the role of magma mixing in the petrogenesis of mafic alkaline lavas rockeskyllerkopf volcanic complex west eifel germany the quaternary rockeskyllerkopf volcanic complex rvc comprises three spatially and temporally distinct volcanic centers that can also be distinguished on the basis of their geochemical signatures all the volcanic products in the complex are olivine basanites whose major and trace element compositions span almost the entire range defined for the west eifel field as a whole the rvc lavas have lower al2o3 na2o and y contents and higher tio2 cao k2o sc v co rb and ba than the tertiary lavas in nearby hocheifel volcanic field within the complex the oldest south east lammersdorf center sel comprises primitive lavas with an average mgo content of 11 wt and lan ybn of 29 2 the second center mauseberg has similar mgo to sel but is distinct in its much higher lan ybn of 42 2 the rockeskyllerkopf center which was erupted after a break in activity comprises lavas similar in composition to the sel center but with distinctly higher al2o3 and lower mgo contents given the lack of evidence for significant fractionation or assimilation in the rvc lavas we attribute the compositional variations within and between the centers of the rvc to be due to variations in the composition of the source region in combination with magma mixing our preferred model involves 1 5 partial melting of lree enriched mantle in the garnet stability field likely within the thermal boundary layer at the base of the lithospheric mantle these melts mixed to variable degrees with 2 4 partial melts of phlogopite spinel peridotite formed at higher levels in the modally metasomatised lithospheric mantle

analysis of high pressure fluid flow in fractures with application to yucca mountain nevada slug test data abstract increases in water pressure if large enough can be sufficient to open existing fractures in a fractured rock water system such large water pressure increases are expected during earthquake activity and are also produced artificially in high pressure hydraulic fracturing and slug injection tests in an in situ slug injection test the slug of water is initially released into a packed off interval of the borehole where the contained fluid is at ambient pressures we recognize three separate stages in the behaviour of the fracture as the water pressure decreases due to drainage namely opening closing and finally completely closed in the first stage the water will initially drain out along conduits between the faces of the opening fracture as the fracture opens and grows it can become long enough to intersect any pre existing network of open joints and fractures if this connection occurs the opened fracture will stop growing and there will be further rapid flow of fluid out along these open conduits even if connection to an open conduit does not occur as the pressure drops the fracture will stop growing and eventually halt at the pressure where the fracture tip begins to close drainage into any open conduits will cease and drainage during fracture closing will thus be by flow into the porous walls of the fracture and borehole this effect of the conduit being shut off may manifest as a kink in the observed height decay of the slug at this pressure due to the effect of the different drainage terms as the water pressure decreases the fracture will continue to close until the water pressure drops below the critical pressure and the fracture becomes completely closed this total closure occurs at the same pressure as that necessary to re open the fracture and has been taken equal to the minimum principal stress this total closure of the fracture also may manifest as a kink in the observed height decay of the slug as below this closure pressure is the third and final stage where drainage is at the usual low pressures controlled by the permeability of the rock just around the packed off interval of the borehole we develop the most general mathematical model for this phenomenon using conservation of mass of the water in the borehole fracture system for each separate pressure stage this model of fracture behaviour with separate flow stages and pressure regimes explains the physical basis for the increasingly used technique in high pressure injection tests of measuring the so called re opening pressure at the sharp change in slope of the rate of change of water height vs height analytic and numerical solutions yield the rate at which the water height drops during the slug test and comparison with high pressure test data confirms the accuracy of the model analysis of data from yucca mountain nevada gives values for the fracture opening pressures that indicate the presence of extensional stresses of significant magnitude and of zones of pre existing open fracture networks in the vicinity of the proposed repository site

eruption processes and deposit characteristics at the monogenetic mt gambier volcanic complex se australia implications for alternating magmatic and phreatomagmatic activity the 5 ka mt gambier volcanic complex in the newer volcanics province australia is an extremely complex monogenetic volcanic system that preserves at least 14 eruption points aligned along a fissure system the complex stratigraphy can be subdivided into six main facies that record alternations between magmatic and phreatomagmatic eruption styles in a random manner the facies are 1 coherent to vesicular fragmental alkali basalt effusive hawaiian spatter and lava flows 2 massive scoriaceous fine lapilli with coarse ash strombolian fallout 3 bedded scoriaceous fine lapilli tuff violent strombolian fallout 4 thin medium bedded undulating very fine lapilli in coarse ash dry phreatomagmatic surge modified fallout 5 palagonite altered cross bedded medium lapilli to fine ash wet phreatomagmatic base surges and 6 massive palagonite altered very poorly sorted tuff breccia and lapilli tuff phreato vulcanian pyroclastic flows since most deposits are lithified to quantify the grain size distributions gsds image analysis was performed the facies are distinct based on their gsds and the fine ash to coarse fine ash ratios these provide insights into the fragmentation intensities and water magma interaction efficiencies for each facies the eruption chronology indicates a random spatial and temporal sequence of occurrence of eruption styles except for a magmatic horizon of effusive activity occurring at both ends of the volcanic complex simultaneously the eruption foci are located along nw se trending lineaments indicating that the complex was fed by multiple dykes following the subsurface structures related to the tartwaup fault system possible factors causing vent migration along these dykes and changes in eruption styles include differences in magma ascent rates viscosity crystallinity degassing and magma discharge rate as well as hydrological parameters

influences of human activities on sediment discharge from devastated weathered granite hills of southern china effects of 4 year elimination of human activities abstract sediment discharge is a serious problem in the weathered granite mountains of southern china human activities such as the harvesting of ferns and litter for fuel are the main source of sediment but the details of the processes and mechanisms leading to sediment discharge are unclear data on sediment yields percentages of peak storm runoff and fern undergrowth and litter cover extent in the two basins one a control from which people have been excluded since 1997 and the other where normal harvesting practices are permitted were used to evaluate how human activity affects sediment discharge the annual sediment discharge decreased immediately after implementing control practice despite no marked changes in the 4 years after 1997 in the percentages of peak storm turnoff and the fern and litter cover extent and density the 4 year period of control practice was too short to affect the relationship between peak rainfall and peak storm runoff and the fern and litter covers and their amounts but long enough to contribute to the reductions in sediment discharge in the control basin by decreasing erodibility thus sediment discharge was probably reduced to some extent by the elimination of human impacts even though a well developed vegetation layer did not develop

drivers of explosivity and elevated hazard in basaltic fissure eruptions the 1913 eruption of ambrym volcano vanuatu sw pacific abstract fissure eruptions along linear structures can extend for several tens of kilometres with distinct separate manifestations of volcanism along their length they typically involve low viscosity mafic magmas forming long lava flows and cinder cones eruptions in 1894 and 1913 on ambrym volcano vanuatu showed how these mildly explosive eruptions can rapidly transform into violent explosive events producing significant hazard and widespread volcanic ash clouds during the 1913 episode a fissure began in the central caldera and basaltic magmas broke out in a series of locations down the island s western flank in all sites over 100 m in elevation fissure outbreaks produced vigorous lava fountains and highly fluid lava flows that travelled rapidly to the shoreline when the outbreaks propagated along the island s axis into coastal plain areas a climactic series of explosive eruptions occurred producing a 1 2 km long by 600 m wide maar and tephra ring a further small tuff ring was formed later creating a temporary island 400 m offshore the onshore tephra ring destroyed a hospital and associated buildings its last evacuating occupants were close witnesses to the eruption processes deposits exposed in the lower portion of the tephra ring show that this part of the eruption began with a mild phreatomagmatic explosive eruption from a narrow vent followed by a magmatic scoria producing phase subsequently a complex sequence of highly explosive phreatomagmatic eruptions occurred producing pyroclastic surges along with repeated distinctive breccia horizons rich in coral and lava country rock these features tally with eye witness accounts to indicate that the main eruption phase was produced by a periodically shifting locus of phreatomagmatic fragmentation and eruption along a single e w fissure the glassy and vesicle poor pyroclasts produced during this eruption phase were dominantly fragmented in a brittle manner by magma water interaction low volatile content of the magma upon fragmentation is confirmed by ftir analysis showing

the geohydrologic setting of yucca mountain nevada abstract this paper provides a geologic and hydrologic framework of the yucca mountain region for the geochemical papers in this volume the regional geologic units which range in age from late precambrian through holocene are briefly described yucca mountain is composed of dominantly pyroclastic units that range in age from 11 4 to 15 2 ma the principal focus of study has been on the paintbrush group which includes two major zoned and welded ash flow tuffs separated by an important hydrogeologic unit referred to as the paintbrush non welded ptn the regional structural setting is currently one of extension and the major local tectonic domains are presented together with a tectonic model that is consistent with the known structures at yucca mountain streamflow in this arid to semi arid region occurs principally in intermittent or ephemeral channels near yucca mountain the channels of fortymile wash and amargosa river collect infrequent runoff from tributary basins ultimately draining to death valley beneath the surface large scale interbasin flow of groundwater from one valley to another occurs commonly in the region regional groundwater flow beneath yucca mountain originates in the high mesas to the north and returns to the surface either in southern amargosa desert or in death valley where it is consumed by evapotranspiration the water table is very deep beneath the upland areas such as yucca mountain where it is 500 750 m below the land surface providing a large thickness of unsaturated rocks that are potentially suitable to host a nuclear waste repository the nature of unsaturated flow processes which are important for assessing radionuclide migration are inferred mainly from hydrochemical or isotopic evidence from pneumatic tests of the fracture systems and from the results of in situ experiments water seeping down through the unsaturated zone flows rapidly through fractures and more slowly through the pores of the rock matrix although capillary forces are expected to divert much of the flow around repository openings some may drip onto waste packages ultimately causing release of radionuclides followed by transport down to the water table

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

petrology and geochronology of metamorphosed volcanic rocks and a middle cretaceous volcanic neck in the east central sierra nevada california metamorphosed mesozoic volcanic rocks from the east central sierra nevada range in composition from basalt to rhyolite and have ages based on whole rock rb sr and u pb zircon dating of about 237 224 185 163 134 and 100 m y the major plutons of the batholith in this area are of triassic 215 200 m y and cretaceous 94 80 m y ages initial 87sr 86sr values for the metamorphosed volcanic rocks of the area are in the range from 0 7042 to 0 7058 and are generally different from the values for the surrounding batholithic rocks 0 7056 0 7066 a circular zoned granitic pluton with an outcrop area of 2 5 km2 similar in appearance to a ring dike complex was apparently a conduit for some or possibly all of the middle cretaceous metamorphosed volcanic rocks exposed about 5 km to the south in the western part of the ritter range samples from the metamorphosed volcanic rocks and the pluton yield a rb sr whole rock isochron age of 99 9 2 2 m y with an initial 87sr 86sr of 0 7048 0 0001 major element variation diagrams of the pluton and volcanic rocks define coincident compositional trends the pluton intruded into early jurassic metamorphosed volcanic rocks rb sr whole rock isochron age of 185 6 m y initial 87 86sr 0 70474 0 00009 is composed of a central body of granite that is intruded into and almost completely surrounded by a crescent shaped outer rim of quartz monzodiorite contact relations between the granitic rocks intrusive in some places and completely gradational at other places indicate that the quartz monzodiorite was not completely crystallized prior to the intrusion of the granite modal minerology within the pluton is also consistent with this inferred crystallization history the granitic rock textures are cataclastic characterized by a groundmass of feldspar and quartz that surrounds larger grains of feldspar hornblende and biotite widely spaced aplite dikes from the granite intrude the quartz monzodiorite along the contact between the granitic rocks the aplite dikes and interstitial alkali feldspar associated with myrmekite in the pluton being undeformed indicate crystallization of a small amount of silicate liquid after cataclasis aplite compositions suggest a minimum crystallization pressure of 0 5 kb 1 2 km this depth is consistent with crystallization near the base of a large stratovolcano the pluton is characterized by steep linear features defined by mineral clots and inclusions that probably formed during the upward movement of the nearly crystallized magma in the volcanic conduit the ages of volcanic events relative to the ages of the major intrusive epochs and the major element and isotopic compositions of the volcanic rocks relative to the major plutons indicate that the volcanic rocks are not simply or directly related to the major plutons in the sierra nevada

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

improved spatial resolution for u series dating of opal at yucca mountain nevada usa using ion microprobe and microdigestion methods two novel methods of in situ isotope analysis ion microprobe and microdigestion were used for 230th u and 234u 238u dating of finely laminated opal hemispheres formed in unsaturated felsic tuff at yucca mountain nevada proposed site for a high level radioactive waste repository both methods allow analysis of layers as many as several orders of magnitude thinner than standard methods using total hemisphere digestion that were reported previously average growth rates calculated from data at this improved spatial resolution verified that opal grew at extremely slow rates over the last million years growth rates of 0 58 and 0 69 mm m y were obtained for the outer 305 and 740 m of two opal hemispheres analyzed by ion microprobe and 0 68 mm m y for the outer 22 m of one of these same hemispheres analyzed by sequential microdigestion these pleistocene growth rates are 2 to 10 times slower than those calculated for older secondary calcite and silica mineral coatings deposited over the last 5 to 10 m y dated by the u pb method and may reflect differences between miocene and pleistocene seepage flux the microdigestion data also imply that opal growth rates may have varied over the last 40 k y these data are the first indication that growth rates and associated seepage in the proposed repository horizon may correlate with changes in late pleistocene climate involving faster growth during wetter cooler climates glacial maximum slower growth during transition climates and no growth during the most arid climate modern data collected at this refined spatial scale may lead to a better understanding of the hydrologic variability expected within the thick unsaturated zone at yucca mountain over the time scale of interest for radioactive waste isolation

water and sediment yield from a small catchment in the hilly granitic region south china abstract shenchong experimental basin is located in subtropical deqing county in the hilly region of south china it has a catchment area of 0 73 km2 and is underlain by granitic rocks with a weathering mantle of about 30 m water and sediment yield were monitored at the basin outlet and at a location about 230 m upstream such that the section between the two stations coincides with the concentration of large gullies these gullies produce most of the sediment yield of the basin and the pattern of sediment discharge mirrors that of rainfall however gullies contribute comparatively little runoff to the basin outflow other surface types including bare slopes bare rills and the valley floor together yield considerable runoff because of their large areal coverage

hot dry rock geothermal energy in the jemez volcanic field new mexico abstract large young calderas possess immense geothermal potential due to the size of shallow magma bodies that underlie them through the example of the valles and toledo calderas new mexico and older more deeply eroded and exposed calderas it is possible to reconstruct a general view of geothermal environments associated with such magmatic systems although a zone of anomalous heat flow extends well beyond caldera margins high to moderate temperature hydrothermal systems appear to be restricted to zones along intracaldera faults and may account for only about five percent of the thermal energy available from the magmatic system much of the remaining thermal energy resides within caldera fill and basement rocks under and along the flanks of the caldera and can only be extracted by manmade geothermal systems depending upon the age and cooling history considerable thermal energy may still reside in crystallizing magma

stable isotopic evidence for a pedogenic origin of carbonates in trench 14 near yucca mountain nevada layered carbonate and silica encrust fault fractures exposed in trench 14 near yucca mountain site of the proposed high level nuclear waste repository in southern nevada comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely formed in the presence of vegetation and rainfall typical of a glacial climate their isotopic composition differs markedly from that of carbonate associated with nearby springs the regional water table therefore remained below the level of trench 14 during the time that the carbonates and silica precipitated a period probably covering parts of at least the last 300 000 years

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

comparison of soil physicochemical properties and mineralogical compositions between noncollapsible soils and collapsed gullies abstract this study aimed to compare soil physicochemical properties and mineralogical compositions including the cohesive force and internal friction angle using direct shear tests with designed water contents and temperatures between noncollapsible soil and collapsed gullies two pedons were collected from longmen town anxi county fujian province with severely collapsed gullies that developed from granitic rocks and another two pedons were collected from metamorphic regions gande town without soil erosion the samples were subjected to x ray diffraction xrd analysis and their soil physicochemical properties were compared noncollapsible soils had superior physicochemical characteristics e g these soils contained higher amounts of cations especially total iron oxides fet furthermore noncollapsible soils were able to resist shearing due to their greater cohesive force and the internal friction angle did not differ considerably from that of the collapsed soils kaolinite illite hydroxy interlayered vermiculite hiv and gibbsite were the dominant clay minerals in the noncollapsible soils however in the collapsed soils kaolinite accounted for 85 of the total clay mineral composition the cohesive force and internal friction angle were significantly correlated with sesquioxides of all non collapsible and collapsed pedons such as fed free fe oxides 0 762 0 637 and total iron fet 0 783 0 708 as well as magnetic susceptibility 0 650 0 740 p

origin of temporal compositional variations during the eruption of lake purrumbete maar newer volcanics province southeastern australia the pleistocene lake purrumbete maar eruption sequence of the newer volcanics province of southeastern australia records stratigraphic temporal and geochemical variations that cannot be explained by crustal processes such as fractional crystallisation and crustal contamination samples from the lake purrumbete maar have distinct trace element trends that correlate with stratigraphic height with decreasing incompatible element concentrations from the bottom of the sequence to the top indicating that the most enriched melts were ejected during the earliest eruption stages with the least enriched melts erupted in the final stages variations in rare earth element ratios indicate that these melts were formed by dynamic melting of garnet lherzolite mantle material consistent with other volcanic centres within the basaltic cones subprovince of the newer volcanics province the geochemistry of the erupted units at lake purrumbete also record minor differentiation of the melts by olivine fractionation although these processes alone cannot explain the observed geochemical variations in the eruption sequence further differentiation of the melts by different processes such as deep clinopyroxene fractionation or assimilation of metasomatised lithosphere may be responsible for the observed geochemical trends at lake purrumbete this shows the complexity of the plumbing system of monogenetic volcanoes but also shows the opportunities that these volcanoes provide to study these processes in detail as the geochemical variations that are preserved in this type of volcanism by fast magma ascent through the crust as evidenced by the presence of fresh mantle xenoliths predominantly reflect processes that occurred in the mantle rather than in the crust

traces of epigenetic hydrothermal activity at yucca mountain nevada preliminary data on the fluid inclusion and stable isotope evidence samples of opal quartz calcite crusts from the 7 8 km long tunnel excavated under yucca mountain were studied to determine their origin calcite in these crusts commonly forms relatively large up to 1 5 cm euhedral crystal terminations in some crusts layers of chalcedony and patches of opal alternate with calcite layers chalcedony commonly grades into euhedral quartz crystals quartz also forms microdruses of individual crystals up to 8 mm in size fluorite was identified in four samples fluid inclusion studies on calcite revealed formation temperatures of 35 85 c gas filled inclusions are apparently of low density p 1 bar at room temperature and contain aromatic hydrocarbons in four studied calcite samples values of 18o remain virtually constant across crusts 10 6 to 12 1 v pdb in one sample the earliest part of calcite had 18o of 19 in this part of the sample the highest fluid inclusion temperatures 70 85 c were measured the secondary calcite found at yucca mountain is commonly interpreted as being formed through a pedogenic process from rain waters percolating in the vadose zone and carrying dissolved carbonate from overlying soils e g stuckless j s peterman z e muchs d r 1991 u and sr isotopes in ground water and calcite yucca mountain nevada evidence against upwelling water science 254 551 554 nas nrc 1992 ground water at yucca mountain how high can it rise national academy press washington dc roedder e whelan j f vaniman d t 1994 fluid inclusion studies of calcite veins from yucca mountain nevada tuffs environment of formation high level radioactive waste management proc int conf am nucl soc la grande park il pp 1854 1860 our data indicate that the calcite opal quartz with minor fluorite crusts from the presently unsaturated vadose zone of yucca mountain were formed from low temperature hydrothermal aqueous fluids in the saturated phreatic environment the issue has direct bearing on the suitability of yucca mountain as a site for permanent geological disposal of the high level nuclear waste

quantification of unsaturated zone alteration and cation exchange in zeolitized tuffs at yucca mountain nevada usa abstract zeolitized horizons in the unsaturated zone uz at yucca mountain nevada usa are an important component in concepts for a high level nuclear waste repository at this site the use of combined quantitative x ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open system zeolitization at yucca mountain this approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange mass balance analysis of zeolitized horizons with extensive cation exchange drill hole uz 16 and with only minimal cation exchange drill hole sd 9 shows that al is essentially immobile although zeolitization occurred in an open system the mass transfer of constituents other than water is relatively small in initial zeolitization in contrast to the larger scales of cation exchange that can occur after zeolites have formed cation exchange in the clinoptilolite mordenite zeolitized horizons is seen in downward diminishing concentration gradients of ca mg and sr exchanged for na and to lesser extent k comparison with data from drill hole sd 7 which has multiple zeolitized horizons above the water table shows that the upper horizons accumulate ca mg and sr to such an extent that transport of these elements to the deepest uz zeolitized horizon can be blocked quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site such analysis also yields information not provided by or contradicted by some models of flow and transport the results include the following 1 evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons 2 evidence that alkaline earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils 3 validation of the very effective operation of unsaturated zeolitic horizons as cation exchange barriers 4 independent support of models that indicate average water infiltration rates of 5 mm yr over the past 10 ma and 5 evidence that the presence or absence of cation exchange profiles can be used to identify those portions of the site where transport through the uz is concentrated this last point is relevant to repository design because a knowledge of where transport takes place can be used to advantage in defining the boundaries of a repository such that high flux portions of the site can be avoided

spatial analysis of an intra plate basaltic volcanic field in a compressional tectonic setting south eastern australia abstract the newer volcanics province nvp is a pliocene to recent intra plate basaltic volcanic field bvf that has formed in a compressive tectonic setting v

granite residual soil properties in collapsing gullies of south china spatial variations and effects on collapsing gully erosion abstract collapsing gully erosion a special erosion phenomenon in the hilly granitic regions is an important factor responsible for the deterioration of the ecological environment in southern china the granite residual soil properties tend to vary with soil depth and their spatial variations have an important impact on the formation and development of collapsing gullies here two typical granitic soil profiles in the north boundary of collapsing gully erosion in south china were selected to investigated the spatial variations of soil physicochemical hydraulic and mechanical properties along the profile and their influences on collapsing gully erosion the upper two soil layers surface soil layer and red soil layer were significantly different from the lower two soil layers sandy soil layer and detritus layer in the investigated properties the soil texture performed a large variation along the profile which might be a positive factor for the formation of secondary vertical joints faults and weak structural planes meanwhile the lower soil layers had a lower value of pl ll organic matter and iron aluminum oxides demonstrating their poor structure and vulnerability to erosion under rainfall conditions additionally the upper soil layers had a higher water holding capacity but a lower decreasing rate in the unsaturated coefficient of permeability leading to the overburdening of the lower soil layers under rainfall conditions and the low soil layers had a low shear strength which could also lead to the sliding of the gully head and sidewall especially under saturated conditions collectively the special geological structure of the granite residual soil layers plays an important role in the occurrence and development of collapsing gully erosion the data reported in this paper may facilitate a better understanding of soil mass failure on the gully head and the collapsing gullies

overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both calcite opal deposits cod at yucca mountain were studied with respect to their regional and field geology petrology and petrography chemistry and isotopic geochemistry and fluid inclusions they were also compared with true pedogenic deposits tpd groundwater spring deposits gsd and calcite vein deposits cvd in the subsurface some of the data are equivocal and can support either a hypogene or pedogenic origin for these deposits however sr c and o isotope fluid inclusion and other data favor a hypogene interpretation a hypothesis that may account for all currently available data is that the cod precipitated from warm co2 rich water that episodically upwelled along faults during the pleistocene and which upon reaching the surface flowed downslope within existing alluvial colluvial eluvial or soil deposits being formed near or on the topographic surface the cod acquired characteristics of pedogenic deposits this subject relates to the suitability of yucca mountain as a high level nuclear waste site

gully erosion and sediment transport in a small subtropical catchment south china discharge and sediment concentration were monitored at two dams as well as gully erosion at four locations during 1988 1989 in the shenchong experimental basin 0 73 km2 located in subtropical deqing county guangdong province the temporal pattern of sediment concentration at the basin outlet is closely related to gully discharge and due to the proximity of the gully sediment source to the gauging station the hysteresis pattern at the lower dam is dominantly clockwise discharge thresholds exist in the sediment concentration discharge relationships at both the upper and the lower dams at the upper dam they are related to the presence of local wetlands which act as a buffer to sediment transport in the channel at the lower dam they result from variable sources of sediment as well as early flow cessation in gullies computation of sediment yield from gullies confirms that they accounted for over 85 of the sediment load that passed through the lower dam

effects of fractal dimension and water content on the shear strength of red soil in the hilly granitic region of southern china abstract deep residual soil formed by the long term weathering of large granite under the impact of high temperature and abundant rainfall in southern china is prone to instability and deformation which has caused a large number of collapsing gullies in this study five different soil grading ratios and five water contents were employed to systematically investigate the effects of the soil fractal dimension and water content on the red soil shear strength the soil fractal dimension increased with soil fine particle content clay and silt the soil saturated hydraulic conductivity ks decreased with the soil fractal dimension whereas the soil air entry value and residual water content r showed a positive relationship with the fractal dimension shearing tests showed that the soil shear strength increased with normal stress but decreased with the soil water content this reduction in the soil shear strength caused by the increasing water content was more notable for the soil with a lower fractal dimension analyses of the main effect tests showed that the water content presented greater effects on the soil cohesion and friction angle than the soil fractal dimension a stepwise regression analysis showed that a linear relationship occurred between soil matric suction and soil cohesion average r 0 981 and p 004 or friction angle average r 0 951 and p 016 for the same matric suction the soil cohesion and friction angles decreased with the soil fractal dimension and the relationship between the soil fractal dimension with the soil cohesion r 0 951 and p 013 and friction angles r 0 922 and p 026 could be described by logarithmic functions soil fractal dimensions influenced both the soil hydraulic properties and shear strength parameters and the overall effects of fine particles loss would decrease the shear strength of gully red soil

the temporal evolution of three magmatic systems in the west eifel volcanic field germany abstract the quaternary west eifel volcanic field is the surface expression of a mantle plume that is thought to contain 1 melt the volcanoes range in age from 0 7 ma to 10 000 yr bp and the average recurrence rate of volcanism is around 3 5 10 4 eruptions per year giving a mean time between eruptions of 2875 years assuming that the field is monogenetic the presence of mafic and ultramafic xenoliths is taken as evidence for rapid single stage emplacement of magmas at velocities around 0 5 km h however the presence of clinopyroxene that preserves evidence of polybaric crystallisation belies this simple model this study uses variations in the fo content of olivine in mantle derived xenoliths and in olivine xenocrysts enclosed in cumulate xenoliths to calculate the time scale of evolution of three volcanic centres in the eifel field core rim variations in olivine are interpreted to result from fe mg interdiffusion between it and a surrounding melt using experimental determinations of the interdiffusion coefficient and approximations of magma temperature contact times have been calculated using planar and radial diffusion models the three volcanic centres studied were meerfelder maar gemundener maar and baarley the cumulate xenoliths at meerfelder maar formed at a depth of 13 km and record a magma emplacement event at between 1 and 3 years prior to eruption two suites of mantle derived olivine clinopyroxenites record a further two events at 1 8 days and 3 h prior to eruption the final event is interpreted to record the eruption of this volcano and the 3 h contact time records the time required for transport of peridotite xenoliths from the mantle to surface giving an average emplacement velocity of around 15 km h the cumulate xenoliths at gemundener maar crystallised at depths of between 4 and 22 km there are four distinct events recorded by the zoned olivine grains in the clinopyroxene rich cumulates from this locality the maximum residence time is similar to that at meerfelder maar however in this case the final magma resided in the chamber for between 23 days and 2 7 months prior to eruption allowing enough time for any entrained peridotite xenoliths to be filtered out the cumulate xenoliths from the baarley locality record a much longer history than those at the other localities in this case initially peridotitic olivine has been completely re equilibrated over 175 years prior to eruption in common with the other two localities there is evidence of multiple intrusive events at depths up to 7 km prior to final eruption the duration of the final eruption event and the interpreted depth to source of the xenoliths indicate an emplacement velocity of around 3 km h the data derived from modelling of diffusion profiles in olivine from cumulate xenoliths indicate that the magmatic systems feeding these three volcanoes were dynamic and very short lived in addition these data can be used to place constraints on the rate of cumulate formation in subvolcanic magma chambers on the basis of the data presented here it would seem that an appreciable thickness of cumulates can form over relatively short time spans days to a few years

limited hydrologic response to pleistocene climate change in deep vadose zones yucca mountain nevada abstract understanding the movement of water through thick vadose zones especially on time scales encompassing long term climate change is increasingly important as societies utilize semi arid environments for both water resources and sites viewed as favorable for long term disposal or storage of hazardous waste hydrologic responses to pleistocene climate change within a deep vadose zone in the eastern mojave desert at yucca mountain nevada were evaluated by uranium series dating of finely layered hyalitic opal using secondary ion mass spectrometry opal is present within cm thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface uranium concentrations in opal fluctuate systematically between 5 and 550 g g age calibrated profiles of uranium concentration correlate with regional climate records over the last 300 000 years and produce time series spectral peaks that have distinct periodicities of 100 and 41 ka consistent with planetary orbital parameters these results indicate that the chemical compositions of percolating solutions varied in response to near surface climate driven processes however slow micrometers per thousand years relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates

ages and stable isotope compositions of secondary calcite and opal in drill cores from tertiary volcanic rocks of the yucca mountain area nevada stable isotope compositions of fracture and cavity filling calcite from the unsaturated zone of three drill cores at yucca mountain tertiary volcanic complex indicate that the water from which the minerals precipitated was probably meteoric in origin a decrease in 18 o in the calcite with depth is interpreted as being due to the increase in temperature in drill holes corresponding to an estimated average geothermal gradient of 34 per kilometer a few of the calcite samples and all of the opal samples yielded uranium series ages older than 400 000 yr although most of the calcite samples yielded ages between 26 000 and 310 000 yr the stable isotope and uranium series dates from precipitated calcite and opal of this reconnaissance study suggest a complex history of fluid movement through the volcanic pile and episodes of fracture filling predominantly from meteoric water during at least the past 400 000 yr

geochemical and c o sr and u series isotopic evidence for the meteoric origin of calcrete at solitario wash crater flat nevada usa calcite rich soils calcrete in alluvium and colluvium at solitario wash crater flat nevada usa contain pedogenic calcite and opaline silica similar to soils present elsewhere in the semi arid southwestern united states nevertheless a ground water discharge origin for the solitario wash soil deposits was proposed in a series of publications proposing elevation dependent variations of carbon and oxygen isotopes in calcrete samples discharge of ground water in the past would raise the possibility of future flooding in the unsaturated zone at yucca mountain nevada site of a proposed high level nuclear waste repository new geochemical and carbon oxygen strontium and uranium series isotopic data disprove the presence of systematic elevation isotopic composition relations which are the main justification given for a proposed ground water discharge origin of the calcrete deposits at solitario wash values of 13c 4 1 to 7 8 per mil 18o 23 8 17 2 87sr 86sr 0 71270 0 71146 and initial 234u 238u activity ratios of about 1 6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits at yucca mountain and are incompatible with a ground water origin for the calcrete variations in carbon and oxygen isotopes in solitario wash calcrete likely are caused by pedogenic deposition from meteoric water under varying quaternary climatic conditions over hundreds of thousands of years

structure and stratigraphy beneath a young phreatic vent south inyo crater long valley caldera california an 861 m long hole has been cored on a slanted trajectory that passed directly beneath south inyo crater in the west moat of long valley caldera california the purpose of the hole was to investigate the magmatic behavior that led to surface deformation and phreatic activity during the 600 year old eruption of the inyo vent chain the hole was sited 216 m southwest of the crater passed beneath its center at a depth of 566 m and terminated 79 m northeast of the crater center at a depth of 810 m metamorphic basement was encountered at a depth of 779 m the volcanic and sedimentary sequence consists solely of post bishop tuff caldera fill including 319 m of moat basalt and 342 m of early rhyolite and is nearly 900 m thinner than in a unocal corporation well 900 m to the southeast apparently a major fault lies between the two holes and forms part of the western structural boundary of the caldera 3 4 km inboard of its topographic boundary breccia zones that intrude the caldera fill were intersected at 12 0 9 3 m and 1 2 0 8 m sw and 8 5 25 1 m ne of the crater center the largest breccia unit is symmetrically zoned from margins rich in vesicular rhyolite and locally derived rhyolite wall rock with most clasts 0 1 m to a center of up to 50 vol basalt with individual basalt clasts to 1 m in intersected length the basalt appears to be an early feeder for the moat basalt sequence the vesicular rhyolite is chemically distinct from both the rhyolite wall rock and previously recognized 600 year old inyo eruptives but matches fresh appearing pyroclasts in the crater ejecta this component of the breccia is therefore interpreted as representing juvenile magma that vesiculated and fragmented as it rose along the margins of an older basalt intrusion during this process wall rock fragments were ejected from depths extending to at least 800 m progression to a magmatic eruption was probably prevented by rapid influx of groundwater into the feeder the chemical data do not support the hypothesis that a single simple dike exists under the entire segment of the inyo chain that was active 600 years ago if such a dike exists it apparently tapped different magma chambers along its 10 km length the excess of surface extension over that needed to accommodate the intruded juvenile material may reflect the presence of a larger intrusion at depth below the level of fragmentation or the contribution of tectonic activity to the surface deformation

a sr isotopic comparison between thermal waters rocks and hydrothermal calcites long valley caldera california abstract the 87 sr 86 sr values of thermal waters and hydrothermal calcites of the long valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks five thermal waters display 87 sr 86 sr of 0 7081 0 7078 but show systematically lighter values from west to east in the direction of lateral flow we believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression all types of pre syn and post caldera volcanic rocks in the west and central caldera have 87 sr 86 sr m between about 0 7060 and 0 7072 and values for sierra nevada granodiorites adjacent to the caldera are similar sierran pre intrusive metavolcanic and metasedimentary rocks can have considerably higher sr isotope ratios 0 7061 0 7246 and 0 7090 0 7250 respectively hydrothermally altered volcanic rocks inside the caldera have 87 sr 86 sr m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites 0 7068 0 7105 occupy a midrange of values between the volcanic plutonic rocks and the sierran metamorphic rocks these data indicate that the long valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks reequilibration of sr isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill

compositional evolution of magma from paricutin volcano mexico the tephra record the birth of paricutin volcano mexico in 1943 provides an unprecedented opportunity to document the development of a monogenetic cinder cone and its associated lava flows and tephra blanket three type sections provide a complete tephra record for the eruption which is placed in a temporal framework by comparing both bulk tephra and olivine phenocryst compositions to dated samples of lava and tephra our data support the hypothesis of luhr 2001 that the first four months of activity were fed by a magma batch phase 1 that was distinct from the magma that supplied the subsequent eight years of activity we further suggest that the earliest erupted vanguard magma records evidence of temporary residence at shallow levels prior to eruption suggesting early development of a dike and sill complex beneath the vent depletion of this early batch led to diminished eruptive activity in june and july of 1943 while arrival of the second magma batch phase 2 reinvigorated activity in late july phase 2 fed explosive activity from mid 1943 through 1946 although most of the tephra was deposited by the end of 1945 phase 3 of the eruption began in mid 1947 with rapid evolution of magma compositions from basaltic andesite to andesite and dominance of lava effusion the combined physical and chemical characteristics of the erupted material present a new interpretation of the physical conditions that led to compositional evolution of the magma we believe that syn eruptive assimilation of wall rock in a shallow complex of dikes and sills is more likely than pre eruptive assimilation within a large magma chamber as previously assumed we further suggest that waning rates of magma supply from the deep feeder system allowed evolved shallowly stored magma to enter the conduit in 1947 thus triggering the rapid observed change in the erupted magma composition this physical model predicts that assimilation should be observable in other monogenetic eruptions particularly those with low pressure melt inclusions and with eruption durations of months to years

flow driven soil erosion processes and the size selectivity of eroded sediment on steep slopes using colluvial deposits in a permanent gully abstract colluvial deposits with loose coarse material are easily erodible in permanent gullies but the mechanisms of erosion and sedimentation during overland flow remain obscure hence the processes and mechanisms of the transportation of soil particles by overland flow were investigated in this study experiments were carried out in a 5 0 m long by 1 0 m wide flume using colluvial deposits the slope gradient varied from 36 to 84 and the flow rate ranged from 0 72 l m 2 min 1 to 2 88 l m 2 min 1 the runoff rate and sediment yield rapidly increased with increasing overland duration runoff and sediment were highly variable when the flume was treated with a high flow rate compared with a low flow rate with the fluctuation of sediment concentration under the high flow rate usually reaching 500 g l 1 the slope gradient and overland flow rate have strong impacts on sediment transport capacity the mean flow velocity and the unit stream power can be an optimal composite force predictor for estimating sediment transport capacity experimental results also revealed that the percentage of gravel sized particles increased with increasing flow rate and slope gradient but silt and clay fractions observed opposite trend the average enrichment ratio er of gravel was usually 2 16 l m 2 min 1 the bed load transport became an important mechanism however the simulation model overestimated these values

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

u and sr isotopes in ground water and calcite yucca mountain nevada evidence against upwelling water hydrogenic calcite and opaline silica deposits in fault zones at yucca mountain nevada have created considerable public and scientific controversy because of the possible development of a high level nuclear waste repository at this location strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep seated waters the vein deposits are isotopically distinct from ground water in the two aquifers that underlie yucca mountain indicating that the calcite could not have precipitated from ground water the data are consistent with a surficial origin for the hydrogenic deposits

u pb ages of secondary silica at yucca mountain nevada implications for the paleohydrology of the unsaturated zone abstract uranium th and pb isotopes were analyzed in layers of opal and chalcedony from individual mm to cm thick calcite and silica coatings at yucca mountain nevada usa a site that is being evaluated for a potential high level nuclear waste repository these calcite and silica coatings on fractures and in lithophysal cavities in miocene age tuffs in the unsaturated zone uz precipitated from descending water and record a long history of percolation through the uz opal and chalcedony have high concentrations of u 10 to 780 ppm and low concentrations of common pb as indicated by large values of 206pb 204pb up to 53 806 thus making them suitable for u pb age determinations interpretations of u pb isotope systems in opal samples at yucca mountain are complicated by the incorporation of excess 234u at the time of mineral formation resulting in reverse discordance of u pb ages however the 207pb 235u ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0 6 and 9 8 ma for chalcedony subsamples showing normal age discordance these ages may represent minimum times of deposition typically 207pb 235u ages are consistent with the microstratigraphy in the mineral coating samples such that the youngest ages are for subsamples from outer layers intermediate ages are from inner layers and oldest ages are from innermost layers 234u and 230th in most silica layers deeper in the coatings are in secular equilibrium with 238u which is consistent with their old age and closed system behavior during the past 0 5 ma the ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the topopah spring tuff yield slow long term average growth rates of 1 to 5 mm ma these data imply that the deeper parts of the uz at yucca mountain maintained long term hydrologic stability over the past 10 ma despite significant climate variations u pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from fractures in the shallower part of the uz welded part of the overlying tiva canyon tuff indicate larger long term average growth rates up to 23 mm ma and an absence of recently deposited materials ages of outermost layers are 3 5 ma these differences between the characteristics of the coatings for samples from the shallower and deeper parts of the uz may indicate that the nonwelded tuffs ptn located between the welded parts of the tiva canyon and topopah spring tuffs play an important role in moderating uz flow

the role of vegetation in the retardation of rill erosion abstract large rills with catchment areas measuring tens to hundreds of square metres pose serious soil erosion problems to south china after deforestation has exposed the deeply weathered granitic slopes to the impacts of tropical rainstorms runoff and sediment discharges of rills respond rapidly to rainfall but compared with bare rills vegetated rills show considerably lower amounts of flow and sediment yield from unit rainfall input rainfall interception is one main reason for reduced runoff and enhanced infiltration also lowers surface flow from vegetated areas potential sediment yield from unit runoff is greatly reduced when the rills are grown with fern and this provides a far more effective mechanism for soil erosion control than the more temporary measures of installing sediment traps along the rills

reservoir processes and fluid origins in the baca geothermal system valles caldera new mexico at the baca geothermal field in the valles caldera new mexico 19 deep wells were drilled in an attempt to develop a 50 mwe megawatts electric power plant the chemical and isotopic compositions of steam and water samples have been used to indicate uniquely the origin of reservoir fluids and natural reservoir processes two distinct reservoir fluids exist at baca these fluids originate from the same deep high temperature 335 c saline 2500 mg kg cl parent water but have had different histories during upflow one fluid from wells 4 and 13 is isotopically light high in radiogenic noble gases co2 and hco3 and low in ca it has a temperature of 290 295 c and a reservoir chloride near 1900 mg kg this fluid resulted from rapid upward flow through 1 1 to 1 4 m y old bandelier tuff reservoir rocks after long residence in pre bandelier 7 m y sediments and precambrian basement rocks and 25 dilution with high altitude cold groundwater from redondo peak the other water from wells 15 19 and 24 moved slowly through the bandelier tuff and cooled conductively with minor steam loss for well 19 from 335 c to 280 260 c apparently short residence in old basement rocks has left this water with low radiogenic gases conductive cooling without mixing has kept the original chloride and relatively heavy isotope composition of the deep water the recharge to the deep parent water is not well understood but may be from lower elevation precipitation outside the valles caldera area gases are in equilibrium in all liquid reservoir fluids at near reservoir temperatures and the concentrations of atmospheric gases are similar to those of air saturated water indicating little boiling and steam loss all water solutes and gases in the reservoir fluids originate from air saturated meteoric recharge water watermineral reactions and rock leaching with the possible exception of excess 3he that must have an ultimate mantle source this gas could originate directly from magma or from leaching of intrusive volcanic rocks beneath the bandelier

source parameters of the june 29 1992 little skull mountain earthquake from complete regional waveforms at a single station the june 29 1992 m sub b 5 5 little skull mountain earthquake occurred 20 km southeast of yucca mountain within the boundaries of the nevada test site this event was recorded at a very broadband station located about 310 km to the east at kanab utah both body and surface waves from this single station were used in a grid search technique for the best fitting double couple moment tensor the technique minimizes the misfit between reflectivity generated complete synthetic seismograms and the three component displacement data via a search over the strike dip and rake of the source in the passband of 50 15 s period the grid search results in a well defined nearly pure normal mechanism with a strike of 35 degrees a dip of 54 degrees a rake of minus 87 degrees and a seismic moment of 4 1 x 10 sup 17 n m applying the same technique to the large aftershock on july 5 1992 the authors obtain a somewhat less well defined minimum with a strike of 358 degrees a dip of 36 degrees a rake of minus 177 degrees and a moment of 4 3 x 10 sup 15 n m the minimum compression axes of these mechanisms are consistent with northwest southeast extension in the basin and range 14more refs 7 figs less

high field strength element ratios in archean basalts a window to evolving sources of mantle plumes abstract in terms of high field strength element ratios nb th zr nb nb y and zr y most basalts from non arc type archean greenstones are similar to oceanic plateau basalts suggestive of mantle plume sources a large number of these basalts have ratios similar to primitive mantle composition perhaps the archean mantle was less fractionated than at present and primitive mantle comprised much of the deep mantle and made a significant contribution to mantle plumes the near absence of archean greenstone basalts similar to nmorb in composition is also consistent with a relatively unfractionated mantle in which a shallow depleted source dm was volumetrically insignificant the element ratios in basalts also indicate the existence of recycled components himu em1 em2 in the mantle by the late archean this suggests that oceanic lithosphere was recycled into the deep mantle and became incorporated in some mantle plumes by the late archean high field strength element ratios also indicate an important contribution of continental crust or and subcontinental lithosphere to some non arc archean greenstone basalts this implies that at least thin continental lithosphere was relatively widespread in the archean

deep seismic images and the tectonic framework of early rifting in the otway basin australian southern margin abstract the otway basin is one of a number of basins formed along australia s southern continental margin during the late jurassic early cretaceous rifting of australia from antarctica it lies on a transitional area of extended lithosphere between the margin to the west where continental separation took place close to the australian craton and the region to the east where separation failed to develop through bass strait but instead switched to the south of tasmania seven agso regional deep seismic profiles recorded during 1992 across onshore parts of the basin provide images of synrift basin bounding faults that dip predominantly towards the continent basin sequences in half graben rift segments at two way times greater than 4 s and mid crustal detachments with ramp and flat geometry at mid crustal levels when combined with industry seismic data trend variations on faults indicate that extensional strain direction varied along the rift system probably locally controlled by pre existing palaeozoic geology but consistent with general north south lithospheric extension basement highs between some of the rift segments are interpreted as accommodation or transfer zones multiple basin bounding faults in some places mirror features within basement and may indicate a component of local strike slip during early rifting the syn rift segments form part of the first stage early cretaceous failed rift system in the otway bass strait region crustal thickness is interpreted to be 31 km 10 3 10 5 s twt near the northern basin margin thinning to about 25 km 9 s twt 40 reduction in thickness of palaeozoic crust seaward of the tartwaup fault zone this fault zone and the timboon fault system farther east are interpreted to be headwall faults landward limit of a late cretaceous second stage rifting system along a lower plate margin which ultimately separated australia from antarctica

erosion control in south china abstract severe soil erosion is common in south china where torrential rainfall erodes the deeply weathered and denuded granitic hills locally developed control measures have been applied successfully to reduce erosion including the benching of steep slopes the construction of check dams and reforestation of particular importance is the treatment of large gullies locally called broken hills these have led to the disintegration of hillslopes and the deposition of colluvium and fines on the agricultural land gully treatment includes the stabilization of the headwalls the containment of sediments in the gully floor zone and the reclamation of flatland below the gully mouth re vegetation of the slopes is essential and the planting of economic crops provides incentive to the farmers to preserve the vegetation cover

assessing the sources of sediment transported in gully systems using a fingerprinting approach an example from south east china abstract eroded sediment is an important feature of permanent gully s development however obtaining the specific characteristics of the sediment transport in the gully can be difficult thus a composite fingerprinting technique incorporating uncertainty analysis has been employed to investigate the mean relative contribution of sediment sources in permanent gullies in this study 31 tracers were measured at 62 different sampling sites from three layers of a gully wall surface layer sl sandy soil layer ssl and semi weathering rock layer swl and 36 sediment samples from the slumping deposit and alluvial fan of the gullies the sediment source tracing procedure was therefore used to assess the relative contribution of each source the mean relative contribution from the sl to the sediment of the slumping deposit is higher in the active gully g1 and is relatively lower in the potentially stable g2 and stable gullies g3 thus there was no obvious gully bank retreat in g2 and g3 in different places of the g1 alluvial fan the mean relative contribution of the sl ssl and swl ranged from 9 11 36 43 and 46 55 respectively however the sediment contribution of the sl increased in g2 and g3 due to the changes in the erosion type the mean relative contributions of the sl were 33 5 g2 and 30 3 g3 these findings have important implications for the establishment of a scientific basis for permanent gully sediment transport management and control policies

physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada abstract calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at yucca mountain the potential site of a high level radioactive waste repository these secondary mineral deposits are heterogeneously distributed in the unsaturated zone uz with fewer than 10 of possible depositional sites mineralized the paragenetic sequence compiled from deposits throughout the uz consists of an early stage assemblage of calcite fluorite zeolites that is frequently capped by chalcedony quartz intermediate and late stage deposits consist largely of calcite commonly with opal on buried growth layers or outermost crystal faces of the calcite coatings on steep dipping fractures usually are thin 3 mm with low relief outer surfaces whereas shallow dipping fractures and lithophysal cavities typically contain thicker more coarsely crystalline deposits characterized by unusual thin tabular calcite blades up to several cms in length these blades may be capped with knobby or corniced overgrowths of late stage calcite intergrown with opal the observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips fluid inclusion studies have shown that most early stage and some intermediate stage calcite formed at temperatures of 35 to 85 c calcite deposition during the past several million years appears to have been at temperatures 18 o values although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository the authors conclude that the temperatures and fluid inclusion assemblages are consistent with deposition in a uz environment that experienced prolonged heat input from gradual cooling of nearby plutons the physical restriction of the deposits and therefore fluid flow to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick uz at yucca mountain the textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a uz setting from meteoric waters percolating downward along fracture flow paths

sediment yield on a devastated hill in southern china effects of microbiotic crust on surface erosion process in southern china most of the forests consist of pinus massoniana but they are usually poor thin and deteriorated due to human intervention such as cutting removal of litter for fuel and over grazing therefore exposed bare soil is found in many devastated hills as a consequence both the direct runoff percentage and the sediment yield are very high in order to understand the surface erosion processes in this environment we measured sediment yield and surface erosion depth in terms of catchment scale and carried out in situ sprinkling experiments focusing on the spatial variability of surface conditions and sediment sources the results of sediment yield measurements at the end of headwater catchment suggest the following characteristic 1 the surface water is capable of transporting more material than is supplied by detachment that is the sediment discharge process is detachment limited in situ sprinkling experiments indicate that 2 in the lower part of the hillslope where the surface is covered by microbiotic crust the ratio of surface runoff to rainfall is high but sediment yield is small 3 in the upper part of the hillslope where there is no microbiotic crust the ratio of surface runoff to rainfall is low but sediment yield is large measurements of surface erosion depths indicate that 4 microbiotic crusts provide a high degree of protection against soil erosion even though the surface runoff ratio is large at the lower hillslope consequently the surface erosion depth is almost zero at the lower part of hillslope 5 the main source of sediment was the upper part of hillslope based on these indications it can be concluded that when the sediment discharge process is detachment limited the effect of the surface crust and or the vegetation cover on the sediment discharge process is great that is the spatial variation of the surface crust and or the vegetation cover controls the source of sediment

volcano tectonic setting of the intraplate pliocene holocene newer volcanic province southeast australia role of crustal fracture zones 1 the pliocene holocene newer volcanic province in victoria southeast australia is a wide volcanic field site of the most recent volcanic activity of australia the intraplate signature and the localization on the northern side of the southern ocean have been used in the past to ascribe the volcanic activity either to the presence of a mantle hot spot or to thermal anomalies inherited from the seafloor spreading that separated australia from antarctica during the gondwana breakup the spacing and distribution of groups of eruption points suggests the presence of a 32 km deep mantle thermal anomaly alignments of eruption points indicate a strong tectonic control on magma emplacement mainly along nw se mesozoic cenozoic structures and along n s palaeozoic and e w late cretaceous structures this volcano tectonic setting relates to the interference of the left lateral kinematics of the major n s trending faults associated with the tasman fracture zone and the extensional structures of the otway basin this interpretation is also coherent with stress in situ data and focal mechanisms of earthquakes shmax oriented n150 this interpretation enhances the role of the tasman fracture zone a major sinistral transform on the reactivation of transtensional structures and on triggering the magmatism of the newer volcanic province

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

thermal history of the unsaturated zone at yucca mountain nevada usa abstract secondary calcite silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry temperatures and timing of past fluid movement in the unsaturated zone at yucca mountain nevada the proposed site of a high level radioactive waste repository the distribution and geochemistry of these deposits are consistent with low temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone however the discovery of fluid inclusions in calcite with homogenization temperatures th up to 80 c was construed by some scientists as strong evidence for hydrothermal deposition this paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition mineral precipitation temperatures in the unsaturated zone are estimated from calcite and fluorite hosted fluid inclusions and calcite 18o values and depositional timing is constrained by the 207pb 235u ages of chalcedony or opal in the deposits fluid inclusion th from 50 samples of calcite and four samples of fluorite range from 35 to 90 c calcite 18o values range from 0 to 22 smow but most fall between 12 and 20 the highest th and the lowest 18o values are found in the older calcite calcite th and 18o values indicate that most calcite precipitated from water with 18o values between 13 and 7 similar to modern meteoric waters twenty two 207pb 235u ages of chalcedony or opal that generally postdate elevated depositional temperatures range from 9 5 to 1 9 ma new and published 207pb 235u and 230th uages coupled with the th values and estimates of temperature from calcite 18o values indicate that maximum unsaturated zone temperatures probably predate 10 ma and that the unsaturated zone had cooled to near present day temperatures 24 26 c at a depth of 250 m by 2 4 ma the evidence of elevated temperatures persisting in ash flow tuffs adjacent to parent calderas for as much as 8 ma is a new finding but consistent with thermal modeling simulations using the heat code demonstrate that prolonged cooling of the unsaturated zone is consistent with magmatic heat inputs and deep seated sub water table hydrothermal activity generated by the large magma body 8 km to the north that produced the 15 11 ma ash flows and ash falls that make up yucca mountain the evidence discussed in this and preceding papers strongly supports unsaturated zone deposition of the secondary minerals from descending meteoric waters although depositional temperatures reflect conductive and possibly vapor phase convective heating of the unsaturated zone related to regional magmatic sources until perhaps 6 ma depositional conditions similar to the present day unsaturated zone have prevailed for at least the past 2 4 ma

a strontium isotope study of the vc 1 core hole and associated hydrothermal fluids and rocks from valles caldera jemez mountains new mexico chemical and strontium isotopic analyses have been performed on 10 geothermal waters from the valles caldera jemez mountain region as well as 10 rock samples collected in the vc 1 scientific core hole the 87sr 86sr values of other rocks sampled in the jemez mountains have also been used in this study to understand relations between the fluids and rocks of the volcanically driven geothermal system and the lateral outflow plume discharging down the jemez fault zone the strontium content of groundwater is linked to the host rock composition the aquifer temperature and therefore the solubility of sr containing minerals low sr concentrations in the fluid are found with a high temperature and or volcanic host rocks whereas high sr concentrations are characteristic of a low temperature and or a paleozoic sedimentary aquifer important variations of the 87sr 86sr value in hydrothermal waters 0 70842 0 72193 are related to chemical composition sr content and host rocks for vc 1 core samples the sr isotopic ratios are also markedly variable 0 70459 0 75686 low for the quaternary volcanics and high for the paleozoic sedimentary rocks the same observation is made for other jemez mountains rocks 0 70465 0 8163 with in addition high 87sr 86sr values for precambrian crystalline rocks a good correspondence is generally found between the waters and the reservoir rocks studied here which indicates that isotopic equilibrium is rapidly attained the following suite of hydraulically related fluids displays a progressive enrichment in radiogenic strontium baca wells 87sr 86sr 0 7084 0 7094 vc 1 core hole at 483 m 0 7152 0 7154 main jemez spring 0 7217 and soda dam 0 7219 this trend is associated with flow through paleozoic rocks and with the length of the flow path from the center of valles caldera primary geothermal fluids toward san diego canyon along the jemez fault zone derivative waters

response to stuckless and others 1998 on overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both

the influence of magma plumbing complexity on monogenetic eruptions jeju island korea terra nova 23 70 75 2011 abstract continuous pyroclastic successions from monogenetic volcanoes in the jeju island volcanic field korea were targeted for detailed geochemical investigations of juvenile ejecta to show that multiple distinct magma pulses may be erupted during a single monogenetic eruption deeply derived and possibly multiply sourced evolving magma pulses may erupt sequentially from the same vent and form generally uninterrupted depositional sequences with continuous chemical trends alternatively pulses can rise independently resulting in breccia horizons and truncation surfaces in depositional sequences and in stepped and mixed chemical trends we infer that uninterrupted eruptions result from clear plumbing systems in which a single large dyke system feeds an eruption and where differently sourced magmas are erupted independently congested plumbing systems consisting of dyke complexes give rise to vent shifts asymmetrical eruptive centres and composite depositional sequences integration of chemical variation and eruptive dynamics provides a powerful means of understanding monogenetic volcanoes

recycling of magmatic clasts during explosive eruptions estimating the true juvenile content of phreatomagmatic volcanic deposits the juvenile content of phreatomagmatic deposits contains both first cycle juvenile clasts derived from magma at the instant of eruption and recycled juvenile clasts which were fragmented and first ejected by earlier explosions during the eruption but fell back or collapsed into the vent recycled juvenile clasts are similar to accessory and accidental lithics in that they contribute no heat to further magma water interaction but previously no effective criteria have been defined to separate them from first cycle juvenile clasts we have investigated componentry parameters vesicularity clast morphology and extent of mud coating which in specific circumstances can distinguish between first cycle juvenile clasts involved in only one explosion and such recycled juvenile clasts phreatomagmatic fall deposits commonly show gross grainsize and sorting characteristics identical to deposits of purely dry or magmatic eruptions however the abundance of non juvenile clasts in pyroclastic deposits is a sensitive indicator of the involvement of external water if this component is calculated including recycled juvenile clasts with accidental and accessory clasts the contrast is even more striking data from a holocene maar deposit in taupo volcanic zone new zealand suggest that the first cycle juvenile component of the deposits is less than one third of that determined by simple juvenile lithic crystal componentry

18o 16o evidence for an early short lived 10 yr fumarolic event in the topopah spring tuff near the proposed high level nuclear waste repository within yucca mountain nevada usa abstract 18 o 16 o analyses of rock samples from the exploratory studies facility esf and from three other locations in the vicinity of yucca mountain nevada suggest that the uppermost 5 20 m of the 12 8 ma topopah spring tuff displays a characteristic 18 o 16 o pattern that is indicative of short lived 10 yr high temperature 500 c fumarolic meteoric hydrothermal activity hydrothermally altered rock is characterized by 1 3 m thick zones of 18 o depleted groundmass down to 18 o 5 5 located above and locally within the upper vitrophyre as well as complementary 2 4 m thick overlying zones of 18 o enriched as high as 18 o 13 7 mineralogically altered groundmass thirty four samples of the topopah spring tuff collected below the upper vitrophyre are not hydrothermally altered and correspondingly display a more uniform set of 18 o values 18 o 8 6 to 11 1 sanidine phenocrysts from fumarolically altered tuff in the upper cooling unit are petrographically pristine and also display uniform 18 o values 18 o 7 80 0 45 which are in isotopic equilibrium with other phenocryst phases at magmatic temperatures the 18 o 16 o signature displayed by the upper part of the topopah spring tuff is analogous to that produced by short lived 10 25 yr high temperature 500 c fumarolic activity in the bishop tuff and in the 1912 ash flow sheet in the valley of ten thousand smokes alaska the remarkable preservation of a fragile fumarolic 18 o 16 o signature in the upper part of the topopah spring tuff indicates that no subsequent hydrothermal alteration of this part of the tuff has occurred

mineralogy and origin of rhizoliths on the margins of saline alkaline lake bogoria kenya rift valley abstract a wide range of rhizoliths occurs around the margins of lake bogoria kenya these include root casts moulds tubules rhizocretions and permineralised root systems these rhizoliths are variably composed of opaline silica calcite zeolites mainly analcime fluorite and possibly fluorapatite either alone or in combinations some rhizoliths are infilled moulds with detrital silicate grains most rhizoliths are in situ showing both vertical and horizontal orientations reworked rhizoliths have been concentrated locally to form dense rhizolites hot spring fluids concentrated by evapotranspiration and capillary evaporation have provided most of the silica for the permineralisation of the plant tissues precipitation involved the growth of silica nanospheres and microspheres that coalesced into homogeneous masses calcite rhizoliths formed following evaporative concentration evapotranspiration and or co2 degassing of ca bearing runoff water that infiltrated the sediment or by mixing of runoff with saline alkaline groundwater fluorite precipitated in areas where mixing of hot spring and meteoric waters occurred or possibly where hot spring fluids came into contact with pre existing calcite zeolitic rhizoliths formed during a prolonged period of aridity when capillary rise and evaporative pumping brought saline alkaline waters into contact with detrital silicate minerals around roots

suction stress characteristics in granite red soils and their relationship with the collapsing gully in south china abstract the main goal of this research is to study the relationship between the soil suction stress and soil properties within four different soil profiles of collapsing gullies in the hilly granitic region of southern china large differences were found in the four soil layers between granite red soils which are manifested in terms of soil bulk density porosity particle composition clay minerals micromorphology organic matter cation exchange capacity permeability oxide and hydraulics properties the suction stress of the upper soils increases rapidly and almost linearly monotonously with the increase of matric suction whereas c layers increases rapidly first followed by a slow increase the suction stress of the lower soils is significantly smaller than the upper soils under the same matric suction these findings illustrate that the collapsing gully starts from the lower part of the granite red soil and finally caused the gravity collapse in the upper soils which is the main aspect that is different from the other types of soil erosion furthermore suction stress has a very significant correlation with soil properties with a positive correlation to the fine particle content iron and aluminum oxide and a negative correlation to coarse particles in addition suction stress can also be explained as being directly proportional to weathering degree our research provides a theoretical basis for the mass failures of the granite derived red soil in southern china

the origin of a large 3 km maar volcano by coalescence of multiple shallow craters lake purrumbete maar southeastern australia lake purrumbete maar is located in the intraplate monogenetic newer volcanics province in southeastern australia the extremely large crater of 3000 m in diameter formed on an intersection of two fault lines and comprises at least three coalesced vents the evolution of these vents is controlled by the interaction of the tectonic setting and the properties of both hard and soft rock aquifers lithics in the maar deposits originate from country rock formations less than 300 m deep indicating that the large size of the crater cannot only be the result of the downwards migration of the explosion foci in a single vent vertical crater walls and primary inward dipping beds evidence that the original size of the crater has been largely preserved detailed mapping of the facies distributions the direction of transport of base surges and pyroclastic flows and the distribution of ballistic block fields form the basis for the reconstruction of the complex eruption history which is characterised by alternations of the eruption style between relatively dry and wet phreatomagmatic conditions and migration of the vent location along tectonic structures three temporally separated eruption phases are recognised each starting at the same crater located directly at the intersection of two local fault lines activity then moved quickly to different locations a significant volcanic hiatus between two of the three phases shows that the magmatic system was reactivated the enlargement of especially the main crater by both lateral and vertical growth led to the interception of the individual craters and the formation of the large circular crater lake purrumbete maar is an excellent example of how complicated the evolution of large seemingly simple circular maar volcanoes can be and raises the question if these systems are actually monogenetic

double porosity models for a fissured groundwater reservoir with fracture skin theories of flow to a well in a double porosity groundwater reservoir are modified to incorporate effects of a thin layer of low permeability material or fracture skin that may be present at fracture block interfaces as a result of mineral deposition or alteration the commonly used theory for flow in double porosity formations that is based upon the assumption of pseudo steady state block to fissure flow is shown to be a special case of the theory presented in this paper the latter is based on the assumption of transient block to fissure flow with fracture skin under conditions where fracture skin has a hydraulic conductivity that is less than that of the matrix rock it may be assumed to impede the interchange of fluid between the fissures and blocks resistance to flow at fracture block interfaces tends to reduce spatial variation of hydraulic head gradients within the blocks this provides theoretical justification for neglecting the divergence of flow in the blocks as required by the pseudo steady state flow model coupled boundary value problems for flow to a well discharging at a constant rate were solved in the laplace domain both slab shaped and sphere shaped blocks were considered as were effects of well bore storage and well bore skin resultsmore obtained by numerical inversion were used to construct dimensionless type curves that were applied to well test data for a pumped well and for an observation well from the fractured volcanic rock terrane of the nevada test site less

hydraulic fracturing stress measurements at yucca mountain nevada and relationship to the regional stress field hydraulic fracturing stress measurements and acoustic borehole televiewer logs were run in holes usw g 1 and usw g 2 at yucca mountain as part of the nevada nuclear waste storage investigations for the u s department of energy eight tests in the saturated zone at depths from 646 to 1288 m yielded values of the least horizontal stress s h that are considerably lower than the vertical principal stress s v in tests for which the greatest horizontal principal stress s h could be determined it was found to be less than s v indicating a normal faulting stress regime the borehole televiewer logs showed the presence of long in excess of 10 m vertical drilling induced fractures in the first 300 m below the water table these are believed to form by the propagation of small preexisting cracks under the excess downhole fluid pressures up to 5 2 mpa applied during drilling the presence of these drilling induced hydrofractures provides further confirmation of the low value of the least horizontal stresses a least horizontal principal stress direction of n60 w n65 w is indicated by the orientation of the drilling induced hydrofractures n25 e n30 e and the orientation of stress induced well bore breakouts in the lower part of usw g 2 n65 w this direction is in good agreement with indicators of stress direction from elsewhere at the nevada test site the observed stress magnitudes and directions were examined for the possibility of slip on preexisting faults using these data the coulomb criterion for frictional sliding suggests that for coefficients of friction close to 0 6 movement on favorably oriented faults could be expected for coefficients of friction of 1 0 preexisting faults of all orientations should be stable laboratory studies on the yucca mountain tuffs reported elsewhere yield coefficients of friction ranging from 0 6 to 0 9

a detailed assessment of global rare earth element resources opportunities and challenges rare earth elements ree are indispensable to infrastructure technology and modern lifestyles which has led to an increasing demand for these elements the current global rare earth oxides reo market is dominated by chinese production which peaked in 2006 at 133 000 tonnes reo per year accounting for some 97 1 of global production causing concern about the long term supply of ree resources although the ree consist of 17 individual elements 15 lanthanides plus scandium and yttrium that are hosted by numerous types of mineralization the relatively modest scale of the global ree mining sector has limited our knowledge of ree mineral resources and mineralizing systems compared to metals such as copper and iron which are produced in much larger quantities in order to quantitatively analyze the mineralogy concentrations and geologic types of ree deposits we compiled a global dataset of ree mineral resources based on the most recently available data 2013 2014 this compilation yields minimum global contained total rare earth oxides plus yttrium oxide treo y resources of 619 5 mt split between 267 deposits deposits with available grade and tonnage data 260 of the 267 deposits in our database contain some 88 483 mt of mineral resources at an average concentration of 0 63 treo y hosting 553 7 mt treo y of the 267 total deposits in our database some 160 have mineral resources reported using statutory mining codes e g jorc ni43 101 samrec with the remaining 107 projects having crirsco noncompliant mineral resources that are based on information available in the industry literature and peer reviewed scientific articles approximately 51 4 of global reo resources are hosted by carbonatite deposits and bastnasite monazite and xenotime are the three most significant ree minerals accounting for 90 of the total resources within our database in terms of ree resources by individual country china dominates currently known treo y resources 268 1 mt accounting for 43 of the global reo resources within our database with australia russia canada and brazil having 64 5 62 3 48 3 and 47 1 mt of contained treo y resources respectively some 84 3 mt treo y is hosted within tailings dominated by tailings from bayan obo but with smaller resources at palabora steenkampskraal and mary kathleen and 12 4 mt treo y is hosted by monazite within heavy mineral sands projects illustrating the potential for reo production from resources other than traditional hard rock mining global ree resources are dominated by the light ree having an average light reo lreo la gd to heavy reo tb lu and y ratio of 13 1 these ree deposits contain an average of 81 ppm th and 127 ppm u indicating that radioactive waste associated with ree extraction and refining could be a concern modeling the 2012 global production figures of 110 kt treo y combined with an assumed 5 annual growth in ree demand indicates that known ree resources could sustain production until 2100 and that geologic scarcity is not an immediate problem this suggests that other issues such as environmental economic and social factors will strongly influence the development of ree resources

long lived shield volcanism within a monogenetic basaltic field the conundrum of rangitoto volcano new zealand drilling through the edifice of rangitoto the youngest and largest volcano in the monogenetic auckland volcanic field reveals the multistage eruptive and magmatic history of a small basalt shield volcano activity commenced calendar year cal 6000 cal yr b p involving minor effusive and pyroclastic volcanism until 650 cal yr b p this period either represents an early less productive phase of a single polygenetic volcano or alternatively rangitoto is better described as a volcanic complex that includes one or more buried edifices concealed by the main structure a voluminous shield building phase occurred 650 550 cal yr b p erupting isotopically uniform subalkalic basalts mg 60 64 four batches of magma distinguished by trace element chemistry were erupted sequentially but they lack genetic connection via fractional crystallization or assimilation two of the magma batches display linear trends of decreasing incompatible trace element abundance and increasing ratios of moderately incompatible to highly incompatible elements with decreasing age this is consistent with cycles of progressive partial melting at the source the final phase of activity ca 550 500 cal yr b p was explosive and less voluminous producing scoria cones at the summit this phase involved more diversity in magma compositions including more mafic subalkalic basalt and alkali basalt pointing to sourcing of magmas simultaneously from different depths in the mantle rangitoto volcano contributes to a growing body of evidence showing that major periods of volcanism in monogenetic basalt fields occur at centers that have experienced multiple eruption episodes changes in magma composition accompany changes in eruption style but a lack of an obvious shared pattern in magmatic evolution at various volcanoes points to the localized mantle heterogeneity and conduit systems hazard scenarios for regions traditionally classified as monogenetic need to encompass the possibility of prolonged episodes of activity and reawakening of volcanoes a significant implication where infrastructure is built on such regions

geohydrological models and earthquake effects at yucca mountain nevada yucca mountain the proposed site for the high level nuclear waste repository is located just south of where the present water table begins a sharp rise in elevation this large hydraulic gradient is a regional feature that extends for over 100 km yucca mountain and its vicinity are underlain by faulted and fractured tuffs with hydraulic conductivities controlled by flow through the fractures close to and parallel with the region of large hydraulic gradient and surrounding the core of the timber mountain caldera there is a 10 to 20 km wide zone containing few faults and thus most likely few open fractures consequently this zone should have a relatively low hydraulic conductivity and this inference is supported by the available conductivity measurements in wells near the large hydraulic gradient also slug injection tests indicate significantly higher pressures for fracture opening in wells located near the large hydraulic gradient compared to the opening pressures in wells further to the south hence implying that lower extensional stresses prevail to the north with consequently fewer open fractures there analytical and numerical modeling shows that such a boundary between media of high and low conductivity can produce the observed large hydraulic gradient with the high conductivity medium having a lower elevation than the water table further as fractures can close due to tectonic activity the conductivity of the yucca mountain tuffs can be reduced to a value near that for the hydraulic barrier due to strain release by a moderate earthquake under these conditions simulations show that the elevation of the steady state water table could rise between 150 and 250 m at the repository site this elevation rise is due to the projected shift in the location of the large hydraulic gradient to the south in response to a moderate earthquake near magnitude 6 along one of the major normal faults adjacent to yucca mountain as the proposed repository would only be 200 400 m above the present water table this predicted rise in the water table indicates a potential hazard involving water intrusion

reconstructing the eruption magnitude and energy budgets for the pre historic eruption of the monogenetic 5 ka mt gambier volcanic complex south eastern australia understanding explosive volcanic eruptions especially phreatomagmatic eruptions their intensities and energy budgets is of major importance when it comes to risk and hazard studies with only a few historic occurrences of phreatomagmatic activity a large amount of our understanding comes from the study of pre historic volcanic centres which causes issues when it comes to preservation and vegetation in this research we show that using 3d geometrical modelling it is possible to obtain volume estimates for different deposits of a pre historic complex monogenetic centre the mt gambier volcanic complex south eastern australia using these volumes we further explore the energy budgets and the magnitude of this eruption vei 4 including dispersal patterns eruption columns varying between 5 and 10 km dispersed towards north east to south to further our understanding of intraplate monogenetic eruptions involving phreatomagmatic activity we also compare which thermodynamic model fits best in the creation of the maar crater of mt gambier the major explosion dominated model or the incremental growth model in this case the formation of most of the craters can best be explained by the latter model

an oxygen isotope study of hydrothermal alteration in the lake city caldera san juan mountains colorado abstract a 23 m y old fossil meteoric hydrothermal system in the lake city caldera 11 14 km has been mapped out by measuring 18o values of 300 rock and mineral samples 18o varies systematically throughout the caldera reaching values as low as 2 great topographic relief regional tilting and variable degrees of erosion within the caldera all combine to give us a very complete section through the hydrothermal system from the surface down to a depth of more than 2000 m the initial 18o value of the caldera fill sunshine peak tuff was very uniform 7 2 0 1 making it easy to determine the exact amount of 18o depletion experienced by each sample during hydrothermal alteration also we have excellent stratigraphic control on depths beneath the mid tertiary surface quantitative information on mineralogical alteration products and accurate data on the shape of the central resurgent intrusion which was the principal heat engine that drove the hydrothermal circulation major conclusions are 1 although pristine mid tertiary meteoric waters in this area had 18 o 14 these fluids were 18o shifted upward to about 18o 8 to 5 prior to entering the shallow convective system associated with the resurgent intrusive rocks although there was undoubtedly radial inflow toward the caldera from all directions the highly fractured eureka graben southwest of the caldera was probably the principal source of recharge groundwater for the lake city system 2 fluid flow within the caldera was dominated by three major categories of permeable zones the porous megabreccia units which dip outward from the resurgent dome vertical fractures and faults related to resurgence and the caldera ring fault itself all of these zones exhibit marked 18o depletions and they are also typically intensely mineralogically altered 3 the resurgent intrusive stock and its contact metamorphic aureole of hornfels both experienced water rock ratios lower than the permeable zones however they have similarly low 18o values because they were altered at higher temperatures 4 throughout the caldera the 18o of sunshine peak tuff decreases with increasing depth about 6 per mil km indicative of a shallow thermal gradient typical of a convective hydrothermal system the near surface portion of this gradient was controlled by the temperature drop associated with boiling in the uprising fluid 5 deeply circulating meteoric water rose along permeable ring fractures 3 to 5 km beneath the mid tertiary surface these fluids were drawn into the shallow convective system through the lower porous megabreccia units near the resurgent intrusions fluid flow was again directed upward where resurgence related near vertical fractures intersect the megabreccia units

uranium thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the salton sea geothermal field southeastern california naturally occurring u and th series radionuclides have been analyzed in high temperature brines 300 c 25 wt dissolved solids and associated rocks from two deep geothermal wells located on the northeastern margin of the salton sea geothermal field ssgf these data are part of a study of the ssgf as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds and permit evaluation of some characteristics of water rock interaction in the ssgf rock brine concentration ratios rc dpm g rock dpm g brine were found to vary from near unity for isotopes of ra pb and rn to about 5 105 for 232th the high sorptivity of 232th is closely followed by that of 238u and 234u rc 5 104 suggesting that u is retained in the 4 oxidation state by the reducing conditions in the brines the relatively high solubility of 210pb and 212pb is attributed to formation of chloride complexes while the high ra solubility is attributed to chloride complexing a lack of suitable adsorption sites due to the high brine salinity and temperature and the reducing conditions that prevent mno2 and raso4 from forming the 228ra226ra ratios in the brines are approximately equal to those of their parents 232th230th in associated rocks indicating that ra equilibration in the brine rock system is achieved within the mean life of 228ra 8 3 years the 224ra228ra ratios in these brines are about 0 7 indicating that either 1 brine composition is not homogeneous and 224ra decays in fracture zones deficient in ra and th as the brine travels to the wellhead or 2 ra equilibration in the brine host rock system is not complete within the mean life of 224ra 5 2 days because the desorption of 224ra from the solid phase is impeded the 228ac228ra activity ratio in the ssgf brines studied is 0 1 and from this ratio the residence time of 228ac in the brine before sorption onto solid surfaces is estimated to be 70 minutes indicating the potential for rapid removal of reactive isotopes fom brines the brine is greatly enriched in 226ra 2 3 dpm g about 104 105 times that of its parent 230th while reservoir rocks are about 10 deficient in 226ra relative to 230th material balance calculations for 2226ra and 18o suggest that brines reside in the reservoir for 102 103 years that the ssgf formed 10 000 40 000 years b p and that porosity cannot be more than 20