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

oxygen isotope evidence for hydrothermal alteration within a quaternary stratovolcano lassen volcanic national park california brokeoff volcano a quaternary stratocone located in the lassen volcanic center in northern california has been deeply eroded exposing a 10 km2 meteoric hydrothermal alteration zone at the core of the volcano portions of the former volcanic edifice are sufficiently well preserved that an unusual opportunity exists wherein the alteration pattern can be correlated with the position of the volcanic cone the 18o analyses of more than 100 whole rock samples consisting primarily of andesitic lavas vary from 9 8 to 0 6 per mil the highest 18o values occur in bleached solfatarically altered rocks that have interacted with low ph fumarolic hot springs associated with the present day hydrothermal system low 18o values are found in propylitically altered rocks that underwent isotopic exchange with meteoric hydrothermal fluids at elevated temperatures mostly during the stratovolcanic stage 650 400ka of the hydrothermal system but probably continuing today at depth electron microprobe analyses of secondary layer silicate minerals in strongly propylitized samples 18o 5 0 revealed the presence of discrete chlorite suggesting that temperatures up to 200 to 250 c were attained in the shallow levels of the system two zones of pervasive meteoric hydrothermal alteration defined by concentric 18o contours that are probably interconnected at depth are located within the original topographic edifice of the volcano the most intensely altered rocks within these equant zones of alteration define nnw trends that coincide with stream valleys and with regional structural patterns a comparison of the characteristics of the 18o depleted zone at brokeoff with those of more deeply eroded volcanic centers such as the comstock lode mining district criss and champion 1991 permits the construction of composite 18o cross sections through a hypothetical intact stratovolcano at both brokeoff and comstock hydrothermal fluids were strongly focused into plumelike zones of intense 18o depletion at comstock these low 18o plumes are associated with faults although major fault displacements are not observed at brokeoff the topographic and alteration patterns are consistent with the presence of a linear array of faults that acted as conduits for fluid flow up into the shallow levels of the volcano

precambrian basement geology of the permian basin region of west texas and eastern new mexico a geophysical perspective because most of the permian basin region of west texas and southern new mexico is covered by phanerozoic rocks other means must be found to examine the precambrian upper crustal geology of the region we have combined geologic information on the precambrian from outcrops and wells with geophysical information from gravity and magnetic surveys in an integrated analysis of the history and structure of basement rocks in the region geophysical anomalies can be related to six precambrian events formation of the early proterozoic outer tectonic belt igneous activity in the southern granite rhyolite province an episode of pre grenville extension the grenville orogeny rifting to form the delaware aulacogen and eocambrian rifting to form the early paleozoic continental mar in two geophysical features were studied in detail the abilene gravity minimum and the central basin platform gravity high the abilene gravity minimum is shown to extend from the delaware basin across north central texas and is interpreted to be caused by a granitic batholith similar in size to the sierra nevada batholith in california and nevada this batholith appears to be related to formation of the southern granite rhyolite province possibly as a continental margin arc batholith because of this interpretation we have located the grenville tectonic front southward from its commonly quoted position closer to the llano uplift middle proterozoic mafic intrusions are found to core the central basin platform and the roosevelt uplift these intrusions formed at about 1 1 ga and are related in time to both the mid continent rift system and the grenville orogeny in texas because these features are likely to be rift related they suggest that the concept of a delaware aulacogen needs to be revised only to the extent that the rifting is proterozoic in age not eocambrian precambrian basement structures and changes in lithology have influenced the structure and stratigraphy in the overlying permian basin and thus have potential exploration significance interpretation of the gravity and magnetic data with geologic information also leads us to suggest the existence of pre ellenburger basins which may be extensive and of potential exploration interest

boron geochemistry from some typical tibetan hydrothermal systems origin and isotopic fractionation the tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters hydrochemistry and b isotope samples from geothermal waters in tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential b reservoirs b concentrations range from 0 35 to 171 90 mg l and isotopic values vary between 16 57 and 0 52 geothermal fields along the indus yarlung zangbo suture zone and n s rifts are observed with high b concentrations and temperatures the similar hydrochemical compositions of high b geothermal waters with magmatic fluid and consistent modeling of b isotopic compositions with present 11b values imply that the b in high b geothermal waters is mainly contributed by magmatic sources probably through magma degassing in contrast geothermal fields in other regions of the lhasa block have relatively low b concentrations and temperatures after considering the small fractionation factor and representative indicators of na ca cl hco3 na k and si the conformity between modeling results and the isotopic compositions of host rocks suggests that the b in low temperature geothermal fields is mainly sourced from host rocks according to simulated results the b in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10 it was anticipated that this study would provide useful insight into the sources and fractionation of b as well as further understanding of the relationships between b rich salt lakes and geothermal activities in the tibetan plateau

sedimentologic to metamorphic processes recorded in the high pressure low temperature mesozoic rosetta marble of anatolia anatolia s high pressure metamorphic belts are characterized in part by a neotethyan stratigraphic succession that includes a mid cretaceous hemi pelagic marble sequence this unit contains towards its stratigraphic top dm to m long radiating calcitic rods forming rosette like textures here we refer to these features as rosetta marble the remarkable textural similarity of non metamorphic selenite crystals and radiating calcite rods in the rosetta marble strongly suggests that these textures represent pseudomorphs after selenites metamorphosed hemi pelagic limestones dominated by rosetta selenite pseudomorphs are alternating with siliceous meta sediments containing relictic radiolaria tests this stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non evaporative hemi pelagic deposition from normal marine seawater the regional distribution of rosetta marble exposures over 600 km is indicative of basin scale evaporitic intervals high pressure low temperature metamorphism of these rocks is witnessed by sr rich up to 3500 ppm fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz peak metamorphic conditions of 1 2 gpa and 300 350 c are attested by high si white mica thermobarometry the rosetta marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta sedimentary rocks

feldspar saturation state in natural waters the saturation state of feldspar minerals in natural waters ranging from 0 c to over 300 c was studied waters above 200 c have closely approached equilibrium with microcline and low albite this is consistent with the occurrence of these minerals as hydrothermal minerals in active geothermal systems with temperature in excess of some 200 c the na k activity ratio of geothermal waters with temperature as low as 50 c closely approaches that predicted from thermodynamic data for the reaction low albite k microcline na suggesting that na and k ion activities in these geothermal waters are controlled by simultaneous equilibrium with these two feldspars geothermal waters are undersaturated with primary disordered plagioclases and alkali feldspars of compositions typically found in volcanic rocks accordingly these feldspars tend to dissolve in such waters simultaneously with precipitation of ordered alkali feldspars surface and non thermal groundwaters are usually undersaturated with respect to igneous and metamorphic feldspars regardless of composition and al si ordering and tend therefore to dissolve under weathering conditions

lithium isotopes in island arc geothermal systems guadeloupe martinique french west indies and experimental approach abstract we report lithium li isotopic measurements in seawater derived waters that were discharged from geothermal wells thermal springs and sub marine springs located in volcanic island arc areas in guadeloupe the bouillante geothermal field and martinique lamentin plain and the diamant areas while li isotopic signatures of the geothermal fluids collected from deep reservoirs were found to be homogeneous for a given site the 7li signatures for each of these reservoirs were significantly different the first low temperature 25 250 c experiments of li isotope exchange during seawater basalt interaction confirmed that li isotopic exchange is strongly temperature dependent as previously inferred from natural studies li isotopic fractionation ranged from 19 4 solution solid at 25 c to 6 7 at 250 c these experiments demonstrated the importance of li isotopic fractionation during the formation of li bearing secondary minerals and allowed us to determine the following empirical relationship between isotopic fractionation and temperature solution solid 7847 t 8 093 application of experimental results and literature data to the bouillante area suggested that geothermal water was in equilibrium at 250 260 c it likely has a deep and large reservoir located in the upper sheeted dike complex of the oceanic crust just below the transition zone between andesite volcanic flows and the basaltic dikes the upper dike section from which li is extracted by hydrothermal fluids was characterized by light li isotopic values in the rocks indicating retention of 6li by the altered rocks for the lamentin and diamant areas the geothermal fluids appeared to be in equilibrium with reservoir volcano sedimentary rocks at 90 120 c and 180 c respectively further evidence for this argument is provided by the fact that only the na li thermometric relationship determined for sedimentary basins yielded temperature values in agreement with those measured or estimated for the reservoir fluids this suggests the importance of a sedimentary signature in these reservoir rocks altogether this study highlights that the use of li isotopic systematics is a powerful tool for characterizing the origin of geothermal waters as well as the nature of their reservoir rocks

the behavior of lithium and its isotopes in oilfield brines evidence from the heletz kokhav field israel twenty four brine samples from the heletz kokhav oilfield israel have been analyzed for chemical composition and li isotope ratios the chemical composition of the brines together with geological evidence suggests derivation from messinian seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization the present salinity of the samples 18 47 g cl l was achieved by dilution of the original evaporitic brine by local fresh waters like brines from other sedimentary basins the li cl ratios in the heletz kokhav samples show a prominent li enrichment five fold to eight fold relative to modern seawater the isotopic ratios of li expressed in the 6 li notation vary from 26 3 to 17 9 all values being significantly higher than that of modern seawater 32 irrespective of their corresponding li concentration 1 0 2 3 mg l the isotopic composition of li and the li cl ratio in the oilfield brines were acquired in two stages a the original evaporated seawater gained isotopically light li during the diagenetic interaction between the interstitial messinian brine and the basin sediments a parent brine with an elevated li cl ratio was formed the brine was later diluted in the oilfields b the 6 li values of the final brines were determined during epigenetic interaction with the heletz kokhav aquifer rocks at the same time the li cl ratio inherited from stage a remained largely unchanged this work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins copyright 2002 elsevier science ltd

mudstone petrology of the mesoproterozoic unkar group grand canyon u s a provenance weathering and sediment transport on intracratonic rodinia abstract the synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance weathering regime hydrodynamic effects and diagenesis of the mesoproterozoic unkar group unkar mudstones were derived largely from the grenville orogen go of southwest texas and the adjacent yavapai mazatzal ym and southern granite rhyolite sgr terranes detrital zircon data indicate distinct pulses of go derived sediment during hakatai and dox formation deposition whereas shinumo sediment contains a larger component of ym and sgr material an increase in plagioclase and biotite abundances in the dox further suggest an orogenic pulse bulk chemistry including elevated cr and ni abundances and ree systematics implicate a heterogeneous provenance for unkar sediment best approximated by a mix of granite or granodiorite with some basalt weathering of unkar sediment as determined from mudstone and crystalline source bulk chemical trends is characterized as moderate cia values between 55 and 70 indicative of a temperate climate in an orogenic setting small less than 10 wt amounts of detrital kaolinite and chlorite are consistent with a moderate temperate weathering regime illite the dominant clay mineral in the unkar group is largely the 2m1 polytype and detrital in origin however it is estimated that 7 of the k in the escalante creek member results from k metasomatism and may form up to 15 wt authigenic 1m or 1md illite the clay size fraction and zircon are the chief contributors to the ree budget in unkar mudstones lithostratigraphic variations in the hree distributions can be attributed partially to variable zircon abundance in the silt size fraction a likely function of hydrodynamic sorting age constraints on the duration of unkar group sedimentation range from 30 to 100 my for the 1100 m conformable shinumo dox succession and result in compacted sedimentation rates of between 1 0 and 3 6 cm 103 yr these rates are comparable to mesozoic foreland basin settings

from source to surface tracking magmatic boron and chlorine input into the geothermal systems of the taupo volcanic zone new zealand the magmatic contribution into geothermal fluids in the central taupo volcanic zone tvz new zealand has been attributed to either andesitic arc type fluids or rhyolitic rift type fluids to explain the compositional diversity of discharge waters however this model relies on outdated assumptions related to geochemical trends associated with the magma at depth of typical arc to back arc settings current tectonic models have shown that the tvz is situated within a rifting arc and hosts magmatic systems dominated by distinct rhyolite types that are likely to have evolved under different conditions than the subordinate andesites therefore a new appraisal of the existing models is required to further understand the origin of the spatial compositional diversity observed in the geothermal fluids and its relationship to the structural setting here we use volatile concentrations i e h2o cl b from rhyolitic and andesitic mineral hosted melt inclusions to evaluate the magmatic contribution to the tvz geothermal systems the andesite and two different types of rhyolites r1 and r2 are each distinct in cl h2o and b cl which will affect volatile solubility and phase separation vapor vs hydrosaline liquid of the exsolved volatile phase ultimately these key differences in the magmatic volatile constituents will play a significant role in governing the concentration of cl discharged into geothermal systems we estimate bulk fluid compositions b and cl in equilibrium with the different melt types to show the potential contribution of parent fluids to the geothermal systems throughout the tvz the results of this analysis show that the variability in fluid compositions partly reflects degassing from previously unaccounted for distinct magma source compositions we suggest the geothermal systems that appear to have an arc type andesitic fluid contribution are actually derived from a rhyolite melt in equilibrium with a highly crystalline andesite magma this model is in better agreement with the current understanding of magma petrogenesis in the central tvz and its atypical rifted arc tectonic setting and show that the central tvz records an arc not back arc fluid signature

hydrothermal water rock interaction and the redistribution of li b and cl in the taupo volcanic zone new zealand abstract lithium b and cl occur as trace elements in the dominant protoliths rhyolite andesite and greywacke underlying high temperature hydrothermal systems in the taupo volcanic zone tvz the fluid mobility of li decreases substantially at 200 c 20 c with the pervasive deposition of quartz chlorite regardless of protolith and altering fluid compositions boron and cl are more fluid mobile than li at all temperatures with mobility affected by the rock type composition of circulating aqueous solutions and to a limited extent by incorporation of the trace elements in hydrothermal minerals uptake of b by clays decreases its mobility at 320 c occur compared to volcanic rocks the mobility of b and cl in greywackes is very low and thus the b cl signature of greywacke in hydrothermal aqueous solutions of the tvz is overwhelmed by the effects of rhyolite and andesite dissolution temperature dependent transitions from mg fe clays and phyllosilicates to k bearing illitic clays tend to decrease the mg li ratios in aqueous solutions at 200 c

new improved equations for and sio2 geothermometers by outlier detection and rejection abstract we present new improved equations for three still widely used na k na li and sio 2 geothermometers obtained by statistical treatment of the data and application of outlier detection and rejection as well as theory of error propagation and compare them with those by fournier and others new equations are also developed for estimating errors associated with the use of these new geothermometric equations and comparing them with the performance of the original equations the errors in the use of the new na k equation for temperatures ranging from 80 to 350 c vary from about 19 to 34 which is lower than the corresponding errors 24 43 for the original fournier equation similarly for temperatures ranging from about 50 to 320 c our new equation for na li geothermometer for cl 2 2 geothermometer we have proposed a linear equation for the temperature range of 210 to 310 c sio 2 295 ppm which shows considerably smaller total propagated errors 2 3 than for the original equation 5 29

clay minerals related to the hydrothermal activity of the bouillante geothermal field guadeloupe abstract the geothermal field of bouillante guadeloupe fwi is a high enthalpy hydrothermal system emplaced in submarine volcanoclastic formations hyaloclastites scarce lava flows and subaerial formations andesitic lava flows pyroclastites lahars which belong to the lesser antilles arc three directional wells were drilled in 2001 to optimize the productivity of the geothermal field up to 15 mwe and to investigate the vertical distribution of clay alteration from the surface area down to a depth of 1000 m where temperatures exceed 250 c special attention has been paid to the clay signature of the fractured zones which channel the present geothermal fluids three successive zones dominated respectively by dioctahedral smectite illite and chlorite were identified at increasing depths alteration petrography indicates that these mineralogical clay zones result from the spatial superimposition of at least two successive alteration stages the first one assimilated to a propylitic alteration stage affected all parts of the system and consisted of crystallization of trioctahedral phyllosilicates chlorite or corrensite ca silicates heulandite clinoptilolite prehnite pumpelleyite wairakite and epidote quartz and minor calcite in replacement of most of the primary minerals of the intersected volcanic or volcanoclastic formations the later stage of alteration is related to the circulation of the present geothermal fluids and is assimilated to argillic or phyllic alteration it consists of a more or less intense argillization which results from the crystallization of aluminous dioctahedral clay phases smectite illite i s mixed layers and accessory kaolinite associated with quartz calcite hematite or pyrite the permeable zones which channel most of the present geothermal fluids are fracture controlled and do not contain specific clay parageneses however the illite i s mixed layers minerals differ from those of the surroundings by specific properties including both crystal structure and texture these specific properties decrease in the expandable component of the illitic material increase of the illite crystallinity can be controlled by the nucleation growth rates operating in zones of active flow regime being mainly a product of the earlier propylitic alteration stage chlorites are much less informative on the fracture controlled permeable levels however the compositional variations of chlorites recorded within the shallower fractured zone suggest a significant change in fo 2 conditions related to early circulation of fluids along the major near west striking normal faults plateau fault

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

geothermometry from brine analyses lessons from the gulf coast u s a abstract geothermometers based on mineral water equilibria are of limited use at temperatures characteristic of hydrocarbon production from sedimentary basins metastable detrital phases such as alkali feldspars and plagioclase persist to temperatures characteristic of the deepest wells sasmpled approaching 200 c and equilibria involving stable phases such as albite illite and quartz are not commonly achieved empirical relations such as that between mg and li are more successful in predicting subsurface formation water temperatures than are equilibrium relations involving quartz carbonates or feldspars the concentrations of most components in saline formation waters seem to be governed by kinetic rather than by equilibrium considerations

characterising the hydrothermal alteration of the broadlands ohaaki geothermal system new zealand using short wave infrared spectroscopy abstract hydrothermal clay minerals present in the broadlands ohaaki geothermal field were characterised by field portable short wave infrared spectroscopy three major alteration zones an upper smectite a middle illite and a lower illite chlorite are spectrally separable the zoning pattern is generally consistent with the thermal structure of the geothermal field although occasionally zone boundaries cut present day isotherms the data indicate that temperature is the major control on clay zoning and permeability plays a subordinate role both beidellite and montmorillonite are common in the upper low temperature smectite zone kaolinite mainly of low crystallinity marks the margin of the field where cool acidic ground waters inflow in the middle alteration zone illite dominantly k rich shows a narrow compositional variability some highly permeable zones are characterised by illite with low octahedral al contents ammonium bearing illite and buddingtonite are present locally in permeable horizons within the illite zone where temperatures are above 200 c chlorite is most abundant in the lower alteration zone temperature 250 c although it also occurs unevenly in the upper and middle alteration zones chlorite varies from mg to fe rich varieties but mostly with mg values

depositional history of the middle proterozoic castner marble and basal mundy breccia franklin mountains west texas abstract the ca 1260 ma castner marble is composed of six metamorphosed lithologies stromatolitic limestone cryptalgalaminite massive limestone hornfels mudstone and tuff rhythmite and flat pebble conglomerate on the basis of the associations of these lithologies the castner marble can be divided into three distinct intervals a lower section containing stromatolitic and cryptalgalaminite units a middle section with thick hornfels and massive limestone beds and an upper section of rhythmites interlaminated to thinly interbedded carbonate and hornfels with interbedded flat pebble conglomerate the castner succession was deposited during a transgressive event on a low energy carbonate ramp the contact between the castner marble and the overlying basaltic mundy breccia marks a catastrophic event or series of events in which rhythmite units were disrupted and or displaced along arcuate detachment surfaces and redeposited as lenses of rhythmite megabreccia unconformably overlying intact rhythmite sequences these megabreccia lenses consist of large locally deformed rhythmite blocks in a matrix of muddy flat pebble conglomerate one megabreccia lens contains intervals bearing irregular shaped basalt clasts possible hyaloclastite layers and pod like basalt intrusions this polymictic lens may have been produced by submarine syn eruptive mixing of basalt and sediment local basalt intrusions may be part of the feeder system for this material and also the overlying basaltic mundy breccia the mundy breccia covered the irregular topography created by the megabreccia lenses locally loading and deforming the megabreccia into flame like structures the polymictic carbonate and basalt nature of one lens and presence of load features suggests that little time elapsed between deposition of the castner marble and the mundy breccia and therefore that the mundy breccia was most likely deposited in a submarine setting

variations in neoarchean microbialite morphologies clues to controls on microbialite morphologies through time the neoarchean carawine formation hamersley group western australia is a carbonate ramp that preserves diverse microbial structures which are characteristic of specific depositional environments these distinctive structures are distributed in five shallow subtidal and two deeper water facies in the oakover area of the carawine formation the shallow subtidal facies are composed of biohermal and bedded stromatolites centimetre scale ridge shaped microbialites and wavy laminated microbialites the deeper water facies are composed of fenestrate microbialites planar laminated dolostone and dolostone with rolled up microbial laminae microbialites in the carawine formation lie within a continuum of archean to proterozoic microbial facies some shallow water microbial facies in the carawine formation are similar to proterozoic facies such as large bioherms internally composed of a variety of stromatolite morphologies in contrast fenestrate microbialites grew in quiet subtidal environments and are common in archean rocks but have not been documented in similar proterozoic environments the similarity of shallow water facies across the archean proterozoic transition before and after the oxidation of the atmosphere and surface oceans indicates that stromatolite growth in shallow subtidal environments was not strongly affected by the chemical changes associated with oxidation of the oceans or by biological responses to those chemical changes rather stromatolite morphology was controlled mostly by the physical environment and the corresponding biological responses to that environment in contrast the absence of fenestrate microbialites from proterozoic deep subtidal environments suggests that the morphology of deep subtidal microbial structures was influenced by chemical or biological changes that occurred in association with oxidation of the surface oceans

helium isotope studies of geothermal fields in the taupo volcanic zone new zealand abstract we report new measurements of 3he 4he and ne on 69 samples of gas from geothermal fields in the central section of the ne sw trending taupo volcanic zone tvz we find 3 he 4 he ratios in the range 5 9 7 3 times the atmospheric ratio 5 9 7 3ra typical of subduction zone systems in some areas near the boundaries of the volcanic zone the ratio is much lower 2 4ra the values in the wairakei field are extremely uniform and vary by only a few per cent from 7 2 ra in contrast the wells in the ohaaki broadlands field show a striking factor of two variation with the west bank section characterised by values near 6 ra while the east bank section has values as low as 3 0 ra this suggests that mixing of two types of geothermal source fluids may be occurring at ohaaki broadlands an inverse relationship has been found between the 3 he 4 he ratio of the gases and the b cl ratios in the associated fluids thus the helium isotope ratios appear to be affected both by the flux of mantle helium associated with mantle subduction and also by the presence of sedimentary rocks beneath the geothermal field leaching by the hot ascending fluid of radiogenic 4he together with boron from the underlying high boron low chloride mesozoic greywacke basement is thought to be the cause of this inverse relationship the co 2 3 he ratio in the tvz exceeds the morb ratio by a factor of up to 100 with higher values corresponding to higher b cl fluid ratios suggesting that the greywacke may also be the major source of the co2 we have also measured argon concentrations and isotopes on 19 samples in the ohaaki broadlands area in order to further elucidate the nature of the striking helium isotope variations the argon isotope ratios are relatively close to atmospheric indicating that the majority of the argon comes from recirculated groundwater the simplified boiling model of mazor et al 1990 has been used to calculate the 3 he heat ratio in the ohaaki broadlands and wairakei fields the values obtained fall within the range previously reported for mid ocean ridge systems this model has been extended and has led us to the conclusion that compared to the 3 he 4 he ratio the 3 he 36 ar asw ratio is a much better indicator of the potential geothermal heat the 4 he 40 ar na where na non atmospheric ratio of both the high mantle derived and low crustal derived 3 he 4 he end members of the analyses reported here is about 3 6 but for samples with low 3 he 36 ar ratio this ratio falls to values below 0 5 the value of 3 6 is in the range which is expected for the radiogenic component and although considerably lower than that often found in subduction type mantle gases it is still within the accepted range of values

grenville age a type and related magmatism in southern laurentia texas and new mexico u s a abstract large grenville age plutons are known to be present in the 1340 1370 ma basement in texas and eastern new mexico but their distribution and compositional ranges are poorly known new u pb zircon dates shrimp rg stanford university on subsurface samples have identified widespread presence of compositionally diverse grenville age 1070 1110 ma plutonic rocks in the texas panhandle core from a 175 m thick sill like gabbroic intrusion yielded a date of 1081 8 3 ma in situ differentiation of this tholeiitic magma led to a 7 fold increase in incompatible element concentrations as ree patterns remained essentially flat trace element data suggest an e morb like source to the south alkali feldspar granite with a type affinities was recovered from drill core from the abilene gravity minimum near albany texas it yielded a date of 1078 23 ma similar to undeformed post orogenic granites in the llano uplift further west an anorthosite xenolith from the eocene three sisters intrusion in el paso texas yielded a date of 1068 30 ma which is within error of the 1110 19 ma age determined for the main stage of the nearby a type red bluff granitic suite xenoliths from potrillo maar volcano in the center of the southern rio grande rift include monzonitic xenoliths with granulitic texture which yielded dates of 1072 ma in contrast potrillo maar xenoliths with igneous textures yielded u pb dates of 27 ma development of the granulitic texture is interpreted to reflect granulite facies metamorphism during tertiary time 26 27 ma on the basis of age zoning and u concentrations in the zircon crystals our results show that grenville age magmatism in the texas and new mexico subsurface was widespread and was coeval with syn and post deformation granites in the llano uplift of central texas the compositions of dated samples suggest that mafic magmas were broadly tholeiitic in character and that granitic magmas were a type these magmatic affinities are thought to be associated with crustal extension rather than with subduction moreover the presence of anorthosite xenoliths in the el paso kilbourne hole region the broadly tholeiitic character of mafic rocks and the a type nature of the granitic rocks are broadly similar to amcg anorthosite mangerite charnockite granite suites present in the grenville province of eastern laurentia

bbe systematics in subduction related metamorphic rocks characterization of the subducted component the mobility of b and be in h2o rich fluids and felsic silicate liquids produced during metamorphism of subducted oceanic slab and sediments has been investigated through analysis of subduction zone metamorphic rocks of the catalina schist california in metasedimentary rocks b be and the range in b be decrease with increasing metamorphic grade mean 72 std dev 41 for lowest grade lawsonite albite fades rocks mean 21 std dev 11 for higher grade greenschist and epidote amphibolite facies equivalents this decrease to more uniformly low b be may be attributed to the preferential removal of b in h2o rich fluids produced by devolatilization reactions over the approximate temperature interval of 350 600 c metamafic rocks do not show pronounced decrease in b be with increasing metamorphic grade however all metamafic samples have b be 30 lower than values for many altered seafloor basalts in amphibolite grade exposures felsic leucosomes and pegmatites reflecting partial melting have low b be similar to their metasedimentary and metamafic hosts which presumably experienced prior reduction in b be during lower temperature devolatilization this evidence for b and be mobility during high p t metamorphism complements studies of b be systematics in arc volcanic rocks in further characterizing mechanisms by which slab derived elements can be added to the source regions of arc lavas before subducted mafic and sedimentary rocks reach wadati benioff zone depths beneath arcs 80 150 km the b be of these rocks is likely to have decreased to 30 thus highly fractionated slab derived hydrous fluids may be necessary to generate the high b be signatures observed in many arcs b be of up to 200 the b be data together with previously presented stable isotope data for the catalina schist demonstrate that subduction zone metamorphic processes are capable of homogenizing presubduction variability in the concentrations of particularly fluid mobile elements in rocks and may through mixing produce fluids which trend toward uniform trace element and isotopic compositions these homogeneous fluids could infiltrate parts of the mantle wedge and contribute to the characteristic trace element and isotopic signatures of arc magma source regions in hotter subduction zones e g involving subduction of young hot oceanic lithosphere silicate melts derived from previously devolatilized sedimentary and mafic rocks may contribute relatively low b be signatures to arc source regions thus significant variations among arcs in the ranges of b be observed in front rank volcanoes e g for the bismarck arc b be 20 190 for the cascades arc b be 5 may be related in part to varying thermal structure which could govern both the b be of hydrous fluids and the relative proportions of hydrous fluid and silicate melt derived from the subducted slab and sediments

sources of solutes and heat in low enthalpy mineral waters and their relation to tectonic setting new zealand abstract approximately 90 of the low enthalpy spring systems in new zealand are distributed along the present day convergence of the pacific and australian plates which varies from subduction to oblique plate collision forearc subducted waters rising in the hikurangi accretionary prism consist of pore waters containing labile organic material water of hydration from clays and seawater these subducted waters are traceable in the north island axial ranges and the northern marlborough fault system in the south island albeit modified by temperature mixing with surface and heated meteoric waters and protracted interaction with the rock the signature of subducted marine sediments in the hikurangi trench is retained in the chemical and isotopic compositions of the taupo volcanic zone magmatic arc type waters the concentrations of b ba br ca cl i k li mg na rb and sr solutes found in high concentrations in forearc subducted waters increase from northeast to southwest towards the incipient subduction zone in the puysegur trench southwest of south island most thermal mineral waters in the south island are expelled along the alpine fault zone where plate collision results to rapid uplift of the southern alps elevated geothermal gradients and fault shearing of rocks in the alpine fault zone variations in temperatures 175 30 c and mineral water compositions are affected by elevation hydrological gradient intensity of tectonic activity permeability fluid volume and rate of throughput and rates of uplift as the main trace of the alpine fault zone is approached concentrations of cl and other solutes generally increase suggesting increasing contributions from ascending cl rich metamorphic waters outside the active convergent zone low enthalpy springs discharge diagenetically modified ancient forearc waters na cl sedimentary formation waters and heated seawater na hco 3 cl waters and na hco 3 deep circulating heated meteoric waters the total surface heat flow in the north island low enthalpy mineral waters is more than 10 higher than in the south island with projected subsurface temperatures as high as 250 c this is because of the widespread occurrence of shallow magmatic and mantle sources associated with pliocene to holocene volcanism and back arc continental rifting the sources of heat and solutes in low enthalpy mineral waters outside the taupo volcanic zone and ngawha are decoupled except for rapidly ascending hot pore waters in the hikurangi accretionary prism and low temperature serpentinization ca cl waters in fiordland

the rare alkalies in hydrothermal alteration at wairakei and broadlands geothermal fields n z abstract drillcores and waters from wairakei and broadlands geothermal areas new zealand have been analyzed for li rb cs na k mg ca al ti mn and be the drillcores were altered to various degrees at temperatures below 300 c in slightly alkaline chloride water probably derived from rock water interaction in untapped horizons at higher temperature it changes its composition as it leaches ca and na from the rock and adds k rb cs and li evaluation of these changes in relation to the dimensions of the altered zone under observation suggests that a high mass ratio of water to rock e g 100 and a period of up to 1 million years are responsible for the present stage of alteration increase of k and rb in the altered rocks is a result of the formation of abundant adularia in addition to illite the k rb ratio of the rock decreases during alteration but remains higher than that of the fluid only clay materials and zeolites that preferentially absorb rb give slightly lower k rb ratios than the fluid the mineral phases responsible for the uptake of lithium during alteration are chlorite 300 ppm li and quartz up to 430 ppm li li uptake in quartz is considered to be the mechanism by which al rich quartz crystallises from alumino silicates li al atomic ratios of 0 3 0 57 and al concentrations up to 3000 ppm have been observed relatively small concentrations of cs are found in potassic minerals e g 10 ppm cs in adularia 44 ppm cs in illite however 240 ppm cs are found in wairakite from wairakei equilibrated at 235 c lower equilibration temperatures may lead to higher cesium concentrations this effect in conjunction with a more concentrated hydrothermal fluid could explain a content of 4500 ppm cs in wairakite extracted from a drillcore taken in the el tatio geothermal field in chile

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

behavior of li rb and cs during basalt glass and olivine dissolution and chlorite smectite and zeolite precipitation from seawater experimental investigations and modelization between 50 and 300 c abstract this study investigates experimentally the behavior of li rb and cs during the hydrothermal alteration of a basalt glass and of forsterite the behavior of trace alkalis during the dissolution of a basalt glass and forsterite has been followed between 150 and 300 c rb and cs are preferentially leached from the glass while li exhibits a stoichiometric release with respect to silica on the other hand incongruent loss of li relative to si during forsterite dissolution reflects a crystallographic site energy control of the release of trace elements from crystalline silicates the partitioning of li rb and cs between hydrothermal solutions and chlorites smectites and zeolites has been experimentally investigated between 50 and 260 c the alteration phases were synthesized by altering silicate glasses in solutions containing the trace alkalis the lower the temperature the higher the exchange capacity of the mineral or the lower the ionic hydration energy then the more the element is incorporated into the solid phases computer simulations generated with the eq3 6 software package and our experimental data on distribution coefficients account for the behavior of alkali trace elements during the alteration of basalt glasses by seawater at mid ocean ridges

trace element mobility and lithium isotope exchange during hydrothermal alteration of seafloor weathered basalt an experimental study at 350 c 500 bars abstract the relative mobility of trace incompatible elements and exchange of lithium isotopes during alteration of basalt previously altered by exposure to seawater at low temperatures seafloor weathered were experimentally determined at 350 c 500 bars these data are important as a means to test models calling for hydrothermal alteration of weathered basalt as a source of alkali elements for hot spring vent fluids at mid ocean ridges weathered basalt used for the experiment was characterized by high cs rb b k and li concentrations high cs rb and low k rb and ba rb ratios respectively relative to fresh basalt the basalt is enriched in 7li consistent with a history involving li uptake during seafloor weathering the experiment involved a na ca k cl fluid and flexible cell hydrothermal equipment which permitted periodic sampling of the fluid phase at experimental conditions the extraction efficiency of all trace incompatible elements was significant and ranged from 40 to 80 cesium rubidium lithium and boron were particularly mobile whereas ba sr and to a lesser degree k were taken up by alteration minerals early stage release of li was dominated by 7li most probably as a consequence of the dissolution of low temperature alteration phases in the weathered basalt that were rendered unstable at the elevated temperatures of the experiment subsequently however an increase in 6li in solution was observed owing to a combination of mineral dissolution from li bearing components in fresh basalt and isotopic equilibration effects owing to the mobility of li during hydrothermal alteration of weathered basalt it is unlikely that dissolution of weathered basalt components in subseafloor reaction zones 350 400 c could occur without noticeably affecting the lithium isotope composition of vent fluids as inferred previously from field studies thus the relatively high cs rb ratios of some vent fluids which were thought to be the result of hydrothermal alteration of weathered basalt may be caused by other effects such as partitioning of rb relative to cs into hydrothermal minerals at temperatures in excess of 400 c cs rb ratios in vent fluids from a wide range of pacific and atlantic ridge localities however reveal relatively large variations in space and time which suggest that a single process is unlikely to account for all of the data the relative mobility of trace alkali elements in weathered basalt not only constrains models of alkali element enrichment in hot spring vent fluids at mid ocean ridges but also provides data bearing on potential sources of alkali elements for arc magmas in subduction zones

boron isotopic geochemistry of carbonates and pore waters ocean drilling program site 851 abstract we have determined the boron content and isotopic composition of bulk carbonates and associated pore waters from ocean drilling program site 851 the 11b of the carbonates range from 23 to as low as 5 5 greatly extending the range of reported carbonate 11b values in contrast pore fluid isotopic compositions are relatively constant based on the correlation of 11b and 1 b r 0 99 we conclude that the bulk carbonate at this site is a mixture of a biogenic component 7 ppm with 11b of 23 and a recrystallized component 2 5 ppm with 11b of 5 5 the empirical low ph water carbonate fractionation factor implied by the data is 0 959 0 003 a boron concentration minimum occurs in pore waters at a depth of approximately 200 m below the seafloor and this is interpreted as reflecting essentially quantitative uptake of b at this depth and the horizontal advection of pore fluids with water residence times below the minimum on the order of 3 600 years

the boron isotope geochemistry of smectites from sodium magnesium and calcium bentonite deposits abstract the mineralogical chemical and isotopic analyses of smectites with variable interlayer cation occupancies from bentonite deposits in various depositional environments reveal new insights into the boron sources and the fluids involved in bentonitization in marine and non marine environments smectites from bentonites have non exchangeable structural boron concentrations of 0 2 to 196 g g b smectites from sodium bentonites have higher boron concentrations 30 g g than those from magnesium or calcium bentonites most smectites have a small interstratified illitic component that has a major influence on boron concentrations requiring the use of modified fluid mineral boron partitioning coefficients which indicate that bentonites formed from fluids of highly variable boron concentrations of 100 mg l b and a chlorine content of 76 4 mg l to 59 076 mg l the sodium bentonites formed from boron rich saline fluids or brines whereas the fluids involved in calcium and magnesium bentonite formation have a more variable boron composition and salinity the 11b values of the structural boron in tetrahedral sites of smectites range from 30 1 to 12 2 the smectites from terrestrial depositional settings have 11b values of 30 1 to about 0 whereas smectites from marine depositional settings have negative as well as positive 11b values the boron isotope values indicate that all examined bentonites from terrestrial depositional settings as well as many bentonites from marine depositional settings formed from basinal fluids or brines the boron isotope geochemistry of smectites is demonstrated to be a tool for elucidating the fluids involved in the formation of clay mineral deposits it also has great potential for tracing fluids in other settings involving authigenic clay minerals such as sedimentary basins and surficial crystalline rocks as well as man made applications such as in disposal sites for highly active nuclear waste

formation and evolution of the changbaishan volcanic geothermal system in a convergent plate boundary back arc region constrained by boron isotope and gas data abstract the goal of this study is to analyze fluid geochemistry boron isotope and gas data to reassess the formation and evolution processes of the changbaishan volcanic geothermal system jilin china due to the presence of hot fumaroles with temperatures of higher than 100 c and sinters we believe that phase separation is occurring underground which is also indicated by the characteristics of the b and gas data based on their hydrochemical data and b cl ratios the thermal water samples in this area can be divided into three groups 1 group 1 is steam heated condensate water group 1 1 jj jlq group 1 2 sbdg xrq 2 group 2 is karst water cr3 and lsd and 3 group 3 is residual water cr1 and cr2 the preliminary discrimination of samples using b and gas data implies that group 1 1 around the crater is controlled by a second phase separation process which is induced by the input of hot magmatic material group 1 2 in the basin area is controlled by the transformation of clay minerals and the xrq water sample shows contamination by sewage group 2 represents karst water that has leached metamorphic rock and been directly heated by the input of hot magmatic volatiles and group 3 is the result of one seawater phase separation process the mixing and fluid rock interaction models based on the mass balance of boron concentration and isotope imply that the phase separation and input of magmatic volatiles are more important than fluid rock interactions in the formation of the changbaishan geothermal system and the first phase separation process in the deep carbonate reservoir occurred in a late stage with approximately 75 87 5 of water becoming vapor additionally the rayleigh distillation of b isotope implies that new magma is being generated below this area with the low b concentrations and high boron isotopic values of its gases implying that the mixed component may be derived from the subducted pacific plate e g marine sediment the addition of excess heat due to the continued subduction of the pacific plate has further encouraged the phase separation process and the subduction process has also accelerated the transition of the hydrothermal system into a non hydrothermal system

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

clay mineral signatures of fossil and active hydrothermal circulations in the geothermal system of the lamentin plain martinique whereas the study of clay minerals using parameters such as structure modifications crystal chemistry has proved to be an effective approach in order to mark the circulation zones and fluid temperatures in high temperature systems there is an important lack of data dealing with such problems in moderate to low temperature systems this paper proposes to fill this lack by studying the site of the lamentin plain martinique characterized by a lowtemperature geothermal activity 50 c6 t6 90 c preliminary data acquired on the three studied exploration wells la01 la02 and la03 show that the current low temperature geothermal activity is particularly well expressed through the la03 well this low temperature activity is superimposed on evidence of a high temperature fossil activity particularly well expressed in the non productive levels of the la01 and la02 wells after a petrographic characterization this work focuses on the textural and microstructural properties of the low temperature hydrothermal clay phases utilizing x ray diffraction xrd fourier transform infrared ftir spectrometry and scanning electron microscope sem the petrographic observations have permitted successive hydrothermal events to be recognized which express the thermal collapse of the system as shown by the superposition of ancient episodes characterized by vein and pervasive alterations of high to moderate temperatures and recent episodes characterized by alterations associated with present day circulations of low temperature fluids the fossil activity results from several hydrothermal episodes with fluid temperatures ranging from 100 to over 200 c illitic phases i e i s r 1 to illite appear as the main markers of the fossil solution paths due to their abundant development close to major veins and fractures while chloritic phases chlorite corrensite seem to mark a pervasive alteration better preserved further from the fossil solution channels on the other hand the recent hydrothermal alteration is characterized by the massive presence of kaolinite dioctahedral smectite and siderite whereas smectites are only observed abundantly farther from the current solution channels kaolinite appears to be the dominant clay mineral in these channels or in the surroundings of sealed fractures which do not currently drain any more hydrothermal fluids the crystallinity estimations on xrd and ftir patterns from the 6 2 wm fraction along with sem morphological observations clearly show that the microstructural and textural properties of the kaolinites can be related to fluid temperatures indeed kaolinites with the best crystallinity or the best ordered are located in the fractures carrying the hottest fluid

lithium isotope evidence for light element decoupling in the panama subarc mantle the systematics of fluid mobile trace elements in arc lavas from panama relative to their li isotopic compositions provide unique evidence for the fertilization and subsequent differential extraction of mobile species from the subarc mantle calc alkaline lavas that crystallized between 20 and 5 ma old group that possess 7 li as high as 11 2 have low b be otherwise identical and similarly old calcalkaline lavas with high b be to 23 have mid ocean ridge basalt morb like 7 li 4 7 to 5 6 adakite lavas 3 ma young group possess 7 li from 1 4 to 4 2 and have consistently lower b be than old group lavas consistent with derivation from melting of a devolatilized morb slab if li and b had comparable fluid mobility in the subarc mantle then slab fluids would carry both high b concentrations and elevated 7 li signatures into arc sources and samples with the highest 7 li would also have the highest b be our data suggest that although both li and b are initially derived from the slab older 7 li signatures may be preserved in the mantle beneath arcs as a result regions of the lithospheric mantle will develop li isotope signatures that are heavier than typical morb mantle

the broadlands ohaaki geothermal system new zealand part 1 strontium isotope distribution in well bro 29 abstract well bro 29 at the broadlands ohaaki geothermal system new zealand penetrates a mixed volcanic sedimentary rock sequence whose 87 sr 86 sr ratios display linear distributions when plotted against 1 sr values these linear distributions do not indicate binary mixing between unaltered lithological units and a single fluid endmember the linear distribution in the volcanic pyroclastic sequences is related to the permeability of the host rocks the degree of leaching of 86 sr rich primary plagioclase laths and secondary crystallisation of the groundmass by a recharge fluid represented by modified taupo rainwater the greywacke argillite basement from the same well displays a separate linear isotopic trend when their 87 sr 86 sr ratios are plotted against 1 sr values in addition to yielding a sr sr vs rb sr errorchron with an age of 88 6 ma bp mswd 9 48 based upon supporting petrographic observations the two isotopic trends in the greywacke argillite basement are believed to be an inherited metamorphic feature from the rangitata orogeny 141 3 ma which has been modified by geothermal fluids preferentially leaching 87 sr and 87 rb from primary micas

element redistribution during hydrothermal alteration of rhyolite in an active geothermal system yellowstone drill cores y 7 and y 8 abstract hydrothermal alteration of the 0 54 ma biscuit basin rhyolite flow in yellowstone drill cores y 7 and y 8 has involved significant changes in ti normalized whole rock concentrations of li mg ca na k mn rb sr sb cs ba and u whereas such changes have generally not occurred for al fe sc co y zr ree hf ta and th the relatively mobile elements have been redistributed over distances from 2 5 cm to more than 10 100 m and are associated mainly with zeolites and clays in thoroughly altered samples average whole rock changes in ti normalized mass range from about 0 5 17 g kg 9 49 for major elements and 0 1 280 mg kg 19 4260 for minor and trace elements compositional changes correlate with hydrothermal mineralogy the relatively immobile elements have been redistributed over a distance of at least 10 100 m but less than 2 5 cm and are associated mainly with clays in thoroughly altered samples addition of sio2 ranges from 110 890 g kg in samples where porosity has been thoroughly sealed by silica deposition thermal water is not in oxygen isotopic equilibrium with any primary or secondary phases analyzed except calcite modest depletions of 18o 1 2 due to exchange with thermal water apparently have occurred in y 8 plagioclase and obsidian oxygen isotope ratios in obsidian replacing smectite and in veinlet celadonite and cristobalite suggest that these phases precipitated from water locally enriched in 18o up to 8 heavier than present thermal water the minimum integrated water rock mass ratio in y 7 and y 8 is 103 104 assuming advective transport

deep water circulation at the northern pyrenean thrust implication of high temperature water rock interaction process on the mineralization of major spring water in an overthrust area abstract in an overthrust context of the northern pyrenean area groundwater is affected by high mineralization sources a multi isotopic approach was used to track the origin of mineralization in a complex multilayer aquifer system through the study of a major regional spring the oeillal spring water osw which shows a not yet investigated geochemical singularity the aims of this study are to understand the hydrogeochemical evolution and the mineralization mechanisms of groundwater in a large scale aquifer extending over the northern pyrenean overthrust oriental corbieres based on an adequate set of geochemical and isotopic tracers including cosmogenic stable and radiogenic isotopes we have revealed complex hydrogeochemical processes that cannot be tracked with traditional hydrochemical and isotopic tracers the high 87 sr 86 sr ratios of the osw associated with relatively high concentrations in trace elements cs rb sr b li suggest the influence of brine from the triassic deposits containing saliferous clay orsaline fluids from the fractured basement the basement hypothesis may be considered regarding the hydro geochemical fingerprint of the paleozoic basement as demonstrated in previous study and further data would be required to validate the contribution of basement fluids contrasting with marine primary brine and current seawater the relatively high 37 cl 0 22 and 0 39 of osw attests the non marine origin of the chloride ion 36 cl cl shows that the osw is issued from a mixing process between recently recharged water lightly mineralized and significantly marked in 36 cl by the thermonuclear bomb pulse and a saline deep end member at secular equilibrium this indicates that cl in these springs is primarily derived from subsurface non meteoric sources the osw s low br cl molar ratio suggests the influence of simple dissolution of halite and or the contribution of more complex secondary brine the deep saline water may results from meteoric infiltration into the lower jurassic aquifer in contact with triassic deposits or deeper high temperature promotes water rock interaction enhancing leaching of mg k rich saliferous clay this is supported by environmental scanning electron microscopy esem analyses showing that i cl is found in accessory minerals from the kcl mgcl 2 h 2 o system of the triassic deposits and ii cs rb molar ratio is similar to that of osw ranging between 0 13 and 0 7 and from 0 13 to 0 4 respectively laboratory experiments carried out on triassic material show that high temperature water rock interaction is suitable to explain the relatively high 87 sr 86 sr observed in groundwater such process can be investigated to confirm the deep origin of the osw and to explain the signature of deep brines in contact with the triassic deposits under high temperature conditions basement fluid contribution may also be considered regarding the hydro geochemical fingerprint of the paleozoic basement as shown in previous studies further data would be required to validate this hypothesis

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

book review the variscan fold belt in the british isles hancock p l editor 1983 adam hilger 217 pp price hardcover 34 00

the partitioning behaviour of boron from tourmaline during ashing of coal abstract boron is an environmentally sensitive element that may be present in high concentrations in some coals three modes of occurrence for boron in coal are commonly recognised namely bound to the organic fraction locked into clay minerals mainly illite and bound within the crystal lattice of tourmaline the organically bound mode is generally considered to be the most likely following combustion in a pulverised fuel utility boron is generally enriched in the fine fly ash waste but in some cases it may also escape with the flue gas suggesting variable partitioning behaviour there is concern that boron may be leached from fly ash disposal impounds at concentrations toxic to higher land plants a coal sample from the d seam of the strongman no 2 mine west coast south island new zealand has been used to test the hypothesis that boron present in tourmaline is less volatile in coal combustion implying that mode of occurrence is a key control on the partitioning behaviour of this element six sample subsets were doped with increasing amounts of ground tourmaline one subsample from each set was analysed by prompt gamma inaa to determine the concentration of boron in the coal two subsamples were ashed at 1000 c one ash sample from each set was analysed for boron while the other ash sample was leached according to australian standards it was found that the relationship between boron in the doped coal and boron in the ash is approximately linear with some losses noted during ashing indicating boron present in tourmaline was substantially retained in the ash furthermore no relationship was found between the boron content of the ash and boron leached from the ash samples by reagent water the results suggest boron present in coal as tourmaline is retained in the ash and is unavailable to the environment following fly ash disposal

intrusive and basement rock sources of lead in hydrothermal systems of the taupo volcanic zone new zealand abstract the taupo volcanic zone is a complex volcanic tectonic region over 250 km long corresponding to the volcanic arc of the taupo hikurangi subduction system volcanism is dominantly rhyolitic with minor amounts of andesite dacite and basalt the volcanics overlie a downfaulted basement of mesozoic metasediment waipapa and torlesse terranes over twenty major geothermal systems are active related to the young volcanism samples of sulfides galena sphalerite chalcopyrite and pyrite from five of the geothermal systems were collected from drill core and their pb isotopic compositions measured representative fresh samples from all volcanic and basement rock types of the region were also analyzed and show a range of values by which they may be distinguished sulfides from the broadlands and waiotapu geothermal systems are homogeneous in their pb isotopic compositions with values similar to the average for the fresh rhyolites and andesites the results indicate that the source of pb and possibly other metals in the broadlands and waiotapu hydrothermal fluids is related to the parent magma of the volcanics a magmatic fluid could be the source consistent with independent geochemical and isotopic evidence for other magmatic fluid derived components at broadlands and to a lesser extent at waiotapu which are both anomalously mineralized in precious and base metals in contrast pyrite pb from the unmineralized kawerau geothermal system has isotopic compositions which vary over a range similar to that of the underlying waipapa metasedimentary basement present at depths of only 1000 m this observation suggests that the pb at kawerau was mainly leached from the basement rocks with a component of isotopically homogenous magma related pb not present in the hydrothermal fluids isotopic compositions of pb from the unmineralized wairakei and mokai systems are intermediate between the broadlands and kawerau examples these data are interpreted to result from leaching of pb from both the basement and volcanic rocks consistent with the thick at least 3 km sequence of volcanics in the center of the zone where wairakei and mokai are located these results suggest that epithermal gold prospects may be distinguished on the basis of their pbisotopic signature those exhibiting a homogeneous and magmatic signature have a higher potential to contain ore all else being equal because of the potential for higher magmatic derived metal concentrations in the hydrothermal fluid this suggestion appears to be applicable only to dilute hydrothermal systems perhaps because the low salinity precludes leaching as an effective process to solubilize metals

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

element transport and enrichment during propylitic alteration in paleozoic porphyry cu mineralization systems insights from chlorite chemistry abstract chlorite is one of the most widely developed minerals in propylitic alteration around porphyry deposits and can be used to investigate element transport and enrichment processes during hydrothermal alteration the paleozoic tuwu porphyry cu deposit metal reserve 0 7 mt cu 0 67 located in the southern margin of the central asian orogenic belt is one of the most economical and largest porphyry cu deposits in nw china the tuwu porphyry cu deposit comprises an early porphyry cu mineralization including potassic propylitic and phyllic alteration stages and later overprinting cu mineralization periods with chlorite found in both chlorite from the propylitic zone at tuwu is geochemically similar to propylitic chlorite in younger cenozoic porphyry systems but enriched in mg and k and depleted in fe and al relative to the overprinting chlorite scandium v ti and ga are enriched and li sr mn and zn are depleted in the tuwu propylitic chlorite proximal to the orebody consistent with cenozoic deposits compared with metamorphic chlorite from proterozoic metamorphic terranes in australia tuwu propylitic chlorite has higher mg and k lower fe al and as our results suggest propylitic alteration in the tuwu district is probably the product of cooling of fluids derived from the magmatic hydrothermal system but not from peripheral waters and trace element variations in chlorite are mainly controlled by temperature although other factors such as fault development could affect variation trends the common elemental features of chlorite in both paleozoic and cenozoic porphyry cu deposits indicate it could act as a potential tool for mineral exploration

architecture of a 1 38 1 34 ga granite rhyolite complex as revealed by geochronology and isotopic and elemental geochemistry of subsurface samples from west texas usa abstract during the evolution of laurentia a mesoproterozoic felsic igneous belt extended from fennoscandia through canada to the southwestern united states this belt referred to as the granite rhyolite province in north america forms much of the west texas and eastern new mexico basement we present data from 41 closely spaced wells in west texas that penetrated several hundred meters into the southern granite rhyolite province and provide the first opportunity to develop a three dimensional view of the basement from subsurface samples the felsic rock types include hornblende bearing quartz monzonite ignimbritic rhyolite and comagmatic granite with eutectic textures these rocks plot in the high k to ultra high k field quartz syenite which plots exclusively in the ultra high k field is the final felsic phase of magmatism all of the felsic magmas were variably oxidizing based on biotite compositions u pb chronology supports the intrusive relations established by petrography the quartz monzonite is oldest 1380 ma and is followed by the granite rhyolite sequence 1360 ma and the quartz syenite 1340 ma nd model ages range from 1520 to 1740 ma indicating involvement of older proterozoic crust in many wells thick mafic sills intrude the granite rhyolite sequence nd model ages for the mafic rocks range from 1560 to 1440 ma implying that they are mesoproterozoic in age the mafic rocks include an alkaline oib like suite which is not supportive of a subduction origin u pb ages are also reported for the mescalero well 1 in eastern new mexico in this well metasedimentary and metavolcanic rocks of the debaca sequence unconformably overlie a quartz syenite similar to the quartz syenite from the west texas wells detrital zircons from the basal meta arkose of the sequence are 1690 and 1320 ma indicating a maximum age of 1300 ma for this sequence

eolian aqueous interactions in the development of a proterozoic sand sheet shikaoda formation hosangabad india abstract a 40 m thick eolian sand sheet deposit characterizes the upper part of the proterozoic shikaoda formation near hosangabad it sharply overlies shoreface deposits and comprises wind ripple strata 50 adhesion strata 17 and subaqueous strata 33 each stratification type defines stratal packages tens of centimeters thick and few meters wide that are superposed upon one another in a nearly random fashion the eolian facies is inferred to have been deposited in a low gradient sandy supratidal setting the subaqueous deposits of the sand sheet also reflect a tide affected westward opening coastal setting with an approximately north south shoreline abundance of aqueous and adhesion strata coupled with the absence of granule rich coarse grained layers corrugated erosion surfaces and evaporites are the typical features of the shikaoda eolian sand sheet these features indicate that in spite of abundant sand supply from the coastal sources and a net aggradational setting repeated flooding and high surface moisture were the principal factors that inhibited dune building processes and favored the growth of a flat bedded eolian sand sheet in the shikaoda sandstone numerous subhorizontal nearly flat bounding surfaces split the sand sheet succession into tabular sediment bodies 50 100 cm thick each of the bounding surfaces can be traced for a few tens of meters and can be correlated to an event of aqueous flooding vertical stacking of tabular sandstone bodies implies that long term sediment aggradation rate in the low lying supratidal region kept pace with that of basin subsidence the sedimentological features of the shikaoda sand sheet facies when compared with known modern and ancient sand sheet deposits suggest that the shikaoda sand sheet developed independent of an erg in a comparatively wet climatic setting the sub humid coastal eolian sedimentary system of padre island texas is probably the closest modern analogue of the shikaoda sand sheet facies

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

compositional multivariate statistical analysis of thermal groundwater provenance a hydrogeochemical case study from ireland abstract thermal groundwater is currently being exploited for district scale heating in many locations world wide the chemical compositions of these thermal waters reflect the provenance and circulation patterns of the groundwater which are controlled by recharge rock type and geological structure exploring the provenance of these waters using multivariate statistical analysis msa techniques increases our understanding of the hydrothermal circulation systems and provides a reliable tool for assessing these resources hydrochemical data from thermal springs situated in the carboniferous dublin basin in east central ireland were explored using msa including hierarchical cluster analysis hca and principal component analysis pca to investigate the source aquifers of the thermal groundwaters to take into account the compositional nature of the hydrochemical data compositional data analysis coda techniques were used to process the data prior to the msa the results of the msa were examined alongside detailed time lapse temperature measurements from several of the springs and indicate the influence of three important hydrogeological processes on the hydrochemistry of the thermal waters 1 salinity and increased water rock interaction 2 dissolution of carbonates and 3 dissolution of sulfides sulfates and oxides associated with mineral deposits the use of msa within the coda framework identified subtle temporal variations in the hydrochemistry of the thermal springs which could not be identified with more traditional graphing methods or with a standard statistical approach the msa was successful in distinguishing different geological settings and different annual behaviours within the group of springs this study demonstrates the usefulness of the application of msa within the coda framework in order to better understand the underlying controlling processes governing the hydrochemistry of a group of thermal springs in a low enthalpy setting

petrogenesis of mid proterozoic granitic magmas examples from central and west texas abstract circa 1 1 ga granitic magmatism in texas was manifested as two compositional groups 1 the 1 12 ga red bluff granitic suite in west texas and 2 1 12 1 07 ga granites of the llano uplift of central texas both suites share some characteristics typical of anorogenic granites e g potassium and iron rich bulk compositions fe rich hydrous silicates emplacement conditions involving low oxygen fugacities and water contents and exhibit similar isotopic characteristics however rock associations mineral chemistries and trace element compositions of the two suites are distinct and no single petrogenetic model for the two suites is possible the red bluff granitic suite includes cogenetic syenites quartz syenites and granites transitional ferrobasaltic dikes are also present in contrast syenitic and mafic rocks are not associated with the llano granites the llano granites contain biotite and calcic amphibole with lower fe fe mg ratios compared to those occurring in the red bluff rocks alkali amphiboles e g arfvedsonite occur in the red bluff granites but not in the llano granites the red bluff granitoids are characterized by high feo t mgo ratios high na2o k2o high concentrations of hfse and rare earth elements ree and other features typical of a type within plate granites e g the pikes peak batholith ppb the llano granites are geochemically distinct with generally higher p2o5 and sr lower na2o feo t mgo zr y and ree and much lower ta and nb nd isotopic data overlap between the two granite suites and have juvenile signatures however trace element data suggest different petrogeneses for the two suites the red bluff suite is interpreted as having a direct derivation from mantle sources via extended fractional crystallization of basaltic parental magmas with minor crustal assimilation the llano granites appear to represent anatectic melts derived from slightly older juvenile crustal sources some melts underwent fractional crystallization controlled by feldspar and accessory minerals the petrology and geochemistry of 1 1 ga granites in texas indicate that they should not be considered as part of a single anorogenic magmatic event the red bluff granitic suite was emplaced into a shelf sequence north of the grenville front within a broad zone characterized by mild extension in contrast llano granites are late stage intrusions emplaced into multiply deformed and metamorphosed crust south of the grenville front during or after waning stages of grenville orogenesis

lithium isotopic composition of central american volcanic arc lavas implications for modification of subarc mantle by slab derived fluids abstract li contents and isotopic compositions were determined for a suite of well characterized basaltic lavas from the central american volcanic arc cava variable li y 0 2 0 5 li sc 0 1 0 4 and 6 li values 2 6 to 7 7 attest to significant compositional heterogeneity in the subarc mantle within specific arc segments these parameters correlate strongly with each other and with a number of other constituents e g k rb ba b la 10 be 9 be 87 sr 86 sr u ce and 230 th 232 th among others these correlations are particularly strong for nicaragua samples coupling of this particular set of constituents is best explained in terms of addition of subduction components to the subarc mantle moreover their selective enrichment with respect to relatively fluid immobile incompatible elements signifies the dominance of fluid vs silicate melt transport of slab components to the subarc mantle several interesting nuances are revealed by the li data first although li and b are strongly correlated in both costa rica and nicaragua there are systematic along strike variations in li b that are consistent with these elements having different fluid release patterns from subducted slab segments for example li b is highest in costa rica where auxiliary evidence indicates higher subduction zone temperatures apparently b is preferentially depleted and li retained in the slab under warmer conditions the same relations are reflected in li 10 be and other subduction tracer systematics all of which point to larger subduction contributions below nicaragua yet even nicaragua lavas vary widely in levels of subduction enrichment high ti basalts from nejapa are the least enriched and have the highest 6 li 1 4 to 2 6 these values are greater than in fresh morb ca 4 and are not easily explained by additions of subducted li because most oceanic crustal rocks and marine sediments have lower 6 li than morb with typical values between 8 and 20 thus it appears the nejapa data may be representative of isotopically light mantle domains relatively light 6 li values in an undepleted spinel lherzolite 11 3 from zabargad is red sea and in primitive backarc basalts 1 6 to 0 5 from lau basin support this conclusion considering representative fluid and mantle endmember compositions the cava data are consistent with limited up to a few percent additions of slab derived fluids to a heterogeneous mantle containing variably depleted and enriched domains to form the respective magma sources in our view the subarc mantle is heterogeneous on a small scale but some arc sectors clearly received greater slab inputs than others

the evolution of the hercynides of central sw england towards the end of lower carboniferous times sedimentation accompanied by widespread igneous activity proceeded in a tectonically active unstable and constricted basinal zone visean flysch and olistostromic sequences were generated in front of an advancing deformation front which caused erosion of submarine rises and heralded the beginning of the hercynian orogeny in this region between dartmoor and bodmin moor upper devonian basin and rise facies sediments were thrust northwards over both upper devonian and lower carboniferous northern equivalents which were themselves incorporated onto the allochthon the tectonic deformation history began in the late visean and early namurian with the gravity sliding dl of the bulk of the lower carboniferous northwards to form the greystone nappe subsequently the main thrusting event d2 from late lower namurian times onwards led to the successive overthrusting and emplacement of the heathfield petherwin and tredorn nappes towards the end of the namurian and in the westphalian the intrusion of the granite batholith caused the fold belt to tighten which resulted in the formation of numerous low angle normal faults d3 offsetting earlier thrusts to the n overall the regime is one of very thin skinned thrust and nappe tectonics with the allochthon probably not exceeding 1 km in thickness

grenville magmatism in west texas petrology and geochemistry of the red bluff granitic suite zone of regional extension as suggested by recent geophysical and the red bluff granitic suite rbgs underlies part of the franklin petrological studies mountains in west texas it was emplaced into a middle proterozoic shelf sequence at 1120 35 ma the suite is predominantly metaluminous it consists of early granitic to quartz syenitic sills a main mass of alkali feldspar granite small bodies of alkali feldspar syenite leucogranitic dikes and late stage peralkaline

boron isotopic composition of subduction zone metamorphic rocks abstract many arc lavas contain material derived from subducted oceanic crust and sediments but it remains unresolved whether this distinctive geochemical signature is transferred from the subducting slab by aqueous fluids silicate melts or both boron isotopic measurements have the potential to distinguish between slab transfer mechanisms because 11 b fractionates preferentially into aqueous fluids whereas little fractionation may occur during partial melting previous studies have shown that 11 b values of island arc lavas 6 to 7 overlap the range of 11 b values for altered oceanic crust 5 to 25 and pelagic sediments and turbidites 7 to 11 secondary ion mass spectrometry sims analyses of minerals in subduction zone metamorphic rocks yield 11 b 11 to 3 suggesting that slab dehydration reactions significantly lower the 11 b values of subducted oceanic crust and sediments in order to explain the higher 11 b values reported for arc lavas as compared to subduction zone metamorphic rocks the b bearing component derived from the metamorphosed slab must be enriched in 11 b relative to the slab favoring an aqueous fluid as the slab transfer mechanism