a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

processing correlating and interpreting converted shear waves from borehole data in southern alberta borehole measurements coupled with phase information from zoeppritz equation modeling has assisted in accurate correlation between a vsp converted s wave section and both the surface and vsp p wave sections from southern alberta for the most part both the character and polarities of the sections agree however there are some differences some reflections are stronger and more distinct on the s wave section than on the p wave section spectral analysis of the time domain upgoing p wave and s wave energy shows that the frequency content of the s waves is comparable to the p waves thus the slower velocity s waves have a shorter wavelenght and provide better vertical resolution of some interfaces other upgoing s wave modes can interfere with the p sv mode and contribute to the differences between the p and s wave sections the match between p wave and s wave velocities vp and vs determined from vsp traveltime inversion and the full waveform sonic log is best in the paleozoic carbonate section ther

reconstruction of reflecting structures from vertical seismic profiles with a moving source when a vertical seismic profile vsp is recorded the illuminated part of a reflector depends upon the shape and position of the reflector itself as well as on the seismic velocities and the positions of sources and receivers a preferable arrangement for the investigation of structures of reflectors is to fix the receiver s at constant depth s in the well and move the source horizontally along a line at the earth s surface usually called a multioffset vsp msp or walkaway vsp as a test of the resolution power of this survey geometry synthetic records were generated from a subsurface model by inverse kirchhoff migration three different methods were applied for the reconstruction wavefront construction leads to the correct shape of the reflectors thus assuring the validity of the modeling method applied reflection point mapping delivered a near similarity to the model but without focusing fault edges kirchhoff migration resulted in a detailed image of the reflectors with fault edges focuse

sediment dewatering and pore fluid migration along thrust faults in a foreland basin inferred from isotopic and elemental geochemical analyses eocene southern pyrenees spain abstract the lower eocene ainsa basin was formed during the first stages of the south pyrenean foreland basin evolution due to southwestward migration of imbricated thrust folds isotopic and elemental geochemistry of syn kinematic veins calcite and celestite and their marly host rock sampled in three thrust fault zones and one footwall syncline allows us to characterize the origin of pore fluids and the early stages of their evolution and circulation during the early deformation of the basin fill the isotopic composition of sulfur and the 87 sr 86 sr ratios of calcites and celestites from the veins in the footwall syncline show that the original fluid had the isotopic composition of eocene seawater the different 87 sr 86 sr ratio in veins from the thrust fault zones compared with the same ratio in the marly host rock of the footwall syncline indicates that the thrust fault zones acted as conduits for advective fluids the relatively high 87 sr 86 sr ratio in the veins related to the thrust fault zones indicates that the fluid originated from the interaction of seawater with an external fluid coming from deeper sources or from the meteoric weathering of the emerged part of the belt 18o and 13c values of calcites show that the isotopic composition of the calcite cements in veins was controlled by the isotopic composition of the marly host sediment depletion of both 18o and 13c with respect to eocene seawater composition together with elemental geochemistry of calcite cements in the veins points to burial transformations of a seawater derived fluid to a formation water composition the distribution of 18o and 13c values of the marly host rock and calcite cements in veins of the four outcrops probably resulted from differences in the meteoric water influences the hydrogeological regime at the toe of the submarine thrust system was dominated by tectonically induced dewatering of the foreland basin sediments the thrust fault zones were the channelizing paths for migration of fluids expelled from the surrounding sediments as well as fluids derived from more internal parts of the belt

stress field in the lithosphere caused by terrain topography and crustal density inhomogeneities abstract the methods and results of computing the two dimensional stress field along the zakopane salgotarjan international profile in central europe are given the loads arising from terrain topography and crustal density inhomogeneities were considered as the stress sources using a floating elastic plate model the horizontal stress which has magnitudes of about 70 mpa is shown to be the most important component

fault controlled sequential vein dilation competition between slip and precipitation rates in the austin chalk texas abstract multi layered calcite veins in a dilatant jog of a left stepping left slipping shallowly buried fault segment are composed of alternating millimeter to submillimeter thick calcite veinlets and host lithons forming a coarse crack seal texture the grain fabrics in calcite veinlets are mostly equant or irregular suggesting face controlled grain growth in a fluid filled cavity the relatively thick veinlets can be developed by progressive fault slip and veinlet opening simultaneously with calcite precipitation under low effective stress continuous changes in the oxygen isotopic compositions of the calcite veinlets along the length of veins suggest that the individual calcite veinlets were sequentially developed from the footwall to the hanging wall there is no particular evidence that these veins represent excursions in fluid pressure or instantaneous fracture opening related to episodic fault slip the fracture formation and filling cycle could have taken place along a continuously slipping fault contained within a porous rock with normal fluid pressure

gold quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting gold quartz vein fields in metamorphic terranes such as greenstone belts provide evidence for the involvement of large volumes of fluids during faulting and may be products of seismic processes near the base of the seismogenic regime in the val d or district of the abitibi greenstone belt canada quartz tourmaline carbonate veins form a vein field 30 15 km in the hanging wall of a crustal scale fault zone which was the main channelway for upward migration of the deeply generated fluids the veins occur in small high angle reverse faults and in adjacent horizontal extensional fractures extending up to 75 m in intact rocks they have formed incrementally during active reverse faulting in response to crustal shortening at depths corresponding to those at the base of the seismogenic zone in actively deforming crust detailed structural and fluid inclusion studies provide evidence for generally lithostatic but fluctuating fluid pressures p of the order of 200 mpa and for cyclic stress reversals during vein formation and provide good support for the fault valve model a comparison of vein characteristics with standard earthquake rupture parameters suggests that each slip increment along veins in reverse faults was accompanied by a small earthquake 4 m 3 or less the large vein field thus represents both the extent of fluid dispersion in the hanging wall of a crustal scale channelway and the distribution of small earthquakes integrated over the lifetime of the hydrothermal system it is proposed that such small earthquakes along veins in reverse faults are related to large earthquakes m 6 nucleating near the base of the seismogenic regime along the nearby crustal scale fault either as aftershocks or as a precursory smarm

crack seal mechanism in a limestone a factor of deformation in strike slip faulting abstract a repeated crack seal mechanism may play a major part in the deformation process in a shear zone this paper develops a microscopic approach to the association of shear planes and tension cracks between two en echelon faults the simultaneous development of these fractures yields a very specific pattern the structure discovered in a cretaceous limestone of the arc basin bouches du rhone france is located between two left stepping sinistral strike slip faults the horizontal displacement does not exceed a few centimeters therefore the structure may be representative of the early stage of deformation within a brittle shear zone each strain increment includes both shearing and tensile fracturing inhomogeneous conditions of friction seem to be prevailing

cleavage development within a foreland fold and thrust belt southern pyrenees spain abstract in the southern pyrenees lithologically distinct cleavage fronts are each parallel to bedding and dip 20 towards the foreland pressure solution was the dominant mechanism of cleavage development the mudstone cleavage front is coincident with the 195 c paleoisotherm and is associated with a pressure solution strain of 5 a mechanical twin strain of 4 and a deviatoric stress magnitude of 65 mpa illite crystallinity measurements define a geothermal gradient of 15 c km 1 and indicate that the paleoisotherms are bedding parallel deviatoric stress magnitudes from calcite twins were regionally constant at 65 mpa and principal stress axes were perpendicular to cleavage temperature was the primary control on deformation micromechanisms and the position and orientation of the cleavage front within the foreland thrust wedge deformation below the cleavage front occurs predominantly by pressure solution which in conjunction with mechanical twinning and microfracturing produces a quasi plastic rheology stress magnitudes determined from mechanical twinning of carbonate grains and long term 10 6 10 76 y strain rates determined for regional folds and faults suggest an apparent macroscopic viscosity of 9 8 10 18 to 7 2 10 19 pa s for the lower thrust wedge above the cleavage front temperature pressure solution strain total strain and mesoscale deformation diminish the region of the thrust wedge above the 100 c paleoisotherm is characterized by large brittle faults with cataclastic fault zones and negligible grain scale deformation indicating an elastico frictional rheology

thermochronology constraints for the propagation sequence of the south pyrenean basement thrust system france spain 1 in this work we combined apatite fission track and biotite k feldspar 40ar 39ar ages with tectonic data in the west central part of the axial zone of the pyrenees we discuss the exhumation ages and rates of the neouvielle bordere louron and bielsa variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the pyrenean orogenic prism the 40ar 39ar ages on k feldspars from the neouvielle massif sample nv7 seem to indicate tectonic movements on the eaux chaudes thrust during the early middle eocene fission track results suggest that the exhumation of the neouvielle massif occurred around 35 ma and exhumation of the bordere louron massif around 32 ma in relation to thrusting on the gavarnie thrust the bielsa massif was exhumed from around 19 ma by out of sequence movements on the bielsa thrust we thus show that whereas most of the pyrenean basement thrust faults here the eaux chaudes gavarnie and guarga thrusts were active in sequence toward the southern foreland from the early eocene to the earliest miocene some of them here the bielsa thrust were activated out of sequence in the hinterland later than the generally accepted aquitanian age for the end of the pyrenean compression finally the apatite fission track modeling indicate a last cooling episode starting around 5 ma which is most certainly related to the pliocene reexcavation of the southern and northern flanks of the pyrenees

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

synthetic fluid inclusions in natural quartz i compositional types synthesized and applications to experimental geochemistry synthetic fluid inclusions having a wide range of geologically applicable compositions in the c o h s na k ca cl cu fe system have been formed by healing fractures in inclusion free natural quartz and by precipitating new quartz overgrowths on an original seed crystal inclusion types synthesized include 1 1 liquid rich pure h2o inclusions of primary and secondary origin 2 2 pure h2o inclusions with the critical density 3 3 liquid rich inclusions containing undersaturated aqueous solutions of nacl or kcl or cacl2 or mixtures of the three salts 4 4 h2o nacl inclusions containing halite daughter minerals 5 5 h2o nacl kcl inclusions containing halite and sylvite daughter minerals 6 6 h2o co2 inclusions of various compositions containing liquid h2o and either co2 vapor or co2 liquid or both at 25 c 7 7 h2o co2 nacl inclusions containing an aqueous phase liquid and vapor co2 and halite at 25 c 8 8 c o h inclusions containing liquid h2o a co2 ch4 liquid phase and graphite daughter minerals at 25 c 9 9 h2o nacl inclusions that contain a chalcopyrite daughter mineral and 10 10 inclusions representing trapping of the coexisting immiscible fluids in the h2o nacl h2o co2 nacl and na c o h systems the inclusions exhibit uniform phase ratios at room temperature and the temperatures of various phase changes within individual inclusions agree with those predicted from experimental and theoretical data indicating that the inclusion fluid has the same composition and density as the parent solution these miniature autoclaves thus may be used to study various problems related to fluid inclusion research to calibrate analytical equipment used to study natural inclusions and to study phase equilibria solubility and pvt relations of a variety of chemical systems

rapid map and inversion of p sv waves multicomponent seismic recordings are currently being analyzed in an attempt to improve conventional p wave sections and to find and use rock properties associated with shear waves e g dohr 1985 danbom and dominico 1986 mode converted p sv waves hold a special interest for several reasons they are generated by conventional p wave sources and have only a one way travel path as a shear wave through the typically low velocity and attenuative near surface for a given frequency they will have a shorter wavelength than the original p wave and thus offer higher spatial resolution this has been observed in several vertical seismic profiling vsp cases e g geis et al 1990 however for surface seismic data converted waves are often found to be of lower frequency than p p waves e g eaton et al 1991

integrated lithospheric modeling combining thermal gravity and local isostasy analysis application to the ne spanish geotransect a two dimensional algorithm to determine the steady state thermal structure of the lithosphere that integrates thermal gravity and local isostasy analyses is presented gravity analyses together with seismic data are used to constrain spatial variations in density and crustal structure while absolute elevation is used to determine the lithospheric mantle thickness the calculation is performed using a finite element technique that links the different physical equations the program optionally calculates the temperature at any material boundary and with given rheological parameters the strength distribution and the total lithospheric strength in selected columns we apply the algorithm to the northeastern spanish geotransect which extends from the pyrenees to the balearic promontory and along which a strong variation in crustal and lithospheric thickness is evident we assess the use of two different inferred density models for the lithospheric mantle the first assumes a linear decrease in density with increasing temperature using the asthenospheric density as a reference the second model assumes a constant density for the whole lithospheric mantle although conceptually the two hypotheses differ substantially the results obtained do not show significant differences lithospheric thicknesses of 120 130 km below the pyrenees 60 65 km in the valencia trough and 65 75 km below the balearic promontory are deduced in all cases the mean lithospheric mantle density has to be 40 60 kg m 3 higher than the asthenospheric density the algorithm is shown to be a powerful tool in lithospheric thermal modeling especially in areas where surface heat flow is poorly constrained because of the temperature density elevation relationship

offset source vsp surveys and their image reconstruction zero offset source vsp surveys provide information about the subsurface only within the fresnel zone centered at the well offsetting the source location moves the reflection zones away from the well thus providing lateral cover conventional processing of this type of data gives rise to a distorted image of the subsurface using a simple ray tracing scheme this image may be reconstructed into the more familiar coordinate system of the surface seismic section this simple data independent mapping is based on the assumption of horizontal layering and requires a vertical velocity profile the technique of placing the source away from the borehole was first applied to the single offset source vsp survey however data from any survey geometry such as deviated well with rig source walkaway vsp etc can be mapped to the coordinate system defined by the appropriate seismic section to obtain the best results from this type of survey the target area must be defined and simple modeling techniques used to optimize the source location s these pre survey modeling methods may also be used to anticipate and hence avoid a number of problem areas which experience has highlighted the data from any vsp survey is the result of a realizable experiment and as such obeys the wave equation this implies that the wave equation may be used to migrate the data to its true subsurface location theoretically such a process is more secure than ray tracing techniques although its practice presents many difficulties

main results of the ecors pyrenees profile abstract the 250 km long deep seismic reflection survey across the pyrenees from one foreland ebro basin to the other aquitaine basin was designed to study the structure of the deformed mesozoic boundary between the iberian and european plates the results are 1 1 the entire crust shows well defined reflectors with a general fan shape geometry 2 2 a deep layered domain is evident above the moho discontinuity 3 3 near the surface in the external domains reflectors accurately define the geometry of major thrusts and structures affecting the mesozoic and cenozoic cover of the pyrenees 4 4 the middle crust shows two major sets of seismic events interpreted as hercynian structures using these results a balanced structural section of the pyrenean belt is proposed the mode of thickening of the crust during the alpine orogeny is briefly discussed only the iberian crust was significantly thickened by a southward stacking of slabs

attached or not attached evidence from crustal stress observations for a weak coupling of the vrancea slab in romania abstract the crustal stress pattern of romania provides key insights into whether the vrancea slab with its seismogenic volume between 70 and 175 km depth is still coupled to the crust and thus acts as a stress guide or whether it is already in a state of detachment from the crust knowledge of the state of the slab under vrancea is particularly critical because the slab attached to the crust can result in future strong earthquake occurrence in the crust and even in the currently aseismic zone between 40 km and 70 km depth potentially causing severe damage our analysis of the contemporary tectonic stress observations in the context of potential stress sources and the comparison with numerical modelling shows that the crustal stress pattern in romania is heterogeneous and does not contain a long wave length stress pattern that would be expected if there is a strong present day coupling between the subducted slab and the upper plate or if lateral plate boundary forces would control the regional stress pattern therefore we conclude that the crustal stress pattern of romania is characterised by small differential horizontal stresses where local stress sources third order effects are responsible for the observed heterogeneity of stress orientations and that the subducted slab under vrancea is only weakly coupled to the crust

rock lithology and porosity determination from shear and compressional wave velocity data examined in this study are previously published laboratory shear s and compressional p wave velocity measurements on water saturated sandstone calcareous sandstone dolomite and limestone cores as well as laboratory porosity measurements on the sandstone and limestone cores sandstone and limestone porosities range from 092 to 299 and from 006 to 229 respectively differential pressure was varied from 500 to 6000 psi corresponding to approximate burial depths from 290 to 3460 m respectively sandstone limestone and dolomite are effectively separated by poisson s ratio or equivalently by the ratio of p to s wave velocity separation of sandstone and limestone appears to result from the difference in of the matrix material namely quartz 056 and calcite 316 respectively an empirical function 1 v a b was fit by regression analysis to sandstone and limestone velocity vs and vp versus porosity values at each differential pressure in this equation a and b are const

full waveform processing and interpretation of kilohertz cross well seismic data high frequency cross well seismic data from the midale oil field of southeastern saskatchewan are analyzed for direct and reflected energy the goal of the analysis is to produce interpretable sections to assist in enhanced oil recovery activities co2 injection in this field direct arrivals are used for velocity information while reflected arrivals are processed into a reflection image raw field data show a complex assortment of wave types that includes direct compressional and shear waves and reflected shear waves a traveltime inversion technique layer stripping via ray tracing is used to obtain p and s wave interval velocities from the respective direct arrivals the velocities from the cross well inversion and the sonic log are in reasonable agreement the subsurface coverage of the cross well geometry is investigated it covers zones extending from the source well to the receiver well and includes regions above and below the source receiver depths upgoing and downgoing primary reflections

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

experimental investigation into the microstructural and mechanical evolution of phyllosilicate bearing fault rock under conditions favouring pressure solution abstract mature crustal fault zones are known to be zones of persistent weakness this weakness is believed to result from microstructural modifications during deformation such as grain size reduction and foliation development around the brittle ductile transition phyllosilicates are expected to have a significant effect on fault strength in particular under conditions favouring pressure solution to study such effects we performed rotary shear experiments on brine saturated halite kaolinite mixtures aimed at investigating the relation between microstructural and mechanical evolution in a system where pressure solution and cataclasis dominate the results show significant strain weakening and a transition with progressive strain towards more rate sensitive and less normal stress sensitive behaviour this was accompanied by a microstructural evolution from a purely cataclastic microstructure to a mylonitic microstructure consisting of elongate asymmetric clasts in a fine grained foliated matrix the results demonstrate that strain weakening and the development of a typical mylonitic microstructure can occur as a consequence of grain size reduction by cataclasis and a transition to pressure solution accommodated deformation even in the absence of dislocation creep the data raise questions regarding the reliability of microstructures as rheology indicators as well as on the use of low strain monomineralic flow laws for modelling crustal dynamics

thermochronology of a convergent orogen constraints on the timing of thrust faulting and subsequent exhumation of the maladeta pluton in the central pyrenean axial zone abstract the pyrenees mountains of spain and france are a collisional orogen cored by a south vergent antiformal stack of paleozoic basement thrust sheets the axial zone thrusting accommodated shortening due to convergence between iberia and europe granitic plutons intruded during the hercynian orogeny form an important component of the basement units thermochronology of granodioritic samples collected from a vertical age elevation profile from the south central maladeta pluton provide new constraints on the timing of thrust faulting and rock exhumation of the pyrenean orogen the maladeta massif lies within the orri thrust sheet presently occupying the immediate footwall of the gavarnie thrust a major axial zone alpine age thrust fault new biotite and k feldspar 40ar 39ar and apatite u th he ahe data combined with previous apatite fission track aft thermochronology and structural studies of the maladeta pluton constrain the thermal evolution of this massif biotite weighted mean plateau and k feldspar maximum 40ar 39ar ages from the highest elevations of the maladeta pluton 2850 m are 280 ma close to the age of intrusion and are interpreted to date the timing of rapid cooling in the hercynian subsequently the maladeta massif remained close to the surface as indicated by the presence of unconformable triassic continental sediments k feldspar 40ar 39ar multiple diffusion domain thermal models from two samples at lower elevations 1780 m and 1400 m indicate heating initiated at 65 ma reaching maximum temperatures of 270 to 280 c these data are interpreted to record thrust burial of the maladeta pluton to depths of 6 10 km in the footwall of the gavarnie thrust burial and heating were followed by a period of relatively rapid cooling beginning at 50 ma recorded in three k feldspar thermal models from samples at different elevations 2850 m 1780 m and 1400 m aft thermal models in conjunction with the aft and apatite ahe age elevation profile interpretation reveal a lower temperature portion of the thermal history these data indicate the onset of rapid cooling that began at 30 35 ma slowed dramatically at 25 30 ma and continued at a reduced rate until 15 ma finally aft thermal models from the lowest elevation samples record rapid cooling in the late miocene pliocene most likely due to re excavation of the southern flank of the pyrenean orogen following burial by syn tectonic conglomerates the integrated thermochronologic data set from the age elevation profile within the maladeta pluton illustrates the potential for obtaining age constraints related to processes operating within the interior portions of convergent orogenic systems e g the onset and or duration of thrust fault activity that are otherwise unobtainable

the origin of tectonic stress in the lithosphere abstract the sources of lithospheric stress and their distinctive features are briefly reviewed it is suggested that there are two main categories of lithospheric stress renewable stress which persists despite continuing stress relaxation and non renewable stress which can be dissipated by relief of the initial strain the two most important types of renewable stress arise from plate boundary forces and from isostatically compensated loads non renewable stress systems include bending stresses membrane stresses and thermal stresses an important phenomenon generating large stresses at shallow depth is stress amplification caused by lower lithospheric creep this applies to renewable stresses but not to the non renewable type it is suggested that only renewable stresses contribute significantly to tectonic activity however bending and thermal stresses are locally important in subducting lithosphere

seismic imaging of the shallow subsurface shear wave case histories obtaining high resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics the methods which are commonly used such as compressional wave surveys and ground penetrating radar often suffer from adverse effects caused by the near surface conditions changes in water saturation and various sources of noise this paper demonstrates some of the advantages offered by the use of shear wave seismology and by the combination of shear and compressional wave seismic methods in shallow subsurface investigations multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near surface geological conditions near surface conditions encountered at the sites included thick clays clay sand sequences overlying chalk mudstone overlying granodiorite bedrock and landfill material under all conditions shear wave data acquisition was found to have advantages over compressional wave acquisition for the investigation of the shallow subsurface shear head waves being unaffected by water saturation achieved penetration to greater depths at a site in crewkerne dorset where compressional head wave penetration was limited to the near surface layers better vertical resolution was achieved at shallow depths using shear wave reflection energy at a landfill site shear wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional wave reflections combinations of shear and compressional wave data recording allowed the measurement of a poisson s ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present

vertical seismic profiling separation of p and s waves in vertical seismic profile s vsp s shot with a large source offset rays from shot to receiver can have large angles of incidence shear waves generated by the source and by conversions at interfaces are likely to be recorded by both the vertical and the horizontal geophones varying angles of incidence may give strong variations in the recorded amplitudes separation of p and sv waves and recovery of their full amplitudes are important for proper processing and interpretation of the data a p s separation filter for three component offset vsp data is presented which performs this operation the separation filter is applied in the k f domain and needs an estimate of the p and s velocities along the borehole as input implementation and stability aspects of the filter are considered the filter was tested on an 1800 m offset vsp and appeared to be robust large velocity variations along the borehole could be handled and results were superior to those obtained by velocity filtering

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

thick plate flexure summary we derive analytical expressions for the displacements and stresses due to loading of a floating uniform elastic plate of arbitrary thickness by a plane or axisymmetric harmonic load the solution is exact except for assumptions of small strains and linear boundary conditions and gravitation within the plate is neglected for typical earth parameters its predictions are comparable to those of the usual thin plate theory frequently assumed in studies of lithospheric flexure gravity and regional isostasy even for a very thick lithosphere which may exist in some regions of mars the thin plate theory is a better approximation to the thick plate solution than the elastic half space limit except for short wavelength loads

oxygen isotope thermometry of quartz calcite veins unraveling the thermal tectonic history of the subgreenschist facies morcles nappe swiss alps combined structural analysis and oxygen isotope thermometry of syntectonic quartz calcite fibrous veins can be used to correlate the thermal history of deformed rocks with specific structural and tectonic events results are presented for the morcles nappe in the western helvetic alps switzerland where mineral parageneses illite crystallinity and fluid inclusion chemistry record an apparent peak metamorphic temperature gradient that increased across the morcles nappe from anchizonal conditions in the foreland to epizonal conditions in its hinterland root zone twenty seven quartz calcite veins were analyzed in this study in order to determine the temperatures of veining during formation and deformation of the nappe peak metamorphic temperatures ranged from 260 to 290 c in the shallower foreland localities and to 330 to 350 c in the deeper more hinterland localities at the end of s1 foliation formation related to large scale folding temperatures gradually decreased throughout the nappe during subsequent development of the s2 foliation and s3 crenulation cleavage uplift and erosion of the overlying nappe pile resulted in slow cooling of the morcles nappe during the waning stages of the alpine orogeny the dominant foliation forming deformation of the morcles nappe occurred at elevated temperatures over the course of 10 to 15 ma combined structure oxygen isotope analyses of quartz calcite veins yield better temperature and temporal constraints on the thermal histories of subgreenschist vein bearing tectonites than do other geothermometers

conditions during syntectonic vein formation in the footwall of the absaroka thrust fault idaho wyoming utah fold and thrust belt abstract the twin creek limestone in the footwall of the absaroka thrust sheet contains three sets of bed normal syntectonic calcite veins vein formation occurred during cretaceous motion along the absaroka thrust fault as indicated by 1 crosscutting relationships among these vein sets 2 a previously dated solution cleavage and 3 calcite twin analysis fluid inclusions in the veins and overburden estimates constrain inclusion entrapment temperatures to be between 175 c and 328 c results from stable oxygen isotopes indicate that the host and vein fluid compositions were in near isotopic equilibrium applying both reasonable geothermal gradients and constraints on overburden temperature yields fluid pressures during vein precipitation that are near hydrostatic all data taken together suggest both that vein formation within the twin creek formation occurred in a relatively closed system and that the veins filled near hydrostatic fluid pressure because the veins fill precursory cracks vein filling might not reflect the maximum fluid pressure that existed during the complete vein forming process

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

long lasting interactions between tectonic loading unroofing post rift thermal subsidence and sedimentary transfers along the western margin of the gulf of mexico some insights from integrated quantitative studies abstract after jurassic rifting numerous carbonate platforms i e the orizaba cordoba and golden lane tuxpan platforms developed during the lower and middle cretaceous episode of thermal subsidence along the western passive margin of the gulf of mexico with intervening basinal domains i e the tampico misantla zongolica veracruz and deep gulf of mexico dgm basins during the late cretaceous paleocene the east verging sierra madre oriental thrust belt developed resulting in tectonic uplift and unroofing of the allochthonous units i e tectonic units made up of former orizaba and cordoba platforms and zongolica basin series this new topography provided also an important source of clastics to feed the adjacent foredeep where coeval tectonic loading accounted for the bending of the foreland lithosphere however shallow water facies or even emersion persisted until the eocene in the forebulge area at the present location of the golden lane preventing locally the clastics to reach the dgm this topographic barrier was ultimately bypassed by the clastics only during the oligocene and neogene once 1 the prograding clastic wedge had exceeded accommodation and 2 the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink numerous paleo thermo meters tmax ro paleo thermo barometers fluid inclusions pvt and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the oligocene to plio quaternary clastic sedimentary wedge of the passive margin where gravitational gliding of post eocene series occurred during the neogene along major listric faults mantle dynamics are advocated as the main process accounting for post orogenic uplift and regional tilting of the basement which initiated a massive transfer of sediments from the cordillera towards the gulf of mexico from oligocene onward resulting in a destabilization and gravitational collapse of the western slope of the gulf of mexico in neogene times

shear veins observed within anisotropic fabric at high angles to the maximum compressive stress some faults seem to slip at unusually high angles 45 relative to the orientation of the greatest principal compressive stress1 2 3 4 5 this implies that these faults are extremely weak compared with the surrounding rock6 laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre existing frictionally weak surface7 8 9 weakening from chemical reactions10 elevated fluid pressure11 12 13 or dissolution precipitation creep14 15 here we describe shear veins within the chrystalls beach accretionary melange new zealand the melange is a highly sheared assemblage of relatively competent rock within a cleaved anisotropic mudstone matrix the orientation of the shear veins compared with the direction of hydrothermal extension veins that formed contemporaneously indicates that they were active at an angle of 80 5 to the greatest principal compressive stress we show that the shear veins developed incrementally along the cleavage planes of the matrix thus we suggest that episodic slip was facilitated by the anisotropic internal fabric in a fluid overpressured heterogeneous shear zone a similar mechanism may accommodate shear at high angles to the greatest principal compressive stress in a range of tectonic settings we therefore conclude that incremental slip along a pre existing planar fabric coupled to high fluid pressure and dissolution precipitation creep may explain active slip on severely misoriented faults

disentangling magnetic subfabrics and their link to deformation processes in cleaved sedimentary rocks from the internal sierras west central pyrenees spain abstract here we present a detailed study of the magnetic fabrics and subfabrics of remagnetized upper cretaceous limolites that crop out in the internal sierras west central pyrenees affected by a penetrative pressure solution cleavage the bulk magnetic fabrics of these rocks rt ams show variable orientations that do not conform to what is typically reported for cleaved sedimentary rocks in contrast the paramagnetic subfabrics lt ams show remarkably constant directional properties so that their k max and k min axes cluster parallel to the intersection lineation and to the poles to bedding respectively these lt ams subfabrics indicate a preferred orientation of phyllosillicates that is consistent with a syn sedimentary late cretaceous period of nne oriented layer parallel shortening noticeably these phyllosillicate subfabrics are not further altered by the subsequent formation of cleavage in the late eocene early oligocene the ferrimagnetic subfabrics aarm also show remarkably constant orientation so that their k max axes are strikingly parallel to the shortening direction in the area we interpret this preferred orientation of ferrimagnetic grains as being caused by subhorizontal shear associated to cleavage formation which is consistent with the age and mechanisms authigenic growth and rotation of pre existing magnetite grains proposed for the pervasive remagnetization that affects the studied rocks

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

syn diagenetic evolution of shear structures in superficial nappes an example from the northern apennines nw italy abstract in the superficial nappes of the northern apennines meso and microstructures in sheared mudstones and fine grained turbidites consist mainly of networks of striated faults and calcite vein arrays the striated faults correspond to the first generation of structures they form two sets respectively synthetic and antithetic to the general shearing locally a sigmoidal microfabric is associated with the synthetic faults in scaly deformation bands up to a few metres thick late laterally extensive calcite veins are superposed on these structures they result from the opening of multiple releasing oversteps between shear surfaces the crack seal mechanism of deformation played a major role in their formation structures of the first generation result from heterogeneous ductile deformation of initially poorly lithified and water rich sediments the late formation of the calcite veins corresponds to a transitional ductile brittle behaviour in sufficiently lithified sediment evolution of structures probably depended on a strain hardening process and was dependent on the progressive compaction and dewatering of the sediment the gently dipping faults and veins probably formed the main pathway for the interstitial fluids possibly overpressured expelled from the sediment we emphasize that the geometry of the structures described provides important shear sense criteria for the study of superficial nappe tectonics

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

quantification of fabrics in clay gouge from the carboneras fault spain and implications for fault behavior abstract clays in fault rocks have the potential to control fault behavior the formation of frictionally weak clays in fault rocks can lead to fault zone weakening and the development of fabrics through authigenesis and mechanical rotation in clay rich fault rocks can influence fault zone permeability structures the left lateral carboneras fault of southwestern spain is a ca 1 km wide fault zone with anastomosing layers of clay rich gouge up to 50 m thick the gouge derived largely from mica schist is composed of neoformed illite and chlorite anisotropy of magnetic susceptibility 201 measurements and x ray pole figures 144 measurements show comparable oblate clay fabrics with the axis of maximum anisotropy sub parallel to strike this dimensional fabric contrasts with previously published maximum permeability results that are sub vertical this observation coupled with the generally poor clay fabric measured in the samples indicates that the orientation of clays is not likely to be the primary control of the permeability anisotropy of clay rich fault gouge becoming important only when gouge zones are 10s of meters thick which is very unusual even in a fault zone like that of the carboneras fault with thick very clay rich gouge zones with a visible foliations and slip surfaces the degree of clay preferred orientation is low above the millimeter scale showing that any strong clay fabric associated with the foliation are extremely localized phenomena this suggests that processes operating below the millimeter scale may significantly influence fault behavior a result compatible with earlier characterizations of faults in a variety of geologic settings highlighting the importance of understanding how the formation and fabric of fault related authigenic clays influence fault behavior

downhole seismic imaging of a massive sulfide orebody with mode converted waves halfmile lake new brunswick canada multioffset multiazimuth downhole seismic data were acquired at halfmile lake new brunswick to image known massive sulfide lenses and to investigate the potential existence of a steeply dipping mineralized zone connecting them the massive sulfide lenses which have significantly higher elastic impedances than host rocks produce strong scattering the downhole seismic data show prominent scattered p p and s s and modeconverted p s and s p waves originating from the deposit such complex scattering from massive sulfide ore was not observed previously in vertical seismic profiling data migration of the scattered and mode converted waves from several shot points imaged different parts of the deepest lens the scattered s waves and modeconverted waves provide additional imaging capabilities that should be considered when selecting downhole seismic methods for mining exploration

fluid pressure and salinity variations in shear zone related veins central pyrenees france implications for the fault valve model abstract fluid inclusion microthermometry data is presented from quartz veins associated with high angle reverse shear zones cutting the neouvielle massif in the central french pyrenees a complex series of veins were formed during both normal and reverse movement on brittle faults within the shear zone brittle structures developed contemporaneously with quasi plastic deformation in the shear zones fluid inclusion data are presented from a variety of vein types and shows that a wide variation in fluid density and salinity is present in the fault system these variations occur both within individual veins and between different vein types temperatures at the time of vein filling are constrained to be in the range 310 360 c by chlorite microthermometry the variation in homogenisation temperature is too large to be accounted for by variations in the fluid temperature and is interpreted to reflect variations in fluid pressure between lithostatic 500 mpa and hydrostatic 200 mpa values at the time of quartz growth in the veins the shear zones carry modest displacements and may not themselves have been seismogenic a model is presented in which fluid pressure variations and stress cycling within the steeply dipping shear zones is controlled by the seismogenic cycle on large underlying thrust structures the model predicts that the highest maximum trapping pressures should occur in fluid inclusions from low angle veins formed in a high pfluid compressional regime immediately before earthquake rupture lower maximum pressures are expected in steep veins related to extension and normal fault movement across the shear zones immediately after rupture the fluid inclusion data support this model when maximum trapping pressures are considered but the majority of inclusions in all vein types formed at pressures well below lithostatic values this suggests that the dominant factor causing quartz precipitation was the sudden pressure drop immediately after earthquake rupture regardless of vein type

a plane wave decomposition for elastic wave fields applied to the separation of p waves and s waves in vector seismic data we describe a method to decompose a two dimensional 2 d elastic wave field recorded along a line into its longitudinal and transverse parts that is into compressional p waves and shear s waves separation of the data into p waves and s waves is useful when analyzing vector seismic measurements along surface lines or in boreholes the method described is based on a plane wave expansion for elastic wave fields and is illustrated with a synthetic example of an offset vertical seismic profile vsp in a layered elastic medium

the use of a combined structural stable isotope and fluid inclusion study to constrain the kinematic history at the northern variscan front zone bettrechies northern france abstract a detailed structural stable isotope and fluid inclusion study of distinct vein generations has been performed in a kilometre scale syncline to correlate the temperature pressure conditions of vein formation with specific deformation episodes the structural relationship of the veins with cleavage folds faults and with one another allows the identification of pre syn and post variscan carbonate vein generations the stable isotope composition of the vein calcites and dolomites is very similar to that of the surrounding limestones and dolostones respectively this indicates that the cements were precipitated from fluids buffered by the host rock and implies that the temperature pressure characteristics of the fluids reflect the thermal history of the deformation history within the syncline microthermometric data of primary fluid inclusions were used to estimate the temperature pressure conditions at precipitation time and thus of the deformation pressure corrected trapping temperatures for the veins show a temperature evolution from pre variscan 310 c to variscan 260 200 c and post variscan 75 c this evolution indicates that the syncline developed not at a specific depth but rather as an active progressive deformation process during transport along the northern variscan thrust front

kinematics and strain distribution in an orogen scale shear zone insights from structural analyses and magnetic fabrics in the gavarnie thrust pyrenees abstract this work aims to characterize the gavarnie thrust one of the large scale thrusts that define the alpine structure of the west central sector of the pyrenees a detailed comparison of structural analysis and magnetic fabrics is carried out for the paleozoic phyllonites of the gavarnie thrust in order to decipher strain distribution and transport direction the ams at room rt ams and low lt ams temperature and the airm can be correlated with the structural patterns kmin axes are mainly parallel to the pole of the s c or c planes and kmax axes are parallel to the transport direction and related to ductile s c structures furthermore the pj t changes across the shear zone characterize strain variations larger pj and t are found in the basal most deformed part of the shear zone and lower values are found where the interaction between alpine and variscan related petrofabrics is stronger we also interpret the reactivation of variscan inherited fabrics within the alpine shear zone in spite of the heterogeneous strain markers indicate a common top to the south n190e alpine transport direction which contrasts with the strong obliquity of the genetically related structures developed in the southern mesozoic sedimentary cover in this sense our data suggest a complete decoupling between basement and cover units during the alpine compression

crustal stress in the northern north sea as inferred from borehole breakouts and earthquake focal mechanisms the regional stress field in the northern north sea offshore western norway has been studied through the acquisition and analysis of directions of maximum horizontal compression sh as extracted from borehole breakouts and from earthquake focal mechanism solutions the results indicate that the regional stress field is dominated by nw se compression with good consistency between shallow borehole breakouts 2 5 km depth and deeper earthquakes 10 25 km depth the broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin and the results are in good agreement with the western europe trend found in earlier investigations the tampen spur region in the northern north sea has been subjected to particularly complex deformation with two dominating fault directions trending nw se and ne sw from tampen spur in the west to the sogn graben in the east an anomalous stress field is indicated with ne sw oriented maximum horizontal compressions this anomaly is clearly seen both in the borehole breakout data and in the earthquake data possible sources for this anomaly are discussed and include postglacial uplift and or lateral variations in the physical properties of the crust

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

converted wave seismic exploration methods multicomponent seismic recording measurement with vertical and horizontal component geophones and possibly a hydrophone or microphone captures the seismic wavefield more completely than conventional single element techniques in the last several years multicomponent surveying has developed rapidly allowing creation of converted wave or p s images these make use of downgoing p waves that convert on reflection at their deepest point of penetration to upcoming s waves survey design for acquiring p s data is similar to that for p waves but must take into account subsurface vp vs values and the asymmetric p s ray path p s surveys use conventional sources but require several times more recording channels per receiving location some special processes for p s analysis include anisotropic rotations s wave receiver statics asymmetric and anisotropic binning nonhyperbolic velocity analysis and nmo correction p s to p p time transformation p s dip moveout prestack migration with two velocities and wa

stress and fluid control on decollement within competent limestone abstract the larra thrust of the pyrenees is a bedding parallel decollement located within a competent limestone unit it forms the floor of a thrust system of hectometric scale imbrications developed beneath a synorogenic basin the fault rock at the decollement is a dense stack of mainly bedding parallel calcite veins with variable internal deformation by twinning and recrystallization veins developed as extension fractures parallel to a horizontal maximum compressive stress cemented by cavity type crystals conditions during vein formation are interpreted in terms of a compressional model where crack arrays develop at applied stresses approaching the shear strength of the rock and at fluid pressures equal to or less than the overburden pressure the cracks developed in response to high differential stress which was channelled in the strong limestone and high fluid pressure in or below the thrust plane ductile deformation although conspicuous cannot account for the kilometric displacement of the thrust which was mostly accommodated by slip on water sills constituted by open cracks a model of cyclic differential brittle contraction stress reorientation slip and ductile relaxation at a rheological step in the limestone is proposed as a mechanism for episodic decollement movement the model accounts for the peculiar microstructural character of the fault zone for alternating sequences of bedding parallel shortening leading to crack dilation and bedding parallel shear leading to decollement slip and for hanging wall imbrication consequent upon decollement slip

episodic discrete and distributed deformation consequences and controls in a thrust culmination from the central pyrenees abstract the pic de port vieux culmination is a 0 5 km long thrust culmination in the footwall of the gavarnie thrust in the central pyrenees the culmination comprises a set of blind thrusts that imbricate a 50 m thick mesozoic cover sequence comprising triassic red beds and upper cretaceous limestone sandwiched between underlying hercynian basement and the overlying palaeozoic strata of the gavarnie thrust sheet an intense cleavage developed within the culmination associated with the oblique tip lines of the thrusts as they climbed from the basement into the cover strata detailed mapping shows that the distributed strain associated with the fault tips locally re activated earlier folded thrusts creating upper detachments to the system and produced a set of new overstepping isolated faults the main detachment occurred along the roof of the culmination using the back limbs of folds in the roof thrust the movement on these detachments can be demonstrated to have been episodic with periods of fault slip producing splays that were then folded during periods when distributed deformation was dominant the main control on this episodic deformation is modelled as the result of feedback between increase in fluid pressure associated with inelastic porosity reduction during cleavage development and fluid pressure bleed off associated with fault zone dilatancy in the culmination

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget