chemistry of hydrothermal fluids from the 17 s active site on the north fiji basin ridge sw pacific abstract in june 1989 a diving cruise of the french submersible nautile was made along the north fiji basin spreading ridge the objective was the geological and geochemical study of the active spreading axis and of the hydrothermal processes discovered during the kaiyo cruise in 1988 active anhydrite chimneys associated with underlaying sulfide deposits were studied in the central spreading ridge the transparent venting fluid showed significant salinity depletion the extrapolated concentrations of all the chemical species in the pure end member showed a signature similar to that of the cl depleted hydrothermal fluid from the ashes vent site in the juan de fuca ridge these features suggest that the present hydrothermal end member resulted from subcritical phase separation which generated a low salinity vapor phase followed by condensation and mixing with normal seawater in the last part of the plumbing system of the vents

interferometer studies of equatorial f region irregularities and drifts a radar interferometer technique developed at jicamarca peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial f region our first results have shown that the most turbulent echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east west direction this slab may very well be the wall of a depleted region a plasma bubble sometimes the irregularities can be tracked as they move eastward or westward velocity profiles for the evening period obtained in this way show a strong shear with westward velocities at the lowest altitudes observed and eastward velocities above a plausible explanation for this shear is that the westward drifts are driven by electric fields produced by westward e region winds and mapped up along magnetic field lines while at higher heights where the electron density is greater the drifts are controlled by the f region dynamo driven by eastward winds

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

the recent crustal stress field in central europe trajectories and finite element modeling the recent crustal stress field of central europe and especially of the adjoining areas to the east is presented in terms of the directions of maximum horizontal stress shmax the analysis is based on fault plane solutions in situ stress measurements geologic fault slip determinations and repeated precise geodetic triangulations a bending of the direction of shmax from the well known nw se direction in the western part of the study area to directions of ne sw to e w in the eastern part is shown first results on the recent crustal stress field of the study area were presented by grunthal and stromeyer 1986 who substantiated this tendency of bending in the central and eastern parts of the study area by few observations only therefore one aim of this paper was to compile observations on the areas with few data points generally these additional data confirm the previously established pattern in some areas especially in the pannonian basin the stress features became more complicated compared with those solely based on a few data points the second part of the paper presents steady state elastic finite element model calculations to provide some possible explanations of the observed stress orientations as a result of plate driving forces simulation of the north atlantic seafloor spreading and the northward directed motion of the african plate by appropriate boundary loads produces a pattern of shmax directions for the western part of the eurasian plate which is compatible with the broad scale observed stress directions subregional anomalies such as the fanlike stress pattern perpendicular to the arc of the western alps or the radial directions around the pannonian basin can be explained only when additional stress producing features are introduced overmodulating the regional field rigorous introduction of physically constrained model parameters for all these features was not feasible to date therefore the preliminary empirical model calculations presented in this paper are attempts to discuss which features have the most influence on the stress field they are in a regional scale the north atlantic seafloor spreading the northward motion of the african and the arabian plate and obviously subregionally increased stiffness of the apulian promontary as well as of the bohemian massif

radar studies of long wavelength waves associated with mid latitude sporadic e layers the cornell university portable radar interferometer cupri a 50 mhz doppler radar system was operated during may and august september 1983 on the island of st croix 17 7 n 64 8 w to study the plasma instabilities associated with nighttime sporadic e layers two events on may 7 and august 22 show evidence of large amplitude waves with apparent horizontal wavelengths of 10 12 km and periods of 2 6 min these apparent wavelengths are upper limits for the true wavelengths the cupri beam was directed over arecibo puerto rico and on may 7 concurrent electron density profiles within the cupri scattering volume were measured by the arecibo observatory s 430 mhz radar during the stronger event of august 22 radar echoes were received from several altitudes up to 130 km large mean doppler velocities at times exceeding 250 m s were observed during this event and the power spectra closely resemble those obtained at the magnetic equator during type 1 conditions we believe 1 that the mid latitude large scale waves are generated by the same gradient drift instability mechanism responsible for equatorial large scale waves and 2 that the type 1 3 m waves can be generated at mid latitudes with drift velocities well below the sound speed because of the very sharp plasma density gradients associated with metallic ion sporadic e layers

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

orientation of in situ stresses in the oceanic crust two in situ measurements of principal stress directions have been made in dsdp holes 504b south of the costa rica rift on the nazca plate and 597c west of the east pacific rise on the pacific plate in both cases the orientations of in situ principal stresses determined from borehole breakouts are consistent with the stress directions inferred from intraplate earthquakes located near the sites

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

evidence of thermally induced borehole elongation a case study at soultz france abstract when they occur borehole breakouts are considered strong markers of principal stress directions at depth an innovative processing method for automatically identifying breakouts from ultrasonic borehole wall images has been developed it has been applied to data sets from two deep sub vertical wells gpk1 and gpk2 at the soultz geothermal site in eastern france in well gpk1 below 3 km depth compression breakouts with a 95 7 azimuth increasingly occur with depth they result from time dependent compression failure at sub critical stress levels and are indicators of the minimum horizontal principal stress orientation however in the uppermost logged section of well gpk2 1 6 2 9 km depth continuous borehole elongations share roughly the same azimuth with so called drilling induced fractures 164 18 and 175 17 azimuth respectively both features concomitantly vanish with depth together with the amplitude of the thermal perturbation induced by drilling it is proposed that these latter borehole elongations result from a pervasive cooling induced tensile micro cracking process prior to macroscopic failure localization they are termed thermal elongations and are indicators of the maximum horizontal principal stress orientation had a simple logging caliper tool been used for this work these thermal elongations might have been confused with classical compression breakouts a simple criterion for differentiating compression breakouts from thermal elongation is proposed

long term observations of the arctic mesosphere with the mst radar at poker flat alaska in this report we summarize the results of 22 months of observations of arctic mesosphere echoes with the 50 mhz radar at poker flat alaska operation with a partially complete system began in february 1979 and has continued on a nearly continuous basis to the present time the altitude range of the mesospheric echoes obtained during this period shows a pronounced seasonal variation during summer months the mesospheric echoes are relatively continuous in time and extend from about 80 to 100 km with an unexpectedly strong peak in signal to noise ratio at about 85 km in contrast in nonsummer months mesospheric echoes are less intense and occur at lower altitudes in the range from 55 to 80 km these lower altitude nonsummer echoes are observed primarily during daytime hours when energetic auroral particle precipitation as determined by the poker flat 30 mhz riometer is present

stress orientations from oil well fractures in alberta and texas many oil wells in alberta exhibit spalling of the walls known as breakouts which elongates the holes with the longer axis aligned northwest southeast this alignment is observed over an area in excess of 4 105 km2 in siltstones sandstones carbonate sediments and one shale formation through the stratigraphic column from devonian to cretaceous it is unrelated to dip of the beds we have elsewhere suggested that these breakouts are produced through stress concentration near the hole walls in a stress field having large unequal horizontal principal stresses and with the larger compression oriented northeast southwest it is probable that this northeast southwest principal stress is 1 this paper adds new data from oil wells in alberta and northern british columbia and shows that the breakouts and by inference the stress orientations are consistent through much of the western canadian sedimentary basin it also uses evidence from hydraulic fracturing in west central alberta and from steam injec

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

a reassessment of the stress and natural fracture orientations from analysis of image logs in the chinese continental scientific drilling program borehole at donghai county jiangsu province china abstract the chinese continental scientific drilling ccsd project has drilled a 5100 m deep research borehole in the sulu ultra high pressure uhp metamorphic belt eastern china the uhp metamorphic belt is thought to be a product of continent continent collision and has consequently experienced very intensive structural deformation based on a more complete well log data set of ccsd borehole we can have a more detailed and reliable study on the structure features of borehole wall and other rock physical properties than a previous study published in 2009 abundant data related to borehole breakouts bos drilling induced tensile fractures ditfs and natural fractures were collected from the image logs the bo and ditf data indicate that the average direction of the maximum horizontal principal stress sh of the ccsd borehole site is about 79 2 which is consistent with the convergent direction e w of the pacific sea plate with respect to the eurasian plate analysis of ditfs indicated that in the case of the ccsd borehole axial drilling induced tensile fractures aditfs occur occasionally in the upper section 0 2300 m of the borehole with low dipping angle 0 10 while transverse drilling induced tensile fractures tditfs occur significantly in the lower section 3800 5000 m with high dipping angle 10 30 the natural fracture distribution at depth in the metamorphic rocks of the ccsd borehole indicates that 1 the failure strength of rocks and borehole depth are two factors that affects natural fracture frequency 2 most of the dip azimuth of natural fractures is consistent with the dip azimuth of foliations observed in the core 3 the development of most of the natural fractures probably was dominated by the development of foliations and both the natural fractures and foliations developed in response to the subduction and exhumation of the sulu terrene

wellbore breakouts of the main borehole of chinese continental scientific drilling ccsd and determination of the present tectonic stress state abstract the sulu dabie high pressure hp ultrahigh pressure uhp metamorphic belt as the product of subduction collision between the northern china plate and yangtze plate underwent a process of formation and evolution from deep subduction exhumation extension slow uplift the study of its modern tectonic stress field has great significance for a complete understanding of the process of formation and evolution of the hp uhp metamorphic belt especially the exhumation and uplift of the belt wellbore breakouts are the most visual tectonic phenomenon which can characterize the modern stress action in the main borehole of chinese continental scientific drilling ccsd ultrasonic borehole televiewer reflection wave data show that wellbore breakouts began to occur at 1216 m depth of the main borehole a total of 143 borehole televiewer images were collected from 1216 to 5118 m depth hole completion depth after data processing and statistics the average azimuth of the long dimension of the wellbore breakout obtained was 319 5 3 5 indicating that the average azimuth of the maximum horizontal principal stress causing wellbore breakout initiation was 49 5 3 5 the maximum and minimum horizontal principal stress values at 52 depths in the interval of 1269 to 5047 m were estimated using the elements of wellbore shapes wellbore depth and width combined with the cohesive strength and internal frictional angle of the rock obtained by rock mechanical tests on samples and the static load stresses at corresponding depths were calculated according to the rock density logging data the results indicate that the maximum and minimum horizontal principal stresses are 41 4 and 25 3 mpa at 1269 m depth respectively and 164 7 and 122 mpa at 5047 m depth respectively the maximum vertical stress is 141 3 mpa at 5047 m depth with a density of 2 8 g cm 3 the in situ stresses increase nearly linearly with depth the magnitudes and directions of the three principal stresses reflect that the regional stress field around the ccsd main borehole is mainly in a strike slip state which is consistent with the basic features of the regional stress field determined using other methods

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

recent stress field and neotectonics in the eastern jura mountains switzerland the regional stress field and its local variation were determined for the northern part of central switzerland fig 1 by using overcoring techniques doorstopper triaxial strain cell and observations of breakouts in deep boreholes the results are compared with fault plane solutions of earthquakes and with the orientation of horizontal stylolites in the northern part of central switzerland the nw se orientation of the maximum horizontal stress sh which is characteristic for central europe was observed only in the crystalline basement in the folded jura and south of it in one well the greatest principal horizontal stress above the triassic decollement horizon is oriented approximately in a n s to nne ssw direction this direction persists into the western tabular jura and the southernmost rhine graben only in the eastern part of the tabular jura the greatest principal horizontal stress shows a nnw sse to nw se orientation comparison of the near surface stress field as determined by in situ stress measurements and borehole breakouts with the directions of horizontal stylolites generated during the evolution of the folded jura indicates that the orientation of the recent stress field near the earth s surface is the same as that which prevailed during the upper miocene to lower pliocene the central part of northern switzerland is therefore the first area in central europe where it is possible to demonstrate that the near surface stress field is decoupled from that in the crystalline basement the difference in the orientation of the greatest principal horizontal stress is about 50

manganese methane iron zinc and nickel anomalies in hydrothermal plumes from teahitia and macdonald volcanoes abstract hydrothermal vents discharging turbid water have recently been discovered at teahitia and macdonald seamounts which are situated at the southeast ends of two south pacific hotspot systems mixtures of the plumes with ambient seawater were sampled during the 1989 cyapol cruise and found to contain significant amounts of ch4 mn fe zn and ni which are comparable in concentration to those found over hydrothermal fields on the epr and in megaplumes over the juan de fuca ridge above teahitia volcano ch4 shows maximum concentrations of 8 nmol kg mn concentrations of 19 nmol kg and fe concentrations of 125 nmol kg the concentrations were much higher during an earlier so 47 cruise in 1987 reaching maximum values of 14 nmol ch4 kg and 60 nmol mn kg by contrast the macdonald seamount plume shows an opposite trend reaching very high concentrations of 350 nmol kg ch4 250 nmol mn kg and 3920 nmol fe kg during the cyapol cruise when the volcano was at an eruptive stage with high seismic activity the fe mn ratio of the plume is variable between the two active volcanoes and at different hydrocast stations reflecting the balance between input and removal of these two elements mapping of the element concentrations in the water column shows the plume ceiling or anomaly maxima to occur to several hundred metres above the seafloor and up to several kilometres 5 km from the vents on macdonald seamount multiple maxima in hydrocast profiles indicate the presence of several distinct hydrothermal vents at different water depths on teahitia and on the western flank of macdonald seamount ree data from a single hydrocast over the active macdonald summit indicate a mobility of the ree which probably results from high temperature basalt seawater interaction

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

orientation of the stress field from breakouts in a crystalline well in a seismic active area abstract the orientation of the regional stress field in the swabian jura was determined from borehole breakouts caused by stress accumulation at the borehole wall the analysis is based on caliper data recorded in the urach 3 geothermal well within an intervall of about 1450 m the azimuths of the breakouts are consistent with depth and indicate a stress direction which is in good agreement with the interpretation of fault plane solutions of nearby earthquakes

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

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

regional stress alignments in the kutai basin east kalimantan indonesia a contribution from a borehole breakout study abstract borehole breakout data from 134 wells located within the kutai basin region east kalimantan were analyzed to determine the present day regional horizontal stress alignments the data were extracted from various types of dipmeter logs the study reveals that the majority of the data give a coherent picture of breakout orientation the mean azimuths for the entire unweighted ellipticity weighted and magnitude weighted data sets are preferentially aligned in the regional mean direction of 48 9 n or 128 9 n most of the data have a low dispersion value s o and the ranking of reliability in zoback s classification is a there is no significant azimuth variation with depth these relatively consistent alignments of breakout azimuths indicate that the maximum regional stress direction in the study area is nw se this regional mean of breakout azimuths deviates from the axis of the anticlinorium trends and from the strike of the thrust fault patterns in the region it is believed that these structural patterns are influenced by reactivation of weak zones related to sediment loading structural inversion

distribution and composition of hydrothermal plume particles from the ashes vent field at axial volcano juan de fuca ridge in 1986 and 1987 buoyant and neutrally buoyant hydrothermal plume particles from the ashes vent field within axial volcano were sampled to study their variations in composition with height above the seafloor individual mineral phases were identified using standard x ray diffraction procedures elemental composition and particle morphologies were determined by x ray fluorescence spectrometry and scanning electron microscopy x ray energy spectrometry techniques the vent particles were primarily composed of sphalerite anhydrite pyrite pyrrhotite chalcopyrite barite hydrous iron oxides and amorphous silica grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume the neutrally buoyant plume consisted of a lower plume which was highly enriched in fe s zn and cu and an upper plume which was highly enriched in fe and mn the upper plume was enriched in fe and mn oxyhydroxide particles and the lower plume was enriched in suspended sulfide particles in addition to the fe and mn oxyhydroxide particles the chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles short term sediment trap experiments indicate that the fallout from the ashes vent field is not as large as some of the other vent fields on the juan de fuca ridge

state of lithospheric stress and borehole stability at deep sea drilling project site 504b eastern equatorial pacific hole 504b in the eastern equatorial pacific is the deepest hole to penetrate oceanic basement extending more than 1500 m beneath the seafloor two borehole televiewer bhtv logs were obtained in this hole one through the upper 1000 m of basement during deep sea drilling project leg 83 and the other extending an additional 260 m deeper into the crust during ocean drilling program leg 111 the two bhtv records have been combined and processed in terms of both acoustic amplitude and travel time in order to evaluate the extent and distribution of rock failure along the borehole wall a histogram of borehole enlargements versus azimuth depicts a dominant breakout azimuth of n122 5 e which corresponds to the direction of minimum principal stress sh and correlates well with stress orientations inferred from solutions to regional earthquake focal mechanisms furthermore the bimodality of this histogram with a secondary mode orthogonal to sh indicates that a significant number of enlargements are coalesced tensile fractures occurring along the orientation of sh the maximum principal stress the appearance of this orthogonal bimodal distribution suggests that the regional horizontal stress field is highly anisotropic a condition supported by seismic data which show all of the earthquakes in the area to be strike slip the frequency of borehole enlargements increases with increasing depth and depicts a systematic structural deterioration of the well bore the tensile fractures along the sh azimuth contribute to this degradation and appear to be induced by thermal stresses due to the injection of cold water into hot rock the frequency of these extensional features does not increase with depth rather their appearances can be directly correlated with shipboard efforts at deliberately cooling the well and or with the sudden resumption of drilling after the hole had been allowed to reequilibrate thermally for several days these latter borehole enlargements are more pronounced then those commonly associated with hydraulic fracturing the mechanisms for fracture initiation and growth based upon temperature contrasts between the well bore fluid and the adjacent rock may enhance rock failure

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

in situ observations of dissolved iron and manganese in hydrothermal vent plumes juan de fuca ridge in situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the juan de fuca ridge using a submersible chemical analyzer scanner the scanner was deployed as part of a ctd transmissometer rosette instrument package on both tow yos and vertical casts during the vents leg i cruise in 1989 dissolved manganese and total dissolved iron concentrations along with temperature and light attenuation anomalies were determined over the ridge crest every 5 s discrete samples for laboratory analyses of dissolved iron ii total dissolved iron ii iii and manganese were also collected metal to heat ratios me q measured in situ were extremely variable in one steady state plume while an event plume had constant me q uniform values of mn q in the event plume demonstrate that mn behaves conservatively in the near field plume variability in the mn q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct me q values a simple mixing model shows that the contribution of mn from high me q sources with a composition characteristic of black smoker vents varies between 1 and 99 within the core of the steady state plume with an average value of 55 on average over 50 of the excess heat within the plume originates from low me q ratio sources with a composition characteristic of low temperature diffuse flow vent fluids less than 4 of the volume of hydrothermal fluids in the plume originates from black smokers the fe ii concentrations were used to provide an estimate of plume age on a transect across the ridge axis plume ages were about 2 5 days on axis and 12 days off axis these plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222rn

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

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

field and laboratory studies of metal uptake and release by hydrothermal precipitates data for suspended particles from hydrothermal plumes on the mid atlantic ridge mar support uptake of dissolved v and as during formation of fe oxides and release of cu and cd during alteration of sulfides to complement these field observations we carried out laboratory time series experiments to determine the stability of v as cu and cd in precipitates from hydrothermal plumes on the mar and juan de fuca ridge for v and as the metal fe ratio in plume particles remained uniform after sampling in contrast to v and as particulate cu and cd values decreased relative to fe over time in laboratory studies using both plume particles and mound derived sulfides the combined field and laboratory results show that scavenging is an important removal mechanism for seawater v and as whereas oxidative dissolution of hydrothermal precipitates in seawater adds cu and cd to the ocean

vhf radar echoes observed in the summer and winter polar mesosphere over andoya norway the mobile sousy vhf 53 5 mhz radar has been operated on a campaign basis on the island of andoya in northern norway 69 17 n 16 01 e with the aim of investigating the backseattering structures and dynamics of the polar middle atmosphere since november 1983 during winter the occurrence of mesospheric echoes at altitudes from 50 to 90 km is strongly correlated with radio wave absorption events measured with a riometer on 32 5 mhz individual structures are observed for up to 8 hours and in general appear as thin layers separated by 3 5 km with typical maximum signal to noise ratios snrs of 5 25 db many of these are related to variations in the background wind produced by long period gravity waves and tidal period motions and in as much are similar to mesospheric layers at middle and low latitudes in summer the echo region is largely restricted to a height interval from 75 to 95 km with 80 of the echoes occurring in the 80 to 93 km height range and on average it has a distinct maximum in snr near 86 km in the 83 to 91 km height region echoes are detected almost continuously with a minimum occurrence rate of 85 there is a low correlation 0 26 between echo strength and absorption many of the weaker echoing regions those with snrs up to 30 db are related to the background wind shear spectral analysis of time series of both snr and zonal velocity for a period of 9 days reveals 54 24 12 and 8 hour components with the 12 hour component dominating strong bursts in backscattered power tend to occur in the late afternoon and early morning hours so they coincide with the time of maximum westward velocity of the semidiurnal tide this suggests that the bursts are due to an increase in the turbulent intensity produced by dynamical instability of this mode layers consistent with dynamically unstable upward propagating inertio gravity waves are also often observed to move down through the 93 to 80 km height range thus dynamical instability of the semidiurnal tide and long period gravity waves appears to play a major role in determining much of the structure observed in the backscatter region however the strongest summer polar mesopause echoes those with peak snrs greater than 30 db while showing modulation due to the background winds often show no clear relation to the background wind shear this supports the view that the production mechanism of the very strong snrs associated with this layer is different in character from that of winter echoes observed in the polar mesosphere by vhf radars and to those mesospheric layers observed at mid latitudes using the same technique

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

trace metals in hydrothermal solutions from cleft segment on the southern juan de fuca ridge concentrations of trace metals in fe and cl rich hydrothermal solutions from the southern juan de fuca ridge sjfr have been determined and corrected for residual precipitates formed in the sampler precipitate corrections for ag cd cu mo pb sb and zn were variable contributing an average of 20 to total solution concentrations whereas corrections for co averaged less than 5 and essentially no corrections were required for fe and mn values for cu co and mo in these solutions showed a strong dependence on temperature with sharp decreases in concentrations as temperatures decreased to less than 320 c in addition and unlike most other metals studied all vent fluids from the sjfr were almost completely depleted in mo relative to seawater values of about 110 nmol kg 1 in contrast to the cu co mo group concentrations of ag cd sb and pb correlated well with those for zn and are presumed to follow a distribution that is influenced less by temperature over the 246 to 332 c range encountered in this study and more by the combined chemical processes that control zn levels along the transport pathway from the deep reaction zone to the vent orifice

stress orientations from borehole wall fractures with examples from colorado east texas and northern canada azimuthally aligned breakouts in oil wells are explained as shear fractures in the zone of amplified stress difference near the borehole in a stress field having unequal horizontal principal stres

the seismotectonic character of the september 3 1978 swabian jura earthquake series abstract the year 1978 should be regarded as a period of relatively high seismic activity in the western swabian jura of southwestern germany the main shock on september 3 1978 with a surface wave magnitude ml 5 1 was recorded world wide and felt within a radius of 330 km prochaskova et al 1979 from over 300 shocks recorded in 1978 24 have been chosen for closer study these have a local magnitude of 3 0 or more and include earthquakes before and after the main shock the results of the study are summarized below 1 1 21 of the 24 earthquakes studied indicate left lateral horizontal strike slip 2 2 from the epicentral locations and the fault plane solutions two dominant fault plane strike directions are present these are n7 e and n22 e 3 3 a the average orientation of the tectonic stress field as determined from the 24 fault plane solutions is azimuth of major stress axis n146 e azimuth of minor stress axis n57 e b based on theoretical considerations in situ measurements and the results of the 24 fault plane solutions the angle of the maximum stress axis is n157 2 e 4 4 the hohenzollern graben does not influence the orientation of the tectonic stress field at depths greater than a few hundred metres the apparent influence on the direction of maximum stress is related to the definition of this direction and to the strike of the disturbance zone below the graben structure

cupri system configuration for nlc 91 and observations of pmse during salvo a the cornell university portable radar inter ferometer cupri provided nearly continuous monitor ing of the mesosphere above esrange sweden during the noctilucent cloud rocket and radar campaign of the sum mer of 1991 nlc 91 cupri probed the mesosphere above esrange from 78 to 91 km altitude with 300 meter resolution and was sensitive to the enhanced polar meso spheric summer echoes pmse that occur in the same altitude range as nlc formations out of the total of 264 hours of cup ri observation time p mse were present for 140 hours rocket salvo a was flown on the night of august 9 10 into an nlc event that occurred simul taneously with a thin and weakening pmse layer high resolution doppler spectrograms of this pmse event re vealed sawtooth like discontinuities at 83 km altitude which we interpret to be a distorted partial reflection layer which was advected across the radar beam

theory applied to the mid atlantic ridge hydrothermal plumes the finite difference approach a system of differential equations describing the entrainment of ambient seawater during the rise of a buoyant hydrothermal plume has been solved by an explicit finite difference method chosen for its ease of application an equation for tracer concentration has been added so that concentrations in the neutrally buoyant plume can be calculated for those elements whose background profiles vary over the depth range of the buoyant plume the height of plume rise can be related directly to the thermal and hydrothermal vent flux for the tag vent field 26 n mar five plume layers have been identified the calculated heat flux is 500 940 mw and the fluid flux is 0 210 0 392 m3 s 1 the fluid flux to the neutrally buoyant plume is 1460 2740 m3 s 1 calculated plume concentrations of mn compared with measurements made at tag in 1988 indicate that there is either 50 removal of manganese in the buoyant plume or that low temperature vent fluids contribute about 50 of the total thermal output of the tag vent field