new insights into the geology and tectonics of the san dimas mining district sierra madre occidental mexico abstract the san dimas district is a world class silver gold low sulfidation epithermal deposit located in the central part of the sierra madre occidental of mexico within the eastern part of the gulf of california extensional province previous works assumed a single period of mineralization between 38 5 and 31 9 ma which is at odds with the existence of vein systems with two different orientations and ag au ratios we present a re evaluation of this district based on new zircon u pb and apatite fission track ages as well as petrographic and field observations of mineralization styles our study also includes two new prospective areas of causita and mala noche located to the south of the main district within the lower volcanic complex we identify a late cretaceous volcanic succession 77 to 69 ma correlative with the tarahumara formation from southern sonora and coeval with the san ignacio batholith exposed to the west this volcanic succession hosts au rich mineralized sub volcanic felsic bodies yielding slightly younger ages and is covered by paleocene intermediate lavas with hypabyssal intrusions with ages around 48 ma a voluminous intrusive suite piaxtla batholith and associated dike swarms was emplaced in the region between 49 and 44 ma early extensional basins were filled by a continental sedimentary sequence palmas formation which yielded u pb age peaks at 66 and 56 ma from detrital zircons and a maximum depositional age of 43 ma the last magmatic activity as in the rest of the sierra madre occidental consists of silicic ignimbrites and less basaltic lava flows clustered in two pulses of 31 5 29 ma and 24 20 ma nnw sse extensional fault systems expose the mineralization and tilted all the succession prior to the emplacement of a 24 ma ignimbrite package this late oligocene extension associated to the early stage of the gulf of california rift is confirmed by apatite fission track dating of samples from the piaxtla batholith which consistently indicate an episode of cooling at 25 23 ma followed by a second episode at 12 5 ma our absolute ages and geologic mapping allow to infer that an older wsw ene trending normal fault system with up to 1 km of displacement must exist between the san dimas district and the causita area to the south this fault system currently buried beneath oligocene miocene ignimbrites may have controlled the intrusion of the piaxtla batholith and played a crucial role in the preservation of large vein systems of san dimas in a tectonic depression setting the main epithermal mineralization is associated with two kinds of structures ag au veins with wsw ene to e w orientation and au ag veins with nnw sse to n s orientation the dominant ag au veins slightly post date the piaxtla intrusive suite and partly recycled older felsic intrusion with porphyry mineralization the nnw sse to n s au ag veins are most probably associated with the oligocene silicic volcanism

offshore granulites from the bay of biscay margins fission tracks constrain a proterozoic to tertiary thermal history over short distances partly as pebbles from albian conglomerates we chose the granulite samples for our fission track study anticipating that they have recorded most of the history of the continental crust in the area and because the origin and emplacement of these rocks is still not clear the results have important implications and show that fission track studies on offshore basement have great potential for furthering our under standing of continental margin pro cesses abstract zircon and apatite fission track ages were determined on granulites dredged along the bay of biscay margins a sample from ortegal spur iberia margin yielded 725 67 ma zircon a sample from le danois bank iberia margin yielded 284 58 ma zircon indicating post variscan cooling apatite from this sample gave 52 2 ma interpreted as final cooling after pyrenean thrust imbrication two other samples from le danois bank have early cretaceous apatite ages 138 7 and 120 8 ma interpreted to result from exhumation during rifting finally a granulite from goban spur armorican margin gave 212 10 ma apatite coinciding with a precursory rifting phase together with published radiometric results these data indicate a precambrian high grade terrane at the site of the current margins the distribution of the granulites on the seafloor reflects tectonic and erosional processes related to a mesozoic rifting and b early tertiary incipient subduction of the bay of biscay beneath iberia

evidence for reflectors in the lower continental crust before rifting in the valencia trough the past decade has seen a rapid advance in our understanding of the deep structure of the continental crust especially in europe1 3 australia4 and north america5 where seismic profiling has revealed a highly reflective layer in the lower crust on many profiles the reflective layer is associated with regions of extension6 7 suggesting that the reflectors originate by some form of ductile flow or magmatic intrusion during rifting8 9 to test this hypothesis we have examined geophysical and geological data from the valencia trough a rift basin10 12 of late oligocene early miocene age from a comparison of profiles in different parts of the trough and independent constraints on the initial crustal thickness we argue that the reflective layer in this basin was probably already in the crust before rifting and that a mid tertiary extensional event is not required to explain it

application of neural networks for the prediction of the unconfined compressive strength ucs from equotip hardness abstract this paper presents the application of a neural network for the prediction of the ucs from hardness tests on rock samples to investigate the suitability of this approach the results of the network are compared to predictions obtained by conventional statistical relations the network was trained to predict the ucs based on the hardness porosity density grain size and rock type information of a rock sample a dataset containing 194 rock sample records ranging from weak sandstones to very strong granodiorites was used to train the network with the levenberg marquardt training algorithm two sets each containing 17 rock samples were used to validate the generalization and prediction capabilities of the network

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

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

a 2 5d interpretation of the eastern galicia magnetic anomaly northwestern spain geodynamical implications abstract the eastern galicia magnetic anomaly egma shows intensities up to 190 nt and is one of the major features of the magnetic field in northwestern spain taking into account the seismic refraction and surface geological data a 2 5d model of the magnetic properties of the crust in the area of the egma has been carried out models show that the anomaly can be produced by a middle to lower crustal layer a few kilometers thick with magnetic susceptibility of approximately 0 045 si emplaced with a ramp flat like geometry in higher crustal levels and giving rise to horizontal displacements of about 50 km on the basal eastern galicia thrust this structure is in close agreement with surface geology since the culmination of the lugo dome and the extensional viveiro fault can be interpreted in relation with the displacement along the eastern galicia thrust the southern termination of the egma can be related to the termination of the anomalous layer on a lateral hanging wall ramp of this thrust rocks in the magnetic layer are interpreted as mainly lower crust mafic and or ultramafic rocks in the northern sector at least part of the anomaly must be attributed to ultramafic hercynian intrusives cropping out in the vicinity of the viveiro fault

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

predicting the deformation moduli of rock masses abstract predictive empirical models for the mechanical properties of rock masses have been used in rock engineering because direct measurement of the properties is difficult due to the presence of discontinuities such empirical models are open to improvement because they are based on collected data the purposes of the present study are to assess the existing empirical equations and to develop a new empirical approach for this reason in the first stage of the study the prediction performance of the existing models proposed for predicting the deformation modulus of rock masses were evaluated statistically by using a database including 115 data values obtained from in situ plate loading and dilatometer tests a new empirical approach with higher prediction capacity than the existing empirical models was developed in the subsequent stage of the study the new empirical model considers the modulus ratio of intact rock e i ucs rock quality designation rqd and weathering degree wd although data obtained from very weak and weak rock masses were included in the development of the new empirical equation the type of rocks employed in the study were limited therefore a crosscheck between the new empirical equation and previous empirical approaches should be performed in the design stage

the deep seismic reflection marconi 3 profile role of extensional mesozoic structure during the pyrenean contractional deformation at the eastern part of the bay of biscay abstract the new marconi 3 deep seismic profile allows recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution it denotes that the easternmost part of the bay of biscay consists of a thick wedge of uppermost cretaceous to cenozoic synorogenic sediments lying unconformably on the top of a thinned continental crust with the mesozoic parentis basin to the north and the coeval landes high to the south the parentis basin appears as a major half graben bounded southwards by a north dipping planar fault it is filled by a thick sequence of jurassic upper cretaceous carbonates affected by salt domes and squeezed diapirs made up of triassic evaporites and mudstones these salt tectonic structures also affect the overlying uppermost cretaceous to lower miocene synorogenic deposits which are folded upon these structures the landes high includes a thin pre upper cretaceous cover tilted to the south in the basque shelf it is deformed by a basement involving thrust wedge emplaced during the late eocene miocene that constitutes the north pyrenean contractional front geometric relationships and thickness variations depict that this overall structure results from the following mesozoic extensional stage which includes a late jurassic late aptian syn rift stage in which the parentis basin formed and an albian early late cretaceous post rift stage in which diapirs of triassic evaporites grew close to this major fault compressive deformational stage coeval to the pyrenean orogeny which led to 1 the development of a latest cretaceous up to middle miocene foreland basin and 2 from late eocene the formation of a basement involving thrust wedge in the innermost foreland basin the squeezing of the diapiric structures formed previously in the parentis basin and later middle miocene the partial inversion of some pre existent faults located in the southern parentis basin margin this geodynamic evolution together with the structure of the area evidences that the extensional structure resulting from the opening of the bay of biscay played an important role both in the location of the north pyrenean front and in the north pyrenean foreland contractional deformation features specially the lack of significant inversion structures in the parentis basin despite that it belongs to a severely thinned crustal area before the alpine compression denotes that the mesozoic landes high acted as an important buffer for the propagation of the pyrenean contractional deformation to the north this deformational buffer was active until early miocene and probably vanished afterwards during the last stages of pyrenean orogen development when some basement faults reactivated in the parentis basin

a review of intermediate sulfidation epithermal deposits and subclassification abstract intermediate sulfidation is veins is one of the subtypes of epithermal deposits formed in subduction related arc settings or post collisional orogenic belts the economic and scientific significance of is deposits has been highlighting importance in ag au pb zn exploration and study of porphyry epithermal systems this epithermal clan of deposits typically have a close relationship with andesitic dacitic volcanic subvolcanic rocks and formed at a depth of 0 3 to as much as 1 km is deposits are typically related to oxidized calcic to calc alkaline magmatism fluid homogenization temperatures and salinities range between 150 and 350 c and 0 and 23 wt nacl equivalent respectively the o and h isotope compositions are consistent with a mixture of magmatic and meteoric water with an increase in meteoric diluent as the hydrothermal system wanes most of the is deposits in the world particularly those in circum pacific metallogenic belts formed during cenozoic time several mesozoic and paleozoic is deposits in the central asian orogenic belt imply great exploration potential for pre cenozoic is deposits in this area the presence of mn carbonate such as rhodochrosite and manganocalcite locally mn silicate e g rhodonite helvite typically in mid to late hydrothermal stages is a common diagnostic feature to discern is from low sulfidation ls deposits in addition the occurrence of intermediate sulfidation state sulfides such as pyrite chalcopyrite sphalerite galena and tetrahedrite tennantite associations are another indicator of the is type light colored fe poor sphalerite is typical of is deposits consistent with relatively oxidized fluids elevated fluid salinity is another characteristic with maximum salinity values of base metal rich is veins usually 5 wt nacl equiv the reported is deposits worldwide show that they develop in compressional volcanic arcs as well as in some extensional settings in this review is deposits are subdivided into nc neutral compressional type is with a low ag au ratio 60 formed in extensional settings such as extensional intra arc post collisional orogenic belts and back arc settings another notable feature of e type is deposits is their large ag endowment compared to nc type is nc type is au ag deposits can be associated with porphyry cu au and or high sulfidation hs au cu deposits and their economic metals are mainly gold and or silver by contrast some e type is deposits can occur on the flanks of porphyry molybdenum deposits e type is veins can also occur together with ls precious metal veins in back arcs or extensional continental margins the most representative examples occurring in mexico the occurrence of the two subtypes of is are largely controlled by the parent magma with parent magma of nc type is primarily derived from depleted mantle or juvenile crust while parent magma of e type is mainly from ancient continental crust the occurrence of is deposits is presumably controlled by tectono magmatic settings and fluid evolution paths neutral to compressive stress regime relatively great depth to an exsolving magma 4 km and low exsolution rate of magmatic fluids plus the presence of syn ore dikes in conjunction with the development of interconnected fracture networks above the porphyry stock could be conducive for the occurrence of is and also hs au veins upon porphyry copper deposits pcds confirmation of sub types and variations of is veins can aid in exploration for spatially and genetic related mineralization types such as porphyry and hs deposits

genesis of the telescoped eocene silver and oligocene gold san dimas deposits sierra madre occidental mexico constraints from fluid inclusions oxygen deuterium and noble gases isotopes abstract the san dimas district is a world class ag au deposit developed as a telescoped eocene oligocene ag au mineralization located in the sierra madre occidental smo of western mexico san dimas exhibits multiple mineralization events during different magmatic and tectonic episodes from late cretaceous to early oligocene the well preserved magmatic hydrothermal system provides an excellent opportunity to determine the source of silver and gold the evolution of the hydrothermal fluids and the controls on the mineralization precipitation mineralogical fluid inclusions fi stable and noble gases isotope analyses suggest that the san dimas deposit consist of two different mineralization styles 1 ag dominant epithermal eocene veins that occurred at temperatures up to 350 c developed at ca 2 3 km depth associated to the final stages of intrusion of the piaxtla batholith with fi dominated by a crustal component and 2 epithermal low sulfidation au dominant oligocene veins which were developed at 250 c at shallower depths

prediction of engineering properties of a selected litharenite sandstone from its petrographic characteristics using correlation and multivariate statistical techniques abstract the determination of rock strength and elastic parameters in laboratory tests requires high quality core samples which are not always available from fractured and or weathered strata the purpose of this study is to apply a correlation analysis in conjunction with multivariate statistical techniques to petrographical and laboratory geomechanical data for the investigation of correlations that exist between these properties of a selected sandstone and to suggest inexpensive predictive models in a preliminary investigation sandstone samples from a borehole drilled for a preliminary investigation of a shaft location at a hard coal region black sea turkey were tested to determine uniaxial compressive strength elastic parameters unit weight porosity point load index and quality index secondly fifteen selected samples were subjected to petrographic examination which included fifteen parameters and modal analysis based on the statistical analysis results polynomial prediction equations were developed for estimating mechanical properties from petrographic characteristics and index properties the study revealed that the influence of textural characteristics appear to be more important than mineralogy for predicting engineering properties it is also noted that type of contacts grain shape and size rock fragments with packing density and proximity are the petrographic characteristics which have significant influence upon engineering properties of the sandstones results of this study were presented in the form of correlation coefficient models and predictive models

constraints imposed by rift inheritance on the compressional reactivation of a hyperextended margin mapping rift domains in the north iberian margin and in the cantabrian mountains the alpine pyrenean cantabrian orogen developed along the plate boundary between iberia and europe involving the inversion of mesozoic hyperextended basins along the southern biscay margin thus this margin represents a natural laboratory to analyze the control of structural rift inheritance on the compressional reactivation of a continental margin with the aim to identify former rift domains and investigate their role during the subsequent compression we performed a structural analysis of the central and western north iberian margin based on the interpretation of seismic reflection profiles and local constraints from drill hole data seismic interpretations and published seismic velocity models enabled the development of crustal thickness maps that helped to constrain further the offshore and onshore segmentation based on all these constraints we present a rift domain map across the central and western north iberian margin as far as the adjacent western cantabrian mountains furthermore we provide a first order description of the margin segmentation resulting from its polyphase tectonic evolution the most striking result is the presence of a hyperthinned domain e g asturian basin along the central continental platform that is bounded to the north by the le danois high interpreted as a rift related continental block separating two distinctive hyperextended domains from the analysis of the rift domain map and the distribution of reactivation structures we conclude that the landward limit of the necking domain and the hyperextended domains respectively guide and localize the compressional overprint the le danois block acted as a local buttress conditioning the inversion of the asturian basin

relationships between chemical weathering indices and physical and mechanical properties of decomposed granite abstract chemical weathering is one of the dominant mechanisms for weathering of granite in subtropical and tropical regions resulting in modifications of its chemical physical and mechanical properties thus the changes in chemical properties may provide insight about the changes in physical and mechanical properties of weathered granite in this paper three quantitative chemical weathering indices are correlated to the dry density of decomposed granite a linear relationship is found between each chemical weathering index and dry density for granitic saprolites mobiles index i mob gives the highest coefficient of correlation among the three chemical weathering indices further investigations were conducted to establish the relationships between i mob and other physical and mechanical properties of granitic saprolites the test results showed that fines content increases with increasing i mob but peak strength increases with decreasing i mob the peak states of granitic saprolites are consistent with rowe s stress dilatancy relationship dilatancy increases with decreasing i mob that contributes to a higher peak strength based on some test results presented in this study it seems that i mob could be a good indicator to quantify the effects of chemical weathering on physical and mechanical properties of granitic saprolites

moho topography beneath the iberian western mediterranean region mapped from controlled source and natural seismicity surveys abstract the complex tectonic interaction processes between the european and african plates at the western mediterranean have left marked imprints in the crustal architecture of this area particularly concerning the lateral variations in crustal thicknesses the detailed mapping of such variations is hence of large interest as it provides a major constraint to geophysical and geodynamic modeling at different scales controlled source seismic profiling and receiver functions from natural seismicity are widely considered as major tools to constrain moho topography we compile here the moho depths determined from a comprehensive number of both types of seismic surveys to end up with a new 3d moho depth map of the iberian peninsula its continental margins and north morocco since the 1970s the lithospheric structure beneath this study area has been extensively investigated using multichannel normal incidence seismic reflection and refraction wide angle reflection profiling in the last few years some high resolution surveys at sea and inland have been acquired the latter ones involving 1000 land stations on the other hand the topoiberia iberarray experiment has triggered the investigations on crustal and lithospheric structure using natural seismicity providing a homogeneous spatial resolution never achieved before the availability of good quality results from both methodologies in a common area provides an excellent opportunity to check the consistency of the moho depth estimations the integration of both datasets has resulted in a new high resolution map of the crustal thickness variations the final grid evidences large moho topography variations including crustal imbrication in the pyrenean range a large and relatively undisturbed variscan massif in the center of iberia and a probable delamination process beneath the gibraltar arc the crustal thicknesses vary from 15 km in continental margins up to values exceeding 50 km beneath the pyrenees or the rif cordillera

generic transformation models for some intact rock properties a global intact rock database of nine parameters including uniaxial compressive strength and young s modulus is compiled from 184 studies this database labeled as rock 9 4069 consists of 27

no water no granites no oceans no continents water is essential for the formation of granite and granite in turn is essential for the formation of continents earth the only inner planet with abundant water is the only planet with granite and continents the moon and the other inner planets have little or no water and no granites or continents

the determination of uniaxial compressive strength from point load strength for pyroclastic rocks abstract the point load test has often been reported as an indirect measure of compressive strength it has been used widely in practice due to easy testing the simplicity of specimen preparation and possible field applications many researchers have investigated the relation between uniaxial compressive strength ucs and point load index is for different rock types however there are limited studies in the literature for soft rocks such as pyroclastic rocks in this study the relation between ucs and is was investigated for pyroclastic rocks having ucs values are less than 50 mpa very strong exponential relations were found for dry rocks saturated rocks and both dry and saturated rocks the results were also compared to the studies in the literature

prediction of unconfined compressive strength of carbonate rocks using artificial neural networks the unconfined compressive strength ucs of intact rocks is an important geotechnical parameter for engineering applications determining ucs using standard laboratory tests is a difficult expensive and time consuming task this is particularly true for thinly bedded highly fractured foliated highly porous and weak rocks consequently prediction models become an attractive alternative for engineering geologists the objective of study is to select the explanatory variables predictors from a subset of mineralogical and index properties of the samples based on all possible regression technique and to prepare a prediction model of ucs using artificial neural networks ann as a result of all possible regression the total porosity and p wave velocity in the solid part of the sample were determined as the inputs for the levenberg marquardt algorithm based ann lm ann the performance of the lm ann model was compared with the multiple linear regression reg model when training and testing results of the outputs of the lm ann and reg models were examined in terms of the favorite statistical criteria which are the determination coefficient adjusted determination coefficient root mean square error and variance account factor the results of lm ann model were more accurate in addition to these statistical criteria the non parametric mann whitney u test as an alternative to the student s t test was used for comparing the homogeneities of predicted values when all the statistics had been investigated it was seen that the lm ann that has been developed was a successful tool which was capable of ucs prediction

side resistance of large diameter bored piles socketed into decomposed rocks the design of large diameter bored piles socketed into rock has received considerable attention in sedimentary rocks but has only occasionally been addressed in igneous and metamorphic rocks design methods based on the performance of sockets in sedimentary rocks have been proposed in literature but it is uncertain how applicable they are to other rock types large diameter 600 mm rock socketed piles were used in several recent developments in hong kong which involved 13 large scale pile load tests in various decomposed rocks the test piles varied in length from 20 to 60 m and in diameter from 1 0 to 1 3 m the test loads were as high as 30 mn this provides a golden opportunity for a study of the performance of piles socketed in igneous volcanic and metasedimentary rocks decomposed as a result of subtropical weathering in total 35 pile tests including 13 in hong kong in decomposed rocks together with 44 other tests in sedimentary rocks are reviewed side resistance is analyzed with regard to rock type and is compared to the findings and correlations published by others the rate of mobilization of side resistance was generally scattered in the test results as were the general shapes of the resistance displacement relationships a trend line was established relating the unconfined compressive strength to side resistance for granitic rocks during bidirectional multistage tests a reduction in the socket stiffness was observed with the second test stage for a given displacement the side resistance mobilized in the second stage was less than in the first

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

inverted turtle salt anticlines in the eastern basque cantabrian basin spain abstract halokinetic structures are sometimes masked by subsequent compression in inverted salt related basins making their study difficult the eastern basque cantabrian basin is an outstanding area to study salt tectonics and sedimentation relationships because precursor salt structures have maintained undeformed geometries after the alpine contraction phase based on the interpretation of subsurface data with surface geology a structural model of some of the area s salt structures is proposed according to the model the formation of listric faults and raft tectonics during the first extensional rifting stage resulted in the sinking and collapse of the late jurassic early cretaceous formations giving rise to a turtle back anticline structure with a semicircular geometry the upper triassic keuper salt migrated towards the outer zones of the structure and peripherial troughs were subsequently filled with albian late cretaceous post rift sediments during the eocene alpine contraction the whole area was folded and moved southwards maintaining much of the geometry of the previously formed salt anticlinal structures traditionally the presence of an nne ssw alignment of triassic diapirs in the eastern zone of the basin has been used to place the southern segment of the so called pamplona fault rather than being associated with fault these diapirs are interpreted to rise along the eastern edge of the collapsed extensional turtle structure existing below the eocene urbasa andia synclines no evidence of fault affecting the mesozoic cover series is observed in several composite profiles that cross the pamplona fault alignment it is suggested that the alignement of the triassic diapirs is due to the incidence of the later alpine compression in a previous expulsion rollover rather than the effect of a major alpine strike slip fault

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

crustal thickening and deformation sequence in the footwall to the suture of the variscan belt of northwest spain abstract the sequence of formation and propagation of structures as well as the evolution of crustal thickening in the variscan belt of northwest spain are proposed in this paper the foreland of this mountain belt shows thin skinned tectonics a polyphase deformation with associated regional metamorphism is recognized in the hinterland zones two important culminations the narcea and lugo antiforms are present in an e w cross section through the footwall to the suture of this orogen such culminations are derived from the stacking of several thrust systems generated during two successive periods the sequence of thrust emplacement helps to clarify the formation of different types of structures at the same time in different places in the orogen

crustal structure of the external variscides in northwest spain from deep seismic reflection profiling abstract recent deep crustal seismic reflection profiling escicantabrica 1 provides a detailed image of the external parts of the variscan belt in northwest spain these seismic data together with surface geological information provide constraints on the crustal structure of the foreland thrust and fold belt cantabrian zone and the transition to the hinterland areas narcea antiform area the image in the cantabrian zone includes strong inclined reflections in the upper 5 s that correspond to mappable paleozoic rocks at the surface which have been deformed by thrusting and folding during the carboniferous some of the major thrust faults imaged show a ramp flat geometry at depth and merge into a highly reflective band between 5 and 6 s that corresponds to the cantabrian zone detachment the precambrian basement is almost transparent underneath the cantabrian zone detachment there are a few subhorizontal discontinuous reflections at 11 s that may correspond to the reflection moho at the transition to the hinterland the seismic profile includes short inclined reflections grouped in several reflective bands in the upper 6 s these correspond to the narcea antiform which comprises at the surface a stack of thrust sheets containing precambrian rocks the narcea antiform is placed above a crustal scale ramp imaged by strong w dipping reflections between 6 and 9 s these reflections merge upwards into the cantabrian zone detachment at 6 s and downwards into a reflective lower crustal zone located between 9 and 12 s these midcrustal reflectors are interpreted as a major variscan shear zone that marks the transition between the thin skinned tectonics of the external areas and the thick skinned tectonics of the hinterland areas the lower crust is highly reflective below the narcea antiform area and reflectivity fades out to the east beneath the foreland thrust and fold belt the different seismic responses at middle and lower crustal levels in the foreland and hinterland areas suggest that variscan tectonics strongly affected deep crustal levels in the hinterland areas whereas they remained undeformed beneath the foreland

evolution of salt structures during extension and inversion of the offshore parentis basin eastern bay of biscay the late jurassic cretaceous parentis basin eastern bay of biscay illustrates a complex geological interplay between crustal tectonics and salt tectonics salt structures are mainly near the edges of the basin where jurassic lower cretaceous overburden is thinner than in the basin centre and allowed salt anticlines and diapirs to form salt diapirs and walls began to rise reactively during the late jurassic as the north atlantic ocean and the bay of biscay opened some salt cored drape folds formed above basement faults from the upper jurassic to albian during albian late cretaceous times passive salt diapirs rose in chains of massive salt walls many salt diapirs stopped growing in the mid cretaceous when their source layer depleted during the pyrenean orogeny late cretaceous cenozoic the basin was mildly shortened salt structures absorbed almost all the shortening and were rejuvenated to form squeezed diapirs salt glaciers and probably subvertical welds some of which were later reactivated as reverse faults no new diapirs formed during the pyrenean compression and salt tectonics ended with the close of the pyrenean orogeny in the middle miocene using reprocessed industrial seismic surveys we document how salt tectonics affected the structural evolution of this offshore basin largely unknown to the international audience during the last decade or two the important role of salt in facilitating shortening in sedimentary basins has been highlighted with examples around the world see reviews by jackson 1995 letouzey et al 1995 rowan et al 2004 hudec jackson

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

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

crustal structure beneath north west iberia imaged using receiver functions abstract in the last years the deep crustal structure of the north western part of the iberian peninsula has been explored using teleseismic receiver function rf analysis of p to s conversions at main crustal interfaces this area has been previously investigated by seismic reflection and refraction experiments and therefore provides an excellent opportunity to compare the results of both approaches the region shows the imprint of two orogenic events the variscan and alpine ones that exhibit different reverse intensities from west to east in a first stage a n s transect across the cantabrian mountains was instrumented to study the area affected by the alpine compressional tectonics later on the limit between the undisturbed variscan units and the reworked alpine zones was explored by n s and e w transects finally an array was deployed in the nw edge of iberia over the variscan hinterland zone the receiver functions are calculated by inverse filtering deconvolution of the l component from the q component and the resulting rf are processed using a simple form of migration to obtain images in depth of the lithosphere that can be compared to the 2 d velocity depth models from active seismic experiments the deep crustal structure constrained by both techniques is remarkably consistent and provides further evidence on the crustal doubling and wedging between the iberian and european crusts throughout the northern part of the iberian peninsula affected by the alpine tectonics the undisturbed variscan domains characterized by a clear subhorizontal moho and few intracrustal convertors show up at the southern edge of the n s transects southward of the alpine deformation front and over the variscan hinterland in the e w transect the crust resulting from alpine reworking presents a complex structure with short and frequently dipping convertors which in some cases seem to image preserved variscan structures

new geological geochronological and geochemical characterization of the san dimas mineral system evidence for a telescoped eocene oligocene ag au deposit in the sierra madre occidental mexico abstract the san dimas district is a historical world class ag au epithermal deposit located in the sierra madre occidental smo of western mexico san dimas has been classified as a classic low to intermediate sulfidation ag au epithermal deposit quartz adularia sericite type developed during a single hydrothermal pulse of 10 ma associated to the emplacement of intermediate intrusive bodies of eocene k ar ages however this metallogenetic model includes several ambiguities such as k ar cooling ages incompatible with the local and regional magmatic pulses as well as wide differences in ag au ratios between individual veins which were also emplaced in two different structural systems based on a detailed study of mineralized veins including new petrographic observations new geochronological data zircon u pb adularia 40ar 39ar and titanite fission track ages ft zircon trace element composition and geochemistry of gold and silver minerals we demonstrate that san dimas exhibits multiple mineralization events developed during different magmatic and tectonic episodes from late cretaceous to early oligocene the earliest episode is represented by late cretaceous copper gold porphyry mineralization associated with fertile and oxidized magmas during the development of the laramide arc the second most abundant ore mineralization is represented by a ag dominant vein system adularia rhodochrosite type which developed into east west striking fractures new 40ar 39ar ages on adularia as well as new titanite ft ages for this mineralization event together with one published 40ar 39ar age indicate the formation of ag rich veins at 41 40 ma shortly after the final emplacement of the piaxtla batholith 45 ma which formed from multiple fertile and oxidized magma intrusions in an extensional environment the third mineralization episode is represented by au dominant epithermal veins quartz sericite type which were emplaced at 31 ma into north south to nne sse striking fractures at regional scale these fractures also host rhyolitic domes associated with the first silicic ignimbrite flare up of the smo in an extensional setting the formation of the san dimas district with its exceptionally rich ag au mineralization is interpreted to be related to an extension related late eocene early oligocene regional uplift that allowed the overprinting of originally deeper ag veins by a shallower au mineralizing event

uncertainties in geologic profiles versus variability in pile founding depth how the design and actual founding depths of foundations correspond to the variability of geological conditions has long been a concern this paper evaluates the spatial variability characteristics of as built and estimated founding depths of driven steel h piles with reference to the spatial variability characteristics of geologic profiles at a weathered soil site in hong kong spatial variability characteristics are evaluated in terms of variance and scale of fluctuation the variability of three founding depth indicators i e the depth of grade iii bedrock the depth of standard penetration test blow count n of 200 blows 0 3 m spt 200 and the depth of completely decomposed granite over the site was estimated it is found that pile founding depths exhibit greater variations than those of the geologic profiles due to the presence of design model errors judgment errors and construction effects the as built founding depths are mostly between the spt 200 profile and the grade iii bedrock profile

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

multivariate probability distribution for some intact rock properties a multivariate probability distribution model for nine parameters of intact rocks including unit weight porosity n l type schmidt hammer hardness rl shore scleroscope hardness sh bra

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

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

evaluation of geo mechanical properties of very weak and weak rock materials by using non destructive techniques ultrasonic pulse velocity measurements and reflectance spectroscopy abstract the main purpose of this study is to evaluate the geo mechanical properties of very weak and weak rock materials by using ultrasonic pulse velocity measurements and considering specifically detailed mineralogical compositions for the purpose p wave velocity v p measurements of 66 core samples of the sedimentary rocks including claystones and mudstones collected from firuzkoy area of istanbul turkey were carried out unconfined compressive strength ucs tests were then conducted the axial deformations recorded during the ucs tests were also evaluated and the elastic moduli of the rock materials e i were calculated statistical relations were investigated between the values of p wave velocity measurements and the ucs and e i in order to evaluate the effects of detailed mineralogical compositions on the prediction performances of the empirical equations v p ucs and v p e i the reflectance spectroscopy was introduced 1035 spectral measurements were taken from smooth and fresh surfaces of the failed core samples different genetic rock types were defined according to crystal field effect and charge transfer absorptions of transition elements and water and oh vibrational spectral diagnostics the statistical relations were reinvestigated and the individual empirical equations were reproduced for each genetic rock type the mean values of the multiple coefficients of correlations r were obtained to be 0 904 and 0 916 for the equations of v p ucs and v p e i considering the maximum values of r the increment rates for the values of the explained variances reach up to 14 3 and 13 5 for the equations respectively additionally according to the results of the analysis of variance anova evaluations the empirical equations of v p ucs and v p e i reproduced for each genetic rock type were found to be statistically significant at the significance level of 0 05 as a consequence the non destructive techniques v p measurements and reflectance spectroscopy could be efficiently used together for the evaluation of the geo mechanical properties of very weak and weak rock materials in particular

seismicity analysis at the prestige oil tanker wreck area galicia margin nw of iberia an evaluation of the geological hazard related to the sinking of the prestige oil tanker in november 2002 in the galicia margin nw of iberia was supported by the spanish research agency it included a specific seismic study of the local activity and of the regional seismicity in this margin results of which are presented here published global catalogues show that diffuse seismicity of moderate magnitude events up to 5 6 mb can be associated with the northern flank of the galicia margin with a roughly e w distribution however event locations in this area are poorly constrained due to the inappropriate geometry of permanent seismic networks we collected and analyzed new data from a dense deployment of 10 obs around the wreck site and from a network of 12 land stations at the nw corner of iberia during a 7 months operation period the land network permitted location of 120 events with magnitudes ranging from 1 6 to 4 8 more than 30 of which were not reported by the spanish permanent array confirming the existence of a moderate seismicity in this area five new focal solutions have been obtained for events on land providing additional information about the active faults in the region the obs network ran for 1 month and allowed the location of three earthquakes of magnitude 2 5 near the sinking site four more events have been identified with just a rough determination of their epicenters based on polarization of the p wave arrivals besides these earthquakes the obs data recorded numerous seismic events of different types they include i groups of very short and regularly spaced pulses that can be explained as acoustic calls generated by finback whales ii a large number of short duration seismic events 2 3 s long identified only at individual obs iii local intense monochromatic signals lasting for up to 4 h that can be described as harmonic tremors these last two types of seismic events might be related to hydrothermal activity within the uppermost sediments and deserve additional studies to appropriately establish the seismic hazard of this area 2007 elsevier b v all rights reserved

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

isrm suggested method for determination of the schmidt hammer rebound hardness revised version with its portable simple and affordable attributes the schmidt hammer sh is an ideal index apparatus which underlies its increasing popularity and expanding range of applications the sh rebound hardness value r is perhaps the most frequently used index in rock mechanics practice for estimating the uniaxial compressive strength ucs and the modulus of elasticity e of intact rock both in laboratory conditions and in situ the sh is also widely used for estimating the ucs of discontinuity walls and assessing the workability excavatability and boreability of rocks by mechanical means cutting polishing milling crushing and fragmentation processes in quarrying drilling and tunneling

predictive model for uniaxial compressive strength for grade iii granitic rocks from macao abstract determination of the uniaxial compressive strength ucs of rocks is an important task for rock and geotechnical engineering applications direct measurement is expensive time consuming and even infeasible in some circumstances due to the difficulty in obtaining core samples therefore empirical models are particularly favorable to engineers especially in the preliminary design stage however there is a lack of predictive ucs model for granite of weathering grade iii but it is well recognized to be crucial to the design of pile foundations on granitic bedrocks in this study a reliable predictive model will be developed under the bayesian framework an extensive experimental program was performed in this study to construct a comprehensive database of the measurements of uniaxial compressive strength point load index schmidt rebound hammer value p wave velocity effective porosity specific gravity and dry density it has been proven that the proposed model possesses satisfactory predictive performance

morphosedimentary features and recent depositional architectural model of the cantabrian continental margin abstract multibeam bathymetry high sleeve airguns and very high resolution parametric system topas seismic records were used to define the morphosedimentary features and investigate the depositional architecture of the cantabrian continental margin the outer shelf down to 180 245 m water depth displays an intensively eroded seafloor surface that truncates consolidated ancient folded and fractured deposits recent deposits are only locally present as lowstand shelf margin deposits and a transparent drape with bedforms the continental slope is affected by sedimentary processes that have combined to create the morphosedimentary features seen today the upper down to 2000 m water depth and lower down to 3700 4600 m water depth slopes are mostly subject to different types of slope failures such as slides mass transport deposits a mix of slumping and mass flows and turbidity currents the upper slope is also subject to the action of bottom currents the mediterranean water mw that interact with the le danois bank favouring the reworking of the sediment and the sculpting of a contourite system the continental rise is a bypass region of debris flows and turbidity currents where a complex channel lobe transition zone cltz of the cap ferret fan develops the recent architecture depositional model is complex and results from the remaining structural template and the great variability of interconnected sedimentary systems and processes this margin can be considered as starved due to the great sediment evacuation over a relatively steep entire depositional profile sediment is eroded mostly from the cantabrian and also the pyrenees mountains source and transported by small stream river mountains to the sea it bypasses the continental shelf and when sediment arrives at the slope it is transported through a major submarine drainage system large submarine valleys and mass movement processes down to the continental rise and adjacent biscay abyssal plain sink factors controlling this architecture are tectonism and sediment source dispersal which are closely interrelated whereas sea level changes and oceanography have played a minor role on a long term scale

gravity and magnetic anomalies in the allochthonous ordenes complex variscan belt northwest spain assessing its internal structure and thickness 1 the ordenes complex is the largest variscan allochthonous structure of nw iberia and preserves the suture of a long standing paleozoic ocean probably the rheic gravity and magnetic data the latter specifically acquired on land for this study show that the complex occupies the core of an open synform with a maximum depth of 9 10 km which contrasts with the flat geometry of the lower crust and moho discontinuity beneath the maximum depth reached by the ophiolitic rocks marking the suture is around 7 km the allochthonous units formed by basic and ultrabasic rocks are lens shaped in section and occur not only at the periphery of the complex but form wide ribbons trending ne sw to n s the bouguer anomaly related with the longest of them the fornas unit previously used to support an autochthonous interpretation of the complexes is modeled as a rootless massive amphibolite body with a maximum thickness of 6 km located at the downthrown block of a large normal fault cutting across previous thrust faults and extensional detachments the main magnetic anomalies are associated with ultrabasic rocks cropping out in the nw and se but a weak wide anomaly in the central part of the complex is related with one or more thin layers of amphibolite partly mineralized with massive sulphides the weakly arcuate geometry of this anomaly and of the bouguer anomaly caused by the fornas unit may reflect the ne flank of the central iberian arc an orocline whose core is occupied by the allochthonous complexes

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

estimation of uniaxial compressive strength of rock materials by index tests using regression analysis and fuzzy inference system abstract this paper presents a comparative evaluation of efficacies of different index tests and analysis techniques i e regression analyses and fuzzy inference system in predicting uniaxial compressive strength ucs of granite schist and sandstone ucs and indices such as block punch index point load strength schmidt rebound hardness ultrasonic p wave velocity and physical properties effective porosity and density were determined for the concerned rocks from simple regression analyses it was apparent that for granite and sandstone performances of all six indices are reasonably good in predicting ucs in case of granite block punch index and point load strength are the best indices whereas effective porosity point load strength and schmidt rebound hardness are the most efficient indices for sandstone in case of schist however ultrasonic p wave velocity does not seem to be a competent index unlike other indices where point load strength proves to be the best one from the critical analysis of the tests results it was demonstrated and subsequently concluded that index test results of different rock types with different geology should not be clubbed together for statistical correlation with any rock mechanical parameter like ucs both multiple regression analyses and the fuzzy inference system exhibited better predictive performances for ucs than simple regression analyses in addition to the coefficient of correlation the variance account for vaf and the root mean square error rmse were also calculated to check the predictive performances of these two models and it was found that the predictive performances of both models are comparable however one should be cautious while employing multiple regression analysis in predicting ucs as there is always a chance of cumulating plausible errors that might have remained within individual index test results on the other hand fuzzy inference system seems to be an efficient tool in predicting ucs of rock materials from indices because of its efficacy in handling uncertainties in the test results with transparency

geomorphology of the iberian continental margin abstract the submarine features and processes around the iberian peninsula are the result of a complex and diverse geological and oceanographical setting this paper presents an overview of the seafloor geomorphology of the iberian continental margin and the adjacent abyssal plains the study covers an area of approximately 2 3 million km 2 including a 50 to 400 km wide band adjacent to the coastline the main morphological characteristics of the seafloor features on the iberian continental shelf continental slope continental rise and the surrounding abyssal plains are described individual seafloor features existing on the iberian margin have been classified into three main groups according to their origin tectonic and or volcanic depositional and erosional major depositional and erosional features around the iberian margin developed in late pleistocene holocene times and have been controlled by tectonic movements and eustatic fluctuations the distribution of the geomorphological features is discussed in relation to their genetic processes and the evolution of the margin the prevalence of one or several specific processes in certain areas reflects the dominant morphotectonic and oceanographic controlling factors sedimentary processes and the resulting depositional products are dominant on the valencia catalan margin and in the northern part of the balearic promontory strong tectonic control is observed in the geomorphology of the betic and the gulf of cadiz margins the role of bottom currents is especially evident throughout the iberian margin the galicia portuguese and cantabrian margins show a predominance of erosional features and tectonically controlled linear features related to faults

study on uniaxial compressive strength point load strength index dynamic and physical properties of serpentinites from central greece test results and empirical relations although many studies have been carried out to determine physical dynamic and mechanical properties and to establish relationships among them for several rocks only few have been focused on serpentinites determination of the mechanical properties such as uniaxial compressive strength the most fundamental property in any geotechnical work is usually difficult for these types of rocks because preparation of the standard size cores from serpentinites is quite difficult this paper presents the physical dynamic and mechanical properties investigates the relationships among them and attempts to derive reliable empirical approaches for the determination of uniaxial compressive strength formed from the above mentioned properties for serpentinites for this purpose a variety of serpentinite samples taken from the othrys and kallidromo mts central greece were tested in accordance with astm and isrm standards the same samples were subjected to petrographic studies the results were statistically described and analyzed using the method of least squares regression

hydrothermal evolution in the formation of silver gold veins in the tayoltita mine san dimas district the tayoltita mine located in the states of durango and sinaloa mexico is a major example of a tertiary volcanic hosted silver gold epithermal vein deposit significant silver and gold values and base metal sulfides as well as most of the vein quartz and accompanying chlorite calcite rhodonite and adularia are restricted to a vertical interval in the veins between approximately 500 and 1 000 m beneath the original surface fluid inclusion studies indicate that ore deposition was from fluids averaging approximately 260 degrees c and was accompanied by some boiling the salinity of the fluid inclusions is estimated at 0 1 m nacl equivalent greater apparent salinities indicated by lower freezing temperatures probably reflect some dissolved co 2 correlation of ag au values with the apparent salinities and with vein mineral paragenesis shows that during ore deposition the fluids evolved in time and space from relatively concentrated to dilute conditions owing to gas loss and possibly some fluid mixing ag au ratio zoning orebody distribution and vein mineral zoning patterns are all consistent with vein formation from fluids flowing predominantly in horizontal flow patterns

geophysical constraints on the deep structure of a limited ocean continent subduction zone at the north iberian margin 1 late cretaceous to cenozoic convergence between iberia and europe led to the partial closure of the bay of biscay with limited southward subduction of oceanic crust below the north iberian margin inclined sub moho reflections and diffractions observed in deep seismic reflection profiles shot across the margin are especially well represented in two reflection profiles escin 3 2 and escin 3 3 these two profiles have been chosen to test if the sub moho reflections correspond to true primary deep events and provided that they are reflecting off the subduction zone to investigate its deep structure spectral analysis together with travel time estimation and migration allow us to characterize a number of these sub moho events as deep source low frequency 19 hz reflections and diffractions synthetic seismograms were generated by three dimensional seismic modeling of a sub moho southward dipping surface interpreted to correspond to the top of subducted oceanic crust comparison between the real and synthetic data show that inclined low frequency sub moho reflections in both escin 3 2 and escin 3 3 profiles may correspond to reflections from southward subducted bay of biscay oceanic crust geoid free air gravity and absolute topography modeling provides additional constraints on the lithospheric scale structure of this limited ocean continent subduction zone beneath the north iberian margin

basinal brines at the origin of the imiter ag hg deposit anti atlas morocco evidence from la icp ms data on fluid inclusions halogen signatures and stable isotopes h c o a discussion we congratulate essarraj et al 2016 for their paper on the polymetallic ag hg imiter deposit anti atlas morocco which is one of the most intensely investigated yet still discussed mineral deposits in term of ore genesis in their contribution essarraj et al have employed fluid inclusion halogen and isotopic analyses in an attempt to constrain the genesis of the imiter ag hg deposit it is through detailed geochemical studies such as this that the origin s of this world class orebody will be deciphered their contribution represents a significant advance in the investigation of polymetallic hydrothermal deposits of the anti atlas however we feel compelled to stress certain problems with their interpretation important geologic attributes of the imiter deposit have been documented by numerous workers ouguir et al 1994 pasava 1994 baroudi et al 1999 cheilletz et al 2002 essarraj et al 2005 barral et al 2011 levresse et al 2005 2016 however there is a lack of direct age information to constrain the timing of hydrothermal activity and duration of vein filling during the silver mineralizing event s this age uncertainty has resulted in the proposal of several conflicting models involving different fluid sources and genetic processes that have been ignored by essarraj et al in their contribution essarraj et al relate the genesis of silver ore at imiter to a single regional scale hydrothermal circulation of basinal brines but do not mention preexisting models that emphasize the polyphase character of the mineralization the authors point out the role of triassic evaporitic brines and development of the central atlantic magmatic province as the main ore forming processes that triggered formation of the imiter ag hg ores key evidence for their proposed model is based on the late permian and triassic ages of borisenko et al 2014 that were determined on a

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

the foreland deformation in the south western basque cantabrian belt spain abstract in the south western portion of the cenozoic basque cantabrian belt structural data collected in pre orogenic upper cretaceous limestones were combined with aerial images interpretation in flat lying areas observations about fracture strike type orientation and overprinting relationships both at the macro and mesoscales allow to constrain the pre thrusting and pre folding deformational sequence that affected the area when it was forming part of the foreland basin wnw ese striking extensional structures represent the oldest elements developed during the very late stages of the mesozoic rifting associated with the opening of the bay of biscay the onset of convergence is marked by the development of extensional structures striking roughly nnw sse and wsw ene which are associated with belt parallel stretching in the foredeep and outer arc extension in the peripheral bulge respectively and developed in a non fluid assisted environment these elements are postdated by a pre folding layer parallel shortening pattern which includes wsw ene striking pressure solution cleavages and reverse faults both of them frequently reactivating inherited early orogenic wsw ene striking extensional elements and right lateral reactivation of wnw ese striking pre orogenic extensional structures this stage was followed by a syn to post folding e w oriented belt parallel compression wnw ese striking left lateral faults being the most outstanding elements associated with this stage the presence of such elements in upper cretaceous sediments provides support to the idea that left lateral shear zones of the area related with a cenozoic intrabelt lateral extrusion tectonics our results indicate coherently with previously published works in the pyrenean orogen that most of the mesoscale deformation has been acquired before layer s tilting

assessing the uniaxial compressive strength of extremely hard cryptocrystalline flint cryptocrystalline flint is an extremely hard siliceous rock that is found in chalk formations the chalk is frequently a prefered rock type which in recent decades is often used as a host for underground rock caverns and tunnels in europe and north america a reliable estimation of the uniaxial compressive strength ucs of the extremely strong flint with an average ucs of about 600 mpa will provide guidance for a proper engineering design where flint is encountered thereby avoiding project progress delay litigation as well as economic consequences conventional ucs measurement using core samples is cumbersome for flint due to the extreme strength and hardness of the rock for which the core sample preparation process is often extremely difficult in this study the ucs prediction models of flints collected from the north west europe were developed and the validity of the developed models was investigated a series of laboratory index tests comprising the three point bending point load ultrasonic velocity density shore hardness and cerchar abrasivity tests were perfomed the index test results were correlated with the ucs values previously determined in the laboratory using both cylindrical and cuboidal specimens to develop the ucs prediction models regression analysis of the ucs and the index test results was then performed to evaluate for any potential correlations that can be applied to estimate the ucs of the cryptocrystalline flint intensive validity and comparison studies were performed to assess the performance of the proposed ucs prediction models this study showed that ucs of the tested flint is linearly correlated with its point load strength index tensile strength and compressional velocity and is parabolically correlated with its density the present study also demonstrated that only a couple of the previously developed empirical ucs models for estimating ucs are suitable for flint which should be used with care

crustal structure beneath the iberian peninsula and surrounding waters a new compilation of deep seismic sounding results abstract we present here an updated compilation of crustal parameters beneath the iberian peninsula and surrounding waters inferred from extensive deep seismic exploration performed in the last three decades firstly the more relevant experiments developed in both terrestrial and marine domains are revisited together with the corresponding seismic velocity depth models published that reveal the characteristics of the different tectonic domains sampled including oceanic zones continental margins orogenic and rift belts the results are summarized in three crustal transects sketched along representative directions secondly we compiled the moho depths along all the available seismic profiles to produce a geo referred database this database has then been interpolated using kriging algorithms to obtain a continuous moho depth model in the form of a regular grid file this integrative moho map for a key area in the western mediterranean documenting the interaction between european and african plates can contribute to constrain further regional studies either at crustal lithospheric or mantle scales

estimating the deformation modulus of rock masses a comparative study although the modulus of deformation of rock masses has crucial importance for geotechnical projects such as tunnels and dams the determination of this parameter by in situ tests requires considerable costs and involves difficult operational processes for this reason empirical equations for the indirect estimation of the modulus of deformation are an interesting issue for rock engineers and engineering geologists this study includes assessment of the prediction performances of some existing empirical equations using in situ plate loading test data and rock mass properties producing an empirical equation depending on the new data construction of a fuzzy inference system for the estimation of modulus of deformation and making a comparison between results obtained from the empirical equations and fuzzy inference system a series of calculations and statistical analyses were undertaken it is concluded that the performance of the empirical equations and fuzzy inference system obtained in this study is satisfactory however the prediction models developed in this study are limited by the number of the data used and the rock types employed for these reasons a cross check should be performed before using these prediction models for design purposes

seismic image of the deep crust at the eastern margin of the alps austria indications for crustal extension in a convergent orogen abstract a 39 km long deep seismic reflection profile recorded during two field campaigns in 1996 and 2002 provides a first detailed image of the deep crust at the eastern margin of the eastern alps austria the ese wnw trending low fold seismic line crosses austroalpine basement units and extends approximately from 20 km west of the penninic window group of rechnitz to 60 km sse of the alpine thrust front the explosive source seismic data reveals a transparent shallow crust down to 5 km depth a complexly reflective upper crust and a highly reflective lowermost crust the upper crust is dominated by three prominent west dipping packages of high amplitude subparallel reflections the upper two of these prominent packages commence at the eastern end of the profile at about 5 and 10 km depth and are interpreted as low angle normal shear zones related to the miocene exhumation of the rechnitz metamorphic core complex in the western portion of the upper crust east dipping and less significant reflections prevail the lowermost package of these reflections is suggested to represent the overall top of the european crystalline basement along the western portion of the line the lower crust is characterised by a 6 8 km thick band of high amplitude reflection lamellae typically observed in extensional provinces the moho can be clearly defined at the base of this band at approximately 32 5 km depth due to insufficient signal penetration outstanding reflections are missing in the central and eastern portion of the lower crust we speculate that the result of accompanying gravity measurements and lower crustal sporadic reflections can be interpreted as an indication for a shallower moho in the east preferable at about 30 5 km depth the high reflectivity of the lowermost part of the lower crust and prominent reflection packages in the upper crust the latter interpreted to represent broad extensional mylonite zones emphasises the latest extensional processes in accordance with eastward extrusion

2 d seismic modeling of the variscan foreland thrust and fold belt crust in nw spain from escin 1 deep seismic reflection data abstract the foreland thrust and fold belt cantabrian zone of the variscan belt in nw spain and the transition to the hinterland westasturian leonese zone was the location of a seismic experiment in 1991 the seismic reflection profile escin 1 is 140 km long and runs in an e w direction the interpretation and seismic modeling of the main reflective interfaces in the profile were made integrating available geological and geophysical data including surface geology deep seismic reflection data from escin 1 transmission velocities from a borehole refraction and laboratory data the geological and velocity model of the crust was tested obtaining synthetic seismograms and can be correlated with surface geology the velocity model images the main crustal structures interpreted from escin 1 the basal detachment of the foreland thrust and fold belt dips gently from 12 km in the easternmost part of the profile to 16 km in the transition to the hinterland to the west a new interpretation is proposed for the structure above the basal detachment in the eastern end of the profile where the basal detachment at a depth of 12 km is duplicated at 6 5 km by a n dipping alpine thrust that also duplicates part of the basement in the western part two deep reflective bands dip westward and the most conspicuous one can be followed from 16 27 km depth the two bands previously interpreted as crustal ramps join a reflective lower crust that is located between 25 and 29 km and fades westwards a reflective moho interpreted at the base of the reflective lower crust dips and fades in the same direction from 30 34 km

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

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

sedimentary evolution of the le danois contourite drift systems southern bay of biscay ne atlantic a reconstruction of the atlantic mediterranean water circulation since the pliocene abstract the evolution of the le danois contourite depositional systems cds during the pliocene and quaternary was investigated based on high resolution seismic reflection data from old to young six seismic units u1 u6 bounded by major discontinuities h1 h6 were identified regarding variations of the bottom current circulation four evolution stages of the le danois cds were identified including onset 5 3 to 3 5 3 0 ma initial 3 5 3 0 to 2 5 2 1 ma intermediate 2 5 2 1 to 0 9 0 7 ma and drift growth 0 9 0 7 ma to present day stages the cds associated with the atlantic mediterranean water amw along the middle continental slope initiated at 3 5 3 ma and was widely built after the mid pleistocene transition mpt 0 9 07 ma at a shallower water depth a second cds associated with the eastern north atlantic central water enacw started to develop from the late quaternary 0 47 ma onwards in the amw related drift system the le danois drift was generated both under glacial and interglacial climatic oscilations repeated internal structures in unit 5 that consist of acoustically transparent lower parts moderate amplitude upper parts and high amplitude erosional surfaces at the top are compared with interglacial glacial cycles since the middle pleistocene to the present day these cyclic features suggest coarsening upward sequences of the le danois drift and processes related to enhanced amw during glacial stages the estimated sedimentation rate of the le danois cds reached a maximum during the mpt at least 27 cm ky and then decreased until present day 5 cm ky variations of sedimentary stacking patterns and processes of the le danois cds imply full domination of the intermediate water mass along the central atlantic and southwest european continental slopes from the late pliocene 3 5 3 0 ma onwards

an empirical approach for estimating shear strength of decomposed granites in galicia spain decomposed granites are often found in galicia spain where they are referred to as jabres similar decomposed granites are also found in many other parts of the world granite weathering rarely produces an homogeneous altered rock mass with all material decomposed to the same degree or even a simple weathering profile where the degree of alteration decreases progressively with depth this paper presents an empirically based approach that allows estimation of the shear strength of this type of materials in terms of mohr coulomb cohesion and internal friction angle values the approach is based on back analysis of failed slopes in decomposed granites and it is implemented through simple in situ testing and classification of the weathered granite treating it as a soil material an advantage of the used approach is that it allows prediction of shear strength values at different locations within the deposit in a quick and economical way from which average values of shear strength parameters can be computed this is particularly important when considering the heterogeneous nature of decomposed granite formations in relation to the scale of the engineering work involved analysis of three slopes instability cases in jabres in galicia illustrating the approach are described in detail these correspond to a road cut a natural slope and the wall of an open pit mine

origin structure and exposure history of a wave cut platform more than 1 ma in age at the coast of northern spain a multiple cosmogenic nuclide approach abstract along the asturian coast of northern spain an uplifted wave cut platform extends for 100 km east west the steep cliff which bounds the gently seaward dipping platform to the north increases in height from 30 m in the west to 100 m in the east and reflects the overall eastward increase in platform elevation the southern edge of the 2 4 km wide platform runs along the foothills of the cantabrian mountains as constrained by a high resolution digital elevation model the marine platform which was carved into deformed paleozoic bedrock with abundant quartzite beds is largely covered by weathered marine and continental sediments quartzite samples from flat bedrock outcrops which are currently not covered by sediment or soil yield cosmogenic nuclide concentrations 21ne 10be and 26al that demonstrate a long and complex exposure history including periods of burial with partial or complete shielding from cosmic rays the combination of multiple cosmogenic nuclides yields a minimum age of 1 2 ma for the platform taking into account i the horizontal and vertical extent of the platform ii the high resistance to erosion of the quartzitic bedrock and iii published data on the magnitude of past sea level fluctuations we suggest that the wave cut platform formed in the pliocene subvertical faults cutting the platform at high angles to the coastline offset the southern edge of the platform by 20 to 40 m and reactivate the pre existing anisotropy in the paleozoic bedrock uplift and crustal deformation of the coastal region have occurred after platform formation in the pliocene and may still be active the slow deformation of the northern edge of the iberian plate including the cantabrian mountains may result from the ongoing slow convergence at an incipient subduction zone extending along the coast of northern spain

the transition from thick skinned to thin skinned tectonics in the basque cantabrian pyrenees the burgalesa platform and surroundings interpretation of seismic data in the margins of the burgalesa platform in the basque cantabrian pyrenees has allowed proposition of a new structural model that combines different modes of deformation during oblique tectonic inversion conditioned by the distribution of triassic salts deformation was decoupled by the presence of the salt horizon between basement involved thrusts inverting formerly triassic and late jurassic early cretaceous extensional faults and a detached thrust system involving the upper triassic to neogene sedimentary package structural units experiencing different styles of deformation are not only stacked vertically above and below the salt but most importantly they change from one to the other along strike across the transversal edges of the triassic salts the burgalesa platform detached thrust system was confined between the basement involved structures of the cantabrian mountains westward and the nw tip of the iberian basement involved structures san pedro southward this together with the obliquity between the pyrenean shortening direction and the strike of the previous extensional faults mostly during the late stages of deformation determined the strike slip reactivation of the basement involved inverted faults and the lateral extrusion of the burgalesa platform detached mesozoic successions above the salt towards the se to form a prominent thrust salient oblique to the main pyrenean trend the proposed model combines thick skinned with thin skinned structural styles during oblique tectonic inversion and is consistent with the surface data including the fracture system the available subsurface data and the mechanical stratigraphy

the late variscan ht lp metamorphic event in nw and central iberia relationships to crustal thickening extension orocline development and crustal evolution

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

jurassic to holocene tectonics magmatism and metallogeny of northwestern mexico the present metallic distribution in northwestern mexico is the culmination of superposed magmatism tectonism erosion and burial over more than 150 m y detailed palinspastic reconstructions of preextensional configurations the first study of its kind for this region clarify the interplay among these features on the present distribution and character of mineralized geologic systems this new synthesis goes beyond previous metallogenic investigations of northwestern mexico by separating events into specific timing and structural relationships and by restoring the geology to its preextensional configuration metallogenic factors such as enrichment preservation and erosion play major roles in the present distributions and for the first time are related to the overall metallogenic framework of northwestern mexico the analysis concludes that modern metallogenic patterns are the result of the complex superposition and subsequent redistribution of geologic systems in a way that is related directly to the regional history rather than simply metallic belts or interpreted angle of a subducting slab three main extensional events in the oligocene holocene have been restored and the palinspastic distributions have been analyzed reconstructions reveal the following 1 mineralization events igneous centers and sedimentary sequences are continuous across the gulf of california and other areas with large amounts of extension 2 middle tertiary gold silver mineralization in baja california may be the western part of the sierra madre oc present address bhp billiton avenida america vespucio sur 100 8th floor las condes santiago chile e mail john mark g staude bhpbilliton com cidental metallogenic province thus expanding the previously recognized extent of this province s mineralization 3 late cretaceous early tertiary porphyry copper deposits and intrusive centers form a narrower belt than previously noted and are traceable for over 400 km with parts of the belt buried beneath the younger sierra madre occidental volcanic fields 4 interpreted alignments of older geologic features including lineaments of ore deposits are displaced in the reconstructions 5 sedimentary rock hosted gold deposits and low angle detachment gold systems are closely related and occur around core complexes by using structurally restored time slices it becomes clear that older deposit types tend to be those formed at greater depths and more proximal to intrusions whereas younger deposits formed at shallower depths are less eroded and are more commonly volcanic rock hosted these characteristics express themselves in the regional distribution of deposit types second mineralization of widely differing ages is spatially superposed commonly associated with coeval magmatic and tectonic events the structural and magmatic events together with paleodistribution of ore deposits define a new framework to interpret the metallogenic history of northwestern mexico

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

paleoconstraints during rifting of the northeast atlantic passive margins the northeast atlantic passive margins formed during the early cretaceous phase of rifting from goban spur to galicia bank these margins are characterized by a tilted fault block geometry well defined by numerous single channel and multichannel seismic data stress directions cannot be deduced from these structural data but recently withjack and jamison 1986 have described the strain states and fault patterns produced by oblique rifting using experimental and analytical techniques we have applied these techniques to the northeast atlantic continental margins all types of extensional margins are represented there with pure extensional rifting goban spur and west galicia margins oblique rifting north spanish and celtic margins and close to pure wrenching armorican margin the rifting directions are parallel to the adjacent oceanic fracture zones or flow lines defined in the northeast atlantic and in the bay of biscay except for the west galicia margin where a 20 difference exists this difference could be within the error range of the method or could be due to a slight relative motion between galicia bank and iberia during rifting globally the coherence between rifting and spreading directions is an argument in favor of the validity of the method on the basis of kinematic arguments the motion of iberia with respect to eurasia has an eastward component related to the west to east motion of africa with respect to eurasia while iberia was a small plate whose motion was roughly coupled to africa this is confirmed by our analysis we conclude that during both the rifting and spreading episodes in the bay of biscay the motion of iberia with respect to eurasia was in the southeastward direction recently boillot 1984 suggested that iberia moved about 150 km southwestward with respect to eurasia during the rifting phase and then moved in the southeastward direction during the spreading phase we suggest that the boillot hypothesis could be wrong

of what is the centre of the ibero armorican arc composed abstract the ibero armorican arc is a large structural bend known between france and iberia a related structure may exist in the crust of the grand banks of newfoundland european geological studies suggest that this now segmented structure developed during the carboniferous but this deformation has not been recognised in the easternmost mainland of canada in france the centre of the arc is occupied by an ancient craton that formed the southern hercynian foreland the northern part of this craton presently lies beneath the mesozoic and cenozoic cover of the aquitaine basin france interpretation of the new ecors gascogne deep seismic reflection lines and gravity modelling suggests that the old aquitaine basement has thinned beneath the mesozoic parentis basin north of the basin the deep variscan structures dip northeast in the south the centre of the aquitaine basement corresponds with the landes high analysis of the ecors refraction seismic data shows the absence of any shallowing of the lower crust beneath this uplift at the same level a high velocity dense body resting on the lower crust has been imaged this body which is probably a metamorphic block of archaean basement at depth lies in line with the spanish le danois bank in a reconstruction where the biscay bay is closed it is postulated that this high velocity and high density block is the only french remnant of the undeformed nucleus of the ibero armorican arc now dismembered by the opening of the biscay bay

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

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

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

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

spatial variability of in situ weathered soil the founding depths of pile foundations depend primarily on the loading conditions of the superstructure and the strength of subsoil the depth of grade iii weathered rock the top of completely decomposed granite cdg and standard penetration test n value of 200 spt 200 are often used as indicators for decision making in arriving at the preliminary founding depth of piles in hong kong the work reported in this paper focuses on evaluation of the spatial variability characteristics of the above founding depth indicators at a construction site using statistical models based on random field theory spatial variability characteristics are evaluated using the measured data in terms of scale of fluctuation geostatistics is used to obtain additional data at unsampled locations for mapping profiles of founding depth indicators over the site using the measured data from borehole records and site investigation results it is observed from the results that if faults are not present the depth of the grade i