseismicity evidence for subduction of the caribbean plate beneath the south american plate in northwestern venezuela over 1100 microearthquakes with body wave magnitude mb 4 have been located in western venezuela and the southwestern caribbean region since the installation in 1980 of the venezuelan seismological array together with 120 events of mb 4 one of them with surface wave magnitude ms 6 this tectonically complex region is part of the boundary between the caribbean and the south american plates the main seismically active feature inland in western venezuela is the northeast striking 600 km long 100 km wide right lateral strike slip bocono fault zone along the venezuelan andes about 80 of the earthquakes located in the entire region in the period 1980 mid 1995 have occurred on this fault zone at focal depths 20 km microearthquake activity at lower rates also occurs northwest of the venezuelan andes both in the continental and caribbean sea regions part of this activity takes place at depths down to 150 km northwest oriented seismicity depth profiles show the existence of a benioff zone dipping to the southeast beneath northwestern venezuela and northern colombia this indicates the presence of a northeast striking southeast dipping subducted slab of the caribbean plate beneath the south american plate hypocentral locations show that the northeastern end of this subduction occurs northwest of the curacao aruba region in the vicinity of a northwest trending right lateral strike slip fault zone that joins up with the northeastern end of the bocono fault zone this latter place turns out to be the western end of the east west striking san sebastian fault along the venezuelan coast

coral mortality increases wave energy reaching shores protected by reef flats examples from the seychelles in the granitic seychelles many shores and beaches are fringed by coral reef flats which provide protection to shores from erosion by waves the surfaces of these reef flats support a complex ecology about 10 years ago their seaward zones were extensively covered by a rich coral growth which reached approximately to mean low water level but in 1998 this was largely killed by seawater warming the resulting large expanses of dead coral skeletons in these locations are now disintegrating and much of the subsequent modest recovery by new coral recruitment was set back by further mortalities a mathematical model of wave energy reaching shorelines protected by coral reef flats has been applied to 14 seychelles reefs it is derived from equations which predict 1 the raised water level or wave set up on reef flats resulting from wave breaking which depends upon offshore wave height and period depth of still water over the reef flat and the reef crest profile and 2 the decay of energy from reef edge to shoreline that is affected by width of reef flat surface roughness sea level rise and pseudo sea level rise created by increased depth resulting from disintegration of coral colonies the model treats each reef as one entity but because biota and zonation on reef flats are not homogenous all reefs are divided into four zones in each cover by both living and dead biota was estimated for calculation of parameters and then averaged to obtain input data for the model all possible biological factors were taken into account such as the ability of seagrass beds to grow upwards to match expected sea level rise reduction in height of the reef flat in relation to sea level as zones of dead corals decay and the observed rounding of reef crests as erosion removes corals from those areas estimates were also made of all these factors for a time approximately a decade ago representing a time before the mass coral mortality and for approximately a decade in the future when the observed rapid state of dead coral colony disintegration is assumed to have reached an end point results of increased energy over the past decade explain observations of erosion in some sites in the seychelles most importantly it is estimated that the rise in energy reaching shores protected by fringing reefs will now accelerate more rapidly such that the increase expected over the next decade will be approximately double than that seen over the past decade c 2005 elsevier ltd all rights reserved

continent ocean transition and voluminous magmatic underplating derived from p wave velocity modelling of the east greenland continental margin summary deep seismic refraction data were gathered across the entire east greenland rifted margin north of the jan mayen fracture zone between 72 n and 75 n in 2003 investigations of the deep crustal structure of this continental margin provide constraints on the formation of the margin and its structural evolution during and after late cretaceous early tertiary rifting and continental break up we present here the results along two profiles located in the prolongation of the godthab gulf and the kejser franz joseph fjord regional p wave velocity models were derived from forward traveltime modelling of land stations and ocean bottom hydrophone obh recordings for the first time long deep seismic sounding transects off east greenland provide a full insight into the crustal architecture of the transition from continental to oceanic crust a mean result is the identification of voluminous magmatic underplating which is wider and thicker than previously thought p wave velocities of the underplated material range between 7 1 and 7 4 km s 1 and the horizontal extents on the profiles are 225 and 190 km the maximum thickness of the underplated material is 15 16 km furthermore the p wave velocity models reveal a 120 130 km wide continent ocean transition zone cot based on an interpretation of the extent of cretaceous syn rift sediments mixed with basaltic intrusions and the lateral increase of velocities in the crustal layers excess magmatism must have been present during a long term rifting process accompanying the extension of the continental crust and giving rise to the voluminous magmatic underplating a consequence of our interpretation of the seismic refraction data is a likely rift propagation in the greenland sea from north to south additionally a comparison of p wave velocity models of the east greenland margin and voring margin reveals significantly asymmetric crustal architectures the voluminous magmatic underplating and asymmetrical conjugate margins formations are considered as a mirror of complex pre and syn rift processes

the 1967 caracas earthquake fault geometry direction of rupture propagation and seismotectonic implications the fault plane orientation of the july 30 1967 caracas earthquake mw 6 6 has been a source of controversy for several years this strike slip event was originally thought to have occurred on an east west oriented fault plane reflecting the relative motion between the caribbean and south american plates more recently however the complex seismic radiation from this event was interpreted as being indicative of a north south striking fault that ruptured along three en echelon segments in this study we synthesize evidence based on the intensity and damage reports the distribution of aftershocks and the results of a joint formal inversion of the p and sh waves and show that these data clearly indicate that the rupture of the 1967 earthquake occurred on an east west trending fault system using a master event technique the largest aftershock which occurred 40 min after the main event is shown to lie 50 km east of the epicenter of the mainshock the epicentral distances of small aftershocks registered in caracas based on the s p arrival time differences and the polarizations of the p waves are also consistent with these events occurring on an east west oriented fault system north of caracas a joint inversion of the teleseismic p and sh waves recorded on long period seismographs of the world wide standardized seismographic network shows that in a time frame of 65 s four distinct bursts of seismic moment release subevents occurred with a total seismic moment of 8 6 1018 n m the first three subevents triggered sequentially from west to east in a direction that is almost identical to the east west trending nodal planes of the source mechanisms the average depth of these three subevents is 14 km the fourth and last identifiable subevent of the sequence shows a reverse faulting mechanism with the nodal planes oriented roughly east west it occurred at a 21 km depth about 50 km to the north of the fault zone defined by the strike slip subevents this fourth subevent appears to reflect compressional deformation of the southern caribbean possibly related to underthrusting along the proposed curacao trench the complexity of the fault system causing the 1967 earthquake suggests that the relative motion along the caribbean south america plate boundary in central venezuela is taken up over a broad highly faulted and highly stressed zone of deformation and not by a simple major throughgoing fault

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

giant submarine landslides on the colombian margin and tsunami risk in the caribbean sea abstract a series of three giant previously unrecognized submarine landslides are defined on a 16 000 line km grid of multi channel 2d seismic reflection profiles along the active margin of northern colombia in the western caribbean sea these deposits record the collapse and mobilization of immense segments thousands of cubic kilometers of the submarine slope and are comparable in scale to the largest known landslides on earth we show that the breakaway zone for these events corresponds to the tectonically over steepened slopes of the magdalena fan an extensive submarine fan composed of sediments sourced from the northern andes and deposited by the magdalena river an over pressured zone of weakness at the base of the gas hydrate stability layer within the fan likely facilitates slope failure timing of these massive slope failures is constrained by well control and occurred from the mid to late pliocene to mid pleistocene to understand the tsunamigenic hazards posed by the recurrence of such an event today we model the potential tsunami source created by a submarine landslide of comparable thickness 400 m and lateral extent 1700 km 2 derived from the over steepened upper slopes of the present day magdalena fan our modeling indicates the recurrence of an analogous slope failure would result in a major tsunami that would impact population centers along the caribbean coastlines of colombia central america and the greater antilles with little advance warning

the role of fringing coral reefs on beach morphodynamics article i nfo this paper examines the degree of energy dissipation provided by a fringing coral reef and its role on the morphodynamics of adjacent beaches in terms of volumetric sediment transport morphological data were collected from the microtidal mexican caribbean beaches of puerto morelos fringed by a reef and cancun without a reef from september 2007 to may 2011 being exposed to the same offshore wave conditions the morphodynamics of the coral reef fronted beach were compared with those of the adjacent beach without a coral reef spatio temporal changes in beach morphology were determined applying empirical orthogonal functions eof to the shorelines extracted from the topographic data and it was concluded that puerto morelos was considerably less dynamic than cancun the longshore energy fluxes were larger in cancun and the subaerial morphological differences in both beaches and under the same offshore conditions demon strated that puerto morelos was particularly stable under shore normal easterly waves a calibrated phase averaged wave model was implemented to determine the amount of wave energy dissipation across the coral reef for energetic shore normal waves the model determined that the semi emerged coral reef was ca pable of reducing up to 85 of the incident wave height the reef crest height controlled the amount of wave energy dissipation and the distance between the reef crest and the shore determined the vulnerability of the beach to morphological changes reef crest degradation by 1 m resulted in a 10 increase in incoming wave energy which resulted in 0 9 m 3 h m of sand being mobilised along the beaches closer to the reef

crustal structure of the ne rockall trough from wide angle seismic data modeling two wide angle seismic lines located in the northern rockall trough were acquired in may 2000 one line line e crosses the trough from the continental shelf off lewis to normal oceanic crust west of lousy bank in nw se direction the other line line d intersects with line e crosses the wyville thomson ridge in a sw ne direction and ends in the faeroe shetland basin sonobuoy data and expanding spread profiles acquired in the same area have been remodeled analysis of the seismic data using travel times and amplitudes reveals an up to 5 km thick sedimentary basin including an up to 1 5 km thick basaltic layer which is present in most of the trough further conclusions of this study are that the rockall trough is underlain by highly stretched continental crust of 13 km thickness the crust thickens to 24 km beneath lousy bank which is interpreted to be of continental nature beneath the hebrides continental shelf a three layer continental crust of 26 km is modeled an up to 12 km thick high velocity layer is observed underneath the ocean continent boundary and is interpreted as magmatic underplating resulting from excess volcanism during rifting no evidence for an underplate layer could be distinguished beneath the trough area modeling of the structure of the wyville thomson ridge revealed no existing igneous core of the ridge confirming existing theories that it is a compressional structure

crustal structure and evolution of the southern voring basin and voring transform margin ne atlantic abstract the dominantly passive volcanic voring and more margins ne atlantic are separated by the 200 km long voring transform margin vtm the southern voring basin and the vtm have been studied by use of four regional ocean bottom seismograph obs profiles combined by gravity modelling the models demonstrate a complex pattern of magmatism along the transform margin the distribution of magmatism seems to be related to the existence and trend of a lower crustal 8 km s body interpreted as eclogitized rocks present in the southern voring basin early tertiary breakup related magmatic leakage across the continent ocean transition cot appears to be facilitated where this layer is absent these results support earlier workers who have concluded that the jan mayen fracture zone originated from a caledonian zone of weakness we propose that partly eclogitized rocks were uplifted into the lower crust close to this zone during the caledonian orogeny and that this body acted as a barrier to magma emplacement during the late cretaceous early eocene phase of rifting breakup the eclogitized terrain also appears to have caused northeastward channeling of the late cretaceous early tertiary intrusions within the voring basin an up to 10 km thick pre cretaceous sedimentary basin in the southern voring basin may be genetically related to the ns trending late paleozoic and mesozoic rift basins in north east greenland

reworking processes and deposits in coral reefs during very high energy events example from a pleistocene coral formation 125 ka la desirade island lesser antilles abstract abundant literature has documented the ecological impact of very high energy hurricane type events and high energy storm type events on modern coral reefs and sediment transport in previous studies sedimentary processes are often deduced from geophysical image analysis and scuba diving observations few field based studies have been devoted to the impact of very high energy disturbance on the structure and ecology of holocene and pleistocene coral reefs and very few to the sedimentary processes acting around these reefs this research examines the structure of the late pleistocene end of mis5e stage reefs of la desirade island guadeloupe archipelago lesser antilles and focuses on the poorly known reworking processes and related coral breccia sedimentation surrounding these reefs fieldwork was performed to document two coral fragment rich breccia interbedded with coral patches the breccia predominantly show the same petrography but differ in their internal structure showing a massive breccia type and a stratified breccia type this work infers that these breccia are the result of gravity induced high density mass flows triggered by high to very high energy events such as storms and hurricanes damage and reworking vary according to the type of very high energy event prior to transport storms are thought to have broken the heads of branching and columnar coral colonies and broken and overturn isolated lamellar and massive colonies hurricanes particularly their eye walls may have reworked much more sediment than storms and may have also destabilised entire several metre sized columnar colonies from the flank of coral patch reefs we propose the name coral debrite for these coral breccia deposits caused by gravity induced debris flows the reworked deposits are interbedded between two coral reef levels of which the main coral species vertical succession should record the end of marine isotope stage 5e sea level rise thus reworking is believed to occur during the transitional stage between a glacial and an interglacial period

the t reflection and the deep crustal structure of the voring margin offshore mid norway seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust we have completed a detailed 2d seismic interpretation of the deep crustal structure of the voring margin offshore mid norway where high quality seismic data allow the identification of high amplitude reflections locally referred to as the t reflection using a dense seismic grid we have mapped the geometry of the t reflection in order to compare it with filtered bouguer gravity anomalies and seismic refraction data the t reflection is identified between 7 and 10 s sometimes it consists of one single smooth reflection however it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries amplitudes and contact relationships the t reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults the spatial correlation between the filtered positive bouguer gravity anomalies and the deep dome shaped reflections indicates that the latter represent a high impedance boundary contrast associated with a high density and velocity body in 50 of the outer voring margin the depth of the mapped t reflection is found to correspond to the depth of the top of the lower crustal body lcb which is characterized by high p wave velocities 7 km s we present a tectonic scenario where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high grade metamorphic rocks deep intrusions into the faulted crustal blocks are responsible for the rough character of the t reflection whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km s the result is a heterogeneous lcb that likely represents a complex mixture of pre to syn breakup mafic and ultramafic rocks cumulates and sills and old metamorphic rocks such as granulites and eclogites an increasing degree of melting towards the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

the moho depth distribution in fennoscandia and the regional tectonic evolution from archean to permian times abstract from a variety of seismic refraction and reflection profiling results a new detailed moho depth map for the fennoscandian part of the baltic shield has been compiled a complementary crystalline crustal thickness map was compiled for denmark the skagerrak sea offshore western norway and adjacent areas where sedimentary strata reach maximum thicknesses of 10 km and even more these maps are discussed in relation to tectonic evolution and crustal ages of fennoscandia seismic velocities bouguer gravity and seismicity areas deviating from the proposed age thickness relationships are the kola peninsula archean and the oslo rift permian the average crustal thickness in the former area is around 44 km while the latter area is associated with a moho elevation of 3 5 km maximum crustal thicknesses in excess of 50 km have been found in southwestern and central finland and correlate with a crust of proterozoic age the caledonides of western norway do not exhibit as elsewhere a crustal root sub moho p n and s n seismic velocities are relatively small in that area and bouguer gravity values are strongly negative intracrustal p velocity variations do not seem to reflect geological age or specific tectonic features although the seismicity is moderate in fennoscandia most of the earthquake activity and in particular the largest earthquakes are confined to areas where the crustal thinning is most pronounced

lower crustal composition and crustal lineaments on the voring margin ne atlantic a review abstract a prominent lower crustal high velocity layer observed in the voring basin ne atlantic has been investigated with regard to composition and spatial link to crustal scale lineaments in the southernmost part of the basin the lower crustal layer is interpreted as eclogites based on anomalously high p wave velocities 8 4 km s in the remainder of the basin the layer is preferably interpreted as mafic intrusions emplaced during the last phase of rifting but it cannot be excluded that the body consists of older caledonian mafic rocks direct link with high grade caledonian rocks to the east and westwards to east greenland cannot be made since these rocks are mainly of felsic composition the crustal scale lineaments inferred from wide angle seismic data appear to represent the oceanward extension of post caledonian detachments the spatial variation in the thickness of the layer is within the late rifting magmatic hypothesis partly interpreted in terms of pre magmatic variations in thickness of the lithosphere in addition lateral variations in extension mantle upwelling and decompressional melting during the last phase of rifting may also have contributed

north atlantic volcanic margins dimensions and production rates early tertiary lithospheric breakup between eurasia and greenland was accompanied by a transient 3 m y igneous event emplacing both the onshore flood basalts of the north atlantic volcanic province navp and huge extrusive complexes along the continent ocean transition on the rifted continental margins seismic data show that volcanic margins extend 2600 km along the early eocene plate boundary in places underlain by high velocity 7 2 7 7 km s lower crustal bodies quantitative calculations of navp dimensions considered minimum estimates reveal an areal extent of 1 3 106 km2 and a volume of flood basalts of 1 8 106 km3 yielding a mean eruption rate of 0 6 km3 yr or 2 4 km3 yr if two thirds of the basalts were emplaced within 0 5 m y the total crustal volume is 6 6 106 km3 resulting in a mean crustal accretion rate of 2 2 km3 yr thus navp ranks among the world s larger igneous provinces if the volcanic margins are considered the velocity structure of the expanded crust seaward of the continent ocean boundary differs from standard oceanic and continental crustal models based on seismic velocities this volcanic margin crust can be divided into three units of which the upper unit corresponds to basaltic extrusives the regionally consistent velocity structure and geometry of the crustal units suggest that the expanded crust including the high velocity lower crust which extends some distance landward of the continent ocean boundary was emplaced during and subsequent to breakup the volcanic margin crust was formed by excess melting within a wide zone of asthenospheric upwelling probably reflecting the interaction of a mantle plume and a lithosphere already extending

crustal structure of the central part of the voring basin mid norway margin from ocean bottom seismographs abstract regional ocean bottom seismograph obs data acquired in the central and northern part of the voring basin mid norway margin have been modelled by use of two dimensional 2 d ray tracing the regional dataset comprises thirty obss deployed along seven 100 170 km long profiles the deeper part of the voring basin is difficult to map using multichannel reflection data due to the presence of sills at intermediate sedimentary levels 2 5 km below sea floor but the modelling of the obs data reveals that this technique provides a reliable estimate of structures and seismic velocities from the sea floor to the upper mantle the shallow and intermediate sediments to 5 km below sea floor are characterized by a vertical increase in velocity due to increased confining pressure there is also considerable lateral variation in the velocities within sedimentary layers at all levels the obs data confirm that intrusions of sills are important at intermediate and deep sedimentary levels 2 10 km below sea floor in most parts of the area the sills seem to vary in lateral extent from about 20 km to more than 100 km and their thickness is generally inferred to be about 200 m the low velocity in the upper crystalline crust 6 2 km s confirms that the crust in the voring basin is of continental origin in most parts of the area the velocity of the lower crust is as high as 7 3 7 6 km s this high velocity layer is interpreted as a magmatic underplated body with strong lateral variations in thickness the base of the 7 3 km s layer is interpreted as the moho and the upper mantle velocity is estimated to 8 2 km s

the moho boundary above upper mantle peridotites or lower crustal eclogites a global review and new interpretations for passive margins abstract we have performed a global study of 2d crustal scale wide angle profiles across passive margins with regard to local elevations in the moho which could possibly be interpreted as indicative of lower crustal eclogites a total of 16 candidates have been found mainly in the north atlantic and around australia these cases make up c 6 only of the total profile length studied confirming the interpretation of the moho generally representing the top of the mantle the interpreted candidates for lower crustal eclogites indicate that there may be a link between eclogite bodies and continental suture zones in the barents sea off mid norway in the newfoundland appalachians and in the yilgarn craton western australia it is also possible that there is a genetic link between the formation of caledonian eclogites and the jan mayen fracture zone which is the only major fracture zone in the north atlantic several of the inferred lower crustal eclogite bodies are located close to lines of major changes in strain such as coastlines and shelf edges indicating that lower crustal eclogite bodies may be important in guiding the evolution of basin architecture interpreting the moho beneath the bedout high on the northwest shelf of australia as the top of a body of lower crustal eclogites may imply that the northern termination of the lambert shelf represents a paleo suture zone and that the western termination of the broome platform acted as a major transfer zone the significant increase in crustal thickness implied by the eclogite model has important implications for estimates of stretching history subsidence and hydrocarbon maturation modelling

crustal inhomogeneities in the northern north sea from potential field modeling inherited structure and serpentinites abstract a new crustal model for the northern north sea was developed by gravity and magnetic modeling along the deep seismic line nsdp84 1 utilizing vertical gradients allowed distinguishing between shallow and deep crustal sources the upper crust is characterized by low magnetic susceptibilities and low densities which is typical for felsic rocks a new finding was that the deep crust below the western viking graben and the east shetland basin is the source of high magnetic anomalies combined with low gravity anomalies which was interpreted to represent rocks with very high magnetic susceptibilities and low to intermediate densities such rock parameters may indicate serpentinites but intermediate intrusives or a combination of both is also possible honoring the string of three near equidistant magnetic maxima which follow the trend of the nne ssw striking east shetland basin in the map plane it is suggested that this area is part of an island arc of the iapetus ocean which has been assembled during the collision between laurentia and baltica in late silurian times partly serpentinized peridotites and intermediate intrusives will relate in such a model to slab dehydration of the subducting oceanic plate below the island arc these inherited or synorogenic serpentinites are expected to persist in the geothermal regime of the caledonian orogeny to a depth of at least 50 km increased heat flow by later rift phases will have caused metamorphism of the remaining serpentinites to meta peridotites at depth below the present day moho fluid release related to dehydration of the serpentinites may have triggered further serpentinization of the inherited partly serpentinized rocks at shallower depth an alternative origin for the suggested serpentinites valid only for the area under the western part of the viking graben may be synrift serpentinization due to the heavy faulting during the jurassic rift phase

controls on forearc basin formation and evolution insights from oligocene to recent tectono stratigraphy of the lower magdalena valley basin of northwest colombia abstract mechanisms of forearc basin evolution remain not very well understood mostly because of insufficient resolution of their temporal evolution and potential drivers the convergent margin of northwest colombia where the san jacinto and lower magdalena valley forearc basins are located offers a unique opportunity to study such mechanisms the formation of the lower magdalena amagmatic forearc basin occurred in a stable setting from the oligocene to the present characterized by the slow and nearly orthogonal low angle subduction of the caribbean plateau we use an exceptional regional database to reconstruct the subsidence extension sedimentation and paleo geographic history of the lower magdalena forearc basin we propose possible mechanisms controlling its evolution in the absence of major changes in plate kinematics and in a low angle subduction setting following the collapse of a pre oligocene magmatic arc late oligocene to early miocene fault controlled subsidence allowed initial basin fill at relatively low sedimentation rates after the connection of the lower and middle magdalena valleys the proto magdalena river in the north and the proto cauca river in the south both started delivering high amounts of sediments in middle miocene times fault controlled subsidence was gradually replaced by subsidence due to increased sedimentary load increase in sediment flux would have also caused the formation of an accretionary prism weakened the plate interface through lubrication with fluid rich sediment and initiated underplating with the development of forearc highs in the san jacinto area inherited basement structures allowed the tectonic segmentation of the basin with the formation its two depocenters plato and san jorge our results highlight the fundamental role of sediment flux of the basement structure and of flat subduction on the evolution of forearc basins such as the lower magdalena

conjugate volcanic rifted margins seafloor spreading and microcontinent insights from new high resolution aeromagnetic surveys in the norway basin we have acquired and processed new aeromagnetic data that cover the entire oceanic norway basin located between the more volcanic rifted margin and the jan mayen microcontinent jmmc the new compilation allows us to revisit the structure of the conjugate volcanic rifted margins and the spreading evolution of the norway basin from the early eocene breakup time to the late oligocene when the aegir ridge became extinct the volcanic margins in a strict sense that formed before the opening of the norway basin have been disconnected with the previous jurassic mid cretaceous episode of crustal thinning we also show evidence of relationships between the margin architecture the breakup magmatism distribution along the continent oceanic transition and the subsequent oceanic segmentation the norway basin shows a complex system of asymmetric oceanic segments locally affected by episodic ridge jumps the new aeromagnetic compilation also confirms that a fan shaped spreading evolution of the norway basin was clearly active before the cessation of seafloor spreading and extinction of the aegir ridge an important mid eocene kinematic event at around magnetic chron c21r can be recognized in the norway basin this event coincides with the onset of diking and increasing rifting activity and possible oceanic accretion between the proto jmmc and the east greenland margin it led to a second phase of breakup and microcontinent formation in the norwegian greenland sea 26 myrs later in the oligocene

deep structures and breakup along volcanic rifted margins insights from integrated studies along the outer voring basin norway three dimensional multichannel seismic survey and well data allows a deeper insight into rifting mechanisms and crustal structure of the norwegian volcanic rifted margin a surprising high velocity lower crustal dome marked by a strong amplitude reflection t reflection is described below the north gjallar ridge ngr near the volcanic plateau formed during the late paleocene early eocene breakup faulting along the ngr occurs during early campanian paleocene and is controlled by the crustal dome the t reflection was previously related to either the top of mafic underplated crust or soft lower crust updomed during the continental breakup the influence and timing of the crustal dome on the basin structure shows clearly that the dome predates the continental breakup based on the structural relationship and the results of the modelling it is therefore concluded that the t reflection does not necessarily originate from an anomalous tertiary magmatic event related to the breakup underplated material but could be also partly attributed to pre breakup mafic material or and inherited high pressure granulite eclogite rocks in the continental domain q 2004 elsevier ltd all rights reserved

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

high resolution topography for understanding earth surface processes opportunities and challenges abstract in the last decade a range of new remote sensing techniques has led to a dramatic increase in terrain information providing new opportunities for a better understanding of earth surface processes based on geomorphic signatures technologies such as airborne and terrestrial lidar light detection and ranging to obtain high resolution topography have opened avenues for the analysis of landslides hillslope and channellization processes river morphology active tectonics volcanic landforms and anthropogenic signatures on topography this review provides an overview of the recent flourishing literature on high resolution topographic analyses underlining their opportunities and critical issues such as their limitations the goal is to provide answers to questions such as what kind of processes can be analyzed through high resolution topographic data and how to do it the review focuses on two different environments natural and engineered landscapes in both contexts high resolution topography offers opportunities to better understand geomorphic processes from topographic signatures particular attention is given to engineered landscapes in which the direct anthropic alteration of processes is significant the last part of the review discusses future challenges

strength of slightly serpentinized peridotites implications for the tectonics of oceanic lithosphere we deformed cores of peridotite with 10 15 lizardite and chrysotile serpentine to determine the influence of serpentine content on the strength and the style of deformation the strength the pressure dependence of strength and the nominally nondilatant mode of brittle deformation of slightly serpentinized peridotites are comparable to those of pure serpentinites these results indicate that deformation is accommodated primarily by serpentine while olivine despite being the more abundant component remains nominally undeformed on the basis of these data and previous work we determine that the transition from a strong dilatant dunite rheology to a weak nondilatant serpentinite rheology is not a linear function of the degree of serpentinization instead an abrupt transition in strength is observed at low degrees of serpentinization the pressure of the transition from localized to distributed deformation also decreases abruptly from 1000 mpa to 150 350 mpa the change in rheological behavior occurs at a serpentine content of 10 15 or less which corresponds to published compressional seismic velocity of 7 8 7 5 km s at a pressure of 200 mpa the seismic velocity of the oceanic lithosphere particularly of that formed at slow spreading ridges can thus provide constraints on its mechanical properties at depth because slightly serpentinized peridotites have a rheology similar to that of pure serpentinite significant lithospheric weakening may occur after the onset of alteration near or at the ridge axis

high velocity breakup related sills in the voring basin off norway multichannel seismic reflection profiles in the hel graben v0ring basin reveal a sill complex at approximately 5 km depth it is associated with exceptionally high 7 4 km s 1 seismic wide angle velocities the existence of observable wide angle arrivals shows that the sills act as efficient waveguides seismic reflection data and amplitude modeling constrain the thickness of individual sills to approximately 100 m sonic logs from sills of similar thickness on the nearby utgard high show an average velocity of 7 0 km s 1 such high velocities require an olivine gabbroic sill composition and emplacement under conditions which allowed growth of relatively large crystal sizes a possible reason for such an emplacement environment is the hei graben s role as an intrusion center during breakup volcanism this would provide the necessary duration of the magmatic activity as well as locally increased melt volumes and cooling times sill complexes of this kind decrease the accuracy of determined velocity fields and crustal geometries below the top of the sill complex affecting depth conversion and gravity modeling furthermore the results question the concept of lower crustal bodies as large scale homogeneous accumulations of mafic melt

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

styles of extension offshore mid norway and implications for mechanisms of crustal thinning at passive margins 1 eocene magmatic breakup along the mid norway rifted margin was preceded by extreme jurassic cretaceous crustal thinning in a magma poor environment along the se borders of the rift top basement detachment faults with heaves on the order of 15 40 km evolved in at least two stages to become the boundaries between moderately thinned 20 30 km thick crust and a 100 200 km wide highly extended area with crustal thicknesses generally between 2 and 12 km under the present day more and voring basins in the footwalls of the basin flank detachments lower and middle crust was exhumed in extensional domes that became incised by a younger set of normal faults under the most highly thinned areas a more distal set of deep seated basin floor detachments incised and extended remnant crust and probably the upper mantle leaving as little as 5 km of continental crust to be preserved under thick synrift and postrift deposits we suggest that basin flank detachments such as the ones described above hold the potential to reduce the crustal thickness down to the critical value required for embrittlement of continental crust thus they prepare the ground for incision by the basin floor detachments which may become responsible for exhumation of deep crust or continental mantle if extension is allowed to proceed

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

a hierarchical tectonic model of the gulf of mexico and caribbean region abstract a quantitative computer graphic methodology hierarchical tectonic analysis has been used to model the tectonic evolution of the gulf of mexico and caribbean region this method employs a highly structured hierarchical description of the relative motions of pairs of tectonic elements in order to quantify the timing and style of plate interactions the main features described in this model are 1 1 a revised fit of pangea 2 2 the opening of the gulf of mexico in the middle late jurassic 3 3 the formation of a proto caribbean ocean due to the separation of north and south america during the early cretaceous 4 4 the formation of the greater antilles arc along the western margin of the proto caribbean ocean 5 5 the insertion of the farallon plate between north and south america during the middle cretaceous resulting in the northeastward advance of the greater antilles arc and the subduction of proto caribbean oceanic crust 6 6 the complete subduction of the proto caribbean ocean and the collision of the greater antilles arc with the bahamas platform in the late cretaceous 7 7 the truncation of the caribbean section of the farallon plate from its pacific counterpart and the formation of the panama arc latest cretaceous and 8 8 the westward movement of north and south america with respect to the caribbean plate resulting in the opening of the yucatan basin paleocene and subsequently in the evolution of the cayman trough and e w zone of strike slip

four phase tectonostratigraphic development of the southern caribbean abstract although the stratigraphy of northern south america and the southern caribbean has been studied in detail in many areas a clear understanding of the sequence of tectonic events and their relation to regional stratigraphy has not been forthcoming since northern south america collided with southern north america in the late palaeozoic we identify four discrete tectonic phases from the stratigraphy of the area that is now the southern caribbean these phases derived from a synthesis of regional stratigraphy were 1 panama arc collistion with colombia in the late miocene early pliocene which drove a complex triangular wedge bounded by strike slip faults northward into the caribbean 2 right lateral strike slip faulting associated with post eocene eastern motion of the caribbean ocean floor into the gap between the separating americas 3 island arc development and collision associated with the entry of the present caribbean ocean floor an area of buoyant ocean crust into the gap between the separating americas and 4 continental rifting and passive margin development in the late jurassic early cretaceous associated with the separation of north and south america approximately along the palaeozoic suture zone overprinting of younger structures on inherited structures from previous phases is responsible for the overall complexity of the region

continent ocean transition on the voring plateau ne atlantic derived from densely sampled ocean bottom seismometer data 1 a 180 km long seismic wide angle profile was acquired across the voring plateau ne atlantic using a tuned air gun array and three component ocean bottom seismometers deployed with 5 km spacing the seismic p wave data have been modeled by ray tracing inversion and the model has been constrained by s wave and gravity modeling the data and modeling have allowed us to depict the crustal structure and nature of the continent ocean transition cot in a classical volcanic margin case the p wave velocity near the top of the main crustal layer is estimated to 6 0 km s landward of the 25 km wide cot the seaward increase to 6 5 km s in the cot is conformable with heavily intruded continental crust within this zone farther seaward the velocity increase to 6 9 km s in the same layer suggests the presence of oceanic crust the abundant magmatism landward of and within the cot is primarily observed as extrusives forming wedges of seaward dipping reflectors and mafic lower crustal intrusions underplating the maximum thickness of the oceanic crust is measured to 23 5 km at the seaward termination of the cot

origin of seaward dipping reflectors in oceanic crust off the norwegian margin by subaerial sea floor spreading a remarkable layered acoustic stratification is observed in the upper oceanic crust adjacent to the norwegian continental margin it comprises a seaward dipping complex of reflectors in the form of a wedge we suggest that it is a layered igneous sequence that results when crustal accretion occurs at a subaerial spreading axis and that this phenomenon may commonly occur during the earliest phase of ocean basin genesis

testing techniques to quantify drumlin height and volume synthetic dems as a diagnostic tool glacial bedform height h and volume v likely preserve important information about the behaviour of former ice sheets however large systematic errors exist in the measurement of h and v three semi automated methods to isolate drumlins from other components of the landscape e g trees hills as portrayed by nextmap have recently been devised however it is unclear which is most accurate this paper undertakes the first quantitative comparison of such readily implementable methods illustrating the use of statistically representative synthetic landscapes as a diagnostic tool from this analysis guidelines for quantifying the 3d attributes of drumlins are proposed specifically to avoid obtaining incorrect estimates caused by substantial systematic biases interpreters should currently take three steps declutter the digital elevation model for estimating h but not v remove height data within the drumlin then interpolate across the resultant hole to estimate a basal surface using delaunay triangulation results are demonstrated through analysis of drumlins in an area in western central scotland the guidance arguably represents the best current advice for subglacial bedforms in general highlighting the need for more studies into the quality of mapped data using synthetic landscapes copyright 2014 john wiley sons ltd

along strike variations in rifted margin crustal architecture and lithosphere thinning between northern voring and lofoten margin segments off mid norway abstract an extensive geophysical and geological database is used to integrate observations and structural and stratigraphic modelling along the northern voring and lofoten margins off mid norway subsidence and fault analysis demonstrates depth dependent lithosphere stretching along both margin segments and the modelling concurs with an emergent or relatively shallow water emplacement environment for the breakup lavas along the northern voring margin however off lofoten subsidence modelling predicts 1500 m of bathymetric relief during breakup in contradiction to the view of subaerial volcanic emplacement environment off mid norway a distinct early eocene bathymetric gradient from voring to lofoten margin is suggested exhibiting depths in the order of 500 1000 m on the latter margin and thus an environment for submarine lava emplacement the water depth may even have reached 1250 m following breakup due to an initial rapid margin subsidence of the lofoten margin along a deep rooted low angle detachment fault the differences between northern voring and lofoten margin segments in pre and post breakup evolution are attributed to the bivrost lineament a transfer zone separating the two margin segments which appears as a major across margin boundary in terms of margin physiography and paleogeography differential sediment accommodation space crustal and lithosphere scale structure and breakup magmatism furthermore gravity inversion results appear to independently predict a significantly greater volcanic addition on the voring than on the lofoten margin

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

inconsistent correlation of seismic layer 2a and lava layer thickness in oceanic crust the oceanic crust makes up two thirds of the earth s surface and has been studied for many years yet the processes by which it is formed are still not fully understood one problem is inaccessibility only a tiny fraction of it has been subjected to drilling and sampling the tools of geology so much relies on remote sensing techniques such as seismic exploration the tools of geophysics these two approaches have led to some confusion over crustal structure christeson et al set out to reconcile the two by a direct comparison between seismic interpretations and geologic mapping the new data question the idea that seismic layer 2a correlates with lava layer thickness instead the layer 2a reflection seems to correspond to an alteration boundary within the lava layer at mid ocean ridges with fast to intermediate spreading rates the upper section of oceanic crust is composed of lavas overlying a sheeted dyke complex these units are formed by dykes intruding into rocks overlying a magma chamber with lavas erupting at the ocean floor seismic reflection data acquired over young oceanic crust commonly image a reflector known as layer 2a which is typically interpreted as defining the geologic boundary between lavas and dykes1 2 3 an alternative hypothesis is that the reflector is associated with an alteration boundary within the lava unit4 5 6 many studies have used mapped variability in layer 2a thickness to make inferences regarding the geology of the oceanic crust including volcanic construction dyke intrusion and faulting7 8 9 10 however there has been no link between the geologic and seismological structure of oceanic crust except at a few deep drill holes here we show that although the layer 2a reflector is imaged near the top of the sheeted dyke complex at fast spreading crust located adjacent to the hess deep rift it is imaged significantly above the sheeted dykes section at intermediate spreading crust located near the blanco transform fault although the lavas and underlying transition zone thicknesses differ by about a factor of two the shallow seismic structure is remarkably similar at the two locations this implies that seismic layer 2a cannot be used reliably to map the boundary between lavas and dykes in young oceanic crust instead we argue that the seismic layer 2a reflector corresponds to an alteration boundary that can be located either within the lava section or near the top of the sheeted dyke complex of oceanic crust

intermediate depth seismicity in northern colombia and western venezuela and its relationship to caribbean plate subduction the recent intermediate depth seismicity in northern colombia and western venezuela was analyzed to understand its origin and its presumed relationship to a subducted lithospheric slab in northwestern south america the area included in this study is located to the north and east of the bucaramanga nest which is a particular region beneath bucaramanga northern colombia that presents a high concentration of intermediate depth earthquakes to the north of the nest the seismicity of the area is sparse and most of the events are of low magnitude mb 5 l thus only 23 earthquakes were large enough to be investigated using teleseismic data the focal parameters of the two largest events mb 5 4 were obtained from the formal inversion of long period body waves recorded at teleseismic distances the focal mechanisms of 10 more events were determined from first motion data in total the focal mechanisms of 12 events were determined from both the inversion of p and s h waveforms and the polarities of first arrivals for the smaller earthquakes the focal depths were calculated by measuring the observed pp p interval time and comparing it to the theoretical travel time tables the isodepth curves reflect a slab striking in a nne ssw direction and dipping approximately at 25 32 to the southeast this observation is corroborated by the direction and plunge of the t axes of the focal mechanisms which are generally parallel to the gradient of the slab defined by the spatial distribution of hypocenters these results indicate that the intermediate depth earthquakes in western venezuela and northern colombia are apparently related to the presence of a continuous lithospheric slab subducted near the northern coast of colombia the two largest earthquakes located at a significant distance from the bucaramanga nest present similar fault plane solutions moreover they also agree with those of the two largest earthquakes reported inside the nest this similarity suggests that the bucaramanga nest lies on the same subducted slab where the other earthquakes occur there is not enough shallow seismicity to define the location where the caribbean lithosphere subducted beneath the south american plate however the extension of the slab toward the surface inferred from the intermediate depth seismicity suggests that the subducted lithosphere may still be attached to the caribbean plate

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

symmetric and asymmetric lithospheric extension relative effects of frictional plastic and viscous strain softening 1 strain dependent rheologies may play a critical role in the deformation of the lithosphere and particularly in the development of focused shear zones we investigate the effects of strain softening on lithospheric extension using plane strain thermomechanical finite element model experiments parametric softening is specified as a linear decrease of the effective internal angle of friction the effective viscosity or both in the model rheologies the sensitivity of deformation to the choice of softening parameters is investigated in cases where the crust is either strongly or weakly coupled to the mantle lithosphere results are classified according to the symmetry s or asymmetry a of the deformation of the upper and lower lithosphere during rifting strain softening is required for rifting asymmetry but is not always sufficient a range of model tectonic styles occurs including pure and simple shear modes with focused shear zones mode selection is mostly determined by the feedback between two primary controls the dominant rheology and the parametric strain softening mechanisms listed above softening of the dominant rheology promotes asymmetric extension of that part of the lithosphere controlled by the dominant rheology model results are consistent with the proposed primary controls and the factors that contribute to these controls in particular decreasing and increasing the rifting velocity can change the mode by changing the dominant rheology asymmetry is strongest in coupled models which include a decrease in the internal angle of friction and have low rifting velocities

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

residual relief separation digital elevation model enhancement for geomorphological mapping geomorphologically mapped data form a primary set of observations that can be used to infer former environmental conditions thus objective and consistent mapping of landforms from remotely sensed data e g satellite imagery digital elevation models dems is paramount for reconstructing palaeoenvironments this paper proposes a technique residual relief separation to enhance landforms in dems prior to visualization and digital mapping this is applied to a 600 km2 region surrounding lough gara ireland where drumlins 200 m wide overlie a regional relief of hills 10 km wide here residual relief separation uses this difference in width scale regional relief is approximated by a 1 km wide median filter then subtracted to leave the drumlins in a residual topography in a second step the residual relief is normalized to allow for amplitude variations in the drumlins across the area 5 40 m high finally visualization uses a simple black to white colour scale for height although not numerically outperforming other visualization techniques this method performs equally well and as the data are not illuminated there is no azimuthal bias additional benefits include the relatively simple calculation intuitive visual comprehension no emphasis of noise and the possibility of using any desired visualization technique after the landscape has been topographically manipulated

morphological characterization of coral reefs by combining lidar and mbes data a case study from yuanzhi island south china sea the correlation between seafloor morphological features and biological complexity has been identified in numerous recent studies this research focused on the potential for accurate characterization of coral reefs based on high resolution bathymetry from multiple sources a standard deviation std based method for quantitatively characterizing terrain complexity was developed that includes robust estimation to correct for irregular bathymetry and a calibration for the depth dependent variablity of measurement noise airborne lidar and shipborne sonar bathymetry measurements from yuanzhi island south china sea were merged to generate seamless high resolution coverage of coral bathymetry from the shoreline to deep water the new algorithm was applied to the yuanzhi island surveys to generate maps of quantitive terrain complexity which were then compared to in situ video observations of coral abundance the terrain complexity parameter is significantly correlated with seafloor coral abundance demonstrating the potential for accurately and efficiently mapping coral abundance through seafloor surveys including combinations of surveys using different sensors

crustal structure and evolution of the outer more margin ne atlantic abstract five regional ocean bottom seismic profiles from the northwestern part of the more margin ne atlantic have been modeled with regard to crustal structure and the interpretations have been supported by the use of multi channel seismic and potential field data the chi squared values uncertainty for the studied profiles are generally in the range 1 3 and the uncertainty in the moho depth is estimated to 1 km the continent ocean transition is found to be relatively sharp 10 40 km wide expressing a change in physical properties corresponding to felsic continental crust along the landward part of the marginal high vp 6 2 6 5 km s and thick mafic oceanic crust further northwestwards the early eocene breakup was associated with excessive magmatism and the models document direct continuity between this magmatism and a lower crustal high velocity layer in the more basin vp 7 1 7 3 km s suggesting a genetic link the jan mayen lineament is observed across the entire study area as northeastward termination of the lower crustal body as well as structuring in the top of the crystalline basement and the moho we present a speculative model involving lower crustal bodies of eclogites vp 8 km s inferred in the easternmost part of the more basin linking the jan mayen lineament to the post caledonian nordfjord sogn detachment

erosion processes in calanchi in the upper orcia valley southern tuscany italy based on multitemporal high resolution terrestrial lidar and uav surveys a 125 000 m2 calanchi badland in the province of siena tuscany was monitored with an unmanned aerial vehicle uav and terrestrial laser scanning over the period of one year tls terrestrial laser scanning was carried out on two sample slopes whereas the image acquisition of the uav covered the entire catchment in combination with ground control points the uav images were used to create orthophotos and 3d point clouds using the structure from motion sfm software photoscan the tls surface models indicate seasonal differences in erosion and deposition the surface change measured with sfm showed nearly 6 700 m3 of net material loss resulting from 8 700 m3 erosion and 2 000 m3 deposition these values reveal a mean annual surface lowering of 5 3 cm for the catchment additionally several geomorphological processes such as rill erosion slope wash and translational slides could be detected in the one year monitoring period a comparison of tls and sfm results showed differences in the calculated volumes of mobilised material these discrepancies resulted from shadowing effects and low point densities of the tls point clouds

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

sinkholes subsidence and subrosion on the eastern shore of the dead sea as revealed by a close range photogrammetric survey abstract ground subsidence and sinkhole collapse are phenomena affecting regions of karst geology worldwide the rapid development of such phenomena around the dead sea in the last four decades poses a major geological hazard to the local population agriculture and industry nonetheless many aspects of this hazard are still incompletely described and understood especially on the eastern dead sea shore in this work we present a first low altitude our analysis reveals a kilometer scale sinuous depression bound partly by flexure and partly by non tectonic faults the estimated minimum volume loss of this subsided zone is 1 83 106 m3 with an average subsidence rate of 0 21 m yr 1 over the last 25 years sinkholes in the surveyed area are localized mainly within this depression the sinkholes are commonly elliptically shaped mean eccentricity 1 31 and clustered nearest neighbor ratio 0 69 their morphologies and orientations depend on the type of sediment they form in in mud sinkholes have a low depth to diameter ratio 0 14 and a long axis azimuth of nne ne in alluvium sinkholes have a higher ratio 0 4 and are orientated nnw n from field work we identify actively evolving artesian springs and channelized sediment laden groundwater flows that appear locally in the main depression consequently subrosion i e subsurface mechanical erosion is identified as a key physical process in addition to dissolution behind the subsidence and sinkhole hazard furthermore satellite image analysis links the development of the sinuous depression and sinkhole formation at ghor al haditha to preferential groundwater flow paths along ancient and current wadi riverbeds