chlorine cycling during subduction of altered oceanic crust eclogitic rocks that have experienced devolatilization with little or no interaction with external fluid sources can be viewed as analogues of crustal material which may be transferred back into the mantle during subduction thus they can be used to evaluate the extent of the recycling of volatile elements such as chlorine we report new oxygen isotope ratios of omphacite and fluid inclusion data determined from eclogitic metagabbros of the rocciavre massif italian alps the data are compared with those obtained for the monviso cyclades and the franciscan complex high pressure rocks in all localities relics of early dehydration fluids are preserved as primary fluid inclusions in the cores of omphacite megacrysts rocciavre monviso and franciscan complex or garnet cyclades salinity estimates of the inclusion fluids range from 32 to 45 wt nacl in rocciavre 17 to 21 wt nacl in monviso and are similar to seawater in other areas omphacite and bulk rock 18o values of rocciavre 5 1 6 8 and monviso 3 0 5 3 metagabbros are markedly lower than those of cyclades 6 8 14 3 and the franciscan 6 7 13 1 metabasites the fluid salinity 18o systematics of eclogitic rocks is similar to that documented along a typical section of the altered oceanic crust and unmetamorphosed ophiolites this suggests that high pressure metamorphism and associated processes did not modify significantly the variability in chlorine concentrations and oxygen isotope ratios inherited from a stage of sea floor hydrothermal alteration under low basaltic layer and high temperature gabbroic layer conditions respectively extrapolating the estimated h2o and cl contents of eclogitic rocks to a representative section of the subducted oceanic crust indicates that a minimum of 100 to 200 ppm cl could be recycled into the mantle during subduction this yields a cl h2o ratio of 3 6 to 7 5 10 2 for the subducted oceanic crust which is similar to e morb on the basis of available cl isotopic data we infer that a large proportion 70 of the cl stored in the altered crust should be recycled to the mantle to generate an isotopic composition of the subducted crust equivalent to the source of unaltered mid ocean ridge basalt 37cl 4 7

effects of short term variations in sea level on dissolved oxygen in a coastal karst aquifer quintana roo mexico sea level rise should cause salt water intrusion into coastal aquifers and limit fresh submarine groundwater discharge pargos spring offshore of puerto morelos quintana roo mexico intermittently discharges brackish water and allows intrusion of lagoon water with seawater salinity to the aquifer lagoon water intrusion occurred when sea level was 0 08 m above mean observed values during the study period salt water intrusion will be permanent within a few decades at the current eustatic sea level rise rate of 3 mm yr a mixing model demonstrates that oxygen dissolved in the lagoon water is reduced as it intrudes the spring dissolved oxygen do reduction is greater at the spring vent than at sensors 10 m inside the conduit reflecting rapid reaction kinetics do reduction results from organic carbon remineralization which also releases n and p to the water increased frequency of intrusion events or continuous intrusion may alter microbially mediated biogeochemical reactions thereby increasing aquifer vulnerability to sea level rise

high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

electromagnetic surveying in current middle eastern archaeology application and evaluation since 1977 the smithsonian institution has had a major research program on the human biological history of the near east as part of this program electromagnetic em surveying methods have been extensively used to identify anomalies of potential archaeological significance below the surface an em 31 noncontacting terrain conductivity meter was used in jordan bahrain kuwait and egypt with excellent results in addition to the successful application of em equipment to archaeological problems we investigated the equipment s response to changing environmental and climatic conditions we have developed efficient methods for recording em data the following results were obtained recording accuracy is better than previously reported 0 97 percent repeatability error between two observers the degree of accuracy is primarily a function of operator error and less a function of equipment reliability and the em 31 produces helpful highly reproducible results in the arid and semiarid environment of the mi

the chlorine isotopic composition of martian meteorites 1 chlorine isotope composition of martian mantle and crustal reservoirs and their interactions the martian meteorites record a wide diversity of environments processes and ages much work has been done to decipher potential mantle sources for martian magmas and their interactions with crustal and surface environments chlorine isotopes provide a unique opportunity to assess interactions between martian mantle derived magmas and the crust we have measured the cl isotopic composition of 17 samples that span the range of known ages martian environments and mantle reservoirs the 37cl of the martian mantle as represented by the olivine phyric shergottites nwa 2737 chassignite and shergotty basaltic shergottite has a low value of approximately 3 8 this value is lower than that of all other planetary bodies measured thus far the martian crust as represented by regolith breccia nwa 7034 is variably enriched in the heavy isotope of cl this enrichment is reflective of preferential loss of 35cl to space most basaltic shergottites less shergotty nakhlites chassigny and allan hills 84001 lie on a continuum between the martian mantle and crust this intermediate range is explained by mechanical mixing through impact fluid interaction and assimilation fractional crystallization

chlorine stable isotopes and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean abstract chlorine stable isotopes 37cl and halogen concentrations e g br cl in 168 pore fluids and 23 serpentines and other solids from three subduction zones the nankai trough costa rica and mariana forearc provide critical information on fluid sources flow paths and reaction conditions the 37cl values of pore fluids at the nankai and costa rica subduction zones are significantly more negative minimum 7 8 2 0 3 than seawater value 0 at nankai trough the minimum 37cl value is situated below the decollement and evolves laterally from 7 8 at the most arcward odp site 808 to 7 1 at site 1174 2 km seaward from site 808 and to 5 8 at the reference site 1173 at costa rica along the decollement the minimum 37cl value evolves from 5 5 at the most arcward odp site 1040 1254 to 3 2 at site 1043 1255 1 km seaward and to 0 at the reference site 1039 1253 at both subduction zones the br cl ratios are higher than the seawater value 1 5 10 3 and also show seaward evolutions these pore fluids originate from greater depth arcward at 250 c from hydrous mineral formation that preferentially incorporates 37cl and excludes br in contrast the 37cl values in the pore fluids at the mariana serpentine mud volcanoes are higher than the seawater value 0 3 to 1 8 and the br cl ratios are lower these pore fluid values and the high cl concentrations with positive 37cl values 1 2 to 6 0 in the serpentines support that the upwelling pore fluid originates from dehydration of the subducting slab that releases water enriched in 37cl into the fluid phase the constancy of the ocean 37cl over the past 200 ma suggests that the isotopically fractionated chlorine in serpentinites and the cl exchanged in subduction zones are efficiently recycled back into seawater if the efficiency is

dehydration of subducting serpentinite implications for halogen mobility in subduction zones and the deep halogen cycle we investigated the halogen cl f br and i chemistry of serpentinites that record progressive dehydration during subduction from shallow oceanic environments via increased pressure and temperature conditions to complete breakdown of antigorite the aim is to evaluate the relevance of serpentinites for halogen recycling in subduction zones and for deep mantle recharge of these elements the halogen compositions of the analyzed samples indicate input from seawater and sedimentary sources during initial serpentinization of either subducting lithospheric mantle during slab bending or forearc mantle by uprising slab fluids during the first dehydration stage antigorite brucite olivine h2o fluids with high br cl and i cl ratios are released resulting in residual serpentinites with lower br cl and i cl ratios veins associated with this event and with the final antigorite breakdown antigorite olivine orthopyroxene h2o show higher halogen ratios compared to their adjacent wall rocks and they are similar to those found in arc volcanoes f cl and i cl between ca 0 083 1 5 and ca 0 00038 0 0013 respectively all measured deserpentinization samples show a narrow range in 37cl values between 0 42 and 0 92 overlapping the 37cl values of seafloor serpentinites and confirming that no significant cl isotope fractionation occurs during subduction dehydration of serpentinites our findings document the conservative behavior of halogens during subduction mass balance constraints reveal that serpentinites strongly control the halogen chemistry of deep subduction zone fluids and that descent of rock residues after deserpentinization strongly affects the halogen budget of the mantle

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

quantification of point source groundwater discharges to the ocean from the shoreline of the big island hawaii aerial thermal infrared imaging has revealed that submarine groundwater discharge sgd along the western coast of the big island of hawaii is often focused as point source discharges that create buoyant groundwater plumes that mix into the coastal ocean we quantified the sgd fluxes associated with several plumes using natural geochemical tracers offshore transects of 222rn and 224ra show elevated activities and corresponding low salinities in the nearshore waters within the plumes indicating that these naturally occurring radionuclides can be useful tracers of groundwater inputs in this area using a series of simultaneous mass balance equations for water salt and radon we determined the groundwater fluxes of six plumes near kona hawaii the average sgd fluxes ranged from 1100 m3 d21 to 12 000 m3 d21 of total fresh saline sgd the fresh meteoric groundwater equivalents for the same flows modeled by adjusting the groundwater end member to reflect freshwater rather than brackish groundwater composition ranged from 630 m3 d21 to 8600 m3 d21 these fluxes are in general agreement with earlier results obtained by hydrological water budgets and physical oceanographic analyses of fresh sgd rates in this region

chlorine isotope chemistry of serpentinites from elba italy as an indicator of fluid source and subsequent tectonic history chlorine concentrations and 37cl and d values are reported for serpentinites in different tectonic positions on elba italy serpentinites from high in the nappe sequence contain 0 01 0 1wt cl with 37cl values from 0 9 to 1 4 samples with positive 37cl values occur beneath gabbro and basalt and are interpreted as having been serpentinized by interaction with seawater samples with negative 37cl values are in direct contact with sedimentary rocks these samples were juxtaposed against and or buried by sediments in response to low angle normal faulting on the seafloor and serpentinization probably occurred by subsequent interaction with sedimentary pore fluids most samples from a structurally lower nappe and from areas affected by contact metamorphism lost their original cl during heating low d values for all samples suggest postserpentinization interaction with meteoric water but neither cl nor o isotope ratios were affected by this interaction our results demonstrate that chlorine can be retained in obducted serpentinites up to low greenschist conditions and that the cl isotope composition of such serpentinites preserves a record of seafloor tectonic processes

source of fluorine and petrogenesis of the rio grande rift type barite fluorite galena deposits abundant fluorite in the rio grande rift barite fluorite galena deposits is anomalous in comparison to typical mississippi valley type mvt deposits the source of fluorine in these deposits is controversial we have tested two hypothesized sources for the origin of fluorine in these deposits including release of gaseous hf from magmas associated with rifting and the leaching of fluorine from proterozoic basement granites that underlie the deposits in this study chlorine isotopes were measured from fluorite fluid inclusions from eight rio grande rift deposits stable chlorine isotope ratios were used as a proxy for determining the possible source of the fluorine because chlorine unlike fluorine has more than one isotope and thus can be used as an isotopic tracer chlorine and fluorine exhibit chemically similar behavior and therefore are likely to be derived from the same source if chlorine is associated with rift related magmatism as a complement to the chlorine isotope measurements br cl ratios were measured from the fluorite fluid inclusions and applied as additional tracers in addition sr and nd isotopes were measured from fluorites regionally related granites carbonates and asthenospheric basalts to aid in understanding the petrogenesis of rio grande rift deposits sr and nd isotope ratios of the fluorites 87 sr 86 sr 0 71986 0 74078 143 nd 144 nd 0 51177 0 51234 are distinctly different from local basalts 87 sr 86 sr 0 70304 0 70465 143 nd 144 nd 0 51277 0 51297 and pennsylvanian limestones 87 sr 86 sr 0 70858 0 72926 143 nd 144 nd 0 51198 0 51245 but similar to the proterozoic bingham granite 87 sr 86 sr 0 73285 143 nd 144 nd 0 51208 the relatively radiogenic sr and unradiogenic nd signatures of the fluorites indicate that the sr and nd were derived largely from a granitic source with some influence from a carbonate and or asthenospheric source this is consistent with previously published pb isotope data on galena from hansonburg mining district 37 cl values from fluorite fluid inclusions range from 0 66 to 3 07 per mil relative to smoc and the br cl ratio by weight for all the fluorite samples ranges between 0 00008 and 0 00050 except for san diego mountain which has a relatively high br cl ratio of 0 00242 the positive correlation between fluorite 37 cl and br cl ratio is attributed to mixing of cl from asthenospheric magmatic and evaporite sources the calculated range of cl derived from an asthenospheric source is 40 to 49 percent for the mex tex mine sample and between 13 and 35 percent for the sunshine no 2 sample these ranges in the asthenospheric component of cl probably represent minimum possible values because f and cl closely follow one another during magma degassing and exhibit similar chemical behavior the presence of asthenospheric cl is consistent with an asthenospheric magmatic source of f in the rio grande rift deposits

apatite compositions from oceanic cumulates with implications for the evolution of mid ocean ridge magmatic systems apatite distributions and compositions from cumulates from the epr at hess deep the mar at the kane transform and the swir at odp hole 735b were determined to assess the variability at each setting and to evaluate the potential utility of apatite in understanding the evolution of the lower ocean crust apatite in cumulates with low p 2 o 5 contents are heterogeneously distributed along linear arrays or in tight clusters suggesting they crystallized from planar or pipe like channels of evolved liquid most of the variation in the apatite composition is in the halogen site the x f a and x cl ap are inversely correlated defining trends at near constant x oh ap with epr x oh ap 0 25 mar x oh ap 0 45 and swir x oh ap 0 65 these trends are defined both by sample averages and by the range of individual analyses in samples with large ranges in their f cl ratio these trends are interpreted to reflect the reequilibration of apatite from variably evolved liquids fluids that moved through the crystal mush comparison of the f cl oh contents of apatite with the f cl oh contents of glasses recovered from the same ridges show approximate correspondence apatite and glasses from the epr have the highest halogen contents while apatite and glasses from the mar and swir have more oh some of the higher cl contents in the apatite are interpreted to be produced by degassing of the cumulus pile while others reflect the assimilation of a seawater component we suggest that systematic analysis of apatite from oceanic cumulates might allow cumulates that crystallized at shallow depths and assimilated seawater derived components to be distinguished from those that crystallized below the level of seawater interaction

stable isotope δ18o δd δ37cl evidence for multiple fluid histories in mid atlantic abyssal peridotites odp leg 209 abstract serpentinized abyssal peridotites sampled by the ocean drilling program leg 209 along the mid atlantic ridge near the 15 20 n fracture zone have been analyzed for oxygen hydrogen and chlorine isotope compositions in order to determine isotopic behavior under a wide range of serpentinization conditions and place constraints on fluid history oxygen and hydrogen thermometry suggests peak serpentinization temperatures of 300 500 c serpentine separates have low d values possibly due to a magmatic fluid component or low temperature exchange during seafloor weathering chlorine geochemistry focused on three holes 1274a and 1272a serpentinized peridotites and 1268a serpentinite locally altered to talc concentrations of both water soluble chloride wsc and structurally bound chloride sbc are significantly lower at hole 1268a compared to holes 1274a and 1272a the 37cl values for wsc and sbc of serpentinites in holes 1274a and 1272a are slightly positive avg wsc 0 20 n 22 and avg sbc 0 35 n 22 representing typical seawater hydration conditions commonly determined for abyssal peridotite the sbc of serpentinites from hole 1268a are also positive avg 0 63 whereas the sbc in talc dominated samples is negative avg 1 22 the wsc of both talc and serpentine dominated samples are also negative avg 0 15 we interpret the chlorine isotope data to preserve a record of multiple fluid events as seawater hydrated the peridotite 37cl was preferentially incorporated into the forming serpentine and water soluble salts yielding similar 37cl values on a regional scale as sampled by holes 1268a 1274a and 1272a the resultant pore fluid was left depleted in 37cl locally hole 1268a this evolved fluid was remobilized possibly due to the initiation of hydrothermal circulation in response to emplacement of a mafic magma body the low 37cl pore fluids attained elevated sio2 and sulfur concentrations due to interaction with the gabbroic intrusion and when ascending through the surrounding serpentinite caused formation of isotopically negative talc this secondary fluid also flushed the preserved serpentinite of its previously formed salts resulting in negative 37clwsc values the 37clsbc values of the serpentinite samples remained unmodified by reaction with the secondary fluid

chlorine isotope evidence for multicomponent mantle metasomatism in the ivrea zone abstract metasomatism of the finero peridotite ivrea zone italy has previously been ascribed to mantle melts generated in a rift or plume setting and or to subduction fluids we combine cl h and o stable isotope geochemistry with petrologic and major and trace element data to further constrain sources and setting of the metasomatic agents and to assess fluid infiltration mechanisms relatively unmetasomatized samples from the balmuccia peridotite serve as our control population 37cl 0 7 to 0 4 n 13 we analyzed 47 samples from four finero rock types 1 spinel harzburgite with minor amphibole phlogopite 2 harzburgite with several percent phlogopite amphibole 3 amphibole rich segregations and 4 phlogopite segregations 37cl values range from 2 0 to 2 1 and cannot be reconciled with metasomatism by a single homogeneous fluid three components describe most of the sample variability a endmember spinel peridotite as represented by the balmuccia samples b a hydrated clinopyroxenite component with low 37cl and high si al ca and d responsible for formation of type 3 amphibole segregations and c a component with high 37cl d cl cr lile and hfse that formed type 4 phlogopite segregations type 1 and 2 peridotite compositions are consistent with different degrees of mixing between these three components centimeter scale isotopic gradients indicate that much of the fluid infiltration was channelized rather than pervasive the data support metasomatism in a forearc wedge with fluids sourced from at least two subducted components with distinct chemical and isotopic compositions e g 37cl 2 overall our results show that relatively shallow and heterogeneous fluid release events from the downgoing slab can profoundly modify the mantle wedge

chlorine stable isotope composition of the oceanic crust implications for earth s distribution of chlorine abstract this first investigation of the cl stable isotope composition of seafloor rocks reveals systematic variations in 37 cl 35 cl of the oceanic crust and its mantle source s relative to seawater chlorine isotopic measurements expressed as 37 cl relative to the seawater 37 cl 35 cl ratio of fresh morb glass hydrothermally produced amphibole containing whole rocks and smectite veins are presented all the samples analyzed are isotopically enriched 0 2 7 5 relative to seawater 0 uptake of cl into amphibole during axial hydrothermal alteration fractionates cl relative to seawater the isotopic compositions of morb glasses are between 0 2 and 7 2 this range appears to be partially due to the assimilation of cl from hydrothermally altered wallrock into morb magmas samples which are unaffected by assimilation have 37 cl between 3 and 7 2 overall the data imply that cl is isotopically fractionated between the surface and mantle reservoirs of earth calculations based on the degree of fractionation suggest that approximately 40 of the cl originally in the degassed mantle now resides on earth s surface

aerial infrared imaging reveals large nutrient rich groundwater inputs to the ocean 1 regional high resolution 0 1 c 0 5 m low altitude thermal infrared imagery tir reveals the exact input locations and fine scale mixing structure of massive cool groundwaters that discharge into the coastal zone as both diffuse flows and as 30 large point sourced nutrient rich plumes along the dry western half of the large volcanic island of hawaii these inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting water column profiling and nutrient sampling show that the plumes are cold buoyant nutrient rich brackish mixtures of groundwater and seawater by way of example we illustrate in detail one of the larger plumes which discharges ca 12 000 m3 d 1 ca 8 600 m3 d 1 freshwater rates comparable in volume to high flux groundwater outputs in better known tropical karst terrains we further show how nutrient mixing trends may be integrated into tir sea surface temperatures to produce surface water nutrient maps of regional extent

nonconservative behavior of br cl ratios during alteration of volcaniclastic sediments abstract other than halite diagenesis and organic matter degradation cl and br are considered to be conservative in marine pore fluids consequently br cl ratios should remain constant during most diagenetic reactions nonetheless br cl molar ratios decrease to 1 27 10 3 18 less than seawater value in pore fluids from site 833 in the aoba basin of the new hebrides convergent margin despite the lack of halite diagenesis and little organic matter sediment at this site is largely volcanic ash which becomes hydrated with depth as it converts to clay and zeolite minerals these hydration reactions remove sufficient water to increase the concentrations of most solutes including cl and br the resulting concentration gradients drive diffusion but calculations indicate that diffusion does not decrease the br cl ratio some cl may be leached from the ash but insufficient amounts are available to cause the observed decrease in br cl ratio the limited source of cl suggests that proportionately more br than cl is lost from the fluids to the diagenetic solids similar nonconservative behavior of cl and br may occur during fluid circulation at ridge crests and flanks thereby influencing the halide distribution in the crust

geophysical surveys of burial sites a case study of the oaro urupa a maori family burial site was surveyed using shallow electromagnetic em magnetometer gradiometer and ground penetrating radar gpr techniques the locations of some older graves are no longer known partly through the loss of markers and partly through the loss of the oral record there are at least 150 such burial sites throughout new zealand and similar problems occur elsewhere in the world the knowledge that maori graves are traditionally set out facing east made survey design easier background trends are removed and possible anomalous features are identified despite the complicating presence of metal fencing the em in phase response the vertical gradient of the total magnetic field and the gpr response were particularly useful in combination gpr surveys were carried out using two frequencies 450 and 200 mhz the higher frequency radar surveys were limited in extent because these data had a limited depth of penetration and were prone to signal ringing in the surficial clay the lower

chlorine isotopic composition in seafloor serpentinites and high pressure metaperidotites insights into oceanic serpentinization and subduction processes bulk rock chlorine content and isotopic composition 37 cl were determined in oceanic serpentinites high pressure metaperidotites and metasediments in order to gain constraints on the global chlorine cycle associated with hydrothermal alteration and subduction of oceanic lithosphere the distribution of insoluble chlorine in oceanic serpentinites was also investigated by electron microprobe the hydrothermally altered ultramafic samples were dredged along the south west indian ridge and the mid atlantic ridge the high pressure metamorphic samples were collected in the western alps metaperidotites in the erro tobbio unit and metasediments in the schistes lustres nappe oceanic serpentinites show relatively large variations of bulk rock cl contents and 37 cl values with mean values of 1105 596 ppm and 0 7 0 4 o respectively n 8 1 serpentines formed after olivine meshes show lower cl content than those formed after orthopyroxene bastites in bastites of two different samples cl is positively correlated with al 2 o 3 and negatively correlated with sio 2 these relationships are interpreted as reflecting preferential cl incorporation into the bastite structure distorted by al substituted for si rather than different alteration conditions between olivine and orthopyroxene minerals high pressure metaperidotites display relatively homogeneous cl contents and 37 cl values with mean values of 467 88 ppm and 1 4 0 1 respectively n 7 1 a macroscopic high pressure olivine bearing vein formed from partial devolatilization of serpentinites at 2 5 gpa and 500 600 c shows a cl content and a 37 cl value of 603 ppm and 1 6 o respectively metasediments n 2 show low whole rock cl contents 15 ppm cl that did not allow cl isotope analyses to be obtained the range of negative 37 cl values observed in oceanic serpentinites is likely to result from water rock interaction with fluids that have negative 37 cl values the homogeneity of 37 cl values from the high pressure olivine bearing vein and the metaperidotite samples implies that progressive loss of cl inherited from oceanic alteration throughout subduction did not significantly fractionate cl isotopes chlorine recycled in subduction zones via metaperidotites should thus show a range of 37 cl values similar to the range found in oceanic serpentinized peridotites

shallow submarine seep of abiotic methane from serpentinized peridotite off the island of elba italy abstract abiotic methane ch4 is today widely reported in gas seeps and hyperalkaline springs in ophiolites and peridotite massifs characterized by low temperature continental serpentinization origin and distribution of this gas have far reaching implications in microbiology astrobiology and carbon cycle we report an in depth study of a recently described abiotic ch4 seep occurring in shallow seafloor along the western coast of elba island tyrrhenian sea italy the gas is characterized by stable c and h isotopic compositions of ch4 13c 18 2h 141 and a very low co2 content that are typical of abiotic gas in continental ultramafic rock systems based on local geothermal gradients the temperature of methane production is estimated to be below 100 c the isotope signature of methane is similar to that occurring in the liguria region about 200 km north of elba island where the same ophiolite unit exposed a mantle co2 component suggested by relatively high 3he 4he ratios has likely acted as ch4 precursor the reconstruction of the geological structural setting of elba ophiolite sequence highlighted that the seep occurs in correspondence with a faulted reverse limb of the antiform of the ophiolite unit the gas bearing fault forms a contact between mafic and ultramafic serpentinized rocks as typically observed in other continental seeps and springs related to ophiolites magmatic intrusions in the island may have contributed to the c feedstock of methane

turbulent fountains in an open chamber the flow and density distribution produced by injecting dense fluid upwards at the bottom of a homogeneous fluid have been investigated experimentally and theoretically both axisymmetric and line sources have been studied using small scale laboratory experiments in which salt water is injected into a tank of fresh water the turbulent fountain formed in this way rises to a maximum height which can be related to the froude number of the inflow and then falls back and spreads out along the floor continuing the inflow builds up a stable stratification in a similar manner to that discussed earlier for the plume filling box model of baines turner 1969 which is complementary to the present work the fountain flows considered here have the important new feature that the volume of the inflow is significant so the total volume of fluid in the open container increases with time the evolution is determined by the rate of entrainment into the fountain from its surroundings which is found directly by experiment re entrainment of fluid into the fountain continually changes the density profile in the mixed fluid collecting at the bottom of the chamber below the level of the fountain top and controls the rate of rise of a front of marked fluid the top of the fountain rises linearly in time at a rate which for axisymmetric fountains has been shown both experimentally and theoretically to be close to half the rate of rise of the free surface due to the inflow thus at a certain time the front rises above the top of the fountain once the mixed fluid at the bottom of the chamber has risen above the fountain its density profile remains unchanged the front velocity the fountain height and the density profile have all been obtained as functions of time using a theory which is in good agreement with the experimental results for a large range of input froude numbers for line fountains the results are less precise owing to an instability which causes the flow to switch irregularly from a symmetrical state to one in which the downflow occurs on one side only and with a smaller maximum height in concluding we discuss the applications which motivated the work particularly the development of a stratified hybrid layer in magma chambers replenished from below and the dynamically identical but inverted problem of heating large buildings through ducts located near the roof

using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off crescent beach florida abstract a spectacular submarine spring is located about 4 km east of crescent beach fl in the atlantic ocean the single vent feature of crescent beach spring provides a unique opportunity to examine onshore offshore hydrogeologic processes as well as point source submarine ground water discharge the floridan aquifer system in northeastern florida consists of tertiary interspersed limestone and dolomite strata impermeable beds confine the water bearing zones under artesian pressure miocene and younger confining strata have been eroded away at the vent feature enabling direct hydrologic communication of eocene ground water with coastal bottom waters the spring water had a salinity of 6 02 which was immediately diluted by ambient seawater during advection mixing the concentration of major solutes in spring water and onshore well waters confirm a generalized easterly flow direction of artesian ground water nutrient concentrations were generally low in the reducing vent samples and the majority of the total nitrogen species existed as nh 3 the submarine ground water tracers rn 222 1174 dpm l 1 dpm methane 232 nm and barium 294 5 nm were all highly enriched in the spring water relative to ambient seawater the concentrations of the reverse redox elements u v and mo were expectedly low in the submarine waters the strontium isotope ratio of the vent water 87 sr 86 sr 0 70798 suggests that the spring water contain an integrated signature indicative of floridan aquifer system ground water additional sr isotopic ratios from a series of surficial and lower floridan well samples suggest dynamic ground water mixing and do not provide clear evidence for a single hydrogeologic water source at the spring vent in this karst dominated aquifer such energetic mixing at the vent feature is expected and would be facilitated by conduit and fractured flow radium isotope activities were utilized to estimate flow path trajectories and to provide information on potential travel times between an onshore well and the spring using either 223 ra and 224 ra or 228 ra and qualifying this approach with several key assumptions estimates of water mass travel times from an upper floridan well in crescent beach to the submarine vent feature distance 4050 m are in the order of 0 01 0 1 m min 1

images of buried graves in bayat afyon turkey from high resolution magnetic data and their comparison with preliminary excavations dedemezari necropolis the site of our study is located in the west of turkey near afyon archaeologists think that it belongs to the middle bronze age a high resolution magnetic survey identified buried material highly accurately in particular anomalies which are transformed by the analytic signal method clarify the observed magnetic anomalies magnetic surveying was applied in three different areas in this study the map of analytic signal transformed anomalies presented good results on preliminary excavation in trenches a and b two types of graves are found in the study area one is made of clay and the second is carved in the rocks shapes of the buried graves are mainly cylindrical and elliptical most of the magnetic anomalies are elliptical and reflect the shape of the buried materials future excavations in dedemezari necropolis will be able to be carried out more easily due to the known locations of the buried graves

water soluble chlorides in massive seafloor serpentinites a source of chloride in subduction zones abstract dissolved cation and anion species were measured in the water soluble fraction of massive seafloor serpentinites leached with distilled h 2 o soluble chloride contents ranged from 0 09 to 0 51 wt average 0 26 wt so 4 2 to 0 09 wt mg 2 to 0 16 wt and na to 0 09 wt the concentration of evolved ions was the same in samples equilibrated with water at 25 and 230 c demonstrating that a significant amount of cl present in serpentinites occurs as water soluble salts a nearly equal amount of cl exists in the leached serpentinite likely sited in serpentinite itself the formation of intergranular salts in the serpentinite can be explained by seawater hydrothermal alteration of peridotite hydration reactions and h 2 o incorporation in the serpentine leave the residual fluid with ever increasing salinity and ultimately lead to precipitation of water soluble chlorides chlorine isotope ratios in the water soluble fraction average 1 49 vs standard mean ocean chlorine smoc from a core at the iberian abyssal plain and 0 16 from a much younger core at hess deep the 37 cl value of insoluble cl is 0 33 higher than the soluble fraction the nonzero 37 cl values demonstrate that the cl in the serpentinites is not an artifact of seawater incorporation during drilling the following conclusions are presented 1 serpentinite may be the major conduit for surficial chlorine transfer to mantle depths and an important part of the global chlorine cycle the cl flux in serpentinites into the mantle is larger than all other previously identified fluxes 2 cl is sited in both a water soluble and insoluble component 3 a high salinity fluid plume is evolved during serpentinite dehydration of a subducting slab the high salinity fluid affects metamorphic reactions and melting properties above the slab and can cause intense metasomatism the unusual bulk composition of the whiteschist from dora maira can be explained by channeled passage of a high salinity fluid 4 high salinity fluids reduce the stability field of serpentine causing its dehydration to occur over a broad interval which may partly explain the broad locus of intermediate depth earthquakes

stable chlorine isotopes in hydrothermal processes abstract values of 37cl can now be routinely measured with an analytical precision of 0 2 as reported herein on fluid inclusion leachates from the elmwood gordonsville mississippi valley type deposit and formation waters from its host formation basin brines from the gulf coast and palo duro basins and fluid inclusion leachates and biotites from the bingham silver bell and panguna porphyry copper deposits isotopic measurements are not affected by reaction yield in the range 85 100 or by generation of free i2 during sample preparation in the elmwood gordonsville deposit five successive paragenetic stages of ore and gangue sphalerite fluorite calcite 2 barite and calcite 3 each yielded multiple 37cl measurements ranges of 37cl vary in alternating fashion between stages with more negative values sphalerite calcites 2 and 3 and those with more positive values fluorite barite an interface between two brine systems with 37 cl and 0 0 appears to have moved back and forth across the zone of mineralization brines from the gulf coast and palo duro basins are apparently bimodal in 37cl with modes near 0 9 and 0 0 consistent with the variation in 37cl observed in fluid inclusion leachates from elmwood gordonsville biotite in the bingham deposit has 37cl values up to 1 7 and chlorine isotopes that are fractionated with respect to salt rich hydrothermal fluid hydrothermal fluids in all three porphyry copper deposits studied have a 37cl range of 0 1 to 0 4 with the one exception of a 0 5 value at bingham loss of low 37 cl chloride in vapor may balance chloride with a net 37 cl 0 in the porphyry deposits

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

unveiling the prehistoric landscape at stonehenge through multi receiver emi abstract archaeological research at stonehenge uk is increasingly aimed at understanding the dynamic of the wider archaeological landscape through the application of state of the art geophysical techniques unprecedented insight is being gathered into the buried archaeological features of the area however applied survey techniques have rarely targeted natural soil variation and the detailed knowledge of the palaeotopography is consequently less complete in addition metallic topsoil debris scattered over different parts of the stonehenge landscape often impacts the interpretation of geophysical datasets the research presented here demonstrates how a single multi receiver electromagnetic induction emi survey conducted over a 22 ha area within the stonehenge landscape offers detailed insight into natural and anthropogenic soil variation at stonehenge the soil variations that were detected through recording the electrical and magnetic soil variability shed light on the genesis of the landscape and allow for a better definition of potential palaeoenvironmental and archaeological sampling locations based on the multi layered dataset a procedure was developed to remove the influence of topsoil metal from the survey data which enabled a more straightforward identification of the detected archaeology the results provide a robust basis for further geoarchaeological research while potential to differentiate between modern soil disturbances and the underlying sub surface variations can help in solving conservation and management issues through expanding this approach over the wider area we aim at a fuller understanding of the human landscape interactions that have shaped the stonehenge landscape

mexican site for k t impact crater research throughout the caribbean suggests that the geophysical anomalies in the yucatan first noted by penfield and camargo 1981 and called the chicxulub crater could be the site of the impact purported to have caused the k t extinctions a semicircular ring of sink holes known locally as cenotes which correlates with the geophysical anomalies has been identified and it is argued that the origin of the cenote ring is related to postimpact subsidence of the chicxulub crater rim if there is indeed a crater the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km if confirmed as a site of impact the chicxulub crater would be the largest terrestrial impact crater known which is consistent with the uniqueness of the k t global catastrophe

determining geophysical responses from burials in graveyards and cemeteries abstractgraveyards and cemeteries around the world are increasingly designated as full therefore there is a requirement to identify vacant spaces for new burials or to identify existing ones to exhume and then reinter if necessary geophysical methods offer a potentially noninvasive target detection solution however there has been limited research to identify optimal geophysical detection methods against burial age we have collected multifrequency 225 900 mhz ground penetrating radar gpr electrical resistivity and magnetic susceptibility surface data over known graves with different burial ages and soil types in three uk church graveyards results indicate that progressively older burials are more difficult to detect but this decrease is not linear and is site specific medium to high frequency gpr and magnetic susceptibility was optimal in clay rich soils medium to high frequency gpr and electrical resistivity in sandy soils and electrical resistivity and low frequency gpr in coarse sand

chlorine isotope and cl br fractionation in fluids of poas volcano costa rica insight into an active volcanic hydrothermal system abstract halogen rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems this paper reports a long term record of cl br concentrations and 37cl signatures of lake water and fumaroles from the active crater of poas volcano costa rica where surface expressions of magmatic hydrothermal activity have shown substantial periodic changes over the last decades both the hyperacid water of its crater lake laguna caliente and subaerial fumaroles show significant temporal variability in cl br concentrations br cl ratios and 37cl reflecting variations in the mode and magnitude of volatile transfer the 37cl signatures of the lake covering the period 1985 2012 show fluctuations between 0 02 0 06 and 1 15 0 09 condensate samples from adjacent fumaroles on the southern shore collected during the interval 2010 2012 with strong changes in gas temperature 107 763 c display a much larger range from 0 43 0 09 to 14 09 0 08 most of the variations in cl isotope br cl and concentration signals can be attributed to interaction between magma derived gas and liquid water in the volcanic hydrothermal system below the crater the 37cl were lowest and closest to magmatic values in 1 fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway and 2 water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation in contrast elevated 37cl can be explained by partial scavenging and fractionation during subsurface gas liquid interaction hence strong cl isotope fractionation leading to very high 37cl in poas fumaroles indicates that they followed a wet pathway highest 37cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low ph caused hcl evaporation it is concluded that combined monitoring of 37cl and br cl in laguna caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of poas

origin of fluids in iron oxide copper gold deposits constraints from δ 37 cl 87 sr 86 sr i and cl br the origin of the hypersaline fluids magmatic or basinal brine associated with iron oxide cu u au ree deposits is controversial we report the first chlorine and strontium isotope data combined with cl br ratios of fluid inclusions from selected iron oxide copper gold iocg deposits candelaria raul condestable sossego a deposit considered to represent a magmatic end member of the iocg class of deposit gameleira and a magnetite apatite deposit el romeral from south america our data indicate mixing of a high 37cl magmatic fluid with near 0 37cl basinal brines in the candelaria raul condestable and sossego iocg deposits and leaching of a few weight percent of evaporites by magmatic hydrothermal fluids at gameleira and el romeral the sr isotopic composition of the inclusion fluids of candelaria raul condestable and el romeral confirms the presence of a non magmatic fluid component in these deposits the heavy chlorine isotope signatures of fluids from the iocg deposits candelaria raul condestable sossego reflecting the magmatic hydrothermal component of these fluids contrast with the near 0 37cl values of porphyry copper fluids known from the literature the heavy chlorine isotope compositions of fluids of the investigated iocg deposits may indicate a prevailing mantle cl component in contrast to porphyry copper fluids an argument also supported by os isotopes or could result from differential cl isotope fractionation processes e g phase separation in fluids of iocg and porphyry cu deposits

springs and streams of the taro ceno valleys northern apennine italy reaction path modeling of waters interacting with serpentinized ultramafic rocks article i nfo in the area of the taro ceno valleys northern apennine emilia romagna region italy waters of meteoric origin interact with ophiolite rocks of the external ligurides fresh water springs issuing from basalts have a ca hco3 composition whereas freshwater springs from ultramafites vary in composition from ca hco3 or mg hco3 to na oh or na so4 types and in ph values from 7 3 8 8 up to ph 11 respectively in addition the boron content of the alkaline waters is up to 13 mg l which is unusually high for freshwaters in general and ultramafites that have undergone oceanic serpentinisation in particular and gives a boric alkalinity to the waters the springs waters show evidence of recent low temperature continental serpentinisation and the process is modeled by reaction paths using an updated geochemical thermodynamic database consistent with the local primary and secondary serpentinite paragenesis for the model bicarbonate waters evolve to alkaline waters supersaturated in ca mg carbonate based on the assumption that the dissolution of serpentinite results in supersaturation with respect to kaolinite ferrihydrite vermiculite fe 2 mg 2 saponite and poorly crystalline serpentine the alkaline composition and the chloride content of the waters suggest a prolonged interaction with the rocks at depth that led to dissolution of albite and leaching of olivine hosted fluid inclusions a similar evolution is also proposed for the more developed springs issuing from the ultramafic rocks of the voltri group liguria region where solutions are supersaturated in brucite and are in equilibrium with enstatite and or chlorite

230th 238u disequilibrium systematics in oceanic tholeiites from 21 n on the east pacific rise significant disequilibrium occurs between 230 th and its parent 238 u in a suite of fresh basalt glasses from the rise project study area at 21 n on the east pacific rise the 230 th 232 th activity ratios observed for eight of nine samples from the crest of the axis at this site are constant within analytical uncertainty with a value of 1 22 this observed homogeneity of 230 th 232 th has two possible interpretations first the measured 230 th 232 th can be considered to indicate a mantle source for the rise basalts with th u of 2 5 this interpretation however conflicts with the proposed correlation between 230 th 232 th and 87 sr 86 sr 1 which predicts that 230 th 232 th should equal 1 33 at the rise site a second possible interpretation is that radioactive decay of 230 th in the basalts themselves or in a magma chamber has decreased 230 th 232 th from 1 33 to the observed values the required time span is 11 000 to 100 000 years however petrologic arguments rule against long residence time in a magma chamber and the spreading rate of this section of the east pacific rise 6 cm yr predicts that the maximum age for axis basalts is 27 000 years both interpretations of the measured 230 th 232 th imply a low th u ratio for the rise basalt source and suggest that the morb source at this location is depleted in th with respect to u relative to primitive mantle or bulk earth in spite of their constant 230 th 232 th the basalts from 21 n have wide ranges of measured th u and thorium and uranium concentrations in apparent conflict with the common assumption that these two elements have very small similar crystal liquid partition coefficients participation of an accessory phase with high th and u concentrations during partial melting or fractional crystallization appears to be required to explain this anomaly major and other trace element compositions provide more information about petrogenetic processes although fractional crystallization can explain the variations in major element composition a more complex process such as continuous melting is required to account for the observed trends in trace element compositions in addition to its use as a tracer the 230 th 238 u disequilibrium technique is capable of putting some constraints on the timing of fractionation events and it may eventually lead to a method for dating very young mid ocean ridge basalts

chlorine stable isotope studies of old groundwater southwestern great artesian basin australia abstract stable cl isotope ratios 37 cl 35 cl were measured in groundwater samples from the southwestern flow system of the great artesian basin australia to gain a better understanding of the cl sources and transport mechanisms 37 cl values range from 0 to 2 5 smoc and are inversely correlated with cl concentration along the inferred flow direction the cl isotopic compositions in conjunction with other geochemical parameters suggest that cl in groundwaters is not derived from salt dissolution mixing of the recharge water with saline groundwater cannot explain the relationship between 37 cl and cl concentration measured marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the cl concentrations observed in wells that are close to the recharge area and in groundwaters sampled along the southern transect 37 cl values measured in the leachate of the bulldog shale suggest that the aquitard is the subsurface source of cl for the majority of groundwater samples studied diffusion is likely the mechanism through which cl is transported from the pore water of the bulldog shale to the aquifer however a more detailed study of the aquitard rocks is required to verify this hypothesis

elemental and isotopic chloride geochemistry and fluid flow in the nankai trough 1 the first transect of pore fluid cl profiles across the deformation front of an accretionary prism and underthrust section nankai trough and the first cl isotopic profile in this environment are presented these demonstrate that there is channelized horizontal episodic flow through most of the section arcward of the deformation front and in the lowermost section seaward of the deformation front in the underthrust sediments channels appear to be continuous fluid velocities within the channels based on cl gradients are 13 5cm year the near balance of depth integrated flow and the subduction of pore fluid indicates that flow episodes are frequent 37cl values are lower than seawater throughout the section averaging 6 1 per mil this demonstrates fluid mineral exchange of cl and suggests that subducted solids carry enriched 37cl that is efficiently recycled from deeper levels in the subduction zone back into seawater and may be responsible for the seawater mantle 37cl fractionation

a new assessment of the abundance of serpentinite in the oceanic crust the gabbro model of the composition of the oceanic crust has prevailed for more than two decades but serpentinites are common along much of the mid atlantic ridge and elsewhere leading to renewed debate over the abundance of serpentinites in crust created at slow spreading ridges based on data from both oceanic and ophiolite samples it has also been suggested that serpentinites are not distinguishable from meta gabbros and diabases by their seismic properties we have made new statistical analyses of the relationship between vs and vp in oceanic gabbro and diabase samples and serpentinized peridotites and compared them to in situ s wave and p wave velocities derived from expanding spread profiles esps acquired in the atlantic our findings demonstrate 1 that there is some overlap of the properties of gabbroic samples taken from ophiolites with the properties of serpentinites but 2 over the range of typical layer 3 seismic velocities the seismic properties of oceanic gabbros and diabases are distinctly different from the properties of serpentinites and 3 that in situ seismic velocities are in excellent agreement with the properties of the gabbros while the shear velocities in serpentinites are significantly lower partially serpentinized peridotite is certainly present but not abundant in normal oceanic crust

chlorine isotopes in fluid inclusions determination of the origins of salinity in magmatic fluids abstract thermal ionisation mass spectrometry tims of the cs 2 cl ion has been used to determine the 37 cl value of paleofluids trapped in fluid inclusions modifications to the existing published method have lowered the precision by a factor of 2 0 09 1 thereby allowing real differences to be measured with greater certainty the method has been applied to determine 37 cl of two sets of magmatic fluids trapped in fluid inclusions samples were studied from the capitan pluton in new mexico and the sw england batholith both of which have high temperature fluids whose d and 18 o signatures are distinctly magmatic relative to standard mean ocean chloride smoc the 37 cl values of the capitan samples cluster around 0 whereas those from sw england cluster around 1 8 the br cl ratios of the capitan fluid inclusions are low indicative of halite dissolution and are comparable to local high salinity waters derived from leaching permian evaporites the br cl ratios of the sw england fluid inclusions are much higher and within the range of values normally considered to be magmatic we conclude that the 37 cl value of the capitan magmatic fluids confirms the evidence from br cl ratios that cl was derived from an evaporite source whereas the 37 cl value of the sw england fluids appears to be more representative of a deep magmatic source

calibration of br cl fractionation during subcritical phase separation of seawater possible halite at 9 to 10 n east pacific rise abstract experiments were conducted to assess br cl fractionatiodn during phase separation of seawater at 400 c and 250 to 275 bars these conditions are applicable to the 9 10 n epr system where low cl concentrations and low br cl rations in vent fluids have been attributed to phase separation of seawater at conditions below the critical point of seawater 408 c 300 bars the level of br cl fractionation observed in experiments is well below that needed to account for br cl systematics at epr 9 10 n based on our experimental results we propose an alternative model involving dissolution and precipitation of halite to account for the anomalous br cl data at 9 10 n halite can be predicted to form at pressure and temperature conditions prevailing during eruption of magma at mid ocean ridges subsequent changes in physical conditions however would induce halite to dissolve and thus decrease br cl ratios of vent fluids

inside a mound applied geophysics in archaeological prospecting at the kings mounds gamla uppsala sweden a combined geophysical prospection with slingram gradiometer and ground penetrating radar is described the prospection is carried out at the eastern mound and the thing mound gamla uppsala middle sweden in an attempt to detect the internal structure of the mounds at the eastern mound we were able to identify the fossil ground surface a centre cairn a possible older grave under the mound and a few other anomalies some of them most possibly depending on historical activities and some more likely on prehistoric human activities the thing mound was found being of geological origin and only prepared to become a grave the project shows that a combined use of several geophysical methods improves and simplifies the interpretation

roof assimilation at fast spreading ridges an investigation combining geophysical geochemical and field evidence 1 the role of assimilation at the roof of the axial magma chamber amc at fast spreading mid ocean ridges is investigated using field geophysical and geochemical data field observations from ophiolites indicate that roof assimilation is a common process but provide little constraint on the amount of material assimilated arguments based on geophysical data that include the subsidence of the layer 2a 2b boundary across the width of the amc and the depth of large axial summit troughs require at least 50 100 m of assimilation however significant variations in the depth of the amc on the east pacific rise epr over short along axis distances suggest up to 500 m fluctuations in the depth of the amc may be common on short timescales geochemical modeling of the over enrichment of chlorine in epr basalts suggests that 20 of the oceanic crust may go through a cycle of crystallization alteration then assimilation this is far more than can be accounted for by roof subsidence and suggests that fluctuations in the level of the roof must account for the majority of the assimilation assimilation most likely occurs on a number of different timescales ranging from decadal due to perturbations in the thermal regime related to diking to longer period fluctuations controlled by magma supply from the mantle large scale roof assimilation has implications for the accretion of the lower crust due to heat losses associated with assimilation and for the interpretation of the geochemistry of the oceanic crust

imaging skeletal remains with ground penetrating radar comparative results over two graves from viking age and medieval churchyards on the stora seyla farm northern iceland detailed ground penetrating radar surveys were conducted at separate viking age and medieval churchyards on the stora seyla farm in skagafjor ur northern iceland surveying over a previously unknown site ca ad 1000 that is located just a few meters above the skagafjor ur valley bottom delineated the remnants of a buried circular turf wall that encloses a church structure and several graves the radar profiles over the graves contain strong hyperbolic reflections that emanated from the skeletal remains over one of the graves an air filled void within the chest cavity had been detected as noted by reflections with normal polarity which indicated a boundary towards increasing microwave velocity during excavation the soil surrounding an intact rib cage collapsed thus confirming the presence of the void in general the skeletal remains were very well preserved and yielded strong reflections which permitted the orientation of the body to be determined conversely the radar profiles over a grave from a more recent churchyard ca ad 1200 show ground disturbance but lack hyperbolic reflections upon excavation only teeth were recovered the poor preservation of the skeletal remains is attributed to increase contact with infiltrating groundwater from an overlying gravel layer interpretations were aided by time slice overlay imaging forward modeling and analysis of the reflection coefficient

origin and evolution of fluids from mud volcanoes in the barbados accretionary complex a large collection of fluids 54 interstitial fluids and four expelled fluids were sampled at the manon site at the outer edge of the barbados accretionary complex these warm fluids up to 20 c are expelled by sub marine 5000 mbsl mud volcanoes consisting of diapirs unchanneled flow and diatremes channeled chlorine stable isotope ratios of these fluids were measured by irms with a reproducibility of 0 05 1 versus smoc standard mean ocean chloride a large range of 37cl between 5 3 and 0 1 is observed data from each volcanic structure describe a mixing between seawater and a low 37cl fluid the whole set of data is interpreted as the result of a mixing between two deep components and seawater the two deep fluids are chemically distinct e g in ca mg k li sr and br contents and br cl ratio they display low and significantly different 87sr 86sr ratios 0 707790 and 0 707892 respectively and 37cl values 4 51 and 5 24 respectively physicochemical processes such as mineralogical transformation diffusion compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative 37cl values ion filtration due to sediment compaction appears to be the more likely process to explain the negative 37cl values observed at the manon site a model for the generation of these signatures is proposed where a residual negative 37cl fluid reservoir is created at the bottom of the prism or the sediment pile further compaction fracturing and or dewatering of the slab may flush out these fluids and focus them towards the decollement zone mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures

chlorine isotope variations along the central american volcanic front and back arc volcanic outputs ash tephra and lava samples of 23 volcanic centers from the volcanic front secondary front and back arc in central america were analyzed for their 37cl values with the goal of using chlorine isotopes as a tracer of fluids sourced from the subducting cocos slab 37cl values range from 2 6 to 3 0 with systematic variations along the length of the front values from the northernmost guatemala and el salvador and southernmost costa rica ends of the front have mantle like signatures in contrast 37cl values are both positive and negative in the center of the front nicaragua implying a sediment and or serpentinite derived component geophysical observations are consistent with extensive hydration of the cocos plate offshore of nicaragua in support of a serpentinite derived fluid source fluids from dehydrating serpentinites may also incorporate cl from overlying sediments resulting in a multiple source chlorine signature

chlorine stable isotope composition of granulites from lofoten norway implications for the cl isotopic composition and for the source of cl enrichment in the lower crust abstract the cl isotopic composition of lower crustal rocks as revealed from granulites from the lofoten islands northern norway centres around the value of standard mean ocean chloride smoc the investigated rocks and mineral separates of cl amphibole and cl biotite have 37 cl values 37 cl 35 cl normalized to smoc of 1 12 to 0 79 with most values concentrated in the range of 0 3 to 0 11 and an average of 0 15 samples from gabbroic and from dry granitic rocks magmatic mangerites and charnockites with highly cl enriched hydrosilicates and from a later amphibolite with low cl amphiboles show no distinct differences in their 37 cl values the results indicate that there was only minor involvement of mantle derived cl in fluid involving processes in the middle and lower crust assuming a 37 cl of 4 7 for the undegassed mantle 1 cl isotopic values of the granulites do not support the influx of significant amounts of mantle derived cl the maximum possible mantle contribution to the sample with the highest 37 cl is about 33 thus the common occurrence of cl enriched minerals in granulite facies terrains is regarded as a product of remobilized crustal cl either during magmatism or during later fluid activity the results support the hypothesis that the crust can be regarded as a reservoir with cl isotopic values very similar to smoc

subtidal hydrodynamics in a tropical lagoon a dimensionless numbers approach abstract observations in a tropical lagoon of the yucatan peninsula motivated a non dimensional number analysis to examine the relative influence of tidal stress density gradients and wind stress on subtidal hydrodynamics a two month observation period in chelem lagoon covered the transition from the dry to the wet season chelem lagoon is influenced by groundwater inputs and exhibits a main sub basin central sub basin a west sub basin and an east sub basin subtidal hydrodynamics were associated with horizontal density gradients that were modified seasonally by evaporation precipitation and groundwater discharge a tidal froude number fr 0 a wedderburn number w and a stress ratio s 0 were used to diagnose the relative importance of dominant subtidal driving forces the froude number fr 0 compares tidal forcing and baroclinic forcing through the ratio of tidal stress to longitudinal baroclinic pressure gradient the wedderburn number w relates wind stress to baroclinicity the stress ratio s 0 sizes tidal stress and wind stress s 0 is a new diagnostic tool for systems influenced by tides and winds and represents the main contribution of this research results show that spring tide subtidal flows in the tropical lagoon had log fr 0 0 and log s 0 0 i e driven mainly by tidal stresses advective accelerations neap tides showed log fr 0 0 and log s 0 0 i e flows driven by baroclinicity especially at the lagoon heads of the east and west sub basins however when the wind stress intensified over the lagoon the relative importance of baroclinicity decreased and the wind stress controlled the dynamics log w 0 each sub basin exhibited a different subtidal response according to the dimensionless numbers the response depended on the fortnightly tidal cycle the location and magnitude of groundwater input and the direction and magnitude of the wind stress

detection and characterisation of black death burials by multi proxy geophysical methods the construction of the new crossrail railway discovered 25 well preserved skeletons shallowly buried in central london in 2013 subsequent carbon dating and adna analysis confirmed the archaeological age and presence of the yersinia pestis black death plague epidemic strain here we present the non invasive multi proxy geophysical survey of the adjacent charterhouse square rapidly undertaken to detect any further burials and characterise the site historical records suggested the area was a burial ground for black death plague victims before subsequent cemetery and urban land use following initial trial surveys surveys imaged 200 isolated and similar sized burials in the south west of the site there were also two contrasting burial orientations present at various depths which suggested a series of controlled phased burials a well defined eastern burial boundary taking the form of a ditch and bank was also discovered geophysical surveys also identified a subsequent complex site history with multiple aged features this study revises knowledge of black death aged burials and provides important implications for successful geophysical burial detection with significant time and space limited site constraints

microstructures and lattice preferred orientations in experimentally deformed clinopyroxene aggregates microstructures and lattice preferred orientations lpo were analysed on experimentally deformed natural and hot pressed clinopyroxene aggregates in order to understand the relationship between deformation processes and evolving microstructures the lpo was measured using electron backscatter diffraction techniques in the scanning electron microscope sem microstructures were observed by polarized light microscopy and by orientation contrast in the sem natural samples sleaford bay pyroxenite were deformed in axial compression stepping tests up to 16 shortening these samples deformed mainly by twinning and dislocation glide with very little recrystallization no clear lpo evolution apart from the initial lpo could be attributed to deformation synthetic clinopyroxenite samples were hot pressed from powders of the same material with three different grain size ranges and deformed in compression stepping experiments up to 28 shortening in the samples with coarse 30 m and intermediate 20 m grain sizes deformation was dominated by dislocation creep accommodated by subgrain rotation recrystallization the recrystallized grains have sizes up to 8 m and represent 15 25 of the sampled area the sample with the finest initial grain size 5 m deformed dominantly by diffusion creep accompanied by grain boundary migration all of the hot pressed samples deformed in compression have a similar texture consisting of a girdle of c 001 axes normal to compression and a point maximum of b 010 axes and a 100 poles parallel to the compression direction the lpo of recrystallized grains was separated on spatially resolved orientation maps and shows an s type fabric with b 010 parallel to the compression axis and a random a 100 distribution the bulk fabric was largely present in the hot pressed starting material and is interpreted as the result of compaction during cold pressing at moderate strains in axial compression the initial compaction fabric has been weakly overprinted by the recrystallization fabric one hot pressed sample coarse grain size was deformed in torsion to a shear strain of 0 1 the microstructure indicates dominant dislocation creep and contains about 20 recrystallized grains the texture evolved from the rotationally symmetric compaction lpo to an oblique fabric

chlorine isotope behavior during prograde metamorphism of sedimentary rocks abstract chlorine stable isotope compositions of two sedimentary sequences and their metamorphic equivalents were measured in order to study fractionation effects during prograde metamorphism and devolatilization protoliths n 25 were collected from a 50 m section of triassic fluvial and playa lake strata and jurassic liassic marine black shales in a well characterized quarry low greenschist to middle amphibolite facies equivalents n 80 were collected from the glarus alps urseren zone and lucomagno region bulk 37 cl values are constant within individual sedimentary layers but vary from 2 0 to 2 4 in triassic rocks and from 3 0 to 0 in the black shales dolomitic and gypsiferous samples have positive 37 cl values but marls and shales are isotopically negative bulk cl contents show only small declines during the earliest stages of metamorphism metamorphic equivalents of the triassic and liassic protoliths record the same overall ranges in 37 cl as their protoliths samples with highly correlated bulk compositions but different metamorphic grade show no statistically significant difference in 37 cl these data lead to the following conclusions 1 terrestrial and marine sedimentary rocks display large primary heterogeneities in chlorine isotope composition as a result an unambiguous sedimentary signature does not exist in the chlorine stable isotope system 2 no isotopic fractionation is discernable during metamorphic devolatilization even at low temperatures alpine style metamorphism thus has little to no effect on bulk chlorine isotopic compositions despite significant devolatilization 3 cl is largely retained in the rocks during devolatilization contrary to the normally assumed hydrophilic behavior of chlorine continuous release of mixed volatile c o h fluids likely affected cl partitioning between fluid and minerals and allowed chlorine to remain in the rocks 4 there is no evidence for fluid communication across meta sedimentary layers except within the urseren shear zone these data contribute to a relatively closed system view of metamorphic devolatilization from anchizone through mid amphibolite facies conditions

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

chlorine isotope constraints on fluid rock interactions during subduction and exhumation of the zermatt saas ophiolite 1 chlorine isotope compositions of high pressure 2 3 gpa serpentinite rodingite and hydrothermally altered oceanic crust aoc differ significantly from high and ultrahigh pressure 3 2 gpa metasedimentary rocks in the aosta region italy texturally early serpentinites rodingites and aoc have bulk 37cl values indistinguishable from those of modern seafloor analogues 37cl 1 0 to 1 0 in contrast serpentinites and aoc samples that recrystallized during exhumation have low 37cl values 2 7 to 0 5 37cl depletion correlates with progressive changes in bulk chemistry hp uhp metasediments have low 37cl values median 2 5 that differ statistically from modern marine sediments median 0 6 cl in metasedimentary rocks is concentrated in texturally early minerals indicating modification of seafloor compositions early in the subduction history the data constrain fluid sources during both subduction and exhumation related phases of fluid rock interaction 1 marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction 2 no pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial 3 localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel most samples however preserved protolith signatures during subduction to near arc depths

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

cl br ratios and stable chlorine isotope analysis of magmatic hydrothermal fluid inclusions from butte montana and bingham canyon utah a bulk geochemical study has been carried out on fluid inclusion leachates extracted from quartz veins from porphyry cu deposits in butte montana usa and bingham canyon utah usa the leachates mostly represent low salinity magmatic hydrothermal fluid inclusions their halogen ratios br cl of fluid inclusion leachates were determined by ion chromatography and 37cl values of the leachates were measured by continuous flow isotope ratio mass spectrometry br cl ratios from early pre main stage and later main stage veins at butte range from 0 60 to 1 88 10 3 m ratios are similar in pre main stage veins with sericite bearing selvages and main stage samples ranging from 0 81 to 1 08 10 3 and from 0 92 to 1 88 10 3 m respectively clustering below seawater 1 54 10 3 m and overlapping mantle values 1 2 10 3 m two samples associated with early pre main stage potassic alteration yield distinctly lower br cl ratios of 0 60 and 0 64 10 3 m butte 37cl values range from 0 8 to 2 3 with no significant difference between pre main stage and main stage samples br cl ratios for quartz veins from bingham canyon range from 0 18 to 3 68 10 3 m br cl ratios from bingham range above and below previously reported for porphyry copper deposits in contrast to butte 37cl values for bingham are lower ranging from 0 9 to 4 1 in the absence of any processes which can significantly fractionate chlorine isotopes at high temperatures we suggest that the porphyry system at bingham and to a lesser extent at butte have inherited negative chlorine isotopic signatures from the subducting slab generated at low temperatures

stable cl isotopes in subduction zone pore waters implications for fluid rock reactions and the cycling of chlorine stable cl isotope ratios measured in marine pore waters associated with the barbados and nankai subduction zones extend significantly to 8 the range of 37 cl values reported for natural waters these relatively large negative values together with geologic and chemical evidence from barbados and nankai and recent laboratory data showing that hydrous silicate minerals i e those with structural oh sites are enriched up to 7 5 in 37 cl relative to seawater strongly suggest that the isotopic composition of cl in pore waters from subduction zones reflects diagenetic and metamorphic dehydration and transformation reactions these reactions involve clays and or other hydrous silicate phases at depth in the fluid source regions chlorine therefore cannot be considered geochemically conservative in these systems the uptake of cl by hydrous phases provides a mechanism by which cl can be cycled into the mantle through subduction zones thus stable cl isotopes should help in determining the extent to which cl and companion excess volatiles like h 2 o and co 2 cycle between the crust and mantle

a chlorine isotope study of dsdp odp serpentinized ultramafic rocks insights into the serpentinization process abstract eight dsdp odp cores were analyzed for major ion concentrations and 37cl values of water soluble chloride 37clwsc and structurally bound chloride 37clsbc in serpentinized ultramafic rocks this diverse set of cores spans a wide range in age temperature of serpentinization tectonic setting and geographic location of drilled serpentinized oceanic crust three of the cores were sampled at closely spaced intervals to investigate downhole variation in cl concentration and chlorine isotope composition the average total cl content of all 86 samples is 0 26 0 16 wt 0 19 0 10 wt as water soluble cl xwsc and 0 09 0 09 wt as structurally bound cl xsbc structurally bound cl concentration nearly doubles with depth in all cores there is no consistent trend in water soluble cl content among the cores chlorine isotope fractionation between the structurally bound cl site and the water soluble cl site varies from 1 08 to 1 16 averaging to 0 21 samples with negative fractionations may be related to reequilibration of the water soluble chloride with seawater post serpentinite formation six of the cores have positive bulk 37cl values 0 05 to 0 36 the other two cores 173 1068a leg hole and 84 570 have negative bulk 37cl values 1 26 and 0 54 the cores with negative 37cl values also have variable cl so42 ratios in contrast to all other cores the isotopically positive cores 153 920d and 147 895e show no isotopic variation with depth the isotopically negative core 173 1068a decreases by 1 with depth for both the water soluble and structurally bound cl fractions non zero bulk 37cl values indicate cl in serpentinites was incorporated during original hydration and is not an artifact of seawater infiltration during drilling cores with positive 37cl values are most likely explained by open system fractionation during hydrothermal alteration with preferential incorporation of 37cl from seawater into the serpentinite and loss of residual light cl back to the ocean fluid rock ratios were probably low as evidenced by the presence of water soluble salts the two isotopically negative cores are characterized by a thick overlying sedimentary package that was in place prior to serpentinization we believe the low 37cl values of these cores are a result of hydration of ultramafic rock by infiltrating aqueous pore fluids from the overlying sediments the resulting serpentinites inherit the characteristic negative 37cl values of the pore waters chlorine stable isotopes can be used to identify the source of the serpentinizing fluid and ultimately discern chemical and tectonic processes involved in serpentinization

magnitudes of submarine groundwater discharge from marine and terrestrial sources indian river lagoon florida 1 magnitudes of terrestrial fresh and marine saline sources of submarine groundwater discharge sgd are estimated for a transect across indian river lagoon florida two independent techniques seepage meters and pore water cl concentrations show terrestrial sgd decreases linearly to around 22 m offshore and these techniques together with a model based on the width of the outflow face indicate a cumulative discharge of between 0 02 and 0 9 m3 d per meter of shoreline seepage meters and models of the deficiencies in 222rn activity in shallow sediments indicate marine sgd discharges of roughly 117 m3 d per meter of shoreline across the entire 1800 m wide transect two surface streams nearest the transect have an average discharge of about 28 m3 d per meter of shoreline marine sgd is thus 4 times greater then surface water discharge and more than 2 orders of magnitude greater than terrestrial sgd the magnitude of the terrestrial sgd is limited by the amount of regional precipitation evaporation recharge and groundwater usage while marine sgd is limited only by processes circulating marine water into and out of the sediments the large magnitude of marine sgd means that it could be important for estuarine cycling of reactive components such as nutrients and metals with only slight modification from estuarine water compositions the small magnitude of terrestrial sgd means that large differences from estuarine water composition would be required to affect chemical cycling

alteration of oceanic crust and geologic cycling of chlorine and water we report new estimates of transport rates for h2o and cl between the mantle and surface reservoirs our estimates take into consideration alteration of oceanic crust especially that of plutonic rocks and possible subduction of sediments the effect of hydrothermal alteration on the cl budget seems to be negligible but the effect on the h2o budget is significant altered oceanic crust excluding sediments contains about 10 times as much h2o as the unaltered crust and its subduction may result in a net transport of h2o to the upper mantle in subduction zones however the rate of expulsion of h2o from the mantle by subduction zone magmatism is comparable to the amount released by ridge magmatism and is only about 10 of the amount subducted therefore about 90 of the subducted h2o must be returned to the mantle or returned to the crust by other processes in addition subduction of oceanic sediments to mantle depths will result in 1 1 a further increase in the return rate of h2o to the mantle reservoir 2 2 possible net transfer of cl to the mantle depending on the rate of pore water expulsion

halogens of bushveld complex south africa δ37cl and cl f evidence for hydration melting of the source region in a back arc setting abstract the bushveld complex is one of only a few layered intrusions anomalously enriched in chlorine this study presents the first chlorine stable isotope analyses of bushveld and associated rocks designed to constrain the source of bushveld cl most samples overlap the range of values for pristine morb and altered seafloor samples 37 cl 4 relative to sea water this contrasts with distal metasedimentary floor rocks 37 cl 0 with little evidence of contamination away from the marginal rocks the cl isotope composition and high cl f ratio is therefore a fundamental characteristic of the lower and critical zone magmas and not derived from infiltration from the country rock these results the high cl f ratio and the boninitic arc like character of bushveld magma are consistent with hydration partial melting of a depleted source in a subduction related setting with cl supplied either by the dehydration of a subducted slab with a heavy cl signature or an overridden wet mantle hotspot

the fate of b cl and li in the subducted oceanic mantle and in the antigorite breakdown fluids we present an inventory of b cl and li concentrations in a key minerals from a set of ultramafic samples featuring the main evolutionary stages encountered by the subducted oceanic mantle and in b fluid inclusions produced during high pressure breakdown of antigorite serpentinite samples correspond to i nonsubducted serpentinites northern apennine and alpine ophiolites ii high pressure olivine bearing antigorite serpentinites western alps and betic cordillera iii high pressure olivine orthopyroxene rocks recording the subduction breakdown of antigorite serpentinites betic cordillera two main dehydration episodes are recorded by the sample suite partial serpentinite dewatering during formation of metamorphic olivine followed by full breakdown of antigorite serpentine to olivine orthopyroxene fluid ion probe and laser ablation icp ms la icp ms analyses of cl b and li in the rock forming minerals indicate that the hydrous mantle is an important carrier of light elements the estimated bulk rock b and cl concentrations progressively decrease from oceanic serpentinites 46 7 ppm b and 729 ppm cl to antigorite serpentinites 20 ppm b and 221 ppm cl to olivine orthopyroxene rocks 9 4 ppm b and 45 ppm cl this suggests release of oceanic cl and b in subduction fluids apparently without inputs from external sources lithium is less abundant in oceanic serpentinites 1 3 ppm and the initial concentrations are still preserved in high pressure antigorite serpentinites higher li contents in olivine ti clinohumite of the olivine orthopyroxene rocks 4 9 ppm bulk rock li as well as in the coexisting fluid inclusions suggest that their budget may not be uniquely related to recycling of oceanic li but may require input from external sources laser ablation icp ms analyses of fluid inclusions in the olivine orthopyroxene rocks enabled an estimate of the li and b concentrations in the antigorite breakdown fluid the inclusion compositions were quantified using a range of salinity values 0 4 2 wt naclequiv as internal standards yielding maximum average fluid rockdb 5 and fluid rockdli 3 5 we also performed model calculations to estimate the b and cl loss during the two dehydration episodes of serpentinite subduction the first event is characterized by high fluid rock partition coefficients for cl 100 and b 60 and by formation of a fluid with salinity of 4 8 wt naclequiv the antigorite breakdown produces less saline fluids 0 4 2 wt naclequiv and is characterized by lower partition coefficients for cl 25 60 and b 12 30 our calculations indicate that the salinity of the subduction fluids decreases with increasing depths fluid rockdb fluid rockdcl 1 0 5 indicates that cl preferentially partitions into the evolved fluids relative to b and that the b cl of fluids progressively increases with increasing depths and temperatures despite light element release in fluids appreciable b cl and li are still retained in chlorite olivine and ti clinohumite beyond the antigorite stability field this permits a bulk storage of about 10 ppm b 45 ppm cl and 5 ppm li i e concentrations much higher than in mantle reservoirs chlorite is the cl repository and its stability controls the cl and h2o budget beyond the antigorite stability b and li are bound in olivine and clinohumite the subducted oceanic mantle thus retains light elements beyond the depths of arc magma sources potentially introducing anomalies in the upper mantle

tidal variability of salinity and velocity fields related to intense point source submarine groundwater discharges into the coastal ocean velocity and hydrography measurements were used to determine the tidal variability and detailed structure of an intense 43 200 m3 d 1 point source submarine groundwater discharge from a spring located in the coastal ocean of the yucatan peninsula mexico measurements were obtained during a dry season with a combination of towed profiling and fixed instrumentation the goal of these observations was to understand the effects of tides on the velocity and salinity structure of the water column that determine mixing and dispersion processes at spatial scales from meters to kilometers tidally averaged flows were characterized by an upward jet flanked by asymmetric downdrafts the asymmetry was caused by a 0 1 m s 1 ambient horizontal flow and by the 40 angle relative to the vertical of discharge the spatially averaged salinity distributions exhibited lowest values at low tides and highest values at high tides this was attributed to tidal variations of hydrostatic pressure acting on the spring outflow which allowed 1 m s 1 vertical flows at low tides and 0 05 m s 1 vertical velocities at high tides the vertical momentum balance consisted of upward accelerations produced by buoyancy and inertia from the spring and downward accelerations from gravity on the basis of this balance and of energetic considerations the vertical extent of the spring discharge likely depends on the density contrast between ambient and discharge waters buoyancy forces the upward speed of the spring inertia forces and the depth of the water column hydrostatic pressure force all of which vary with tides

contrasting serpentinization processes in the eastern central alps stable isotope compositions have been determined for serpentinites from between davos arosa platta nappe switzerland and the valmalenco italy d and 18o values 120 to 60 and 6 10 respectively in the arosa platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water one sample of chrysotile has a 18o value of 13 providing evidence of high w r ratios and low formation temperature of lizardite chrysotile in this area in contrast relatively high d values 42 to 34 and low 18o values 4 4 7 4 for serpentine in the eastern part of the valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water the antigorite in the valmalenco is the first reported example of continental antigorite with an ocean water signature an amphibole sample from a metasomatically overprinted contact zone to metasediments d 36 indicates that the metasomatic event also took place in the presence of ocean water lower d values 93 to 60 of serpentines in the western part of the valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism low water rock ratios during regional metamorphism and metasomatism have to be assumed for both regions

nutrient biogeochemistry in a gulf of mexico subterranean estuary and groundwater derived fluxes to the coastal ocean we hypothesize that biogeochemical processes in a subterranean estuary in the northeastern gulf of mexico significantly alter nutrient concentrations that are discharged into the ocean via submarine groundwater discharge sgd this subterranean estuary is a site of steep gradients over small spatial scales so selecting the appropriate groundwater endmember for flux calculations is difficult two endmember mixing models typically applied to investigate biogeochemical processes in surface estuaries are not useful in this case because of aquifer heterogeneity and complex solid fluid interactions groundwater residence times redox potential source strength and aquifer matrix appear to be the most important drivers for dissolved organic carbon doc and nutrient concentrations in this pristine coastal plain aquifer the distribution of dissolved species was consistent with a sequence of reactions in a narrow 2 m surface layer in which nitrate is initially exhausted likely because of denitrification organic nitrogen is remineralized releasing ammonium and some doc remains on the basis of a 222rn derived non steady state box model total terrestrial marine sgd rates were estimated to oscillate around 11 cm d21 the sgd is composed almost entirely of recirculated seawater accounting for 95 of total sgd fluxes conservative estimates of groundwater derived nitrogen inputs into the coastal ocean were 8 2 6 1 2 mmol m22 d21 consisting of ammonium 58 organic nitrogen 28 and nitrate 14 we suggest that these mainly represent recycled rather than new nutrient additions when extrapolated to the florida gulf coast the nitrogen and doc fluxes were comparable to the main regional rivers supporting the proposition that sgd plays a major role in coastal biogeochemistry the biogeochemical implications of submarine groundwater discharge sgd into coastal environments are becoming increasingly recognized globally groundwater discharge has been estimated to be only a few percent of the total freshwater flux to the oceans burnett et al 2006 in spite of that small fraction the input of nutrients to coastal environments via groundwater pathways could be globally more important because nutrient concentrations in groundwater are often much higher than those in river water in addition high dissolved n p ratios in groundwater relative to surface waters might drive the coastal ocean toward p limitation within the coming decades perhaps changing the present n limited coastal primary production slomp and van cappellen 2004

the search for graves with ground penetrating radar in connecticut the search for unmarked and clandestine graves is a labor intensive time consuming and often frustrating task several geo physical methods are available which can be expediently used with little or no disturbances to sites among which ground penetrating radar gpr is often considered the most useful tool to delineate possible graves this paper is the result of many years of gpr testing for unmarked graves in connecticut natural and cultural conditions are considered in the failure and or success of detection and the use of gpr in archaeological studies

the search for graves over the decades grave markers in old cemeteries have been lost geophysical exploration can sometimes locate the unmarked burials the two techniques which may be best for this search are a ground penetrating radar survey and a soil conductivity survey a ground penetrating radar survey with its capability for estimating the depth and shape of buried objects is particularly suitable with an electromagnetic induction survey the disturbed soil in the grave shaft can sometimes be detected as a change in electrical conductivity both of these surveys also can locate large metal objects these surveys have limitations at some sites the radar cannot profile deeply enough at others the soil strata are so complex that graves cannot be distinguished a conductivity survey can be degraded by metallic trash and other small objects in the topsoil it can give the best results where the earth is distinctly stratified results from nine surveys are illustrated here the sites are all in the u s a and the gra

stable chlorine isotopes in phanerozoic evaporites abstract modern seawater has a uniform 37cl value 0 0 with an exception in the upper current of the bosphorus 0 4 marine halite ranging in age from cambrian to miocene has 37cl values of 0 0 0 9 with most of the data in the range 0 0 0 5 mean 37cl values differ measurably between basins with no evident relationship to basin size or to age smaller evaporite bodies have the largest 37cl ranges potash facies halite has mean 37cl values lower than those of halite facies salt in the east siberia and zechstein basins the bulk 37cl of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions during the phanerozoic a detectable change in the 37cl values of the oceans is unlikely as a result of cl fluxes to and from the mantle and evaporites in halite the values of 37cl that cannot be explained by fractionation occurring on crystallization are best explained by the addition of non marine cl with 37cl 0 0 to evaporite brine

salt intrusion at a submarine spring in a fringing reef lagoon variations in discharge and turbulent kinetic energy tke were studied at a point source submarine groundwater discharge sgd within a fringing reef lagoon from quadrature neap to syzygy spring tides the principal factors affecting discharge and tke variations were tides and waves field data indicated discharge and tke varied with high and low tides and with quadrature and syzygy maximum discharge and tke values were observed during low tides when the hydrostatic pressure over the jet was minimal while the lowest discharge and tke values were found at high tides syzygy tides produced consistent saltwater intrusion during high tides while quadrature tides produced the greatest tke values in general as the discharge intensified during low tides jet temperatures decreased suggesting that waters originated further within the aquifer at the same time jet salinities increased suggesting a mixing of aquifer and seawater to reconcile these two seemingly opposing views it is proposed that the jet conduit is connected to a stratified chamber with seawater below brackish water the greatest subtidal discharge occurred during quadrature tides syzygy produced low subtidal discharge driven by flow reversals flow into the aquifer observed throughout syzygy high tides in conjunction with the peak wave setup 5 cm observed during a storm while tides were the primary driving force of the discharge waves played a nonnegligible role wave effects on the discharge were most evident during syzygy high tides combined with a storm when the subtidal spring discharge was weakest and salt intrusion developed

halogens in atlantis bank gabbros sw indian ridge implications for styles of seafloor alteration abstract the processes controlling halogen f cl br i abundances in gabbroic ocean crust recovered from the 809 m deep hole u1473a drilled on the atlantis bank during international ocean discovery program iodp expedition 360 were investigated the aims were to provide new constraints on hydrothermal alteration and the abundances of halogens potentially transported to subduction zones in oceanic crust produced on a slow spreading ridge halogens in 51 gabbros and felsic veins have concentrations of 20 260 ppm f 15 840 ppm cl 44 1230 ppb br and 1 2490 ppb i on average the gabbros retain a melt derived magmatic f component of 58 26 but are dominated by 96 hydrothermal cl br i and h2o the abundances of hydrothermal cl br and i are consistent with alteration at a seawater rock ratio of downhole variations show f cl br and h2o are most abundant in amphibole and clay rich alteration zones at the top of the hole the highest i concentrations of 1 2 5 ppm delineate an oxidised co2 rich alteration zone in which seawater iodate was incorporated into carbonate and fe oxyhydroxide alteration the role of iodate which is more reactive than other halides in generating i rich alteration can be distinguished from alteration by i rich sedimentary pore waters because the oxidised alteration is characterised by high i cl together with low br cl whereas organic matter in pore waters is enriched in both br cl and i cl the halogens have inferred compatibilities of f io 3 oh cl br i in the investigated alteration assemblage epma and shrimp analyses indicate amphibole contains 1000 3000 ppm cl in amphibolite facies alteration at the top of the hole amphibole chlorite and talc in greenschist facies alteration have much lower concentrations typically in the range of 20 800 ppm cl median 100 ppm cl and f cl ratios of

chlorine isotope variations across the izu bonin mariana arc chlorine isotope ratios were determined for volcanic gas geothermal well ash and lava samples along the izu bonin mariana volcanic front serpentinite clasts and muds from serpentine seamounts conical south chamorro torishima basalts from the guguan cross chain and sediments from ocean drilling program odp sites 800 801 802 and 1149 there is no systematic variation in 37 cl values along the volcanic front in either gas or ash samples in contrast distinct variations occur across the arc implying variations in the fluid source at different depths within the subduction zone serpentinite clasts and serpentine muds from the seamounts tap a source of 30 km depth and have 37 cl values of structurally bound chloride of 0 4 0 4 n 24 identical to most seafloor serpentinites suggesting a serpentinite chrysotile and or lizardite to antigorite transition fluid source tapping deeper levels of the subduction zone 115 130 km depth volcanic gases and ashes have 37 cl values averaging 1 1 1 0 n 29 precisely overlapping the range measured in sediments from odp cores 1 1 0 7 n 11 and limited altered oceanic crust aoc both sediments and aoc are possible cl sources in the volcanic front the guguan cross chain basalts come from the greatest depths and have an average 37 cl value of 0 2 0 2 n 3 suggesting a second serpentine derived source in this case from antigorite breakdown at 200 km depth

comment to chlorine stable isotopes and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean by wei et al a review of the cl isotope composition of serpentinites and the global chlorine cycle abstract wei et al wei w kastner m spivack a 2008 chlorine stable isotope and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean earth planet sci lett 266 90 104 published chlorine isotope data for pore fluids and serpentinites from three subduction zones and two obducted serpentinites the measured 37cl values of serpentinites ranged from 1 2 to 6 0 vs smoc far higher than all other published data for serpentinites the explanation for these high 37cl values defies known fractionation mechanisms instead the anomalous 37cl values are almost certainly due to analytical artifacts known to exist for the method the authors employed wei et al wei w kastner m spivack a 2008 chlorine stable isotope and halogen concentrations in convergent margins with implications for the cl isotopes cycle in the ocean earth planet sci lett 266 90 104 concluded that if high 37cl serpentinites 6 were subducted into the mantle then a change in the 37cl value of the crustal reservoir would be observed in the evaporite record over the last 200ma because the cl isotope composition of the crustal reservoirs has been constant over this time period as constrained by evaporites they argue that cl in serpentinites is recycled back to the oceans this argument is flawed for two reasons first the 37cl values of serpentinites is close to 0 not 6 as suggested in their paper second the 37cl value of the crustal reservoir would change immeasurably over 200ma even if serpentinites of 6 were subducted into the mantle in fact it has been shown that the crust mantle and chondritic reservoir all have 37cl values close to 0 sharp z d barnes j d brearley a j fischer t p chaussidon m kamenetsky v s 2007 chlorine isotope homogeneity of the mantle crust and carbonaceous chondrites nature 446 1062 1065 no secular variation in the 37cl value of the crust is expected a conclusion that is supported by chlorine isotope data on sediments extending back over 3 5ga sharp z d barnes j d brearley a j fischer t p chaussidon m kamenetsky v s 2007 chlorine isotope homogeneity of the mantle crust and carbonaceous chondrites nature 446 1062 1065

theoretical estimates of equilibrium chromium isotope fractionations equilibrium chlorine isotope 37 cl 35 cl fractionations have been determined by using published vibrational spectra and force field modeling to calculate reduced partition function ratios for cl isotope exchange ab initio force fields calculated at the hf 6 31g d level are used to estimate unknown vibrational frequencies of 37 cl bearing molecules whereas crystalline phases are modeled by published lattice dynamics models calculated fractionations are principally controlled by the oxidation state of cl and its bond partners molecular mass or the absence of c h bonds also appears to play a role in determining relative fractionations among simple cl bearing organic species molecules and complexes with oxidized cl i e cl 0 cl etc will concentrate 37 cl relative to chlorides substances with cl at 298 k clo 2 containing cl 4 and clo 4 containing cl 7 will concentrate 37 cl relative to chlorides by as much as 27 and 73 respectively in rough agreement with earlier calculations among chlorides 37 cl will be concentrated in substances where cl is bonded to 2 cations i e fecl 2 mncl 2 micas and amphiboles relative to substances where cl is bonded to 1 cations such as nacl by 2 to 3 at 298 k organic molecules with c cl bonds will be even richer in 37 cl 5 to 9 at 298 k precipitation experiments in combination with our results provide an estimate for cl isotope partitioning in brines and suggest that silicates to the extent that their cl atoms are associated with nearest neighbor 2 cations analogous with fecl 2 and mncl 2 will have higher 37 cl 35 cl ratios than coexisting brine by 2 to 3 at room temperature calculated fractionations between hcl and cl 2 and between brines and such alteration minerals are in qualitative agreement with both experimental results and systematics observed in natural samples our results suggest that cl bearing organic molecules will have markedly higher 37 cl 35 cl ratios by 5 8 to 8 5 at 295 k than coexisting aqueous solutions at equilibrium predicted fractionations are consistent with the presence of an isotopically heavy reservoir of hcl that is in exchange equilibrium with cl aq in large marine aerosols

the sources and evolution of mineralising fluids in iron oxide copper gold systems norrbotten sweden constraints from br cl ratios and stable cl isotopes of fluid inclusion leachates we have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated fe oxide cu au mineralising systems in norrbotten sweden fluid inclusions in late stage veins in fe oxide apatite deposits contain saline brines and have a wide range of br cl molar ratios from 0 2 to 1 1 10 3 and 37cl values from 3 1 to 1 0 leachates from saline fluid inclusions from the greenstone and porphyry hosted cu au prospects have br cl ratios that range from 0 2 to 0 5 10 3 and 37cl values from 5 6 to 1 3 finally the cu au deposits hosted by the nautanen deformation zone ndz have br cl molar ratios from 0 4 to 1 1 10 3 and 37cl values that range from 2 4 to 0 5 although the bulk of the data fall within 0 0 5 the br cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite most of the isotopic data from the fe oxide apatite and greenstone deposits are consistent with a mantle derived source of the chlorine with the exception of the four samples with the most negative values the origin of the low 37cl values in these samples is unknown but we suggest that there may have been some modification of the cl isotope signature due to fractionation between the mineralising fluids and cl rich silicate assemblages found in the alteration haloes around the deposits if such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low 37cl values would be significantly larger the source of cl in the ndz deposits has a crustal signature which suggests the cl in this system may be derived from meta evaporites or from input from crustal melts such as granitic pegmatites of the lina suite