vanadiferous minerals from the nereus deep red sea the chemical analysis by emp eds of 140 samples in cores from six red sea troughs and basins has led to the discovery in the nereus deep of high vanadium concentrations up to 1 3 v2o3 in several bulk samples and to the isolation of a major magnetite phase this vanado magnetite remarkable for its high content of vanadium mean 1 45 v2o3 and its lack of titanium is frequently zoned the v content decreasing toward the outer zones oxides with up to 42 v2o3 have also been found since the origin of the magnetite is clearly authigenic its high vanadium and low titanium concentrations are traced back to the differential hydrothermal leaching of fe ti oxides which occur profusely in basic eruptive rock clasts actually present in some of the overlying seams authors

heat and salt fluxes in the atlantis ii deep red sea abstract the atlantis ii deep is located on the red sea axial rift it is a topographic depression enclosing a volume of about 17 km3 between 1 900 m and 2 200 m depth that contains layered brines of temperatures up to 66 c and salinities up to 270 previous geochemical investigations showed that the hot brines result from discharge of hydrothermal solutions that have exchanged heat and chemical components with the basaltic substratum the last investigation of the deep in 1992 showed that the brines occurred in four well mixed layers with the shallowest at a depth of 2 000 m the temperature and salinity profiles describe a transition zone from 2 000 m to 1 900 m above which red sea water occurs the distribution of temperature and salt in this transition zone appears to be controlled by the topography of the deep the hydrographic structure of the brine column has been documented in the literature for seven time intervals between 1966 and 1992 examination of these data shows that the system changed with time the evolution of the entire package of brines that fill the deep shows the following changes 1 the temperature of the brines increased 2 the salinity of the solutions increased 3 the two brine layers described in 1966 still existed in 1992 but new layers appeared above them 4 for 26 years almost all additional heat and salt supplied in the deep were confined to the depression and were not dispersed into the overlying seawater the fourth point indicates that a heat and salt balance for the deep can be calculated the calculation of the heat that entered into the system was divided into two components the temperature increase of the brines and the heat loss at the wall rock the latter component was negligible the rate of heat input to the deep was constant during the period considered and amounted to 0 54 109 w the salt input was also constant and equalled 250 350 kg s during the period 1966 1992 heat and salt were most probably supplied by a hydrothermal solution with an average range of flow rate temperature and salinity of 670 1000 kg s 195 310 c and 270 370 respectively

hydrothermal alteration of graywacke and basalt by 4 m nacl separate experiments at 350 degrees c and 500 bars at a rock fluid ratio of 1 10 illite dolomite and quartz amounting to 67 percent of the original graywacke were converted to albite and smectite the rock gained na and released ca k heavy metals and co 2 to solution in sharp contrast the reaction of 4 m nacl with basalt produced only minor alteration albitization of graywacke produces h super whereas albitization of basalt apparently consumes h super all experiments to date that have reacted basalt with sea water natural brine and fully saturated nacl over a variety of conditions have been unsuccessful in producing a spilite alteration assemblage modified journal abstract

hydrographic structure of brine filled deeps in the red sea new results from the shaban kebrit atlantis ii and discovery deep abstract hydrographic profiles with ctd and water samples from four brine filled deeps in the red sea shaban kebrit atlantis ii and discovery deep were taken during the meteor 31 2 expedition in february march 1995 in the shaban deep area two smaller basins containing high saline brine were found in addition to the already known southern basins corresponding salinities 150 7 cl in the upper brine section and near equal brine levels around 1325 m water depth suggest subbottom connections below the sills separating the northern and southern basins an insignificant decrease in temperature to about 24 1 c has occurred in the upper brine since detection of the shaban deep in 1981 and no changes were found for the brine seawater level no significant changes have been observed in the kebrit deep over the last 23 years in temperature 24 3 c chlorinity 154 0 0 3 cl and brine level 1466 1 m the transition from high saline brine to normal seawater salinity probably extends over a depth of only a few decimetres or less strong changes however were registered for the atlantis ii deep the temperature increase known from numerous earlier investigations continued the gradient of increase was the steepest during the last 2 5 years and a temperature of 71 7 c was reached in the lower brine of the sw basin the structure of the lower transition zone between about 1990 m water depth and high saline brine has also changed significantly now containing two convective layers with nearly constant temperatures 61 and 55 c respectively the neighbouring discovery deep also shows evidence of increased hydrothermal activities while the temperature was nearly constant near 44 7 c until 1977 it has since increased to almost 50 c and the brine level has risen by about 17 m

3 d inversion of deep tow magnetic data on the atlantis ii deep red sea hydrothermal and geodynamic interpretation abstract to study the magnetic signature of hydrothermal oceanic crust areas data were collected using a magnetometer towed a few hundred meters above the sea floor within an acoustic transponder net the experiment was performed in the red sea over the atlantic ii deep near 21 20 n 38 05 e this deep created during the brunnes epoch is well known for its intense hydrothermal activity and the presence of hot brines overlying metalliferous sediments the magnetic field was inverted to obtain the distribution pattern of crustal magnetization including the effects of topography and irregular depth of the magnetic sensor the procedure however does not produce any unique solution it is approximated using probabilistic linear methods tarantola and valette 1982 which require the introduction of constraints in the form of gaussian probability density functions the resultant magnetization pattern then follows a gaussian law the mean and standard deviation are then computed the results show contrary to what has been suggested formerly rona 1978a b that the strongest magnetization as well as the most frequent hydrothermal and magmatic occurrences are found in the southwest basin the high magnetic intensities are thus associated with a recent magmatism which initiates the hydrothermal circulation two hypotheses explain this 1 1 the freshness of the basalts and the low temperature alteration are the principal causes of magnetization contrasts and represent respectively the discharge and recharge zones of the hydrothermal plumbing 2 2 in the general framework of the red sea opening by progressive tearing the formation of the atlantis ii was extremely fast according to the elastic rebound theory reid 1911 this hypothesis is applicable to some other deeps

mineralogy and geochemistry of epigenetic features in metalliferous sediment atlantis ii deep red sea finely laminated and undisturbed except in the area of the southwest basin in this part bedding resedimentation and brecciation are common in addition some sediment cores contain vein minerals precipitated in open fissures which crosscut unlithified metalliferous sediments these veins are the conduits by which new hot brine vents into the deep vein mineralogy is dominated by anhydrite talc smectite pyrite sphalerite and chalcopyrite vertical zonation due to cooling and reaction of the incoming brine as it rises through the metalliferous sediment near the southwest basin west basin transition metalliferous sediment has been locally recrystallized to a hematite magnetite pyroxene assemblage probably due to the intrusion of basalt into the metalliferous sediments modified journal abstract

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

evidence for episodic hydrothermal activity in the red sea from the composition and formation of hydrothermal sediments thetis deep abstract sediments obtained from the ne thetis deep during the sonne cruise so 29 consist of a manganite facies and various types of fe facies hematite magnetite goethite and lepidocrocite facies the sediments have a chemical and mineralogical composition similar to some of the lithological units previously described from the atlantis ii deep 160 km to the southeast in contrast to the atlantis ii deep no stable brine pool recently exists in the ne thetis deep however based on the fe mn fractionation in the fe facies types an intermittent brine filling of the ne thetis deep has probably existed we propose that the formation of the brine pools correlate to the volume of discharging fluids the chronology of hydrothermal deposition in the ne thetis deep seems to correlate with similar events in the atlantis ii deep suggesting that major tectonic events in the red sea may have caused large scale pulses of hydrothermal activity

atlantis ii deep geothermal brine system chemical processes between hydrothermal brines and red sea deep water water samples and suspended matter taken in the atlantis ii deep area red sea during the expedition so 2 with rv sonne in november 1977 were investigated for chemical composition only slight changes have been found for most components since 1966 a strong decrease of the cu content from 100 500 g kg 1 according to brooks et al 1969 to values below 1 g kg 1 has however become evident comparison between theoretical concentrations in the intermediate brine layers resulting when using the lower or the upper homothermal layers respectively as end members of mixing processes with red sea deep water and the concentrations measured prove that precipitation and resolution processes have considerable influence on the concentrations found in solution components strongly involved in such processes are iron manganese copper oxygen sulfate and silica as could be shown from comparison of theoretical and measured concentration profiles along the water column investigations of the metals suspended in the brine confirm these processes compared to 1971 1972 the cu and zn values in suspension preferring the southwestern basin at that time are clearly reduced thus being in agreement with the recently lowered hydrothermal activity remarks on the hypothetical composition of the unknown hydrothermal brine discharging into the deepest basin are also included

double diffusive convection in this paper we present a rather personal view of the important developments in double diffusive convection a subject whose evolution has been the result of a close interaction between theoreticians laboratory experimenters and sea going oceano graphers more recently applications in astrophysics engineering and geology have become apparent in the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists

chemical mass balances in metalliferous deposits from the atlantis ii deep red sea abstract in order to assess the quantitative distribution of mineral species within the sedimentary series of the atlantis ii deep we have examined the chemical composition mineralogy and physical properties of 120 sediment samples from two cores that sampled the entire sediment sequences in the west and south west basins biostratigraphic correlations and chemical budget calculations indicate that the nonmetalliferous solid fractions i e detrital and biogenic particles in the older sedimentary unit unit 1 in the west basin represent 46 wt of the total and that they were deposited between 23 000 and 15 12 000 years bp with a mass accumulation rate between 109 and 150 kg per thousand years per square metre the muddy sediment in the upper part of the west basin core units 2 3 and 4 consists mainly of metalliferous particles which account for less than 15 wt of the mud and yield a mass accumulation rate 130 162 kg k y m 2 close to that of nonmetalliferous particles deposited simultaneously nonmetalliferous particles were probably the major source of si and a significant source of pb through dissolution in the brine system and diagenesis in the metalliferous mud the metalliferous sediments in the upper unit of the south west basin unit u 1100 cm were deposited at the same time as those of the upper unit in the west basin unit 4 335 cm the calculated mass accumulation rate is about 700 kg k y m 2 for unit u the recent sediments of the south west basin are more enriched in zn and cu and more depleted in mn relative to fe than the contemporary sediments in the west basin suggesting that the hydrothermal source has been in or near the south west basin during the last 2 250 years assuming that a salton sea like solution supplies all the fe contained in the west basin metalliferous sedimentary pile the mineralizing brine flowed at a minimum rate of 30 l s except for the period of mn oxide deposition the difference between the metal fe ratios in oxide rich and sulphide rich facies is attributed to changes in the chemical composition of the mineralizing fluid rather than to chemical processes acting in the brine system of the atlantis ii deep

sr nd and pb isotope constraints on the formation of the metalliferous sediments in the nereus deep red sea previous chemical analyses of sediments from nereus deep core 412 located in the northern part of the red sea at about 23 20 n have demonstrated the occurrence of v rich authigenic magnetites associated with fe zn and cu sulphides mostly located at the bottom of the core the evolutionary stage of nereus deep is intermediate between that of the immature shaban deep and the more evolved atlantis ii deep previous studies have proposed either morb basalts by analogy with east pacific rise sulphide deposits or sediments as possible sources of the metals in the red sea metalliferous sediments sr nd and pb isotope systematics observed at ten levels in nereus core 412 lead us to distinguish three types of sediments 1 with predominantly basaltic fragments associated with loose titanomagnetite crystals 0 70413 87sr86sr 0 70622 0 51271 143nd144nd 0 51300 18 618 206pb204pb 18 673 2 detrital or biogenic sediments with a continental isotopic imprint 0 70938 87sr86sr 0 71323 0 51242 143nd144nd 0 51262 18 848 206pb204pb 18 890 and 3 v rich metalliferous sediments 0 70872 87sr86sr 0 70895 0 51260 143nd144nd 0 51274 18 717 206pb204pb 18 851 on sr nd and pb pb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups our data suggest that the sr nd and pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins red sea morb and continental arabo nubian shield these data clearly support a model of convective circulation within the nereus deep sedimentary pile this model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of v rich magnetites and fe zn and cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core a driving force represented by magmatic activity located near the 412 core in the nereus deep is required to explain the presence of hot convective fluids these data also suggest that for sedimented ridges the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals

chemical and isotopic 87sr 86sr δ18o δd constraints to the formation processes of red sea brines abstract about twenty deeps filled with hot brines and or metalliferous sediments are located along the red sea axis these brines present a well suited framework to study the hydrothermal activity in such a young ocean the present study outlines the results of a geochemical approach combining major trace element and isotopic oxygen hydrogen strontium analyses of brines in six of the deeps to evaluate different processes of brine formation and to compare the evolution of each deep important heterogeneities in temperature salinity hydrographic structure and chemistry are recorded each brine having its own characteristics the intensity of hydrothermal circulation varies among the deeps and ranges from being strong atlantis ii and nereus to weak port soudan and even to negligible valdivia and suakin and it varies along the entire red sea axis these observations do not favour a unique formational model for all of the brines for example the brines of the suakin deep appear to have been formed by an old sea water which dissolved evaporite beds without significant fluid circulation and hydrothermal input while others such as atlantis ii or nereus deeps appear to be dominated by hydrothermal influences a striking feature is the absence of a relationship between the position of the deeps along the axis and their evolutionary maturity

the development of layering fluxes through double diffusive interfaces and location of hydrothermal sources of brines in the atlantis ii deep red sea the brines in the atlantis ii deep of the red sea occur in horizontally uniform well mixed layers with the hottest and saltiest water at the bottom separated from the successively cooler and fresher layers above by very sharp vertical temperature and salinity gradients data acccumulated over 3 decades are used to test the widely accepted hypothesis that all heat and salt for the brine layers are supplied from below and that the layered brine structure is the result of double diffusion using the changes in temperature and salinity in each layer over successive time intervals one can deduce the corresponding fluxes of heat and salt across the interfaces it is found that the required flux of salt cannot be sustained by double diffusion alone an alternative calculation shows that most of the salt in the successively forming upper layers must have been injected directly from the bottom of the deep through one or more vents located above the level of the lowest brine interface for the bottom layer however it is not possible to obtain the observed salinity and temperature changes unless hot saline water is injected directly into that layer and some of the heat and a smaller fraction of the salt are transferred upward through the interface this process will also maintain convection in each of the layers and keep them well mixed as is observed the new interpretation in terms of separate inputs at various levels in the atlantis ii deep is also supported by recent geochemical evidence

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

tectonic development of passive continental margins of the southern and central red sea with a comparison to wilkes land antarctica abstract the continental margins of the southern and central red sea and most of wilkes land antarctica have bulk crustal configurations and detailed structures that are best explained by a prolonged history of magmatic expansion that followed a brief but intense period of mechanical extension extension on the red sea margins was spatially confined to a rift that was 20 30 km in width the rifting phase along the arabian margin of the central and southern red sea occurred 25 32 ma ago primarily by detachment faulting at upper crustal levels and ductile uniform stretching at depth rifting was followed by an early magmatic phase during which the margin was invaded by dikes and plutons primarily of gabbro and diorite at 20 24 ma after the crust was mechanically thinned from 40 km to 20 km we infer continued spreading after that in which broad shelves were formed by a process of magmatic expansion because the offshore crust is only 8 15 km thick including sediment and seismic reflection data do not depict horst and graben or half graben structures from which mechanical extension might be inferred the wilkes land margin is similar to the arabian example the margin is about 150 km in width the amount of upper crustal extension is too low to explain the change in sub sediment crustal thickness from 35 km on the mainland to

origin of fluids and the evolution of the atlantis ii deep hydrothermal system red sea strontium isotope study abstract atlantis ii is the largest and most mineralized of the deeps along the axis of the red sea spreading center its basaltic substratum is covered by recent layered metalliferous sediments which precipitated from an overlying brine pool the 87 sr 86 sr ratio and the strontium concentration of interstitial waters within these sediments range between 0 70708 and 0 70725 and between 43 and 53 ppm respectively they are close to what is found for the present day deep brine pool 0 707105 45 10 ppm the strontium concentration and the 87 sr 86 sr ratio of the atlantis ii deep brines can be derived from those of the interstitial waters of the surrounding miocene evaporite by hydrothermal interaction with oceanic basaltic rocks at a maximal water rock ratio of 2 3 this water rock ratio is similar to that calculated for oceanic hydrothermal systems on sediment free ridges interstitial waters show a linear trend on a plot of 87 sr 86 sr vs 1 sr the highest strontium concentration and the most radiogenic interstitial waters correspond to sediment samples enriched in iron and manganese oxide minerals these waters reflect the diagenetic release of strontium by oxide minerals that initially precipitated at the interface between the brine pool and more radiogenic seawater the solid fraction of the sediment has 87 sr 86 sr isotopic compositions intermediate to those of the brines and seawater the most radiogenic strontium values were observed in samples strongly enriched in marine microbiota the gradual isotopic evolution in the lowest part of the western basin sediments testifies to the gradual influence of the hydrothermal activity in the deep in the beginning of the atlantis ii deep sedimentary history the strontium isotopic composition of solid samples from younger metalliferous facies is fairly uniform and close to that of the present day brine this isotopic homogeneity indicates that the isotopic composition of mineralizing fluids did not change during the time of deposition of the metalliferous sediment

the chemical evolution of kurnub group paleowater in the sinai negev province a mass balance approach abstract the chemical evolution of the kurnub group paleowater was studied starting from rainwater in recharge areas of the sinai and along groundwater flowpaths leading to the natural outlets of this regional aquifer this was achieved by investigating the chemical composition of groundwater ionic ratios degrees of saturation with common mineral species normative analysis of dissolved salts and by modeling of rock water interaction and mixing processes occurring along groundwater flow paths the initial groundwater composition used is from the nakhel well in sinai it evolves from desert rainwater percolating through typical kurnub group lithology in sinai this rainwater dissolves mainly gypsum halite and dolomite together with smaller amounts of marine aerosol and k feldspar at the same time it precipitates calcite sio 2 smectite and degasses co 2 between the area of nakhel and the northern negev the chemistry of kurnub group waters is influenced by dissolution of halite and lesser amounts of gypsum of surficial origin in recharge areas small amounts of feldspars and of dolomite cement in sandstones eroded from the arabo nubian igneous massif of sinai and organic degradation derived co 2 concomitantly there is precipitation of calcite smectite sio 2 and probably analcime characteristic of sediments in continental closed basins north of the negev the kurnub group fluids are diluted and altered by mixing with judea group aquifer groundwaters on the e there is mixing with residual brines from the water body ancestral to the dead sea prior to discharge into the arava valley rock water interaction indicated by netpath and phreeqc modeling is in agreement with lithology and facies changes previously observed in the kurnub group sequence

stable isotope signatures of water rock interaction in mid ocean ridge hydrothermal systems sulfur oxygen and hydrogen reaction path models of seawater basalt interaction at mid ocean ridges similar to those presented by bowers and taylor 1985 are extended to include sulfur isotopic exchange equilibria the effects of variable contribution of sulfur from basalt and of high and low temperature reduction of sulfate in the fluid are considered results of the model calculations are compared with 34s analyses of disseminated sulfides in altered basalts chimney sulfides and fluids collected from mid ocean ridge hot springs the calculations indicate that under the physical conditions of water rock interaction in mid ocean ridge circulation systems the overwhelming influence on the sulfur isotope signature of exiting fluids is basaltic sulfur no trace of 34s enrichment by reduction of seawater sulfate is recorded in hot spring fluids unless the reduction occurs at high temperature 350 c or near the venting areas a comparison of recent oxygen and hydrogen isotope data from several vent sites suggests that contributions of altered basalt and fluid with a significant history of low temperature interaction with basalt can be qualitatively assessed

punctiform initiation of seafloor spreading in the red sea during transition from a continental to an oceanic rift transition from a continental to an oceanic rift occurs in the red sea by initial emplacement of oceanic crust in regularly spaced hot points which serve as nuclei for axial propagation into segments of oceanic crust accretion and for initiation of seafloor spreading hot points develop above upwelling mantle diapirs caused by density viscosity inversion beneath continental and oceanic rifts

sediments of the active rift zone in the western woodlark basin and the development of hydrothermal and volcanic activity abstract in the western woodlark basin within the neovolcanic zone sediments form ponds in fissures and between individual pillows and tubes a continuous thin sediment cover appears only at the base of the neovolcanic zone its thickness increases with the distance from the zone data on the lithology mineralogy and chemistry of sediment cores from the spreading centre in the western woodlark basin and adjacent areas show that these calcareous sediments avg 44 1 caco 3 contain significant amounts of terrigenous arc volcanic hyaloclastic and hydrothermal material the latter constituting up to 15 of the non carbonate fraction two types of sedimentary sequences occur in the studied area those of the first type were formed by particle by particle sedimentation horizons of redeposited sediments occur in sequences of the second type redeposition of sediments is widespread and is tentatively correlated with cycles of volcanic activity at swells along the spreading centre these alternate with hydrothermal cycles which were determined by the presence of hydrothermal matter in sediments radiocarbon dating of sediments showed that both cycles are of similar duration of the order of 10 000 years they are not synchronous along the spreading axis each swell having a specific evolution based on these determinations we can say that within the studied spreading centre only the franklin seamount swell is prospective for contemporary hydrothermal activity

deuterium in interstitial water from deep sea cores as part of the joint oceanographic institutions deep earth sampling project the interstitial waters of cores from 69 holes were sampled for deuterium analysis sixteen of the cores penetrated sediments as old as eocene and several sampled cretaceous sediments which allowed us to examine changes in the deuterium content of the oceans with time deuterium is shown to be a conservative constituent of the pore water its abundance in the pore fluids can be changed by diffusion but the rate is slow and corrections for this effect have been made changes in the abundance of deuterium can be related to changes in the amount of ice stored in continental glaciers inasmuch as precipitation in the form of snow is highly depleted in deuterium compared with the oceans many of the cores show a change in isotopic composition of samples from early to late miocene that can be ascribed to the buildup of the antarctic ice sheets after correcting for the role of diffusion in reducing the isotopic contrast between samples from a single core we estimate an increase of 10 per mil d corresponding to a 18o change of about 1 2 between the early and late miocene a similiar analysis of pleistocene to holocene changes indicates a d rise of 8 during the time of maximum continental ice which corresponds to a 18o increase of about 1 0 on the basis of limited data we find no d change in the oceans from cretaceous to miocene

the anhydrite saturation index of the ponded brines and sediment pore waters of the red sea deeps abstract we compiled the available chemical analyses of the ponded brines and of the sediment interstitial waters for the atlantis ii discovery suakin and valdivia deeps in the red sea central valley along with the dsdp data for interstitial waters of several cores in the rift axis sites 225 228 of leg 23 recent advances in the calculation of the thermodynamic properties of concentrated solutions at high temperatures and pressures allow the study of the equilibrium conditions between anhydrite and halite and the brines we first tested the influence of various parameters as temperature pressure and solution composition on the calculated anhydrite saturation index in order to provide a clear criterion for equilibrium which is assumed when the saturation index lies within 0 9 and 1 1 we found that at 62 c and 200 bar the pressure effect on the saturation indices is of the same magnitude as that of temperature our calculations point to the overall undersaturation of the free brines with respect to halite the calculated halite saturation state of the pore waters at the four dsdp sites is consistent with the mineralogical description of the sediments in which halite is not reported except at site 225 where the calculated undersaturation is in contradiction with the reported presence of halite at the base of the core from the hypothesis of equilibrium between anhydrite and the pore waters in the dsdp cores we have estimated values of the geothermal gradients off the rift axis which fall within the highest values obtained by extrapolation of direct temperature measurements this suggests that at the latitude of the atlantis ii and suakin deeps the high heat fluxes measured along the axial trough extend off the rift axis our calculations show that the upper convective layer ucl of the atlantis ii hydrothermal system has always been undersaturated over the studied period 1965 1985 which is consistent with the absence of anhydrite in sediment underlying this brine the calcium and sulfate contents of the lower convective layer lcl show a parallel evolution they decrease when temperature increases although this behaviour suggests control of brine chemistry by equilibrium with anhydrite our calculations show that anhydrite has reached saturation in the lower brine only in 1966 and 1976 the general regime leading to the loss of calcium and sulfate outside these periods is tentatively attributed to diffusion calculations show that throughout the whole stratified brine column from the sediment to normal red sea water there is no chemical potential gradient for calcium sulfate whereas the chemical potential of sodium chloride regularly decreases we tentatively advocate the coupling of calcium sulfate diffusion with the large sodium chloride gradient to account for the loss in ca and so 4 finally the pore water chemistry of the atlantis ii and discovery deep sediments record two parallel evolutions from anhydrite undersaturation in 1966 to saturation or a state close to in 1976 these data are consistent with a periodical brine overspill from atlantis ii into discovery

pb and sr isotopic systematics of some basalts and sulfides from the east pacific rise at 21 n project rita abstract tholeiitic basalts and sulfide deposits from the cyana and alvin diving programs rita project on the east pacific rise were analyzed for pb and sr isotopes the basalt data plot within the field defined previously by other east pacific rise basalts 206 pb 204 pb 18 35 18 58 207 pb 204 pb 15 48 15 53 208 pb 204 pb 37 8 38 1 87 sr 86 sr 0 7022 0 7025 pb u and sr contents 0 5 0 05 and 110 ppm respectively and values 6 are typical of morb whereas th u ratios 3 5 are significantly higher the pb isotopic ratios of the sulfide samples are very homogeneous 206 pb 204 pb 18 47 207 pb 204 pb 15 49 208 pb 204 pb 37 90 and plot in the middle of the basalt field this indicates that 1 the sulfide pb was derived from the basaltic crust without any significant contribution from either seawater or hemipelagic sediments and 2 the solutions from which the sulfides were deposited had uniform pb isotopic composition the pb contents of three sulfide samples is relatively high 170 1310 ppm the sr contents of five sulfide samples are widely scattered from 12 to 210 ppm with 87 sr 86 sr ratios intermediate between basaltic and seawater values 0 70554 0 00005 to0 70795 0 00011 leaching experiments show that both basalt derived sr and seawater sr were present in the solutions which deposited the sulfides in some cases sr was also adsorbed from seawater onto the sulfides following their deposition basalt derived sr and seawater sr are also present in associated non sulfide phases

new stratification in the hydrothermal brine system of the atlantis ii deep red sea temperature and salinity records from the redsed cruise september 1992 reveal a new stratification in the hydrothermal brine system of the atlantis ii deep this stratification consists of the preexisting lower and upper convective layers lcl and ucl1 with temperatures of about 66 c and 55 c respectively and two additional upper convective layers ucl2 and ucl3 that formed more recently and have distinct temperature salinity and thickness in accordance with the physical process that leads to the formation of brine layers i e double diffusive convection a flow rate of about 200 l s has been estimated for the hydrothermal discharge

chalcophile element processing beneath a continental arc stratovolcano the chalcophile elements are important both in terms of their economic value and as potential tracers of magmatic processes at convergent margins however because of analytical difficulties comprehensive datasets of chalcophile element concentrations for volcanic rocks are rare here we present analyses of a near complete suite of chalcophile elements s cu ag se as sb sn w mo pb bi tl zn ga co for volcanic rock samples collected from a typical continental arc stratovolcano in southern chile antuco enrichment in pb bi w tl sb and as relative to parental morb indicates that these elements have been mobilised from the subducting slab into the sub arc mantle wedge in contrast to cu and ag very low se concentrations suggest that se like s was lost during co eruptive degassing of the antuco magmas previous studies on oceanic arcs have demonstrated that as higher fo2 subduction related magmas ascend through the overlying lithosphere magnetite fractionation may trigger sulfide fractionation during crystallisation if such a process is extensive and has a sharp onset this would result in a plummet in the cu se and ag contents of the residual melt at antuco although a decrease in the fe2o3 t and tio2 concentrations at 55 wt sio2 3 wt mgo indicates magnetite fractionation this is not associated with a corresponding drop in cu contents instead we observe a general decrease in cu and a decrease in cu ag with increasing sio2 and decreasing mgo furthermore cu ag in the most primitive antuco rocks are lower than the global morb array indicating that the melts were sulfide saturated at an early stage in their crustal evolution through modelling fractional crystallisation we show that only a minor volume 0 5 0 6 vol of fractionating sulfide is needed to produce divergent trends in cu and ag as observed in the antuco samples our results show that sulfide fractionation occurred from an early stage during the crustal evolution of antuco s magmas we infer that this was promoted by stalling in the lower crust which for oxidised magmas at depths 20 km is within the sulfide stability field however elevated dyn ybn of the antuco magmas compared to oceanic island arc magmas provides an additional or alternate mechanism to inducing sulfide fractionation in the lower crust prior to ascent through initial garnet fractionation fractional crystallisation within this depth range meant that later magnetite fractionation had only a minor impact on the partitioning behaviour of the chalcophile elements in contrast arc magmas transiting thinner crust may not experience sulfide saturation until a later stage in their evolution induced by magnetite fractionation our results imply that convergent margin crustal thickness and therefore the depth range of magmatic differentiation determines the dominant control on initial magmatic sulfide saturation and therefore the primary distribution of chalcophile elements this implies that secondary processes are required to explain the transport and concentration of sulfides and chalcophile elements at shallower crustal levels

chemistry and geothermometry of brine produced from the salton sea scientific drill hole imperial valley california the december 29 30 1985 flow test of the state 2 14 well also known as the salton sea scientific drill hole produced fluid from a depth of 1865 1877 m at a reservoir temperature of 305 5 c another flow test at a depth of 3170 m produced brine contaminated by drilling fluid and diesel oil therefore we focus on the first flow test samples were collected at five different flashing pressures the brines are na ca k cl type waters with very high metal and low so4 and hco3 contents compositions of the flashed brines were normalized relative to the 25 c densities of the solutions and an ionic charge balance was achieved by adjusting the na concentration the composition of the preflashed reservoir fluid was calculated using enthalpy chloride relations applied to the normalized and charge balanced brines the calculated total dissolved solids in the preflashed reservoir fluid ranges from about 24 8 wt assuming insignificant thermal losses from the erupting fluid before sampling to 26 0 wt assuming a 10 enthalpy loss by conduction of thermal energy through casing and surface piping the preferred total dissolved solids of the reservoir fluid is 25 05 wt the calculated specific density of the preflashed reservoir fluid at 305 c and 1870 m depth ranges from 0 9980 no thermal loss prior to sampling to 1 0107 0 0023 g cm 3 10 thermal loss of the various cation geothermometers that are now in common use the na k ca method gives a temperature 310 c closest to the measured temperature 305 c in the production horizon calculated na k geothermometer temperatures using equations suggested by different investigators range from 326 to 364 c the mg k2 method gives a temperature of about 350 c mg li2 about 282 and na li 395 418 c