on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 2 applicability of a u leach model to mineral separates abstract preliminary u series data are presented on the disequilibria of mineral separates of surface samples from the eye dashwa lakes granite canada most analyses of the ferromagnesian quartz plus feldspar and zircon plus sphene grains show that leaching of u has taken place such that 234 u 239 u 1 and 230 th 234 u 1 the simple leach model presented in a companion paper was used to explain these characteristic ratios it is suggested that the leach model may be used on zircon and sphere grains to estimate u leach rates and this is relevant to the suggestion of using sphene like hosts as the primary barrier in the safe disposal of nuclear waste a full analysis of u mobility within a given rock volume was not possible due to our limited data base and to our inability to monitor labile u directly

new views of lunar geoscience an introduction and overview beyond the earth the moon is the only planetary body for which we have samples from known locations the analysis of these samples gives us ground truth for numerous remote sensing studies of the physical and chemical properties of the moon and they are invaluable for our fundamental understanding of lunar origin and evolution prior to the return of the apollo 11 samples the moon was thought by many to be a primitive undifferentiated body e g urey 1966 a concept shattered by the data returned from the apollo and luna missions ever since new data have helped to address some of our questions but of course they also produced new questions in this chapter we provide a summary of knowledge about lunar geologic processes and we describe major scientific advancements of the last decade that are mainly related to the most recent lunar missions such as galileo clementine and lunar prospector 1 1 the moon in the planetary context compared to terrestrial planets the moon is unique in terms of its bulk density its size and its origin fig 1 1a c all of which have profound effects on its thermal evolution and the formation of a secondary crust fig 1 1d numerous planetary scientists considered the moon as an endmember among the planetary bodies in our solar system because its lithosphere has been relatively cool rigid and intact throughout most of geological time a one plate planet and its surface has not been affected by plate recycling an atmosphere water or life therefore the moon recorded and preserved evidence for geologic processes that were active over the last 4 4 5 b y and offers us the unique opportunity to look back into geologic times for which evidence on earth has long been erased fig 1 1c d impact cratering an exterior process is considered the most important surface process on the moon internal

distribution of uranium thorium and rare earth elements in the eye dashwa lakes pluton a study of some analogue elements abstract the distribution of u th and rare earth elements ree s in the eye dashwa lakes pluton near atikokan ontario is examined materials analysed include a unaltered granite b altered granite c highly altered granite adjacent to open fractures and d fracture filling minerals distinct distribution patterns are noted for u and some ree s among the four types of samples th shows higher concentrations in materials c and d compared with unaltered and altered granite the highly altered granite and some fracture fillings have greater concentrations of u th and ree s the large concentrations of u th and ree s in these materials are due to both sorption on selective materials and precipitation as mineral phases containing these elements the occurrence of uraninite bastnaesite and thorogummite coatings on fracture fillings are examples of this precipitation

review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

applications of uthpb isotope systematics to the problems of radioactive waste disposal abstract concentrations of u th and pb and the isotopic composition of pb for whole rock samples of granitoids show 1 that open system behavior is nearly universal in the surface and near surface environment and 2 that elemental mobility is possible to depths of several hundred meters several identified or at least postulated factors that control u and or pb mobility include 1 the mineralogical sites for u and its daughter products 2 access of groundwater to these sites 3 the volume of circulating water and 4 the chemistry of the groundwater studies of granitic samples from peralkaline complexes in the arabian shield have shown that most samples lost less than 20 of their u during recent exposure to the near surface environment most of the u in these samples appears to be firmly bound in zircons in contrast most surface and shallow drill core samples of the granite of lankin dome granite mountains wyoming have lost 70 of their u most of the u in these samples is weakly bound in biotite and epidote family minerals the granite recovered during the illinois deep drill hole project stephenson county illinois is mineralogically similar to the granite of lankin dome but this granite lost radiogenic pb rather than u probably as a result of exposure to groundwater that had a markedly different chemistry from that in the granite mountains studies of the sherman granite wyoming and the gotemar granite southeastern sweden have shown that u and or pb mobility is greatest in and near fractured rock the greater mobility is interpreted to be the result of both a larger water rock ratio in the fractured rock and exposure to water over an increased surface area and consequently a greater number of uranium sites several types of geochemical and mineralogic data can be used to identify rock water interaction in granites however if rock samples have favorable radiogenic to common pb ratios both the amount and approximate timing of u or pb mobility can be obtained through the use of isotopic studies such information can be extremely important in the search for favorable hosts for containment of radioactive waste rocks such as the gotemar granite have undergone considerable rock water interaction most of which occurred 400 myr ago and little in recent times thus a search for zones that have experienced only a little interaction with water may provide a misleading prediction as to the ability of such zones to shield radioactive wastes from the modern biosphere from an isotopic point of view an ideal candidate for evaluation as a host rock for radioactive wastes would have the following characteristics 1 a high ratio 2 of radiogenic to common pb in order to optimize precision of the results 2 a simple two stage geologic history so that results could be interpreted without multiple working hypotheses and 3 an originally high percentage 50 of labile u so that the results would be highly sensitive to even small amount of rock water interaction these characteristics should produce rocks with marked radioactive disequilibrium in surface samples the disequilibrium should grade to radioactive equilibrium with increasing depth until zones in which water has not circulated are found extensive regions of such zones must exist because u th pb systematics of most analyzed granitoids demonstrate closed system behavior for almost all of their history except for their recent history in the near surface environment

migration of radionuclides in fissured rock the influence of micropore diffusion and longitudinal dispersion the migration of radionuclides in the fissures in the bedrock surrounding a repository is discussed a one dimensional transport model is presented it includes diffusion of the nuclides into the microfissures of the rock and linear sorption and longitudinal dispersion in the bedrock an analytical solution to the model is given in terms of an infinite integral the integrand is a sometimes highly oscillatory function of the system parameters a special integration method is developed to evaluate the infinite integral the method utilizes the oscillatory behavior of the integrand the assessment of input parameters is discussed in some detail dimensionless breakthrough curves are given for the approximate range of variation of the input parameters calculations are made for a repository of spent fuel surrounded by fissured but fairly good rock kp 10 9 m s and fissure spacing s 50 m longitudinal dispersion may significantly affect the amount of radioactive material reaching the biosphere radionuclides which would decay completely without longitudinal dispersion may arrive in nonnegligible concentrations dispersion effects of the magnitude considered in this study can significantly diminish the retardation effects of matrix diffusion

a new scheme for the very deep geological disposal of high level radioactive waste a case is presented for reconsidering deep borehole disposal for high level radioactive waste hlw in the light of recent discoveries about the hydrogeology and hydrogeochemistry of the continental crust a new multi barrier concept is proposed for very deep elevated temperature disposal of vitrified hlw spent fuel and ex military and other fissile materials which involves melting and recrystallization of a granitic host rock utilizing the heat from the waste this scheme is fundamentally different from previously proposed borehole disposal scenarios in its key aspects particularly in utilizing only partial melting and a surviving container the perceived advantages of the scheme are discussed in general and in relation to previous deep disposal ideas particularly from the standpoint of safety it is concluded that the scheme offers a potentially safer and environmentally more acceptable option for the permanent disposal of high level waste

235u fission tracks and238u series disequilibria as a means to study recent mobilization of uranium in archaean pyritic conglomerates uranium transport in archaean sediments was investigated by means of two carefully selected suites of variably weathered sediment samples from different localities of the pongola supergroup kaapvaal craton south africa u remobilization on a micron to meter scale was analyzed using u fission track micromapping and spectrometry bulk measurements these studies were supported by ore microscopy neutron activation analysis and spectrometry by combining particle track technique and spectrometry detailed information is obtained on the u transport history of weathered surface samples a simple model of u redistribution processes in geologic systems based on238u series disequilibria is developed and applied to the samples investigated some implications for radiometric field methods are discussed

the chemical and isotopic record of rock water interaction in the sherman granite wyoming and colorado chemical isotopic radiographic and rock leaching data are combined to describe the effects of rock water interactions in core samples of petrographically fresh 1 43 b y old sherman granite the data serve to identify sensitive indicators of incipient alteration and to estimate the degree pathways and timing of element mobilization unfractured core samples of sherman granite are remarkably fresh by most chemical or isotopic criteria but incipient alteration is indicated by the abundance and distribution of uranium and the degree of radioactive equilibration of uranium with its decay products uranium abundances which are out of equilibrium with lead decay products indicate remobilization of a portion 3 to 60 percent of original uranium in late phanerozoic time association of uranium with minor but pervasive secondary alteration products also indicates some remobilization the amount of apparent uranium mobility in unfractured sherman granite 3 to 60 percent is small compared to the results of similar studies of archean granites from nearby localities chemical and isotopic data evaluated as a function of core sample depth suggest a uranium migrational pathway involving near surface leaching and reconcentration at depth movement of solutions through the upper 200 ft 60 m of sherman granite is fracture controlled and brecciated granite shows more obvious petrographic chemical and isotopic evidence of alteration and multi element redistribution laboratory experiments using freshly crushed sherman granite confirm that uranium is leached in preference to elements such as si mg ca and k and that leachable uranium is situated close to the solid liquid interface perhaps as uranium along grain boundaries in crystal defects or on cleavage traces of minerals that exclude uranium from their structure

electrical conductivity and temperature in the canadian cordilleran crust abstract high electrical conductivity and high heat flow coexist in much of the canadian cordillera a region of recent accretion of crustal terranes to north america the relationship between temperature and electrical conductivity in the crust is investigated by means of results from 251 heat flow determinations and 301 magnetotelluric mt soundings we first compared maps of mt phase at period 10 s and of heat flow larger phases correlate with higher heat flows in some areas but the relationship is complicated by other causes of variation in these two parameters to give a more focussed comparison we map the depth d 450 to the 450 c isotherm for two assumed distributions of reduced heat flow and the depth d c to the top of the lower crustal conductor at mt sites away from major fracture zones the map of d c visually resembles both of the maps of d 450 and readings at 76 points of a grid give correlation coefficient 0 80 this supports a relationship between high conductivity in the crust and temperatures above 450 c both the lower crustal conductor and the 450 c isotherm occur at depths near 30 km above the subducting oceanic plate under vancouver island at 15 20 km in the intermontane belt and of 10 15 km in the omineca belt if there is an upcurrent in the mantle beneath the continent behind the subduction as proposed elsewhere its axis may now be under the omineca belt this location is in harmony with evidence of recent extension and uplift there

lunar floor fractured craters as magmatic intrusions geometry modes of emplacement associated tectonic and volcanic features and implications for gravity anomalies lunar floor fractured craters are a class of 170 lunar craters with anomalously shallow fractured floors two end member processes have been proposed for the floor formation viscous relaxation and subcrater magmatic intrusion and sill formation recent morphometric analysis with new lunar reconnaissance orbiter laser altimeter lola and image lroc data supports an origin related to shallow magmatic intrusion and uplift we find that the distribution and characteristics of the ffc population correlates strongly with crustal thickness and the predicted frequency distribution of overpressurization values of magmatic dikes for a typical nearside lunar crustal thickness dikes with high overpressurization values favor surface effusive eruptions medium values favor intrusion and sill formation and low values favor formation of solidified dikes concentrated lower in the crust we develop a model for this process make predictions for the morphologic morphometric volcanic and geophysical consequences of the process and then compare these predictions with the population of observed floor fractured craters in our model the process of magmatic intrusion and sill formation begins when a dike propagates vertically towards the surface as the dike encounters the underdense brecciated region beneath the crater the magmatic driving pressure is insufficient to continue vertical propagation but pressure in the stalled dike exceeds the local lithostatic pressure the dike then begins to propagate laterally forming a sill which does not propagate past the crater floor region because increased overburden pressure from the crater wall and rim crest pinch off the dike at this boundary the sill then continues to inflate further raising and fracturing the brittle crater floor when the intrusion diameter to intrusion depth ratio is smaller than a critical value the intrusion assumes a laccolith shape with a domed central region when the ratio exceeds a critical value the intrusion concentrates bending primarily at the periphery resulting in a flat tabular intrusion we predict that this process will result in concentric fractures over the region of greatest bending this location is close to the crater wall in large flat floored craters as observed in the crater humboldt and interior to the crater over the domed floor in smaller craters as observed in the crater vitello a variety of volcanic features are predicted to be associated with the solidification and degassing of the intrusion these include 1 surface lava flows associated with concentric fractures e g in the crater humboldt 2 vents with no associated pyroclastic material from the deflation of under pressurized magmatic foam e g the crater damoiseau and 3 vents with associated pyroclastic deposits from vulcanian eruptions of highly pressurized magmatic foam e g the crater alphonsus the intrusion of basaltic magma beneath the crater is predicted to contribute a positive component to the bouguer gravity anomaly we assess the predicted bouguer anomalies associated with ffcs and outline a process for their future interpretation we conclude that our proposed mechanism serves as a viable formation process for ffcs and accurately predicts numerous morphologic morphometric and geophysical features associated with ffcs these predictions can be further tested using grail gravity recovery and interior laboratory data

the formation of floor fractured craters in xanthe terra floor fractured craters ffc are a peculiar form of degradation of impact craters defined by the presence of crevice networks and mesas affecting crater floors they are preferentially distributed near chaotic terrains and outflow channels the scope of this paper is to present a detailed systematic analysis of ffc at xanthe terra ffc morphologies in this region are classified into five types making a picture of different stages of the same degradation process ffc are geographically intermixed with un fractured normal craters non ffc young craters are less prone to show this type of degradation as suggested by fresh ejecta layer with preserved crater floor size distributions of ffc and non ffc indicate that larger craters are preferentially fractured careful examinations of the crater floor elevations reveal that the crevices often extend deeper than the original crater cavity furthermore an onset depth for the formation of ffc is evidenced from the difference of spatial distributions between ffc and non ffc roof collapsed depressions observed in the same region have been also documented and their characteristics suggest the removal of subsurface material at depth from about 1200 to 4000 m these observations taken together suggest a subsurface zone of volume deficit at depth from 1 to 2 km down to several kilometers responsible for ffc formation then a scenario of ffc formations is presented in the context of groundwater discharge events at the late hesperian this scenario involves two key processes earth fissuring and piping erosion known to occur with rapid groundwater migrations on earth

shear wave velocity structure in the northern basin and range province from the combined analysis of receiver functions and surface waves a new method based on the joint inversion of receiver functions and surface wave phase velocities results in well determined shear velocity structures that are consistent with the compressional wave structure gravity heat flow and elevation data in the northern basin and range this new inversion method takes advantage of average velocity information present in the surface wave method and differential velocity information contained in the receiver function method thus min imizing the nonuniqueness problem that results from the velocity depth trade off an unusually thick 38 kin and relatively faster crust and upper mantle are found in central and eastern nevada compared to the thin 28 to 34 km and slower crust and upper mantle of the western basin and range we interpret the regions of thicker and faster crust and upper mantle as zones that have undergone less cenozoic ex tension relative to the surrounding regions to the west and north the thick crust and consequently greater depth to the dense mantle material is consistent with the gravity low pattern in central and eastern nevada simple gravity modeling shows both local and regional isostatic compensation occur within 40 km of the surface indicating a near classical airy type of compensation in the province we analyze in detail the shear wave s wave velocity model derived from the receiver functions at station bmn and compressional wave p wave velocity models derived from the 1986 passcal experiment in northwestern nevada the most interesting feature of these models is the presence of negative velocity gradients in the s wave model with no corresponding velocity decrease in the p wave models between depths of 10 and 24 km this combined velocity model may be explained by high pore fluid pressures at these depths this model favors a layered fluid porosity model proposed in the literature to explain extensive middle to lower crust conti nental seismic reflections and high electrical conductivity an upper mantle grada tional low velocity zone is present between 32 and 38 km in the s wave model this upper mantle shear wave low velocity zone is consistent with partial melt which may be the source material for magmatic underplating in this region

a study of rock alteration in the eye dashwa lakes pluton atikokan northwestern ontario canada abstract as a part of the research pertaining to evaluation of the suitability of crystalline rocks for the disposal of nuclear fuel waste a study of core samples from five boreholes in the eye dashwa lakes pluton reveals several types and degrees of alteration the different degrees of alteration are related to the intensity of pink coloration and the amounts of plagioclase and ferromagnesian minerals that are affected the alteration process has reconstituted plagioclase to pure albite in highly altered rocks whereas in unaltered and slightly altered rocks it occurs as oligoclase the alteration products chlorite and sericite are relatively fe rich in the highly altered rocks unaltered to slightly altered moderately altered and highly altered samples each occupy a distinct field in a cao mgo feo variation diagram a close association exists between alteration and fractures a model relating fractures alteration and fracture infillings is proposed distinct differences in chemical and some physical properties between altered and unaltered rocks indicate that significant changes have occurred the distinct physical and chemical characteristics of the alteration and its close association with faults and fractures suggest the need to consider alteration as an important parameter in evaluating crystalline rocks for nuclear fuel waste disposal

ages and stratigraphy of lunar mare basalts in mare frigoris and other nearside maria based on crater size frequency distribution measurements 1 we report on ages derived from impact crater counts for exposed mare basalt units in the northern part of the lunar nearside hemisphere mare frigoris the eastern and northeastern part of the nearside hemisphere lacus temporis joliot hubble goddard mare marginis and mare smythii the central part of the nearside hemisphere palus putredinis mare vaporum and sinus medii and the southwestern part of the nearside hemisphere grimaldi cruger rocca a lacus aestatis and schickard in mare frigoris we dated 37 basalt units showing ages from 2 61 to 3 77 gyr with most units being formed in the late imbrian period between 3 4 and 3 8 gyr ago in mare vaporum we dated six spectrally homogeneous units that show model ages of 3 10 to 3 61 gyr our model ages of basalts in mare marginis range from 3 38 to 3 88 gyr and are mostly older than basalts in mare smythii 3 14 3 48 gyr the model ages of four units in sinus medii indicate that the basalts in this region formed 3 63 to 3 79 gyr ago we find an excellent agreement of our crater size frequency model ages of the palus putredinis area which contains the apollo 15 landing site with the radiometric ages of apollo 15 samples according to our crater counts basalts in palus putredinis are 3 34 gyr old and this compares favorably with the radiometric ages of 3 30 3 35 gyr of the olivine normative and quartz normative basalts of the apollo 15 landing site lacus aestatis is a small irregular shaped mare patch in the southwestern nearside and shows an imbrian age of 3 50 gyr basalts in lacus temporis in the northeastern nearside formed between 3 62 and 3 74 gyr ago and are therefore older than the basalts in lacus aestatis we found that basalts in craters of the southwestern nearside schickard grimaldi cruger and rocca a are also mostly younger than basalts in craters of the northeastern nearside hubble joliot and goddard while basalt ages vary between 3 16 and 3 75 gyr in the southwest basalts in the northeast are 3 60 3 79 gyr old these results confirm and extend the general distribution of ages of mare basalt volcanism and further underline the predominance of older mare basalt ages in the eastern and southern nearside and in patches of mare peripheral to the larger maria in contrast to the younger basalt ages on the western nearside oceanus procellarum

the steepest slopes on the moon from lunar orbiter laser altimeter lola data spatial distribution and correlation with geologic features abstract we calculated topographic gradients over the surface of the moon at a 25 m baseline using data obtained by the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter lro spacecraft the relative spatial distribution of steep slopes can be reliably obtained although some technical characteristics of the lola dataset preclude statistical studies of slope orientation the derived slope frequency distribution revealed a steep rollover for slopes close to the angle of repose slopes significantly steeper than the angle of repose are almost absent on the moon due to 1 the general absence of cohesion strength of the fractured and fragmented megaregolith of the lunar highlands and 2 the absence of geological processes producing steep slopes in the recent geological past the majority of slopes steeper than 32 35 are associated with relatively young large impact craters we demonstrate that these impact craters progressively lose their steepest slopes we also found that features of early imbrian and older ages have almost no slopes steeper than 35 we interpret this to be due to removal of all steep slopes by the latest basin forming impact orientale probably by global seismic shaking the global spatial distribution of the steepest slopes correlates moderately well with the predicted spatial distribution of impact rate however a significant paucity of steep slopes in the southern farside remains unexplained

evidence for intrusive activity on mercury from the first messenger flyby images from messenger s first flyby of mercury have shown convincing evidence for surface volcanism here we report on evidence in the new data for several features that are characterized by fractures and graben rare features on a planet dominated by contractional deformation that may be linked to intrusive activity these features include 1 a floor fractured crater interpreted to have been the site of laccolith like sill intrusions the feature is similar to some floor fractured craters on the moon and shows evidence for individual fractured dome like uplifts on the floor 2 a concentric complex of graben observed inside the peak ring on the floor of the 250 km diameter raditladi basin and associated with dark plains and possibly embayed by them the feature may represent an unusual type of floor fracturing associated with deeper intrusions and related ring dikes or cone sheets or the graben may instead be the product of non magmatic uplift of the basin floor 3 a large radial graben swarm pantheon fossae located near the center of the caloris basin thus far unique on mercury and characterized by hundreds of individual graben segments ranging from 5 km to 110 km in length in the nexus graben crosscut one another and produce a local polygonal pattern others curve away from the center as the nexus is approached two scales of graben length are observed the radius of the dense radially symmetric plexus of graben is 175 km and a few graben extend to greater radial distances to the north and southwest out to distances that intersect with a ring of generally concentric graben around the outer basin floor two width scales of graben are observed a large graben about 8 km wide emerges from the nexus and extends for 100 km most graben are less than half this width some graben walls appear cuspate with convex outward wall segments that resemble crater chain segments one crater chain with distinctive raised rims parallels nearby graben locally some graben appear in en echelon patterns and smaller graben sometimes show cross cutting superposition relationships abundant impact craters the most prominent being apollodorus and secondary crater clusters and chains are superposed on the graben system there is little evidence that craters greater than 5 km in diameter have been cut by a graben this relation implies that the graben swarm formed soon after the emplacement of the caloris floor plains these graben are interpreted to be the surface expression of a radial dike swarm emanating from a subsurface magma reservoir similar features in which the dikes contribute to a near surface stress field that favors radial graben are known on the earth venus and mars the location of pantheon fossae in the center of the caloris basin suggests that formation of the radial graben structure is linked to basin evolution

albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository hydrothermal alteration resulting in albitization and quartz dissolution has been identified in paleoproterozoic metagranites down to 1000 m elevation at forsmark sweden the alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository in general albitization occurs extensively but it is also observed locally adjacent to minor intrusive bodies of amphibolite the altered rocks show a marked decrease in k feldspar and an increase in quartz relative to the unaltered equivalents resulting in an epitonalitic composition plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks it is inferred that albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1 87 1 86 ga the mineralogy of the epitonalites gives rise to an increased thermal conductivity and thereby a positive influence for the design and safety of a deep geological repository for spent nuclear fuel however the increased frequency of low conductive amphibolite in the albitized volumes consistent with the proposed mechanism for alteration gives a negative influence in sharp contrast to the albitization a majority of the occurrences of quartz dissolution which resulted in the formation of episyenite are located along fracture zones quartz dissolution took place between or after 1 8 1 7 ga when the bedrock was able to respond to deformation in a brittle manner most of the vugs left after the removal of quartz are to a variable extent refilled by hydrothermal assemblages including quartz albite k feldspar hematite chlorite and calcite the geometry and spatial distribution of episyenite argue against an extreme fluid rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 degrees c the dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe like volumes the close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and thereby reduce the negative mechanical and hydrogeological aspects for a deep geological repository c 2012 elsevier b v all rights reserved

history of actinide and minor element mobility in an archean granitic batholith in manitoba canada abstract surface and borehole core samples from the lac du bonnet granite manitoba canada have been analysed for major element concentrations fe 3 fe total ratios rare earth element ree content and actinide isotopic abundances this work forms part of the geological investigations of the canadian nuclear fuel waste management program performed by atomic energy of canada limited aecl the study attempts to understand the history of and processes governing mobilisation of elements and naturally occurring radionuclides during high and low temperature alteration events in fluid bearing fractures in the granite one surface sample and two core samples from 150 m and 730 m are each in contact with fractures in the granite and show evidence of alteration events that penetrated the rock matrix over distances of at least 3 cm loss of ca and na is seen in cores from a depth of 150 m from the highly altered hematite rich rock adjacent to sub horizontal fracture zones at the underground research laboratory url of aecl near lac du bonnet in contrast k fe fe 3 fe and u concentrations increase towards the fracture surface due to formation of illite and association of u with hematite and the illite at the fracture surface u continues to increase but fe and thefe 3 fe ratio decrease indicating fe removal by reduction the ree also show some enrichment in more altered rock at intermediate depths but the total ree concentration is lower than in the surface and deep core samples no clear trends are visible for parent and fracture surface ree in surface and deep core samples however disequilibrium values of 234 u 238 u and 230 th 234 u ratios in surface and intermediate depth core samples indicate that u has been mobilised in recent geological time the last ma but th has remained relatively immobile high th u and 230 th 234 u ratios in surface samples are indicative of rapid leaching of u but little isotopic fractionation probably within the last 10 5 a apparently unaltered rock several centimetres distant from the fracture in surface and intermediate depth samples has lost appreciable u but evidence from u series disequilibrium studies suggests that this process occurred more than one million years ago perhaps during deuteric or hydrothermal alteration core from a fracture at depth in the granite shows little hematite or clay formation and lacks evidence of ree and recent or ancient actinide mobilisation the u series results are correlated with the observed concentrations and isotope activity ratios of u in groundwaters sampled from the same or adjacent fractures analyses of samples of highly altered rubble recovered from centre portions of fracture zones at the url show both excesses and deficiencies of 234 u and 230 th in neighbouring locations possibly due to the presence of a redox front whose position is controlled by modern groundwater composition the implications of these results are discussed for the concept of disposal of nuclear fuel waste at depth in plutonic rock on the canadian shield

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

the relative mobility of u th and ra isotopes in the weathered zones of the eye dashwa lakes granite pluton northwestern ontario canada radioisotope activity ratios of weathered surface rocks from the eye dashwa lakes granite pluton show that in the 238u decay series 226ra has been leached more rapidly than the grandparent 234u and 238u isotopes the observation of 238th232th disequilibria in the 232th decay series shows that either 228th half life of 1 9 yrs or 228ra half life of 5 75 yrs have been removed from these rocks very rapidly indeed isotope ratios of separated mineral fractions appear to show that whereas uranium tends to be removed from all mineral fractions ra is strongly readsorbed onto feldspars presumably as these undergo alteration to clay minerals this necessitates making a distinction between intermineral mobility of u or ra and the net loss of u or ra from the whole rock an attempt has been made to model quantitatively the transport rate of ra though with little success failure of the modelling appears to indicate that the mobility of 228ra is higher than might be predicted by the mobility of 226ra that is the two isotopes are not strict analogues of one another in their response to initial weathering

isotopic composition of uranium and thorium in crystalline rocks the 238u 234u 230th 232th system has been investigated in 84 silicic crystalline rocks obtained from drill cores surface and near surface samples in california wyoming colorado and illinois results of these analyses displayed on ternary diagrams with apexes for 238u 234u and 230th indicate five predominant geochemical processes that affected uranium in the rock 1 bulk uranium leaching where 238u and 234u were removed with little or no fractionation 2 preferential 234u leaching by alpha recoil displacement 234u recoil loss with lesser 238u loss 3 234u recoil loss with little or no 238u loss 4 uranium assimilation where both 238u and 234u were added with present day 234u 238u activity ratios varying from 0 8 to 1 2 and 5 addition of 234u and 230th by daughter emplacement processes 234u 230th recoil gain evidence for the existence of 234u and 230th recoil gain in rocks is the most important finding of this investigation radioactive disequilibrium occurs in the majority of rocks analyzed where 234u recoil loss is the predominant process associated with incipient weathering u assimilation and 234u 230th recoil gain occur under conditions of substantial water penetration along fractures and into weathered zones in the rocks relatively unfractured and petrographically fresh rocks from the uph 3 drill hole in northern illinois are closest to being in radioactive equilibrium for any suite of rocks included in this study and they demonstrate that equilibrium during the last 0 5 m y can be maintained over a substantial vertical distance where there has been little or no movement of water in the basement rock the 238u 234u 230th system can be a sensitive indicator of geologically recent u mobility and rock water interaction both in petrographically fresh core samples and in sealed fracture zones

234u238u and 230th234u activity ratios in mineral phases of a lateritic weathered zone abstract a selective phase extraction procedure was developed for the identification of the significant phases of a typical deep soil profile sampled in the vicinity of the ranger no 1 uranium ore body alligator rivers region n t australia the significant phases were identified as amorphous iron oxide crystalline iron oxide and a clay quartz resistate the distribution of 238 u 234 u 230 th and 226 ra between the phases was measured the results indicated that the amorphous iron oxide phase is in adsorption desorption equilibrium with the ground water the crystalline iron oxide phase contains a chemical control the kinetics of which are commensurate with or less than the half life of 230 th 7 52 10 4 y the clay quartz resistate is enriched in 238 u descendants in such a way that they are not readily accessible to the ground water

testing the viability of topographic relaxation as a mechanism for the formation of lunar floor fractured craters historically two modes of origin for lunar floor fractured craters have been proposed subcrater laccolith emplacement and topographic relaxation to test the viability of the topographic relaxation model we employ an elastoviscoplastic finite element model and ductile rheology measurements of a devolatilized terrestrial diabase an analog to lunar crustal materials trials were run under two situations 1 under extreme conditions e g high heat flow to determine the maximum degree of relaxation that the model can accommodate and 2 under more nominal conditions in order to resolve how much relaxation can be expected to occur under more plausible lunar conditions we find that in the extreme case topographic relaxation is a viable means only for explaining the observed shallowing of the largest floor fractured craters 100 km in diameter results from the less extreme case demonstrate that lunar materials are simply too rigid to experience degrees of relaxation as large as those observed in the floor fractured crater population these results indicate that topographic relaxation is not the primary mechanism for the formation of floor fractured craters because the topographic relaxation model does not apply for the vast majority of floor fractured craters i e those with diameters less than 60 km we conclude that the laccolith intrusion model is a more viable alternative

lunar floor fractured craters modes of dike and sill emplacement and implications of gas production and intrusion cooling on surface morphology and structure abstract lunar floor fractured craters ffcs represent the surface manifestation of a class of shallow crustal intrusions in which magma filled cracks dikes rising to the surface from great depth encounter contrasts in host rock lithology breccia lens rigid solidified melt sheet and intrude laterally to form a sill laccolith or bysmalith thereby uplifting and deforming the crater floor recent developments in the knowledge of lunar crustal thickness and density structure have enabled important revisions to models of the generation ascent and eruption of magma and new knowledge about the presence and behavior of magmatic volatiles has provided additional perspectives on shallow intrusion processes in ffcs we use these new data to assess the processes that occur during dike and sill emplacement with particular emphasis on tracking the fate and migration of volatiles and their relation to candidate venting processes ffcs result when dikes are capable of intruding close to the surface but fail to erupt because of the substructure of their host impact craters and instead intrude laterally after encountering a boundary where an increase in ductility base of breccia lens or rigidity base of solidified melt sheet occurs magma in dikes approaching the lunar surface experiences increasingly lower overburden pressures this enhances co gas formation and brings the magma into the realm of the low pressure release of h2o and sulfur compounds both factors adding volatiles to those already collected in the rising low pressure part of the dike tip high magma rise velocity is driven by the positive buoyancy of the magma in the part of the dike remaining in the mantle the dike tip overshoots the interface and the consequent excess pressure at the interface drives the horizontal flow of magma to form the intrusion and raise the crater floor if sill intrusion were controlled by the physical properties at the base of the melt sheet dikes would be required to approach to within 300 m of the surface and thus eruptions rather than intrusions would be very likely to occur instead dynamical considerations strongly favor the sub crustal breccia lens as the location of the physical property contrast localizing lateral intrusion at a depth of several kilometers the end of lateral and vertical sill growth occurs when the internal magma pressure equals the external pressure the intrusion just supports the weight of the overlying crust dynamical considerations lead to the conclusion that dike magma volumes are up to 1100 km3 and are generally insufficient to form ffcs on the lunar farside the estimated magma volumes available for injection into sills on the lunar nearside up to 800 km3 are comparable to the observed floor uplift in many smaller ffcs and thus consistent with these ffcs forming from a single dike emplacement event in contrast the thickest intrusions in the largest craters imply volumes requiring multiple dike contributions these are likely to be events well separated in time rather than injection of new magma into a recently formed and still cooling intrusion we present a temporal sequence of 1 dike emplacement 2 sill formation and surface deformation 3 bubble rise foam layer formation and collapse 4 intrusion cooling and a synthesis of predicted deformation sequence and eruption styles initial lateral injection of the sill at a depth well below the upper dike tip initiates upbowing of the overburden leveraging deformation of the crater floor melt sheet above this is followed by lateral spreading of the sill toward the edges of the crater floor where crater wall and rim deposit overburden inhibit further lateral growth and the sill grows vertically into a laccolith or bysmalith uplifting the entire floor above the intrusion subsidiary dikes can be emplaced in the fractures at the uplift margins and will rise to the isostatic level of the initial dike tip if these contain sufficient volatiles to decrease magma density eruptions can also occur this initial phase of intrusion sill lateral spreading and floor uplift occurs within a few hours after initial dike emplacement during the subsequent cooling of the sill bubbles can rise hundreds of meters to the top of the intrusion to create a foam layer when drainage of gas bubble wall magma occurs in the foam layer a continuous gas layer forms above the foam gas formation and upward migration produces an increase in sill thickness while subsequent cooling and solidification cause a thickness decreases and subsidence the total topographic evolution history following an initial 2 km thick sill intrusion and floor uplift hours includes further floor uplift by gas formation and migration decades 30 m followed by cooling solidification and subsidence a century 350 m an initial 2 km thick sill is predicted to have a final thickness of 1 7 km this predicted sequence of events can be compared with the sequence of floor deformation and volcanism in ffcs in order to test and refine this model

floor fractured craters in mare smythii and west of oceanus procellarum implications of crater modification by viscous relaxation and igneous intrusion models endogenic modification in lunar floor fractured craters can constrain spatial variations in early lunar conditions the nature of these constraints however depends on the assumed mecha nism of crater modification for viscous relaxation the extent of crater modification depends on the surrounding crustal viscosity and thus provides loose constraints on the history of crustal heat ing within a region for igneous intrusion models the extent of crater modification reflects mag matically driven deformation and can be inverted to estimate both local magma pressure and intru sion depth both models indicate clear differences between regional conditions at mare smythii and in the highlands west of oceanus procelm the uniformly shallow crater depths in mare smythii probably indicate a long lived period of extreme crater relaxation whereas the wide range of modified crater depths in the western highlands suggest a much shorter period of partial crater relaxation for comparable relaxation times the average viscosity derived for mare smythii is over 10 times lower than the average viscosity inferred for the western highlands alternatively if modification reflects deformation over crater centered laccolithlike intrusions the derived magma pressures indicate a broad uniform magma source beneath mare smythii whereas the spatial vari ation of estimated magma pressures in the western highlands suggests the presence of several smaller magma sources the derived intrusion depths are partly a function of crater size but range from 1 to 10 km in depth for both regions and may be slightly greater on average in the western highlands while both viscous relaxation and igneous intrusions can explain the modification of individual craters the regional variations in these derived modification conditions also allow fur ther testing of each modification model in particular the correlation of the lowest viscosities or the longest relaxation times with the smallest craters in both mare smythii and the western high lands seems inconsistent with crater modification by the relaxation mechanism the onset of total relaxation at progressively smaller topographic wavelengths over time might produce such a trend in mare smythii but total relaxation cannot be invoked for the western highlands where many large craters still preserve significant fractions of their initial relief in addition the relaxation of the smallest craters in both regions suggests the presence of exceptionally high near surface ther mal gradients 150 200 k km since the observed regional variations in crater modification can be easily attributed to variations in magma pressure as a function of mantle topography we con clude that crater floor fracturing in both regions is more consistent with the igneous intrusion mechanism than with viscous relaxation during a crustal heating event

diversity of basaltic lunar volcanism associated with buried impact structures implications for intrusive and extrusive events abstract relatively denser basalt infilling and the upward displacement of the crust mantle interface are thought to be contributing factors for the quasi circular mass anomalies for buried impact craters in the lunar maria imagery and gravity observations from the lunar reconnaissance orbiter lro and dual gravity recovery and interior laboratory grail missions have identified 10 partially or fully buried impact structures where diversity of observable basaltic mare volcanism exists with a detailed investigation of the characteristics of associated volcanic landforms we describe their spatial distribution relationship with respect to the subsurface tectonic structure of complex impact craters and propose possible models for the igneous processes which may take advantage of crater related zones of weakness and enable magmas to reach the surface we conclude that the lunar crust having been fractured and reworked extensively by cratering facilitates substance and energy exchange between different lunar systems an effect modulated by tectonic activities both at global and regional scales in addition we propose that the intrusion caused contribution to gravity anomalies should be considered in future studies although this is commonly obscured by other physical factors such as mantle uplift and basalt load

radioelements radiogenic helium and age relationships for groundwaters from the granites at stripa sweden abstract the solution of radioelements and radiogenic 4he by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock water interface the 234 u 238 u activity ratio and the dissolved u rn and he contents of such groundwaters respond to changes in the flow regime with time although 234 u 238 u activity ratios change with groundwater residence time as a consequence of 234th recoil induced solution of 234u the activity ratio is strongly influenced by the u distribution within fractures by the extent of the rock water interface and by the amount of 238u in solution a model for the quantitative evaluation of these effects is presented groundwaters from depths up to 880 m in the stripa granite have variable dissolved uranium contents and 234 u 238 u activity ratios the uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age dissolved radiogenic 4he in the groundwaters increases with their depth of origin and is dependent upon the u content of the granite and upon its fracture porosity it increases with groundwater residence time but movement of 4he by diffusion and transport processes make the actual groundwater age indeterminate

lunar intrusive domes morphometric analysis and laccolith modelling abstract this study examines a set of lunar domes with very low flank slopes which differ in several respects from the frequently occurring lunar effusive domes some of these domes are exceptionally large and most of them are associated with faults or linear rilles of presumably tensional origin accordingly they might be interpreted as surface manifestations of laccolithic intrusions formed by flexure induced vertical uplift of the lunar crust or alternatively as low effusive edifices due to lava mantling of highland terrain or kipukas or structural features all of them are situated near the borders of mare regions or in regions characterised by extensive effusive volcanic activity clementine multispectral uvvis imagery indicates that they do not preferentially occur in specific types of mare basalt our determination of their morphometric properties involving a combined photoclinometry and shape from shading technique applied to telescopic ccd images acquired at oblique illumination reveals large dome diameters between 10 and more than 30 km flank slopes below 0 9 and volumes ranging from 0 5 to 50 km 3 we establish three morphometric classes the first class in1 comprises large domes with diameters above 25 km and flank slopes of 0 2 0 6 class in2 is made up by smaller and slightly steeper domes with diameters of 10 15 km and flank slopes between 0 4 and 0 9 and domes of class in3 have diameters of 13 20 km and flank slopes below 0 3 while the morphometric properties of several candidate intrusive domes overlap with those of some classes of effusive domes we show that a possible distinction criterion are the characteristic elongated outlines of the candidate intrusive domes we examine how they differ from typical effusive domes of classes 5 and 6 defined by head and gifford head j w gifford a 1980 lunar mare domes classification and modes of origin moon planets 22 235 257 and show that they are likely no highland kipukas due to the absence of spectral contrast to their surrounding these considerations serve as a motivation for an analysis of the candidate intrusive domes in terms of the laccolith model by kerr and pollard kerr a d pollard d d 1998 toward more realistic formulations for the analysis of laccoliths j struct geol 20 12 1783 1793 to estimate the geophysical parameters especially the intrusion depth and the magma pressure which would result from the observed morphometric properties accordingly domes of class in1 are characterised by intrusion depths of 2 3 3 5 km and magma pressures between 18 and 29 mpa for the smaller and steeper domes of class in2 the magma intruded to shallow depths between 0 4 and 1 0 km while the inferred magma pressures range from 3 to 8 mpa class in3 domes are similar to those of class in1 with intrusion depths of 1 8 2 7 km and magma pressures of 15 23 mpa as an extraordinary feature we describe in some detail the concentric crater archytas g associated with the intrusive dome ar1 and discuss possible modes of origin in comparison to the candidate intrusive domes terrestrial laccoliths tend to be smaller but it remains unclear if this observation is merely a selection effect due to the limited resolution of our telescopic ccd images an elongated outline is common to many terrestrial laccoliths and the putative lunar laccoliths while the thickness values measured for terrestrial laccoliths are typically higher than those inferred for lunar laccoliths but the typical intrusion depths are comparable

a model for the dynamics of crater centered intrusion application to lunar floor fractured craters lunar floor fractured craters are a class of craters modified by post impact mechanisms they are defined by distinctive shallow floors that are convex or plate like sometimes with a wide floor moat bordering the wall region radial concentric and polygonal floor fractures suggest an endogenous process of modification two mechanisms have been proposed to account for such deformations viscous relaxation and spreading of a magma intrusion at depth below the crater to test the second assumption and bring more constraints on the intrusion process we develop a model for the dynamics of magma spreading below an elastic overlying layer with a crater like topography as predicted in earlier more qualitative studies the increase in lithostatic pressure at the crater wall zone prevents the intrusion from spreading laterally leading to the thickening of the intrusion additionally our model shows that the final crater floor appearance after the uplift which can be convex or flat with or without a circular moat bordering the wall zone depends on the elastic thickness of the layer overlying the intrusion and on the crater size our model provides a simple formula to derive the elastic thickness of the overlying layer hence a minimum estimate for the intrusion depth finally our model suggests that crust redistribution by cratering must have controlled magma ascent below most of these craters

early fracture evolution within the eye dashwa lakes pluton atikokan ontario canada abstract the fracture history of part of the eye dashwa lakes pluton near atikokan ontario was investigated from drill core and surface fracture data the earliest fractures contain aplite and compose less than 5 of the population they developed during the initial stages of plutonic cooling and contraction in response to local magma related pressures internal pressures decreased as the pluton cooled subsequent fractures comprising more than 90 of the population formed soon afterwards under the influence of a regional subhorizontal nw se compression statistical analysis and field evidence indicate that subhorizontal and moderately dipping dip slip fractures are filled mainly with epidote these were followed by formation of steeply dipping to subvertical strike slip fractures that are filled mainly with chlorite the resulting fracture framework was well established by the end of the archaean minor stress changes since then have rejuvenated the old fracture zones rather than creating new zones

reconstruction of past u migration in a sedimentary deposit coutras france implications for a radwaste repository this study is focused on ancient u mobility in unconsolidated kaolinite bearing sediments from the outcrop area of the coutras u deposit gironde france the analysis of radiation induced defects by electron paramagnetic resonance spectroscopy shows significant variations among the investigated samples and provides the paleodoses due to u at coutras the highest paleodose does not correspond to the highest u concentrations indicative of a past concentration of uranium different from the present one the paleodose gives an estimate of the equivalent u concentrations eu responsible for the defect concentration assuming an age for the kaolinites and considering extreme degrees of disequilibrium among u decay chain as uncertainties of the method the comparison between the equivalent eu and normalized present day u concentrations u norm reveals past migration of u when these two concentrations are different past occurrence of u and daughters is revealed even when this radioelement has been subsequently leached indeed surface sandy beds show a slight barely significant leaching evidence of u eu u norm in contrast several samples show u norm much greater than eu which suggests past accumulation of u younger than the sediment deposition particularly in organic rich clay layers these late enrichments may reach several hundreds ppm u isotopic constraints from the literature imply that accumulation is older than 1 ma in the organic clayey beds although the time of transfer or spatial dispersion of u cannot be specified from the methodology and the limited set of samples the quantitative analysis of radiation induced defects in clays yields intensity of past radioisotope transfers at the geological timescale it is relevant for the analysis of u mobility in sedimentary natural analogues of high level nuclear waste repositories it is also complementary to classical isotopic analysis of u and th series

tectonic analysis of fracturing associated with occator crater abstract occator crater a ceres crater that hosts multiple bright spots on its floor has several sets of fractures associated with it a tectonic analysis of each of these fracture sets suggests that the concentric and radial fractures around the central pit and the concentric fractures high on the crater wall near the rim most likely formed due to well known impact cratering processes uplift of the crater floor due to magmatic injection is suggested to have resulted in the concentric floor fractures at the base of the crater wall as well as the cross cutting fractures in the lower part of the southwestern wall a mathematical analysis shows that a cryomagmatic plume diapir could have both reached the height necessary to cause fracturing within occator and that the stresses required are reasonable expansion a lobate flow from beneath is proposed to have formed those linear fractures associated with the vinalia faculae circumferential fractures surrounding occator appear to have formed due to the volumetric compaction of the ejecta blanket over the buried pre existing topography

density temperature and rheological models for the southeastern canadian cordillera implications for its geodynamic evolution two dimensional density temperature and rheological models are constructed for a 350 km northeast trending transect of the southeastern canadian cordillera all models highlight several major physical differences between foreland and hinterland lithosphere significant features of the density model are the presence of an anomalously low density 3 10 103 kg m 3 layer with a maximum thickness of 12 km beneath the moho in the hinterland the similar densities of the monashee terrane and the cratonic crust of the foreland and an increase in crustal thickness beneath the southern rocky mountain trench the temperature model shows steeper gradients and higher moho temperatures beneath the hinterland than beneath the foreland in the rheological model the hinterland is characterized by a thin brittle upper crust beneath which the entire lithosphere is hot weak and ductile in contrast the foreland is composed of a thick brittle upper crust with an additional brittle zone in the upper mantle the

fractures and fracture infillings of the eye dashwa lakes pluton atikokan ontario fractures in the eye dashwa pluton near atikokan ontario can be subdivided on the basis of their filling materials these materials include aplite epidote chlorite and gypsum carbonate clay listed in order of decreasing age established from crosscutting relations textures indicate that infilling occurred during fracture growth continuous cooling of the pluton during fracturing is inferred from the expected crystallization temperatures of fillings fracturing began before the pluton was completely solidified 650 600 c and continued to temperatures below 100 c many fractures appear to have been sealed by the filling materials after initiation but were subsequently sheared and filled by lower temperature materials apparently the majority of fractures formed during or immediately after pluton solidification and new fractures became smaller and more restricted in location as cooling progressed fractures and filling materials are seen as important features in assessing the possibility of movement

uranium series disequilibrium studies of granitic rocks abstract igneous plutons of the canadian shield which are to be considered as possible storage sites for radioactive waste should be free from any evidence of past mobility of chemical species through the rock however cores taken from some plutons to depths of up to 1 km reveal the presence of hydrous low temperature alteration along joints and fractures and within the body of the rock to test whether such rocks or any others have been subjected to chemical transport in geologically recent times we may study the state of radioactive equilibrium between 238 u 235 u and 232 th and their short lived daughterisotopes members of the decay series of these parent isotopes have half lives ranging from a few hours to 0 25 ma also the chemical characteristics of the various daughters vary significantly allowing us to test the mobility of isotopes of similar half life but differing chemistry if the rock has been chemically undisturbed for 10 ma or more then the activity in d p m g of each daughter in these decay schemes will be equal to that of its parent isotope conversely if the rock was chemically disturbed 10 n a ago then some daughter isotopes with half lives t 10 n a will be out of equilibrium with their parents preliminary results are presented showing disequilibrium effects in samples from atikokan ontario

coincident conductive and reflective middle and lower crust in southern british columbia summary processing and interpretation of magnetotelluric data recorded as part of the lithoprobe southern cordillera transect studies across the boundary of the intermontane and omineca morphogeological belts reveals a high electrical conductivity in the middle and lower parts of the crust everywhere and b a depth dependency of geoelectric strike the data have been modelled using two different inversion algorithms and different methods for correcting static shifts the two different approaches gave similar results the depth to the top of a conductive layer decreases from 15 17km in the west across the intermontane belt to 8 10km across the transition to the omineca belt the top of this conductive layer is closely coincident with a layer of increased seismic reflectivity as shown by reprocessing of collocated lithoprobe seismic reflection data the eastward shallowing is associated with an increase in heat flow such that the top of the conductive and reflective zones remains at 400 450 c this coincidence suggests that the increased reflectivity and the high electrical conductivity observed in the middle crust may have a common cause and that their presence is limited to where the present temperature exceeds a critical value one explanation that meets these conditions is that both the conductivity and reflectivity are produced by a small amount of aqueous fluid porosity we propose that fluids are trapped in the middle crust by a ductile shear zone previously interpreted from the seismic sections as the okanagan valley fault to the west of okanagan lake the geoelectrical strike varies from n25 w for the first 5 10 km of the crust to n20 e for the middle lower crust and to n60 e for the upper mantle this variation indicates that the exotic terrane material is concentrated in the uppermost part of the crust and that the remainder of the crust is composed of ancestral north american rocks

small scale lunar graben distribution dimensions and formation processes abstract the lunar reconnaissance orbiter camera lroc is the first instrument to provide widespread coverage with a range of incidence angles at the resolution required to detect small scale landforms a sample n 238 of globally distributed small scale graben average 26 m wide and 179 m long when dividing the population into those located within mare and highland regions we observe that graben located within mare tend to be narrower shorter and more irregularly spaced than those in highland terrane for graben associated with contractional landforms those in mare are smaller in width and length than those in highlands the same is true for graben independent of contractional landforms assuming a simple geometry widths of mare graben associated with scarps or ridges are used to estimate the minimum depth range to a mechanical discontinuity e g base of the regolith resulting in values of 4 48 m these values are similar to the ranges estimated for regolith thickness from previous workers using apollo 14 seismic data 3 9 8 5 m crater counting techniques 8 33 m crater morphology techniques 2 5 9 m and crater blockiness 8 31 m widths of highland graben yield minimum depths of faulting of 209 296 m while this range agrees well with models for regolith production an older surface will have thicker regolith this estimate likely does not represent the thickness of a mechanical unit due to the fragmented nature of the highland crust it does not provide a defining boundary between bedrock and regolith spacing of mare graben not associated with contractional landforms is used to estimate maximum local mare unit thickness for two graben groups 190 m for posidonius and 296 m for vitello maximum graben ages range from late eratosthenian to early copernican based on superposed and crosscut crater ages with a group of graben deforming ejecta from copernicus crater data presented here provide further evidence of a globally distributed young small scale graben population that has formed as a result of localized extension either from flexural bending or dilation due to contractional faulting or volcanic uplift indicating a significant level of recent geologic activity

an analogue validation study of natural radionuclide migration in crystalline rocks using uranium series disequilibrium studies abstract concentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water conducting fractures deep in the bedrock radioactive disequilibria resulting from rock water interactions were observed in two of the cores these indicated u migration along distances of 40 cm or more on a time scale of 1 myr in conjunction with th immobility under the same conditions fracture surface minerals showed a high affinity for radionuclide retardation and a limit of 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock this limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels

early diagenesis impact on precise u series dating of deep sea corals example of a 100 200 year old lophelia pertusa sample from the northeast atlantic deep sea coral has proved useful for paleoceanographic reconstructions and for documenting 14 c ages of water masses using 230 th ages however for precise and accurate u series dating further information on coral age structure growth rate and diagenetic evolution is still needed to document such processes we used u th 226 ra systematics in a 40 cm diameter lophelia pertusa specimen collected in 1912 from the eastern atlantic sea of the hebrides external parts of the specimen are thought to have been alive when collected whereas more internal parts were likely dead the live collected and dead parts of the skeleton were sampled and analyzed for their 230 th 232 th 234 u 238 u 226 ra and ba contents by thermal ionization and multicollector inductively coupled plasma mass spectrometry 230 th 234 u ratios in the most recent parts yielded ages of 86 6 a and 92 9 a in agreement with the date of recovery the older parts yielded 230 th ages ranging from 169 15 to 211 10 a n 5 but had a 31 higher u content than more recent parts of the skeleton this raises concerns about the possibility of secondary diagenetic u uptake although an environmentally controlled u ca shift between coral growth stages cannot be ruled out 226 ra ba measurements were made and model 226 ra ba ages averaging 250 12 yr were calculated for the older part assuming a constant initial 226 ra ba ratio in bottom waters these ages are slightly older than 230 th ages suggesting either that 226 ra ba ratios of ambient seawater changed over time or that a diagenetic phenomenon have affected the u series system or both scanning electron microscope observations revealed bioerosion and secondary biomineralization in the older part of the coral skeleton supporting the hypothesis that diagenetic processes may have influenced the ages obtained by the u series toolbox modeled u series ages for such an open system are discussed however a comparison between 14 c and 230 th ages performed on both pristine and bioeroded parts of the coral gives coherent values ca 450 a for the preindustrial 14 c reservoir age of north atlantic waters it remains to be determined however whether diagenesis occurs rapidly over a short period of time or whether it continues for longer periods in the latter case diagenetic processes would hamper paleoceanographic interpretations as well as the precise calculation of 14 c ages of deep water masses based on comparative u th and 14 c chronologies copyright 2005 elsevier ltd

lunar floor fractured craters classification distribution origin and implications for magmatism and shallow crustal structure 1 floor fractured craters ffcs are a class of lunar craters characterized by anomalously shallow floors cut by radial concentric and or polygonal fractures additional interior features are moats ridges and patches of mare material two formation mechanisms have been hypothesized floor uplift in response to shallow magmatic intrusion and sill formation and floor shallowing in response to thermally driven viscous relaxation this study combines new lunar orbiter laser altimeter lola and lunar reconnaissance orbiter camera lroc data to characterize and categorize the population of ffcs and map their distribution on the moon and uses variations in floor fractured crater morphology and regional distribution to investigate the proposed formation mechanisms the population of ffcs was categorized according to the classes outlined by schultz 1976 the distribution of these ffc categories shows an evolution of crater morphology from areas adjacent to lunar impact basins to areas in the lunar highlands we propose that this trend is supportive of formation by shallow magmatic intrusion and sill formation crustal thickness determines the magnitude of magmatic driving pressure and thus either piston like floor uplift for high magnitude or a convex floor profile for low magnitude predictions from previous studies modeling viscous relaxation are inconsistent with the observed altimetric profiles of ffcs hence our analysis favors ffc formation by shallow magmatic intrusion with the variety of ffc morphologies being intimately linked with location and crustal thickness and the driving pressure of the intrusion data from the grail gravity recovery and interior laboratory mission will help to test these conclusions

the origin of lunar concentric craters abstract lunar concentric craters are a unique class of impact craters because the interior of the craters contains a concentric ridge but their formation mechanism is unknown in order to determine the origin of concentric craters we examined multiple working hypotheses which include eight impact related and endogenic processes we analyzed data sets that originated from instruments onboard clementine kaguya and the lunar reconnaissance orbiter to characterize the morphology spatial distribution composition and absolute model ages of 114 concentric craters concentric craters contain five key properties 1 a concentric ridge 2 anomalously shallow floors 3 their occurrence is concentrated near mare margins and in mare pond regions 4 the concentric ridge composition is similar to the surrounding area and 5 concentric crater ages are eratosthenian and older these five key properties served as constraints for testing impact related and endogenic mechanisms of formation we find that most impact related hypotheses cannot explain the spatial and age distribution of concentric craters as for endogenic hypotheses we deduce that igneous intrusions are the likely mechanism that formed concentric craters because of the close relationship between concentric craters and floor fractured craters and the concentration of both features near mare highland boundaries and in mare ponds furthermore we observe that floor fractured craters are common at crater diameters 15 km whereas concentric craters are common at crater diameters 15 km produce floor fractured craters

crater centered laccoliths on the moon modeling intrusion depth and magmatic pressure at the crater taruntius abstract many floor fractured craters on the moon show surface deformation like that seen over terrestrial laccoliths consequently terrestrial laccoliths provide one model for such crater modification this model directly relates surface deformation to the growth of a shallow crater centered intrusion and it estimates intrusion size and magma pressure it also yields a minimum estimate for intrusion depth maximum intrusion depths cannot be directly constrained but a range of likely intrusion depths can be derived with additional assumptions when the model is applied to the crater taruntius the surface record indicates an intrusion 30 km across and 1900 m thick the calculated excess magma pressure is 9 mpa 90 bar and the estimated intrusion depths range from 1 to 5 km if magma pressure reflects a hydrostatic magma column beneath taruntius these values suggest a total magma column length of 65 km during crater modification

interpretation of magnetic susceptibility a new approach to geophysical evaluation of the degree of rock alteration magnetic susceptibility measurements on cores from boreholes in the eye dashwa lakes pluton an archean granitic pluton near atikokan ontario give a quantitative evaluation of the alteration leve

actinide and rare earth element characteristics of deep fracture zones in the lac du bonnet granitic batholith manitoba canada the history of major trace and actinide element mobility and fluid infiltration has been studied in two deep fractures 1 km in the lac du bonnet batholith as part of the canadian nuclear fuel waste management program core samples collected from two fracture zones fr1 and fr2 1175 m deep containing saline groundwater tds 50 g l were investigated mineralogically chemically and isotopically 238u series o and h several sequentially overprinting alteration stages were identified from early high temperature to later low temperature hydrothermal alteration k feldspar illite chlorite and later kaolinite formed during these stages subsequent infiltration of oxidizing fluids produced alteration of the chlorite to hydrous iron oxides fracture zone fr1 contains predominantly hematite coating fracture zone fr2 is characterized by the formation of a breccia and by an intense alteration of the granite in contact with this breccia to illitic clay alteration occurred during infiltration either of formation brines or of isotopically evolved meteoric water where 18o 8 to 12 and d 65 to 20 at calculated temperatures between 250 and 25 c loss of ca na and sr and to some extent ba was observed in all the altered samples relative to fresh granite a sharp increase in k mg u th and ree was observed in the illitic clay rich zone pronounced disequilibria of 234u238u 0 5 230th234u 0 7 and 226ra230th 0 9 exist in the illitic clay indicating loss of 234u 230th and 226ra to the groundwater within the last 1 5 ma in contrast an excess of 234u 230th and 226ra was measured in the brecciated samples the disequilibria are consistent with a model involving loss of 234u 230th and 226ra to groundwater by recoil from u deposited on the illitic clay surfaces these radionuclides were deposited subsequently in the nearby brecciated zone