tectonic implications of paleomagnetic research into upper cretaceous magmatic rocks in the apuseni mountains romania the paleomagnetism of upper cretaceous magmatic rocks from 47 collecting sites 172 samples 692 specimens in the apuseni mountains was studied after af cleaning characteristic magnetizations were identified for various collecting areas in the study zone which defined a few spatial and temporal units for which paleomagnetic poles could be derived statistically at 21 sampling sites the paleomagnetic directions showed a high level of intrasite and intersite consistency with a mean direction of if 38 and df 100 with 95 6 the paleomagnetic results show that to reach their present day position the apuseni mountains moved to the north around 14 with respect to europe or around 25 with respect to the geographic poles between the campanian and probably late miocene while a clockwise rotation of around 80 was taking place

one hundred million years of geomagnetic polarity history since 1968 absolute ages have been assigned to the late cretaceous cenozoic geomagnetic reversal time scale by fixing the ages of two or more calibration points in a composite marine magnetic anomaly profile and interpolating between or extrapolating beyond these points assuming constant spreading rates in each interval previously no more than 4 calibration points were used but it is now possible to specify 11 calibration points in addition to the 0 m y datum this improvement is based on magnetostratigraphic studies in italian pelagic limestones these studies closely tie the geomagnetic reversal sequence to the foraminiferal and coccolith zonations absolute ages of calibration points are provided by the best available dates on stage boundaries which are located from the biostratigraphic zonation the greatest changes from previous scales come in the late paleocene early eocene where the new ages are as much as 3 m y younger than in the 1977 scale of labrecque and others and as much as 1 8 m y younger than in the 1980 scale of ness and others

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

regional setting and geochronology of the late cretaceous banatitic magmatic and metallogenetic belt the 1 500 km long banatitic magmatic and metallogenetic belt bmmb of romania serbia and bulgaria is a complex calc alkaline magmatic arc of late cretaceous age it hosts a variety of magmatic hydro thermal cu au mo zn pb and fe deposits including europe s only world class porphyry copper deposits regional metallogeny can be linked to subduction of the vardar ocean during the late cretaceous as part of the closure of the neotethys ocean that had separated europe and africa in the mesozoic porphyry cu au mo and intimately associated epithermal massive sul phides dominate in the central segments of the belt in southernmost banat romania serbia and north west bulgaria these districts are the economically most im portant today including major active cu au mines at moldova noua in romania majdanpek veliki krivelj and bor in serbia and elatsite assarel and chelopech in bulgaria more numerous and mostly mined in the past are fe cu and zn pb skarns which occur mainly at the two ends of the belt in eastern bulgaria and in romania this paper summarises some of the deposit characteristics within the geodynamic framework of terminal vardar subduction heterogeneous terranes of the belt including the apuseni mountains at the western end are aligned parallel to the vardar front following continental collision of the dacia and tisza blocks all available geochronological data numerous k ar and some u pb and re os ages are compiled and are complemented by a new high precision re os date for the dognecea skarn deposit south west romania 76 6 0 3 ma these data indicate that magmatism extended over at least 25 million years from about 90 to 65 ma in each segment of the belt within apuseni mountains and banat where magma emplacement was related to syn collisional extension in the orogenic belt of carpathians ore formation seems to be restricted in time and maybe constrained by a shared tectonic event

magnetic polarity stratigraphy of the tertiary igneous rocks of skye scotland summary palaeomagnetic results are given for 115 sites mainly from the central igneous intrusive complex and also radiometric dates by the 40ar 39ar step heating method these are combined with published dates and palaeomagnetic results for the lavas and regional dyke swarms with the aim of establishing the magnetic polarity stratigraphy igneous activity spanned at least the approximate interval 61 54 ma and a polarity sequence of at last r n r n r but could span seven polarity intervals r n r n r n r depending on the age of the loch ainort epigranite however these polarities cannot be identified with specific chrons of either the harland et al 1982 or berggren et al 1985 polarity time scales the skye igneous activity therefore spans more polarity intervals than in mull ardnamurchan or rhum and this is consistent with the radiometric ages interpretations of the results for the coire uaigneich and related granites and for the loch ainort epigranite present problems and partial solutions are offered

timing of rotational motion of apuseni mountains romania paleomagnetic data from tertiary magmatic rocks paleomagnetic results are reported from 8 sites in eocene to oligocene magmatic rocks and 27 sites in middle miocene to upper miocene volcanic rocks of the apuseni mountains following af demagnetization 29 sites were selected for tectonic interpretation these results together with previously published data imply a northward displacement of the area studied between the late cretaceous and oligocene followed by a large clockwise rotation prior to the middle miocene after which no significant movement has occurred these results agree with other data from the carpatho pannonian domain showing a period of great mobility during the early miocene

engineering behaviour of phyllites abstract the physico mechanical behaviour of intrinsically anisotropic rocks cannot be assessed through common engineering experiences due to a number of governing intrinsic factors e g variation of mineral assemblage fabric and physical and mechanical properties the study of such rocks under the stress conditions existing within the drilling reach of the earth s crust has not been given due attention not even in laboratory simulated conditions therefore it seemed worthwhile to undertake a comprehensive study using three varieties of intrinsically anisotropic phyllites obtained from the vicinity of the chamera hydroelectric project site in the himalayan region attention has been paid to their petrographic and petrofabric analyses through thin sections x ray diffraction and scanning electron microscopy and the physical and geotechnical properties with special reference to their anisotropyp compression tests were run from unconfined to a maximum confining pressure 3 of 70 mpa for the three phyllites at specified orientation angles angle between the plane of weakness and the direction of the major principal stress 1 of 0 15 30 45 60 75 and 90 thus the physico mechanical response of the phyllites as a function of confining pressure and the orientation angle has been determined and the degree of anisotropy could be quantified in terms of physically measureable parameters

structural applications and discussion of a paleomagnetic post paleozoic data base for the central mediterranean abstract a post paleozoic paleomagnetic data base has been compiled for the central mediterranean with the intention of listing directions at the highest possible level of data combination the value of the entries depends on the number and quality of data available the most reliable data are those based on regionally distributed localities and sites where the age is known to a stage and where tectonic correction has been made these represent a whole tectonic unit in a given period of time the lowest quality directions are those based on few samples and isolated in space and time in the tectonic interpretation of the listed data this variation in quality of data has been taken into consideration indications for cenozoic movements having a fundamental influence on the now observable distribution of the clockwise and counter clockwise rotated paleomagnetic directions were treated first and those for older movements afterwards microplate block and nappe movements were considered as possible mechanisms for the rotation of these the last two mechanisms explained satisfactorily the occasional local deviations from a general pattern other differences however such as those which exist between the northern calcareous alps or the tisza unit and the counter clockwise rotated superunit of the central mediterranean which are large and persisted through a longer period of time are best explained by independent movement of the whole unit

geodynamical models of lithospheric deformation rotation and extension of the pannonian basin of central europe article i nfo the two major crustal blocks of the pannonian basin alcapa alpine carpathian pannonian and tisza underwent a complex process of rotation and extension of variable magnitude during the tertiary the northward push of the adriatic block initiated the eastward displacement and rotation of both the alcapa and tisza blocks we have constructed geodynamical models of the rotation and extension of the two pannonian blocks we analyse this process in terms of the competing influences of a ne push by the adriatic block a ne pull from a retreating subduction zone on the eastern carpathians and the internal buoyancy forces arising from crustal thickness variations deformation of the blocks included substantial strike slip movements together with shortening and possible extension across the mid hungarian line which now separates the two domains we use an idealised thin viscous sheet model of the continental lithosphere in which deformation is described by a nonlinear viscous constitutive relationship our approach is based on the finite element method and we consider several distinct models of initial geometry boundary conditions and constitutive parameters rotation and deformation vary across both blocks with anticlockwise rotation occurring in the alcapa plate and clockwise rotation in the tisza block the opposite rotations of the two plates led to nw se convergence in the space between the two intra carpathian terranes subsequently both domains underwent extension dominantly in the ne sw direction extension and internal rotation can be represented using a thin sheet model in which deformation is driven by an east or northeast directed outward traction of order 1 to 3 mpa internal buoyancy forces produced by thick crust from a prior phase of alpine style convergence appear to be a necessary element in the force balance that drives the extension process

effect of planar structures on the anisotropy of ranyah sandstone saudi arabia the anisotropy of metamorphic and sedimentary rocks is mainly due to the presence of a single set of discontinuity surfaces such as cleavage foliation schistosity joints microfissuring or bedding the uniaxial compressive strength anisotropy curve is usually u shaped however the presence of more than one discontinuity modifies the shape of the anisotropy curve therefore ranyah sandstone having two sets of mutually perpendicular discontinuities was selected and tested the investigation includes the geological and engineering geological descriptions as well as the classification of the rock mass it also includes the determination of the physical mechanical and dynamic properties of the rock material the most sensitive engineering property to the anisotropic behaviour for ranyah sandstone was found to be the compressive strength a w shaped anisotropy curve was obtained this shape is due the superimposed effects of the two directions of bedding and microfissures acting almost at right angles to each other and is in line with hoek and brown s hoek e brown e t 1980 underground excavations in rock the institution of mining and metallurgy london p 165 hypothesis for two mutually perpendicular discontinuities a comparison of the anisotropic behaviour of the ranyah sandstone with same foreign sandstones of different origin was also made

shear fractures in anisotropic ductile materials an experimental approach abstract analogue models have been used to investigate the influence of planar mechanical anisotropy on the orientation of shear fractures in an elastoviscous brittle material multilayered models consisting of a mixture of plasticine vaseline and preferentially oriented paper flakes have been coaxially deformed for this purpose the evolution of the orientation length and connectivity of fracture sets has been systematically analysed with progressive coaxial deformation the experimental results show that the orientation of fractures with respect to the deformation axes depends on the orientation of transverse anisotropy two symmetrical sets of shear fractures are formed in models with layering parallel to the extension axis x while the fracture network is asymmetrical with respect to the deformation axes for cases with oblique anisotropy the average dihedral angles between fracture sets are higher than 100 with the obtuse bisector between the two sets oriented perpendicular to layers the stress fields calculated from fracture data differ from the boundary conditions applied by the deformation apparatus this misorientation is related to the degree of anisotropy in models with high oblique anisotropy both fracture arrays rotate in a dextral sense together with layers towards the x axis indicating that the presence of a strong anisotropy controls their evolution with progressive deformation

intrusion of igneous rocks physical aspects igneous rocks occur in two predominant modes the plutonic mode is characterized by intrusive emplacement under compressional tectonic stress regimes the volcanic mode is dominated by the eruption of large volumes of magma through fault controlled dyke structures in extensional tectonic stress regimes

exhumation of the danubian nappes system south carpathians during the early tertiary inferences from kinematic and paleostress analysis at the getic danubian nappes contact abstract a detailed kinematic study based on the analysis of brittle structures combined with a description of structures in the adjacent foredeep allows for the definition of three major tectonic episodes during the late cretaceous tertiary evolution of the central part of the south carpathians following middle cretaceous and older orogenic phases the first tectonic event that affected the studied area was a late cretaceous nnw sse oriented contraction which led to the final major emplacement of the danubian and getic nappes during the paleogene early miocene an extension event induced rapid exhumation of the danubian units leading to the formation of large normal faults dipping towards both the foreland and the hinterland this extension together with dextral rotation of the south carpathians around the western corner of the moesian platform allows for the ne ward movement of the internal continental blocks with respect to the foreland platforms in the late miocene e ward translation of the internal south carpathians units with respect to the moesian platform was accommodated through a large scale e w oriented strike slip corridor within the south carpathians the general paleogene early miocene ne to e ward rotation and the late miocene e ward translation of the rhodopian fragment allowed for the accommodation of roll back and contraction taking place in the east carpathians

engineering properties of quartz mica schist quartz mica schist which is a highly anisotropic metamorphic rock usually presents a geotechnical challenge in construction projects to ensure a safe and economical design a comprehensive in situ and laboratory investigation scheme is necessary for projects to be built in quartz mica schist in this study such a comprehensive laboratory study of the engineering behavior of quartz mica schist has been carried out the p wave velocity tests tensile and uniaxial compressive strength tests and creep deformation tests conducted on specimens with differently oriented schistose planes all reveal the strong anisotropic characters of the rock the relevant crack initiation stress and crack damage stress analysis in uniaxial compression test which has not been previously applied to studying schistose rock has been performed in the present study when loading is parallel to schistose planes crack initiation stress and crack damage stress are lower than those in other loading directions as the compressive loading is applied parallel to schistose planes local tensile stresses are preferentially induced normal to the relatively weak schistose planes cracks are thus easier to develop than in any other loading directions since schistose plane orientation is one of the key factors to control the formation of macro cracks and hence failures of unloading test specimens these engineering geological characters should be taken into consideration in engineering design

the transylvania basin transfer zone between coeval extending and contracting regions inferences on the relative importance of slab pull and rift push in arc back arc regions 1 structural analysis and paleostress fault slip inversion of the transylvanian basin and its border regions with the surrounding east and south carpathians and the pannonian basin e g the apuseni mountains reveal at least two distinct tectonic phases for the neogene evolution for the eastern part of the pannonian basin system our main focus is on the role of the transylvanian basin and its border regions in the neogene as a transition zone between the extending pannonian basin and the converging east and south carpathians the results provide constraints on the mechanisms responsible for as well the formation of the transylvanian basin itself as on the relation between the basin formational processes operating in the pannonian basin and the contractional history of the east and south carpathian mountain belt in the middle miocene 17 14 12 myr the transylvanian basin underwent e w extension coeval with the first and major phase of overall e w extension affecting the pannonian basin and with submarine accretionary wedge tectonics in the east carpathian arc in the late miocene to early pliocene 12 8 6 myr the transylvanian basin experienced a strong pulse of e w oriented shortening coeval with the climax of compression in the east carpathians and a second rift phase affecting the pannonian basin continued contractional deformation affected the transylvanian basin during the pliocene and pleistocene with compression directions shifting to ese wnw directions

a refined apparent polar wander curve for the transdanubian central mountains and its bearing on the mediterranean tectonic history abstract recently obtained palaeomagnetic data have given a fairly detailed apparent polar wander a p w curve for the mesozoic of the transdanubian central mountains which has been compared with other a p w curves from the mediterranean area the similarity of the a p w curves enabled a unified a p w curve to be constructed for the central mediterranean region it has been shown that the new mediterranean a p w curve is in full agreement even in details with the updated a p w curve for africa this confirms the existence during the entire mesozoic of a single central mediterranean megatectonic unit rigidly attached to africa its positions with respect to the pole can now be traced back in more detail than before

palaeomagnetic study of some neogene magmatic rocks from the oas ignis văratec tibles mountains romania summary for this palaeomagnetic study 199 sites were sampled in the northern part of the east carpathians oas ignisl v ratec tibles sector after af alternating field demagnetization 155 sites were selected for further analyses a good agreement between the measured palaeomagnetic poles for the pontian the pannonian and the reference polar wander path of eurasia was made evident in the southern part of the ignis mountains the sarmatian volcanic rocks were affected by a 30 counterclockwise rotation with respect to europe post emplacement

the paleomagnetism of the upper cretaceous magmatic rocks in the banat area of south carpathians tectonic implications abstract forty four sites were sampled in upper cretaceous magmatic rocks in the western part of the southern carpathians banat area for a paleomagnetic study after detailed af demagnetization only 10 sites yielded primary remanent magnetizations the directions of which are similar to those identified in senonian magmatic rocks from the apuseni mountains and the ha eg and rusca montan basins the mean paleomagnetic pole for these three areas is compared with those from coeval formations of stable europe and stable africa this comparison shows a large clockwise rotation both with respect to africa and europe and a northward transport to reach their present day position during the tertiary the relations with adjacent zones of the tethys mobile belt are also discussed

structural evolution of the transylvanian basin romania a sedimentary basin in the bend zone of the carpathians abstract the transylvanian basin with its up to 10 km thick upper cretaceous to pliocene fill is one of the most important sedimentary basins of southeastern europe upper cretaceous coarse grained clastics lie unconformably on basement strongly tectonized during early cretaceous and older stages upper cretaceous sediments were mainly deposited along roughly n s trending grabens and were subsequently folded before the end of the paleocene eocene to middle oligocene rocks record mostly quiet sedimentation n s tension and extension took place in the oligocene and was followed by widespread nw se compression and contraction important thrusts are associated with this phase in the northwestern and southeastern parts of the basin widespread n s contraction followed during the early miocene in association with s vergent thrusting in the northern part of the basin a southward thinning clastic wedge developed during this stage the badenian basal unconformity marked a major change in the sedimentary and tectonic pattern of the transylvanian basin with new depocenters developing in the central parts of the present day basin late miocene e w extension affected vast areas and caused some important normal faulting in the southeast the youngest deformation recorded is associated with e w contraction and is of pliocene or younger age

quantification of strength anisotropy of metamorphic rocks of the hamedan province iran as determined from cylindrical punch point load and brazilian tests abstract in this research different experimental techniques have been used to determine the strength of five types of anisotropic foliated rocks selected from different parts of the hamedan province west of iran for this purpose after sample preparation and assessment of mineralogical and physical properties selected samples were subjected to cylindrical punch point load and brazilian tests and their strengths were evaluated with respect to different angles beta i e 0 15 30 45 60 75 and 90 between anisotropy planes and the major loading directions data analyses show that the types and amounts of minerals have an influence on the physical and mechanical properties of the tested anisotropic rocks porosity and water absorption also have a dominant control on the mechanical indices such as cylindrical punch index cpi point load index is 50 and brazilian tensile strength bts on the basis of the test result two empirical equations eqs 3 and 5 are proposed for calculating cpi and is 50 other empirical equations relating studied indices are also presented

subsidence analysis and tectonic evolution of the external carpathian moesian platform region during neogene times abstract the miocene pliocene subsidence of the tectonic platforms in the romanian carpathians foreland is analysed using standard 1d backstripping techniques for individual wells combined in two regional sections and six contour maps the subsidence patterns were integrated together with previous paleostress and kinematic studies in order to derive the tertiary kinematics of the buried faults in the carpathians lower plate the study revealed accelerated subsidence during the early miocene in the western part of the moesian platform getic depression in direct relationship with the opening of a wsw ene trending extensional basin the largest subsidence recorded in the front of the carpathians took place during the late miocene due to final e ward emplacement of the thrust sheets the late miocene subsidence showed anomalous high values between the intramoesian and trotus faults as a result of the orogenic collision with the east european platform northward and acceleration of the subduction process in the se carpathians corner further pliocene subsidence continued only in the latter region the depocenter being shifted southward near the junction with the south carpathians foreland

anisotropic strength and deformational behavior of himalayan schists abstract anisotropy which is characteristic of metamorphic rocks such as schists is due to a process of metamorphic differentiation preferred orientation of minerals like mica and chlorite in response to tectonic stresses makes schistose rocks foliated as a result their engineering properties vary with the direction of loading the influence of transverse anisotropy on strength and deformational responses of four schistose rocks obtained from the foundation of two underground powerhouse sites in the himalayas has been critically examined specimens at different orientation of the foliations varying from 0 to 90 with respect to the axial stress 1 in the unconfined state and also in the confined states up to 100 mpa of confining pressure were tested to evaluate the applicability of the non linear strength criterion for the prediction of triaxial compressive strength and modulus based on the analysis of large experimental results it has been possible to predict strength and modulus with minimum pre evaluation experimental data i e only with three uniaxial compressive strength tests at 0 30 and 90 and two triaxial compression tests conducted at convenient confining pressures at 90 orientation predicted non linear stress strain curves using predicted values of strength and modulus have been found to match well with the experimental stress strain curves even at higher confining pressures

tectonics of the banat srednogorie rift abstract the banat srednogorie rift is located on the balkan peninsula in the northeastern part of the alpine system it is superimposed on a continental type basement which cuts across older structures the rift is filled with a 3 8 km thick layer of upper cretaceous sedimentary and volcanogenic rocks the volcanic and plutonic formations belong to four series calc alkaline tholeiitic potassic alkaline and peralkaline the rift was formed in three stages 1 1 the formation of the sedimentary trough 2 2 subsidence accompanied by intense volcanic activity and tephroidal flysch sedimentation 3 3 inversion expressed in the laramide deformation the epicontinental rifting occurred in the preorogenic stage of the geotectonic development of the balkanide dinarides after the closure of the vardar paleo ocean and the formation of an embryonal orogenic arc

paleomagnetic aspects of plate tectonics in the carpatho pannonian region paleomagnetic data available from the carpatho pannonian region are unevenly distributed at some places observations are sporadic at others the concentration is high in the latter case it is possible to decide whether the movements indicated are related to plate microplate displacements or are of local significance the paleomagnetically best known parts of the carpatho pannonian region belong to the transdanubian central range to the cserhat matra bukk area and to the mecsek villany zone comparison among paleomagnetic data sets characterizing each of them reveals fundamental differences i e points to their independent displacements during the mesozoic and cenozoic most of the isolated observations can be tied to one of the above mentioned paleomagnetic units via coeval mostly late cretaceous cenozoic data thus further subdivision of the carpatho pannonian area at least in the cenozoic does not seem required by available paleomagnetic observations

on the formation and evolution of the pannonian basin constraints derived from the structure of the junction area between the carpathians and dinarides 1 the large number and distribution of rollback systems in mediterranean orogens infer the possibility of interacting extensional back arc deformation driven by different slabs the formation of the pannonian back arc basin is generally related to the rapid miocene rollback of a slab attached to the european continent a key area of the entire system that is neglected by kinematic studies is the connection between the south carpathians and dinarides in order to derive an evolutionary model we interpreted regional seismic lines traversing the entire serbian part of the pannonian basin the observed deformation is dominantly expressed by the formation of miocene extensional detachments and half grabens the extensional geometries and associated synkinematic sedimentation that migrated in time and space allow the definition of a continuous and essentially asymmetric early to late miocene extensional evolution this evolution was followed by the formation of few uplifted areas during the subsequent latest miocene quaternary inversion the present day extensional geometry changing the strike across the basin is an effect of the clockwise rotation of the south carpathians and apuseni mountains in respect to the dinarides our study infers that the carpathian rollback is not the only mechanism responsible for the formation of the pannonian basin an additional middle miocene rollback of a dinaridic slab is required to explain the observed structures furthermore the study provides constraints for the pre neogene orogenic evolution of this junction zone including the affinity of major crustal blocks obducted ophiolitic sequences and the sava suture zone

paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic abstract we first re examined the apparent polar wander curves for stable eurasia and africa since the triassic these curves were then combined together with curves of north and south america according to the kinematics of the atlantic ocean and a synthetic polar wander curve was given then most of the paleomagnetic results from the tethys mobile belt from the atlantic to the pamirs were analysed several groups of plates microplates and blocks can be seen first relatively stable regions like maghreb and sicily which have not moved much then we have a group formed by iberia sardinia italy and to a lesser extent corsica and the western and central alps for these blocks movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of africa but they are sometimes stronger to the east a major change takes place the north of the aegean sea and the ionian zone are clockwise rotated and these rotations are recent oligocene miocene for the first part pliocene to the present for the second part a major problem arises in turkey caucasus and iran paleomagnetic results indicate a position far to the south of eurasia and at the same time geological evidence is in favour of a position close to eurasia we discuss these discrepancies

alpine polyphase tectono metamorphic evolution of the south carpathians a new overview abstract the main terrains involved in the cretaceous tertiary tectonism in the south carpathians segment of the european alpine orogen are the getic supragetic and danubian continental crust fragments separated by the severin oceanic crust floored basin during the early middle cretaceous times the danubian microplate acted initially as a foreland unit strongly involved in the south carpathians nappe stacking multistage folding thrusting events uplift erosion and extensional stages and the development of associated sedimentary basins characterize the south carpathians during cretaceous to tertiary convergence and collision events the main cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the south carpathians are mid cretaceous austrian phase and latest cretaceous laramide or getic phase in age the architecture of the south carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom the getic supragetic basement cover nappes the severin and arjana cover nappes and danubian basement cover nappes all tectonically overriding the moesian platform the severin nappe complex including obarsia and severin nappes with late jurassic early cretaceous ophiolites and turbidites is squeezed between the danubian and getic supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred mid to late cretaceous subduction collision followed by tectonic inversion processes early cretaceous thick skinned tectonics was replaced by thin skinned tectonics in late cretaceous thus the former middle cretaceous austrian nappe stack and its albian lower senonian cover got incorporated in the intra senonian laramide getic stacking of the getic supragetic severin arjana nappes onto the danubian nappe duplex the two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the banatitic magmas 84 73 ma the overthrusting of the entire south carpathian cretaceous nappe stack onto the fold thrust foredeep units and to the moesian platform took place in the late miocene intra sarmatian times and was followed by extensional events and sedimentary basin formation

shear behavior of inherently anisotropic rocks abstract the effect of schistosity plane orientations on failure mechanism and effective shear strength response of inherently anisotropic rocks are dealt with in this paper with an emphasis on shear parameters of the weak planes the study employed an oblique shear apparatus to apply shear and normal stress on specimens at three predetermined shear inclinations the concurrent application of confinement and shear loading was made to the apparatus both stresses were developed as a result of vertical loading confined stress conditions and hence their failure mechanisms the results indicate a transition state of shear strength values fluctuating from a minimum to a maximum based on angle due to the anisotropic effects of schistosity plane orientation coupled with confinement stress is the angle between strike of weak planes and the predetermined shear loading plane hence the anisotropic effect of weak planes orientation is a significant occurrence that must be noted in the analysis and failure mechanism studies it was also observed that different shearing failure modes were built up depending on the orientations of a family weak planes with respect to confinement stresses as 1 tensile fracture across the weak planes non sliding mode 2 tensile split along the weak planes non sliding mode and 3 sliding failure along the weak planes and or combination of these mechanisms the experimental results demonstrated that the failure modes were changed from non sliding into sliding along weak planes when dip of weak planes increases it was also noticed that due to the influence of confinement stresses failure occurred through rock material together with tensile splitting of weak planes this was more prominent for higher values of strike direction of weak planes investigations were extended to examine the influence of effective shear stresses on the failure mechanisms considering various dip and strike directions of weak planes

pore geometry as a control on rock strength the strength of rocks in the subsurface is critically important across the geosciences with implications for fluid flow mineralisation seismicity and the deep biosphere most studies of porous rock strength consider the scalar quantity of porosity in which strength shows a broadly inverse relationship with total porosity but pore shape is not explicitly defined here we use a combination of uniaxial compressive strength measurements of isotropic and anisotropic porous lava samples and numerical modelling to consider the influence of pore shape on rock strength micro computed tomography ct shows that pores range from sub spherical to elongate and flat ellipsoids samples that contain flat pores are weaker if compression is applied parallel to the short axis i e across the minimum curvature compared to compression applied parallel to the long axis i e across the maximum curvature numerical models for elliptical pores show that compression applied across the minimum curvature results in relatively broad amplification of stress compared to compression applied across the maximum curvature certain pore shapes may be relatively stable and remain open in the upper crust under a given remote stress field while others are inherently weak quantifying the shape orientations and statistical distributions of pores is therefore a critical step in strength testing of rocks

experimental and theoretical study of the anisotropic properties of shale abstract the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated with an emphasis on the shear parameters of the bedding planes this study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well developed stratification the tested cylindrical specimens were prepared by coring at 30 intervals from the direction of the bedding planes the results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress the shear parameters such as strength cohesion and internal friction angle reach their maximum and the minimum values at 60 and 0 respectively where is the angle between the bedding planes and the coring orientation which is also the direction of normal stress during the laboratory tests it is demonstrated that the bedding planes are weak not only with regards to cementing strength but also with regards to friction three different shear failure modes were built up depending on the shearing angle 1 sliding failure across the bedding planes 2 sliding failure along the bedding planes and 3 sliding failure across the bedding planes combined with tensile splitting along the bedding planes an expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength