influence of rotation on the metal rain in a hadean magma ocean 1 today it is widely accepted that during its early evolution the earth experienced a magma ocean that covered most of its surface the separation of metal from silicate was much facilitated in the environment of such a magma ocean the differentiation mechanism is known as the metal rain scenario our study will focus on the settling dynamics of these metal droplets because of the low viscosity of molten silicate and a higher rotation period of the earth at that time the rotation has a potentially strong influence on the dynamics of the magma ocean we use numerical 3d fluid simulations to analyze the combined effects of strong rotation and convection on the settling of the iron droplets we show that the influence of rotation on the settling depends on the latitude at the poles the influence of rotation is only marginal at the equator three different scenarios can be distinguished first at low rotation rates the particles form a dense layer at the bottom second for strong rotation the particles stay mostly suspended and layers form in the temperature field third at higher rotation rates the particles form a ribbon like structure in the middle of the box the influence of rotation on the iron droplets may lead to a scenario where part of the iron is kept in the mantle instead of transported to the core this would have a strong influence on the later states of the differentiation process and the amount of siderophile elements in the mantle

melting curve of mg fe sio3 perovskite to 96 gpa evidence for a structural transition in lower mantle melts the melting temperature of mg fe sio3 perovskite the dominant mineral phase of the earth s lower mantle has been measured to a pressure of 96 10 gpa below 60 gpa we find good agreement with the previous measurement of heinz and jeanloz 1987a and above 60 gpa the melting curve of silicate perovskite has a small positive slope of 19 5 5 5 k gpa the melting point of mg0 9fe0 1 sio3 perovskite is 3800 300 k at 96 gpa by extrapolation to 136 gpa it is 4500 500 k at the core mantle boundary these values provide an upper limit to the geotherm through the solid mantle and they are compatible with recent estimates of the temperature in the core being high 4500 k at the core mantle boundary our melting curve implies that the volume change on melting increases at 60 gpa from vm 0 0 0 2 cm mole to vm 0 16 0 03 cm mole we derive an equation of state for the melt from our data and find that a highly coordinated structure is required to explain the molar volume of liquid mg fe sio3 at pressures above 20 gpa

hf w chronometry of lunar metals and the age and early differentiation of the moon the use of hafnium tungsten chronometry to date the moon is hampered by cosmogenic tungsten 182 production mainly by neutron capture of tantalum 181 at the lunar surface we report tungsten isotope data for lunar metals which contain no 181 ta derived cosmogenic 182 w the data reveal differences in indigenous 182 w 184 w of lunar mantle reservoirs indicating crystallization of the lunar magma ocean 4 527 0 010 billion years ago this age is consistent with the giant impact hypothesis and defines the completion of the major stage of earth9s accretion

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

seismic characterization of multiple fracture sets does orthotropy suffice as geophysicists rely increasingly on effective media theories to characterize naturally fractured reservoirs they become more and more interested in evaluating the accuracy of different theories estimating their limits of applicability and assessing their usefulness for practice with this in mind we compare two popular seismological theories of hudson and schoenberg with the theory of kachanov developed in the context of mechanics of materials by performing finite element simulations of effective media for models that contain several sets of nonintersecting circular vertical fractures embedded in otherwise isotropic host rock we examine the accuracy of these theories our numeric study reveals that predictions of both the first and second order hudson s theories are typically inferior to those of others especially when the fractures are dry while on average the theories of schoenberg and kachanov fit finite element computations with comparable accuracy the latter appears to be more useful

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

dynamics of core formation and equilibration by negative diapirism 1 we investigate dynamically the timing and metal silicate equilibration processes during core formation by negative diapirism using numerical modeling in 3 d axisymmetric geometry we follow the sinking of iron rich diapirs through a viscous silicate mantle we carried out a parameter study in which shear heating as well as several viscous rheologies are considered and systematically varied general scaling laws are derived for the diapir sinking velocity as well as for the silicate melt generation and distribution around the diapir using these scaling laws we show that metal diapirs of a radius 1 100 m sinking through a partially molten silicate mantle can chemically equilibrate within the timescales suggested by geochemical constraints therefore negative diapirism can contribute significantly to metal silicate equilibration processes during core formation

the hf w isotopic system and the origin of the earth and moon abstract the earth has a radiogenic w isotopic composition compared to chondrites demonstrating that it formed while 182hf half life 9 myr was extant in earth and decaying to 182w this implies that earth underwent early and rapid accretion and core formation with most of the accumulation occurring in 10 myr and concluding approximately 30 myr after the origin of the solar system the hf w data for lunar samples can be reconciled with a major moon forming impact that terminated the terrestrial accretion process 30 myr after the origin of the solar system the suggestion that the proto earth to impactor mass ratio was 7 3 and occurred during accretion is inconsistent with the w isotope data the w isotope data is satisfactorily modeled with a mars sized impactor on proto earth proto earth to impactor ratio of 9 1 to form the moon at 30 myr

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

compressibility of porous rocks four compressibilities are defined for porous rock relating changes in the bulk and pore volumes to changes in the pore and confining pressures using a micromechanical theory based on classical linear elasticity three relations are found between these compressibilities two of these relations are verified experimentally for berea and bandera sandstone bounds are derived for these compressibilities involving only the porosity and the elastic moduli of the rock forming minerals for the strains to be unique functions of the stresses the compressibilities must be functions only of the difference between the confining and pore pressures this dependence is verified for berea bandera and boise sandstone while the strains cannot be expressed as functions of an effective stress regardless of how it is defined the elastic volumetric behavior of porous rocks can be studied through tests conducted at zero pore pressure

dynamics of a terrestrial magma ocean under planetary rotation a study in spherical geometry abstract during a later stage of the earth s accretion impacts of mars sized bodies on the earth caused one or more deep terrestrial magma oceans of global extent during that time the earth rotated very fast with a rotation period between two and five hours accordingly the effect of planetary rotation is not only of key importance for the chemical structure and the development of chemical heterogeneities but also sets the stage for the initiation of plate tectonics on earth this study investigates the effect of planetary rotation on the dynamics of silicate crystals in spherical geometry during an early stage of magma ocean solidification our results in a rotating spherical shell reveal a substantial influence of planetary rotation on the early magma ocean crystallization leading to crucial differences in solidification with respect to crystal accumulation depth and latitude without and with slow planetary rotation crystals are kept in suspension at all latitudes differently at moderate and high rotation rate clear dependencies of the crystal dynamics on latitude do arise at the poles all crystals settle at the bottom while in the equatorial region they stay entrained in the bottom half however at mid latitudes they are kept in suspension and are distributed over the entire depth of the magma ocean at even higher rotation rate all crystals accumulate at the bottom of the spherical shell suggesting that crystallization would start at the bottom at lower latitudes crystals are repeatedly re entrained by convective motions hindering the development of a stable layering at low latitudes whereas at higher latitudes a potentially stable gravitational layering does develop our numerical experiments reveal that planetary rotation is likely to induce an inhomogeneous solidification of a terrestrial magma ocean with respect to depth and latitude depending on the rotational strength this has important consequences on the solidification time and further favors major chemical segregation resulting in large scale chemical heterogeneities developing during magma ocean crystallization the origin and distribution of mantle heterogeneities like the llsvps could be an imprint of planetary rotation on the magma ocean crystallization during earth s early evolution

on the relationship between stress and elastic strain for porous and fractured rock modeling the mechanical deformations of porous and fractured rocks requires a stress strain relationship experience with inherently heterogeneous earth materials suggests that different varieties of hooke s law should be applied within regions of the rock having significantly different stress strain behavior we apply this idea by dividing a rock body conceptually into two distinct parts the natural strain volume change divided by rock volume at the current stress state rather than the engineering strain volume change divided by the unstressed rock volume should be used in hooke s law for accurate modeling of the elastic deformation of that part of the pore volume subject to a relatively large degree of relative deformation i e cracks or fractures this approach permits the derivation of constitutive relations between stress and a variety of mechanical and or hydraulic rock properties we show that the theoretical predictions of this method are generally consistent with empirical expressions from field data and also laboratory rock experimental data

characterizing production induced anisotropy of fractured reservoirs having multiple fracture sets since natural fractures in petroleum reservoirs play an important role in determining fluid flow during production knowledge of the orientation and density of fractures is required to optimize production this paper outlines the underlying theory and implementation of a fast and efficient algorithm for upscaling a discrete fracture network dfn to predict the fluid flow elastic and seismic properties of fractured rocks potential applications for this approach are numerous and include the prediction of fluid flow elastic and seismic properties for fractured reservoirs model based inversion of seismic amplitude versus offset and azimuth avoa data and the optimal placement and orientation of infill wells to maximize production given that a single fracture network may comprise hundreds of thousands of individual fractures the sheer size of typical dfns has tended to limit their practical applications this paper demonstrates that with efficient algorithms the utility of discrete fracture networks can be extended far beyond mere visualization

dynamics of metal silicate separation in a terrestrial magma ocean in a terrestrial magma ocean the metal silicate separation involved small metal droplets our goal is to better understand the dynamics of the metal droplet scenario the mechanism of sedimentation in a vigorously convecting and strongly rotating magma ocean may differ significantly from settling droplets in a still fluid in order to systematically study the parameter dependence on the style of motion we utilize two dimensional and three dimensional numerical convection models combined with a tracer based sedimentation method we investigate the characteristic flow patterns resulting from the competing effects of convection and droplet settling and find three styles of motion a temperature dominated style where most droplets remain suspended a droplet dominated style where the droplets separate from the fluid and a style of repetitive motion we find that the droplet dominated style is relevant to the magma ocean in this scenario the droplets settle and form a dense bottom layer one of the key findings of this work is that the formation of the dense bottom layer and therefore the separation of metal droplets from the liquid silicate occurs on a characteristic timescale which is identical with the stokes settling time finally we study the chemical interaction of settling metal droplets and liquid silicate and discuss how accurately a simple parameterized model can describe the chemical equilibration in the metal rain scenario of a terrestrial magma ocean we find agreement between the parameterized model and our two dimensional model our simulations which include thermal convection into the metal rain model confirm the fundamental observation that metal droplets are not permanently suspended in the convecting silicate melt but that they sink and rapidly form a dense layer at the base of the magma ocean

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

earth s core formation aided by flow channelling instabilities induced by iron diapirs abstract the core formation mechanism remains poorly known an unstable gravitational configuration of a dense molten metallic layer overlying a cold chondritic protocore is predicted by most studies which leads to the formation of a rayleigh taylor rt instability recent results dahl t w 2005 turbulent mixing during planet accretion and core formation interpretation of the hf w chronometer and implications for the age of the moon m sc thesis university of copenhagen indicate that additionally iron cores of predifferentiated planetesimals are also able to plunge mostly intact into the cold protocore and create large iron diapirs for both scenarios we propose the application of the stress induced melt channelling mechanism stevenson d j 1989 spontaneous small scale melt segregation in partial melts undergoing deformation geophys res lett 16 1 067 1 070 in the region surrounding an incipient iron diapir we therefore perform numerical experiments solving the two phase two composition flow equations within a 2d rectangular box with symmetrical boundary conditions we apply the compaction boussinesq approximation cba and include a depth dependent gravity for simplicity we use a constant viscosity for the solid phase and a melt fraction dependent rheology for the partially molten region around the diapir we investigate the physical conditions under which the melt channels can form and whether they are applicable to the early earth as a result for sufficiently small melt retention numbers iron rich melt channels develop within a region of approximately twice the diapir s size this could lead to effective draining of the surrounding region and might initiate cascading daughter diapirs the region of the protocore drained by this cascading mechanism is expected to significantly increase with depth and thus indicates an effective mechanism to also extract iron melt from deeper parts of the initially chondritic protocore this mechanism could effectively accelerate the process of core formation

viscosity of mafic magmas at high pressures while it is accepted that silica rich melts behave anomalously with a decrease of their viscosity at increased pressures p the viscosity of silica poor melts is much less constrained however modeling of mantle melts dynamics throughout earth s history including the magma ocean era requires precise knowledge of the viscous properties of silica poor magmas we extend here our previous measurements on fayalite melt to natural end members pyroxenite melts mgsio 3 and casio 3 using in situ x ray radiography up to 8 gpa for all compositions viscosity decreases with p rapidly below 5 gpa and slowly above the magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the ca end member within pyroxene melts the anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 gpa while the p dependence of viscosity beyond this remains to be measured these results imply that mantle melts are very pervasive at depth

acoustic emissions monitoring during inelastic deformation of porous sandstone comparison of three modes of deformation in some reservoirs large deformations can occur during oil or gas production because of the effective stress change for very porous rocks these production operations can be sufficient to cause inelastic deformation and irreversible damage rock formations can undergo deformation by different mechanisms including dilatancy or pore collapse in the laboratory it has been shown that the inelastic deformation and failure mode of porous rocks are pressure sensitive indeed when subjected to an overall compressive loading a porous rock may fail by shear localization compaction localization or by cataclastic compaction acoustic emission ae records provide important information to understand the failure mode of rocks the spatial evolution of damage as well as the source mechanisms can be followed using this technique in this paper we present three different laboratory axisymmetric compression experiments performed on bleurswiller sandstone which enable us to compare the acoustic emission signature of these three modes of deformation our data show that compaction localization and cataclastic compaction are characterized by similar acoustic signatures in terms of ae sources characteristics and evolution of ae number in comparison to the acoustic signature from shear localization this implies similar micromechanisms involved during compaction bands formation and cataclastic compaction

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

active hydrothermal vents and sulfide deposits on the southern juan de fuca ridge massive sulfide deposits rich in zinc and silver were recovered from the juan de fuca ridge 500 km west of oregon in september 1981 the samples recovered are composed largely of zinc sulfide with lesser amounts of iron lead and copper sulfide most of the deposits occur at a series of hydrothermal vents within a relatively continuous depression in the center of a smooth 1 km wide valley along the ridge axis the depression appears to be formed by collapse of a lava lake possibly modified by extensional faulting the axial valley floor outside the depression is underlain by fresh glassy ferrobasalt sheet and lobate flows two types of sulfide mineral deposits were dredged from one of the hydrothermal vents 1 angular slabs of dark gray zinc sulfide and 2 subrounded fragments of porous light gray zinc sulfide the samples contain fresh sphalerite zoned wurtzite pyrite and minor amounts of marcasite galena and chalcopyrite cubanite the spreading rate of the juan de fuca ridge and the composition of the sulfide samples are generally similar to the east pacific rise lat 21 n site however the texture and geologic setting of the sulfide deposits are significantly different

direct numerical simulation of an iron rain in the magma ocean core formation in terrestrial planets is a complex process possibly involving several mechanisms this paper presents a direct numerical simulation of one of these the separation of an emulsion of metal in a magma ocean the model using a fully lagrangian approach called the moving particle semi implicit method solves the equations of fluid dynamics including a proper treatment of surface tension it allows investigation of the balances controlling the distribution of drop size and velocity in both two and three dimensional situations a scaling analysis where buoyancy is balanced by both surface tension and inertia correctly predicts the average values in these quantities the full calculation gives an average drop radius of 1 5 cm falling at a velocity of about 30 cm s 1 analysis of the full distribution remains interesting and shows that a significant part of the smallest droplets is entrained upward by the return flow in molten silicate and might be entrained by succeeding thermal convection in addition we investigate the conversion of gravitational energy into viscous heating and the thermal equilibration between both phases we find that viscous heating is essentially produced at the surface of iron drops and that thermal equilibration is dominated by advection scaling thermal diffusion to chemical diffusion leads to the estimation that the latter would happen in less than 100 m in the magma ocean

in situ observations of dissolved iron and manganese in hydrothermal vent plumes juan de fuca ridge in situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the juan de fuca ridge using a submersible chemical analyzer scanner the scanner was deployed as part of a ctd transmissometer rosette instrument package on both tow yos and vertical casts during the vents leg i cruise in 1989 dissolved manganese and total dissolved iron concentrations along with temperature and light attenuation anomalies were determined over the ridge crest every 5 s discrete samples for laboratory analyses of dissolved iron ii total dissolved iron ii iii and manganese were also collected metal to heat ratios me q measured in situ were extremely variable in one steady state plume while an event plume had constant me q uniform values of mn q in the event plume demonstrate that mn behaves conservatively in the near field plume variability in the mn q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct me q values a simple mixing model shows that the contribution of mn from high me q sources with a composition characteristic of black smoker vents varies between 1 and 99 within the core of the steady state plume with an average value of 55 on average over 50 of the excess heat within the plume originates from low me q ratio sources with a composition characteristic of low temperature diffuse flow vent fluids less than 4 of the volume of hydrothermal fluids in the plume originates from black smokers the fe ii concentrations were used to provide an estimate of plume age on a transect across the ridge axis plume ages were about 2 5 days on axis and 12 days off axis these plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222rn

effects of earth s rotation on convection in magma chambers abstract the rotation of the earth is predicted to have a strong influence on the convective motions in basaltic magmas which cool at high and intermediate latitudes on the earth s surface convection in layers greater than 100 m deep is characterised by large taylor numbers and small rossby numbers for which laboratory experiments provide evidence of strong rotationally induced flows in the case of convection driven by either thermal or compositional buoyancy fluxes from horizontal top or bottom boundaries coriolis forces induced by the earth s rotation are expected to cause the turbulent convective motions to form into intense vortices whose axes tend to be close to the vertical these vortices should be tall and thin be very unsteady and have rapid vertical motion in their cores earth s rotation is likely to have little or no effects on convection in very shallow convecting layers

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

the scavenging of u 230th and 231pa during pulsed hydrothermal activity at 20 s east pacific rise abstract uranium th and pa isotopes were measured in eight box cores from two transects to the west of the east pacific rise at 10 s and 20 s sediment geochemistry al ca fe mn and water column paniculates mn suggest that highly metalliferous plumes rich in fe and mn are emanating from the rise crest at 19 s measurements of 230thxs and 231paxs indicate decreasing sediment accumulation rates from the rise flank 0 4 cm ky 1 to the tiki basin 0 23 cm ky 1 over this geographical area al is found to have a constant flux of 3 6 10 4 g cm 2 ky 1 application of an al constant flux model to ridge crest metalliferous sediment reveals two 1 000 year pulses of hydrothermal activity during the holoccne since 11 000 y bp these hydrothermal pulses are characterised by hydrothermal fe mn ratios 3 5 1 enhanced 230th and 231pa scavenging and low 230thxs 231paxs ratios 3 4 the similarity of the 230thxs and 231paxs ratio to the dissolved seawaterrauo suggests that in fracuonation of the isotopes occurs during scavenging supplementary supply of dissolved 230th and 231pa in a westwards moving water mass is suggested

corrigendum 146 sm 142 nd evidence from isua metamorphosed sediments for early differentiation of the earth s mantle nature 423 428 432 2003 in this letter the subscripts l and k were accidentally transposed so coefficient a in equation 4 should have read

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

thermal and chemical evolution of the terrestrial magma ocean abstract the earth is likely to have experienced a magma ocean stage during accretion thermal and chemical evolution of magma ocean is investigated based on a one dimensional two phase flow heat and mass transfer model differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere if the magma ocean is formed by the blanketing effect of a solar type proto atmosphere extensive differentiation proceeds at lower mantle pressure if the magma ocean is formed by the blanketing effect of an impact induced steam atmosphere no differentiation at lower mantle pressure is likely if a very deep magma ocean is formed by a giant impact whether differentiation proceeds at lower mantle pressure or not depends on grain size viscosity of melt and or properties of a transient atmosphere on the contrary chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type a shallow magma ocean can remain for 100 200 my without any heating processes

hydrothermal particle plumes over the southern juan de fuca ridge hydrothermal particles originate in buoyant plumes emanating from seafloor thermal vents1 4 and accumulate as metalliferous sediments found along oceanic spreading centres5 7 observational evidence of the transport pathway of hydrothermal particles is scarce however and the structure extent and particle concentrations of hydrothermal plumes remain largely conjectural to evaluate the potential of hydrothermal plumes as particle transport agents we mapped their distribution along and across the 80 100 m deep axial valley of the southern juan de fuca ridge in the north east pacific ocean 44 30 n 130 w an area of known hydrothermal activity8 11 continuous light scattering measurements reported here defined numerous particle plumes centred 30 120 m above bottom m a b elemental analysis of the plume particles and the theta potential temperature s salinity signatures of the plume water verified their hydrothermal origin concentrations of hydrothermal particles remained elevated at ridge crest depths at least 100 km from the ridge indicating distant off axis dispersal of hydrothermal emissions

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

changes in geophysical properties caused by fluid injection into porous rocks analytical models author s pride sr berryman jg commer m nakagawa s newman ga vasco dw abstract 2016 european association of geoscientists a engineers analytical models are provided that describe how the elastic compliance electrical conductivity and fluid flow permeability of rocks depend on stress and fluid pressure in order to explain published laboratory data on how seismic velocities and electrical conductivity vary in sandstones and granites the models require a population of cracks to be present in a possibly porous host phase the central objective is to obtain a consistent mean field analytical model that shows how each modeled rock property depends on the nature of the crack population the crack populations are described by a crack density a probability distribution for the crack apertures and radii and the averaged orientation of the cracks the possibly anisotropic nature of the elasticity conductivity and permeability tensors is allowed for however only the isotropic limit is used when comparing to laboratory data for the transport properties of conductivity and permeability the percolation effect of the crack population linking up to form a connected path across a sample is modeled however this effect is important only in crystalline rock where the host phase has very small conductivity and permeability in general the importance of the crack population to the transport properties increases as the host phase becomes less conductive and less permeable

imaging of a fluid injection process using geophysical data a didactic example author s commer m pride sr vasco dw finsterle s kowalsky mb abstract the authors in many subsurface industrial applications fluids are injected into or withdrawn from a geologic formation it is of practical interest to quantify precisely where when and by how much the injected fluid alters the state of the subsurface routine geophysical monitoring of such processes attempts to image the way that geophysical properties such as seismic velocities or electrical conductivity change through time and space and to then make qualitative inferences as to where the injected fluid has migrated the more rigorous formulation of the time lapse geophysical inverse problem forecasts how the subsurface evolves during the course of a fluid injection application using time lapse geophysical signals as the data to be matched the model unknowns to be estimated are the multiphysics forward modeling parameters controlling the fluid injection process properly reproducing the geophysical signature of the flow process subsequent simulations can predict the fluid migration and alteration in the subsurface the dynamic nature of fluid injection processes renders imaging problems more complex than conventional geophysical imaging for static targets this work intents to clarify the related hydrogeophysical parameter estimation concepts

a re evaluation of metal diapir breakup and equilibration in terrestrial magma oceans abstract due to mechanisms such as impact heating early atmospheric thermal blanketing and radioactive heating the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable in such a context a key question to constrain the early thermo chemical evolution of the earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean in the past years several workers have focused on this question using however various approaches and making different assumptions while most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean therefore leading to metal silicate disequilibrium to clarify the discrepancies and the differences among studies i have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size sinking through a silicate magma ocean with a large range of plausible viscosity values the obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates i show that for plausible magma ocean viscosities diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0 2 m at which metal silicate equilibration is rapidly achieved

fractured reservoirs an analysis of coupled elastodynamic and permeability changes from pore pressure variation equivalent medium theories can describe the elastic compliance and fluid permeability tensors of a layer containing closely spaced parallel fractures embedded in an isotropic background we propose a relationship between effective stress background or lithostatic stress minus pore pressure and both permeability and elastic constants this relationship uses an exponential decay function that captures the expected asymptotic behavior i e low effective stress gives high elastic compliance and high fluid permeability while high effective stress gives low elastic compliance and low fluid permeability the exponential decay constants are estimated for physically realistic conditions with relationships coupling pore pressure to permeability and elastic constants we are able to couple hydromechanical and elastodynamic modeling codes a specific coupled simulation is demonstrated where fluid injection in a fractured reservoir causes spatially and temporally varying changes in pore pressure permeability and elastic constants these elastic constants are used in a 3d finite difference code to demonstrate time lapse seismic monitoring with different acquisition geometries changes in amplitude and traveltime are seen in surface seismic p to s reflections as a function of offset and azimuth as well as in vertical seismic profile p to s reflections and in crosswell converted s waves these observed changes in the seismic response demonstrate seismic monitoring of fluid injection in the fractured reservoir

the use of effective medium theories for seismic wave propagation and fluid flow in fractured reservoirs under applied stress summary methods for predicting the permeability and elastic properties of hydrocarbon reservoirs containing natural fractures are important for the production optimization and seismic characterization of fractured reservoirs effective medium theories may be used for this purpose but need to be validated using numerical calculations of the fluid flow and seismic properties for realistic fracture networks the prediction of effective permeability and elastic properties using effective medium theories of fractured media are compared with numerical simulations using a discrete fracture network dfn containing two sets of non orthogonal vertical fractures discrepancies between the permeability obtained from the simulations and using effective medium theory are attributed to an oversimplified treatment of fracture interconnectivity in the effective medium theory used the simulations indicate that the effect of interconnectivity on fluid flow varies with stress and flow direction by contrast the effective elastic compliances obtained from numerical simulation and effective medium theory are in good agreement even for relatively complicated fracture networks although permeability and seismic anisotropy both vary with stress the relation between them is not simple the variation in reflection amplitude with offset and azimuth is found to be sensitive to the ratio of the normal to shear compliance of the fractures whereas permeability is less sensitive to this ratio for the dfn studied the permeability rapidly increases at high level of stress due to dilation of the fractures when the in situ stress field is strongly anisotropic

effective elasticity of rocks with closely spaced and intersecting cracks the noninteraction approximation nia is the simplest effective media theory that describes the overall elasticity of fractured rocks if the nia is used for fracture characterization its accuracy and the range of applicability must be estimated we do it by performing a series of 3d finite element simulations of effective elasticity for models that contain several sets of fractures embedded in otherwise isotropic host rock we intentionally place the cracks close to each other to create strong interactions in their local stress fields in addition we allow the cracks to intersect in such a way that they do not break a rock specimen apart perhaps surprisingly we find that fracture interactions and intersections have little influence on the effective elasticity and the nia performs well in all cases while it has a tendency to slightly underestimate the effective stiffnesses the incurred errors are small their typical magnitudes are just a few percent in the entire range of the crack densities expe