structural analysis of a transform fault rift zone junction in north iceland abstract on the north coast of iceland the rift zone in north iceland is shifted about 120 km to the west where it meets with and joins the mid ocean kolbeinsey ridge this shift occurs along the tjornes fracture zone an 80 km wide zone of high seismicity which is an oblique non perpendicular transform fault there are two main seismic lineaments within the tjornes fracture zone one of which continues on land as a 25 km long wnw trending strike slip fault this fault referred to as the husavik fault meets with and joins north trending normal faults of the theistareykir fissure swarm in the axial rift zone the most clear cut of these junctions occurs in a basaltic pahoehoe lava flow of holocene age where the husavik fault joins a large normal fault called gudfinnugja at this junction the husavik fault strikes n55 w whereas gudfinnugja strikes n5 e so that they meet at an angle of 60 the direction of the spreading vector in north iceland is about n73 w which is neither parallel with the strike of the husavik fault nor perpendicular to the strike of the gudfinnugja fault during rifting episodes there is thus a slight opening on the husavik fault as well as a considerable dextral strike slip movement along the gudfinnugja fault consequently in the holocene lava flow there are tension fractures collapse structures and pressure ridges along the husavik fault and pressure ridges and dextral pull apart structures subparallel with the gudfinnugja fault the 60 angle between the husavik strike slip fault and the gudfinnugja normal fault is the same as the angle between the tjornes fracture zone transform fault and the adjacent axial rift zones of north iceland and the kolbeinsey ridge the junction between the faults of husavik and gudfinnugja may thus be viewed as a smaller scale analogy to the junction between this transform fault and the nearby ridge segments using the results of photoelastic and finite element studies a model is provided for the tectonic development of these junctions the model is based on an analogy between two offset cuts mode i fractures loaded in tension and segments of the axial rift zones or parts thereof in the case of the husavik fault the results indicate that the tjornes fracture zone in general and the husavik fault in particular developed along zones of maximum shear stress furthermore the model suggests that as the ridge segments propagate towards a zero underlapping configuration the angle between them and the associated major strike slip faults gradually increases this conclusion is supported by the trends of the main seismic lineaments of the tjornes fracture zone

origin of trace gases in submarine hydrothermal vents of the kolbeinsey ridge north iceland two hydrothermal fields of the kolbeinsey ridge area north of iceland show vent gas characteristics which can be related to the subsurface conditions helium isotopes r r air 9 8 10 9 indicate a mantle derived origin and can be considered as a mixture of more helium and a deep mantle plume helium component the carbon isotope composition of co2 ranges between 2 4 and 7 8 parts per thousand the less negative delta 13 c co2 values were found at grimsey the data from grimsey are very similar to those previously published and regarded as being characteristic for the icelandic magmatic source however small amounts of biogenic co2 and or subsurface calcite precipitation are responsible for the lighter isotope values of co2 from kolbeinsey ch4 he 3 ratios which are higher than in morb indicate an additional sedimentary methane source for kolbeinsey and grimsey hydrothermal gases the presence of higher hydrocarbons up to butane together with the carbon isotope values of methane delta 13 c 26 1 to 39 8 parts per thousand suggest a probably high mature organic source within thick sediments of the tjornes fracture zone and smaller depressions on the west side of the kolbeinsey ridge crest geochemical characteristics of hydrocarbons present in kr hydrothermal fluids are however typical for a mixed thermogenic and high temperature hydrothermal e g epr type origin moreover it is likely that secondary processes such as bacterial oxidation and thermal cracking determined the geochemical characteristics of the gases c 1999 elsevier science b v all rights reserved

growth history of a diffusely venting sulfide structure from the juan de fuca ridge a petrological and geochemical study centimeter scale mineralogical and chemical analyses of a diffusely venting 280 c sulfide structure called roane from the mothra hydrothermal field on the juan de fuca ridge reveal a complex growth history these analyses document four well defined zones which from the exterior to the interior of the structure include a barite silica zone fossil worm tube zone a silica sulfide zone silica zone a sulfide silica zone outer sulfide zone and a sulfide gordaite silica zone inner sulfide zone these features are a product of a myriad of processes that include extensive mineral replacement ingress of seawater fracturing and breakout of hot hydrothermal fluids significant conductive cooling and the sustained broad scale outflow of warm fluids from the walls through a porous and permeable matrix roane lacks an open throughgoing chalcopyrite lined central conduit instead it hosts an anastomosing discontinuous network of tortuous channels within the interior of a sponge like matrix of amorphous silica sulfide sulfate and clay minerals megafaunal communities at the summit and sides of this mature diffusely venting chimney provide a constructional framework for new growth isolation of hydrothermal fluid from seawater during progressive fossilization of megafauna and the early formation of barite silica assemblages promote flow of higher temperature fluids within the interior continued isolation of interior higher temperature fluids through increased mineral precipitation and expansion of the structure leads to a zn sulfide pyrite dominated permeable matrix and a network of tortuous channels that form a central porous conduit this conduit is shielded by a weakly silicified metal sulfide inner wall and a strongly silicified outer wall the most outer portions of the walls are highly porous and sites of significant advection and mixing between hydrothermal fluids and seawater the mineralogy and chemistry of roane are strongly affected by ammonia ammonium buffering of the ph during cooling of the hydrothermal fluids the two major results of the buffering are 1 precipitation of zn sulfide at higher temperatures than are typical for bare rock systems leading to the correlation of cu zn cd and se and 2 increased deposition of amorphous silica and clay minerals

new gas geothermometers for geothermal exploration calibration and application calibration of five gas geothermometers is presented three of which used co2 h2s and h2 concentrations in fumarole steam respectively the remaining two use co2h2 and h2sh2 ratios the calibration is based on the relation between gas content of drillhole discharges and measured aquifer temperatures after establishing the gas content in the aquifer gas concentrations were calculated in steam formed by adiabatic boiling of this water to atmospheric pressure to obtain the gas geothermometry functions it is shown that the concentrations of co2 h2s and h2 in geothermal reservoir waters are fixed through equilibria with mineral buffers at temperatures above 230 c epidote prehnite calcite quartz are considered to buffer co2 two buffers are involved for h2s and h2 and two functions are therefore presented for the geothermometers involving these gases for waters containing less than about 500 ppm chloride and in the range 230 300 c pyrite pyrrholite epidote prehnite seem to be involved but pyrite epidote prehnite magnetite or chlorite for waters above 300 c and waters in the range 230 300 c if containing over about 500 ppm the gas geothermometers are useful for predicting subsurface temperatures in high temperature geothermal systems they are applicable to systems in basaltic to acidic rocks and in sediments with similar composition but should be used with reservation for systems located in rocks which differ much in composition from the basaltic to acidic ones the geothermometry results may be used to obtain information on steam condensation in upflow zones or phase separation at elevated pressures measured aquifer temperatures in drillholes and gas geothermometry temperatures based on data from nearby fumaroles compare well in the five fields in iceland considered specifically for the present study as well as in several fields in other countries for which data were inspected the results of the gas geothermometers also compare well with the results of solute geothermometers and mixing models in three undrilled icelandic fields

high b values in the leaky segment of the tjornes fracture zone north of iceland are they evidence for shallow magmatic heat sources near the seamount holl in the tjornes fracture zone tfz north of iceland two anomalies of high seismic b values have been found in a depth shallower than 10 km according to the results of similar b value anomalies beneath volcanic edifices such as mt st helens a magma chamber was suspected in the region on first view the existence of a long living magma body between the island of kolbeinsey and holl seamount appears to be confirmed by reflection seismic surveys conducted in the area with shallow water depths of 400 m they show a clear deep reflector however the reflector is best imaged in a migrated record at 1500 m s i e the speed of sound in water and it can be modeled by single scattering from the bathymetry in the area which leads to the conclusion that the apparent reflection images the seafloor rather than a magma chamber the recent volcanism along manareyjar ridge with the last eruption in 1868 69 and the hydrothermalism east of grimsey island would be trivially explainable by a magma chamber in the subsurface however there is no evidence for a magma chamber in this more southern part of the grimsey lineament gl even in a volcanic area such as the gl as the leaky part of the tfz neither the existence of high b values nor an apparent deep reflector prove the existence of a magma chamber instead the seismic imaging of magma chambers in areas of intermediate to slow spreading ridge areas appears to be questionable

distributions of hydrothermal activity along the mid atlantic ridge interplay of magmatic and tectonic controls abstract hydrothermal activity has been investigated along three different sections of the slow spreading mid atlantic ridge mar 11 20 30 n 36 38 n and the reykjanes ridge 57 45 63 06 n when considered in total the incidence of venting along these three sections of the mar compares well with the predictions of a model in which frequency of venting is linearly related to ridge crest spreading rate at the scale of individual study areas however departure from the model is observed by up to an order of magnitude venting is anomalously rare along the reykjanes ridge but anomalously abundant along the mar 36 38 n whilst such variability may be within the error of the linear spreading rate model we note that the interplay between magmatic and tectonic processes also differs between the three study areas in the case of the reykjanes ridge we propose that the low incidence of venting reported may reflect a limitation of the sampling investigative strategy because the style of venting which predominates may not give rise to conventional black smoker hydrothermal plumes along the oblique and broadly segmented mar 36 38 n we propose that vigorous hydrothermal venting in broad segment end non transform discontinuities may be focussed along deeply penetrating active faults with the requisite heat supply being supported through some combination of along axis magmatic intrusions and thermal release associated with the serpentinisation of crustal peridotites

mineral chemical studies of metamorphosed hydrothermal alteration in the kristineberg volcanogenic massive sulfide district sweden the massive sulfide deposits of the kristineberg area sweden occur within a 2 to 3 km thick succession of felsic volcaniclastic rocks belonging to the skellefte group the volcanic pile is intruded by a synvolcanic jorn type granitoid viterliden intrusive complex and is overlain by a thick sequence of metasedimentary rocks vargfors group mineralization occurs at two main stratigraphic levels at the base of the felsic volcanic succession and at the contact with the metasedimentary rocks of the vargfors group the kristineberg cu zn mine is the largest deposit approximately 21 mt and occurs at the base of the volcanic pile close to the contact with the viterliden intrusive complex four smaller deposits ravliden ravlidmyran horntrask and nyliden occur along the upper ore horizon these deposits are thought to be related to a late intrusive phase of the viterliden complex which cuts the altered volcanic rocks at the kristineberg deposit within an area of about 50 km2 surrounding the kristineberg deposit felsic volcanic rocks between the two ore horizons are affected by extensive albite destructive alteration sodium depletion and development of chlorite and muscovite strong co enrichment in magnesium and potassium the kristineberg deposit is enveloped by a large and partly transposed quartz chlorite alteration zone approximately 2 km in diameter and a distal but coherent pyrite quartz muscovite alteration zone extending as far as 4 km from the deposit chlorite talc in the mine area is notably magnesium rich and contains anomalous f ba zn and mn high fluorine is also present in coexisting muscovite and phlogopite the magnesium rich chlorite alteration contrasts sharply with the iron enrichment observed in many other felsic volcanic hosted precambrian massive sulfide deposits this may indicate fixation of iron by large amounts of pyrite in the section or entrainment of large amounts of seawater in the hydrothermal upflow zones kyanite is developed locally in the chlorite rich pipe at kristineberg in response to regional thermal metamorphism of highly aluminous alteration in the immediate foot wall rocks spectacular andalusite bearing quartz muscovite schists and quartz biotite cordierite schists also occur where the altered felsic volcanic rocks are intruded by the late revsund granite however similar metamorphic mineral growth is not observed where the volcanic rocks at the contact are less altered deposits near the top of the felsic volcanic succession are characterized by magnesium rich chlorite alteration in the foot wall and proximal calc silicate assemblages dolomite calcite tremolite garnet margarite where the host sedimentary rocks are carbonate rich in general the calc silicate alteration is restricted to the immediate hanging wall and zones lateral to the deposits and does not represent a regionally extensive exploration target the two main ore horizons in the kristineberg area are not linked by any obvious discordant structures or alteration zones however mineral chemical studies highlight several possible fluid flow pathways leading from the kristineberg deposit to the ravliden ore horizon more than 2 km upsection overprinting regional metamorphic minerals have inherited the hydrothermal signature of the ore related alteration electronic supplementary material is available at http dx doi org 10 1007 s00126 002 0299 y on that page frame on the left side a link takes you directly to the supplementary material

formation of hydrothermal deposits at kings triple junction northern lau back arc basin sw pacific the geochemical perspectives an inactive hydrothermal field was discovered near kings triple junction ktj in northern lau back arc basin during 19th cruise of r v akademik mstislav keldysh in 1990 the field consisted of a large elongated basal platform the pedestal with several small chimneys on its periphery and one main mound superposed over it the surrounding region is carpeted with lava pillows having ferromanganese precipitate as infillings the adjoining second field consisted of small chimney like growths termed as christmas tree field the basal pedestal the peripheral chimneys and small christmas tree like growths samples collected by mir submersibles though parts of the same hydrothermal field differ significantly in their mineralogy and elemental composition indicating different history of formation the pedestal slab consisting of chalcopyrite and pyrite as major minerals and rich in cu is likely to have formed at higher temperatures than sphalerite dominated peripheral chimney extremely low concentration of high field strength elements e g zr hf nb and ta and enrichment of light ree in these sulfides indicate prominent influence of aqueous arc magma rich in subduction components the oxide growths in the christmas tree field have two distinct layers fe rich orange red basal part which seems to have formed at very low temperature as precipitates from diffused hydrothermal flows from the seafloor whereas mn rich black surface coating is formed from hydrothermal fluids emanated from the seafloor during another episode of hydrothermal activity perhaps this is for the first time such unique hydrothermal oxide growths are being reported in association with hydrothermal system here we discuss the possible processes responsible for the formation of these different hydrothermal deposits based on their mineralogy and geochemistry

simulation of the argo observing system in an ocean general circulation model 1 the main goal of this study is to determine how well large scale temperature salinity upper ocean heat content uohc and surface mixed layer fields and their variability can be reconstructed from the argo observing system the approach is to sample and reconstruct these oceanic fields from a coarse resolution ocean general circulation model ogcm quantify the errors in the reconstructed fields and analyze the factors controlling these errors in particular this study analyzes the effects of float movements on the spatial coverage and reconstruction of temporal variability overall performance of the simulated argo array is good and the reconstructed climatological means of such key quantities as the temperature salinity uohc and mixed layer depth are very close to the actual ogcm simulated values in most of the global ocean however the differences between the reconstructed and actual fields reconstruction errors are more significant in several regions with strong currents such as the antarctic circumpolar current acc the results also suggest that the detection of the year to year changes in uohc in the acc in high latitude north atlantic and near the coasts can be particularly problematic as illustrated by sensitivity experiments the main effect of float movements is to increase reconstruction errors this adverse effect of float movements is the main cause of large errors in the uohc interannual difference in the acc when the spatial sampling coverage is improved for example by increasing the number of floats the accuracy of reconstruction improves substantially

pyrite and other sulphur minerals in giant aquic spodosols western australia abstract thirty very deep aquic spodosols in swales of the bassendean dune system western australia were investigated for their potential to acidify due to their contents of acid forming sulphur minerals pyrite commonly occurs in b bh c and sometimes a and e horizons of these soils two morphologies of pyrite are present single crystals of pyrite are euhedral cubic or octahedral 1 m and framboidal pyrite aggregate grains range from 1 to 10 m elemental sulphur in the form of anhedral particles 10 500 nm may occur in e b and bh horizons and is strongly associated with organic matter and jarosite sometimes occurred in the a horizon rare marcasite and mackinawite are other acid generating sulphide minerals and indicate the diverse redox and other chemical conditions that exist in these spodosols consequently drying and aeration of these soils due to drainage and possibly also to climate change acidifies both soil and groundwater these spodosols are therefore acid sulphate soils acid buffering is mostly minor and is provided by organic matter and allophane these observations of acid generating sulphides in spodosols may indicate that very acid nonaquic spodosols elsewhere were once saturated and contained pyrite before the profiles experienced permanent or episodic oxidising conditions

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

first observations of high temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of iceland high temperature 250 c hydrothermal vents and massive anhydrite deposits have been found in a shallow water sediment filled graben near 66 36 n in the tjornes fracture zone north of iceland the site is located about 30 km offshore near the small island of grimsey the main vent field occurs at a depth of 400 m and consists of about 20 large diameter up to 10 m mounds and 1 3 m chimneys and spires of anhydrite and talc a north south alignment of the mounds over a 1 km strike length of the valley floor suggests that their distribution is controlled by a buried fault widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1 km2 area occupied by the vents is thermally active a 2 man research submersible jago was used to map the area and to sample vent waters gases and chimneys actively boiling hydrothermal vents occur on most of the mounds and extensive two phase venting indicates that the field is underlain by a large boiling zone 200 300 m the presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring the highest temperature pore fluids were encountered in talc and anhydrite rich sedimentary layers that occur up to 7 m below the mounds baked muds underlie the talc and anhydrite layers and pyrite is common in stockwork like fractures and veins in the hydrothermally altered sediments however massive sulfides pyrite marcasite crusts were found in only one relict mound subseafloor boiling has likely affected the metal carrying capacity of the hydrothermal fluids and deposition of sulfides may be occurring at greater depth although the mounds and chimneys at grimsey resemble other deposits at sedimented ridges e g middle valley escanaba trough guaymas basin the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system

mineralogy and geochemistry of clay samples from active hydrothermal vents off the north coast of iceland active hydrothermal vent sites were sampled during 1997 in a series of submersible dives at the active grimsey ghf and kolbeinsey khf hydrothermal fields off the north coast of iceland this study focuses on secondary clay minerals which were formed in two different settings the ghf is characterized by the presence of clay minerals precipitated within active chimneys by contrast the khf is characterized by the presence of secondary clay minerals which are the products of hydrothermal alteration of lava fragments based on xrd electron microprobe and icp ms analyses the dominant clay mineral in both hydrothermal fields is saponite mg rich smectite chlorite and chlorite smectite mixed layer minerals also occur at the khf the mg rich nature of saponite from the ghf chimneys suggests intense mg metasomatism in the mixing zone where hydrothermal fluids interact with seawater at temperatures of 250 c saponite formation resulted in the additional uptake of cu zn and pb enrichment in ba is evident in the almost pure saponite from the khf based on oxygen isotope data the saponite formation at the khf occurred at 148 c which is close to the maximum measured fluid temperature of 131 c in this field

the influence of magmatic fluids and phase separation on b systematics in submarine hydrothermal vent fluids from back arc basins abstract the composition of submarine hydrothermal vent fluids is affected by a variety of processes such as interaction of heated seawater with rocks and sediments addition of magmatic fluids as well as phase separation and segregation how these processes specifically affect the vent fluid composition is still poorly understood in particular the relative role of phase separation and magmatic degassing which is common in arc back arc hydrothermal systems is not well known to provide new insights into these processes we analysed b contents and isotope ratios in hydrothermal vent fluids and volcanic rocks from the manus basin papua new guinea and nifonea volcano new hebrides back arc these fluids show a range of salinities gas contents acidities and host rock compositions many of them are influenced by phase separation and by addition of magmatic volatiles both co2 and so2 previous studies of hydrothermal vents in arc back arc settings suggest that b contents and isotopic composition of vent fluids are controlled by interactions between seawater basement and sediments and propose that phase separation and magmatic fluids play only a subordinate role in our study we demonstrate that vent fluids with minor magmatic input indeed reflect the interaction between seawater and oceanic crust in contrast the low salinity nifonea fluids and some of the acid sulphate fluids from the manus basin have higher b contents as expected whereas other volatile rich fluids from the manus basin show b depletions the lack of correlation between b contents and the intensity of magmatic fluid influx co2 and so2 may indicate that magma degassing is not responsible for the b enrichments or depletions in these vent fluids b enrichments might be related to preferential partitioning of b into the vapour phase during phase separation under pt conditions well above the two phase curve and critical line i e t tcritical p pcritical however this cannot explain the low b concentrations in the vapour rich vent fluids from the manus basin and the low b isotope ratios in the nifonea fluids instead we propose that b concentrations and isotope ratios in submarine vent fluids largely depend on the residence and reaction time of the vent fluid in the subsurface in general all vent fluids are still influenced by water rock interaction during hydrothermal circulation however vent fluids with short residence times define a trend towards lower b concentrations and isotope ratios which can be explained by mixing between hydrothermal and magmatic fluid which is similar to the composition of the host rock in contrast the b signature of the magmatic fluid can be overprinted due to preferential mobilisation of b from the oceanic crust into vapour rich fluids at longer reaction times thus b may provide a tool for estimating the extent of b leaching and hence hydrothermal alteration in the subseafloor

crystal chemistry of interstratified mg fe clay minerals from seafloor hydrothermal sites abstract seafloor hydrothermal sites generate abundant mg and fe rich clays these clays are structurally and compositionally interesting because these environments are characterized by large dynamic temperature and chemical gradients in their deposition environment which promote the formation of chemically and structurally complex clays including interstratified phases the system is also interesting as a proxy for the study of the large mg and fe rich phyllosilicate deposits on mars which are broadly characterized as smectitic clay of hydrothermal volcanic or sedimentary origin thirty submarine samples and four terrestrial ones for comparison were studied by means of x ray diffraction xrd thermogravimetry tg mid ir and mossbauer spectroscopies and chemical analysis the samples include nontronite and the mixed layer phases glauconite nontronite talc nontronite and talc saponite some of the talc saponite samples have fe contents well above those typical for these mg rich trioctahedral phases up to 1 69 fe per o 10 oh 2 in the tetrahedral and octahedral sheets tetrahedral fe ranges from 0 to 0 66 atoms per o 10 oh 2 across the samples as found in previous studies of similar specimens fe promotes the retention of molecular water that is released upon heating above 200 c and is mainly emplaced in non expandable layers talc and glauconite layers in talc nontronite and talc saponite octahedral fe both di and trivalent appears to be bound to this trapped molecular water whereas in glauconite nontronite the bond appears to be with tetrahedral fe samples typically show more than one dehydroxylation event in the tg analysis the weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of xrd but there is no good correlation between both by contrast the weight loss at each dehydroxylation event correlates with the chemistry of the layers where certain cations promote chemical domains in the octahedral sheet e g trioctahedral nontronite like and montmorillonite like that dehydroxylate at the several temperatures the correlations found for talc nontronite and glauconite nontronite samples suggest that the distribution of cations in the octahedral sheets of most but not all samples is intermediate between total dispersion and total segregation perhaps random the talc nontronite samples have talc layers with cation deficient octahedral sheets the above results are best explained by layers of polar character where the octahedral sheets are composed of domains with different chemical characteristics corresponding to the two types of layers in the interstratified clay the existence of molecular water bands at 1635 and 3300 3500 cm 1 or 6 1 and 2 9 3 1 m respectively bound in non expanding layers is relevant to the mineral characterization of martian fe rich clays with spectroscopic methods where molecular water is so far assumed to be linked to smectite the variety of mixed layer clays in which fe is found in the submarine samples suggests that mixed layering may be important in martian clays which are spectroscopically variable but generally fe rich

salt formation associated with sub surface boiling and supercritical water abstract laboratory experiments have demonstrated that supercritical water has extremely low solubility for normal sea salts this fact opens up the possibility for the precipitation of salt from seawater that circulates in faults and fractures close to a heat source in tectonically active basins typically extensional pre rifts and rift settings seawater attains supercritical conditions at depths exceeding 2800 m corresponding to a pressure of 300 bars and temperatures above 405 c salts may also precipitate by the boiling of seawater in sub surface or submarine settings this is demonstrated by a simple laboratory experiment the theoretical basis for the precipitation of salts from seawater attaining supercritical condition has been examined by molecular modelling these processes of salt precipitation constitute a new approach to the geological understanding of salt deposits and two regions are selected to examine whether salt may have deposited under such hydrothermal conditions today the atlantis ii deep in the red sea marine setting and lake asale dallol ethiopia continental setting

extensional transform zones and oblique spreading centers extensional transform zones etzs are plate boundary segments of order 100 km long that strike at angles between 15 and 45 to the extension direction they are characterized by neovolcanic tectonic zones comprising overlapping en echelon volcanic systems and or faults that trend 30 75 to the extension direction sometimes accompanied by a riedel shear below these surficial en echelon structures the deformation is aseismic and ductile and the plate boundary is probably continuous etzs occur in fast and slow spreading and rifting environments and may persist in a stable configuration for several million years etzs link oblique spreading segments to transform faults in the manus and probably the lau backarc basins the reykjanes peninsula and tjornes fracture zone in iceland and the mak arrasou in afar are etzs that link subaerial to submarine spreading or rifting segments the brawley and cerro prieto seismic zones appear to be etzs in the imperial and mexicali valleys that link the san andreas imperial and cerro prieto transform faults experimental and analytical models of transtensional deformation in brittle ductile systems match many of the observed characteristics of etzs and oblique spreading centers including variably sigmoidal to straight en echelon faults that are not parallel to the extension direction the contrasting fault patterns reflect the rheology of the models and lithosphere they are more sigmoidal when the strain in the lower ductile layer is more focused causing the axial faults to curve as they propagate toward parallelism with the less ductile rift margins the angle o between the faults and the extension direction decreases with the angle between the strike of the zone and the extension direction etzs occur in the range 15 45 whereas oblique spreading centers have 45 90 and transform relay zones have 0 15 oblique fast spreading segments exhibit ridge parallel faults and volcanic systems o presumably reflecting locally rotated stress fields whereas at oblique slow spreading centers o is closer to orthogonal o 90

the influence of hydrothermal fluid composition and advection rates on black smoker chimney mineralogy insights from modeling transport and reaction abstract a detailed study of black smoker chimneys was carried out by drawing together mineralogical observations and measured fluid compositions the modeling technique which establishes a link between vent fluid chemistry and vent deposit mineralogy is used to examine the influence of the physical environment on transport across short length scales centimeters which are subject to steep thermal 350 c and chemical gradients and to predict saturation states of minerals as functions of position within chimney walls owing to short length scales steep gradients and constancy of bounding fluid compositions concentration profiles are controlled by transport the effect of reaction rates on profiles is assumed to be negligible precipitation at points within the chimney wall is thus kinetically controlled local equilibrium does not apply and precipitation must be suppressed when calculating distributions of species and saturation states of minerals model calculations are performed in a series of four steps the first is speciation of measured fluid compositions at in situ temperature and pressure conditions results of calculations are plotted on stability diagrams of log fo2 log f s2 and log fo2 log a fe 2 a cu 2 to examine how closely the predicted saturation states fit with observations of minerals coexisting with the hydrothermal fluid at the vent sites the second step is calculation of heat and mass transport across the chimney wall the third is speciation of the pore fluid compositions calculated to exist in the wall subsequent to transport and the fourth is comparison of calculated mineral saturation states to observations of naturally occurring chimney samples application of the modeling technique to five vent sites which exhibit distinct fluid compositions allows reproduction of observed mineralogy model results demonstrate the sensitivity of geochemical processes to the physical environment porosity tortuosity permeability mineral composition to rates of advection of seawater inward or hydrothermal fluid outward across chimney walls and to endmember fluid composition

geochemistry of hydrothermal fluids from the pacmanus northeast pual and vienna woods hydrothermal fields manus basin papua new guinea abstract processes controlling the composition of seafloor hydrothermal fluids in silicic back arc or near arc crustal settings remain poorly constrained despite growing evidence for extensive magmatic hydrothermal activity in such environments we conducted a survey of vent fluid compositions from two contrasting sites in the manus back arc basin papua new guinea to examine the influence of variations in host rock composition and magmatic inputs both a function of arc proximity on hydrothermal fluid chemistry fluid samples were collected from felsic hosted hydrothermal vent fields located on pual ridge pacmanus and northeast ne pual near the active new britain arc and a basalt hosted vent field vienna woods located farther from the arc on the manus spreading center vienna woods fluids were characterized by relatively uniform endmember temperatures 273 285 c and major element compositions low dissolved co 2 concentrations 4 4 mmol kg and high measured ph 4 2 4 9 at 25 c temperatures and compositions were highly variable at pacmanus ne pual and a large newly discovered vent area fenway was observed to be vigorously venting boiling 358 c fluid all pacmanus fluids are characterized by negative d h 2 o values in contrast to positive values at vienna woods suggesting substantial magmatic water input to circulating fluids at pual ridge low measured ph 25 c values 2 6 2 7 high endmember co 2 up to 274 mmol kg and negative 34 s h 2 s values down to 2 7 in some vent fluids are also consistent with degassing of acid volatile species from evolved magma dissolved co 2 at pacmanus is more enriched in 13 c 4 1 to 2 3 than vienna woods 5 2 to 5 7 suggesting a contribution of slab derived carbon the mobile elements e g li k rb cs and b are also greatly enriched in pacmanus fluids reflecting increased abundances in the crust there relative to the manus spreading center variations in alkali and dissolved gas abundances with cl at pacmanus and ne pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents in further contrast to vienna woods substantial modification of pacmanus ne pual fluids has taken place as a result of seawater ingress into the upflow zone consistently high measured mg concentrations as well as trends of increasingly non conservative so 4 behavior decreasing endmember ca cl and sr cl ratios with increased mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment decreased ph and endmember fe mn ratios in higher mg fluids indicate that the associated mixing cooling gives rise to sulfide deposition and secondary acidity production several low temperature 80 c fluids at pacmanus ne pual also show evidence for anhydrite dissolution and water rock interaction fixation of b subsequent to seawater entrainment hence the evolution of fluid compositions at pual ridge reflects the cumulative effects of water rock interaction admixing and reaction of fluids exsolved from silicic magma phase separation segregation and seawater ingress into upflow zones

siliceous sublacustrine spring deposits around hydrothermal vents in lake taupo new zealand chimneys around hydrothermal vents at a depth of c 140 m in the horomatangi reefs area in lake taupo new zealand are composed of amorphous silica opal a with lesser amounts of mn fe and hg rich precipitates detrital quartz and feldspar grains are found in the surrounding sediments the associated biota includes fish bacteria sponges crayfish amphipods copepods ostracodes annelids and other unidentified organisms much of this biota however is not preserved in the opal a deposits instead the silicified biota includes filamentous microbes and diatoms scattered coccoid microbes fungal hyphae and spores rare sponge spicules and rare worm tubes the diatoms coccoid microbes and fungi were brought into the area with the detrital sediment in ancient successions distinction between sublacustrine terrestrial and some marine hot spring deposits may be difficult because the precipitates share many similarities distinction based on the biota is viable only if palaeoecological information can be inferred from accurately identified organisms unfortunately silicification commonly disguises microbes and precludes their accurate identification diagenetic transformation of opal a to its more stable polymorphs also destroys many original depositional fabrics and silicified microbes distinction between the different types of spring deposit may therefore depend on the interpretation of their overall sedimentological and stratigraphic setting

jarosites and their application in hydrometallurgy the alunite supergroup consists of more than 40 minerals with the general formula dg 3 t o4 2 oh h2o 6 wherein d represents cations with a coordination number greater or equal to 9 and g and t represent sites with octahedral and tetrahedral coordination respectively smith et al 1998 the supergroup is commonly subdivided into various groups but the simplest primary subdivision is on the basis of the g cations for all of the minerals in the supergroup the dominant g cation is trivalent most of the minerals have g represented by fe3 or al3 but exceptions are the rare minerals gallobeudantite in which g is ga3 and springcreekite in which g is v3 table 1 thus the primary grouping adopted here is on whether formula fe3 exceeds or is subordinate to al3 the hierarchical sequence in mineralogy seems to be variable but here the decreasing sequence is given as supergroup family group and subgroup minerals with fe3 al3 are referred to as belonging to the jarosite family and those with a13 fe3 are allocated to the alunite family view this table table 1 minerals of the alunite supergroup subdivision of the alunite and jarosite families has also been variable scott 1987 for example used seven groups novak et al 1994 used six gaines et al 1997 used four and mandarino 1999 used three the arbitrary decision here is to use three groups which differ from those of mandarino 1999 but which in general indicate whether sulfate phosphate or arsenate predominates in the t o4 tetrahedra the three groups are the alunite group in which t o4 is dominated by so4 the crandallite group in which po4 is

evidence for hydrothermal venting and sediment volcanism discharged after recent short lived volcanic eruptions at deception island bransfield strait antarctica abstract the results of a combined geophysical and geochemical research programme on deception island an active volcano at 62 43 s 60 57 w in bransfield strait antarctica are presented ultrahigh resolution acoustic data obtained with a topas topographic parameter sonar system and multibeam bathymetry simrad em1000 allow a detailed analysis of submarine vents in port foster the submerged caldera of deception island the data show three different types of seafloor structures low relief mounds high relief mounds wasp nest like and spire like structures we interpret these structures as products of sediment volcanism and seeps caused by heating and boiling of pore fluids in gas charged sediments and related to recent short lived volcanic events possibly those that occurred in 1967 1969 and 1970 in addition subsurface vertical disturbed zones formed by increased amplitude and phase inverse reflectors beneath the mounds suggest the presence of fluidised and brecciated sediments within hydrofracture systems a key finding of this study is that there appears to be a close relationship between the submarine mounds detected by our ultrahigh resolution seismic study geochemical haloes fault pathways and present day thermal anomalies in surface waters we suggest that seafloor hydrofracture systems and subsurface pipes can be re used as fluid migration pathways resulting in hydrothermal seeps and vents on the seafloor possibly up to decades after coeval volcanic eruptions

origin of fluids and anhydrite precipitation in the sediment hosted grimsey hydrothermal field north of iceland the sediment hosted grimsey hydrothermal field is situated in the tjornes fracture zone tfz which represents the transition from northern iceland to the southern kolbeinsey ridge the tfz is characterized by a ridge jump of 75 km causing widespread extension of the oceanic crust in this area hydrothermal activity occurs in the grimsey field in a 300 m 1000 m large area at a water depth of 400 m active and inactive anhydrite chimneys up to 3 meters high and hydrothermal anhydrite mounds are typical for this field clear metal depleted up to 250 c hydrothermal fluids are venting from the active chimneys anhydrite samples collected from the grimsey field average 21 6 wt ca 1475 ppm sr and 3 47 wt mg the average molar sr ca ratio is 3 3 10 3 sulfur isotopes of anhydrite have typical seawater values of 22 0 7 34s indicating a seawater source for so42 strontium isotopic ratios average 0 70662 0 00033 suggesting the precipitation of anhydrite from a hydrothermal fluid seawater mixture the endmember of the venting hydrothermal fluids calculated on a mg zero basis contains 59 8 mol kg sr 13 2 mmol kg ca and a 87sr 86sr ratio of 0 70634 the average sr ca partition coefficient between the hydrothermal fluids and anhydrite of about 0 67 implies precipitation from a non evolved fluid a model for fluid evolution in the grimsey hydrothermal field suggests mixing of upwelling hydrothermal fluids with shallowly circulating seawater before and during mixing seawater is heated to 200 250 c which causes anhydrite precipitation and probably the formation of an anhydrite rich zone beneath the seafloor

characterization of jarosite natrojarosite in two northern scandinavian soils abstract jarosite type minerals mfe 3 so 4 2 oh 6 m k jarosite m na natrojarosite were studied in two sulfic cryaquepts developed in sulfidic sediments deposited in the baltic between 7000 and 4000 bp the jarosites were characterized by x ray diffraction xrd and a selective dissolution technique selective dissolution showed that the k na molar ratio in the jarosites was 0 32 1 27 and the xrd patterns indicated that the jarosite and natrojarosite components formed solid solutions saturated pastes of soil samples were equilibrated for different periods 6 hours to 8 days in order to estimate solubility product constants k so for the jarosite and natrojarosite estimated values of k so for jarosite 10 94 1 10 94 2 corresponded well with literature values for pure or nearly pure synthetic jarosite for natrojarosite only one determination or k so was found in the literature the discrepancy between this value and the k so values obtained in the present study 10 93 1 10 93 9 is about four orders of magnitude which is too large to be explained as an effect of solid solution formation thus we suggest that the literature value is not valid for the pedogenic natrojarosite in these soils i e it is less soluble than the value indicates we hypothesize that natrojarosite forms mainly where the supply of k limits jarosite formation e g under conditions where marine or brackish water has a minor influence the weathering of silicate minerals might be the main source of k and na in such a case by contrast in coastal areas concentrations of k na and so 4 are high and jarosite formation probably is limited by fe oxidation in such environments mainly jarosite is formed owing to its more rapid formation kinetics

role of deep sourced fluids on the initiation and growth of isolated carbonate build ups abstract the relative role of the various mechanisms responsible for the formation of isolated carbonate build ups occurring on the seafloor along continental margins is still uncertain the interpretation of an extensive seismic dataset in the central vulcan sub basin nw australia allowed to evaluate the possible role of migration and seepage of deep sourced fluids during the initial growth of isolated carbonate build ups the neogene tectonic activity along the margin generated extensional fault systems that commonly displaced the seafloor thus apparently creating a substratum to the initiation of various carbonate build ups during the pleistocene the seismic data show reflections with enhanced amplitude respect to background values which are associated with both isolated carbonate build ups and normal faults the seismic character of these reflections supports the presence of fluids that migrated within the sedimentary pile throughout the investigated area the interpreted occurrence of methane derived authigenic carbonates mdac on the seismic surface upon which the carbonate build ups lay suggests that seepage of hydrocarbons likely occurred at the time of their initial formation the fluid migration appears focused in the areas above extensional faults which breached the seals of the mesozoic reservoirs combined tectonic activity and seepage are suggested to support the initial growth of the carbonate build ups various smaller buried carbonate build ups developed contemporaneously to those on the present day seafloor in sites that lack evidence of past hydrocarbon seepage their shorter life compared to those on the present day seafloor suggests their inability to keep up with the frequent relative sea level variations during the quaternary and the importance of deep sourced fluids for the carbonate build ups growth in the central vulcan sub basin the initiation of the numerous carbonate build ups documented along continental margins worldwide must be explained considering the complex and dynamic interplay of all factors potentially involved such as geological and oceanographic settings and an active petroleum system in particular the migration and seepage of deep sourced fluid can have an important role in controlling the genesis and growth of isolated carbonate build ups

postglacial tectonic activity within the skjalfandadjup basin tjornes fracture zone offshore northern iceland based on high resolution seismic stratigraphy abstract multibeam bathymetric and high resolution seismic reflection data chirp have been used to illuminate the structural framework and tectonic evolution of the 300 km2 skjalfandadjup basin one of three large rift basins within the tjornes fracture zone a complex transform zone offshore northern iceland the skjalfandadjup basin together with the nafir seamounts form the nascent nafir skjalfandadjup volcanic system of the oblique grimsey volcanic zone the skjalfandadjup basin is made up of normal faults with maximum displacement of 50 60 m and a dominant strike of n10 20 w correlation of chirp data with tephrochronology from sediment core md99 2275 provided constraints on tectonic movements along individual faults from late glacial time throughout holocene maximum vertical displacement is observed on three listric normal faults marking the eastern boundary of the main basin postglacial tectonic activity commenced as early as 14 15 kyr bp followed by three major rifting episodes prior to 10 kyr bp and three smaller rifting episodes during the last 4 2 kyr the 10 12 kyr period of enhanced tectonic activity was accompanied by eruptions within the tjornes fracture zone isostatic rebound following rapid deglaciation caused rifting with significant vertical displacement on normal faults offshore n iceland

anhydrite bearing rocks from the rožna district moldanubian zone czech republic high grade metamorphosed exhalites several types of anhydrite bearing rocks have been found in the amphibolite facies metamorphosed rocks at the north eastern margin of the moldanubian zone anhydrite either forms monomineralic bands up to 40 cm thick or occurs in the form of disseminated grains in surrounding calc silicate gneiss together with feldspar scapolite amphibole pyroxene epidote and pyrite the isotopic composition of sulphur 34s 30 6 to 32 3 and strontium 87sr 86sr 0 70797 to 0 70781 in anhydrite may indicate a marine source of sulphate the isotopic ratio of strontium is in the same range as that of metamorphosed strata bound barite sulphide ores which have been previously described in the same area the 34s values of coexisting pyrite range from 21 4 to 22 5 the 34sanhydrite pyrite corresponding to the metamorphic temperature of 600 to 660 c in contrast to many submarine exhalative deposits the oxygen isotopic compositions of anhydrite 18o 9 3 to 10 2 are lighter than that of barite 18o 10 4 to 13 8 this indicates that the both minerals are not in isotopic equilibrium therefore it is probable that anhydrite and barite from the ro na district were deposited from fluids that contained different proportions of seawater and hydrothermal fluids or from hydrothermal fluids that underwent variable extent of oxygen isotope exchange with seafloor rocks the 13c values in calcite 13c 17 2 to 18 7 from anhydrite bearing rock are lower than those in distant marbles as graphite is absent in anhydrite and calcite bearing rocks impoverishment in the 13c isotope cannot be attributed to the graphite carbonate isotopic exchange during metamorphism it is proposed that low 13c values in carbonates are caused by pre metamorphic oxidation of organic matter in course of hydrothermal processes anhydrite and anhydrite bearing calc silicate gneiss from the north eastern part of the moldanubian zone are interpreted to be the high grade metamorphosed analogue of anhydrite rich exhalites commonly found in submarine exhalative hydrothermal deposits

hydrothermal activity on the reykjanes ridge the steinaholl vent field at 63 06 n we have completed a systematic survey for hydrothermal activity along the reykjanes ridge from 57 45 n to 63 09 n shipboard determinations of total dissolvable mn tdmn and dissolved si ch4 and h2 have revealed evidence for only one site of hydrothermal activity along this section of ridge crest the steinaholl vent field at 63 06 n 1 our measurements confirm this site to be a stable hydrothermal convection cell of at least two years duration the site is situated in just 250 350 m of seawater and unlike deeper sited vent fields e g tag 3650 m 26 n mar is notable for the formation of bubble rich plumes which have been imaged using a high frequency 38 khz echo sounder high dissolved gas concentrations of up to 18 nmol l ch4 and 30 nmol l h2 coincide with these bubble rich plumes the steinaholl plume is also characterised by high total dissolvable mn tdmn anomalies up to 60 nmol l and dissolved si anomalies 2 mol l yielding molar tdmn ch4 and tdmn si ratios of 3 5 and 0 03 respectively directly comparable to the tag hydrothermal plume the absence of any indication of hydrothermal activity along the remainder of the reykjanes ridge is intriguing between 11 n and 40 n on the mid atlantic ridge previous studies have revealed evidence for hydrothermally active sites approximately every 150 km for the 300 km of ridge crest studied in detail here 750 km total only one site has been found thus despite its proximity to the iceland hot spot the incidence of hydrothermal activity along this section of ridge crest appears to be only 20 50 of that measured elsewhere along the slow spreading mid atlantic ridge

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

vertical and lateral splitting of a hydrothermal plume at steinaholl reykjanes ridge iceland abstract the generation of multiple neutrally buoyant intrusions by a single bubble rich plume asaeda and imberger j fluid mech 249 1993 35 57 and plume bifurcation ernst et al bull volcanol 56 1994 159 169 lavelle j geophys res 102 1997 3405 3420 are predicted from theory and experiments but have yet to be documented for hydrothermal plumes in contrast bifurcation of volcanic plumes which are dynamically analogous to hydrothermal plumes is very common ernst et al bull volcanol 56 1994 159 169 and thus bifurcation of hydrothermal plumes should be expected lavelle j geophys res 102 1997 3405 3420 ernst et al bridge newslett 10 1996 76 77 recent 38 khz echo sounder and water column chemical tracer studies near the steinaholl vent site reykjanes ridge iceland identified a bubble rich hydrothermal plume intruding at three levels two main ones and a subsidiary one before reaching the sea surface and spreading there ernst et al bridge newslett 10 1996 76 77 olafsson et al ridge events 2 1991 35 38 german et al earth planet sci lett 121 1994 647 654 the two main intrusions ca 100 and 200 m above the vent show lateral development of two lobes away from the vent and are consistent with the 350 m rise of a bubble plume yielding seafloor and surface gas fluxes of 2 5 10 3 and 0 75 10 1 m3 s respectively the bubble rich core of the hydrothermal plume also penetrates the 150 m deep thermocline and generates an intrusion visible at the sea surface although bifurcation of the bent over plume could have been initiated by crossflow alone ernst et al bull volcanol 56 1994 159 169 several other processes may also have enhanced plume bifurcation including interaction with the thermocline and entrainment of the plume lobes by horseshoe eddies in the lee of a 150 m high hill on the seafloor

processes influencing extreme as enrichment in shallow sea hydrothermal fluids of milos island greece abstract arsenic as is naturally enriched in most terrestrial and marine hydrothermal systems its discharge from shallow sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems shallow sea hydrothermal venting of acidic ph 5 hot 40 116 c and highly sulfidic up to 3 1 mm h2s fluids occurs at palaeochori and spathi bays off the southeast coast of milos island greece two distinct types of fluids both extremely as enriched were collected from the submarine vents often within a few meters of each other 1 a high cl fluid enriched in cl by up to 47 relative to seawater depleted in mg and so4 and enriched in major na ca k b sr and br and minor trace elements si li rb ce as fe mn and ba and 2 a low cl fluid depleted in cl by up to 66 relative to seawater also depleted in na mg so4 and br the maximum concentration of as reached 39 m in the high cl fluids and up to 78 m in the low cl fluids this is approximately 3000 times the concentration of as in seawater and far exceeds the concentrations typically found in mid ocean ridge mor and back arc basin bab fluids which are typically we used a combination of elemental analyses and stable and radiogenic isotope data oxygen deuterium and strontium to understand the primary controls on as enrichment those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water rock interaction subcritical phase separation boiling and vapor brine segregation since as was extremely enriched in both the high cl and the low cl thermal fluids we conclude that this element readily partitions into the vapor phase in the milos hydrothermal system the original source of as is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite it is possible that these veins were deposited from as rich magmatic fluids similar to some epithermal au deposits a poorly crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater and removes much of the dissolved as prior to discharge

submarine hydrothermal activity and mineralization on the kurile and western aleutian island arcs n w pacific the kurile arc consists of at least 100 submarine volcanoes and 5 submarine caldera located mainly in the rear arc the arc is seismically very active particularly in the south and is characterized by extensive volcanism and hydrothermal activity at least one subaerial volcano on the arc medvezhy located on iturup island has an extremely shallow magma chamber and is intensely active three types of submarine hydrothermal deposit were recovered from this area hydrothermal manganese crusts nontronite and hydrothermal manganese crusts overlain by hydrogenous manganese oxides in addition submarine hydrothermal fe oxyhydroxides enriched in p were sampled from the submerged caldera of kraternaya bight in the central part of the arc these deposits appear to be analagous to deposits from santorini caldera on the aegean arc piip submarine volcano located in the western aleutian arc is characterized by two shallow summit craters both intermediate temperature anhydrite gypsum barite amorphous silica pyrite calcite and aragonite and low temperature nontronite fe oxyhydroxides hisingerite and ferromanganese crusts hydrothermal minerals were recovered from this seamount together with bacterial mats and giant clams the maximum measured temperature of the hydrothermal fluids was 133 c although the actual temperature may have reached 250 c both the kurile and aleutian arcs have the potential to host major submarine hydrothermal systems detailed exploration of these poorly studied areas using modern geophysical geochemical and sampling techniques is therefore strongly recommended

a newly emerged august 2013 artificially triggered fumarole near the fiumicino airport rome italy abstract early in the morning of 24 august 2013 following by hours the drilling of a shallow borehole in the same spot a new fumarole producing emissions of co2 rich gas water and mud suddenly appeared at a crossroad along the fenced area of the fiumicino international airport of rome italy similar episodes have been scientifically documented or simply reported in recent and past years to understand why gases are easily entrapped in the shallow subsurface of the fiumicino area we used five borehole cores drilled by us analyzed the stratigraphy of these and other nearby cores acquired a 2d seismic refraction tomogram and performed chemical and isotopic analyses of water samples collected from aquifers intercepted by two drilled boreholes our boreholes were realized with proper anti gas measures as while drilling we recorded the presence of pressurized gases at a specific permeable gravel level results show that in the study area gases become mainly entrapped in a mid pleistocene gravel horizon at about 40 50 m depth this horizon contains a confined aquifer that stores the endogenous upwelling gases the gravel is interposed between two silty clayey units the lower unit very hard and overconsolidated is affected by fractures that allow ascending gases to bypass the otherwise impermeable shale permeate the gravel and dissolve into the aquifer in contrast the upper unit is impermeable to fluids and seals the gas pressurized aquifer which therefore constitutes a source of hazard during human activities such as well drilling quarrying and various building related excavations as the stratigraphy of the fiumicino area is very common in large portions of the densely populated roman area and as the adjacent volcanic districts are hydrothermally active we conclude that phenomena similar to that observed at fiumicino could again occur both at fiumicino and elsewhere in the surrounding region as a prompt confirmation of our conclusion we signal that while writing this paper new artificially triggered degassing phenomena occurred off fiumicino in connection with the construction of the new harbor

reduction of jarosite by shewanella oneidensis mr 1 and secondary mineralization abstract jarosite is a common mineral in a variety of environments formed by the oxidation of iron sulfide normally accompanying with the generation of acid mine drainage amd in mining areas or acid rock drainages ard in many localities decomposition of jarosite by dissimilatory iron reducing bacteria dirb influences the mobility of many heavy metals generally accommodated in natural jarosite this study examined the anaerobic reduction of synthesized jarosite by shewanella oneidensis strain mr 1 a typical facultative bacteria the release of ferrous and ferric ion as well as sulfate and potassium in the inoculated experimental group lasting 80 days is much higher than that in abiotic control groups the detection of bicarbonate and acetate in experimental solution further confirms the mechanism of microbial reduction of jarosite in which lactate acts as the electron donor the produced ferrous iron stimulates the subsequent secondary mineralization leading to precipitation and transformation of various iron containing minerals green rust and goethite are the intermediate minerals of the microbial reduction process under anoxic conditions and the end products include magnetite and siderite in aerobic environments goethite magnetite and siderite were also detected but the contents were relatively lower while in abiotic experiments only goethite has been detected as a product thus the microbial reduction and subsequent mineral transformation can remarkably influence the geochemical cycling of iron and sulfur in supergene environments as well as the mobility of heavy metals commonly accommodated in jarosite

mid ocean ridge sulfide deposits evidence for heat extraction from magma chambers or cracking fronts numerous seafloor observations show that the sizes of high temperature hydrothermal sulfide edifices vary dramatically with spreading rate on fast spreading ridges venting occurs from spindly chimneys which reach heights of about 10 m while on slow spreading ridges vents are frequently located near the tops of large sulfide mounds whose volumes may reach 105 106 m3 we argue that such variations are the result of a profound difference in the nature of hydrothermal heat extraction between fast spreading ridges where spreading occurs predominantly by magmatism and slow spreading ridges where there is a significant component of tectonic extension along fast spreading ridges a steady state axial magma chamber can be insulated by a relatively thick conductive boundary layer because heat extraction is limited by low permeability in such systems episodes of vigorous venting are linked to diking events not only because these introduce a significant heat source into the upper crust but also because the intrusion of a dike is the primary source of increased permeability near the ridge axis over a time scale of the order of a decade mineral deposition tends to clog the reaction and upflow zones and there is a high probability that young sulfide structures will be buried by subsequent eruptions on slow spreading ridges tectonic extension maintains the fluid pathways necessary to support vigorous convection in the waning stages of magmatism hydrothermal circulation driven by a downward migrating cracking front can cool the entire crust leading to the formation of very large sulfide deposits as the depth of circulation increases overburden pressures reduce the permeability and the hydrothermal heat fluxes decrease progressively once hydrothermal fluids penetrate the moho serpentinization clogs the fluid pathways and high temperature venting ceases until it is reactivated by a fresh magmatic intrusion

submarine volcanoes and high temperature hydrothermal venting on the tonga arc southwest pacific submarine hydrothermal vents and associated seafloor mineralization on the tonga arc have been found for the first time in the summit calderas of two shallow water volcanoes greatly extending the known areas and diversity of seafloor hydrothermal activity in the western pacific region the highest temperature vents 245 265 c occur at water depths of 385 540 m near the summit of one volcano at 24 s the vents are spatially related to basaltic dike swarms exposed at a summit cone and in the caldera walls clusters of large to 10 m high barite anhydrite and sulfide chimneys on the summit cone are vigorously discharging clear hydrothermal fluids with temperatures on the seawater boiling curve there is abundant evidence of phase separation which can be seen as flame like jets of steam h2o vapor at the chimney orifices pyrite marcasite sphalerite and chalcopyrite line the interiors of the highest temperature vents similar to black smoker chimneys on the mid ocean ridges

occurrence of kaolinite and mixed layer kaolinite smectite in hydrothermal sediments of grimsey graben tjornes fracture zone north of iceland the sediments at a site situated among high temperature vents in the grimsey graben tjornes fracture zone north of iceland exhibit features of strong hydrothermal alteration 1 almost total dissolution of the volcaniclastic material composing the background sediment 2 sulfate and sulfide precipitation 3 kaolinitisation smectite precipitated in the shallowest sediment is gradually replaced downward by mixed layer kaolinite smectite and pure well crystallised kaolinite the kaolinite smectite is interstratified with up to 10 swelling smectitic layers according to the oxygen isotope composition kaolinite smectite mixed layer mineral most likely formed at temperatures near 160 degrees c the vertical sequence kaolinite kaolinite smectite smectite as well as the distinct zonation across the kaolinitic veins almost pure kaolinite in the central zone and kaolinite smectite along the rim suggest hydrothermal transformation of initially formed smectite kaolinite smectite kaolinite most probably this conversion occurred in an evolving from alkaline to slightly acidic hydrothermal environment c 2004 elsevier b v all rights reserved

chemical microenvironments within sulfide structures from the mothra hydrothermal field evidence from high resolution zoning of trace elements abstract massive portions of a 300 c black smoker finn and a diffusely venting intermediate temperature 200 c chimney roane recovered from the mothra hydrothermal field on the juan de fuca ridge have been analyzed in detail for bulk chemistry the size of the recovered pieces of chimney enabled physical segregation and analysis of distinct chemical zonation within the structures in particular large variations in the concentrations of minor and trace elements in the different mineralogical zones provide new insight into the processes involved in chimney growth that are not evident from the bulk mineralogy systematic zonation of trace and minor elements is strongly influenced by redox conditions multiple host phases single or dual fluid source and the mixing cooling history of the fluids even within an individual mineralogical zone distinct chemical microenvironments within the chimneys are recognized that provide a basis for detailed reconstruction of the changing conditions in the interiors of the chimneys during their growth in finn 14 discrete chemical microenvironments are recognized in 80 of 90 samples based on high resolution zoning of major and trace elements four of the microenvironments are cu rich three are zn rich one is fe rich with low cu two are ca rich three are sio2 rich and one is ba and sio2 rich in roane 24 discrete chemical microenvironments are recognized six of the microenvironments are sio2 poor

magnetic surveys of iceland abstract data from a 1968 1980 aeromagnetic survey of iceland and a 1972 1973 marine magnetic survey of a part of the shelf around iceland have been digitized and upgraded additional aeromagnetic survey lines were flown in 1985 1986 after appropriate low pass filtering and regridding a new multicolor map of geomagnetic field intensity anomalies over the island and its surroundings was produced the main features of the anomaly field are of two types the first 1 a comprises broad lineations subparallel to currently active or extinct spreading zones these are believed to be mostly due to tilled basalt lava flows of alternating remanence polarity in quaternary regions other extrusives of subglacial origin also contribute to the lineations the second 2 b comprises localized anomalies of the order of 10 km or less at individual volcan c centers we describe some of these features in terms of current knowledge of the age structure and magnetic properties of the uppermost crust in iceland

primary igneous anhydrite progress since its recognition in the 1982 el chichon trachyandesite abstract primary igneous anhydrite was first identified in 1982 el chichon pumices analysis of the sulfur budget for the eruption provided compelling evidence that the pre eruptive magma contained a significant gas phase at 7 km depth in order to account for the excess gas release of 5 9 million tons of so2 to the stratosphere by the eruption primary igneous anhydrite and a larger excess gas release of 20 million tons of so2 were noted for the significantly larger eruption of mount pinatubo in 1991 for which a separate gas phase at 7 9 km depth was also required by the sulfur budget pumices from both eruptions have mineral assemblages dominated by plagioclase and hornblende with minor biotite and show evidence for co nucleation and mutual inclusions of anhydrite and apatite both magmas were also very water rich and highly oxidized with oxygen fugacities 1 log unit above the synthetic ni nio buffer furthering the similarities between these two eruptions ion microprobe analyses of sulfur isotopic compositions of anhydrites in pumices from el chichon and mount pinatubo both showed that individual crystals are isotopically homogeneous but inter crystalline variations in 34s are well beyond analytical error this study reviews the history of thought regarding primary igneous anhydrite ten volcanic and plutonic analogues to the el chichon and mount pinatubo magmas are discussed all were similarly water rich and highly oxidized magmas hornblende is the dominant mafic phenocryst in all but one plutonic example in that case so much early anhydrite precipitated that no calcium remained to form hornblende biotite is very abundant in that exceptional plutonic case and is present in six of the other examples with primary igneous anhydrite sphene is known as an indicator mineral of high magmatic oxygen fugacity it was present in the 1982 el chichon pumices and in 6 of the other anhydrite bearing samples hornblende and biotite phenocrysts are also characteristic of the intermediate to felsic plutonic rocks that typically host porphyry cu deposits such magmas are also known to be water rich and highly oxidized a close spatial and petrogenetic connection exists between magmas with primary igneous anhydrite and magmatic hydrothermal ore deposits

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

mineral precipitation in the walls of black smoker chimneys a quantitative model of transport and chemical reaction a quantitative model of transport and chemical reaction is developed to examine the interplay of physical and chemical processes controlling the evolution of black smoker chimneys diffusion and advection yield steady state profiles of temperature and concentration across a porous wall bound on one side by hydrothermal fluid and on the other by seawater the pressure gradient is estimated from the fluid dynamics of high velocity flow inside the chimney parametric studies reveal the importance of diffusion driven by gradients in activity coefficients resulting from the strong thermal gradient the model wall is a series of vertical layers each with specified physical properties chemical reaction calculated assuming chemical equilibria for the local temperature and concentration conditions significantly modifies the physical properties of the wall as it evolves model calculations demonstrate the sensitivity of mineral zonation to the physical environment and can be used to re create the aging of chimneys inferred from petrologic studies

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

mechanisms for anhydrite and gypsum formation in the kuroko massive sulfide sulfate deposits north japan the sr ba and rare earth elements rees concentrations and sr isotopic composition of anhydrite and gypsum have been determined for samples from the matsumine shakanai and hanaoka kuroko type massive sulfide sulfate deposits of northern japan to evaluate the mechanisms of sekko anhydrite and gypsum ore formation the sr isotopic compositions of the samples fall in the range of 0 7077 0 7087 intermediate between that for middle miocene 13 15 ma seawater 0 7088 peterman et al geochim cosmochim acta 34 105 120 1970 and that for country rocks e g 0 7030 0 7050 shuto assn geol collab japan monograph 18 91 105 1974 the kuroko anhydrite samples exhibit two types of chondrite normalized ree patterns one with a decrease from light rees lrees to heavy rees hrees type i and another with a lree depleted pattern type ii

the stability and composition of sulfate melts in arc magmas the stability field and composition of immiscible sulfate melts in equilibrium with silicate magmas has been determined using experiments over a range of crustal pressures allowing an assessment of their possible role in transporting sulfur into the sub volcanic arc and porphyry copper deposit systems experimental starting materials were based on natural trachyandesite and trachydacite compositions with 3 5 7 wt h2o and 3 5 5 5 wt sulfur added to produce large analyzable amounts of sulfate phases conditions ranged over 800 1200 c 0 2 1gpa and o2 nno 2 5 sulfate melts formed at temperatures above 1000 c at 0 75 and 1 gpa and above 900 c at 0 2 gpa suggesting some pressure dependence on their stability at temperatures below 1100 c sulfate melts and anhydrite crystals commonly coexist sulfate melts quenched to an intergrowth that was difficult to prepare for analysis however the composition was approximated by epma and further constrained by mass balance calculations sulfate melts were dominated by cao and so3 but also contained in order of decreasing abundance na2o k2o mgo feo cl and p2o5 chlorine showed a particular preference for the sulfate melt relative to the coexisting silicate melt and calculated partition coefficients for sulfate silicate melts were 5 13 at 1200 c 0 75 1 gpa experimental data show that in the absence of an exsolved hydrous fluid phase sulfate melts can form in natural arc magmas at near liquidus temperatures 1000 c assuming that magmas are oxidized and contain sufficient sulfur 2000 3000 ppm s these results suggest that sulfate melt could be an important component in transporting sulfur as well as chlorine to shallow levels in the crust for hydrous magmas under a specific range of conditions both the non quenchable and water soluble nature of sulfate melts and anhydrite make them difficult to identify unless trapped as mineral inclusions similar to the wormy anhydrite trapped in high temperature amphiboles from yanacocha peru

transform margins development controls and petroleum systems an introduction this paper provides an overview of the existing knowledge of transform margins including their dynamic development kinematic development structural architecture and thermal regime together with the factors controlling these this systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock seal rock and reservoir rock distribution expulsion timing trapping style and timing and migration patterns the paper then introduces individual contributions to this volume and their focus supplementary material location table and map of specific transform examples structural elements of the romanche transform margin and glossary of terms used in this article is available at https doi org 10 6084 m9 figshare c 3276407 gold open access this article is published under the terms of the cc by 3 0 license this volume shows dynamic linkage between new transform margin research and increasing transform margin exploration it offers a critical set of predictive tools via an understanding of the mechanisms involved in the development of play concept elements at transform margins and their controlling factors our introduction to this volume reviews the current knowledge of the transform margins focusing on their dynamic development kinematic development structural architecture thermal regimes and petroleum systems the last part of this paper introduces the contributions to this volume

deposition of talc kerolite smectite smectite at seafloor hydrothermal vent fields evidence from mineralogical geochemical and oxygen isotope studies abstract talc kerolite smectite smectite chlorite smectite and chlorite samples from sediments chimneys and massive sulfides from six seafloor hydrothermal areas have been analyzed for mineralogy chemistry and oxygen isotopes samples are from both peridotite and basalt hosted hydrothermal systems and basaltic systems include sediment free and sediment covered sites mg phyllosilicates at seafloor hydrothermal sites have previously been described as talc stevensite or saponite in contrast new data show tri octahedral mg phyllosilicates ranging from pure talc and fe rich talc through kerolite rich kerolite smectite to smectite rich kerolite smectite and tri octahedral smectite the most common occurrence is mixed layer kerolite smectite which shows an almost complete interstratification series with 5 to 85 smectitic layers the smectite interstratified with kerolite is mostly tri octahedral the degree of crystal perfection of the clay sequence decreases generally from talc to kerolite smectite with lower crystalline perfection as the proportion of smectite layers in kerolite smectite increases our studies do not support any dependence of the precipitated minerals on the type subtype of hydrothermal system oxygen isotope geothermometry demonstrates that talc and kerolite smectite precipitated in chimneys massive sulfide mounds at the sediment surface and in open cracks in the sediment near seafloor are high temperature 250 c phases that are most probably the result of focused fluid discharge the other end member of this tri octahedral mg phyllosilicate sequence smectite is a moderate temperature 200 250 c phase forming deep within the sediment 0 8 m chlorite and chlorite smectite which constitute the alteration sediment matrix around the hydrothermal mounds are lower temperature 150 200 c phases produced by diffuse fluid discharge through the sediment around the hydrothermal conduits in addition to temperature other two controls on the precipitation of this sequence are the silica activity and mg al ratio i e the degree of mixing of seawater with hydrothermal fluid higher silica activity favors the formation of talc relative to tri octahedral smectite vent structures and sedimentary cover preclude complete mixing of hydrothermal fluid and ambient seawater resulting in lower mg al ratios in the interior parts of the chimneys and deeper in the sediment which leads to the precipitation of phyllosilicates with lower mg contents talc and kerolite smectite have very low trace and rare earth element contents some exhibit a negative or flat eu anomaly which suggests eu depletion in the original hydrothermal fluid such eu depletion could be caused by precipitation of anhydrite or barite sinks for eu2 deeper in the system ree abundances and distribution patterns indicate that chlorite and chlorite smectite are hydrothermal alteration products of the background turbiditic sediment

application of radium isotopes to determine crustal residence times of hydrothermal fluids from two sites on the reykjanes peninsula iceland radium isotopes were used to determine the crustal residence times of hydrothermal fluids from two geothermal wells svartsengi and reykjanes from the reykjanes peninsula iceland the availability of rock samples from the subsurface to depths of 2400 m allowed direct comparison of the radium isotopic characteristics of the fluids with those of the rocks within the high temperature and pressure reaction zone the 226 ra activity of the svartsengi fluid wasone fourth of the reykjanes fluid and the 228 ra 226 ra ratio of the svartsengi fluid wastwice that of reykjanes the fluid isotopic character istics were relatively stable for both sites over the 6 years 2000 2006 of the study it was determined using a model that predicts the evolution of the fluid 228 ra 226 ra ratio with time that both sites had fluid residence times from the onset of high temperature water rock reaction of less than 5 years measurement of the short lived 224 ra and 223 ra allowed estimation of the recoil input parameter used in the model the derived timescale is consistent with results from similar studies of fluids from submarine systems and has implications for the use of terrestrial systems in iceland as an exploited energy resource 2007 elsevier ltd all rights reserved

the fluid geochemistry of icelandic high temperature geothermal areas abstract icelandic high temperature geothermal systems are considered to number thirty three thereof three are submarine and seven subglacial all are briefly described but the chemistry of fluids from twenty four of them is considered the fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater the rest contain dilute fluids the fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly krafla area which is inland and the oxarfjor ur area which is close to the sea appear to be a mixture of local and central highland water but those in the inland hengill geysir namafjall and theistareykir areas appear to have travelled relatively long distances from the central highlands the gas observed is magmatic except in the northerly oxarfjordur area close to the sea where it is apparently derived from organic sediments

relationships between lava types seafloor morphology and the occurrence of hydrothermal venting in the ashes vent field of axial volcano deep towed and submersible photographic surveys within the caldera of axial volcano have been integrated with high resolution bathymetry to produce a geological map of the most active vent field axial seamount hydrothermal expeditions ashes in the caldera the ashes vent field encompasses an approximately 200 m 1200 m area of active venting which is located adjacent to the southwest caldera wall locations for over 2000 photographs in and near the vent field were determined using a seafloor transponder network then each photograph was described utilizing a classification system which provides detailed information concerning lava type hydrothermal activity sediment cover geological structure and biology resulting data were entered into a digital data base and computer generated maps were created that portray spatial relationships between selected geological variables in general the entire ashes field is characterized by pervasive low temperature venting the most vigorous venting is concentrated in an approximately 80 m 80 m area where there are several high temperature vents including some which are producing high temperature vapor phase fluids derived from a boiling hydrothermal system lava types within the ashes vent field are grouped into three distinct morphologies 1 smooth flat surfaced ropy and whorled sheet flows 2 lobate flows and 3 jumbled sheet flows the most intense hydrothermal venting is concentrated in the smooth sheet flows and the lobate flows the location of the ashes field is mainly attributable to faulting which defines the southwest caldera wall but the concentration of intense venting appears to be related also to the spatial distribution of lava types in the vent field and their contrasting permeabilities other structural trends of faults and fissures within the field also influence the location of individual vents

subaqueous hot springs in koycegiz lake dalyan channel and fethiye gocek bay sw turkey locations chemistry and origins abstract in this study horizontal temperature measurements along organized grids have been used to detect subaqueous hot springs the study area located in the southwest of turkey and comprised of koycegiz lake dalyan channel and fethiye gocek bay was scanned by measuring temperatures horizontally 2 3 m above the bottom of the lake or sea after analyzing the temperature data along the grids the locations with anomalous temperature values were detected and divers headed here for further verification accordingly among these anomalies the divers confirmed seven of them as subaqueous hot springs three of these hot springs are located in the koycegiz lake three of them are located in the dalyan channel and one hot spring is located in the fethiye gocek bay at the locations where temperature anomalies were detected the divers collected samples directly from the subaqueous hot spring using a syringe type sampler we evaluated these water samples together with samples collected from hot and cold springs on land and from local rivers lakes and the sea with an aim to generate a conceptual hydrogeochemical model of the geothermal system in the study area this model predicts that rainwater precipitating in the highlands percolates through fractures and faults into the deeper parts of the earth s crust here it is heated and ascends through the sea bottom via buried faults pervious carbonate nappes that are underlain and overlain by impervious rocks create a confined aquifer the southern boundary of the carbonate marmaris nappes is buried under alluvium and or sea lake water bodies and this phenomenon determines whether hot springs occur on land or subaqueous the chemical and isotopic properties of the hot springs point to seawater mixing at deep levels thus the mixing most probably occurs while the water is ascending through the faults and fractures the gas geochemistry results reveal that the lowest mantle he contributions occur in the samples from koycegiz lake whereas the highest ones are found in samples from the dalaman plain for the first time we made use of the micro xrf sediment core scanning itrax scanner for exploring the relation between subaqueous geothermal occurrence and chemical properties of the surrounding sediments the spatial elemental distribution of sea lake bottom sediments suggests that depending on the surrounding rock units and the temperature of the hot spring the sediments around the spring can be enriched with certain elements

massive sulfides in a sedimented rift valley northern juan de fuca ridge a number of mounds each several hundred meters across and up to sixty meters high have been observed with seamarc ii acoustic imagery and seabeam bathymetry in the sediment filled axial valley at the northern end of the juan de fuca ridge the mounds are located a few kilometers west of the eastern valley bounding normal fault scarp where the local sediment fill is approximately 300 m thick all of the mounds are believed to be of hydrothermal origin and one is associated with anomalously high heat flow in excess of 1 w m 2 a piston core collected from that mound comprises coarse clastic sulfide units interbedded with sulfidic muds hydrothermal minerals present in the 2 3 m section include pyrrhotite pyrite marcasite sphalerite chalcopyrite iss intermediate solid solution in the cufezns system chalcopyrrhotite galena talc barite and amorphous silica mineral fabrics of the clasts indicate that the material was precipitated at or near the sea floor by mixing of hot hydrothermal fluids with cold seawater low concentrations of zn cu cd and ag relative to those found in unsedimented ridge hydrothermal deposits and the presence of pyrrhotite as an early phase mineral indicates that the vent fluids have been modified by reaction with sediments beneath the mound rapid sedimentation in a rift valley is clearly conducive to the formation of large hydrothermal mineral deposits like those believed to be present within and beneath these mounds the relatively impermeable sediment cover insulates the crust inhibits groundwater recharge promotes long lived discharge at a restricted number of sites provides a substrate for the efficient subsurface precipitation of minerals and through continued sedimentation protects surficial deposits from the corrosive effects of seawater no reliable estimate of the bulk composition of the mounds can be made with existing data but their size is comparable to major hydrothermal mineral deposits found on land ancient settings in which many land deposits formed are in many ways similar to the one in which the features described here are currently forming

iron isotope exchange and fractionation between jarosite and aqueous fe ii abstract jarosite is one of the critical minerals that regulates acidity and contaminants in acid sulfate environments and its fe isotope composition may shed light on its formation transformation and recrystallization over time interpretation of its fe isotope composition requires understanding the equilibrium fe isotope fractionation factor between jarosite and other fe bearing minerals and aqueous species here we explore fe isotope exchange and fractionation between jarosite and fe ii aq under acidic conditions using the three isotope method 54fe 56fe 57fe a reversal approach to equilibrium was applied by reacting synthetic jarosite and natural natrojarosite with two 57fe enriched fe ii aq solutions that had initial 56fe 54fe ratios above and below the predicted equilibrium value no change in dissolved fe ii concentrations were observed with time but the 57fe 56fe ratio of fe ii aq decreased towards the system mass balance suggesting a high degree of equilibration of the fluid with the solid phase despite no net fe ii sorption within error there is a negative relationship between ph and fe isotope exchange with fe isotope exchange proceeding as ph decreases this may be explained by dissolution of hydronium jarosite and reprecipitation of natrojarosite coupled h3o na exchange or jarosite decomposition although no fe oxyhydroxide phases were identified from xrd calculation of the amount of fe atoms in jarosite that exchanged with fe ii aq indicates that jarosite recrystallization was limited to a few percent when the initial 56fe value of fe ii aq was greater than the presumed equilibrium value its isotopic value substantially decreased with time whereas the 56fe values of fe ii aq increased with time when it had an initial value below the suspected equilibrium composition in each case the isotopic composition of fe ii aq approached similar values providing a high degree of confidence of an attainment of equilibrium calculation of the fe ii aq jarosite and fe ii aq natrojarosite equilibrium fractionation factors at 22 c were 2 26 0 27 2 and 2 19 0 18 2 respectively this indicates that during jarosite recrystallization in the presence of fe ii jarosite is expected to become isotopically heavier as lighter isotopes are fractionated into fe ii these values differ from the estimated fractionation factors derived from nrixs spectroscopy and molecular modeling the differences between experiments and theory may reflect surface exchange which was likely in our study versus predicted bulk thermodynamic properties of the mineral