some effects of weathering on joints in granitic rocks abstract standard engineering weathering classifications most of which are based on weathered granite typically describe the appearance and condition of the weathered material e g whether or not it is friable the condition of individual minerals e g degree of pitting and micro cracking and changes in mineral composition and the degree of staining on joint surfaces or the distance that staining extends into rock from the joints these classifications do not address changes in frequency length and appearance of joints in the rock mass as weathering progresses this account of work on vertical or steeply dipping joints in granitic rocks shows that not only are there statistically significant differences in mean joint spacings and mean trace lengths with increased weathering but that the physical appearances of joints also changes as weathering progresses mean joint spacing is wide in fresh rock becomes closer in moderately weathered rock and then becomes progressively wider from moderately weathered rock through highly and completely weathered rock mean joint lengths follow a similar but inverse pattern mean trace lengths become shorter from fresh to slightly weathered rock lengthen in moderately weathered rock then progressively become shorter from moderately weathered rock through highly and completely weathered rock furthermore joint appearance changes with increased weathering joints in fresh rock are sharp edged and typically straight the edges begin to round in moderately weathered rock and in highly weathered rock joint traces become sinuous and discontinuous around mineral grains in completely weathered rock the only visible joints are filled with minerals or marked with iron staining it is proposed that this evolution in joint pattern and appearance results from increased cracking along grain boundaries and thermal expansion of individual mineral grains and within grain micro cracking as weathering proceeds these factors allow individual mineral grains to move into the spaces between joint surfaces thus obscuring individual joints and making them appear shorter these apparent changes in joint properties could lead to incorrect rock mass classification and thus to inappropriate engineering design and costly errors during construction

stresses in the lithosphere and sedimentary basin formation abstract seven fundamental questions on the relationship of lithospheric stresses and sedimentary basin origin and evolution are posed and elaborated these are 1 1 how is the evolution of sedimentary basins tied to lithospheric dynamics 2 2 what are the sources of stress that lead to formation of sedimentary basins 3 3 how does the interaction between internally and externally applied stresses affect the formation and evolution of sedimentary basins 4 4 how do space and time variations of rheology and pore pressure affect stress transmission strain vertical motions and stratigraphy during basin evolution 5 5 what factors influence spatial and temporal variations of rheology in and around different kinds of sedimentary basins 6 6 what is the role of magmatism in basin formation and what deep seated processes does it reflect 7 7 what is the relationship between basin evolution thermal history and fluid flow these fundamental questions can be investigated by developing fully dynamic models of processes at the basin and sub basin scale models must incorporate or honour basin history and plate reconstructions the intregration of structural and sedimentological data direct observations of the physical state and the synthesis of geological and geophysical data including tectono dynamic stratigraphy petrological and geochemical data and geophysical data gravity magnetics heat flow deep and shallow seismics a number of type basins in passive margin foreland rift and strike slip tectonic settings suitable for modelling studies elucidating the fundamental questions are identified

shear localization in transformation induced faulting first order similarities to brittle shear failure abstract transformation induced faulting a leading candidate for the mechanism of deep focus earthquakes leads to catastrophic shear failure in laboratory specimens by the growth and coalescence of microscopic mode i anticracks or packets of denser microcrystalline transformed material we have studied this phenomenon in mg 2 geo 4 olivine undergoing a polymorphic phase transformation to its denser spinel phase at 2 7 gpa and 1200 k under applied stress in order to better understand the details of anticrack growth and coalescence which leads to localized shear zones and macroscopic failure here we report observations that address the early stages of shear localization preserved in one experiment of this series are microstructures typical of anticrack nucleation and growth as well as those involved in the self organization of these features during the shear localization process we have analyzed sem and optical images of individual anticrack reaction interfaces and coalesced structures from this experiment and another experiment conducted under similar conditions but with a different strain history we have isolated the reaction boundaries in these images and have performed fractal analysis of these boundary lines we find that the fractal dimension of isolated uncoalesced anticrack structures is consistently higher than that of structures formed from coalescence and coarsening of fine grained reaction products this result is consistent with the varying effects of stress and thermal feedback at these interfaces and also represents an interesting parallel with the fractal nature of brittle cracks and fault surfaces we also measured the length of the long axis of uncoalesced anticrack structures found in the experiment arrested at failure and find a roughly log normal distribution of sizes very similar to the distribution of microcrack lengths reported in experiments involving brittle shear failure microcracks and microanticracks both also commonly nucleate on grain boundaries intracrystalline flaws and phase boundaries shear zones faults formed by either of these mechanisms also regularly form at 30 to maximum compression from this set of observations we conclude that the general phenomenon of shear failure creates similar features in both systems perhaps in any system which generates a shear instability despite the major differences in the detailed microphysics because of the detailed and unambiguous measurements that are possible with images of transformation induced faulting experiments further studies of this faulting mechanism may provide new insights into brittle failure and shear localization processes

fractal analysis of fracture patterns using the standard box counting technique valid and invalid methodologies abstract on the basis of results of simple box counting analysis it has been suggested in several recent publications that natural fracture patterns are fractal fractal patterns are characterized by self similarity of structure on a range of scales and provide straight line distributions on box counting plots new analysis of a fracture pattern that provided the most convincing straight line box counting curve previously published shows that the curve is non linear and therefore that the fracture pattern is not fractal non linear box counting curves are also characteristic of other natural fracture patterns analysed but spurious linear curves can be obtained if the area analysed extends beyond the mapped area

numerical study of critical behaviour of deformation and permeability of fractured rock masses abstract the connectivity of fractures in rock masses is determined using a numerical simulation method there is a continuous fracture cluster throughout a fractured rock mass if fracture density d is at or above a threshold fracture density d c fractal dimension d f is used to describe the connectivity and compactness of the largest fracture clusters d f increases with increasing fracture density percolation theory is used to determine the universal law d f a f d d c f which describes the critical behaviour of connectivity of fractures in rock masses the results from numerical modeling show that the deformability of fractured rock masses increases greatly with increasing fracture density i e fractal dimension and the critical behaviour of deformability can be described by b s a d d f s also the overall permeability of a fractured rock mass occurs at or above a critical fracture density d c and increases with increasing fracture density the critical behaviour of permeability can be described by q a p d d c p the critical behaviour of connectivity and permeability of naturally fractured rock masses is examined using the universal forms

no moho uplift below the baikal rift zone evidence from a seismic refraction profile across southern lake baikal 1 the late cenozoic baikal rift zone brz in southern siberia is composed of several individual topographic depressions and half grabens with the deep lake baikal at its center we have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the baikal explosion seismic transects best project across the rift zone in the southern part of lake baikal the seismic velocity structure along the profile is determined by tomographic inversion of first arrival times and 2 d ray tracing of first arrivals and reflections the velocity model shows a gently deepening moho from the siberian platform 41 km depth into the sayan baikal fold belt 46 km depth we can exclude the presence of any moho uplift around the 10 km deep sedimentary graben structure of southern lake baikal the lower crust includes a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s slightly offset to the northeast from the rift axis we interpret this feature as resulting from mafic intrusions their presence may explain the flat moho by compensation of lower crustal thinning by intrusion of mafic melts the pn wave velocities 8 15 8 2 km s are normal for the area and do not show any sign of decompression melting in the sub moho mantle such that possible lithosphere thinning has not reached the base of the crust on the basis of the results of the best project we suggest that the brz is formed by passive rifting in the rheologically weak suture between the siberian platform and the amurian plate

fault spacing in the el teniente mine central chile evidence for nonfractal fault geometry we utilize the excellent rock exposure provided by the network of mining tunnels in el teniente mine central chile to test the applicability of fractal fault spacing laws to a 2 km 3 km 1 3 km body of crystalline rock in an andean shear zone fractal spacing laws can be particularly useful because they allow prediction of fault spacing at unsampled scales because of the restrictions of tunnel geometry in the mine we use only scanline one dimensional analyses the large number of parallel tunnels allows us to assess the consistency of one dimensional scanline samples over a two dimensional area we use two methods 1 an interval counting technique and 2 standard cumulative statistics to test the hypothesis of fractal fault geometry in the shear zone the interval counting method produces deceptively good fits to a fractal distribution in fact by analyzing the residuals and differential slopes of interval counting and cumulative statistical plots and by comparison with synthetic fractal negative exponential and log normal distribution data we conclude that a negative exponential distribution best describes fault spatial distribution at the mine we present three possible explanations for the negative exponential spacing distribution 1 the rock body is at the earliest stage in a deformational path that will produce varying spacing distributions as deformation proceeds 2 the spacing distribution is inherited through joint reactivation and 3 the present spacing distribution is the result of a superposition of two spacing distributions each of which is not necessarily negative exponential additionally we attempt to use the deviation of mean spacings in parallel scanlines after wu and pollard 1995 to further classify deformational maturity we show that this method cannot be used to compare population development in faults which follow a negative exponential spacing distribution because of the negative exponential s equivalence of mean and standard deviation instead we use a relative measure of parallel scanline deviation to compare regions the distinctly smaller standard deviation of mean spacings in one region the t3 isla region may be a signature of increased local finite strain accumulation

the moho in extensional tectonic settings insights from thermo mechanical models the lithospheric memory is key for the interplay of lithospheric stresses and rheological structure of the extending lithosphere and for its later tectonic reactivation other important factors are the temporal and spatial migration of extension and the interplay of rifting and surface processes the mode of extension and the duration of the rifting phase required to lead to continental break up are to a large extent controlled by the interaction of the extending plate with slab dynamics the finite strength of the lithosphere has an important effect on the formation of extensional basins this applies both to the geometry of the basin shape as well as to the record of vertical motions during and after rifting we demonstrate a strong connection between the bulk rheological properties of europe s lithosphere and the evolution of some of europe s main rifts and back arc systems the thermo mechanical structure of the lithosphere has a major impact on continental break up and associated basin migration processes with direct relationships between rift duration and extension velocities thermal evolution and the role of mantle plumes compressional reactivation has important consequences for post rift inversion borderland uplift and denudation as illustrated by poly phase deformation of extensional back arc basins in the black sea and the pannonian basin region

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

neural network analyses of stress induced overpressures in the pannonian basin summary artificial neural networks can learn relationships between sediment characteristics burial depth composition coordinates and thickness of overlying quaternary deposits and overpressures from well data after which they can interpolate and extrapolate to areas and depths not covered by wells we analyse data from the south eastern part of the pannonian basin we use a neural network for analysing fluid overpressures because of the complex interaction of the key variables making it difficult to derive the functional relationships required for a statistical analysis the optimal topology of the network number of hidden layers and neurons is found by minimizing the network s training and testing errors the optimal design of the network resembles the interactions scheme of the key variables the pannonian basin originally formed in an extensional regime has been in a compressive state of stress since late pliocene causing anomalous subsidence patterns numerical forward modelling of compaction driven fluid overpressures shows that due to an increase in the level of compressive interplate stress the fluid overpressures in the deep subbasins have increased substantially since late pliocene giving rise to a very high overpressure up to 45mpa at present the neural network analyses provide an independent estimate of the current amount of overpressuring in this basin complementing the numerical forward modelling results the overpressure profiles obtained by the two modelling approaches are in excellent agreement showing the same magnitude of overpressures a reversal of the overpressure in the deepest parts of the subbasins and a general decrease of the overpressure from sw to ne

the connectivity of two dimensional networks of spatially correlated fractures 1 continuum percolation thresholds for fracture systems are based on models with random fracture locations resulting in uniformly clustered systems in which all connections are fracture intersections fractures in natural systems can be either clustered or anticlustered and a significant portion of the connectivity is achieved through fracture abutments or splays analytical and numerical methods are combined to define critical properties of isotropic networks of constant length lines as a function of fracture clustering and of the ratio of abutments to intersections a second suite of numerical results indicates that the influence of these parameters varies as a function of the fracture length distribution a preliminary predictor of critical density of anisotropic nonrandom systems with lognormal length distributions is derived and applied to a suite of natural fracture systems predicted connectivities are closer to the observed connectivities when the predictor is used than when connectivity is estimated from the random threshold

evidence for active tilting of the nw german basin from correlations between fluvial landscape and geological subground the catchment basin of the river hunte lower saxony nw german basin was studied on a mesoscale length of 90 km to investigate the influence of the geological subground on modern morphology a geo information system gis was used to calculate linear correlation coefficients between the depth of geological strata base zechstein to base quaternary and the height of the modern landscape holocene alluvial plain lower weichselian terrace catchment basin and watershed high linear correlation coefficients between the base of tertiary and the height of the modern topography catchment basin r2 0 87 lower weichselian terrace r2 0 95 and holocene alluvial plain r2 0 95 indicate control of the modern topography by the depth of the geological subsurface via tilting of the entire basin most likely northward tilting of the nw german basin forces the river hunte to flow in a northerly direction by relative uplift of the hinterland wiehengebirge rhenish massif and subsidence of the north sea area

relative importance of strain rate and rheology for the mode of continental extension summary both extension rate and rheology have been shown to influence the style of continental rifting so far their effect on the dynamics of extension has been discussed separately in the literature leading to diverging conclusions the rate of extension mostly affects the dynamics of rifting through the occurrence of syn rift cooling at low extension rates this cooling results in an increase of strength if the lithosphere has a temperature dependent rheology england 1983 first suggested that this effect will limit the amount of extension that an area may undergo kusznir park 1987 argued more generally that it will induce a widening of the rift and concluded that extension rate is the major control on wide versus narrow rifting later studies bassi 1991 bassi keen potter 1993 however have demonstrated the importance of rheological layering within the lithosphere for the mode of continental extension by showing that a plasticity dominated rheology will lead to rapid and narrow necking while a creep dominated rheology results in wider rifts and margins gravitational stresses arising from density anomalies due to lithosphere thinning also affect the style of rifting buck 1991 in this paper we examine the combined effect of these different parameters in order to reconcile earlier studies and assess the importance of syn rift cooling for the process of lithospheric necking the approach introduced in a previous study bassi 1991 uses a finite element technique to simulate extension of a vertical cross section of the lithosphere the effect of cooling on the necking pattern depends strongly on the rheology of the thinned lithosphere when it starts to cool if heat diffusion always induces strengthening and delays rupture in time it only modifies significantly the geometry of the rift when the upper mantle is weak and viscous in this case the locus of maximum strain rate migrates laterally once the central area starts to cool and harden as hypothesized by kusznir park 1987 eventually strain concentrates at the transition between deformed and undeformed lithosphere we predict that this pattern will induce asymmetric breakup and produce a very narrow margin and a wide uniformly thinned conjugate margin in all other cases i e when the upper mantle is initially in the low plasticity regime or if it reaches the yield stress during extension the rate of extension appears to have little effect on the rifting pattern

fractured but not fractal fragmentation of the gulf of suez basement recent geophysical studies revealed that the palaeozoic basement of the gulf of suez consists of an enormous number of fault blocks whose network qualitatively resembles the contractioncrack polygons which can be found in nature in a wide variety of materials and on all scales mud cracks hardening concrete age cracking in paintings etc the fault network of the gulf of suez basement forms a rather uniformly spaced polygonal pattern most of the blocks are four sided the lengths of block sides parallel with the gulf of suez axis are exponentially distributed the power law size distribution associated with the fractal scale free fragmentation can be possibly ruled out

fractal dimension of fault systems in japan fractal structure in rock fracture geometry at various scales based on fault maps whether or not the fracture geometry of rocks is self similar was examined by using a box counting algorithm the statistical self similarity fractal structure of the fault fracture systems holds well at the scale of about 2 to 20 km the fractal dimension in japan varied from 1 05 to 1 60 the fractal dimension is about 1 5 1 6 at the central part of the japan arc and decreases with distance from the center at a smaller scale the fractal structure also holds well in the rock fracture geometry the fractal dimension of the north izu peninsula fault system branching faults is 1 49 at the scale of 0 625 to 10 km the fractal dimension of rock fracture geometry at the scale order of 10 1 to 10 2 meters is about 1 49 1 61 the upper limit of the fractal dimension of rock fracture geometry is about 1 6 judging from the estimation of fractal dimension on actual fracture geometry of rocks this value may impose a restraint on modeling of faulting and the fracture process of rocks

structural and statistical characterization of joints and multi scale faults in an alternating sandstone and shale turbidite sequence at the santa susana field laboratory implications for their effects on groundwater flow and contaminant transport abstract this paper describes the properties of faults and fractures in the upper cretaceous chatsworth formation exposed at santa susana field laboratory and its surroundings simi hills california where groundwater flow and contamination have been studied for over three decades the complex depositional architecture of this turbidite consisting of alternating sandstones and shales interacting with formative stress conditions are responsible for multi scale fault hierarchies and permeable fractures in which nearly all groundwater flow occurs intensity and distribution of background fractures and their relation to bedding thickness are established for sandstones the dominant lithology the architecture of faults with increasing displacement is described and relationships among fault dimensional parameters captured data from 400 boreholes and piezometers reveal the effect of faults and fractures on groundwater flow large hydraulic head differences observed across fault zones with shale rich cores indicate these structures as cross flow barriers moreover hydraulic head profiles under ambient conditions and pumping tests suggest strong hydraulic connectivity in all directions to depth of hundreds of meters this outcrop based structural characterization relates the horizontal hydraulic conductivity to the observed well connected fracture network and explains the strong vertical connectivity across low hydraulic conductivity shales as faults and sheared fractures provide flow pathways

tectonics and global change inferences from the late cenozoic subsidence and uplift patterns in the atlantic mediterranean region summary quantitative subsidence analysis for a number of rifted basins in the northern atlantic mediterranean region provides evidence for rapid phases of plioquaternary subsidence the observed acceleration in tectonic subsidence occurs after a phase of general quiescence in subsidence in these basins and deviates from predictions of stretching models the latter indicate a decay of subsidence with time after mesozoic tertiary basin formatioh and a slow tectonic subsidence in plio quaternary times a possible explanation for the observed patterns of anomalous subsidence could be an increase in the level of intraplate compression in the northern atlantic region intraplate stress changes in the plio quaternary are related to the dynamics of african eurasian collision processes and a reorganization of spreading directions in the atlantic possibly reflecting a plate reorganization of global nature it seems that the plio quaternary record reflects a period of increased levels of neotectonic activity interplaying with periods of de glaciation stress induced topography in the onshore parts of continental margins coupled with the stress induced subsidence in the offshore deeper parts of the basins could have contributed to recent phases of uplift in fennoscandia augmenting the uplift induced by glacial unloading estimates of ice thicknesses are directly inferred from the observed uplift ignoring other driving mechanisms whereas topography plays a crucial role in the dynamics of glaciation it is therefore important to quantdy the interplay of rapid tectonic uplift and subsidence phases with climatic effects during the plio quaternary

the neogene evolution of the outer carpathian flysch units poland ukraine and romania kinematics of a foreland fold and thrust belt system abstract various techniques of geometric and kinematic analyses including cross section balancing and forward modeling have been applied successfully to the outer carpathian flysch units along regional geologic profiles crossing the belt from its undeformed foreland to the pieniny klippen belt western carpathians poland or to the central east carpathian allochthon eastern carpathians ukraine and romania the amounts of neogene shortening as well as the mode and the location of basement consumption are discussed on the basis of balanced cross sections compiled along the three most representative regional traverses in addition the complete kinematic evolution of complex carpathian structures such as the fore dukla triangle zone southeastern poland the borislav pokut duplexes ukraine and the marginal folds romania are described in more detail by using a forward modeling approach major results concern the tectonic heritage of laramian inverted structures mesozoic normal faults reactivated as reverse faults during the late cretaceous paleocene compression or transpression in the development of the neogene outer carpathian edifice pre eocene deformation and erosion effectively induce discontinuities in the mid cretaceous blackshale detachment horizon and help to localize the neogene deformations in complex triangle zones the thrust sequence itself evolves alternatively in a piggyback or in an out of sequence mode clearly the critical taper of the outer carpathians is preserved by a constant balance between erosion and thrust reactivations in the inner part of the wedge and sedimentation and tectonic accretion at its front

the link between tectonics and sedimentation in back arc basins new genetic constraints from the analysis of the pannonian basin the architecture of sedimentary basins reflects the relationship between accommodation space and sediment supply their rates and localization being variable during basin evolution the mechanisms driving the interplay between tectonics and sedimentation in extensional back arc basins overlying rheological weak zones inherited from an earlier orogenic evolution are less understood a typical example is the pannonian back arc basin of central europe it is floored by continental lithosphere and was affected by large amounts of extension driven by the subduction rollback that took place in the carpathians and or dinarides a novel kinematic and seismic sequence stratigraphic interpretation calibrated by wells allows the quantification of the link between the formation of half grabens and coeval sedimentation in the great hungarian plain part of the basin while the lower order tectonic induced cycles characterize the main phases of extension in various subbasins the higher order cyclicity and associated unconformities define individual moments of fault re activation our novel interpretation of a temporal and spatial migration of extension during miocene times explains the contrasting present day strike of various subbasins as a result of their gradual clockwise rotation incorporating the observed asymmetry in particular the associated footwall exhumation infers that the amount of extension is much larger than previously thought the quantitative link between tectonics and sedimentation has allowed the definition of a novel model of sedimentation in asymmetric basins that can be ported to other natural scenarios of similarly hyperextended back arc basins observed elsewhere

identifying the characteristics of groundwater flow in the classical karst area slovenia italy by means of tracer tests tracer tests are a widely used research method in karst hydrology in the classical karst area on the border between slovenia and italy they have a long history and for the most part they have been used to research the underground flow in the main karst conduits between the ponors and the springs the results of the tracer test from 2013 presented in the article revealed new knowledge about the central part of the aquifer less well researched to date where the density of caves and the level of karstification are lower two tracers uranine and amidorhodamine g were used at two injection points a research borehole in the central part of the aquifer and the karst surface at a distance of 2 5 km from a drinking water pumping station and six springs a pumping station three boreholes and four karst caves were observed for tracer breakthrough for a full year after injection the results were compared with findings from three other selected older tracer tests in which uranine was likewise used as a tracer but where hydrological conditions varied very low low and medium water levels as did the methods of injecting tracer in a sinking stream in a fracture on the karst surface the comparison showed how different modes of aquifer recharge and the heterogeneity of aquifer structure affect the characteristics of water flow and solute transport in complex karst aquifers

geometrical and fractal analysis of a three dimensional hydrothermal vein network in a fractured granite abstract a three dimensional study of a fracture network has been performed on a 0 66 m 3 block of fine grained granite from la peyratte deux sevres france the block was sawn in nine parallel plates the fractures associated with altered haloes were mapped for each plate using a photographic method the nine fracture sets were subjected to an analysis of the percolated network based on a measurement of the width of altered haloes developed around fractures hydrothermal alteration is created by circulation of a certain amount of fluid flow in the rock we assume that the alteration zone width is proportional to fluid mass flow the width of alteration zones will give a good idea of the path preferentially followed by fluids the relation between fracture length and width of the alteration zone shows that the total fracture network consists in fact of two sorts the largest fractures surface 0 1 m 2 create a loose and poorly interconnected pattern in the block however they have developed wide alteration zones 3 mm and have then had a great role in fluid conduction they represent only 10 of the fractures but are responsible for 47 of alteration in volume approximately 80 of these fractures with wide alteration zones are oriented in the same direction this main network is linked to a more dense highly interconnected system made of shorter fractures with narrower altered zones fractal analysis has also been performed on pictures of the fracture patterns using the linear cantor s dust method fractal dimension values d indicate an anisotropy of fracture distribution on each plane moreover when the planes are compared to one another in succession variations of d values can be noticed indicating an inhomogeneity in the third dimension the study of such a three dimensional fracture set shows that fluids follow preferential paths within a fracture network and helps the understanding of fracture distribution

modelling of piggyback basin stratigraphy record of tectonic evolution abstract the tectono stratigraphic evolution of foreland basins is influenced by processes acting on local regional and global scale in this paper the effects of these processes on the basin evolution are investigated using a forward reconstruction model based on the principles of balanced cross section the modelling incorporates the consequences of thrust deformation sedimentation erosion basement subsidence and sealevel changes on the basin stratigraphy basement subsidence due to lithospheric loading is the main cause of foreland basin formation but appears to have minor implications for the occurrence of angular unconformities in the stratigraphie record of piggyback basins thrusting is probably the dominant factor in the control of the stratigraphie evolution of piggyback basins overprinting the effect of eustasy detailed analyses of stratigraphie data enable the reconstruction of the structural evolution of the underlying thrust system modelling of the northern apenninic po basin shows that neogene stratigraphie sequences of the proximal part of the basin can be explained by tectonic activity of the apenninic fold and thrust belt strong basement subsidence accompanied with deep seated mid pliocene thrusting controls the stratigraphie record of the po piggyback basins

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

thermo mechanical modelling of black sea basin de formation abstract we present the results of a thermo mechanical modelling study carried out to investigate the effect of pre rift rheology on subsequent basin de formation in the black sea area important differences are inferred for the bulk lithosphere structure and mechanical properties expressed in terms of different estimates for levels of necking in the western and eastern black sea respectively gravity data provide constraints on the mode of flexure in the black sea pointing to significant lateral variations in pre rift lithospheric strength these features strongly affect predictions for mesozoic cenozoic basin stratigraphy and have implications for the presence and development of rift shoulder topography on the margins of the black sea basins differences in lithosphere strength affect the mode of stress propagation from the basin margins into the central parts of the black sea basins during the post rift phase these post rift compressional stresses could be of key importance for long wavelength late neogene differential motions within the basins superimposed on vertical motions induced by rifting and subsequent sediment loading thermo mechanical modelling of integrated lithospheric strength points to a rapid increase of strength during the later stages of post rift evolution and the presence of relatively strong lithosphere in the centre of the basin these features predict preferential shortening induced by compressional activity of surrounding orogens to be primarily accommodated at the basins margins

lithosphere rheology and sedimentary basins introduction the dynamics of sedimentary basins is re flected in the wide range of observational scales inside sedimentary basins the advent of high qu ality data sets have significantly improved the resolution of the record of near surface tectonic processes crustal thinning mechanical and thermal sub sidence sediment filling are involved in exten sional basin evolution and controlled by complex interactions between ductile and brittle modes of deformation of the whole lithosphere the rate of loading extension and sediment filling and the thermal evolution are among the most important controlling parameters these nonlinear interac tions do possess a memory of the evolution his tory and loading quantitative understanding of basin subsidence and the offlap onlap strati graphic patterns of a specific basin obviously benefits from progress in understanding the geo dynamical context horvlth 1993 this issue in compressional settings foreland basins re sult from the flexural lithospheric response to loading most of the models proposed so far have considered the lithosphere as a rheological unit and have been based on classical elastic and viscoelastic plate theory the wavelength and am plitude of the flexural response is not an intrinsic property of the lithosphere but result from the history of the competitive interactions between rate of loading and rate of viscous dissipation thermally activated a clear physical description of this flexural mode has not yet been proposed even though some recent results on the mecha nisms of uplift shoulder formation during rifting evolution may be considered bassi 1991 chery et al 1992 the geodynamical context of those basins is complex and the relationship between the transition of extensional and compressional domains is a topic of vigorous research current models for extensional and compressional basins are strongly based on a bulk rheological descrip tion of the whole lithosphere and on a kinematic description of the deformation mechanisms sawyer 1985 houseman and england 1986 quinlan et al 1993 this issue the basin record does reveal to some extend the memory of the deformation history starting from the construction of the internal structure of the basins i e from the processes leading to the formation of rocks sedimentation diagenesis compaction including possible buildup of fluid overpressures and the pattern of the large de formations by faulting or folding to enhance the understanding of the formation and evolution of sedimentary basins it is important to fully address the physical mechanisms operating at different scale in the continental lithosphere for example faulting forms a most important expression at least at the surface of large scale deformation in the basins how those basins are related to the faulting process and the fault interactions is an unsolved question pull apart basins are certainly

interplay of extensional and compression in basin formation this volume contains a collection of papers on the interplay of extension and compression in basin dynamics presented at the 4th annual workshop of the international lithosphere project task force origin of sedimentary basins in benevento italy 25 september l october 1993 previous workshops of the ilp task force have been held in rueil malmaison france 19901 in matrahaza hungary 1991 on the rim of the pannonian basin and in sundvollen in the oslo rift 1992 meeting reports have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 cloetingh sassi and task force team 1994 the 5th task force meeting focusing on basin extension and strike slip tectonics was held in the dead sea rift israel 29 september 5 october 1994 a selection of papers presented at the 5th task force workshop will be published in a forthcoming special volume of tectonophysics the 1995 workshop has taken place in the southern pyrenean foreland basin to examine the relationships between tectonics and eustasy in foreland fold and thrust belts the emphasis of the benevento workshop was on

the role of rheology in extensional basin formation modelling the rheology of the lithosphere determines its deformation under given initial and boundary conditions this paper presents a critical discussion on how rheological properties are taken into account in extensional basin modelling since strength envelopes are often used in models we review the uncertainties in temperature and rheological parameters and assumptions in type of rheology and mode of deformation involved in their construction models of extensional basins are classified into three groups kinematic kinematic with rheological constraints and dynamic rheology enters kinematic models only implicitly in the assumption of an isostatic compensation mechanism we show that there is a critical level of necking that reconciles local isostasy with the finite strength of the lithosphere which requires a flexural response kinematic models with rheological constraints make use of strength envelopes to assess the initial lateral variations of lithospheric strength and its evolution with time at the site of extension dynamic models are the only ones to explicitly introduce rheological constitutive equations usually in plane strain or plane stress they usually however require the presence of an initial perturbation thickness variations pre existing faults thermal inhomogeneities rheological inhomogeneities the mechanical boundary conditions kinematic and dynamic and the thermal boundary conditions constant temperature or constant heat flux at the lower boundary of the lithosphere may result in negative positive feedbacks leading to cessation acceleration of extension we conclude that while kinematic models with rheological constraints if possible are very successful in accounting for the observed characteristics of sedimentary basins dynamic models are necessary to gain insight into the physical processes underlying basin formation and evolution

morphotectonic evolution of rifted continental margins inferences from a coupled tectonic surface processes model and fission track thermochronology we use a numerical model to study the topographic evolution and erosional history of rifted continental margins the model combines a kinematic description of lithospheric extension tectonic model with a surface processes model that includes short range hillslope and long range fluvial transport the tectonic model predicts the evolution of the lithospheric temperature and strength elastic thickness distribution as well as the tectonic uplift through time this is input into the surface processes model which calculates the degradation of topography and associated isostatic rebound modeled denudation histories across the margin are used to predict apatite fission track age and length patterns modeling results indicate that depending on the adopted parameters an uplifted rift flank should degrade by erosion within 50 100 m y without significant retreat of the topographic elevation maximum the development of an escarpment system at rifted continental margins is in itself not an indication of tectonic rift flank uplift but results from the existence of a high elevation interior plateau erosional base level lowering as a consequence of rifting and regional isostatic response to erosion of the margin however apatite fission track thermochronology reveals that the areas seaward of the escarpment at a number of rifted margins have been exhumed from several kilometers depth such amounts of denudation cannot be accommodated with isostatic rebound alone and require additional tectonic uplift of the rift flanks modeling of apatite fission track patterns suggests that fission track thermochronology dates the onset of rapid erosion which coincides with the initiation of strong relief i e initiation of rifting fission track ages which are younger than the age of rifting thus cannot be unambiguously interpreted as excluding prerift uplift the timing of margin uplift can be established only by careful track length analysis and integration with regional stratigraphic data the model is applied to the saudi arabian red sea margin and the southeastern australian highlands where it is constrained by present day topography and apatite fission track data as well as seismic and gravity data for the saudi arabian red sea margin synrift regional plateau uplift with a magnitude of approximately 1 km is inferred possibly as a result of asthenospheric upwelling flexurally induced tectonic uplift of the rift flank with a magnitude of 2 km is superimposed on this regional uplift the relatively high elevation of the southeastern australian highlands their steep front and the relatively high amounts of erosion suggest that apart from mesozoic synrift flexural uplift tertiary rejuvenation of topography has occurred possibly as a result of renewed lithospheric thinning and underplating the low elevation of the australian interior would inhibit the evolution of a major escarpment in the absence of such renewed uplift

relationship between deeper lithospheric processes and near surface tectonics of sedimentary basins interactions between upper lithosphere deformation as manifested in the structure and evolution of sedimentary basins and lower lithospheric deformation presumably reflect large scale regional or global tectonic events we review the current state of knowledge regarding these interactions and suggest areas of research which may lead to an improvement in this knowledge understanding the development of sedimentary basins requires insight into the processes responsible both for basin subsidence and also for distribution and preservation of sediments within the basins while some classes of basins are better understood than others there remain significant gaps both in our ability to account for available data and also in the data available to test current models and develop new ones subsidence in some classes of basins can be related to lithospheric scale processes occurring as part of the overall plate tectonic paradigm for example it is widely accepted that passive margin basins subside as a result of lithospheric extension mckenzie 1978 and that foreland basins are flexural consequences of collision between a continent and outboard terranes beaumont 1981 on the other hand models for the origin of intracratonic forearc and trans tensional basins are essentially still at cartoon level involving processes that are difficult to quantify and evaluate in the following we review a number of fundamental questions of vital interest for understanding of the relationship between deeper lithospheric processes and near surface tectonics

fault growth in brittle ductile experiments and the mechanics of continental collisions using laboratory models of continental collisions we study the mechanisms responsible for large scale deformation and the nature of the penetrative deformation localized or homogeneous and its characteristic scales and structure in order to focus the study one of the most spectacular cases of continental collisions namely the india asia collision is considered different models with varying rheologies are analyzed which attempt to respect the brittle ductile stratification corresponding to the crust and mantle structure in the earth each experiment is quantified by studying the strain field and the fault pattern as a function of the position p of the indenter within the system the strain field is characterized by 1 the second invariant of the two dimensional strain tensor and its variation with position for a fixed p the evolution of its average as a function of p 2 the evolution with p of the participation ratio s2 which quantifies the fraction of the system surface area which participates in the deformation 3 the evolution of the escape ratio calculated as the surface increase gained by the system during its eastward lateral escape divided by the surface covered by the indenter penetration qualitatively we find that the deformation first spreads out but later on undergoes localization once the fault pattern is mature the cumulative fault length does not increase anymore we observe that the strain field is essentially controlled by the kinematics of the larger faults each fault pattern is quantified by studying 1 the histograms of fault orientations 2 the capacity and barycenter fractal dimensions 3 the multifractal generalized dimensions and 4 the distribution of fault lengths the fractal dimension d is found to almost constant within experimental uncertainty d 1 7 0 1 and thus appears rather insensitive to the particular chosen rheology we find a correlation between the generalized multifractal dimensions and two exponents the barycenter fractal dimension b and the exponent a of the fault length distribution this shows that the scaling properties of fault patterns can be characterized by the knowledge of only two exponents b and a of the spatial and length distributions of faults our main results are 1 observation of the growth of self similar fault patterns 2 complete characterization of the fault patterns with two scaling exponents a and b 3 wide distribution of undeteriorated domains and large heterogeneity of the deformation field 4 maturation of the fault structure corresponding to a localization of the deformation on a few large faults in the late stage of the deformation

thermo mechanical modeling of the tyrrhenian sea lithospheric necking and kinematics of rifting we present the results of quantitative forward modeling of the sardinian rifted margin of the tyrrhenian sea the purpose of this study is to investigate the thermo mechanical structure that affects the thinning of the lithosphere across the margin the role of lithospheric necking during basin formation constrained by basement topography moho depth and gravity anomalies is modeled for different compensation models independent constraints are obtained from the analysis of the predicted thermal structure a deep level of necking 25 km is required to explain the observed crustal geometries and gravity anomaly signature the model predicts spatial and temporal variations in rheology during extension with important implications for kinematics of lithospheric thinning prerift lithospheric conditions strain rate and temperature during extension appear to be the key controls on the style of lithospheric rifting and necking in the tyrrhenian sea a forward model for basin stratigraphy is presented for the polyphase history of the tyrrhenian rifting this model provides quantitative estimates of time space dependent crustal thinning and rates of extension

fractal and multifractal measures of natural and synthetic fracture networks we have analyzed the fractal and multifractal nature of a series of 17 natural fracture trace maps representing a wide variety of scales geological settings and lithologies as well as a number of typical synthetic fracture networks in which fracture locations orientations and lengths are drawn from various probability distribution functions recent studies have shown that multifractal methods can be used to investigate fracture networks at greater depth since the fractal dimension represents only part of the scaling spectrum characterizing each network we find that the real and synthetic fracture maps display fractal and multifractal properties moreover the properties of the synthetic networks are very similar to those of the real networks with nontrivial fractal dimensions and multifractal spectra we suggest that different fracturing mechanisms can lead to two or more distinct subranges over which a fractal dimension can be defined while the heterogeneity of the rock and the nature of the fracturing mechanisms lead to multifractal properties we also find that the fractal dimension of a synthetic fracture network is relatively insensitive to parameters such as fracture length and orientation but can be controlled by appropriate choice of the relative fracture density

quantitative characterization of fracture structure in coal based on image processing and multifractal theory abstract the characterization of fracture structures is key for evaluating the permeability of coalbed methane cbm reservoirs and an interconnected fracture network is essential for the production of cbm taking the upper permian coal in the eastern yunnan and western guizhou region as an example we systemically studied the characteristics of coal deformation and fracture development through direct observation of coal faces and hand specimens an image processing technique was used to obtain high resolution fracture images with an actual resolution of approximately 2 m followed by the statistics of the porosity parameters such as micro fracture density intersection point density and plane areal porosity the multifractal theory was applied to study the micro fracture structures of the coal and a practical algorithm and corresponding technical procedure was proposed to characterize the multifractal characteristics of coal fractures the quantitative characterization of the heterogeneity of the whole and partial fracture structure was then performed and the indicating significance of the generalized dimension spectrum the singularity spectrum and the calculated characteristic parameters was described our results suggest that the micro fracture structures of coal are multifractal which can be measured by combining image processing and multifractal methods the fracture development and the distribution heterogeneity in the target coal seams show significant differences both vertically and laterally coal seam groups with well developed fracture systems and high connectivity were identified by combining macro and micro scale fracture observations and multifractal characterization including the 8 12 coal seam group in the tucheng mining area the 3 7 group of the yueliangtian mine in the pan guan mining area the 8 12 group in the pan guan mining area the 13 18 group in the enhong mining area and the 3 7 group in the laochang mining area

a finite difference technique to incorporate spatial variations in rigidity and planar faults into 3 d models for lithospheric flexure summary we present a finite difference formulation for 3 d elastic flexure of the lithosphere which is solved by a direct matrix method to incorporate the effect of spatial variations in rigidity additional terms for the bi harmonic 3 d flexure equation have been derived from a variational displacement formulation as used in finite element methods additionally planar faults are treated as discontinuities these are implemented by an additional degree of freedom for fault heave and a coupled continuum equation for zero differential tilting across the fault the 3 d finite difference results have been tested for line loads point loads and disc loads by analytical solutions and for spatial variation in effective elastic thickness eet by 2 d finite difference solutions fault related flexure patterns are compared to the 2 d analytical broken plate model developed by vening meinesz 1950 we subsequently apply the 3 d fault model to investigate fault controlled 3 d basement geometries in lake tanganyika east africa we show that our model is capable of predicting 3 d basement geometries characteristically observed in rifted basins the modelling results indicate that fault controlled upper crustal flexure patterns are associated with low values for eet a comparison with regional scale model studies showing a superposition of high eet flexure effects supports a multilayered rheological control on continental rifting

late cretaceous early tertiary tectonic evolution of the central european basin system cebs constraints from numerical modelling abstract the results obtained from a suite of spherical thin sheet finite element model calculations on the late cretaceous early tertiary tectonic evolution of the area of the central european basin system cebs are presented and discussed the calculations incorporate the effects of variations in lithospheric structures and compositions and changes in the imposed boundary conditions the impact of lateral contrasts such as pre existing weak domains is quantified through a thermo mechanical model for the entire cebs the obtained predictions have been constrained by comparisons with more recent observed field data and resemble the present day dynamics and kinematics a trial and error reconstruction of the development through time of the dynamic of the alpine orogeny as well as of the early atlantic extension have been considered in order to investigate the role of boundary forces in the late cretaceous early tertiary tectonic evolution of the cebs the observed evolution of subsidence depocentres and areas of uplift for the cebs during this time span has been reconstructed the results are in agreement with previous studies which have related the large scale late cretaceous early tertiary inversion within the cebs to long wavelength intra plate compressive stresses exerted mainly by the alpine thrust the models show that lateral heterogeneities have to be considered in order to model more local features such as the observed differential response of adjacent areas to the large scale stress regime this indicates that both intra plate tectonic forces and rheological structural contrasts must be taken into account to reconcile the style of intra plate deformation and to model the evolution through time of complex basin systems

fractal analysis of fracturing in two african regions from satellite imagery to ground scale abstract in two test areas of africa the fractal character of fracture fields was analyzed at very different scales on fracture maps from satellite images and from interpretation of drainage networks on topographical maps aerial photographs and ground photographs three different methods were used and the results criticized it was generally found that the area studied in western africa displays more fractal features than the area examined in central africa this might be related to the number and mechanism of fracturing phases in each region

structural controls on sedimentary basin evolution introduction this volume contains a collection of papers on structural controls on sedimentary basin evolution presented at the sixth annual workshop of the international lithosphere program task force origin of sedimentary basins in sitges at the rim of the ebro basin september 1995 previous workshops of the ilp task force had been in rueil malmaison france 1990 in matrahaza hungary 1991 on the rim of the pannonian basin in sundvollen norway 1992 in the oslo graben in benevento italy 1993 in the southern apennines fold andthrust belt and in the dead sea rift of israel 1994 the task force also organized a number of sessions during the 1992 and 1996 european geophysical society and the 1993 and 1995 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 1995a b 1996 stephenson 1993 stephenson et al 1996 a position paper cloetingh sassi and task force team 1994 published in m a r i n e a n d p e t r o l e u m geo logy has outlined the task force strategy to pursue the development of a new generation of basin models using natural laboratories with high quality data sets obtained through close partnership with industry the 7th task force workshop was held on the faroe islands northern atlantic in 1996 with the aim of examining the dynamics of rifting

a fractal constitutive model for unsaturated flow in fractured hard rocks abstract a physical conceptual model for water retention in self similar fractured hard rocks is presented the geometric pattern of the fracture network is described using a classical fractal object known as the sierpinski carpet assuming this type of geometry a relatively simple closed form expression for the water content is obtained all model parameters can be calculated from the density of the main fractures the maximum and minimum values of the fracture aperture and the residual water content the resulting water content expression is then used to estimate the unsaturated hydraulic conductivity of the fractured medium based upon the well known model of burdine it is found that for large enough ranges of fracture apertures the new constitutive model converges to the empirical brooks corey model

the legacy of the ne german basin reactivation by compressional buckling in contrast to previously published models for the area the seismic reflection moho is essentially flat beneath the ne german basin along the dekorp deep seismic profile basin 96 this raises the question whether the present structure of the crust and flat moho reflect the initial formation of the basin or modification by more recent processes a 2d flexural model developed for a thin elastic plate is presented together with lithospheric strength profiles calculated along the basin 9601 reflection seismic line the analysis shows a southward decrease of lithospheric strength below the basin with a lithospheric decoupling between the crust and the mantle the modelling supports the hypothesis that the present moho topography is caused by flexural buckling which caused subsidence of the ne german basin during the upper cretaceous early cenozoic inversion event this suggests that the basin is in isostatic disequilibrium and that compressive stresses are required to keep the present basin geometry

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

fractal analysis of fractures applied to soultz sous forets hot dry rock geothermal program abstract a fractal analysis has been performed on a fracture set observed on granite cores in order to determine preferential paths for fluids injected during hot dry rock hdr geothermic experiments this analysis was based on the sorting of fractures on criteria such as their direction according to the present stress field their dip their hydrothermal filling thickness vein width which is linked to the intensity of alteration and thus to the physico chemical properties of the surrounding rock the results show a global increase of the fractal dimension d with depth which may be related to the lithostatic pressure gradient analysis of the total fracture set has showed zones in which fractures are clustered low d values while others are characterized by regularly spaced fractures higher d values fractures parallel to the maximum horizontal stress narrow veins and fractures with a dip greater than 40 represent 35 to 79 of the total fracture set their fractal dimensions are similar to those of the total fracture set large veins linked with high porosity zones show a cluster pattern all along the drilling in the context of hdr geothermics one should seek highly fractured zones especially if the fractures they contain are clustered and if they have developed wide alteration zones linked to a high porosity these conditions may optimize the hdr heat exchanger possibilities

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

the fractal nature of structural controls on ore formation the case of the iron oxide copper gold deposits in the carajas mineral province brazilian amazon the formation of ore minerals in hydrothermal deposits is the result of a complex interplay between physical and chemical processes that are conditioned by the geologic environment in which they occur in the last decades research has increasingly indicated that many of these processes display different forms of scale invariance i e they show fractal geometry this suggests that behind the apparent disorder and irregularity of the geometry of mineral deposits at different scales an underlying regular pattern is present if properly understood this regular geometrical pattern could be useful in a variety of theoretical and applied fields a great portion of this scale invariance is given by the structural framework during mineralization because structures are a dominant factor controlling fluid flow here we assess the geometry of iron oxide copper gold iocg mineralization in the world renowned carajas mineral province focusing on one of the largest and most economically important orebodies the sossego deposit the geometry of mineralization is evaluated at the microscale ore minerals in thin sections local scale orebodies in mine maps and regional scale deposit distribution on regional maps we show that the spatial distribution and shape of ore minerals at the microscale is largely nonrandom presents fractal geometry and displays defined trends in spatial distribution and anisotropy additionally the geometric trends observed at the microscale mimic those of the local scale geometry of orebodies as well as the regional scale distribution of mineralization the main property controlling the observed scale invariance is permeability which is intrinsically associated with structures at multiple scales these results contribute to further understanding the fractal nature of processes controlling mineral deposit formation and revealing new multiscale approaches to investigate structural controls on ore deposition

fractal clustering of metamorphic veins metamorphic veins record the fracture controlled flow of fluids throughout the oceanic and continental crust i show that the spatial distributions of veins from three diverse metamorphic settings are fractal and self similar vein densities were measured by counting the number of macroscopic veins intersected along linear transects the localities included wol lastonite quartz veins in marbles for which the fractal dimension d is 0 46 actinolite chlorite veins in hydrothermally altered oceanic diabases d 0 81 and epidote quartz veins in contact metamorphosed basalts d 0 25 0 63 the fractal clustering of veins provides a geometric framework for understanding spatial and temporal patterns of fluid flow and mineral reaction during metamorphism