tungsten accumulation in pacific ferromanganese deposits tungsten has often been reported in marine ferromanganese deposits and the question arises as to how the large oxyanionic species wo42 enters the appropriate phases very low w concentrations in seawater less than 0 0002 g kg suggest that it is not directly related to precipitation processes of all the comparable marine samples manganese micronodules have the highest w contents in the range 1 4 to 3 6 times 3 higher than in the associated macronodules a depositional record for more than 60 million years obtained for a thick manganese crust shows that the tungsten distribution with depth correlates best with as and to a lesser extent with fe the mechanism favoured for enrichment of w is precipitation onto fine hydrothermal manganese rich particles supplied by ridge volcanic activity such particle plumes are usually released in cycles stay for comparatively long periods in the water column and are then transported from the hydrothermal centres to the deep basins where they settle and probably contribute to the growth of ferromanganese oxide phases on the ocean floor which is mainly by diagenetic and hydrogenetic processes

fast and slow spreading ridges structure and hydrothermal activity ultramafic topographic highs and ch4 output different parts of the world ridge system have quite different morphologies which reflect different constructional processes it appears that hydrothermal circulation at all spreading centers is an important exchange process between the ocean and the newly formed oceanic crust this hydrothermal circulation may vary according to morphology and crustal composition and may also affect ridge constructional processes the tag 26 n and snake pit 23 n hydrothermal sites on the mid atlantic ridge mar display mn ch4 ratios in overlying seawater similar to those of nonsedimented east pacific rise sites i e about 0 2 mol l in contrast large methane anomalies with very low mn ch4 ratios of 0 005 mol l are associated with ultramafic topographic highs near 15 n close to the axis and on ultramafic walls of the rift valley the association of ultramafic bodies and ch4 anomalies in seawater indicates active serpentinization processes ch4 is produced during serpentinization according to the fisher tropsch reaction charlou et al 1991 many ultramafic rock assemblages have been sampled on the mar away from fracture zones in particular by the deep sea drilling project changes of mechanical properties and of density of uplifted deep material in the accreting plate boundary zone caused by serpentinization may play an important role in the construction of slow spreading ridges

petrogenesis of syn orogenic rare metal pegmatites in the chinese altai evidences from geology mineralogy zircon u pb age and hf isotope abstract recently an increasing number of anatetic pegmatites have been confirmed in contrast to the granitic pegmatite the anatetic pegmatite has no relation to granite it is therefore necessary to reacquaint the origin and classification of pegmatitic rocks as one of the largest pegmatite provinces the chinese altai provides a natural laboratory for pegmatite study to date the type age source and tectonic setting of the syn orogenic pegmatites in the chinese altai remain unclear in this work the cms chemical composition mineral assemblage structural geology classification is primarily applied on the pegmatitic rocks in the chinese altai five types pegmatitic rocks including metapegmatite pegmatoid pegmatite pseudopegmatite and granite pegmatite are identified by their cms features in addition the geology mineralogy zircon u pb ages and hf isotopes of six pegmatites are presented in this work the pegmatites numbered jmhb02 qbl02 tlt01 aljk01 amlg01 and tmlt01 are dated at 394 8 4 0 ma 402 6 5 5 ma 385 9 3 5 ma 368 0 4 0 ma 358 3 4 6 ma and 333 0 6 0 ma respectively indicating that they were formed during the syn orogenic stage of the altai orogenic process they are exposed in the qiongkuer domain in the southern chinese altai juxtaposed with the late and or post orogenic pegmatites in the same pegmatite field no parental granite can be confirmed for all these pegmatites comparatively the synorogenic pegmatites are scarce and have lower mineralization grades than the late and postorogenic pegmatites zircon hf isotopic compositions of the syn orogenic pegmatites have positive hf t values of 2 06 8 28 and old t dm2 ages of 1 234 860 ma and are consistent with those of most of the syn orogenic i and s granites which indicates that the pegmatites and granites have a common immature crustal source from the early paleozoic metasedimentary rocks compared to the post orogenic pegmatites in the central altai domain the syn orogenic pegmatites in this work have larger positive hf t values and younger t dm2 ages indicating that more juvenile components were involved in their magma sources combining this study with previous works we suggest that the anatexis of metasediments induced by decompression and injection of heat energy and mantle derived materials under a forearc extensional setting led to the formation of the syn orogenic pegmatites in the chinese altai

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

helium radon and manganese at the tag and snakepit hydrothermal vent fields 26 and 23 n mid atlantic ridge abstract 3 he 4 he and 222 rn have been measured in samples of vent fluids from the tag and snakepit hydrothermal vent fields and in samples from the neutrally buoyant plume at tag the hydrothermal end member 3 he 4 he at tag normalised to the ratio in air is r r a 7 5 0 9 222 rn 187 dpm kg 1 and 226 ra 13 5 0 4 dpm kg 1 at snakepit r r a 7 86 1 85 222 rn 82 dpm kg 1 and 226 ra 10 3 0 2 dpm kg 1 helium isotope tracer systematics have been described which allow hydrothermal end member properties to be estimated from plume data or non conservative behaviour in the buoyant plume to be identified comparison of plume mn concentrations and he isotope data shows that mn behaves conservatively in the plume system over the time scale considered in contrast 222 rn is highly non conservative and there is a large 222 rn excess in the neutrally buoyant plume the hydrothermal end member accounts for less than 2 5 of the excess 222 rn enrichment at the top of the buoyant plume attributed to entrainment of 222 rn enriched fluids during buoyant plume rise 222 rn 3 he ages of the tag plume give values of around 1 2 days close to the vent field and up to 10 days in adjacent waters 222 rn mn ages are similar except for a region of anomalous water at the level of neutral buoyancy which is enriched in 222 rn and si but not 3 he and mn and which may be derived from the walls of the axial valley at the depth of the neutrally buoyant plume

tonian fe ti p ferronorite and alkali anorthosite in the northern appalachian orogen southern new brunswick canada amazonian basement in ganderia abstract the lower coverdale plutonic suite is located in the ganderian brookville terrane of southern new brunswick canada it does not outcrop at surface but has been intersected in 11 drill holes at depths of 100 200 m below unconformably overlying carboniferous sedimentary rocks and extends to a depth of at least 1100 m no host rocks are present in the drill core which consists entirely of plutonic and meta plutonic rocks the dominant rock types are anorthosite mela anorthosite and ferronorite with layers of ilmenite and ilmenite apatite rocks they are intruded by abundant undated mafic dykes and minor ca 390 ma felsic dykes a ferronorite sample yielded a tonian age of 975 5 2 3 ma interpreted to be the igneous crystallization age of the plutonic suite a mela anorthosite sample yielded a similar but less precise age of 979 16 ma likely also the igneous crystallization age the anorthosite has characteristics of alkali anorthosite massifs including andesine an30 35 commonly with exsolution lamellae of k feldspar the lower coverdale suite is interpreted to have been emplaced during orogen scale extension following crustal thickening associated with the grenvillian orogeny the lower coverdale anorthosite and ferronorite have more isotopically evolved signatures higher 206pb 204pb and 207pb 204pb and lower nd compared to typical laurentian grenville age plutons we infer from these data that the lower coverdale plutonic suite originated in the amazonian part of the grenville orogen during the early stages of tonian breakup of rodinia it was then incorporated into ganderia before accreting to laurentia as part of the brookville terrane during the pangean phase of supercontinent assembly

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

in situ filtration and preliminary molecular analysis of microbial biomass from the rainbow hydrothermal plume at 36 15 n on the mid atlantic ridge abstract elevated microbial biomass levels play a significant role in altering the chemical composition of hydrothermal plumes in this work a procedure was developed for collecting sufficient quantities of microbial biomass from a hydrothermal plume to allow the extraction of dna suitable for use in molecular analyses of the plume microbial populations during a geophysical survey along 200 km of the mid atlantic ridge mar southwest of the azores triple junction several new sites of hydrothermal activity were identified including the rainbow hydrothermal plume at 36 15 n the strongest such feature yet reported from the mar during the survey in situ filtration systems were used to collect microbial biomass from the water column onto 293 mm diameter 0 2 m pore membrane filters by pumping large volumes 300 500 l of seawater through the filters filter samples were collected from both the neutrally buoyant portion of the rainbow plume at a depth of 2050 m and from above it in the water column at 1500 m microgram quantities of genomic dna were extracted and purified from the biomass on these filters the suitability of the purified dna for use in molecular analyses was demonstrated by polymerase chain reaction pcr amplification of the small subunit ribosomal rrna ssu rrna gene from the two primary prokaryotic domains the bacteria and the archaea as indicated by the binding of domain specific oligonucleotide hybridisation probes to the purified dna the plume microbial populations contained a higher proportion of members of the domain archaea than the populations in the surrounding ambient sea water

the stommel and arons model and geothermal heating in the south pacific abstract the model of joyce and speer 1987 2 for the large scale influence of a geothermal heat source in an ocean basin is applied to the south pacific taking into account observed isopycnal depth variations and tracer distributions these observations are used with the model to estimate the required geothermal heating and strength of the background stommel and arons flow both heating and background flow are necessary in the model for agreement with observations

lava seawater interactions at shallow water submarine lava flows hydrothermal plumes associated with nearshore lava flows from kilauea volcano hawaii were studied on five occasions during 1989 1990 to address the current lack of data on direct lava seawater interactions the following enrichments were found in the sea surface hydrothermal plumes above the active underwater lava flows h2 15 000x ambient seawater concentrations mn 250x and si 20x water temperatures reached 46 c lower concentrations and temperatures were observed in the plumes with increasing distance from shore with h2 si and mn concentrations linearly related to seawater temperature unlike deep sea spreading center hydrothermal plumes no ch4 enrichment was observed the elevated h2 is likely to be from water rock reactions rather than from the release of magmatic gas the plume mass heat ratios presented here suggest that submarine flood basalts although aerially large should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust

226ra and222rn contents of galapagos rift hydrothermal waters the importance of low temperature interactions with crustal rocks abstract hydrothermal waters collected by alvin from the galapagos spreading center are enriched in 222 rn by factors of 50 200 over bottom waters the 226 ra in the same samples however is enriched by less than a factor of four over bottom waters enrichments of 222 rn result primarily from recoil from rock surfaces while 226 ra enrichments are dominantly produced by high temperature alteration of cooling ridge volcanics the abundances of both nuclides exhibit positive correlations with temperature the data extrapolate to bottom water temperatures and compositions demonstrating the importance of seawater mixing different vents however have different mixing lines and vents with high 222 rn have low 226 ra we propose these patterns result from variations in the extent of low temperature crustal interaction with the hydrothermal fluids low temperature crustal waters can maintain high steady state 222 rn contents due to the recoil additions to the fluids the 226 ra however is strongly adsorbed at low temperatures resulting in low concentrations of this nuclide in low temperature crustal waters thus physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and 222 rn 226 ra values of the hot springs the 222 rn 226 ra value appears to be a sensitive indicator of low temperature crustal interaction values 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust values of 222 rn 226 ra between 10 3 and 10 4 are indicative of interaction of the hydrothermal fluids with sediments such values are observed in water samples from the galapagos hydrothermal mounds

flow rates in the axial hot springs of the east pacific rise 21 n implications for the heat budget and the formation of massive sulfide deposits abstract the first in situ measurements of flow rates in submarine hot springs temperatures between 275 and 350 c were made in the hot springs of the east pacific rise at 21 n during november 1981 the flow rates ranged between 0 7 and 2 4 m s we estimate that the total rates at which heat and mass are transported from the three hot spring areas obs national geographic and southwest vents are ca 2 2 108 w and 150 kg of fluid s respectively the very high rate of heat loss precludes the existence of hot springs as steady state features of the east pacific rise at 21 n we estimate that hot springs are active for a maximum of ca 40 000 years chemical and or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs using a simple model of plume development 1 we calculated that less than 3 of the sulfide particles that are entrained in the hydrothermal plumes at 21 n settle from the plumes before dispersal by a lateral submarine current at a height of ca 250 m above the seafloor 2 the time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca 70 85 years the current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the mavrouni deposit on cyprus 3 within the time limits that are suggested by our thermal energy balance calculations

manganese geochemistry in the guaymas basin gulf of california manganese geochemistry in the guaymas basin gulf of california is dominated by hydrothermal processes the concentration of particulate mn in the subsill basin is about four times higher than in the non hydrothermally active basins of the southern gulf this excess mn closely matches the predicted anomaly from a model of hydrothermal fluxes based on dissolved silica and sup 3 he the hot spring flux of mn is about 4 times greater than the benthic flux from the sediments on the slopes of the basin dissolved hydrothermal mn has a residence time of about one week in the water column the particulate mn phase consist of 2 5 mu m size particles that are distinct from all other suspended particulate matter these mn rich particles are responsible for the observed turbidity in the water column hydrothermal clouds above vents and chimneys in the guaymas basin and bear a striking resemblance to the mn oxidizing bacterium metallogenium the rapid conversion of mn to a particulate phase in these clouds is consistent with bacterial catalysis this contrasts with the particles at 21 sup 0 n east pacific rise where mn is more slowly co precipitated with or adsorbed onto an iron oxyhydroxide phase

deep methane maxima and 3he anomalies across the pacific entrance to the celebes basin methane and 3he measurements have been performed in deep waters across the sills between the pacific ocean and celebes basin the in situ analyses of dissolved methane have led to the identification of several methane seeps along the flanks of the two south mindanao submarine ridges sangihe and talaud east mindanao 3he excesses in the celebes basin and east of talaud east mindanao ridge at 2000 3000 meter depths are in the range 21 22 a few percent above the philippine sea 3he background the isotopic ratio of the added he is 1 8 times the atmospheric ratio which indicates an input of hydrothermal fluids involving both mantle and crustal sedimentary components methane anomalies are partially associated with these 3he excesses the order of magnitude of the ch43he ratios is comparable to those observed in spreading axis hydrothermal fields at a few tens of kilometers from the top of the sangihe ridge conversely a major methane anomaly 90 times greater than the ch4 background of the philippine sea deep waters was measured at a depth where the waters show no 3he enrichment or anomalous water temperature versus the philippine sea background this result implies that methane could originate largely from shallow sedimentary layers

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

methane sources distributions and fluxes from cold vent sites at hydrate ridge cascadia margin to constrain the fluxes of methane ch4 in the water column above the accretionary wedge along the cascadia continental margin we measured methane and its stable carbon isotope signature 13c ch4 the studies focused on hydrate ridge hr where venting occurs in the presence of gas hydrate bearing sediments the vent ch4 has a light 13c ch4 biogenic signature 63 to 66 pdb and forms thin zones of elevated methane concentrations several tens of meters above the ocean floor in the overlying water column these concentrations ranging up to 4400 nmol l 1 vary by 3 orders of magnitude over periods of only a few hours the poleward undercurrent of the california current system rapidly dilutes the vent methane and distributes it widely within the gas hydrate stability zone ghsz above 480 m water depth the methane budget is dominated by isotopically heavier ch4 from the shelf and upper slope where mixtures of various local biogenic and thermogenic methane sources were detected 56 to 28 pdb the distribution of dissolved methane in the working area can be represented by mixtures of methane from the two primary source regions with an isotopically heavy background component 25 to 6 pdb methane oxidation rates of 0 09 to 4 1 per day are small in comparison to the timescales of advection this highly variable physical regime precludes a simple characterization and tracing of downcurrent plumes however methane inventories and current measurements suggest a methane flux of approximately 3 104 mol h 1 for the working area 1230 km2 and this is dominated by the shallower sources we estimate that the combined vent sites on hr produce 0 6 104 mol h 1 and this is primarily released in the gas phase rather than dissolved within fluid seeps there is no evidence that significant amounts of this methane are released to the atmosphere locally

an assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry profiles of 210pb over the endeavour and north cleft segments of the juan de fuca ridge are used to model a time scale for the scavenging by hydrothermal plumes of reactive elements in seawater the hydrothermal plumes above these ridge segments are sites of intense scavenging removal of 210pb at endeavour the total 210pb activities within the plume are as low as 8 dpm 100 l and dissolved activities are as low as 3 dpm 100 l at the north cleft which is characterized by higher particulate fe concentrations the total 210pb activities are 4 5 dpm 100 l the dissolved activities are 1 2 dpm 100 l and the 210pb activities are deficient with respect to the activity of the 210po daughter these are perhaps the lowest 210pb activities ever measured in the deep sea the large gradient of 210pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport the implication therefore is that this process might impact the ocean on a scale larger than that local to the ridge crest by coupling published measurements of particle flux from endeavour with 210pb activities on particles trapped at that site the total volume of seawater stripped of 210pb per year for that site was calculated to be 7 4 1012 l y globally the extrapolated volume flux of seawater stripped of reactive constituents is 5 7 1015 l y such that the entire ocean is processed in this manner in 2 4 105 y the geochemical cycle of elements with ocean residence times much shorter than this e g pb and th will not be greatly affected by hydrothermal scavenging on the other hand this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes such as p and v whose ocean residence times are 104 y

diffuse venting and background contributions to chemical anomalies in a neutrally buoyant ocean hydrothermal plume plumes originating in high temperature hydrothermal discharges entrain background water and often entrain diffuse source fluids during convective ascent the mixing of fluid from those three different sources determines the chemical composition of the ensuing neutrally buoyant plumes here convection models and aluminum data from the trans atlantic geotraverse tag site are used to examine relative contributions of focused diffuse and background sources to anomalies in the plume our analysis shows that anomalously high al values observed just above the seafloor at tag which we assume stem from diffuse flows can contribute as much as 50 to the al anomaly in the neutrally buoyant plume found 350 m above bottom background water contributes nearly an equal fraction of al to the anomaly more generally entrained contributions depend on gradients in profiles external to the rising plume entrainment also depends on effective source area distributed high temperature vents entrain more fluid than a single composite high temperature vent larger effective source area is particularly significant for entrainment of diffuse source or other tracers trapped within a few tens of meters of the seafloor downstream cross stream and temporal variabilities exhibited in the three dimensional model plume also underscore problems of sampling and interpreting actual plume data

submarine magmatic hydrothermal systems at the monowai volcanic center kermadec arc the monowai volcanic center is located at the midpoint along the 2 530 km long tonga kermadec arc system the monowai volcanic center is comprised of a large elongate caldera monowai caldera area 35 km2 depth to caldera floor 1 590 m which has formed within an older caldera some 84 km2 in area to the south of this nested caldera system is a large composite volcano monowai cone which rises to within 100 m of the sea surface and which has been volcanically active for the past several decades mafic volcanic rocks dominate the monowai volcanic center basalts are the most common rock type recovered from the cone whereas basaltic andesites are common within the caldera hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone 1 the summit of the cone 2 low temperature venting 60 c mussel ridge on the southwestern wall of the caldera and 3 a deeper caldera source with higher temperature venting that has yet to be observed the cone summit plume shows large anomalies in ph a shift of 2 00 ph units and 3he 358 and noticeable h2s up to 32 m and ch4 up to 900 nm the summit plume is also metal rich with elevated total dissolvable fe tdfe up to 4 200 nm tdmn up to 412 nm and tdfe tdmn up to 20 4 particulate samples have elevated fe si al and ti consistent with addition to the hydrothermal fluid from acidic water rock reaction plumes extending from 1 000 to 1 400 m depth provide evidence for a major hydrothermal vent system in the caldera the caldera plume has lower values for tdfe and tdmn although some samples show higher tdmn concentrations than the cone summit plume caldera plume samples are also relatively gas poor i e no h2s detected ph shift of 0 06 ph units ch4 concentrations up to 26 nm the composition of the hydrothermal plumes in the caldera have higher metal contents than the sampled vent fluids along mussel ridge requiring that the source of the caldera plumes is at greater depth and likely of higher temperature minor plumes detected as light scattering anomalies but with no 3he anomalies down the northern flank of the monowai caldera most likely represent remobilization of volcanic debris from the volcano flanks we believe the monowai volcanic center is host to a robust magmatic hydrothermal system with significant differences in the style and composition of venting at the cone and caldera sites at the cone the large shifts in ph very high 3he values elevated tdfe and tdfe tdmn and the h2s and ch4 rich nature of the plume fluids together with elevated ti p v s and al in hydrothermal particulates indicates significant magmatic volatile metal contributions in the hydrothermal system coupled with aggressive acidic water rock interaction by contrast the caldera has low tdfe tdmn in hydrothermal plumes however elevated al and ti contents in caldera particulate samples combined with the presence of alunite pyrophyllite sulfide minerals and native sulfur in samples from mussel ridge suggest past and perhaps recent acid volatile rich venting and active fe sulfide formation in the subsurface

radioisotopic studies of submarine hydrothermal vents the importance of mid ocean ridge hydrothermal systems has been recognized for their role in the regulation of ocean and sediment chemistry as well as for providing a chemosynthetic source of carbon which drives a unique population of animals found at hydrothermal vents despite the importance of these systems the rates length and depth scale of submarine hydrothermal processes are not precisely known because they are for the most part inaccessible to observational tools we must therefore rely on indirect methods to quantify these processes one way of investigating the rates or timescales of processes in a hydrothermal or any natural system is through the study and modeling of naturally occurring radioisotopes disequilibria among the naturally occurring radioactive decay series in vent fluids associated mineral deposits and overlying effluent plume have provided geochemical tools to investigate the rates of various processes occurring in submarine hydrothermal systems because the half lives of the radioisotopes vary from days to many years processes which encompass a wide range of spatial and temporal scales can be studied this paper presents a review of methods that estimate the residence time of hydrothermal fluids in the ocean crust establish the geochronology of seafloor sulfide deposits investigate the rates of chemical reactions within hydrothermal effluent plumes and derive the heat and mass flux from seafloor hydrothermal areas

onset and duration of zn pb mineralization in the talate pb zn fe skarn deposit nw china constraints from spessartine u pb dating abstract distal pb zn skarn commonly displays ambiguous relationships with the nearby intrusions leading to poorly constrained and often controversial skarn metallogenic models in this study we discuss the potential usage of spessartine a common u bearing gangue mineral in many pb zn skarn deposits in u pb dating spessartine from the talate skarn pb zn deposit xinjiang nw china can be divided into two types gi and gii based on mineral assemblage gi spessartine sp56 5 al28 3 gr12 4 to sp66 0 al22 3 gr8 5 is coarse grained with core rim texture occasionally well preserved disseminated magnetite and magmatic ti titanite grains are hosted within the spessartine gi core indicating that the spessartine gi is slightly postdate the magmatic titanite ti and disseminated magnetite gii massive spessartine sp64 2 al24 8 gr2 7 to sp69 6 al20 1 gr1 2 occurs with hydrothermal titanite tii and shows a close relationship with coarse grained hydrothermal magnetite and is cut by quartz or fine sulfide e g pyrite pyrrhotite and chalcopyrite veins the flat time resolved signals obtained from the depth profile analyses and inclusion free trace element mapping of u in spessartine indicate that the u is structurally bounded in the lattice both gi and gii spessartine show clear positively correlation between u al and mn but no apparent correlation is present between u and fe which indicates that al and mn are more important in the u incorporation in spessartine integrating with the positive correlations with u and lrees in spessartine which suggest u is incorporated in the lattice by a substitution of u4 viii 2 al3 iv ca2 viii 2 si4 iv in situ u pb dating of the two spessartine types yielded a weighted average 206pb 238u age of 231 7 7 2 ma gi mswd 0 56 n 35 and 211 5 5 8 ma gii mswd 1 1 n 47 considering the errors caused by common pb and matrix mismatch the corrected gi and gii spessartine ages are consistent with the ti 228 0 4 6 ma mswd 2 n 28 and tii 209 8 3 6 ma mswd 1 03 n 39 titanite ages suggesting that spessartine u pb dating is robust and reliable the least 8 1 my gap between the formation of the two titanite and spessartite types reflects two mineralization events suggesting an influx of magmatic fluids during the retrograde alteration mineralization our study represents a new way of directly constraining the timing of skarn alteration mineralization

manganese and methane in hydrothermal plumes along the east pacific rise 8 40 to 11 50 n abstract in november 1991 we surveyed the water column for hydrothermal plumes along 350 km of the east pacific rise axis from 8 40 to 11 50 n using a combination of physical and chemical measurements our survey included the two major ridge segments north and south of the clipperton transform fault at about 10 10 n both limbs of the overlapping spreading centers osc s at 9 03 n and 11 45 n and a 30 km section of the next ridge segment to the south we found vigorous plumes along most of this ridge axis in keeping with its magmatically robust cross section axial summit caldera and shallow magma related seismic reflector these plumes were detectable by both physical temperature and light attenuation and chemical dissolved mn and ch4 measurements although the chemical measurements were more sensitive the least active sections were the southern third of the northern segment from 10 20 to 52 n and the oscs especially the osc at 11 45 n plumes there had weak mn and ch4 signals and were barely detectable by physical methods these axial sections were the only ones surveyed that lie deeper than 2600 m and appear to be magma starved the most active sections on the northern segment gave stronger signals for mn and temperature than for ch4 and light attenuation whereas the opposite was true on the southern segment which was the site of a volcanic eruption at 9 45 52 n only seven months prior to our cruise on the northern segment the four physical and chemical plume tracers correlated positively and linearly with one another suggesting that the segment was fed by relatively uniform end member fluids with a mean ch 4 mn molar ratio of 0 075 the southernmost section surveyed from 8 42 to 9 08 n closely resembled the northern segment the rest of the southern segment fell into three sections with different ch 4 mn ratios 9 39 to 53 n with ch 4 mn as high as 10 9 08 to 39 n with ch 4 mn of 0 51 and 9 53 to 10 07 n with ch 4 mn of 0 85 the section with the highest ch 4 mn was the site of the volcanic eruption which produced high temperature low salinity gas rich vent fluids carrying abundant bacterial particles the high ch4 concentrations are clearly associated with the volcanic eruption but the origin of the ch4 is unclear

composition and dissolution of black smoker particulates from active vents on the juan de fuca ridge during two atlantis ii alvin cruises to the juan de fuca ridge in 1984 active high temperature 140 284 c vents were sampled for black smoker particulates using the grassle pump individual mineral phases were identified using standard x ray diffraction and petrographic procedures in addition elemental compositions and particle morphologies were determined by x ray energy spectrometry and scanning electron microscope x ray energy spectrometry techniques the vent particulates from the southern juan de fuca ridge vent sites were highly enriched in s si fe zn and cu and were primarily composed of sphalerite wurtzite pyrite pyrrhotite barite chalcopyrite cubanite hydrous iron oxides and elemental sulfur two additional unidentified phases which were prevalent in the samples included an fe si phase and a ca si phase the grain sizes of the individual particle phases ranged from 100 m for the fe si particles grain size and current meter data were used in a deposition model of individual phase dispersal for many of the larger sulfide and sulfate particles the model predicts dispersal to occur over length scales of only several hundreds of meters the high temperature black smokers from the more northerly endeavour segment vents were highly enriched in fe s ca cu and zn and were primarily composed of anhydrite chalcopyrite sphalerite barite sulfur pyrite and other less abundant metal sulfide minerals the grain sizes of the individual particles ranged from 10 m to slightly larger than 500 m the composition and size distributions of the mineral phases are highly suggestive of high temperature mixing between vent fluids and seawater a series of field and laboratory studies were conducted to determine the rates of dissolution of several sulfate and sulfide minerals the dissolution rates ranged over more than 3 orders of magnitude from 3 2 10 8 cm s 1 for anhydrite to 1 2 10 12 cm s 1 for chalcopyrite the results indicate that for some minerals particularly anhydrite and marcasite total dissolution occurs within a few hours to a few weeks of their formation for other more stable minerals including pyrite sphalerite and chalcopyrite the time required for total dissolution is much longer and consequently individual crystals may be expected to persist in the sediments for considerable periods of time after deposition

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

methane in the northern atlantic controlled by microbial oxidation and atmospheric history during may august 1997 the distributions of dissolved methane and ccl3f cfc11 were measured in the atlantic between 50 and 60 n in surface waters throughout the region methane was observed to be close to equilibrium with the atmospheric mixing ratio implying that surface ocean methane is tracking its atmospheric history in regions of north atlantic deep water formation despite the different atmospheric history and ocean chemistry of ch4 and cfc11 their spatial distribution patterns in the water column are remarkably similar one dimensional distributions have been simulated with an advection diffusion model forced by the atmospheric histories the results suggest that the similar patterns result from the increasing input of ch4 and cfc11 to newly formed deep waters over time combined with the effect of horizontal mixing and the oxidation of methane on a 50 year time scale

hydrothermal plumes at the rodriguez triple junction indian ridge water column anomalies of light transmission mn fe al and ch4 concentrations were searched in the central southeastern and southwestern indian ridge segments centered on the rodriguez triple junction rtj 25 32 s 70 02 e for the purpose of locating hydrothermally active areas in july to august 1993 we found an active zone in the central indian ridge segment 25 18 20 s approximately 12 miles north of the rtj where significant hydrothermal plumes were observed at 2 200 2 400 m depth intensive tow yo observations using a ctd rosette multi sampling system equipped with a transmissometer revealed that the plumes show temporal as well as spatial variations discrete water samples within the plumes were enriched in mn fe and ch4 with maximum concentrations of 9 8 nm 40 2 nm and 3 3 nm respectively judging from the spatial and chemical characteristics of the plumes especially from transmission anomalies andc h4mn ratios we speculate that the hydrothermal venting site might be not in the rift valley but on the eastern off axis zone several miles distant from the rift valley

methane dynamics in hydrothermal plumes over a superfast spreading center east pacific rise 27 5 32 3 s 1 samples were collected from hydrothermal plumes along the east pacific rise epr from 28 to 32 s during the ridge axis plume and neotectonic unified investigation rapanui cruise 5 march to 12 april 1998 forty five vertical casts and tow yos were conducted 3 off axis and 42 over the axes of two overlapping propagating ridges the west and east ridges these ridges are composed of several nontransform offset ridge segments spreading rates range from 149 mm yr in the segment interiors to 0 mm yr at the propagating rifts these maximum spreading rates are considered the fastest on the mid ocean ridge system and affect the structure of the ridge segment averaged methane plume maxima ranged from 1 7 to 7 2 nm mean methane concentrations on the west ridge were nearly double those of the east ridge westwardly advecting hydrothermal methane persisted to our most distal station nearly 480 km west of the east pacific rise background concentrations were less than 1 nm the highest methane concentration measured was 50 nm in a buoyant plume methane did not covary with manganese or any other hydrothermal tracer in plumes over portions of a segment that exhibited recent magmatic activity possibly as a result of the hydrothermal system s recovery from a phase separation event in contrast methane manganese ratios on the other segments ranged from 0 077 to 0 091 methane 13c values in plume maxima ranged from 27 to 33 versus peedee belemnite background values were around 40 these data are compared with hydrothermal plume methane data from slower spreading ridges and illustrate similarities in hydrothermal processes and sources between these systems

geochemistry and morphology of metalliferous sediments and oxyhydroxides from the endeavour segment juan de fuca ridge abstract we present first data on the geochemistry mineralogy and morphology of near vent sediments 35 and 200 m from active vent and ridge flank sediments approximately 3 km from the vent field as well as oxyhydroxide deposits from the endeavour segment juan de fuca ridge the purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains hydrothermal components in sediments are fe si s rich and mn fe si rich phases sulfides and barite which were exclusively derived from plume fallout sulfides are only a minor constituent of near vent sediments 2 4 wt and were not detected in ridge flank sediments the study suggests that the distribution of hydrothermal phases and associated elements in near vent and ridge flank sediments is affected mainly by processes of agglomeration dissolution absorption and settling that take place within a plume and to a lesser extent post depositional processes rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the cu concentrations in sediments with increasing distance from the vents besides sulfides important carriers of pb cu zn and co in near vent sediments are fe mn oxyhydroxides that occur together with silica as aggregates of gel like material and flaky particles and as coatings on filaments away from the vents trace metals are mostly in fe mn oxyhydroxides and authigenic fe rich montmorillonite oxyhydroxides at the main endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary fe oxyhydroxide silica from low temperature fluids at the mothra field seafloor deposits and chimney crusts composed of fe oxyhydroxide mn silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities

carbon isotopic distribution of methane in deep sea hydrothermal plume myojin knoll caldera izu bonin arc implications for microbial methane oxidation in the oceans and applications to heat flux estimation the concentration and stable carbon isotopic composition 13c of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the myojin knoll caldera izu bonin arc in the western north pacific the hydrothermal end member concentrations and 13c of methane show near homogeneity among vents 41 2 mol kg and 16 3 0 8 pdb respectively while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation 2 1 11 nmol kg and 29 0 to 11 3 pdb respectively comparison of concentration and 13c data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume assuming steady state emission of methane from the vents 1 kinetic isotope effect due to the microbial oxidation k12 k13 2 methane flux from the vents fvents 3 heat flux from the vents q and 4 average turnover time of hydrothermal methane tall are estimated to be k12 k13 1 005 0 001 fvents 90 340 mol d q 30 110 mw and tall 60 240 d respectively the estimated turnover times however are not uniform within the water column around the vents a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean while those at the distant points correspond to values more typical for deep ocean water

late paleozoic to early triassic multiple roll back and oroclinal bending of the mongolia collage in central asia abstract the architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined because of unavailable data the central asian orogenic belt caob provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage in this paper we review several lines of available evidence which enable us to propose a new tectonic model of huge roll back in the formation of the accretionary tectonics of the mongolian collage in central asia in the early paleozoic the mongolia collage comprised the southern siberian and the tuva mongol oroclines the siberia craton and the mongolia collage jointly formed a giant tadpole shape within the paleo asian and panthanlassic oceans its head siberia was to the south and the tail tuva mongol to the northwest the structures and tectonic zonation of the mongolia collage are characteristic of multiple arcs which have been separately described in detail in different segments southwards from the southern siberia east sayan west sayan gorny altai chara via the lake zone junggar tianshan gobi altai beishan alxa to the manlay hegenshan baolidao solonker segments almost all segments underwent early paleozoic to permian or even triassic frontal subduction and accretion while rifting in the late carboniferous to permian or triassic occurred in the outward oceanward westward advancing mongolian collage therefore we suggest that a huge complex roll back active from the carboniferous to permian or even to late triassic facilitated the formation of the mongolian collage the outward multiple roll back process was compatible and almost coeval with the start of the tuva mongol orocline and rotation of the siberian craton as confirmed by paleomagnetic and structural data during the roll back processes an archipelago paleogeography was formed behind the frontal subduction and accretion in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times the roll back process was affected by the collision of the kazakhstan collage along the chara and karamay zones in the early permian the collision of the tarim craton along the south tianshan zone in the early permian the collision of the dunhuang block along the liuyuan zone in the early permian triassic the collision of the alxa block along the qugan qulu zone in the permian and the collision of the north china craton along the solonker zone in the middle late triassic the tectonic styles and architecture of accretionary orogenic belts like the caob are characterized both by the amalgamation of multiple terranes and by oroclinal bending the systematic anatomy of the multiple roll back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens

lithology and fluid prediction from prestack seismic data using a bayesian model with markov process prior lithology and fluid prediction from prestack seismic data using a bayesian model with markov process prior

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

hydrothermal activity on the ultra slow spreading southern knipovich ridge we report first evidence for hydrothermal activity from the southern knipovich ridge an ultra slow spreading ridge segment in the norwegian greenland sea evidence comes from optical backscatter anomalies collected during a systematic side scan sonar survey of the ridge axis augmented by the identification of biogeochemical tracers in the overlying water column that are diagnostic of hydrothermal plume discharge mn ch4 atp analysis of coregistered geologic and oceanographic data reveals that the signals we have identified are consistent with a single high temperature hydrothermal source located distant from any of the axial volcanic centers that define second order segmentation along this oblique ridge system rather our data indicate a hydrothermal source associated with highly tectonized seafloor that may be indicative of serpentinizing ultramafic outcrops consistent with this hypothesis the hydrothermal plume signals we have detected exhibit a high methane to manganese ratio of 2 3 1 this is higher than that typical of volcanically hosted vent sites and provides further evidence that the source of the plume signals reported here is most probably a high temperature hydrothermal field that experiences some ultramafic influence compare to rainbow and logachev sites mid atlantic ridge while such sites have previously been invoked to be common on the sw indian ridge this may be the first such site to be located along the arctic ultra slow spreading ridge system

famous and amar segments on the mid atlantic ridge ubiquitous hydrothermal mn ch4 δ3he signals along the rift valley walls and rift offsets dynamic hydrocast experiments enabled mn tdm ch4 concentrations and 3he ratio to be recorded through vertical cross sections of hydrothermal plumes along the famous segment and the southern part of the amar segment on the mid atlantic ridge between 36 n and 37 n mn ch4 and 3he figures all along both segments are well above the seawater background in the open ocean they are interpreted to be the result of time integrated hydrothermal discharges dispersed and mixed in a closed basin delineated by the rift valley and the segment ends hydrothermal activity along the famous and amar segments appears to be similar a comparison of the residence times of the three tracers from the dispersed time integrated signals is proposed although the background values in these closed basin are high some proximal and or large hydrothermal inputs overprinted on the general time integrated plume can be detected i e the rainbow site south of amar based on the depth and the location of plumes hydrothermal activity is not by far limited to the neo volcanic inner floor of the valley and should involve the walls and complex offsets of the rift valley considering the mn and ch4 concentrations in these plumes two types of ocean mantle interaction may be represented hot focused discharges on ultramafic exposures rainbow site and low temperature diffuse serpentinisation

fe ni co o s phase relations in peridotite seawater interactions serpentinization of abyssal peridotites is known to produce extremely reducing conditions as a result of dihydrogen h2 aq release upon oxidation of ferrous iron in primary phases to ferric iron in secondary minerals by h2o we have compiled and evaluated thermodynamic data for fe ni co o s phases and computed phase relations in fo2 g fs2 g and ah2 aq ah2s aq diagrams for temperatures between 150 and 4008c at 50 mpa we use the relations and compositions of fe ni co o s phases to trace changes in oxygen and sulfur fugacities during progressive serpentinization and steatitization of peridotites from the mid atlantic ridge in the 15820 0 n fracture zone area ocean drilling program leg 209 petrographic observations suggest a systematic change from awaruite magnetite pentlandite and heazlewoodite magnetite pentlandite assemblages forming in the early stages of serpentinization to millerite pyrite polydymite dominated assemblages in steatized rocks awaruite is observed in all brucite bearing partly serpentinized rocks apparently buffering of silica activities to low values by the presence of brucite facilitates the formation of large amounts of hydrogen which leads to the formation of awaruite associated with the prominent desulfurization of pentlandite sulfide is removed from the rock during the initial stage of serpentinization in contrast steatitization indicates increased silica activities and that highsulfur fugacity sulfides such as polydymite and pyrite vaesite solid solution form as the reducing capacity of the peridotite is exhausted and h2 activities drop under these conditions sulfides will not desulfurize but precipitate and the sulfur content of the rock increases the co evolution of fo2 g fs2 g in the system follows an isopotential of h2s aq indicating that h2s in vent fluids is buffered in contrast h2 in vent fluids is not buffered by fe ni co o s phases which merely monitor the evolution of h2 activities in the fluids in the course of progressive rock alteration the co occurrence of pentlandite awaruite magnetite indicates h2 aq activities in the interacting fluids near the stability limit of water the presence of a hydrogen gas phase would add to the catalyzing capacity of awaruite and would facilitate the abiotic formation of organic compounds

manganese scavenging and oxidation at hydrothermal vents and in vent plumes abstract hydrothermal vents provide a major source of dissolved mn ii to the oceans where concentrations range from 5 mm within the 350 c hot smokers to just above ambient seawater concentration in far field vent plumes the mn ii rich environments within warm vents and vent plumes provide a suitable habitat for mn ii oxidizing bacteria in order to compare rates of scavenging and oxidation of mn ii proximally within vent fields

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

shear wave velocity estimation in porous rocks theoretical formulation preliminary verification and applications shear wave velocity logs are useful for various seismic interpretation applications including bright spot analyses amplitude versus offset analyses and multicomponent seismic interpretations measured shear wave velocity logs are however often unavailable we developed a general method to predict shear wave velocity in porous rocks if reliable compressional wave velocity lithology porosity and water saturation data are available the precision and accuracy of shear wave velocity prediction are 9 and 3 respectively the success of our method depends on 1 robust relationships between compressional and shear wave velocities for water saturated pure porous lithologies 2 nearly linear mixing laws for solid rock constituents 3 first order applicability of the biot gassmann theory to real rocks we verified these concepts with laboratory measurements and full waveform sonic logs shear wave velocities estimated by our method can improve formation evaluation our method has been successfully tested with data from several locations

particle recycling in the tag hydrothermal plume abstract analysis of th isotope distributions in the tag hydrothermal plume yields evidence for pronounced 234 th 230 th isotope fractionation this fractionation can be attributed to a combination of four processes 1 particle ageing 2 differential scavenging of 234 th and 230 th 3 differential focusing of 234 th and 230 th and 4 recycling of old particles we present arguments for the importance of the last of these processes particle recycling particles in the tag hydrothermal plume exhibit grain sizes which fall in the range 1 10 m applying the range of densities reported for amorphous iron oxyhydroxide and iron oxide mineral phases stokes law predicts that these particles should achieve terminal settling velocities ranging between 4 and 8 m d 1 for coarse grained 5 m radius particles and 0 2 0 3 m d 1 for fine grained particles 1 m radius these velocities have been used in a physical model of re entrainment and recycling in neutrally buoyant plumes our results indicate that particle recycling and re entrainment in hydrothermal plumes may be important over length scales of 1 10 km the model predicts that the proportion of particles re entrained is independent of particle size but increases with plume strength for plumes with volumetric fluxes greater than 10 3 m 3 s 1 the proportion of particles re entrained exceeds 50 in agreement with previous calculations based upon 230 th distributions sampling strategies in the past have typically concentrated upon processes operating within 1 km of active vent fields and will need to be revised accordingly in the future

improved resolution in bayesian lithology fluid inversion from prestack seismic data and well observations part 1 methodology the focus of our study is lithology fluid inversion with spatial coupling from prestack seismic amplitude variation with offset avo data and well observations the inversion is defined in a bayesian setting where the complete solution is the posterior model the prior model for the lithology fluid lf characteristics is defined as a profile markov random field model with lateral continuity each vertical profile is further given as an inhomogeneous markov chain model upward through the reservoir the likelihood model is defined by profile and it relates the lf characteristics to the seismic data via a set of elastic material parameters and a convolution model the likelihood model is approximated the resulting approximate posterior model is explored using an efficient block gibbs simulation algorithm the inversion approach is evaluated on a synthetic realistic 2d reservoir seismic avo data and well observations are integrated in a consistent manner to obtain predictions of the lf characteristics wi

a review of oceanographic and meteorological controls on the north sea circulation and hydrodynamics with a view to the fate of north sea methane from well site 22 4b and other seabed sources abstract the north sea hydrodynamics are key to the redistribution of methane released at the 22 4b site located at 57 55 n 1 38 e in the uk central north sea 200 km east of the scottish mainland this review summarizes the current state of knowledge on the north sea circulation stratification and variability therein and briefly discusses the potential consequences for the distribution and fate of methane released from site 22 4b or other seabed sources astronomical tidal waves follow a counter clockwise path and tide topography interaction generates a residual circulation in the same direction wind stress forcing can enhance reduce or even reverse this circulation variations in the strength of the fair isle current fic are important the fic enters the north sea between the orkneys and shetland follows approximately the 100 m isobath passes along site 22 4b and ends up in the norwegian trench the north atlantic oscillation nao also causes variability a positive negative nao index is associated with stronger weaker than normal westerly winds nao situations strengthen the circulation in the north sea whereas it weakens during nao conditions and is directed northeastward high positive correlations exist between the sst at site 22 4b and the nao index climate change can have a long term effect on the hydrodynamics of the north sea seasonal stratification has potentially the most important imprint on methane derived from the well 22 4b site summertime heating stratifies the northern part of the north sea in autumn loss of heat to the atmosphere causes the stratification to breakdown until tides and storms mix the entire water column during the period of stratification the bulk of dissolved methane released from site 22 4b gets trapped below the thermocline the loss of methane to the atmosphere thus becomes a function of the relative time scales of transport and horizontal and vertical mixing processes versus the time scale of microbial degradation oxidation in the water column

geology and hydrothermal evolution of the mothra hydrothermal field endeavour segment juan de fuca ridge detailed characterization of the mothra hydrothermal field the most southern and spatially extensive field on the endeavour segment of the juan de fuca ridge provides new insights into its geologic and hydrothermal development meter scale bathymetry side scan sonar imagery and direct dive observations show that mothra is composed of six actively venting sulfide clusters spaced 40 200 m apart chimneys within each cluster have similar morphology and venting characteristics and all clusters host a combination of active and extinct sulfide structures black smoker chimneys venting fluids above 300 c are rare while more common lower temperature diffusely venting chimneys support dense colonies of macrofauna and bacterial mat hydrothermal sediment and extinct sulfide debris cover 10 15 m of the seafloor surrounding each vent cluster obscuring the underlying basaltic substrate of light to moderately sedimented pillow lobate sheet and chaotic flows basalt talus and collapse terrain extinct sulfide chimneys and debris between the clusters indicate that hydrothermal flow was once more widespread and that it has shifted spatially over time the most prominent structural features in the axial valley at mothra are regional 020 trending faults and fissures and north south trending collapse basins the location of actively venting clusters within the field is controlled by 1 localization of fluid upflow along the western boundary fault zone and diversion of these fluids by antithetic faults to feed vent clusters near the western valley wall and 2 tapping of residual magmatic heat in the central part of the axial valley which drives flow beneath vent clusters directly adjacent to the collapse basins 70 90 m east of the western valley wall these processes form the basis for a model of axial valley and hydrothermal system development at mothra in which the field is initiated by an eruptive diking episode and sustained through intense microseismicity and non eruptive diking events

enhanced scavenging of210pb and210po by processes associated with the east pacific rise near 8 45 n in 1977 and 1981 a hydrothermal plume was detected at the east pacific rise epr near 8 45 n and at manop site m 25 km east of the epr by anomalous222rn and mn concentrations in 1981 samples were also taken for210pb 210po and226ra analyses to determine if enhanced scavenging of these elements occurred in the plume at both the ridge crest and at site m the 210pb 226ra ratios range from 0 09 to 0 35 which are among the lowest values ever measured it appears that removal of the210pb is occurring by processes operating at or near the seafloor there is also significant 210po 210pb disequilibrium at both locations which appears to increase away from the seafloor towards the plume as indicated by elevated mn concentrations an in situ water column scavenging process is suggested by correlation of 210pb 210po and mn concentrations in the plume the residence time of the210po is only about 1 year which is close to its residence time in surface waters but quite short compared to typical deep sea values thus rapid scavenging of the polonium in the plume and relatively rapid settling of particles from the plume is suggested

trace element geochemistry of magnetite implications for ore genesis of the talate skarn pb zn fe deposit altay nw china abstract the talate skarn pb zn fe deposit is hosted in the kangbutiebao formation of the abagong polymetallic belt altay nw china the talate magnetite comprises the magmatic hydrothermal hydrothermal disseminated and massive magnetite types and formed during the early skarn and quartz magnetite stage the magmatic hydrothermal disseminated magnetite is nb ta ti depleted whereas the hydrothermal disseminated magnetite associated with skarn alteration is geochemically similar to the ca skarn with slight ta mg ni depletions the massive magnetite ores have similar ni concentrations with the ca skarn but contain minor depletions in sn sc ta nb mg and co probably attributed to magma host rock interactions the talate hydrothermal disseminated magnetite contains lower sn than magnetite from typical skarn deposits and likely resulted from cassiterite crystallization as it is found co precipitated with disseminated magnetite both magmatic hydrothermal and hydrothermal disseminated magnetite are characterized by narrow ti concentration range and variable co ni ratios which likely reflect rapid cooling rate and significant fluid rock interaction during multiple successive stages of skarn alteration as the co has a higher solubility over the ni in the ore forming fluid whereas the talate massive magnetite contains wider ti concentration range and in some cases with 120 triple junctions the co ni ratios mostly

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

petrogenesis of the permian intermediate mafic dikes in the chinese altai northwest china implication for a postaccretion extensional scenario abstractthe central asian orogenic belt is a long lived accretionary orogen and the late paleozoic has been considered to be a critical period for the terminal amalgamation of its three tectonic collage systems however the exact timing of amalgamation and the geological process of such a huge accretionary orogenic belt are poorly understood this study presents new geochronological and geochemical data for permian intermediate mafic dikes in the chinese altai a key region between the mongolian and the kazakhstan collage systems according to mineral assemblages and petrographic textures the intermediate mafic dikes can be categorized as gabbronorite and quartz diorite the gabbronoritic and quartz dioritic dikes have zircon u pb ages of 276 7 2 9 and 273 2 4 3 ma respectively the gabbronorites are characterized by low sio2 47 1 51 3 wt and high mgo 5 33 8 46 wt together with medium cr 71 2 95 7 ppm and ni 80 6 192 ppm contents geochemical modeling indicates that the parental magma w

bayesian lithology and fluid prediction from seismic prestack data a fast bayesian inversion method for 3d lithology and fluid prediction from prestack seismic data and a corresponding feasibility analysis were developed and tested on a real data set the objective of the inversion is to find the probabilities for different lithology fluid classes from seismic data and geologic knowledge the method combines stochastic rock physics relations between the elastic parameters and the different lithology fluid classes with the results from a fast bayesian seismic simultaneous inversion from seismic data to elastic parameters a method for feasibility analysis predicts the expected modification of the prior probabilities to posterior probabilities for the different lithology fluid classes the feasibility analysis can be carried out before the seismic data are analyzed both the feasibility method and the seismic lithology fluid probability inversion were applied to a prospect offshore norway the analysis improves the probability for gas sand from 0 1 to about 0 2 0 4 with s

chemical reaction rates and entrainment within the endeavour ridge hydrothermal plume the aging of the hydrothermal plume over the endeavour segment of the juan de fuca ridge was estimated by measuring the222rn3he ratio in the plume as it dispersed despite uncertainties in the source function of hydrothermal input it wa determined that the relative sequence of removal from the plume ish2 c 222rn ch4 mn where c is a measure of particle concentration and the mean life of222rn is 5 5 days h2 is removed from the plume within hours of input while mn is not removed within the two week timescale of the radon helium clock entrainment of bottom water within the buoyant plume may introduce additional chemical signatures into the spreading effluent layer over that which would be introduced by hydrothermal discharge alone this is particularly significant for those chemical species which are not greatly enriched in the vent fluids relative to bottom water concentration and which display a nutrient like profile in the deep ocean thus we found that significant fractions of the si and226ra anomalies in the plume were not of hydrothermal origin but were derived from entrained bottom water which has a higher concentration of these elements than ambient water at plume height

particle size distributions within hydrothermal plumes over the juan de fuca ridge abstract the particle size distributions of suspended particles in neutrally buoyant hydrothermal plumes from two vent sites on the juan de fuca ridge were measured with a coulter counter hydrothermal particle populations were characterized by high volume concentrations of particles with diameters of m particle populations dominated by larger particles were rare and observed only very near active vent sources because of rapid settling and dilution particle size distributions from particle plumes of hydrothermal origin can be readily distinguished from those of benthic nepheloid layers by the fine particle tail which is expressed on a cumulative number distribution by a slope much steeper than the oceanic norm of 3 the predominance of particles with diameters m within neutrally buoyant hydrothermal plumes demonstrates that the bulk of hydrothermal precipitates are capable of being dispersed over wide areas

bayesian wavelet estimation from seismic and well data a bayesian method for wavelet estimation from seismic and well data is developed the method works both on stacked data and on prestack data in form of angle gathers the seismic forward model is based on the convolutional model where the reflectivity is calculated from the well logs possible misties between the seismic traveltimes and the time axis of the well logs errors in the log measurements and seismic noise are included in the model the estimated wavelets are given as probability density functions such that uncertainties of the wavelets are an integral part of the solution the solution is not analytically obtainable and is therefore computed by markov chain monte carlo simulation an example from sleipner field shows that the estimated wavelet has higher amplitude compared to wavelet estimation where well log errors are neglected and the uncertainty of the estimated wavelet is lower

stable isotopic compositions of methane and carbon monoxide in the suiyo hydrothermal plume izu bonin arc tracers for microbial consumption production abstract effluent hydrothermal water samples in and around the water column of the suiyo seamount caldera ca 2 km diameter izu bonin arc were taken to determine concentrations and stable carbon isotopic compositions 13c of methane ch4 and carbon monoxide co in the plume venting fluids on the caldera floor ca 1370 m depth were also examined using the manned submersible shinkai 2000 to compare the chemical composition and isotopic composition of ch4 and co with those in the hydrothermal plume strong ch4 enrichment was detected not only in the water column within the caldera but also on those outside the caldera at the depth of ca 1100 m the sill depth of the caldera wall within the plume we also detected significant co enrichment the 13c of co in the plume however exhibited highly 13c depleted values 110 vpdb to 60 vpdb compared with those in seafloor venting hydrothermal fluids around 31 vpdb besides the plume samples exhibited higher co ch4 ratios depending on the distance from the seafloor venting site we conclude that in situ microbial activity in the plume causes the co enrichment in the hydrothermal plume the present results suggest that co enrichment in deep sea water could act as a new tracer for unidentified seafloor hydrothermal activities especially for detecting plumes distant from venting sites as well as for quantifying in situ microbial activity related to co production in hydrothermal plumes

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

hydrothermal particle plumes over the southern juan de fuca ridge hydrothermal particles originate in buoyant plumes emanating from seafloor thermal vents1 4 and accumulate as metalliferous sediments found along oceanic spreading centres5 7 observational evidence of the transport pathway of hydrothermal particles is scarce however and the structure extent and particle concentrations of hydrothermal plumes remain largely conjectural to evaluate the potential of hydrothermal plumes as particle transport agents we mapped their distribution along and across the 80 100 m deep axial valley of the southern juan de fuca ridge in the north east pacific ocean 44 30 n 130 w an area of known hydrothermal activity8 11 continuous light scattering measurements reported here defined numerous particle plumes centred 30 120 m above bottom m a b elemental analysis of the plume particles and the theta potential temperature s salinity signatures of the plume water verified their hydrothermal origin concentrations of hydrothermal particles remained elevated at ridge crest depths at least 100 km from the ridge indicating distant off axis dispersal of hydrothermal emissions

microorganisms in deep sea hydrothermal plumes the study of hydrothermal vents at oceanic spreading centres has led to a re evaluation of some basic tenets concerning energy flux through oceanic ecosystems and the sources and sinks for dissolved ions in sea water hydrothermal vents vary considerably from relatively low temperature 25 c fluid discharges to the spectacular high temperature 350 c black smokers1 3 the high temperature vents give rise to buoyant plumes which can be detected hundreds of kilometres away from ridge crests4 5 in the immediate vicinity of hydrothermal vents chemoautotrophic bacteria are present in vent fluids6 8 attached to rock surfaces9 10 and as endosymbionts in certain macro fauna11 deep sea hydrothermal plumes have not as yet been examined for the presence of bacteria we now report the presence of elevated bacterial biomass in a hydrothermal plume originating from the juan de fuca ridge and discuss the potential geochemical significance of these microorganisms

joint avo inversion wavelet estimation and noise level estimation using a spatially coupled hierarchical bayesian model the main objective of the avo inversion is to obtain posterior distributions for p wave velocity s wave velocity and density from specified prior distributions seismic data and well log data the inversion problem also involves estimation of a seismic wavelet and the seismic noise level the noise model is represented by a zero mean gaussian distribution specified by a covariance matrix a method for joint avo inversion wavelet estimation and estimation of the noise level is developed in a bayesian framework the stochastic model includes uncertainty of both the elastic parameters the wavelet and the seismic and well log data the posterior distribution is explored by markov chain monte carlo simulation using the gibbs sampler algorithm the inversion algorithm has been tested on a seismic line from the heidrun field with two wells located on the line the use of a coloured seismic noise model resulted in about 10 lower uncertainties for the p wave velocity s wave velocity and density compared with a white noise model the uncertainty of the estimated wavelet is low in the heidrun example the effect of including uncertainty of the wavelet and the noise level was marginal with respect to the avo inversion results

methane manganese and helium in hydrothermal plumes following volcanic eruptions on the east pacific rise near 9 50 n 1 as part of a rapid response cruise in may 2006 we surveyed water column hydrothermal plumes and bottom conditions on the east pacific rise between 9 46 0 n and 9 57 6 n where recent seafloor volcanic activity was suspected real time measurements included temperature light transmission and salinity samples of the plume waters were analyzed for methane manganese helium concentrations and the 13c of methane these data allow us to examine the effects of the 2005 2006 volcanic eruption s on plume chemistry methane and manganese are sensitive tracers of hydrothermal plumes and both were present in high concentrations methane reached 347 nm in upper plume samples 250 m above seafloor and exceeded 1085 nm in a near bottom sample mn reached 54 nm in the upper plume and 98 nm in near bottom samples the concentrations of methane and mn were higher than measurements made after a volcanic eruption in the same area in 1991 but the ratio of ch4 mn at 6 7 is slightly lower though still well above the ratios measured in chronic plumes high concentrations of methane in near bottom samples were associated with areas of microbial mats and diffuse venting documented in seafloor imagery the isotopic composition of the methane carbon shows evidence of active microbial oxidation however neither the fractionation factor nor the source of the eruption associated methane can be determined with any certainty considerable scatter in the isotopic data is due to diverse sources for the methane as well as fractionation as methane is consumed one sample at 21 versus peedee belemnite standard is among the most enriched methane carbon values reported in a hydrothermal plume to date

estimation of heat and chemical fluxes from a seafloor hydrothermal vent field using radon measurements the circulation of seawater through newly formed ocean crust at mid ocean ridge spreading centres is important in the oceanic heat and chemical budgets the heat transfer in submarine hydrothermal systems accounts for 25 of the total global heat loss1 the transfer of mass resulting from basaltic alteration affects the geochemistry of seawater2 and is responsible for the formation of ore deposits on and beneath the seafloor3 various geophysical techniques have been employed in efforts to determine the heat output from hydrothermal vent fields4 9 however the magnitudes of the heat and chemical fluxes through these systems remain uncertain here we introduce a geochemical approach for estimating the flux from a vent field based on radon 222rn measurements in the overlying effluent plume this method was applied successfully in september 1986 during a 23 day expedition to an active vent field on the 170 km endeavour segment of the juan de fuca ridge fig la we estimate the heat flux from this site to be l 5 l09 w

is the south pacific helium 3 plume dynamically active it is suggested that the hydrothermal vents of the south pacific rise produce a beta governed circulation at mid depth and that perhaps the associated plume of excess3he lupton and craig 1 points westward because of the dynamics of this circulation rather than as a passive tracer

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

abiotic hydrogen h2 sources and sinks near the mid ocean ridge mor with implications for the subseafloor biosphere free hydrogen h2 is a basal energy source underlying chemosynthetic activity within igneous ocean crust in an attempt to systematically account for all h2 within young oceanic lithosphere

topographic control of a dispersing hydrothermal plume deep sea hydrothermal vents represent a major source of heat and chemicals to the oceans and support endemic chemosynthetic biological communities to fully understand the impact of hydrothermal activity upon the oceans however requires investigation of both the physical and the biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans we have recently conducted a detailed multidisciplinary study of the lateral dispersion of the hydrothermal plume emitted from the rainbow vent site near 36 15 n mid atlantic ridge combining velocity measurements from a lowered adcp optical back scatter measurements from a deep tow ctd and methane measurements from bottle samples we are able for the first time in the atlantic to trace a neutrally buoyant plume for a distance of over 50 km the path of the plume is seen to be heavily controlled by the local topography with a general northeast movement of water both particle and methane concentrations decrease downstream over the length of the observed plume the dataset provides an excellent opportunity to study the mixing and biogeochemical processes active in a hydrothermal plume and estimate fluxes of biogeochemical constituents

hydrothermal methane plumes in the mariana back arc spreading centre submarine hydrothermal vents were first unequivocally detected by measurement of 3he 4he ratio anomalies coupled with deviations from ambient t s relationships on the galapagos spreading centre1 2 since then the existence of hydrothermal vents along the entire length of the east pacific rise has been demonstrated by shipboard observations of 3he methane and manganese in the effluent plumes3 5 we have extended our studies of vent fields at mid ocean ridge spreading centres to search for effluent plumes in back arc basins which are also thought to be active regions of seafloor spreading where new oceanic crust is formed6 and thus where rifting and assuring along the axis of extension should provide similar opportunities for the downward penetration of sea water and the development of active hydrothermal systems we have detected large plumes of methane enriched water in the mariana trough back arc basin7 and also in the summit crater of loihi seamount7 at the present site of the hawaiian hotspot thus establishing the widespread existence of off ridge hydro thermal vents in the ocean however although the loihi vents produce plumes enriched in both 3he and methane7 we find that surprisingly the mariana vents are enriched in methane without a corresponding enrichment in 3he this is the first time such a decoupling of these two effluent plume tracers has been observed

methane anomalies in seawater above the loihi submarine summit area hawaii hydrothermal activity above loihi submarine volcano was characterized by water column distributions of methane ph and helium 3 it was found that the southern loihi summit is almost covered with hydrothermal plumes which have anomalously high concentrations of methane maximum 569 10 6cm3kg 1 accompanied by high concentrations of helium 3 and low ph values minimum 7 18 the plumes consist of two layers a shallow plume about 200 m above the summit and a deep plume about 100 m above the summit probably derived from different hydrothermal vents the shallow and deep plumes showed different ch43he and ch4ph ratios with the same 3heph ratio which implies that methane concentrations differ between the hydrothermal end members for the two plumes the variation of methane between the end members is suggested to result from inter vent inhomogeneity of bacterial activities that consume or produce methane within the vents comparison of the ch43he ratios of the two plumes with the previous data for loihi and other submarine hydrothermal areas confirms that the loihi hotspot has one to two orders of magnitude smaller ch43he value than those of the east pacific rise and the galapagos spreading centers

the effect of plume processes on the fe isotope composition of hydrothermally derived fe in the deep ocean as inferred from the rainbow vent site mid atlantic ridge 36 14 n abstract the rainbow hydrothermal vent site which is the largest known point source for dissolved fe delivered to the deep north atlantic ocean has remained invariant in its fe isotope composition over at least the past 16 000 years based on analysis of metalliferous sediments beneath the plume because of the conservative behavior of fe in the rainbow plume 56 fe values of particles in the neutrally buoyant plume 0 18 0 05 and underlying sediments 0 19 0 05 are indistinguishable from the 56 fe values of the high temperature fluid sources 0 23 0 04 particles from the near vent buoyant stage of the plume however have higher 56 fe values 0 15 to 1 20 relative to the original vent fluid consistent with fractionation during oxidation of fe ii aq to fe iii aq isotope compositions become invariant in the plume once all fe ii aq is fully oxidized preserving the original composition of the vent fluid the constant fe isotope compositions of the vent fluids over time implies that changes in seawater fe isotope composition of the north atlantic ocean as they are recorded in fe mn crusts requires changes in the relative fluxes of fe to the ocean

locating hydrothermal vents by detecting buoyant advected plumes an improved method of detecting buoyant hydrothermal plumes and locating their source vents is introduced plumes are detected by computing fluid stability from conductivity temperature and depth measurements acquired during navigated towed vertically oscillating casts over the endeavour segment of the juan de fuca ridge for each instability detected the maximum range to its hydrothermal source is estimated by multiplying a theoretical plume equilibration time by a measured current velocity using an estimate of current direction the method reliably locates plume sources where they are known to exist in all of the focused vent fields mapped by submersible and in several isolated diffuse flow sites the method generates a distribution of hydrothermal sources that is more consistent with variations in surface permeability than with circulation cells spaced evenly along a uniformly permeable axis axial instabilities are nearly continuous along the heavily fissured and fractured western wall of the axial valley beyond the axial valley instabilities evidence that hydrothermal upflow penetrates the outer slopes of the ridge crest probably along a boundary between sheet and pillow flows