the effect of fluorine boron and excess sodium on the critical curve in the albite h 2 o system experiments to define the critical curve for a series of silicate melts in equilibrium with a hydrous fluid were carried out in a hydrothermal diamond anvil cell silicate compositions studied were albite with several wt excess na2o b2o3 and f2o 1 complete miscibility between melt and water was observed at lower pressure and temperature conditions compared to pure albite for all compositions for albite excess na2o the critical curve had been lowered by 143 and 247 c at 10 kbar for 5 and 10 wt excess na for albite 5 and 10 wt f the difference at 10 kbar was 147 and 246 c respectively and for albite 5 and 10 wt b differences of 168 and 262 c were found these results are likely to be additive with the presence of more than one of the components depressing the critical curve to even lower temperatures and pressures the results suggest that in complex pegmatitic systems complete miscibility between melt and fluid may be important in the final stages of crystallisation the unusual properties of fluid phases under conditions close to the critical curve in a silicate melt water system may be essential for the enrichment of trace elements in pegmatites as well as for the formation of typical pegmatite textures

an accurate model for the solubilities of quartz in aqueous nacl and or co2 solutions at temperatures up to 1273 k and pressures up to 20 000 bar abstract a simple and general relation between the solubility of quartz and the density of solution is derived rigorously based on this relation and the pressure volume temperature composition model of mao et al 2010 an accurate density based model is developed for the solubility of quartz in aqueous nacl and or co2 solution up to 1273 k and 20 000 bar the model parameters are regressed with carefully assessed experimental data compared to a large number of experimental data the average absolute deviations of calculated quartz solubilities in water aqueous nacl solution and aqueous co2 solution are 5 50 5 24 and 7 55 respectively which are within experimental uncertainties and are much better than the most competitive models in literature particularly this model can predict the experimental solubility of quartz in aqueous nacl and co2 solution without using any additional parameter this model can be incorporated in software for accurate geochemical modeling the strategy of this model should be promising for the solubilities of other minerals in water or multicomponent aqueous solutions

a multi isotope b sr o h and c and age dating 3h 3he and 14c study of groundwater from salinas valley california hydrochemistry dynamics and contamination processes 1 the chemical and isotope 11b 10b 87sr 86sr 18o 16o 2h h 13c 12c 14c and 3he 3h compositions of groundwater from the upper aquifer system of the salinas valley in coastal central california were investigated in order to delineate the origin and processes of groundwater contamination in this complex system the salinas valley has a relatively deep confined 400 foot aquifer overlain by a 180 foot aquifer and a shallower perched aquifer all made up of alluvial sand gravel and clay deposits groundwater from the aquifers have different 14c ages fossil 14c 21 3 percent modern carbon pmc for the 400 foot aquifer and modern 14c 72 2 98 2 pmc for the 180 foot aquifer fresh groundwater in all aquifers is recharged naturally and artificially through the salinas river the two modes of recharge can be distinguished chemically we identified several different saline components with distinguishable chemical and isotopic fingerprints 1 saltwater intrusion in the northern basin has c1 concentrations up to 1700 mg l a na cl ratio less than seawater a marine br cl ratio a ca cl ratio greater than seawater 11b between 17 and 38 and 87sr 86sr between 0 7088 and 0 7096 excess dissolved ca relative to the expected concentration for simple dilution of seawater correlates with 87sr 86sr ratios suggesting base exchange reaction with clay materials 2 agriculture return flow is high in no3 and so4 with a 87sr 86sr 0 7082 11b 19 and 13c between 23 and 17 the 3h 3he ages 5 17 years and 14c data suggest vertical infiltration rates of irrigation water of 3 10 m yr 3 nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg l high so4 na cl ratio 1 11b between 24 and 30 and 87sr 86sr 0 70852 this groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the coast range marine deposits of mesozoic to early cenozoic age the combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the so4 enriched no3 depleted saline plume that is located west of the city of salinas we suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination

the solubility of corundum in h2o at high pressure and temperature and its implications for al mobility in the deep crust and upper mantle abstract the solubility of corundum in h 2 o was measured at 700 1100 c and 0 5 2 0 gpa using a piston cylinder apparatus and weight loss methods at 700 c 0 5 gpa al concentration is 0 41 0 15 millimolal 1 analytical error corundum solubility increases strongly with pressure p and temperature t reaching 2 57 0 15 millimolal at 700 c 2 0 gpa and 27 3 1 5 millimolal at 1100 c 2 0 gpa the results were fitted with the equation log m al 1 131 3827 t 2 277 7336 t log h 2 o where m al is molality of al h 2 o is the density of h 2 o in g cm 3 and t is in kelvin the data indicate that al can have significant solubility in h 2 o during metamorphic and metasomatic processes in the deep crustal and upper mantle

implications of nonsynchronous rotation on the deformational history and ice shell properties in the south polar terrain of enceladus abstract numerous studies of the south polar region of saturn s moon enceladus have focused on the four main fractures the tiger stripes their associated water plume and the effects of diurnal tidal stresses on these fractures however due to their small magnitude 10 100 kpa diurnal stresses alone are unable to completely explain the initial formation of the tiger stripes and the many additional fractures in the region we suggest nonsynchronous rotation nsr stresses induced by a freely rotating ice shell over a global ocean are large enough to overcome the tensile strength of the ice shell and initiate fracturing on enceladus using the tidal stress calculation program satstressgui we demonstrate the dependence of the magnitude of the nsr stress on the thickness of the ice shell particularly the brittle outer layer of the ice shell we suggest the brittle layer in the south polar region is 2 4 km thick whereas in the more northern regions it is 6 8 km the difference is most likely due to the elevated energy flux at the south pole compared to the regions to the north resulting in a warmer and thinner ice shell in the south polar region the thinner ice around the south pole permits nsr tensile stresses of 5 mpa enough to fracture the ice however the thicker ice to the north reduces the nsr stress to less than 2 mpa making fracturing less likely the difference in ice shell thickness and resultant nsr stress can help explain the activity in the south but relative quiescence in the north our modeled nsr stress magnitudes and orientations suggests a nsr period on the order of 1 myr and advocate that the tiger stripes have rotated 45 clockwise about the south pole since their initial formation in response to nsr of the ice shell if the ice shell is rotating at a constant rate the tiger stripes would thus be up to 100 000 years old an apparent decreasing angular separation between consecutive fracture sets that formed in the south polar region suggests an ice shell that has weakened in strength over the course of its recent geologic history this could be a result of increased heating thinning of the ice shell or a combination of the two as the ice shell thinned the nsr stresses were enhanced making fracturing more likely after a smaller amount of nsr compared to the previous fracturing episode

strontium isotope evidence on the history of oilfield brines mediterranean coastal plain israel abstract the isotopic composition of sr in oil field brines from the mediterranean coastal plain was determined in 18 drillholes 13 of which are oil producing wells the brines are characterized by salinities ranging from 35 to 93 g l tds sr from 28 to 350 mg l sr ca molar ratios from 0 011 to 0 053 and 87 sr 86 sr ratios from 0 7075 to 0 7090 e a 0 7081 0 0004 2 the brines are classified into two groups 1 a mavqi im group brines with relatively high 87 sr 86 sr ratios 0 7087 and 0 7090 sampled from elastics dolomites and anhydrites of upper miocene age 2 b heletz group brines with relatively low 87 sr 86 sr ratios 0 7075 to 0 7081 sampled from sandstones and dolomites of lower cretaceous age equations were derived to show the relations between 87 sr 86 sr ratio of the brines and the processes through which they evolved dolomitization and dissolution reprecipitation it is suggested that both groups of brines originated from mediterranean evaporated seawater during the messinian desiccation the strontium isotope composition of the seawater is reflected in that of both groups of brines the mavqi im group containing the original 87 sr 86 sr ratio 0 7088 the heletz group evolved later on through exchange reactions of those primary brines with a carbonate sequence of cretaceous age and consequently new 87 sr 86 sr ratios 0 7078 could have been developed the effect of the dissolution reprecipitation reactions on the carbonate rocks is estimated to be very slight only around 1 by weight

the hydrogeochemistry of a heavily used aquifer in the mexican wine producing guadalupe valley baja california the guadalupe valley aquifer is the only water source for one of the most important wine industries in mexico and also the main public water supply for the nearby city of ensenada this groundwater is monitored for major ion n no3 p po4 fe as se mo cd cu pb zn and sb concentrations as well as tds ph dissolved oxygen and temperature high concentrations of n no3 26 mg l 1 se 70 g l 1 mo 18 g l 1 and cu 4 3 g l 1 suggest that groundwater is being polluted by the use of fertilizers only in the western section of the aquifer known as el porvenir graben unlike the sites located near the main recharge area to the east of the aquifer the water in el porvenir graben has low tritium concentrations 1 9 tu indicating a pre modern age and thus longer water residence time no significant variations in water quality generally 10 were detected throughout 2001 2002 in the aquifer suggesting that reduced rainfall and recharge during this dry period did not significantly affect water quality however the wells nearest to the main recharge area in the eastern aquifer show a slight but constant increase in tds with time probably as a result of the high 200 l s 1 uninterrupted extraction of water at this specific recharge site relatively high as concentrations for the aquifer 10 5 g l 1 are only found near the northern limit of the basin associated with a geological fault

structure and equilibria among silicate species in aqueous fluids in the upper mantle experimental sio2 h2o and mgo sio2 h2o data recorded in situ to 900 c and 5 4 gpa experiments to determine silicate structural species in silicate saturated aqueous fluids in equilibrium with silica polymorphs quartz and coesite enstatite and enstatite forsterite in the sio2 h2o and mgo sio2 h2o systems have been carried out in situ in the 0 4 5 4gpa and 700 900 degrees c pressure and temperature ranges respectively microraman spectroscopy was the structural probe in the sio2 h2o system 1 6 5 4gpa 700 900 degrees c the detected silicate species are q 0 sio44 q 1 0 5 si2o76 and q 2 sio32 the expression 2q 1 q 0 q 2 describes the equilibrium among these species with h and v values from the isochoric temperature and isothermal pressure dependence of its equilibrium constant k xq0xq2 x q1 2 range from 23 to 69kj mol and 1 to 2cm 3 mol respectively in the system mgo sio2 h2o the calculated silica solubility using literature algorithms is approximately 50 of that in the sio2 h2o system at similar temperature and pressure only q 1 and q 0 species were detected in the mgo sio2 h2o fluids whether in equilibrium with enstatite forsterite p 3gpa the temperature and pressure dependence of the equilibrium constant k x q1 x q0 for this system yields average values of h 405kj mol and v 2 30 4cm 3 mol the speciation of silicate in aqueous fluids resembles that in hydrous melts as a function of temperature and pressure at deep crustal and upper mantle temperature and pressure conditions and they become increasingly similar with depth as the silicate speciation and solubility in the aqueous fluid depend on silicate composition the pressure and temperature at which complete miscibility occurs will also vary with silicate composition the structural similarity between fluids and melts will also lead to fluid melt element partition coefficients trending toward 1 and mineral fluid partition coefficients trending toward mineral melt values in the upper mantle as the silicate h2o systems approach complete miscibility with increasing temperature and pressure

premelting polymerization of crustal and mantle fluids as indicated by the solubility of albite paragonite quartz in h2o at 1 gpa and 350 620 c abstract the composition and structure of dissolved silicates in model crustal and upper mantle fluids was assessed by measuring the solubility of the assemblage albite paragonite quartz in h 2 o from 350 to 620 c at 1 gpa natural low albite and quartz were equilibrated with h 2 o paragonite grew in all experiments due to incongruent dissolution of albite quartz melting occurred at 635 5 c solute concentrations at subsolidus conditions were determined by analysis of quenched fluids or mineral weight loss and mass balance bulk solubility of the mineral assemblage increased from 1 to 8 oxide wt with rising temperature si al and na all increase in concert the solutions were slightly peralkaline and possess si na al 1 5 molar at all conditions studied extrapolated thermodynamic data were used to predict solubility at the conditions investigated experimentally calculated solubility agreed with that measured from 350 to 500 c however above 500 c the calculations underpredict solubility to an increasing degree as the hydrothermal melting point is approached the excess measured solubility points to increasing abundance of aqueous si al si and na al si polymers polymerized solutes predominate in all near solidus solutions rising to 80 of total dissolved solids at the melting point the observations support a conceptual model in which as the temperature of the system rises isobarically at 1 gpa the silicate components dissolved in the aqueous phase begin to polymerize significantly within 100 c of the melting point the polymerized solutes may facilitate condensation of more polymerized hydrous silicate liquid at the hydrothermal melting point from the perspective of isobaric cooling the fluid crossing the solidus retains na al si o clusters or fragments that are less polymerized than those which comprised the melt but more polymerized than has previously been inferred for the aqueous phase the high concentrations of na al and si in the form of polymeric clusters will yield substantial mass transfer by near solidus metamorphic and magmatic fluids in the crust and mantle and likely promote dissolution transport and precipitation of nominally insoluble refractory rock components

thermodynamics of sio2 h2o fluid near the upper critical end point from quartz solubility measurements at 10 kbar abstract quartz solubility in sio 2 h 2 o fluid was measured at 10 kbar and 750 1130 c in a piston cylinder apparatus at 1035 c solubility was determined by weight loss of single crystals equilibrated with h 2 o rich fluid at higher temperature t the fluid phase coexisting with quartz quenched to a glass and solubility was determined by phase assemblage bracketing quartz present or absent with glass in quenched charges at 700 to 1000 c quartz solubility increases at an accelerating rate from 1 2 mol to 8 9 mol sio 2 above 1000 c there is a sharp increase to nearly equimolar fluids in equilibrium with quartz at 1080 c at t 1080 c sio 2 concentration increases less strongly the data confirm the existence of a critical end point on the hydrous melting curve of quartz and imply it lies at 1080 c and 9 5 10 kbar two independent approaches to calculating sio 2 activity at 1080 c from a mixing model for aqueous sio 2 extrapolated from lower temperatures and from depression of the melting temperature of quartz by h 2 o indicate nearly constant values over the wide compositional range of 20 60 mol sio 2 the activity of h 2 o a h at the same conditions calculated by integration of the gibbs duhem relation shows a plateau of very high a h 0 93 in the same broad composition range at 60 mol there is an abrupt change in h 2 o dissolution mechanism as sio 2 activity becomes proportional to its mole fraction at high silica concentration the activity concentration relations at 1080 c and 10 kbar were fitted to a subregular solution model giving interchange energies for sio 2 and h 2 o of respectively 25 3 and 14 3 kj mol roughly constant sio 2 activity of the near critical fluid despite a factor of 3 increase in x h2o can be explained by progressively greater amounts of hydrogen bonding of h 2 o molecules to polymerized silica units so that the effective concentration of these units remains nearly constant as h 2 o increases the sudden onset of critical phenomena in the system sio 2 h 2 o as temperature and pressure increase over narrow intervals approaching 1080 c and 10 kbar is thus explained as mainly a convergent or cooperative compositional effect in which polymerization and hydrogen bonding both play important roles

hydrous albite magmas at lower crustal pressure new results on liquidus h2o content solubility and h2o activity in the system naalsi3o8 h2o nacl at 1 0 gpa the system albite h2o serves as an important model for the generation of granitic magmas yet relatively few experimental investigations have focused on phase relations at high pressure this study reports new experimental results at 1 0 gpa and 690 1050 c on the temperature and liquid composition at vapor saturated melting the h2o content of undersaturated silicate liquids in equilibrium with albite the solubility of albite in h2o nacl fluids immediately below the solidus and the activity of h2o in hydrous naalsi3o8 liquids along the liquidus albite melts and dissolves congruently at all temperatures and salinities in the nacl absent system the temperature of vapor saturated melting of low albite confirmed by x ray diffraction is 695 5 c and the liquid composition is 18 14 1 35 wt h2o the temperature dependence of the fluid undersaturated liquidus curve in the system naalsi3o8 h2o varies with h2o wt w text h 2 text o according to t 2 0331 times 10 3 w text h 2 text o 3 1 6497w text h 2 text o 2 58 963w text h 2 text o 1235 5 circ text c indicating positive curvature in temperature composition coordinates and a dry melting temperature of 1235 c at 690 c immediately below the solidus albite solubility decreases drastically with nacl content of the fluid phase from 8 8 0 6 wt in the nacl free fluid to 2 at nacl concentration of only 10 mol experiments determining the activity of h2o a text h 2 text o in liquids at vapor saturated melting exploited low cl solubility in liquids and low albite solubility in the presence of h2o nacl fluids the maximum cl content of quenched glasses only 0 95 wt and very low albite solubility together make possible h2o activity measurement in melts equilibrated with nacl h2o solutions when combined with activity data for h2o nacl fluids experimentally determined a text h 2 text o along the liquidus is described by t 469 16a h 2 o l frac 1 2 93 382a h 2 o l 1235 5 circ c at 1 gpa h2o activities in hydrous albitic melts in h2o nacl fluids agree with those in the presence of h2o co2 fluids provided appropriate fluid mixing data are used our results constrain an asymmetric regular solution model for the mixing of na1 8al1 8si3 8o and h2o yielding margules parameters of w ab 25 56 0 54 and w text h 2 text o 10 50 pm 0 74 text kj text mol the results imply critical mixing of liquid and vapor at 1100 c using existing speciation models our results imply that h2o dissolved in hydrous albitic liquids is almost entirely in the form of molecular h2o oh concentration is negligible at temperatures near vapor saturated melting the results provide a more complete experimental foundation for modeling the system naalsi3o8 h2o at high pressure

the formation of enceladus tiger stripe fractures from eccentricity tides abstract enceladus has a young tectonically active south polar region which is erupting material from a prominent set of fractures called tiger stripes no comparable activity is observed at the north pole which is heavily cratered with limited tectonism given the many lines of evidence supporting a global ocean under enceladus icy shell the reason for the dichotomy in geologic activity is unclear we model the formation of the tiger stripes as tidally driven fractures and examine the magnitudes of tidal stresses with different ice shell structures in order to explore whether and how tidal stress might explain enceladus distribution of tectonic activity we find that eccentricity driven tidal stresses would produce fractures of nearly identical orientations to the observed tiger stripe fractures and that a 10 km difference in ice shell thickness between the north and south poles can result in substantially different tidal stress magnitudes providing a natural explanation for the hemispheric dichotomy in tectonic activity on enceladus finally we synthesize these results with enceladus global geologic record to offer insight into the evolution of this enigmatic moon

quartz solubility in sodium carbonate solutions at high pressure and temperature abstract we present new experimental data on the synthetic quartz qtz solubility in the na2co3 aqueous solutions ranging in salt concentration from 0 3 3 5 m mole kg h2o the data have been collected in the temperature t range 500 700 c at pressure p 4 kbar and 600 c 5 kbar in an internally heated pressure vessel with phase assemblage bracketing as a solubility monitor in quench experiments first disappearance of crystalline qtz in a succession of runs with constant na2co3 concentration but decreasing the qtz solution weight ratio was taken for the solubility value it was possible to bracket the solubility within about 1 wt by carefully observing the presence or absence of crystalline qtz in the run products qtz solubility varies systematically with p t and particularly with the na2co3 molality increasing from 0 7 m for the 0 3 m na2co3 to 4 m for the 3 5 m na2co3 at 600 c 4 kbar in all cases the sio2 molality in the solutions exceeds that of na2co3 which suggests the presence of polymerized silica species in the solutions quantum chemical computations showed the dimer h5si2o7 as the most stable species which corresponds to the dehydrated species si2o4oh in the framework of the revised helgeson kirkham flowers equation of state hkf a complete set of thermodynamic quantities for si2o4oh consistent with the revised hkf and the dew model sverjensky et al 2014 has been retrieved from the experiments calculations with the obtained set of thermodynamic parameters reproduce very well the qtz solubility experiments performed in a simpler h2o naoh fluid at 600 c 4 kbar model calculations of silica and ca solubility in the 15 wt 3 m nacl aqueous solution interacting with a siliceous carbonate rock qtz calcite saturated along a 13 km geotherm which take into account si2o4oh predict much higher bulk si and ca contents in the fluid phase than in equilibrium with the corresponding individual minerals for p above 4 5 kbar

complete miscibility between silicate melts and hydrous fluids in the upper mantle experimental evidence and geochemical implications the phase relationships between silicate melts and hydrous fluids were studied by direct visual observation in an externally heated diamond anvil cell complete miscibility of silicate melt and water was observed for a wide range of melt compositions including nepheline jadeite dacite haplogranite and ca bearing granite some evidence for complete miscibility was also observed in the system basalt h2o the critical temperatures in all systems decrease rapidly with pressure at 15 kbar the critical temperature for nepheline is around 550 c for jadeite around 800 c and for granitic compositions it is close to 900 c in general the critical temperatures appear to increase with silica content in the system our results suggest that there is complete miscibility between silicate melts and water in most of the upper mantle except at very shallow depths this means that a water saturated solidus cannot be defined any more in the deeper parts of the upper mantle very silica rich melt inclusions found in spinel lherzolites associated with fluid inclusion are probably the result of the unmixing of a supercritical fluid containing comparable amounts of water and silicate components the decomposition of amphibole in a subducted slab occurs at conditions where the miscibility gap between fluid and silicate melt is not yet closed while the decomposition of phengite and lawsonite occurs far beyond the critical curve accordingly the fluids released by the breakdown of these minerals should have very different properties highly mobile hydrous fluids containing little dissolved silicate should be produced by amphibole breakdown while the decomposition of lawsonite and phengite will lead to much more silicate rich and less mobile fluid phases

occurrence and formation of high fluoride groundwater in the hengshui area of the north china plain although high f groundwater was observed in the hengshui of the north china plain the depth dependence of groundwater f and its relation to aquifer sediments remains unknown both shallow groundwater and deep groundwater were collected for chemical and isotopic characterization sediments were taken from different depths down to 130 m for total element analysis and f form determination with sequential extraction procedure results show that f concentration ranges from 0 37 to 3 28 mg l and from 0 28 to 3 6 mg l in shallow and deep groundwater respectively high f water from shallow aquifers are of cl so4 na mg hco3 cl so4 na and so4 cl na mg types while hco3 so4 cl na and cl so4 na types are from deep aquifers high f waters are mainly found at the depths of 50 200 and 300 m along the flow path groundwater shows an increasing trend in f concentration from the northwest to the southeast isotopes of 18o and d in deep groundwater are more depleted in comparison with shallow groundwater suggesting that shallow and deep groundwater replenish through different ways with longer retention time of deep groundwater 13c of dissolved inorganic carbon are between 11 9 and 8 8 in shallow groundwater and between 10 6 and 7 5 in deep groundwater respectively which indicates that groundwater dic comes from both rock weathering and biodegradation of organic matter fluoride content in the sediment ranges from 140 to 1690 mg kg showing a decreasing trend with depth good correlations between f and al2o3 and fe2o3 are observed demonstrating that f contents in sediments are significantly influenced by the minerals containing fe2o3 and al2o3 in terms of adsorption sequential extraction procedure shows that exchangeable f form f1 and fe mn oxides bound f f3 generally decrease with depths while organic matter or sulfide bound f f4 keeps relatively stable and carbonate bound f f2 exhibits highly variable the relationships between f concentration and fe or mn imply that f in f1 is more inclined to be scavenged by fe and mn oxides hydroxides which have a stronger affinity for f although a variety of hydrogeochemical processes affected f concentrations dissolution precipitation is a vital process in the study area in comparison with shallow groundwater cation exchange may exhibit more significantly effect on f enrichment in deep groundwater competitive adsorption of hco3 and oh with f leads to the release of f from aquifer matrix into solution which increases groundwater f concentration evaporation is another control on f concentration especially in shallow groundwater

curtain eruptions from enceladus south polar terrain observations of the south pole of the saturnian moon enceladus revealed large rifts in the terrain that were found to be the sources of the observed jets of water vapour now it is shown that much of the eruptive activity can be explained by broad curtain like eruptions many of which were probably misinterpreted previously as discrete jets images taken by the cassini probe have revealed large fractures bounded by rifts towards the south pole of saturn s moon enceladus these features popularly known as tiger stripes reach higher temperatures than their surroundings and are thought to be the sources of observed jets of water vapour and icy particles joseph spitale et al compare cassini images with simulated curtains of material erupting from enceladus south polar terrain to produce detailed maps of the emissions at various times much of the eruptive activity can be explained by broad curtain like eruptions many of which were probably misinterpreted previously as discrete jets phantom jets in the synthesized curtains correspond closely to regions of enhanced brightness in the cassini images observations of the south pole of the saturnian moon enceladus revealed large rifts in the south polar terrain informally called tiger stripes named alexandria baghdad cairo and damascus sulci these fractures have been shown to be the sources of the observed jets of water vapour and icy particles1 2 3 4 and to exhibit higher temperatures than the surrounding terrain5 6 subsequent observations have focused on obtaining close up imaging of this region to better characterize these emissions recent work7 examined those newer data sets and used triangulation of discrete jets3 to produce maps of jetting activity at various times here we show that much of the eruptive activity can be explained by broad curtain like eruptions optical illusions in the curtain eruptions resulting from a combination of viewing direction and local fracture geometry produce image features that were probably misinterpreted previously as discrete jets we present maps of the total emission along the fractures rather than just the jet like component for five times during an approximately one year period in 2009 and 2010 an accurate picture of the style timing and spatial distribution of the south polar eruptions is crucial to evaluating theories for the mechanism controlling the eruptions

silicate coh melt and fluid structure their physicochemical properties and partitioning of nominally refractory oxides between melts and fluids abstract structural characterization of silicate melts and aqueous fluids equilibrated at pressures and temperatures corresponding to the earth s interior requires measurements in situ while the samples are at the pressure and temperature of interest to this end structure and structure property relations of melts and coexisting fluids in silicate coh systems have been determined at temperatures up to 1000 c and at pressures to 2 0 gpa the water component of silicate h 2 o systems shows aqueous fluids supercritical fluids and hydrous melts to comprise molecular h 2 o h 2 o 0 and oh groups bonded to si 4 and likely al 3 the abundance ratio oh h 2 o 0 is positively correlated with temperature the extent of hydrogen bonding diminishes with temperature and cannot be detected at above 450 c and 0 4 gpa its h is near 10 kj mol for water dissolved in hydrous melt as compared with 20 kj mol for pure h 2 o hydrogen bonding cannot therefore be the cause of property behavior in hydrous magmatic systems because the temperature in hydrous magmatic systems exceeds 600 c in sio 2 h 2 o fluid silicate solute comprises q 0 and q 1 species with a h of the polymerization reaction of 15 kj mol assuming no pressure effect in the q n notations the value of n indicates the number of bridging oxygen in a silicate or aluminosilicate polymeric species in chemically more complex alkali aluminosilicate systems the silicate speciation in melts in aqueous fluid and in supercritical fluids comprises the same q species but their abundance and proportions differ with the more polymerized species dominant in melt silicate water interaction in the fluids melts and supercritical fluids is described with the expression 12 q 3 13h 2 o 2 q 2 6 q 1 4 q 0 with h 400 450 kj mol the solubility of geochemically important trace elements such as for example hfse in silicate saturated aqueous fluid under deep crustal and upper mantle pressure and temperature conditions is orders of magnitude greater than in pure h 2 o at the same temperature and pressure for example the fluid melt partition coefficients for structural species such as po 4 p 2 o 7 and q n p are in the 0 15 0 7 range and increases rapidly with silica content of the fluid the fluid melt partition coefficient of tio n species in similar ti bearing systems increases from 0 1 to 0 5 in the 200 500 c and 0 4 1 0 gpa temperature and pressure range the ti abundance in aqueous fluids coexisting with rutile in the same pressure and temperature range is about 2 orders of magnitude lower these differences reflect solute dependent structural roles of ti 4 and p 5 in pure h 2 o fluid and in silicate saturated h 2 o other hfse likely behave similarly in silicate melt coh systems oxygen fugacity f o 2 is an additional variable affecting solubility and solution mechanisms from haplobasalt to haploandesite melt coh the carbon solubility at upper mantle pressures and temperatures decreases from 2 wt to 1 wt in equilibrium with co 2 gas oxidized carbon is dissolved dominantly as co 3 groups the solubility of reduced carbon in the coh system on the other hand is less than 50 of oxidized carbon reduced carbon in the coh system is dissolved in melts as a mixture of ch 3 groups and ch 4 molecules when coexisting fluid is ch 4 the isotope fractionation between coexisting coh saturated silicate melt and silicate saturated coh fluid is correlated with the ch 3 ch 4 abundance ratio in the melt by changing f o 2 from oxidized to reduced resultant changes of c solution mechanisms in melt coh systems cause nbo t changes this change can cause crystal melt element partition coefficients to vary by several tens of percent within natural abundance ranges of coh in magmatic liquids variable redox conditions will also result in variable q speciation of melts this variability in turn governs configurational properties of magmatic liquids as a result their transport properties such as viscosity and diffusion also vary with redox conditions

fluoride nitrate and water hardness in groundwater supplied to the rural communities of ensenada county baja california mexico the hydrogeochemistry of 26 wells belonging to ten different aquifers in the county of ensenada baja california is studied these wells are all used to supply the rural communities in the region which comprise 37 000 inhabitants excluding the city of ensenada high total dissolved solids tds concentrations maximum 7 35 g l 1 indicate that salt is a ubiquitous contaminant in the aquifers due to seawater intrusion the aquifers that support extensive agriculture activities maneadero san quintin san simon and el rosario are characterized by higher n no3 concentrations maximum 20 mg l 1 derived from fertilizers fluoride concentrations exceed the 1 5 mg l 1 mexican official limit in only four wells the enrichments of f in the southern aquifers are thought to be associated to water rock interactions controlled mainly by na ca equilibrium reactions with fluorite as suggested from high dissolved na concentrations in these waters in the northern aquifer of maneadero no enrichment of na is found and a geothermal source for f is likely water is hard to moderately hard with ca mg ratios 1 although drinking water directly from the tap is not a common practice in these localities most sources have concentrations of major ions and tds that exceed the mexican official limits

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

experimental determination of liquidus h 2 o contents of haplogranite at deep crustal conditions the liquidus water content of a haplogranite melt at high pressure p and temperature t is important because it is a key parameter for constraining the volume of granite that could be produced by melting of the deep crust previous estimates based on melting experiments at low p 0 5 gpa show substantial scatter when extrapolated to deep crustal p and t 700 1000 c 0 6 1 5 gpa to improve the high p constraints on h2o concentration at the granite liquidus we performed experiments in a piston cylinder apparatus at 1 0 gpa using a range of haplogranite compositions in the albite ab naalsi3o8 orthoclase or kalsi3o8 quartz qz sio2 h2o system we used equal weight fractions of the feldspar components and varied the qz between 20 and 30 wt in each experiment synthetic granitic composition glass h2o was homogenized well above the liquidus t and t was lowered by increments until quartz and alkali feldspar crystalized from the liquid to establish reversed equilibrium we crystallized the homogenized melt at the lower t and then raised t until we found that the crystalline phases were completely resorbed into the liquid the reversed liquidus minimum temperatures at 3 0 4 1 5 8 8 0 and 12 0 wt h2o are 935 985 875 900 775 800 725 775 and 650 675 c respectively quenched charges were analyzed by petrographic microscope scanning electron microscope sem x ray diffraction xrd and electron microprobe analysis empa the equation for the reversed haplogranite liquidus minimum curve for ab36 25or36 25qz27 5 wt basis at 1 0 gpa is t 0 0995 w text h 2 text o 3 5 0242w text h 2 text o 2 88 183 w text h 2 text o 1171 0 for 0 le w text h 2 text o le 17 wt and t is in c we present a revised p t diagram of liquidus minimum h2o isopleths which integrates data from previous determinations of vapor saturated melting and the lower pressure vapor undersaturated melting studies conducted by other workers on the haplogranite system for lower h2o 5 8 wt and higher temperature our results plot on the high end of the extrapolated water contents at liquidus minima when compared to the previous estimates as a consequence amounts of metaluminous granites that can be produced from lower crustal biotite amphibole gneisses by dehydration melting are more restricted than previously thought

the solubility of fluorite in h2o and h2o nacl at high pressure and temperature abstract the solubility of fluorite in h2o and h2o nacl has been measured at 600 1000 c 0 5 2 0 gpa in a piston cylinder apparatus fluorite dissolves congruently at all conditions investigated the data indicate that the concentration of fluorite dissolved in h2o is low at 600 c and 0 5 gpa 0 0014 mol kg h2o but increases strongly with temperature t and pressure p to 0 247 mol kg h2o at 1000 c 2 gpa the data were fit with the equation log mcaf2 6 587 2 774p1 2 2 266 10 3 4 699 10 4p t where mcaf2 is molality of caf2 t is in kelvin and p is in gpa fluorite solubility was also measured in h2o nacl fluids at 800 c and 1 0 gpa results indicate a strong increase in dissolved fluorite concentration with increasing nacl content from 0 028 mol kg h2o at xnacl 0 to 1 673 mol kg h2o at xnacl 0 486 where xnacl is the mole fraction of nacl in the fluid the data were fit to mcaf2 0 01035 1 141xnacl 4 694xnacl2 the results indicate that f mobility will be further enhanced by saline brines in high p t igneous and metamorphic environments high f solubility in h2o and h2o nacl in the deep crust and upper mantle can promote mobilization of high field strength elements rare earth elements u and th through transport as f bearing complexes

pit chains on enceladus signal the recent tectonic dissection of the ancient cratered terrains abstract enceladus is the first outer solar system body on which pit chains have been positively identified we map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on enceladus s surface concentrated in the cratered plains centered on enceladus s saturnian and anti saturnian hemispheres pit chains on enceladus are interpreted as the surface expressions of subsurface dilational fractures underlying a cover of unconsolidated material which we infer to be a geologically young cover of loose regolith that mantles the surface of enceladus a widespread layer of regolith may act to insulate the surface which has implications for the thermal state of enceladus s ice shell the widespread distribution of pit chains across the cratered plains indicates that this ancient surface has recently been tectonically active

a geochemical and 3d geometry geophysical survey to assess artificial groundwater recharge potential in the pacific coast of baja california mexico a geophysical and geochemical study was carried out in the maneadero aquifer baja california mexico with the aim of identifying potential recharge locations for reclaimed water rw this coastal aquifer shows a significant decline in water quality both as a result of salinization and the pollution by nitrates total dissolved solids tds in an extreme case increased from 4 g l 1 in 2000 to 27 g l 1 in 2011 nitrate as n no3 reaches 46 mg l 1 based on their geochemistry and location four water quality zones are identified a fresh water with tds 1 g l 1 in the upper creeks b mixture between seawater and freshwater in the coast proximal sections c water significantly enriched in nitrate below and adjacent to the town of maneadero and d brackish water with no signs of current interaction with freshwater the 3d geophysics identifies the influence of modern recharge areas and also buried flow paths down to at least 30 m depth the locations best suitable for aquifer recharge are those with equal or higher tds concentrations 2 5 g l 1 than rw which are located at the brackish water zone and or at the coastal limits of the mixing zones

quantification of groundwater seawater interaction in a coastal sandy aquifer system a study from panama sri lanka the panama coastal aquifer system is an important water resource in the southeast coast of sri lanka that provides adequate supplies of water for agriculture and domestic uses one of the biggest threats to these fragile aquifers is the sea water intrusion in this study recharging mechanism and geochemical evaluation of groundwater in the coastal sandy aquifer of panama were evaluated using chemical and stable isotope techniques thirty groundwater samples were collected and analyzed for their major ion concentrations and stable isotope ratios of oxygen 18o 16o and hydrogen d h all studied samples showed a ranking of major anions in the order cl hco 3 so 4 2 n no3 while cations showed a decreasing order of abundance with na ca2 mg2 k dominant groundwater hydrogeochemical types were na cl and mixed ca mg cl results of saturation index calculations indicate that the investigated groundwater body was mostly saturated with respect to calcite dolomite and gypsum in addition stable isotope and geochemical data suggest that fresh groundwater in the aquifer is recharged mainly by local precipitation with slight modification from evaporation and saline water intrusions isotope data suggest that mixing of salt water with freshwater occurs in aquifers which are located towards the lagoon since the communities in the study area depend entirely on groundwater an understanding of the hydrogeochemical characteristics of the aquifer system is extremely important for the better water resource management in the region

sustained eruptions on enceladus explained by turbulent dissipation in tiger stripes spacecraft observations suggest that the plumes of saturn s moon enceladus draw water from a subsurface ocean but the sustainability of conduits linking ocean and surface is not understood observations show eruptions from tiger stripe fissures that are sustained although tidally modulated throughout each orbit and since the 2005 discovery of the plumes peak plume flux lags peak tidal extension by 1 rad suggestive of resonance here we show that a model of the tiger stripes as tidally flexed slots that puncture the ice shell can simultaneously explain the persistence of the eruptions through the tidal cycle the phase lag and the total power output of the tiger stripe terrain while suggesting that eruptions are maintained over geological timescales the delay associated with flushing and refilling of o 1 m wide slots with ocean water causes erupted flux to lag tidal forcing and helps to buttress slots against closure while tidally pumped in slot flow leads to heating and mechanical disruption that staves off slot freezeout much narrower and much wider slots cannot be sustained in the presence of long lived slots the 10 6 y average power output of the tiger stripes is buffered by a feedback between ice melt back and subsidence to o 10 10 w which is similar to observed power output suggesting long term stability turbulent dissipation makes testable predictions for the final flybys of enceladus by cassini our model shows how open connections to an ocean can be reconciled with and sustain long lived eruptions turbulent dissipation in long lived slots helps maintain the ocean against freezing maintains access by future enceladus missions to ocean materials and is plausibly the major energy source for tiger stripe activity

supercritical fluids at subduction zones evidence formation condition and physicochemical properties abstract there is a general consensus that at subduction zones mass transfer from the subducted slab to the overlying mantle wedge is mediated by a hydrous mobile phase however it is under intense debate whether this phase is an aqueous fluid hydrous silicate melt or supercritical fluid with intermediate composition h 2 o concentration in the range of 30 wt 70 wt supercritical fluids with fluid like viscosity and melt like wetting and element carrying capability are an ideal agent for chemical transport at subduction zones after clarifying the phase relations of silicate h 2 o systems and the definition of supercritical fluids this contribution reviews existing evidence for the presence of supercritical fluids at subduction zones mostly from experimental investigation of phase relations of mineral h 2 o and rock h 2 o systems and the atomic structure and physicochemical properties of supercritical fluids h 2 o rich multi phase solid inclusions from continental subduction zones once their bulk water contents can be confirmed may provide a direct record of supercritical fluids experimental results generally indicate that supercritical fluids can derive from the slab at 160 km depth but there is still significant discrepancy between different studies on h 2 o saturated solidus fluid melt critical curve and the second critical end point scep some novel experimental methods are proposed to resolve the controversies over the formation condition of supercritical fluids the special physicochemical properties of supercritical fluids arise fundamentally from their intermediate composition and intermediate degree of polymerization that are distinctive from aqueous fluids or silicate melts probing the structure and properties of supercritical fluids which are required for understanding of their petrological and chemical behavior and geophysical characteristics relies mainly on in situ spectroscopy but first principles molecular dynamics is becoming a potentially powerful alternative approach

linking europa s plume activity to tides tectonics and liquid water abstract much of the geologic activity preserved on europa s icy surface has been attributed to tidal deformation mainly due to europa s eccentric orbit although the surface is geologically young 30 80 myr there is little information as to whether tidally driven surface processes are ongoing however a recent detection of water vapor near europa s south pole suggests that it may be geologically active initial observations indicated that europa s plume eruptions are time variable and may be linked to its tidal cycle saturn s moon enceladus which shares many similar traits with europa displays tidally modulated plume eruptions which bolstered this interpretation however additional observations of europa at the same time in its orbit failed to yield a plume detection casting doubt on the tidal control hypothesis the purpose of this study is to analyze the timing of plume eruptions within the context of europa s tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on europa and enceladus to do this we determine the locations and orientations of hypothetical tidally driven fractures that best match the temporal variability of the plumes observed at europa specifically we identify model faults that are in tension at the time in europa s orbit when a plume was detected and in compression at times when the plume was not detected we find that tidal stress driven solely by eccentricity is incompatible with the observations unless additional mechanisms are controlling the eruption timing or restricting the longevity of the plumes the addition of obliquity tides and corresponding precession of the spin pole can generate a number of model faults that are consistent with the pattern of plume detections the locations and orientations of these hypothetical source fractures are robust across a broad range of precession rates and spin pole directions analysis of the stress variations across the fractures suggests that the plumes would be best observed earlier in the orbit true anomaly 120 our results indicate that europa s plumes if confirmed differ in many respects from the enceladean plumes and that either active fractures or volatile sources are rare

spatial variations in the dust to gas ratio of enceladus plume abstract on day 138 of 2010 the plume of dust and gas emerging from enceladus south polar terrain passed between the sun and the cassini spacecraft this solar occultation enabled cassini s ultraviolet imaging spectrograph uvis and the visual and infrared mapping spectrometer vims to obtain simultaneous measurements of the plume s gas and dust components along the same lines of sight the uvis measurements of the plume s gas content are described in hansen et al 2011 grl 38 11202 while this paper describes the vims data and the information they provide about the plume s particle content together the vims and uvis measurements reveal that the plume material above baghdad and damascus sulci has a dust to gas mass ratio that is roughly an order of magnitude higher than the material above alexandria and cairo sulci similar trends in the plume s dust to gas ratio are also found in data obtained when cassini flew through the plume in 2009 during which time the ion and neutral mass spectrometer inms radio and plasma wave science instrument rpws and cosmic dust analyzer cda instruments made in situ measurements of the plume s gas and dust densities dong et al 2015 jgr 120 915 937 these and other previously published systematic differences in the material erupting from different fissures likely reflect variations in subsurface conditions across encealdus south polar terrain

partial melting of metabasic rocks and the generation of tonalitic trondhjemitic granodioritic ttg crust in the archaean constraints from phase equilibrium modelling abstract rocks of tonalitic trondhjemitic granodioritic ttg composition preserved in archaean terranes represent fragments of the earth s earliest formed continental crust and are thought to have formed via partial melting of hydrated metabasalt the geodynamic environments in which such high grade metamorphism and anatexis may have occurred in the early earth is strongly debated constraining the pressure p and temperature t conditions at which melts of appropriate composition can be derived from protoliths containing plausible mineral assemblages is central to addressing this question phase equilibrium modelling has been undertaken for an enriched archaean tholeiite bulk composition a suggested protolith for early earth ttg magmas using newly parameterised thermodynamic models that were specifically developed to evaluate the anatectic behaviour of metabasalt assuming minimal h 2 o saturation at the wet solidus the potential fertility of the studied metabasalt is greatest if the solidus is crossed at a pressure of 11 kbar where the solidus temperature reaches a minimum of 610 c major element compositions and proportions of calculated partial melts show the best correlation with those of natural archaean ttgs when in the p t range 800 950 c and 10 18 kbar which we suggest are optimal conditions for their petrogenesis normative geochemistry suggests that these melts would crystallise to broadly trondhjemitic or tonalitic lithologies calculated modal proportions of garnet plagioclase amphibole and rutile in the residuum which control diagnostic trace element signatures in the melt also show the best agreement with natural and experimental data at these conditions importantly although partial melts calculated outside of this p t range still produce ttg like major element compositions and normative mineralogies they would poorly match the diagnostic trace element signatures of natural archaean examples owing to the absences of key minerals in the residuum this optimal p t range of 800 950 c and 10 18 kbar defined herein is most likely to characterise metamorphism of hydrated basalt at the base of a 40 km thick archaean oceanic plateau overthickened crust or else tectonic underplating via shallow subduction which we therefore suggest are the most likely tectonic settings for the formation of the first voluminous continental crust on the early earth