tectonic classification of cenozoic iberian foreland basins abstract the iberian microcontinent stands out because of its intense alpine intraplate deformation this is reflected in a large number of cenozoic basins of very different sizes most of the contacts between topographic highs and basins are thrust or strike slip faults all these basins seem to have undergone a common sedimentary evolution comprising four stages initiation of sedimentation intense syn tectonic infilling change from endorheic to exorheic drainage and accelerated erosion related to fluvial incision this simple evolutionary model shows a migration from east to west in which basins are still tectonically active at the atlantic margin of iberia this common evolution is also found in a series of geometrical characteristics such as the ratio r of length of strike slip fault and length of thrust fault that are very similar in both types of basin border settings thrust related basins are mainly associated with segmented pop downs whereas the main basins have the characteristics of open ramp basins strike slip related basins are mostly transpressive structures although small pull apart basins are usual along the vilarica and messejana faults for basin areas larger than 100 1000 km 2 a constant r value of 0 6 is found including the ebro duero madrid lower tagus and badajoz basins within the iberian microcontinent the total amount of cenozoic contractional deformation was distributed between strike slip and thrust faults with an r ratio close to 0 6 however for small basins this parameter seems to depend on the type of fault range or deformation belt pure strike slip transtension transpression and pop up independently of its local tectonic development

tracking bubble evolution inside a silicic dike abstract pressure estimates from rapidly erupted crustal xenoliths constrain the depth of intrusion of the silicic lavas hosting them this represents an opportunity for tracking magmatic bubble s evolution and quantifying the variation in bubble volume during rapid magma ascent through a volcanic dike just prior to eruption the petrology stable isotope geochemistry and x ray micro tomography of dacites containing crustal xenoliths erupted from a neogene volcano in se spain showed an increase in porosity from 1 7 to 6 4 from 19 to 13 km depth at nearly constant groundmass and crystal volumes this result provides additional constraints for experimental and numerical simulations of subvolcanic magma crust degassing processes in silicic systems and may allow the characterization of volcanic eruptive styles based on volatile content

on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

palaeolithic engravings and sedimentary environments in the coa river valley portugal implications for the detection interpretation and dating of open air rock art the pre magdalenian phase of the coa river valley open air rock art is mostly distributed at the boundary between the rocky valley slopes and the floodplain that correspond to the most favourable geomorphological setting for the preservation of pecked and deeply superposed engravings of the most famous artistic phase of the area the natural vertical panels of the engraved art located at this geomorphological interface have suffered weathering during two cold events of the lateglacial they were buried by several colluvial and alluvial deposits the reconstruction of the sedimentary and archaeological context of the coariver valley engraving permits a better assessment of the preservation processes and interpretation of palaeolithic open air rock art

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

clay fabrics in relation to the burial history of shales quantitative appraisal of compaction strain is essential for the study of the burial history of shales in sedimentary basins the results of a preliminary fabric analysis of westphalian and zechstein shales in the campine basin belgium show that clay fabric analysis using an x ray pole figure goniometer is suitable for this purpose clay fabrics in the range studied are independent of depth and therefore cannot be used as depth indicators this suggests that in the early stages of the burial history a stable clay fabric has to develop which will basically remain unchanged during the subsequent burial history the degree of clay particle preferred orientation not only reflects the compaction strain but is also determined by mineralogical parameters the presence of non platy particles and the relative concentrations of the different clay minerals this degree of preferred orientation furthermore determines the degree of fissility of the shales these mineralogical factors limit the use of clay fabrics as truly quantitative strain markers their use as semi quantitative strain markers remains advantageous mainly because of the common occurrence of clay fabrics in the geological record moreover the relative ease of measurement and the possibility of distinguishing compaction from tectonic strains favour the use of clay fabrics in the quantitative strain analysis of argillaceous rocks

microlite orientation in obsidian flow measured by synchrotron x ray diffraction clinopyroxene and plagioclase andesine microlites in an obsidian flow from glass mountain ne california usa display strong alignment synchrotron x ray diffraction coupled with rietveld analysis was used to quantify crystallographic preferred orientation cpo clinopyroxene with a rod shaped morphology shows a strong alignment of 001 in the flow direction and 010 aligned parallel to the inferred flow plane andesine with a platy morphology displays an alignment of 010 platelets in the flow plane some pole densities exceed 90 multiples of random distribution applying a model of rigid ellipsoidal inclusions in a viscous matrix the local pure shear strains are between 2 and 3

high resolution 3d analyses of the shape and internal constituents of small volcanic ash particles the contribution of sem micro computed tomography sem micro ct abstract the morphology of small volcanic ash particles is fundamental to our understanding of magma fragmentation and in transport modeling of volcanic plumes and clouds until recently the analysis of 3d features in small objects 20 m3 3 5 m in diameter can be successfully reconstructed and quantified in addition new functionalities of the blob3d software were developed to allow the particle shape factors frequently used as input parameters in ash transport and dispersion models to be calculated this study indicates that sem micro ct is very well suited to quantify the various aspects of shape in fine volcanic ash and potentially also to investigate the 3d morphology and internal structure of any object

wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation we obtain the wave velocities and quality factors of clay bearing sandstones as a function of pore pressure frequency and partial saturation the model is based on a biot type three phase theory that considers the coexistence of two solids sand grains and clay particles and a fluid mixture additional attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas fluid mixing law that satisfies the wood and voigt averages at low and high frequencies respectively pressure effects are accounted for by using an effective stress law by fitting a permeability model of the kozeny carman type to core data the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies including the effects of partial saturation testing of the model with laboratory data shows good agreement between predictions and measurements

misalignment of the orientation of fractures and the principal axes for p and s waves in rocks containing multiple non orthogonal fracture sets summary azimuthal anisotropy in rocks can result from the presence of one or more sets of partially aligned fractures with orientations determined by the stress history of the rock a shear wave propagating in an azimuthally anisotropic medium splits into two components with diverent polarizations if the source polarization is not aligned with the principal axes of the medium in the presence of two or more non orthogonal sets of vertical fractures the symmetry of the medium may be approximated as monoclinic with a horizontal plane of mirror symmetry if in the absence of fractures the rock is transversely isotropic ti with the symmetry axis perpendicular to the bedding plane for such a medium the fast and slow polarization directions for vertically propagating shear waves are not parallel or perpendicular to any of the fracture planes but lie in directions given by the principal axes of a second rank fracture compliance tensor this tensor is independent of the normal compliance of the fractures it follows that for vertical propagation of shear waves in a vertically fractured ti medium any number of arbitrarily oriented vertical fracture sets is equivalent to two mutually perpendicular fracture sets provided that the seismic wavelength is large compared to the size of the fractures for ovsets typical of surface seismic acquisition the p wave velocity at fixed ovset varies with azimuth as cos 2 w w 0 where w is the azimuth measured with respect to the fast polarization direction for a vertically polarized shear wave w 0 depends on both the normal and the shear compliance of the fractures and may diver from zero if the ratio of the normal to shear compliance of the fractures varies significantly between fracture sets if this ratio is similar for all fractures w 0 0 and the principal axes of the variation in p wave velocity with azimuth for fixed ovset are determined by the principal axes of the second rank fracture compliance tensor

vesiculation in magmas from stromboli and implications for normal strombolian activity and paroxysmal explosions in basaltic systems 1 we performed a series of x ray tomographic experiments and lattice boltzmann permeability simulations on pyroclastic products from explosive activity at stromboli between december 2004 and may 2006 we reconstructed the 3 d textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes scoriae from normal strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 0 2 we ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state shallow magma system that supplies normal strombolian activity volume distributions and textures of vesicles in pumice clasts from the 5 april 2003 and 15 march 2007 paroxysmal activity are markedly different from those in the scoriae besides a power law function with a higher exponent portions of these distributions can be also fit by an exponential function suggesting the attempt of the system to reach near equilibrium conditions the investigated pumice clasts also lack the large connecting vesicles responsible for the development of degassing pathways in the stromboli magma that erupts the scoriae this testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth by comparison with degassing experiments on basaltic melts we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at stromboli

flow resistance and momentum flux in compound open channels new formulations are presented for flow resistance and momentum flux in compound open channels as implemented in the st venant equations these formulations facilitate a physically enhanced approach to evaluating conveyance roughness stage discharge relationship and unsteady flood routing in compound open channels an analysis using steady flow data from the well controlled experiments at the large scale flood channel facility hr wallingford demonstrates the ability of the present approach to properly resolve the discontinuity of overall roughness across the main channel bankfull level also the proposed formulations are shown to be conducive to obviating the long standing computational difficulty in unsteady flood routing due to small flow depths over flat and wide floodplains the present work should find general applications in one dimensional computation of river flows

an example of intraplate neotectonic activity vilarica basin northeast portugal the vilarica tectonic basin nw iberian peninsula is presented as an example of intraplate neotectonic activity the regional geological setting is first introduced then followed by a brief view on the neotectonic activity in portugal the basin consists of an elongated depression approximately 20 km long and 2 to 3 km wide trending nne ssw it is located astride a late variscan strike slip fault the manteigas braganca fault suggesting that it might correspond to a structural depression related to reactivation movements on that fault mapping of neogene and quaternary cover deposits preserved in the basin and its vicinity was accomplished and numerous evidence of tectonic deformation tilting and faulting affecting the sediments were found other geomorphological criteria are discussed showing the structural origin of the vilarica basin and its neotectonic activity attending to its location on the manteigas braganca fault the vilarica depression is interpreted as a pull apart basin resulting from left lateral strike slip displacement on that fault in the quaternary average fault slip rates are estimated with values comprised between 0 2 mm yr and 0 5 mm yr these slip rates are typical of moderate to moderately high degrees of fault activity and are compatible with the regional faulting geomorphic expression and the relatively important historical and instrumental seismicity affecting the vilarica region finally a geodynamical model is proposed and the studied area is presented in the geodynamic framework

anisotropy of experimentally compressed kaolinite illite quartz mixtures the anisotropy of physical properties is a well known characteristic of many clay bearing rocks this anisotropy has important implications for elastic properties of rocks and must be considered in seismic modeling preferred orientation of clay minerals is an important factor causing anisotropy in clay bearing rocks such as shales and mudstones that are the main cap rocksofoilreservoirs thepreferredorientationofclaysdepends mostly on the amount of clays and the degree of compaction to studytheeffectoftheseparameters wepreparedseveralsamples compressingattwoeffectiveverticalstressesamixtureofclays illite and kaolinite and quartz silt with different clay quartz ratios the preferred orientation of the phases was quantified with rietveld analysis on synchrotron hard x ray images pole figures for kaolinite and illite display a preferred orientation of clay platelets perpendicular to the compaction direction increasing in strength with clay content and compaction pressure quartz particles have a random orientation distribution aggregate elastic properties can be estimated by averaging the singlecrystal properties over the orientation distribution obtained from the diffraction data analysis calculated p wave velocity anisotropy ranges from 0 pure quartz sample to 44 pure clay sample highly compacted but calculated velocities are much higher than measured velocities this is attributed to uncertainties about single crystal elastic properties and oriented micropores and limited grain contacts that are not accounted for in themodel inthiswork wepresentaneffectivemethodtoobtain quantitative data helping to evaluate the role of clay percentage and compaction pressure on the anisotropy of elastic properties ofclay bearingrocks

texture analysis of volcanic rock samples quantitative study of crystals and vesicles shape preferred orientation from x ray microtomography data abstract in the texture analysis of volcanic rocks the preferred orientation of the constituents can provide useful information for the interpretation of the processes involved in the rock formation we present here a new data analysis technique based on x ray microtomography measurements and on shape preferred orientation analysis to obtain the orientation distribution functions of the constituents of volcanic rocks this procedure proved to be very suitable for volcanic samples where diffraction based techniques developed for crystallographic preferred orientation studies are of limited utilization in addition to the fact that they cannot provide any information about vesicles or bubbles moreover the analysis performed directly in three dimensions 3d overcomes the problems that usually occur when employing stereological methods for the analysis of the images obtained via microscopy based techniques in this study two scoriae from stromboli and etna and a tube pumice from campi flegrei were measured via x ray microtomography and then the resulting volumes were analyzed following the proposed procedure results highlight little preferred orientation for the vesicles in the two scoria samples whereas the pumice shows a marked preferred orientation crystals also divided by mineral species were taken into account as well and in the two scoria samples there is no crystal preferred orientation in contrast with the pumice where crystal preferred orientation features are very similar to the ones found for the vesicles overall we found strong differences in preferred orientation weak for vesicles in scoriae showing an axial symmetry with the axis parallel to the elongation axis of the sample and a stronger and more complex orientation texture in the pumice sample for both crystals and vesicles the promising results obtained suggest that this procedure is potentially very useful for the analysis of preferred orientation in volcanic rocks and geomaterials in general

the 3d quantitative lattice and shape preferred orientation of a mylonitised metagranite from monte rosa western alps combining neutron diffraction texture analysis and synchrotron x ray microtomography abstract two complementary 3d techniques neutron diffraction and synchrotron x ray microtomography sxr ct were used to compare the shape and lattice preferred orientations of a mylonitised metagranite from the monte rosa unit western alps italy the goal of using these techniques was to obtain two different orientation distribution functions although the two functions describe relatively independent characteristics of the rock fabric nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures thereby highlighting 3d features that cannot be obtained with either technique if used independently we describe an approach that can be potentially useful in various disciplines e g structural geology rock mechanics tectonics and geophysics when a complete data set of preferred orientations and size distribution is needed micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic spo and lpo whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and lpo these observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz feldspar layers this mechanical decoupling occurred during the alpine subduction collision when the monte rosa unit was part of the insubric line system and accommodated large vertical strain

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

choosing between sides in the battle for pioneer colonization of schist in the coa valley archaeological park a community ecology perspective lichens and bryophytes are the dominant colonizers of rock art on schist in the coa valley archaeological park vila nova de foz coa north east portugal they should play an important role in the process of biologically induced deterioration of the engraved surfaces yet little is known about the composition and distribution of these communities and how they respond to local environmental constraints this study provides a first detailed survey of lichen and bryophyte species assemblages on vertical schist surfaces in the coa valley and assesses the effect of slope aspect on the composition of those assemblages with the aim of providing a selection of the most appropriate species for future approaches of biologically induced rock art deterioration ninety lichens and forty one bryophytes were identified on a set of twenty four rock surfaces with significant variation in the composition of their assemblages dependent on slope aspect here analysed in detail the potential implications of such variation for differential rock art deterioration are also discussed based on their frequency and abundance at opposite slopes in the coa valley three crustose lichens aspicilia hoffmanniana caloplaca subsoluta and lecanora pseudistera were selected to address the phenomenon of lichen induced weathering under the effect of major environmental constraints an emphasis is given on the need to directly quantify the impacts of individual species and species assemblages before assuming the effective role of biological activity in differential rock surface weathering

the measurement of velocity dispersion and frequency dependent intrinsic attenuation in sedimentary rocks a series of experiments to determine the elastic properties of a sequence of saturated sedimentary rocks over as wide a frequency range as possible was carried out at the imperial college borehole test site these experiments fall into four categories vertical seismic profiles vsps within the frequency range 30 280 hz crosshole surveys 0 2 2 3 khz sonic logging 8 24 khz and laboratory measurements 300 900 khz the intrinsic attenuation and velocity of compressional and shear waves were measured whenever possible velocity dispersion is observed for both compressional and shear waves the intrinsic attenuation of compressional waves is frequency dependent with a peak in the attenuation in the sonic frequency band the data were modeled assuming the attenuation is caused by local fluid flow in pores of small aspect ratio the modeling indicates that the intrinsic attenuation may be dominated by cracks with aspect ratios of around 10 super 3 to 10 super 4

effective elastic properties of solid clays clay minerals are perhaps the most abundant materials in the earth s upper crust as such their elastic properties are extremely important in seismic exploration seismic reservoir characterization and sonic log interpretation because little exists in the literature on elastic properties of clays we have designed a method of measuring effective elastic properties of solid clays clays without pores in this method clay minerals are mixed with a material with known elastic properties to make composite samples elastic properties of these clay minerals are then inverted from the measured elastic properties of the composite samples using the weighted hashin shtrikman average using this method we have measured 66 samples of 16 types of clays in this paper we present a comprehensive data set of elastic properties of solid clays that commonly occur in or are related to petroleum reservoirs although uncertainties up to 10 exist the data set reported here is by far the most comprehensive set of e

preferred orientation of phyllosilicates effects of composition and stress on resedimented mudstone microfabrics abstract development of a preferred orientation of clay minerals is investigated in response to changes in vertical effective stress and composition in resedimented material boston blue clay boston blue clay bbc an illitic glacio marine clay composed of 57 clay sized particles

a 3d imaging textural characterization of pyroclastic products from the 1538 ad monte nuovo eruption campi flegrei italy abstract the explosive volcanic event of the 1538 ad monte nuovo eruption volcanic explosivity index vei 2 in the campi flegrei high risk caldera italy has a strategic significance in the framework of volcanology and volcanic hazard of caldera forming magmatic systems in fact it represents the last and unique historical eruption of the highly populated phlegraean restless caldera and its precursory and eruptive phenomena are well known because they were described in detail by contemporaneous eyewitnesses in this study a set of samples representative of the complete stratigraphic sequence of the monte nuovo eruption was characterized using phase contrast synchrotron radiation computed microtomography and quantitatively investigated through the development of a new protocol for 3d textural analysis of highly vesiculated volcanic rocks previous studies of products from this eruption are available in the literature mostly based on 2d imaging techniques and thus provide a useful data set for comparison the 3d textural measurements allow us to investigate the subvolcanic processes mechanisms and timing of magma degassing that occurred during magma ascent in the conduit for each stage of the eruption and their relationship with the variations in the eruptive style described in the contemporaneous accounts of the eruption this information is fundamental for the definition of a volcanic eruption scenario for such low vei events often recurrent in the history of the caldera and is useful both for hazard assessment and emergency planning

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

synchrotron x ray computed microtomography studies on vesiculated basaltic rocks synchrotron x ray computed microtomography cmt was applied to five basalt samples from different locations in order to determine the microgeometrical structures and physical properties of vesicles two vesiculated basaltic lavas and one calcite filled vesiculated basaltic lava were collected from the lesotho highland south africa and two basaltic scoria tephra were taken from the lungkuan volcano group in northeast china they were examined with cmt on the x27c beam line of the brookhaven national synchrotron light source the voxel size varied from 10 to 20 m depending on the chosen field of view of the tomographic instrument a fast filtered back transform ffbt algorithm was employed in the tomographic reconstruction a 3d image geometry analysis package was used to measure the vesicularity specific surface area and interconnectivity of the vesicles the results of the analyses showed that the bubbles have roughly spheroidal forms of different sizes vesicularity ranged from 45 for lavas to 80 for scoria at least 90 of the vesicles are interconnected specific surface area was determined both by counting voxel faces and by use of two point correlation functions

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

stress pattern in portugal mainland and the adjacent atlantic region west iberia the portuguese mainland territory is located close to the azores gibraltar plate boundary in a tectonic setting responsible for significant neotectonic and seismic activities however few data concerning the present regional lithospheric stress field were available as testified by recently published maps of stress indicators for the europe and mediterranean regions one of the authors already presented a synthesis on this subject cabral 1993 where geological and geophysical stress indicators were considered in this paper we introduce new information mainly a considerable amount of borehole breakout data the updated data set comprises 32 reliable stress indicators showing a mean azimuth of 145 standard deviation 21 for the maximum horizontal stress direction shmax on the average the geological data are rotated clockwise and the focal mechanism data deviated anticlockwise to that azimuth while the borehole elongation results are consistent with the mean shmax trend these differences in stress trend suggest a regional progressive rotation of the shmax direction from nnw sse to wnw ese since the upper pliocene to estimate stress trajectories new and published stress indicators in the adjacent atlantic area and northern africa were also investigated showing a very uniform nw se shmax trend in west iberia a high level of horizontal compressive stress acting oblique to the western portuguese continental margin is inferred and interpreted in view of a proposed regional geodynamical model of activation of this passive margin with the nucleation of a subduction zone in the atlantic sw of iberia at the gorringe submarine bank which is propagating northward along the base of the continental slope at the transition between thinned and normal continental crust

syn and post fragmentation textures in submarine pyroclasts from lō ihi seamount hawai i abstract the extent and timing of vesiculation and microlite formation in ascending basaltic melts are relatively well understood for subaerial eruptions but they have not been studied thoroughly for submarine eruptions this is largely due to a lack of samples of appropriate volume and grain size we present a quantitative textural evaluation of coarse lapilli from two cone forming deposits at 1 km depth on l ihi seamount hawai i collected during a sampling intensive submersible dive series in 2006 lapilli from the deposits named the northern and southern cones have modal bulk vesicularities of 55 and 42 respectively and vesicle populations dominated by sub spherical non interconnected vesicles with number densities on the order of 10 4 to 10 5 cm 3 clasts of modal vesicularity have margin parallel zonation with seawater quenched rims interpreted to preserve syn fragmentation magmatic textures in microlite free sideromelane glass enclosing post fragmentation tachylitic interiors with vesicle and microlite textures that progressively coarsen from rim to core degassing scenarios are linked to syn fragmentation vesicle textures to demonstrate that both magmas degassed in dominantly closed systems diffusion controlled cooling rates of basaltic pyroclasts in contact with water are linked to post fragmentation evolution of vesicle and microlite textures to make inferences about transportation and dispersal of the pyroclasts in low submarine jets the textural analysis shows that the northern and southern cone eruptions were not strictly analogous to any classical subaerial eruption type they were uniquely submarine with ambient seawater playing a crucial role in the processes of degassing vesiculation crystallization and dispersal

seismic and mechanical properties of opalinus clay comparison between sandy and shaly facies from mont terri switzerland for the safe disposal of high level radioactive waste different host rocks are currently being considered the favorable properties of clay are low permeability some retention capacity concerning radionuclides and the ability to self seal cracks and fissures e g by swelling or time dependent compaction creep in switzerland the jurassic opalinus clay is envisaged as a potential host rock which at mont terri is subdivided into the sandy shaly and carbonate rich facies the latter being less abundant for long term safety assessments the understanding of the relations of properties e g mineralogical composition and microstructure and performance e g mechanical behavior of clays and claystones is essential in the case of the sandy opalinus clay the mechanical strength increases with increasing carbonate content because carbonates form the matrix the mineralogical investigation of a set of sandy facies samples proved a significantly larger carbonate content 20 40 mass when compared to the shaly facies 10 20 mass the carbonates of the shaly opalinus clay on the other hand are mostly localized fossils aligned parallel to the bedding acting as predetermined breaking points image analysis of sem images of polished sections proved the determined microstructural differences in addition carbonate particles of the sandy facies are mostly isometric whereas carbonate particles of the shaly facies cover a greater range of shapes the mechanical tests were accompanied by investigations of the p and s wave velocities which revealed that the anisotropy of the sandy facies is less pronounced than sedimentological analyses would suggest the mechanical strength which for the first time presents results of real triaxial tests of the sandy facies the samples of the sandy facies exhibit a failure strength of eff b approximately twice as high as was found for the shaly facies considering the deformation axis parallel to the bedding similar values were obtained when measuring perpendicularly to the bedding

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

microstructural evolution of an incipient fault zone in opalinus clay insights from an optical and electron microscopic study of ion beam polished samples from the main fault in the mt terri underground research laboratory abstract slickensided shear surfaces are ubiquitous in many fault zones however the internal structure the micromechanics and the evolution of these structures are not fully understood and the contributions of crystal plasticity grain boundary sliding microfracturing solution precipitation and mineral transformation under different conditions are subject of debate we studied well preserved core samples from the main fault an up to 3 m wide zone of approximately 10 m offset in the mont terri underground research laboratory ch a site to evaluate long term safety of radioactive waste disposal the drill core breaks easily along many slickensided shear surfaces indicating reverse slip which form an anastomosing network connected by branch lines broad ion beam polishing and scanning electron microscopy shows that the slickensides are invariably revealed by fracture of the drill core along a few m thick shear zone which acts as a crack guide for fracturing the samples in this zone a complex set of processes is inferred leading to extreme localization of strain development of strong particle preferred orientation the formation of nanoparticles and local precipitation of calcite veins in releasing sections in lenses between shear zones homogeneous gouge is formed with a well developed oblique foliation and removal of calcite grains by pressure solution we infer that with progressive deformation the number and density of slickensided shear surfaces increases generating tectonically derived scaly clay and more homogeneous gouge in all deformed elements of the main fault porosity is much smaller than in the undeformed opalinus clay an interesting observation is the almost complete absence of cataclastic microstructures transmission electron microscopy tem of focused ion beam lamellae of this micron wide shear zone shows a strong preferred orientation of clay minerals including nano sized illite particles in tem the shear zones envelop hard particles and confirm an almost complete loss of porosity compared to the protolith we propose that inter and transgranular microcracking pressure solution clay neoformation crystal plasticity and grain boundary sliding are important micro scale processes during the early stages of faulting in opalinus clay and thus need to be considered in extrapolating laboratory results to long term mechanical behavior

elastic properties of anisotropic synthetic calcite muscovite aggregates 1 a set of synthetic aggregates containing mixtures of calcite and muscovite were compacted with varying uniaxial loads ranging from 20 mpa up to 400 mpa their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 mpa measured seismic velocities are shown to depend on 1 the ratio of calcite to muscovite 2 the uniaxial load used during sample manufacturing and 3 the porosity amount prior to velocity measurements the matrix framework may also affect the seismic velocities but this effect is not easily quantifiable in general measured seismic velocities decrease with increasing muscovite content and porosity elastic properties have been calculated based on texture measurements which were obtained by neutron diffraction the calculated velocities are based on the calcite and muscovite single crystal elastic tensors their orientation distribution functions and their modal fractions a large discrepancy is apparent between calculated and measured velocities where the former always overestimate the actual velocities shear waves display less of a difference between calculated and measured values than do compressional waves indicating that waves propagating by shearing are less affected by sample porosity and matrix framework a better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account using a differential effective medium model seismic anisotropy is evident from both measured and calculated velocities and is low for samples containing pure calcite but becomes prominent as the muscovite concentration increases the intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity

palaeostress evolution of the iberian peninsula late carboniferous to present day abstract three main stages can be differentiated in iberia from the upper carboniferous to the present the end of the variscan orogeny late carboniferous the permian early cretaceous rifting and the alpine orogeny late cretaceous to present in this contribution the main features of the stress fields determined in each of these stages are compiled and revised from the analysis of the brittle deformations mainly microfault population stresses are related to the development of the principal structures of each stage in the late variscan fracturing stage sinistral strike slip faults prevailed in a stress field with ne sw subhorizontal compression in the permian to early cretaceous rifting stage the extensional trends varied in each sector during the alpine orogeny primarily the margins of the iberian massif the betic and pyrenee mountain chains were deformed however numerous deformations are also identified in its interior where large mountain chains such as the central system and the iberian chain developed these deformations occurred in a complex stress field where zones of nw se to nne ssw horizontal compression prevailed albeit predominantly extensional zones existed as well at present the stress field in most of iberia has a nw se compressive trend associated with active deformations in the betic cordillera where a continental subduction developed however simultaneously there are zones in which extensional settings predominate such as the internal zones of the betic cordillera and the gulf of valencia region making for quite a complex current stress field

revisiting elastic anisotropy of biotite gneiss from the outokumpu scientific drill hole based on new texture measurements and texture based velocity calculations abstract a sample of biotite gneiss from the outokumpu deep drilling project in finland was investigated by kern et al 2008 for crystal preferred orientation and elastic anisotropy considerable differences between measured acoustic velocities and velocities calculated on the basis of texture patterns were observed measured p wave anisotropy was 15 1 versus a voigt average yielding 7 9 here we investigate the same sample with different methods and using different averaging techniques analyzing time of flight neutron diffraction data from dubna skat and lansce hippo diffractometers with the rietveld technique much stronger preferred orientation for biotite is determined compared to conventional pole figure analysis reported previously the comparison reveals important differences hippo has much better counting statistics but pole figure coverage is poor skat has better angular resolution using the new preferred orientation data and applying a self consistent averaging method that takes grain shapes into account close agreement of calculated and measured p wave velocities is observed 12 6 this is further improved by adding 0 1 vol flat micropores parallel to the biotite platelets in the simulation 14 9

magma degassing during the plinian eruption of novarupta alaska 1912 1 we have modeled the nucleation and isothermal growth of bubbles in dacite from the 1912 plinian eruption of novarupta alaska bubble growth calculations account for the exsolution of h2o and co2 beginning with bubble nucleation and ending when bubble sizes reproduced the observed size distribution of vesicles in novarupta pumice clasts assuming classical nucleation theory bubbles nucleated with a diameter of the order of 10 8 m and grew to sizes ranging from 10 6 m to greater than 10 3 m the typical range of vesicle sizes found in novarupta pumice the smallest vesicles in novarupta pumices are also the most abundant and bubbles with radii of 10 6 m to 10 5 m comprise almost 90 of the entire bubble population we find that these bubbles must have nucleated and grown to their final size within a few 100 milliseconds despite these extremely fast growth rates the pressures of exsolved volatiles contained within the bubbles remained high up to about 107pa in excess of ambient pressure assuming a closed system the potential energy of these compressed volatiles was sufficient to cause magma fragmentation even though only a fraction of the pre eruptive volatiles had exsolved unless the matrix glasses of novarupta pyroclasts retains a large fraction of pre eruptive volatiles the majority of magmatic volatiles 80 90 was likely lost by open system degassing between magma fragmentation and quenching

phyllosilicate preferred orientation in relation to strain path determination in the lower paleozoic stavelot venn massif ardennes belgium abstract phyllosilicate preferred orientation measured by means of an x ray pole figure goniometer allows a quantitative exploration of the slaty cleavage development the relationship between phyllosilicate preferred orientation and strain as demonstrated in the march model furthermore enables the application of phyllosilicate pole figures in a strain determination in slate belts both applications are illustrated in this paper in which the results are presented of a crystallographic fabric analysis of argillites in the southern domain of the lower paleozoic stavelot venn massif belgium in these argillites the development of a phyllosilicate preferred orientation is primarily defined by the low grade metamorphism and the deformation history the metamorphism causing recrystallisation to be active during cleavage development assures the development of a high degree of preferred orientation on the other hand the deformation history defines the type of phyllosilicate pole figure pattern based on the distinction of different pole figure patterns a possible strain path for the argillites in the southern domain of the stavelot venn massif is proposed an axially symmetric pole figure pattern indicates a caledonian cleavage development in a pure flattening regime the variscan cleavage development on the other hand is characterised by an additional extensional component in the cleavage plane if the primary phyllosilicate fabric due to a pre deformational compaction or a caledonian cleavage development underwent a complete reorientation caused by syntectonic recrystallisation a typical orthorhombic pole figure pattern is formed otherwise a transition pole figure pattern develops reflecting the superposition of the variscan cleavage development on a pre existing caledonian cleavage fabric the general deformation history of the southern domain of the stavelot venn massif differs substantially from that described for the northern domain contrary to the northern domain the southern domain seems to have undergone considerable variscan deformation

3d particle size distributions from 2d observations stereology for natural applications abstract we have developed a general formulation for stereological analysis of particle distributions which is applicable to any particle size or size distribution not limited to log normal unimodal etc we have applied numerical techniques to define intersection probability distributions for any shapes previously only known for spheres and quantified the errors involved in using spherical coefficients for various non spherical particles this stereological technique is based on knowing the probability distribution of random cross sections through various particles so that small circle cross sections can be subtracted from an observed population to provide the 3d size distribution of particles the results indicate that the most important parameter controlling calculated size distribution is particle aspect ratio for a distribution of particles with a specific aspect ratio or range of aspect ratios variations of particle form spherical vs cubic rectangular vs elliptical do not alter the results so the technique can be applied to a range of particle shapes applications can be made in a petrology volcanology and other fields only a few of which can also be treated using expensive x ray techniques

quantitative 3d petrography using x ray tomography application to bishop tuff pumice clasts abstract textures are traditionally studied using the petrographic microscope which limits observations to 2d sections of 3d objects given the difficulty in retrieving information on shapes sizes and spatial distribution of objects in 3d from random sections a method that can yield observations in 3d is highly desirable x ray tomography yields a 3d map of the linear x ray attenuation coefficient which is a function of the atomic number and density of the material and the x ray energy used based on the compositional contrasts between different phases various phases can be identified in a rock pumice clasts characterized by isolated crystals surrounded by a low density matrix are ideal for the application of this technique we present our first results obtained using x ray tomography for pumice clasts from the bishop tuff samples studied are from units f7 and f8 and are representative of the variability in density and crystal contents observed in the early erupted bishop tuff data were collected on the geosoilenvironcars beamline at the advanced photon source argonne national laboratory using a 22 kev monochromatic x ray beam image analysis was performed using the software blob3d brightness contrasts in the resulting images allow the separation of magnetite sanidine quartz including minor plagioclase glass and vesicles crystals smaller than 5 voxels in diameter cannot be quantified properly mostly due to noise in the images this constrains the spatial resolution of the resulting images such that there is a trade off between sample size and spatial resolution we employed two runs with samples of varying sizes 5 and 10 mm to obtain adequate resolution voxel sizes ca 8 and 17 m we have previously studied quartz size distributions in bishop pumice clasts using a crushing sieving and winnowing procedure the agreement between our new and previous results is excellent quartz size distributions obtained using the tomography data are concave upward on population density vs size plots and resemble the size distributions for all quartz crystals including both whole crystals and fragments these size distributions were probably generated by fragmentation through which large crystals were converted in a larger number of small crystals petrographic observations suggest fragmentation occurred mostly under magmatic conditions sanidine size distributions are similar to those observed for quartz magnetite size distributions are typically linear indicating a simple magmatic history in contrast with the tektosilicates

anisotropy in shale from mont terri anisotropy of shales is the subject of this report and we use an example of the jurassic opalinus clay from mont terri switzerland that is being investigated in the context of radioactive waste disposal the study is targeted at the geomechanical characterization of shale by laboratory testing the overall aim is to improve the constitutive material laws and their application in numerical models

elastic anisotropy modeling of kimmeridge shale 1 anisotropy of elastic properties in clay rich sedimentary rocks has been of long standing interest these rocks are cap rocks of oil and gas reservoirs as well as seals for carbon sequestration elasticity of shales has been approached by direct velocity measurements and by models based on microstructures here we are revisiting the classical kimmeridge shale studied by hornby 1998 by first quantifying microstructural features such as phase volume fractions grain shapes and grain orientations and pore distributions with advanced analytical methods and then using this information in different models to explain bulk elastic properties it is shown that by application of a self consistent algorithm based on eshelby s 1957 model of inclusions in a homogeneous medium it is possible to explain most experimental elastic constants though some discrepancies remain which may be due to the interpretation of experimental data using a differential effective medium approach an almost perfect agreement with experimental stiffness coefficients can be obtained though the physical basis of this method may be questionable the influence of single crystal elastic properties grain shapes preferred orientation and volume and shapes of pores on elastic properties of shale is explored

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

characterizing high energy explosive eruptions at stromboli volcano using multidisciplinary data an example from the 9 january 2005 explosion abstract stromboli is well known for its persistent normal explosive activity consisting of intermittent mild to moderate strombolian explosions that typically occur every 10 20 min all tephras erupted during this activity usually fall back into the crater terrace and consist of volatile poor scoriae fed by highly porphyritic hp magma more occasionally large explosions or paroxysms eject a greater quantity of tephra mainly consisting of hp scoriae and pumice clasts of low porphyritic lp magma but also including large lithic blocks in addition to this activity between 2004 and 2006 high energy explosions displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height duration and tephra dispersal were observed to occur at a frequency of one to eight events per year while many volcanological geochemical and geophysical studies have focused in the last few years on the two end members of activity i e normal or paroxysmal a detailed investigation on these intermediate types of events has not been carried out yet here we report of a study on the 9 january 2005 explosion one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m and of ash and lapilli to 200 m an accompanying ash plume rose up to 500 m at the end of the explosion we present a multidisciplinary approach that integrates the results from analysis of live camera images with compositional and textural characterization of the erupted products major element composition of glassy groundmass and 3d views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity for which we use the term intermediate by comparing the video camera images of the 9 january 2005 explosion with volcanological features of other high energy explosions that occurred at stromboli between june 2004 and october 2006 we find that three additional events can be considered intermediate explosions suggesting that this type of activity may be fairly common on this volcano the results of this study although preliminary given our limited dataset clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity potentially improving our capability of eruption forecasting and assessing volcanic hazard at stromboli

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

two dimensional solution for straight and meandering overbank flows this paper presents a practical method to predict depth averaged velocity and shear stress for straight and meandering overbank flows an analytical solution to the depth integrated turbulent form of the navier stokes equation is presented that includes lateral shear and secondary flows in addition to bed friction the novelty of the present approach is not only its inclusion of the secondary flows in the formulation but also its applicability to straight and meandering channels the analytical solution is applied to a number of channels at model and field scales and is also compared with other available methods such as that of shiono and knight and the lateral distribution method the present formulation gives much better predictions of velocity and shear stress particularly in those cases where the secondary flows are dominant

the role of syn eruptive vesiculation on explosive basaltic activity at mt etna italy abstract we investigated the dynamics of explosive activity at mt etna between 31 august and 15 december 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active summit crater the analysed scoria clasts present large connected vesicles with complex shapes and smaller isolated spherical vesicles the content of which increases in scoriae from the most explosive events gas geochemistry reports co 2 so 2 and so 2 hcl ratios supporting a deep derived gas phase for fire fountain activity by integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of mt etna activity in 2006 were driven by a previously accumulated co 2 rich gas phase but we highlight the lesser role of syn eruptive vesicle nucleation driven by water exsolution during ascent we conclude that syn eruptive vesiculation is a common process in etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation

magma vesiculation and infrasonic activity at stromboli open conduit volcano abstract explosive activity at stromboli is explained in terms of dynamics of large gas bubbles that ascend in the magma conduit and burst at the free surface generating acoustic pressure that propagates as infrasonic signals in the atmosphere the rate and the amplitude of the infrasonic activity is directly linked to the rate and the overpressure of the bursting gas bubbles and thus reflects the rate at which magma column degasses under non equilibrium pressure conditions we investigate the link between explosive degassing and magma vesiculation by comparing the rate of infrasonic activity with the bubble size distributions bsds of scoria clasts collected during several days of explosive activity at stromboli bsds of scoria show a characteristic power law distribution which reflect a gas bubble concentration mainly controlled by a combined process of bubble nucleation and coalescence the cumulative distribution of the infrasonic pressure follows two power laws indicating a clear separation between the frequent but weak bursting of small gas bubbles puffing and the more energetic explosions of large gas slugs the exponents of power laws derived for puffing and explosive infrasonic activity show strongly correlated 0 96 changes with time indicating that when the puffing rate is high the number of energetic explosions is also elevated this correlation suggests that both puffing and explosive activity are driven by the same magma degassing dynamics in addition changes of both infrasonic power law exponents are very well correlated 0 92 with puffing and 0 87 with explosions with variations of the bsd exponents of the scoria clasts providing evidence of the strong interplay between scoria vesiculation and magma explosivity our analysis indicates that variable magma vesiculation regimes recorded in the scoria correlate with the event number and energy of the explosive activity we propose that monitoring infrasound on active volcanoes may be an alternative way to look at the vesiculation process in open conduit systems

the late variscan fault network in central northern portugal nw iberia a re evaluation abstract the fault network in central northern portugal especially the fault system with mean strike n25 has been used to help deduce the late palaeozoic dynamics of western europe on the other hand the n80 strike slip fault system was recognized in previous works as late variscan and left lateral but was scarcely mapped and its importance neglected this study shows that the n25 faults were dextral in the late stages of the variscan orogeny and sinistral during the alpine cycle due to pervasive reactivation fault rocks and intrusions are clearly different according to age mostly high temperature quartz infillings but locally muscovite tourmaline and aplite dykes in late variscan times and low temperature cataclasites fault gouges and mesozoic mafic dykes in younger alpine times we dated dextral n45 segments of the n25 fault system because they are less prone to reactivation by the nnw sse alpine compression and can thus preserve the variscan record we used k ar in muscovite concentrates and obtained a minimum age of the analysed faults of ca 312 ma which sets a lower limit to the so called late variscan wrench faulting period the present study shows that the n80 fault set is pervasive and sinistral in central northern portugal and therefore that it only admits one brittle dextral conjugate the n25 fault system both were generated by a maximum compressive stress bearing between n50 and n55 in azimuth we did not find evidence of a variscan sinistral strike slip movement in the n25 fault system and therefore this kinematics is believed to represent only the displacements accommodated during the alpine cycle

near liquidus growth of feldspar spherulites in trachytic melts 3d morphologies and implications in crystallization mechanisms the nucleation and growth processes of spherulitic alkali feldspar have been investigated in this study through x ray microtomography and electron backscatter diffraction ebsd data here we present the first data on shape preferred orientation spo and crystal preferred orientation cpo of alkali feldspar within spherulites the analysis of synchrotron x ray microtomography and ebsd datasets allowed us to study the morphometric characteristics of spherulites in trachytic melts in quantitative fashion highlighting the three dimensional shape preferred orientation branching of lamellae and crystal twinning providing insights about the nucleation mechanism involved in the crystallization of the spherulites the nucleation starts with a heterogeneous nucleus pre existing crystal or bubble and subsequently it evolves forming bow tie morphologies reaching radially spherulitic shapes in few hours since each lamella within spherulite is also twinned these synthetic spherulites cannot be considered as single nuclei but crystal aggregates originated by heterogeneous nucleation a twin boundary may have a lower energy than general crystal crystal boundaries and many of the twinned grains show evidence of strong local bending which combined with twin plane creates local sites for heterogeneous nucleation this study shows that the growth rates of the lamellae 10 6 10 7 cm s in spherulites are either similar or slightly higher than that for single crystals by up to one order of magnitude furthermore the highest volumetric growth rates 10 11 10 12 cm3 s show that the alkali feldspar within spherulites can grow fast reaching a volumetric size of 10 m3 in 1 s

seismic properties of the upper mantle beneath lanzarote canary islands model predictions based on texture measurements by ebsd abstract we present a petrophysical analysis of upper mantle xenoliths collected in the quaternary alkali basalt fields series iii and iv from the island of lanzarote the samples consist of eight harzburgite and four dunite nodules 5 to 15 cm in size and exhibit a typical protogranular to porphyroclastic texture an anomalous foliation resulting from strong recovery processes is observed in half of the specimens the lattice preferred orientations lpo of olivine orthopyroxene and clinopyroxene were measured using electron backscatter diffraction ebsd in most samples olivine exhibits lpos intermediate between the typical single crystal texture and the 100 fiber texture occasionally the 010 fiber texture was also observed simultaneous occurrence of both types of fiber textures suggests the existence of more than one deformation regime probably dominated by a simple shear component under low strain rate and moderate to high temperature orthopyroxene and clinopyroxene display a weaker but significant texture the lpo data were used to calculate the seismic properties of the xenoliths at pt conditions obtained from geothermobarometry and were compared to field geophysical data reported from the literature the velocity of p waves 7 9 km s obtained for a direction corresponding to the existing seismic transect is in good agreement with the most recent geophysical interpretation our results are consistent with a roughly w e oriented fastest p wave propagation direction in the uppermost mantle beneath the canary islands and with the lithosphere structure proposed by previous authors involving a crust mantle boundary at around 18 km in depth overlaid by intermediate material between 11 and 18 km

three dimensional grain fabric measurements using high resolution x ray computed tomography abstract high resolution x ray computed tomography hrxct provides detailed imagery of the interiors of rocks up to hand sample size non destructively and in three dimensions new tools described here allow these data to be used for analysis of grain fabrics two separate sets of measurement techniques have been developed the first concentrates on quantifying individual crystals phenocrysts porphyroblasts or other discrete objects or void spaces within a sample quantifiable properties include location size shape orientation and contact relationships with adjacent objects the second set of techniques performs a more general fabric analysis on any distinguishable component in a sample a fabric tensor can be computed based on a number of metrics including the star volume distribution svd star length distribution sld and mean intercept length mil methods the fabric tensors provide principal component directions and magnitudes which in turn provide a measure of degree of anisotropy and shape indices because the svd and sld measure only the material of interest whereas the mil is also influenced by spatial distribution results can be divergent for sparse phases also introduced is a three dimensional rose diagram that can be viewed interactively and inspected to reveal further details about non orthogonal directional components these techniques are demonstrated through analysis of a garnet kyanite schist from mica dam british columbia

the clay fabric of shales is a strain gauge abstract shales with their large clay fraction are prone to deform in an almost ductile way under tectonic loading here we propose to monitor and quantify the evolution of strained shales clay fabric in the field of illite diagenesis by using magnetic fabric in the footwall of a south pyrenean thrust 281 shales samples have been collected along a 2 km long exceptional exposure the cleavage evolves from pencil structures at 1 km of the thrust to pencil cleavage at 850 m and slaty cleavage at 170 m the average magnetic foliation of illite remains nearly parallel to bedding over a distance of 600 m despite development of pencil cleavage it is at 600 m of the thrust that illite foliation shifts gradually from bedding to cleavage by contrast the magnetic fabric scalar data reflect a more continuous evolution of the deformation the application of a rigid rotation model of the clays allows to quantify the strain magnitude using eigen values of tensor this strain magnitude is consistent with distance to the thrust and conforms favorably with a trishear modelling of this thrust damage we demonstrate therefore that the magnetic fabric of illite rich shales is a strain gauge

crystal size distributions csd in three dimensions insights from the 3d reconstruction of a highly porphyritic rhyolite growth histories and residence times of crystals in magmatic systems can be revealed by studying crystal sizes size distributions and shapes in this contribution serial sectioning has been employed on a sample of porphyritic rhyolite from a permo carboniferous laccolith from the halle volcanic complex germany to reconstruct the distribution of felsic phenocrysts in three dimensions in order to determine their true shapes sizes and three dimensional size distributions a model of all three phenocryst phases quartz plagioclase k feldspar with 217 crystals and a larger model containing 1599 k feldspar crystals was reconstructed in three dimensions the first model revealed a non touching framework of crystals in three dimensions suggesting that individual crystals grew freely in the melt prior to quenching of the texture however crystal shapes are complex and show large variation on a zingg diagram intermediate over long axis plotted against short over intermediate axis they often do not resemble the crystallographic shapes expected for phenocrysts growing unhindered from a melt indicating complex growth histories in contrast the three dimensional size distribution is a simple straight line with a negative slope stereologically corrected size distributions from individual sections compare well with stereologically corrected size distributions obtained previously from the same sample however crystal size distribution csd data from individual sections scatter considerably it is shown that csds can be robustly reproduced with a sampling size of greater than 200 crystals the kind of shape assumed in stereological correction of csds however has a large influence on the calculation and estimation of crystal residence times

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

elastic properties of clay minerals clay minerals are the most abundant materials in sedimentary basins the most common like kaolinite illite chlorite and smectite are found in various amounts in mudstones and are also often found in clastic and nonclastic reservoir rocks their presence alters the elastic behavior of reservoir rocks significantly as a function of mineral type volume and distribution thus two sandstones with the same clay amount might have different elastic properties due to differences within the clay population the elastic properties of clay minerals are therefore important in rock physics modeling to understand the seismic and sonic log responses of shaley sequences and clay bearing reservoir rocks

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

lateral depth averaged velocity distributions and bed shear in rectangular compound channels this paper presents a method to predict depth averaged velocity and bed shear stress for overbank flows in straight rectangular two stage channels an analytical solution to the depth integrated navier stokes equation is presented that includes the effects of bed friction lateral turbulence and secondary flows the shiono and knight method accounts for bed shear lateral shear and secondary flow effects via three coefficients f and respectively a novel boundary condition at the internal wall between the main channel and the adjoined floodplain is proposed and discussed along with other conventional boundary conditions the analytical solution using the novel boundary condition gives good prediction of both lateral velocity distribution and bed shear stress when compared with experimental data for different aspect ratios

non invasive assessment of the formation of tourmaline nodules by x ray microtomography and computer modeling tourmaline nodules occurring in the capo bianco elba island italy aplitic rocks are here investigated by x ray microtomography 3d imaging this non invasive technique provides 3d images of the tourmaline nodules revealing an irregular morphology consisting of branches that extend radially from the cores the nodules present scale invariant features that can be described by a box counting fractal dimension the value of the fractal dimension is proportional to the size of the nodules and tends asymptotically to a value of 2 5 in agreement with the results obtained from the simulation of virtual nodules by means of a diffusion limited aggregation model based on a monte carlo metropolis algorithm in which the growth probability at the tips of the nodule is an inverse function of the diffusion coefficient the results support the hypothesis that tourmaline formed by a disequilibrium magmatic process in which diffusion represents the rate limiting step inducing the formation of nodules with irregular shapes this study shows the potential of x ray microtomography in combination with numerical modeling as a probe for accessing the 3d microstructural information of complex mineral morphologies with a non invasive approach the combination of numerical and experimental non invasive 3d techniques represents a fundamental step forward in bridging the gap between the observation of microstructures and the interpretation of the associated processes

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

orientation distribution of microlites in obsidian abstract the shape and three dimensional orientation distribution of microlites are measured in obsidian from little glass mountain ca measurements are made from thin sections using an image series of high magnification digital micrographs taken serially through different focal depths these measurements agree well with the theoretically predicted and experimentally measured distribution of long slender rods in a newtonian fluid undergoing simple shear flow in this type of flow rods in a dilute suspension rotate periodically spending most of the time aligned with the flow measurements of the detailed orientation distribution integrated with theoretical models provide a tool for inferring flow dynamics and the timing of magmatic processes

quartz use in the absence of flint middle and upper palaeolithic raw material economy in the coa valley north eastern portugal abstract differing from most of european upper palaeolithic record the coa valley lithic assemblages reveal an intensive use of a large variety of quartz and quartzite available locally new surveys of the lower coa valley quartz veins were carried out in order to establish potential areas of raw material exploitation by hunter gatherers through the identification of the raw material sources present in the archaeological record upper palaeolithic lithic assemblages are produced on local quartz varieties regional fine grained quartz veins and flint and silcrete from long distance sources the proportion of raw material and their choice for different tool types reveal some variation through the upper palaeolithic sequence but present the same diversity and large geographical range of supply middle palaeolithic assemblages from the same region are essentially based on local lithic material showing a more restricted exploitation area and revealing different technology and procurement strategies possibly evidence of changes in mobility and social networks

three dimensional investigation of volcanic textures by x ray microtomography and implications for conduit processes 1 synchrotron x ray computed microtomography ct was applied for the first time to clasts of pumice and scoria generated by active explosive volcanoes characterized by a range of eruptive styles mild strombolian to plinian and magmatic composition basaltic to trachytic the obtained two dimensional 2d tomographic images corresponding to sample views at different rotation angles were processed to reconstruct three dimensional 3d volumes and then used to make 3d measurements of vesicularity vesicle number density volume and connectivity for quantitative characterization of the investigated tephras the results indicate a positive correlation between vesicle number density and eruption intensity that is used to investigate modes of magma degassing in explosive eruptions in addition the vesicle geometry affecting the connected gas flow pathways in pyroclasts from strombolian eruptions is determined and related to the known permeabilities implications on the dynamics of explosive eruptions is discussed and ultimately used to quantitatively discriminate between different eruptive styles

nature vs culture present day spatial distribution and preservation of open air rock art in the coa and douro river valleys portugal abstract late glacial and iron age open air rock art of the coa river valley shows a similar spatial distribution with several clusters along the coa and douro river tributaries that are mostly exposed to the southeast in this report we try to determine whether the artists of both periods deliberately chose the same natural panels for rock art or its present day spatial distribution is imposed by formation and weathering processes previous or subsequent to the engraving geological structural analysis from regional to field scales shows a nne ssw sinistral strike slip fault system that crosses the study area together with a set of fracture joints with the same orientation and formed by the same tectonic stress direct field measurement and the description of 713 natural panels engraved and un engraved reveal that the preserved rock art panels correspond to the most common tectonic fracture joint systems nne ssw of the study area locally the hydrographic network is conditioned by the same structural control differential weathering exists between the panels exposed on opposite margins of watercourses with preferential degradation of the rock art panel surfaces exposed to the nw we propose that on the scale of the valley the surface weathering of the rock art panels results from differential solar radiation humidity lichen and bryophyte colonisations interpretation of field observations a frequency probabilistic procedure pair wise comparison matrix and geographic information system analysis were combined to evaluate a coa panel formation and preservation predictive model using archaeological topographical and hydrological data four variables were extracted and weighted from the collected data including topographic slope and aspect solar radiation and cost weighted distance to watercourses which were used as environmental input data the archaeological input data rock art occurrences were used to calculate the variable ratings and to evaluate both the coa panel formation and preservation predictive model and external validation maps with the results showing an agreement of 80 and 70 respectively field verification revealed unknown rock art panels in areas with high and very high values the coa panel formation and preservation predictive model provides a useful framework to guide survey and heritage management

magnetic fabric welding texture and strain fabric in the nuraxi tuff sardinia italy anisotropy of magnetic susceptibility ams has been used to interpret flow directions in ignimbrites but no study has demonstrated that the ams fabric corresponds to the flow fabric in this paper we show that the ams and strain fabric coincide in a high grade ignimbrite the nuraxi tuff a miocene rhyolitic ignimbrite displaying a wide variability of rheomorphic features and a well defined magnetic fabric natural remanent magnetization nrm data indicate that the magnetization of the tuff is homogeneous and was acquired at high temperatures by ti magnetite crystals comparison between the magnetic fabric and the deformation features along a representative section shows that ams and anisotropy of isothermal remanent magnetization airm fabric are coaxial with and reproduce the shape of the strain ellipsoid magnetic tests and scanning electron microscopy observations indicate that the fabric is due to trails of micrometer size pseudo single domain magnetically interacting magnetite crystals microlites formed along discontinuities such as shard rims and vesicle walls mimicking the petrofabric of the tuff the fabric was thus acquired after deposition before late rheomorphic processes and accurately mimics homogeneous deformation features of the shards during welding processes and mass flow

turbulent open channel flows with variable depth across the channel the flow of water in straight open channels with prismatic complex cross sections is considered lateral distributions of depth mean velocity and boundary shear stress are derived theoretically for channels of any shape provided that the boundary geometry can be discretized into linear elements the analytical model includes the effects of bed generated turbulence lateral shear turbulence and secondary flows experimental data from the science and engineering research council serc flood channel facility are used to illustrate the relative importance of these three effects on internal shear stresses new experimental evidence concerning the spatial distribution of reynolds stresses yx and zx is presented for the particular case of compound or two stage channels in such channels the vertical distributions of zx are shown to be highly nonlinear in the regions of strongest lateral shear and the depth averaged values of yx are shown to be significantly different from the depth mean apparent shear stresses the importance of secondary flows in the lateral shear layer region is therefore established the influence of both reynolds stresses and secondary flows on eddy viscosity values is quantified a numerical study is undertaken of the lateral distributions of local friction factor and dimensionless eddy viscosity the results of this study are then used in the analytical model to reproduce lateral distributions of depth mean velocity and boundary shear stress in a two stage channel the work will be of interest to engineers engaged in flood channel hydraulics and overbank flow in particular

the grizzly lake complex yellowstone volcano usa mixing between basalt and rhyolite unraveled by microanalysis and x ray microtomography abstract magma mixing is a widespread petrogenetic process it has long been suspected to operate in concert with fractional crystallization and assimilation to produce chemical and temperature gradients in magmas in particular the injection of mafic magmas into felsic magma chambers is widely regarded as a key driver in the sudden triggering of what often become highly explosive volcanic eruptions understanding the mechanistic event chain leading to such hazardous events is a scientific goal of high priority here we investigate a mingling event via the evidence preserved in mingled lavas using a combination of x ray computed microtomographic and electron microprobe analyses to unravel the complex textures and attendant chemical heterogeneities of the mixed basaltic and rhyolitic eruption of grizzly lake in the norris mammoth corridor of the yellowstone plateau volcanic field yvf we observe evidence that both magmatic viscous inter fingering of magmas and disequilibrium crystallization dissolution processes occur furthermore these processes constrain the timescale of interaction between the two magmatic components prior to their eruption x ray microtomography images show variegated textural features involving vesicle and crystal distributions filament morphology the distribution of enclaves and further textural features otherwise obscured in conventional 2d observations and analyses although our central effort was applied to the determination of mixing end members analysis of the hybrid portion has led to the discovery that mixing in the grizzly lake system was also characterized by the disintegration and dissolution of mafic crystals in the rhyolitic magma the presence of mineral phases in both end member for example forsteritic olivine sanidine and quartz and their transport throughout the magmatic mass by a combination of both mixing dynamics and flow imposed by ascent of the magmatic mass and its eruption might have acted as a geometric perturbation of flow fields further fuelling mass exchange between magmas in terms of both chemical diffusion and crystal transfer these results illuminate the complexity of mixing in natural magmatic systems identifying several reaction related textural factors that must be understood more deeply in order to advance our understanding of this igneous process

three dimensional petrography of metal phases in equilibrated l chondrites effects of shock loading and dynamic compaction abstract to examine the role of impacts in the evolution of asteroids as seen through their chondritic offspring we have performed a quantitative three dimensional 3d study of metal grains in a suite of increasingly shocked l chondrites with synchrotron x ray microtomography xmt our data allow rigorous quantification of size number distributions and collective morphology of fe ni metal phases in chondritic meteorites at the resolution of our xmt measurements 8 4 17 9 m voxel the number of metal particles increase with higher degrees of petrographically identified shock loading indicating a coalescing of fe ni metal at or below this scale our results demonstrate that collective degrees of metal grain preferred orientation increase with greater degrees of impact related compaction and shock loading ductile metal grains in l chondrites begin to show foliation at peak shock pressures

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

texture and anisotropy the study of preferred orientation of minerals in rocks dates back to omalius d halloy 1833 who attributes a special significance to the alignment of crystals as an indicator of the formation process much later the influence of crystal alignment on physical properties was quantified e g weissenberg 1922 voigt 1928 reuss 1929 only recently has this field emerged as a coherent part of earth science research linking such branches as mineralogy petrology structural geology geodynamics and seismology the reason for this was the emergence of quantitative methods to analyze preferred orientation or texture as it was first called by naumann 1850 these methods were largely developed in collaboration with materials science and mechanics quantitative measurements detailed field studies rigorous data analysis theories to predict textures and improvements in characterizing seismic anisotropy in the earth are leading to a coherent picture that is now being refined though seismologists have long accepted that there is a causal relationship between anisotropic propagation of seismic waves the deformation field and crystal orientation the prevailing view is still largely the mythological concept that seismic fast directions align with the flow direction while this may be approximately the case for olivine deformed under certain conditions it is certainly no universal law as we will try to illustrate in this review the fast direction of a crystal depends on the mineral species and its crystal structure the alignment of crystals depends on microscopic intra crystalline deformation systems and the deformation history both relationships are complex and not intuitive but there are well established theories to compute single crystal physical properties as well as orientation patterns simulations can be compared with experimental data and then applied with some caution to the macroscopic earth this review is intended to provide a brief introduction highlighting some of the issues with

anisotropic approximations for mudrocks a seismic laboratory study an experimental technique for determining the in situ elastic properties of mudrocks with horizontal alignments in the microstructure is used to study the accuracy of a set of three nested scalar anisotropic approximations for transversely isotropic ti media each subsequent approximation adds one more velocity parameter and includes the previous as a special case these approximations are convenient and robust because of their close relationship to standard geophysical measurements there exists no good theory to predict the effects of an imposed stress on the elasticity of mudrocks in this study the tensor of elastic moduli of a single test specimen of mudrock subjected to an anisotropic stress field is determined from ultrasonic group velocity measurements involving pointlike transducers the mechanical characterization performed at constant pore pressure is accompanied by detailed microscopic observations and analysis the method was used to obtain accurate elastic constants for five well defi

preferred orientation of phyllosilicates comparison of fault gouge shale and schist abstract samples of fault gouge from the san andreas fault drill hole safod a shale from the north sea sedimentary basin and schists from metamorphic rocks in the alps have been analyzed with high energy synchrotron x rays to determine preferred orientation of mica and clay minerals the method relies on obtaining 2d diffraction images which are then processed with the crystallographic rietveld method implemented in the software maud allowing for deconvolution of phases and extraction of their orientation distributions it is possible to distinguish between detrital illite muscovite and authigenic illite smectite kaolinite and chlorite and muscovite and biotite with strongly overlapping peaks in the diffraction pattern the results demonstrate that phyllosilicates show large texture variations in various environments where different mechanisms produce the rock microfabrics fault gouge fabrics are quite weak and asymmetric with maxima for 001 in the range of 1 5 2 5 multiples of random distribution m r d this is attributed to heterogeneous deformation with randomization as well as dissolution precipitation reactions shale fabrics have maxima ranging from 3 to 9 m r d and this is due to sedimentation and compaction the strongest fabrics were observed in metamorphic schists 10 14 m r d and developed by deformation as well as recrystallization in a stress field in the analyzed samples fabrics of co existing quartz are weak all phyllosilicate textures can be explained by orientation of 001 platelets with no additional constraints on a axes

quantifying the three dimensional shapes of spheroidal objects in rocks imaged by tomography abstract the shapes of objects in rocks are sometimes measured through tomographic sections either physical sections or virtual x ray computed tomography approximation of these objects as ellipsoids is often sufficient in these analyses here we present an easily implemented algorithm to best fit an ellipsoid to a set of n points n 9 distributed on the surface of a spheroidal object observed in tomographic sections the method is demonstrated on x ray computed tomography data of 90 chondrules in a cr2 chondrite by averaging the ellipsoids for all the objects measured in a rock one can then readily describe its fabric by an average ellipsoid and if that average ellipsoid is interpreted as a strain ellipsoid and assuming all objects have undergone the same strain each object can be retro deformed and the inferred initial population of objects studied