fluid flow in metamorphic environments the study of fluid flow in metamorphic environments progressed over the last quadrennium mainly from a focus on the tenets of continuum mechanics in which rock properties such as porosity and tortuosity that control flow are assumed to be homogeneous over a specified finite volume advances have been afforded by these principles not only from their direct application but also from tests of their veracity assumptions inherent in the continuum approach are based on the scale of observation and in conjunction with the advent of new analytical technologies have given new impetus for examining mechanisms of material transfer between fluids and metamorphic rocks at smaller and smaller scales thus even as continuum mechanics has laudably come to be widely utilized in the study of metamorphic fluid flow the empirical adequacy oreskes et al 1994 of the methodology is being assessed through access to previously unattainable scales of observation

getting over continent ocean boundaries the idea of a simple linear boundary between continental and oceanic crust at extended continental margins is widely recognized to be an oversimplification despite this such boundaries continue to be mapped because of their perceived utility in palinspastic and plate kinematic reconstructions to examine whether this perception is justified we review the data and models on which basis continent ocean boundaries are interpreted and map a set of such interpretations worldwide from more than 150 publications the maps show that the location of the continent ocean boundary is rarely consistently estimated within the 10 100 km observational uncertainty that might be expected of the geophysical data used for doing so that this is the case regardless of whether the transition zone behind the boundary is classified as magma rich or magma poor and that the geographical separation of estimates exceeds the width of single study continent ocean transition zones the average of global maximum separations across sets of three or more estimates is large 167 km and mostly a consequence of interpretations published over the last decade we interpret this to indicate an extra component of uncertainty that is related to authors understanding of the range of features that are interpretable at extended continental margins we go on to discuss the implications of this uncertainty for palinspastic and plate kinematic modelling using examples from the literature and from the south atlantic ocean we conclude that a precise continent ocean boundary concept with locational uncertainty defined from the ensembles is of limited value for palinspastic reconstructions because the reconstruction process tends to bunch the ensemble within a region that is i of similar width to the observational uncertainties associated with continent ocean boundary estimates ii narrower than the regions of uncertainty about rotated features implied by the propagation of uncertainties from plate rotation parameters and iii coincident within all the above uncertainties with the more easily mapped continental shelf gravity anomaly secondly we conclude that estimated continent ocean boundaries are of limited use in developing or testing plate kinematic reconstructions because i reconstructions built using them as markers do not within uncertainty limits defined from the ensembles differ greatly from those using more easily determined bathymetric or gravity anomaly contours and ii because it is impossible to segment and date them with useful precision to use as markers of the edges of rigid oceanic lithosphere outside of the constraints of a pre existing plate kinematic model

transverse tectonics in the sikkim himalaya evidence from seismicity and focal mechanism data abstract in the present study about 356 local earthquakes in the region of the sikkim himalaya have been accurately located and analyzed using 2181 p travel times and 2161 s travel times from a network of 11 broadband seismic stations operated by the national geophysical research institute during january 2006 to november 2007 further refinement of the hypocentral parameters using the hypodd relocation program resulted in 198 well constrained locations interestingly this study reveals several characteristic features that distinguish sikkim from the rest of the himalaya the seismicity distribution is found to be confined mostly between the main boundary thrust mbt and the main central thrust mct but not quite associated with either while the entire himalayan front is generally characterized by shallow angle thrust faulting focal mechanisms in this region are predominantly of strike slip type in conformity with a right lateral strike slip mechanism along the northwest trending tista and gangtok lineaments the p axis trends of earthquake focal mechanisms are clearly oriented north northwest marking a clear transition from the ambient north northeast trending direction of indian plate motion with respect to the eurasian plate all along the himalayan front moderate sized earthquakes occur down to 70 km depth in this region compared to an average focal depth of 15 20 km in the rest of the himalaya also a high average crustal p velocity of 6 66 km sec and a fairly low b value of 0 83 0 04 are obtained indicating the probability of occurrence of a higher magnitude earthquake in the future a north south section in the sikkim region shows a relatively flat topography unlike in the rest of the himalayan mountain chain and suggestive of lower rates of convergence in the recent geologic past it is proposed that crustal shortening in the sikkim himalaya has been substantially accommodated by transverse tectonics rather than underthrusting in recent times

correlation analysis of fracture arrangement in space abstract we present new techniques that overcome limitations of standard approaches to documenting spatial arrangement the new techniques directly quantify spatial arrangement by normalizing to expected values for randomly arranged fractures the techniques differ in terms of computational intensity robustness of results ability to detect anti correlation and use of fracture size data variation of spatial arrangement across a broad range of length scales facilitates distinguishing clustered and periodic arrangements opposite forms of organization from random arrangements moreover self organized arrangements can be distinguished from arrangements due to extrinsic organization traditional techniques for analysis of fracture spacing are hamstrung because they account neither for the sequence of fracture spacings nor for possible coordination between fracture size and position attributes accounted for by our methods all of the new techniques reveal fractal clustering in a test case of veins or cement filled opening mode fractures in pennsylvanian marble falls limestone the observed arrangement is readily distinguishable from random and periodic arrangements comparison of results that account for fracture size with results that ignore fracture size demonstrates that spatial arrangement is dominated by the sequence of fracture spacings rather than coordination of fracture size with position fracture size and position are not completely independent in this example however because large fractures are more clustered than small fractures both spatial and size organization of veins here probably emerged from fracture interaction during growth the new approaches described here along with freely available software to implement the techniques can be applied with effect to a wide range of structures or indeed many other phenomena such as drilling response where spatial heterogeneity is an issue

proterozoic accretionary tectonics in the east kimberley region australia abstract the east kimberley region contains well preserved tectonic structure dating back to the earth s most significant stage of continental growth the assembly of the nuna supercontinent an integrated geological geophysical investigation of this region has been conducted and reveals insight into its tectonic evolution including potential influence of significant crustal scale structures in the development of regional architecture the emplacement of magma and the relationship of these structures to large scale deformation some newly interpreted features include a north trending structure and three north west trending structures that segment the north east trending orogen the central segment of the orogen is a zone of higher metamorphic grade and is host to a distinct gravity high this gravity high can be explained by excess mass in the mid crust this anomaly is consistent with either a large mafic ultramafic intrusion or a high density crustal fragment possible tectonic models to explain the geophysical and metamorphic anomalies involve in the latter case the accretion of a crustal fragment to the kimberley craton prior to the 1865 1850 ma hooper orogeny or in the former case intrusion of voluminous mafic magmas into the middle crust whether by igneous or structural means we consider the development of this anomalous region to be a result of along strike variations in subduction dynamics these were perhaps driven by variations in slab geometry accommodated by the orogen normal structures we identify the orogen normal structures are interpreted to be crustal scale faults along which significant vertical displacement occurred when a crustal fragment collided with kimberley craton and exhumed high grade metamorphic rocks to the surface

automatic gravity optimization of 2 5d strike listric fault sources with analytically defined fault planes and depth dependent density an automatic gravity inversion technique in the space domain simultaneously estimates the parameters of strike limited listric fault sources and regional gravity background from a set of observed bouguer gravity anomalies the fault profile and regional effect are described by unknown polynomial functions of arbitrary but prescribed degree furthermore the density contrast within the fault structure is presumed to be known according to a prescribed parameterized nonlinear function of depth in geologic settings where the detached downthrown block consists of a series of sedimentary beds whose density increases with depth the inversion is automatic in that it initializes and determines polynomial coefficients for the fault boundary and regional gravity background from a set of observed bouguer gravity anomalies and improves them iteratively until the modeled gravity anomalies mimic the observed anomalies an analysis of a set of gravity anomalies attributable to a synthetic model of a listric fault structure in the presence of pseudorandom noise with and without regional background has disclosed that the algorithm yields reliable interpretations with modest error in model geometry even in the presence of pseudorandom noise in the presence of regional gravity background and pseudorandom noise the estimated parameters of the structure deviate marginally from the true ones the derived density depth model of the jharia coal basin in india a pull apart basin has been used to analyze the observed bouguer gravity anomalies of a boundary fault the interpretation has yielded information consistent with drilling results and geologic setting of the basin

potential field data in integrated frontier basin geophysics successes and challenges on australia s continental margin abstract offshore frontier sedimentary basins are characterised by a lack of constraining geological and geophysical data this lack of data is generally the result of deep water 500 m difficult geology volcanics and salt remoteness and harsh met ocean conditions these characteristics present significant challenges to marine surveying which means that frontier basins tend to be underexplored with continuing interest in exploration for energy resources in frontier regions many frontier basins around the world have been the focus of increasingly sophisticated geophysical studies that integrate a range of methodologies including those based on potential field gravity and magnetic data underexplored frontier basins around australia s continental margin have received increased attention during the last decade largely as a result of government funded programs of precompetitive data acquisition and analysis the components of this work that have relied heavily on potential field data include first pass depth to basement estimation using spectral techniques applied to magnetic data enhancement of gravity and magnetic images to aid the identification of basin depocentres and to facilitate onshore offshore geological interpretation of basement structure multi scale edge detection applied to gravity and magnetic data to aid the interpretation of basement structure 3d forward and stochastic inverse modelling of gravity data to guide seismic interpretation of sediment thickness and basement structure and using supercomputers for high resolution regional scale 3d inverse modelling of magnetic and gravity data to constrain the physical properties of the crust despite the additional insight offered by this work efforts to understand frontier basins are not without challenges one of the most fundamental of which is to ensure that non specialists are not misinterpreting data e g wrongly interpreting artefacts arising from specific processing the other main challenge in australian frontier basins arises from a lack of constraints on crustal structure this leads to significant ambiguity when using gravity data to infer sediment thickness or to understand the nature of basement this ambiguity could be vastly reduced through the acquisition of seismic refraction data that focuses on imaging crustal structure further opportunities exist in using alternative methods for automated depth to basement estimation incorporating process oriented rather than static potential field modelling and in applying 3d forward and inverse gravity and magnetic modelling to other australian frontier basins

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

fractal vein distributions within a fault fracture mesh in an exhumed accretionary melange chrystalls beach complex new zealand a well developed fault fracture mesh is observed in the chrystalls beach complex an accretionary melange within the otago schist on the south island of new zealand in this study an analysis of vein thicknesses and clustering of veins is presented both shear and extension veins have a power law thickness distribution measures of vein spacing best fit a power law distribution but a small data set limits this interpretation to a small fractal range vein clustering varies from random to moderately clustered between outcrops and is the greatest where a large proportion of relatively competent blocks occurs within the melange fractures are distributed within the melange matrix and this localized deformation requires heterogeneity in rheology and or fluid pressure distribution whereas pervasive distributed deformation occurs in relatively homogeneous rock the overall trend of this deformation being mainly accommodated by thin veins required that new fractures formed preferentially over refracturing existing veins which highlights the distributed nature of deformation within a fault fracture mesh the predominance of new fractures may result from vein material being stronger than the cleaved wall rock such that wall rock failure occurred instead of reopening of pre existing shear and extension veins

power law vein thickness distributions and positive feedback in vein growth the thicknesses of veins of a single generation from the kodiak accretionary complex show a power law distribution with an exponent of d 1 33 this value d 1 indicates that a significant portion of the vein related extension is accommodated by the thinnest veins thick vein segments are typically confined to southeast dipping brittle ductile shear zones textural observations of veins within these zones indicate a progressive evolution from crack seal to euhedral growth of quartz with an increase over time in the duration that fractures remained open model simulations of vein thickness distributions show that a constant growth model results in a negative exponential distribution and that it is necessary to assume size proportional growth to produce a power law distribution textures and power law thickness distributions for the kodiak veins are thus consistent with an increasing time averaged growth rate as vein thickness increased comprising a positive feedback the positive feedback resulted in the progressive evolution from fractures to brittle ductile shear zones and ultimately to faults

gravimetric determination of the continental oceanic boundary of the argentine continental margin from 36 s to 50 s fil arecco maria alejandra universidad de buenos aires facultad de ingenieria argentina

pegmatite dyke emplacement and the state of stress during cratonization an example from the dharwar craton south india abstract in this study we measured orientations of 797 pegmatite dykes intruding the 2 5 ga koppal pluton dharwar craton south india and use the data to evaluate the state of stress prevalent during dyke emplacement we infer that the dykes were emplaced synchronously with late d3 regional deformation that was controlled by nw se directed shortening dykes within the koppal pluton kp have a restricted range of orientations which is indicative of fluid pressure pf

giant mounded drifts in the argentine continental margin origins and global implications for the history of thermohaline circulation abstract partially buried giant drifts are located in the southern most sector of the argentine continental margin generating a bathymetric jump at the base of the slope they are characterised as giant asymmetrical elongated mounded contourite drifts and are described in detail here for the first time this description is mainly based on the bathymetric and multichannel seismic reflection profiles data their origin and evolution in the argentine basin are decoded and their implications in an area crucial for geologic and palaeoceanographic reconstruction between the atlantic and antarctica are discussed the buried giant drifts are divided into two zones by a large seamount the major giant drift 50 km wide 300 km long and having a sedimentary thickness of nearly 1 km is located to the south of this seamount and oriented to the north where its summit outcrops at present seafloor here its asymmetric external shape is characterised by a steep western side and a gently dipping smooth eastern side with internal reflections prograding eastward based on its position morphology and internal characteristics it has been deduced that this giant drift was generated in the argentine basin by the southward branch of a confined large loop of the antarctic bottom deep water from the eocene oligocene boundary coevally with the drake passage opening until the middle miocene however after a major palaeoceanographic change in the mid to late miocene a new oceanographic scenario was established that fossilised these giant drifts these changes produced a new depositional style in the margin resulting in initiation of the present contourite depositional system and morphologic features over the slope extension of north atlantic deep water circulation into the southern hemisphere and deepening of antarctic bottom water circulation in the argentine basin are herein postulated as the factors that controlled said changes these giant drifts show strong seismic evidence of hydrates and free gas that are ripe for energy resources exploration thus demonstrating the economic potential of contourite deposits in deep marine environments

geology age and origin of supracrustal rocks at akilia west greenland new mapping geochronology and geochemistry of the supracrustal enclave and associated orthogneisses at akilia west greenland support a 3825 6 ma age for the sequence and a chemical sedimentary origin for the controversial fe rich quartz pyroxene gneisses lithologies of the enclave comprise laterally continuous mappable units of mafic amphibolite ultramafic rocks and two fe rich quartz pyroxene units a minor anthophyllite garnet rock with chemical characteristics suggesting a sedimentary protolith was identified the earliest foliation parallels lithologic contacts this foliation was isoclinally folded about a steep hinge surface and then tightly refolded about a steep ns hinge plane the latest folding produced limbs exhibiting contrasting strains the full deformation history is shared by all lithologies of the enclave two previously unidentified orthogneiss sheets preserve deformed magmatic crosscutting relations with amphibolite and ultramafic units in the low strain limb the supracrustal anthophyllite garnet rock experienced zircon growth at 3600 and 2700 ma in common with amphibolites these ages are interpreted to reflect metamorphism at granulite and amphibolite facies respectively consistent with independent regional evidence the crosscutting orthogneiss sheets preserve a complex history of zircon growth but only earliest cores indicate th u exchange equilibrium with the bulk rock at magmatic conditions weighted mean 207 pb 206 pb ages of cores of 3730 7 ma and 3825 6 ma date the crystallization ages of the sheets indicating that the akilia supracrustal rocks were deposited 3819 ma quartz pyroxene rocks on akilia have been interpreted as metamorphosed chemical sediments that may preserve carbon isotope evidence for life at the time of their formation an alternative proposal is an origin by metasomatic alteration our results show that these rocks experienced a history of deformation and zircon growth identical to other lithologies of the supracrustal body metamorphic zircons give a minimum 207 pb 206 pb age of 3589 13 ma regardless of origin the two models of formation of quartz pyroxene rocks were evaluated using field petrologic and geochemical tests the distribution of the units the absence of field or petrologic indicators of metasomatism and geochemistry oxygen and nontraditional stable isotopes immobile elements and ree together support a sedimentary but not a metasomatic origin because their protolith was sedimentary the quartz pyroxene rocks are a primary part of the supracrustal sequence and have the same minimum age despite strong deformation and polymetamorphism the akilia supracrustal enclave contains information about terrestrial surficial processes at 3819 ma

reconstruction of the southwestern african continental margin by backward modeling abstract as the evolution of the southwestern african passive continental margin and in particular the vertical movements in this area are still a matter of debate this study aims to quantify the past vertical movements by reconstructing the paleobathymetric evolution of the southwestern african margin during the post rift phase to quantify the vertical movements inferred from paleobathymetries different subsidence components that have affected the passive continental margin are calculated and interpreted with respect to the generating processes our investigation takes advantage of information on the present day sedimentary thicknesses and the crustal configuration along the sw african margin by using this detailed information and modeling backward in time we attempt to separate different subsidence components such as the load induced subsidence and the thermal subsidence for different time intervals during the post rift phase calculating the amounts of each subsidence component and subtracting them from the present day configuration yields paleobathymetries which are interpreted with respect to the evolution of the southwestern african passive margin these restored paleobathymetries for different time steps during the post rift phase indicate spatial and temporal variations of vertical movements including phases of seafloor uplift as a result our investigation allows to give minimum estimates of the vertical movements that have occurred during the post rift phase in addition to predominant subsidence about 1000 m of seafloor uplift are deduced for the northern and southern parts of the sw african margin quantifying the amounts of vertical movements cannot finally clarify the generating processes behind these movements but the timing and magnitude of seafloor uplift indicate a deep mantle mechanism

fractal models for ore reserve estimation abstract traditional geometric and geostatistic methods for reserve estimation in a single deposit are difficult to use with skewed distribution mineralization variables including grade orebody thickness and grade thickness a common characteristic of most deposits and require complex data processing it has been shown that the skewed mineralization variables can be described by the number size model in a fractal domain based on the number size model assuming that orebody thickness and grade thickness are continuous variables the fractal model for reserve estimation fmre in a single deposit can be established in the fmre ore tonnage can be estimated given the orebody area and the fractal parameters of orebody thickness distribution and metal tonnage can be estimated based on the orebody area and the fractal parameters of grade thickness distribution the reserve estimated by the fmre can denote actual ore tonnage and metal tonnage that can be mined out of the deposit the frme was applied to the dayingezhuang gold deposit in the jiaodong gold province in china the gold reserves via the fmre and the traditional geometric block method are similar with relative errors of 3 11 in ore tonnage and 0 29 in metal tonnage compared to traditional reserve estimation the fmre is much easier in calculation process and is more reasonable in dealing with the skewed distribution however this new method fails to calculate local reserve which can be derived via any of the traditional estimation methods

structural features of the southwest african continental margin according to results of lithosphere scale 3d gravity and thermal modelling abstract to understand the structure of the southwest african continental margin a lithosphere scale 3d structural model has been developed covering the marginal cretaceous cenozoic orange luderitz walvis and namibe basins the easternmost walvis ridge offshore onshore the model includes two late proterozoic owambo etosha and nama basins this 3d model integrates published thickness maps sediment isopach maps shallow seismic and well data as well as published deep seismic information and has been additionally constrained by 3d gravity and thermal modelling using 3d gravity modelling the first order configuration of the crystalline crust has been resolved with respect to the location of the continent ocean boundary the distribution of a high density lower crustal layer indicates a continuous body extending below the cretaceous cenozoic depocentres and aligned parallel to the coast line in addition high density zones within the continental crystalline crust had to be included in the model to fit observed and calculated gravity the obtained moho topography correlates with the major tectonic units of this continental margin the results of the 3d thermal modelling indicate that there is a clear relationship between the location of thickened sediments and areas with increased temperatures within the upper 10 km of the 3d model this indicates that the low thermal conductivity of the sediments increases heat storage within the areas covered by thick sediments within the deeper crust the main feature of the temperature distribution is the transition across the continental margin from the relatively cold oceanic part to the warm continental one this regional pattern is controlled by the thickness of the crystalline continental crust which is characterized by an increased radiogenic heat production at a depth of 80 90 km the temperature becomes higher beneath the oceanic domain than beneath the continent reflecting the configuration of the lower thermal boundary which is represented by an isothermal lithosphere asthenosphere boundary

oxygen isotope constraints on the petrogenesis of the sybille intrusion of the proterozoic laramie anorthosite complex the origin of monzonitic intrusions that are associated with proterozoic massif type anorthosite complexes is controversial a detailed oxygen isotope study of the sybille intrusion a monzonitic intrusion of the laramie anorthosite complex wyoming indicates that either derivation from a basaltic magma of mantle origin with a metasedimentary component 20 incorporated early in its magmatic history or a partial melt of lower crustal rocks is consistent with the data the oxygen isotope compositions of plagioclase pyroxene and zircon from the sybille monzosyenite the dominant rock type in the sybille intrusion were analyzed in order to establish the isotopic composition of the source of the magma plagioclase 18o values range from 6 77 to 9 17 we interpret the higher plagioclase 18o values average 8 69 0 30 n 19 to be magmatic in origin lower plagioclase 18o values average 7 51 0 44 n 22 to be the result of variable subsolidus alteration and pyroxene 18o values average 6 34 0 38 n 19 to be the result of closed system diffusional exchange during cooling low magnetic zircons which have been shown to retain magmatic oxygen isotope values despite high grade metamorphism and extensive subsolidus hydrothermal alteration have 18o values 7 40 0 24 n 11 which are consistent with our interpretation of the plagioclase and pyroxene results oxygen isotope data from all three minerals indicate that the magmatic oxygen isotope composition of the sybille intrusion is enriched in 18o relative to the composition of average or normal mantle derived magmas this enrichment is approximately twice the oxygen isotope enrichment that could result from closed system fractionation rendering a closed system comag matic petrogenetic model between the sybille intrusion and the mantle derived anorthositic lithologies of the laramie anorthosite complex improbable

oxygen isotope evidence for short lived high temperature fluid flow in the lower oceanic crust at fast spreading ridges millimeter scale amphibole veins in the lower oceanic crust record fracture controlled fluid flow at high temperatures but the importance of this fluid flow for the thermal and chemical evolution of the lower oceanic crust is unclear in the section of lower oceanic crust recovered at hess deep from odp hole 894g which formed at the fast spreading east pacific rise these veins are randomly distributed with an average spacing of 1 m we unravel the history of fluid flow through one of these veins by combining in situ o isotope analyses of wall rock plagioclase with major element analyses geothermometry and diffusion modeling thermometry indicates vein sealing by amphibole at 720 c over a narrow temperature interval 20 c in situ oisotope analyses by ion microprobe with a precision of b0 5 reveal zoning of o isotopes in plagioclase adjacent to the vein the zoning profiles can be reproduced using a diffusion model if the duration of o isotope exchange was 100 yr a similar interval of fluid rock exchange is suggested by modeling potassium depletion in plagioclase adjacent to the vein if representative of fracture controlled fluid flow in the lower oceanic crust the limited duration of fluid flow and its occurrence over a narrow temperature interval suggest that high temperature fluid flow in this porosity network does not transport significant heat 2007 elsevier b v all rights reserved

linear to non linear relationship between vein spacing and layer thickness in centimetre to decimetre scale siliciclastic multilayers from the high ardenne slate belt belgium germany abstract typical spacing distributions have frequently been described for fractures in thin sedimentary layers 40 cm vein spacing tends to increase to a maximum value becoming more or less independent of layer thickness the resemblance with fracture spacing suggests that in an unfractured rock vein saturation can occur high fluid pressures are responsible for vein nucleation but the stress state around the initial veins controls the spacing pattern subsequently in a vein saturated rock or the existing veins will thicken by the process of crack sealing or a new cross cutting vein generation will develop in case the regional stress field changes relatively with respect to the existing veins

anisotropy quantification the application of fractal geometry methods on tectonic fracture patterns of a hercynian fault zone in nw sardinia abstract three different fractal geometry methods for pattern analysis are applied on a quartz filled late hercynian fracture zone in nw sardinia fragment size distribution analysis and the box counting method offer the possibility to i detect self similarity of patterns and therefore argue for a specific pattern forming process and ii allow the quantification of the patterns and their comparison with other patterns from similar natural and artificial environments the failure of these methods in analyzing pattern anisotropies can be overcome by the cantor dust method direction related and based on the analysis of 1 d distribution of material in relation to its 2 d orientation with the aid of fractal dimension orientation diagrams dod a specific parameter the azimuthal anisotropy of fractal dimension aad can be determined it quantifies the pattern anisotropy and consequently provides the basis for analyzing the pattern forming processes in addition the cantor dust method shows the existence of two different pattern forming processes

tectonics alteration and the fractal distribution of hydrothermal veins in the lower ocean crust abstract gabbros from hole 735b preserve the igneous structural and metamorphic history beneath the southwest indian ridge down to middle amphibolite facies conditions the gabbro was isolated from the zone of lithospheric necking by detachment faulting unroofing and block uplift at the inside corner high of the atlantis ii transform lower crustal accretion as preserved in the core is a complex integration of igneous hydrothermal and tectonic processes alteration began at anhydrous granulite conditions as surface faulting penetrated the brittle ductile transition to form brittle ductile shear zones in the amphibolite facies hydrous alteration around these zones was extensive while undeformed sections remained virtually unaltered amphibole veins formed during the brittle ductile deformation have a high fractal dimension reflecting an unclustered distribution consistent with high strain and cracking rates in the zone of lithospheric necking beneath the ridge however the fractal dimensions of the two major gneissic amphibolite zones in hole 735b are different and suggest that they represent discrete fault zones formed at different times below middle amphibolite facies a dramatic drop in the extent of alteration reflects cooling cracking and alteration under static conditions similar to layered intrusions initially fracture and vein formation exploited undeformed sections where elastic strain accumulated during cooling from high temperatures was unrelieved by recrystallization plagioclase diopside veins formed at this time have the same orientation as higher temperature veins but a mineralogy reflecting much lower rock permeabilities and a low fractal dimension reflecting a tight clustering of veins as would be anticipated for crack formation at low strain rates late zeolite and carbonate veins and irregular smectite lined near vertical cracks also have a very low fractal dimension reflecting clustering appropriate to low strain near static conditions these however show no preference for undeformed sections of the core and are oriented with subvertical and subhorizontal maxima this indicates crack formation under the present day stress field thus elastic strain due to cooling from high temperatures and extension during lithospheric necking dissipated after plagioclase diopside vein formation

the use of gravity anomaly data for offshore continental margin demarcation analysis of gravity anomaly data can be an effective and economical means of demarcating the world s offshore continental margins

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