mineral and gas chemistry of hydrothermal fluids on an ultrafast spreading ridge east pacific rise 17 to 19 s naudur cruise 1993 phase separation processes controlled by volcanic and tectonic activity during the naudur cruise in december 1993 23 dives using the french submersible nautile were conducted on the axis of the east pacific rise between 17 and 19 s where the spreading rate is among the fastest in the ocean 14 to 16 cm yr twenty hydrothermal fluids located at the topographic high of each segment in the axial domain were collected between 2573 and 2669 m depth on three segments centered respectively at 17 25 s 18 15 s and 18 26 s the fluids exhibit a very wide range of temperature chemical and gas compositions on the 17 25 s and 18 26 s segments fluids have quite uniform compositions low chlorinities are gas enriched and are low in dissolved metals relative to fluids from the 18 15 s segment which show high chlorinities are less gas enriched and show high metal concentrations chloride and metal depletion associated with gas enrichment is consistent with phase separation whereas ch 4 end members show large variations between sites the 13 ch 4 data are very similar with 13 c values in a narrow range 22 0 to 23 9 versus pee dee belemnite pdb 13 co 2 measured in fluids within the 18 15 s and 18 26 s segments are respectively 7 9 and 5 8 versus pdb similar to 13 c of co 2 trapped in mid oceanic ridge basalts suggesting a magmatic origin the variability in fluid composition is linked to the variability of the accretion process observed on the three segments the uniform venting of low chlorinity fluids in the 17 25 s and 18 26 s segments is connected with volcanic activity which causes boiling with preferential venting of vapor enriched fluids high salinity fluids are emitted on the 18 15 s segment where the ridge is tectonics dominated and subseafloor circulation controlled by faults phase separated effluents induced by volcanic and tectonic activity are delivered to the deep ocean in this area as previously observed on the juan de fuca ridge or in the north fiji basin ridge

accelerated ice mass depletion revealed by low degree gravity field from satellite laser ranging greenland 1991 2011 1 we detect the acceleration of ice mass depletion in greenland for the period 1991 2011 from the low degree gravity field up to degree and order 4 derived from the satellite laser ranging slr data between 2003 and 2011 during the era when the grace gravity recovery and climate experiment satellite data are available our slr results of gravity changes agree well with grace showing significant negative patterns in greenland prior to that the slr linear trend maps show a near balance in greenland ice mass during 1991 2002 after the glacial isostatic adjustment is accounted for using model values we further confirm the consistency of our slr results with the vertical crustal uplift of the region observed by the global positining system gps which manifests ice mass loading unloading thus the slr data series constitute a continuous benchmark for the time history of the greenland ice mass changes for over two decades

continuous sampling of hydrothermal fluids from loihi seamount after the 1996 event for at least 9 years prior to july 1996 hydrothermal fluids flowed from pele s vents on loihi seamount hawaii in july august 1996 a tectonic volcanic event occurred that destroyed pele s vents creating a pit crater pele s pit and several sites with hydrothermal venting in october 1996 we deployed two new continuous water samplers osmosamplers at two of these hydrothermal sites and collected fluids using traditional sampling techniques to monitor the evolution of crustal and hydrothermal conditions after the event the samplers were recovered in september 1997 and additional discrete vent fluid samples were collected the osmosampler located along the south rift at naha vents captured a change in composition from a low chlorinity high k fluid relative to bottom seawater to a high chlorinity low k fluid these changes are consistent with the fluid cooling during ascent and being derived from several different sources which include high 330 c and low 330 c into which magmatic volatiles were added during the deployment thermal and fluid fluxes decreased at naha the transport of heat and chemicals was decoupled the chemical and thermal evolution of hydrothermal fluids after the event on loihi is consistent with previous models based on events that have occurred along mid ocean ridges the event at loihi clearly had an effect on the local hydrography however the integrated effect of chemical fluxes to global budgets from similar events is uncertain chemical fluxes from similar events may have a global impact if ratios of chemical e g co2 fe mn mg sulfate and k to thermal anomalies greatly exceed or are in the opposite direction to fluxes from mid ocean ridge hydrothermal systems

bromide chloride fractionation in seafloor hydrothermal fluids from 9 10 n east pacific rise hydrothermal fluids collected from 9 10 n epr during 5 cruises between 1991 and 1994 were analyzed for br and cl the chlorinity of these fluids ranges between 32 6 and 860 mmol kg in comparison to local seawater values of 540 mmol kg these very low chlorinity fluids some with temperatures high enough to be within the vapor stability field were collected following a volcanic eruption in 1991 1 although fluids with chlorinities less than 250 mmol kg had been sampled once previously at axial volcano 2 the vent fluid chlorinities at 9 10 n epr were much lower than at axial volcano fluids with cl 250 mmol kg hadbr cl ratios identical to seawater in agreement with previous studies in contrast fluids with cl 250 mmol kg collected from this area hadbr cl ratios as much as 40 less than the seawater value bromide depletions observed in the low chlorinity fluids from 9 10 n epr were probably the result of fractionation of br from cl during subcritical phase separation this fractionation process appeared to be limited to fluids with cl 250 mmol kg and to require open system phase separation to produce vapors with cl 250 mmol kg at pressure and temperature conditions appropriate for 9 10 n epr requires conditions that are close to the critical point where the properties of the vapor and liquid phases are quite similar resulting in lack of fractionation in thebr cl ratio between the two phases

the quantum event of oceanic crustal accretion impacts of diking at mid ocean ridges seafloor diking eruptive events represent the irreducible quantum events of upper oceanic crustal accretion they record events by which a large portion of the oceanic crust has formed through geological history since 1993 the u s navy s real time sound surveillance system has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast pacific these diking eruptive events trigger a sequence of related rapidly evolving physical chemical and biological processes magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms some of which thrive in high temperature anaerobic environments many of the organisms identified from these systems are archaea if microorganisms can thrive in the water saturated pores and cracks within deep volcanically active portions of our planet other hydrothermally active planets may harbor similar life forms

analysis of fluid inclusions in seafloor hydrothermal precipitates testing and application of an integrated gc ic technique the principal research objective was to test an integrated gas gc and ion chromatographic ic technique for analysis of trapped fluids in seafloor hydrothermal precipitates and to compare the results with independently analyzed vent fluids twenty three samples of chalcopyrite pyrite sphalerite barite and anhydrite from hydrothermal chimneys from four seafloor sites axial seamount juan de fuca ridge the vai lili vent field lau basin the tag hydrothermal field mid atlantic ridge and the 21 n vent field east pacific rise as well as of pyrite marcasite and quartz from the tag mound were analyzed a new type of blank for sulphides and sulphates was also developed water contents obtained by gc analysis are in agreement with known compositions of seafloor hydrothermal solutions also the volatiles occur in the same order of abundance as in vent fluids co2 n2 co ar o2 ch4 cos c2 c3 hydrocarbons for all analyzed hydrothermal fluids the mean cl concentrations are similar to those for the respective measured vent fluid compositions furthermore the gc ic results are directly comparable to salinity data determined by microthermometric methods nh4 can be enriched and is most probably formed by decomposition of organic matter volatile concentrations in fluid inclusions and data from vent fluids differ significantly for some of the investigated sites furthermore the gc data indicate systematic variations regarding the volatile contents of trapped fluids from different active seafloor hydrothermal systems fluid inclusion volatile data of samples from the ashes vent field at axial seamount define an inclined array consistent with phase separation

axial summit trough of the east pacific rice 9 10 n geological characteristics and evolution of the axial zone on fast spreading mid ocean ridge the nature and morphological characteristics of axial summit troughs on fast 90 130 mm yr 1 full spreading rate and superfast spreading 130 mm yr 1 mid ocean ridge crests reflect the time integrated effects of long term magmatic cycles short term volcanic episodicity and the tensional stress regime imposed on young ocean crust two principal types of axial trough morphology have been identified and associated with distinct volcanic and tectonic processes occurring at fast and superfast spreading mid ocean ridge crests 1 narrow axial troughs 300 2000 m wide and 30 100 m deep on the east pacific rise crest are classified as axial summit graben the dimensions of axial summit graben as well as the morphological and structural character of their walls and floors suggest a primary tectonic origin an axial summit graben may contain a nested axial summit collapse trough implying that processes responsible for these endemic features may be linked near bottom side looking sonar and observational data collected using the towed vehicle argo i and submersible alvin have been used to characterize the axial summit trough of the fast spreading east pacific rise between 9 and 10 n a four stage model is presented for the evolution of this axial summit collapse trough as well as for other well studied portions of the east pacific rise crest from 21 n to 20 s we propose that the transition from a narrow surface collapse dominated axial trough to a broader fault bounded graben is controlled by the relative importance of diking volcanism hydrothermal cooling and tectonism along a ridge segment over time periods 104 years

phase separation and fluid mixing in subseafloor back arc hydrothermal systems a microthermometric and oxygen isotope study of fluid inclusions in the barite sulfide chimneys of the lau basin fluid inclusions in barite and sulfide in chimneys both active and inactive from three hydrothermal sites of the back arc lau basin were studied with microthermometric and isotopic methods to determine the chemistry and evolution of hydrothermal aqueous fluids strontium isotope compositions of sulfides from the lau basin reflect the presence of anhydrite and barite inclusions the 87sr 86sr ratios of these two sulfate minerals vary from 0 7045 to 0 7078 and are interpreted as the result of mixing between various proportions of the hydrothermal end member and pure seawater the microthermometric study of fluid inclusions reveals that mixing with seawater involved different kinds of aqueous fluid end members a high temperature mg depleted end member of high salinity 5 5 wt eq nacl was found at the vai lili site a uncommon low temperature mg rich end member was also identified at the hine hina site in association with barite deposition at the vai lili site very low salinity fluids were produced in addition to a very saline brine 30 wt nacl that was trapped inside anhydrite precipitated from an active vent at a temperature of 342 c oxygen isotope ratios of water inclusions range from 2 to 4 4 for chalcopyrite barite and sphalerite minerals the 18o enrichment and the high salinities of many fluids from the lau basin are accounted for by the specificity of the back arc setting this non mid ocean ridge setting is characterized by the shallow depth of the hydrothermal systems that allows frequent unmixing of high temperature liquids the abundance of silicic magmas also provided magmatic fluids including brines that mixed with seawater derived aqueous fluids

test of the predictability of the pi method for recent large earthquakes in and near tibetan plateau five large earthquakes of m 7 0 based on the magnitude scale of the china earthquake networks center occurred in and near the tibetan plateau during 2008 2014 including the wenchuan m8 0 earthquake on may 12 2008 bjt in this paper the tibetan plateau was chosen to be the study region and calculating parameters of pattern informatics pi method with grid of 1 1 and forecasting time interval of 8 years were employed for the retrospective study according to the previous studies for m7 earthquake forecasting the sliding step of forecasting interval was 1 year and the hotspot diagrams of each forecasting interval since 2008 were obtained year by year the relationships among the hotspots and the m 7 0 earthquakes that occurred during the forecast intervals were studied the predictability of pi method was tested by verification of receiveroperating characteristic curve roc and r score the results show that the successive obvious hotspots occurred during the sliding forecasting intervals before four of the five earthquakes while hotspots only occurred in one forecasted interval without successive evolution process before one of the five earthquakes which indicates that four of the five large earthquakes could be forecasted well by pi method test results of the predictability of pi method by roc and r score show that positive prospect of pi method could be expected for long term earthquake forecast

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

rare earth element distribution in 400 c hot hydrothermal fluids from 5 s mar the role of anhydrite in controlling highly variable distribution patterns abstract two submarine hydrothermal vent fields at 5 s mid atlantic ridge mar turtle pits and comfortless cove emanate vapor phase fluids at conditions close to the critical point of seawater 407 c 298 bars in this study the concentration and distribution of rare earth element ree and yttrium y has been investigated independent of the major element composition the fluids display a strong temporal variability of their ree y concentrations and relative distributions at different time scales of minutes to years chondrite normalized distributions range from common fluid patterns with light ree enrichment relative to the heavy ree accompanied by positive eu anomalies type i to strongly ree y enriched patterns with a concave downward distribution with a maximum enrichment of sm and weakly positive or even negative eu anomalies type ii the larger the sum of ree the smaller cecn ybcn and eu eu we also observed a strong variability in fluid flow and changing fluid temperatures correlating with the compositional variability as evident by the positive correlation of total ree ca and sr concentrations in turtle pits and comfortless cove fluids precipitation dissolution of hydrothermal anhydrite controls the variability in ree concentrations and distributions in these fluids and the transformation of one fluid type to the other the variable distribution of ree can be explained by the accumulation of particulate anhydrite with concave downward ree distribution and negative eu anomaly into a fluid with common ree distribution type i followed by the modification of the ree fluid signature due to dissolution of incorporated anhydrite a second model in which the type ii fluids represent a primary ree reaction zone fluid pattern which is variably modified by precipitation of anhydrite can also explain the observed correlations of total ree fractionation of lree hree and size of eu anomaly as well as ca sr the emanation of such a fluid may be favored in a young hydrothermal system in its high activity phase with short migration paths and limited exchange with secondary minerals however this model is not as well constrained as the other and requires further investigations the strongly variable ree fluid signature is restricted to the very hot actively phase separating hydrothermal systems turtle pits and comfortless cove at 5 s and has not been observed at the neighboring red lion vent field which continuously emanates 350 c hot fluid and displays a stable ree distribution type i

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

time variable gravity from grace first results eleven monthly grace gravity field solutions are now available for analyses we show those fields can be used to recover monthly changes in water storage both on land and in the ocean to accuracies of 1 5 cm of water thickness when smoothed over 1000 km the amplitude of the annually varying signal can be determined to 1 0 cm results are 30 better for a 1500 km smoothing radius and 40 worse for a 750 km radius we estimate the annually varying component of water storage for three large drainage basins the mississippi the amazon and a region draining into the bay of bengal to accuracies of 1 0 1 5 cm

integrated fe and s isotope study of seafloor hydrothermal vents at east pacific rise 9 10 n abstract in this study we report on coupled fe and s isotope systematics of hydrothermal fluids and sulfide deposits from the east pacific rise at 9 10 n to better constrain processes affecting fe isotope fractionation in hydrothermal environments we aim to address three fundamental questions 1 is there significant fe isotope fractionation during sulfide precipitation 2 is there significant variability of fe isotope composition of the hydrothermal fluids reflecting sulfide precipitation in subsurface environments 3 are there any systematics between fe and s isotopes in sulfide minerals the results show that chalcopyrite precipitating in the interior wall of a hydrothermal chimney displays a limited range of 56fe values and 34s values between 0 11 to 0 33 and 2 2 to 2 6 respectively the 56fe values are on average slightly higher by 0 14 relative to coeval vent fluid composition while 34s values suggest significant s isotope fractionation 0 6 0 2 during chalcopyrite precipitation in contrast systematically lower 56fe and 34s values relative to hydrothermal fluids by up to 0 91 and 2 0 respectively are observed in pyrite and marcasite precipitating in the interior of active chimneys these results suggest isotope disequilibrium in both fe and s isotopes due to s isotopic exchange between hydrothermal h2s and seawater so42 followed by rapid formation of pyrite from fes precursors thus preserving the effects of a strong kinetic fe isotope fractionation during fes precipitation in contrast 56fe and 34s values of pyrite from inactive massive sulfides which show evidence of extensive late stage reworking are essentially similar to the hydrothermal fluids multiple stages of remineralization of ancient chimney deposits at the seafloor appear to produce minimal fe isotope fractionation similar affects are indicated during subsurface sulfide precipitation as demonstrated by the lack of systematic differences between 56fe values in both high temperature fe rich black smokers and lower temperature fe depleted vents

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

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

210po 210pb dating of recent volcanic eruptions on the sea floor the globe encircling mid ocean ridge system accounts for most of the earth s volcanism and influences its heat budget morphology and the composition of the oceans it is therefore important to constrain the size frequency and compositional variability of ridge eruptions but this is made difficult by the remoteness of much of the sea floor and the paucity of applicable radioactive chronometers remote monitoring has provided indirect evidence for active ridge volcanism1 3 which in some cases has been strengthened by submersible observations4 5 but it has not been possible to date these eruptions directly here we present a new chronometer based on 210po 210pb radioactive disequilibrium which allows us to date glassy eruption products within a few years of their eruption our first results on lavas from 9 50 n on the east pacific rise confirm that the ridge erupted only months before sample collection and indicate that the eruptions extended over at least one year the chronometer begins with po volatilization during eruption all glasses analysed were 75 100 degassed a crystalline pillow interior was 20 degassed however implying that the flow surface may control po degassing during deep submarine eruptions although the 210po 210pb chronometer is useful for only a short time frame it should prove valuable for dating recent but unobserved submarine eruptions and determining details of eruptive sequences

geochemistry of north cleft segment vent fluids temporal changes in chlorinity and their possible relation to recent volcanism hydrothermal vent fluids from the north cleft segment of the juan de fuca ridge between 44 54 and 45 00 n were sampled in 1988 1990 1991 and 1992 in 1988 chloride depleted relative to seawater diffuse fluids with low dissolved metal concentrations relative to other mid ocean ridge mor fluids were sampled over a distance of 10 km along axis in 1990 and 1991 both high temperature 200 c and diffuse vents were consistently metal and chloride enriched the end member compositions of high temperature vents and nearby diffuse vents were very similar there were small but significant correlated changes in diffuse and high temperature composition from 1990 to 1991 the large scale but temporary venting of low chlorinity fluids over the entire north cleft segment provides a resolution to the apparent mass imbalance implied by observations of continuous venting of chloride enriched fluids it is possible that a volcanic event along the north cleft segment prior to 1987 for which there is firm geologic evidence initially caused a boiling event which resulted in the preferential venting of vapor enriched fluids through 1988 followed by a transition to brine enriched fluids by 1990 high iron low sodium and low sr ca ratios in the high chlorinity fluids suggest that the brine phase has continued to react and approach reequilibration with an alteration mineral assemblage after the phase separation event the absence of chloride depleted fluids from 1990 onward and the systematics of lithium boron and manganese with chloride in the high temperature fluids from north cleft suggest that the evolution toward lower chlorinity at monolith vent from 1990 to 1992 is caused by progressive dilution of a brine with hydrothermal seawater

geophysical interpretation of observed geocenter variations geocenter variations are caused by mass redistribution within the earth system especially the atmosphere oceans and continental water using surface pressure fields and soil moisture and snow depth fields of the ncep ncar climate data assimilation system i cdas i 1 we estimate contributions from variations in atmospheric surface pressure and continental water storage to the earth s geocenter center of mass variation in addition sea surface anomalies determined by the topex poseidon altimeter are used to investigate geocenter variations resulting from ocean mass redistribution these sea surface height data were corrected using a simplified steric model a comparison with observed geocenter variations derived from lageos 1 and 2 satellite laser ranging data indicates that the atmosphere oceans and continental hydrological cycle all provide significant contributions at different frequencies geocenter variations estimated in this paper are in reasonably good agreement with results given by dong et al 1997 for atmospheric and ocean contributions but not for the estimates of continental hydrological contributions

quartz solubility in the two phase and critical region of the nacl kcl h2o system implications for submarine hydrothermal vent systems at 9 50 n east pacific rise abstract experiments were performed to investigate quartz solubility in cl bearing aqueous solutions at temperature 365 430 c and pressure conditions 219 381 bars near and within the two phase region of the nacl kcl h2o system dissolved sio2 concentrations increased with pressure along a given isotherm although the magnitude of this decreased with increasing proximity to the two phase boundary upon intersection of the two phase boundary however significant concentrations of dissolved sio2 characterized vapor rich fluids at both subcritical and supercritical conditions for these fluids dissolved silica concentrations ranged from 2 81 to 14 6 mmolal increasing with dissolved chloride concentration the experimental data permit regression of a density based relationship taking account of non ideal activity concentration effects which can be used to better constrain temperatures and pressures from dissolved sio2 and chloride in high temperature vent fluids at mid ocean ridges accordingly pressure and temperature conditions in subseafloor hydrothermal reaction zones at 9 50 n east pacific rise epr were estimated applying data from this experimental study to interval 1991 2002 and new field data 2004 results indicate reaction zone at conditions ranging from 420 to 430 c at 600 to 1500 m below seafloor thus conditions predicted for 9 50 n east pacific rise epr vent fluids suggest that supercritical phase separation might be more common than previously thought

geochemistry of hydrothermal fluids from the ultramafic hosted logatchev hydrothermal field 15 n on the mid atlantic ridge temporal and spatial investigation abstract mantle derived ultramafic rocks commonly occur on the seafloor at slow spreading axes and are tectonically emplaced along shear zones since the early 1990s a growing number of hydrothermal systems have been detected in ultramafic settings but chemical data for fluid compositions in active systems are still limited besides the logatchev field at 15 n on the mid atlantic ridge mar the only other active high temperature 300 c hydrothermal field known to be strongly influenced by ultramafics is the rainbow field at 36 n on the mar the field at logatchev consists of six active vent sites at about 3000 m water depth situated along a nw se trending line with distances of 50 200 m between the individual sites the vent sites were mapped in detail and re sampled during two cruises in 2004 and 2005 using a rov the geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen up to 3 5 mm and 19 mm respectively related to serpentinization processes in the reaction zone together with moderate si concentrations of 9 mm a depletion in b compared to seawater and li concentrations lower than in basaltic systems this fluid composition has been identified as characteristic signature of high temperature hydrothermal fluids reacting with ultramafic rocks however additional alteration of gabbroic intrusions is likely the fluid composition is very similar at all vent sites indicating a common source in the reaction zone and little variation during upflow spatial differences in fluid composition were observed between smoking craters and the complex chimney system irina ii but are restricted to elements with strong temperature controlled solubility as cu and co these differences can be related to different exit temperatures up to 350 c and as it is known that more ultramafic hosted hydrothermal systems exist along slow spreading ridges this type of hydrothermal systems might have a significant influence on the elemental budget of the oceans detailed information about the fluid geochemistry and its spatial and temporal variations is an important prerequisite for an estimation of elemental fluxes in ultramafic hosted systems and their relative importance compared to basaltic hosted systems

parameters of subsurface brines and hydrothermal processes 12 15 months after the 1999 magmatic event at the main endeavor field as inferred from in situ time series measurements of chloride and temperature 1 phase separation at mid ocean ridge hydrothermal systems is a widely distributed frequently occurring process it is highly sensitive to dynamic subsurface pressure and temperature conditions and has a significant impact on chloride concentrations of hydrothermal fluid although vapor phases produced by phase separation are observed in a variety of hydrothermal settings observation of conjugate brines that must be produced concurrently are more rare and the fate of subsurface brines is still not well understood here we use an array of in situ chloride sensors deployed at the main endeavor field on the juan de fuca ridge in the wake of a magmatic event to monitor the behavior of hydrothermal vent effluent with high temporal resolution our results provide evidence of near critical chloride depleted fluids within the crust up to 486 m beneath the seafloor we estimate that a brine reservoir stored beneath the main endeavor field is constrained to temperatures between 131 c and 326 c for chloride concentrations ranging from 6 to 25 wt nacl respectively our data suggest that subsurface fluids and circulation pathways vary widely over spatial scales on the order of meters under these circumstances simultaneous measurements of multiple fluid parameters at a high temporal resolution are essential to understanding subsurface hydrothermal processes associated with magmatic events

sub sea floor boiling of red sea brines new indication from noble gas data hydrothermal brines from the atlantis ii deep red sea have been sampled in situ and analyzed for noble gases the atmospheric noble gas concentrations ne aratm kr xe in the deepest layer lcl are depleted by 20 to 30 relative to the initial concentrations in ambient red sea deep water without a systematic mass fractionation between the different noble gases sub surface boiling during the hydrothermal circulation and subsequent phase separation is shown to be a consistent explanation for the observed depletion pattern using a conceptual model of phase separation under sub critical conditions in which gases are partitioned according to henry s law we reconstruct the fluid history before injection into the atlantis ii deep after having circulated through evaporites and young oceanic crust where it becomes enriched in hemorb and armorb the ascending fluid boils and the residual liquid becomes depleted in noble gas concentrations the depleted fluid rises to the sediment surface and feeds the atlantis ii basin the relatively low boiling degree of about 3 i e the percentage of fluid removed as vapor derived from the model indicates that the atlantis ii system represents an early stage of boiling with relatively small gas loss in contrast to hydrothermal systems at sediment free mid ocean ridges

tectonic evolution of the mesozoic songpan ganze orogenic belt in the eastern margin of tibetan plateau constraints from structural analyses and 40ar 39ar dating

alaskan mountain glacial melting observed by satellite gravimetry abstract we use satellite gravity measurements from the gravity recovery and climate experiment grace as an indication of mass change to study potential long term mountain glacial melting in southern alaska and west canada the first 3 5 yr of grace monthly gravity data spanning april 2002 november 2005 show a prominent glacial melting trend in the mountain regions around the gulf of alaska goa grace observed surface mass changes correlate remarkably well with available mass balance data at gulkana and wolverine two benchmark glaciers of the u s geological survey usgs although the grace signals are smaller in magnitude in addition terrestrial water storage tws changes estimated from an advanced land surface model show significant mass loss in this region during the same period after correcting for the leakage errors and removing tws contributions using model estimates we conclude that grace observed glacial melting in the goa mountain region is equivalent to 101 22 km 3 yr which agrees quite well with the assessment of 96 35 km 3 yr based on airborne laser altimetry data and is consistent with an earlier estimate based on the first 2 yr of grace data this study demonstrates the significant potentials of satellite gravity measurements for monitoring mountain glacial melting and regional climate change

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

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

chemistry of vent fluids and its implications for subsurface conditions at sea cliff hydrothermal field gorda ridge we report here the first compositional data for fluids from the sea cliff hydrothermal field northern gorda ridge collected in 2000 2002 and 2004 an unusual aspect of this site is its location 2 6 km east of the axis of spreading leading to speculation since its discovery in 1988 that this may be an older hydrothermal field as it occurs on crust that the spreading rate would predict to be 100 000 years old our results suggest this hydrothermal system is being driven by subsurface magma as evidenced by 1 elevated 3he heat ratios 2 relatively high concentrations of he and 3 chloride contents less than seawater in the hydrothermal fluids the measured fluid temperatures were 308 c but we infer they were 400 c at depth in spite of these elevated temperatures the fluids exiting from these vents are clear a consequence of extremely low transition metal concentrations we attribute the low transition metal contents to loss of these metals below the seafloor most likely as a result of the slightly elevated ph of the fluids neither the fluid compositions nor the setting provides evidence that buried sediments and or organic matter are responsible for raising the fluid ph our favored explanation for the elevated ph is that calcite deposited as a vein filling mineral at this site perhaps when it was closer to the axis and a hydrothermal downflow zone is currently being dissolved by the hydrothermal fluids this hypothesis is supported by our geochemical modeling results that suggest the fluids are close to saturation with calcite at in situ conditions elevated fluid ph is observed at a number of hydrothermal sites on the global mid ocean ridge system and the reason for this has not been well understood dissolution of previously deposited calcite may be a heretofore unrecognized mechanism that can explain these observations finally our data suggest the compositions of these fluids are unchanged from 2002 to 2004 and are consistent with water column observations first made at this site in 1985 we therefore interpret the sea cliff site to be another hydrothermal area marked by long term stability in fluid compositions and temperatures

sr isotope variations in vent fluids from 9 46 9 54 n east pacific rise evidence of a non zero mg fluid component abstract sr isotopic variations in vent fluids from six high temperature hydrothermal vents from between 9 46 n and 9 54 n on the east pacific rise are reported the mg sr 87sr 86sr systematics of one vent biovent require the presence of a fluid component that has experienced significant mg depletion 50 but has undergone very little sr exchange with local basalts this fluid component accounts for 3 to 10 of the biovent samples by volume similarities between the composition of the inferred fluid component and that of bore hole fluids sampled from hole 504b suggest that this fluid component is modified seawater partially reacted with basalt at temperatures less than 150 c and subsequently entrained by high temperature vent fluids previously reported vent fluid data from 12 50 n east pacific rise suggest that the presence of the additional lower temperature fluid component admixed in biovent samples may not be unique among seafloor hydrothermal systems if such a fluid component is common in seafloor hydrothermal systems it will need to be considered in estimates of axial hydrothermal fluxes if not accounted for properly the presence of an additional fluid component can bias calculated end member 87sr 86sr ratios after correction for the influence of the additional fluid component on the biovent samples the calculated end member 87sr 86sr ratio of this vent is 0 7041 other nearby vents p vent and bio9 are slightly more radiogenic 0 7042 a and l vents from the southern portion of the study area have end member 87sr 86sr ratios that are less radiogenic 0 7039 and 0 7037 respectively the reason for the greater influence of seawater derived sr in the more northern vents is not known but it may be related to entrainment of seawater in the upflow zone

time variable gravity from space and present day mass redistribution in theearth system abstract since 2002 the us german grace gravity recovery and climate experiment mission has been providing a precise survey of earth s time variable gravity field with unprecedented temporal and spatial sampling grace time variable gravity fields provide a means of measuring temporal and spatial variations of mass redistribution within the earth system the grace mission has launched a new era in studying a series of geophysical problems ranging from deep earth structure to tracking mass redistribution on and near the surface of the earth grace has greatly improved understanding of mass redistribution in various compartments of the climate system atmosphere oceans terrestrial water and cryosphere in this review we use examples to show how grace has fundamentally enriched a number of fields including but not limited to the global water cycle and land hydrology mass balance of polar ice sheets and mountain glaciers ocean mass and global sea level change and solid earth geophysics

postseismic signature of the 2004 sumatra earthquake on low degree gravity harmonics 1 we perform an extensive analysis of the low degree gravity field harmonics measured by the grace mission in order to find a signature of the postseismic relaxation following the 2004 sumatra earthquake we find a statistically significant perturbation in the secular trend of low degree zonal coefficients jl in correspondence of the 2004 sumatra earthquake and a similar perturbation but with weak associated statistical significance also in the nonzonal coefficients technical features and results of such analysis are discussed the time dependent postseismic evolution of harmonic coefficients is modeled for various asthenosphere viscosity values using a theoretical model of global postseismic deformation the observed change in secular trend is found to be consistent with our modeling results but it cannot be used to discriminate between viscosities a forward modeling of the perturbations to time dependent zonal variation rates following the sumatra earthquake for various asthenospheric viscosities is provided as a result an evident signature of the sumatra earthquake on l time series is expected for asthenospheric viscosity values below 1018 pa s therefore long term l time histories from satellite laser ranging will be able to put constraints on the asthenosphere viscosity if such a signature is evidenced from data or at least put lower limits if no significant perturbation will be observed

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

prokaryote communities at active chimney and in situ colonization devices after a magmatic degassing event 37 n mar emso azores deep sea observatory the mixing zone between high temperature hydrothermal fluids and seawater produces redox gradients promoting the development of unique ecosystems based on chemotrophy the structure of microbial communities depends on their environment which can vary according to space and time hydrothermal circulation within the oceanic crust determines the chemical composition and flow of fluids depending on underground events earthquakes volcanic episodes and impacts the development of microbial communities this link between hydrothermal vent communities and deep geological events is the focus of the present study the first of its kind for slow spreading ridge in this study we present a unique set of multidisciplinary data collected from 2008 to 2011 on the eiffel tower hydrothermal site lucky strike vent field mid atlantic ridge we benefit from continuous geophysical monitoring temperature seismicity of the site annual sampling of hydrothermal fluids hot and diffuse for geochemistry analyses sampling of hydrothermal chimneys and an in situ microbial colonization experiments over a year for microbial study the high co2 content and concentrations of major elements cl ca si and so4 in the end member fluids collected in 2010 indicate that a magmatic degassing occurred between 2009 and 2010 under the lucky strike hydrothermal field this is supported by the large temperature variations observed in march april 2010 these magmatic co2 inputs seem to have affected microbial communities colonizing the high temperature chimney as well as the basalts in the more diffuse and mixed zone promoting the development of thermophilic anaerobic archaea and bacteria archaeoglobales nautiliales nitratiruptoraceae

independent patterns of water mass anomalies over australia from satellite data and models the gravity recovery and climate experiment grace products allow the quantification of total water storage tws changes at global to regional scales however the quantity measured by grace represents mass signals integrated over vertical columns requiring their separation into their original sources such a separation is vital for australia for which grace estimates are affected by leakage from the surrounding oceans the independent component analysis ica method that uses higher order statistics is implemented here to separate grace derived water storage signals over the australian continent from its surrounding oceans covering from october 2002 to may 2011 the performance of ica applied to grace is then compared to the ica of watergap global hydrology model wghm and the ica of the australian water resources assessment awra system to study the influence of rainfall variability on the derived independent patterns use is made of tropical rainfall measuring mission trmm data set from january 2000 to may 2011 implementing ica on grace tws showed a remarkable improvement in separating the continental hydrological signals from the surrounding oceanic anomalies which was not achievable using a conventional principle component analysis reconstructing the continental tws changes using only those independent components of grace that were located over the continent showed a high correlation with wghm tws and awra tws mass concentrations over the oceans and particularly s2 semi diurnal aliased pattern were separated as independent modes correlation analysis between the independent components of grace and climate teleconnections showed that the mass anomalies over the northern ocean gulf of carpentaria and north eastern parts of australia were significantly correlated with the el nino southern oscillation while those over south and south eastern parts of australia were mainly linked to the indian ocean dipole

low degree spherical harmonic influences on gravity recovery and climate experiment grace water storage estimates we estimate terrestrial water storage variations using time variable gravity changes observed by the gravity recovery and climate experiment grace satellites during the first 2 years of the mission we examine how treatment of low degree gravitational changes and geocenter variations affect grace based estimates of basin scale water storage changes using independently derived low degree harmonics from earth rotation eop and satellite laser ranging slr observations grace based water storage changes are compared with estimates from nasa s global land data assimilation system gldas results from the 22 grace monthly gravity solutions covering the period april 2002 to july 2004 show remarkably good agreement with gldas in the mississippi amazon ganges ob zambezi and victoria basins combining grace observations with eop and slr degree 2 spherical harmonic coefficient changes and slr observed geocenter variations significantly affects and apparently improves the estimates especially in the mississippi ob and victoria basins

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

low degree gravitational changes from grace validation and interpretation 1 we examine low degree gravitational variations c21 s21 and c20 observed by the gravity recovery and climate experiment grace satellites during the first 2 years of this gravity mission the grace observations are compared with independent estimates from accurately measured earth rotational changes and predictions from atmospheric oceanic and hydrological models the 18 grace monthly gravity solutions covering the period april 2002 to march 2004 show strong seasonal variability in the c21 s21 and c20 time series and generally agree with earth rotation derived changes and geophysical model estimates in particular for s21 and c20 the reason for the poorer agreement between the grace results and the earth rotation derived estimates for c21 is unclear we demonstrate that the omission of the ocean pole tide in the grace data processing does have significant effects on the estimated c21 and s21

a fluorescein tracer release experiment in the hydrothermally active crater of vailulu u volcano samoa 1 on 3 april 2001 a 20 kg point source of fluorescein dye was released 30 m above the bottom of the active summit caldera of vailulu u submarine volcano samoa vailulu u crater is 2000 m wide and at water depths of 600 1000 m with the bottom 200 m completely enclosed it thus provides an ideal site to study the hydrodynamics of an active hydrothermal system the magmatically driven hydrothermal system in the crater is currently exporting massive amounts of particulates manganese and helium the dispersal of the dye was tracked for 4 days with a fluorimeter in tow yo mode from the u s coast guard icebreaker polar sea lateral dispersion of the dye ranged from 80 to 500 m d 1 vertical dispersion had two components a diapycnal diffusivity component averaging 21 cm2 s 1 and an advective component averaging 0 025 cm s 1 these measurements constrain the mass export of water from the crater during this period to be 8 1 3 4 6 107 m3 d 1 which leads to a turnover time for water in the crater of 3 2 days coupled with temperature data from ctd profiles and mn analyses of water samples the power output from the crater is 610 100 350 mw and the manganese export flux is 240 kg d 1 the mn heat ratio of 4 7 ng j 1 is significantly lower than ratios characteristic of hot smokers and diffuse hydrothermal flows on mid ocean ridges and points to phase separation processes in this relatively shallow hydrothermal system

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

origin of a barite sulfide ore deposit in the mykonos intrusion cyclades trace element isotopic fluid inclusion and raman spectroscopy evidence abstract the polymetallic mykonos vein system in the cyclades greece consists of 15 tension gashes filled with barite quartz pyrite sphalerite chalcopyrite and galena in ca 13 5 ma i type mykonos monzogranite zones of silica and chlorite muscovite alteration are associated with the veins and overprint pervasive silicification phyllic and argillic alteration that affected large parts of the monzogranite the mineralization cements breccias and consists of an early barite silica pyrite sphalerite chalcopyrite assemblage followed by later argentiferous galena a combination of fluid inclusion and stable isotope data suggests that the barite and associated mineralization were deposited from fluids containing 2 to 17 wt nacl equivalent at temperatures of 225 to 370 c under a hydrostatic pressure of 100 bars the mineralizing fluids boiled and were saturated in h 2 s and so 2 calculated 18 o h2o and d h2o initial 87 sr 86 sr isotope compositions and the trace and rees elements contents are consistent with a model in which the mineralizing fluids were derived during alteration of the mykonos intrusion and subsequently mixed with miocene seawater heterogeneities in the calculated 34 s so4 2 and 34 s h2s compositions of the ore fluids indicate two distinct sources for sulfur namely of magmatic and seawater origin and precipitation due to reduction of the so 4 2 during fluid mixing the physicochemical conditions of the fluids were ph 5 0 to 6 2 log f s2 13 8 to 12 5 log f o2 31 9 to 30 9 log f h2s g 1 9 to 1 7 log f te2 7 9 and log so 4 2 aq h 2 s aq 2 6 to 5 5 we propose that retrograde mesothermal hydrothermal alteration of the mykonos monzogranite released barium and silica from the alkali feldspars barite was precipitated due to mixing of so 4 2 rich miocene seawater with the ascending ba rich magmatic fluid venting upwards in the pluton

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

hydrothermal alteration processes at midocean ridges experimental and theoretical constraints from ca and sr exchange reactions and sr isotopic ratios diabase and basalt were reacted with na ca k cl fluids of seawater chlorinity at 375 425 c 375 400 bars and fluid rock mass ratios of 0 5 1 0 to assess the role of basalt chemistry and texture on sr and ca mobility during high temperature hydrothermal alteration an additional experiment utilizing an 84sr spiked fluid was performed to help quantify reaction rates of processes affecting sr mobility the experimental results help to constrain reaction processes responsible for the chemistry of hot spring fluids at midocean ridges alteration of basalt and diabase is characterized by formation of tremolite actinolite smectite chlorite and clinozoisitic epidote smectite chlorite respectively diabase alteration produced dissolved sr ca ratios similar to those observed for ridge crest hot spring fluids whereas alteration of a mostly crystalline basalt produced significantly lower ratios this observation supports the premise that the sr ca ratios observed in vent fluids may be produced during deep seated reaction of the hydrothermal fluids with diabase dikes and or gabbro at relatively low fluid rock ratios and suggests that hydrothermal alteration of primary igneous minerals at relatively high temperatures 400 c leads to formation of a mineral with low dsr ca possibly hydrothermal plagioclase results of the 84sr spiked experiment indicated that only 4 of the sr in basalt was mobilized after 800 hours of reaction despite the fact that b and li were nearly quantitatively leached it is thus suggested that b and li are good indicators of the amount of fresh rock encountered by fluids while sr concentration and isotopic data can be used to estimate the degree of alteration that the sr bearing primary minerals have undergone the degree of alteration of subsurface reservoirs may be estimated by dividing the fluid rock ratio obtained for highly mobile elements by the fluid rock ratio obtained from path integrated sr isotope and concentration data based on this method for example it can be estimated that only 5 of the primary sr bearing minerals encountered by fluids in the subsurface at epr 21 n are actually converted to secondary phases

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

hydrothermal fe fluxes during the precambrian effect of low oceanic sulfate concentrations and low hydrostatic pressure on the composition of black smokers abstract modern mid ocean ridge hydrothermal systems typically release vent fluids to the ocean with dissolved h2s in excess of fe these fluids are the consequence of high temperature interactions between sulfate rich seawater and mid ocean ridge basalt at conditions near the critical point for seawater the precipitation of fes and fes2 during venting titrates most of the fe from the fluid significantly reducing the net flux of fe to the open ocean here we suggest that hydrothermal fluids emanating from precambrian seafloor systems older than 1 8 ga had fe h2s ratios 1 and with fh2 higher than today because seawater lacked its primary oxidant dissolved sulfate ion this predominance of fe over h2s would have promoted the establishment of an iron rich deep ocean and the deposition of banded iron formations bif accordingly the end of bif deposition at 1 8 ga was the result of the buildup of sulfate in seawater from oxidative weathering and its return at 750 ma the result of reductions in seawater sulfate concentrations during snowball earth episodes enhanced by elevated fe concentrations during depressurization of hydrothermal systems by large eustatic sea level falls moreover precambrian chemosynthetic vent communities may have been based on h2 synthesis rather than on h2s oxidation as they largely are today

structural style and tectonic significance of the jianglang dome in the eastern margin of the tibetan plateau china abstract the jianglang tectonic dome jtd lies on the eastern margin of the tibetan plateau and consists of three tectono stratigraphic units separated by two extensional detachment faults a schist complex a middle ductile slab and an overlying sedimentary unit the schist complex is composed of quartz mica schists and amphibolites of possible mesoproterozoic age and exhibits two early foliations s 1 and s 2 overprinted by two later foliations s 3 and s 4 the ductilely deformed middle slab consists of paleozoic quartzite phyllite marble amphibolite and meta basalt it is characterized by pervasive intrafolial and intraformational recumbent folds with a penetrative axial foliation s 1 an equivalent of s 3 in the basement rocks the cover unit the triassic xikang group of flysch sedimentary rocks experienced shallow level buckling and flattening deformation with an axial cleavage defining s 1 an equivalent of s 4 in the middle slab and basement rocks the jtd appears to have experienced three stages of extension immediately after orogeny the earliest d 1 recorded by an axial surface s 1 of s 0 intrafolial folds and sub parallel to s 0 in the schist complex probably occurred prior to the collision between the south china and north china blocks this extensional event was followed by subduction of the yangtze block to the west towards the eastern margin of the tibetan plateau the two detachment faults are characterized by structures formed by ductile brittle to brittle shear deformation which are sub parallel to the layer of s 2 in the lower detachment and to s 0 in the upper detachment these faults mark the second stage of extension and may have caused thinning and selective removal of the sinian and paleozoic strata as well as exhumation of the schist complex and the middle slab in the middle jurassic 177 ma the final stage of extension d 5 shown by brittle deformation and thermo metamorphism from the lower detachment to the xikang group was associated with the indian eurasia collision

zinc stable isotopes in seafloor hydrothermal vent fluids and chimneys many of the heaviest and lightest natural zinc zn isotope ratios have been discovered in hydrothermal ore deposits however the processes responsible for fractionating zn isotopes in hydrothermal systems are poorly understood in order to better assess the total range of zn isotopes in hydrothermal systems and to understand the factors which are responsible for this isotopic fractionation we have measured zn isotopes in seafloor hydrothermal fluids from numerous vents at 9 10 n and 21 n on the east pacific rise epr the tag hydrothermal field on the mid atlantic ridge and in the guaymas basin fluid 66zn values measured at these sites range from 0 00 to 1 04 of the many physical and chemical parameters examined only temperature was found to correlate with fluid 66zn values lower temperature fluids 250 c had both heavier and more variable 66zn values compared to higher temperature fluids from the same hydrothermal fields we suggest that subsurface cooling of hydrothermal fluids leads to precipitation of isotopically light sphalerite zn sulfide and that this process is a primary cause of zn isotope variation in hydrothermal fluids thermodynamic calculations carried out to determine saturation state of sphalerite in the vent fluids support this hypothesis with isotopically heaviest zn found in fluids that were calculated to be saturated with respect to sphalerite we have also measured zn isotopes in chimney sulfides recovered from a high temperature 383 c and a low temperature 203 c vent at 9 10 n on the epr and in both cases found that the 66zn of chimney minerals was lighter or similar to the fluid 66zn the first measurements of zn isotopes in hydrothermal fluids have revealed large variations in hydrothermal fluid 66zn and suggest that subsurface zn sulfide precipitation is a primary factor in causing variations in fluid 66zn by understanding how chemical processes that occur beneath the seafloor affect hydrothermal fluid 66zn zn isotopes may be used as a tracer for studying hydrothermal processes

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

direct observation of the evolution of a seafloor black smoker from vapor to brine a single hydrothermal vent f vent occurring on very young crust at 9 16 8 n east pacific rise was sampled in 1991 and 1994 in 1991 at the measured temperature of 388 c and seafloor pressure of 258 bar the fluids from this vent were on the two phase curve for seawater these fluids were very low in chlorinity and other dissolved species and high in gases compared to seawater and most sampled seafloor hydrothermal vent fluids in 1994 when this vent was next sampled it had cooled to 351 c and was venting fluids 1 5 times seawater chlorinity this is the first reported example of a single seafloor hydrothermal vent evolving from vapor to brine the 1991 and 1994 fluids sampled from this vent are compositionally conjugate pairs to one another these results support the hypothesis that vapor phase fluids vent in the early period following a volcanic eruption and that the liquid phase brines are stored within the oceanic crust and vent at a later time in this case 3 years these results demonstrate that the venting of brines can occur in the same location in fact from the same sulfide edifice where the vapor phase fluids vented previously

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

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

ensemble prediction and intercomparison analysis of grace time variable gravity field models precise measurements of the earth s time varying gravitational field from the nasa deutsches zentrum fur luft und raumfahrt gravity recovery and climate experiment grace mission allow unprecedented tracking of the transport of mass across and underneath the surface of the earth and give insight into secular seasonal and subseasonal variations in the global water supply several groups produce these estimates and while the various gravity fields are similar differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns this study examined the spatial temporal and spectral variations between the different gravity field products and developed an ensemble gravity field solution from the products of four such analysis centers the solutions were found to lie within a certain analysis scatter regardless of the local relative water height variation and the ensemble model is clearly seen to reduce the noise in the gravity field solutions within the available scatter of the solutions

hydrothermal mineral deposits and fossil biota from a young 0 1 ma abyssal hill on the flank of the fast spreading east pacific rise evidence for pulsed hydrothermal flow and tectonic tapping of axial heat and fluids heat flow data indicate that most hydrothermal heat loss from ocean lithosphere occurs on the flanks of the mid ocean ridge but few ridge flank hydrothermal sites are known we describe the first nonseamount abyssal hill hydrothermal mineral deposits to be recovered from the fast spreading east pacific rise epr flanks deposits were sampled at two sites on an abyssal hill 5 km east of the epr axis just north of clipperton fracture zone at 10 20 n on 0 1 ma lithosphere tevnia site is on the axis facing fault scarp of the hill and ochre site is located 950 m farther east near the base of the outward facing slope clusters of fragile biodegradable tevnia worm tubes at both sites indicate that hydrothermal fluids carried sufficient h2s to sustain tevnia worms and that fluid flow waned too recently to allow time for tube destruction presence of microbial mats and other biota also are consistent with recent waning of flow the deposits are mineralogically zoned from nontronite celadonite to hydrous fe oxide opaline silica to mn oxide birnessite and todorokite this places them into a distinctive class of fe si mn hydrothermal deposits found along tectonic cracks and faults in young oceanic crust and suggests that 1 deposits precipitated along an o2 gradient between ambient seawater and hydrothermal fluid 2 fluid temperatures were 150 c and 3 undiluted fluids were mg depleted and fe k si and mn enriched these fluids may derive from high temperature seawater basalt interaction phase separation proximal to the axial melt zone and lose cu and zn before venting due to conductive cooling and or ph increase ochre site samples are purely hydrothermal however tevnia site samples incorporate volcanic sedimentary and fossil components and exhibit at least three generations of fracturing and hydrothermal cementation the tevnia site breccias accumulated on the exposed fault scarp possibly during multiple slip events and hydrothermal pulses as the abyssal hill was uplifted we hypothesize that frequent earthquakes rejuvenate young abyssal hill hydrothermal systems episodically over 104 105 years tapping axial heat and hydrothermal fluids sustaining biota and likely helping to chill the margins of the axial melt zone

optimized smoothing of gravity recovery and climate experiment grace time variable gravity observations 1 high degree and high order spherical harmonics of time variable gravity fields observed by the gravity recovery and climate experiment grace gravity mission are dominated by noise we develop two smoothing methods that suppress these high degree and high order errors with results superior to more commonly used gaussian smoothing these optimized smoothing methods considerably improve signal to noise levels of grace terrestrial water storage estimates relative to residual signal and noise over the oceans and show significantly better spatial resolution and lower leakage error on the basis of analysis using an advanced land surface model the equivalent spatial resolution from these optimized smoothing estimates is about 500 km compared to the roughly 800 1000 km gaussian smoothing that is required to suppress high degree noise in the grace fields

chemistry of hot springs along the eastern lau spreading center abstract the eastern lau spreading center elsc is the southernmost part of the back arc spreading axis in the lau basin west of the tonga trench and the active tofua volcanic arc over its 397 km length it exhibits large and systematic changes in spreading rate magmatic tectonic processes and proximity to the volcanic arc in 2005 we collected 81 samples of vent water from six hydrothermal fields along the elsc the chemistry of these waters varies both within and between vent fields in response to changes in substrate composition temperature and pressure ph water rock ratio and input from magmatic gases and subducted sediment hot spring temperatures range from 229 to 363 c at the five northernmost fields with a general decrease to the south that is reversed at the mariner field the southernmost field vai lili emitted water at up to 334 c in 1989 but had a maximum venting temperature of only 121 c in 2005 due to waning activity and admixture of bottom seawater into the subseafloor plumbing system chloride varies both within fields and from one field to another from a low of 528 mmol kg to a high of 656 mmol kg and may be enriched by phase separation and or leaching of cl from the rock concentrations of the soluble elements k rb cs and b likewise increase southward as the volcanic substrate becomes more silica rich especially on the valu fa ridge iodine and 7li increase southward and 11b decreases as b increases apparently in response to increased input from subducted sediment as the arc is approached species that decrease southward as temperature falls are si h2s li na cl fe mn and 87sr 86sr whereas ph alkalinity ca and sr increase oxygen isotopes indicate a higher water rock ratio in the three systems on valu fa ridge consistent with higher porosity in more felsic volcanic rocks vent waters at the mariner vent field on the valu fa ridge are significantly hotter more acid and metal rich less saline and richer in dissolved gases and other volatiles including h2s co2 and f than the other vent fields consistent with input of magmatic gases the large variations in geologic and geophysical parameters produced by back arc spreading along the elsc which exceed those along mid ocean ridge spreading axes produce similar large variations in the composition of vent waters and thus provide new insights into the processes that control the chemistry of submarine hot springs

composition of hydrothermal fluids and mineralogy of associated chimney material on the east scotia ridge back arc spreading centre abstract the east scotia ridge is an active back arc spreading centre located to the west of the south sandwich island arc in the southern ocean initial exploration of the ridge by deep tow surveys provided the first evidence for hydrothermal activity in a back arc setting outside of the western pacific and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments e2 and e9 here we report the chemical and isotopic composition of high and low temperature vent fluids and the mineralogy of associated high temperature chimney material for two sites at e2 dog s head and sepia and four sites at e9 black white ivory tower pagoda and launch pad the chemistry of the fluids is highly variable between the ridge segments fluid temperatures were 350 c at all vent sites except black white which was significantly hotter 383 c end member chloride concentrations in e2 fluids 532 536 mm were close to background seawater 540 mm whereas cl in e9 fluids was much lower 98 220 mm indicating that these fluids are affected by phase separation concentrations of the alkali elements na li k and cs and the alkaline earth elements ca sr and ba co vary with cl due to charge balance constraints similarly concentrations of mn and zn are highest in the high cl fluids but by contrast fe cl ratios are higher in e9 fluids 3 8 8 1 10 3 than they are in e2 fluids 1 5 2 4 10 3 and fluids with lowest cl have highest cu although both ridge segments are magmatically inflated there is no compelling evidence for input of magmatic gases to the vent fluids fluid d values range from 0 2 to 1 5 ph values 3 02 3 42 are not especially low and f concentrations 34 6 54 4 m are lower than bottom seawater 62 8 m the uppermost sections of conjugate chimney material from e2 and from ivory tower and pagoda at e9 typically exhibit inner zones of massive chalcopyrite enclosed within an outer zone of disseminated sulphide principally sphalerite and pyrite in an anhydrite matrix by contrast the innermost part of the chimneys that currently vent fluids with lowest cl black white and launch pad is dominated by anhydrite by defining and assessing the controls on the chemical composition of these vent fluids and associated mineralisation this study provides new information for evaluating the significance of hydrothermal processes at back arc basins for ocean chemistry and the formation of seafloor mineral deposits