crystals stirred up 1 direct numerical simulations of crystal settling in nondilute magmatic suspensions 1 this is the first paper in a two part series examining the fluid dynamics of crystal settling and flotation in the lunar magma ocean a key challenge in constraining solidification processes is determining the ability of individual crystals to decouple from vigorous thermal convection and settle out or float the goal of this paper is to develop a computational methodology capable of capturing the complex solid fluid interactions that determine settling and flotation in the second paper we use this computational approach to explore the conditions under which plagioclase feldspar would be able to buoyantly float and form the earliest crust on the moon the direct numerical method described in this paper relies on a fictitious domain approach and captures solid body motion in 2d and 3d with little overhead beyond single fluid calculations the two main innovations of our numerical implementation of a fictitious domain approach are an analytical quadrature scheme which increases accuracy and reduces computational expense and the derivation of a multibody collision scheme advantages of this approach over previous simulations of crystal bearing magmatic suspensions include the following 1 we fully resolve the two way interaction between fluid and solid phases implying that crystals are not only passively advected in an ambient flow field but are also actively driving flow and 2 we resolve the flow around each individual crystal without assuming specific settling speeds or drag coefficients we present several benchmark problems and convergence tests to validate our approach

an assessment of dynamically recrystallized grainsize as a palaeopiezometer in quartz bearing mylonite zones abstract recrystallized grainsize has been measured in quartz and in some cases feldspar in about 200 samples from 22 mylonite zones from 3 discrete tectonic settings 1 1 supracrustal low temperature shallow dipping thrusts 2 2 deeper level major 100 km thrusts in high grade metamorphic rocks and 3 3 steeply dipping fault zones in granite within a low grade palaeozoic fold belt the concept of a steady state dynamically recrystallized grainsize largely unaffected by post creep processes e g static grain growth receives strong support especially from the microstructures and the independence of finite strain and grainsize in most mylonite zones however the usefulness of this grainsize for predicting stress magnitudes is limited by the apparently independent influence of metamorphic environment on grainsize the available theoretical and empirical stress grainsize relationships do not account for these effects the concept of a steady state grainsize and the ease of accurate measurement offer a potentially powerful method for predicting stress intensity during deformation predicted deviatoric stresses have been computed using twiss theoretical model for comparison with other crustal stress estimates and most samples fall in the range from 20 to 150 mpa in a few cases where discrete high strain mylonite zones occur within contemporaneously regionally deformed rocks the recrystallized grainsize indicates that stresses were 1 5 to 2 times higher within the zones there is a clear need for improved theoretical and or empirical stress grainsize relationships for quartz and other minerals before extensive further application of this technique

crystals stirred up 2 numerical insights into the formation of the earliest crust on the moon 1 this is the second paper in a two part series examining the fluid dynamics of crystal settling and flotation in the lunar magma ocean in the first paper we develop a direct numerical method for resolving the hydrodynamic interactions between crystals and their feedback on the flow field in magmatic liquid in this paper we use this computational technique to test the leading model for the formation of the earliest crust on the moon the anorthositic lithology of the lunar crust is thought to have been formed by the flotation of buoyant plagioclase crystals at a time when the lunar mantle was still wholly or largely molten this model is appealing from an observational point of view but its fluid dynamical validity is not obvious because 1 plagioclase probably started crystallizing very late i e when the magma ocean was already 80 solidified and 2 a significant portion of the shallow lunar crust consists of almost pure plagioclase 90 vol requiring very efficient plagioclase segregation the goal of this study is to better understand the fluid dynamical conditions that hinder or facilitate crystal settling or flotation our approach complements earlier studies by explicitly linking the petrological and fluid dynamical evolution and by focusing on the effect of increasing crystal fraction we find that crystal settling was probably possible throughout the entire solidification history of the lunar magma ocean as long as crystal sizes were sufficiently large r 1 mm and crystal fraction sufficiently low 13

grain growth kinetics in olivine aggregates abstract grain growth kinetics were studied in hot pressed fine grained olivine aggregates experimental conditions include pressures of 0 1 mpa 300 mpa and 1 gpa and temperatures of 1473 1573 and 1673 k with or without the presence of water at the initial stage of grain growth growth of larger grains occurs rapidly consuming smaller grains which results in significant pore entrapment almost homogeneous grain size distribution is established in this process after this stage grain size distribution remains almost homogeneous in most cases it was found that the presence of water enhances the grain growth kinetics when the amount of water is limited however when the amount of water is large the water containing pores significantly inhibit the grain boundary migration therefore the enhancement of grain growth due to the presence of water is due to the role of dissolved water in olivine rather than the mass transport through water abnormal grain growth was found in some samples in these cases normal grain growth was inhibited by the presence of a significant amount of water filled pores or grains with significantly larger size than the rest occurred in the starting materials in 0 1 mpa runs significant porosity developed and the grain growth rates were significantly lower than in those at high confining pressures these results show that both water and pores have important effects on grain growth kinetics in olivine when the effects of pores or secondary phases in inhibiting grain growth are unimportant the grain growth rate in olivine is very fast growth to 100 m size will occur in 102 to 103 hours at 1500 k thus fine grain size in olivine will be maintained only for a short geological time unless the grain boundaries are effectively pinned by secondary particles

robust characteristics method for modelling multiphase visco elasto plastic thermo mechanical problems abstract we have extended our previous 2d method gerya t v yuen d a 2003 characteristics based marker in cell method with conservative finite differences schemes for modeling geological flows with strongly variable transport properties phys earth planet interiors 140 295 320 which is a combination of conservative finite differences with marker in cell techniques to include the effects of visco elasto plastic rheology self gravitation and a self consistently derived evolving curvilinear planetary surface this code is called i2elvis and can solve a new class of computationally challenging problems in geodynamics such as shear localization with large strains crustal intrusion emplacement of magmas bending of realistic visco elasto plastic plates and core formation by vigorous shell tectonics activities related to a global rayleigh taylor instability of a metal layer formed around silicate rich lower density primordial core during planetary accretion we discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location we show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology subducting slab bending with a visco elasto plastic rheology and equilibrium spherical configurations from self gravitation we have also tested possibilities of future applications by addressing 3d geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities

forsterite to wadsleyite phase transformation under shear stress and consequences for the earth s mantle transition zone we have studied the phase transformation of forsterite to wadsleyite under shear stress at the earth s transition zone pressure and temperature conditions two step experiments were performed using a multi anvil press first we hot pressed iron free forsterite at 6 or 11 gpa and 1100 c then we deformed a slab of this starting material using a direct simple shear assembly at 16 gpa and 1400 c for 1 15 35 40 or 60 min both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations cpo by electron back scattered diffraction ebsd transmission electron microscopy tem and fourier transform infrared spectroscopy ftir the phase transformation occurs very rapidly in less than 1 min and metastable forsterite relics are not observed after deformation the grain size of wadsleyite is slightly smaller than the forsterite starting material the water contents obtained from ftir analyses in forsterite and wadsleyite are 65 124 wt ppm h2o and 114 736 wt ppm h2o respectively which are well below water solubility at similar conditions in the presence of free water wadsleyite aggregates display weak cpo patterns with 1 0 0 axes concentrated at low angle to the shear direction 0 1 0 axes perpendicular to the shear plane and nearly random 0 0 1 axes only a few dislocations were observed in wadsleyite with tem this observation is consistent with the assumption that most dislocations formed during the initial high stress stages of these stress relaxation experiments were consumed in the phase transformation probably enhancing the transformation rate cpo patterns vary as a function of the water content with increasing water content the density of 1 0 0 axes parallel to the shear direction decreases and the density of 0 0 1 axes increases viscoplastic self consistent modeling of cpo evolution using previously reported glide systems for wadsleyite i e 1 0 0 0 k l and 1 2 111 101 cannot reproduce the measured cpo unless the 0 0 1 0 1 0 system for which dislocations have not been observed by tem is also activated in addition wadsleyite grain growth suggests the participation of diffusion assisted processes in deformation calculated anisotropies for p and s waves using measured cpo are always below 1 this very low anisotropy is due to both the low finite strain achieved in the experiments which leads to weak wadsleyite cpo and to the diluting effect of added majorite the present experiments emphasize the importance of stress grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone

quantifying magma segregation in dykes abstract the dynamics of magma flow is highly affected by the presence of a crystalline load during magma ascent it has been demonstrated that crystal melt segregation constitutes a viable mechanism for magmatic differentiation moreover crystal melt segregation during magma transport has important implications not only in terms of magma rheology but also in terms of differentiation of the continental crust however the influences of the crystal volume percentage of their geometry their size and their density on crystal melt segregation are still not well constrained to address these issues we performed a parametric study using 2d direct numerical simulations which model the ascension of a crystal bearing magma in a vertical dyke using these models we have characterised the amount of segregation as a function of different physical properties including the density contrast between crystals and the melt phase the size of the crystals ac and their aspect ratio r results show that small values of r do not affect the segregation in this case the amount of segregation depends upon four parameters segregation is highest when and ac are large and lowest for large pressure gradient pd and or large values of dyke width wd these four parameters can be combined into a single one the snumber which can be used to quantify the amount of segregation occurring during magma ascent based on systematic numerical modelling and dimensional analysis we provide a first order scaling law which allows quantification of the segregation for an arbitrary snumber and encompassing a wide range of typical parameters encountered in terrestrial magmatic systems although developed in a simplified system this study has strong implications regarding our understanding of crystal segregation processes during magma transport our first order scaling law allows to immediately determine the amount of crystal melt segregation occurring in any given magmatic dyke system

evidence of chemical heterogeneity within lunar anorthosite parental magmas abstract lunar anorthosites are known for displaying a limited range of plagioclase an content an 94 to 98 here we demonstrate that plagioclase trace element variations from apollo ferroan anorthosites fan samples collected by the apollo 15 and 16 missions display more significant chemical heterogeneity e g chondrite normalized la sm 0 33 5 42 than previously reported we report mineral plagioclase pyroxene and olivine major and trace element abundances for a suite of apollo fan samples in addition to anorthositic clasts within apollo 16 regolith breccias this suite of data extends the compositional range currently reported for apollo anorthosites and for anorthositic clasts previously found within lunar meteorites petrological classifications of the regolith breccia clasts e g anorthosite versus noritic anorthosites cannot always be accurately assessed due to the limited size

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

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

numerical modelling of magma transport in dykes the rheology and dynamics of an ascending pure melt in a dyke have been extensively studied in the past from field observations it is apparent that most dykes actually contain a crystalline load the presence of a crystalline load modifies the effective rheology of such a system and thus the flow behaviour indeed the higher density and viscosity of each crystal compared to the melt cause a decrease of the ascent velocity and modify the shape of the velocity profile from a typical poiseuille flow to a bingham type flow a common feature observed in the field is the arrangement of crystals parallel or at a very low angle to the edge of the dyke such a structural arrangement is often interpreted as the result of magma flow which caused the crystals to rotate and align within the flow direction but this process remains unclear another issue related to the introduction of a crystalline load concerns the possibility for crystals to be segregated from a viscous granitic melt phase during magma ascent the implications of such a process on magmatic differentiation have not previously been considered nor has such a process been previously investigated via numerical models in this study we examine the flow dynamics of a crystal bearing granitic melt ascending in a dyke via numerical models in our models both the crystal and melt phases are represented as highly viscous fluids in a stokes regime our results reveal that the presence of crystals in the melt modifies the magma velocity profile across the dyke furthermore we observe that whilst crystals continually rotate in the shear flow over one period of revolution their major axis has a high probability to be aligned parallel to the flow direction moreover some experiments showed that the melt phase can effectively be squeezed out from a crystal rich magma when subjected to a given pressure gradient range this demonstrates that crystal melt segregation in dykes during granitic magma ascent constitutes a viable mechanism for magmatic differentiation

evolution of crystal settling in magma chamber convection abstract the motion of negatively buoyant particles embedded within kinematically prescribed convective velocity fields is used to study the evolution of crystal settling in magma chambers we consider the effects of stokesian settling velocity crystal growth aspect ratio of the convective domain and the site of crystal nucleation on mixing and transport of heavy crystals in this system the percentage of particles retained in a convecting fluid is very sensitive to the site of nucleation particles nucleating along the cold roof or within the wall boundary layers are generally not retained as a consequence crystal settling can occur even in rapidly convecting magma chambers equilibrium crystal densities are reached relatively quickly within one overturn and the distribution of particles deposited on the bottom of the chamber is always asymmetric this feature may facilitate the formation of primary sedimentary structures in plutons laboratory experiments using small negatively buoyant spheres in a highly viscous fluid with axisymmetric thermal convection confirm the basic predictions of this model

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

reconciling pyroclastic flow and surge the multiphase physics of pyroclastic density currents abstract two end member types of pyroclastic density current are commonly recognized pyroclastic surges are dilute currents in which particles are carried in turbulent suspension and pyroclastic flows are highly concentrated flows we provide scaling relations that unify these end members and derive a segregation mechanism into basal concentrated flow and overriding dilute cloud based on the stokes number s t the stability factor t and the dense dilute condition d d we recognize five types of particle behaviors within a fluid eddy as a function of s t and t 1 particles sediment from the eddy 2 particles are preferentially settled out during the downward motion of the eddy but can be carried during its upward motion 3 particles concentrate on the periphery of the eddy 4 particles settling can be delayed or fast tracked as a function of the eddy spatial distribution and 5 particles remain homogeneously distributed within the eddy we extend these concepts to a fully turbulent flow by using a prototype of kinetic energy distribution within a full eddy spectrum and demonstrate that the presence of different particle sizes leads to the density stratification of the current this stratification may favor particle interactions in the basal part of the flow and d d determines whether the flow is dense or dilute using only intrinsic characteristics of the current our model explains the discontinuous features between pyroclastic flows and surges while conserving the concept of a continuous spectrum of density currents

stability of clinopyroxene at pressure temperature conditions of the transition region abstract the stability of diopside at conditions of 16 19 gpa and 1250 1900 c was determined using a 6 8 type multi anvil apparatus at pressures of 17 18 gpa diopside undergoes a decomposition reaction to an assemblage of casio3 perovskite ca mg sio3 garnet or ilmenite depending on temperature the clapeyron slope for the breakdown reaction download download full size image is 2 mpa k 1 when coupled with a re examination of clinopyroxene stability in other more complex peridotite systems the experimental data are consistent with a recent proposal that the 520 km discontinuity in the transition region is caused by the exsolution of casio3 rich perovskite from garnet rich in majorite component

paleo viscometry of magma bodies abstract viscosity and water content are among the most important characteristics of magma bodies however once magma has erupted or solidified such properties of the original magma are difficult to constrain directly for an ensemble of rhythmically layered magmatic sills and dikes we present a simple model of crystallization and crystal settling that allows one to obtain a melt viscosity estimate when combined with field observations if the composition of the parental magma is roughly known and an estimate of its liquidus temperature is known the viscosity can be used to infer water content

the origin of eucrites diogenites and olivine diogenites magma ocean crystallization and shallow magma chamber processes on vesta the asteroid 4 vesta is one of the very few heavenly bodies to have been linked to samples on earth the howardite eucrite diogenite hed meteorite suite this large and diverse suite of meteorites provides a detailed picture of vesta s igneous and postigneous history we have used the range of igneous rock types and compositions in the hed suite to test a series of chemical models for solidification processes following peak melting magma ocean conditions on vesta fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive fe enrichment in the melt models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates diogenites our best models invoke 60 70 equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush magmatic recharge can produce all of the igneous hed lithologies noncumulate and cumulate eucrites diogenites dunites harzburgites and olivine diogenites magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites we predict an internal structure for vesta that permits excavation of the heds during the formation of the rheasilvia basin while remaining consistent with observations from the dawn mission and most impact models

the yield strength of subliquidus basalts experimental results yield strength is an important property of particle fluid suspensions in basaltic lavas that crystallize during flow emplacement the onset of yield strength may result in threshold transitions in flow behavior and flow surface morphology however yield strength crystallinity relations are poorly known particularly in geologic suspensions where difficulties of experimental and field measurements have limited data acquisition in the subliquidus temperature range here we describe two complementary experimental approaches designed to examine the effect of particle shape on the low shear yield strength of subliquidus basalts the first involves melting cubes of holocrystalline basalt samples with different initial textures to determine the temperature crystallinity at which these samples lose their cubic form these experiments provide information on the minimum crystal volume fractions 0 20 0 35 required to maintain the structual integrity of the cube the second set of experiments uses suspensions of corn syrup and neutrally buoyant particles to isolate the effect of particle shape on yield strength development from these experiments we conclude that the shape is important in determining the volume fraction range over which suspensions exhibit a finite yield strength as anisotropic particles may orient during flow the effect of particle shape will be controlled by the orientation distribution of the constituent particles we find that the so called excluded volume can be used to relate results of experiments on anisotropic particles to those of suspensions of spherical particles recent measurements of yield strength onset in basaltic melts at crystal volume fractions near 0 25 are consistent with our observations that crystal frameworks develop at low to moderate crystal volume fractions when crystals are anisotropic e g plagioclase we further suggest that conditions leading to yield strength onset at low crystallinities include rapid cooling increased crystal anisotropy heterogeneous nucleation which promotes extensive crystal clustering and large cluster anisotropy and static conditions random crystal orientations

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

the timeline of the lunar bombardment revisited abstract the timeline of the lunar bombardment in the first gy of solar system history remains unclear basin forming impacts e g imbrium orientale occurred 3 9 3 7 gy ago i e 600 800 my after the formation of the moon itself many other basins formed before imbrium but their exact ages are not precisely known there is an intense debate between two possible interpretations of the data in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail end here we revisit the work of morbidelli et al 2012 that examined which scenario could be compatible with both the lunar crater record in the 3 4 gy period and the abundance of highly siderophile elements hse in the lunar mantle we use updated numerical simulations of the fluxes of asteroids comets and planetesimals leftover from the planet formation process under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation we conclude that only the cataclysm scenario can explain the data the cataclysm should have started 3 95 gy ago however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization due to iron sulfide exsolution o neil 1991 rubie et al 2016 we show that this is likely true also for the moon if mantle overturn is taken into account based on the hypothesis that the lunar magma ocean crystallized about 100 150 my after moon formation elkins tanton et al 2011 and therefore that hses accumulated in the lunar mantle only after this timespan we show that the bombardment in the 3 4 gy period can be explained in the accretion tail scenario this hypothesis would also explain why the moon appears so depleted in hses relative to the earth we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars the accretion tail scenario requires a global resurfacing event on mars 4 4 gy ago possibly associated with the formation of the borealis basin and it is consistent with the hse budget of the planet moreover it implies that the noachian and pre noachian terrains are 200 my older than usually considered

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

the development of discrete shear zones in a granite stress strain and changes in deformation mechanisms abstract the development of millimetre scale continuous shear zones in the sidi ali bou nab algeria granite and their progressive transformation into discrete shear zones are presented increases in strain stress and strain rate magnitudes as well as changes of deformation mechanisms are suggested by an evolution of the microstructure across these narrow shear zones temperatures are assumed to be constant from boundaries to core the most striking aspects of this evolution are 1 1 a decrease in the angle between the foliation and the shear zone 2 2 a decrease in the recrystallized grain size of quartz together with the development of a crystallographic orientation characterized by a strong concentration of c axes around the y axis of the finite strain ellipsoid 3 3 the development of very fine grained feldspathic aggregates or layers probably through dynamic recrystallization of original large crystals and 4 4 the replacement of original biotite by muscovite and a new generation of biotite in the continuous shear zones the deformation is controlled by the behaviour of quartz this mineral undergoes extensive dynamic recrystallization which probably favours a higher strain rate and a change in the active slip system from a dominant basal one in the outermost part of the structures to a dominant prismatic one in its core paleopiezometry and strain computations show a shear strain up to 10 and an inferred steady state differential stress to 100 130 mpa respectively the high stress level is suspect because the estimates are derived from recrystallized grain size which may be sensitive to strain and variations of chemical environment discrete shear zones develop in relation with dynamic recrystallization of feldspars in the core of continuous shear zones dynamic recrystallization of feldspars produces very fine grained aggregates grain size of 6 7 m which coalesce and form a continuous layer at the central part of the shear zones this fabric may result from 1 1 a change in the driving flow mechanism from dislocation creep of quartz to dislocation creep or and grain boundary sliding of feldspar neoblasts and 2 2 a large strain softening that would favour strain concentration in the fine grained matrix and the development of sharp shear zone boundaries

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

effects of sediment pulses on channel morphology in a gravel bed river sediment delivery to stream channels in mountainous basins is strongly episodic with large pulses of sediment typically delivered by infrequent landslides and debris flows identifying the role of large but rare sediment delivery events in the evolution of channel morphology and fluvial sediment transport is crucial to an understanding of the development of mountain basins in july 2001 intense rainfall triggered numerous debris flows in a severely burnt watershed in the sapphire mountains of montana ten large debris flow fans were deposited on the valley floor and investigations focused on the channel response to these sediment pulses the channel has aggraded immediately upstream of each fan and braided in reaches immediately downstream channel incision through the fans has created sets of coarse grained terraces the deposition upstream of the pulses consists almost exclusively of fine material resulting in a median bed material size d 50 1 2 orders of magnitude lower than the ambient channel material the volume of sand being transported is so great that these aggrading reaches can extend hundreds of meters upstream of the fans with 1 2 m of sand deposited across the entire valley floor along a 10 km study reach cross section surveys longitudinal profiles and pebble counts chronicle channel response to a punctuated increase in sediment supply and provide insight on the processes of sediment wave dispersal

monomineralic glomerocrysts textural evidence for mineral resorption during crystallization of igneous rocks monomineralic aggregates or glomerocrysts are a distinctive feature of many igneous rocks those with crystals joined along prominent euhedral crystal faces form by synneusis while the mineral is crystallizing other glomerocrysts comprised of crystals joined along irregular embayed margins arguably formed while the crystals were being resorbed a model for glomerocryst formation during mineral resorption is described during resorption a boundary layer melt which envelops the dissolving crystals is produced when two or more dissolving crystals come into close proximity the intervening portion their respective boundary layer melts becomes isolated from chemical communication with the surrounding granitic liquid contributions from both dissolving crystals to this isolated portion of the boundary layer melt creates a melt composition that eventually becomes supersaturated with respect to the dissolving crystals this results in crystallization of new material from the intervening melt that bonds th

two phase natural convection implications for crystal settling in magma chambers abstract crystal settling is no longer thought to be the most likely mechanism operating in the formation of layered igneous intrusions the main objection raised against its feasibility is the prediction that crystal settling velocities are likely to be orders of magnitude smaller than convective velocities and that vigorous convection would therefore keep crystals well mixed within the interior of a magma chamber in previous theoretical and numerical investigations of crystal settling no account has been taken of compositional buoyancy gradients created by the interpenetration of crystals and melt this paper includes these effects the results of two dimensional numerical simulations show that parameter regimes exist in which effective crystal settling occurs in infinite prandtl number thermally convecting two phase fluids even for small ratios of settling to convective velocity

potential causes for the non newtonian rheology of crystal bearing magmas experimental studies indicate that crystal bearing magma exhibits non newtonian behavior at high strain rates and solid fractions we use a zero dimensional 0 d inversion model to reevaluate rheological parameters and shear heating effects from laboratory data on crystal bearing magma the results indicate non newtonian behavior with power law coefficients of up to n 13 5 it has been speculated that finite strain effects shear heating power law melt rheology or plasticity are responsible for this non newtonian behavior we use 2 d direct numerical crystal scale simulations to study the relative importance of these mechanisms these simulations demonstrate that shear heating has little effect on aggregate bulk rheologies finite strain effects result in both strain weakening and hardening but the resulting power law coefficient is modest maximum n 1 3 for simulations with spherical crystals the strain weakening and hardening behavior is related to rearrangement of crystals rather than strain rate related weakening finite strain effects were insignificant in a numerical simulation with naturally shaped crystals strain partitioning into the melt phase may induce microscopic stresses that are adequate to provoke a nonlinear viscous response in the melt large differential stresses and low effective stresses revealed by the simulations are sufficient to cause crystals to fail plastically numerical experiments that account for plastic failure show large power law coefficients n 50 in some simulations we conclude that this effect is the dominant cause of the strong nonlinear viscous response of crystal bearing magmas observed in laboratory experiments