statistical probability distribution of snow depth at the model sub grid cell spatial scale comprehensive snow depth data collected using georadar and hand probing were used for statistical analyses of snow depths inside 1 km grid cells the sub grid cell spatial scale was 100 m statistical distribution functions were found to have varying parameters and an attempt was made to connect these statistical parameters to different terrain variables the results showed that the two parameters mean and standard deviation of snow depth were significantly related to the sub grid terrain characteristics linear regression models could explain up to 50 of the variation for both of the snowcover parameters mentioned copyright 2004 john wiley sons ltd

the blanketing effect of sediments in basins formed by extension a numerical model application to the gulf of lion and viking graben abstract a numerical finite difference model is employed to reconstruct the time temperature history of sediments in basins formed by extension in which crustal thinning by stretching as well as the effects associated with sedimentation and compaction are taken into account two extreme cases of basins were investigated to identify the scale of this mechanism the gulf of lion illustrates a case of a young basin in which the average sedimentation rate is high 620 m ma and the viking graben in the north sea offers a case of a basin formed in the triassic but where average sedimentation rate is much less 37 m ma in the former the sediments absorb 30 of the surface heat flow while in the latter the effect is only 10

persistence in intra annual snow depth distribution 1 measurements and topographic control 1 terrestrial and airborne laser scanning tls and als techniques have only recently developed to the point where they allow wide area measurements of snow distribution in varying terrain in this paper we present multiple tls measurements showing the snow depth development for a series of precipitation events we observe that the pattern of maximum accumulation is similar for the two years presented here correlation up to r 0 97 storms arriving from the northwest show persistent snow depth distributions and contribute most to the final accumulation pattern snow depth patterns of maximum accumulation for the two years are more similar than the distribution created by any two pairs of individual storms based on the strong link between accumulation patterns and terrain we investigated the ability of a model based on terrain and wind direction to predict accumulation patterns this approach of winstral et al 2002 which describes wind exposure and shelter was able to predict the general accumulation pattern over scales of slopes but failed to match observed variance furthermore a high sensitivity to the local wind direction was demonstrated we suggest that winstral et al s model could form a useful tool for application from hydrology and avalanche risk assessment to glaciology

modelling of hydrocarbon generation in the cenozoic song hong basin vietnam a highly prospective basin abstract the cenozoic song hong basin situated on the northern part of the vietnamese shelf has been only sporadically explored for hydrocarbons a review of the results of the exploration efforts so far shows that the distribution of potential source rocks and their time of hydrocarbon generation are the critical risks for finding commercial amounts of hydrocarbons in the song hong basin including the hanoi trough the rocks most likely to have source potential are 1 oil prone eocene lower oligocene lacustrine mudstones and coals 2 oil and gas prone middle miocene coal beds 3 gas prone upper oligocene lower miocene coals and 4 gas and oil prone miocene marine mudstones to assess the time of hydrocarbon generation from these units relative to the formation of traps the generation history was modelled at 32 well and pseudo well locations the modelling demonstrates that the two first mentioned source rock units are especially important in the northern and northeastern part of the basin and along its western margin traps may have been charged by eocene lower oligocene source rocks in the hanoi trough the excellent middle miocene coal beds have probably generated hydrocarbons within the last few million years thus the huge and still underexplored song hong basin provides attractive areas for further exploration

the variation of temperature with time and hydrocarbon maturation in sedimentary basins formed by extension abstract when a sedimentary basin is formed by extension both the subsidence history and the temperature gradient can be calculated hence the time temperature history of any stratum can be obtained three types of behaviour occur the temperature of material which never reaches depths greater than about 4 km increases at all times the time temperature history of material which finally sinks to greater depths reaches a maximum during the subsidence history the time at which this maximum occurs decreases as the depth increases at greater depths the maximum temperature occurs at the time the basin is formed the time temperature history is then used to calculate lopatin s maturation index for each stratum as a function of time and the index plotted as a function of depth and time for different amounts of extension the maximum temperature at a given depth and hence lopatin s index is almost independent of the amount of extension when the age of the basin is greater than about 150 ma similar calculations taking account of sediment compaction show the same behaviour though the maturity of the material at a given depth is increased because both lopatin s index and its calibration are empirical it is important to develop new maturation indices based on individual molecular reactions whose activation energies can be determined in the laboratory

an improved method for reconstructing the stratigraphy and bathymetry of continental margins application to the cenozoic tectonic and sedimentary history of the congo margin a number of techniques such as backstripping and forward modeling have been previously used to reconstruct the tectonic sedimentary and thermal history at passive margins still these techniques are generally inaccurate in places such as the west african margin where the stratigraphic record is disrupted by continuous faulting of the sediment pile caused by salt tectonics and by erosional unconformities the ability to reconstruct the stratigraphy salt thickness and water depth along profiles of these types of margins is important for determining the factors controlling the geological history of the margin and the evolution of hydrocarbon systems to reconstruct the stratigraphy paleowater depths and salt flowage on a profile across the congo margin we combined backstripping and palinspastic reconstruction this enabled us to restore the faulting and salt flowage and simultaneously to take into account the isostatic response of the lithosphere to sediment loading and unloading this method allowed us to estimate the paleowater depth as well as the stratigraphy and the geometry of the sedimentary section on the profile through time the determination of the regional isostatic response of the lithosphere is performed with the use of a new model to estimate the flexural rigidity of continental lithosphere to demonstrate this method we perform the cenozoic reconstruction of the congo margin the results yield a coherent geological history of the margin from the eocene to the present in the eocene the margin was a carbonate ramp with a deep seated shelf break 600 m during the eocene oligocene transition intermediate water depth oceanic currents triggered submarine erosion of the eocene slope and shelf from the miocene to the present we observe a large increase in the input of terrigenous clastic sediments as a result the shelf prograded 40 km across the eocene ramp as the clastic sediments prograded across the margin into the deep basin faulting of the sediment pile and salt withdrawal caused the formation of grabens in places where salt swells had previously formed finally the reconstruction suggests that the congo margin was uplifted by at least 330 m between the late oligocene and the middle miocene

thermal effects of normal faulting during rifted basin formation 1 a finite difference model abstract a finite difference model is presented describing the thermal structure of a region undergoing fault controlled extension the model is two dimensional and time dependent we combine temperature changes resulting from conduction advection due to fault movements sediment blanketing and heat production cooling curves can be derived at chosen points in the area this study mainly investigates the effect of the extension rate on the thermal field which turns out to be very important 20 km of extension with extension rates of 0 2 2 0 and 20 mm yr yield maximum deviations in temperatures from the steady slate situation of 2 26 and 84 the sediment blanketing effect can even be reversed by variations in the sedimentation rates fast sedimentation leads to crustal cooling slow sedimentation to crustal heating the turning point value is lithology dependent and corresponds to 2 0 mm yr for shale 2 2 mm yr for clay and 1 4 mm yr for sand a sandstone will cause an increased cooling at both high and low velocities our modelling shows that footwall cooling during or immediately after a rifting event cannot be explained by the downwards movement of the adjacent relatively cold hanging wall consequently in areas where such a cooling is observed other cooling mechanisms must play an important role these can be phenomena like footwall uplift or the fading out of an older thermal anomaly

subsidence maturation and migration history of the tampen spur area abstract a complete study of the petroleum system of the tampen spur area has been carried out the approach used was a two dimensional temispack analysis of a seismic line crossing the area where various hypotheses could be tested and later applied in a three dimensional sense the profile crosses from the deepest part of the tampen graben across the visund ridge and the marflo ridge to the sogn graben in the east four source rocks have been taken into account two marine the draupne the most prolific and the heather and two deltaic the brent and the dunlin two different prospect types can be defined the brent at the top of the tilted blocks and heather sand bodies at the foot of the eroded tilted blocks various hypotheses about the geometry of these sand bodies and about the contact between the rich draupne source rocks and the sands have been tested maturation started in the middle cretaceous between 100 ma in the deepest eastern part of the section sogn graben and 80 ma for the draupne on the tampen spur west graben at this time the structures were already sealed by the cretaceous shales apart from the visund ridge all the prospects are currently in the condensate or gas window overpressures are compatible with large closed faults more data are required about the possible sealing of minor faults before any conclusions can be drawn there is no easy migration path from the rich draupne rocks to the brent reservoir and various hypotheses are discussed to explain the regional petroleum potential one possible explanation for the regional charge is the contribution of the other source rocks the heather the brent and the dunlin

source rock maturation characteristics of symmetric and asymmetric grabens inferred from integrated analogue and numerical modeling the southern viking graben north sea abstract we present the results of an integrated analogue and numerical modeling study with a focus on structural stratigraphic and thermal differences between symmetric and asymmetric grabens these models enable fault interpretation and subsidence analyses in studies of active rifting and graben migration we imported the surface topography and crustal thinning factors from the analogue models into tectono stratigraphic forward models which allowed an assessment of the relative importance of sediment stacking in the generation of symmetric and asymmetric grabens effects on source rock maturation zones were calculated through 1d thermal modeling for different graben types combined analogue numerical modeling appears to be a useful method to simulate natural examples as shown in this study of the southern viking graben in the northern north sea this area was formed by early permian late jurassic extension with rifting most intense during the late jurassic the thermal structure of the model constrained by lithospheric and sedimentary parameters for this region compares well with actual source rock maturation data on the southern viking graben

relationship between thermal maturation gradients geothermal gradients and estimates of the thickness of the eroded foreland section southern alberta plains canada abstract analysis of post laramide tertiary uplift and erosion in the southern alberta plains indicates that the greatest erosion occurred in regions where the youngest stratigraphic units are preserved this is consistent with geological structure and the few preserved stratigraphic constraints on erosional history throughout this region erosion is pervasive and the uplift history is commonly constrained by coalification data the analysis of coalification erosion and paleogeothermics are interrelated and knowledge of them is important to understand hydrocarbon generation and tectonic history several independent attempts to analyse coalification erosion and paleogeothermics in this area have given different results the most striking differences are those between estimates derived from the analysis of well profile coalification gradient and those determined using a commonly accepted relationship between the amount of eroded section and the equilibrium moisture content of near surface coals the match between present and paleogeothermal gradient fields is better when the latter technique is used correlation is expected between the late orogenic and present geothermal gradient fields because the hydrodynamically controlled advective heat flow pattern that now dominates geothermal gradients in the mesozoic and tertiary foreland succession was initiated by the growth of topography in the west throughout cordilleran orogeny well profile coalification gradients have significant though commonly unacknowledged uncertainties these uncertainties are propagated in erosion and paleogeothermal gradient calculations ideally the relationship between erosion estimates using well profile coalification gradients and near surface coal properties can be compared unfortunately the uncertainties in well profile coalification gradients prevent this

the dynamics of extensional sedimentary basins constraints from subsidence inversion on the continents sedimentary basins are generally formed by small amounts of lithospheric extension extension might cease because the lithospheric mantle has cooled and strengthened or because the driving force is removed in the former case a relationship should exist between the maximum strain rate during extension and the final stretching factor attained we explore how this relationship depends on the rheology of the lithospheric mantle and of the crust as well as on sedimentation and prior rifting events we also present strain rate information obtained by inverting subsidence data from a variety of sedimentary basins there is evidence of a systematic relationship between strain rate and stretching factor in each basin implying that lithospheric rheology is consistent with the rheology of olivine measured in laboratory experiments our data are difficult to explain if removal of the driving force governs the magnitude of stretching factors

gps estimate of relative motion between the caribbean and south american plates and geologic implications for trinidad and venezuela global positioning system gps data from eight sites on the caribbean plate and five sites on the south american plate were inverted to derive an angular velocity vector describing present day relative plate motion both the caribbean and south american velocity data fit rigid plate models to within 1 2 mm yr the gps velocity uncertainty the caribbean plate moves approximately due east relative to south america at a rate of 20 mm yr along most of the plate boundary significantly faster than the nuvel 1a model prediction but with similar azimuth pure wrenching is concentrated along the approximately east striking seismic el pilar fault in venezuela in contrast transpression occurs along the 068 trending central range warm springs fault in trinidad which is aseismic possibly locked and oblique to local plate motion

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

arguments for the pre rift uplift and rift propagation in the ligurian provencal basin northwestern mediterranean in the light of pyrenean provencal orogeny the cenozoic provencal orogeny and the subsequent opening of the ligurian provencal basin were caused by a geodynamic mechanism that originated in the cretaceous it is evident from the arguments presented that 1 regional doming preceded rifting of the continental margin and this uplift widened and or migrated during the ensuing opening of the ligurian provencal basin 2 clastic sedimentation on the provencal platform was initiated during the early cenomanian 3 deformation in the provencal block which varies from late cretaceous to miocene reflects a migration of the north south compression from west to east accross the block 4 the languedoc provencal fold belt was initiated during the eocene as a result of tectonic uplift and sinistral displacement of the paleozoic basement toward the north significant geologic features of the region associated with these events include 1 similarities in shape of the languedoc virgation and the provencal thrust front with the shape of geophysical features over the golfe du lion 2 the unusual width of the young stretched continental margin in the golfe du lion 3 the distinctive v shaped form of the ligurian oceanic crust and 4 the concordance in age of the earliest post rift deposits which increasingly young toward the east and magnetic anomalies that parallel the basin axis these events and structures are attributed to the uplift of a paleozoic block situated to the south in the golfe du lion and previously buried under the mesozoic cover the development of this crustal uplift since upper aptian and its northeastwards migration and or gradual widening account for both sedimentary events and tectonic deformation that occurred on the provencal platform until upper eocene and the later stage of rifting and formation of the provencal margin in the ligurian provencal basin the synthesis of marine data as well as relevant terrestrial data indicates that rifting propagated towards the gulf of genoa while the corsica sardinia block rotated to the southeast

numerical modeling of simultaneous extension and compression the valencia trough western mediterranean a two dimesional kinematic model which incorporates lateral accommodation of extension and differential stretching is used to investigate the geodynamic evolution of the valencia trough this neogene basin located between the iberian peninsula and the balearic promontory underwent two rifting episodes the first one being coeval with compression model predictions are compared with observations of tectonic subsidence bouguer gravity anomaly surface heat flow and the present day crustal structure the best fitting model assumes three stages in the evolution of the basin during the first stage late oligocene early miocene extension is mainly restricted to the central and northwestern parts of the basin whereas its southeastern margin is locked by the alpine deformation front the material expelled from the axial area is partly accommodated under the balearic promontory producing compression and crustal thickening during the second rifting stage middle miocene extension affects a much broader area including the balearic promontory and the algero provencal basin the third stage late miocene to recent corresponds to a postrift thermal relaxation phase our results put further constraints on the geodynamic evolution of the area

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

topographic meteorologic and canopy controls on the scaling characteristics of the spatial distribution of snow depth fields 1 in this study lidar snow depths bare ground elevations topography and elevations filtered to the top of vegetation topography vegetation in five 1 km 2 areas are used to determine whether the spatial distribution of snow depth exhibits scale invariance and the control that vegetation topography and winds exert on such behavior the one dimensional and mean two dimensional power spectra of snow depth exhibit power law behavior in two frequency intervals separated by a scale break located between 7 m and 45 m the spectral exponents for the low frequency range vary between 0 1 and 1 2 for the one dimensional spectra and between 1 3 and 2 2 for the mean twodimensional power spectra the spectral exponents for the high frequency range vary between 3 3 and 3 6 for the one dimensional spectra and between 4 0 and 4 5 for the mean two dimensional spectra such spectral exponents indicate the existence of two distinct scaling regimes with significantly larger variations occurring in the larger scale regime similar bilinear power law spectra were obtained for the fields of vegetation height with crossover wavelengths between 7 m and 14 m further analysis of the snow depth and vegetation fields together with wind data support the conclusion that the break in the scaling behavior of snow depth is controlled by the scaling characteristics of the spatial distribution of vegetation height when snow redistribution by wind is minimal and canopy interception is dominant and by the interaction of winds with features such as surface concavities and vegetation when snow redistribution by wind is dominant

temperature subsidence and hydrocarbon maturation in extensional basins a finite element model the thermo mechanical history of extensional basins is of great importance in determining their hydrocarbon potential because of the great variation of geologic conditions a flexible method is needed to model this history a one dimensional finite element method is particularly suited for this purpose its use shows that the temperature distribution is out of equilibrium if the rate of sedimentation exceeds 100 m ma 300 ft ma favorable conditions for hydrocarbon production in three models are found between 100 and 225 c but this is not a general rule in areas of reasonably flat interfaces the method yields excellent results at very little cost it shows the interplay among sedimentation temperature and subsidence more clearly than has been possible heret fore

velocity field across the southern caribbean plate boundary and estimates of caribbean south american plate motion using gps geodesy 1994 2000 global positioning system gps observations between 1994 and 2000 at twenty two sites in the lesser antilles and northern south america indicate that the caribbean plate along its southern boundary slips at a rate of 20 5 2 mm a with an azimuth of n 84 2 e at 65 w relative to the south american plate east of 68 w 80 of the dextral slip is contained within a 80 km wide shear zone centered on the el pilar san sebastian fault system west of 68 w the plate boundary broadens to more than 300 km with dextral shear shared between the northeast trending bocono fault 9 11 mm a in western venezuelan and an offshore system near the northern coast

thermal and compaction processes in a young rifted basin containing evaporites gulf of lions france the gulf of lions northwestern mediterranean is a young oligocene miocene rifted basin characterized by the presence of a thick evaporitic sequence observed data surface heat flow well temperatures geopressures below the evaporites crustal thinning are used to model 1 the basin forming mechanisms and 2 the intrasedimentary processes that influence the temperature history and thus the maturation of source rocks a two dimensional finite difference basin model temispack simulates the sedimentation compaction and overpressures related to the low permeability of the post rift sequence the heat transfer from the rifted lithosphere into the sediments and the level of maturation by using a kinetic approach the classic passive margin model which relates the history of heat flow and the rate of subsidence to a uniform thinning factor yields subsidence and heat flow predictions that agree with observations the recently accelerated subsidence observed in the deep margin is probably an effect of recent regional compression rather than the consequence of alternative rifting mechanisms the history of maturation of organic matter was influenced by the variation of the regional heat flow due to the rifting the effect of sedimentation or blanketing and the variability of the lithologies and porosities the undercompaction of sediments underlying the evaporites is accounted for by the model which suggests that hydraulic fracturing is taking place at present in the overpressured sediments fluid flow associated with the compaction disequilibrium has negligible thermal effect undercompacted shales below the evaporites have lower thermal diffusivity and thus higher temperatures which has a significant effect on maturation

scaling properties and spatial organization of snow depth fields in sub alpine forest and alpine tundra this paper reports on a study analysing the spatial distribution functions the correlation structures and the power spectral densities of high resolution lidar snow depths 1 m in two adjacent 500 m 500 m areas in the colorado rocky mountains one a sub alpine forest the other an alpine tundra it is shown how and why differences in the controlling physical processes induced by variations in vegetation cover and wind patterns lead to the observed differences in spatial organization between the snow depth fields of these environments in the sub alpine forest area the mean of snow depth increases with elevation while its standard deviation remains uniform in the tundra subarea the mean of snow depth decreases with elevation while its standard deviation varies over a wide range the two dimensional correlations of snow depth in the forested area indicate little spatial memory and isotropic conditions while in the tundra they indicate a marked directional bias that is consistent with the predominant wind directions and the location of topographic ridges and depressions the power spectral densities exhibit a power law behaviour in two frequency intervals separated by a break located at a scale of around 12 m in the forested subarea and 65 m in the tundra subarea the spectral exponents obtained indicate that the snow depth fields are highly variable over scales larger than the scale break while highly correlated below based on the observations and on synthetic snow depth fields generated with one and two dimensional spectral techniques it is shown that the scale at which the break occurs increases with the separation distance between snow depth maxima in addition the breaks in the forested area coincide with those of the corresponding vegetation height field while in the tundra subarea they are displaced towards larger scales than those observed in the corresponding vegetation height field

probing connections between deep earth and surface processes in a land locked ocean basin transformed into a giant saline basin the mediterranean gold project during the last decade the interaction of deep processes in the lithosphere and mantle with surface processes erosion climate sea level subsidence glacio isostatic readjustment has been the subject of heated discussion the use of a multidisciplinary approach linking geology geophysics geodesy modelling and geotechnology has led to the awareness of coupled deep and surface processes deep earth dynamics topography erosion tectonics are strongly connected to natural hazards such as earthquakes landslides and tsunamis sedimentary mass transfers have important consequences on isostatic movements and on georesources geothermal energy repartitions the ability to read and understand the link between deep earth dynamics and surface processes has therefore important societal impacts ground truthing at carefully selected sites of investigation is imperative to better understand these connections due to its youth 30 ma and its subsidence history the almost land locked gulf of lion sardinia continental margins system provides a unique record of sedimentary deposition from the miocene to present due to its high subsidence rate palaeoclimatic variations tectonic events and vertical evolution are all recorded here at very high resolution the late miocene isolation and desiccation of the mediterranean the youngest and most catastrophic event the messinian salinity crisis msc induced drastic changes in marine environments widespread deposition of evaporite gypsum anhydrite and halite in the central basin and intense subaerial erosion along its periphery these extraordinary mass transfers from land to sea induced strong isostatic re adjustments that are archived in the sedimentary record and represent a window to the lithospheric rheology and the deep processes the gold gulf of lion drilling project proposes to explore this unique sedimentary record as well as the nature of the deep crustal structure providing valuable information about the mechanisms underlying vertical motions in basins and their margins

heat flow heat production and fission track data from the hercynian basement around the provencal basin western mediterranean abstract in the complex structural framework of the western mediterranean hercynian areas are expected to be thermally preserved from the recent tectonic evolution the thermal regime of these areas is studied using heat flow heat production and fission track data the surface heat flow is significantly higher in corsica 76 10 mw m 2 than in the maures and esterel 58 2 mw m 2 neither heat production nor erosion subsequent to the alpine orogeny in corsica can explain such a difference it is suggested that a deep thermal source related to the asymmetric evolution of the provencal basin could explain the higher heat flow in corsica a model of thermal structure based on the present day thermal regime of the maures and esterei is proposed for the stable hercynian crust in this area the mantle heat flow is 20 25 mw m 2 and the temperature at moho level is 375 500 c depending on the thermal parameter distribution with depth

reconstruction of low temperature 100 c burial in sedimentary basins a comparison of geothermometer in the intracontinental paris basin abstract the thermal evolution of sediments in the shallowest part of sedimentary basins is challenging to investigate as most of the geothermometers are at their application limits this is typically the case of the callovian oxfordian claystones at the eastern border of the paris basin a recent 2000 m deep well penetrated the entire jurassic and triassic sedimentary series and permitted coring of sediments never reached by previous drilling in this part of the basin thanks to the use of several independent geothermometers apatite fission track thermochronology fluid inclusion microthermometry clay mineralogy and sedimentary organic matter evolution the burial history of the mesozoic series has been reconstructed modeled and calibrated using kinetic algorithms relevant to the various paleothermometers used in addition to these conventional methods an innovative approach was developed using the temperature dependence of the magnetic mineral assemblage within clay rich sediments mageval thermal modeling indicates that the callovian oxfordian and the lower triassic experienced maximum burial temperatures of 50 5 c and 90 10 c respectively i e about 25 c higher than present day this temperature offset implies the erosion of several hundred meters of sediments which depending on the thermal flux and conductivity considered most likely constituted upper cretaceous chalk deposits falling sea level resulted in the exposure and subsequent dismantling of the chalk cover at the beginning of cenozoic times the eastern border of the basin was then subjected to slow erosion and discrete tectonic deformation

thermal state in the north viking graben north sea determined from oil exploration well data we can deduce thermal conductivities and thermal gradients from extensively available oil exploration data geophysical well logs cores cuttings formation thicknesses and temperatures thermal conductivity is predicted at three significant scales first it is computed at the scale of well log electrofacies thicknesses from 1 to 10 m using a geometric mean model calibrated on laboratory measurements made on the main sedimentary rocks the electrofacies conductivity is calculated as a function of the mineralogy the porosity and the saturating fluids second it is estimated at formation scale at each well site thicknesses from 100 to a few thousand meters using a serial model that accounts for the anisotropy due to sediment stacking and for temperature effects finally for each formation thicknesses on the order of 1 km the average conductivity field is mapped at basin scale extent on the order of 100 km using a geostatistical treatment accounting for lateral facies and or porosity changes fo

flexural and gravity modelling of the merida andes and barinas apure basin western venezuela abstract the kinematic evolution of the barinas apure basin and the southern merida andes from lower miocene to the present is numerically modelled using flexural isostatic theory and geophysical and geological data two published regional transects are used to build up a reference section which is then used to constrain important parameters e g shortenings and sedimentary thicknesses for the flexural modelling to control the location of the main fault system in the flexural model earthquake information is also used the estimated flexural elastic thickness of the south american lithosphere beneath the barinas apure basin and the merida andes range is 25 km the value for the final total shortening is 60 km the flexural isostatic model shows that the andean uplift has caused the south american lithosphere subsidence and the development of the barinas apure basin in addition gravity modelling was used to understand deep crustal features that could not be predicted by flexural theory consequently the best fit flexural model is used to build a gravity model across the merida andes and the barinas apure basin preserving the best controlled structural features from the flexural modelling e g basin wavelength and depth and slightly changing the main bodies density values and deep crustal structures the final gravity model is intended to be representative of the major features affecting the gravity field in the study area the predicted morphology in the lower crustal level of the final gravity model favours the hypothesis of a present delamination or megathrust of the maracaibo crust over the south american shield this process would use the conrad discontinuity as a main detachment surface within an incipient nw dipping continental subduction

late paleozoic rotations of corsica and sardinia new evidence from paleomagnetic and k ar studies abstract a detailed paleomagnetic investigation of so called permian volcanics was undertaken in southeastern and northwestern sardinia k ar dating on separate minerals representing 30 sites on corsica and sardinia showed that the first calc alkaline cycle had taken place in westphalo stephanian times and the second alkaline one at the end of the stephanian 246 paleomagnetic specimens from 28 sites of southeastern sardinia and 2 sites from the northwest were demagnetized by alternating field and thermal processes the directions of characteristic magnetizations are d 85 i 6 95 5 for the volcanics of southeastern sardinia and d 126 i 1 for the nurra samples these mean directions differ from those of northwestern corsica and northern sardinia gallura the paleomagnetic results display good grouping for each volcanic complex but exhibit a geographical dispersion of the mean directions this scattering suggests significant motions in late hercynian times

types of crust beneath the ligurian sea the structural setting beneath the ligurian sea resujts from several tectonic events reflected in the nature of the crust the central western sector called the ligurian basin is part of the northwestern mediterranean it is a marginal basin that was generated in oligocene miocene time by subduction of the adriatic plate beneath the european plate and by the eastward drift of the corsica sardinia block the eastern sector belongs to the tyrrhenian basin system and is characterized by extensional activity which since tortonian time superimposed an earlier compressional regime our effort has been addressed in particular towards simplifying the complex nature of the crust of the ligurian basin by modelling its genesis using uniform extension and sea floor depth variation with age in the rift stage of the basin s evolution the initial subsidence reaches the isostatic equilibrium level of the asthenosphere by a thinning factor of 3 15 the additional passive process corresponding to the cooling of the lithosphere since 21 ma leads to a total tectonic subsidence of 3 4 km representing the boundary of the extended continental crust for values up to 4 1 km a transitional type crust is expected whereas for higher tectonic subsidence values a typical oceanic crust should exist after setting these constraints the boundaries of the different crust types have been drawn based on total tectonic subsidence observations deduced from bathymetry and post rift sediment thickness although there is a general agreement with the previous reconstructions deduced from other experimental data the oceanic realm has wider extent and more complex shape the northernmost part of this realm shows crust of sub oceanic type altemating basement highs with lower subsidence values the observed surface heat flux is consistent with the predicted geothermal held in the alpine provencal continental margin and in the oceanic domain however a characteristic thermal asymmetry is clearly visible astride the basin due to the enhanced heat flux of the corsica margin even if the uniform extension model accounts well at a regional level for the present basement depth a remarkable tectonic subsidence excess has been found in the alpine provencal continental margin this evidence agrees with the reprise in compression of the margin the direction of the greatest principal stress is n120 e on average

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america we used seismic tomography to investigate the complex structure of the upper mantle below northwestern south america images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted caribbean pacific lithosphere beneath the study area beneath western venezuela and colombia we distinguish two slabs a maracaibo and a redefined bucaramanga slab the maracaibo slab coinciding with most of the bucaramanga slab previously defined by w d pennington dips in a direction of 150 at an angle of 17 to a depth of 275 km and correlates to the subducted late cretaceous oceanic plateau of the caribbean plate farther south a second slab dips at an angle of 50 in a direction of 125 to a depth of at least 500 km and correlates to the subducted oceanic crust of the nazca plate and the downdip extension of the panama island arc we refer to this slab as the redefined bucaramanga slab because it is different from the bucaramanga slab segment defined by pennington the area of the south american plate overriding both slabs is characterized by the absence of an active volcanic arc an anomalously wide topographically uplifted and tectonically active area and the northward escape of the maracaibo block along active strike slip faults in support of earlier studies we attribute this to the underthrusting of the caribbean oceanic plateau our shallowly dipping maracaibo slab along the base of the south american lithosphere and to the recent collision of the panama island arc rafted in on more steeply dipping crust of the nazca plate our redefined bucaramanga slab

an upper limit to palaeo heat flow theory and examples from the danish central graben abstract the surface heat flow yields a condensed expression of the subsurface thermal regime while the present heat flow can be measured as the product of thermal conductivity and temperature gradient resolution of the past surface heat flow variations calls for indirect methods such as the modelling of vitrinite reflectance and other organic maturity indicators which represent integrals of the past temperature history this paper argues that regarding the reflectance of vitrinite which is the most common maturity indicator the feature of the past thermal regime which can survive the effects of measuring and modelling uncertainties is the maximum temperature present or past how the maximum temperature was obtained is only rarely resolved given maximum temperature burial history thermal conductivity structure and surface temperature history the one dimensional steady state heat equation yields an approximate upper limit to the surface heat flow artificial examples show that the past heat flow may be similar to the maximum heat flow constraint when the past was significantly warmer than the present however this requires a delicate balancing of burial history and heat flow history to occur the thermal relaxation rate of the hot past must compensate for heating due to burial generally the past heat flow may be well below the maximum constraint examples from the central graben show that vitrinite reflectance samples of upper jurassic age constrain the maximum palaeo heat flow back to 150 ma this is due to the very rapid and significant sedimentation of upper jurassic sediments resulting in immediate deep burial of vitrinite the data of the present study are consistent with a early cretaceous heat flow elevated by about 20 30 above the present and with a heat flow throughout the cenzoic only marginally higher than the present however the data are also fully consistent with a time independent background heat flow history this illustrates the limits of resolution in palaeo thermal reconstruction based on vitrinite reflectance and temperature data the problem is one of finding the space of admissible solutions rather than one of finding a single solution

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

probabilistic tectonic heat flow modeling for basin maturation assessment method and applications tectonic modeling is often neglected in the basin modeling workflow and heat flow is most times considered a user input such heat flows can therefore result in erroneous basin modeling outcomes resulting in false overoptimistic identification of prospective areas or failure to identify prospects this is particularly true for areas with limited data control such as frontier basin areas or deep unexplored plays in mature basins three major factors obstruct routinely use firstly because of the focus of most tectonic models on lithosphere scale processes a large range of models including the mckenzie rift model fail to take into account effects which are of paramount importance for basement heat flow such as transient effects of sediment infill and erosion and changes in crustal heat production over time secondly lithosphere tectonic models often fail to allow inversion of basin data making forward tectonic modeling a cumbersome exercise non vertical sediment movements and 2d and 3d loading effects can play an important role hampering a unique inversion thirdly lithosphere tectonic models generally fail to aid the user to understand the sensitivity of the model results in terms of basin maturation for permissible ranges of tectonic model parameters and for uncertainties in tectonic scenarios such as absence or presence of underplating or two layered stretching vs a mckenzie model for this reason we have developed a multi 1d probabilistic tectonic heat flow model which is capable of calculating tectonic heat flows incorporating a variety of tectonic scenarios the model is capable of inversion of burial histories calibrated to temperature and maturity data calibration and sensitivity analysis is done through monte carlo sampling analysis using an experimental design technique for computational efficiency the tectonic heat flows can easily be used as input for basin modeling in commercially available 3rd party software 2009 elsevier ltd all rights reserved

thermal structure and source rock maturity of the north peruvian forearc system insights from a subduction sedimentation integrated petroleum system modeling abstract basin modeling is commonly used for the hydrocarbon potential evaluation of underexplored areas taking into account the full basin history to assess its thermicity and fluid distributions in the case of forearc basins however the influence of the subduction on the internal thermal structure is difficult to predict the existing subduction thermal models usually focus on the present day lithosphere and do not consider the sediment infill history while industrial modeling tools handle the thermal evolution of sedimentary basins but not the subduction process in this paper we propose a solution model in which the cooling engendered by the subduction is represented by the advective term of the heat conservation energy equation throughout the sedimentation this study focuses on the talara tumbes lancones petroleum province part of the north peruvian forearc system despite the long term exploration of the talara basin the origin of its massive oil fields still remains questioned the new subduction sedimentation integrated petroleum system modeling presented here calibrated by numerous structural and thermometric data allows to better constrain the thermal structure and source rock maturity history of this forearc system we show that the exposure of the sedimentary basin to the subducting cold lithosphere the sedimentation rate and erosion are important factors impacting the maturity of the source rocks consequently even in the same subduction setting each depocenter of the north peruvian forearc system presents a different thermal history and maturity timing and each basin presents an independent petroleum system

interannual persistence of the seasonal snow cover in a glacierized catchment knowledge of the spatial snow distribution and its interannual persistence is of interest for a broad spectrum of issues in cryospheric sciences in this study snow depths derived from airborne laser scanning are analyzed for interannual persistence of the seasonal snow cover in a partly glacierized mountain area 36 km2 at the end of five accumulation periods the snow covered area varied by 16 of its temporal mean mean snow depth of the total area ranged by a factor of two 1 31 2 58 m with a standard deviation of 0 42 m interannual correlation coefficients of snow depth distribution were in the range 0 68 0 84 of the investigated area 75 was found to be interannually persistent the remaining area showed variable snow cover from year to year caused by occasional avalanches and changes in surface topography as a result of glacier retreat snow cover underwent a change from a homogeneous distribution on the former glacier surface to a more heterogeneous snow cover in the recently deglaciated terrain a geostatistical analysis shows interannual persistence in scaling behavior of snow depth in ice free terrain with scale break distances at 20 m scale invariant behavior of snow depth is indicated over 100 m on smooth glacier surfaces

tearing and breaking off of subducted slabs as the result of collision of the panama arc indenter with northwestern south america we present two regional lithospheric cross sections that illustrate eastward and southeastward dipping subducted slabs to depths of 315 km beneath the surface of colombia in northwestern south america these cross sectional interpretations are based on relocated earthquake hypocentral solutions models supported on gravity and magnetic regional data and coda q q c tomography the method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system mapping of earthquake defined benioff zones combined with tomographic imaging reveals the presence of an 240 km long east west striking slab tear named here the caldas tear the proposed caldas tear separates a zone of shallow 20 30 dipping southeastward subduction in the area of colombia adjacent to panama and the caribbean sea which is not associated with subduction related volcanism from an area of steeper 30 40 dipping slab adjacent to the eastern pacific ocean that is associated with an active north south chain of active arc volcanoes we propose that the caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the panama indenter an extinct island arc that began subducting beneath northwestern south america about 12 ma the area south of the panama indenter is miocene oceanic crust of the nazca plate which subducts eastward beneath northwestern south america at normal angles and melts to form a north south trending active volcanic arc in addition to the formation of the caldas tear we propose that impedance of the thicker crustal area of the panama arc indenter over the past 12 ma may have led to down dip break off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate depth earthquakes beneath east central colombia

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

lidar measurement of snow depth a review laser altimetry lidar is a remote sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications recently lidar has seen a dramatic widening of applications in the natural sciences resulting in technological improvements and an increase in the availability of both airborne and ground based sensors modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies typical vertical accuracies for airborne datasets are decimeter scale with order 1 m point spacings ground based systems typically provide millimeter scale range accuracy and sub meter point spacing over 1 m to several kilometers many system parameters such as scan angle pulse rate and shot geometry relative to terrain gradients require specification to achieve specific point coverage densities in forested and or complex terrain additionally snow has a significant volumetric scattering component requiring different considerations for error estimation than for other earth surface materials we use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions this paper presents a review of lidar mapping procedures and error sources potential errors unique to snow surface remote sensing in the near infrared and visible wavelengths and recommendations for projects using lidar for snow depth mapping

scaling properties of wind and snow depth distribution in an alpine catchment 1 the spatial variability of the snow cover is driven by wind induced snow transport processes the main aim of this study is to investigate the link between the scaling behavior of snow depths and the wind induced processes driving the spatial structure of snow depths we used very high resolution atmospheric and snow transport simulations to compare their spatial characteristics with snow depths obtained from airborne and terrestrial laser scans the directions of the strongest autocorrelations of snow depths and wind velocities were predominantly perpendicular to the modeled local flow direction independent of whether more homogeneous lee slope loading in one area was considered or the formation of drifts in another area in the case of homogeneous lee slope loading the same direction of anisotropy was only found in the modeled preferential deposition of precipitation as for both wind and snow distribution this deposition process appears to dominate homogeneous lee slope loading in contrast saltation driven processes seem to dominate the formation of drifts and snow dunes furthermore the fractal analysis suggests similar scale breaks for the modeled wind velocity field and measured snow depths defining the upper scale of landscape smoothing through snow

quaternary tectonics and present stress tensor of the inverted northern falcon basin northwestern venezuela abstract the tertiary falcon basin in northwestern venezuela has a privileged position in the geodynamic puzzle of northwestern south america occurring in a region where several major plates caribbean south america and nazca and minor lithospheric blocks maracaibo bonaire and western colombia are interacting a combination of good exposures due to aridity and a near continuous sedimentary record in a now inverted basin helps to unravel the neogene and quaternary geodynamic evolution of this region a neotectonic and microtectonic investigation of the plio quaternary sedimentary rocks of the northern falcon basin reveals that this region is subject to a compressive to transpressive regime at present this regime is characterized by a nnw sse oriented maximum horizontal stress and a ene wsw trending intermediate or minimum horizontal stress as is confirmed by focal mechanism solutions this stress field is in agreement both with the nne directed extrusion of the maracaibo and bonaire blocks in western venezuela where the falcon basin is located and present day transpression along the caribbean south america plate boundary zone

lithosphere dynamics and tectono stratigraphic evolution of the mesozoic betic rifted margin southeastern spain abstract quantitative subsidence analysis demonstrates that mesozoic sediments in the eastern betic cordilleras have been deposited on a thermally subsiding rifted margin the dynamics of rifting are related to regional trans tension in the atlantic realm modelling of this phase of rifting at the southern iberian margin shows that the associated stretching of the lithosphere significantly altered its geometrical and mechanical structure and exerted a major control on subsequent convergence tectonics the mesozoic stretching led to the formation of a ramp at the margin due to strong lateral variations in the effective elastic thickness eet of the lithosphere and the thickness of the crust in a direction perpendicular to the margin the existence of a ramp structure in the late mesozoic at the iberian margin which is also supported by stratigraphic and structural data is important for the style of subsequent deformation of the lithosphere in late cretaceous tertiary times the lateral variations in eet inferred from forward modelling of rifted margin stratigraphy could explain the observed multiple collapse of the betic margin and the partitioning of deformation between the converging units involved in the betic orogeny modelling of depth dependent palaeo rheological profiles of the margin shows that the mechanical properties of the lithosphere after stretching differed distinctly from those before stretching lithospheric deformation in the betic cordilleras during the tertiary orogeny seems therefore to be largely controlled by the previous rifting phase a comparison of the palaeo and present day rheologies in terms of estimates for eet during late cretaceous and present times indicates that the mechanical properties of the lithosphere underlying the betic orogen were also affected by rifting during late oligocene aquitanian times this phase of rifting is coeval with extension in the valencia trough the gulf of lions and the west european rift system which supports a causal relation with regional lithospheric processes the lateral and spatial variations in thermo mechanical properties of the lithosphere underlying the betics therefore reflect the dynamics of lithospheric extension on a larger scale

on the accuracy of modelling hydrocarbon generation and migration the egersund basin oil find norway abstract quantitative estimates of kerogen transformation and hydrocarbon charge to the structure of block 9 2 norwegian north sea were obtained by integrated basin modelling a probability distribution was assigned to each input parameter and the sensitivity to these parameters was investigated by subsequently varying each parameter within the assigned ranges the inaccuracy in the modelling results were mainly due to imprecise knowledge of hydrocarbon generation kinetics depth conversion and present day virgin rock temperature kerogen transformation modelling and source rock richness thickness areal extent volumetric charge calculations monte carlo latin hypercube sampling based on the probability distribution of each parameter was performed giving a 40 probability for a dry structure a mean value of 10 7 106sm3 recoverable oil and a considerable high side potential 4 probability for more than 50 106sm3

the crustal structure of the guayana shield venezuela from seismic refraction and gravity data abstract we present results from a seismic refraction experiment on the northern margin of the guayana shield performed during june 1998 along nine profiles of up to 320 km length using the daily blasts of the cerro bolivar mines as energy source as well as from gravimetric measurements clear moho arrivals can be observed on the main e w profile on the shield whereas the profiles entering the oriental basin to the north are more noisy the crustal thickness of the shield is unusually high with up to 46 km on the archean segment in the west and 43 km on the proterozoic segment in the east a 20 km thick upper crust with p wave velocities between 6 0 and 6 3 km s can be separated from a lower crust with velocities ranging from 6 5 to 7 2 km s a lower crustal low velocity zone with a velocity reduction to 6 3 km s is observed between 25 and 25 km depth the average crustal velocity is 6 5 km s the changes in the bouguer anomaly positive 30 mgal in the west and negative 20 mgal in the east cannot be explained by the observed seismic crustal features alone lateral variations in the crust or in the upper mantle must be responsible for these observations

receiver function study of the crustal structure of the southeastern caribbean plate boundary and venezuela 1 we have investigated crustal thickness and composition across the southeastern caribbean plate boundary with the receiver function technique we used teleseismic data recorded by a temporary broadband array deployed under the bolivar project and the permanent national seismic network of venezuela we used the primary p to s conversion and crustal reverberations to estimate crustal thickness and average crustal vp vs ratio over the region we observe large variations in crustal thickness and poisson s ratio estimated moho depth ranges from 16 km beneath the southeastern caribbean sea to 52 km beneath northeastern venezuela and the venezuelan andes there is a good correlation between crustal structure and tectonic terranes data from the precambrian guayana shield suggest that the underlying crustal structure is relatively uniform with a moderate thickness 37 km and an intermediate composition a thick crust is found below the foreland basins the two mountain systems in northern venezuela the serrania del interior and the serrania del falcon have a thin crust with arc composition and are likely dynamically supported by elastic rebound or underthrusting of the oceanic plateau that characterizes the southern caribbean on the other hand the venezuelan andes and perija range on the western side of the country are probably isostatically balanced by thick crustal roots

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

orogenic float of the venezuelan andes abstract the venezuelan or merida andes are a ne trending intracontinental orogen that started to rise from the middle miocene due to the e w far field convergence between the maracaibo block to the northwest and the guyana shield to the southeast oblique convergence is responsible for strain partitioning with thrusting along both foreland basins and right lateral strike slip faulting along the ne sw bocono fault cutting the venezuelan andes along strike the central part of the belt is also cut by the n s left lateral strike slip valera fault that connects the bocono fault both faults bounding the trujillo block that escapes towards the nne even though the regional geology of belt is well known its structure at depth remains a matter of debate our work based on the integration of geological and geophysical data aims to better constrain the deep geometry of faults and the tectonic evolution of the mountain belt we used the orogenic float model to construct two nw se trans andean crustal scale balanced sections the late neogene quaternary shortening varies from 40 km in the south to 30 km in the north across the trujillo block indicating that a quarter of the deformation seems to be absorbed by the tectonic escape process more importantly a major reorganization in the crust took place in the early pliocene it is characterized by the imbrication of the maracaibo crust into the guyana crust this resulted in the subduction of the guyana lower crust and the formation of a nw vergent basement thrust propagating upwards and surfacing along the las virtudes thrust rapid uplift of the northern flank of the belt subsequently occurred together with massive deposition of the plio quaternary coarse grained betijoque formation in the northwestern foreland basin

age thermal evolution and history of the black sea basin based on heat flow and multichannel reflection data abstract multichannel reflection data tugolessov et al 1985 have revealed two deeps in the basement topography of the black sea which are filled with sediments from 12 to 15 km thick the deeps lack the granitic layer and are underlain by oceanic type crust which we assume to be generated by seafloor spreading processes the age of the deeps was interpreted previously in a highly controversial manner as being from the paleozoic early mesozoic to the recent in the paper age estimations were undertaken using surficial heat flow data assuming that they are related to deep seated age dependent heat flow generated by the cooling oceanic lithosphere but that they are strongly distorted by the heating of continuously accumulating sediments as well as by additional heat input from radiogenic production within sediments using reliable thermophysical parameters of compacting sediments the distorted heat flow in the sediments was evaluated numerically this allowed us to estimate the age of the black sea deeps floor the results show that the west black sea deep is 130 to 95 m y old and the east black sea deep is nearly 110 m y old these figures support an interpretation of the black sea deeps as remnants of a late mesozoic back arc basin that evolved behind the lesser caucasian pontide island arc the inferred middle cretaceous age of the deeps is the first estimate obtained quantitatively and corresponds well with available heat flow and multichannel reflection data

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

mantle flow beneath northwestern venezuela seismic evidence for a deep origin of the merida andes abstract we measured shear wave splitting from sks data recorded by the national seismic network of venezuela and a linear broadband passcal rice seismic array across the merida andes the linear array was installed in the second phase of the passive seismic component of the bolivar project to better understand the complicated regional tectonics in western venezuela using the method proposed by wolfe and silver 1998 sks waveforms from 2 to 36 earthquakes mostly from the tonga subduction zone were selected for each of the 23 stations in the region in order to do splitting analysis the fast polarization directions can be divided into 3 zones all in agreement with local gps data the first zone comprises the stations north of the dextral strike slip oca ancon fault these stations show the largest split times 1 6 3 2 s oriented in a roughly ew direction and are similar to splitting observations made further to the east along the strike slip plate boundary growdon et al 2009 we attribute this to trench parallel mantle flow that passes around the northwest corner of the subducting caribbean plate and along the northern edge of south america as proposed by russo and silver 1994 forming an eastward flow beneath the southern caribbean plate zone two is the merida andes with the right lateral bocono fault in the center where split orientations are at n45 e suggesting that the observed seismic anisotropy is likely caused by lithospheric deformation parallel to the bocono fault zone three is east of the bocono fault inside the barinas apure basin where the measured split times are smaller 0 8 s with an ew fast direction that is consistent with those observed at the guarico basin maturin basin and the guayana shield in the east and are interpreted as orientation with the motion of the continent

heat flow in the westernmost part of the alpine mediterranean system the rif morocco abstract heat flow density hfd and thermal gradient calculated on the basis of oil well data in the rif vary from 50 to 90 mw m 2 and from 20 to 50 c km respectively short term variations in the west can be attributed to water circulation and lateral heat conductivities contrast along the pre rif thrusting front and at the limits between the main structural units the gharb basin the south rifian ridges and the pre rif nappe high hfd and thermal gradient values are determined in the southwest of the study area this zone extends the central moroccan massif which is well known by its high thermal manifestations the external rif shows a tendency of increasing hfd toward northeastern morocco and the alboran sea in agreement with the geophysical observations electrical conductive structures great negative bouguer anomaly shear velocity attenuation high upper mantle p velocity the thermal structure of the external rif would be a consequence of the presence at subcrustal depths of hot and low density asthenospheric material overlying a high velocity lithospheric body beneath the rif betic belt

self similarity in glacier surface characteristics catchment wide information on glacier snow cover depth surface albedo and surface roughness is important input data for distributed models of glacier energy balance in this study we investigate the small scale mm to 100 m spatial variability in these properties with a view to better simulating this variability in such models data were collected on midre lovenbreen a 6 km 2 valley glacier in northwest svalbard the spatial variability of all three properties was found to be self similar over the range of scales under investigation snow depth and albedo exhibit a correlation length within which measurements were spatially autocorrelated late winter and summer properties of snow depth differed with smaller depths in summer due to melt and shorter correlation lengths similar correlation lengths for snow depth and surface albedo may suggest that snow depth variation is an important control on the small scale spatial variability of glacier surface albedo for surface roughness the data highlight a possible problem in energy balance studies which use microtopographic surveys to calculate aerodynamic roughness in that the scale of the measurements made affects the calculated roughness value this suggests that further investigations of the relationships between surface form and aerodynamic roughness of glacier surfaces are needed

kinematics exhumation and sedimentation of the north central andes bolivia an integrated thermochronometer and thermokinematic modeling approach quantifying mountain building processes in convergent orogens requires determination of the timing and rate of deformation in the overriding plate in the central andes large discrepancies in both timing and rate of deformation prevent evaluating the shortening history in light of internal or external forcing factors geologic map patterns age and location of reset thermochronometer systems and synorogenic sediment distribution are all a function of the geometry kinematics and rate of deformation in a fold thrust belt foreland basin ftb fb system to determine the timing and rate of deformation in the northern bolivian andes we link thermokinematic modeling to a sequentially forward modeled balanced cross section isostatically accounting for thrust loads and erosion displacement vectors in 10 km increments are assigned variable ages to create velocity fields in a thermokinematic model for predicting thermochronometer ages we match both the pattern of predicted cooling ages with the across strike pattern of measured zircon fission track apatite fission track and apatite u th he cooling ages as well as the modeled age of fb formations to published sedimentary sections results indicate that northern bolivian ftb deformation started at 50 ma and may have begun as early as 55 ma acceptable rates of shortening permit either a constant rate of shortening 4 5 mm yr or varying shortening rates with faster rates 7 10 mm yr at 45 50 ma and 12 8 ma significantly slower rates 2 4 mm yr from 35 to 15 ma and indicate the northern bolivian subandes started deforming between 19 and 14 ma

palaeozoic to early jurassic history of the northwestern corner of gondwana and implications for the evolution of the iapetus rheic and pacific oceans abstract the palaeozoic to mesozoic igneous and metamorphic basement rocks exposed in the merida andes of venezuela and the santander massif of colombia are generally considered to define allochthonous terranes that accreted to the margin of gondwana during the ordovician and the carboniferous however terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains a general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the merida andes and the santander massif we present new zircon u pb icp ms data from 52 igneous and metamorphic rocks which we combine with whole rock geochemical and pb isotopic data to constrain the tectonic history of the precambrian to mesozoic basement of the merida andes and the santander massif these data show that the basement rocks of these massifs are autochthonous to gondwana and share a similar tectono magmatic history with the gondwanan margin of peru chile and argentina which evolved during the subduction of oceanic lithosphere of the iapetus ocean the oldest palaeozoic arc magmatism is recorded at 500 ma and was followed shortly by barrovian metamorphism peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at 477 ma and the intrusion of synkinematic granitoids until 472 ma subsequent retrogression resulted from localised back arc or intra arc extension at 453 ma when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement continental arc magmatism dwindled after 430 ma and terminated at 415 ma coevally with most of the western margin of gondwana after pangaea amalgamation in the late carboniferous to early permian a magmatic arc developed on its western margin at 294 ma as a result of subduction of oceanic crust of the palaeo pacific ocean intermittent arc magmatism recorded between 294 and 225 ma was followed by the onset of the andean subduction cycle at 213 ma in an extensional regime extension was accompanied by slab roll back which led to the migration of the arc axis into the central cordillera of colombia in the early jurassic

pattern of mantle thinning from subsidence and heat flow measurements in the gulf of suez evidence for the rotation of sinai and along strike flow from the red sea we have undertaken a combined analysis of tectonic subsidence heat flow and uplift data for the gulf of suez results show significant differences along the length of the rift the heat flow and subsidence in the northern gulf of suez can be fitted by close to uniform extension in the early miocene with minimal extension since the middle miocene in contrast the southern gulf of suez requires that the early miocene extension is followed by both continuous slow 1 mm yr extension and mantle thinning greatly in excess of the crustal thinning the continued extension of the southern gulf of suez is interpreted as indicating a counterclockwise rotation of the sinai peninsula that allows the southern gulf of suez to accommodate 10 15 of the motion of the dead sea transform our best estimate of the net crustal and mantle extension factors for southern suez are 1 4 1 5 and 2 2 2 6 respectively while these values are approximate they indicate a significant input of heat into the southern gulf of suez rift that is in excess of that directly advected by extension modeling indicates that while 1 2 of the extension occurred in the early miocene most of the lithospheric thinning and virtually all of the excess thinning of the mantle lithosphere developed since then in addition the gulf of suez is bordered by large and growing rift flank uplifts particularly on the sinai peninsula the geometry of the motions at the sinai triple junction region has created a large contrast in extension between the red sea and gulf of suez sinai since the middle miocene these lateral temperature gradients drove the flow of hot material that is responsible for the extra heating beneath southern suez and sinai the rift flank uplift along most of the gulf of suez is interpreted as resulting from a combination of secondary convection and flexure the much greater uplift in southern sinai is produced by the additional convective flow from the red sea

heat flow and hydrothermal circulation at the ocean continent transition of the eastern gulf of aden abstract in order to investigate the importance of fluid circulation associated with the formation of ocean continent transitions oct we examine 162 new heat flow hf measurements in the eastern gulf of aden obtained at close locations along eight seismic profiles and with multi beam bathymetry the average hf values in the oct and in the oceanic domain 18 m y are very close to the predictions of cooling models showing that the overall importance of fluids remains small at the present time compared to oceanic ridge flanks of the same age however local hf anomalies are observed although not systematically in the vicinity of the unsedimented basement and are interpreted by the thermal effect of meteoric fluids flowing laterally we propose a possible interpretation of hydrothermal paths based on the shape of hf anomalies and on the surface morphology fluids can circulate either along dip or along strike but are apparently focussed in narrow pipes in several locations in the oct there is no detectable hf anomaly while the seismic velocity structure suggests serpentinization and therefore past circulation we relate the existence of the present day fluid circulation in the eastern gulf of aden to the presence of unsedimented basement and to the local extensional stress in the vicinity of the socotra hadbeen fault zone at the scale of rifted margins fluid circulation is probably not as important as in the oceanic domain because it can be inhibited rapidly with high sedimentation rates serpentinization and stress release after the break up

characterizing the caribbean south american plate boundary at 64 w using wide angle seismic data 1 we present wide angle velocity modeling results from profile 64 w of the broadband ocean land investigation of venezuela and the antilles arc region bolivar project line 64w is a 460 km long approximately north south onshore offshore reflection refraction transect located approximately at 64 w longitude the profile extends across the transform plate boundary between the southeastern caribbean car and south american sa plates east of the profile the plate boundary bends to the north and sa subducts beneath car we utilize first arrival tomography to resolve a smooth velocity field for the sediments and upper middle crust and then use a layered approach to resolve a sharp velocity contrast for the moho simultaneously inverting refracted pn and reflected pmp arrivals we image crustal and upper mantle structure across the plate boundary zone we interpret that the strike slip system that accommodates relative motion between car and sa extends near vertically through the entire crust and offsets the moho we see no evidence supporting a major component of convergence and rather than a wide boundary zone of overlapping lithospheric plates we interpret the plate boundary to be confined to the 33 km wide near vertical strike slip system previously interpreted thrust faults flanking the strike slip system appear to be confined to the upper middle crust and may be related to the detachment of subducting south american lithosphere at the southern terminus of the lesser antilles subduction zone east of 64 w

high resolution heat flow density in the lower congo basin 1 heat flow density hfd has been derived in the lower congo basin from 293 conventional probe measurements 424 oil exploration data and about 1 000 000 bottom simulating reflector bsr values each set of data provides independent estimates of temperature gradients associated with specific uncertainties and geographic distributions but a statistical comparison in overlapping domains shows a relatively good consistency in situ conductivity has been measured in conventional surveys and estimated from rock composition and porosity in oil exploration boreholes in the deep offshore measurements and estimates are consistently low and increase significantly toward the shelf domain thermal conductivity does not change significantly in the interval between the water bottom and the bsr and can be estimated from the surface measurements to provide an inference of hfd the combined sets of hfd in the lower congo basin cover the overall domain of the continental margin and a part of the oceanic domain high resolution imaging of the bsr by three dimensional 3 d seismic studies provides in addition good quality nominal resolution of 500 m in the deep offshore at short length scales on the order of kilometers large variations of hfd from 30 to 140 mwm 2 exist above salt diapirs and canyons related to heat refraction on the other hand no small scale effect related to fluid flow has been detected although active venting is known at larger length scale hfd in the deep offshore is different on both sides of the congo submarine channel 54 8 mwm 2 to the north and 48 12 mwm 2 to the south which are also characterized by different basin tectonic styles at the margin scale hfd is significantly different in the oceanic domain 42 3 mwm 2 the deep continental offshore 52 10 mwm 2 and the continental shelf 65 15 mwm 2 a progressive reduction of the radiogenic heat contribution in the extended continental crust is the more likely the cause of these differences mantle heat flow below the continental margin is consequently high compared to that expected 15 mwm 2 for old shields such as congo

effects of asthenospheric heat flow in basin modelling exemplified with the danish basin a mathematical model is developed to simulate the process of basin formation by rifting subsidence is driven by crustal thinning and influenced by the transient temperature variation within the lithosphere the model offers possibilities for multiple phases of rifting superimposing non steady state conditions important features in the model are two layered heat production and a definition of the lower boundary in terms of heat flow instead of one of constant temperature as opposed to other models furthermore phase transformations caused by rift induced pressure and temperature changes are suggested as an additional syn rift subsidence mechanism the relevant phase transformations are assumed to be those occurring during an amphibolite to granulite facies transition perturbation of the steady state temperature profile is performed by one or several phases of rifting with finite stretching rates by sill intrusion or by changes in asthenospheric heat flow the greatest deviation from the steady state geotherm occurs at the lower boundary because of the flow definition of the lower boundary the consequence of this is a much longer duration of anomalous heat flow the model is applied to the danish basin north jylland denmark this basin was formed in permian times and since then it has been thermally subsiding apart from a minor event of stretching in the late cretaceous the higher present day heat flow in the basin compared to the adjacent fennoscandian shield area is successfully explained by the model presented in this paper it is concluded that transient temperature conditions still today contribute significantly to present surface heat flow although main rifting took place for more than 240 m y ago this cannot be explained by models using a fixed temperature definition of the lower boundary the modelled contribution by phase transformations to subsidence explains why the syn rift early and middle triassic subsidence was accompanied by insignificant faulting activity as evidenced by the seismic data available

snow depth structure fractal behavior and interannual consistency over haut glacier d arolla switzerland snow depth patterns over glaciers are controlled by precipitation snow redistribution due to wind and avalanches and the exchange of energy with the atmosphere that determines snow ablation while many studies have advanced the understanding of ablation processes less is known about winter snow patterns and their variability over glaciers we analyze snow depth on haut glacier d arolla switzerland in the two winter seasons 2006 2007 and 2010 2011 to 1 understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas and 2 investigate the snow pattern consistency over the two accumulation seasons we perform this analysis on a data set of high resolution lidar derived snow depth using variograms and fractal parameters our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior with a scale break around 20 m after which the fractal dimension increases indicating more autocorrelated structure before the scale break than after second this behavior is consistent over the two years with fractal parameters and their spatial variability almost constant in the two seasons we also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment with longer correlation distances on the tongue in the direction of the main winds suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples

small scale spatial structure of shallow snowcovers the results of a field study of the small scale spatial structure of the depth of shallow seasonal snowcovers in prairie and arctic environments are presented it is shown that the spatial distribution of snow depth is fractal at small scales becoming random at scales beyond some limiting length this is due to the autocorrelation of depth at small sampling distances the transition of fractal to random behaviour is indexed by a cutoff length which is defined by the intersection of the fractal slope and horizontal tangent of a logarithmic plot of the standard deviation of depth versus sampling distance the magnitude of the cutoff length is related to the degree of macroscopic variability of the underlying topography an increase in length due to the effects of macroscopic topographic variability on snowcover accumulation is confirmed by de trending field measurements the de trended data shown a cutoff length for wheat stubble and fallow surfaces of approximately 30 m which is consistent with the distance determined from measurements on flat fields the implications of the transition of snow depth from fractal to random structure on the scales of snow sampling and modelling are presented the cutoff length may provide a statistic for stratifying shallow snowcovers by linking snowcover properties to the underlying topography

understanding the thermal evolution of deep water continental margins areas of exploration for new hydrocarbons are changing as the hydrocarbon industry seeks new resources for economic and political reasons attention has turned from easily accessible onshore regions such as the middle east to offshore continental shelves over the past ten years there has been a marked shift towards deep water continental margins 500 2 500 m below sea level in these more hostile regions the risk and cost of exploration is higher but the prize is potentially enormous the key to these endeavours is a quantitative understanding of the structure and evolution of the thinned crust and lithosphere that underlie these margins

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

automated thermotectonostratigraphic basin reconstruction viking graben case study we present a generic algorithm for automating sedimentary basin reconstruction automation is achieved through the coupling of a two dimensional thermotectonostratigraphic forward model to an inverse scheme that updates the model parameters until the input stratigraphy is fitted to a desired accuracy the forward model solves for lithospheric thinning flexural isostasy sediment deposition and transient heat flow the inverse model updates the crustal and mantle thinning factors and paleowater depth both models combined allow for automated forward modeling of the structural and thermal evolution of extensional sedimentary basins the potential and robustness of this method is demonstrated through a reconstruction case study of the northern viking graben in the north sea this reconstruction fits present stratigraphy borehole temperatures vitrinite reflectance data and paleowater depth the predictive power of the model is illustrated through the successful identification of possible targets along the transect where the principal source rocks are in the oil and gas windows these locations coincide well with known oil and gas occurrences the key benefits of the presented algorithm are as follows 1 only standard input data are required 2 crustal and mantle thinning factors and paleowater depth are automatically computed and 3 sedimentary basin reconstruction is greatly facilitated and can thus be more easily integrated into basin analysis and exploration risk assessment

surface heat flow and the mantle contribution on the margins of australia 1 we present thermal data from 473 oil exploration wells in australia and new zealand approximately 2300 bottom hole temperatures are corrected to form a homogeneous set along with 86 temperatures from reservoir tests thermal conductivity profiles are estimated from a set of geophysical well logs using a recently developed neural network approach retaining wells in which temperature and thermal conductivity data overlap over an interval greater than 1000 m we estimate 10 heat flow values in the taranaki basin of new zealand and 270 values in the northwestern western and southern margins and in the intracontinental canning basin of australia the values are in the range 30 80 mw m 2 as a result of several differences in the data and methods our heat flow values are 10 20 mw m 2 lower compared to previously published estimates for the same wells in new zealand for australia our values are consistent with previously measured values and trends in the continental and marine regions on the northwestern and southeastern margins we interpret the variations as reflecting changes in the nature of the underlying basement consistent with onshore data it is inferred that the archean crust is depleted in radiogenic elements compared to proterozoic regions and that recent volcanism affects the eastern paleozoic area after removing from surface heat flow the sediment contributions including a permanent radiogenic heat component and a transient sedimentation effect a simple crustal model suggests that mantle heat flow on the continental margin bordering the pilbara craton is higher than below the craton itself moreover heat flow corrected for the sediment contributions is markedly lower in the petrel intracontinental basin than in the adjacent margin although the crust is thinner below this latter region as both are underlaid by the same basement this observation may indicate that the mantle contribution is also higher below that margin such a higher mantle heat flow on old continental margins is consistent with experiments of fluid convection below an insulating lid and suggests that the thermal regime of the continental lithosphere never returns to its prerift state as usually assumed by several thermomechanical models of evolution of continental margins

crustal density structure in northwestern south america derived from analysis and 3 d modeling of gravity and seismicity data abstract this paper presents a three dimensional 3 d interpretation of new gravity and seismicity datasets for northern south america a 3 d forward density model was constructed on the basis of deep wide angle seismic refraction sections moho depth from receiver functions and surface geology density values were estimated from published borehole data for sediments by using empirical velocity density functions and considering mineralogical chemical composition variations under typical pressure temperature conditions for upper and lower crustal rocks the modeled 3 d density structure was kept as simple as possible the continental and oceanic plates were formed by two sedimentary bodies one crustal body and one mantle lithosphere body overlying a sub lithospheric mantle the caribbean plate was modeled with an atypical crustal thickness of 18 km including sediments the geometry of the caribbean plate was modeled using a combination of gravity modeling and analyses of the seismicity and focal mechanism solutions intermediate seismicity and the orientation of the t axes appeared aligned along the predicted position of the slab as a result the estimated slab dip angle under maracaibo and the merida andes was 15 and increases up to 20 after 100 km depth the model shows two orientations in the slab strike n150 e 5 in western colombia and southward underneath the maracaibo block the modeling results suggest that the northern south american upper and lower crusts are relatively light and the density of the caribbean crust is typical for an oceanic crust

geodetic exploration of strain along the el pilar fault in northeastern venezuela we use global navigation satellite systems observations in northeastern venezuela to constrain the el pilar fault epf kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth the velocity field exhibits an asymmetric velocity gradient on either side of the epf we use five different approaches to explore possible models to explain this asymmetry first we infer a 1 6 km locking depth using a classic elastic half space dislocation model second we infer a 1 5 km locking depth and a 0 33 asymmetry coefficient using a heterogeneous asymmetric model including contrasting material properties on either side of a vertical fault suggesting that the igneous metamorphic terranes on the northern side are 2 times more rigid than the sedimentary southern side third we use a three dimensional elastostatic model to evaluate the presence of a compliant zone suggesting a 30 reduction of rigidity in the upper 3 km at the depth of a 1 to 5 km wide fault zone fourth we evaluate the distribution of fault slip revealing a widespread partial creep pattern in the eastern upper segment while the upper western segment exhibits a partially locked area which coincides with the rupture surface of the 1797 and 1929 earthquakes to supplement these models we upgrade the previously published displacement simulation method using nonvertical dislocations with data acquired between 2003 and 2013 the localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity

formation of the rocky mountains western united states a continuum computer model one hypothesis for the information of the rocky mountain structures in late cretaceous through eocene time is that plate of oceanic lithosphere was underthrust horizontally along the base of the north american lithosphere the horizontal components of the motion of this plate are known from paleomagnetism and the edge of the region of flat slab can estimated from reconstructed patterns of volcanism new techniques of finite element modeling allow prediction of the thermal and mechanical effects of horizontal subduction on the north american plate a model that has a realistic temperature dependent rheology and a simple plane layered initial condition is used to compute the consequences of horizontal underthrusting in the time interval 75 million to 30 million years before present successful prediction of this model include i the location amount and direction of horizontal shortening that has been inferred from laramide structures ii massive transport of lower crust from southwest to northeast iii the location and timing of the subsequent extension in metamorphic core complexes and the rio grande rift and iv the total area eventually involved in basin and range style extension in a broad sense this model has predicted the belt of laramide structures the transport of crust from the coastal region to the continental interior the subsequent extension in metamorphic core complexes and the rio grande rift and the geographic region of late tertiary basin and range extension its principal defects are that i many events are predicted about 5 million to 10 million years too late and ii the wave of crustal thickening does not travel far enough to the east reasonable modifications to the oceanic plate kinematics and rheologies that were assumed may correct these defects the correspondence of model predictions to actual geology is already sufficiently close to show that the hypothesis that horizontal subduction caused the laramide orogeny is probably correct the rocky mountain thrust and reverse faults formed in an environment of east west to northeast southwest compressive stress that was caused by the viscous coupling between the oceanic plate and the base of the north american crust nonuniform crustal thickening by simple shear transport also caused relative uplifts therefore this model is consistent with both of the range forming mechanisms that have been inferred 1 a new proposal that arises from this simulation is that horizontal subduction also caused the subsequent extensional basin and range taphrogeny by stripping away the mantle lithosphere so that the crust was exposed to hot asthenosphere after the oceanic slab dropped away

subduction in the southern caribbean images from finite frequency p wave tomography 1 the eastern boundary of the caribbean plate is marked by subduction of the atlantic under the lesser antilles the southeastern plate boundary is characterized by a strike slip margin while different configurations of subduction of the southwest caribbean under south america have been proposed we investigate the slab geometry in the upper mantle using multiple frequency teleseismic p wave tomography waveforms from p and pkpdf phases from 285 mb 5 0 events occurring at epicentral distances from 30 to 90 and greater than 150 were bandpass filtered and cross correlated to obtain up to three sets of delay times for each event the delay times were inverted using approximate first fresnel zone sensitivity kernels our results show the subducting atlantic slab as well as a second slab in the west of the study area that we interpret as a subducting fragment of the caribbean plate both slabs have steep dips where imaged and can be traced to depths greater than 600 km these results are consistent with transition zone boundary topography as determined by receiver function analysis the atlantic slab extends continent ward south of the plate bounding strike slip margin we interpret this extension as continental margin lithospheric mantle that is detaching from beneath south america and subducting along with the oceanic atlantic slab the steep subduction of the caribbean occurs 500 km landward from the trench implying an initial stage of shallow subduction as far to the east as the lake maracaibo merida andes region as has been inferred from intermediate depth seismicity

aseismic continuation of the lesser antilles slab beneath continental south america 1 we present results of travel time inversions of teleseismic p and s waves recorded at the secasa92 southeast caribbean south america 1992 temporary broadband array in northeastern venezuela and trinidad the inversions reveal the unusual structure of the southern termination of the lesser antilles subduction zone a minimum 2 relatively high velocity anomaly trends wsw from the seismically defined lesser antilles slab beneath and nw of the paria peninsula to a point below the venezuelan serrania del interior well south of the caribbean coast resolution tests utilizing actual ray geometries and densities of the source data indicate that the regional scale structure beneath the study area is reasonably well resolved thus a detached and detaching subducted south american slab appears to lie beneath continental south america we infer that oceanic south american lithosphere has been overridden to a significant degree by continental south america the detached slab now lying beneath continental south america was driven into its current position after detaching from the former eastward striking mesozoic ocean continent passive margin as this margin entered the subduction zone because oceanic and continental south america are still attached without apparent relative motion between them along the atlantic passive margin southeast of our study region the slab must be the actively moving element during continental overriding thus the slab and its surrounding mantle both caribbean and south america beneath northeastern south america are mobile and have moved ese relative to the stable guyana shield craton

skagerrak evolution derived from tectonic subsidence abstract stratigraphic data gathered from 32 points in the continental skagerrak basin have been analyzed by basin modelling methods non tectonic effects of sediment loading were removed by backstripping giving the observed tectonic subsidence this was compared to synthetic subsidence curves constructed on the basis of a combined lithospheric extension and metamorphism model where gabbroic magma which was emplaced during the permian is transformed to granulits eclogite facies the overall picture is that prior to 230 ma subsidence was roughly similar north and south of the fennoscandian border zone fbz after this time the northern area sagged due to the still preserved lithospheric thermal anomaly and continued metamorphism whereas the southern area was also affected by extension a physical explanation for this contrast in evolution is given by considering the relative lithospheric strength history of the areas the northern area becoming progressively stronger with time relative to the southern area as crustal thicknesses are reduced total post 570 ma extension is approximately 1 4 40 north of the fbz and 1 5 50 south of it north of the fbz the average thickness of the metamorphic layer is between 3 and 7 km whereas south of the zone a thickness of 1 2 km is estimated this difference may reflect variations in the degree of permian magmatism the temperature history of the sediments and the degree of organic maturation has been calculated by the tti method the youngest sediments to have experienced temperatures high enough for significant oil generation are estimated to be of bathonian age the present model heat flow of about 57 mw m 2 is in agreement with observations lateral displacements along the fbz are of the order of 10 20 km and have consequently only played a minor role in the development of the skagerrak basin a thermal lithosphere thickness of about 125 km is inferred

thermal history of the eastern margin of the gulf of suez i reconstruction from borehole temperature and organic maturity measurements abstract the gulf of suez is a tertiary continental rift associated with prominent flank uplift despite numerous studies which focused mainly on the western and central parts of the graben the thermo mechanics controlling the tectonic evolution of the gulf of suez is still enigmatic we have integrated borehole temperatures and organic maturity measurements in the eastern margin of the gulf of suez in order to study rift related paleothermometry and the present day thermal regime the data obtained suggest that the present thermal regime represents the maximum heat flow and temperatures for the sedimentary section in the basin furthermore lateral distributions of geothermal gradient and heat flow in the gulf of suez do not correlate mainly because of extensive variability in lithology and thermal conductivity rift related heat flow increases systematically and subparallel to the rift axis from about 60 mw m2 in the darag subbasin in the north to about 80 mw m2 in the ras garra area in the south both values are higher than 45 mw m2 the average heat flow assumed for the pre rift stage and the characteristic level for the present day heat flow away from the rift the north to south increase in heat flow probably reflects the southward increase of extension as well as lateral transfer of heat flow from the red sea this latter conclusion is supported by the fact that heat flow in the southern gulf of suez recorded by the paleothermometric reconstructions and borehole temperature data is somewhat higher than that estimated by model calculations for the extension derived from structural and subsidence reconstruction