dynamics of paleoenvironments in the cis ural steppes during the mid to late holocene the multi layered settlement of turganik in the tok river valley steppe region west of the urals has been studied using paleopedological and microbiomorphical methods early humans lived in the settlement during the eneolithic epoch the fifth millennium bc and in the early bronze age the fourth millennium bc the cultural layers attributable to the atlantic period of the holocene developed under conditions of a rather dry climate with the landscapes being dominated by the grass and herb steppe the settlement area was above the flood water level and was suitable for habitation the soils in its vicinity were kastanozems endosalic protosodic the final stages of the cultural layer formation bear traces of strong though short term floods with the deposits of the latter partly concealed traces of the preceding long term arid phase maximum aridity was during the final interval of the atlantic period the subboreal and subatlantic periods were noted for meadow chernozem soil formation luvic chernozems stagnic and an increasing proportion of arboreal species in the pollen assemblages some phytoliths of aquatic plants were found in the assemblages dominated by those of meadow grasses the climate was more humid and cool although short episodes of aridity were possible

u sr isotopic speedometer fluid flow and chemical weathering rates in aquifers abstract both chemical weathering rates and fluid flow are difficult to measure in natural systems however these parameters are critical for understanding the hydrochemical evolution of aquifers predicting the fate and transport of contaminants and for water resources water quality considerations 87 sr 86 sr and 234 u 238 u activity ratios are sensitive indicators of water rock interaction and thus provide a means of quantifying both flow and reactivity the 87 sr 86 sr values in ground waters are controlled by the ratio of the dissolution rate to the flow rate similarly the 234 u 238 u ratio of natural ground waters is a balance between the flow rate and the dissolution of solids and recoil loss of 234 u from the solids by coupling these two isotope systems it is possible to constrain both the long term ca 100 s to 1000 s of years flow rate and bulk dissolution rate along the flow path previous estimates of the ratio of the dissolution rate to the infiltration flux from sr isotopes 87 sr 86 sr are combined with a model for 234 u 238 u to constrain the infiltration flux and dissolution rate for a 70 m deep vadose zone core from hanford washington the coupled model for both 234 u 238 u ratios and the 87 sr 86 sr data suggests an infiltration flux of 5 2 mm yr and bulk silicate dissolution rates between 10 15 7 and 10 16 5 mol m 2 s the process of recoil enrichment while primarily responsible for the observed variation in 234 u 238 u of natural systems is difficult to quantify however the rate of this process in natural systems affects the interpretation of most u series data models for quantifying the recoil loss fraction based on geometric predictions surface area constraints and chemical methods are also presented the agreement between the chemical and theoretical methods such as direct measurement of 234 u 238 u of the small grain size fraction and geometric calculations for that size fraction is quite good

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

routine characterization and interpretation of complex alkali feldspar intergrowths almost all alkali feldspar crystals contain a rich inventory of exsolution twin and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions sometimes multiple microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering they are central to the retention or exchange of trace elements and of radiogenic and stable isotopes this review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process we suggest a systematic approach that employs methods available in most well founded laboratories the crystallographic relationships of complex feldspar intergrowths were established by the 1970s mainly using single crystal x ray diffraction but such methods give limited information on the spatial relationships of the different elements of the microtexture or of the mode and chronology of their formation which require the use of microscopy we suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections sections cut parallel to the perfect 001 and 010 cleavages are the easiest to locate and most informative techniques described are light microscopy scanning electron microscopy using both backscattered and secondary electrons including the use of surfaces etched in the laboratory electron probe microanalysis and analysis by energy dispersive spectrometry in a scanning electron microscope transmission electron microscopy we discuss the use of cathodoluminescence as an auxiliary technique but do not recommend electron backscattered diffraction for feldspar work we review recent publications that provide examples of the need for great care and attention to pre existing work in microtextural studies and suggest several topics for future work

experimental partitioning of sr and ba in kiglapait feldspars new electron microprobe analyses of sr and ba in feldspars and coexisting experimental glasses show very strong correlations of the partition coefficients with the ternary or content of the feldspar the correlations therefore scale inversely with temperature as also found in the literature the sr content of feldspars is maximized in mesoperthite and decreases with evolution of feldspar to the ternary minimum the relationship of d sr l to decreasing x an is initially flat at a value of 1 8 but curves sharply upward past 6 5 after the arrival of apatite at an 38 a similar concave up curve at much higher values of d is found in the literature the value of d nine points scales linearly with ternary or r 2 0 99 experimental feldspars are consistently richer in sr than natural ones at comparable an they jump from 200 ppm higher to 400 ppm higher at ap experimental glass compositions are correspondingly low in sr so the material balance is conserved inversion of natural feldspars to liquid compositions using the experimental partition coefficients fails because the experimental crystals contain enhanced values of sr from the apatite and feldspar components of the melted rock compositions the partitioning of ba five points range 0 4 to 6 1 also scales with ternary or r 2 0 99 and there is no systematic difference between the natural and experimental concentrations of ba in the feldspars the inversion of d to liquid compositions may be safe for ba but must be approached with caution for sr

anthropogenic impacts on mineral weathering a statistical perspective abstract correspondence analysis was adopted as tool for investigating the statistical structure of hydrochemical and weathering datasets of groundwater samples with the main purpose of identifying impacts on mineral weathering caused by anthropogenic activities namely fertilizing of farmlands the hydrochemical dataset comprised measured concentrations of major inorganic compounds dissolved in groundwater namely bicarbonate silica usually by products of chemical weathering chloride sulphate and nitrate typically atmospheric plus anthropogenic inputs the weathering dataset consisted of calculated mass transfers of minerals being dissolved in loess sediments of a region located in sw hungary szigetvar area namely na plagioclase calcite and dolomite and of pollution related concentrations of sodium magnesium and calcium a first run of correspondence analysis described groundwater composition in the study area as a system of triple influence where spots of domestic effluents dominated chemistries are surrounded by areas with agriculture dominated chemistries both imprinted over large regions of weathering dominated chemistries a second run revealed that nitrification of n fertilizers is promoting mineral weathering by the nitric acid reaction anthropogenic pathway in concurrence with the retreating of weathering by carbonic acid natural pathway it also indicated that dolomite and calcite are being players in a dedolomitization process driven by dissolution of gypsum fertilizers and nitrification of n fertilizers

the system fayalite albite anorthite and the syenite problem the presence in a magma of fayalite the iron end member of the olivine binary series affects the feldspars at pressure by lowering the temperatures at which they crystallize from the magma starting with estimates from published literature it becomes obvious that at pressure fayalite becomes important because the pressure effects on the melting temperatures are very different large for albite and small for anorthite in this experimental study a powder of fayalite composition was combined with six finely ground natural feldspars from ab to an 97 to make six bulk compositions using graphite crucibles in piston cylinder apparatus at a pressure of 5 kbar a cotectic in the ternary system was found to range from 1141 c at an fa to 1124 c at ab fa with fayalite contents from 68 to 17 wt respectively the results can be used to show that ternary feldspars saturated with fayalite and fe monoclinic pyroxene will crystallize at a 5 kbar multiphase eutectic 1010 c 56 c below a calculated azeotropic point on the ab or join the results are used to compare the end points of two very different layered intrusions skaergaard and kiglapait and to illuminate the nature and origins of syenite and trachyte which are leucocratic rocks unsaturated with mafic minerals because fayalite saturated melts are responsive to pressure unequally on the feldspar end members olivine of intermediate composition will have a damped but potentially significant effect on feldspar fractionation in the lower crust of the earth possibly affecting the origin of anorthosite and syenite

can fe isotope fractionations trace the pedogenetic mechanisms involved in podzolization abstract stable fe isotopes have shown the potential for tracing pedogenetic processes large isotopic fractionations were especially observed in podzols nevertheless a clear link between isotopic fractionation and elementary processes still needs to be established to spatially distinguish the mechanisms successively involved in pedogenesis we studied a podzolic chronosequence from vancouver island british columbia canada we analyzed depth variations in soil properties ph particle size fractions organic carbon si al ratio zr ti fe concentrations in different fe pools and fe isotopic compositions the si al ratio zr and ti demonstrated that the cox bay podzols developed from the same parental material satisfying the requirements of a chronosequence we showed that acidification to a ph of 4 7 was a prerequisite for the start of podzolization this first phase took place after 270 years furthermore we observed that once the required ph was reached 4 7 podzolization occurred rapidly over 50 years we found that fe isotope fractionation in the a e horizon was linked to mineral dissolution while in the podzolic b horizons this fractionation was clearly associated with the accumulation of fe organic complexes and poorly crystalline fe oxyhydroxides

mineral weathering processes in podzolic soils on granitic materials and their implications for surface water acidification many areas where concern has arisen over the recent acidification of their surface waters contain podzolic soils developed upon granitic materials the mineral weathering processes in these soils are reviewed and the ways in which such processes could be altered by acid deposition are considered the most weatherable primary minerals are plagioclase feldspar biotite and fine grained dioctahedral mica and their decomposition which is mediated by organic acids leads to the formation of proto imogolite allophane vermiculite and smectite other clay minerals occurring in podzols such as kaolinite and halloysite as well as gibbsite are probably inherited from previous weathering cycles although a present day pedogenic origin should not be ruled out entirely the possibility is considered that the partial replacement of soil organic acids by mineral acids introduced through precipitation could bring about significant differences in mineral weathering leading to more acid soils with more dissolved ionic aluminium in soil and stream waters the weathering products involved in the mobilization of aluminium from podzols are likely to be proto imogolite allophane and hydroxy al interlayered vermiculite or smectite another possibility is that sand and silt sized plagioclase feldspars are more reactive than previously realized

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

transport of 234u in the opalinus clay on centimetre to decimetre scales the opalinus clay formation in north switzerland is a potential host rock for a deep underground radioactive waste repository the distribution of u 238 u 234 and th 230 was studied in rock samples of the opalinus clay from an exploratory borehole at benken canton of zurich using mc icp ms the aim of u 234 was to assess the in situ long term migration behaviour in this rock very low hydraulic conductivities of the opalinus clay reducing potential of the pore water and its chemical equilibrium with the host rock are expected to render both u 238 and th 230 immobile if u is heterogeneously distributed in the opalinus clay gradients in the supply of u 234 from the rock matrix to the pore water by the decay of u 238 will be established diffusive redistribution separates u 234 from its immobile parent u 238 resulting in bulk rock u 234 u 238 activity disequilibria these may provide a means of estimating the mobility of u 234 in the rock if the diffusion rate of u 234 is significant compared to its decay rate sampling was carried out on two scales drilling of cm spaced samples from the drill core was done to study mobility over short distances and elucidate possible small scale lithological control homogenized 25 cm long portions of a 2 m long drill core section were prepared to provide information on transport over a longer distance variations in u and or th content on the cm scale between clays and carbonate sandy layers are revealed by beta scanning which shows that the dominant clay is richer in both elements samples were digested using aqua regia followed by total hf dissolution yielding two fractions in all studied samples u was found to be concentrated in the hf digestion fraction it has a high u th ratio and a study by sem eds points to sub mu m up to several mu m in size zircon grains as the main u rich phase this fraction consistently has u 234 u 238 activity ratios below unity the minute zircon grains constitute the major reservoir of u in the rock and act as constant rate suppliers of u 234 into the rock matrix and the pore water the aqua regia leach fraction was found to be enriched in th and complementary to the hf fraction having u 234 u 238 activity ratios above unity it is believed that these u activity ratios reflect the surplus of having u 234 delivered from the zircon grains some cm spaced samples show bulk rock u 234 u 238 activity ratios that are markedly out of equilibrium in most of them a striking negative correlation between the total u content and the bulk rock u 234 u 238 activity ratios is observed this is interpreted to indicate net u 234 transfer from regions of higher supply of u 234 towards those of lower supply which is in most cases equivalent to transfer from clayey towards carbonate sandy portions of the rock in contrast the 25 cm averaged samples all have uniform bulk rock u 234 u 238 activity ratios in equilibrium indicating u immobility in the last 1 1 5 ma on this spatial scale it is concluded that the small scale lithological variations which govern u spatial distribution in the opalinus clay are the major factor determining u 234 in situ supply rates regulating its diffusive fluxes and controlling the observed bulk rock u 234 u 238 activity ratios a simple box model is presented to simulate the measured bulk rock u 234 u 238 activity ratios and to give an additional insight into the studied system c 2008 elsevier ltd all rights reserved

kiglapait mineralogy iv the augite series based on twenty five new chemical analyses augites from the upper zone of the kiglapait layered intrusion labrador span the range from en 7 3 to en 0 disposed about a straight line sloping slightly upward from wo 4 0 to wo 4 2 in the pyroxene quadrilateral they contain little tetrahedral al which decreases with fe enrichment as tetrahedral ferric fe 3 increases little or no jadeite or ca tschermaks component is present titanium rises only slightly with fe and the acmite component is scattered near mole fraction 0 03 excess cations relative to 6 oxygen atoms occur chiefly by solid solution toward olivine the only co crystallizing mafic silicate phase values of n increase linearly over the range 1 670 at fictive en 1 0 0 to 1 7448 at en 0 the position of the 150 powder x ray diffraction peak shifts regularly from 5 0372 to 4 1727 degrees away from the 220 peak of silicon metal over the same composition range exsolution of orthopyroxene near 100 is succeeded up stratigraphy by that of pigeonite near 001 and the switch occurs at about the same augite composition as the switch from external orthopyroxene to pigeonite in the skaergaard intrusion exsolution of ilmenite in or near 100 and magnetite ulvospinel near the a and c directions in 010 produces the black color of these augites in hand specimen subsolidus augite olivine tie lines and exchange relations in fe mg allow the distinction between equilibrium pairs and those affected by exchange with external fe ti oxide minerals or with intercumulus liquid in upper border zone lithologies liquids producing augite and olivine with plagioclase follow a ca depletion trend until crystallization of abundant olivine and titanomagnetite drives them on a ca enrichment trend to a point near mg free augite activities of silica consistent with augite olivine pairs range from 0 6 to 0 98 the kiglapait augite series exemplifies the crystallization of a magma occupying the narrow regime between silica saturation and undersaturation in extreme fractionation from troctolite to mg free syenite

determining rates of chemical weathering in soils solute transport versus profile evolution abstract sio 2 fluxes associated with contemporary solute transport in three deeply weathered granitoid profiles are compared to bulk sio 2 losses that have occurred during regolith development climates at the three profiles range from mediterranean to humid to tropical due to shallow impeding alluvial layers at two of the profiles and seasonally uniform rainfall at the third temporal variations in hydraulic and chemical state variables are largely attenuated below depths of 1 2 m this allows current sio 2 fluxes below the zone of seasonal variations to be estimated from pore water concentrations and average hydraulic flux densities mean annual sio 2 concentrations were 0 1 1 5 mm hydraulic conductivities for the investigated range of soil moisture saturations ranged from 9 to 10 6 m s 1 estimated hydraulic flux densities for quasi steady portions of the profiles varied from 6 10 9 to 14 10 9 m s 1 based on darcy s law and field measurements of moisture saturations and pressure heads corresponding fluid residence times in the profiles ranged from 10 to 44 years total sio 2 losses based on chemical and volumetric changes in the respective profiles ranged from 19 to 110 kmoles sio 2 m 2 of land surface as a result of 0 2 0 4 ma of chemical weathering extrapolation of contemporary solute fluxes to comparable time periods reproduced these sio 2 losses to about an order of magnitude despite the large range and non linearity of measured hydraulic conductivities solute transport rates in weathering regoliths can be estimated from characterization of hydrologic conditions at sufficiently large depths the agreement suggests that current weathering rates are representative of long term average weathering rates in the regoliths

207 pb 206 pb and 238 u 230 th dating of uranium migration in carbonate fractures from the palmottu uranium ore southern finland precambrian u ore deposits such as oklo cigar lake or palmottu constitute invaluable analogues of nuclear waste repositories that provide direct evidence of u mobility or sequestration over very large time intervals in geological formations in this study pervasive millimeter thick calcite veins filling microfractures in gneiss and granite surrounding the palmottu u ore finland were analysed as fingerprints of past fluid circulation through the site stable pb isotopes and short halflife 234u 230th isotopes all products of the u decay chain have been chosen to investigate long term over a ga and recent within the last 500 ka u migrations respectively lead u and th isotopes have been analysed by thermo ionisation mass spectrometry on mg size bulk carbonate samples and ion probe analyses of pb isotopes performed on microinclusions of pyrite monazite and coffinite a striking contrast was found between the preservation of a well defined pb pb isochron 1925 70 ma msdw 2 47 n 17 on the one hand and fractionated 230th 238u ratios 230th 238u 1 on the other hand this shows that although the veins were formed simultaneously to the ore itself during the fennoscandian orogeny and behaved mainly as a closed system for several billion years u migrations did occur in the last 0 5 ma the recent u mobility is probably related to changes in the groundwater circulation through the bedrock nowadays the dispersion of the u is however restricted to within a few meters around the u ore it is shown that complex processes of dissolution and re adsorption or re crystallisation took place within these tiny carbonate fracture fillings relatively unradiogenic 206pb 204pb ratios measured by sims in coffinite micro inclusions demonstrate recent precipitation of this mineral coffinite being the main u bearing phase in the carbonate fracture fillings its crystallization probably played a major role in u redistribution within the fractures and in the relatively restricted dispersion of u through the bedrock

plagioclase fractionation in troctolitic magma troctolitic intrusive rocks poor in augite are common in certain proterozoic anorthosite complexes and related rocks the lower zone of the kiglapait intrusion labrador consists of 1570 km troctolite today and possibly 2900 km before erosion in this augite free lower zone plagioclase fractionation is as low as 1 6 an km of cumulate thickness and averages 3 an km when augite crystallizes after 84 of the magma has crystallized the fractionation becomes as much as 17 an km of cumulate why such a difference it is clear from first principles of phase equilibria that fractionation accelerates with saturation in augite but not so clear that the difference should be so great the answer is to be found in the silica poor nature of troctolitic magma that is critically undersaturated in silica this low silica effect reduces the activity of the nasi albite component relative to the caal anorthite component in the plagioclase thereby favoring the an component of the liquid and crystals and weakening the fractionation process as the normative augite component in the magma rises from the base of the lower zone to the base of the upper zone the activity of silica also rises slightly and its consequent effect on plagioclase composition tends to diminish liquid fractionation paths derived from observed crystal paths when plotted in the system diopside anorthite albite rise across the liquidus fractionation lines toward diopside and reach augite saturation near the 1atm cotectic they produce plagioclase compositions 10 mol higher in an than pure liquidus fractionation lines predict the key criterion for the troctolitic fractionation of plagioclase composition is the absence of ca poor pyroxene from the rocks noritic magmas by contrast have higher activities of silica and more effective fractionation of plagioclase a parallel fractionation of olivine is also retarded in the lower zone by the accumulation of ferric iron in the liquid until augite and titanomagnetite crystallize in the upper zone key word plagioclase fractionation troctolite melts silica activity layered intrusions kiglapait intrusion

kiglapait geochemistry iii potassium and rubidium abstract the regular geometry and completeness of the kiglapait intrusion permit its bulk composition to be obtained by summation and the composition of successive liquids to be obtained by subtraction the summations for k and rb give 1806 and 1 08 ppm yielding r frsol k rb 1670 for the intrusion taken as equal to the parent magma r increases slightly from this initial value to 2000 at the end of crystallization where mgo approaches zero in the rocks k and rb are therefore closely coherent and their distribution coefficients can differ only by a small amount in the kiglapait system apparent feldspar liquid distribution coefficients d f l can be estimated from detailed plots of feldspar and liquid compositions against f l the kiglapait data imply that these coefficients are linear 1 1 functions of plagioclase composition within experimental error having values given by d k f l 1 42 x an d rb f l 1 13 x an with minimum values of 0 75 and 0 49 respectively the ratio r f r l lies in the range of 1 53 0 03 for the plagioclase composition range x an 0 34 to 0 67 showing that high r rocks such as anorthosite crystallized from high r liquids the apparent feldspar distribution coefficients are much closer to 1 0 than common literature values they can be reduced by assuming that the cumulate pile was continuously recharged by the circulating magma until an advanced stage of differentiation was reached and assuming that alkalies were exchanged to the feldspars from the magma when such an aquifer recharge model is calibrated using olivine liquid equilibria as a time marker for the liquid the inferred minimum equilibrium values of the distribution coefficients are d k f l 0 42 d rb f l 0 25 at the base of the intrusion their variation is given by d k f l 1 66 1 88x an d rb f l 1 17 1 41x an the equilibrium values are considered to be appropriate for deducing liquid compositions in plutonic bodies where alkali exchange can be shown or inferred to have been inhibited such as in small intrusions the apparent values are considered to be appropriate even though they may be artificial for large intrusions similar to the kiglapait the bulk k and rb concentrations in the kiglapait intrusion are consistent with a plagioclase rich abyssal tholeiite magma clinopyroxene and olivine fractionation in the mantle may contribute to the production of such high r magmas

weathering in three podzolized pedons on glacial deposits in northern sweden and central finland abstract chemical weathering losses were calculated for three conifer stands in relation to ongoing studies on chemical status soil solution chemistry and soil genesis weathering losses were based on elemental depletion trends in soil profiles since deglaciation and exposure to the weathering environment gradients in total geochemical composition were assumed to reflect alteration over time study sites were nyanget and heden in northern sweden and hyytiala in central finland the nyanget site is located on sandy loamy weichselian till at an altitude of 310 m a s l and the heden and hyytiala sites on water deposited coarse silt and out wash sand at an altitude of 175 and 150 m respectively volume determined samples from different soil levels were fused with lithium metaborate dissolved in hno 3 and analysed by icp aes results indicated highest cumulative weathering losses at heden and lower but similar values for nyanget and hyytiala the weathering losses for the elements are in the following order mg ca na k al fe mn si p total annual losses for ca mg k expressed in mmol c m 2 yr 1 amounted to 27 2 16 6 and 19 at heden nyanget and hyytiala respectively variations between study sites were consistent with differences in geochemistry and mineralogy the accumulated weathering losses after deglaciation were much larger in e than in b horizons for all elements studied for fe al and si this was partly due to the retention by precipitation of secondary minerals

production redistribution and loss of helium and argon isotopes in a thick sedimentary aquitard aquifer system molasse basin switzerland abstract in a rock water system an apparent residence time for he can be derived from the bulk he concentration in the rock and the porewater and the he production rate provided that 1 the system is at steady state and 2 the he flux from external sources is negligible this second condition is crucial and needs to be assessed by identifying the various he sources in a given hydrologic environment he and ar isotope abundances were investigated in whole rock samples and mineral separates of the alternating shale sandstone rock sequence of the permo carboniferous trough pct of the molasse basin in northern switzerland 4 he concentrations and 40 ar 36 ar ratios in groundwater in the bounding aquifers are lower than those in pct groundwaters thus eliminating a possible external source of radiogenic noble gases the elements producing radiogenic helium isotopes u th and li are mainly concentrated in the shales where they reside in biotite muscovite clay minerals and organic matter contents of these elements as well as chronological and chemical data allow us to calculate maximum closed system he isotope concentrations and the retention coefficients e g 3 he measured 3 he calculated ratios as deduced from the low retention coefficients almost all helium 3 that has been produced in these minerals since their deposition has been lost into the complementary reservoir i e the porewater the same conclusion is valid for 4 he this is also indicated by the similarity between the calculated 4 he 3 he production ratio of the shales and that observed in pct groundwater 1 3 10 7 moreover similar 4 he 3 he ratios are measured in quartz and plagioclase mineral grains from the sandstone layers by far exceeding the production ratios derived for these minerals also the measured concentrations of he isotopes especially 3 he are higher than the calculated production capacities of these minerals these observations suggest that some of the he produced in the shale and released from these rocks migrates via the porewater into the sandstone layers and penetrates further into some rock forming minerals such as quartz and plagioclase measurements of the migration rate of he atoms through quartz crystals showed that equilibrium between internal gas fluid vesicles and external porewater he concentrations is reached on a short time scale of 10 4 years at an in situ temperature of 70 c the equilibrium allows the he concentrations in the porewater across the pct sequence to be quantified using quartz crystals as detectors for the pct segment opened by the weiach borehole these quartz derived concentrations as well as those directly measured in pct groundwaters are rather high implying a long residence time for the he atoms in the pct rock porewater system well exceeding 10 7 years

a reactive transport model for weathering rind formation on basalt abstract saprolite formation rates influence many important geological and environmental issues ranging from agricultural productivity to landscape evolution here we investigate the chemical and physical transformations that occur during weathering by studying small scale saprolites in the form of weathering rinds which form on rock in soil or saprolite and grow in thickness without physical disturbance with time we compare detailed observations of weathered basalt clasts from a chronosequence of alluvial terraces in costa rica to diffusion reaction simulations of rind formation using the fully coupled reactive transport model crunchflow the four characteristic features of the weathered basalts which were specifically used as criteria for model comparisons include 1 the mineralogy of weathering products 2 weathering rind thickness 3 the coincidence of plagioclase and augite reaction fronts and 4 the thickness of the zones of mineral reaction i e reaction fronts four model scenarios were completed with varying levels of complexity and degrees of success in matching the observations to fit the model to all four criteria however it was necessary to 1 treat diffusivity using a threshold in which it increased once porosity exceeded a critical value of 9 and 2 treat mineral surface area as a fitting factor this latter approach was presumably necessary because the mineral water surface area of the connected accessible porosity in the costa rica samples is much less than the total porosity navarre sitchler et al 2009 the model fit surface area here termed reacting surface area was much smaller than the bet measured surface area determined for powdered basaltic material in the parent basalt reacting surface area and diffusivity are low due to low pore connectivity and early weathering is therefore transport controlled however as pore connectivity increases as a result of weathering the reacting surface area and diffusivity also increase and weathering becomes controlled by mineral reaction kinetics the transition point between transport and kinetic control appears to be related to a critical porosity 9 at which pore connectivity is high enough to allow rapid transport based on these simulations we argue that the rate of weathering front advance is controlled by the rate at which porosity is created in the weathering interface and that this porosity increases because of mineral dissolution following a rate that is largely surface reaction controlled

the behavior of u and th series nuclides in groundwater groundwater has long been an active area of research driven by its importance both as a societal resource and as a component in the global hydrological cycle key issues in groundwater research include inferring rates of transport of chemical constituents determining the ages of groundwater and tracing water masses using chemical fingerprints while information on the trace elements pertinent to these topics can be obtained from aquifer tests using experimentally introduced tracers and from laboratory experiments on aquifer materials these studies are necessarily limited in time and space regional studies of aquifers can focus on greater scales and time periods but must contend with greater complexities and variations in this regard the isotopic systematics of the naturally occurring radionuclides in the u and th decay series have been invaluable in investigating aquifer behavior of u th and ra these nuclides are present in all groundwaters and are each represented by several isotopes with very different half lives so that processes occurring over a range of time scales can be studied table 1 within the host aquifer minerals the radionuclides in each decay series are generally expected to be in secular equilibrium and so have equal activities see bourdon et al 2003 in contrast these nuclides exhibit strong relative fractionations within the surrounding groundwaters that reflect contrasting behavior during release into the water and during interaction with the surrounding host aquifer rocks radionuclide data can be used within the framework of models of the processes involved to obtain quantitative assessments of radionuclide release from aquifer rocks and groundwater migration rates the isotopic variations that are generated also have the potential for providing fingerprints for groundwaters from specific aquifer environments and have even been explored as a means for calculating groundwater ages view this table table 1 radionuclides important in groundwater studies the highly fractionated nature of the

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

controls on rind thickness on basaltic andesite clasts weathering in guadeloupe abstract a clast of low porosity basaltic andesite collected from the b horizon of a soil developed on a late quaternary volcaniclastic debris flow in the bras david watershed on basse terre island guadeloupe exhibits weathering like that observed in many weathered clasts of similar composition in other tropical locations specifically elemental profiles measured across the core rind interface document that primary minerals and glass weather to fe oxyhydroxides gibbsite and minor kaolinite in the rind the earliest reaction identified in the core is oxidation of fe in pyroxene but the earliest reaction that creates significant porosity is plagioclase dissolution elemental loss varies in the order ca na k mg si al fe p ti consistent with the relative reactivity of phases in the clast from plagioclase pyroxene glass apatite ilmenite the rind surrounds a core of unaltered material that is more spherical than the original clast the distance from the core rind boundary to a visually prominent rind layer l was measured as a proxy for the rind thickness at 36 locations on a slab cut vertically through the nominal center of the clast this distance averaged 24 4 3 1 mm maximum and minimum values for l 35 8 and 20 6 mm were observed where curvature of the core rind boundary is greatest 0 12 mm 1 and smallest 0 018 mm 1 respectively extrapolating from other rinds in other locations the rate of rind formation is estimated to vary by a factor of about 2 from 4 to 7 10 14 m s 1 from low to high curvature the observation of a higher rate of rind formation for a higher curvature interface is consistent with a diffusion limited model for weathering rind formation the diffusion limited model predicts that like rind thickness values of the thickness of the reaction front h for a given reaction defined as the zone over which a parent mineral such as plagioclase completely weathers to rind material should also increase with curvature values of h were quantified as a function of interface curvature using bulk chemical analysis 500

petrology and mineral compositions of the middle banded series of the stillwater complex montana the two olivine beating zones of the middle banded series of the stillwater complex are characterized by an increase in the number of cumulus minerals with height in each anorthosite and anorthositic troctolite dominate the lower part whereas olivine gabbro and gabbronorite form much of the upper portions electron microprobe analyses of cumulus minerals indicate little or no variation of average mineral compositions with height in addition no significant lateral variations in cumulus mineral compositions occur along 8 km of section plagioclase from throughout these zones shows the complex reverse and oscillatory zpnation patterns also seen in plagioclase from the thick 500 m anorthosites that sandwich the zones the data suggest that the entire middle banded series is genetically related and therefore requires models for the origin of the thick anorthosites to also explain the olivine bearing rocks between them however textural features such as discordant troctolites pegmatoids slump structures and variably developed mineral laminations and chemical features such as zpnation in clinopyroxene produced by intergranular exchange with orthopyroxene and large within sample variations in the mg number of olivine in lowolivine troctolites indicate that significant modification of these rocks by postcumulus processes has taken place thereby obscuring evidence of their genesis

origin of strongly reversed rims on plagioclase in cumulates abstract narrow reversed rims on plagioclase are ubiquitous in troctolites and olivine gabbros of the kiglapait intrusion and may be a common feature of all such cumulates the rims occur at plag plag plag ol and less strongly at plag aug grain boundaries they are optically obvious at an and can reach an 32 mol or more in parallel k na drops sharply although ubiquitous from sample to sample the reversed rims are only locally present at grain boundaries even for the same pair of crystals in contact they are prominent in linear networks suggesting the last trace of intercumulus liquid a subsolidus origin is ruled out by the absence of reactants at plag plag and plag ol boundaries and by the local rather than pervasive development of rims the rims are required to grow from intercumulus liquid in which the partition of an component between crystals and liquid increases with the trapped augite component of the liquid calculations from published experimental data show that an 30 can easily be achieved by such a process it is also probable that the trapped liquid is part of an an rich boundary layer generated by solute rejection during adcumulus growth the ability of the rims to sustain steep k na gradients despite a long subsolidus cooling history proves that the k na exchange rate is vanishingly small over a geologic time scale in an rich feldspar suggesting that at low k content the potassium is site bound to the tetrahedral al si distribution reversed rims therefore provide important information on diffusion limits as well as on the late stage solidification history of plagioclase rich cumulates moreover they demonstrate that plagioclase geothermometry cannot be divorced from effects of liquid composition and structure as monitored for example by augite content

the role of phytolith formation and dissolution in controlling concentrations of silica in soil solutions and streams abstract by integrating the results of recent studies on the concentration and flux of si in european forest soils podzols and acid brown soils with published evidence on the amounts of si cycled through forest vegetation we conclude that phytoliths must be the principal immediate source and sink of silica in soil solution although mineral weathering is the ultimate source during the growing season forest vegetation takes up most of the si made available by weathering of soil minerals and by phytolith dissolution and converts it into phytoliths phytoliths will be the principal source of si leached from the soil during winter rains and spring snowmelt this work accounts for the plateau concentrations of si observed in laboratory equilibrations of bs horizon soils for the maximum si concentration reported for b horizons in the field for a deep sink for si in bs horizons and for the fact that the concentrations of si in soil drainage water and in streams all fall in or below the range expected for phytolith solubility concentrations of si in surface horizons can exceed these levels during droughts the common assumption that the concentration of si in soil solution is a result of a dynamic balance between si released by mineral weathering and that lost by leaching is untenable for bs horizons

large scale magmatic layering in the main zone of the bushveld complex and episodic downward magma infiltration the bellevue drillcore intersects 3 km of main and upper zone cumulates in the northern limb of the bushveld complex main zone cumulates are predominately gabbronorites with localized layers of pyroxenite and anorthosite some previous workers using bulk rock major trace and isotopic compositions have suggested that the main zone crystallized predominantly from a single pulse of magma however density measurements throughout the bellevue drillcore reveal intervals that show up section increases in bulk rock density which are difficult to explain by crystallization from a single batch of magma wavelet analysis of the density data suggests that these intervals occur on length scales of 40 to 170 m thus defining a scale of layering not previously described in the bushveld complex upward increases in density in the main zone correspond to upward increases in modal pyroxene producing intervals that grade from a basal anorthosite with 5 pyroxene to gabbronorite with 30 40 pyroxene we examined the textures and mineral compositions of a 40 m thick interval showing upwardly increasing density to establish how this type of layering formed plagioclase generally forms euhedral laths while orthopyroxene is interstitial in texture and commonly envelops finer grained and embayed plagioclase grains minor interstitial clinopyroxene was the final phase to crystallize from the magma plagioclase compositions show negligible change up section average an62 with local reverse zoning at the rims of cumulus laths average increase of 2 mol in contrast interstitial orthopyroxene compositions become more primitive up section from mg 57 to mg 63 clinopyroxene similarly shows an up section increase in mg pyroxene compositions record the primary magmatic signature of the melt at the time of crystallization and are not an artefact of the trapped liquid shift effect combined the textures and decoupled mineral compositions indicate that the upward density increase is produced by the downward infiltration of noritic magma into a previously emplaced plagioclase rich crystal mush fresh noritic magma soaked down into the crystallizing anorthositic mush partially dissolving plagioclase laths and assimilating fe enriched pore melt the presence of multiple cycles showing upward increases in density in the bellevue drillcore suggests that downward magma infiltration occurred episodically during crystallization of the main zone

melt assisted interior to margin switch from dislocation to diffusion creep in coarse grained plagioclase evidence from a deformed anorthosite pluton abstract at bolangir eastern india massive anorthosites in the pluton interior grade into anorthosites with outward dipping margin parallel foliation neighboring the pluton margin sheets and veins of ferrodiorites residual melts of anorthosite crystallization concordant and discordant to the margin parallel foliation suggest pluton deformation at near magmatic conditions t 950 c and p 6 12 kbar in the pluton interior the larger than centimeter sized magmatic plagioclase grains are replaced by aggregates of smaller 100 600 m dynamically recrystallized internally strained grains with un equilibrated boundaries neighboring the pluton margin poly sized 200 2500 m plagioclase grains in anorthosites are of two types strain free rectangular shaped plagioclase grains with high energy an richer margins indenting neighboring plagioclase grains formed by diffusion creep whereas unstrained end to end touching euhedral plagioclase grains showing tilling represent magmatic flow textures the pluton interior to margin switch in plagioclase deformation from grain boundary migration accommodated dislocation creep to grain boundary diffusion creep is attributed to the increasing melt fraction melt crystal ratio during syn deformation pluton emplacement plagioclase grains in the bolangir pluton are significantly coarser compared to plagioclase aggregates

solidification of trapped liquid in rocks and crystals trapped liquid in an igneous cumulate solidifies over a range of time and temperature that can be retrieved by use of the lever rule in binary solutions applied to plagioclase using the range in the an content found for the individual rock studied the an range so called when measured in sufficient detail defines the solidification history the instantaneous solid composition along the solidus defines the zoning of the plagioclase as it follows the trapped liquid on the liquidus the reference bulk composition of the trapped liquid is given by an intercept on the initial solid liquid lever defined by the fraction of plagioclase in the trapped parent magma times the residual porosity the mafic fraction is assumed to solidify by reaction independently of the plagioclase zoning the residual porosity is estimated from the content of evolved components in the trapped liquid and can also be calculated from the an range itself when that is calibrated to a value independently determined from the evolved components examples from a recent treatment of residual porosity are given for the solidification of selected rock compositions from the kiglapait and skaergaard intrusions the same principles apply to the solidification of melt inclusions with the difference that the latter tends to sample an evolved sheath by capture rather than a parent magma trapped by closure of a cumulate because only the cumulate has had time to exchange the evolved rejected solute owing to its slow solidification experimental examples of melt inclusions trapped at liquidus conditions demonstrate the highly evolved composition of the sheath compared to the bulk glass composition the application of the solidification principle to presumed liquid immiscibility in the skaergaard intrusion suggests that the melt inclusions are evolved during the capture process and then solidified as given by the an range in the plagioclase the hypothesis of liquid immiscibility is not needed in this analysis the very different end stage feldspar histories of the two intrusions is attributed to the sequestering of low melting feldspar components in the trapped liquids of the skaergaard cumulates compared to the lesser amounts trapped in the kiglapait cumulates

origin of anorthosite by textural coarsening quantitative measurements of a natural sequence of textural development the textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite such textures have been quantified in a troctolite anorthosite from the proterozoic lac st jean anorthosite complex canada crystal size distributions csds indicate that initially plagioclase nucleated and grew in an introduction environment of linearly increasing undercooling producing a straight the textures of plutonic rocks are one of their most line csd during this phase latent heat of crystallization was striking aspects but they have been little used to elucidate largely removed by circulation of magma through the porous crystal petrological processes as compared with chemical and mush by about 25 solidification the crystallinity was such that isotopic methods where used discussion has tended it reduced but did not eliminate the circulation of magma resulting to be qualitative in contrast to quantitative chemical in the retention of more latent heat within the crystal pile the methods hence reducing the weight of this approach temperature rose until it was buvered by the solution of plagioclase indeed it is not possible to verify physical models if close to the liquidus temperature of plagioclase nucleation of quantitative data are not available quantitative textural plagioclase was inhibited and conditions were suitable for textural studies of volcanic rocks are becoming more common coarsening of both plagioclase and olivine to occur ostwald and these methods are applied here to the development ripening in this process small crystals were resorbed whereas of anorthosite larger crystals grew from both material recycled by the resorption of quantitative textural studies of plutonic rocks really crystals smaller than the critical size and new material brought in started with jackson s studies of the stillwater complex by the circulating magmatic fluid the results of this process resemble in 1961 jackson 1961 he measured crystal size disthose of high temperature metasomatism but there is no necessity for tributions but did not record the area that he measured a magmatic fluid with a diverent composition the shapes of the hence his data cannot be completely compared with plagioclase csds fit better the communicating neighbours equation of modern data his pioneering work was not really followed textural coarsening rather than the classic lifshitz slyozov wagner up and since then most studies have looked only at equation as do other examples drawn from the literature if olivine average or typical crystal sizes these data are much started to nucleate at a higher temperature than plagioclase then less revealing of petrological processes than crystal size during the textural coarsening phase olivine would have been more distributions partly because they only give one parameter undercooled than plagioclase and would have had a higher maximum for each sample the few existing studies of crystal size growth rate in these conditions olivine would coarsen more rapidly distributions in plutonic rocks have not treated than plagioclase and engulf it hence the order of crystallization plagioclase determined from the textures would be the reverse of the order of one problem especially pertinent to quantitative texfirst nucleation of the two phases from equilibrium phase diagrams tural studies is the way that many igneous petrologists maintenance of the temperature near the plagioclase liquidus may look at rocks they commonly try to reconstruct how a rock has formed by examining the final fully crystallized also inhibit the nucleation and growth of other phases

weathering release rates of base cations from soils within a boreal forested catchment variation and comparison to deposition litterfall and leaching fluxes long term 10 200 years average annual weathering rates mass losses of base cations ca mg and k for ten podzolic soil profiles in a remote forested catchment in eastern finland were determined using the zr depletion method three of the profiles were developed in sorted glaciofluvial parent material sand overlying till and seven developed in stony till parent material the aims were to determine the variation in base cation weathering rates within the catchment to determine if weathering rates differed between the two types of parent material and to compare the weathering rates with other ecosystem fluxes of base cations namely total deposition td litterfall lf and soil leaching 40 cm soil and parent material were sampled to a depth of 3 5 m and total elemental concentrations in the 2 mm fraction determined using xrf annual mean 1989 1997 td lf and leaching fluxes have been determined at two of the plots as part of long term ecosystem monitoring programmes there was no significant p 0 05 difference in ca mg k weathering rates between the two deposit types with rates averaging 15 3 and 14 9 mmolc m 2 year 1 for glaciofluvial sand and till profiles respectively the coefficient of variation in ca mg k weathering rates across all ten profiles was 31 the weathering rates were similar in size to the lf and leaching fluxes of base cations and were also sufficient to neutralize the td load of so4 2 acidity our results indicate that soil weathering is an important source of base cations and essential to the sustainability of site productivity of boreal catchments receiving low deposition loads even when having soil parent material dominated by acidic silicate minerals

kiglapait mineralogy iii olivine compositions and rayleigh fractionation models olivints present throughout the layered cumulates of the kiglapait intrusion record extreme iron enrichment during fractional crystallization mn is less compatible than fe the exchange coefficient kd for mn fe ol liq has values near 0 95 but they drop to 0 7 near the lower one upper one boundary ca is depleted by more than a factor of 30 relative to experimental values at 5 kbar pressure attempts to find a sink for ca in the lower zone without invoking liquid as a reactant are unconvincing and questions of metastability arise cumulus olivines vary systematically to lower fo contents with stratigraphic height using equilibrium values for the exchange coefficient kd fe mg ol ljq j and the observed mode of olivine and residual porosity a rayleigh fractionation calculation reproduces the observed lower zone trend without recourse to multiple injections of magma an anomalously fe rich region above the main ore band in the upper zone ascribed to ponding of fe rich magma at the floor of the intrusion until later buoyant residual magma entrained the fe rich residua such fe rich ponds probably account for the abnormal fe enrichment shown by some other fenner trend layered intrusions summation over the observed crystal compositions yields values of xjug that do not represent the equilibrium liquid but that reduce to it by a simple multiplier p 0 78 this result means that if ko is known the high temperature liquidus olivine compositions can be retrieved or vice versa because the observed olivine compositions are supported by realistic forward models there is no need to invoke evolved boundary layer liquids to explain the in situ crystallization of kiglapait cumulates classical cumulate theory suffices

geochemistry of the nain massif anorthosite labrador magma diversity in five intrusions abstract the petrography and major and trace element concentrations of the anorthositic bird lake massif blm susie brook slab sbs lister massif lm port man vers run pmr and kikkertavak area kik in the nain plutonic suite nps labrador delineate the mineralogical and composition ranges of these large intrusions from these a variety of magmas and staging histories can be inferred the blm and sbs are mainly noritic anorthosites of the western region exposed along tikkoatokhakh bay tik tilting and stretching deformation distinguish sbs from blm but the two units show no mineralogical or chemical differences the kik and pmr intrusions are mainly troctolitic to noritic anorthosites of the eastern region and they contain more mafic components than the tik bodies chemically all the anorthositic rocks are high in ba sr and the ratio k rb and low in zr rb and rb sr the three plutonic bodies blm sbs and lm along tik are similar and can be clearly distinguished from kik and pmr intrusions by element concentrations and ratios diagrams of element pairs show that each intrusion or group has its own evolutionary trend and variable style indicating that they represent independent magma batches rather than fractionally related volumes of the same magma ree patterns show light ree enrichment and heavy ree depletion and strong positive eu anomalies correlated with cumulus plagioclase in chemical comparison with adjacent plutons one pmr chilled leucotroctolite after subtraction of 18 cumulus plagioclase is similar to the kiglapait magma ki one melatroctolite in kik is close to the comb layered melatroctolite of the snowflake zone in the hettasch intrusion hi and the average leucotroctolite and leuconorite in kik are similar to the leucotroctolite unit and the upper leuconorite respectively at paul island pi therefore the magmas from pmr and kik are similar to those of wellknown troctolitic bodies and their feldspar rich cumulates kik differs from pmr in having somewhat higher an and xmg values all these lines of evidence show that at least three types of magma existed in the study area sodic noritic magma accumulating plagioclase in tik troctolitic magma in kik and a magma similar to but more evolved than kik in pmr the methods used also illustrate the feasibility of characterizing magma compositions from diverse types of cumulates regional differences in modal and chemical composition occur in the nps noritic compositions with pale plagioclase are located in the western and southern regions and troctolitic compositions with darker plagioclase are located in the eastern region a reasonably accurate boundary can now be drawn between the two regions which differ in the nature of their transport from the mantle in comparison with a primitive mantle composition high ba pb k sr ti and low rb nb zr in the nain anorthositic rocks are distinctive these anomalies and the isotopic results of other investigators are consistent with mantle source enrichment followed by variable contamination during magma ponding at the base of the depleted crust

changes in the rate of release of ca and mg and normative mineralogy due to weathering along a 5300 year chronosequence of boreal forest soils changes in the normative mineralogy and chemical weathering rates elemental loss of ca and mg from the uppermost mineral soil horizon were determined at five forested sites in the boreal zone forming a chronosequence the sites were all located on the same glaciofluvial esker deposit well sorted sand over a distance of 27 km in the coastal region of the gulf of bothnia in finland and had estimated ages from 339 to 5276 years because of isostatic land uplift the region is continually emerging from the sea the rates of which are known allowing the age of current surfaces to be dated soil profile development progressed from gleyic arenosols youngest and nearest the coast through haplic arenosols to haplic podzols 3 oldest and furthest away from the coast elemental concentrations of soil 2 mm were determined using xrf and icp ms from a hot aqua regia digest normative mineralogy was determined using these data and a stoichiometric mineral distribution model weathering elemental loss rates were calculated using xrf concentrations and normative quartz as the conservative reference component quartz was increasingly enriched in the uppermost horizon with soil age commensurate with the loss of easily weathered minerals using quartz as the conservative component the mass residual fraction remaining in the uppermost soil horizon of the oldest soil was 0 27 0 35 and 0 57 respectively for biotite hornblende and anorthite which are important sources of ca and mg b e horizon ratios of hydrous aluminosilicate contents increased from 1 to 14 with soil age clearly indicating the increase in degree of podzolisation the losses of ca and mg increased with soil age but at a decreasing rate ca and mg losses for the youngest soil were respectively 3 3 and 1 8 mol m 2 corresponding values for the oldest soil were 10 6 and 10 5 mean rates of loss for the youngest soil were 10 and 5 mmol m 2 yr 1 for ca and mg respectively and corresponding values for the oldest soil were 2 mmol m 2 yr 1 for both ca and mg the loss of these base cations from the soil will have resulted in a lower acid neutralizing capacity and increased sensitivity of these soils to acidic deposition and represents a reduction in the soil reserve of important plant nutrients

the normative mineralogy of 10 soil profiles in fennoscandia and north western russia abstract the mineralogical composition of soil horizons in different soil types of different ages was estimated by applying the norma software which was developed originally for calculating the normative mineralogical composition of young podsols ten soil profiles from six sites in nw russia two in finland and one in ne norway were sampled in 1999 as a part of the pilot phase of a large geochemical mapping project total element concentrations were determined from the 4 extraction extractable concentrations for al ca cr fe k mn mg na p s ti zr and ba were determined by icp ms or icp aes after aqua regia a 1 3 mixture of strong hcl and hno 3 extraction total c was determined using a thermal conductivity detector from a sample burned in an o 2 stream the norma software was used to calculate the percentage of normative soluble minerals pyrite apatite titanite calcite biotite chlorite weathered albite hydrous al silicate goethite and soluble residue the percentages of non soluble normative minerals rutile hornblende k feldspar albite anorthite tremolite wollastonite kaolinite magnetite zircon quartz carbon graphite and non soluble residue were calculated after soluble minerals the calculated mineralogical composition of c horizon samples in each profile reflected the known geological composition of the bedrock from which the soil parent material was derived during geological processes secondary minerals including goethite and hydrous al silicates were detected in upper soil horizons reflecting the development of soils rather than age the local bedrock geology together with the mineralogical composition and chemical properties of the parent material proved to be the controlling factor in the formation of secondary minerals the results showed that the norma method can be used in defining the mineralogy of soil horizons in a large variety of soil types

textural immaturity of cumulates as an indicator of magma chamber processes infiltration and crystal accumulation in the rum eastern layered intrusion textural maturity describes the extent to which rocks have approached textural equilibrium for igneous rocks this is a function of the time integrated thermal history in the sub solidus which for cumulate rocks generally translates to the cooling history via the rate of solidification of the accumulating crystal mush the most straightforward way to quantify the textural maturity of orthocumulates sensu lato is to measure the angle subtended at the corners of interstitial grains texturally mature cumulates have angle populations with median values of c 120 whereas texturally immature cumulates have lower medians inherited by the interstitial phase which infills either an impingement texture in the accumulating mush or a texturally equilibrated pore topology textural observations of allivalites from the rum layered suite demonstrate that stratigraphically localized excursions towards textural immaturity are the result of either transient relatively rapid solidification rates perhaps a result of the arrival of cold crystal laden bodies of fluid on the chamber floor or late stage infiltration of fully solidified cumulates by evolved liquids expelled upwards by compaction of underlying horizons these two processes have distinct textural and compositional signatures

introduction to u series geochemistry during the last century the earth sciences underwent two major revolutions in understanding the first was the recognition of the great antiquity of the earth and the second was the development of plate tectonic theory these leaps in knowledge moved geology from its largely descriptive origins and established the modern quantitative earth sciences for any science and particularly for the earth sciences time scales are of central importance until recently however the study of time scales in the earth sciences was largely restricted to the unraveling of the ancient history of our planet for several decades earth scientists have used a variety of isotope chronometers to unravel the long term evolution of the planet a fuller understanding of the physical and chemical processes driving this evolution often remained elusive because such processes occur on time scales 1 105 years which are simply not resolvable by most conventional chronometers the u series isotopes however do provide tools with sufficient time resolution to study these earth processes during the last decade the earth sciences have become increasingly focused on fundamental processes and u series geochemistry has witnessed a renaissance with widespread application in disciplines as diverse as modern oceanography and igneous petrology the uranium and thorium decay series contain radioactive isotopes of many elements in particular u th pa ra and rn the varied geochemical properties of these elements cause nuclides within the chain to be fractionated in different geological environments while the varied half lives of the nuclides allows investigation of processes occurring on time scales from days to 105 years u series measurements have therefore revolutionized the earth sciences by offering some of the only quantitative constraints on time scales applicable to the physical processes that take place on the earth the application of u series geochemistry to the earth sciences was thoroughly summarized in 1982

plagioclase an range and residual porosity in igneous cumulates of the kiglapait intrusion the range in an content of plagioclase in grain mounts of igneous cumulates provides a measure of diversity that is uniquely preserved in plagioclase because of its well known refractory nature to a first approximation such data provide when calibrated an estimate of the residual porosity or fraction of trapped liquid in each specimen the ensemble of specimens then provides a model for the stratigraphic variation of residual porosity the raw data however include pre cumulus zoning that can be isolated from in situ zoning by textural analysis in thin section the baseline of residual porosity determinations was earlier determined for the lower zone of the kiglapait intrusion from the content of excluded components in the solid rock compared with their content in the melt as calculated by summation and rayleigh fractionation the baseline equation was then used to calibrate the residual porosity obtained from the an range in grain mounts this calibration is now extended to the remainder of the intrusion the an range and the calculated residual porosity decrease to zero at 99 solidified pcs and then rise to the end of crystallization the data suggest initial porosities smaller than 0 35 allowing for pre cumulus zoning the data suggest a dominance of adcumulates in the intrusion and these impermeable barriers occupy 75 of the rocks in the lower zone they occur at intervals of 1 to rarely 15 m and thereby restrict the likelihood of compaction over thick mushy zones variations in the fo range of olivine are also observed in grain mounts and they follow those in plagioclase however they are in part due to subsolidus equilibration with fe ti oxides and augite the new calibration is successfully applied to the skaergaard intrusion to supplement the published results from excluded components with some interesting contradictions

petrology of a leucogabbroic interval within basal layered gabbros at north arm mountain bay of islands ophiolite data from detailed sample traverses in the layered gabbro unit of the north arm mauntain massif bay of islands ophiolite allow meter scale resolution of magmatic processes in spreading ridge magma chambers one suite of 46 samples from a 195 m interval near the base of the layered gabbro unit contains cumulus plagioclase an73 7 87 5 average modal abundance 75 clinopyroxene mg 80 3 86 0 18 and olivine fo76 6 82 1 6 with intergranular orthopyroxene mg 78 0 83 3 1 and accessory cr al spinel cr 32 3 41 4 ilmenite rims spinel in one sample whole rock zr contents range from 6 to 15 ppm plots of stratigraphic height in the traverse versus petrogenetic indicators e g mg s of mafic phases and an in plagioclase reveal both normal and reverse cryptic variation patterns the patterns for all indices are generally correlated the normal portions of the patterns formed during fractional crystallization of basalt batches ranges of mineral compositions in the normal trends suggest that 29 38 crystallization of each batch of basalt occurred before magmatic replenishment the reverse cryptic trends formed by crystallization of hybrid magmas produced during periods of magma mixing other evidence for magma mixing is the systematic association of spinel and reversely zoned plagioclase with the reverse trends experiments and observations of natural assemblages indicate that 55 modal plagioclase crystallizes from basalts at the olivine plagioclase clinopyroxene liquid piercing point the average plagioclase content of this suite of leucogabbros from north arm mountain is too high to have formed from simple crystallization at the piercing point petrologic modeling indicates the leucogabbros may have formed from basalts into which a small amount 10 of plagioclase was resorbed during mixing the initial compositions of these hybrid basalts lie in the plagioclase primary phase volume other suites of layered gabbros from north arm mountain are not so plagioclase rich as the leucogabbros described above crystallization of basalts in the plagioclase primary phase volume and the consequent formation of plagioclaserich gabbros may occur in restricted portions of zoned magma chambers underlying oceanic spreading centers or may occur episodically in the overall lifetimes of the magma chambers

in situ radionuclide transport and preferential groundwater flows at ineel idaho decay series disequilibrium studies uranium and thorium decay series disequilibria in groundwater occur as a result of water rock interactions and they provide site specific natural analog information for assessment of in situ long term migration of radionuclides in the far field of a nuclear waste disposal site in this study a mass balance model was used to relate the decay series radionuclide distributions among solution sorbed and solid phases in an aquifer system to processes of water transport sorption desorption dissolution precipitation radioactive ingrowth decay and recoil isotopes of u 238u 234u th 232th 230th 228th 234th ra 226ra 228ra 224ra and rn 222rn were measured in 23 groundwater samples collected from a basaltic aquifer at the idaho national engineering and environmental laboratory ineel idaho the results show that groundwater activities of th and ra isotopes are 2 4 orders lower than those of their u progenitors which average 1 35 0 40 dpm 238u l with 234u 238u ratios of 1 6 3 0 222rn activities range from 20 to 500 dpm l modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water rock interaction at ineel 1 time for sorption is minutes for ra and th time for desorption is days for ra and years for th and time for precipitation is days for th years for ra and centuries for u 2 retardation factors due to sorption average 106 for 232th 104 for 226ra and 103 for 238u 3 dissolution rates of rocks are 70 to 800 mg l y 4 ages of groundwater range from 10 to 100 years contours of groundwater age as well as spatial patterns of radionuclide disequilibria delineate two north south preferential flow pathways and two stagnated locales relatively high rates of dissolution and precipitation and recoil of 222rn occur near the groundwater recharging sites as well as in the major flow pathways decay of the sorbed parent radionuclides e g 226ra and 228ra on micro fracture surfaces constitutes an important source of their daughter 222rn and 228th activities in groundwater

plagioclase fractionation and the common basalt a labor saving device is recalled which predicts the course of plagioclase fractionation in hat creek basalt within 2 mole an until the system is 80 crystallized referred to the smoothed hat creek data the effective plagioclase liquid partition coefficient d a an eff is estimated from d eff 1 81f dt prime 1 04 where f di prime is the cipw normative fraction di di fsp in this case 0 2 the data for hat creek basalt suggest an intercept constant equal to 1 08 rather than 1 04 this method of predicting plagioclase fractionation emphasizes the importance of initial liquid composition and structure and its success shows that the effects of temperature are minor and submerged in the general empirical expression for d eff experimental verification of the augite effect is found in earlier data for the system di an ab

the effect of site fertility and climate on current weathering in finnish forest soils results of a 10 16 year study using buried crushed test rock material abstract knowledge of the weathering rates in forest soils is needed when nutrient balances and the sustainability of silvicultural practices are estimated the effects of site fertility and climate on weathering rates were studied in boreal coniferous forest soils in finland by following transformations in crushed rock spectrolite a dark anorthosite feldspar dominated gabbro confined in porous bags inserted into e b and c horizons along fertility and climate gradients and left to weather for 10 11 or 16 years organic carbon oc was accumulated in e horizon incubated crushed test rock material and it was more acidified and weathered than that deeper in the soil there was a tendency for faster weathering of the c horizon bags in the fertile sites than in the poor sites multivariate analyses indicated that more oc was accumulated in the bags in fertile sites than in poor sites and that the crushed rock was more weathered in north than in south finland although temperature sum and precipitation decreased northwards the results suggest that humidity is an important climatic factor determining weathering rates and that fertile sites have greater potential to release base cations through weathering and sequester c to mineral surfaces than do poor sites

a method for determining the normative mineralogy of tills a new computer program norma was developed for calculating the normative mineral composition of till from analytical data the norma program manipulates concentrations of elements totally dissolved by hot aqua regia and total element concentrations measured by either total dissolution or x ray fluorescence method minerals dissolving in aqua regia are presumed to be trioctahedral micas biotite clay minerals chlorite and primary and secondary salts and hydroxyoxides the abundances of the main silicates quartz k feldspar albite anorthite and hornblende and resistant oxides ilmenite magnetite are determined by subtracting the concentrations of elements soluble in aqua regia from the element concentrations of the total analyses norma gave a reliable distribution of the main minerals in reconnaissance scale till sampling in finland

sediment transport time measured with u series isotopes results from odp north atlantic drift site 984 abstract high precision uranium isotope measurements of marine clastic sediments are used to measure the transport and storage time of sediment from source to site of deposition the approach is demonstrated on fine grained late pleistocene deep sea sediments from ocean drilling program site 984a on the bjorn drift in the north atlantic the sediments are siliciclastic with up to 30 carbonate and dated by 18o of benthic foraminifera nd and sr isotopes indicate that provenance has oscillated between a proximal source during the last three interglacial periods volcanic rocks from iceland and a distal continental source during glacial periods an unexpected finding is that the 234u 238u ratios of the silicate portion of the sediment isolated by leaching with hydrochloric acid are significantly less than the secular equilibrium value and show large and systematic variations that are correlated with glacial cycles and sediment provenance the 234u depletions are inferred to be due to recoil loss of 234th and are used to calculate comminution ages of the sediment the time elapsed between the generation of the small 50 m sediment grains in the source areas by comminution of bedrock and the time of deposition on the seafloor transport times the difference between comminution ages and depositional ages vary from less than 10 ky to about 300 to 400 ky for the site 984a sediments long transport times may reflect prior storage in soils on continental shelves or elsewhere on the seafloor transport time may also be a measure of bottom current strength during the most recent interglacial periods the detritus from distal continental sources is diluted with sediment from iceland that is rapidly transported to the site of deposition the comminution age approach could be used to date quaternary non marine sediments soils and atmospheric dust and may be enhanced by concomitant measurement of 226ra 230th 230th 234u and cosmogenic nuclides

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

uranium series radionuclide and element migration around the sanerliu granite hosted uranium deposit in southern china as a natural analogue for high level radwaste repositories abstract the sanerliu uranium deposit located in hunan province south china has a number of features analogous to aspects considered in the performance assessment of concepts for the disposal of high level radwaste deep in granite the deposit is hosted by medium to coarse grained porphyritic granite with a rb sr isochron age of 215 2 6 3 ma the orebodies have a burial depth of more than 160 400 m under the surface of the ground the major uranium mineralizations have u pb ages pitchblende of 103 2 0 6 88 3 0 5 and 51 2 0 4 ma and a hydrothermal origin the isotopic data show that the rb sr systems in the whole rock samples of less and un fractured host granite around the orebodies have been little disturbed since the altered granite formed 132 ma ago such samples have close to secular equilibrium activity ratios for 234 u 238 u 230 th 234 u and 226 ra 230 th indicating that obvious water rock interactions have not taken place in them within the interval of at least the last 1 ma the migration of uranium thorium and most trace elements in the ores and the host granite are limited often less than 30 35 m over 51 ma the alpha activity ratios 234 u 238 u 230 th 234 u and 226 ra 230 th for the samples from the fracture zones show obvious deviations from secular equilibrium indicating the deposition of uranium during the last 1 ma and of radium during the last 10 3 yr the fracture zones are channels for groundwater flow however the migration of uranium series radionuclides along the fracture zones is limited by adsorption onto the clays this is confirmed by the absence of any hydrogeochemical indication on the ground surface of the orebodies the ores have been well preserved in a natural aquifer system without any specially designed artificial barriers the migration behavior of radionuclides in the ores of the sanerliu deposit may be termed a worse case scenario for the safety assessment of a high level radwaste disposal repository hosted by granitic rocks

sidewall crystallization in the klokken intrusion zoned ternary feldspars and coexisting minerals the syenitic layered series in the klokken intrusion is surrounded by a zone 500 m thick of nearly structureless unlaminated syenite followed outwards by a zone of vertically banded gabbro 200 m thick at the outer rim the unlaminated syenite is intrusive into the gabbro and develops a thin 2 m transition zone of syenodiorite at the contact a traverse across the vertical transition zone and inwards towards the layered series was sampled with a portable drill mafic silicates olivine clinopyroxene biotite show inward evolution in fe fe mg across the syenodiorite unlaminated syenite zones feldspars change rapidly across the syenodiorite zone from rocks dominated by plagioclase in some cases together with two alkali feldspars one a mesoperthite or cryptomesoperthite the other a cryptoperthite to rocks in which plagioclase is seen only rarely as cores to cryptomesoperthitic alkali feldspar crystals plagioclase is absent from the layered series

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

consequences of slow growth for 230th u dating of quaternary opals yucca mountain nv usa thermal ionization mass spectrometry and data are reported for uranium rich opals coating fractures and cavities within the silicic tuffs forming yucca mountain nv the potential site of a high level radioactive waste repository high uranium concentrations up to 207 ppm and extremely high activity ratios up to about 106 make microsamples of these opals suitable for precise dating conventional ages range from 40 to greater than 600 ka and initial activity ratios between 1 03 and 8 2 isotopic evidence indicates that the opals have not experienced uranium mobility however wide variations in apparent ages and initial ratios for separate subsamples of the same outermost mineral surfaces positive correlation between ages and sample weights and negative correlation between ages and calculated initial are inconsistent with the assumption that all minerals in a given subsample was deposited instantaneously the data are more consistent with a conceptual model of continuous deposition where secondary mineral growth has occurred at a constant slow rate up to the present this model assumes that individual subsamples represent mixtures of older and younger material and that calculations using the resulting isotope ratios reflect an average age ages calculated using the continuous deposition model for opals imply average mineral growth rates of less than 5 mm m y the model of continuous deposition also predicts discordance between ages obtained using different radiometric methods for the same subsample differences in half lives will result in younger apparent ages for the shorter lived isotope due to the greater influence of younger materials continuously added to mineral surfaces discordant and u pb ages obtained from outermost mineral surfaces at yucca mountain support this model

uranium series disequilibrium in tuffs from yucca mountain nevada as evidence of pore fluid flow over the last million years abstract samples of tuff from boreholes drilled into fault zones in the exploratory studies facility esf and relatively unfractured rock of the cross drift tunnels at yucca mountain nevada have been analysed by u series methods this work is part of a project to verify the finding of fast flow paths through the tuff to esf level indicated by the presence of bomb 36cl in pore fluids secular radioactive equilibrium in the u decay series i e when the radioactivity ratios 234u 238u 230th 234u and 226ra 230th all equal 1 00 might be expected if the tuff samples have not experienced radionuclide loss due to rock water interaction occurring within the last million years however most fractured and unfractured samples were found to have a small deficiency of 234u weighted mean 234u 238u 0 95 0 01 and a small excess of 230th weighted mean 230th 234u 1 10 0 02 the 226ra 230th ratios are close to secular equilibrium weighted mean 0 94 0 07 these data indicate that 234u has been removed from the rock samples in the last 350 ka probably by pore fluids within the precision of the measurement it would appear that 226ra has not been mobilized and removed from the tuff although there may be some localised 226ra redistribution as suggested by a few ratio values that are significantly different from 1 0 because both fractured and unfractured tuffs show approximately the same deficiency of 234u this indicates that pore fluids are moving equally through fractured and unfractured rock more importantly fractured rock appears not to be a dominant pathway for groundwater flow otherwise the ratio would be more strongly affected and the th and ra isotopic ratios would likely also show disequilibrium application of a simple mass balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at esf level is about 400 a processes of u sorption precipitation and re solution are believed to be occurring and would account for these anomalous results but have not been included in the model despite the difficulties the u series data suggest that fractured rock specifically the sundance and drill hole wash faults are not preferred flow paths for groundwater flowing through the topopah spring tuff and by implication rapid flow within 50 a from the surface to the level of the esf is improbable

the use of natural analogues to assess radionuclide transport abstract predicting the long term safety and performance of a repository for intermediate to high level radioactive wastes requires the evaluation of various scenarios which may influence the integrity of the repository system one such scenario radionuclide transport is described and some of the geochemical processes which serve to enhance or retard transport are illustrated with examples selected from natural analogue or natural system studies these studies as distinct from laboratory simulations help considerably in understanding how near and far field radionuclide transport mechanisms work over geological timescales thousands to hundreds of thousands of years more in line with the anticipated lifespan of a repository processes addressed include stability of the spent fuel uo 2 matrix bentonite backfill as a barrier to radionuclide diffusion retention of radionuclides by absorption on fracture minerals transport and diffusion of radionuclides controlled by interconnected bedrock porosity geochemical influence and behaviour of repository construction materials on radionuclide transport

the hydromagnesite playas of atlin british columbia canada a biogeochemical model for co2 sequestration abstract anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide co2 through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals the hydromagnesite mg5 co3 4 oh 2 4h2o playas of atlin british columbia canada provide a natural model to examine mineral carbonation on a watershed scale at near surface conditions co2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals the purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for co2 sequestration with emphasis on microbial processes that accelerate mineral carbonation regions with ultramafic bedrock such as atlin represent the best potential sources of feedstocks for mineral carbonation elemental compositions of a soil profile show significant depletion of mgo and enrichment of sio2 in comparison to underlying ultramafic parent material polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years upon retrieval the cube surfaces as seen using scanning electron microscopy had been colonized by bacteria that were associated with surface pitting degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium rich bedrock at atlin stable carbon isotopes of groundwater from a well situated near a wetland in the southeastern playa indicate that 12 of the dissolved inorganic carbon has a modern origin from soil co2 the mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments 1 the wetland characterized by biologically aided precipitation of carbonate minerals from waters concentrated by evaporation 2 isolated wetland sections that lead to the formation of consolidated aragonite sediments and 3 the emerged grassland environment where evaporation produces mounds of hydromagnesite examination of sediments within the southeastern playa wetland suggests that cyanobacteria sulphate reducing bacteria and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals the atlin site as a biogeochemical model has implications for creating carbon sinks that utilize passive microbial geochemical and physical processes that aid in mineral carbonation of magnesium silicates these processes could be exploited for the purposes of co2 sequestration by creating conditions similar to those of the atlin site in environments artificial or natural where the precipitation of magnesium carbonates would be suitable given the vast quantities of mg rich bedrock that exist throughout the world this study has significant implications for reducing atmospheric co2 concentrations and combating global climate change

kiglapait mineralogy v feldspars in a hot dry magma the lithology of the 1 305 ga kiglapait intrusion is dominated by a lower zone of troctolite succeeded by an upper zone of olivine gabbro ferrodiorite and syenite with olivine composition of pure fayalite the feldspar composition of the intrusion varies from an 68 to an 9 over a thickness of 8 4 km from the base to a sandwich horizon under an upper border zone the anhydrous nature of the kiglapait syenites is shown by their high temperature by the loss of minor biotite up stratigraphy in the intrusion and the absence of amphibole the end stage feldspar of the kiglapait syenites is that of a solidus embedded in a solvus in a 3 kbar eutectic at 1000 c the end member assemblage at temperature and pressure is invariant the final bulk composition is relatively an rich an 11 with a composition of x or 1 3 when projected to the ab or sideline the experimental feldspar solvus when corrected for the effects of an and ba and referred to 3 kbar penetrates the solidus and fits the experimental tie lines these conditions precede a stage of local coarsening under subsolidus conditions that is found in colloform symplectites invading mesoperthite the oligoclase orthoclase symplectites are iso compositional with their host mesoperthites the coarsening is assumed to be related to a plausibly f rich vapor phase that is locally consumed with time the observed phase compositions indicate the end of exsolution at 800 c at 3 kbar on the binodal solvus

234u 238u evidence for local recharge and patterns of ground water flow in the vicinity of yucca mountain nevada usa uranium concentrations and 234u 238u ratios in saturated zone and perched ground water were used to investigate hydrologic flow and downgradient dilution and dispersion in the vicinity of yucca mountain a potential high level radioactive waste disposal site the u data were obtained by thermal ionization mass spectrometry on more than 280 samples from the death valley regional flow system large variations in both u concentrations commonly 0 6 10 g l 1 and 234u 238u activity ratios commonly 1 5 6 are present on both local and regional scales however ground water with 234u 238u activity ratios from 7 up to 8 06 is restricted largely to samples from yucca mountain data from ground water in the tertiary volcanic and quaternary alluvial aquifers at and adjacent to yucca mountain plot in 3 distinct fields of reciprocal u concentration versus 234u 238u activity ratio correlated to different geographic areas ground water to the west of yucca mountain has large u concentrations and moderate 234u 238u whereas ground water to the east in the fortymile flow system has similar 234u 238u but distinctly smaller u concentrations ground water beneath the central part of yucca mountain has intermediate u concentrations but distinctive 234u 238u activity ratios of about 7 8 perched water from the lower part of the unsaturated zone at yucca mountain has similarly large values of 234u 238u these u data imply that the tertiary volcanic aquifer beneath the central part of yucca mountain is isolated from north south regional flow the similarity of 234u 238u in both saturated and unsaturated zone ground water at yucca mountain further indicates that saturated zone ground water beneath yucca mountain is dominated by local recharge rather than regional flow the distinctive 234u 238u signatures also provide a natural tracer of downgradient flow elevated 234u 238u in ground water from two water supply wells east of yucca mountain are interpreted as the result of induced flow from 40 a of ground water withdrawal elevated 234u 238u in a borehole south of yucca mountain is interpreted as evidence that natural downgradient flow is more likely to follow southerly paths in the structurally anisotropic tertiary volcanic aquifer where it becomes diluted by regional flow in the fortymile system