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

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

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

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

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

fluid flow in the resurgent dome of long valley caldera implications from thermal data and deep electrical sounding abstract temperatures of 100 c are measured at 3 km depth in a well located on the resurgent dome in the center of long valley caldera california despite an assumed 800 c magma chamber at 6 8 km depth local downflow of cold meteoric water as a process for cooling the resurgent dome is ruled out by a peclet number analysis of temperature logs these analyses reveal zones with fluid circulation at the upper and lower boundaries of the bishop tuff and an upflow zone in the metasedimentary rocks vertical darcy velocities range from 10 to 70 cm a 1 a 21 km long geoelectrical profile across the caldera provides resistivity values to the order of 10 0 to 10 3 m down to a depth of 6 km as well as variations of self potential interpretation of the electrical data with respect to hydrothermal fluid movement confirms that there is no downflow beneath the resurgent dome to explain the unexpectedly low temperatures in the resurgent dome we challenge the common view that the caldera as a whole is a regime of high temperatures and the resurgent dome is a local cold anomaly instead we suggest that the caldera was cooled to normal thermal conditions by vigorous hydrothermal activity in the past and that a present day hot water flow system is responsible for local hot anomalies such as hot creek and the area of the casa diablo geothermal power plant the source of hot water has been associated with recent shallow intrusions into the west moat the focus of planning for future power plants should be to locate this present day flow system instead of relying on heat from the old magma chamber

eastern boundary currents and coastal upwelling abstract the adjustment of the eastern coastal zone of an inviscid ocean with vertical walls to a change in wind conditions occurs in two stages after the propagation of a kelvin wave across the forced region in a time tk which is of the order of a day or two the coastal upwelling zone is temporarily in equilibrium with the wind further adjustment occurs after a time tr which is of the order of a few mouths when westward rossby dispersion of the coastal jet becomes important these time scales define three frequency ranges that characterize the response to fluctuating winds with period p 1 at high frequencies p tk short kelvin waves can destroy coherence between the forcing and response alonshore coherence of oceanic variables is small and the spectrum of the response is red even if that of the forcing is white the offshore wale of the response is the radius of deformation poleward phase propagation at kelvin wave speed c in unforced regions and at speed 2c in the forced region is prominent

deep water nutrient and oxygen gradients in a modern coastal upwelling zone and their paleoceanographic implications dissolved phosphate and oxygen data from the waters at 300 m depth beneath the peru upwelling system imitate observed onshore offshore surface productivity data positive onshore phosphate gradients and negative onshore oxygen gradients are greater in deeper water up to 1000 m reflecting the decreasing degree of horizontal mixing at depth mass balance reconstructions of surface productivity nutrient remineralization and onshore offshore chemical gradients suggest that the lack of wide continental shelves during glacial climates would lead to more pronounced dissolved nutrient and oxygen gradients in the deep water adjacent to continental margins horizontal 13c gradients in sediments beneath highly productive coastal upwelling zones may have been as high as 0 5 1 0 per 100 km suggesting caution in the interpretation of benthic 13c samples adjacent to continental margins during low sea level stands

carbon dioxide emissions from vegetation kill zones around the resurgent dome of long valley caldera eastern california usa abstract a survey of diffuse co2 efflux soil temperature and soil gas chemistry over areas of localized vegetation kill on and around the resurgent dome of long valley caldera california was performed to evaluate the premise that gaseous and thermal anomalies are related to renewed intrusion of magma some kill sites are long lived features and others have developed in the past few years total anomalous co2 emissions from the thirteen areas average around 8 7 t per day but the majority of the emissions come from four sites west of the casa diablo geothermal power plant geochemical analyses of the soil gases from locations west and east of the plant revealed the presence of isobutane related to plant operations the 13c values of diffuse co2 range from 5 7 to 3 4 similar to values previously reported for co2 from hot springs and thermal wells around long valley at many of the vegetation kill sites soil temperatures reach boiling at depths 20 cm soil temperature depth profiles at two of the high emissions areas indicate that the conductive thermal gradient in the center of the areas is around 320 c m 1 we estimate total heat loss from the two areas to be about 6 1 and 2 3 mw given current thinking on the rate of hydrothermal fluid flow across the caldera and using the co2 concentration in the thermal fluids the heat and co2 loss from the kill areas is easily provided by the shallow hydrothermal system which is sourced to the west of the resurgent dome we find no evidence that the development of new areas of vegetation kill across the resurgent dome are related to new input of magma or magmatic fluids from beneath the resurgent dome our findings indicate that the areas have developed as a response to changes in the shallow hydrologic system some of the changes are likely related to fluid production at the power plant but at distal sites the changes are more likely related to seismicity and uplift of the dome

gas geochemistry of the valles caldera region new mexico and comparisons with gases at yellowstone long valley and other geothermal systems abstract noncondensible gases from hot springs fumaroles and deep wells within the valles caldera geothermal system 210 300 c consist of roughly 98 5 mol co 2 0 5 mol h 2 s and 1 mol other components 3 he 4 he ratios indicate a deep magmatic source r r a up to 6 whereas 13 c co 2 values 3 to 5 do not discriminate between a mantle magmatic source and a source from subjacent hydrothermally altered paleozoic carbonate rocks regional gases from sites within a 50 km radius beyond valles caldera are relatively enriched in co 2 and he but depleted in h 2 s compared to valles gases regional gases have r r a values 1 2 due to more interaction with the crust and or less contribution from the mantle carbon sources for regional co 2 are varied during 1982 1998 repeat analyses of gases from intracaldera sites at sulphur springs showed relatively constant ch 4 h 2 and h 2 s contents the only exception was gas from footbath spring 1987 1993 which experienced increases in these three components during drilling and testing of scientific wells vc 2a and vc 2b present day valles gases contain substantially less n 2 than fluid inclusion gases trapped in deep early stage post caldera vein minerals this suggests that the long lived valles hydrothermal system ca 1 myr has depleted subsurface paleozoic sedimentary rocks of nitrogen when compared with gases from many other geothermal systems valles caldera gases are relatively enriched in he but depleted in ch 4 n 2 and ar in this respect valles gases resemble end member hydrothermal and magmatic gases discharged at hot spots galapagos kilauea and yellowstone

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

sr isotope diversity of hot spring and volcanic lake waters from zao volcano japan abstract the ratio of 87 sr 86 sr was measured from different water samples of thermal mineral hot spring as well as crater lake and meteoric origins in order to specify the location and to verify the detailed model of a volcano hydrothermal system beneath zao volcano the ratio showed a trimodal distribution for the case of thermal mineral water 0 7052 0 7053 type a zao hot spring 0 7039 0 7043 type b okama crater lake and shin funkiko hot spring and 0 7070 0 7073 type c gaga aone and togatta hot springs respectively however in comparison the ratio was found to be higher for meteoric waters 0 7077 0 7079 the water from the central volcanic edifice type b was found to be similar to that of nearby volcanic rocks in their sr isotopic ratio this indicates that the sr in water was derived from shallow volcanic rocks the 87 sr 86 sr ratio for water from the zao hot spring type a was intermediate between those of the pre tertiary granitic and the quaternary volcanic rocks thus suggesting that the water had reacted with both volcanic and granitic rocks the location of the vapor liquid separation was determined as the boundary of the pre tertiary granitic and the quaternary volcanic rocks by comparing the results of this strontium isotopic study with those of kiyosu and kurahashi kiyosu y kurahashi m 1984 isotopic geochemistry of acid thermal waters and volcanic gases from zao volcano in japan j volcanol geotherm res 21 313 331

mapping 87sr 86sr variations in bedrock and water for large scale provenance studies abstract although variation in 87sr 86sr has been widely pursued as a tracer of provenance in environmental studies forensics archeology and food traceability accurate methods for mapping variations in environmental 87sr 86sr at regional scale are not available in this paper we build upon earlier efforts to model 87sr 86sr in bedrock by developing gis based models for sr isotopes in rock and water that include the combined effects of lithology and time using published data we fit lithology specific model parameters for generalized equations describing the concentration of radiogenic sr in silicate and carbonate rocks the new model explained more than 50 of the observed variance in measured sr isotope values from independent global databases of igneous metaigneous and carbonate rocks but performed more poorly explaining 33 of the variance for sedimentary and metasedimentary rocks in comparison a previously applied model formulation that did not include lithology specific parameters explained only 20 and 8 of the observed variance for igneous and sedimentary rocks respectively and exhibited an inverse relationship with measured carbonate rock values building upon the bedrock model we also developed and applied equations to predict the contribution of different rock types to 87sr 86sr variations in water as a function of their weathering rates and strontium content the resulting water model was compared to data from 68 catchments and shown to give more accurate predictions of stream water 87sr 86sr r2 0 70 than models that did not include lithological weathering parameters we applied these models to produce maps isoscapes predicting 87sr 86sr in bedrock and water across the contiguous usa and compared the mapped sr isotope distributions to data on sr isotope ratios of us marijuana crops although the maps produced here are demonstrably imperfect and leave significant scope for further refinement they provide an enhanced framework for lithology based sr isotope modeling and offer a baseline for provenance studies by constraining the 87sr 86sr in strontium sources at regional scales

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

determination of isopycnal diffusivity in the sargasso sea abstract using observed space and time derivatives of the distribution of 3he tritium and tritium helium age in the sargasso sea and the tritium helium age equation the isopycnal eddy diffusivity is estimated to be 1840 sw 440 m2s 1 within the main thermocline

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

water rock interactions in the basement beneath long valley caldera an oxygen isotope study of the long valley exploratory well drill cores abstract the long valley exploratory well at the center of the resurgent dome of long valley caldera penetrated pre caldera basement rocks at a depth of 2101 72 2313 0 m beneath the caldera forming bishop tuff and post caldera early rhyolite the basement rocks contain prominent quartzites with ubiquitous milky white quartz veins with minor calcite and pyrite and fractures of varied orientation and geometry the other members of the basement sequence are very fine grained quartz rich graphitic pelites with calcite veins spotted hornfels and shallow intrusive rocks previous studies established the presence of a post caldera paleohydrothermal system 500 100 ka to a depth of 2000 m that affected the bishop tuff and a recent 40 ka to present hydrothermal system at shallow depth

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

boron sr o and h isotope geochemistry of groundwaters from mt etna sicily hydrologic implications combined b o h and sr isotopic studies of groundwaters from mt etna provide new constraints on their origin and the consequences of fluid rock interaction within this hydrologic system variations in d 18 o 29 7 to 27 2 and d d 262 to 223 mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation however small shifts in d 18 o and variable 87 sr 86 sr 0 70355 to 0 70879 and d 11 b 25 2 to 125 8 indicate that subsequent interactions occurred between the fluids and local rocks high b cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and in some samples elevated 87 sr 86 sr and d 11 b two general end member water types are recognized on the basis of their chemistry these apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks either basaltic lavas of etna or the underlying sediments respectively high d 11 b in the sediment hosted end member points to a significant marine carbonate contribution subsequent mixing between these or similar end members produced a range of intermediate composition groundwaters certain anomalous water compositions require the presence locally of a distinct component with high b and moderate d 11 b ca 110 but relatively low 87 sr 86 sr an anthropogenic source for this component is plausible one unusual sample has b and sr isotopic compositions similar to the other volcanic rock hosted waters but anomalously high cl content that likely reflects local magmatic outgassing near this sampling locality in general this study indicates that groundwater b and sr isotopic compositions are rock dominated these data provide useful constraints on the origin and evolution of groundwaters copyright 2000 elsevier science ltd

the hydrothermal outflow plume of valles caldera new mexico and a comparison with other outflow plumes stratigraphic temperature gradient hydrogeochemical and hydrologic data have been integrated with geologic data from previous studies to show the structural configuration of the valles caldera hydrothermal ouflow plume hydrologic data suggest that 25 50 of the discharge of the valles outflow is confined to the jemez fault zone which predates caldera formation thermal gradient data from bores penetrating the plume show that shallow gradients are highest in the vicinity of the jemez fault zone up to 190 c km shallow heat flow above the hydrothermal plume is as high as 500 mw m 2 near core hole vc 1 jemez fault zone to 200 mw m 2 at fenton hill jemez plateau chemical and isotopic data indicate that two source reservoirs within the caldera redondo creek and sulphur springs reservoirs are parents to mixed fluids flowing in the hydrothermal plume however isotopic data borehole data basic geology and inverse relations between temperature and chloride content at major hot springs indicate that no single reservoir fluid and no single diluting fluid are involved in mixing the valles caldera hydrothermal plume is structurally dominated by lateral flow through a belt of vertical conduits jemez fault zone that strike away from the source reservoir stratigraphically confined flow is present but dispersed over a wide area in relatively impermeable rocks the valles configuration is contrasted with the configuration of the hydrothermal plume at roosevelt hot springs which is dominated by lateral flow through a near surface widespread permeable aquifer data from 12 other representative geothermal systems show that outflow plumes occur in a variety of magmatic and tectonic settings have varying reservoir compositions and have different flow characteristics although temperature reversals are commonly observed in wells penetrating outflow plumes reversals are not observed in all plumes less information is available on the absolute age of hydrothermal outflow plumes although the data show that they can be as old as 106 years and display episodic behavior

radiocarbon application in dating complex hot and cold co2 rich mineral water systems a review of case studies ascribed to the northern portugal abstract the use of radioactive isotopes plays a very important role in dating groundwater providing an apparent age of the systems in the framework of the aquifers conceptual modelling making available important features about the water fluxes such as recharge horizontal flow rates and discharge in this paper special emphasis has been put on isotopic constraints in the use of 13 c and 14 c content as a dating tool in some hot 76 c and cold 17 c co 2 rich mineral waters discharging in the vilarelho da raia pedras salgadas region n portugal the radiocarbon content determined in these co 2 rich mineral waters 14 c activity from 4 3 up to 9 9 pmc is incompatible with the systematic presence of 3 h from 1 7 to 7 9 tu the 13 c values of the studied co 2 rich mineral waters indicate that the total c in the recharge waters is being masked by larger quantities of co 2 14 c free introduced from deep seated upper mantle sources this paper demonstrates that a good knowledge of mineral water systems is essential to allow hydrologists to make sound conclusions on the use of c isotopic data in each particular situation

horizontal transport and the distribution of nutrients in the coastal transition zone off northern california effects on primary production phytoplankton biomass and species composition conductivity temperature depth surveys during 1988 encountered strong baroclinic jets that were evident in acoustic doppler current profiler and hydrographic data during june and july 1988 a filament with high surface nitrate high chlorophyll abundant populations of neritic centric diatoms and higher rates of primary production was evident perpendicular to the coast between point arena and point reyes however the high nutrient and phytoplankton regions were not in the baroclinic jets but were south and inshore of them surface water transported offshore by the strong baroclinic jets was found to have relatively low nutrient content suggesting that the jets themselves do not carry significant levels of coastally upwelled high nutrient water to the ocean interior the low nutrient and salinity content of the jet suggests that the water originated several hundred kilometers upstream although the jets themselves do not appear to transport significant levels of nutrients directly from the coastal regime to the oceanic regime dynamic processes associated with a meandering jet are likely responsible for high surface nutrients found several hundred kilometers offshore processes such as upwelling along the southern edge of the seaward jet result in significant enrichment of the coastal transition zone and in large blooms of neritic diatoms during 1988 the high nutrient high phytoplankton filament was present when the survey sequence began but then decayed after a month the surface and subsurface nitrate fields were coherent with the dynamic topography field throughout the survey sequence however the surface and integrated chlorophyll fields were coherent only through the first two surveys a decrease in phytoplankton biomass began during the third survey coincident with physical changes which occurred in that time frame 1 an intensification of the undercurrent and 2 changes in the surface circulation from predominantly offshore to predominantly longshore understanding the processes responsible for the uncoupling between biology and physics is paramount for realistic biological models of this region

structural controls on the emission of magmatic carbon dioxide gas long valley caldera usa we present a degassing study of long valley caldera that explores the structural controls upon emissions of magmatic carbon dioxide gas a total of 223 soil gas samples were collected and analyzed for stable carbon isotopes using a field portable cavity ring down spectrometer this novel technique is flexible accurate and provides sampling feedback on a daily basis sampling sites included major and minor volcanic centers regional throughgoing faults caldera related structures zones of elevated seismicity and zones of past and present hydrothermal activity the classification of soil gases based on their 13c and co2 values reveals a mixing relationship among three end members atmospheric biogenic and magmatic signatures dominated by biogenic contributions 4 vol 24 are found on the caldera floor the interior of the resurgent dome and areas associated with the hilton creek and hartley springs fault systems with the introduction of the magmatic component 100 vol 4 5 samples acquire mixing and hydrothermal signatures and are spatially associated with the central caldera and mammoth mountain in particular they are concentrated along the southern margin of the resurgent dome where the interplay between resurgence related reverse faulting and a bend in the regional fault system has created a highly permeable fracture network suitable for the formation of shallow hydrothermal systems this contrasts with the south moat where despite elevated seismicity a thick sedimentary cover has formed an impermeable cap inhibiting the ascent of fluids and gases to the surface

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

paleocene to early eocene paleoceanography of the middle east the δ13c and δ18o isotopes from foraminiferal calcite paleocene to early eocene benthic foraminiferal 13c and 18o records from southern tethyan sections at ben gurion israel paleodepth 500 700 m and gebel aweina egypt paleodepth 150 200 m show generally similar trends but 1 3 more negative values than coeval deep sea isotopic records in both tethyan sections a negative 13c excursion of 2 5 3 marks the benthic extinction event in the latest paleocene for at least 1 m y after this event 13c values were 1 5 2 more negative on the shelf than at upper bathyal depths reflecting a deepening of the oxygen minimum zone possibly related to an increase or spatial shift in upwelling benthic 18o records indicate a 2 4 c temperature gradient between the shelf and upper bathyal depths temperature salinity reconstructions suggest that upwelling was a dominant mechanism for surface water formation in this part of the southern tethys during the late paleocene

influence of magmatic hydrothermal activity on brine evolution in closed basins searles lake california evaporites in a 700 m long core km 3 from searles lake california preserve a record of the chemical evolution of inflow waters chemical analyses of fluid inclusions in halite and evaporite minerals show that the major ion composition of inflow waters to searles lake was changed by distant hydrothermal activity associated with magmatism at long valley caldera between 1 27 and 1 0 m y ago below core depths of 291 m the evaporites consist of ca bearing sulfates anhydrite glauberite and halite fluid inclusions in the halite show that parent waters were na cl so42 rich waters above 291 m the evaporites include sodium carbonates pirssonite trona and halite and fluid inclusion brines are na k hco3 co32 cl so42 rich these fluctuations in mineralogy and brine chemistry document an alkalinity spike beginning between 1 27 and 1 0 ma when inflow waters to searles lake crossed the caco3 chemical divide and began to produce alkaline brines that precipitated trona upon evaporation the owens river is a modern chemical analog for inflow water into searles lake beginning between 1 27 ma and 1 0 ma a major contributor of solutes to the owens river is hot creek in long valley caldera which is fed by hydrothermal springs with high alkalinity from magmatically derived co2 the timing of magmatism in owens valley and the appearance of sodium carbonate minerals in core km 3 suggest a causal relationship volcanism and hydrothermal activity provided co2 and elevated alkalinity to searles lake inflow waters 0 5 0 2 m y before the eruptions that formed the bishop tuff and long valley caldera

a model that helps explain sr isotope disequilibrium between feldspar phenocrysts and melt in large volume silicic magma systems feldspar phenocrysts of silicic volcanic rocks are commonly in sr isotopic disequilibrium with groundmass in some cases the feldspar is more radiogenic and in others it is less radiogenic several explanations have been published previously but none of these is able to accommodate both senses of disequilibrium we present a model by which either more or less radiogenic feldspar or even both within a single eruptive unit can originate the model requires a magma body open to interaction with biotite and feldspar bearing wall rock magma is incrementally contaminated as wall rock melts incongruently biotite preferentially melts first followed by feldspar such melting behavior which is supported by both field and experimental studies first contaminates magma with a relatively radiogenic addition followed by a less radiogenic addition feldspar phenocrysts lag behind melt groundmass of volcanic rock in incorporating the influx of contaminant thus resulting in sr isotopic disequilibrium between the crystals and melt the sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process this model is testable by isotopic fingerprinting of individual feldspar crystals for a given set of geologic boundary conditions specific core to rim sr isotopic profiles are expectable moreover phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history initial results of sr isotopic fingerprinting of sanidine phenocrysts from the taylor creek rhyolite are consistent with the model more tests of the model are desirable

oxygen isotope study of the long valley magma system california isotope thermometry and convection in large silicic magma bodies products of voluminous pyroclastic eruptions with eruptive draw down of several kilometers provide a snap shot view of batholith scale magma chambers and quench pre eruptive isotopic fractionations i e temperatures between minerals we report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite pyroxene and zircon from individual pumice clasts of ignimbrite and fall units of caldera forming 0 76 ma bishop tuff bt pre caldera glass mountain 2 1 0 78 ma and post caldera rhyolites 0 65 0 04 ma to characterize the long lived batholith scale magma chamber beneath long valley caldera in california values of 18o show a subtle 1 decrease from the oldest glass mountain lavas to the youngest post caldera rhyolites older glass mountain lavas exhibit larger 1 variability of 18o quartz the youngest domes of glass mountain are similar to bt in 18o quartz values and reflect convective homogenization during formation of bt magma chamber surrounded by extremely heterogeneous country rocks ranging from 2 to 29 oxygen isotope thermometry of bt confirms a temperature gradient between late 815 c and early 715 c bt the 18o quartz values of early and late bt are 8 33 and 8 21 consistent with a constant 18o melt 7 8 0 1 and 100 c temperature difference zircon melt saturation equilibria gives a similar temperature range values of 18o quartz for different stratigraphic units of bt and in pumice clasts ranging in pre eruptive depths from 6 to 11 km based on melt inclusions and document vertical and lateral homogeneity of 18o melt worldwide five other large volume rhyolites lava creek lower bandelier fish canyon cerro galan and toba exhibit equal 18o melt values of earlier and later erupted portions in each of the these climactic caldera forming eruptions we interpret the large scale 18o homogeneity of bt and other large magma chambers as evidence of their longevity 105 years and convection however remaining isotopic zoning in some quartz phenocrysts trace element gradients in feldspars and quartz and zircon crystal size distributions are more consistent with far shorter timescales 102 104 years we propose a sidewall crystallization model that promotes convective homogenization roofward accumulation of more evolved and stagnant volatile rich liquid and develops compositional and temperature gradients in pre climactic magma chamber crystal melt gas bubbles mush near chamber walls of variable 18o gets periodically remobilized in response to chamber refill by new hotter magmas one such episode of chamber refill by high ti sr ba zr and volatile richer magma happened 103 104 years prior to the 0 76 ma caldera collapse that caused magma mixing at the base mush thawing near the roof and walls and downward settling of phenocrysts into this hybrid melt

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

helium isotope and gas discharge variations associated with crustal unrest in long valley caldera california 1989 1992 the onset of anomalous seismic activity in 1989 beneath mammoth mountain on the southwestern rim of the long valley caldera california was followed within approximately 4 months by a large increase in sup 3 he sup 4 he in vapor discharged from a fumarole on the north side of the mountain the helium isotopic ratio at this vent rose to a maximum of 6 7 r sub a in july 1990 and subsequently declined to values near 5 r sub a potential sources of the sup 3 he rich vapors include degassing of fresh magma degassing from fresh surfaces generated in newly fractured igneous rocks and volatile release from a sup 3 he rich gas chamber situated above previously emplaced intrusives the magnitude of the increase in helium isotopic composition from 3 8 to 6 7 r sub a the persistence of relatively high values 5 r sub a over a period of 3 years the increase in the flux of total he relative to gases in air saturated water and the increases in the rates of discharge of steam and gas from this fumarole indicate that magmatic intrusion did in fact begin in 1989 beneath mammoth mountain seismic activity and limited measurements of extensional deformation at the surface suggest that the depth of intrusion maymore be as shallow as 2 km consistent with the prompt appearance of increased sup 3 he sup 4 he ratios in the fumarolic gas and that the intrusive process may have persisted for approximately 1 year in contrast a similar combination of magmatic intrusion and anomalous seismic activity beneath the resurgent dome south moat region during the 1989 1991 period resulted in at most relatively small changes in sup 3 he sup 4 he in fumarolic discharge at the southern edge of the resurgent dome the more subdued response may result from a combination of greater intrusive depths and greater dilution of sup 3 he rich inputs to thermal fluid reservoirs in the shallow hydrothermal system in this area compared with mammoth mountain 60 refs 11 figs 4 tabs less

the isotopic and chemical composition of co2 rich thermal waters in the mont dore region massif central france chemical and isotope compositions of fluid samples collected between 1974 and 1986 from 52 springs or shallow boreholes located in the mont dore region massif central france were examined some springs and wells were sampled several times during this period the fluids emerge from quaternary volcanic rocks or paleozoic granite at temperatures between 4 and 62 c and the origin of the h2o is meteoric the waters can be classified into three groups bicarbonate fluids mixed bicarbonate chloride fluids with a mineralization up to 8 g l and acid sulfate fluids only two fluids contain sufficient cl to be considered as mature waters previous work has demonstrated that they all contain partly mantle derived co2 gas and that the co2 rich gas phase and bicarbonate chloride waters are separated at substantial depth mineralized fluids circulate at depth and undergo several processes such as cooling or dilution with recent freshwater during their ascent to the surface therefore the co2 rich gas phase can be partly dissolved in the freshwater or in deep fluids after their dilution this process leads to the dissolution of surrounding rocks such dissolution is discussed on the basis of major element concentrations na k ca mg as well as the sr 87 86 isotope ratio dissolution of s bearing minerals has also been demonstrated the presence of the co2 rich gas phase also leads to isotope exchange between co2 and h2o some mineralized fluids are less affected by these processes than others in which case they display the chemical and isotopic characteristics of the original deep fluids it was shown that the applicability of geothermometer calculations for these waters is hampered by several processes that modify the chemical composition however some geothermometers can be used for estimating the temperature of the deep fluids using the chemical composition of the less modified fluids they indicate that fluids emerging from volcanic rocks in the dordogne valley reach temperatures of around 100 130 c at depth while the temperature of the fluid that issues from the granite at saint nectaire is 160 175 c at depth

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

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

first coupled sr and pb isotopic measurements in volcanic gas condensates and groundwaters of vulcano island italy 1 for the first time coupled sr pb concentrations and isotopic compositions have been measured on four crater fumaroles and six groundwaters sampled between 1999 and 2001 at vulcano island southern italy sr concentrations and isotopic compositions of groundwaters show that the sr budget results mainly from the leaching of volcanic rock by groundwaters leaching intensity is controlled by the variable dissolution of volcanic gases into shallow aquifers the data do not reveal any influence of seawater except at one coastal site low pb concentrations together with calculated saturation indexes with respect to mineral phases indicate that pb content in groundwaters is strongly influenced by adsorption and or precipitation processes pb isotopic ratios of two steam heated waters display a clear anthropized meteoric water signature suggesting gas dissolution or wall rock alteration to be a negligible process for this element in this particular context low 0 5 and high 102 103 enrichment factors were calculated for sr and pb respectively indicating their refractory and volatile behavior in volcanic gases most of the gas samples display sr and pb isotopic ratios similar to parent rocks these data suggest that sr is mainly derived from wall rock or particle contamination during gas ascent whereas pb results mainly from magma degassing however two gas condensates collected from two different fumarolic vents and at different periods show a dramatic pb and sr isotopic shift with a clear atmospheric anthropogenic signature episodic permeability variations of the volcanic structure probably arising from microseismicity swarms changes of local stress field and migration of self sealing processes lead to changing interactions between freshly infiltrated meteoric water and volcanic gases that temporarily modify the trace metal signature of the fumarolic gas

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

the green river salt mystery what was the source of the hyperalkaline lake waters abstract bicarbonate rich source waters were needed to form the largest sodium carbonate evaporite deposits in the geologic record the early and middle eocene green river trona nahco 3 na 2 co 3 2h 2 o in the bridger basin wyoming and nahcolite nahco 3 in the piceance creek basin colorado large modern and pleistocene trona deposits are associated with magmatic activity and na hco 3 rich hydrothermal inflow waters either within the depositional basin lake magadi kenya or at great distances searles lake california no evidence exists for magmatic sources of co 2 near the green river formation several regional volcanic centers were active 300 km or more to the north but drainage reconstructions show that waters from these areas did not discharge into the green river formation lakes during evaporite deposition alternatively na hco 3 rich waters could have drained northwestward from the colorado mineral belt to the bridger basin via the proposed aspen river a river originating in the colorado mineral belt sawatch uplift could also have provided source waters to the piceance creek basin field evidence however has not yet documented these flow paths and specific eocene volcanic centers and hydrothermal source areas have yet to be identified other explanations for the elevated alkalinities needed to form thick sodium carbonate evaporites include accelerated silicate mineral weathering rates during a period of high atmospheric p co 2 and eocene warmth amplified chemical weathering may explain the cluster of sodium carbonate evaporites in the usa and china that are eocene in age another possible source of alkalinity to the green river lakes is fault controlled upward migration of a deep sedimentary source of co 2 the large amount of organic matter preserved in the evaporitic wilkins peak and parachute creek members raises the possibility that decay of organic matter in green river lakes could have added sufficient co 2 and alkalinity to produce waters capable of precipitating trona and nahcolite although such degradation of organic matter has not created hyperalkalinity in modern lakes

age and origin of base and precious metal veins of the coeur d alene mining district idaho ore bearing quartz carbonate veins of the coeur d alene mining district yield 87sr 86sr ratios of 0 74 to 1 60 for low rb sr carbonate gangue minerals similar to current ranges measured in middle proterozoic high rb sr rocks of the belt supergroup stable isotope and fluid inclusion studies establish a genetic relationship between vein formation and metamorphic hydrothermal systems of the region these extraordinary 87sr 86sr ratios require accumulation of radiogenic 87sr in a high rb sr system over an extended period prior to incorporation of sr into the hydrothermal veins evaluation of the age and composition of potential sources of highly radiogenic sr indicates that the ore bearing veins of the coeur d alene district formed during the cretaceous from components scavenged from rocks of the belt supergroup the primary host rocks of the district proterozoic pb isotope ratios observed in galena from many coeur d alene veins were established when pb separated from uranium during deposition or diagenesis of the belt supergroup at 1400 to 1500 ma possibly as disseminated syngenetic deposits k ar and rb sr apparent ages and 18o values of belt supergroup rocks decrease from the coeur d alene district toward the idaho and kaniksu batholiths approximately normal to the trends of metamorphic isograds fold axes foliation and the major reverse faults of the district isoclinal folding thrust faulting high temperature metamorphism granitic plutonism and regional scale metamorphic hydrothermal activity is documented in the region between 140 and 45 ma representing the only such combination of events in the coeur d alene region subsequent to about 1300 ma the sr and oxygen results and geologic evidence favor formation of the ore bearing carbonate veins by fluids related to a complex metamorphic hydrothermal system during the cretaceous pb with proterozoic isotopic compositions was probably mobilized and incorporated like other metals into the hydrothermal veins during this event the ore bearing veins were sheared and displaced during early tertiary northwest trending dextral strike slip faulting along the osburn fault and related structures of the lewis and clark line

strontium 87 strontium 86 ratios as tracers in groundwater and surface waters in mono basin california the 87sr 86sr isotope ratios in spring waters in mono basin california are highly variable and reflect contact with different rock types whole rock 87sr 86sr ratios throughout the basin range between 0 7054 and 0 7281 ratios in surface water samples differ greatly between runoff from the mainly granitic sierra 0 7094 0 7097 and runoff from the volcanic regions 0 7054 0 7064 the ratio in mono lake water 0 7096 is similar to the ratios of streams from the sierra nevada springs close to the western shoreline have more radiogenic sr ratios 0 7092 0 7100 while those on the east side have ratios 0 7081 0 7088 indicative of a mixture of water from the volcanic terrain and mono lake thermal springs at the south side of the lake have 87sr 86sr ratios of 0 7081 0 7089 and might originate in paleozoic limestones at depth

contrasting iron isotopic compositions in river suspended particulate matter the negro and the amazon annual river cycles abstract iron isotopic compositions fe irmm 14 56 of suspended particulate matter spm from two major rivers in the amazon basin the amazon river itself at the obidos station and the negro river at the serrinha station were investigated in the present study the main objective was to search for temporal variations during their annual river cycles fe irmm 14 56 values for the amazon river at obidos range between 0 00 and 0 15 indistinguishable from the average continental crust value in contrast the iron isotopic compositions of the negro river serrinha station spm vary between 0 34 and 0 82 whereas the dissolved matter is isotopically heavier in this river the lack of significant isotopic variations in the amazon river indicates that one individual spm subsurface sample is representative of the river during the whole annual river cycle in opposition to results obtained for the negro river the data suggest that in organic poor white water rivers such as the amazon iron isotopic signatures of the suspended fraction reflect a detrital crustal component with little isotopic fractionation on the other hand in the organic rich negro river which has tropical podzols as the main iron source the iron redox cycling at the water soil interface influences the iron isotopic composition