topography at the core mantle boundary analysis of the earth s gravity field using ratio of gravity to geoid g n and cumulative degree contribution curve techniques improves resolution of the mass depth and dimensions of anomalous mass sources within the planet the source for four of the ten major geoid anomalies of the earth has large contributions from harmonic degrees 2 and 3 lie at the core mantle boundary and the greatest has a mass anomaly of 4 2 1022 grams that boundary has a density contrast 4 4 gm cm which is greater than at any other location including the contrast at the earth s surface with space thus relatively small vertical undulations of that boundary produce very large mass anomalies topographic relief of less than 3 km at the core mantle boundary occurs and accounts for the existence of the largest geoid anomalies occurring on the earth

a study of flow wetted surface area in a single fracture as a function of its hydraulic conductivity distribution the contact area between flowing water and rock the flow wetted surface fws is a main factor controlling the rock matrix diffusion and sorption of flowing solute in a rock fracture flow channeli

how late are k feldspar megacrysts in granites abstract various petrologists have suggested that k feldspar megacrysts grow in granites that are extensively crystallized even at subsolidus conditions however experimental evidence indicates that though k feldspar nucleates relatively late in the crystallization history abundant liquid is available for development of large crystals a great deal of evidence involving many different factors favours a magmatic phenocrystic origin for k feldspar megacrysts in granites namely simple twinning oscillatory zoning euhedral plagioclase inclusions and concentric crystallographically controlled arrangements of inclusions in addition abundant evidence has been presented of 1 mechanical accumulation of k feldspar megacrysts in granites 2 alignment of megacrysts and megacryst concentrations in magmatic flow foliations 3 involvement of megacrysts in zones of magma mixing in granite plutons and 4 occurrence of megacrysts in some volcanic rocks implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains

aspherical structure of the core mantle boundary from pkp travel times maps of aspherical structure in the vicinity of the core mantle boundary have been constructed from a tomographic analysis of p df and p ab travel times in the distance range 150 180 these maps reveal long wavelength features not previously detected by mantle tomography the peak to peak amplitude of these features is on the order of 1 s in vertical travel time too large to be explained by conventional thermal boundary layer models or dynamically supported topography on the core mantle boundary we hypothesize the existence of one or more chemical boundary layers whose large scale accumulations on the surface of the core may in some ways be analogous to continents at the earth s surface

coupling of the core dynamo and mantle thermal or topographic static features in the earth s magnetic field and fixed sources of secular variation suggest the dynamo is anchored to the lowermost mantle via either thermal or topographic coupling here we show a correspondence with dynamic core topography which is related to mantle temperature and suggest further effects due to topography associated with subducting slabs the two coupling mechanisms may occur on different time scales providing a potential means for discriminating between them

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

simple model representations of transport in a complex fracture and their effects on long term predictions 1 a complex fracture model for fluid flow and tracer transport that incorporates many of the important physical effects of a realistic fracture including advection through a heterogeneous fracture plane partitioning of flow into multiple subfractures in the third dimension and diffusion and sorption into fracture filling gouge small altered rock matrix blocks within the fracture zone and the unaltered semi infinite rock matrix on both sides of the fracture zone was previously developed it is common however to represent the complex fracture by much simpler models consisting of a single fracture with a uniform or heterogeneous transmissivity distribution over its plane and bounded on both sides by a homogeneous semi infinite matrix simple model properties are often inferred from the analysis of short term one to a few days site characterization sc tracer test data the question addressed in this paper is how reliable is the temporal upscaling of these simplified models are they adequate for long term calculations that cover thousands of years in this study a particle tracking approach is used to calculate tracer test breakthrough curves btcs in a complex fracture model incorporating all the features described above for both a short term sc tracer test and a 10 000 year calculation the results are considered the real world next two simple fracture models one uniform and the other heterogeneous are introduced properties for these simple models are taken either from laboratory data or found by calibration to the short term sc tracer test btcs obtained with the complex fracture model then the simple models are used to simulate tracer transport at the long term timescale results show that for the short term sc tracer test the btcs calculated using simple models with laboratory measured parameters differ significantly from the btcs obtained with the complex fracture model by adjusting model properties the simple models can be calibrated to reproduce the peak arrival time and height of the complex fracture model btcs but the overall match remains quite poor using simple models with short term sc calibrated parameters for long term calculations yields btcs with order of magnitude errors peak arrival time is 10 to 100 times too late and peak height is 50 to 300 times too small on the other hand using simple models with laboratory measured properties of unfractured rock samples for 10 000 year calculations yields btcs with peak arrivals and heights up to a factor of 50 too early and large respectively the actual magnitudes of the errors made by using the simple models depend on the parameter values assumed for the complex fracture model but in general simple models are not expected to provide reliable long term predictions the paper concludes with some suggestions on how to improve long term prediction calculations

deformation of internal boundaries in a viscoelastic earth and topographic coupling between the mantle and core summary in a two layer self gravitating viscoelastic maxwell earth is solved analytically and the behaviour of the internal interface which is non monotonic in time is shown to be due to the buoyancy effect across the interface deformation inside realistic earth models is calculated using the new normal mode method some modes with long relaxation times which do not contribute significantly to surface deformations are found to be significant for deformations inside the mantle flow patterns inside the mantle and the topograph at the core mantle boundary cmb due to surface glacial loads have been calculated glacial induced topography at the cmb unless suitably located is shown to be too small to significantly alter the total coupling mechanism and thus flow in the fluid core if there is any causal relationship between climatic changes and geomagnetic reversals then it is probably due to the transfer of rotational energy from the mantle to the core a revised estimate of 100 m drop in sea level is required to cause changes in the flow pattern in the core

tracer transport in a stochastic continuum model of fractured media a stochastic continuum model of a fractured medium conditioned on a specific set of field data is developed both the more conductive fractures and the less permeable matrix are generated within the framework of a single continuum stochastic model based on nonparametric indicator geostatistics in the stochastic model the fracture zones are distinguished from the matrix by imposing a long range correlation structure for a small fraction the highest approximately 11 of the hydraulic conductivity in the preferred planes of fracture zones results of flow arid transport simulation in three dimensions 3d are used to illustrate the large spatial variability of point measurements but for spatially integrated quantities the variability is reduced and results become less sensitive to correlation structure therefore it is suggested that spatially integrated quantities may be a more appropriate choice for predicting flow and transport in a strongly heterogeneous medium in that they are more commensurate with the level of our ignorance of the site the issue of spatial variability giving rise to uncertainty in the site characterization of a heterogeneous medium and the prediction of transport results is also addressed simulations are carried out for 3d transport from point tracer sources at hundreds of locations in the medium the breakthrough curve from each point source release is characterized by two parameters the mean transport velocity and the dispersion coefficient the results are presented as a statistical distribution of the transport parameters thus quantifying the uncertainty in predicting flow and transport based on a limited amount of site characterization data

orbital signature of interglacials a specific orbital configuration high obliquity combined with the june perihelion marked the beginning of the past three interglacials this suggests that the primary cause of the glacial cycle may be astronomical an astronomical climate index aclin is introduced which combines the three orbital variables in the time lag bivariant model designed to predict the major climate changes in the late and middle pleistocene and in the near future aclin closely correlates with the major climatic events revealed by independently dated proxy climate indicators of the past 130 000 yr it successfully differentiates the interglacials and displays a 100 000 yr periodicity it predicts an early end of the present inter glacial and the start of a new one in 114 000 yr

interpreting tracer breakthrough tailing from different forced gradient tracer experiment configurations in fractured bedrock 1 conceptual and mathematical models are presented that explain tracer breakthrough tailing in the absence of significant matrix diffusion model predictions are compared to field results from radially convergent weak dipole and push pull tracer experiments conducted in a saturated crystalline bedrock the models are based upon the assumption that flow is highly channelized that the mass of tracer in a channel is proportional to the cube of the mean channel aperture and the mean transport time in the channel is related to the square of the mean channel aperture these models predict the consistent 2 straight line power law slope observed in breakthrough from radially convergent and weak dipole tracer experiments and the variable straight line power law slope observed in push pull tracer experiments with varying injection volumes the power law breakthrough slope is predicted in the absence of matrix diffusion a comparison of tracer experiments in which the flow field was reversed to those in which it was not indicates that the apparent dispersion in the breakthrough curve is partially reversible we hypothesize that the observed breakthrough tailing is due to a combination of local hydrodynamic dispersion which always increases in the direction of fluid velocity and heterogeneous advection which is partially reversed when the flow field is reversed in spite of our attempt to account for heterogeneous advection using a multipath approach a much smaller estimate of hydrodynamic dispersivity was obtained from push pull experiments than from radially convergent or weak dipole experiments these results suggest that although we can explain breakthrough tailing as an advective phenomenon we cannot ignore the relationship between hydrodynamic dispersion and flow field geometry at this site the design of the tracer experiment can severely impact the estimation of hydrodynamic dispersion and matrix diffusion in highly heterogeneous geologic media

geomagnetic reversals from impacts on the earth the impact of a large extraterrestrial object on the earth can produce a geomagnetic reversal through the following mechanism dust from the impact crater and soot from fires trigger a climate change and the beginning of a little ice age the redistribution of water near the equator to ice at high latitudes alters the rotation rate of the crust and mantle of the earth if the sea level change is sufficiently large 10 meters and rapid in a few hundred years then the velocity shear in the liquid core disrupts the convective cells that drive the dynamo the new convective cells that subsequently form distort and tangle the previous field reducing the dipole component near to zero while increasing the energy in multipole components eventually a dipole is rebuilt by dynamo action and the event is seen either as a geomagnetic reversal or as an excursion sudden climate changes from other causes such as volcanic eruptions could also trigger reversals this mechanism may not be the sole cause of geomagnetic reversals but it can account for the rapid drop of the dipole component preceding a reversal the predominance of multipole components during a transition the associations of microtektites temperature drops and extinctions with reversals and the possible correlation between peaks in the geomagnetic reversal rate and the times of mass extinctions the model may also account for the long term changes in the average rate of reversals we make several testable predictions

the origin of k feldspar megacrysts hosted in alkaline potassic rocks from central italy a track for low pressure processes in mafic magmas abstract in situ sr isotope and microchemical studies were used to determine the provenance of k feldspar megacrysts hosted in mafic alkaline potassic ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central italy at monte cimino volcanic complex mafic leucite free ultrapotassic megacryst bearing rocks of olivine latitic composition are associated with evolved latite and trachyte here latites and trachytes straddle the sub alkaline field age corrected 87sr 86sr values sri of the analysed cimino olivine latites vary from 0 71330 and 0 71578 and strongly increase at constant mg value latite and trachyte have lower sri than olivine latites ranging between 0 71331 and 0 71361 sri of k feldspar megacrysts from olivine latites are between 0 71352 and 0 71397 but core and rim 87sr 86sr ratios within individual megacryst are indistinguishable in all the mafic rocks the megacrysts are not in isotopic equilibrium with the hosts k feldspar megacrysts from both the latite and trachyte have similar sr isotope compositions sri 0 71357 0 71401 to those in the olivine latites however sri of megacryst in the trachyte vary significantly from core to rim sri from 0 71401 to 0 71383 as with the olivine latites the k feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte at vico volcano megacryst bearing rocks are mafic leucite free potassic rocks mafic leucite bearing ultrapotassic rocks and old trachytic rocks the mafic leucite bearing and leucite free rocks are a tephri phonolite and an olivine latite respectively a megacryst in vico trachyte is isotopically homogeneous sri core 0 71129 rim 0 71128 and in equilibrium with the host rock sri bulk rock 0 71125 sri of megacryst from tephri phonolite is clearly not in isotopic equilibrium with its host sri bulk rock 0 71158 and it increases from core sri 0 71063 to rim sri 0 71077 a megacryst in vico olivine latite is isotopically homogeneous sri core 0 71066 rim 0 71065 but not in equilibrium with the host rock sri bulk rock 0 71013 the sr isotope microdrilling technique reveals that cimino megacrysts were crystallised in a cimino trachytic magma and were subsequently incorporated by mixing mingling processes in the latitic and olivine latitic melts a model invoking the presence of a mafic sub alkaline magma which was mixed with the olivine latite is proposed to justify the lack of simple geochemical mixing relation between cimino trachytes and olivine latites this magmatological model is able to explain the geochemical characteristics of cimino olivine latites otherwise ascribed to mantle heterogeneity the similarity of core sri of megacrysts hosted in vico tephri phonolite and olivine latite suggests that the k feldspar megacrysts are co genetic isotopic equilibrium between megacryst and vico host trachyte indicates that the trachyte is the parent of this megacryst on the contrary the megacrysts hosted in tephri phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim sr isotope increase of the xenocryst hosted in the tephri phonolite the megacrysts hosted in the vico mafic rocks might derive from a trachytic melt similar in composition to the old vico trachytes

effective matrix diffusion in kilometer scale transport in fractured crystalline rock concentrations of tritium 3h and dichlorodifluoromethane cfc 12 in water samples taken from glacial drift and fractured crystalline rock over 4 km2 in central new hampshire are interpreted to identify a conceptual model of matrix diffusion and the magnitude of the diffusion coefficient dispersion and mass transfer to and from fractures has affected the 3h concentration to the extent that the peak 3h concentration of the 1960s is no longer distinguishable because of heterogeneity in the bedrock the sparsely distributed chemical data do not warrant a three dimensional transport model instead a one dimensional model of cfc 12 and 3h migration along flow lines in the glacial drift and bedrock is used to place bounds on the processes affecting kilometer scale transport arid model parameters are varied to reproduce the measured relation between 3h and cfc 12 rather than their spatial distributions a model of mass exchange to and from fractures that is dependent on the time varying concentration gradient at fracture surfaces qualitatively reproduces the measured relation between 3h and cfc 12 with an upper bound for the fracture dispersivity approximately equal to 250 m and a lower bound for the effective matrix diffusion coefficient equal to 1 m2 yr 1 the diffusion coefficient at the kilometer scale is at least 3 orders of magnitude greater than laboratory estimates of diffusion in crystalline rock the large diffusion coefficient indicates that diffusion into an immobile fluid phase rock matrix is masked at the kilometer scale by advective mass exchange between fractures with large contrasts in trarismissivity the measured transmissivity of fractures in the study area varies over more than 6 orders of magnitude advective mass exchange from high permeability fractures to low permeability fractures results in short migration distances of a chemical constituent in low permeability fractures over an extended period of time before reentering high permeability fractures viewed at the kilometer scale this process is analogous to the chemical constituent diffusing into and out of an immobile fluid phase

pb isotopic zoning of k feldspar megacrysts determined by laser ablation multi collector icp ms insights into granite petrogenesis this study investigates pb isotopic zoning in magmatic k feldspar megacrysts from the monte capanne pluton elba italy using laser ablation multi collector icpms the studied crystals provide an ideal opportunity to use in situ techniques to assess the extent of open system processes and better characterize the components involved in the genesis of complex magma systems earlier investigations of the pluton identified the importance of magma mixing between mantle and crustal derived magmas the investigated k feldspar megacrysts exhibit strong zoning in 207pb 206pb and 208pb 206pb correlated with lead elemental variations we interpret these variations as reflecting growth zoning as opposed to secondary diffusive exchange despite a great variety of zoning patterns we were able to correlate different events of megacryst growth reflecting crystallization in a dynamic magma system our two step model includes 1 growth of a granitic magma chamber by addition of low 208pb 206pb magma to a high 208pb 206pb magma contaminated with crustal material i e the megacryst cores and 2 recharge by mantle derived magma i e the megacryst rims we interpret the thorogenic nature of the megacryst rims to reflect the mantle derived component involved in the mixing process taking account of other data from the tuscan magmatic province the mantle source is inferred to have been metasomatized by continental material during subduction tims sr isotopic data from microdrilled cores in one megacryst provides general support for the model but show that the two isotopic systems are decoupled

a new approach to account for fracture aperture variability when modeling solute transport in fracture networks a simple yet effective method is presented to include the effects of fracture aperture variability into the modeling of solute transport in fracture networks with matrix diffusion and linear sorpti

shelf to basin transition in the cambrian lower ordovician of sardinia italy reply in southern and central sardinia two different cambrian lower ordovician sedimentary belts occur the former is exposed in southwestern sardinia iglesiente and sulcis and is characterized by shallow marine siliciclastic and carbonate sediments settled on a continental shelf with lowangle morphology the latter exposed in the nappe zone central and southeastern sardinia consists of a thick monotonous sequence of siliciclastic deposits settled in a deeper water basin

hydraulic characterization and upscaling of fracture networks based on multiple scale well test data hydraulic properties and upscaling characteristics of low permeability fractured rock are analyzed based on systematic well test data from three different measurement scales first tests are simulated in a large number of geological fracture network realizations and the acceptable fracture transmissivity distribution parameters that produce the observed statistics of the two smallest measurement scales i e 2 m and 10 m scales are defined instead of a single value a range of acceptable parameter values can be found to produce the observed result second upscaling simulations are carried out with the calibrated networks these indicate that the investigated system cannot be properly modeled by means of a continuum tensor presentation but would better be represented by means of equivalent fracture statistics third the conductive characteristics of the calibrated 30 m network blocks are compared to well test results from the same scale the results from this preliminary analysis indicate that one dimensional borehole observations interpreted with standard continuum based methods may considerably underestimate the three dimensional conductive characteristics of heterogeneous noncontinuum fractured media

multiple early paleozoic volcanic events at the northern gondwana margin u pb age evidence from the southern variscan branch sardinia italy abstract in sardinia one of the southernmost remains of the european variscan belt a crustal section through different gondwanan paleodomains is largely preserved laser ablation icp ms u pb ages on undoubtedly igneous sites of the zircons were determined on the lower palaeozoic volcanic rocks constrained by defined field relationships thus evidencing three subsequent volcanic events i intermediate and felsic 491 7 3 5 ma 479 9 2 1 concordia ages transitional volcanic rocks embedded within a cambro ordovician terrigenous succession that occurs with continuity in external and inner nappes bounded to the top by the sardic unconformity ii this cambrian lower ordovician succession is cut by calc alkalic rhyodacites which yielded a concordia age of 465 4 1 4 ma confirming their pertinence to the huge bimodal mid ordovician arc volcanism commonly interpreted as the widespread marker of the rheic ocean subduction iii alkalic metaepiclastites in the external nappe within the post caradocian transgressive sequence dated at 440 1 7 ma likely related to rifting and collapse of the mid ordovician volcanic arc in the reshaped lower palaeozoic stratigraphy of sardinia the timing of the early steps of the variscan wilson cycle can be inferred

industrial mineral occurrences associated with cenozoic volcanic rocks of sardinia italy geological mineralogical geochemical features and genetic implications the most important industrial mineral im deposits associated with the cenozoic volcanics of sardinia include kaolin bentonite and zeolites though of less significance perlite and potassium feldspar are also important in local and national markets bentonite and to a lesser extent kaolin and perlite form economically viable deposits and zeolites appear as very important industrial mineral commodities for future economic development the market situation for potassium feldspar is still under evaluation for use in ceramics all these deposit types occur as alteration products of cenozoic volcanic rocks which were emplaced during three main volcanic cycles in the eocene ec 55 to 51 ma oligocene miocene omc 32 to 13 ma and pliocene pleistocene ppc 5 to 0 1 ma kaolin bentonite zeolites and potassium feldspar occur as alteration products of the omc volcanites perlite occurs as an alteration product of the ppc volcanites all deposits have generally derived from the alteration of the most acidic members of the cenozoic volcanic rocks rhyolites to rhyodacites but differences among the associated ore forming phenomena are recognized hydrothermal sensu stricto deuteric alteration and weathering are the most important processes involved in ore formation weathering although of minor importance can also contribute to enhance the alteration of the deposits formed by hydrothermal and deuteric processes the extent and type of occurrences are mainly controlled by the local geological and structural features and the environmental geochemical conditions kaolin occurs in three main districts at romana and tresnuraghes it is hosted within ignimbritic sequences while at serrenti furtei it is found in pyroclastic flows and ash flow tuffs kaolin formed by hydrothermal processes occurs in high sulfidation romana and serrenti furtei and low sulfidation tresnuraghes type epithermal systems the alteration is proximal to the feeder conduits and structural setting controls kaolin formation bentonite is widespread throughout sardinia deposits occur as stratiform mineral bodies in situ altered within poor welded pumice rich and ash rich layers and also as distal fall out deposits as lenticular bodies interlayered within the miocene sedimentary sequences the former originated by deuteric alteration and formation is mainly controlled by lithology whereas the second type originated by weathering which altered the volcanic ash lenses deposited in lacustrine and or fluvial deltaic environments

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

an unusual occurrence of an exploitable k feldspar deposit hosted in the ordovician porphyroids southern sardinia geology mineralogy geochemical features and economic potential abstract an atypical potassium feldspar deposit of real economic potential has been found at arcu de su bentu southern sardinia italy the massive mineralization occurs in the middle ordovician porphyroids metavolcanic complex which consists of dominant metarhyolite and minor metarhyodacite lavas and or ignimbritic flows erupted in a sub aerial environment during variscan orogenesis the mineralized area was affected by low grade anchizone to greenschist facies metamorphism the deposit generally shows uniform macroscopic textural features over the entire outcrop the significant presence of k feldspar sanidine and quartz megacrystals the latter being generally smaller than the former mafic minerals do not occur in significant proportions although minor amounts of biotite and muscovite occur locally besides the uncommon lithological type the typical feature of this deposit is the unusual coarseness 10 to 20 cm in diameter of the potassium feldspar crystals the favourable geomorphological conditions of the area high k 2 o contents 6 to 8 wt high proportion of k feldspar in the mineralized rock 35 to 51 vol and large reserves estimated at 4 368 000 t in just one restricted part of the deposit are all favourable conditions for future economic exploitation in spite of this mineralogical and chemical impurities may adversely affect the possible use of k feldspar from arcu de su bentu in some conventional applications e g manufacture of high quality products such as ceramics to assess the real future economic development of the deposit market specific beneficiation is required although it is important to note that the bulk raw materials even if they have a lower market value could be still be targeted to specific industrial sectors e g red gres

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

a novel three dimensional discrete fracture network model for investigating the role of aperture heterogeneity on fluid flow through fractured rock masses abstract effect of anisotropic aperture on the hydraulic properties of single rock fractures has been systematically investigated yet the aperture variability of individual fractures in 3d discrete fracture networks dfns is commonly negligible by using parallel plate fractures the present study proposed a 3d dfn model with fractures having heterogeneous apertures to estimate the influence of fracture variability on fluid flow in total a set of 1280 3d models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code the influences of aperture heterogeneity and network topology on the flow pattern and permeability of 3d dfns are estimated the results show that the network topology provides a first order frame of geometrical connectivity and the heterogeneous aperture further allows the flow to select some most transmissive channels within these connected fractures the dfn model with identical apertures generates a large number of medium flow rate regions whereas the dfn model with fractures having heterogeneous apertures results in extremely low and high flow rate regions the permeability ratio of the two models is widely spread in terms of a small variation in the average mechanical aperture as a result of strong dependence on the aperture distribution the average permeability ratio increases significantly first and then approaches to 1 0 with increasing the average mechanical aperture this allows for the definition of a critical mechanical aperture above which the permeability can be properly predicted using the dfn model with fractures having identical apertures and below which the permeability is much altered by the aperture variability and the dfn model with fractures having heterogeneous apertures should be employed