analysis of a gradual change in stress regime example from the eastern iberian chain spain abstract the compression extension passage in the eastern iberian chain during the miocene is analyzed structural data suggest that it is a gradual change in stress regime which does not involve rotation but interchange of 1 and 2 axes one of them remaining always vertical the gradual stress evolution is interpreted by a numerical graphic method y r diagram which optimizes combinations of y azimuth of the maximum horizontal axis and r stress ratio explaining groups of fault movements the y r diagrams of some fault populations measured in the castellon region provide optimum tensors appearing within a continuous cloud of solutions from the compressional field to the extensional one movement sequences obtained from superimposed striations indicate a systematic stress change between these two regimes

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

biogenic origin of intergrown mo sulphide and carbonaceous matter in lower cambrian black shales zunyi formation southern china abstract the lower cambrian zunyi formation in southern china hosts complex intergrown phases of mo sulphides and anthracite like carbonaceous matter and graphite mosc pyrite and ni sulphides these sulphides occur in a few centimeters thick polymetallic stratiform layer in black shales above phosphorites cherts dolomites and barite the ore horizon contains 7 wt mo 2 wt ni 19 wt s and 13 wt c org and c tot co 2 58 wt 14 wt cao 1 2 wt as 2000 ppm se 5400 ppm zn 450 ppm u and v and up to 1 ppm platinum group elements three types of mosc phases always including framboidal pyrite are distinguished 1 rounded structures few hundred microns large 2 relict inclusions in diagenetic pyrite 3 grains interstitial to sulphurised and phosphatised organic matter at the nanoscale mosc is represented by nanometric porous rounded structures of mos 2 finely intergrown with carbonaceous matter of typical nano onion structures mosc also contains nanocrysts of quartz clays ca sulphate carbonate and ni sulphides micro raman spectroscopy shows that the carbon phase has a maturation grade of anthracite indicating temperatures below 300 c mosc is mainly composed of 25 wt mo 23 wt s 5 6 wt fe 2 5 wt ni 33 wt c 1 5 wt o 0 6 wt n and several hundreds of ppm of cu as se sb pd zn co and sn electron energy loss spectra show that n is related to nanosized carbonaceous matter the mean c n ratio 57 of mosc is similar to those observed in marine organic matter and those reported from zooplankton at hydrothermal vents the mineralized shales are crosscut by hydrothermal veins composed of carbonate or barite always associated with quartz apatite and fe and zn sulphides a paragenesis also observed as nanocrysts in mosc although mo originated from seawater its extreme concentration is due to an enhanced growth of bacterial consortia in a diffuse hydrothermal vent system these consortia may be dominated by nitrogen fixing and mo dependant hyperthermophilic or mesophilic species containing nitrogenase composed also of mo s fe organic matter decay led thus to the formation of mosc and the included framboidal pyrite

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

paleostress inversion a multi parametric geomechanical evaluation of the wallace bott assumptions wallace 1951 and bott 1959 were the first to introduce the idea that the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface however this simplified hypothesis is questionable since fault mechanical interactions may induce slip reorientations earlier numerical geomechanical models confirmed that the slickenlines slip vectors are not necessarily parallel to the maximum resolved shear stress but are consistent with local stress perturbations this leads us to ask as to what extent the wallace and bott simplifications are reliable as a basis hypothesis for stress inversion from fault slip data here a geomechanical multi parametric study using a 3d boundary element method covering i fault geometries such as intersected faults or corrugated fault surfaces ii the full range of andersonian state of stress iii fault friction iv fault fluid pressure v half space effect and vi rock properties is performed in order to understand the effect of each parameter on the misfit angle between geomechanical slip vectors and the resolved shear stresses it is shown that significant misfit angles can be found under specific configurations invalidating the wallace and bott assumptions even though fault friction tends to minimize the misfit we therefore conclude that in such cases stress inversions based on fault slip data should be interpreted with care

forty years of paleostress analysis has it attained maturity abstract powerful methods of paleostress analysis from fault slip data have been used since the 1970 s and have demonstrated their capacity for reconstructing stress fields with tectonic significance however in some cases these methods have been applied to samples that do not fulfill basic requirements or developed on the basis of unsound conceptual models most methods of fault slip are based on the wallace bott principle dynamic paradigm while others invoke the necessity of remaining within the alternative kinematic paradigm therefore inferring only finite strain or strain rate axes the scientific community shares neither standard procedures for applying these methods nor standard parameters for assessing the quality of results this indicates that paleostress analysis has not attained maturity it is necessary to see back to the conceptual and methological bases following accurate procedures of data collection using additional field observations and critically assessing the results within the tectonic setting spatial and temporal heterogeneity of stress fields over all scales makes the mean stress tensor obtained from site analysis just an abstract notion though indispensable for understanding lithosphere dynamics

structural analysis of faults related to a heterogeneous stress history reconstruction of a dismembered gold deposit stawell western lachlan fold belt australia in the internationally significant victorian goldfields a complex system of faults dismembers the 5 million ounce magdala gold deposit these faults represent a combination of neoformed faults and inherited faults that reflect deformation associated with stress tensors of variable orientation and stress shape ratio the fault geometry is strongly controlled by the pre existing rheology faults have propagated around the flanks of an antiformal basalt dome along earlier ductile cleavages and the margins of porphyry dykes many of the faults do not have andersonian geometries and there is no correlation between the orientation of the faults and the palaeostress directions much of the faulting is associated with the emplacement of porphyry dykes additional gold mineralisation related to plutonism and late stage deformation post dating the intrusion of the stawell pluton systematic mapping of extension veins associated with faults striations and conjugate joint sets allowed the construction of a revised and more robust history of brittle deformation this successfully predicted the offset direction of the currently mined magdala ore body beneath the studied system of faults the use of extension veins was a critical aspect of the analysis if striations on the fault surfaces had solely been used the offset direction of the new golden gift orebody would not have been correctly ascertained the palaeostress history was delineated via use of compression and tension dihedra stress inversion of slip data and calculation of theoretical resolved shear stress for faults with orientations similar to those mapped the calculation of theoretical resolved shear stress directions highlights the importance that the intermediate stress has on the slip direction for faults whose pole does not lie in the plane containing 1 and 3

a stress inversion procedure for polyphase fault slip data sets palaeostress estimation from striated fault data is frequently frustrated by the fact that natural fault data are heterogeneous in the sense that they cannot satisfactorily be explained by reactivation brought about by a single stress tensor in many instances there is clear evidence to show that striation data can record the effects of multiple stress events any attempt to find the tensor which best fits or explains such dynamically mixed data sets risks determining a spurious stress state which is some form of compromise between the real stress states corresponding to different tectonic phases to avoid this problem a strategy is proposed here which involves an initial separation of the raw data into coherent sub sets prior to formal stress inversion this separation is performed by assigning attributes to each fault which describe the fault s compatibility with trial stress tensors using these attributes faults can be grouped into dynamically homogeneous families using the statistical techniques of cluster analysis

interaction between perpendicularly trending thrust wedges and its impact on foreland deformation insights from analogue modelling abstract in this work we used analogue models in order to better understand how two orthogonal fold and thrust belts may interact in the foreland and influence the geometry and kinematics of the resulting structures our experimental device has two vertical mobile backstops oriented perpendicular with respect to each other independent and moving coevally with variable or equal velocities there are strong contrasts between our models results and thrust wedges generated using a unique indenter and simple convergence thrust wedge deformation in front of two perpendicular indenters overlying a basal viscous decollement progressed following two major stages i independent growth of each tectonic wedges then ii formation of major oblique and continuous structures that nucleated in the foreland of both indenters in some models the two indenters moving at different velocities favoured the interference and superimposition of structures strain partitioning structure curvature and vertical axis rotation comparison with the friulian venetian basin southern alps and the altomira loranca thrust belt iberian chain central spain supports the hypothesis that foreland deformation can strongly vary if a basal viscous decollement is present during the interaction of two mutually indenters

morphostructural analysis and cenozoic evolution of elephant island southern scotia arc antarctica elephant island located in the vicinity of the present day active boundary of the south shetland block and the antarctic and scotia plates is a region of particular interest for understanding the past and present geodynamic evolution of the southern scotia arc lineament from different data sources field measured fractures and geomorphological evidences have been analysed in this context the lineaments extracted from aerial photographs 1 624 from a dem 348 and from radarsat 2 satellite data 1 365 indicate four dominant lineament sets with ne sw nw se n s and w e strikes all data sources identified similar lineament families but differences in the frequency distributions and subsequently on the dominant orientations were observed the measurements direct of fractures were obtained from 23 sites in the field at which 278 planes were measured fracture planes indicate main modes trending in the nne ssw and nnw sse directions and a secondary mode in the e w the major trends of the fracture measurements and the lineaments display a good correlation in the e w direction however there is an angular variation in the azimuth values of the nne sse and nnw sse fractures with respect to the n s ne sw and nw se orientations of the lineaments of approximately 20 this trend deviation may be due to the fact that mapped lineaments are composed of small fracture sets that may be related to shear fractures that cannot be distinguished at the aerial photograph or radar satellite data scales submerged sea floor morphological feature orientations match the studied morphostructures on the island and the main tectonic structures in this part of the scotia arc a linkage of the main lineament families to the tectonic stages from the oligocene to the present has been proposed taking into account the information of the orientation and sense of movement of the fractures and stresses in the elephant island region

analysis of solution lineations in pebbles kinematical vs dynamical approaches abstract solution lineations in conglomerates resulting from indentation of non soluble grains of the matrix into the surface of soluble pebbles make up a morphological and genetic continuum with gradual transition between orthogonal stylolites oblique slickolites and parallel striations the distributions of incidence angles of matrix grains have been analyzed in individual pebbles in order to discern their kinematical or dynamical meaning as a general rule they fit theoretical models of flow trajectories determined by the bulk strain kinematical hypothesis in contrast they are not consistent with dynamical hypotheses based upon relationships with stress vectors in particular they do not fit the model of frictional sliding which would give rise to a sharp discontinuity between slickolites parallel to the maximum principal stress 1 and true striations parallel to the resolved shear stress therefore solution lineations all around a pebble cannot be considered as an analogue of multiple fault slip data and they should not be generally analysed by methods of stress inversion based upon bott s principle under certain conditions high pebble solubility active pressure solution processes able to accommodate the strain rate earlier cementation the solution lineations tend to be parallel to each other and to the maximum shortening compression axis they therefore assume a double kinematical and dynanical meaning and the deformation involves maximum volume reduction

a geometric test for possible andersonian stress using striated faults a graphical compilation of the rake guides of fault striations of known sense facilitates a simple test for their compatibility with andersonian stress conditions a compilation of negative double strike angles on tracing paper is superimposed on the rake guide plot if the two register the candidate generating stress is given by the relative position and orientation of the two plots

the inverse problem in microtectonics and the separation of tectonic phases abstract the algorithm of inverse problems is applied to three cases in microtectonics a collection of striations measured on pre existing faults may be processed automatically and interpreted in terms of tectonic stress a comparison is made between two different methods formerly proposed by the authors both methods are tested with field data the theoretical results agree with independent field criteria for a separation of tectonic phases

understanding the mesozoic kinematic evolution in the cameros basin iberian range ne spain from magnetic subfabrics and mesostructures abstract analysis of anisotropy of magnetic susceptibility ams and brittle mesostructures hydroplastic synsedimentary faults and tension gashes is applied in this study in order to characterize the mesozoic tectonic events in the cameros basin nw iberian range formed between tithonian and albian times low field ams at room and low temperature lf ams at rt and lf ams at lt respectively together with high field ams hf ams measurements allow separating ferro and paramagnetic fabrics the combination of lf ams at lt and hf ams torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the ams magnetic fabric results combined with the analyses of synsedimentary faults indicate a nw se extension direction during aptian and probably barremian times this extension direction is perpendicular to the main extension direction ne sw prevailing during early and late stages of basin evolution it is also consistent with extension direction deduced from large scale bending folds and tension gashes developed after partial lithification cleavage development during albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression

palaeogene evolution of deformation in the northeastern iberian peninsula during the palaeogene alpine compression three units were differentiated in the studied area south of the ebro basin the catalan coastal range dominated by ne sw major basement faults with a sinistral movement the iberian range where the important basement faults have a nw se direction and a reverse movement often with a dextral component the linking zone between these two ranges where an e w dominant structural direction is marked by an array of folds and thrusts with a northward vergence in the mesozoic cover from the analysis of both these major structures and the small scale structures it can be deduced that the compression in the studied area has evolved from a nw se direction lower middle eocene to a n s direction and to a ne sw one uppermost oligocene the major structures are due to the n s compression later the stress field progressively changed to a distensive regime we suggest a relation between the compressive phases and the displacement direction of the iberian plate with reference to the european plate

stress field and thrust kinematics a model for the tectonic inversion of the cameros massif spain abstract alpine tectonics of the cameros thrust has been studied from several points of view geometry surface and sub surface structure three dimensional outline of the thrust kinematics transport direction and dynamics characterization of the regional compressional stress field all three aspects are related by means of a model based on bott s equation under a n to nne horizontal compression with an average stress ratio r z x y x 0 2 the eastern ramp of the cameros thrust oriented 155 30 w underwent a strike slip right lateral movement with a small reverse component this gave rise to rigid displacement of the cameros block towards the nnw and produced a guided movement on the western frontal ramp oriented 060 13 s

deflection of a compressional stress field by large scale basement faults a case study from the tertiary almazan basin spain abstract palaeostresses deduced from brittle mesostructures more than 50 sites and 1500 structures measured in the mesozoic and tertiary rocks of the almazan basin located in the northwestern iberian chain indicate a regional nne sse directed compression that lasted during all the tertiary shortening stage the stress regime corresponding to this compression ranges from thrust to wrench n s directed compression was the responsible for most macrostructures folds and thrusts forming a s vergent system with ne sw to e w and nw se orientations and mesostructures mainly faults stylolytes and impressed pebbles we propose that the stress trajectories are deflected following anderson s model in the western part of the almazan basin by the ne sw striking left lateral strike slip soria fault this basement fault was inherited from the late variscan fracturing stage and controlled the deposition in the mesozoic basins as well as the location of tertiary compressional macrostructures in the eastern border of the almazan basin palaeostress trajectories were deflected both by right lateral strike slip faults and nw se trending thrusts near which the regional n s directed compression becomes perpendicular to them three minor compression directions have also been recorded in several sites ne sw e w and nw se the ne sw directed compression is interpreted as a deviation of the main n s directed compression at a regional scale whereas the nw se directed stress field corresponds to the regional field responsible for the main tertiary shortening stage in the spanish central system the age of compression ranges from eocene to miocene

carbonate cemented stylolites and fractures in the upper jurassic limestones of the eastern iberian range spain a record of palaeofluids composition and thermal history abstract dolomite and calcite cements fill open stylolites fractures and pipe shaped structures related to faulting in tithonian berriasian limestones of the maestrat basin in the iberian range spain due to the grater susceptibility of the dolomitised limestones to brittle fracturing during the alpine tectonism their location and distribution may have important implications for hydrocarbon prospectively within the studied region iberian range three generations of structures were recognised open stylolites extensional fractures and faults based on field observations cross cutting relationships and cement mineralogy petrographic cathodoluminesence and geochemical analyses electron microprobe fluid inclusion oxygen carbon and strontium isotopes of the carbonates helped unravel the origin and evolution of the fluids from which these carbonates have been precipitated these cements occur in the following structures a the first generation nne trending fractures formed during the late eocene miocene compressional stage were filled by calcite cement 18 o vpdb 8 8 and 13 c vpdb 0 8 b the second generation represented by subvertical extensional fractures and the third generation by pipe shaped structures which are considered to be formed during the miocene pliocene extensional stage contain four carbonate cement phases 1 isolated rhombic dolomites 2 saddle dolomite with fluid inclusions characterised by high salinity 21 5 to 23 5 wt eq nacl radiogenic sr enriched 0 70796 to 0 70857 in relation to the marine standard high temperatures t h 110 155 c and low 18 o values vpdb 11 5 to 11 3 3 calcitized saddle and rhombic dolomite with variable 18 o vpdb 12 2 to 6 8 and 13 c vpdb 4 4 to 0 2 and 4 two phases of calcite cements with moderate to high temperatures t h 110 125 c 15 to 19 7 wt eq nacl and 160 198 c 5 5 to 9 5 wt eq nacl low 18 o vpdb values 13 4 to 10 and positive carbon values 13 c vpdb 0 1 to 1 8 the diagenetic fluid is interpreted to be initially hot saline hydrothermal temperature higher than the estimate of the ambient temperature and sr enriched 0 70800 the dolomitisation event was followed by an input of meteoric water which was related to the extensional stage finally late calcite cement precipitated from fluids which had initially moderate salinity and moderate to high temperature and later evolved to a lower temperature and higher salinity fluid both sr enriched these fluids were probably derived from the progressive mixing of late triassic evaporitic brines with descending meteoric water that migrated via fractures during the miocene pliocene alpine extensional stage major vug filling calcite cement is probably late in timing and related to hydrothermal karst associated with the pipe shaped structure c bed parallel stylolites and subvertical extensional fractures containing idiomorphic quartz crystals for which make it difficult to deduce the timing of its precipitation idiomorphic quartz has homogenisation temperatures of 140 180 c and salinities of 13 6 wt eq nacl the high homogenisation temperature of this quartz and its association with dickite suggest precipitation from hydrothermal fluid

late cenozoic stress field and fracturing in the iberian chain and ebro basin spain detailed study of mesoscopic faults and joints affecting neogene and pleistocene deposits in the iberian chain and the ebro basin involving statistical study of fracture directions and palaeostress analysis from striated fault planes together with analysis of macrostructures suggest a complex late cenozoic stress field in which both primary and secondary stress systems are superposed 1 regional n s compression was caused by convergence between the iberian and african plates 2 multidirectional extension was caused by crustal doming in the iberian chain 3 stress trajectories were deflected near major faults 4 small scale swapping of the horizontal tension axes 2 and 3 was caused by development of fractures at right angles to either the primary or the deflected 3 axis

superposed buckle folding in the eastern iberian chain spain abstract the aliaga area eastern iberian chain shows large scale examples of buckle superposition developed during tertiary folding in most cases ene trending folds overprint earlier nnw sse trending ones the resulting structures are mapped analysed and genetically classified by comparison with analogue models described by several authors the following types are found standard type 1 1a dome and basin structure 1b unequal wavelength overprinted folds modified type 1 1c t shaped joined folds 1d t shaped abutting folds 1e l shaped folds 1f snake like folds standard type 2 2a non cylindrical buckling of earlier axial surfaces involving hinge replacement different superposed sets of flexural slip striations record successive folding episodes in snake like folds and hinge replacement in the case of type 2a superpositions types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90 respectively which fits the results of analogue modelling and theoretical analysis by previous authors types 1b and 1d are associated with higher w1 w2 wavelength ratios than types 1a and 1c other controlling factors are viscosity contrast and erosion processes specifically erosion of competent limestone beds in the hinge zone of a nnw sse trending anticline allowed the near vertical eastern limb to be refolded into snake like folds