dimensional threshold for fracture linkage and hooking fracture connectivity in rocks depends on spatial properties of the pattern including length abundance and orientation when fractures form a single strike set they hardly cross cut each other and the connectivity is limited linkage probability increases with increasing fracture abundance and length as small fractures connect to each other to form longer ones a process for parallel fracture linkage is the hooking where two converging fracture tips mutually deviate and then converge to connect due to the interaction of their crack tip stresses quantifying the processes and conditions for fracture linkage in single strike fracture sets is crucial to better predicting fluid flow in naturally fractured reservoirs for 1734 fractures in permian shales of the lodeve basin se france we measured geometrical parameters in 2d characterizing three stages of the hooking process underlapping overlapping and linkage we deciphered the threshold values shape ratios and limiting conditions to switch from one stage to another one the hook set up depends on the spacing s and fracture length lh with the relation s 0 15 lh once the hooking is initiated with the fracture deviation length l l 0 4 lh the fractures reaches the linkage stage only when the spacing is reduced to s 0 02 lh and the convergence c is 0 1 l these conditions apply to multi scale fractures with a shape ratio l s 10 and for fracture curvature of 10 20

gravity anomalies and dynamics of the swiss alps an interpretation of the gravity observations in switzerland is presented the gravity anomalies are mainly caused by crustal effects taking 0 5 g cm3 as the average density contrast between crust and upper mantle the remaining positive residual field of 50 mgal can be explained as the effect of the so called lithospheric root underneath the swiss alps this root must be considered as a relatively cold body with increased density in order to calculate the thermally induced density distribution in the upper mantle a kinematic and geothermal model has been constructed simulating the alpine history for a time span covering the last 40 m y at the same time the moving lithospheric body crustal uplift and subsidence of the lower lithosphere is analysed from a dynamical point of view in order to test the kinematic conditions the calculation leads to a mantle subsidence rate of 1 mm y for the present period

hydraulic fracturing modeling using a discrete fracture network in the barnett shale abstract hydraulic fracturing has been a successful stimulation method for enhancing recovery in very low permeability shale gas reservoirs proper modeling of multistage hydraulic fracturing in shale reservoirs requires an accurate representation of the pre existing natural fractures in the shale the objective of this study is to utilize a 3d discrete fracture network model to simulate hydraulic fracturing in five horizontal wells a e in the barnett shale each horizontal well had 10 stages of hydraulic fracturing stimulation only the well c has comprehensive logging data including an fmi formation microresistivity imager log of the well we characterize stochastic realizations pre existing natural fracture network in the reservoir integrating different types of data from limited wellbore data to the geologic setting two fracture sets clustered using fisher distribution after correcting for the observation biases fractures size constrained by induced microseismicity magnitude happened during hydraulic fracturing while fracture intensity correlated to clay contents gamma ray and distance from the fault crossing the well c we have modeled the hydraulic fracturing in the five wells and predict that how pre existing fractures induced to slip and contribute to permeability enhancement of the reservoir

multiscale fracture network characterization and impact on flow a case study on the latemar carbonate platform a fracture network arrangement is quantified across an isolated carbonate platform from outcrop and aerial imagery to address its impact on fluid flow the network is described in terms of fracture density orientation and length distribution parameters of particular interest is the role of fracture cross connections and abutments on the effective permeability hence the flow simulations explicitly account for network topology by adopting discrete fracture and matrix description the interior of the latemar carbonate platform dolomites italy is taken as outcrop analogue for subsurface reservoirs of isolated carbonate build ups that exhibit a fracture dominated permeability new is our dual strategy to describe the fracture network both as deterministic and stochastic based inputs for flow simulations the fracture geometries are captured explicitly and form a multiscale data set by integration of interpretations from outcrops airborne imagery and lidar the deterministic network descriptions form the basis for descriptive rules that are diagnostic of the complex natural fracture arrangement the fracture networks exhibit a variable degree of multitier hierarchies with smaller sized fractures abutting against larger fractures under both right and oblique angles the influence of network topology on connectivity is quantified using discrete fracture single phase fluid flow simulations the simulation results show that the effective permeability for the fracture and matrix ensemble can be 50 to 400 times higher than the matrix permeability of 1 0 10 14 m2 the permeability enhancement is strongly controlled by the connectivity of the fracture network therefore the degree of intersecting and abutting fractures should be captured from outcrops with accuracy to be of value as analogue

noble gas and carbon isotopes in mariana trough basalt glasses abstract noble gas elemental and isotopic compositions have been measured as well as the abundance of c and its isotopic ratios in 11 glasses from submarine pillow basalts collected from the mariana trough the 3he 4he ratios of 8 22 and 8 51 ratm of samples dredged from the central mariana trough 18 n agree well with that of the mid ocean ridge basalt morb glasses 8 4 0 3 ratm whereas a mean ratio of 8 06 0 35 ratm in samples from the northern mariana trough 20 n is slightly lower than those of morb one sample shows apparent excess of 20ne and 21ne relative to atmospheric ne suggesting incorporation of solar type ne in the magma source there is a positive correlation between 3he 4he and 40ar 36ar ratios which may be explained by mixing between morb type and atmospheric noble gases excess 129xe is observed in the sample which also shows 20ne and 21ne excesses observed 13c values of 20 n samples vary from 3 76 to 2 80 and appear higher than those of morb and the corresponding co2 3he ratios are higher than those of mara samples at 18 n suggesting c contribution from the subducted slab

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

variable so2 emission rates for anatahan volcano the commonwealth of the northern mariana islands implications for deriving arc wide volatile fluxes from erupting volcanoes 1 we report new spectroscopic derived so2 emission rates for anatahan volcano mariana islands measurements of so2 fluxes reveal large fluctuations over the 2003 2005 period from 78 kg s 1 which occurred on the same day as resurgent volcanic activity march 2005 to 50 kg s 1 and 25 kg s 1 made days weeks after the start of eruptive sequences in 2003 and 2004 respectively even the lowest values make anatahan a major global source of so2 over the past decade these so2 emission rates are used to estimate the co2 flux from the arc as a whole 3 6 40 107 mol km 1 yr 1 such values are significantly higher than estimates derived using other approaches they are also high compared to other convergent margins e g central america where the input flux of co2 is substantially greater our results caution against including volatile fluxes from actively degassing volcanoes to produce volatile outputs considered representative of entire arc fronts

stable isotopic composition of upper oceanic crust formed at a fast spreading ridge odp site 801 1 odp legs 129 and 185 sampled the upper 474 m of 170 ma ocean crust in the western pacific in order to investigate alteration processes in fast spread crust and to determine inputs to subduction fourteen composite bulk samples of altered upper oceanic crust from site 801 have 18o 8 7 25 7 d 69 4 to 90 4 and 13c 2 7 to 1 8 the intensity of alteration and the amount of sediment within the basement decrease with depth leading to corresponding decreases in 18o and d a super composite constructed to estimate the bulk composition of the upper crust has 18o 12 0 d 87 0 and 13c 0 7 compared to core descriptions and geophysical logs the super composite contains too much 18o rich sediment 18o 25 7 and a corrected 18o value of 10 8 is more reasonable for the upper crust at site 801 these values are higher than those for other bulk upper oceanic basement sections 18o 8 0 10 0 and result in part from 1 intense low temperature 100 c hydrothermal alteration of the upper 100 m of tholeiitic basement at site 801 that may not be representative of material subducting in the western pacific and 2 an aging effect whereby progressive addition of 18o rich secondary carbonate in veins and breccia cements contributed to the high bulk 18o of this old upper crustal section

palaeomagnetism magnetic fabrics and the structural style of the hornelen old red sandstone western norway the old red sandstone of the hornelen district western norway forms part of a major fold terrane and the principal magnetization is associated with the late devonian to early carboniferous svalbardian solundian orogeny the present fault margins of the hornelen massif claimed by various authors to represent subordinate devonian splay faults associated with megashearing in the north atlantic or lateral ramps in a regional extensional tectonic setting are shown to be post devonian structures and the present outline of the hornelen massif is a mesozoic jurassic graben

inter well scale natural fracture geometry and permeability variations in low deformation carbonate rocks regional natural fracture networks often show variations on a scale below that captured by seismic reflection data this variability is not considered in most reservoir models but likely impacts uncertainties in permeability we quantify this uncertainty using a database of 13 000 fractures in nine outcrops digitised in the carbonate jandaira formation potiguar basin brazil distance between outcrops is on average 11 km with a minimum of 300 m which is comparable to the distance between wells in naturally fractured reservoirs in between outcrops significant variations exist in orientation intensity length and topology using discrete fracture matrix flow models we model the permeability of each deterministic pattern and find that small changes in geometry and topology result in permeability variations that are not captured by connectivity based analyses such as percolation probabilities particularly when the matrix is permeable the permeability variations associated with subseismic scale fracture variability are not captured in conventional stochastic models but can be captured using deterministic outcrop models with flow through discrete fractures the deterministic models provide a permeability range associated with subseismic fracture variability that can be assigned to grid cells of fractured reservoir flow models as an alternative to assuming constant permeability in the absence of subseismic scale deformation

improved statistical multi scale analysis of fractured reservoir analogues abstract this paper includes the results of the application of novel methodologies for the statistical analysis of tensile fracture attributes spacing density and aperture the statistical methods have been applied to a fractured lower cretaceous carbonate succession cropping out in the sorrento peninsula naples area italy representing a geological analogue of buried reservoirs of southern apennines major oil fields as fracture networks observable from outcrop to the crystal scale can significantly affect the hydraulic behavior of a fractured reservoir the definition of appropriate models of fracture spacing and aperture probability distribution at various scales represents an important goal of structural analysis in order to achieve such an objective sampling has been carried out at different scales by means of traditional scan lines at outcrop as well as micro scan lines carried out both by a digital micro camera 50 and by the optical microscope 200 fracture spacing and density analysis are mainly aimed at establishing the characteristics of joint spatial distribution over a range of scales aperture analysis is aimed at verifying that the aperture cumulative frequency is described by a power law and in the latter instance to provide an effective method for a more precise determination of the exponent of the power law finally new expressions are provided in closed form in order to calculate the confidence interval of the power law exponent the proposed criteria provide handy and effective methods for a significantly improved statistical analysis of fracture attributes

the evolution of the hornelen basin detachment system western norway implications for the style of late orogenic extension in the southern scandinavian caledonides abstract the geology of the devonian hornelen basin and the surrounding western gneiss region wgr western norway has been examined in detail structural clast provenance and geothermobarometric data have been combined to reconstruct the motion history of part of a major late orogenic extensional shear zone in the southern scandinavian caledonides the nordfjord sogn detachment nsd the nsd in the hornelen basin area is a zone of mylonites 4 6 km thick tectonostratigraphically constrained within the lower and middle allochthons lma and the uppermost part of the wgr it separates eclogite bearing gneisses of the wgr from greenschist and amphibolite facies rocks of the middle and upper allochthons marking a profound metamorphic break and indicating major excision of crustal section kinematic indicators give a consistent top to the west shear sense indicating a reversal of the movement sense of the scandian nappes with the ductile strain being distributed through the entire lma section the wgr was exhumed from depths of up to 100 km in the footwall of the shear zone partly aided by pure shear vertical flattening below the nsd and extension and erosion of the hanging wall the majority of the movements on the nsd in the hornelen basin area occurred under amphibolite facies conditions prior to 410 ma subsequent shear caused limited greenschist retrogression along extensional crenulation cleavages depending on interpretation of mica 40 ar 39 ar ages this lower grade shearing may be due to a continuation of movements or renewal of motion associated with opening of the hornelen basin at about 385 ma the lack of clear evidence of penetrative greenschist facies mylonites in the hornelen area may be due to the faulted omission of tectonites of this grade following scandian a subduction and eclogite facies metamorphism at 425 ma the p t t path of the wgr shows very rapid decompression associated with early slip on the extensional detachment horizons unroofing was initially near isothermal followed by a phase of rapid near isobaric cooling after 410 ma decompression and cooling slowed as slip on the nsd slowed or even ceased by the middle devonian the wgr lay at about 10 15 km depth and the crust had almost returned to isostatic equilibrium at this time a brittle fault splaying from the nsd ramped upwards through the upper allochthon opening a scoop shaped west facing half graben the hornelen basin a further 50 km of heave on the nsd occurred during alluvial infilling of the basin subsequently the basin fill was folded by late devonian n s compression and the basin margins were modified by mesozoic faulting these features are consistent with an orogenic collapse model for southern scandinavia that involves large scale backsliding of the scandinavian caledonides within tectonostratigraphic units by this mechanism the baltic shield could have been efficiently unloaded with tectonic translations producing significant metamorphic breaks within a seemingly preserved tectonostratigraphic sequence the model favours orogenic collapse driven by an external pull rather than internal body forces

a statistical scaling model for fracture network geometry with validation on a multiscale mapping of a joint network hornelen basin norway 1 fracture patterns are characterized by a complex geometry which involves a large length distribution and nonhomogeneous density distributions here we address the issue of the modeling of this complex geometry over scales through a first order model providing the characterization of the number of fractures of a given length and at a given scale we propose that the simplest model is a power law in both space and fracture length with three main parameters the exponent a of a power law length distribution the fractal dimension d which fixes the scale dependence of the number of fractures and the fracture density we verify the applicability of this model on seven fracture patterns mapped from the metric scale up to almost the kilometric scale in the hornelen basin the model efficiently describes fracture network properties at all scales with a single set of parameters for the hornelen fracture networks we found a simple relationship between basic exponents a d 1 implying that the fracture network is self similar through this analysis we present different methodological developments for deriving the basic exponents a and d and for verifying the consistency of the model overall the main methodological development is about the normalization of the measurements made from different scales of observation finally we discuss both the limitations and the uses of such a model for analyzing the hydraulic and mechanical properties of fracture networks

hybrid veins from the southern margin of the bristol channel basin uk sinistral and dextral en echelon hybrid calcite veins are exposed on the southern margin of the bristol channel basin north somerset on a liassic carbonate platform these hybrid veins are transitional between pure extensional mode i and shear fractures mode ii mode iii and experienced both extensional and shear displacements during their formation in the study area they occur in conjugate sets with the conjugate angle ranging between 10 and 50 based on the kinematic analysis of these veins a new model for the opening of the bristol channel is proposed

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

stochastic fracture generation accounting for the stratification orientation in a folded environment based on an implicit geological model article i nfo this paper presents a new approach in generating stochastic discrete fracture networks the particularity of the approach isthatitallows us tosimulate thetheoreticalfamiliesoffractures thatare expected ina foldedenviron ment the approach produces fractures that are consistent with the local stratigraphic orientation the fractures are modeled as simplerectangular planarobjects whenthey are modeled they arerotatedaccordingtothe local stratigraphic orientation as the stratigraphy is modeled using an implicit approach we use the gradient of this geological potential field to retrieve the information about the geological orientation the fracture number and size are following user defined probability density functions 2015 elsevier b v all rights reserved

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

effect of shallow level contamination on the helium isotope systematics of ocean island lavas the bimodal distribution of helium isotope ratios in ocean island lavas has provided powerful constraints on the composition and evolution of the earth s mantle1 3 high 3he hotspot ratios 3he 4he greater than in mid ocean ridge basalt morb found on hawaii4 and iceland5 are thought to trace pristine plumes from the deep er mantle whereas low 3he hotspot values 3he 3he morb value at tristan da cunha6 and st helena7 are considered to characterize plumes composed in part of recycled oceanic or continental crust here we report the observation of both high 3he and 6low 3he characteristics8 in lavas from a single ocean island heard island in the indian ocean whereas the high 3he lavas provide unambiguous evidence for the involvement of a deep seated plume in their genesis we argue that the low 3he 4he ratios in other lavas result from shallow level contamination by radiogenic helium before eruption these observations call into question the presumed association between low 3he ratios at heard island and elsewhere and ancient crustal material recycled back into the mantle

forecasting etna eruptions by real time observation of volcanic gas composition it is generally accepted but not experimentally proven that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data by discussing the results of two years of real time observation of h2o co2 and so2 in volcanic gases from mount etna volcano we unambiguously demonstrate that increasing co2 so2 ratios can allow detection of the pre eruptive degassing of rising magmas quantitative modeling by the use of a saturation model allows us to relate the pre eruptive increases of the co2 so2 ratio to the refilling of etna s shallow conduits with co2 rich deep reservoir magmas leading to pressurization and triggering of eruption the advent of real time observations of h2o co2 and so2 combined with well constrained models of degassing represents a step forward in eruption forecasting

the petrology of seafloor rodingites insights from geochemical reaction path modeling abstract thermodynamic reaction path models were applied to provide insights into the formation of rodingites at mafic ultramafic boundaries the models were set up to investigate the shifts in fluid rock equilibria as fluids move from peridotite undergoing serpentinization into a gabbroic body phase relations were investigated in the direction of increasing extent of reaction of the serpentinization fluid with gabbro at 200 c 300 c and 400 c phase assemblages typical of rodingite grossular diopside chlorite are predicted to form at 200 c and 300 c but only in areas where the fluid is essentially unaffected by reactions with gabbro i e near the contact with ultramafic rock or adjacent to a fissure filled with serpentinization fluid as the fluid becomes more affected by reactions with the gabbro prehnite or epidote ss replace garnet and tremolite replaces clinopyroxene once the fluid chemistry is completely reset by reactions with gabbro the predicted assemblage is typical of greenschist facies albitic plagioclase actinolite chlorite and epidote ss these transitions predicted in the model are very similar to what is observed in natural rodingites from different settings our model results hence support the hypothesis that rodingites form during serpentinization and only in areas where fluids controlled by serpentinization reactions are present our calculations further indicate that the formation of mineral assemblages and spatial mineralogical variability within rodingites from the ocean floor is mainly driven by steep activity gradients in protons and aqueous silica in pore fluids mass transfer of ca is likely by diffusion of the caoh species which is predicted to show a very steep concentration gradient across a mafic ultramafic boundary rodingites act as ca traps because of the great stability of diopside and garnet at low sio 2 activities our model calculations further predict the formation of diopsidite from gabbroic and clinopyroxenite precursor rocks at 200 c and 300 c suggesting that very high temperatures on the order of 800 c are not required in the formation of diopsidite veins

investigation of the he solubility in h2oâco2 bearing silicate liquids at moderate pressure a new experimental method we have designed the first available experimental method capable to investigate the solubility of inert gases in h2o co2 bearing silicate melts in a large range of pressures the method overcomes the difficulties imposed by the physical state of volatiles at room conditions experiments were done by using an internally heated pressure vessel where sealed capsules containing the sample are introduced the peculiarity of the method consists in the capability of loading in accurately known proportions even lower than ppm volatiles in a gaseous state at room conditions gas is loaded as a weighed amount of a gas bearing glass which was previously prepared by using the same gas as a pressure medium of a superliquidus experimental run by analyzing the gas concentration in the prepared glass the glass itself can be used as a gas source we applied this method in order to investigate the helium solubility in silicate melts having dissolved volatile mixtures mostly composed of h2o and co2 in a range of pressure suitable to provide useful information regarding pre eruptive magma degassing our results indicate that helium solubility is strongly affected by the h2o content in silicate liquid displaying an increase by about a factor three as a consequence of the addition of 3 wt h2o to the melt taking into account the physical mechanism of he dissolution the sites of the silicate melt structure where noble gases can be accommodated drastically increase by adding modest aliquots of h2o the influence of dissolved co2 on helium solubility is not certain although few signs would suggest an opposite effect with respect to h2o at least in basalt melts on the basis of the obtained results we could reasonably expect that the helium behavior during the degassing of h2o co2 bearing magmas is sensibly different with respect to a h2o co2 free silicate liquid therefore the effect of the major volatiles on noble gas solubility in magmas should be taken into account in the investigation of several geological processes such as magma genesis ascent and degassing or mantle evolution

evidence for an 18o depleted mantle plume from contrasting 18o 16o ratios of back arc lavas from the manus basin and mariana trough abstract back arc basin glasses from the mariana trough and manus basin display contrasting oxygen isotope characteristics that require differences in their mantle sources in both basins the lavas that are most depleted in high field strength elements possess 18o values of around 6 0 that are elevated with respect to mid ocean ridge basalt morb this characteristic is consistent with a mantle source that has been infiltrated by fluids released from subducted oceanic lithosphere the nature of the more fertile mantle component differs between the two basins the lowest 18o values in the mariana trough are similar to morb and suggest that the ambient upper mantle interacts with a subduction modified mantle to produce mariana trough back arc basin basalts oxygen isotope ratios of basaltic glasses from the manus basin display a negative correlation with helium isotope ratios the subduction modified component is associated with 3he 4he ratios typical of the upper mantle glasses with 3he 4he ratios greater than average morb characteristic of a deep mantle plume have 18o values that are lower than expected for upper mantle melts this suggests that the manus basin plume taps a reservoir that is 18o depleted relative to the source of morb two mechanisms are identified that might generate this reservoir deep recycling of oceanic crust that has been hydrothermally altered at high temperature may provide large 18o depleted domains in the deep mantle alternatively we propose that interactions between silicate and iron alloy during the segregation of the earth s core may have the potential to generate such reservoirs resolution between these mechanisms requires further experimental investigation of oxygen partitioning between silicates and iron alloy each of these mechanisms has distinct implications for the origins and dynamics of the manus basin plume

scaling of fault displacements from the badajoz cordoba shear zone sw spain faulting occurs over a large range of scale parts of which are sampled by various techniques e g microscopy outcrop measurement mapping seismic reflection and other forms of remote sensing use of a single technique to measure displacement or strain will not sample faults at all scales and hence will give a biased estimate in order to assess this bias a knowledge of the distribution over all scales is needed many samples of fault displacement appear to follow a power law distribution with departures which can be attributed to sampling effects the number of faults with a displacement u is given by n u cu d the power law distribution of displacement is consistent with similar distributions of other fault parameters and earthquake magnitudes when sampling along a line e g a bedding trace on a map or section a self similar fault population would have d 1 whereas self affine geometries yield d 1 displacement and extension are dominated by small faults when d 1 and by large faults when d 1 when sampling over areas or volumes these critical values are 2 and 3 respectively a set of strike slip faults from the badajoz cordoba shear zone spain were sampled at two different scales using 1 50000 maps and outcrop measurements displacement ranges over 6 orders of magnitude these and other fault populations typically have d ranging from 0 6 to 1 5 the power law relationship may be integrated to yield estimates of the displacement or extension for faults which lie beyond the resolution of the sampling system for example a knowledge of d allows the extension measured on a map or seismic section to be corrected for faults whose displacement is below the resolution of the survey based on an overall estimate of d 0 9 for the badajoz cordoba data only some 40 of the extension would be recorded by map scale faults a corrected extension of 41 along the shear zone is estimated which if typical for the entire 300 km zone represents some 87 km of along strike extension thus work suggests that significant displacement occurs on faults which are too small to be interpreted from conventional seismic profiles and geological maps

the geometry of listric growth faults in the devonian basins of sunnfjord w norway thick devonian clastic sequences accumulated in fault bounded basins in w norway at the close of the caledonian orogeny and mark the beginning of a phase of crustal extension traditionally the eastern boundary fault to the devonian basins has been regarded as a thrust but cross sections based on the use of a branch line reveal it to be an extension fault there is clear omission of structural section across the boundary and by matching up metamorphic rocks in the hanging and foot walls of the boundary fault over 40 km of extensional dip slip can be measured at the n end of the fault the boundary fault is a flat lying listric fault with rollover anticlines in the hanging wall the fault also cuts up and down section along strike to form lateral ramps parallel to the movement direction these ramps appear as wrench faults in outcrop the ramp flat geometry of the fault may have been inherited from a precursor caledonian thrust fault which reversed its sense of slip in early middle devonian times to form the basins over 25 km of onlapping sediment accumulated in the largest basin during faulting in 14 ma with an average slip rate on the fault of 3 mm yr 1

meso to microscale fracture porosity in tight limestones results of an integrated field and laboratory study abstract the complex fluid saturation distribution and influence of microscale and mesoscale fractures on the fluid accumulation and flow properties of carbonates are still interesting challenges for petroleum geologists for this reason in order to know the relative role played by the aforementioned features on the storage and migration properties of tight limestones the present work focuses on a surface analogue cropping out in southern italy by first applying a deterministic discrete fracture network dfn modelling to a 1 m3 geocellular volume an amount of 0 3 of fracture porosity and a fracture connectivity configuration above the percolation threshold are computed in addition to mesoscale fracture porosity in order to gather information on matrix porosity and microscale fractures we investigate the pore type geometry and textural anisotropy of selected rock plugs by mean of integrated petrophysical ultrasonic and optical microscopy analyses experiments results show values of connected porosity ranging between 1 and 6 presence of vugs localized along pre existing structural heterogeneities and the predominance of stiff pores within the carbonate matrix the rare microfractures are mainly oriented orthogonal to bedding the estimated crack density 0 19 shows that the contribution of fracture porosity at microscale 0 078 is very low if compared to that of matrix porosity and also a structural configuration above the percolation the present study therefore documents that the carbonate matrix forms an isotropic medium which profoundly affects the storage capability of the study limestones in fact the amount of storage provided by carbonate matrix and microscale fractures is greater than that due to mesoscale fractures moreover we document that the matrix contribution on porosity is much more significant than the contribution provided by microfractures finally the present work shows the importance of integrating different methodologies on the assessment of fracture porosity at different scales of observation in fact a great benefit for development and production operations can be obtained by performing studies of surface analogs which allow the detailed investigation of rock masses below seismic resolution

hydrothermal fluids assisted crustal scale strike slip on the argentat fault zone abstract the role of hydrothermal fluids in assisting the activity of strike slip faults is investigated using a range of new geological geophysical and geochemical data obtained on the argentat fault massif central france this fault zone 180 km long and 6 to 8 km width has experienced coeval intense channeling of hydrothermal fluids and brittle deformation during a short time span 300 295 ma according to seismic data the fault core is a 4 km wide vertical zone of high fracture density that rooted in the middle crust 13 km and that involved fluids in its deeper parts 9 13 km depth if stress analyses in the fault core and strain analyses in the damage zone both support a left lateral movement along the fault zone it is inferred that hydrothermal fluids have strongly influenced fault development and the resulting fault has influenced fluid flow fluid pressure made easier fracturing and faulting in zones of competent rocks units and along rheological boundaries repeated cycles of increase of fault fracture permeability then overpressure of hydrothermal fluids at fault extremity favored strong and fast development of the crustal scale strike slip fault the high permeability obtained along the fault zone permitted a decrease of coupling across the weak fault core connections between shallower and lower crustal fluids reservoirs precipitate the decrease of fault activity by quartz precipitation and sulfides deposition the zones of intense hydrothermal alteration at shallows crustal levels and the zones of fluid overpressure at the base of the upper crust both controlled the final geometry of the crustal scale fault zone

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

transport of conservative solutes in simulated fracture networks 1 synthetic data generation 1 this paper investigates whether particle ensembles in a fractured rock domain may be adequately modeled as an operator stable plume if this statistical model applies to transport in fractured media then an ensemble plume in a fractured rock domain may be modeled using the novel fokker planck evolution equation of the operator stable plume these plumes which include the classical multi gaussian as a subset are typically characterized by power law leading edge concentration profiles and super fickian growth rates to investigate the possible correspondence of ensemble plumes to operator stable densities we use numerical simulations of fluid flow and solute transport through largescale 2 5 km by 2 5 km randomly generated fracture networks these two dimensional networks are generated according to fracture statistics obtained from field studies that describe fracture length transmissivity density and orientation a fracture continuum approach using modflow is developed for the solution of fluid flow within the fracture network and low permeability rock matrix while a particle tracking code random walk particle method for simulating transport in heterogeneous permeable media rwhet is used to simulate the advective motion of conservative solutes through the model domain by deterministically mapping individual fractures onto a highly discretized finite difference grid 1 m 1m 1 m here the modflow continuum simulations can faithfully preserve details of the generated network and can approximate fluid flow in a discrete fracture network model an advantage of the modflow approach is that matrix permeability can be made nonzero to account for any degree of matrix flow and or transport

melt inclusion record of the conditions of ascent degassing and extrusion of volatile rich alkali basalt during the powerful 2002 flank eruption of mount etna italy 1 two unusual highly explosive flank eruptions succeeded on mount etna in july august 2001 and in october 2002 to january 2003 raising the possibility of changing magmatic conditions here we decipher the origin and mechanisms of the second eruption from the composition and volatile h2o co2 s cl content of olivine hosted melt inclusions in explosive products from its south flank vents our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive volatile rich 4 wt basaltic magma that rose from 10 km depth below sea level bsl and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading this magma the most primitive for 240 years probably represents the alkali rich parental end member responsible for etna lavas evolution since the early 1970s few of it was directly extruded at the eruption onset but its input likely pressurized the shallow plumbing system several weeks before the eruption this latter was subsequently fed by the extrusion and degassing of larger amounts of the same but slightly more evolved magma that were ponding at 6 4 km bsl in agreement with seismic data and with the lack of preeruptive so2 accumulation above the initial depth of sulphur exsolution 3 km bsl we find that while ponding this magma was flushed and dehydrated by a co2 rich gas phase of deeper derivation a process that may commonly affect the plumbing system of etna and other alkali basaltic volcanoes

chemical composition of hydrothermal fluids in the central and southern mariana trough backarc basin abstract we present a geochemical data set from hydrothermal fluids collected from the central and southern mariana trough during dive programs conducted in the 1990s the fluid samples were collected from two hydrothermal fields 1 the alice springs field 18 13 n 144 42 e water depth 3600 m on the axial ridge crest of the central marana trough and 2 the forecast field 13 24 n 143 55 e water depth 1470 m on peak b seamount one of a cluster of small volcanic seamounts which represents a unique tectonic setting in the southern mariana trough gas geochemistry of the alice springs fluid showed he and c isotope ratios in the range of morb whereas that of the forecast fluid showed a higher co 2 3 he ratio and 13 c enriched isotope ratio both of which are commonly recognized in hydrothermal fluids from intraoceanic arc volcanoes the major and minor element composition of the alice springs fluid is characterized by enrichment in mobile alkali elements such as k rb and cs this geochemical signature is in accordance with the well known characteristics of basaltic lava collected from the same area which show substantial enrichment in incompatible elements as interpreted in previous petrological studies this signature is considered to be an arc geochemical signal reflecting contribution from the subduction component the b concentration of the alice springs fluid is also high and is another arc geochemical signal the forecast fluid by contrast did not show enrichment in the mobile alkali elements although its b concentration is high the forecast fluid is characterized instead by enrichment in ca and sr coupled with depletion in na and li as discussed in previous studies this signature is attributed to hydrothermal reactions at rather low temperature due to the shallow water depth we recognize two different arc geochemical signals in these two hydrothermal fluids mobile alkali elements in the alice spring fluid and gaseous species in the forecast fluid this difference could reflect different behaviors of these species during magmatic processes in the mantle wedge beneath the mariana trough backarc spreading center

multi scale fracture network analysis from an outcrop analogue a case study from the cambro ordovician clastic succession in petra jordan abstract a regional multi scale fracture network is prominently exposed in the cambro ordovician sedimentary succession in south western jordan this succession consists of marine deposits overlain by heterogeneous deltaic sediments culminating in 500 m of massive to cross bedded fluvial sandstones a data set acquired from high resolution satellite imagery and field measurements enables the quantification of the geometry and spatial characteristics of the fracture network in three dimensions five directional fracture sets are identified from the satellite data with mean strikes of 000 040 065 120 and 145 large fracture zones longer than 600 m composed of tightly spaced joints confined in fracture swarms exhibit a log normal trace length distribution and the fracture swarms are regularly spaced the trace length distribution of intermediate fractures 40 600 m long exhibits power law characteristics and the fractures are clustered reflecting different fracture system styles and stratigraphic controls as a function of scale the small scale fracture network is strongly dependent on the distribution of bedding plane discontinuities throughout different parts of the succession the multi scale fracture network is categorized in a three tier hierarchical fracture model that reflects underlying stratigraphic controls in the study area this type of model can be used to improve the representation of fracture networks in fluid flow simulations of fractured reservoirs with hybrid models that combine elements of discrete fracture networks and continuum models

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

the lepontine alps as an evolving metamorphic core complex during a type subduction evidence from heat flow mineral cooling ages and tectonic modeling new surface heat flow data are presented for the valle maggia region within the high grade metamorphic core of the lepontine alps the steady state values range from 44 4 to 55 2 mw m2 and are anomalously low compared with those measured around the periphery of the lepontine these differences are considered to reflect the combined effects of differential uplift and erosion superimposed on a transient low heat flow regime which has existed since the miocene the uplift denudation history of the lepontine is modeled by using various mineral geochronometers two major pulses of accelerated uplift are recognized at circa 22 m y b p and circa 10 m y b p respectively these events directly coincide with times of dominant crustal convergence in the helvetic and jura stages of a subduction from known pmax tmax conditions of oligocene metamorphism estimates of low mantle heat flow and experimentally determined values of crustal heat production best fit thermal models are presented to explain surface heat flow and mineral cooling age data for the metamorphic core a two stage underplating model is shown to be consistent with the excavation history of the lepontine and with geological and geophysical data from more external parts of the central alps this information is integrated to explain the establishment of a crustal scale duplex in the metamorphic core complex contemporaneous with thin skinned tectonics in the foreland

two dimensional simulation of controls of fracture parameters on fracture connectivity two dimensional fracture simulation is conducted to analyze the controls of different fracture parameters variations in fracture orientation density and length on fracture network connectivity three different scenarios which are commonly encountered in natural fracture systems are analyzed 1 a single fracture set 2 two fracture sets with one primary through going set and 3 two fracture sets with approximately equal parameters the modeling reveals that certain parameters are more dominant in controlling the connectivity for each of the settings for a single set of fractures increases in length and dispersion and a decrease in spacing all result in higher fracture parallel connectivity but the decrease in spacing is the most important in increasing fracture normal connectivity especially where the dispersion in fracture strike is very low simulations of two sets of fractures reveal that the density length and angle between the two sets are important factors in producing complete connectivity in cases where one set of fractures is a systematic throughgoing set a critical combination of length of the second set and the angle between the two sets results in complete connectivity where both sets of fractures have varying length and density the influence of increasing density of one set has a great effect on connectivity when the other set is short and a more subtle to insignificant change when the other set is long the network also shows higher connectivity with increasing angles up to 90 between the two sets

water saturated oceanic lavas from the manus basin volatile behaviour during assimilation fractional crystallisation degassing afcd we have analysed volatiles h 2 o he ar co 2 in differentiated basaltic andesite dacite volcanic glasses dredged at a depth of ca 2000 m in the eastern part of the manus basin between 151 20 and 152 10 e these samples have sr o b isotopic ratios that show that they most likely represent lavas evolved from a common magma source since these glasses are very fresh they provide a unique opportunity to study the behaviour of magmatic volatiles during assimilation fractional crystallisation degassing afcd the samples are highly vesicular up to 18 and the volatiles trapped in vesicles consist predominantly of h 2 o with minor amounts of co 2 and the concentration of water in the glasses indicates that h 2 o saturation was attained rare gases except helium are atmospheric in origin and the 3 he 4 he ratios and the co 2 3 he ratios are respectively lower and higher than those typical of mid ocean ridge basalt morb and appear to correlate with the degree of differentiation afcd allows efficient degassing of mantle derived volatiles and contribution of crust derived and atmosphere derived volatiles given the widespread occurrence of differentiated magmatism at arcs we suggest that afcd is responsible for large scale occurrence of 3 he rich crustal fluids and of atmospheric like rare gases in arc emanations and that most of the volatiles are lost continuously during fractional crystallisation rather than catastrophically during eruptions

active submarine eruption of boninite in the northeastern lau basin subduction of oceanic crust and the formation of volcanic arcs above the subduction zone are important components in earth s geological and geochemical cycles subduction consumes and recycles material from the oceanic plates releasing fluids and gases that enhance magmatic activity feed hydrothermal systems generate ore deposits and nurture chemosynthetic biological communities among the first lavas to erupt at the surface from a nascent subduction zone are a type classified as boninites these lavas contain information about the early stages of subduction yet because most subduction systems on earth are old and well established boninite lavas have previously only been observed in the ancient geological record here we observe and sample an active boninite eruption occurring at 1 200 m depth at the west mata submarine volcano in the northeast lau basin southwest pacific ocean we find that large volumes of h2o co2 and sulphur are emitted which we suggest are derived from the subducting slab these volatiles drive explosive eruptions that fragment rocks and generate abundant incandescent magma skinned bubbles and pillow lavas the eruption has been ongoing for at least 2 5 years and we conclude that this boninite eruption is a multi year low mass transfer rate eruption thus the lau basin may provide an important site for the long term study of submarine volcanic eruptions related to the early stages of subduction boninite lavas are erupted during the early stages of subduction however they have previously been found only in the ancient geological record discovery of an active boninite eruption shows that abundant volatile gases derived from the subducting slab drive this violent eruptive activity even in the deep sea

enrichment of h2o and fluid soluble trace elements in the troodos ophiolite evidence for a near trench origin abstract the troodos ophiolite on the island of cyprus is a cretaceous supra subduction zone ophiolite it formed by seafloor spreading in the vicinity of a subduction zone but the exact tectonic setting in which it formed is debated we determined h2o contents together with other volatiles s cl and co2 and sr nd and pb isotope compositions of fresh troodos volcanic glasses previously measured for major and trace element contents glass compositions range from boninite to tholeiitic andesite the least degassed glasses have h2o contents of 1 7 to 2 7 wt and h2o ce ratios of 4400 to 33 600 the most depleted glasses with low zr yb have the highest fractionation corrected h2o contents and h2o ce and the highest subduction zone input highest th la ba zr and 87sr 86sr the high h2o contents enrichment in fluid mobile elements and depletion in zr hf and heavy rare earth elements are consistent with formation above a subduction zone very close to a trench in a fore arc position likely at water depths of 5000 m the enrichment in both fluid mobile e g rb cs and melt soluble e g th elements indicate that the troodos ophiolite formed by propagation of a back arc rift into the fore arc region of an active subduction zone

the origin of tensile fracture lineaments abstract fracture controlled lineaments commonly seen where brittle basement is exposed at the earth s surface are generally restricted to a small number of sets with angles of 45 90 between sets the length frequency distribution of lineaments in each set follows a truncated poisson function such lineaments usually show almost no shearing offset suggesting a tensile origin a simple mechanical model of tensile fracturing is used to explain the spacing directions and length of lineaments as well as their depth frequency distribution results suggest that the penetration depth of tensile fractures which produce lineaments at the earth s surface is directly related to their length and that the fracture density is inversely proportional to fracture depth finally the angles between lineament sets may be controlled by the ratio of strength of unfractured rock to that of pre existing fractures which might heal with time the most likely source of tension is tectonic uplift fractures due to typical uplifts of 0 5 1 km over distances of 10 100 km may penetrate as brittle fractures to several kilometres into the crust perhaps to the depth at which seismic activity ceases

no slab derived co2 in mariana trough back arc basalts implications for carbon subduction and for temporary storage of co2 beneath slow spreading ridges the southern mariana trough is particularly well suited to study mass balance in subduction zones because the flux of material recycled from the subducted slab has been shown to diminish to negligible levels in the southernmost part of the area we present new he and ar concentration and isotopic data for 16 back arc basaltic glasses and combine these with previously published co2 and h2o concentration and 13c data to explore the recycling of carbon and light noble gases in the mariana back arc degassing has affected all samples and is particularly extensive in more water rich samples i e those containing the largest recycled component the degassing history features three stages 1 deep degassing which commenced when the melt reached saturation of co2 and noble gases in the mantle 2 preeruptive degassing during storage in the crust mantle transition zone which involved addition of extraneous co2 to the vapor phase and 3 eruption co2 released during stage 1 was at least partially incorporated into wall rock and subsequently remobilized during stage 2 degassing of later magma batches reconstructed parental values for 3he 4he 13c co2 3he and co2 40ar are indistinguishable from those of mid ocean ridge basalt this implies that there is negligible recycling of subducted carbon helium or argon into the source of mariana trough basalt

volatile lines of descent in submarine plutonic environments insights from stable isotope and fluid inclusion analyses microthermometric and isotopic analyses of fluid inclusions in primitive olivine gabbros oxide gabbros and evolved granitic material recovered from ocean drilling program hole 735b at the southwest indian ridge provide new insights into the evolution of c o h nacl fluids in the plutonic foundation of the oceanic crust the variably altered and deformed plutonic rocks span a crustal section of over 1500 m and record a remarkably complex magma hydrothermal history magmatic fluids within this suite followed two chemically distinct paths during cooling through the subsolidus regime the first path included formation of co21ch41h2o1c fluids with up to 43 mole ch 4 the second path produced hypersaline brines that contain up to 50 nacl equivalent salinities subsequent to devolatilization respeciation of magmatic co2 attendant graphite precipitation and cooling from 800 c to 500 c promoted formation of ch 4 enriched fluids these fluids are characterized by average d 13 c ch4 values of 227 1 6 4 3 n5 45 with associated d 13 c co2 compositions ranging from 224 9 to 21 9 n539 and average dd values of exsolved vapor of 241 6 12 n523 in pods veins and lenses of highly fractionated residual material hypersaline brines formed during condensation and by direct exsolution in the absence of a conjugate vapor phase entrapped co21ch41h2o rich fluids within many oxide bearing rocks and felsic zones are significantly depleted in 13 c with d 13 c co2 values down to about 225 and contain co 2 concentrations higher than those predicted by equilibrium devolatilization models we hypothesize that lower effective pressures in high temperature shear zones promoted infiltration of highly fractionated melts and compositionally evolved volatiles into focused zones of deformation significantly weakening the rock strength in felsic rich zones volatile build up may have driven hydraulic fracturing of gabbroic wall rocks resulting in the formation of magmatic breccias comparison of isotopic compositions of fluids in plutonic rocks from 735b the mark area of the mid atlantic ridge and the mid cayman rise indicate 1 that the carbon isotope composition of the lower oceanic crust may be far more heterogeneous than previously believed and 2 that carbon bearing species in the oceanic crust and their distribution at depth are highly variable copyright 2001 elsevier science ltd

distinct regional differences in crustal thickness along the axis of the mariana trough inferred from gravity anomalies we have compiled extensive gravity and bathymetry data for the whole mariana trough which were collected during several japanese scientific cruises over the last few years this study aims to clarify the lateral distribution of the local differences in geochemical signatures which have been observed locally in the mariana trough shipboard free air gravity anomaly data from eight japan agency for marine earth science and technology jamstec cruises were compiled with those crossover errors of 2 85 mgal mantle bouguer anomalies mba were calculated by subtracting the predictable gravity signal due to the seawater crust and crust mantle density boundaries the crustal thickness variation along the spreading axis was estimated from the mba different features in crustal thickness its variation and segment length for each segment allow us to identify four distinct regional differences in magmatic activity along the spreading axis of the mariana trough segment in region a to the north of 20 35 n shows the largest sectional dimensions of crust along the axis and it is probably affected by an additional supply from island arc magma sources a variety of crustal thickness values and of along axis crustal thickness variations in region b between 15 38 n and 20 35 n suggests two types of segments one is similar to a slow spreading ridge segment that has a plume like mantle upwelling under the spreading axis and the other is a magma starved segment region c between 14 22 n and 15 38 n is a less magmatic region individual crustal thickness averages of 3 4 4 1 km region d to the south of 14 22 n has higher individual crustal thickness averages of 5 9 6 9 km suggesting higher magmatic activity with a sheet like mantle upwelling under the spreading axis different features in the mba for off axis areas suggest that these four regions have existed since the mariana trough started spreading moreover comparison between our results of crustal thickness and previous geochemical results indicates that less magmatic spreading segments with thin crust which are locally distributed in both regions b and c probably result from mantle source depleted of water and incompatible elements this suggests that lateral compositional variation of water and incompatible elements exists on a segment scale in the mantle source beneath the spreading axis of the mariana trough

melt inclusions track pre eruption storage and dehydration of magmas at etna at mount etna italy vigorous gas rich eruptions in a d 2001 2002 and 2003 were followed by gas poor eruptions in 2004 2006 and 2007 analyses of volatile co2 h2o s cl f semivolatile cu and involatile nb la elements trapped in olivine hosted melt inclusions from these latest eruptions reveal the effects of the sustained interaction between a percolating gas phase and the stored magma melt inclusion compositions indicate that magmas erupted from 2004 to 2007 were residual from the 2001 2003 eruptions and show significant evolution in the volatile content of the melt these melt inclusion observations and variations in the c s of volcanic gases can be accounted for if melts reequilibrated with co2 rich gases during storage and prior to entrapment as melt inclusions sustained gas percolation caused loss of water and enhancement of co2 in the evolving melt and may strongly influence the behavior of cu which potentially partitions into the gas phase vapor melt interactions during magma storage are important controls on magma evolution at persistently degassing volcanoes

boulder coastal deposits at favignana island rocky coast sicily italy litho structural and hydrodynamic control abstract boulders are frequently dislodged from rock platforms transported and deposited along coastal zones by high magnitude storm waves or tsunamis their size and shape are often controlled by the thickness of bedding planes as well as by high angle to bedding fracture network we investigate these processes along two coastal areas of favignana island by integrating geological data for 81 boulders 49 rupture surfaces called sockets and fracture orientation and spacing with four radiocarbon dates numerical hydrodynamic analysis and hindcast numerical simulation data boulders are scattered along the carbonate platform as isolated blocks or in small groups which form as a whole a discontinuous berm underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform boulders are composed of ruditic to arenitic size clastic carbonates their size ranges from 0 6 to 3 7 m 0 55 to 2 4 m and 0 2 to 1 m on the major a medium b and minor c axes respectively the highest value of mass estimation is 12 5 t almost all of boulders and sockets are characterized by a tabular or bladed shape the comparisons between a the fractures spacing and the length of a and b axes and b the frequency peaks of c axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho structural control in the size and shape of joint bounded boulders these comparisons together with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets suggest that blocks originate by detachment from the platform edge thus the most common pre transport setting is the joint bounded scenario hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from 2 m to 8 m for joint bounded boulders and from few tens of centimeters up to 11 m for submerged boulders the comparison between the wave heights at the breaking point of the coastal zones with the results of hydrodynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders our data suggest that boulders have been transported by several storm events even in very recent times

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

geothermal problems in mountain ranges alps abstract an attempt has been made to model the temperature distribution taking into account simultaneously the effects of regional uplift and erosion present topography development of topography with time and paleoclimatic variations two time intervals were considered a long period 30 m y for the uplift history and a relatively short period 200 000 y for the surface history topography climate the calculations were based on finite differences in space and time an example is presented for an area in the swiss alps where observed rock temperatures in a tunnel and paleotemperature data are available a simple uplift history can fit the paleotemperatures but leads to unrealistic high temperatures in greater depths to improve the model frictional heat sources due to crustal overthrusting were introduced

oman diopsidites a new lithology diagnostic of very high temperature hydrothermal circulation in mantle peridotite below oceanic spreading centres abstract mafic ultramafic dykes scattered in the mantle section of ophiolites are generally crystallisation products from common silicate melts in the frame of a global survey of these melt migration relics in the oman mantle harzburgites we discovered a peculiar lithology made essentially of pure diopside 0 95 m g m g f e total 1 whose characteristics do not match a magmatic or mantle origin arguments against a magmatic or mantle origin for these diopsidites combine compositional and textural evidence in spite of their refractory composition they are strongly depleted in cr cr2o3 0 2 wt by the same way other minor elements al ti na and rare earth elements have peculiarly low abundances and plot away from magmatic differentiation trends in a few samples the paragenetic association includes pure anorthite an up to 0 99 minor amounts of forsterite fo 0 95 or traces of andradite when not deformed the diopsides are automorphic and their texture points to metamorphic growth in a matrix composed of antigorite and or carbonate diopsidites have textures reminiscent to that of skarns developing in contact metamorphic halos or that of rodingite frequently present in the serpentine bodies of the ophiolitic crust they frequently appear as dykes former cracks with a few mm to few tens of cm wide transitional zones which contain high amounts of hydrous minerals between the diopsidite facies and its host rock the diopsidites are not randomly distributed in the oman ophiolite being more abundant near former asthenospheric diapirs emplaced at shallow depth in the lithosphere we interpret the diopsidites as the footprint of very high temperature circulation of seawater and carbonated fluids 800 c which may have leached plagioclase rich lithologies before penetrating the mantle as shown by a well developed positive eu anomaly our data confirm the prediction of mccollom and shock t m mccollom e l shock fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration j geophys res 103 b1 1998 547 575 who proposed that common anhydrous minerals like pyroxene plagioclase and olivine may crystallise from high temperature fluids intermediate between silicate melts and supercritical water this confirms that there is no clear cut thermal and chemical boundary between the fields of magmatic and hydrothermal crystallisations

helium and argon isotope systematics of the central lau basin and valu fa ridge evidence of crust mantle interactions in a back arc basin abstract we report helium and argon isotope analyses of fresh lau basin volcanic glasses from six sites within the central basin 18 s six localities along the valu fa ridge 21 22 4 s and a single site from the northeastern basin 15 s central basin basalts have 3 he 4 he ratios r between 8 2 8 5 r a r a air 3 he 4 he 40 ar 36 ar ratios significantly greater than atmosphere up to 4900 and 4he contents from 3 5 9 4 10 6cm3 stp g similar to n morbs worldwide these results are consistent with trace element and other radiogenic isotope data on these samples which indicate derivation from a depleted mantle source region in contrast evolved lavas from the valu fa ridge all have r r a and show evidence of mixing with a component rich in radiogenic helium there is a clear relationship between the 3 he 4 he ratios of these samples and their chemistry basaltic andesites have 6 02 r c r a andesites have lower ratios 2 37 2 65 ra and a dacite has the lowest value of the entire sample suite 1 19 ra all lavas have 40 ar 36 ar ratios similar to the atmospheric value and low helium concentrations from 3 11 10 8cm3 stp g or between 30 and 300 times less than the central basin basalts although the helium isotope results of the valu fa lavas mirror the shift to more radiogenic values of other isotope systems e g 206 pb 204 pb 87 sr 86 sr which indicate addition of subducted sediment to these magma sources we find no evidence that the radiogenic helium has a mantle or slab derivation or is in any way coupled to these other tracers instead the most plausible mechanism to explain its incorporation into the valu fa lavas is by assimilation of old lau crust in the near surface environment by previously degassed magma we argue that this mechanism has general applicability and can explain a number of hitherto apparently paradoxical geochemical features of some back arc and ocean ridge lavas such as their high volatile and lil element contents with low rare gas concentrations and their mantle 3 he 4 he ratios with hydrated oceanic crustal d h values the realisation that the helium and argon systematics of the valu fa lavas are controlled by crust mantle interactions has important implications for distinguishing between a number of models proposed for the formation of such evolved lavas and we show that fractional crystallisation processes can most readily account for the low concentrations of and systematic trends in the mantle derived helium and argon component of these lavas in addition because pre existing crust in the lau basin must be old and or altered enough to supply the radiogenic helium and atmospheric like 40 ar 36 ar component to the valu fa lavas the occurrence of crust mantle interactions implies that old forearc crust may have been trapped within the lau basin such a scenario has a clear bearing on ideas of the tectonic development of the basin finally because of the potential of crust mantle interactions to modify 3 he 4 he and 40 ar 36 ar ratios of mantle derived melts we assess the implications for using he and ar tracers to characterise mantle sources in arcs back arcs and spreading ridges and consider the consequences for the combined use of rare gases with other radiogenic isotopic tracers of magma provenance at such settings the basaltic andesite from the northeastern basin may also be influenced by the same kind of crustal interaction as the valu fa lavas as it falls within the 3 he 4 he range 6 9ra of the other basaltic andesites interestingly other helium isotope studies indicate that this part of the basin is characterised by a wide range in 3 he 4 he ratios from morb values up to 22ra the low 3 he 4 he ratio of the basaltic andesite therefore serves to illustrate the possible effects of magma chamber processes on the rare gas and other volatile characteristics of hotspot lavas an observation which is important not only for this part of the lau basin but for other localities worldwide

co 2 13 c 12 c and h 2 o variability in natural basaltic glasses a study comparing stepped heating and ftir spectroscopic techniques abstract a comparison of two independent techniques was used to assess the homogeneity of co 2 and h 2 o concentrations in a number of natural basaltic glasses variations in carbon concentration and isotopic ratio were determined by comparison of stepped heating data obtained in two different laboratories dissolved volatile concentrations were also obtained by stepped heating and fourier transform infrared ftir spectroscopy replicate stepped heating analyses of a mid ocean ridge basaltic glass show that the concentration and 13 c 12 c of bulk magmatic and dissolved co 2 vary by less than 10 and 0 5 respectively a similar degree of correlation is observed for replicate stepped heating analyses of mariana trough glasses conducted in two different laboratories dissolved co 2 concentrations determined by stepped heating also correlate well with concentrations measured by ftir spectroscopy the correspondence of results obtained in these experiments provide an upper limit to the degree of natural variation in concentrations and isotopic ratios of these volatiles in basaltic glasses and suggest that intrinsic magmatic carbon has a relatively homogeneous distribution in these glasses water concentrations determined through extraction by heating and ftir also show excellent agreement

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

a geothermic method for the reconstruction of the uplift history of a mountain range applied to the central alps vertical movements of a crustal block in connection with denudation sedimentation or overthrusting respectively lead to a change in the temperature field this process can be used to correlate the uplift and temperature history of a rock sample in a quantitative way the uplift rate may change over a period of time the effect of the radiogenic heat sources has been taken into account in the calculations

statistical mechanics and scaling of fault populations with increasing strain in the corinth rift scaling properties of fracture fault systems are studied in order to characterize the mechanical properties of rocks and to provide insight into the mechanisms that govern fault growth a comprehensive image of the fault network in the corinth rift greece obtained through numerous field studies and marine geophysical surveys allows for the first time such a study over the entire area of the rift we compile a detailed fault map of the area and analyze the scaling properties of fault trace lengths by using a statistical mechanics model derived in the framework of generalized statistical mechanics and associated maximum entropy principle by using this framework a range of asymptotic power law to exponential like distributions are derived that can well describe the observed scaling patterns of fault trace lengths in the rift systematic variations and in particular a transition from asymptotic power law to exponential like scaling are observed to be a function of increasing strain in distinct strain regimes in the rift providing quantitative evidence for such crustal processes in a single tectonic setting these results indicate the organization of the fault system as a function of brittle strain in the earth s crust and suggest there are different mechanisms for fault growth in the distinct parts of the rift in addition other factors such as fault interactions and the thickness of the brittle layer affect how the fault system evolves in time the results suggest that regional strain fault interactions and the boundary condition of the brittle layer may control fault growth and the fault network evolution in the corinth rift

arctic sea ice leads from advanced very high resolution radiometer images a large number of advanced very high resolution radiometer avhrr images from throughout 1989 are analyzed to determine lead characteristics the units of analysis are square 200 km cells and there are 270 such cells in the data set clouds are masked manually leads are determined from images of the potential open water a scaled version of the surface temperature or albedo that weights thin ice by its thermal or brightness impact the lead fraction is determined as the mean the monthly mean lead fraction ranges from 0 02 in winter to 0 06 in summer in the central arctic and is near 0 08 in the winter in the peripheral seas a method of accounting for lead width sampling errors due to the finite sample areas is introduced in the central arctic the observed mean lead width for a threshold of 0 1 ranges from 2 or 3 km near the resolution of the instrument in the winter to 6 km in the summer in the peripheral seas it is about 5 km in the winter width distributions are often more heavily weighted in the tail than exponential distributions and are well approximated by a power law the along track number density power law n aw b has a mean exponent of b 1 60 standard deviation 0 18 and shows some seasonal variability mean floe widths in the central arctic are 40 to 50 km in the winter dropping to about 10 km in the summer for floes the power law has a mean exponent of 0 93 and exhibits a clearer annual cycle lead orientation is determined with a method based on the direction of maximum extent

spatial distribution scaling and self similar behavior of fracture arrays in the los planes fault baja california sur mexico we present a case of detailed analysis of fracture arrays spanning four orders of magnitude in length all of them measured at a single natural site by acquiring images at progressively larger scales there is a high dispersion of cumulative length exponents box dimensions and fracture densities however the fractal analysis supports the fractal nature of fracture arrays our data indicate the existence of an upper limit for the density parameters as similarly reported by other authors we prove that box dimension is in inverse relation with fracture concentration and in direct relation with fracture density these relations are also observed in our data and additionally there is an upper limit for the box dimensions we interpret the dispersion in our results as more fundamental than methodological problems it represents a truncation in the complete evolution of the fracture systems because in natural cases strain initiates overprinting of previous fracture arrays considering that larger fractures accommodate strain more efficiently than small fractures the generation of small fractures is inhibited in the presence of pre existing larger fractures maximum values of fracture density prevent accommodating an excess of strain in a single or restricted range of scales we claim this condition produces migration of fracturing to larger scales originating fracture scaling

helium 3 and deuterium in back arc basalts lau basin and the mariana trough samples of fresh basalt glass from the mariana trough and the lau basin were analyzed for their isotopic composition of water and helium in order to identify the sources of the volatiles in back arc basin basalts in the mariana trough basalts the concentration 0 64 2 1 wt and d h ratio d 46 to 32 of the water provide important evidence for a water rich component from the subducting lithosphere extrapolation to infinite water content gives an end member d h ratio of d 25 3he 4he ratios are in general similar to morb values 8 ra and indicate that mariana trough basalts represent a mixture of a morb type mantle and an alkali and water rich component from the descending slab in contrast the lau basin produces both hydrous 1 3 wt h2o and relatively anhydrous 0 12 0 35 wt basalts the d h ratio d 43 in the hydrous lau basin basalt resembles those of mariana trough lavas the low water contents 0 12 0 35 wt and morb like d h ratios d 63 to 70 in three of five lau basin samples show that the water rich component observed in all mariana trough lavas is absent in some lau basin lavas and not essential for the production of back arc basalts the high3he 4he ratio of rochambeau bank in the northern lau basin 11 ra confirms an earlier analysis by lupton and craig and provides evidence for an enriched mantle source region beneath the lau basin which is perhaps related to the high 3he samoan hotspot

the scaling of hydraulic conductivity in rock fracture zones beyond the scale of a few meters fracture traces as viewed on aerial photographs represent fracture zones thus for bulk fractured rock permeability the hydraulic properties of fracture zones are important here observations on joint zones in sandstones from western norway are used to build a quantitative model relating joint zone length and effective hydraulic conductivity using simple rules for hydraulic conductors in series and parallel applied to joint zone geometry the effective hydraulic aperture the aperture of a single parallel walled channel that conducts the same flow is estimated for 72 joint zones of known length a power law relation between trace length l and effective hydraulic aperture be with an effective exponent of around 0 27 is found which may extend to km scales this exponent contrasts with values of 0 5 to 2 0 reported for veins

scaling and geometric properties of extensional fracture systems in the proterozoic basement of yemen tectonic interpretation and fluid flow implications abstract multi scale mappings of fracture systems in the crystalline basement of yemen are presented fracture datasets are described through statistical analyses of direction length spacing density and spatial distribution results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks from multi kilometric to decametric scales the fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir backbone and matrix respectively these two end members reveal contrasting geometrical reservoir and scaling properties in tectonic systems multi scale geometries are self similar the fracture network shows fractal behavior power law length distribution and clustered spacing and fault zones show hierarchical organization of geometrical parameters such as length thickness and spacing in joint systems the fracture network is scale dependent with exponential length distribution and shows anti clustered spacing however these two end members have both well connected properties with fault zones acting as main drain and joint systems acting as the fluid supply

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

volatile element isotopes of submarine hydrothermal mineral deposits in the western pacific the abundance and isotopic compositions of volatile elements trapped in fluid inclusions of submarine hydrothermal mineral deposits in western pacific subduction zones okinawa trough izu bonin arc mariana trough and lau basin and in kuroko ores in northeastern japan are presented the helium isotopic compositions corrected for air contribution of the okinawa and mariana troughs ranging 4 49 7 68 ra are lower than those of the izu bonin and lau basin 7 62 8 91 ra this characteristic might reflect the differences in regional tectonic setting the okinawa and mariana troughs are related to back arc spreading with strong graben sedimentary signature whereas the izu bonin arc is associated with island arc magmatism the arc contribution to the lau basin volcanism is significantly strong even though it is assigned to back arc spreading nitrogen isotopes can also be explained by a similar hypothesis whereas argon and carbon isotopes cannot be used to discriminate tectonic setting 13c co2 3he and 15n n2 36ar diagrams elucidate the source of carbon and nitrogen the mor type mantle contributions to carbon are mostly smaller in the okinawa and mariana troughs ranging 0 06 8 9 with the average of 2 4 than in the izu bonin and lau basin 2 1 25 with the average of 7 7 the sedimentary contributions to nitrogen are larger in the okinawa and mariana troughs 11 65 with the average of 35 than in the izu bonin and lau basin 4 24 with the average of 15 and the kuroko samples agree well with the latter carbon and nitrogen fluxes are again higher in okinawa trough than in izu bonin arc

carbon isotope variations of co2 in central lau basin basalts and ferrobasalts co2 abundance and carbon isotope data are reported for basalt glasses from three spreading centres in the central lau basin abundances of co2 dissolved in glasses vary from 9 ppm to 217 ppm with 13c ranging from 16 4 to 8 8 evolved ferrobasalts from the propagating rift tip of the central lau spreading centre have both the lowest co2 concentrations and 13c values while more magnesian basalts from the intermediate and eastern lau spreading centres have higher co2 abundances with higher and less variable 13c values variations in abundance and carbon isotope ratios of dissolved co2 can be modelled by degassing during eruption of melts originally containing 410 440 ppm co2 with 13c of 7 7 using a vapour melt isotope fractionation of 2 3 the type of degassing experienced by melts is related to their style of eruption which is in turn governed by their eruption site central lau basin glasses along with glasses from other marginal basins display carbon isotope ratios which are lower than morb while the variations within the suite are adequately described by various degrees of degassing carbon isotope heterogeneity between sources of oceanic basalts can not be discounted

heterogeneous large total co2 abundance in the shallow magmatic system of kilauea volcano hawaii 1 due to its very low solubility in silicate melts co 2 concentrations in melt inclusions mis within crystals are commonly orders of magnitude less than the total concentration in the multiphase magma strongly limiting the possibility to constrain co 2 abundance based on the dissolved quantities here we develop a statistical method to process mi data which allows analytical uncertainties to be taken into account together with the peculiar features of the local saturation surface the method developed leads to retrieve total h 2 o and co 2 concentrations in magma as well as the gas phase abundance at the time of magma crystallization application to a set of 29 high resolution secondary ion mass spectrometry sims mi data from a single specimen of the 1842 1844 eruption of kilauea hawaii reveals the existence of heterogeneous total co 2 abundance and of at least 2 6 wt total co 2 in some magma batches two orders of magnitude higher than the dissolved amounts and 30 50 times more abundant than the corresponding total h 2 o content heterogeneous total volatile concentrations are interpreted as due to a combination of degassing and gas flushing in magma subject to convective motion at shallow depth where p 1 wt is likely to characterize the 30 km deep magma not represented in the analyzed inclusions from which a co 2 rich gas phase exsolves and decouples from the liquid

evolution of permeability in sand injectite systems abstract sand injectite complexes comprise kilometer scale clastic intrusion networks that act as effective conduits for the migration accumulation and then recovery of hydrocarbons and other fluids an equivalent continuum model is constructed to represent a sand injectite reservoir coupling stress and fluid flow in fractured rock using the continuum simulator toughreact coupled with flac3d to follow deformation and fluid flow a permeability model which uses staged percolation models is proposed to improve permeability estimation of fracture networks by accommodating four different levels of fracture connectivity this permeability model is confirmed against field and laboratory data corresponding to the different connectivities of fracture networks the new constitutive permeability model is incorporated into the coupled hydro mechanical simulator framework and applied to sand injectites with the analysis of permeability evolution mechanisms and mechanical sensitivity the results indicate that when the magnitudes of principal stresses increase in a constant ratio normal closure is the dominant mechanism in reducing fracture aperture and thereby permeability conversely the evolution of stress difference can accentuate aperture and permeability due to an increase in shear dilation for critically or near critically oriented fractures also the evolution of aperture and related permeability of fractured rock are more sensitive at lower stress states than at higher stress states due to the hyperbolic relationship between normal stress and normal closure of the fractures

fluid velocity fields in 2d heterogeneous porous media empirical measurement and validation of numerical prediction the scale invariance of geological material and the consequent absence of a length scale on which to base the upscaling of measurements made on geological samples represent a serious challenge to the prediction of fluid behaviour in rock at economically interesting scales numerical simulation is an important tool for understanding constraints in this problem and current discrete fluid models in which complex boundary conditions can be represented have the potential for testing many possible upscaling schemes at present however there are no accurate empirical data on the distributions of fluid velocities in complex scale invariant geometries with which to validate such models to address this fluid velocity fields in complex 2d media with fractal heterogeneity were measured digital models of rock geometries were created and translated into physical form using electric discharge machining and stereolithography these physical models were then enclosed between parallel sheets of glass and perspex forming a hele shaw cell which was permeated with water doped with small neutrally buoyant spheres and pumped at accurately steady and reproducible velocities local velocity vectors were estimated by the analysis of sequential images captured using high resolution video precision digital control systems were used to move the cell relative to the camera and repeated measurements allowed the construction of full 2d velocity fields the accuracy of the technique was assessed by comparison between automated and manual measurements confirming the accuracy over approaching three orders of magnitude in velocity the results have been compared to the output of lattice boltzmann lb simulations of flow in identical geometries showing that the correlation between simulated and measured velocity fields is strongly dependent on the viscosity used in the numerical simulation in particular the lb scheme used in these tests is incapable of simulating correct viscosities for complex geometries some important effects are shown to be strongly viscosity dependent and it is concluded that some simulations may be able to predict the behaviour of high viscosity fluids only nonlinear effects between fracture and matrix flow are likely to be more important in these cases