structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

the impact of hydrodynamics authigenesis and basin morphology on sediment accumulation in an upwelling environment the miocene monterey formation at shell beach and mussel rock pismo and santa maria basins central california u s a abstract in the sections at shell beach pismo basin and mussel rock santa maria basin both along the central california coast the miocene monterey formation is composed of laminated biosiliceous organic rich and phosphate rich sediments which are intercalated with carbonates and volcanogenic deposits the presence of small and large scale scours conglomerates gravity flow deposits slumps and condensed intervals reveals the importance of sediment reworking which is related to the presence of bottom currents the general morphology of the basins and recurrent high energy events of likely seismic origin the lithologies reflect strong upwelling enhanced primary productivity and the presence of an oxygen minimum zone which is indicated by ubiquitous lamination a general absence of bioturbation with the rare exception of traces related to the gravity flow displacement of trace makers high pyrite mo and u concentrations and molar ratios of total organic carbon and organic phosphorus toc p org of up to 2000 oxygen depletion was particularly severe during the early langhian and the late serravallian and early tortonian and favored the preservation of organic matter episodes of deposition of organic rich sediment were followed by longer phases of subdued sediment accumulation and early diagenetic phosphogenesis which resulted in the formation of a low porosity less permeable lid in the near surface sediments that assisted in preserving organic matter phosphogenesis occurred throughout the time interval considered approximately 17 5 6 5 ma and phosphate rich sediments formed especially during periods of sedimentary condensation in the langhian and earliest serravallian and the latest tortonian and early messinian a comparison of temporal trends in the type and quantity of deposited sediments between the two sections at shell beach and mussel rock and three sections of the santa barbara basin el capitan state beach naples beach and haskell beach confirms that towards the top of the monterey formation sediments become enriched in biosilica in all three basins the transition into this lithology occurred diachronously during the serravallian in the pismo and santa maria basins and tortonian in the santa barbara basin and was probably related to a diachronous shift to more intense upwelling in all three basins a phase of important condensation and phosphogenesis terminated monterey type sedimentation during the latest tortonian and early messinian in both the santa maria and santa barbara basins the uniform expression of this phase is interpreted as the result of improved connections between the two basins

strike slip duplexes abstract strike slip fault systems often contain zones of steep imbricate faults geometrically similar to imbricate fans and duplexes in dip slip thrust and normal fault systems they are evident in map view rather than in vertical sections examples of duplexes are cited from both active and ancient systems and from theoretical and physical models duplexes may form at bends on strike slip faults by a process kinematically analogous to the sequential imbrication of ramps on dip slip faults however some may form and many may initiate as non sequential riedel fractures at fault offsets or on straight fault segments this process is more marked than in dip slip systems where primary anisotropy such as bedding exerts more control on fault geometry strike slip duplexes may be shunted along the fault system parallel to the regional slip vector however duplexes or individual horses will usually also move up or down perpendicular to the slip vector because of the unconstrained upper surface to the fault system these factors mean that no section through a strike slip system should be expected to area balance the faults of strike slip duplexes and imbricate fans may root in kinematically necessary low dip faults or may converge downwards and appear in vertical sections as flower structures

lateral interaction between metamorphic core complexes and less extended tilt block domains the alpujarras strike slip transfer fault zone betics se spain abstract the alpujarras area in southeastern spain exhibits one of the scant documented examples of extension related strike slip faults bordering core complexes in the world faults of the alpujarras fault zone define a regional scale complex ene striking transfer zone that marks the boundary among the sierra nevada elongated dome a highly extended constricted core complex and a less extended domain formed by large scale tilt blocks detailed mapping and structural analysis show that the alpujarras fault zone is an integral part of the wsw directed normal fault systems that thinned the betic hinterland during the middle miocene to recent time fault patterns and palaeostress analysis both indicate that dextral movement along the strike slip faults was induced by a local stress field with a sub horizontal e w to ese wnw trending maximum principal stress axis which is synchronous with the regional stress field driving the normal fault systems palaeostress analysis also indicates subsequent variations in the stress field with a sub horizontal nw se to n s trending maximum principal stress axis thus producing both the tectonic inversion of the northern fault of the alpujarras system and shortening of the unloaded extensional detachment footwall a simplified kinematic model for the tectonic evolution of the alpujarras area from the middle miocene to recent emphasizes the kinematic coupling of normal faults and strike slip transfer zones in the extensional process

effects of water content and particle crushing on the shear behaviour of an infilled joint soil ring shear tests were carried out on a compacted low plasticity infilled joint soil from beihetan site in china different initial water contents 5 0 9 0 and 13 5 were considered it was observed that the failure envelope is linear for the peak deviator stress but highly non linear for the residual deviator stress in the range of high normal stresses higher than 400 kpa evidencing the particle crushing effect on the residual strength furthermore this particle crushing effect was dependent on water content the residual friction angle is larger at higher water content further grain size analysis was performed on the portion taken in the zone of shear band after each test and changes of the fractions of 75 m and 2 m were compared for different water contents the results indicate clearly that the effect of water content on particle crushing depends on particle size for large particles 75 m water content increase enhances the particle crushing by the fracture mechanism on the contrary f

geology and petrology of the hormuz dolomite infra cambrian implications for the formation of the salt cored halul and shraouh islands offshore state of qatar abstract geological investigations of the halul and the shraouh islands offshore qatar indicate that most of their calcareous rocks which display abundant stromatolitic bedding belong to the infra cambrian hormuz series mineralogical petrological and geochemical analyses show that these calcareous rocks consist dominantly of dolomite and have formed in a reducing depositional environment faint laminations and small streaks of organic matter furnish evidence for the involvement of algal mats in their genesis and indicate their formation in an intertidal to supratidal setting the halul and shraouh dolomites experienced extensive recrystallization and sulfatization during the emplacement of the halul and shraouh salt domes that form the cores of the islands during mobilization and ascent of the salt the dolomite recrystallized and its sr initial ratios were abnormally enhanced by the incorporation of 87sr from a source which is more radiogenic than the attendant seawater at the time of the dolomite formation near the proterozoic cambrian boundary geochemical analysis show that si al ti zr and of insoluble residue are highly correlative suggesting the presence of detrital minerals such as rutile and zircon a paleosabkha model may well agree with this chemical signature however the infra cambrian age of the hormuz rocks and the presence of stromatolitic layers containing organic materials in the studied rocks suggest that organogenic dolomitization could be an alternative dolomitization model

an evaporite bearing accretionary complex in the northern front of the betic rif orogen the guadalquivir accretionary complex forms a largely oblique prism at the northern edge of the betic rif orogen where miocene sediments plus allochthonous evaporite bearing units were accreted during the displacement of the alboran domain towards the west traditional interpretations end the tectonic structuring of the betic cordillera at the present topographic front beyond which gravitational and or diapiric processes would predominate however this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics which is achieved through an alternation of roughly n s arcuate thrust systems connected by e w transfer fault zones these structures accord well with the geophysical models that propose westward rollback subduction the main stage of tectonic activity occurred in the early middle miocene but deformation lasted until the quaternary with the same kinematics evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area s and l gypsum tectonites scaly clay fabrics and brittle fabrics coexist and consistently indicate westward motion top to 290 with subordinate n s contraction almost perpendicular to the transfer zones this work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic melanges involving evaporites above the decollement level of accretionary wedges

the alpujarride nevado fibabride extensional shear zone betic cordillera se spain in the betic cordillera the initial thickening of the alboran domain produced an alpine high pressure low temperature hp lt metamorphism in the alpujarride and nevado filabride complexes after 19 ma this thickening process evolved to an extensional stage with uplift rates of between 1 and 2 mm year 1 the extensional stage generated structures in a heterogeneous shear regime with a top to the west sense of movement the present day alpujarride nevado filabride contact is a detachment fault generated in this shearing regime in the footwall the first structure developed in this extensional stage is a planar linear fabric characterized by constrictive strain that is axial planar to kilometric recumbent tight to isoclinal folds the planar linear fabric is folded by inclined close to open folds with axes parallel to the stretching lineation the planar linear fabric and folds are deformed by a late extensional crenulation cleavage near the detachment surface finally brittle deformation was generated within the same kinematic framework as that of the ductile structures in the hanging wall meanwhile deformation had a brittle character producing faults and joints

strontium isotopic chronostratigraphy and correlation of the miocene monterey formation in the ventura and santa maria basins of california the sr isotopic composition of authigenic marine carbonates can be used effectively with the known sr isotopic evolution of sea water to decipher chronostratigraphic relationships and correlate the monterey formation the sr isotopic chronostratigraphy of both the oakview and mussel rock sections agrees with published biostratigraphic ages correlations of lithologic members between the two sections are also in accord with the published lithologic and biostratigraphic correlations time and stratigraphic resolutions of sr isotopic chronostratigraphy are dependent upon the slope of the sea water sr evolution curve sedimentation rates inherent sr isotopic variability and analytical precision on the average individual analyses yield time resolutions of 0 5 ma and stratigraphic resolutions of 10 70 m of section 24 references 3 figures 3 tables

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

role of fluids in faulting inferred from stress field signatures the stress orientation signature of weak faults containing high pressure fluids has been observed for segments of the san andreas fault system in southern california the inferred lithostatic fluid pressures extend into the surrounding relatively intact rock in a zone scaling with the width of the interseismic strain accumulation repeated strain related fracturing and crack sealing may have created low permeability barriers that seal fluids into the network of currently active fractures

isotopic constraints on the genesis and age of autochthonous glaucony in the oligo miocene torquay group south eastern australia the oligo miocene torquay group at bird rock in south eastern australia comprises a sequence of fine grained skeletal carbonates and argillaceous and glauconitic sandstones deposited in a cool water mid shelf environment the bird rock glaucony is autochthonous and consists predominantly of randomly interstratified glauconitic smectite which constitutes bioclast infills and faecal pellet replacements the results of rb sr and oxygen isotopic analysis of samples taken from a single glauconitic horizon the bw horizon indicate that the glaucony developed through a series of simultaneous dissolution crystallization reactions which occurred during very early diagenesis in a closed or isochemical system isolated from the ambient marine environment the constituent ions of the glaucony were derived primarily from terrigenous clay minerals but considerable potassium may have been sourced indirectly from sea water through potassium enrichment of clay precursors the pore fluids associated with glauconitization were marine derived but progressively modified by the dissolution crystallization of detrital clay minerals and autochthonous glaucony rb sr data for the bw horizon indicate that dating glauconies may be somewhat problematic as co genetic glauconitic minerals can show a range of initial strontium compositions which reflect the incorporation of strontium derived from mineralogical precursors and or contemporaneous sea water rb sr isochrons indicate that the glaucony of the bw horizon formed at 23 a 3 ma this age is in good agreement with both the established biostratigraphy and a 87 sr 86 sr age for the horizon 23 a 1 ma but could only be determined using the independent age constraint and the estimate of the 87 sr 86 sr ratio of contemporaneous sea water provided by

high resolution dating of cenozoic sediments from northern north sea using 87sr 86sr stratigraphy we demonstrate the potential of sr isotope stratigraphy as a tool in basin analysis by dating bioclastic carbonate and phosphate fragments from eight seismic units in cenozoic sedimentary rocks along two east west profiles in the northern north sea the dates which agree well with available rb sr glauconite dates have precisions in the range 0 5 to 3 m y thereby providing important chronostratigraphic information for sediments that otherwise are difficult to date basinward southwest in this area the most important seismic sequence boundaries are dated at approximately 53 ma 33 ma 22 ma 8 ma and 2 ma northeastward toward the basin margin these boundaries represent important periods of erosion or nondeposition deep water sedimentation predominated from he paleocene until the early oligocene 33 ma a time of high global sea levels close to the basin margin local tectonic activity contributed turbiditic clastic sediments an important sequence boundary at 30 ma involves erosion in the northern area and correlates with a sharp eustatic drop in sea level post early oligocene seismic sequence boundaries are controlled mainly by basin margin tectonics related to uplift events in fennoscandia and in the shetland platform area

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

stress field variation related to fault interaction in a reverse oblique slip fault the alhama de murcia fault betic cordillera spain abstract the interpretation of kinematic data from microstructural observations has led many authors to propose a complex dynamic development for the eastern betic cordillera from the late miocene to the present in which different and sometimes contradictory stress fields explain the generation of the same structures the main aim of this work is to determine whether the dynamic variability of the study area observed during the neotectonic period is coherent with a single regional stress field the structure of the area was analysed through the detailed mapping of the alhama de murcia fault amf and the associated structures further microtectonic data from shear veins in an interaction zone between the main and secondary faults were studied by the stress inversion method of reches tectonics 6 1987 849 a hierarchy is proposed for stress fields and their interpretation with respect to the interaction between structures of different scales relative movements of fault bounded blocks with different sizes produce this hierarchy these movements depend on boundary conditions of blocks and their position relative to the alhama fault zone the study shows that adequate cartography and understanding the context of micro and mesotectonic data is necessary for determining the dynamic significance of microtectonic data the use of stress inversion methods without taking the local tectonic context into consideration can give rise to incorrect interpretations incorrect processing of previous data and extrapolations inappropriate at other scales

coseismic vs climatic factors in the record of relative sea level changes an example from the last interglacials in se spain abstract trying to decipher how paleoseismic activity has influenced the altitudinal disposition of interglacial deposits is one of the main challenges to be confronted before quantifying relative sea level changes between consecutive highstands at the same time identifying paleoseismic features in an area with low instrumental seismic activity can complement the seismic record thereby contributing to better seismic hazard knowledge in this regard cope basin se spain meets all the requirements necessary for these kinds of analysis firstly on account of its excellent outcrop conditions and secondly because its sea level record is undoubtedly conditioned by both factors climatically driven changes and local and regional seismotectonics the morpho sedimentary sequence presented in this paper provides evidence from three different highstands two littoral sedimentary units separated by terrestrial deposits and affected by liquefaction paleoseismic activity and a younger paleo cliff and its associated wave cut platform carved into those sedimentary units this wave cut platform now tilted and folded reaches heights ranging from 0 to 8 m which has been interpreted as a consequence of cosesimic effect the age of this wave cut platform last interglacial or holocene supports uplift rate estimations of from 0 016 to 0 15 mm yr since the last interglacial holocene active deformation observed on pleistocene holocene sea level geomarkers can not only furnish useful information about seismic activity within the major structure of the aguilas arc but also offer new insight into the cope basin s geodynamic model

determination of the tectonic stress tensor from slip along faults that obey the coulomb yield condition a new method to calculate the stress tensor associated with slip along a population of faults is derived here the method incorporates two constraints first the stresses in the slip direction satisfy the coulomb yield criterion and second the slip occurs in the direction of maximum shear stress along the fault the computations provide the complete stress tensor normalized by the vertical stress and evaluation of the mean coefficient of friction and the mean cohesion of the faults during the time of faulting the present method is applied to three field cases dixie valley nevada wadi neqarot israel and yuli microearthquakes taiwan it is shown that the coefficieet of friction of the three cases varies between 0 1 to 0 8 further it is demonstrated that previous stress inversion methods implicitly assume zero friction along the faults

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

the landslide of cortes de pallas spain a large landslide in cretaceous limestone and marl formations reactivated by quarry excavations has been stabilized by weight transfer procedures designed by using a conventional limit equilibriu

the recent upper miocene to quaternary and present tectonic stress distributions in the iberian peninsula a general synthesis of the recent and present stress situation and evolution in the iberian peninsula was obtained from microstructural and seismological analysis the stress evolution was deduced from 1 fault population analysis fpa from 409 sites distributed throughout the iberian peninsula 2 paleostress indicators given by 324 stations taken from the bibliography and 3 seismic data corresponding to 161 focal mechanisms evenly spread in the studied region the application of fpa together with the determination of stress tensors and focal mechanisms for the whole iberian microplate has provided two main results 1 the iberian peninsula is undergoing a nw se oriented compression except for the northeastern part pyrenees ebro basin and iberian chain where it is n s to ne sw and the gulf of cadiz where it seems to be e w and 2 the main trends of the stress field have remained almost constant since the upper miocene the analysis performed by zones suggests the presence of local heterogeneities in the stress field

mode of extensional tectonics in the southeastern betics se spain implications for the tectonic evolution of the peri alboran orogenic system the gibraltar arc which closes the westernmost part of the mediterranean basin is a miocene a type subduction arc formed by the continental collision of various pre miocene terranes in the major zone of collision between the iberian and african cratons the hanging wall block known as the alboran domain has undergone more than 300 km migration from a more easterly position where it was the continuation of the alpine cretaceous paleogene orogen contemporaneous with thin skinned thrusting in the footwall the alboran domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a nnw sse system orthogonal to the belt axis in the late burdigalian langhian to a wsw directed orogen parallel one in the serravallian the superposition of these two systems resulted in a chocolate tablet megastructure this extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust nevertheless orogen parallel extension is more difficult to explain in this context we advocate that the wsw directed low angle normal faults formed during large scale extension in connection with important westward arc migration the driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model constraints on both the timing and the kinematics of extension as presented in this paper seem to support the contribution of both mechanisms convective removal may have started the process but continued n s convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination

dating phosphogenesis with strontium isotopes authigenic and replacement francolites in modern phosphorite have values of sup 87 sr sup 86 sr within error of that of modern marine sr 0 70916 plus minus 2 during the phosphatisation of carbonate sr is not inherited from the carbonate but is totally exchanged with sr in ambient water the sup 87 sr sup 86 sr in shallow marine pore waters is indistinguishable from the value for modern marine sr so authigenic francolite which precipitates from pore water accurately records the isotopic ratio of contemporary marine sr by comparing the sup 87 sr sup 86 sr in francolite with published curves for the isotopic evolution of tertiary marine sr we have dated phosphogenetic events affecting the chatham rise 4 90 plus minus 0 35 ma the nambian margin 1 15 plus minus 0 25 ma and 4 70 plus minus 0 35 ma and the sechura desert peru 11 8 plus minus 0 5 ma

constraints on the strength of the upper crust from stress inversion of fault slip data the coefficient of friction of small faults in the field are estimated here by stress inversion of fault slip data the small faults that were measured in israel and the grand canyon arizona are considered as representing natural friction experiments the stresses associated with the faulting are determined by a stress inversion method which incorporates the coulomb failure criterion reches 1987 the coefficients of friction determined for 27 fault clusters in limestone sandstone and basalt range from 0 0 to 1 3 with mean value of 0 58 0 37 these values are in general agreement with the friction of 0 6 0 85 determined from laboratory experiments the magnitudes of the calculated principal stresses are compared with in situ stress measurements in similar tectonic environments

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale