evidence of active ground deformation on the mid ocean ridge axial seamount juan de fuca ridge april june 1988 since september 1987 a precision bottom pressure recorder bpr has been deployed within the summit caldera of axial seamount on the central juan de fuca ridge the instrument is capable of measuring pressure to 1 mbar resolution and recording these measurements at 64 samples per hour for up to 15 months after removal of oscillatory signals due to tidal and oceanographic effects and linear trends caused by sensor drift any significant change in the pressure record should indicate a change of depth associated with vertical ground movement in subaerial volcanic systems such ground movements commonly indicate active inflation or deflation of underlying magma bodies and are frequently coincident with rift eruptions axial seamount was selected for this pilot study for three primary reasons 1 its tectonic setting 2 the presence of a well formed summit caldera and 3 observational evidence of geologically recent volcanic activity results from the first 9 months of the bpr deployment revealed a significant change in pressure which is interpreted to represent a 15 cm subsidence of the caldera floor during two 2 to 3 week periods in april june 1988 also during these periods an anomalous decline in temperature at the site was recorded that is correlated with an apparent increase in current velocity at the axial seamount hydrothermal emissions study ashes vent field suggesting vigorous advection of cold water into the caldera concurrent oceanographic data from geosat and from current meter arrays do not indicate any large scale oceanographic phenomena capable of generating these simultaneous events one mechanism to explain simultaneous ground subsidence and temperature decline at the caldera center and increased bottom current at the caldera margin is the generation of a buoyant parcel of heated water in response to the intrusion or the eruption of magma associated with volcanic deflation such a parcel must have been sufficiently buoyant and proximal to induce horizontal entrainment currents capable of producing the bottom water conditions that were observed at both sites similar volcanic events also may have generated large midwater plumes that have been described previously along the southern juan de fuca ridge

chemical weathering in high sediment yielding watersheds new zealand 1 we have determined the chemical erosion yields for fifteen watersheds in new zealand ranging in size from 12 2 to 2928 km2 these rates coupled with previously measured physical erosion yields allow us to compare these two modes of landscape denudation the physical erosion yields are some of the highest measured in the world although in most instances the chemical erosion yields are only a small fraction of the total erosion yields the absolute values are very high our data strongly support the notion that chemical erosion rates are greatly influenced by the yield of physical erosion and that the rapid production of fresh surfaces as a result of high physical erosion rates and subsequent denudation is critical to the high chemical erosion yields observed

middepth flow near hydrothermal venting sites on the southern juan de fuca ridge long term moored current measurements around the southern end of the juan de fuca ridge show that flow parallels the ridge and may be intensified by its presence the mean flow is northward on the west side and southward on the east thus plumes emanating from the ridge probably are advected along the ridge before flowing away from the ridge other topographic features may be responsible for westward or eastward turning along the west side of the ridge we hypothesize a regional flow pattern with southward flow north of axial seamount northward flow south of axial and a convergence somewhere south of axial resulting in westward flow along the east side the flow may be southward everywhere above the ridge crest the long term mean flow is weaker and more variable and it includes tidal inertial and a dominant broadband 4 day oscillation this 4 day energy is maximum in the rift valley where the inertial is least decreases upward and away from the ridge and is more energetic in winter this oscillation is predominately a clockwise rotating feature which along with the presence of inertial oscillations suggests that it may be storm induced from the sea surface these observations along with those by cannon and pashinski 1990 suggest northward propagation flow variations across the ridge lasting one to a few months have mean speeds of 1 3 cm s and are capable of transporting plumes off axis to the west or east into the northerly or southerly flows respectively

geothermal heating and the properties of bottom water in cascadia basin 1 a new compilation of ctd data sheds light on the circulation and properties of bottom water within cascadia basin a relatively high salinity water mass is revealed in a region of likely bottom water inflow east of the blanco fracture zone water mass distributions and the deep geostrophic shear field are consistent with a general cyclonic circulation within the basin and suggest a northward flowing boundary current next to the deep continental slope shifts in temperature salinity relationships are consistent with a vertical transition from waters of northern origin to waters of southern origin approaching the seafloor this vertical water mass transition complicates the interpretation of temperature anomalies we redefine the temperature anomaly due to geothermal activity and the thickness of the layer influenced by seafloor heating simple heat budget calculations lead to a residence time of about one year for the bottom water shorter than suggested by previous studies

coherent and subsequent incoherent ringwoodite growth in olivine of shocked l6 chondrites abstract pervasive replacement of original olivine grains by ringwoodite adjacent to a shock melt vein of yamato 791384 l6 chondrite was observed with a feg sem in these olivines we observed three distinct olivine ringwoodite textures arranged in a spatially successive arrangement from the wall of the shock melt vein into the olivine grains 1 polycrystalline ringwoodite 2 oriented several sets of ringwoodite lamellae and 3 oriented single lamellae tem images show that the polycrystalline and oriented several sets of lamellae parts consist of polycrystalline ringwoodite indicating that phase transformation from olivine to ringwoodite is controlled by incoherent growth mechanism on the other hand the set of oriented single lamellae consists of thin ringwoodite platelets

mechanisms of ringwoodite formation in shocked meteorites evidence from l5 chondrite dhofar 1970 the formation of the high pressure compositional equivalents of olivine and pyroxene has been well documented within and surrounding shock induced veins in chondritic meteorites formed by crystallization from a liquid or solid state phase transformation typically polycrystalline ringwoodite grains have a narrow range of compositions that overlap with those of their olivine precursors whereas the formation of iron enriched ringwoodite has been documented from only a handful of meteorites here we report backscattered electron images quantitative wavelength dispersive spectrometry wds analyses qualitative wds elemental x ray maps and micro raman spectra that reveal the presence of fe rich ringwoodite fa44 63 as fine grained 500 nm polycrystalline rims on olivine fa24 25 wall rock and as clasts engulfed by shock melt in a previously unstudied l5 chondrite dhofar 1970 crystallization of majorite magnesiowustite in the vein interior and metastable mineral assemblages within 35 m of the vein margin attest to rapid crystallization of a superheated shock melt 2300 k from 20 25 gpa to ambient pressure and temperature the texture and composition of bright polycrystalline ringwoodite rims fa44 63 mno 0 01 0 08 wt surrounding dark polycrystalline olivine fa8 14 mno 0 56 0 65 wt implies a solid state transformation mechanism in which fe was preferentially partitioned to ringwoodite the spatial association between ringwoodite and shock melt suggests that the rapidly fluctuating thermal regimes experienced by chondritic minerals in contact with shock melt are necessary to both drive phase transformation but also to prevent back transformation

high pressure phases in a shock induced melt vein of the tenham l6 chondrite constraints on shock pressure and duration abstract the microtexture and mineralogy of a 580 m wide melt vein in the tenham l6 chondrite were investigated using field emission scanning electron microscopy and transmission electron microscopy to better understand the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide grains that crystallized from immiscible melts and sub rounded fragments of the host chondrite that have been entrained in the melt and transformed to polycrystalline high pressure silicates the melt vein matrix contains two distinct textures and mineral assemblages corresponding to the vein edge and interior the 30 m wide vein edge consists of vitrified silicate perovskite ringwoodite akimotoite majorite with minor metal sulfide the 520 m wide vein interior consists of majorite magnesiowustite with irregular metal sulfide blebs although these mineral assemblages are distinctly different the pressure stabilities of both assemblages are consistent with crystallization from similar pressure conditions the melt vein edge crystallized at about 23 25 gpa and the vein interior crystallized at about 21 25 gpa this relatively narrow pressure range suggests that the melt vein either crystallized at a constant equilibrium shock pressure of 25 gpa or during a relatively slow pressure release using a finite element heat transfer program to model the thermal history of this melt vein during shock we estimate that the time required to quench this 580 m wide vein was 40 ms because the entire vein contains high pressure minerals that crystallized from the melt the shock pressure duration was at least 40 ms using a synthetic hugoniot for tenham and assuming that the sample experienced a peak shock pressure of 25 gpa near the impact site we estimate that the tenham parent body experienced an impact with collision velocity 2 km s based on a one dimensional planar impact model we estimate that the projectile size was 150 m in thickness

compositional variability in the ascending fluxes from a hydrothermal plume 1 sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast pacific ocean between july 1994 and may 1995 one mooring was deployed near the main vent field on endeavour ridge on axis site 47 57 0 n 129 05 7 w a second 3 km west of the main vent site west site and the third 43 km northeast of the main vent site east or background site ascending and descending particles were collected near 1600 and 2000 m depth well above and within the top of laterally spreading hydrothermal plumes the elemental composition of particles was used to evaluate their origins biogenic fluxes were indicated by elevated ca or si hydrothermal fluxes by elevated fe mn and cu and lithogenic fluxes by elevated ti we link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean the relatively low hydrothermal fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material these results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below

a numerical study of stratified tidal rectification over finite amplitude banks part ii georges bank abstract tidal rectification over a two dimensional finite amplitude symmetrical bank is studied using the blumberg and mellor primitive equation coastal ocean circulation model ecom si in the homogeneous case the nonlinear interaction of tidal currents with the variable bottom topography generates an along isobath residual circulation over the bank which tends to increase as either the slope or height of the bank is increased in the stratified case internal waves at tidal and higher frequencies are generated over the sloping sides of the bank tidal mixing occurs in the bottom boundary layer leading to horizontal tidal mixing fronts the resulting stratified tidal rectification associated with the tidal mixing front the generation of internal tides and the modification of internal friction due to stratification leads to a subsurface intensification of the along isobath residual current at the front and at the top of the bottom mixed layer over the slope and a cross bank double cell circulation

high pressure minerals in shocked meteorites heavily shocked meteorites contain various types of high pressure polymorphs of major minerals olivine pyroxene feldspar and quartz and accessory minerals chromite and ca phosphate these high pressure minerals are micron to submicron sized and occur within and in the vicinity of shock induced melt veins and melt pockets in chondrites and lunar howardite eucrite diogenite hed and martian meteorites their occurrence suggests two types of formation mechanisms 1 solid state high pressure transformation of the host rock minerals into monomineralic polycrystalline aggregates and 2 crystallization of chondritic or monomineralic melts under high pressure based on experimentally determined phase relations their formation pressures are limited to the pressure range up to 25 gpa textural crystallographic and chemical characteristics of high pressure minerals provide clues about the impact events of meteorite parent bodies including their size and mutual collision velocities and about the mineralogy of deep planetary interiors the aim of this article is to review and summarize the findings on natural high pressure minerals in shocked meteorites that have been reported over the past 50 years

fate of event hydrothermal plumes on the juan de fuca ridge current meter moorings were deployed in august 1993 at the megaplume site of the june 1993 seismic event on the coaxial segment of the juan de fuca ridge and were recovered in april 1994 record averaged flow was about 2 cm s across axis which is sufficiently large to advect plumes off axis in a few days during july two megaplumes 1800 m level disappeared between repeated ctd tows a deeper plume 2150 m had a relatively strong signature during august and extended southeastward in agreement with the observed flow a ctd tow along the east flank of axial volcano did not locate remnants of the megaplumes but did find deeper plumes which could have come from off axis advection from the coaxial sources followed by southward advection along the east side of ridge

lagrangian measurement of mid depth currents in the eastern tropical pacific helium tracer data and basin scale steric height maps imply that there is an eastward flowing intermediate depth 1000 m countercurrent near 20 n in the eastern tropical pacific to measure this current directly we deployed profiling autonomous lagrangian current explorer p alace drifters at depths of 1000 and 1300 m near hawaii 19 n 156 w in june 1997 the deployment site marks the summit of loihi seamount an active hydrothermal venting region thought to be the source for the helium anomaly contrary to expectation the drifters first moved to the southwest then turned abruptly westward along 18 n the drifters maintained their westward trajectories for one year before stalling in an eddying region near 165 to 168 w the westward intermediate flow and location of the current reversal region observed by the drifters appear to be at variance with the average flow fields derived from the helium and steric height data

long term monitoring of hydrothermal heat flux using moored temperature sensors cleft segment juan de fuca ridge heat flux from submarine vent fields can vary gradually on interannual scales or nearly instantaneously in response to volcano tectonic events in the underlying crust neither case is well documented because measurements of vent field scale heat flux are scarce we report here a new approach to hydrothermal plume monitoring sensitive to both progressive changes and hydrothermal events from june 1991 to may 1992 we moored 35 self contained temperature sensors and six current meters on seven moorings located in and around the plume from a vent field on the cleft segment juan de fuca ridge the hydrothermal plume was identified by a local temperature anomaly of 0 01 to 0 03 c in the lowermost 200 m of the water column plume heat flux defined as the net advection of this temperature anomaly averaged about 250 mw during the deployment this flux is less than previous estimates and thus supports speculation that the heat flux is declining after a sudden reinvigoration triggered by a seafloor rifting event in 1986

a 6 year time series of hydrothermal plumes over the cleft segment of the juan de fuca ridge the causal links between magmatic tectonic processes and hydrothermal venting along the mid ocean ridge axis will be difficult to discern without broadband observations of the temporal variability of hydrothermal activity i report here on temporal variability in the intensity and distribution of chronic and event plumes generated by continuous and episodic hydrothermal discharge at two vent fields on the cleft segment of the juan de fuca ridge hydrothermal temperature and light attenuation c anomalies were comprehensively mapped between 1 and 4 times per year during nine cruises from 1986 to 1991 intensity of and c in the chronic plume overlying the north cleft vent field showed more variability between years than within a given year both and c were exceptionally high in 1986 fell to moderate levels during 1988 to 1990 and declined to minimum values in 1991 the chronic plume over the south cleft vent field varied similarly superimposed on the chronic plumes were brief and intense releases of hydrothermal fluid that created event plumes distinguishable by their symmetry and exceptional rise height event plumes at the north cleft field ranged from the 1986 megaplume with a rise height exceeding 1000 m to smaller events in 1987 and 1989 with rise heights of 400 m chronic hydrothermal heat 660 277 1 mw and mass 204 86 1 g s 1 fluxes from the north cleft field were determined by assuming these fluxes were equivalent to the long term net advection of a mean cross section of the vertically integrated and c in the plume this 6 year history of hydrothermal plumes indicates that episodic discharge has been an important component of the recent hydrothermal flux and that the aggregate heat and mass fluxes declined significantly though not consistently between 1986 and 1991

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

on the dynamics of current jets trapped to the flanks of mid ocean ridges 1 time mean abyssal current observations over the flanks of the east pacific rise epr at 9 10 n and at the juan de fuca ridge at 45 n document the occurrence of paired along ridge current jets that are trapped to the ridge flanks and sheared across the ridge in an anticyclonic sense a coincident feature where local hydrothermal discharge effects are not in play is the upward bowing of isopycnals over ridge crests and isopycnals plunging into ridge flanks it would be tempting to explain the jets primarily as geostrophic responses to the doming plunging isopycnal distribution though that should lead to the question as to how the isopycnal perturbations originate a numerical model of time dependent flow on a cross ridge x z transect forced in a way to be consistent with a yearlong hourly sampled record of currents measured at the epr ridge crest is used to investigate some of the underlying physics it will be shown that the jets can arise from oscillatory flows via eddy momentum eddy heat and eddy salt fluxes that ultimately cause the isopycnals to dome over the ridge as the probable offspring of velocity velocity and velocity density correlations that depend upon oscillatory motion the jets are likely examples of stratified topographic flow rectification an ancillary feature is a slight yearlong averaged downward current o 0 1 0 5 mm s over the epr ridge crest that crosses the time mean upward bowing isopycnals in a counter intuitive vertical direction

characteristics of 4 day oscillations trapped by the juan de fuca ridge current meter observations from different studies along the crest of the juan de fuca ridge have been combined to show new features of the relatively large broad spectral peak centered near a period of about 4 days the coherence range of the 4 day oscillations has been extended to the extreme ends of the ridge and the trapped waves appear to propagate northward along the entire length of the ridge at about 1 m s spectral amplitudes are about double on the south end compared to the north end and a recent model for bottom trapped subinertial waves over topography shows this may be due to variations in ridge width allen and thomson 1993 new observations show coherence between temperatures and currents near the south cleft vent field and suggest 4 day oscillations can play a major role in the local advection of hydrothermal plumes these observations combined with earlier results demonstrate that 4 day oscillations are a significant ridge trapped feature and they suggest that other ridges may be important in transmitting energy over much longer distances

from olivine to ringwoodite a tem study of a complex process the study of shock metamorphism of olivine might help to constrain impact events in the history of meteorites although shock features in olivine are well known so far there are processes that are not yet completely understood in shock veins olivine clasts with a complex structure with a ringwoodite rim and a dense network of lamellae of unidentified nature in the core have been reported in the literature a highly shocked s5 6 l6 meteorite asuka 09584 which was recently collected in antarctica by a belgian japanese joint expedition contains this type of shocked olivine clasts and has been therefore selected for detailed investigations of these features by transmission electron microscopy tem petrographic geochemical and crystallographic studies showed that the rim of these shocked clasts consists of an aggregate of nanocrystals of ringwoodite with lower mg fe ratio than the unshocked olivine the clast s core consists of an aggregate of iso oriented grains of olivine and wadsleyite with higher mg fe ratio than the unshocked olivine this aggregate is crosscut by veinlets of nanocrystals of olivine with extremely low mg fe ratio the formation of the ringwoodite rim is likely due to solid state diffusion controlled transformation from olivine under high temperature conditions the aggregate of iso oriented olivine and wadsleyite crystals is interpreted to have formed also by a solid state process likely by coherent intracrystalline nucleation following the compression shock release is believed to have caused opening of cracks and fractures in olivine and formation of olivine melt which has lately crystallized under postshock equilibrium pressure conditions as olivine

circulation hydrography and transport over the summit of axial seamount a deep volcano in the northeast pacific a numerical model of ocean flow hydrography and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around axial seamount a destination node of nsf s ocean observatories initiative s cabled array using an inverse method the model is made to approximate measured deep ocean flow around this site during a 35 day time period in the year 2002 the model is then used to extract month long mean patterns and examine smaller scale spatial and temporal variability around axial like prior observations model month long mean currents flow anti cyclonically around the seamount s summit in toroidal form with maximum speeds at 1500m depth of 10 11 cm s as a time mean the temperature salinity anomaly distribution takes the form of a cold briny dome above the summit passive tracer material continually released at the location of the ashes vent field exits the caldera primarily through its southern open end before filling the caldera once outside the caldera the tracer circles the summit in clockwise fashion fractionally re entering the caldera over lower walls at its north end while gradually bleeding southwestward during the modeled time period into the ambient ocean a second tracer release experiment using a source of only two day duration inside and near the casm vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8 9 days

dispersal of hydrothermal vent larvae at east pacific rise 9 10 n segment author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 123 11 2018 7877 7895 doi 10 1029 2018jc014290

mean hydrographic and velocity sections near pipe organ vent at juan de fuca ridge a composite cross ridge hydrographic and velocity section near the pipe organ vent site on the juan de fuca ridge is presented the hydrographic section is composed of surveys obtained from 1990 to 1994 the potential temperature field shows pronounced downward sloping of the isotherms below 1 9 centered at about 150 m above the bottom on either side of the ridge crest the horizontal scale is about 2 km comparable to the local rossby deformation radius the maximum potential temperature anomaly is greater than 0 03 c significant light attenuation anomalies are also present the mean along ridge velocity section is constructed from the records of 85 current meters the mean flow is southward at and to the east of the vent and northward to the west largest velocities occur at the depth of the neutrally buoyant plume the cross ridge shear is thus anti cyclonic with a characteristic value of 0 05f geostrophic velocity fields obtained from the density section differ significantly from the field produced from the current meter data an estimate of the net mean flux of anomalous heat gives 780 400 mw to the south

entrainment and bending in a major hydrothermal plume main endeavour field juan de fuca ridge 1 we measure expansion rate and bending in a 23 hour time series of acoustic images of the lower 25 m section of a buoyant hydrothermal plume rising from grotto vent in the main endeavour field juan de fuca ridge we then calculate entrainment coefficient the constant of proportionality relating mean inflow velocity at the plume edge to maximum mean upward velocity within the plume the plume section alternately bends southwest at relatively high inclinations 37 and northeast at lower inclinations at irregular intervals twice during this time period apparently driven by current reversals in the mixed semi diurnal tidal cycle the measured expansion rates 0 11 0 25 m m and calculated entrainment coefficients 0 07 0 18 are directly proportional to the degree of bending r2 0 75 the loss of buoyancy flux related to enhanced mixing in a stratified environment during bending may contribute to reduction of potential rise height consistent with predicted 400 m and measured 300 350 m plume tops

on subinertial oscillations trapped by the juan de fuca ridge northeast pacific spectra of currents measured along the 2100 m deep juan de fuca ridge in the northeast pacific have prominent tidal inertial and weather band 3 7 day period spectral peaks the weather band peak in particular has a number of interesting features it is strongest in close lateral proximity to the ridge and strongest near ridge depth intensification near the ridge is characteristic of trapped motion spectral peak intensities vary seasonally with largest amplitudes occurring in autumn and winter seasonal variation suggests that surface weather is forcing flow at depth together trapping and seasonality indicate opportunistic amplification of oscillatory motion at the ridge at all frequencies forcing topography and stratification together shape current and hydrographic distributions near the ridge effects of those interactions for subinertial motion are quantified here using a primitive equation numerical model forcing period 1 10 days and friction are the principal dependencies examined results show that flow over the juan de fuca ridge can be amplified by factors of 3 4 for diurnal and up to a factor of 7 for weather band frequencies amplification is ridge trapped with effects extending many hundreds of meters upward and extending 5 10 km laterally for 5 day period flow the strength and area of amplification increase with increasing period over the 1 to 10 day period band oscillatory weather band flow leads to vertical velocities on the order of 0 3 cm s 1 on ridge flanks which in turn cause periodic temperature t and salinity s variations with amplitudes of as much as 0 05 c and 0 01 practical salinity units respectively the vertical motion and consequent vertical displacement 100 m lead to isotherms that plunge below the crest alternately each side of the ridge a distribution observed in conductivity temperature depth transect data near the ridge crest cross ridge baroclinic pressure gradients caused by cyclically plunging isopycnals are in near geostrophic balance with the coriolis force associated with along ridge flow along ridge current amplification is therefore closely tied to isopycnal movement up and down ridge flanks since weather band oscillations lead to much larger cross ridge baroclinic pressure gradients than do diurnal motions of the same amplitude weather band forcing causes greater along ridge current amplification results vary strongly with forcing period and direction of forcing with respect to the ridge but depend only moderately on friction and turbulent mixing coefficients

composition and sedimentation of hydrothermal plume particles from north cleft segment juan de fuca ridge in 1990 and 1991 particles from buoyant and neutrally buoyant hydrothermal plumes above hydrothermal vents at the north cleft segment of the juan de fuca ridge were sampled to study their changing composition and fluxes away from the vent field in the rising buoyant plume 75 of the p v cr and as scavenging from seawater by hydrothermal precipitates occurs in the first 50 m above the vent cu and zn are most enriched in buoyant plume particles collected from the first few meters above the vent however the degree of enrichment decreases very rapidly with increased height above the vents due to sedimentation of the more dense cu and zn rich sulfide phases using the plume data coupled with the results of our analysis of sediment trap samples we estimated that more than 99 and 99 9 respectively of the total hydrothermal fe and mn produced at the vent field are transported beyond the vent field and dispersed in the open ocean

experiments on baroclinic vortex shedding from hydrothermal plumes laboratory experiments have been conducted to examine the effects of rotation on the structure and stability of hydrothermal plumes it is shown that the plume forces a baroclinic vortex consisting of an anticyclonic eddy at the neutral buoyancy level and cyclonic circulation in the ambient fluid around the rising plume these features agree qualitatively with speer s 1989 model however the experiments show that this state is unstable leading to the breakup of the plume and the unsteady generation of baroclinic vortices hetons that propagate away from the source two nearby plumes interact repulsively for separations nzs and initially coalesce for smaller separations here n is the buoyancy frequency is the coriolis frequency and zs is the height of the spreading level it is suggested that oceanic hydrothermal plumes may shed isolated baroclinic vortices which are capable of retaining anomalous properties temperature salinity 3he etc over large distances

short term variations in the distribution of hydrothermal plumes along a superfast spreading center east pacific rise 27 30 32 20 s 1 a multidisciplinary expedition to the southern east pacific rise 27 30 32 20 s provided an opportunity to compare the efficiency and effectiveness of two methods for mapping hydrothermal plumes the standard conductivity temperature depth optical ctdo tow yo method and a towed fixed array of hydrographic and optical sensors miniature autonomous plume recorders maprs six second order segments were mapped twice once with ctdo tow yos and then again with a fixed array of maprs attached to the cable of a deep towed side scan sonar we found a high degree of overall agreement between the two methods in both the distribution and optical intensity of hydrothermal plumes between survey differences increased as time between surveys increased from 6 days presumably because of advection of the plumes by local currents plume locations changed by as much as 10 km implying a confidence limit in predicting vent site location using segment scale hydrothermal plume surveys towed mapr arrays proved an efficient and effective method for acquiring coregistered geological and hydrothermal plume data

a forced baroclinic vortex around a hydrothermal plume a steady frictional flow around a hydrothermal plume is described which is forced by the entrainment of water into the buoyant part of the plume as it rises above its source the circulation is anticyclonic clockwise in the northern hemisphere near the equilibrium density level or spreading level of the plume and cyclonic below this level the strength of this flow is adequate to trap anomalous properties from the hydrothermal fluid near the source in the presence of weak background flow some observational support for such a flow is presented

transmission electron microscope observation of α β and γ mg fe 2sio4 in shocked meteorites planar defects and polymorphic transitions abstract high pressure polymorphs of olivine mg fe 2sio4 have been observed by transmission electron microscopy in the shocked tenham and catherwood meteorites planar defects are characterized in and polymorphs and their possible role in polymorphic transitions is assessed and discussed in relation with the published literature the stacking fault 1 2 1 01 010 observed in the phase can produce a shear transformation to the phase if it occurs on every other 010 plane conversely the stacking fault 1 2 1 1 2 110 observed in the phase can be transformed to the phase if it is repeated on every other 110 plane and to an intermediate yet unobserved e phase if it is repeated on every 110 plane shear transformation between olivine and spinel could involve the e phase as an intermediate stage

near inertial motions over a mid ocean ridge effects of topography and hydrothermal plumes we investigate the spatial structure of near inertial motions in the vicinity of the endeavour segment of juan de fuca ridge approximately 48 n 129 w in the northeast pacific ocean on the basis of time series current and water property data collected from september 1984 to september 1987 near inertial motions are ubiquitous features of the 2200 m water column with root mean square rms current speeds comparable to those of the dominant m2 tidal currents within the lower 1000 m of the water column where most of the observations were obtained near inertial oscillations have rms current speeds of o 1 cm s and vertical isotherm displacements of o 10 m the fluctuations are confined to the frequency band 0 966 1 079 f f is the local coriolis parameter and have characteristic event durations of 1 week although the spectra of subsurface motions are dominated by the blue shifted superinertial band significant spectral peaks are found also in the subinertial and inertial frequency bands marked alteration of the near inertial current amplitudes occurs over two well defined depth zones within the study region within the 200 m zone immediately above the 2100 m ridge crest current amplitudes are amplified by a factor of 1 2 1 7 because of bottom reflection and or scattering of the downward propagating energy evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross slope rotation of the near inertial current ellipses with increased proximity to the top of the ridge reflection would occur at grazing angles of less than 1 and would be associated with surface generated waves originating at distances of over 100 km from the observational site in contrast to the enhanced amplitudes immediately above the top of the ridge near inertial currents within the 1600 to 1800 m depth range undergo pronounced attenuation and frequency alteration amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow the increased shear is most likely associated with buoyancy induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest but it could also be related to bottom trapped oscillations over the steep ridge topography near inertial motions are estimated to have vertical coherence scales of the order of 10 100 m while horizontal coherence scales exceed the 50 km separation between the mooring locations minimum vertical and horizontal coherences are found for the depth zone 1600 1800 m while maximum correlation occurs for near bottom motions immediately above the crest of the ridge weak near inertial motions are observed within the 100 m deep axial valley

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

deep ocean circulation and transport where the east pacific rise at 9 10 n meets the lamont seamount chain 1 we report the first 3 d numerical model study of abyssal ocean circulation and transport over the steep topography of the east pacific rise epr and adjoining lamont seamount chain in the eastern tropical pacific we begin by comparing results of hydrodynamical model calculations with observations of currents hydrography and sf6 tracer dispersion taken during larval dispersal on the deep east pacific rise ladder field expeditions in 2006 2007 model results are then used to extend observations in time and space regional patterns are pronounced in their temporal variability at m2 tidal and subinertial periods mean velocities show ridge trapped current jets flowing poleward west and equatorward east of the ridge with time varying magnitudes weekly average maximum of 10 cm s 1 that make the jets important features with regard to ridge originating particle larval transport isotherms bow upward over the ridge and plunge downward into seamount flanks below ridge crest depth the passage p1 between the epr and the first lamont seamount to the west is a choke point for northward flux at ridge crest depths and below weekly averaged velocities show times of anticyclonic flow around the lamont seamount chain as a whole and anticyclonic flow around individual seamounts results show that during the ladder tracer experiment sf6 reached p1 from the south in the western flank jet a short lived change in regional flow direction just at the time of sf6 arrival at p1 started the transport of sf6 to the west on a course south of the seamounts as field observations suggest approximately 20 days later a longer lasting shift in regional flow from west to sse returned a small fraction of the tracer to the epr ridge crest

circulation near axial seamount year long moored current measurements from 1987 to 1988 on the saddle 1860 m between axial volcano and brown bear seamount show an oscillating flow with a broadband frequency centered at about 4 days and a long term average flow of about 4 cm s southward the measurements at sill depth also suggest a possible alternating exchange of water north and south of the cobb eickelberg seamount chain with warmer water 0 05 c coming from the north however measurements near the top of the volcano at about 1400 m show a weaker but northward mean flow and the 4 day oscillation barely exists conductivity temperature and depth ctd observations on the east side of the volcano infer possible intensification of southward flow adjacent to the juan de fuca ridge similar to that found with combined ctd and current meter observations about 100 km to the south southward flow is hypothesized along the entire east side of the ridge on the west side the axial brown bear saddle may be near a convergence zone between southward and northward currents which then flow westward the highly energetic environment on the saddle suggests other gaps in the ridge and seamount chains may be important in determining the fate of the hydrothermal effluents the general oceanic flow at the top of the caldera however is more tenuous and the depth of change between these two regimes cannot be determined

variations in mean currents affecting hydrothermal plumes on the juan de fuca ridge a summary of current meter observations near the juan de fuca ridge shows new features of topographic steering of flow that determine the fate of plumes from hydrothermal vents an anticyclonic circulation exists over the ridge with north and south mean flows along the west and east flanks speeds are up to 2 3 cm s 1 near the ridge and decrease to zero about 25 km from the crest contributions from hydrothermal forcing and tidal rectification may generate the along ridge flows average anomalous heat fluxes associated with the north and south flows were estimated at 1400 and 2600 mw respectively and they are larger than previous estimates based on single point current measurements variability of flow occurs on several time scales and space scales daily average currents over a 4 day period can rotate over the entire ridge with sufficient cross axis speeds to move plumes away from the vents into the stronger north south flows over the flanks currents along the west side of north cleft diverge with near ridge flow 10 km from the ridge turning eastward around the north end of the segment and offshore flow turning westward farther west in winter off axis currents can be several times as large as the long term mean and could advect plume water relatively long distances significant cross axis flow occurs on the north side of axial volcano that may be the result of interaction between the general circulation and topography generating eddy circulations around or near axial or the entire axial cobb massif

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

thermal modeling of shock melts in martian meteorites implications for preserving martian atmospheric signatures and crystallization of high pressure minerals from shock melts the distribution of shock melts in four shergottites having both vein and pocket geometry has been defined and the conductive cooling time over the range 2500 c to 900 c calculated isolated 1 mm2 pockets cool in 1 17 s and cooling times increase with pocket area an isolated vein 1 7 mm in northwest africa nwa 4797 cools to 900 c in 4 5 s interference between thermal haloes of closely spaced shock melts decreases the thermal gradient extending cooling times by a factor of 1 4 to 100 this is long enough to allow differential diffusion of ar and xe from the melt small pockets 1 mm2 lose 2 2 ar and 5 2 xe during cooling resulting in a small change in the ar xe ratio of the dissolved gas over that originally trapped with longer cooling times there is significant fractionation of xe from ar and the ar xe ratio increases rapidly the largest pockets show less variation of ar xe and likely preserve the original trapped gas composition considering all of the model calculations even the smallest isolated pockets have cooling times greater than the duration of the pressure pulse i e 0 01 s the crystallization products of these shock melts will be unrelated to the peak shock pressure experienced by the meteorite

the nature and significance of stacking faults in wadsleyite natural β mg fe 2sio4 from the peace river meteorite abstract the phase spinelloid polymorph of mg fe 2 sio 4 makes up a major part of the transition of the earth s mantle naturally occurring mg fe 2 sio 4 wadsleyite from the peace river meteorite was found to carry a variety of stacking faults the nature of which have been studied using high resolution transmission electron microscopy the faults lie on 010 and are generally of a complex nature best described in terms of various stacking sequences of the component spinelloid units the stacking faults locally transform the cation distribution so that in the plane of the fault the structure is that of spinel the development of such stacking faults is consequently a significant feature of the martensitic transformation of spinel to phase the possible occurrence of transformation enhanced plasticity associated with this inversion is discussed and the probable deformation mechanisms of mg fe 2 sio 4 are outlined

distribution and behavior of dissolved hydrogen sulfide in hydrothermal plumes through the deep ocean hydrothermal plumes disperse high concentrations of key chemical tracers including he 3 ch4 mn fe h2s etc this paper focuses on the distribution and behavior of total dissolved sulfide sulfide hereafter in hydrothermal plumes to show that its plume concentration decreases to subnanomolar a few kilometers from the vents we also report on sulfide removal rates determined at in situ conditions we observe that they are two orders of magnitude greater than for open ocean seawater consistent with sulfide being detected only in the vicinity of hydrothermal vents from our observations we infer that the sole presence of sulfide in hydrothermal plumes locates active venting at thekilometer scale

vertical and temporal vorticity observations at juan de fuca ridge hydrothermal signatures moored current measurements made from april 1994 to june 1995 reveal the vertical and temporal structure of the vorticity over the northern segment of the juan de fuca ridge at a depth of 2100m near the thermal and particle maximum associated with the neutrally buoyant hydrothermal plume the relative vorticity is anticyclonic with a mean value of nearly 0 09f with variability of the same magnitude this arises from cross ridge shear in the horizontal currents at this level in the vertical the anticyclonic shear has a peak value at plume level decreasing in magnitude both upward and downward from depths of 2100 2150m as the bottom is approached the transverse shear changes sign with cyclonic values of up to 0 09f below 2250m depth this vorticity signature is suggestive of dynamics of a line source of buoyant fluid entering the plume at its neutral density horizon and not due to individual point sources

excess 222rn above the cleft segment of the juan de fuca ridge the distributions of excess 222rn above the north cleft segment of the juan de fuca ridge were determined from 1988 to 1991 in order to obtain a better understanding of the temporal variability of heat flux from this ridge segment based on the inventories of excess 222rn the hydrothermal heat flux was estimated to be 2 7 1 3 gw in 1990 the large uncertainty results from errors in calculating the standing crop of 222rn the difficulty in determining the 222rn to heat ratio and the problem of entrainment of low temperature waters into the rising plume the high resolution sampling program carried out in 1990 permitted the mapping of apparent plume ages for different sections of the neutrally buoyant plume about 3 km to the east of the ridge axis there is a sharp gradient in the apparent age of the plume while to the west the plume appears to be younger this plume age distribution could indicate a current flow to the northwest during the time this transect was sampled the mean 222rn heat ratios for the high and low temperature vent fluids were 0 0017 disintegrations per minute dpm g 1 c 1 and 0 0044 dpm g 1 c 1 respectively the extrapolated end member concentrations of excess 222rn in low temperature vent fluids are a factor of 6 greater than the high temperature fluids based on the regressions of excess 222rn activity and mg concentration in north cleft segment vent fluid samples

iron ii distribution and oxidation kinetics in hydrothermal plumes at the kairei and edmond vent sites indian ocean deep sea hydrothermal activity cycles the entire volume of the global ocean through deep sea hydrothermal plumes at least every 4 8 103 a a rapid timescale that is comparable to global deep ocean mixing an important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids leading to the co precipitation of many other vent sourced metals thus modifying gross hydrothermal fluxes to the deep ocean and acting as a net sink in the ocean chemical budgets of certain key tracers here we report direct measurements of dissolved fe ii oxidation rates from two recently discovered indian ocean vent sites that are intermediate between pacific and atlantic values thus demonstrating that the rate of iron oxidation and formation of scavenging fe iii solid phases in hydrothermal plumes varies systematically along the global deep ocean conveyor the average pseudo first order rate constant for the oxidation reaction is 0 303 h 1 and the corresponding half life 2 31 h the rate plots show some curvature however indicating additional processes possibly interactions with organic matter may also influence the net oxidation removal rate different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge crest and ridge flank sediments

effects of the fieberling seamount group upon flow and thermohaline structure in the spring of 1991 the circulation and thermohaline structure around fieberling fieberling ii and hoke seamounts are examined on the basis of two high resolution surveys in april and may 1991 the large scale flow approached the seamounts from the southeast impinging first on hoke then splitting with one branch meandering westward in jetlike fashion over the fieberling ii and fieberling seamounts and the other turning to the northeast the jets were typically 10 20 km wide with core speeds of 0 2 0 5 m s and were accompanied by pairs of cyclonic and anticyclonic eddies with diameters of 10 30 km located near the seamounts while the large scale flow pattern persisted over a week significant changes were observed in the shape of the meanders and the locations of the eddies over this period transient bottom intensified upwelling cones 20 km in diameter and 150 220 m high were encountered on all three seamounts investigated as were pronounced 60 m deep mixed layers above the summits their persistence at a given location was less than a week geopotential height perturbations of the order of 0 8 j kg equivalent to 0 08 m in elevation were observed in the vicinity of the seamounts these perturbations are dominated by mesoscale ridges troughs peaks and depressions the positions of which vary with depth as well as time in general the surface geopotential topographies differ in shape from those observed at depths where the seamount peaks occur which is attributed to the vanishing influence of the california current beneath 200 m

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

tracing southwest pacific bottom water using potential vorticity and helium 3 abstractthis study uses potential vorticity and other tracers to identify the pathways of the densest form of circumpolar deep water in the south pacific termed southwest pacific bottom water spbw along the 28 2 kg m 3 surface this study focuses on the potential vorticity signals associated with three major dynamical processes occurring in the vicinity of the pacific antarctic ridge 1 the strong flow of the antarctic circumpolar current acc 2 lateral eddy stirring and 3 heat and stratification changes in bottom waters induced by hydrothermal vents these processes result in southward and downstream advection of low potential vorticity along rising isopycnal surfaces using 3he released from the hydrothermal vents the influence of volcanic activity on the spbw may be traced across the south pacific along the path of the acc to drake passage spbw also flows within the southern limb of the ross gyre reaching the antarctic slope in places and contributes via entrainment to the formation of

estimating compositions of natural ringwoodite in the heavily shocked grove mountains 052049 meteorite from raman spectra a combined raman spectroscopy and electron probe microanalysis study of the heavily shocked grove mountains grv 052049 meteorite revealed the largest chemical fractionation of natural ringwoodite and composition dependent variation of the intensities and or wavenumbers of raman bands with fa content atomic ratio of fe fe mg of ringwoodite varying from 27 8 to 81 6 mol the peak position of the single band around 290 cm 1 sb1 which relates to the sio4 translation mode shifts from 296 0 to 284 6 cm 1 and one of the doublets around 790 cm 1 db1 which relates to the symmetric stretching of sio4 shifts from 796 3 to 782 7 cm 1 in addition the relative intensities of sb1 and the other band of the doublet around 840 cm 1 db2 which relates to asymmetric stretching of sio4 increases with fa content based on the paired raman epma data single peak and two peak calibrations were established which can be used to derive fa contents of ringwoodite from the raman spectra the accuracy of raman derived fa content of ringwoodite is better than 5 mol the correlation of sb1 intensity with the fa content of ringwoodite suggests that the vibration of sb1 is enhanced with the substitution of mg2 by fe2 the correlation between raman spectra and the chemical composition of ringwoodite have potential applications in on line measurement of high pressure experiments and in situ mineralogical determination in future planetary explorations

shock metamorphism of elephant moraine a79001 implications for olivine ringwoodite transformation and the complex thermal history of heavily shocked martian meteorites abstract lithology a of martian meteorite elephant moraine eet a79001 contains fragments entrained within a 100 m thick shear induced shock vein these fragments the shock vein matrix and walls of olivine along the vein as well as shock deformation and transformation in rock forming minerals in the bulk rock were investigated using scanning electron microscopy the electron microprobe and raman spectroscopy the presence of ringwoodite the spinel structured high pressure mg fe 2 sio 4 polymorph has been confirmed in eeta79001 for the first time ringwoodite occurs within and around the shock vein exhibiting granular and lamellar textures in both textures ringwoodite consists of 500 nm size distinct grains ringwoodite lamellae are 115 nm to 1 3 m wide planar fractures in olivine provided sites for heterogeneous nucleation of ringwoodite analyses performed on the largest grains 1 m show that ringwoodite is consistently higher in iron fa 27 4 32 4 relative to surrounding olivine fa 25 1 267 7 implying that there was fe mg exchange during their transformation and therefore their growth was diffusion controlled in the shock environment diffusion takes place dynamically i e with concurrent deformation and grain size reduction this results in enhanced diffusion rates 10 8 m 2 s over nm m distances shock deformation in host rock minerals including strong mosaicism pervasive fracturing polysynthetic twinning pyroxene only extensive shock melting local transformation of olivine to ringwoodite and complete transformation of plagioclase to maskelynite in the bulk rock indicate that eeta79001 was strongly shocked the short shock duration 0 01 s combined with a complex thermal history resulted in crystallization of the 100 m thick shock vein in eeta79001 during the pressure release and partial back transformation of ringwoodite to olivine based on the pressure stabilities of clinopyroxene ringwoodite crystallization at the shock vein margin began at 18 gpa olivine and clinopyroxene crystallized at

tracking the dispersal of hydrothermal plumes from the juan de fuca ridge using suspended matter compositions in 1988 and 1989 particles from on and off axis neutrally buoyant plumes over the juan de fuca ridge were sampled to study their changing composition with distance from the ridge crest plume depth and particle composition in off axis hydrothermal plumes were used to identify plume sources and trajectories iron and phosphorus concentrations and in particular p fe molar ratios were found to be sensitive indicators of hydrothermal phases in the suspended matter phosphorus vanadium and arsenic are scavenged from solution where dissolved iron from hydrothermal vents oxidizes in seawater and forms submicrometer sized particles of fe oxyhydroxide the p fe molar ratio 0 23 is essentially the same for vent fields along cleft and endeavour segments indicating that the scavenging processes are the same for both regions high p fe ratios are observed over the south and north cleft segment vent fields and to the west along the vance seamount chain the seamounts evidently function as a barrier bathymetrically steering the hydrothermal plumes to the west away from the ridge crest since particles from the endeavour vent field are greatly enriched in copper relative to hydrothermal plumes from other vent fields along the juan de fuca ridge copper concentrations in the plumes can be used to distinguish plume sources based on water column depth and elemental composition hydrothermal plume particles from specific vent fields on the juan de fuca ridge may be tracked as much as several tens of kilometers from their source using particle compositions