boron lithium relationships in rhyolites and associated thermal waters of young silicic calderas with comments on incompatible element behaviour abstract this study had three goals 1 1 to study b distribution in a rhyolitic volcanic sequence already extensively investigated for other elements 2 2 to interpret the joint behaviour of b and li during the interaction of such rocks with subsurface waters 3 3 to assess the manner in which water affects the behaviour of incompatible elements such as b and gd new b gd and sm analyses have been made on a suite of yellowstone rhyolites including fresh and partially devitrified glassy obsidian from surface exposures of several flows drill core of increasing degrees of alteration in the biscuit basin flow and two drill cores from other flows within the biscuit basin flow the sm and gd concentrations remain rather constant 9 12 and 8 10 ppm respectively and behave conservatively independent of alteration boron decreases from about 10 to 3 ppm with progressive alteration and li increases from about 40 ppm by a factor of 2 3 in the most altered rocks thermal waters reflect leaching from the fresh rocks but contain much less li than b b li 3 compared with 0 8 in fresh obsidian retention of li was favoured by abundant illitic alteration obsidians from the valles and long valley calderas show greater li loss during alteration all the rhyolitic rocks lose b during aqueous alteration the waters acquire both b and li but proportionately much more b natural waters of all kinds including those from the three calderas show six orders of magnitude range in aqueous b and li with a high degree of linear correlation and an average ratio b li essentially constant at 4 0 the linearity mainly expresses processes of dilution and concentration reactions specific to b or li engender waters with deviating b li the patterns of sm gd b li variation in rocks exemplify two kinds of behaviour in petrological processes with no hydrous phase lunar rocks mantle fresh seafloor basalt the lower continental crust these elements are incompatible and behave similarly when an aqueous phase is present b and li behave independently of sm and gd

evidence for li rich brines and early magmatic fluid rock interactionin the larderello geothermal system abstract the geochemical features of fluids accompanying the first stages of geothermal activity linked to magmatic intrusions have been documented for the larderello geothermal system italy deep drilling has provided samples which preserve evidence of this early geothermal activity four wells san pompeo 2 monteverdi 7 sasso 22 and serrazzano vc 11 penetrated the deeper parts of the larderello system located in a metamorphic basement underlying the tertiary nappe complex which constitutes the main aquifer at larderello the drill holes terminated close to the inferred roof of a granitic complex thought to be responsible for geothermal activity fluid inclusion data were obtained from recrystallized quartz lenses and quartz veins in samples displaying high temperature assemblages plagioclase actinolite biotite tourmaline clinopyroxene andradite wollastonite and also from magmatic quartz in a leucogranite dike the inclusions are mainly secondary in origin oriented in fluid inclusion planes fip related to hydrothermal circulation in the larderello system several generations of high temperature fluids were trapped and include 1 1 h2o co2 dominated vapors displaying variable but significant contents of ch4 and n2 2 2 aqueous vapors containing licl with variable salinity 3 3 aqueous licl brine often oversaturated with respect to halite at room temperature 4 4 complex brine always oversaturated at room temperature with respect to two halite and sylvite or more n 4 salts the presence of licl was confirmed by identification of the salt hydrate licl 5h2o at very low temperature using raman spectroscopy bulk salinities could be roughly estimated at around 30 wt eq licl for the licl brine geometric and chronologic relationships between fip reveal close relationships and mutual contamination between the h2o co2 vapors and licl brine indicating synchronism in their trapping these fluids were generated and trapped at pressures of 100 130 mpa nearly 23 mpa above the estimated present day lithostatic pressure this implies a denudation rate between 0 2 and 0 5 mrn a 1 since the onset of hydrothermal activity compatible with the setting of larderello in a young tortonian collision belt fluid inclusion trapping temperatures 425 650 c show a monotonous increase towards the inferred granite and are around 100 200 c higher than the highest present day temperatures the results are interpreted as recording the interaction between magmatic and contact metamorphic fluids in the early larderello system the h2o co2 vapors resulted from the reheating of the basement metamorphic series often c rich under relatively high temperatures during contact metamorphism lirich fluids expelled from an underlying li rich leucogranite migrated through the metamorphic series and the already cooled granite dikes and experienced local boiling the fluid inclusion data demonstrate the involvement of magmatic fluids during the initial development of this high energy geothermal field

interplay between biotic and environmental conditions in pre salt messinian microbialites of the western mediterranean upper miocene mallorca spain microbial buildups that predate the messinian salinity crisis including one of the few phanerozoic examples of giant microbialites crop out upon the island of mallorca w mediterranean sedimentological and geochemical data from microbialites and associated deposits both essentially dolomitic indicate that they grew in shallow marine conditions but relatively restricted from the open marine realm two microbialite bearing sequences occur both consisting of subtidal to supratidal deposits periods of restriction led to evaporative and hypersaline conditions that favored the development of microbialites and local precipitation of sulfates by contrast ephemeral periods marked by more open conditions were devoid of microbialites and allowed production of bioclastic deposits microbialites range from decameter to decimeter scale reflecting differences in accommodation space despite contrasting sizes all microbialite bodies record similar mesostructure evolution through time from thrombolites to stromatolites with a sharp transition between these endmembers the change from subtidal to shallower more restricted and saline intertidal environments triggered biotic substitution of thrombolite generating microbial communities to stromatolite generating ones furthermore a wide variety of microstructures from agglutinated to micritic with fossilized microbes indicates that two main accretion processes occurred microbially influenced primary dolomite precipitation and grain trapping and binding which were controlled by the interaction between microbes and changes in environmental conditions e g grain supply hydrodynamics and hydrochemistry therefore the diversity of macro meso and microstructures of these microbialites was caused by a complex interplay between depositional biotic and hydrological parameters which offers useful insights for the palaeoecological interpretation of other examples at any scale and throughout geological time

moment tensor inversions of m 3 earthquakes in the geysers geothermal fields california microearthquakes have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields hydrofracturing and co2 sequestration sites characterizing and understanding the faulting process of induced earthquakes which is generally achieved through moment tensor inversion could both help in risk prediction and in reservoir development monitoring however this is a challenging task because of their lower signal to noise ratio at frequencies typically used in earthquake source analyses therefore higher resolution velocity models and modeling of seismic waves at higher frequencies are required in this study we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions we utilize a short period seismic network located in the geysers geothermal field in northern california and limit our study to that which would be achieved by industry in a typical reservoir environment we obtain full moment tensor solutions of m 3 earthquakes using waveform modeling and first motion inversions we find that these two data sets give complimentary but yet different solutions some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially this illuminates the presence of fluids at depth and their role for the generation of these small magnitude earthquakes finally since first motions are routinely obtained for all magnitude earthquakes our approach could be extended to small earthquakes where noise level and complex green s functions prohibit using waveforms in moment tensor inversions

large scale right slip displacement on the east san francisco bay region fault system california implications for location of late miocene to pliocene pacific plate boundary a belt of northwardly younging neogene and quaternary volcanic rocks and hydrothermal vein systems together with a distinctive cretaceous terrane of the franciscan complex the permanente terrane exhibits about 160 to 170 km of cumulative dextral offset across faults of the east san francisco bay region esfbr fault system the offset hydrothermal veins and volcanic rocks range in age from 01 ma at the northwest end to about 17 6 ma at the southeast end in the fault block between the san andreas and esfbr fault systems where volcanic rocks are scarce hydrothermal vein system ages clearly indicate that the northward younging thermal overprint affected these rocks beginning about 18 ma the age progression of these volcanic rocks and hydrothermal vein systems is consistent with previously proposed models that relate northward propagation of the san andreas transform to the opening of an asthenospheric window beneath the north american plate margin in the wake of subducting lithosphere the similarity in the amount of offset of the permanente terrane across the esfbr fault system to that derived by restoring continuity in the northward younging age progression of volcanic rocks and hydrothermal veins suggests a model in which 80 110 km of offset are taken up 8 to 6 ma on a fault aligned with the bloomfield tolay franklin concord sunol calaveras faults an additional 50 70 km of cumulative slip are taken up 6 ma by the rogers creek hayward and concord franklin sunol calaveras faults an alternative model in which the permanente terrane is offset about 80 km by pre miocene faults does not adequately restore the distribution of 8 12 ma volcanic rocks and hydrothermal veins to a single northwardly younging age trend if 80 110 km of slip was taken up by the esfbr fault system between 8 and 6 ma dextral slip rates were 40 55 mm yr such high rates might occur if the esfbr fault system rather than the san andreas fault acted as the transform margin at this time major transpression across the boundary between the pacific and north american plates at about 3 to 5 ma would have resulted in the transfer of significant slip back to the san francisco peninsula segment of the san andreas fault since that time the esfbr fault system has continued to slip at rates of 11 14 mm yr if this interpretation is valid the esfbr fault system was the pacific north american plate boundary between 8 and 6 ma and this boundary has migrated both eastward and westward with time in response to changing plate margin geometry and plate motions

fluorescent bands in massive corals result from terrestrial fulvic acid inputs to nearshore zone the discovery of yellow green fluorescent bands in the skeletons of massive corals from inshore waters of the great barrier reef and the temporal and spatial correlations of these bands with adjacent river flow1 prompted an investigation into the substances responsible for the phenomenon we have determined that all regions of the coral skeleton contain fulvic acids2 3 which impart a blue background fluorescence the yellow green fluorescent bands found only in inshore coral appear to result from enhanced concentrations of low relative molecular mass 10 000 fulvic acids from adjacent river input these compounds are ubiquitous and the yellow green banding phenomenon can be expected to occur in massive corals located near to significant river systems in the widely distributed genus porites4 the great age of the largest colonies1 means that extremely long highly resolvable records of coastal runoff exist throughout tropical nearshore seas

dating of deformation phases using k ar and 40ar 39ar techniques results from the northern apennines abstract paleozoic to oligocene metasedimentary rocks present in the alpi apuane region of the northern apennines italy have been sequentially deformed during a tertiary progressive deformation in an attempt to date the individual deformation episodes over 50 conventional k ar and 1140 ar 39ar incremental gas release analyses have been carried out on fine grained white micas separated from samples whose structural settings were well known mineralogy x ray diffractometry and thin section analyses indicate that the constituent muscovite and phengite formed under metamorphic conditions of 3 4 kbars and 300 400 c during all deformational phases pre existing micas were variably crenulated during each subsequent deformational phase both k ar and 40ar 39ar analyses were carried out on 0 6 2 m 2 6 m and 6 20 m size separates of the phengitic white mica although the k ar apparent ages range from 11 to 27 ma and are consistent with available stratigraphic constraints the 40ar 39ar age spectra display variable internal discordancy these isotopic data indicate that 1 both the k ar and 40ar 39ar total gas ages decrease as the degree of crenulation increases 2 the k ar and 40ar 39ar total gas ages decrease as grain size decreases 3 for each sample characteristics of the 40ar 39ar age spectra depend upon grain size with fine sizes yielding discordant patterns which systematically increase in apparent age from low to high temperature and 4 phengitic micas associated with earliest structures yield generally older ages than micas associated with later structures the isotopic results are interpreted to indicate that the major deformation phase d1 occurred at approximately 27 ma with subsequent pulses ending by c 10 ma these results may be combined with finite strain data to suggest that the region was deformed at strain rates between 10 15 and 10 14 s 1 a 27 ma age indicates mid oligocene initiation of plate tectonic activity in the western mediterranean and concomitant deformation in the northern apennines

activators of photoluminescence in calcite evidence from high resolution laser excited luminescence spectroscopy abstract laser excited luminescence spectroscopy of a red algal biogenic calcite and a synthetic mn calcite can make the distinction between organic and trace element activators of photoluminescence organic activated photoluminescence in biogenic calcite is characterized by significant peak shifts and increasing intensity with shorter wavelength excitation and by significant decreases in intensity after heating to 400 c in contrast mn activated photoluminescence shows no peak shift greatest intensity under green excitation and limited changes after heating examination of samples with a high sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators

chronological control of coral records using luminescent lines and evidence for non stationary enso teleconnections in northeast australia eight multicentury porites coral cores were used to develop a 373 year chronology by cross dating techniques adapted from dendrochronology characteristic patterns of distinct luminescent lines within the coral skeletons were matched between coral cores from inshore and mid shelf reefs in the central great barrier reef australia skeleton plots of luminescent banding were produced for each core and combined into a master chronology back to ad 1615 in addition to improving dating control the luminescence master chronology provides a proxy for burdekin river runoff and queensland summer rainfall variations in the magnitude of the correlation between the luminescence master and the mann et al 2000 nino3 sea surface temperature reconstruction provides insights into the long term stability of el nino southern oscillation enso telecon nections burdekin river runoff was significantly inversely related to enso variability for much of the period from the ad 1650s to 1800 suggesting that enso related te

tropical river flow and rainfall reconstructions from coral luminescence great barrier reef australia 1 rainfall and river flow in northeast queensland australia are highly seasonal and show high interannual and decadal variability that is modulated by el nino southern oscillation enso events and the pacific decadal oscillation pdo reconstructions of october september freshwater input to the great barrier reef lagoon and october september queensland rainfall are developed from visual assessment of the occurrence and intensity of luminescent lines in massive porites from up to 25 coral cores from 15 nearshore reefs regularly influenced by river flood plumes separate reconstructions are developed for four rivers herbert burdekin pioneer and fitzroy and these are used to reconstruct total annual freshwater flow into the great barrier reef 69 74 variance calibrated and an index of queensland rainfall 53 57 variance calibrated the reconstructions extend back to 1631 but are most reliable from 1661 and capture significant decadal variability the reconstructions provide insights into long term tropical rainfall and river flow variability and the behavior of enso and the pdo over several centuries significant though weak relationships are found between these reconstructions and an independent reconstruction of enso the reconstructions highlight that observations from the instrumental records of high interannual and decadal rainfall and river flow variability in northeast australia also characterize the past few centuries although there appears to be no overall trend toward wetter or drier conditions the reconstructions suggest that the variability of rainfall and river flow has increased during the twentieth century with more very wet and very dry extremes than in earlier centuries as projected for the region as a consequence of global warming

elucidating the dynamics and mixing agents of a shallow fjord through age tracer modelling abstract the mixing agents and their role in the dynamics of a shallow fjord are elucidated through an eulerian implementation of artificial tracers in a three dimensional hydrodynamic model the time scales of vertical mixing in this shallow estuary are short and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields the fjord s response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing transport time scales of fresh water runoff and estuarine circulation in relation to external forcing using age tracers released at surface and bottom we quantify the time scales of downward mixing of surface water and upward mixing of bottom water wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom the time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0 7 h to 9 0 days with an average age of 2 7 days for the year 2004 the fjord receives fresh water from two streams entering the innermost part of the fjord and the distribution and age of this water are studied using both ageing and conservative tracers the salinity variations outside this fjord are large and in contrast to the salinity the artificial tracers provide a straight forward analysis of river water content the ageing tracer is used to estimate transport time scales of river water i e the time elapsed since the water left the river mouth in may 2004 the typical age of river water leaving the fjord mouth is 5 days as the major vertical mixing agent is wind it controls the estuarine circulation and export of river water when the wind stress is set to zero the vertical mixing is reduced and the vertical salinity stratification is increased and the river water can be effectively exported out of the fjord we also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind induced straining of the along estuary density gradient we find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord and with an overall decrease in vertical stratification and river water content at the surface thus our results show no apparent signs of wind induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events

regional variations in water quality and relationships to soil and bedrock weathering in the southern sacramento valley california usa abstract regional patterns in ground and surface water chemistry of the southern sacramento valley in california were evaluated using publicly available geochemical data from the us geological survey s national water information system nwis within the boundaries of the study area more than 2300 ground water analyses and more than 20 000 surface water analyses were available ground waters from the west side of the sacramento valley contain greater concentrations of na ca mg b cl and so 4 while the east side ground waters contain greater concentrations of silica and k these differences result from variations in surface water chemistry as well as from chemical reactions between water and aquifer materials sediments that fill the sacramento valley were derived from highlands to the west the coast ranges and east the sierra nevada mountains the former having an oceanic provenance and the latter continental these geologic differences are at least in part responsible for the observed patterns in ground water chemistry thermal springs that are common along the west side of the sacramento valley appear to have an effect on surface water chemistry which in turn may affect the ground water chemistry

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

aliphatic hydrocarbons in surface sediments from the north queensland coast and great barrier reef effects of tropical cyclone winifred abstract aliphatic hydrocarbons were determined in inner shelf and reef lagoon surface sediments off the north queensland coast near innisfail in february 1986 immediately after tropical cyclone winifred passed through the region causing severe rainfall runoff and disturbance of bottom sediments lagoon sediments from feather gilbey and potter reefs 25 50 km offshore were characterized by a suite of c 15 c 25 n alkanes and alkenes derived predominantly from algal sources terrestrial hydrocarbons were not present in contrast inner shelf sediments contained relatively large amounts of terrestrial derived c 25 c 33 n alkanes which decreased in concentration with distance from the coast inner shelf sediments collected after the cyclone also contained a suite of petroleum derived hydrocarbons the concentrations of terrestrial derived hydrocarbons increased in samples collected from the inner shelf after the cyclone however the distribution of terrestrial hydrocarbons was largely confined to the inner shelf after the cyclone and only occurred in trace concentrations in midshelf sediments these results indicate that cyclone related outwelling of suspended sediments and presumably nutrients from rivers was confined to the inner shelf and did not reach the reef zone the post cyclone phytoplankton bloom was probably caused by resuspension of bottom sediments and release of porewater nutrients rather than advection of river plumes to the offshore reefs

seasonal rainfall in the sinai desert during the late quaternary inferred from fluorescent bands in fossil corals skeletal bands of alternating high and low density in massive coral species have been used to record their growth history1 2 in the red sea living colonies of the genus porites deposit low density skeletal bands during summer and high density bands during winter3 additionally yellow green fluorescence can sometimes be seen in these massive corals imparted to them by the incorporation of humic material carried by coastal runoff4 annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near shore environment5 6 here we report the finding of similar yellow green fluorescent bands in fossil porites from late quaternary reef terraces in southern sinai which are absent from living porites in the nearby fringing reefs the periodic sequences of the fluorescing humics were found to be superimposed on the low density sub bands of the fossil corals we interpret our observations as evidence that during the late quaternary reef forming peaks the climate was wetter than the extreme desert conditions now prevailing with a possible summer rainfall regime

the hydrothermal system of the calabozos caldera central chilean andes abstract active thermal springs associated with the late pleistocene calabozos caldera complex occur in two groups the colorado group which issues along structures related to caldera collapse and resurgence and the puesto calabozos group a nearby cluster that is chemically distinct and probably unrelated to the colorado springs most of the colorado group can be related to a hypothetical parent water containing 400 ppm cl at 250 c by dilution with 50 of cold meteoric water the thermal springs in the most deeply eroded part of the caldera were derived from the same parent water by boiling the hydrothermal system has probably been active for at least as long as 300 000 years based on geologic evidence and calculations of paleo heat flow there is no evidence for economic mineralization at shallow depth the calabozos hydrothermal system would be an attractive geothermal prospect were its location not so remote

oxygen isotope systematics in an evolving geothermal system coso hot springs california abstract oxygen isotope and clay mineralogy studies have been made on whole rock samples and feldspar separates from three wells along the high temperature west flank of the coso geothermal system california the reservoir rocks have experienced variable 18o 16o depletion with 18o values ranging from primary values of 7 5 down to 4 6 spatial patterns of clay mineral distributions in the three wells are not closely correlated with the distributions expected from measured pre production temperature profiles but do correlate with spatial patterns of 18o 16o depletion indicating that the stability of clay minerals in the three wells is a function of fluid rock interaction in addition to temperature detailed 18o measurements in the three wells identify a limited number of localized intervals of extensive 18o 16o depletion these intervals document localized zones of higher permeability in the geothermal system that have experienced significant fluid infiltration water rock interaction and oxygen isotopic exchange with the geothermal fluids the local zones of maximum 18o 16o depletion in each well correspond closely with current hot water production zones most feldspar separates have measured 18o values too high to have completely attained oxygen isotope exchange equilibrium with the reservoir fluid at pre production temperatures in general the lower the 18o value of the feldspar the closer the feldspar approaches exchange equilibrium with the geothermal fluid this correlation suggests that fracture induced increases in permeability increase both fluid infiltration and the surface area of the host rock exposed to geothermal fluid promoting fluid rock interaction and oxygen isotope exchange the two most 18o 16o depleted feldspar samples have 18o values too low to be in exchange equilibrium with the pre production reservoir fluid at pre production temperatures these discrepancies suggest that the reservoir fluid in the west flank of the coso geothermal system was hotter and or had a lower 18o value due to fluid rock interaction at higher permeability in the past

high resolution isotopic records from corals using ocean temperature and mass spawning chronometers abstract we present a 6 year long 1978 1984 18 o and 13 c record from a great barrier reef pandora reef porites lutea coral based on near weekly sample intervals a sampling technique was designed to minimise any smoothing or distortion of the isotopic record due to complex coral growth calyx architecture and calcification at depth within the tissue layer the arrival time of the mid winter minimum sea surface temperature is very consistent 2 weeks near pandora reef and provides an annual time marker offering more precision than the traditional density band chronometer the improved chronology and high resolution record demonstrate that signal distortion in porites due to calcification within the tissue layer and variable intra annual coral extension is generally negligible also confirmed is that the arrival time of monsoonal floods is precisely preserved 1 week within the skeleton of porites the sensitivity of weekly sampling allows the detection of a subtle warm to cool sea surface temperature anomaly which preceded by more than one year a similar temperature anomaly associated with the 1982 83 el nin o in the east pacific sharply higher 13 c values coincide with the time of the annual coral mass spawning event in the great barrier reef recognition of this mass spawning signal should simplify the interpretation of coral 13 c records and provides an additional precise time marker with which to adjust chronologies when intra annual coral extension is not constant

nature and origin of organic matter in carbonates from speleothems marine cements and coral skeletons organic matter in speleothem calcite marine carbonate cements and aragonitic coral skeletons was studied to determine its location molecular structure functionality and effect on mineral growth sem analyses showed that inorganically precipitated carbonates incorporate during growth adsorbed organic matter between submicroscopic subunits of the crystals whereas biologically secreted carbonates incorporate biogenic tissue between the crystals molecular fluorescence spectroscopy indicated that low molecular weight fulvic acids are the most important constituents of the organic matter the fulvic acids are probably derived from soils speleothem calcite dissolved organic matter marine carbonates and biological decay products aragonitic coral skeleton

tracer dating and ocean ventilation the interpretation of transient tracer observations depends on difcult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions recent studies have attempted to circumvent this problem by making use of a derived quantity age based on the simultaneous distribution of two complementary tracers such as tritium and its daughter helium 3 the age is defined with reference to the surface such that the boundary condition takes on a constant value of zero we use a two dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms an interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age we define an idealized ventilation age tracer that is conservative with respect to mixing and we explore how its behavior compares with that of the tracer based ages over a range of advective and diffusive parameters transient tracers such as tritium and tritiugenic helium 3 chlorofiuorocarbons especially cfc 11 and cfc 12 and radiocarbon produced by nuclear bomb tests have entered the oceans primarily during the past 30 years the inherent time scale of these tracers matches very well typical time scales for thermocline ventilation as well as other important oceanic processes such as deep water formation they have been used with some success to study the time scales of thermocline ventilation e g sarrniento 1983 jenkins 1987 and oxygen utilization rates our e g jenkins 1977 1980 1982 1987 as well as other processes such as equatorial upwelling rates broecker et al 1978 quay et al 1983 wunsch 1984 and transport of upper north atlantic deep water weiss et al 1985 the problem of coping with the nonsteady state aspect of these tracers has been dealt with in many ways few of them truly satisfactory for example rooth and ostlund 1972 chose to estimate the diapycnic diffusivity in a region where there was some evidence that the tracer distributions were approximately in steady state at the time of their measurements wunsch 1984 used a similar steady state assumption in his study of equatorial upwelling using bomb radiocarbon such an argu ment cannot be applied in most regions of the ocean however indeed one can question whether it applies even in the above situations therefore one generally would expect that it would be necessary to know something about the evolution of the tracer concentration in time as well as the time history of the boundary conditions for that tracer over the same span of time for example sarrniento s 1983 tritium box model of the thermocline solved the conserva tion equation for the period of time between 1952 before nuclear bomb tests had injected a significant amount of tritium into the oceans and 1972 when a single realization of the tracer field was obtained by a series of field studies the surface concentration time history of dreisigacker and roether 1978 was used as a boundary condition such an l now at deutsche forschungs und versuchasanstalt ftir luft

hydrology of lake eyre australia el nino link abstract all major ephemeral rivers of australia lie in the lake eyre basin dry for years on occasions they carry enormous floods with annual volumes of 40 km 3 and instantaneous discharges of the order of 30 000 m 3 s 1 mean annual runoff of the basin is 4 km 3 or 3 5 mm significantly less than the 57 mm for the whole of australia this paper examines lake eyre and its drainage basin describing the historical hydrology of the catchment both in terms of instrument records and inflows hindcast using a model based on the technique of coral fluorescence palaeohydrological reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs reconstruction coral fluorescence is a function of nearby river discharge and can be used to reconstruct annual river outputs beyond the instrument period the burdekin river catchment runoff history is strongly paralleled by the volumes of lake eyre inflows during the period of common reliable instrument gaugings the burdekin runoff data have been extended back to 1735 a d using the correlation between river discharge and annual growth band fluorescence in an old coral from pandora reef off the north queensland coast for the instrument period 1952 to 1980 73 of the variance between coral fluorescence and burdekin discharge is common during the period 1949 1980 41 of the variance between coral fluorescence and lake eyre inflow data is common modelled inflows to lake eyre for the period 1885 1948 are based on the latter data set

fracturing processes due to temperature and pressure nonlinear waves propagating in fluid saturated porous rocks a model is proposed of rock deformation fracturing in the subsurface of hydrothermal systems in response to deep fluid rock temperature and pore fluid pressure perturbations carried upward by hot and pressurized fluid fronts since during these episodes of unrest one also has to take into account that rock parameters can evolve a model of fluid diffusivity change as a function of pore fluid pressure is described through reformulating the linear thermoporoelastic equations rock deformation fracturing is thus thought of as being associated with migration of thermomechanical nonlinear waves which travel upward associated with an increase in concurrent fluid diffusivity on dynamical grounds it is assumed that on the boundary of the two superimposed horizons the overlying rock suddenly starts rupturing caused by the arrival of supercritical water from below which drives up a pore fluid pressure excess in this connection the purpose of this analysis is to investigate the general evolution of the subsurface pressure and temperature fields assuming that the original signal is itself strong enough to generate fracturing processes of the overburden rock on its arrival a general formulation provides evidence of nonlinear thermal waves compensated waves and residual pressure burgers waves that can be found for every value of the system parameters a mechanical analogy is also presented which is treated analytically and numerically allowing one to gain intuitive insight into such complex phenomena a characteristic of these nonlinear processes is that the resulting timescales of the order of years for the case of the campi flegrei and the izu peninsula can be particularly small corresponding to quick hyperthermal phenomena during the filtrating movement of fluid toward the earth s surface

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

the geysers cobb mountain magma system california part 2 timescales of pluton emplacement and implications for its thermal history abstract over 400 ion microprobe u pb isotopic ages measured for zircons extracted from 24 geothermal wells that penetrate the geysers plutonic complex gpc allow us to conclude that the entire known extent of the gpc crystallized during the early pleistocene nine samples of the microgranite porphyry that forms the shallow cupola 100 1 500 m below sea level mbsl of the gpc yield the oldest model u pb age 1 75 0 01 ma after correction for initial u series disequilibrium errors 1 twelve samples from the main intrusive phase orthopyroxene biotite granite present at depths 1 250 mbsl define a crystallization age of 1 27 0 01 ma this coincides with the age determined for a structurally and compositionally distinct body of granodiorite 1 25 0 01 ma n 5 samples that is intruded over a similar depth range two petrographically distinct varieties of orthopyroxene biotite granite yield ages of 1 46 0 03 gpc21 6000 and 1 16 0 02 ma ca5636 74f 21 three samples u pb zircon ages for dikes intruded in metagraywacke country rocks overlap with those obtained from the main body of the gpc and include the youngest material identified dike sample negu2 st1 7700 1 11 0 03 ma overall the u pb results demonstrate that the main body of the gpc 300 km3 was emplaced and crystallized within the upper crust over a short time interval 0 2 ma that overlaps with zircon crystallization ages of overlying silicic volcanic units

fluid rock interactions in co2 saturated granite hosted geothermal systems implications for natural and engineered systems from geochemical experiments and models abstract hydrothermal experiments were conducted and geochemical models constructed to evaluate the geochemical and mineralogical response of fractured granite and granite epidote in contact with thermal water with and without supercritical co 2 at 250 c and 25 45 mpa illite smectite zeolite precipitate as secondary minerals at the expense of k feldspar oligoclase and epidote illite precipitates in experiments reacting granite and granite epidote with water metastable smectite forms in the experiments injected with supercritical co 2 waters are supersaturated with respect to quartz and saturated with respect to chalcedony in co 2 charged experiments but neither mineral formed carbonate formation is predicted for experiments injected with supercritical co 2 but carbonate only formed during cooling and degassing of the granite epidote co 2 experiment experimental results provide insight into the buffering capacity of granites as well as the drivers of clay formation metastable smectite in the experiments is attributed to high water rock ratios high silica activities and high co 2 and magnesium iron concentrations smectite precipitation in supercritical co 2 bearing geothermal systems may affect reservoir permeability silicate formation may create or thicken caps within or on the edges of geothermal reservoirs carbonate formation as desired for carbon sequestration projects coinciding with geothermal systems may require extended periods of time cooling and degassing of co 2 saturated waters leads to carbonate precipitation potentially plugging near surface production pathways

convective hydrothermal c02 emission from high heat flow regions abstract in addition to volatiles released from volcanoes the flux of co2 to the atmosphere from other sources e g metamorphism and subsurface magmatism represents an important aspect of the global carbon cycle we have obtained a direct estimate of the present day atmospheric co2 flux from convective hydrothermal systems within subaerial seismically active high heat flow regions geothermal systems of the salton trough california u s a and the taupo volcanic zone new zealand provide benchmarks for quantifying convective hydrothermal co2 fluxes from such regions co2 fluxes from the salton trough 109 mol yr 1 and the taupo volcanic zone 8 109 mol yr 1 were computed using data on convective heat flow and the temperatures and co2 concentrations of reservoir fluids the similarity in specific co2 flux 106 mol km 2 yr 1 from these two disparate geologic tectonic settings implies that this flux may be used as a baseline to compute convective hydrothermal co2 emission from other areas of high heat flow if this specific flux is integrated over high heat flow areas of the circum pacific and tethyan belts the total global co2 flux could equal or exceed 1012 mol yr 1 adding this flux to a present day volcanic co2 flux of 4 1012 mol yr 1 the total present day earth degassing flux could balance the amount of co2 consumed by chemical weathering 7 1012 mol yr 1

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

isotope geochemistry of mercury in source rocks mineral deposits and spring deposits of the california coast ranges usa abstract we present here the first study of the isotopic composition of mercury in rocks ore deposits and active spring deposits from the california coast ranges a part of earth s crust with unusually extensive evidence of mercury mobility and enrichment the franciscan complex and great valley sequence which form the bedrock in the california coast ranges are intruded and overlain by tertiary volcanic rocks including the clear lake volcanic sequence these rocks contain two types of mercury deposits hot spring deposits that form at shallow depths the franciscan complex and great valley sequence contain clastic sedimentary rocks with higher concentrations of mercury than volcanic rocks of the clear lake volcanic field mean mercury isotopic compositions 202hg for all three rock units are similar although the range of values in franciscan complex rocks is greater than in either great valley or clear lake rocks hot spring and silica carbonate mercury deposits have similar average mercury isotopic compositions that are indistinguishable from averages for the three rock units although 202hg values for the mercury deposits have a greater variance than the country rocks precipitates from spring and geothermal waters in the area have similarly large variance and a mean 202hg value that is significantly lower than the ore deposits and rocks these observations indicate that there is little or no isotopic fractionation

particles in fluid inclusions from yellowstone national park bacteria micrometre sized particles resembling microorganisms have been found in liquid rich fluid inclusions in hydrothermal quartz crystals from a research drill hole in yellowstone national park wyoming the particles are moving apparently in brownian motion the 1 2 mm long quartz crystals were obtained from fractures in late pleistocene rhyolite at depths of 59 5 102 1 and 102 5 m the measured temperature and pressure at 102 1 m where about 99 of the moving particles were found were about 190 c and 1 24 mpa respectively homogenization temperatures 190 280 c of fluid inclusions at this depth mostly exceed measured temperatures which suggests that the fluid inclusions probably did not form under present day conditions instead the fluid inclusions probably formed 45 000 14 000 b p at a much higher pressure owing to the weight of at least 490 m of glacial ice only 3 of the more than 200 quartz crystals examined contain up to several hundred rodlike threadlike or irregular shaped moving particles fluid inclusions in 17 other quartz crystals each contain one or two moving particles that were observed only because of their continuous brownian motion

fluid mineral equilibria in a hydrothermal system roosevelt hot springs utah the availability of fluids and drill cuttings from the active hydrothermal system at roosevelt hot springs allows a quantitative comparison between the observed and predicted alteration mineralogy calculated from fluid mineral equilibria relationships comparison of all wells and springs in the thermal area indicates a common reservoir source and geothermometer calculations predict its temperature to be higher 288 c 10 than the maximum measured temperature of 268 c the composition of the deep reservoir fluid was estimated from surface well samples allowing for steam loss gas release mineral precipitation and ground water mixing in the well bore this deep fluid is sodium chloride in character with approximately 9700 ppm dissolved solids a ph of 6 0 and gas partial pressures of o2 ranging from 10 32 to 10 35 atm co2 of 11 atm h2s of 0 020 atm and ch4 of 0 001 atm comparison of the alteration mineralogy from producing and nonproducing wells allowed delineation of an alteration pattern characteristic of the reservoir rock theoretical alteration mineral assemblages in equilibrium with the deep reservoir fluid between 150 and 300 c in the system na2o k2o cao mgo feo fe2o3 al2o3 h4sio4 h2o h2s co2 hcl were calculated minerals theoretically in equilibrium with the calculated reservoir fluid at 240 c include sericite k feldspar quartz chalcedony hematite magnetite and pyrite this assemblage corresponds with observed higher temperature 210 c alteration assemblage in the deeper parts of the producing wells the presence of montmorillonite and mixed layer clays with the above assemblage observed at temperatures 210 c corresponds with minerals predicted to be in equilibrium with the fluid below 240 c alteration minerals present in the reservoir rock that do not exhibit equilibrium with respect to the reservoir fluid include epidote anhydrite calcite and chlorite these may be products of an earlier hydrothermal event or processes such as boiling and mixing or a result of errors in the equilibrium calculations as a result of inadequate thermochemical data

age intercalibration of 40ar 39ar sanidine and chemically distinct u pb zircon populations from the alder creek rhyolite quaternary geochronology standard abstract we report results from a 40 ar 39 ar sanidine and ca tims 238 u 206 pb zircon dating study of eruption and crystal residence timescales of the alder creek rhyolite acr california extruded during the cobb mountain normal polarity subchron c1r 2n a 40 ar 39 ar acr sanidine date of 1 1850 0 0016 ma 2 external uncertainty determined relative to the astronomically dated a1 tephra sanidine is interpreted as the acr eruption age this age is supported by ca tims u pb zircon dating guided by la icpms trace element analyses titanium in zircon tizr thermometry and cathodoluminescence cl imaging using these data two compositionally distinct zircon populations were revealed pre acr group b zircon exhibit oscillatory zoning large positive ce and negative eu anomalies high incompatible trace element contents tizr temperatures of 650 c 750 c and th u disequilibrium corrected 238 u 206 pb dates of 1 38 1 24 ma these crystals are interpreted as antecrysts inherited from earlier intrusives in the geysers cobb mountain magma source region acr related group a zircon present as discrete grains and overgrowths on group b zircon display less intense cl with diffuse zoning and have less pronounced positive ce and negative eu anomalies lower incompatible trace element contents higher tizr temperatures that range up to 840 c and significantly younger dates the youngest group a dates yield a weighted mean of 1 1978 0 0046 ma 2 including systematic uncertainties that is interpreted as the mean age of zircon crystallization prior to eruption the 13 5 ka offset between the 40 ar 39 ar and 238 u 206 pb dates can be attributed to zircon magma residence time recognition of a young population of acr zircon is consistent with the 40 ar 39 ar eruption age which coincides with the astronomical age estimate for the cobb mountain subchron determined by correlating the oxygen isotope record of the giant piston core md972143 to the la93 1 1 orbital solution on the basis of independent radio isotopic and orbital forcing results we propose the refined age of 1 1850 0 0016 ma 2 external uncertainty for the quaternary acr 40 ar 39 ar sanidine standard

palaeohydrological variation in a tropical river catchment a reconstruction using fluorescent bands in corals of the great barrier reef australia massive long lived corals in inshore waters of the great barrier reef contain yellow green fluorescent bands these bands are due to terrestrial humic and fulvic compounds incorporated into the coral skeleton during high river flow events fluorescence measurements are presented for two colonies of porites spp from locations in the path of the burdekin river floodwaters the major river in north queensland draining into the coral sea the records extend from ad 1737 to 1980 and 1644 to 1986 respectively the two independent coral records show a high degree of similarity the two series are combined and used to reconstruct burdekin river runoff for the period ad 1644 to 1980 the regression model accounts for 83 of the annual water year variability of burdekin river flow and is verified over independent data the 337 year reconstruction thus increases by threefold the length of record for considering interannual to decadal climate variations in northeast australia instrumental and reconstructed burde

extensional tectonics at the geysers geothermal area california comparisons between the yearly volume of steam withdrawn from the geysers california geothermal reservoir and the number of earthquakes indicate that most of the seismicity is induced to establish the inducing mechanism an estimate of the stress field orientation was calculated from inversion of 210 fault plane solutions below 1 km depth the geysers is undergoing uniaxial extension with the least principal stress 3 oriented near horizontal at approximately 105 azimuth the consistency between the local and regional stress fields indicates that the regional tectonic stress is much larger than the stresses induced locally through geothermal activities the stress data are equivocal as to whether earthquakes are induced due to conversion of aseismic to seismic slip or by increased shear stresses arising from reservoir contraction the observed tendency for downward growth of seismicity may arise from a preferential fracture orientation that is near vertical in conjunction with a stress state where the gradient of 1 exceeds that of 3 evidence of extension at the geysers and in the surrounding clear lake region indicates a direct relationship to the presence of the quaternary clear lake volcanics

trace element distribution in an active hydrothermal system roosevelt hot springs thermal area utah abstract chemical interaction of thermal fluids with reservoir rock in the roosevelt hot springs thermal area utah has resulted in the development of characteristic trace element dispersion patterns multielement analyses of surface rock samples soil samples and drill cuttings from deep exploration wells provide a three dimensional perspective of chemical redistribution within this structurally controlled hot water geothermal system five distinctive elemental suites of chemical enrichment are recognized each characteristic of a particular combination of physical and chemical conditions within the geothermal system these are 1 concentrations of as sb be and hg associated with siliceous material at locations of liquid discharge fluid mixing or boiling 2 concentrations of mn ba w be cu co as sb and hg in manganese and iron oxide deposits 3 high concentrations of hg in argillized rock near fumaroles and lower concentrations in a broad diffuse halo surrounding the thermal center 4 concentrations of as in sulfides and li in silicate alteration minerals immediately surrounding high temperature fluid flow controlling fractures 5 deposits of caco 3 at depth where flashing of brine to steam has occurred due to pressure release the geochemical enrichments are not in general widespread pervasively developed zones of regular form and dimension as are typical in many ore forming hydrothermal systems as the geothermal system develops changes and eventually declines through time the chemical deposits are developed remobilized or superimposed upon each other thus preserving within the rocks a record of the history of the geothermal system recognition of trace element distribution patterns during the exploration of a geothermal system may aid definition of the present geometry and interpretation of the history of the system

age and thermal history of the geysers plutonic complex felsite unit geysers geothermal field california a 40ar 39ar and u pb study abstract sixty nine ion microprobe spot analyses of zircons from four granite samples from the plutonic complex that underlies the geysers geothermal field yield 207pb 206pb vs 238u 206pb concordia ages ranging from 1 13 0 04 ma to 1 25 0 04 1 ma the weighted mean of the u pb model ages is 1 18 0 03 ma the u pb ages coincide closely with 40ar 39ar age spectrum plateau and terminal ages from coexisting k feldspars and with the eruption ages of overlying volcanic rocks the data indicate that the granite crystallized at 1 18 ma and had cooled below 350 c by 0 9 1 0 ma interpretation of the feldspar 40ar 39ar age data using multi diffusion domain theory indicates that post emplacement rapid cooling was succeeded either by slower cooling from 350 to 300 c between 1 0 and 0 4 ma or transitory reheating to 300 350 c at about 0 4 0 6 ma subsequent rapid cooling to below 260 c between 0 4 and 0 2 ma is in agreement with previous proposals that vapor dominated conditions were initiated within the hydrothermal system at this time heat flow calculations constrained with k feldspar thermal histories and the present elevated regional heat flow anomaly demonstrate that appreciable heat input from sources external to the known geysers plutonic complex is required to maintain the geothermal system this requirement is satisfied by either a large underlying convecting magma chamber now solidified emplaced at 1 2 ma or episodic intrusion of smaller bodies from 1 2 to 0 6 ma

luminescence and density banding patterns in massive porites corals around the thai malay peninsula southeast asia we characterized the annual luminescent and skeletal density banding patterns in 51 massive porites corals from 15 reefs from six locations around the thai malay peninsula in southeast asia and explored the seasonal environmental cues drivers of band formation location specific recurrent annual luminescent banding patterns were found at all study locations with a brighter band occurring toward the end of the year october november december at five locations and in june one location annual density banding patterns could only be discerned at four locations and were categorized into those that formed a dense band commencing november december and those starting may june overall compared to luminescence variations in skeletal density provided a less clear signal for demarcation of annual growth increments seasonal variations in luminescence showed clearest relationships with salinity as a proxy for freshwater river runoff no convincing relationship between intra annual luminescence intensity and density variations was found which supports the notion that luminescent banding is due to inclusions of fluorophores into the coral skeleton rather than variations in skeletal architecture the relationships between seasonal density variations and significant wave height and rainfall suggest density banding in this region is likely related to wave energy or some other correlated environmental parameter s the large variability in skeletal banding patterns not only highlights the current relatively poor understanding of their nature and causes but also the need for replication in their interpretation especially in settings with complex seasonal hydrodynamic hydrological patterns such as those found around the thai malay peninsula

variation in sericite compositions from fracture zones within the coso hot springs geothermal system two types of white micas are found in drillhole samples within the geothermal system at coso hot springs low permeability zones of the crystalline basement contain coarse grained relict muscovite whereas rock alteration near fracture zones at temperatures 150 c is characterized by abundant finegrained sericite in association with secondary calcite and quartz and unaltered relict microcline in this hydrothermal sericite there is an increase in interlayer k octahedral mg fetotal and tetrahedral al with increasing temperature between 215 to 250 c thermodynamic activity of the al2si4o10 oh 2 component of serielles calculated using site mixing approximations of helgeson and aagaard 1985 decreases with increasing temperature between 215 and 250 c as a consequence of the observed variations in the interlayer octahedral and tetrahedral site occupancies the activity of kal2 alsi3o10 oh 2 is essentially constant in the coso seriates over this temperature range the calculated equilibrium distribution of aqueous species in the hydrothermal solutions produced from well 16 8 together with cation activity phase diagrams that account for variations in sericite composition requires a ph of 6 7 6 8 at temperatures between 236 and 250 c comparison of predicted and observed phase relations with fluid compositions indicate that seriates are in local equilibrium with the geothermal reservoir fluid whereas relict metamorphic muscovites are metastable although the compositions of hydrothermal sericites are a complex function of temperature pressure and geothermal fluid composition compositional relations observed at coso together with published compositions of hydrothermal dioctahedral layer silicates from the salton sea geothermal system demonstrates that elemental compositions of interlayer k and tetrahedral al increase systematically with increasing temperature despite the dramatic differences in fluid compositions between these two geothermal systems this suggests that the observed variations in interlayer and tetrahedral site occupancy is largely dependent on the enthalpy of hydrolysis reactions representing equilibrium between sericite solid solutions and the geothermal reservoir fluids

on the propagation of nonlinear transients of temperature and pore pressure in a thin porous boundary layer between two rocks abstract the dynamics of transients of fluid rock temperature pore pressure pollutants in porous rocks are of vivid interest for fundamental problems in hydrological volcanic hydrocarbon systems deep oil drilling this can concern rapid landslides or the fault weakening during coseismic slips and also a new field of research about stability of classical buildings here we analyze the transient evolution of temperature and pressure in a thin boundary layer between two adjacent homogeneous media for various types of rocks in previous models this boundary was often assumed to be a sharp mathematical plane here we consider a non sharp physical boundary between two adjacent rocks where also local steady pore pressure and or temperature fields are present to obtain a more reliable model we also investigate the role of nonlinear effects as convection and fluid rock frictions often disregarded in early models these nonlinear effects in some cases can give remarkable quick and sharp transients all of this implies a novel model whose solutions describe large sharp and quick fronts we also rapidly describe transients moving through a particularly irregular boundary layer

the geysers clear lake area california thermal waters mineralization volcanism and geothermal potential manifestations of a major thermal anomaly in the geysers clear lake area of northern california include the late pliocene to holocene clear lake volcanics the geysers geothermal field abundant thermal springs and epithermal mercury and gold mineralization the epithermal mineralization and thermal springs typically occur along high angle faults within the broad san andreas transform fault system that forms the western boundary of the north american plate in this area the young volcanic rocks overlie mesozoic marine rocks of the great valley sequence which have been thrust above the coeval franciscan complex and penecontemporaneously dropped back down along low angle detachment faults many of the waters of the region are nonmeteoric as defined by their isotopic signature one type of isotopically shifted water emerges from or near great valley sequence rocks and is the most chloride rich it is interpreted to be evolved connate in origin a second type evolved meteoric water has moderate chloride contents high boron contents and high b cl ratios and is found locally in franciscan rocks notably at the sulphur bank mercury mine where it probably results from near closed system repeated boiling of meteoric water in host rocks that also contribute organic components to the water at the sulphur bank mine fracturing of otherwise impermeable franciscan rocks by faulting has created a localized zone of permeability in which thermal water boils repeatedly with limited venting to the surface boron rich fluids were apparently present at depth in the geysers geothermal field when intrusion of silicic magma occurred because the concealed intrusion of felsite is surrounded by a halo of tourmaline bearing hornfels the volume of this poorly dated early to middle quaternary intrusive body probably exceeds the 100 km 3 of erupted clear lake volcanics similar intrusions may have occurred in the eastern part of the area at wilbur springs and the mclaughlin mine where gold deposition and evidence of hydrothermal phenomena suggest more magmatic activity than is indicated by the small exposed bodies of early quaternary basaltic lava the clear lake volcanics are the present locus of volcanism in the northern coast ranges and progressively older volcanic centers occur to the south geophysical data suggest that a large silicic magma body may be centered north of the geysers steam field providing the heat for the geothermal field geothermal power production has peaked at the geysers and pressure declines indicate significant depletion of the fluid resource the vapor dominated field evolved from a preexisting hydrothermal system within fractured otherwise impermeable franciscan metamorphic rocks a deep water table of saline fluid has been postulated to be present under the steam field but no chloride rich water has been found at drillable depth we propose that recently discovered isotopically shifted steam in the northwest geysers area indicates the presence not of deep connate water but xather of boiled down boron rich franciscan evolved meteoric water this water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at the geysers field or from the main clear lake volcanic field

modelling of modern mercury vapor transport in an ancient hydrothermal system environmental and geochemical implications mercury has been used in some mineralizing hydrothermal systems as a significant pathfinder of au and other elements in addition its geochemical behaviour reflects some characteristics related to the transport mechanism of metal bearing fluids in this work the authors analyse the geochemical aspects and the environmental impact of hg mobilization from the old mining area of valle del azogue va from smelting slags mining waste and the partially exploited mineralization that remains a few metres underground the main pathway of hg is the transport of vapor from different foci therefore a mathematical simulation of the process of hg vapor transport was carried out in the valle del azogue va mineral deposit this is one of the two sites in spain the other being the famous district of almaden where hg vapor emissions have been cited the results obtained by means of mathematical simulation were compared with both the real hg concentration values detected in the field upper part of the mining area and with the geochemical distribution patterns of au and other elements related to the mineralization a close relationship between the simulated hg vapor distribution and soil gas concentrations was identified it is proposed that the transport of hg emissions from this old mining area could be the cause of present contamination of marine sediments in the area

evidence of reduced mid holocene enso variance on the great barrier reef australia this study was funded by the national environmental research programme nerp tropical ecosystems hub project 1 3 characterising the cumulative impacts of global regional and local stressors on the present and past bio diversity of the gbr to j xz jmp sgs trc y xf and others and australian research council lief grant le0989067 for the purchase and installation of the mc icp ms essential for this study to jxz jmp y xf and others as well as an australian postgraduate award apa to ndl we are grateful to eric matson from the australian institute of marine science aims for technical assistance in obtaining the fossil coral cores and to hard rock earth works rod morelli and associates in townsville for allowing access to the corals we also thank st vincent s private hospital brisbane for ct scans and queensland diagnostic imaging indooroopilly for x rays we thank an anonymous reviewer for helpful comments on an earlier manuscript the data used in this study are available through the cited references figures and tables as well as in the supporting information to this manuscript

holocene and paleogene arkoses of the massif central france mineralogy chemistry provenance and hydrothermal alteration of the type arkose abstract paleogene arkoses of the auvergne region of france represent the type arkose originally described by brongniart 1826 they are alluvial fan and fluvial deposits including traction current sandstones arenites and matrix rich debris flow deposits wackes locally they have been extensively altered by geothermal waters related to nearby tertiary holocene volcanic activity the alteration is typified by leaching of detrital grains and precipitation of ubiquitous chert cement the average gazzi dickinson composition of unaltered arenites is q40f60l0 with k f potash feldspar total feldspar 0 63 altered arenites have an average composition of q55f43l2 with k f 0 73 reflecting loss of plagioclase due to intense a teration when secondary chert is included with detrital quartz and chert the altered rocks have an average composition of q66f32l1 emphasizing silica enrichment associated with alteration holocene sands derived from crystalline basement of the massif central have the same provenance as the paleogene sandstones they have an average gazzi dickinson composition of q46f49l5 with k f 0 52 and compare favorably with their unaltered ancient counterparts arkosic alluvium at roosevelt hot springs utah is believed to represent a modern analog for alteration of the auvergne sandstones the alluvium has been altered and cemented with silica by geothermal waters at near surface conditions in the epithermal zone chemical analyses of 130 sand and rock samples demonstrate original sediment compositions and changes due to hydrothermal alteration holocene sands and unaltered paleogene clastics are compositionally similar and show variation trends similar to feldspathic clastics derived from granitic basement in other basins silica enrichment in the altered sandstones causes dilution of all other elements as an effect of constant summation consequently most element abundances decline proportionately with silica dilution na and rb however are reduced below the levels predicted by dilution due to plagioclase and biotite destruction as a result k rb ratios are higher in the altered sandstones ba s so4 as and sb are enriched in the altered rocks by precipitation from hydrother al solutions barium is in barite as fracture filling veins and scattered patches in sandstone matrix destruction of mafic minerals during alteration released fe co cr ni zn pb and th that later precipitated as oxides and sulfides in fractures and locally in chert matrix in the sandstones

evidence for suppressed mid holocene northeastern australian monsoon variability from coral luminescence summer monsoon rainfall in northeastern ne australia exhibits substantial interannual variability resulting in highly variable river flows the occurrence and magnitude of these seasonal river flows are reliably recorded in modern inshore corals as luminescent lines here we present reconstructed annual river flows for two 120 year mid holocene windows based on luminescence measurements from five cores obtained from three separate coral colonies we were able to cross date the luminescence signatures in four cores from two of the colonies providing confidence in the derived reconstruction present day ne australian rainfall and river flow are sensitive to el nino southern oscillation enso variability with la nina el nino events typically associated with wetter drier monsoon seasons thus our replicated and annually resolved coral records provide valuable insights into the northern australian summer monsoon and enso variability at a key period 6 ka when greenhouse gas levels and ice sheet cover were comparable to the preindustrial period but orbital forcing was different average modern and mid holocene growth characteristics were very similar suggesting that sea surface temperatures off ne australia at 6 kyr were also close to present values the reconstructed river flow record suggests however that the mid holocene australian summer monsoon was weaker less variable from year to year possibly indicative of reduced enso variability and characterized by more within season flood pulses than present in contrast to today the delivery of moisture appears to have been dominated by eastward propagating convective coupled waves associated with the madden julian oscillation

regional 18o depletion of neoproterozoic igneous rocks from avalonia cape breton island and southern new brunswick canada neoproterozoic igneous rocks of the avalonian mira terrane cape breton island and caledonia terrane southern new brunswick have experienced regional 18 o depletion the majority of these rocks have 18 o wr values between 1 and 6 markedly different from igneous rocks of the inboard ganderian terranes which have normal high 18 o wr values of 7 to 12 the 18 o depletion of these avalonian terranes resulted from pervasive hydrothermal alteration all of the igneous rocks contain classic propylitic alteration assemblages of turbid feldspar chlorite epidote sericite and calcite and host multiple generations of veins containing the same phases the 18 o values of the rock forming minerals show strong disequilibrium with qtz fs ranging from 2 5 to 11 0 and kfs plg from 0 5 to 1 0 such values are indicative of post magmatic hydrothermal alteration the hydrothermal alteration occurred at ca 560 550 ma during initial transcurrent rifting of avalonia at the gondwanan margin the development of rift wrench basins with associated bimodal volcanism allowed large volumes of hydrothermal fluids to penetrate and circulate within mira and caledonia terrane crust before its submergence in the early cambrian ca 540 530 ma the hydrothermal fluids were predominantly meteoric although the presence of a significant seawater component cannot be ruled out the almost ubiquitous 18 o depletion exhibited by the neoproterozoic rocks in these avalonian terranes is absent in the associated ganderian terranes suggesting that avalonia remained separate from ganderia until at least the cambrian ordovician this 18 o depletion provides an additional geochemical tool for identification of avalonian crust in other areas of the appalachians and europe

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

geomorphic controls on mercury accumulation in soils from a historically mined watershed central california coast range usa abstract historic hg mining in the cache creek watershed in the central california coast range has contributed to the downstream transport of hg to the san francisco bay delta different aspects of hg mobilization in soils including pedogenesis fluvial redistribution of sediment volatilization and eolian transport were considered the greatest soil concentrations 30 mg hg kg 1 in cache creek are associated with mineralized serpentinite the host rock for hg deposits upland soils with non mineralized serpentine and sedimentary parent material also had elevated concentrations 0 9 3 7 mg hg kg 1 relative to the average concentration in the region and throughout the conterminous united states 0 06 mg kg 1 erosion of soil and destabilized rock and mobilization of tailings and calcines into surrounding streams have contributed to hg rich alluvial soil forming in wetlands and floodplains the concentration of hg in floodplain sediment shows sediment dispersion from low order catchments 5 6 9 6 mg hg kg 1 in sulphur creek 0 5 61 mg hg kg 1 in davis creek to cache creek 0 1 0 4 mg hg kg 1 these sediments deposited onto the floodplain during high flow storm events yield elevated hg concentrations 0 2 55 mg hg kg 1 in alluvial soils in upland watersheds alluvial soils within the cache creek watershed accumulate hg from upstream mining areas with concentrations between 0 06 and 0 22 mg hg kg 1 measured in soils 90 km downstream from hg mining areas alluvial soils have accumulated hg released through historic mining activities remobilizing this hg to streams as the soils erode

evaluation of mineral aqueous chemical equilibria of felsic reservoirs with low medium temperature a comparative study in yangbajing geothermal field and guangdong geothermal fields abstract classical geothermometers are useful tools for estimating reservoir temperatures of geothermal systems however their application to low medium temperature reservoirs is limited because large variations of temperatures calculated by different classical geothermometers are usually observed in order to help choose the most appropriate classical geothermometer for calculating the temperatures of low medium temperature reservoirs this study evaluated the mineral aqueous equilibria of typical low medium temperature felsic reservoirs in the yangbajing geothermal field and guangdong geothermal fields the findings of this study support that reservoirs in the guangdong geothermal fields have no direct magma influence also natural reservoirs may represent the intermediate steady state before reaching full equilibrium which rarely occurs for the low medium temperature geothermal systems without the influence of magma even with seawater intrusion the process of minerals reaching mineral aqueous equilibrium is sequential chlorite and chalcedony are the first then followed by k feldspar kaolinite and k mica chlorite may reach equilibrium at varying activity values and the equilibrium between k feldspar and kaolinite or k feldspar and k mica can fix the contents of k and al in the solutions although the sio2 and al attain equilibrium state albite and laumontite remain unsaturated and thus may affect low medium temperature calculations in this study the chalcedony geothermometer was found to be the most suitable geothermometer for low medium temperature reservoirs the results of k mg geothermometer may be useful to complement that of the chalcedony geothermometer in low medium temperature reservoir systems na k geothermometer will give unreliable results at low medium temperatures and na k ca will also be unsuitable to calculate reservoir temperatures lower than 180 c probably caused by the chemical imbalance of laumontite

fluid inclusion and isotopic systematics of an evolving magmatic hydrothermal system the geysers california is the site of a long lived hydrothermal system that initially developed 1 5 2 m y ago in response to the intrusion of a hypabyssal granitic pluton although wells drilled into the geysers produce only dry steam fluid inclusion isotopic and mineralogic data demonstrate that the present vapor dominated regime evolved from an earlier and more extensive liquid dominated hydrothermal system circulation of these early fluids produced veins characterized by tourmaline biotite actinolite clinopyroxene within the pluton and adjacent biotite rich hornfels actinolite ferroaxinite epidote and epidote chlorite within the intermediate parts of the thermal system and calcite in the outer parts potassium feldspar and quartz are present in all assemblages pressure corrected homogenization temperatures and apparent salinities of fluid inclusions trapped in vein minerals range from 440 c and 44 wt nacl equivalent within the hornfels 600 m from the pluton to 325 c and 5 wt nacl equivalent at distances of approximately 1500 m from the intrusion we suggest that the shallow moderate salinity fluids are connate waters modified by water rock interactions while the high salinity fluids are interpreted as magmatic brines halite dissolution temperatures of inclusions in the hornfels and pluton indicate that the magmatic fluids were trapped at lithostatic pressures 300 900 bars in contrast homogenization temperatures of the connate fluids suggest trapping under hydrostatic pressures of less than several hundred bars whole rock 18o values of samples from the geysers display systematic variations with respect to depth location within the field and grade of alteration at depths below 610 m relative to mean sea level the 18o values are strongly zoned around a northwest southeast trending low located near the center of the steam reservoir as the pluton beneath the geysers is approached the 18o values decrease from approximately 14 per mil near the surface to 4 to 7 per mil within the hornfels the 18o values then increase to 8 to 10 per mil at the intrusive contact and thereafter vary little within the pluton calculated rock water fractionation factors suggest that temperature was the dominant control on the vertical decrease in the isotopic values of the reservoir rocks in contrast the increase in the 18o values within the hornfels suggest equilibration with an isotopically heavy fluid and or decreasing water rock ratios the formation of vapor dominated conditions is reflected in the abrupt appearance of low salinity 0 0 0 4 wt nacl equivalent fluid inclusions with homogenization temperatures near 265 c these inclusion fluids are thought to represent steam condensate that formed as the early liquid dominated system boiled off bladed calcite which is corroded in places and late stage clays provide mineralogic evidence of boiling and the formation of an acidic condensate in the upper part of the reservoir and in the overlying caprock at greater depths however clear mineralogic evidence of boiling is lacking the present vapor dominated regime at the geysers consists of two hydraulically connected steam reservoirs within the main steam reservoir pressures are vaporstatic and temperatures are nearly constant at 240 c beneath this reservoir in the northwestern third of the field temperatures as high as 342 c have been encountered wells drilled into this deeper reservoir discharge corrosive cl bearing steam

the evolution of volcano hosted geothermal systems based on deep wells from karaha telaga bodas indonesia temperature and pressure surveys fluid samples and petrologic analyses of rock samples from deep drill holes at the karaha telaga bodas geothermal field on the volcanic ridge extending northward from galunggung volcano west java have provided a unique opportunity to characterize the evolution of an active volcano hosted geothermal system wells up to 3 km in depth have encountered temperatures as high as 353 c and a weakly altered granodiorite that intruded to within 2 to 3 km of the surface the intrusion is shallowest beneath the southern end of the field where an acid lake overlies a nearly vertical low resistivity structure 10 ohm m defined by magnetotelluric measurements this structure is interpreted to represent a vapor dominated chimney that provides a pathway to the surface for magmatic gases four distinct hydrothermal mineral assemblages document the evolution of the geothermal system and the transition from liquid to vapor dominated conditions the earliest assemblage represents the initial liquid dominated system generated during emplacement of the granodiorite between 5910 76 and 4200 150 y bp tourmaline biotite actinolite epidote and clay minerals were deposited contemporaneously at progressively greater distances from the intrusive contact assemblage 1 at 4200 150 y bp flank collapse and the formation of the volcano s crater kawah galunggung resulted in catastrophic decompression and boiling of the hydrothermal fluids this event initiated development of the modern vapor dominated regime chalcedony and then quartz were deposited as the early low salinity liquids boiled assemblage 2 both vapor and liquid rich fluid inclusions were trapped in the quartz crystals liquid rich fluid inclusions from the southern part of the field record salinities ranging from 0 to 26 weight percent nacl cacl 2 equivalent and locally contain fluorite daughter crystals we suggest based on temperature salinity relationships and evidence of boiling that these fluids were progressively concentrated as steam was lost from the system however mixing with fluids derived from the underlying intrusion or generated during the formation of acid so 4 water on the vapor dominated chimney margins could have contributed to the observed salinities as pressures declined co 2 and so 4 rich steam heated water drained downward depositing anhydrite and calcite assemblage 3 in the fractures limiting further recharge fluid inclusions with salinities up to 31 weight percent nacl equivalent were trapped in these minerals as the descending water vaporized the final assemblage is represented by precipitates of nacl kcl and fecl x deposited on rock surfaces in portions of the vapor dominated zone that boiled dry vapor dominated conditions extend over a distance of at least 10 km and to depths below sea level deep wells drilled into the underlying liquid dominated reservoir in the northern and central part of the volcanic ridge produce low salinity fluids representing recent recharge of meteoric and steam heated water the evolution of volcanic hosted vapor dominated geothermal systems can be described by a five stage model stage 1 involves the formation of an over pressured liquid dominated geothermal system soon after magmatic intrusion in stages 2 and 3 pressures progressively decrease and a curtain of steam heated water surrounding a magmatic vapor dominated chimney at 350 c and 14 2 mpa develops the relatively low pressure near the base of the chimney causes liquid inflow adjacent to the intrusion and the development of a secondary marginal vapor dominated zone in stage 4 the magmatic vapor discharge from the intrusion becomes small vapor pressure declines and the secondary vapor dominated zone expands above the intrusion in stage 5 the vapor dominated zone floods because heat from the intrusion is insufficient to boil all liquid inflow a more common liquid dominated volcanic hosted system then develops

tracking crystallinity in siliceous hot spring deposits siliceous hot spring deposits sinters entrap paleoenvironmentally significant components and are used as extreme environment analogs in the search for early earth and extraterrestrial life however sinters undergo a series of textural and mineralogical changes during diagenesis that can modify and overprint original environmental signals for ancient hydrothermal settings including those close to the dawn of life these transformations have long since occurred so that study of diagenetic processes and effects is best undertaken in much younger deposits still undergoing change three young sinters preserve the entire diagenetic sequence of silica phases from opal a to quartz the 6000 to 11 500 years bp 70 years sinter at steamboat springs nevada the 1600 1900 160 years bp opal mound sinter at roosevelt hot springs utah and the 456 35 years bp deposit at sinter island taupo volcanic zone new zealand provide an opportunity to track crystallographic mineralogic and morphologic transitions of sinter diagenesis using standard and new analytical approaches worldwide sinter forms from cooling alkali chloride waters as noncrystalline opal a transforming first into noncrystalline opal a ct then paracrystalline opal ct moganite paracrystalline opal c and eventually to microcrystalline quartz in this study these changes were identified by the novel and combined application of electron backscatter diffraction x ray powder diffraction and scanning electron and optical microscopy techniques we show that mineralogical changes precede morphological and accompanied crystallographic transformations during this modification silica particles grow and shrink several times from the micron to nano meter scales via dissolution reprecipitation and recrystallization and diagenesis follows the ostwald step rule all deposits followed nearly identical diagenetic pathways with time as the only variable in the march toward physicochemically stable quartz crystals diagenesis alters original environmental signatures trapped within sinters after five silica phase changes filamentous microfossils are modified but still remain recognizable within sinter from the opal mound and steamboat springs deposits and during the opal a to opal ct silica phase transformations at sinter island therefore delineating diagenetic components and how they affect sinters is necessary to accurately identify biosignals from ancient hot spring deposits

fluorescent bands in massive corals record centuries of coastal rainfall massive coral colonies on the great barrier reef grow outwards at 5 25 mm yr 1 ref 1 skeletal density varies seasonally in all massive corals from the great barrier reef and an exact temporal record of growth can be obtained by x radiography of appropriately cut sections of the colony2 3 environmental influences on coral growth have been described from such analyses4 6 this is the first report from the skeletons of massive corals of yellow green fluorescent bands which appear under long wave uv light such fluorescence is confined to corals growing within 20 km of the shore and is not present in massive corals from mid and outer shelf reefs of the central great barrier reef region the timing width and intensity of the fluorescent bands correlate strongly with summer monsoonal rainfall and coastal runoff large colonies several centuries old can provide long records of the strength and periodicity of terrestrial runoff to the tropical nearshore environment such records are potentially important to climatology meteorology agriculture civil engineering and management of the great barrier reef

cathodoluminescence in quaternary carbonate deposits abstract the cathodoluminescent oscillatory and sectoral growth zones common in crystals formed in ancient limestone successions in a variety of putative environments appear to be rare or absent from recent and pleistocene marine carbonate sequences the factors controlling cathodoluminescence and reasons for this disparity are examined the cathodoluminescent zones in the cements of ancient rocks have been interpreted as responses to variations in the redox potential of formative pore waters during crystal growth although similar cathodoluminescent behaviour is recorded from some deposits including travertines and quaternary speleothems formed in what are thought to have been strongly oxidizing environments the apparent absence of cathodoluminescence in the most recent and pleistocene marine deposits that presumably reflect deposition and diagenesis in environments that are also characteristically oxidized therefore seems anomalous the controlling influences on cathodoluminescence are reviewed together with evidence relating to observations of pleistocene marine deposits and likely conditions of formation but where it is present the mechanism s for its development remain elusive

belemnite taphonomy upper jurassic western tethys part ii fossil diagenetic analysis including combined petrographic and geochemical techniques abstract fossil diagenetic features were analyzed on 56 belemnite rostra from the pozo canada section external prebetic as well as 31 belemnite rostra from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian they mainly correspond to hibolithes and secondarily to belemnopsis fossil diagenetic processes were analyzed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy and geochemical elemental and stable isotopes techniques the most common fossil diagenetic processes are dissolution calcite cementation and recrystallization of the apical zone and outer growth rings of belemnite rostra these processes may appear enhanced by fracturing and stylolite formation petrographic study also reveals that the alternation of cloudy and clear concentric growth areas displayed by many belemnite rostra corresponds to an early diagenetic feature in origin however an original concentric growth pattern is also observed under epifluorescent microscopy and bsem this growth pattern fits with changes in the mg and s content of the rostra although fossil diagenetic processes typically make specimens non suitable for paleoenvironmental interpretations microsampling of petrographically altered and non altered areas from the same specimens performed directly from thin sections after petrographic study allowed us to obtain excellent geochemical results suitable for paleoenvironmental interpretations these geochemical analyses moreover demonstrates that caution should be taken if elemental analyses are used as the most significant criteria for discriminating diagenetically altered and non altered belemnite samples

stable oxygen isotopic composition of corals from the gulf of guinea as indicators of periods of extreme precipitation conditions in the sub sahara stable oxygen isotopic analyses of scleractinian coral skeletons from the gulf of guinea in the eastern atlantic reveal that the corals from this region can be used to identify periods of severe drought and above average precipitation in sub sahara africa data presented in this paper show an inverse correlation between precipitation in the sahel and the 18 o values of a coral skeletons of the species siderastrea spp collected from the island of principe in the gulf of guinea this is opposite to the correlation expected as previous work has suggested that higher sea surface temperatures occur in the gulf of guinea during periods of low rainfall in the sahel such an association would lead to a positive correlation between sahel precipitation and skeletal 18 o the explanation for the observed inverse correlation is that the salinity of the gulf of guinea is strongly influenced by the outflow from the niger and congo rivers these periods of high freshwater input also correlate with periods of higher rainfall in the sub sahara and therefore affect the 18 o values of the coral skeleton the correlation between 18 o values of the coral skeleton and temperature in the northern subtropical atlantic ocean r 0 34 the magnitude of the dipole r 0 45 and the latitudinal position of the intertropical convergence zone r 0 37 illustrate that the 18 o values in the coral skeleton reflect climate dynamics of the region that affect the precipitation patterns in sub sahara africa

evidence for oxygen isotope disequilibrium in selected geothermal and hydrothermal ore deposit systems abstract there is ample evidence from geothermal systems that temperatures estimated from the oxygen isotope fractionation between alteration phases and coexisting aquifer fluids agree closely 25 c with measured bore hole temperatures conversely many hydrothermal systems exhibit varying degrees of apparent fluid rock oxygen isotope disequilibrium measured rock water equilibrium rock water a comparison of data from a variety of hydrothermal systems indicates that an increase in the degree of isotopic equilibration can be related in a general way to an increase in the temperature salinity and intensity of fracturing this relationship is entirely consistent with calculations carried out for a simple closed system model that estimates the fraction of isotope exchange between rock and fluid as a function of temperature rock type salinity of the fluid grain size water rock ratio and the rate of isotope exchange the fact that many silicate fluid reactions and their isotopic counterparts are fast leads us to conclude that observed variations in the degree of exchange may have resulted from local self sealing of the fracture network prior to equilibration the ability for fractures to remain open or to propagate allowing continued fluid flow may be the deciding factor in the attainment of isotopic equilibration

hydrothermal petroleums from yellowstone national park wyoming u s a abstract in yellowstone national park oil is actively discharging with thermal waters at several widely separated thermal areas samples from two locations were studied petroleum from calcite springs occurs as vapor condensates in steam vents detailed geochemical analyses show a complex origin for the petroleum fluid deeply buried hydrothermally altered sedimentary rocks are believed to have contributed a high temperature pyrolysate consisting largely of polynuclear aromatic hydrocarbons and heterocyclic compounds shallow sedimentary rocks which are also hydrothermally altered have contributed large amounts of aromatic and polar compounds as well as minor amounts of hydrocarbons the permian phosphoria formation is suggested as a likely source rock for the bulk of the oils autochthonous pyrolysates and lipids from thermally altered surface and near surface bacterial and land plant debris have also been introduced to the vents the latter may have been introduced by downward percolating meteoric water the oil from rainbow springs is a highly paraffinic low s crude oil depleted in light hydrocarbons unlike the calcite springs samples the oil from rainbow springs is believed to have originated from a single sedimentary source rock with little or no hydrocarbon contributions from surface biota the oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input and places the age of the source unit in the tertiary consideration of the local stratigraphy and water temperatures limits the probable source zone to the eocene aycross formation an intra volcanic lacustrine mudstone calculation of deep water temperatures indicates that this unit is exposed to thermal waters in an extensive near surface aquifer such conditions are consistent with the widespread surface manifestations and biomarker kinetic models consideration of the petroleum chemistry and regional hydrodynamics indicates that the yellowstone park oils did not migrate into the park from distant sources the chemical data are also inconsistent with the oils being generated and trapped prior to tertiary volcanism at both calcite springs and rainbow springs oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively shallow sedimentary rocks by hydrothermal fluids

altering avalonia oxygen isotopes and terrane distinction in the appalachian peri gondwanan realmlaboratory for stable isotope science lsis the university of western ontario contribution 236 distinct 18o depletion is characteristic of a large majority of the 620 550 ma felsic igneous rocks of avalonia in the northern appalachian orogen neoproterozoic rocks in the boston avalon terrane have the lowest 18owr values 3 1 followed by the mira terrane in cape breton island and the caledonia terrane in new brunswick 1 2 the avalon terrane in newfoundland 2 8 and the antigonish highlands in nova scotia 5 3 in contrast this depletion of 18o is observed in very few of the paleozoic felsic igneous rocks from these avalonian terranes and also in very few of the neoproterozoic and paleozoic felsic igneous rocks from the inboard ganderian terranes the low 18o character of the neoproterozoic igneous rocks is related to regional pervasive post magmatic alteration by predominantly meteoric hydrothermal fluids 18oh2o 6 to 4 at 200 450 c the alteration likely occurred during late neoproterozoic transtensional extension of avalonia large scale fluid infiltration and circu

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

geophysical characterization of the northwest geysers geothermal field california abstract the clear lake volcanic field in northern california is the youngest and northern most part of a long lived volcanic system that has produced recent 10 ka eruptions adjacent to the clear lake volcanic field is the world s largest energy producing geothermal field the geysers the hottest part of the geyser s geothermal field is in the northwest where temperatures reach 400 c at 3 km depth low permeability high thermal gradients and low steam saturation prescribed development of an enhanced geothermal system egs in the northwest geysers to increase energy producing capacity though the northwest geysers is known to be the hottest part of the field geophysical methods have failed to adequately image any inferred heat source this project aims to image the heat source of the northwest geysers using newly collected gravity and magnetotelluric mt measurements gravity data were jointly modeled with existing magnetic data along a two dimensional profile aligned with an existing geologic cross section the key feature of the potential field model is a low density low susceptibility body at 5 km depth bmsl under the egs mt data were modeled in three dimensions to characterize subsurface resistivity structure where the upper 3 km of the resistivity model agrees well with existing data lithologic and steam saturation are estimated from modeled resistivity values using existing geophysical data below 3 km depth bmsl the resistivity model images a possible young intrusion under the egs a possible zone of partial melt

boiling and fluid mixing in the chlorite zone of the larderello geothermal system abstract the geochemical features of the geothermal fluids produced within the boiling zone in the relatively shallow parts of the larderello geothermal system italy have been documented as a result of deep drilling which provided samples from 1480 to 2500 m depth four wells monteverdi 1 monteverdi 2a sasso 22 and capannoli 2b have been sampled in the intermediate parts of the larderello aquifer located in a metamorphic basement underlying the tertiary nappe complex which constitutes the shallow aquifer at larderello fluid inclusions from recrystallized quartz lenses and quartz veins in samples displaying a predominant quartz chlorite epidote adularia paragenesis have been studied by microthermometry and raman spectroscopy the inclusions are primary and pseudo secondary in origin when formed in authigenic quartz or of secondary origin when located in fluid inclusion planes related to microfracturing of metamorphic quartz lenses several generations of fluids are present and include h 2 o co 2 dominated vapours and liquids and a series of aqueous liquids for the most part of relatively low salinity the t m ice of both early and late inclusions are mostly between 0 0 and 4 5 c indicating that the salinities of the hydrothermal fluid were very low to moderate however rare fluid inclusions with lower t m ice from 4 9 to 25 0 c were also observed these inclusions may record the occasional input of saline fluids which may be derived from the interaction of the hydrothermal waters with the evaporites present in the shallow part of the larderello field at capannoli 2b earliest h 2 o co 2 liquids were trapped under minimal pressures of 610 645 bars which bracket the estimated present day lithostatic pressure 640 bars in all other samples the main stage of quartz chlorite crystallization occurs under boiling conditions attested by the presence of liquid and vapour rich inclusions that in some instances can be texturally interpreted to be coeval their trapping conditions 350 375 c 160 215 bars are higher than the present day temperatures at the same depth later fluid inclusions attest to a significant cooling of the fluids down to temperatures similar to the present day temperatures during this time pressures were close to hydrostatic conditions most fluid inclusions were trapped within the liquid field this indicating that a significant pressure drop has since affected the main aquifers or fractured zones which are at present under vaporstatic conditions

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

origin of warm springs in banks peninsula new zealand abstract thermal springs present rare opportunities to locate and interpret the geological drivers of upper crustal fluid flow interpreting the conditions through which crustal fluids are heated and released to the surface is important for advancing our understanding of crustal deformation and geothermal resource potential across tectonic contexts in new zealand the majority of thermal springs are associated with magmatic hydrothermal systems in the central north island or with the rapidly uplifting bedrock in the south island s convergent fault systems however low enthalpy systems outside of these areas represent attractive targets for potential geothermal resource development the low enthalpy warm springs of banks peninsula located immediately adjacent to christchurch represent a highly understudied but potentially significant resource to the south island s most densely populated metropolitan area hosted within the eroded 11 5 8 ma volcanic complex of banks peninsula these warm springs 14 5 33 6 c represent an anomalous hydrothermal system that has been perturbed by the 2010 2016 canterbury earthquake sequence ces the february 22 2011 mw 6 2 earthquake induced observable changes to the banks peninsula warm springs system including the appearance of new warm springs within the peninsula s north western hillsborough valley we assess the origins of the volcanically hosted banks peninsula warm springs post ces using an integrated isotopic geochemical and soil gas flux approach additionally we elucidate the tectonic context and geological drivers of upper crustal fluid flow in the banks peninsula warm spring system aqueous phase emissions from the springs predominantly plot within the na k hco3 type waters and exhibit 18 o d and 13 c values of 8 30 to 9 26 v smow 60 15 to 64 19 v smow and 12 37 to 15 06 v pdb respectively soil gas flux surveys of the springs at rapaki bay revealed co2 fluxes that average 6 93 10 gm 2 day 1 with an average 13 c value of 19 81 5 v pdb and ch4 fluxes that average 5 58 12 gm 2 day 1 with an average 13 c value of 59 52 1 v pdb our results suggest that the banks peninsula warm springs are a structurally controlled upper crustal metamorphic hydrothermal heated system sourced from high altitude southern alps derived meteoric waters carbon isotope compositions of gaseous emissions associated with the banks peninsula thermal springs are consistent with an upper crustal metamorphic decarbonation and decarboxylation carbon source based on their geochemistry we propose that the banks peninsula warm springs should be considered an outboard extension of the south island s plate boundary hydrothermal system such connectivity implies that long lived low enthalpy geothermal resources may be associated with permeable and distributed fault networks in the periphery of convergent margins

oxygen and carbon isotope ratios of hydrothermal minerals from yellowstone drill cores abstract oxygen and carbon isotope ratios were measured for hydrothermal minerals silica clay and calcite from fractures and vugs in altered rhyolite located between 28 and 129 m below surface in situ temperatures ranging from 81 to 199 c in yellowstone drill holes the purpose of this study was to investigate the mechanism of formation of these minerals the 18o values of the thirty two analyzed silica samples quartz chalcedony cristobalite and cristobalite range from 7 5 to 2 8 about one third of the silica 7samples have 18o values that are consistent with isotopic equilibrium with present thermal waters most of the other silica samples appear to have precipitated from water enriched in 18o up to 4 7 relative to present thermal water assuming precipitation at present in situ temperatures available data on fluid inclusion homogenization temperatures in hydrothermal quartz indicate that silica precipitation occurred mostly at temperatures above those measured during drilling and imply that 15o enrichments in water during silica precipitation were generally larger than those estimated from present conditions similarly clay minerals celadonite and smectite have 18o values higher by 3 5 to 7 9 than equilibrium values under present conditions in contrast all eight analyzed calcite samples are close to isotopic equilibrium with present thermal waters the frequent incidence of apparent 18o enrichment in thermal water from which the hydrothermal minerals precipitated may indicate that a higher proportion of strongly 18o enriched deep hydrothermal fluid once circulated through shallow portions of the yellowstone system or that a recurring transient 18o enrichment effect occurs at shallow depths and is caused either by sudden decompressional boiling or by isotopic exchange at low water rock ratios in new fractures the mineralogy and apparent 18o enrichments of hydrothermal fracture filling minerals are consistent with deposition during transient boiling or rock water exchange fracturing events

nitrogen isotopic composition of organic matter from a 168 year old coral skeleton implications for coastal nutrient cycling in the great barrier reef lagoon abstract ongoing human activities are known to affect nitrogen cycling on coral reefs but the full history of anthropogenic impact is unclear due to a lack of continuous records we have used the nitrogen isotopic composition of skeleton bound organic matter cs 15 n in a coastal porites coral from magnetic island in the great barrier reef as a proxy for n cycle changes over a 168 yr period 1820 1987 ad the magnetic island inshore reef environment is considered to be relatively degraded by terrestrial runoff given prior cs 15 n studies from other regions there was an expectation of both secular change and oscillations in cs 15 n since european settlement of the mainland in the mid 1800s surprisingly cs 15 n varied by less than 1 5 despite significant land use change on the adjacent mainland over the 168 yr measurement period after 1930 cs 15 n may have responded to changes in local river runoff but the effect was weak we propose that natural buffering against riverine nitrogen load in this region between 1820 and 1987 is responsible for the observed stability in cs 15 n in addition to coral derived skeletal 15 n we also report for the first time 15 n measurements of non coral derived organic n occluded within the coral skeleton which appear to record significant changes in the nature of terrestrial n inputs in the context of previous cs 15 n records most of which yield cs 15 n changes of at least 5 the magnetic island coral suggests that the inherent down core variability of the cs 15 n proxy is less than 2 for porites

soluble humic substances from in situ precipitated microcrystalline calcium carbonate internal sediment and spar cement in a cretaceous carbonate mud mound albian carbonate mud mound limestones exposed near iraneta northern spain show a fabric and particle specific fluorescence intense fluorescence is restricted to in situ precipitated microcrystalline automicritic fabrics calcified demosponges and coralline sponges intermediate intensity derives from micritized bioclasts pellets and a rim of marine bladed cement most invertebrate skeletons late diagenetic equant cement and crosscutting zones of dolomitization are weakly to nonfluorescent internal microcrystalline sediment allomicrite and red algae debris have variable fluorescence correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite allomicrite and cement time resolved laser induced fluorescence spectroscopy trlfs with ultra short pulses on two extracrystalline fractions naoh soluble and two intracrystalline fractions hcl soluble and naoh soluble showed that most of the soluble humic substances of automicrite are within the crystals but conversely are significantly enriched on outer surfaces of allomicrite spar cement is close to detection limits fluorescence lifetimes are in the range of 0 5 2 ns and 3 5 6 ns we conclude that precipitation of automicrite took place during oxidative organic matter diagenesis i e during condensation reactions of degradation products of marine biopolymers by contrast allomicrite formed by skeletal breakdown followed by ingestion organic coating and reingestion during deposit feeding a humic substance based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds so typical of phanerozoic mud mounds in deeper water settings

pharmacokinetic modelling of multi decadal luminescence time series in coral skeletons abstract as corals grow they incorporate chemical indicators of seawater conditions into their aragonite skeleton after they have traversed an outer living tissue layer long lived massive coral skeletons can record decade and century long time series of seawater status one such environmental clue is luminescence intensity which can correspond to river flow patterns and has been attributed to humic acid incorporation seawater humic acid levels are linked to river flow as rainfall extracts them from catchment soils to then flow into rivers and coastal seas however discrepancies exist when validating coral luminescence records against river flow data with intense luminescence sometimes occurring in the absence of increased flows this contributes to uncertainty when reconstructing pre instrumental river flows and rainfall from coral luminescence here we demonstrate that a major portion of coral core luminescence time series can be explained using a single compartment pharmacokinetic model that incorporates river flow measurements as the equivalent of drug dose the model was robust for luminescence series in corals from near shore reefs regularly influenced by river flow the model implies that after floods a proportion of subsequent luminescence peaks can be derived from the initial flood this explains why some luminescence peaks after floods often do not correspond to additional significant river flows this provides the first mechanism based explanation for temporal changes in coral skeleton luminescence that incorporates a mathematical link between two independent time series making this proxy even more robust for reconstructing river flow and rainfall

thermal history of the acoculco geothermal system eastern mexico insights from numerical modeling and radiocarbon dating abstract acoculco is a geothermal prospective area hosted by a volcanic caldera complex in the eastern trans mexican volcanic belt surface manifestations are scarce and consist of gas discharges co2 rich and acid sulfate springs of low temperature whereas hydrothermal explosive activity is profusely manifested by meter scale craters and mounds of hydrothermal debris and breccias silicic alteration extends for several square kilometers around the zone with gas manifestations and explosive features affecting surficial volcanic rocks primarily tuffs and breccias in the subsurface an argillic alteration zone ammonium illite extends down to a depth of 600 m and underneath it a propylitic zone epidote calcite chlorite occurs down to 1000 m thermal logs from an exploratory borehole eac 1 drilled in 1995 down to 1810 m showed a conductive heat transfer regime under high geothermal gradient 140 c 1000 m in contrast the thermal profile established from temperatures of homogenization of fluid inclusions measured on core samples from the same drill hole suggests that convection occurred in the past through the upper 1400 m of the geothermal system a drop in permeability due to the precipitation of alteration minerals would have triggered the cessation of the convective heat transfer regime to give place to a conductive one with the purpose of determining when the transition of heat transfer regime occurred we developed a 1d model that simulates the time depth distribution of temperature according to our numerical simulations this transition happened ca 7000 years ago this date is very recent compared to the lifespan of the geothermal system in addition radiocarbon chronology indicates that the hydrothermal explosive activity postdates the end of the convective heat transfer regime having dated at least three explosive events at 4867 5295 1049 1417 and 543 709 y cal bp therefore hydrothermal explosions arise from the self sealing of the acoculco geothermal system involving a natural hazard that could affect future geothermal power infrastructure

stable isotope studies of rocks and secondary minerals in a vapor dominated hydrothermal system at the geysers sonoma county california the geysers a vapor dominated hydrothermal system is developed in host rock of the franciscan formation which contains veins of quartz and calcite whose 18 o values record the temperatures and isotopic compositions of fluids prevailing during at least two different episodes of rock fluid interaction the first episode took place at about 200 c during which marine silica and carbonate apparently interacted with ocean water entrapped in the sediments to form veins of quartz and calcite whose 18 o values were around 19 and 16 respectively the calculated water mineral ratios were less than unity the water may have profoundly influenced the 18 o values of spilitic basalts during their metamorphism to greenstones serpentinization and structural emplacement of ophiolite slabs were isotopically unrelated to this episode which was essentially a low grade post cretaceous burial metamorphism d h ratios of actinolite chlorite and micas in host rocks were more profoundly altered during this episode than were 18 o 16 o ratios a paleogeothermal gradient of about 53 c km has been inferred for this episode from 18 o depth distributions of vein minerals the second episode in part recorded by cogenetic vein quartz and calcite 18 o values of 4 to 6 and 1 to 3 respectively began with large quantities of meteoric water circulating in fractures in the rock at temperatures of 160 180 c in response to the initiation of the pliocene pleistocene clear lake magmatism the temperature rose and with the restricted circulation of fluids the ancestral hot water system evolved into the presently active vapor dominated system which according to the cogenetic vein quartz and calcite 18 o values involved temperatures as high as 320 c and fluid mineral ratios near unity the change in the oxygen isotopic composition of the serpentinite within the host rock during this later activity was negligible the 13 c values of vein calcite at the geysers reflect both a marine carbonate and organic component of carbon but carbon isotope exchange has been facilitated by the vapor dominated hydrothermal fluid to a greater degree than in any other episode or in other hot water systems